US2487788A - Processing oil shale - Google Patents

Description

Nov., l59 1949 F. E. BUCHAN PROCESS ING OIL SHALE Filed Sept. 5, 1945 Patented Nov. 15, 1949 2,487,788 PROCESSING OIL SHALE Frederick E. Buchan, Washington, D. C., assignor to the United States of America as represented by the Secretary of the Interior Application September 5, 1945, Serial No. 614,588

(Granted under the act of March 3, 1883, as

6 Claims.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

This invention relates to the recovery of hydrocarbon liquids and/or gases from carbonaceous mineral materials, more particularly to the production of high quality liquid fuel fractions from kerogen rocks.

It is an object of the invention to increase the yield of useful products from kerogen rocks, especially oil shales such as occur in the United States. Another object of the invention is the recovery of crude liquid hydrocarbons that may be further processed satisfactorily either by conventional refining operations or, at the most, with only minor modication thereof. A further object is the provision of an improved heating method whereby the percentage recovery as a liquid of the organic matter initially present in the rock is materially increased over prior methods, without excessive decomposition and consequent formation of carbon in the residual material. Other objects will be apparent or will appear hereinafter.

Kerogen rocks are defined by Down and Himus (Classification of Oil Shales and :Cannel Coals (1940)) as sedimentary rocks containing organic matter which, on destructive distillation, yield an oil equivalent to approximately 50 percent of the organic content. They occur in continuous seams scattered all over the world, and the western deposits in the United States are particularly suitable for development, although large quantities of lean oil shale occur in the Kentucky-Indiana area. A typical sample of Green River shale from Colorado according to Bradley (Geol. Survey Prof. Paper 168 (1931)) consists of kerogen 46 percent, clay 2l. percent, excess silica l0 percent, and magnesium carbonate 9 percent. Kerogen itself, according to Brown (Shale Oil- R. N. McKee (1925)) is the material in Scottish shales, which, on destructive distillation, yields oil. It is neither petroleum nor bitumen, but an organic substance yielding petroleum and nitrogenous compounds upon pyrolytic conversion.

It has been the common practice for many years to distill destructively kerogen rocks. such as Scottish shale in large vertical retorts thereby decomposing the kerogen and recovering part of it in the form of oils resembling crude petroleum while a part of it is lost as fixed gases and residual carbon. However, the percentage recovery, as oil, of the organic matter present in the shale is low and this fact has led to the development of many types of retorts to improve the process. In spite of all these efforts, to date the total recovery of the kerogen in the shale remains relatively low, as some of it is always reduced to carbon and permanent gases, which have some usefulness but m .M+ as aannam@ 'nv-minets as the crude oils.

amended April 30, 1928; 370 O. G. 757) In order to overcome this diculty, it has been proposed to extract the kerogen from the shale with liquid solvents, and thereby increase the recovery of crude oils and avoid the formation of excess carbon and permanent gases. Numerous patents have been granted covering the broad aspects of this idea, but so far a successful process to compete with the established retort methods, has not been developed.

In my investigations of the broad problem of extractive recovery of organic matter in oil shales and other kerogen rocks, I have discovered the following pertinent facts:

l. Kerogen itself is not soluble in the usual liquid solvents and various fractions of shale oil and similar liquids, previously proposed for its extraction.

2. On heating at various temperatures for varying periods of time, kerogen is converted to bituinen, the percentage conversion increasing with the temperature and time of heating.

3. The resulting bitumen is soluble in certain fractions of shale oil, including the heavier fractions.

4. Prolonged contact of the extracted bitumen with the remaining shale results in cracking of the bitumen to yield various lower boiling fractions of liquid hydrocarbons, such as gas, gasoline, fuel oil, etc., the extent of the cracking depending on the time of contact and temperature.

The correlation of temperature and time of digestion with respect to items 2 and 4 above in the batch treatment of a Colorado oil shale are summarized in the tables below:

Heating Time (Hours) I. T=707 F. (375 C.)

Kerogen converted 6. 9 13. 4 19. 4 25. 0 Gas 2.4 4.9 7. 2 8.7 Light Oils (l. 6 1.2 1. 7 2. 2 Heavy Oils 3. 9 7.3 l0. 5 14.1 Carbon II. T=752 F. (400 O.)

Kerogen converted 22.1 39. 4 52.8 63. 2 as 3.0 5. 9 8.5 10.9 Light Oils 2. 6 4. 6 6.2 7. 9 Heavy Oils 16. 5 28. 9 38.1 44. 5 Carbon Nil Nil (7) C?) III. T=797 F. (425 C.)

Kerogcn converted. 51.8 76.8 88. 8 96. 0 4. 7 9. 0 13. 0 18. 9 6. 2 11. 0 14. 9 19.0 34. 9 44. S 42. 9 33.1 (G. 0) (12.0) (18. 0) (25. 0)

NOTE: Figures represent percentage by weight based on the kerogen initially present in shale.

These data indicate that under the conditions version of kerogen to liquid fuels, such as gaso-JA line and heavier oils, and a minimumconversion to gases and residual carbon. Obviously-with other shales, the yields and products distribution may vary from those given above for likeA conditions, and the optimum conversion conditions for yields of liquid productsmay differ with shales of Varying kerogen content. f

Based on experimental evidence available at this time, my treating process-.may be considered as involving the following stages:

1. Initial heating of shale to a predetermined temperature andto drive on" free moisture vin the shale.

2; Conversion of kerogenof the shale to bitumen and some lighter products.

3. Cracking ofbitumen and heavy-oil to lighter products.

This theory is advanced merely by way of explanation and it will-be understoodthat the description of my inventionis'not intended to be limited to any particular theory as to the mechanism of the reaction'wherebykerogenof the shale is recoveredas usefulliquid products.

In a batch treatment', as described herein, by reasonof lack-of uniformity in the chemical composition and physical character of the charge, the heatingy rate and other factors, obviously these stages will not appear to be separate and distinct. Some conversion of' kerogen to bitumen and cracking-of bitumen and heavy oil may occur duringA the initial heating stage. Likewise there may be appreciable cracking of heavier products concurrently with thel conversion of kerogen to'bitumenin the second stage of the process. In general, however, each stage will be characterized by the predominant physical.. or chemical changes occurringat the time.

In my combined'heating and extracting method for the recovery of shale oil, I have, found that it' is unnecessary to resort to line grinding of the raw shale and that the process is effective ifN the shale is coarsely crushedto about one-half inch size.

A suitable procedure for-v realizing the desired optimum conditionsfor conversion ofthe kerogen of oil shale to useful liquid products is described in connection with the accompanying drawing.

A Colorado oil shale, crushed to approximately one-half inchsize, isfed into a vertical reactor I, which isY preferably lagged tominimize heat loss. When the desiredV quantity of material has been placed in the. reactor, a high boiling fraction of shale oil is withdrawn from tank 3 passing throughvalve controlled line I5 andA pump I (i` to heater 4. In heater4, the heavy oil is heated to about 425 C; andV passes to reactor I through line I'll. The overflow from reactor I passes through line I to separator 2 where water vapor and lighter oils are separated and oils heavier than furnace oils are withdrawn through line 8 to heater 4 and back to reactor I. Heavy oil over and above that required for the extractive treatment of the shale is accumulated in tank 3 and maybe withdrawn from the system by line 20. The flow of heavy oil to tank 3 is controlled by closing valve 9' and opening valve 22.

Lighter products, including gases and water, removed from the circulating stream in separator 2, ow through line I2 to stripper 6. Gases are taken off overhead from stripper 6 through line I4l` while the light liquid products flow out through line I3v for further treatment.

The gases taken off at I4 may be used as fuel in heater 4 or may be separated into various fractions asis well known in the refining art.

YFractions of intermediate boiling range, such Vasfurnace oil, gas-oil, and the like may be withdrawn in one or'more side streams, as at I I, from Separator '2.

.For a maximum recovery of liquid fuels from' Colorado oil shale,A circulation of the heavy oil at about 425 C. is maintained for not in excess of one and one-half hours after the oil shale charge is brought to this temperature. Under these conditions, as-shown in the above tables, approximately percent off the kerogen is converted to extractable material, andv at least 18 percent lightzoil and 42 percent heavy oils will be recovered. This is equivalent to a conversion of 60f`percent of the total kerogen to liquid products, of which the major'portion representsv desirable liquid fuel fractions;

By operating ata lower temperature for a longer period of time, a higher proportion. of the eX- tracted bitumen may-be recoveredlas useful liquid fuels, althoughthere-Will1 be afcorre'sponding decrease in kerogen conversionandtl'ie total amount of these liquidV products recoveredt may be lower than when the conditionsare zasdescribed in the foregoing example. From. a two and one-half hour treatment atv400' C., the recovery of liquid products on `the basis of kerogen convertedV 57/71)=80 percent` as compared' with (60/9'0)-=67 percent under the higher temperature and shorterl time conditions. Where an vincreased recovery of heavier'oils is desirable such conditions obviously areindicated';

At the'en'd of the treatingi period, circulation of the heavy voil throughzheaterA 4 is discontinued and valve 23 is closed. Liquid materials in reactor I arefa'llowed todrain into surge tank 5 through Vline I8vby openingfvalve 24 and closing valve I9. Any-oil remaining iny or on the treated shale ink reactor I may be recovered by displacement with steam or-gasesaadmitted'through valve controlled` line 2|. The spent shalein reactor I'is then discharged andthe reactor is relled with freshY oil shale; The contents of tank 5 are pumped through` liney I-'I and-heater 4'V into reactor I: by-c1osingfvalve 24'open1ng'valves 23Vv and `2li-and starting pump, I6; Additional oil to ll the reactor is drawn from tank 3 and theA treating cycle isrepeated.

For-'reasons of. economy'of operation, a pluralityy of reactors I may be employed with suitable connections to. heater 4, surge tank4 5` and separator 2, sothat at'the close-of the treating cycle in one reactor, treatment of fresh vshale may be continued in alsecond reactor. In this manner heavy oiland any: material' dissolvedv thereinmay be continuous-1y.I circulated through` maintained at a temperature within the range of about 375-425 C. and for a period of time not in excess of two and one-half hours thereby converting a substantial portion of the kerogen of said rock to predominantly liquid products, miscible with said oil, removing fluids from contact with the treated rock and fractionating the thus separated uids into fractions of desired boiling ranges.

2. A process as in claim 1 in which the hydrocarbon treating oil comprises a fraction of the heavy oils produced from kerogen containing rock, said fraction having an initial boiling point above 200 C.

3. A process as in claim 1 in which the treating period is between one and two hours.

4. A process as in claim 1 in which the yield of liquid products is equivalent to at least fty percent of the kerogen initially present in the rock.

5. A process for increasing the percentage recovery of normally liquid hydrocarbons from the pyrolytic conversion of kerogenous materials which comprises subjecting kerogen containing solids in the form of coarsely crushed lumps to the action of a heavy hydrocarbon oil at a temperature within the range of from 375 C. to 425 C. for at least one hour and not substantially in excess of two hours, separating the thus treated solids from the said oil and liquid conversion products, distillng the separated eilluent and recovering fractions of desired boiling ranges.

6. A process for the production of hydrocarbon oils from oil shales which comprises passing a shale oil fraction heavier than furnace oil in contact with shale in a conversion Zone maintained within the range 375425 C., fractionating eluent from said reaction zone to separate lighter products and to recover a fraction heavier than furnace oil, heating said heavier fraction to the temperature of said conversion zone and returning said heated fraction to said conversion zone, circulation of said heavier fraction being continued for from one to two hours, whereby substantial conversion of kerogen to hydrocarbon oils is effected, separating the thus treated shale from further contact with said oil and conversion products and recovering fractions of desired boiling ranges from said oil and conversion products.

FREDERICK E. BUCHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 17,762 Reeve I Aug. 5, 1930 1,327,572 Ryan Jan. 6, 1920 1,467,758 Day II Sept. 11, 1923 1,643,521 Reeve II Sept. 27, 1927 1,778,515 Hampton Oct. 14, 1930 1,833,155 Danner et al. Nov. 24, 1931 1,903,749 Carter Apr. 11, 1933 2,397,432 Records Mar. 26, 1946

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