Ppg Industries, Inc.

Ppg Industries Ohio, Inc.

Bernard A Maloney

Donald W DuBois

Stanley R Pickens

Colonel R Dilmore

Thomas A Rechlicz

John E Carbaugh

Jerry N Kinney

A method of forming a liquid-permeable asbestos-free diaphragm for use in an electrolytic cell (e.g., a chlor-alkali cell) is described. The method comprises, (a) forming a liquid-permeable diaphragm base mat of asbestos-free material on a foraminous structure (e.g., a foraminous cathode structure); (b) drawing through the base mat a topcoat slurry comprising an aqueous medium (e.g., deionized water), water-insoluble inorganic particulate material (e.g., attapulgite clay) and alkali metal polyphosphate (e.g., tetrasodium pyrophosphate decahydrate); and (c) drying the formed diaphragm. The inorganic material of the topcoat slurry is deposited on and within the diaphragm base mat.

Method of preparing a diaphragm for an electrolytic cell

A method of operating a chlor-alkali electrolytic cell comprising a catholyte compartment containing a cathode, an anolyte compartment containing an anode, and a liquid-permeable diaphragm partitioning the catholyte and anolyte compartments, is described. The method comprises adding water-insoluble inorganic particulate material, e.g., clay mineral, and alkali metal polyphosphate, e.g., tetrasodium pyrophosphate, to the anolyte compartment of the electrolytic cell while the cell is operating. The water-insoluble inorganic particulate material and alkali metal polyphosphate may be added to the anolyte compartment in the form of an aqueous slurry.

Method of operating chlor-alkali electrolytic cells

A method of forming a liquid-permeable asbestos-free diaphragm on a cathode structure is described. The method comprises forming a liquid-permeable diaphragm base mat comprising fibrous synthetic polymeric material, e.g., polytetrafluoroethylene, on a cathode structure, e.g., a foraminous cathode; drawing a liquid slurry comprising an aqueous medium containing a wetting amount of surfactant and water-insoluble inorganic particulate material through the base mat, thereby to deposit said inorganic particulate material on and within the pre-formed base mat; and drying the resultant diaphragm at temperatures less than the temperature at which decomposition by-products of the surfactant are formed. The liquid slurry is substantially free of alkali metal halide and alkali metal hydroxide; and the inorganic particulate material comprises at least one oxide or silicate of a valve metal, e.g., zirconium oxide, having a median diameter of 0.1 to 5 micrometers, and optionally clay mineral and/or hydrous oxide of zirconium and/or magnesium. In a further embodiment of the present invention, the base mat is dried prior to deposition of the inorganic particulate material.

Diaphragm for electrolytic cell

Describes adding an anolyte soluble amphoteric material, e.g., an aluminum compound, to the anolyte of a chlor-alkali diaphragm cell having a synthetic diaphragm during the start-up period of the cell to reduce the permeability of the diaphragm. Complementary inorganic porosity modifying materials, e.g., magnesium materials such as magnesium chloride, and clays are also added to the anolyte during the start-up period of the cell.

Method for starting a chlor-alkali diaphragm cell

Disclosed is an improved method of making chlorine and alkali metal hydroxide, e.g., sodium hydroxide, in an electrolytic cell of the type wherein a liquid permeable diaphragm separates the anolyte from the catholyte, said method comprising adding to the anolyte, while the cell is operating, a hydrated aluminum silicate containing clay mineral, followed by lowering the pH of the anolyte by the addition of an inorganic acid and maintaining the anolyte at said lowered pH for a time sufficient to restore the cell to a predetermined current efficiency.

Method of operating chlor-alkali cells

A liquid permeable diaphragm for use in an electrolytic chlor-akali cell, the diaphragm being made of fibrous material and having deposited thereon and cementitiously bonded to the anode face thereof at least one topcoating of inorganic, particulate, refractory material. The interstices of the fibrous matrix of the diaphragm may also have particulate zirconia deposited therein.

Diaphragm for use in chlor-alkali cells

A process for the removal of essentially chromium-free sulfate from a chromate and sulfate-containing chlorate liquor which includes mixing the chlorate liquor having a pH of between about 2.0 and 6.0 with a calcium-containing material at a temperature and for a time sufficient to form a sulfate-containing precipitate predominantly of glauberite, Na.sub.2 Ca(SO.sub.4).sub.2, and separating the substantially chromium-free glauberite from the chlorate liquor.

Sulfate removal from alkali metal chlorate solutions

Disclosed is a method of starting up a permionic membrane chloralkali electrolytic cell by hydrolyzing the permionic membrane inside the cell. The permionic membrane is hydrolyzed by maintaining one side in contact with aqueous alkali metal hydroxide, and the opposite side in contact with aqueous alkali metal chloride, where the concentration of the alkali metal chloride is maintained low enough to avoid osmotic concentration of the alkali metal hydroxide solution.

Treatment of permionic membrane

Disclosed is a method of preparing an asbestos diaphragm containing a thermoplastic resin. According to the method disclosed herein, an asbestos mat is prepared by drawing the asbestos mat from a salt free, aqueous, asbestos slurry, providing the resin, and thereafter heating the mat to form the resin reinforced mat.

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Murrysville, PA, United States of America

Bernard A Maloney