Method and apparatus for controlling anode pH in membrane chlor-alkali cells
AssigneeIonics, Incorporated
InventorWayne A. McRae
Life of this patent
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Abstract
An improved process and apparatus for pH control in the anode compartments of membrane chlor-alkali cells is disclosed wherein an anode is used having an oxygen evolution efficiency substantially equivalent chemically to the hydroxide ion transfer efficiency of the membrane.
Claims16
In a process wherein an aqueous alkali metal chloride solution is electrolyzed in a chlor-alkali appartus including a cell having an anode compartment containing an anode capable of generating chlorine and lesser amounts of oxygen from aqueous chloride solution, a cathode compartment containing a cathode and a substantially fluid impervious, cation permselective membrane separting said anode compartment from said cathode compartment, the improvement comprising controlling the pH of the anolyte by operating said anode to have an oxygen evolution efficiency substantially chemically equivalent to the hydroxide ion transfer efficiency of the said membrane whereby the formation of excessive chlorates and hypochlorites in said anolyte and insoluble metallic hydroxide in said membrane is substantially reduced.
A chlor-alkali apparatus including a cell comprising an anode compartment containing an anode, a cathode compartment containing a cathode, a substantially fluid impervious cation permselective membrane separating said anode and cathode compartments, said membrane having a hydroxide ion transfer efficiency, said anode having an oxygen evolution efficiency substantially equivalent chemically to said hydroxide ion transfer efficiency of said membrane.
A chlor-alkali apparatus comprising:
- (a) at least one electrolytic cell comprising an anode compartment containing an anode, a cathode compartment containing a cathode, a substantially fluid impervious cation permselective membrane separating said anode and cathode compartments, said membrane having a finite hydroxide ion transfer efficiency, said anode having an oxygen evolution efficiency substantially equivalent chemically to said hydroxide ion transfer efficiency of said membrane;
- (b) means for controlling the temperature of the fluid immediately effluent from said cathode compartment to the range of from about 70.degree. to about 95.degree. C.;
- (c) means for controlling the concentration of the effluent from said cathode compartment to at least about 8 percent by weight of alkali hyroxide;
- and
- (d) means for controlling the current density at said membrane to the range of from about 10 to about 35 amperes per square decimeter.
A chlor-alkali apparatus including:
- (a) at least one electrolytic cell comprising an anode compartment containing a coated electrolytic valve metal anode, a cathode compartment containing a cathode, a substantially fluid impervious perfluorocarbon cation permselective membrane having active groups selected from the group consisting of sulfonate, sulfonamide, carboxylate and phosphonate separating said anode and cathode compartments, said membrane having a hydroxide ion transfer efficiency in excess of about 5 percent, said anode having an oxygen evolution efficiency substantially equivalent chemically to said hydroxide ion transfer efficiency of said membrane;
- (b) means for separating the liquid effluent from the cathode compartment from the gaseous effluent therefrom;
- (c) means for cooling the liquid effluent by evaporation to a temperature of substantially less than about 70.degree. C.;
- (d) means for measuring the temperature of the liquid immediately effluent from said cathode compartment;
- (e) temperature responsive means for controlling the temperature of said liquid immediately effluent to the range of from about 70.degree. to about 95.degree. C. by exchanging heat between said cooled liquid effluent and the influent to said cathode compartment.
A chlor-alkali apparatus including:
- (a) an array of electrolytic cells arranged in stages with each cell comprising an anode compartment containing a coated metallic anode, a cathode compartment containing a metallic cathode, a substantially fluid impervious perfluorocarbon cation permselective membrane separating said anode and cathode compartments, said membrane having a hydroxide ion transfer efficiency of more than about 5 percent, but less than about 30 percent, said anode having a chlorine evolution efficiency of less than about 98 percent but more than about 70 percent;
- (b) means for passing at least part of the combined liquid effluent from the cathode compartment(s) from a first stage of such array as influent to the cathode compartment(s) of a second stage of such array;
- (c) means for recycling the remainder of said combined liquid effluent and adder water as influent to the cathode compartment(s) of said first stage;
- and
- (d) means for controlling the concentration of the combined liquid effluent from the cathode compartment(s) of such first stage to the range of from about 9 to about 13 percent by weight.
Dependencies are inferred from the claim text.