Recycle of unconverted hydrocracked residual to hydrocracker after removal of unstable polynuclear hydrocarbons

A process for upgrading unconverted residuals by the removal of degraded unstable polynuclear hydrocarbons and recycling said uprgraded residual to the hydrocracker so as to increase liquid yields while at the same time decrease fouling of the hydrocracker and preheater upstream of said hydrocracker comprising feeding a heavy crude feedstock to a hydrocracking reactor;

• hydrocracking said heavy crude feedstock in said reactor under the following conditions:
• pressure about between 500 to 4000 psi, LHSV of about between 0.1 to 2 HR.sup.-1, hydrogen-crude ratio of about between 3,000 to 30,000 SCF/B and temperature of about between 770.degree. to 900.degree. F. wherein an effluent overhead is produced;
• feeding said effluent to a hot separator;
• treating said effluent in said hot separator wherein a light hydrocarbon stream and a slurry hydrocracked product residual are produced;
• feeding said slurry hydrocracked product residual to a separator;
• mixing a solvent selected from the group consisting of kerosenes, naphthas, butanes, pentanes, hexanes, heptanes, octanes and mixtures thereof with said hydrocracked residual in a ratio of from about 0.5/1 to 10/1 by volume in said separator so as to reduce the viscosity of said hydrocracked residual and thereby increase the incompatibility of the polynuclear hydrocarbons in said hydrocracked residual allowing for efficient separation of the polynuclear hydrocarbons;
• separating out the polynuclear hydrocarbons from said hydrocracked residual so as to produce an upgraded hydrocracked solvent rich residual substantially free of said polynuclear hydrocarbons;
• and recycling only said upgraded hydrocracked solvent rich residual substantially free of said polynuclear hydrocarbons to a preheater and thereafter to said hydrocracking reactor for further treatment.