JPH0735444B2 - Method for producing anion exchange membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an anion exchange membrane having excellent alkali resistance.

[Problems to be Solved by Conventional Techniques and Inventions] In recent years, development of a process using a membrane has been active, and among them, a process using an ion-exchange membrane has received a great deal of attention from the viewpoint of energy saving.

Among the ion exchange membranes, a so-called perfluorocarbon-based membrane represented by Nafion (DuPont) has been developed as a cation exchange membrane. The skeleton of this type of membrane is composed of a perfluorocarbon polymer, and its durability is extremely superior to that of a conventional cation exchange membrane.

On the other hand, the anion exchange membrane has been a problematic field from the viewpoint of durability. Therefore, one of the inventors of the present invention has already proposed an anion exchange membrane having a completely novel structure in which the main chain is a perfluorocarbon polymer, as an anion exchange membrane having excellent durability (Japanese Patent Laid-Open No. 61-7312). Gazette). Although this type of film has extremely excellent durability as compared with conventional films, it has the following problems in the manufacturing process.

Japanese Unexamined Patent Publication No. 61-7312 discloses the following process.

[However, Rf p '/ q' is about 6.5. ] When using this type of membrane in the presence of alkali, -SO ₂ N
H- becomes -SO ₂ NNa- and forms a complex with a quaternary ammonium group, resulting in an increase in the membrane resistance and unusability (see Comparative Example).

Therefore, the following process has been proposed as a method for solving this problem (the above publication).

However, although the film obtained by this process has solved the above-mentioned problems, the alkyl group of CH ₃ NH- of the reacting amine (here, —CH ₃ ) becomes a steric hindrance to decrease the reaction rate, At the same time, there is a problem that the film resistance becomes incomplete and there is still room for lowering the membrane resistance, and at the same time, there is a drawback that the amine used is limited.

The present invention has been made from the above viewpoint, and an object thereof is to provide a method for producing an anion exchange membrane having extremely low membrane resistance and excellent alkali resistance in a short reaction time.

[Means for Solving Problems] The inventors of the present invention have conducted intensive studies based on such a background, and have completed the present invention.

That is, the method for producing an anion exchange membrane of the present invention is represented by the following general formula (1) [X is F or CF ₃ , l is an integer of 0 to 5, m is 0 or 1, n is an integer of 1 to 5, p and q are positive numbers, and the ratio p / q is 2 ~ 16. same as below. ] And a film having a structure represented by the following general formula (2) H ₂ NCH ₂ rNR ₁ R ₂ (2) [r is 2 to 7, R ₁ and R ₂ are C _{1 to} C ₆ alkyl groups,
R ₁ and R ₂ are the same or different. same as below. ], Then with alkali metal hydroxide, and then with alkali iodide.

This will be specifically described below.

In the above case, the copolymer having (1) is a copolymer of tetrafluoroethylene and, for example, the following comonomer CF ₂ = CFO-CF ₂ -CF ₂ -SO ₂ F CF ₂ = CFO-CF ₂ CF ( the _{CF 3) OCF 2 -CF 2 -SO} 2 F CF 2 = CF (OCF 2 CF (CF 3)) 2 OCF 2 -CF 2 -SO 2 F CF 2 = CFCF 2 -CF 2 -SO 2 F can get. The copolymerization can be obtained in the range of 0 to 200 ° C. and 1 to 200 atm in the presence of a free radical initiator.

Of course, the structure of the film used in the present invention is not limited to the above.

These copolymers are molded into a film. For this molding, a general technique of melting and forming a thin film can be used.

The thickness of the film used in the present invention is usually 50 μm or
The thickness of 500 μm is used, and an appropriate thickness can be selected in consideration of the strength of the film, the specific electric conductivity, the current efficiency, etc. Further, such a film may be reinforced with a Teflon fiber cloth or the like in order to improve the strength of the film.

The film may have a flat film shape or a tube shape.

R ₁ and R ₂ shown in the general formula (2) have 1 to 6 carbon atoms.
However, if the number of carbon atoms exceeds that, steric hindrance will occur at the alkylation stage, and the alkylation will not proceed efficiently.

The film having the above-mentioned structure (1) is converted into a film having a sulfonamide group by reacting it with an amine represented by the following general formula H ₂ NCH ₂ rNR ₁ R ₂ (2). Examples of the amine represented by the general formula (2) include dimethylaminoethylamine, diethylaminoethylamine, dipropylaminoethylamine, dimethylaminopropylamine,
Examples thereof include diethylaminopropylamine, dibutylaminopropylamine, dimethylaminobutylamine and the like.

The reaction of these amines can be carried out in the amine or using a solvent.

When a solvent is used, ethers such as diethyl ether, tetrahydrofuran and dioxane; hydrocarbons such as benzene, toluene and hexane can be used.

A reaction temperature of room temperature to 80 ° C and a reaction time of 60 hours are sufficient.

The film having a sulfonamide group thus obtained is converted into an alkali metal salt of a sulfonamide group by acting an alkali metal hydroxide.

Although an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide or the like can be used as the alkali metal hydroxide, the use of a solvent such as methanol is excellent in terms of reaction efficiency. A reaction temperature in the range of room temperature to 90 ° C is sufficient.

The film of the obtained alkali metal salt of sulfonamide group is converted into an anion exchange membrane by alkylating the film with an alkylating agent.

As the alkylating agent, for example, methyl iodide, ethyl iodide, butyl iodide or the like can be used.

At this time, methynol, ethanol, dimethylformamide or the like can be used as a solvent.

When it is necessary to exchange the counterion of the membrane having an anion exchange group obtained here, it can be exchanged by treating with an alkali metal salt by a conventional method.

[Effects of the Invention] As described above, it is possible to obtain an anion exchange membrane having extremely low membrane resistance and excellent alkali resistance in a short reaction time.

EXAMPLES Next, the present invention will be described in more detail with reference to examples.

In the following examples, the resistance of the membrane is measured at a temperature of 25 ° C. for 1000 cycles after being sufficiently equilibrated with 0.5N saline and 1N sodium hydroxide aqueous solution.

Example 1 CF ₂ = CF ₂ and _{CF 2 = CFO-CF 2 CF} (CF 3) O-CF 2 -CF 2 -SO 2 F
The copolymer obtained by copolymerization with
125 μ, p / q = 7.6).

Then, the film was immersed in dimethylaminopropylamine and reacted at 40 ° C. for 50 hours. After the reaction, wash with water (conversion rate 97% in this case, based on elemental analysis), soak in 10 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1), treat at 50 ° C for 30 hours, and then with water Washed and air dried.
Then ethyl iodide / dimethylformamide (volume ratio 1:
In 4), it was treated at 60 ° C for 7 days. Then, after washing with methanol, in a methanol solution of lithium chloride (10 wt%),
It was treated at 50 ° C. for 24 hours.

In the dyeing test, the obtained film was colored yellow-orange with cresol red and was not dyed with crystal violet at all.

The membrane resistance was 3.8 Ω · cm ² in 0.5N saline. Next, the film was immersed in a 20 wt% sodium hydroxide aqueous solution for 10 days, and then the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 0.9 Ω · cm ² .

Comparative Example 1 The same film as used in Example 1 was used.

The film was immersed in dimethylaminopropylethylamine and reacted at 40 ° C. for 50 hours. After the reaction, the product was washed with water (conversion rate in this case was 72%, based on elemental analysis) and air-dried.
Then ethyl iodide / dimethylformamide (volume ratio 1:
In 4), it was treated at 60 ° C for 7 days. Then, after washing with methanol, in a methanol solution of lithium chloride (10 wt%),
It was treated at 50 ° C. for 24 hours.

In the dyeing test, the obtained film was colored yellow-orange with cresol red and light blue with crystal violet.

The membrane resistance was 5.2 Ω · cm ² in 0.5N saline. Next, the film was dipped in a 20 wt% sodium hydroxide aqueous solution for 10 days, and then the film resistance was measured in a 1N sodium hydroxide aqueous solution and found to be 30 Ω · cm ² .

Comparative Example 2 A film was obtained in the same manner as in Example 1 except that the treatment of the 10 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1) in Example 1 was not performed.

The membrane resistance of the obtained film is 4.2 Ω · cm ^{2 in} 0.5N saline.
Met. Next, after the film was immersed in a 20 wt% sodium hydroxide aqueous solution for 10 days, the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 852 Ω · cm ² .

Example 2 A copolymer obtained by copolymerization of CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) O-CF ₂ -CF ₂ -SO ₂ F was formed into a film (film thickness 17
0 to 160 μ, p / q = 6.5).

Then, the film was immersed in dimethylaminopropylamine and reacted at 40 ° C. for 50 hours. After the reaction, wash with water,
(Conversion rate in this case was 97%, based on elemental analysis) It was immersed in a 10 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1), treated at 50 ° C. for 30 hours, washed with water and air-dried.
Then methyl iodide / dimethylformamide (volume ratio 1:
In 4), it was treated at 60 ° C for 7 days. The obtained film was washed with methanol and then treated in a methanol solution of lithium chloride (10 wt%) at 50 ° C. for 24 hours.

In the dyeing test, the obtained film was colored yellow-orange with cresol red and was not dyed with crystal violet at all.

The membrane resistance was 4.0 Ω · cm ² in 0.5N saline.

Next, the film was placed in a 20 wt% sodium hydroxide aqueous solution at 10%.
After soaking for one day, the film resistance was measured in a 1N sodium hydroxide aqueous solution and found to be 1 Ω · cm ² .

Comparative Example 3 A film was obtained in the same manner as in Example 2 except that the treatment of 10 wt% aqueous sodium hydroxide solution / methanol (volume ratio 1: 1) in Example 2 was not performed.

The membrane resistance of the obtained film is 4.5 Ω · cm ^{2 in} 0.5N saline.
Met. Next, after the film was immersed in a 20 wt% sodium hydroxide aqueous solution for 10 days, the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 758 Ω · cm ² .

Example 3 A film was obtained in the same manner as in Example 2 except that dimethylaminoethylamine was used instead of dimethylaminopropylamine in Example 2.

In the dyeing test, the obtained film was colored yellow-orange with cresol red and was not dyed with crystal violet at all.

The membrane resistance was 4.3 Ω · cm ² in 0.5N saline.

Next, the film was placed in a 20 wt% sodium hydroxide aqueous solution at 10%.
After immersion for 1 day, the film resistance was measured in a 1N sodium hydroxide aqueous solution and found to be 1.5 Ω · cm ² .

Comparative Example 4 A film was obtained in the same manner as in Example 3, except that the treatment of the 10 wt% sodium hydroxide aqueous solution / methanol in Example 3 was not performed.

The membrane resistance of the obtained film is 4.5 Ω · cm ^{2 in} 0.5N saline.
Met. Next, after the film was immersed in a 20 wt% sodium hydroxide aqueous solution for 10 days, the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 985 Ω · cm ² .

Example 4 CF ₂ = CF ₂ and _{CF 2 = CFO-CF 2 CF} (CF 3) O-CF 2 -CF 2 -SO 2 F
The copolymer obtained by copolymerization with
0.63 mm, outer diameter 0.88 mm, p / q = 6.5) and then immersed in dimethylaminopropylamine and reacted at room temperature for 4 days. After the reaction, the product was washed with water (conversion rate in this case was 95%,
10 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1) was introduced into the tube and treated at 50 ° C. for 30 hours. After washing with water, introduce methyl iodide / dimethylformamide (volume ratio 1: 4) into the tube and
It was treated at 7 ° C for 7 days.

The obtained tube was washed with methanol and then treated in a methanol solution of lithium chloride (10 wt%) at 50 ° C for 24 hours.

The resulting tube was colored yellow-orange with cresol red in the dyeing test and was not dyed with crystal violet at all.

Claims (6)

[Claims] 1. The following general formula [X is F or CF ₃ , l is an integer of 0 to 5, m is 0 or 1, n is an integer of 1 to 5, p and q are positive numbers, and the ratio p / q is 2 A film having a structure represented by the formula: H ₂ NCH ₂ rNR ₁ R ₂ [r is 2 to 7, R ₁ and R ₂ are C _{1 to} C ₆ alkyl groups,
R ₁ and R ₂ are the same or different] and then reacted with alkali metal hydroxide and then with alkyl iodide. 2. The method according to claim 1, wherein the film is a flat film. 3. A method according to claim 1, wherein the film is tubular. 4. The method according to any one of claims 1 to 3, wherein the alkali metal hydroxide is lithium hydroxide. 5. The method according to any one of claims 1 to 3, wherein the alkali metal hydroxide is sodium hydroxide. 6. The method according to any one of claims 1 to 3, wherein the alkali metal hydroxide is potassium hydroxide.