US3850738A - Bituminous coal liquefaction process - Google Patents

Abstract

Economical and efficient carbonaceous material liquefaction is achieved to provide high yields of aralkanes for liquid fuels. Comminuted carbonaceous material as an aqueous slurry is combined with supercritical water at temperatures and pressures to provide thermal cracking of alkane bonds in the presence of hydrogen. This process converts the carbonaceous material to liquids, primarily aralkanes, gaseous hydrocarbons and undissolved ash. The supercritical effluent is then separated into a product fluid stream and a solid fraction. The pressure of the fluid phase is reduced, resulting in formation of a gaseous fraction comprised mainly of hydrogen, water vapor and low molecular weight gaseous hydrocarbons, and a liquid fraction, which separates into an organic phase and an aqueous phase. The organic phase which is rich in aralkanes is then scrubbed to remove any acidic or basic constituents and is processed in accordance with conventional techniques. The aqueous phase may be recycled after impurity rejection.

Description

United States Patent 1191' Stewart, Jr. et al.

1451 Nov. 26, 1974 BITUMINOUS COAL LIQUEFACTION 3,755,136 8/1973 Fields et al. 208/8 E S 3,775,071 11/1973 Hoffertet al... 208/8 PROC S 3,808,119 4/1974 Bull et al. 208/10 [75] Inventors: A. Theodore Stewart, Jr., Woodside;

Dyer San Rafael both of Primary Examiner-Delbert E. Gantz Cahf- Assistant Examiner-Veronica OKeefe [73] Assignee: Bechtel International Corporation, Y Agent, Firm-Townsend and Townsend San Francisco, Calif. 1221 Filed: Dec. 6, 1973 [57] {*BSTRACT Economlcal and eft'lclent carbonaceous materlal llque- PP 422,497 faction is achieved to provide high yields of aralkanes for liquid fuels. Comminuted carbonaceous material [52] us. c1. 208/8 as an aqueous Slurry is Combined with supercrhha' [51] Int. Cl C10g l/06 Water at temperatures and pressures to provide [58] Field 61 Search 208/8 cracking of a'kahe hhds the Presence f drogen. This process converts the carbonaceous mate- 56 R f d I ml to liquids, prlmarlly aralkanes, gaseous hydrocar- UNITE]; gl lizf ZZ bons and undissolved ash. The supercritical effluent is then separated into a product fluid stream and a solid .lannek et al fraction The pressure f the phase is reduced gf 2 1 resulting in formation of a gaseous fraction comprised 5x936 8 5 8 mainly of hydrogen, water vapor and low molecular 7/1936 Lowry Jr 208/8 weight gaseous hydrocarbons, and a liquid fraction, 2:871:18] 1/1959 Kulik ....,:::I::::.... I: 208/8 which separates into an Organic Plhase and an aqueous 3.109.803 11/1963 Bloomer et a]. 208/8 P The Organic Phase WhiCh is rich in aralkanes is 3,240,566 3/1966 Bullough et al 208/8 then scrubbed to remove any acidic or basic constitu- 3.375,188 3/1968 Bloomer 208/8 ents and is processed in accordance with conventional 3,453,206 7/1969 Gatsis 208/210 techniques. The aqueous phase may be recycled after t e au ey 3.694.342 9/1972 Sprow et =11 208/ 5 C m 1 awing igur SCRUBBER 24 CONZSSSER LIQUID HEAT 1 SEPARATOR IO EXCHANGER 34 1, I4 SOLIDS 36 REACTOR SEPARATOR 1 BITUMINOUS COAL LIQUEFACTION PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention The ever increasing requirements for liquid fuels and the uncertainties of supply from the major known proven oil reserves have accelerated interest in alternative sources for liquid fuels. One source which has received extensive study over a long number of years is coal, particularly bituminous and subbituminous coal. Coal is comprised of a substantial amount of high molecular weight hydrocarbon, particularly polymers having arylene and alkylene links, which can serve as a source of liquid fuels by cracking under reducing conditions.

Coking of coal produces about 1 percent by weight of light oils, which are primarily aromatic hydrocarbons. A large amount of the hydrocarbon content of the coal is converted to char and highly aromatic solid hydrocarbons. In order to enhance the yield of the light oil fractions, numerous processes have been proposed.

Upon pyrolysis of the hydrocarbons in the solid coal phase, there is ample opportunity for the resultant free radicals or other high energy products of the pyrolysis to react with each other and form asphaltenes, we well as other high molecular weight materials. To minimize asphaltene formation, it is desirable. to both maintain the hydrocarbon fraction of the coal relatively fluid and esily mobile, and to provide a sufficient amount ofa hy-' drogen source, so that the hydrogen will react with the highly reactive pyrolytic fractions, so as to prevent them from recombining into high molecular weight products.

In processing the coal, it is desirable to use inexpensive agents which do not require recovery or can be easily or inexpensively recovered in reusable form. Furthermore, the materials employed should allow easy separation of the ash and undissolved components, should be easily separable from the desired liquid product and should not interfere with the formation of the liquid fuel fraction. Since catalytic systems frequently require pretreatment of the coal, as well as recovery and rejuvenation of the catalyst, a preferred system should not require a catalyst.

2. Description of the Prior Art US Pat. Nos. 1,695,914; 1,936,819; 2,012,318 and 2,041,858 employ water, coal and a reducing metal, i.e. iron or zinc in processing comminuted coal to provide liquid carbonaceous materials. US. Pat. Nos. 1,931,550 and 3,488,280 teach catalytic hydrogenation of coal in the presence of water. U.S. Pat. No. 3,660,269 teaches employing a small amount of water with coal, a hydrocarbon solvent and hydrogen in a fluidized bed to reduce asphaltene formation. U.S. Pat. No. 3,453,206 treats oils with water and hydrogen at elevated temperatures and pressures to reduce sulfur and asphaltene content.

SUMMARY OF THE INVENTION Economic and efficient production of liquid fuel fractions from carbonaceous materials, particularly coal, is provided. Using coal as illustrative, comminuted coal as an aqueous slurry is contacted with supercritical water at temperatures and pressures to provide thermal cracking of alkane bonds in the presence of hydrogen. The method of contacting the coal with the water minimizes the time required to raise the coal to the desired cracking temperature. The process converts the coal to liquids, primarily aralkanes, gaseous hydrocarbons and undissolved ash. The supercritical effluent is separated into a product fluid stream and a solid fraction which may be combusted to provide heat for the process. The pressure of the fluid phase is then reduced to allow for the formation of a gaseous fraction comprised mainly of hydrogen, low molecular weight gaseous hydrocarbons and water vapor and a liquid fraction containing hydrocarbons and water. The organic phase is separated from the aqueous phase. After the separation, the organic phase may be scrubbed free of acidic andbasic materials and processed according to conventional techniques. The aqueous phase may be recycled after provision is made for impurity rejection.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a flow sheet diagram of a method according to this invention.

BRIEF DESCRIPTION OF THE SPECIFIC EMBODIMENTS The effluent from the reactor is then transferred to a solids separation zone and separated into a fluid phase and a solid phase. The solid phase containing ash and undissolved organic material may be combusted for process heat. The pressure of the fluid phase is transferred to a subsequent zone in which the temperature and pressure are reduced in one or more stages. The condensation occurs in heat exchanging relationship with water, which is then employed in the reactor after being brought to the desired temperature and pressure. Gaseous products are taken overhead and the unreacted hydrogen may be recovered and reused. The liquid phase is transferred to a separation zone and separated intotwo phases, an aqueous phase and an organic phase. The organic phase may then be scrubbed free of acidic and basic. materials and processed according to conventional techniques. Various naturally occurring carbonaceous materials may be employed as a source of the carbonaceous material. Coal, other than anthracite, such as bituminous or subbituminous coal may be employed. In addition, lignite, peat, shale, and the like may also be used.

The carbonaceous material will be employed as an aqueous slurry. The carbonaceous material will be comminuted to particles in the size range of from about 200 Tyler mesh to about A: inch, more usually from about Tyler mesh to about V4 inch, and preferably in the range of about 200 to 100 Tyler mesh.

The comminuted carbonaceous material will then be slurried with water, so as to provide a. conveniently mobile stream. The amount of water employed should be the minimum required to provide a conveniently flowable slurry. Normally, the water will be less than about one-half, frequently equal to or less than about onethird the total amount of water introduced into the reactor. Usually, the amount of water in the slurry will be from about 0.25 to about 0.75 parts by weight per part of coal, more usually from about 0.4 to 0.6 parts by weight per part of coal. The less water employed in the slurry, the lower the temperature requirement for the supercritical water introduced into the reactor.

The carbonaceous material which is employed need not be treated to remove ash or moisture. In this way, processing of the coal or other carbonaceous material prior to introduction into the reactor is minimized.

In the reaction zone the process may be carried out as a batch process or a continuous process, but is preferably carried out as a continuous process.

While many different carbonaceous materials may be used, coal is preferred and will be employed as illustrative.

Concomitant with the introduction of the coal slurry, water under supercritical conditions and hydrogen are introduced into the reaction zone. The primary source of heat for the reaction is introduced by heating the feed water, elevating it to supercritical conditions. Additional heat is added in the reaction zone as a result of the exothermic nature of the reaction. The temperature of the heated water will be sufficient to bring the reaction medium to a temperature of at least 380C, and not greater than about 650C, more usually in the range of about 400500C. The total amount of water, including the water employed in providing the slurry, will be at least about 0.5 parts by weight per part of coal and not exceed about parts by weight per part of coal. Usually, the total amount of water will be in the range of about 1-5 parts by weight per part of coal and preferably from about 1 to 2 parts by weight per part of coal.

Hydrogen can be employed by itself, or as a mixture with water and carbon monoxide as obtained with water gas, synthesis gas, and the like. The amount of water present with the hydrogen is included in the total amount of water employed. Other gases may also be present which do not interfere with the reaction. The hydrogen can be introduced as a separate stream or can be mixed with the supercritical water, so that only two streams are simultaneously metered into the reaction zone. The amount of hydrogen employed will be at least about 0.5 weight percent based on coal and not exceed about weight percent based on coal, more usually being from about 1 to 10 weight percent based on coal and preferably from about i to 4 weight percent based on coal.

The contact time in the reaction zone will generally be at least one minute and not exceed about 10 minutes, more usually being in the range of about i to 5 minutes. The particular contact time will vary with the temperature employed, the carbonaceous material, the ratio of reactants, and the like. The time required to bring the coal to reaction temperature will be less than about 0.5 min.

The pressure in the reactor will be at least about 3,300 psi (about 230 atm.) and generally not exceed 10,000 psi (about 700 atm.) preferably being in the range from about 3,500 psi (about 245 atm.) and not exceeding about 5,000 psi (about 350 atm.). By maintaining high pressures, a dense compact reaction medium is employed which insures efficient extraction from the coal of the desired hydrocarbons, minimizing side reactions to undesirable products.

The streams entering the reaction zone are brought together so as to provide agitation and effective contact of the coal with the gases. By not heating the coal slurry significantly prior to its rapid contact in the reactor with water at supercritical temperatures, the coal is rapidly brought up to pyrolytic temperatures without significant residence time at temperatures below the reaction temperature.

While still at a supercritical temperature, the reaction mixture is transferred to a solids separation zone to separate the fluid stream from the solids. The solids may be separated by filtration, centrifugation, sedimentation, or other convenient means, and recovered to be used as a fuel, a source of hydrogen, or otherwise processed according to known procedures. Because of the high efficiency of the conversion to liquid fractions, the amount of solids will only be a small proportion of the total solids charged.

The fluid stream is flashed into a condensing and heat exchanging zone were gaseous products, mainly hydrogen and small amounts of gaseous hydrocarbons, e.g. methane, are carried overhead, while the organic and aqueous phases are cooled to below their boiling points C.) at ambient pressures.

The condensing and heat exchanging zone may be comprised of one or more stages and may be separate or combined for the gaseous and liquid phase cooling. The first stage can provide heat exchange with the vapors under the exit conditions of temperature and pressure from the solids separation zone. A second stage can provide adiabatic and condensation expansion of the vapors.

The gaseous effluent may be processed to remove any undesirable reactive minor constituents, such as hydrogen sulphide, and then recycled to the reaction zone. The hydrogen can be separated from gaseous hydrocarbons, and acidic gases prior to introduction into the reaction zone.

in order to conserve energy, the water stream which is to be fed to the reaction zone is heated by indirect heat exchange with the vapor phase in the coolingcondensing zone, providing the necessary cooling of the vapor phase, while absorbing the heat from the vapor phase. in this manner, once the process has been initiated, only minor amounts of supplemental heat is required to maintain the reaction mixture at the reaction temperature. This supplemental heat can be derived from the use of the solids from the separation zone as a fuel.

The combined liquid phases are now transferred to a separation zone, where the aqueous phase is separated from the organic phase. Centrifugation, chemical demulsifiers, ultrasonic treatment or the like may be employed. Any emulsification which results can be rapidly broken by mechanical or physical means.

The aqueous phase will contain a major portion of low molecular weight sulfur and nitrogen containing compounds, such as any hydrogen sulphide and low molecular weight amines. The water may be processed for reuse. The organic phase, after separation from the aqueous phase, may be further processed by percolating through one or more scrubbers having strong aqueous alkali or acid to remove any residual acidic or basic materials which may be present in the organic phase.

The resulting organic fraction may now be processed according to conventional techniques. The organic fraction may be fractionally distilled, hydrofined, extracted, or the like.

The resulting organic fraction provides a high yield of aromatic hydrocarbons, particularly aralkanes in the C -C range. Efficient conversion of the carbonaceous material is achieved with minimal formation of undesirable high molecular weight products, such as asphaltenes. Conversions will exceed weight percent of the carbonaceous material charged, usually exceeding weight percent.

To further understand this invention, the drawing will now be considered. Into reactor 10 via line 12 is introduced an aqueous slurry of comminuted coal. Simultaneously, via line 14, a mixture of supercritical water and hydrogen are introduced into reactor 10. The reaction mixture is maintained in the reactor for sufficient time to insure efficient pyrolysis of the coal, the transformation to the desired hydrocarbon liquid fractions. The reaction mixture is then transferred to solids separator 16 via line 20, while maintaining the elevated temperatures and pressures. The solids are withdrawn from solids separator 16 via line 22 and the supercritical fluid transferred via line 24 and flashed into condenser 26.

The gaseous effluent, primarily hydrogen, is processed to remove any adventitious undesirable reactive materials and recycled via line to line 14 to augment the hydrogen combined with the supercritical water. The mixed liquid phases in condenser 26 are transferred via line 32 to liquid separator 34.

After separation of the organic phase from the aqueous phase, the aqueous phase is withdrawn through line 36, and the organic phase passed via line 40 through. scrubber 42. The organic effluent free of acidic and basic constituents may then be fractionally distilled and the various fractions processed in accordance with conventional techniques.

in accordance with this invention, carbonaceous materials are liquefied to desirable liquid fuel fractions, particularly C Asphaltene and coal tar formation is minimized. By the use of water and hydrogen as the sole agents, separation is easily achieved, and excess hydrogen may be recovered and recycled. High economy and efficiency is obtained in the consumption of hydrogen.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.

What is claimed is:

l. A method for liquefying bituminous and subbituminous coal to provide high yields of C liquid fuel fractions which comprises:

contacting for a period of 1 to 5 minutes in a reaction zone a charge consisting of comminuted coal as a relatively cool flowable aqueous slurry, supercritical water, and hydrogen, wherein said water is at a temperature sufficient to maintain a temperature in the reaction zone in the range of 380 to 650C, and the pressure in the reaction zone is maintained in the range of about 230 to 700 atm., whereby said coal is rapidly raised to the temperature of the reaction zone, and wherein the weight ratio of total water to coal in the reaction zone is in the range of from about 1 to 10:1, and the amount of water in said slurry is less than about one-half of the total amount of water introduced into said reaction zone;

separating said effluent into a solid phase and a supercritical fluid phase while substantially maintaining the temperaturesand pressures of said reaction zone,

condensing said supercritical fluid phase into an organic phase enriched in C-,+ hydrocarbons and an aqueous phase; and

recovering said organic phase.

2. A method according to claim 1, wherein said hydrogen is present in from about 1 to 10 weight percent based on coal.

3. A method according to claim 2., including the steps of flashing said supercritical fluid phase prior to condensing to obtain a gaseous phase of gaseous hydrocan bons and hydrogen; and

recovering said gaseous phase.

4. A method according to claim 1, wherein the weight ratio of total water to coal inthe reactor is from about 1 to 5 parts by weight per part of coal and the amount of water in said aqueous slurry is from about 0.4 to 0.6 parts by weight per part of coal.

5. A method according to claim 1 wherein said temperature is in the range of about 400 to 500C, said pressure is in the range of about 245 to 350 atm., the total amount of water is in the range of from about 1 to 2 parts by weight per part of coal, and the hydrogen is present in from 1 to 4 weight percent based on coal.

Claims (5)

1. A METHOD FOR LIQUEFYING BITUMINOUS AND SUBBITUMINOUS COAL TO PROVIDE HIGH YIELDS OF C7+ LIQUID FUEL FRACTIONS WHICH COMPRISES, CONTACTING FOR A PERIOD OF 1 TO 5 MINUTES IN A REACTION ZONE A CHARGE CONSISTING OF COMMINUTED COAL AS A RELATIVELY COOL FLOWABLE AQUEOUS SLURRY, SUPERCITICAL WATER, AND HYDROGEN, WHEREIN SAID WATER IS AT A TEMPERATURE SUFFICIENT TO MAINTAIN A TEMPERATURE IN THE REACTION ZONE IN THE RANGE OF 380* TO 650*C, AND THE PRESSURE IN STHE REACTION ZONE IS MAINTAINED IN THE RANGE OF ABOUT 230 TO 700 ATM., WHEREBY SAID COAL IS RAPIDLY RAISED TO THE TEMPERATURE OF THE REACTION ZONE, AND WHEREIN THE WEIGHT RATIO OF TOTAL WATER TO COAL IN THE REACTION ZONE IS IN THE RANGE OF FROM ABOUT 1 TO 10.1, AND THE AMOUNT OF WATER IN SAID SLURRY IS LESS THAN ABOUT ONE-HALF OF THE TOTAL AMOUNT OF WATER INTRODUCED INTO SAID REACTION ZONE, SEPARATING SAID EFFULENT INTO A SOLID PHASE AND A SUPERCRITICAL FLUID PHASE WHILE SUBSTANTIALLY MAINTAINING THE TEMPERATURES AND PRESSURES OF SAID REACTION ZONE; CONDENSING SAID SEPERCRITICAL FLUID PHASE INTO AN ORGANIC PHASE ENRICHED IN C7+ HYDROCARBON AND AN AQUEOUS PHASE; AND RECOVERING SAID ORGANIC PHASE.

2. A method according to claim 1, wherein said hydrogen is present in from about 1 to 10 weight percent based on coal.

3. A method according to claim 2, including the steps of flashing said supercritical fluid phase prior to condensing to obtain a gaseous phase of gaseous hydrocarbons and hydrogen; and recovering said gaseous phase.

4. A method according to claim 1, wherein the weight ratio of total water to coal in the reactor is from about 1 to 5 parts by weight per part of coal and the amount of water in said aqueous slurry is from about 0.4 to 0.6 parts by weight per part of coal.

5. A method according to claim 1 wherein said temperature is in the range of about 400* to 500*C, said pressure is in the range of about 245 to 350 atm., the total amount of water is in the range of from about 1 to 2 parts by weight per part of coal, and the hydrogen is present in from 1 to 4 weight percent based on coal.

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