PROCESS FOR ENHANCED PROPYLENE YIELD FROM CRACKED HYDROCARBON FEEDSTOCKS AND REDUCED BENZENE IN RESULTING NAPHTHA FRACTIONS
First Claim
1. A catalytic cracking process comprising:
- (a) introducing a hydrocarbon feedstock into a reaction zone of a catalytic cracking unit which feedstock is characterized as having;
an initial boiling point from about 120°
C. with end points up to about 850°
C.;
(b) catalytically cracking said feedstock in said reaction zone employing a cracking catalyst, temperature, catalyst-to-oil ratio, pressure, steam dilution and space velocity such that an olefin yield from the unit is enhanced to produce a product comprising olefin, naphtha and benzene, wherein the product comprises about 6 to about 20% propylene based on the weight of the hydrocarbon feedstock introduced in step (a) above;
(c) fractionating the product into at least a light olefin-containing fraction, and a benzene-containing naphtha fraction;
(d) recovering the light olefin-containing fraction;
(e) contacting the benzene-containing naphtha fraction with a membrane having a sufficient flux and selectivity to separate a benzene-enriched permeate fraction and a benzene-deficient naphtha retentate fraction, said benzene-enriched permeate fraction being enriched in benzene compared to the retentate;
(f) recovering the benzene-deficient naphtha retentate fraction; and
(g) routing the benzene-enriched permeate fraction for further processing.
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Abstract
A process in which a catalytic cracking unit is operated to crack a hydrocarbon feedstock in a manner to enhance light olefin yields. The accompanying benzene-containing naphtha product stream is further processed through a benzene selective membrane to provide a low content benzene stream. Refiners frequently operate their cracking units to optimize light olefin yields, e.g. propylene, in response to needs in the petrochemical industry, and it has been discovered that units operated in this manner frequently produce naphtha containing increased amounts of benzene. The method of this invention therefore allows one to operate the unit when it is desired to optimize light olefin yields, yet at the same time produce a naphtha yield having a low benzene content. The invention is particularly useful when the cracking unit utilizes pentasil zeolites at increased concentrations to enhance light olefins yield.
54 Citations
32 Claims
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1. A catalytic cracking process comprising:
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(a) introducing a hydrocarbon feedstock into a reaction zone of a catalytic cracking unit which feedstock is characterized as having;
an initial boiling point from about 120°
C. with end points up to about 850°
C.;(b) catalytically cracking said feedstock in said reaction zone employing a cracking catalyst, temperature, catalyst-to-oil ratio, pressure, steam dilution and space velocity such that an olefin yield from the unit is enhanced to produce a product comprising olefin, naphtha and benzene, wherein the product comprises about 6 to about 20% propylene based on the weight of the hydrocarbon feedstock introduced in step (a) above; (c) fractionating the product into at least a light olefin-containing fraction, and a benzene-containing naphtha fraction; (d) recovering the light olefin-containing fraction; (e) contacting the benzene-containing naphtha fraction with a membrane having a sufficient flux and selectivity to separate a benzene-enriched permeate fraction and a benzene-deficient naphtha retentate fraction, said benzene-enriched permeate fraction being enriched in benzene compared to the retentate; (f) recovering the benzene-deficient naphtha retentate fraction; and (g) routing the benzene-enriched permeate fraction for further processing. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of producing light olefins and low benzene-containing naphtha in a catalytic cracking unit from a hydrocarbon feedstock, the method comprising:
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(a) selecting catalyst, temperature, catalyst-to-oil ratio, pressure, steam dilution and/or space velocity to enhance olefin yield in the catalytic cracking unit; (b) contacting the feedstock with cracking catalyst in the unit, thereby producing a product comprising olefin, naphtha and benzene; (c) fractionating the product into at least a light olefin-containing fraction, and a benzene-containing naphtha fraction; (d) recovering the light olefin-containing fraction; (e) contacting the benzene-containing naphtha fraction with a membrane having a sufficient flux and selectivity to separate a benzene-enriched permeate fraction and a benzene deficient naphtha retentate fraction, said benzene-enriched permeate fraction being enriched in benzene compared to the retentate; (f) recovering the benzene deficient naphtha retentate fraction; and (g) routing the benzene-enriched permeate fraction for further processing. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification