JPH0146529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel cation exchange membrane for electrolysis of aqueous alkali metal salt solutions.

Today, in our country, the technology for obtaining alkali metal hydroxide, halogen gas, hydrogen gas, oxygen gas, etc. by electrolyzing an aqueous alkali metal salt solution is changing from the conventional mercury method to the diaphragm method. However, the alkali metal hydroxide obtained by this diaphragm electrolysis is impure and its purification cost is high. Therefore, as an alternative to this method, a method for electrolyzing alkali metal salts using a diaphragm having a dense structure, that is, an ion exchange membrane, has attracted attention and has been partially industrialized. Methods for electrolyzing alkali metal salts using such ion exchange membranes as diaphragms are roughly divided into those using oxidation-resistant cation exchange membranes, such as fluorine-containing cation exchange membranes, and those using hydrocarbon-based cation exchange membranes that do not have oxidation resistance. A cation exchange membrane may be used.

However, although the alkali metal hydroxide obtained in the electrolysis of alkali metal salts using a cation exchange membrane as a diaphragm has a high purity, the concentration of the alkali metal hydroxide obtained from the cathode chamber is generally 10 to 10%.
As low as 20%. Of course, it is possible to electrolyze an alkali metal salt in an electrolytic cell using an ion exchange membrane to increase the concentration of alkali metal hydroxide obtained from the cathode chamber to 50% or more, but due to the natural properties of the ion exchange membrane, As a result of increasing the concentration of alkali metal hydroxide in the cathode chamber, the current efficiency of alkali metal hydroxide acquisition decreases significantly. For this reason, efforts are being made to develop techniques for maintaining high current efficiency even when a high concentration of alkali metal hydroxide is obtained, and improvements to the cation exchange membrane itself and improvements to the electrolysis method have been proposed.

On the other hand, the rayon industry, which requires the most highly purified alkali metal hydroxide, requires approximately 25 to 30% caustic soda, although this varies depending on the process. That is, since such a high concentration of alkali metal hydroxide is required, an evaporator should be installed to collect 10 to 20% alkali metal hydroxide obtained by the electrolysis method of alkali metal salts using an ion exchange membrane. must be concentrated. Therefore, even in the electrolysis of alkali metal salts using the above-mentioned ion exchange membrane, it is most preferable that 25% or more, especially 30% or more of alkali metal hydroxide can be obtained directly from the cathode chamber. However, to date, there has been no cation exchange membrane that satisfies the above conditions and can be used on an industrial scale.

The present invention provides a cation exchange membrane of a different type from conventional cation exchange membranes that have been used in aqueous alkali metal salt electrolysis.

That is, the present invention has a fluorine-containing cation exchange membrane having a water permeability of 10 ⁻⁷ to 10 c.c./hr·cm ² ·cmH ₂ O and an ion exchange group on one surface of the fluorine-containing cation exchange membrane. This is a cation exchange membrane for electrolysis of aqueous alkali metal salt solutions with a diaphragm arranged in close contact with each other.

In the present invention, any conventionally known cation exchange membrane may be used as the cation exchange membrane. for example,
Contains a sulfonic acid group, a carboxylic acid group, a thiol group, a phenolic hydroxyl group, a sulfuric acid ester group, a phosphoric acid group, a phosphorous acid group, a phosphoric acid ester group, a phosphite group, and a dissociable hydrogen group as a cation exchange group. A fluorine-containing cation exchange resin membrane having one or more selected from acid amide groups and the like is used. Examples of cation exchange membranes having oxidation resistance include fluorine-containing cation exchange membranes, such as tetrafluoroethylene and perfluoro(3,6-dioxer-4).
Various sulfonic acid type cation exchange membranes with different ion exchange capacities are used, which are obtained by hydrolyzing a polymer membrane obtained from a copolymer of methyl-7-octensulfonyl fluoride. In addition, in order to improve the electrochemical performance of the above-mentioned fluorine-containing cation exchange membrane, we have developed a cation exchange membrane in which two or more types of membranes with different ion exchange capacities are adhered or fused together, and also a surface or internal layer of the cation exchange membrane. A cation exchange membrane that is treated with ammonia, primary amines, secondary amines, etc. to form acid amide bonds, and also has an anionic thin layer, a neutral thin layer, and an amphoteric thin layer on the surface of the membrane. An improved cation exchange membrane in which different layers are combined, such as a thin layer having a carboxylic acid group or a thin layer having a high concentration of fixed ions, is also preferably used.

The average pore diameter of the water-permeable diaphragm used in the present invention is 10 ^-7 to 10 c.c./hr·cm ² ·cmH ₂ O, particularly 10 ^-4 to 5
cc/hr·cm ² ·cmH ₂ O is preferred.

In the present invention, the water permeable diaphragm disposed in close contact with one surface of the cation exchange membrane has a water permeability of 10 ⁻⁷ to 10 c.c./hr·cm ² ·cmH ₂ O as described above. There are no particular restrictions if the electrical resistance is 25℃.
Porous cation exchange membranes having a uniform pore size distribution of 15 Ω-cm ² or less, particularly 5 Ω-cm ² or less, and an average pore size generally from 10 ^-2 to 9 microns in 6.0 N NaOH are preferred. In addition, in order to reduce the electrical membrane permeation of hydroxide ions in the cathode side chamber to the anode side, it is generally preferable that the membrane has a higher cation exchange capacity.
0.001meq/g (dry film) or more is preferable. Also,
The above-mentioned water-permeable diaphragm may be fluorine-containing, hydrocarbon-based, or inorganic-based as long as it maintains constant electrical resistance, water permeability, and mechanical strength in an aqueous solution of alkali metal hydroxide over a long period of time. It can be used regardless of. For example, (1) so-called deposits in which conventional asbestos, that is, asbestos commonly used in ordinary diaphragm electrolysis, such as olaceite asbestos and orionite asbestos, is appropriately dispersed with barium sulfate and deposited on the cathode or reinforcing material. Tuto type neutral membrane.

(2) Mix the above asbestos fibers with an emulsion of oxidation-resistant polymers such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, difluoroethylene, monofluoroethylene, etc. Asbestos paper is obtained by dispersing paper making, then baking it and melting and bonding the added resin parts to integrate it.

(3) Polymers obtained by polymerizing oxidation-resistant fluorine-based monomers such as ethylene tetrafluoride, ethylene trifluoride, ethylene difluoride, and ethylene monofluoride are pressure-molded into films. A porous neutral membrane obtained by adding extractable fluorine-based solvents, other solvents, and polymer compounds, and then performing an extraction process when the membrane is fused into a lump and cut into a film.

(4) In (3) above, a porous neutral membrane that can be decomposed by thermal decomposition or other means after forming the solvent and polymer compound added when forming the film into a film.

(5) A membrane-like material (nonwoven fabric) made from short fibers of polyfluoroethylene mentioned above.

(6) A film-like material obtained by heating the nonwoven fabric obtained in (5) above.

(7) A membrane material made from a mixture of the above-mentioned asbestos and polyfluoroethylene fibers.

(8) A film-like material obtained by adding short glass fibers to the polyvinyl fluoride lump or sheet, mixing them uniformly, and eluting the glass fibers with hydrofluoric acid, etc.

(9) A monomer capable of introducing a cation exchange group such as styrene-divinylbenzene or a monomer capable of introducing an anion exchange group such as chloromethylstyrene or vinylpyridine into a polyvinyl fluoride compound sheet or fine powder is required. Impregnation polymerization is carried out under heating and pressure, and in the case of a fine powder, this is formed into a sheet form, after which a cation exchange group or anion exchange group is introduced by a conventional method, and then this is formed into an iron mold or other type. A porous neutral membrane that undergoes oxidative decomposition or thermal decomposition in the form of transition metals or their complex salts.

(10) Fine powders such as colloidal silica, magnesium carbonate, calcium carbonate, etc. are uniformly dispersed in a polymer such as polyvinyl fluoride or polypropylene, and this is formed into a film by a conventional method and eluted with an appropriate acid. Treated porous neutral membrane.

(A) The porous neutral membrane of (1) to (10) above is impregnated with a polymerizable vinyl monomer into which a cation exchange group can be introduced, along with a polyvinyl compound as a crosslinking agent and other additives, if necessary, and pressurized. A porous cation exchange membrane in which cation exchange groups are introduced by sulfonation or other methods under harsh conditions that cause cracks to form in the cation exchange resin.

(B) A deposit film formed by mixing extremely fine powder of cation exchange resin into a liquid when making the asbestos deposit film in (1) above.

(C) A functional group (sulfonic acid group, phosphonic acid group,
A sheet-like product made by mixing a perfluoro compound (phosphinic acid group, carboxylic acid group, phenolic hydroxyl group, thiol group, etc.) bonded with an inert fiber compound, such as asbestos, and molding the mixture. Other soluble components and degradable components are added to form a film-like material, and if necessary, it is extracted or decomposed to make it porous.

(D) Fluorine-based, porous neutral membranes exemplified in (1) to (10)
Adsorbed with hydrocarbon surfactant. Furthermore, if necessary, it is fired.

(E) A porous neutral membrane exemplified in (1) to (10) impregnated with an aqueous solution or an organic solvent solution of a polymer electrolyte having an ion exchange group having cationic or amphoteric ion exchange properties. Furthermore, if necessary, it is fired.

(F) Porous fluorinated ethylenes or copolymers with other vinyl monomers, allyl monomers, or polyvinyl compounds are treated with a reaction product of an alkyl ketone and an alkyl metal compound, or a reaction product with an alkyl metal hydroxide. , sulfonated to introduce a sulfone group, hydrolyzed to have a hydroxyl group, or other cation exchange group. In addition, other porous polyfluoroethylene compounds can be used with fuming sulfuric acid,
A compound that combines cation exchange groups by reacting with chlorsulfonic acid, etc. under harsh conditions.

(G) In making some of the porous neutral membranes and porous cation exchange resin membranes listed above, polyvinyl fluoride compounds such as polytetrafluoroethylene are used, but instead of polytetrafluoroethylene, ethylene chloride,
Copolymers of ethylene trifluoride, ethylene difluoride, ethylene monofluoride, perfluoropropylene, etc. may be used, and copolymers of polyolefins such as ethylene, propylene, butene, etc. may also be used to facilitate processability. A similar treatment may be performed using a copolymer of a vinyl monomer or an aryl monomer having properties.

(H) When making (17), other vinyl monomers and aryl monomers that can be introduced with cation exchange groups are copolymerized with the fluorine-based vinyl monomer, and when molding into a sheet, the eluted components are mixed and molded. A porous cation exchange membrane in which the eluted components were eluted simultaneously with the introduction of the cation exchange group, or before or after the introduction of the cation exchange group.

(I) Use of materials other than fluorine-containing materials as the base material for the various porous, ion exchange, or neutral diaphragms in (2) to (10) or (A) to (H) above. Porous, ion-exchange membrane (J) A porous neutral membrane in which a specific metal ion is introduced into a known ion-exchange membrane and then treated with hydrogen peroxide to give water permeability, or a porous neutral membrane with cation-exchange groups. The remaining porous membrane is used.

The present invention is a cation exchange membrane in which the water-permeable diaphragm is adhered to one surface of a fluorine-containing cation exchange membrane as described above. When this cation exchange membrane is used for electrolysis of an aqueous alkali metal salt solution, it is preferable to use it so that the water-permeable diaphragm faces the cathode side. By using it in this way, a highly concentrated alkali metal hydroxide can be obtained with high current efficiency.

When electrolyzing an aqueous alkali metal salt solution, conventionally known anodes such as carbon electrodes, noble metal electrodes, and insoluble anodes can be used without restriction, and a saturated aqueous alkali metal salt solution is usually used as the anolyte. However, it does not necessarily have to be saturated, and in order to control the hydration number of sodium ions passing through the membrane, as described in U.S. Pat. may also be used. Further, as the cathode, an electrode made of iron, stainless steel, nickel, etc. can be used. Furthermore, the present invention can be practiced in a form in which a plurality of electrolytic cells are connected by using bipolar negative and positive electrodes. In addition, in actual electrolysis, the current density can be carried out between 10 and 70 A/dm ² .

The present invention will be further explained in Examples below, but the present invention is not limited to these Examples in any way. In the electrolysis in the examples, a container with an effective current carrying area of 1 dm ² was used, a titanium mesh coated with ruthenium oxide and titanium oxide was used as the anode, and an iron mesh was used as the cathode. Further, the average pore diameter of the water-permeable diaphragm used in the Examples was measured using a mercury porosimeter.

Example Tetrafluoroethylene and perfluoro(3,
6-Dioxa-4-methyl-7-octensulfonyl fluoride) copolymer with 0.05 mm of sulfonyl fluoride and ion exchange capacity with an ion exchange capacity of 5.6 meq/g (dry membrane). A film-like material having a sulfonyl fluoride group of 0.10 mm with a thickness equivalent to 0.91 meq/g (dry film) was fused to form a single film-like material, into which a plain woven fabric made of tetrafluoroethylene was placed. After immersing this membrane in ethylenediamine for 48 hours at room temperature,
The remaining sulfonyl fluoride that did not form an acid amide bond with ethylenediamine was hydrolyzed by immersion in 6.0N-KOH and converted to potassium sulfonate. Using the above cation exchange membrane, arrange the surface with the acid amide bond layer toward the cathode side of the electrolytic cell, and then place a cathode chamber on the cathode side of the cation exchange membrane with a polypropylene microporous membrane ( Celanese (trade name: Jyuraguard 2400W) was immersed in a 1:1 mixture of sulfuric acid and chlorosulfonic acid at 30°C for 5 hours (exchange capacity: 0.1 meq/g dry resin, water permeability: 6 c.c./ Electrolysis was carried out in an electrolytic cell divided into two by a cation exchange membrane layered with hrcm ² cmH ₂ O).
Electrolysis is 30A/ ^dm2 , electrolysis temperature is 70℃, and the anolyte is
NaCl was electrolyzed at 2.6N with a decomposition rate of 18%. Sodium ions and water molecules that had passed through the cation exchange membrane were moved to the cathode chamber through the microporous membrane. The battery voltage is 3.9V, 41.7% from the cathode chamber.
NaOH could be obtained with a current efficiency of 90%.

Claims (1)

[Claims] 1. A diaphragm having a water permeability of 10 ^-7 to 10 c.c./hr.cm ² cmH ₂ O and having an ion exchange group is closely attached to one surface of a fluorine-containing cation exchange membrane. A cation exchange membrane for electrolysis of aqueous alkali metal salt solutions.