GB767103A - Electrolytic production of weak acids - Google Patents

Abstract

767,103. Electrolytically preparing weak acids. ROHM & HAAS CO. Oct. 6, 1953 [Oct. 17, 1952], No. 27396/53. Drawings to Specification. Class 41. A water-soluble salt of a weak acid is converted into the weak acid by passing D.C. through a cell including one or more identical groups of two compartments, one containing a strong mineral acid, e.g. hydrochloric or sulphuric acid and the other the water-soluble salt of the weak acid, the first mineral acid compartment housing the anode and the last weak acid water-soluble salt compartment being adjacent a cathode compartment containing an aqueous electrolyte, e.g. of the hydroxide of the metal of weak acid salt typically an alkali metal, all of the compartments being separated by cationically permeable diaphragms containing a cation exchange resin. The process can be applied to the preparation of organic acids such as acetic, propionic, butyric, itaconic, maleic, fumaric, acrylic, tartaric, citric, sebacic, ascorbic, oleic, and stearic acids as well as of inorganic acids such as sulphurous, arsenious and silicic acids. Typically the strong mineral acid is sulphuric acid, the weak acid salt is sodium acetate, and the catholyte is caustic soda solution, hydrogen and oxygen being evolved. If only one weak acid salt compartment is employed between the anode and cathode compartments, it is only necessary to add water to the anolyte which may be removed at will, to add sodium acetate to the intermediate compartment and to remove acetic acid as a solution, and to add dilute electrolyte, e.g. sodium hydroxide, to the catholyte removing the more concentrated caustic soda solution formed. If hydrochloric acid is used in the anode compartment chlorine is evolved instead of oxygen and hydrochloric acid must be added. Valve supply pipes are provided above the levels of the solutions in the compartments and draw-off pipes are provided at the bottom of the compartments. If a number of weak acid salt and strong mineral acid compartments are provided, the weak acid and its salt are continuously successively transferred from the compartment nearest the cathode which receives further weak acid salt to those nearer the anode and the weak acid is removed from that adjacent the anode, water, if sulphuric acid is used, or hydrochloric acid being supplied to the intervening mineral acid compartments. The cationically permeable diaphragms are preferably of the kind described and claimed in Specification 719,315 typically of polyethylene, polyvinyl chloride, natural or synthetic rubber containing a sulphonated copolymer of styrene and divinyl benzene prepared by the process of U.S.A. Specification 2,366,007. A potential of 11-12 volts is applied to the cell to pass between platinum electrodes a current of 60 amps/sq. ft. initially, falling to 6 amps/sq. ft. at the end of operation. Specifications 489,437, 498,251, 515,517, 516,609, 521,207, [all in Group IV], 693,166, 720,002, and U.S.A. Specification 2,340,111 also are referred to.