Process for refractory compound rejection from a hydrocracker recycle liquid

Claim 1

A catalytic hydrocracking process which comprises: (a) contacting a hydrocarbonaceous feedstock having a propensity to form heavy polynuclear aromatic compounds and a liquid recycle stream in a hydrocracking zone with added hydrogen and a metal promoted hydrocracking catalyst at elevated temperature and pressure sufficient to convert a substantial portion of the hydrocabonaceous components in said feedstock to lower boiling products; (b) recovering a hydrocarbon effluent from said hydrocracking zone and partially condensing the hydrocarbon effluent from said hydrocracking zone and separating the same into a lower boiling hydrocarbon product stream and an unconverted hydrocarbon stream having at least a portion boiling above about 400° F. and comprising trace quantities of heavy polynuclear aromataic compounds; (c) introducing at least a portion of said unconverted hydrocarbon stream having at least a portion boiling above about 400° F. and comprising trace quantities of heavy polynuclear aromatic compounds into a hydrogen stripping flash zone with a first hydrogen-rich gaseous stream having a temperature greater than said hydrocarbon stream at flash conditions thereby increasing the temperature of said hydrocarbon stream and vaporizing at least a portion thereof to produce a vapor stream comprising hydrogen and hydrocarbon compounds and produce a liquid hydrocarbon stream comprising heavy polynuclear aromatic compounds; (d) contacting said vapor stream comprising hydrogen and hydrocarbon compounds with a hydrogenation catalyst in a hydrogenation reaction zone at hydrogenation conditions to increase the hydrogen content of the hydrocarbon compounds contained in said vapor stream; (e) condensing at least a portion of the resulting effluent from said hydrogenation reaction zone to produce a second hydrogen-rich gaseous stream and a liquid stream comprising hydrogenated hydrocarbon compounds; (f) recycling at least a portion of said liquid stream comprising hydrogenated hydrocarbon compounds recovered in step (e) to said hydrocracking zone in step (a) as at least a portion of said liquid recycle stream; and (g) recycling at least a portion of said second hydrogen-rich gaseous stream to said first hydrogen-rich gaseous stream in step (c).