Claims
- 1. A process for hydroconverting coal to produce a hydrocarbonaceous liquid, which comprises:
- (a) in a pretreatment zone, forming a slurry of water-containing coal in an organic solvent, wherein the ratio of water-to-dry coal at conditions is below 0.5:1 and the ratio of organic solvent-to-dry coal is 4:1 to 1:1, and subjecting the slurry to an effective amount of carbon monoxide at a temperature in the range of 550.degree.-700.degree. F. and an elevated pressure to cause deploymerization and hydrogenation of the coal thereby increasing the coal's solubility in the solvent and to extract a portion of the coal into the organic solvent;
- (b) separating the pretreated coal slurry into two phases, an organic solvent phase comprising a substantial amount of soluble hydrocarbonaceous materials extracted from the coal, and a second solid residue phase comprising substantially all of the inorganic ash from the coal;
- (c) forming an essentially ashless mixture comprising said extract and a catalyst, wherein the catalyst is comprised of dispersed particles of a sulfided metal containing compound, said metal being selected from the group consisting of Groups VA, VIA, VIIA and VIIIA of the Periodic Table of the Elements and mixtures thereof;
- (d) reacting the essentially ashless mixture of coal extract and catalyst with a hydrogen-containing gas under coal hydroconversion conditions, in a hydroconversion zone to obtain a hydrocarbonaceous liquid; and
- (e) hydrotreating at least an portion of the hydrocarbonaceous liquid from step (d) to produce an upgraded product.
- 2. The process of claim 1, wherein following the pretreatment of step (a), the pretreated coal slurry is further extracted in an extraction zone prior to separation of the coal material in step (b) into solid and liquid phases.
- 3. The process of claim 1, wherein the inlet ratio of water-to-dry coal in step (a) is below about 1:1.
- 4. The process of claim 1, wherein said hydroconversion zone is at a temperature of 650.degree. to 950.degree. F.
- 5. The process of claim 1, wherein said hydroconversion zone is at a temperature between about 650.degree. and 800.degree. F.
- 6. The process of claim 1, wherein said pretreatment zone is at a temperature of 600.degree. to 675.degree. F.
- 7. The process of claim 1, wherein said catalyst is a conversion product of an organic oil-soluble metal compound.
- 8. The process of claim 1, wherein said compound is molybdenum sulfide.
- 9. The process of claim 1, wherein the hydrocarbonaceous liquid is fractionated to obtain a liquid product and a solvent for recycle.
- 10. The process of claim 1, wherein the coal extract of step (b) is separated from a residue comprising ash-containing coal solids by filtration, sedimentation, cycloning, centrifugation, or settling.
- 11. The process of claim 10, wherein said residue is subjected to partial oxidation, whereby carbon monoxide for step (a) is produced and hydrogen for step (d) is produced.
- 12. The process of claim 1, wherein the organic solvent is a distillate boiling in the range of about 440 to 650.degree. F. or a vacuum gas oiling boiling in the range of about 650 to 1000.degree. F. or a combination thereof.
- 13. The process of claim 7, wherein the metal constituent of said oil soluble metal compound is selected from the group consisting of molybdenum, chromium and vanadium.
- 14. The process of claim 13, wherein said oil soluble metal compound is molybdenum naphthenate.
- 15. The process of claim 14, wherein said oil soluble metal compound is phosphomolybdic acid.
- 16. The process of claim 1, wherein an effective amount of catalyst is employed in step (d) to convert the extract to a nearly finished product characterized by a nitrogen level of 0 to 1500 ppm, a sulfur level of 200 to 4900 ppm, an oxygen level of 1300 to 15,000 ppm and a hydrogen-to-carbon ratio of at least about 1.7.
- 17. The process of claim 16, wherein the metal is present in said mixture at a concentration of between 1% and 10% by weight.
BACKGROUND OF THE INVENTION
The invention relates to a process for liquefying coal, in particular, a multi-stage process comprising in sequence a pretreatment stage, an extraction stage, and a catalytic hydroconversion stage.
1. Field of the Invention
The petroleum industry has long been interested in the production of "synthetic" liquid fuels from non-petroleum solid fossil fuel sources. It is hoped that economic non-petroleum sources of liquid fuel will help the petroleum industry to meet growing energy requirements and decrease dependence on foreign supplies.
Coal is the most readily available and most abundant solid fossil fuel, others being tar sands and oil shale. The United States is particularly richly endowed with well distributed coal resources. Addi-tionally, in the conversion of coal to synthetic fuels, it is possible to obtain liquid yields of about three to four barrels per ton of dry coal, or about four times the liquid yield/ton of other solid fossil fuels such as tar sands or shale, because these resources contain a much higher proportion of mineral matter.
Despite the continued interest and efforts of the petroleum industry in coal hydroconversion technology, further improvements are necessary before it can reach full economic status. Maximizing the yield of coal liquids is important to the economics of coal hydroconversion.
The present invention relates to an improved process for converting coal to liquid hydrocarbon products in a catalytic hydroconversion process. The improvement relates to a coal pretreatment stage comprising subjecting a slurry of coal, dispersed in an organic solvent, to carbon monoxide under specific pressure and temperature conditions. This pretreatment results in a higher reactivity of an extract of the pretreated coal in the subsequent hydroconversion stage.
2. Description of the Prior Art
The known processes for producing liquid fuels from coal can be grouped into four broad categories: direct hydrogenation, donor solvent hydrogenation, Fischer-Tropsch synthesis (via gasification), and pyrolysis (see Kirk Othmer --Fuels).
The direct hydrogenation of coal in the presence of solvent and catalyst was first developed in Germany prior to World War II. In such a process, a slurry of coal in a suitable solvent was reacted in the presence of molecular hydrogen at an elevated temperature and pressure.
A number of previous co-assigned patents disclose coal liquefaction processes utilizing hydroconversion catalysts which are micron-sized particles comprised of a metal sulfide in a carbonaceous matrix. These catalysts are generally formed from certain soluble or highly dispersed organometallic compounds or precursors. These precursors are converted into catalyst particles by heating in the presence of an hydrogen-containing gas. The catalyst particles are highly dispersed in the feed being treated during hydroconversion. Among the various patents in this area are U.S. Pat. No. 4,077,867; U.S. Pat. No. 4,094,765; U.S. Pat. No. 4,149,959; U.S. Pat. No. 4,298,454; and U.S. Pat. No. 4,793,916. Other patents disclose catalysts similar to the above except that the catalytically active metal compound is supported on finely divided particles of solid metals and metal alloys, for example as disclosed in U.S. Pat. Nos. 4,295,995 and 4,357,229.
The conversion of coal in the presence of high temperature steam and carbon monoxide is well known, dating back to Fischer and Schrader in 1921 (F. Fisher & H. Schrader, Bennst. Chem., 2, 257, 1921). Several hydroconversion processes, including the U.S. Bureau of Mines COSTEAM process (H. R. Appell, E. C. Moroni, R. D. Miller, Energy Sources, 3, 163, 1971), have been developed based on using steam/carbon monoxide or steam/syngas at 750-850.degree. F. in a primary conversion block.
One of the problems encountered in coal hydroconversion is the separation of slurried catalyst from solid by-products, such as undissolved organic coal and ash. Such solid materials are typically dispersed throughout the reaction mixture during the hydroconversion operation, and are thus present in the coal liquid recovered after hydroconversion. Such solid materials are present in the coal liquids in a finely divided, particulate state, and are typically separated from the coal liquid products by distillation.
Another problem inherent in coal hydroconversion processes has been the requirement for large amounts of hydrogen. It has been suggested that this problem of hydrogen consumption could be reduced by converting only a relatively small fraction of the coal, which fraction is rich in hydrogen. However, to be economical, there is a need for a process which converts a relatively large fraction of the coal to valuable liquid hydrocarbon products. The present process, while not necessarily reducing the requirement for hydrogen, allows coal to be taken to a higher conversion level. Hydrogen utilization is therefore more efficient. For a given amount of liquid products less gas is produced, resulting in a better liquid to gas selectivity.
An object of the present invention is to provide a novel process for the hydroconversion of coal in order to produce valuable liquid hydrocarbonaceous products.
A further object of the present invention is to provide an improved process for producing liquid hydrocarbonaceous products from coal by utilizing a pretreatment step wherein the coal, slurried in an organic solvent phase, is subjected to reaction with carbon monoxide.
A still further object of the present invention is to pretreat coal in a specific temperature range to enhance extraction and generate a more reactive coal material for hydroconversion, thereby obtaining more product, with better liquid to gas selectivity.
Another object of the present invention is to improve the utilization efficiency of molecular hydrogen, in the transformation of coal to valuable liquids, by hydrogenating less of the original coal feed, as well as effecting better liquid-to-gas selectivity.
Still another object of the present invention is to liquefy coal by a process comprising in sequence a pretreatment stage, an extraction stage (ex-situ or in-situ), and a catalytic hydroconversion stage.
Additional advantages of the present coal hydroconversion process will become apparent in the following description.
In accordance with the present invention, there is provided a process for liquefying coal to produce an oil, comprising: (a) forming a mixture comprising coal, carbon monoxide and an organic solvent in a pretreatment zone and subjecting the mixture to a temperature and pressure effective to cause mild depolymerization of the coal; (b) removing gases from the coal mixture in a separation zone; (c) extracting the pretreated coal with an organic solvent in an extraction zone to obtain an extract comprising a substantial amount of soluble hydrocarbonaceous coal; (d) forming a subsequent mixture of said extract and a catalyst wherein the catalyst comprises a sulfided metal-containing compound, said metal being selected from the group consisting of Groups VA, VIA, VIIA and VIIIA of the Periodic Table of Elements and mixtures thereof; and (e) reacting the mixture of coal extract and catalyst with hydrogen under coal hydroconversion conditions in a hydroconversion zone to obtain a hydrocarbonaceous liquid product.
In accordance with another embodiment of the invention, there is provided a process for liquefying coal to produce an oil, which comprises: (a) subjecting a mixture of coal, organic solvent and carbon monoxide to a temperature of 550.degree. F. to 700.degree. F. and a carbon monoxide partial pressure of 500 to 5000 psi for a period of at least 10 minutes, (b) removing gases from the coal mixture; (c) extracting the pretreated coal with an organic solvent in an extraction zone to obtain an extract comprising a substantial amount of soluble hydrocarbonaceous coal; (d) forming a subsequent mixture of said extract, an organic solvent, preferably coal derived, and a catalyst, wherein the catalyst comprises a sulfided metal compound and has an average particle size of 0.02 to 2 microns, preferably a conversion product of an organic oil-soluble metal containing compound, said metal being selected from the group consisting of Groups VA, VIA, VIIA and VIIIA of the Periodic Table of the Elements and mixtures thereof; and (e) reacting the latter mixture with a gas comprising molecular hydrogen under coal hydroconversion conditions, in a hydroconversion zone to obtain a hydrocarbonaceous liquid product.
US Referenced Citations (12)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 0264743 |
Apr 1988 |
EPX |
Patent Grant
5110450
