US3503864A

US3503864A - Coal liquefaction method

Info

Publication number: US3503864A
Application number: US694522A
Authority: US
Inventors: Edwin F Nelson
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1967-12-29
Filing date: 1967-12-29
Publication date: 1970-03-31
Anticipated expiration: 1987-03-31

Description

Solvenf /A/VENTOR: Edwin F. Nelson /nog as/aog/ TTO-R/VEYS United States Patent O 3,503,864 COAL LIQUEFACTION METHOD Edwin F. Nelson, Arlington Heights, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Dec. 29, 1967, Ser. No. 694,522 Int. Cl. Cg 1/04, 1/06 U.S. Cl. 208-10 3 Claims ABSTRACT 0F THE DISCLOSURE 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 obtaining valuable liquid hydrocarbons from coarse particulate coal utilizing steps of solvation, hydrogenation, and coking.

It has long been known that hydrocarbon gases, liquids, pitch and chemicals 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 developed for obtaining useful fuels and chemicals from coal whereby the coal is contacted with a selective solvent which acts as a hydrogen donor for supplying suilicient hydrogen to the coal to aid in converting it into a liquid state. Following such a 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. However, none of the aforementioned prior art procedures have been commercially efficient or feasible to warrant widespread commercial exploitation of converting coal into liquid products. Generally, the deficiencies in the prior art schmese have not only involved capital investment problems, but also involved disposal problems of the residue or waste frequently having high metals content, but also involves liquid product quantity and quality problems which have yet to be solved in an economical and facile manner.

Since it 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 techniques, particularly the solvent extraction technique in order to reduce the cost of obtaining high quality 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 liquid hydrocarbons are obtained therefrom.

' It is a specilic object of this invention to provide an improved method for subjecting pulverized coal to solvent extraction for the conversion thereof into valuable liquid hydrocarbons.

It is another specific object of this invention to provide an improved method for the liquefaction of coarse particulate coal via solvent extraction in a facile and economical manner.

Therefore, in accordance with the practice of one embodiment of this invention, there is provided a method for obtaining valuable liquid hydrocarbons fromy coarse particulate coal which comprises: (a) passing said coal and coal solvent into a pulverization zone under conditions suihcient to reduce the size of coal and to at least partially dissolve said coal; (b) introducing the pulverized coal-solvent including dissolved coal into a digestion zone under conditions including the presence of an added hydrogen-containing gas suiiicient to substantially dissolve said coal, thereby producing liquid coal extract having increased hydrogen content; (c) passing said liquid coal extract into a reaction zone maintained under coking conditions; (d) withdrawing from said reaction zone coke and hydrocarbons including normally liquid hydrocarbons; and, (e) recovering valuable liquid hydrocarbons from said withdrawn hydrocarbons.

Another embodiment of this invention includes the method hereinabove wherein said digestion zone conditions include the presence of hydrogenation catalyst.

Thus, it is to be noted from the description of the present invention presented hereinabove that the benefits to be derived from the practice thereof are predicated on the presence of solvent in the pulverization zone, the presence of hydrogen and, preferably, a hydrogenation catalyst in the digestion zone, and the utilization of a coking unit in a facile and economical manner for producing valuable liquid hydrocarbons from coarse particulate coal. It is believed that one of the reasons the practice of the present invention produces such desirable results is theA manner in which hydrogen balance is maintained in the system. For example, during the pulverization operation, it is believed that hydrogen is transferred from the solvent to the coal, thereby aiding in the conversion of at least part of the coal into a liquid. It follows, therefore, that in the pulverization zone, the solvent becomes reduced in hydrogen content. The product from the pulverization zone is next passed into a digestion zone in the presence of an added hydrogen-containing gas. It isbelieved that the presence of hydrogen still further facilitates the conversion of coal into a liquid while simultaneously restoring the hydrogen content to the solvent. By operating in this manner, preferably utilizing a hydrogenation catalyst in the digestion zone, one of the ultimately recovered hydrocarbon products is now imminently suitable for recycle to the pulverization zone, since its hydrogen content has been restored to the proper level. Still further, the utilization of the coking operation on the entire liquid coal extract, rather than a selected portion thereof, produces signicantly upgraded hydrocarbons in both quantity and quality over the processing schemes previously disclosed by the prior art.

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 subsequent hydrogenation step, i.e., digestion results in a decreased use of solvent for obtaining at least the same amount of liquid coal extract as obtained in the prior art process.

With respect to he 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 than if the coal is pulverized prior to contact with the sOlvent. In addition, the smaller particles of coal Which are sheared away from a relatively large lump immediately exposes not only the highly reactive shear site to the solvent, but also exposes an extremely large surface area to the solvent, thereby enabling the resulting small particles of coal to almost immediately dissolve in the solvent and become a part of the liquid coal extract.

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 difficult for the coal to react properly with the suitable solvents for the conversion thereof into liquid coal extract. It is further believed, therefore, that by pulverizing or by 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 further enabling the transfer of the hydrogen from the solvent to the coal to become significantly 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 solids content greater than about 20 wt. percent of maf. coal (moisture and ash-free coal). Although the invention will be described with reference to the conversion of bituminous coal to valuable liquid hydrocarbons, it is Within the concept of the present invention to apply the i11- ventive method to sub-bituminous coal, lignite, and other solid carbonaceous materials of natural origin.

The extraction of coal .by means of a selective solvent is, by definition, a partial conversion of the coal since not only is the coal reacted with the hydrogen which is transferred from the solvent, but is also reacted with the hydrogen which is added during the digestion step. In addition, there is also a solution phenomenon which actually dissolves the 4coal which has accepted the hydrogen into the solvent. Therefore, as used herein, the terms liquid coal extract and liquefied coal fraction or other Words of similar import are intended to include the liquid product which is obtained from the solvent extraction of the coal with the selective solvent, including the liquid product obtained from the digestion step as practiced herein, and generally will be described on the basis of being solventfree even though a portion of the extract comprises hydrocarbon Suitable for use as the solvent. The practice of the present invention is preferably performed under conditions which increase the kinetics of the reaction while maintaining the components there in primarily liquid phase, although in some cases it may be desirable to practice this invention in the presence of a vapor-ized solvent by using a vaporous pulverization technique. It is recognized, however, that the coking operation will produce hydrocarbons primarily in a vaporous state and will be preferably transferred in its vaporous state from the coking unit directly into separation facilities, such as fractionation equipment.

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 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 iinal 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), decahydronaphtalene (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 corn'- pounds such as phenols, cresols, and xylenols. It is also to be recognized that in some casesit 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 parafnic 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 the solvent rnust have the ability t0 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 pulverization zone having coal dissolved therein has a reduced hydrogen content compared to the hydrogen content of the lean solvent which is added to the pulverization zone in admixture with the feed. It has also lbeen explained that another critical feature -of this invention is the selective hydrogenation of the solvent during digestion in order to increase its hydrogen content so that hydrogen may be more easily transferred from the solvent to the coal during the pulverization step, as previously mentioned.

One of the convenient ways of optimizing the specific 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 I-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 paraiiin hydrocarbons, have an ionization level above l0 volts, the ionization chamber is thus maintained at a potential of about 7 volts so that only the aromaic 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 compound. Thus, the technique permits characterization of the aromatic hydrocarbons by means of the general formula CnH2n J where I is the herein referred to T-factor for the practice of the present invention. The following table shows the relationship between the J-factor and the type of aromatic.

I -factor number: Type of aromatic hydrocarbon 6 Alkyl benzenes and benzene.

8 Indanes, Tetralins.

10 Indenes.

12 Alkyl naphthalenes and naphthalene. 14 Acenaphthenes, tetrahydroanthracene. 16 Acenaphthalenes, dihydroanthracenes. 18 Anthracenes, phenanthrenes.

Using this J-factor analysis in characterizing the hydrotreating step of the present invention allows for the optimum treatment of said solvent to produce a 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 pulverization 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 pulverization zone is less than the hydrogen content of the solvent leaving the digestion zone and being recycled to the pulverization zone. The .T-factor analysis is simply a convenient means for optimizing the hydro'- treating step in the prac-tice 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. Conventiontal ball mills or rod mills may be used with satisfactory results. Preferably, the apparatus must be able to pulverize lump of coarse coal in the presence of signicant 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:

Average diameter 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 temperfature, 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 invention.

The amount of solvent which is used in the present invention generally will range from 0.2 to pouds of solvent per pound of coal. Satisfactory results may be obtained in utilizing approximately equal amounts of S01- vent 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 maf. 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 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 10, a residence time from 30 seconds to 5 hours, and the presence of hydrogen, sufficient 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 lighter, may be lower, o1' may be any different configuration 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 temperature and pressure in the digestion zone be maintained essentially at the same levelas 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 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 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 cobaltmolybdate catalyst or any other hydrogenation catalyst known to those skilled in the art and applicable to the solvent-coal 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 the above. Homogenous catalysts may be introduced with the coal, or hydrogen donor compounds, in the pulverization step of the extraction zone. Examples of catalyst 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 gaseous materials, including hydrogen, undissolved coal residue, and catalyst, if any, from the total eflluent of the digestion zone, the liquid coal extract is passed, preferably in its entirety, into a conventional coking zone. However, if desired, a portion of the total liquid coal extract can be recycled without further treatment to the pulverization zone and/or digestion zone. The coking zone is preferably a delayed coker and comprises a plurality of coke drums. The heated liquid coal extract is passed into a first coking drum wherein it is decomposed into coke and a vaporous effluent containing normally gaseous hydrocarbons. Following reaction in the first drum, the charge is alternated to a second coking drum and the operation is repeated while the first drum is cooled down and the coke removed therefrom. Those skilled in the art are familiar with the delayed coking technique, so detailed instructions thereon need not be presented here. However, briefly, coking conditions include a temperature from 400 C. to 800 C., sufficient to produce coke having a volatile content from 5% to 30% by weight.

Following the coking operation, the efiluent therefrom is passed, preferably in its vaporous state, directly into separation facilities. which typically comprise a fractionation column for the separation therein of the effluent into valuable liquid hydrocarbons, such as normally gaseous hydrocarbons, a relatively light hydrocarbon comprising essentially middle oil, a relatively 'heavy hydrocarbon comprising materials suitable for use as a coal solvent, and a bottoms fraction comprising residue material which is suitable as fuel. In essence, therefore, the valuable liquid hydrocarbons recovered from the efuent of the coking zone include, for example, gasoline boiling range products and/or chemicals, aromatic hydrocarbon-containing fractions, heavy fuel oil fractions, and the like, the utility of which being well known to those skilled in the art.

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 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.

Solvent having dissolved therein at least a portion of the coal plus undissolved pulverized coal is admixed with hydrogen-containing gas via line 26 and passed via line 17 into digestion zone 19 which may be 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 suicient high level. Furthermore, hydrogenation catalyst (from means not shown) may advantageously be used in the digestion step. Make-up hydrogen, if any, may be added to the system via line 27. Preferably, the amount of hydrogen present in the digestion zone is from 1,000 to 100,000 standard cubic feet per barrel of coal-solvent entering digester 19 via line 17.

The entire effluent from rigestion zone 19 is passed via line 20 into filtration zone 21 wherein solid residue, including solid hydrogenation catalyst, if any, is sepa-rated from the liquid material and removed from the system via line 2'2. Filtration zone 21 preferably is a rotary lter defvice precoated with conventional tilter aids and is typically operated at a pressure 0f from 50 to 100 p.s.i.g. sucient to effect removal of substantially all of the suspended solid matter, including undissolved carbonaceous matter. The filter cake is washed and dried by conventional means to recover adsorbed liquid material. The mother liquor, comprising hydrogen gas, if any, and solvent having dissolved therein coal, 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 ltration zone 21 in an effort to further aid in removing tars and solid materials from the desired solvent and liquid hydrocarbons making up the liquid :coal ex-tract. If an anti-solvent is used, then the material in line 23 will also contain such added light hydrocarbons.

The liquid effluent, therefore, from filtration zone 21 is passed via line 23 into separator 24 for the separation therein of the hydrogen gas from the other hydrocarbonaceous material. Although separator '24 has been shown in a position following filtration zone 21, it is within the concepts of the present invention to arrange for separation of the hydrogen gas prior to filtration zone 21. In other words, another embodiment of this invention would include a hydrogen separation zone, not shown, in line 20 between digester 19 and filter 21. However, for purposes of illustration only, separator 24 has been placed between ltration zone 21 and coking unit 29, more fully discussed hereinbelow.

In keeping with the present illustration, hydrogen gas is removed from separator 24 via line 26 and returned to digester 19, as previously discussed. Separator 24 may also include means, not shown, for the separation of the added light hydrocarbon (anti-solvent) -which may have been added during the filtration step previously discussed. rTherefore, the liquid coal extract, substantially free of solid matter, hydrogen gas, and normally gaseous hyd-rocarbons, is removed from separator 24 via line 25.

The material in line 25 is passed into delayed coking zone 29 which is operated under coking conditions sufficient to produce coke having a volatile content of about 20% by weight. As previously mentioned, if desired, a portion of the liquid coal extract in line 25 may be bypassed around coking zone 29 via line 28 for return to either -mill 14 and/or digester 19. Coke is removed from the coking unit via line 30 and disposed of by means not shown. The eluent of coking zone 29 containing normally liquid hydrocarbons is withdrawn via line 31 and passed into fractionator 33.

Fractionator 33 is operated under conditions sufficient to remove normally gaseous hydrocarbon produced during the coking operation from the system via line 35. A relatively light hydrocarbon material, -such as a kerosene fraction is withdrawn from fractionator 33 via line 36. A relatively heavy hydrocarbon is withd-rawn via line 37 and, preferably, comprises sufficient solvation properties for use in the coal liquefaction step previosuly discussed. Therefore, the material in line 37 is recycled to mill 14 and/or digester 19 via line 28, 11 and/or 18, as discussed hereinabove. A residual fraction comprising heavy fuel oil is withdrawn from fractionator 33 via line 34. Added solvent external of the process may be added to the system via line 32, if desired.

PREFERRED EMBODIMENT From the discussion presented hereinabove, the preferred embodiment of the present invention includes a method for obtaining valuable liquid hydrocarbons from coarse particulate coal which comprises: (a) admixing coarse size bituminous coal with a solvent comprising aromatic hydrocarbons; (fb) introducing the solvent-coarse Coal admixture into a pulverization zone under conditions including a temperature from 300 C. to 500 C., pressure from atmopsheric to 10,000 p.s.i.g., solvent to coal ratio from 0.2 to l0, and including from 1,000 to 100,000 standard cubic feet of hydrogen per barrel of admixture, suicient to reduce said coarse coal to at least -8 Tyler screen size and at least partially dissolve coal into said solvent; (c) passing the pulverized coal-solvent product including dissolved coal 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 ratio from 0.2 to l0, a residence time from 30 seconds to 5 hours, and the presence of a hydrogen-containing gas sufficient to dissolve Coal such that a total in excess of 50% by weight maf. coal is liqueed as liquid coal extract; (d) separating the liquid coal extract from the digester product stream; (e) passing said separated liquid coal extract into a delayed coking zone maintained under coking conditions including a temperature from 400 C. to 800 C. sufficient to produce coke having a Ivolatile content from to 30% and, (f) recovering Valuable liquid hydrocarbons from the euent of said coking zone.

The invention claimed: 1. Method for obtaining valuable liquid hydrocarbons from coarse particulate coal which comprises:

(a) admixing coarse size bituminous coal with a solvent comprising aromatic hydrocarbons; (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, and including from 1,000 to 10,000

lstandard cubic feet of hydrogen per barrel of admixture, suicient to reduce said coarse coal to at least -8 Tyler screen size and at least partially dissolve coal into said solvent;

(c) passing the pulverized coal-solvent product including dissolved coal 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 ratio from 0.2 to 10, a residence time from 30 seconds to 5 hours, and the presence of a hydrogen-containing gas sucient to dissolve coal such that a total in excess of 50% by Weight m.a.f. coal is liqueed as liquid coal extract; y

(d) separating the liquid coal extract from the digester product stream;

(e) passing at least an aliquot part of the entire separated liquid coal extract Without distilaltion into a delayed coking zone maintained under coking conitions including a temperature from 400 C. to 800 C. sulicient to produce coke having a volatile content from 5% to 30% and,

(f) recovering valuable liquid hydrocarbons from the efuent of said coking zone.

2. Method according t0 claim 1 wherein -said digestion zone conditions includes the presence of solid particulate hydrogenation catalyst, and hydrogen in an amount from 1,000 to 100,000 standard cubic feet per barrel said coal-solvent product.

3.' Method according to claim 1 wherein a portion of the efuent from the coking zone is recovered as solvent forcoal and recycled to said pulverization zone of step References Cited UNITED STATES PATENTS 1,934,023 11/1933 Wright 208-10 1,940,648 12/1933 Russel 208-8 2,174,184 9/1939 Bywater 208-8 3,018,242 1/1962 Gorin 208-10 2,738,311 3/1956 Frese etal 208-8 3,075,912 1/1963 Eastman 208-8 DELBERT E. GRANTZ, 'Primary Examiner VERONICA OKEEFE, Assistant Examiner 'U.S. Cl. X.R.