Process for removing SO2 from effluent gases and for removing heat stable salts from systems in which they accumulate using an anion exchange resin

Claim 1

In a process for the selective removal of sulfur dioxide with respect to carbon dioxide from a gas mixture containing same wherein (a) said gas mixture is contacted with a mainstream of an aqueous absorbent solution to remove sulfur dioxide from said gas mixture and form a rich aqueous absorbent solution enriched in sulfur dioxide removed from the gas mixture, (b) a mainstream of said rich aqueous absorbent solution is moved to a stripping zone where sulfur dioxide is removed to form a lean aqueous absorbent solution depleted in sulfur dioxide content, and (c) a mainstream of said lean aqueous absorbent solution is recycled from the stripping zone and re-contacted with said gas mixture, the improvement comprising 1. using an aqueous alkanolamine or sulfites thereof as the aqueous absorbent solution; 2. performing the stripping step of step (b) so that the residence time of said aqueous absorbent solution in said stripping zone is from about 3 to about 30 minutes and said stripping zone is operated at a reduced pressure of about 50 to about 350 mm. Hg. and a temperature of about 80° to 100° C. to thereby minimize the formation of sulfate, thiosulfate and thionate anions; 3. separating a portion of said aqueous absorbent solution containing accumulated sulfate, thiosulfate and thionate anions from said mainstream of lean aqueous absorbent; 4. contacting said separate portion with an anion exchange resin having hydroxyl anions displaceable by said sulfate, thiosulfate and thionate anions to remove same from said portion whereby the hydroxyl anions of the resin are replaced by said sulfate, thiosulfate and thionate anions; 5. returning said portion after contact with said anion exchange resin to one of said mainstreams; and 6. regenerating said anion exchange resin by contacting it with aqueous alkaline inorganic hydroxide to replace the sulfate, thiosulfate and thionate anions on said resin with hydroxyl anions thereby forming a waste stream containing said sulfate, thiosulfate and thionate anions, whereby sulfate, thiosulfate and thionate anions are removed from said aqueous absorbent solution.