Process for cracking to light olefins

Abstract

A process for catalytic production of olefins comprises contacting a first hydrocarbon stream and a first stream of fluid catalyst in a first riser to produce a first cracked product stream and a spent catalyst stream. The first cracked product stream is separated in a main column. An overhead stream from the main column is separated into a second hydrocarbon stream. The second hydrocarbon stream is contacted with a second stream of fluid catalyst in a second riser to produce a second cracked product stream and a first stream of cool catalyst. A third hydrocarbon stream is obtained from the overhead stream and/or from the second cracked product stream. The third hydrocarbon stream is contacted with a third stream of fluid catalyst in a third riser to produce a third cracked product stream and a second stream of cool catalyst.

1 . A process for catalytic production of olefins comprising:
 contacting a first hydrocarbon stream and a first stream of fluid catalyst in a first riser to produce a first cracked product stream and a spent catalyst stream;   separating said first cracked product stream in a main column;   separating an overhead stream from the main column into a second hydrocarbon stream;   contacting said second hydrocarbon stream with a second stream of fluid catalyst in a second riser to produce a second cracked product stream and a first stream of cool catalyst; and   obtaining a third hydrocarbon stream from said overhead stream and/or from said second cracked product stream; and   contacting said third hydrocarbon stream with a third stream of fluid catalyst in a third riser to produce a third cracked product stream and a second stream of cool catalyst.   
     
     
         2 . The process of  claim 1  wherein said second hydrocarbon stream is more olefinic and/or more crackable than said third hydrocarbon stream. 
     
     
         3 . The process of  claim 1  wherein said second hydrocarbon stream is a light cracked naphtha stream and further comprising separating said overhead stream from the main column into a first C4 hydrocarbon stream and taking said first C4 hydrocarbon stream as said third hydrocarbon stream. 
     
     
         4 . The process of  claim 1  further comprising washing said second cracked product stream in a wash column and obtaining said third hydrocarbon stream from said wash column. 
     
     
         5 . The process of  claim 3  wherein said second hydrocarbon stream is a first C4 hydrocarbon stream and said third hydrocarbon stream is a second C4 hydrocarbon stream. 
     
     
         6 . The process of  claim 1  further comprising compressing an overhead stream from said wash column to provide a compressed overhead stream and depropanizing said compressed overhead stream to provide a depropanized compressed overhead stream and taking said third hydrocarbon stream from said depropanized compressed overhead stream. 
     
     
         7 . The process of  claim 6  further comprising separating a depropanized compressed overhead stream into a second C4 stream and a second light cracked naphtha stream and taking said third hydrocarbon stream from said second light cracked naphtha stream and/or from said second C4 stream. 
     
     
         8 . The process of  claim 1  wherein said second stream of fluid catalyst and said third stream of fluid catalyst contain about 0.005 to about 1.2 wt % coke. 
     
     
         9 . The process of  claim 1  wherein said third riser operates at a higher outlet temperature and/or a lower hydrocarbon partial pressure and/or a different catalyst density than said second riser. 
     
     
         10 . The process of  claim 1  further comprising regenerating said stream of spent catalyst by combustion of coke from said spent catalyst to provide hot regenerated catalyst and heat exchanging a portion of said second stream of fluid catalyst with a portion of said hot regenerated catalyst before contacting said second stream of fluid catalyst with said second hydrocarbon stream. 
     
     
         11 . The process of  claim 1  further comprising regenerating said stream of spent catalyst by combustion of coke from said spent catalyst to provide hot regenerated catalyst and heat exchanging a portion of said third stream of fluid catalyst with a portion of said hot regenerated catalyst stream before contacting said third stream of fluid catalyst with said third hydrocarbon stream. 
     
     
         12 . The process of  claim 1  wherein the third hydrocarbon stream has more than 20 wt % olefins. 
     
     
         13 . The process of  claim 1  further comprising recycling a C4+ stream to a catalyst pipe that provides catalyst to the second riser and/or to the third riser. 
     
     
         14 . A process for catalytic production of olefins comprising:
 contacting a first hydrocarbon stream and a first stream of fluid catalyst in a first riser to produce a first cracked product stream and a spent catalyst stream;   separating said first cracked product stream in a main column;   obtaining a second hydrocarbon stream from said main column;   contacting said second hydrocarbon stream with a second stream of fluid catalyst in a second riser to produce a second cracked product stream and a first stream of cool catalyst; and   separating said second cracked product stream in a wash column and obtaining said third hydrocarbon stream from said wash column; and   contacting said third hydrocarbon stream with a third stream of fluid catalyst in a third riser to produce a third cracked product stream and a second stream of cool catalyst.   
     
     
         15 . The process of  claim 14  further comprising compressing an overhead stream from said wash column to provide a compressed overhead stream and depropanizing said compressed overhead stream to provide a depropanized compressed overhead stream and taking said third hydrocarbon stream from said depropanized compressed overhead stream. 
     
     
         16 . The process of  claim 14  wherein the third hydrocarbon stream has more than 20 wt % olefins. 
     
     
         17 . A process for catalytic production of olefins comprising:
 contacting a first hydrocarbon stream and a first stream of fluid catalyst in a first riser to produce a first cracked product stream and a spent catalyst stream;   separating said first cracked product stream in a main column;   obtaining a second hydrocarbon stream from an overhead line of said main column system;   contacting said second hydrocarbon stream with a second stream of fluid catalyst in a second riser to produce a second cracked product stream and a first stream of cool catalyst; and   obtaining a third hydrocarbon stream from said first cracked product stream or said second cracked product stream; and   contacting said third hydrocarbon stream with a third stream of fluid catalyst in a third riser to produce a third cracked product stream and a second stream of cool catalyst.   
     
     
         18 . The process of  claim 17  wherein said second hydrocarbon stream is more olefinic and/or more crackable than said third hydrocarbon stream. 
     
     
         19 . The process of  claim 17  wherein the third hydrocarbon stream has more than 20 wt % olefins. 
     
     
         20 . The process of  claim 17  further comprising operating the third riser at a greater severity than the second riser.