System and method for selective component cracking to maximize production of light olefins

Abstract

A process for the fluid catalytic cracking of hydrocarbons includes contacting relatively heavy hydrocarbons with a fluidized particulate catalyst in a reaction zone under catalytic cracking conditions to convert at least some of the heavy hydrocarbons to light olefins having from 3 to 4 carbon atoms, conveying a reaction mixture containing spent catalyst particles and a gaseous stream containing the light olefins and other reaction products to a cyclone separation system directly connected to the reaction zone, at least part of the cyclone separation system being positioned within an interior space enclosed by a vessel, the interior space including a stripping region and an upper region in which the cyclone separation system is positioned. The cyclone separation system includes at least one cyclone connected directly to the reaction zone and having an interior pressure at least 0.05 psig lower than the pressure in the stripping region.

1 . A process for the fluid catalytic cracking of hydrocarbons comprising: 
 a) contacting a primary feed of relatively heavy hydrocarbons with a fluidized particulate catalyst in a reaction zone under catalytic cracking conditions to convert at least some of the heavy hydrocarbons to light olefins having from 3 to 4 carbon atoms;    b) conveying a reaction mixture containing spent catalyst particles and a gaseous stream containing the light olefins and other reaction products to a cyclone separation system directly connected to the reaction zone, at least part of said cyclone separation system being positioned within an interior space enclosed by a vessel, said interior space including a stripping region and an upper region in which the at least part of the cyclone separation system is positioned, said cyclone separation system including at least one cyclone connected directly to the reaction zone and having an interior first pressure and said stripping region having a second pressure, said interior first pressure being at least 0.05 psig lower than the second pressure;    c) separating the spent catalyst particles from the gaseous fluid within said at least one cyclone, said gaseous fluid being ejected as effluent from the separation vessel through an exit port and said spent catalyst particles being transferred to the stripping region; and,    d) contacting said spent catalyst particles with a stripping gas to remove entrained hydrocarbons, said stripping gas with entrained hydrocarbons being moved through the at least one cyclone through the exit port.    
     
     
         2 . The process of  claim 1  further including the step: 
 e) transferring the stripped catalyst particles to a regeneration zone for decoking.    
     
     
         3 . The process of  claim 2  further including the step: 
 f) decoking at least a portion of the stripped catalyst to provide regenerated catalyst.    
     
     
         4 . The process of  claim 1  wherein the catalyst comprises one or more zeolitic material selected from the group consisting of USY, ZSM-X, ZSM-Y, ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.  
     
     
         5 . The process of  claim 1  wherein the hydrocarbon feed comprise a petroleum fraction having a boiling range of from about 250° C. to about 625° C.  
     
     
         6 . The process of  claim 1  wherein the catalytic cracking conditions include a temperature of from 500° C. to about 600° C., a pressure of from about 10 to 25 psig, a residence time of from about 0.5 seconds to about 10.0 seconds and a hydrocarbon partial pressure of from about 3 psig to about 10 psig.  
     
     
         7 . The process of  claim 1  further comprising the step of injecting at least a second feed component into said reaction zone separately from said primary feed, said second feed component comprising a recycled portion of the effluent from the separation vessel, said recycled portion of the effluent being separated from the effluent downstream of the separation vessel by fractionation.  
     
     
         8 . The process of  claim 1  wherein the reaction zone comprises a vertically oriented riser reactor wherein the primary feed is introduced into the riser reactor at a position in the vicinity of a bottom portion of the riser reactor and exits the reaction zone at a top portion of the riser reactor.  
     
     
         9 . The process of  claim 7  wherein the second feed component comprises a hydrocarbon fraction which is lighter than the saturated hydrocarbons of the primary feed and which is introduced in the riser reactor through multiple points downstream of the position at which the primary feed is introduced.  
     
     
         10 . The process of  claim 3  wherein the step of transferring the stripped catalyst particles to a regeneration zone comprises conducting the catalyst particles through a square bend transfer line.  
     
     
         11 . The process of  claim 10  wherein the regeneration zone includes a fluidized bed and the stripped catalyst particles are introduced in the vicinity of the center of the fluidized bed.  
     
     
         12 . The process of  claim 11  wherein the decoking step includes contacting the stripped catalyst particles in the fluidized bed of the regeneration zone with an oxidizing gas.  
     
     
         13 . The process of  claim 12  further comprising the step of: 
 transferring at least a portion of regenerated catalyst to the reaction zone.    
     
     
         14 . The process of  claim 13  wherein the transferred portion of regenerated catalyst is conducted through a stand pipe and recycled to the reaction zone.