Patent ID: 6193872
Filing Date: 2001-02-27
Classification: C02F,C07C

Abstract:
A process for treating an aqueous waste stream from a chemical production plant, which aqueous waste stream contains at least one alkali metal carboxylate containing at least 3 carbon atoms, to produce a solution of an alkali metal hydroxide for recycle to the chemical production plant, which process comprises:(a) admixing the waste stream with a dilute aqueous solution of an inorganic acid selected from phosphoric acid, sulphuric acid, or a mixture thereof so as to generate from said at least one alkali metal carboxylate a corresponding carboxylic acid or acids and to produce an acidic liquor having a pH of less than about 3.5 and containing an alkali metal salt of the inorganic acid;(b) separating free carboxylic acid or acids from the acidic liquor of step (a) to form an acidic predominantly aqueous phase containing the alkali metal salt of the inorganic acid;(c) providing an electrolysis zone comprising an anode compartment and a cathode compartment, the anode compartment containing an anode and the cathode compartment containing a cathode, and the anode compartment being separated from the cathode compartment by means of an ion permeable membrane permeable to alkali metal ions;(d) supplying the acidic predominantly aqueous phase resulting from step (b) to the anode compartment of the electrolysis zone;(e) supplying water to the cathode compartment of the electrolysis zone;(f) passing a current between the anode and the cathode thereby to subject the acidic predominantly aqueous phase to electrolysis, to cause alkali metal ions to pass through the ion permeable membrane from the anode compartment to the cathode compartment and form alkali metal hydroxide therein, and to regenerate inorganic acid in the anode compartment;(g) recovering from the cathode compartment an alkali metal hydroxide solution for recycle to the chemical production plant; and(h) recycling a solution containing the inorganic acid produced in step (f) to step (a).