Catalyst demetallization

Claim 1

IN A METHOD FOR REMOVING VANADIUM FROM A SYNTHETIC GEL, SILICA-BASED CRACKING CATALYST WHICH HAS BEEN POISONED BY CONTAMINATION WITH VANADIUM DUE TO USE OF SAID CATALYST IN A CRACKING SYSTEM, SAID CRACKING SYSTEM INCLUDING A CATALYTIC CRACKING ZONE IN WHICH CATALYST CONTACTS A ELEVATED TEMPERATURE A HEAVIER HYDROCARBON FEEDSTOCK CONTAINNIG VANADIUM, IN WHICH GASOLINE IS PRODUCED AND IN WHICH VANADIUM DEPOSITS ON THE CATALYST, SAID CRACKING SYSTEM INCLUDING ALSO A CATALYST REGENERATION ZONE BETWEEN WHICH ZONE AND THE CRACKING ZONE THE CATALYST IS CYCLED, AND IN WHICH REGENERATION ZONE CARBON IS OXIDZED AT AN ELEVATED TEMPERATURE AND THEREBY REMOVED FROM THE CATALYST, SAID METHOD FOR REMOVING VANASIUM COMPRISING BLEEDING A PORTION OF THE VANADIUM-CONTAMINATED CATALYST FROM THE CRACKING SYSTEM, CONTACTING BLED, SUBSTANTIALLY CARBON-FREE CATALYST AT AN ELEVATED TEMPERATURE FOR AT LEAST ABOUT 15 MINUTES WITH A GAS CONSISTING ESSENTIALLY OF MOLECULAR OXYGEN IN AN AMOUNT SUFFICIENT TO ENHANCE LATER VANADIUM REMOVAL, DISCONTINUING CONTACT WITH SAID GAS CONTAINING MOLECULAR OXYGEN, SUBSEQUENTLY REMOVING VANADIUM FROM THE OXYGEN-TREATED CATALYST WITHOUT UNDUE DELERTIOUS CHANGE IN THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE CATALYST AND RETURNING RESULTING DEVANADIZED CATALYST TO A HYDROCARBON CRACKING SYSTEM, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID CONTACT OF CARBON-FREE CATALYST WITH OXYGEN-CONTAINING GAS IN THE PRESENCE OF AN ADDED AMOUNT OF AN OXIDE OF NITROGEN AND AT A TEMPERATURE OF ABOUT 600 TO 1300*F., SAID OXIDE OF NITROGEN BEING PRESENT IN AN AMOUNT SUFFICIENT TO ENHANCE VANADIUM REMOVAL FROM THE CATALYST.