High-Pressure Pyrolysis of Green River Oil Shale - ACS Symposium

18

H i g h - P r e s s u r e P y r o l y s i s of G r e e n R i v e r Oil S h a l e

Downloaded by PENNSYLVANIA STATE UNIV on February 12, 2016 | http://pubs.acs.org Publication Date: August 1, 1983 | doi: 10.1021/bk-1983-0230.ch017

ALAN K. BURNHAM and MARY F. SINGLETON Lawrence Livermore National Laboratory, Livermore, CA 94550 Oil yields, compositions and rates of evolution are reported for heating rates from 1 to 100°C/h and pressures of 1.5 and 27 atm. Pyrolysis occurred in an autogenous atmosphere and volatile products were allowed to escape the pyrolysis region continuously. Higher pressures and lower heating rates during pyrolysis cause a decrease in oil yield, although the effects are not additive. The lowest oil yield was approximately 72 wt% or 79 vol% of Fischer assay. Lower oil yield is generally accompanied by lower boiling point distribution, nitrogen content and density and higher H/C ratios. Oils produced at high pressure and slow heating rates are a clear amber color instead of the usual opaque brown. The effect of pyrolysis conditions on biological markers and other diagnostic hydrocarbons is also discussed. Existing kinetic expressions for o i l evolution slightly overestimate the shift in the o i l evolution rate vs temperature with a decrease in heating rate. Finally, the rate of o i l evolution is retarded by pressure, a factor not taken into account by current kinetic expressions. Pyrolysis of kerogen-rich rocks under pressure provides information that is useful for evaluating oil-shale-processing schemes (1-5) and understanding the formation of petroleum (j>>_7)« Reliable extrapolation from laboratory experiments to commercial situations generally requires a kinetic model that can properly describe the effects of temperature (or heating rate), pressure, residence time and gas atmosphere on o i l yield and composition. None of the existing studies have been designed to separate and quantify these dependencies, so such a model has not yet been derived. 0097-6156/83/0230-0335S06.00/0 © 1983 American Chemical Society

In Geochemistry and Chemistry of Oil Shales; Miknis, Francis P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


336

GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES

In t h i s work, we p y r o l y z e d Green R i v e r o i l shale i n a r e a c t o r w i t h an i n i t i a l t o t a l p o r o s i t y o f 29% wjiere the products are allowed to escape as they are produced. This s e l f - p u r g i n g design r e s u l t s i n the p y r o l y s i s o c c u r r i n g i n a n e a r l y autogenous atmosphere, u n l i k e most other s t u d i e s where the gas atmosphere i s dominated by an added p r e s s u r i z i n g f l u i d . We d i s c u s s the e f f e c t of i n i t i a l p o r o s i t y , hence product r e s i d e n c e time at h i g h temperatures, on the p y r o l y s i s r e s u l t s . The experiments were designed t o simulate the temperature-pressure h i s t o r i e s a n t i c i pated i n radio-frequency i n - s i t u o i l - s h a l e p r o c e s s i n g (8) so that o i l y i e l d s c o u l d be estimated more r e l i a b l y . The r e s u l t s presented here may a l s o be u s e f u l f o r understanding petroleum formation i n the U i n t a b a s i n (Utah) and from other type I source r o c k s . We do not c o n s i d e r the present r e p o r t to be d e f i n i t i v e ; f u t u r e experimental work and a n a l y s i s w i l l be d i r e c t e d at developing a t r a c t a b l e k i n e t i c model o f high-pressure p y r o l y s i s . Experimental Procedures The sample i n t h i s study was a 94-L/Mg (22.4-gal/ton) Green R i v e r o i l shale (marl) from the A n v i l P o i n t s mine near R i f l e , CO. The p a r t i c l e s i z e was 0.42 to 0.84 mm (-20 +40 mesh). I t contained by weight 10.88% o r g a n i c C, 4.76% m i n e r a l C, 1.64% H, 0.42% N, and 0.59% S. The sample i s approximately r e p r e s e n t a t i v e of mine-run s h a l e , which covers most o f the Mahogany zone. The apparatus i s shown s c h e m a t i c a l l y i n F i g u r e 1. To reduce the p o r o s i t y i n the r e a c t o r , hence residence time o f the v o l a t i l e products, the f o l l o w i n g procedures were used. The sample was compressed i n t o 3.2-cm-diam. by 4-cm-long p e l l e t s u s i n g a pressure of 165 MPa. Two o f these p e l l e t s , weighing a t o t a l o f about 110 g, were placed i n t o the sample can (3.3 cm diam.) along w i t h quartz sand above and around the p e l l e t s , and a top was welded on. We determined the t o t a l p o r o s i t y of the p e l l e t s to be about 24% from the helium-buoyancy d e n s i t y o f the raw shale and the weight and dimensions of the p e l l e t s . T o t a l p o r o s i t y i n the r e a c t o r averaged 29%, o r e q u i v a l e n t l y , the t o t a l v o i d volume was about 20 cm . The sample was heated from room temperature to 500°C at h e a t i n g r a t e s ranging from 1 to 110°C/h. Previous experience i n d i c a t e s that the d i f f e r e n c e i n temperature across the sample i s l e s s than 5°C f o r t h i s s i z e sample and h e a t i n g r a t e s l e s s than 120°C/h. For the near-atmospheric pressure experiments, a thermocouple was used to measure the temperature near the c e n t e r of the o i l shale sample. For the high-pressure experiments, t h i s sample thermocouple was o m i t t e d , and the sample temperature was estimated from the furnace temperature. The d i f f e r e n c e between the sample and furnace temperatures was determined i n the nearatmospheric pressure experiments. The sample and o i l c o l l e c t i o n system was evacuated and then p r e s s u r i z e d w i t h argon to prevent o x i d a t i o n . The pressure was 3



BURNHAM AND SINGLETON

Green River Oil Shale Pyrolysis

337

Figure 1. Apparatus for pyrolysis under an autogenous atmosphere.



338


maintained approximately constant during the experiment by a back-pressure r e g u l a t o r r e l e a s i n g gas at approximately the same r a t e as i t i s produced. The pressure i n the r e a c t o r increased somewhat (^

/ Φ

I

rit _

'

A

I A

1

/

/

A #

A A

—

/·

A

_

A A

~~ —

A

0.0

1

/ ^ / " 1°C/h

10°C/h

Α

8

> 0.5 >

349


BURNHAM AND SINGLETON

400

I

500

/? /·

A* • Λ * Α ±

350

Α

A m

A ,

— 1

450

~~

Γ

•uL/^AA|

300

A

I

400

Temperature, °C Figure 6. Experimental (points) and calculated (lines) volumes of oil evolved as a function of temperature as the sample is heated at the indicated heating rate. Key: ·, 1.5 atm; and A, 27 atm.



350

Table V. Experimental (+5°C) and c a l c u l a t e d temperatures f o r 99% o f o i l e v o l u t i o n .


Heating r a t e (°C/h)

Pressure (atm) 1.5 27

Calculated Shih and Campbell Sohn (19) et a l . (18)

110

465

495

460

465

10

435

455

415

415

1

400

410

380

375

r a t e i f the r a t e o f evaporation i s comparable t o o r slower than the r a t e o f g e n e r a t i o n . Campbell's treatment o f o i l e v a p o r a t i o n i s too e m p i r i c a l t o account f o r pressure e f f e c t s . An accurate d e s c r i p t i o n o f o i l evaporation i s needed t o untangle the v a r i o u s c o n t r i b u t i o n s t o changes i n o i l y i e l d and composition. I t i s e s p e c i a l l y important when a p p l y i n g the r e s u l t s o f t h i s work t o s i t u a t i o n s where the t r a n s p o r t mechanisms are d i f f e r e n t than i n our experiments, e.g., petroleum formation. Conclusions Pressure causes a decrease i n o i l y i e l d i n an autogenous atmosphere, but the e f f e c t o f pressure i s s m a l l e r a t slow h e a t i n g r a t e s . The changes i n o i l composition r e l a t e d t o decreased o i l y i e l d a t e l e v a t e d pressure are somewhat d i f f e r e n t than the corresponding changes w i t h h e a t i n g r a t e a t atmospheric p r e s s u r e . Heating r a t e p r i n c i p a l l y determines n i t r o g e n content w h i l e pressure determines s u l f u r content. Pressure s i g n i f i c a n t l y r e t a r d s the o i l - e v o l u t i o n r a t e even though a l o w e r - b o i l i n g product i s formed. In f a c t , the longer residence times caused by increased pressure may cause the decrease i n b o i l i n g p o i n t by i n c r e a s i n g o i l c r a c k i n g . A k i n e t i c model that can a c c u r a t e l y c a l c u l a t e y i e l d s , compositions and r a t e s o f e v o l u t i o n w i l l have to t r e a t the e f f e c t o f pressure on o i l evaporation and i t s r e l a t i o n s h i p t o c r a c k i n g and coking o f o i l . F u r t h e r experiments w i t h v a r i a b l e p o r o s i t y , hence residence time, would be h e l p f u l i n developing such a k i n e t i c model. Acknowledgments We a p p r e c i a t e the design o f the apparatus by E. Huss, W. M i l l e r and R. T a y l o r and the c o n s t r u c t i o n and c o n t i n u i n g support by J . T a y l o r and C. H a l l . We a l s o thank L. Gregory, J . C l a r k s o n , J . Cupps, C. M o r r i s , C. Otto, and R. Ryan f o r


17. burnham and singleton


351

analytical support, and R. Taylor for numerous helpful discussions· Work performed under the Auspices of the U. S. Department of Energy at Lawrence Livermore National Laboratory under contract #W-7405-Eng-48.


Literature Cited 1. Bae, J . H. Soc. Petrol. Eng. J., 1969, 278-292. 2. Wise, R. L.; Miller, R. C.; George, J . H. ACS Div. Fuel Chem. Preprints 1979, 21(6), 87. 3. Noble, R. D.; Wang, C.-C. "Kerogen Decomposition Under Elevated Pressures" Rept. DOE/LC/01761-T2, 1981 (Aval. NTIS). 4. Weil, S. A. Symposium Papers; Synthetic Fuels from Oil Shale 1980, p. 353. 5. Sresty, G. C.; Dev H.; Snow, R. H.; Bridges, J . E. 15th Oil Shale Symposium Proceedings 1982, p. 411. 6. Lewan, M. D.; Winters, J . C.; McDonald, J . H. Science 1979, 203, 897-899. 7. Bandurski, E. Energy Sources 1982, 6, 47-66. 8. Mallon, R. G. "Economics of Shale Oil Production by Radio Frequency Heating," Lawrence Livermore National Laboratory Rept. UCRL-52942, 1980. 9. Singleton, M. F . ; Koskinas, G. J.; Burnham, A. K.; Raley, J . H. "Assay Products from Green River Oil Shale," Lawrence Livermore National Laboratory Rept. UCRL-53273, 1982. 10. Campbell, J . H.; Koskinas, G. J.; Stout, N. D.; Coburn, T. T. In Situ 1978, 2, 1. 11. Evans, R. Α.; Campbell, J . H. In Situ 1979, 3, 33. 12. Stout, N. D.; Koskinas, G. J.; Raley, J . H . ; Santor, S. D.; Opila, R. J.; Rothman, A. J . Colorado School of Mines Quart. 1976, 71, 153. 13. Jackson, L. P.; Allbright, C. S.; Poulson, R. E. Anal. Chem. Liq. Fuel Sources, P. C. Uden, Ed., ADVANCES IN CHEMISTRY SERIES No.170, ACS: Washington, D. C., 1978, p. 232. 14. Burnham, A. K. Oil Shale, Tar Sands and Related Materials, W. C. Stauffer, Ed., ACS SYMPOSIUM SERIES No. 163, ACS: Washington, D. C., 1981, p. 39. 15. McKee, R. H. "Shale O i l , " Chemical Catalog Co., 1925, p. 82. 16. Burnham, A. K.; Clarkson, J . E . ; Singleton, M. F.; Wong, C. M.; Crawford, R. W. Geochim. Cosmochim. Acta 1982, 46, 1243. 17. Slettevold, C. Α.; Biermann, A. H.; Burnham, A. K. "A Surface-Area and Pore-Volume Study of Retorted Oil Shale," Lawrence Livermore National Laboratory Rept. UCRL-52619, 1978. 18. Campbell, J . H.; Koskinas, G. J.; Stout, N. D. Fuel 1978, 57, 372. 19. Shih, S. M.; Sohn, H. Y. I&EC, Process Design and Devel. 1980, 19, 420-426. RECEIVED April 25, 1983


High-Pressure Pyrolysis of Green River Oil Shale - ACS Symposium

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