US3520794A - Solvent extraction method - Google Patents

Description

July14, 1970 J. c. GATSIS SOLVENT EXTRACTION METHOD 2 Sheets-Sheet 1 Filed March 29, 1968 ES QE sta w ub v 59;

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SOLVENT EXTRACTION METHOD 2 Sheets-Sheet 2 Coal Efacf v M m t tt i 0 l m k g I f g N x 3 E, L Ls F N a r B 8 9.) k a P1 //v vnvron- John 6. Gafs/s Lk BY- ATTORNEYS I United States Patent 3,520,794 SOLVENT EXTRACTION METHOD John G. Gatsis, Des Plaines, Ill., assignor to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Filed Mar. 29, 1968, Ser. No. 723,341 Int. Cl. C10g 1/00 US. Cl. 208-8 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for liquefying coal via solvent extraction. Coal and solvent are introduced into the tubes via a vertical shell and tube extraction zone. The tube is perforated in such a manner that coal extracted may be removed through the perforations into the shell side with the remaining solid material being removed from the tubes. Hydrocarbons useful as fuel and/ or chemicals may be obtained from the liquid coal extract.

BACKGROUND OF THE INVENTION This invention relates to a solvent extraction method. It also relates to a method for liquefying coal using a selective solvent. It particularly relates to a method for liquefying coal utilizing a novel extraction zone design.

It has long been known that hydrocarbon gases, liquids, pitch, and the chemicals derived from or allied to these hydrocarbons may be obtained in some form from coal which is mined from the earth. Usually, the prior art has employed destructive distillation or other gasification processes for the conversion of coal into these more valuable and useful products. Recently, the prior art has developed a high pressure hydrogenation of coal technique to effectuate such conversion. Still more recently, methods involving solvent extraction techniques have been perfected by the prior art for obtaining useful fuels and chemicals from coal wherein the crushed coal is contacted with a selective solvent which acts as a hydrogen-donor for supplying sufiicient hydrogen to the coal to aid in converting it to a liquid phase. Following the solvent extraction step, the prior art schemes have generally utilized various produce recovery procedures, such as hydrogenation of the liquid coal extract, for increasing its value and utility together with retorting or coking of the residual materials obtained from the solvent extraction step to still further convert these coal derived priducts into more useful and valuable products.

One of the main difficulties in the liquefaction of coal using the solvent extraction process is in the separation step following extraction, i.e., the separation of the undissolved coal and inorganic material from the liquid. The prior art has attempted to make this separation by filtration methods using a precoated filter at temperatures which approach atmospheric temperatures. However, the prior art methods of separating the insoluble material from the liquid coal extract have been, for the most part, unsatisfactory in the commercial sense.

Since it is clear to those skilled in the art that the vast mineral reserves of bituminous coal represent an extreme ly important supply of energy, it would be desirable to improve upon the prior art processes, particularly the solvent extraction process in order to reduce the cost of obtaining typical petroleum-type products from coal.

SUMMARY OF THE INVENTION Therefore, it is an object if this invention to provide a method for the liquefaction of coal whereby valuable hydrocarbon products may be obtained therefrom.

It is a specific object of this invention to provide an ice improved method for subjecting pulverized coal to solvent extraction using solvent which is selective for dissolving the coal, e.g., Tetralin.

It is another specific object of this invention to provide an improved method for liquefying coal via solvent extraction whereby increased efliciency of the separation step is significantly increased in a facile and economical manner.

This invention has both apparatus and method aspects. In accordance with the practice of one embodiment of the apparatus aspect, there is provided apparatus which comprises in combination a vertically disposed enclosed shell having at least one conduit extending through said shell in parallel relationship with the vertical axis of said shell, means for introducing a mixture of solid and liquid materials into the lower end of said conduit, first outlet means for removing solid material from the upper end of said conduit, perforate means in the upper section of said conduit providing a passageway for liquid between said con duit and said shell, and second outlet means for withdrawing liquid from said shell.

A specific embodiment of the apparatus aspect includes the apparatus hereinabove wherein said perforations comprise orifice openings having a small enough diameter to prevent the passage therethrough of solid particles having an average diameter of five (5) microns or larger.

Further, in accordance with the practice of one method embodiment of this invention, there is provided a method for liquefying coal which comprises passing granular coal and solvent into the lower end of an extraction zone maintained under coal extraction conditions; said zone comprising at least one vertically disposed conduit having an imperforate lower section and perforate upper section; withdrawing liquefied coal from said upper section through the perforations therein while retaining solid material within said conduit; and removing solid material from the upper end of said conduit.

In a specific method embodiment of the present invention there is provided a method for liquefying coal which comprises contacting granular coal with a solvent selective for coal in the lower end of at least one smaller conduit disposed concentrically in a larger conduit, passing the coal and solvent upwardly through said smaller conduit under coal extraction conditions; withdrawing liquefied coal and solvent through at least one opening in the upper section of said smaller conduit into the larger conduit in a manner such that solid material is substantially retained in said smaller conduit; removing liquefied coal and solvent from said larger conduit; and, removing solid material from the upper end of said smaller conduit.

In other words, the method of the present invention utilizes a reactor consisting of two concentric tubes with the upper section of the inner tube consisting of a perforated or filter element. In operation, the ground coal is mixed with the solvent and the mixture is passed upwardly in the reactor through the inner tube. Preferably, a temperature gradient is applied across the reaction or liquefying zone with the temperature increasing from the bottom of the inner tube to the top of the tube. As the coal proceeds upwardly through the liquefaction zone, the coal is dissolved into the solvent and as it proceeds through the perforated section of the inner tube the liquid will pass through the filter and the unreacted coal passed upwardly and out of the extraction zone.

DESCRIPTION OF THE INVENTION The coal preferred for use in the practice of the present inventive method is of the bituminous type such as Pittsburgh seam coal. More preferably, however, the bituminous coal is a high volatile content coal having a volatile content greater than about 20% by weight of 1m.a.f. coal (moisture and ash-free coal).

The extraction of coal by means of solvent has been described (by definition) as a partial conversion of the coal since not only is the coal reacted with the hydrogen which is transferred from the solvent, but there is also a solution phenomenum which actually dissolves the coal which has accepted the hydrogen from some source into the solvent liquid phase. Therefore, as used herein, the term liquid coal extract, liquefied coal fraction, liquefied coal, or other words of similar import, is intended to include the liquid product which is obtained from the solvent extraction of the coal with the selective solvent and, generally, will be described on the basis of being solvent-free even though a portion of the liquid coal extract comprises hydrocarbons suitable for use as the selective solvent. The practice of the present invention is performed under conditions which increase the kinetics of the reaction while maintaining the components therein primarily liquid phase; although, in some cases it may be desirable to practice this invention in the presence of a vaporized solvent by using a gaseous extraction technique.

Suitable solvents for use in the practice of this invention are those which are of the hydrogen-donor type and are at least partially hydrogenated and include naphthalenic hydrocarbons. Other aromatic type hydrocarbons are suitable if an extraneous source of hydrogen is provided. Preferably, the solvent is one which is in liquid phase at the recommended temperature and pressure for the extraction and/or pulverization step. Mixtures of hydrocarbons are generally employed and preferably are derived from intermediate or final products obtained from subsequent processing following the practice of this invention. Typically, these solvent hydrocarbons or mixtures of hydrocarbons boil between about 260 C. and 425 C. Examples of suitable solvents are tetrahydronaphthalene (Tetrahn), Decalin, biphenyl, methylnaphthalene, dimethylnaphthalene, etc. Other types of solvents which may be added to the preferred solvents of this invention for special reasons include phenolic compounds, such as phenols, cresols, and xylenols. It is also to be recognized that it some cases it may be desirable during a subsequent separation step prior to the removal of the solvent from the liquid coal extract to add an antisolvent, such as saturated paraflinic hydrocarbon like hexane, to aid in the precipitation of tarry and solid residue from the coal extract of the invention.

However, in the selection of a suitable solvent it must be recognized that unless hydrogen is added to the extraction zone the solvent must have the ability to transfer hydrogen to the pulverized coal during the extract step. In other words, in the absence of added hydrogen, it is a requirement of this invention that the rich solvent leaving the extraction zone having liquid coal extract dissolved therein has a reduced hydrogen content compared to the hydrogen content of the lean solvent which is added to the extraction zone in admixture with the feed.

A particularly preferred embodiment of this invention includes the use of the selective solvent during the pulverization step whereby relatively coarse size coal is reduced to granular coal of optimum size for extraction. This preferred embodiment is predicated on the theory that having the presence of a hydrogen-rich solvent during the pulverization step of the coal results in a substantial increase in the efficiency of the operation and in many cases results in a decreased use of solvent for obtaining the same amount of liquid coal extract.

With respect to the benefit gained from having the solvent present during the pulverization step, it is believed that at the point of shear for the crushing and grinding of the coal the shear site is extremely reactive and hydrogen, therefore, can be transfercd into that site more easily then if the coal is pulverized prior to contact with the solvent. In addition, the small particles of coal which are sheared away from a large lump immediately expose not only the highly reactive shear site to the solvent, but also exposes an extremely large surface area to the solvent, thereby enabling the small particles of coal to almost immediately dissolve in the solvent and become a part of the liquid coal extract. While not desiring to be limited by this theory, the practice of this preferred embodiment of the invention is at least explained to those skilled in the art so that future work may be used along these lines to further improve upon the inventive concepts contained herein.

Apparatus for use in pulverizing the lump or coarse coal feed as practiced in the present invention may be any type known to those skilled in the art. Conventional ball mills or rod mills may be used with satisfactory results. Preferably, the apparatus must be able to pulverize lump or coarse coal in the presence of significant quantities of liquid solvent without difficulty. Those skilled in the art are familiar with the kinds of apparatus for processing wet solids and the crushing and grinding thereof, such that no detailed discussion of the apparatus need be presented herein. The primary requirement for crushing and grinding of the lump coal is that coarse coal usually having an average particle diameter in excess of 0.08 inch and, typically, about 0.25 to 2.0 inches must be processed thereto and reduced in size to an average particle diameter which would be of at least a 8 Tyler screen size and, preferably, would be reduced to an average particle size for 14 Tyler screen size. As used herein the term Tyler screen refers in all instances to the commercial Tyler Standard Screens. The correlation between Tyler screen mesh and average particle diameter is as follows:

Tyler screen mesh-Average diameter of particles D in.

The conditions during the pulverization step may be varied widely according to the desires of those skilled in the art and practicing this invention. The temperature, of course, may be varied over a relatively broad range, from essentially atmospheric temperature to a relatively high temperature. It is distinctly preferred in the practice of this invention that the temperature of the coal and the solvent be maintained at a relatively high temperature, say, from 300 C. to 500 C. The pressure, in similar manner, may be varied over an extremely wide range from atmospheric pressure to, say, 10,000 p.s.i.g. with a preferred pressure being about p.s.i.g. or, typically, about 70 p.s.i.g.

The operation of the pulverization equipment is preferably performed so that the oversized material; that is, greater in size than the 8 Tyler screen size, be separated and returned to the apparatus for further pulverization. The utilization of the closed circuit technique is well known to those skilled in the art and is preferred in the practice of this invention. Unless otherwise stated, closed circuit operation of the pulverization equipment will be deemed inherent in the practice of this invention.

The amount of solvent which is used in the present invention generally will range from 0.2 to 10 pounds of solvent per pound of coal. Satisfactory results may be obtained in utilizing approximately equal amounts of solvent to coal on a weight basis. In the practice of the preferred embodiment of this invention, the conditions during the pulverization step should be chosen such that the coarse coal is reduced in size to at least a -8 Tyler screen size and the solvent has a chance to react and dissolve the coal to an extent such that the coal particles are at least partially dissolved in the solvent. As more fully developed hereinbelow, the conditions are chosen in the pulverization step such that from 10% to 40% of the m.a.f. coal is dissolved in the solvent with at least an additional 50% by weight being dissolved during the subsequent digestion zone.

Following the size reduction step wherein at least part of the coal has been dissolved in the solvent and oversized solid materials have been separated, the effluent product comprising solvent having dissolved therein liquid coal extract and undissolved solid coal is passed into the concentric tube a digestion zone which is a reaction zone of the present invention for the substantial conversion of the coal into liquid coal extract. The operating conditions for the digestion zone include a temperature from 300 C. to 500 C., a pressure from atmospheric to 10,000 p.s.i.g., a solvent to coal weight ratio from 0.2 to 10, and a residence time from 30 seconds to 5 hours, suflicient to dissolve coal such that a total in excess of 50% by weight of m.a.f. coal has been liquefied. It is to be noted that the temperature and pressure conditions during the digestion zone may be the same, may be higher, may be lower, or may be any different configuration desired by those skilled in the art over those conditions maintained in the pulverizatipn zone. It has been found satisfactory in the practice of this invention that the temperature and pressure in the digestion zone be maintained essentially at the same level as the temperature and pressure maintained in the pulverization zone. Additionally, it has been found that significant efficiencies of operation of the concentric tube digestion zone may be obtained by imposing an increasing temperature gradient across the digestion zone. In other words, the lower end of the inner tube should be maintained at a relatively low temperature whereas the withdrawal of the liquid extract through the perforations in the upper section of the tube should be at a relatively high temperature. Preferably, the relatively low temperature in the lower section of the tube should be from 350 C. to 400 C., preferably, 380 C. and the relatively high temperature at the upper section of the tube should be from 400 C. to 500 C., typically, 430 C.

Since the purpose of the digestion zone, including in the preferred embodiment the pulverization and the digestion zones, is to substantially complete the conversion of the coal into a liquid coal extract, it may be desirable to add to the digestion zone additional solvent, add a hy drogen-containing gas to the digestion zone, and/or utilize a catalyst in the digestion zone. The catalyst used may be conventional, may be homogenous or heterogenous and may be introduced in the pulverization zone and/ or digestion zone in admixture with the liquid solvent or with the solid coal. Those skilled in the art, from a knowledge of the characteristics of the coal, solvent and the properties desired for the end product will know whether or not it may be desirable to use any or all of these desirable features in the digestion zone. Conventional hydrogenation catalyst may be desirable, such as palladium on an alumina support or a cobalt-molybdate catalyst or any other hydrogenation catalyst known to those skilled in the art and applicable to the solventcoal system environment maintained in the digestion zone including the use of a slurry-catalyst system. Hydrogenation in the digestion zone generally accomplishes the following functions: transfer of hydrogen directly to coal molecules; transfer of hydrogen to hydrogen donor molecules; transfer of hydrogen from hydrogen donor molecules to coal molecules; and, combinations of above. Homogenous catalysts may be introduced with the coal, or hydrogen donor compounds, in the pulverization step of the digestion zone. Examples of catalysts suitable include compounds containing tin, nickel, molybdenum,

tungsten, and cobalt. By way of emphasis, as used herein, the term extraction zone is intended to include the pulverization step, the digestion step, or the combined pulverization-digestion step.

After separation of the solvent and undissolved coal residue (and catalyst, if any) from the total effluent of the digestion zone, the liquid coal extract is further processed by means known to those skilled in the art, such as conventional hydrogenation treatment to convert the liquid coal extract into more valuable products, such as fuel, e.g., gasoline boiling range products and/or chemicals, such as aromatic hydrocarbons, the utility of which is well known. The invention may be more fully understood with reference to FIG. 1 and FIG. 2 which are detailed schematic representations of apparatus for practicing the present invention.

DESCRIPTION OF THE DRAWINGS Referring now to FIG. 1, coarse coal having an average particle diameter generally in excess of 0.08 inch is introduced into the system via line 10. A suitable selective solvent enriched in hydrogen content is introduced into admixture with the coarse coal from line 11, the source of which is more fully discussed hereinafter. As previously mentioned, the oversized solid material from the pulverization zone is also preferably returned to the pulverization zone via line 12. The entire admixture of coarse coal and solvent is passed via line 13 anto mill 14 which conventionally may be of the ball mill type.

Suitable pulverization conditions including a temperature of about 380 C., a pressure of about 70 p.s.i.g., and a solvent to coal weight ratio of about 1 is maintained in mill 14 such that the coarse coal is reduced to an average particle diameter between 0.08 inch and 0.04 inch and at least a portion of the coal, say, about 17% by weight is dissolved into the solvent.

The effluent from mill 14 containing solvent having dissolved therein the liquid coal extract, undissolved coal of proper small particle size, and undissolved coal of oversize is passed via line 15 into separator 16 which may be of the cyclone type. Conditions are maintained in separator 16 whereby the oversized coal particles, preferably, in admixture with at least a portion of the liquid material is removed via line 12 and returned to mill 14 in a manner previously discussed.

The solvent having dissolved therein the liquid coal extract plus undissolved pulverized coal (and insoluble inorganic material) is passed via line 17 into digestion zone 19 which contains concentric tube 22 placed in shell 33. Inner tube 22 contains perforations 23 which are just large enough to allow the passage of liquid therethrough while prohibiting the passage of any substantial amounts of solid material therethrough. Added solvent, if any, may be introduced into the system via line 18 in an amount sufficient to maintain the solvent-coal ratio at the desired level and/ or to maintain the hydrogen content of the solvent present in digestor 19 at a sufficiently high level. Furthermore, catalyst (from means not shown) may be advantageously used in the digestion and/ or extraction step. The material in inner tube 22 passes upwardly until it reaches the perforation zone 23 wherein liquid coal extract plus solvent pass through the perforations into the shell 33 of digestor 19. Since the operation is continuous, the retained solid material wet with solvent and oil is removed from digestor 19 via line 21. Typically, the solid material removed from line 21 may contain from 25% to 50% by weight liquid. In any event, at least by volume of the liquid material is passed into shell 33. As previously mentioned, if desired, by means not shown an antisolvent, such as a light hydrocarbon of the hexane type, may be added into the inner tube 22 at a location close to perforation zone 23 in an effort to further aid in removing tars and solid materials from the desired solvent and liquid coal extract. If an antisolvent is used, then, of course, the material in the shell 33 also will contain such light hydrocarbon.

The liquid coal extract plus solvent is passed out of shell 33 via line 20 into fractionation zone 24 which may be of a conventional distillation column type. Suitable conditions are maintained therein such that a distillate fraction comprising light hydrocarbons may be withdrawn via line 26 and the liquid coal extract may be removed via line 25 for further processing in accordance with the practices known to those skilled in the art, including hydrogenation techniques for upgrading the liquid coal extract to the desired valuable products of motor fuel and/or chemicals. Means (not necessarily shown) for removing the antisolvent, if any, may be also incorporated broadly into fractionation zone 24.

In the practice of the present invention, a material suitable in boiling range, in characteristics as a selective solvent for the coal, is withdrawn from fractionation zone 24 via line 27 and, in a preferred embodiment of this invention, passed into hydrogenation zone 29. Hydrogen is introduced into hydrotreater 29 through conduit 30 to supply the required hydrogen. Generally, this hydrotreating step may be carried out by any means known to those skilled in the art of hydrotreating. The purpose of the hydrogenation zone is to restore hydrogen balance to the solvent in order to maintain efliciency of extraction both in the pulverization step and digestion step previously discussed. Preferably, hydrotreating catalyst is loaded into a fixed bed, not shown, within reaction zone 29. The material in line 27 is mixed with fresh hydrogen from line 30, by means not shown, and recycle gas from a source not shown, heated and passed at once through the fixed bed of catalyst. A hydrotreated efiluent is withdrawn from the reaction zone and cooled and introduced into a separator, all by means not shown. The efiluent is separated into a normally hydrotreated product and a normally gaseous stream. As those in the art are familiar, the normally gaseous stream containing hydrogen is recycled to the reaction zone by means not shown. The

normally liquid product stream may be fractionated or stripped to remove dissolved gases, such as hydrogen or hydrogen sulfide or, if desired, this step may be omitted.

By way of emphasis, it is to be noted that the sequence of steps and equipment required for hydrogenation is well known to those skilled in the art and has not been shown in the drawing; rather, all steps and equipment necessary for practicing hydrogenation are embodied in the box shown as hydrogenation zone 29 in the drawing.

The hydrogenation catalyst is preferably sulfur resistant and comprises a silica-alumina support having at least one metal or metal compound of Group VI of the Periodic Table and one metal or metal compound of Group VIII of the Periodic Table. Especially preferable in the practice of this invention are those hydrogenation catalysts having tungsten and/or molybdenum along with nickel and/or cobalt on silica-alumina supports. Other supports such as alumina, silica-zirconia, silica-magnesia, faujasite, mordenite, inorganic oxide matrix containing at least one crystalline aluminosilicate, etc., are also suitable. Other metals which are also satisfactory include the noble metals such as platinum or palladium. These latter noble metal catalysts are generally satisfactory without the presence of a Group VIII metal.

The hydrotreating conditions employed in hydrogenation zone 29 are selected to convert the solvent separated from the eflluent of the extraction zone to a product having increased hydrogen content. Suitable pressure ranges are from about 400 p.s.i.g. to about 2,000 p.s.i.g., preferably, from 600 p.s.i.g. to 900 p.s.i.g. Suitable liquid hourly space velocity by weight (LHSV) is from about 0.5 to about 20, preferably, from 3 to 10. The hydrogen-to-oil mole ratio may be from 2 to 20, preferably, from to 15. Typically, the temperature will be in the range from 232 C. to about 454 C.

The properly hydrogen enriched solvent stream is removed from hydrogenation zone 29 via line 31 and returned to the digestion zone via line 11 and/or line 1 8, as previously mentioned. Additional suitable solvent, if necessary, may be added to the system from a source not shown via line 32. In addition, for control purposes a by-pass of solvent material around hydrogenation zone 29 may be accomplished by means of line 28. Normally, a small amount of material will always be flowing in line 28 so as to provide flexibility of control on the hydrogen content of the material flowing in line 31.

As previously mentioned, it may be highly desirable to add hydrogen gas and a catalyst to digestion zone 19. The means by which such materials may be additionally added to digestor 19 have not been shown since those skilled in the art from general knowledge and the teachings presented herein would know how to add these further improvements to the inventive method of the present invention.

Referring now to FIG. 2, there is shown an apparatus in combination which comprises a vertically disposed shell 33 having at least one conduit 22 extending through the shell in concentric fashion. Means for introducing liquids and solids into the inner tube 22 via line 17 can be by any means known to those skilled in the art. One such means would be a screw conveyor which would carry the feed material through the filter section 23, would compress the solids in the filter section, thereby forcing the liquid through the holes in zone 23 into the space 37 of shell 33. Another method of reaching the same result would be to have a higher pressure in tube 22 than is maintained in space 37. Additionally, the apparatus includes outlet means 21 for withdrawing solid material from the inner tube 22 and outlet means 20 for removing liquid from shell 33.

In addition, there is shown inlet means 34 for introducing hydrogen gas into admixture with the feed material in line 17 and additional outlet means 38 located in the upper section of shell 33 to remove gaseous materials from the eflluent which passed through perforations 23 into space 37.

In operation, pulverized coal including solvent and catalyst, if desired, is passed via line 17 as a slurry into the lower end of inner tube 22. Hydrogen gas may also be introduced with the feed material via line 34. The entire mixture passes upwardly through inner tube 22 until it reaches filtration zone 23 containing a series of orifice openings having a small enough diameter to prevent the passage through of solid materials having an average diameter of five (5) microns or larger.

The liquid coal extract plus solvent, hydrogen gases, and other light gases pass through the perforations in zone 23 into space 37 of shell 33. The insoluble material comprising inorganic material, such as ash, plus any undissolved coal pass out of the system from inner tube 22 via line 21. The material which has passed through filtration zone 23 into space 37 of shell 33 is separated therein with the gaseous materials being removed from shell 33 via line 35. The accumulated liquid coal extract plus solvent is withdrawn from shell 33 via line 20. If desired, a portion of the liquid coal extract may be returned to the digestion zone via line 35. In addition, should there be a significant quantity of undissolved coal in the solid material being removed via line 21, a portion thereof may be returned to the extraction step via line 36.

It is to be noted that the digestion zone comprising shell 33 and tube 22 is, in effect, of well known shell and tube design. The embodiments of the present invention include the use of at least one tube 22 within shell 33, but may include a plurality of tubes 22 depending upon the design parameters utilized by those skilled in the art. A typical commercial configuration would include a shell having a diameter of eight (8) feet and containing 1,000 to 5,000, typically, 4,000 tubes 22 of 2 to 3 inches in diameter. The perforations in zone 23 of tube 22 may be placed in any manner desired by those skilled in the art. It is distinctly preferred, however, that the perforated area of tube 22 occur over less than 75% of the length of the conduit. However, the perforations may occur over any portion of tube 22 with the preferred arrangement being that all of the perforations be contained in the upper one-half of tube 22. The diameters of the holes or orifices may range from five microns to .093 inch in diameter sufiicient to prevent the passage therethrough of any significant amount of solid material. The geometry of the hole spacing is not critical in the practice of this invention.

PREFERRED EMBODIMENT A preferred embodiment of the invention includes a method for liquefying coal which comprises the steps of: (a) admixing coarse size bituminous coal with solvent selective for dissolving coal; (-b) introducing the solventcoarse coal admixture into a pulverization zone under conditions including a temperature from 300 C. to 500 C., pressure from atmospheric to 10,000 p.s.i.g., solvent to coal ratio from 0.2. to sufficient to reduce said coarse coal to at least a 8 Tyler screen size and to partially dissolve coal into said solvent; (c) passing the pulverized coal-solvent product including dissolved coal at a relatively low temperature into the lower end of at least one smaller conduit disposed concentrically in a larger conduit; (d) passing said coal-solvent product upwardly through said smaller conduit under digestion conditions including a temperature from 300 C. to 500 C. pressure from atmospheric to 10,000 p.s.i.g., solvent to coal weight ratio from 0.2 to 10, and a residence time from seconds to 5 hours sufficient to dissolve coal such that a total in excess of 50% by weight of m.a.f. coal is liquefied as liquid coal extract; (e) Withdrawing said liquid coal extract at a relatively high temperature through at least one opening in the upper section of said smaller conduit into the larger conduit such that solid material is substantially retained in said smaller conduit; (f) removing solid material from the upper end of said smaller conduit; and (g) recovering liquid coal extract from said larger conduit.

Another preferred embodiment of the present invention includes the method hereinabove wherein said digestion conditions include the presence of hydrogen gas and still further includes the presence of a catalyst.

I claim:

1. Method for liquefying coal which comprises the steps of:

(a) admixing coarse size bituminous coal with solvent selective for dissolving coal;

(b) introducing the solvent-coarse coal admixture into a pulverization zone under conditions including a temperature from- 300 to 500 0, pressure from atmospheric to 10,000 p.s.i.g., solvent to coal ratio from 0.2 to 10 suificient to reduce said coarse coal to at least a 8 Tyler screen size and to partially dissolve coal into said solvent;

(0) passing the pulverized coal-solvent product including dissolved coal at a relatively low temperature into the lower end of at least one smaller conduit disposed concentrically in a larger conduit;

(d) passing said coal-solvent product upwardly through said smaller conduit under digestion conditions including a temperature from 300 C. to 500 C., pressure from atmospheric to 10,000 p.s.i.g., solvent to coal weight ratio from 0.2 to 10, and a residence time from 30 seconds to 5 hours suflicient to dissolve coal such that a total in excess of 50% by weight of m.a.f. coal is liquefied as liquid coal extract;

(e) withdrawing said liquid coal extract at a relatively high temperature through at least one opening in the upper section of said smaller conduit into the larger conduit such that solid material is substantially retained in said smaller conduit;

(f) removing solid material from the upper end of said smaller conduit; and

(g) recovering liquid coal extract from said larger conduit.

2. Method according to claim 1 wherein said digestion conditions include the presence of hydrogen gas.

3. Method according to claim 2 wherein said digestion conditions include the presence of a hydrogenation catalyst.

4. Apparatus comprising in combination: a vertically disposed, enclosed shell having at least one conduit extending through said shell in parallel relationship with the vertical axis of said shell, means for introducing a mixture of solid and liquid materials into the lower end of said conduit, first outlet means for removing solid material from the upper end of said conduit, perforate means in the upper section of said conduit occurring over less than of the length of said conduit providing a passageway for liquid between said conduit and said shell, and second outlet means for withdrawing liquid from said shell.

5. Apparatus according to claim 4 wherein said perforations comprise orifice openings having a small enough diameter to prevent the passage therethrough of solid particles having an average diameter of five (5) microns or larger.

References Cited UNITED STATES PATENTS 2,595,979 5/1952 Pevere et a1. 2088 2,453,633 11/1948 Logan 19614.52

769,531 9/1904 Bremer 202-254 2,851,396 9/1958 Myers 19614.52

690,693 1/1902 Von Boyen 2088 2,885,337 5/1959 Keith et a1. 2088 2,784,148 3/1957 Edmonds et a1. 2088 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner US. 'Cl. X.R.

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