US 3505203 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
April 7, 1970 E. F. NELSON SOLVENT EXTRACTION METHOD Filed June 26. 196'? United States Patent O 3,505,203 SOLVENT EXTRACTION METHOD Edwin F. Nelson, Arlington Heights, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed June 26, 1967, Ser. No. 648,872 Int. Cl. Cg 1/00 U.S. Cl. 208-8 7 Claims ABSTRACT OF THE DISCLOSURE Method for the liquefaction of coal via solvent extraction using a hydrogen-donor selective solvent. The method contacts pulverized coal with a solvent, such as Tetralin, to produce a liquefied coal extract dissolved in the solvent which now has a lower hydrogen content. Following separation of the liquid coal extract from the hydrogen deficient solvent, the solvent is regenerated via selective catalytic hydrogenation. 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 using a hydrogen-donor solvent wherein the hydrogen content of the recycle solvent stream is increased via selective hydrogenation.
It has long been known that hydrocarbon gases, liquids and 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 for obtaining useful fuels and chemicals from a coal whereby the coal is contacted with a selective solvent which acts as a hydrogen donor for supplying suflicient hydrogen to the coal to aid in converting it into a liquid phase. Following the solvent extraction step, the prior art schemes have utilized various 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 products into more valuable products.
Sinceit is clear to those skilled in the art that the vast mineral reserves of bituminous coal represent an extremely important supply of energy, it would be desirable to improve upon the prior art process, 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 of 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 improved method for subjecting pulverizer coal to solvent extraction using, for example, Tetralin as the solvent.
It is another specific object of this invention to provide an improved method for the liquefaction of coal via solvent extraction whereby increased eiiiciency of the solvent recovery step is significantly increased in a facile and economical manner.
Therefore, in accord-ance with the particle of one em- 3,505,203 Patented Apr. 7, 1970 ICC bodiment of this invention, there is provided a method for liquefying coal which comprises passing bituminous coal and a hereinafter specified hydrogen-rich solvent into an extraction zone under conditions suicient to convert said coal substantially to liquid coal extract dissolve in solvent having reduced hydrogen content, separating the solvent containing liquid coal extract into a residual fraction comprising substantially solvent-free liquid coal extract and a fraction comprising solvent having reduced hydrogen content, passing at least a portion of said solvent fraction into a hydrogenation zone under conditions sufficient to increase the hydrogen content of the solvent, thereby producing a hydrogen-rich solvent, and returning hydrogen-rich solvent to the extraction zone as specified.
Another embodiment of the invention includes the method hereinabove wherein said extraction zone includes the step of pulverizing coarse size feed coal in the presence of said hydrogen-rich solvent.
Thus, it is to be noted from the description of the present invention presented thus far that the benefits to be derived from the practice thereof are predicated on the continual recycle of the solvent to the extraction zone in a manner which utilizes a hydrogenation step to maintain the ability of the solvent to transfer needed hydrogen from the solvent to the coal in order to aid in the liquefying process.
Another benefit to be derived from the practice of the present invention is predicated on the theory that having the presence of the hydrogen-rich solvent during the pulverization step of the coal results in a substantial increase in the efficiency of the operation and complementing the hydrogenation step results in a decreased use of solvent for obtaining the same 4amount 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 transferred 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 are 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 furt-her improve upon the inventive concepts contained herein.
Additionally, there has been some discussion in the prior art that the presence of oxygen or oxygen compounds on the surface of the coal makes it diiiicult for the coal to react properly with the suitable solvents for the conversion thereof into liquid coal extract. Therefore, by pulverizing or crushing the coal in the presence of a liquid solvent, oxygen compounds or the presence of oxygen have been excluded from the highly reactive shear sites along the coal thereby enabling the transfer of the hydrogen from the solvent to the coal to become of signiiicantly increased efficiency.
The coal preferred for use in the practice of the present inventive method is of the bituminous type, such as Pittsburg 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 m.a.f. coal (moisture and ash-free coal).
The extraction of coal by means of solvent has been proposed Iby delinition as partial conversion of the coal since not only isthe coal reacted with the hydrogen which is transferred from the solvent, but there is also a solution phenomenon which actually dissolves the coal which has accepted the hydrogen into the solvent. Therefore, as used herein, the term liquid coal extract and liquefied coal fraction 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 extract comprises hydrocarbons suitable for use as the solvent. The practice of the present invention is performed under conditions which increase the kinetics of the reaction while maintaining the components therein in 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 vaporous pulverization technique.
Suitable solvents for use in the practice of this invention are those which are of the hydrogen-donor type and are d at least partially hydrogenated and include naphthenic hydrocarbons. 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 (Tetralin), 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 in 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 anti-solvent, such as saturated parainic 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 the suitable solvent it must be recognized that the solvent must have the ability to transfer hydrogen to the pulverized coal during the extract step. In other words, 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. it has also been explained that another critical feature of this invention is the selective hydrogenation of the separated recycle solvent in order to increase its hydrogen content so that hydrogen may be more easily transferred from the solvent to the coal during the extraction step, as previously mentioned.
One of the convenient Ways of optimizing the speciiic hydrotreating operation is to use the J-factor analysis for determining the degree to which hydrogen has been added to the hydrogenation reaction zone feed. This analytical technique permits the characterization of various types of aromatics in a hydrocarbon mixture by means of the J-factor analysis. The technique utilizes mass spectrometer analysis employing a low ionizing voltage. The ionizing voltage is chosen such that only those hydrocarbons to be characterized are ionized While other hydrocarbon types are not ionized under the potential chosen. For example, since compounds more saturated than aromatic hydrocarbons, such as the paraiin hydrocarbons, have an ionization level above 10 volts, the ionization chamber is thus maintained at a potential of about 7 volts so that only the aromatic hydrocarbons are ionized and the saturated compounds will not be observed on the mass spectrum. As those skilled in the analytical art know, the mass spectrum reveals molecular ion peaks which correspond to the molecular Weight of the aromatic cornpound. Thus, the technique permits characterization of the aromatic hydrocarbons by means of the general formula CH2n J where J is the herein referred to i-factor for the practice of the present invention. The following table shows the relationship between the J-factor and the type of aromatic.
J-factor number: Type of aromatic hydrocarbon 6 Alkyl benzenes and benzene.
' 8 Indanes, Tetralins.
10 Indenes. 12 Alkyl naphthalenes and naphthalene. 14 Acena-phthenes, tetrahydroanthracene. 16 Acenaphthalenes, dihydroanthracenes. 18 Anthracenes, phenanthrenes.
Using this I-factor analysis in characterizing the hydrotreating step of the present invention allows for'the optimum treatment of said solvent to produce Va high quality hydrogen enriched solvent for use in converting coal into liquid coal extract. However, as previously mentioned, the important control technique of the present invention is that a hydrogen content of the initial solvent charged to the extraction zone in admixture with the coal is greater than the solvent leaving the extraction zone having dissolved therein the liquid coal extract. In similar manner, the other control technique is that the hydrogen content of the solvent which has been recovered from the effluent of the extraction zone is less than the hydrogen content of the solvent leaving the hydrogenation zone and being recycled to the extraction zone. The .i-factor analysis is simply a convenient means for optimizing the hydrotreating step in the practice of this invention.
Apparatus for use in pulverizing the lump or coarse coal feed to the present invention may be of 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 signicant quantities of liquid solvent without diiculty. 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:
Average diameter of Tyler screen mesh: particles Davg 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 atmospherictemperature 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 temperaure,
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 100 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 invenion.
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 resultsmay 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 thesolvent 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%4 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 efliuent product comprising solvent having dissolved therein liquid coal extract and undissolved solid coal is passed into a digestion zone which is a reaction zone 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 l0 and a residence time from 30 seconds to 5 hours suicient to dissolve coal such thata 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 conguration desired by those skilled in the art over those conditions maintained in the pulverization zone. It has been found satisfactory in the`practice of this invention that the temperaure and pressure in the digestion zone be maintained essentially at the same level as the temperature and pressure maintained in the pulverization zone.
Since the purpose of the extraction zone, including in the preferred embodiment the pulverization and 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 hydrogencontaining gas to the extraction zone, and/or utilize a catalyst in the extraction zone, including specifically 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 o r tions: 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 extraction zone. Examples of catalysts which are 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 pulverizationdigestion step.
After separation of the solvent and undissolved coal residue (and catalyst, if any) from the total eiuent 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,l 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 the appended drawing which is a schematic representation of apparatus for practicing one embodiment of the present invention.
DESCRIPTION OF THE DRAWING Referring now to the drawing, 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 into 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 and 0.04 inch and at least a portion of the coal, say, about 17% by weight is dissolved into the solvent.
The eluent 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 is passed via line 17 into digestion zone 19 which may be of a jacketed stirred type vessel. Added solvent, if any, may be introduced into the system via line 18 in an amount sufficient to maintain the solvent to coal ratio at the desired level and/or to maintain the hydrogen content of the solvent present in digester 19 at a suiciently high level. Further, catalyst (from means not shown) may advantageously be used in the digestion step.
The entire eluent from digestion zone 19 is passed via line 20 into filtration zone 21 wherein solid residue is separated from the rich solvent and removed'from the system via line 22. The mother liquor comprising solvent having dissolved therein liquid coal extract is removed from ltration zone 21 via line 23. As previously mentioned, if desired, by means not shown, an anti-solvent such as a light hydrocarbon of the hexane type may be added to filtration zone 21 in an eifort to further aid in removing tars and solid materials from the desired solvent and liquid coal extract. If an anti-solvent is used, then, of course, the material in line 23 also will contain such light hydrocarbon.
The liquid effluent from filtration zone 21 is passed via line 23 into fractionation zone 24 which may ibe 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 2S 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 product of motor fuel and/or chemicals. Means (not necessarily shown) for removing the anti-solvent, if any, may be also incorporated -broadly into fractionation zone 24.
In the practice of the present invention, a material suitable in boiling range as solvent for the coal is Withdrawn from fractionation Zone 24 via line 27 and passed into hydrogenation zone 29. Hydrogen is introduced into hydrotreater 29 through conduit 30 to supply the required hydrogen. Generally, the hydrotreating step may be carlied out by any means known to those skilled in the art of hydrotreating taking into account the previously mentioned J-factor analysis technique for controlling the degree of hydrogenation which is accomplished in hydrotreater 29. Preferably, hydrotreating catalyst is loaded into a fixed bed, not Shown, within the reaction zone. 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 once-through the fixed bed of catalyst. A hydrotreated effluent is withdrawn from the reaction zone and cooled and introduced into a separator, all by means not shown. The eiuent is separated into a normally liquid hydrotreated product and a normally gaseous stream. The normally gaseous stream contains hydrogen and is recycled to the reaction zone by means of a recycle compressor, again by means not shown. The normally liquid product stream may be llashed or stripped to remove dissolved gases, such as hydrogen and 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 the practice of hydrogeneration is well known to those skilled in the art and have not been shown in detail 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 v` 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. l
The hydrotreating conditions employed in hydrogenation Zone 29 are selected to convert the solvent separated from the effluent of the extraction zone to a product having increased hydrogen content such as an aromatic hydrocarbon of the 1 8 type, previously defined. Then, correspondingly, the rich solvent separated from the extraction zone has 1 12 as the major single type of laromatic hydrocarbon. Therefore, the hydrogenation process variable are controlled themaximize the 1 12 to 1 8 conversion reaction without substantial conversion of the polyfcyclic aromatic compounds to monocyclic aromatic compounds' of the 1 6 type. Suitable pressure ranges are from about 400 p.s.i.g. to about 2000 p.s.i.g., preferably,from 600 p.s.i.g. to 900 .p.s.i.g. Suitable liquid hourly space velocity by weight (LI-ISV) is from about 0.5 to about in Step (a) comprises Tetralin.
20, preferably, from 3 to 10. The hydrogen-to-oil mole ratio may be from 2 to 20, preferably, from 5 to 15. When these conditions are selected, the temperature is then adjusted to miximize the 1 12 to 1 8 conversion'. Normally, this temperature will be in the range from 232 C. to about 454 C. The most straight-forwardway of obtaining the proper operating conditions is to select the independent variables, conduct a 1 -factor analysis of the streams flowing in lines 27 and 31, and adjust the temperature to obtain the maximum conversion of 1 12 to 1 8. If the hydrotreating conditions are too severe, the 1-12 type compounds may be converted to the undesirable 1 6 compounds.
The properly hydrogen enriched solvent stream is removed from hydrogenation zone 29 via line 31 and returned to the extraction zone via line 11 and/or line 18, 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 bypass 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.
PREFERRED EMBODIMENT A preferred embodiment of the present invention includes a method for the liquefaction of coal which comprises the steps of: (a) admixing coarse size bituminous coal with a solvent comprising aromatic hydrocarbons substantially of the 1 8 type; (b) introducing the solventcoarse coal admixture into a pulverization zone under conditions including a temperature from 300 C. to 500 C., a pressure from atmospheric to 10,000 p.s.i.g., solvent to coal ratio from 0.2 to 10 suicient to reduce said coarse coal to at least a -8 Tyler screen size and at least partially dissolved coal into said solvent thereby simultaneously converting at least part of said 1 8 type aromatic hydrocarbons to 1 12 type; (c) passing the pulverized coal-solvent 4product including dissolved coal from the pulverization zone into a digestion zone maintained under 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 sufficient to dissolve coal such that a total in excess of 50% by weight of maf. coal is liquefied as liquid coal extract thereby converting additional 1 8 type hydrocarbons in the solvent to 1 12 type; (d) separating the total effluent from said digestion zone into a solid coal fraction, a fraction comprising liquid coal extract, and a solvent fraction containing 1-12 type aromatic hydrocarbons; (e) subjecting at least a portion of said solvent fraction to VVcatalytic hydrogenation in the presence of added hydrogen under conditions including a temperature from 232 C. to 454 C., pressure from 400 p.s.i.g. to 2000 p.s.i.g, liquid hourly space velocity (weight) from 0.5 to 20, and a hydrogen-to-oil mole ratio from 2 to 20 sufficient to convert 1 12'ty'pe aromatic hydrocarbons to 1 8 type; (f) returning hydrogenated solvent from Step (e) to Step (a-); and, (g) recovering liquid coal extract in high concentration.v v l l v vAnother preferred embodiment of the present invention includes the method hereinabove wherein said solvent The invention claimed: y 1.'Method forliquefying coal which comprises the steps of: 'Y l .v y YA.. .7..
(a) passing coarse size bituminous feed coal and a here- `in'after specified: solvent comprising aromatic hydrocarbons substantially ofthe 1 8 type into an extraction zone wherein said-coarse feed. coal is pulverized, maintaining ksaid extraction zone under conditions i sutiicient to substantially convert coal to liquid coal l extract thereby simultaneously converting at least part of said 1 8 type aromatic hydrocarbons to 1-12 type;
(b) separating the total eluent from said extraction zone into a solid coal fraction, a fraction comprising liquid coal extract, and a solvent fraction containing I l2 type aromatic hydrocarbons;
(c) subjecting at least a portion of said solvent fraction to catalytic hydrogenation in the presence of an added hydrogen-containing gas under conditions sufficient to convert 1 12 type aromatic hydrocarbons to 1 8 type, said conditions being controlled to obtain substantial `l-l2 to 1 8 conversion without substantial conversion of polycyclic aromatic compounds to monocyclic aromatic compounds of 1 6 type;
(d) returning hydrogenated solvent to Step (a) as said specified solvent; and,
(e) recovering said liquid coal extract fraction.
2. Method according to claim 1 wherein said specified solvent comprises Tetralin.
3. Method according to claim 2 wherein said extraction zone conditions include 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 10.0, and a residence time from 30 seconds to 5 hours sutiicient to convert coal to liquid coal extract in an amount exceeding 50% by weight of maf. coal.
4. Method according to claim 1 wherein said catalytic hydrogenating conditions include a temperature from 232 C. to 454 C., pressure from 400 p.s.i.g. to 2000 p.s.i.g. liquid hourly space velocity (weight) from 0.5 to 20, and a hydrogen-to-oil mole ratio from 2 to 20.
5. Method for the liquefaction of coal which comprises the steps of:
(a) admixing coarse size ybituminous coal with a solvent comprising aromatic hydrocarbons substantially of the I-8 type;
(b) introducing the solvent-coarse 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 10 suicient to reduce said coarse coal to at least a -8 Tyler screen size and at least partially dissolve coal into said solvent thereby simultaneously converting at least part of said 1 8 type aromatic hycarbons to 1 12 type;
(c) passing the pulverized coal-solvent product including dissolved coal from the pulverization zone into a digestion zone maintained under 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 l0, and a residence time from 30 seconds to 5 hours suicient to dissolve coal such that a total in excess of by weight of maf. coal is liqueed as liquid coal extract thereby converting additional 1 8 type hydrocarbons in the solvent to J- 12 type; (d) separating the total effluent from said digestion zone into a solid coal fraction, a fraction comprising liquid coal extract, and a solvent fraction containing J l2 type aromatic hydrocarbons;
(e) subjecting at least a portion of said solvent fraction to catalytic hydrogenation in the presence of added hydrogen under conditions including a temperature from 232 C. to 454 C., pressure from 400 p.s.i.g. to 2000 p.s.i.g., a liquid hourly space velocity (weight) from 0.5 to 20, and a hydrogen-to-oil mole ratio from 2 to 20 sufcient to-convert 1 12 type aromatic hydrocarbons to 1 8 type without substantial conversion of polycyclic aromatic compounds to monocyclic aromatic compounds of 1 6 type;
(f) returning hydrogenated solvent from Step (e) to Step (a); and,
(g) recovering liquid coal extract in high concentration.
6. Method according to claim 5 wherein said coarse coal is reduced in Step (b) to an average particle diameter between 0.08 inch and 0.04 inch.
7. Method according to claim 5 wherein said solvent in Step (a) comprises Tetralin.
References Cited UNITED STATES PATENTS 3,018,242 l/l962 Gorin 208-10 1,940,648 12/1933 Russell 208-8 1,934,023 11/1933 Wright 208-10 3,018,241 1/1962 Gorin 208-8 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner U.S. Cl. X.R. 208-10