GB1564829A - Hydrogen-donor solvent coal liquefaction process - Google Patents

Description

(54) HYDROGEN-DONOR SOLVENT COAL LIQUEFACTION PROCESS (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a hydrogendonor solvent coal liquefaction process.

Processes for the conversion of coal into useful petroleum-like liquid products have been known for many years. Of particular interest are those which utilize a hydrogen transfer, or hydrogen donor solvent to hydrogenate and liquefy the coal. In such processes, crushed coal is contacted at elevated temperature and pressure with a selective solvent, often a liquid fraction derived from within the process, which acts as a hydrogen donor to supply hydrogen to the hydrogen-deficient coal molecules, as molecules are thermally cracked and cleaved from disintegrating coal solids.

In breaking coal molecules, since coal largely comprises polymerized multi-ring hydroaromatic structures, each bond rupture results in the formation of two extremely reactive free radicals. These moieties are stabilized by the addition of a hydrogen atom, and those which are sufficiently small are evolved as a portion of the liquid product. If excessively large, the fragments remain with the char that is produced. If insufficient hydrogen is available, polymerization of the moieties occurs, thus producing char or coke.

Coal is not a pure hydrocarbon and, whereas much of the coal has been successfully converted to useful petroleum .like liquids, the amount of such liquids which can be produced is quite variable.

The liquid products themselves vary considerably in composition, and liquids are only a portion of the total products that are produced. Coal contains bitumin and humin which have large, flat, aromatic, lamellar structures that differ in molecular weight, degree of aromaticity, oxygen and nitrogen contents and degree of cross-linking. The product liquids produced from coal thus vary widely in composition. Coal also contains volatile matter, fusain, mineral matter, and sulfur, such as pyritic sulfur, inorganic sulfates and organic sulfur compounds. The product liquids thus contain fusinite and ash, as well as char and sludge, which must be separated from the liquids.The heavy products from such coal liquefaction processes, characterized as "liquefaction bottoms" and consisting of 1000"F. + organics, ash and carbon residue (fusinite), consist largely of carbon, 6070 weight percent, and about 20 weight percent ash. The liquefaction bottoms, which are less useful than the 1000"F. - liquids, generally contain 4W50 weight percent of the original feed coal to the process.

Such processes thus leave much to be desired in terms of carbon effeciency, which can be defined as the amount of conversion of carbon to useful liquid products. It is desirable to obtain higher levels of conversion, and to reduce the level of formation of the excessively high molecular weight hydrocarbons which occur in the process.

One approach to the improvement in carbon efficiency, whatever the mechanism, is due to an improvement in the quality of the hydrogen donor solvent used in the coal liquefaction zone.

It is accordingly an object of the present invention to provide an improved coal liquefaction process, employing solvents which are suitable for improving carbon feed efficiencies by better utilization of coal feeds to produce greater quantities of the more useful liquids.

According to the present invention there is provided a process for producing coal liquids, comprising liquefying a slurry of coal in a hydrogen-donor solvent under coal liquefaction conditions which include a temperature of 7500 F to 9500 and a pressure of 300 psia to 3000 psia; the liquefaction being conducted in the presence of at least added liquefaction promoter selected from polar heterocyclic compounds which (i) either have a single 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen atom, or have 2 to 6 fused rings of which at least one is a 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen, sulfur or oxygen atom, and (ii) have up to a total of 36 carbon atoms per molecule.

In a preferred embodiment the liquefaction comprises a series of steps which include (a) subjecting a said slurry in a liquefaction zone to a temperature and pressure in said ranges, to hydro-convert and liquefy the coal; (b) separating the product from the liquefaction zone by distillation into fractions including a liquid fraction boiling within the range 350 to 850"F and which contains at least 30wt.% hydrogen donor compounds; (c) hydrogenating said liquid fraction in a hydrogenation zone to form a hydrogendonor solvent; (d) adding to the thus formed solvent a total of 3 to 50%, based on the weight of total sovent of said heterocyclic compound(s); and (e) recycling the product of step (d) to the said liquefaction zone.

The heterocyclic compound(s) employed is/are polar. To be effective they must, of course, be stable at the conditions of operation, and must be capable of promoting liquefaction of high molecular weight hydrocarbons within the reaction mixture, particularly the 10000 F + hydrocarbons.

When the said heterocyclic compound is one having a ring fused to another ring, or to more than one other ring, each other ring can be heterocylic or non-heterocyclic or non-heterocyclic, particularly aromatic.

Generally, the heterocyclic compound's molecule(s) can be substituted or unsubstituted, and in terms of carbon atoms the total molecule will preferably contain 8 to about 2-0 carbon atoms, and most preferably from 8 to about 12 carbon atoms.

Ring substituents which increase the polarity of the total molecule are particularly desirable, such groups as oxy, hydroxy, nitro, amino, acetamide, carboxy, carboxy amide, halo, alkyl, alkoxy, phenoxy and the like being preferred substituents, notably the methyl, methoxy, ethyl and ethoxy substituents. The substituting groups themselves can be substituted or unsubstituted, and more than one substituent, or substituting group can be present in the molecule. The substituent group, or groups, can contain oxygen, nitrogen, or sulfur within the ring, or attached to a ring carbon atom.Exemplary of heterocyclic oxygen compounds of this character are benzofuran, naphthenobenzofuran, dibenzofuran, naphthenodibenzofuran, phenanthrenofuran, naphthenophenanthrenofuran, 1,2-beuzopyran, 2 furo[3,4-cl-pyrazole, 2,7-dioxapyrene, spiro [benzofuran-3(2),4'-piperidinel and the like, and exemplary of heterocyclic sulfur compounds of this character are benzothiophene, naphthenobenzothiophene, dibenzothiophene, naphthenodibenzothiophene, phenanthrenothiophene, naphthenophenanthrenothiophene, 2-(o-nitrophenyldithio)benzothiazole, 10-thiaxanthenol and the like.Exemplary of such heterocyclic nitrogen compounds of this character are pyrrole, pyrrolidone, n-methyl pyrrolidone, pyridine, P-picoline, p-phenoxy-picoline, p- cresyl-picoline, 2-acetoamido-pyridine, 1acetylpiperidine, 1,2,3,4-tetrahydroquinoline, 2-acetamidoquinoline, 10-benzylacridine, and the like.

The heterocyclic compound must be one which is polar, and desirable one which also either posses or can be hydrogenated such that it will possess donatable hydrogen in or near the ring, or both Where the hydrogen donor quality does not exist in the heterocyclic oxygen, sulfur or nitrogen compound, however, this function can and must be added by admixture with a compound, or admixture of compounds, which supplies this characteristic. The heterocyclic oxygen, sulfur or nitrogen compound in its role as a hydrogen donor is thus an unsaturated compound of considerable stability at coal liquefaction conditions which can be further hydrogenated, preferably an aromatic compound which can be hydrogenated in situ or ex situ of the coal liquefaction zone.

On donation of the hydrogen at coal liquefaction conditions, the stability of the now unsaturated compound is retained. In the instance of an aromatic compound, the aromatic compound, e.g., contains hydroaromatic hydrogen which it donates, but remains stable at coal liquefaction conditions. In general, the heterocyclic oxygen, sulfur or nitrogen compound, or admixture of such compounds, boils within the range of from 250"F to 8500 F., and preferably from about 290"F. to about 700 F.

In accordance with the practice of this invention, the heterocyclic oxygen, sulfur or nitrogen compound, or admixture of such compounds, is added to a liquid fraction separated from the liquid products obtained from within the process, suitably a fraction boiling within the range of from about 350"F. to about 850"F., and preferably from about 4000 F. to about 7000 F. These fractions have been found admirably suitable as a solvent donor, solvent donor vehicle or precursor, and generally contain about 30 percent, and most often about 50 percent, of an admixture of hydrogen donor compounds, adequate to supply the necessary hydrogen under coal liquefaction conditions, based on the total weight of the recycled solvent.Where such amounts of hydrogen donor compounds are not present in a given solvent vehicle, additional amounts of these materials can be added.

Suitably, the heterocyclic oxygen, sulfur or nitrogen compound is added to the solvent fraction in quantity ranging from about 3 to about 50 percent, preferably from about 5 to about 20 percent, based on the weight of total solvent fed into the coal liquefaction zone.

Preferred hydrogen donor compounds added to, or originally contained within a suitable solvent donor vehicle, include indane, dihydronaphthalene, C10-C12 tetrahydronaphthalenes, hexahydrofluorine, the dihydro-, tetrahydro-, hexahydro-, and octahydro-phenanthrenes, C12- C13 acenaphthenes, the tetrahydro-, hexahydroand decahydro-pyrenes, the dihydro-, tetrahydro-, hexahydro-, and octahydroanthracenes, and other derivates of partially saturated aromatic compounds.In terms of hydrogen donor potential, the solvent to which the heterocyclic oxygen, sulfur or nitrogen compound is added, at the time of its introduction into use or within the coal liquefaction zone, very preferabfy contains at least 0.8 percent, and even more preferably from 1.2 to 3 percent of donatable hydrogen, based on the weight of total solvent introduced into the coal liquefaction zone. The preferred hydrogen donor solvent is one produced within the coal liquefaction process, and to which the heterogeneous oxygen, sulfur or nitrogen compound is added. Suitably, the solvent is added to the coal in concentration adequate to provide a solvent-to-coal ratio ranging from about 0.8:1 to about 4:1.

The reason for the effectiveness of the heterogeneous oxygen, sulfur or nitrogen compound, or admixture thereof, added to the solvent for increasing the conversion of coal to lower molecular weight, more useful liquid petroleum-like products is not understood. It is believed that the high solvency power of the heterogeneous oxygen, sulfur or nitrogen compound progressively enhances dispersion of the high molecular weight compounds, notably those boiling at 1000 F. +, as liquefaction proceeds. The free radicals produced by the thermal cracking of the large coal molecules are thus known to be extremely short-lived and are formed principally at the solid interfaces wherein the coal solids particles are being dissolved.By improving contact between the hydrogen donor solvent and these moieties, repolymerization of some of these moieties with other molecules or with each other is suppressed. The greater effectiveness of the hydrogen donor molecules in their role of reaching the extremely reactive-free radicals as they are formed, and more effectively hydrogenating said radicals. is thus believed to account largely for these improvements.

During liquefaction, it is thus believed that the coal molecule is dispersed by the solvent to form aggregates of colloidal nature. In general, an aggregate has a polyaromatic nuclei of the coal micelle at its center. The polyaromatic nuclei is surrounded by high and low molecular weight aromatics. The high molecular weight aromatics are formed from disintegration of coal, and the low molecular weight aromatics from the hydroaromatic solvent after donation of hydrogen to the free radicals of coal. The outer layer of aromatics is surrounded by hydroaromatics and the latter are surrounded by more saturated compounds.

The solvent, it is believed, tends to disperse or pull apart the aggregate, thereby enabling the donor solvent to contact the polyaromatic nuclei. Penetration of the liquefaction barrier, made possible by the addition of the solvent, has the effect of accelerating the hydrogen transfer to the thermally cracked coal free radicals.

In the best mode of practicing the present invention, the heterocyclic oxygen, sulfur or nitrogen containing compound, or admixture thereof, is added to a hydrogen donor solvent fraction produced from within the coal liquefaction process. In such process, schematically illustrated by reference to the figure, the required process steps generally include (a) a mixing zone 10 within which particulate coal is slurried with an internally generated liquids fraction, suitably one within which the heterocyclic oxygen, sulfur or nitrogen compound has been added, (b) a coal liquefaction zone 20 within which the coal slurry and hydogen are fed, and the coal liquefied, (c) a distillation and solids separation zone 30 within which a solvent fraction, a 1000"F. + heavy bottoms fraction, and liquid product fraction are separated, and (d) a catalytic solvent hydrogenation zone 40 wherein the solvent fraction is hydrogenated prior to its being recycled to said coal liquefaction zone 20.

In the mixing zone 10, particulate coal of size ranging up to about 1/8 inch particle size diameter, suitably 8 mesh (Tyler), is slurried in recycle solvent. The heterocyclic oxygen, sulfur or nitrogen compound is added to the solvent in concentrations ranging from about 3 to about 50 weight percent, preferably from about 5 to about 20 weight percent. The total solvent and coal are admixed in a solvent-to-coal ratio ranging from about 0.8:1 to about 4:1, preferably about 1.2.: 1 to about 1.6:1, based on weight.In general, the solvent to which the heterocyclic oxygen, sulfur or nitrogen compound is added is one which boils within the range of 2500 F. to 8500 F., advantageously from 3500 F. to 8500 F, preferably from 290"F. to 700"F. The coal slurry is fed, preferably with molecular hydrogen, into the coal liquefaction zone 20.

Within the coal liquefaction zone 20, liquefaction conditions include a temperature ranging from a minimum of at least 750"F. (as in all Examples herein) to a maximum of 9500 F. As shown by the majority of the Examples the minimum temperature is at least 7600 F. A preferred range is 800"F. to 850"F. Pressures range from 300 psia to 3000 psia, preferably from about 800 psia to about 2000 psia.

Preferably, molecular hydrogen is also added to the liquefaction zone 20 at a rate from about 1 to about 6 weight percent (MAF coal basis), liquid residence times ranging from about 5 to about 130 minutes, and preferably from about 10 to about 60 minutes.

The product from the coal liquefaction zone 20 consists of gases and liquids, the liquids comprising a mixture of undepleted hydrogen-donor solvent, depleted hydrogen-donor solvent, heterocyclic oxygen, sulfur or nitrogen compound, or compounds, dissolved coal, undissolved coal and mineral matter. The liquid mixture is transferred into a separation zone 30 wherein light fractions boiling below 4000 F.

useful as fuel gas are recovered and intermediate fractions boiling, e.g., from 4000 F. to 7000F. are recovered for use as a hydrogen donor solvent. Heavier fractions boiling from about 700"F. to 10000 F. are also recovered, and bottoms fractions boiling over 10000 F., including char, are withdrawn for use in the gasification process or for coking, as desired.

The solvent fraction or 400 F.

fraction is introduced into a catalytic solvent hydrogenation zone 40 to upgrade the hydrogen content of that fraction. The conditions maintained in hydrogenation zone 40 hydrogenate, and if desired, conditions can be provided which produce substantial cracking. Temperatures normally range from about 650"F. to about 850"F., preferably from about 700"F. to about 800"F., and pressures suitably range from about 650 psia to about 2000 psia, preferably from about 1000 psia to about 1500 psia. The hydrogen treat rate ranges generally from about 1000 to about 10,000 SCF/B, preferably from about 2000 to about 5000 SCF/B.

The hydrogenation catalyts employed are conventional. Typically, such catalysts comprise an alumina or silica-alumina support carrying one or more Group VIII non-noble, or iron group metals and one or more Group VI-B metals of the Periodic Table. In particular, combinations of one or more Group VI-B metal oxides or sulfides with one or more Group VIII metal oxides or sulfides are preferred. Typical catalyst metal combinations include oxides and/or sulfides of cobalt-molybdenum, nickel molybdenum, nickel-tungsten, nickel molybdenum-tungsten, cobalt-nickel molybdenum and the like.A suitable cobalt molybdenum catalyst is one comprising from about I to about 10 weight percent cobalt oxide and from about 5 to about 40 weight percent molybdenum oxide, especially about 2 to 5 weight percent cobalt and about 10 to 30 weight percent molybdenum.

Methods for the preparation of these catalysts are well known in the art. The active metals can be added to the support. or carrier, typically alumina, 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, can also be employed.

These and other features of the present process will be better understood by reference to the following demonstration of prior art runs conducted without benefit of the added heterocyclic oxygen, sulfur or nitrogen compound, and to exemplary comparative data obtained by liquefying the coal slurries in accordance with this invention, i.e., with added heterocyclic oxygen, sulfur or nitrogen compounds. All units are in terms of weight unless otherwise specified.

Example 1.

Stainless steel tubing bombs of 30 ml.

capacity were charged with slurries of -100 mesh (Tyler) Illinois No. 6 coal in various solvents at solvent-to-coal ratios of 2:1, with 2 percent added molecular hydrogen, based on the weight of coal. One set of the bombs was agitated at 120 cycles per minute for 130 minutes (Runs 1, 2, 3 and 4) and another was agitated at the same rate for 40 minutes (Runs 5, 6 and 7) in a fluidized sandbath heated sufficiently to provide reaction temperatures. Various other conditions of operation, the nature of the solvent systems, and the results of these runs are given in Tables I and 2.

The data in Tables I and 2 thus clearly show, inter alia, the following advantages, to wit: TABLE 1 Run No. 1 2 3 4 Liquefaction Information Temperature, F. 760 760 760 760 Pressure, psig 1675 1675 1500 1500 Residence Time, min. 130 130 130 130 Solvent Type Tetralin + Tetralin + Tetralin + Tetralin cyclopentanone tetrahydrofuran dibenzothiophene Dry Feed, g 3.00 3.00 3.00 3.00 Solvent, g 4.80 + 1.20 4.80 + 1.20 4.80 + 1.20 6.00 H2 Feed, Wt. % Dry Coal 2.00 2.00 2.00 2.00 Chemical Analysis Ash, Wt. % Solid Residue 15.56 17.75 18.18 15.77 Yields, Wt. % Dry Coal H2 Consumption 0.18 - 0.24 0.04 Gas Make 5.10 12.36 4.53 4.50 H2 - 0.11 - COx 2.73 6.27 1.75 1.80 H2S 0.33 0.26 0.47 0.44 C1-C3 1.86 4.99 2.15 2.10 C4 + 0.18 0.84 0.16 0.16 H2O Make 6.00 3.71 6.29 6.77 Solid Residue 57.1 50.0 48.8 56.3 Liquid Make 32.0 33.9 40.6 32.5 Conversion 42.9 50.0 51.2 43.7 TABLE 2 Run No. 5 6 7 Liquefaction Information Temperature, F. 813 813 820 Pressure, psig 2250 1675 1800 Residence Time, min. 40 40 40 Solvent Type Tetralin + Tetralin + Tetralin tetrahydrofuran dibenzofuran Dry Feed, g 3.00 3.00 3.00 Solvent, g 4.80 + 1.20 4.80 + 1.20 6.00 H2 Feed, Wt. % Dry Coal 2.0 2.0 2.0 Chemical Analysis Ash, Wt. % Solid Residue 22.55 21.35 19.39 Yields, Wt. % Dry Coal H2 Consumption - 0.22 0.15 Gas Make 17.36 5.83 6.52 H2 0.65 - COx 9.09 1.65 1.97 H2S 0.33 0.88 0.71 C1-C3 6.82 2.99 3.62 C4 + 0.47 0.31 0.22 H2O Make 3.71 6.75 8.32 Solid Residue 44.7 47.2 Liquid Make 34.3 40.5 33.4 Conversion 55.3 52.8 48.1 Referring first to Table 1, comparison of Runs 3 and 4 shows that the presence of dibenzothiophene produces a major advantage in increasing liquids yield, and in the amount of conversion. These data thus show an increase of 8.1 percent liquids (40.6-32.5), and an increase of 7.5 percent in the level of conversion when the solvent used in the reaction contains dibenzothiophene, as contrasted with a solvent which did not include dibenzothiophene.

The gas make in the two runs is essentially the same.

Referring to Table 2, comparison of Runs 6 and 7 also shows advantages in the use of a solvent which contains dibenzofuran as contrasted with a solvent otherwise similar except that it contains no dibenzofuran.

Referring to the data, it will thus be observed that the solvent used in Run 6 contained dibenzofuran whereas the solvent used in Run 7 did not. The run which employed dibenzofuran, i.e. Run 6, thus produced 7.1 percent more liquid than was produced in Run 7, and 4.7 percent higher conversion than was produced in Run 7.

Whereas tetrahydrofuran (Runs 2 and 5) provided high conversion, the excess gases that were produced make the use of these species undesirable. It is also to be noted (Run I) that the use of cyclopentanone was ineffective.

Example 2.

Two 30 ml. stainless steel tubing bombs were charged with a slurry of Illinois No. 6 coal in tetralin at a solvent-to-coal ratio of 2:1, and 2 percent molecular hydrogen, based on the weight of coal. The bombs were agitated at 120 cycles per minute for 130 minutes in a fluidized sandbath heated to a temperature sufficient to provide a reaction temperature of 7500 F., and a pressure of 1500 psig. The liquid products recovered from the bombs illustrative of runs made without an added heterocyclic oxygen, sulfur or nitrogen compound showed an average cyclohexane conversion of 54 weight percent (dry coal).

The following are illustrative of comparative runs made with benefit ofan added heterocyclic nitrogen compound.

Two bombs, as used in the foregoing demonstration, were charged with slurries of Illinois No. 6 coal in a solvent mixture consisting of 80 percent tetralin and 20 percent p-picoline, the mixture providing a 2:1 solvent-to-coal ratio.

Reaction conditions were otherwise precisely the same as in the foregoing demonstration. The liquid recovered from the bombs showed an average cyclohexane conversion of 61 weight percent (dry coal).

These comparative results are summarized in Table 3 below.

Table 3.

Cyclohexane Conversion, Wt. Percent Dry Coal Run: No added heterocyclic 54 nitrogen compound p-picoline 61 Clearly, liquid yields measured by cyclohexane conversion were notably increased by inclusion of the heterocyclic nitrogen compound in the slurried coal.

Additional comparative runs were conducted, at different conditions, to show various other advantages achieved via use of the heterocyclic nitrogen compounds in coal liquefaction reactions. The results of these runs are set out in the following examples.

Example 3.

A series of bombs, as used in Exmple 1, were charged with coal slurries of 100 mesh No. 6 Illinois coal in various solvents in a solvent-to-coal ratio of 2:1, and agitated at a rate of 120 cycles per minute throughout the entire period of reaction. Various other conditions of operation, the nature of the solvent system, and the results of these runs are given in Table 4.

TABLE 4 Run No. 1 2 3 4 5

Liquefaction Information Temperature, F. 800 800 750 750 800 Pressure, psig 3040 2350 1581 1597 2004 Residence Time, Min. 94 130 130 130 130 Solvent Type 1,2,3,4-tetra Tetralin Tetralin Tetralin (80%) Tetralin (80%) hydroquinoline ss-Picoline (20%) Pyridine (20%) Dry Feed, g. 7.0000 6.9999 3,0003 3,0011 3,0018 Solvent, g. 14.0082 14.0149 6.0019 4.8020 4.8029 H2 Feed, Wt.% Dry Coal - - 1.95 1.95 1.92 Chemical Analysis (A) 28.45 28.96 19.45 22.88 29.14 Ash, Wt. % Solid Residue* # (B) 28.28 24.55 20.04 22.90 28.02 S, Wt. % Liquid 0.53 0.42 0.36 0.46 N, Wt. % Liquid 9.79 0.49 0.21 4.17 Yields, Wt. % Dry Coal H2 Consumption - - 0.47 0.94 0.82 Gas Make 9.17 7.09 3.09 3.15 5.91 H2 0.27 0.26 - - COx 1.39 2.19 1.34 0.59 0.49 H2S 0.19 0.21 0.10 0.06 0.07 C1-C3 6.92 4.23 1.58 2.20 4.99 C4+ 0.82 0.20 0.09 0.30 0.36 H2O Make - 6.11 4.81 4.66 3.37 (A) 31.07 30.52 45.66 38.81 30.44 Solid Residue* # (B) 31.36 36.13 44.26 38.73 31.66 Liquid Make - 56.29 46.91 54.32 61.10 * Determinations by two different analytical groups, A and B.

The data in Table 4 thus clearly show, inter alia, the following advantages, to wit: Comparison of Runs 1 and 2 shows that the presence of 1,2,3,4-tetrahydroquinoline produces a major advantage in reducing the quantity of solids residue. These data thus show a solids residue of only 31 percent when the solvent used in the reaction contains 1,2,3,4-tetrahydroquinoline vis-avis 33 percent (average of two methods) as contrasted with a solvent which did not include 1,2,3,4-tetrahydroquninoline, albeit the residence time of the coal liquids in the reactor was only 94 minutes as contrasted with 130 minutes for the reaction which did not contain 1,2,3,4-tetrahydroquinoline.

Advantages are also shown in the use of a solvent which contained A-picoline as contrasted with a solvent otherwise similar except that it contained no p-picoline.

Referring to the data, it will be observed that the solvent used in Run 4 contained p- picoline whereas the solvent used in Run 3 did not. The run which employed p-picoline, i.e., Run 4, thus produced 7 percent less solids than was produced in Run 3, and 7 percent more total liquids was produced in Run 4.

The same improvements are manifest in Run 5 wherein pyridine was included as a part of the solvent employed in the reaction, this example showing a 5 percent increase in total liquids as contrasted with Run 2.

WHAT WE CLAIM IS: 1. A process for producing coal liquids, comprising liquefying a slurry of coal in a hydrogen-donor solvent under coal liquefaction conditions which include a temperature of 750"F to 9500F and a pressure of 300 psia to 3000 psia; the liquefaction being conducted in the presence of at least one added liquefaction promoter selected from polar heterocyclic compounds which (i) either have a single 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen atom, or have 2 to 6 fused rings of which at least one is a 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen, sulfur or oxygen atom, and (ii) have up to a total of 36 carbon atoms per molecule.

2. A process according to claim 1 wherein a total of 3 to 50%, based on the weight of total solvent, of said added compound(s) is employed.

3. A process according to claim 1 or claim 2, wherein the heterocyclic compound(s) is or are present ab initio in the hydrogendonor solvent employed in slurrying the coal.

4. A process according to claim 1, wherein the liquefaction comprising a series of steps which include (a) subjecting a said slurry in a liquefaction zone to a temperature and pressure in said ranges to hydroconvert and liquefy the coal; (b) separating the product from the liquefaction zone by distillation into fractions including a liquid fraction boiling within the range 350 to 8500F and which contains at least 30 wt.% hydrogen donor compounds; (c) hydrogenating said liquid fraction in a hydrogenation zone to form a hydrogendonor solvent; (d) adding to the thus formed solvent a total of 3 to 50%, based on the weight of total solvent of said heterocyclic compound(s); and (e) recycling the product of step (d) to the said liquefaction zone.

5. A process according to claim 4, wherein the said liquid fraction contains at least 50 wit.% hydrogen donor compounds.

6. A process according to any one of claims 3 to 5, wherein the hydrogen donor solvent contains from 5 to 20 wt.% of said added compound.

7. A process according to any preceding claim, wherein the hydrogen donor solvent contains at least 0.8% donatable hydrogen, based on the weight of the solvent.

8. A process according to claim 7, wherein there is 1.2 to 3% of said donatable hydrogen.

9. A process according to any preceding claim, wherein the said hydrogen-donor solvent is one boiling within the range 2500 F to 8500 F.

10. A process according to any preceding claim, wherein the hydrogen donor solvent is admixed with the coal to provide a solvent-to-coal ratio of 0.8:1 to 4:1.

I I. A process according to any preceding claim, wherein the slurry of coal is also contacted with molecular hydrogen at a treat rate of from about 1 to 6 wit.% (MAF coal basis).

12. A process according to any preceding claim, wherein the heterocyclic compound(s) boil in the range 2500F to 850"F.

13. A process according to any preceding claim, wherein the heterocyclic compound(s) employed contain only one heterocyclic atom in the nucleus.

14. A process according to any preceding claim, wherein the heterocyclic compound(s) contain 2 or 3 fused rings, at least one of which contains one heterocyclic atom in the nucleus.

15. A process according to any preceding claim, wherein the heterocyclic atom is oxygen or sulfur.

16. A process according to any one of claims 1 to 14 wherein the heterocyclic atom is nitrogen 17. A process for producing coal liquids as claimed in claim 1 and substantially as

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. The data in Table 4 thus clearly show, inter alia, the following advantages, to wit: Comparison of Runs 1 and 2 shows that the presence of 1,2,3,4-tetrahydroquinoline produces a major advantage in reducing the quantity of solids residue. These data thus show a solids residue of only 31 percent when the solvent used in the reaction contains 1,2,3,4-tetrahydroquinoline vis-avis 33 percent (average of two methods) as contrasted with a solvent which did not include 1,2,3,4-tetrahydroquninoline, albeit the residence time of the coal liquids in the reactor was only 94 minutes as contrasted with 130 minutes for the reaction which did not contain 1,2,3,4-tetrahydroquinoline. Advantages are also shown in the use of a solvent which contained A-picoline as contrasted with a solvent otherwise similar except that it contained no p-picoline. Referring to the data, it will be observed that the solvent used in Run 4 contained p- picoline whereas the solvent used in Run 3 did not. The run which employed p-picoline, i.e., Run 4, thus produced 7 percent less solids than was produced in Run 3, and 7 percent more total liquids was produced in Run 4. The same improvements are manifest in Run 5 wherein pyridine was included as a part of the solvent employed in the reaction, this example showing a 5 percent increase in total liquids as contrasted with Run 2. WHAT WE CLAIM IS:

1. A process for producing coal liquids, comprising liquefying a slurry of coal in a hydrogen-donor solvent under coal liquefaction conditions which include a temperature of 750"F to 9500F and a pressure of 300 psia to 3000 psia; the liquefaction being conducted in the presence of at least one added liquefaction promoter selected from polar heterocyclic compounds which (i) either have a single 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen atom, or have 2 to 6 fused rings of which at least one is a 5 or 6 membered heterocyclic ring having in the nucleus 4 or 5 carbon atoms and at least one nitrogen, sulfur or oxygen atom, and (ii) have up to a total of 36 carbon atoms per molecule.

2. A process according to claim 1 wherein a total of 3 to 50%, based on the weight of total solvent, of said added compound(s) is employed.

3. A process according to claim 1 or claim 2, wherein the heterocyclic compound(s) is or are present ab initio in the hydrogendonor solvent employed in slurrying the coal.

4. A process according to claim 1, wherein the liquefaction comprising a series of steps which include (a) subjecting a said slurry in a liquefaction zone to a temperature and pressure in said ranges to hydroconvert and liquefy the coal; (b) separating the product from the liquefaction zone by distillation into fractions including a liquid fraction boiling within the range 350 to 8500F and which contains at least 30 wt.% hydrogen donor compounds; (c) hydrogenating said liquid fraction in a hydrogenation zone to form a hydrogendonor solvent; (d) adding to the thus formed solvent a total of 3 to 50%, based on the weight of total solvent of said heterocyclic compound(s); and (e) recycling the product of step (d) to the said liquefaction zone.

5. A process according to claim 4, wherein the said liquid fraction contains at least 50 wit.% hydrogen donor compounds.

6. A process according to any one of claims 3 to 5, wherein the hydrogen donor solvent contains from 5 to 20 wt.% of said added compound.

7. A process according to any preceding claim, wherein the hydrogen donor solvent contains at least 0.8% donatable hydrogen, based on the weight of the solvent.

8. A process according to claim 7, wherein there is 1.2 to 3% of said donatable hydrogen.

9. A process according to any preceding claim, wherein the said hydrogen-donor solvent is one boiling within the range 2500 F to 8500 F.

10. A process according to any preceding claim, wherein the hydrogen donor solvent is admixed with the coal to provide a solvent-to-coal ratio of 0.8:1 to 4:1.

I I. A process according to any preceding claim, wherein the slurry of coal is also contacted with molecular hydrogen at a treat rate of from about 1 to 6 wit.% (MAF coal basis).

12. A process according to any preceding claim, wherein the heterocyclic compound(s) boil in the range 2500F to 850"F.

13. A process according to any preceding claim, wherein the heterocyclic compound(s) employed contain only one heterocyclic atom in the nucleus.

14. A process according to any preceding claim, wherein the heterocyclic compound(s) contain 2 or 3 fused rings, at least one of which contains one heterocyclic atom in the nucleus.

15. A process according to any preceding claim, wherein the heterocyclic atom is oxygen or sulfur.

16. A process according to any one of claims 1 to 14 wherein the heterocyclic atom is nitrogen

17. A process for producing coal liquids as claimed in claim 1 and substantially as

herein described with reference to any one of the Examples.

18. A process for producing coal liquids as claimed in claim 1 and substantially as herein described with reference to the accompanying drawing.

19. Coal liquids produced by a process according to any preceding claim.