Hydrodealkylation process with promoted group vib metals and promoters

Abstract

A process for the hydrodealkylation of alkyl-substituted aromatic hydrocarbons, including contacting the alkyl-substituted aromatic hydrocarbons with a catalyst comprising a metal of Group VIB of the Periodic System, such as chromium, molybdenum, and tungsten, and mixtures thereof, in an amount of about 5 to 15 per cent by weight of the finished catalyst, and a promoter selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and mixtures thereof, such as potassium, rubidium, cesium, calcium, strontium, barium, cerium, thorium, etc., in an amount between about 1 to 10 percent by weight of the finished catalyst, at a temperature of about 1,050* to 1,200*F, a pressure of about 100 to 1,000 psig., a liquid hourly space velocity of about 0.1 to 5, and a hydrogento-hydrocarbon mole ratio between about 3 and 15 to 1.

Claims

2. A process in accordance with claim 1 wherein the promoter metal is calcium. 3. A process in accordance with claim 1 wherein the promoter metal is strontium. 4. A process in accordance with claim 1 wherein the promoter metal is barium. 5. A process in accordance with claim 1 wherein the promoter metal is thorium. 6. A process in accordance with claim 1 wherein the promoter metal is rubidium. 7. A process in accordance with claim 1 wherein the promoter metal is cesium. 8. A process in accordance with claim 1 wherein the alumina carrier is a gamma alumina.
United States Patent 1 Patrick et al. [451 Sept. 18, 1973 HYDRODEALKYLATION PROCESS WITH PROMOTED GROUP VIB METALS AND PROMOTERS [75] Inventors: Ralph E. Patrick, Flatwoods; Ronald A. Kmecak; Stephen M. Kovach, both of Ashland, all of Ky. [73] Assignee: Ashland Oil, Inc., Ashland, Ky. [22] Filed: Apr. 26, 1971 [21] App]. No.: 137,666 Related (1.8. Application Data [63] Continuation of Ser. No. 769,735, Oct. 22, 1968, abandoned. [521 US. Cl. 260/672 R, 208/112, 208/136, I 252/462, 252/465 [51] Int. Cl B0lj 11/06, C07c 3/58 [58] Field of Search 260/672 R [56] References Cited UNITED STATES PATENTS 2,958,643 11/1960 Friedman 208/60 2,858,348 10/1958 Bosmajian et al. 260/668 2,895,905 7/1959 Kimberlin 208/137 3,193,592 7/1965 Eubank 260/672 2,963,518 12/1960 Amos 260/672 Mason 260/668 Doumani 260/672 [57] ABSTRACT A process for the hydrodealkylation of alkylsubstituted aromatic hydrocarbons, including contactingthe alkyl-substituted aromatic hydrocarbons with a catalyst comprising a metal of Group VlB of the Periodic System, such as chromium, molybdenum, and tungsten, and mixtures thereof, in an amount of about 5 to 15 per cent by weight of the finished catalyst, and a promoter selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and mixtures thereof, such as potassium, rubidium, cesium, calcium, strontium, barium, cerium, thorium, etc., in an amount between about 1 to 10 percent by weight of the finished catalyst, at a temperature of about 1,050 to 1,200F, a pressure of about 100 to 1,000 psig., a liquid hourly space velocity of about 0.1 to 5, and a hydrogen-to-hydrocarbon mole ratio between about 3 and 15 to l. 8 Claims, No Drawings 1 HYDRODEALKYLATION PROCESS WITH PROMOTED GROUP VIB METALS AND PROMOTERS RELATED APPLICATIONS The present application is a continuation of Ser. No. 769,735, filed Oct. 22, 1968, now abandoned. Other related applications are Ser. No. 769,729, filed Oct. 22, 1968, now U.S. Pat. No. 3,700,745 and Ser. No. 769,733, filed Oct. 22, 1968, now U.S. Pat. No. 3,679,768. BACKGROUND OF THE INVENTION The present invention relates to a process for the hydrodealkylation of alkyl aromatics to the present aromatic hydrocarbons. More specifically, the present invention relates to a process for the hydrodealkylation of alkyl aromatic hydrocarbons to the parent aromatic hydrocarbons, utilizing a unique catalyst system. The hydrodealkylation of alkyl aromatics has been practiced for many years. The principal processes involve the conversion of toluene and like alkylsubstituted benzenes to benzene, and coal tar light oils and coal tar methyl naphthalene to benzene and naphthalene, respectively. These processes may be catalytic or non-catalytic in nature. The non-catalytic system which involves thermal dealkylation, in the presence of hydrogen, requires high temperatures and pressures. While the catalytic processes require lower temperatures and pressures, these temperatures and pressures are still quite high and therefore result in short catalyst life. Most commerical catalytic processes employ chromia-magnesia deposited on an alumina base as a catalyst Since the development of this catalyst, there has really been no improvement in catalysts for this reaction. It is therefore an object of the present invention to provide a new process for the hydrodealkylation of alkyl aromatic employing a novel catalyst system. In a more specific aspect, the present invention relates to a process, for the hydrodealkylation of alkyl aromatics wherein catalysts which improve conversion are em-' ployed. Another and .further object of the present invention is to provide a process for the hydrodealkylation of aromatics wherein catalysts of higher selectivity are utilized. A still further object of the present invention is to provide an improved process for the hydrodealkylation of alkyl aromatics wherein catalysts which reduce carbon lay-down on the catalyst are employed. A further object of the present invention is to provide an improved hydrodealkylation process for the hydrodealkylation of alkyl aromatics wherein novel catalysts are employed which permit operation at lower than conventional temperatures. Another and further object of the present invention is to provide an improved system for the hydrodealkylation of alkyl aromatics wherein-catalysts are employed which permit the use of lower hydrogen partial pressures. SUMMARY OF THE INVENTION Briefly, in accordance with the present invention, alkyl aromatics are hydrodealkylated to their parent aromatic hydrocarbons by contacting the alkyl aromatic with a catalyst comprising a Group VIB metal oxide and an oxide selected from the group consisting of an alkali metal, an alkaline earth metal and a rare earth metal. DESCRIPTION OF THE PREFERRED EMBODIMENTS Suitable feedstocks for use in accordance with the present invention include toluene, polymethyl benzenes, coal tar light oils, coal tar methylnaphthalene concentrates, and bicyclic concentrates from light cycle oils and heavy reformates. Feedstock preparation includes fractionation to remove front ends or bottoms to thereby remove undesired fractions such as unsaturates, indanes and resinous materials. For example, it hasbeen found the coal tar'methylnaphthalene concentrates, as received from the coke oven, contain a large amount of contaminants, such as polymers, resins and free carbon. Distillation of such raw materials to yield a percent overhead leaves these materials as a bottoms. Hydrogenation and hydrotreating of the overhead fraction removes sulfur, nitrogen and oxygen contaminants, but, due to the thermal instability of the feedstocks, a heavy resinous material is produced through thermal polymerization. Distillation of the hydrotreated product is required to remove these resins and thereby reduce carbon lay-down on 1 the hydrodealkylation catalyst and reduce hydrogen consumption due to hydrocracking of the resins and polymers. The processing conditions for the hydrodealkylation reaction of the present invention include a temperature between about l,050 and l,200F, a pressure between about and 1,000 psig., a liquid hourly space velocity between about 0.1 and 5, and a hydrogen-tohydrocarbon mole ratio of about 3 to 15/1. The catalysts to be employed in accordance with the present invention include metal oxides from Group VIB of the Periodic System, particularly chromium, molybdenum and tungsten. The promoters include alkali metal oxides of Group I of the Periodic System and, alkaline earth metal oxides of Group II of the Periodic System and the rare earth metals. Examples of materials of this nature which may be employed include potassium, rubidium, and cesium; magnesium, calcium and strontium, and cerium and thorium, etc. The active metal and the promoter are deposited on an inert oxide support, which preferably includes a high area alumina having a boehmite, bayerite, beta, or eta crystalline form, or other aluminas, silica-alumina, silica, silicamagnesia, silica-zirconia, alumina-magnesia, etc. The optimum active metal content of the catalyst is about 5 to 15 percent by weight based on'the final catalyst. The metal oxide promoter should be present in amounts of about 1 to 10 percent by weight. The catalysts of the present invention may be prepared by well-known techniques in the art. Typical examples are coprecipitation or impregnation techniques. One may employ extrudates or pellets for impregnation or powders followed by pelletization or extrusion to yield the finished catalyst. The active metal and the promoter may be added through the use of water- Example I. To 200 ml. of distilled water was added 15 g. of cesium nitrate and 40 g. of chromic acid. This solution was added to 200 ml. of a boehmite alumina and after contact for fifteen minutes, the unadsorbed liquid was decanted from the catalyst pellets. The resulting im- We claim: 1. A process for hydrodealkylating alkyl aromatic hydrocarbons in a mixture comprising; contacting the hydrocarbon mixture with a catalyst consisting essentially pregnated catalyst was dried at 250F for one hour and 5 of about 5 to 15 percent of an active metal of Group calcined in air at 950F for sixteen hours in a muffle VIB of the Periodic System and about 1 to percent furnace. This yielded a catalyst of the following compoby weight of a promoter metal selected from the group SitiOn: consisting of rubidium, cesium, calcium, strontium, barium, and thorium, and mixtures thereof, both im- 10 percent Cr2o3 4 percent CS2O A12O3 10 pregnated on an alumina carrier selected from the group consisting of boehmite, bayerite, beta, alumina- Example magnesia, and mixtures thereof, under conditions suffi- To 500 ml. of distilled water was added 41 g. of cecient to effect said hydrodealkylation reaction, includrous nitrate hexahydrate and 100 g. of chromic nitrate. ing a temperature of about l,050 to l,200F., a pres- This solution was added to 500 ml. of a bayerite alusure of about 100-],000 psig., a liquid hourly space vemina and after contact for fifteen minutes, the unadlocity of about 0.1 to 5.0 and a hydrogen-tosorbed liquid was decanted from the catalyst pellets. hydrocarbon mole ratio between about 3 and 15 to l. The resulting impregnated catalyst was dried at 250F 2. A process in accordance with claim 1 wherein the for one hour and calcined in air at 950F in a muffle promoter metal is calcium. furnace for 16 hours. This yielded a catalyst of the fol- 20 3. A process in accordance with claim 1 wherein the lowing composition: promoter metal is strontium. . 4. A process in accordance with claim 1 wherein the 10 percent Cr O -2 percent Ce O Al O promoter metal is ri m- 5. A process in accordance with claim 1 wherein the The following Table illustrates the advantages of the promoter metal is thorium. catalysts of the present invention as compared with a 6. A process in accordance with claim 1 wherein the commerical chromia-magnesia on alumina catalyst. promoter metal is rubidium. TABLE 1 [Feed: toluene. Standard conditions: l,150 F., 500 psig., 0.5 LHSV, .3/1 lIz/II'C] Run Catalyst 12 (Jr-2 Mil-A1203 10 Cr-t K-Al O; w Cr-lCs-AlgO; 12 cm C0-Al20 12 cm tit-A1203 Liquid recovery volume percent feed 8-1 83 80 77.0 83. U Product distribution Benzene. U. 8 0. 7 I), u 1. l o. 3 Benzene... 66.8 75.6 81.5 80.0 71.8 Toluene s2. 4 23.1 11. 3 13. s 38.0 Weight percent feed: Toluene conversion 72. 8 80. 2 86. 2 80. 4 To. Selectivity to benzene 92 93 {)2 8!! -94 Carbon on catalyst; weight percent iced 0.- 0. 1!) 0. 07 .005 .005 7. A process in accordance with claim 1 wherein the promoter metal is cesium. 8. A process in accordance with claim 1 wherein the alumina carrier is a gamma alumina. * t It!

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    EP-0098538-A3June 06, 1984Air Products And Chemicals, Inc.Process for the hydrodealkylation of alkyl-aromatic hydrocarbons, process for the hydrodesulfurization of a hydrocarbon gas stream, and catalyst therefor
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    US-3978004-AAugust 31, 1976Rhone-ProgilCatalysts for the treatment of gases containing various derivatives of sulphur
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