Fcc process with an integrated secondary reactor for increased light olefin yields

Abstract

A process for increasing the yields of propylene is presented. The process is an FCC process for producing light olefins, and utilizes a smaller secondary reactor that uses the same catalyst, or a different catalyst as in the FCC reactor. The FCC effluent is separated, and C4 and C5 olefins are recovered. The C4 and C5 olefins are passed to the secondary reactor for cracking to generate increased light olefin yields.

What is claimed is: 
     
         1 . A process for improving light olefin yields, comprising:
 passing a hydrocarbon stream to an FCC reactor to generate an FCC effluent stream comprising light olefins;   passing the FCC effluent stream to a product recovery unit to generate a first stream comprising light components, a second stream comprising C4 and C5 hydrocarbons, and a third stream comprising C6+ compounds;   passing the second stream to an extractive distillation unit to generate a fourth stream comprising C4 and C5 olefins, and a fifth stream comprising paraffins;   passing the fourth stream to a secondary reactor to generate a sixth stream comprising light olefins; and   passing the sixth stream to the light olefins separation unit.   
     
     
         2 . The process of  claim 1  wherein the secondary reactor is a bubbling bed reactor, a slow fluidized bed reactor or a fast fluidized bed reactor with, or without, partial regeneration. 
     
     
         3 . The process of  claim 1  further comprising passing a catalyst to the secondary reactor, thereby generating a catalyst effluent stream. 
     
     
         4 . The process of  claim 3  further comprising passing the catalyst effluent stream to the FCC reactor. 
     
     
         5 . The process of  claim 4  wherein the FCC reactor comprises a riser section, a catalyst separation section and a stripper section, and wherein the catalyst effluent stream is passed to the stripper section. 
     
     
         6 . The process of  claim 1  wherein the catalyst comprises a cracking catalyst selected from the group consisting of Y-zeolite, ZSM-5, ST-5, ZSM-11, ZSM-22, beta, erionite, ZSM-34, SAPO-11, non-zeolitic amorphous silica-alumina, faujasite, chabazite, modernite, and mixtures thereof. 
     
     
         7 . The process of  claim 6  wherein the catalyst comprises ZSM-5. 
     
     
         8 . The process of  claim 1  further comprising:
 passing a regenerated catalyst stream to the FCC reactor, to generate an intermediate stream of catalyst and reactants; 
 passing the intermediate stream to a reactor separation stage to generate the FCC effluent stream and an intermediate catalyst stream; 
 passing the intermediate catalyst stream to a stripping section to generate a stripped catalyst stream; and 
 passing the stripped catalyst stream to a regenerator to generate the regenerated catalyst stream. 
 
     
     
         9 . The process of  claim 1  wherein the hydrocarbon stream is a VGO stream. 
     
     
         10 . The process of  claim 1  wherein the extractive distillation unit comprises a selective olefin absorption process utilizing a solvent to generate the fourth stream comprising olefins and the fifth stream comprising paraffins. 
     
     
         11 . The process of  claim 10  wherein the solvent is selected from the group consisting of NMP (n-methyl-2-pyrrolidone), DMF (dimethylformamide), THF (tetrahydrofuran), ACN (acetonitrile), and mixtures thereof. 
     
     
         12 . A process for improving light olefin yields, comprising:
 passing a hydrocarbon stream to a cracking reactor, wherein the reactor includes a cracking catalyst, to generate a cracking effluent stream comprising light olefins;   passing the cracking effluent stream to a separation unit to generate a first stream comprising C3 and lighter compounds, a second stream comprising C4 and C5 hydrocarbons, and a third stream comprising C6+ compounds;   passing the second stream to an extractive distillation unit to generate a fourth stream comprising C4 and C5 olefins, and a fifth stream comprising paraffins; and   passing the fourth stream to a secondary reactor, wherein the secondary reactor includes a cracking catalyst, to generate a sixth stream comprising light olefins.   
     
     
         13 . The process of  claim 12  wherein the cracking reactor is a fluidized catalytic cracking reactor comprising a riser reactor. 
     
     
         14 . The process of  claim 12  further comprising:
 passing a regenerated catalyst stream to the cracking reactor. 
 
     
     
         15 . The process of  claim 12  further comprising passing the sixth stream to the light olefins separation unit. 
     
     
         16 . The process of  claim 12  further comprising passing a cracking catalyst to the secondary reactor to generate a secondary catalyst effluent stream. 
     
     
         17 . The process of  claim 16  further comprising passing the catalyst effluent stream to the cracking reactor, thereby generating a cracking reactor catalyst effluent stream. 
     
     
         18 . The process of  claim 12  further comprising:
 passing a regenerated catalyst stream to the cracking reactor thereby generating a spent catalyst effluent stream; and 
 passing the spent catalyst effluent stream to a regenerator thereby generating the regenerated catalyst stream. 
 
     
     
         19 . The process of  claim 18  further comprising:
 passing a fresh catalyst stream to the secondary reactor thereby generating a spent secondary catalyst stream; and 
 passing the spent secondary catalyst stream to the cracking reactor. 
 
     
     
         20 . The process of  claim 12  wherein the secondary reactor can comprise a bubbling bed reactor, a slow fluidized bed reactor, or a fast fluidized bed reactor, and wherein the secondary reactor utilizes the same catalyst as in the FCC reactor.