Regulating a hydrocracking process, with a crystalline zeolite catalyst, containing a platinum group metal, to obtain a constant octane gasoline

Claim 1

IN THE HYDROCRACKING OF HYDROCARBON FRACTION S BOILING ABOVE 300*F. BY CONTACT AT A HYDROCRACKING TEMPERATURE OF 500 TO 800*F. WITH A HYDROCRACKING CATALYST COMPRISING A CRYSTALLINE ALUMIN-SILICATE ZEOLITE HAVING UNIFORM PORE OPENINGS OF 6 TO 15 ANGSTROMS AND CONTAINING A CATALYTIC AMOUNT OF A PLATINUM GROUP METAL AND LESS THAN 10 WT. PERCENT NA2O, SAID CATALYST HAVING AN INITIAL HYDROCRACKING ACTIVITY WHICH IN THE ABSENCE OF A CATALYST POISON PRODUCES EXCESSIVE CRACKING TO UNDESIRED PRODUCTS AT THE DESIRED HYDROCRACKING TEMPERATURE WITHIN SAID TEMPERATURE RANGE, THE IMPROVED MEANS FOR OBTIAINING HIGH QUALITY PRODUCT OF RELATIVELY CONSTANT OCTANE NUMBER AT A RELATIVELY CONSTANT CONVERSION LEVEL, HYDROCARBON FEED RATE AND HYDROCRACKING TEMPERATURE WHICH COMPRISES (1) INITIALLY CONDUCTING THE HYDROCRACKING REACTION AT SAID DESIRED TEMPERATURE IN THE RESENCE OF A RELATIVELY HIGH CONCENTRATION OF CATALYST POISON SUFFICIENT TO TEMPORARILY SUPPRESS SAID INITIAL ACTIVITY TO THEREBY PREVENT SAID EXCESSIVE CRACKING TO UNDESIRED PRODUCTS, AND (2) THEREAFTER REDUCING THE CONCENTRATION OF SAID CATALYST POISON IN PROPORTION TO THE LOSS OF CATALYST ACTIVITY AS THE CATALYST AGES DURING SAID HYDROCRACKING REACTION WHILE (3) MAINTAINING THE HYDROCARBON FEED RATE, CONVERSION LEVEL, REACTION TEMPERATURE, AND PRODUCT OCTANE NUMBER SUBSTANTIALLY CONSTANT.