THREE-COMPARTMENT CELL WITH A PRESSURIZED BUFFER COMPARTMENT

摘要

The invention describes a pressurized threecompartment membrane cell for electrolyzing aqueous alkali metal halide solutions at low cell voltages and high cathodic current efficiencies. Unitary electrode-electrolyte structures, in the form of electro-chemically active electrodes physically bonded to ion-exchange permselective membranes, divide the cell into anode, cathode and buffer compartments. The buffer compartment feed is pressurized to maintain a positive pressure differential with respect to the anode and cathode compartment feeds. The flexible unitary electrode-electrolyte structures are forced outwardly against electronically-conductive anode and cathode current collectors to provide uniform, constant and controllable contact between the bonded electrodes and their corresponding current collectors and thereby minimizing ohmic losses. A three-compartment cell operated in this fashion not only minimizes the voltage required to electrolyze the halide solution, but also increases the cathodic current efficiency at high caustic concentrations by providing multiple hydroxide rejection stages in a single cell process. The improvement in cathodic current efficiency is realized by forming a lower caustic concentration in the buffer compartment than in the cathode compartment, thereby reducing backmigration of OH- ions into the anode compartment.