GB1087090A - Process for the manufacture of anhydrous sodium sulphite - Google Patents

Abstract

Anhydrous Na2SO3 is prepared by the reaction of a gaseous mixture containing SO2 and at a temperature of 200-600 DEG C. with an aqueous solution containing sodium sulphite, the SO2 content of the gas being such that the heat of neutralization together with the sensible heat of the gas stream is sufficient to dehydrate the reaction solution such that subsequent addition of Na2CO3, or NaOH to the residual solution precipitates anhydrous Na2SO3 which is removed, the mother liquor being recycled as said solution containing sodium sulphite. In the Figure (not shown) hot SO2-containing gases are contacted first with a falling thin film of solution containing solution, then this solution is sprayed into the gas, and then the residual gases are contacted with a further quantity of the solution in a packed column. The resulting solution from all three stages is collected and neutralized, the resulting slurry separated and mother liquor recycled. The gaseous mixture is preferably obtained by burning one or more of elemental sulphur, sulphur ore, a metal sulphide or hydrogen sulphide and the mixture may also contain SO3 and oxygen. Any solid or mist may be separated from the combustion gases by an appropriate separator before the gases are used. The gas mixture preferably contains 2 to 18% by volume of SO2 and the aqueous solution contains a total content of sodium compounds of between 16% by weight and saturation. The preferred neutralizing agent is sodium hydroxide.