Production of sodium dithionite from sulfur dioxide, sodium formate, and

Abstract

A convenient batch process for producing anhydrous sodium dithionite at high productivity by reduction of sulfur dioxide with formate ion in aqueous methanolic solution is described in which sodium carbonate, in the form of a dry powder, is the source of alkali. Minimum amounts of water, in which sodium formate is dissolved, and of methanol, in which sulfur dioxide is dissolved, are used. In one aspect, SO.sub.2 -methanol solution, aqueous sodium formate solution, and powdered sodium carbonate are added to a methanol puddle solution, obtained from a preceding run which contains methyl formate in an equilibrium amount which is usually 4-8%, according to specific schedules which are proportioned to the rate of solution of sodium carbonate in the aqueous methanolic solvent and to the rates of reaction of sulfur dioxide with sodium carbonate and with sodium formate to form sodium metabisulfite. The process has a productivity, measurable as pounds of anhydrous sodium dithionite produced per gallon of reactor volume per hour, that is at least as high as the optimum productivity of the process of U.S. Pat. No. 3,887,695, without requiring hazardous dissolving temperatures and possibilities of freeze-up in supply pipes from slight drops in temperatures.