Oxidative Desulfurization of Coal - ACS Symposium Series (ACS

13 Oxidative Desulfurization of Coal SIDNEY FRIEDMAN, ROBERT B. LACOUNT, and ROBERT P. WARZINSKI

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

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.

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FRIEDMAN ET

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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.


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



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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



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 .



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



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


FRIEDMAN

Oxidative Desulfurization of Coal

E T A L .


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



172

COAL

DESULFURIZATION

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.


Oxidative Desulfurization of Coal - ACS Symposium Series (ACS

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