Multi-stage reforming process using rhenium-containing catalyst in the final stage

Abstract

This is a process for upgrading a petroleum naphtha fraction. The naphtha is subjected to reforming and the reformate is cascaded to a benzene and toluene synthesis zone over a benzene and toluene synthesis catalyst comprising a molecular sieve of low acid activity. The preferred molecular sieve is steamed ZSM-5. The benzene and toluene synthesis zone is operated under conditions compatible with the conditions of the reformer such as temperatures of above about 800° F. (427° C.). In one aspect on the invention, the benzene and toluene synthesis catalyst includes a metal hydrogenation component from group VII(B), specifically rhenium. In one mode of operation, the benzene and toluene synthesis catalyst replaces at least a portion of the catalyst in the reformer. The process produces a product containing an increased proportion of benzene, toluene, and/or xylenes, and a reduced portion of alkylated aromatics, as compared to reformate.

What is claimed is:  
     
         1 . A multistage integrated process for upgrading a petroleum naphtha comprising the steps of: 
 (a) introducing the naphtha to a catalytic reforming stage comprising a plurality of operatively connected catalyst zones including a first catalyst zone and a last catalyst zone, the last catalyst zone being maintained under reforming conditions of temperature ranging from at least 800° F. (427° C.) to 1050° F. (565° C.) and pressure of 50 psig (446 kPa) to 500 psig (3,549 kPa) to provide an intermediate product comprising aromatics and paraffins;    (b) transferring at least a portion of the intermediate product of the last catalyst zone to a benzene and toluene synthesis zone comprising at least one benzene and toluene synthesis catalyst operatively connected to the last catalyst zone of the reforming stage of step (a), the benzene and toluene synthesis zone being maintained under conditions of hydrogen-to-hydrocarbon mole ratio and pressure compatible with the last catalyst zone of the reforming stage and temperature of greater than 800° F. (427° C.), the benzene and toluene synthesis catalyst zone containing a catalyst, which comprises a hydrogenation component from Group VIIB and further comprises a molecular sieve of low acid activity, as determined by an alpha value of less than 60, to provide a hydrocarbon product comprising more benzene, toluene, xylenes content than the intermediate product of the last catalyst zone of the reforming stage;    wherein the intermediate product of step (a) that is fed to the benzene, toluene, and xylenes synthesis zone of step (b) has not been subjected to intermediate    separation.    
     
     
         2 . The process as described in  claim 1  in which the catalyst of step (b) comprises a molecular sieve selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38, MCM-22, MCM-36, MCM-48, MCM-56, and zeolite beta.  
     
     
         3 . The process as described in  claim 2  in which the catalyst of step (b) comprises ZSM-5 having an alpha value less than 50.  
     
     
         4 . The process as described in  claim 1  in which the benzene, toluene, or xylenes content of the intermediate product of step (a) is increased by at least 10% in step (b).  
     
     
         5 . The process as described in  claim 1  in which the metal hydrogenation component of step 1 (b) is selected from the group consisting of Pd, Pt, Re, and Mo.  
     
     
         6 . The process as described in  claim 1  in which the catalyst of step (b) comprises a catalyst deactivated in another refinery oxygenate or hydrocarbon conversion process.  
     
     
         7 . The process as described in  claim 1  which the hydrocarbon product of step (b) further comprises branched C6+ paraffins, the process further comprising step (c) of contacting the hydrocarbon product of step (b) over a catalyst zone comprising another catalytic reforming stage which isomerizes the branched C6+ paraffins.  
     
     
         8 . The process as described in  claim 1  in which the catalyst of step (b) further comprises sulfur.  
     
     
         9 . The process as described in  claim 8  in which a source of sulfur is a cofeed introduced in step (b).  
     
     
         10 . The process of  claim 1  in which at least the catalyst zone of step (a) is a radial flow reactor zone.  
     
     
         11 . The process of  claim 1  in which at least the zone of step (b) is a radial flow reactor zone.  
     
     
         12 . The process of  claim 3  in which the catalyst of step (b) is self-bound ZSM-5.  
     
     
         13 . The process of  claim 12  in which the zone of step (b) is a fixed bed zone.  
     
     
         14 . The process of  claim 1  in which the hydrocarbon product of step (b) comprise C9+ hydrocarbons, the process further comprising separating the C9+ hydrocarbons from the product of step (b) and recycling the C9+ hydrocarbons to step (a) or step (b).  
     
     
         15 . The process of  claim 1  which further comprises a C9+ aromatic cofeed in step (a) or step (b).  
     
     
         16 . The process of  claim 1  in which the petroleum naphtha is free of C6− hydrocarbons.  
     
     
         17 . The process of  claim 2  in which the catalyst of step (b) is subjected to steaming.  
     
     
         20 . The process of  claim 1  in which the product of step (b) further comprises a xylenes content which is higher than the intermediate of the last catalyst zone of the reforming stage.