United States Patent (19) 11) 4,229,320 Slaugh 45) Oct. 21, 1980 54 CATALYST FOR MAKING PARA-XYLENE (56) References Cited U.S. PATENT DOCUMENTS 75) Inventor: Lynn H. Slaugh, Houston, Tex. 3,291,564 12/1966 Kearby ............... ... 252/463 X s O 3,755,556 8/1973 Aldridge ................. 252/476 X 73) Assignee: Shell Oil Company, Houston, Tex. 3,830,866 8/1974 D'Alessandro et al. ............. 585/417 21 Appl. No.: 5 653 Primary Examiner-W.J. Shine 9 57 ABSTRACT (22) Filed: Jan. 22, 1979 Isobutylene is selectively converted to para-xylene over a coupling catalyst consisting essentially of a neutral or 51) Int. Cl......................... B01J 21/04; B01J 21/08; weakly acidic support impregnated with a non-halogen B01J 23/04; B01J 23/14; B01J 23/36 containing water soluble rhenium compound and an 52 U.S. C. .................................... 252/454; 252/463; alkali metal hydroxide or stannate and then reduced 252/476; 585/417 with hydrogen at elevated temperatures. 58) Field of Search ....................... 252/454, 463,476; 585/417 - 6 Claims, No Drawings 4,229,320 1. 2 dehydrocoupling reaction which yields the p-xylene CATALYST FOR MAKNG PARA-XYLENE isomer. The prior art also discloses catalysts which contain BACKGROUND OF THE INVENTION rhenium for the isomerization of xylene isomers to p This invention relates to a process for the preparation xylene. See for example U.S. Pat. Nos. 3,642,925 and of p-xylene as well as the catalytic composition used 3,557,022 and German Pat. No. 2,221,863. These three therein. More particularly, this invention is directed patents again teach the presence of additional metals, toward a process for the selective conversion of isobu such as platinum or tin, in the catalytic compositions. tylene to p-xylene over a supported catalyst impreg Furthermore, an isomerization reaction differs radically nated with a non-halogen containing water soluble rhe O from the types of coupling reactions claimed herein. nium compound and an alkali metal hydroxide or stan nate and then reduced with hydrogen at elevated tem SUMMARY OF THE INVENTION peratures. A process has now been discovered for the selective Dehydrocoupling reactions, such as the conversion conversion of isobutylene to p-xylene over a novel of isobutylene to various aromatics, are of interest as a 15 coupling catalyst comprising rhenium in oxide or metal means of utilizing the isobutylene often produced in lic form deposited on a neutral or weakly acidic support large amounts as a by-product of such commercial re which has been additionally impregnated with an alkali fining processes as hydrocarbon cracking. It would be metal hydroxide or stannate and subsequently reduced especially desirable to selectively convert an isobutyl with hydrogen at elevated temperatures. The rhenium ene feed to para-xylene while avoiding the formation of 2 is provided by a non-halogen containing water soluble ortho-xylene and meta-xylene isomers. Para-xylene is rhenium compound which is reduced after deposit on the more valuable xylene isomer and finds applications said support. This process provides a means for obtain as an octane booster in motor fuels or as a precursor to commercially important intermediates such as terep ing the more valuable p-xylene isomer from the olefinic thalic acid. While other aromatics like benzene or tolu 25 feed stream while avoiding the troublesome formation ene that may be formed are comparatively easy to distill of the ortho-xylene and meta-xylene isomers. The cata off, the separation of the xylene isomers is more diffi lytic composition obviates the problems of low selectiv cult, requiring costly recrystallization and filtration ity, commercial infeasibility or system corrosion ob which may often prove impractical in large scale opera tained with catalysts in the prior art. By producing tions. With the instant invention, a simple and effective 30 solely the para-xylene isomer, the costly and impracti process has been devised to obtain the desired para cal recrystallization normally required for the separa Xylene product in the absence of the troublesome meta tion of the three xylene isomers is avoided. The catalyst and/or ortho-isomers. is conveniently prepared in a two step process where The prior art discloses several methods for the prepa the non-halogen containing water-soluble rhenium ration of aromatics from aliphatic or olefinic hydrocar 35 compound and an alkali metal hydroxide or stannate are bon streams with the use of catalysts containing some deposited on the appropriate support and the rhenium form of rhenium. For example, U.S. Pat. No. 3,546,138 component is subsequently reduced by treatment with discloses a catalyst consisting of oxides of antimony and hydrogen at elevated temperatures. It is believed that iron promoted with an oxide of rhenium for use in the the catalysts prepared in this manner contain sites oxidative dehydrogenation of olefins to diolefins and which promote the dimerization of isobutylene selec aromatics. However, it is specifically mentioned that tively to a 2,5-dimethylhexyl structure which leads isobutylene should not be in the feed in large amounts. exclusively to the para-isomer of xylene. U.S. Pat. No. 3,856,880 discloses the use of rhenium to DESCRIPTION OF THE PREFERRED promote ferrite catalysts for the oxidative dehydrogena EMBODEMENTS tion of organic compounds; the conversion of a pentene 45 to a mixture of xylenes is specifically taught. In U.S. Suitable supports for the coupling catalysts above are Pat. No. 3,374,281, a catalyst consisting of an acidic such neutral or weakly acidic supports as silicas and support with a metal or oxide of a metal such as rhe alumina, many of which are commercially available. nium as a dehydrogenation component is disclosed for Alumina is the support of choice. Generally, highly the conversion of paraffinic hydrocarbons to various 50 acidic supports should be avoided as they may cause alkylated aromatics. Similarly, a form of rhenium is some undesired isomerization. Silica-alumina supports employed in the catalyst in the following U.S. Pat. Nos. and zeolites are examples of supports which may cause patents which disclose cyclization or aromatization isomerization problems. The support is suitably impreg reactions: 4,003,957; 3,855, 115; 3,541,001 and 3,129,243. nated with a non-halogen containing water soluble rhe It should be noted that the listed patents do not describe 55 nium compound. Ammonium perrhenate and rhenium the selective conversion of an olefinic stream to a single heptaoxide are the rhenium compounds of choice. Halo Xylene isomer. The prior art which utilizes a rhenium genated rhenium compounds are too acidic in nature, component often does so in conjunction with some causing undesirable side reactions. As will be more fully other metal and nowhere discloses further treatment discussed below, the rhenium compound is deposited on with an alkali metal hydroxide or stannate as herein. 60 the support by reaction with a warm aqueous solution The selective production of p-xylene from isobutyl of the rhenium compound and subsequently calcined ene and/or other olefinic charge stocks is disclosed in with air. The supported rhenium catalyst is also treated the following patents: U.S. Pat. Nos. 4.007,231; (doped) with an alkali metal hydroxide or stannate. 3,830,866; 3,769,237; 3,730,957; 3,644,551 and 3,644,550. Sodium or potassium are the preferred alkali metals; However, none of these patents disclose catalysts con 65 thus sodium hydroxide, sodium stannate, potassium taining any form of a rhenium component. Serious cor hydroxide or potassium stannate are the preferred com rosion problems may also arise in some cases from com pounds for doping the catalyst in this manner. Of these, pounds that are added to the catalyst to promote the sodium hydroxide and sodium stannate are more pre 4,229,320 3 4 ferred. After both components are deposited on the isobutylene reactant passed through the tube, optionally support, the composition is then treated with hydrogen and preferably with a concurrent stream of an inert at elevated temperatures. This treatment serves to re diluent gas as above. The product stream containing duce the rhenium component to its metallic state while p-xylene is then collected by conventional means, for leaving the hydroxide or stannate largely unreduced. example, condensation in externally cooled heat ex Accordingly, the preferred catalytic composition changers. The reaction may be suitably conducted at herein is an alumina support impregnated with rhenium pressures ranging from atmospheric pressure to 1000 heptaoxide or ammonium perrhenate, calcined, addi psig, most preferably from atmospheric pressure to 200 tionally treated with sodium hydroxide or sodium stan psig. The reaction suitably takes place at elevated tem nate and finally reduced with hydrogen at elevated 10 peratures of from 400 to 600° C., with temperatures of temperatures. The process according to the invention 450 to 550° C. preferred. Above temperatures of 550 may be carried out batchwise or continuously and is C., small amounts of other xylene isomers may begin to suitably conducted by passing the isobutylene reactant, contaminate the desired p-xylene. Methane and isobu optionally and preferably in the presence of an inert tane are the main by-products of the reaction. The diluent gas such as nitrogen, into a reaction Zone con 15 taining the supported rhenium catalyst as a fixed or isobutane may be dehydrogenated to yield isobutylene fluidized bed at elevated temperatures and recovering and fed through the reactor tube again so as to increase the p-xylene formed from the reaction zone effluent. the total level of conversion to p-xylene. Alternatively, The support is impregnated with the non-halogen the by-products each may be utilized as a feed for a containing rhenium compound by completely wetting 20 number of conventional processes whereby they are the surface of the support with a warm aqueous solution converted to more valuable chemicals or intermediates.