Electrolytic prodn. of alkali metal carbonate - using two-compartment cell with fluorinated copolymer membrane

摘要

Electrolytic prodn. of alkali metal carbonates is effected as described in the parent patent, by electrolysing an alkali metal chloride soln. at a current intensity >=0.155 A/cm2 in a cell with anode and cathode compartments sepd. by a semipermeable, cation-exchanging, hydraulically impermeable membrane made of a fluorinated copolymer, while CO2 is introduced into the cathod compartment. In this addition, (a) the copolymer contains repeating units of formulae (I) or (I') and -C(X')X-CF2 (II); and (b) the electrolysis conditions are such that the catholyte solids comprise =400 ppm of alkali metal chloride. In the formulae R is -CR'F-CF2-O-(CYF-CF2-O)-m; R' is F or 1-10C perfluoroalkyl; Y is F or CF3; m=1-3; n = 0 or 1; A is H, Na or K; D is H or the residue of an amine; X is F, Cl or CF3; X' is X or CF3(CF2)2-; z = 0-5; with the proviso that units of formula (I) and (I') are present in amts. such that the SO3H equiv. wt. is 1000-1400 (pref. 1050-1250) and the copolymer has a water-absorption capacity of >=15 wt.% at 100 degrees C. Process gives high purity prods. with high current efficiencies ( >= 95%). The current consumption is comparable with that of conventional diaphragm and mercury cells and the cell can be operated at high current densities (e.g. >=0.31 A0cm2) over long periods.