JP2624424B2 - Bipolar membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar membrane having a low water electrolysis voltage, excellent chemical resistance and durability, and more particularly to a water splitting method capable of decomposing a neutral salt and efficiently obtaining an alkali and an acid. The present invention relates to a bipolar membrane useful in electrodialysis.

[0002]

2. Description of the Related Art A bipolar membrane has a structure in which a cation exchange membrane and an anion exchange membrane are bonded to each other, and various production methods have been proposed. For example, a method of laminating and bonding a cation exchange membrane and an anion exchange membrane with a mixture of polyethyleneimine-epichlorohydrin (Japanese Patent Publication No. 32-3962), a method in which a cation exchange membrane and an anion exchange membrane are bonded with an ion exchange adhesive Adhesion method (Japanese Patent Publication No. 34-3961), a method of applying a paste-like mixture of a fine powder of an anion or cation exchange resin and a thermoplastic substance to a cation exchange membrane and an anion exchange membrane and compressing the mixture (Japanese Patent Publication No. 35-19635) 14531), a method of applying a paste-like substance composed of vinyl pyridine and an epoxy compound to the surface of a cation exchange membrane and irradiating the applied substance (Japanese Patent Publication No. 38-16633). A method in which a sulfonic acid type polymer electrolyte and an allylamine are attached to the surface and then cross-linked by irradiating with ionizing radiation (Japanese Patent Publication No. 51-4) No. 13), a method of depositing a mixture of the dispersion and maternal polymer ion exchange resin having an opposite charge to the surface of the ion exchange membrane (JP 53-371
No. 90), a sheet material obtained by impregnating and polymerizing a polyethylene film with styrene and divinylbenzene was sandwiched in a stainless steel frame, one side was sulfonated, the sheet was removed, and the remaining portion was chloromethylated. Amination treatment (US Pat. No. 3,562,139) and the like. However, in the bipolar membrane obtained by these methods, when water is generally decomposed, a voltage much higher than the theoretical electrolysis voltage of water (0.83 volts) is applied, and high power consumption is required. There is.

In addition, an electro-chemical actor (Ele)
trochemica Acta) Vol. 31, N
o9, PP1175 to 1176 (1986), a cation exchange membrane and an anion exchange membrane previously surface-treated with one or more inorganic electrolyte solutions such as sodium tungstate, chromium nitrate, sodium metasilicate, and ruthenium trichloride. A method for producing a bipolar membrane having a low water electrolysis voltage by press-fitting has been reported. However, in the bipolar membrane having a low water electrolysis voltage by this manufacturing method, the water electrolysis voltage rises relatively quickly at the time of use, and furthermore, the bipolar membrane itself is easily separated into a cation exchange membrane and a cation exchange membrane. There is a problem in durability, such as being lost.

[0004]

Means for Solving the Problems The present inventors have solved the above-mentioned problems of the prior art, and have found that the rise in water electrolysis voltage is small, the current efficiency is high, and We worked on the development of a bipolar membrane with excellent durability.
As a result, by using a styrene-based block copolymer having no unsaturated bond in the main chain as a base of the anion exchange layer, a bipolar membrane that achieves a desired purpose is obtained,
It has already been proposed (Japanese Patent Application No. 4-121742). An object of the present invention is to provide a bipolar membrane based on the above-mentioned novel bipolar membrane, which is further excellent in chemical resistance and durability for long-time use.

That is, according to the present invention, a cation exchange membrane and an anion exchanger having a crosslinked structure of a polyvalent amine based on a styrene-based block copolymer having no unsaturated bond in the main chain are used. A bipolar membrane is provided.

[0006] The cation exchange membrane in the present invention is not particularly limited, and is a known cation exchange membrane. For example, a cation exchange membrane having an ion exchange group such as a sulfonic acid group and a carboxylic acid group can be used, but a cation exchange membrane having a sulfonic acid group in which the ion exchange group is dissociated even under acidic conditions from the use of a bipolar membrane. A membrane is preferred. The cation exchange membrane may be of any type, such as a polymerization type, a uniform type, a non-uniform type, or a type and a type of a cation exchange membrane derived from the presence or absence of a reinforcing material and a production method. In addition, even if the cation exchange membrane has some anion exchange groups in the cation exchange membrane, the cation exchange membrane of the present invention is sufficient if the cation transport number is 90% or more. is there.

The cation exchange membrane used in the present invention is of a heavy metal ion type in which at least the counter ion of the ion exchange group present on the surface is ion-exchanged to a heavy metal ion in order to further reduce the increase in water electrolysis voltage. You can also.
The heavy metal ion referred to in the present invention is an ion excluding halogen and an inert gas element having an atomic number of 20 to 90, and is generally iron (II, III), titanium (IV), tin (II, IV). , Zirconium (IV), palladium (II),
Ruthenium (III) is desirable. As a method for obtaining a heavy metal ion-type cation exchange membrane, a known ion exchange method can be adopted.In general, a method in which the cation exchange membrane is immersed in a solution of a heavy metal salt, or a solution of the heavy metal salt is applied to or sprayed on the cation exchange membrane. It is achieved by such methods. Heavy metal ions in such a heavy metal ion type cation exchange membrane,
It is not necessary that the film is uniformly distributed in the thickness direction of the membrane, and it is sufficient that the film is present at least on the side on which the anion exchanger film is formed.
100%, particularly preferably 0.01 to 50%.

In the present invention, the styrenic block copolymer having no unsaturated bond in the main chain serving as a base of the anion exchanger is specifically a copolymer comprising a polystyrene segment (block) and a polyolefin segment (block). Styrene, which is a block copolymer of a polystyrene and a hydrogenated polymer such as polybutadiene and polyisoprene in addition to polystyrene and, for example, polyethylene, poly (ethylene-propylene), poly (ethylene-butylene), etc. Is a saturated thermoplastic elastomer. Furthermore, when the segment of the polyolefin is shown by the formula,

[0009]

Embedded image

And so on.

The content of polystyrene in such a styrenic block copolymer is generally 10 to 85% by weight, preferably 30 to 70% by weight. In other words, a copolymer having a polystyrene content of less than 10% by weight is not preferred because the electrical resistance of the resulting anion exchanger coating increases and the water electrolysis voltage increases. On the other hand, a copolymer having a polystyrene content of more than 85% by weight is not preferable because the resulting anion exchanger film is brittle and the mechanical strength is reduced.

In general, the bipolar membrane of the present invention is formed on a cation exchange membrane by using a solution of a polymer obtained by introducing a conventionally known anion exchange group, using the above-mentioned styrene block copolymer as a base. It is obtained by forming a coating of an anion exchanger. That is, in general, a predetermined styrene-based block copolymer is halomethylated,
Then, the copolymer is dissolved in a suitable solvent, cast on a cation exchange membrane to form a coating, and then reacted with a polyvalent amine to form a coating of an anion exchanger having a crosslinked structure. A method in which a polyvalent amine is added to a halomethylated copolymer dissolved in a solvent to amination and cast on a cation exchange membrane to form a coating of an anion exchanger having a crosslinked structure;
A method in which a halomethylated copolymer is aminated with a polyvalent amine to form an aminated copolymer, which is then dissolved in a solvent and cast on a cation exchange membrane to form a film of an anion exchanger having a crosslinked structure. Is adopted.

The above-mentioned halomethylation method is not particularly limited, and a known method can be used. For example, the styrenic block copolymer can be dissolved in a solvent stable in the halomethylating agent and reacted with the halomethylating agent. Halogenated hydrocarbons such as chloroform and dichloroethane are used as the solvent. As the halomethylating agent, chloromethyl methyl ether or hydrochloric acid-paraformaldehyde can be used. Tin chloride or zinc chloride can be used as the catalyst.

The solvent used for dissolving the halomethylated copolymer or aminated copolymer includes, for example, tetrahydrofuran, chloroform, dichloroethane,
A single system such as dimethylformamide or a mixed system such as chloroform-methanol and dichloroethane-methanol is appropriately selected and used. Solutions of halomethylated or aminated copolymers are generally prepared at a concentration of 0.1 to 35% by weight.

As the polyvalent amine, 2 per molecule is used.
There is no particular limitation as long as it has at least one or more primary to tertiary amino groups, for example, ethylenediamine, trimethylenediamine, N, N, N ′, N′-tetramethyl-1,3-propanediamine, N, N , N ', N'-tetramethyl-
Diamines such as 1,6-hexanediamine, triamines such as iminobispropylamine and diethylenetriamine, and polyamines such as polyethyleneimine and polyvinylpyridine are used. Among them, diamines having two tertiary amino groups in one molecule are particularly preferably used because they have high reactivity with halomethyl groups and can be easily obtained.

Further, after the solution of the halomethylated copolymer or the aminated copolymer is cast, the solvent is evaporated by natural drying or heating to obtain a desired anion exchanger film.

The ion exchange capacity of the thus obtained anion exchanger film of the present invention is not particularly limited, but is generally from 0.2 to 4.0 meq / g (dry resin), preferably from 0.5 to 4.0 meq / g (dry resin). ~ 2.5 meq / g (dry resin). That is, if the ion exchange capacity of the anion exchanger film is greater than 4.0 meq / g (dry resin), the current efficiency at the water electrolysis voltage is undesirably low. On the other hand, if the ion exchange capacity of the anion exchanger film is smaller than 0.2 meq / g (dry resin), the electric resistance increases and the water electrolysis voltage increases, which is not preferable.

In the present invention, the surface of the cation exchange membrane is sufficiently dried when casting the solution of the halomethylated copolymer or the aminated copolymer, and is roughened with sandpaper or the like. As a result, a well adhered anion exchanger film is formed, and a bipolar membrane having excellent durability can be obtained. As a method of surface roughening,
In general, the surface of the cation exchange membrane is treated with sandpaper to provide fine irregularities, or a long cation exchange membrane is manufactured, and the rolls are provided with irregularities on the guide roll during winding. A method of making the surface of the film uneven.

[0019]

According to the present invention, a bipolar membrane having a low water electrolysis voltage, excellent chemical resistance, and excellent long-term durability can be easily obtained. Therefore, in such water electrolysis using the bipolar membrane of the present invention,
This has the effect of significantly reducing power consumption. Especially recently,
Since the salt, which is a neutralized product of an acid and an alkali, is difficult to dump in the open sea due to stricter drainage regulations, the bipolar membrane of the present invention is extremely useful in a method for regenerating an acid and an alkali from an aqueous solution of such a salt.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The characteristics of the bipolar films in Examples and Comparative Examples were obtained by the following measurements. That is,
Platinum electrodes were provided in both chambers of a two-room acrylic cell separated by a bipolar membrane having an effective energization area of 10 cm ² , and 100 ml of a 1.00 N aqueous sodium hydroxide solution was provided on the anode chamber side.
And a 100 m aqueous 1.00 N hydrochloric acid solution on the cathode chamber side.
After applying a DC current of 1 A for 5 to 10 hours, the amounts of acid, base and salt in both chambers are measured to determine the water electrolysis efficiency of the bipolar membrane and the generation efficiency of hydroxyl ions (ηOH). The hydrogen ion generation efficiency (ηH) was determined. Further, platinum wire electrodes were provided very close to both sides of the bipolar membrane, and the water electrolysis voltage of the bipolar membrane was measured.

In the case of long-time energization, 4.00 N is applied to the anode chamber side using the above-described two-chamber type acrylic cell.
An aqueous sodium hydroxide solution and 4.0
Each of the 0N-hydrochloric acid aqueous solutions was supplied, and a DC current of 1 A was applied in a constant temperature water bath at 40 ° C.

Example 1 A cation exchange membrane having a sulfonic acid group as an ion exchange group (trade name: Neosepta CM-1, manufactured by Tokuyama Soda Co., Ltd.) was previously treated with sandpaper to roughen one surface, And air-dried.

Also, 100 g of a copolymer having no unsaturated bond in the main chain composed of a polystyrene segment (65% by weight) and a hydrogenated segment of polyisoprene (35% by weight) was dissolved in 1000 g of chloroform.
00 g of chloromethyl methyl ether and 10 g of tin chloride were added, reacted at 40 ° C. for 15 hours, precipitated in methanol, washed, and dried to obtain a chloromethylated copolymer.

Next, the chloromethylated copolymer was dissolved in a mixed solvent of chloroform / methanol (volume ratio: 5: 1) to obtain an 18% by weight chloromethylated copolymer solution. And dried to form a chloromethylated copolymer film having a thickness of 25 μm.

Further, the cation exchange membrane having the chloromethylated copolymer coating was added to a methanol solution of N, N, N ', N'-tetramethyl-1,3-propanediamine (10% by weight). After immersion at 50 ° C. for 50 hours and washing with water, a bipolar membrane was obtained.

When the characteristics of the obtained bipolar membrane were measured, the water electrolysis efficiency was ηOH = 98.5%, ηOH
At H = 98.5%, the water electrolysis voltage was 1.9 volts.
The characteristics of this bipolar film did not change even after 4 months of energization, and no bubbles or water bubbles were observed in the bipolar film.

Comparative Example 1 The same cation exchange membrane as in Example 1 was previously treated with sandpaper to roughen one surface. Next, an anion exchange membrane (trade name: Neosepta AM-1, manufactured by Tokuyama Soda Co., Ltd.) was placed on the roughened side of the cation exchange membrane to produce a bipolar membrane.

When the characteristics of the obtained bipolar membrane were measured, the water electrolysis voltage was initially 3.5 volts, but increased to 5.8 volts after 24 hours of energization, and the water electrolysis efficiency was ηOH = 98. 0.0% and ηH = 98.1%. Further, in the bipolar film, bubbles were generated in the film after 6 hours, and the generated bubbles became large after 50 hours, so that water electrolysis could not be performed substantially.

Example 2 The same cation exchange membrane as in Example 1 (trade name: Neosepta C)
M-1; manufactured by Tokuyama Soda Co., Ltd.) was previously treated with sandpaper to roughen one surface, immersed in a 2% by weight aqueous solution of stannous chloride at 25 ° C. for 1 hour, and then sufficiently washed with ion-exchanged water. Washed and air dried at room temperature.

Next, the chloromethylated copolymer obtained in Example 1 was mixed with chloroform / methanol (volume ratio: 5:
After dissolving in the mixed solvent of 1) to obtain a chloromethylated copolymer solution of 18% by weight, the solution is applied to the roughened surface of the tin ion type cation exchange membrane, dried and dried to obtain a chloromethylated copolymer having a thickness of 20 μm. A polymer coating was formed.

Further, the tin ion type cation exchange membrane having the chloromethylated copolymer coating was used for N, N, N ',
Immersed in a methanol solution of N'-tetramethyl-1,3-propanediamine (10% by weight) at 30 ° C. for 70 hours,
After sufficiently washing with water, a bipolar membrane was obtained.

When the characteristics of the bipolar membrane thus obtained were measured, the water electrolysis efficiency was ηOH = 99.4.
%, ΗH = 99.3% and the water electrolysis voltage was 1.3 volts. Further, the bipolar membrane was immersed in a mixed solution of chloroform / methanol (volume ratio: 3: 1) for 3 hours, washed sufficiently with water, and the characteristics of the bipolar membrane were measured. The water electrolysis efficiency was ηOH = 99.1% , ΗH = 99.1
% And the water electrolysis voltage was 1.3 volts. The characteristics of this bipolar film did not change even after 4 months of energization, and no bubbles or water bubbles were observed in the bipolar film.

Comparative Example 2 A tin ion type cation exchange membrane having a chloromethylated copolymer film obtained in Example 2 was immersed in a trimethylamine aqueous solution (10% by weight) at 30 ° C. for 48 hours, washed with water, A bipolar membrane was obtained.

When the obtained bipolar membrane was immersed in a mixed solution of chloroform / methanol (volume ratio: 3: 1) for 3 hours, the coating of the anion exchanger was dissolved, and the characteristics of the bipolar membrane were measured. Could not.

Example 3 The same cation exchange membrane as in Example 2 (trade name: Neosepta C)
M-1 (manufactured by Tokuyama Soda Co., Ltd.) was previously treated with sandpaper to roughen one surface, immersed in a 2% by weight aqueous ferrous chloride solution at 25 ° C. for 1 hour, and then sufficiently ion-exchanged with water. Washed and air dried at room temperature.

Next, the chloromethylated copolymer obtained in Example 1 was dissolved in tetrahydrofuran to form a 20% by weight solution, and N, N, N ', N'-tetramethyl-1, 3% by weight of 6-hexanediamine was added.
The solution thus prepared was applied to the roughened side of the iron ion type cation exchange membrane and dried to prepare a bipolar membrane having a thickness of the aminated copolymer film of 30 μm.

When the characteristics of the bipolar membrane thus obtained were measured, the water electrolysis efficiency was ηOH = 98.8.
%, ΗH = 99.0% and the water electrolysis voltage was 1.3 volts. Further, when the bipolar membrane was energized for 4 months and the characteristics of the bipolar membrane were measured, the water electrolysis efficiency was ηO
H = 98.6%, ηH = 98.8%, and the water electrolysis voltage was 1.
3 volts. Further, generation of bubbles and water bubbles in the bipolar film was not observed.

Comparative Example 3 The chloromethylated copolymer obtained in Example 1 was dissolved in tetrahydrofuran to form a 20% by weight solution, and 3% by weight of triethylamine was added to this solution. The solution prepared in this manner is applied to the roughened side of the iron ion type cation exchange membrane obtained in Example 3, and dried to form a bipolar membrane having a coating of an aminated copolymer having a thickness of 32 μm. Was prepared.

When the characteristics of the bipolar membrane thus obtained were measured, the water electrolysis efficiency was ηOH = 98.5.
%, ΗH = 98.5% and the water electrolysis voltage was 1.4 volts. Further, when the bipolar film was energized for 4 months and the characteristics of the bipolar film were measured, no bubbles and bubbles were generated in the bipolar film. However, the water electrolysis efficiency was ηOH = 81.1%, ηH = It decreased to 81.0%. The water electrolysis voltage rose to 1.9 volts.

Example 4 50 g of a copolymer having no unsaturated bonds in the main chain composed of segments of polystyrene (42% by weight) and hydrogenated segments of polyisoprene (58% by weight) were dissolved in 1000 g of chloroform. 50 g of chloromethyl methyl ether and 10 g of tin chloride were added, reacted at 35 ° C. for 40 hours, precipitated in methanol, washed and dried to obtain a chloromethylated copolymer.

Next, this chloromethylated copolymer was dissolved in tetrahydrofuran to adjust to 20% by weight.
3% by weight of N, N, N ', N'-tetramethyl-1,6-hexanediamine was added. This solution was applied to the roughened side of the tin ion type cation exchange membrane obtained in Example 2, dried, and the thickness of the anion exchanger film was 28 μm.
Was fabricated.

When the characteristics of the bipolar membrane thus obtained were measured, the water electrolysis efficiency was ηOH = 99.4.
%, ΗH = 99.3% and the water electrolysis voltage was 1.4 volts. Next, the bipolar membrane was immersed in a mixed solution of acetone / methanol (volume ratio: 1: 1) for 8 hours, washed sufficiently with water, and the characteristics of the bipolar membrane were measured. The water electrolysis efficiency was ηOH = 99.1. %, ΗH = 99.1% and the water electrolysis voltage was 1.4 volts.

Further, the characteristics of the bipolar membrane were measured by energizing the bipolar membrane for 6 months. The water electrolysis efficiency was ηOH = 98.8%, ηH = 98.9%, and the water electrolysis voltage was 1.4 volts. Met. Further, generation of bubbles and water bubbles in the bipolar film was not observed.

Comparative Example 4 The chloromethylated copolymer obtained in Example 4 was dissolved in a mixed solvent of chloroform / methanol (volume ratio: 5: 1) to obtain a 18% by weight chloromethylated copolymer solution.
3% by weight of triethylamine was added to this solution. The solution prepared in this manner was applied to the roughened side of the tin ion type cation exchange membrane obtained in Example 2, and dried to form a bipolar membrane having an aminated copolymer film thickness of 35 μm. Produced.

When the characteristics of the thus obtained bipolar membrane were measured, the water electrolysis efficiency was ηOH = 98.4.
%, ΗH = 98.5% and the water electrolysis voltage was 1.5 volts. Next, this bipolar membrane was immersed in a mixed solution of acetone / methanol (volume ratio: 1: 1) for 8 hours, washed sufficiently with water, and the characteristics of the bipolar membrane were measured. The water electrolysis efficiency was ηOH = 78.9. %, ΗH = 80.0%. In addition, the water electrolysis voltage rose to 2.2 volts.

When the bipolar membrane was energized for 6 months and the characteristics of the bipolar membrane were measured, no bubbles and water bubbles were found in the bipolar membrane. However, the water electrolysis efficiency was ηOH = 62.3%. , ΗH = 62.0%. The water electrolysis voltage rose to 2.7 volts.

Claims (1)

(57) [Claims] 1. A bipolar membrane comprising a cation exchange membrane and an anion exchanger having a crosslinked structure of a polyamine based on a styrene-based block copolymer having no unsaturated bond in the main chain.