Abstract: An improved hydrocarbon catalytic cracking process which comprises determining the concentrations of carbon dioxide and carbon monoxide in the gaseous effluent from the catalyst regeneration zone and adjusting the rate of addition of a selective treating agent to the hydrocarbon feed to the cracking zone so as to maintain a volume ratio of carbon dioxide to carbon monoxide of at least 2.2 in said effluent.

Abstract: A process is described for fixed bed hydrodesulfurizing a non-asphaltic oil feed blend for a zeolitic FCC riser cracking system in which cracking occurs at a space velocity sufficiently high to prevent formation of a catalyst bed. It is shown that sulfur dioxide emissions from the zeolite catalyst regenerator associated with the riser are reduced to a lower extent than total sulfur removal from the feed oil. This indicates uneven sulfur removal in the hydrodesulfurization step whereby a smaller portion of sulfur is removed from the heavy portion of the feed from which the coke is derived than from the lighter portion of the feed. The present invention demonstrates a synergistic effect upon sulfur removal from the heavy portion of the feed by widening the boiling range of the feed and this synergistic effect is converted to practical advantage by reducing the amount of hydrodesulfurization catalyst in proportion to said synergistic effect, thereby keeping hydrocracking to a specified low level.

Abstract: A method of negating the effects of metals poisoning on a cracking catalyst which comprises contacting the catalyst containing metal contaminants with a bismuth or manganese compound.