The Composition of Liquids From Coals of Different Rank - ACS

1 The Composition of Liquids From Coals of Different Rank G.P.STURM, JR., J. E. DOOLEY,J.S.THOMSON, P. W. WOODWARD, andJ.W.VOGH

Downloaded by UNIV OF MISSISSIPPI on June 23, 2015 | http://pubs.acs.org Publication Date: June 20, 1981 | doi: 10.1021/bk-1981-0156.ch001

U.S. Department of Energy, Bartlesville Energy Technology Center, Bartlesville, OK 74003

Among the many r e p o r t s i n the l i t e r a t u r e on c o a l l i q u e f a c t i o n , s e v e r a l i n d i c a t e a r e l a t i o n s h i p between the rank of the c o a l and the complexity of the hydrocarbon groups i n the c o a l and i n i t s l i q u e f a c t i o n products. This subject was reviewed i n some d e t a i l i n previous r e p o r t s (l.,2_) and w i l l only be summarized and updated here. Background E a r l y German work i n d i c a t e d that the lower-rank brown c o a l s ( l i g n i t e ) are more r e a c t i v e , r e q u i r e l e s s hydrogen pressure, and produce smaller polynuclear hydrocarbon u n i t s (3) than bituminous c o a l s . A l s o , the asphaltene content o f the c o a l l i q u i d s decreases w i t h the c o a l rank t o a minimum f o r sub-bituminous c o a l s . E a r l y work by the U.S. Bureau of Mines produced s i m i l a r r e s u l t s ( . Low-rank c o a l s were found t o be so r e a c t i v e t h a t , a t a r e a c t i o n temperature o f 430° C, high hydrogen pressure was r e q u i r e d t o prevent r e p o l y m e r i z a t i o n of r e a c t i v e fragments t o coke. More recent s t u d i e s have shown that the product from the l i q u e f a c t i o n o f a Utah sub-bituminous c o a l w i t h hydrogen donor solvent (5) contains l e s s benzene i n s o l u b l e m a t e r i a l than that from P i t t s b u r g h b i t u m i n ous c o a l . Although the l i t e r a t u r e suggests that the complexity of hydrocarbon groups i n c o a l and c o a l l i q u e f a c t i o n products can d i f f e r s u b s t a n t i a l l y w i t h the rank of the c o a l , s p e c i f i c data are l i m i t e d and sometimes appear t o be c o n t r a d i c t o r y . A recent report on the comparison of s o l v e n t - r e f i n e d l i g n i t e and s o l v e n t - r e f i n e d subbituminous and bituminous c o a l s (6) i n d i c a t e s h a r d l y any d i f f e r e n c e among the products i n terms of gross combustion a n a l y s i s ; a c i d and b a s i c t i t r e s ; molecular weight; and nuclear-magnetic resonance, u l t r a v i o l e t , and electron-spin-resonance s p e c t r a . Only the n i t r o gen content o f the c o a l was r e f l e c t e d i n the s o l v e n t - r e f i n e d products. However, i n another recent study of a l i g n i t e , a b i t u m i n ous c o a l , and an a n t h r a c i t e c o a l , a n a l y s i s of the organic compounds trapped i n the c o a l s and contained i n the products o f s e l e c t i v e This chapter not subject to U.S. copyright. Published 1981 American Chemical Society In Upgrading Coal Liquids; Sullivan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


2

UPGRADING COAL LIQUIDS

o x i d a t i o n i n d i c a t e d an i n c r e a s e d condensation of aromatic r i n g s w i t h i n c r e a s i n g rank (_7) . A n a l y s i s was performed by gas chromatography/ t i m e - o f - f l i g h t mass spectrometry and h i g h - r e s o l u t i o n mass spectrometry. Furthermore, an e x t e n s i v e , d e t a i l e d study revealed c o m p o s i t i o n a l d i f f e r e n c e s i n the p y r i d i n e e x t r a c t s of three c o a l s of d i f f e r e n t rank and a l s o i n t h e i r l i q u e f a c t i o n products produced by the S y n t h o i l process (8). For example, l a r g e r q u a n t i t i e s of s a t u r a t e s and higher percentages of lower ring-number s a t u r a t e compound types were observed i n the two higher rank c o a l e x t r a c t s . However, the r i n g d i s t r i b u t i o n s of the aromatic f r a c t i o n s from the c o a l e x t r a c t s i n d i c a t e d s l i g h t l y higher average r i n g numbers f o r the higher rank c o a l s . S i m i l a r r e s u l t s were obtained i n a study c h a r a c t e r i z i n g l i q u i d products obtained from s i x c o a l s of d i f f e r e n t rank by treatment of the c o a l s w i t h NaOH-alcohol f o r 1 hour at 300° to 350° C ( 9 ) . C h a r a c t e r i z a t i o n by elemental a n a l y s i s , molecular-weight determina t i o n , and proton NMR i n d i c a t e d that the younger (lower-rank) c o a l s gave s i m p l e r products w i t h p r i m a r i l y t w o - r i n g , t e t r a l i n - t y p e n u c l e i and more abundant ether l i n k a g e s than the higher-rank bituminous c o a l s which y i e l d e d products w i t h f i v e to s i x r i n g s , about two of which were naphthenic. S i m i l a r l y , i n Japanese s t u d i e s of p y r i d i n e e x t r a c t s of c o a l s of d i f f e r e n t rank (10), a n a l y s i s by proton NMR i n d i c a t e d more condensed aromatic r i n g s w i t h l e s s s u b s t i t u t i o n and s h o r t e r a l i p h a t i c chains i n the h i g h e r - r a n k - c o a l e x t r a c t s . Ext r a c t s from bituminous c o a l s contained an average of four or f i v e aromatic r i n g s w i t h s i d e chains averaging three or four carbons i n l e n g t h , whereas a l i g n i t e e x t r a c t had an average of one or two aromatic r i n g s w i t h seven- or e i g h t - c a r b o n , a l i p h a t i c s i d e c h a i n s . F i n a l l y , a study u s i n g carbon-13 NMR to c h a r a c t e r i z e a h a r d - c o a l - t a r p i t c h and a brown-coal-tar p i t c h i n d i c a t e d a predominance of fuseda r o m a t i c - r i n g systems w i t h s m a l l amounts of methyl and hydroaromatic methylene groups f o r the h a r d - c o a l - t a r p i t c h (11). The r e s u l t s f o r the brown-coal-tar p i t c h i n d i c a t e d p r i m a r i l y l o n g , s t r a i g h t - c h a i n a l i p h a t i c s estimated at 25 to 40 carbon atoms i n length. The c o a l l i q u i d s c h a r a c t e r i z e d at the B a r t l e s v i l l e Energy Technology Center previous to t h i s study have come from d i f f e r e n t p r o j e c t s i n which the primary o b j e c t i v e was the development of a s p e c i f i c process. This precluded a systematic study of the r e l a t i o n s h i p of c o a l rank to c o a l l i q u i d composition, which i s the o b j e c t i v e of t h i s study. Eight c o a l l i q u i d s prepared from s i x c o a l s (1,2) of w i d e l y d i f f e r i n g rank were c h a r a c t e r i z e d by procedures p r e v i o u s l y developed f o r petroleum (12^,13,14) and by ASTM methods. The l i q u i d s were prepared and upgraded by hydrogenation i n a batch autoclave under c o n d i t i o n s intended to minimize c r a c k i n g of the hydrocarbons ( e s p e c i a l l y those of c y c l i c and aromatic s t r u c t u r e ) and yet produce most of the l i q u i d hydrocarbons p o t e n t i a l l y o b t a i n a b l e from a given c o a l . The extent of the hydrogenation/hydrogenolysis (henceforth r e f e r r e d to as hydrogenation) of the raw c o a l l i q u i d s

In Upgrading Coal Liquids; Sullivan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

1.

STURM E T AL.

Composition of Coal Liquids

3

was adjusted as r e q u i r e d t o decrease the n i t r o g e n content t o about 0.2 t o 0.3 weight-percent w i t h the a d d i t i o n a l i n t e n t o f p r o v i d i n g a predominantly hydrocarbon l i q u i d f o r a n a l y s i s . D e t a i l s of the c o a l l i q u i d p r e p a r a t i o n s have been r e p o r t e d p r e v i o u s l y (1,2). This r e p o r t covers the c h a r a c t e r i z a t i o n of the c o a l l i q u i d s and p o s s i b l e i m p l i c a t i o n s i n r e l a t i o n t o r e f i n i n g .


Experimental Procedures Coal L i q u i d P r e p a r a t i o n s . The c o a l l i q u i d s were produced i n two stages as p r e v i o u s l y d e s c r i b e d i n d e t a i l ( 1 ) . I n the f i r s t stage, crude c o a l l i q u i d s were produced by hydrogenation of a c o a l / t e t r a l i n s l u r r y i n a batch autoclave w i t h 60-100 mesh Cyanamid Aero HDS-3A c a t a l y s t (3.2 wt-pct NiO and 15.1 wt-pct M0O3 on an alumina support) a t about 2,500 p s i g t o t a l pressure over a temperature program which increased s l o w l y t o a maximum of 400° C. In subsequent runs w i t h a given c o a l , f i l t e r e d product l i q u i d from the previous run was used to s l u r r y the c o a l . A f t e r the t e t r a l i n content of the l i q u i d product decreased t o 5 percent or l e s s , three or four a d d i t i o n a l runs were made. A l l l i q u i d s w i t h l e s s than 5 percent t e t r a l i n were combined as the crude c o a l l i q u i d . In the second stage of c o a l l i q u i d p r e p a r a t i o n , the crude c o a l l i q u i d s were upgraded i n the batch a u t o c l a v e w i t h p r e s u l f i d e d Aero HDS-3A c a t a l y s t under c o n d i t i o n s designed to decrease the n i t r o g e n content t o a targeted range of 0.2 t o 0.3 weight percent. One e x c e p t i o n was a sample of l i q u i d from the Wyodak c o a l which, f o r comparison purposes, was upgraded on the same time-temperature program as that r e q u i r e d t o upgrade the I l l i n o i s No. 6 run 2 crude l i q u i d . In every case the maximum temperature employed was 400° C or l e s s . Distillations. The upgraded c o a l l i q u i d s were d i s t i l l e d w i t h a metal-mesh-spinning-band s t i l l under the c o n d i t i o n s shown i n Figure 1 to produce cuts a t 200°, 325°, and 425° C. Asphaltenes were then p r e c i p i t a t e d from each >425° C residuum d i s s o l v e d i n benzene by a d d i t i o n of 50 volumes of normal pentane (15). F u r t h e r d i s t i l l a t i o n s on the a s p h a l t e n e - f r e e m a t e r i a l s , a t 202° C and 4 micron pressure u s i n g a wiped-wall molecular s t i l l , produced 425° t o 540° C d i s t i l l a t e c u t s and r e s i d u a f r a c t i o n s . Separations and Analyses. A f t e r removal of t r a c e amounts o f a c i d s and bases from the 325° C RESIDUUM

DISTILLATION AT 180° C , 0.1 TORR

325-425° C DISTILLATE \ >425° C RESIDUUM

ASPHALTENE SEPARATION

ASPHALTENE FRACTION

>425° C ASPHALTENEFREE RESIDUUM

DISTILLATION AT 202° C , 4 ^PRESSURE 425-540° C DISTILLATE

>540° C RESIDUUM

Figure 1.

Distillation scheme for coal liquids



STURM E T AL.


r r o

O

2 O

O

ON


1.

STURM E T AL.


1

The h i g h e r - b o i l i n g d i s t i l l a t e s were c h a r a c t e r i z e d by methods adapted from the c h a r a c t e r i z a t i o n of heavy ends of petroleum (12, 14). A schematic of the procedure i s shown i n F i g u r e 3. D e t a i l s of the procedures have been r e p o r t e d p r e v i o u s l y (12,14,16,17). Analyses of s u b f r a c t i o n s of aromatic concentrates separated by g e l permeation chromatography (GPC) were performed on a l o w - r e s o l u t i o n CEC 21-103C mass spectrometer (MS) u s i n g l o w - i o n i z i n g - e n e r g y e l e c t r o n s to produce predominantly molecular i o n s . Compound-type assignments were made by means of p r e v i o u s l y e s t a b l i s h e d GPC-MS c o r r e l a t i o n s and h i g h - r e s o l u t i o n mass s p e c t r a l data f o r s e l e c t e d f r a c t i o n s . H i g h - r e s o l u t i o n , 70 eV, mass s p e c t r a were obtained on an AEI MS 3074 mass spectrometer. High- and l o w - r e s o l u t i o n f i e l d - i o n i z a t i o n s p e c t r a of s e l e c t e d f r a c t i o n s , p r i m a r i l y p o l y aromatic-polar c o n c e n t r a t e s , were obtained at Oklahoma S t a t e U n i v e r s i t y on a CEC Model 21-110 B mass spectrometer f i t t e d w i t h a r a z o r blade source (18). Results P r o p e r t i e s of Coals and Coal L i q u i d s . D e s c r i p t i o n s and a n a l yses of the s i x c o a l samples used to prepare the c o a l l i q u i d s are summarized i n Table I . P h y s i c a l and chemical p r o p e r t y data f o r the e i g h t c o a l l i q u i d s prepared from the s i x c o a l s are summarized i n Table I I . Included i n Table I I are data f o r repeat runs on I l l i n o i s No. 6 and Wyodak c o a l s . The repeat run f o r the I l l i n o i s No. 6 c o a l was made because of changes i n the procedure i n s t i t u t e d d u r i n g the f i r s t l i q u e f a c t i o n run, I l l i n o i s No. 6 run 1. The changes i n v o l v e d a s w i t c h from CoMo to NiMo c a t a l y s t and a decrease i n the maximum temperature from 425° to 400° C ( 1 ) . A l s o , upgrading of the f i r s t I l l i n o i s crude l i q u i d d i d not achieve the t a r g e t e d value of 0.2 to 0.3 percent n i t r o g e n . The second Wyodak c o a l l i q u i d was prepared from the same crude l i q u i d as the f i r s t by upgrading according to the time-temperature p r o f i l e used f o r the I l l i n o i s No. 6 run 2 l i q u i d . I t was noted p r e v i o u s l y , that the lower-rank c o a l s r e a c t e d more r e a d i l y and under m i l d e r c o n d i t i o n s than those of higher rank f o r both the i n i t i a l l i q u e f a c t i o n and the upgrading of the raw c o a l l i q u i d s ( 1 ) . Thus, the second Wyodak run was made to determine the e f f e c t s of i n c r e a s e d upgrading upon l i q u e f a c t i o n - p r o d u c t composition. D i s t i l l a t i o n R e s u l t s and D i s t i l l a t e P r o p e r t i e s . Distillation r e s u l t s f o r the upgraded c o a l l i q u i d s are a l s o summarized i n Table I I . The r e s u l t s showed no l a r g e d i f f e r e n c e s f o r the l i q u i d s , except f o r the e x t e n s i v e l y upgraded second Wyodak l i q u i d which had a higher percentage of l o w - b o i l i n g m a t e r i a l . Asphaltene content of the s i x "normally" upgraded l i q u i d s ranged from about 1 to 7 percent. I n c l u s i o n of the second Wyodak and f i r s t I l l i n o i s l i q u i d s extended the range of asphaltene content from 0.1 to 14 percent. The asphaltene content c o r r e l a t e d w i t h the n i t r o g e n content of the l i q u i d s , thus supporting the use of n i t r o g e n content to monitor the extent of c o a l - l i q u i d upgrading.


UPGRADING COAL LIQUIDS


8

Table I.

Analysis of Coals, Weight Percent Montana

Source

PA-WV

Seam

Pittsburgh

Rank

hvb A

Illinois No. 6 hvb B/C

Wyoming (Wyodak)

N . Dakota

Rosebud

Lower

Beulah S t d . II

subb. A

subb. C

W. KY

(Colstrip)

hvb B/C

Lignite

Proximate analysis, (as received): 1.7 35.9

2.9

4.2

10.9

V o l a t i l e matter

38.4

34.4

39.5

31.0

Fixed carbon . .

34.2

55.1

51.4

48.8

48.5

42.7

33.3

7.3

6.6

9.9

12.9

6.9

5.1 76.9

4.9 75.2

70.2

4.9

4.3 65.2

66.8

1.5

1.6

1.4

0.6

1.6

4.3 8.8

14.5

19.2

19.1

10.2

13.5

7.8

10.7

Ash

7.8

28.0

7.7

Ultimate analysis, (moisture free):

Sulfur

O x y g e n (diff) .

7.6

1.5 9.7

Ash

7.4

7.1

1.8

4.8

1.0 0.5

hvb B/C — high volatile bituminous B or C subb. — subbituminous


4.5

63.5 0.9 1.3


4.7

Ky.

1.28 2.09 .02

0.64 1.61

The Composition of Liquids From Coals of Different Rank - ACS

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