Process and catalysts for C8 alkylaromatic isomerization

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 MFI-type.

1 . A process for the isomerization of xylenes comprising contacting an aromatics-containing hydrocarbon feed stream with a catalyst system comprising a beta zeolite and a pentasil zeolite selected from the group of zeolite types consisting of MFI, MEL, MTW, TON or mixtures thereof, under isomerization conditions and recovering a product stream comprising a greater amount of para-xylene than in the feed stream, wherein the amount of para-xylene in the product is at least 90 mol-% of the approach to an equilibrium amount of para-xylene to total xylenes and wherein the conversion of ethylbenzene over the catalyst system is at least 20 mol-%.  
     
     
         2 . The process of  claim 1  wherein the catalyst system is contacted under at least partial liquid phase conditions.  
     
     
         3 . The process of  claim 2  wherein the at least partial phase liquid conditions include the absence of added hydrogen.  
     
     
         4 . The process of  claim 1  wherein the isomerization conditions comprise a space velocity from about 0.1 to about 20 hr −1 , a temperature from about 100° to about 400° C. and a pressure from about 10 kPa to about 5 MPa absolute.  
     
     
         5 . The process of  claim 4  wherein the isomerization conditions comprise a space velocity from about 0.5 to about 10 hr −1 , a temperature from about 150° to about 300° C. and a pressure from about 100 kPa to about 3 MPa absolute.  
     
     
         6 . The process of  claim 1  wherein the catalyst system is essentially free of a hydrogenation metal component.  
     
     
         7 . The process of  claim 6  wherein the catalyst system is essentially free of hydrogenation metal component by containing less than 0.1 mass-% amount of said metal.  
     
     
         8 . The process of  claim 1  wherein the catalyst system further comprises a binder selected from the group consisting of alumina, silica, and mixtures thereof.  
     
     
         9 . The process of  claim 8  wherein the binder is alumina.  
     
     
         10 . The process of  claim 1  wherein the pentasil zeolite is a MFI-type zeolite.  
     
     
         11 . The process of  claim 1  wherein the beta zeolite is a surface modified beta zeolite.  
     
     
         12 . The process of  claim 11  wherein the surface modified beta zeolite results from acid washing of a templated native zeolite.  
     
     
         13 . A process for the isomerization of xylenes comprising contacting a C 8  aromatics containing hydrocarbon feed stream, which comprises ethylbenzene, with a catalyst system comprising a beta zeolite catalyst and a MFI-zeolite catalyst under at least partially liquid phase at isomerization conditions, and recovering a product stream comprising para-xylene, wherein the amount of para-xylene in the product is at least 90 mol-% of the approach to an equilibrium amount of para-xylene to total xylenes and wherein the conversion of ethylbenzene over the catalyst system is at least 20 mol-%.  
     
     
         14 . The process of  claim 13  wherein the binder is selected from the group consisting of alumina, silica, zeolites, and mixtures thereof.  
     
     
         15 . The process of  claim 13  wherein the beta zeolite catalyst is essentially free of a metal hydrogenation component.  
     
     
         16 . The process of  claim 13  wherein the isomerization conditions comprise a space velocity from about 0.5 to about 10 hr −1 , a temperature from about 150° to about 300° C. and a pressure from about 100 kPa to about 3 MPa absolute.  
     
     
         17 . The process of  claim 16  wherein the isomerization conditions further comprise the absence of a substantial amount of hydrogen.  
     
     
         18 . The process of  claim 17  wherein the substantial amount of hydrogen is less than or equal to the hydrogen solubility in the liquid phase.  
     
     
         19 . The process of  claim 17  wherein the substantial amount of hydrogen is less than 1 wt-%.