Process for efficiently purifying industrial gas

Claim 1

A process for efficiently removing sulfur dioxide and ammonia from an industrial waste gas containing each of them in a proportion lower than about 300 ppm by volume, comprising the steps of: a. contacting the waste gas with a dilute aqueous solution of ammonium sulfate, to absorb sulfur dioxide and ammonia and form ammonium sulfites dissolved in said dilute ammonium sulfate solution at a concentration of about 0.02-0.5 mole of ammonium sulfite per liter; b. separating resultant purified gas from the solution obtained in step (a); c. dividing the separated solution into separate portions; d. passing a first portion of separated solution to the anodic compartment of an electrochemical cell having a cation-permeable membrane separating the anodic compartment from the cathodic compartment, and passing a second portion of said separated solution to the cathodic compartment of said cell and electrolyzing said portions in said compartments to convert sulfite to sulfate in the anodic compartment and transfer ammonium ions through said cation-permeable membrane to produce a solution of neutral ammonium sulfite in the cathodic compartment; e. discharging the solution of neutral ammonium sulfite from the cathodic compartment and thereafter contacting it with a molecular oxygen containing gas, thereby converting said neutral ammonium sulfite to ammonium sulfate; f. admixing at least a fraction of the solution discharged from the anodic compartment with at least a fraction of the solution discharged from the cathodic compartment and subsequently contacted with a molecular oxygen containing gas; and g. recycling at least a portion of said admixed fractions to the step (a) as the dilute aqueous solution of ammonium sulfate.