13 Oxidative Desulfurization of Coal SIDNEY FRIEDMAN, ROBERT B. LACOUNT, and ROBERT P. WARZINSKI
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Pittsburgh Energy Research Center, U.S. Energy Research and Development Administration, 4800 Forbes Ave., Pittsburgh, PA 15213
It is becoming increasingly apparent that the solution to our national energy problems will require a variety of approaches and that these must be compatible with environmental restrictions. Coal, only recently considered destined for obscurity, has been rescued by a combination of international political events and increasing difficulties in developing a nuclear power industry. Although coal as an energy source presents problems, at least it is available and can be utilized. The Federal Government, as part of the program administered by the Energy Research and Development Administration, is carrying out research on many phases of coal utilization to overcome the environmental problems involved in the combustion of coal. One research project, which has been in progress at the Pittsburgh Energy Research Center since 1970, is concerned with chemical beneficiation of coal and most specifically with removal of sulfur from coal prior to combustion. Experimental Batch Experiments. Thirty-five grams of -200 mesh coal and 100 ml water were placed in a liner (glass or teflon) in a 1-L, magnetically stirred, stainless steel autoclave. The autoclave was p r e s s u r i z e d w i t h c y l i n d e r a i r t o t h e r e q u i r e d gauge p r e s s u r e (800 p s i i n t h e e x p e r i m e n t s i n T a b l e s I , I I , a n d I I I ) and t h e n was h e a t e d w i t h s t i r r i n g a t 800-1000 rpm u n t i l t h e s p e c i f i e d t e m p e r a t u r e was r e a c h e d ( a p p r o x i m a t e l y 1 h r h e a t - u p t i m e ) . O p e r a t i n g p r e s s u r e f o r 800 p s i i n i t i a l e x p e r i m e n t s was 1000-1200 p s i , d e p e n d i n g o n t e m p e r a t u r e and e x t e n t o f r e a c t i o n . After a s p e c i f i e d time a t r e a c t i o n temperature, r a n g i n g from 5 min t o 2 h r , t h e a u t o c l a v e was c o o l e d b y a n i n t e r n a l c o o l i n g c o i l . Final p r e s s u r e a t room t e m p e r a t u r e was b e t w e e n 650 a n d 750 p s i . The c o n t e n t s w e r e removed, f i l t e r e d , washed u n t i l t h e pH o f t h e f i l t r a t e was n e u t r a l , and t h e n e x t r a c t e d i n a S o x h l e t t h i m b l e w i t h w a t e r u n t i l s u l f a t e ( p r e s e n t a s CaSO,) was no l o n g e r p r e s e n t i n the fresh extract. The c o a l was t h e n d r i e d t h o r o u g h l y i n a
164
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
13.
FRIEDMAN ET
AL.
Oxidative Desulfurization of Coal
vacuum oven a t 100°C and U.S. B u r e a u o f M i n e s .
a n a l y z e d by
165
the Coal A n a l y s i s S e c t i o n ,
Semicontinuous Experiments. Using a s i m i l a r autoclave f i t t e d w i t h p r e s s u r e r e g u l a t i n g v a l v e s , the a u t o c l a v e c o n t a i n i n g t h e c o a l and w a t e r was h e a t e d t o t h e s p e c i f i e d t e m p e r a t u r e u n d e r 1 atra ( i n i t i a l p r e s s u r e ) N . At temperature, or s h o r t l y b e f o r e r e a c h i n g i t , a i r was a d m i t t e d t o t h e d e s i r e d p r e s s u r e , w h i c h was 1000 p s i e x c e p t f o r e x p e r i m e n t s d e s i g n e d t o i n v e s t i g a t e t h e e f f e c t of p r e s s u r e . T e m p e r a t u r e was k e p t a t t h e r e q u i r e d v a l u e by h e a t i n g and cooling ( c o o l i n g c o i l ) while a i r (approximately 2 c u f t / h r ) flowed through the a u t o c l a v e . A f t e r t h e r e q u i r e d t i m e a t temp e r a t u r e , t h e a u t o c l a v e was c o o l e d , and t h e p r o d u c t s were w o r k e d up a s i n t h e p r e v i o u s example.
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?
R e s u l t s and
Discussion
A l t h o u g h t h e p r o j e c t was i n i t i a l l y d i v i d e d i n t o r e m o v a l o f o r g a n i c and o f i n o r g a n i c s u l f u r (1), i t was s o o n e v i d e n t t h a t , t h o u g h one c o u l d remove p y r i t i c s u l f u r w i t h o u t r e m o v i n g o r g a n i c s u l f u r , t h e r e v e r s e was n o t t r u e . Any p r o c e s s w h i c h removed o r g a n i c s u l f u r w o u l d a l s o remove p y r i t i c s u l f u r . So t h e a p p r o a c h t o t h e p r o b l e m became one o f f i n d i n g c h e m i c a l r e a c t i o n s s u i t a b l e f o r removing o r g a n i c s u l f u r from c o a l . The c h e m i s t r y w h i c h we c h o s e t o e x p l o r e was b a s e d on two premises: t h e m a j o r p o r t i o n o f t h e o r g a n i c s u l f u r i n c o a l was of the dibenzothiophene (DBT) t y p e , and, t h e r e a g e n t s had t o be inexpensive. W h i l e we now b e l i e v e t h a t a t l e a s t a s i z a b l e f r a c t i o n o f t h e o r g a n i c s u l f u r i n c o a l i s n o t d i b e n z o t h i o p h e n i c , we have no r e a s o n t o d o u b t t h a t o v e r 50% o f i t may be. T h e s e p r e m i s e s l e d us t o t h e f o l l o w i n g h y p o t h e t i c a l twostep removal of o r g a n i c s u l f u r from c o a l . (1). O x i d a t i o n of o r g a n i c (or d i b e n z o t h i o p h e n i c ) s u l f u r to sulfone.
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
166
COAL
DESULFURIZATION
B o t h o f t h e s e r e a c t i o n s a r e i n t h e l i t e r a t u r e , so we had to m o d i f y and i m p r o v e them so t h a t t h e y c o u l d be a p p l i e d t o d e s u l f u r i z a t i o n of c o a l . The s e c o n d s t e p — t h e r e m o v a l o f SO^ f r o m DBT s u l f o n e by b a s e — was e s s e n t i a l l y q u a n t i t a t i v e when t h e s u l f o n e was h e a t e d t o 300°C i n the p r e s e n c e o f aqueous NaOH and n e a r l y as e f f i c i e n t w i t h Na CO~. T h i s was an improvement on t h e nonaqueous treatment The f i r s t s t e p i n t h e r e a c t i o n — o x i d a t i o n t o s u l f o n e — a l t h o u g h e x t e n s i v e l y documented i n t h e l i t e r a t u r e , p r e s e n t e d more o f a c h a l l e n g e . T h e r e a r e numerous o x i d a n t s r e p o r t e d w h i c h c a n e f f e c t t h e c o n v e r s i o n o f o r g a n o s u l f u r compounds t o s u l f o n e s , i n c l u d i n g KMnO^, HNC> , CrO^, H ^ / H O A c , and h y d r o p e r o x i d e s ( 3 ) . T h e s e o b v i o u s l y do n o t f i t t h e s e c o n d p r e m i s e t h a t t h e r e a g e n t s must be i n e x p e n s i v e . I t was a g r e e d t h a t t h e o n l y r e a g e n t w h i c h c o u l d be used as an o x i d a n t was t h e o x y g e n i n a i r . But DBT, and presumably the o r g a n i c s u l f u r i n c o a l , i s i n e r t to a i r at r e l a t i v e l y h i g h p r e s s u r e and t e m p e r a t u r e . T r a n s f e r o f o x y g e n t o a c a r r i e r t o f o r m a h y d r o p e r o x i d e , f o l l o w e d by r e a c t i o n o f t h e h y d r o p e r o x i d e w i t h DBT, d i d g i v e s u l f o n e . We f o u n d t h a t w i t h many h y d r o c a r b o n s , s u c h as t e t r a l i n , d e c a l i n , and c y c l o h e x a n e , m e r e l y h e a t i n g DBT w i t h a i r u n d e r p r e s s u r e i n t h e p r e s e n c e o f the hydrocarbon r e s u l t e d i n f o r m a t i o n of s u l f o n e ( 4 ) , presumably as a r e s u l t o f i n s i t u f o r m a t i o n o f h y d r o p e r o x i d e s . Benzene, w h i c h does n o t f o r m a h y d r o p e r o x i d e , a f f o r d s no s u l f o n e f o r m a t i o n under comparable c o n d i t i o n s . A p p l y i n g o u r t w o - s t e p r e a c t i o n — a i r o x i d a t i o n f o l l o w e d by t r e a t m e n t w i t h aqueous b a s e — t o c o a l , we removed up t o 50% o f o r g a n i c s u l f u r , and a l m o s t c o m p l e t e l y e l i m i n a t e d p y r i t i c s u l f u r as a b o n u s . A l t h o u g h t h i s scheme a p p e a r e d p r o m i s i n g , i t d i d r e q u i r e a s u i t a b l e o r g a n i c l i q u i d and a l s o NaOH. We a l s o e x p l o r e d a n o t h e r o x i d a t i o n s y s t e m w h i c h u s e s a i r as t h e u l t i m a t e s o u r c e o f o x y g e n . N i t r o g e n d i o x i d e ( N 0 ) i s a good r e a g e n t f o r c o n v e r t i n g s u l f i d e s t o s u l f o n e s , and i t can be u s e d i n an e a s i l y r e g e n e r a b l e s y s t e m .
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We f o u n d t h a t we c o u l d i n d e e d o x i d i z e DBT t o i t s s u l f o n e u s i n g NO^ and a i r . When t h e r e a c t i o n was e x t e n d e d t o c o a l , h o w e v e r , a s i g n i f i c a n t amount o f c o n c u r r e n t r e a c t i o n t o o k p l a c e , i n c l u d i n g n i t r a t i o n o f t h e c o a l , w h i c h consumed t h e n i t r o g e n o x i d e s and t h u s w o u l d have n e c e s s i t a t e d a c o n t i n u o u s a d d i t i o n o f NO^ r a t h e r t h a n t h e r e c y c l i n g shown i n E q u a t i o n s 3 and 4. I n t h e meantime, o u r e x p e r i m e n t s on a i r o x i d a t i o n o f o r g a n o s u l f u r u s i n g h y d r o p e r o x i d e p r e c u r s o r s l e d us t o t h e u l t i m a t e e x p e r i m e n t , t h e one i n w h i c h H«0 was u s e d i n p l a c e o f an o r g a n i c l i q u i d p h a s e . T h i s r e a c t i o n o f c o a l w i t h w a t e r and c o m p r e s s e d a i r almost q u a n t i t a t i v e l y c o n v e r t e d the p y r i t i c s u l f u r i n c o a l
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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13.
FRIEDMAN
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Oxidative
Desulfurization
of
167
Coal
t o H^SO^. I n a d d i t i o n , we a l s o removed 2 5 % o f t h e o r g a n i c sulfur. H e r e was e v i d e n c e t h a t t h e r e was some o r g a n o s u l f u r i n c o a l w h i c h was n o t D B T - l i k e , s i n c e DBT f a i l e d t o r e a c t w i t h a i r and w a t e r u n d e r t h e s e c o n d i t i o n s . I n i t i a l experiments on t h e a i r - w a t e r o x y d e s u l f u r i z a t i o n o f c o a l were c a r r i e d o u t u s i n g a b a t c h , s t i r r e d a u t o c l a v e s y s t e m . In t h i s a p p a r a t u s , i n o r d e r t o r e p l a c e o x y g e n a s i t was u s e d , i t was n e c e s s a r y t o c o o l t h e a u t o c l a v e t o n e a r room t e m p e r a t u r e , v e n t t h e s p e n t a i r , r e p r e s s u r e , a n d r e h e a t . A l t h o u g h t h i s gave s a t i s f a c t o r y d e s u l f u r i z a t i o n , i t was a n i m p r a c t i c a l a p p r o a c h f o r s t u d y i n g r e a c t i o n parameters. The r e s u l t s c i t e d i n T a b l e s I , I I , and I I I a r e f r o m 1-hr b a t c h s t u d i e s w i t h o u t r e p r e s s u r i z a t i o n a n d t h u s r e p r e s e n t l e s s t h a n maximum d e s u l f u r i z a t i o n i n some c a s e s . A l l c o a l s , except those noted, a r e bituminous. The a p p a r a t u s h a s b e e n m o d i f i e d t o a l l o w a i r t o f l o w through t h e s t i r r e d r e a c t o r w h i l e the coal-water s l u r r y remains as a b a t c h r e a c t a n t . T h i s i s o u r c u r r e n t s y s t e m . I n t h i s way, we a r e s t u d y i n g many o f t h e v a r i a b l e s a s t h e y w i l l a f f e c t t h e r e a c t i o n i n a continuous system. Our newest a p p a r a t u s , now b e g i n n i n g o p e r a t i o n , i s a f u l l y c o n t i n u o u s u n i t , f e e d i n g b o t h a i r and c o a l - w a t e r s l u r r y i n t o a r e a c t o r tube. T h i s sytera i s d e s i g n e d t o o b t a i n d a t a on r e a c t i o n r a t e s , d e v e l o p i n f o r m a t i o n f o r e c o n o m i c e v a l u a t i o n , a n d answer those q u e s t i o n s which a r i s e concerning e n g i n e e r i n g aspects o f the p r o c e s s . H e a t i n g h i g h - p y r i t e c o a l s i n aqueous s l u r r y w i t h c o m p r e s s e d a i r a t 1000-1200 p s i and a t 150°-160°C d e c r e a s e s p y r i t i c s u l f u r to n e a r t h e l o w e r l i m i t o f d e t e c t i o n b y s t a n d a r d a n a l y t i c a l procedure. Some r e s u l t s o f 1 h r b a t c h e x p e r i m e n t s a r e shown i n T a b l e I . The s u l f u r w h i c h i s removed i s c o n v e r t e d p r i m a r i l y t o aqueous s u l f u r i c a c i d , w i t h s m a l l amounts o f f e r r i c a n d f e r r o u s sulfates i nsolution. A t i n i t i a l p r e s s u r e s o f 800 p s i a n d above and a t t e m p e r a t u r e s above 160°C, 8 0 % o r more o f t h e p y r i t i c s u l f u r i n t h e M i n s h a l l Seam ( I n d i a n a ) c o a l i s removed i n 5 m i n at temperature. S i m i l a r p y r i t i c s u l f u r r e m o v a l was o b s e r v e d i n a s e r i e s o f 10 m i n e x p e r i m e n t s a t 1000 p s i i n t h e c o n t i n u o u s unit. TABLE I . P y r i t e Removal f r o m R e p r e s e n t a t i v e C o a l s by Oxydesulfurization
Seam
State
Temp (°C)
I l l i n o i s No. 5 Minshall L o v i l i a No. 4 Pittsburgh Lower F r e e p o r t Brookville
Illinois Indiana Iowa Ohio Pennsylvania Pennsylvania
150 150 150 160 160 180
P y r i t i c S u l f u r (wt %) Treated Untreated 0.9 4.2 4.0 2.8 2.4 3.1
0.1 0.2 0.3 0.2 0.1 0.1
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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168
C O A L DESULFURIZATION
A t 200 p s i , t h e r e a c t i o n i s much s l o w e r , r e q u i r i n g s e v e r a l h o u r s t o a c h i e v e even 6 0 % p y r i t i c s u l f u r r e m o v a l . F o r some c o a l s , a t l e a s t , t h e d e s u l f u r i z a t i o n i s a l m o s t a s r a p i d a t 500 p s i a s a t 1000 p s i . The o x i d a t i o n o f p y r i t i c s u l f u r i s temp e r a t u r e dependent, but a t the c o n d i t i o n s of our experiments, r e a c t i o n i s s u f f i c i e n t l y f a s t t h a t above 150°C l i t t l e i m p r o v e ment i s n o t e d . I n a few c a s e s , where a c o a l a p p e a r s t o h a v e some r e s i d u a l p y r i t e w h i c h i s n o t o x i d i z e d r e a d i l y a t 150°C, i t may be removed a t 180°C. As t h e t e m p e r a t u r e a t w h i c h t h e o x i d a t i o n i s c o n d u c t e d i s i n c r e a s e d a b o v e 150°C, a n i n c r e a s i n g amount o f o r g a n i c s u l f u r i s removed f r o m t h e c o a l . A l t h o u g h t h e p e r c e n t a g e o f o r g a n i c s u l f u r removed p a r a l l e l s t h e t e m p e r a t u r e r i s e , so does t h e amount o f c o a l w h i c h i s o x i d i z e d . To p r e v e n t e x c e s s i v e l o s s o f c o a l , a p r a c t i c a l l i m i t o f 200°C h a s been c h o s e n f o r c a r r y i n g o u t t h e r e a c t i o n on most c o a l s . Removal o f o r g a n i c s u l f u r f r o m a s e r i e s o f c o a l s , shown i n T a b l e I I , v a r i e s f r o m 20 t o o v e r 40%. Further reduction of organic s u l f u r content i s probably p o s s i b l e w i t h some o f t h e s e c o a l s w i t h o u t s a c r i f i c i n g c o a l recoverability. An upper l i m i t on o r g a n i c s u l f u r r e m o v a l a p p e a r s t o be b e t w e e n 40 and 5 0 % , and v a r i e s f r o m c o a l t o c o a l . We b e l i e v e t h i s i s c a u s e d by t h e f u n c t i o n a l i t y o f t h e o r g a n i c s u l f u r , and g i v e s some r o u g h measure o f o x i d a t i o n r e s i s t a n t o r DBT t y p e o f sulfur. O b v i o u s l y , t h a t s u l f u r w h i c h i s removed by o x y d e s u l f u r i z a t i o n must be i n some o t h e r s t r u c t u r e w h i c h i s r e a d i l y o x i d i z e d , such as t h i o l , s u l f i d e , and/or d i s u l f i d e . A s i m i l a r amount o f o r g a n i c s u l f u r i s removed f r o m c o a l when i t i s h e a t e d a t 300°C w i t h aqueous a l k a l i , a r e a g e n t w h i c h does n o t a t t a c k DBT (_5,6) . TABLE I I .
O r g a n i c S u l f u r Removal f r o m R e p r e s e n t a t i v e C o a l s by O x y d e s u l f u r i z a t i o n
Seam
State
Temp (°C)
Bevier Mammoth Wyoming No. 9 Pittsburgh Lower F r e e p o r t I l l i n o i s No. 6 Minshall
Kansas Montana Wyoming Ohio Pennsylvania Illinois Indiana
150 150 150 180 180 200 200
O r g a n i c S u l f u r (wt %) Untreated Treated 2.0 0.5 1.1 1.5 1.0 2.3 1.5
1.6 0.4 0.8 0.8 0.8 1.3 1.2
Subbituminous. Even a t 150°-160°C many c o a l s , i n c l u d i n g some w i t h r a t h e r h i g h s u l f u r c o n t e n t s , c a n be d r a m a t i c a l l y d e s u l f u r i z e d a s shown i n Table I I I .
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Indiana Illinois Iowa Montana Pennsylvania Wyoming Ohio Pennsylvania
Minshall I l l i n o i s No. 5 L o v i l i a No. 4 Mammoth Pittsburgh Wyoming No. 9 Pittsburgh Upper F r e e p o r t
Subbituminous.
State 150 150 150 150 150 150 160 160
Temp (°C) 5.7 3.3 5.9 1.1 1.3 1.8 3.0 2.1
2.0 2.0 1.4 0.6 0.8 0.9 1.4 0.9
T o t a l S u l f u r (wt %) Untreated Treated
Oxydesulfurization of Representative
Seam
TABLE I I I . 6
4.99 2.64 5.38 0.91 0.92 1.41 2.34 1.89
1.81 1.75 1.42 0.52 0.60 0.78 1.15 0.80
Sulfur ( l b / 1 0 Btu) Treated Untreated
Coals
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170
COAL
DESULFURIZATION
The r e a c t i o n c o n d i t i o n s w h i c h we have f o u n d t o be s u i t a b l e for o x y d e s u l f u r i z a t i o nare: t e m p e r a t u r e b e t w e e n 150° and 220°C, o p e r a t i n g p r e s s u r e b e t w e e n 220 and 1500 p s i , and r e s i d e n c e t i m e of 1 h r or l e s s . Most o f o u r e x p e r i m e n t s h a v e b e e n c a r r i e d o u t b e l o w 220°C a n d a t a p p r o x i m a t e l y 1000 p s i . R e c o v e r i e s o f f u e l v a l u e s a r e e x c e l l e n t , g e n e r a l l y 9 0 % o r b e t t e r . The o n l y b y p r o d u c t o f t h e r e a c t i o n i s d i l u t e H«S0^ c o n t a i n i n g i r o n sulfates. T h i s c a n be r e c y c l e d w i t h no o b s e r v a b l e e f f e c t on desulfurization for at least five cycles. When t h e H^SO^ becomes t o o c o n c e n t r a t e d f o r f u r t h e r u s e , i t c a n be c o n v e r t e d to a commercial grade o f s u l f u r i c a c i d i f a s u i t a b l e , economic m a r k e t e x i s t s , o r i t c a n be d i s p o s e d o f by l i m e s t o n e n e u t r a l i z a t i o n a s a r e a d i l y f i l t e r a b l e CaSO,. The p r o c e s s , o u t l i n e d i n F i g u r e 1, n e e d s no n o v e l technology t o produce c o a l having over 95% o f i t s p y r i t i c s u l f u r and a s much a s 4 0 % o f i t s o r g a n i c s u l f u r removed. O t h e r t h a n t h e c o a l , a i r , and w a t e r , t h e o n l y o t h e r m a t e r i a l needed f o r t h e p r o c e s s i s t h e l i m e s t o n e u s e d t o n e u t r a l i z e t h e H^SO^. No s l u d g e i s f o r m e d , much o f t h e w a t e r c a n be r e c y c l e d , and t h e o n l y w a s t e p r o d u c t i s s o l i d CaSO^. S i m i l a r o x i d a t i v e d e s u l f u r i z a t i o n s u s i n g a i r and w a t e r (7) and o x y g e n and w a t e r (8) have been r e p o r t e d . A p r e l i m i n a r y estimate f o r t h i s process i n d i c a t e s a cost o f $8.00-$10.00 p e r t o n . A t t h i s p r i c e , t h e p r o c e s s w o u l d s t i l l be c o n s i d e r a b l y l e s s e x p e n s i v e t h a n c o a l c o n v e r s i o n t o gas o r l i q u i d f u e l . A s s u m i n g r e m o v a l o f 9 5 % p y r i t i c s u l f u r and 40% o r g a n i c s u l f u r , an e s t i m a t e d 4 0 % o f t h e c o a l mined i n t h e e a s t e r n U.S. c o u l d be made e n v i r o n m e n t a l l y a c c e p t a b l e a s b o i l e r f u e l a c c o r d i n g t o EPA s t a n d a r d s f o r new i n s t a l l a t i o n s . And t h e s u l f u r c o n t e n t o f t h e r e m a i n d e r o f t h e e a s t e r n c o a l c o u l d be d r a s t i c a l l y r e d u c e d , m a k i n g i t e n v i r o n m e n t a l l y acceptable f o r e x i s t i n g b o i l e r s . Conclusions T r e a t m e n t w i t h c o m p r e s s e d a i r a n d w a t e r a t 150°-200°C r e p r e s e n t s a p r a c t i c a l method t o d e s u l f u r i z e t o a c c e p t a b l e l e v e l s a s i z a b l e percentage of the a v a i l a b l e c o a l i n the e a s t e r n U n i t e d S t a t e s a t a c o s t i n money and f u e l v a l u e w h i c h i s l e s s t h a n c o a l c o n v e r s i o n and t o an e x t e n t w h i c h i s g r e a t e r t h a n c a n be a c h i e v e d b y p h y s i c a l d e p y r i t i n g methods. Abstract
Both pyritic and organic sulfur in coal can be removed by a variety of oxidation techniques, including treatment with NO , peroxygen compounds, air in the presence of specific organic media, or air and water at elevated temperature and pressure. The most promising method involves contacting an aqueous slurry of coal with air at pressures up to 1000 psi x
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
FRIEDMAN
Oxidative Desulfurization of Coal
E T A L .
Downloaded by IMPERIAL COLL LONDON on June 28, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch013
COMPRESSOR AIR
-CPGRINDING DESULFURIZED COAL FOR POWER PLANTS AND INDUSTRIAL BOILERS
HIGH-SULFUR COAL
MIXING TANK
DRYER
γ
HEAVY MINERALS WAT^R]
FILTER
+ LIMESTONE
CtS0
Figure 1.
4
Air-water oxydesulfurization process
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Downloaded by IMPERIAL COLL LONDON on June 28, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch013
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and temperatures of 140°-200°C. Coals from different geo graphic areas of the U.S. have been treated with air and water in this way, resulting in removal of more than 90% of pyritic sulfur and up to 40% of organic sulfur as sulfuric acid, which is separated from the desulfurized coal by filtration. Fuel value losses are usually less than 10%. Costs for processing coal by this procedure will be somewhere between the less efficient, less thorough and less costly physical coal cleaning methods and the more thorough but much more costly coal conversion techniques. Oxidative desulfurization potentially can upgrade up to 40% of the bituminous coal in the U.S. to environmentally acceptable boiler fuel and can bring most of the rest of the bituminous coals at least close to acceptability with relatively little loss in total fuel value. Literature Cited 1. Reggel, L., Raymond, R., Wender, I., Blaustein, B. D., Am. Chem. Soc., Div. Fuel Chem. Preprints, (1972) 17 (2), 44. 2. Wallace, T. J., Heimlich, Β. Ν., Tetrahedron (1968), 24, 1311. 3. Reed, Ε., "Organic Chemistry of Bivalent Sulfur," Vol. II, p. 64, Chemical Publishing Co., Inc., New York, 1968. 4. LaCount, R. Β., Friedman, Sidney, J. Org. Chem (1977), 42, 2751. 5. Worthy, W., Chem. Eng. News, (July 7, 1975), pp. 24-25. 6. Friedman, Sidney, Warzinski, R. P., Trans. ASME, J. Eng. Power, (1977) 99A, 361. 7. Thomas, J., Warshaw, Α., U.S. Pat. 3,824,084 (Assigned to Chemical Construction Corp.) July 16, 1974. 8. Agarwal, J. C., Giberti, R. Α., Irminger, P. F., Petrovic, L. F., Sareen, S. S., Min. Congr. J., (1975) 61 (3), 40.
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.