US 3532617 A
Description (OCR text may contain errors)
R. HODGSON 3,532,617
HYDROCONVERSION OF COAL WITH COMBINATION OF CATALYSTS Oct. 6, 1970 Filed July 23, 1968 INVENTOR R- L- HODGSON BY:
HIS ATTORNEY United States Patent 3,532,617 HYDROCONVERSION OF COAL WITH COMBINATION OF CATALYSTS Russell L. Hodgson, Lafayette, Calif., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 23, 1968, Ser. No. 746,820 Int. Cl. Cg l/06, 1/08 U.S. Cl. 20810 7 Claims ABSTRACT OF THE DISCLOSURE A process for hydroconversion of coal to refinable liquid products in which the coal is hydrogenated in the presence of at least two catalysts, one being impregnated on the coal, to obtain both increased conversion and improved selectivity to gasoline and gas oil components.
BACKGROUND OF THE INVENTION Field of the invention This invention relates to the hydroconversion of coal to liquid products. More particularly it relates to a process for hydrogenation of coal wherein coal is impregnated with a catalyst to enhance conversion and the impregnated coal is contacted with a heterogeneous catalyst in the presence of hydrogen to improve product selectivity.
Description of the prior art A practical process for converting coal to liquid fuels as a means of utilizing the extensive energy reserves in the worlds coal deposits has been a much sought after goal since it was first demonstrated nearly 60 years ago that coal could be hydrogenated to liquid products. Particularly large research efforts were carried out in Germany prior to and during World War II and in the United States by the Bureau of Mines following the war. The number of publications and patents in this area is astronomical, as witnessed by a Bureau of Mines bibliography compiled at the outset of their efforts in the late 1940s containing over 6,000 entries. [1. L. Wiley and H. C. Anderson, Bureau Mines Bull. 485: Part I (1950); Part II 1951); Part III (1952)]. Work on coal hydrogenation has not waned in recent years; in fact, it is approaching fruition in the form of economical processes for converting coal into refinable liquid products.
Several unique problems associated with the conversion of coal to refinable liquid products result from its chemical and physical nature. Not only is the starting raw material a solid, but even when complete conversion of the organic matter'is obtained, an appreciable amount of inorganic ash remains. The condensed nature of the coal molecule results in a low hydrogen/ carbon ratio, necessitating the addition of large amounts of hydrogen.
In general, processes developed for conversion of coals into liquid products require that the coal be first broken down to a liquid state which can be processed further by more or less conventional petroleum refining techniques such as hydrofining, hydrocracking, reforming, etc. While the first step may be merely a thermal treatment, there are significant advantages for catalytic hydrogenative decomposition or liquefication. However, the most effective means known require very high pressures in the range of 2000 to 6000 p.s.i.
In recent years several schemes have been undergoing rather extensive development to obtain commercially feasible processes. Basically, three rather different schemes are employed. In one, coal is extracted with a solvent to remove ash and residue, the extract hydrogenated and the residue and char coked or carbonized. Eln another, lique- 3,532,617 Patented Oct. 6, 1970 'ice fication is accomplished by successively higher temperature stages of pyrolysis or thermal decomposition. In the third the coal is subjected to hydrogenation in a reaction zone wherein a particulate hydrogenation catalyst is maintained in an ebullating bed. Exemplary of the various publications describing these developments is Chemical and Engineering News, June 12, 1967, pp. 96-100.
One major drawback of all the proposed processes is the relatively large amount of refractory residues and coke which are produced. These fractions are usually further treated by coking (or carbonization) and/or extensive recycle to the hydrogenation zone.
Obviously any proposal which reduces production of residue and coke (or char), especially when accompanied by increased production of lower boiling refinable products is of a major significance.
The present invention is such a process, accomplishing a high degree of conversion and greatly improved selectivity to gasoline and gas oil boiling range products. This is accomplished by the use of a combination of at least two catalysts; one being intimately dispersed or impregnated on the coal and the other a heterogeneous catalyst. The dispersed catalyst increases conversion and speeds hydrogenation while the second acts primarily to improve product selectivity and product boiling range distribution.
SUMMARY OF THE INVENTION In broad aspect, the invention is a process for hydroconversion of coal using a combination of at least two catalysts; one of which is impregnated on the coal, the other contacted with the impregnated coal in the presence of hydrogen at elevated temperature and pressure. One catalyst which is impregnated on the coal or intimately dispersed thereon, increases initial breakdown of the com plex coal structure; the second catalyst eifects and improves product selectivity to distillate (as opposed to residual) products.
The process of the invention may be carried out for the hydrogenation of any type of coal, as for example, bituminous, sub-bituminous or lignite coal. The coal should desirably be ground or pulverized to increase the efliciency of catalyst contacting.
According to the invention, coal is first impregnated with a catalyst, the impregnate solvent or vehicle optionally removed and the resulting catalyst-impregnated coal contacted with a second particualte hydrogenation catalyst (preferably a hydrogenation metal or metal compound supported on a solid carrier) in the presence of hydrogen at elevated temperature and pressure.
In the first step, e.g., catalyst impregnation, coal is slurried with a catalyst which is dissolved or dispersed in a liquid vehicle. Thus efficient dispersion of the catalysts. necessarily used in small amounts, with the coal is accomplished.
Catalysts which are elfective include metal compounds, particularly metal halides and metal sulfides. Another class of catalysts are metal naphthenates. Naphthenates have the advantage of being soluble in hydrocarbons allowing the use of a hydrocarbon or organic impregnation vehicle and thus better contact and dispersion.
Especially preferred are catalysts which are prepared in situ on the coal. For example, metal naphthenates are dispersed on the coal by impregnation of the coal with either a metal salt or a naphthenic acid followed by conversion to the metal naphthenate. Another class of in situ prepared catalysts are metal sulfides which are dispersed on the coal by impregnation of coal with a metal salt followed by gaseous sulfiding to the metal sulfide. The method of in situ catalysts preparation and its advantages are included in my copending patent application Ser. No. 686,345, filed Nov. 28, 1967, the pertinent disclosure of 3 which is hereby made a part of and incorporated into this application.
In many cases, for example, when the first catalyst is impregnated from an aqueous solution, it will -be highly desirable to remove the solvent, e.g., by evaporation or drying.
The particulate catalyst of the invention is a hydrogenation catalyst, preferably a catalyst composite comprising a hydrogenation metal or metal compound (oxide or sulfide) on a solid support. The preparation of such catalysts is well known in the art. Suitable hydrogenation components include metals, metal oxide and sulfides, especially metals of Group VI and Group VIII of the Periodic Table of the Elements, their compounds and mixtures thereof.
Particularly suitable solid carriers are refractory oxides, for example, silica, alumina, zirconia, magnesia, etc. or mixtures thereof. In general, carriers having high intrinsic acid cracking activity are not required although some acidic cracking function is desirable, the degree of cracking ability is dependent inter alia upon the desired conversion selectivity between low and high boiling products. Crystalline alumino-silicates are also desirable and effective catalyst carriers and in some cases are particularly effective as will be discussed more fully below. Faujasites, particularly synthetic Y-faujasite, are especially preferred crystalline alumino-silicate catalyst supports. Exemplary of suitable catalysts which have been found to accomplish the advantages of the invention are cobalt/molybdenum on alumina and palladium on Y-faujasite aluminosilicates.
It will be understood that the metal component of both the impregnated catalyst and the particulate catalyst may, in some instances, be the same. However, it is well recognized that the chemical form, as well as the physical form of metal and metal compound catalysts, are highly significant factors in catalytic performance. Thus, the reference herein and in the claims to two catalysts are not intended to exclude catalysts containing the same metal component.
In the process of the invention, hydrogenation with the combination of catalyst is carried out at temperatures in the range of 200-600" C. and hydrogen pressures from about 500-3000 p.s.i.g. One significant advantage of the invention is, in fact, the ability to effect high coal conversion at pressures which are lower than required in previously proposed processes. Pressures in the range of 2500-5000 p.s.i.g. are generally required with known processes.
Hydrogenation can be carried out, of course, over a wide range of conditions depending upon the catalysts used, the type of coal being processed and the desired degree of conversion.
In one embodiment of the invention, hydrogenation of impregnated coal is carried out in the presence of particulate catalyst maintained in random motion within a reaction zone by upfiowing recycle liquid, hydrogen and/ or other gases. Suitable for this purpose is a reaction system with an ebullating catalyst bed as described in Johanson, U.S. Re. 25,770, issued April 1965.
Unlike other coal hydrogenation processes based on the use of an ebullating bed hydrogenation zone, the present invention involves the use of at least two catalysts which result in greatly improved product conversion and selectivity to nonresidual products. Moreover, the process is operable at lower pressures than previously proposed processes.
DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENT The invention will be more completely understood by reference to the accompanying drawing which is a diagrammatic representation of a preferred embodiment of the invention.
Coal enters the process via line 11 to a crusher pulverizer 1 where it is reduced in size for efficient impregnation. The crushed coal is transferred to an impregnation vessel 2 where it is mixed with a catalyst such as, for example, ammonium molybdate, in aqueous solution. The catalyst slurry or solution is introduced via line 21. Sullicient solution is added to give the desired amount of catalyst on the coal.
Any hydrogenation metal salt which can be converted to metal sulfides and/or naphthenates are suitable for the practice of the invention. Nickel, tin, molybdenum, cobalt, iron and vanadium salts are especially preferred.
Any suitable solvent may be used as a carrier for the impregnate, water being of course a logical choice in many instances. However, a lower boiling solvent which can be easily recovered is desirable in some applications. The requirements are solubility of the impregnate in the solvent and nonreactivity or at least limited reactivity of the solvent with the coal. For example, ether has proved a particularly suitable solvent for impregnation of such salts as molybdenum chloride. The concentration of the impregnate in the solvent is not critical. It should be as high as possible to minimize solvent requirements and recovery but not so high as to impair the dispersion or to render the physical properties of the solution unmanageable. Use of appropriate concentrations within these broad limits is within the skill of those in the art.
When a metal salt catalyst is used, the amount should be in the range of about 0.01 to 5.0% by weight; an amount between 0.05 and about 1.0% weight being preferred.
From the impregnation step the coal and impregnating solution is transferred via line 13 to a drying vessel 3 where solvent is removed. This may be done in various ways well known in the art, as for example, by passing a hot inert gas through a fluidized bed of coal. Solvent is removed via line 31 and the coal containing the intimately mixed catalytic metal or salt passes via line 14 to vessel 4 where the metal salt is converted to the catalytically active form. Sulfiding is optional but is preferred for use with many metal catalysts used in the present invention. The advantages of sulfiding to convert the catalyst metal to an active metal compound or to a sulfided form are more completely outlined in my copending application, Ser. No. 686,345, filed Nov. 28, 1967.
When the catalyst is converted, in situ, to the sulfide, any sulfur compound which gives the sulfide compound, i.e., which reacts with the impregnated metal salt is suitable. Hydrogen sulfide is preferred. Again, concentration is not critical and any available hydrogen sulfide-containing gas may be used as, for example, hydrogen sulfide off-gas from refinery streams is appropriate. Relatively pure hydrogen sulfide may, of course, be used. Elevated temperatures are desirable for sulfiding, for example, temperatures in the range of 2 0O-500 C. In general, suflicient sulfur should be added to convert substantially all the metal to the sulfide form.
Sulfur compound gas enters the sulfiding reactor through line 22. From unit 4, if sulfiding is used, or vessel 3 if sulfiding is not practiced, the impregnated coal enters a hydrogenation zone 5 via line 15. In the hydrogenation zone it is preferred that an ebullating bed of heterogeneous catalyst be used as explained hereinbefore. Hydrogen-containing gas enters the zone via line 34, gaseous products leave the zone via line 36 and liquid product, suspended char and ash and catalyst fines, if any, are removed via line 16.
In the hydrogenation zone, temperatures in the range of 350450 C. and hydrogen pressures in the range of 1000-2000 p.s.i. are preferred conditions which allow maximum advantage to be taken of the dual catalyst system. Of course, higher temperatures and/ or pressures may be used if desired. Gaseous products and any excess hydrogen and/ or gases used in the hydrogenation zone are removed via line 36 where they pass to separator 7. Hydrogen gas which is separated in separator 7 may be recycled via line 32, mixed with incoming fresh hydrogenation gas from line 23 and returned to the hydrogenation zone 5. Recycle of hydrogenation gas is optional and should not be practiced if the product gas contains excessive poisons which would reduce the effectivepractice and to point up the advantages of the present invention.
EXAMPLE I A series of experiments were made on the hydrogenation-liquefaction of Illinois No. 6 coal. Representative ness of the hydrogenative catalysts in the hydrogenation analysis of this coal is shown in Table L zone. Of course, where undesirable components are prescut, the gas may be purified before recycling. Table I Fresh hydrogenation gas, preferably a concentrated hydrogen stream, enters the system via line 23. It is not gii i (percentw') nhnols 6 $2 necessary to employ pure hydrogen-containing gas such H dro as off-gases from e.g., the catalytic reforming of naphy g Nitrogen 1.5 thas belng suitable and expedient. Other hydrogen-con- Sulfur 4 3 taining gases from processes which produce hydrogen OX en from hydrocarbons are also suitable. yg T H/C (atomic ratlo) 0.8 In an ebullatlng bed reaction system, a substantial MOlSlZUIC (percent w.) 10.9 portion of the converted coal 1s removed as a liquid via Ash ercent w 13 3 line 16. In the present invention, this stream will be p somewhat lower boiling than in previously proposed lAmlysls on mmstule and ash-free (MAP) basisschemes due to the increased gasoline make resulting The use of combinations of catalysts was examined from the use of two catalysts. The liquid fraction will using powdered palladium on Y-zeolite catalyst (obtained contain not only converted coal, but also ash, char, and from Linde Company and designated as SK100) lmixed a minor amount of catalyst fines. One advantage of the with powdered, impregnated Illinois No. 6 coal. The ebullating bed operation is the attrition of catalyst which mixed solids were treated with a 200 cc./min. flow of tends to keep fresh catalyst surface available. This mixed hydrogen at 1500 p.s.i for 5 hours at 425 C. The results stream passes via line 16 to separation zone 6 where distilare summarized in Table II. For comparison purposes, lable oil is taken overhead as the major product. This frac- SiO which has no catalytic hydrogenation activity was tion, which contains primarily gasoline and gas oil boiling used instead of the zeolite with untreated raw coal, sulrange liquids, may be further refined by conventional pefided coal, and molybdenum impregnated and sulfided troleum refining means. The residue is discharged via coal. Sulfiding the coal had little effect in the absence of line 35. The residue contains unconverted coal, if any, an impregnated catalyst. Impregnating with -0.1%- tar, heavy residual liquids, and ash which was introduced 0.2% w. molybdenum and then sulfiding increased both with the coal, and the impregnated catalyst. The tar, heavy conversions and yield of liquid products. The use of palresidual liquids and unconverted coal can be separated ladium on Y-zeolite in place of the Si0 did not aflfect from the ash and if desired recycled via line 37 to hythe conversion appreciably but did alter the distribution drogenation zone 5. Alternatively, it may be used to imof products so that almost all the recovered products pregnate fresh coal with catalyst contained in a residual boiled below about 200 C. With palladium on Y-zeolite stream or as a parting liquid from the impregnated coal. as the heterogeneous catalyst, sul-fiding the coal or im- The quantity of this material is less with the present inpregnating with molybydenum increased conversion while vention than in known processes. The hydrocarbon resi- 40 still giving good product selectivity. When the coal was due can be coked to recover additional refinable prodimpregnated with molybdenum, sulfided, and then used nets and coke, or total hydrocarbon residue or char gasiwith palladium on Y-zeolite, the best results were ob fied to produce hydrogen. Recovery and reuse of catalysts tained: 57% w. basis moistureand ash-free coal (MAP) will depend upon the total economics of the particular liquid product in the gasoline range (C -200 C.) at a system. If small quantities of inexpensive catalyst are coal conversion of -85% w. (MAP). In these experiments, used, recovery may not be justified. Catalyst reuse is not the molybdenum was impregnated to a level of -01- considered a vital part of the present invention, but the 0.2% w. from an ether solution of MoCl Similar impossibility of reuse in some cases is a definite advantage. pregnation to -0.0l% w. Mo was less eflective; however, For example, catalyst contained in the recycle residual impregnation with aqueous ammonium molybdate at liquid may be used to impregnate fresh coal. 0.6% w. Mo was equally effective. Nickel chloride im- The process scheme described is an efficient means of pregnated and sulfided was also effective when used with utilizing the present invention and a preferred embodithe palladium on Y-zeolite heterogeneous catalyst.
TABLE II Products (percent w. MAF) Conversion Heterogeneous C4- 200- (percent w. catalyst n Coal treatment b 200 0. 400 C. Char MAF) SiO None 14 23 33 67 Si02 Su ed. 15 26 33 2 S102" MoClr, (I) (S) 22 37 22 78 Pd/Y one 31 0 41 59 Pd/Y sulfided.-. 44 1 27 73 Pd/Y- M0015 d (I) 46 7 9 91 Pd/Y. M0Cl5 d (I) (S) 57 3 14 86 Pd/Y M0015 (I) 45 4 22 7g Pd/Y (NH4 6M07024 (1) (S). 57 1 15 Pd/Y NiCLz B (I) (S) 45 11 15 85 Caleined and sulfided (-10 g.) mesh), SiOz not calcined or sulfided. Illinois N0. 6 (-10 g.) (100-200 mesh), (I) Impregnated; (S) Sulfided. Material recovered from 200 0. lines and traps.
8 -0.01% w. Mo.
1 -0.6% w. Mo. 8 -0.5% w. Ni.
ment, but is not to be considered a limitation thereon. Many variations within the scope of the invention which may be employed to improve the operation in any particular system will occur to those in the art.
EXAMPLE II Another set of experiments were made using a particulate catalyst consisting of cobalt and molybdenum impregnated on alumina, a known catalyst for petroleum The following examples further serve to illustrate the 75 refining and available commercially. The results are summarized in Table III. Compared to SiO which like alumina has no catalytic hydrogenation activity, the Co/Mo/ A1 shows increased conversion and yields with raW coal, sulfided coal and molybdenum-impregnated and sul fided coal. The Co/Mo/Al O functions to improve the product distribution. Impregnated FeSO also showed good activity with Co/Mo/Al O TABLE III.DOWNFLOW TUBE REACTOR Hz-200 ccJmin. for 5 hrs. at 1,500 p.s.i.
Products (percent w. MAF) selected from a group consisting of metals of Group VI and Group VIII of the Periodic Table of Elements, and compounds and mixtures thereof and the refractory oxide support is selected from a group consisting of silica, alumina, zirconia, magnesia and mixtures thereof.
3. The process of claim 1 wherein the refractory oxide is a crystalline alumino-silicate.
a Calcined and sulfided (-10 g.) 100 mesh). SiOz not calcined or Sulfidcd.
b Illinios No. 6 (-10 g.) (100-200 mesh).
0 Material recovered from 200 0. lines and traps.
The most striking feature of the results of the experiments outlined in Examples I and II is the greatly improved selectivity of the dual catalyst system. In all experiments carried out according to the method of the invention, the char or residue is significantly reduced and gasoline and gas oil product significantly increased. This improvement not only directly enhances the feasibility of coal conversion to usable petroleum products but greatly reduces the problems associated with the residue treating and/or disposal necessitated by the processes heretofore proposed.
I claim as my invention:
1. A process for hydroconversion of coal to liquid products boiling in the gasoline and gas oil range comprising impregnating coal with a first catalyst selected from halide, sulfide, or naphthenate of a metal having catalytic activity to promote hydrogenation, and contacting the catalyst-impregnated coal with a second catalyst of a hydrogenative metal component supported on a refractory oxide support having acid cracking activity at a temperature from ZOO-600 C. and under a hydrogen pressure of from 5003000 p.s.i.g.
2. The process of claim 1 wherein the hydrogenative metal component of the second particulate catalyst is 4. The process of claim 1 wherein the first impregnated catalyst is prepared by forming the catalytic compound in situ on the coal by impregnating one component of the catalytic component on the coal followed by reacting the component to the desired catalytic species.
5. The process of claim 1 wherein the impregnated coal and particulate catalyst are contacted in a reaction zone wherein the particulate catalyst is an ebullating catalyst bed.
6. The process of claim 1 wherein the impregnated catalyst is used in an amount in a range of between 0.01 to 5.0% W. basis impregnated coal.
7. The process of claim 1 wherein the impregnated catalyst is recovered and used to impregnate fresh coal feed to the process.
References Cited UNITED STATES PATENTS 2,377,728 7/1969 Thomas 208-10 PAUL M. COUGHLAN, 111., Primary Examiner V. OKEEFE, Assistant Examiner