Abstract: In a process for chlorine-alkali electrolysis, use is made of an oxygen depletion cathode. The process is run with a high excess of oxygen. The oxygen needed for this is provided for a device of the gas separation, for example a VPSA plant or an air fractionation plant. The large quantities of oxygen produced lead to considerable costs of the process. According to the invention, the oxygen-rich atmosphere remaining after passing through the process is fed back into the device for gas separation as input gas. The device the gas separation is therefore operated with an oxygen-rich input gas and therefore produces a larger quantity of oxygen-rich gas, which in turn is fed to the oxygen depletion cathode. As a result of the circulation of the gas, the economy of the overall process is increased considerably.

Abstract: A membrane electrolysis cell comprising an anodic compartment and a cathodic compartment is described, wherein at least one of the two compartments contains an electrode fed with gas and a porous planar element is interposed between the membrane and the gas-fed electrode. A flow of chemically aggressive electrolyte crosses the porous planar element downwards under the effect of the gravity force. The planar element consists in a plastic element withstanding the aggressive operative conditions: The use of perfluorinated plastics such as ECTFE, PTEFE, FEP, PFA is preferred, even though they are strongly hydrophobic. When the gas-fed electrode is a cathode and the gas contains oxygen, the gas crosses the cathodic compartment upwardly so as to minimize the risk of hydrogen build up. The cell equipped with the oxygen cathode is particularly advantageous for the sodium chloride electrolysis.

Abstract: Provided is a process which permits, upon preparation of chlorine and a caustic alkali by electrolyzing an aqueous alkali chloride solution in an ion-exchange-membrane-method alkali chloride electrolytic cell equipped with a gas diffusion cathode, decrease of an excess ratio of an oxygen containing gas to be fed newly to the gas diffusion cathode and facilitates temperature control of the electrolytic cell. A process for electrolyzing an alkali chloride comprising: introducing saline water into an anode chamber of an ion-exchange-membrane-method alkali chloride electrolytic cell equipped with a gas diffusion cathode; and introducing an oxygen-containing gas into a gas chamber of a gas diffusion cathode, to thereby obtain chlorine in the anode chamber and an aqueous caustic alkali solution in the cathode chamber.

Abstract: The invention relates to a method for shutting down an electrolysis cell with a membrane and an oxygen-reducing cathode, which comprises, after the electrical power and oxygen supplies have been disconnected, in emptying the oxygen compartment and filling it with demineralized water having a pH≦7 and in keeping this water in the oxygen compartment throughout the shutdown period.

Abstract: The present invention relates to an electrochemical cell and a process for producing a hydroxide solution, sulfuric acid and a halogen gas from a hydrogen halide and a sulfate solution. In particular, the sulfate solution may be an alkali metal sulfate solution, such as sodium or potassium sulfate solution, an alkaline earth metal sulfate solution or an ammonium sulfate solution. The cell and the process may use either an anhydrous or an aqueous hydrogen halide, namely, hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, to a respective dry halogen gas, such as chlorine, fluorine, bromine, or iodine, to produce hydrogen ions in order to split the alkali metal solution and form the sulfuric acid. The cell has two membrane-electrode assemblies, where an anode is disposed in contact with one membrane, and a cathode is disposed in contact with another membrane. The sulfate solution is fed in between the membrane-electrode assemblies.

Abstract: The present invention relates to an electrochemical cell and a process for using a halogen halide and splitting a sulfate solution and producing a hydroxide solution, sulfuric acid and a halogen gas. In particular, the sulfate solution may be an alkali metal sulfate solution, such as sodium or potassium sulfate solution, an alkaline earth metal sulfate solution or an ammonium sulfate solution. The cell and the process may use either an anhydrous or an aqueous hydrogen halide, namely, hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, to a respective dry halogen gas, such as chlorine, fluorine, bromine, or iodine, to produce hydrogen ions in order to split the sulfate solution and form the sulfuric acid. The cell has two membrane-electrode assemblies, where an anode is disposed in contact with one membrane, and a cathode is disposed in contact with another membrane. The sulfate solution is fed in between the membrane-electrode assemblies.