Diamond Shamrock Corporation

Stanley K Baczek

G Howard McCain

Michael J Covitch

Leo L Benezra

Craig S Warburton

An improved process for producing high purity caustic in a chlor/alkali cell utilizing a sulfonamide membrane allowing for improved current efficiency with approximately constant voltage by increasing the caustic concentration of the catholyte substantially above the normal level used in this type of cell.

Membrane cell at increased caustic concentration

Coatings made from soluable cross-linkable elastomers are shown. Particularly, techniques for solution cross-linking perfluorocarbon copolymers to generate resistant coatings for lining and coating applications are disclosed.

Method for making linings and coatings from soluble cross-linkable

Normally solid copolymers of a fluorinated vinyl monomer and a perfluorinated vinyl compound having a carboxyl and/or sulfonyl group attached directly to the perfluorinated vinyl group or indirectly through an alkyl or ether linkage have been found to be soluble in low molecular weight polymers of perhalogenated alkyl ethers, low molecular weight polymers of perhalogenated alkyls and perfluoro kerosenes, each of said solvent materials having boiling points between about 200.degree. C. and 350.degree. C. The copolymeric material dissolved in accordance with the instant invention can readily be resolidified by solvent removal and hydrolyzed or converted to the salt form to become a cation exchange material having an equivalent weight in the range of 1000 to 1600.

Method of making sheet or shaped cation exchange membrane

Normally solid copolymers of a fluorinated vinyl monomer and a perfluorinated vinyl compound having a carboxyl and/or sulfonyl group attached directly to the perfluorinated vinyl group or indirectly through an alkyl or ether linkage have been found to be soluble in low molecular weight polymers of perhalogenated alkyl ethers, low molecular weight polymers of perhalogenated alkyls and perfluoro kerosenes, each of said solvent materials having boiling points between about 200.degree. C. and 350.degree. C. The copolymeric material dissolved in accordance with the instant invention can readily be resolidified by solvent removal and hydrolyzed or converted to the salt form to become a cation exchange material having an equivalent weight in the range of 1000 to 1600. Membrane coated cathodes can be formed using the dissolved copolymeric material and may be made by casting or coating a foraminous cathode followed by removal of the solvent to result in a continuous, pore-free coating of membrane on the cathode. Multiple coatings or other techniques can be used to build up the desired thickness of the membrane. Reinforced membrane may be produced by similar manufacturing techniques wherein the casting or coating of the membrane is upon a reinforcing backing fabric, which can be polytetrafluoroethylene mesh or the like is first wrapped around the foraminous cathode. The copolymeric material which is used in making the membrane coated cathode can be a single material or it can be of various equivalent weights, structures (carboxyl or sulfonyl, mixtures of same, or can be layers of the same or different materials).

Method of depositing cation exchange membrane on a foraminous cathode

Normally solid copolymers of a fluorinated vinyl monomer and a perfluorinated vinyl compound having a carboxyl and/or sulfonyl group attached directly to the perfluorinated vinyl group or indirectly through an alkyl or ether linkage have been found to be soluble in low molecular weight polymers of perhalogenated alkyl ethers, low molecular weight polymers of perhalogenated alkyls and perfluoro kerosenes, each of said solvent materials having boiling points between about 200.degree. C. and 350.degree. C. The copolymeric material dissolved in accordance with the instant invention can readily be resolidified by solvent removal and hydrolyzed or converted to the salt form to become a cation exchange material having an equivalent weight in the range of 1000 to 1600. When these cation exchange materials in the salt form become damaged or contaminated during operation, for example in an electrochemical cell, they may now be reclaimed rather than discarded. The process involves conversion of the salt form of the cation exchanger to the precursor sulfonyl fluoride, carbonyl fluoride, sulfonate ester, or carboxylate ester form followed by dissolution in one of the solvents mentioned above. Dissolved impurities are then removed, e.g., by filtration, and the purified precursor cation exchange material in dissolved state may be shaped into the desired form by solvent removal and hydrolyzed back to the purified cation exchange polymeric material.

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Painesville, OH, United States of America

Stanley K Baczek