JP3044784B2 - Method for producing fluorine-containing bipolar membrane - Google Patents

Description

The present invention relates to a method for producing a fluorine-containing bipolar film. A bipolar membrane is a membrane having a two-layer structure, having a cation exchange group in one layer and an anion exchange group in the other layer, and regenerating the salt generated as industrial waste by decomposition into acid and base. It can be used for utilization, recovery of various acid waste liquids, production of acids and bases, and the like.

[Prior Art] Conventionally, many proposals have been made as a method for manufacturing such a bipolar film.

For example, JP-B-60-31860 and JP-A-63-95235 describe that a cation exchange group is introduced by sulfonation on one surface of a polymer membrane containing a benzene ring, and a quaternary anion exchange group is formed on the other surface. A method for introducing an ammonium halide group is disclosed. Japanese Patent Publication No. 60-35936 discloses a bipolar membrane produced by applying a solution of polyvinylbenzyl chloride and polyvinylidene fluoride.Furthermore, Japanese Patent Publication No. There is disclosed a film bonded to an interface with an inorganic compound such as iron chloride interposed therebetween.

Furthermore, Japanese Patent Publication No. 60-1234 discloses a fluorine-based bipolar membrane whose main chain skeleton is a perfluorocarbon polymer for the purpose of improving mechanical strength and chemical resistance.

A conventional method for producing a fluorine-containing bipolar membrane is to convert a sulfonic acid group into a carboxylic acid group on only one side using a homogeneous fluorinated sulfonic acid membrane as a starting material, introduce an amine after esterification, and quaternize. A method in which one side is a sulfonic acid type cationic membrane and the other side is a quaternary ammonium type anionic membrane. After diamine is introduced into only one side of the homogeneous fluorine-based fluoronyl fluoride membrane, the entire membrane is alkali-treated and the amine portion is quaternized, so that one side has a sulfonic acid type cation membrane and the other side has four sides. There is a method of forming a grade ammonium type anion membrane. However, when performing a reaction on only one side, there was a problem that it was difficult to finely control the reaction thickness. In particular, it was practically impossible to produce a bipolar membrane having a cation layer thinner than an anion layer.

[Problems to be Solved by the Invention] An object of the present invention is to improve the problems of the conventional method for producing a fluorinated bipolar film and to provide a novel method for producing a fluorinated bipolar film. It is in.

[Means for Solving the Problem] The present inventors have a two-layer structure, have a sulfonyl fluoride group on a pendant chain of one layer, and add the sulfonyl fluoride group to water on a pendant chain of the other layer. This is a layer converted to a sulfonic acid group by hydrolysis by acting, and a main chain of a membrane made of a perfluorocarbon polymer is reacted with an amine, and a sulfonyl group is converted to a sulfonylfluoryl group without denaturing the sulfonic acid group. A tertiary amine was introduced through the method, and a nitrogen atom of the tertiary amine was quaternized to find a method for producing a fluorinated bipolar membrane, thereby completing the present invention.

[Operation] An example of the present invention will be described.

Ethylene tetrafluoride and, for example, the following comonomers And 0 to 200 ° C. in the presence of a free radical initiator
And a copolymer having sulfonyl fluoride in a pendant chain by copolymerizing under conditions in the range of 1 to 200 atm. Can be obtained. Of course, the film used in the present invention is not limited to those obtained by the above-mentioned comonomer. These copolymers are
It is molded into a film. For this molding, a general technique of molding a thin film by melting usually can be used. The thickness of the film used in the present invention is usually 50 μm to 500 μm, and an appropriate thickness can be selected in consideration of the strength, specific conductivity, current efficiency and the like of the film. Such a membrane may be reinforced with a Teflon fiber cloth or the like to improve the strength of the membrane.

The shape of the film may be a flat film or a tube.

Water is allowed to act on only one side of such a membrane under an alkaline atmosphere or an acid atmosphere to cause hydrolysis, thereby converting a sulfonyl fluoride group into a sulfonic acid group. The water to be acted on may be either a liquid or a gas, and the thickness of the layer that converts to sulfonic acid groups can be controlled by the time for which the water acts, and as a result, the thickness of the cation exchange layer can be controlled. .

Alternatively, it is also possible to obtain a sulfonyl fluoride / sulfonic acid bilayer membrane by laminating a film having a sulfonic acid group and a film having a sulfonyl fluoride group.

In this way, it is composed of two layers, one layer is the above-mentioned sulfonyl fluoride layer, and the other layer has the following formula having a sulfonic acid group in a pendant chain. Can be obtained. Of these, the layer having a sulfonyl fluoride group becomes an anion exchange layer by introducing a quaternary ammonium group which is an anion exchange group by a reaction described below. On the other hand, the alkali metal salt layer of sulfonic acid remains as a cation exchange layer without being changed by the reaction. Therefore, if the thickness of the first layer having a sulfonyl fluoride group and the thickness of the alkali metal salt layer of sulfonic acid are specified, the bipolar ion exchange membrane in which the thickness of the anion exchange layer / cation exchange layer is arbitrarily controlled. Can be manufactured.

Hereinafter, the reaction of converting the sulfonyl fluoride base layer into a quaternary ammonium group will be described below.

Diamine represented by the following general formula H2N- (CH2) nC (R1) (R2)-(CH2) m-N (R
3) (R4), To introduce an amine into the sulfonyl fluoride moiety. As the structure of the amine represented by the above general formula, And the like.

Further, the reaction with these amines can be carried out in the amine or using another solvent. When a solvent is used, diethyl ether, tetrahydrofuran,
Ethers such as dioxane and hydrocarbons such as benzene, toluene and hexane can be used.

A reaction temperature of room temperature to 80 ° C. and a reaction time of 100 hours are sufficient.

The thus-obtained film having a sulfonamide group is converted into an alkali metal salt of a sulfonamide group by the action of a sodium chloride solution, and at the same time, a sulfonyl fluoride group is converted into an alkali metal salt of sulfonic acid.

As the sodium solution, a mixed system of an aqueous solution of an alkali metal hydroxide and an alcohol, an alcohol solution of an alcoholate, or the like can be used. The reaction temperature is between room temperature and 90 ° C
Is sufficient.

Sulfonic acid, which is a cation exchange group, is obtained by subjecting the obtained film composed of two layers of an alkali metal salt of a sulfonamide group and an alkali metal salt of a sulfonic acid to alkylation by acting a mixed system of dimethyl sulfoxide and alkyl iodide. By introducing a quaternary ammonium group which is an anion exchange group without destroying the group, a bipolar ion exchange membrane can be obtained. This bipolar ion exchange membrane is a membrane in which the thicknesses of the anion exchange layer and the cation exchange layer are controlled.

As the alkyl iodide, for example, methyl iodide, ethyl iodide, butyl iodide and the like can be used.

When it is necessary to exchange the counter ion of the membrane having a cation exchange group and an anion exchange group obtained here, it can be exchanged by treating with a alkali metal halide, an acid, or an alkali by a conventional method.

[Effects of the Present Invention] The present invention is characterized in that it passes through a two-layer film of a sulfonyl fluoride base layer / a sulfonic acid alkali base. With this feature, it is possible to manufacture a bipolar ion exchange membrane in which the thickness of the anion exchange layer / cation exchange layer is arbitrarily controlled.

[Examples] Examples will be shown below, but the present invention is not particularly limited to the following examples.

In the following examples, the resistance of the film was measured by immersing it sufficiently in a 0.5N aqueous solution of sodium chloride or a 1N aqueous solution of sodium hydroxide at 1,000 cycles of AC at a temperature of 25 ° C.

Example 1 The copolymer obtained by copolymerization with 02F was molded into a flat film (film thickness 170 μm, p / q = 6.5).

One side of the membrane was contacted with water vapor for 2 hours to effect hydrolysis to obtain a two-layer membrane of sulfonyl fluoride / sulfonic acid. The bilayer film was immersed in an amine having a structure of H2N-CH2-C (CH3) 2-CH2-N (CH3) 2 and reacted at 40 ° C for 60 hours. After the reaction, the resultant was immersed in a 10 wt% aqueous solution of sodium hydroxide / methanol (volume ratio of 2: 7), treated at 60 ° C. for 6 days, and then washed with methanol. Then, it was treated in ethyl iodide / dimethyl sulfoxide (1:20 by volume) at 50 ° C. for 2 days.

Then in a 10 wt% methanol solution of lithium chloride at 60 ° C
After the treatment for 24 hours, it was immersed in a 0.5N aqueous sodium chloride solution for 3 days. When the obtained membrane was stained with cresol red, only one side of the anion exchange layer (film thickness = 150 μm) was colored. On the other hand, when stained with crystal violet, only the cation exchange layer (film thickness = 20 μm) on the other side was colored.

Example 2 A bipolar ion exchange membrane was produced under the same conditions as in Example 1 except that the hydrolysis time was changed to 8 hours. When the obtained membrane was stained with cresol red, only one side of the anion exchange layer (film thickness = 130 μm) was colored. On the other hand, when stained with crystal violet, only the other one side of the cation exchange layer (film thickness = 40 μm) was colored.

Example 3 The copolymer obtained by copolymerization with 02F was molded into a flat film (film thickness 170 μm, p / q = 6.5).

A part of this film was cut off (film thickness = 20 μm), hydrolyzed, washed well with water, and dried. Hydrolyzed film (film thickness = 20 μm) and non-hydrolyzed film (film thickness = 15
0 μm) by pressure bonding to obtain a two-layer membrane of sulfonyl fluoride / sulfonic acid. A bipolar ion exchange membrane was produced from this two-layer membrane in the same manner as in Example 1.

When the obtained membrane was stained with cresol red, only one side of the anion exchange layer (film thickness = 150 μm) was colored. On the other hand, when stained with crystal violet, only the cation exchange layer (film thickness = 20 μm) on the other side was colored.

Table 1 shows the resistance of the obtained film and the anion transport number with respect to the aqueous potassium chloride solution.

Example 2 The amine represented by H2N-CH2-CH2-CH2-CH2-N (CH3) 2 instead of the amine having the structure of H2N-CH2-C (CH3) 2-CH2-N (CH3) 2 in Example 1. A fluorinated bipolar membrane was obtained in the same manner as in Example 1 except for using. When the obtained membrane was stained with cresol red, only one side of the anion exchange layer (film thickness = 150 μm) was colored. On the other hand, when stained with crystal violet, only the cation exchange layer (film thickness = 20 μm) on one side was colored.

Table 1 shows the membrane resistance and the anion transport number with respect to the aqueous potassium chloride solution.

Claims (1)

(57) [Claims] 1. A sulfonic acid group which has a two-layer structure and has a sulfonyl fluoride group on a pendant chain of one layer, and hydrolyzes the sulfonyl fluoride group on the pendant chain of the other layer by the action of water. Is a layer converted to, and the main chain reacts an amine with a membrane made of a perfluorocarbon polymer, and introduces a tertiary amine via a sulfamide group to a sulfonyl fluoride group without denaturing a sulfonic acid group, A method for producing a fluorinated bipolar membrane, further comprising quaternizing a nitrogen atom of a tertiary amine.