Two stage catalytic cracking process

Abstract

A two-stage cascade flow fluid catalytic cracking process capable of converting high molecular weight hydrocarbons containing catalyst poisons into products of lower molecular weight with high activity cracking catalyst susceptible to catalyst poisons, the cascade flow process resulting in higher yields of desired motor fuel fractions than those obtainable with conventional riser flow fluid catalytic cracking processes. Catalyst poisons, e.g. nitrogen compounds, sulfur compounds, heavy metal compounds and high Conradson Carbon Residues, are removed from the heavy hydrocarbon charge stocks by first contacting the charge stock containing catalyst poisons with a low activity catalyst comprising used catalyst from the process under fluid catalytic cracking reaction conditions effective for the conversion of a minor portion of the heavy feed hydrocarbons to hydrocarbons of lower molecular weight, recovering gas oils from the products of said first fluid catalytic cracking reactor and subjecting the gas oils to more severe cracking conditions in the presence of high activity cracking catalyst, e.g. a molecular sieve catalyst.