JPH082975B2 - Method for producing anion exchange membrane having excellent alkali resistance - 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 Prior Art and Invention]

In recent years, development of a process using a membrane has been actively conducted, 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 in terms of durability. Therefore, one of the present inventors, Kiyota et al., Has already proposed an anion exchange membrane having a completely new structure in which the main chain is made of a perfluorocarbon polymer as an anion exchange membrane having excellent durability (Japanese Patent Laid-Open No. Sho 61-61). −731
2). This type of film has extremely excellent acid resistance and oxidation resistance as compared with conventional films, but has a problem in durability especially against alkali.

The present invention has been made from such a viewpoint,
Its purpose is to provide an anion exchange membrane having excellent alkali resistance.

[Means for solving problems]

The present inventors have conducted intensive studies based on such a background and completed the present invention.

That is, the method for producing an anion exchange membrane of the present invention comprises 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. A film made of a polymer having a structure represented by the following general formula (2) H ₂ N- (CH ₂ ) _r- C (R ₁ ) (R ₂ )-(CH ₂ ) _s -N
(R ₃ ) (R ₄ ) ... (2) (r and s are integers from _{1 to} 8, R ₁ is hydrogen or a C _{1 to} C ₄ alkyl group, R ₂ is a C _{1 to} C ₄ alkyl group, R ₃ and R ₄ are C ₁
After reacted with the compound represented by -C ₆ alkyl group), is reacted with an alkali metal hydroxide, followed consists in reacting with alkyl iodide.

 This will be specifically described below.

The copolymer having the above structure (1) is a copolymer of tetrafluoroethylene and, for example, a comonomer shown below CF ₂ ═CF—O—CF ₂ —CF ₂ —SO ₂ F CF ₂ ═CF—O— _{CF 2 -CF (CF 3) -O} -CF 2 -CF 2 -SO 2 F CF 2 = CF-O-CF 2 -CF (CF 3) -O-CF 2 -CF (CF 3) -
_{O-CF 2 -CF 2 -SO 2} F CF 2 = is obtained by _{CF-CF 2 -CF 2 -SO 2} F. The copolymerization can be obtained in the presence of a free radical initiator under conditions ranging from 0 to 200 ° C and 1 to 200 atm.

Of course, the film used in the present invention is not limited to that obtained by the above-mentioned comonomers.

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 to 500 μm, and an appropriate thickness can be selected in consideration of the strength, specific electric conductivity, current efficiency, etc. of the film. Further, such a film may be reinforced with a Teflon fiber cloth or the like for improving the strength of the film.

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

In the general formula (2), r and s are 1 to 8 and R ₁
Is hydrogen or a C ₁ -C ₄ alkyl group, R ₂ is a C ₁ -C ₄ alkyl group, but if the number or carbon number exceeds the above range, the amidation reaction rate decreases, The reaction may be incomplete. R ₃ and R ₄ are C _{1 to} C ₆ alkyl groups, but if the number of carbon atoms is 7 or more, steric hindrance occurs at the alkylation stage, and the alkylation does not proceed efficiently.

The film having the above structure (1) is reacted with the amine represented by the general formula (2) to convert it into a film having a sulfonamide group.

Structure of the amine represented by the above general formula (2) _{is, H 2 N-CH 2 -C} (CH 3) 2 -CH 2 -N (CH 3) 2 H 2 N-CH 2 -C (CH 2 CH 3 _{) 2 -CH 2 -N (CH 3} ) 2 H 2 N-CH 2 -CH 2 -C (CH 3) 2 -CH 2 -CH 2 -N (CH 3) 2 H 2 N-CH 2 -CH 2 _{-C (CH 3) 2 -CH 2} -CH 2 -N (CH 2 CH 3)
_{2 H 2 N-CH 2 -CH} 2 -C (CH 3) 2 -CH 2 -CH 2 -N (CH 2 CH 2 CH
₂ CH ₃ ) _{2 and the} like can be exemplified.

The reaction with these amines can be carried out in these amines or using other solvents.

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 100 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.

As the alkali metal hydroxide, an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide or the like can be used, but 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 obtained film of the alkali metal salt of sulfonamide group is converted to an anion exchange membrane by alkylating the film with alkyl iodide.

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

At this time, methanol, 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.

[Work]

Japanese Unexamined Patent Publication (Kokai) No. 61-7312 describes that the durability is improved by synthesizing using a linear amine, but the present invention is characterized by using a branched amine.

It is unclear why the anion exchange membrane synthesized using a branched amine has a greater effect on alkali resistance than the one synthesized using a linear amine, but it can be explained as follows.

It is considered that this is because the quaternary ammonium group, which is an exchange group, becomes stable due to the electron donating effect of the branched alkyl group.

〔The invention's effect〕

By using the anion exchange membrane according to the present invention as a diaphragm for various electrolysis, which particularly requires alkali resistance such as recovery of alkali from an inorganic salt, it becomes possible to use a highly concentrated alkaline liquid, and the membrane is used for a long time. In order to withstand, it is possible to put into practice many processes that were not possible in the past.

〔Example〕

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

In the following examples, the resistance of the membrane is measured after fully equilibrating it with a 1N sodium hydroxide aqueous solution and then at 1000 cycles of alternating current at a temperature of 25 ° C.

Example 1 CF ₂ = CF ₂ and _{CF 2 = CF 2 -O-CF} 2 -CF (CF 3) -O-CF 2 -C
The copolymer obtained by the copolymerization of F ₂ -SO ₂ F were filmed.
(Thickness 170 μm, p / q = 6.5) Then, the film was formed into H ₂ N—CH ₂ —CH ₂ —C (CH ₃ ) ₂ —CH
_It is immersed in an amine having a structure of _2- CH ₂ -N (CH ₃ ) ₂ at 60 ° C for 60
Allowed to react for hours. After the reaction, the product was washed with methanol (conversion rate in this case 97%, confirmed by elemental analysis), immersed in 20 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1), and treated at 60 ° C. for 7 days , Washed with methanol. Then, it was treated in ethyl iodide / dimethylformamide (volume ratio 1: 4) at 60 ° C. for 7 days.

Next, in a 10 wt% methanol solution of lithium chloride at 50 ° C
After treating for 24 hours, it was immersed in a 0.5N sodium chloride aqueous solution for 3 days.

When the obtained film was dyed with cresol red, it was colored yellow orange and was not dyed with crystal violet at all.

The membrane resistance was 0.9 Ω · cm ² in 1N aqueous sodium hydroxide solution.

Next, the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, and then the film resistance was measured in a 1N sodium hydroxide aqueous solution. As a result, there was no change at 0.9 Ω · cm ² .

Comparative Example 1 H ₂ N—CH ₂ —CH ₂ —C (CH ₃ ) ₂ —CH ₂ —CH _{2 in} Example 1
_{-N (CH 3) H 2 N} -CH 2 instead represented by the amine ₂
Except for using the _{-CH 2 -CH 2 -CH 2 -CH 2} -N (CH 3) 2 , the
A film was obtained in the same manner as in Example 1. The conversion of amidation was 97% (from elemental analysis).

When the obtained film was dyed with cresol red, it was colored yellow orange and was not discolored by crystal violet at all.

The membrane resistance was 0.9 Ω · cm ² in 1N aqueous sodium hydroxide solution.

Next, after the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 900 Ω · cm ² .

Comparative Example 2 The procedure of Example 1 was repeated, except that the treatment of the 20 wt% aqueous sodium hydroxide solution / methanol (volume ratio 1: 1) in Example 1 was not performed.

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

The membrane resistance was 1.8 Ω · cm ² in 1N sodium hydroxide aqueous solution.

Next, after the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, the film resistance was measured in a 1N sodium hydroxide solution, and it was 1400 Ω · cm ² .

EXAMPLE ₂ CF 2 = CF 2 and _{CF 2 = CF-O-CF} 2 -CF (CF 3) -O-CF 2 -
The copolymer obtained by the copolymerization with CF ₂ —SO ₂ F was formed into a film (film thickness 120 μ, p / q = 7.6). Then the film
_{H 2 N-CH 2 -CH 2} -C (CH 3) 2 -CH 2 -CH 2 -N (CH 3) 2
It was immersed in an amine having the structure of and reacted at 40 ° C. for 60 hours. After the reaction, it was washed with methanol (conversion rate in this case 97%, from elemental analysis), immersed in 20 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1), treated at 60 ° C for 7 days, and then with methanol. Washed. It was then treated in methyl iodide / dimethylformamide (volume ratio 1: 4) at 60 ° C. for 7 days.

Next, in a 10 wt% methanol solution of lithium chloride at 50 ° C
After the treatment for 24 hours, it was immersed in a 0.5N sodium chloride aqueous solution for 3 days.

When the obtained film was dyed with cresol red, it was colored yellow orange and was not dyed with crystal violet at all.

The membrane resistance was 1.1 Ω · cm ² in 1N aqueous sodium hydroxide solution.

Then, the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, and the film resistance was measured in a 1N sodium hydroxide aqueous solution. As a result, there was no change of 1.1 Ω · cm ² .

Comparative Example 3 A film was obtained in the same manner as in Example 2 except that the treatment of the 20 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1) used in Example 2 was not performed.

The film obtained was colored yellow-orange with cresol red and not crystal violet in the dyeing test.

The membrane resistance of the obtained film was 1.6 Ω · cm ² in a 1N sodium hydroxide aqueous solution.

Next, after the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 1500 Ω · cm ² .

Example 3 H ₂ N—CH ₂ —CH ₂ —C (CH ₃ ) ₂ —CH ₂ —CH _{2 in} Example ₂
-N (CH _{3) 2} in place in the H ₂ N-CH ₂ -C amine (CH ₃₎
Except for using _{2 -CH 2 -N (CH 3)} 2 amine structure,
A film was obtained in the same manner as in Example 2. The conversion of amidation was 97% (from elemental analysis).

When the obtained film was dyed with cresol red, it was colored yellow orange and was not dyed with crystal violet at all.

The membrane resistance of the obtained film was 1.0 Ω · cm ² in a 1N sodium hydroxide aqueous solution.

Next, the film was dipped in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, and the film resistance was measured in a 1N sodium hydroxide aqueous solution. As a result, there was no change at 1.0 Ω · cm ² .

Comparative Example 4 A film was obtained in the same manner as in Example 3 except that the treatment of 20 wt% sodium hydroxide / methanol (volume ratio 1: 1) used in Example 3 was not performed.

When the obtained film was dyed with cresol red, it was colored yellow orange and was not dyed with crystal violet at all.

The membrane resistance of the obtained film was 1.8 Ω · cm ² in a 1N sodium hydroxide aqueous solution.

Next, the film was immersed in a 10 wt% sodium hydroxide aqueous solution at 60 ° C. for 10 days, and the film resistance was measured in a 1N sodium hydroxide aqueous solution, and it was 1200 Ω · cm ² .

Example 4 CF ₂ = CF ₂ and _{CF 2 = CF-O-CF} 2 -CF (CF 3) -CF 2 -CF 2
And the tube of the copolymer obtained by copolymerization of -SO ₂ F (inner diameter 0.63 mm, outer diameter 0.88mm, p / q = 6.5) .

Then the tube _{H 2 N-CH 2 -CH 2} -C (CH 3) 2 -CH
₂ -CH ₂ -N (CH ₃₎ was immersed in the amine of the _second structure, 8 at 40 ° C.
Reacted for 0 hours. After the reaction, wash with methanol (conversion rate in this case 97%, from elemental analysis), immerse in 20 wt% sodium hydroxide aqueous solution / methanol (volume ratio 1: 1), 60 ° C
After being treated for 7 days, it was washed with methanol. Then, in methyl iodide / dimethylformamide (volume ratio 1: 4), 6
It was treated at 0 ° C. for 7 days. Then, the mixture was treated in a 10 wt% methanol solution of lithium chloride at 50 ° C. for 24 hours and then immersed in a 0.5N sodium chloride aqueous solution for 3 days.

When the obtained film was dyed with cresol red, it was colored yellow orange 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 made of a polymer having a structure represented by the following general formula H ₂ NCH _{2 r} C (R ₁ ) (R ₂ ) CH _{2 s} N (R ₃ ) (R ₄ ) (r And s is an integer of 1 to 8, R ₁ is hydrogen or a C _{1 to} C ₄ alkyl group, R ₂ is a C _{1 to} C ₄ alkyl group, and R ₃ and R ₄ are both C _{1 to} C ₆ alkyl. A compound represented by the formula (1), which is reacted with an alkali metal hydroxide and then with an 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.