Fuel Gasification

12 Catalytic Gasification of Shale O i l

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P. L. COTTINGHAM and H. C. CARPENTER U.S. Department of the Interior, Bureau of Mines, Laramie Petroleum Research Center, Laramie, Wyo. Crude shale oil was hydrogasified at 1000 lbs. pressure over depleted uranium and cobalt molybdate catalysts at temperatures in the range 880°-1102°F. with depleted uranium and 974°-1196°F. with cobalt molybdate. With both catalysts, the higher reaction temperatures produced greater hydrocarbon gas yields, greater percentages of methane in the gas, and greater methane yields expressed as percentage of conversion of the feedstock. The largest methane yields— 4340 cu. ft. per barrel—and largest hydrocarbon gas yield— of 5725 cu. ft. per barrel—were obtained at the highest temperature (1196°F.) and lowest space velocity (0.25 V /V /hr.) used. At these conditions, methane yield was 75.8 vol.% of the hydrocarbon gas and 49.7 percent of stoichiometric. o

c

A lthough the United States has large reserves of natural gas, our annual marketed production increased from less than 4 trillion cu. ft. in 1945 to nearly 16 trillion cu. ft. in 1964 ( 9), an increase of about 400% in 19 years. This increase, coupled with our decreasing ratio of reserves to production and the need for peak-shaving, has stimulated interest in possible methods for supplementing our future natural gas supply. The large quantities of oil shale in the western United States suggest using oil shale or shale oil for such supplemental purposes. Various authors have reported on the thermal gasification of these materials (5, 6, 7, 8). The present study is concerned with catalytic hydrogasification of crude shale oil, using depleted uranium and cobalt molybdate on alumina supports as catalysts. Previous experiments in catalytic hydrogénation of crude shale oil at the Laramie Petroleum Research Center (3,4) showed that pressures in excess of 2000 lbs. per sq. in. greatly suppressed the formation of methane, ethane, and catalyst deposits. At 500 lbs. pressure, catalyst deposits became excessive. The gasification experiments were, therefore, run at 180 In Fuel Gasification; Schora, Frank C.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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Shale OH

181

1000 lbs. pressure to obtain high gas yields with moderate catalyst deposits.


Experimental Apparatus and Procedure. A simplified flow diagram of the apparatus used for the gasification study is shown in Figure 1. The reactor was a vertical 2-9/16-in.-i.d. by 32-in.-long stainless steel vessel; it was modified for these experiments by a stainless steel sleeve that was inserted to reduce the internal diameter to 1 in. This modification improved temperature control. The reactor contained 18 in. of alundum granules at the top to serve as a preheater, 12.5 in. of catalyst (150 c c ) , and 1.5 in. of alundum granules at the bottom. Catalyst temperatures were determined by five thermocouples, spaced at 2.25-in. intervals in a central thermowell in the catalyst bed.

Figure I.

Hydrogénation unit

Hydrogen and oil were mixed at the inlet to the reactor and passed downward through the catalyst. Liquid products were separated in two high-pressure separators, operated in series at 350° and 40°F. Gas from the cold receiver was metered and stored until it could be sampled for mass spectrometer analysis. Each gasification experiment was run for 6 hours with 12,000 cu. ft. of hydrogen per barrel. At the end of an experiment, liquid products were distilled into a light-ends fraction collected in a dry-ice trap, a naphtha fraction boiling up to 400°F., and a recycle fraction containing everything boiling above 400°F. The light ends from the cold trap were analyzed by the mass spectrometer, and appropriate weights were added to the

In Fuel Gasification; Schora, Frank C.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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Table I.

Properties of Crude Shale CHI


Specific gravity at 60°-60°F.

0.9408

Elemental analysis, wt.% Sulfur Nitrogen Carbon Hydrogen Oxygen (by diff.) Hydrogen/carbon atomic ratio

0.68 2.18 83.96 11.40 1.78 1.61

Carbon residue, wt.% Iron, p.p.m. Zinc and arsenic, p.p.m. Viscosity at 140°F., cs. at 210°F.

3.5 40 present 28.30 8.23

ASTM gas-oil distribution (760 mm.) I.B.P., °F. Max. (cracking), °F. Recovery, vol.% Residue, vol.%

407 695 37.5 62.5

gaseous and liquid products. Carbon deposits in the reactor were determined by measuring the carbon dioxide obtained when passing air through the reactor to regenerate the catalyst. Catalysts. The catalysts used were commercial cobalt molybdate and a laboratory-prepared depleted uranium catalyst. The cobalt molybdate consisted of cobalt and molybdenum oxides on 6- to 8-mesh alumina granules. The uranium catalyst consisted of 7.7% depleted uranium (uranium from which the U-235 has been removed) in the oxide form on 1/8-in. H-151 alumina balls. This catalyst had produced high gas yields in previous hydrogénation experiments with shale oil, and these results suggested its possible use as a hydrogasification catalyst. Both catalysts were maintained under a hydrogen atmosphere at approximate reaction temperature and pressure for about 12 hours before each experiment. Feedstock. The crude shale oil used for these studies was prepared in the Bureau of Mines gas-combustion retort at Rifle, Colo. It was filtered before use, and the ash content was reduced to 0.03 wt.%. Properties of the oil are shown in Table I. It contains a large amount of sulfur-, nitrogen-, and oxygen-containing compounds, and more than half of it may consist of nonhydrocarbons (2). It has a high viscosity and contains no gasoline-boiling range material. The hydrogen-carbon atomic ratio of 1.61 shows that additional hydrogen must be added to the oil to convert it to pipeline gas.


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Calculations. A l l gas measurements are reported at 60 °F. and 760 mm. mercury pressure. The hydrogen feed rate of 12,000 cu. ft. per barrel was 1.1 times the stoichiometric amount of about 10,890 cu. ft. needed to convert the crude oil completely to methane, hydrogen sulfide, ammonia, and water. The yield of methane as volume percent of stoichiometric was calculated by dividing the volume in cubic feet per barrel by 8740, which was the stoichiometric yield at the given conditions. The hydrocarbon gas yields were considered to consist of the C i through C hydrocarbons. The percentages of C hydrocarbons were added to the percentages of liquid products to obtain C -plus liquid yields. Weight percent conversion of the feed was defined as 100 minus the weight percent of C -plus liquid product. Therefore, conversion would include the weight percent of feed converted to C through C hydrocarbons and to such things as ammonia, hydrogen sulfide, water, and coke. Methane yields as percent of conversion were obtained by dividing the weight percent methane by the weight percent conversion and multiplying by 100.


3

4

4

4

x

3

Table II. Gasification of Crude Shale Oil over Depleted Uranium Catalyst" 0.5V /V /hr. 0

c

954 979 1840

1010 1035 3080

1053 1074 3980

1102 1125 4170

Hydrocarbon gases (std. cu. ft/barrel) Methane 365 Ethane 200 Propane 146 Ethylene 18 Propylene 33 Total 762 Heat value, gross ( B.t.u./cu.ft.) 1589

598 387 247 4 0 1236 1570

76.4 23.6 5.1 2.0 0.6 1.6

67.5 32.5 4.7 2.0 0.7 2.0

1152 693 441 29 44 2359 1565 44.9 55.1 4.9 2.0 0.7 2.1

1507 971 536 18 40 3072 1550 32.9 67.1 4.0 2.0 0.7 2.5

1767 1059 459 18 0 3303 1481 30.6 69.4 5.5 2.0 0.7 2.4

4.7 19.9 47.9 4.2

7.7 23.7 48.4 6.8

14.8 26.9 48.8 13.2

19.3 28.8 49.0 17.2

22.6 32.6 53.5 20.2

Temp, (av.) °F. Temp, (max.) °F. H consumed (std. cu. ft./barrel) 2

C liquid (wt.%) Conversion (wt.%) Catalyst deposit (wt.% ) Water (wt.%) Hydrogen sulfide (wt.% ) Ammonia (wt.% ) Methane wt.% wt.% of conv. vol.% of gas vol.% of stoich. 4

a

+

880 906 1340

Pressure 1000 p.s.i.g.; hydrogen feed 12,000 std. cu. ft./barrel.


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Gross heating values were calculated from component heating values used by the Bureau of Mines in reporting the analyses of natural gases (I). The values were calculated at 760 mm. mercury pressure to agree with the volume measurements.


Results Depleted Uranium Catalyst. Table II shows the results from five experiments in hydrogasifying crude shale oil over depleted uranium catalyst at a space velocity of 0.5 volumes of oil per volume of catalyst per hour. Average reaction temperatures varied from 880° to 1102 °F. Table III.

Liquid Products from Gasification over Depleted Uranium Catalyst

Temp, (av.) °F. H consumed (std. cu. ft. /barrel) 2

880 1340

954 1840

1010 3080

1053 3980

1102 4170

13.4 11.1 16.7 Naphtha (wt. % of feed) 26.5 26.6 Sp. gr. at 60°-60°F. 0.7655 0.7799 0.8279 0.8711 0.8874 Sulfur (wt.%) 0.08 0.04 0.08 0.02 0.04 Nitrogen (wt.%) 0.68 0.61 0.86 0.34 0.52 Hydrocarbon types (vol.% ) 8 25 Paraffins 34 35 ο Naphthenes 11 14 4 4 3 Olefins 29 18 10 3 1 Aromatics 26 32 61 85 96 0

Recycle oil (wt.% of feed) Sp. gr. at 60°-60°F. Sulfur (wt.%) Nitrogen (wt.%) 6

40.7 0.9247 0.18 1.74

19.4 0.9973 0.22 1.76

15.7 1.0555 0.28 2.02

10.7 1.0695 0.16

—

9.5 1.0763 0.22 1.28

* Not including C from gas. * Insufficient sample where analysis is not shown. 4

+

Total hydrocarbon gas volumes increased from 762 cu. ft. per barrel at 880°F. to 3303 cu. ft. at 1102°F.; at the same time, the methane content of the gas increased from 47.9 to 53.5 vol.%, resulting in a change in the volume of methane from 365 to 1767 cu. ft. A corresponding decrease in the heating values of the gas occurred, from 1589 to 1481 B.t.u. per cu. ft., as the heating values tended to approach that of methane. Expressed on the weight basis, the yield of methane increased from 4.7% at 880°F. to 22.6% at 1102°F., and total conversion increased from 23.6 to 69.4% ; the corresponding change in methane yield expressed as weight percent of conversion was from 19.9 to 32.6%.



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Table III shows the properties of the liquid products from the hydrogasification experiments with depleted uranium catalyst. Sulfur percentages in the liquid products were considerably lower than the percentage in the feed, but nitrogen percentages were high. The naphthas became aromatic as the operating temperature was raised from 880° to 1102°F. Cobalt Molybdate Catalyst. Yields of products from hydrogasifying crude shale oil over cobalt molybdate catalyst at a space velocity of 1.0 volume of oil per volume of catalyst per hour are shown in Table IV, and properties of the liquid products are shown in Table V. The average reaction temperatures from 974° to 1183°F. were higher than those used with depleted uranium catalyst. Consequently, greater gas yields were obtained. However, similar trends were shown in the results obtained with both catalysts. Conversion increased from 34.1 to 85.1% as the average temperature was increased from 974° to 1183°F. At the same time, methane yield, as weight percent of conversion, increased from 24.6 to 46.6%. Also, the Table IV. Gasification of Crude Shale Oil over Cobalt Molybdate Catalyst e

l.OVJVJhr. Temp, (av.) °F. Temp, (max.) °F. H consumed (std. cu. ft./barrel)

1018 2680

974

1004 1049 3210

1106 1172 4850

1183 1226 5980

Hydrocarbon gases (scf/bbl) Methane Ethane Propane Ethylene Propylene Total Heat value, gross ( B.t.u./cu.ft.

652 427 288 27 30 1424 1601

972 663 435 48 57 2175 1611

1945 1292 504 5 0 3746 1490

3090 1699 109 0 5 4903 1315

C liquid (wt.%) Conversion (wt.%) Catalyst deposit (wt.%) Water (wt.%) Hydrogen sulfide (wt.%) Ammonia (wt.%)

65.9 34.1 2.4 2.0 0.7 2.6

50.5 49.5 2.0 2.0 0.7 2.6

24.9 75.1 2.4 2.0 0.7 2.6

14.9 85.1 4.2 2.0 0.7 2.6

Methane wt.% wt.% of conv. vol.% of gas vol.% of stoich.

8.4 24.6 45.8 7.5

12.5 25.3 44.7 11.1

25.0 33.3 51.9 22.2

39.7 46.6 63.0 35.4

2

4

a

+



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methane content of the hydrocarbon gas increased from 45.8 to 63.0 vol. %. The increased percentage of methane in the gas at the higher temperature and conversion levels was reflected in the heat content of the gas, which decreased from 1,601 B.tu. per cu. ft. for the gas obtained at 974°F. to 1315 B.t.u. per cu. ft. for the gas obtained at 1183°F.


Table V. Liquid Products from Gasification over Cobalt Molybdate Catalyst Space velocity

L0V /V /hr. o

Temp, (av.) ° F . H consumed (std. cu. ft./barrel) 2

Naphtha" (wt.% of feed) Sp. gr. at 6 0 ° - 6 0 ° F .

Sulfur (wt.%) Nitrogen (wt.% ) Hydrocarbon types* (vol.%) Paraffins Naphthenes Olefins Aromatics Recycle oil (wt.% of feed) Sp. gr. at 6 0 ° - 6 0 ° F .

Sulfur (wt.%) Nitrogen (wt.%)

2680

1004 3210

1106 4850

39.5 0.7562 0.00 0.02

24.9 0.7821 0.00 0.01

12.0 0.8741 0.00 0.02

— — — —

— — — —

974

15.3 1.0303 0.00 0.22

Not including C from gas. * Insufficient sample where analysis is not shown.

a

4

c

9.5 1.0543 0.00

—

«J 2 95 7.2 1.1181 0.00 0.20

1183 5980 7.8 0.8801 0.00 0.01

100

0 0 0

6.3 1.0699 0.03 0.27

+

Yields of products from hydrogasifying crude shale oil over cobalt molybdate catalyst at space velocities of 0.50 and 0.25 are shown in Table VI, and properties of the liquid products are shown in Table VII. Results of two experiments at different temperatures are shown for each space velocity. The highest methane yield (4341 cu. ft. per barrel) and highest gas yield (5725 cu. ft. per barrel) were obtained at the highest temperature (1196°F. average or 1208°F. maximum) and lowest space velocity (0.25) used. The greatest conversion of feed stock, 88.1%, and greatest yield of methane as percent of conversion, 63.3%, were also obtained under these conditions. Methane content of the hydrocarbon gas was 75.8 vol. %, or 49.7% of stoichiometric. Heating value of the gas was 1202 B.tu. per cu. ft. Sulfur percentages in the liquid products were low. Nitrogen percentages were much lower than those of the liquid products obtained by hydrogasification over depleted uranium catalyst. The percentages of



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Shale OH

aromatic hydrocarbons in the naphthas were high, and at a reaction temperature of 1114°F. with a space velocity of 0.50 they approached 100% of the hydrocarbons. The naphthas produced in small percentages at a space velocity of 0.25, although not analyzed, also would be expected to be almost 100% aromatic. Decreasing the space velocity had much the same effect as increas ing the reaction temperature. Comparing results obtained at 1106°F. average temperature and 0.25 space velocity with those obtained at 1114°F. and 0.50 space velocity shows that greater methane yield, greater total gas yield, greater conversion, and greater methane yields expressed Table V I . Gasification of Crude Shale Oil over Cobalt Molybdate Catalyst 0

0.50V /V /hr. 0

c

0.25V /V /hr. o

c

Temp, (av.) °F. Temp, (max.) °F. H consumed (std. cu. ft./barrel)

1062 1089 3803

1114 1141 4985

1106 1129 5460

1196 1208 6852

Hydrocarbon gases (std. cu. ft./barrel) Methane Ethane Propane Ethylene Propylene Total Heat value, gross (B.t.u./cuit.)

1465 995 461 9 24 2954 1530 35.5 64.5 4.7 2.0 0.7 2.6

2141 1379 407 23 18 3968 1451 23.2 76.8 2.6 2.0 0.7 2.6

2485 1683 231 0 18 4417 1393 20.2 79.8 1.4 2.0 0.7 2.6

4341 1357 25 1 1 5725 1202 11.9 88.1 4.1 2.0 0.7 2.6

18.8 29.1 49.6 16.8

27.5 35.8 54.0 24.5

31.9 40.0 56.2 28.4

55.8 63.3 75.8 49.7

2

C liquid (wt.%) Conversion (wt.%) Catalyst deposit (wt.%) Water (wt.%) Hydrogen sulfide (wt.%) Ammonia (wt.%) Methane wt.% wt.% of conv. vol. % of gas vol.% of stoich. 4

β

+


either as percent of conversion or percent of total gas were obtained at the lower space velocity. Heating value of the hydrocarbon gas was lower for the gas produced at the lower space velocity because of the higher methane content. These comparisons can be extended to the results shown in Table IV for the experiment at 1106°F. and 1.0 space velocity.


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Table VII. Liquid Products from Gasification over Cobalt Molybdate Catalyst 0.50 V /V /hr. 0

Temp, (av.) °F. H consumed (std. cu. ft./barrel)

1062 3803

2

Naphtha (wt.% of feed) 16.8 Sp. gr. at 60°-60°F. 0.8482 Sulfur (wt. %) — Nitrogen (wt. %) 0.14 Hydrocarbon types (vol.%) Paraffins 15 Naphthenes 2 Olefins 0 Aromatics 83 a


6

6

c

0.25 V /V /hr. 0

1114 4985

1106 5460

10.2 0.8832 0.01 0.04

10.1 0.8869 — 0.02

c

1196 6852 6.4 0.8986 — —

6

Recycle oil (wt.% of feed) Sp. gr. at 60°-60°F. Sulfur (wt.%) Nitrogen (wt.%) a 6

8.0 1.0635 0.12 0.34

0

—

—

0 99

— —

— —

5.8 1.1064 0.02 0.16

2.8 1.0730 0.08 0.15

3.4 1.1074 0.06 0.11

Not including C from gas. Insufficient sample where analysis not shown. 4

+

Conditions used with the cobalt molybdate were generally not the same as those with the depleted uranium catalyst. However, the gas yields obtained at 1062°F. and 0.50 space velocity over cobalt molybdate were similar to those obtained at 1053°F. and 0.50 space velocity over depleted uranium. Better elimination of nitrogen from the liquid products was achieved with the cobalt molybdate. No special advantages were found for the depleted uranium, but further research would be needed to evaluate it fully over the entire range of conditions investigated with the cobalt molybdate. Summary Cobalt molybdate on alumina and depleted uranium on alumina were tested as catalysts for hydrogasifying crude shale oil at 1000 lbs. pressure and a hydrogen feed rate of 1.1 times the stoichiometric, with on-stream periods of 6 hours for each experiment. Reaction temperatures were in the range 880°-1102°F. with depleted uranium and 974° to 1196°F. with cobalt molybdate. With both catalysts the higher reaction temperatures produced greater hydrocarbon gas yields, greater percentages of methane in the gas, and greater methane yields expressed as percentage of conversion of feedstock. Lowering the space velocity through the range 1.00.25 with cobalt molybdate produced effects similar to those obtained when raising the temperature.


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Acknowledgment This work was conducted under a cooperative agreement between the Bureau of Mines of U.S. Department of the Interior and the Univer sity of Wyoming. The depleted uranium used in this work was obtained from the Atomic Energy Commission, Oak Ridge, Tenn.


Literature Cited (1) Boone, W. J., Jr., U.S. Bur. MinesBull.576 (1958). (2) Cady, W. E., Seelig, H. S., Ind. Eng. Chem. 44, 2632 (1952). (3) Carpenter, H. C., Cottingham, P. L., U.S. Bur. Mines Rept. Invest. 5533 (1959). (4) Cottingham, P. L., White, E. R., Frost, C. M., Ind. Eng. Chem. 49, 679 (1957). (5) Feldkirchner, Harlan L., Quart. Colo. School Mines 60, (3), 147 (1965). (6) Linden, Henry R., Chem. Eng. Progr.Symp.Ser. No. 54, 61, 76 (1965). (7) Schultz, Ε. B., Jr., Linden, Henry R., Ind. Eng. Chem. 51, 573 (1959). (8) Schultz, Ε. B., Jr., Chem. Eng. Progr. Symp.Ser.No. 54, 61, 48 (1965). (9) Zaffarano, R. F., Avery, Ivan F., Minerals Yearbook (U.S. Bur. Mines) 2, 319-352, (1964). RECEIVED November 28, 1966.


Fuel Gasification

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