Electrolysis of aqueous solution of potassium chloride

Claim 1

In a process of producing potassium hydroxide by electrolysis of an aqueous solution of potassium chloride utilizing a fluorinated cation exchange membrane having an ion-exchange capacity of 0.8 to 2.0 meq/g dry polymer and having carboxylic acid groups as functional groups comprised of a copolymer having units ##STR4## wherein X represents fluorine, chlorine or hydrogen atom or --CF 3 ; X' represents X or CF 3 (CF 2 ) m -- ; m represents an integer of 1 to 5 and Y represents ##STR5## p, q and r respectively represent an integer of 1 to 10; Z and Rf represents --F or a C 1 -C 10 perfluoroalkyl group; A represents --COOH, --COOM or --CN, --COF, --COOR 1 , ##STR6## as a functional group which can be converted to carboxylic acid group by a hydrolysis or a neutralization; R 1 represents a C 1 -C 10 alkyl group; M represents an alkali metal or a quaternary ammonium group; R 2 and R 3 respectively represent a C 1 -C 10 alkyl group and maintaining a potassium hydroxide concentration of from about 20 to about 45 weight % in the aqueous solution in the cathode compartment, in the improvement comprising maintaining said aqueous potassium chloride solution a calcium concentration lower than 0.05 mg/liter and a magnesium concentration lower than 0.03 mg/liter.