Ancillary cracking of heavy oils in conjuction with FCC unit operations

Abstract

The production of light hydrocarbons consisting of ethylene, propylene, butylenes, and of gasoline is enhanced by introducing a heavy oil feedstream derived from an external source into an ancillary downflow reactor that utilizes the same catalyst composition as an adjacent FCC unit for cracking the heavy oil and withdrawing the desired lighter hydrocarbon reaction product stream from the downflow reactor and regenerating the catalyst in the same regeneration vessel that is used to regenerate the spent catalyst from the FCC unit. The efficiency of the recovery of the desired lighter olefinic hydrocarbons is maximized by limiting the feedstream to the downflow reactor to heavy oils that can be processed under relatively harsher conditions, while minimizing production of undesired by-products.

Description

FIELD OF THE INVENTION[0001]This invention relates to the processing of heavy hydrocarbons, such as gasoils, vacuum gasoils and residues for the purpose of increasing the production of lighter hydrocarbons, such as ethylene, propylene and the butylenes, and gasoline in conjunction with the operation of a fluidized catalytic cracking process.BACKGROUND OF THE INVENTION[0002]Propylene is second in importance only to ethylene as a petrochemical raw material building block. Propylene has traditionally been obtained as a by-product from steam cracking to produce ethylene and from refinery fluidized catalytic cracking processes to produce gasoline. The projected growth in demand for propylene has started to exceed that of ethylene so that existing processes cannot satisfy the foreseeable future growth in the demand for propylene.[0003]Fluidized catalytic cracking, or FCC, is a well-known and widely practiced process for converting heavy hydrocarbons, gasoils and residues into lighter hydr...

AI Technical Summary

Benefits of technology

[0016]The above objects and other advantages are achieved by the improved process and apparatus of the invention in which a downward flow fluidized catalyst reactor is added as an ancillary reactor to an existing FCC process unit operation. The ancillary downflow reactor system utilizes the same hot regenerated catalyst as is used in the FCC unit, thereby minimizing capital investment for new equipment and operating costs. The regenerated catalyst and a heavy hydrocarbon or gasoil feedstream that can be derived from a source that is the same as, or independent of the FCC unit are introduced and thoroughly mixed in an upper portion of the downflow reactor that is above the reaction zone.

[0020]The efficient operation of the auxiliary process of the invention is dependent upon the optimization of cracking conditions for a given feedstream that consists of one or more heavy hydrocarbon feeds. The relatively low residence times and higher catalyst-to-oil ratios of 20 to 40 percent by weight when compared to the FCC primary reaction zone are specific to the heavy hydrocarbon feedstream.

[0030]The improved ancillary process of the invention can be utilized with prior art FCC units, whether they employ riser cracking in an upward or downward flow reaction scheme, or bed cracking, to catalytically convert the feedstock into the desired lighter hydrocarbons, and particularly to provide an enhanced propylene yield for the overall unit operation.

Problems solved by technology

The projected growth in demand for propylene has started to exceed that of ethylene so that existing processes cannot satisfy the foreseeable future growth in the demand for propylene.

However, none of these disclosures provides a solution to the problem of enhancing the production of light olefins, and particularly of propylene in significant measure as an adjunct to existing FCC unit processes.

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