Dual riser catalytic cracking process for making middle distillate and lower olefins

Abstract

A dual riser catalytic cracking process for preferentially making middle distillate and lower olefins. The system and process provide for the processing of multiple hydrocarbon feedstocks so as to selectively produce middle distillate boiling range product and lower olefins. The system and process uses two riser reactors, a single vessel for separating the cracked product and cracking catalyst received from both riser reactors, and a regenerator for regenerating coked or spent cracking catalyst.

1 . A dual riser catalytic cracking process for making middle distillate and lower olefins, wherein said process comprises:
 catalytically cracking a first hydrocarbon feedstock within a first riser reactor zone by contacting under first catalytic cracking conditions within said first riser reactor zone said first hydrocarbon feedstock with a combination of a clean spent catalyst and a first portion of a regenerated cracking catalyst to yield a first riser reactor product comprising a first cracked product and a coked spent catalyst;   catalytically cracking a second hydrocarbon feedstock within a second riser reactor zone by contacting under second catalytic cracking conditions within said second riser reactor zone said second hydrocarbon feedstock with a second portion of said regenerated cracking catalyst to yield a second riser reactor product comprising a second cracked product and said clean spent catalyst;   passing said first riser reactor product to a single vessel separator/stripper providing means for separating said first riser reactor product into a separated first cracked product and a separated coked spent catalyst;   passing said second riser reactor product to said single vessel separator/stripper providing means for separating said second riser reactor product into a separated second cracked product and a separated clean spent catalyst;   using at least a portion of said separated clean spent catalyst as said clean spent catalyst of said combination; and   passing said separated coked spent catalyst and the remaining of said separated clean spent catalyst to a regenerator that defines a regeneration zone and provides means for regenerating said separated coked spent catalyst to yield said regenerated cracking catalyst.   
     
     
         2 . A process as recited in  claim 1 , which further comprises: passing said separated first cracked product and said separated second cracked product to a fractionator defining a fractionation zone and providing fractionation means for separating either said separated first cracked product or said separated second cracked product, or both, into one or more product streams including a naphtha product stream. 
     
     
         3 . A process as recited in  claim 2 , which further comprises: using at least a portion of said naphtha product stream as at least a portion of said second hydrocarbon feedstock. 
     
     
         4 . A process as recited in  claim 3 , wherein said single vessel separator/stripper defines a separation zone that includes first separation means for separating said first riser reactor product into said separated first cracked product and said separated coked spent catalyst and second separation means for separating said second riser reactor product into said separated second cracked product and said separated clean spent catalyst, and wherein said single vessel separator/stripper further defines a stripping zone that includes a first stripping zone and a second stripping zone provided by segregation means for defining said first stripping zone and said second stripping zone contained within said single vessel separator/stripper, and wherein within said first stripping zone said separated coked spent catalyst is stripped of hydrocarbons, and wherein within said second stripping zone said separated clean spent catalyst is stripped of hydrocarbons. 
     
     
         5 . A process as recited in  claim 4 , wherein said single vessel separator/stripper further includes a clean catalyst withdrawal conduit and a catalyst standpipe conduit, wherein said clean catalyst withdrawal conduit provides fluid communication between said second stripping zone and said first riser reactor zone to thereby allow for withdrawing said at least a portion of said separated clean spent catalyst from said second stripping zone and introducing said separated clean spent catalyst into said first riser reactor zone, and wherein said catalyst standpipe conduit provides fluid communication between said stripping zone and said regeneration zone to allow withdrawing said remaining portion of said separated clean spent catalyst and said separated coked spent catalyst and introducing said remaining portion of said separated clean spent catalyst and said separated coked spent catalyst into said regenerator zone. 
     
     
         6 . A process as recited in  claim 5 , wherein said single vessel separator/stripper further includes a product withdrawal conduit in fluid communication between said separation zone and said fractionation zone and providing product withdrawal means for withdrawing said separated first cracked product or said separated second cracked product, or both, from said separation zone and introducing said separated first cracked product or said separated second cracked product, or both, into said fractionation zone. 
     
     
         7 . A process as recited in  claim 1 , which further comprises: passing a remaining portion of said separated clean spent catalyst to said regenerator that provides means for regenerating said remaining portion of said separated clean spent catalyst to yield said regenerated cracking catalyst.