Plant Biomass Conversion

The development of biofuels and green chemistry has escalated rapidly in recent years, and with increased interest there is now a great demand for scientific information on the development of biomass crops and conversion of biomass into fuels and chemicals. Plant Biomass Conversion provides coverage of a broad range of key topics that are directly tied to the sustainable and profitable development of the biofuels industry. Plant Biomass Conversion covers topics ranging from the development of dedicated biomass crops to the evolution of conversion processes. Chapters also look at sustainability issues and the economic considerations to profitably develop fuels and industrial chemicals from biomass. Bringing together contributions from scientific researchers and industry personnel, Plant Biomass Conversion will provide the reader with thorough understanding of this evolving industry. Broad ranging in scope and written in a succinct, scientific style, Plant Biomass Conversion will be an essential reference for all researchers and industrial personnel interested in the production and development of biofuels.

KEY FEATURES: • Provides an overview of plant biomass conversion for plant and crop scientists, biofuels researchers, and industry personnel • Addresses both development of biomass crops and conversion techniques • Discusses sustainability and economic issues around the development of bio-based fuels and chemicals

EDITORS: Elizabeth E. Hood is a Distinguished Professor of Agriculture at Arkansas State University. Peter Nelson is Co-Founder and Director of Business Development with BioDimensions, Inc. Memphis, Tennessee. Randall Powell is Technology Consultant and Program Manager for Sugar Platform with BioDimensions, Inc, Memphis Tennessee.

RELATED TITLES: Biofuels from Agricultural Wastes and Byproducts Editors: Hans P. Blaschek, Thaddeus Ezeji, Jurgen Sheffren 9780813802527

ISBN: 978-0-8138-1694-4

www.wiley.com/wiley-blackwell

HOOD, NELSON, & POWELL

Anaerobic Biotechnology for Bioenergy Production: Principles and Applications Samir Kumar Khanal 9780813823461

PLANT BIOMASS CONVERSION

PLANT BIOMASS CONVERSION

BIOMASS AND BIOFUELS SERIES

PLANT BIOMASS CONVERSION

ELIZABETH E. HOOD, PETER NELSON, & RANDALL POWELL

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Plant Biomass Conversion Editors Elizabeth E. Hood Arkansas Biosciences Institute Arkansas State University Jonesboro, Arkansas, USA

Peter Nelson BioDimensions, Inc. Memphis, Tennessee, USA

Randall Powell BioDimensions, Inc. Memphis, Tennessee, USA

A John Wiley & Sons, Ltd., Publication

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C 2011 by John Wiley & Sons Inc. This edition first published 2011


Wiley-Blackwell is an imprint of John Wiley & Sons, formed by the merger of Wiley’s global Scientific, Technical and Medical business with Blackwell Publishing. Registered office:

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For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: 978-0-8138-1694-4/2011. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Library of Congress Cataloging-in-Publication Data Plant biomass conversion / editors: Elizabeth E. Hood, Peter Nelson, Randall Powell. p. cm. Includes bibliographical references and index. ISBN 978-0-8138-1694-4 (hardcover : alk. paper) 1. Plant biomass. 2. Biomass conversion. 3. Biomass conversion–Environmental aspects. 4. Biomass energy. I. Hood, Elizabeth E. II. Nelson, Peter (Peter Allan), 1974– III. Powell, Randall Worth. TP248.27.P55P554 2011 662 .88–dc22 2010040942 A catalogue record for this book is available from the British Library. This book is published in the following electronic formats: ePDF 9780470959053; Wiley Online Library 9780470959138; ePub 9780470959091 R Inc., New Delhi, India Set in 10/11.5 pt Times New Roman by Aptara


1 2011

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Contents

Contributors Preface 1 The Bioeconomy: A New Era of Products Derived from Renewable Plant-Based Feedstocks Peter Nelson, Elizabeth Hood, and Randall Powell 1.1 1.2 1.3

1.4 1.5 1.6 1.7 1.8 1.9 1.10

Introduction Market Opportunity for Biofuels and Biobased Products Feedstocks 1.3.1 Biobased Feedstock Availability and Issues 1.3.2 Characterization of Lignocellulosic Feedstocks 1.3.3 The Role of Agricultural Biotechnology 1.3.4 Biomass Agricultural Equipment Development The Biochemical Technology Platform Investment and Major Players The Role of the Farmer Opportunities for Rural Development Environmental Benefits Economic Comparison of the Biochemical and Thermochemical Technology Platforms Conclusions and Future Prospects References

2 Agricultural Residues James Hettenhaus 2.1 2.2

Introduction 2.1.1 Key Issues Feedstock Supply 2.2.1 Residue Markets 2.2.2 Harvest Window 2.2.3 Residue Removal 2.2.4 Residue Management 2.2.5 Ag Equipment Needs 2.2.6 Operating Costs 2.2.7 Residue Nutrient Value 2.2.8 Land for Energy Crops

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3 3 5 6 6 8 9 11 11 12 14 16 17 17 18 19 21 21 22 23 26 27 27 28 29 33 33 33 v

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2.3

2.4

2.2.9 Farmer Outlook 2.2.10 Crop Research and Development Feedstock Logistics 2.3.1 Bulk Density 2.3.2 Storage 2.3.3 Regional Biomass Processing Centers Conclusion Endnotes References

3 Growing Systems for Traditional and New Forest-Based Materials Randall Rousseau, Janet Hawkes, Shijie Liu, and Tom Amidon 3.1 3.2 3.3

34 34 34 35 36 43 48 49 49 51

Introduction Natural Regeneration Overall Growing Systems 3.3.1 The Beginnings of Biomass Plantation Production 3.3.2 Short Rotation Woody Crops 3.3.3 Other Types of Hardwood Plantations 3.3.4 Southern Pine New Genetic Tools Agroforestry Products from Woody Biomass 3.6.1 Hemicellulosic Products 3.6.2 Biorefineries Using Woody Biomass 3.6.3 Hot-Water Extraction of Hemicellulose 3.6.4 Wood Extracts: Processing and Conversion 3.6.5 Residual Solid Wood Biomass: Processing and Conversion of the wood mass after extraction, an example Summary References

51 54 54 55 56 59 61 62 63 67 69 71 73 75

4 Dedicated Herbaceous Energy Crops Keat (Thomas) Teoh, Shivakumar Pattada Devaiah, Deborah Vicuna Requesens, and Elizabeth E. Hood

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3.4 3.5 3.6

3.7

4.1 4.2

4.3

4.4

Introduction Miscanthus 4.2.1 Characteristics That Make Miscanthus a Potential Biomass Crop 4.2.2 Agronomy Sweet Sorghum 4.3.1 Biology of Sweet Sorghum 4.3.2 Production 4.3.3 Potential Yields 4.3.4 Economic and Environmental Advantages of Sweet Sorghum 4.3.5 Production Challenges Switchgrass 4.4.1 Physiology 4.4.2 Switchgrass Ecotypes

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85 85 87 87 90 92 92 94 94 96 97 97 98

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4.4.3 Advantages 4.4.4 Disadvantages 4.4.5 Yields 4.4.6 Switchgrass as a Bioenergy Crop Conclusions and Future Prospects References

98 99 100 101 101 104

5 Municipal Solid Waste as a Biomass Feedstock David J. Webster

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4.5

5.1 5.2 5.3

5.4 5.5

5.6

5.7 5.8

Introduction Definitions 5.2.1 Second-Generation Conversion Technologies for Biofuels Disposal Infrastructure and Transfer Stations 5.3.1 Collection Practices 5.3.2 Cost Parameters Waste Generation Waste Characterization 5.5.1 Composition of Generated MSW Prior to Disposal or Processing 5.5.2 Landfilled Waste Compared to Waste Generation 5.5.3 Water in MSW 5.5.4 Heavy Metals in MSW Preparing MSW for Conversion Processing—Mixed Waste Material Recovery Facilities (MRFs) 5.6.1 Presorting 5.6.2 Mechanical Sorting Operations 5.6.3 Manual Sorting Operations 5.6.4 Recovery Rates of the MRF System Cellulosic Content of MSW 5.7.1 Glucose and Ethanol Yields from MSW Framing the Potential References

6 Water Sustainability in Biomass Cropping Systems Jennifer L. Bouldin and Rodney E. Wright 6.1 6.2 6.3

6.4

Introduction Water Use in Bioenergy Production Water Quality Issues in Bioenergy Crops 6.3.1 AGNPS Watershed Model 6.3.2 Water Quality and the Gulf Hypoxic Zone Conclusions—Water Quantity and Quality References

7 Soil Sustainability Issues in Energy Crop Production V. Steven Green 7.1 7.2

Soil Sustainability Concepts Bioenergy Crops and Soil Sustainability

109 110 110 110 112 112 113 114 114 115 116 117 119 121 122 123 123 124 124 125 126 129 129 130 133 135 138 138 139 143 143 145

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7.3

7.4 7.5

7.2.1 Crop Residues 7.2.2 Dedicated Energy Crops Resource Use in Biomass Production 7.3.1 Water and Soil 7.3.2 Land Use Soil Sustainability Solutions Conclusion References

8 Fermentation Organisms for 5- and 6-Carbon Sugars Nicholas Dufour, Jeffrey Swana, and Reeta P. Rao 8.1 8.2 8.3 8.4 8.5 8.6

Introduction Fermentation Metabolic Pathways Fermenting Species 8.4.1 Brief Description of Major Species Other Relevant Products Summary Endnotes References

9 Pretreatment Options Bradley A. Saville 9.1

9.2

9.3

9.4

9.5 9.6

Overview of Pretreatment Technologies 9.1.1 History 9.1.2 Mechanistic Assessment of Pretreatment 9.1.3 Severity Factor Concept Pretreatment Classification 9.2.1 Mechanical Pretreatment Processes 9.2.2 Chemical Pretreatment Processes 9.2.3 Thermochemical Pretreatment Processes 9.2.4 Impact on Moisture Content and Hydraulic Load Laboratory vs. Commercial Scale Pretreatment—What Do We Really Know? 9.3.1 Laboratory Studies 9.3.2 Pilot/Demonstration Scale Studies 9.3.3 Limitations of Laboratory-Scale Comparisons of Pretreatment Methods Process Issues and Trade-Offs 9.4.1 Inhibitors 9.4.2 Hydrolysis Efficiency and Enzyme Loadings 9.4.3 Solvent/Catalyst Recovery 9.4.4 Viscosity Reduction and Hydraulic Load Economics Conclusions References

145 146 149 149 150 150 154 154 157 157 159 160 161 175 180 183 183 184 199 199 199 200 203 205 206 206 209 210 211 211 211 214 215 215 218 218 218 220 224 224

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10 Enzyme Production Systems for Biomass Conversion John A. Howard, Zivko Nikolov, and Elizabeth E. Hood 10.1 10.2 10.3

10.4 10.5

Introduction The Challenge: Volume and Cost of Enzymes Required Theoretical Ways to Address the Challenge of Quantity of Enzyme and Cost Requirements 10.3.1 Increase Susceptibility for Biomass Deconstruction 10.3.2 Decrease Exogenous Enzyme Load 10.3.3 Increase Accumulation of Enzymes in Production Host Cost of Producing Exogenous Enzymes 10.4.1 Cost Analysis Summary and Future Prospects References

11 Fermentation-Based Biofuels Randy Kramer and Helene Belanger 11.1 11.2

11.3

11.4

11.5

11.6

Introduction First-Generation Biofuels 11.2.1 Starch-Based Ethanol—United States 11.2.2 Sugar-Based Ethanol—Brazil 11.2.3 Biodiesel Policy and Biofuel Implementation Status 11.3.1 North America 11.3.2 South America 11.3.3 Europe 11.3.4 Asia Second-Generation Biofuels 11.4.1 Cellulosic Ethanol 11.4.2 Biobutanol Issues for Biofuels Commercial Success 11.5.1 Transport by Pipeline 11.5.2 Decentralized Production and Local Distribution 11.5.3 Optimized Engine Performance 11.5.4 Value of Biorefinery Co-products Summary References

12 Biobased Chemicals and Polymers Randall W. Powell, Clare Elton, Ross Prestidge, and Helene Belanger 12.1 12.2 12.3

12.4

Introduction Biobased Feedstock Components Biomass Conversion Technologies 12.3.1 Technology Platforms Overview 12.3.2 Lignocellulose Fractionation Overview Biobased Products 12.4.1 Oil-Based Products 12.4.2 Sugar/Starch-Based Products

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227 227 227 228 229 231 236 240 242 245 246 255 255 256 256 257 258 260 260 262 262 263 265 265 268 269 269 270 271 272 272 272 275 275 276 277 277 279 287 287 289

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12.4.3 Polymer Products 12.4.4 Lignin Products Summary References

13 Carbon Offset Potential of Biomass-Based Energy Gauri-Shankar Guha 13.1

13.2

13.3

13.4

13.5

Emerging Public Interest in Carbon 13.1.1 Overview 13.1.2 Initiatives to Address Anthropogenic Climate Change 13.1.3 GHG Mitigation and Carbon Sequestration Strategies Theory of Carbon Markets 13.2.1 Tradable Permits and the Market for Emissions 13.2.2 Concept of Carbon Markets 13.2.3 Demand and Supply of Carbon Credits Creation of Carbon Markets 13.3.1 Carbon Credits 13.3.2 Global Carbon Trade 13.3.3 Carbon Trading in the United States 13.3.4 The CCX Offset Program Role of Biomass-Based Energy in Carbon Markets 13.4.1 Economic Significance of Bioenergy 13.4.2 Bioenergy Policies, Practices, and Trends 13.4.3 Carbon Offset Opportunities for Biofuels Prognosis of Carbon Markets References

14 Biofuel Economics Daniel Klein-Marcuschamer, Brad Holmes, Blake A. Simmons, and Harvey W. Blanch 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8

14.9 14.10 14.11 14.12 14.13 Index

Introduction Production Processes Biomass Transportation and Handling Conversion of Biomass into Sugars Conversion of Sugars into Biofuels Separation and Purification Co-product Handling Major Cost Drivers 14.8.1 Biomass-Associated Costs 14.8.2 Capital Expenses 14.8.3 Operating Costs Risks Policy Support Infrastructure and Vehicle Modifications Conclusions Acknowledgments References

293 299 303 304 311 311 311 311 314 314 314 315 316 317 317 318 318 318 319 319 321 323 324 325 329

329 330 331 332 335 337 337 338 338 340 342 343 345 346 347 348 348 355

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Contributors

Tom Amidon, SUNY, Syracuse, NY, USA. Helene Belanger, Vertichem Technology Limited, Toronto, Ontario M5H 3B7, Canada. Harvey W. Blanch, Joint Bioenergy Institute, Lawrence Berkeley National Laboratory, and University of California-Berkeley; Berkeley, CA, USA. Jennifer L. Bouldin, Department of Biological Sciences, Ecotoxicology Research Facility, Arkansas State University, Jonesboro, AR, USA. Shivakumar Pattada Devaiah, Arkansas Biosciences Institute, Arkansas State University, Jonesboro, AR, USA. Nicholas Dufour, Worcester Polytechnic Institute, Worcester, MA, USA. Clare Elton, Vertichem Technology Limited, Toronto, Ontario M5H 3B7, Canada. Steven Green, Agricultural Studies, College of Agriculture and Technology, Arkansas State University, Jonesboro, AR, USA. Gauri-Shankar Guha, Economics and Finance Department, Arkansas State University, Jonesboro, AR, USA. Janet Hawkes, HD1, LLC, Ithaca, NY, USA. James Hettenhaus, Chief Executive Assistance, Inc, Charlotte, NC, USA. Brad Holmes, Joint Bioenergy Institute and Lawrence Berkeley National Laboratory, Berkeley, CA, USA. Elizabeth E. Hood, Arkansas Biosciences Institute, Arkansas State University, Jonesboro, AR, USA. John A. Howard, Applied Biotechnology Institute, San Luis Obispo, CA, USA. Daniel Klein-Marcuschamer, Joint Bioenergy Institute and Lawrence Berkeley National Laboratory, Berkeley, CA, USA. xi

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Contributors

Randy Kramer, Kramer Energy Group, Rapid City, SD, USA. Shijie Liu, SUNY, Syracuse, NY, USA. Peter Nelson, BioDimensions, Inc., Memphis, TN, USA. Zivko Nikolov, Texas A&M University, College Station, TX, USA. Randall W. Powell, BioDimensions, Inc., Memphis, TN, USA. Ross Prestidge, Vertichem Technology Limited, Toronto, Ontario M5H 3B7, Canada. Reeta P. Rao, Worcester Polytechnic Institute, Worcester, MA, USA. Deborah Vicuna Requesens, Arkansas Biosciences Institute, Arkansas State University, Jonesboro, AR, USA. Randall Rousseau, Forestry Department, Mississippi State University, Starkville, MS, USA. Bradley Saville, University of Toronto, Department of Chemical Engineering and Applied Chemistry, Toronto, Canada. Blake A. Simmons, Joint Bioenergy Institute, Lawrence Berkeley National Laboratory, and Sandia National Laboratories, Livermore, CA, USA. Jeffrey Swana, Worcester Polytechnic Institute, Worcester, MA, USA. Keat (Thomas) Teoh, Arkansas Biosciences Institute, Arkansas State University, Jonesboro, AR, USA. David J. Webster, Ark Resources, LLC, Birmingham, AL, USA. Rodney E. Wright, Ecotoxicology Research Facility, Arkansas State University, Jonesboro, AR, USA.

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Preface

A host of motivations is driving the development of the “renewables” industry—a desire for energy independence in the United States, biodegradable products, global warming, and hopefully, making money. All energy utilized on the earth is ultimately derived from the sun through photosynthesis—the only truly renewable commodity. Capitalizing on this productive process in a balanced way is crucial to our survival as a species. Crude oil represents an ancient capture of carbon and sunlight by plants. However, the rate at which we are utilizing oil releases ancient fixed carbon into the atmosphere and upsets the balance of nature in a way that is unprecedented in global history. Nature’s checks and balances are not able to accommodate this huge increase in carbon from man’s activities. Thus, development of a new source of energy and products is imperative. Many models that describe processes for generating energy from biomass exist. No one book can describe them all. This work focuses on the biochemical (enzymatic) digestion of plant biomass to produce the raw materials that make up plant cell wall polymers. These raw materials can then be used as feedstocks for ethanol and other bio-based products. This volume also is focused on solving the issues for biomass conversion into ethanol and bio-based products now—not the longer-term solutions with modified microbes and modified feedstocks. The chapters review existing technologies and future expectations for those technologies. They describe multiple feedstocks, multiple pretreatment technologies, enzyme production models, fermentation models, and manufacturing of products in biorefineries. While this is a snapshot in time of the state of the industry, this volume should serve as a guide and model for describing what is possible and where the issues are, which must be solved. We hope you enjoy our book. Elizabeth E. Hood, PhD Arkansas State University

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Plant Biomass Conversion

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Chapter 1

The Bioeconomy: A New Era of Products Derived from Renewable Plant-Based Feedstocks Peter Nelson, Elizabeth Hood, and Randall Powell

1.1 Introduction The first two decades of the 21st century will be marked as the turning point when large investments, technology breakthroughs, and new strategic alliances set the stage for the eventual widespread replacement of fossil feedstocks with renewable, plant-based alternatives for the production of fuels, chemicals, and energy. This is not a new idea, as humankind in the pre-industrial era utilized plant-derived chemicals such as proteins, sugars, and cellulose as the primary feedstocks to make a range of necessary materials and industrial products. However, as non-renewable fossil resources now become increasingly scarce, expensive, and produce negative environmental impacts, the need has never been so great to develop and expand agriculture and forestry as the source of sustainable feedstocks to serve a growing global population. Ultimately, renewable resources must feed, clothe, shelter, fuel, and provide for material goods for the planet’s inhabitants, while also addressing vexing environmental problems including climate change, pollution, access to clean water, and long-term soil health. In the 20th century, incredible technological improvements in agriculture and forestry were made. These advances included dramatic yield increases, drought tolerance, insect resistance in agricultural crops, and new production methodologies such as conservation tillage, which builds soil health and requires less energy. These productivity and environmental improvements offer much promise for a future bioeconomy in which agriculture and forestry will provide the predominant feedstocks for much more than food, feed, and fiber. Agricultural successes such as the Green Revolution have dramatically increased global crop yields, reduced hunger in the developing world, and expanded access to nutritious foods, but are still heavily dependent upon fossil-derived energy and chemicals. Fortunately, agricultural and forestry-based companies and institutions are now collaborating in new ways with industries traditionally dependent on fossil fuels to expand the use of renewable raw materials in a range of manufactured goods.

Plant Biomass Conversion, First Edition. Edited by Elizabeth E. Hood, Peter Nelson and Randall Powell.
C 2011 John Wiley & Sons Inc.

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Over the coming decades, this will lead to a more sustainable, closed-loop-systems-based approach to the production of food, energy, and materials. This biobased transition requires development and integration of a range of technologies encompassing energy, process efficiency, environmental compatibility, and even more advanced agricultural production systems. The increasing application of biotechnology tools—previously focused on human health—to improve agricultural crops and practices, enable clean manufacturing processes, and provide sustainable products is the essential catalyst for this transition. A renewable “bioeconomy” is now starting to become a reality, but the concept is not new. In the early days of the 20th century, industrial and agricultural leaders such as Henry Ford and George Washington Carver were proponents and practitioners of the use of plant-derived materials in a range of nonfood products. These innovators demonstrated the commercial utility of renewable biobased feedstocks in hundreds of products, such as automotive composites, glues and adhesives, dyes and inks, plastics, and, of course, biofuels. Unfortunately, the rapid emergence of petroleum as an available and inexpensive feedstock, albeit with unrecognized long-term environmental consequences, drove manufacturers to develop fossil-based rather than renewable products as the initial outputs of the Industrial Revolution. A century later, as the true costs of fossil fuels are realized, renewable feedstocks are re-emerging at commercial scale, largely through innovative partnerships across the value-chain linking agriculture, biotechnology, and the chemical process industries in new ways. Evidence of this transition has become increasingly apparent over the last 30 years as some organizations began decoupling themselves from traditional businesses to focus on agricultural biotechnology. A leading example is Monsanto Company, which has aggressively divested its mainstay fossil-based chemical manufacturing business to focus on the commercial opportunity to develop new agricultural biotechnology traits in commodity crops such as corn, cotton, and soybeans. Major agricultural commodity companies such as Archer Daniels Midland (ADM) and Cargill have also expanded chemical and fuel product offerings based upon their plant-based raw material resources. More recently, a number of multinational chemical companies—notably Dow and DuPont—are pursuing biobased product platforms, with initial commercial products now entering the marketplace. Increasingly, many traditional agricultural commodity companies, fossil-based chemical companies, and newer industrial biotechnology firms are partnering to integrate knowledge of biobased feedstocks, new conversion processes, and operational expertise in order to solve future challenges related to energy and useful materials. The transition to a photosynthesis-based bioeconomy offers commercial opportunity, resource and environmental sustainability, and more equitable global economic development than has been the recent case with fossil resources. However, more intensive agricultural and forestry utilization, and the accompanying deployment of technology must be the products of clear strategic planning and sustainable development practices. If managed correctly, the transition to a renewable-based economy can create new rural and urban opportunities, offer unique environmental solutions, and create wealth. The new economy based on renewable agricultural and forestry raw materials and clean processes will also serve as a major catalyst for realignment of some of the world’s largest companies and institutions, creating many new partnerships across the value-chain. This is an exciting time in which entrepreneurial companies as well as established industries can innovate new farm-to-factory supply chains and establish an early position in the emerging bioeconomy. Although there are multiple technology platforms and an expanding portfolio of biobased raw materials, which will comprise a future biobased economy, this book will focus on biochemical processing technologies, applied primarily to sugar, starch, and lignocellulosic

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1 The Bioeconomy: A New Era of Products Derived from Renewable Plant-Based Feedstocks

5

biomass feedstocks. This platform will be a significant game changer, lend itself to a wide range of potential chemical products, and provide opportunities for new players in the supply chain. In particular, sugars derived from lignocellulosic biomass represent an abundant feedstock resource that does not compete with food and feed supplies. Commercially viable processes for converting lignocellulosic biomass to biobased products must address two overriding issues: efficient nonseasonal feedstock supply and logistics, and cost-effective deconstruction of cellulose and hemicellulose polymers to fermentable simple sugars. Feedstock supply and cost issues are being addressed by new crops, new harvesting/storage practices, and decentralized processing models. Technology issues to access sugars (and lignin) within lignocellulosic feedstocks are being addressed through new pretreatment options, genetically modified fermentation organisms, biotechnology-enhanced plants, and plant-based enzyme production systems. The development and commercialization of these new technologies and the requisite biobased supply chain will be profiled in this publication. Despite the early stage and dynamic nature of the industrial bioprocessing industry, the authors hope that the current status and perspectives presented will prove beneficial to the diverse industry stakeholders.

1.2 Market Opportunity for Biofuels and Biobased Products Liquid biofuels including corn-based ethanol, as well as advanced biofuels such as biobutanol or cellulosic ethanol, are assured of a growing market over the next 50 years. As petroleum costs escalate with diminishing supplies, liquid transportation fuels will still be preferred due to energy density, safety, and distribution infrastructure, with increasing growth of biofuels between now and 2035 (IEA, 2008). The biofuels market represents the largest and most consistent demand from which to build a strong sugar and biomass supply chain from field to factory. The global biofuels market is already estimated to be $150 billion per year (UN, 2009). According to one report focused on the United States market: Rapid growth in the consumption of renewable fuels results mainly from the implementation of the US Renewable Fuel Standard (RFS) for transportation fuels and State renewable portfolio standard (RPS) programs. Biofuels production will grow over the next two decades, though is likely to fall short of the 36 billion gallons of RFS target in 2022. However, it may exceed expectations for 2035 including fuels from cellulosic ethanol, renewable diesel, and first generation biofuels. (Newell, 2009)

Beyond biofuels, companies are increasingly targeting higher value biobased chemical products and biomaterials. Liquid fuels are the ultimate commodity chemicals, representing the highest volume, but lowest value products whether produced from fossil or renewable feedstocks. In the United States, the petroleum-based liquid fuels industry and related energy services account for approximately 67% of petroleum consumed, with an overall industry value of $350 billion dollars. In contrast to commodity fuels, the goods and services resulting from the highervalue plastics, coatings, resins, and related consumer products utilize only 7% of petroleum consumed while resulting in an approximate $255 billion impact (Frost, 2005). Cargill and McKinsey & Company estimate that there is a potential to produce up to two-thirds of chemicals from biobased materials representing over 50,000 products, a $1 trillion annual global market (Jarrel, 2009).

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Commercial examples of higher value biobased products are emerging with increased frequency, as profiled in Chapter 12 of this review. By 2007, internal corporate investment in research and development related to biobased chemicals and biomaterials was as much as $3.4 billion, which far outpaced biofuels. This was due primarily to internal research and development investments from a few large pharmaceutical companies, which was in contrast to the United States Government’s continued focus during the same time period on liquid transportation biofuels (Lundy et al., 2008). While some biobased products are direct replacements for fossil-derived materials, others possess novel properties unique to their biogenic origin. An interesting example is Canadian-based EcoSynthetix (www.ecosynthetix. com) that is producing a starch-based coating product for the paper industry that outperforms its competitive products by requiring less water and heat in production, while exhibiting superior ink adhesive properties. This product is competitive with its petroleum-based counterpart when the price of oil is as low as $30 per barrel. Recent grants from United States Department of Energy (DOE) to support biomass work have not just focused on biofuels. For example a sizable $600 million round of funding awarded in late 2009, included support for Myriant Technologies’ succinic acid project and Amyris Biotechnology’s process to produce a range of biobased products to complement their biofuel program. It is expected that this trend will continue with both public and private investment focused on a range of high-value biomaterials and chemicals, as opposed to exclusively on biofuels.

1.3 Feedstocks 1.3.1

Biobased Feedstock Availability and Issues

Globally, ample supplies of renewable feedstocks are available for developing a robust and profitable biobased products industry, including agricultural crops, residues, and forestry materials, as well as future sources such as algae. Lignocellulosic biomass is globally dispersed and can be found in many forms, including agricultural crop and processing residues, forestry resources, dedicated energy crops such as miscanthus and switchgrass, and municipal solid waste. In the United States alone, resources associated with agriculture and forestry were calculated at 1.3 billion dry tons per year of biomass potential (Perlack et al., 2005). There are additional chapters in this volume that provide detailed information from a variety of perspectives on the availability of lignocellulosic biomass. It is important to note that the theoretical availability of biomass does not necessarily mean that it is economically feasible or environmentally viable to collect. For example, many primary row crop regions in the United States would produce excellent yields of perennial bioenergy crops, but the economics do not currently support substitution. The availability of agricultural crop residues must also be carefully considered. Crop residues include sustainably removable materials left after harvesting primary crops such as corn and wheat. Such residue availability has often been calculated based on 1:1 corn stover-to-grain ratios provided in the “Billon-Ton Report” published by the United States Department of Agriculture (USDA) and DOE (Perlack et al., 2005). Corn stover is widely considered a prime candidate for bioprocessing, although the actual availability within a working farm system, as well as collection incentives to farmers, may not be understood adequately. Additionally, regional (and global) variables affecting crop residue supply are acknowledged in the Billion Ton Report. For example, in northern climates, corn stover, the stalks and residues left after harvesting the grain, does not degrade quickly due to the cold winter temperatures. This sometimes creates a problem in that there is too

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much stover for field preparation activities for the next spring. As corn yields increase due to biotechnology, this problem may increase and it will be necessary to remove stover. This is not the case in southern climates, as stover degrades quickly in the wet, relatively warm winters and is counted on by the farmer as a valuable source of organic matter in the soil. Rice straw is another potential crop residue source that is widely available. In this case it would be an environmental benefit to remove the straw because currently it must be burned or otherwise disposed of every year to avoid diseases in the following year’s rice crop. It would be a great benefit for air quality and the farmer to develop a market for this straw in a biomass application. In California, there has been much work, with limited success, in trying to develop markets for rice straw as a reaction to the Rice Straw Burning Reduction Act of 1991 (AB1378). Projects included the development of construction products and packaging materials from rice straw. Unfortunately, the straw is high in silica, which damages existing harvesting and handling equipment, making it impractical to develop a widespread harvesting system. However, if alternative technologies could extract higher value silica products, economics might support the development of more robust harvesting systems. The use of wheat straw in biomass processing and biomaterials has potential, as the straw is already harvested in the United States and globally for use in animal bedding and for other applications. Over the last two decades, wheat straw has been used for composite construction materials, filler materials in plastics, and in the development of cellulosic ethanol. Iogen (www.iogen. ca) has based its cellulosic ethanol demonstration plant on wheat straw as a major raw material. The company is planning its first commercial facility in Saskatchewan that will utilize cereal straw feedstocks. In the near term, especially in the United States, corn cobs may represent the most accessible crop residue for early commercial lignocellosic processing. Harvesting of corn cobs in a onepass system is feasible and is being developed as a component of the United States’ corn ethanol industry. There is already an existing market in some regions for corn cobs at approximately $80.00 per ton, to be used in the production of chemicals such as furfural. Companies such as POET Biomass, a division of POET (www.poetenergy. com), and DuPont Danisco Cellulosic Ethanol, LLC (www.ddce. com) are developing conversion technologies specifically targeting corn cobs as feedstocks for biochemical conversion using enzymes. There is also significant work by major equipment companies, including CNH America LLC. (www.cnh. com) and Deere & Co. (www.deere. com), on one-pass harvesting systems for corn cobs. Another potential source for lignocellulosic biomass is dedicated energy crops, both perennials and annuals. Perennials include crops such as miscanthus and switchgrass which have recently been the focus of attention by crop biotechnology and cellulosic ethanol companies. Perennials offer options to farmers and land owners for use of marginal land that is currently in pasture or other use. These crops sequester carbon in their root systems, as well as utilize relatively small amounts of inputs such as fertilizers and pesticides. The economics of producing these crops does not lend itself to replacing prime row crops, but their production may be part of farm-based crop diversification strategies in the future or as part of a program to utilize marginal and unproductive farm land. Annual crops include sweet sorghum and forage sorghums, both of which require minimal inputs and produce significant biomass. In the case of sweet sorghum, a large sugar content in the crop can be easily converted to ethanol or other biobased products with current technology, while the bagasse could serve as feedstock for lignocellulosic conversion technologies. Markets for these crops are being developed for biopower applications, even as other higher value uses are being commercialized. There is a growing market in Europe and in certain

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regions in the United States for densified wood and energy crop pellets and briquets for home heating, industrial use, and co-firing with coal. The latter use is increasingly being driven by regulatory requirements directed toward renewable power generation and greenhouse gas reduction. Forestry and wood-processing residues and byproducts, as well as short-rotation woody crops, also represent important biomass feedstocks. Collectively referred to as “woody biomass,” these resources are often advantaged by an existing year-round harvesting and collection infrastructure. A detailed analysis of all of the crops, trees, and residues is provided in this volume.

1.3.2

Characterization of Lignocellulosic Feedstocks

Woody and herbaceous biomass, or lignocellulosic biomass, primarily comprises three major components—lignin, cellulose, and hemicellulose—along with lesser amounts of minor and trace constituents. Cellulose and hemicellulose are polysaccharides or sugar polymers composed of repeating monomer sugar units bonded together into long chains, much like rail cars are coupled together to form a train. Combined with lignin, these biopolymers comprise the structural components of plant matter and are produced by the photosynthetic process, whereby atmospheric carbon dioxide (CO2 ) is absorbed by the plant, chemically transformed, and “fixed” into these other useful chemical materials. Lignin is a natural polymer found in all plant materials, which combines with cellulose and hemicellulose to provide structural strength to the plant. It is not a sugar polymer, but rather an aromatic polymer, meaning its component phenylpropyl molecular units contain the highly stable benzene-ring chemical structure, which is also the basis for many commercially useful materials produced from petroleum. The aromatic chemical structure also imparts a high caloric value to the lignin molecule, which is valuable for combustion (heat) and also chemical transformations. The lignin polymer can have significant variability in its chemical structure, often differing based upon the biomass source. Cellulose and hemicellulose are referred to as carbohydrates because they are aliphatic polymers composed only of carbon, hydrogen, and oxygen. Cellulose is the most abundant biopolymer on earth and is made of six carbon or C-6 glucose (sugar) monomers. Cellulose obtained from wood pulp, cotton, and other plants has been used for centuries to produce paper and cardboard, as well as derivative products. Often referred to as dietary fiber, it is not digestible by humans, but with recent technology developments, it can now be commercially hydrolyzed by chemical, enzymatic, or biological processes to its monomer sugars, which can then be readily utilized as feedstocks for bioprocessing. Yeast fermentation of glucose to ethanol (mostly for beverages) has been practiced for centuries, and other natural and genetically modified organisms can convert glucose to various useful chemical molecules. Hemicellulose is a polymer primarily composed of various five carbon or C-5 sugar monomers with some C-6 sugars as well. Unlike cellulose, it is an amorphous polymer with little structural strength and is easily hydrolyzed to its monomeric sugars with acid/base or enzymes. Unfortunately, C-5 or xylose sugars cannot be fermented using natural yeasts. However, aggressive research and development programs are developing new organisms and genetically modified yeasts to utilize these readily available C-5 sugars as bioprocessing feedstocks, as described in Chapter 8 of this volume. Fractionation, or separation, of petroleum into its component constituents has been the key methodology to develop high value petrochemical end products. A similar biobased example

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is corn wet milling, in which the corn kernel is separated into its different components, from which value-added products are produced. As noted above, lignocellulosic biomass feedstocks possess comparable compositional diversity, and several leading technology developers are pursuing fractionation, or separation, of these components in order to facilitate more efficient and targeted downstream conversion of each component to value-added products. Historically, lignocellulose fractionation originated in the pulp and paper industry, where processes were designed to remove hemicellulose and “de-lignify” wood pulp in order to obtain a purified cellulose fraction for paper manufacturing (Agenda 2020 Technology Alliance, 2006). More recent approaches have used a combination of physical and thermal pre-processing followed by aqueous and/or solvent extractions, to afford substantially purified fractions of hemicellulose, lignin, and cellulose for further processing that is specific to each component. As a supporting technology, lignocellulose fractionation may prove to be extremely valuable as an integrated component of biochemical processing, providing sugars for fermentation and also a purified lignin stream as an aromatic chemical platform feedstock. Developmental and commercial lignocellulosic fractionation technologies are fully described in Chapter 12 of this volume.

1.3.3

The Role of Agricultural Biotechnology

In order to provide sustainable food, fuel, and material needs of humans, it will be necessary to dramatically increase the yields of agricultural crops and forest resources, as well as develop crops with specific attributes for biomass feedstocks. Currently, biotechnology traits used to reduce farmers’ costs and increase profitability are widely deployed in canola, corn, cotton, soybeans, and sugarbeets, predominantly in the United States. However, more than 13 million farmers in 25 countries currently grow agricultural biotechnology crops. In 2008, the global biotechnology crop area grew by 9.4%, or 26.4 million acres, to reach a total of 309 million global acres. Between 2007 and 2008, the United States alone increased its biotechnology crop acreage from 143 million acres to 154 million, phenomenal growth considering that the first biotechnology crops were not introduced until the mid-1990 s (ISAAA, 2008). To date, the vast majority of commercialized agricultural biotechnology-derived crops have focused on genetic “input traits,” which add value to the farmer and/or environment by reducing the production costs of the farm operation. Examples include RoundupTM Ready soybeans that are resistant to the herbicide glyphosate, allowing soybean farmers to more widely adapt conservation tillage practices. There are other examples related to insect and herbicide resistance. In addition to input traits in commodity crops, plant biotechnology has developed new crops for bioenergy and pharmaceutical applications with enhanced “output traits,” which allow the crop to produce certain characteristics desired by food, health, or industrial customers. While the value proposition for input traits is directed to the farmer, output traits are directed to those making products from the crops and ultimately to the consumer. Output traits allow crops to have higher protein and other nutritional properties, stronger fibers, specific oil profiles, novel health benefits, and to produce new products within green plants. In short, output traits enhance the value of the plant as a feedstock for the production of plant-based products. Not all of these technology improvements are created through gene transfer. Some use mutation, breeding, and other novel techniques to create new crop performance. Numerous examples of enhanced crop products have been commercialized or are in development for food, feed, and industrial applications, as summarized in Table 1.1. In the mid-1990s, Monsanto Company had a designer fiber unit that attempted to match specialized end uses for

10 Low-linolenic soybeans Phytase

Mirel Vistive QuantumTM Phytase

Metabolix

Monsanto

Syngenta Seed

Amylase and cellulase (under development) New oilseeds

Syngenta Seeds

Targeted Growth Inc.

2006.

Ricinoleic acid

Linnaeus Plant Sciences Inc.

a Grooms,

Cellulase

Infinite Enzymes LLC./ Applied Biotechnology Institute

Plant-based plastic and chemicals

Improved biomass characteristics, yields

Bioenergy Seeds

Low linolenic soybeans

Mendel Biotechnology

Partnership with Bunge

DuPont/Pioneera

40% more oil than No.2 yellow corn

Plant-made industrial enzymes

Supercede HE High Energy

Dow AgroSciences (Mycogen Seeds)a

High oleic/low linolenic fatty acids

Infinite Enzymes, LLC.

Nexera

Dow AgroSciences

Improved biomass characteristics, yields

Improved biomass characteristics and plant-made enzymes

Blade

Ceres, Inc.

Trait

Camelina

Corn

Camelina

Corn

Corn

Soybeans

Switchgrass

Miscanthus and other biomass crops

Biofuels

High amylase corn for conventional ethanol production

Green chemistry/biomaterials

Plant production system for cellulase used in green chemistry/cellulosic ethanol

Animal feed ingredient

Food/feed, reduce trans fats, increase shelf life and oil stability

Biomaterials and bioenergy

Advanced biofuels and biopwoer

Green chemicals and advanced biofuels

Biomaterials and advanced biofuels

Switchgrass and corn

Corn

Food/feed, future products include high-oleic and Omega-3

Animal feed—increases energy in metabolism

Food—no trans fats and low in saturated fat

Advanced biofuels, biobased chemicals, and biopower

Applications

Soybeans

Corn

Canola and sunflower

Switchgrass, biomass sorghum, sweet sorghum and other biomass crops

Crops

20:45

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Brand

Selected plant biotechnology companies and products.

Company

Table 1.1.

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cotton with specific, genetically engineered characteristics in a cotton variety. Other examples include products for reagent use that ProdiGene, Inc. commercialized. Trypsin (trade name TrypZean), beta-glucuronidase, and avidin are all sold by Sigma Chemical Co. Significant research is also being conducted to improve the fatty acid profile in camelina, a crop pioneered by United States producer groups in the Great Plains and companies such as Targeted Growth, Inc. (www.targetedgrowth. com). Targeted Growth, Inc. began a breeding program for camelina in 2005, employing a three pronged approach: classical and molecular breeding, mutation breeding, and transgenics (Panter, 2008). Other companies, such as Linnaeus Plant Sciences (www.linnaeus.net), are seeking to change the oil profile of the crop for various novel biobased product applications. Researchers are also working to adapt modern biotechnology tools to the development of new bioenergy crops. Examples of these include miscanthus, switchgrass other herbaceous crops, and short rotation woody crops. Companies working in this area include Ceres, Inc. (www.ceres.net); Chromatin, Inc. (www.chromatininc.com); Edenspace Systems Corporation (www.edenspace. com); Infinite Enzymes, LLC (www.infiniteenzymes.com), Mendel Biotechnology, Inc. (www.mendelbio.com), and Metabolix (www.metabolix. com). For both large multinational biotechnology firms and small boutique trait developers, a key hurdle is navigating a confusing and costly regulatory environment. A streamlined approach to getting crops deregulated and into commercial applications will have to be coordinated to attract the significant capital needed to grow this part of the industry.

1.3.4

Biomass Agricultural Equipment Development

As discussed in this chapter and the subsequent chapters in the volume, there is significant activity in the development of biomass feedstocks, conversion processes, and end-use applications. Increasingly, there is also investment by major farm equipment manufacturers in developing biomass harvest systems such as one-pass corn cob harvesters or systems to remove tree residues in harvesting. Noteworthy projects include commercial scale harvesting demonstrations of corn cobs by POET Energy and switchgrass by Genera Energy, LLC. (www.generaenergy.net). Equipment manufacturers actively engaged in biomass development activities include AGCO (www.agcorp. com); CLAAS (www.claasofamerica. com); CNH America, LLC. (www.cnh.com); Deere & Company; and Vermeer Corporation (www.vermeer. com). The involvement of these prominent companies in both agriculture and forestry-based biomass development addresses another major link in the new supply chain and promises innovative solutions for farmers and processors.

1.4 The Biochemical Technology Platform Biomass or components of biomass can be used as feedstocks by molecular modification of the constituents, a process often referred to as bioprocessing. There are three distinct technology platforms for these molecular transformations—chemical, thermochemical, and biochemical. Each platform has specific characteristics for commercial processing, including range of feedstocks and products, co-products, cost, scale, and stage of technology development. The focus of this book is on the biochemical technology platform that utilizes enzymes and microorganisms to effect molecular transformations, often with incredible energy efficiency and product specificity. Biochemical processing, sometimes referred to as the “sugar” or

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carbohydrate platform, seeks to convert C-6 and C-5 sugars derived from biomass through fermentation processes to biofuel and biobased chemical products. In the United States and globally, much recent biochemical platform R&D has focused on the development of pretreatment systems and enzymes that can depolymerize cellulose and hemicellulose into monomeric sugars to allow yeast fermentation to “cellulosic” ethanol. As a second-generation biofuel, ethanol derived from lignocellulosic feedstocks eliminates the food-fuel issue associated with sugar/starch feedstocks and has also been shown to have a much more favorable net energy balance and lifecycle GHG reduction than corn (starch-based) ethanol. Also within the biochemical platform, other research is developing new bacterial organisms and genetically modified yeasts to convert both C-6 and C-5 sugars to other biofuel and chemical products (see Chapters 11 and 12 in this volume), with perhaps the most advanced efforts directed at butanol, an important industrial chemical and possible second-generation biofuel, and succinic acid, a multifunctional platform chemical. Significant progress has been made in developing biochemical technologies to use lignocellulosic feedstocks. The overall process requires several steps, including feedstock pretreatment, depolymerization, sugar fermentation, and distillation/product isolation. Several pretreatment methodologies have been developed, generally combining heat, pressure, and chemical reaction to make the cellulose and hemicellulose polymers more accessible to enzymatic and microorganism attack (as described in Chapter 9 in this volume). Pretreatment processing must be designed to minimize introduction or formation of contaminants that would be toxic to the downstream fermentation organisms. While significant hydrolysis of the hemicellulose can occur during pretreatment, cellulase and other enzymes must be added to convert the more recalcitrant cellulose to its component C-6 sugars and complete conversion of hemicellulose to C-5 sugars. Remarkable advancements in cellulase enzyme cost and effectiveness have been made in the last 5 years and are continuing (see Chapter 10 in this volume). Novel approaches to enzyme production are also being developed, for example: A major technical challenge in making cellulosic ethanol economically viable is the need to lower the costs of enzymes needed to convert biomass to fermentable sugars. The expression of cellulases and hemicellulases in crop plants and their integration with existing ethanol production systems are key technologies that will significantly improve the process economics of cellulosic ethanol production. (Sainz, 2009)

While C-6 sugars are readily fermented to ethanol by natural yeasts, current R&D programs seek to develop new organisms that can effectively convert the C-5, as well as the C-6 lignocellulosic sugars to ethanol and other chemical products. Some R&D programs are pursuing organisms that can both hydrolyze cellulose and hemicellulose and ferment the resulting mixed sugars to ethanol, referred to as consolidated bioprocessing. These efforts will be more fully described in other Chapters throughout this volume.

1.5 Investment and Major Players Despite the recent global economic downturn, $16.9 billion was invested in new biofuels in 2008 (UN, 2009) and the cleantech sector emerged as the leading investment category for venture capitalists in 2009. Recognizing the complexities of introducing new biobased

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technologies, strategic partnerships are becoming a preferred route to commercial products in the biobased supply chain. This is leading to a business environment that includes direct investments in entrepreneurial ventures, as well as many strategic partnerships and joint ventures, often leveraging existing competencies and assets. Table 1.2 summarizes key biobased product companies and their investors/partners.

Table 1.2.

Selected investments and joint ventures in biobased product companies.

Company

Feedstock/Product

Investors/Partners

Abengoa Bioenergy

Corn ethanol and experimental lignocellulosic biomass fuels and chemicals

DOE

Amyris Biotechnology

Development of advanced biofuels and chemicals from sugar-based feedstocks including sweet sorghum and sugar cane.

DAG Ventures, Khosla Ventures, Kleiner Perkins, TPG Ventures, Total

Butamax Advanced Biofuels

Biobutanol, sugarbeets

DuPont, British Petroleum

Catchlight Energy LLC.

Feedstocks, supply chain, technology licensing and deployment

Joint ventures between Chevron & Weyerhauser

Coskata

Wood, MSW

Khosla Ventures, Great Point Ventures, Advanced technology Ventures, General Motors, Globespan

Dupont Danisco Cellulosic Ethanol, LLC.

Corn cobs, switchgrass

DuPont, Danisco, Genera Energy (University of Tennessee).

Dupont Tate&Lyle

Sugar

DuPont, Tate&Lyle

Elevance Renewable Sciences

Oilseeds

Cargill Inc., Materia Inc., California Institute of Technology, TPG Growth, TPG Biotechnology Partners

Gevo Development LLC.

Biobutanol, other biobased products.

Cargill, ICM, Khosla Ventures, Virgin Fuels, Burrill & Company, Malaysian Life Sciences Capital Fund

Iogen Corporation

Wheat straw, other feedstocks, cellulosic ethanol

Royal Dutch Shell, Goldman Sachs, Volkswagen, Petro-Canada, Government of Canada, DSM

Mascoma Corporation

Biomass feedstocks, cellulosic ethanol

Khosla Ventures, Flagship Ventures, General Catalyst, Kleiner Perkins, Vantage Point, Atlas Ventures, Pinnacle Ventures

Range Fuels

Wood and other biomass feedstocks, cellulosic ethanol

Passport Capital, BlueMountain, Khosla Ventures, Leaf Clean Energy Company, PCG Clean Energy & Technology Fund

Verenium Corporation

Wood, sugarcane bagasse

British Petroleum, Khosla Ventures, Braemar Energy Ventures, Charles River and Rho Ventures

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Significant investments were made in advanced biofuels and green chemistry by a range of biotechnology, petroleum, and chemical companies in 2008 and 2009. Funding directed toward developing biobased chemicals has risen steadily since 2004 and reached $3.4 billion in 2007 in the United States (Lundy et al., 2008). From 2004 to 2009, major investments were made by large multinational petroleum and chemical companies, including Chevron, DuPont, Dow, Dutch Royal Shell, and Exxon Mobil. Venture capital investment also grew substantially, with the cleantech sector moving into a leadership position through the economic downturn of 2008–2009. As an example, new funds were announced by leading cleantech investor Khosla Ventures (www.khoslaventures.com), as well as Finistere Ventures (www.finistereventures.com). Partnerships among established global producers in the agriculture, biotechnology, chemical, and petroleum sectors are becoming commonplace. An early example was the Cargill-Dow, LLC venture started in 1997, which is now NatureWorks, LLC (www.natureworksllc. com) (wholly owned by Cargill), which invested approximately $1 billion to commercialize cornbased polylactic acid (PLA). British Petroleum and DuPont have formed Butamax Advanced Biofuels, LLC (www.butamax. com) to commercialize biobutanol as an advanced biofuel, while British Petroleum is also investing in Verenium and other advanced cellulosic biofuels businesses. More recently, Exxon Mobil announced in 2009 a $600 million investment to produce biofuels from algae in a joint venture with Synthetic Genomics founded by human genome pioneer J. Craig Venter (Mouawad, 2009). Royal Dutch Shell PLC increased its investment to $60 million in 2009 in Codexis (www.codexis) to explore biofuels production (Gold, 2009) while continuing to partner with Canada-based Iogen (www.iogen. ca). DuPont has formed Dupont Danisco Cellulosic Ethanol, LLC (www.ddce. com) to commercialize cellulosic ethanol and is in a joint venture with sugar company Tate & Lyle (called Dupont Tate & Lyle Bioproducts) to produce 1,3-propanediol (www.duponttateandlyle. com). These are a few of the hundreds of new business divisions, companies, and partnerships being developed globally to pursue renewable fuels and chemicals. Major venture capital funders such as Khosla Ventures (www.khoslaventures. com) and Burrill & Company (www.burrillandco. com) announced new funds in 2009 that will focus on biofuels and related technologies, including two new funds totaling $1 billion by Khosla Ventures. Khosla Ventures has led investment in numerous advanced biofuels companies, including Amyris (www.amyris. com), Coskata (www.coskata. com), Gevo (www.gevo. com), LS9 (www.ls9. com), Mascoma (www.mascoma. com), Range Fuels (www.rangefuels. com), and Verenium (www.verenium. com), providing strong strategic direction and momentum to the industry at a crucial time. Coskata has also received investment from General Motors, another example of the cross-industry, strategic investments made in this space between 2005 and 2009. Incorporating the forestry sector, Catchlight Energy is a joint venture between Chevron and Weyerhaeuser dedicated to combining the strengths of the two organizations to commercialize biofuels (www.catchlightenergy. com). The formation of domestic and foreign strategic alliances has grown from 532 new industrial biotechnology alliances in 2004 to 1,367 new alliances in 2007. Patent and trademark activity has intensified as firms seek to protect, commercialize, and license their new discoveries and brands. Trademark registrations in particular have shown strong growth, increasing from 197 new registrations in 2004 to 1,027 in 2007, reflecting the increasing prominence of biobased brands as the field moves from early discoveries to the commercialization of innovative technologies and products (Lundy et al., 2008). The Federal Government’s significant investments since 2000 have helped many of the early companies develop technologies, improve processes, and leverage private investment, as

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Table 1.3.

15

Selected USDA and DOE grants (2002–2009) for biomass projects.

Year

Program

Total Funding

Awarded Projects

Partial List of Recipients

2002

Biomass R&D Joint

$79,350,000.00 8 awards

Broin & Associates (now POET), Cargill, DuPont, Abengoa, National Corn Growers Association, Iowa Corn Promotion Board

2003

Biomass R&D Joint

$23,803,802.00 19 awards

Dartmouth (Mascoma), University of Florida (now partnering with Buckeye Technologies), Pure Vision Technology, Metabolix, Cargill, ADM

2004

Biomass R&D Joint

$26,357,056.00 13 awards

Rohm & Haas Co., Weyerhaeuser Company

2005

Biomass R&D Joint

$12,626,931.00 11 awards

Samuel Robert Noble Foundation

2006

Biomass R&D Joint

$17,492,507

17 awards

Increasing focus on feedstock development: Ceres Inc., SUNY, Edenspace Systems

2007

Biomass R&D Joint

$18,449,090.00 21 awards

GE Global Research, Ceres Inc., Agrivida Inc.

2007

DOE Commercial Scale Biorefinery

$385,000,000.00 6 awards

Abengoa Bioenergy, BlueFire Ethanol, Broin Companies (now POET), Iogen, Range Fuels

2008

DOE Small Scale Biorefinery

$200,000,000.00 7 awards

Verenium, Lignol Innovations, ICM, UT/Genera

2009

DOE Advanced Biorefinery

$564,000,000.00 19 awards

ADM, Amyris Biotechnology Inc., Elevance Renewable Sciences, BioEnergy International LLC (Myriant)

summarized in Table 1.3. For example, the recent $564 million DOE investment in advanced biorefinery projects leveraged a private investment of $1.3 billion. The Obama Administration is continuing to invest heavily in advanced biofuels, regional innovation clusters, renewable energy jobs, and biotechnology. On the feedstock side, substantial investment is occurring in the development of dedicated energy crops and crop-based synergies such as enhanced traits or downstream processability. These initiatives include the commercialization of plant-made enzymes by Syngenta and startup companies, and the commercialization of dedicated energy crops by companies such as Arborgen, Ceres, and Mendel Biotechnology.

1.6 The Role of the Farmer An essential component of the value chain for biobased products is the alignment of companies seeking to commercialize biobased products with feedstock providers, namely the farmers, logistics, and preprocessing producers. All too often biobased products industry proponents tout the ability of biorefineries to revitalize rural regions without understanding the overall value proposition or fully considering the vital linkages necessary with the farmer. Three

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primary models have emerged for companies and processors to access lignocellulosic biomass, as described below (Nelson, unpublished). (1) Farm gate—In this model, farmers are paid a set price and/or contracted price for biomass baled and delivered to the factory, storage site, or made available at field for pickup. Generally, this price is between $30 and $70 per dry ton according to most publications. In discussions with farmers, it is clear that this model will require a guaranteed long-term contract that includes one or more of the following: an independent ability to market carbon credits, a contract price (especially for perennial energy crops) indexed to corn or petroleum, and a guaranteed price floor. The Biomass Crop Assistance Program (BCAP) authorized in the 2008 Farm Bill was recently released, which will provide assistance to farmers producing biomass crops within this scenario. (2) Access fee/land rental—In this model, farmers are essentially land owners, similar to the pulp and paper industry, in which companies pay to have dedicated energy crops produced and the companies handle the planting and harvesting. Although the farmers may have some role in maintenance, they are essentially operating as absentee land owners. This model is not considered viable in major row crop farming regions, but may be of interest to small, part time farmers or those that own marginal land. (3) Value-added farmer participation—In this model, farmers participate in a value-added enterprise, possibly formed as a cooperative, in which their biomass production includes some component of preprocessing, logistics, and/or value-added processing or service to the end clients. As an example, a University of Tennessee-sponsored program through its subsidiary company Genera Energy, LLC (www.generaenergy.net) has formed a biomass processing cooperative to support scale up of switchgrass in East Tennessee. In the United States, the development of farmer-owned businesses to process biomass into pellets or briquettes to cofire with coal or other biopower applications may serve to establish a reliable supply chain for lignocellulosic biomass destined for future higher-value applications, other than combustion. Show Me Energy Cooperative LLC. of Centerview, Missouri (www.goshowmeenergy.com) is a great example. Show Me Energy has over 400 farmers who own part of the cooperative and are supplying waste straw and dedicated energy crops to their pellet operation. Logistics and storage considerations for commercial lignocellulosic feedstock supply are not insignificant. For example, within each of these models, some scenarios envision biomass materials being baled and stored at the fields for delivery throughout the year to the processing facility. It remains to be seen whether off-season on-field storage of lignocellulosic crops will be accepted by high production commercial row crop farming operations. For a given project or program, the successful model must involve farmers and supporting logistics providers as more than an afterthought. To attract serious, large-scale farmers who can professionally deliver large volumes of biomass as well as invest in the supporting infrastructure will require new business models that make a compelling case to each participant in the supply chain.

1.7 Opportunities for Rural Development A pressing need exists for rural development to provide jobs and long-term sustainable opportunities in rural areas in the United States and across the world. In the United States, poverty is consistently higher in rural as opposed to urban areas, with over 500 rural counties defined as being in “persistent poverty.” Agriculture is often a significant economic sector in these regions, but its role as a job and local wealth creator has declined in recent years (Cowan,

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2002). New biobased feedstocks may offer the opportunity to grow, process, and transport lignocellulosic biomass for new products and rebuild these local agriculture-based economies. The conversion of lignocellulosic biomass to biobased products promises to have significant impact on rural communities. The low bulk density of lignocellulosic biomass dramatically changes logistics and processing dynamics. Grain crops such as corn and soybeans can be economically transported via barge and rail for remote processing and consumption, whereas at least the first phase of commercial lignocellulosic feedstock processing will necessarily be located in close proximity to the harvested biomass due to transport economics. This is especially true for herbaceous biomass such as processing and crop residues and dedicated energy crops, while forestry materials or densified feedstocks may be transported longer distances. Most models indicate that the viable transport radius of harvested herbaceous energy crops around a rural biorefinery or preprocessing facility is approximately 25–50 miles. This will necessitate smaller decentralized biorefineries across rural areas that will at least incorporate preprocessing and/or initial refining of lignocellulosic biomass substrates. To give an example of what this opportunity can mean for rural regions, the corn ethanol industry can be examined at its high growth period from 2006 to 2008. One report summarized the economic impact during this period as follows: The industry spent $12.5 billion on raw materials, other inputs, goods and services to produce an estimated 6.5 billion gallons of ethanol during 2007. An additional $1.6 billion was spent to transport grain and other inputs to production facilities. Within the corn ethanol industry, new jobs are created as a consequence of increased economic activity resulting from ongoing production and construction of new capacity supported the creation of 238,541 jobs in all sectors of the economy during 2007. These include more than 46,000 jobs in America’s manufacturing sector – American jobs making ethanol from grain produced by American farmers (Urbanchuk, 2008).

Despite its significant rural economic impact in the United States, it is generally recognized that starch-based ethanol is an important, but ultimately limited, first-generation biofuel. As such, its economic impact on rural communities may have been largely realized. Furthermore, the germplasm, production inputs, and processing of corn are controlled by a relatively small number of multinational companies such as DuPont Pioneer, Monsanto and Syngenta on the seed side, and ADM, Bunge, and Cargill on the processing side, leaving little room for entrepreneurial technology developers and farmer value participation. Fortunately, the fully realized bioeconomy will require diverse and flexible feedstocks and technologies to produce a comprehensive range of biobased products, as well as biofuels. The multiproduct “biorefinery” will increasingly utilize more globally abundant lignocellulosic feedstocks to produce both commodity and value-added products. As a result, the lignocellulosic processing opportunity is substantially larger in terms of volume, and the low bulk density will dictate that processing be located in proximity to feedstock production. In contrast to corn and other grains with fully developed food-centric supply chains, the lignocellulosic feedstock supply chain is largely undeveloped and unconsolidated. A recent comprehensive United States study concluded that in a 98-county area in the Mid-South Mississippi Delta region, lignocellulosic feedstock processing utilizing 10% of cropland, 25% of idle lands, 25% of conservation reserve program land, and 15% of pasture land would support a biomass industry valued at over $8 billion annually. This industry would create 25,000 new jobs within a decade and 50,000 jobs by 2030 in the study area alone (Tripp et al., 2009).

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1.8 Environmental Benefits The environmental benefits of biobased products and related technologies are just beginning to be fully understood. For example, studies have shown that the life cycle analysis for cellulosic ethanol produced from certain dedicated energy crops has a 90% reduction in greenhouse gas (GHG) emissions compared to petroleum gasoline (Farrell et al., 2006). Case studies have shown that energy and water use for biobased processes decreased 10–80%, while the use of petrochemical solvents was reduced by 90% or eliminated completely (OECD, 2001). Additional benefits can be found in product recyclability, air emissions, and reduced overall energy consumption from locally sourced foods, materials, and fuels. However, sustainable crop production is necessary to avoid soil and water depletion, as described in Chapters 6 and 7 of this volume.

1.9 Economic Comparison of the Biochemical and Thermochemical Technology Platforms According to a recent report by the International Energy Agency (IEA), the thermochemical and biochemical routes have comparable potential energy yields, converting dry biomass at about 20 GJ/ton to about 6.5 GJ/ton of biofuels, for an overall conversion efficiency of about 35%. The report further projects potential ethanol yield of about 80 gallons/dry ton from biochemical processing and a synthetic diesel yield of 53 gallons/dry ton from thermochemical conversion. Experience with each platform, utilizing biomass feedstocks, is limited to pilot and precommercial scale at present, so accurate production cost information remains to be confirmed (see Chapter 14 in this volume). Furthermore, leading private-sector technology developers do not generally publish proprietary process cost information. IEA has estimated production costs of second-generation biofuels to be in the range of $3.02–3.79/gallon for ethanol and at least $3.79/gallon for synthetic diesel, comparable to the wholesale petrochemical fuel prices when crude oil is in the range of $100–130/bbl. The IEA report concludes that there is presently not a clear commercial or technical advantage between the platforms for the production of biofuels and that widely fluctuating crude oil prices impart high risk to investment in second-generation biofuels (IEA, 2008). The IEA report does not take into account the value of biobased products and the benefit of added flexibility of diverse end product applications.

1.10 Conclusions and Future Prospects The bioeconomy represents a disruptive technological, social, and economic change that will be realized over decades, not years. The opportunities—as described in this volume—are many, as are the challenges. These will be met and exploited by a diverse combination of traditional foodbased agribusiness, the fossil-based fuel and chemical industries, entrepreneurs, financiers, and farmers. The market for biobased products is potentially higher value than for biofuels, and biochemical processing technologies likely offer more value-added specialty chemical product options than thermochemical technologies. Sugars derived from globally abundant and dispersed

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lignocellulosic feedstocks would serve as the predominant raw materials for rural biorefineries, which in turn could transform declining rural economies and create new “local” supply chains for energy, liquid transportation fuels, and other products. Positive environmental impacts from the use of renewable feedstocks, lower intensity manufacturing, and more efficient local supply and consumption would be significant. A vision for plant-based renewable resources was published in 1998 (http://www1. eere.energy.gov/biomass/pdfs/technology roadmap.pdf). This document was the result of a workshop comprising industry and trade group representatives assembled to discuss what it would take to convert the US industrial base to a more sustainable economy. The goals were modest by most standards: 10% of bio-based products and 40% of fuels would be from plantbased sources by the year 2050. Over a decade later, progress down this path has been slow at best. More aggressive goals than those stated in the 1998 document have been set in the US 2007 Energy Independence and Security Act—36 billion gallons of renewable transportation fuels per year (∼20–30% replacement) to be reached in 2022. Because corn-starch-based ethanol is nearly maximal at 9 billion gallons per year (∼25% of the grain crop), the balance of the ethanol should be derived from lignocellulosic biomass. The ultimate requirement to replace finite fossil feedstocks with renewable resources is perhaps best described by Italian Chemist and holocaust survivor Primo Levi in his 1975 chronicle of the elements (Levi, 1975): Carbon, in fact, is a singular element: it is the only element that can bind itself in long stable chains without a great expense of energy, and for life on earth (the only one we know so far) precisely long chains are required. If the elaboration of carbon were not a common daily occurrence, on the scale of billions of tons a week, wherever the green of a leaf appears, it would by full right deserve to be called a miracle. Man has not tried until now to compete with nature on this terrain, that is, he has not striven to draw from the carbon dioxide in the air the carbon that is necessary to nourish him, clothe him, warm him, and for the hundred other more sophisticated needs of modern life. He has not done it because he has not needed to: he has found and is still finding (but for how many more decades?) gigantic reserves of carbon already organized, or at least reduced. Besides the vegetable and animal worlds, these reserves are constituted by deposits of coal and petroleum: but these too are the inheritance of photosynthetic activity carried out in distant epochs, so that one can well affirm that photosynthesis is not only the sole path by which carbon becomes living matter, but also the sole path by which the sun’s energy becomes chemically usable.

The chapters of this volume describe the current state of the transformation to a renewable and sustainable bioeconomy and suggest the opportunities that await its realization.

References Agenda 2020 Technology Alliance, American Forest & Paper Association. Integrated Forest Products Biorefinery. Available: www.agenda2020.org/PDF/IFPB Brochure.pdf. Cowan, T. 2002. Value-Added Agricultural Enterprises in Rural Development Strategies. Washington, DC: Congressional Research Service, The Library of Congress. DOE. 2007. Top Value-Added Chemicals from Biomass, Volume II—Results of Screening for Potential Candidates from Biorefinery Lignin. Available: www1.eere.energy.gov/ biomass/pdfs/pnnl-16983.pdf.

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Frost, J. W. 2005. Redefining chemical manufacture, replacing petroleum with plant-derived feedstocks. Industrial Biotechnology, 1(1), 23–25. Gold, R. 2009. Shell, other oil firms bolster biofuels spending. Wall Street Journal (newspaper), December 30. Grooms, L. 2006. Farm Industry News, September. Farrell, A. E., et al. 2006. Ethanol can contribute to energy and environmental goals. Science 311(5760), 506–508. IEA. 2008. 1st to 2nd Generation Biofuel Technologies: An Overview of Current Industry and RD&D Activities. Available: www.iea.org/Textbase/Publications/free new Desc. asp?PUBS ID=20742. International Service for the Acquisition of Agri-biotech Applications (ISAAA). 2008. ISAAA Report for 2008. Jarrell, K. A. 2009. Synthetic biology and the sustainable chemistry revolution. Industrial Biotechnology, 5(4), 210–212. Levi, P. (1975). The Periodic Table. Penguin Books, London, UK. Lundy, D., et al. 2008. Industrial Biotechnology: Development and Adoption by the U. S. Chemical and Biofuel Industries. Washington, DC: U. S. International Trade Commission. Mouawad, J. 2009. Exxon to invest millions to make fuel from algae. New York Times, July 13. Organisation for Economic Co-Operation and Development (OECD). 2001. The Application of Biotechnology to Industrial Sustainability. Paris. Nelson, P. 2006. Developing an Ag-based biomass supply chain: What is the role of the farmer? Presented at The World Congress on Industrial Biotechnology, Toronto, Canada, July 14. Newell, R. 2009. Annual Energy Outlook 2010, Reference Case, U. S. Energy Information Administration, Washington, DC, December 14. Panter, D. 2008. Sustainable Oils LLC, Conference Presentation, Memphis, Tennessee, November. Perlack, R. D., Wright, L. L., Turhollow, A. F., Graham, R. L., Stokes, B. J., & Erbach, D. C. 2005. Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply. Oak Ridge: Oak Ridge National Laboratory. Sainz, M. 2009. Commercial cellulosic ethanol: The role of plant-expressed enzymes. In Vitro Cellular & Developmental Biology, 45, 314–329. Tripp, S., Nelson, P., & Powell, R. 2009. Regional Strategy for Biobased Products in the Mississippi Delta, Report by Battelle Technology Partnership Practice. United Nations. 2009. Global Trends in Sustainable Energy Investment. Available: www.indiaenvironmentportal.org.in/node/277152. Urbanchuk, J. M. 2008. Contribution of the Ethanol Industry to the Economy of the United States. Prepared for the Renewable Fuels Association.

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Chapter 2

Agricultural Residues James Hettenhaus

2.1 Introduction The present US ethanol industry has grown rapidly using cereal grain, mainly corn, as its primary feedstock. Corn grain has been a global commodity for more than a century, with the supply and demand inextricably linked. Infrastructure is in place to grow, harvest, store, and transport corn to global markets. When the US demand for corn increased to supply newly constructed ethanol plants over the last decade, the only concern was locating those plants to economically source the corn, convert it to biofuels, and ship the products to market. The availability and quality of corn was not in question, just the price relative to other costs of goods sold. In 2007, Congress enacted the Energy Independence and Security Act, establishing a Renewable Fuel Standard (RFS) goal for advanced biofuels. Advanced biofuel is defined as the total production from cellulosic biomass and biomass-based diesel and biogas produced through the conversion of organic matter from renewable biomass. Cellulosic biofuels make up the major portion of the mandate by 2016 (Table 2.1). The basic platform for building advanced biofuels is the cellulosic biofuels segment. The RFS mandates growth from a few research and early commercialization efforts now to 16 billion gallons by 2022. Massive investment of resources across the supply chain will be required in a relatively short time frame to meet this goal. New technology must be validated, plants designed and constructed, feedstock sourced, and logistical systems in place to move cellulosic biomass feedstocks to facilities and finished biofuels to customer markets. For example, five 100 MGPY facilities could meet the cellulosic goal of 500 million gallons in 2012. An examination of the 100 MGPY corn-based facilities gives some ideas of the size and logistics of this undertaking. Each 100 MGPY corn-based facility requires about 36 million bushels of corn, supplied from about 200,000 acres. Because of improved seeds,

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Table 2.1. EISA 2007 biofuel goals.

Year

Advanced Biofuel (in Billion Gallons)

Cellulosic Biofuel (in Billion Gallons)

Cellulosic (% Advanced Biofuels)

Cellulosic Feedstock (Million Dry Tons)

2012 2014 2016 2018 2020 2022

2.0 3.8 7.2 11.0 15.0 21.0

0.5 1.6 4.2 7.0 10.5 16.0

25% 47% 59% 64% 70% 67%

500 1,600 4,200 7,000 10,500 16,000

corn yields increase 2–3 bu/ac annually. An additional 10–15 million bushels will be produced on the 5 million acres within a 50-mile radius of the facility. Depending on the relative cost, the farmer can increase the amount of corn planted or adjust the inputs to grow more corn on the same acres. The corn is usually delivered by truck over this distance. The facility may also choose to purchase the corn outside of the immediate area. Delivery could be by truck or rail, depending on the distance and relative cost. River Barge shipments are common and ocean-going shipments are also routine. The situation is somewhat different for biomass-derived products. The five cellulosic 100 MGPY facilities, necessary to reach the 2012 RFS goal, are estimated to require 1 million or more dry tons of cellulosic feedstock. Thermochemical facilities convert the lignin and the carbohydrates to fuels, producing 100–110 gallons per ton. Biochemical facilities use the cellulose and a portion of the hemicellulose for fuels, producing 80–90 gallons per ton. Their lignin is being evaluated for a multitude of uses, including supplying the process energy needs, selling the excess as power, or as raw material for value-added products (Simmons et al., 2010). Unlike corn, currently no system is in place to supply 1 million tons of feedstock to each of these facilities. In fact, this biomass supply requirement is 20 times greater than the largest corn stover or cereal straw collection supplied to a single site, currently 50,000 tons. This stover collection project for 50,000 tons required reaching agreement with 400 farmers and contracting with more than 30 custom operators for baling and hauling (Glassner et al., 1998; Hettenhaus, 2006). Thus, one can imagine the increased complexity of logistics. Cellulosic feedstock is also unlike corn and other cereal grains and sugar, i.e., no quality standards for biomass exist. Biomass is not fungible, and it has no asset value to provide source of liquidity to the owner until sold. The challenge is to overcome these and other obstacles in order to reach the goal of tripling biomass production between 2012 and 2014 and then increasing production ten times over the subsequent 8 years, between 2014 and 2022.

2.1.1

Key Issues

One of the key issues is that farmers and landowners control the cellulosic feedstock supply. They will decide when to provide their crop residues, deliver forest biomass, and make the decision to grow dedicated energy crops. Unless there is a significant benefit for farmers to change current production and crop management practices, cellulosic feedstock in large quantities from crop residues will be difficult to source for industrial use. A reliable market is needed for the farmer to commit to producing biomass, while the processor requires a reliable supply of feedstock. Unlike corn, bulky agricultural residues are

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limited to a local market due to transport costs. A win-win relationship between the farmer and the processor is needed for the feedstock supply chain to flourish. Economics must benefit the farmer and the processor. Once cellulosic technology is proven: farmer participation in the value chain would help overcome the current “chicken or egg” obstacle of sourcing and supplying crop residues to biorefineries. The “Minnesota Model” provided incentives for Minnesota farmers to participate in the corn grain-to-ethanol value chain through offering ownership of corn ethanol plants. The State-funded program resulted in the formation of 12 farmer-owned ethanol processing cooperatives (Morris, 2008). Currently, over 30% of Minnesota farmers are investors in corn ethanol plants and a “Minnesota Model 2” is underway with Minnesota farmers collecting corn cobs for biomass gasification in their plants, while evaluating grasses, straw, and other cellulosic feedstocks (Kleinschmit, 2008). The feedstock must be competitive with natural gas pricing. Sustainable harvest systems must be in place to ensure that soil quality is maintained. Farmers are the stewards of the soil. However, processors and their customers expect validation of sustainable feedstock. This dichotomy requires a solution for moving agriculture residues ahead as feedstocks. Quality of feedstock is still loosely defined at the present stage of industry development. There is a consensus that feedstock needs to be free of dirt and relatively consistent in composition. Feedstock containing dirt accelerates equipment wear, increases maintenance cost, and causes lost production. Preferably, the material is collected while still standing in the field. During grain harvest, some residues inevitably end up on the ground as vehicles pulling trailers and grain carts drive alongside the combine to off-load the grain, knocking down a portion of the crop residues. A final issue is that feedstock composition varies, and any move towards more consistent composition would improve operating stability. Participants in stakeholder sessions considered consistency more important for biochemical processing than for thermochemical due to the more narrow selectivity of bioprocessing. Some processors said they would pay based on dry weight, but would eventually prefer to pay based on composition and “ease of processing.”

2.2 Feedstock Supply Sourcing an adequate, reliable, and economic supply of cellulosic feedstock is a major obstacle in commercializing renewable fuels. Studies at a macro level found the supply potential to be 900 million tons of agricultural biomass and nearly 400 million tons of forest biomass feedstock (Table 2.2; Perlack, 2005). These quantities of feedstock are based on a sustainable harvest using “best crop practices” for maintaining soil quality. The quantities will shift based on markets, government policies, and local economics. Crop residues are available in significant quantities now. However, removing large quantities for a biorefinery is a serious challenge to the farmer as well as the biomass buyer representing the biorefinery. Establishing sustainable crop systems for removal requires changing to new methods, acquiring new knowledge, and investing in different equipment. An estimated 900 MDTY of agricultural biomass is available now if “best crop systems” are practiced to maintain soil quality and achieve sustainable removal. Only 200 MDTY is required to meet the EISA 2022 goal of 16 billion gallons of cellulosic biofuels. The actual amount that can be removed in a sustainable and economic manner depends on cropping practices,

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Table 2.2.

US cellulosic biomass feedstock supply potential.

Biomass Source

MDT

Agricultural biomass Crop residues Perennial crops Others: e.g., process residues Forest biomass Forest products industry residues Logging residues Forest thinning Urban wood residues Energy crops

900 430 370 100 370 150 60 60 50 50

MDT, million dry tons.

especially till or no-till, and geophysical parameters—soil type, field slope, and length, as well as weather. The largest component of agricultural biomass is 430 MDTY of crop residues (Table 2.2), mostly corn stover. Stover production is 300 MDTY. Other residues are largely straw from cereal grains—wheat and barley. There is a 1:1 stover to grain weight ratio in most grain crops. A field producing 180 bu/ac corn leaves 5 tons/ac of stover in the field. Straw residues in dryland farming amount to 1–2 tons per acre. Some amount is often left on the field to retain soil moisture and prevent wind and water erosion. Larger residue quantities provide a harbor for fungi, weed seeds, and pests that can damage the crop. In the northern parts of the Corn Belt, the surface cover prevents the cold damp soil from warming in the spring, delaying seed germination. A rule of thumb is that each day delay in soil warming reduces the yield by 1 bu/ac. For these reasons, there is a clear advantage to the farmer for removing the stover, which will increase as corn yields increase. Continued trait improvement of corn is expected to raise corn yield 3 bu/ac/year in the near term. Seed companies project 300 bu/ac corn yields by 2030 due to advances in molecular breeding and biotechnology. The 1:1 ratio is expected to remain unchanged and stover, now at 8.4 tons/ac, becomes even more difficult to manage. Until now, there has been little market for stover. Most is on-farm use for animal bedding and cattle grazing after the grain harvest. As a result, the fields are tilled to bury most of the surface residue and compensate for soil compaction. Tilling adds $15/ac cost, increases soil erosion, and results in a loss of soil organic material, reducing soil quality. Process residues, 100 MDTY, include cotton gin trash, bagasse, and oat hulls. Available in smaller quantities at the processing plant, they enjoy an economic advantage, as they do not have to be collected and transported from the field. Forest products and energy crops are discussed in other chapters in this volume (Chapters 3 and 4) and will not be addressed here. As mentioned previously, conventional biofuel is ethanol produced from corn starch, while advanced biofuel is defined as renewable fuel that has life-cycle greenhouse gas emissions that achieve at least a 50% reduction over baseline life-cycle greenhouse gas emissions. Cellulosic biofuel is renewable fuel derived from any cellulose or lignocellulose that is derived from renewable biomass. Included within the definition of feedstocks for advanced biofuels are sugar or starch (other than corn starch), crop residues, vegetative waste material, food waste, and yard waste.

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While the current data provide some idea of estimated feedstock, the future is not likely to maintain the agronomic system status quo. The segments in the agricultural production and processing pie will shift due to new and varied markets and technology improvement of the crops. Future feedstock availability will depend on the following: r Crops will be planted to meet the demands of new and existing markets. As markets

change, crops will be adjusted to meet customer demand.

r Cropping practices will be required to ensure soil quality maintenance. When a market

for crop residues develops, new residue management practices are likely that lead to economic and sustainable removal. ◦ No-till is assumed in most studies of crop residue management systems that will yield excess cellulosic biomass feedstock. Presently, only one out of five corn and wheat farmers use no-till today (CTIC, 2007). ◦ New cropping systems that include cover crops are needed for erosion control and to maintain soil carbon on many fields to allow for sustainable residue removal. r Accurate models for “soil quality” based on soil organic material must be developed. Several models are in development, but validation is required (See Chapter 7 in this volume). r Changes in farm and energy policies will be needed, with stronger connections between farm policy and energy policy, which can incentivize cellulosic feedstock production. Significant regional differences exist in soils, weather, and crop characteristics, as well as differences in harvesting mechanics for stover and straw. In dryer areas, more residue is currently left in the field to retain moisture in the soil. More cover must also be left on highly erodible soils and sloping fields to protect the soil from water and wind erosion. More corn stover is produced than straw, but straw is more readily removed. Corn stover yields are 3–5 times greater per acre than straw from cereal crops. Unless cereal crops are irrigated, there is little straw left to collect. For example, the average dryland wheat straw yield is 2,500 pounds per acre compared to 10,000 pounds per acre or more for corn stover. The equivalent of 1,200 pounds per acre of straw must be left on the surface to comply with erosion guidelines with no-till. The excess is less than 1 ton of straw per acre that is removable. In contrast, leaving 2,000 lbs of stover with no-till is often sufficient and the excess is 8,000 lbs or more of stover per acre. Straw collection infrastructure is generally well developed, while corn stover collection is not. When cereal grain is ready to harvest, straw usually contains 20% moisture or less, suitable for baling. In contrast, stover contains 50% moisture and must remain in the field to dry and be collected later, depending on the weather. A wet harvest season can prevent its collection entirely. Farmers generally agree that $50/acre pretax margin would raise some interest in harvesting crop residues, but only if the grain harvesting was not hindered in any way. Cash crop values—$3–$5/bu corn, $7–$10/bu for soybeans and wheat—make the relative value of residues small in comparison. Collecting the stover can add $100–$200/ac sales ($50/dry ton, collecting 2–4 dt of the 4.8 dt produced). However, some estimate $70–$100/dry ton delivered would likely be required to raise farmer interest. Most processors base their cost for biomass on $30–$50/dry ton delivered, a $40–$70 million annual difference in costs for a 100 MGPY plant. This discrepancy has not been adequately evaluated by potential purchasers of crop residues and other biomass feedstocks.

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Realizing this profit from residue sales requires overcoming related issues with harvesting and transporting crop residues that must be addressed on the farm level. Farmers routinely raise the following issues in evaluating this opportunity: r r r r r r r r r

Residue markets Residue harvest window Residue removal cost Corn yield and residue management Ag equipment needs Operating costs Residue nutrient value Farmer outlook Crop R&D lead times.

2.2.1

Residue Markets

Currently, there is a limited market for cellulosic crop residues and no market for energy crops. Crop residues that are collected are mostly for on-farm use—bedding and animal feed. Corn cobs are an exception. Corn cobs are 15%–20% of the stover. They are currently used for a wide variety of applications ranging from abrasives for polishing metal and wood (no silica hazard), as a carrier for pesticides and fertilizers, and as an absorbent for hazardous liquid spills (high absorbency properties). The price for a 40 lb bag of ground cobs for polishing metal is $25 FOB facility, equivalent to $1,250/ton (Soda-Blast.com, LLC). Collecting just the corn cobs during the grain harvest is less disruptive than collecting stover. The yield is about 0.5–0.6 tons per acre. Collecting 30% of all the cobs results in 10–15 million dry tons of feedstock nationwide. The cobs are discharged with the husk and usually spread over the field surface behind the combine after the grain is removed. Collecting the cobs and husks as they are discharged from the combine is one possibility. The cobs do not touch the ground, so they are free of dirt, rocks, and other foreign material, a common problem when baling material left on the ground. Because of recent government and economic incentives, several agricultural equipment suppliers and processors are evaluating two methods for cob collection: r Pulling a caddy behind the combine to collect cobs as they are discharged after shelling.

Questions have been raised concerning whether this process will slow the harvest too much. r Collecting the cob with the grain and screening the grain enroute to storage. A key question that must be addressed is whether the additional step in the logistics infrastructure will be cost effective. Trials to look at both methods are in progress. Two companies evaluating the methods for feedstock are Chippewa Valley Ethanol Co. (www.cvec.com), who is working to replace natural gas, and Poet, Inc. (www.poetenergy.com) for conversion to fuel ethanol. Residue sales are limited to local markets, typically within a 50-mile radius. The bulky, lowdensity properties make them expensive to load and transport. The biomass is not fungible, so there is little spot market. Sales are arranged a year in advance many times with no contract and only with a handshake.

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Another market for residue is leasing the harvested corn fields for grazing cattle. Most fields can provide several months of grazing after harvest. A rule of thumb is 1 cow/acre. Typical lease rates are $7–$10/acre. The only cost involved for the leaser is fencing the fields and providing drinking water for the livestock. A one-wire electric fence is generally used to contain the cattle. The fence can be easily moved from one area to another as the cattle consume the stover and is reused from year to year. Obviously, this use of agricultural residues competes with the ethanol and biobased products market.

2.2.2

Harvest Window

The harvest window for residues is the time between the grain harvest and the next field operation. For no-till fields, this is the planting time for the next crop. For tilled fields, fall tilling is usually done immediately after the harvest of the current crop, weather permitting. Fields must be dry enough to permit good ground conditions to support the equipment operations in tilled systems. According to the last USDA survey, 85% of the wheat acres and 80% of the corn acres are tilled (CTIC, 2007). The wheat ripens in early June and is harvested much earlier in the season than corn, which is harvested in mid-August through early September. Weather conditions are more favorable for field operations in June than in the fall, and therefore, wheat straw is generally more accessible for baling. Because corn harvest is later when days are shorter and cooler, wet weather may delay fields and crop from drying adequately, extending the harvest beyond 30 days. Additionally, the physiology of wheat straw is very similar to commercial hay and there is no special equipment required, while corn stover is not a homogeneous material and presents some issues in harvesting. For stable storage, the residue needs to be below 20% moisture or above 60% moisture. Between 20% and 60% moisture, microbial activity is high, thereby digesting the cellulosic material and reducing the yield. In the worst case scenario, the heat is not dissipated from the reaction and auto ignition of the material can occur. The physical structure of straw and the timing of harvest ensure conditions will be right for collection. Corn stalks are more difficult. The stalk contains about 30% more moisture than the grain and must be left in the field after the harvest to dry. Wet weather can prevent drying well past the time when the farmer would do fall tilling. Harvesting wet corn above 20% moisture is common. Its high value justifies drying in equipment designed for that purpose. The lower value of stover and its heterogeneous character prevent economic drying. Corn cobs are the exception as whole cobs dry well and store well in the open.

2.2.3

Residue Removal

The crop residue removal cost has two components: cost per acre and cost per dry ton collected. The more collected per acre, the lower the cost per ton. The quantity of residue for harvesting after the erosion requirement is met depends on cropping practices. Tillage greatly affects availability when following USDA guidelines for erosion control. No-till practice allows most of the residue to be removed, especially when cover crops are employed. In contrast, conventional tillage leaves less than 30% of the surface covered, and there is no excess residue. Baling dry material is common practice. Collecting the stover with existing equipment requires multiple passes through the field. Conventional baling requires additional passes to

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Table 2.3. Custom Bale & Haul economics for corn residues.

1:1 ratio, 15% moisture, sell Sale, $70/dt P&K nutrient credit, $10/dt Reduced field operations, $14/ac Total revenue increase Less stalk chopping (corn only), $9/ac Less raking, $6/ac Less custom baling $23/dt Handling, storage $5/dt Strinkage, 10% Hauling, 23 mile radius, $10/dt Net to farmer, $/ac

130 bu/ac

170 bu/ac

200 bu/ac

2 dt/ac $140 (20) 14 $134 (9) (6) (46) (10) (14) (20) $29

3 dt/ac $210 (30) 14 $194 (9) (6) (69) (15) (21) (30) $44

3.8 dt/ac $266 (38) 14 $242 (9) (6) (87) (19) (27) (38) $56

Assumptions: $70/dry ton delivered, 1 million acres, 23 miles radius collection site, 1 dt/ac left in field.

Table 2.4. One-pass harvest and transport economics for corn residues.

1:1 ratio, 15% moisture, sell Sale, $70/dt P&K nutrient credit, $10/dt Reduced field operations, $10/ac Total revenue increase Less one-pass harvest $18/ac Field to collection site transport $10/dt Handling, storage $6/dt Shrinkage, 3% Transport from collection site $7/dt Net to farmer, $/ac

130 bu/ac

170 bu/ac

200 bu/ac

2 dt/ac $140 (20) 14 $134 (18) (20) (12) (14) (20) $56

3 dt/ac $210 (30) 14 $194 (18) (30) (18) (21) (30) $86

3.8 dt/ac $266 (38) 14 $242 (18) (38) (23) (27) (38) $109

Assumptions: $70/dry ton delivered, 1 million acres, 3–13 miles radius collection site, 1 dt/ac left in field.

chop, rake, bale, and remove the bales from the field. Estimated baling costs are summarized in Table 2.3. Baling cost is about $30/dt for round or square bales at the roadside. Storing, stacking, and transporting bales add $14–$25/dt to the cost. The example assumes $70/dry ton delivered price. Collection is within a 23-mile radius encompassing 1 million acres. Costs are based on the average value from the 2008 Iowa Farm Custom Rate Survey. To achieve $50/ac pretax income, grain yields need to be 200 bu/ac, while leaving 1 dry ton in the field. One-pass harvest, bulk storage, and transporting the feedstock from regional collection centers is estimated to reduce the costs and nearly double the margins for the farmer but remains to be demonstrated (Table 2.4).

2.2.4

Residue Management

The emerging market for cellulosic feedstock and increasing yields of corn present new opportunities for better reside management. Continued trait improvement of corn by seed companies, including Monsanto (www.Monsanto.com), Pioneer (www.pioneer.com), and Syngenta

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(www.syngenta.com), is expected to raise the yield 3 bu/ac/year in the near term. The ratio of stover to corn grain remains unchanged, producing an additional 150 lbs/ac of stover annually. Advances in breeding will boost the average to 300 bushels per acre by 2030. For the same 90 million acres in corn now, stover increases from 3.7 to 7.4 dt/ac, doubling stover to 600 million dt of residue to be managed. A major challenge is managing residue in an economically and environmentally sustainable way. An evolution in crop tilling practices toward no-till cropping is needed in order to supply adequate feedstock while complying with erosion guidelines and maintaining soil quality. No-till cropping is increasingly practiced but not widely utilized in regions of the country with the greatest potential to supply crop residues, as calculated based on their average yields of corn. Farmers need relevant information on the effects of biomass removal to establish a better basis for sustainable removal as biorefining opportunities emerge. A series of colloquies, or informal discussions, was held to discuss needs to accelerate cellulosic biofuels commercialization. Participants were a multidisciplinary group of industry leaders in a position to influence the future direction of the industry. Topics traced the supply chain from the farmer’s field to the marketplace. Discussion focused on increasing feedstock availability, logistical challenges to transport agricultural biomass, and financing commercial scale plants with new technology supplied with a nonfungible feedstock (Hettenhaus, 2006). All participants concurred that residue management needs to extend beyond the field, considering other portions of the supply chain. Additional infrastructure in collection, storage, and transportation are also needed, including equipment for one-pass harvesting and investments for alternatives to trucking collected material, including pipelines and short-line rail.

2.2.5

Ag Equipment Needs

Several general statements were made in the colloquies describing Agricultural Equipment needs: r To supply clean feedstock to the biorefinery, the feedstock should contain little to no dirt,

preferably the material collected never touches the ground. The dirt causes severe wear on piping, conveyors, and equipment. r To not slow down the grain harvest, crop planning is premised on collecting 10–12 acres per hour, completing the harvest within 30–40 days. The acres planted, the size of the harvest crews, and supporting equipment and infrastructure are sized to operate accordingly. If the harvest is slowed, there is increasing danger of losing a portion of the crop due to high winds and wet weather, exposing the crop to fungi and risk of more deterioration of the grain in the field. The harvest window is especially important for corn, since it is harvested late in the season with cooler weather and shorter days. Several one-pass prototypes are being investigated that do not slow down the grain harvest. The base case shown (Table 2.5) assumes the stalk and ear are removed together in one truck from the field. Grain is separated at the collection center. Locating collection centers at existing grain elevators, the “grain elevator model,” makes use of existing infrastructure to store the corn. These assets are often underutilized since much of local corn is sold to nearby ethanol plants. Land may need to be acquired at some locations to accommodate the additional cellulose storage.

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Table 2.5. One-pass harvester requirements: 200 bu/ac example. Harvest Days Stover Collected in Million dt

30

1 2

Harvesters required 28 21 17 56 42 34

40

50

To collect 1 million dry tons of stover in the example above, 30 one-pass harvesters would be required based on the following assumptions: (1) 12 ac/h average harvest rate, (2) 200 bu/ac average yield, (3) 20 hours per day operating time, and (4) two spare harvesters for back up. The number of harvesters drops as the harvest days are increased (Table 2.5). There are no spare harvesters included in the table values. To maintain the harvest rate at 14 ac/h, a 12 head combine in a 200 bu/ac field harvests 40 bu/min, filling a trailer to legal weight (20 tons) in 15 minutes. A one-pass harvester will fill the truck in 5 minutes. The number of trucks required per harvester triples, and the trucks are volume-limited (3,000 ft3 , 8 lbs/ ft3 , 12 tons as is). Depending on yield and distance, present corn harvesters operate with a minimum of 3–4 trucks/combine. Therefore, for similar distances, 10–12 trucks will be required per one-pass harvester. One-Pass Investment The list price of a 12 row, 375 horse power (hp) rotary combine is about $300,000. Assuming trucks can be contracted with no additional investment and the same harvest cost can be achieved when the additional handling is done off site, the investment in new one-pass harvest equipment is $9 million (30 × $300,000) per 1 million dry tons of stover collected. Large operators lease their combines, and if the economics work, the opportunity would warrant serious consideration. Baling Investment The equipment investment for baling in the same example as above, i.e., 1 million dry tons of stover in 30 days, is $15 million. The capital is the same for round or square bales (Table 2.6). Cost of equipment for moving the bales from the field, storing, and transporting are not included. The baling-related units required are based on the same values used for the one-pass harvest example: (1)feedstock, 1,000,000 dt/year, (2) yield, 200 bu/ac, (3) stover (1:1 ratio), 4.8 dt/ac, (4) cover left, 1.0 dt/ac, (5) stover baled, 3.8 dt/ac, and (6) area baled, 265,000 ac. The units required are shown in Table 2.7. They are based on the September 2009 University of Minnesota Extension Machinery Estimates for Net Cost of a New Unit and Work Performed, acres per hour. The stalk chopper is widely used now to help microbes attack stover residue. For baling, the stalks are chopped immediately after the harvest to accelerate drying. After the chopped material dries to less than 18% moisture, it is raked to form a windrow. The windrow reduces the number of passes the baler makes across the field, improving the baling rate. Windrows

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Table 2.6.

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Capital equipment investment for baling. Harvest Days

Capital Equipment

Unit Cost $(000)

Stalk chopper Rake Square baler Round baler Tractor, 60 HP w/rake Tractor, 60 HP w/rnd baler Tractor, 130 HP MFWD, chop Tractor, 130 HP MFWD, sq baler Chop, rake, square bale only Chop, rake, round bale only

20 27 75 21 26 26 106 106

Table 2.7.

30

40

50

Capital required $ (Millions) 1.1 0.8 1.7 1.3 2.1 1.5 2.3 1.7 1.5 1.1 2.9 2.1 5.0 4.5 2.9 2.2 15.3 11.4 15.4 11.6

0.7 1.0 1.2 1.4 0.9 1.7 3.6 1.7 9.1 9.3

Baling equipment requirments. Harvest Days

Harvest hours Collection rate required Equipment employed Stalk chopper Rake Square baler Round baler Tractor, 130 HP MFWD Tractor, 60 HP

20 h days ac/h Equip. rate ac/h 7.8 6.8 16.0 4.0 NA NA

30

40

50

600 439 Units required 56 64 27 110 83 174

800 329

1000 263

42 48 21 82 63 130

34 39 16 66 50 105

once wet due to rain or even a heavy dew are difficult to dry back down, so raking is scheduled just prior to baling. Tractors are multipurpose. A 60 HP tractor can rake and pull the round baler. The 130 HP Mechanical Front Wheel Drive tractor can handle all the assignments, but is only required for the stalk chopper and the square baler. Harvest Choices While baling can fit other residues and energy crops, for stover, the collection choice appears to favor one-pass harvest. Several reasons drive this conclusion. First, the grain is harvested when it is mature, usually after drying below 20% moisture. However, in a wet season, the grain is harvested when field conditions permit and dried in specially designed dryers. One-pass harvests the wet stover material with the grain. The stover is stored wet, adding water as required to be at 60% or more moisture. In contrast, baling requires material to be 18% moisture or below. Wet weather keeps residue moisture too high for baling and feedstock remains in the field. One-pass harvesters replace existing combines for corn harvest. The grain and stover are collected in one pass (with more trucks). Stalk chopping in one-pass harvested

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Table 2.8.

Bale staffing requirment, 1 million dry tons.

Operation

Positions

Stalk choppers Rakes Rotary balers, 30% of balers Square balers, 70% of balers Baling support crew, 15% Field operators, bales left in the field

56 64 33 20 27 200

fields is eliminated. Conventional combines continue to be used when residue is baled. The baling equipment is an additional investment and its utilization is weather dependent. Second, during the seasonal harvest, operations are planned to continue around the clock, supplementing the regular workforce with all able-bodied persons including spouses, retirees, students during nonschool times, and contract labor. There is little to no slack, as 12 or more hours per day are normal. Any additional work, including harvesting, transporting, and storing residues, will require additional people. For one-pass harvesting of 1 million dry tons of stover in 30 days, farmers must plan for four more trucks per combine, 30 harvesters, and 120 additional trucks (240 drivers, as workers would rotate through positions working 24/7) to remove the grain and stover from the field to collection centers. Replacing existing combines with one-pass harvesters is a trade-off for operators. Support crews are deployed for combines now. A similar crew would support one-pass harvest. To match existing combine harvest rates, one-pass harvesters require more trucks—one loaded every 5 minutes for ear and stalk in contrast to one every 20 minutes for grain. When baling stover, 1 million dry tons produces 2 million bales. Nearly 200 additional positions are needed to operate the equipment (Table 2.8) Since the work week is 24/7, 400 people are required to staff the baling operation not including administrative needs. Three operations are employed: chop, rake, and bale, leaving the bales in the field. Stalk chopping follows the combine to hasten the stalk drying. When the residue reaches the required moisture, a baling crew is deployed. Raking and baling are done together, collecting the windrow immediately to prevent it from getting wet. Heavy dew on a cloudy day or a local shower will add moisture and delay baling. Thus, advance scheduling is difficult. In this example, 30% are round bales and 70% square bales are produced. The net wrapping protects round bales from weather. They can be left in the field for collection until the next field operation. For no-till, this is spring. Square bales are not protected and must be removed from the field and stacked. In most areas, they must be covered to protect them from the weather. This additional movement is not included in the above operations. When wet weather curtails collection, there are limited other assignments for the baling crews, and their fixed costs continue to accumulate.

Soil Quality and Compaction When making a choice to remove stover, the impact on soil quality is a serious factor. Traffic in the field can cause excessive soil compaction, damaging the soil structure. Compacted soil inhibits root growth, increases water runoff, and reduces the flow of nutrients to nourish the plant . . . all reducing crop yields. In both harvest cases, more traffic will occur on the field.

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Compaction can be avoided in several ways, including wide tires that have better distributive weight, limiting traffic to tracks between rows and tilling the compacted area. Tilling is the least attractive, because of added cost and it releases soil organic matter.

2.2.6

Operating Costs

Farmers make annual crop planting and selling decisions based on their historical operating costs and yields, and the expected market for their crops that year. The average age for farmers is 62. Over the many crop seasons, they have accumulated much experience, and they know their operating costs well. Their focus is increasingly on cost of inputs, especially fertilizer, emphasizing costs per acre, not yield per acre. Farmers are generally conservative in their approach, diversifying their fields and crops to produce a profit across the board, in dry years and in wet years. Changes for existing crops are adjustments made in an evolutionary way, trying several rows, then several acres, increasing acreage after results meet expectations. When considering a new practice—no-till, drill planting, removing crop residues, and growing energy crops—many questions arise. The answers vary depending on many conditions, including the soil types, crop system needs, and the weather. Accumulating the information to arrive at a satisfactory answer requires years.

2.2.7

Residue Nutrient Value

The present market for residues—grazing, bedding, and animal feed supplement—recycles the nutrients back to the soil. With grazing, nutrients remain in the same field. Bedding and manure from feedlots can be recycled to local fields where needed. The major nutrient components in the residues are phosphorus, potassium, and nitrogen. The phosphorous and potassium content (P&K nutrients) in straw and stover is typically 0.1% and 1%, respectively. The composition varies depending on the soil and local conditions. Rain quickly washes out these soluble nutrients. If a dry season, the P and K value removed with the stover is $10 per dry ton, $8 for the K, and $2 for P. The nitrogen fertilizer value is more complex and depends on local conditions. The N content in the stover is 0.5%–2.0% depending on the length of time in the field after the plant has matured. However, there is conflicting information regarding its value. If the residue is plowed under the surface, microbes desire a 10/1 ratio of C/N for breaking down residue. Since the C/N ratio of straw and stover is 40–70/1, 20 lbs N fertilizer addition per ton of residue is recommended to avoid denitrification of the next crop. If left on the surface, there is some evidence that shows that the same N deficiency occurs, but the results are not conclusive.

2.2.8

Land for Energy Crops

Energy crops provide another source of feedstock. The quantity depends on the incentives for replacing the existing land use. The Corn Belt is an unlikely area for growing energy crops due to the profitability of current cash crops. See Chapter 4 for a discussion of energy crop production.

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Farmer Outlook

Farmers embrace change at a conservative pace. Will farmers bother with supplying corn stover, the most abundant cellulosic feedstock available? Moreover, how can they participate in the value-added prospects? Farming, efficiently supplying commodity crops at a low cost, planting improved seeds with better traits, and employing improved crop practices with equipment that covers more acres per hour remains the primary focus. Removing the residues will be approached cautiously. When results are proven, expansion on their lands will occur. On average, farmers own 40% of the land they farm, renting the rest. Landlord approval is important to increase supply. Agricultural equipment and seasonal demands are planned around the total acres. Changing crops or crop practices on the rented lands is usually done with the consent of the landowner. Agreement on land use is in their mutual interest—keeping the equipment utilized and the rented land farmed. Downstream Value-Added Prospects: Farmer-owned dry mill ethanol plants are a shining example of how farmers can prosper from downstream “value-added” processing. In the areas surrounding these facilities, the farmers have enjoyed a stronger market for their corn since the facilities began operation. In addition, operating margins from their ethanol plants have increased due to higher gasoline prices. The farmer-investors and others in the community are benefitting from the increased dividends and higher value of their investment. The local economy has also benefitted from the jump in local expenditures to improve and expand plant operations. The corn to ethanol process was well proven when farmers began to invest in the dry mill plants. States, especially Minnesota, added incentives for farmer ownership. Similar programs may help to include the farmer in the value-added downstream prospects.

2.2.10 Crop Research and Development To supply the cellulosic feedstock market, new crop systems are needed. Energy crops and present cash crops that have a cellulosic feedstock component offer new opportunities for growth, but bringing a new crop to the market requires 5–7 years in the United States. A “disruptive” technology takes 10 years. To improve crop breeding, regional centers that conduct parallel crop development programs are needed. In addition to switchgrass, the possibility of other new feedstocks including cover crops, forage soybeans and sorghum, high fiber sugar cane, miscanthus, willows, and poplars are some that are being investigated. Improving plant traits, including enzymes in the plants to lower the processing costs, are related projects that could accelerate commercialization.

2.3 Feedstock Logistics Cellulosic feedstocks face several logistical hurdles, including low density for transportation and storage stability. Additional trucks and drivers are required to transport the bulky material, increasing the traffic at a time already prone to congestion. Collecting the annual supply of feedstock during the fall harvest to supply the facility over the next years requires secure storage conditions.

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Table 2.9.

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Densification of dry material. Feedstock Density (dry lbs/ft3 )

2.3.1

Form

Operating Cost $/dt

Bulk Milled Baled Pellets

NA $15–$25 $25–$30 $25–$30

Corn Stover

Straw

Cobs

40

4 8 8–12 25–35

8–10

Bulk Density

Grain density is about 40 lbs/ft3 . Stover or straw bulk density is 4 lbs/ft3 , thus requiring 10 times the volume to transport and store it, unless compacted or finely milled. A trailer with the standard dimensional limits, 3,000 ft3 , holds 60 tons of grain, nearly triple the usual legal load of 20 tons of baled or ground biomass. Thus, hauling logistics will be difficult, but critical, to resolve. During harvest season, most states provide an overweight allowance for trucks since the crops must be harvested during a short time period and varying water content makes it difficult to estimate actual harvest weight. The temporary limit is based on maximum safe weights for roads, especially bridges. For example, Wisconsin permits a 15% overweight allowance between September and November. Nevertheless, biomass bulk density is too low to take advantage of the higher weight limits. Chopped corn stalks or straw is about 4 lbs/ ft3 . Without some compaction or grinding, the same trailer would contain just six (6) tons, more than tripling the transportation costs of grain. Permitting larger trailer dimensions would help, but then equipment is nonstandard, limiting the utilization after the seasonal harvest. Increasing the bulk density—incurring cost for baling, pelletizing, or compressing in other ways—can lower transport cost. The most economic trade-off depends on transportation distances, and the costs of handling, storing, and processing. Densification Processing the material removed from the field through a mill or grinder to reduce its size can increase density to 8 lbs/ft3 (Table 2.9). The same density, 8 lbs/ft3 , can be achieved with a one-pass harvest, collecting corn stalks with the ears. Baling, round or square bales, further increases density to 8–12 lbs/ ft3 . Pellets are the densest at 25–35 lbs/ft3 . However, they can be friable, i.e., easily broken apart if not processed properly or if handled in a rough manner. Pelletizing cost Transportation cost is offset by densifying the feedstock. Dry feedstock is usually baled when removed from the field after harvest. Dense square bales, pellets, and cobs readily fill trucks to capacity while remaining in legal dimension limits. Round bales are most efficiently handled by a “load and go” wagon that picks bales off the field and carries them over the road with a high-speed tractor in less than a 10-mile radius. Pelletizing occurs in series. Bales are broken and pelletized at a collection center and then transported to their final destination. Pelletizing requires significant investment and the

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relatively high fixed pelletizing cost depends on the volume. For example, Green Circle’s pelletizing plant in Cottondale, FL, recently began production. The $65 million plant has 13 pelletizer machines scaled to produce 550,000 tons of wood pellets per year from regionally sourced yellow pine. Extending this example, pelletizing 1 million dry tons annually would require a $100 million investment (Kotrba, 2009).

2.3.2

Storage

Storage stability is mostly a function of moisture. Many methods for storing crop residues have been investigated over the years. An early patent (Lanthrop and Munroe, 1926) claimed that one of two conditions must exist during storage for good fiber properties and minimum storage losses: either the moisture content must be below 20% during storage so that the microbial activity is nearly dormant, or the material must be kept wet, above 60% moisture. Dry storage of cellulosic feedstock is seen as the most likely practice for supplying biomass in the United States today. Baling and bale handling equipment are readily available from Ag machinery suppliers. While baling adds cost, it supplies needed compaction for economic transport. Wet storage of silage is a common practice for feeding cattle. Wet storage is also used for bagasse, the fiber residue left after removing the juice from sugar cane. Dry Storage The first industrial scale application of crop residues occurred in the sugar cane industry in the last century. Bagasse exits the sugar cane refinery at 50% moisture, too damp for stable storage. Some is burned to supply process energy. The excess is used as a component in building materials like fiberboard and as a pulp mill feedstock. Production of building materials is a dry process. Producers pursued ways to economically dry the feedstock for storage. This effort resulted in using the heat from microbial fermentation to dry bales from 50% to less than 20% moisture (Munroe and Lathrop, 1933). The bales were sized and stacked to dissipate heat and acid fumes without fiber damage (Figure 2.1). Sheltered from the weather, bales are kept for several years without serious deterioration or fiber loss (Hay and Lathrop, 1941; Lathrop and Munroe, 1926). Classical bale storage is pictured in Figures 2.2 and 2.3.

Figure 2.1.

Bale stacking, about 1930.

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Figure 2.2.

Bale storage, 1930–1960.

Figure 2.3.

Bale storage, 1997 winter.

37

This original dry storage method was used for more than 40 years. However, a change to wet storage occurred in the 1960s due to increasing recognition of dry storage disadvantages, including that the bales were relatively small, weighing 250 lbs “as is,” mechanical handling was slow and costly; the bales had to be precisely stacked to vent fumes and dissipate heat; procedures were labor intensive; several months were required to dry bales from 50% to 15% moisture; and as fire loss was high, fire insurance costs were increasing. While some progress in handling has occurred, experience in baling, storing, and transporting has demonstrated that the issues above are still unresolved today. Corn stover bales harvested in 1997 for furfural feedstock are shown in Figures 2.3–2.6. The bales survived the cold weather well (Figure 2.3). However, warm weather disclosed serious decomposition of round and square bales (Figures 2.4 and 2.5). Inspection of the round bales showed they were loosely made. Evidently, that bale operator had not tightened the belt to better compact the bale. The loosely packed bale absorbed excessive water so that microbial activity was high since air was more able to diffuse into the bale. Consistent, dense bales and covered storage on well-drained pads can minimize the feedstock loss. Other hazards remain, such as fire. Once ignited, bale fires cannot be extinguished. Figure 2.6 shows the results from a fire in Harlan, IA, started when a small flame caused by a welder’s spark blew into the stacks on a windy day. The blaze destroyed much of the inventory (Figure 2.6), which burned for several weeks. The Harlan Tribune reported “by far the most notable incident during the year was the corn bale fire at Penn Chemical Company, south of Harlan, on October 7–8, 1999. Thousands of corn bales burned, keeping the department, as well as other area fire departments, on call for both days” (Harlan Tribune, 2000).

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Figure 2.4.

Round bale loss.

Figure 2.5.

Square bale loss.

Figure 2.6.

Storage area after bale fire.

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Process water

Feedstock

Washshred(pump)

Wet storage pad

Cellulosic process

Circulation liquor Water management • Remove dirt • Recycle nutrients

Figure 2.7.

Wet storage platform.

Figure 2.8.

Wet storage mound with pumping arm.

Wet Storage Since pulping is a wet process, companies in the pulp and paper industry investigated wet storage of nonwood fibers for feedstock. The results were more successful than dry storage. Even companies with a dry process abandoned bales in favor of wet storage. Wet storage of sugar cane bagasse has been in wide use on a commercial scale since 1960 (Atchison and Hettenhaus, 2002). Unlike ensiling forage for animal feed, the biomass material is typically slurried to 3% solids and piped to a storage pad (Figure 2.7). The liquor drains through the pile and is recirculated until a height limited by the pump performance is reached—typically more than 100 feet (Figure 2.8). The Imperial Young Farmers and Ranchers Assn, Imperial, NE, validated wet storage for corn stover, as part of a USDA funded project (Hettenhaus and Mosier, 2010). A 700 dt pile was built in 2005. Samples over the next 8–16 months were pretreated, hydrolyzed with cellulase enzymes, and fermented to ethanol. The feedstock from wet storage showed improved results over dry material since inorganic solubles were dissolved in the circulating liquor when the pile was constructed (Figure 2.9).

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Figure 2.9.

Corn stover wet storage; Imperial Young Farmers & Ranchers Assn, Imperial, NE.

Adapting wet storage to a crop that has “damp” feedstock like high fiber cane, silage sorghum, and corn stover fits well into a wet biorefinery process. Harvesting when the crop is mature, including the excess wet stover, can reduce the weather risk and soil compaction in addition to lowering cost.

Storage Comparison A comparison of dry bale and wet bulk storage shows there are significant advantages for the wet method in most categories (Table 2.10).

Storage Area Wet storage density is 12.5–14 dry lbs/ft3 of average pile density (Bruijn et al., 1974; Moebius, 1966). The height of a wet pile is only limited by the pump head capacity, how high is it economic to pump? Bales require ten times or more the wet storage space due to bale stacking limits, access corridors, and a measure of fire protection. The total area required for 1 million dry tons is about 500 acres for square bales. Annual rent at $300/acre would be $150,000. Square bales, 10 dry lbs/ft3 , can be stacked about 300 lbs/ft2 or 30 feet high before the weight begins to compress the lower bales, causing the stack to shift in storage and possibly fall. Round bales, stacked three high require about 140% more storage area, 170–200 dry lbs/ft2 . Using “cotton modules” to compress the feedstock, even more area is needed for a

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Table 2.10.

41

Dry and wet storage comparison.

Parameter

Dry (Bales)

Wet Storage (Ritter Method)

Dry density, lbs/ft3 Storage areas Storage loss Foreign matter and soil nutrients Solubles removal Weather risk Fire hazard Investment Storage quantity

8–12 10× >5% High Process residue Rain High Low to high Small, mostly farm use

12–14 1× mid-rotation > juvenile. At the Hill Farm Research Station, an older similar study has shown that yields of fully mature switchgrass (greater than age 3) when grown under loblolly pine without fertilization averaged 2.5 tons per acre per year, with a maximum of 3.5 tons per acre per year (Michael Blazier, personal communication). Catchlight Energy, LLC is a joint venture between Chevron and Weyerhaeuser, whose objective is to develop the next generation of renewable transportation fuels from non-food sources. This unique venture will capitalize on the biological expertise of Weyerhaeuser and the advanced fuels expertise of Chevron. Currently, the Catchlight group is exploring the possibility of combining a bioenergy crop that can be harvested annually with trees that are managed for wood products and fiber. Their concept is very similar to that of many agroforestry systems where alternate rows of trees and an annual biomass crop are grown and used to feed a second-generation biofuels plant (http://www.catchlightenergy.com).

3.6 Products from Woody Biomass The US DOE and US Department of Agriculture estimated potential lignocellulosic biomass production for fuels in the United States at more than 1.3 billion tons annually, sufficient to replace more than 30% of current transportation fuel use (Perlack et al., 2005). Although age-old processes are available for converting the starch content of grain into sugars, which can then be fermented to ethanol, the conversion of lignocellulose to sugars is much more difficult. The recalcitrance of lignocellulose lies in its structure, which has evolved to provide long duration resistance to pests and pathogens. Thus, the development of processes for converting lignocellulosic biomass to fuels is hampered by the lack of energy-efficient and cost-effective processes for the deconstruction and conversion of this feedstock (Lynd et al., 1999). Trees and herbaceous material are made of three basic components plus many trace materials. The most abundant components are structural natural organic polymers: cellulose, hemicelluloses, and lignin. Cellulose is the long strong and flexible natural linear polymer in fibers that predominately gives trees and woods their strength. Cellulose fibers are held together in part by hydrogen bonds with itself but also by lignin, natural phenolic glue. Hemicelluloses are heteropolysaccharides of lower degree of polymerization than cellulose that are found encrusting the cellulose and lignin and also provide some bonding in the natural structure. Structural wood is simply the tree with all these components cut and shaped to the desired form. White paper is made predominantly from the cellulose fibers with most of the hemicellulose and almost all of the lignin removed.

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68

CH2OH

HO

OH

4 O

O HO

HO

O

O OH

1

1

4

CH2OH

CH2OH O

OH OH OH

n

Figure 3.3. Sterochemical structure of cellulose.

Cellulose consists of long chains of the six-carbon sugar glucose that are connected end to end as a polymer (Figure 3.3). It would seem simple to break that connection, by mechanical means or with enzymes, so that a long fiber of cellulose would become thousands of simple glucose molecules. However in practice, it is very difficult. The glucose molecules are connected by the more difficult to break β-O-4 linkages (Figure 3.3) and are arranged in regions with high crystallinity, which limits accessibility. Thus, cellulose is much more difficult to break up than starch molecules with their α-O-4 linkages that connect the glucose. Natural selection has resulted in cellulose that does not break apart easily. Fortunately, cellulose fibers are more valuable than their derived sugars because paper products can be made from them at present. However, as the demand for fuel and energy is increasing more than the demand for paper, conversion of cellulose to platform sugars will become more important as fossil energy sources diminish. Relatively pure cellulose can be hydrolyzed to glucose in formic acid media (Sun et al., 2007) and many other methods have been used in the past and are being developed now. It has been demonstrated that a woody biomass hot-water hemicellulose hydrolyzate stream can be separated into products and the sugars used for fermentation to ethanol. This sequential deconstruction of woody biomass is expected to become the dominant commercial method for production of new forest-based materials as it preserves the original value of components and allows their recovery for society’s use. The general process flow is to remove the easiest major component first, the hemicellulose, followed by application of a separate separation technique to fractionate the lignin and cellulose. Past techniques have focused on removing the lignin from cellulose, as in Kraft pulping and pulp bleaching, to provide fiber for papermaking. This approach may not be preferable to removing the cellulose from the lignin when the goal is to produce monomeric or oligomeric sugars from the cellulose. Current research is taking both approaches to continued deconstruction after hemicellulose removal without a clear winner yet clear. The method of deconstruction has significant implications for development of growing systems for traditional products integrated with new forest-based materials. The relative value of some components in traditional products may be trivial or even negative while the same component might be as valuable as cellulose, or significantly higher, as a new forest-based material. One example of this is the Ac, which stands for acetyl group, shown in the hemicelluloses galactoglucomannan and glucuronoxylan in Table 3.1. The acetyl group when recovered in an aqueous medium as acetic acid has values that can range from equal to that for relatively pure cellulose pulp to three times as valuable per unit of mass. This is important as the most dominant method of making relatively pure cellulose pulp (white pulp) is an alkaline system (using NaOH), and the acetyl groups use up alkali by neutralization while producing sodium acetate that is burned to recover the sodium. The fuel value of sodium acetate is very small, a few pennies per pound while the acetic acid could have recovered from $0.25 to $0.65 per pound.

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Table 3.2.

69

Major components of hemicelluloses and extractives. Distribution (wt%) Type

Hemicelluloses Galactoglucomannan (1:1:3)

G−M−M−M−G−M−M−M → | | | | Ga Ac Ac Ga

(Galacto) glucomannan (0.1:1:4) Glucomannan (1:2–1:1) Arabinoglucuronoxylan

Glucuronoxylan Extractives Aliphatic and alicyclic Phenolics Carbohydrates Inorganics Others

G−M−M−G−M →
 X −X −X−X−[X]5 → | | Gu 2 A
 X− X− X −[X] → | | Ac 7 Gu

Softwoods

Hardwoods

25–30

25–35

5–8

0

10–15

0

0

2–5

7–10

Trace

Trace

15–30

5–8 2–4 Terpenes: terpenoids, esters, fatty acids, alcohols Phenols: stilbenes, lignans, isoflavones Arabinose, galactose, glucose, xylose, raffinose, starch, pectic material Ca, K, Mg, Na, Fe, SO4 2− , Cl− Cyclitols, tropolones, amino acids, protein, alkaloids

Ash

0.2–0.5

0.2–0.8

G, glucose unit; Ga, galactose unit; M, mannose unit; X, xylose unit; A, arabinose unit; Ac, acetyl group (H3 C-CO-); and Gu, 4-O-methyl-glucuronic acid unit; all the linkages shown in the table are through –O–.

Discussion of the wood components will begin with hemicelluloses as they represent a significantly underutilized component of wood, which are most frequently lost during current chemical conversion processes used to purify cellulose, most commonly the Kraft pulping process followed by a bleaching sequence. These hemicelluloses will likely become targeted for enhancement in future growing systems, as their sugar complement will eventually be equal in value to glucose and their easier disassembly and high value substituents recommend increasing their content in the raw material.

3.6.1

Hemicellulosic Products

Hemicelluloses are heteropolymers of 5- and 6-carbon sugars with side chains. Table 3.2 shows major hemicellulose constituents together with wood biomass extractives. If one considers cellulose as a one-dimensional polymer, most hemicelluloses are two-dimensional polymers. Hemicellulose oligomers can be partially extracted from hardwood chips through solution in water at high temperatures (Amidon et al., 2008; Liu and Amidon, 2007; Liu et al., 2006), and xylose or hemicellulose sugars can be fermented to ethanol by microorganisms (Jeffries and Jin, 2004; Liu and Amidon, 2007; Qureshi et al., 2006). Hemicellulosic sugars may also be used as building blocks for biodegradable plastics (Keenan et al., 2004) or other products and chemicals that are currently made from petroleum (Liu et al., 2006). The residual woodchips can be processed into pulp to make paper, burned for renewable energy, or converted to

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γ

CH2OH

CH2OH

CH2OH

β

α 1

2

6

3

5 4

OCH3

OH a. trans-Coniferyl alcohol

OCH3

H3CO OH

b. trans-Sinapyl alcohol

OH c. trans-p-Coumaryl alcohol

Figure 3.4. The precursors of lignin (Al´en, 2000).

reconstituted wood products such as fiberboard or pellets (Amidon, 2006; Amidon and Liu, 2009). This process would add additional products to the current paper and wood energy business starting an evolution towards wood-based biorefineries (Myerly et al., 1981). Making pulp and/or paper products from cellulose remains attractive today due to cellulose having a higher value as pulp than as sugar. However, the pulp and paper industry in the United States and Canada has actually been declining steadily in recent years as production shifts to higher growth areas such as China and Brazil. Further conversion of cellulose into sugars and/or other chemicals/liquid fuel is highly desirable because of higher future demand. A purpose-built biorefinery will include all these process alternatives, though adaptations of current processing locations may not include all alternatives. Lignin is a heteropolymer composed primarily of methoxylated phenylpropylene alcohol monomeric units interconnected by a variety of stable carbon–carbon and carbon–oxygen–carbon (ethers and esters) linkages (Dence and Lin, 1992). Structurally, lignin is a three-dimensional macromolecule. While the lignin of gymnosperms (also called softwoods, conifers, needle trees, or evergreens) is primarily an enzyme-initiated dehydrogenative polymerization product of coniferyl alcohol (Fengel and Wegener, 1984), the lignin of angiosperms (also hardwoods, deciduous or broad-leaved trees, grasses, etc.) is derived primarily from a mixture of coniferyl and sinapyl alcohols. Figure 3.4 shows the three cinnamyl alcohols, lignin precursors. The oxygen to carbon ratio in the lignin precursors (Figure 3.4) is less than 4/11. One can infer that lignin is much less oxygenated than carbohydrates, where approximately each carbon atom is accompanied by one oxygen atom. Therefore, lignin has the highest heating value in woody biomass. Lignin aromatic structure also provides excellent functional chemical sources, e.g., aromatic monomers. Lignin phenylpropane units, guaiacyl (G) and syringyl (S) derived from coniferyl and sinapyl alcohol, respectively, are linked together by different bonds (Figure 3.5) (Pu et al., 2007). The β-O-4 inter-unit linkages are the most abundant in lignin, estimated to be as high as 50% in softwoods and almost 60% in hardwoods. In general, more than two-thirds of the phenylpropane units are linked by ether bonds and the rest by carbon–carbon bonds. Depending on the hardwood species, GS-lignin as a copolymer of coniferyl and synapyl alcohols varies in the G/S ratio from 4:1 to 1:2. G-lignin occurring in almost all softwood is largely a polymerization product of coniferyl alcohol. Different contribution of p-hydroxycinnamyl alcohols in the biosynthesis of hardwood and softwood lignins causes significant differences in their structure, including the contents of different types of bonds and main functional groups (for example, methoxyl (OMe), phenolic hydroxyl (PhOH), aliphatic hydroxyl, carbonyl, and carboxyl groups). Softwood lignin is more condensed than hardwood lignin due to the difference in substitution of the lignin

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C C O

C

C

C

C

C

C O

C

C O

C

O

O

C

C O

O

O β-O-4

C

α-O-4

71

O

β-1

dibenzodioxocin

C C

C C

O

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C C

O O

O β-5

O β-β

O

O 5-5

O 4-O-5

Figure 3.5. Common linkages between phenylpropane units in lignin (Pu et al., 2007).

precursors; substituted C3 and unsubstituted C5 in coniferyl alcohol versus substituted C3 and C5 in synapyl alcohol. Significant differences observed between hardwood and softwood lignin structures lead to different physical and chemical properties of these two lignin types (Argyropoulos and Menachem, 1997).

3.6.2

Biorefineries Using Woody Biomass

Current technologies for the chemical utilization of wood use a “destructive strategy” to obtain a single, relatively pure, component (cellulose). Other fractions are either wasted or used for power generation that gives a low added-value. The “biorefining” philosophy provides an alternative approach for utilization of lignocellulosic biomass. Lignocellulosic biomass can be “fractionated” into its main components by sequential treatments to give separate streams used for different product applications, maximizing the benefits of a renewable and complex resource by preserving as much of the value inherent in its original structures as possible. Wide applications of the carbohydrate oligomer streams exist. For example, xylooligomers are currently used as novel sweeteners in food additives (Aoyama, 1996; Ichikawa and Mitsumura, 1996). Health applications of indigestible oligosaccharides have been recently reported: for example, Imaizumi et al. (1991) found that a xylooligosaccharide-based diet reduced the blood concentrations of sugars and lipids on diabetic rats, and Toyoda et al. (1993) reported that xylooligosaccharides improved calcium absorption by rats. The phagocytic activity of neutrophils in mice was enhanced by either oral or intraperitoneal administration

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of xylooligosaccharides (Aoyama, 1996); increased resistance of mice towards infection by Clostridium difficile caused by xylo- and fructo-oligosaccharides was reported by May et al. (1995). Improvements in the gastrointestinal health of rats caused by a xylooligosaccharidecontaining diet have been reported by Campbell et al. (1997). In relation to human health, xylooligosaccharides selectively enhance the growth of bifidobacteria, thus promoting a favorable intestinal environment (Okazaki et al., 1990; 1991). Sequential incremental deconstruction of wood into cellulosic, hemicellulosic, and ligninbased streams holds significant promise for industrial development. Each of these streams can be further processed to yield valuable products in a biorefinery setting. Papermaking pulps can be produced from the cellulosic components, biofuels including ethanol and bioplastics produced by fermentation from the hemicellulosic and cellulosic streams, and other chemical components from lignin. We address the fundamental challenges of biomass conversion to both conventional products—materials, chemicals and energy—and unconventional (new) ones not currently used in our daily life. In cellulose fibers, cellulose molecules fit together snugly lengthwise via hydrogen bonding. In conversion of woody biomass to chemicals, materials, and energy, systematic incremental deconstruction can lead to energy-efficient synthesis of revolutionary new forms of matter with tailored properties. For example, paper today is made of cellulose fibers. If we further split fibers into fibrils and make paper with fibrils, the outcome can be significantly different. Deconstruction of woody biomass one component at a time reduces the chances of forming undesired side products. We can more effectively control the conversion process and make better use of the released products with sufficient scientific knowledge applied. When biomass or a constituent of woody biomass is oxidized, it produces carbon monoxide, carbon dioxide, and water. The composition depends on oxygen availability. Incremental deconstruction of woody biomass requires transformation in a controlled way, far away from equilibrium. For example, partial oxidation of aromatic compounds or lignin to aldehydes requires the oxidation reaction to stop before completion, or equilibrium. Much knowledge is needed to allow the necessary control to develop effective commercial processes. The knowledge developed in the fundamental characterization of biomass and the identification of chemical linkages that make it difficult to convert lignocellulose will positively impact the development of engineered plants specifically tailored for fuel conversion. These engineered plants are envisioned to (1) contain weak links within the cell wall components that make them more amenable to deconstruction, (2) have certain chemical, genetic, and/or environmental triggers that initiate the deconstruction process, and/or (3) have been engineered so that certain structural and cross-linking elements no longer exist. The key to obtaining benefits associated with success is the development of the science underlying biomass disassembly, separation, and conversion processes. This will allow an increase in production and economic utilization of currently underutilized components of woody and agricultural biomass available in the United States. Woody biomass crops such as willow, cottonwood, aspen, alder, and Loblolly Pine could very significantly increase the amount of biomass available for processing when the science is developed that relates the different properties among species to disassembly, separation, and conversion methods. The method of growing the wood, the age of the wood, the height above ground, and the competitive situation of the tree producing the wood all affect the wood chemical, anatomical, and physical traits that affect its value and the preferred use and disassembly method (Amidon, 1975). As new forest-based materials become a larger component of the forest or purpose-grown biomass value, the agricultural and silvicultural systems employed will adapt to enhance the production of other value components or to make the disassembly easier.

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3.6.3

73

Hot-Water Extraction of Hemicellulose

One currently used disassembly procedure that is moving to commercial use is an example to show some of the key concepts. The method is Hot-Water Extraction of Hemicellulose. The key to this hot-water extraction process is to provide a beginning for systematic sequential deconstruction of woody biomass. Fractionation of woody feedstocks into their respective process streams (cellulose, hemicelluloses, lignin, extractives, etc.) is of interest for commercial operations. The elementary processes occurring during the conversion of biomass depended on the rate and extent of treatments that affect the structure and chemical composition of the woody biomass. The use of water as the sole solvent is a strength of this approach. The major constituents of lignocellulosic biomass (cellulose, hemicelluloses and lignin) cannot be simultaneously isolated as polymers. Extraction or prehydrolysis (e.g., Amidon et al., 2008; Conner and Lorenz, 1986; Garrote et al., 1999; 2001; Liu and Wyman, 2005; Overend et al., 1987; Weil et al., 1997) has a wide range of applications, including (Heitz et al., 1991) (1) fractionation or pulping processes, in which there is removal of hemicelluloses with selectivity towards cellulose degradation and splitting the α and β aryl ether bonds of lignin (Lora and Wayman, 1978; Schultz et al., 1984); (2) defibration for fibreboard production, in processes using high pressure steam; and (3) as a pretreatment for the enzymatic hydrolysis of cellulose (Dekker and Wallis, 1983; Grethlein and Converse, 1991). Since xylan is the main component of hardwood and grass hemicelluloses, xylooligomers and xylose are the main products obtained in hydrothermal treatments of this raw material. Sugar-degradation products (such as furfural or hydroxymethylfurfural) and acetic acid (generated from acetyl groups) can also appear in the reaction media. Extraction and subsequent acid hydrolysis are commonly carried out in water media. There are many advantages of using water as the sole solvent. However, harsh reaction conditions, i.e., either high temperature or a combination of high temperature and strong acid, are required and thus limit the processes to large-scale operations for economic success. Enzymatic hydrolysis is a slow process and is still in the process of developments (Gan et al., 2009; Zhang and Lynd, 2003). In reactions involved with woody biomass, either by pulping or extraction/autohydrolysis, a homogeneous model has largely been implicitly applied. For example, the kinetics of the Kraft pulping process is expressed through the following empiricism: −

dL = (ka [OH − ]a + kb [OH − ]b [HS − ]c )L d dt

(3.1)

where L is the concentration of lignin in wood, [OH− ] is the alkali or hydroxyl ion concentration in the cooking liquor, [HS− ] is the hydrosulfide ion concentration in the cooking liquor, and ka and kb are reaction rate constants. Different values of parameters a, b, and c were found for each stage during the delignification process. The transition points between the stages depend on the lignin content and the cooking conditions and are determined empirically by plotting carbohydrate content versus lignin content. There are two imperfections in the simplistic Equation 3.1, first, the rate of reaction is represented simply as rate change of reactant, and second, the mechanism is lost. A direct challenge to this empiricism is the gradual changing of order of reaction as it progresses (Li et al. 2002; Yang and Liu 2005) despite its popularity in dealing with woody biomass. On the basis of the surface reaction theory, Liu (2004; Liu and Wyman, 2005) and Yang and Liu (2005) inserted more fundamental kinetic approaches into developing bleaching and

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pulping reactions involving wood and fibers. This introduction did explain why the orders of reaction in regard to the reactants in the liquid phase change with concentration range. In Yang and Liu (2005), the Kraft pulping kinetics was described by seven steps: (1) transport of hydroxide and hydrosulfide ions from the bulk liquor to the exterior surface of the chip, (2) diffusion of the chemical ions to the interior of the chip, (3) chemisorptions occur on the interior surface, (4) surface reaction between the chemical ions and lignin, (5) desorption of the soluble lignin degradation products, (6) diffusion of the soluble lignin degradation products to the chip exterior, and (7) transport of the soluble lignin degradation products in the bulk liquor. This is appropriate in kinetics of complex materials and reactions. However, the solid phase is not acting as a catalyst. The solid phase contains both reactant and the desired product. Under normal conditions, transport steps 1 and 7 are probably unimportant but the diffusion steps of 2 and 6 may play a significant role unless the effective thickness of the biomass particles is less than the critical thickness, say 2–3 mm (e.g., Hatton and Keays, 1973; Wilder and Daleski, 1965). Under 2–3 mm thickness conditions, these transport steps are negligible in effect on the overall observed pulping rate. The chemical reactions involved are said to be the rate-controlling steps, which means the overall reaction rate is dependent on steps of 3–5 directly, provided that the wood chips with the thickness of 4 mm or less are cooked. In many cases, our interests are on the intrinsic kinetics, i.e., steps 3–5, only. For the aqueous hydrolysis of woody biomass catalyzed by acid, the underlying principles of chemical kinetics are similar. However, the reactive sites are known not to be at the end of the molecular chain. The hydronium ion needs to access the O at β-1→4, forming the H. + .. complex as the first step towards the dissolution–hydrolysis reaction. Therefore, swelling −O− of the biomass matrix to expose the β-O-(1,4) linkage to the surface or solid–liquid interface is highly desirable. While the true mechanistic steps of the hydrolysis reactions catalyzed by acid can be very complex, we use a simplistic preliminary model to describe the behavior:

R1 − O − R 2 + H

H+ • R1 − O − R 2

+

H+ • + H2O R1 − O − R 2

H+

H

R1 − O

O

H

H+

H

R1 − O

O

(3.2)

H (3.3)

R2

R 1OH + R 2OH • H +

(3.4)

R2

R2 OH•H +

R 2 OH + H +

(3.5)

In the above model, Equations 3.2–3.5, the hydronium ion (H+ ) is a catalyst. Reactions 3.2 and 3.3 can be considered as adsorption steps, while reaction 3.5 is a desorption step.

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R1 and R2 can be carbohydrate groups, acetyl group, or methoxyl group. If the ROH is a small enough molecule, it effectively dissolves in the solvent (water) and becomes part of the solution. Reaction 3.4 is a hydrolysis reaction. Therefore, this hydrolysis reaction is the key reaction in the woody biomass conversion in aqueous medium. After the carbohydrates dissolve in the water, the hydrolysis reaction continues. The kinetics can be again represented by reactions 3.2–3.5). The only difference is that in the “extraction” stage, the carbohydrates are in the solid phase, whereas the carbohydrates are in the liquid phase during hydrolysis or “post-hydrolysis.” The hydrolysis ends when all the carbohydrates are converted to monosaccharides. In an acid medium, carbohydrate monomers (xylose and glucose, for example) can be dehydrated and thus form undesired products if the sugars are the desired products. The most common dehydration products are hydroxylmethylfufural (HMF, from 6-carbon sugars) and furfural (from 5-carbon sugars). Many more products can form from furfural and HMF, including levulinic acid, succinic acid, etc. Furfural, HMF, and organic acids, such as acetic acid, are potent inhibitors of the subsequent fermentation processes for biofuels. In order to control the conversion process, we must understand the chemical reactions occurring in the process. Therefore, kinetic studies are essential in the commercialization of the biomass conversions. The solid residue after complete hydrolysis can be recovered by filtration (number 3 porosity glass filter) and considered to be Klason lignin. The monosaccharides, acetic acid, and other compounds contained in the hot-water extract liquor can be determined by 1 H NMR spectroscopy (Kiemle et al., 2004). Wood extracts and hydrolyzate have been characterized by 1 H NMR extensively using the method developed at ESF (e.g., Kiemle et al., 2004). While the NMR analysis is reliable when the compositions are predominantly monomers and dilute, it does present challenges to complex mixtures. These challenges have made any research program more interesting. Figure 3.6 shows a 2D HSQC NMR (Two Dimensional Heteronuclear Single Quantum Correlation Nuclear Magnetic Resonance) spectrum we have been able to obtain on a wood extract sample. On the top, it is shown a 1 H NMR spectrum. One can observe the challenge of distinguishing the different molecules as shown inside the box by this top curve. Analytical technique development will continue, as knowledge of the complex mixture is needed for fundamental understanding that can lead to expanded commercial efforts.

3.6.4

Wood Extracts: Processing and Conversion

The conversion of woody biomass to platform chemicals, materials and energy can be achieved via two main routes: biochemical and thermochemical, with some overlap. A biochemical route has been the focus of this description. When dealing with cellulose and hemicellulose utilization, water as the solvent holds advantages over all other choices because of environmental and product recovery advantages. However, ionic liquids as solvents are also showing promise and may become major methods in the future. Recent work has shown that a cellulose solubility of up to 30 wt% can be achieved in ionic liquid solvents (Heinze et al., 2005). Ionic liquids in combination with acidic catalysts could also be used to promote the hydrolytic deconstruction of cellulose and hemicelluloses to five- and six-carbon sugars (Zhao et al., 2007). Many scientific strides are needed to push the utilization opportunities enough to enable biorefinery commercialization.

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ppm 92 GluN Glu Gal GluA Ara Xyl

94 GluN Rha

96

Man

Man Rha

Glu

Gal

GluA

98 Ara 100

Xyl

Oligomers

β-Region

13C

102 104

α-Region Oligomers

106 108

5.6

5.5

5.4

5.3

5.2

5.1

5.0

4.9

4.8

4.7

4.6

4.5

4.4

4.3

ppm

1H

Figure 3.6. 2D HSQC NMR spectrum for a concentrated wood extract sample. Credit Dr. B. Bujanovic, SUNYESF.

Fractionation and Concentration of Wood Extracts Microfiltration of extracts is conducted to separate colloidal and particulate material in the extract. Following microfiltration, separation processes are applied for the removal of acetic acid and other small molecules from the wood hydrolyzates, leaving purified sugar streams for fermentation. These processes include nano and reverse osmosis membranes and adsorptive membrane systems. Hot-Water Wood Extract Hydrolysis One method of hydrolysis of hot-water wood extract is to add xylanase to reduce oligomeric xylose to monomers. This will not hydrolyze non-xylan/xylose-derived oligomers and can take a long time. A second hydrolysis method of hydrolysis of hot-water wood extracts in aqueous media is to use mineral acid(s). Challenges remain on the enzymatic xylan hydrolysis due to the complex mixture generated during the hot-water extraction process. Microorganism adaption/evolution is being carried out to meet the challenges. Kinetic studies of the hydrolysis have focused on the molecular level mechanistic evaluations, coupled with computational modeling (Liu, 2008). The ability to control, separate, and analyze the low molecular weight polysaccharides is of great importance. Both proton and carbon NMR can be combined (i.e., 2D NMR) to identify and characterize the polysaccharides.

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P

Permeate holding tank

Feed and concentrate tank

Figure 3.7. Schematic of the Nano Filtration unit setup. Multiple passes are required for obtaining the substrate for ethanol and PHA fermentation: sugars and levulinic acid stream from the wood hydrolyzate.

Hydrolysate Fractionation and Sugar Stream Purification One critical problem in fermenting wood extracts is the toxicity of various lignin-derived components and phenolics to the microorganisms. Furthermore, small molecules such as acetic acid, furfural, and 2-hydroxy methyl-furfural are potent inhibitors affecting the commercial viability of a biorefinery processes. The success of manufacturing bioproducts is dependent upon reliable and efficient means to separate and purify these wood extract liquors to render them easily fermentable, while recovering additional products. Selective removal of various toxic compounds such as acetic acid, furfural, and other aromatics prior to fermentation is necessary. Development of a comprehensive database for the selection, design, and optimization of separation and purification processes for the extracts is ongoing. The ability to co-flocculate, adsorb, and recover inhibitory compounds is also a developing technology. The dispersed phases can then be separated by (1) sedimentation, (2) centrifugation, (3) dead-end (cake) filtration, and (4) cross flow filtration. Parameters for scale-up of these separation operations such as the specific filtration resistance, permeability, and compressibility of the sediments or dispersed phases are still being developed. For the membrane separation/purification processes, flux–transmembrane pressure maps to identify optimal operating conditions have been obtained. A schematic of the membrane unit is shown in Figure 3.7. The objective of using the membrane is to eliminate the commonly referred to detoxification steps in most cellulosic ethanol process. This is a unique approach at SUNY ESF (Liu, 2008; Amidon et al. 2008). Product recovery is promoted over the generation of a waste stream by detoxification procedures.

Hot-water Wood Hydrolysate Fractionation and Ethanol and PHA Fermentations The sugars solutions, after membrane separation as described above, have been found to be directly usable by Burkholderia cepacia, E. coli fbr5, and Pichia stipitis to convert the separated sugars to PHA and ethanol.

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Plant Biomass Conversion

Residual Solid Wood Biomass: Processing and Conversion of the wood mass after extraction, an example

Pulping Cellulose fiber currently enjoys extensive utilization by the paper industry. One of the most surprising results from recent research is the observation that when hot-water extraction is used to extract ∼15% of the chip mass or more prior to pulping, the cooking time in the Kraft process can be decreased from 120 minutes to