Abstract: A method for purifying a dipeptide ester by electrolysis in an electrolytic cell comprising an anode compartment, a cathode compartment and a central compartment partitioned by anion exchange membranes, which comprises supplying an aqueous dipeptide ester solution containing an inorganic acid to the central compartment defined by said anion exchange membranes, an aqueous solution containing a basic substance or an aqueous electrolyte solution containing a basic substance to the cathode compartment and an aqueous electrolyte solution to the anode compartment, supplying hydroxyl ions from the cathode compartment to the central compartment through the anion exchange membrane to neutralize the aqueous dipeptide ester solution containing the inorganic acid and removing anions of the inorganic acid in the aqueous dipeptide ester solution from the central compartment to the anode compartment through the anion exchange membrane.

Abstract: A method for producing a metal salt by electrolysis in an electrolytic cell comprising an anode compartment and a cathode compartment partitioned by a diaphragm, characterized by supplying to the cathode compartment an aqueous solution of a water-soluble metal compound, and electrolytically reducing metal ions or metal complex ions to electroplate the metal on a cathode, wherein the diaphragm is a fluorinated anion exchange membrane made of a copolymer having repeating units of the formula: ##STR1## wherein X is F or CF.sub.3, l is an integer of from 0 to 5, m is 0, or 1, n is an integer of 1 to 5, each of p and q is a positive number and the ratio of p/q is from 2 to 16, and Y is a group involving a quaternary ammonium group.

Abstract: A process for preparing an anion exchange membrane, which comprises subjecting a carboxylate membrane made of a copolymer having repeating units of the formula: ##STR1## wherein X is F or CF.sub.3, l is an integer of from 0 to 5, m is 0 or 1, n is an integer of from 1 to 5, and p/q is from 4 to 16, and R is an alkyl group, to an acid or base treatment, and then introducing anion exchange groups thereinto.

Abstract: A method for producing a metal salt by electrolysis in an electrolytic cell comprising an anode compartment and a cathode compartment partitioned by a diaphragm, disposing in the anode compartment a metal anode soluble in the aqueous solution, and conducting electrolysis to dissolve the metal anode, wherein the diaphragm is a fluorinated anion exchange membrane made of a copolymer having repeating units of the formula: ##STR1## wherein X is F or CF.sub.3, l is an integer of from 0 to 5, m is 0 or 1, n is an integer of 1 to 5, each of p and q is a positive number and the ratio of p/q is from 2 to 16, and Y is a group involving a quaternary ammonium group.

Abstract: A method for recovering acids from an aqueous solution of a mixture of the acids and metal salts by dialysis, characterized in that a fluorinated anion exchange membrane made of a copolymer having repeating units of the formula: ##STR1## wherein X is F or CF.sub.3, l is an integer of from 0 to 5, m is 0 or 1, n is an integer of from 1 to 5, p/q is from 2 to 16, and Y is a quaternary ammonium group, is used as a dialysis membrane.

Abstract: A method for separating an acid and an alkali from an aqueous solution of a salt by an ion exchange membrane electrolysis wherein anion and cation exchange membranes are used as diaphragms and wherein the acid is formed in an anode compartment, and the alkali is formed in a cathode compartment, characterized in that the cation exchange membrane is a fluorinated cation exchange membrane and the anion exchange membrane is a fluorinated anion exchange membrane with the ion exchange capacity varied from one side to the other side.