ROLE OF METAL CONTAMINANTS IN THE PRODUCTION OF CARBON-DIOXIDE DURING THE REGENERATION OF CRACKING CATALYSTS

An investigation of the factors which affect the ratio of combustion products in the flue gas from a catalytic cracking unit has been conducted. Units which process resids have been found to suffer feed throughput penalties as a result of high CO2/CO ratios. This study describes the effect of contaminant metals (nickel, vanadium and iron) on the combustion of carbon in the regenerator. Effects of these metals were investigated since they are deposited on the catalyst during the catalytic cracking process. Typical zeolite cracking catalysts were used in this study. The metal activity for the production of carbon dioxide increases from iron < vanadium << nickel. Results of this investigation show that nickel catalyzes carbon directly to carbon dioxide. Therefore, the amount of active nickel should be minimized to prevent high CO2/CO ratios in the regenerator. In addition, the active catalytic species can be effectively passivated by antimony when nickel and antimony are allowed to interact under reducing conditions.