Organic chemistry of coal

Organic Chemistry of Coal John W. Larsen, EDITOR Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.fw001 Uni...

Author: John W. Larsen

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Organic Chemistry of Coal John W. Larsen,

EDITOR

Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.fw001

University of Tennessee

A symposium sponsored by the Division of Fuel Chemistry at the 174th Meeting of the American Chemical Society, Chicago, Illinois, August 29— September 1, 1977.

ACS

SYMPOSIUM

SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C. 1978

In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

71


Library of Congress CIP Data Main entry under title: Organic chemistry of coal. (ACS symposium series; 71 ISSN 0097-6156) Includes bibliographies and index. 1. Coal—Analysis—Congresses. I. Larsen, John W . , 1940. II. American Chemical Society. Division of Fuel Chemistry. III. Series: American Chemical Society. ACS symposium series; 71. TP325.0685 ISBN 0-8412-0427-6

662'.622 ASCMC8

78-8114 71 1-327 1978

Copyright © 1978 American Chemical Society A l l Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATES OF AMERICA


ACS Symposium Series


Robert F. Gould, Editor

Advisory Board Kenneth B. Bischoff

Nina I. McClelland

Donald G. Crosby

John B. Pfeiffer

Jeremiah P. Freeman

Joseph V. Rodricks

E. Desmond Goddard

F. Sherwood Rowland

Jack Halpern

Alan C. Sartorelli

Robert A. Hofstader

Raymond B. Seymour

James P. Lodge

Roy L. Whistler

John L. Margrave

Aaron Wold



FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974

to provide

a medium for publishing symposia quickly in book form. The format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.


Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.pr001

PREFACE X T 7 i t h the Arab oil embargo the American political structure became * * aware that oil and gas resources are finite and that ours would not suffice to fuel our economy. This has led to the current, awkward attempts to develop a rational, long-term energy policy for the United States. Since coal constitutes more than 90 percent of American fossil fuels which can be used with current technology, a natural result of governmental attention has been the flow of money into chemical research on coal. This area had been badly neglected since the last time the government was worried about oil supplies. Previous government commitments to coal research have not been sufficiently long lived to allow the development of satisfactory coal conversion technologies. There is hope that the current commitment to coal research will last long enough to allow both an increase in our knowledge of coal chemistry and the application of this knowledge to improve old processes and to develop new ones. The new money for coal research has attracted some new people; various corporations have increased their activities in the area; and some individuals have discovered that the organic chemistry of coal is a fascinating research area. Thus, there has been a great increase in activity and much of it is now resulting in significant increases in our understanding. In each of the past several years there has been a meeting dedicated to the organic chemistry of coal. The papers in this volume were given at the 1977 meeting. Unfortunately, time limitations prevented the presentation of several excellent papers. Coals are extraordinarily complex, insoluble organic mixtures. Complete elucidation of their structures has remained beyond the capabilities of the organic chemist and his instruments. However, the increased attention has begun to give results. Comparison of the proceedings of our annual coal chemistry meetings ( University of Tennessee, 1975; Stanford Research Institute, 1976; this book, 1977) and conversations with workers active in the field will show that we are now just entering the rapid growth region of an exponential curve. We remain a long way from good structural models for coals and from a reasonable understanding of their chemistry, but the quality and quantity of work now being done is such that we will probably find answers to some of the fundamental questions in time to be of some aid to the development of conversion and cleaning processes. vii In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

But even without this practical goal, the problem of the structure and reactivity of this extraordinary complex material is worth solving simply because it is so complex and challenging. JOHN W. LARSEN

University of Tennessee

Knoxville, Tennessee

Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.pr001

February, 1978

viii In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1 A Primer on the Chemistry and Constitution of Coal D.D.WHITEHURST

Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.ch001

Mobil Research and Development Corp., P.O. Box 125, Princeton, NJ 08540

The purpose of this paper i s to review what i s known about the structure of coal and show how this information relates to the ultimate conversion of coal to conventional liquid fuels. Let us f i r s t consider some common beliefs about coal, as shown below: • • • • • •

Coal is highly aromatic. Its structure contains predominantly condensed polycyclic aromatic rings. The high degree of condensation makes coal d i f f i c u l t to liquify. Extreme pressures and temperatures are required for coal conversion. Organic sulfur is much more d i f f i c u l t to remove than organic oxygen. Liquefaction requires high hydrogen consumption.

By the end of this paper I hope to have shown that all of these statements are wrong. To initiate this discussion, I propose to present three aspects of coal and coal product structure. These include, aromaticity, functionality, and molecular weight. I w i l l then discuss reactivity of coal in non-catalytic hydrogenative processes and f i n a l l y , how structure and reactivity interrelate. Concerning the structure of coal, I would f i r s t like to say a few words about the origin of coal. It is generally agreed that coal originates primarily from plants. Through a series of evolutionary changes the primary products of the original decomposed plant matter becomes transformed through a series of steps in which the f i r s t product is humic acid. The humic acid 0-8412-0427-6/78/47-071-001$10.00/0 ©

1978 American Chemical Society


ORGANIC CHEMISTRY OF COAL


2

i s then transformed s e q u e n t i a l l y i n t o peat, l i g n i t e , subbituminous c o a l , b i t u m i n o u s c o a l , and f i n a l l y t o a n t h r a c i t e as shown i n F i g u r e 1. With t h e s e t r a n s f o r m a t i o n s , the c a r b o n c o n t e n t i n c r e a s e s and the oxygen content decreases. The r e s u l t i s t h a t the c a l o r i f i c v a l u e o f the c o a l i n c r e a s e s w i t h rank. A l s o shown i n F i g u r e 1, i s the f a c t t h a t c o a l as we know i t today, can be i d e n t i f i e d as composed o f a s e r i e s o f macérais, o r f o s s i l i z e d p l a n t fragments. These f o s s i l i z e d p l a n t fragments are r e l a t e d t o the o r i g i n a l p l a n t m a t t e r from which t h e y are d e r i v e d . The c o n s t i t u e n t s o f p l a n t s which c o u l d p o s s i b l y g i v e r i s e t o c o a l and commonly a s s o c i a t e d s t r u c t u r e s are shown i n F i g u r e 2. The s t r u c t u r e s t h a t we f i n d i n c o a l , o r c o a l l i q u i d s , must be t h o s e r e l a t e d t o the most s t a b l e o f the s t r u c t u r e s from the o r i g i n a l p l a n t fragments. There are two s c h o o l s o f thought on the major c o n s t i t u e n t o f c o a l . United States c o a l s c o n s i s t of p r i m a r i l y v i t r i n i t e , u s u a l l y 80% o r more. The c o m p o s i t i o n o f t h i s v i t r i n i t e i s b e l i e v e d t o be the r e s u l t o f the c o a l i f i c a t i o n o f e i t h e r c e l l u l o s e or l i g n i n s t r u c t u r e s , which c o n s t i t u t e the m a j o r i t y o f the p l a n t components (jL) . I t has been shown by G i v e n and o t h e r s , however, t h a t c e l l u l o s e undergoes v e r y r a p i d biodégradation i n p l a n t s which are decomposing t o d a y (2). The same i s t r u e f o r p r o t e i n . P l a n t c o n s t i t u e n t s which are most r e s i s t a n t t o b a c t e r i a l a t t a c k are t h o s e o f waxes, r e s i n s , t a n n i n s , l i g n i n s , f l a v o n o i d s , and p o s s i b l y a l k a l o i d s (_3) . A l t h o u g h the p r e v i o u s l y d i s c u s s e d s t r u c t u r e s are p r e s e n t i n p l a n t s today, and c o u l d be s i m i l a r t o t h o s e o f p l a n t s o f p r e h i s t o r i c t i m e s , i t i s not a n t i c i p a t e d t h a t the s t r u c t u r e s would s u r v i v e i n t a c t o v e r the l o n g p e r i o d s o f time r e q u i r e d f o r t h e i r t r a n s f o r m a t i o n t o coal. Some o f the s t r u c t u r a l f e a t u r e s however may p o s s i b l y be r e c o g n i z a b l e even i n t o d a y ' s c o a l . I t has r e c e n t l y been shown by G i v e n t h a t c e r t a i n components o f c o a l can be r e l a t e d t o s t r u c t u r e s e v o l v e d from l i g n i n s (4). I t s h o u l d a l s o be remembered t h a t the U.S. coals were l a y e d down i n two d i f f e r e n t g e o l o g i c a l ages; about 160 m i l l i o n y e a r s a p a r t , and the s t r u c t u r e s a s s o c i a t e d w i t h two g e o l o g i c a l ages may be s u b s t a n t i a l l y d i f f e r e n t . Aromaticity

of

Coal

T h e r e i s c o n t r o v e r s y on the p r o p o s e d p r i m a r y b a c k bone s t r u c t u r e o f c o a l . Some workers c o n t e n d t h a t c o a l i s p r i m a r i l y g r a p h i t e - l i k e , o t h e r s argue t h a t c o a l i s of a diamond-like s t r u c t u r e .


1.

wmTEHURST

Chemistry and Constitution of Coal

ORIGINAL PLANT

MATERIAL

3

COAL M A C E R A L (VISUAL

RESINOUS

MATERIAL


CUTICLES, SPORES CELLWALLS,RES1NS

PLANT

MICROSCOPY)

EXINiTc RESIN1TE

N

FRAGMENTS

WOOD, CORK SPORES,?OLLEN

V i T R I N l T E j 6 SUBSTANCES CARBONIZATION

FUSINITE M1CRONITE

RANK % C % 0

Ρ E A T — ^ L ! G Ν I T E — * 5 U S B I T U MI N O U S — * B I T U M I N O U S — * A N T H R A C I T E HIGH M E D . L O W CBA 60 70 80 93 35

CALORIFIC 12000 VALUE Bru/^-fnaf)

25 13000

Figure 1.

15 14000

3 16000

15500

Mode of formation of coal


4


C-OH

Cellulose

\

*

OH

C-OH /h

Protein

c-s-s-c-ç-cC^.ô

3

NH

f*o

COJ

2

OH

c,

Waxes

(C, -C ) 7

26

XOOR

Resins Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.ch001

(C -C32>

3I

,COOR C-C

Terpenes

COOH

•C-C-C-C-OH HO"

Sterols HO'

Flavonoids

CO"® 0

OH OH

Tannins

^

OH Ο

COO-Sugar

^ O H

OH

OH

OH

OCH

3

Lignins

CHj-OH OH OH COOH

c-c

Alkaloids CH3O.

Figure 2.

Structures of coal precursors



1.

WHITEHURST

5


Graphite

Diamond

B o t h o f t h e s e s t r u c t u r e s a r e low i n H/C r a t i o which i s consistant with the composition o f c o a l s . To g a i n i n s i g h t on t h e s t r u c t u r e o f c o a l , p a s t workers have attempted t o b r e a k c o a l down i n t o r e c o g n i z a b l e u n i t s and t h e n p i e c e them back t o g e t h e r as i s done i n n a t u r a l p r o d u c t c h e m i s t r y today. The most common t e c h n i q u e p r e s e n t l y p u r s u e d i s t h a t o f o x i d a t i v e degradation. W i t h o x i d a n t s such as HNO3, K2Cr207/HN03, KMNO4/OH"-, BuOOH/AIBN, o r p e r a c e t i c a c i d , workers have come t o t h e c o n c l u s i o n t h a t c o a l i s p r e d o m i n a t e l y a r o m a t i c and c o n t a i n s many condensed r i n g s (J5,6) . Other a u t h o r s u s i n g NaOCl/OH" have come t o a d i f f e r e n t conc l u s i o n , i n that they b e l i e v e c o a l contains large amounts o f q u a r t e r n a r y a l i p h a t i c carbon, o r i s diamonl i k e i n s t r u c t u r e and c o n t a i n s 50% a r o m a t i c c a r b o n o r l e s s (_7) . The p r e c e e d i n g methods o f o x i d a t i o n s e l e c t i v e l y oxidize only the a l i p h a t i c p o r t i o n of c o a l . A new method p i o n e e r e d b y Dieno u s e s t r i f l u o r o a c e t i c a c i d s i n c o m b i n a t i o n w i t h hydrogen p e r o x i d e . T h i s method s e l e c t i v e l y o x i d i z e s the aromatic r i n g s . Combination o f t h e s e two t e c h n i q u e s c o u l d be a v e r y p o w e r f u l i n s t r u c t u r a l c h a r a c t e r i z a t i o n o f c o a l (8) . Because o f t h e d i f f i c u l t y o f p i e c i n g back t o g e t h e r t h e fragmented p r o d u c t s o f c o a l , a number o f workers have attempted t o do d i r e c t c h a r a c t e r i z a t i o n o f coal. D i r e c t t e c h n i q u e s s u f f e r from t h e problem t h a t c o a l i s an opaque s o l i d which i s i n s o l u b l e i n i t s n a t u r a l form and r e l a t i v e l y few t o o l s have been a v a i l a b l e up u n t i l t h e p r e s e n t time f o r such d i r e c t measurements. I n t h e p a s t , t e c h n i q u e s such as X - r a y s c a t t e r i n g have



6


been u s e d and c o n f l i c t i n g i n t e r p r e t a t i o n s as t o t h e predominant s t r u c t u r e o f c o a l have been r e p o r t e d . H i r s c h f i r s t r e p o r t e d t h a t c o a l was from 50-80% aromat i c , w i t h p r i m a r i l y 89% o r d e r e d s t r u c t u r e (9). Ergun l a t e r , using X-ray s c a t t e r i n g , concluded that c o a l i s l e s s a r o m a t i c and c o n t a i n s l a r g e q u a n t i t i e s o f amorphous r e g i o n s (10). F r i e d e l using u l t r a v i o l e t techn i q u e s c o n c l u d e d t h a t c o a l c o u l d not be p o l y a r o m a t i c and c o n t a i n e d l a r g e amounts o f a l i p h a t i c s t r u c t u r e (11). Given^ i n c h a r a c t e r i z i n g c o a l e x t r a c t s by polarographic r e d u c t i o n c o n c l u d e d t h a t low rank c o a l s were g r e a t e r than 20% a r o m a t i c and h i g h rank c o a l s were g r e a t e r than 50% a r o m a t i c (12)· P o l y c y c l i c a r o m a t i c r i n g s were bel i e v e d t o be p r e v a l e n t . R e c e n t l y , new t o o l s have e v o l v e d and f o r the f i r s t time c o a l can be c h a r a c t e r i z e d d i r e c t l y i n i t s n a t u r a l form. The most p r o m i s i n g o f t h e s e t o o l s i s a s o l i d s t a t e CP-C^ n m r d e v e l o p ed by P i n e s (JL3) . Working i n c o n j u n c t i o n w i t h P r o f e s s o r P i n e s , we have found t h a t t h e r e i s r e l a t i v e l y l i t t l e c o r r e l a t i o n between the hydrogen c a r b o n mole r a t i o and the p e r c e n t a r o m a t i c c a r b o n found i n c o a l or c o a l l i q u i d s , as shown i n F i g u r e 3. These d a t a g i v e some i n d i c a t i o n as t o why t h e r e has been so much d i f f i c u l t y i n the p a s t c o r r e l a t i n g a r o m a t i c c a r b o n c o n t e n t w i t h the e l e m e n t a l compos i t i o n o f the c o a l . T h e r e is,however, some c o r r e l a t i o n between the rank o f t h e c o a l and i t s a r o m a t i c i t y . This i s shown i n F i g u r e 4. I t can be seen t h a t the a r o m a t i c c a r b o n c o n t e n t i n c r e a s e s from about 40-50% f o r subb i t u m i n o u s c o a l t o over 90% f o r a n t h r a c i t e . I t w i l l be shown l a t e r t h a t t h i s a r o m a t i c i t y changes w i t h c o n v e r s i o n o f the c o a l under l i q u e f a c t i o n c o n d i t i o n s . The CP-C13 t e c h n i q u e i s somewhat new and s t i l l e v o l v i n g . I t does show p r o m i s e , however, i n c h a r a c t e r i z a t i o n o f c o a l i n t o a l i p h a t i c and a r o m a t i c components, but i n a d d i t i o n , h o l d s p r o m i s e f o r f u r t h e r s u b - d i v i s i o n o f the s t r u c t u r a l types. As shown i n F i g u r e 5, i t i s p o s s i b l e t o d i s t i n g u i s h i n model compounds, a r o m a t i c , a l i p h a t i c , a l i p h a t i c e t h e r , and condensed a r o m a t i c c a r b o n . We hope e v e n t u a l l y t o use t h e s e same s u b - d i v i s i o n s i n the c h a r a c t e r i z a t i o n of c o a l . As r e p r e s e n t a t i v e examples o f the s p e c t r a t h a t one can a c h i e v e , F i g u r e 5 shows t y p i c a l model compounds, the p a r e n t c o a l , SRC derived from a c o a l , u n c o n v e r t e d r e s i d u e and the s p h e r i c a l coke formed on extended t h e r m a l r e a c t i o n (14). 3

F u n c t i o n a l i t y of

Coal

F i g u r e 6 shows the major f u n c t i o n a l group t y p e s identified in coal. Oxygen o c c u r s p r e d o m i n a t e l y as




WHiTEHURST

1.1

Figure 3.

Aromatic carbon vs. H/C


8



Figure 4.

Aromaticity increase with rank


1.

wmTEHURST



p-Pt«thoxvb«n««n« (391)*

2.3-Dla«thrln«ohth«l«n« (480)

Mcnf rmγ Coal (7300)

Monf rmv SBC (S000) AC-70

M ^ t f f y R««û« (8800) AC-70

Soh«ric»l Cok« (9200)

*The numbers i n p a r e n t h e s e s i n d i c a t e t h e number o f s p e c t r a accumulated t o g e n e r a t e t h e spectrum p r e s e n t e d . Note t h a t t h e s c a l e s a r e n o t a l l the same. Figure 5.

CP- C 13

NMR spectra of representative samples


9


10


p h e n o l i c or e t h e r i c groups w i t h l e s s amounts o f c a r b o x y l i c a c i d s or e s t e r s ; some c a r b o n y l s have a l s o been i d e n t i f i e d . S u l f u r has s i m i l a r c h e m i s t r y t o oxygen and a l t h o u g h s u l f o x i d e s have been i d e n t i f i e d i n t a r sands t h e i r p r e s e n c e i n c o a l i s l e s s w e l l d e f i n e d . N i t r o g e n o c c u r s p r e d o m i n a t e l y as p y r i d i n e o r p y r r o l i c t y p e r i n g s . M e t a l s are found as s a l t s or a s s o c i a t e d with porphyrins. Some r e c e n t work c o n d u c t e d by Ruberto i s summarized i n F i g u r e 7 (15). Shown t h e r e are q u a n t i t a t i v e a n a l y s i s o f the major t y p e s o f f u n c t i o n a l i t y , oxygenated s p e c i e found i n c o a l s and one s o l v e n t r e fined coal. I t can be seen t h a t subbituminous c o a l c o n t a i n s c o n s i d e r a b l y more c a r b o x y l i c a c i d t h a n b i t u minous c o a l s and somewhat more c a r b o n y l . After react i o n under l i q u e f a c t i o n c o n d i t i o n s , the c a r b o x y l i c a c i d s and c a r b o n y l s are almost c o m p l e t e l y absent, and the prédominent p r o d u c t s are p h e n o l i c t y p e oxygen. Our r e s u l t s i n d i c a t e t h a t i n a d d i t i o n t o p h e n o l i c type oxygen, e t h e r i c t y p e oxygen i s a major oxygenated s p e c i e (14). As c o a l i s c o n v e r t e d i n p r e s e n t day p r o c e s s e s , the above d e s c r i b e d f u n c t i o n a l i t y , o f c o u r s e , changes w i t h s e v e r i t y , b u t i n a d d i t i o n the s t r u c t u r e o f the c o a l and i t s e l e m e n t a l c a r b o n t o hydrogen r a t i o must a l s o change. F i g u r e 8 shows a comparison o f the hydrogen t o c a r b o n mole r a t i o f o r c o a l and a number o f o t h e r n a t u r a l p r o d u c t s , i n comparison w i t h t h a t o f p e t r o l e u m and the premium p r o d u c t s t h a t are d e s i r e d from the c o a l . It can be seen t h a t t h e r e i s a v e r y l o n g p a t h n e c e s s a r y i n the c o n v e r s i o n o f c o a l t o premium p r o d u c t s such as g a s o l i n e , s i n c e c o a l s c o n t a i n about .8 hydrogen/carbon. The d e s i r e d p r o d u c t s c o n t a i n about 2. This indicates t h a t i n any c o n v e r s i o n p r o c e s s o f c o a l , one o f the p r i mary g o a l s w i l l be e x t r e m e l y e f f i c i e n t use o f hydrogen. Most p r o c e s s e s p r e s e n t l y u s e d today are i n i t i a l l y t h e r m a l i n n a t u r e s i n c e c a t a l y s t s cannot c o n t a c t the b u l k o f the c o a l m a t r i x . But j u s t where does the t h e r m a l c h e m i s t r y o f c o a l become s i g n i f i c a n t ? F i g u r e 9 shows a s u p e r i m p o s i t i o n o f t h r e e t h e r m a l a n a l y s e s o f coal. These c o n s i s t o f t h e r m a l g r a v i m e t r i c , t h e r m a l m e c h a n i c a l , and d i f f e r e n t i a l t h e r m a l a n a l y s i s o f c o a l . T h i s f i g u r e i n d i c a t e s t h a t c o a l undergoes p r i m a r y dec o m p o s i t i o n i n the range o f 400-450°, a s s o c i a t e d w i t h t h i s temperature range i s the b u l k o f the s w e l l i n g o f the c o a l and s i g n i f i c a n t changes i n the t h e r m a l behavior of c o a l . I t i s not s u r p r i s i n g , t h e r e f o r e , t h a t most o f the p r e s e n t p r o c e s s e s b e i n g d e v e l o p e d today, o p e r a t e i n the range o f 400-450°C. But, a t t h i s temperature j u s t how f a s t does c o a l r e a c t ? We have shown t h a t i n the p r e s e n c e o f hydrogen donors



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I n c o n j u n c t i o n w i t h t h e l o s s o f m o l e c u l a r weight and i n c r e a s e i n a r o m a t i c i t y , the f u n c t i o n a l i t y o f t h e i n i t i a l l y d i s s o l v e d c o a l undergoes major change. Oxygen i s t h e p r i m a r y element o f c o n c e r n as f a r as f u n c t i o n a l i t y and s o l u b i l i t y c l a s s determination. I f one examines t h e e l e m e n t a l c o m p o s i t i o n o f c o a l and p r o d u c t s o f c o a l a t s h o r t and l o n g t i m e s , a r a t h e r i n t e r e s t i n g r e s u l t c a n be found. As shown below f o r e v e r y 100 c a r b o n atoms i n a c o a l , c o n v e r s i o n a t e i t h e r s h o r t o r l o n g time causes e s s e n t i a l l y no change i n t h e c o n t e n t o f n i t r o g e n . The hydrogen c o n t e n t i s s i m i l a r t o t h e p a r e n t c o a l a t s h o r t time, b u t becomes l e s s a t l o n g e r t i m e s . The oxygen c o n t e n t and s u l f u r c o n t e n t s b o t h a r e reduced s l i g h t l y a t s h o r t time b u t a r e s i g n i f i c a n t l y r e d u c e d a t l o n g e r times.

General Monterey C o a l

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C ^ ^ g N ^ g O ^ S j ^

Number Heteroatoms/ 100 C 14.9 12.0 7.5


24



Oxygen i s l o s t p r i m a r i l y as c a r b o n d i o x i d e and water, w i t h s m a l l e r amounts o f c a r b o n monoxide. The r a t e o f oxygen l o s s p a r a l l e l s the r a p i d i n i t i a l d i s s o l u t i o n o f c o a l and r a p i d l o s s o f h i g h m o l e c u l a r weight m a t e r i a l . About 40-50% o f the oxygen i s r e l a t i v e l y easy t o r e move (17). The l o s s o f s u l f u r i s k i n e t i c a l l y p a r a l l e l t o the l o s s o f oxygen as shown i n F i g u r e 17. This might be a n t i c i p a t e d i n view o f the o r i g i n o f the o r g a n i c s u l f u r o f c o a l , which i s b e l i e v e d t o be the r e s u l t o f exchange o f OH o r c a r b o n y l oxygen b y s u l f u r , due t o b i o l o g i c a l a c t i v i t y i n the sediment (20,21). The s i g n i f i c a n c e o f t h i s i s t h a t 40-50% o f the o r g a n i c s u l f u r i s a l s o e a s i l y removed. The r e m a i n i n g s u l f u r i s much more r e s i s t a n t t o a t t a c k and i s p r o b a b l y p r e sent i n h e t e r o c y c l i c r i n g s t r u c t u r e s . Hydrogen Consumption and

Reactive

Moieties

In c o n j u n c t i o n w i t h the l o s s o f oxygen and s u l f u r , as w e l l as m o l e c u l a r weight r e d u c t i o n o f the s o l u b l e c o a l s p e c i e , t h e r e i s hydrogen consumption r e q u i r e d f o r the p r o c e s s . T h i s hydrogen i n t h e c a s e o f s o l v e n t r e f i n i n g i s donated from the s o l v e n t t o the c o a l o r c o a l fragments. I n i t i a l l y , the l o s s o f oxygen r e q u i r e s r e l a t i v e l y l i t t l e hydrogen consumption and i s v e r y c l o s e t o s t o i c h i o m e t r i c r e q u i r e m e n t s (16,17). T h i s i s shown i n F i g u r e 18, where i t can be seen t h a t o n l y a f t e r about 30% o f the oxygen i s l o s t does the hydrogen consumption become g r e a t e r t h a n s t o i c h i o m e t r y . This h y d r o g e n consumption i n e x c e s s o f s t o i c h i o m e t r y i s due p r i m a r i l y t o the f o r m a t i o n o f gaseous p r o d u c t s o r lowe r m o l e c u l a r weight d i s t i l l a t e s such as s o l v e n t and not due t o the i n p u t o f hydrogen i n t o the h i g h e r molecu l a r weight p r o d u c t s o f c o a l . A n o t h e r way t o l o o k a t the c o n v e r s i o n o f oxygen i s t o compare the p r o d u c t c o m p o s i t i o n * o v e r a l l , w i t h the p e r c e n t oxygen removed from the t o t a l p r o d u c t . F i g u r e 19 shows t h a t i n o r d e r t o a c h i e v e maximum s o l u b i l i t y o f the c o a l about 60% o f the oxygen must be lost. A t the same time the SRC y i e l d maximizes. The f o r m a t i o n o f s o l v e n t range m a t e r i a l and l i g h t gases such as methane, t h e n become major p r o d u c t c o n s t i t u e n t s as the oxygen c o n t e n t i s r e d u c e d f u r t h e r . What t h e s e r e s u l t s i n d i c a t e i s t h a t h i g h hydrogen consumpt i o n i s n o t n e c e s s a r y i n o r d e r t o j u s t d i s s o l v e the c o a l o r t o remove a major p o r t i o n o f the oxygen. I n o r d e r t o g a i n an u n d e r s t a n d i n g o f what k i n d s o f r e a c t i o n s can be e n v i s i o n e d t o e x p l a i n the above r e s u l t s , we c o n d u c t e d a s e r i e s o f e x p e r i m e n t s u s i n g model compounds and r e a c t i o n s w i t h t y p i c a l s o l v e n t s


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0.0

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0.6

0.8

MOLES 0 REMOVED

Figure 18.

Hydrogen consumption vs. moles oxygen removed



26


f o r c o a l under c o n d i t i o n s o f c o a l l i q u e f a c t i o n . I n t h e s e s t u d i e s we i d e n t i f i e d a number o f c h e m i c a l c l a s s e s w h i c h c o u l d be c o n v e r t e d a t r a t e s t h a t were comparable t o t h o s e o f r a p i d d i s s o l u t i o n o f c o a l (14). These a r e summarized i n F i g u r e 20, where f a s t r e a c t i o n s a r e t h o s e i n which 80% o r h i g h e r c o n v e r s i o n c a n be a c h i e v e d i n t e n m i n u t e s a t 800°F. I t c a n be seen t h a t b e n z y l i c e t h e r s o r b e n z y l i c t h i o e t h e r s c e r t a i n e s t e r s and q u i n o n e s r e a c t r a p i d l y enough t o account f o r t h e v e r y s h o r t c o n t a c t time c o a l d i s s o l u t i o n . I n a d d i t i o n , r i n g s t r u c t u r e s such as d i h y d r o p h e n a n t h r e n e s w i l l r a p i d l y dehydrogenate under t h e same c o n d i t i o n s . By c o n t r a s t w i t h t h e s e r e l a t i v e l y f a s t r e a c t i o n s we have a l s o i d e n t i f i e d a number o f low r e a c t i v i t y s p e c i e which can be r u l e d o u t as b e i n g r e s p o n s i b l e f o r c o a l d i s s o l u t i o n , t h e s e a r e summarized i n F i g u r e 21. Here i t c a n be seen t h a t s t r u c t u r e s such as a r o m a t i c e t h e r s , o r r i n g s t r u c t u r e d e t h e r s , h e t e r o c y c l i c hydrogen compounds, p o l y c o n d e n s e d r i n g s b o t h a r o m a t i c and a l i p h a t i c , have r e l a t i v e l y low r e a c t i v i t y . I f a r o m a t i c r i n g s a r e subs t i t u t e d o n t o a number o f t h e s e s t r u c t u r e s , t h e r e a c t i v i t y increases dramatically. This increase i n react i v i t y with higher aromatic s u b s t i t u t i o n c o u l d p o s s i b l y account a t l e a s t i n p a r t f o r t h e h i g h e r r e a c t i v i t y o f b i t u m i n o u s c o a l s r e l a t i v e t o subbituminous c o a l s . Speculations

on C o a l

Structure

Up t o t h i s p o i n t , I have d i s c u s s e d p r i m a r i l y t h e c h e m i s t r y o f d i s s o l v e d c o a l and how t h e c h e m i c a l n a t u r e o f t h e c o a l p r o d u c t s change w i t h t h e s e v e r i t y o f c o n version. I t s h o u l d be n o t e d t h a t a t v e r y s h o r t c o n t a c t times the i n i t i a l products o f c o a l d i s s o l u t i o n are very s i m i l a r i n b o t h a r o m a t i c i t y and f u n c t i o n a l i t y t o t h a t of the parent c o a l . I w i l l now d i s c u s s how t h i s i n f o r m a t i o n c a n be used t o h e l p g a i n a b e t t e r u n d e r s t a n d i n g o f t h e o r i g i n a l s t r u c t u r e o f p a r e n t c o a l . A number o f workers have attempted t o d e r i v e a r e p r e s e n t a t i v e s t r u c t u r e o f c o a l which i s c o n s i s t e n t i n i t s o b s e r v e d chemistry. One o f t h e f i r s t was t h a t o f P r o f e s s o r G i v e n , shown i n F i g u r e 22. T h i s s t r u c t u r e was n o t i n t e n d e d t o be t h e s t r u c t u r e f o r c o a l b u t m e r e l y t o r e p r e s e n t what k i n d s o f s t r u c t u r e s one s h o u l d e n v i s i o n as c o n s t i t u t i n g c o a l ( 2 2 ) . The s t r u c t u r e i s c o n s i s t e n t w i t h h i g h l y s u b s t i t u t e d a r o m a t i c s , which a r e n o t h i g h l y condensed, w i t h f u n c t i o n a l i t i e s which a r e known t o be p r e s e n t i n c o a l and w i t h i t s e l e m e n t a l c o m p o s i t i o n . A more r e c e n t , more s o p h i s t i c a t e d model, was p r e s e n t e d b y P r o f e s s o r W i s e r (23) and i s g i v e n i n F i g u r e 23. The s i g n i f i c a n c e o f t h i s f i g u r e i s t h e l o c a t i o n o f a number o f


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Product yields vs. percent oxygen conversion for West Kentucky coal

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n e a r l y imperceptible. V i t r i n i z a t i o n , on the other hand, i n v o l v e s a p r o g r e s s i v e change throughout a l l stages of rank development. The r e l a t i o n s h i p between the g values of the l i t h o t y p e s and c o a l rank (Figures 5 and 6) a l s o supports S c h o p f s t h e o r i e s of v i t r i n i z a t i o n and f u s i n i z a t i o n . The l a r g e g values found f o r the v i t r a i n s from meta-anthracites i s i n accord with the f i n a l step i n v i t r i n i z a t i o n being the f u s i n g of aromatic r i n g s i n t o g r a p h i t e - l i k e s t r u c t u r e s . The g value of each of the v i t r a i n s and f u s a i n s i s higher than that of the f r e e e l e c t r o n and l i e s i n the s p e c t r a l r e g i o n expected f o r simple organic free radicals. The only exceptions are v i t r a i n s from the more h i g h l y metamorphized c o a l s , one of which e x h i b i t e d a g value of 2.011. The f a c t that esr g values of organic f r e e r a d i c a l s are g r e a t e s t f o r r a d i c a l s i n which the unpaired e l e c t r o n i s l o c a l i z e d or p a r t i a l l y l o c a l i z e d on atoms having high s p i n - o r b i t coupling constants can be used to e x p l a i n the g value r e s u l t s for vitrains. Since the heteroatom contents of c o a l s decrease w i t h i n c r e a s i n g rank, the high g values f o r peats and l i g n i t e s can be i n t e r p r e t e d i n terms of aromatic r a d i c a l s with some p a r t i a l l o c a l i z a t i o n of the unpaired e l e c t r o n s on heteroatoms, p a r t i c u l a r l y but not e x c l u s i v e l y oxygen. As c o a l i f i c a t i o n progresses the g values decrease, suggesting that the r a d i c a l s become more "hydrocarbon-like. The g values of many of the v i t r a i n s from bituminous and young a n t h r a c i t i c c o a l s compare f a v o r a b l y with those e x h i b i t e d by aromatic hydrocarbon r a d i c a l s . During the f i n a l stages of c o a l i f i c a t i o n , the g values become q u i t e l a r g e as one would expect i f continued condensat i o n of the aromatic r i n g s i n t o g r a p h i t e s t r u c t u r e s occurs. The o b s e r v a t i o n of a s m a l l , but r e p r o d u c i b l e , anisotropy i n the g value of c e r t a i n a n t h r a c i t e s (Figure 7) suggests that some o r d e r i n g of the polynuclear condensed aromatic r i n g s i s o c c u r r i n g . 11

Coal-Derived Asphaltenes. To b e t t e r understand the chemist r y of c o a l l i q u e f a c t i o n , an esr i n v e s t i g a t i o n of c o a l - d e r i v e d asphaltenes was i n i t i a t e d . P r e l i m i n a r y r e s u l t s are presented here. Of p a r t i c u l a r concern was the temperature v a r i a t i o n of the esr i n t e n s i t i e s of asphaltenes and t h e i r a c i d / n e u t r a l and base components (Figure 8). The most s i g n i f i c a n t f i n d i n g to date i s that the weighted average of the temperature dependencies of the two components reproduces the temperature dependence of the t o t a l asphaltene (before separation) e x c e p t i o n a l l y w e l l . T h i s suggests that charge t r a n s f e r i n t e r a c t i o n s , at l e a s t i n the M u l l i k a n sense, are r e l a t i v e l y unimportant b i n d i n g f o r c e s between the a c i d / n e u t r a l and base components of the asphaltenes.




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162


the s i m i l a r i t y o f the products from the three bituminous c o a l s s u g g e s t t h e f o l l o w i n g mechanism: Hg + hv Hg* + H

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(4)

products

In o t h e r w o r d s , t h e s i m i l a r i t y o f t h e p r o d u c t d i s t r i b u t i o n s f r o m t h e d i f f e r e n t b i t u m i n o u s c o a l s i s p r o p o s e d t o be a r e s u l t o f t h e s i m i l a r i t y o f s e c o n d a r y H atom c r a c k i n g o f t h e p r o d u c t p r e c u r s o r s f r o m r e a c t i o n (3) u n d e r t h e i d e n t i c a l r e a c t o r c o n d i t i o n s , r a t h e r t h a n an i n d i c a t i o n t h a t t h e s e t h r e e c o a l s , w i t h d i f f e r e n t h i s t o r i e s and d i f f e r e n t p h y s i c a l p r o p e r t i e s , have s u r f a c e s t h a t a r e s i m i l a r . A t t h i s p o i n t , t h e o n l y l i k e n e s s i n s u r f a c e t h a t can be i n f e r r e d i s t h e a b i l i t y o f H atoms t o l i b e r a t e t h e h y d r o g é n a t i o n p r e c u r s o r s f r o m t h e s u r f a c e o f I l l i n o i s #6, P i t t s b u r g h Hi-Seam, and Utah-Emery b i t u m i n o u s c o a l s . R e a c t i o n (3) must be s i m i l a r i n r a t e arid r e a c t i o n p r o d u c t s t o a c c o u n t f o r t h e s i m i l a r i t y o f F i g u r e s 2, 3, and 4. K i n e t i c i n f o r m a t i o n a b o u t r e a c t i o n (4) i s a p p e a r i n g (7_, 8) and s h o u l d a i d i n t h e i n t e r p r e t a t i o n o f f u t u r e e x p e r i m e n t s i n v o l v i n g more u n i f o r m c o n c e n t r a t i o n s . F i n a l l y , t h e f a i l u r e o f Wyoming-Wyodak c o a l t o r e a c t u n d e r i d e n t i c a l c o n d i t i o n s must be a t t r i b u t e d t o a s l o w n e s s o f r e a c t i o n (3). A g r e a t e r d i v e r s i t y of products from a sub-bituminous coal m i g h t have been e x p e c t e d s i n c e i t s o r g a n i c s t r u c t u r e s had been s u b j e c t e d t o l e s s s t r i n g e n t c o a l i f i c a t i o n c o n d i t i o n s and i t c o n t a i n s more v o l a t i l e o r g a n i c m a t t e r . S i n c e F i g u r e 5 l o o k s r e m a r k a b l y s i m i l a r to r e s u l t s from experiments e a r l y i n t h i s program u s i n g I l l i n o i s #6 c o a l a t a m b i e n t t e m p e r a t u r e , one m i g h t e x p e c t a g r e a t l y e n h a n c e d ESR s p e c t r u m s u c h as was o b s e r v e d t h e n . That i s , a r e s u l t o f H atom bombardment i s t h e p r o d u c t i o n o f n o n v o l a t i l e f r e e r a d i c a l s . F u r t h e r work i s c l e a r l y w a r r a n t e d . N o n e t h e l e s s , i t has now been d e m o n s t r a t e d t h a t p h o t o - p r o d u c e d H atoms do i n t e r a c t w i t h t h e s u r f a c e o f b i t u m i n o u s c o a l s a t 200°C t o y i e l d C t o C h y d r o c a r b o n s . However, t h e a u t h o r s f e e l t h a t f u r t h e r e x p e r i m e n t s , some a l t e r i n g t h e s t e a d y s t a t e H atom c o n c e n t r a t i o n and a d d i n g s u s p e c t e d p r e c u r s o r s , a r e r e q u i r e d t o e l u c i d a t e t h e mechanisms. A l s o , an a c c u r a t e method f o r d e t e r m i n i n g c o a l p a r t i c l e c o n c e n t r a t i o n s i n t h e p h o t o r e a c t o r needs t o be f o u n d b e f o r e r e l i a b l e r a t e d a t a can be f o r t h c o m i n g . F i n a l l y , o t h e r s u b - b i t u m i n o u s c o a l s need t o be examined t o see i f t h e Wyodak r e s u l t s , r e p r o d u c e d s e v e r a l t i m e s , a r e common t o t h i s r a n k o f c o a l . Whether H atoms w i l l p r o v e an e f f e c t i v e c o a l s u r f a c e 2

8



11.

MAINS ET AL.

Photochemical

TIME

Hydrogen

163

Atoms

(MINUTES)

Figure 4. Gas chromatogram of Η-atom produced gaseous products from Emery-Utah Coal at 185°-200°C. V-OCT/PORACIL C, Va" χ IV column; 60°C; 8% Η in He carrier gas; 25 cc injection loop. 2

>H Lu

Ρ ο *

< o

S LU oc i 40

LU Lu Χ Ω

30

20

10

TIME (MINUTES) Figure 5. Gas chromatogram of Η-atom produced gaseous products from Wyodak-Wyoming Coal at 185°-200°C. η -OCT/PORACIL C, Vs" χ 10' column; 60°C; 8% H in He carrier gas; 25 cc injection loop. 2


164


probe remains to be proven. couraging i n some r e s p e c t s .

These p r e l i m i n a r y r e s u l t s are en

Acknowledgments We wish to thank Dr. Fred Radd, Continental O i l Company, who e n t h u s i a s t i c a l l y encouraged us to begin coal r e s e a r c h , and Mr. Ed O b e r m i l l e r , CONOCO Coal Development, f o r both encouragement and the coal samples. L a s t , but c e r t a i n l y not l e a s t , we thank E . R . D . A . f o r a research grant that supported these experiments. Abstract Hydrogen atoms, produced by the mercury p h o t o s e n s i t i z a t i o n of H , were made to i n t e r a c t with coal d u s t , -53 to +38 microns, at 200°C i n a flow r e a c t o r . Illinois No. 6, P i t t s b u r g h Seam, and Utah-Emery c o a l s produced a l a r g e number o f saturated hydrocarbon products i n the C to C range. Wyoming-Wyodak coal was c o n s i d e r a b l y l e s s r e a c t i v e . The kinetic, q u a n t i t a t i v e , and s t r u c t u r a l i m p l i c a t i o n s o f these r e s u l t s are d i s c u s s e d . Experimentation with d i f f e r e n t r e a c t o r c o n d i t i o n s c o n t i n u e s .


2

2

8

Literature Cited (1) (2) (3) (4) (5) (6) (7) (8)

Avaremko, V. J., J. Phys. Chem. (U.S.S.R.), (1946), 20, 1299. P i n c h i n , F. T., Brit. Coal Util. Res. A s s o c . , Monthly Bulletin, (1965), 29, 105. Sanada, Y., B e r k o w i t z , N., F u e l , (1969), 48, 375. Kobayashi, K., B e r k o w i t z , N., F u e l , (1971), 50, 254. Solomon, J. Α., Mains, G. J., F u e l , (1977), 56, 302. S n e l s o n , Α., A . C . S . D i v . Fuel Chem. P r o c . , (1973), 18, 101. Kim, P., Lee, J., Bonnano, R . , Timmons, R . , J. Chem. P h y s . , (1973), 59, 4593. Amano, Α . , H o r i e , O., Hanh, W., I n t . J. Chem. Kinetics, (1976), 8, 321.

RECEIVED March 13, 1978


12 Isotopic Studies of Thermally Induced Reactions of Coal and Coal-Like Structures CLAIR J. COLLINS, BEN M. BENJAMIN, VERNON F. RAAEN, PAUL H. MAUPIN, and W. H . ROARK (1)


Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, T N 37830

We r e c e n t l y (2) reported that under c o n d i t i o n s o f coal conv e r s i o n (tetralin, 400°) several d i a r y l a l k a n e s undergo carbon-carbon cleavage, and that the scission o f carbon-carbon bonds must t h e r e f o r e be considered as an important process i n asphaltene formation ( 3 ) . We also reported (2) t h a t vitrinite (from Illinois No. 6 c o a l ) was a " b e t t e r hydrogen t r a n s f e r agent" than tetralin itself f o r the hydrogenolysis o f 1 , 1 , 2 - t r i p h e n y l e t h a n e t o diphenylmethane and toluene. We have now extended these s t u d i e s to e s t a b l i s h a) t h a t vitrinite i s indeed a b e t t e r hydrogen donor than tetralin toward several organic s t r u c t u r e s ; b) that tetralin, i n a d d i t i o n t o its f u n c t i o n as a hydrogen donor, can undergo c e r t a i n other r e a c t i o n s w i t h coal and coal-like s t r u c t u r e s which i n v o l v e both carbon-carbon bond formation and bond cleavage. A Comparison o f T etralin an d V itrinite as H-donors When 1 , 2 - d i p h e n y l - 1 - p - t o l y l e t h a n e i s heated a t 400° ( e i t h e r i n g l a s s capillaries or i n s t a i n l e s s s t e e l tubes) w i t h an excess of tetralin, the major products are toluene and phenyl-p-tolylmethane. The same products are obtained when 1 , 2 - d i p h e n y l - l - p t o l y l e t h a n e i s heated a t 400° i n the presence o f an excess o f v i t r i n i t e (handpicked from I l l i n o i s No. 6 c o a l ) . Given i n Table I i s a comparison o f the extent r e a c t i o n - as determined by g . c . a n a l y s i s o f the products - a f t e r various contact times with t e t r a l i n or w i t h v i t r i n i t e . Another d i a r y l a l k a n e which i s e a s i l y decomposed i n the presence o f excess t e t r a l i n o r excess v i t r i n i t e i s 1,3-diphenylpropane. The major products i n both cases are toluene and e t h y l benzene, although a m u l t i p l i c i t y o f minor products are produced. Also given i n Table I are comparisons o f the extent r e a c t i o n o f 1,3-diphenylpropane (400° f o r 30 minutes) a) with excess t e t r a l i n ; b) with excess t e t r a l i n and v i t r i n i t e ; and c) with excess v i t r i n i t e . The extent r e a c t i o n i n each case was estimated from the g . c . t r a c e .

0-8412-0427-6/78/47-071-165$05.00/0 © 1978 American Chemical Society In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

166


Table I A Comparison o f T e t r a l i n and I l l i n o i s No. 6 V i t r i n i t e as Hydrogen Donors

Reactants


1,2-Diphenyl-1-ptolylethane

Conditions 400°, 5 min tetralin

Percent Reaction 2%

a

II

4 0 0 ° , 30 m i n tetralin

II

400°, 5 min vitrinite 4 0 0 ° , 30 m i n tetralin

b

50%

a

1 , 3 - d i p h e n y l propane

b

23%

b

43%

b

65%

II

4 0 0 ° , 30 m i n tetralin & vitrinite

II

4 0 0 ° , 30 m i n vitrinite

The oven was a t 4 0 0 ° , b u t t h e warm-up t i m e i s 15 m i n u t e s , t h e a c t u a l t e m p e r a t u r e was c o n s i d e r a b l y l e s s t h a n 4 0 0 ° . b

94%

thus

3 0 m i η i n c l u d e d warm up t i m e .

S i n c e t h e r e a c t i o n s were m o n i t o r e d by g . c , w h i c h would d e t e c t n e i t h e r n o n v o l a t i l e polymeric m a t e r i a l , nor high molecular weight products o f r e a c t i o n with v i t r i n i t e , i t i s p o s s i b l e t h a t t h e v i t r i n i t e i s a c t i n g n o t as a hydrogen d o n o r , b u t m e r e l y as a c a t a l y s t , and t h a t t h e s o u r c e o f t h e h y d r o g e n f o r t h e h y d r o g e n o l y s e s comes f r o m t h e 1 , 2 - d i p h e n y l - l - £ - t o l y l e t h a n e or from the 1,3-diphenylpropane. To c i r c u m v e n t t h i s p r o b l e m , we h e a t e d benzophenone t o 4 0 0 ° f o r one hour a) i n t h e p r e s e n c e o f e x c e s s t e t r a l i n , and b) i n t h e p r e s e n c e o f e x c e s s v i t r i n i t e . The m a j o r p r o d u c t s a r e d i p h e n y l m e t h a n e and w a t e r , w i t h t r a c e s o f t o l u e n e and benzene. The r e a c t i o n i n t e t r a l i n p r o c e e d e d t o t h e e x t e n t o f o n l y 12%, whereas i n t h e p r e s e n c e o f v i t r i n i t e 35% r e a c t i o n had o c c u r r e d . (6,7) R e a c t i o n s o f T e t r a l i n o t h e r t h a n Hydrogen D o n a t i o n T e t r a l i n - l - ^ C r e a c t s w i t h Wyodak c o a l a t 4 0 0 ° (1 hour) t o the extent t h a t the p y r i d i n e - i n s o l u b l e r e s i d u e c o n t a i n s c h e m i c a l l y bound c a r b o n - 1 4 e q u i v a l e n t t o 5% t e t r a l i n by w e i g h t . F u r t h e r , when t h e r e s i d u e was r e h e a t e d i n normal t e t r a l i n ( 4 0 0 ° , one h o u r ) t h e r e i s o l a t e d s o l v e n t c o n t a i n e d no m e a s u r a b l e amount o f e i t h e r


12.

Isotopic

COLLINS ET AL.

Studies of Thermally


l l f

Induced

Reactions

167

ll

t e t r a l i n - C o r o f n a p h t h a l e n e - * C . T h e r e were, however, t r a c e s o f l a b e l e d a l k y l a t e d n a p h t h a l e n e s , w h i c h were i d e n t i f i e d by g.c. r e t e n t i o n t i m e s as 1- and 2 - s u b s t i t u t e d m e t h y l - and e t h y l n a p h t h a l e n e s . These p r o d u c t s u n d o u b t e d l y a r i s e as a r e s u l t o f f r e e r a d i c a l i n t e r m e d i a t e s . We t h e r e f o r e i n v e s t i g a t e d t h e p o s s i b i l i t y t h a t m e t h y l - o r e t h y l n a p h t h a l e n e s c o u l d be p r o d u c e d by t h e r e a c tion of t e t r a l i n with structures containing aromatic moieties s e p a r a t e d by two o r more m e t h y l e n e g r o u p s , o r w i t h a r y l a l k y l e t h e r s . Both t y p e s o f s t r u c t u r e (4,5) a r e known t o be p r e s e n t i n d i f f e r e n t k i n d s and r a n k s o f c o a l . We h e a t e d s e v e r a l d i a r y l a l k a n e s and a r y l a l k y l o r a r a l k y l e t h e r s t o 4 0 0 ° i n t e t r a l i n f o r v a r y i n g p e r i o d s o f t i m e . Many o f t h e s e r e a c t i o n s y i e l d e d m e a s u r a b l e q u a n t i t i e s o f m e t h y l - and ethyl naphthalenes i n a d d i t i o n to other products. Typical are the r e a c t i o n s o f 1 , 3 - d i p h e n y l p r o p a n e and o f p h e n e t o l e , b o t h o f w h i c h were i n v e s t i g a t e d w i t h c a r b o n - 1 4 — l a b e l e d s p e c i e s . The p r o d u c t s were a n a l y z e d a) by gas c h r o m a t o g r a p h y combined w i t h r a d i o a c t i v i t y m o n i t o r i n g o f c a r b o n - 1 4 — l a b e l e d p r o d u c t s ; b) by gas c h r o m a t o g r a phy e q u i p p e d w i t h mass s p e c t r o g r a p h s a n a l y z e r s ; and c ) by i s o l a t i o n o f s p e c i f i c p r o d u c t s u s i n g p r e p a r a t i v e g.c. f o l l o w e d by nmr a n a l y s i s ( V a r i a n XL-100 S p e c t r o m e t e r ) . G i v e n i n T a b l e s II and I I I a r e t h e m a j o r p r o d u c t s o b t a i n e d - t o g e t h e r w i t h a p p r o p r i a t e y i e l d s - f r o m t h e r e a c t i o n s o f 1 , 3 - d i p h e n y l propane and phenetole, respectively, with t e t r a l i n . T a b l e II 3

M a j o r P r o d u c t s and Y i e l d s O b t a i n e d on H e a t i n g 1 , 3 - D i p h e n y l propane w i t h T e t r a l i n One Hour a t 4 0 0 °

Toluene E t h y l benzene 1- and 2 - ( 2 - P h e n y l e t h y l ) t e t r a l i n s 1,4-Diphenylbutane 1- and 2 - M e t h y l n a p h t h a l e n e s Styrene 1,3-Diphenylpropene Methyldi hydronaphthalenes 1,2-Diphenylethane 1- and 2 - ( 2 - P h e n y l e t h y l ) n a p h t h a l e n e s Other a

B a s e d on 1 , 3 - d i p h e n y l p r o p a n e

28% 19 8 5 3 1. 1. 34

consumed.

The 1- and 2 - m e t h y l n a p h t h a ! e n e s were i s o l a t e d and i d e n t i f i e d by nmr a n a l y s i s . T h e i r g e n e s i s f r o m t h e r e a c t i o n o f 1 , 3 - d i p h e n y l p r o p a n e - 2 - C ( C=*) and t e t r a l i n was d e t e r m i n e d as follows: lif

llf


168


CH P h C H C H C H P h + (0Q 2

2

-

2

00}

CH CH Ph

3

2

+

2

00)

Table III


M a j o r P r o d u c t s and Y i e l d s O b t a i n e d on H e a t i n g P h e n e t o l e w i t h T e t r a l i n E i g h t e e n Hours a t 4 0 0 °

Phenol M e t h y l n a p h t h a l enes Toluene E t h y l benzene Ethylnaphthalenes Methyltetralins Ethyl phenol Ethyltetralins E t h y l m e t h y l benzene Methylindane B u t y l benzene

37J » 7 ' 7

3 / 0

4 3 3 %

From D e c o m p o s i t i o n of Tetralin

The m i x t u r e o f e t h y l n a p h t h a l e n e s was i d e n t i f i e d by g . c . r e t e n t i o n t i m e s and r a d i o a c t i v i t y a s s a y by means o f t h e g . c . r a d i o a c t i v i t y m o n i t o r . T r a c e s o f m e t h y l i n d a n e and o f b u t y l benzene were a l w a y s p r e s e n t a f t e r r e a c t a n t s were h e a t e d w i t h t e t r a l i n . T h a t t h e s e l a t t e r two p r o d u c t s were d e r i v e d f r o m t e t r a l i n was d e m o n s t r a t e d by t h e f a c t t h a t t h e y c o n t a i n e d c a r b o n - 1 4 when t e t r a l i n - * C was u s e d i n t h e r e a c t i o n . In l i k e manner, l a b e l e d p h e n e t o l e and t e t r a l i n were s u b j e c t e d t o t h e c o n d i t i o n s o f r e a c t i o n w i t h t h e f o l l o w i n g results: l l

It i s c l e a r from the i s o t o p i c l a b e l i n g experiments t h a t t e t r a l i n has e n t e r e d i n t o t h e r e a c t i o n b o t h w i t h 1 , 3 - d i p h e n y l p r o p a n e and w i t h p h e n e t o l e . The r e s u l t s a r e n i c e l y accommodated by t h e p o s t u l a t i o n o f r a d i c a l i n t e r m e d i a t e s . A p o s s i b l e mechanism f o r t h e r e a c t i o n o f 1 , 3 - d i p h e n y l p r o p a n e i s i n d i c a t e d i n T a b l e IV.


COLLINS ET AL.

12.

Isotopic Studies of Thermally Induced Reactions

169

TABLE IV P o s s i b l e Mechanism f o r t h e R e a c t i o n o f T e t r a l i n w i t h 1 , 3 - D i p h e n y l propane PhCH CH CH Ph

>• PhCH -

+

PhCH -

*

+

2

2

2

+

2

PhCH

3

PhCH CH - +

*• PhC,H CH

2PhCH CH -

*~

2

2

2


2

2

2

(00

PhCH CH - + 2

2

CH CH Ph 2

2

-CH CH Ph 2

2

+

3

PhCH CH CH CH Ph 2

2

2

2

CH CH Ph

-

®3 ©0

2

2

CH '

?

2

+

PhCH 2

α & g

€0

CH 2

+

.

CH

0D - OOêO ^ .CHs 3

a

α,β A c k n o w l e d g e m e n t s : We a c k n o w l e d g e w i t h t h a n k s t h e a s s i s t a n c e o f Mr. L. L. Brown i n r u n n i n g t h e nmr s p e c t r a , and o f Dr. W. T. R a i n e y , Mr. Ε. H. McBay and Mr. D. C. Canada o f t h e A n a l y t i c a l C h e m i s t r y D i v i s i o n , f o r c a p i l l a r y g . c . a n d mass s p e c t r o g r a p h ! c a n a l y s e s o f s e v e r a l o f t h e h y d r o g e n o l y s i s p r o d u c t s . We thank t h e S a h a r a M i n i n g Co., H a r r i s o n b u r g , 111., f o r a g e n e r o u s sample o f I l l i n o i s No. 6 c o a l ; t h a n k s a r e a l s o due D r s . L. A. H a r r i s and A. S. Dworkin f o r a f i e l d t r i p t o t h e mine s i t e .

Literature Cited 1. 2.

Research sponsored by the Division o f Basic Energy Sciences of the Department o f Energy under contract with the Union Carbide Corporation. C o l l i n s , C. J., Raaen, V. F., Benjamin, Β. M . , and Kabalka, G. W., Fuel (1977), 56, 107.


170

3.

4. 5. 6.


7.


S e e also S h o z d a , R. J., Depp, Ε. Α . , Stevens, C. Μ . , and Neuworth, M. B., J. Amer. Chem. S o c . ( 1 9 5 6 ) , 78, 1716; Depp, Ε . Α . , Stevens, C. Μ . , and Neuworth, M. B., Fuel ( 1 9 5 6 ) , 35, 437. H e r é d y , L. Α . , K o s t y o , A. E . , and Neuworth, M. B., Fuel ( 1 9 6 5 ) , 44, 125. Brücker, R. a n d Kölling, G., Brennst. Chem. ( 1 9 6 5 ) , 46, 4 1 ; Kölling, G. a n d H a u s i g k , D., ibid. (1969) 50, 1. For information on "Catalylic D e h y d r o g e n a t i o n of Coal" s e e R e g g e l , L . , Wender, I., a n d Raymond, R., Fuel ( 1 9 7 3 ) , 52. 162-163 (1973) a n d the previous six papers in this series cited therein. C o a l s have previously been d e h y d r o g e n a t e d w i t h p - b e n z o q u i n o n e , P e o v e r , M. E . , J. Chem. S o c . (London) ( 1 9 6 0 ) , 5020.

RECEIVED February 10,

1978


13 Supercritical Solvents and the Dissolution of Coal and Lignite JAMES E. BLESSING and DAVID S. ROSS


SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025

The unique solvent properties of supercritical fluids suggest their use in coal extraction as a novel scheme for isolating syncrude-like materials. One advantage such a process might offer is the ease of separating solvent from extract. We have studied the degree of coal dissolution possible with a number of solvents in the supercritical state and examined the importance of system parameters, such as solvent type, density, and temperature, on the success of extractions. Shortly after we began our work, Bartle, Martin, and Williams of the National Coal Board of Britain reported a 17% yield of low -ash, high-H/C material from the extraction of coal with superc r i t i c a l toluene at 350°C (1). Since then, Maddocks and Gibson have reported greater yields, with up to one-third extraction of an I l l i n o i s No. 6 coal with toluene at 400°C (2). They estimated that their process would be economically competitive with the COED and SRC operations. This paper reviews the fundamentals of supercritical extraction, discusses our data in terms of theoretical expectations, and draws some conclusions regarding the role of extraction per se i n obtaining products from coal. Background A "supercritical" fluid i s one that i s above i t s c r i t i c a l temperature (T ), the point beyond which a phase boundary no longer exists between gas and liquid. In the supercritical region, the density of a f l u i d is a continuous function of i t s pressure, no distinction exists between gas and liquid, and the f l u i d has no surface tension. One hundred years ago, Hannay and Hogarth observed the dissolution of KI in supercritical ethanol (3). Yet, until now, little practical use has been made of supercritical extractants. Paul and Wise have described the theoretically based expectations of the use of supercritical fluids as solvents or extractants, both c

0-8412-0427-6/78/47-071-171$05.00/0 © 1978 American Chemical Society In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

172



g e n e r a l l y and with some emphasis on c o a l d i s s o l u t i o n (4). Given below are some of the p r o p e r t i e s of s u p e r c r i t i c a l f l u i d s , d i s cussed i n t h e i r monograph: •

At low d e n s i t i e s , gases have no solvent power, and the concentration of a compound s o l u t e i n the gas phase i s described by i t s p a r t i a l pressure. However, at a given temperature, the solvent power of any gas increases d r a m a t i c a l l y as i t s density approaches that of l i q u i d s .

•

For a given pressure, a gas i s at i t s highest d e n s i t y near i t s c r i t i c a l temperature, where i t i s l e a s t i d e a l .

•

For a given gas density, the concentration of a s o l u t e i n a gas increases with i n c r e a s i n g temperature due to increased s o l u t e v o l a t i l i t y , but solvent pressures r i s e r a p i d l y as the temperature exceeds T and the solvent gas becomes more i d e a l . Theory p r e d i c t s that the solvent power of such a gas i s p r i m a r i l y a f u n c t i o n of i t s p h y s i c a l p r o p e r t i e s and i s r e l a t i v e l y independent of i t s chemical s t r u c t u r e and f u n c t i o n a l i t y . c

•

Because a gas i s g e n e r a l l y l e s s viscous than a l i q u i d , i t can b e t t e r penetrate porous substrates, such as coal.

•

Though the solvent power of a dense gas may not be high compared with l i q u i d s , the gas i s more e a s i l y separated from m a t e r i a l s l i k e c o a l , and solvent r e c o v e r i e s can therefore be b e t t e r .

The conclusions of Paul and Wise thus suggest that superc r i t i c a l e x t r a c t i o n i s a promising procedure f o r c o a l conversion. The r e s u l t s of our research v e r i f y the a p p l i c a b i l i t y of these p r i n c i p l e s to c o a l e x t r a c t i o n , but a l s o point to the importance of processes other than simple e x t r a c t i o n s i n the production of c o a l products. Experimental Procedures A v a r i e t y of experiments were performed using s e v e r a l s o l vents over a range of c o n d i t i o n s to e x t r a c t samples of I l l i n o i s No. 6 c o a l and North Dakota l i g n i t e . The coals are c h a r a c t e r i z e d i n Table I. A l l experiments were done i n batch mode, i n a 300 cm , 316 SS AE MagneDrive autoclave. Most experiments were run f o r 90 min at 335°C. The run procedure i s summarized i n Figure 1. The workup procedure i s shown i n Figure 2. Each r e a c t i o n product i s separated i n t o a f i l t r a t e and a s o l i d s f r a c t i o n . In every case, the f i l t r a t e s were f u l l y p y r i d i n e s o l u b l e . The p y r i d i n e s o l u b i l i t i e s of the s o l i d s were determined by s t i r r i n g 0.5 g s o l i d i n 50 ml p y r i d i n e f o r 1 hr at room temperature, and 3



COAL OR LIGNITE

Figure 1.

Run procedure

CAREFULLY COLLECT REACTOR CONTENTS

HEAT-UP (50 MIN) HOLD COOL-DOWN (60 MIN)

FILL AND V E N T 1000 psig OF NITROGEN, TWICE

3

A E MAGNEDRIVE 300 c m , 316 SS AUTOCLAVE STIRRING 1500 rpm

DRY A T 120°C, < 1 TORR

REACTION SOLVENT

Figure 2.

Low melting solids. Typical MW_ « 450

Wt% Filt. based on MAF starting coal.

REACTION MIXTURE

"SOLIDS"

Workup procedure

Typical MW

n

* 1100

Wt% solids pyr. sol based on MAF 0.5 g sample

EVAPORATE SOLVENT AND DRY, 120°C, < 1 TORR

MED. POROSITY FILTER

STIR 0.5 g IN 50 ml PYRIDINE FOR 1 HOUR A T ROOM T E M P E R A T U R E

DRY, 120°C, < 1 TORR

MEDIUM POROSITY FRITTED FILTER (10-15 Mm)

EVAPORATE SOLVENT AND DRY, 120°C, < 1 TORR

"FILT"


174


Table I CHARACTERISTICS OF COAL AND LIGNITE SAMPLES


Analyses

Beneficiated I l l i n o i s No. 6 Coal Dried Over night at 120°C and < 1 t o r r . ASTM HVC (PSOC-26?

%C %H Molar H/C %N %S org %S. morg %0 Δ %Ash % Pyridine solubility % Solubility i n a l l reac tion solvents

North Dakota L i g n i t e Dried Overnight a t 120°C and < 1 t o r r (PSOC-246)'

77.2 5.1 0.79 1.7 2.1

62.0 4.5 0.87 1.0 0.7

b

% 0 11.9

14.8

2.0 13

17 2

Λ

* £ the duced d e n s i t y of l i q u i d s , taken to be about 2.66. Thus δ i s a l i n e a r f u n c t i o n of the experimental d e n s i t y , a l l other v a r i a b l e s i n the equation being constant f o r any given s o l v e n t . Product p y r i d i n e s o l u b i l i t y versus δ i s p l o t t e d i n F i g u r e 4. The data f o r a l l the s o l v e n t s appear to f a l l about a l i n e . * Regardless of t h e i r s t r u c t u r a l d i f f e r e n c e s , a l l these compounds l a r g e l y perform i n accordance with t h e i r solvent c a p a b i l i t i e s . Thus, the media are a c t i n g simply as solvents and are apparently not chemically a c t i v e . Since the p y r i d i n e s o l u b i l i t y of the s t a r t i n g c o a l i s 13%, the use of these solvents at lower den s i t i e s i s a c t u a l l y counterproductive. c

a n c

r

p

i s

r e

C

A comparable run with T e t r a l i n and c o a l y i e l d s a product that i s about 50% p y r i d i n e s o l u b l e .



BLESSING AND Ross

Figure 4.

Supercritical

Solvents

Product pyridine solubilities vs. 8 (reaction conditions: 90 min, 335°C, approx. 500-5000 psig)


182



Conclusion The conclusions presented here are based on the r e s u l t s of our experiments with c o a l . On the b a s i s of some l i m i t e d research with l i g n i t e , we suggest that these conclusions a l s o apply to lignite. The y i e l d s f o r l i g n i t e , however, were g e n e r a l l y lower than those f o r c o a l under comparable c o n d i t i o n s . The c o r r e l a t i o n of p y r i d i n e s o l u b i l i t y of the c o a l products with the Hildebrand s o l u b i l i t y parameter coupled with the tempera ture dependence of the product y i e l d s leads us to suggest that the s o l u b l e product m a t e r i a l s r e s u l t from an i n i t i a l , thermally induced fragmentation of the c o a l i n v o l v i n g the a c t i o n of a dense solvent. Thermochemical c o n s i d e r a t i o n s suggest that the r a t e of thermal fragmentation i s too slow to account f o r the r e s u l t s . As s t a t e d , however, these thermochemical c a l c u l a t i o n s are f o r a gas phase system, a t d e n s i t i e s s e v e r a l orders of magnitude lower than those used i n our experiments. Wiser has suggested that c o a l thermolysis r a t e s may be s i g n i f i c a n t l y enhanced i n the presence of a s o l v e n t (10). Although n e i t h e r t h e o r e t i c a l nor independent experimental j u s t i f i c a t i o n e x i s t s f o r t h i s suggestion,* our data, and p a r t i c u l a r l y , our f i n d i n g of a correspondence between the d e n s i t y of the medium and the conversion to p y r i d i n e - s o l u b l e products, are best explained that way. Thus, a model c o n s i s t e n t with the data i s

c

_

c

solvent participation 1

c

m

2

C-0 bonds can be considered s i m i l a r l y .

(i)

Hydrogen-transfer coal, —C-

(ii)

conversion to s t a b l e products

Step (2) may i n v o l v e e i t h e r

from a hydrogen-rich p o r t i o n of the

+ RH—^R- +

—CH

D i s p r o p o r t i o n a t i o n of the r a d i c a l s p e c i e s , 2

—CH-CH

3

—*~

—CH=CH

2

+ —CH -CH 2

3

or ( i i i ) β-scission, s p l i t t i n g o f f a s m a l l , r e l a t i v e l y f r e e r a d i c a l (R=H, a l k y l , benzyl) —C-C-R — — C = C

stable

+ R-

* For the simple, thermal homolysis, R-R 2R«, no evidence e x i s t s that the r a t e i s s i g n i f i c a n t l y enhanced by the presence o f s o l vent. Moreover, i f the process i s s t r i c t l y one i n which no charge s e p a r a t i o n occurs i n the t r a n s i t i o n s t a t e , there i s no t h e o r e t i c a l expectation of a s i g n i f i c a n t solvent e f f e c t .



13.

BLESSING AND Ross

Supercritical

183

Solvents

(An a l t e r n a t i v e mechanism i s discussed i n the Appendix.) S u p e r c r i t i c a l s o l v e n t s , t h e r e f o r e , c l e a r l y can provide moderate y i e l d s of s y n c r u d e - l i k e m a t e r i a l s from c o a l , and these y i e l d s are not p r i m a r i l y due to any unique c h a r a c t e r i s t i c s of s u p e r c r i t i c a l c o n d i t i o n s . Since high solvent d e n s i t i e s are d e s i r a b l e , solvents that are l i q u i d at l i q u e f a c t i o n temperatures could prove at l e a s t as e f f e c t i v e as those that are s u p e r c r i t i c a l , and at lower pressures. L i q u i d s , however, are subject to the l i m i t a t i o n s of surface t e n s i o n and higher v i s c o s i t i e s , which dimi n i s h t h e i r usefulness i n t h i s scheme. A d d i t i o n a l l y , s o l v e n t s that are l i q u i d at l i q u e f a c t i o n temperatures are very d i f f i c u l t to separate from c o a l products. Thus, s u p e r c r i t i c a l s o l v e n t s o f f e r solvent f l u i d i t y , a r e l a t i v e l y wide range of usable types of compounds, and e a s i l y o b t a i n a b l e high solvent r e c o v e r i e s i n the e x t r a c t i o n of low molecular weight m a t e r i a l s from c o a l . An understanding of the importance of the thermal processes i n v o l v e d i n the treatment of c o a l with hot, dense solvents and the p r i n c i p l e s of s u p e r c r i t i c a l e x t r a c t i o n , as enumerated at the outset of t h i s paper, could l e a d to an e f f e c t i v e use of s u p e r c r i t i c a l solvents i n c o a l and l i g n i t e processing.

Appendix An a l t e r n a t i v e scheme i n v o l v i n g charge s e p a r a t i o n i s suggested f o r c o a l t h e r m o l y s i s : coal + coal ^ ± r w

+· coal

/

.+· (coal ....coal

solvent )

solvent ^ separated

pair

+·

> coalH coal or H-donor

2

As u n l i k e l y as t h i s suggestion may seem at the o u t s e t , the propos i t i o n i s c o n s i s t e n t with the f o l l o w i n g : •

As discussed i n the t e x t , an i n c r e a s e i n d e n s i t y of the media increases the degrees of c o a l conversion. The conversion process, i n turn, e n t a i l s i r r e v e r s i b l e changes i n the c o a l , and thus i s not j u s t a simple s o l v e n t - s o l u t e interaction.

•

Wiser s t a t e s that c o a l p y r o l y s i s i n the absence of T e t r a l i n i s second order i n c o a l , and when T e t r a l i n i s present the process i s f i r s t order i n both T e t r a l i n and c o a l (10).



184

ORGANIC CHEMISTRY OF

COAL

•

T e t r a l i n r e a d i l y donates hydrogen to electron-poor systems at 50 to 160°C. T y p i c a l Η-acceptors are quinones. The r e a c t i o n i s a c c e l e r a t e d by electron-withdrawing subs t i t u e n t s on the quinone, i s a c c e l e r a t e d by polor s o l v e n t s , and i s unaffected by f r e e r a d i c a l i n i t i a t o r s (11) .

•

R a d i c a l cations r e a d i l y accept H (12) .

•

The e s t a b l i s h e d acid-base character of c o a l - d e r i v e d asphaltenes (13) suggests that charge separation, i . e . , donor-acceptor complexes, e i t h e r are present i n c o a l i t s e l f or form thermally.

•

Poly-condensed aromatic s t r u c t u r e s , l i k e those i n c o a l , are known to form r e a d i l y both r a d i c a l c a t i o n s and r a d i c a l anions (15) .

2

from hydrocarbon donors

This suggested model could provide p r a c t i c a l i n s i g h t i n t o the a c t i o n of c a t a l y s t s i n conversion processes. One might consider, thus, the use of c a t a l y s t s that promote C-C s c i s s i o n by r a d i c a l c a t i o n intermediates.* The i m p l i c a t i o n s of t h i s scheme await the r e s u l t s of f u r t h e r research i n t o the Η-donor process and c o a l con v e r s i o n chemistry. Acknowledgment We acknowledge the support of the Department o f Energy f o r t h i s work on Contract EF-76-C-01-2202. Literature Cited 1. 2. 3. 4.

B a r t l e , K e i t h D., Martin, Terence G., and Williams, Dereck F., F u e l (1975), 54, 226. Maddocks, R. R., and Gibson, J . , Chem. Eng. Prog. (June 1977), 73, 6, 59-63. Hannay, J . B., and Hogarth, J . , Proc. Roy. Soc. (London), Ser. A (1879), 29, 324-26. Paul, P.F.M., and Wise, W.S., "The P r i n c i p l e s of Gas E x t r a c t i o n , " M i l l s and Boon Limited, London, 1971.

*Trahanovsky and B r i x i u s have shown that at temperatures below 100°C, Ce(IV) promotes the cleavage of PhCH -CH Ph, y i e l d i n g o x i d a t i o n products by way of a r a d i c a l c a t i o n intermediate (16). I t would be of i n t e r e s t to c a r r y out the r e a c t i o n with H-donor solvents present. 2

2


BLESSING AND Ross 5.

6.

7. 8. 9.


10. 11. 12.

13. 14.

15.

16.

Supercritical

Solvents

185

Ross, D. S., and B l e s s i n g , J . Ε., " I s o r p o p y l A l c o h o l as Coal L i q u e f a c t i o n Agent," F u e l D i v i s i o n P r e p r i n t s f o r the 173rd N a t i o n a l Meeting of the Amer. Chem. Soc., New Orleans, LA, (March 1977). Manuscript i n p r e p a r a t i o n . Benson, S. W., and O'Neal, Η., N a t i o n a l Standard Refer ence Data S e r i e s — NBS 21, U.S. Government P r i n t i n g O f f i c e , Washington, D.C., 1970. Blanks, R., and Peausnitz, J . , Ind. Eng. Chem. Funda mentals (1964), 3, 1. Angelovich, J . , Pastor, G., and S i l v e r , Η., Ind. Eng. Chem. Process Des. Dev. (1970), 9, 160. Giddings, J . , Myers, Μ., McLaren, L., and K e l l e r , R., Science (4 October 1968), 162, 67. Wiser, N., F u e l (1968), 47, 475. Braude, Ε. Α., Jackman, L., and L i n s t e a d , R., J . Chem. Soc. (1954), 3548, 3564, 3569. Doepker, R., and Ausloos, P., J . Chem. Phys. (1960), 44 (5), 1951; Kramer, G., and Pancirov, R., J . Org. Chem. (1973), 38, 349. Sternberg, Η., Raymond, R., and Schweighardt, F., Science (4 April 1975), 188, 49. F r a n k l i n , J . , Dillard, S., Rosenstock, Η., Herron, J . , and D r a x l , Κ., " I o n i z a t i o n P o t e n t i a l s , Appearance P o t e n t i a l s , and Heats of Formation of Gaseous P o s i t i v e Ions," N a t i o n a l Standard Reference Data S e r i e s — NBS 26, U.S. Government P r i n t i n g O f f i c e , Washington, D.C., 1969. Compton, R., and Huebner, R., in "Advances in R a d i a t i o n Chemistry," Burton, Μ., and Magee, J . , Ed., V o l . 2., 1970 p. 281; Christophorou, L., and Compton, R., Heath P h y s i c s (1967), 13, 1277. Trahanovsky, W., and B r i x i u s , W., J . Amer. Chem. Soc. (1973), 95 (20), 6778.

RECEIVED February 10,

1978


14 Homogeneous Catalytic Hydrogenations of Complex Carbonaceous Substrates J. L. COX, W. A. WILCOX, and G. L. ROBERTS


Battelle, Pacific Northwest Laboratories, Richland, WA 99352

Hydrogenation of unsaturated organic compounds with homogeneous catalysts has been known and practiced for some time. Such hydrogenations have been of both an academic and commercial interest. Some of the more extensively studied catalysts include Co(CN) (1), RhCl (ΡΦ ) (2), Ir(CO)Cl(ΡΦ ) (3,4), IrH(CO)(PΦ ) (3,4), OsHCl(CO)(PΦ ) (3,4) and Ziegler-type catalysts (5,6). These catalysts, except for the Ziegler-type, have not been observed to hydrogenate aromatics. In fact, very few homogeneous catalysts have been reported that will hydrogenate aromatics. Wender, et al. (7) have shown that polynuclear aromatics are partially hydrogenated with Co (CO) Efimov, et al., (8,9) have observed rapid hydrogenation of polynuclear aromatics in the presence of a rhodium complex of N-phenylanthranilic acid (NPAA), formulated as (RhNPAA) . This rhodium catalyst is more active than the dicobalt octacarbonyl and shows a greater hydrogenation activity toward polynuclear aromatics than the Ziegler catalyst. Holly et al. (10) investigated the use of this rhodium complex and other homogeneous catalysts for coal liquefaction, concluding that such catalysts do not appear to offer a viable route to coal liquefaction. Muetterties and Hirsekorn (11) have reported the hydrogenation of benzene to cyclohexane at 25°C and 1 atm pressure in the presence of n -allylcobalt phosphite; n -C H Co[P(0CH ) ] . Here we report the results of homogeneous catalytic hydrogénation of complex unsaturated substrates including coal and coal-derived materials. -35

3

3

3

3

2

3

3

2

8

·

2

3

3

3

5

3

3

3

Hydrogénations U s i n g o r g a n i c s o l u b l e m o l e c u l a r c o m p l e x e s as c a t a l y s t s , a number o f h y d r o g é n a t i o n s o f v a r i o u s o r g a n i c s u b s t r a t e s (a Hvab c o a l , s o l v e n t r e f i n e d c o a l (SRC) and COED p y r o l y s a t e ) were p e r f o r m e d . The a n a l y s i s o f t h e s e f e e d m a t e r i a l s i s c o n t a i n e d i n T a b l e I . The h y d r o g é n a t i o n s were c a r r i e d o u t i n a 300 c c s t i r r e d a u t o c l a v e by m i x i n g c o a l w i t h c a r r i e r s o l v e n t c o n t a i n i n g s o l u b i 0-8412-0427-6/78/47-071-186$05.00/0 This chapter not subject to U.S. copyright. Published 1978 American Chemical Society


3

14.

Homogeneous

COX ET AL.

Catalytic

Hydrogénations

187

1 i z e d c a t a l y s t u n d e r p r e s c r i b e d c o n d i t i o n s . Upon c o m p l e t i o n o f the r u n t h e g a s e s were m e a s u r e d w i t h a c a l i b r a t e wet t e s t m e t e r and a n a l y z e d b y r o u t i n e g a s c h r o m a t o g r a p h y p r o c e d u r e s . T h e s o l i d c a r b o n a c e o u s r e s i d u e was s e p a r a t e d f r o m c a r r i e r s o l v e n t by f i l t r a t i o n , t h e n t h o r o u g h l y washed w i t h benzene and f i n a l l y d r i e d i n a vacuum o v e n .


TABLE I . A n a l y s i s o f Feed M a t e r i a l s Hydrogenated Coal C o a l (a) Run 25 SRC COED As R e c e i v e d Vacuum D r i e d Moisture Ash H C 0 Ν S

1.1 14.5 4.8 68.8 6.0 1.2 4.6

0.0 14.7 4.6 68.3 6.1 1.2 4.6

0.0 0.3 5.6 87.7 4.0 2.2 0.5

0.0 0.1 7.3 85.0 7.2 1.1 1.3

1.8 27.0 4.4 55.0 5.9 0.2 4.0

B o t h samples were -200 mesh. A l l catalysts except the Ni-Ziegler are commercially available and were u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . The N i - Z i e g l e r was p r e p a r e d u n d e r a n i t r o g e n a t m o s p h e r e b y r e a c t i n g 4 moles o f t r i e t h y l aluminum w i t h 1 m o l e o f n i c k e l n a p h t h e n a t e i n a n h y d r o u s η - h e p t a n e . T h e a c t i v i t y o f t h i s c a t a l y s t was f i r s t t e s t e d w i t h b e n z e n e b e f o r e p r o c e e d i n g t o more complex s u b s t r a t e s . Hence, 10 ml benzene were h y d r o g e n a t e d i n 40 ml η - h e p t a n e c o n t a i n i n g 4 χ 1 0 " m o l e s o f t h e N i - Z i e g l e r c a t a l y s t f o r 1 hour a t 150°C and 1000 p s i g H ( a m b i e n t t e m p e r a t u r e ) . Even t h o u g h t h e h y d r o g é n a t i o n c o v e r e d a 1 hour p e r i o d t h e a u t o c l a v e p r e s s u r e r a p i d l y d r o p p e d t o 650 p s i g once 150°C was r e a c h e d , s i g n a l i n g r a p i d h y d r o g é n a t i o n o f t h e benzene. L i q u i d p r o d u c t a n a l y s i s by gas c h r o m a t o g r a p h y r e v e a l e d 9 9 % c o n v e r s i o n o f t h e benzene t o c y c l o hexane. H y d r o g é n a t i o n c o n d i t i o n s and r e s u l t s f o r c o a l and c o a l d e r i v e d m a t e r i a l s a r e summarized i n T a b l e I I . The change i n a t o m i c h y d r o g e n - c a r b o n r a t i o (Δ) i s t h e p r i n c i p a l c r i t e r i o n f o r c o m p a r i n g c a t a l y s t a c t i v i t y and e x t e n t o f h y d r o g é n a t i o n . S i n c e no a t t e m p t has been made t o a c c o u n t f o r t h e l i g h t e r h y d r o c a r b o n s t h a t were removed w i t h t h e c a r r i e r s o l v e n t by f i l t r a t i o n t h e h y d r o g é n a t i o n c r i t e r i o n i s v e r y c o n s e r v a t i v e . The Δ v a l u e has been o b t a i n e d b y s u b t r a c t i n g t h e e x p e r i m e n t a l l y d e t e r m i n e d atomic hydrogen-carbon r a t i o o f carbonaceous s u b s t r a t e from that o f t h e p r o d u c t . The c a r b o n - h y d r o g e n a n a l y s i s was p e r f o r m e d on a P e r k i n E l m e r model 240 e l e m e n t a l a n a l y z e r . S i n c e a s m a l l amount 3

2



5.7 mmole N i - Z i e g l e r / 1 7 . 2 g COED/THF

40

(e)

(d)

(c)

(b)

8 mmole N i - Z i e g l e r / 1 0 g

38 200/3850/21

200/1200/23

200/1300/22

200/2770/2

8.28

7.29

5.88

74. .8

77. .1

63. ,6

55. ,8

70. ,7

4.94

220/2720 V2

4.48

65. ,9

(E

4.56

71. ,8

5.26

200/2830^/2

69. ,0

67. .4

68. .6

Ç_

5.16

4.69

4.64

H

c

?

0.291 0.377 0.290

1.13 1.32

V a r i a b l e s temperature, pressure and time reported as °C, psig and h r . , r e s p e c t i v e l y .

2

Gas composition of 25%C0, 75%H , used i n h y d r o g é n a t i o n .

Pressures are those at r e a c t i o n temperature and due to hydrogen and solvent unless otherwise stated.

Δ, i s the change i n atomic H/C r a t i o between substrate and product.

0.148 1.10

0.957

0.021

0.015

0.824 0.833

0.064

0.082

0.891 0.873

0.020

-0.003

Δ(atomic

0.829

0.806

At.H/C

Feed materials i n c l u d e : C o n s o l i d a t i o n coal (C), 4.64%H, 68.3%C, At.H/C = 0.809; Solvent Refined Coal (SRC), 5.55%H, 87.7%C, At.H/C = 0.753; FMC p y r o l y s a t e (COED), 7.32%H , 85.0%C, At.H/C = 1.03.

SRC/THF

C/heptane


?

36

c

C/decalin

?


c

25

0

7 mmole N i [ ( P h O ) , P ] ( C O ) / 1 5 g C/ decalin

C/decalin

19

3

8

13 mmole Fe (C0)-j /30g

2

Q

2

400/3400^/2

7 mmole C o ( C 0 ) / 1 5 g C / d e c a l i n

20

18

300/3080^/2

2

200/2950^/2


8

21

2


300/2880/2

17

C/decalin

P r e s s u r e ^ V"Time^

Temperature/

No c a t a l y s t / 1 5 g

Catalyst/Feed^ Vsol vent a

31

Run No.

TABLE I I . Summary o f Homogeneous C a t a l y t i c H y d r o g é n a t i o n s o f Carbonaceous Substrates


H/C)

(c)

1

î

ο

i

W

00

14. COX ET AL.

Homogeneous

Catalytic

189

Hydrogénations

o f unremoved s o l v e n t i n t h e p r o d u c t c a n s e r i o u s l y a f f e c t t h e i n t e r p r e t a t i o n o f r e s u l t s , extreme p r e c a u t i o n was t a k e n t o ensure i t s complete removal. T h i s was a c c o m p l i s h e d by w a s h i n g w i t h a v o l a t i l e s o l v e n t ( t e t r a h y d r a f u r a n ) f o l l o w e d by vacuum d r y i n g w i t h a n i t r o g e n b l e e d a t 1 1 0 ° C f o r a t l e a s t 24 h o u r s . I n o r d e r t o c h e c k t h o r o u g h n e s s o f s o l v e n t removal a d r i e d sample showing H/C o f 1.10 was f u r t h e r d r i e d and r e a n a l y z e d . T h e r e was e s s e n t i a l l y no change i n t h e H/C ( i . e . , 1.10 v e r s u s 1.09). I t i s apparent from T a b l e II t h a t t h e N I - Z i e g l e r c a t a l y s t i s more a c t i v e t h a n C o ( C 0 ) , N i [ ( P h 0 ) P ] ( C 0 ) and F e ( C 0 ) . In Run 25 a Δ o f 0.148 f o r t h e Hvab c o a l was o b s e r v e d o v e r a 2-hour r e a c t i o n t i m e a t 200°C and 2770 p s i g . T h i s change i n a t o m i c H/C r a t i o f r o m hydrogénation c o r r e s p o n d s t o a hydrogen usage o f o n l y 0.85% (w/w) o f c o a l . Even i n Run 36 where a Δ o f 0.291 was e f f e c t e d a t 200°C a n d 1300 p s i g H a f t e r 22 h o u r s o n l y 1.7% (w/w) H i s consumed i n t h e h y d r o g é n a t i o n . T h e s e h y d r o g é n a t i o n s may be compared t o Run 31 where a s l i g h t d e c r e a s e i n Δ, -0.003, was o b s e r v e d i n t h e hydrogénation o f t h e Hvab c o a l w i t h no c a t a l y s t f o r 2 hours a t 300°C a n d 2880 p s i g . I n c o n t r a s t t o t h e s e h y d r o g e n c o n s u m p t i o n s a b o u t 2% H (w/w maf c o a l b a s i s ) i s used i n t h e SRC p r o c e s s , 2.5% i n S y n t h o i l and 4% f o r Η - C o a l . Homogeneous c a t a l y t i c h y d r o g é n a t i o n s were a l s o c o n d u c t e d on s o l i d p r o d u c t s f r o m t h e SRC a n d COED c o a l l i q u e f a c t i o n p r o c e s s e s . The a n a l y s e s o f t h e s e s u b s t r a t e s a r e c o n t a i n e d i n T a b l e I . E x a m i n a t i o n o f t h e hydrogénation r e s u l t s summarized i n T a b l e I I r e v e a l s t h a t t h e e a s e o f hydrogénation under t h e s e homogeneous c a t a l y t i c c o n d i t i o n s i s SRC > COED > Hvab, a l t h o u g h some r e s e r v a t i o n must be made s i n c e t h e hydrogénations were n o t made under i d e n t i c a l c o n d i t i o n s . That the c o a l - d e r i v e d substrates a r e more r e a d i l y h y d r o g e n a t e d t h a n t h e c o a l i s n o t t o o s u r p r i s i n g s i n c e t h e y a r e l i q u i d s a t r e a c t i o n t e m p e r a t u r e s (>200°C) and quite soluble i n carrier solvent permitting effective catalysts u b s t r a t e i n t e r a c t i o n . D i f f u s i o n a l r e s i s t a n c e s t o hydrogénation a r e a l s o e x p e c t e d t o be l e s s f o r t h e s e m a t e r i a l s t h a n t h e s o l i d coal. P r o d u c t g a s a n a l y s i s o n each e x p e r i m e n t a l hydrogénation r u n r e v e a l e d p r e d o m i n a n t l y r e a c t a n t g a s e s . In Runs 17, 18, 19, 20 and 21 t h e p r o d u c t gas c o n s i s t e d o f >98% H and CO, w h i l e Runs 25, 3 1 , 36, 38 a n d 40 showed a t l e a s t a s g r e a t a c o n c e n t r a t i o n o f h y d r o g e n . E x c e p t f o r Run 20, C 0 a n d CH4 c o n t r i b u t e d methyl i n d a n ( C O — C H ) >benzene ( Q ) , C^-benzene ( Q — C ^ H g ) > d e c a l i n ( 0 0 ) . O f t h e s e f i v e compounds t h e f i r s t t h r e e a c c o u n t f o r a t l e a s t 8 0 % o f t h e l i g h t o i l i n e a c h sample. T h e b r o a d n e s s o f many o f t h e chromatogram peaks, p a r t i c u l a r l y those a t t h e l o n g e r r e t e n t i o n t i m e , i s a good i n d i c a t i o n t h a t t h e y c o n s i s t o f more t h a n one component. Hence, t h e number o f c h e m i c a l compounds a c t u a l l y i n t h e l i g h t o i l sample i s p r o b a b l y a t l e a s t t w i c e t h e number o f i n t e g r a t e d gas c h r o m a t o g r a p h peaks. 3


cox ET AL.

Homogeneous

Catalytic

Hydrogénations


14.

Figure 3.

Gas chromatogram of light oil from hydrogenolysis of hydrogenated Hvab coal


199


200

TABLE V. G. C. Mass S p e c t r a l A n a l y s i s o f L i g h t O i l

G. C. Retention Time, Area %


Hvab Coal

H -Hvab Coal 2

Mass Spec Assignments

18.59

0.58

16.02

benzene

0.44

0.93

0.52

toluene

0.15

1.19

0.20

0.67

1.59

1.32

xylene

0.35

2.17

0.52

xylene

0.46

2.97

0.68

C^-benzene

2.06

4.39

2.03

decalin

8.10

5.78

10.37

C^-benzene

20.47

7.51

22.74

1-methylindane

0.93

8.41

1.04

40.54

12.35

40.61

0.80

13.17

0.49

0.50

14.12

0.14

0.82

14.67

0.60

0.65

15.33

0.29

0.42

16.17

0.05

1.17

17.18

0.54

0.32

17.88

0.08

0.68

18.53

0.10

18.95

0.03

0.31

19.47

0.10

0.04

20.40

0.12

0.04

20.93

0.12

0.05

21.87

0.07

0.29

22.89

0.28

0.12

24.28

0.27

0.66

25.20

0.52

0.00

26.19

0.02

0.18

28.07

0.12

naphthalene methyl-tetrahydronaphthalene

methyl-naphthalene

C -tetralin 2

methyl-biphenyl


14.

cox ET AL.

Homogeneous

Catalytic

Hydrogénations

201


Utility Even t h o u g h homogeneous c a t a l y t i c h y d r o g é n a t i o n has had c o n s i d e r a b l e p r a c t i c a l u t i l i t y i n the hydrogénation o f s p e c i a l i z e d c h e m i c a l s such a s c e r t a i n f a t s , o i l s and p h a r m a c e u t i c a l s , i t s e c o n o m i c and t e c h n i c a l u t i l i t y i n p r o c e s s i n g c a r b o n a c e o u s f e e d s t o c k s such as c o a l , o i l o r t h e i r d e r i v e d i n t e r m e d i a t e s i s very uncertain. We have seen t h a t p r e h y d r o g e n a t i o n o f c o a l c a n s i g n i f i c a n t l y i n c r e a s e t h e amount o f l i q u i d s o b t a i n e d by p y r o l y s i s compared t o t h e u n h y d r o g e n a t e d c o a l . I t has a l s o been shown t h a t the hydrogenolysis o f prehydrogenated coal produces l e s s a s p h a l t e n e s and more l i g h t o i l and gas t h a n t h e c a t a l y t i c h y d r o g e n o l y s i s o f t h e p a r e n t c o a l . F i n a l l y i t was shown t h a t homogeneous c a t a l y t i c h y d r o g é n a t i o n c a n e f f e c t i v e l y i n c r e a s e t h e atomic hydrogen t o carbon r a t i o o f the carbonaceous m a t e r i a l s i n c l u d i n g c o a l and m a t e r i a l s d e r i v e d from c o a l by p y r o l y s i s and solvent refining. A l t h o u g h t h e amount o f e x p e r i m e n t a l d a t a g e n e r a t e d here i n s u p p o r t o f homogeneous c a t a l y t i c h y d r o g é n a t i o n i s i n f i n i t e s i m a l i n r e g a r d t o t h a t needed f o r a sound t e c h n i c a l j u d g m e n t concerning i t s u t i l i t y i n the area of f u e l s processing, there i s a c l e a r i n d i c a t i o n t h a t t h e a p p r o a c h has m e r i t . The e x t r a p o l a t i o n o f t h e e x p e r i m e n t a l d a t a i n d i c a t e s t h a t homogeneous c a t a l y t i c h y d r o g é n a t i o n has c o n s i d e r a b l e p o t e n t i a l a s a p r e l i m i n a r y p r o c e s s i n g s t e p f o r i n c r e a s i n g t h e a t o m i c H/C r a t i o o v e r c o n v e n t i o n a l methods f o r c a r b o n a c e o u s m a t e r i a l s such a s c o a l , and p o s s i b l y o i l s h a l e and t a r s a n d s . T h e d e r i v e d b e n e f i t from s u c h a u n i t o p e r a t i o n a s i d e from t h e a d d i t i o n o f h y d r o g e n t o t h e s e h y d r o g e n - d e f i c i e n t m a t e r i a l s i s t o i n c r e a s e t h e y i e l d and q u a l i t y o f t h e p r o d u c t s o v e r t h a t now o b t a i n a b l e b y c o n v e n t i o n a l p r o c e s s i n g techniques a t such m i l d c o n d i t i o n s . Y e t another p o t e n t i a l a p p l i c a t i o n o f homogeneous c a t a l y t i c h y d r o g é n a t i o n i s as a n i n t e r m e d i a t e s t e p i n f u e l p r o c e s s i n g o r c o n v e r s i o n schemes i n w h i c h t h e H/C r a t i o i s i n c r e a s e d t o p r o d u c e a s u p e r i o r q u a l i t y p r o d u c t . F i n a l l y , p o t e n t i a l a p p l i c a t i o n s o f homogeneous c a t a l y t i c hydrogénation a r e foreseen i n the area o f b a s i c r e s e a r c h s t u d i e s where i t i s used a s a n a n a l y t i c a l t o o l o r t e c h n i q u e f o r i n v e s t i g a t i n g complex c a r b o n a c e o u s s u b s t r a t e s . Much o f t h e i m p e t u s f o r t h e u s e o f homogeneous c a t a l y s t s i s t h e p r o s p e c t o f r e d u c i n g t e m p e r a t u r e and p r e s s u r e r e q u i r e d f o r c o n v e r s i o n , i n c r e a s i n g r e a c t i o n s p e c i f i c i t y and o b t a i n i n g t h e most e f f i c i e n t u s e p o s s i b l e o f t h e a c t i v e metal component. I n some i n s t a n c e s o f homogeneous c a t a l y t i c h y d r o g é n a t i o n , a l l t h e s e p r o s p e c t s have been r e a l i z e d . I t i s r e a s o n a b l e t o e x p e c t t h a t homogeneous c a t a l y s t s w i l l e v e n t u a l l y be d e v e l o p e d t h a t a r e c a p a b l e and e f f e c t i v e i n h y d r o g e n o l y s i s r e a c t i o n s o f c a r b o n c a r b o n bonds. T h i s i n d e e d w o u l d be a n e x t r e m e l y s i g n i f i c a n t break-through with respect t o coal l i q u e f a c t i o n . The m a j o r t e c h n i c a l drawback t o t h e u s e o f homogeneous a s well as heterogeneous c a t a l y s t s i s the d i f f i c u l t y o f recovery



202


f r o m p r o c e s s i n g s t r e a m s and p o i s o n i n g . S i n c e c a t a l y s t s a r e extremely expensive processing m a t e r i a l s , as a r e s u l t o f t h e i r m a n u f a c t u r i n g c o s t s and c o s t o f t h e i r component c o n s t i t u e n t s , o n l y s m a l l l o s s e s c a n be e c o n o m i c a l l y t o l e r a t e d . In homogeneous c a t a l y t i c h y d r o g é n a t i o n Run 25 where 7 mmole o f N i - Z i e g l e r c a t l y s t were employed p e r 15 g c o a l , t h e c o s t o f n i c k e l a l o n e a t z e r o r e c o v e r y ( i . e . , 54.8 l b / t o n c o a l ) w o u l d amount t o a b o u t $110/ton coal hydrogenated. I f t h e c o s t o f t h e t r i e t h y l aluminum and t h e c a r b o x y l a t e o f n i c k e l a r e t a k e n i n t o c o n s i d e r a t i o n t h e c o s t o f c a t a l y s t m a t e r i a l s a l o n e i s estimated t o exceed $150/ton coal hydrogenated. C l e a r l y , i n o r d e r t o c o n t e m p l a t e such a u s e o f t h e s e c a t a l y s t s , t h e y must e i t h e r be r e c o v e r e d o r used i n a much r e d u c e d c o n c e n t r a t i o n o r p r e f e r a b l y b o t h . Even though no a t t e m p t s were made a t c a t a l y s t r e c o v e r y o r u s e o f r e d u c e d amounts i n t h i s s t u d y i t was f o u n d t h a t t h e h y d r o g e n a t e d c o a l i n Run 25 c o n t a i n e d 1.2% N i . T h i s f i g u r e s t o be 3 1 % o f t h e n i c k e l used i n t h e homogeneous c a t a l y t i c h y d r o g é n a t i o n . T h e r e m a i n i n g 6 9 % o f the n i c k e l c a t a l y s t a p p a r e n t l y remained i n t h e c a r r i e r s o l v e n t , w h i c h i n p r a c t i c e w o u l d be r e c y c l e d . O b v i o u s l y , even h i g h e r c a t a l y s t r e c o v e r y i s n e c e s s a r y t o promulgate i t s economic viability. T h a t c a t a l y s t s c a n be used e f f e c t i v e l y and e c o n o m i c a l l y i n b u l k c h e m i c a l p r o c e s s e s i s amply d e m o n s t r a t e d i n t h e h y d r o c a r b o n p r o c e s s i n g i n d u s t r i e s . A l t h o u g h t h e s e c a t a l y s t s have been f o r t h e most p a r t h e t e r o g e n e o u s , homogeneous c a t a l y s t s have f o u n d a home i n a t l e a s t two n o t a b l e a r e a s . One i s t h e u s e o f Z i e g l e r c a t a l y s t s i n c o o r d i n a t i o n p o l y m e r i z a t i o n and t h e o t h e r i s i n t h e h y d r o f o r m y l a t i o n p r o c e s s . T h e s e two examples show t h a t t h e t e c h n i c a l and e c o n o m i c p r o b l e m s so o f t e n a s s o c i a t e d w i t h t h e u s e o f homogeneous c a t a l y s t s i n i n d u s t r i a l p r o c e s s e s c a n be overcome. Acknowledgement The a u t h o r s w i s h t o a c k n o w l e d g e t h e D i v i s i o n o f B a s i c Energy S c i e n c e s , Department o f Energy f o r f i n a n c i a l support o f t h i s work. Literature Cited 1. 2. 3. 4. 5.

K w i a t e k , J., Mador, I . L . , and Seyler, J.K., Adv. in Chem. Ser. (1963) ( 3 7 ) , 201-215. O s b o r n , J.Α., Jardine, F.H., Young,J.F.,a n d Wilkerson, G., J. Chem. S o c . , A, ( 1 9 6 6 ) , 1711-32. V a s k a , L . , a n d Rhodes, R.E., J. Amer. Chem. S o c . , (1965) 87, 4970. V a s k a , L . , Inor. N u c l . Chem. Lett., ( 1 9 6 5 ) , 1, 89. L a p p o r t e , S . J . , A n n . N.Y. A c a d . Sci., ( 1 9 6 9 ) , 158, ( 2 ) , 510.



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Homogeneous Catalytic Hydrogénations

203

6. Bressan, G . , and Broggi, R., Chem. Abstr., (1969), 70, 37257k. 7. Friedman, S., Metlin, S., Svedi, Α . , and Wender, I., J. Org. Chem., (1959), 24, 1287-89. 8. Efimov, O.N., et al., J. Gen. Chem., USSR, (1968) 38, (12), 2581. 9. Efimov, O.N., et al., Izv. Akad. Nauk. SSSR, Ser. Khim. (1969), (4), 855-8. 10. Holy, Ν . , Nalesnik, T., and McClanahan, s., Fuel, (1977), 56, (10) 272-77. 11. Muetterties, E.L., and Hirsekon, F.J., J. Amer. Chem. Soc. (1974), 96, (12), 4063-7. 12. Cotton, F . Α . , and Wilkinson, G . , "Advanced Inorganic Chemistry", 3rd Edition, 772-6, Interscience Publishers, New York, 1972. 13. Coates, G.E., Green, M.L.H., Powell, P . , and Wade, Κ., "Principles of Organometallic Chemistry", 197-8, Methuen and Co., L t d . , London, 1968. 14. Heredy, L.A., and Neuworth, M.B., Fuel (London), (1962), 41, 221. 15. Ouchi, K . , Imuta, K . , and Yamashita, Y . , Fuel, (London), (1965), 44, 29. 16. Gan,H.,Nandi, S.P., and Walker, P.L. Jr., Fuel (London) (1972), 51, (10), 272-77. 17. Howard, H . C . , in "Chemistry of Coal Utilization, Supplemental Volume", H.H. Lowry, e d . , 363-70, John Wiley & Sons, New York, 1963. 18. Jones, J.F., "Project COED: Clean Fuels from Coal Symposium" Institute of Gas Technology, Chicago, Ill., September 1014, 1973. RECEIVED February 10, 1978


15 Hydrotreatment of Coal with AlCl /HCl and Other 3

Strong Acid Media J. Y. LOW

and D. S. ROSS


SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025

Most current processes for upgrading coal to cleaner fuels require stringent reaction conditions of high temperatures and pressure. Less severe reaction conditions are needed to make coal upgrading economically feasible. The objective of this work was to investigate catalyst systems for upgrading coal to clean fuels under moderated conditions. In this work, homogeneous acid catalysts are of particular interest because they allow intimate contact with the coal and are not liable to coal ash founding. The most common homogeneous catalysts studied i n coal upgrading belong to the general class of molten salt catalyst (1-5) and include halide salts of antimony, bismuth, aluminum, and many of the transition metals. Most often, these molten salts have been studied at high temperature and i n massive excess (1-5). We have performed a systematic study of the use of some of these molten salts as homogeneous acid catalysts for upgrading of coal at relatively low temperatures and i n moderate quantities. In our i n i t i a l work to establish relatively mild reaction conditions that would still give relatively good conversions, we conducted a series of experiments to determine the role of HCl, A1C1 , and H i n coal hydrocracking. We examined the effects of temperature and residence time, studied catalyst/coal weight ratios of 1/1 to 3/1, then chose the standard reaction conditions for the screening of several acid catalysts. The effectiveness of the catalysts was judged by the solubility of the treated coal in THF and pyridine or both, and by the gas yields. In some cases where gasification was significant, gas yields were the only c r i t e r i a used. 3

2

Experimental Studies We used I l l i n o i s No. 6 coal pulverized by b a l l milling under nitrogen to -60 mesh and then usually dried i n a vacuum oven at 115°C overnight. Pennsylvania State University supplied beneficiated coal samples (PSOC-26) as well as an unbeneficiated sample (PSOC-25) for use i n some experiments. The beneficiated 0-8412-0427-6/78/47-071-204$05.00/0 © 1978 American Chemical Society In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


15.

LOW AND ROSS

Hydrotreatment

of

205

Coal

c o a l has the f o l l o w i n g elemental a n a l y s e s : C, 77,2%; H, 5.05% N, 1.69%; S, 2.08%; ash, 2.0%. The experiments were c a r r i e d out i n e i t h e r a r o c k i n g 500-ml autoclave f u l l y l i n e d w i t h T e f l o n or i n a 300 m l - H a s t e l l o y C MagneDrive s t i r r e d autoclave from Autoclave Engineers. In general, the r e a c t o r was charged with c o a l and c a t a l y s t , evacuated, then f i l l e d with 0.7 mole of HC1 ^~ 500 p s i ) and 800 p s i of hydrogen. The r e a c t i o n mixture was heated to and kept a t the r e a c t i o n temperature f o r a given p e r i o d . A f t e r the r e a c t i o n , the r e a c t o r was cooled slowly to room temperature. The gases were analyzed by gas chromatography to determine hydrogen, methane, ethane, and propane contents. The r e a c t o r was then depressurized and the r e a c t i o n mixture washed w i t h water u n t i l the washings were neutral. The f i l t e r e d c o a l products were then allowed to dry i n a vacuum oven at 115°C overnight. The t r e a t e d product c o a l was u s u a l l y c h a r a c t e r i z e d by elemental analyses (C, Η, Ν ) , by molecular weight determinations, and by s o l u b i l i t i e s i n THF and p y r i d i n e . THF and p y r i d i n e s o l u b i l i t i e s were determined by s t i r r i n g a 0.50 g sample of the product c o a l i n 50 ml THF or p y r i d i n e at room temperature f o r 1 hr, f i l t e r i n g the mixture i n a medium p o r o s i t y s i n t e r e d g l a s s f i l t e r , and then washing the r e s i d u e with f r e s h solvent (~ 50 ml) u n t i l the washings were c l e a r . Results and D i s c u s s i o n AlCl /HCl. In a s e r i e s of runs i n a r o c k i n g T e f l o n - l i n e d autoclave, we f i r s t studied the r o l e of HC1, A1C1 , and H i n c o a l hydrocracking using 5 g each of A1C1 and c o a l , at 190°C ( j u s t above the melting point of A1C1 ), f o r 15 hr. As shown i n Figure 1, one or more of the three components were absent i n Runs 1 to 6 and i n Run 9, and i n each case, no i n c r e a s e i n THF and p y r i d i n e s o l u b i l i t i e s was observed. In Run 10, where a l l three components were present, s o l u b i l i t i e s increased s u b s t a n t i a l l y , suggesting that the A1C1 /HC1 system was a c t i v e . The purpose of Runs 7 and 10 was to assess the importance of HC1 i n the system under these c o n d i t i o n s ; however, the r e s u l t s are not unequivocal. Here, the presence i n the c o a l of proton sources, such as phenolic groups and traces of water, undoubtedly hydrolyzes some of the A1C1 , producing HC1. These runs i n d i c a t e that no added HC1 i s r e q u i r e d f o r c o a l hydrocracking at these lower temperatures At higher r e a c t i o n temperatures (210°C) and shorter r e a c t i o n time (5 h r ) , the added HC1 c l e a r l y i n c r e a s e s the conversion (Runs 21 and 25), suggesting that the e f f e c t i v e c a t a l y s t i n the system must c o n t a i n the elements of HCl and A1C1 . We a l s o studied the e f f e c t of p o t e n t i a l Η-donor hydrocarbons and temperature. We based our work on the r e s u l t s of S i s k i n (6), who found that saturated, t e r t i a r y hydrocarbons serve as e f f e c t i v e hydride donors i n the strong acid-promoted hydrogenolysis of benzene. In our system, they proved i n e f f e c t i v e (Runs 17, 22, 24, a

3

2

3

3

3

3

3


In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. IS

THF Solubility

50 60

RUN NO.

2

3

2

a) DMB = 2,3-Dimethylbutane b) MCP = Methylcyclopentane

AICI3/H2

AICI /H /HCI

H

Figure 1.

a

a

2

3

2

AICI /H /HCI/MCP

AICI3/H2

3

b

a

210°C, 5 hr

X

30

40

S O L U B I L I T Y (%) 20

1 9 5 C , 15 hr

10

Acid-catalyzed hydrocracking of beneficiated Illinois No. 9 coal

Pyridine Solubility

2

AICI /N /HCI/DMB

3

AICI /N /DMB

Coal Heated Alone In Evacuated Bulb

2

AICI /H /HCI 3

2

2

2

AICI3

AICI3/HCI

3

AICI /HCI/N

3

3

3

AICI /H /HCI

AICI /H /HCI (5 hr)

190 C, 15 hr

40

HCI/H

2

30

SOLUBILITY (%) 20

AICI /H /HCI/DMB

2

10

HCI

Untreated Coal

RUN| NO.


50

60


15.

LOW AND ROSS

Hydrotreatment

of

Coal

207

and 26, Figure 1). Higher temperatures allowed s h o r t e r r e a c t i o n times. The r e s u l t s f o r Run 17 (only 5 hr at 195°C) are comparable to those f o r Runs 7 and 10 (15 hr, 190°C). Runs at 195°C f o r 15 hr were f a r more e f f e c t i v e , and the conversion f o r Run 15 at 210°C f o r 5 hr i s about the same as that f o r Run 16 at 195°C f o r 15 hr. Next, we s t u d i e d the e f f e c t s of the c a t a l y s t / c o a l weight r a t i o on product character and c o a l product y i e l d s i n both the T e f l o n - l i n e d and the H a s t e l l o y C a u t o c l a v e s . At a weight r a t i o of 1.0, the two systems y i e l d e d products w i t h s t r i k i n g l y d i f f e r e n t pyridine s o l u b i l i t i e s : about 13% and 60% with the metal and Tefl o n equipment, r e s p e c t i v e l y (Figure 2). Increasing the c a t a l y s t / c o a l r a t i o to 2.0 increased s o l u b i l i t i e s to above 90% f o r both systems, but a f u r t h e r r a t i o increase a c t u a l l y caused s o l u b i l i t i e s to decrease s l i g h t l y . The s o l i d product recovery a l s o decreased with i n c r e a s i n g c a t a l y s t / c o a l r a t i o . As shown i n Figure 2, at a 2.0 r a t i o only about h a l f the c o a l was recovered as a s o l i d product. The other h a l f was converted to a mixture of methane and ethane. The s o f t e n i n g p o i n t f o r the THF-soluble fraction was about 150°C; however, the p y r i d i n e - s o l u b l e f r a c t i o n d i d not melt even a t temperatures up to 280°C. Figure 3 presents data on the H/C r a t i o s f o r products from both systems. The c o a l products from the T e f l o n - l i n e d r e a c t o r have c o n s i s t e n t l y higher H/C r a t i o than those from the H a s t e l l o y C reactor. R e s u l t s i n the H a s t e l l o y C autoclave were unchanged when a l o o s e l y f i t t i n g T e f l o n l i n e r was used. We have no d e t a i l e d explanation f o r the e f f e c t of autoclave s u r f a c e on the r e s u l t s , but p a s s i v a t i o n of the metal s u r f a c e by some minimum q u a n t i t y of c a t a l y s t i s part of the answer. Whatever the mechanism, the Teflon surface i s h e l p f u l . The c a t a l y s t system g a s i f i e s some of the c o a l d i r e c t l y to methane and ethane. This r e s u l t and the e f f e c t s of temperature on c o a l conversion are shown i n Table I. The t a b l e shows data from runs at 210°C f o r r e a c t i o n times from 45 min to 5 hr, and at 300°C f o r a 90 min r e a c t i o n time. The 210°C data are from an e a r l i e r phase of our work, where the g a s i f i c a t i o n was not q u a n t i f i e d , and the g a s i f i c a t i o n was determined by d i f f e r e n c e . For the 300°C work, the q u a n t i t i e s of gases and r e s i d u e were determined independently, and thus, the mass balances f o r these runs are not e x a c t l y 100%. The 300°C runs are a l l f o r 90 min, and Runs 83 and 85 show s t r i k i n g degrees of g a s i f i c a t i o n . More than 90% of the carbon i n the c o a l was converted to a 50/50 mixture of methane and ethane i n these experiments. In the next three runs, no HC1 was present, and we observe a cumulative e f f e c t of i t s absence. The degrees of g a s i f i c a t i o n d e c l i n e s e v e r e l y , and a l l the s o l i d c o a l products recovered have d e c l i n i n g p y r i d i n e s o l u b i l i t i e s and H/C r a t i o s . Kawa et a l . (2) observed a s i m i l a r e f f e c t f o r HC1.



208


CATALYST/COAL

Figure 2.

(wt/wt)

Effect of autoclave surface and catalyst I coal ratio on coal conversion.

The AlClj/HCl system was used with reaction temperature of 210°C, for 5 hr in a stirring Hastelloy C autoclave or rocking Teflon-lined autoclave.



LOW AND ROSS

Hydrotreatment

of

Coal

2 CATALYST/COAL

3 (wt/wt)

Figure 3. Comparison of H/C atomic ratio of treated product coal vs. effects by different reactors and catalyst/coal ratios. For runs at 210°Cand5hr.



210

Table I THE EFFECT OF RESIDENCE TIMES ON COAL GASIFICATION (4 g I l l i n o i s No. 6 c o a l , 8 g A1C1 , 500 p s i HC1, 800 p s i H , i n 2 300 ml s t i r r e d H a s t e l l o y C autoclave) 3

2

Run

Residence Time

67

5 hr

Coal Residue %Recovered %Pyridine Solubility a

% H/C

Coal , Gasified

0.83

61

b


210°C

46

C

39

97

5 hr

48

87

0.82

52

b

41

4 hr

49

91

0.84

51

b

66

90 min

47

96

0.85

53

b

45 min

72

93

0.82

28

b

71

45 min

66

97

0.82

34

b

83

90 min

18

78

0.72

96

d

85

90 min

18

83

0.74

90

d

69

C

300°C

86

e

90 min

30

60

0.75

72

d

87

e

90 min

49

31

0.68

56

d

88

e

90 min

68

28

0.64

36

d

°Based on 4 g of c o a l . ^Based on unaccounted f o r s o l i d product. Run with 3 g c o a l and 6 g A1C1 . 3

^Determined independently. CHz,/C H - 1/1. Traces of propane were seen i n Runs 86, 87, and 88. 2

e

6

Run without HC1


15.

LOW AND ROSS

Hydrotreatment

of

211

Coal

These data can be explained by the f o l l o w i n g scheme: 1 Coal H/C = 0.79

2 Coal product

2Ί l ^ peak enhancement. The high b o i l i n g l i q u i d i s composed of s p e c i e s with a very wide range of b o i l i n g p o i n t s . S t a r t i n g with phenol (181°C) a t the low end and n-C^ffl^ (497°C) a t the upper end. A careful examination of Table I I r e v e a l s that f r a c t i o n a l d i s t i l l a t i o n or s u b l i m a t i o n can be e f f e c t i v e l y used to separate the high b o i l i n g l i q u i d i n t o separate f r a c t i o n s enriched w i t h phenols (180-230°C), aromatic hydrocarbons (230-300°C) and alkanes (300-500°C). Sim i l a r l y the low b o i l i n g l i q u i d s can a l s o be f r a c t i o n a t e d i n t o en r i c h e d samples. The minor components of the high and low b o i l i n g l i q u i d s are concentrated i n these f r a c t i o n s and can be i d e n t i f i e d by use of GC and GC-MS. The proton nmr s p e c t r a show the d i s t r i b u t i o n of c h e m i c a l l y bound hydrogen among the aromatic r i n g s , a l i p h a t i c chains and other carbon atoms with v a r y i n g chemical s h i f t s due to d i f f e r e n t f u n c t i o n a l groups. The s p e c t r a g i v e o n l y a very q u a l i t a t i v e p i c t u r e about the chemical nature of the numerous components present i n the l i g n i t e d e r i v e d products. An approximate estima t i o n of the aromatic and the a l i p h a t i c m o i e t i e s i n the sample could be attempted with reasonable success. F i g u r e 5 shows the proton nmr s p e c t r a of four d i f f e r e n t samples. Most of the com ponents of the sample i n F i g u r e 5b and 5c a r e l i s t e d i n Table I and I I . F l u i d s d e r i v e d from hydrogenated West V i r g i n i a subbituminous c o a l a r e composed of more a l k y l a t e d aromatics com pared to Texas l i g n i t e d e r i v e d products. Hydrogénation of Texas l i g n i t e c l e a v e s the l a t t i c e s t r u c t u r e r e l e a s i n g the aromatic and a l i p h a t i c c o n s t i t u e n t s w h i l e simple benzene e x t r a c t i o n of l i g n i t e r e l e a s e s only a small amount of alkanes (Figure 5c and 5d). Since the comparative nature of products d e r i v e d from one hydrogénation experiment to another does not change much, proton nmr can be used to see the products d i s t r i b u t i o n and the extent of the r e a c t i o n . Compared to GC and GC-MS, proton nmr r e q u i r e s a short time and the sample c o n t a i n i n g n o n v o l a t i l e s can be used. The proton nmr s p e c t r a of complex mixtures such as c o a l a

a

n

e



268

Table I I . I d e n t i f i c a t i o n of Major Components i n the High B o i l i n g L i q u i d s Peak No. 1 2


3 4 5 6 7 8 9

10 11

12 13 14 15 16 17 18 19

20 21 22 23 24 25 26 27 28 29 30 31 32 33

34 35 36

37 38

39 40 41 42

43

Compound Phenol l-Ethyl-3-methylbenzene plus Decane 0-Cresol p-Cresol n-Undecane plus m e t h y l c r e s o l 13) s a l t water (3 NaOH: 10 NaCl: 50 H 0) and continuously e x t r a c t e d with THF to y i e l d a b l a c k THF l a y e r , a c o l o r l e s s H 0 l a y e r and a darkc o l o r e d p r e c i p i t a t e . A p o r t i o n of t h i s p r e c i p i t a t e could be d i s s o l v e d by re-suspension i n H 0 (pH = 6) followed by THF extraction. This behavior i s suggestive of amphoteric m a t e r i a l s . The o r i g i n a l hot THF l a y e r was f i l t e r e d then evaporated t o dryness. The dry p r e c i p i t a t e was s t i r r e d with warm water f o r 12 hours, i n order to remove extraneous c h l o r i d e i o n , followed by f i l t r a t i o n of the p r e c i p i t a t e . This p r e c i p i t a t e was washed w i t h water u n t i l a negative t e s t f o r c h l o r i d e i o n was obtained. The SRC bases were then r e - c o n s t i t u t e d i n THF, f i l t e r e d , solvent removed and d r i e d i n vacuo a t 75°C. 2

2

2

Scheme I I o u t l i n e s the i s o l a t i o n of SRC n e u t r a l s and a c i d s . The THF f i l t r a t e was i n i t i a l l y e x t r a c t e d with b a s i c (pH > 13) s a l t water to y i e l d a b l a c k THF l a y e r , a black H 0 l a y e r and i n s o l u b l e m a t e r i a l which was removed by f i l t r a t i o n . The THF l a y e r which contained SRC n e u t r a l s was evaporated t o dryness, washed to remove r e s i d u a l c h l o r i d e i o n and r e c o n s t i t u t e d i n the same manner as the SRC bases. The i n s o l u b l e m a t e r i a l and H2O l a y e r were combined, a c i d i f i e d and extracted with THF. The black THF l a y e r which r e s u l t e d was evaporated, washed and r e c o n s t i t u t e d 2



280


P4 W H

H •J PU
υ pu M CO

H M

CM

< & PQ

33

H H

SS ss H

S,

I H I

W W PM

co

Ο

CO

33

Ο W >2

Pu 33 H

5!

W

W Pu

CO

P3

CO

H :=> H

H

M

H

W H

CO

§ « w

Pu C§ 33 Ο H Pj 53 M

> W

CO ' CO

Organic chemistry of coal

Fundamentals of Organic Chemistry

Organic Chemistry