US3645885A

US3645885A - Upflow coal liquefaction

Info

Publication number: US3645885A
Application number: US34224A
Authority: US
Inventors: Grady W Harris; Frank B Sprow
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1970-05-04
Filing date: 1970-05-04
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28

Abstract

COAL IS LIQUEFIED WITHOUT EMPLOYING INTERNAL MIXING (BY STIRRERS, ETC.) IN A TURBULENCE-FREE UPFLOW LIQUEFACTION ZONE, PROVIDING IMPROVED YIELDS AND SELECTIVITY OF DESIRABLE LIQUID PRODUCTS THAN A WELL-MIXED LIQUEFACTION ZONE. BEFORE INTRODUCTION TO THE UPFLOW LIQUEFACTION ZONE, A SLURRY OF THE COAL IN A HYDROGEN-DONOR SOLVENT IS PREHEATED TO A TEMPERATURE WITHIN THE RANGE FROM ABOUT 700*F. TO ABOUT 900%F. AND SUBJECTED TO CONDITIONS OF TURBULENCE, A TREATMENT WHICH CAUSES THE COAL PARTICLES, ESPECIALLY CAKING-TYPE COAL PARTICLES, TO DISINTEGRATE WITHOUT AGGLOMERATION. INTRODUCED INTO A LOWER PORTION OF THE LIQUEFACTION ZONE, THE COAL, IN MIXED SOLID AND LIQUID PHASE, IS PLUG FLOWED UPWARDLY AT A SUPERFICIAL LIQUID VELOCITY SUFFICIENT TO CARRY UPWARD ALL PARTICLES WHICH HAVE A MAXIMUM SETTLING VELOCITY OF FROM ABOUT 0.01 TO ABOUT 0.04 FT./SEC. PARTICLES OF HIGHER SETTLING VELOCITIES SETTLE THROUGH THE ZONE. CONTINUED DISSOLUTION OF LARGE CONVERTIBLE COAL PARTICLES DECREASES THEIR SIZE UNTIL THEY TOO RISE THROUGH THE LIQUEFACTION ZONE. SETTLED ASH-FORMING PARTICLES ARE REMOVED FROM A LOWER PORTION OF THE ZONE. A LIQUEFACTION PRODUCT IS REMOVED FROM AN UPPER PORTION OF THE ZONE. THE LIQUEFACTION PRODUCT CONTAINS FROM ABOUT 70 TO ABOUT 96 WEIGHT PERCENT OF MEK SOLUBLE MATERIALS. SOLIDS RECOVERED FROM A LOWER PORTION OF THE LIQUEFACTION ZONE CONTAIN FROM ABOUT 25 WEIGHT PERCENT TO ABOUT 35 WEIGHT PERCENT OF MEK INSOLUBLES AND FROM ABOUT 35 TO ABOUT 45 WEIGHT PERCENT OF ASH. CONDITIONS IN THE LIQUEFACTION ZONE INCLUDE A TEMPERATURE WITHIN THE RANGE FROM ABOUT 700*F. TO ABOUT 100*F., A PRESSURE WITHIN THE RANGE FROM ABOUT 350 P.S.I.G. TO ABOUT 3000 P.S.I.G. AND AN AVERAGE LIQUID RESIDENCE TIME WITHIN THE RANGE FROM ABOUT 5 MINUTES TO ABOUT 60 MINUTES. THE HYDROGEN-DONOR SOLVENT MAY BE SUPPLEMENTED WITH FROM ABOUT 0.1 TO ABOUT 10 WEIGHT PERCENT OF HYDROGEN IN GASEOUS FORM IN THE LIQUEFACTION ZONE. PREFERRED HYDROGEN DONORS INCLUDE INDANE, C10-C12 TETRALINS, C12 AND C13 ACENAPHTHENES, DI-, TETRA-, AND OCTAHYDROANTHRACENE, AND TETRAHYDROACENAPHTHENE.

Description

Feb. 29, 1972 Filed May 4,. 1970 4 Sheets-Sheet l SLURRY RHEO LOGICAL BEHAVIOR 45 WT. COAL/HYDROGENATED CREOSOTE OIL SLUR RY HYDROGENATION zone 34 S/C i2 N Cool Type Illinois No.6

3 Cool SizeMinus lOOMesh 3 Moisture Conienti-34 (Wi.)/ I 8 Temperature 5.42F.(Ai Equilibrium) Pressure 420 psiu a m w E m m 1 1 LL] :7;

IOO

I l l l I l l i l i i l 0 I00 200 300 FIG. 4. SHEAR RATE,SEC 28 GASES COAL NAPHTHA :38

UPFLOW 26 GAS-LIQUID HYDROGEN-DONOR ggijg s5 PA RATOR SOLVENT l2 if mxme 39 ZONE 24 FRACTIONATING STRIPPING ZONE ZONE 3| 29 GAS I6 30 32 2 I-NAPHTHA i 23 34 PREHEATING ZONE 25 ASHFORMING 33 HEAVY souos GAS on.

INVENTORS. GRADY W. HARRIS BY FRANK B. SPROW,

ATTORNEY.

Feb. 29, 1972 w HARRIS ETAL 3,645,885

'UPFLOW COAL LIQUEFACTION Filed May 4, 1970 4 Sheets-Sheet 2 EFFECT OF TEMPERATURE ON VISCOSITY 45 WT.% COAL/HYDROGENATED CREOSOTE OIL SLURRY s/c-|.2 24 Min. 3 Cool Typ '-lllinois No. 6 T i Coal Size Minus IOO Mesh Moisture Conienil.34 (W'r.)% r ShearRaie 289 sec- IHr. at v 654F.

T' =07 50- i i- I 6 Time=|8. 5 Min. 0 U m K Newtonian Non-Newtonian Behavior Behavior 5 l I i 1 TEMPERATURE ,F.

FIG. 2.

INVENTOR.S. GRADY W. HARRIS, FRAN B. SPROW,

ATTORNEY.

Feb. 29, 1972 UPFLOW 00 Filed May 4, 1970 VISCOSITY,CP

G. W. HARRIS E-TAL AL LIQUEFACTION 4 Sheets-Sheet 5 NON NEWTONIAN BEHAVIOR OF 45 WT.% COAL/HYDROGENATED CREOSOTE OIL SLURRY AT 542 F.

IOOO

Coal Type Illinois No.6

Cool Size Minus I00 Mesh 800 1 Moisture Content I. 34 (W1.

7OO Shear Ruie Viscosity (Sec") (CP) 600 I6 783 BZI O l I l 1 l i l i i l l SHEAR RATE,SEC"

FIG. 3.

INVEN'IORJ.

GRADY w HARRIS,

FRANK B. SPROW ATTORNEY Feb. 29, 1972 I I G. w. HARRIS ETAL 3,645,885

UPFLOW COAL LIQUEFACTION Filed May 4, 1970 4 Sheets-$heet 4.

INFLUENCE OF TEMPERATURE ON VISCOSITY 45 WT./o COAL/HYDROGENATED CREOSOTE OIL I I I I Sample Shear Rafe ViscosH/F H\ T MB (5%) (CPI I8 Min.

868 Cu? OF I I Scale For 0 5Min. I

( 7OCP) 7 I45 2|O 5o- I Cool Type-Illinois No.6 g- Cool Size Minus I00 Mesh Shear Rate 868 Secf 40 8 32Mln.' o (n 5 Sample TE HEATING lo I O COOLING \Q Sample zzmh, .ATSTIF o IP- *I'l -'I I 200 300 400 500 600 700 TEMPERATURE ,F.

FIG. 5.

INVENTORS,- GRADY w. HARRIS, BY FRANK B.sPRow,

ATTORNEY.

United States Patent O 3,645,885 UPFLOW COAL LIQUEFACTION Grady W. Harris, Cambridge, Mass., and Frank B. Sprow,

Houston, Tex., assignors to Esso Research and Engineering Company Filed May 4, 1970, Ser. No. 34,224 Int. Cl. C10g 1/04 US. Cl. 208-8 12 Claims ABSTRACT OF THE DISCLOSURE Coal is liquefied without employing internal mixing (by stirrers, etc.) in a turbulence-free upflow liquefaction zone, providing improved yields and selectivity of desirable liquid products than a well-mixed liquefaction zone. Before introduction to the upliow liquefaction zone, a slurry of the coal in a hydrogen-donor solvent is preheated to a temperature within the range from about 700 F. to about 900 F. and subjected to conditions of turbulence, a treatment which causes the coal particles, especially caking-type coal particles, to disintegrate without agglomeration. Introduced into a lower portion of the liquefaction zone, the coal, in mixed solid and liquid phase, is plug flowed upwardly at a superficial liquid velocity sufficient to carry upward all particles which have a maximum settling velocity of from about 0.01 to about 0.04 ft./sec. Particles of higher settling velocities settle through the zone. Continued dissolution of large con vertible coal particles decreases their size until they too rise through the liquefaction zone. Settled ash-forming particles are removed from a lower portion of the zone. A liquefaction product is removed from an upper portion of the zone. The liquefaction product contains from about 70 to about 96 weight percent of MEK soluble materials. Solids recovered from a lower portion of the liquefaction zone contain from about 25 weight percent to about 35 weight percent of MEK insolubles and from about 35 to about 45 weight percent of ash. Conditions in the liquefaction zone include a temperature within the range from about 700 F. to about 1000 F., a pressure within the range from about 350 p.s.i.g. to about 3000 p.s.i.g. and an average liquid residence time Within the range from about minutes to about 60 minutes. The hydrogen-donor solvent may be supplemented with from abouut 0.1 to

about 10 weight percent of hydrogen in gaseous form in the liquefaction zone. Preferred hydrogen donors include indane, C -C Tetralins, C and C acenaphthenes, di-, tetra-, and octahydroanthracene, and tetrahydroacenaphthene.

BACKGROUND OF THE INVENTION This invention involves the production of liquid hydrocarbon products from solid coal, and more particularly, the step in such a process which utilizes a hydrogen-donor solvent in the liquefaction zone.

Heretofore, as illustrated by US. Pats. 3,018,241, 3,075,912 and 3,117,921, liquefaction of solid coals utilizing a hydrogen-donor solvent has been carried out in a well-mixed reactor using stirrers, agitators etc. with attendant problems of costly power consumption and associated mechanical difliculties. In these reactors, incomplete liquefaction of larger convertible coal particles commonly occurs, particularly in continuous process operations. In addition, extensive and costly mechanical separations equipment has to be used downstream of the 3,645,885 Patented Feb. 29, 1972 liquefaction zone to separate the unliquefied convertible coal and nonconvertible coal solids from the liquefied product. All of this contributes greatly to the cost of recovering liquid hydrocarbon products from solid coal. Representing a recent attempt to escape these difliculties, US. Pat. 3,488,278 suggests that ground coal particles be settled through a countercurrent stream of solvent (and hydrogen gas) flowed upwardly at increasing velocities effected by vertically-staged solvent inlets. This approach, however, falls short of overcoming the aforesaid difiiculties in a manner providing materially improved economies of operation. It is therefore highly desirable and plainly important that the difficulties and shorcomings in the present level of the art of liquefying coal using a hydrogen-donor solvent be reduced or eliminated.

SUMMARY OF THE INVENTION Liquefaction of coal in a hydrogen-donor solvent is accomplished without internal mixing in the liquefaction zone in a continuous new process which provides improved yields and selectivity in the liquefaction of convertible coal and which minimizes the presence of ashforming particles in the liquefaction product. According to this process, the coal in particulate form and slurried in a hydrogen-donor solvent is prepared for plug flow in a turbulence-free upflow liquefaction zone by preheating the slurry to a temperature sufiiciently high to cause the slurried coal particles to disintegrate and partially dissolve while subjecting the heated slurry to turbulence to prevent particle agglomeration. The preheated coal slurry in mixed solid and liquid phase is then introduced into a lower portion of an upflow liquefraction zone and passed upwardly under conditions of nonturbulent plug flow at a superficial liquid velocity sufficient to support coal fines and to permit the settling of heavier particles. Conditions in the liquefaction zone include a temperature high enough to permit a hydrogen-transfer reaction between the hydrogen-donor solvent and moistureand mineral-free portions of the coal, a pressure high enough to prevent appreciable vaporization of the solvent, and an average liquid residence time sufiicient to produce a liquefaction product in an upper portion of the reaction zone. The liquefaction product is withdrawn from an upper portion of the liquefaction zone and contains from about to about 96 Weight percent of methyl-ethyl ketone (MEK) soluble materials. Settled solids are withdrawn from a lower portion of the liquefaction zone. These solids consist essentially of from about 25 to about 35 weight percent of MEK insoluble materials and from about 35 to about 45 weight percent of ash-forming materials. Thus in addition to a better yield and selectivity than a well-mixed liquefaction zone, the high ash concentration of the solids withdrawn from the lower portion of the zone reduces the load on downstream solids removal equipment and eliminates expense in mechanical separations equipment to remove essentially unconvertible parts of the coal.

For a better understanding of the present invention, each of the aspects of the complete overall process scheme will be separately discussed.

Preparation of the coal The basic feedstock to the process of the present invention is a solid, particulate coal such as bituminous coal, subbituminous coal, lignite, and brown coal, or a mixture thereof. Although it is desirable to grind the coal to a particle size distribution from about 8 mesh and finer, it has been found that the preheating treatment hereinafter described and the solvation reaction carried out in the liquefaction zone will result in adequate conversion even if particles as large as one-fourth inch on the major dimension are charged to the preheating zone. The preheating treatment is especially useful for cakingtype coals, as hereinafter described in greater detail. A typical proximate and ultimate analysis of an Illinois No. 6 coal (a caking-type Eastern bituminous coal mined in Macoupin County, Illinois) and of Gillette coal (a noncaking type Western subbituminous coal mined in Campbell County, Wyoming) which have been utilized in this process is set out in Table I, which follows:

TABLE I.CHEMICAL ANALYSIS OF COAL WT. PERCENT DRY ANALYSIS Illinois coal The coal preferably is dried to remove excess water, although it is feasible to utilize coal which is not moisture free if the liquefaction facilities have been sized to allow the withdrawal of evolved steam. The coal can be dried by convention techniques prior to mixing it with the hydrogen-donor solvent to form the slurry feed for liquefaction. It is preferred, however, to mix the wet coal with a hot hydrogen-donor oil in a mixing zone to volatilize water in the mixing zone, thereby reducing the feed slurry moisture content to less than about two weight percent. Thus, the mixing zone also serves the function of a drier zone.

Hydrogen-donor solvent In the mixing zone, the coal feedstock at ambient temperature is mixed with a hydrogen-donor solvent which has a tempeature of from about 500 F. to about 700 F. The solvent/coal weight ratio is within the range from about 0.8:1 to about 2: 1, resulting in a slurry temperature within the range from about 300 F. to about 350 F. A mechanical propeller or other agitating device may suitably be provided in the mixing zone to obtain a uniform slurry concentration.

The hydrogen-donor solvent boils within the range from about 300 F. to about 900 F., preferably from about 375 F. to about 800 F., at atmospheric pressure, so as to remain in the liquid phase at the elevated temperatures employed in the liquefaction zone. Desirably, the solvent will contain at least 30 weight percent, preferably at least 50 weight percent, of compounds which are known to be hydrogen donors under the conditions used in the liquefaction zone. The hydrogen-donor solvent stream suitably contains one or more hydrogen-donor com-pounds in admixture with non-donor compounds or with one another, compounds such as indane, C -C Tetralins, C and C acenaphthenes, di-, tetra-, and octahydroanthracene, and tetrahydroacenaphthene being preferred hydrogen-donor compounds, as are other derivatives of the partially saturated hydroaromatic compounds.

It is preferred that the solvent stream be a hydrogenated recycle solvent fraction. The composition of such a fraction will vary somewhat, depending upon the source of the coal used as the feedstock to the system, the operating conditions in the overall process, and the conditions used in hydrogenating the solid fraction for recycle after liquefaction. However, a typical description of a hydrogenated recycle solid fraction will be simiar to that shown in Table II.

TABLE Ill-TYPICAL RECYCLE SOLVENT Distillation-Glass spiral Cumulative wt. percent over Sp. git, 60 F./60 F.

Temp.,F.-760 mm.

Mass spec. analysis W t Typical compound percent Elemental analysis Carbon Hydro gen Oxygen CHEM-6 Alkylbenzene--. O nHh-B Tetralin C nHZnl-O Indene OnH2n'l-2 Naphthalene" Gn 2u' Acenaphthene-.- CHEM-16 Acenaphthylene- Callas-l8 Phenanthrene.--

C H2n-20 C Hz r22 C 11: 2 11- Nitrogen.

Sulfur 0. 03

Naphthenoanthracene.

Pyrene Ohrysene Cliolanthrenes Beuzopyrenes--.

Total... 100. 00

Preheating zone The slurry of coal in the hydrogen-donor solvent is passed into a preheating zone before charging it to a liquefaction zone. In the preheating zone, the slurry is heated from its temperature in the mixing zone (preferably about 300 to about 350 F. when mixed with hot solvent) to a temperature within the range from about 700 F. to about 900 F. while being subjected to conditions of turbulence. The particular temperature(s) within the range from about 700 (F. to about 900 F. to which the slurry is heated preferably will approximate the temperature(s) employed in the liquefaction zone with allowance for any cooling which the slurry may undergo in passing from the preheating zone to the liquefaction zone. I

As the temperature of the slurry increases in the preheating zone to the desired level, the particles in the hyrogen-donor slurry solvent disintegrate into smaller sizes and become .very plastic and sticky and will agglomerate with other coal particles and with each other. In order to minimize the problem of agglomeration, it is part of this invention that the slurry is maintained in a turbulent condition in the preheating zone, at least-at temperatures above which disintegration occurs. The turbulent regime of the slurry is a function of the Reynolds number of the slurry and occurs at Reynolds numbers of about 4000 and greater. High shear rates produced by high shearing stresses exerted upon the slurry are conducive to turbulent flow, and shear rates above 100 secs:- are employed, preferably being used at' a level above about 300 secs- Infinite shear rates are best. High shearing stresses are provided by passing the slurry through the preheating zone at high superficial liquid velocities.

Liquefaction zone The preheated slurry in mixed solid and liquid phase is passed into a lower portion of the liquefaction zone, where the convertible portion of the coal, already disintegrated and partially dissolved, is caused to depolymerice to form free radicals. The free radicals can recombine to form material which is insoluble even in pyridine if a hydrogen-donor solvent prevents recombination of the freeradicals. The degree to which recombination is prevented depends upon the amount of donor solvent which is present. Where the donor solvent contains about 50 weight percent of hydrogen-donor constituents, and the solvent/coal ratio is from about 0.8:1 to about 2:1, the concentration of hydrogen-donor constitutents in the liquefaction zone can be seen to range initially from about 22 weight percent to about 33 /3 weight percent and will be depleted by the liquefaction reaction. However, molecular hydrogen can be added to the liquefaction zone to partially replenish the hydrogen-donor solvent by in situ hydrogena tion of the depleted molecules. For example, naphthenes may be hydrogenated to Tetralins.

Thus, it is preferred to include a hydrogen-rich gas with the hydrogen-donor solvent in the liquefaction zone which provides from about 0.1 to about weight percent of hydrogen. Preferably, the hydrogen-rich gas is fed through the preheating zone with the hydrogen-donor solvent so that the temperature of the gas is increased to the temperatures employed in the liquefaction zone. Inclusion of the gas in this slurry as it passes through the preheating zone does not cause appreciable hydrogenation of the coal in the preheating zone.

In accordance with this invention, the preheated slurry in mixed solid and liquid phase is plug flowed upwardly under conditions of nonturbulent flow in a liquefaction zone in which no internal mixing, back mixing etc. is employed. Upflow occurs in the reactor at a superficial liquid velocity which preferably is sufficient to carry upward particles having a maximum settling velocity within the range from about 0.01 to about 0.04 ft./sec., or stated conversely, to permit particles having a settling velocity greater than within the range from about 0.01 to about 0.14 ft./sec. to settle. Such particles are of course settling through a rising liquid phase carrying a slurry or suspension of particles. In accordance with Stokes Law, the maximum settling velocity of a particle is therefore dependent upon the density or specific gravity of that particle and upon the bulk suspension, the size of the particle, and the viscosity of the bulk suspension. The slurry in the liquefaction zone will preferably have an effective specific gravity within the range from about 1.4 to about 1.7. The viscosity of the slurry in the liquefaction zone preferably will be within the range from about 0.1 centipoise to about 1.0 centipoise.

In the liquefaction zone, dissolution of disintegrated convertible coal particles of various sizes, specific gravities and compositions occurs. The upflow liquid velocity of the reactor liquid is adjusted relative to the effective specific gravity of the liquefaction zone so that the larger convertible particles or any portion of the original coal which may liquefy very slowly can remain in the liquefaction zone until size reduction allows them to be carried overhead. Certain parts of the coal (e.g. pyrite, clay and fusinite) are not liquefied in the liquefaction zone, but are instead freed from their original matrix in the zone and are present in the reacting slurry as distinct and separate particles. The upflow liquid velocity is adjusted so that the bulk of these nonconvertible particles are contained within the liquefaction zone, from which they may be withdrawn separately instead of being carried overhead with the reactor liquid product. Thus, the upflow liquefaction zone provides a plug flow residence time distribution with its associated advantages of higher conversion and better yield and selectivity as compared to a well-mixed reactor. The liquefaction zone may suitably be comprised of one or more vessels.

Conditions in the liquefaction zone include a temperature high enough to permit the hydrogen-transfer reaction between the hydrogen-donor solvent and the moistureand mineral-free portions of the coal to occur and apressure high enough to. prevent appreciablevaporization of the solvent at the temperatures employed and in consideration of the hydrogen-input rate utilized. Suitable liquefaction conditions include a temperature within the range from about 700 F. to about 1000 F., a pressure within the range from about 350 p.s.i.g. to about 3000 p.s.i.g.,- and an average liquid residence time within the range from about 5 minutes to about 60 minutes. Thus, in a low severity process, in which, for example, the pressure is about 500 p.s.i.g., a temperature of about 775 F. may be employed in the liquefaction zone if about 1 weight percent of hydrogen is utilized. In a moderately high severity operation, in which the pressure ranges, for example, from about 1500 p.s.i.g. to about 3000 p.s.i.g., a temperature of about 850 F. is suitably employed where hydrogen is used in amounts of from about 5 to about 10 weight percent.

The conditions of the liquefaction zone produce a liquefaction product taken from the upper portion of the liquefaction zone which contains from about 60 to about 96 Weight percent of MEK soluble materials. This M-EK conversion is expressed as the percent of moisture and ash free coal that is converted to materials which are soluble in methyl-ethyl ketone. It is calculated by the equation:

Percent convers1on=100 m wherein Before measuring S MEK is added to the product slurry as a solvent, in the ratio of 1 volume of MEK for each volume of product slurry. The results so obtained are referred to as MEK conversion.

As aforesaid, in the liquefaction zone the hydrogendonor solvent reacts with the free radicals resulting from depolymerization. As a result, even though hydrogen may be charged into the liquefaction zone to replenish the donor solvent, a portion of the hydrogen-donor solvent becomes hydrogen depleted. The degree of depletion is a function of the specific solvent and of the conditions employed. A typical recycle solvent will contain about 50 Weight percent of compounds which will donate hydrogen and, during about one hour within the liquefaction zone with molecular hydrogen being added, will be depleted to the extent that only 25 weight percent of the solvent is made up of hydrogen-donor compounds.

A gaseous phase product is removed from the liquefaction zone as well as the liquefaction product. Exemplary compositions of the gas product and liquid product (without separation from solids in the slurry) are given below in Table III.

TABLE III.EXEMPLARY GAS AND LIQUID PRODUCTS Liquid product Gas product Cumula- Wt. tive wt. Sp. gr. Compound percent percent 60/60 F.

1. 2 IE? 21.8 7. 4 0. 9014 17. 7 14. 7 0. 9496 5. 2 22. 6 0. 9667 4. 7 31. 4 1. 0089 20.1 40. 2 1. 0370 15. 8 49. 0 1. 0560 0. 4 53. 4 1. 0791 7. 3 59. 1 Solid 0. 5 30. 9 Solid The foregoing description of the invention will be further illustrated by a discussion of the preferredmode of carrying out the invention, taken with adescription of the accompanying drawings.

7 DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a preferred mode of carrying out this invention.

FIG. 2 is a plot depicting the change in viscosity with DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, particulate coal is introduced by way of line to a mixing zone 12, where it is combined with a hot hydrogenated heavy distillate recycle oil stream introduced thereinto by way of line 14 to form a slurry having a temperature of about 350 F. The solvent/ coal ratio in the mixing zone is preferably about 2:1. The slurry is conducted from the mixing zone by way of line 16 and passes through a valve 18 by which about 1 weight percent of hydrogen is metered from line 19 into the slurry. From valve 18, the slurry with hydrogen is passed by line 20 into a preheating zone 21, in which the temperature of the slurry is raised to approximately the temperature to be utilized in the upfiow liquefaction zone. This temperature depends upon the severity of conditions employed in the upfiow liquefaction zone. For a suitable low severity liquefaction operation, the slurry is heated to about 775 F. in the preheating zone. Conditions of turbulence including high shear rates, greater than about 100 seesand providing a Reynolds Number greater than 4000 are maintained in the preheating zone to prevent agglomeration of the slurry particles during swelling, dispersion and to some extent, dissolution.

From preheating zone 21, the preheated slurry in mixed solid and liquid phase is conducted by line 23 into a lower portion of an upfiow liquefaction zone 24. In a suitable low severity operation, upfiow liquefaction zone 24 is maintained at a temperature of about 875 F. and a pressure of about 500 p.s.i.g. The effective specific gravity of the liquefaction zone is preferably about 1.5. A superficial liquid velocity of about one foot per minute, sufficient to carry upward particles which have a maximum settling velocity of about 0.02 ft./sec. is employed. Viscosity in the zone is preferably about 1 centipoise. Residence time of the slurry as it moves through the zone is about minutes.

The upfiow liquefaction zone 24 contains no internal mixing by stirrers or other means, and is turbulence free. The slurry moves through the liquefaction zone in a plugflow manner.

Solids having a settling velocity greater than about 0.02 ft./sec. are collected in the bottom of upfiow liquefaction zone 24, from which they may be withdrawn by line 25. Products of the liquefaction zone are withdrawn from an upper portion thereof by way of line 26 for further treatment to obtain the useful liquid products of coal liquefaction, in accordance with the art.

Thus, the products are suitably discharged from line 26 into a gas-liquid separator 27, which is operated to permit volatile coal gases to separate from the liquid product and to escape by way of line 28 for further use as desired. The liquid product from the gas-liquid separator 27 is suitably discharged by way of line 29 into a fractionating zone 30 which may be operated to produce a gas stream which is recovered by way of line 31, a naphtha stream boiling up to about 400 P. which is recovered by way of line 32 and a heavy gas oil stream boiling within the range from about 700 to about 1000 F., which is recovered by way of line 33. A recycle solvent stream boiling within the range from about 400 to about 700 F.

is recovered by way of line 34 for use as a hydrogen-donor solvent.

The recycle solvent is contacted in a hydrogenation zone 35 with hydrogen which is introduced by way of line 36 in the presence of a hydrogenation catalyst such' as cobalt molybdate under hydrogenation conditionssuch as a temperature of about 700 F.', a pressure of" about 1350 p.s.i.g. and a space velocity of about2 weights of liquid per hour per weight of catalyst. The hydrogenated recycle solvent is then suitably conducted by way of "line' 36 to a stripping zone 37 where naphtha is recovered-. from it by way of line 38. The hydrogenated solvent leavesv the stripping zone through line 38 and is thus discharged back into mixing zone 12 for formation of the slurry.

The following examples further illustrate'aspects of this invention. The first specifically sets out a full example of the invention. The remaining examples show the neces-"- EXAMPLE 1 In a typical operation of the 'presentinvention,'two'" preheat stages were employed, one being ft. of 0.159

inch inner diameter tubing held at isothermal conditions} in heated sand baths. The reactor itself was in-two upfiow stages, each of which had an inner diameter of 1 inches and was 30 ft. tall, with no mechanical mixing being employed.

A 33 weight percent slurry of -l00 mesh Illinois No."

'6 coal in hydrogenated creosote oil was fed at the rate of '90 lbs./hr. (about 1 v./v./hr.) into a first preheater maintained at 500 F., at a superficial liquid velocity of about 2 ft./ sec. and a residence time of about 0.2 minute, and thence into a second preheater maintained at 775 F., again at a superficial liquid velocity of about 2 ft./sec'. for about a 0.2 minute residence time. From the preheaters, the slurry was fed to the upfiow reactors, which were operated under low severity conditions, employing a pressure within the range from about'350 p.s.i.g. to about 500 p.s.i.g. The average temperature for both stages of the reactors was 750 F. The superficial liquid velocity through the reactors was about 0.02 ft. /sec. Solids were withdrawn from the bottom of each stage of the reactor at the rate of 3-6 lbs./hr.

The liquefaction product taken from the'top of the upper reactor contained about 6 weight percent methylethyl ketone insoluble materials and about 19 weight per cent benzene insoluble materials. The solids withdrawn from the bottom of each reactor stage contained about 30 weight percent MEK insoluble materials, about 40 weight percent benzene insoluble materials and about 40 percent ash. i

Examples 2 and 3 illustrate the particular'application' of this invention to caking-type coals.

EXAMPLE 2 6 coal (a caking-type Eastern coal) in hydrogenated creosote oil was continuously recycled through a slurry viscometer apparatus for about 4% hours while information was collected on its rheological behavior at various temperatures. The results of this run are shown in FIGS.- 2-4. I FIG. 2 illustrates the influence of temperature on viscosity at a shear rate of 289 secsr Observe that the viscosity decreases from about centipoise at 84 F, to about 20-21 centipoise at 306 F. Note also that the viscosity does not change significantly with temperature between about 306 and 487 F. The rheological behavior of this slurry was Newtonian up to 411 'F., but at higher temperatures, it was non-Newtonian. Furthermore, the viscosity increased significantly with temperature between 487 F. and 590 F. At 542 F., the slurry was initially rheopectic (viscosity increased with time) for about 5 /2 minutes and then became thixotropic (viscosity -.de-

creased with time) for the next 13 minutes, until equilibrium was obtained. The viscosity readings were off the scale of the slurry viscometer apparatus atthe shear rate utilized of 289 secs- I FIG. 3 shows the reheological behavior of this slurry at 542 F. after equilibrium was obtained. Theslurry appears to behave as a Bingham plastic. Its yieldvalue appears to be higher than 100 dynes/cm. A turbulence produced by a shear rate in excess of about a 100 sec? is necessary to overcome and prevent the particle agglomeration which causes these slurries to behave as a plastic material.

FIG. 4 shows the influence of shear rate on the viscosity of the slurry at 542 F. after equilibrium was obtained. Observe that the viscosity decreases from about 783-821 centipoise at 16 secs.* to about 125 centipoises at 100 secsr and levels of about 25 centipoises at infinite shear rate.

EXAMPLE 3 A 45 weight percent slurry of 100 mesh Illinois No. 6 coal in hydrogenated creosote oil was recycled through the same slurry viscometer apparatus utilized in Example 1, except that a high viscosity attachment was utilized. The maximum shear rate with this high viscosity attachment was 145 secs- The slurry was recycled through the slurry viscometer apparatus for 1 hour at 400 F. and then heated up to 675 F. in about 50 minutes. The results of this run are shown in FIG. 5 and in Table III.

FIG. 5 is a plot of a slurry viscosity against temperature. As in Example 1, slurry viscosity initially decreased with increasing temperature, but at a temperature above about 550 F. in this instance suddenly changed direction and exhibited a dramatic rise with a further increase in temperature, finally peaking out, here at about 675 F. and thereafter falling off. In this example, samples from the viscometer were taken at the beginning of the high viscosity range (Sample A), at the maximum viscosity (Sample B), and immediately after the high viscosity range (Sample C), at the temperatures indicated by arrows in FIG. 4.

Microscopic examinations of Sample A showed no evidence of coal dissolution. Small particles were in abundance and the edges of the larger particles were intact. Small cavities were present in the coal particles, indicating that gas generation and subsequent coal swelling was just beginning. MEK ash analysis indicated that no coal conversion had occurred.

Microscopic examination of Sample B showed that some large particles had developed gas vacuoles or cavities indicating softening and gas bloating. Edge destruction was evident and a smaller quantity of fine particles than seen in Sample A were observed, indicating that coal dissolution had begun. However, MEK ash conversion analysis again indicated that no conversion or upgrading had occurred.

Microscopic examinations of Sample C showed that no identifiable coal particles existed and that the sample consisted of reagglomerated material. It appeared as if the coal may have been dispersed as fragments of collodial material, but these colloids then appeared to be reagglomerated. MEK ash conversion was 6.9%

Table IV shows the influence of shear rate on the maximum slurry viscosity in the swelling range.

TABLE IV Influence of shear rate on maximum slurry viscosity in swelling range of Illinois No. 6 coal in hydrogenated creosote oil, at 667 F.

Shear rate (sec- Viscosity (cp.)

Examples 2 and 3, taken together, and especially FIGS. 2-5, show that the sharp increase in the viscosity of the slurry as the temperature is increased is due to a swelling of the coal particles. Thisswelling is apparently the initial stage 'of-"the coal disintegration/dissolution process and results in non-Newtonian slurry characteristics. As the coal disintegration and dissolution proceeds, the viscosity decreases again. High shear rates (turbulent fiow conditions) are elfective in controlling agglomeration of the plastic coal particles, as evidenced by the decrease in slurry viscosity at high shear rates.

Having fully and particularly disclosed our invention, including a preferred mode of carrying it out, what is desired by Letters Patent is defined by the appended claims.

We claim:

1. A process of liquefying coal, which comprises:

(a) introducing (1) a slurry (la) of coal particles suspended in (1b) a hydrogen-donor solvent maintained in liquid phase (2) into a preheating zone (2a) where the slurry is heated to a temperature within the range from about 700 F. to about 950 F.

(2b) and subjected to conditions of turbulence (2c) for a residence time sufficiently long to cause the coal particles to disintegrate and to partially dissolve without agglomerating,

(b) passing the preheated slurry in mixed solid and liquid phase (1) upwardly through (2) a turbulence-free liquefaction reaction zone maintained at (2a) a temperature high enough to permit a hydrogen-transfer reaction to occur between the hydrogen-donor solvent and moistureand mineral-free portions of the coal, and

(2b) a pressure high enough to prevent appreciable vaporization of the solvent,

(3) at a superficial liquid velocity sufficient to support coal fines and to permit the settling of heavier particles,

(4) for a residence time sufiicient to produce a liquefaction product in an upper portion of the reaction zone, and

(c) withdrawing (1) from an upper portion of the liquefaction reaction zone (la) liquefaction product including at least 70 weight percent methyl-ethyl ketone soluble materials, and

(2) from a lower portion of the reaction zone,

(2a) undissolved solids settled from the reaction zone.

2. The process of claim 1 in which the slurry is comprised of caking-type coal particles.

3. The process of claim 1 in which the conditions of turbulence in said preheating zone include a Reynolds number of at least 4000.

4. The process of claim 1 in which the superficial liquid velocity in said liquefaction zone is within the range from about 0.01 to about 0.04 ft./sec.

5. A process of liquefying coal which comprises continuously:

(a) forming a slurry of (1) coal particles having a size range of about 8 mesh (Tyler) and smaller 2) in a hydrogen-donor solvent (2a) boiling within the range from about 300 F. to about 900 F. and

(2b) containing at least 30 weight percent of .hydrogen donors chosen from the group consisting of C to C Tetralins, indane, C and ci acenaphthenes, ditetra-, and

octahydroanthracene and tetrahydroacenaphthen e, and mixtures of two or more thereof, I

[(3) at a solvent/coal ratio within the range from I about 0.8:1 to about 2: l,

(b) passing the slurry through a preheating zone (1) in which the slurry is heated to a temperature within the range from about 700 F. to about 900 F.,

(2) under conditions of turbulent flow,

(3) whereby disintegration and partial dissolution of the coal particles occurs therein,

() flowing the preheated slurry in mixed solid and liquid phase under conditions of non-turbulent plug flow upwardly through an unmixed liquefaction zone (1) with a hydrogen-rich gas providing from about 0.1 to about weight percent of hydrogen (2) under liquefaction conditions including (2a) a temperature within the range from about 700 F. to about 1000 R,

(2b) a pressure within the range from about 350 p.s.i.g. to about 3000 p.s.i.g.

(2c) for an average liquid residence time within the range from about 5 minutes to about 60 minutes,

(3) at a superficial liquid velocity sufiicient to carry upward particles which have a maximum settling velocity within the range from about 0.01 to about 0.04 ft./sec., and

(d) withdrawing (1) from an upper portion of the liquefaction zone (1a) a liquefaction product containing from from about 70 to about 96 weight percent of methyl-ethyl ketone soluble materials and (2) from a lower portion of the liquefaction zone (2a) solids consisting essentially of from about Weight percent to about weight percent of methyl-ethyl ketone insoluble materials, and from about 35 to about weight percent of ash.

6. The process of claim 5 in which the slurry is comprised of caking-type coal particles.

7. The process of claim 5 in which the slurry in the preheating zone has a Reynolds Number greater than about 4000.

8. The process of claim 5 in which the slurry in the preheating zone is subjected to a shear rate greater than about 100 secsf p f 9. The process of claim 5 in which the said slurry in said liquefaction zone has an effective specific gravity "within the range from about 1.4 to about 1.7.

10. The process of claim 5.in which the viscosity of the slurry in the liquefaction zone is within the range from about from about 0.1 centipoise to about 1.0 centipoise.

11. The process of claim 5 in which the superficial liquid velocity in the liquefaction zone is about one foot per minute.

12. A process for liquefying caking-type coals, compris- (a) introducing a slurry of caking-type coal particles in a hydrogen-donor solvent in liquid phase into a preheating zone under conditions of turbulence including a shear rate exceeding 100 secs- (b) heating said slurry in said preheating zone under said conditions of turbulence to a temperature within the range from 700 F. to 900 F., efiective to cause said coal particles to undergo disintegration and partial dissolution without agglomeration,

(c) passing said preheated slurry in mixed solid and liquid phase upwardly in plug flow through a turbulence-free liquefaction zone at a temperature within the range from about 700 F. to about 950 F.,' a' pressure within the range from-about 300 p.s.i.g. to about 3000 p.s.i.g. for a residence time of from about 5 minutes to about minutes at a superficial liquid velocity sutficient to carry upward particles having'a settling velocity within the range from about 0.01 ft./ sec. to about 0.04 ft./sec.,

(d) withdrawing a liquefaction product comprising at least about weight percent of methyl-ethylket'one UNITED STATES PATENTS 9/1967 Bull et al 2088 OTHER REFERENCES Alan S. Foust et al.,' Principles of United Operations, John Wiley, New York, p. 141, 1966, Fourth Printing.

PAUL M. COUGHLAN, JR., Primary Examiner V. OKEEFE, Assistant Examiner I