Selective hydrocracking process

Claim 1

A PROCESS FOR HYDROCRACKING A MINERAL OIL FEEDSTOCK CONTAINING BOTH POLYCYCLIC HYDROCARBONS AND HYDROCARBONS CONTAINING LESS THAN TWO CYCLIC STRUCTURES, WHICH COMPRISES: (A) SUBJECTING SAID FEEDSTOCK TO A HYDROCARBON SEPARATION STEP, AND RECOVERING THEREFROM A FRACTION RELATIVELY RICH IN POLYCYCLIC HYDROCARBONS AND A FRACTION RELATIVELY LEAN IN POLYCYCLIC HYDROCARBONS; (B) SUBJECTING SAID POLYCYCLIC-RICH FRACTION PLUS ADDED HYDROGEN TO CATALYTIC HYDROCRACKING IN CONTACT WITH A CATALYST CONSISTING ESSENTIALLY OF A COMPOSITE OF SILICA GEL COPRECIPITATED WITH AT LEAST ONE OTHER GEL FROM THE CLASS CONSISTING OF ALUMINA, ZIRCONIA, TITANIA AND MAGNESIA, AND UPON WHICH IS DEPOSITED A SMALL PROPORTION OF A GROUP VIII METAL HYDROGENATING COMPONENT; (C) SUBJECTING SAID POLYCYCLIC-LEAN FRACTION PLUS ADDED HYDROGEN TO CATALYTIC HYDROCRACKING IN CONTACT WITH A CATALYST CONSISTING ESSENTIALLY OF A CRYSTALLINE, ZEOLITIC ALUMINO-SILICATE MOLECULAR SIEVE CRACKING BASE HAVING A SIO2/AL2O3 MOLE-RATIO BETWEEN ABOUT 3 AND 10, RELATIVELY UNIFORM CRYSTAL PORE DIAMETERS BETWEEN ABOUT 6 AND 14A., AND WHEREIN THE ZEOLITIC CATIONS ARE PREDOMINANTLY HYDROGEN IONS AND/OR POLYVALENT METAL IONS, AND UPON WHICH IS DEPOSITED A SMALL PROPORTION OF A GROUP VIII METAL HYDROGENATING COMPONENT; AND (D) RECOVERING DESIRED LOW-BOILING HYDROCARBONS FROM EACH OF STEPS (B) AND (C).