Process for removing sulfur dioxide from a gas and producing sulfur therefrom

Claim 1

Process for removing sulfur dioxide from a gas containing the same, wherein said gas is contacted, in a first step (a), with an aqueous ammonia absorbing solution, so as to absorb sulfur dioxide in the form of ammonium sulfites, then, in a second step (b), the solution resulting from (a) is heated, so as to decompose the sulfites to a gas containing sulfur dioxide and ammonia, then, in a third step (c), the gas from step (b) is heated at 150°-600° C. with gas capable of reducing SO 2 to H 2 S, in contact with a catalyst for reducing SO 2 to H 2 S so as to produce a gas essentially containing hydrogen sulfide, sulfur dioxide and ammonia in a molar ratio of H 2 S to SO 2 of 1.7-2.3, and in a fourth step (d), the gas from (c), which has a molar ratio H 2 S/SO 2 of from 1.7:1 to 2.3:1 is contacted at 200°-400° C. with a catalyst for the reaction of H 2 S and SO 2 to sulfur, and a gas containing free sulfur, ammonia and residual sulfur dioxide and hydrogen sulfide is recovered, and, in a fifth step (e), said gas recovered from step (d) is cooled to about 150° C. in contact with an organic solvent in the liquid phase, so as to be made free of residual sulfur without substantial formation of ammonium thiosulfate or sulfate, and the resulting ammonia containing effluent gas is used to reconstitute the absorbing solution of (a).