Ancillary cracking of heavy oils in conjuction with FCC unit operations

Abstract

The production of light hydrocarbons consisting of ethylene, propylene, butylenes, and of gasoline is enhanced by introducing a heavy oil feedstream derived from an external source into an ancillary downflow reactor that utilizes the same catalyst composition as an adjacent FCC unit for cracking the heavy oil and withdrawing the desired lighter hydrocarbon reaction product stream from the downflow reactor and regenerating the catalyst in the same regeneration vessel that is used to regenerate the spent catalyst from the FCC unit. The efficiency of the recovery of the desired lighter olefinic hydrocarbons is maximized by limiting the feedstream to the downflow reactor to heavy oils that can be processed under relatively harsher conditions, while minimizing production of undesired by-products.

1 . A method of enhancing the conversion of a heavy oil feedstream derived from a crude distillation unit into a lighter hydrocarbon product stream consisting of ethylene, propylene, butylenes and gasoline, the method comprising:
 a. directing a separate feedstream of heavy oil into the top of an ancillary downflow reactor that contains fresh or regenerated catalyst of the same composition as the catalyst used in an FCC unit with which the downflow reactor is associated;   b. operating the downflow reactor with a residence time of the feedstream in the reaction zone of from 0.1 seconds to 5 seconds at an operating temperature in the range of 990° F. to 1300° F. and with a catalyst-to-feedstream ratio in the range from 10 percent to 50 percent by weight to produce a lighter hydrocarbon reaction product by cracking the heavy oil feedstream;   c. separating the lighter hydrocarbon reaction product stream produced in the downflow reactor cracking process from spent catalyst downstream of the reaction zone; and   d. recovering the lighter hydrocarbon reaction product stream.   
   
   
       2 . The method of  claim 1  which includes combining and commingling the spent catalyst from the downflow reactor with spent catalyst from the FCC unit and regenerating the combined spent catalysts for reuse in the FCC unit and the downflow reactor. 
   
   
       3 . The method of  claim 1 , wherein the downflow reactor is operated with a feedstream residence time in the range of from 0.2 seconds to 2 seconds. 
   
   
       4 . The method of  claim 1 , wherein the catalyst-to-feedstream ratio is in the range of from 20 percent to 40 percent by weight. 
   
   
       5 . The method of  claim 1 , wherein the recovered lighter hydrocarbon reaction product stream from the downflow reactor is subjected to fractionation. 
   
   
       6 . The method of  claim 1 , wherein the recovered lighter hydrocarbon reaction product stream from the downflow reactor is combined with an effluent stream from the FCC unit for fractionation. 
   
   
       7 . The method of  claim 2  which is operated continuously. 
   
   
       8 . The method of  claim 1  in which the hydrocarbon reaction product stream is separated from the spent catalyst by a cyclone separator process. 
   
   
       9 . The method of  claim 1  which includes applying a quenching fluid to the reaction product and catalyst below the reaction zone. 
   
   
       10 . The method of  claim 1  which includes stripping the spent catalyst downstream of the reaction zone. 
   
   
       11 . A method of producing a product stream consisting primarily of the light olefins ethylene, propylene and butylenes, and gasoline in conjunction with the processing of a petroleum feedstock in a fluidized catalytic cracking (FCC) unit containing a catalyst of specified composition, the catalyst used in the FCC unit being regenerated from spent catalyst, the method comprising:
 a. introducing a separate heavy oil feedstream into an upper portion of a downflow reactor that is proximate the FCC unit;   b. introducing regenerated catalyst of the same type used in the FCC unit into the downflow reactor for mixing with the heavy oil feedstream in a ratio of catalyst-to-heavy oil feedstream of from 10 percent to 50 percent by weight;   c. passing the catalyst and heavy oil mixture through a reaction zone in the downflow reactor that is maintained at a temperature in the range of from 990° F. to 1300° F. for a residence time of from 0.1 seconds to 5 seconds;   d. separating the resulting reaction product stream of light olefins and gasoline from spent catalyst;   e. recovering the reaction product stream; and   f. passing the spent catalyst from the downflow reactor to a separate regeneration vessel that also contains spent catalyst from the FCC unit for regeneration.   
   
   
       12 . The method of  claim 11 , wherein the downflow reactor is operated with a feedstream residence time in the range of from 0.2 seconds to 2 seconds. 
   
   
       13 . The method of  claim 11 , wherein the catalyst-to-feedstream ratio is in the range of from 20 percent to 40 percent by weight. 
   
   
       14 . The method of  claim 11 , wherein the recovered reaction product stream from the downflow reactor is combined with an effluent stream from the FCC unit for fractionation. 
   
   
       15 . The method of  claim 11 , wherein the recovered reaction product stream from the downflow reactor is subjected to fractionation.