Fluid cat cracking with high olefins prouduction

Abstract

The propylene production of a fluid catalytic cracking unit employing a large pore zeolite cracking catalyst, produces more propylene by adding a naphtha cracking riser and a medium pore zeolite catalytic component to the unit, and recycling at least a portion of the naphtha crackate to the naphtha riser. The large pore size zeolite preferably comprises a USY zeolite and the medium pore size is preferably ZSM-5. Propylene production per unit of naphtha feed to the naphtha riser is maximized, by using the 60-300° F. naphtha crackate as the feed.

What is claimed is:  
     
         1 . A fluid cat cracking process with increased C 3  olefins production which comprises the steps of: 
 (a) contacting an FCC feed with a particulate, hot, regenerated cracking catalyst comprising large and medium pore zeolite components in a first cracking reaction zone at reaction conditions effective to catalytically crack said feed and produce lower boiling hydrocarbons comprising naphtha, propylene-containing light olefins, and spent catalyst particles which contain strippable hydrocarbons and coke;    (b) separating said lower boiling hydrocarbons produced in step (a) from said spent catalyst particles in a separation zone and stripping said catalyst particles in a stripping zone, to remove said strippable hydrocarbons to produce stripped, coked catalyst particles, wherein said separation and stripping zones are in the same vessel;    (c) contacting at least a portion of said naphtha produced in said first reaction zone with said hot, regenerated, particulate cracking catalyst in a second and separate cracking reaction zone at reaction conditions effective to catalytically crack said naphtha and produce lower boiling hydrocarbons comprising more propylene-containing light olefins, and spent catalyst particles which contain strippable hydrocarbons and coke;    (d) separating said lower boiling hydrocarbons from said spent catalyst particles in said separation zone and stripping said particles in said stripping zone, to remove said strippable hydrocarbons to produce stripped, coked catalyst particles;    (e) passing said stripped, coked catalyst particles produced in steps (b) and (d) into a regeneration zone in which said particles are contacted with oxygen at conditions effective to burn off said coke and produce said hot, regenerated catalyst particles, and    (f) passing said hot, regenerated particles into said first and second cracking reaction zones, each of which is in a separate riser.    
     
     
         2 . A process according to  claim 1  wherein said catalyst also comprises at least one inorganic refractory metal oxide binder material.  
     
     
         3 . A process according to  claim 2  wherein said binder material has an acid cracking function.  
     
     
         4 . A process according to  claim 3  wherein said large pore zeolite component has an internal porous cell structure having cross-sectional dimensions ranging from 6 to more than 8 Å for a mesoporous zeolite and preferably from 6 to 8 Å.  
     
     
         5 . A process according to  claim 4  wherein said medium pore zeolite component has an internal porous cell structure having cross-sectional dimensions ranging from 4 to 6 Å.  
     
     
         6 . A process according to  claim 5  wherein said catalyst includes a phosphorous component.  
     
     
         7 . A process according to  claim 6  wherein more than 50 wt. % of said naphtha feed for said second cracking reaction zone boils within the range of from 60-300° F.  
     
     
         8 . A process according to  claim 5  wherein said medium pore zeolite component has an internal porous cell structure having cross-sectional dimensions ranging from 4 to 6 Å.  
     
     
         9 . A process according to  claim 7  wherein the respective pore sizes of said large and medium pore zeolites range from 6.5-7.6 Å and 6 4.4-5.4 Å.  
     
     
         10 . A process according to  claim 9  wherein said large pore zeolite comprises a USY zeolite and said medium pore zeolite comprises ZSM-5.  
     
     
         11 . A process according to  claim 10  wherein more than 75 wt. % of said naphtha feed boils within the range of from 60-300° F.  
     
     
         12 . A process according to  claim 7  wherein said contacting occurs in the presence of steam added to said second cracking reaction zone.  
     
     
         13 . A fluid cat cracking process with increased C 3  olefins production which comprises the steps of: 
 (a) contacting an FCC feed with a particulate, hot, regenerated cracking catalyst comprising USY and ZSM-5 zeolite catalytic components and a porous, amorphous, inorganic refractory metal oxide having an acid cracking function, in a first cracking reaction zone at reaction conditions effective to catalytically crack said feed and produce lower boiling hydrocarbons comprising naphtha, propylene-containing light olefins, and spent catalyst particles which contain strippable hydrocarbons and coke;    (b) separating said lower boiling hydrocarbons produced in step (a) from said spent catalyst particles in a separation zone and stripping said catalyst particles in a stripping zone, to remove said strippable hydrocarbons to produce stripped, coked catalyst particles, wherein said separation and stripping zones are in the same vessel;    (c) contacting at least a portion of said naphtha produced in said first reaction zone with said hot, regenerated, particulate cracking catalyst in a second cracking reaction zone at reaction conditions effective to catalytically crack said naphtha and produce lower boiling hydrocarbons comprising more propylene-containing light olefins, and spent catalyst particles which contain strippable hydrocarbons and coke;    (d) separating said lower boiling hydrocarbons from said spent catalyst particles in said separation zone and stripping said particles in said stripping zone, to remove said strippable hydrocarbons to produce stripped, coked catalyst particles;    (e) passing said stripped, coked catalyst particles produced in steps (b) and (d) into a regeneration zone in which said particles are contacted with oxygen at conditions effective to bum off said coke and produce said hot, regenerated catalyst particles, and    (f) passing said hot, regenerated particles into said first and second cracking reaction zones, each of which is in a separate riser.    
     
     
         14 . A process according to  claim 13  wherein said USY zeolite has an equilibrated unit cell size no greater than 24.30 Å.  
     
     
         15 . A process according to  claim 14  wherein said catalyst also comprises a phosphorous component.  
     
     
         16 . A process according to  claim 15  wherein said catalyst comprises an admixture of particles comprising said USY zeolite and particles containing said ZSM-5 zeolite.  
     
     
         17 . A process according to  claim 16  wherein the amounts of said ZSM-5 and USY zeolites respectively comprise from 1-20 wt. % and from 10-50 wt. % of said catalyst, based on the total weight of the catalyst.  
     
     
         18 . A process according to  claim 17  wherein said phosphorous component is contained in an aluminum-containing binder component of said particles containing said ZSM-5.  
     
     
         19 . A process according to  claim 18  wherein said USY zeolite has an equilibrated unit cell size no greater than 24.26 Å.  
     
     
         20 . A process according to  claim 18  wherein said phosphorous present in said binder component in an amount such that the binder P/A 1  mole ratio lies between 0.1 and 10.  
     
     
         21 . A process according to  claim 19  wherein said P/A 1  mole ratio is between 0.2 and 5.0.  
     
     
         22 . A process according to  claim 21  wherein more than 50 wt. % of said naphtha feed for said second cracking reaction zone boils within the range of from 60-300° F.  
     
     
         23 . A process according to  claim 13  wherein said contacting occurs in the presence of steam added to said second cracking reaction zone.  
     
     
         24 . A process according to  claim 22  wherein said contacting occurs in the presence of steam added to said second cracking reaction zone.  
     
     
         25 . A method for improving the propylene productivity of a fluid cat cracking unit which produces a crackate comprising propylene and naphtha, said naphtha crackate comprising a lower boiling fraction which boils in the range of from 60-300° F., from a fluid cat cracking feed, said unit comprising (i) a single regenerator vessel, (ii) a single combined separator-stripper vessel, (iii) at least one riser reaction zone for catalytically cracking said feed and (iv) a particulate cracking catalyst comprising a USY zeolite and an amorphous binder material, said method comprising: 
 (a) adding at least one separate riser to said unit;  
 (b) adding a particulate catalyst comprising ZSM-5 to said cracking catalyst in said unit to form a combined particulate catalyst;  
 (c) recovering at least a portion of said naphtha crackate comprising a fraction of which more than 50 wt. % boils in the range of from 60-300° F. and feeding it into said separate riser, in which it contacts said combined catalyst particles at reaction conditions effective to catalytically crack said naphtha and produce more propylene.  
 
     
     
         26 . A method according to  claim 25  wherein said ZSM-5 catalyst includes an aluminum and a phosphorus component, in which the P/A 1  mole ratio ranges between 0.1 and 10.