Process for removing sulfur oxides from a gas

A process for the cyclic, fluidized catalytic cracking of a hydrocarbon feedstock containing from about 0.2 to about 6 weight percent sulfur as organic sulfur compounds wherein:

• (i) said feedstock is subjected to cracking in a reaction zone through contact with a particulate cracking catalyst at a temperature in the range from 430.degree. to 700.degree. C.;
• (ii) cracking catalyst, which is deactivated by sulfur-containing coke deposits, is separated from reaction zone effluent and passes to a stripping zone wherein volatile deposits are removed from said catalyst by contact with a stripping gas comprising steam at a temperature in the range from 430.degree. to 700.degree. C.;
• (iii) stripped catalyst is separated from stripping zone effluent and passes to a catalyst regeneration zone and non-stripped, sulfur-containing coke deposits are removed from the stripped catalyst by burning with an oxygen-containing regeneration gas at a temperature in the range from 565.degree. to 790.degree. C., thereby forming sulfur oxides;
• and (iv) resulting catalyst is separated from regeneration zone effluent gas and recycled to the reaction zone;
• and wherein emissions of sulfur oxides in the regeneration zone effluent gas are reduced by the method which comprises:
• (a) absorbing sulfur oxides in said regeneration zone with a fluidizable particulate solid which comprises magnesium oxide in association with at least one free or combined rare earth metal selected from the group consisting of lanthanum, cerium, praseodymium, samarium and dysprosium, wherein said magnesium oxide and rare earth metal or metals are present in the particulate solid in sufficient amount to effect the absorption of at least about 50 percent of the sulfur oxides produced by the burning of sulfur-containing coke deposits in the regeneration zone and the ratio by weight of magnesium oxide to rare earth metal or metals is from about 1.0 to about 30,000;
• and
• (b) removing said absorbed sulfur oxides from the fluidizable particulate solid as a sulfur-containing gas which comprises hydrogen sulfide by contacting said particulate solid with the hydrocarbon feedstock in said reaction zone.

A process for the cyclic, fluidized catalyst cracking of a hdyrocarbon feedstock containing organic sulfur compounds wherein:

• (i) said feedstock is subjected to cracking in a reaction zone through contact with a particulate cracking catalyst at a temperature in the range from 430.degree. to 700.degree. C.;
• (ii) cracking catalyst, which is deactivated by sulfur-containing coke deposits, is separated from reaction zone effluent and passes to a stripping zone wherein volatile deposits are removed from said catalyst by contact with a stripping gas comprising steam at a temperature in the range from 430.degree. to 700.degree. C.;
• (iii) stripped catalyst is separated from stripping zone effluent and passes to a catalyst regeneration zone and non-stripped, sulfur-containing coke deposits are removed from the stripped catalyst by burning with an oxygen containing regeneration gas at a temperature in the range from 565.degree. to 790.degree. C., thereby forming sulfur oxides;
• and (iv) resulting catalyst is separated from regeneration zone effluent gas and recycled to the reaction zone;
• and wherein emissions of sulfur oxides in the regeneration zone effluent gas are reduced by the method which comprises:
• (a) absorbing sulfur oxides in said regeneration zone with a fluidizable particulate solid other than said cracking catalyst which comprises magnesium oxide in association with at least one free or combined rare earth metal selected from the group consisting of lanthanum, cerium, praseodymium, samarium and dysprosium, wherein the ratio by weight of magnesium oxide to rare earth metal or metals is from about 1.0 to about 1,000 and said particulate solid is physically admixed with said cracking catalyst;
• and
• (b) removing said absorbed sulfur oxides from the fluidizable particulate solid as a sulfur-containing gas which comprises hydrogen suldife by contacting said particulate solid with the hydrocarbon feedstock in said reaction zone.