Short contact time FCC process

Abstract

This invention relates to a short contact time (SCT) fluid catalytic cracking (FCC) process for improving the yield of distillates and gasoline. An SCT FCC process combines staging the FCC conversion process with interstage molecular separation of multi-ring aromatic species wherein separation of cat bottoms and recycling the separated stream containing saturates and 1- and 2-ring aromatics to the FCC unit results in improved yields of gasoline and other distillates while decreasing bottoms yields.

1 . A fluid catalytic cracking process which comprises: 
 (a) contacting hydrocarbon feed with regenerated catalyst in a fluid catalytic cracking reactor operating under short contact time cracking conditions including a contact time of less than 5 seconds to form a cracked product;    (b) separating cracked product from catalyst;    (c) passing the separated cracked product into a fractionating zone and separating from the cracked product a bottoms stream;    (d) passing the bottoms stream to a separation zone and separating the bottoms stream into a stream containing saturates and 1- and 2-ring aromatics and a stream containing predominantly aromatics having 3 or more rings;    (e) combining the stream containing saturates and 1- and 2-ring aromatics with hydrocarbon feed in step (a) to form a combined feed and contacting combined feed with catalyst of step (a).    
   
   
       2 . A fluid cracking process which comprises: 
 (a) contacting hydrocarbon feed with regenerated catalyst in a fluid catalytic cracking reactor operating under short contact time cracking conditions including a contact time of less than 5 seconds to form a cracked product;    (b) separating cracked product from catalyst;    (c) passing the separated cracked product into a fractionating zone and separating from the cracked product a bottoms stream;    (d) passing the bottoms stream to a separation zone and separating the bottoms stream into a stream containing saturates and 1- and 2-ring aromatics and a stream containing predominantly aromatics having 3 or more rings;    (e) passing the stream containing saturates and 1- and 2-ring aromatics to step (a) wherein hydrocarbon feed and the stream containing saturates and 1- and 2-ring aromatics are separately contacted with regenerated catalyst.    
   
   
       3 . The process of claims  1  or  2  wherein the catalyst is amorphous, crystalline or a mixture thereof.  
   
   
       4 . The process of  claim 3  wherein the amorphous catalyst is silica-alumina.  
   
   
       5 . The process of  claim 3  wherein the crystalline catalyst is a zeolite which is isostructural to zeolite Y.  
   
   
       6 . The process of  claim 3  wherein the catalyst includes an additive which is a medium pore zeolite having a Constraint Index of about 1 to 12.  
   
   
       7 . The process of claims  1  or  2  wherein short contact time conditions include riser outlet temperatures from 482 to 621° C., pressures from 0 to 100 psig (101 to 790 kPa) and residence times from 1 to 5 seconds.  
   
   
       8 . The process of claims  1  or  2  wherein the separation zone comprises solvent extraction, membrane separation or liquid chromatography.  
   
   
       9 . The process of  claim 8  wherein the separation zone comprises solvent extraction.  
   
   
       10 . The process of  claim 9  wherein solvent for solvent extraction comprises at least one of dimethyl sulfoxide, dimethyl formamide, n-methylpyrrolidone, phenol and furfural.  
   
   
       11 . The process of  claim 8  wherein liquid chromatography is simulated moving bed liquid chromatography.  
   
   
       12 . The process of  claim 8  wherein membrane separation contains supported polymeric membranes.  
   
   
       13 . The process of claims  1  or  2  wherein the stream containing saturates and 1- and 2-ring aromatics contains from 25 to 85 wt. % saturates and 1- and 2-ring aromatics.  
   
   
       14 . The process of claims  1  or  2  wherein the stream containing predominantly aromatics having 3 or more rings comprises greater than 75 wt. % of aromatics having 3 or more rings.