Claims
- 1. A process for cracking a normally liquid, light hydrocarbon feed boiling below the gas oil range and a heavy liquid hydrocarbon feed comprising hydrocarbons boiling above 650.degree. F. comprising:
- a. catalytically cracking said heavy feed in a catalytic riser cracking zone operating at catalytic cracking conditions including a severity sufficient to convert at least 50 wt % of the feed into lighter products by contacting said feed in the base of a riser reactor with a supply of hot regenerated cracking catalyst to produce a riser cracking zone effluent mixture having an effluent temperature and comprising cracked products and cracking catalyst containing less than 1.5 wt % coke and strippable hydrocarbons;
- b. separating in a reactor vessel said cracking zone effluent mixture into a cracked product vapor phase having an elevated temperature and a spent catalyst phase comprising catalyst containing less than 1.5 wt % coke;
- c. stripping in a stripping means at least a portion of said spent catalyst to produce stripped catalyst;
- d. regenerating, in a catalyst regeneration means operating at catalyst regeneration conditions, said stripped catalyst to produce a supply of hot, regenerated catalyst;
- e. recycling at least a portion of said regenerated catalyst to the base of said riser reactor to contact said heavy feed;
- f. removing said cracked product vapor phase from said reactor vessel via a transfer line and charging same to a main fractionator;
- g. fractionating the cracked product vapor into a spectrum of products including normally liquid hydrocarbons boiling below 650.degree. F.;
- h. removing from said reactor vessel at least a portion of the spent catalyst containing less than 1.5 wt % coke and charging same to a recracking reactor vessel;
- i. charging said light, normally liquid hydrocarbon feed to said recracking reactor and catalytically cracking said light feed at low severity recracking conversion conditions selected to convert less than 30 wt % of the light feed to lighter components and to convert less than 10 wt % of the light feed to heavier products;
- j. recovering from said recracking reactor catalytically cracked products including gasoline boiling range hydrocarbons; and spent recracking catalyst; and
- k. recycling from said recracking reactor to said FCC riser reactor, FCC catalyst stripper, or FCC catalyst regenerator, said spent recracking catalyst.
- 2. The process of claim 1 wherein:
- said light feed to said recracking reactor is a naphtha or heavy naphtha boiling range feed having an octane number; and
- low severity recracking conditions are sufficient to increase the octane number of said naphtha at least 2.0 and to convert from 10 to 30 wt % of said cracked naphtha or heavy naphtha fraction to lighter products and less than 7.5 wt % to heavier products.
- 3. The process of claim 1 wherein said light feed to said recracking reactor is a thermally or catalytically cracked naphtha or heavy naphtha fraction.
- 4. The process of claim 1 wherein said recracking reactor is a turbulent or fast fluidized bed reactor.
- 5. The process of claim 1 wherein said recracking reactor operates at naphtha recracking conditions including a temperature of 800.degree. to 1100.degree. F., a cat:naphtha feed weight ratio of 1:1 to 20:1, and a vapor residence time of 1-100 seconds.
- 6. The process of claim 1 wherein said recracking reactor is a riser reactor and operates at naphtha recracking conditions including a riser top temperature of 850.degree. to 1050.degree. F., a cat:naphtha feed weight ratio of 5:1 to 10:1, and a vapor residence time of 2-5 seconds.
- 7. The process of claim 1 wherein the recracking catalyst comprises a mixture of 50 to 95 wt % spent FCC catalyst and 5 to 45 wt % regenerated FCC catalyst.
- 8. The process of claim 1 wherein said light feed to said recracking reactor is a hydrocracked naphtha or heavy naphtha fraction.
- 9. The process of claim 1 wherein said light feed to said recracking reactor is a furfural raffinate.
- 10. The process of claim 1 wherein spent catalyst from said recracking reactor is returned to said FCC unit without stripping.
- 11. A method of increasing gasoline yields during riser catalytic cracking comprising:
- adding to the base of a riser cracking reactor preheated, heavy hydrocarbon feed comprising 650.degree. F.+ hydrocarbons and a supply of hot regenerated cracking catalyst having a zeolite content of at least 20 wt % large pore zeolite, to form a mixture of feed and catalyst;
- cracking said feed at riser cracking condition to produce a mixture of cracked products comprising heavy naphtha boiling in the range of 300.degree. to 425.degree. F. and having an octane number and spent catalyst;
- separating said mixture in a reactor vessel downstream of said riser to produce a cracked product vapor phase and a spent catalyst phase containing less than 1.5 wt % coke;
- stripping said spent catalyst to produce stripped catalyst;
- regenerating at least a portion of said stripped catalyst to produce a supply of hot regenerated catalyst containing less than 0.2 wt % coke and recycling at least a portion of said hot regenerated catalyst to said riser cracking reactor;
- fractionating in an FCC main column said cracked products to produce cracked products including an FCC heavy naphtha product having an octane number and including hydrocarbons boiling in the range of 300.degree. to 425.degree. F.;
- charging at least a portion of said FCC heavy naphtha to a recracking reactor vessel;
- charging a stream of spent catalyst containing from 0.2 to 1.5 wt % coke from said FCC reactor vessel to said recracking reactor;
- catalytically recracking said FCC heavy naphtha at naphtha recracking conditions including a temperature of 800.degree. to 1100.degree. F., a catalyst:FCC heavy naphtha weight ratio of 1:1 to 20:1, and a vapor residence time of 1-100 seconds and sufficient to increase the octane number of said heavy naphtha fraction at least 2.0 and convert from 10 to 30 wt % of said FCC heavy naphtha to lighter products and produce spent recracking catalyst;
- separating in a catalyst/vapor separation means said catalytically recracked naphtha products from spent recracking catalyst;
- recovering catalytically recracked naphtha products; and
- recycling to said FCC unit said spent recracking catalyst.
- 12. The process of claim 11 wherein the naphtha recracking catalyst is 50 to 95% spent FCC catalyst and 5 to 50% regenerated FCC catalyst.
- 13. The process of claim 11 wherein said FCC main column produces an overhead vapor fraction comprising gasoline boiling range hydrocarbons which is charged to the base of a recontacting vessel and said catalytically recracked vapor product is cooled and at least partially condensed to produce a recracked gasoline liquid phase, and at least a portion of the recracked gasoline liquid phase is charged to an upper portion of said recontacting vessel to adsorb and recover from said FCC main column overhead vapor fraction gasoline boiling range hydrocarbons and produce a recontacting drum liquid stream of recracked gasoline and recovered gasoline and a vapor stream.
- 14. The process of claim 11 wherein a liquid FCC heavy naphtha product from the FCC main column is heat exchanged with catalytically recracked vapor from said recracking reactor to produce a heat exchanged FCC heavy naphtha product which is charged to said recracking reactor.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of our prior copending application No. 749,483 filed Aug. 15, 1991 and now U.S. Pat. No. 5,154,818 granted Oct. 13, 1992, which is a continuation of Ser. No. 527,985, filed May 24, 1990 and now abandoned.
US Referenced Citations (13)
Continuations (1)
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527985 |
May 1990 |
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Continuation in Parts (1)
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749483 |
Aug 1991 |
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