Oil Shale, Tar Sands, and Related Materials - American Chemical

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Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: September 3, 1981 | doi: 10.1021/bk-1981-0163.ch021

The Chemistry of Shale Oil and Its Refined Products DONALD M. FENTON, HARVEY HENNIG, and RYDEN L. RICHARDSON Union Oil Company of California, Science and Technology Division, P.O. Box 76, Brea, CA 92621

"Oil Shale" is a term used to cover a wide range of materials which are found in many parts of the United States. The Green River oil shales are particularly high grade and are the only U.S. deposits having adequate size and availability for potential commercial value with present technology. The Green River formation contains the equivalent of 1.8 trillion barrels of shale oil. Assuming that only 600 billion barrels or one third of this oil is ultimately recoverable, this would still be 20 times the U.S. proved crude oil reserves. The Green River oil shale is a marlstone (calcareous mud-stone) that was formed in shallow lakes about 45 million years ago (1). The climate at this time probably varied from subtropical to arid. During wet periods these lakes may have been as large as 75 to 100 miles in diameter. Sediment, mineral salts, minor plant debris and wind-transported pollen were carried into the lakes by small local streams, but the majority of the organic material that is in the oil shale came from colonies of algae that thrived in the lakes. The organic matter found i n the Green River shales formed i n the deeper, c e n t r a l part of the l a k e . Rocks formed under these c o n d i t i o n s a r e c h a r a c t e r i z e d by t h i n , a l t e r n a t i n g l a y e r s o f c a r bonate and organic matter. The l a y e r s vary i n thickness from 0.01 to 10 m i l l i m e t e r s . The l a y e r s are b e l i e v e d to have been formed by the p r e c i p i t a t i o n of calcium carbonate i n e a r l y summer, when the s u r f a c e water temperature r i s e s , followed by the seasonal high p r o d u c t i v i t y of algae which occurs i n l a t e summer. The heavy carbonate m a t e r i a l s were deposited q u i c k l y ; the organic matter s e t t l e d more s l o w l y — w h i c h gave an a l t e r n a t i o n of l i g h t and dark l a m i n a t i o n s . The t y p i c a l composition of Green R i v e r o i l shale i s composed of around 0-15% bitumen, e x t r a c t a b l e o r g a n i c s , and 85-100% kerogen, unextractable o r g a n i c s , see Table I . The kerogen i s an organic matrix of high molecular weight, c o n t a i n i n g on the average s e v e r a l saturated r i n g s with hydrocarbon chains having an occ a s i o n a l i s o l a t e d carbon-carbon double bond and a l s o c o n t a i n i n g ,

0097-6156/81/0163-0315 $05.00/0 © 1981 American Chemical Society

In Oil Shale, Tar Sands, and Related Materials; Stauffer, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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SHALE, TAR SANDS, AND RELATED MATERIALS

i n a d d i t i o n to small amounts of n i t r o g e n and s u l f u r , approximately 6% oxygen. There i s a l s o the p o s s i b i l i t y that c o n s i d e r able amounts of non-crosslinked, long-chain compounds are trapped i n the matrix. I f the n i t r o g e n and s u l f u r are f o r m a l l y replaced by oxygen, f o r example by h y d r o l y s i s with each n i t r o g e n and s u l f u r being replaced by the two oxygens and one hydrogen, then a simple


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formula weight i s ^ g 2 8 ° 2 8 / 7.7. T h i s i s about what would be expected f o r algae d e r i v e d organics, s i n c e algae produce f a t t y a c i d s i n the C^g range as w e l l as other hydrocarbons such as cartenoids a t C ^ Q . I t has been shown that the e x t r a c t a b l e hydrocarbons from o i l shale have a bimodal d i s t r i b u t i o n at and supporting t h i s contention (2) . Strong evidence f o r the biogenesis of kerogen was shown when i t was found that the r a t i o of odd to even number of carbon atoms i n the extracted hydrocarbons was as high as four to one. A r a t i o of one to one would be expected from a n o n b i o l o g i c a l source. The higher p r o p o r t i o n of the odd number hydrocarbons would be a n t i c i p a t e d i f t h e i r source was the d e c a r b o x y l a t i o n of a l g a l f a t t y a c i d s , s i n c e these a c i d s are predominantly even number a c i d s . An i n t e r e s t i n g question i s : how d i d these predominantly a l g a l a c i d s become c r o s s l i n k e d to form kerogen? I t can be seen from the kerogen formula that there a r e on the average four u n i t s of u n s a t u r a t i o n , while i t i s known that under some c o n d i t i o n s algae form f a t t y a c i d s that are 95% unsaturated, and with some a c i d s , such as a r a c h i d o n i c , an e s s e n t i a l f a t t y a c i d , there are four o l e f i n i c l i n k a g e s . I t has a l s o been shown that these polyunsaturated a l g a l a c i d s , under m i l d heating, become c r o s s linked. I t i s c l e a r that the unsaturated a c i d s on diagenesis i n the o i l shale r e a c t to form naphthenes, the c y c l i c compounds found i n kerogen. One r e a c t i o n of t h i s type i s the D i e l s - A l d e r r e a c t i o n which can occur at m i l d temperatures ( 3 ) . While the D i e l s - A l d e r r e a c t i o n i s thought to be r e s p o n s i b l e f o r the organic c r o s s l i n k i n g r e a c t i o n , i t i s a l s o proposed that there i s a chemical attachment of the organic to the i n o r g a n i c matrix. T h i s attachment could a r i s e from the i n t e r a c t i o n of the c a r b o x y l group of the f a t t y a c i d with the calcium and magnesium ions on the i n o r g a n i c s u r f a c e , which could l e a d to the formation of i n s o l u b l e calcium and/or magnesium soaps. In a d d i t i o n to the n i t r o g e n found i n porphyrins and r e l a t e d compounds, i t i s a l s o proposed that the s u l f u r and n i t r o g e n moieties found i n kerogen r e s u l t from a t t a c k of ammonia and p o l y s u l f i d e s on the unsaturated f a t s l e a d i n g to W i l l g e r o d t - t y p e r e a c t i o n products. One b i g advantage of shale o i l as compared to c o a l i s the more f a v o r a b l e atomic composition of kerogen noted i n Table I I . The hydrogen content of kerogen i s almost twice that of many c o a l s , and the oxygen content i s lower. The s u l f u r content of kerogen i s s i m i l a r to that of c o a l . The n i t r o g e n i s higher i n kerogen. Consequently, l e s s hydrogen i s r e q u i r e d to remove the


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TABLE I TYPICAL COMPOSITION OF GREEN RIVER OIL SHALE

(25 Gal/Ton Shale O i l ) Wt%


Kerogen Content 15 wt% Kerogen Composition: Carbon Hydrogen Nitrogen Sulfur Oxygen (Varies with Depth)

80.5 10.3 2.4 1.0 5.8 100.0 H

Simple Chemical Formula (Sulfur & Nitrogen Replaced by Oxygen) M i n e r a l Content

^20 32°2

85 wt%

Carbonates Feldspars Quartz Clays Analcite & Pyrite

48.0 21.0 15.0 13.0 3.0 100.0

TABLE I I KEROGEN VS COAL

Kerogen

Weight Percent Coal Bit Subb

Lignite

Moisture and Ash Free Carbon Hydrogen Oxygen Nitrogen Sulfur C/H Ratio

80 .5 10 .3 5 .8 2 .4 1 .0

78 .8 5 .7 8 .9 1 .4 5 .2

73. 5 5. 3 19. 7 1. 0 0.5

72.5 4.9 20.8 1.1 0.7

7 .8

13 .8

13. 9

14.8



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unwanted oxygen, n i t r o g e n and s u l f u r , and l e s s hydrogen i s needed to b r i n g the carbon/hydrogen r a t i o down to values r e quired i n l i q u i d f u e l s such as g a s o l i n e , turbine and d i e s e l f u e l s or h e a t i n g o i l s . Because of the impervious nature of the o i l shale and the chemical nature of the kerogen, i t i s necessary to heat the shale to around 450°C (900°F) to thermally break up the kerogen. Under these c o n d i t i o n s , kerogen decomposes to give o i l (65-70%), gas (10-15%), coke (15-20%) and water (2-7%). A l s o , during the r e t o r t i n g operation, there i s s i g n i f i c a n t l o s s of oxygen. About two-thirds i s l o s t as carbon d i o x i d e and about o n e - t h i r d as water. Because of the l o s s of carbon d i o x i d e , the C/H r a t i o has b e n e f i c i a l l y decreased from 7.8 i n kerogen to 7.3 i n shale o i l . Some i n s i g h t i n t o the u t i l i t y of shale o i l can be gained by comparing i t s composition w i t h c o a l - d e r i v e d l i q u i d s and petroleum crude o i l . See Table I I I . Two r e p r e s e n t a t i v e l i q u i d products from c o a l a r e shown: COED product, produced by c a r b o n i z a t i o n or coking, which, l i k e r e t o r t i n g o f shale, i s a thermal step (4), and a l i q u i d from the H-Coal process by c o a l hydrogenat i o n (5). Arabian L i g h t crude o i l i s a l s o shown. Of the two thermally produced l i q u i d s , shale o i l has a b e t t e r (lower) carbon-to-hydrogen r a t i o , and a lower s p e c i f i c g r a v i t y which i n d i c a t e s the absence of h i g h b o i l i n g aromatics. Both have h i g h pour p o i n t s ; shale o i l because of long-chain p a r a f f i n s , COED l i q u i d because of heavy polyaromatics. The l i q u i d y i e l d s per t o n of raw m a t e r i a l mined are i n the same order of magnitude. The s o l i d r e s i d u e of shale r e t o r t i n g i s l a r g e l y mineral matter, w h i l e the s o l i d residue from c o a l c a r b o n i z a t i o n , c a l l e d a char, i s a usable f u e l c o n t a i n i n g more energy than the o i l f r a c t i o n . Conversion of the COED l i q u i d product to t r a n s p o r t a t i o n f u e l s , however, i s a more d i f f i c u l t task because of i t s h i g h t a r , lower hydrogen and higher hetero atom contents. The hydrogenated product from c o a l , H-Coal l i q u i d , i s more aromatic than shale o i l but somewhat comparable i n hetero atom content even though a c o n s i d e r a b l e amount of hydrogen has already been added to the product. Arabian L i g h t crude i s a wider b o i l i n g m a t e r i a l than crude shale o i l and i s lower i n a l l hetero atoms except s u l f u r . I t has a more f a v o r a b l e carbon/hydrogen r a t i o because i t contains fewer aromatics and no o l e f i n s . In the upgrading of crude shale o i l , s o l i d s removal i s f i r s t achieved by optimal c e n t r i f u g i n g , s e t t l i n g and f i l t e r i n g . Next, a r s e n i c removal i s achieved with a c a t a l y s t - a b s o r b e n t . In the t h i r d step, the h y d r o t r e a t i n g step, the s u l f u r , n i t r o g e n , and oxygen c o n t a i n i n g compounds a r e hydrogenated over m e t a l l i c s u l f i d e c a t a l y s t s to hydrogen s u l f i d e , ammonia, water and hydrocarbons. O l e f i n s present i n the raw shale o i l are a l s o hydrogenated. The hydrotreated shale o i l (or syncrude) now, save f o r pour


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TABLE I I I CRUDE SHALE OIL, COAL LIQUIDS, CRUDE OIL

Crude Shale Oil

Coal L i q u i d s COED* H-Coal

Gravity, Specific °API

0.92 22.2

1.13 -4

B o i l i n g Range, °C

60-540

Composition, Nitrogen Sulfur Oxygen

Arabian Light Crude

0.92 23.0

0.85 34.7

30-525

5-575+

Wt%

C/H Ratio

1.8 0.9 0.8

1.1 2.8 8.5

0.1 0.2 0.6

0.8 1.7

7.3

11.2

8.1

6.2

Pour P o i n t , °F

60

100

Oil Shale, Tar Sands, and Related Materials - American Chemical

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