US3642927A

US3642927A - Process for desulfurization of aromatics

Info

Publication number: US3642927A
Application number: US703585A
Authority: US
Inventors: Stephen M Koyach; Ralph E Patrick
Original assignee: Ashland Oil Inc
Current assignee: Ashland LLC
Priority date: 1968-02-07
Filing date: 1968-02-07
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15

Abstract

THE SULFUR-PARTICULARLY THAT PRESENT AS THIOPHENESCONTAINED IN AROMATIC HYDROCARBONS IS SUBSTANTIALLY REMOVED BY TREATING THE HYDROCARBONS WITH METALS, AND OXIDES THEREOF HAVING HYDROGENATING ACTIVITY. IN ONE EMBODEMENT, THE AROMATIC HYDROCARBON IS CONTACTED WITH NICKEL, COBALT, NICKEL AND TUNGSTEN, COBALT AND TUNGSTEN, OR THEIR OXIDES AT A TEMPERATURE OF ABOUT 200 TO 600*F. AND A PRESSURE OF ABOUT 50-500 P.S.I.G. IN ANOTHER EMBODIMENT, THE AROMATIC HYDROCARBON IS CONTACTED WITH NICKEL, COBALT, NICKEL AND MOLYBDENUM, COBALT AND MOLYBDENUM, NICKEL AND TUNGSTEN, COBALT AND TUNGSTEN, OR THEIR OXIDES AT A TEMPERATURE OF ABOUT 600-900*F. AND A PRESSURE OF ABOUT 0-50 P.S.I.G.

Description

United States Patent 3,642,927 PROCESS FOR DESULFURIZATION F AROMATICS Stephen M. Kovach, Ashland, and Ralph E. Patrick,

Flatwoods, Ky., assignors to Ashland Oil & Refining Company, Houston, Tex.

Filed Feb. 7, 1968, Ser. No. 703,585 Int. Cl. C07c 7/00 US. Cl. 260-674 18 Claims ABSTRACT OF THE DISCLOSURE The sulfur-particularly that present as thiophenescontained in aromatic hydrocarbons is substantially removed by treating the hydrocarbons with metals, and oxides thereof having hydrogenating activity. In one embodiment, the aromatic hydrocarbon is contacted with nickel, cobalt, nickel and tungsten, cobalt and tungsten, or their oxides at a temperature of about 200 to 600 and a pressure of about 50-500 p.s.i.g. In another embodiment, the aromatic hydrocarbon is contacted with nickel, cobalt, nickel and molybdenum, cobalt and molybdenum, nickel and tungsten, cobalt and tungsten, or their oxides at a temperature of about 600-900 F. and a pressure of about 0-50 p.s.i.g.

FIELD OF THE INVENTION The present invention relates to the purification of aromatic hydrocarbons. In a more specific aspect, the present invention relates to the removal of sulfur compounds from aromatic hydrocarbons. In a still more specific aspect, the present invention relates to the removal of thiophene and alkylated thiophenes from aromatic hydrocarbons.

SUMMARY OF THE PRIOR ART The commercial demand for monoand polycyclic aromatics, such as benzene and naphthalene, is wellknown to those skilled in the art. It is equally well-known that the commercial value of such monoand polycyclic hydrocarbons resides to a large extent in the purity of the material. For example, high purity naphthalene is used as an intermediate in the production of phthalic anhydride, which requires high purity naphthalene. Similarly, the chemical industry requires high grade benzene for nitration and like treatments.

At the present time, the vast majority of naphthalene and a considerable portion of the benzene produced in the United States is obtained by the distillation of coal tar products. The coal tar products are generally produced as a by-product of the high temperature carbonization of coal to yield coke. Another source of such coal products is the solvent extraction of coal to yield hydrocarbon liquids and combinations of solvent extraction and carbonization. Monoand polycyclic hydrocarbons are also present in crude petroleum. While the amounts present in crude petroleum vary with the source, the total amount of all aromatic hydrocarbons in crude petroleum is only about Separation by fractionation of the desired aromatics from crude petroleum has not proven feasible because of the large volumes of other hydrocarbons, boiling in substantially the same range, which are present in the crude. However, certain fractions of petroleum products, from processes such as catalytic reforming, catalytic cracking, and thermal cracking, do contain significant amounts of monoand polycyclic aromatics which can be economically recovered.

Hydrocarbon fractions rich in monocyclic and polycyclic aromatics, particularly those derived from coal, contain rather substantial volumes of impurities, particularly sulfur compounds, such as thiophenes, alkyl thiophenes,

3,642,027 Patented Feb. 15, 1972 thionaphthenes, etc. These compounds complicate the recovery and purification of monoand polycyclic aromatics, since they display boiling points close to the desired hydrocarbons. In order to produce chemical grade monocyclic and polycyclic aromatics, such as benzene and naphthalene, these sulfur compounds, as well as nitrogen compounds and small amounts of non-aromatic hydrocarbons, must be removed from the product or their contents be substantially reduced. For example, chemical grade benzene specifications require 0.5 ppm. thiophene or less. Similar specifications apply to chemical grade naphthalene.

Benzene in coal liquids is concentrated in what is usually referred to as a light oil fraction. This light oil is high in benzene, toluene, and xylene, but contains high concentrations of sulfur and nitrogen compounds and small amounts of non-aromatics. The coal tar light oils are generally considered to be coal liquids boiling up to about 400 F., but more generally such liquids boiling up to about 340 F. to 360 F. Commercially, these light oils have been processed to recover benzene, toluene and xylene by hydrotreating, followed by solvent extraction, such as extraction with a triethylene glycol-water system or by hydrotreating followed by hydrodealkylation. The hydrodealkylation, in addition to removing alkyl groupsfrom the toluene and xylene, and thus increasing benzene production, also serves to remove a portion of the sulfur impurities when certain types of catalytic hydrodealkylation schemes are utilized. However, the product of such a dealkylation-desulfurization unit still contains from 1 to 50 and generally 1 to 2 ppm. of thiophene, all of which are over the specification for commercial grade benzene. Similar low-boiling refinery streams are also treated by similar tion of coal liquids boiling above the previously mentioned light oil and below the pitch or tar fractions. This broad boiling range can be from about 340 to about 680 F. However, as a practical matter, it is highly desirable that a heart-cut of this so-called middle oil, boiling between about 400 and 600 F., be utilized as a source of naphthalene. This out also contains the usual sulfur and nitrogen contaminants as well as alkyl naphthalenes. Consequently, the fraction is generally treated in essentially the same way as the light oil fraction in order to pro duce substantial quantities of high purity naphthalene. In other words, the ideal treatment is the previously mentioned deal'kylation-desulfurization treatment. However, as is the case with the benzene product of the dealkylation-desulfurization treatment, the naphthalene product also contains undesirable quantities of thiophenes and alkyl thiophenes which must be removed or substantially reduced in amount. These products, however, also contain trace quantities of indene or indan compounds which cause discoloration of the product and make it undesirable as a commercial grade naphthalene. In accordance with conventional practice, this discoloration may be remedied by subjecting the product to treatment with hot clay at temperatures between about 450 to 500 F. While this hot clay treatment has been found effective in removing non-sulfur contaminants, it has been found ineffective in the removal of the sulfur compounds previously mentioned.

-In addition to the hot clay treatment previously mentioned, several other schemes have been investigated for the removal of thiophene and alkyl thiophenes from monocyclic and polycyclic aromatics. One of these involves a sodium treatment with a sodium dispersion or a sodium impregnated clay. This technique has numerous drawbacks, the principal of which is the presence of water and olefins which lead to high sodium consumption. The aromatic products can also be treated with acid, such as sulfuric acid, and the sulfur compounds effectively removed in this manner. However, the recovery of aromatics is quite low since it is well-known that the sulfuric acid treatment of aromatics is effective in the production of aromatic sulfonates. Desulfurization has also been practiced under conventional desulfurization conditions, i.e., at relatively high temperatures and pressures and at low space velocities, as by the commonly hydrotreating process. While such treatments are highly successful for the removal of thiophene and thiophene compounds, this process, as commercially practiced, is uneconomical. If a platinum-containing catalyst is utilized, complete desulfurization can be obtained, but the aromatic products are also hydrogenated, thereby producing contaminating amounts of cyclohexenes, methylcyclopentanes, etc. It would, of course, also be effective to re-process the material produced in the previously-mentioned dealkylationdesulfurization operation in a similar unit, or to treat relatively pure benzene and naphthalene produced by the other techniques in a dealkylation-desuliurization unit. However, by the time products of the purity referred to herein have been produced by any of the previously outlined methods, it is wholly uneconomical to process these products through a hydrodealkylation unit.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an improved process for the production of purified aromatic hydrocarbons. Another and further object of the present invention is to provide an improved process for the production of aromatic hydrocarbons by the removal of sulfur compounds therefrom. Yet another object of the present invention is to provide an improved process for the removal of sulfur compounds from monocyclic and polycyclic aromatic hydrocarbons. Another and further object of the present invention is to provide an improved process for the removal of thiophenes and alkyl thiophenes from aromatic hydrocarbons. Still another object of the present invention is to provide an improved process for the purification of benzene, naphthalene, and like monoand polycyclic aromatic hydrocarbons. A still further object of the present invention is to provide an improved process for the removal of thiophenes and alkyl thiophenes from high purity benzene, naphthalene and like monocyclic and polycyclic aromatic hydrocarbons. Yet another object of the present invention is to provide an improved process for purification of monocyclic and polycyclic aromatic hydrocarbons without destruction of the aromatic compounds themselves. A further object of the present invention is to provide an improved process for the removal of small amounts of thiophenes and alkyl thiophenes from monocyclic and polycyclic aromatic hydrocarbons, such as benzene and naphthalene, without the consequent loss of a portion of the aromatics. Another and further object of the present invention is to provide an improved process for the removal of thiophene and alkyl thiophenes from monocyclic and polycyclic hydrocarbon streams, such as benzene and naphthalene streams containing less than 100 ppm. of such thiophenes, wherein the hydrocarbon stream is catalytically treated under conditions for the removal of the thiophenes without the consequent hydrogenation of the aromatic materials. A yet further object of the present invention is to provide an improved process for the purification of aromatic hydrocarbons comprising subjecting the hydrocarbon to a dealkylationdesulfurization reaction and thereafter removing substantially all of the sulfur contaminants remaining without hydrogenation of the aromatics. These and other objects and advantages of the present invention will be apparent from the following description.

Briefly, in accordance with the present invention, aromatic hydrocarbons containing small amounts of sulfur compounds are subjected to treatment with a hydrogeneation-dehydrogenation metal catalyst, particularly a metal selected from the group consisting of nickel, cobalt, or mixtures of these metals with molybdenum or tungsten,

under conditions such that the sulfur compounds are removed without hydrogenation of the benzene nucleus of the aromatic hydrocarbons. Where the feed material is treated at a high temperature, in the presence of the specified catalysts, essentially atmospheric pressure is maintained and small amounts of hydrogen are added from an external source and high velocities are employed; whereas, treatment at lower temperatures required high pressurees and no external hydrogen introduction. In the preferred operation, the aromatic hydrocarbons contain alkyl aromatic hydrocarbons and the aromatic hydrocarbons are first subjected to a dealkylation treatment to produce a material concentrated in aromatics, with substantially no non-aromatics, and relatively small amounts of sulfur compounds. Therefter, the dealkylation product is subjected to the previously-mentiened treatment with a hydrogenation-dehydrogenation catalyst under select conditions for the removal of the remaining sulfur compounds without hydrogenation ef the aromatic compounds.

The details of the present invention will be set forth with specific reference to the single sheet of drawings, which represents a typical flow diagram for carrying out the preferred process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the drawing, a feed material is introduced through line 10 to hydrodealkylation reactor 12. The total product of hydrodealkylation reactor 12 is discharged through line 14 to condenser 16. The effiuent of condenser 16 passes through line 18 to fractionator 20. In fractionator 20, the hydrodealkylation product is separated into a gas, which is discharged through line 22, a bottoms product or heavy oil, suitable for use as a fuel or for a variety of other purposes, and a concentrated aromatic product. The bottoms product is discharged through line 24 while the concentrated aromatic is discharged through line 26. Whether the concentrated aromatic product be benzene or naphthalene or some other aromatic product, it still contains undesirable quantities of impurities which must be removed to produce chemical grade aromatics. In order to remove certain of these impurities, the product is subjected to a hot clay treatment in hot clay treater 28. In the hot clay treater 28, the aromatic product is treated at a temperature of about 450 to 500 F. to remove indenes, indan and like contaminants. Partially purified aromatic product, which yet contains thiophenes and alkyl thiophenes in amounts of 1 to 50 parts per million or even higher, is discharged through line 30. The partially purified aromatic then passes to desulfurization unit 32, where it is treated with a hydrogenation-dehydrogenation catalyst, under select conditions as set forth herein, to remove substantially all of the remaining sulfur compounds. The purified aromatic is then discharged through line 34 to storage or other receptacle for use or sale. In those instances where hydrogen is added to the desulfurization reactor, such addition is through line 36. This hydrogen may be derived from a wide variety of refinery gases, including the off gas of hydrodealkylation unit 12.

The feed material to hydrodealkylation unit 12 may be derived from any source of hydrocarbonaceous material, including coal, petroleum, etc. For example, coke oven or coal tar oils and pitches derived from the carbonization of coal, liquids extracted from coal by solvent extraction with Tetralin, Decalin, etc., and liquids obtained by combinations of solvent extraction and carbonization may be uti lized. As previously indicated, these liquids may be further concentrated by fractionation or like separations to obtain a feed rich in benzene or a feed rich in naphthalene. The feed material to the hydrodealkylation unit 12 may also be a process stream from a petroleum or coal refinery, such as catalytic reformate, obtained by contacting petroleum or coal liquids with a precious metal catalyst, such as platinum, at a temperature of about 900 to 950 F., a pressure of about 200 to 600 p.s.i.g., at a weight hourly space velocity between about 1.5 and 5, and using a hydrogen-to-hydrocarbon ratio between about 3 to 1 and to 1. The lower-boiling fraction of reformate boiling below about 400 F. is the preferred feed when benzene is to be the end product; whereas, a reformate fraction boiling between about 400 and 600 F. is the preferred feed when naphthalene is the preferred product. The reformer product may be further treated prior to introduction to the hydrodealkylation reactor, as by solvent extraction, such as with a triethylene glycol-water solvent system, or by other known means of concentration. Other petroleum fractions which may be used as a feed for the hydrodealkylation unit may include kerosene which has been extracted with an aromatic selective solvent, such as sulfur dioxide, a catalytic cracking light cycle oil, such light cycle oils which have been subjected to solvent extraction, as with sulfur dioxide, or hydrocracking or a similar light cycle oil from a thermal cracking operation.

Hydrodealkylation unit 12 is preferably a catalytic hydrodealkylation unit utilizing a catalyst and operating under conditions such that it not only concentrates the desired aromatic and produces additional amounts thereof, but also clarifies and desulfurizes the product. A preferred catalyst operation of this type is one carried out in the presence of a catalyst containing from 10 to about of chromia on a gamma alumina carrier. A highly effective catalyst of this character is designated G-41 by its manufacturer, the Girdler Corporation of Louisville, Ky. When utilizing such a catalyst, the hydrodealkylation may be carried out at temperatures between about 1000 and 1400 F., preferably between about 1250 and 1300 F.; at a pressure of about 100 to 1000 p.s.i.g., and preferably between 400 and 1000 p.s.i.g.; at a weight hourly space velocity between about 0.5 and 5, and preferably between about 0.5 and 3; and at a hydrogen-to-hydrocarbon ratio between about 3 and 10' moles of hydrogen per mole of hydrocarbon, and preferably between about 6 and 7 to 1. It is possible to carry out the hydrodealkylation without a catalyst, in which case the temperature is above about 1200 F., the pressure above about 500 p.s.i.g., and the hydrogen-to-hydrocarbon ratio is about 1400 to 1900 cubic feet of hydrogen per barrel of feed. However, the catalytic operation has been found to be substantially more effective.

The product of the hydrodealkylation unit includes a normally gaseous material and a normally liquid material. The residual light gases are drawn OE and used as a plant fuel or in variety of other manners. The highest boiling or bottoms product, boiling above the boiling point of the desired concentrated aromatic, is normally drawn off and utilized as a fuel oil stock. The cut point between the concentrated aromatic and the bottoms fraction depends primarily on the type of feed and consequently upon the concentrated aromatic to be recovered. When benzene is the desired concentrated aromatic, the cut point would be about 300 to 350 F. Where naphthalene is the primary end product, the cut point should be about 400 to 600 F., and ideally 440 to 525 F.

As previously pointed out, the concentrated aromatic product is essentially free of non-aromatic materials but contains minor amounts of contaminants, despite the highly eifective nature of the hydrodealkylation reaction. Therefore, in order to remove certain of these contaminants, it is desirable to subject the concentrated aromatic to a hot clay treatment. In this hot clay treatment, the maerial is subjected to temperaures of about 450 to 550 F., and certain of the contaminants are adsorbed on the clay. This is a known process and therefore will not be discussed in any great detail. The hot clay treatment removes substantially all of the non-sulfur containing, contaminating materials from the partially purified aromatic but fails to remove the small amounts of thiophene and alkylated thiophenes which are still present in the aromatic and render it unfit as a chemical grade product. Consequently, the partially purified aromatic is subjected to the selective desulfurization reaction which forms a significant step in the present process.

In the desulfurization reactor 32, the partially purified aromatic is contacted with a hydrogenation-dehydrogenation metal catalyst under conditions selective to the removal of the sulfur compounds but ineffective to hydrogenate any of the aromatic present.

One of the primary factors in the novel process of the present invention is the utilization of a specific group of hydrogenation-dehydrogenation catalysts in desulfurization reactor 32. Any active hydrogenation-dehydrogenation catalyst, such as, platinum, rhodium, palladium, nickel, cobalt, etc., may be used. While the precious metals of this group are adequate, the amounts necessary for long on-stream periods limit their use from an eco nomic standpoint. However, it has been found that excellent results in the removal of thiophene from aromatics can be obtained by utilizing a catalyst selected from the group consisting of nickel, cobalt, and mixtures of these metals with molybdenum and tungsten. Preferably the metal is deposited on an inert carrier material, such as kieselguhr, alumina, silica-alumina, etc. Such catalysts are relatively inexpensive, can be pro-reduced or in their oxide state and, therefore, reduced during the operation to the extent that hydrogen is present to effect such reduction. The metal should be present on the carrier in amounts ranging from about 1 to 60% by weight. However, in order to guarantee long cycle time, it is necessary to have from 10 to 60% and preferably between about 10 and 55% by weight. While it is not desired to be limited to any particular theory of operation, it is believed that the metal, in its free metal state, combines with the sulfur compounds to eventually form metal sulfides and olefins. 'If a low concentration of hydrogen is also present during the reaction, the olefins will be converted to saturates which can be more readily removed. The spent metal sulfide may be effectively restored to its original activity by air regeneration and reduction of the metal oxide with hydrogen to the free metal state. To confirm this theory of operation, a nickel catalyst was converted to nickel sulfide by treatment with hydrogen sulfide and the sulfided catalyst was tested under the process conditions of this invention for the removal of thiophene. The thiophene content of the product remained unchanged and at times was greater than that in the feed. Consequently, it appears that the postulated conversion of the metal to metal sulfide is the primary mechanism by which the sulfur is removed from the aromatic product. By the same token, however, under the conditions practiced herein, no hydrogenation of the aromatic product occurs.

While the conditions of operation of the desulfurization reactor may vary over rather wide ranges, these conditions are critical to the operation and certain of the conditions are critically interdependent upon one another. More specifically, the temperature of the operation may vary from about 200 to 900 F.; the pressure may vary from 0 to 500 p.s.i.g.; the liquid hourly space velocity may be between about 0.1 and 10; and the hydrogen-tohydrocarbon ratio may vary from 0 to 1. Since the primary purpose of the treatment is to convert the metallic hydrogenation-dehydrogenation catalyst to a metal sulfide and to avoid any appreciable hydrogenation of the aromatic being treated, the temperature of operation has been found to be a critical factor. If the temperature is maintained between about 200 and 600 F., or a matter of convenience, between about 450 and 500 F., (the usual temperature of the product passing from the hot clay treating operation), the pressure of the operation should be at the higher limits, usually between about 50 to 500 p.s.i.g., and no hydrogen should be added from an external source. The following example will illustrate an operation of this character.

A hydrodealkylation benzene product containing about 5 ppm. of thiophene was treated with a catalyst comprising 55% nickel oxide deposited on a kieselghur carrier. The catalyst was first reduced with hydrogen at a temperature of about 450 F. and under presusre. The benzene product was then processed over the catalyst at a temperature of about 450 F., at a pressure of about 400 p.s.i.g., while maintaining a liquid hourly space velocity of about 4, and without the addition of hydrogen from an external source. The product of this treatment was analyzed and found to contain 0.7 p.p.m. of thiophene. This, of course, represents the removal of about 86% of the original thiophene, and, based on the data set out in the other examples given herein as well as related work, a benzene product containing from 1.5 to 2% thiophene would be reduced to a product containing about 0.2 p.p.m. of thiophene.

Where the monocyclic or polycyclic aromatic to be desulfurized can be conveniently heated to a higher temperature, desulfurization at such higher temperature has certain advantages. For example, no aromatic hydrogenation will occur at temperatures between about 600 and 900 F., and preferably between about 650 and 750 F., even in the presence of small amounts of hydrogen from an external source. The hydrogen should, of course, be added in extremely low concentrations sufficient only to convert olefins produced by the desulfurization to saturates and to the extent that the hydrogenation-dehydrogenation metal is in its oxide form to reduce the oxide to free metal. It has been found that this can be accomplished in accordance with the present invention by utilizing a hydrogen-to-hydrocarbon mole ratio between about 0.01 to 1 to 1, and preferably between about 0.1 and 1 to 1. At these high temperatures, the operation should also be carried at essentially atmospheric pressure, the only pressure, therefore, being that sufficient to introduce the external hydrogen. Accordingly, a pressure of about p.s.i.g. would be employed, but may range up to about 50 p.s.i.g. As previously indicated, the liquid hourly space velocity may vary from 0.1 to 10, and preferably should be between about 1 and 5.

The results of three such high temperature treatments are illustrated in the following Table I. In these three runs, benzene from a hydrodealkylation unit had added thereto varying amount of thiophene, as indicated in the table. The material was then contacted with the indicated catalyst under the conditions set forth in the table.

Conditions:

Tempcrature, F." 700-730 730. 740 Pressure, p.s.l.g 0 0 0 LHSV 1 1 H2/HC,molc/mole 1/3 1/3 1/3 Product: Thlophene, 0.09 0.9 1

p.p.m.

The results of Table I above indicate that 99% desulfurization was obtained irrespective of the amount of thiophene contained in the sample. Consequently, it can readily be observed that in order to obtain an aromatic product containing less than 0.5 p.p.m. of thiophene from a contaminated product, the product may contain up to 50 p.p.m. of thiophene. Such a product, as previously indicated, will meet chemical grade specifications after treatment in accordance with the present invention.

Having described the present invention with reference to a specific flow diagram and specific examples, it is to be understood that these are illustrative only and that the invention is to be limited only in accordance with the appended claims.

We claim:

1. A method for the purification of aromatic hydrocarbons containing small amounts of thiophenes, alkyl thiophenes and thionaphthenes, comprising, contacting said aromatic hydrocarbons with a hydrogenation-dehydrogenation metal catalyst selected from the group consisting of oxides and free metals of metals selected from the group consisting of nickel, cobalt, mixtures of nickel with tungsten and mixtures of cobalt with tungsten, under conditions sufiicient to convert said thiophenes, alkyl thiophenes and thionaphthenes to metal sulfides and olefins, to dehydrogenate sufficient of said aromatic hydrocarbons to hydrogenate said olefins, to hydrogenate said olefins and to prevent hydrogenation of said aromatic hydrocarbons including, a temperature of about 200 to 600 F., a pressure of about 50 to 500 p.s.i.g., a liquid hourly space velocity of about 0.1 to 10 and in the absence of hydrogen from an external source.

2. A method in accordance with claim 1 wherein the aromatic hydrocarbons additionally contain substantial quantities of alkyl aromatic hydrocarbons and said aromatic hydrocarbons are first subjected to dealkylation conditions suflicient to convert substantially all of said alkyl aromatic hydrocarbons to unsubstituted aromatic hydrocarbons.

3. A method in accordance with claim 2 wherein the dealkylation conditions are selected to remove a part of the thiophenes, alkyl thiophenes and thionaphthenes from the aromatic hydrocarbons.

4. A method in accordance with claim 2 wherein the dealkylation is carried out in the presence of a dealkylation catalyst.

5. A method in accordance with claim 4 wherein the dealkylation catalyst comprises 10 to 15% chromia deposited on a gamma alumina carrier.

6. A method in accordance with claim 1 wherein the sulfur compounds are thiophenes in amounts less than about p.p.m.

7. A method in accordance with claim 1 wherein the aromatic hydrocarbons are derived from a solid carbonaceous material.

8. A method in accordance with claim 7 wherein the solid carbonaceous material is coal.

9. A method in accordance with claim 1 wherein the aromatic hydrocarbons are derived from crude petroleum.

10. A method for the purification of aromatic hydrocarbons containing small amounts of thiophenes, alkyl thiophenes and thionaphthenes, comprising, contacting said aromatic hydrocarbons with a hydrogenation-dehydrogenation metal catalyst, selected from the group consisting of oxides and free metals of metals selected from the group consisting of nickel, cobalt, mixtures of nickel with molybdenum, mixtures of cobalt with molybdenum, mixtures of nickel with tungsten, and mixtures of cobalt with tungsten, under conditions sufficient to convert said thiophenes, alkyl thiophenes and thionaphthenes to metallic sulfides and olefins, to saturate said olefins and to prevent hydrogenation and dehydrogenation of said aromatic hydrocarbons, including, a temperature of about 600 to 900 F., a pressure of about 0 to 50 p.s.i.g., a liquid hour- 1y space velocity of about 0.1 to 10, and in the presence of hydrogen, from an external source, in amounts of about 0.01 to 1 mol hydrogen per rnol of aromatic hydrocarbons.

11. A method in accordance with claim 10 wherein the aromatic hydrocarbons additionally contain substantial quantities of alkyl aromatic hydrocarbons and said aromatic hydrocarbons are first subjected to dealkylation conditions sufficient to convert substantially all of said alkyl aromatic hydrocarbons to unsubstituted aromatic hydrocarbons.

12. A method in accordance with claim 11, wherein the dealkylation conditions are selected to remove a part of the thiophenes, alkyl thiophenes and thionaphthenes from the aromatic hydrocarbons.

13. A method in accordance with claim 11 wherein the dealkylatiori is carried out in the presence of a dealkylation catalyst.

14. A method in accordance with claim 13 wherein the dealkylation catalyst comprises 10 to 15% chromia deposited on a gamma alumina carrier.

15. A method in accordance with claim 10 wherein the sulfur compounds are thiophenes in amounts less than about 100 p.p.m.

16. A method in accordance with claim 10 wherein the aromatic hydrocarbons are derived from a solid carbonaceous material.

17. A method in accordance with claim 16 wherein the solid carbonaceous material is coal.

18. A method in accordance with claim 10 wherein the aromatic hydrocarbons are derived from petroleum.

References Cited UNITED STATES PATENTS 2,951,034 8/ 1960 Stuart 208-244 2,951,886 9/1960 Paulsen 260-674 3,198,846 8/1065 Kelso 260-672 3,222,410 12/1965 Swanson 260-672 3,310,592 3/1967 Fukuda et a1 260-672 3,116,234 12/ 1963 Douwes ct a1. 260-674 3,484,367 12/1969 Winsor 260-674 10 OTHER REFERENCES Emmett, Catalysis, vol. V, Reinhold Pub. Corp., New York, 1958, pp. 444 and 445.

Horne et al., Advances in Petroleum Chemistry and Refining, vol. 3, Interscience Publishers, Inc., New York, 1960, pp. 215-217, 225-227.

Gully et al., Advances in Petroleum Chemistry and Refining, vol. 7, Interscience Publishers, Inc., New York, 1963, pp. 248-249, 260-269.

Elgin et al., Industrial and Engineering Chemistry, vol. 22, No. 12, pp. 1284-1290.

Elgin, Industrial and Engineering Chemistry, vol. 22, No. 12, pp. 1290-1293.

Ellis, The Chemistry of Petroleum Derivatives (1934), TP690E5, pp. 461-463.

CURTIS R. DAVIS, Primary Examiner US. Cl. X.R.