Recracking mixture of cycle oil and cat naphtha for maximizing light olefins yields

Abstract

A process for increasing the yield of C 3 and C 4 olefins by injecting light cat naphtha and cat cycle oil together with steam into an upstream reaction zone of a FCC riser reactor. The products of the upstream reaction zone are conducted to a downstream reaction zone and combined with fresh feed in the downstream reaction zone.

What is claimed is:  
     
         1 . A fluid catalytic cracking process to increase yields of C 3  and C 4  olefins which comprises: 
 (a) conducting hot regenerated catalyst to an FCC unit having at least one riser reactor containing a downstream and an upstream reaction zone,    (b) contacting hot catalyst with a cycle oil, a light cat naphtha, and steam in the upstream reaction zone at a temperature of from about 620 to 775° C. and a vapor residence time of cycle oil, naphtha, and steam of less than 1.5 sec. wherein at least a portion of the C 5  to C 9  olefins present in the light cat naphtha is cracked to C 3  and C 4  olefins, and wherein at least a portion of the saturates in the cycle oil is converted to lower boiling point products including C 3  and C 4  olefins,    (c) contacting at least the catalyst products of cycle oil and naphtha cracking, and steam from the upstream reaction zone with a heavy feedstock in the downstream reaction zone at an initial temperature of from about 600 to 750° C. with vapor residence times of less than about 20 seconds,    (d) conducting spent catalyst, cracked products and steam from the first and second reaction zones to a separation zone,    (e) separating from the cracked products a cycle oil fraction, a light cat naphtha fraction, and steam from spent catalyst and recycling at least a portion of the cycle oil fraction and light cat naphtha fraction to the upstream reaction zone in step (b),    (f) conducting spent catalyst to a stripping zone and stripping spent catalyst under stripping conditions, and    (g) conducting stripped spent catalyst to a regeneration zone and regenerating spent catalyst under regeneration conditions.    
     
     
         2 . The process of  claim 1  wherein the amount of steam in the upstream reaction zone is from 2 to 50 wt. %, based on total weight of light cat naphtha and cycle oil.  
     
     
         3 . The process of  claim 1  wherein the residence time of cycle oil, naphtha, and steam in the upstream reaction zone is less than about 1 sec.  
     
     
         4 . The process of  claim 1  wherein process conditions in step (b) include catalyst/oil ratios of 75-150 (wt/wt) at pressures of 100-400 kPa.  
     
     
         5 . The process of  claim 1  wherein process conditions in step (c) include catalyst/oil ratios of 4-10 at pressures of 100-400 kPa and vapor residence times of 2-20 sec.  
     
     
         6 . The process of  claim 1  wherein the feedstock in step (c) includes from 1 to 15 wt. %, based on feedstock, of a higher boiling fraction with initial boiling point greater than 565° C.