During coal pyrolysis, the break up of the coal macromolecular network is controlled by the relative rates of bond breaking, crosslinking and mass transport.
CROSSLINKING REACTIONS G.V.
Deshpande, P.R.
Advanced Fuel Research, Inc.,
IN COAL PYROLYSIS
Solomon, and M.A.
Serio
87 Church S t r e e t , East H a r t f o r d , CT 06108 INTRODUCTION
During coal p y r o l y s i s , t h e break up o f t h e coal macromolecular network i s c o n t r o l l e d by the r e l a t i v e r a t e s o f bond breaking, c r o s s l i n k i n g and mass t r a n s p o r t . C r o s s l i n k i n g r e a c t i o n s are important because t h e u l t i m a t e t a r y i e l d and t a r molecular weight d i s t r i b u t i o n are dependent on t h e e x t e n t o f these r e a c t i o n s . C r o s s l i n k i n g , as measured by s o l v e n t s w e l l i n g experiments, i s observed t o be rank dependent, w i t h l i g n i t e s c r o s s l i n k i n g a t l o w e r temperatures than bituminous coals.
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I n a recent study o f c r o s s l i n k i n g , Suuberg e t a l . (1) observed t h a t t h e This c r o s s l i n k i n g r a t e appeared t o c o r r e l a t e w i t h t h e e v o l u t i o n o f CO It appears t t a t c r o s s l i n k i n g c o r r e l a t i o n was confirmed by Solomon e t al. (2.3). may be r e l a t e d t o the decomposition o f carboxyl groups (whose c o n c e n t r a t i o n i s rank dependent) t o form Cop. Recent research ( 4 ) has a l s o demonstrated t h a t s u b s t a n t i a l r e d u c t i o n s i n t h e c r o s s l i n k i n g r e a c t i o n s can be achieved by u l t r a r a p i d heating. The h i g h h e a t i n g r a t e c o n d i t i o n s f o r l i g n i t e s produce m e l t i n g and s w e l l i n g o f char, higher y i e l d s of s o l u b l e products, and product molecular weight d i s t r i b u t i o n s p r e v i o u s l y seen o n l y f o r m e l t i n g , e a s i l y s o l u b l e coals. T h i s paper describes a study o f c r o s s l i n k i n g behavior i n which chars o f a number o f coals have been pyrolyzed under a v a r i e t y o f temperature h i s t o r i e s and analyzed a t i n t e r m e d i a t e e x t e n t s o f p y r o l y s i s f o r s o l v e n t s w e l l i n g behavior, f u n c t i o n a l group compositions and gas e v o l u t i o n . The behavior i s c o n s i s t e n t w i t h t h e hypothesis t h a t l o w temperature c r o s s l i n k i n g i s r e l a t e d t o t h e decomposition o f carboxyl groups t o form CO2. EXPERIMENTAL Coals Exanined Experiments were done w i t h North Dakota (Zap), B i g Brown Texas, and perdeutero-methylated B i g Brown Texas l i g n i t e s , Wellmore Kentucky #9, P i t t s b u r g h Seam ( h i g h ash), P i t t s b u r g h Seam (Argonne sample) bituminous c o a l s and o x i d i z e d P i t t s b u r g h Seam ( h i g h ash) bituminous coal. The u l t i m a t e a n a l y s i s of each coal i s given i n Table I. Char P r e p a r a t i o n The ex eriments described here were c a r r i e d out on chars formed from the c o a l s given i n Tagle I. The chars were formed by h e a t i n g i n an i n e r t gas w i t h i n an e n t r a i n e d f l o w r e a c t o r [EFR) and a heated t u b e r e a c t o r (HTR) f o r a v a r i e t y o f residence times and maximum temperatures, o r by h e a t i n g i n a Thermogravimetric Analyzer (TGA) a t 30"C/min t o 9 0 0 Y where t h e v o l a t i l e s a r e analyzed o n - l i n e by F o u r i e r Transform I n f r a r e d (FT-IR) spectroscopy (TG-FTIR). A more d e t a i l e d d e s c r i p t i o n can b e found i n Ref. 5. Char C h a r a c t e r i z a t i o n The chars were analyzed by q u a n t i t a t i v e FT-IR spectroscopy u s i n g t h e K B r p e l l e t method (6.7). The chars were a l s o analyzed using t h e s o l v e n t s w e l l i n g techniques developed by J.W. Larsen and coworkers ( 8 3 ) t o q u a n t i f y and m o n i t o r t h e densities o f covalent c r o s s l i n k s i n s i d e t h e macromolecular framework o f coal chars. 3 10
RESULTS AllD DISCUSSION
Rank Dependence o f C r o s s l i n k i n g Reactions Measurements o f t h e appearance o f c r o s s l i n k s d u r i n g coal p y r o l y s i s were r e c e n t l y reported by Suuberg e t a l . ( 1 ) . T h e i r r e s u l t s showed t h a t l i g n i t e s c r o s s l i n k a t temperatures (650 K) f a r below those where bituminous c o a l s c r o s s l i n k This m o t i v a t e d t h e present study o f s y s t e m a t i c a l l y measuring t h e e x t e n t (800 K). of c r o s s l i n k i n g i n coal p y r o l y s i s . Figure 1 shows t h e v o l u m e t r i c s w e l l i n g r a t i o f o r Zap and Big Brown Texas l i g n i t e s and Wellmore Kentucky #9, P i t t s b u r g h Seam (Argonne sample) and Oxidized P i t t s b u r g h Seam ( h i g h ash) bituminous c o a l s measured as a f u n c t i o n o f temperature. The s w e l l i n g r a t i o p r o f i l e s are presented as (1-X) where X i s the change i n the solvent s w e l l i n g r a t i o between the coal and char, normalized by t h e maximum change. The curves are q u i t e d i f f e r e n t among t h e f i v e samples. The l i g n i t e s c r o s s l i n k a t much lower temperatures than t h e bituminous coals, w h i l e t h e o x i d i z e d bituminous coal i s an i n t e r m e d i a t e case. The e x t e n t o f l o w temperature c r o s s l i n k i n g c o r r e l a t e s w i t h t h e carbonyl c o n c e n t r a t i o n o f t h e coal as measured by FT-IR. The carbonyl c o n c e n t r a t i o n i s d i r e c t l y r e l a t e d t o t h e c o n c e n t r a t i o n o f carboxyl groups. The high rank c o a l s have a very low c o n c e n t r a t i o n o f carboxyl groups, as seen by a l o w i n t e n s i t y carbonyl band a t 1700 wavenumbers, i n Fig. 2. The o x i d i z e d P i t t s b u r g h Seam coal and the low rank coals have much h i g h e r carbonyl peaks. B i q Brown Texas l i p i t e shnws a s l i 9 h t l y s l o w e r r a t e n f cross!inkin; than Z:p lignite; Schobert e t a l . (10) compared t h e ESCA s p e c t r a o f Big Brown Texas and Beulah Zap l i g n i t e s and found t h a t the c a r b o x y l i c peak t o be l e s s pronounced i n the B i g Brown spectrum. Spackman (11) has a l s o reported t h a t B i g Brown Texas l i g n i t e had a lower c a r b o x y l i c content than t h e N o r t h Dakota Zap l i g n i t e . When b o t h l i g n i t e s a r e heated a t 30°C/min t o 6OO0C, Big Brown Texas l i g n i t e evolves l e s s COP (8%) than Zap l i g n i t e (11.3%). The area corresponding t o t h e carbonyl peak i n t h e FT-IR spectrum o f B i g Brown Texas l i g n i t e i s a l s o l e s s (1.29) than f o r t h e Zap, l i g n i t e (1.69). These observations are c o n s i s t e n t w i t h t h e hypothesis t h a t e a r l y c r o s s l i n k i n g r e a c t i o n s i n l i g n i t e s occur w i t h l o s s o f carboxyl groups and e v o l u t i o n of carbon d i o x i d e and t h e e x t e n t o f c r o s s l i n k i n g i s d i r e c t l y r e l a t e d t o t h e amount o f these l a b i l e carboxyl groups present i n coal. Bituminous coals which do not have a l a r g e c o n c e n t r a t i o n of these groups do not undergo e a r l y c r o s s l i n k i n g reactions. A major c o n t r i b u t i o n o f hydroxyl groups i n e a r l y c r o s s l i n k i n g r e a c t i o n s i s n o t l i k e l y because bituminous c o a l s have a l a r g e r c o n c e n t r a t i o n o f hydroxyl groups than the carboxyl groups and do n o t c r o s s l i n k a t l o w temperatures.
Heating Rate Dependence o f C r o s s l i n k i n g Reactions
An important o b s e r v a t i o n was made t h a t c r o s s l i n k i n g r e a c t i o n s could be minimized by c a r r y i n g o u t t h e py.rolysis a t a very h i g h h e a t i n g r a t e . I n Fig. 3, t h e e f f e c t of h e a t i n g r a t e on t a r y i e l d and v o l u m e t r i c s w e l l i n g r a t i o i n p r i d i n e f o r North Dakota (Zap) l i g n i t e i s compared f o r r a p i d p y r o l y s i s (20,000°C/s~ and slow p y r o l y s i s (0.5"C/s). It can be c l e a r l y seen t h a t t h e l i g n i t e s t a r t s t o c r o s s l i n k p r i o r t o t h e t a r e v o l u t i o n i n slow p y r o l y s i s , whereas c r o s s l i n k i n g occurs simultaneously w i t h t a r e v o l u t i o n i n r a p i d p y r o l y s i s . The t a r y i e l d obtained d u r i n g r a p i d p y r o l y s i s i s h i g h e r than t h a t obtained a t low h e a t i n g r a t e by more than a f a c t o r o f two. F i g u r e 4 compares scanning e l e c t r o n rnicro2raphs o f l i g n i t e chars produced a t 800°C w i t h h e a t i n g r a t e s o f 6OO0C/s and 20,000 C/s. The 6OO0C/s char shows l i t t l e evidence o f f l u i d i t y w h i l e t h e 20,000"C/s char shows f l u i d i t y , bubbling, and s w e l l i n g . T h i s i s b e l i e v e d t o be due t o reduced c r o s s l i n k i n g reactions. 31 1
Chemical M o d i f i c a t i o n o f C r o s s l i n k i n g Reactions I n o r d e r t o t e s t t h e hypothesis o f l o w temperature c r o s s l i n k i n g i n l i g n i t e s due t o carboxyl groups, slow p y r o l y s i s ( h e a t i n g r a t e , 0.5 K / s ) o f B i g Brown Texas and perdeutero-methylated B i g Brown Texas l i g n i t e s were c a r r i e d o u t i n t h e TG-FTIR. The sample o f perdeutero-methylated B i g Brown Texas l i g n i t e was provided f o r t h i s study by Dr. Ron L i o t t a . The gas e v o l u t i o n r a t e p r o f i l e s ( i n a r b i t r a r y u n i t s ) f o r gas species CO, C02, p a r a f f i n s , CH4, and H20 a r e shown i n Figs. 5a-5e, r e s p e c t i v e l y , f o r Big Brown Texas and perdeutero-methyl ated B i g Brown Texas l i g n i t e s . The amount o f gas species evolved i s p r o p o r t i o n a l t o t h e area under t h e curve. It can be seen t h a t d u r i n g t h e p y r o l y s i s stage (Time < 2000 s) t h e amount of CO2, CO, and H20 evolved i s l e s s f o r t h e perdeutero-methylated coal w h i l e t h e amount o f CH4 evolved i s s l i g h t l y more. The amount o f p a r a f f i n evolved (which i s r e l a t e d t o t h e amount o f t a r evolved) i s also h i g h e r f o r t h e perdeutero-methylated coal. The weight l o s s p r o f i l e f o r these two c o a l s i s shown i n Fig. 5 f . The i n i t i a l weight l o s s p r o f i l e (Time < 800 s, T < 300°C) i s d i f f e r e n t w h i l e t h e r e s t o f t h e weight l o s s p r o f i l e d u r i n g t h e p y r o l y s i s stage (800 < Time < 2000 s; 300 < T < 900OC) seems t o be v e r y s i m i l a r . The increase i n weight a t 2040 sec i s due t o noise i n t h e balance and i s n o t a r e a l effect. CO, CO2, and H20 e v o l u t i o n i s lower and CH4 and p a r a f f i n (300 < T < 900°C) i s h i g h e r f o r t h e perdeutero-methylated coal. Hence t h e d i f f e r e n c e i n t h e weight l o s s p r o f i l e s o f the two l i g n i t e s . The e f f e c t o f r e d u c t i o n i n c r o s s l i n k i n g r e a c t i o n s observed i n p y r o l y s i s o f perdeutero-methylated coal i s n o t o n l y on t h e t o t a l amount o f t a r evolved b u t a l s o on the molecular weight d i s t r i b u t i o n o f t h e t a r . F i g u r e 6 compares t h e FIMS spectra f o r raw and perdeutero-methylated Big Brown Texas 1 i g n i t e s . The average molecular weight i s s u b s t a n t i a l l y increased from t h a t o f t h e unmethylated coal and now resembles t h a t o f a bituminous coal.
Effects o f M i n e r a l s on C r o s s l i n k i n g Reactions Several i n v e s t i g a t o r s (12-15) have s t u d i e d t h e r o l e o f exchangeable c a t i o n s i n g a s i f i c a t i o n and p y r o l y s i s o f low rank coals. The ion-exchange technique as o u t l i n e d by Schafer (16.17) i s used t o exchange c a t i o n s w i t h ammonium i o n s o r l o a d t h e coal w i t h a c e r t a i n c a t i o n (e.g. calcium) i n d i f f e r e n t amounts. T y l e r and Schafer (13) found t h a t t h e removal o f c a t i o n s from G e l l i o n d a l e c o a l s increased t h e y i e l d s o f b o t h t a r and t o t a l v o l a t i l e matter. The converse was a l s o observed i n t h a t t h e a d d i t i o n o f Ca2+ i o n s t o an acid-form coal reduced t h e y i e l d s . 4 h e r e v e r s i b i l i t y o f t h e phenomena shows t h a t t h e increase i n y i e l d s on c a t i o n removal i s n o t t h e r e s u l t o f any permanent chemical m o d i f i c a t i o n o r degradation o f t h e organic s t r u c t u r e o f t h e coal d u r i n g t h e a c i d treatment (2N HC1 a t room temperature). T h i s m o t i v a t e d t h e study o f . e f f e c t o f m i n e r a l s on c r o s s l i n k i n g r e a c t i o n s . As calcium has been t h e c a t i o n most e x t e n s i v e l y studied and l o w rank c o a l s have a l a r g e amount o f calcium c a t i o n s attached t o t h e c a r b o x y l a t e anions, I n d i a n Head Zap l i g n i t e was used i n t h i s study. Two techniques were used t o remove t h e c a l c i u m I n the f i r s t c a t i o n s , t h e d e t a i l s o f which can be found elsewhere (18,19), technique, c a l c i u m ions were i o n exchanged w i t h 1N.ammonium acetate f o r t h r e e 24 hour periods. The c a l c i u m content a f t e r i o n exchange was reduced from 1.66 t o 0.2%. I n t h e second technique, d e m i n e r a l i z a t i o n w i t h HC1 and HF was used. The calcium c o n t e n t a f t e r d e m i n e r a l i z a t i o n decreased t o 0.01%. The s w e l l i n g r a t i o p r o f i l e s presented as (1-X) where X i s t h e change i n t h e s o l v e n t s w e l l i n g r a t i o between t h e coal and char normalized by t h e maximum change
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f o r i o n exchanged Zap l i g n i t e , demineralized Zap l i g n i t e and Zap l i g n i t e are canpared i n Fig. 7. The c r o s s l i n k i n g behavior f o r ion-exchanged Zap l i g n i t e i s s i m i l a r t o raw l i g n i t e and shows e a r l y c r o s s l i n k i n g . It should be noted here t h a t t h e calcium has n o t t o t a l l y been removed by t h e ion-exchange technique i n t h i s study. The c r o s s l i n k i n g behavior of demineralized Zap l i g n i t e i s s t r i k i n g l y d i f f e r e n t from t h a t o f Zap l i g n i t e . It shows a s h i f t t o a h i g h e r temperature f o r t h e same l o s s i n s w e l l i n g due t o c r o s s l i n k i n g reactions. Both the raw and demineralized Zap l i g n i t e s were pyrolyzed i n t h e TG-FTIR apparatus. The t a r evolved was higher ( d a f b a s i s ) and t h e CO and COP e v o l u t i o n s were l o w e r f o r t h e demineralized case. An increase i n t a r e v o l u t i o n i s expected due t o reduced c r o s s l i n k i n r e a c t i o n s . When p y r o l y s i s o f two l i g n i t e s were c a r r i e d out a t h i g h h e a t i n g r a t e q5000 K / s ) i n t h e entrained flow r e a c t o r , t h e t a r y i e l d was increased from 14% ( f o r raw l i g n i t e ) t o 22% due t o d e m i n e r a l i z a t i o n . S i m i l a r increase i n t a r y i e l d has been found f o r increase i n h e a t i n g r a t e d u r i n g p y r o l y s i s which has been discussed i n t h e s e c t i o n e n t i t l e d “Heating Rate Dependence o f Cross1 i n k i n g Reactions”. This f u r t h e r supports the idea o f reduced c r o s s l i n k i n g due t o demineralization. It should be noted t h a t t h e increase i n t a r y i e l d due t o the removal o f calcium found by T y l e r and Schafer (13) was f o r coals whose c a t i o n s were removed by Both t h e l i g n i t e and t h e demineralized l i g n i t e s were e x h a u s t i v e l y a c i d treatment. e x t r a c t e d by p y r i d i n e i n a soxhlet apparatus t o determine whether any The amount o f p y r i d i n e e x t r a c t a b l e depolymerization o f l i g n i t e had occurred. m a t e r i a l was 0% f o r t h e raw l i g n i t e and 2.6% f o r t h e demineralized l i g n i t e . The volumetric s w e l l i n g r a t i o i n p y r i d i n e was 2.4 f o r t h e r a w l i g n i t e and 2.5 f o r t h e demineralized l i g n i t e . Both r e s u l t s show t h a t a very small degree o f d e p o l p e r i z a t i o n had occurred, If :ny, 36; t o t h e deiiiirierai i z a i i o n procedure employed t o remove t h e cations. Hence t h e increase i n t a r amount and s h i f t o f t h e c r o s s l i n k i n g curve t o a higher temperature f o r t h e same amount o f l o s s i n s w e l l i n g due t o c r o s s l i n k i n g for demineralized Zap l i g n i t e appears t o be due t o t h e reduced mineral content.
E f f e c t o f O x i d a t i o n on C r o s s l i n k i n g Reactions To f u r t h e r study t h e r o l e o f carboxyl groups i n c r o s s l i n k i n g , P i t t s b u r g h Seam bituminous coal was o x i d i z e d i n an oven i n a i r t o add carboxyl groups t o t h e coal and see whether t h e o x i d i z e d coal behaved l i k e a l i g n i t e i n slow h e a t i n g r a t e p y r o l y s i s . A f t e r 239 hours o f o x i d a t i o n , a l a r g e increase i n the a b s o r p t i o n o f I R due t o carbonyl band a t 1700 wavenumbers i s observed which i s shown i n Fig. 2. There i s a s l i g h t change i n t h e OH band a t 3300 wavenumbers, a l a r g e decrease i n t h e a l i p h a t i c C-H a t 2900 wavenumbers. This was c o n s i s t e n t w i t h t h e f i n d i n g s o f o t h e r (20-22) i n v e s t i g a t o r s . The chars o f t h e o x i d i z e d coal formed a t i n t e r m e d i a t e temperatures were swelled i n p y r i d i n e t o determine t h e c r o s s l i n k d e n s i t i e s . These r e s u l t s are shown i n Fig. 1. The o x i d i z e d coal shows e a r l i e r c r o s s l i n k i n g . as seen by t h e decrease i n s w e l l i n g r a t i o (decrease i n value o f (1-X)) a t temperatures above 300yC. The decrease i s n o t as l a r g e as t h a t f o r t h e l i g n i t e s because t h e c o n c e n t r a t i o n o f carboxyl groups formed d u r i n g o x i d a t i o n i s n o t as l a r g e as t h a t found i n t h e l i g n i t e s . The h e i g h t o f t h e shoulder peak a t 1700 wavenumbers corresponding t o carbonyl band f o r o x i d i z e d coal i s s m a l l e r than b o t h t h e Zap l i g n i t e and t h e B i g Brown Texas l i g n i t e . The o n - l i n e FT-IR spectra o f t h e gas e v o l u t i o n products from t h e raw coal and t h e o x i d i z e d coal were taken d u r i n g p y r o l y s i s and are shown f o r d i f f e r e n t temperatures d u r i n g p y r o l y s i s i n Fig. 8. There i s a l a r g e r amount o f CO e v o l u t i o n a t low temperatures f o r t h e o x i d i z e d coal than f o r t h e raw coal. T h i s was also
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found by Ignasiak e t a l . (21) i n t h e i r study o f p y r o l y s i s o f o x i d i z e d bituminous coals. The amount of C02 and CO evolved were higher f o r the o x i d i z e d bituminous coal. This i s c o n s i s t e n t w i t h t h e l a r g e r carbonyl peak i n t h e FT-IR spectrum o f the o x i d i z e d coal. The amount o f t a r e v o l u t i o n ( a s seen from a b s o r p t i o n o f C-H band a t 2900 wavenumbers) a t temperatures between 400'C and 550°C i s g r e a t e r f o r t h e raw coal than t h e o x i d i z e d coal. This i s c o n s i s t e n t w i t h t h e f i n d i n g s o f Furimsky e t a l . (20). The t a r , as i t flows o u t o f t h e p y r o l y s i s chamber o f t h e TGFTIR i n t o t h e FT-IR c e l l , forms an aerosol which causes s c a t t e r i n g and r e s u l t s i n increased absorption a t high wavenumbers. The s c a t t e r i n g i s maximum a t temperatures between 450 and 5OOOC and i s a l s o found t o be g r e a t e r f o r t h e raw coal than t h e o x i d i z e d coal.
CONCLUSIONS
1.
For the l o w rank coals, t h e amount o f t a r obtained i n a p y r o l y s i s process increases w i t h t h e increase i n t h e h e a t i n g r a t e .
2.
The i n i t i a l c r o s s l i n k i n g r e a c t i o n s i n l o w rank c o a l s appear t o be due t o t h e presence o f carboxyl groups. High rank coals which do n o t have these grou s i n l a r g e c o n c e n t r a t i o n do n o t show t h i s k i n d o f behavior i n py roPy s is
.
3.
Chemical m o d i f i c a t i o n o f carboxyl groups i n 1 i g n i t e s by m e t h y l a t i n g r e s u l t s i n increased t a r y i e l d and molecular weight d i s t r i b u t i o n o f t a r l o o k s l i k e t h a t o f a bituminous c o a l .
4.
D e m i n e r a l i z a t i o n o f t h e l i g n i t e r e s u l t s i n decrease i n t h e r a t e o f c r o s s l i n k i n g r e a c t i o n and i n c r e a s e i n t a r y i e l d and t h e increase i s h i g h e r when p y r o l y s i s i s c a r r i e d out a t a h i g h e r heating r a t e . The amount o f CO and C02 e v o l u t i o n i s a l s o decreased due t o d e m i n e r a l i z a t i o n . These r e s u l t s are c o n s i s t e n t w i t h i o n exchanged minerals p l a y i n g an i m p o r t a n t r o l e i n t h e cross1 i n k i n g reactions.
5.
O x i d a t i o n o f bituminous coal r e s u l t s i n e a r l y c r o s s l i n k i n g d u r i n g p y r o l y s i s due t o t h e presence o f carboxyl groups introduced d u r i n g t h e o x i d a t i o n process.
ACKNOWLEOGEIIENT The authors wish t o thank t h e P i t t s b u r g h Energy Technology Center o f t h e Department of Energy f o r t h e support o f t h i s work under Contract No. DE-FG22-85PC80910. The authors would a l s o l i k e t o thank Dr. Ron L i o t t a f o r samples o f perdeuteromethylated B i g Brown Texas l i g n i t e .
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Lee,
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TABLE I ULTIMATE ANALYSES OF COALS USE0 (ZDAF) C
H
N
S
Zap N. Dakota
66.5
4 .E
1.1
1.1
26.5
Big Brown
72.4
5.5
1.4
1.2
19.5
Wellmore Kentucky #9 Bituminous
86 .O
5.4
1.5
1.2
5.9
Pittsburgh Seam #8 Bituminous
82.1
5.6
1.7
2.4
8.2
Pittsburgh Seam #8 (Argonne sample) Bi t umi no us
83.3
5.9
1.6
2.3
6.9
0 (diff)
Lignite
Texas Lignite
Zap Big Brown A Wellmore Ky.#9 X Pitts Seam (OX) + Pitts Seam (Arg)
0
X I
r(
Y I
0
200
400 600 800 Temperature (“C)
Figure 1. Comparison of Swelling Data of Zap Lignite, Big Brown Texas Lignite, Wellmore Bituminous Coal, Pittsburgh Seam Bituminous (high ash) Oxidized Coal and Pittsburgh Seam (Argonne sample) Bituminous Coal in a TG-FTIR at Various Final Temperatures (Heating Rate = 0.5 Ws).
3 16
1000
.75 -
.30-
4000 3600 sa00 2800 2k00 2000 1600 1400 S'OO
4b0
Wavenumbers Comparison of the FT-IRSpectra of a) Zap Lignite, b) Big Brown Texas Lignite, c) Pittsburgh Seam Bituminous (high ash) Oxidized Coal, d) Pittsburgh Seam (Argonne) Bituminous, and e) Wellmore Coals Dry, Mineral Matter Corrected.
Figure 2.
317
.23
E
6
0 0
7
100
Figure 3. Effect of Temperature on Tar Yield and Pyridine Swelling Ratio of Char for Rapid Pyrolysis of Zap Lignite in Carbon Dioxide (solid line) and Slow Pyrolysis of Zap Lignite in Helium (dashed line).
I
Figure 4. Scanning Electron Micrographs of North Dakota Lignite Chars. a) GOO"C/sec Heating Rate and b) 20,000°C/sec Heating Rate.
318
5. Thermogravimetric/Evolved Gas Analysis of Big Brown Texas and Perdeutero Methylated Big Brown Texas Lignites. a-e) Evolution Rate in Arbitrary Units for Individual Gas Species, and 0 Measured Weight Loss. (HeatingRate = 0.5 Ws). 1 = Big Brown Texas Lignite and 2 = Perdeutero Methylated Big Brown Texas Lignite. figUre
319
Figure 6. Comparison of FlMS Spectra for Raw and Perdeutero-methylated Big Brown Texas Lignite.
+ Zap Lignite X zap Lignite
Ion-Exchanged
1.61
0 DemineralizedZap Lignite
1.2X 3
0.
'
e 0.4-
\L
0.0
0
I
I
I
100
200
SO0
*-= +-
- -0-- - --0
I
I
400
500
Temperature ("C)
Y
I.
600
T
700
I
800
900
Figure 7. Effect of Removal of Ca by Ion Exchange or Demineralization on Crosslinking Behavior of Zap Lignite. 320
=--"1
* bQ
Q
zoz A0
65O'C
1.6
.oo..MI,
I
,
,
4#l
,
~
,
, SMO
, , ,
, , ,
do00
, I loo0
Absorbance FT-IR Spectra of Evolved Products from Pyrolysis of Figure& Pittsburgh Seam Bituminous (high ash) Coal and Pittsburgh Seam Bituminous (high ash) Oxidized Coal.
321
