Handbook of Detergents, Part D: Formulation (Surfactant Science)

HANDBOOK OF DETERGENTS Part D: Formulation © 2006 by Taylor & Francis Group, LLC SURFACTANT SCIENCE SERIES FOUNDING...

Author: Michael Showell

5926 downloads 19167 Views 7MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form

DOWNLOAD PDF

HANDBOOK OF DETERGENTS Part D: Formulation

© 2006 by Taylor & Francis Group, LLC

SURFACTANT SCIENCE SERIES

FOUNDING EDITOR

MARTIN J. SCHICK 1918–1998 SERIES EDITOR

ARTHUR T. HUBBARD Santa Barbara Science Project Santa Barbara, California

ADVISORY BOARD

DANIEL BLANKSCHTEIN Department of Chemical Engineering Massachusetts Institute of Technology Cambridge, Massachusetts

ERIC W. KALER Department of Chemical Engineering University of Delaware Newark, Delaware

S. KARABORNI Shell International Petroleum Company Limited London, England

CLARENCE MILLER Department of Chemical Engineering Rice University Houston, Texas

LISA B. QUENCER The Dow Chemical Company Midland, Michigan

DON RUBINGH The Procter & Gamble Company Cincinnati, Ohio

JOHN F. SCAMEHORN Institute for Applied Surfactant Research University of Oklahoma Norman, Oklahoma

BEREND SMIT Shell International Oil Products B.V. Amsterdam, The Netherlands

P. SOMASUNDARAN Henry Krumb School of Mines Columbia University New York, New York


JOHN TEXTER Strider Research Corporation Rochester, New York

1. Nonionic Surfactants, edited by Martin J. Schick (see also Volumes 19, 23, and 60) 2. Solvent Properties of Surfactant Solutions, edited by Kozo Shinoda (see Volume 55) 3. Surfactant Biodegradation, R. D. Swisher (see Volume 18) 4. Cationic Surfactants, edited by Eric Jungermann (see also Volumes 34, 37, and 53) 5. Detergency: Theory and Test Methods (in three parts), edited by W. G. Cutler and R. C. Davis (see also Volume 20) 6. Emulsions and Emulsion Technology (in three parts), edited by Kenneth J. Lissant 7. Anionic Surfactants (in two parts), edited by Warner M. Linfield (see Volume 56) 8. Anionic Surfactants: Chemical Analysis, edited by John Cross 9. Stabilization of Colloidal Dispersions by Polymer Adsorption, Tatsuo Sato and Richard Ruch 10. Anionic Surfactants: Biochemistry, Toxicology, Dermatology, edited by Christian Gloxhuber (see Volume 43) 11. Anionic Surfactants: Physical Chemistry of Surfactant Action, edited by E. H. Lucassen-Reynders 12. Amphoteric Surfactants, edited by B. R. Bluestein and Clifford L. Hilton (see Volume 59) 13. Demulsification: Industrial Applications, Kenneth J. Lissant 14. Surfactants in Textile Processing, Arved Datyner 15. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications, edited by Ayao Kitahara and Akira Watanabe 16. Surfactants in Cosmetics, edited by Martin M. Rieger (see Volume 68) 17. Interfacial Phenomena: Equilibrium and Dynamic Effects, Clarence A. Miller and P. Neogi 18. Surfactant Biodegradation: Second Edition, Revised and Expanded, R. D. Swisher 19. Nonionic Surfactants: Chemical Analysis, edited by John Cross 20. Detergency: Theory and Technology, edited by W. Gale Cutler and Erik Kissa 21. Interfacial Phenomena in Apolar Media, edited by Hans-Friedrich Eicke and Geoffrey D. Parfitt 22. Surfactant Solutions: New Methods of Investigation, edited by Raoul Zana 23. Nonionic Surfactants: Physical Chemistry, edited by Martin J. Schick 24. Microemulsion Systems, edited by Henri L. Rosano and Marc Clausse


25. Biosurfactants and Biotechnology, edited by Naim Kosaric, W. L. Cairns, and Neil C. C. Gray 26. Surfactants in Emerging Technologies, edited by Milton J. Rosen 27. Reagents in Mineral Technology, edited by P. Somasundaran and Brij M. Moudgil 28. Surfactants in Chemical/Process Engineering, edited by Darsh T. Wasan, Martin E. Ginn, and Dinesh O. Shah 29. Thin Liquid Films, edited by I. B. Ivanov 30. Microemulsions and Related Systems: Formulation, Solvency, and Physical Properties, edited by Maurice Bourrel and Robert S. Schechter 31. Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato 32. Interfacial Phenomena in Coal Technology, edited by Gregory D. Botsaris and Yuli M. Glazman 33. Surfactant-Based Separation Processes, edited by John F. Scamehorn and Jeffrey H. Harwell 34. Cationic Surfactants: Organic Chemistry, edited by James M. Richmond 35. Alkylene Oxides and Their Polymers, F. E. Bailey, Jr., and Joseph V. Koleske 36. Interfacial Phenomena in Petroleum Recovery, edited by Norman R. Morrow 37. Cationic Surfactants: Physical Chemistry, edited by Donn N. Rubingh and Paul M. Holland 38. Kinetics and Catalysis in Microheterogeneous Systems, edited by M. Grätzel and K. Kalyanasundaram 39. Interfacial Phenomena in Biological Systems, edited by Max Bender 40. Analysis of Surfactants, Thomas M. Schmitt (see Volume 96) 41. Light Scattering by Liquid Surfaces and Complementary Techniques, edited by Dominique Langevin 42. Polymeric Surfactants, Irja Piirma 43. Anionic Surfactants: Biochemistry, Toxicology, Dermatology. Second Edition, Revised and Expanded, edited by Christian Gloxhuber and Klaus Künstler 44. Organized Solutions: Surfactants in Science and Technology, edited by Stig E. Friberg and Björn Lindman 45. Defoaming: Theory and Industrial Applications, edited by P. R. Garrett 46. Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe 47. Coagulation and Flocculation: Theory and Applications, edited by Bohuslav Dobiás


48. Biosurfactants: Production Properties Applications, edited by Naim Kosaric 49. Wettability, edited by John C. Berg 50. Fluorinated Surfactants: Synthesis Properties Applications, Erik Kissa 51. Surface and Colloid Chemistry in Advanced Ceramics Processing, edited by Robert J. Pugh and Lennart Bergström 52. Technological Applications of Dispersions, edited by Robert B. McKay 53. Cationic Surfactants: Analytical and Biological Evaluation, edited by John Cross and Edward J. Singer 54. Surfactants in Agrochemicals, Tharwat F. Tadros 55. Solubilization in Surfactant Aggregates, edited by Sherril D. Christian and John F. Scamehorn 56. Anionic Surfactants: Organic Chemistry, edited by Helmut W. Stache 57. Foams: Theory, Measurements, and Applications, edited by Robert K. Prud’homme and Saad A. Khan 58. The Preparation of Dispersions in Liquids, H. N. Stein 59. Amphoteric Surfactants: Second Edition, edited by Eric G. Lomax 60. Nonionic Surfactants: Polyoxyalkylene Block Copolymers, edited by Vaughn M. Nace 61. Emulsions and Emulsion Stability, edited by Johan Sjöblom 62. Vesicles, edited by Morton Rosoff 63. Applied Surface Thermodynamics, edited by A. W. Neumann and Jan K. Spelt 64. Surfactants in Solution, edited by Arun K. Chattopadhyay and K. L. Mittal 65. Detergents in the Environment, edited by Milan Johann Schwuger 66. Industrial Applications of Microemulsions, edited by Conxita Solans and Hironobu Kunieda 67. Liquid Detergents, edited by Kuo-Yann Lai 68. Surfactants in Cosmetics: Second Edition, Revised and Expanded, edited by Martin M. Rieger and Linda D. Rhein 69. Enzymes in Detergency, edited by Jan H. van Ee, Onno Misset, and Erik J. Baas 70. Structure-Performance Relationships in Surfactants, edited by Kunio Esumi and Minoru Ueno 71. Powdered Detergents, edited by Michael S. Showell 72. Nonionic Surfactants: Organic Chemistry, edited by Nico M. van Os 73. Anionic Surfactants: Analytical Chemistry, Second Edition, Revised and Expanded, edited by John Cross


74. Novel Surfactants: Preparation, Applications, and Biodegradability, edited by Krister Holmberg 75. Biopolymers at Interfaces, edited by Martin Malmsten 76. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications, Second Edition, Revised and Expanded, edited by Hiroyuki Ohshima and Kunio Furusawa 77. Polymer-Surfactant Systems, edited by Jan C. T. Kwak 78. Surfaces of Nanoparticles and Porous Materials, edited by James A. Schwarz and Cristian I. Contescu 79. Surface Chemistry and Electrochemistry of Membranes, edited by Torben Smith Sørensen 80. Interfacial Phenomena in Chromatography, edited by Emile Pefferkorn 81. Solid–Liquid Dispersions, Bohuslav Dobiás, Xueping Qiu, and Wolfgang von Rybinski 82. Handbook of Detergents, editor in chief: Uri Zoller Part A: Properties, edited by Guy Broze 83. Modern Characterization Methods of Surfactant Systems, edited by Bernard P. Binks 84. Dispersions: Characterization, Testing, and Measurement, Erik Kissa 85. Interfacial Forces and Fields: Theory and Applications, edited by Jyh-Ping Hsu 86. Silicone Surfactants, edited by Randal M. Hill 87. Surface Characterization Methods: Principles, Techniques, and Applications, edited by Andrew J. Milling 88. Interfacial Dynamics, edited by Nikola Kallay 89. Computational Methods in Surface and Colloid Science, edited by Malgorzata Borówko 90. Adsorption on Silica Surfaces, edited by Eugène Papirer 91. Nonionic Surfactants: Alkyl Polyglucosides, edited by Dieter Balzer and Harald Lüders 92. Fine Particles: Synthesis, Characterization, and Mechanisms of Growth, edited by Tadao Sugimoto 93. Thermal Behavior of Dispersed Systems, edited by Nissim Garti 94. Surface Characteristics of Fibers and Textiles, edited by Christopher M. Pastore and Paul Kiekens 95. Liquid Interfaces in Chemical, Biological, and Pharmaceutical Applications, edited by Alexander G. Volkov 96. Analysis of Surfactants: Second Edition, Revised and Expanded, Thomas M. Schmitt 97. Fluorinated Surfactants and Repellents: Second Edition, Revised and Expanded, Erik Kissa 98. Detergency of Specialty Surfactants, edited by Floyd E. Friedli


99. Physical Chemistry of Polyelectrolytes, edited by Tsetska Radeva 100. Reactions and Synthesis in Surfactant Systems, edited by John Texter 101. Protein-Based Surfactants: Synthesis, Physicochemical Properties, and Applications, edited by Ifendu A. Nnanna and Jiding Xia 102. Chemical Properties of Material Surfaces, Marek Kosmulski 103. Oxide Surfaces, edited by James A. Wingrave 104. Polymers in Particulate Systems: Properties and Applications, edited by Vincent A. Hackley, P. Somasundaran, and Jennifer A. Lewis 105. Colloid and Surface Properties of Clays and Related Minerals, Rossman F. Giese and Carel J. van Oss 106. Interfacial Electrokinetics and Electrophoresis, edited by Ángel V. Delgado 107. Adsorption: Theory, Modeling, and Analysis, edited by József Tóth 108. Interfacial Applications in Environmental Engineering, edited by Mark A. Keane 109. Adsorption and Aggregation of Surfactants in Solution, edited by K. L. Mittal and Dinesh O. Shah 110. Biopolymers at Interfaces: Second Edition, Revised and Expanded, edited by Martin Malmsten 111. Biomolecular Films: Design, Function, and Applications, edited by James F. Rusling 112. Structure–Performance Relationships in Surfactants: Second Edition, Revised and Expanded, edited by Kunio Esumi and Minoru Ueno 113. Liquid Interfacial Systems: Oscillations and Instability, Rudolph V. Birikh,Vladimir A. Briskman, Manuel G. Velarde, and Jean-Claude Legros 114. Novel Surfactants: Preparation, Applications, and Biodegradability: Second Edition, Revised and Expanded, edited by Krister Holmberg 115. Colloidal Polymers: Synthesis and Characterization, edited by Abdelhamid Elaissari 116. Colloidal Biomolecules, Biomaterials, and Biomedical Applications, edited by Abdelhamid Elaissari 117. Gemini Surfactants: Synthesis, Interfacial and Solution-Phase Behavior, and Applications, edited by Raoul Zana and Jiding Xia 118. Colloidal Science of Flotation, Anh V. Nguyen and Hans Joachim Schulze 119. Surface and Interfacial Tension: Measurement, Theory, and Applications, edited by Stanley Hartland


120. Microporous Media: Synthesis, Properties, and Modeling, Freddy Romm 121. Handbook of Detergents, editor in chief: Uri Zoller Part B: Environmental Impact, edited by Uri Zoller 122. Luminous Chemical Vapor Deposition and Interface Engineering, HirotsuguYasuda 123. Handbook of Detergents, editor in chief: Uri Zoller Part C: Analysis, edited by Heinrich Waldhoff and Rüdiger Spilker 124. Mixed Surfactant Systems: Second Edition, Revised and Expanded, edited by Masahiko Abe and John F. Scamehorn 125. Dynamics of Surfactant Self-Assemblies: Micelles, Microemulsions, Vesicles and Lyotropic Phases, edited by Raoul Zana 126. Coagulation and Flocculation: Second Edition, edited by Hansjoachim Stechemesser and Bohulav Dobiás 127. Bicontinuous Liquid Crystals, edited by Matthew L. Lynch and Patrick T. Spicer 128. Handbook of Detergents, editor in chief: Uri Zoller Part D: Formulation, edited by Michael S. Showell


HANDBOOK OF DETERGENTS Part D: Formulation

Edited by Michael S. Showell Procter & Gamble Company Cincinnati, Ohio, U.S.A.

Boca Raton London New York Singapore

A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.


Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8247-0350-2 (Hardcover) International Standard Book Number-13: 978-0-8247-0350-9 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Catalog record is available from the Library of Congress

Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com Taylor & Francis Group is the Academic Division of T&F Informa plc.


and the CRC Press Web site at http://www.crcpress.com

Preface We are all familiar with the most common form of detergent formulations—household cleaners, laundry detergents, dishwashing detergents, shampoos, body washes, bar soaps, toothpastes, etc. While pervasive in developed markets in a variety of forms for a variety of uses, even developing markets offer an array of such products for consumer use. However, detergents, a term applied to any material which either aids in the removal of foreign matter from surfaces or promotes the dispersion and stabilization of one or more ingredients in a bulk matrix, are widely used in a number of applications and industries not generally familiar to the public (the reader is referred to Volume C of this series: Applications). These include additives to lubricants to aid the removal of deposits from internal surfaces of engines, formulations to aid in the cleanup of, or to enhance the biodegradation of, oil spills and other environmental contaminants, paper and textile processing aids, and as components in the formulation of paints, inks, and colorants. The purpose of this volume, Part D in the Handbook of Detergents series, is to provide an overview of the full range of detergent formulations used today, from common household products to the more esoteric specialty applications. Detergents, although thousands of years old, continue to evolve, providing the end user with an array of benefits and services. In their most common form, as aids in household cleaning and personal care, detergents generally offer not only a basic cleaning benefit but also a range of ancillary benefits intended to better meet the needs of the consumer. For example, today’s laundry detergents provide good general cleaning of fabrics while delivering additional benefits like increased fabric wear, color rejuvenation, and longlasting fresh scent. The increasing complexity of detergent formulations, which combine surface-active agents, builders, sequestering agents, bleaches, enzymes, and other components, places a high demand for creativity and innovation on the part of the detergent formulator. Furthermore, economic constraints and an increasing expectation that detergent formulations meet the ever-increasing demands of sustainability place even more demand on, and require more responsibility from, the formulator. This, in turn, requires that the formulator be knowledgeable of the conditions under which the product will be used, stored, and shipped as well as the end user’s needs and constraints so that formulations are designed which are shelf stable, have acceptable consumer aesthetics, and provide the intended benefit with each particular use. In addition, the increasing volume of detergents and their use across a range of product segments, categories, and industries increases the load on the environment to which they are eventually released. This makes it necessary for the detergent formulator to consider the use of environmentally friendly, and ultimately biodegradable, raw materials whenever possible, creating additional formulation challenges.

iii


iv

Preface

This volume of the Handbook of Detergents series provides a review of the process and chemical technologies involved in producing various detergent formulations. Attention is given to formulations in the consumer products area—laundry detergents, dishwashing products, and household cleaning formulations (Chapters 3–7) as well as a number of specialty areas like Auto Care and Industrial/Institutional Products (Chapter 8), Textile Processing (Chapter 9), Separation Science (Chapter 10), Oil Recovery (Chapter 11), Environmental Cleanup (Chapter 12), Paints and Colorants (Chapter 13), Polymerization Processes (Chapter 14), and Lubricants (Chapter 15). Formulations based on N-alkyl amide sulfates are covered in Chapter 16. A major aim of this book is to provide the reader with some general guidance on formulation approaches. To that end, Chapter 2 provides an overview of the use of statistical mixture design in detergent formulations. This book should serve as a useful reference for scientists, engineers, technicians, managers, policymakers, and students having an interest in detergents and emerging technology trends and formulations that will sustain the industry for years to come. I would like to thank the contributing authors for their time in preparing the highly authoritative individual chapters for this volume, Dr. Uri Zoller for his helpful suggestions and guidance, and Helena Redshaw for her patience, encouragement, and support. Michael S. Showell


About the Editor Michael S. Showell joined Procter & Gamble in 1984 in the Packaged Soap Division and has had various assignments with increasing responsibilities within P&G’s laundry and cleaning product research and development community. He currently is associate director of R&D in the Fabric & Home Care Technology Division at P&G’s Miami Valley Innovation Center in Cincinnati, Ohio. His research interests include: enzymes and their application in laundry and cleaning products, enzyme/detergent interactions, protein engineering to improve enzymes for use in consumer product applications, enzymatic synthesis of detergent ingredients, bioremediation, bioprocessing, and detergents. He is author or coauthor of a number of articles, book chapters, and presentations on the use of enzymes in laundry and cleaning products. In 1999 he was one of the recipients of the American Chemical Society award for Team Innovation. Mike received a B.S. in chemistry from Willamette University in 1978, and M.S. and Ph.D. degrees in physical chemistry from Purdue University in 1980 and 1983, respectively.

v


Contributors Thanaa Abdel-Moghny, tute, Cairo, Egypt Achim Ansmann, Shoaib Arif,

Application Department, Egyptian Petroleum Research Insti-

Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany

Noveon, Inc., Cleveland, Ohio

Samir S. Ashrawi, Surface Sciences Division, The Austin Laboratories, Huntsman Corporation, Austin, Texas Alessandra Bianco Prevot, Torino, Italy

Dipartimento di Chimica Analitica. Università di Torino,

Jean-François Bodet, Brussels Technical Center, Procter & Gamble Eurocor NV, Strombeek-Bever, Belgium Peter Busch,


Jeffrey H. Harwell, School of Chemical Engineering and Materials Science and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma Hermann Hensen, Karlheinz Hill,


Cognis Deutschland GmbH & Co. KG, Monheim, Germany

Krister Holmberg, Department of Applied Surface Chemistry, School of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, Sweden Tze-Chi Jao, Research & Development Department, Afton Chemical Corporation, Richmond, Virginia Glenn T. Jordan, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Robert C. Knox, School of Chemical Engineering and Materials Science and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma Hans-Udo Krächter,


Hiromoto Mizushima, Wakayama, Japan Felix Mueller, Michael Müller,

Material Development Research Laboratories, Kao Corporation,

Degussa AG Goldschmidt Home Care, Essen, Germany Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany vii


viii

Contributors

Charles A. Passut, Research & Development Department, Afton Chemical Corporation, Richmond, Virginia Jörg Peggau,

Degussa AG Goldschmidt Home Care, Essen, Germany

Gianmarco Polotti,

Lamberti SpA, Albizzate, Italy

Edmondo Pramauro, Italy

Dipartimento di Chimica Analitica, Università di Torino,Torino,

Kenneth N. Price, Global Household Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio David A. Sabatini, School of Civil Engineering and Environmental Science, and School of Chemical Engineering and Materials Science, and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma William M. Scheper, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Stefano Scialla, Pescara, Italy

Italia SpA, Pescara Technical Center, The Procter & Gamble Company,

Jichun Shi, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Ben Shiau,

Surbec-ART Environmental, LLC, Norman, Oklahoma

Michael S. Showell, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Mark R. Sivik, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio George A. Smith, Surface Sciences Division, The Austin Laboratories, Huntsman Corporation, Austin, Texas Brian X. Song, Home Care Product Development, Ivorydale Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Oreste Todini, Household Care, Bruxelles Innovation Center, The Procter & Gamble Company, Bruxelles, Belgium Jiping Wang, Fabric & Home Care Technology Division, The Procter & Gamble Company, Cincinnati, Ohio Randall A. Watson, Beijing, P.R. China

Beijing Technical Center, The Procter & Gamble Company,

Yong Zhu, Fabric & Home Care Technology Division, The Procter & Gamble Company, Cincinnati, Ohio


Table of Contents 1.

Introduction to Detergents Michael S. Showell

1

2.

Statistical Mixture Design for Optimization of Detergent Formulations Samir S. Ashrawi and George A. Smith

27

3.

Laundry Detergent Formulations Randall A. Watson

51

4.

Dishwashing Detergents for Household Applications Jichun Shi, William M. Scheper, Mark R. Sivik, Glenn T. Jordan, Jean-François Bodet, and Brian X. Song

105

5.

The Formulation of Liquid Household Cleaners Stefano Scialla

153

6.

Liquid Bleach Formulations Stefano Scialla and Oreste Todini

179

7.

Personal Care Formulations Achim Ansmann, Peter Busch, Hermann Hensen, Karlheinz Hill, Hans-Udo Krächter, and Michael Müller

207

8.

Special Purpose Cleaning Formulations: Auto Care and Industrial/Institutional Products Felix Mueller, Jörg Peggau, and Shoaib Arif

261

9.

Surfactant Applications in Textile Processing Jiping Wang and Yong Zhu

279

10.

Detergent Formulations in Separation Science Edmondo Pramauro and Alessandra Bianco Prevot

305

11.

Surfactant Formulations in Enhanced Oil Recovery Thanaa Abdel-Moghny

325

ix


x

Table of Contents

12.

Surfactant-Based Systems for Environmental Remediation David A. Sabatini, Robert C. Knox, Jeffrey H. Harwell, and Ben Shiau

347

13.

Paints and Printing Inks Krister Holmberg

369

14.

Surfactant Formulations in Polymerization Gianmarco Polotti

387

15.

Detergent Formulations in Lubricants Tze-Chi Jao and Charles A. Passut

437

16.

N-Alkyl Amide Sulfates Hiromoto Mizushima

473

17.

Future Outlook for Detergent Formulations Kenneth N. Price

483


1 Introduction to Detergents Michael S. Showell

CONTENTS I. II.

Introduction ............................................................................................................... 2 Common Detergent Ingredients ................................................................................ 4 A. Surfactants ..................................................................................................... 4 B. Dispersing Polymers ..................................................................................... 4 C. Builders and Chelants ................................................................................... 8 D. Bleaching Systems ........................................................................................ 9 E. Solvents ....................................................................................................... 10 F. Performance Enhancing Minor Ingredients................................................ 11 III. Representative Detergent Formulations ................................................................. 13 A. Laundry Detergent Formulations ................................................................ 13 B. Dishwash Detergent Formulations.............................................................. 13 C. Hard Surface Cleaning Formulations ......................................................... 13 D Personal Care Detergent Formulations ....................................................... 13 E Oral Care Detergent Formulations.............................................................. 13 F. Agricultural Detergent Formulations .......................................................... 13 G. Automobile Detergent Formulations........................................................... 13 H. Detergent Formulations for Cleaning Food Processing Equipment .......... 14 I. Detergent Formulations for Metal Component Cleaning........................... 15 IV. Detergency Theory and Mechanisms...................................................................... 15 A. Removal Mechanisms ................................................................................. 19 B. Suspension Mechanisms ............................................................................. 23 Acknowledgments............................................................................................................. 24 References ......................................................................................................................... 25

1


2

Showell

I. INTRODUCTION Generally, the term “detergents” is applied to materials and/or products that provide the following functions: 1. 2.

Promote removal of material from a surface, e.g., soil from a fabric, food from a dish, or soap scum from a hard surface; Disperse and stabilize materials in a bulk matrix, e.g., suspension of oil droplets in a mobile phase like water.

The ability of a detergent to perform either of these functions depends on the composition of the formulation, the conditions of use, the nature of the surfaces being treated, the nature of the substance to be removed and/or dispersed, and the nature of the bulk phase. Accordingly, detergent formulation is a complex process driven by the specific needs of the end user, economics, environmental considerations, and the availability of specific “actives” that can provide the required functionality. By far the most common and familiar detergents are those used in household cleaning and personal care. These products can be grouped into four general categories: 1.

2.

3.

Laundry detergents and laundry aids. These comprise mainframe laundry detergents in powder, liquid, tablet, gel, and bar form, fabric conditioner products typically in liquid or sheet form, and an array of specialty products like pretreaters (as sticks, gels, sprays, bars), presoaks (liquids, powders), and bleaches (liquids, powders). Typical laundry detergents are formulated to provide general cleaning, which includes removal of soils and stains as well as the ability to maintain whiteness and brightness. In addition, many premium laundry detergents offer additional benefits like fabric softening, dye lock, fiber protection, and disinfectancy. Dishwashing products. These include detergents for hand and machine dishwashing and are typically provided in liquid, gel, powder, or tablet form. Hand dish wash products are formulated to remove and suspend food soils from a variety of surfaces. They also must deliver long-lasting suds, even at high soil loads, and they must be mild to skin. Products designed for automatic dishwashing must provide soil removal and suspension, control of water hardness and sheeting of water off dish surfaces in order to achieve a spot- and film-free finish, and produce little or no suds that would otherwise interfere with the operation of the machine. Rinse aids are specialty detergent formulations for automatic dishwashing designed to promote drainage of water from surfaces via lowering of surface tension. This helps minimize spotting and filming during drying. Household cleaning products. Because no single product can provide the range of cleaning required on the various surfaces found in the home a broad range of household cleaning products are currently marketed. These are typically formulated either in liquid or powder form although gel, solid, sheet, and pad products are also available. So-called “all-purpose” cleaners are designed to penetrate and loosen soil, control water hardness, and prevent soil from redepositing onto clean surfaces. Many of these products also contain low levels of antibacterial actives like Triclosan to sustain disinfectancy claims. Powdered abrasive cleaners remove heavy accumulations of soil via the use of mineral or metallic abrasive particles. Some of these products may also bleach and disinfect through the incorporation of a bleach precursor like sodium perborate, sodium percabonate, or sodium dichloroisocyanurate.


Introduction to Detergents

4.

3

Personal cleansing products. These include products for hand and body washing as well as shampoos, conditioners, and toothpastes. They are marketed primarily in bar, gel, and liquid forms. A major consideration in formulation of such products is the desired consumer aesthetic such as lather, skin feel, rinsability, smell, and taste. Formulations designed for cleaning may also provide moisturizing benefits, disinfectancy, conditioning, and styling effects.

Within each of these categories products are formulated with specific ingredients selected on the basis of their ability to perform the desired function and deliver “consumer preferred” aesthetics while meeting specific cost constraints, environmental regulations, and human safety guidelines. In addition to these familiar consumer products, detergent formulations are used in a number of other applications and industries. These include: 1.

Environmental remediation. Surfactant systems have been developed to aid in the clean up of contaminated groundwater supplies [1]. 2. Enhanced oil recovery. Micellar and surfactant “floods” are among the most successful methods of enhancing recovery of oil from depleted reservoirs [2]. 3. Nanoegineering. Researchers have used the phase behavior of surfactants to generate self-assembling nanosystems [3]. 4. Formulation of paints and printing inks. Paints and inks comprise formulations wherein a pigment is dispersed into a liquid phase. The dispersion is typically achieved with surfactants and/or dispersing polymers [4]. 5. Preparation and application of synthetic polymers. Emulsion polymerization and the preparation of latexes represent one of the largest uses for surfactants outside the cleaning arena [5]. 6. Industrial/metal parts cleaning. Detergent compositions based on a CO2 bulk phase have application in the cleaning of microelectronic components [1]. 7. Medical applications. Mimics of human lung surfactants have been developed to treat respiratory distress syndrome in premature infants [1]. 8. Lubricants. While highly diverse, lubricant formulations utilize the same basic additives: surfactants, dispersants, antiwear actives, antioxidants, corrosion inhibitors, and viscosity modifiers. 9. Textile processing. Detergent formulations are used to clean fibers prior to manufacture into finished textiles as well as lubricate the fibers during spinning and weaving. 10. Agricultural preparations. Pesticide and herbicide preparations are often formulated as aqueous dispersions with specific functional actives to promote even distribution of the active during application and fast penetration of the active upon contact with plants [6]. This diversity of application of detergents presents a rather formidable challenge when compiling a volume such as this on detergent formulations. Accordingly, rather than try to cover authoritatively all aspects of detergent formulations—a monumental task in its own right— I have elected instead in this chapter to provide some general background on detergency, the common ingredients used in detergent formulations, and general approaches to detergent processing or manufacture. This should provide a solid framework for the more in-depth discussions found in later chapters of this book. In addition, there are several good reference books available on the topic of detergent formulations [7– 9].


4

Showell

II. COMMON DETERGENT INGREDIENTS Modern detergents can comprise 20 or more ingredients depending on what benefits the detergent is meant to deliver. It is not within the scope of this chapter to provide an extensive review of the myriad ingredients used in detergent formulations. Rather, the intent of this section is to provide a general overview of the more common elements— surfactants, dispersing polymers, builders and chelants, bleaching systems, solvents, and performance enhancing minors — in order to familiarize the reader with the general chemistry of detergent formulation. Subsequent chapters will provide significantly more detail on many of these ingredients and there are several reference books available on the topic [6–12]. A. Surfactants Surfactants are arguably the most common ingredient of the detergent formulations described in this book. Their primary function is to modify the interface between two or more phases in order to promote the dispersion of one phase into another. In cleaning formulations, for example, surfactants serve to wet surfaces and reduce the interfacial tension between soil and water such that the soil is removed from the surface to be cleaned and dispersed in the aqueous phase. The ability of surfactants to concentrate at interfaces derives from their amphiphilic character—the combination of hydrophilic and hydrophobic moieties within the same molecule. Generally, surfactants are classified according to their hydrophilic component as nonionic, anionic, cationic, or amphoteric. The nonionic surfactants have a hydrophilic component that is not ionized. Typical nonionic groups consist of polyoxyethylene, polyoxypropylene, alkanolamides, or sugar esters. As the name implies, the hydrophilic component of anionic surfactants comprises an anionic group, typically a sulfate, sulfonate, or carboxylate moiety. Likewise, the cationic surfactants comprise molecules containing a positively charged group such as a quaternary amine. The amphoteric surfactants are perhaps the most unique in that they comprise a hydrophilic group containing both anionic and cationic character such as the amino acids. Typical hydrophobes for surfactants are the alkyl chains between C10 and C20. However, in some specialty surfactants the hydrophobe may consist of polysiloxane or perfluorocarbon backbones. Examples of common surfactants are shown in Table 1. Until the 1940s detergents were formulated principally with the sodium or potassium salts of C12–C18 chain length fatty acids. The synthesis of surfactants from petroleum feed stocks in the late 1940s spurred the development of soap-free synthetic detergents that proved much more effective for cleaning in cooler wash temperatures and in hard water. Today, the linear alkyl benzene sulfonates, alkyl sulfates, alkyl ethoxy sulfates, and alkyl ether ethoxylates are the workhorse surfactants for most detergent formulations. Alkyl polyglucosides, alkyl glucosamides, and methyl ester sulfonates are also widely used [13]. Recent attention has been given to the use of internal methyl branched alkyl chains as the hydrophobe for certain anionic surfactants [14]. Such branching promotes improved solubility, particularly in cold, hard water. For systems where water is not the continuous phase a variety of specialty surfactants are used. Examples include the polydimethylsiloxane-based surfactants for use in highly hydrophobic media and the acrylate-polystyrene co-polymers designed by DiSimone and colleagues for applications in cleaning systems utilizing condensed phase CO2 [15]. B. Dispersing Polymers The suspension of solids or liquids in a continuous phase is a critical aspect in the formulation of paints, inks, coatings, and agricultural products such as herbicides. Suspension of soil after removal from a surface is important in cleaning applications to


Introduction to Detergents Table 1

5

Common Surfactants Used in Detergent Formulations

Type

Structure

Anionic

CH3-(CH2)n-CH-(CH2)m-CH3

Linear Alkyl Benzene Sulfonate

SO3Na CH3-(CH2)n-CH-(CH2)m-CH3

Paraffinsulfonate

SO3Na Alkyl Ether Sulfate

CH3-(CH2)n-O-(CH2-CH2-O)xSO3Na

Fatty Acid Soap

O CH3-(CH2)nCONa

Methyl ester sulfonate

O CH3-CH2-(CH2)nCO-CH3 SO3Na

Cationic Quaternary monoalkylammonium chloride

CH3-(CH2)n-N+(CH3)3Cl-

Nonionic

CH3-(CH2)n-O-(CH2-CH2O)nH

Fatty alcohol ethoxylate

CH3-(CH2)n-N(CH3)2

Amine oxide

O

CH3-(CH2)n-C-NH-CH2-CH2OH

Alkyl monoethanolamide

O N-methylglucosamide

OH OH CH3-(CH2)n-C-N-CH2-CH-CH-CH-CH-CH2OH O CH3 OH OH

Amphoteric

CH3-(CH2)n-C-NH-(CH2)3-N+(CH3)2-CH2-C-OAmidopropyl betaine

Alkyl sulfobetaine

O

O

CH3-(CH2)n-N+(CH3)2-CH2-CH-CH2-SO3OH

avoid redeposition of the soil back onto the cleaned surface. Generally speaking, the particles to be suspended are sufficiently large that definite surfaces of separation exist between the dispersed phase and the dispersion medium [16]. In order to keep the dispersed phase stable it is important to adsorb functional actives at these surfaces to prevent aggregation. This is one of the critical functions of surfactants. However, another class of detergent actives has been developed to assist in particle suspension—the polymeric dispersants.


6

Showell

In general two types of polymeric dispersants are used in detergent formulations—polymers comprising ionically charged groups and nonionic polymers. Typical of the ionic dispersing polymers are the homopolymers of acrylic acid and copolymers of acrylic and maleic acids which are widely used in laundry detergent formulations:

H

H

C

C

Z

COOH

n

where Z is either hydrogen, in the case of homopolymers of acrylic acid, or a carboxyl group in the case where the monomer unit is maleic acid. Polymers of this type are commonly found in powdered laundry detergent formulations where they assist in cleaning by acting as a dispersant for soil and inorganic salts, provide alkalinity control, and serve as crystal growth inhibitors [17]. Anionic dispersing polymers comprising carboxyl and sulfonate groups in the same backbone have been developed for use in water treatment where they act to prevent formation of inorganic scale. The polymers are generally of the following hybrid type:

A Sulfonated monomer(s)

B

C

D

Carboxylate monomer(s)

Optional neutral monomer(s)

Optional charged monomer(s)

The key features are A and B. A, the sulfonated monomers, include the following groups:

H

R1

N

R

SO3H

O

O

O R2

SO3H

(OR)nSO3H (OR)qSO3H

n

SO3H

O

(CH2)nSO3H

H SO3H

N

q

SO3H

O SMS

AMPS SSS

SO3H

OH O AHPS

SO3H

HO3S

O

OH R

SPMS



7

B usually comprises maleic, acrylic, or methacrylic acid. C and D are optional but can include acrylamide, vinyl acetate (alcohol), acrylate esters, cationics, or phosphonates [18]. Carboxymethylcellulose is another example of an anionic dispersing polymer widely used in laundry detergent applications

CH2OCH2COO− O

O OH O OH n

Considerable attention has been paid over the years to the preparation of biodegradable dispersants [19–21]. Examples include polyamino acid polymers such as polyaspartate prepared from the catalytic condensation of polyaspartic acid [22] and functionalized polysaccharides such as oxidized starches [23]. Recently, a novel process was reported for the preparation of functionalized polyaspartic acid polymers that expands the utility of these materials as dispersants for a variety of applications [24]. Cationic dispersants are less commonly used although some amphiphilic structures have been described as effective dispersants in high salt content media [25]:

[CH2-CH]n

CH]m

[CH O

C

C

O

N CH2 H3C

N+ CH3 Cl− CH3

Amphoteric dispersing polymers of the types shown below have also been reported to be good clay and particulate dispersants in certain laundry detergent formulations [26]:

(CH2CH2O)24SO3Na NaO3S-(OCH2CH2)24N +

N-(CH2CH2O)24SO3Na

Cl−

(CH2CH2O)24SO3Na

CH3

(CH2CH2O)20SO3Na NaO3S(OCH2CH2)20-N + Cl−


CH3 + Cl−

(CH2CH2O)20SO3Na N + Cl−

(CH2CH2O)20SO3Na + Cl−

N-(CH2CH2O)20SO3Na

8

Showell

Nonionic polymers include polyethylene glycol, polyvinyl alcohol, and random and block ethoxy propoxy copolymers. Graft copolymers of polyalkylene oxide and vinyl acetate are reported to be effective antiredeposition agents for hydrophobic surfaces like polyester fabric [27]. C. Builders and Chelants Metal ion control is a common need in many detergent formulations. For example, in aqueous cleaning applications the presence of Ca2+ in the water can lead to the precipitation of anionic surfactant reducing the effective concentration available for cleaning. Fatty acids can precipitate as calcium soaps resulting in the formation of soap scum on hard surfaces, and many soils, especially inorganic clays, will precipitate with calcium leading to redeposition of the soil onto the surface being cleaned. Builders—a generic term used to refer to any number of materials whose primary function is the removal of Ca2+ and Mg2+ ions from aqueous solutions—and chelants are widely used in the formulation of various detergents. Sodium tripolyphosphate (STPP) is among the best known and widely used detergent builder. In laundry detergent formulations it serves not only as an extremely effective calcium control agent but also provides dispersion, suspension, and anti-encrustation benefits. However, environmental concerns associated with large-scale release of phosphates into the environment lead to the development of a number of substitutes. Citric acid and sodium nitrilotriacetate are representative of soluble detergent builders

CH2COONa

CH2COOH

HO

C

COOH

CH2COOH Citric Acid

N

CH2COONa CH2COONa

Sodium nitrilotriacetate

Sodium carbonates and noncrystalline sodium silicate form sparingly soluble precipitates with calcium and are frequently used in powdered detergent formulations where they also provide a source of alkalinity. However, to avoid encrustation of the calcium carbonate/silicate onto surfaces these building agents generally are co-formulated with a dispersing polymer like the polyacrylate/maleic acid copolymers described above and crystal growth inhibitors like HEDP (1-hydroxyethane diphosphonic acid). Insoluble builders include the zeolites and layered silicates, which bind calcium via an ion exchange mechanism [28]. Zeolite A, Na12(AlO2)12(SiO2)12∑27H2O, is the principal alternative to phosphate as a detergent builder. The Na+ ions are exchangeable for Ca2+ while the larger hydration shell around Mg2+ tends to impede exchange. Citric acid is also an excellent chelant for metal ions other than calcium and can be employed where the removal of transition metals such as copper, zinc, and iron is important. Other commonly used detergent chelants include ethylenediaminetetraacetate (EDTA)


Introduction to Detergents NaOOCCH2

9

CH2COONa N-CH2CH2-N CH2COONa

NaOOCCH2

and diethylenetriaminepentaacetate (DTPA)

NaOOCCH2

CH2COONa N-CH2CH2-N-CH2CH2-N

NaOOCCH2

CH2COONa

CH2COONa

D. Bleaching Systems Bleaches are common components of laundry, automatic dish wash, and hard surface cleaning detergent formulations where they act to destroy chromophoric groups responsible for color in soils via oxidative attack. Four basic technology approaches have been taken to deliver bleaching in these products—chlorine-based bleaches, peroxide-based bleaches, activated peroxide systems, and metal catalysts. Chlorine-based systems are common in some powdered abrasive hard surface cleaners and automatic dishwashing products. Typically, hypochlorite bleach is delivered via precursor like sodium dichloroisocyanurate according to the reaction:

Na

Na N

O C

C

N

N

O

H2O

Cl

Cl

2HClO

+

N

O C

C

N

N

O

H

H O

O

Peroxide-based bleaches either use hydrogen peroxide directly or appropriate precursors like perborate monohydrate, which generate peroxide according to the reaction: (NaBO2H2O2)2 Æ H2O2NaBO2 + 2H2O2 + H2O Activated peroxide systems rely on perhydrolysis of a precursor molecule (generally referred to as an “activator” to generate a peracid bleach in situ: RCO2H + H2O2 Æ RCO3H + H2O The two most common activators used in laundry detergents are N¢N≤-tetraacetyl ethylene diamine (TAED) and nonanoyloxybenzene sulfonate (NOBS). In an aqueous environment TAED undergoes perhydrolysis with the perhydroxyl anion from peroxide to


10

Showell

generate peracetic acid. NOBS reacts in much the same way but generates the more hydrophobic pernonanoic acid. A frequently studied approach to bleaching involves the use of transition metal catalysts [29]. Complexes of metals like Mn, Fe, Cu, and Co with certain organic ligands can react with peroxygen compounds to form reactive intermediates, which can potentially result in powerful bleaching action. Typical of these systems are the structures shown below:

H3N

Co

Cl

N

N

NH3

2+

Me

Me

NH3

O Me

N Me

MnIV O MnIV

N

NH3

(PF6−)2

O NH3

From US Patent 5, 798, 326

N

N

Me

Me

From US Patent 5, 246, 612

E. Solvents The selection of solvents for use in detergent formulation depends on the nature of the actives being formulated, the intended application of the detergent, and economics. Water is the dominant solvent in most household and industrial cleaning formulations. Generally speaking, water-based detergents are less toxic, more environmentally friendly, cheaper, more surface compatible, and easier to handle than petroleum-based solvents. However, many common detergent actives have limited solubility in water requiring formulation of a co-solvent and/or hydrotrope. Typical co-solvents used in household cleaning formulations include ethanol, glycerol, and 1,2-propanediol. A hydrotrope, also called a “coupling agent,” is an organic compound that increases the ability of water to dissolve other molecules. Hydrotropes are commonly used in aqueous-based detergent formulations containing high concentrations of surfactant in order to achieve a shelf-stable, clear, isotropic fluid. Common hydrotropes are sodium xylene sulfonate, sodium toluene sulfonate, and sodium cumene sulfonate. A typical liquid dishwashing formulation, shown below in Table 2, is a good example of a surfactant-rich aqueous-based detergent system comprising both a co-solvent (in this case ethanol) and a hydrotrope (sodium cumene sulfonate): Of course there are applications where water must be avoided. Perhaps the most recognizable of these is in the dry cleaning of fine textiles like silk and wool. Historically, this process has used volatile organic solvents like perchloroethylene as the bulk cleaning fluid. Concerns that such solvents may represent human and environmental safety hazards has recently lead to the development of alternative processes utilizing condensed phase CO2 [30] and certain silicone oils like cyclic decamethylpentasiloxane, D5 [31]. Detergent formulations for use in such systems will typically comprise a solvent compatible with the bulk phase (e.g., polydimethylsiloxane in the case of the D5 system) and capable of solublizing the cleaning actives to be introduced into the bulk phase.



11

Typical Hand Dishwash Formulation Ingredient

C12-C13 Alkyl ethoxy (E1.4) sulfate C12-C14 Polyhydroxy fatty acid amide C14 Amine oxide C11 Alcohol ethoxylate E9 MgCl2 Calcium citrate Polymeric suds booster Ethanol Sodium cumene sulfonate Minors and water

Weight % 33 4 5 1 0.7 0.4 0.5 1 0.5 Balance

Other areas where water is not a suitable solvent include the cleaning of certain metal parts and electronic circuit boards. Here chlorinated hydrocarbons like perchloroethylene or methylene chloride, or volatile organics like methyl ethyl ketone have historically been used but regulatory pressure has resulted in a shift to more environmentally friendly solvents like terpenes and dibasic esters. F. Performance Enhancing Minor Ingredients Depending upon the end use of the detergent formulation and the benefits to be delivered a number of performance enhancing minor ingredients may be used. These include: 1.

2.

3.

Enzymes. Used primarily in cleaning formulations enzymes promote soil removal by the catalytic breakdown of specific soil components. Proteases (enzymes that degrade protein) are the most common of all the detergent enzymes but amylases (starch degrading), lipases (lipid degrading), and cellulases (cellulase degrading) are also used [32]. Brighteners/fabric whitening actives. These materials enhance the visual appearance of white surfaces, typically cotton fabrics, by absorbing ultraviolet (UV) radiation and emitting via fluorescence in the visible portion of the spectrum. Typical whitening actives are built from direct linkage or ethylenic bridging of aromatic or heteroaromatic moieties. Among the most commonly used whiteners in laundry detergents are the derivatives of 4,4-diaminostilbene-2,2-disulfonic acid. Foam boosters. In some applications, most notably hand dishwashing and shampoos; it is desirable for the detergent formulation to generate a large-volume, stable foam. While most surfactants are capable of generating and sustaining foam in the absence of soil, these foams rapidly collapse in the presence of soil, especially particulate and fatty soils. In applications where foam must be maintained throughout the course of detergent use, specific boosters may be added. Proteins have been shown to promote foaming in certain systems [33] especially in food and beverage applications [34]. Alkanolamides, particularly mono- and diethanolamides, are effective foam stabilizers used in dishwashing liquids and


12

Showell

shampoos [7]. Polymeric foam boosters of the type shown below have also proved effective in hand dish wash applications [35]:

n

N O

4.

5.

6.

O

Antifoam agents. In many applications it is desirable to minimize foam generation. For example, in automatic dishwashing foam generation can interfere with rotation of the spray arm leading to degradation in the performance of the dishwasher. Antifoam agents act to reduce or eliminate foams. They either prevent formation of the foam or accelerate its collapse. Alkyl ethoxylate nonionic surfactants are commonly used as foam control agents in detergents where application temperatures exceed the cloud point of the surfactant—the temperature at which the surfactant becomes insoluble. The insoluble nonionic-rich surfactant phase acts to break foam lamella promoting foam collapse. Hydrophobic particulate antifoam agents physically break foams by lodging in the foam film promoting rapid localized draining in the region of the film in contact with the particles. The calcium soaps of long-chain fatty acids are effective at foam control as are hydrophobic silica particles. Particularly effective antifoams are comprised of colloidal hydrophobic silica particles suspended in a silicone oil like polydimethyl siloxane. The hydrophobic oil promotes spreading of the particles at the air-water interface thereby ensuring entrapment in the foam film and subsequent foam disruption [7]. Thickeners. It is often desirable to modify the rheology of a detergent formulation to fit a particular application. For example, gel-type automatic dishwashing detergents are thickened to help suspend phosphate and other solids that would otherwise separate out from the liquid phase. Thickening can be achieved through the use of inorganic electrolytes, e.g., NaCl; clays, such as laponite or hectorite; or a high-molecular-weight polymer like carboxymethylcellulose, guar, or xanthan gum. The Carbopol“ series of polymers from Noveon, homoand copolymers of acrylic acid cross linked with polyalkenyl polyether, are particularly effective thickeners for household cleaning detergent formulations. Soil release polymers. Soil release refers to the enhanced removal of soil from a surface as a result of modification of that surface with a specific agent, typically a polymer that alters surface polarity thereby decreasing adherence of soil. Used primarily in laundry detergent formulations soil release polymers provide significant changes in surface energy, which in turn can lead to dramatic improvements in the removal of soils. Carboxymethyl cellulose (CMC) is the archetypical soil release polymer. CMC absorbs onto cotton fabric owing to the similarity in structure between the cellulose backbone of CMC and the cellulose polymer of cotton fibers. Once absorbed, the carboxyl moiety creates a high net negative charge on the fabric surface effectively repelling negatively charged soils, especially clays [7].



13

Other soil release polymers used in detergents are derivatives of polyester-polyether block copolymers that are capped with nonionic (ethoxylates), anionic (typically sulfonates), or cationic (typically quaternary amines) groups to achieve deposition and release from specific formulations [36].

III. REPRESENTATIVE DETERGENT FORMULATIONS This section provides examples of detergent formulations comprising the ingredients discussed in Section II. This is by no means an exhaustive compilation. Rather, the intent is to illustrate the variety of detergent formulations and how the composition of the formulation varies depending on the intended use. Subsequent chapters of this book will provide more detail on detergent formulations for specific applications. A. Laundry Detergent Formulations Examples of granular laundry detergent formulations are shown in Table 3. Table 4 illustrates typical liquid laundry detergent formulations. B. Dishwash Detergent Formulations Examples of typical liquid hand dishwash formulations are provided in Table 5. Examples of granular detergent formulations for use in automatic dishwashing applications are illustrated in Table 6. C. Hard Surface Cleaning Formulations Examples of liquid hard surface cleaning formulations are illustrated in Table 7. D. Personal Care Detergent Formulations Table 8 provides examples of typical shampoo formulations. Examples of body washes are provided in Table 9. E. Oral Care Detergent Formulations An oral mouthwash formulation is illustrated in Table 10. Examples of Toothpaste formulations are provided in Table 11. In the toothpaste formulations illustrated in Table 11 note the use of silica as an abrasive cleaning agent. F. Agricultural Detergent Formulations Herbicidal compositions typically comprise an aqueous emulsion of the active with appropriate surfactants to insure effective spreading and penetration of the herbicide into plants. Typical compositions comprising the well-known herbicidal active glyphosphate are illustrated in Table 12. G. Automobile Detergent Formulations A variety of detergent compositions are used in the care and maintenance of automobiles. Chapter 8 provides an extensive review of the components used in such formulations. The composition in Table 13 illustrates a formulation designed to clean and provide a waxed finish to the exterior of automobiles. A formulation designed to remove grease from automobile engines and engine compartments is illustrated in Table 14.


14 Table 3

Showell Representative Granular Laundry Detergent Formulations Weight %

Ingredients Examples

A

B

C

C11-C13 Linear alkyl benzene sulfonate C12-C16 Alkyl ethoxy (E2) sulfate C14-C16 Secondary alkyl sulfate C14-C15 Alkyl sulfate C16-C18 Alkyl sulfate C14-C15 Alkyl ethoxy (E2) sulfate C12-C15 Alcohol ethoxylate E7 C14-C15 Alcohol ethoxylate E7 STPP Zeolite A Carbonate Silicate Sodium sulfate Na perborate tetrahydrate Na perborate monohydrate TAED NOBS HEDP DTPA Proteasea Amylasea Lipasea Cellulasea Acrylic/maleic copolymer CMC Polyester-based soil release polymer Minors

8 — 2 — 2 — 3.4 — — 18 13 1.4 26 9 — 1.5 — 0.3 — 0.8 0.8 0.2 0.15 0.3 0.2 0.2 Balance

10 — — 7 — 1 — 1 — 22 19 1 10 — 1 — 4 — 0.4 0.3 0.1 — — 1 — 0.4 Balance

— 5.3 — — — — — 3.3 10.7 10.7 6 7 40 5 — 0.5 — — — 0.3 0.1 0.2 0.3 0.8 0.2 — Balance

a

Enzymes are added in granulated form where typical enzyme level in the granulate ranges from 1 to about 8% by weight of the granulate formulation. Source: From U.S. Patents 6,326,348 B1 and 6,376,445 B1.

H. Detergent Formulations for Cleaning Food Processing Equipment Processing of food contaminates surfaces with lipids, carbohydrates, and proteins. A variety of detergent formulations have been developed specifically for cleaning food processing and preparation equipment. Table 15 provides an example of one such detergent utilizing high alkalinity as the major detersive component: More user friendly and environmentally compatible formulations can be built around enzyme technology to facilitate the removal of protein bound to surfaces. Examples are illustrated in Table 16.



15

Representative Liquid Laundry Detergent Formulations

Ingredients Examples C11-C13 Linear alkyl benzene sulfonate C12-C15 Alkyl sulfate C14-C15 Alkyl sulfate C14-C15 Alkyl ethoxy (E2.5) sulfate C12-C13 Alcohol ethoxylate (E7) C11-C13 Alcohol ethoxylate (E8) C16-C18 Alkyl N-methyl glucamide C12-C14 Fatty acids Oleic acid Citric acid Sodium cumene sulfonate NaOH Ethanol 1,2 propanediol Monoethanolamine Proteasea Amylasea Lipasea Cellulasea Polyester-based soil release polymer Water + minors

Weight % A

B

C

12 — — 12 3 — — 2

— 18 — 2 4 — 8 11 — 5 — — 3 10 9 0.8 0.3 0.1 0.1 0.2 Balance

28 — 14 — — 3 2 — 3.4 5.4 — 0.4 7 6 17 1 — — — — Balance

3 4 6 — 3 3 0.8 — — — 0.2 Balance

a

Enzymes are added from liquid stocks where typical enzyme levels in the stock ranges from 1 to about 8% by weight of the liquid stock formulation. Source: From U.S. Patent 6,376,445 B1.

I. Detergent Formulations for Metal Component Cleaning Industries involved in repair and replacement of mechanical parts often require that those parts be cleaned prior to inspections, repair, or replacement. Generally, mechanical parts have been exposed to a wide variety of contaminants including dirt, oil, ink, and grease that must be removed for effective repair or service. A variety of metal cleaners have been developed to clean such surfaces. For example, solvent-based cleaners containing either halogenated or nonhalogenated hydrocarbons are common. However, the use of these cleaners carries certain environmental and worker safety issues. Where appropriate, aqueous-based cleaners are preferred for cost, safety, and environmental concerns. Table 17 provides example formulations of aqueous-based metal cleaning formulations:

IV. DETERGENCY THEORY AND MECHANISMS As noted in the introduction the two major functions of detergents are to remove materials from surfaces and keep materials suspended in a bulk phase. Each function requires work


16 Table 5

Showell Representative Liquid Hand Dishwash Detergent Formulations Weight %


A

B

C

C12-C13 Alkyl ethoxy (E3.5) carboxylate C11-C17 Alkyl ethoxy (E2.5) sulfate C12-C13 Alcohol ethoxylate (E3.5) Polyhydroxy fatty acid amide C12-C13 Alkyl sulfate C12-C14 Amidopropyl diemethyl betaine C14 Amine oxide MgCl2 Mg(OH)2 Methyldiethanol amine Ethanol Xylene sulfonate Water + minors

22 — 1.3 — 6 3 3 0.6 — 10 9 — Balance

— 29 — — — 0.9 3 3.3 — — 4 2 Balance

— 34 — 7 — 2 3 — 2 — 9 2 Balance

Source: From U.S. Patents 5,376,310 and 6,376,445 B1.

Table 6 Representative Granular Automatic Dishwashing Detergent Compositions

Ingredients Examples STPP Carbonate Silicate Sodium perborate monohydrate Alcohol ethoxylate Metal bleach catalyst TAED Proteasea Amylasea Sulfate Minors a

Weight % A

B

54 14 15 8 2 0.01 — 2 0.3 5 Balance

30 31 7.4 4.4 1.2 — 1 2.5 0.5 23.4 Balance

Enzymes are added in granulated form where typical enzyme level in the granulate ranges from 1 to about 8% by weight of the granulate formulation. Source: From U.S. Patent 6,376,445 B1.



17

Representative Liquid Hard Surface Cleaning Compositions

Ingredients Examples Hydrogen peroxide C10 Alkyl sulfate Na octyl sulfate Na dodecyl sulfate C12-C13 Alcohol ethoxylate (E3) C9-C11 Alcohol ethoxylate (E10) Betaine Butyl octanol Butyl carbitol Isopropanol Butoxypropanol Sodium hydroxide Silicate Monoethanolamine Quaternary ammonium disinfectant Tartaric acid Water + minors

Weight % A

B

C

7 2 — — 2 2 — 0.5 — — — — — — — — Balance

— — 2 4 — — — — 4 — — 0.8 0.04 — — — Balance

— — — — — — 0.8 — — 30 15 — — 2.5 0.5 0.1 Balance

Source: From U.S. Patents 6,277,805 and 6,376,445.

Table 8

Representative Shampoo Formulations Weight %


A

B

C

D

Ammonium lauryl sulfate Isostearamidopropyl morpholine lactate Cocoamidopropylbetaine Sodium cocosulfate Polyquaternium-10 Trimethylolpropane caprylate caprate Cocamide MEA Cetyl alcohol Stearyl alcohol Glycerol stearate Ethylene glycol distearate Dimethicone EDTA Water + minors

14 — 2.7 — 0.3 0.3 0.8 — — — 1.5 1 — Balance

12.5 — 4.2 — 0.3 0.3 — 0.4 0.2 — 1.5 1 — Balance

48 3 — 4 — — — — — 1.5 — — — Balance

50 6 — 3 — — — — — 1.5 — — 0.4 Balance

Source: From U.S. Patent 6,007,802 and HAPPI, February 2001.


18

Showell

Table 9

Representative Body Wash Formulations Weight %


A

B

Sodium cocoamphoacetate Cocaminopropyl betaine Disodium lauryl sulfosuccinate Disodium oleamido MEA sulfosuccinate Disodium laureth sulfosuccinate Sodium laureth sulfate Isostearamidopropyl morpholine lactate Hydrolyzed wheat protein derivative Polyquaternium–7 Glycol distearate Sodium chloride Water + minors

5 10 — 5 5 17 2 1 2 — — Balance

14 10 30 — — — 6 — 3 3.5 3 Balance

Source: Courtesy of T. Schoenberg, The McIntyre Group Ltd.

Table 10

Oral Mouthwash Formulation

Ingredients tb Glycerine Betaine Ethanol Propylene glycol Flavoring Triclosan Water

Weight % 10 10 1.4 10 7 0.2 0.06 Balance

Source: From U.S. Patent 5,681,548.

(W) to be done on the system. In the case of removal that work, defined here as WR, is a measure of the energy required to move a substance from a surface into the bulk phase. In general, surface-active agents like surfactants promote removal from surfaces by lowering the interfacial energy between the substrate and the bulk phase. In the case of suspension, the work, WS, to suspend in the bulk phase is a measure of the energy required to keep materials from aggregating, flocculating, or adhering to a surface. Generally, suspension is achieved either by electrostatic repulsive effects or steric stabilization. Subsequent chapters of this book provide extensive detail on how to remove and suspend materials via chemical means. The purpose of this section is to provide a general thermodynamic underpinning to the phenomena of soil removal and particulate suspension so that the reader can better understand the mechanisms by which detergent chemicals function.



19

Representative Toothpaste Formulations Weight %


A

B

C

Glycerin Polyethylene glycol Xanthan gum CMC Water Sodium saccharin Sodium fluoride Xylitol Poloxamer Sodium alkyl sulfate Cocamidopropyl betaine Flavoring Sodium carbonate Titanium dioxide Silica Sodium bicarbonate Propylene glycol Tetrasodium pyrophosphate Calcium peroxide

27 2 0.3 0.2 5 0.5 0.2 10 2 6 — 1.1 2.6 1 20 1.5 15 5 0.5

29 1 0.4 0.2 7 0.4 0.2 10 3 4 — 1 3 1 20 1 11 7 1

29 3 0.3 0.2 5 0.5 0.2 10 — 4 2 1 3 1 20 1 12 7 1


Table 12

Representative Herbicidal Formulations Weight %


A

B

C

Butyl stearate Span 80 Tween 20 C12-15 Alcohol ethoxylate (E20) Glyphosphate (as g a.e./liter) Water

18 3 5 — 100 Balance

1 — — 10 163 Balance

7.5 3 5 — 160 Balance

Note: a.e. = active ether Source: From U.S. Patent 6,479,434.

A. Removal Mechanisms For simplicity, in the following discussion, materials to be removed from a surface will be generically referred to as soils. The basic concept illustrated here will be for surfactant-


20 Table 13

Showell Detergent Formulation for Cleaning and Care of Automobile Exteriors Ingredients

Weight %

Micronized polymer wax Amino functional silicone Polydimethylsiloxane Paraffinic hydrocarbon solvent Alkyl alcohol ethoxylate Fluoroamide polymer Water

6 3 1 15 0.5 0.2 Balance


Table 14

Automobile Engine Cleaner Ingredients

Dodecyl oxydibenzene disulfonate Nonylphenol-9 ethoxylate Sodium orthosilicate Tetra potassium pyrophosphate C18 tall oil Heavy aromatic naphtha Water

Weight % 6 1.2 1.2 8 9.5 14 Balance

Source: From U..S Patent 3,717,590.

Table 15

Detergents for Cleaning Food Processing Equipment

Examples Sodium hydroxide Sodium polyacrylate 1,2,4 Tricarboxylic acid 1-Hydroxyethylidene-1,1-disphosphonic acid Sodium hypochlorite Water Source: From U.S. Patent 4,935,065 to Ecolab Inc.


A 15 2.7 0.8 — 2 Balance

B 15 2.7 — 0.3 3 Balance

C 15 2.7 — 0.8 3 Balance


21

Enzymatic Based Detergents for Cleaning Food Processing Equipment

Ingredients Examples Triethanolamine Sodium metabisulfite Propylene glycol Sodium xylene sulfonate Ethoxylated propoxylated nonionic Protease Water

Weight % A

B

2 1 12 20 25 6.3 Balance

2 1 12 20 25 6.3 Balance

C 2 1 15 20 25 3.1 Balance

D 2 1 15 20 25 3.1 Balance

Source: From U.S. Patent 6,197,739 B1 to Ecolab Inc.

Table 17

Representative Aqueous-Based Metal Cleaning Detergents

Ingredients Examples Sodium carbonate Borax N-octylpyrrolidone 1,2,3-Benzotriazole C9-C11 Alcohol ethoxylate (E2.5) C9-C11 Alcohol ethoxylate (E6) C12-C15 Alcohol ethoxylate (E9) C14-C15 Alcohol ethoxylate (E7) Acrylic acid polymer NaOH Sodium silicate Sodium nonanoate Water

Weight % A

B

3 0.3 — 0.3 2 2 — — 0.5 0.5 2 6.5 Balance

3 0.3 — 0.3 — — 4 — 0.5 0.5 2 6.5 Balance

C 3 0.3 — 0.3 — — — 4 0.5 0.5 2 6.5 Balance

D 3 0.3 2 0.3 2 2 — — 0.5 0.5 2 6.5 Balance

Source: From U.S. Patent 6,124,253 to Church & Dwight Co.

mediated removal of soil from a surface. Soil removal mechanisms can be considered to comprise several steps: 1.

2.

Surfactant transport to an interface. This can occur with the surfactant in the monomeric form, in which case kinetics of transport are fairly rapid (10–5 cm2/sec), or with the surfactant in aggregated or micellar form in which case the kinetics of transport are relatively slow (10–7 cm2/sec). The kinetics of surfactant transport and adsorption at the interface can be measured via dynamic interfacial tensiometry [37–41]. Adsorption of surfactant at the solution/soil interface, solution/atmosphere interface, and surface/solution interface. This step results in lowering of the interfa-


22

Showell

3.

4.

5.

6.

cial energies at each of these interfaces. Adsorption is driven by the surfactant packing parameter (P = V/aoI) where V is the volume described by the hydrophobic portion (alkyl chain) of the surfactant, ao is the mean cross-sectional area of the surfactant head group, and l is the all trans alkyl chain length of the hydrophobe (alkyl chain) [42]. Surfactants with 0 < P < 1/3 form micelles in aqueous solution. Surfactants with 1/3 < P < 1/2 form wormlike micelles and surfactants with 1/2 < P < 1 display vesicle formation. Controlling the surfactant packing parameter close to 1 (flat surfactant film) promotes strong adsorption and delivers very low-soil/bulk phase equilibrium interfacial tensions. Formation of a surfactant:soil complex. This typically is represented as surfactant coating the soil to be removed either in a monolayer, or, at high enough surfactant concentrations with bilayer structures. During this step surfactant can promote solid soil softening and liquifaction. This is a critical step to promote roll-up or emulsification that takes place only with liquid soils. Desorption of the surfactant:soil complex. For oily soils this occurs either via the classical roll-up mechanism or by solubilization of the oil into micellar surfactant aggregates. In the case of liquid soil, the energy required to remove the soil can be expressed as gow (1+cosq) where gow is the soil/solution interfacial tension and q is the soil/substrate contact angle. For large contact angle (180o) roll-up of the soil occurs. For small contact angles emulsification via low gow is the major mechanism of soil removal. Transport of the surfactant:soil complex away from the surface. In the case of greasy soils that have lower density than the bulk solution, the soil simply floats to the surface. In other cases, mechanical energy or agitation is critical to move the surfactant:soil complex away from the interface. Stabilization of the dispersed soil to prevent redeposition (see Section IV B).

The work, WR, to move soil (o) from the surface (s) to the bulk phase (w) can be directly related to the interfacial tensions of the various interfaces through the following [7]: WR = gsw + gow - gos

(1)

where gsw is the interfacial tension between the surface and bulk phase, gow is the interfacial tension between the soil and the bulk phase, and gos is the interfacial tension between the soil and the surface. From this equation it can be seen that the work required to remove soil from a surface is reduced when the interfacial tensions between the surface and bulk phase and soil and bulk phase are minimized and the interfacial tension of the soil-surface is increased. This is exactly the effect that surfactants have. By adsorbing at the surface, bulk-phase, and soil interfaces surfactant lowers interfacial energies, decreasing the free energy associated with moving the soil from the surface into the bulk phase. Surfactant adsorption causes the surface/bulk phase (gsw ) and soil/bulk phase (gow) interfacial tensions to drop while the interfacial tension between soil and surface (gos) increases thereby facilitating movement of the soil into the bulk phase. One aspect of the above that is often ignored is step one, transport of surfactant to the various interfaces. The presence of monomeric surfactant is critical to rapid transport of surfactant to the interface and rapid lowering of the interfacial tensions (IFT). However, solubilization is dependent on the presence of micelles. As surfactant concentration in solution is raised aggregates (micelles) form and at a certain concentration (critical micelle concentration, CMC) the monomer concentration of surfactant remains constant and addi-



23

tional surfactant resides in micelles. The formation of micelles reduces the capacity of the surfactant to adsorb at the interface and reduce IFT that is critical in step 2. Therefore, there is an optimum CMC that must be achieved in order to optimize steps 1 and 2 above while still allowing efficient solubilization. This optimum is dependent on the nature of the soil being removed, the substrate (hydrophobicity), and the surfactant system used. The mechanism outlined above is generally applicable for oily soils. For particulate soils consideration of the electrostatic and van der Waals forces of attraction between the particle and the surface need to be considered because most particulate dirt and most surfaces tend to be charged due to the presence of surface exposed silicic acid, hydroxyl, or carboxyl groups [43]. . Again, the process can be described in a series of steps [44]. In the first step a soil particle, P, adhering to a surface, S, is removed a distance d with no penetration of liquid between the soil and the surface. The process requires work input, w1, to overcome the van der Waals attraction between P and S. Then detergent solution penetrates the space between P and S, allowing surfactant to adsorb at the solution-particle interface and the surface-solution interface, and a net sum of work, w2 , is obtained. The total work done in this first step is: W1 = w1 - w2

(2)

In the second step the particle is removed from the surface to a distance large enough that there are effectively no forces of interaction between P and S. The work for this second step, W2, is composed of contributions from van der Waals attractions and the electrostatic repulsions between P and S, and is equal to the total potential energy of the system at the distance d such that W2 = -jd and the work done for the total process of removing an adhering particle, P, from surface S is equal to the sum of W1 and W2 or: SW = W1 + W2 = w1 - w2 - jd

(3)

The work, w2, created when surfactant adsorbs onto the particle and the surface can, in the first approximation, be described as the sum of various interfacial energies, similar to Eq. (1): w2 = gsp - gsw - gpw

(4)

where gpw is the interfacial tension between the particle and the solution phase. According to Eq. (3) the removal of particulate soil becomes easier as the total work to remove the particle, SW, becomes smaller. The addition of surfactant reduces both gsw and gpw such that w2 increases, which helps to lower the total work of removal. In addition, the total potential energy of the system jd is the sum of the attractive van der Waals interactions, jd,A, and the repulsive interactions, jd,R, due to surface charges. The adsorption of surfactant, especially anionic surfactant, at the surface-solution and particle-solution interfaces serves to decrease the attractive force and increase the repulsive force thereby promoting removal to a distance where there are no longer any attractive forces between particle and surface. B. Suspension Mechanisms Once material is removed from a surface it must be suspended in the bulk phase to avoid redeposition. For hydrophobic liquid soils in aqueous media, suspension is typically accomplished by entrapment of the soil within the surfactant micelle or vesicle. For particulate soils suspension is often best achieved by adsorption of a charged polymer onto the surface of the particle thereby increasing electrostatic repulsion between particle-


24

Showell

particle and particle-surface interactions. There are two general mechanisms for suspending soil in solution— electrostatic repulsion and steric stabilization. In polar media, most substances will acquire a surface electric charge as a result of ionization of surface chemical groups, ion adsorption, and ion dissolution [16]. In aqueous solutions most surfaces and most soil particles are negatively charged. As a result both soil and surface possess an electrical double layer. The electrical double layer is comprised of a compact layer of ions of opposite charge to the surface and a more diffuse double layer comprised of counter- and co-ions distributed in a diffuse manner in the polar medium. As described in Section IV A, the total potential energy for a system comprised of a particle at some distance, d, from a surface is the sum of the attractive force, jd,A, and the repulsive force jd,R. When two particles of the same net surface charge approach one another, or when a particle approaches a charged surface, they repel each other as their double layers start to overlap. The particles have to overcome this electrical barrier in order to get close enough for van der Waals attraction to take over. When the potential energy barrier jd,R is high particles tend to stay dispersed in the bulk phase. However, if the electrical double layer is compressed by high ionic strength or shielded by adsorption of an organic layer coalescence and aggregation can occur resulting in redeposition of soil particles back onto the surface. Electrostatic repulsion is best achieved in low ionic strength media where the electrical double layer on particles and surfaces is diffuse. An alternative strategy is to adsorb a charged polymer, such as the acrylic acid polymers described in Section II B, or a charged surfactant onto the surface. When particles having adsorbed layers (polymer or surfactant) collide, their adsorbed layers may be compressed without penetrating. This results in reduced configurations available to the adsorbed layer. In thermodynamic terms the reduction in potential configurations is expressed as a decrease in entropy for the system or an increase in free energy. This increased free energy of stabilization results from the “elastic” effect of colliding adsorbed layers and is referred to as steric stabilization. The positive free energy change is related to both the enthalpy and entropy change by DG = DH – TDS. Stabilization can therefore come either as a result of a positive change in enthalpy or a decrease in entropy. A positive DH reflects the release of bound solvent from the polymer chains as they interact and a negative DS results from the loss of configurational freedom of the polymer [16]. Steric stabilizers are usually block copolymers that make up a hydrophobic part (e.g., polyethyleneterepthalate) which attaches to the particle surface and a hydrophilic part (e.g., polyethylene glycol) which trails out into the bulk solution. Effective detergency results when the detergent formulation is designed to maximize four basic properties; penetration, wetting, dispersion, and emulsification. These four factors combined determine the ultimate effectiveness of the detergent formulation. Subsequent chapters of this book provide significantly more detail on how to design effective detergents for a variety of specific applications.

ACKNOWLEDGMENTS I thank each of the authors of the individual chapters in this work for their effort and dedication in bringing the vision to life. Thanks to all of my friends and colleagues at Procter & Gamble who contributed their time and expertise to review and critique of the contributions.



25

REFERENCES 1. 2. 3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19. 20. 21. 22. 23. 24. 25. 26. 27.

INFORM, Vol. 13, pp. 682–695 (September 2002). J. W. B. Gogarty, Petroleum Techn., pp. 1475–1483 (1976). X. Zheng, Y. Xie, L. Zhu, X. Jiang, and A. Yan, Ultrasonics Sonochem., 9(6):311 (2002). R. W. Bassemir, A. Bean, O. Wasilewski, D. Kline, W. Hills, C. Su, I.R. Steel, and W. E. Rusterholz, in: Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 14, 4th ed., New York, Wiley, pp. 482–503 (1995). H. Hendricks and C. Nootens, J. Eur. Coat., 6:710 (2003). T. F. Tadros, Surfactants in Agrochemicals, Vol. 54, Marcel Dekker Surfactant Science Series, New York (1995). L. H. Tan Tai, Formulating Detergents and Personal Care Products, AOCS Press, Champaign, Illinois (2000). Liquid Detergents, Vol. 67, ed. K-Y. Lai, Marcel-Dekker Surfactant Science Series, New York (1997). Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel-Dekker Surfactant Science Series, New York (1998). Nonionic Surfactants, Vols. 1(1967) and 23 (1987), ed. M. J. Schick, Marcel Dekker Surfactant Science Series, New York. Anionic Surfactants: Organic Chemistry, ed. H. W. Stache, Vol. 56, Marcel Dekker Surfactant Science Series, New York (1995 ). Novel Surfactants: Preparation, Applications, and Biodegradability, ed. K. Holmberg, Vol 74, Marcel Dekker Surfactant Science Series (1998). Detergency of Specialty Surfactants, ed. F. E. Friedli, Vol. 98, Marcel Dekker Surfactant Science Series, New York (2001). P. K. Vinson, P. R. Foley, T. A. Cripe, D. S. Connor, and K. W. Willman, U.S. Patent 6,326,348 to The Procter & Gamble Co. (2001). J. B. McClain, D. E. Betts, D. A. Canelas, E. T. Samulski, J. M. DeSimone, J. D. Londono, H. D. Cochran, G. D. Wignall, D. Chillura-Martino, and R. Triolo, Science, 274:2049 (1996). D. J. Shaw, Introduction to Colloid and Surface Chemistry, 3rd ed., Butterworth & Co. Ltd., London (1980). G. Swift in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). (a) A. M. B. Austin, A. M. Carrier, and M. L. Standish, U.S. Patent 5547612 to National Starch and Chemical Investment Holding Corp. (1996); (b) A. M. B. Austin, A. M. Carrier, and M. L. Standish, U.S. Patent 5,698,512 to National Starch and Chemical Investment Holding Corp. (1997); (c) E. Penzel, G. Franzmann, A. Maximilian, J. Pakusch, and B. Schuler, U.S. Patent 5604272 to BASF Aktiengesellschaft (1997); (d) W. Denzinger, A. Kisternmadner, J. Perner, A. Funhoff, B. Potthoff-Karl, and H-J. Raubenheimer, U.S. Patent 5,658,993 to BASF Aktiengesellschaft (1997). A. duVosel, F. Francalanci, and P. Maggiorotti, Eur. Patent Application 454,126-A1 to Montedipe S.r.l. (1991). T. Cassata, U.S. Patent 5,219,986 to Cygnus Corporation (1993). M. Kroner, G. Schornick, W. Denzinger, R. Baur, K. Alexander, B. Potthoff-Karl, V. Schwendemann, German Patent Application DE 4,308,426-A to BASF AG (1993). M. B. Freeman, Am. Oil Chemists Soc. Annual Meeting, San Antonio, Texas (1995). S. W. Heinzman and S. J. Dupont, Eur. Patent 542,496-B1 to The Procter & Gamble Company (1998). S. C. Sikes, L. Ringsdorf, and G. Swift, U.S. Patent 6,495,658 to Folia, Inc. (2002). D. T. Nzudie and C. Collette, U.S. Patent 6,221,957 to Elf Atochem S. A. (2001). (a) K. N. Price, U.S. Patent 6,444,633 B2 to The Procter & Gamble Company (2002); (b) K. N. Price U.S. Patent 6,479,451 B2 to The Procter & Gamble Company (2002). J. V. Boskamp, Eur. Patent Apps. 0358473-A2 and 0358472-A2 to Unilever NV (1990).


26

Showell 28. H.-P. Rieck in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). 29. See, e.g., U.S. Patents 5,132,431; 5,208,340; 5,246,612; 5,279,757; 5,310,934; 5,391,324; 5,415,796; 5,466,825; 5,798,326. 30. C. Wu, Science News Online, August 16, 1997. www.sciencenews.org/pages/sn—arc97 /8—16—97/bob1.htm 31. D. Halvorsen, Minnesota Star Tribune, July 6, 2001. www.greenearthcleaning.com/newsarticles.asp 32. Enzymes in Detergency, Vol. 69, ed. J. H. van Ee, O. Misset, and E. J. Baas, Marcel-Dekker Surfactant Science Series (1997). 33. A. Prins, F. J. G. Boerboom, and H. K. A. I. Vankalsbeeck, in Colloids and Surfaces A: Physiochemical and Engineering Aspects, Vol. 143, Issues 2–3:395 (1998). 34. (a) W. P. Hsu, T. W. Foley, and H. J Haller in U.S. Patent 5,387,425 to Rhone-Poulenc Specialty Chemicals Co. (1995), (b) Y. Ishibashi, T. Kakui, K. Nakatani, and Y. Terano in U.S. Patent 6,080,405 to Suntory Ltd. (2000). 35. C. Kasturi, M. G. Schafer, M. R. Sivik, W. B. Kluesner, and M. W. Scheper in PCT WO9927058 to the Procter & Gamble Co. (1999). 36. E. Gosselink in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). 37. J. Chatterjee, J. Colloids and Surfaces, A:Physiochemical and Engineering Aspects, 204(1–3) (2002). 38. J. R. Campanelli and X. Wang, and J. Coll., Int. Sci., 213:340 (1999). 39. A. Bonfillon, F. Sicoli, and D. Langevin, J. Coll. Int. Sci. 168:497 (1994). 40. Nasr-El-Din, A. Hisham, K. C. Taylor, Colloids and Surfaces, 66(1):23 (1992). 41. A. W. Adamson and A. P. Gast in Physical Chemistry of Surfaces, Wiley-Interscience, p. 33, New York (1997). 42. D. J. Mitchell and B. W. Ninham, J. Chem. Soc. Faraday Trans., 2, 77:601 (1981). 43. H. Schott in Detergency Part I, Vol. 5, eds. W. G. Cutler and R. C. Davis, Marcel Dekker Surfactant Science Series, New York (1972). 44. H. Lange in Detergency Part I, Vol. 5, eds. W. G. Cutler and R. C. Davis, Marcel Dekker Surfactant Science Series, New York (1972).


2 Statistical Mixture Design for Optimization of Detergent Formulations Samir S. Ashrawi and George A. Smith

CONTENTS I. II. III.

Introduction ............................................................................................................ Mixture Design Experiments ................................................................................. Examples of Mixture Design Experiments............................................................ A. Heavy Duty Liquid Detergent Optimization ............................................. B. Light Duty Liquid Detergent Optimization ............................................... C. Detergent Concentrate Robustness Study.................................................. IV. Conclusions ............................................................................................................ References ........................................................................................................................

27 29 31 32 39 45 49 49

I. INTRODUCTION Development of new cleaning formulations can be a very arduous and time-consuming task. The formulator must choose from literally hundreds of raw materials. The individual ingredients must be combined in the proper ratio to obtain the best cost performance while satisfying a myriad of physical property and stability criteria. The formulation must also be robust enough to be produced on a commercial scale with little or no rework required to meet product specifications. Traditionally, formulators of cleaning products have used a trial-and-error approach to arrive at cost-effective, robust formulations. The formulator selects ingredients based on experience, availability, and cost in order to develop an initial starting formulation. The starting formulation is tested against competitive products and the results are analyzed to determine which physical and performance properties need improvement. The formulation is then modified and the process repeated in an iterative fashion until acceptable performance is obtained. It is common to optimize the formulation components one at a time to avoid confounding the response with other variables. 27


28

Ashrawi and Smith

In the trial-and-error approach, component variations are usually fairly small, which limits the composition space that is investigated to small perturbations around the starting formulation. Because responses are optimized one at a time, one is never quite sure that all properties and performance responses have been optimized. Furthermore, one is not sure if the observed optimum is local within the small composition space that was investigated, or global within a much larger composition space. Finally, since this approach does not yield maps of performance over the composition space, it is not possible to predict the behavior of new formulations without continuous tweaking. An alternative, and more informative, approach is the use of statistical experimental design to optimize formulations. We have used various types of statistically designed experiments in our laboratories to help develop and optimize formulations for different applications [1,2]. Factorial screening designs are extremely helpful in identifying the vital factors or components that affect the desired product. Response surface designs are useful in locating the ideal criteria or process settings that yield optimum performance. And finally, mixture designs yield performance maps over a defined composition space, enabling us to discover the optimum formulation and to predict performance in other regions of the defined composition space. Figure 1 describes the framework of our statistical experimental approach to formulation development. Beginning with a well-defined goal of achieving certain performance criteria, physical properties, and cost, we conduct screening experiments to determine the components that would be vital to achieving our goal. Once the trial mixtures are prepared and the desired property or performance response is measured, the results can be analyzed

Goal Definition

Screening Design

Properties

Mixture Design

Performance

Data Analysis

Optimization

Figure 1

Model Generation & Validation

Scenario Analysis

Framework for formulation development using statistical experimental design.


Statistical Mixture Design for Optimization of Detergent Formulations

29

to determine how each component affects a particular response as the amount of that component is changed. Next, we use the components that most affect the measured response to develop a suitable mixture design. The mixture design trial formulations are prepared and the physical properties and performance responses are measured and recorded. A model that best fits the data is then generated and validated by exploring its statistical significance. With a good-fit model, one can then proceed to optimization of the composition to meet the required performance criteria. The authors have used mixture design experiments to optimize different types of cleaning formulations. Examples include laundry liquids, dishwashing liquids, and hard surface cleaners. Many times the results indicate that improvements in one property come at the expense of another. By measuring multiple responses it is possible to optimize the formulation to get the best overall performance for a wide variety of performance factors. Mixture design experiments can also be used to optimize formulation robustness. This allows us to obtain a product that can be easily manufactured on a commercial scale.

II. MIXTURE DESIGN EXPERIMENTS It is not the purpose of this chapter to delve into all the mathematical details of mixture design experiments. Our intent is to present only the major salient points to better understand the basic assumptions behind the technique. For a more complete discussion of statistics as applied to mixture designs, the reader is invited to peruse the pertinent literature [3–5]. In a mixture design experiment, two or more individual ingredients are blended together to produce a final product or formulation. Measurements of the physical properties and the performance for several different trial blends are made and the results used to find the best overall result. The measured properties depend only on the relative proportions of the individual ingredients and not on the total amount present. The defining feature of a mixture design is that the proportions of the ingredients sum to unity. In mathematical terms, if the number of ingredients in the system is given by q, and the proportion of the ith component is given by xi For xi ≥ 0 and i = 1, 2,..., q

(1)

q

∑χ = χ + χ i

1

2

+ ..... + χq = 1

(2)

i =1

Because of the restrictions imposed by Eqs. (1) and (2), the experimental region of interest is a (q-1) dimensional space. For q = 2, the dimensional space is a straight line and can be represented on a conventional x-y plot. For q = 3, the dimensional space is an equilateral triangle and can be represented in triangular coordinates. For q = 4, the dimensional space is a tetrahedron. Since the proportions sum to unity, the xi are constrained variables; varying the proportion of one component will change the proportion of at least one other component in the mixture. In mixture design experiments, the experimental data are defined in a quantitative fashion, the purpose of which is to model the mixture behavior using some form of a mathematical equation. This allows for predictions of the response for any combination of ingredients and allows for a measure of the influence for each component or combination of components on the measured response.


30

Ashrawi and Smith

The data from a mixture design experiment are modeled in the following fashion. Assuming that the response factor η depends only on the proportions of the individual components: η = f (χ1, χ2 ,.....χq )

(3)

We assume that the function is continuous for all χi, and can be represented by a first- or second-order polynomial. Only on rare occasions is a third-degree (cubic) polynomial necessary to represent the data. In actual practice, it is convenient to use a canonical form for the polynomial fitting equation. This acts to reduce the number of fitting parameters compared to a standard power series polynomial expression. Canonical polynomial expressions were developed by Henri Scheffé in the early 1950s specifically for mixture design experiments [6,7]. The Scheffé quadratic polynomial for two components is given by q

η=

∑ i

βi χi +

q

q

i

j

∑∑β χ χ ij

i

j

(4)

The Scheffé form of the fitting equation is also easy to interpret. The coefficients for the main effects βi are responses for the pure components. The coefficients for the mixed terms βij give a measure of positive or negative deviation from the response predicted for ideal mixing of the individual components. Up until this point, we have not discussed the experimental error associated with the measured responses. Experimental error can arise from various sources including sample preparation, analytical methodology, mechanical noise, and equipment problems. In an experimental program consisting of N trials, the observed value of the response in the uth trial is given by yu and is assumed to vary about the mean of η with a common variance σ2. The observed response value contains experimental error εu

( )

( )

yu = η + ε u 1 ≤ u ≤ N

(5)

where the errors are assumed to be independent with a common variance. The Scheffé expression for two components becomes yu = β1χ1 + β2 χ2 + εu

(6)

With N ≥ 2 observations collected on yu, we can obtain the estimates b1 and b2 of the parameters β1 and β2 , respectively. The parameters of Eq. (6) can be replaced by their respective estimates to give the approximating equation yˆ ( x ) = b1χ1 + b2 χ2

(7)

where yˆ ( x ) is the predicted value of η for given values of x1 and x2. The estimated parameters contain the main effects plus any error associated with measurement of the response variables. In practice, the magnitude of error associated with the measured responses can be determined by replicating some of the trial blends. Differences in the response values of the replicate samples are taken as a measure of the experimental error. Lack of fit tests



31

can be used to make certain that the level of noise arising from the experimental error is not greater than the effect one is trying to measure. After the experiments are performed and the data collected, the best-fit parameters given in Eq. (7) are determined using least squares analysis. Initially the fitting parameters are estimated to give a predicted response, which is compared to the measured response. The parameters are then optimized to minimize the sum of squares between the measured and predicted response values. q

Sum of squares =

∑ (y − yˆ ) i

2

(8)

i

1

A variety of optimization methods have been developed for determining the best-fit parameters. For simple, well-defined mixture designs, the fitting parameters can be calculated in closed form. For more complicated designs, multivariable optimization techniques are required. Many of these techniques are based on matrix inversion algorithms. A complete discussion of multivariable optimization methods is beyond the scope of this chapter. For a more complete discussion, the reader is invited to peruse the pertinent literature [8]. In the early days of design of experiments (DOE), determination of the best-fit parameters was a tedious and labor-intensive task. With the advent of the personal computer, the calculations involved in determining the best-fit parameter values for the fitting equation became relatively easy. There are several software packages available for running mixture design experiments, some of which are listed in Table 1. Many of these programs will perform screening designs, response surface designs and mixture designs. The reader is invited to contact the software manufacturers for more details.

III. EXAMPLES OF MIXTURE DESIGN EXPERIMENTS In the last few years, there have been a number of published works using design of experiments to study and optimize detergent formulations. Response surface designs have been used to model the critical micelle concentration (CMC) of ternary surfactant mixtures. Results agree with those obtained using thermodynamic modeling [9]. Mixture design has

Table 1 Commercially Available Design of Experiments (DOE) Software Software Design Expert 6 DoE Fusion JMP 4 Minitab 13 MultiSimplex 2.1 Sirius Stratgrapics Plus


Company Stat-Ease S-Matrix Corp. SAS Institute Inc. Minitab Inc. MultiSimplex AB PRS Manugistics, Inc.

URL www.statease.com www.s-matrix.com www-jmpdiscovery.com www.minitab.com www.multisimplex.com www.prs.no www.statgraphics.com

32

Ashrawi and Smith

been used to optimize the ratio of amphoteric, nonionic, and anionic surfactants in a shampoo formulation. The authors report that the methodology offered the maximum return in terms of information about the interplay of multiple factors at the minimum investment [10]. Mixture design experiments have been used to optimize surfactant blend ratio to obtain low foaming and good detergency at high and low use levels [11]. Mixture design experiments have been used to solve solubilization problems in light-duty liquid detergents [12]. Factorial and mixture design methods have been used to develop solid esterquats and ensure compatibility with other formulation components [13]. A.

Heavy Duty Liquid Detergent Optimization

Mixture designs have been used extensively in our laboratory to help develop and optimize formulations for different cleaning applications. This technique can be used to solve a variety of problems. In some cases, the goal is to optimize the ratio of different formulation components to get the best performance at the lowest formulation cost. In other cases, the goal is to understand the role of different ingredients in a formulation and to identify any interactions or synergies between the components. There are also cases where we are interested in establishing product specifications based on the accuracy to which the manufacturing plant can charge the individual raw materials. Formulation optimization always starts with the goal clearly defined. Key information includes performance criteria, physical property requirements, and finished formulation costs. To illustrate the mixture design approach, we will examine the development of an economical laundry detergent formulation with performance comparable to a leading national brand. Product requirements include performance at a given dose level and finished formulation costs. In developing the formulation, a combination of different surfactants was used, based on single-surfactant screening experiments. Figure 2 shows a schematic factorial screening design using two components, A and B. In this design, one prepares at least five mixtures (dark shaded points) that include the apexes of the composition space and a centroid point. The centroid is duplicated to get a measure of the variation in the measurement. Four more points (light shaded) can be added to determine any curvature in the response of the performance criteria.

Component A

High

Centroid

Low Low

Figure 2

Component B

High

Schematic of a two-component factorial screening design.



33

Once the mixtures are prepared and the desired property or performance response is measured, the results can be plotted in a manner that demonstrates how each component affects that particular response as the amount of that component is changed away from its level at the centroid. This is schematically shown for a four-component screening design, with a response Y, in Fig. 3, where it can be seen that components A and B have opposing effects, while component C has no effect on response Y. For the purpose of our working example, we conducted three screening experiments, each comprising six surfactants. These surfactants included various salts of linear alkylbenzene sulfonate, and a host of nonionic surfactants including different types of amine ethoxylates. All told, we screened 18 surfactants in four families, and selected three components for our next step, the mixture design. These surfactants were a linear alkylbenzene sulfonate (LAS), linear alcohol ethoxylate (LAE), and a polyetheramine ethoxylate (PEA). Linear alkylbenzene sulfonate (LAS) was used because of its relatively low price, good detergency for oily soils and because it provides the formulator the ability to adjust formulation viscosity through the salt effect (14,15). In this study, high 2-phenyl, lowdialkyl tetralin LAS with an average alkyl chain length of 12 was used. The free acid was neutralized with caustic to give the sodium salt (NaLAS). Typically, the high 2-phenyl grades of LAS are used in liquid formulations due to solubility and stability issues [16–18]. An alcohol ethoxylate (AE) was used because it is reasonably inexpensive and shows good performance on greasy soils [19,20]. The properties of AE depend primarily on the alcohol source and the degree of ethoxylation. Oxo alcohols contain both even and odd carbon chain lengths and have 10 to 20% branching in the hydrophobe. Natural and Ziegler alcohols contain only even carbon chain lengths and are relatively linear. In this study, a C12–14 Ziegler alcohol was reacted with 7 Mol of ethylene oxide using a base catalyst (L24–7). Polyetheramine ethoxylates (PEA), a relatively new type of nonionic surfactant, show excellent detergency for dust sebum and help prevent dye transfer in the laundry process [21]. In this study, a C12–14 Ziegler alcohol was reacted with 2 moles of propylene oxide using a base catalyst. The alcohol propoxylate was then reacted with ammonia using

120

D

A

60

C

Response Y

90

30 B 0 −10

−5

0

5

10

Deviation from centroid

Figure 3

Schematic results for a four-component screening design.


34

Ashrawi and Smith

a heterogeneous catalyst to form the primary amine. The amine was reacted with 10 Mol of ethylene oxide. The nominal structure of the resulting material is C 12–14 –2PO–N–10EO(PEA210). To understand the effect of each surfactant on the overall performance and to identify regions of optimum performance, a three-component mixture design was developed. The concentration of each surfactant was varied from 0 to 100%, holding the surfactant actives in the formulation constant at 20%. Each trial blend contained 1% monoethanolamine (MEA) to increase alkalinity and avoid variations in formulation pH as a function of surfactant blend ratio. No dyes, fragrance, or optical brighteners were added to the formulation since we were mainly concerned with the effect of surfactant blend ratio on the cleaning performance. To model the system, an augmented simplex lattice design was used. The dimensional space and the mixture design points covered in this example are shown in Fig. 4. To express the composition of the design points, a ternary diagram is used. The diagram is normalized so that any point on the surface represents 100% surfactant actives. The apices of the triangle correspond to single surfactants, the sides represent binary surfactant mixtures and the interior points correspond to mixtures of all three surfactants. Sufficient mixture points were used to model any interactions between the surfactants. Several of the design points were replicated to determine the experimental uncertainty in the measured response factors. Cleaning performance was determined by washing standard soil swatches in a sixpot Tergtometer (Model 7243ES, Instrument Marketing Services, Inc., Fairfield, New Jersey) under carefully controlled conditions. The wash temperature and water hardness were held constant at 100oF and 150 ppm (Ca+2/Mg+2 = 2/1). This corresponds to standard warm-water wash and average water hardness conditions in the United States [22]. The wash cycle and agitation rate were held constant at 15/5 minutes (wash/rinse) and 100 RPM, respectively. The detergent was charged to each Terg pot by weight. The amount of detergent corresponds to a 1/2 -cup formulation in a conventional top-loading, verticalaxis washing machine

NaLAS (100/0/0)

(50/50/0)

(50/0/50)

(33/33/33)

(0/0/100)

(0/100/0)

L24-7

Figure 4

(0/50/50)

PEA

Heavy duty liquid detergent mixture design space.



35

Cleaning performance was determined for different soil types and fabrics. Soils of interest included dirty motor oil (DMO), dust sebum (synthetic sebum/air conditioner filtrate), EMPA 101 and 104 (olive oil/carbon black, Eldgenossiche Materials Prufings Anstalt, St. Gall, Switzerland) and clay on both cotton and polyester/cotton fabrics. Dust sebum and clay soil swatches were obtained from Testfabrics (Testfabrics, Inc., West Pittston, Pennsylvania). DMO swatches were prepared using spent 10W40 motor oil. Each soil/fabric type combination was run in triplicate and the results were averaged to obtain the measured response data. Soil redeposition was assessed by including clean cotton and polyester/cotton swatches along with the standard soil swatches in the wash. Redeposition swatches were washed three times to determine the effect of multiple wash cycles. The optical reflectance of each soil swatch was measured before and after cleaning using a HunterLab Labscan XE reflectometer (HunterLab, Reston, Virginia). A 1-in.-diameter view port was used to average the reflectance over a wider area of fabric. An in-line ultraviolet (UV) filter was used to suppress any fluorescence effects, which could affect the measured reflectance. The reflectance was measured using the tristimulus L a b scale. The change in measured reflectance was used as a measure of the cleaning performance. For soil detergency, greater differences in reflectance indicate greater amount of soil removed from the fabric. Similarly, for soil redeposition, smaller changes in reflectance indicate smaller amounts of soil deposited on the clean fabric during the washing process. The actual mixture design and cleaning performance data are shown in Table 2. The design consisted of 12 trial formulations, which were run in standard order. The composition of each trial formulation is given as a percentage of the total surfactant in the formulation. The pH and viscosity averaged 11.5 and 27 cP, respectively. No attempt was made to adjust formulation viscosity because all of the detergency samples were charged by weight. The change in reflectance is the average of three different experiments. The raw detergency data was analyzed using Design-Expert 6 software (DesignExpert is a registered trademark of Stat-Ease, Inc., Minneapolis, Minnesota). The program analyzes the raw data using several different statistical models and data transformations to determine the empirical best fit for the data. The empirical best-fit model can be used to determine how each response factor changes as a function of surfactant composition either numerically or graphically. Graphical results can be viewed as a perturbation plot, a contour plot or a three-dimensional response surface. The contour plots generated by the Design-Expert software are shown in Fig. 5. The detergency results for cotton and polyester/cotton blends have been combined to obtain the total cleaning performance. Also included is the formulation cost given in dollars per pound of the finished detergent. For each response variable, a contour plot has been superimposed on the surface of the design space. Three of the responses are best represented using a linear model indicating little interaction between the individual components. The other three responses show interactions between the components and are best represented using a quadratic model. We can now examine each of the responses, one at a time. For dirty motor oil (DMO), cleaning performance on cotton is much better than on polyester/cotton. This is somewhat expected since motor oil is a hydrophobic material which would adhere more strongly to a hydrophobic substrate. A linear model gives the best fit of the experimental data. The cleaning performance increases with increasing concentration of nonionic surfactant and decreases with increasing concentration of NaLAS. L24-7 and PEA210 give about the same level of cleaning performance. For the ubiquitous ground-in clay, the cleaning performance is about the same on either cotton or polyester/cotton. A linear model gives the best representation of the experimental data. Clay detergency increases with increasing concentration of L24-7 in the formulation and decreases with increasing concentration of PEA210. Under alkaline


36

Table 2 Heavy Duty Liquid (HDL) Detergent Mixture Design and Performance Data

RUN ORDER

1 2 3 4 5 6 7 8 9 10 11 12

NaLAS (%)

0.0 100.0 50.0 16.7 66.7 33.3 0.0 50.0 100.0 0.0 16.7 0.0

L24-7 (%)

0.0 0.0 0.0 16.7 16.7 33.3 50.0 50.0 0.0 100.0 66.7 0.0

PEA (%)

VISCOSITY (cps)

pH (as is)

COSTS ($/LB)

REDEP

DUST SEBUM

DMO

OLIVE OIL

CLAY

C

PC

C

PC

C

PC

C

PC

C

PC

100.0 0.0 50.0 66.7 16.7 33.3 50.0 0.0 0.0 0.0 16.7 100.0

8.6 19.0 9.0 6,4 36.8 10.8 10.0 112.0 19.0 68.0 24.6 4.4

11.3 11.9 11.7 11.7 11.8 11.7 11.0 11.8 11.8 10.8 11.4 10.9

0.20 0.09 0.15 0.17 0.12 0.14 0.16 0.10 0.09 0.11 0.13 0.20

-2.0 -1.4 -2.2 -2.2 -1.8 -1.8 -1.9 -1.5 -1.1 -2.2 -2.1 -2.0

-1.1 -15.7 -1.9 -1.3 -1.8 -1.3 -1.2 -1.6 -16.1 -1.0 -1.1 -0.9

25.0 25.2 25.5 25.4 25.6 26.0 26.1 26.6 24.8 26.0 26.2 25.3

9.0 2.0 6.0 7.3 6.2 7.6 9.4 6.0 1.9 7.3 7.4 10.0

15.1 11.0 14.0 14.1 13.8 13.7 15.0 13.9 11.5 14.1 14.4 14.2

15.6 3.4 12.4 13.7 9.8 11.3 14.2 9.8 2.9 11.6 12.3 15.3

15.9 15.9 13.8 15.0 14.1 13.8 16.2 14.0 14.2 14.5 14.2 16.6

24.7 19.6 18.2 21.3 18.7 19.6 22.1 18.7 19.8 21.4 19.5 23.1

12.1 13.9 13.6 12.5 14.1 14.0 13.0 13.4 14.1 14.2 13.2 13.2

13.6 14.5 15.7 15.6 16.4 15.9 15.6 16.0 17.0 20.9 21.5 21.7

AVE STDEV

27.4 32.0

11.5 0.4

0.1 0.0

-1.8 0.3

-3.7 5.7

25.6 0.5

6.7 2.5

13.7 1.3

11.0 4.1

14.9 1.0

20.6 2.0

13.4 0.7

17.0 2.8

Ashrawi and Smith


Statistical Mixture Design for Optimization of Detergent Formulations NaLAS

NaLAS

37

NaLAS

29 0.11 30

Dirty Motor Oil

31

Formulation Costs ($/LB)

Clay 30

33 34 34

L24-7

0.17 0.19 PEA

L24-7

NaLAS

NaLAS −11.6 −9.0

19.8

33.3 32.7 32.5

−4.0 −3.2

Dust Sebum

Olive Oil

24.9 26.6

−1.9

−2.2

27.5

Figure 5

PEA

L24-7

32.7 33.3 34.7

28.9

36.1

−3.2 L24-7

PEA NaLAS

22.4

−6.5 Redeposition

0.15 27

33 PEA

L24-7

0.13

29

32

PEA

L24-7

37.4

38.8 PEA

Heavy duty liquid detergent response contour plots.

conditions, the clay particles carry a negative charge. It appears that the nitrogen atom in the PEA head group acts to neutralize some of this charge, thus reducing the amount of soil removed from the fabric. The concentration of anionic surfactant has little effect on the cleaning performance. There is no interaction observed between the surfactants. For dust sebum detergency, a quadratic model gives the best empirical fit of the experimental data. The cleaning performance on cotton is about the same as on polyester/cotton except at the higher levels of NaLAS, where it is much lower. Overall, cleaning performance increases with increasing concentration of PEA210 in the formulation. We hypothesize that the amine in the surfactant head group forms salts with the fatty acid in the soil, thus improving detergency. The model shows a slight synergy between the anionic (NaLAS) and the nonionic surfactants (L24-7 and PEA210) so that combination of the two gives better performance than either of the two pure surfactants. No interaction is observed between the two nonionic surfactants. For olive oil detergency, a quadratic model gives the best fit of the experimental data. Cleaning performance on polyester/cotton is higher than on cotton. Olive oil detergency increases with increasing concentration of PEA in the formulation. The model shows an antagonism between the anionic (NaLAS) and the nonionics (L24-7 and PEA210). Anionic to nonionic surfactant ratios of 3:1 give the worst cleaning performance. Considering soil redeposition, we find that a quadratic model provides the best fit of the experimental data. Redeposition on polyester/cotton is slightly higher on average than on cotton. Redeposition increases with increasing concentration of NaLAS in the formulation especially on polyester/cotton fabric. This result indicates that NaLAS is relatively poor at keeping soil suspended in the wash liquor after it has been removed form the fabric. There is a significant interaction between NaLAS and the two nonionic surfactants. A nonionic to anionic surfactant ratio of 3 to 1 gives the lowest amount of soil redeposition. © 2006 by Taylor & Francis Group, LLC

38

Ashrawi and Smith

For the cost ($/lb) of the finished formulation, a linear model gives an exact representation of the data. Formulation cost is a calculated value based on the price of the individual components, so it will always be a linear function. The formulation cost increases with increasing concentration of PEA210 since it has the highest raw material cost. The results from the various contour plots illustrate a common difficulty in detergent formulation work. Different types of surfactants are required to clean different types of soils. One of the most difficult tasks facing the formulator is determining the optimum surfactant ratio to achieve the best performance for a variety of different soil types. One of the features of mixture design experiments is the ability to simultaneously optimize each response to find compositions that give the best overall performance. Alternatively, a formulator could choose to favor particular performance criteria in order to support a desired marketing claim. The Design-Expert software provides both numerical and graphical optimization options where the user specifies the response factors and the performance criteria and the program identifies compositions that meet a defined level of performance. Results from a graphical optimization treatment are shown in Fig. 6. In the overlay plot, the darkly shaded area represents compositions that satisfy the defined performance criteria. The results from the optimization show that the best overall cleaning performance is obtained with mixtures that are rich in L24-7. The optimum ratio of L24-7 to PEA 210 is around 3:1. The model shows that only a small amount of LAS is needed to get the overall best performance. The size of the optimized region gives an indication of product robustness. In general, the larger the size of the optimized region, the more robust the formulation will be to small changes in product composition. While only a small amount of NaLAS was needed to optimize cleaning performance, the amount of NaLAS, in actual practice, needs to be at least 10% in order to provide viscosity building through the salt effect. This could have been demonstrated by including salt as a component in the mixture design experiments.

NaLAS

DMO REDEP Dust Sebum Clay $/LB Olive Oil

L24-7

PEA Overlay Plot

Figure 6

Heavy duty liquid detergent graphical optimization plot.



39

The optimization procedure is completely general. An unlimited number of response factors can be optimized. We can combine different types of response factors including performance, physical properties, and cost to arrive at the optimum formulation. Often several iterations of mixture designs are used. A broad design is used to identify the general composition; a second design then focuses on this region to elucidate the fine details of the optimized region. To help validate the model and compare performance to a commercial laundry detergent, a dose-response experiment was performed on the optimized HDL formulation. In this experiment, the ratio of surfactants was held constant and the total actives was varied from 5 to 30%. The cleaning performance as a function of surfactant actives was determined in the Terg pot along with a commercial HDL formulation of known surfactant actives. The total detergency for each sample was determined by summing the change in reflectance over each soil and fabric type. The dose-response curve is shown in Fig. 7. The solid points represent the total detergency scores for the optimized HDL formulation at five different actives levels. The star represents the performance of the commercial HDL. Because the commercial HDL gives lower performance than the optimized HDL, it is possible to get better performance at equal surfactant actives. Alternatively, it is possible to get equal cleaning performance at lower surfactant actives, which results in a raw material cost savings. B. Light Duty Liquid Detergent Optimization Another example of the usefulness of mixture design techniques is the formulation of a light duty liquid detergent (LDL). Our goal is to develop a high-active, premium liquid dish product with the lowest formulation cost possible. In this example, we look at using a combination of alkyl ether sulfate (AES), linear alkylbenzene sulfonate (LAS), linear alcohol ethoxylate (LAE), and fatty acid monoethanolamide (FAMA). Performance factors of interest include the total amount of foam, the persistence of the foam under a soil load, soil emulsification, and the formulation cost. Before we discuss the mixture design, we need to say a few words about surfactant selection. In this work, the sodium salt of a 3-mole ether sulfate based on C12–14 Ziegler fatty alcohol was used. The 30% active grade was used to avoid handling issues associated with the high-viscosity paste. In general, AES surfactants show good detergency, generate a large amount of foam and are relatively mild to the skin [23]. The latter is especially true when the ether sulfate is partially neutralized with magnesium. The magnesium salt is also more surface active than the sodium salt which results in better soil emulsification and cleaning performance [24].

Total Detergency

120 110 L24-7 = 70% PEA = 20% NaLAS = 10%

100 90 0%

10%

20%

30%

Surfactant Actives

Figure 7

Optimized heavy duty liquid detergent dose-response curve.


40

Ashrawi and Smith

Linear alkylbenzene sulfonate (LAS) was used because it is inexpensive, is a moderate foamer and shows good detergency for oily types of soils. For this study, the triethanolamine (TEA) salt of a low 2-phenyl, low-tetralin LAS was used. While low 2phenyl LAS is not commonly used in liquid formulations, addition of a hydrotrope will increase its solubility. Propylene glycol and denatured alcohol are commonly used as hydrotropes in LDL formulations. LAS will also interact with calcium or magnesium ions to increase mildness and surface activity [25]. Linear alcohol ethoxylate (LAE) was used because it is inexpensive and shows good cleaning performance for greasy soils commonly encountered in hand dishwashing. In this work, a C12–14 Ziegler fatty alcohol was reacted with 7 Mol of ethylene oxide using a base catalyst. The structure of the material was confirmed using hydroxyl number titration and supercritical fluid chromatography. Fatty acid monoethanolamide (FAMA) was used as a foam booster. Foam boosters are known to improve the performance of LDL formulations by increasing foam volume and stabilizing the foam in the presence of food soils [26]. In this work, the C12–14 coconut fatty acid was reacted with monoethanolamine under dehydrating conditions. To reduce the melting point of the MEA amide and improve its handling characteristics, the reaction product was dissolved in an aqueous solution of sodium xylene sulfonate (SXS) to give a low-melting, 40%-active mixture. Until recently, it was common to use diethanolamine (DEA) amides in this type of formulation. DEA amides are liquid products whereas the MEA amides are hard waxy solids at room temperature. Concerns with nitrosamine formation in the DEA amides have largely limited their use in applications that require human contact [27]. Foam is one of the main performance criteria for an LDL formulation. Consumers equate foam and foam persistence with cleaning performance. So, more is always better. To produce large amounts of persistent foam, the formulation should be rich in anionic surfactant. Rather than look at the entire dimensional mixture space as we did in the case of the HDL, we concentrate on anionic-rich compositions and constrain the variables as shown in Table 3. AES and LAS were varied from 0 to 100% of the surfactant actives while the nonionics were limited from 0 to 20%. Because some of the components are constrained, a d-optimal mixture design was used. Each of the 16 trial formulations was prepared holding the total surfactant actives constant at 30%. To increase the solubility of the LAS and FAMA, 5% SD3A alcohol was added to each of the formulations. The amount of TEA in each formulation varied with the amount of LAS. In general, each formulation was prepared with sufficient TEA to give a pH in the range of 6 to 7. The amount of water in each formulation was varied to give 30%-active surfactant. The trial formulations were run in the standard order as randomized by the software. Several of the formulations were replicated to assess the degree of experimental error associated with measurement of the response factors. A number of response factors were examined including initial foam, foam under soil load, soil emulsification, and formulation costs. The initial foam was determined by diluting the concentrated samples to 0.2% surfactant active in 150 ppm hard water (Ca+2/Mg+2 = 2/1) and mixing the solution in a commercial Waring blender for 10 sec. Under the resulting high-shear conditions, a large amount of foam was generated. The contents of the Waring blender were then transferred to a 1000-ml graduated cylinder and the foam height measured. Since we are working with four formulation variables, it is not possible to view the entire response surface. The analyzed results for the mixture design model are most easily visualized using a perturbation plot. The perturbation plot in Fig. 8 shows how the initial foam changes as the concentration of each surfactant moves from the chosen reference


Light Duty Liquid (LDL) Detergent Mixture Design and Performance Data

RUN ORDER

AES (%)

LAS (%)

LAE (%)

FAMA (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0 0 20 0 45 0 30 0 70 60 80 100 0 20 50 45

80 80 60 60 45 80 30 80 0 20 0 0 100 50 20 45

10 0 15 20 10 0 20 20 20 5 0 0 0 15 15 0

10 20 5 20 0 20 20 0 10 15 20 0 0 15 15 10 AVE STDEV

TERGE (GMS SOIL0

INITIAL FOAM (ML)

FOAM WIHT SOIL (ML)

COSTS $/LB

30 35 30 39 30 25 34 18 28 39 30 30 16 35 37 30

400 425 425 320 500 460 375 420 475 500 575 600 500 425 450 450

225 225 240 230 275 225 240 240 300 275 310 340 290 250 240 280

0.173 0.191 0.182 0.186 0.198 0.191 0.213 0.156 0.234 0.236 0.263 0.250 0.160 0.198 0.225 0.216

30.3 6.5

456.3 70.0

261.6 35.1

0.2 0.0


Table 3

41


42

Ashrawi and Smith

A

600

530

B

Initial Foam

D

B

460

390

C

A

320 −0.417

−0.167

0.083

0.333

0.583

Deviation from Reference Blend Actual Components A: AES = 41.67 C: LAE = 8.33 B: LAS = 41.67 D: FAMA = 8.33

Figure 8

Liquid duty liquid detergent initial foam height perturbation plot.

point, while holding all other factors constant. By default, the software sets the reference point at the center of the design space but it is possible to view the results from any reference point within the design space. This is useful in determining the robustness of a formulation if the reference point is set at the optimized composition. Taking AES as an example, as we change the concentration of AES in the reference blend, the foam height varies from 400 to 600 ml. Overall, increasing the concentration of AES increases the foam height. This is the major effect in the model. As we change the concentration of LAS from the reference point, there is little change in the foam height. Increasing the concentration of either LAE or FAMA decreases the initial foam height. Using the perturbation plot as a tool to determine which components have the most effect on the measured response, it is possible to construct contour plots for slices of the response surface. Contour plots for a number of different response factors are shown in Fig. 9. The initial foam height ranges from 325 to 600 ml. A quadratic model best represents the initial foam data. The initial foam increases with increasing concentration of AES and decreases with increasing concentration of LAS. There is a slight antagonism between the foam booster and the anionic surfactants. Intermediate levels of FAMA give slightly lower foam heights. For perception reasons, a light duty liquid detergent must maintain foam in the presence of food soils. To study the effectiveness of different surfactants in the formulation, we examined foam in the presence of an artificial soil using a 0.2%-active solution prepared in 150 ppm hard water (Ca+2/Mg+2 = 2/1). Two grams of an artificial soil consisting of 12.5% egg powder, 37.5% vegetable shortening, and 50% 150 ppm hard water were added



43

AES

AES

306

527 492

Foam under Soil Load

Initial Foam

291

457 275 260 431 245

LAS

FAMA

FAMA

LAS

AES

AES 34

Formulation Costs ($/lb)

32

Soil Emulsification

0.2407 0.2262

29 0.2117

26

0.1972 23

LAS

Figure 9

0.1828

FAMA

LAS

FAMA

Light duty liquid detergent response contour plots.

to each solution and mixed for 10 sec in the Waring blender. With the addition of soil, the foam height was reduced to about half of the initial value. Foam height increased with increasing AES and decreased with increasing concentration of LAS. The foam height in the presence of soil decreased slightly with increasing concentration of FAMA. We also examined soil emulsification using the six-pot Tergtometer holding the temperature and water hardness constant at 110oF and 150 ppm (Ca+2/Mg+2 = 2/1). In the soil emulsification test, we determine the amount of soil required to dissipate a known volume of foam. Each of the trial formulations is diluted to 0.2% active surfactant, charged to a Terg pot, and suds are generated using a paddle impeller. To each Terg pot is pipetted 1 gram of artificial soil, every minute, until the suds dissipate. The grams of soil required to completely break the foam are recorded. The soil emulsification response shows a different trend than that observed for foam height. The amount of soil emulsified increased with increasing concentration of FAMA. The increase is greater for mixtures that are rich in AES. These results are quite informative. They help us understand the role of different surfactants in the formulation. The foam test measures the total volume of foam while the soil emulsification test measures the amount of soil required to completely break the foam. Anionic surfactants are responsible for producing large amounts of foam. AES produces more foam than LAS and the foam is more persistent under soil load. Nonionic surfactants are responsible for emulsifying soil and stabilizing the foam produced by the anionic surfactants in the formulation. FAMA is more effective than LAE at stabilizing the foam. To complete the mixture optimization, we examined the relative formulation costs. The cost of each formulation was calculated using surfactant raw material costs and the


44

Ashrawi and Smith AES Initial Foam

Foam with Soil

Terge

Initial Foam

LAS

FAMA Overlay Plot LAE = 0

Figure 10

Light duty liquid detergent graphical optimization plot.

concentration in each trial formulation. The formulation costs increase most with increasing concentration of AES. This is not surprising since AES is the most expensive surfactant in the formulation. Formulation costs decrease with increasing concentration of LAS. LAE and FAMA do not have a large effect on the overall formulation cost since both surfactants were used at relatively low levels in the mixture. These results are similar to those observed for the HDL formulation. Performance increases with increasing concentration of AES but so do the formulation costs. To obtain the best cost performance, the response models can be optimized simultaneously as before. Results for this treatment are shown in Fig. 10. The optimization treatment shows LAE does little to increase performance. The results also indicate that it is not possible to obtain the optimum performance at the minimum formulation costs. Using performance as the main criteria, the optimum formulation is obtained for compositions rich in AES using FAMA as a foam stabilizer. To determine the amount of LAS which could be added before performance decreases dramatically and to validate the optimized formulation, experiments were performed varying the concentration of AES and LAS, holding the amount of FAMA constant. Results are given in Fig. 11. The initial foam decreases with increasing concentration of LAS in the formulation. At low levels of LAS, the foam height decreases only slightly. Above 40% LAS, the foam height decreases rapidly with increasing concentration. The inflection point represents the highest level of LAS, and the lowest formulation cost, before performance starts to fall off rapidly.



LAS + AES = 90% FAMA = 10% LAE = 0%

500

Foam Height (ml)

45

400

300

200

0

20

40

60

80

100

Percent LAS (LAS + AES = 100)

Figure 11

Optimized light duty liquid detergent initial foam plot.

C. Detergent Concentrate Robustness Study One last example involves the manufacture of a concentrated detergent blend developed for use in a heavy duty liquid (HDL) detergent. By preblending the ingredients, the customer avoids having to inventory and store separate components. Preblending also results in shorter production times since only one component must be charged versus many. To avoid shipping water, the concentration of the blend should be as high as possible. In this case, the blend contained 20% water to prevent the product from stratifying in the customer’s storage tanks. The composition of the blend was optimized using mixture design experiments as shown in previous examples. In order to manufacture the blend consistently, we must determine how small changes in the composition affect the physical properties. This information allows us to determine the amount of variability we can expect in the finished product and provides information on how best to correct production batches to meet product specifications. The blend is composed of the six components given in Table 4. Nonylphenol ethoxylate with 9.5 Mol of ethylene oxide (N-95) is the main component of the blend. In general, nonylphenol ethoxylates are excellent detergents due to their low cost, ease of handling, and good cleaning performance [28]. Linear alkylbenzene sulfonate (LAS) is used as the main anionic surfactant. Again we used a low 2-phenyl, low-tetralin grade with an average carbon chain length of 13. Tallowamine ethoxylate with 15 Mol of ethylene oxide (T-15) is used as a secondary nonionic surfactant. T-15 has properties similar to the polyetheramine surfactant described previously [29]. Because the nitrogen atom in the surfactant head group is basic, T-15 acts to neutralize some of the LAS in the formulation. On a molar basis, the amount of T-15 is insufficient to neutralize all of the LAS so MEA is used to fully neutralize the LAS in the formulation. Polyethylene glycol with a molecular weight of 300 (PEG 300) is added to reduce formulation viscosity and to prevent gel phase formation when the blend is diluted down to use concentration. Water is added to reduce blend viscosity and prevent stratification of the blend in storage. Because we are interested in how changes in the blend ratio affect the physical properties, all of the component ranges were constrained. The blend has six components,


Table 4

Concentrated Detergent Blend Mixture Design and Physical Properties MEA (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

15.4 15.4 17.2 15.4 19.4 15.4 19.4 19.4 19.4 17.2 19.4 19.4 17.4 19.4 15.4 15.4 19.4 15.4 15.4 15.4 19.4 19.4 17.4 15.4 18.5 19.4 17.6

2.2 2.2 2.6 2.6 2.2 2.2 2.2 2.4 2.6 2.6 2.6 2.2 2.4 2.2 2.6 2.2 2.2 2.6 2.2 2.2 2.4 2.4 2.4 2.6 2.2 2.6 2.2

PEG 300 (%)

T-15 (%)

N-9.5 (%)

WATER (%)

ACIDITY (meq/gm)

pH (1%)

SOLIDS (%)

8.1 10.0 10.0 10.0 8.2 10.0 6.0 8.0 7.9 10.0 6.0 6.0 6.0 8.1 6.0 8.2 6.0 7.8 6.0 10.0 10.0 6.0 8.0 7.8 10.0 7.8 6.0

17.5 19.4 15.4 15.4 19.4 17.6 17.5 15.4 15.4 19.4 19.4 17.6 15.4 17.5 17.2 15.4 15.4 19.4 19.4 19.4 17.4 19.4 17.4 19.4 15.4 15.4 19.4

36.8 35.0 36.8 34.6 32.8 32.8 34.9 36.8 34.7 32.8 34.6 32.8 36.8 34.9 36.8 36.8 36.8 32.8 35.0 35.0 32.8 32.8 34.8 36.8 32.8 32.8 36.8

20.1 18.0 18.0 22.0 18.0 22.0 20.1 18.0 19.9 18.0 18.0 22.0 22.0 18.0 22.0 22.0 20,2 22.0 22.0 18.0 18.0 20.0 20.0 18.0 21.1 22.0 18.0

0.48 0.49 0.55 0.49 0.62 0.49 0.62 0.62 1.32 0.55 0.61 0.62 0.55 0.62 0.49 0.49 0.61 0.49 0.49 0.49 0.62 0.62 0.55 0.49 0.58 0.62 0.56

8.9 8.9 8.6 9.0 3.5 8.7 3.4 3.5 4.0 8.9 8.0 3.5 7.9 3.4 9.0 8.5 3.3 9.1 8.8 8.8 3.5 4.2 8.4 9.1 3.5 4.1 7.5

78.0 82.0 82.0 78.0 82.0 78.0 80.0 82.0 80.0 82.0 82.0 78.0 78.0 81.0 78.0 78.0 79.0 77.0 78.0 82.0 82.0 80.0 80.0 82.0 79.0 78.0 82.0

AVE STDEV


0.58 0.2

6.6 2.5

79.9 1.8

VISCOSITY (gm/ml)

577 497 460 428 550 526 11300 589 577 442 561 12900 3860 580 515 538 10760 578 563 504 532 10900 579 532 580 5880 548

2475 4013

DENSITY (gm/ml)

COLOR (GARDNER)

1.0646 1.0668 1.0678 1.0663 1.0665 1.0660 1.0650 1.0668 1.0658 1.0663 1.0650 1.0609 1.0642 1.0648 1.0630 1.0654 1.0663 1.0628 1.0629 1.0669 1.0679 1.0634 1.0658 1.0610 1.0593 1.0612 1.0630

5 5 4 4 4 4 3 3 3 5 5 3 4 3 4 4 3 5 5 5 3 4 5 5 3 4 5

1.065 0.002

4.1 0.8

Ashrawi and Smith

LAS (%)

46

RUN ORDER


47

which requires 27 trial formulations using a d-optimal mixture design. In general, the constraints are based on the accuracy to which the plant can charge individual components. For N-95 LAS, PEG 300, T-15, and water, the constraint is ±2 weight percent using load cells to charge the mixing vessel. For MEA, the constraint was ±0.2 weight percent using a micro-motion flow controller. Each of the 27 trial formulations was prepared and the physical properties measured. Physical property responses included acidity, pH, nonvolatiles, viscosity, and color. Because we have six components it is impossible to view the response surface for this design. To determine which variables are important, we use perturbation plots. For pH of the blend, the main factors are LAS, MEA, and T-15. Since LAS is a strong acid, whereas MEA and T-15 are weak bases, this is not unexpected. The contour plot for pH with respect to the three main components is given in Fig. 12. The pH varies from 3.5 to 9 depending on the ratio of the three components. MEA is more effective at increasing pH than T-15 since it has a lower molecular weight and is a stronger base. Formulation nonvolatiles were measured using a moisture balance (Denver Instruments, Arvada, CO) at 140oC. Solids varied from 77 to 82% depending to a large extent on the amount of water in the formulation. Surprisingly, the ratio of MEA to LAS also has a small effect. Formation of the MEA/LAS salt reduces the volatility of MEA and increases the measured solids. The color of each trial formulation was measured with a HunterLab ColorQUEST II spectrophotometer (HunterLab, Reston, Virginia) using the Gardner scale. The color of the blend varies from 3 to 5 depending on the amount of LAS, MEA, and T-15 in the mixture. The color increases most with the amount of T-15 in the mixture, in general,

LAS Acid

LAS Acid 4.9

81.6

Solids pH (1%)

79.8

6.8

Color (gardner) LAS Acid = 19.6

7.8

PEG 300 = 8 N-9.5 = 34.8 WATER = 20 MEA

79.3

3.3

8.7

T-15

PEG 300 = 8 T-15 = 17.4 N-9.5 = 34.8

3.7 3.9

LAS Acid

78.7

MEA

4.1

Water LAS Acid

Viscosity (cps)

MEA = 2.4 T-15 = 17.4 N-9.5 = 34.8

80.9

5.9

4.3

PEG 300 = 8 N-9.5 = 34.8 Water = 20

7531 5854 4178 2502

Acidity (meq/gm)

4.5 4.9

0.67 0.63 0.59

MEA = 6.4

T-15 = 19.6

826 0.55 826

PEG 300 = 8 N-9.5 = 34.8 Water = 20

2502

Water

PEG 300 MEA

Figure 12

Concentrated detergent blend response contour plots.


0.52

T-15

48

Ashrawi and Smith

Table 5 Optimized Concentrated Detergent Product Specifications Specifications pH, 1% SOLUTION SOLIDS (%) VISCOSITY (cps @ RT) LVT#2 @ 30 RPM ---COMPOSITION, WT%

C C C

LOADING MEASURE

Min

Max

Target

7.5 77 1

9.5 82 1000

8.5 80 575

Min

Max

Typical 0–1 3–7

C

LAS ACID MEA POGOL 300 SURFONIC T-15 SURFONIC N-95 WATER TYPI

Additional Information: ACID VALUE (meq/gm) COLOR, GARDNER, PT-CO APPEARANCE

CLEAR, AMBER LIQUID

tallowamine ethoxylates tend to be amber in color so this is not too surprising. The color decreases with increasing concentration of LAS but also depends on the amount of MEA in the mixture. It appears that the color of the LAS increases with increasing level of neutralization. The viscosity of each trial formulation was measured with a Brookfield LVT viscometer using a #2 LVT spindle (Brookfield Engineering Laboratories, Middleboro, MA) at 25oC. The viscosity varies from 440 to 13,000 cP depending primarily on the amount of LAS, water, and PEG 300 in the mixture. In general, viscosity increases with increasing concentration of LAS and decreases with increasing concentration of water and PEG 300 in the mixture. PEG 300 is more effective at reducing the viscosity than water. There is a slight interaction between LAS and PEG 300, which acts to further reduce viscosity at intermediate levels of both components. Acidity was determined by titration of each trial formulation with a strong base. The acidity of the blend provides a consistency check that the acidic (LAS) and basic (T15 and MEA) components of the blend are present in the correct ratio. Acidity increases with increasing concentration of LAS and decreases with increasing concentration of MEA and T-15. This response is very nearly the same as pH. MEA is more effective at decreasing acidity that T-15 because of its lower molecular weight. The results for each of the models are used to set product specification ranges. These must be wide enough to account for small changes in the ratio of the different components. In addition, the model provides a tool for manufacturing personnel to use in adjusting production batches to meet specifications. The proposed manufacturing specifications are given in Table 5. The pH, solids and viscosity are all primary product specifications along



49

with the loading measure for each component. All of these properties appear on the certificate of analysis. Additional tests which are measured but not reported include acidity, color and appearance of the blend. The specification range for each property was set wide enough to cover the variability seen in the mixture design.

IV. CONCLUSIONS Experimental mixture design can be used to optimize detergent cleaning formulations. The method is simple, fast, and greatly reduces the amount of work required to optimize detergent formulations. The results can be used to predict behavior for mixtures within the design space. Mixture design experiments can also be used to determine the robustness of a formulation prior to scale-up and manufacture. Setting appropriate specification ranges to cover the variability observed from small changes in the mixture ratios can reduce cycle times in the manufacturing of the product. The information from the robustness study can also be used to adjust batches as needed to meet the product specifications.

REFERENCES 1. SS Ashrawi, GA Smith. Use of experimental mixture design to optimize cleaning formulations. Proceeding of the 5th World Surfactants Congress, Florence, Italy, 2000, pp. 1253–1261. 2. SS Ashrawi, CM Elsik, HM Stridde, GA Smith. Strategies for agricultural formulations: a statistical design approach. In: Pesticide Formulations and Application Systems: A New Century for Agicultural Formulations, Vol. 21, ASTM STP 1414, JC Mueninghoff, AK Viets, and RA Downer, Eds., American Society for Testing and Materials, West Conshohocken, PA, 2001. 3. J Cornell. In: S. Ghosh, Ed. Statistical Design and Analysis of Industrial Experiments. New York: Marcel Dekker, 1990, pp. 175–209. 4. J Cornell. Experiments with Mixtures: Designs, Models, and the Analysis of Mixture Data. New York: John Wiley & Sons, 1981. 5. GEP Box, WG Hunter, JS Hunter. Statistics for Experimenters. New York: John Wiley & Sons, 1978. 6. H Scheffé. J Royal Statist Soc B 20:344–360, 1958. 7. H Scheffé. J Royal Statist Soc B 25:235–263, 1963. 8. PR Adby, MAH Dempster. Introduction to Optimization Methods. London: Chapman and Hall, 1974. 9. J Coret, A Shiloach, P Berger, D Blankschtein. J Surfactants Deterg 2(1): pp 51–58, 1999. 10. G Marti-Mestres, F Nielloud, R Marti, H Maillols. Drug Dev Ind Pharm 23(10): 993–998, 1997. 11. C Verite. Utilization of the simplex experimental design for optimization of a low foaming household detergent. Phys Chem Snwendungstech Grenzflaechenaktiven Stoffe Int Kongr, 1973, pp 203–212. 12. JP Narcy, J Renaud. J Am Chem Soc 49:598–608, 1972. 13. R Pi. Comun Horn Com Esp Deterg 25: pp 267-279, 1994. 14. JC Drozd, W Gorman. J Am Oil Chem Soc 65: 398–404, 1988. 15. KL Matheson, TP Matson. J Am Oil Chem Soc 69: 1693–1609, 1983. 16. DL Smith. J Am Oil Chem Soc 74: 837–845, 1997. 17. L Cohen, R Vergara, A Moreno, JL Berna. J Am Oil Chem Soc 72: 115–122, 1995. 18. MF Cox, DL Smith. Inform 8: 19–24, 1997.


50

Ashrawi and Smith 19. MJ Schick. In: MJ Schick, ed. Nonionic Surfactants: Physical Chemistry. New York: Marcel Dekker, 1987, pp. 753–833. 20. MF Cox. J Am Chem Soc 66: 367–371, 1989. 21. E Garcia, R Smadi, GA Smith. Physical chemical characterization of ethoxylated polyetheramine surfactants. Proceedings of the 5th World Surfactant Congress, Florence, Italy, 2000, pp. 1341–1348. 22. ASTM D-459, West Conshohocken, Pennsylvania. 23. MF Cox. J Am Oil Chem Soc 66: 1637–1646, 1989. 24. MJ Schwuger. J Am Chem Soc 59: 265, 1982. 25. L Cohen, A Moreno, JL Berna. Tenside Surf Det 35: 265–269, 1998. 26. FE Friedli. In: JM Richmond, Ed. Cationic Surfactants: Organic Chemistry. New York: Marcel Dekker, 1990, pp. 51–99. 27. HM Fishman. HAPPI 45, April 2001. 28. KW Dillan, ED Goddard, DA McKenzie. J Am Chem Soc 57: 230–237, 1980. 29. A Shoaib. HAPPI 67–72, February 1997.


3 Laundry Detergent Formulations Randall A. Watson

CONTENTS I.

II. III.

IV.

V.

Introduction ............................................................................................................. 52 A. Scope of Chapter......................................................................................... 52 B. Why Different Forms? ................................................................................ 52 Unifying Formulation Concepts.............................................................................. 54 Typical Laundry Detergent Ingredients .................................................................. 56 A. Surfactants ................................................................................................... 56 1. Anionic Surfactants ............................................................................... 56 2. Nonionic Surfactants ............................................................................. 56 3. Cationic Surfactants............................................................................... 58 4. Others..................................................................................................... 58 B. Builders........................................................................................................ 58 C. Polymers ...................................................................................................... 59 D. Enzymes ...................................................................................................... 61 E. Bleach .......................................................................................................... 62 F. Chelating Agents ......................................................................................... 63 G. Perfumes ...................................................................................................... 63 H. “Minors” ...................................................................................................... 65 Heavy Duty Granules.............................................................................................. 66 A. Phosphate vs. Nil-Phosphate....................................................................... 67 B. Low Density vs. High Density ................................................................... 69 C. Machine Wash vs. Handwash ..................................................................... 70 Heavy Duty Liquids ................................................................................................ 71 A. Isotropic Liquids ......................................................................................... 71 B. Structured Liquids ....................................................................................... 76 C. Bleach-Containing Liquids ......................................................................... 79 D. Dual-Bottle Liquids..................................................................................... 81

51


52

Watson

VI.

Unit Dose Detergents............................................................................................. 82 A. Tablets.......................................................................................................... 82 B. Liqui-Tabs.................................................................................................... 87 C. Sheets........................................................................................................... 89 VII. Laundry Bars ........................................................................................................... 90 VIII. Specialty Detergents................................................................................................ 93 A. Care Formulas ............................................................................................. 94 B. 2-in-1 Detergents......................................................................................... 96 IX. Summary.................................................................................................................. 99 Acknowledgments........................................................................................................... 100 References ....................................................................................................................... 100

I. INTRODUCTION A. Scope of Chapter A chapter on laundry detergent formulations would have been significantly shorter and less complex a few decades ago. It wasn’t so long ago that the same basic detergent was used for clothes, dishes, floors, and even the body! In the search for ever better cleaning and value, and larger market shares, there has been an incredible multiplication of laundry detergents. Not all of the forms and formulations are available or relevant in every market. Nonetheless, today in most markets the choices presented to consumers in the laundry detergent section of their local store is nothing short of bewildering. Likewise, the number of choices and demands faced by the detergent formulator continues to grow. This chapter is designed to first present the logic behind the plethora of laundry detergent forms and formulations. Despite the growing diversity of forms and formulas, the underlying chemistry and general concepts remain essentially unchanged. A brief discussion of the key unifying formulation concepts is therefore presented, along with a brief description of the key ingredients used in these formulations. The bulk of this chapter is devoted to discussion and examples of each of the key laundry detergent forms available today. Some general conclusions and discussion of future trends closes the chapter. The reader will appreciate that each of the topics covered in this chapter could be, and in many cases are, the subject of entire chapters or books in and of themselves. As such, it is not the aim of this chapter to provide an exhaustive discussion of each topic. Rather, it is intended to provide an overview of the many different products and product forms that fall generally under the heading of “home laundry detergent.” For those looking for still more details, the references will direct them to more in-depth reviews. B. Why Different Forms? The number of different laundry products and types available today is nothing short of remarkable. So is the level of effort from the large number of different formulators in different companies around the world. On one level the reason for this is clear. Consumers have become more demanding and more discriminating in their purchases of all types of consumer goods. They are also looking for more and more customization. “One size fits all” no longer works in much of the world. These trends are also reflected in laundry products. As companies have responded to these new consumer demands they have also realized that the company who best meets their needs can reap rich rewards. Why there should be so many different formulas and forms is perhaps less obvious, though for most there are equally clear answers. These answers are usually related to differences in con-


Laundry Detergent Formulations

53

sumer habits and wash conditions, differences in the targeted benefits, and differences in consumer preferences. Different laundry habits and conditions are the most obvious reasons for different laundry formulations. Wash conditions range in concentration from several thousand ppm of detergent in the typical European front-loading washing machine, to only a few hundred ppm in Japanese machines. These same two countries also illustrate the extremes in wash temperatures. Though the average washing temperature is falling everywhere in the world due to energy and environmental concerns, the typical front loading machine still includes a boil-wash cycle. On the other hand, in Japan and several others countries consumers often use ambient wash-water temperatures, meaning that in the winter the wash can be as low as 2°C. Add onto these variations the differences in wash/rinse times—where in a U.S. top-loading machine it can be as short as 12 minutes and in a European front loader as long as almost 2 hours—and one can easily see the challenge. Of course many consumers in the world don’t even use washing machines. When considering the various ways that handwash laundry is executed around the world the variables multiply even more. One of the more interesting variables the formulator encounters in handwash laundry is the reuse of the laundry liquor for more than one load. This is done both to conserve often-precious water supplies, and to stretch the value of their detergent purchase. In this situation consumers often start with a load of whites and then reuse the wash solution for one or more loads of their colored or more delicate items. Providing good performance throughout this habit is extremely challenging. Also, hand washers can spend several hours each week with their hands immersed in laundry liquors. Hand skin mildness is therefore another concern largely absent from machine wash geographies. Even within a given laundry habit, a single detergent formulation that can work for all clothes under all conditions remains unobtainable. The same formulation that delivers superior dingy cleaning and whiteness can result in unacceptable fading of colored garments. In a similar vein, formulas containing protease enzymes provide superior stain removal, but can prove disastrous when used to wash fine wool or silk garments. For formulas that deliver through-the-wash softening via clay, the challenge is to provide acceptable base cleaning while still depositing enough softening clay for a benefit. These are just a few of the many dichotomous challenges faced by the formulator. The result is a number of detergents formulated specifically against targets such as softness, delicate care items, brightly colored items, etc.

Table 1

Average Global Machine Wash Conditions

Wash water volume (L) Washing Time (min) –Total wash cycle –Main wash duration Ave. wash temp. (˚C) Water Hardness Detergent Concentration (ppm)


Europe

North America

Japan

13

64

49

115a 75a aLong cycle 40–90 2.5 mmol 5000–7500

35 12

na 10

10–45 1.0 mmol 1200–2000

4–20 0.5 mmol 600–1000

54

Watson

Table 2 Representative Global Handwash Conditions

Wash water volume (L) Washing time (min) - Soak - Wash Duration Avg. wash temp. (˚C) Water hardness Detergent concentration (ppm)

Russia

Brazil

China

India

24

20

5

4.5

— 24 40 2.5 mmol 8300

22 n/a 22 0.3 mmol 4000

10 10 25 1.4 mmol 4800

30 n/a 25 0.5–3.4mmol 5555

Note: n/a, not applicable.

A final driver for multiple laundry formulations is consumers’ preferences themselves. Some prefer granular detergents and others liquids. Still others, at least in the handwash world, prefer bars or pastes. Some want to be able to adjust their dosage freely and others prefer the simplicity of predetermined doses as found in laundry tablets or liquitabs. But perhaps the best example is odor. There are those consumers who want as much perfume odor on their clothes as possible, as well as those who will go to great lengths to avoid perfume altogether. Likewise, not every scent pleases every consumer, so often you can find the exact same cleaning formula sold under the same brand name, but in multiple scent variations. There are also consumers who have real or perceived skin sensitivity to perfumes, dyes or enzymes, and for these consumers “free” products are available that contain none of these items.

II. UNIFYING FORMULATION CONCEPTS The key, unifying concept of all the different forms and formulations is that consumers expect their laundry detergent to clean their clothes. As such, the underlying chemistry of detergents is, not unexpectedly, quite similar. With a few exceptions that have been touched on above and will be discussed later, their primary job is the same—clean clothes. Briefly, following the laundry mechanism laid out by Venegas [1], all detergents in one way or another need to: (1) hydrate the soil, (2) remove the soil from the fabric, (3) fragment the soil to aid suspension, (4) prevent the redeposition of said soils, (5) bleach any residual soils to lessen their visual impact, and (6) provide any final modification to the fabric as desired (e.g., deposit perfume, brighteners, etc.). The general approach to meeting these needs looks quite similar in all detergents. In all cases one or more surfactants provide the primary wetting and soil removal power (excluding the very large impact of water via machine or hand agitation alone). Surfactants provide the basis and bulwark of the cleaning power as illustrated in Figure 1 [2]. Builders of one sort or another are included to protect anionic surfactant from precipitation as calcium salts, aid in removal of calcium sensitive soils like clay and particulate soils, and depending on the builder, aid in peptization and suspension of soils. Very few if any detergents exist that lack one or the other of these two actives.



55

Performance Contribution to Detergency 40

% Contribution

35 30 25 20 15 10 5 0 Surfactant

Figure 1

Bleach

Polymer

Builder

Enzyme

Relative Contribution of Actives to the Cleaning Process.

The actual selection of surfactant(s) and builder and their relative ratios can vary widely however. The level of cleaning and overall price desired largely determines the presence and level of additional actives besides surfactant and builder. In less expensive, more basic detergents there may be nothing additional besides a buffer system to maintain pH and some level of perfume. In top-tier, flagship detergents, typically one or more enzymes, soil suspension polymers, and/or bleaching agents are also added. There are a number of variants of each available to the formulator (see below). The exact choice and number is often dictated by questions of availability of proprietary materials, mutual compatibility with other actives present in the detergent, and the particular role the detergent is designed for. Technologies that work very well in one habit or in one form may not work at all in another. An obvious example is heavy duty granules (HDG) vs. heavy duty liquids (HDL), where there is a big difference in the actual wash pH. While both commonly use a protease enzyme, they must use different strains of the enzyme to obtain maximum activity at wash pH. The kinetics can also be vastly different between habits. In the short, cool wash cycles of Japan or North America, only technologies that work very quickly are useful. In the longer, warmer, European wash cycle the kinetics are still important, though not to the same degree. This difference can often be observed in the chain length of surfactants used, and also accounts for the relative efficiency of some builders in each habit. Regardless of the form, for a detergent whose focus is primarily cleaning you can expect to see surfactant and builder at the core, with one or more cleaning adjuncts added to boost the performance further and some level of perfume. The exception to this is those detergents that are designed to deliver a different primary benefit, plus a base level of cleaning. Examples of this include 2-in-1 detergents, which seek to soften clothes as they clean, and color-care or fabric-care detergents that strive to maintain the look and feel of clothing as close to the original, store-bought, appearance as possible. In these cases the formulator is often forced to make tradeoffs in absolute cleaning (either for cost or chemical reasons) to facilitate delivering these benefits. More will be said about this in the section on specialty detergents (Section VIII).


56

Watson

III. TYPICAL LAUNDRY DETERGENT INGREDIENTS A. Surfactants A number of excellent reference works are available covering every aspect of surfactant chemistry and use [3]. Today’s formulator has an extensive pallet of surfactants to choose from. What surfactant is chosen, and what level is used in product, is determined by a number of different factors. These include cost and supply availability of course. Additional requirements are often dictated by machine type and wash conditions, compatibility with the rest of the formulation, concerns with mildness where handwash is involved, and existing local regulations regarding biodegradability, to name a few. 1. Anionic Surfactants Anionic surfactants, especially the sulfates and sulfonates, dominate laundry detergent formulations. Their ready supply, generally low cost, and excellent performance make them a clear choice [4]. Linear alkylbenzene sulfonate (LAS) remains the most important of the anionic surfactants. When used as the sole surfactant it suffers due to its hardness sensitivity and generally poor surface activity. As a result LAS is usually formulated along with a lower level of cosurfactant to ameliorate these weaknesses. A recent interesting development involves introducing a mono-methyl substitution in the alkyl chain and increasing the percentage of terminal-phenyl isomers to nearly 100%. [5] This has the effect of improving the overall surface activity and eliminating the internal phenyl isomers that are most responsible for the hardness sensitivity of LAS. The alcohol sulfates and alcohol ether sulfates account for most of the remaining anionic surfactants in common detergent usage. The ether sulfates in particular are useful for boosting the hardness tolerance of LAS containing systems. They also have the benefit (or issue, depending on your point of view) of being high foaming. Other sulfates and sulfonates such as secondary alkane sulfonates, and sulfo fatty acid esters (e.g., MES) [6], are also known, but are currently less widely used. Methyl substituted versions of AS and AES, similar to the methyl-substituted LAS discussed above, have also been developed [7]. There are several other anionic surfactants known (e.g., phosphate esters, sulfosuccinates, taurates, isethionates, carboxylates), but aside from the simplest of the carboxylates—soap—they are seldom widely used. Soap is sensitive to low pH, and to polyvalent cations such as calcium, and hence is not used much as the primary surfactant in laundry detergents. Having said that, in situations where these factors can be controlled, soap provides excellent cleaning properties. In Japan, for instance, soap bars represent the gold standard for collar and cuff soil removal. Figure 2 presents exemplary structures of common surfactants in detergents. 2. Nonionic Surfactants Almost by definition nonionic surfactants [8] are insensitive to hardness ions. As such they can make excellent cosurfactants with anionics as discussed above. They also have the advantage of being relatively mild toward dyes and delicate fabrics, making them good candidates for color-care or delicate garment formulations. Nonionics are generally kinetically slower than anionics though, sometimes limiting their cleaning contribution in shortwash cycle, cold water conditions. Alcohol ethoxylates are by far the most important of the nonionic surfactants. By proper balance of the alkyl chain length with the number of ethoxy groups a wide range of surfactants with varying properties is possible. As a result, interaction and compatibility



57

Linear Alkylbenzene Sulfonate (LAS) (CH2)x

H3C

CH

(CH2)y

CH3

SO3Na Alcohol ether sulfate (AES) O(CH2CH2O)xSO3Na Alcohol sulfate (AS) OSO3Na Alcohol ethoxylated (AE) O(CH2CH2O)xH Alkyl N-methyl glucose amide O R

OH

OH OH

N CH3

OH

OH

Alkyl dimethyl hydroxyethyl ammonium chloride CH3Cl− R

N+

(CH2CH2)OH

CH3 Alkyl dimethyl amine oxide

CH3 N

O

CH3

Figure 2

Exemplary Structures of Common Surfactants in Detergents

with other surfactants and detergent actives, overall performance for a given wash condition, and stain removal performance on various soils, can be accurately optimized. Versions using an alkyl phenol instead of a simple alcohol are known to provide even better performance, but environmental concerns have limited their use in household products. There are other important nonionics as well, though their significantly higher cost and lower supply availability limit the actual volumes used. Included here are amine oxides, alkanolamides, EO/PO block copolymers, and various surfactants made from polysaccharides. Amine oxides are often used as suds boosters, and can sometimes play a similar role in surfactancy as cationic surfactants.


58

Watson

3. Cationic Surfactants Cationic surfactants [9] present a series of different opportunities and challenges to the formulator. Since most fabric surfaces and many soils are negatively charged at wash pH, cationic surfactants have a natural affinity and can build up in significant amounts. This can be a positive or a negative depending on the desired outcome. Likewise, the interaction of cationics with anionic surfactants is important (formulating a laundry detergent with all cationic surfactants is not done). When used at the right ratio cationics can significantly boost the cleaning power of an anionic surfactant like LAS. Use at too high a level results in precipitation and loss of both. The most common cationic surfactants are quaternized ammonium compounds. These can be as simple as a single alkyl chain of typical detergent length, along with three methyl groups on the nitrogen. Others incorporate various levels of ethoxylation on the nitrogen along with methyl groups. These quaternary compounds are often referred to as “true quats.” Regardless of the pH of the wash solution they remain cationic. A “pseudoquat” then, is a surfactant like an alkyl amine, which becomes protonated below it’s pKa and behaves as a quat. Above its pKa it is a neutral surfactant. Materials like this can be important, for example, in heavy duty liquids where formulating a true quat along with anionic surfactant can pose significant formula stability issues. 4. Others The simple classification of anionic, cationic, and nonionic above easily captures the lion’s share of surfactants actually used in laundry detergent formulations today. There are also amphoteric surfactants [10] like the betaines and sultaines that are also used occasionally. There are some specialty surfactants like the chelating surfactant N-acyl ED3A marketed by Hampshire Chemical (Nashua, NH) [11], and short-chain surfactants that are more often used as hydrotropes, though they can provide good cleaning benefits if present in high enough concentration as in a specialty pretreater. Research continues as well on Gemini, twin-tail surfactants, on polymeric surfactants, and others. To date none of these new developments offers a suitable cost/performance value to be used extensively in laundry detergents. B. Builders The primary role of builders in a laundry detergent is sequestering calcium and magnesium ions. All other considerations are secondary. There are numerous reasons why this is important, not the least of which is that calcium and magnesium lead to precipitation of anionic surfactants, or help form multilamellar vesicles, both situations leading to significant loss of performance. Both the rate of sequestration and the absolute capacity for sequestration are important considerations in the choice of builder. Beyond removal of hardness ions, builders can also play a variety of additional roles. Depending on the builder they can also provide dispersancy and peptization of soils, can serve as a source of alkalinity, and in granular and tablet detergents can be important carriers of other organic actives in the formula. The number of practically important builders for laundry detergents remains relatively small [12]. Sodium tripolyphosphate (STPP) is the standard by which all other builders are measured. It delivers rapid sequestration of hardness ions while also serving as an excellent peptization and soil suspension agent. It is also inexpensive, readily available and easy to formulate in a granular product (isotropic liquid products are a different matter as discussed later in this chapter). Today it is largely limited in use to handwash countries due to concerns over its role in eutrophication of waterways. As a result of these concerns, the development and use of a variety of substitutes has ensued.



59

Zeolites, primarily Zeolite A and Zeolite MAP, are the primary replacement for STPP in granular detergents today. Like STPP, Zeolite A is readily available and relatively cheap, and it has high capacity for calcium ions. The primary drawback of zeolite builders is that they are kinetically slower in the uptake of calcium (something that becomes more and more important as wash temperatures and wash times decrease), and are relatively ineffective in removal of magnesium. Also, because they are insoluble, concerns with deposition and buildup on fabrics is also always present. Recent work [13] has looked at reducing the primary particle size of the zeolite in an attempt to increase the rate of calcium ion exchange, but as of this writing it is not yet commercially common. Builders based on carboxylic acids become more important for liquid detergents than granular ones, but they are used in both. The simplest form of this type of builder is soap. In liquid detergents, fatty acids sometimes represent the only builder present in the formula. Citric acid is also an effective carboxylate builder, used most often in liquid detergents. Polycarboxylate polymers are effective dispersants that also deliver some building power. Use is largely limited to granules due to formulatability concerns in liquids. Amino carboxylic acids, like nitrilo triacetic acid (NTA), are excellent builders, though their use is limited by toxicological concerns. Other builders include amorphous silicates, materials common in granular detergents as a source of alkalinity and as anticorrosion aids. Layered silicates are a more recent development used in some markets. Calcium carbonate is ubiquitous in granular detergents and tablets, and its role as a builder is sometimes overlooked. By forming insoluble calcium carbonate it efficiently removes calcium from solution, but brings with it the concern of inorganic encrustation of fabrics. As often as not, this trait of carbonate is viewed more as a liability in detergents than as a positive. C. Polymers The use of polymers has increased as detergent formulations have evolved. Initially, as phosphate use was curtailed, the focus was on polyacrylate-type polymers with the goal of replacing some of the lost building and dispersancy power of STPP. Carboxymethyl cellulose is another of the oldest polymers and represents one of earlier attempts at soil release. From these successful beginnings, a large number of polymers for a variety of purposes have emerged [14]. Several new dispersants have been commercialized, as have polymers for dye transfer inhibition, soil release and soil repulsion, for structuring liquid detergents and for aiding dissolution of tablets. For every new polymer actually commercialized there are myriad additional ones patented, attesting to the level of interest in the area. Dispersancy and soil removal remains the primary role of polymers today [15]. The choice of dispersant is governed by a number of factors. The formulator must first be clear on what it is they want to disperse and where. Is it clay-type soils in the wash, solids in the crutcher of their spray-tower, dyes in the rinse, hydrophobic soils in the wash, etc.? Poly(acrylic acid) or poly(acrylic/maleic) copolymers are the most popular dispersants for granules, but their use in liquids is limited due to solubility concerns and limited efficacy at the lower pH. For HDLs, smaller polymers, such as ethoxylated polyamines are more common. Recently, more specialized (and more expensive) polymers have been developed to broaden the spectrum of soils against which they work. These include a variety of ethoxylated polyamines, and zwitterionic polymers [16]. Figure 3 presents exemplary structures of common polymers in detergents. Soil release polymers are another important class [17]. In simple terms, these are polymers deposited on fabrics through the wash cycle (this discussion excludes polymers applied in the mill for similar benefits) such that they form a “protective layer” between the fabric and subsequently encountered soil. In it’s most common application the polymer


60

Watson

Poly(acrylic)/Poly(maleic) acid (PAA/PMA) H2 C

H C

x

CO2H

H C

H C

CO2H

CO2H

y

Ethoxylated tetraethylene pentaimine EO15

EO15

N

N

EO15

EO15 N

N

N

EO15

EO15

EO15

Ethoxylated Polyethyleneimine EO20

EO20 N EO20

EO20 N N EO20 N

EO20

N

N

EO20 N

N

EO20

EO20 EO20

N

N EO20 EO20

N

N

N

N EO 20

EO20

EO20

EO20

Soil Release Polymers O NaO3S(CH2CH2O)2 C

O

O CO

O

O

CH2CHO C

CH2CHO C

C O

O CH2CH2OCH2CH2SO3Na

C O

R

R

y

x SO3Na

O CH3O(CH2CH2O)x

O

O

O (OCH2CH2)yOCH3

OCHCH2O CH3 z

PVNO n

N O

Figure 3

Exemplary Structures of Common Polymers in Detergents

is based on a terephthalate polyester backbone and builds up primarily on synthetic fabrics over multiple cycles. This buildup makes the otherwise hydrophobic (and therefore hard to wet and clean) fabric more hydrophilic thereby aiding in soil removal. CMC has also been claimed to provide some soil release benefits on cotton, though the size of benefits are rather limited. The last main class of polymers currently in use are dye transfer inhibition polymers. These polymers are included to trap fugitive dyes released from fabrics and prevent them



61

from depositing on other fabrics. The fugitive dyes can be released due to the nature of dye used on a new garment initially, or due to the action of the detergent itself. Whatever the primary cause of dye release, these polymers work by complexing with the dyes, usually via dipole-dipole interactions, and keeping them well solubilized. The most common DTI polymers are based on poly(vinylpyridine) and related derivatives. New developments in nondispersant polymers are focused on delivering totally new “fabric-care” benefits. The ultimate goal is to repair damaged fibers and/or prevent damage in the first place to keep clothes looking like new. Work in this area is still in the early stages, but some materials have already been introduced into the market. Recent developments in this area are covered in Section IXA—Care Detergents. D. Enzymes Enzymes offer a great deal to the detergent formulator. By definition they work catalytically and hence take up little formulation space. They are also biodegradable, making them a good choice for today’s increasingly environmentally conscious consumer. Enzymes have also proven beneficial in keeping performance high as wash temperatures have fallen. Some have predicted that enzymes will become the single most important detergent component as environmental pressures continue to mount on other actives. While this may still be some time away, detergents containing as many as four or five different enzymes are already on the market. Several different enzymes are commercially available today for detergents and research continues apace to discover and develop new ones [18]. In choosing an enzyme the formulator needs to consider what the target soil or benefit is. The answer to this question determines what enzymatic activity is required. The formulator also needs to consider the wash pH and wash temperature. All enzymes have a pH and temperature window in which activity is maximized. Moving too far out of this window can make the enzyme so inefficient that it becomes cost prohibitive, or perhaps even impossible, to formulate an efficacious amount. Finally, the formulator needs to consider the mutual compatibility of the enzyme and other detergent actives. By far the most common enzyme in use today is protease. Not coincidentally it was also the first enzyme to be successfully commercialized in detergents. Protease works by cleaving peptide chains found in proteins, producing smaller, more soluble or easy to disperse fragments. Since proteins are found in some of the most common and important consumer stains (e.g., grass, blood, skin cells, sweat, many foods) it is a natural fit in most detergents. Protease presents a unique challenge for formulators (especially of liquid detergents) since it can also undergo autolysis and degrades other enzymes that are present in the formula. This is a well-understood phenomenon and solutions generally take the form of a reversible inhibitor that releases the protease on dilution into the wash. Amylases, more specifically alpha-amylases, are the second most commonly used enzyme in detergents. By hydrolyzing glycosidic bonds in starch, amylase can deliver significant stain removal benefits on food stains such as chocolate, gravy, and spaghetti, as well as body soil removal benefits. Also, amylase can sometimes deliver multicycle whiteness benefits by removing starch that could otherwise serve as a “glue” to attract other soils to the garment. Because amylases require calcium ions to maintain their threedimensional structure, care must be given to how they are formulated, with liquid detergents again providing the largest challenge. Lipases offer great potential in principle, though their actual impact in detergents thus far has been limited. Lipases work by hydrolyzing triglycerides and fatty esters to the corresponding fatty acids. The fats and oils that are susceptible to hydrolysis by lipase are often difficult to remove by surfactants alone, especially in colder water. Hydrolyzing


62

Watson

them to fatty acid and glycerol makes removal by surfactants much easier. The issue has been that today’s lipases require multiple cycles to provide benefits. Also, lipases generally require the presence of calcium ions for maximum activity, and these same calcium ions can form a hard soap layer over the oily stain, blocking further action. Cellulase rounds out the roll call of today’s commonly used enzymes. It is different from those listed above in that it does not work directly on any stains, but rather directly on the fabric itself. By hydrolyzing the glycosidic β-1,4 bonds of cellulose, cellulase can remove the topmost layer of microfibers from cotton garments. The result can include stain removal by loosening the cloth “fingers” that help trap soils, but the focus has generally been on depilling, color restoration and softness. The obvious challenge with cellulases is balancing the benefits obtained with damage to the strength of the cotton garment itself over several cycles. As mentioned above, there is a great deal of ongoing work by enzyme suppliers, academics, and detergent makers themselves to discover and develop new enzymes. This work involves screening of natural isolates and “evolution” of existing enzymes, with the goal of both improving on existing activities (where improving can mean higher activity, greater stability, wider temperature and pH applicability, etc.) and developing new ones. One recent example of a newly commercialized enzyme activity for detergents is mannanase [19]. Mannanase hydrolyzes the mannan backbone of galactomannans and glucomannans. Because these materials are common rheology modifiers in a variety of foods and consumer care products, they can form a gluey film on fabrics. By removing this film, mannanase helps prevent fabric dinginess. E. Bleach Bleach contributes to stain removal by either oxidatively modifying the stain such that it becomes more water soluble and easier to remove, or by decolorizing the stain such that it is no longer visible. In some cases the oxidative bleach can also provide antibacterial benefits. There are also reductive bleaches available, but generally speaking they are not popular in laundry detergents for a variety of reasons. There are several oxidative bleaches available to the formulator today, though like most actives discussed in this chapter, a relative few dominate commercially [20]. The simplest and most common bleach is hydrogen peroxide. The ability of peroxide to decolorize and help remove hydrophilic stains like tea, coffee, and wine has been known for a very long time. It has been used in granular detergents for over 100 years. Of course hydrogen peroxide itself cannot be formulated in a granular detergent, so it is usually formulated as the stable perborate salt. Also available is percarbonate, which is actually carbonate with the hydrogen peroxide trapped in the crystal lattice. Just which material is used is based on a number of factors. Stability, dissolution rates, environmental legislation all comes into play. Whichever form one chooses, the performance of the resulting peroxide is most powerful at high temperature and long wash times. In all other situations, an additional bleaching agent is needed for strong performance. This “additional bleaching agent” takes the form of a bleach activator. A bleach activator is a peracid precursor that reacts with peroxide in the wash solution to form a peracid. They have the advantage being more reactive and therefore more effective than peroxide. Also, because they are hydrophobic, they offer better performance on body soils and hydrophobic stains. The combined bleaching profile of hydrogen peroxide and peracid gives a much broader performance profile, both in terms of stains affected and conditions in which good performance is observed. By far the two most common bleach activators are tetraacetylethylenediamine (TAED) that generates two equivalents of peracid, and nonanoyloxybenzenesulfonate (NOBS) that generates one [21].



63

Preformed peracids are also known. They offer a weight efficiency advantage since no hydrogen peroxide is required and there is no “wasted” leaving group. The main issue with preformed peracids is stability—both of the raw material itself and in finished product. Phthalimidoperoxycaproic acid (PAP) is probably the best known. Metal bleach catalysts also offer great promise of weight efficiency. Bleach catalysts are transition metal compounds, typically Mn, Fe, Cu, or Co, with various chelating organic ligands. They react with appropriate oxygen sources to form high valent metal oxides that are potent oxidizing agents. Most are designed for use with hydrogen peroxide, but the obvious goal is to develop a catalyst that works with molecular oxygen. To date there is no successful commercial example, but the search continues within many academic and corporate labs. In some regards photobleaches (normally metal phthalocyanines) could be considered as bleach catalysts. They generate singlet oxygen, a powerful bleaching species, on exposure to light and air. Because of the need for sunlight, and because the bleach is only really effective while the clothing is still wet, the utility of photobleach is greatest in areas where consumers air dry their laundry outside. Figure 4 presents the exemplary structure of common bleaches and chelants. F. Chelating Agents Chelants are often formulated in detergents because metal ions in the wash are almost always a detriment to end performance. Many highly colored stains incorporate metals. Removal of the metal can often decolorize the stain and/or make it easier to remove by destabilizing its structure. Examples include porphyrins found in blood and tannins in tea. Metal ions can also catalytically decompose bleach in a formulation, leading to significantly reduced performance. Finally, metals often find their way onto fabric surfaces, either as insoluble salts as with calcium or magnesium fatty acids, or as metal oxides. Both lead to a multicycle dinginess and fabric feel issues. What chelant is used depends largely on local environmental regulations. Diethylene triamine pentaacetic acid (DTPA) is commonly used in North America. It’s an analog of the more well-known ethylenediaminetetraacetate (EDTA), but has a better environmental profile. In Europe, however, DTPA is banned due to concerns with aquatic toxicity. As a result, European formulations rely more on phosphonate-based chelants such as diethylene triamine penta(methylene phosphonic) acid (DTPMP) or ethylene diamine tetra(methylene phosphonic) acid (DDTMP). In an interesting twist, these materials cannot be used in North America due to bans on phosphorous in laundry detergents. In environmental terms, ethylene diamine disuccinic acid (EDDS) represents the best achievement thus far. The molecule has two chiral centers and only the S,S-isomer is fully biodegradable. This makes it a more expensive chelant than the phosphonate chelants mentioned previously. It is used in some European granules today. HEDP, 1hydroxyethyidene-1,1-diphosphonic acid, is not truly a chelant in the sense of the materials mentioned above, but because it also helps control deposition of metals on fabrics it deserves mention in the same section. HEDP works more by inhibiting crystal growth. G. Perfumes In a technical sense perfumes add no cleaning power to a detergent. However, from a consumer point of view perfumes have a major impact on the overall impression of how well a detergent works. Even a perfectly clean garment can be judged substandard due to lack of a “fresh and clean” odor. Odor has been proven to be an important driver for consumer acceptance, and thus should be carefully considered when formulating a product. As a result, as much effort is put into formulating different perfumes [22] as goes into formulating the rest of the laundry product, it’s just done by a different set of people—perfumers. Perfumers


64

Watson

PB1 2

HO

2Na+

O

O

O

O

B HO

B

OH OH

NOBS O SO3Na

O

C8 TAED

O

CH3

O N

N

H3C H3C

CH3 O

O

PAP O O

N OOH O Photobleach SO3Na

N NaO3S

N N

N

N

Mn

N

N

N

SO3Na

SO3Na

Figure 4A Exemplary Structure of Common Bleaches and Chelants.

are highly trained technologists skilled in the science and art of creating unique winning perfumes with odor performance profiles meeting consumer needs. Perfumes are complex mixtures of organic compounds. For example, a detergent perfume may be composed of 30, 50, or even over 100 different organic materials. Given this nature, perfumes can have complex interactions with detergent actives that affect both the perfume character and possibly the actives’ performance. In addition, detergent actives often have odor properties themselves, and these “base odors” should also be considered



65

DTPA Ac Ac

Ac N

N

Ac

N Ac DDTMP

O−

O

O−

P

O−

−O

P N

O N

O P −O

−

P

O

O−

O

−O

EDDS CH2 CH2 COOH

CH COOH

NH

CH2 NH

CH

CH2

COOH COOH

Figure 4B

when formulating detergents since they can impact the final product odor profile. The detergent formulator should work in partnership with the perfumer to ensure the final product odor profile best meets consumer’s needs. Most of the perfume formulated in laundry detergent ends up being washed down the drain. Deposition onto fabric is inefficient. To further complicate things, what perfume does deposit on a fabric is relatively short lived. As a result, there has been a great deal of research in recent years to aid in delivery and sustained release of perfumes. The result is a number of additional technologies available to the formulator, including those that aid in deposition of traditional perfumes, those that extend the longevity (usually via delayed release) of perfume on fabrics, and even those that only generate perfume after some triggering event such as heat, sun, or moisture exposure. All of these new developments are beyond the scope of this chapter to describe. H. “Minors” Whether a detergent ingredient is a “minor” or not is all in the eye of the beholder. In this section, “minor” simply refers to actives that are included at a relatively low level in detergent, or have no direct cleaning benefit (these items are sometimes referred to as “fillers”). “Minor” should not be taken as statement of the importance of these actives, as their absence will generally result in overall poorer performance. Discussion here is limited and the list should not be considered as exhaustive. Fluorescent whitening agents (FWA) are included at some level in most detergents today [23]. The primary benefit of FWAs is observed over multiple cycles as white


66

Watson

garments begin to become dingy. By absorbing ultraviolet (UV) light and emitting it in the violet-blue visible region, FWAs increase the apparent whiteness of a garment. FWAs are also added at the mill as garments are made, but these FWAs are removed with multiple washes and need to be replenished. FWAs additionally have a benefit in solid detergents by making the granule appear whiter, and hence more attractive to consumers. The watch out, especially in liquid detergents that are often used for pretreating fabrics, is that when applied in excess to light-colored clothing, the fluorescence in the violet-blue region can appear as a light-colored stain. By careful selection of the right FWA this issue is easily avoided in most situations. In liquid detergents there is often a need for solvents or hydrotropes to ensure formula stability across the wide range of temperatures it will experience from plant to the consumer’s home. Typical solvents and hydrotropes include ethanol, propanediol, toluene sulfonate, or xylene sulfonate. The effect of solvents and hydrotropes on liquid stability and physical properties (e.g., viscosity) is not always straightforward. Effects can reverse depending on the formulation, and stability issues may not materialize for many months. Optimization of the solvent system for a product is therefore an involved process involving many samples and various rapid aging techniques. Liquid detergents, especially the more dilute ones where water makes up a greater fraction of the total product, also often contain an antibacterial agent of some sort to protect against microbial growth over the lifetime of the product [24]. Liquids are also the biggest users of dyes, pigments, or colorants [25]. In all detergents, maintaining the optimum pH for performance is crucial. As such, most contain a buffering system of some sort. This is much easier in a granular detergent than a liquid where solubility of common buffering salts is problematic. In granules this is accomplished with carbonate, silicate, and STPP. In liquids there is essentially no buffering capacity in the real sense of the word. What pH control exists comes from the degree of neutralization of acid surfactants and fatty acid, as well as the nature of the neutralizing agent itself. Suds control [26] is important as consumers make many judgments relating to the performance of their detergent based on the suds profile. Unfortunately not all consumers want the same suds profile, so knowing the consumer preference is key. It’s not just important from a consumer preference point of view, but in machine wash it is often necessary for correct machine performance. For example, a typical handwash or North American detergent will result in suds flowing out of a European machine, at best making a mess and at worst locking-up the machine such that it shuts down. Some degree of suds control is possible via careful selection of surfactant type and level, but often a separate suds control material is required. The most important type of suds suppressor is based on organic silicone compounds, though metallic soaps of carboxylic acids, insoluble nitrogenous compounds, and branched alcohols are also used.

IV. HEAVY DUTY GRANULES Heavy duty granules (HDG) were the first mass marketed consumer laundry detergents. They remain the dominant laundry form in most markets today, with a few notable exceptions such as in North America where heavy duty liquids have overtaken them in volume sold. Even in markets such as North America, however, HDGs remain a very important and dominant form. The range of different formulations on the market around the world today is quite wide. Extremely basic formulas that contain little more than carbonate, some LAS, and a bit of sulfate that are simply made by stirring them all together are sold very cheaply in some developing markets. Somewhat more complex (but devel-



67

opmentally still very simple) formulas made by spray-drying LAS, STPP, carbonate and fillers are found widely around the world in handwash geographies. In developed machine wash countries one can find very complex products with mixed surfactant systems, mixed builder systems, multiple enzymes, and polymers, and made via agglomeration techniques. As the formulas gain in complexity they also gain in cleaning power, benefits delivered, and cost. In general the HDG form leverages high pH and high builder levels, both made possible by the relative ease of formulating solid buffer like carbonate and solid builders such as STPP or zeolite. Surfactant levels and types are determined in part by cost considerations of course, but manufacturing and flowability concerns have a significant impact as well. As will be seen, these considerations generally limit total surfactant levels to under 25%, and nonionic surfactant to less than 5%. Additional performance is provided by bleach, and a wide variety of enzymes and polymers. Most recent patent art is focused on new developments in these areas versus the fundamental formulation. Processes for making granules also dominate the patent art. In an attempt to bring some clarity, discussion of HDG formulations in this chapter is focused on the basic formulation and is grouped according to three key questions. First, does the desired formulation contain phosphate (usually as STPP) or not? In many markets today the use of phosphate builder is banned or severely limited. Whether or not phosphate is present can have major implications on the remainder of the formulation. Second, is this a low-density (aka “fluffy”) product or a high-density (aka “compact”) product? All markets used to be made up of fluffy products, with a density of around 350–– 500 g/L. In the late 1980s there was a significant shift to compacts with a density of around 600 to 900 g/L [27]. Finally, is this a product intended for use in washing machines or for use in handwashing of clothes? The delineation provided by these questions is somewhat arbitrary as the answers can be combined in many different ways. There are both highdensity and low-density phosphate containing formulas for machine wash for example. Likewise, there are both phosphate and nil-phosphate low-density formulas for handwash, and so on. Examples of all these formulations abound in the patent literature. The discussion below is illustrative of the more common approaches. A. Phosphate vs. Nil-Phosphate Phosphate, typically STPP, has been the preferred builder of formulators for many years. STPP readily sequesters hardness, acts as a soil peptizer and dispersant, provides some buffering capacity and helps carry the organic load in granules. It is still the preferred builder in many parts of the world today. In others, such as North America, the use of phosphate in laundry detergents has been banned and so alternative such as zeolite A are used. Zeolite A replaces the builder function and organic carrying function of STPP, but other actives are required for buffering, soil peptization, and soil suspension. Also, since the calcium binding kinetics and capacity of zeolite is not as high as STPP, more hardness tolerant surfactant systems are often used in nil-P products. Hence, to get equal performance from a nil-P product can mean additional formulation cost to pay for the chemistry needed to offset the loss of STPP. Table 3 illustrates a high-end, phosphate built detergent [28]. Compared to the nilP detergent in Table 4 [29], the biggest apparent difference in the core formula (aside from replacing STPP with zeolite A) is the presence in the nil-P formula of a polyacrylic/maleic acid copolymer and of the soda ash/silicate co-granulate sold commercially by Rhodia under the name Nabion 15. These extra actives help compensate for the dispersancy power lost when STPP is removed. Even with such additions, it is very difficult to achieve the same level of clay stain removal from a nil-P product at equal cost to a P product without


68

Watson

Table 3 Example of Phosphate Built HDG Ingredient

Percent

Sodium C11-13 alkylbenzene sulfonate Sodium C14-15 alcohol sulfate Sodium C14-15 alcohol ethoxylate (0.5) sulfate Sodium C14-15 alcohol ethoxylate (6.5) STPP Sodium carbonate Sodium silicate (1:6 ratio NaO/SiO2) (46%) Sodium sulfate PEG 4000 (50%) Dispersant polymer Soil release polymer Suds suppressor Water and minors

13.7 4.0 2.0 0.5 41.0 12.4 6.4 10.9 0.4 0.76 0.10 0.60 Balance

Table 4 Example of Nil-Phosphate HDG Ingredient

Percent

C9-13 Alkylbenzene sulfonate C12-18 Alcohol sulfate C12-18 Alcohol ethoxylate (5) C12-18 Fatty acid PEG 400 Zeolite A Nabion 15 (Rhodia) Acrylic/maleic copolymer Silicate PB1 Chelant Dusting agent EDTA Protease Suds suppressor Water, misc.

13.6 3.9 3.6 0.7 1.5 17.6 12.0 3.5 1.5 17.4 0.5 1.5 7.0 1.6 3.6 10.3

Note: EDTA, ethylenediaminetetraacetate.

compromising in other areas (e.g., surfactancy). Mixed STPP and zeolite products are also known as illustrated in Table 5 [30]. This complex formula also illustrates the trend to using a mix of agglomerated and/or spray dried particles of varying composition to form the total formulation. This approach provides increased flexibility over a single spraydried or agglomerated particle.



69

Table 5 Example of Mixed Builder HDG Ingredient

Percent

Base Powder STPP Sodium LAS Sodium silicate Sodium sulfate Moisture, minors

51.2 28.3 27.8 11.0 21.0 11.8

LAS Granule Sodium LAS Zeolite 4A Zeolite MAP Moisture, etc.

11.1 70.0 20.0 5.0 5.0

Nonionic granule Sodium carbonate Citric acid AE3 Water

12.0 62.8 8.1 20.9 8.2

Admixes Dense sodium carbonate Sodium sulfate Savinase Lipase Perfume

10.7 13.86 0.754 0.166 0.22

Relying on the building capacity of carbonate is another, less common, approach to nil-P formulas. Whereas STPP is a soluble builder that remains soluble when complexed with calcium, and zeolite is an insoluble builder from the start, carbonate is a precipitating builder. That is to say, it remains soluble until it interacts with calcium. As such it has the additional challenge of controlling the growth of calcium carbonate crystals and the fabric incrustation that can result when too large crystals are formed. Table 6 illustrates one approach that relies on polyacrylic acid and a maleic acid/olefin copolymer to limit encrustation [31]. Another approach to carbonate builders involves the use of very small calcite particles that act as seeds for calcium carbonate growth, resulting in more controlled and smaller crystal sizes [32]. Many other nil-P builders are known: soluble, precipitating, and zeolitic. However, they all come with significant additional cost and are used far less commonly. B. Low Density vs. High Density The choice between high- and low-density products is primarily market driven. In most of the developed world today consumers prefer high-density products. The products take up less shelf space in their homes, have less packaging waste, lower dosages, and are seen as better for the environment and as a better value. Not long ago in these same markets


70

Watson

Table 6 Example of Carbonate Built HDG Ingredient

Percent

Nonionic EO5 Sodium carbonate Sodium bicarbonate Acusol 445ND (polyacrylic acid) Acusol 460ND (maleic acid/olefin copolymer) PB1 Sodium silicate Sodium sulfate

4.0 25.6 4.0 3.4 0.9 4.0 9.6 48.5

consumers looked for large boxes at low prices, and in much of the handwash world this is still the case. The formulation strategy for high- and low-density products is essentially the same. However, because of limitations in the end density that can be provided with different processes, some changes are required. Most low-density products are made via spray-drying. The products contain large amounts of carbonate and sulfate, and the surfactant system is limited somewhat by what can safely and stably go through the spray-drying tower. Additional surfactant and other organics can be sprayed onto the surface of the tower made granule, but only at low levels. Otherwise the granule can become “wet” and sticky, resulting in poor flowability and poor aesthetics. “Dusting” the finished particle with zeolite or other flow-aids is commonly done to prevent stickiness. High-density products are typically made via agglomeration processes, though postspray-tower densification processes are also used. Low-efficiency actives such as sulfate and carbonate are significantly reduced in high-density products relative to their lowdensity counterparts. Within the practical limits of marketed detergents there is not a large difference in the overall formulation beyond this. There is a great deal of patent art related to the challenges of making agglomerated powders that flow and dissolve as readily as low-density, tower-made granules [33]. C. Machine Wash vs. Handwash Much of the world today still does laundry by hand. In most cases handwash consumers use the presence of suds as a signal that sufficient detergent is present in the wash. To meet the cleaning and sudsing needs of handwash consumers, formulators have added high levels of anionic surfactants such as LAS. However, many anionic surfactants can be harsh to skin at high concentrations, especially when the skin is repeatedly exposed for relatively long periods of time as in handwashing. As a result, the formulator needs to be aware and adjust accordingly. In addition, the handwash consumer often has a much higher soil load, either due to environmental reasons or due to a lower overall frequency of garment washing. This results in increased demand on the detergent actives, including enzymes and bleach. A handwash detergent could use the same formulation as a machine wash detergent minus the suds suppressor in the simplest situation. More often though, handwash formulations include higher levels of builder and dispersants, and special care is taken to limit the level of protease and other actives that can be harsh to skin under certain conditions.



71

Table 7 Example of a Simple Handwash HDG Ingredient Sodium LAS STPP CMC Polyacrylic acid Protease Carbonate Silicate Sulfate FWA Perfume Water

Percent 15.0 17.0 0.1 0.1 0.1 12.0 8.0 38.0 0.1 0.2 Balance

Because the handwash habit is predominately found in lower income markets, many handwash formulas are relatively simple, as shown in Table 7. With lower priced formulations consumers frequently “titrate” the dosage and the amount of time scrubbing to get the end benefit they desire. Top performing handwash detergents, however, contain a mixed enzyme system, bleach, chelant and other performance boosting actives. The increased performance allows consumers to dose less and spend less time scrubbing while still obtaining the desired end result. Combined with a surfactant system designed to maximize cleaning while still being mild to hands results in a very mild formulation. Table 8 illustrates this approach [34].

V. HEAVY DUTY LIQUIDS The first heavy duty liquids (HDL) were introduced as early as the 1950s, though it wasn’t until the early eighties that the form really took hold in the United States and Europe. Formulators of HDLs generally fall into two different schools of thought. The first focuses on the intrinsic benefits of the liquid form, allowing for the incorporation of surfactants at high levels and for pretreatment (i.e., direct application of the HDL to the stain prior to addition to the washing machine). This route leads to low viscosity, isotropic liquids and has been the preferred route for Procter & Gamble and Henkel for example. The second school of thought is to make the HDG into a liquid form. This route leads to structured liquid detergents containing high levels of suspended builders such as STPP or zeolites, a route championed by Unilever. These two schools remain dominant today, roughly 50 years after the introduction of the first HDLs [35]. Recently, however, new concepts have emerged including “liquigels” or “liquitabs,” essentially an HDL in a soluble pouch (a form covered in the section on Unit Dose Detergents), and HDLs packaged in dual compartment bottles. A. Isotropic Liquids Isotropic liquids are by far the largest in terms of market share and number of formulations on the market. In many markets in North America in particular, isotropic HDLs have


72

Watson

Table 8 Example of Handwash HDG Designed for Mildness Ingredient C16-18 N-methyl glucose amide C12-14 Dimethyl amine oxide C12-15 Alkyl ethoxylated (EO = 5) C14-15 Alkyl ethoxy (EO = 1) sulfate STPP Sodium polyacrylate (MW = 4500) DTPA CMC Protease Cellulase Amylase Sodium silicate Soil release polymer PB1 NOBS bleach FWA 15 FWA 49 Misc. (sulfate, water, perfume, etc.)

Percent 2.3 1.9 7.3 14.0 15.0 15.0 1.6 0.4 1.0 0.15 0.15 7.0 0.3 2.0 3.2 0.15 0.05 15.1

become the leading seller, surpassing HDGs. HDLs offer a number of intrinsic advantages over HDGs. The form itself makes the pretreatment of stains easy and effective, allowing levels of stain removal not otherwise possible. The advent of dosing cups with built-in rollerballs or pour spouts makes this even easier. Rapid and complete dissolution is another inherent advantage of isotropic liquids. As wash cycles become shorter and temperatures cooler this takes on increasing importance. Liquids also offer the opportunity to formulate much higher levels of surfactant than is possible in a granule, resulting in much better greasy stain removal. Ease of dosing and less mess are also advantages noticed by consumers. The key disadvantage liquids have faced versus powders is poorer cleaning due to lack of bleach. This is the origin for much research in liquids as will be discussed below. The biggest challenge for the formulator of an isotropic liquid is stability—both physical and chemical. These considerations are the primary driving force behind what today’s isotropic liquid formulations look like. Stability must be maintained across a wide range of conditions and for a considerable period of time. From the time product is made and stored in bulk at the manufacturing plant, through bottling and warehouse storage, on to retail outlets and finally into consumer’s homes, the HDL can experience wide swings in storage conditions. Temperatures ranging from below freezing to over 40°C are not unheard of. In well-developed markets where product is made on demand, the time gap between manufacturing and use can be relatively short. In less developed markets, where perhaps product is imported from a manufacturing site in another country, the time gap can stretch to several months. Water is the primary solvent in HDLs, though various cosolvents such as propanediol, and hydrotropes like toluene- or xylen-sulfonate, are also used at low levels.



73

Maintaining solubility of all actives, especially as formulas become more compact (i.e., more concentrated so lower volume doses are needed for each wash), is the main challenge. Surfactants with high Krafft temperatures are particularly troublesome, and longer-chain length hydrophobes are strictly limited. Surfactants that tie up large amounts of water, such as highly ethoxylated nonionics are also troublesome, as can be some of the more commonly used polymers in HDGs. The problem becomes further aggravated as other actives are included and as the ionic strength increases. Several “tricks” can be used such as using monoethanolamine (MEA) or triethanolamine (TEA) neutralized surfactants. Because they have lower hydration demand, these counterions have been key in the development of concentrated HDL formulas. Using potassium instead of sodium as the counterion is also done, but this has limited effect for the increased cost. These solubility issues are a main reason why most HDLs in the market today have a pH of around 7 to 9. It is impractical to try to formulate the amount of buffer that would be required to raise the pH to 10 or higher that is common for HDGs. The lower pH and lack of in-wash buffering is not a major issue though, provided the formulator keeps it in mind when selecting actives such as enzymes. In fact, this lower pH can often have a beneficial effect in reducing dye bleeding and damage to fabrics. Delivering the HDL with the right viscosity is also important. If the viscosity is too low consumers view the product as being dilute and therefore poor cleaning. If the viscosity is too high the rate of dissolution under stressed conditions (e.g., low temperature, short wash cycle, low agitation) can be negatively impacted. Most isotropic HDLs in the market today have a viscosity of between 100 and 400 centipoise (cps), though examples are available outside of this at either extreme. In simple HDLs with high water levels the issue is increasing viscosity without adding expensive thickening chemicals. In top-end HDLs with numerous cleaning actives the issue is often keeping the viscosity from becoming too high. Careful balance of solvent and hydrotrope types and levels, often determined by laborious trial and error, is usually sufficient. Maintaining chemical stability, that is preventing or limiting interactions among the various actives included in an HDL, is also a challenge. The challenge is much higher in isotropic HDLs than in other detergent forms since all actives are dissolved in solution and free to interact with everything else in solution. The most commonly encountered chemical stability issues are reactivity and stability of enzymes, formulation of oppositely charged actives, hydrolysis of actives, and microbial growth. The formulation of bleach also falls into this category, but because there are no isotropic HDLs containing bleach this will be covered in the section on bleach containing liquids (Section V.C.). The issue of autoproteolysis in protease containing HDLs was mentioned briefly in the section on laundry detergent ingredients (Section III). If formulated without a stabilizing system, protease will rapidly consume itself and other enzymes the formulator may have added. A number of different strategies have been examined to overcome this issue. A reversible inhibitor of protease is the most common solution employed. In the relatively concentrated neat formula the inhibitor binds to the active site of the protease, preventing any unwanted reactivity. Once dosed into the wash solution the detergent is diluted and the inhibitor releases, freeing the protease active site. Boric acid and boronic acids are the most commonly used reversible inhibitors. These are added in the form of borate or boric acid and propylene glycol, which form the active stabilizer species in situ. Novozymes has recently begun offering “prestabilized” proteases for sale, which include 4-formyl phenyl boronic acid as the enzyme stabilizer already mixed into the enzyme solution [36]. Other enzymes have additional stability concerns. Amylase for example, requires low levels of free calcium to stabilize their tertiary structure. Without the calcium they


74

Watson

Table 9 Example of Dilute Isotropic HDL Ingredient AES AS AE Citric acid (50%) Protease Propylene glycol Monoethanol amine Borax (38%) NaOH (50%) Na formate (36%) Suds suppressor Dye Perfume w/benzyl salicylate FWA Water

Percent 5.0 5.0 1.0 0.75 0.24 0.28 0.32 0.6 1.4 1.25 0.02 0.016 0.30 0.10 Balance

essentially denature and become inactive. Low levels of calcium are often formulated for this reason. The challenge comes when chelating agents, fatty acids, citric acid, etc. are also formulated. These materials can all effectively bind calcium. Careful consideration and balance are required to include all these actives. The formulation of oppositely charged actives can also present difficulties. Interactions between anionic and cationic surfactants, resulting in the precipitation of their large uncharged complex are an obvious example. Most HDLs today do not include cationic surfactants, but there are examples that have been marketed in the past, where low levels of cationic surfactant were successfully formulated. Pseudoquats, namely tertiary amines that are not fully protonated at the pH of the formulation, are also used. Less obvious are problems that can arise from FWAs, which are also anionic species. The formula shown in Table 9 is illustrative of one way to formulate a “low-cost” dilute HDL while maintaining suitable aesthetics [37]. The challenge in a formula with over 80% water and around 10% surfactant is getting an acceptable viscosity. In this particular case the formulators found that certain perfume raw materials had an added benefit of thickening to greater than 160 cps. Finding actives that can play a dual role such as this is always a challenge. Adding a thickening polymer is also a possible solution. However, since most thickening polymers add nothing in terms of cleaning or odor, this represents an extra cost that is usually avoided. At the other extreme are formulas containing 20 to 30% surfactant, soil release polymer and/or dispersant, chelant, and multiple enzymes. Table 10 illustrates such a detergent that contains a pseudoquat amine surfactant [38]. Compared to the simple formula of Table 9, the increased use of solvent is apparent. There are numerous variations existing between these two formulas with variations on surfactant system, enzyme stabilization system (e.g., see Table 11 where sucrose is added [39]), solvents, and perfume. In all cases the underlying formulation strategy and challenges remain basically the same.



75

Table 10 Example of “Fully Loaded” Isotropic HDL Ingredient LAS C8-10 Propyldimethyl amine C12-14 Alkyl ethoxylated C12-18 Fatty acid Citric acid DTPA Monoethanol amine NaOH Propane diol Ethanol Amylase enzyme Lipase enzyme Protease enzyme Endo-A glucanase enzyme Carezyme Terepthalate polymer Boric acid Suds suppressor Water/various

Percent 18.0 2.0 12.0 11.0 5.0 1.0 11.0 1.0 12.7 1.8 0.1 0.15 0.5 0.05 0.09 0.5 2.4 1.0 balance

Table 11 Example of Isotropic HDL with Sucrose Ingredient NaLAS NaAES AE7 Na borate Sucrose Na citrate Propylene glycol Monoethanol amine Coconut fatty acid Protease enzyme Lipase enzyme NaOH Water

Percent 7.0 11.6 7.0 2.0 3.2 5 3.42 0.24 0.85 0.3 0.4 to pH 8.0 Balance

Both batch and continuous processes are used in the manufacturing of isotropic liquids. The manufacturing process is relatively straightforward and does not normally add additional constraints to the formulator. The primary concern is that the order of


76

Watson

addition is defined to avoid formation of highly viscous phases or generate insoluble precipitates. Since neutralization of acid surfactants can generate considerable heat, care must also be taken to add heat sensitive materials only after the batch has been sufficiently cooled. This usually means items like enzymes and perfumes are added very late in the making process. B. Structured Liquids Those formulators who prefer to formulate the liquid more along the lines of an HDG favor structured liquids. The key difference in structured liquids is the opportunity to suspend solids and possibly to formulate a higher concentration of cleaning actives without stability issues. This makes it possible to include actives that would otherwise not be soluble in an isotropic liquid, and to add actives that might otherwise be too reactive in their dissolved form. The resulting liquids are typically opaque and highly viscous, hence offering an entirely different aesthetic appearance to the consumer as well as a different performance profile. The higher viscosity of typically 500 to 9000 cps can also result in lower pretreat performance since the liquid does not penetrate the fabric as well as an isotropic liquid. The most common structured liquids are based on liquid crystalline surfactant phases. The structure comes from the dispersion of surfactant vesicles in the aqueous phase. The advantage of this method of structuring is that the structurant is also a cleaning agent and does not add extra cost. The surfactant (including fatty acid for purposes of this discussion) concentration is increased, and/or the electrolyte concentration is increased to push the system to form enough of these vesicles to become space filling. In practice this occurs when the vesicles have a solution volume fraction of above around 0.6 [40]. As the volume fraction of vesicles increases, the viscosity increases, as does the stability. Because the viscosity must be low enough to make the product easily pourable from the product bottle, there is a compromise that must be made between stability and pourability. The other common issue is flocculation of the vesicles that can result in significantly increased product viscosity due to the formation of networks, or can result in the destabilization of the structure due to a decrease in the total number of vesicles. Overcoming the viscosity/stability compromise and the flocculation issue is where most recent patent art is focused. Deflocculating or decoupling polymers are the most commonly used solution. These polymers are typically comb-type polymers with a hydrophilic backbone and hydrophobic teeth and there are numerous examples in the patent art. They are thought to perform two functions. First, they stabilize against flocculation by providing a barrier between individual vesicles in solution. Second, by inserting the hydrophobic teeth into the lamellar sheets that make up the vesicle walls, they can increase the size of individual vesicles, thereby increasing stability. The hydrophilic backbone is often a polyacrylate derivative and the hydrophobic teeth a long alkyl chain. Table 12 shows an example of a phosphate containing HDL [41] made in this way. Adding even a fraction of this level of STPP in an isotropic HDL would not be possible. A similar, nil-phosphate version is illustrated in Table 13 [42]. There are alternatives to structuring via surfactant phase. These alternatives typically involve creating a network throughout the solution that reduces the tendency of other materials in solution to coalesce or phase-split. This network can be established via some soluble polymers [43], though this approach is typically very expensive and is not always sheer-thinning, thus making pouring difficult. A more common means of creating this network involves the use of insoluble or sparingly soluble solids. The use of organically modified clay particles to create a “house-of-cards” structure in a liquid is well known and will be discussed briefly in the section on 2-in-1 detergents. A more recent example



77

Table 12 Example of a Phosphate Containing Structured HDL Ingredient NaLAS K Laurate K Oleate AE7 Glycerol Boric acid KOH STPP Gasil 200 Silicon oil FWA NaCMC Dequest 2060S Protease enzyme Perfume Deflocculating polymer Water

Table 13

Percent 6.3 3.8 5.5 10.0 5.0 2.28 1.0 19.0 2.0 0.25 0.1 0.3 0.4 0.5 0.3 0.75 Balance

Example of Nil-Phosphate Structured HDL Ingredient

LAS AES AE Na citrate Borax Glycerine Protease enzyme Deflocculating polymer FWA Colorant Preservative Fragrance Water

Percent 20.0 5.5 10.0 10.0 2.0 4.0 1.5 1.0 0.4 0.75 0.05 0.4 Balance

involves the controlled crystallization of hydroxyl-modified oils to create a fibrous or entangled thread-like network in situ [44]. One such example is trihydroxystearin, sold under the trade name Thixcin by Rheox, Inc. It is possible to generate a stable structured gel without the use of decoupling polymers or other external structurants. An example is shown in Table 14 [45]. In this


78 Table 14

Watson Example of Structured Gel HDL without Deflocculating Polymer Ingredient

C25E1.8S C12 LAS C23 E9 C10 Amidopropylamine Citric acid DTPA C12-16 FA Rapeseed FA Protease enzyme Amylase enzyme Cellulase enzyme FWA Soil suspending polymer Ethanol Propane diol Monoethanol amine NaOH Na sulfate Borax Suds suppressor Perfume Dye Water

Percent 23.5 3.0 2.0 1.5 2.5 0.5 5.0 6.5 0.88 0.1 0.05 0.15 1.2 0.5 4.0 0.48 7.0 1.75 2.5 0.06 0.5 0.02 balance

example the careful balancing of electrolyte levels via citric acid and sodium sulfate is used to move the surfactant into a planar lamellar phase. The result is a shear thinning gel that remains transparent. Gels of this type can be sensitive to fluctuations in raw material quality and process variations that affect electrolyte levels. Otherwise they offer an interesting alternative to the more traditional opaque structured liquids. Transparent gels packaged in transparent bottles open the possibility of delivering unique aesthetics via the suspension of visible particles of various sizes and compositions. Robust, clear gels based on lamellar phase droplets dispersed in an isotropic aqueous phase have been reported [46]. The key is to reduce the size of the lamellar phase droplets via either very high sheer rate during processing, and/or by use of deflocculating polymers. Careful matching of refractive index between the droplets and the continuous phase via addition of sugars can also help. An interesting new issue of such a clear product in a clear product is the effect of UV light on the actives. Degradation of actives such as enzymes or dyes when exposed to normal daylight is well know and must be avoided. Addition of fluorescent dyes, UV absorbers, and antioxidants are all shown to aid stability [47]. Encapsulation of actives in polymers or other protective shells can also work [48]. The production of structured liquids is more problematic than that of isotropic liquids. Depending on the structuring method used the process required can vary dramatically. Also, some systems need to “age” before their full structuring capability is realized. In systems where solids will be suspended this is an important consideration. In a typical



79

batch mixer with blade agitation, large amounts of air can be incorporated into the product. This needs to be removed before the structuring step or it can become entrapped in the liquid. As it slowly deaerates an undesirable foam layer can form on top of the liquid, and the process of deaerating can destabilize suspended solids. C. Bleach-Containing Liquids As mentioned above, one of the largest challenges in liquid detergents is the inclusion of bleach. There are two primary reasons for this, and two primary avenues used to overcome them. First, most of the nonchlorine oxidizing bleaches are unstable as the aqueous solution. Second, even if the bleach is stable, the other actives in the formula are typically not stable toward the bleach. In both cases, by the time the detergent reaches the consumer’s home there is little bleaching power remaining, and often little of anything else. Conceptually the solutions are straightforward—keep the bleach separate from the rest of the detergent and/or make the detergent nonaqueous. Executionally things are less straightforward. One way to keep the bleach separated from the rest of the detergent is to use a bleach that is either insoluble or only very slightly soluble in the detergent matrix. Provided the insoluble bleach is present in small enough (i.e., submicron) particle size it can be suspended directly in a non-structured liquid. More commonly, a structured liquid is utilized. If totally insoluble, such a bleach could theoretically be added into any structured HDL with appropriate suspending power. The bleach is typically an organic peroxy acid, examples of which include: N,N′-terephthaloyl-di-(6-aminopercarboxycaproic acid) (TPCAP); 1,12-diperoxydodecenoic acid (DPDA); and N,N-pthaloylaminoperoxycaproic acid (PAP). The reality is that these bleaches do have limited water solubility—enough to be of concern. Hence thought has to be given to their chemical stability as well. The stability of these peracids is much higher at low pH (i.e., pH 3–6), but for good performance of the detergent the wash pH needs to be higher (i.e., pH 7–9). So formulators have developed “pH-jump” systems. In a pH-jump system the neat product pH remains low, but on dilution in the wash jumps to a suitably high pH of 7 to 8. This is commonly accomplished by formulating borax and a polyol. The polyol complexes the borate in the concentrated neat liquid, keeping the pH low. On dilution they dissociate, releasing borate into solution and thereby raising the pH. Table 15 illustrates a bleach containing HDL formulated around this concept [49]. Another potential problem area for bleach stability is the presence of trace transition metals in the formulation. Even with careful attention to water sources and raw material quality, the presence of trace transition metals in the formulation is all but unavoidable. Transition metals decompose the peracid bleaches via a radical mechanism. To shut down the decomposition pathway the formulator can either add a chelant to sequester the transition metals, or add a radical scavenger such as an amine-oxide or an antioxidant like BHT. An example of a formulation with the later is shown in Table 16 [50]. Suspending the bleach in an anhydrous liquid detergent is another possibility. This also opens the possibility to formulate a bleach activator such as TAED or NOBS for better performance. The challenge in this case is insuring there is no free water to begin decomposition of the bleach, and ensuring the liquid remains stable at a pourable viscosity. These two items are often related since decomposition of activators such as NOBS leads to formation of colloidal fatty acid derivatives that leads to irreversible thickening upon aging. Stable products are obtained by the careful choice of organic solvent and liquid raw materials (such as some nonionic surfactants). The rest of the raw materials are added as fine powders. Table 17 illustrates a formula where butoxy-propoxy-propanol is the primary solvent, and NOBS/percarbonate makes up the bleach system [51]. Processing of


80

Watson

Table 15 Example of pH-Jump with Bleach HDL Ingredient

Percent

DPDA LAS C25 E9 Na borate 10H2O sorbital Na sulfate Na polyacrylate Decoupling polymer Chelant Minors Water

2.0 16.1 6.9 5.0 20.0 0–5 0 – 0.20 0.5 – 1.0 0.30 0.5 Balance

Table 16 Example of Stabilized HDL with Bleach Ingredient HLAS Sorbitol (70%) DI H2O AE9 Na citrate NaOH (50%) Decoupling polymer Sodium borate BHT TPCAP

Percent 29.5 16.1 15.2 12.9 9.7 7.4 1.8 3.7 0.84 3000 ppm AvO

anhydrous formulas such as this is much more complex than for isotropic liquids or even for most structured liquids described above. Bleach catalysts offer perhaps the most promising approach to an HDL with bleach, though to date none have appeared on the market. The reasons for this are tied to the design and performance of the bleach catalyst more than to the HDL itself [52]. As already discussed in the section on raw materials, catalysts react with appropriate oxygen sources to form high valent metal oxides that are potent oxidizing agents. These metal oxides provide enhanced performance at lower temperatures and in shorter time. More importantly for HDLs they take up far less formulation space since they are catalytic. The ultimate goal for an HDL is to have a catalyst that forms the metal oxide bleaching species using molecular oxygen or the low levels of peroxides that preexist in stains. Such a catalyst would remove the challenge of formulating either peroxide sources or preformed peracids in the HDL.



81

Table 17 Example of Anhydrous with Bleach HDL Ingredient

Percent

NaLAS C11E5 BPP Na citrate NOBS Soil suspension polymer EDDS Na carbonate Acrylate polymer Protease enzyme prills Amylase enzyme prills Cellulase enzyme prills Na percarbonate Suds suppressor Perfume TiO2 FWA Thixatrol ST Speckles Misc.

16.0 21.0 19.0 4.0 6.0 1.2 1.0 7.0 3.0 0.4 0.8 0.5 16.0 1.5 0.5 0.5 0.14 0.1 0.4 to 100%

D. Dual-Bottle Liquids One of the goals mentioned above for structured and anhydrous liquids is to keep reactive or incompatible ingredients separate. The same goal can be accomplished in a chemically simpler way by keeping the different actives physically separated via the packaging. That is to say, the bottle is made up of two (or more) separate compartments such that their contents mix only on dosing. This opens up several degrees of freedom to the formulator, but adds packaging complexity and cost. With such a packaging system in hand a number of possibilities emerge. The utility of the dual-bottle approach is currently limited by packaging and production constraints much more so than formulation constraints. Formulating for a dual-bottle approach is not as straightforward as putting a normal HDL in one bottle and a solution of the incompatible active in the other. Unless the dosage volume is doubled, the result would be to dilute the HDL with the second bottle. Where possible then, the main cleaning actives are often formulated into both bottles, with the main incompatible actives formulated more concentrated in separate bottles. In this way, deliver of sufficient actives can be balanced against dosage volume. The degree to which this is an issue depends on the volume ratio delivered by the two bottles on dosing and on how concentrated the particular formula can be. Matching the viscosity between the two liquids is also an important challenge to maintain optimum pouring and mixing properties. An example of a dual-bottle approach delivering softening benefits is shown in Table 18 [53]. In this case the second compartment contains a quaternary softening active that


82

Watson

Table 18 Example of Dual-bottle HDL with Softener Active Ingredient AE Alkyl amine oxide Citric acid Ethoxylated alkyl amine Chelant N,N-dimethyl N,Ndi(tallowacyloxyethyl) ammonium chloride Protease enzyme Amylase enzyme Boric acid Ethanol Propanediol Sodium cumene sulfonate NaOH Monoethanolamine Perfume/minors Water

Percent A

Percent B

15.0 5.0 — 1.0 0.4 —

5.0 — 10.0 — — 15.0

0.10 0.22 2.0 — 10.0 2.0 — to pH 7.5 1.5 Balance

— — — 5.0 — 2.0 to pH 3.0 — 1.5 Balance

would otherwise precipitate with the anionic surfactant in a single bottle HDL. Note that the dual-bottle approach also allows for formulating at the optimum pH for chemical stability of the softener active on the one hand, and the detergent enzymes on the other. Incorporation of a bleach such as PAP in the second bottle is also of key interest [54]. Another interesting possibility disclosed in the same patent application is delivery of “signals” that reinforce to consumers that the detergent is working as intended. Examples could include release of a specific consumer appreciated fragrance, or production of a color that indicates mixing is complete. Table 19 illustrates a formula where the signal is effervescent foaming created by the reaction of catalase enzyme with hydrogen peroxide. The foam is created as the gas generated from the decomposition of peroxide bubbles through the concentrated surfactant solution of the HDL.

VI. UNIT DOSE DETERGENTS A. Tablets Laundry tablets are small “briquettes” of solid laundry detergent. Shapes vary, but the typical tablet contains roughly 40 G of detergent making the normal dose two per wash load. The primary advantage of tablets comes in ease of dosing—aside from deciding how many tablets to add to the wash there is no measuring. Given their highly compact nature, tablets also offer some economy in shipping and storage, but this is secondary. The basic idea of laundry tablets has been around since the 1960s. Initial launches failed due to poor solubility and poor consumer acceptance. Tablets were relaunched in Europe in the late 1990s, where they have taken a firm place in the market. Improvements in



83

Table 19 Example of Dual-bottle Effervescent HDL Ingredient

Percent

Bottle A

MEA C10 APA Na C25 AE1.8S Propylene glycol Neodol 23-9 FWA Na toluene sulfonate NaOH N-cocoyl N-methyl glucamine Citric acid C12–16 real soap Borax Ethanol Ca formate Ethoxylated polyethyleneimine Ethoxylated tetraethylene pentaimine Na formate Fumed silica Soil release polymer Water Dye Protease enzyme Cellulase enzyme Amylase enzyme Silicone Perfume DTPA Catalase enzyme

1.1 0.5 19.35 7.5 0.63 0.15 2.25 2.79 2.5 3.0 2.0 2.5 3.25 0.09 1.3 0.6 0.115 0.0015 0.08 46.08 0.016 1.24 0.043 0.15 0.119 0.35 0.3 0.15

Bottle B

NaOH Hydrogen peroxide Water Titanium dioxide Xanthan gum

3.46 4.0 72.69 2.5 0.45

tablet design and changes in consumer habits and preferences have contributed to the new success. Tablets are the same as HDGs in terms of actual cleaning chemistry delivered to the wash process. The basic cleaning chemistry is reapplied from HDG developments, described previously in this chapter. Most developments in the field of tablets are targeted at overcoming the manufacturing and dosing/dissolution constraints inherent in the form. The first step of manufacturing tablets often involves making a traditional laundry granule


84

Watson

via either spray-drying or agglomeration. These granules are then combined with other actives, a binder of some kind (e.g., polyethylene glycol, water soluble polyacrylates, etc.), and the combination is then “pressed” with high pressures into the tablet form. Due to the force used to compact the tablets, they dissolve slower in the wash compared to the same actives in granule form. If less force is used a more porous, faster dissolving tablet results. Unfortunately such tablets are usually not physically robust enough to withstand the packaging and shipping operations. Developing a tablet with good handling characteristics and good dissolution profile at the same time is the primary challenge. A number of approaches have been developed against this challenge, many of them learned from the pharmaceutical industry that faces related challenges in medicinal tablets. Some solutions do not affect the tablet per se, but rather how the tablet is physically added to the wash. These range from hard plastic devices to simple mesh bags [55]. In all cases the idea is to insert the tablet into the device to help break-up the tablet and to prevent large chunks from becoming lodged in nonproductive places in the washing machine. Once broken into small enough pieces the same dynamics affect dissolution as in HDGs. Approaches that affect the tablet itself usually rely on an added swelling agent, hydrotropes, or disintegrant to help the tablet break apart rapidly and completely in the presence of water. This is the preferred approach for tablets of uniform density and hardness. There are also approaches that involve more complex processing of the tablet to include layers of different hardness, or coatings to protect softer interiors. Combinations of all these approaches are also known. In phosphate-containing tablets it is possible to use materials high in Phase I STPP to aid in rapid disintegration [56]. Phase I STPP, available commercially for example as Rhodiaphos HPA 3.5, is the high temperature stable version of crystalline anhydrous STPP. It hydrates and dissolves more rapidly than phase II material and has been shown to aid dissolution of granules. Additional dissolution aides can also be used at the same time as shown in the example in Table 20, which includes an effervescent system. This example also highlights another common feature of tablet design, the use of multiple layers to separate actives (e.g., the phase I STPP is best separated from other hydrated species), or to provide additional mechanical stability. Table 21 illustrates the use of phase I STPP in a zeolite-containing tablet [57]. In nil-P products a different approach is required. In this case, the use of other higher water-soluble salts is found to be beneficial [58]. Sodium acetate trihydrate is claimed for use in this role [59]. Another approach is to use swellable polymers, which on wetting serve as an “explosive agent” to aid disintegration of the tablet. Henkel, for example, use a form of compacted cellulose sold as “Arbocell” by Rettenmaier, for this purpose [60]. A wide variety of other disintegrants are known from the pharmaceutical industry, including starches, and gums [61]. Generating a tablet with a softer, more readily dispersed and dissolved interior, coated with a harder protective “shell” is another approach to the problem. The shell coating is designed to provide mechanical stability during manufacturing, shipping, and handling, and also to provide some level of moisture protection. The coating should be easily broken in the washing machine, via mechanical action and via interaction with water, to release the softer contents rapidly. The coating can be applied over the already formed tablet interior either in the molten form, or as an aqueous solution. Dicarboxylic acids, such as adipic acid, are the preferred coatings in many applications [62]. The coating can also include a disintegrant as discussed above to aid the breakup of the coating. Likewise, reinforcing fibers (e.g., 100 to 400 µm synthetic or natural fibers) can also be included to help avoid premature cracking of the coating during handling. It should be noted that tablets using a coating such as this generally require a flow wrap of some sort for moisture protection to prevent premature swelling and cracking.



85

Table 20 Example of Tablet with Phase I STPP and Effervescent System Ingredient Base powder Na-LAS Nonionic surfactant Soap AA/MA copolymer (70:30) STPP (builder) Na silicate Na carboxymethyl cellulose Moisture Total

Percent

23.55 10.42 0.72 3.22 40.63 8.63 0.67 12.15 100.0

Tablet Thick Layer Base powder Na percarbonate TAED granules (83%) Rhodiaphos HPA 3.5 Citric acid Na bicarbonate Minors + moisture Total

39.00 — 4.40 49.00 — — 7.60 100.00

Thin Layer 22.00 49.00 — — 9.62 19.30 0.08 100.00

Overall 35.60 9.80 3.52 39.20 1.92 3.96 6.10 100.00

An interesting possibility being explored recently is development of tablets with controlled release of actives. Increased performance and/or delivery of additional benefits can be obtained by controlling the order and timing in which various actives enter the wash process. Tablets offer some additional avenues by which to do this. For example, by changing the pressure used to compress different layers of a tablet, different dissolution rates can be obtained. Generally speaking the higher the compression force used the slower the dissolution. The addition of different binding agents at different levels can complement this effect. Likewise, by using different coating or even the same coating with varying thickness the dissolution rate of different layers of the tablet can be retarded by varying amounts of time. Finally, disintegrants can be added to selected layers to help them dissolve more rapidly. An example of this approach is illustrated in Table 22 [63]. This particular example is a four-phase tablet wherein the surfactants and nonprotease enzymes are released almost immediately in the wash, followed 5 to 10 min later by protease enzyme, builder, and alkali. Bleach follows closely in the third phase, and finally a fabric softener active is added in the final rinse. The advantage to this approach is the separation of actives that normally interfere with each other. The nonprotease enzymes have time to function before protease is added and begins degrading them. All of the enzymes have time to function before bleach is added, and the cationic fabric softener is well separated from the anionic surfactants, thereby preserving the function of both.


86

Watson

Table 21 Example of Tablet with Mixed Zeolite/STPP System Ingredient

Percent

Base Powder

Na-LAS Nonionic surfactant Soap Zeolite 4A Na carbonate STPP (fully hydrated) Moisture/minors Total

22 5 3 35 20 10 5 100%

Tablet

Base powder Rhodiaphos HPA 3.5 Blue speckles Sequestrant, enzymes, perfume Total

Table 22

66 31 1.5 3.5 100%

Example of Tablet Utilizing Controlled Release of Actives

Ingredient C12-18 Alkylbenzene sulfonate C12-18 Alkyl sulfate C12-18 Alkyl ethoxylate EO7 Zeolite A Sodium carbonate Water glass Polycarboxylate polymer Sodium percarbonate TAED Protease Amylase Lipase Cellulase Auxiliary materials (antifoam, perfume) Water Sodium sulfate Esterquat softener


Amount (G/Wash Load) 9.75 1.95 2.93 14.63 7.31 2.91 2.44 11.25 4.5 0.75 0.23 0.75 0.23 3.75 6.5 to 100 7

Phase I

Phase II

Phase III

Phase IV

x x x x x x x x x x x x x x x x x


87

B. Liqui-Tabs Liqui-tabs, i.e., a single dose of liquid detergent contained in a water-soluble pouch, are a relative newcomer in the market. The first versions for laundry began appearing in Europe less than 5 years ago. The main benefit of liqui-tabs, like tablets, is primarily convenience—there is no need to measure the dose or come into contact with the enclosed liquid. The cleaning chemistry is the same as in conventional HDLs, and the water-soluble pouch is typically made of polyvinylalvohol (PVA) or some derivative thereof. The pouches are typically filled and sealed using either vertical form-fill-seal (VFFS) or horizontal form-fill seal (HFFS) processes. In the vertical processes the pouch is formed into a rectangular shape without stretching the film material. In the horizontal processes one sheet of film is drawn into a mould with thermo- and/or vacuum-forming techniques, filled with the liquid and sealed with another (not-stretched) sheet of film. The advantage of the horizontal processes is the higher production speed (translating into a lower production cost) and the possibility to give the pouch a shape that will be more attractive to consumers. Research development in liqui-tabs are primarily addressed at overcoming challenges that come from the water-soluble film itself, and from the need to keep pouches stable during shipping and handling. The major differences between an HDL formulation and a liquitab formulation are driven by these challenges. The most obvious challenge is how to put a formula that normally contains up to 50% or more water into a water-soluble pouch. The obvious answer is to remove the water, though as discussed in the HDL section this is not as easy as it sounds. This is especially true if you do not want to invest a lot of money into expensive nonaqueous solvents. In practice, formulas with 80 96

41

C12E8/C12E4.2 Triton X-100f

100 98–100

42 43

Genapol X-80 Brij 56c

98–100 92–96

44 ”

C12E8/C12E4.2

72–100

42

C8E3 C12E5 Igepal CA-520

35–40 79 97

45 ” 46

Triton X-114 Triton X-114d PONPE-7.5

100 63–77c 76–98 100

47 ” 48 38

C12E8/C12E4.2

84.5-98

42

Igepal CA 620g, 50˚C

79-87

49

Surfactant concentration (w/v): 1% if not indicated otherwise: a0.5%, b0.2%, c2%, d0.25%, e3%, f 2%; g50 mM. Undissociated solutes are considered.

Examples of recent applications of CP extractions of metals using commercial ligands include: use of Triton X-114 to preconcentrate U(VI) as PAN complex prior to the flow injection analysis [61]; preconcentration of Ni(II) and Zn(II) as PAN chelates in micellar Triton X-114 prior to the flame atomic absorption analysis [62]; determination via FIA of Al(III) present at trace levels in parenteral solutions, preconcentrated as Chrome Azurol S (CAS) chelate in the presence of cationic surfactants and nonionic PONPE 7,5 [63]; preconcentration of gadolinium present in urine after reaction with the ligand 2-(3,5dichloro-2-pyridilazo)-5-dimethylaminophenol and CP extraction with: PONPE 7.5 [64].


Detergent Formulations in Separation Science

313

Cloud-point extraction of metals can also exploit the complexing ability of the surfactant oxyethylene units, without the introduction of auxiliary ligands [65]. 3. Micellar Ultrafiltration Micellar-enhanced ultrafiltration (MEUF) is a separation method proposed by Scamehorn and coworkers [66] which combines the good selectivity performances of reverse osmosis with the higher flux rate of ultrafiltration, allowing the separation of dissolved solutes bound to carrier micellar aggregates. The removal of micelles from the bulk solution is performed provided the UF membrane pore-size is small enough to reject micelles (and their guest solutes), leaving them in the retentate phase. Since the mean weight of usual aggregates is in the range 10 to 100 kDa, membranes having pore diameters between 20 and 100 Å are normally suitable, with corresponding acceptable fluxes of the solution to be treated. In most reported frontal ultrafiltration experiments, membranes with MWCO in the range 55 kDa were successfully employed. Various types of hydrophilic (largely cellulose-based) and hydrophobic membranes can be applied under different conditions [67]. Most laboratory ultrafiltration experiments were performed in cylindrical stirred cells, where the feed solution is forced to permeate under the pressure exerted by an inert gas (see Figure 3). Efficient stirring just above the membrane surface reduces the formation of a solute concentration gradient, referred to as concentration polarization, which decreases the flux rate. A surfactant concentration limit exists above which the flux drops to zero (gel point). The use of centrifuge tubes having an incorporated suitable membrane allows to obtain a faster filtration (see Figure 3) The efficiency of micellar ultrafiltration is measured by the rejection coefficient (or rejection factor), defined as: R = 1 – Cp/Co

(6)

where Cp and Co are the solute concentrations in the permeate and in the initial (feed) solution, respectively. Since micelles are completely rejected by the membranes, they accumulate in the retentate phase and the permeate contains only low concentrations (near the cmc) of the amphiphile. a. Preconcentration of Organic Solutes via Micellar Ultrafiltration. Irrespective of the micellar system used and of the substrate structure, complete rejection of solutes in the retentate is achieved when they are completely bound to the aggregates (as for quantitative cloud-point extractions, KB must be higher than ca. 1000 M–1). Several highly hydrophobic compounds satisfy the above requirement, but for more hydrophilic solutes permeation becomes relevant and changes in the operating conditions are necessary in

Inert gas

Permeate

Figure 3

Laboratory ultrafiltration devices: centrifuge tube and stirred cell.


314

Pramauro and Prevot

100 90

4

80

2

%R

70

4

5 3

5

5

6

6

2

60 50 40

HTAB SDS

1

30 20 0

300

600

900

1200

KB

Figure 4 %R vs. KB (M–1) in MEUF experiments performed with ionic micelles. (1) aniline; (2) 4-ethylaniline; (3) 4-tert-buthylaniline; (4) phenol; (5) 4-chlorophenol; (6) 2,4-dichlorophenoxyacetic acid. (From Pramauro, E. Ann Chim (Rome) 80:101–109, 1990 and Pramauro, E. et al. Analyst 118:23–27, 1993.)

order to increase KB. Figure 4 shows the separation performances of various aromatic solutes as a function of KB in ultrafiltrations performed with ionic micelles. Amphiphiles having longer hydrocarbon chains are generally preferred since increased rejection and decreased cmc values are obtained. However, when ionic surfactants are used, the risk of phase separation exists because the Krafft temperature of these compounds rapidly increases with the alkyl chain length [12]. The effect of surfactant concentration on rejection is relevant for partitioned solutes, whereas no significant changes in the bound fraction is observed for highly hydrophobic compounds. For example, the permeation of 4-chlorophenol present in aqueous acidic wastes passes from ca. 40% to ca. 15% of the initial feed concentration (0.1 mM) increasing the SDS concentration from 20 to 80 mM. Under the same conditions, permeation of 3,5dichlorophenol decreases from ca. 3% to ca. 2% [42]. Changes of pH alter the rejection of ionic solutes either in the presence of ionic or nonionic micelles; for ionic aggregates, in particular, the role exerted by electrostatic repulsions or attractions is very important. For example, the preconcentration of aniline from aqueous samples can be achieved with good yields (R > 0.95) using SDS micelles at a working pH at which the analyte is fully protonated [68]. Under these conditions, the loss of hydrophobicity due to protonation is largely compensated by the electrostatic attraction exerted by the anionic aggregates. On the contrary, electrostatic repulsion reduces the rejection factor when HTAB aggregates are used to remove the same compounds from acid solutions (R < 0.10). In Figure 5 the effect of pH variation on rejection is showed for 4ethylaniline and 2,4,5-trichlorophenoxyacetic acid, in presence either of HTAB or SDS micelles. Ionic strength plays an important role when ionic solutes are extracted using oppositely charged ionic aggregates. Shielding effects are observed in these cases, with a corresponding decrease of the rejection coefficients; on the other hand, no significant changes due to ionic-strength have been reported for ultrafiltration of neutral solutes in the presence of nonionic aggregates. b. Ultrafiltration of Inorganic Ions using Micelles Bearing Opposite Charge. M u l ticharged ions can be efficiently removed via micellar ultrafiltration using oppositely charged aggregates, but the system is not selective and is highly sensitive to the ionic strength. Rejection coefficients higher than 99% have been reported, under the same



315

Solute rejected (%)

100 80 60 40 20 0 2

3

4

1SDS

5 pH 1HTAB

6

2SDS

7

8

2HTAB

Figure 5 Effect of pH variation on R values for 4-ethylaniline (1) and 2,4,5-trichlorophenoxyacetic acid (2), in presence either of HTAB or SDS micelles. (From Pramauro, E. Ann Chim (Rome) 80:101–109, 1990 and Pramauro, E. et al. Analyst 118:23–27, 1993.)

experimental conditions, for divalent cations (Co2+, Zn2+, Cu2+, Cd2+) using SDS micelles and similar rejection values were measured for divalent anions in the presence of cationic micelles [69]. The effective removal of Sr2+ present in nuclear wastes is a recent example of these applications [70]. c. Use of Chelating Micelles. The combined use of ligand micelles and UF can be effective either for preconcentration or separation of metals present in complex aqueous mixtures [60,71-77]. Cationic surfactants are in principle the best candidates to form the mixed chelating micelles since uncomplexed cations should be repelled from the aggregates, but partial rejection of the free cations was observed in some cases [78]. Nonionic polyoxyethylene-type amphiphiles do not show these undesirable effects, although they exhibit some complexing ability toward metal ions. Rejections of divalent cations up to ca. 55% were, in fact, observed in blank ultrafiltration runs performed with Triton X-100 aggregates [74]. The increase of ligand hydrophobicity increases the bound chelate fraction, thus improving the metal rejection. For example, the rejection of Cu(II) (present at the trace level in aqueous acidic wastes) passes from less than 10% using mixed micelles of HTAB and the ligand C4-NHMePyr to more than 99% working with C16-NHMePyr [72]. Similarly, the rejection of Fe(III) at pH 3.5, in the presence of host C12E8 micelles, was 84% using Y-PAS-C4 and nearly 100% using Y-PAS-C8, respectively [78]. The structures of some lipophilic ligands used in micellar ultrafiltration work are shown in Figure 6. The stoichiometry of the complexes formed in micellar media is usually different from that observed in homogeneous solutions and tends to 1:1 for hydrophobic ligands. For example, the ligand PAN reacts with Ni(II) in Triton X-100 micelles forming a 2:1 chelate (as in homogeneous water-dioxane solutions) whereas a 1:1 complex is formed when the more hydrophobic derivative PAN-C4 is used [79]. Higher complex stabilities are preferred because the ligand excess can be minimized, thus reducing the costs. PAR, PAN, 8-hydroxyquinoline, etc. (and their lipophilic derivatives) are particularly suitable. The complex formation kinetics also changes dramatically depending on the reaction site (aqueous vs. micellar phase) and is very sensitive to electrostatic repulsion or attraction between the metal ions and the chelating ligands [73,80,81]. In some cases the kinetic effects can be exploited for separation purposes. For example, mixtures of Co2+ and Ni2+


316

Pramauro and Prevot CH3

OH N

CH2CH3

CnH2n+1O

CHCH2CH2CHC4H9

C11-HQ

N

COOH

Cn-PIC: 5-alkoxypicolinic acid

CnH2n+1

COOH OH

N

N HO

NHCOCnH2n+1 Cn-PAS: 4-alkylamido-2-hydroxybenzoic acid

Cn-PAN

CH2COOH HOH2C

CnH2n+1NHCH3

CH3(CH2)11 N CH2COOH

N CnNHMePyr: 6-[(alkylamino)methyl]-2(hydroxymethyl) pyridine

DIDA: dodecyliminodiacetic acid

Figure 6 Molecular structure of some amphiphilic ligands used to form ligand micelles.

(in the ppm range) can be separated using the ligand C11-HQ solubilized in HTAB/butanol microemulsions. The complex formation takes few minutes for Co2+ and hours for Ni2+ at pH ca.6, thus allowing their separation via micellar ultrafiltration [82]. As expected on the basis of chelate formation from ionizable ligands, the ultrafiltration performances are pH-dependent and the corresponding R vs. pH curves are similar to the typical liquid–liquid extraction profiles [72,74,75]. The performances of micellar UF are in many cases comparable with those obtained using usual extraction methods [83]. Figure 7(a) shows the variation of rejection for three different metal ions in the pH range 3 to 7.5, measured after treating the feed with ligand micelles of Triton X-100 and C4-PAN. Quantitative or nearly quantitative recovery of Co(II) is possible by ultrafiltration in the reported pH range. On the contrary, very low retention has been observed for Ca(II), whereas quantitative recovery of Zn(II) is achievable only in the pH range 5 to 7.5. Selective separation and purification of Co(II) from mixtures containing Zn(II) and Ca(II) can be achieved at pH 3, by applying a multistep ultrafiltration (see Figure 7b). C. Micellar Liquid Chromatography In reverse-phase micellar liquid chromatography (RP-MLC) aqueous micellar solutions, usually containing some proper additives such as alcohols or acetonitrile, are used as mobile phases instead of usual hydroorganic mixtures. The peculiar features of micellar eluents and the retention models describing the solutes behavior have been analyzed in detail in some comprehensive reviews [2-4,7,9] and books [10,84]. The micellar HPLC



317

1 Co(II) Zn(II) Ca(II)

0.8 0.6 R 0.4 0.2 0 2.0

4.0

6.0

8.0

pH (a)

0.5

0.5

0.5

0.5

CR

0.4

Co (II) Zn (II)

0.3 0.2

0.14

0.1

0.03

0.01

0 I stage

II stage

III stage

(b)

Figure 7 a. Effect of pH on R values for different metal cations. b. CR (metal ion concentration in the retentate) vs. consecutive MEUF stages. Initial metal concentration: 0.5 mg/l–1. (From Pramauro, E. et al. Talanta 41:1261–1267, 1994.)

equation reported in Table 1 describes the basic Armstrong-Nome retention model, valid for solutes attracted by the micelles. Several advantages related to the use of micellar eluents have been evidenced: enhanced selectivities, lower costs, more safety, specific detection modes, possibility of direct injection of biological samples, and fast gradient elution capabilities. The main inconvenient of RP-MLC is the low efficiency, but this drawback has been at least in part compensated by adding adequate organic modifiers to the eluent. The direct injection of biological fluids samples in RP-MLC is particularly interesting since the development of sensitive methods for HPLC analysis of metabolites and drugs in such matrices requires a careful elimination of proteins to avoid column clogging and interference effects. Protein extraction (or precipitation) preliminary steps increase the analysis time and the possibility of error; these pretreatments can be avoided using micellar eluents due to the solubilization of the proteins through surfactant coating. Several reports appeared during the last 5 to 6 years were focused on both applicative and mechanistic studies on RP-MLC. Contributions to the knowledge and prediction of the MLC performances include: analysis of band broadening [85] and peak shape [86]; examination of the effect of organic modifiers on retention [87,88]; introduction of ionexchange stationary phases for separation of dansylated amino acids [89]; characterization of retention in MLC [90]; retention prediction and modelling studies for pyridine derivatives [91], peptides [92], catecholamines [93], anesthetics [94], metal-dithiocarbamate complexes [95]; prediction of ecotoxicity of various organic pollutants [96,97] from MLC partition data; studies on pharmacokinetics and pharmacodynamics of antihistamines via MLC [98], etc. A systematic optimization of micellar eluents for improved MLC separations has also been examined on chemometric bases [99].


318

Pramauro and Prevot

Table 5 MLC Analysis of Complex Samples Analyzed compounds

Chromatographic Eluent

Samples

Ref.

Pentobarbital Synthetic antioxidants Derivatized amino acids

0.02M CTAB + 15% 1-propanol 0.05-0.15 M SDS + (1–9)% 1-propanol 0.05 M SDS + 1.2% 1-propanol

100 101 102

Parabens

0.1 M SDS + 2.5% 2-propanol, pH 3 (phosphate) 0.05 M SDS + 10-15% 1-propanol, (after derivatization) pH 3 0.01 M HTAB + 20% acetonitrile, pH 6.3 (phosphate) 0.05–0.15 M SDS + 15% 1-propanol +1% triethylamine, pH 3

Plasma, urine Dairy products Aqueous samples Cosmetics Urine

104

River waters

105

Urine

106

Pharmaceutical formulations Pharmaceutical formulations

107

Thiazide diuretics Thiram (fungicide) Antagonists (acebutolol, atenolol, nadolol, metoprolol, celiprolol, etc.) Antihistamines Caffeine

0.15 M SDS + 6% 1-pentanol 0.05 M SDS + 1.5 % 1-propanol, pH 7

103

108

Chromatographic columns: RP-C18.

Table 5 summarizes some recent examples of MLC determinations. D. Micellar Electrokinetic Capillary Chromatography (MECC) This powerful surfactant-based separation technique, introduced by Terabe and coworkers [17] can be considered as a combination of MLC and capillary zone electrophoresis (CZE). In MECC a surfactant is dissolved in the background electrolyte solution at a concentration higher than its cmc; both ionic and non ionic surfactants can be used. Anionic micelles (i.e., SDS) have an electrophoretic mobility and a migration direction opposite to that of the electroosmotic flow (EOF). Being this last usually faster than the aggregates migration velocity, the direction of flow of all the components is the same, but micelles migrate slowly. In these conditions, a chromatographic like system is operative in which two distinct phases, the aqueous (mobile) and micellar (pseudostationary), are present within the capillary column and migrate at different velocities toward the electrode with the same charge as the micelles. Solutes partitioned between these two phases will move more or less slowly depending on their binding constants to the micelles, whereas, if charged analytes are present, they will in addition undergo electrophoretic migration either in the opposite direction of the electroosmotic flow (micelle-like charged analytes) or in the flow direction if they act as micelle counterions. In presence of cationic aggregates (i.e., HTAB) the direction of the electroosmotic flow will be reversed due to the formation of double layer or surfactant hemimicelles at the capillary wall surface. Compared to micellar liquid chromatography (MLC), MECC has the advantages related to the absence of a stationary phase: faster preconditioning and cleaning of the system, higher reproducibility and decreased error caused by intercolumn variability [109];



319

moreover this technique is faster than MLC, needs only few µl of sample and few milliliters of buffer. The present state of the technique has been recently discussed [110–112]. The papers published about MECC can be divided in two main groups: those improving the knowledge on the separation principles and the effect of different surfactants, buffer modifiers, and pH changes on the separation performances, and those devoted to the application of the technique to real samples analysis. Hereafter we will report essentially on the second kind of research. Concerning the surfactant type relevance many studies describe the effect of different surfactants on the retention behavior and chemical selectivity [113–115]. In particular was the use of mixed micelles formed from similar charged surfactant [116], charged and nonionic or zwitterionic surfactants [117], and oppositely charged surfactants was investigated [118]. Considering the applications, many efforts have been done to overcome the principal limit of MECC: the low sensitivity when absorption spectrometry detection is used (most cases). Good results have been obtained by applying on-line preconcertration technique and in particular the sample stacking with reverse migrating micelles [119 and refs. therein]. On the other hand efforts have been done to improve the detection sensitivity, by employing different cells with longer pathlength; in this case the drawback is the loss in separation efficiency. Otherwise more sensitive detector were used, such as fluorescence, in particular laser-induced, because of the importance of having a light source with beams that could be focused on a small volume. For electroactive analytes amperometric detection gave good results. The coupling with mass spectrometry would be able to render this technique very powerful, but, the problem of the introduction of a nonvolatile buffer into the interface is still to be solved. Despite to its limits, MECC is a powerful technique, especially for real samples; due to the absence of the stationary phase, often no sample pretreatment is required, contrary to what HPLC needs. Some examples of recent MECC determinations performed on biological and environmental samples are illustrated in Table 6.

Table 6

Examples of MECC Separations Analytes

Creatinine, uric acid, and antipyrine Heroin, opium alkaloids, amphetamines, benzodiazepine Ibuprofen, codeine phosphate and degradation products Essential and branched-chain amino acids 28 Biogenic amines Postharvest fungicides Explosives and transformations products Herbicides 22 aromatic sulfonate derivatives Tropane alkaloid Sesquiterpene lactone


Sample Type

Ref.

Human plasma and urine Human biological fluids

120 121–123

Commercial tablets

124

Nutraceutical products

125

Red wines Grape, lettuce, orange, and tomato Soil and groundwaters

126 127 128

Lake sediments Industrial effluents Plant extracts Magnolia grandiflora

129 130 131 132

320

Pramauro and Prevot

ACKNOWLEDGMENTS Financial support from Ministero dell’Istruzione, dell’Universitá e della Ricerca (MIUR) (Rome), Programmi di Ricerca di Rilevante Interesse Nazionale (PRIN) 2000 is gratefully acknowledged.

REFERENCES 1. WL Hinze. In KL Mittal, ed. Solution Chemistry of Surfactants. Vol.1. New York: Plenum Press, 1979, pp. 79–113. 2. LJ Cline-Love, JG Habarta, JG Dorsey. Anal Chem 56: 1132A–1148A, 1984. 3. DW Armstrong. Sep Purif Methods 14: 213–238, 1985. 4. E Pelizzetti, E Pramauro. Anal.Chim Acta 169: 1–29, 1985. 5. GL McIntire. Am Lab 18: 173–185, 1986. 6. U Pfüller. Mizellen, Vesikel, Mikroemulsionen. Tensidassoziate und ihre Anwendung in Analytik und Biochemie. Berlin: Veb Verlag, 1986. 7. WL Hinze, DW Armstrong, eds. Ordered Media in Chemical Separations. Washington D.C.: ACS Symp Ser 342, American Chemical Society, 1987. 8. JF Scamehorn, JH Harwell, eds. Surfactant-Based Separation Processes. New York: Marcel Dekker, 1989. 9. GL McIntire. Crit Rev Anal Chem 21: 257–278, 1990. 10. E Pramauro, E Pelizzetti. Surfactants in Analytical Chemistry. Comprehensive Anal. Chem. Vol. XXXI. Amsterdam: Elsevier, 1996. 11. JF Scamehorn, JF Harwell, eds. Surfactant-Based Separations. Science and Technology. Washington D.C.: ACS Symp Ser 740, American Chemical Society, 1999. 12. MJ Rosen. Surfactants and Interfacial Phenomena. 2nd ed. New York: Wiley, 1989. 13. M Almgren, F Grieser, JK Thomas. J Am Chem Soc 101: 279–284, 1979. 14. IV Berezin, K Martinek, A Yatsimirskii. Russ Chem Rev 42: 778–782, 1973. 15. L Sepulveda, E Lissi, FH Quina. Adv Coll Interface Sci 25:1–9, 1986. 16. DW Armstrong, F Nome. Anal Chem 53:1662–1666, 1981. 17. S Terabe, K Otsuka, K Ichikawa, A Tsuchiya, T Ando. Anal Chem 56: 111–113,1984. 18. A Bianco Prevot, E Pramauro, M Gallarate, ME Carlotti, G Orio. Anal Chim Acta 412: 141–148, 2000. 19. MA Garcia, ML Marina, JC Diez-Masa. J Chromatogr A 732: 345–359, 1996. 20. JK Strasters, MG Khaledi. Anal Chem 63: 2503–2508, 1991. 21. MG Khaledi, SC Smith, JK Strasters. Anal Chem 63: 1820–1830, 1991. 22. MA Garcia, JC Diez–Masa, ML Marina. J Chromatogr A 742: 251–256, 1996. 23. CA Bunton, LJ Sepulveda. J Phys Chem 83: 680–683, 1979. 24. C Hirose, LJ Sepulveda. J Phys Chem 85: 3689–3694, 1981. 25. E Pelizzetti, E Pramauro. J Phys Chem 84: 990–996, 1984. 26. V Camel. Trends Anal Chem 19: 229–249, 2000. 27. Test Methods for Evaluating Solid Waste. Method 354., U.S. Environmental Protection Agency (USEPA) SW–846. 3rd ed. Update III. Washington DC: U.S. General Post Office (GPO), 1995. 28. TL Chester, JD Pinkston, D Raynie. Anal Chem 66: 106R–130R, 1994. 29. A Bianco Prevot, M Gulmini, V Zelano, E Pramauro. Anal Chem 73: 3790–3795, 2001. 30. B Vallejo-Pecharromàn, LE Garcia-Ayuso, MD Luque de Castro. Chromatographia 53: 5–10, 2001. 31. M Gulmini, A Bianco Prevot, E Pramauro, V Zelano. Polycyclic Aromatic Compounds 22: 1–16, 2002. 32. A Eiguren Fernandez, Z Sosa Ferrera, JJ Santana Rodriguez. Anal Chimica Acta 433: 237–244, 2001.



321

33. G Karlstrom. J Phys Chem 89: 4962–4967, 1985. 34. V DeGiorgio. In V DeGiorgio, M Corti, eds. Physics of Amphiphiles. Micelles, Vesicles and Microemulsions. Amsterdam: North Holland, 1985, pp. 303–335. 35. WL Hinze, E Pramauro. Crit Rev Anal Chem 24: 133–177, 1993. 36. H Watanabe, H Tanaka. Talanta 25: 585–589, 1978. 37. A Eiguren-Fernandez, Z Sosa-Ferrera, JJ Santana-Rodriguez. Anal Chim Acta 358: 145–155, 1998. 38. WL Hinze, HN Singh, ZF Fu, R Williams, DJ Kippenberger, MD Morris, FS Sadek. In T. Vo Dinh, ed. Chemical Analysis of Polycyclic Aromatic Compounds. New York: Wiley, 1989, pp. 151–169. 39. C Garcia-Pinto, JL Perez-Pavon, B Moreno-Cordero. Anal Chem 66: 874–881, 1994. 40. A Böckelen, R Niessner. Fresenius J Anal Chem 346: 435–440, 1993. 41. D Bai, J Li, SB Chen, BH Chen. Environ Sci Technol 35: 3936–3940, 2001. 42. E Pramauro. Ann Chim (Rome) 80:101–109, 1990. 43. SR Sirimanne, JR Barr, DG Patterson. Anal Chem 68: 1556–1560, 1996. 44. A Eiguren-Fernandez, Z Sosa-Ferrera, JJ Santana Rodriguez. Analyst 124: 487–491, 1999. 45. RP Frankewich, WL Hinze. Anal Chem 66: 944–954, 1994. 46. ND Gullickson, JF Scamehorn, JH Harwell. In JF Scamehorn, JH Harwell, eds. SurfactantBased Separation Processes. New York: Marcel Dekker, 1989, pp. 139–152. 47. C Garcia-Pinto, JL Perez-Pavon, B Moreno-Cordero. Anal Chem 67: 2606–2612, 1995. 48. R Carabias-Martinez, E Rodrìguez-Gonzalo, MG Garcìa-Jimènez, C Garcìa-Pinto, JL PèrezPavòn, J Hernàndez-Mèndez. J Chromatogr A 754: 85–91, 1996. 49. S Sakulwongyai, P Trakultamupatam, JF Scamehorn, S Osuwan, SD Christian. Langmuir 16: 8226–8230, 2000. 50. V Pino, JH Ayala, AM Afonso, V Gonzalez. Fresenius J Anal Chem 371: 526–531, 2001. 51. T Saitoh, WL Hinze. Anal Chem 63: 2520–2525, 1991. 52. T Saitoh, WL Hinze. Talanta 42: 119–127, 1992. 53. X Jin, M Zhu, ED Conte. Anal Chem 71: 514–517, 1999. 54. I Casero, D Sicilia, S Rubio, D Perez-Bendito. Anal Chem 71: 4519–4526, 1999. 55. Q Fang, M Du, CW Huie. Anal Chem 73: 3502–3505, 2001. 56. H Hoshino, T Saitoh, H Taketomi, T Yotsuyanagi. Anal Chim Acta 147: 339–345, 1983. 57. S Kawamorita, H Watanabe, K Haraguchi. Anal Sci 1: 41–45, 1985. 58. T Saitoh, Y Kimura, T Kamidate, H Watanabe, K Haraguchi. Anal Sci 5: 577–581, 1989. 59. T Okada. Anal Chem 64: 2138–2142, 1992. 60. E Pramauro, E Pelizzetti. Trends Anal Chem 7: 260–265, 1988. 61. ME Fernandez-Laespada, TL Pèrez-Pavon, B Moreno-Cordero. Analyst 118: 209–212, 1993. 62. MC Cerrato-Oliveros, O Jimenez de Blas, JL Perez-Pavon, B Moreno-Cordero. J Anal Atomic Spectroscopy 13: 547–550, 1998. 63. L Sombra, M Luconi, MF Silva, RA Olsina, L Fernandez. Analyst 126: 1172–1176, 2001. 64. MF Silva, LP Fernandez, RA Olsina. Analyst 123: 1803–1807, 1998. 65. MO Luconi, MF Silva, RA Olsina, LP Fernandez. Talanta 51: 123–129, 2000. 66. RO Dunn, JF Scamehorn, SD Christian. Sep Sci Technol 20: 257–284, 1985. 67. AS Jönsson, B Jönsson. J Membrane Sci 56: 49–55, 1991. 68. E Pramauro, A Bianco-Prevot, P Savarino, G Viscardi, M de la Guardia, E Peris-Cardells. Analyst 118: 23–27, 1993. 69. SD Christian, SN Bhat, EE Tucker, JF Scamehorn, DA El-Sayed. AIChE J 34: 189–193, 1988. 70. A Paulenova, P Rajec, P Adamcik. J Radioanal Nucl Chem 228: 115–117, 1998. 71. J Klepac, DL Simmons, RW Taylor, JF Scamehorn, SD Christian. Sep Sci Technol 26: 165–173, 1991. 72. C Tondre, SG Son, M Hebrant, P Scrimin, P Tecilla. Langmuir 9: 950–955, 1993. 73. M Hebrant, A Bouraine, C Tondre, A Brembilla, P Lochon. Langmuir 10: 3994–4000, 1994. 74. E Pramauro, A Bianco-Prevot, V Zelano, WL Hinze, G Viscardi, P Savarino. Talanta 41: 1261–1267, 1994.


322

Pramauro and Prevot

75. E Pramauro, A Bianco-Prevot, V Zelano, M Gulmini, G Viscardi. Analyst 121: 1401–1405, 1996. 76. BR Filippi, JF Scamehorn, RW Taylor, SD Christian. Sep Sci Technol 32: 2401–2424, 1997. 77. L Gzara, A Hafiane, M Dhabbi. Rev Sci Eau 13: 289–304, 2000. 78. E Pramauro, A Bianco, E Barni, G Viscardi, WL Hinze. Coll Surfaces 63: 291–300, 1992. 79. E Pramauro, A Bianco-Prevot. Pure & Appl Chem 67:551–559, 1995. 80. HS Kim, C Tondre. Langmuir 5: 395–397, 1989. 81. FP Cavasino, C Sbriziolo, E Pelizzetti, E Pramauro. J Phys Chem 93: 469–473, 1989. 82. M Ismael, C Tondre. Langmuir 8: 1039–1041, 1992. 83. M Hebrant, N Francois, C Tondre. Colloids & Surfaces A 143: 77–88, 1998. 84. A Berthod. Micellar Liquid Chromatography. New York: Marcel Dekker, 2000. 85. BK Lavine, S Hendayana. J Liq Chrom & Rel Technol 19: 101–123, 1996. 86. MA Rodriguez-Delgado, MJ Sanchez, V Gonzàlez, F Garcia-Montelongo. J Liq Chrom & Rel Technol 19: 187–200, 1996. 87. M Angeles-Garcia, ML Marina. J Liq Chrom & Rel Technol 19: 1757–1776, 1996. 88. S Lopez-Grio, MC Garcia Alvarez-Coque, WL Hinze, FH Quina, A Berthod. Anal Chem 72: 4826–4835, 2000. 89. T Takeuchi, T Miwa. Chromatographia 43: 143–148, 1996. 90. P Jandera, J Fischer, H Effemberger. J Chromatogr A 807: 57–70, 1998 91. O Jimènez, I Benito, ML Marina. J Liq Chrom & Rel Technol 19: 2477–2495, 1996 92. TA Walker. J Liq Chrom & Rel Technol 19: 1715–1727, 1996 93. JM Sanchis-Mallols, RM Villanueva-Camañas, S Sagrado, MJ Medina-Hernàndez. Chromatographia 46: 605–612, 1997 94. L Escuder-Gilabert, S Sagrado, RM Villanueva-Camañas, MJ Medina-Hernàndez. Anal Chem 70: 28–34, 1998 95. MP San Andrès, MJ Barroso, S Vera. Chromatographia 48: 517–522, 1998 96. Y Martin-Biosca, L Escuder-Gilabert, ML Marina, S Sagrado, RM Villanueva-Camañas, MJ Medina-Hernandez. Anal Chim Acta 443: 191–203, 2001 97. L Escuder-Gilabert, Y Martin-Biosca, S Sagrado, RM Villanueva-Camañas, MJ MedinaHernandez. Anal Chim Acta 448: 173–185, 2001 98. C Quiñones-Torrelo, S Sagrado, RM Villanueva-Camañas, MJ Medina-Hernandez. J Chromatogr B 761: 13–26, 2001 99. JR Torres-Lapasiò, DL Massart, JJ Baeza-Baeza, MC Garcia-Alvarez-Coque. Chromatographia 51: 101–110, 2000. 100. Y Martin-Biosca, S Sagrado, RM Villanueva-Camañas, MJ Medina-Herninde. J Liq Chrom & Rel Technol 22: 2895–2905, 1999. 101. JF Noguera-Orti, RM Villanueva-Camañas, G Ramis-Ramos. Chromatographia 51: 53–60, 2000. 102. S Lopez-Grio, JR Torres-Lapasio, JJ Baeza-Baeza, MC Garcia-Alvarez-Coque. Anal Chim Acta 418: 153–165, 2000. 103. JF Noguera-Ortì, RM Villanueva-Camañas, G Ramis-Ramos. J Chromatogr Sci 37: 83–87, 1999. 104. S Carda-Broch, MC Garcia-Alvarez-Coque, EF Simò-Alfonso, JS Esteve Romero. Anal Chim Acta 353: 215–226, 1997. 105. A Lòpez-Garcìa, E Blanco-Gonzalez, A Sanz-Medel. Chromatographia 43: 607–611, 1996. 106. I Rapado-Martinez, RM Villanueva-Camañas, MC Garcia-Alvarez-Coque. J Chromatogr Sci 37: 93–102, 1999. 107. M Gil-Agusti, L Monferrer-Pons, J Esteve-Romero, MC Garcia-Alvarez-Coque. J of AOAC International 84: 1687–1694, 2001. 108. I Perez-Martinez, S Sagrado, MJ Medina-Hernàndez. Chromatographia 43: 149–152, 1996. 109. BJ Herbert, JG Dorsey. Anal Chem 67: 744–749, 1995. 110. PG Muijselaar, K Otsuka, S Terabe. J Chromatogr A 780: 41–61, 1997. 111. JP Quirino, S Terabe. J Chromatogr A 856: 465–482, 1999. 112. U Pyell. Fresenius J Anal Chem 371: 691–703, 2001.


Detergent Formulations in Separation Science 113. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132.

323

M Hong, BS Weekly, SJ Grieb, JP Foley. Anal Chem 70: 1394–1403, 1998. SY Yang, MG Khaledi. Anal Chem 67: 499–510, 1995. SY Yang, J Bumgarner, MG Khaledi. J Chromatogr A 738: 265–274, 1996. SY Yang, J Bumgarner, LFR Kruk, MG Khaledi. J Chromatogr A 721: 323–335, 1996. ES Aluja, EL Little, KR Nielsen, JP Foley. Anal Chem 67: 26–33, 1995. M Hong, BS Weekley, SJ Grieb, JP Foley. Anal Chem 70: 1394–1403, 1998. JP Quirino, S Terabe. Anal Chem 70: 149–157, 1998. M Miyake, A Shibukawa, T Nakagawa. J High Res Chromatogr 14: 181, 1991. R Weinberger, IS Lurie. Anal Chem 63: 823–827, 1991. P Wernly, W Thormann. Anal Chem 63: 2878–2882, 1991. P Wernly, W Thormann. Anal Chem 64: 2155–2159, 1992. KP Stubberud, O Astrom. J Chromatogr B 826: 95–102, 1998. R Stancanelli. J of Agricultural and Food Chem 48: 3324–3329, 2000. G Nouadje, N Simeon, F Dedieu, M Nertz, P Puig, F Couderc. J Chromatogr A 765: 337–343, 1997. R Rodriguez, Y Pico, G Font, J .Manes. J Chromatogr A 924: 387–396, 2001. W Kleiböhmer, K Cammann, J Robert, E Mussenbrock. J Chromatogr A 638: 349–356, 1993. Y Yu, RB Cole. Environ Sci Technol 31: 3251–3257, 1997. S Angelino, A Bianco Prevot, MC Gennaro, E Pramauro. J Chromatogr A 845: 257–271, 1999. S Cherkaoui, L Mateus, P Christen, JL Veuthey. Chromatographia 46: 351–357, 1997. M Ganzera, M Mair, H Stuppner, NH Fischer, IA Khan. Chromatographia 54: 665–668, 2001.


11 Surfactant Formulations in Enhanced Oil Recovery Thanaa Abdel-Moghny

CONTENTS I.

II.

Scope ..................................................................................................................... 326 A. Primary Recovery...................................................................................... 326 B. Secondary Recovery.................................................................................. 326 C. Tertiary Oil Recovery................................................................................ 326 Introduction ........................................................................................................... 327 A. Enhanced Oil Recovery............................................................................. 327 B. Chemical Flooding .................................................................................... 327 1. Development of Chemical Flooding ......................................... 327 C. Chemical Surfactant .................................................................................. 329 1. Surfactants.................................................................................. 329 2. Cation Exchange ........................................................................ 332 3. Stability ...................................................................................... 332 D. Surfactant Flooding ................................................................................... 332 1. Mechanism of Surfactant at Reservoir Rocks........................... 333 E. Surfactant Mixture..................................................................................... 333 1. Ideal Mixtures ............................................................................ 334 2. Application of Ideal Mixing ...................................................... 334 3. Nonideal Mixtures ..................................................................... 334 F. Polymer Flooding...................................................................................... 335 G. Alkaline Water Flooding ........................................................................... 336 H. Traditional Surfactant/Polymer Flooding ................................................. 336 I. Surfactant-Polymer Interaction in Solution .............................................. 337 J. Relation between the Interfacial Tension and Residual Oil Saturation ... 338 K. Phase Behavior in EOR ............................................................................ 339 L. Application of Surfactants in Enhanced Oil Recovery ............................ 339 325


326

Abdel-Moghny

1.

Interaction between Surfactant and Polymer at Reservoir Rock ........................................................................................... 340 2. Displacement of Oil by Spontaneous Imbibition of Aqueous Surfactant Solution..................................................................... 340 3. Adsorption of Different Surfactants on Kaolinite..................... 341 4. Acidified Oil/Surfactant Enhanced Alkaline System ................ 341 5. Dual Surfactants—System for Enhanced Oil Recovery at High Salinity .......................................................................... 341 6. Ultralow IFT Using Neutralized Oxidized Hydrocarbon Surfactant ................................................................................... 342 7. Mixed Micelles .......................................................................... 342 8. Biosurfactants as New Surfactant.............................................. 342 Acknowledgments........................................................................................................... 342 References ....................................................................................................................... 343

I. SCOPE A. Primary Recovery A traditional step for increasing oil recovery is to inject gas or water into an oil reservoir for the purpose of delaying the pressure decline during oil production; a technique called pressure maintenance. A well-executed pressure maintenance program can substantially increase the amount of economically recoverable oil over that to be expected with no pressure maintenance. Without either fluid injection or an active natural water drive, oil recovery falls to where further production is no longer economically feasible. In the early days of the petroleum industry, reservoirs were allowed to produce naturally until a certain stage of depletion had been reached, generally when the production rates had become uneconomic. This was known as the primary production phase. B. Secondary Recovery To produce more oil, the pressure in the reservoir must be maintained by injecting another fluid. This second stage of production is called secondary oil recovery. The injection of fluids into the reservoir actually has two closely linked objectives: to maintain the pressure in the reservoir, and to push forward the oil contained in the reservoir toward the producing wells. Several types of fluid injection are used according to the reservoir fluid and rock characteristics. For oil field, the pressure may effectively be maintained by injecting water into the zone at the periphery of the reservoir, or gas into gas cap at the center of the reservoir. C. Tertiary Oil Recovery The major tertiary recovery method falls into two basic categories thermal methods and miscible method. Thermal methods aimed to reducing the viscosity of the oil by heating. The most widely used thermal techniques are in situ combustion, continuous injection of hot fluids such as steam, water, or gases, and cyclic operations such as steam soaking. The chemical method involves the injection of a fluid into the oil-bearing strata for the purpose of overcoming the deficiencies of conventional secondary techniques. The fluids are designed so that they will alter the capillary forces trapping the oil and reduce the tendency of bypassing the oil in the less permeable portions of the reservoir.


Surfactant Formulations in Enhanced Oil Recovery

327

II. INTRODUCTION A. Enhanced Oil Recovery After a successful water or gas injection project as much as 50% of the initial oil in place remains entrapped in the pores of the reservoir rock. This remaining oil needs a very high pressure gradient to be mobilized due to the capillary forces needed to drive the isolated oil bubbles through the narrow necks of the porous medium. To recover this residual oil under the usually applied field pressure gradients, the interfacial tension between the oil and the displacing fluid must be either greatly reduced or completely eliminated. This can be done either thermally by vaporizing the oil and water into a single vapor phase or chemically by injecting solutions completely or partially miscible in both oil and water phase. Recovery methods that are used to recover some or all of the residual oil are termed as enhanced oil recovery (EOR) methods. They may be divided into (1) thermal methods (hot water flooding, steam flooding and in situ combustion), (2) chemical methods (polymer flooding, surfactant flooding, and alkaline flooding), and (3) gas injection methods (hydrocarbon miscible flooding, and carbon dioxide flooding). B. Chemical Flooding Chemical flooding of oil reservoirs is one of the most successful methods to enhance oil recovery from depleted reservoirs at low pressure. Initially, the objective of chemical flooding was to recover additional oil after a waterflood, and it is therefore described as a tertiary oil recovery process. A lot of papers and reviews, both laboratory work and field tests, have been published on this subject since the first work by Marathon Oil Company in the early 1960s [1]. The research declined drastically during the 1990s, but still some research groups were active trying to improve the technique by: (1) simplifying the flooding process, (2) improving the efficiency of surfactants, and (3) developing new chemicals (surfactants). Chemical flooding processes is meant to include the “water-based” processes such as micellar and surfactant floods, alkaline water-floods and polymer floods. These processes are all sensitive to certain environmental elements or factors that are commonly present in oil reservoirs. These are the in-place oil and water, the mineralogy, the geology/ lithology and the temperature. These can influence the process selection and the composition of the chemical slugs [2]. 1.

Development of Chemical Flooding a. In the Laboratory. Essentially, two different methods have developed for using surfactants to enhance oil recovery. One uses a large pore volume (PV) of a low-concentration surfactant solution. The other uses a small pore volume of a high-concentration surfactant solution. Laboratory results reported in the literature indicate that, with low concentration surfactant injection, oil production is sustained at a lower level for a longer period of time than with high-concentration surfactant injection. The two different processes including; (i) displacement, (ii) adsorption, (iii) mobility control, and (iv) scaling. i. Displacement with Surfactant Systems. The displacement results come from different laboratories are reported by [3–5], and are presented in Table 1. All floods took place in Berea cores and petroleum sulfonate as the surfactant. The recoveries indicate that both types of surfactant processes are capable of recovering significant quantities of tertiary oil. Process efficiency can be related to the ratio of oil recovered divided by the amount of surfactant injected.


328 Table 1

Flood Gale 3 Hill 4 Davis 5

Abdel-Moghny Laboratory Displacement with Surfactant Surf. Concs. % 2 1.3 10.4

PV Injected %

CD (in) x Length (ft)

R/P

TOR %

Efficiency Ratio

50 25 2

2x3 2x16 2x4

3 psi 1.4ft/D 44ft/D

70 85 85

0.70 2.62 4.09

Abbreviations: Surf. Concs.= Surfactant concentrations %, PV = pore volume injected %, CD = core dimension diameter (in) x length (ft), R/P = rate/pressure, TOR = tertiary oil recovery, and efficiency ratio = (oil recovery:surfactant injected)

ii. Adsorption. Various methods have been suggested for reducing surfactant loss in low-tension flooding: these methods include the use of different salts and mixtures of petroleum sulfonate with broad equivalent weight distributions. Such broad equivalent weight distribution is reported to increase recovery because the critical portions of the distribution act as sacrificial adsorbates. This adsorption minimizes the loss of the high equivalent weight fraction that is most efficient in lowering the interfacial tension. iii. MC = Mobility Control. Mobility control is necessary for enhanced oil recovery using both high and low-concentration surfactant-flooding processes. With low-concentration surfactant injection, mobility control of the surfactant slug is accomplished by dissolving polymer in the surfactant solution. The mobility of the high-concentration surfactant slug is fixed by adjusting the composition of such micellar components as the co-surfactant and electrolyte. iv. Scaling. Scaling of laboratory results to the field is a difficult problem with any recovery process. The displacement mechanism, associated adsorption, and mobility control with surfactant systems make scaling particularly difficult. b. Field Testing. Field results indicate that higher recovery values are obtained with high- concentration–surfactant, low-pore volume systems than with low-concentration, high-pore-volume systems. In terms of efficient surfactant use, the amount of oil recovered needs to be related to the amount of surfactant injected within the pattern from where the oil is displaced. c. Commercial Application. The key factors in any economic projections for enhanced oil recovery processes using surfactant are investment requirements including chemical and development costs, oil recovered, the time required to obtain that oil, oil price, and tax load. The historical developments of chemical flooding, are reported elsewhere [6–9]. A review by Austad et al. [10] focus on the recent laboratory developments in chemical flooding of oil reservoirs within: (1) traditional chemical flooding of sandstone reservoirs, and (2) imbibition of aqueous surfactant solution into low-permeable chalk. Other reviews reported that the uses of surfactant in flooding oil reservoirs are: (1) alkaline/surfactant/polymer flooding (ASP) is hoped to be a low-cost improvement over micellar /polymer flooding [11]; (2) surfactants based mobility control, i.e., foam generation during gas injection; and (3) partial or complete blocking of high-permeable regions, forcing injected displacing fluid into low-permeability areas of high oil content [12].



C.

329

Chemical Surfactant

1. Surfactants Surfactants are classified by the polar head group. It is common practice to divide surfactants into the classes anionics, nonionics, cationics, and zwitterionics (Fig. 1). • Anionic. Carboxylate, sulfate, sulfonate, and phosphate are the polar group found in anionic surfactants. • Nonionic. Ethoxylated alcohols, ethoxylated alkylphenols, ethoxylated acids, fatty acid alkanolamides, ethoxylated alkanolamides, ethoxylated amine, ester of polyhydroxy compounds, i.e., sorbitan distearate, ethoxylated esters, i.e., ethoxylated sorbitan monostearate, ethylene oxide/propylene oxide block copolymers, amine oxides. • Cationic. Fatty quaternary ammonium salts, benzylalkyldimethylammonium salts. • Zwitterionic. Amino acids. These amphoteric surfactants are generally prepared by reaction of a fatty primary amine with an α-unsaturated methyl ester, followed by hydrolysis of the ester. De Groot [13,14] reported that the polycyclic sulfonic body and wood sulfite liquor could be used as water-soluble surfactants for oil recovery. Other water soluble compounds have been suggested by Holbrook [15] for surfactant flooding; these compounds include organic perfluoro compounds, fatty acids soaps, polyglycol ether, salts of fatty or sulfonic acids, and polyoxyalkylene compounds. Laboratory results were presented showing that these solutions reduced interfacial tension and enhanced oil recovery. Publications since then have stressed coupling different salts with surfactants to reduce the interfacial tension to a minimum value and to prevent the adsorption of surfactants within the reservoir. These techniques have given rise to the low-tension surfactant flooding processes. In low-tension floods, much of the reservoir pore volume (PV) is filled with surfactant solution of a relatively low concentration. For example, a 30% PV slug containing less than 2% surfactant might be used [16]. To reduce surfactant adsorption in water wet formation a 0.1 to 3% surfactant dissolved in low-viscosity hydrocarbon solvent was injected [17]. For the soluble-oil flooding process a mixture of an anhydrous soluble oil and a nonaqueous solvent containing up to about 12% surfactant was injected [18]. The injection of microemulsion into production wells to remove objectionable waxy solids was described by Blair et al [19]. The interfacial surface between oil and water must covered by at least a monolayer of surfactants. High surface coverage is needed in order to obtain low enough IFT. Thus, the surfactant molecules must have strong lateral intermolecular association without forming liquid crystal and gels. Furthermore, the surfactant must also grade smoothly from being oil-to water-soluble over a sufficient length of the molecule. In this way it will be a smooth transition from oil- to waterlike fluid along the interphase. A lot of papers have shown it is possible to synthesize anionic surfactants with these properties that tolerate high concentrations of multivalent cations [20–23]. Anionic surfactants containing multiple units of ethylene oxide and propylene oxide (EO and PO) in their middle section were found to satisfy many of the desired conditions. Examples are:


330

Abdel-Moghny O

O

OCH2COO− Alkyl ethercarboxylate

O

OSO−3

O O O Alkyl ethersulfate

Alkyl sulfate

OSO−3

O

SO−3 Alkylbenzene sulfonate

SO−3

O-C

Dialkyl sulfosuccinate

O-C O

OPO32−

O O O Alkyl etherphosphate

Alkyl phosphate

OPO32−

(a)

O

O

O

O

O

O

O

O

O

O CONH

O

O

O O

O

OH

O

COO

OH

O

O

Fatty alcohol ethoxylate

Alkylphenol ethoxylate O

OH Fatty acid ethoxylate

O

OH Fatty amide ethoxylate

OH

O

N O

O

O

O

Fatty amine ethoxylate

OH

CH2OH OH OH OH O

Alkyl glucoside

O C

O

CH2

OH CH O OH

Sorbitan alkanoate

OH O C

O

O n

O

O CH CH2

m

OH

O

O

m

O

O

OH

Ethoxylated sorbitan alkanoate

OH m

(b)

Figure 1 (a) and (b) Classification of surfactant types. (From Jonsson, Lindman, Holmberg, and Kronberg. Surfactants and Polymers Interfacial Tension Aqueous Solution. John Wiley & Sons, 1998.)



331

NH+3

Fatty amine salt

NH+2

Fatty diamine salt

NH+3

O2C

O

N+

N+

N+ O2C O

Alkyl ‘quat’

Ester ‘quat’

Dialkyl ‘quat’

(c)

N+ –CH2COO

Betaine

N+ –CH2COO−

CONH O

Amidobetaine

CH2CH2OH

CNH–CH2CH2NH

Imidazoline

CH2COO− N

O

Amine oxide

(d)

Figure 1 (c) and (d).

R- (PO) Y– (EO) X–SO3– (alkyl propoxy-ethoxy-sulfonate) R- (PO) Y– (EO) X–OSO3– (alkyl propoxy-ethoxy-sulfate) R- Ph- (PO) Y– (EO) X-SO3– (alkylarylpropoxy-ethoxy-sulfonate) Where y = 0, 1, 2, 3, …., x = 1,2,3,… R 12 -15-O- (CH (CH3) CH2O) 7-(CH2CH2O) 2-(CH2CH (OH) CH2)-SO3–Na+ Pure and highly substituted benzene sulfonates, n-C 12-o-xylene-SO3–, have similar properties regarding low IFT in the two-phase region without using alcohol [24].


332

Abdel-Moghny

The PO/EO sulfonate showed an IFT value close to 10–2 mN/m toward n-heptane in seawater. Also showed a remarkable performance in the presence of high concentration of Ca2+ and Ma2+ ions. This mean that calcium and magnesium salts of these surfactants have a limited solubility in oil, which will reduce possible trapping of surfactant at low concentration in the residual oil phase. Austad et al. [25] found that the small change in IFT is observed by doubling the salinity of seawater. 2. Cation Exchange The most common anionic surfactants (petroleum, alpha-olefin, and alkylaryl sulfonates) have great potential for extracting adsorbed multivalent cations, Mg2+, Ca2+, etc., into the micellar slug, with the consequence of a drastic change in phase properties. Therefore, a preflush of water containing monovalent cations is often performed to obtain a cation exchange. In order to compensate for reservoir parameters, which disturb the phase behavior of the surfactant slug during the process, an imposed phase gradient is normally used. If the phase gradient does not behave properly, a great loss of surfactants may take place due to phase trapping; i.e., the surfactant is trapped in the oil or in the middle phase [10]. 3. Stability Ethoxylated anionic sulfonates are fairly stable regarding desulfonation by breakage of the C-S bond at ordinary reservoir conditions [26]. Water solvolysis, H+ catalyzed hydrolysis, and nucleophilic (HS– and Cl–) displacement reactions have, however, been observed. Each and every one of these reactions can dominate the decomposition rate under different conditions. Even though oil reservoirs have a reducing environment, air or oxygen is usually not excluded from solutions in surfactant flood experiments, and it is therefore important to be sure that the loss of surfactant is not due to chemical decomposition during the experimental period. Under aerobic conditions, oxygen is important in the decomposition of the EO-groups. The main mechanism is believed to be cleavage of the ether bonds in the same way as in the decomposition of polyethylene oxide [27]. The ether bonds are broken by formation of hydroperoxides as intermediates. The peroxides are then decomposed by a radical mechanism, which may initiate chain scission reactions. The decomposition may also be catalyzed by metal ion [28]. The EO-sulfates are cheaper than the corresponding EO-sulfonates, but they are hydrolyzed at high temperatures and low pH. The pH of injected seawater is normally changed from about 8 to 4-6 due to solubilization of CO2 and ion exchange between water and the reservoir rock. At 60°C, the half-life time for EO-sulfates is estimated to be about 7 and 30 years at pH ≈ 5 and pH ≈ 8, respectively [29]. D. Surfactant Flooding Surfactant is characterized by its tendency to adsorb at a surface. The driving force for a surfactant to adsorb at an interface is to lower the free energy of that phase boundary. The interfacial free energy per unit area represents the amount of work required to expand the interface. The term interfacial tension is often used instead of interfacial free energy per unit area. Surfactant flooding process are referred to detergent floods, sulfonate floods, microemulsion floods, emulsion floods, micellar floods, and soluble oil floods (Figure 2a). In this process a slug of surface-active material is injected into reservoir to mobilized the residual oil which can be displaced and produced. The surfactant slug, representing only a fraction of the total pore volume, is driven through the reservoir by a subsequent slug


Surfactant Formulations in Enhanced Oil Recovery Injection Drive

↓

Figure 2a

Water Mobility buffer

333 Production

Slug

Oil Water

↑

Surfactant flood.

of thickened water (polymer solution), which is in turn displaced by water or brine. The mobility’s of each these slugs are adjusted to minimize by–passing and channeling and to improve the volumetric coverage of the process. Ideally, the displacement by surfactant flooding approaches a miscible displacement. It is important that integrity of the slugs be maintained for as long as possible. They are sensitive to certain elements of the reservoir, and these factors can contribute to early attenuation [2]. The goal of the research on surfactant flooding during the 1990s was to develop surfactants that can recover additional oil in a cost-effective manner during a normal water flood using produced brine (due to environmental aspects) or seawater as injection fluid. In order to avoid many of the problems associated with complicated chemical slugs with high concentration of surfactants and cosurfactants/alcohols, the following criteria should apply: (1) The only chemicals used are surfactants and polymers, (2) low chemical concentration (surfactant 0.1 to 0.5 wt%, polymer < 500 ppm), (3) no imposed salinity gradient or other phase gradients, (4) these chemicals should be insensitive to multivalent cations, and (5) the flooding conditions should be a two-phase flood with the surfactant and polymer present in the aqueous phase, forming an oil-in-water microemulsion [10]. Surfactant loss due to phase trapping is minimized if only oil and water phases are present at all times during the flood. Surfactant loss is only related to adsorption onto the mineral surface provided that the surfactant tolerates multivalent cations, i.e., no precipitation [10]. 1. Mechanism of Surfactant at Reservoir Rocks Fluid/rock interactions that affect surfactant flooding are adsorption, cation exchange, precipitation dissolution phenomena, capillary phenomena, and dispersion. All of these directly or indirectly affect the retention of surfactant. Adsorption at the solid liquid interface should be at minimum and be the only retention mechanism for a type oil-in-water microemulsion phase behavior. In case of brines of high hardness, the surfactants will partition in the oil/or in the upper-phase microemulsion formed under these conditions, rather than precipitate. Phase trapping are caused by microscopic capillary forces in the pores of the rock [30]. E. Surfactant Mixture Most practical application of surfactants makes use of mixture of surfactants [31,32]. There are two reasons for this (1) technical–grade surfactants are themselves mixtures of chain lengths/isomers and (2) mixture of different types of surfactants often perform better than individual components. Surfactants in solution undergo two physical processes, which must be understood by the technologist: (1) they adsorbs onto surfaces thereby modifying surface energy, (2) they self-aggregate to form micelles or larger structures such as vesicles and liquid crystalline phase.


334

Abdel-Moghny

Micelle formation is actually an equilibrium process in which micelles are in equilibrium with unassociated surfactant molecules (called monomers). The monomer concentration increases up to the CMC and then becomes essentially constant. Thus, the monomer concentration is always less than or equal to the CMC. This relationship between the monomer concentration and the CMC is one reason why the CMC is such an important measurement for understanding the behavior of surfactants and surfactant mixtures. The interaction which favors micelle formation generally favors also adsorption. Adsorption is a key link between surface activity and many applications because it controls such properties as particle-substrate adhesion, wetting, soil roll-up, emulsification, and particle suspending efficiency. Such a linkage between performance and micellar mixing behavior is supported by data presented by Schambil and Schwuger [31] showing that the mixture composition which corresponds to the minimum CMC also gives the best wetting, highest contact angle, lowest dynamic surface tension (best foam), and best emulsification. In the air–water interface, the hydrocarbon tails interact only weakly with the air molecules, whereas in an oil–water interface, for example, interactions with oil molecules are strong and can be very specific. Such work should be based on adsorption and phase diagram data, and oil-water interfacial tension rather than surface tension. The properties of mixtures of surfactants have been studied in recent years [31–33]. Surfactants are classified according to the nature of their hydrophobic and hydrophilic groups. Typical hydrophobic groups include hydrocarbons, polypropylene oxide, fluorocarbons, and siloxanes, whereas hydrophilic groups consists of polar nonionic species such as polyethylene oxide (POE), anionic groups such as sulfate, or cationic groups such as quaternary ammonium salts. Zwitterionic surfactants contain both an anionic and a cationic group. 1. Ideal Mixtures Mixtures of surfactants that belong to the same hydrophope and hydrophile class, such as a pair of homologous alkyl ethoxylates, have properties, which are simply predictable from the individual components [32,33]. This is done by treating of the micelle as a condensed “phase” in equilibrium with its “vapor”the unassociated monomers (the water in which this equilibrium with takes place is ignored). The CMC is treated as analogous to a vapor pressure. This is referred to as the pseudophase model. 2. Application of Ideal Mixing The addition of a small proportion of a long chain alkyl sulfate to a shorter chain alkyl sulfate improves the brine and water hardness tolerance of the mixture, even though the longer-chain material by itself is much more sensitive to water hardness than the other component [33,34]. The longer-chain surfactant lowers the mixed CMC and, therefore, the monomer concentration, but itself partitions almost entirely into the micelle. This leads to improved detergency over a range of water hardness conditions. 3. Nonideal Mixtures Mixtures of surfactants drawn from different hydrophope or hydrophile classes, such as a mixture of an ionic hydrocarbon surfactant and a nonionic hydrocarbon surfactant, usually show some deviation from ideal behavior. In the case of ionic-nonionic mixtures, the physical origin of the nonideality is a combination of reduction of electrostatic energy and complex formation [32,33].



335

4. Application of Nonideal Mixing. One of the largest potential applications of surfactant mixtures is enhanced oil recovery. This is a vast field with an extensive literature [2,35–39] dealing with the physical and interfacial properties of temperature, pressure, and salinity. Cox et al. [40] investigated the effects of interactions between linear alkyl sulfate (LAS) and several nonionic surfactants on CMC, surface tension, water hardness sensitivity, and detergency performance. They found that nonionic surfactants lowered the CMC of the LAS, promoted micelle formation, and improved hard water detergency. In a related series of studies of studies, Cox and co-workers systematically investigated interactions between water hardness ions and LAS [41–43]. They report precipitation boundary diagrams and detergency results for LAS and mixtures of LAS with other surfactants, which act to promote micelle formation. They found that lowering the CMC led to improved cleaning in hard water. There are many papers and patents, which report synergistic performance of mixtures of alkyl ethoxylate nonionic surfactants with commonly used anionic surfactants such as LAS and sodium dodecyl sulfate (SDS) [31,32]. These systems show strong negative deviation from ideality, and the monomer concentrations above the CMC can be very much lower than either surfactant alone. As for ideal mixing, the composition of the micellar and monomer phases may be quite different. These effects are exploited, as mentioned above, to prevent calcium sensitive anionic surfactants from precipitating in hard water [44]. Nonionics are generally more effective in this regard than the insoluble anionics referred to above because they are more effective at lowering the monomer concentration and they are not susceptible to precipitation themselves. These principles have also been applied to formulating detergents, enhanced oil recovery, ore flotation, and ag-adjuvants [44]. The adsorption of a dual surfactant system of the type nonylphenol-6-ethoxy-sulfonate (6EOS) and dodecyl-benzene-sulfonate (DDBS) in the mole ratio of 1:1 has been studied by: (1) static adsorption onto kaolinite, (2) nonequilibrium long-term dynamic adsorption on a reservoir core, and (3) dynamic slug injection in a Berea core. The studies were conducted at 70°C using artificial seawater. The core floods were performed at residual oil saturation. The static adsorption of the mixture showed that DDBS adsorbed more strongly than 6EOS at surfactant concentration below the CMC. The plateau adsorption appeared to be quite similar, but significantly higher than for pure 6EOS. The logterm dynamic study was conducted by circulating the dual surfactant solution through the core for 16 weeks, and injecting 0.5 PV of the surfactant mixture followed performed the slug injection by a xanthan solution. In both cases it appeared to be a selective adsorption until the surfactant mixture, forming the most stable micelles, was obtained. Further adsorption at surfactant concentration above the CMC seems to be governed by a linear relationship between the two surfactants. Possible impacts on surfactant flooding, using dual surfactant mixtures of this type are discussed [45]. F. Polymer Flooding As mentioned above, in a surfactant flood the polymer solution is injected to aid in obtaining a good volumetric sweep of the reservoir by the process. A polymer solution may also be used in conjunction with a water flood to achieve the same purpose. This is illustrated in Figure 2b. it is if we are looking at only the portion of the surfactant flood with no mobilization of residual oil downstream of the polymer solution. The intent is to reduce the mobility of the water, thus forcing the water to flow through more flow channels in the rock than would be the case with water injection alone [2]. The polymer must be water soluble and of low flexibility to give high viscosity at low polymer concentration and high salinities. The two biopolymers, xanthan and sclero-


336

Abdel-Moghny Injection

Drive

↓ Water

Production Oil

Polymer Solution

↑

Water

Figure 2b

Polymer flood.

Injection ↓

Production Oil Bank

Residual Oil Drive Water

Figure 2c

Buffer slug

NaOH solution

Initial Oil Preflush

↑

Connate Water

NaOH waterflood.

glucan, are good candidates. Xanthan acts as a negatively charged double helix in saline solution, while scleroglucan acts as an unchanged triple helix in solution. Polymers forming a helix usually hide their hydrophobic sections in the interior of the helix, minimizing surfactant–polymer complex formation. Both of the polymers tolerate high salinity and can be in seawater. Hydrolyzed polyacrylamide, HPA, is a good alternative at low salinities, but is not recommended to be used in hard water at high salinities. Copolymers containing sulfonate groups (acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate from Floerger) are designed to tolerate high temperatures and seawater salinities [10]. G. Alkaline Water Flooding In the alkaline waterflood, a slug of water containing caustic is injected into the reservoir and followed by water or brine Figure 2c. The slug might contain up 5% sodium hydroxide and approximate about 15% of the pore volume. The caustic effects an increase in oil recovery by one or more of the following mechanisms (1) a favorable change in the wettability of the rock, (2) a low tension displacement, and (3) improved sweep [2]. H.

Traditional Surfactant /Polymer Flooding Surfactants and polymers are the principal components used in chemical flooding. The surfactants lowers the interfacial tension (IFT) between the reservoir oil and the injected water, while the polymer will create favorable viscosity conditions and good mobility control for the surfactant slug. The viscous forces acting on the oil then displace the oil by the flowing water. For this reason, chemical flooding is also denoted as: (1) micellar/polymer flooding, (2) surfactant /polymer flooding, and (3) microemulsion flooding. In general terms, Fig. 3 illustrates the various regions of immiscible flow during a typical displacement of oil by a surfactant solution. Provided that a water flood was performed prior to the chemical flood, the various zones are described as: Region 1: waterflooded residual oils saturation, only water is flowing. Region 2: an oil bank is formed, both oil and water are flowing. Region 3: surfactant slug forming the low IFT region, two-or three- phase flow of oil, brine, and microemulsion depending on the actual phase behavior. Region 4: polymer solution for mobility control, single-phase flow of water [10].



337

Flow direction

Region 4 polymer

Figure 3

Region 3 surfactant

Region 2 oil bank

Region 1 wros

Phase position in a typical chemical flood.

I. Surfactant-Polymer Interaction in Solution In the traditional way of micellar flooding the surfactant is present most of the time in the microemulsion phase, i.e., the middle phase, and the polymer is present in the excess water phase. Due to the negative salinity gradient usually applied, a high concentration of surfactant is also present in the oil-in-water phase, at the back of surfactant slug. A rather high concentration of polymer must initially be injected to obtain mobility control of the surfactant slug. Thus, at the rear of the surfactant slug, both surfactant and polymer are present in the oil-in-water phase in significant concentration (5 to 10 wt% surfactant and more than 1000 ppm of polymer). It is well documented in the petroleum and chemical literature that mixtures of anionic surfactants and different water soluble polymer tend to phase separate in saline aqueous solutions [46–47]. The incompatibility phenomena can be chemically explained by considering the micelle–polymer system as a colloidal system according to the DLVO theory for the stability of colloids [48–49]. Therefore, the micellar–polymer systems usually contain alcohol in order to obtain gel-free microemulsions and to improve the compatibility of the surfactant–polymer solution. High salinities require larger concentrations of alcohol to prevent phase separation. Piculell and Lindman [50] recently discussed the phase separation of aqueous mixtures of polymer/polymer and polymer/surfactant solutions in terms of association and segregation. When one of the phases is concentrated with both of the components, the phase separation is termed associative, and when the separating phases contain components of comparable total concentrations it is called a segregative phase separation. Mixtures of nonionic polymer and ionic surfactant mainly show an associative phase separation. However, this may be due to the fact that most studies performed in the chemical literature have been specifically concerned with systems where P-S association has been important. Systematic experiments on P-S systems where both are negatively charged are reported to show a segregative phase separation. Taugbøl et al. reported that it is possible to recover more than 50% of water flooded residual oil by performing a low tension polymer water flood (LTPWF), i.e., no complicated phase gradients are used. Core flood experiments in Berea and Bentheim sandstone cores are conducted using a surfactant of the type alkylpropoxy-ethoxy sulfate, xanthan as polymer, model oil (n-heptane), and synthetic seawater. The floods are performed in the two-phase state with the surfactant and the polymer dissolved in the aqueous phase using different polymer concentrations and a low surfactant concentration, 0.5 wt%. In the presence of a polymer, the oil recovery was improved and the retention of surfactant was decreased. The results are discussed in relation to dissociative surfactant polymer interaction in solution and the effect of polymer on the flow performance of the surfactant in the porous media. Depending on the porous media, an important criteria for success is that the surfactant system must be able to decrease the interfacial tension by a factor of about 103 [22].


338

Abdel-Moghny

The presence of polymer and surfactant in injection water will improve the oil recovery during a water flood. The flooding method is termed low-tension polymer water flood. During the flooding process both chemicals are present in the aqueous microemulsion phase. Core flood experiments were conducted using an alkyl xylene sulfonate, xanthan, model oil (n-heptane), NaCl brine, and Berea sandstone cores in the two-phase ° Surprisingly, at low surfactant concentration, the flooding behaviour of region at 50°C. the surfactant is influenced by the presence of polymer in a negative way regarding oil recovery, even though a dissociative surfactant–polymer interaction is observed in static experiments. The polymer appears to have a negative effect of the flow performance of the surfactant in the porous media possibly owing to very large micellar aggregates [51]. It is, however, very important that no association between surfactant and polymer takes place in solution. In the presence of excess polymer, the surfactant monomer concentration will then become lower than the CMC. The monomolecular packing of surfactants at the interface decreases, and the IFT will increase drastically. It is important to note that the association between ethoxylated sulfonates [52] and sulfates [53] and nonionic polymer decreases as the ethoxylation degree increases. Practically no interaction was observed with EO-groups higher than 3-4. This means that the free energy for normal micelle formation is more favorable than for forming micellar aggregates on the polymer. J.

Relation between the Interfacial Tension and Residual Oil Saturation At the end of primary recovery and/or secondary recovery (water flooding), the residual oil trapped in the pore structure due to capillary forces. The displacement of residual phases is strongly influenced by the competition between two forces, viscous and capillary. Viscous force is known to be a driving force to mobilize the residual oil droplet while capillary force is defined as a resistant force to entrap this residual oil drop. Therefore, the trapped drop does not flow until the viscous forces of the displacing fluid exceeds the capillary forces, usually quantitatively presented by the capillary number Nc. The basic correlation between the Nc and the level of the residual oil had been remodified by Tabor [54] in the form equation (1). Nc = µν /σφ

(1)

where Nc capillary number. µ viscosity of the displacing fluid, dyne. Sec/cm2. ν velocity the displacing fluid, cm/sec. σ is the interfacial tension, dyne/cm. φ the porosity. The value of the capillary number is around 10-6 after water flooding and should be increased by 3 to 4 orders for enhanced oil recovery processes [55]. So the interfacial tension between oil and brine, which is usually around 30 mNm, must be reduced by a factor of 103 or 104. This was shown with gas/liquid mixtures without any additives and confirmed with surfactant containing system in the early 1970s. The waterflooded residual oil saturation may be in the range of 30 to 40%. It must be noticed that these data are mainly based on model cores (Berea and other outcrop sandstone cores) which have never been in contact with reservoir crude oil. Much lower



339

values are, however, observed under mixed wet condition [56]. This implies that it is about 10 times more difficult to remobilize capillary-trapped discontinuous oil, compared to continuous oil. In order to be able to mobilize a significant amount of the waterflooded residual oil, it is expected that the capillary number must be increased by a factor of 103 to 104. The only practical way to do this is to reduce the IFT between the reservoir oil and the injected water by the same factor using surfactants, which normally means that the IFT should be between about 0.01 and 0.001 mN/m. K. Phase Behavior in EOR A pseudoternary diagram including surfactants, brine, and oil, respectively, often represents the phase behavior of EOR systems. Possible combinations of oil, water/salt, and surfactant/co-surfactant/alcohol will give different phase behavior depending on actual conditions. The liquid phase containing the surfactant is a thermodynamically stable phase usually termed a microemulsion. In the pseudophase model, microemulsion phases formed from oil/brine/surfactant/alcohol mixtures consist of three microemulsions. Generally, their three phase terminology for microemulsion phases in EOR are divided as follows: (1) Oil in water microemulsion phase that exhibits equilibrium with excess oil is called type II (-). (2) The micromulsion phase which exhibits equilibrium with excess oil and water is called type III. (3) Water in oil microemulsion phase that exhibits equilibrium with excess water is called type II (+) [10]. In general, the phase behavior conditions for oil-water-surfactant system without alcohol present is very sensitive to the oil composition. Polar components in the crude oil may act as cosurfactants, so, a model oils like n-alkane can be used. The Exxon surfactant product termed RL-3011 (dodecyl-o-xylene sulfonate) illustrates the importance of oil composition on the phase behavior regarding changes in reservoir parameters like temperature, pressure, and salinity [57–60]. Forming a thermodynamically stable microemulsion phase between the oil and the water developed complicated formulations of injected flooding. At equal solubilization of oil and water into this middle phase, the IFT between the microemulsion phase and the two excess phases, oil and water, is ultralow and equal, fulfilling the conditions for displacing most waterflooded residual oil. A variety of chemicals, mixtures of surfactants and low molecular weight alcohols, were needed to design a gel-free chemical formulation. The amount of polymer needed for maintaining mobility control must be high because the middle phase microemulsion is normally rather viscous. Because of the complexity of the chemical formulation, the slug is affected by mass transfer and changes in phase behavior as the fluids propagate through the reservoir. The process is sensitive to many parameters including: (1) rock type, (2) mineral content, (3) interstitial brine salinity and composition, (4) pH, (5) injection rate, (6) slug composition, (7) polymer concentration and type, (8) oil viscosity and composition, (9) pressure, (10) temperature, and (11) heterogeneities of the formation [10]. Sanz and Pope [61] have screened combinations of ethoxylated sulfonates and alkylaryl sulfonates for alcohol-free chemical flooding purposes. They observed difficulties in obtaining clean or gel-free, liquid crystals, macroemulsions, and precipitates along the compositional path during a chemical flood if cosurfactants/alcohols are not part of the chemical formulation. Phase trapping and blockage of the porous medium must be avoided. L. Application of Surfactants in Enhanced Oil Recovery Enhanced oil recovery is the additional recovery of oil from a petroleum reservoir over that which can be economically recovered by conventional primary and secondary methods [30].


340

Abdel-Moghny

1. Interaction between Surfactant and Polymer at Reservoir Rock During flooding process such interaction is also affected by chromatographic separation between the chemicals due to size exclusion phenomena, relative diffusion rate between surfactant monomers and polymers and between polymers of different molecular weight, and the access to the surface area. The polymer will move ahead of the surfactant when the chemicals are injected into a porous medium. Mixtures of xanthan, acrylamide, sodium 2-acrylamido-2-methylpropane sulfonate (AN125), crude oil, and synthetic seawater were circulated through clay-containing reservoir cores for several weeks. They injected at constant slug concentration at different slug size, through model sandstone cores. Various adsorption regimes of the surfactant were detected at different contact times between the reservoir core material and the circulated chemical solution, and it was observed that xanthan behaves as a sacrificial adsorbate towards the surfactant by decreasing the surfactant adsorption. In the slug experiments, using model cores, xanthan appeared to decrease the surfactant adsorption when using small surfactant slug sizes, but no measurable effect of xanthan or AN 125 on surfactant adsorption was observed for large slug sizes. A dynamic reversible adsorption model appeared to predict the propagation of the surfactant slug through the porous medium, but the adsorption level was not fitted. Thus, the polymer may decrease the adsorption of surfactant in reservoir rock of high clay content, approximately 20 wt%. In cores of low clay content, approximately 5 wt%, the polymer will probably have negligible effect on the surfactant adsorption onto the rock [25] 2.

Displacement of Oil by Spontaneous Imbibition of Aqueous Surfactant Solution Imbibition of water is a physical process caused by adsorption of water to hydrophilic ion- groups forming a hydrophilic surface. A porous reservoir medium, consisting of a hydrophilic surface, may contain lipophilic liquid such as oil. When such an oil-filled reservoir rock is exposed to water, the water may spontaneously be sucked into the pores and displace the oil. Spontaneous imbibition of water into low-permeable fractured chalk is an wellaccepted method to improve the oil recovery from water to mixed wet rock material [62]. Normally, this process is driven by capillary forces, and it may seem a little strange to lower the capillary forces by adding surfactants to the injected water. In the same way as the viscous forces will mobilize capillary trapped water flooded oil, the gravity forces may be active in displacing the oil by spontaneous imbibition at low IFT [63]. Spontaneous imbibition experiments in nearly oil-wet, low-permeable chalk material saturated with oil are performed at ambient conditions with and without the cationic surfactant dodecyltrimethylammonium bromide present in the aqueous solution. Without surfactant present in the water, the rate of imbibition is, as expected, very small, and only approximately equals 13% of the oil was expelled from the core within 90 days. After that time, a sudden increase in the oil production was observed by exchanging the water with a 1.0 wt% surfactant solution. If the surfactant is present from the beginning, an oil production plateau of approximately equals 65% recovery was obtained within 90 days. The imbibition mechanism at low interfacial tension is discussed in terms of the phase behavior of the oilbrine surfactant system, and the ability of the surfactant to enhance the water wettability [64]. The improved spontaneous imbibition of water into oil saturated, fractured, low permeable (2 to 3 mD) chalk material of the Ekofisk type by means of surfactants was studied. The experiments were performed at room temperature, using long (55 cm) and



341

short (5.0 cm) core samples of different wettabilities, i.e., water-wet, mixed-wet, and nearly oil-wet. For the two former systems, anionic surfactant of the alkyl-propoxy-ethyl sulfate type was used. A cationic surfactant, dodecyltrimethylammonium bromide, was used for the oil-wet condition. The imbibition mechanism in the water and mixed wet system at high IFT was found to be a countercurrent flow governed by capillary forces. At low IFT, the fluid flow appeared to be countercurrent at the start. Later, the oil expulsion was very slow and governed by gravity forces. Surprisingly, spontaneous oil expulsion from the nearly oil-wet core took place in the presence of the cationic surfactants by a countercurrent flow mechanism. The mechanism is discussed in terms of reversed micelle formation turning the chalk more water wet just across the water/oil interface [65). 3. Adsorption of Different Surfactants on Kaolinite The adsorption of anionic, cationic, and nonionic surfactants on kaolinite has been investigated. Anionic surfactants are widely used in enhanced oil recovery. The lower the adsorptions on the oil-bearing rock the higher the advantage of the surfactant to be used. Whilst the adsorption of anionic and nonionic surfactants are negligible, that of cationic surfactants is relatively high. For this reason, the use of cationic reagents in the enhanced oil recovery is not recommended. The adsorption of cationic surfactants was found to follow an ion-exchange mechanism, while that of anionic and nonionic surfactants proceed through electrostatic attraction and precipitation [66]. 4. Acidified Oil/Surfactant Enhanced Alkaline System A model acidic oil has been used to examine the effects of various alkali and added surfactant concentrations on dynamic interfacial tension. Experimental results revealed the existence of a characteristic behavior exhibited by the acidified oil against aqueous solutions. The dynamic interfacial tension is a function of acid concentration, alkali concentration, and added surfactant concentration. It has been found that there exists an optimum concentration with respect to both alkali and added surfactant, at which the interfacial tension is the lowest. The optimum concentration has been found to be dependent on acid concentration. The results suggest that the unionized acid contributed to the lowering of the dynamic interfacial tension between the model acidic oil and alkali and added surfactant solutions. The results also suggest that the unionized acid, ionized acid added surfactant adsorbed simultaneously onto the interface, resulting in low dynamic interfacial tension [67]. 5. Dual Surfactants—System for Enhanced Oil Recovery at High Salinity Surfactants for the enhanced oil recovery of crude oil were studied with a model oil by means of phase experiments and core floods. As single surfactants, alkylphenol ether sulfonates have only a limited potential for enhanced oil recovery at high salinities. If the surfactant is made hydrophilic enough to dissolve in brine it is no longer able to form a microemulsion with the hydrocarbon. This problem may solve by using dual surfactant systems consisting of alkane sulfonate and ether sulfonate. At high salinities these surfactant combinations dissolve in brine to form a homogeneous dispersion. Such mixtures are also cheaper than the ether sulfonate alone. Core floods with model oil demonstrate the efficiency of these surfactant mixtures and their compatibility with a modified polyacrylamide polymer specially developed for high salinity reservoir [68].


342

Abdel-Moghny

6. Ultralow IFT Using Neutralized Oxidized Hydrocarbon Surfactant Surfactants that may be suitable for application in enhanced oil recovery have been produced from C22 and C26 paraffinic and naphthenic petroleum fractions by a two-step process. The hydrocarbon feed stocks were first oxidized in the vapor phase, followed by neutralization of the oxidized products with aqueous alkali. As a result, dilute solutions of organic acid salts were produced that achieved ultralow (less than 10–2 dyne/cm) interfacial tensions against a synthetic oil. Surfactant solutions that exhibited the lowest interfacial tensions (IFTs) were prepared from neutralizations that used low concentrations of sodium hydroxide rather than sodium silicate, sodium tripolyphosphate, or sodium carbonate. Neutralizations that used sodium silicate or sodium carbonate resulted in surfactant solutions having IFT profiles that were less sensitive to the electrolyte concentration. When sodium hydroxide was combined with either sodium silicate or sodium tripolyphosphate in the neutralizations, solutions having intermediate IFT properties were produced [69]. 7. Mixed Micelles Micelles composed of mixed surfactants with different structures (mixed micelles) are of great theoretical and industrial interest. Abdel-Moghny et al. maximize the reduction of the interfacial tension by blending four types of fatty acid amides based on lauric, myristic, palmetic and stearic acid with dodecyl benzene sulfonic acid at molar ratio 4:1 and designated as A1, A2, A3, and A4, respectively. The IFT was measured for each blend against different concentrations using Badri crude oil. The most potent formula (A4) was evaluated for using in enhanced oil recovery (EOR). The IFT was tested in the presence of a different electrolyte concentration with different crude oils at different temperatures. Finally, several runs were devoted to study the displacement of Badri crude oil by A4 surfactant solution using different slug sizes, 10, 20 and 40% of pore volume (PV). The study revealed that, Badri crude oil gave ultra low IFT at lowest surfactant concentration and 0.5% of NaCl. The recovery factor at slug size of 20% PV was 83% of original oil in place (OOIP) compared with 59% in case of conventional water flood [70]. 8. Biosurfactants as New Surfactant Surfactants are widely used for various purposes in industry, but for many years were mainly chemically synthesized. It has only been in the past few decades that biological surface active compounds (biosurfactants) have been described. Biosurfactants are gaining prominence due to their advantages of biodegradability, production on renewable resources and functionality under extreme conditions; particularly those pertaining during tertiary crude oil recovery. However, caution is frequently exercised with respect to their use because of possible subsequent microbial contamination of either underground oil reservoirs or products. The limited successes and applications for biosurfactants production, recovery, use in oil pollution control, oil storage tank clean up and enhanced oil recovery were reviewed from technological points of view [71].

ACKNOWLEDGMENTS I express my thanks to the staff of the Egyptian Petroleum Research Institute (EPRI) particularly, Prof. Dr. Ahmed Kadry Aboul-Gheit, professor of process development, who devoted time and effort to review this text. I am very grateful for his continuous encour-



343

agement. Without his support this entire subject would not have been possible. In addition Prof. Dr. Abdel-Fattah Badawi, professor of petrochemicals, contributed many valuable suggestions. Also, many thanks to Dr. Mahmoud Ramzi, in the production department, for his help and final montage.

REFERENCES 1. Gogarty, W.B. J. Petroleum. Techn. 1976, Dec., 1475–1483. 2. Shah, D.O. and Schechter, R.S. Improved Oil Recovery by Surfactant and Polymer Flooding, 1977, Academic Press, pp. 1–4. 3. Gale, W.W. and Sandvik, E.I. Tertiary Surfactant Flooding: Petroleum Sulfonate Composition Efficiency Studies. Soc. Petroleum Eng. J. 1973, Aug., 191–199. 4. Hill, H.J., Reisberg, J. and Stegemeier, G.L. Aqueous Surfactant Systems for Oil Recovery J. Petroleum Tech. 1973, Feb., 186–194, Trans., AIME, 255. 5. Davis, J.A., Jr. and Jones, S.C. Displacement Mechanism of Micellar Solution, J. Petroleum Tech. 1968, Dec., 1415- 1428, Trans., AIME, 243. 6. Pope, G.A. and Baviere, M. In Basic Concepts in Enhanced Oil Recovery Processes; Baviere, M., ed.; Elsevier Applied Science, 1991, pp. 89–122. 7. Thomas, S. and Farouq, S.M. J. Can. Pet. Techn. 1992, 31, 53–60. 8. Healy, R.N. and Reed, R.L. SPE J 1974, Oct., 491–501. 9. Ling, T.F., Lee, H.K., and Shah, D.O. In Industrial Applications of Surfactants; Karsa, D.R., ed., Royal Society of Chemistry, Special Publication No. 59, 1986, pp. 126–178. 10. Austad, T. and Milter, J. in Surfactants Fundamentals and Applications In the Petroleum Industry, Laurier L. Schramm, ed., 2000, Chap. 6. Cambridge University Press. 11. Baviere, M., Glenat, P., Plazanet, V., and Labride, J. SPE Res. Eng, 1995, 10, 187–193. 12. Hankins, N.P. and Harwell, J.H. J. Pet. Sci. Eng. 1997, 17, 41–62. 13. De Groot, M., Flooding Process for Recovering Oil from Subterranean Oil-Bearing Strata, U.S. Patent No.1, 823, 439, 1929. 14. De Groot, M., Flooding Process For Recovering Fixed Oil from Subterranean Oil-Bearing Strata, U.S. Patent No.1, 823,440, 1930. 15. Holbrook, O.C., Surfactants-Water Secondary Recovery Processs, U.S. Patent No. 3,006,411, 1958. 16. Shah, D.O. and Schechter, R.S. Improved Oil Recovery by Surfactant and Polymer Flooding, 1977, Academic Press, pp. 28–54. 17. Holm, L.W. and Bernard, G.G. Secondary Recovery Waterflood Process, U.S. Patent No. 3,082,822, 1959. 18. Csaszar, A.K., Solvent-Waterflood Oil Recovery Process, U.S. Patent No. 3,163,214, 1961. 19. Blair, C.M., Jr. and Lehmann, S., Jr., Process for Increasing Productivity of Subterranean Oil Bearing Strata, U.S. Patent No. 2,356,205, 1942. 20. Maerker, J.M. and Gale, W.W. SPE Res. Eng. 1992, 7, 36–44. 21. Kalpakci, B., Arf, T.G., Barker, J.W., Krupa, A.S., Morgan, J.C., and Neira, R.D. Proceeding of the 7th Symposium on Enhanced Oil Recovery of SPE; Society of Petroleum Engineers, Tulsa, OK, 1990, Paper SPE 20220. 22. Taugbøl, K., Van Ly, T., and Austad, T. J of Colloids Surface A: Physicochem. EngineeringAspects. Vol. 103, No. 1–2, October 1995, pp. 83–90. 23. Wellington, S.L. and Richardson, E.A. Proceedings of the Annual Technical Conference of SPE; Society of Petroleum Engineers: Dallas, TX, 1995, Paper SPE 30748. 24. Austad, T. and Taugbøl, K. Colloids Surfaces A: Physicochem. Eng. Aspects 1995, 103, 73–81. 25. Austad, Tor, Ekrann, Steinar, Fjelde, Ingebret, and Taugbol, Knut. J of Colloids and Surfaces A: Physicochemical and Engineering Aspects. Vol. 127 No. 1–3 July 2 1997, pp. 69–82. 26. Tally, L.D. Proceedings from of The International Symposium on Oilfield Chemistry of SPE; Society of Petroleum Engineers: Houston, TX, 1989, Paper SPE 18492.


344 27. 28. 29. 30. 31. 32. 33. 34. 35. 36.

37. 38. 39. 40. 41. 42. 43. 44. 45. 46.

47.

48. 49. 50. 51. 52. 53. 54.

55. 56. 57. 58. 59.

Abdel-Moghny Baviere, M., Bazin, B., and Labrid, J. In Situ 1989, 13, 101–120. McGary, C.W. J. Polymer Sci. 1960, XLVI, 51–57. Tally, L.D. SPE Res. Eng. 1988, 3, 235–242. Bavier, M. Basic Concepts in Enhanced Oil Recovery Processes, 1991 published for SCI, Elsevier Applied Science, London and New York. Schambil, F and Schwuger, M.J., In Surfactants In Consumer Products, Theory, Technology and Application, J. Falbe, ed., Springer-Verlag, New York, 1987. Scamehorn, J.F. In Phenomena In Mixed Surfactant Systems, J.F. Scamehorn, ed., ACS Symposium Series 311, American Chemical Society, Washington, D.C., 1986, P.I. Meguro, K., Ueno, M., and Esumi, K., In Nonionic Surfactants, Schick, M.J., ed., Surfactant Science Series 23, Marcel Dekker, Inc., New York, 1987, p.109. Kurzendorfer, C.P., Schwuger, M.J, and Lange, H., Ber. Bunsenges. Phys. Chem. 82:962, 1978. Ling, T.F., Lee, H.K., and Shah, D.O., In Industrial Applications of Surfactants, Karsa, D.R., ed., Royal Society of Chemistry, London, 1987, p. 126. Miller, C.A., and Qutubuddin, S. In Interfacial Phenomena In Apolar Media, Eicke, H.F., and Parfitt, G.D., eds., Surfactant Science Series 21, Marcel Dekker, Inc., New York, 1987, p. 117. Borthakur, A., and Subrahmanyan, B., Chem. Eng. World 21: 33, 50. 1986. Puig, J.E., Scriven, L.E., Davis, H.T., and Miller, W.G. AIChE Symp. Ser. 78:1, 1982. Shah, D.O., Dev. Petroleum. Sci. 13: 1, 1981. Cox, M.F., Borys, N.F., and Matson, T.P. J. Am. Oil Chem. Soc. 62:1139, 1985. Matheson, K.L., Cox, M.F., and Smith, D.L., J.Am.Oil Chem. Soc. 62:1391, 1985. Cox, M.F., and Matson, T.P., J. Am. Oil Chem. Soc. 62:1396, 1985. Smith, D.L., Matheson, K.L., J. Am. Oil Chem. Soc. 62:1399, 1985. Stellner, K.L., and Scamehorn, J.F., J. Am. Oil Chem. Soc. 63:566, 1986. Fjelde, I., Austad, T., and Milter, J., J of Petroleum Science and Engineering. Vol. 13 No. 3–4 November 1995, pp. 193–201. Pope, G., Tsaur, K., Schechter, S., and Wang, B. Proceeding from the First Symposium on Enhanced Oil Recovery of SPE; Society of Petroleum Engineers, Tulsa, OK, 1980, Paper SPE 8826. Lindman, B. and Thalberg, K. In Interactions of Surfactant with Polymers and Proteins; Goddard, E.D., Antanthapadmanabhan, K.P., eds. CRC Press, Boca Raton, 1993, pp. 203–276. Vervey, E.J.W. and Overbeek, J.Th. Theory Of The Stability Of Lyophobic Colloids; Elsevier, Amsterdam, 1948. Yang, C.Z. Proceedings from the 5th Symposium on Enhanced Oil Recovery of SPE; Society of Petroleum Engineers, Tulsa, OK, 1986, Paper SPE 14931. Piculell, L. and Lindman, B. Advances in Colloid and Interface Sci. 1992, 41, 149–178. Austad, Tor and Taugbol, Knut, Colloid and Surface-A: Physicochemical and Engineering Aspects. Vol. 103 No. 1–2 October 2 1995, pp. 73–81. Veggeland, K. and Nilsson, S. Langmuir 1995, 11, 1885–1192. Saito, S. J. Colloid Interface Sci. 1960, 15, 283–286. Tabor, J.J. Research on Enhanced Oil Recovery: Past, Present, and Future, in Surface Phenomena in Enhanced Oil Recovery, Shah, D.O., ed., pp. 13N53, Plenum Publication Co., New York, 1981. Basal, V.K., and Shah, D.O. In Micellization, Solibilization and Microemulsions, Mittal, K.L., ed.,Vol. 1. pp. 87–113, Plenum Press, NewYork, 1977. Morrow, N.R. and Songkran, B. In Surface Phenomena in Enhanced Oil Recovery; Shah, D.O., ed.; Plenum Press, New York, 1981, pp. 387–411. Austad, T., Hodne, H., and Staurland, G. Progress Colloid Polymer. Sci. 1990, 82, 296-310. Austad, T. and Staurland, G. Progress Colloid Polymer. Sci. 1990, 14, 429–454. Austad, T. and Strand, S. Colloids Surfaces A: Physicochem. Eng. Aspects 1996, 108, 243–52.



345

60. Austad, T., Hodne, H., Strand, S., and Veggeland, K. Colloids Surfaces A: Physicochem. Eng. Aspects 1996, 108, 253–262. 61. Sanz, C.A. and Pope, G.A. Proceedings of The SPE International Symposium on Oilfield Chemistry, Society of Petroleum Engineers, San Antonio, TX, 1995, Paper SPE 28956. 62. Thomas, L.K., Dixon, T.K., Evans, C.E., and Vienot, M.E. J. Pet. Tech., Trans., AIME 1987, 283, 221–232. 63. Schechter, D.S., Zhou, D.S., and Orr Jr., F.M. J. Petroleum Sci. Eng. 1994, 11, 283–300. 64. Austad, T., Mater, B., Milter, J., Saevareid, A., and Oyno, L. J of Colloids and Surfaces A: Physicochemical and Engineering Aspects. Vol. 137, No. 1–3, June 15, 1998, pp. 117–129. 65. Austad, T. and Milter, J. Proceedings SPE Symposium on Oilfield Chemistry. 1997, Society of Petroleum Engineers (SPE), Richardson, TX, pp. 257–266. 66. Atia, A.A. and Radwan, N.R.E. Adsorption—Science and Technology Vol. 125, No. 8 1997, pp. 619–626. 67. Touhami, Y., Hornof, V., and Neale-Gh. J of Colloids and Surfaces A: Physicochemical and Engineering Aspects. Vol. 132 No. 1, January 15, 1998, pp. 61–74. 68. Miller, D.J., Von, Halasz, S.P., Schmidt, M., Holst, A., and Pusch, G. J of Petroleum. Sci. Eng. Vol. 6, No. 1, July 1991, pp. 63–72. 69. Huang, H., Donnellan, W.H., and Jones, J.H. J Am Oil Chem. Soc. Vol. 67, No. 6, June 1990, pp. 406–414. 70. EL-Batanoney, M., Abdel-Moghny, Th., and Ramzi, M, The Effect of Mixed Surfactants on Enhancing Oil Recovery, Journal of Surfactants and Detergents, 1999, April, pp. 2,201– 2, 205. 71. Banat, I.M. Bioresource Technology, Vol. 51, No. 1, pp. 1–12, 1995. 1996, Elsevier Science Ltd.


12 Surfactant-Based Systems for Environmental Remediation David A. Sabatini, Robert C. Knox, Jeffrey H. Harwell, and Ben Shiau

CONTENTS I. II. III. IV.

Summary................................................................................................................ 347 The Problem .......................................................................................................... 348 The Approach ........................................................................................................ 350 Surfactant Fundamentals ....................................................................................... 351 A. Key Economic/Technical Factors.............................................................. 353 1. Minimizing Surfactant Losses ................................................... 354 2. Maximizing Contaminant Extraction ........................................ 354 3. Surfactant Regeneration/Reuse .................................................. 355 4. Mitigating Vertical Migration Concerns.................................... 356 B. Field Results.............................................................................................. 358 1. Hill Air Force Base (AFB)—Maximizing Contaminant Extraction ................................................................................... 358 2. Tinker AFB—Surfactant Decontamination for Reinjection...... 361 3. Alameda Point NAS—Mitigating Vertical Migration (Supersolubilization) .................................................................. 362 C. Future Advances/Applications .................................................................. 364 Acknowledgments........................................................................................................... 366 References ....................................................................................................................... 366

I.

SUMMARY

Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in their contamination of valuable ground water supplies. This chapter summarizes key technical and economic issues for surfactant-enhanced remediation of such contamination episodes. 347


348

Sabatini et al.

The major issues considered include: maximizing the amount of contaminant extracted by surfactant injection, minimizing the surfactant losses in the subsurface, mitigating concerns of vertical contaminant migration, and decontaminating and recycling the surfactant solutions. Both laboratory and field results are presented to demonstrate how we address each of these issues. Finally, we will discuss recent innovations in surfactant systems to further improve the economics of subsurface remediation efforts, and describe how these systems may be useful in other applications (e.g., detergency, solvent replacement).

II. THE PROBLEM Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in contamination of valuable ground water resources. Figure 1 is a schematic illustration of an oil spill that occurs at the land surface and migrates downward due to gravity forces. The oil first moves through the unsaturated zone and eventually reaches a depth where the porous media (soil) is saturated with water, known as the water table. In this illustration (Fig. 1) the oil phase continues to migrate downward through the saturated zone, indicating that this oil is denser than water. Finally, the oil reaches a confining layer that it cannot penetrate, and begins to pool at this depth. In the environmental literature these oil phases are referred to as nonaqueous phase liquids, or NAPLs. In Fig. 1 the oil is denser than water, and is thus referred to as a dense nonaqueous phase liquid (DNAPL). Chlorinated hydrocarbons are typical examples of a DNAPL. If the oil is less dense than water, as true for petroleum hydrocarbons, they are known as “light” nonaqueous phase liquids, or LNAPLs. These oil phases are immiscible with water because of the interfacial tension that exists between the phases. Capillary forces cause oil droplets to be trapped in the porous media as the oil phase migrates through the porous media—as illustrated on a macroscopic scale in Fig. 1 and at a mesoscale in Fig. 2. The trapped oil (residual saturation) is held against gravity forces for dense chlorinated solvents and against buoyancy forces for petroleum hydrocarbons; the latter can become trapped in the saturated zone due to a rising water table. The water solubility of

Injection well

Extraction well Treat

Pump Unsaturated zone Water table

Trapped (residual) oil A

Saturated zone

Confining layer

Figure 1 Schematic cross-section of trapped (residual) oil in subsurface and flushing based remediation—Box A is enlarged in Fig. 2.


Surfactant-Based Systems for Environmental Remediation

349

Trapped oil

Porous media

Fluid flow

Dissolved oil Ground water flow

Figure 2 Trapped oil (residual NAPL) in a porous medium and the resulting aqueous solubility during ground water flow/pump-and-treat flushing.

these trapped oil phases is both too high and too low. The high water solubility of these oils causes their ground water concentrations to exceed treatment goals (health standards). At the same time, their low water solubility renders water-based flushing of the contamination highly inefficient (much as washing dirty clothes in water alone is highly inefficient). Nevertheless, water-based flushing, as depicted in Figs. 1 and 2, has been the traditional approach for addressing these contamination scenarios. In water-based flushing, water is injected into the subsurface and flushed through the zone containing the trapped oil. However, the water immiscibility and low solubility of these compounds severely limits the effectiveness of water-based flushing. At the same time, large dissolved contaminant plumes can emanate from these trapped oil “source” zones, as depicted in Fig. 3. For example, a source zone of relatively small size (acres or less) can produce dissolved plumes that are miles in length. While traditional pump-and-treat remediation (water-based flushing) is generally effective for treating dissolved contaminant plumes (Fig. 3), as discussed above it is very inefficient for trapped oil phases (the source zone in Fig. 3). And if the dissolved plume is addressed without removing the source zone, the plume reappears when additional ground water flows through the source zone. For this reason, innovative methods have been developed to significantly enhance the extraction of residual oil saturation. Chemical

Ground Water Flow

Source Zone

Dissolved Contaminant

Figure 3 Top view of trapped oil/source zone which acts as a source to create a dissolved contaminant plume.


350

Sabatini et al.

additives have been widely evaluated for this purpose, with surfactants being a prime candidate [1,2]. This is analogous to adding surfactants to a washing bath in an effort to improve contaminant “extraction” from the clothes. Both surfactants and alcohols can increase the apparent water solubility of the oil phase, and, when these systems are properly designed, can dramatically reduce the interfacial tension responsible for trapping the oil phase. Since the surfactant has little or no impact on treating the dissolved plume, it will be targeted at the trapped oil phase. In this chapter we discuss key technical and economic considerations for successful application of surfactant enhanced aquifer remediation. We then share laboratory and field results from our group that illustrate each of these issues and show how they can be addressed. We conclude by presenting recent advances that are still in the developmental stages. But first, we will provide a brief overview of the surfactant enhanced subsurface remediation technology in the next section, and an introduction to fundamental surfactant concepts critical to this technology in the following section.

III. THE APPROACH

As mentioned above, surfactant enhanced aquifer remediation seeks to overcome the limitations of water-based pump-and-treat remediation. In our approach, a surfactant or surfactant mixture is added to the injection side of the system in Fig. 1 in an effort to significantly increase the contaminant extraction efficiency. This can be accomplished in one of two ways; by increasing the contaminant solubility without significantly reducing the interfacial tension (“solubilization”), or by significantly reducing the interfacial tension and mobilizing the trapped oil phase (“mobilization”). Relative advantages and disadvantages of these two approaches are discussed later. For a chlorinated solvent (e.g., tetrachloroethylene or PCE), water-based flushing of the trapped oil may require 1000 flushing cycles (pore volumes) to dissolve the trapped oil. In contrast, by increasing the PCE solubility 50-fold in surfactant micelles, surfactantenhanced solubilization will accomplish the same level of remediation in 20 pore volumes. In this case the oil remains trapped (as in Fig. 2), but the surfactant solution flowing through the pores achieves significantly higher extraction concentrations. Conversely, by virtually eliminating the interfacial tension causing the oil to be trapped in the first place, surfactant enhanced mobilization will accomplish the same level of removal in several pore volumes. In this case, the oil trapped in Fig. 2 is largely or totally released from the trapped stage. Thus, in the example above the relative efficiencies of water, solubilization and mobilization are 1000:20:2, respectively. While the exact numbers and ratios are system specific, these values give an idea of the relative efficiencies of each system. Using this example, and given that a full-scale remediation system may require months to flush a single pore volume, surfactant enhanced aquifer remediation could reduce the remediation times from hundreds of years for water alone to 5 years for solubilization to less than a year for mobilization. The potential advantages of surfactant enhanced subsurface remediation are therefore obvious. But beyond technical viability, this technology must also be economically viable. Because of the surfactants costs, the surfactant solution is designed to maximize the amount of contaminant extracted per mass of surfactant injected. We must also seek to minimize surfactant losses due to sorption and precipitation in the subsurface. When using multiple flushing cycles, it may be more economical to regenerate (decontaminate) the surfactant solution for recyling (reinjection). Finally, reducing the surfactant concentration necessary



351

to achieve a given solubility enhancement is desirable. But implicit to all this is the basic question: How clean is clean enough? How much of the “oil stain” (residual saturation) must be removed to be successful? Before discussing these points in further detail, we will first discuss surfactant fundamentals critical to this technology.

IV. SURFACTANT FUNDAMENTALS Surfactants (surface active agents) are unique because of their amphiphilic nature, which makes them surface active and causes them to accumulate at interfaces. Thus, when placed in water-oil or water-air systems, surfactants accumulate at the interface with their waterlike moiety in the polar water phase and the oil-like moiety in the nonpolar oil or less polar air phase. In this way, both surfactant moieties are in a preferred phase and the free energy of the system is minimized [3]. By definition, alcohols could be considered as surfactants since they also accumulate at interfaces. However, a unique characteristic of surfactants differentiates them from alcohols. When the aqueous surfactant concentration exceeds a certain level, the surfactant molecules (monomers) self-aggregate into spherical aggregates known as micelles. In contrast, alcohols do not form such micellar aggregates. Surfactant micelles form when increasing surfactant concentrations first exceed the critical micelle concentration (CMC). Surfactant micelles have polar exteriors and nonpolar interiors. The polar exterior makes micelles highly soluble in water, while the nonpolar interior provides a hydrophobic sink for organic compounds, which effectively increases the compound’s solubility. Thus, by adding surfactant well above the CMC, we significantly increase the micelle concentration and thus the contaminant’s apparent solubility. In contrast, adding surfactant near or only slightly above the CMC will have minimal effect on contaminant solubility and extraction efficiency. We therefore desire to be well above the CMC (e.g., 10 to 20 times the CMC) to maximize contaminant solubility and extraction efficiency. Surfactants are capable of producing other structured phases. Some of these phases are undesirable for subsurface remediation (e.g., liquid crystals, gels). In contrast, middle phase microemulsions can be desirable for subsurface remediation. In particular, middle phase microemulsion systems produce ultra-low oil-water interfacial tensions and ultrahigh contaminant solubilization (supersolubilization). Since it is the oil–water interfacial tension that originally trapped the oil in porous media, virtually eliminating the interfacial tension will mobilize the trapped oil phase (i.e., cause the oil to come out as a bulk phase rather than simply increasing its water solubility). While micelles form spontaneously above the CMC, forming middle phase microemulsions is not so simple. The surfactant system must be carefully tailored to each specific contaminant phase. Before describing a middle phase microemulsion we will first discuss two other surfactant systems; micelles, which we have described above, and inverse micelles. While micelles form when water-soluble surfactants are added to an aqueous phase, inverse micelles occur when oil-soluble surfactants are added to an oil phase. For oil-soluble surfactants, the hydrophilic surfactant moiety (head) accumulates in the interior of the aggregate and the hydrophobic moiety (tail) orients toward the oil phase. The inverse micelle thus has a hydrophobic exterior, which makes it oil soluble, and a hydrophilic interior, which acts as a sink to “solubilize” water. For the descriptions of micelles and inverse micelles we considered surfactants in a single phase system (oil or water). If both oil and water phases coexist, as is true with residual oil in a ground water system, the surfactant will partition between the two phases in accordance with the surfactant’s relative hydrophilicity. The hydrophilic-lipophilic balance (HLB)


352

Sabatini et al.

O/S interface

W/S interface

Optimum formulation

I

III

Oil solubilization, %V/V

Interfacial tension, mN/m

is a surfactant property that approximates this partitioning. Surfactants with relatively high HLB values (e.g., 20) are water soluble, while relatively low HLB values (e.g., 5) indicate surfactants that are oil soluble. As the HLB of a surfactant, or surfactant mixture, varies between these extreme values it transitions from being water soluble (micelles) to oil soluble (inverse micelles); this transition occurs at intermediate HLB values (approximately 8 to 12, depending on the oil). By varying system conditions we can force water-soluble surfactants to partition into the oil phase. For example, by increasing the salt concentration we can reduce the HLB of ionic surfactant systems. When the salt concentration is increased sufficiently ionic surfactants will eventually partition into the oil phase. This is illustrated in Fig. 4, which shows aqueous micelles at lower salt concentrations and oil-phase inverse micelles at higher salt concentrations. Increasing the system temperature will likewise decrease the system HLB for nonionic surfactant systems. Middle phase microemulsion systems form when the surfactant system HLB (or effective HLB, as a function of salinity or temperature) is adjusted such that the surfactant is just ready to leave the water phase, but is not yet ready to go into the oil phase. At this point the surfactant system dislikes both the water and oil phases and would prefer to accumulate at the interface. In simple terms, since all the surfactant cannot fit at the oil–water interface, a new phase forms. This new phase, which we call a middle phase microemulsion, combines virtually all of the surfactant with portions of both the oil and water phases, and exists in equilibrium with surfactant-free oil and water phases. Middle phase microemulsions appear at intermediate salt concentrations in Fig. 4. Unlike an oilwater emulsion, which breaks given sufficient time, a middle phase microemulsion system is thermodynamically stable and thus does not break with time. Winsor referred to this new phase as a Type III microemulsion, as opposed to Type I (micelles) and Type II (inverse micelles) microemulsions [3,4].

II

Increase Salinity, Decrease temperature or increase long chain alcohol content

Figure 4 Surfactant scan showing transition from micelles to middle phase microemulsions to inverse micelles. Note that the oil (PCE) is the lower phase in the vials.



353

The middle phase microemulsion occurs over a limited HLB range as the system transitions from a Type I to a Type II system. When salinity is used to adjust the system HLB, this middle phase range is known as the salinity window. Within the salinity window, as the HLB decreases the middle phase system transitions from being under-optimum (more water than oil in the middle phase) to optimum (equal volumes of water and oil) to over-optimum (more oil than water). Optimum here refers to the lowest interfacial tension within the middle phase regime, which experience teaches us occurs when equal volumes of oil and water coexist in the middle phase microemulsion. Recalling that ultralow interfacial tension and superhigh solubilization are two desirable characteristics of middle phase microemulsion systems, we now know that the lowest possible interfacial tension occurs in middle phase microemulsions with equal volumes of oil and water. An obvious question is; When is the supersolubilization potential at its maximum? This question can be answered by considering the Chun-Huh relationship [5], as shown below. S=

C IFT

where S = solubilization ratio (vol/mass) C = constant IFT = interfacial tension (mN/m) The Chun-Huh relationship demonstrates that solubilization potential is inversely proportional to the square root of the interfacial tension. Since interfacial tension continuously decreases as we move towards a middle phase microemulsion system, the ChunHuh relationship demonstrates that the solubilization potential also continuously increases, within both the Winsor Type I and Type III regions (see Fig. 4). We refer to this increased solubilization within the Type I region as supersolubilization [6]. But why operate in a supersolubilization region instead of in the optimum middle phase microemulsion region? Because the supersolubilization system can mitigate vertical migration of released DNAPL droplets. If the interfacial tension is reduced to the point that DNAPL droplets are released in bulk, then gravity forces will cause these released droplets to migrate downward, potentially allowing them to enter zones previously inaccessible to the oil. By operating in a supersolubilization region, the system HLB is adjusted such that the lower interfacial tension does not release the trapped oil but does maximize the solubility enhancement. A. KEY ECONOMIC/TECHNICAL FACTORS Having discussed surfactant fundamentals pertinent to environmental remediation, we now identify key technical and economic issues relative to successful implementation of this technology. In many respects this technology is an outgrowth of surfactant enhanced oil recovery in petroleum reservoirs; Pope and Wade [5] do an excellent job of identifying similarities and differences between these two applications. After discussing economic factors below, we will then summarize our previous laboratory and field results that illustrate successful implementation of this technology relative to each of the key economic factors.


354

Sabatini et al.

Full-scale application of surfactant enhanced subsurface remediation requires that this approach be economically competitive with other methods. Krebbs-Yuill et al. [7] demonstrated that surfactant enhanced subsurface remediation is economically competitive when surfactant losses are minimized, surfactant extraction efficiency is maximized and surfactant regeneration and reuse are implemented. These factors reflect the fact that surfactant capital costs can, and initially were, the single largest expense for these systems. In addition, we will further describe an approach for mitigating vertical migration concerns, a problem introduced above. Another simple alternative for improving the overall system economics is to spatially divide the residual zone into compartments and march the surfactant remediation through the compartments one at a time, thereby reducing the capital expenditure for surfactant. While having the potential to decrease the capital costs, this approach will extend the time necessary to clean up the site, which may have negative repercussions. 1. Minimizing Surfactant Losses Surfactant losses in the subsurface negatively impact system performance and economics, and can potentially result in system failure. Careful surfactant selection can minimize surfactant precipitation and sorption losses. For example, we have demonstrated that disulfonated vs. monosulfonated surfactants [8] and ethoxylated vs. nonethoxylated alkylsulfate surfactants [9] reduce surfactant sorption and precipitation losses, while maintaining good solubilization potential. We have used the disulfonated surfactant Dowfax 8390 in several field demonstrations [10–12]; its robustness and conservative nature have validated its ability to minimize surfactant losses (> 95% recovery of injected surfactant in the above tests). 2. Maximizing Contaminant Extraction Maximizing contaminant extraction is also important to overall system performance. As discussed above, the greatest possible extraction enhancement occurs with middle phase microemulsion systems. In their work with chlorinated solvents, Shiau et al. [13] focused on the use of direct food additive surfactants for both solubilization and mobilization (via middle phase microemulsions). Shiau et al. [13] demonstrated that surfactant selection was much more critical when forming middle phase microemulsions. While initial surfactant scans transitioned from micellar phases (Winsor Type I) to reverse micelles (Winsor Type II), undesirable phases occurred in the transition region (e.g., liquid crystals) instead of the target middle phase microemulsions. Only when the branched surfactant Aerosol OT (AOT) was used did middle phase microemulsion systems occur; the branched AOT surfactant sterically hinders liquid crystal formation and thus promotes formation of middle phase microemulsions. Shiau et al. [13] also demonstrated that middle phase microemulsion formation is temperature and hardness sensitive, especially when using nonionic and anionic surfactants, respectively. Shiau et al. studied PCE, TCE, and 1, 2-DCE individually [13] and in binary and ternary mixtures [14]. Using regular solution theory it was possible to predict ternary and binary system behavior based on binary and single-component system results, respectively. Using column studies, Shiau et al. [15] demonstrated that mobilization was significantly more effective than solubilization (>97% of PCE was extracted in 3 pore volumes with mobilization, while

Handbook of Detergents, Part D: Formulation (Surfactant Science)

Handbook of Detergents, Part A - Properties (Surfactant Science Series)

Handbook of Detergents, Part B: Environmental Impact (Surfactant Science Series)

Liquid Detergents (Surfactant Science Series)

handbook of detergents analysis

Solubilization in Surfactant Aggregates (Surfactant Science)

Organized Solutions (Surfactant Science)

Surfactant Science and Technology

Cationic Surfactants (Surfactant Science)

Surfactant science and technology

Bicontinuous Liquid Crystals (Surfactant Science)

Powdered detergents

Detergency of Specialty Surfactants (Surfactant Science)

Handbook of Psychotherapy Case Formulation, 2nd Edition

Biomolecular Films (Surfactant Science Series)

Colloids in Biotechnology (Surfactant Science)

Detergency of Specialty Surfactants (Surfactant Science)

Analysis of Surfactants (Surfactant Science Series)

Physical Chemistry of Polyelectrolytes (Surfactant Science Series)

Thermal Behavior of Dispersed Systems (Surfactant Science)

Reactions and Synthesis in Surfactant Systems (Surfactant Science Series)

Handbook of Psychotherapy Case Formulation, Second Edition (Handbook of Psychotherapy Case Formulation)

Laundry detergents

Wetting and Spreading Dynamics: 138 (Surfactant Science)

Protein-Based Surfactants (Surfactant Science Series)

Coagulation and Flocculation, Second Edition (Surfactant Science)

Handbook of Macroeconomics, Part 3

Handbook of Macroeconomics, Part 1

Molecular and Colloidal Electro-optics (Surfactant Science)

Protein-Based Surfactants (Surfactant Science Series)

Handbook of Detergents, Part D: Formulation (Surfactant Science)

Handbook of Detergents, Part A - Properties (Surfactant Science Series)

Handbook of Detergents, Part B: Environmental Impact (Surfactant Science Series)

Liquid Detergents (Surfactant Science Series)

handbook of detergents analysis

Solubilization in Surfactant Aggregates (Surfactant Science)

Organized Solutions (Surfactant Science)

Surfactant Science and Technology

Cationic Surfactants (Surfactant Science)

Surfactant science and technology

Bicontinuous Liquid Crystals (Surfactant Science)

Powdered detergents

Detergency of Specialty Surfactants (Surfactant Science)

Handbook of Psychotherapy Case Formulation, 2nd Edition

Biomolecular Films (Surfactant Science Series)

Colloids in Biotechnology (Surfactant Science)

Detergency of Specialty Surfactants (Surfactant Science)

Analysis of Surfactants (Surfactant Science Series)

Physical Chemistry of Polyelectrolytes (Surfactant Science Series)

Thermal Behavior of Dispersed Systems (Surfactant Science)

Reactions and Synthesis in Surfactant Systems (Surfactant Science Series)

Handbook of Psychotherapy Case Formulation, Second Edition (Handbook of Psychotherapy Case Formulation)

Laundry detergents

Wetting and Spreading Dynamics: 138 (Surfactant Science)

Protein-Based Surfactants (Surfactant Science Series)

Coagulation and Flocculation, Second Edition (Surfactant Science)

Handbook of Macroeconomics, Part 3

Handbook of Macroeconomics, Part 1

Molecular and Colloidal Electro-optics (Surfactant Science)

Protein-Based Surfactants (Surfactant Science Series)

Recommend Documents