JPH0585575B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to a novel fluorine-containing three-layer ion exchange membrane. More specifically, the present invention relates to a fluorine-containing three-layer ion exchange membrane having a three-layer structure, with cation exchange groups in both layers and an anion exchange group in the center layer. The fluorine-containing three-layer ion exchange membrane of the present invention can be used as a battery separator, a selective membrane for monovalent and multivalent ions, and the like. [Prior Art] Conventionally, hydrocarbon polymers have been used as such multilayer ion exchange membranes. As these methods, a method has been proposed in which the surface of the ion exchange membrane is treated with a polymer electrolyte, or a method in which both sides are impregnated with a monomer and polymerized. However, problems such as membrane destruction due to repeated drying and swelling and improvements in chemical resistance have not been solved. [Problems to be Solved by the Invention] The present invention solves the above problems. [Means for Solving the Problems] The present inventors have conducted intensive studies on a membrane that will not be destroyed by repeated drying and swelling and has chemical resistance, especially oxidation resistance. structure, the pendant chains on both sides have cation exchange groups, the pendant chains in the middle layer have cation exchange groups, the pendant chains in the middle layer have anion exchange groups, and the main chain is A non-crosslinked fluorine-containing ion exchange membrane made of a perfluorocarbon polymer was discovered and the present invention was completed. In the three-layer membrane of the present invention, preferably the cation exchange group is a sulfonic acid group and the anion exchange group is a quaternary ammonium group. More preferably, in the three-layer ion exchange membrane of the present invention, the layer having a cation exchange group in the pendant chain has the following general formula:

[Chemical _{formula ]} q is a positive number and its ratio p/q is 2-16. The layer consisting of repeating units represented by the general formula

[Image Omitted] This is a fluorine-containing three-layer ion exchange membrane consisting of repeating units where x, l, m, n, p and q are the same as above, and z is a group containing a quaternary ammonium group. In both formulas, l, m and n can take different numbers for each pendant chain even on the same main chain. Furthermore, the value of p/q means an average value in the copolymer, and it goes without saying that the value of p/q includes cases in which each repeating unit takes a different value. Specifically, the layered cation exchange groups forming the layers on both sides of the three-layer structure ion exchange membrane of the present invention can be exemplified by polymers having the following structures.

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embedded image The counter ion of these cation exchange groups may be a hydrogen ion or an alkali metal ion such as a sodium ion or a potassium ion. Specifically, the layered anion exchange group forming the central layer of the three-layer structure ion exchange membrane of the present invention can be exemplified by a polymer having the following group as Z in the above general formula. .

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[Image Omitted] Examples of counter ions for these anion exchange groups include hydroxide ions; halogen ions such as chloride ions, bromide ions, and iodine ions; and trifluoromethanesulfonate ions. The thickness of the layered cation exchange groups and layered anion exchange groups of the present invention is preferably from about 1 μm to about 1 μm.
It is in the range of 200μm. The fluorine-containing three-layer ion exchange membrane of the present invention may be in the form of a flat membrane or a tube. The fluorine-containing three-layer ion exchange membrane of the present invention is
For example, it can be produced using a copolymer film composed of repeating units represented by the following general formula as a raw material.

[Chemical formula] Y' is a group represented by the formula SO ₂ Q, where Q is a halogen atom or a group of the formula OA (where A is hydrogen,
(representing an alkal metal or lower alkyl group), x, l, m, n, p and q
have the same meanings as above. l, m and n can take different numbers for each pendant chain even on the same main chain, and the value of p/q means the average value in the copolymer, and takes different values for individual repeating units. The same applies to cases. in particular,

[ka]

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embedded image The thickness of the copolymer film used as a raw material is preferably in the range of about 10 μm to about 500 μm.
The exchange group concentration can range from 0.3 meq/g dry resin to 1.2 meq/g dry resin. As for the shape, it is preferable to use a flat membrane or a tube-shaped membrane depending on the shape of the intended fluorine-containing three-layer ion exchange membrane of the present invention. The fluorine-containing three-layer ion exchange membrane of the present invention is
It can be obtained by introducing a quaternary ammonium group into the central layer of such a raw material copolymer film by chemical modification, for example, using the following route. Route 1 This route passes through a homogeneous sulfonic acid film, passes through a three-layer film with sulfonic acid on both sides and carboxylic acid in the center, and converts the carboxylic acid layer into a layer containing quaternary ammonium groups. A system three-layer structure ion exchange membrane is obtained. The exchange of terminal groups is shown below using a chemical formula containing only the terminal groups.

[Chemical formula] However, R ¹ , R ² , R ³ = lower alkyl group, however, R ¹ and R ²
may be combined to form a tetramethylene chain or a pentamethylene chain. R ⁴ = halogen atom or lower alkoxy group. D=halogen atom, _-O- ( ^R3 ) _2BF4 , -O-( ^R3 ) _{2SbCl6 ,}

[expression] or

[Formula] Z = halogen anion, BF ₄ , SbCl ₆

[expression] or

[Formula] R ⁵ = lower alkyl group, substituted or unsubstituted phenyl group, or lower perfluoroalkyl group, Q = the same as above. Route 1 will be explained below. The three-layer membrane of sulfonic acid/carboxylic acid/sulfonic acid used as a raw material membrane in this route is, for example, made by converting homogeneous sulfonic acid into sulfonyl chloride,
It can be obtained by hydrolyzing both sides so that a sulfonyl chloride group remains in the center, introducing sulfonic acid on both sides, and further carboxylating the sulfonyl chloride group present in the center (Example 1
reference). The carboxylic acid layer of the resulting three-layer film is converted into a carboxylic ester by reacting with an alcohol in the presence of an acid or by reacting with an orthoformic acid ester. Next, after drying this membrane, it is converted into a carboxylic acid amide by reacting it with a lower dialkylamine represented by the following general formula HNR ¹ R ² (1). Examples of the lower dialkylamine represented by the above general formula (1) include dimethylamine, diethylamine,
Examples include dipropylamine, methylethylamine, pyrrolidone, and piperidine. The reaction with these amines can be carried out by bringing the gaseous amine into contact with the membrane, in a liquid amine, or using a solvent. In this case, ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran, and dioxane, and hydrocarbons such as benzene, toluene, and hexane can be used as the solvent. Note that the same carboxylic acid amide can also be similarly obtained by reacting a lower dialkylamine represented by the general formula (1) with the corresponding carboxylic acid chloride. The carboxylic acid amide thus obtained is
It can be converted into an amine by the action of a reducing agent. As the reducing agent, lithium aluminum hydride, diborane, etc. can be used, but diborane is superior in terms of reaction efficiency. The diborane used can be generated by, for example, reacting a boron trifluoride ether complex with sodium borohydride, or various complexes of borane (such as dimethyl sulfide complex) can be used. The reaction proceeds smoothly in an ether solvent such as tetrahydrofuran, dioxane, or diethylene glycol dimethyl ether. In addition, in the early stage of the reaction, the temperature is kept in the range of ice-cold temperature to room temperature, and then,
Heating to reflux temperature to 100°C is preferred in order to complete the reaction. The obtained amine can be converted into the fluorine-containing three-layer structure ion exchange membrane of the present invention by alkylating (quaternizing) it with an alkylating agent (R ³ D). Examples of the alkylating agent include methyl iodide, methyl bromide, n-propyl bromide, trimethyloxonium fluoroborate ((CH ₃ ) ₃ OBF ₄ ),
Triethyloxonium fluoroborate ((C ₂
H ₅ ) ₃ OBF ₄ ), trimethyloxonium hexachloroantimonate ((CH ₃ ) ₃ OSbCl ₆ ), methyl trifluoromethanesulfonate, etc. can be used. At this time, methanol, ethanol, methylene chloride, chloroform, carbon tetrachloride, etc. may be used as a solvent. If it is necessary to exchange the counter ion of the above-obtained fluorine-containing three-layer ion exchange membrane, this can be done by treating it with an alkali metal salt by a conventional method. Route 2 This route passes from a homogeneous sulfonic acid membrane to a sulfonic acid/carboxylic acid/sulfonic acid trilayer membrane.
A fluorine-containing three-layer ion exchange membrane is obtained by converting the carboxylic acid layer into a layer containing a quaternary ammonium group. The conversion of the terminal group is shown below using the chemical formula of only the terminal group.

embedded image R ⁶ may be a hydrogen atom or a lower alkyl group, R ⁷ and R ⁸ may be lower alkyl groups, or R ⁶ and R ⁷ may be combined to form a polymethylene chain [(CH ₂ ) _b ]. a is an integer of 2 to 4, b is an integer of 2 to 3, R ⁴ , Z and D are the same as above. Route 2 will be explained below. The carboxylic acid ester obtained in the same manner as route 1 is expressed by the following general formula:

By reacting with the diamine represented by
Converts to aminocarboxylic acid amide. As the diamine represented by the above general formula (2),
N,N-dimethylethylenediamine, N,N,
N'-trimethylethylenediamine, N,N-dimethyltrimethylenediamine, N,N,N'-trimethyltrimethylenediamine, N-methylpiperazine, N,N-diethyltrimethylenediamine, N-ethylpiperazine and N-propylpiperazine etc. can be exemplified. At this time, a corresponding silylamine in which the hydrogen atom on the nitrogen atom in the above general formula (2) is replaced with a trimethylsilyl group can also be used in place of the above diamine. Further, the reaction with these diamines can be carried out in a liquid amine or using a solvent. At this time, as a solvent, diethyl ether,
Ethers such as tetrahydrofuran and dioxane, hydrocarbons such as benzene, toluene, hexane, etc. can be used. As the reducing agent, lithium aluminum hydride, diborane, etc. can be used, but diborane is superior in terms of reaction efficiency. The diborane used can be generated by, for example, reacting a boron trifluoride ether complex with sodium borohydride, or various complexes of borane (dimethyl sulfide complex, etc.) can be used. The reaction proceeds smoothly in an ether solvent such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, or the like. In addition, in the initial stage of the reaction, it is preferable to maintain the temperature between ice-cooling temperature and room temperature, and then to heat the temperature between the reflux temperature and 100° C. in order to complete the reaction. By alkylating the obtained diamine with an alkylating agent, it can be converted into a fluorine-containing three-layer ion exchange membrane. Examples of the alkylating agent include methyl iodide, methyl bromide, n-propyl bromide, trimethyloxonium fluoroborate ((CH ₃ ) ₃ OBF ₄ ),
Triethyloxonium fluoroborate ((C ₂
H ₅ ) ₃ OBF ₄ ), trimethyloxonium hexachloroantimonate ((CH ₃ ) ₃ OSbCl ₆ ), methyl trifluoromethanesulfonate, etc. can be used. At this time, methanol, ethanol, methylene chloride, chloroform, carbon tetrachloride, etc. may be used as a solvent. If it is necessary to exchange the counter ion of the above-obtained fluorine-containing three-layer ion exchange membrane, it can be carried out by treatment with an alkali metal salt by a conventional method. Route 3 This route involves hydrolyzing both sides of the homogeneous sulfonyl fluoride membrane to introduce a sulfonic acid so that a sulfonyl fluoride group remains in the center, then reacting the central sulfonyl fluoride group with a diamine, and then forming a quaternary fluoride membrane. By this process, a fluorine-containing three-layer ion exchange membrane is obtained. The conversion of the terminal group is shown below using the chemical formula of only the terminal group.

[Chemical formula] (R ³ , R ⁶ , R ⁷ , R ⁸ , D, a and Z are the same as above) Route 3 will be explained below. The synthesis of a membrane with a sulfonamide group in the center is
This is achieved by reacting a diamine represented by the general formula (2) or the corresponding silylamine described above with a membrane having sulfonic acid on both sides and a sulfonyl fluoride group in the center. At this time, it is preferable to use a large excess of diamines or to coexist a tertiary amine. A solvent can be used in the reaction, such as diethyl ether (ether), ethers such as tetrahydrofuran, benzene, toluene,
Hydrocarbons such as hexane can be used. The reaction is usually carried out at a temperature ranging from 0°C to 150°C. The resulting sulfonamide membrane can be converted into a fluorine-containing three-layer ion exchange membrane by alkylating it with an alkylating agent. Examples of the alkylating agent include methyl iodide, methyl bromide, n-propyl bromide, trimethyloxonium fluoroborate (Me ₃ OBF ₄ ), triethyloxonium fluoroborate (Et ₃
OBF ₄ ), trimethyloxonium hexachloroantimonate (Me ₃ OSbCl ₆ ), methyl trifluoromethanesulfonate, and the like can be used.
At this time, methanol, ethanol, methylene chloride, chloroform, carbon tetrachloride, etc. may be used as a solvent. If it is necessary to exchange the counter ion of the fluorine-containing three-layer ion exchange membrane obtained here, it can be carried out by treatment with an alkali metal salt by a conventional method. The fluorine-containing three-layer ion exchange membrane of the present invention is
Although some of the pendant chains contain hydrocarbon groups, it surprisingly shows extremely good durability under harsh oxidizing atmospheres such as chlorine atmospheres. In particular, it is a non-crosslinked type, withstands repeated drying and swelling, does not peel off, and has excellent chemical resistance and solvent resistance. Therefore, when used, for example, as a diaphragm for batteries or a membrane for separating monovalent and multivalent ions, it not only has remarkable durability, but also resists drying and swelling, which has traditionally been considered impossible. It exhibits extremely excellent performance when applied to associated equipment, used in systems containing solvents, and used under oxidizing conditions. Yet another major advantage is that it can be handled dry. This is an important point when used on an industrial scale. [Example] Next, a method for evaluating the obtained film in Examples will be described. 1 Repeated drying-swelling...Study item A After processing in methanol at 65°C for 48 hours, the moisture content is measured using a membrane in which the process of removing the solvent under vacuum at 40°C is repeated 5 times. 2. Peeling condition...Consideration item B Judgment is made by taking a cross-sectional photograph of the film in 1 above. 3 Chemical resistance...Study item C Measure the water content and exchange capacity (NMR and titration method, quantification of S) of the membrane into which Cl ₂ gas was introduced at 10 to 40 ml/min for 50 hours at 60°C in water. Example 1

The copolymer obtained by _{copolymerization} with
g. Dry film) and then hydrolyzed. next
After treatment with 2N HCl and thorough washing with water, heat at 60°C.
and dried under vacuum. Next, this membrane was treated with a mixed solution of phosphorus pentachloride and phosphorus oxychloride to form a sulfonyl chloride. Next, the mixture was hydrolyzed with 10 wt caustic soda/methanol (1/1; volume ratio) at room temperature so that sulfonic acid was formed in a layer of about 10 μm, and then washed with water. Then, oxidation treatment was performed to carboxylate the remaining sulfonyl chloride layer. The carboxylic acid layer of the sulfonic acid/carboxylic acid/sulfonic acid film thus obtained was esterified with methanol-HCl. The membrane obtained above was immersed in dry ether, dimethylamine gas was passed through it under ice cooling, and the mixture was reacted for 6 hours under cooling and for 18 hours at room temperature. 80℃ with 1.5% sodium bicarbonate water-methanol mixed solution.
Washed for 5 hours and dried under reduced pressure overnight. A colorless and transparent film was obtained, and in the surface infrared spectrum of the layer removed by about 12 to 15 microns from the surface, CH absorption was observed at 2930 and 1420 cm ^-1 and absorption due to amide carbonyl was observed at 1700 cm ^-1 . Next, sodium borohydride was dissolved in dry diethylene glycol dimethyl ether under an argon atmosphere, and then the membrane obtained above was immersed. A dry diglyme solution of boron trifluoride ether complex was added dropwise to the solution under ice cooling. By reacting under cooling for 5 hours and then at 100°C for 18 hours,
The absorption at 1700 cm ^-1 in the infrared spectrum disappeared, indicating that reduction to the amine layer had completely progressed. After washing the obtained membrane with methanol, it was placed in a methanol solution of methyl iodide and reacted at 60°C for 80 hours. After washing the obtained membrane with methanol,
The reaction was carried out in a methanol solution of lithium chloride at 60°C for 24 hours. This film was heated to 60°C in methanol to obtain a film having the desired quaternary ammonium chloride layer. In a dyeing test, the resulting three-layer ion exchange membrane was colored reddish-purple (basic aqueous solution) or yellow-orange (methanol solution) in the central thickness of about 180 μm with cresol red, indicating that quaternary ammonium groups were present. It was shown that it was formed in the central layer. The three-layer ion exchange membrane obtained as described above was treated and evaluated according to the evaluation method described above. The evaluation results are shown below. Meanwhile, the approximately 10μ layer on both sides was colored blue with crystal violet. From the above results, it was found that the obtained membrane was a three-layer ion exchange membrane containing a sulfonate salt in a layer of about 10 μm on both sides and a quaternary ammonium salt in a layer of about 185 μm in the center.

[Table] Also, very good results were shown for study item B. Example 2

The copolymer obtained from the _{copolymerization} with
g. Dry film). So that the sulfonic acid is formed in a layer of about 10μ
After hydrolyzing with 10 wt% caustic soda/methanol (1/1; volume ratio) at room temperature, it was washed with water. N-methylpiperazine was reacted in the resulting dry ether. Thereafter, it was washed with warm water and dried. In the surface infrared spectrum of the layer removed by about 12 to 15 μ from the surface, 2930 cm ^-1 , 2850 cm ^-1 , 1450 to 1430
Absorption due to C-H was observed at cm ^-1 . The resulting membrane was reacted with methyl iodide in methanol at 50°C for 48 hours. It was then washed in methanol and treated with a methanol solution of lithium chloride for 24 hours. It was further washed in methanol at 50°C for 8 hours. In the infrared spectrum of the film after drying, the absorption in the 3000 to 2800 cm ¹ region of the sulfonamide layer was shifted to the higher wavenumber side due to quaternization. As a result of a cresol red staining test, the resulting three-layer ion exchange membrane was colored reddish-purple at a thickness of approximately 130 μm in the center, indicating that quaternary ammonium groups were formed in the center layer. Meanwhile, on both sides approx.
The 10μ layer was colored blue with crystal violet. From the above results, the obtained membrane has approximately
It was found to be a three-layer ion exchange membrane containing a sulfonate salt in the 5μ layer and a quaternary ammonium salt in the central approximately 130μ layer. The exchange capacity was 0.9 meq/g dry membrane for the sulfonic acid base layer and 0.7 meq/g dry membrane for the quaternary ammonium base layer. Evaluation of this three-layer structure ion exchange membrane was carried out in Example 1.
showed similar results. Example 3 A reaction was carried out in the same manner as in Example 2 except that N,N,N'-trimethylethylenediamine was used in place of the N-methylpiperazine used in Example 2 to obtain a three-layer structure ion exchange membrane. The exchange capacity was 0.9 meq/g dry membrane for the sulfonic acid base layer and 0.7 meq/g dry membrane for the quaternary ammonium base layer. Evaluation of this three-layer ion exchange membrane showed the same results as in Example 1. Example 4

The copolymer obtained by _{copolymerization} with
0.92 meq/g dry resin). Next 10wt
% caustic soda/methanol and from both sides.
Hydrolyzed to a depth of 7μ. Using this tube, a reaction was carried out in the same manner as in Example 3. In a staining test, the approximately 110μ central layer was colored reddish-purple with cresol red, and the presence of quaternary ammonium chloride groups was confirmed in the approximately 110μ central layer. Meanwhile, the approximately 7μ layer on both sides was colored blue with crystal violet. From the above results, it can be seen that the obtained membrane is a three-layer ion exchange membrane containing a sulfonate in the approximately 7 μm layer on both sides and a quaternary ammonium salt in the approximately 110 μm layer in the center. The resulting three-layer ion exchange tube had an exchange capacity of 0.92 meq/g dry resin for the sulfonic acid layer and 0.84 meq/g dry resin for the quaternary ammonium chloride layer. The obtained three-layer structure ion exchange tube was evaluated in the same manner as in Example 1 and showed the same results.

[Brief explanation of the drawing]

Figure 1 shows the surface infrared absorption spectrum of the layer containing the quaternary ammonium group of the three-layer structure film obtained in Example 1, and Figure 2 shows the spectrum of the three-layer structure film obtained in Example 1. .

Claims (1)

[Claims] 1. Has a three-layer structure, has a cation exchange group in the pendant chains of both layers, has an anion exchange group in the pendant chain of the central layer, and has a main chain made of a perfluorocarbon polymer. Non-crosslinked fluorine-containing three-layer ion exchange membrane. 2. The fluorine-containing three-layer ion exchange membrane according to claim 1, wherein the cation exchange group is a sulfonic acid group and the anion exchange group is a quaternary ammonium group. ₃ The layer having a cation exchange group on the pendant chain has _the following general formula: or 1, n=1 or an integer from 2 to 5, p and q are positive numbers, and the ratio p/q is from 2 to 16. A layer consisting of repeating units represented by the following and having an anion exchange group in the pendant chain has the general formula: x, l, m, n, p and q are the same as above, z is a group containing a quaternary ammonium group The fluorine-containing three-layer structure ion exchange membrane according to claim 1, which comprises the repeating unit represented by the above formula. 4 Claims 1, 2, or 3 in which the fluorine-containing three-layer ion exchange membrane is in the form of a flat membrane.
The fluorine-containing three-layer structure ion-exchange membrane described in 2. 5. The fluorine-containing three-layer ion exchange membrane according to claim 1, 2 or 3, wherein the fluorine-containing three-layer ion exchange membrane is tube-shaped.