Cracking with spent catalyst
AssigneeMobil Oil Corporation
InventorsMohsen N. Harandi, Hartley Owen
Life of this patent
Estimating the term…
Abstract
A process and apparatus for low cracking or recracking of liquid hydrocarbons with FCC catalyst containing 0.2 to 1.5 wt % coke is disclosed. FCC naphtha, or a thermally or hydrocracked naphtha, contacts spent FCC catalyst in a naphtha recracking reactor for limited conversion to lighter products and an increase in octane number. Spent catalyst from the recracking reactor can be recycled to the FCC reactor without stripping or regeneration. Naphtha recracking products are preferably cooled, then used as an absorbent to recover gasoline boiling range products from the FCC main column overhead vapor. Use of spent catalyst and controlled conversion conditions minimizes overcracking of the light liquid and minimizes formation of heavy ends.
Claims14
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.
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.
Dependencies are inferred from the claim text.