Operation and regeneration of permselective ion-exchange membranes in brine electrolysis cells

Claim 1

A method of operating and regenerating an electrolysis cell which electrolyzes an aqueous alkali metal halide solution (brine) to a halogen at the cell's anode and an alkali metal hydroxide at the cell's cathode, which cell contains a permselective cation exchange membrane disposed between the anode and cathode to form an anolyte and catholyte compartment so as to separate the cell's anolyte from its catholyte, which method comprises the combination of steps of: A. during at least 50% of the cell's normal electrolysis operation, feeding to and electrolyzing in said cell a brine which, at least at the time immediately prior to the brine's becoming part of the anolyte, contains no more than about 5 ppm hardness (expressed as ppm calcium) and no more than about 70 ppm "carbon oxide" (expressed as ppm CO 2 ); B. regenerating the membrane (after it has become fouled with compounds of multivalent cations accumulated from the brine fed to the cell during the normal cell electrolysis step of Step (A) above) by contacting the membrane on at least one of its sides with a solution capable of dissolving the multivalent cation compounds fouling the membrane for a time sufficient to dissolve a substantial amount of said compounds fouling said membrane, said solution having a pH lower than the pH of the electrolyte which contacted that side of the membrane during the normal cell electrolysis step, Step (A) above.

Claim 2

A method of operating and regenerating an electrolysis cell which electrolyzes an aqueous alkali metal halide solution (brine) to a halogen at the cell's anode and an alkali metal hydroxide at the cell's cathode, which cell contains a permselective cation exchange membrane disposed between the anode and cathode to form an anolyte and catholyte compartment so as to separate the cell's anolyte from its catholyte, which method comprises the combination of steps of: A. during at least 50% of the cell's normal electrolysis operation, feeding to and electrolyzing in said cell a brine which, at least at the time immediately prior to the brine's becoming part of the anolyte, contains no more than about 5 ppm hardness (expressed as ppm calcium) and no more than about 70 ppm "carbon oxide" (expressed as ppm CO 2 ); B. regenerating the membrane (after it has become fouled with compounds of multivalent cations accumulated from the brine fed to the cell during the normal cell electrolysis step of Step (A) above) by contacting the membrane on at least one of its sides with a solution capable of dissolving the multivalent cation compounds fouling the membrane for a time sufficient to dissolve a substantial amount of said compounds fouling said membrane, said solution having a pH lower than the pH of the electrolyte which contacted that side of the membrane during the normal cell electrolysis step, Step (A) above.