Electrolytic manufacture of chlorates, using a plurality of electrolytic cells

• US 3,897,320 A
• Filed: 11/01/1973
• Issued: 07/29/1975
• Est. Priority Date: 11/01/1973
• Status: Expired due to Term

• Current Assignee: Occidental Chemical Corporation (Occidental Petroleum Corporation)
• Original Assignee: Edward H. Cook Jr
• Inventors: Cook, Edward H. Jr.
• Primary Examiner(s): Edmundson, F. C.
• Application Number:
  US05/411,622
• Time in Patent Office: 635 Days
• Field of Search: 204/95,98
• US Class Current: 205/345
• CPC Class Codes: C25B 1/34 Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis

Abstract

A sodium chloride solution is electrolyzed to produce a high strength caustic solution and sodium chlorate solution, using two different electrolytic cells. In the first cell, a twocompartment cell in which the compartments are separated by a permselective membrane of a hydrolyzed copolymer of a perfluorinated hydrocarbon and a fluorosulfonated perfluorovinyl ether or of a sulfostyrenated perfluorinated ethylene propylene polymer, the sodium chloride solution is electrolyzed at a pH of about 4 to 7 to produce aqueous sodium hydroxide solution in the cathode compartment and chlorine and cell liquor containing chlorate in the anode compartment. Then, the cell liquor, already containing some chlorate, is further electrolyzed in a conventional chlorate cell or equivalent apparatus to convert chloride therein to chlorate. After separation of the chlorate from chloride present with it the chloride is returned to the first cell.

Claims

1. A METHOD FOR ELECTROLYTICALLY PRODUCING CHLORATE SOLUTION, CHLORINE, HYDROGEN, AND HYDROXIDE SOLUTION WHICH COMPRISES ELECTROLYZING 200 TO 360G./1. OF AQUEOUS CHLORINE SOLUTION HAVING A PH OF ABOUT 2 TO 7 IN AN ELECTROLYTIC CHLORINE CELL SAID CELL HAVING AN ANODE COMPARTMENT AND A CATHODE COMPARTMENT, AN ANODE, A CATHODE, A CATION-ACTIVE PERMSELECTIVE MEMBRANE OF A HYDROLYZED COPOLYMER OF A PERFLUORINATED HYDROCARBON AND A FLUOROSULFONATED PERFLUOROVINYLETHER, OR OF A SULFOSTYRENATED PERFLUORINATED ETHYLENE-PROPYLENE POLYMER, DEFINING A BOUNDARY BETWEEN THE ANODE AND THE CATHODE COMPARTMENTS AND BETWEEN THE ANODE AND CATHODE, TO PRODUCE HIGH-PURITY HYDROXIDE SOLUTION AND HYDROGEN IN THE CATH-

2. A method according to claim 1 wherein the chlorine cell is of two compartments, the cation-active permselective membrane is of a hydrolyzed copolymer of tetrafluoroethylene and a fluorosulfonated perfluorovinyl ether of the formula FSO2CF2CF2OCF(CF3)CF2OCF CF2which copolymer has an equivalent weight of about 900 to 1,600, the concentration of sodium chloride in the chlorine cell anode compartment is from about 200 to 320 grams per liter, the anolyte pH therein is about 3 to 7, the aqueous hydroxide solution made in the catholyte therein is at a concentration of 250 to 450 g./l., the chlorine made contains less than 7.5 percent of oxygen, the anode efficiency is in excess of 85 percent and the caustic efficiency is greater than 75 percent.

3. A method according to claim 2 wherein the temperatures of electrolysis in both cells are maintained from 50 to 95* C., the voltages are from about 2.3 to 6 volts, the current densities are from about 0.5 to 4 amperes per square inch of electrode surface, the surfaces of the cathodes are of a material selected from the group consisting of platinum, iridium, ruthenium, rhodium, graphite, iron and steel and the surfaces of the anodes are of a material selected from the group consisting of noble metals, noble metal alloys, noble metal oxides, mixtures of noble metal oxides and valve metal oxides, or mixtures thereof, on a valve metal.

4. A method according to claim 3 wherein the permselective membrane is from about 0.02 to 0.5 mm. in thickness and is mounted on a network of material selected from the group consisting of polytetrafluoroethylene, asbestos, perfluorinated ethylene propylene polymer, polypropylene, titanium, tantalum, niobium and noble metals, having an area percentage of openings therein from about 8 to 80%.

5. A method according to claim 4 wherein the copolymer equivalent weight is from about 1,100 to 1,400, the cathode is of steel and the anode is of ruthenium oxide on titanium, the aqueous sodium chloride solution electrolyte in the anode compartment is at a concentration of about 250 to 300 g./l., the pH of the anolyte is about 4.5, the temperatures of the electrolytes are in the range of 65* to 95*C., the membrane wall is from 0.1 to 0.3 mm. thick and the network is a screen or cloth of polytetrafluoroethylene filaments having a thickness of 0.01 to 0.3 mm. and having an area percentage of openings therein of 10 to 70 percent.

6. A method according claim 5 wherein after production of chlorate in the chlorate cell, a solution thereof is withdrawn from the cell, chloride is removed from it and chlorate is crystallized out and the chloride and mother liquor are returned to the anode compartment of the chlorine cell for electrolysis.