Electrolytic prodn. of chlorine and alkali phosphate - using ruthenium coated electrodes as cathodes

摘要

In the prodn. of Cl2 by electrolysis of an aq. alkali metal chloride soln. and phosphoric acid in aq. soln., a hot conc. aq. anolyte soln. of the alkali metal chloride is contacted with one side of a cation exchange membrane, and a hot aq. catholyte soln. of phosphoric acid contg. ca 10-70 wt. % H3PO4 is contacted with the other side of the membrane. The cathode used consists of a conducting metal coated with ruthenium metal. A direct current is passed in series through the solns. and the membrane. The cation exchange membrane has a normality of ca 0.2-10 N, and the solns. have attemp. of ca 80-110 degrees C. Cl2 gas is collected from the anolyte soln., while H2 gas is collected from the catholyte soln. At least part of the alkali metal phosphate formed in the catholyte soln. is recovered as a prod. of the process. The process gives highly pure Cl2, H2 and alkali metal phosphates. When a KCl soln. is used as anolyte, highly potassium phosphate salts with any desired K:P molar ratio (suitable for the prodn. of fertilizers or detergents) can be produced. Current consumption is low. The ruthenium-coated cathode is resistant to the corrosive conditions in the cathode space, and gives a low hydrogen potential on the cathode.