Control of emissions in FCC regenerator flue gas

In a process for catalytic cracking of a sulfur containing hydrocarbon charge by contacting said charge at cracking temperature with a circulating inventory of cracking catalyst which inventory includes a component capable of sorbing oxides of sulfur in an oxidizing atmosphere and of reaction in a reducing atmosphere to release sulfur as hydrogen sulfide whereby the catalyst acquires an inactivating carbonaceous deposit containing sulfur, separating vaporous products of reaction including hydrogen sulfide from circulating catalyst inventory containing said deposit, regenerating the so separated inventory by contact with air at a temperature to burn said carbonaceous deposit thus generating oxides of carbon and sulfur and regenerating the catalyst, separating products of combustion from regenerated catalyst and returning regenerated catalyst to renewed contact with hydrocarbon charge with reduction of sulfur associated with the regenerated catalyst;

• the improvement which comprises again contacting said products of combustion and said regenerated catalyst at a temperature substantially below the temperature of regeneration to thereby induce sorption by said catalyst inventory being returned to contact with said charge of an amount of sulfur oxides greater than that sorbed during said regeneration, and to return said regenerated catalyst to contact with said charge at a temperature substantially below the temperature of said regeneration.