Process for reducing sox emissions from catalytic cracking units

Abstract

Reduction of SO.sub.x emissions from the regenerator associated with the fluidized catalytic cracking (FCC) unit for converting hydrocarbon feedstocks into more valuable products is achieved by introducing into the FCC cycle one or more organic, aluminum-containing compounds in dissolved form. In the catalytic cracking zone, the dissolved aluminum-containing compounds are converted to aluminum compounds that deposit relatively uniformly upon the catalyst particles. Also depositing upon the catalyst particles in the catalytic cracking zone are deactivating quantities of sulfur-containing coke. When such catalyst particles are introduced into the regenerator, wherein the sulfur-containing coke present on the catalyst surfaces is removed by combustion, thereby activating the catalyst particles, the SO.sub.x so produced reacts with the deposited aluminum compounds to form one or more stable, sulfur-aluminum oxidic compounds, thus desulfurizing the regenerator flue gas. Once deposited upon the catalyst particles, the aluminum compounds alternately react with the SO.sub.x compounds produced in the regenerator and then, by passage with the recycling catalyst particles through the catalytic cracking and steam stripping zones of the FCC unit, are converted to forms active for once again removing SO.sub.x compounds. Thus, just as the catalyst particles are alternately activated and deactivated for cracking hydrocarbons, the aluminum compounds dispersed on such catalyst particles undergo similar cyclical changes in activity with respect to SO.sub.x removal.