Abstract: Alkali metal hydroxide solutions are purified and concentrated by electrolysis of such solutions in the anode compartment of a hybrid cell comprising an anode compartment and a cathode compartment separated by a cation permeable diffusion barrier. To enable operation, gaseous hydrogen is supplied to the anode, oxygen to the cathode and an aqueous media receptive to alkali metal ions to the cathode compartment. A plurality of the hybrid cells may be operated in hydrodynamic series.

Abstract: Alkali metal hydroxide solutions are purified and concentrated by electrolysis of such solutions in a hybrid cell comprising an anode compartment and a central compartment separated from the anode compartment by a cation permeable diffusion barrier, and a cathode compartment in flow communication with the central compartment and separated from the central compartment by a diaphragm. To enable operation, gaseous hydrogen is supplied to the anode, oxygen to the cathode, an aqueous solution of at least one alkali metal hydroxide to the anode compartment, and an aqueous media receptive to alkali metal ions to the central compartment. A plurality of the hybrid cells may be operated in hydrodynamic series.

Abstract: A flow of an alkali hydroxide solution such as chloralkali cell liquor containing NaOH and NaCl is introduced into the anode compartment of a hybrid cell which also includes a cathode compartment and a central compartment. The anode compartment is defined by a first surface of a gas diffusion type, electrode and a first surface of a gas diffusion type, electrode and a first surface of a cation permeable membrane. The central compartment is defined by a second surface of the cation permeable membrane, which membrane is opposite such first membrane surface and a first surface of a diaphragm. The cathode compartment is defined by a second surface of such diaphragm opposite such first diaphragm surface and a first surface of a gas diffusion type cathode. Gaseous hydrogen is supplied to the anode; air is supplied to the cathode, in each case at the surface opposite the aforementioned first surfaces, and water is supplied to the central compartment which is a flow communication with the cathode compartment.

Abstract: A flow of an alkali hydroxide solution such as chloralkali cell liquor containing NaOH and NaCl is introduced into the anode compartment of a hybrid cell which also includes a cathode compartment separated from the anode compartment by a cation selective, permeable membrane. The anode and the cathode permit gas diffusion. Gaseous hydrogen is supplied to the anode; air to the cathode; and a flow of water or other aqueous solution to the cathode compartment. The chloralkali cell is electrically connected to the hybrid cell. When the same number of coulombs flow through the chloralkali cell and the hybrid cell, the introduced chloralkali cell liquor is depleted of alkali metal ions which pass through the membrane to the water flowing through the cathode compartment. Through electrolytic consumption of water and evaporation of water from the cathode surface, highly purified caustic solutions of up to 50% caustic content can be obtained.