Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/426—Fluorocarbon polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/20—Manufacture of shaped structures of ion-exchange resins
  • C08J5/22—Films, membranes or diaphragms
  • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
  • C08J5/2218—Synthetic macromolecular compounds
  • C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
  • C08J5/2237—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds containing fluorine
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/431—Inorganic material
  • H01M50/434—Ceramics
  • H01M50/437—Glass
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
  • H01M8/1023—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1039—Polymeric electrolyte materials halogenated, e.g. sulfonated polyvinylidene fluorides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1058—Polymeric electrolyte materials characterised by a porous support having no ion-conducting properties
  • H01M8/106—Polymeric electrolyte materials characterised by a porous support having no ion-conducting properties characterised by the chemical composition of the porous support
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
  • H01M8/1081—Polymeric electrolyte materials characterised by the manufacturing processes starting from solutions, dispersions or slurries exclusively of polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0002—Aqueous electrolytes
  • H01M2300/0014—Alkaline electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/429—Natural polymers
  • H01M50/4295—Natural cotton, cellulose or wood
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/44—Fibrous material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• This invention relates to improved methods for the production of foraminous cathodes having a continuous coating of cation exchange copolymers, reinforced and unreinforced, useful as separators in batteries and fuel cells as well as electrochemical cells such as chlor-alkali cells.
• Typical of the cation exchange copolymers involved in the instant invention are the fluorocarbon vinyl ether polymers disclosed in U.S. Patent 3,282,875. This patent discloses the copolymerization of fluorocarbon vinyl ethers having sulfonyl groups attached thereto with fluorinated vinyl compounds. Of the various copolymers listed in U.S. Patent 3,282,875 is the copolymer produced by the copolymerization of tetrafluoroethylene with perfluoro(3, 6-dioxa-4-methyl-7-octene sulfonyl fluoride). This is the base copolymer from which most of the membranes in commercial use today are made from.
• cation exchange resins useful in the instant invention are those described in U.S. Patent 3,718,627.
• the copolymer After polymerization of either of these materials of the prior art, the copolymer must be hydrolyzed to obtain its ion exchange character. Typically, such materials are treated with caustic to convert the sulfonyl halide group to the alkali metal salt thereof.
• These known perfluorocarbon-type cation exchange membranes containing only sulfonic acid groups have been found to have a disadvantage that when used in the electrolysis of an aqueous solution of an alkali metal halide, they tend to permit penetration there through of excessive hydroxyl ions by back migration from the cathode compartment because of the high hydrophilicity of the sulfonic acid group. As a result, the current efficiency during electrolysis at higher caustic concentrations is lower.
• the precursor resin to the cation exchange materials that is, the copolymeric material containing sulfonyl fluoride, carbonyl fluoride, sulfonate ester, or carboxylate esters
• a solvent selected from the group consisting of low molecular weight polymers of perhalogenated alkyl ethers, low molecular weight polymers of perhalogenated alkyls, and perfluoro kerosenes, each of said solvents having boiling points between about 200°C and 350°C.
• This precursor to the polymer containing ion exchange sites is referred to in the instant specification as the Intermediate polymer.
• Such intermediate polymer with high solvent loading readily permits many easily controlled processing techniques which result in more uniform end products formed from the intermediate polymer.
• solvent technique can employ spraying, dipping, rolling, painting and other coating techniques to produce uniform coatings of the intermediate polymer directly on foraminous cathodes or on matting material upon the cathode surface.
• laminar products containing different equivalent weight intermediate polymer can be utilized as well as laminar products containing different intermediate resins and/or different cation exchange groups.
• Copolymeric ion exchange materials are well known in the art. Typically, these are highly fluorinated resins containing sulfonic acid or carboxylic acid groups or salts thereof attached to the copolymer.
• the useful range of equivalent weights i.e., the weight of of resin/mole of cation exchange groups in said resin, found to be useful are generally in the range of 1000 to 1600.
• These highly fluorinated materials in this equivalent weight range however are extremely difficult to process since the highly fluorinated nature makes them somewhat akin to polytetrafluoroethylene which requires special processing techniques.
• the cation exchange materials are not processed in the ionic form, but rather in the precursor form referred to in this application as the intermediate polymer.
• intermediate polymer is meant the form of the copolymeric resin before it is converted to the ionic form.
• the sulfonyl portion of the molecule is in the sulfonyl fluoride or sulfonate ester form.
• the carboxyl group Is present it can be in the carbonyl fluoride or carboxylate ester form.
• This precursor or intermediate resin is thermoplastic or melt processable and, thus, prior art techniques for shaping and forming sheets or other shaped forms involved hot pressing, calendering, molding or the like techniques to bond individual particles of intermediate polymer together to result in the desired form or shape of material.
• the degree of freedom in such processing is extremely limited since the resulting material is quite heat sensitive and overheating in the forming step can, in fact, decrease the utility of the resulting cation exchange material.
• the intermediate polymer which serves as the precursor to the polymer containing Ion exchange sites is prepared from monomers which are fluorine-substituted vinyl compounds.
• the polymers include those made from at least two monomers with at least one of the monomers coming from each of the two groups described below.
• the first group comprises fluorinated vinyl compounds such as vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), tetrafluoroethylene and mixtures thereof.
• fluorinated vinyl compounds such as vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), tetrafluoroethylene and mixtures thereof.
• the second group Includes monomers containing or capable of being converted to cation exchange materials containing pendant sulfonic acid, carboxylic acid and less desirably phosphoric acid groups. Esters or salts which are capable of forming the same ion exchange groups can also be utilized. Furthermore, the monomers of the second group can also contain a functional group in which an ion exchange group can easily be Introduced and would include such groups as oxyacids, salts, or esters of carbon, nitrogen, silicon, phosphorus, sulfur, chlorine, arsenic, selenium, or tellurium.
• One of the preferred family of monomers in the second group is the sulfonyl containing monomers containing the precursor - - SO 2 F br - - SO 3 alkyl.
• the particular chemical content or structure of the radical linking the sulfonyl group to the copolymer chain is not critical and may have fluorine, chlorine or hydrogen atoms attached to the carbon atom to which is attached the sulfonyl group, although the carbon atom must have at least one fluorine atom attached. If the sulfonyl group is attached directly to the chain, the carbon in the chain to which it is attached must have a fluorine atom attached to it.
• the R, radical of the formula above can be either branched .or unbranched, i.e., straight chained, and can have one or more ether linkages.
• CF 2 CFOCF 2 CF 2 SO 2 F
• CF 2 CFCF 2 CF 2 SO 2 F
• the most preferred sulfonyl fluoride containing comonomer is perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride).
• the sulfonyl containing monomers are disclosed in such references as U.S. Pat. No. 3,282,875 to Connolly et al. and U.S. Pat. No. 3,041,317 to Gibbs et al, U.S. Pat. No. 3,560,568 to Resnick and U.S. Pat. No. 3,718,627 to Grot.
• the preferred intermediate copolymers are perfluorocarbon
• perfluorinated although others can be utilized as long as there is a fluorine atom attached to the carbon atom which is attached to the sulfonyl group of the polymer.
• the most preferred copolymer is a copolymer of tetrafluoroethylene and perfluoro(3, 6-dioxa-4-methyl-7-octenesulfonyl fluoride) which comprises 10 to 60 percent, preferably 25 to 40 percent by weight of the latter.
• the intermediate copolymer is prepared by general polymerization techniques developed for homo- and copolymerizations of fluorinated ethylenes, particularly those employed for tetrafluoroethylene which are described in the literature.
• Nonaqueous techniques for preparing the copolymers of the present invention include that of U.S. Pat. No. 3,041,317, to Gibbs et al. by the polymerization of the major monomer therein, such as tetrafluoroethyene, and a fluorinated ethylene containing sulfonyl fluoride in the presence of a free radical initiator, preferably a perfluorocarbon peroxide or azo compound, at a temperature in the range of 0° - 200° C.
• a free radical initiator preferably a perfluorocarbon peroxide or azo compound
• the nonaqueous polymerization may, if desired, be carried out in the presence of a fluorinated solvent.
• Suitable fluorinated solvents are inert, liquid, perflorinated hydrocarbons, such as perfluoromethylcyclohexane, perfluorodimethylcyclobutane, 1, 1, 2-trichlorotrifluoroethane, perfluorooctane, perfluorobenzene, and the like.
• Aqueous techniques for preparing the Intermediate copolymer include contacting the monomers with an aqueous medium containing a free-radical initiator to obtain a slurry of polymer particles in non-water-wet or granular form, as disclosed in U.S. Pat. No. 2,393,967 to Brubaker, contacting the monomers with an aqueous medium containing both a free-radical initiator and a telogenically inactive dispersing agent, to obtain an aqueous colloidal dispersion of polymer particles, and coagulating the dispersion, as disclosed, for example, in U.S. Pat. No. 2,559,752 to Berry and U.S. Pat. No. 2,593,583 to Lontz.
• Transformation of the intermediate polymer to a polymer containing ion exchange sites is by conversion of the sulfonyl groups ( - - SO 2 F or - - SO 3 alkyi)to -SO 3 X where X is hydrogen or alkali metal.
• the converted polymer is a fluorine containing polymer with a plurality of sulfonate groups present as ion exchange sites. These ion exchange sites will be contained in side chains of the polymer and will be attached to Individual carbon atoms to which are attached at least one fluorine atom.
• the conversion of the sulfonyl groups in the intermediate polymer to ion exchange sites may be in accordance with known techniques in the prior art, e.g., U.S. Pat. No. 3,770,567 to Grot and U.S. Pat. No. 3,784,399 to Grot.
• Another preferred family of monomers of the second group is the carboxyl containing monomers of the structure referred to previously in discussing the sulfonyl monomers wherein the carboxyl group replaces the sulfonyl group.
• the final copolymer contains one less carbon atom than the corresponding sulfonyl copolymer due to conversion process such as discussed in U.S. Pat. No. 4,151,053 (See Column 7, lines 37-64).
• Particularly preferred monomers in this group include
• CF 2 CF-O-CF 2 CF(CF 3 )O(CF 2 ) 2 COOCH 3
• Such monomers can be made in accordance with the teachings found in U.S. Pat. No. 4,151,053 or Japanese Published Patent Application 52(1977) 38486. Methods of copolymerization are likewise disclosed therein.
• the preferred soluble copolymer of the present invention is one which comprises 10-60%, more preferably 25-40% by weight of the second monomer so as to yield equivalent weights in the range of 1000 to 1600 or most preferably in the range of 1000-1300.
• the soluble fluoropolymer of the instant invention is also characterized by the presence of the carboxyl and/or sulfonyl groups represented by the formula:
• X is sulfonyl fluoride, carbonyl fluoride, sulfonate ester, or carboxylate ester and Y Is sulfonyl(-SO 2 -) or carbonyl (-CO-).
• the aforedescribed intermediate polymer can be dissolved only by use of the specific solvents disclosed hereinafter.
• the solvents useful in the present invention are low molecular weight polymers of perhalogenated alkyls and/or perhalogenated alkylethers having boiling points in the range of 200°C to 350°C. Particularly preferred are the oligomers or telomers of chlorotrifluoroethylene , - - (CF 2 -CFCl ) n - - wherein n is 5 to 15 having boiling points between about 200°C and 350°C, and perfluorokerosenes having boiling points between about 200°C and 350°C.
• Typical perhalogenated alkyi solvents available commercially are the "Halocarbon Oils" sold by Halocarbon Products Corp., Hackensack, New Jersey.
• Halocarbon Oil 11-14 and Halocarbon Oil 11-21 are Halocarbon Oil 11-14 and Halocarbon Oil 11-21.
• Similar solvents useful in the Instant Invention are the FLUOROLUBES® sold by Hooker Chemical Corporation, Niagara Falls, New York. Preferred among the FLUOROLUBES® are Fluorolube FS-5 and MO-10. Ugine Kuhlmann of Paris, France also offers low molecular weight polymers of chlorotrifluroethylene in their Voltalef® oil line. A typical solvent from this company useful in the present invention would be Voltalef® 10-S.
• One specific embodiment for the instant invention is in the conversion of diaphragm-type cells to membrane cells.
• the membrane separator for a standard diaphragm electrolytic cell electrode assembly and the method for forming such a membrane will overcome many of the disadvantages of the prior art forms listed above and yield the benefits of the use of a membrane in an electrolytic cell without the substantial capital cost associated heretofore with the conversion of a diaphragm electrolytic cell to a membrane electrolytic cell.
• Most of these diaphragm electrolytic cells in use today are of two general types. Both consist of an outer steel shell either cylindrical or rectangular which supports a cathode of perforated iron plate or woven Iron screen inside of the shell, generally referred to as a foraminous electrode element. This constitutes the cathode assembly.
• the actual cathode surfaces are generally lined with a layer of asbestos either in the form of paper wrapped around it or vacuum deposited fibers.
• the type of cathode assembly for which the present invention is especially useful is that known as the Diamond Shamrock Cell wherein the cathode assembly consists of a rectangular steel shell housing with an inner assembly of lateral rows of vertically flattened wire-screen tubes, upon which the diaphragm has been deposited by suction from a cell liquor suspension of asbestos fibers. Since these foraminous electrode assemblies generally have a high porosity it is necessary to reduce the porosity by vacuuming some type of matting material onto the foraminous electrode surface before applying a membrane material.
• the matting material may be an asbestos support made from chrysotile asbestos fibers mixed with 5% (by weight) fluorinated ethylene propylene copolymer particles, or any other material which will form a sufficient mat upon the foraminous electrode.
• Another example would be a cellulosic material.
• sheets of material such as filter paper could be wrapped around the electrode tube. It is believed that the exact nature of the matting material is not of great significance since it is generally of a temporary nature for the purpose of supporting the polymeric materials to form a film upon the foraminous electrode. It is believed that any depositable fiber with suitable thermal properties will serve as an adequate support structure, inertness to chlorine cell environments not being necessary.
• the thickness of the support structure affects the cell potential it Is desirable to obtain the thinnest matting structure consistent with the purpose of substantially reducing the porosity of the foraminous electrode material.
• One way of building a matting which is often used in industry is to suspend the matting material in a fluid medium and in the case of the asbestos fibers usually the cell liquor.
• the foraminous electrode material may then be suspended into the slurry of matting material and a vacuum pulled to the inside of the foraminous electrode material such that the fibers of the matting material will be drawn onto the surface of the foraminous electrode.
• This support structure will then provide a uniform surface on which the dissolved intermediate polymer can be applied.
• the support structure is no longer necessary and the film performs like a membrane on the cathode structure.
• the matting structure itself must have a low enough porosity to retain the dissolved intermediate polymer on the surface without being pulled to the interior portions of the matting material. This is easily controlled by controlling the degree of polymer loading or viscosity of the treating solution. In fact, the intermediate polymer in the dissolved state can be maintained at a high viscosity which minimizes the fineness required of the matting material, as compared to when the melt fabrication techniques of the prior art are utilized.
• Another preferred method is to paint the surface of the matting material, strip the solvent therefrom and repeat as often as needed to obtain a continuous sheet of intermediate polymer on the surface of the matting material.
• the openings in the cathode are small enough, no matting material is needed.
• a reinforcing fabric is utilized, often the openings in the reinforcing fabric are small enough to overcome the need for a matting material when practicing the instant invention.
• the film may then be hydrolyzed into the infusible ion exchange form.
• Hydrolyzing or saponifying of the intermediate polymer is a fairly simple procedure for the conversion of the sulfonyl form, or carboxyl form to the ionic form. This may be accomplished by soaking the coated cathode in a sodium hydroxide solution, sodium hydroxide in dimethyl sulfoxide solution, potassium hydroxide solution, or potassium hydroxide in dimethyl sulfoxide solution. Any of these treatments appear to work equally well although different temperatures and times are required to accomplish the hydrolysis.
• the electrode is then ready for use in a standard diaphragm electrolytic cell. The conditions of the cell should be altered to operate the cell as a membrane electrolytic cell.
• the resultant membrane electrolytic cell will yield a high current density, a lower sodium chloride concentration in the resultant sodium hydroxide solution compared to that of standard diaphragm cell, a higher resultant sodium hydroxide concentration, good utilization of existing cell space, longer life for cell and a lower potential.
• the advantages of the present invention to the chlorine and caustic industry will recognize the advantages of the present invention to the chlorine and caustic industry.
• the deposited membrane has been described as a single type material.
• the membrane coating on the cathode can be built up of various layers of membrane material having different equivalent weights or different chemical structures, as for example, separate layers of carboxylic and sulfonate type membrane.
• Such membranes are made by merely laying down a continuous surface of the desired membrane material and stripping the solvent therefrom.
• membrane contemplated by the Instant invention may be aminated, as with ammonia, monoamines or diamines. Normally such modification is on the cathodic side of the membrane and this also minimizes back migration of hydroxyl ions, improving efficiency of the cell.
• Preferred amination is with ethylene diamine, n-propylamine or ethyl amine and such amination is applied to the cathodic side of the membrane through the cathode after deposition of the membrane material on the cathode.
• Typical examples of the solution coatings of the instant invention are as follows;
• Two 2.5" diameter circular cathodes fabricated from 6-mesh steel screens were fastened tightly together by means of a 3/8 ⁇ 1/4" diameter stud threaded into nuts welded flush into their centers.
• the assembled pair of screens was dipped into a solution of 61 grams of 1200 equivalent weight intermediate resin copolymer of tetrafluoroethylene and perfluoro(3,6-dloxa-4-methyl-7-octenesulfonyl fluoride) in 549 grans Fluorolube FS-5, at 245°C with a dwell time of less than 5 seconds.
• the coated screens were placed in a vapor phase extractor and extracted with methylene chloride for 24 hours.
• the cell When operated in a membrane mode for the electrolysis of aqueous sodium chloride, the cell produced sodium hydroxide at 368 grams per liter concentration with a current efficiency of 80 percent at a cell potential of 3.48 volts (2 asi current density, 90°C).
• cathode screen was placed in a special cylindrical funnel with an internal diameter slightly greater than the diameter of the cathode and having a capacity of about 200 ml.
• a thin cellulose web was deposited on the electrode screen by gravity draining a suspension of 0.5 gram of pulped Whatman #41 filter paper In about 200 ml of water through the steel grid.
• the coated cathode was dried at 100°C for 4 hours, giving a cellulose web density of about 0.15 g/in 2 of cathode surface.
• the back of the cathode was then blanked off by covering it with a 2.25" diameter washer secured by a nut to the center stub and separated from the mesh by a gasket formed from 1/8" Gore-Tex® (W. L.
• Example 1 After ethylene diamine treatment and hydrolysis as in Example 1, the deposited membrane was tested in the laboratory electrolysis cell of Example 1. It produced, under standard conditions (2 asi current density, 90°C), 377 grams per liter sodium hydroxide with a current efficiency of 90.2 percent and a cell potential of 3.52 volts.
• Example 2 was repeated using a cathode coated with chopped Kevlar® fiber (E. I. duPont de Nemours brand of aramide polymer) with a web density of 0.1 g/in 2 and an intermediate resin thickness of 11 mils.
• Kevlar® fiber E. I. duPont de Nemours brand of aramide polymer
• Example 2 was repeated using a cathode coated with Teflon fibrids at a web density of 0.24 g/in 2 and and intermediate resin thickness of 6 mils. After ethylene diamine treatment and hydrolysis, it produced
• Example 2 was repeated using a cathode coated with glass fibers
• a cathode with cellulose precoat (web density of about 0.3 g/in 2 ) was prepared as in Example 2 and dipped In the carboxy intermediate resin solution, used in Example 5 above, at 226°C for 10 seconds. After drying at 225°C for 15 minutes in a mechanical convection oven, the cathode was redipped in intermediate resin solution of Example 6. The resulting laminate was extracted, dried and hydrolyzed as in Example 2 (total resin thickness prior to hydrolysis was about 10 mils). Under standard conditions (2 asi current density, 90°C), in the electrolysis cell of Example 1, it produced 414 grams per liter sodium hydroxide at 81.4 percent current efficiency at a cell potential of 3.91 volts.
• Example 7 was repeated using as a substrate a 71/29(wt) mixture of glass and carbon fibers (web density about 0.1 g/in 2 ). This laminate gave 440 grams per liter sodium hydroxide at a current efficiency of 79.5 percent with a cell potential of 5.96 volts (2 asi current density, 90°C) when tested in the electrolysis cell of Example 1.
• Example 2 was repeated using 1/4" long chopped rayon fiber as a substrate (web density about 0.15 g/in 2 ) and the intermediate resin solution of Example 6 above. After ethylene diamine treatment and hydrolysis, the deposited membrane was tested in the electrolysis cell of Example 1. Under standard conditions (2 asi current density,
• the solvents of the instant invention are capable of dissolving completely depending on equivalent weight the Intermediate polymer up to about 30 weight percent when the intermediate polymer is In the sulfonyl fluoride, carbonyl fluoride, sulfonate ester, or carboxyl ester form.
• the appropriate amount of intermediate polymer and solvent are mixed and heated to temperatures below the boiling point of the solvent. Typically, the heating Is usually done to temperatures in the range of 220°C to 260°C. Using these temperatures, total dissolution of the intermediate polymer takes place anywhere up to 24 hours, depending upon equivalent weight temperature, degree of polymer loading and agita tion.
• the intermediate polymer may be applied to cathode to form membrane coatings of any possible dimension and returned to the solid state merely by stripping off the solvent
• Fabric reinforcement such as Teflon fabrics of various weave, degrees of openness and surface preparations can also be encapsulated in the same manner resulting in a stress-free, reinforced membrane of closely controlled uniform thickness.
• reinforcing fabrics can be dipped into these hot solutions of dissolved intermediate polymer. Multiple dippings can be used if thicker membranes are desired.
• the coated reinforcing cloth on the foraminous cathode may then be dipped into methylene chloride or other given solvent for the preferred chlorotrifluoroethylene telomer solvent, and after a period of time, removed and allowed to dry in air and then placed in an oven for thermal treatment.
• the thermal treatment Is for the purpose of removing any remaining methylene chloride and we have found that treatment at 100°C for four hours followed by a slow temperature rise over approximately a 3-hour period to 220°C is completely satisfactory.
• the previously discussed extraction method using methylene chloride is most useful in the systems wherein the intermediate polymer is in the sulfonyl form.
• the resulting film or reinforced membrane may be cured directly by heating at 225°C for a very short time, as for example, one to fifteen minutes. Prior to the heating, the film or reinforced membrane is cloudy, due to the inclusion of solvent. However, after the heating, the film cloudiness disappears.
• Asymmetric membranes may also be prepared by the above-described techniques, such as by multiple dipping.
• various equivalent weight laminates and asymmetric carboxylic/sulfonate or sulfonamide laminates may be prepared.
• purification of the surface between coatings may be utilized if desired Purification of the surface can be made using Freon-type solvents, but such purification is not necessary.
• the preferred loading of the solutions of the instant invention are those that contain from 1 to 30 weight percent intermediate polymer, as these are easily used in most forming techniques.

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