Production of alkali metal carbonates in a membrane cell

An alkali metal carbonate substantially free of alkali metal chloride is efficiently produced by electrolyzing an alkali metal chloride in an electrolytic cell having anolyte and catholyte compartments separated by a cation-exchange hydraulically impermeable membrane comprised of a thin film of a fluorinated polymer having pendant sulfononate groups and a cathode spaced apart from the membrane, injecting into the catholyte compartment of the cell carbon dioxide in a quantity sufficient to convert substantially all of the alkali metal hydroxide forming therein to the alkali metal carbonate salt, and utilizing a magnitude of electrolyzing current that reduces alkali metal chloride in the carbonate salt to less than 400 ppm.