GB2148936A - Two-stage coal liquefaction process - Google Patents

Abstract

A process for liquefying coal comprises first forming a coal-solvent slurry in a mixing zone (10). In a hydrothermal dissolving-stripping zone (20) the coal in the slurry is substantially dissolved in the solvent to form a mixture comprising solvent, dissolved coal, insoluble solids and light products, while simultaneously the mixture is stripped of substantial amounts of the light products by contacting the slurry countercurrently with a first hydrogen gas stream at elevated temperatures. A gaseous stream comprising the light products is withdrawn from the hydrothermal dissolving-stripping zone. At least a portion of the mixture containing insoluble solids is contacted in a reaction zone (45) with a second hydrogen gas stream and an externally supplied hydrocracking catalyst under hydrocracking conditions to provide an effluent stream (50) having a normally liquid portion. <IMAGE>

Description

SPECIFICATION Two-stage coal liquefaction process This invention relates to the liquefaction of coal. In particular, it relates to a two-stage process for the hydrothermal and hydrocatalytic liquefaction of subdivided coal in a solvent slurry.

The production of liquid products by the high temperature and pressure hydrogenation of a coal and solvent slurry in the presence of a hydrogenation catalyst is well known. The resulting coal liquid, however, has a high average molecular weight and a high viscosity. These properties present considerable difficulty in any need subsequent processing, such as fines removal and/or catalytic hydrocracking. Rosenthal and Dahlberg devised (U.S.Patent 4,330, 391) a two-stage process for the liquefaction of coal in which a subdivided coal is substantially dissolved in a solvent in the presence of hydrogen at 750"F to 900"F (339-482 C) and in which the entire effluent from the disolver stage (gases, liquids, and solids) may be passed directly to a catalytic hydrocracking zone at a temperature below 800"F (427 C) and lower than the temperature in the dissolving zone. This process provides, in high yield, a product having an API gravity of at least - 3. In one embodiment, this process is known to the industry as the "CCLP", which stands for Chevron Coal Liquefaction Process.

In a preferred embodiment of the CCLP, the dissolver and the catalytic reactor are closecoupled. Solids separation takes place downstream of the reactor. Coal conversion and distillate yield are maximized. The product viscosity is low, so solids separated is easier and performed more flexibly. A consequence is higher severity dissolver operation, i.e., more cracked products and light gases are produced in the hydrothermal dissolver stage.

Furthermore, the distillate species formed in the dissolver are further hydrogenated in the catalytic reactor, and although this improves product quality, hydrogen consumption is higher.

The high temperature hydrothermal dissolver which is characteristic of the CCLP, produces saturated light products which can form an unstable mixture with the remaining heavy uncracked materials which are through to be mostly aromatic and other unsaturates. The heavy portion of a coil liquid contains asphaltenes which require an aromatic medium for solubilization. There may be insufficient solvency in the bulk of the material, or cosolvency in the added solvent, to retain the uncracked heavier asphaltenes in solution.

The result may be phase separation and precipitation of asphaltenes which would tend to occur as the temperature is dropped between the dissolver stage and the lower temperature hydrocracking stage. U.S. Patent 4,330,393 teaches that in the Rosenthal-Dahlberg process the small quantities of water and C, to C4 gases produced in the dissolver are preferably removed before the dissolver effluent enters the hydrocracking zone for the purpose of increasing the hydrogen partial pressure in the hydrocracking stage. The physical structuring of the disolving zone in U.S. Patent 4,330,393 is such that the slurry may flow upwardly or downwardly in said zone. In the multi-stage coal liquefaction process of U.S.

Patent 4,110,192, it has been found advantageous to vent most of the gases from the dissolver zone while co-currently passing hydrogen and liquids into the dissolver zone and out of the dissolver zone to the catalytic treatment zone.

The preferred embodiment of CCLP produces the most hydrogenated product among all the major coal liquefaction processes. The CCLP product is of higher hydrogen content throughout the boiling range, and especially in the mid-distillate range. While other coal liquefaction processes reject heavy material and solids upstream of the catalytic reactor (thereby reducing liquid yield), CCLP,in its preferred embodiment, catalytically processes the heavy metal and solids for highest yield.

Thus, CCLP requires more hydrogen, which can be supplied by known processes from natural gas or coal, at a price. The cost of CCLP could be reduced without loss of benefit if (i) light products which consume hydrogen in the catalytic reactors could be separated before the catalytic hydrocracking stage; (ii) some solids or heavy material rejection occured before the catalytic stage; and (iii) milder operating conditions were selected.

It would be advantageous if hydrogen utiiization efficiency could be improved in twostage coal liquefaction processes such as the CCLP by reducing the hydrogenation of the mid-distillate fraction of the product of the two-stage process. This could be accomplished if the lighter fractions, including middistillates, could be continuously removed from the dissolver stages.

It would also be advantageous if the light products, including light saturated hydrocarbons found in the dissolver stage of a twostage coal liquefaction process, could be continuously stripped away from the remaining liquid together with water, carbon monoxide, and other materials which cause instability and are deleterious to the processes of the catalytic hydrocracking stage. By this means the second stage would operate more efficiently and the instability of the product towards asphaltene precipitation would be overcome. This, and other advantages, are achieved by the process of the present invention.

Thus in accordance with the present invention there is provided a process for liquefying coal which comprises forming a coal solvent slurry by mixing subdivided coal with a solvent. In a hydrothermal dissolving-stripping zone the coal is substantially dissoled in the solvent to form a mixture comprising solvent, dissolved coal, insoluble solids, and light products, while simultaneously the mixture is stripped of substantial amounts of the light products by contacting the slurry countercurrently with a first hydrogen gas stream at elevated temperatures. A gaseous stream comprising the light products is withdrawn from the hydrothermal dissolving-stripping zone. At least a substantial amount of the insoluble solids in the remaining mixture is contacted in a reaction zone with a second hydrogen gas stream and an externally supplied hydrocracking catalyst under hydrocracking conditions.An effluent stream having a normally liquid portion is withdrawn from the hydrocracking zone.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing which is a block flow diagram of suitable flow for use in practising a preferred embodiment of the invention.

Referring to the drawing, comminuted coal is slurried with a solvent in a mixing zone 10.

The effluent slurry from zone 10 passes via line 1 5 to a hydrothermal dissolving-stripping zone 20 which it traverses in a generally downflow manner in countercurrent contact with added hydrogen gas entering the hydrothermal dissolving-stripping zone 20 through line 25. The slurry is heated to dissolve at least about 50 weight percent of the coal in the presence of the added hydrogen gas, thereby forming a mixture of solvent, dissolved coal, insoluble solids, and light products. The hydrogen gas traverses zone 20 in a generally upflow manner, thereby stripping substantial amounts of the light products from the mixture and conveying same out of the dissolving-stripping zone via line 28.The mixture from zone 20 passes via line 30 to zone 35 where it is cooled, if desired, to a temperature lower than the temperature of the dissolver and preferably 55"C to 85"C lower than the temperature of the dissolver. Optionally, some solids may be removed from the mixture via line 36. The cooled mixture is then conveyed by line 40 to hydrocracking zone 45 where it is catalytically hydrocracked in the presence of hydrogen supplied via line 38 to produce a relatively low viscosity liquid product which may be readily separated from any remaining coal residue.

Referring to the drawing in more detail, subdivided coal and a solvent are mixed in zone 10 to form a pumpable slurry. The basic feedstock of the invention is a solid particulate coal such as anthracite, bituminous coal, subbituminous coal, lignite, or mixtures thereof.

The bituminous and sub-bituminous coals are particularly preferred. It is also preferred that said coals be comminuted or ground to a particle size smaller than 100 mesh, Tyler Standard Sieve size, although large coal sizes may be processed in this invention. The solvent used in zone 10 may be selected from the various solvents known to the coal liquefaction art, and it may be process-derived.

Hydrogen-donor solvents are known in the coal liquefaction art and comprise polycyclic aromatic hydrocarbons such as tetrahydronaphthalene or dihydronaphthalene, which are capable of being at least partially saturated.

After hydrogenation, these solvents can donate or transfer the acquired hydrogen to hydrogen-deficient dissolved coal molecules.

In general, suitable solvents may be obtained from numerous materials, but it is particularly preferred to use crude petroleum or a 200"C or higher-boiling petroleum fraction, such as a topped napthenic crude or a vacuum residua. Asphaltic or napthenic crudes are generally higher in aromatics and naphthenes in comparison to paraffinic based crudes. As a result, such crudes are preferable over the paraffinic crudes for use as solvents in the present invention. Such crudes are also usually higher in sulfur, nitrogen, and metals than paraffinic crudes and thus create problems in refining processes. The process of the present invention, however, is capable of tolerating the higher metals content in the hydrocracking zone without prior demetalation or pretreatment precautions.A substantial portion of the metals of the crude are bound to or deposit upon the coal residue suspended in the liquid feedstock and thus do not deposit on the cracking catalyst.

While it is understood that suitable solvents can be obtained from many different sources, it is also preferred to use a solvent obtained from the process, or particularly, a portion of the 400'F (204"C) and higher boiling fraction obtained from fractionation of the hydrocraking zone effluent.

The subdivided coal is mixed with a solvent in a solvent to coal weight ratio generally of from 1:2to50:1, preferably from 1:2to5:1 and more preferably from 1:1 to 2:1. The slurry from zone 10 may be heated by conventional means (not shown) such as process heat exchangers, steam coils, or fired heaters.

The slurry is fed or pumped through line 1 5 to a hydrothermal dissolving-stripping zone 20 comprising one or more dissolver-strippers wherein the slurry is heated, with added hydrogen, to a temperature in the range of 400"C to 480"C (750'F to 900 F), preferably 425"C to 455'C (800"F to 850 F) for a length of time to substantially dissolve the coal. At least 50 weight percent and more preferably greater than 70 weight percent, and most preferably more than 90 weight percent of the coal, on a moisture-free and ash-free basis, is dissolved in zone 20, thereby forming a mixture of solvent, dissolved coal, insoluble solids, and light products.Such light products include acid gases, such as carbon monoxide, light saturated hydrocarbons, such as methane, ethane, butane, and the lighter fractions of hydrocarbonaceous oils, including those which are generally known as mid-distillates, i.e., having normal boiling points up to about 370"C (700"F).

It is usually essential that the slurry be heated to at least 400"C (750"F) to obtain 50 weight percent dissolution of the coal. Furthermore, it is usually required that the slurry not be heated to temperatures above 480"C (900"F) in order to prevent excessive thermal cracking which could substantially reduce the overall yield of normally liquid product.

The hydrothermal dissolving-stripping zone 20 basically comprises one or more elongated vessels, preferably free of added external catalysts or contact materials, which are designed so that in at least one vessel of said zone slurry flows downwardly while hydrogen gas flows upwardly in countercurrent contact with the heated slurry, and the mixture resulting from the hydrothermal dissolution of coal in solvent.More generally, the vessel used of continuous contacting of hydrogen gas and the mixture can be a tower filled with solid packing material, or an empty tower into which the mixture may be sprayed and through which the gas flows, or a tower which contains a number of bubble-cap sieve or valve-type plates, but the gas and the mixture flow in substantially countercurrent contact with each other to obtain the greatest concentration driving force and therefore the greatest rate of desorption, i.e., stripping.

Design factors in this unit operation are dealt with in "Chemical Engineers Handbook", Perry and Chilton, 5th Edition, McGraw-Hill, Sections 4, 14, and 18.

The hydrothermal dissolving-stripping zone 20 may comprise one or more dissolving vessels in which slurry and added hydrogen move countercurrently or co-currently, but it is essential that is comprises at least one dissolv ing-stripping vessel in which the hydrothermal product mixture of the coal-solvent slurry flows countercurrently to a hydrogen gas stream. The dissolving-stripping vessel may be operated as a liquid-full vessel with level control to ensure that the vessel operates with a liquid mixture of a certain level thereby regulating the residence time of the mixture in the hydrothermal zone. Level control is exemplified by Perry and Chilton, supra, Section 22.

The latter operating configuration is preferred under conditions where substantial backmixing is not detrimental to the process and its products. Preferably, the dissolving-stripping vessel is operated as a continuous staged reactor of the vertical type (Perry and Chilton, supra, page 4-21) by the use of the aforementioned reactor internals. The latter operating configuration is preferred under conditions requiring minimum backmixing.

The yield structure of products obtained from the hydrothermal dissolving-stripping zone 20 is improved (i.e., less light normal gaseous products are produced) if the vessels comprising zone 20 are temperature staged in series, i.e., going from a higher temperature vessel near the inward to zone 20 at line 1 5 to a lower temperature vessel near the outlet of zone 20 at line 30, with all the temperatures in zone 20 still within the aforementioned range. By dropping the temperature toward the outlet of zone 20 the mixture is not only prepared for the preferred lower temperature subsequent stage in zone 35 and zone 45, but the dissolving and cracking reactions are turned down, temperature control along a series of dissolver vessels is easily achieved by intermediate cooling between vessels by means of heart exchange or quench gas injection.Similar benefits are obtainable in a single vessel dissolving-stripping zone 20 by the use of the aforementioned continuous staged reactor. With back mixing eliminated or reduced in a staged reactor, a descending temperature profile is obtained in the dissolving-stripping vessel by the use of, for example, a downflowing preheated coalsolvent slurry 1 5 and an upflowing hydrogen quench gas stream 25. In an alternative embodiment, hydrogen gas is injected into the vertically elongated dissolving-stripping vessel at several positions along the vertical length of the vessel. In yet another embodiment, cooling stage 35 may not be necessary to achieve the lower temperature preferred for hydrocracking stage 45, which the ranges of temperatures specified, when such a temperature staged dissolving-stripping zone is used.

Depending on operating conditions, and the aforementioned design factors which are within the knowledge of those skilled in the art, the counterflowing hydrogen gas entering through line 25 and comprising fresh and recycle hydrogen, will strip the mixture more or less deeply as to the amount of the light products stripped and the normal boiling points of the light products stripped from the mixture. It is preferred that substantially all gases, i.e., materials, having normal boiling points below about 0 C (32to) be stripped from the hydrothermal dissolving-stripping zone 20 and removed via line 28.In another embodiment, it is also preferred that substantial amounts of all light materials having nor mal boiling points below about 20"C (70"F) be stripped from the hydrothermal dissolvingstripping zone 20 and removed via line 28. In other embodiments, it is preferred that sub stantial amounts of all materials having nor mal boiling points from 35"C to 260"C (100'to 500"F) be stripped from the hydrothermal dissolving-stripping zone 20 and removed via line 28. In one embodiment, substantial amounts of mid-distillate, i.e., a fraction boiling below about 260"C (500'F), is stripped, separated, and optionally recycled as solvent.Hydrogen should be separated from the effluent stream 28 for recycle to the process. The light hydrocarbon products in the effluent stream 28 should be fractionated and used directly, or, if necessary for particular usages, subjected to further treatment.

Operating conditions in the hydrothermal dissolving-stripping zone can vary widely, except for temperature, in order to obtain at least 50 weight percent dissolution of the coal. Other reaction conditions in the hydrothermal dissolving-stripping zone generally include a residence time of 0.01 to 3.0 hours, preferably 0.1 to 1.0 hours: a pressure of 0 to 10,000 psig (1 to 702 kg/cm2), preferably 1,500 to 5,000 psig (104 to 350 kg/cm2), and more preferably 1,500 to 2,500 psig (104 to 1 75 kg/cm2); a hydrogen gas rate of 500 to 20,000 standard cubic feet per barrel of slurry, preferably 500 to 10,000 standard cubic feet per barrel of slurry and most preferably 500 to 4,000 SCF/BBL; and a slurry hourly space velocity of about 0.3 to 100 hr-1 preferably about 1 to 10 her~'.

A remarkable advantage of the process of the present invention is the decoupling of the hydrogen supply to the dissolving and hydrocracking zones 20 and 45 while the dissolving and hydrocracking stages may remain closely coupled, if desired. Consequently, optimal hydrogen pressure and gas rate may be provided to the hydrothermal dissolving-stripping zone 20, while simultaneously, a different optimal hydrogen pressure and gas rate is provided in the catalytic hydrocracking zone 45. In general the dissolver requires less hydrogen than the hydrocracking zone. In the co-current hydrogen gas flow and liquid process this flexibility is not practical. In general, hydrogen gas flow rate should be higher in the hydrocracking zone because of greater hydrogen consumption.By placing a pump (not shown) in line 40 one may operate at a lower hydrogen pressure in zone 20 and a higher pressure in zone 45.

The dissolving zone will, in general, contain no catalyst from any external source, although the mineral matter contained in the coal may have some catalytic effect. The mixture of solvent, dissolved coal and insoluble solids, as well as any remaining light products, is preferably passed via line 30 to a cooling zone 35.

Cooling zone 35 will typically contain a heat exchanger or similar means whereby the effluent from dissolver 20 is cooled to a temperature below the temperature of the dissolving stage and at least below 425"C (800"F).

Some cooling in zone 35 may also be effected by the addition of fresh cold hydrogen. Optionally, some solids may be removed from zone 35 via line 36.

The mixture of solvent, dissolved coal, insoluble solids, and remaining products is fed through line 40 into reaction zone 45 containing a hydrocracking catalyst. Hydrogen comprising fresh and/or recycle hydrogen is fed via line 38 into the hydrocracking zone 45 at the rate of 4,000-50,000 SCF/BBL. In the hydrocracking reaction zone hydrogenation and cracking occur simultaneously and the higher molecular weight compounds are converted to lower molecular weight compounds, the sulfur in sulfur-containing compounds are converted to hydrogen sulfide, the nitrogen in nitrogen-containing compounds are converted to ammonia, and the oxygen in oxygen-containing compounds are converted to water.

Preferably, the catalytic reaction zone is a fixed bed type, but an ebullating or moving bed may also be used. The mixture of gases, liquids, and insoluble solids preferably passes upwardly through the catalytic reaction zone, but may also pass downwardly. Countercurrent or co-current movement of the added hydrogen gas with respect to the liquid flow is also optional.

The primary advantage of passing such a mixture of gases, liquids, and insoluble solids upwardly through the fixed bed of particulate catalysts is that the probability of plugging is reduced. Downflow operation can cause particles in the reactor feed to breach interstices between stationary catalyst particles. Upflow operation, on the other hand, results in opposing forces on the particles, i.e., the gravitational forces and the forces exerted by the flowing liquid. These opposing forces tend to reduce the probability of bridging. In addition, the gravitational force tends to dislodge localized plugs which may form.

A particularly desirable method of operating the process is for the fixed catalyst bed to be operated in an upflow mode, with the lower portion of the catalyst in the bed being removed as the catalyst becomes fouled. Fresh catalyst can be added to the top of the fixed bed to replace the catalyst which is removed from the bottom. This addition and removal of catalyst can take place periodically or in a continuous or semi-continuous manner. Continuous catalyst replacement according to this invention is carried out at such a low rate that the catalyst bed is properly described as a fixed bed.

The catalyst used in the hydrocracking zone may be any of the well known, commercially available hydrocracking catalysts. A suitably catalyst for use in the hydrocracking reaction stage comprises a hydrogenation component and a cracking component. Preferably the hydrogenation component is supported on a refractory cracking base. Suitable bases include, for example, silica, alumina, or composites of two or more refractory oxides such as silica-alumina, silica-magnesia, silica-zirconia, alumina-boria, silica-titania, silica-zirconia-ti tania, acid-treated clays, and the like. Acidic metal phosphates such as aluminia phosphate may also be used. Preferred cracking bases comprise alumina and composites of silica and alumina. Suitable hydrogenation components are selected from Group Vl-B metals, Group VIII metals, and their oxides, or mixtures thereof.Particularly useful are cobalt-molyb- denum, nickel-molybdenum, or nickel-tungsten on silica-alumina or alumina supports.

Hydrocracking zone 45 comprises one or more hydrocracking reactor vessels containing one or more of the aforementioned catalysts in any combination.

It is preferred to maintain the temperature in the hydrocracking zone below 425"C (800"F), preferably in the range of 340"C to 425"C (645"F to 800"F), and more preferably 340"C to 400"C (645"F to 750"F), to prevent catalyst fouling.The temperature in the hydrocracking zone should be preferably maintained below the temperature in the dissolving zone by from 55"C to 85"C. Other hydrocracking conditions include a pressure from 500 to 5,000 psig (34 to 350 kg/cm2), preferably 1,000 to 3,000 psig (70 to 210 kg/cm2), and more preferably 1,500 to 2,500 psig (104 to 175 kg/cm2); a hydrogen gas rate of 2,000 to 20,000 standard cubic feet per barrel of slurry, preferably 3,000 to 10,000 standard cubic per barrel of slurry; and a slurry hourly space velocity in the range of from 0.1 to 2.0, preferably 0.2 to 0.5.

The product effluent 50 from reaction zone 45 is separated in separation zone 55 into a gaseous fraction 60 comprising light oils boiling from 150"C to 260"C (302"F to 500"F), preferably below 200"C (392"F) and normally gaseous component such as hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, and the C1 to C4 hydrocarbons. Preferably, the hydrogen is separated from the other gaseous components and recycled. Liquids-solid fraction 65 is fed to a solids separation zone 70 wherein the stream is separated into a solidslean stream and a solids-rich stream. The insoluble solids are separated by conventional means, for example, hydroclones, filtration, centrifugation, and gravity settling, or any combination of these.Preferably, the insolubcle solids are separated by gravity settling which is a particularly added advantage of the present invention since the effluent from the hydrocracking reaction zone has a particularly low viscosity and a high API gravity of at least - 3. The high API gravity of the effluent allows rapid separation of the solids by gravity settling such that 50 weight percent and generally 90 weight percent of the solids can be rapidly separated in a gravity settler. Preferably, the insoluble solids are removed by gravity settling at an elevated temperature in the range of 100"C to 400"C (212"F to 752"F). Separation of the solids at an elevated temperature and pressure is particularly desirable. The solids-lean product stream produced in zone 70, or any fraction thereof, may be recycled to the mixing zone 10 to provide additional solvent.

The process of the present invention produces extremely clean, normally liquid products. The normally liquid products, that is, all of the product fractions boiling above C4 have an unusually low specific gravity; a low sulfur content of less than 0.2 weight percent; and a low nitrogen content of less than 0.5 weight percent.

Claims (22)

1. A process for liquefying coal which comprises: (a) forming a coal-solvent slurry by mixing subdivided coal with a solvent; (b) in a hydrothermal dissolving-stripping zone substantially dissolving said coal in said solvent to form a mixture comprising solvent, dissolved coal, insoluble solids and light products, and simultaneously, stripping light products from said mixture by countercurrently contacting said mixture with a first hydrogen gas stream at an elevated temperature; (c) withdrawing from said dissolving-stripping zone a gaseous stream comprising said light products; (d) contacting at least a portion of said mixture comprising said insoluble solids in a hydrocracking reaction zone with a second hydrogen gas stream and an externally supplied hydrocracking catalyst under hydrocracking conditions; and (e) withdrawing from said reaction zone an effluent stream having a normally liquid portion.

2. A process according to Claim 1, wherein said dissolving-stripping zone comprises at least one dissolving-stripping vessel containing internals which substatially reduce backmixing.

3. A process according to Claim 1 or 2, wherein the temperature in said dissolvingstripping zone is staged in a descending manner, such that the temperature is lower at the outlet end of the zone than at the inlet end of the zone.

4. A process according to Claim 3, wherein said staged descending temperature is obtained by the use of a plurality of dissolving-stripping vessels connected in series.

5. A process according to Claim 3, wherein said slurry is preheated and said staged descending temperature is obtained in a single vessel by the use of a said first hydrogen gas stream of lower temperature than said slurry and said vessel contains internals which at least partially eliminate backmixing.

6. A process according to any preceding claim, wherein said first hydrogen gas stream has a lower flow rate than said second hydrogen gas stream.

7. A process according to any preceding claim, wherein the hydrogen partial pressure in said hydrothermal dissolving-stripping zone is less than the hydrogen partial pressure in said hydrocracking reaction zone.

8. A process according to any preceding claim, wherein said dissolving-stripping zone is free of externally supplied catalysts or contacted particles.

9. A process according to any preceding claim, wherein the residence time of the slurry in said hydrothermal dissolving-stripping zone is regulated by the use of a level control in a dissolving-stripping zone vessel.

10. A process according to any preceding claim, wherein a mid-distillate fraction is stripped from said mixture and said withdrawn gaseous stream comprises a mid-distillate fraction.

11. A process according to Claim 10, wherein at least a portion of said mid-distillate is recycled as solvent.

1 2. A process according to any preceding claim, wherein a recycle stream of said effluent stream is recycled as solvent to form said slurry.

1 3. A process according to any preceding claim, wherein said portion of said mixture is passed from said dissolving-stripping zone to said reaction zone without an intervening solids separation step.

14. A process according to any preceding claim, wherein a portion of said mixture comprises said insoluble solids is recycled to the dissolving-stripping zone.

1 5. A process according to any preceding claim, wherein said solvent is crude petroleum oil.

16. A process according to Claim 15, wherein said solvent comprises a fraction of a crude petroleum oil boiling above 200"C.

1 7. A process according to any one of Claims 1 to 14, wherein said solvent comprises a petroleum residuum fraction.

18. A process according to any one of Claims 1 to 14, wherein said solvent comprises an asphalted petroleum crude oil fraction boiling above 200"C.

1 9. A process according to any one of Claims 1 to 14, wherein said solvent comprises a petroleum-derived solvent containing metal contaminants.

20. A process according to any preceding claim, wherein the reaction zone temperature is from 55"C to 85"C lower than the temperature of said dissolving-stripping step.

21. A process according to any preceding claim, wherein the dissolving-stripping zone temperature is in the range from 400"C to 480"C.

22. A process for liquefying coal, substantially as hereinbefore described with reference to the accompanying drawing.