Catalytic cracking with reduced emission of noxious gases

Claim 1

In a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds wherein: (i) said feedstock is subjected to cracking in a reaction zone with fluidized solid particles of a cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable, sulfur-containing, carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone; a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas stream which comprises: (a) cracking said feedstock at a temperature from about 850° to about 1,200°F in the presence of particles of a molecular sieve-type cracking catalyst in admixture with fludizable particles which contain a metallic reactant, wherein said metallic reactant consists of at least one free or combined metallic element which is selected from the group consisting of sodium, scandium, titanium, iron, chromium, molybdenum, manganese, cobalt, nickel, antimony, copper, zinc, cadmium, the rare earth metals, and lead, and wherein said metallic reactant is present in sufficient amount to effect the absorption of at least about 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) stripping volatile deposits from the mixture of particles at a temperature from about 850° to about 1,200°F with a stripping gas which contains steam, wherein the ratio by weight of steam to said particles of molecular sieve-type cracking catalyst is from about 0.0005 to about 0.025; (c) regenerating the stripped particles at a temperature from about 1,050° to about 1,450°F; (d) absorbing with the admixture of particles at least about 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (e) conveying the particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (f) withdrawing an effluent gas stream from the regenera-tion zone containing molecular oxygen and having a low concentration of sulfur oxides; and (g) substantially withdrawing said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.