Process for reducing coke formation in heavy feed catalytic cracking

Claim 1

A method for reducing the rate of coke and hydrogen production from a hydrocarbon feedstock cracked to lower molecular weight products in a reaction zone containing cracking catalyst of a catalytic cracking system comprising a reaction zone and a reduction zone where the feedstock contains at least one metal contaminant selected from the class consisting of nickel, vanadium, and iron, and where at least some of said metal contaminant becomes deposited on the catalyst such that at least 50 wt. % of the total of said metal contaminant deposited on the catalyst comprises only one of said metal contaminants, and where said metal contaminant contributes to excessive hydrogen and coke production, said method comprising: A. monitoring the composition of said metal contaminant deposited on the catalyst; B. adding an effective passivating amount of at least one of said metal contaminants not present as the major contaminant on the catalyst; C. passing the coke and metal contaminated catalyst from the reaction zone to a regeneration zone maintained at regeneration conditions having a regeneration gas passing therethrough whereby at least a portion of the coke is removed from the catalyst and thereafter the catalyst is passed through a reduction zone maintained at an elevated temperature for a time sufficient to at least partially passivate said metal contaminants on the catalyst while a reducing environment is maintained in said reduction zone by the addition to the reduction zone of material selected from the class consisting of hydrogen, carbon monoxide and mixtures thereof; and, D. adding a hydrogen donor material into the reaction zone whereby at least a portion of the hydrogen donor material transfers hydrogen to the hydrocarbon feedstock and/or to the cracked lower molecular weight products to decrease the rate of coke formation on the cracking catalyst.

Claim 2

A method for reducing the rate of coke and hydrogen production from a hydrocarbon feedstock cracked to lower molecular weight products in a reaction zone containing cracking catalyst of a catalytic cracking system comprising a reaction zone and a reduction zone where the feedstock contains at least one metal contaminant selected from the class consisting of nickel, vanadium, and iron, and where at least some of said metal contaminant becomes deposited on the catalyst such that at least 50 wt. % of the total of said metal contaminant deposited on the catalyst comprises only one of said metal contaminants, and where said metal contaminant contributes to excessive hydrogen and coke production, said method comprising: A. monitoring the composition of said metal contaminant deposited on the catalyst; B. adding an effective passivating amount of at least one of said metal contaminants not present as the major contaminant on the catalyst; C. passing the coke and metal contaminated catalyst from the reaction zone to a regeneration zone maintained at regeneration conditions having a regeneration gas passing therethrough whereby at least a portion of the coke is removed from the catalyst and thereafter the catalyst is passed through a reduction zone maintained at an elevated temperature for a time sufficient to at least partially passivate said metal contaminants on the catalyst while a reducing environment is maintained in said reduction zone by the addition to the reduction zone of material selected from the class consisting of hydrogen, carbon monoxide and mixtures thereof; and, D. adding a hydrogen donor material into the reaction zone whereby at least a portion of the hydrogen donor material transfers hydrogen to the hydrocarbon feedstock and/or to the cracked lower molecular weight products to decrease the rate of coke formation on the cracking catalyst.