US3726785A

US3726785A - Coal liquefaction using high and low boiling solvents

Info

Publication number: US3726785A
Application number: US00120437A
Authority: US
Inventors: J Keller; J Hochman; J Foster
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1971-03-03
Filing date: 1971-03-03
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10

Abstract

First and second slurries of a particulate coal are formed with low and high boiling fractions of a coal-derived solvent boiling within the range from 300* to 1,000* F., the cut point of the two fractions being from about 500* F. to about 600* F. The slurries are separately liquefied, producing a higher total cylcohexane conversion of the coal than if the coal had been slurried instead in the total coal-derived solvent and liquefied under like conditions.

Description

Keller et al. 1 Apr. 10, 1973 [54] COAL LIQUEFACTION USING HIGH 2,658,861 11/1953 Pevere et a] ..208/8 AND ow BOILING SOLVENTS 3,535,224 10 1970 Corey et al. ....208/8 3,583,900 6/1971 Gatsis ..208/8 [75] Inventors: John E. Keller, Baytown, Tex.; Jack Hochman, Boonton, Ni; James Primary ExaminerDelbert E. Gantz Q- 'a Baytown, Assistant ExaminerVeronica OKeefe [73] Assigneez Esso Research and Engineering AttorneyThomas B. McCulloch, Melvin F. Fincke,

Company, Linden NJ John S. Schneider and Sylvester W. Brock, Jr.

[22] Filed: Mar. 3, 1971 [57] ABSTRACT PP 120,437 First and second slurries of a particulate coal are formed with low and high boiling fractions of a coalderived solvent boilin within the ran e from 300 to US. Cl ..20s 8 g g Int Cl Clog 6 1,000 F., the cut point of the two fractions being [58] Fieid 208/8 from about 500 F. to about 600 F. The slurries are Separately liquefied, producing a higher total y [56] References Cited cohexane conversion of the coal than if the coal had been slurried instead in the total coal-derived solvent UNITED STATES PATENTS and liquefied under like conditions.

1,864,496 6/1932 Pier et a1. .208/8 14 Claims, 1 Drawing Figure I PRODUCT LIOUEFACTION 22 REACTORS LIQUID PRODUCT LIQUID PRODUCT LIQUID COKER FRACTIONATOR f" SOLVENT 11101015111110" REACTORS FURNACE PATEHTED APR 1 01973 JA MES i1. FOSTER JOHNE KELLER, JACK M HOCHMAN,

INVENTOR'S AT ORNEY :3 3; I Z w 6 0 Q H h {r o l: g :3 9

3 283: 222582; m 5:3 I 223: 3 a k 22:: as: 2 $2255 i 1:: 522: N? A 5m 2 A|L| l 22E 3 T on r812; N L Lynn-00 COAL LIQUEFACTION USING HIGH AND LOW BOILING SOLVENTS BACKGROUND OF THE INVENTION This invention relates to the solvent liquefaction of coal in a coal liquid solvent, and more particularly, it involves the separate liquefaction of two slurries of the like coal, one slurry being formed with a high boiling coal liquid solvent and the other with a low boiling coal liquid solvent.

DESCRIPTION OF THE PRIOR ART Normally in the solvent liquefaction of coal, particulate coal is heated in liquefaction reactors at elevated temperatures while slurried in a coal-derived solvent boiling widely at least within a range from 400 to 850 F., usually to as low as about 300 F. to as high as about l,000 F. The solvent normally is hydrogenated either before preparation of the slurry or in situ in the liquefaction reactor, or by both procedures, so that it contains hydrogen-donor molecules when in the liquefaction reactor. Hydrogen-donor molecules have the ability to donate hydrogen to the liquids being made from the coal at the elevated temperatures in the.

liquefaction reactors. Liquids are made from the coal when weaker chemical bonds in the very large coal molecules are thermally cracked. As ameasure of coal liquefaction, cyclohexane conversionthe weight percent of moisture and ash-free (MAF) coal that is converted to materials soluble in cyclohexane-is considered representative of the extent to which MAF coal is converted to liquids boiling below about 1,000 F.

SUMMARY OF THE INVENTION Surprisingly, we have discovered that by forming separate slurries of a coal, one in a low boilingv coalderived solvent and the other in a high boiling coalderived solvent, and then separately liquefying the separate slurries, a total cyclohexane conversion of the coal is obtained which is greater than that which occurs when the coal is slurried in a single wide boiling coalderived solvent and liquefied under like liquefaction conditions. I I

Briefly, then, our invention involves a process for liquefying coal in which a first slurry of a particulate coal is formed with a low boiling coal-derived solvent having an initial boiling point of at least about 300 F. and a final boiling point within the range from about 500 F. to about 600 F., and in which a second slurry of the coal is formed with a high boiling coal-derived solvent having an initial boiling point within the range from about 500 F. to about 600 F. and a final boiling point no higher than about 1,000" F., the final boiling point of the low boiling solvent and the initial boiling of the high boiling solvent being substantially the same. The first and second slurries are then separately liquefied under predetermined liquefaction conditions. The selection of the temperature between 500 F.

and 600 F. which demarcates the low boiling coalderived solvent from the high boiling coal-derived solvent is advantageously made so that substantially all two-ring hydrocarbonaceous compounds derived from the coal are in the low boiling solvent while substantially all of the three-ring or higher hydrocarbonaceous compounds derived from the coal are in the high boiling solvent. Accordingly, the demarcation temperature separating the low boiling coal-derived solvent from the high boiling coal-derived solvent is preferably within the range from about 500 F. to about 550 F.

Separate liquefaction products with improved cyclohexane conversions are produced by separately liquefying the first and second slurries. At least the liquids in the separate liquefaction products are combined and fractionated to obtain liquid product boiling in desired ranges. The low boiling coal-derived solvent and the high boiling coal-derived solvent preferably are recycle streams recovered by fractionating the combined liquids in the two liquefaction products. The cut point in the fractionation for recovering a low boiling coal-derived recycle solvent and a high boiling coalderived recycle solvent is accordingly within the range from about 500 F. to about 600 F., preferably from about 500 F. to about 550 F.

When using recycled solvents for the low and high boiling coal-derived solvents, it is necessary to recover the two solvents from the combined liquids obtained from the separate liquefactions of the separate slurries,

in order to maintain solvent balance. The net production of high boiling coal liquids in the liquefaction of the slurry made with a high boiling coal-derived recycle solvent is insufficient to permit the continued recycle, without makeup, of a high boiling coal-derived solvent recovered by fractionation of the liquids produced on liquefying the high boiling solvent slurry. The same is true of the liquids produced on liquefying the low boiling solvent slurry.

The liquid product stream, which preferably is fractionated to separately recover a low boiling coal liquid recycle solvent and a high boiling coal liquid recycle solvent, may boil, e.g., from about 400 F. to about 700 F. The composition of the equilibrium liquid product stream will vary somewhat, depending upon the source of the coal used as the feedstock to the system and the operating conditions in the liquefaction zone. However, a typical description of a liquids product stream which, in this case is hydrogenated, will be similar to that shown in Table I.

TABLE I Solvent Properties Typical Solvent Distillation Cumulative Volume Percent Vaporized Temperature, F.

400 Initial Cut Overall specific gravity [.0350

Solvent Elemental Composition Element Weight Percent Carbon 9 l .23 Hydrogen 7.67 Nitrogen 0.48 Sulfur 0.05

With a cut point of 550 F., a typical description of a hydrogenated low boiling coal-derived recycle solvent and that of a typical hydrogenated high boiling coalderived solvent will be similar to those shown in Tables 11 and III.

TABLE 11 400l550 F. Solvent Properties Specific Gravity 1.0078

Elemental Composition Element Weight Percent Carbon 91 .03

Hydrogen 8.03

Nitrogen 0.5 1

Sulfur 0.01

TABLE III 5 50/700 F. Solvent Properties Specific Gravity 1.0703

Elemental Composition Element Weight Percent Carbon 91.48 Hydrogen 7.23 Nitrogen 0.44 Sulfur 0.09

The low boiling coal-derived solvent, which can have a hydrogen content as low as about 6 weight percent, and the high boiling coal-derived solvent, which can have a hydrogen content as low as 5 weight percent, suitably are hydrogenated to add from about 0.1 to about 5, preferably from about 0.2 to about 2, weight percent of hydrogen to them, hydrogenation being regulated so that the low boiling coal-derived solvent contains up to about 10.5 weight percent hydrogen, preferably from about 7.5 to about 9.5 weight percent hydrogen, and the high boiling coal-derived solvent has a hydrogen content up to about 9.5 weight percent, preferably from about 7 to about. 9 weight percent.

Where, as preferred, the low boiling and high boiling coal-derived solvents are recycle streams recovered by fractionating the combined liquids from the separate liquefaction reactors, the hydrogenation may be conducted on a combined liquid products stream before such stream is fractionated to recover the low and high boiling coal-derived recycle solvents, or on the low and high boiling coal-derived recycle solvents after fractionation of a combined liquid products stream, or in situ in the liquefaction reactor where liquefaction conditions include a hydrogen treat rate of from about 0.1 to about 6 weight percent hydrogen (MAF coal). Hydrogen-donor compounds present in the low boiling coal-derived recycle solvent as a result of hydrogenation include without limitation one or more of such two-ring compounds as indane, tetrahydronaphthalene,

mcthyltetrahydronaphthalene and dimethyltetrahydronaphthalene. Hydrogen-donor compounds present as a result of hydrogenation in the high boiling coal derived solvent include, without limitation, one or more of such three-ring compounds as tetrahydroacenaphthene, acenaphthene, methylacenaphthene, octahydroanthracene, tetrahydroanthracene and dihydroanthracene.

In preparing the slurry fed to the liquefaction zone, the coal feedstock used to form two slurries is a solid particulate coal such as a bituminous coal, sub-bituminous coal, lignite, brown coal, or a mixture thereof. Although it is desirable to grind the coal to a particle size distribution of from about 8 mesh (Tyler) and smaller, it has been found that the coal suitably liquefies even in particles as large as one fourth inch on the major dimension are in a slurry. A typical proximate and ultimate analysis of a suitable high volatile bituminous coal is set forth in Table [V which follows:

Preferably the coal is dried to remove excess water, either by conventional techniques or preferably by mixing the moisture containing coal with a hot low or high boiling coal-derived solvent to volatilize water therefrom. Moisture in the resultant slurry preferably is less than about 2 weight percent.

The low and high boiling coal-derived solvents are separately suitably mixed with the particulate coal in a solvent-to-coal ratio of from about 0.8:] to about 2:1, preferably about 1.221. The slurry prepared with the low boiling solvent, which has a higher volatility than the high boiling solvent, suitably is prepared at a slightly higher solvent-to-coal ratio than the slurry prepared with the high boiling solvent, so as to main tain a selected solvent-to-coal ratio, e.g., 1.2:1, in the liquefaction reactor, where more of the lower boiling solvent will be in the vapor state.

Each of the separate slurries, the one prepared with the low boiling solvent and the other prepared with the about 0.1 to about 6 weight percent (MAF coal).

Liquefaction conditions in the separate reactors suitably may differ to optimize the liquefactions occurring in the different solvents.

The invention will be better understood byreference to the following detailed description of a preferred embodiment of it, which is depicted in the drawing.

DESCRIPTION OF THE DRAWING The drawing is a schematic flow'diagram of a coal liquefaction process conducted in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a high boiling coal-derived solvent recycle stream and a low boiling coalderived solvent recycle stream 12 are recovered, respectively, from

solvent hydrogenation reactors

52 and 54. The high boiling stream from line 10 suitably initially boils within the range from about 500 F. to about 600 F., e.g., about 550 F., and has a final boiling point of up to about l,000 F., suitably 700 F. The low boiling solvent recycle stream from line 12 suitably initially boils as low as about 300 F., e.g., 400 F., and termally boils within a range from about 500 F. to about 600 F., e.g., about 550 F. The low boiling solvent recycle stream in line 12 is mixed with a particulate coal, suitably 8 mesh (Tyler) and smaller, from line 16, at a solvent-to-coal ratio suitably within the range of about 0.8:1 to 2:1, e.g., about 1.3, to produce a first slurry. The high boiling solvent recycle stream from line 10 is separately mixed with a like coal, also suitably an 8 mesh (Tyler) and smaller, from line 14 at a solvent-to-coal ratio also suitably within the range from 0.811 to 2:1 e.g., about 1.2, to produce a second slurry stream. The first and second slurry streams are then conducted into furnace 18, where they are preheated to a temperature suitably within the range from 700 F. to 950 F., preferably from about 750 F. to about 850 F. The preheated second slurry stream is then led by line 20 into liquefaction reactor 24, and the preheated first slurry stream is carried by line 22 into liquefaction reactor 26. In the separate liquefaction reactors, the first and second slurries are separately liquefiedunder liquefactionconditions suitably including a temperature within the range from about 700 F. to about 950 F., preferably from about 750 F. to about 850 F., and a pressure suitably within the range from about 300 psig to about 3,000 psig, preferably from about 300 psig to about 2,500 psig. Preferably, hydrogen is introduced into

liquefaction reactors

24 and 26 so as to provide a hydrogen treat rate within the liquefaction reactors within the range from 0.1 to about 6 weight percent (MAF coal) to replenish hydrogen depleted hydrogen-donor molecules in the solvents.

After a suitable residencetime, e.g., from about 5 minutes to about 60 minutes, vaporous and gaseous materials are removed overhead from

liquefaction reactors

24 and 26 by way of

lines

34 and 36, respectively, for treatment to recover them in separate streams. Separate liquid liquefaction products comprised of a mixture of undepleted hydrogen donor solvent, depleted hydrogen donor solvent, dissolved coal, undissolved coal and mineral matter are recovered from

reactors

24 and 26, respectively, by

lines

28 and 30.

Lines

28 and 30 are then combined and charged to a fluid coker 40, which is preferably operated with a dense phase bed of coker particles maintained in fluidized state by steam and by evolution of vapor volatilization and cracking of the charge stream, as known in'the art. Within the fluid coker 40, the liquid hydrocarbons from line 32 undergo thermal cracking to produce various products which pass upwardly, usually through a cyclone-type separator (not illustrated), which returns coker particles back to the fluidized bed and permits the vaporous particles to ascend upwardly into a coker fractionator which is suitably mounted atop the fluid coker. In the coker fractionator, the vaporous products are liquefied and distilled according to boiling point. A liquid product boiling above the desired cut point for the solvent is suitably withdrawn by way of line 42, as product or for further upgrading. A heavy fraction, preferably boiling from about 550 F. to about 700 F., is withdrawn by way of line 44, suitably as liquid product, but at least in part, preferably for use as high boiling coal-derived recycle solvent. Similarly, a low boiling fraction, preferably boiling from about 400 F. to about 550 F., is withdrawn by way of line 46, suitably as liquid product, but at least partially, preferably for use as a low boiling coal-derived recycle solvent.

To upgrade its hydrogen content, the heavy solvent fraction in line 44 is carried by way of line 48 into a catalytic solvent hydrogenation reactor 52. Similarly, the low boiling solvent fraction in line 46 is carried by way of line 50 into a catalytic solvent hydrogenation reactor 54 for the same purpose. Hydrogenation conditions maintained in

solvent hydrogenation reactors

52 and 54 suitably include a nondestructive (i.e., noncracking) temperature within the range from about 650 F. to about 850 F., preferably about 700 F., and pressures suitably within the rangefrom about 650 psig to about 2,000 psig, preferably about 1,300 psig. Hydrogen is admixed with

streams

48 and 50, respectively, by way of lines 49 and 51 in sufficient excess to provide a total hydrogen treat rate in the reactors within the range from about 1,000 to about 10,000, preferably up to about 5,000, standard cubic feet of hydrogen per barrel of total feed to each reactor.

The hydrogenation catalysts employed in

reactors

52 and 54 are of conventional nature. Without being limited to any particular catalyst, these catalysts will typically comprise an alumina or silica-alumina support carrying one or more iron group metals and one or more metals of Group VI-B of the Periodic Table in the form of the oxides or sulfides. In particular, combination of one or more Group VI-B metal oxides of sulfides with one or more Group VIII metal oxides or sulfides are preferred. For example, typical catalyst metal combinations contemplated are oxides and/or sulfides of cobalt-molybdenum, nickel-tungsten,. nickel-molybdenum-tungsten', cobalt-nickel-molybdenum, nickel molybdenum, etc. As a typical example, one catalyst will comprise a high metal-content sulfided cobaltmolybdenum-alumina catalyst containing about 1 to 10 weight percent cobalt oxide and about 5 to 40 weight percent molybdenum oxide, especially about 2 to 5 weight percent cobalt and about 10 to 30 weight percent molybdenum. It will be understood thatother oxides and sulfides will be useful, such as those of iron, nickel, chromium, tungsten, etc. The preparation of these catalysts is now well known in the art..The active metals can be added to the relatively inert carrier by impregnation from aqueous solutions followed by drying and calcining to activate the composition. Suitable carriers include, for example, activated alumina, activated alumina-silica, zirconia, titania, etc., and mixtures thereof. Activated clays, such as bauxite, bentonite and montmorillonite, may also be employed.

A high boiling coal-derived recycle solvent stream having a hydrogen content no greater than about 9.5 weight percent is recovered from reactor 52 by way of line 10, and a low boiling coal-derived solvent recycle stream having a hydrogen content no greater than about 10.5 weight percent is recovered from reactor 54 by way of line 12. Each of the streams is then recycled to form separate slurries, as hereinbefore described.

The following example will demonstrate the unexpected increases in cyclohexane conversion obtained with the present process. Cyclohexane conversion is calculated by the equation:

% Conversion [S,S (100)]/[S,(l 0.0l

wherein a ash in the moisture-free coal feedstock S,= solids in the feed slurry, and

S, solids in the product slurry. Before measuring S cyclohexane is added to the product slurry as solvent, in the ratio of one volume per each volume of product slurry.

EXAMPLE Base Case: Liquefaction Using Total Solvent Using two hydrogenated creosote oils normally boiling from 400 F. to 700 F., a first having a hydrogen content of 7.67 weight percent and the second a hydrogen content of 8.42 weight percent, two slurries of Illinois No. 6 coal were prepared at a solvent-to-coal ratio of 1.2:1. Each slurry was introduced into a liquefaction reactor and subjected to a temperature of 775 F. and a pressure of 350 psig in contact with 0.3 weight percent hydrogen gas for a residence time of 30 minutes. Identical such slurries were identically liquefied several times. The cyclohexane conversion of the slurry prepared with the first 400l700 F. solvent was an average 23.9 weight percent (MAF coal), and that of the slurry prepared from the second 400/700" F. solvent was an average 35.2 weight percent (MAF coal).

Split Solvent Liquefaction Case One: Solvent No. l

The first 400/700 F. solvent was fractionated into a low boiling 400/ 50 F. cut and a high boiling 550/700 F. cut. The low boiling cut constituted about 49 volume percent of the 400/700 F. solvent and contained 8.03 weight percent hydrogen. The high boiling cut was 51 volume percent of the total solvent and had a hydrogen content of 7.23 weight percent. A slurry of Illinois No. 6 coal was prepared with each cut at l.2:l solvent-tocoal ratio, and each slurry was introduced into separate liquefaction reactors where each was subjected to the same liquefying conditions used in the base case. identically prepared first and second slurries were subjected to like liquefactions in several repeat experiments. The cyclohexane conversion of the slurry prepared with the 400/550 C. cut was an average 37.8 weight percent (MAF coal) and that of the slurry prepared with the 550/700 F. cut was an average 30.0 weight percent (MAF coal). Case Two: Solvent No. 2

Again using a cut point of 550 F., the second 400/700 F. solvent was fractionated into low and high boiling fractions, the low boiling fraction constituting about 52 volume percent of the total solvent and the high boiling fraction being about 48 volume percent thereof. The hydrogen content of the low boiling fraction was 8.78 weight percent, and that of the high boiling fraction was 8.01 weight percent. As in Case One, slurries were formed with each fraction at solvent-tocoal ratios of 1.2:1, and the slurries were liquefied under the base case conditions. Identically prepared first and second slurries were subjected to like liquefaction conditions in several repeat experiments. The cyclohexane conversion for the slurry prepared with the 400l550 F. fraction was an average 36.2 weight percent (MAF coal) and that of the 550/700 F. fraction was an average 36.3 weight percent (MAF coal).

The results of these liquefactions are summarized below.

Cyclohexane Conversion Wt.

MAF Coal Total Solvent 400l550 F. 50/700 F. 400/700 F. Cut Cut Solvent 1 23.9 37.8 30.0 Solvent 2 35.2 36.2 36.3

Surprisingly, higher cyclohexane conversions were obtained when slurries formed with high and low boiling fractions of a solvent were separately liquefied than when a slurry formed from the total solvent was liquefied under the same conditions. The cyclohexane conversion of each of the parts of the total solventwas greater than the conversion obtained with the whole total solvent, a totally unexpected effect. Thus, the total cyclohexane conversion on combining the liquefaction product of the two parts is greater than obtained with the whole solvent.

Having described our invention, various changes and variations of it will now occur to those skilled in the art, but insofar as these changes are substantially the same way of accomplishing the same end within the spirit and scope of the appended claims, they are deemed part of the invention.

We claim:

1. A process for liquefying coal, which comprises:

forming a first slurry of a particulate coal with a low boiling coal-derived solvent having an initial boiling point of at least about 300 F. and a final boiling point within the range from about 500". F. to about 600 F., and forming a second slurry of such coal with a high boiling coal-derivedsolvent having an initial boiling point within said range from about 500F. to about 600 F. and a final boiling point no higher than about 1,000" F., said final boiling point of said low boiling solvent and said initial boiling point of said high boiling solvent being substantially the same, and separately liquefying said first and second slurries under predetermined liquefaction conditions,

whereby the total cyclohexane conversion of said coal in said slurries is greater than if the coal had been slurried instead in a solvent resulting from the admixture of said. low boiling solvent and said high boiling solvent and then liquefied under like liquefaction conditions.

2. The process of claim 1 wherein said low boiling coal-derived solvent contains up to about 10.5 weight percent hydrogen, and wherein said high boiling coalderived solvent contains up to about 9.5 weight percent hydrogen. 7

3. The process of claim 1 wherein said liquefaction conditions include a hydrogen treat rate of from about 0.l to about 6 weight percent hydrogen (MAF coal).

4. The process of claim 1 wherein said liquefaction conditions include:

a temperature within the range from about 700 F. to

about 950 F.,

a pressure within the range from about 300 psig to about 3,000 psig, and

a liquid residence time within the range from about 5 to about 60 minutes.

5. A process for liquefying coal, which comprises:

forming a first slurry of a particulate coal with a low boiling coal-derived recycle solvent having an initial boiling point of at least about 300 F. and a final boiling point within the range from about 500 F. to about 600 F., and forming a second slurry of such coal with a high boiling coal-derived recycle solvent having an initial boiling point within the range from about 500 F. to about 600 F. and a final boiling point no higher than about 1,000 F., said final boiling point of said low boiling solvent and said initial boiling point of said high boiling solvent being substantially the same,

separately liquefying said first and second slurries under predetermined liquefaction conditions to produce first and second liquefaction products,

combining at least the liquids of said first and second liquefaction products to obtain a liquid products stream, and

fractionating said liquid products stream to separately recover said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent.

6. The process of claim 5 further comprising:

hydrogenating said liquid products stream under hydrogenation conditions correlated to add from about 0.1 to about 5 .0 weight percent of hydrogen to the liquids in said low boiling coal-derived recycle solvent and in said high boiling coal-derived recycle solvent, so that said low boiling coalderived recycle solvent contains up to about 10.5 weight percent hydrogen and said high boiling coal-derived recycle solvent contains up to about 9.5 weight percent hydrogen.

7. The process of claim 5 further comprising:

separately hydrogenating said low boiling coalderived recycle solvent and said high boiling coalderived recycle solvent under hydrogenation conditions correlated to add from about 0.1 to about 5.0 weight percent of hydrogen to said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent, so that said low boiling coal-derived recycle solvent contains up to about 10.5 weight percent hydrogen and said low boiling coal-derived recycle solvent contains up to about 9.5 weight percent hydrogen, and

separately recycling the hydrogenated, low boiling coal-derived recycle solvent and the hydrogenated, high boiling coal-derived recycle solvent for use in forming said first and second slurries.

8. The process of claim 5 in which said liquefaction conditions include a hydrogen treat rate of from about 0.1 to about 6 weight percent hydrogen (MAF coal).

9. The process of claim 5 in which low boiling coalderived recycle solvent boils from about 400 F. to about 550 F. and contains from about 7.5 to about 9.5

weight percent hydro en, and in which said high boilmg coa -der1ved recyc e solvent boils from about 550 F. to about 700 F. and contains from about 7 to about 9 weight percent hydrogen.

10. The process of claim 5 wherein said liquefaction conditions include:

a temperature within the range from about 700 F. to

about 950 F.,

a pressure within the range from about 300 psig to about 3,000 psig, and

a liquid residence time within the range from about 5 to about 60 minutes. 11. The process of claim 5 wherein said first and second slurries are each formed at a solvent-to-coal ratio of from about 0.8:1 to about 2:1.

12. A process for liquefying coal, comprising: forming first and second slurries of a particulate coal 8 mesh (Tyler) and smaller at a solvent-to-coal ratio of about 1.2, the first slurry being formed with a low boiling coal-derived recycle solvent boiling from about 400 F. to about 550 F., and the second slurry being formed with a highboiling coal-derived recycle solvent boiling from about 550 F. to about 700 F.,

separately liquefying said first and second slurries under liquefaction conditions including a temperature from about 700 F. to about 950 F., a pressure from about 300 psig to about 3,000 psig, and a liquid residence time from about 5 to about 60 minutes, to produce first and second liquefaction products,

fractionating said liquid products stream to separately recover. said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent.

13. The process of claim 12 wherein said liquefaction conditions include a hydrogen treat rate within the range from about 0.1 to about 6 weight percent hydrogen (MAF coal).

14. The process of claim 12 wherein said low boiling coal derived recycle solvent contains from about 7.5 to about 9.5 weight percent hydrogen and wherein said high boiling coal-derived recycle solvent contains from about 7 to about 9 weight percent hydrogen.

Claims

2. The process of claim 1 wherein said low boiling coal-derived solvent contains up to about 10.5 weight percent hydrogen, and wherein said high boiling coal-derived solvent contains up to about 9.5 weight percent hydrogen.
3. The process of claim 1 wherein said liquefaction conditions include a hydrogen treat rate of from about 0.1 to about 6 weight percent hydrogen (MAF coal).
4. The process of claim 1 wherein said liquefaction Conditions include: a temperature within the range from about 700* F. to about 950* F., a pressure within the range from about 300 psig to about 3,000 psig, and a liquid residence time within the range from about 5 to about 60 minutes.
5. A process for liquefying coal, which comprises: forming a first slurry of a particulate coal with a low boiling coal-derived recycle solvent having an initial boiling point of at least about 300* F. and a final boiling point within the range from about 500* F. to about 600* F., and forming a second slurry of such coal with a high boiling coal-derived recycle solvent having an initial boiling point within the range from about 500* F. to about 600* F. and a final boiling point no higher than about 1,000* F., said final boiling point of said low boiling solvent and said initial boiling point of said high boiling solvent being substantially the same, separately liquefying said first and second slurries under predetermined liquefaction conditions to produce first and second liquefaction products, combining at least the liquids of said first and second liquefaction products to obtain a liquid products stream, and fractionating said liquid products stream to separately recover said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent.
6. The process of claim 5 further comprising: hydrogenating said liquid products stream under hydrogenation conditions correlated to add from about 0.1 to about 5.0 weight percent of hydrogen to the liquids in said low boiling coal-derived recycle solvent and in said high boiling coal-derived recycle solvent, so that said low boiling coal-derived recycle solvent contains up to about 10.5 weight percent hydrogen and said high boiling coal-derived recycle solvent contains up to about 9.5 weight percent hydrogen.
7. The process of claim 5 further comprising: separately hydrogenating said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent under hydrogenation conditions correlated to add from about 0.1 to about 5.0 weight percent of hydrogen to said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent, so that said low boiling coal-derived recycle solvent contains up to about 10.5 weight percent hydrogen and said low boiling coal-derived recycle solvent contains up to about 9.5 weight percent hydrogen, and separately recycling the hydrogenated, low boiling coal-derived recycle solvent and the hydrogenated, high boiling coal-derived recycle solvent for use in forming said first and second slurries.
8. The process of claim 5 in which said liquefaction conditions include a hydrogen treat rate of from about 0.1 to about 6 weight percent hydrogen (MAF coal).
9. The process of claim 5 in which low boiling coal-derived recycle solvent boils from about 400* F. to about 550* F. and contains from about 7.5 to about 9.5 weight percent hydrogen, and in which said high boiling coal-derived recycle solvent boils from about 550* F. to about 700* F. and contains from about 7 to about 9 weight percent hydrogen.
10. The process of claim 5 wherein said liquefaction conditions include: a temperature within the range from about 700* F. to about 950* F., a pressure within the range from about 300 psig to about 3,000 psig, and a liquid residence time within the range from about 5 to about 60 minutes.
11. The process of claim 5 wherein said first and second slurries are each formed at a solvent-to-coal ratio of from about 0.8:1 to about 2:1.
12. A process for liquefying coal, comprising: forming first and second slurrIes of a particulate coal 8 mesh (Tyler) and smaller at a solvent-to-coal ratio of about 1.2, the first slurry being formed with a low boiling coal-derived recycle solvent boiling from about 400* F. to about 550* F., and the second slurry being formed with a high boiling coal-derived recycle solvent boiling from about 550* F. to about 700* F., separately liquefying said first and second slurries under liquefaction conditions including a temperature from about 700* F. to about 950* F., a pressure from about 300 psig to about 3,000 psig, and a liquid residence time from about 5 to about 60 minutes, to produce first and second liquefaction products, combining at least the liquids of said first and second liquefaction products to obtain a liquid products stream, and fractionating said liquid products stream to separately recover said low boiling coal-derived recycle solvent and said high boiling coal-derived recycle solvent.
13. The process of claim 12 wherein said liquefaction conditions include a hydrogen treat rate within the range from about 0.1 to about 6 weight percent hydrogen (MAF coal).
14. The process of claim 12 wherein said low boiling coal derived recycle solvent contains from about 7.5 to about 9.5 weight percent hydrogen and wherein said high boiling coal-derived recycle solvent contains from about 7 to about 9 weight percent hydrogen.