Production of Paraxylene

Abstract

The process concerns ethylbenzene conversion and xylene isomerization with a catalyst pretreated by sulfiding.

What is claimed is: 
     
         1 . A process for preparing paraxylene comprising:
 (a) contacting a C8 aromatic hydrocarbon mixture including ethylbenzene and at least one xylene isomer other than paraxylene, in the presence of hydrogen and under suitable ethylbenzene de-alkylating conditions, with at least a first catalyst comprising at least a first hydrogenation component, wherein said hydrogenation component is selected from Groups 6-11 and 14-15 of the Periodic Table, preferably rhenium, said component supported on a molecular sieve, wherein said catalyst is suitable for de-alkylation of ethylbenzene and further characterized as having been subjected to a sulfiding treatment prior to said contacting, to produce a ethylbenzene-depleted aromatic hydrocarbon mixture; then   (b) contacting said ethylbenzene-depleted C8 aromatic hydrocarbon mixture, in the presence of hydrogen and under suitable xylene isomerization conditions, with at least a second catalyst comprising at least a second hydrogenation component, preferably rhenium, said component supported on a molecular sieve, wherein said catalyst is suitable for xylene isomerization and further characterized as having been subjected to a sulfiding treatment prior to said contacting, to produce a paraxylene-enriched C8 aromatic hydrocarbon mixture, when compared with said C8 aromatic hydrocarbon mixture of step (a).   
     
     
         2 . The process of  claim 1 , wherein said sulfiding treatment in at least one of steps (a) and (b) is carried out in a hydrogen sulfide current at a temperature of 100° to 450° C. 
     
     
         3 . The process of  claim 1 , wherein at least one of said first and second catalysts is not silica-selectivated. 
     
     
         4 . The process of  claim 1 , wherein at least one of said first and second catalysts is steam-treated prior to said sulfiding treatment. 
     
     
         5 . The process of  claim 1 , wherein at least one of said first and second catalysts comprises a hydrogenation component in the reduced state prior to said sulfiding. 
     
     
         6 . The process of  claim 1 , wherein at least one of said first and second catalysts is/are sulfided by exposure to hydrogen sulfide at a temperature of from above room temperature to 540° C. for a period of time sufficient to provide sulfur in an amount of at least 0.5 equivalents based on the catalyst metal content. 
     
     
         7 . The process of  claim 1 , wherein each of said first and second catalysts comprises an intermediate pore size molecular sieve and characterized by a Constraint Index within the range of 1 to 12, independently selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-57, ZSM-58, and mixtures thereof, and wherein said first and second hydrogenation components are each independently selected from Groups 6-11 and 14-15 of the Periodic Table. 
     
     
         8 . The process of  claim 1 , wherein said at least one first catalyst has a higher alpha value than said at least one second catalyst. 
     
     
         9 . The process of  claim 1 , wherein said at least one first catalyst is in a first bed and said at least one second catalyst is in a second bed and wherein said ethylbenzene-depleted aromatic hydrocarbon mixture is cascaded from the first bed to said second bed without intervening separation of light gases. 
     
     
         10 . The process of  claim 1 , wherein said at least one first catalyst has a crystal size of greater than 1 micron and said at least one second catalyst has a crystal size of from 0.02 to 0.05 microns. 
     
     
         11 . The process of  claim 1 , wherein said first and second hydrogenation compounds are rhenium. 
     
     
         12 . A reactor system comprising, in sequence and in separate but fluidly connected beds, a first catalyst having an average crystal size of greater than 1 micron and a second catalyst having an average crystal size of 0.02 to 0.05 microns, wherein each of said first and said second catalysts comprise a molecular sieve and a sulfided hydrogenation component, wherein each of said molecular sieves is not silica selectivated and is independently selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-57, ZSM-58, and mixtures thereof, wherein said first catalyst has a higher alpha value than said second catalyst, and wherein said first catalyst is in contact with a first C8 aromatic hydrocarbon mixture and said second catalyst is in contact with a second C8 aromatic hydrocarbon mixture. 
     
     
         13 . The reactor system of  claim 12 , wherein said hydrogenation components on said first and second catalyst are independently selected from Groups 6-11 and 14-15 of the Periodic Table. 
     
     
         14 . The reactor system of  claim 12 , wherein said hydrogenation component is rhenium and said molecular sieve is ZSM-5, in both said first and second catalysts. 
     
     
         15 . The reactor system of  claim 12 , wherein said hydrogenation component is rhenium.