Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/44—Ion-selective electrodialysis
  • B01D61/46—Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0002—Organic membrane manufacture
  • B01D67/0006—Organic membrane manufacture by chemical reactions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
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  • B01D69/10—Supported membranes; Membrane supports
  • B01D69/106—Membranes in the pores of a support, e.g. polymerized in the pores or voids
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D69/10—Supported membranes; Membrane supports
  • B01D69/107—Organic support material
  • B01D69/1071—Woven, non-woven or net mesh
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D69/12—Composite membranes; Ultra-thin membranes
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  • B01D69/1213—Laminated layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D71/06—Organic material
  • B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
  • B01D71/82—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74 characterised by the presence of specified groups, e.g. introduced by chemical after-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J39/00—Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
  • B01J39/04—Processes using organic exchangers
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J39/08—Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
  • B01J39/16—Organic material
  • B01J39/18—Macromolecular compounds
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  • B01J41/00—Anion exchange; Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
  • B01J41/04—Processes using organic exchangers
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J41/00—Anion exchange; Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
  • B01J41/08—Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
  • B01J41/12—Macromolecular compounds
  • B01J41/14—Macromolecular compounds obtained by reactions only involving unsaturated carbon-to-carbon bonds
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J47/00—Ion-exchange processes in general; Apparatus therefor
  • B01J47/12—Ion-exchange processes in general; Apparatus therefor characterised by the use of ion-exchange material in the form of ribbons, filaments, fibres or sheets, e.g. membranes
• • 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
• • 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
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  • 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
• • C—CHEMISTRY; METALLURGY
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  • 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
  • C08J5/2243—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds obtained by introduction of active groups capable of ion-exchange into compounds of the type C08J5/2231
• • C—CHEMISTRY; METALLURGY
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  • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
  • C08J5/2275—Heterogeneous membranes
• • C—CHEMISTRY; METALLURGY
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  • C08J5/22—Films, membranes or diaphragms
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• • 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
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/02—Diaphragms; Spacing elements characterised by shape or form
• • 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
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
  • C25B13/08—Diaphragms; Spacing elements characterised by the material based on organic materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
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  • B01D2323/46—Impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/42—Ion-exchange membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/44—Ion-selective electrodialysis
  • B01D61/445—Ion-selective electrodialysis with bipolar membranes; Water splitting
• • C—CHEMISTRY; METALLURGY
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  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2325/00—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 an aromatic carbocyclic ring; Derivatives of such polymers
  • C08J2325/02—Homopolymers or copolymers of hydrocarbons
  • C08J2325/04—Homopolymers or copolymers of styrene
  • C08J2325/06—Polystyrene
• • C—CHEMISTRY; METALLURGY
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  • C08J2325/04—Homopolymers or copolymers of styrene
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• • C—CHEMISTRY; METALLURGY
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• • C—CHEMISTRY; METALLURGY
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  • C08J2325/18—Homopolymers or copolymers of aromatic monomers containing elements other than carbon and hydrogen
• • C—CHEMISTRY; METALLURGY
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• • 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
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  • Y02E60/50—Fuel cells

Definitions

• This invention relates to a bipolar membrane obtained by sticking a cation-exchange membrane and an anion-exchange membrane together, and to a method of producing the same. More specifically, the invention relates to a bipolar membrane having improved adhesiveness between the cation-exchange membrane and the anion-exchange membrane, and having an improved current efficiency, and to a method of producing the same.
• the bipolar membrane is a composite membrane obtained by sticking a cation-exchange membrane and an anion-exchange membrane together, and has a function of dissociating water into protons and hydroxide ions.
• the bipolar membrane is set in an electrodialyzer together with a cation-exchange membrane and/or an anion-exchange membrane, and the electrodialysis is executed to produce an acid and an alkali from a neutral salt.
• the above bipolar membrane requires a high degree of adhesiveness, specifically, between the cation-exchange membrane and the anion-exchange membrane.
• the electrodialysis can be executed while effectively preventing the membranes from swelling, without permitting the membranes to be peeled off and maintaining stability.
• a patent document 1 discloses a bipolar membrane whose at least either the cation-exchange membrane or the anion-exchange membrane contains a chlorinated polyolefin.
• the above bipolar membrane has a high adhesiveness between the cation-exchange membrane and the anion-exchange membrane, and features excellent stability at the time of electrodialysis. From the standpoint of current efficiency, however, there still remains a room for improvement.
• an object of the present invention to provide a bipolar membrane in which a cation-exchange membrane and an anion-exchange membrane are firmly adhered together, and exhibiting an excellent current efficiency even under high-temperature conditions, and a method of producing the same.
• a bipolar membrane in which a cation-exchange membrane and an anion-exchange membrane are joined to each other,
• a leakage ratio of gluconic acid at 60° C. is not more than 1.0%
• the cation-exchange membrane is supported by a polyolefin reinforcing member and, further, contains a polyvinyl chloride.
• An area ratio of a portion where the cation-exchange membrane and the anion-exchange membrane are peeled off is not more than 20% after the bipolar membrane is dipped in a 6N sodium hydroxide aqueous solution of 25° C. for one hour and then in pure water of 25° C. for another one hour; and (2)
• the cation-exchange membrane contains the polyvinyl chloride in an amount of 10 to 45% by mass.
• a method of producing a bipolar membrane including a step of forming a cation-exchange membrane, and
• the step of forming the cation-exchange membrane includes:
• the method of production includes a step of impregnating a polyolefin reinforcing member with the polymerizable composition obtained by mixing the polyvinyl chloride (A) and a monomer (b1) having a cation-exchange group, and the step of forming a membrane of the cation-exchange resin that contains the polyvinyl chloride by the polymerization curing at a temperature of not lower than 100° C.; and (2) The method of production includes a step of impregnating a polyolefin reinforcing member with the polymerizable composition obtained by mixing the polyvinyl chloride (A) and the monomer (b2) having a reaction group capable of introducing a cation-exchange group, a step of forming a membrane of the cation-exchange resin precursor resin by the polymerization curing at a temperature of not lower than 100° C., and a step of introducing a cation-exchange group by acting a cation-exchange group introducing agent
• the step of forming the anion-exchange membrane on the surface of the cation-exchange membrane includes a step of applying a polar organic solvent solution of the anion-exchange resin on the surface of the cation-exchange membrane, and a step of removing the polar organic solvent;
• the step of forming the anion-exchange membrane on the surface of the cation-exchange membrane includes a step of applying, on the surface of the cation-exchange membrane, a polar organic solvent solution of an anion-exchange resin precursor resin having a reaction group capable of introducing the anion-exchange group, a step of forming a membrane of the anion-exchange resin precursor resin on the surface of the cation-exchange membrane by removing the polar organic solvent, and a step of introducing the anion-exchange group into the anion-exchange resin precursor resin; or (5) The step of forming the anion-exchange membrane on the surface of the cation-exchange membrane, further, includes a step of applying a
• the present invention is concerned to a bipolar membrane which uses a cation-exchange membrane as the exchange base membrane (hereinafter also referred to as “cation-exchange base membrane”).
• a solution for forming an anion-exchange resin is applied onto the surface of the cation-exchange base membrane, and the solvent is removed from the layer that is applied in order to form an anion-exchange membrane.
• the cation-exchange base membrane is the one that is obtained by impregnating a polyolefin reinforcing member with a polymerizable composition that contains a polymerization-curable component for forming a cation-exchange resin and a polyvinyl chloride, followed by curing by polymerization.
• the cation-exchange base membrane contains the polyvinyl chloride. This makes it possible to attain both a strong adhesion between the anion-exchange membrane and the cation-exchange membrane and an excellent electric current efficiency under a high temperature condition (60° C.). The reasons for this will now be described in detail.
• the polyvinyl chloride works as a resin for adhering the cation-exchange base membrane and the anion-exchange membrane together. Namely, the polyvinyl chloride exhibits a high degree of affinity to the polymerization-curable component (B) (e.g., styrene, divinylbenzene, etc.) that is used for forming the cation-exchange base membrane, to the cation-exchange resin (e.g., a resin having a specific skeleton that will be described later) or to the precursor resin thereof (e.g., a precursor resin having a specific skeleton that will be described later) and, besides, is highly compatible with various polar organic solvents.
• B polymerization-curable component
• the cation-exchange resin e.g., a resin having a specific skeleton that will be described later
• precursor resin thereof e.g., a precursor resin having a specific skeleton that will be described later
• the polyvinyl chloride has its high molecular chain (specifically, amorphous portion) entangled with a high molecular chain of the cation-exchange resin in the cation-exchange base membrane, and forms a structure that cannot be easily separated from the cation-exchange membrane.
• the polyvinyl chloride present in the cation-exchange base membrane migrates partly into the solvent that forms the anion-exchange resin due to the polar solvent contained in the solvent for forming the anion-exchange resin.
• the polyvinyl chloride is made present in the interface between the cation-exchange base membrane and the anion-exchange membrane in a form being engaged with both membranes.
• the polyvinyl chloride exhibits a high degree of anchoring effect, and the adhesiveness is markedly improved between the two membranes.
• the polyvinyl chloride is added to the anion-exchange membrane, then the polyvinyl chloride does not migrate insufficiently into the cation-exchange base membrane that has been polymerized and cured, and a strong adhesiveness is not obtained.
• the present inventors have discovered that with the cation-exchange base membrane provided with a reinforcing member such as polyolefin woven fabric, the junction was poor between the reinforcing member and the cation-exchange resin, and gaps developed in the interface between the reinforcing member and the cation-exchange resin permitting, therefore, the anions such as hydroxide ions to pass through the gaps and through the cation-exchange membrane during the electrodialysis.
• a reinforcing member such as polyolefin woven fabric
• Such unwanted motion of anions means that an electric current flows without contributing to the hydrolysis reaction at the time of electrodialysis and, therefore, forming the acid and alkali in relatively decreased amounts despite of the amount of electricity that is used causing, therefore, a decrease in the electric current efficiency.
• the chlorinated polyolefin and the cation-exchange resin undergo the separation in phase in the cation-exchange base membrane, causing the chlorinated polyolefin to agglomerate or, in other words, causing the chlorinated polyolefin to be no longer dispersed homogeneously.
• the chlorinated polyolefin is present in decreased amounts in the interface between the anion-exchange membrane and the cation-exchange membrane, the adhesiveness is lost, and the strength of the membrane decreases.
• the present invention does not use the chlorinated polyolefin but, instead, uses the polyvinyl chloride. Even when the cation-exchange resin is formed by the polymerization under such a high temperature condition that the polyolefin reinforcing member partly melts, the polyvinyl chloride does not undergo the phase separation and disperses homogeneously in the cation-exchange resin. This is because the polyvinyl chloride exhibits very higher affinity to the monomer component used for forming the cation-exchange base membrane and to the cation-exchange resin in the membrane and very higher compatibility to various polar solvents than those exhibited by the chlorinated polyolefin.
• the present invention realizes both strong adhesion between the anion-exchange membrane and the cation-exchange membrane and excellent electric current efficiency.
• the Examples appearing later are demonstrating that when the electrodialysis is executed under a high temperature condition (60° C.), the leakage ratio of gluconic acid is suppressed to be not more than 1.0%, proving that anions such as gluconic acid ions are effectively suppressed from passing through the cation-exchange membrane.
• the bipolar membrane of the present invention uses a cation-exchange membrane as the exchange base membrane, and has the anion-exchange membrane formed on one surface of the cation-exchange base membrane.
• the cation-exchange base membrane is supported by the polyolefin reinforcing member and contains the polyvinyl chloride.
• polyvinyl chloride (A) there can be used any known ones without limitation. For instance, there can be used not only a homopolymer of vinyl chloride monomer but also copolymers copolymerized with other monomers so far as they do not impair the properties of the polyvinyl chloride or the object of the invention. As other monomers that are copolymerizable, there can be exemplified ⁇ -olefins such as ethylene, propylene, etc. and vinyl esters such as vinyl acetate, etc. These polyvinyl chlorides may be used alone or in a combination of two or more kinds, as a matter of course.
• the chlorine content of the polyvinyl chloride (A) is in a range of, desirably, 30 to 80% by mass and, specifically, 55 to 70% by mass.
• the polyvinyl chloride (A) having a chlorine content in this range has a high degree of affinity to the polar solvent, and works advantageously in the mechanism of adhesion.
• the polyvinyl chloride has a high softening point, e.g., has a Crash Berg flexible temperature (JIS K6734) of not lower than 60° C. and, more preferably, not lower than 65° C.
• the polyvinyl chloride that lies within the above range is capable of holding a high degree of adhesiveness even under high temperature conditions.
• the polyvinyl chloride has a low bipolar voltage, and does not cause the membrane to peel off even during the electrodialysis under high temperature conditions enabling, therefore, the electrodialysis to be executed maintaining stability.
• the polyvinyl chlorides in general, have Crash Berg flexible temperatures of not higher than 70° C.
• the polyvinyl chloride (A) has an average polymerization degree which usually lies in a range of 500 to 3,000 and, specifically, 800 to 2,000.
• the longer the molecular chain of the polyvinyl chloride the larger the degree of entanglement with the molecules of the cation-exchange resin and the higher the degree of adhesiveness.
• too long molecular chains cause a decrease in the solubility thereof in a solvent, and migration into the anion-exchange resin decreases. As a result, the entanglement becomes loose in the interface between the two membranes, and the adhesiveness decreases between the two membranes. If the average polymerization degree lies within the above-mentioned range, an improved adhesiveness is achieved and, therefore, a bipolar membrane is obtained having a low bipolar voltage.
• the polyvinyl chloride (A) can be put to use in a known form such as powder, pellets or the like. Among them, however, the powdery form is preferred and, more preferably, the powdery form having an average particle size of 0.1 to 30 ⁇ m as measured by the laser diffraction ⁇ light scattering method.
• the powdery polyvinyl chloride has good affinity to the cation-exchange resin (e.g., resin having a specific skeleton that will be described later) or to a precursor resin thereof (e.g., precursor resin having a specific skeleton that will be described later), and can be homogeneously dispersed.
• the powdery polyvinyl chloride can be obtained by a known suspension polymerization method.
• the polyvinyl chloride (A) may be contained in the cation-exchange base membrane. This is because, as described above, the cation-exchange base membrane that is blended with the polyvinyl chloride exhibits the effect for improving adhesiveness more than the anion-exchange membrane. It is allowable, of course, for the anion-exchange membrane to contain the polyvinyl chloride in a range in which it does not impair the properties of the bipolar membrane of the present invention.
• the polyvinyl chloride (A) is polymerized in a state of being made compatible with the monomer (b1) having a cation-exchange group, with the monomer (b2) having a reaction group capable of introducing the cation-exchange group, or with a crosslinking monomer.
• the polyvinyl chloride (A) therefore, is present in a state of being entangled with the molecular chain of the cation-exchange resin.
• the polyvinyl chloride (A) is effectively prevented from separating, and a particularly improved adhesiveness is obtained.
• the polyvinyl chloride (A) is contained in the cation-exchange membrane that contains the cation-exchange resin that is obtained, specifically, by sulfonating a styrene-divinylbenzene copolymer.
• the styrene-divinylbenzene copolymer is obtained by the polymerization of a monomer such as styrene having a very high degree of affinity to the polyvinyl chloride or by the polymerization of a crosslinking component such as divinylbenzene.
• the polyvinyl chloride (A) is contained in the cation-exchange base membrane in an amount of, preferably, 10 to 45% by mass, more preferably, 15 to 35% by mass and, particularly preferably, 20 to 30% by mass (on the dry weight basis). If the amount of the polyvinyl chloride is too small, the effect is not sufficient for improving the adhesiveness between the cation-exchange base membrane and the anion-exchange membrane. If the amount thereof is too large, on the other hand, the resistance of the membrane so increases as to cause such an inconvenience as a rise in the bipolar voltage.
• the invention can use a cation-exchange membrane known per se. as the cation-exchange base membrane.
• the cation-exchange base membrane has a polyolefin reinforcing member which imparts strength and heat resistance to the bipolar membrane.
• polystyrene resin there can be exemplified homopolymers of ⁇ -olefins, such as ethylene, propylene, 1-butene and 4-methyl-1-pentene, or random or block copolymers thereof.
• ⁇ -olefins such as ethylene, propylene, 1-butene and 4-methyl-1-pentene, or random or block copolymers thereof.
• low-density polyethylene high-density polyethylene, polypropylene, poly (1-butene) and poly (4-methyl-1-pentene).
• low-density polyethylene, high-density polyethylene and polypropylene are preferred.
• the polyethylene type polymers are most desirably used, such as low-density polyethylene and high-density polyethylene.
• the polyolefin reinforcing member may assume any form such as woven fabric, nonwoven fabric or porous film but, preferably assumes the form of the woven fabric from the standpoint of strength.
• the filament of the woven fabric may be in the form of either a multi-filament or a mono-filament. The mono-filament, however, is preferred from the standpoint of strength.
• the polyolefin woven fabric has a thickness which is, usually, 50 to 500 ⁇ m and, preferably, 100 to 300 ⁇ m, and the filament has a thickness of, specifically, 10 to 250 deniers (20 to 200 ⁇ m) from the standpoint of taking a balance between the strength and the membrane resistance.
• the cation-exchange resin for forming the cation-exchange membrane there can be used any one that has been known per se.
• a resin having a specific skeleton or a precursor resin that forms the specific skeleton and in which a cation-exchange group has been introduced there can be used.
• the precursor resin for forming the specific skeleton there can be exemplified polymers obtained by polymerizing a monomer having an ethylenically unsaturated double bond such as of vinyl type, styrene type or acryl type, and copolymers thereof; and hydrocarbon type resins having an aromatic ring on the main chain thereof, such as polysulfone, polyphenylene sulfide, polyether ketone, polyether ether ketone, polyether imide, polyphenylene oxide, polyether sulfone, and polybenzimidazole.
• a monomer having an ethylenically unsaturated double bond such as of vinyl type, styrene type or acryl type, and copolymers thereof
• hydrocarbon type resins having an aromatic ring on the main chain thereof such as polysulfone, polyphenylene sulfide, polyether ketone, polyether ether ketone, polyether imide, polyphenylene oxide, polyether sul
• the cation-exchange group if it is a reaction group that is capable of turning into a negative charge in an aqueous solution.
• sulfonic acid group carboxylic acid group and phosphonic acid group.
• sulfonic acid group that is a strong acid group.
• the cation-exchange base membrane may be produced according to a method known per se. Representative methods include a method of impregnating the polyolefin reinforcing member with a polymerizable composition which contains the polyvinyl chloride (A) and the polymerization-curable component (B) that contains the monomer (b1) having a cation-exchange group, and forming a membrane of the cation-exchange resin by polymerizing and curing the polymerizable composition (hereinafter often called “method I”), and a method of impregnating the polyolefin reinforcing member with a polymerizable composition which contains the polyvinyl chloride (A) and the polymerization-curable component (B) that contains the monomer (b2) having a reaction group capable of introducing a cation-exchange group, forming a membrane of the cation-exchange resin precursor resin by polymerizing and curing the polymerizable composition, and introducing a cation-exchange group
• the method I will be described, first.
• This method is capable of forming a membrane of the cation-exchange resin which is the same as the resin obtained by introducing a cation-exchange group into the precursor resin that has the specific skeleton by simply polymerizing and curing the polymerizable composition without requiring the step of separately introducing the cation-exchange group.
• the polymerizable composition is prepared by mixing together the polyvinyl chloride (A) and the polymerization-curable components (B) for forming the cation-exchange resin, such as the monomer (b1) having a cation-exchange group, a crosslinking monomer and a polymerization initiator.
• the polymerizable composition is filled in the gaps in the polyolefin reinforcing member which is in the form of a woven fabric and is, thereafter, polymerized and cured to form the cation-exchange resin. There is thus obtained the desired cation-exchange base membrane.
• the polymerization-curing temperature is nearly so set that the polyolefin reinforcing member melts.
• the lower limit of the polymerization-curing temperature is, usually, a melting point minus 40° C. and, preferably, a melting point minus 20° C. of the polyolefin that constitutes the reinforcing member
• the upper limit of the polymerization-curing temperature is a melting point plus 20° C. and, preferably, a melting point plus 5° C. thereof.
• the lower limit of the polymerization-curing temperature is 100° C. and, preferably, 110° C.
• the upper limit thereof is, preferably, 160° C. If the polymerization is executed at an excessively low temperature, then gaps are made present in the interface between the polyolefin reinforcing member and the cation-exchange resin, and the current efficiency may decrease. If the temperature is too high, on the other hand, the polyolefin reinforcing member may once melt completely, and the strength of the obtained cation-exchange base membrane may decrease strikingly.
• the monomer (b1) having the cation-exchange group contained in the polymerization-curable component (B) may be the one that has heretofore been used for producing the cation-exchange resin.
• sulfonic acid type monomers such as ⁇ -halogenated vinyl sulfonate, styrene sulfonate and vinyl sulfonate
• carboxylic acid type monomers such as methacrylic acid, acrylic acid and maleic anhydride
• phosphonic acid type monomers such as vinyl phosphonate and the like
• salts and esters of the above monomers such as sodium phosphonate and the like.
• the crosslinking monomer is used for densifying the cation-exchange resin, for suppressing the swelling and for increasing the membrane strength, and no specific limitation is imposed thereon.
• the crosslinking monomer is used in an amount of, preferably, 0.1 to 50 parts by mass and, more preferably, 1 to 40 parts by mass per 100 parts by mass of the monomer (b1) that has the cation-exchange group.
• the other monomers there may be added, as required, other monomers capable of copolymerizing with the above monomers.
• the other monomers there can be used styrene, chloromethylstyrene, acrylonitrile, methylstyrene, ethylvinylbenzene, acrolein, methyl vinyl ketone and vinylbiphenyl.
• the amounts of the other monomers may differ depending on the object of addition. Usually, however, the other monomers are added in a total amount of 0 to 100 parts by mass per 100 parts by mass of the monomer (b1) that has the cation-exchange group.
• the other monomers are added in amounts of 1 to 80 parts by mass and, specifically, 5 to 70 parts by mass.
• the polymerization initiator there can be used those known per se. without any limitation. Concretely, there are used organic peroxides such as octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethyl hexanoate, benzoyl peroxide, t-butylperoxyisobutylate, t-butylperoxylaurate, t-hexylperoxybenzoate, di-t-butylperoxide and 1,3,3-tetramethylbutylhydroperoxide.
• the polymerization initiator is used in an amount of, preferably, 0.1 to 20 parts by mass and, more preferably, 0.5 to 10 parts by mass per 100 parts by mass of the monomer (b1) that has the cation-exchange group.
• the polymerizable composition is prepared by blending the above polymerization-curable component (B) with the polyvinyl chloride (A) so that the cation-exchange membrane that is finally obtained will possess the above-mentioned composition.
• the polyvinyl chloride may be stirred together with the polymerization-curable component (B) at room temperature such that a homogeneously mixed polymerizable composition is obtained.
• the polyvinyl chloride may be stirred and mixed together with the polymerization-curable component (B) at a temperature at which the polymerization-curable component (B) does not undergo the polymerization or, concretely, at a temperature of not higher than 50° C.
• the polymerizable composition may, as required, contain a chlorinated polyolefin, a thickener and known additives.
• chlorinated polyolefin there can be exemplified a chlorinated polyolefin that is closely described in, for example, the patent document 1. Though dependent upon the kinds of the cation-exchange base membrane and the anion-exchange membrane, addition of the chlorinated polyolefin further increases the adhesiveness. The amount of addition thereof is 0 to 10 parts by mass per 100 parts by mass of the polyvinyl chloride (A).
• the thickener there can be used saturated aliphatic hydrocarbon type polymers such as ethylene-propylene copolymer and polybutylene; styrene type polymers such as styrene-butadiene copolymer and the like; and polyolefin powder having an average particle size of not more than 10 ⁇ m.
• saturated aliphatic hydrocarbon type polymers such as ethylene-propylene copolymer and polybutylene
• styrene type polymers such as styrene-butadiene copolymer and the like
• polyolefin powder having an average particle size of not more than 10 ⁇ m.
• plasticizers such as dioctyl phthalate, dibutyl phthalate, tributyl phosphate, styrene oxide, tributyl acetylcitrate, or alcohol esters of fatty acid or aromatic acid; and hydrochloric acid-trapping agents such as ethylene glycol diglycidyl ether and the like.
• Impregnation with the polymerizable composition can also be executed by such a method as spray coating or application by using a doctor blade in addition to the dipping.
• the polymerizable composition with which the polyolefin reinforcing member is impregnated as described above is heated in a polymerization apparatus such as heating oven, and is polymerized and cured.
• the step of polymerization in general, a method is employed in which the polyolefin reinforcing member impregnated with the polymerizable composition is held by a polyester film, and the temperature thereof is elevated starting from the normal temperature under a pressurized condition.
• the pressure is, usually, about 0.1 to 1.0 MPa, and is produced by using an inert gas such as nitrogen or by using a roll. Due to the application of pressure, the polymerization is carried out in a state where an excess of the polymerizable composition present on the outer interface of the polyolefin reinforcing member is pushed into voids in the polyolefin reinforcing member, effectively preventing the occurrence of resin reservoirs.
• polymerization-curable component (B) Other polymerization conditions vary depending on the kind of the polymerization-curable component (B), and should be suitably selected from the known conditions and determined.
• the polymerization temperature is set, as described above, to be such that the polyolefin reinforcing member partly melts.
• the polymerization time is, usually, about 3 to about 20 hours though dependent upon the polymerization temperature and the like.
• the cation-exchange base membrane is formed by using a polymerization-curable component for forming the cation-exchange resin precursor resin instead of using the polymerization-curable component for forming the cation-exchange resin used in the method I.
• the cation-exchange base membrane is prepared by blending the polymerizable composition with the monomer (b2) having a reaction group capable of introducing the cation-exchange group instead of the monomer (b1) having the cation-exchange group.
• the cation-exchange base membrane may be prepared in the same manner as in the method I that uses the monomer (b1) having the cation-exchange group but necessitating the step of introducing the cation-exchange group that will be described later.
• the monomer (b2) having the reaction group capable of introducing the cation-exchange group may be the one that has heretofore been used for producing the cation-exchange resin.
• Examples thereof include styrene, vinyltoluene, vinylxylene, ethylvinylbenzene, ⁇ -methylstyrene, vinylnaphthalene and ⁇ -halogenated styrene.
• the monomer (b2) having the reaction group capable of introducing the cation-exchange group and the crosslinking monomer it is also allowable to use any other monomers.
• the other monomers there can be used chloromethylstyrene, acrylonitrile, acrolein and methyl vinyl ketone.
• the step of introducing the cation-exchange group is carried out after the membrane of the cation-exchange resin precursor resin is formed by polymerizing and curing the polymerizable composition.
• the concentrated sulfuric acid, chlorosulfonic acid or phosphoric acid is acted, as the cation-exchange group introducing agent, upon the precursor resin that is obtained so as to be sulfonated, chlorosulfonated or phosphoniated, or the precursor resin that is obtained is hydrolyzed to introduce the cation-exchange group into it. There is thus obtained the desired cation-exchange base membrane.
• the method II that uses the monomer (b2) having the reaction group capable of introducing the cation-exchange group.
• the polymerizable composition that comprises the polymerization-curable component (B) and the polyvinyl chloride (A).
• the polyvinyl chloride (A) dissolves more in the monomer to which no cation group has been introduced than in the monomer (b1) that has the cation-exchange group.
• the method that uses the polymerizable composition is preferred since the polymerization and curing are executed at a temperature near the melting point of the polyolefin reinforcing member contributing to improving the adhesiveness between the reinforcing member and the cation-exchange resin.
• the cation-exchange base membrane prepared as described above has a thickness in a range of 10 to 500 ⁇ m and, more preferably, 100 to 300 ⁇ m. If the thickness is too small, the strength of the exchange base membrane may greatly decrease. If the thickness is too large, inconvenience may occur such as an increase in the bipolar voltage.
• the cation-exchange base membrane has a burst strength of, usually, 0.1 to 3.0 MPa though dependent upon the thickness thereof.
• the thickness of the polyolefin reinforcing member and the amount of the crosslinking monomer in the whole monomers are so set that the burst strength of the cation-exchange base membrane is 0.2 to 1.8 MPa.
• the cation-exchange base membrane has an ion-exchange capacity of, usually, in a range of 0.1 to 4 meq/g and, specifically, 0.5 to 2.5 meq/g from the standpoint of bipolar membrane properties, such as voltage drop and current efficiency.
• the membrane resistance is, desirably, not larger than 10 ⁇ cm 2 and, specifically, in a range of 1 to 5 ⁇ cm 2 .
• an anion-exchange membrane is formed on the surface of the cation-exchange base membrane formed as described above.
• the following three methods can be preferably employed.
• a polar organic solvent solution of the anion-exchange resin precursor resin having the reaction group capable of introducing the anion-exchange group On the surface of the cation-exchange membrane, there is applied a polar organic solvent solution of the anion-exchange resin precursor resin having the reaction group capable of introducing the anion-exchange group. The polar organic solvent is then removed to form a membrane of the anion-exchange resin precursor resin on the surface of the cation-exchange membrane. Next, the anion-exchange group is introduced into the anion-exchange resin precursor resin to thereby form the anion-exchange membrane on the cation-exchange base membrane.
• the arithmetic mean surface roughness Ra is adjusted to be in a range of 0.1 to 2.0 ⁇ m and, specifically, 0.5 to 1.8 ⁇ m.
• the density of the membrane can be increased and, therefore, the anchoring effect can be increased.
• the arithmetic mean surface roughness Ra can be calculated by processing the image on the surface that is photographed by using an ultradeep profile microscope.
• the organic solvent for forming the polar organic solvent solution used in the above-mentioned three methods there can be used the one that does not affect the properties of the cation-exchange base membrane forming the lower layer but that accelerates the polyvinyl chloride (A) in the cation-exchange base membrane to be partly migrated into the anion-exchange membrane.
• the organic solvent for forming the polar organic solvent solution used in the above-mentioned three methods there can be used the one that does not affect the properties of the cation-exchange base membrane forming the lower layer but that accelerates the polyvinyl chloride (A) in the cation-exchange base membrane to be partly migrated into the anion-exchange membrane.
• alcohol ethylene chloride
• tetrahydrofuran dimethylformamide
• N-methylpyrrolidone Among them, the tetrahydrofurane or the dimethylforamide is particularly preferred from the standpoint of accelerating the migration of the polyvinyl chloride.
• the anion-exchange resin is the known one, e.g., is a resin having a specific skeleton or a resin obtained by introducing the anion-exchange group into a precursor resin that has a specific skeleton.
• the precursor resin having the specific skeleton there can be exemplified the same resins as those of the case of the cation-exchange resin.
• the anion-exchange group if it is a reaction group capable of serving as a positive electric charge in an aqueous solution.
• Examples thereof include primary to tertiary amino groups, quaternary ammonium salt group, pyridyl group, imidazole group and quaternary pyridinium salt group.
• the quaternary ammonium salt group and the quaternary pyridinium salt group which are strongly basic groups are preferred.
• the anion-exchange resin precursor resin there can be used a high molecular compound having a monomer unit capable of introducing an anion-exchange group, such as chloromethylstyrene, vinylpyridine and vinylimidazole; and high molecular compounds into which has been introduced a reaction group capable of introducing an anion-exchange group such as chloromethyl group or bromobutyl group into a styrene type elastomer, like polystyrene-poly(ethylene-butylene)-polystyrene triblock copolymer, polystyrene-poly(ethylene-propylene)-polystyrene triblock copolymer, polystyrene-polyisoprene block copolymer, and hydrogenated products thereof.
• a high molecular compound having a monomer unit capable of introducing an anion-exchange group such as chloromethylstyrene, vinylpyridine and vinylimidazole
• the concentration of the precursor resin in the solution may be suitably set by taking the coating property into consideration. Though there is no limitation, the concentration thereof is, usually, 5 to 40% by mass.
• polystyrene polystyrene-poly(ethylene-butylene)-polystyrene triblock copolymer
• polystyrene-poly(ethylene-propylene)-polystyrene triblock copolymer polystyrene-polyisoprene block copolymer
• styrene type elastomers such as hydrogenated products thereof.
• Halogenated alkanes such as methyl iodide, ethyl iodide and methyl bromide; and dibromoalkanes such as dibromobutane and dibromohexane.
• the anion-exchange membrane is formed, more preferably, by the non-precursor resin type one-step method. This is because the process of production can be shortened and the cost of production can be lowered. That is, when the anion-exchange membrane is formed by the non-precursor resin type one-step method, no step is required for introducing the anion-exchange groups. Therefore, the productivity can be increased as compared to the case where the two steps are required for forming the anion-exchange resin precursor resin and for introducing the anion-exchange groups.
• the precursor resin type one-step method comprises preparing a polar organic solvent solution that contains the anion-exchange resin precursor resin and the anion-exchange group introducing agent, and applying the polar organic solvent solution followed by drying.
• introduction of the anion-exchange groups into the anion-exchange resin precursor resin takes place during the period of from when the solution is prepared till when it is dried. Since the anion-exchange groups are introduced while the anion-exchange membrane is being formed as described above, there is easily formed the anion-exchange membrane into which the anion-exchange groups have been introduced homogeneously.
• a crosslinked structure can be introduced into the anion-exchange membrane.
• a diamine compound such as N,N,N′,N′-tetramethyl-1,6-hexanediamine or to use the dibromoalkane such as dibromobutane or dibromohexane, which is effective in improving water-proof property of the anion-exchange membrane and in suppressing the swelling thereof.
• the diamine compound such as N,N,N′,N′-tetramethyl-1,6-hexanediamine is used from the viewpoint of easy handling.
• the anion-exchange membrane produced as described above has a thickness that lies in a range of, preferably, 1 to 200 ⁇ m.
• the anion-exchange membrane has an ion-exchange capacity, usually, in a range of 0.1 to 4 meq/g and, specifically, 0.5 to 2.5 meq/g from the standpoint of bipolar membrane properties. Therefore, the amount of applying the polar organic solvent solution containing the anion-exchange resin or the precursor resin thereof, the composition of the precursor resin (ratio of content of monomer units having the reaction groups) and the amount of the anion-exchange group introducing agent, are so set that the above-mentioned thickness and the anion-exchange capacity can be realized.
• the bipolar voltage it is allowable, as required, to suitably employ a known method of lowering the bipolar voltage by introducing ions of a heavy metal (e.g., ions of iron, tin, chromium or ruthenium) having a catalytic action for hydrolysis, an oxide of the heavy metal or a tertiary amine into the surface of the cation-exchange base membrane (surface on the side where the anion-exchange membrane is to be formed) prior to forming the anion-exchange membrane.
• a heavy metal e.g., ions of iron, tin, chromium or ruthenium
• the content of the heavy metal in the bipolar membrane is in a range of 1 to 5,000 mg/m 2 and, preferably, 5 to 1,000 mg/m 2 .
• tin ions, ruthenium ions or an oxide of tin or ruthenium from the standpoint of not being dissolved in acid or alkali and low toxicity.
• a heat treatment may be suitably executed. This enables the anion-exchange membrane to bite into the rough surface of the cation-exchange base membrane. As a result, adhesiveness or the strength of junction is greatly improved between the cation-exchange base membrane and the anion-exchange membrane. It is desired that the heat treatment is executed at a temperature higher than, for example, the softening point of the polyolefin reinforcing member in the exchange base membrane. In order to improve the anchoring effect due to the rough surface, furthermore, it is desired that the heat treatment is executed under a pressurized condition while, for example, holding the membranes between the steel plates heated in the above-mentioned temperature range or passing the membranes through the rollers.
• the cation-exchange base membrane is blended with the polyvinyl chloride (A). Therefore, the cation-exchange base membrane and the anion-exchange membrane are joined together maintaining a high degree of adhesiveness.
• the area ratio a portion where the cation-exchange membrane and the anion-exchange membrane are separated away from each other has been suppressed to be, generally, not more than 20% and, preferably, not more than 10%.
• the bipolar membrane of the invention having such a high degree of adhesiveness, the membranes are not peeled even when put to use in the electrodialysis which, therefore, can be continued for extended periods of time maintaining stability.
• the bipolar membrane can be employed under a wide range of production conditions such as of temperatures and the like.
• the bipolar voltage is, usually, suppressed to be not higher than 2.0 V and, preferably, not higher than 1.5 V.
• the bipolar membrane of the invention In the cation-exchange base membrane of the bipolar membrane of the invention, further, no gap is present between the polyolefin reinforcing member and the cation-exchange resin. Therefore, an improved current efficiency is observed when the bipolar membrane is put to the electrodialysis. This effect is not impaired in the electrodialysis of even under high temperature conditions.
• the gluconic acid leakage ratio 60° C.
• the hydrolysis efficiency is, usually, not less than 98% as measured in a sodium hydroxide aqueous solution of 60° C. and in a hydrochloric acid aqueous solution.
• Positive electrode (Pt plate) (1.0 mol/L of NaOH)/control bipolar membrane/(1.0 mol/L of NaOH)/sample bipolar membrane/(1.0 mol/L of HCl)/control bipolar membrane/(1.0 mol/L of HCl) negative electrode (Pt plate)
• the bipolar voltages were measured under the conditions of a liquid temperature of 25° C. and a current density of 10 A/dm 2 via platinum wire electrodes placed holding the bipolar membrane therebetween.
• Platinum electrodes were provided in two compartments of a glass cell having two compartments separated by a bipolar membrane having an effective current-carrying area of 4.5 cm 2 .
• An aqueous solution containing 0.8 mol/L of sodium hydroxide was fed in an amount of 60 ml into the positive electrode compartment, and an aqueous solution containing 0.8 mol/L of hydrochloric acid was fed in an amount of 60 ml into the negative electrode compartment.
• a direct current of 0.45 A at 60° C. for 20 hours the quantities of the acid and the base in the two compartments were determined.
• the current efficiencies for forming the acid and the base were calculated from the quantities of the acid and the base that were formed, and an average value of the two was regarded as a hydrolyzing efficiency of the bipolar membrane.
• Platinum electrodes were provided in two compartments of a glass cell having two compartments separated by a bipolar membrane having an effective current-carrying area of 4.5 cm 2 .
• An aqueous solution containing 2.0 mol/L of sodium gluconate was fed in an amount of 50 ml into the positive electrode compartment, and an aqueous solution containing 2.0 mol/L of sodium hydroxide was fed in an amount of 50 ml into the negative electrode compartment.
• a direct current of 0.45 A at 60° C. for one hour the quantity of the gluconic acid in the negative electrode compartment was determined. From the quantity of the gluconic acid that was obtained, the current efficiency of the gluconic acid that has permeated through was calculated and was regarded to be a gluconic acid leakage rate.
• the bipolar membrane was dipped in an aqueous solution containing 6.0 mol/L of sodium hydroxide of 25° C. for one hour, taken out therefrom, and was dipped again in pure water of 25° C. for one hour. After taken out from the pure water, the membrane was analyzed by using an image processing system (IP-1000 PC manufactured by Asahi Engineering Co.), and the ratio of an abnormal portion (that was blistered) in 1 cm 2 of the membrane was calculated as a peeled area (%).
• IP-1000 PC manufactured by Asahi Engineering Co.
• the ion-exchange membrane was dipped in an aqueous solution containing 1 mol/L of HCl for not less than 10 hours.
• the same ion-exchange membrane was dipped in an aqueous solution containing 1 mol/L of NaCl for not less than 4 hours. Thereafter, the ion-exchange membrane was dried at 60° C. under a reduced pressure for 5 hours, and its dry weight (Dg) was measured. From the above measured values, the ion-exchange capacity of the ion-exchange membrane was found according to the following formula,
• the cation-exchange membrane was dipped in an aqueous solution containing 0.5 mol/L of NaCl for not less than 4 hours, and was then washed with the ion-exchanged water to a sufficient degree. Next, without drying, the membrane was measured for its burst strength by using the Meullen burst strength tester (manufactured by Toyo Seiki Co.) in compliance with the JIS-P8112.
• the cation-exchange membranes prepared in Examples and in Comparative Examples were each held in a 2-compartment cell having platinum black electrode plates.
• the cell was filled with an aqueous solution containing 0.5 mol/L of sodium chloride on both sides of the cation-exchange membrane, and the resistance across the electrodes of an AC bridge circuit (frequency of 1,000 cycles per sec.) was measured at 25° C. A difference between the resistance across the electrodes in this case and the resistance across the electrodes measured without installing the cation-exchange membrane was recorded as a membrane resistance.
• the cation-exchange membrane used for the above measurement was the one that had been rendered, in advance, to be in an equilibrium state in an aqueous solution containing 0.5 mol/L of sodium chloride.
• the cation-exchange membrane was dipped in an aqueous solution containing 0.5 mol/L of NaCl for not less than 4 hours. Thereafter, the water on the surfaces of the membrane was wiped away with a tissue paper, and the membrane was measured for its thickness by using a micrometer MED-25PJ (manufactured by Mitsutoyo Co.).
• Ra 1 f ⁇ ⁇ 0 l ⁇ ⁇ f ⁇ ( x ) ⁇ ⁇ dx
• the cation-exchange membrane that has been treated with a catalyst was subjected to the X-ray fluorometric analysis to find a molar ratio of sulfur element and catalyst element.
• the amount of the catalyst was calculated from a ratio of the sulfur element relative to the ion-exchange capacity.
• the following polymerizable composition was prepared.
• Polyvinyl chloride powder (Crash Berg flexible temperature: 68° C., chlorine content: 57%, average polymerization degree: 1,060, average particle size: 1 ⁇ m)
• a polyethylene woven fabric (50 denier, mesh vertical:lateral 156:100/inch, monofilament, filament diameter 86 ⁇ m, melting point 125° C.) was dipped under the atmospheric pressure at 25° C. for 10 minutes. Thereafter, the woven fabric was taken out from the polymerizable composition and was coated on both sides thereof with the Teijin Tetron Film (type S, polyethylene terephthalate) manufactured by Teijin-Du Pont Film Co., 188 ⁇ m in thickness as a peeling material. The woven fabric was then polymerized by being heated at 120° C. for 5 hours under a nitrogen pressure of 0.3 MPa.
• the thus obtained membrane was dipped in a mixture of sulfuric acid of a concentration of 98% and chlorosulfonic acid of a purity of not less than 90% at a weight ratio of 1:1 maintaining a temperature of 40° C. for 60 minutes to thereby obtain a sulfonic acid type cation-exchange membrane.
• the obtained cation-exchange membrane possessed an ion-exchange capacity of 1.9 meq/g, a burst strength of 0.4 MPa and a membrane resistance of 3.0 ⁇ cm 2 .
• the obtained cation-exchange membrane was dipped in an aqueous solution containing 2.0 wt % of ruthenium chloride for 60 minutes. The cation-exchange membrane was then taken out therefrom and was dried at 60° C.
• a styrene type block copolymer comprising a polystyrene segment (65% by mass) and a polyisoprene segment (35% by mass) that has been hydrogenated was dissolved in 1,000 g of a chloroform and to which were added 100 g of a chloromethylmethyl ether and 10 g of tin chloride to prepare a reaction solution.
• the reaction solution was stirred at 40° C. for 15 hour. After the stirring, methanol was added to the reaction solution, and the precipitated solid material was picked up by filtering. The obtained solid material was washed and was then dried. As a result, there was obtained a chloromethylated styrene type block copolymer.
• the solution for forming the anion-exchange membrane that was the same as the one used for forming the bipolar membrane, was applied onto a polyethylene terephthalate film and was dried.
• the membrane formed on the polyethylene terephthalate film was peeled off the film to thereby obtain an anion-exchange membrane for measuring the ion-exchange capacity.
• the anion-exchange membrane was measured for its ion-exchange capacity to be 1.4 meq/g.
• the obtained bipolar membrane was evaluated for its adhesiveness, amount of catalyst, bipolar voltage, hydrolytic efficiency and gluconic acid leakage rate (60° C.).
• the constitution of the bipolar membrane and the evaluated properties thereof were as shown in Table 2.
• Bipolar membranes were prepared according to the same procedure as that of Example 1 but changing the kind and amount of the polyvinyl chloride which was the polymerizable monomer used for preparing the cation-exchange base membrane as shown in Table 1.
• the constitutions and properties of the cation-exchange base membranes were as shown in Table 1 while the constitutions and properties of the bipolar membranes were as shown in Table 2.
• a bipolar membrane was obtained according to the same procedure as that of Example 1 but treating the cation-exchange membrane obtained in Example 1 with an aqueous solution containing 2.0 wt % of tin chloride (II) instead of treating the cation-exchange membrane with the ruthenium chloride aqueous solution.
• the constitution and properties of the bipolar membrane were as shown in Table 2.
• the partly aminated polystyrene was synthesized as described below. First, a monomer mixture of styrene and chloromethylstyrene at a molar ratio of 10:1 was copolymerized in toluene in the presence of a benzoyl peroxide that was a polymerization initiator at 70° C. for 10 hours. The obtained reaction solution was poured into methanol, and the precipitated styrene-chloromethylstyrene copolymer was recovered.
• the chloromethylated polymer solution obtained in Example 1 was applied onto the roughened surface of the cation-exchange membrane treated with the ruthenium chloride aqueous solution obtained in Example 1 followed by drying to thereby forma chloromethylated polymer film of a thickness of 60 ⁇ m. Thereafter, the cation-exchange membrane having the chloromethylated polymer film was dipped in a methanol solution of an N,N,N′,N′-tetramethyl-1,3-propanediamine (10% by mass) at 30° C. for 50 hours. The cation-exchange membrane was, thereafter, washed with water to a sufficient degree, and there was obtained a bipolar membrane. The constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but changing the polyolefin reinforcing member and the polymerization temperature for preparing the cation-exchange base membrane into those shown in Table 1 and using a 1,1,3,3-tetramethylbutylhydroperoxide as the polymerization initiator.
• the constitution and properties of the cation-exchange base membranes were as shown in Table 1 while the constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but changing the polyolefin reinforcing member used for preparing the cation-exchange base membrane into the one shown in Table 1.
• the constitution and properties of the cation-exchange base membranes were as shown in Table 1 while the constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but changing the polymerization temperature to 80° C. at the time of preparing the cation-exchange base membrane and using a t-butyl-2-ethylperoxyhexanoate as the polymerization initiator.
• the constitution and properties of the cation-exchange base membranes were as shown in Table 1 while the constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but preparing the cation-exchange base membrane without adding the polyvinyl chloride that was the polymerizable monomer.
• the constitution and properties of the cation-exchange base membranes were as shown in Table 1 while the constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but preparing the cation-exchange base membrane by using a chlorinated polyethylene (average molecular weight of 20,000, chlorine content of 66%) in an amount as shown in Table 1 instead of using the polyvinyl chloride, executing the polymerization at 80° C. and using the t-butyl-2-ethylperoxyhexanoate as the polymerization initiator.
• the constitution and properties of the cation-exchange base membranes were as shown in Table 1 while the constitution and properties of the bipolar membrane were as shown in Table 2.
• a bipolar membrane was prepared according to the same procedure as that of Example 1 but preparing the cation-exchange base membrane by using the chlorinated polyethylene (average molecular weight of 20,000, chlorine content of 66%) in an amount as shown in Table 1 instead of using the polyvinyl chloride.
• PVC1 Polyvinyl chloride, chlorine content 57%, average polymerization degree 1060
• PVC2 Polyvinyl chloride, chlorine content 57%, average polymerization degree 1200
• CPE Chlorinated polyethylene, chlorine content 66%, average polymerization degree 20,000
• CMPS/CMSEPS TMHDA 1.4 Ru 1000 100 5.1 97.8 1.7 Ex. 2
• CMPS/CMSEPS TMHDA 1.4 Ru 700 0 1.2 97.2 3.0
• Ru 700 100 5.2 99.1 0.8
• CMPS Chloromethylated polystyrene CMSEPS: Chloromethylated styrene type block copolymer SCMS: Styrene-chloromethylstyrene copolymer
• TMHDA N,N,N′,N′-tetramethyl-1.6-hexanediamine
• TMEDA N,N,N′,N′-tetramethyl-1.2-ethanediamine
• TMPDA N,N,N′,N′-tetramethyl-1.3-propanediamine

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