US3607717A

US3607717A - Fractionating coal liquefaction products with light organic solvents

Info

Publication number: US3607717A
Application number: US1818A
Authority: US
Inventors: Jack W Roach
Original assignee: Kerr McGee Corp
Current assignee: Kerr McGee Corp
Priority date: 1970-01-09
Filing date: 1970-01-09
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21

Abstract

Coal liquefaction products are separated into a plurality of fractions of varying softening points and molecular complexity by treatment with light organic solvents having critical temperatures below 800* F. under elevated temperature and pressure conditions. In one variant, coal is liquefied employing selected light organic solvents which are suitable for both liquefaction and fractionation, and thereafter the coal liquefaction products are separated into a plurality of fractions by treatment with the solvent contained in the resultant solution. Preferred solvents for liquefying coal include pyridine and benzene, and preferred fractionating solvents include pyridine, benzene and hexane. In a preferred variant, a solvent phase is recovered directly from the final fractionating stage and is passed in heat exchange relationship with solvent-rich streams to preceding fractionating stages to recover the heat content and provide cooled solvent for recycle. The invention further provides a method of separating finely divided insoluble material derived from coal during liquefaction thereof from an organic-solvent solution of coal liquefaction products.

Description

United States Patent [72] Inventor Jack W. Roach Oklahoma City, Okla. [21] AppLNo. 1,818 [22] Filed Jan. 9, 1970 [45] Patented Sept. 21,197] [73] Assignee Kerr-McGee Corporation Oklahoma City, Okla.

[54] FRACTIONATING COAL LIQUEFACTION PRODUCTS WITH LIGHT ORGANIC SOLVENTS 28 Claims, 2 Drawing Figs.

[52] US Cl 208/8 [5!] Cl0g 1/00 [50] Field of Search 208/10 [56] References Cited UNITED STATES PATENTS 2,221,866 ll/l940 Dreyfus 208/8 2,913,397 ll/l959 Murray et al. 208/8 2,202,901 6/! 940 Dreyfus 208/8 2,9l3,388 ll/l959 Howell et al 208/8 Primary Examiner-Delbert E. Gantz Assistant Examiner Veronica OKeefe Attorney-Shanley and O'Neil ABSTRACT: Coal liquefaction products are separated into a plurality of fractions of varying softening points and molecular complexity by treatment with light organic solvents having critical temperatures below 800 F. under elevated temperature and pressure conditions. In one variant, coal is liquefied employing selected light organic solvents which are suitable for both liquefaction and fractionation, and thereafter the coal liquefaction products are separated into a plurality of fractions by treatment with the solvent contained in the resultant solution. Preferred solvents for liquefying coal include pyridine and benzene, and preferred fractionating solvents include pyridine, benzene and hexane. In a preferred variant. a solvent phase is recovered directly from the final fractionatin g stage and is passed in heat exchange relationship with solventrich streams to preceding fractionating stages to recover the heat content and provide cooled solvent for recycle. The invention further provides a method of separating finely divided insoluble material derived from coal during liquefaction thereof from an organic-solvent solution of coal liquefaction products.

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ATTORNEYS FRACTIONATING COAL LIQUEFACTION PRODUCTS WITH LIGHT ORGANIC SOLVENTS BACKGROUND OF THE INVENTION This invention broadly relates to a method of separating coal liquefaction products into a plurality of fractions employing light organic fractionating solvents under elevated temperature and pressure conditions. The invention further relates to a novel process for liquefying coal and fractionating the resultant products, and a method of separating finely divided insoluble material from a solution of coal liquefaction products.

The potentially soluble substances in fossilized carbonaceous materials such as coal are composed largely of high molecular weight three-dimensional cyclic structures which contain predominantly six-membered rings. For example, coal contains bitumen and humin, which have large, flat, aromatic lamellar structures that differ in molecular weight, degree of aromaticity, oxygen content, nitrogen content and cross-linking, volatile matter, fusain, mineral matter, sulfur and moisture. The sulfur content may be present as pyritic sulfur,

inorganic sulfates, and/or organic sulfur compounds.

The mineral matter remains behind as ash when the coal is burned and fusain, which is a mineral charcoal, is consumed during burning at high temperatures in the presence of sufficient oxygen for complete combustion. The presence of sulfur in the coal in substantial quantities results in contamination of the atmosphere with oxides of sulfur upon combustion, and highly corrosive sulfurous acid and/or sulfuric acid is produced therefrom upon reaction with atmospheric moisture. As a result, air pollution regulations in metropolitan areas often require that the sulfur content of fuels be reduced so as to control atmospheric pollution. The mineral content of the coal may be ll5 percent by weight or higher in some instances, and this reduces the B.t.u. value of the raw coal per unit weight and increases transportation costs. There is an additional cost when the coal is burned as the ash residue must be removed and disposed of in some manner.

The presence of mineral matter, fusain and sulfur in substantial quantities also reduces the value of the coal for specialized uses. For example, if these substances are removed prior to coking, the deashed coal thus produced may be used for preparing high purity anode coke which has a substantially higher value than the usual impure coke produced from raw coal.

For the above and other reasons, it is desirable to reduce the mineral matter, fusain and sulfur contents of coal. One process presently used for removing these substances involves solvation or liquefaction of desirable coal constituents such as bitumen and humin in an organic solvent to produce a solution of coal liquefaction products containing suspended finely divided insoluble material. Thereafter, the undesirable insoluble constituents such as mineral matter, fusain and inorganic sulfur are separated from the solution prior to recovery of the deashed coal liquefaction products.

The methods available heretofore for separating finely divided insoluble material from a solution of coal liquefaction products have left much to be desired. For example, gravity settling has a number of disadvantages due in part to the low settling rates encountered under ambient conditions of temperature and pressure, and especially in instances where the solution is somewhat viscous in nature. Filtration methods also have disadvantages as the solution is often viscous at room temperature and must be heated to obtain sufficiently fast filtration rates. Plugging of the filter pores with finely divided insoluble constituents is an additional problem. In instances where the viscosity of the solution is sufficiently low, centrifuging is usually satisfactory insofar as the physical separation of the solids from the solution is concerned. However, centrifuging equipment is costly and it is difficult to remove the lighter micron-sized particles. As a result of the above and other deficiencies, there has not been an entirely satisfactory method available heretofore for separating suspended finely divided insoluble materials from an organic-solvent solution of coal liquefaction products.

The solvation of coal in an organic-solvent produces a mixture of coal liquefaction products which differ greatly with respect to their chemical and physical properties. For example, the liquefaction products may vary from low boiling liquids to solids which are soluble in the organic solvent and have softening points of 300400 F. and higher. The low boiling liquid products may be recovered by distillation, but a method has not been available heretofore for separating normally solid coal liquefaction products into a plurality of fractions having desired softening points or other physical and/or chemical characteristics. A satisfactory fractionating method would be very useful as coal liquefaction products with widely differing properties could be produced for specific end uses.

The present invention provides an efficient method of separating ash constituents from previously prepared coal liquefaction products, and/or fractionating previously prepared deashed coal liquefaction products into a plurality of fractions. Additionally, it is also possible to liquefy coal employing certain light organic solvents of the invention, and to thereafter deash and/or fractionate the coal liquefaction products in the same solvent. The liquefying and fractionating steps involve the use of large quantities of light organic solvent and heretofore it has been necessary to recover the solvent from the final fractionating stage by flashing and condensation of the solvent vapor. This prior art method of solvent recovery involves the use of expensive equipment with high operating costs as the utility requirements are excessive. The present invention overcomes this disadvantage by providing for the recovery of the solvent directly from the last fractionating stage whereby it may be heat exchanged with incoming streams to recover heat and produce a cooled stream of solvent for recycle.

It is an object of the present invention to provide a novel method of separating coal liquefaction products into a plurality of fractions employing selected light organic solvents.

It is a further object to provide a novel method of separating coal liquefaction products into a plurality of fractions wherein the solvent may be recovered directly from the final fractionating stage and passed in heat exchange relationship with incoming streams to preceding fractionating stages to recover the heat content.

It is a further object to provide a novel process for liquefying coal employing selected light organic solvents, and then separating the coal liquefaction products in the solution thus produced into a plurality of fractions.

It is a further object to provide a novel method of separating suspended finely divided insoluble material derived from coal during liquefaction thereof from an organic-solvent solution of products of coal liquefaction.

Sill other objects and advantages of the invention will be apparent to those skilled in the art upon reference to the following detailed description and the examples.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B of the drawings illustrate one presently preferred arrangement of apparatus for use in practicing the invention.

FIG. 1B is a continuation of FIG. 1A.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED VARIANTS THEREOF The process of the present invention provides a method whereby liquefied coal dissolved in a light-fractionating solvent is introduced into a deashing-fractionating vessel under temperature and pressure conditions such that the solvent density of the light-fractionating solvent is about0.350.55 g./cc. and sufficiently low to cause the rejection or separation of a small amount of the heavy liquefied coal constituents. The lighter solvent-rich liquefied coal solution exiting from the deashing-fractionating vessel may then be introduced into at least one fractionating vessel, in the last of which the temperature and pressure of the solution are adjusted to give a solvent density of about 0.15-0.20 g./cc. to yield a fluid bottom fraction comprising the residual dissolved coal and a lighter solvent phase which may be withdrawn and recycled for heat recovery and reuse. in those instances where more than one fractionating vessel is employed, the solvent densities prevailing in the intermediate fractionating vessels are decreased progressively from the solvent density existing in the deashingfractionating vessel to the solvent density existing in the final fractionating vessel to thereby provide a succession of heavy coal fractions of decreasing softening point and a succession of correspondingly lighter solvent-rich phases. In one variant of the invention, the deashing-fractionating vessel and all subsequent fractionating vessels may be operated at a pressure which is at or below the critical pressure of the fractionating solvent provided that the pressure, temperature and enthalpy are controlled whereby the solvent densities set forth herein are maintained.

Referring now to the drawings, a selected light organic solvent to be defined more fully hereinafter is transferred by pump 10 from solvent surge vessel 11 to mixer 12 via conduit 14 at a rate controlled by valve 15. Makeup solventis supplied to vessel 11 as required via conduit 8 at a rate controlled by valve 9. in the variant to be presently described, which includes liquefying the coal and thereafter fractionating the liquefaction products in the same solvent, finely divided raw coal in storage vessel 16 is passed into mixer 12 via conduit 17 at a rate determined by meter 18. The relative feed rates of solvent and coal may be controlled so that the weight ratio of solvent to coal in mixer 12 is between about 1:1 and 20:1, and preferably between about 2:1 and :1. The best results are usually obtained when the weight ratio of solvent to coal is approximately 3:l.

The coal and solvent in mixer 1 1 are agitated with a motordriven agitator l9, and the slurry thus prepared is withdrawn via conduit 20 and transferred by pump 21 to gas-fired heater 22 where the slurry flowing in coil 23 is heated to an elevated temperature which preferably closely approximates the desired initial temperature of solvation. In the variant presently described, valve 24 in conduit 25 is closed and valve 26 in conduit 27 is open, and the heated slurry is withdrawn via conduit 27 and passed to liquefier 28. While it is not essential, it is usually preferred to carry out the liquefaction in the presence of added gaseous hydrogen. When gaseous hydrogen is added, it may be passed into the slurry flowing in conduit 20 upon opening valve 29 in conduit 30.

The liquefier 28 preferably operates under a high superatmospheric pressure which is determined by the overpressure of gaseous hydrogen when present, the vapor pressure of the solvent at the operating temperature, and/or the hydraulic pressure applied by pump 21. The liquefaction temperature is determined by the initial temperature of the slurry flowing in conduit 27 and by the temperature control fluid which is supplied to coil 31 via conduit 32 at a rate controlled by valve 33 and withdrawn via conduit 34. The solvent is contacted with the coal under the temperature and pressure conditions existing in the liquefier 28 for a sufficient period of time to solubilize a substantial amount of extractable carbonaceous content thereof, and to produce a solution of coal liquefaction products which contains suspended finely divided fusain, mineral ash and other insoluble constituents. The resultant solution usually contains relatively large amounts of dissolved normally solid liquefaction products of widely varying softening points, and in many instances little or no low boiling normally liquid products. The solution is preferably but not necessarily substantially saturated with respect to the dissolved coal liquefaction products under the temperature and pressure conditions existing in liquefier 28, i.e., at the solvent density in liquefier 28.

The solution containing insoluble constituents is withdrawn from liquefier 28 via conduit 35 and is introduced into bulk insoluble coal separator 36. At least 95 percent by weight, and

usually more than 99 percent by weight, of the insoluble constituents separate as a heavy slurry phase 37 which is sufficiently fluid under the existing temperature and pressure conditions to be withdrawn via conduit 39 at a rate controlled by valve 40. The lighter phase 38 containing dissolved coal possessing less than l percent by weight of ash is withdrawn via conduit 41 and is passed through heat exchanger 46. The solution flowing in conduit 41 when withdrawn from separator 36 is at approximately the same temperature and pressure as exist in liquefier 28 and the excess heat content thereof is recovered by heat exchange in heat exchanger 46 with cold solvent flowing in conduit 14. The cold solvent is heated to an elevated temperature in heat exchanger 46 and is then passed into mixer 12 as previously described, and thus the slurry flowing in conduit 20 is likewise at an elevated temperature. The solution flowing in conduit 41 downstream of pressure reduc ing valve 44 is at approximately the desired temperature of operation of deashing-fractionating vessel 47, and the temperature of the solution flowing in conduit 41 may be controlled at a desired level by passing all or a portion thereof around heat exchanger 46 via conduit 42 at a ratio determined by valves 43 and 48. The pressure on the solution flowing in conduit 41 is reduced while passing through pressure-reducing valve 44 to approximately the desired pressure of operation of vessel 47, and the solution is then introduced into gas separator 61. Hydrogen, gaseous hydrocarbons and other gaseous constituents are separated from the solution and withdrawn via conduit 62 at a rate controlled by valve 63. The degassed solution is withdrawn from gas separator 61 via conduit 49 and normally open block valve 45. The temperature and pressure conditions selected for operation of deashing-fractionating vessel 47 are such that the solvent density of the light organic solvent is about 0.35-0.55 g./cc. and sufficiently low to cause the rejection or separation of a small amount of the heavy liquefied coal constituents. While the mechanism is not fully understood, it is believed that the coal liquefaction products thus rejected from the solution tend to coat the micron-sized particles of insoluble material in the solution. This causes the surface of the particles to be tacky, and enlarges the particles somewhat so that they are much easier to agglomerate than would otherwise be true. The amount of coal liquefaction products separated as a heavy phase in vessel 47 need be only sufficient to coat the insoluble particles and, with the attendant solvent, aid in the agglomeration and fluxing thereof, and usually is no more than about 1 or 2 times the weight of insoluble material. However, substantially larger amounts of coal liquefaction products, such as 3-5 times the weight of insoluble material, may be separated if desired, as this does not interfere with the removal of the ash.

The solution containing finely divided insoluble constituents is passed via conduit 49 to header 50. The header 50 is positioned in deashing-fractionating vessel 47 a substantial distance beneath the interface 52 between the relatively heavy slurry phase 53 and the lighter clarified solution of coal liquefaction products 54, and it is provided with a plurality of spaced outlets 51. The fluidlike slurry layer 53 in the bottom portion of vessel 47 contains suspended mineral ash, fusain, and other insoluble material in finely divided form which is fluxed with solvent and coal liquefaction products, and it is withdrawn via conduit 55 at a rate controlled by valve 56, or by operation of a pump which controls the volume. The slurry 53 is withdrawn at a rate to maintain the interface 52 substantially above the outlets 51 on header 50. The solution flowing in conduit 49 is at an elevated temperature and has a low viscosity, and the particles of coated suspended material settle out rapidly when the solution is passed into vessel 47. While the mechanism is not fully understood, it is believed that injecting the solution into the heavy slurry layer 53 and passing the solution upward therethrough into the clarified phase 54 also causes the micron-sized solid particles of insoluble material to agglomerate into larger particles more rapidly and completely, and the larger particles in turn settle much faster. Unexpectedly, the presence of the slurry layer and passing the solution therethrough aids in coating the individual particles of micronrsized solids and in the agglomeration thereof to produce much heavier particles than would otherwise be possible. As a result, the lighter clarified phase 54 in the upper portion of vessel 47 is substantially free of insoluble material and it does not require filtering or centrifuging to remove the last traces of solids. The vessel 47 may be maintained at the desired operating temperature by passing a heat exchange fluid to coil 57 via conduit 58 at a rate controlled by valve 59 and withdrawing it via conduit 60.

The clarified coal solution 54 is withdrawn from the top of vessel 47 via conduit 65 at a rate to provide a sufficient residence time to assure settling of the insoluble material, such as l-30 minutes and preferably about 5-15 minutes. The clarified solution 54 is then passed through heat exchanger 66 in heat exchange relationship with a warm solvent stream which is being recycled through conduit 64 to solvent surge vessel 11. The solution is withdrawn from heat exchanger 66 at a substantially higher temperature and preferably at a temperature closely approximating the desired operating temperature for fractionating vessel 67, and is then introduced into vessel 67 via conduit 65. The solvent density existing in vessel 67 is substantially less than that existing in vessel 47 due to the higher operating temperature and the slightly lower pressure resulting from the drop in line and heat exchanger pressure. The differential in the solvent density is sufficiently large to cause a fluidlike fraction 72 of heavy coal liquefaction products to separate from the solvent rich lighter phase 75 of residual coal solubilization products. The vessel 67 is maintained at a uniform operating temperature which is sufficiently elevated to permit a liquid-to-liquid bulk interface 76 to form between heavy fraction 72 and solvent rich phase 75. The temperature is maintained at the desired level by means of a heat exchange fluid fed to coil 68 via conduit 69 at a rate controlled by valve 70 and withdrawn via conduit 71. The temperature and pressure conditions existing within vessel 67 are selected to provide a solvent density whereby a desired percentage of the heaviest material dissolved in the solution is separated in the form of a fluidlike heavy phase 72. The heavy phase 72 contains sufficient light solvent to lower the viscosity and allow it to be withdrawn via conduit 73 upon opening valve 74 without plugging the same. The light solvent content of the withdrawn heavy phase 72 can be recovered by flashing and condensation of the vapor to produce liquid light solvent for recycling in the process. The residue remaining after flashing the solvent is a hard friable deashed heavy coal fraction having a softening point of about 400 F. or higher.

The solvent-rich phase 75 containing residual liquefied coal products is withdrawn from the top of vessel 67 via conduit 77 and passed through heat exchanger 78 in heat exchange relationship with the warm solvent stream flowing in conduit 64. The solvent rich phase 75 is withdrawn from heat exchanger 78 at a higher temperature and preferably at a temperature closely approximately the desired operating temperature for fractionating vessel 79, and is introduced into vessel 79 via conduit 77. The solvent density existing in vessel 79 is substantially less than that existing in vessel 67 due to the higher operating temperature and the slightly lower pressure level resulting from the drop in line and heat exchanger pressure. The differential in solvent density between

vessels

67 and 79 is sufficiently large to cause a fluidlike heavy fraction 80 of residual liquefied coal products to precipitate from the lighter solvent rich phase 81. The vessel 79 is maintained at a uniform operating temperature which is sufficiently elevated to permit a liquid-to-liquid bulk interface 82 to form between heavy fraction 80 and the solvent-rich phase 81. The temperature is maintained at the desired level by means of heat exchange fluid fed to coil 83 via conduit 84 at a rate controlled by valve 85 and withdrawn via conduit 86. The temperature and pressure conditions existing within vessel 79 are selected so that a desired percentage of the liquefied coal products of intermediate softening point dissolved in solvent rich phase 75 are separated. The heavy phase 80 contains some solvent and has a sufficiently low viscosity to be withdrawable via conduit 87 upon opening valve 88 without plugging the same. The solvent content may be recovered by flashing and condensation of the vapor to produce liquid light solvent for recycling in the process. The residue is a normally solid deashed coal product. lt is understood that the residue withdrawn from successive fractionating vessels will have successively lower softening points. In many instances, the residue obtained from phase will have a softening point below 400 F. and usually has a softening point of about 200 F.400 F.

The solvent rich phase 81 containing dissolved light liquefied coal products is withdrawn from the top of vessel 79 via conduit 90 and passed through heat exchanger 91 in heat exchange relationship with the warm solvent stream being recycled through conduit 64. The solvent-rich phase 81 is withdrawn from heat exchanger 91 at a higher temperature, passed to gas-fired heater 93 where it is heated to a temperature closely approximating the desired operating temperature for fractionating vessel 92, and introduced into vessel 92 via conduit 90. The solvent density existing in vessel 92 is substantially less than that existing in vessel 79 due to the higher operating temperature and the slightly lower pressure level resulting from the drop in line and heat exchanger pressure. The solvent density differential between

vessels

79 and 92 is sufficient to cause a fluidlike fraction of the remaining liquefied coal products 94 to separate from the lighter solvent phase 95. The vessel 92 is maintained at a uniform operating temperature which is sufficiently elevated to reduce the solvent density to a level that causes the solvent to separate from the remaining dissolved liquefied coal products. The operating temperature is also sufficiently elevated to permit a liquid-toliquid bulk interface 96 to form between the separated fraction 94 and the solvent phase 95. The uniform operating temperature is maintained by means of a heat exchange fluid fed to coil 97 via conduit 98 at a rate controlled by valve 99 and withdrawn via conduit 100. The separated fraction 94 contains sufficient solvent to lower the viscosity whereby it is withdrawable via conduit 101 upon opening valve 102 without plugging the same. The solvent content of the withdrawn fraction 94 may be recovered by flashing and the vapor condensed to produce liquid solvent for recycling and a deashed coal fraction which is semisolid to liquid at room temperature. The hot light organic solvent phase is withdrawn from the top of vessel 92 via conduit 64 and passed successively through

heat exchangers

91, 78 and 66 in heat exchange relationship with the relatively cool solvent-rich phases flowing in

conduits

90, 77 and 65, respectively. The solvent-rich phases thereby are heated. The solvent flowing in conduit 64 downstream of heat exchanger 66 is further cooled in heat exchanger 103 by means of a coolant supplied via conduit 104 at a rate controlled by valve 105 and withdrawn via conduit 106. This method of operation allows cool solvent to be recovered directly from the solution of liquefied coal products flowing in conduit 90 without flashing and condensation of the solvent vapor. As a result, the cost of solvent recovery for recycle is much lower. it is also possible to recover the heat content of the phased out hot

heavy phases

53, 72, 80 and 94 and this further reduces the overall costs.

The variant previously discussed is concerned with liqucfying coal to produce a solution of coal liquefaction products in light organic solvent, and thereafter fractionating the products into a plurality of fractions employing the same solvent for both steps. The present invention is also useful for fractionating coal liquefaction products recovered from the liqucfying solvent with or without prior removal of the insoluble constituents. The products are usually recovered in the form of a normally solid-friable material which is capable of being dissolved in light organic-fractionating solvents. Thus, it is possible to liquefy the coal in a highly efficient heavy organic solvent, recover the coil liquefaction products from the resultant solution by flashing off the solvent, and then remove the insoluble constituents and fractionate the coal liquefaction products in accordance with the present invention.

Referring again to FIGS. 1A and 1B of the drawings, previously prepared finely divided normally solid coal liquefaction products substantially free of the liquefying solvent are withdrawn from storage vessel 16 and passed into mixer 12 via conduit 17 at a rate determined by meter 18. Light organic fractionating solvent is introduced into mixer 12 via conduit 14 at a rate controlled by valve 15. The relative feed rates of solvent and coal liquefaction products are controlled so that the weight ratio of solvent to coal liquefaction products existing in mixer 12 is between about 2:1 and 20:1 and preferably between about 3:1 and 5:1. The mixture thus produced is withdrawn from mixer 12 via conduit 20 and transferred by pump 21 to gas fired heater 22 where it is heated in coil 23 to an elevated temperature which preferably closely approximates the operating temperature of vessel 47. The coal liquefaction products dissolve in the light organic fractionating solvent and, upon closing

valves

26, 43 and 48 and opening valve 24, the solution is passed via

conduits

25 and 49 to header 50 and introduced into vessel 47 through outlets 51.

The vessel 47 may be operated as previously described to remove insoluble constituents which are withdrawn as a fluidlike phase via conduit 55. In instances where the coal liquefaction products have been previously deashed, very little if any insoluble material is removed but passing the solution through vessel 47 assures that a small amount of insoluble material is not present in the heavy coal fraction produced in vessel 67. The coal liquefaction products contained in the clarified solution 54 withdrawn via conduit 65 are fractionated in

vessels

67, 79 and 92 to produce heavy, intermediate and light fractions which are withdrawn via

conduits

73, 87 and 101, respectively, in the manner previously discussed. The light organic-fractionating solvent phase 95 is withdrawn via conduit 64 and passed through

heat exchangers

91, 78, 66 and 103 to recover the heat content and produce cool solvent for recycle as previously discussed.

The carbonaceous material fed to mixer 12 and liquefied in liquefier 28 may be coal, which preferably is of a rank lower than anthracite, such as subanthracite, bituminous, subbituminous, and lignite or brown coal. Peat also may be used in some instances. The particle size of the coal may vary over wide ranges and in general the particles only need be sufficiently small to be slurried in the solvent and pumped. For example, the coal may have an aver particle size of one-fourth inch in diameter or larger in some instances, and as small as 200 mesh (Tyler screen) or smaller. The most practical particle size is usually between 30 mesh and l mesh as less energy is required for grinding and yet the particles are sufficiently small to achieve an optimum rate of liquefaction. The particle size is not of great importance, provided extremely large particles are not present as the solvent penetrate the coal particles and the extractable constituents are liquefied rapidly.

Light organic solvents having critical temperatures below 800 F., and preferably below 750 F., are employed for liquefying and/or fractionating the coal. While solvents broadly falling in this classification and as further defined hereinafter are suitable for use as fractionating solvents, not all are suitable for liquefying the coal. Light organic solvents useful for both liquefying the raw coal and fractionating the coal liquefaction products comprise one or more substances selected from the following groups:

1. Hydrocarbons:

a. Aromatic hydrocarbons having a single benzene nucleus and preferably 6-9 carbon atoms, such as benzene, toluene, 0-, m-, and pxylene, ethyl benzene, npropyl or isopropyl benzene, and monocyclic aromatic hydrocarbons in general having normal boiling points below about 310 F., and

. Cycloparaffin hydrocarbons which preferably contain 4-9 carbon atoms, such as cyclobutane, cyclopentane, cyclohexane, cycloheptane, and nonaromatic monocyclic hydrocarbons in general having normal boiling points below about 310 F.

2. Amines, including the following:

a. Mono-, di-, and tri-open chain amines which preferably contain about 2-8 carbon atoms, such as ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl amines;

b. Carbocyclic amines having a monocyclic structure and preferably containing approximately 6-9 carbon atoms, such as aniline and its lower alkyl homologs wherein the alkyl groups contain about 13 carbon atoms and up to 3 alkyl groups are present on each monocarbocyclic structure; and

c. Heterocyclic amines and preferably those containing about 5-9 carbon atoms such as pyridine and its lower alkyl homologs wherein the alkyl groups contain approximately l4 carbon atoms and up to three alkyl groups are present on each hetercyclic structure.

3. Phenol and its lower alkyl homologs, and preferably phenols having 6-9 carbon atoms. The alkyl groups may contain, for example, 1-3 carbon atoms and up to three alkyl groups may be present on each phenolic nucleus.

Additional light organic solvents suitable as fractionating solvents but which are not generally suitable as liquefaction solvents include one or more substances from the following groups:

4. Open chain mono-olefin hydrocarbons having normal boiling points below about 310 F. and preferably con taining about 4-7 carbon atoms, such as butene, pentene, hexene, and heptene, and

5. Open chain saturated hydrocarbons having normal boiling points below about 3 l0 E. and preferably containing about 5-8 carbon atoms such as pentane, hexane, heptane and octane.

Pyridine and benzene are usually the preferred solvents for liquefying coal and pyridine, benzene and hexane for fractionating the coal liquefaction products. Other preferred solvents include light aromatic extracts of reforrnate obtained by extracting a catalytic reformate by a number of commercial processes including the UDEX process, and aromatic or phenolic cuts in general which have critical temperatures below 800 F., including those derived from the destructive distillation of coal or coal tar and light oils. Still other commercially available mixtures including one or more of the foregoing classes of compounds may be employed, and in many instances the mixture need not be purified prior to use.

The presence of added elemental hydrogen during the coal liquefaction step is not necessary, but it is usually beneficial. When hydrogen is added, the feed to the liquefier 28 may include 0.1-2 percent and preferably about 0.25-1 percent by weight of hydrogen based upon the weight of the coal. The excess hydrogen which does not enter into the liquefaction reaction may be recovered from the coal liquefaction products and recycled if desired, and thus higher percentages than 2 percent by weight of the coal may be used such as up to 5 percent by weight or more. The hydrogen content of the vapor phase in contact with the liquid solvent phase may be about 5-50 percent and preferably is about 10-35 percent by volume, but it may be higher or lower as desired in a given instance. As a general rule, the higher the partial pressure of hydrogen, the faster the liquefaction reaction, as more hydrogen is available in the solvent for transfer to the active sites produced on the decomposing or depolymerizing coal.

The temperature employed in operating liquefier 28 should be sufficiently high to result in a fast solvation rate. The upper limit is the temperature at which the carbonaceous material is coked and/or the organic solvent is decomposed substantially during the period of treatment. The temperature of liquefaction may be 550-l ,000 F. for most solvents and coals. ln instances where pyridine is the solvent, the preferred temperature is usually about 650-750 F. as pyridine decomposes at temperatures of about 750800F. and higher. Benzene is much more refractory than pyridine and temperatures above 700 F. are preferred, such as about 700800 F. or somewhat higher. The coking temperature varies from coal to coal, and coals having a higher rank usually have a higher decomposition or coking temperature. Oklahoma bituminous coal cokes at about 800840 F. and the more volatile Wyoming coals at a lower temperature such as 700-800 F. In instances where a tubular reaction is employed and a slurry of coal is passed through the tubes on a continuous basis, then somewhat higher solvation temperatures are suitable due to the dynamic nature of the system. Also, the flow rates through the tubes may be sufficiently fast to reduce coking on the tube surfaces.

The liquefying solvent is contacted with the coal in liquefier 28 for a sufficient period of time to solubilize a substantial amount ofextractable constituents, such as about 0.2-2 hours. For economic reasons, the contact period should not be more than about 1 hour, and preferably no more than about 0.250.5 hour. Usually more than about 50 percent by weight of the coal is liquefied, and often up to 8090 percent.

The minimum ratio of light fractionating solvent to coal liquefaction products in the resultant solution is about 2:1 by weight, and the upper limit is practical in nature and may be as high as 20:1. There is little improvement in the sharpness of fractionation beyond fractionating solvent to coal liquefaction product ratios of 5:1 to :1, and the lowest weight ratio necessary to give a desired sharpness of fractionation is preferred as the cost of handling the solvent increases with the amount used. Usually a fractionating solvent to coal liquefaction products ratio between about 3:1 and 5:1 is preferred.

The pressure in liquefier 28 may be between about 400 and l0,000 pounds per square inch absolute (p.s.i.a.) and should be about l,0007,000 p.s.i.a. for most light organic coal liquefaction solvents. When pyridine is the solvent, preferably the pressure is about 3,0005,000 p.s.i.a. The pressure should be sufficient to provide a solvent density of at least 0.5 g./cc. and preferably at least 0.6 g./cc. at the existing temperature. There is no upper limit on the solvent density during liquefaction as the highest solvent density that can be achieved under practical operating conditions gives improved results due to the increased solubility of the coal liquefaction products. The light liquefying solvents defined herein have a solvent density of about 0.5-0.8 g./cc., and preferably about 0.6-0.7 g./cc. under practical temperature and pressure conditions for use in operating liquefier 28. If the solvent density is too low, then it is necessary to resort to pressure to increase the density. Usually pressurized hydrogen is preferred as a pressurizing medium, but inert gases or gaseous mixtures may be employed such as nitrogen, argon and helium. Also, the pressure existing in liquefier 28 may be imposed by suitable hydrostatic means such as a high-pressure pump.

Suprisingly, light organic solvents are effect liquefying solvents at temperatures above their criticals. In such instances, the liquefying solvent is a supercritical fluid which has the necessary minimum solvent density due to imposing pressure upon the system. When the liquefier 28 is operated within 50 F. below the critical temperature of the solvent or higher, then the solvent is either a supercritical fluid or has properties similar to a supercritical fluid. The solvent has a much lower viscosity and a higher diffusivity, and it penetrates the coal particles faster. Solvation temperatures between 50 F. below the critical temperature of the liquefying solvent and l,000 F. produce unusually good results, and especially when elemental hydrogen is used as a pressurizing gas. The presence of elemental hydrogen also increases solvent recovery as thermal decomposition is reduced.

In instances where the solution flowing in conduit 49 contains low boiling normally liquid liquefaction products, as well as insoluble constituents and/or dissolved liquefaction products which are semisolid to solid at room temperature, then the low boiling products may be removed by fraction distillation prior to removal of the insoluble constituents and/or fractionating the semisolid to solid coal liquefaction products. As a general rule, the average molecular weight and complexity of the coal liquefaction products increase with the boiling points of the normally liquid products and with the softening points of the semisolid to solid products, and products having a similar boiling point or softening point also tend to have similar physical and/or chemical characteristics.

lt is possible to separate one or more distillate fraction of normally liquid products by a prior art fractionating step which is not shown in the drawings in the interest of clarity, and thereafter separate with heavy oils, semisolid and solid products into a plurality of fractions by the method of the invention. While the fractions may differ markedly in chemical and/or physical characteristics, the products within a fraction may have similar chemical and/or physical characteristics and it is possible to produce fractions which are suitable for specific end uses. For example, low boiling normally liquid fractions may be used as fuels, and liquid fractions of higher boiling point may be catalytically or thermally cracked to produce low boiling distillates for use as fuels. The slurry 53 withdrawn from vessel 47 contains a high concentration of sulfur, mineral ash and other undesirable constituents, but it is possible to use the residue remaining after flashing off the solvent as a fuel for firing boilers and the link in areas where air pollution is not a problem. After flashing off the solvent, the heavy fraction of coal liquefaction products 72 withdrawn from vessel 67 is useful as a solid fuel in metropolitan areas where air pollution regulations require the use of low sulfur fuels. The fraction of coal liquefaction products of intermediate softening point withdrawn from vessel 79 has a low sulfur content and it is useful as a solid fuel in metropolitan areas. Additionally, vessel 79 may be operated at a sufficiently elevated temperature and low solvent density to separate a fraction having a softening point below 200 F. and preferably below P. which may be hydrofined and/or hydrocatalytically cracked to produce liquid fuels. The fraction 94 of light coal liquefaction products withdrawn from vessel 92 is normally semisolid to liquid upon flashing off the solvent, and it likewise may be fed to a conventional catalytic hydrofining unit and/or catalytic or hydrocatalytic cracker to produce low boiling distillate fractions useful as fuels.

lt is possible to bypass up to two of the

vessels

47, 67 and 79 in instances where the desired end products will permit it. For example, when the solution flowing in conduit 49 contains an unobjectionable amount of insoluble constituents, vessel 47 may be bypassed and the solution flowing in conduit 49 may be introduced directly into vessel 67. If insoluble constituents are not objectionable in the heavy fraction 72, then vessel 47 may be operated under the conditions described for vessel 67 to thereby cause the separation of heavy fraction 72 and slurry phase 53 simultaneously in vessel 47, vessel 67 may be bypassed, and the solution flowing in conduit 65 may be introduced directly into vessel 79. Similarly, the

heavy fractions

72 and 80 may be rejected along with slurry 53 by operating vessel 47 under conditions described for vessel 79, and the solution flowing in conduit 65 may be introduced directly into vessel 92. It is also possible to bypass vessel 67 and introduce the solution flowing in conduit 65 directly into vessel 79, and thereby separate the insoluble materials in slurry phase 53 in vessel 47 and reject

heavy phases

72 and 80 in vessel 79. Still other modifications may be made in the fractionating scheme illustrated in the drawings and described herein.

The

vessels

47, 67 79 and 92 are operated at a sufficiently elevated temperature to form a liquid-to-liquid bulk interface between the separated fluidlike

heavy fractions

53, 72, 80 and 94 and the lighter solvent-

rich fractions

54, 75, 81 and 95, respectively. The minimum temperature sufficient to form the liquid-to-liquid bulk interface will vary somewhat with the sol vent and the chemical and physical nature of the separated heavy fractions and the lighter solvent-rich fractions. For example, the minimum temperature of at least 400 F. is sufficiently high to form the necessary liquid-to-liquid bulk interface, which temperature may be as high as 500650 F. with some solvents when separating heavy fractions. At lower fractionating temperatures, the solvent may percipitate a fraction, but the fraction has a viscosity whereby it is not fluidlike and freely flowable from the treating zone. The fractions precipitated at lower temperature are semisolids or solids which tend to plug the apparatus as they are withdrawn and thus continuous operation is very difiicult or impossible.

The maximum temperature for operating vessel 67 at practical pressures to separate a fraction containing coal solubilization products having a softening point above about 400 F. is approximately the critical temperature of the light organic fractionating solvent, the pressure being adjusted simultaneously to provide a solvent density about 0.05 g./cc. less than that prevailing in vessel 47. At temperatures above this level, the density change in the fractionating solvent is very rapid and coal liquefaction products having lower softening point than about 400 F. separate along with the higher softening point materials, and this lowers the softening point of fraction 72. By operating vessel 67 near the minimum fractionating temperature, it is possible to separate a heavy fraction having a softening point in excess of about 400 F.

The selection of a specific fractionating temperature between 400 F. and about the critical temperature of the fractionating solvent provides a convenient means of separating varying yields of heavy fractions of coal liquefaction products having high softening point and a high degree of molecular complexity. lnasmuch as some of the heavy constituents often have objectionably characteristics for certain end uses, the invention provides a convenient means for removing the objectionable heavy fraction prior to recovery of the remaining lighter fractions. it is also possible to operate vessel 47 at. a temperature closely approximating the minimum level for forming a liquid-to-liquid bulk interface, and reject a small amount of heavy tarry coal liquefaction products along with the insoluble constituents to flux the same. Thereafter, the temperature may be raised in one or more stages to a level approaching the maximum for separating fractions having softening points of 400 F. or higher, and additional fractions having softening points above 400 F. may be separated.

ln instances, for example, where the heavy fraction 72 has a softening point of 400 F. or above, then vessel 79 may be operated at a temperature higher than about the critical temperature and at a solvent density of, for example, about 0.05 g./cc. less than that prevailing in vessel 67 to separate a fraction having a softening point below about 400 F. Surprisingly, the critical temperature is not the maximum temperature at which a fraction of coal liquefaction products may be recovered from the solvent. Under the proper pressure conditions, the upper temperature limit is the decomposition temperature of the solvent and/or coal liquefaction products. In instances where the temperature is significantly higher than the critical temperature of the solvent, then the coal fraction usually has a lower softening point, such as below l F.

The fractionating vessel 92 is preferably operated above the critical temperature of the organic fractionating solvent to separate the remaining dissolved coal liquefaction products as a heavy phase 94 from the lighter phase 95 of solvent. Vessel 92 may be operated at essentially the same pressure as vessel 79, and the temperature may be increased to a value such that the density of the solvent at the prevailing pressure is about 0.2 g./cc. or lower. Under these conditions, the solvent is phased out and separates from the remaining coal liquefaction products, which appear at the bottom of fractionating vessel 92 as fraction 94. Fraction 94 is usually a heavy liquid or semisolid material at room temperature.

It is apparent from the foregoing discussion that, when operating

vessels

47, 67, 79 and 92 at approximately the same pressure with the exception of line and heat exchanger drop, the temperature may be increased in each successive vessel to provide successively lower solvent densities whereby a phase separation occurs in each vessel. The heat energy required to increase the temperature in the vessels is easily recovered by heat exchange with the returning solvent stream as previously described. When operating

vessels

47, 67, 79 and 92 at substantially the same temperature and making solvent density changes therein by adjusting the pressure, the energy required for adjusting the solvent densities in

vessels

47, 67, 79 and 92 to the necessary successively lower levels for phase separation cannot be recovered conveniently.

The following specification examples further illustrate the invention.

EXAMPLE 1 One hundred pounds per hour of Oklahoma Stigler seam coal containing 12.] weight percent of ash, 25.8 weight percent of volatile matter and 62.1 weight percent of fixed carbon, and having a particle size of 65 mesh is withdrawn from vessel l6 and introduced into mixer 12. One thousand pounds per hour of pyridine is withdrawn from vessel 11 and introduced into mixer 12 where it is admixed with the incoming coal feed. The resultant slurry is withdrawn via conduit 20, pressurized to 3,500 p.s.i.g. by pump 21, and admixed with 2 pounds per hour of hydrogen introduced therein via conduit 30. The slurry is then passed to heater 22 where the temperature is raised to 675 F. and introduced into liquefier 28 via conduit 27. The average residence time in the liquefier 28 is 1 hour and the solvent density is 0.62 g./cc.

The mixture of insoluble coal and pyridine solution of liquefied coal is withdrawn from liquefier 28 via conduit 35 and introduced into bulk insoluble coal separator 36 where the insoluble constituents are allowed to settle as a fluidlike phase 37 and are withdrawn via conduit 39. The separator 36 operates at substantially the same temperature and pressure conditions as liquefier 28. The insoluble coal fraction withdrawn via conduit 39 contains approximately 50 pounds per hour of insoluble coal and ash constituents and 50 pounds per hour of pyridine. The pyridine is flashed from the insoluble constituents, the vapor is condensed, and the liquid pyridine is recycled to vessel 11. The insoluble coal fraction contains 23.0 weight percent of ash, 23.6 weight percent of volatile matter and 53.4 weight percent of fixed carbon.

The solution 38 remaining as the light phase in separator 36 contains approximately 2 pounds per hour of suspended insoluble material which is largely present in the form of micron size particles. The solution 38 is passed via conduit 41 through heat exchanger 46, and its temperature is adjusted so that after passing through valve 44 and reducing the pressure to 1,000 p.s.i.g. the temperature of the solution is about 640 F. The solution is then introduced into gas separating vessel 61, from which released gases such as hydrogen and light hydrocarbons are removed via conduit 62. The degassed solution is then withdrawn from vessel 61 and passed via conduit 49 into deashing-fractionating vessel 47.

Vessel 47 operates at a solvent density of about 0.53 g.lcc., and a heavy slurry phase 53 separates and is withdrawn via conduit 55 at the rate of 12 pounds per hour. The slurry 53 contains the ash mineral brought into vessel 47, about 4 pounds per hour of separated previously dissolved heavy coal liquefaction products, and 6 pounds per hour of pyridine.

The remaining soluble liquefied coal products in the lighter phase 54, now free of ash mineral, are withdrawn via conduit 65, passed through heat exchanger 66, and then introduced into fractionating vessel 67 at a temperature of 660 F. and at substantially the pressure prevailing in vessel 47. The solvent density in vessel 67 is about 0.49 g.lcc. A heavy fluidlike phase 72 separates in the bottom of vessel 67 and is readily withdrawn therefrom via conduit 73 at the rate of 25 pounds per hour of deashed coal containing an equal weight of pyridine. Upon flashing off the pyridine solvent, the residue has a softening point in excess of 400 F., an ash content of 22.3 weight percent, and a fixed carbon content of 76.8 weight percent.

The solution of remaining liquefied coal products existing as solvent rich phase 75 is withdrawn via conduit 77, passed through heat exchanger 78 where it is heated to 680 F., and is then introduced into fractionating vessel 79. The pressure in fractionating vessel 79 is about 975 p.s.i.g., and the solvent density is about 0.35 g./cc. The intermediate fraction of coal liquefaction products which separates as heavy phase 80 in the bottom of vessel 79 is fluidlike and is withdrawn via conduit 87 at the rate of about 10 pounds of coal liquefaction products per hour along with 20 pounds per hour of pyridine. Upon flashing off the pyridine, the residue has a softening point of 200 F., an ash content of 0.81 weight percent, a volatile matter content of 40.9 weight percent, and a fixed carbon content of 8.3 weight percent.

The solvent-rich phase 81 is withdrawn from vessel 79 via conduit 90, passed through heat exchanger 91 and heater 93 where the temperature is raised to 735 F., and introduced into fractionating vessel 92. The vessel 92 operates at substantially the same pressure as vessel 79 and the solvent density is 0.18 g./cc. A fluid heavy phase containing the lightest portion of the liquefied coal products separates in the bottom of vessel 92 and is removed therefrom via conduit 101 at a rate of pounds per hour along with pounds per hour of pyridine. Upon evaporation and recover of the pyridine, the resultant residue has an ash content of 0.38 weight percent, a volatile matter content of 66.1 weight percent, and a fixed carbon content of 33.5 weight percent.

The solvent-rich phase 95 in the upper portion of vessel 92 contains 99.3 weight percent of pyridine. It is removed from the top of vessel 92 via conduit 64, passed successively through

heat exchangers

91, 78 and 66 in heat exchange relationship with the solvent-rich phases flowing in

conduits

90, 77 and 65 to recover its heat content, then through heat exchanger 103 to reduce its temperature sufficiently to produce cool pyridine solvent, and the cooled solvent is introduced into vessel 11 awaiting recycle. The pyridine flashed from the

heavy fractions

53, 72, 80 and 94 is recovered by condensation and returned to surge vessel 11 via conduit 8, and makeup solvent likewise is supplied to vessel 11 via conduit 8 as required.

EXAMPLE 11 Two thousand grams of Oklahoma Stigler seam coal having a particle size of -65 mesh, a volatile matter content of 25.8 weight percent, a fixed carbon content of 63.0 weight percent, a sulfur content of 2.12 weight percent, and an ash content of 12.1 weight percent was treated with 6,000 grams of anthracene oil at 400 C. for 1 hour in the presence of hydrogen at a pressure of 625 p.s.i.g. More than 80 percent of the coal was dissolved. The solution was centrifuged to remove insoluble matter and the anthracene oil was removed by vacuum distillation to produce a deashed and desolvated coal product which analyzed 0.7 weight percent of ash, 0.61 weight percent of sulfur, 36.6 weight percent of volatile matter, and 62.7 weight percent of fixed carbon.

One thousand grams of the above prepared antracene oilfree deashed coal product was placed in a pressure vessel together with 20,000 grams of benzene. The pressure of the contents of the pressure vessel was maintained at approximately 1,000 p.s.i.g. and the temperature was raised periodically to successively higher levels. At each temperature level, a fluidlike heavy phase containing about 50 weight percent coal liquefaction products and about 50 weight percent benzene separated and was withdrawn from the bottom of the pressure vessel. The results are given in the following table:

EXAMPLE in One thousand grams of the deashed and desolvated coal product prepared in accordance with example 11 is introduced 5 into a pressure vessel along with 5,000 grams of normal hex- 10 ture the density of the hexane solvent is 0.39 g./cc., a fluidlike heavy phase forms in the bottom of the pressure vessel consisting of equal parts by weight of hexane and coal liquefaction products. After withdrawing the heavy phase from the pressure vessel and flashing off the hexane, the residue has a volatile matter content of 35.8 weight percent.

Upon raising the temperature of the contents of the pressure vessel to 520 F., at which temperature the density of the hexane solvent is 0.33 g./cc. a fluidlike heavy phase forms in the bottom of the pressure vessel consisting of approximately equal parts by weight of hexane and intermediate coal liquefaction products. After withdrawing the fraction of intermediate coal liquefication products from the pressure vessel and flashing off the solvent, the residue has a volatile matter content of 5 l .8 weight percent.

The temperature of the contents of the pressure vessel is further raised to 570 F., at which temperature the hexane solvent density is 0.27 g./cc., and a fluidlike heavy phase of coal liquefaction products separates which has a hexane content of about 50 percent. Upon withdrawing this heavy phase and flashingoff the hexane, the residue has a volatile matter content of 74.7 weight percent.

The temperature of the contents of the pressure vessel is further raised to 650 F., at which temperature the hexane density is 0.20 g./cc., and a fluidlike phase of coal liquefaction products of very light character separates. Upon withdrawing this phase from the pressure vessel and flashing off the hexane solvent, the residue has a volatile matter content of 84.4 weight percent.

When desired, the various light organic solvents which are disclosed herein as being suitable for both liquefaction and fractionation of coal may be substituted for pyridine as the solvent in example 1 to thereby obtain comparable results. Similarly, the various light organic solvents which are disclosed herein as being suitable for either liquefaction and fractionation or fractionation alone of coal may be substituted for benzene and hexane as a fractionating solvent in examples II and Ill, respectively, to obtain comparable results.

1 claim: 1. A method of fractionating products of coal liquefaction into a plurality of fractions comprising:

treating an organic-solvent solution of products of coal liquefaction in a treating zone at an elevated temperature and pressure to separate a fluidlike first heavy fraction of coal liquefaction products from a lighter first solvent-rich phase containing dissolved coal liquefaction products,

said solution containing initially at least two parts by weight of the organic solvent for each part by weight of the dissolved coal liquefaction products,

the organic solvent consisting essentially of at least one substance having a critical temperature below 800 F. selected from the group consisting of aromatic hydrocarbons having a single benezene nucleus and normally boiling points below about 310 F., cycloparaffin hydrocarbons having normal boiling points below about 310 F., open chain mono-olefin hydrocarbons having normal boiling POlNTS BELOW ABOUT 310 F., open chain saturated hydrocarbons having normal boiling points below about 310 F., mono-, di-, and tri-open chain amines, carbocyclic amines having a monocyclic structure, heterocyclic amines, and phenol and its homologs,

said solution being treated at a temperature of at least 400 F. and the temperature being sufficiently elevated to form a liquid-to-liquid bulk interface between the first heavy fraction and the first solvent rich phase,

the temperature and pressure being adjusted to provide a solvent density in the treating zone of less than about 0.55 g./cc., the solvent density being sufficient low to separate the first heavy fraction from the first solvent-rich phase and sufficiently high to retain the remaining coal liquefaction products in solution in the first solvent-rich phase,

the first heavy fraction having a viscosity under the temperature and pressure conditions existing in the treating zone whereby it is flowable from the treating zone, and

withdrawing the first heavy fraction from the treating zone.

2. The method of claim 1 wherein the organic solvent is selected from the group consisting of pyridine, benzene and hexane.

3. The method of claim 1 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction,

the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.35-0.55 g./cc. when separating the first heavy fraction,

a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of slurry containing the first heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treating zone, and

the slurry is withdrawn from the treating zone.

4. The method of claim 1 wherein the first solvent-rich phase is further treated in a treating zone under elevated temperature and pressure conditions to separate at least one additional fluidlike heavy fraction of coal liquefaction products including a fluidlike final heavy fraction of residual coal liquefaction products which is separated from a lighter organic-solvent phase,

the temperature and pressure being adjusted to provide a solvent density in the treating zone during separation of the final heavy fraction not greater than about 0.15-0.20 g./cc. and sufficiently low to separate the residual coal liquefaction products from the organic-solvent phase,

the final heavy fraction having a viscosity under the temperature and pressure conditions existing in the treating zone during the separation thereof whereby it is flowable from the treating zone, and

withdrawing the final heavy fraction of residual coal liquefaction products from the treating zone.

5. The method of claim 4 wherein the organic solvent is selected from the group consisting of pyridine, benzene and hexane.

6. The method of claim 4 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction, the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.35-0.55 g./cc. when separating the first heavy fraction, a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of the slurry contains the heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treat ing zone, and the slurry is withdrawn from the treating zone.

7. The method of claim 4 wherein the pressure in the treating zone during separation of the first heavy fraction and at least one additional heavy fraction including the final heavy fraction is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density for separation of at least one additional heavy fraction including the final heavy fraction.

8. The method of claim 4 wherein the separated organic-solvent phase is withdrawn from the treating zone and passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in the treating zone.

9. The method of claim 4 wherein at least one fluidlike intermediate heavy fraction of coal liquefaction products is obtained by treating the first solvent-rich phase in at least one treating zone under elevated temperature and pressure conditions providing a solvent density therein which is less than that existing in the treating zone when separating the first heavy fraction and greater than about 0.15-0.20 g./cc.,

at least one intermediate heavy fraction separated by this treatment having a viscosity under the temperature and pressure conditions existing in the treating zone whereby it is freely flowable therefrom, and

withdrawing at least one intermediate heavy fraction from at least one treating zone.

10. The method of claim 9 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction, the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.350.55 g./cc. when separating the first heavy fraction, a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of slurry contains the heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treating zone, and the slurry is withdrawn from the treating zone.

11. The method of claim 10 wherein the pressure in the treating zone during separation of the first heavy fraction and at least one additional heavy fraction including the final heavy fraction is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density for separation of at least one additional heavy fraction including the final heavy fraction.

12. The method of claim 11 wherein the separated organicsolvent phase is withdrawn from the treating zone and passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in the treating zone.

13. A process for liquefying and fractionating coal comprising intimately contacting coal in particulate form with an organic solvent in a coal liquefaction zone to produce a solution containing products of coal liquefaction and suspended finely divided insoluble material.

the organic solvent consisting essentially of at least one sub stance having a critical temperature below 800 F. selected from the group consisting of aromatic hydrocarbons having a single benzene nucleus and normal boiling points below about 3l0 F., cycloparaffin hydrocarbons having normal boiling points below about 310 F., mono-, di-, and tri-straight chain amines, carbocyclic amines hav ing a monocyclic structure, heterocyclic amines, and phenol and its homologs,

the coal being contacted with the solvent in the liquefaction zone at a temperature of about 550-] ,000 F. and under a pressure of about 400-] 0,000 p.s.i.a., said temperature being below the solvent decomposition temperature and the solution thus produced containing at least two parts by weight of the organic solvent for each part by weight of the coal liquefaction products and having finely divided insoluble material therein, the temperature and pressure in the liquefaction zone being adjusted to provide a solvent density of at least 0.5 g./cc.,

withdrawing the organic-solvent solution of coal liquefaction products from the liquefaction zone and introducing it into a first treating zone,

treating the organic-solvent solution of coal liquefaction products in the first treating zone at an elevated temperature and pressure to separate a fluidlike first heavy fraction containing coal liquefaction products and said finely divided insoluble material and a lighter first organic solvent-rich phase containing dissolved coal liquefaction products,

said solution being treated in the first treating zone at a temperature of at least 400 F. and the temperature being sufficiently elevated to form a liquid-to-liquid bulk interface between the first heavy fraction and the first solvent-rich phase,

the temperature and pressure being adjusted to provide a solvent density of less than about 0.55g./cc. in the first treating zone, the solvent density in the first treating zone being less than the solvent density at which the coal was contacted with the solvent in the coal liquefaction zone and sufficiently low to separate the first heavy fraction from the first solvent-rich phase and sufficiently high to retain the remaining coal liquefaction products in the first solvent-rich phase,

the first heavy fraction having a viscosity under the temperature and pressure conditions existing in the first treating zone whereby it is flowable from the first treating zone, and

withdrawing the first heavy fraction from the first treating zone.

14. The process of claim 13 wherein said organic solvent is selected from the group consisting of pyridine and benzene.

15. The process of claim 13 wherein said organic solvent solution of coal liquefaction products is withdrawn from the liquefaction zone and introduced into an insoluble coal-separating zone,

the said solution is maintained in the insoluble coal-separating zone at approximately the same temperature and pressure as exist in the liquefaction zone and for a residence time sufficient to separate a heavy slurry phase which contains a major amount of the insoluble material and a lighter phase which contains dissolved coal liquefaction products and some insoluble material, the heavy slurry phase being flowable under the temperature and pressure conditions existing in the insoluble coal separating zone,

the heavy slurry phase is withdrawn from the insoluble coalseparating zone, and

the lighter phase containing dissolved coal liquefaction products and some insoluble material is withdrawn from the coal-separating zone and introduced into the first treating zone.

16. The process of claim 13 wherein the residence time of said solution in the first treating zone is sufficient to settle insoluble material therefrom, and

the temperature and pressure in the first treating zone are adjusted to provide a solvent density of about 0.35-0.55 g./cc. and sufficiently low to separate coal liquefaction products from said solution in an amount to flux the settled insoluble material whereby it may be withdrawn as a fluidlike phase.

17. The process of claim 13 wherein said first solvent-rich phase is withdrawn from the first treating zone and is introduced into at least one additional treating zone including a final treating zone,

the first solvent-rich phase is further treated under elevated temperature and pressure conditions to separate at least one additional fluidlike heavy fraction of coal liquefaction products including a fluidlike final heavy fraction of residual coal liquefaction products which is separated in the final treating zone from a lighter organic solvent phase,

the temperature and pressure are adjusted to provide a solvent density in the final treating zone during separation of the final heavy fraction not greater than about 0. 1 5-020 g./cc. and sufficiently low to separate the residual coal liquefaction products from the organic-solvent phase,

the final heavy fraction has a viscosity under the temperature and pressure conditions existing in the treating zone during the separation thereof whereby it is flowable from the treating zone, and

the final heavy fraction of residual coal liquefaction products is withdrawn from the treating zone.

18. The process of claim 17 wherein the organic solvent is selected from the group consisting of pyridine and benzene.

19. The process of claim 17 wherein the pressure in the treating zones during separation of the heavy fractions is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density in the treating zones for separation of the heavy fractions.

20. The process of claim 17 wherein the separated organicsolvent phase is withdrawn from the final treating zone and is passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in at least one treating zone.

21. The process ofclaim 17 wherein at least one fluidlike intermediate heavy fraction of coal liquefaction products is obtained by treating the first solvent-rich phase in at least one treating zone under elevated temperature and pressure conditions providing a solvent density therein which is less than that existing in the treating zone when separating the first heavy fraction and greater than about 0.15-0.20 g./cc.,

22. The process of claim 21 wherein the pressure in the treating zones during separation of the heavy fractions is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density in the treating zones for separation of the heavy fractions.

23. The process of claim 22 wherein the separated organicsolvent phase is withdrawn from the final treating zone and is passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in at least one treating zone.

24. A method of separating suspended finely divided insoluble material from products of'coal liquefaction comprising introducing an organic-solvent solution of products of coal liquefaction into a settling zone having upper and lower portions,

said solution containing at least two parts by weight of organic solvent for each part by weight of dissolved coal liquefaction products, and having therein suspended fine- 1y divided insoluble material derived from the coal during liquefaction,

the lower portion of the settling zone having therein a rela tively heavy fluidlike body of slurry containing said insoluble material in a markedly higher concentration than present in said solution initially,

the upper portion of the settling zone having therein a relatively tight body of an organic-solvent solution of coil liquefaction products containing said insoluble material in a substantially lower concentration than present in said solution initially,

said solution being injected into the lower portion of the settling zone beneath the surface of the body of slurry and passing upward therefrom into the upper portion of the settling zone,

said finely divided insoluble material being agglomerated and retained in the body of slurry,

withdrawing slurry from the lower portion of the settling zone, and

withdrawing from the upper portion of the settling zone an organic-solvent solution of coal liquefaction products having a substantially lower concentration of insoluble material than present in solution initially.

25. The method of claim 24 wherein the body of slurry contains finely divided insoluble material fluxed with a fraction of coal liquefaction products and organic solvent, and the slurry has a viscosity whereby it may be withdrawn from the settling zone as a fluidlike phase.

26. The method of claim 24 wherein a fraction of coal liquefaction products is separated from said solution and deposited on the suspended particles of insoluble material whereby the particles of insoluble material may be agglomerated in the settling zone.

27. The method of claim 24 wherein the organic solvent comprises at least one substance having a critical temperature below 800 F. selected from the group consisting of aromatic Patent No.

UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION Inventor(s) Column 7, line 4-5, line 52, line 14, line 28, line 3, line 67, line 1, line 17, line 1, line 15,

Column 8,

Column 9,

Column 10,

Column Column Dated September 21, 1971 Jack W. Roach It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"aver" should read average "penetrate" should read penetrates "hetercyclic" should read heterocyclic "310? E." should read 310 F. "reaction" should read reactor "fraction should read fractional "fractionfshould read fractions "link" should read like "specification" should read specific "recover" should read recovery in the table appearing at the bottom of the column the print is not discernible and should read:

Withdrawn heavy phase (solvent free) Weight Weight Solvent percent Weight percent density, Weight, volatile percent fixed Temperature, F. g./cc. g. matter ash carbon 535 0.55 260 p 30.0 0.3 68.4 610 0.29 400 32.2 0.3 69.0 660 0.19 170 33.0 0.l 68.0 720 0.15 150 36. 9 0.l' 63.1

Column 14, line 67, "POINTS BELOW ABOUT" should read points below about [Column 15, line 10, "sufficient" should read sufficiently Column 17, line 73, "0 15" should read 0.15

Signed and sealed this 25th day of April 1972. r

(SEAL) Attest:

EDWARD MFLETCHER Attesting Officer QM PO-IOSO (10-69) ROBERT GOTTSCHALK Commissioner of Patents L USCOMM-DC 60376-P69 i us GOVERNMENT mmrms Orncz; 1969 0-36b-l8l

Claims

2. The method of claim 1 wherein the organic solvent is selected from the group consisting of pyridine, benzene and hexane.
3. The method of claim 1 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction, the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.35-0.55 g./cc. when separating the first heavy fraction, a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of slurry containing the first heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treating zone, and the slurry is withdrawn from the treating zone.
4. The method of claim 1 wherein the first solvent-rich phase is further treated in a treating zone under elevated temperature and pressure conditions to separate at least one additional fluidlike heavy fraction of coal liquefaction products including a fluidlike final heavy fraction of residual coal liquefaction products which is separated from a lighter organic-solvent phase, the temperature and pressure being adjusted to provide a solvent density in the treating zone during separation of the final heavy fraction not greater than about 0.15-0.20 g./cc. and sufficieNtly low to separate the residual coal liquefaction products from the organic-solvent phase, the final heavy fraction having a viscosity under the temperature and pressure conditions existing in the treating zone during the separation thereof whereby it is flowable from the treating zone, and withdrawing the final heavy fraction of residual coal liquefaction products from the treating zone.
5. The method of claim 4 wherein the organic solvent is selected from the group consisting of pyridine, benzene and hexane.
6. The method of claim 4 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction, the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.35-0.55 g./cc. when separating the first heavy fraction, a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of the slurry contains the heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treating zone, and the slurry is withdrawn from the treating zone.
7. The method of claim 4 wherein the pressure in the treating zone during separation of the first heavy fraction and at least one additional heavy fraction including the final heavy fraction is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density for separation of at least one additional heavy fraction including the final heavy fraction.
8. The method of claim 4 wherein the separated organic-solvent phase is withdrawn from the treating zone and passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in the treating zone.
9. The method of claim 4 wherein at least one fluidlike intermediate heavy fraction of coal liquefaction products is obtained by treating the first solvent-rich phase in at least one treating zone under elevated temperature and pressure conditions providing a solvent density therein which is less than that existing in the treating zone when separating the first heavy fraction and greater than about 0.15-0.20 g./cc., at least one intermediate heavy fraction separated by this treatment having a viscosity under the temperature and pressure conditions existing in the treating zone whereby it is freely flowable therefrom, and withdrawing at least one intermediate heavy fraction from at least one treating zone.
10. The method of claim 9 wherein said solution contains initially finely divided insoluble material derived from coal during liquefaction, the temperature and pressure are adjusted to provide a solvent density in the treating zone of about 0.35-0.55 g./cc. when separating the first heavy fraction, a body of slurry containing the insoluble material and the first heavy fraction is separated in a lower portion of the treating zone, the body of slurry contains the heavy fraction in an amount to flux the insoluble material present therein under the temperature and pressure conditions existing in the treating zone, and the slurry is withdrawn from the treating zone.
11. The method of claim 10 wherein the pressure in the treating zone during separation of the first heavy fraction and at least one additional heavy fraction including the final heavy fraction is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density for separation of at least one additional heavy fraction including the final heavy fraction.
12. The method of claim 11 wherein the separated organic-solvent phase is withdrawn from the treating zone and passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same aT elevated temperature and pressure in the treating zone.
13. A process for liquefying and fractionating coal comprising intimately contacting coal in particulate form with an organic solvent in a coal liquefaction zone to produce a solution containing products of coal liquefaction and suspended finely divided insoluble material. the organic solvent consisting essentially of at least one substance having a critical temperature below 800* F. selected from the group consisting of aromatic hydrocarbons having a single benzene nucleus and normal boiling points below about 310* F., cycloparaffin hydrocarbons having normal boiling points below about 310* F., mono-, di-, and tri-straight chain amines, carbocyclic amines having a monocyclic structure, heterocyclic amines, and phenol and its homologs, the coal being contacted with the solvent in the liquefaction zone at a temperature of about 550-1,000* F. and under a pressure of about 400-10,000 p.s.i.a., said temperature being below the solvent decomposition temperature and the solution thus produced containing at least two parts by weight of the organic solvent for each part by weight of the coal liquefaction products and having finely divided insoluble material therein, the temperature and pressure in the liquefaction zone being adjusted to provide a solvent density of at least 0.5 g./cc., withdrawing the organic-solvent solution of coal liquefaction products from the liquefaction zone and introducing it into a first treating zone, treating the organic-solvent solution of coal liquefaction products in the first treating zone at an elevated temperature and pressure to separate a fluidlike first heavy fraction containing coal liquefaction products and said finely divided insoluble material and a lighter first organic solvent-rich phase containing dissolved coal liquefaction products, said solution being treated in the first treating zone at a temperature of at least 400* F. and the temperature being sufficiently elevated to form a liquid-to-liquid bulk interface between the first heavy fraction and the first solvent-rich phase, the temperature and pressure being adjusted to provide a solvent density of less than about 0.55g./cc. in the first treating zone, the solvent density in the first treating zone being less than the solvent density at which the coal was contacted with the solvent in the coal liquefaction zone and sufficiently low to separate the first heavy fraction from the first solvent-rich phase and sufficiently high to retain the remaining coal liquefaction products in the first solvent-rich phase, the first heavy fraction having a viscosity under the temperature and pressure conditions existing in the first treating zone whereby it is flowable from the first treating zone, and withdrawing the first heavy fraction from the first treating zone.
14. The process of claim 13 wherein said organic solvent is selected from the group consisting of pyridine and benzene.
15. The process of claim 13 wherein said organic solvent solution of coal liquefaction products is withdrawn from the liquefaction zone and introduced into an insoluble coal-separating zone, the said solution is maintained in the insoluble coal-separating zone at approximately the same temperature and pressure as exist in the liquefaction zone and for a residence time sufficient to separate a heavy slurry phase which contains a major amount of the insoluble material and a lighter phase which contains dissolved coal liquefaction products and some insoluble material, the heavy slurry phase being flowable under the temperature and pressure conditions existing in the insoluble coal separating zone, the heavy slurry phase is withdrawn from the insoluble coal-separating zone, and the lighter phase containing dissolved coal liquefaction products and some insoluble material is withdrawn From the coal-separating zone and introduced into the first treating zone.
16. The process of claim 13 wherein the residence time of said solution in the first treating zone is sufficient to settle insoluble material therefrom, and the temperature and pressure in the first treating zone are adjusted to provide a solvent density of about 0.35-0.55 g./cc. and sufficiently low to separate coal liquefaction products from said solution in an amount to flux the settled insoluble material whereby it may be withdrawn as a fluidlike phase.
17. The process of claim 13 wherein said first solvent-rich phase is withdrawn from the first treating zone and is introduced into at least one additional treating zone including a final treating zone, the first solvent-rich phase is further treated under elevated temperature and pressure conditions to separate at least one additional fluidlike heavy fraction of coal liquefaction products including a fluidlike final heavy fraction of residual coal liquefaction products which is separated in the final treating zone from a lighter organic solvent phase, the temperature and pressure are adjusted to provide a solvent density in the final treating zone during separation of the final heavy fraction not greater than about 0.15-0.20 g./cc. and sufficiently low to separate the residual coal liquefaction products from the organic-solvent phase, the final heavy fraction has a viscosity under the temperature and pressure conditions existing in the treating zone during the separation thereof whereby it is flowable from the treating zone, and the final heavy fraction of residual coal liquefaction products is withdrawn from the treating zone.
18. The process of claim 17 wherein the organic solvent is selected from the group consisting of pyridine and benzene.
19. The process of claim 17 wherein the pressure in the treating zones during separation of the heavy fractions is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density in the treating zones for separation of the heavy fractions.
20. The process of claim 17 wherein the separated organic-solvent phase is withdrawn from the final treating zone and is passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in at least one treating zone.
21. The process of claim 17 wherein at least one fluidlike intermediate heavy fraction of coal liquefaction products is obtained by treating the first solvent-rich phase in at least one treating zone under elevated temperature and pressure conditions providing a solvent density therein which is less than that existing in the treating zone when separating the first heavy fraction and greater than about 0.15-0.20 g./cc., at least one intermediate heavy fraction separated by this treatment having a viscosity under the temperature and pressure conditions existing in the treating zone whereby it is freely flowable therefrom, and withdrawing at least one intermediate heavy fraction from at least one treating zone.
22. The process of claim 21 wherein the pressure in the treating zones during separation of the heavy fractions is approximately the same, and the temperature of the solvent is adjusted to provide the desired solvent density in the treating zones for separation of the heavy fractions.
23. The process of claim 22 wherein the separated organic-solvent phase is withdrawn from the final treating zone and is passed in heat exchange relationship with at least one relatively cool solvent-rich phase to raise the temperature thereof prior to treating the same at elevated temperature and pressure in at least one treating zone.
24. A method of separating suspended finely divided insoluble material from products of coal liquefaction comprising introducing an organic-solvent sOlution of products of coal liquefaction into a settling zone having upper and lower portions, said solution containing at least two parts by weight of organic solvent for each part by weight of dissolved coal liquefaction products, and having therein suspended finely divided insoluble material derived from the coal during liquefaction, the lower portion of the settling zone having therein a relatively heavy fluidlike body of slurry containing said insoluble material in a markedly higher concentration than present in said solution initially, the upper portion of the settling zone having therein a relatively tight body of an organic-solvent solution of coil liquefaction products containing said insoluble material in a substantially lower concentration than present in said solution initially, said solution being injected into the lower portion of the settling zone beneath the surface of the body of slurry and passing upward therefrom into the upper portion of the settling zone, said finely divided insoluble material being agglomerated and retained in the body of slurry, withdrawing slurry from the lower portion of the settling zone, and withdrawing from the upper portion of the settling zone an organic-solvent solution of coal liquefaction products having a substantially lower concentration of insoluble material than present in solution initially.
25. The method of claim 24 wherein the body of slurry contains finely divided insoluble material fluxed with a fraction of coal liquefaction products and organic solvent, and the slurry has a viscosity whereby it may be withdrawn from the settling zone as a fluidlike phase.
26. The method of claim 24 wherein a fraction of coal liquefaction products is separated from said solution and deposited on the suspended particles of insoluble material whereby the particles of insoluble material may be agglomerated in the settling zone.
27. The method of claim 24 wherein the organic solvent comprises at least one substance having a critical temperature below 800* F. selected from the group consisting of aromatic hydrocarbons having a single benzene nucleus and normal boiling points below about 310* F., cycloparaffin hydrocarbons having normal boiling points below about 310* F., open chain mono-olefin hydrocarbons having normal boiling points below about 310* F., open chain saturated hydrocarbons having normal boiling points below about 310* F., mono-, di-, and tri-open chain amines, carbocyclic amines having a monocyclic structure, heterocyclic amines and phenol and its homologs.
28. The method of claim 27 wherein the organic solvent is selected from the group consisting of pyridine, benzene and hexane.