Ancillary cracking of paraffinic naphtha in conjunction with fcc unit operations

Abstract

The production of light hydrocarbons consisting of ethylene, propylene, butylenes, and of gasoline is enhanced by introducing a virgin paraffinic naphtha 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 naphtha 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 paraffinic naphtha that can be processed under relatively harsher conditions, while minimizing production of undesired by-products and reducing the formation of coke on the catalyst.

1 . A method of enhancing the conversion of a feedstream consisting essentially of paraffinic naphtha boiling up to 450° F./233° C. derived from a crude distillation unit into a lighter hydrocarbon product stream consisting of ethylene, propylene, butylenes and gasoline, the feedstream having a low concentration of olefins, the method comprising:
 a. directing a separate feedstream of the paraffinic naphtha into the top of an ancillary downflow reactor that contains fresh or regenerated hot catalyst of the same composition as the catalyst used in a fluidized catalytic cracking (FCC) unit with which the downflow reactor is associated, the regenerated catalyst being at a temperature that is sufficient to provide the heat required to promote the endothermic cracking of the paraffinic naphtha; 
 b. introducing a heavy oil or gas oil as the feedstream to the associated FCC 
 c. introducing the paraffinic naphtha through a plurality of injection nozzles into a mixing zone and into contact with a controlled flow of the hot catalyst to provide a uniform mixture; 
 d. 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 900° F. to 1200° F. and with a catalyst-to-feedstream ratio in the range from 25 to 50 by weight to produce a lighter hydrocarbon reaction product stream by cracking the paraffinic naphtha feedstream; 
 e. separating the lighter hydrocarbon reaction product stream produced in the downflow reactor cracking process from spent catalyst in a rapid separation section that is downstream of the reaction zone; and 
 f. recovering the lighter hydrocarbon reaction product stream, wherein the lighter hydrocarbon reaction product stream contains a greater combined proportion of ethylene, propylene and butylenes as compared to a product stream from the associated FCC unit. 
 
     
     
         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 25 to 40 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 heavy oil or gas as the feedstream to the FCC unit;   b. introducing a separate paraffinic naphtha feedstream into an upper portion of a downflow reactor that is proximate the FCC unit;   c. introducing a controlled flow of hot regenerated catalyst that is the same catalyst used in the FCC unit into a mixing zone of the downflow reactor along with the paraffinic naphtha feedstream which is injected into the mixing zone through a plurality of nozzles for uniform mixing with the catalyst in a ratio of catalyst-to-paraffinic naphtha feedstream of from 25 to 50 by weight, the temperature of the catalyst being sufficient to provide the heat required to promote the catalytic cracking of the paraffinic naphtha feedstream;   d. passing the catalyst and paraffinic naphtha mixture through a reaction zone in the downflow reactor that is maintained at a temperature in the range of from 900° F. to 1200° F. for a residence time of from 0.1 seconds to 5 seconds;   e. separating the resulting reaction product stream of light olefins and gasoline from spent catalyst in a rapid separation section of the reactor that is downstream of the reaction zone;   f. recovering the reaction product stream of the light olefins ethylene, propylene and butylenes, and gasoline, wherein the reaction product stream contains a greater combined proportion of ethylene, propylene and butylenes as compared to a product stream from the proximate FCC unit; and   g. 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 25 to 40 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 1  wherein the recovered reaction product stream from the downflow reactor is subjected to fractionation. 
     
     
         16 . The method of  claim 1 , wherein the flow rate of hot catalyst into the mixing zone of the downflow reactor is adjusted to control the temperature in the reaction zone. 
     
     
         17 . The method of  claim 11 , wherein the flow rate of hot catalyst into the mixing zone of the downflow reactor is adjusted to control the temperature in the reaction zone. 
     
     
         18 . The method of  claim 1  which includes stabilizing the temperature of the hot catalyst prior to its controlled introduction into the reaction mixing zone. 
     
     
         19 . The method of  claim 11  which includes stabilizing the temperature of the hot catalyst prior to its controlled introduction into the reaction mixing zone. 
     
     
         20 . The method of  claim 1 , wherein the spent catalyst is recovered from the separation section and is separately returned to a regenerator where it is mixed with the catalyst from the FCC unit. 
     
     
         21 . (canceled) 
     
     
         22 . (canceled)