Production of alkali metal carbonates in a membrane cell

Claim 1

In a method for producing an alkali metal carbonate wherein: A. an alkali metal chloride is electrolyzed in an electrolytic cell having an anode and cathode in anolyte and catholyte compartments separated by a permselective cation-exchange membrane that is impervious to hydraulic flow and is spaced apart from the cathode; B. carbon dioxide is injected into the catholyte compartment to give catholyte solids wherein substantially all of the alkali metal hydroxide formed therein is converted to alkali metal carbonate; and C. catholyte containing the alkali metal carbonate is removed from the catholyte compartment; the improvement which comprises: D. utilizing a membrane which: 1. consists essentially of a film having a thickness not exceeding 8 mils of a copolymer having recurring structural units of the formula: ##STR4## wherein R represents the group ##STR5## in which R' is fluorine or perfluoralkyl of 1 to 10 carbon atoms, Y is fluorine or trifluoromethyl, and m is 1, 2 or 3; n is 0 or 1; A is H, Na, or K; X is fluorine, chlorine, or trifluoromethyl; and X' is X or CF 3 --CF 2 -- z wherein z is 0 or an integer from 1 to 5; the units of formula (I) being present in an amount to provide a copolymer having in the acid form an --SO 3 H equivalent weight of about 1000 to 1400; and 2.