Patent ID: 6554990
Filing Date: 2003-04-29
Classification: B01D,C01D

Abstract:
A process for concentrating an aqueous solution of an alkali metal hydroxide, in an electrodialysis cell containing three compartments, comprising:circulating an aqueous alkali metal halide solution in a saline compartment of the cell, delimited between an anionic membrane and a cationic membrane, introducing an alkali metal halide into an acidic compartment of the cell, which is delimited between the anionic membrane and a cationic face of a bipolar membrane, and extracting a more concentrated aqueous alkali metal hydroxide solution from an alkaline compartment of the cell, delimited between the cationic membrane and an anionic face of the bipolar membrane, and extracting an aqueous solution of a hydrohalic acid and an alkali metal halide from said acidic compartment; wherein said process further comprises adjusting the amount of the alkali metal halide which is introduced into the acidic compartment so that the aqueous solution extracted from the alkaline compartment substantially contains from 3 to 10 moles of alkali metal hydroxide per litre.