Characterization of Organosulfur Compounds in Oklahoma Coals by

Chapter 20 Characterization in

of

Organosulfur Compounds

Oklahoma Coals

by P y r o l y s i s — G a s

Chromatography Allen J. Bakel, R. Paul Philp, and A. Galvez-Sinibaldi

Downloaded by UNIV LAVAL on February 25, 2013 | http://pubs.acs.org Publication Date: June 29, 1990 | doi: 10.1021/bk-1990-0429.ch020

School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019

Extracted coals from eastern Oklahoma were analyzed using pyrolysis-gas chromatography and a flame photometric detector (FPD) to characterize the organosulfur compounds produced by pyrolysis of coals. A l l coals from the Croweburg seam with calorific values below 13,000 BTU (Table I) were shown to produce similar distributions of organosulfur compounds. The ratio of dibenzothiophenes to thiophenes produced by pyrolysis was shown to be proportional to the c a l o r i f i c value of the coal. A great deal of recent organic geochemical research has been devoted to the study of organosulfur compounds in organic rich geological samples. Many organosulfur compounds have been identified in crude o i l s (1,2), rock extracts (3.) , o i l asphaltenes (4) and kerogen pyrolysates (5) . The distributions of organosulfur compounds in geochemical samples have been shown to be affected by maturity (1/6) and depositional environment of the original organic matter (4,7) . Special attention has been given to the occurrence of organosulfur compounds in samples thought to be derived from organic matter deposited in hypersaline environments. The Rozel Point o i l (7) and extracts from a marl deposited in a Messinian 0097-6156/90/0429-0326$06.00/0 © 1990 American Chemical Society

In Geochemistry of Sulfur in Fossil Fuels; Orr, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


20. BAKEL ET AL.

Characterization of Organosulfur Compounds

327

e v a p o r i t i c b a s i n i n the northern Appennines o f I t a l y (3.) have been found t o c o n t a i n a v a r i e t y o f thiophenes (structure i in Appendix I ) , thiolanes ( i i ) (tetrahydrothiophenes), t h i a n e s ( i i i ) and benzothiophenes (iv) . The d i s t r i b u t i o n s of o r g a n o s u l f u r compounds i n the p y r o l y s a t e s o f o i l asphaltenes have been shown t o resemble those of the aromatic f r a c t i o n o f the o i l from which they were i s o l a t e d (8), and vary a c c o r d i n g t o the depositional environment of the o r i g i n a l organic m a t e r i a l . P h i l p and Bakel (4) r e p o r t e d t h a t p y r o l y s a t e s of asphaltenes i s o l a t e d from limestone-sourced o i l s contained h i g h c o n c e n t r a t i o n s o f benzothiophenes and dibenzothiophenes (v) r e l a t i v e t o thiophenes, w h i l e asphaltenes from shale-sourced o i l s produced more thiophenes than benzo- and dibenzothiophenes. P y r o l y s i s of a v a r i e t y o f kerogens has been shown t o y i e l d primarily thiophenes, with smaller amounts of benzothiophenes, dibenzothiophenes (4) and t h i o l a n e s (5) . C h a r a c t e r i z a t i o n and i d e n t i f i c a t i o n o f o r g a n o s u l f u r compounds i n v a r i o u s c o a l d e r i v e d l i q u i d s i n c l u d i n g hydrogenates (9) , c o a l t a r s , and c o a l l i q u i d vacuum r e s i d u e s (10) have been s t u d i e d i n many l a b o r a t o r i e s . These systems have been s t u d i e d i n order t o understand the p o t e n t i a l p o l l u t i o n problems c r e a t e d i f the l i q u i d s are t o be used as f u e l s . Organosulfur compounds i d e n t i f i e d i n c o a l products i n c l u d e : benzothiophene, hydroxy-, and alkylbenzothiophenes, dibenzothiophene, alkyldibenzothiophenes, benzonaphthothiophenes (vi) , phenanthrothiophenes ( v i i ) , naphthothiophenes (viii), triphenylenothiophenes (ix) andbenzophenanthrothiophenes (x) (see s t r u c t u r e s i n Appendix I ) . Coal e x t r a c t s have been found t o c o n t a i n benzo- and dibenzothiophenes (11,12). A v a r i e t y of techniques, i n c l u d i n g flash p y r o l y s i s have been used t o d e s c r i b e the form o f s u l f u r i n the c o a l matrix (13). F l a s h p y r o l y s i s o f e x t r a c t e d c o a l s has been shown t o y i e l d thiophenes, benzothiophenes and dibenzothiophenes (4.) . Coals are generated by b u r i a l o f peats, which are formed i n swamps and marshes. Geographic and t e c t o n i c requirements f o r formation of t h i c k peat d e p o s i t s i n c l u d e slow subsidence, p r o t e c t i o n o f the swamp from e r o s i o n by marine inundation or f l u v i a l flood waters and a restricted supply of fluvial sediment. These requirements are met on c o a s t a l p l a i n s where most Recent peat swamps are l o c a t e d . M i c r o b i a l a c t i v i t y i s capable of degrading great q u a n t i t i e s o f the p l a n t m a t e r i a l which i s the u l t i m a t e source of peat. Therefore, c o n d i t i o n s which i n h i b i t m i c r o b i a l a c t i v i t y are f a v o r a b l e f o r the



328

GEOCHEMISTRY OF SULFUR IN FOSSIL FUELS

accumulation of l a r g e peat d e p o s i t s . The c o n d i t i o n s i n peat swamps which i n h i b i t a e r o b i c m i c r o b i a l degradation and thus f a v o r accumulation of peat such as low pH and Eh a l s o f a v o r anaerobic s u l f a t e r e d u c t i o n (14). Organic s u l f u r i n peat i s d e r i v e d from two sources, s u l f u r from the o r i g i n a l p l a n t m a t e r i a l , and i n o r g a n i c s u l f u r compounds which r e a c t with o r g a n i c m a t e r i a l present i n peat. Peat i s known t o c o n t a i n more s u l f u r than i s present i n the original plant material, suggesting an e x t e r n a l source of s u l f u r such as s u l f a t e r i c h waters, hydrogen s u l f i d e (H2S) from the metabolic a c t i v i t y of s u l f a t e reducing b a c t e r i a (15) or elemental sulfur (16). H2S, a metabolic product of anaerobic s u l f a t e reducing b a c t e r i a present i n peat swamps, i s known t o r e a c t with organic matter i n such a way as t o permit i n c o r p o r a t i o n of s u l f u r i n t o the s t r u c t u r e of complex o r g a n i c molecules (Γ7) and has t h e r e f o r e been proposed as an important agent i n s u l f u r enrichment d u r i n g e a r l y d i a g e n e s i s of peat. In l a b o r a t o r y s t u d i e s , Casagrande e t a l . (16) found t h a t peats from the Okefenokee Swamp became enriched i n s u l f u r when exposed t o H2S a t room temperature i n a matter of days. A l a r g e enrichment was observed i n the humic a c i d f r a c t i o n , which i s thought t o be a p a r t i c u l a r l y important p r e c u r s o r of c o a l macérais. Peats can accumulate i n environments of v a r y i n g s a l i n i t y . Peats deposited under p a r t i c u l a r l y saline c o n d i t i o n s tend t o have high s u l f u r contents, as do peats covered by marine sediments d u r i n g marine t r a n s g r e s s i o n s . The source of the s u l f u r i n these m a r i n e - i n f l u e n c e d peats i s thought t o be the s u l f a t e i o n i n the marine waters, which i s reduced t o hydrogen s u l f i d e by s u l f a t e reducing b a c t e r i a present i n anaerobic sediments. Much of the s u l f i d e r e a c t s with i r o n t o form i r o n s u l f i d e s , w h i l e excess hydrogen s u l f i d e r e a c t s with organic m a t e r i a l such as carbohydrates or humic a c i d s . In support of t h i s model, a c o r r e l a t i o n has been observed between h i g h c o n c e n t r a t i o n s of p y r i t e and h i g h c o n c e n t r a t i o n s of o r g a n i c s u l f u r i n peats and c o a l s (14). In order t o determine the o r i g i n of s u l f u r i n c o a l s , Hackley and Anderson (18) s t u d i e d the s u l f u r i s o t o p i c composition of v a r i o u s c o a l s from the western U n i t e d S t a t e s . Coals from the Powder R i v e r Basin, Wyoming were found t o have anomalously low δ ^ v a l u e s (-18.7 t o 3.9 p a r t s per m i l ) . The unusual δ ^ v a l u e s of these c o a l s suggest t h a t o r i g i n a l p l a n t m a t e r i a l and i s o t o p i c a l l y l i g h t secondary s u l f u r from b a c t e r i a l a c t i v i t y were the major c o n t r i b u t o r s t o the s u l f u r content o f these c o a l s . 3

3


20.

BAKELET AL.

Characterization of Organosulfur Compounds 3/

The Hanna Basin c o a l s from Wyoming had higher 6 S values than c o a l s from the Powder R i v e r Basin. The p a t t e r n of s u l f u r i s o t o p i c composition found i n c o a l s from the Hanna Basin revealed t h a t c o a l s near the top of the c o a l seam contained more of the heavy s u l f u r isotope than c o a l s s t r a t i g r a p h i c a l l y lower i n the c o a l seam. The s u l f u r isotope p a t t e r n observed i n the Hanna Basin coals suggests t h a t s u l f u r was introduced i n s u l f a t e - r i c h water from the top of the c o a l seam. Many c o a l p y r o l y s i s s t u d i e s have reported only bulk r e s u l t s , such as the amounts of char, water, and NH + H2S + H produced (19). More d e t a i l e d a n a l y t i c a l p y r o l y s i s has been performed on i s o l a t e d c o a l macérais. I t has been found t h a t the d i s t r i b u t i o n of phenols i n the p y r o l y s a t e s of v i t r i n i t e are a f f e c t e d by the rank, or maturity of the c o a l (20). Saiz-Jimenez and de Leeuw (21) proposed t h a t c e r t a i n p y r o l y s i s products of l i g n i n (guaiacyl and s y r i n g y l compounds) are of p o t e n t i a l use i n determination of source m a t e r i a l of c o a l s and l i g n i n s . P h i l p e t a l . (22) found t h a t brown c o a l s with s i m i l a r chemical and pétrographie p r o p e r t i e s (lithotype) yielded s i m i l a r p y r o l y s i s products, and t h a t the hydrocarbon d i s t r i b u t i o n i n the p y r o l y s i s products changed with increasing maturity. P y r o l y s i s products of s e v e r a l components of the c o a l ( c u t i c l e , r e s i n and s o f t brown c o a l woods) were compared t o the p y r o l y s i s products of l i g n i n s . A number of p y r o l y s i s products of these c o a l components, i n c l u d i n g s y r i n g y l d e r i v a t i v e s and s e v e r a l p h e n o l i c compounds, were found t o be u s e f u l i n d i f f e r e n t i a t i n g angiosperm from gymnosperm sources f o r the c o a l s . P h i l p and Bakel (4.) examined organosulfur compounds i n the p y r o l y s a t e s of e x t r a c t e d Pennsylvanian c o a l s from eastern Oklahoma and i d e n t i f i e d thiophenes, benzothiophenes, dibenzothiophenes and benzonaphthothiophenes. The c o a l reserves i n eastern Oklahoma d e f i n e the southern edge of the i n t e r i o r c o a l province of North America. Oklahoma c o a l s can be divided into two c a t e g o r i e s (Figure 1) , the Arkoma b a s i n c o a l s , which occur i n Coal, P i t t s b u r g , H a s k e l l , Latimer, Sequoyah and Le F l o r e counties at the southern extremity of the i n t e r i o r c o a l province, and the northeastern Oklahoma s h e l f c o a l s , which occur from the Arkoma b a s i n , north t o the Kansas border. The c o a l s found i n the northeastern s h e l f area tend to have higher s u l f u r content (>3%) than the c o a l s from the Arkoma Basin (

Tebo ( E R A M ? ) WEIR-PITTSBURG Stuort Shole 0 - 3 7 5 Thurmon Ss 0-25*

>CO

Boggy

125-2,140

Lu CL

Drywood Savanna

180-2,500

KREBS

ROWE (LOWER WITTEVILLE) CAVANAL

Upper McAlester MC A L E S T E R (STIGLER) Mc Alester

Hartshorne

140-2,830

3-316

HARTSHORNE

F i g u r e 2 . Geologic column o f northeastern Oklahoma showing c o a l beds. Coals i n c l u d e d i n t h i s study are marked (·). (Reproduced with permission from r e f e r e n c e 25) .


332


Desmoinesian c o a l seams i n e a s t e r n Oklahoma (Figure 2), t h i s study w i l l examine only f i v e d i f f e r e n t c o a l seams: Hartshorne, S t i g l e r , McAlester, Croweburg and Iron Post.


Experimental The e a s t e r n Oklahoma c o a l s were obtained from the Oklahoma G e o l o g i c a l Survey Organic Petrography Laboratory where they had been crushed t o -20 mesh and analysed on an as r e c e i v e d b a s i s (Table I ) . The whole, crushed c o a l s were e x t r a c t e d f o r 48 hours with a 1:1 (v/v) mixture of chloroform/methanol u s i n g a s o x h l e t apparatus. Exhaustive e x t r a c t i o n ensures t h a t s o l u b l e compounds are removed and t h a t the compounds produced d u r i n g p y r o l y s i s are d e r i v e d from the o r g a n i c matrix of the c o a l . The e x t r a c t e d c o a l s were p y r o l y s e d a t a temperature s e t t i n g of 800°C f o r 20 seconds u s i n g the c o i l probe of the Chemical Data Systems Pyroprobe 122 system. I t should be noted t h a t an attempt was made t o p y r o l y z e s i m i l a r amounts of each sample. The p y r o l y s a t e s were r a p i d l y removed from the heated i n t e r f a c e (300°C) under a stream of helium (1.8 ml/minute) onto a fused s i l i c a DB-5 c a p i l l a r y column (J&W S c i e n t i f i c , 30m χ 0.32mm i.d.) i n s t a l l e d i n a V a r i a n 3300 gas chromatograph equipped with both a flame i o n i z a t i o n d e t e c t o r (FID) f o r d e t e c t i o n of hydrocarbons and a flame photometric d e t e c t o r (FPD) f o r d e t e c t i o n of o r g a n o s u l f u r compounds. A column e f f l u e n t s p l i t t e r was i n s t a l l e d a t the end of the column t o a l l o w f o r simultaneous a c q u i s i t i o n o f data from the FID and FPD d e t e c t o r s . The column oven temperature was held at -25°C f o r four minutes, and r a i s e d t o 300°C at the r a t e of 4°C/minute. T e n t a t i v e i d e n t i f i c a t i o n s of the FPD peaks (Figure 3) were made by comparison with chromatograms p u b l i s h e d by Hughes (1), and comparisons of r e t e n t i o n times of a u t h e n t i c standards (thiophenes, benzothiophene and dibenzothiophene) analyzed under i d e n t i c a l chromatographic c o n d i t i o n s (Table Π). I t should be noted t h a t the flame pnotometric d e t e c t o r is more sensitive to thiophenes than i t i s to benzothiophenes (23.) . S t u d i e s i n our l a b o r a t o r y have shown t h a t the flame photometric d e t e c t o r response t o thiophene i s approximately 25% g r e a t e r than t h a t f o r the corresponding q u a n t i t y of benzothiophene. Hence a consequence of t h i s n o n - l i n e a r i t y of response i s t h a t the thiophenes are not as quantitatively dominant as suggested by some of the FPD pyrograms.


20. BAKELETAL.



Results Hartshorne. The Hartshorne c o a l occurs i n the Arkoma Basin, and i n some areas can be s p l i t i n t o upper and lower s t r a t a , separated by shales and sandstones. The average t o t a l s u l f u r content o f the Hartshorne c o a l i s 1.8%. Higher c a l o r i f i c values o f a c o a l can be c o r r e l a t e d with a higher abundance o f dibenzothiophenes r e l a t i v e t o thiophenes i n the FPD pyrograms (Figure 4) . I t i s i n t e r e s t i n g t o note t h a t the t o t a l s u l f u r contents o f the two Hartshorne c o a l s shown i n F i g u r e 4 are very s i m i l a r (Table I) , suggesting t h a t rank i s more important than t o t a l s u l f u r content i n determining the d i s t r i b u t i o n o f o r g a n o s u l f u r compounds i n the p y r o l y s i s products from these c o a l s . McAlester. The d i s t r i b u t i o n o f o r g a n o s u l f u r compounds i n the pyrogram o f McAlester c o a l s i s dependent on t h e i r rank as was the case f o r the Hartshorne c o a l s (Figure 5) . The McAlester c o a l o f lowest rank (#497) a l s o has the h i g h e s t t o t a l s u l f u r content (Table I) . The McAlester c o a l o f lower rank (#497) y i e l d s higher c o n c e n t r a t i o n s of a l l o r g a n o s u l f u r compounds than c o a l s from the same seam but o f higher rank (#499). Stialer. The S t i g l e r coal i s stratigraphically e q u i v a l e n t t o the McAlester c o a l , and t y p i c a l l y occurs a t shallower depths than the McAlester. S t i g l e r c o a l s o f lower rank (#508) y i e l d a broad range o f o r g a n o s u l f u r compounds upon pyrolysis, including thiophenes, benzothiophenes and dibenzothiophenes and the o r g a n o s u l f u r compound d i s t r i b u t i o n o f c o a l #508 i s dominated by thiophenes (Figure 6 ) . In c o n t r a s t , p y r o l y s a t e s o f a higher rank c o a l (#452) c o n t a i n a mixture of organosulfur compounds dominated by dibenzothiophenes (Figure 6). Iron Post. The Iron Post c o a l i s a high s u l f u r c o a l (Table I) from the northeastern Oklahoma s h e l f , which i s a s s o c i a t e d with p y r i t i c s h a l e s . FPD chromatograms o f the p y r o l y s i s products of two Iron Post c o a l s o f s i m i l a r rank show t h a t the d i s t r i b u t i o n s o f o r g a n o s u l f u r compounds produced by p y r o l y s i s o f these two c o a l s are q u i t e similar (Figure 7 ) . T h i s supports the idea o f a r e l a t i o n s h i p between rank and o r g a n o s u l f u r compound d i s t r i b u t i o n i n the p y r o l y s a t e s o f c o a l s .


333

334



Table

SAMPLE //

FORMATION

COUNTY

TWN/RNG

1.

CALOR.VAL. (BTU) (D-2015)^

%R 0

General Data For Coals

%M0ISTURE (D-3302) (D-3173)

@ @

%ASH (D-3174)^

419

Hartshorne

Latimer

T5N R17E

13448

NA

6.4

512

Hartshorne

Haskell

T9N R21E

14176

NA

3.0

6.5

497

McAlester

Latimer

T6N R21E

12486

NA

4.5

14.3

499

McAlester

Latimer

T6N R21E

13544

0.85

3.0

8.5

452

Stigler

Haskell

T9N R22E

14592

1.25

2.3

4.4

508

Stigler

Haskell

T8N R21E

10120

NA

9.6

21.5

466

Iron

Post

Craig

T26N R18E

13412

NA

3.9

5.5

515

Iron

Post

Rogers

T24N R17E

13384

NA

4.0

7.2

227

Croweburg

Wagoner

T16N R15E

8709

0.57

3.7

32.3

3.6

517

Croweburg

Rogers

T24N R17E

13167

NA

7.6

3.5

397

Croweburg

Okfuskee

TION R12E

9150

NA

3.0

31.0

395

Croweburg

Okfuskee

TION R12E

1 1723

NA

2.4

16.9

* - determined at two different particle sizes. ** - determined as difference of total weight and the sum of %moisture, %ash, and %volatile. @ - determined as difference of total sulfur and the sum of %S-pyrite and %S-sulfate. @ @ - ASTM method used to determine these values. Method taken from ref. 26.


20.

BAKEL ET AL.


Examined

in This

%VOL.MATT. (D-3175)^

335


Study

%FIXED C

%S-total (D-3177)^

%S-organic

%S-pyrite (D-2492)^

%S-sulfate (D-2492)^

%EXTRACT

38..5

51,.5

2,.2

0..80

1 .40 .

0..03

2.42

24..2

66,.3

2,.4

0..40

1 .91 .

0..04

0.23

30..0

51,.2

5,.2

0..70

4,.48

0..02

NA

33..9

54,.6

2,.6

0..60

1 .95 ,

0..01

0.43

25..5

67,.8

0,.7

0..50

0,. 17

Characterization of Organosulfur Compounds in Oklahoma Coals by

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