Catalysts for C8 alkylaromatic isomerization process

Abstract

A liquid or partially liquid phase process for isomerizing a non-equilibrium mixture of xylenes and ethylbenzene uses a zeolitic catalyst system preferably based on zeolite beta and on pentasil-type zeolite. The invention obtains an improved yield of para-xylene from the mixture relative to prior art processes in a more economical manner. A preferred beta zeolite is a surface-modified zeolite beta resulting from acid washing of a templated native zeolite at conditions insufficient to effect bulk dealumination. A preferred pentasil zeolite is a MTW-type with a silica-to-alumina ratio between 20 and 45.

1 . A catalyst system for the isomerization of xylenes comprising a combination of a first catalyst comprising beta zeolite and a second catalyst comprising MTW-type zeolite.  
     
     
         2 . The catalyst system of  claim 1  wherein the second catalyst further comprises a platinum-group metal.  
     
     
         3 . The catalyst system of  claim 1  wherein either catalyst further comprises a zeolite-free inorganic oxide binder.  
     
     
         4 . The catalyst system of  claim 3  wherein the binder is selected from the group consisting of alumina, silica, and mixtures thereof.  
     
     
         5 . The catalyst system of  claim 4  wherein the binder is alumina.  
     
     
         6 . The catalyst system of  claim 1  wherein the beta zeolite is a surface modified beta zeolite.  
     
     
         7 . The catalyst system of  claim 6  wherein the surface modified beta zeolite results from acid washing of a tetraalkylammonium salt templated native zeolite.  
     
     
         8 . The catalyst system of  claim 1  wherein either catalyst further comprises a halogen component.  
     
     
         9 . The catalyst system of  claim 1  wherein a first:second mass ratio is from about 1:50 to about 50:1.  
     
     
         10 . The catalyst system of  claim 1  wherein the combination is a physical mixture of first particles comprising the beta zeolite and second particles comprising the MTW-type zeolite.  
     
     
         11 . The catalyst system of  claim 1  wherein the proportion of beta zeolite in the first catalyst is from about 10 to about 80 mass-% of the first catalyst.  
     
     
         12 . The catalyst system of  claim 1  wherein the proportion of MTW-type zeolite in the second catalyst is from about 50 to about 90 mass-% of the second catalyst.  
     
     
         13 . The catalyst system of  claim 1  wherein the MTW-type zeolite is characterized by silica to alumina ratio greater than about 20 and less than about 45.  
     
     
         14 . The catalyst system of  claim 1  wherein the first catalyst is essentially free of a metal hydrogenation component by containing less than 0.1 mass-% amount of said metal.  
     
     
         15 . A catalyst system for the at least partial liquid phase isomerization of xylenes comprising a combination of a first catalyst comprising beta zeolite and a zeolite-free inorganic oxide binder, and a second catalyst comprising MTW-type zeolite and a zeolite-free inorganic oxide binder, wherein the catalyst system is essentially free of a hydrogenation metal component by containing less than 0.1 mass-% amount of said metal.  
     
     
         16 . The catalyst system of  claim 15  wherein either binder is selected from the group consisting of alumina, silica, and mixtures thereof.  
     
     
         17 . The catalyst system of  claim 15  wherein the beta zeolite is a surface modified beta zeolite.  
     
     
         18 . The catalyst system of  claim 15  wherein the combination is contained within the same catalyst particle.  
     
     
         19 . The catalyst system of  claim 15  wherein the MTW-type zeolite is characterized by silica to alumina ratio greater than about 20 and less than about 45.  
     
     
         20 . A catalyst system for the at least partial liquid phase isomerization of xylenes comprising a combination of a first catalyst comprising a surface modified beta zeolite and a zeolite-free inorganic oxide binder, and a second catalyst comprising MTW-type zeolite characterized by silica to alumina ratio greater than about 20 and less than about 45 and a zeolite-free inorganic oxide binder, wherein the catalyst system is essentially free of a hydrogenation metal component by containing less than 0.1 mass-% amount of said metal and wherein either binder is selected from the group consisting of alumina, silica, and mixtures thereof.