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

Abstract

A fluidized catalytic cracking process and system that provide for the processing of hydrocarbon feedstocks to selectively produce a middle distillate boiling range product and lower olefins. The inventive process uses two riser reactors each having associated therewith a separator/stripper for separating the cracked product and cracking catalyst received from the respective riser reactor and a single regenerator for regenerating coked or spent cracking catalyst received from the separator/strippers. The two riser reactors, two separator/strippers and regenerator are operatively integrated to provide a process system for carrying out the process of the invention.

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 first 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 a second separator/stripper providing means for separating said second riser reactor product into a separated cracked 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 a remaining portion of said separated clean spent catalyst to a regenerator that defines a regeneration zone and provides means for regenerating said separated coked spent catalyst and said remaining portion of said separated clean 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 first separator/stripper defines a first 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 wherein said first separator/stripper further defines a first stripping zone, and wherein within said first stripping zone said separated coked spent catalyst is stripped of hydrocarbons. 
     
     
         5 . A process as recited in  claim 4 , wherein said second separator/stripper defines a second separation zone that includes 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 second separator/stripper further defines a second stripping zone, and wherein within said second stripping zone said separated clean spent catalyst is stripped of hydrocarbons. 
     
     
         6 . A dual riser 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 first 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 a second separator/stripper providing means for separating said second riser reactor product into a separated cracked second cracked product and a separated clean spent catalyst; and   passing said separated coked spent catalyst to a regenerator and passing said separated clean spent catalyst to said regenerator, wherein said regenerator defines a regeneration zone and provides means for regenerating said separated coked spent catalyst and said separated clean spent catalyst to yield said regenerated cracking catalyst.