Removal of nickel and vanadium from silica based cracking catalysts

Claim 1

IN A METHOD FOR TREATING A SYNTHETIC GEL, SILICA-BASED CATALYST WHICH HAS BEEN POISONED BY CONTAMINATION WITH VANADIUM DUE TO USE OF SAID CATALYST IN CRACKING AT ELEVATED TEMPERATURE A HYDROCARBON FEEDSTOCK CONTAINING VANADIUM, SAID CRACKING INCLUDING A CATALYTIC CRACKING ZONE AND A CATALYST REGENERATION ZONE BETWEEN WHICH THE CATALYST IS CYCLED AND IN WHICH CRACKING ZONE THE CATALYST BECOMES CONTAMINATED WITH VANADIUM OF SAID HYDROCARBON FEEDSTOCK AND IN WHICH REGENERATION ZONE CARBON IS OXIDIZED AT AN ELEVATED TEMPERATURE AND THEREBY REMOVED FROM THE CATALYST, THE STEPS COMPRISING BLEEDING A PORTION OF THE VANADIUM-CONTAMINATED CATALYST FROM THE CRACKING SYSTEM, CONTACTING BLED CATALYST WITH AN AQUEOUS SOLUTION HAVING A BASIC PH AND CONTAINING AMMONIUM IONS SUFFICIENT TO REMOVE VANADIUM FROM THE CATALYST, AND RETURNING RESULTING DEVANADIZED CATALYST TO THE CRACKING SYSTEM, SAID AMMONIUM IONS BEING PROVIDED IN THE AQUEOUS SOLUTION BY A MEMBER SELECTED FROM THE GROUP CONSISTING OF AMMONIUM HYDROXIDE, AMMONIUM CARBONATE AND METHYLAMINE.