JPH06145379A - Bipolar membrane - Google Patents

Abstract

PURPOSE:To obtain the title membrane excellent in water dissociation efficiency, acid resistance, heat resistance, etc., by joining an anion exchange membrane to a cation exchange membrane comprising a specified aromatic polymer having a sulfo group on the aromatic ring. CONSTITUTION:A cation exchange membrane is prepared which comprises an aromatic polymer having a group of the formula -X-Ar-Y wherein X and Y are each -O-, -S-, 1-13C alkylene or a single bond; Ar is a group of formula I, II or III; R<1> to R<5> are each a substituent having a negative Hammett substituent constant; a is 0 to 3; b+c is 0 to 5; and d+e is 0 to 5 in the repeating unit and having a sulfo group on the aromatic ring. An example of the desirable cation exchange membrane is one made from a polyphenylene oxide/ polyethersulfone copolymer. The cation exchange membrane is joined to an anion exchange membrane (e.g. one made from a styene/divinylbenzene copolymer having a quaternary ammonium group introduce thereinto) to produce the title membrane.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a bipolar membrane which is particularly useful in the water splitting method by electrodialysis.

[0002]

2. Description of the Related Art When a voltage is applied with the anion-exchange membrane side of a bipolar membrane as the anode side and the anion-exchange membrane side as the cathode side, water splits and dissociates into hydrogen ions and hydroxide ions. This was reported by Friette in 1956 and is widely known.

A bipolar membrane is useful because it has this ability. By appropriately using the bipolar membrane and an anion exchange membrane and / or a cation exchange membrane, a neutral salt such as Glauber's salt is used as a raw material to form sulfuric acid. It is known to produce acids and alkalis such as caustic soda. Since such a bipolar membrane is used in large quantities, it must be manufactured inexpensively and easily, and since it contacts acid and alkali, the cation exchange membrane has acid resistance, Is required to have alkali resistance.

Further, from the viewpoint of the production cost of acid and alkali, the bipolar membrane is required to have heat resistance because the voltage drop and the liquid resistance due to the membrane become small when it is operated at a high temperature, and at the same time, the dissociation of water is required. High efficiency is required.

Several bipolar films have already been reported. For example, a cation-exchange group is introduced on one side of a film based on a styrene-divinylbenzene copolymer by a treatment such as sulfonation, and an anion-exchange group consisting of a quaternary ammonium group is introduced on the other side. Such a bipolar film is disclosed in JP-B-60-31860 and JP-A-63-95235. Also,
Japanese Patent Publication No. 60-35936 discloses a bipolar membrane in which a cation-exchange resin of fine particles and a dispersion of polyvinylidene fluoride are applied on a quaternary ammonium salt membrane of a mixed membrane of polyvinylbenzyl chloride and polyvinylidene fluoride.

Further, a bipolar membrane manufactured by fusing an anion exchange membrane and a cation exchange membrane produced in advance by heat and pressure is disclosed in US Pat. No. 3,372,101.
JP-A-59-4 discloses a bipolar film manufactured by post-pressing with an inorganic compound interposed at the lamination interface.
No. 7235 and Japanese Patent Publication No. 3-505894.

However, all the conventional cation exchange membranes of bipolar membranes have poor acid resistance and heat resistance, and cannot exhibit stable performance for a long period of time when operated at high temperature in a high concentration of acid.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of conventional bipolar membranes and provides a bipolar membrane having high water dissociation efficiency, excellent acid resistance and heat resistance, and stable performance for a long period of time. It is provided.

[0009]

Means for Solving the Problems The above-mentioned object is to provide a compound of the general formula (1) --X--Ar--Y-- (wherein X and Y are --O--, --S--, and 1 carbon atoms in the repeating unit). Is an alkylene group or a single bond of Ar.

[0010]

[Chemical 3]

[0011] Here, R ^{1 to} R ⁵ are the same or different Hammett's substituent having a negative substituent constant. a
To e are all positive integers, a is 0 to 3, and b + c and d + e are all 0 to 5. And a cation-exchange membrane having a sulfonic acid group on the aromatic ring and an anion-exchange membrane are joined to each other.

The above cation exchange membrane constituting the bipolar membrane of the present invention has an aromatic ring in the main chain and therefore is excellent in mechanical properties, heat resistance, chemical resistance and thin film formability.
Specific preferred examples of the aromatic ring-containing polymer having the general formula (1) include polymers having the repeating unit of the following chemical formula 4. Here, p is 2 to 200.

[0013]

[Chemical 4]

In the above cation exchange membrane, the aromatic ring-containing polymer is a block copolymer composed of two kinds of repeating units, and a sulfonic acid group is introduced into the aromatic ring of one of the repeating units. The cation exchange membrane thus obtained is preferable from the viewpoint of obtaining a membrane having high dissociation efficiency of water and excellent mechanical properties.

Examples of such copolymers include polyphenylene oxide / polyether sulfone copolymer, polyphenylene sulfide / polyether sulfone copolymer, polyaryl ether sulfone / polyether sulfone copolymer or polyaryl ether sulfone / polythioether sulfone. Examples of copolymers include, for example

[0016]

[Chemical 5]

And the like. However, m and n are 2 to 20
It is 0. Preferably, m / n is 100/1 to 1/10. These polymers are described in JP-A 1-215348.
Japanese Unexamined Patent Publication No. 2-245035 and Japanese Unexamined Patent Publication No. 2-248434.
It can be obtained by the method described in No.

The cation exchange membrane has a thickness of 5 μm to 300 μm.
It is usually used in the range of μm, but from the viewpoint of membrane resistance and strength, it is preferably used in the range of 20 μm to 150 μm. The ion exchange capacity, which is the content of sulfonic acid groups in the polymer, is 0.5 to 2.0 meq / g dry resin, particularly 0.8 to 1.5 meq / g.
It is preferably a dry resin.

As the anion exchange membrane constituting the bipolar membrane of the present invention, an anion exchange membrane having a high permeability of hydroxide ions generated in the bipolar membrane and a minimum permeability of cations is used. To be done. Examples thereof include a membrane obtained by introducing a quaternary ammonium group into a copolymer of styrene and divinylbenzene, an anion-exchange group or a monomer having a functional group capable of being converted to the group, which is a porous olefin-based or fluorine-containing polymer. An anion exchange membrane graft-polymerized on a substrate such as a body, a woven fabric, a non-woven fabric or a film can be used.

Of these, a base material of polyolefin such as polypropylene or polyethylene is preferably used because it has excellent chemical resistance such as alkali resistance, and a copolymer of styrene and divinylbenzene, or further, is used as the base material. If desired, an anion exchange membrane having a quaternary ammonium group in which a part of a copolymer obtained by polymerizing vinylbenzyl chloride is graft-polymerized to the above-mentioned polyolefin substrate by electromagnetic rays such as radiation is desirable.

The anion exchange membrane has a thickness of 5 μm to 300 μm.
It is usually used in the range of μm, but from the viewpoint of membrane resistance and strength, it is preferably used in the range of 20 μm to 150 μm. About the ion exchange capacity, 0.5 to 4.0
It is desirable that it is a meq / g dry resin, especially 0.8 to 3.0 meq / g dry resin.

It is preferable that the cation exchange membrane and the anion exchange membrane forming the bipolar membrane, particularly the anion exchange membrane, be treated with the metal ion-containing aqueous solution before bonding, because the voltage drop becomes small.

The metal ion forming the above metal ion-containing aqueous solution is not particularly limited, but for example, Zr ⁴⁺ , Ti
⁴⁺ , Ru ³⁺ , Cr ³⁺ , Fe ^{3+ and the} like are preferably used. In order to treat the ion exchange membrane with the metal ion-containing aqueous solution, is it preferable to coat the ion exchange membrane with an aqueous solution of 0.1 to 20% by weight, particularly 1 to 10% by weight of a metal sulfate or hydrochloride. Can be achieved by immersing the ion exchange membrane in the metal ion-containing aqueous solution.

As the metal ion-containing aqueous solution, an aqueous solution of a complex anion of metal ions may be used. Examples of complex anions of metal ions include [FeCl ₄ ] ^- ,
[CoCl ₄ ] ^2- , [ZrCl ₆ ] ^2- , [PbCl ₆ ]
^2- , [TiCl ₆ ] ^2- , [FeF ₆ ] ^3- , [AlF ₆ ]
^{_{3-, [CrO 3 F] -}} , [ZnI 4] 2-, [Cu (C
N) ₄ ] ^3- , [Fe (CN) ₆ ] ^3- , [Sn (OH)
₆ ] ^2- etc. can be used.

The ion-exchange membrane treated with the metal ion-containing aqueous solution can be directly joined, but if it is further treated with an alkali such as being dipped in an alkaline aqueous solution before joining, the voltage drop due to the obtained bipolar membrane is reduced. It can be further improved. As the alkaline aqueous solution, preferably, 0.1 to 20% by weight aqueous solution of NaOH, KOH, Na ₂ CO ₃ or the like can be used.

The method of fusing by heat and pressure is the most simple and preferable method for joining the anion exchange membrane and the cation exchange membrane,
The bonding strength is also large. The bonding depends on the type of the membrane material, the reinforcing material and the ion exchange group, but the temperature is preferably 100 to 25
It is carried out at 0 ° C. and a pressure of 10 to 100 kg / cm.

[0027]

The present invention will be described below with reference to examples, but the present invention is not limited to the examples.

Example 1 A precursor composed of an aromatic polysulfone unit was prepared by reacting 4,4-diphenol with dihalodiphenyl sulfone in the same manner as in the synthesis method described in JP-A-61-168629. Was synthesized, and then the precursor, dihalophenyl sulfone and sodium sulfide were reacted to obtain a copolymer having an equimolar amount of aromatic polysulfone and polythioether sulfone.

Next, the copolymer was dissolved in 1,1,2,2-tetrachloroethane, chloromethyl methyl ether and anhydrous tin chloride were added and reacted at 110 ° C. for 4 hours, and then methyl alcohol was added. The precipitate was washed with and washed to obtain a chloromethylated copolymer. The obtained chloromethylated copolymer was dissolved in tetrachloroethane to obtain a 10% by weight solution. Then, the polymer solution was cast on a glass plate and then heat-dried at 150 ° C. for 2 hours to obtain a cast film having a film thickness of 50 μm. Then, the cast membrane was sulfonated with 98% by weight of concentrated sulfuric acid at 90 ° C. for 6 hours to obtain a cation exchange membrane A having an ion exchange capacity of 1.5 meq / g dry resin.

An anion exchange membrane made of a styrene-divinylbenzene copolymer and reinforced with a polypropylene woven fabric and having a quaternary ammonium group (ion exchange capacity 3.0 meq / g dry resin, film thickness 120 μm) and a cation. The ion exchange membrane A was added to a 10 wt% chromium chloride aqueous solution at 70 ° C. for 30 minutes.
It was soaked for a minute and thoroughly washed with water. The film was thoroughly dried and then pressed at 190 ° C. and 70 kg / cm to produce a bipolar film. After the bipolar membrane was stored in a 0.5N sodium chloride aqueous solution, its performance was evaluated in the electrodialysis tank shown in FIG.

In the electrodialysis tank of FIG. 1, the bipolar chambers 13,
15% by weight sodium sulfate aqueous solution is supplied to 14 and the neutral salt chambers 9 and 10, and ion-exchanged water is adjusted to the alkali generation chamber 5 so that the concentration of sodium hydroxide produced is 20% by weight. At the same time as the supply, the amount of ion-exchanged water supplied to the acid generation chamber 6 was adjusted so that the concentration of the sulfuric acid aqueous solution generated was 10% by weight.

The cation exchange membranes 7, 11 and 12 are styrene-divinylbenzene copolymer type strongly acidic cation exchange membranes (ion exchange capacity 3.3 meq / g dry resin, film thickness 1).
40 μm), and the anion exchange membrane 8 is a styrene-divinylbenzene copolymer system weakly basic anion exchange membrane (ion exchange capacity 2.0 meq / g dry resin, film thickness 120).
μm) was used. When electrodialysis was performed at a current density of 10 A / dm ² at 60 ° C., the voltage drop due to the bipolar membrane 1 was 1.9 V, and the water dissociation efficiency was 95%. This performance did not change after three months.

Example 2 The same anion exchange membrane as used in Example 1 was immersed in a 10% by weight iron chloride 4N hydrochloric acid aqueous solution at 70 ° C. for 16 hours. The anion-exchange membrane was thoroughly washed with water and dried, and then the same cation-exchange membrane used in Example 1 was pressed at 190 ° C. and 70 kg / cm to produce a bipolar membrane. The performance was evaluated in the same electrodialysis tank as in Example 1. The voltage drop due to the bipolar membrane was 1.8 V, and the water dissociation efficiency was 95%. This performance did not change after three months.

[Example 3] The same cation and anion exchange membrane used in Example 1 was immersed in a 10 wt% zirconium oxychloride aqueous solution at 70 ° C for 16 hours. After that, both ion-exchange membranes were thoroughly washed with water and dried, then at 190 ° C, 70
A bipolar film was manufactured by pressing at kg / cm ² . The performance was evaluated in the same electrodialysis tank as in Example 1. The voltage drop due to the bipolar membrane was 1.6 V, and the water dissociation efficiency was 95%. This performance did not change after three months.

Example 4 A cation and anion exchange membrane treated with an aqueous zirconium oxychloride solution in the same manner as in Example 3 was used.
Before joining, it was immersed in a 5 wt% sodium hydroxide aqueous solution, thoroughly washed with water and dried, and then at 190 ° C. and 70 kg / c.
A bipolar film was manufactured by pressing at m ² . The performance was evaluated in the same electrodialysis tank as in Example 1. The voltage drop due to the bipolar membrane is 1.1V and the water dissociation efficiency is 95.
%Met. This performance did not change after three months.

[0036]

EFFECTS OF THE INVENTION The bipolar membrane of the present invention has a higher water dissociation efficiency than that of the conventional method, is excellent in acid resistance and heat resistance, and exhibits stable performance for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrodialysis device for evaluating a bipolar membrane.

[Explanation of symbols]

 1: Bipolar membrane 2: Cation exchange layer 3: Interface area of both ion exchange layers 4: Anion exchange layer 5: Alkali generation chamber 6: Acid generation chamber 7, 11, 12: Cation exchange membrane 8: Anion exchange Membrane 9, 10: Neutral salt chamber 13: Anode chamber 14: Cathode chamber 15: Anode 16: Cathode

Claims (6)

[Claims] 1. A compound of the general formula (1) --X--A within a repeating unit.
r-Y- (In the formula, X and Y are -O-, -S-, an alkylene group having 1 to 13 carbon atoms or a single bond. Ar
Is Have. Here, R ^{1 to} R ⁵ are the same or different Hammett's substituent having a negative substituent constant. a to e are all positive integers, a is 0 to 3, and b + c and d + e are all 0 to 5. And a cation exchange membrane having a sulfonic acid group on the aromatic ring, and an anion exchange membrane are joined together. 2. The aromatic ring-containing polymer is composed of a block copolymer having two kinds of repeating units, and substantially has a sulfonic acid group on the aromatic ring of one repeating unit.
Bipolar membrane. 3. The bipolar film according to claim 2, wherein the block copolymer having two kinds of repeating units has the following chemical formula 2.
However, both m and n are 2 to 200. [Chemical 2] 4. The bipolar membrane according to claim 1, wherein the anion exchange membrane is composed of a copolymer of styrene and divinylbenzene supported on a polyolefin base material and has a quaternary ammonium group as an anion exchange group. 5. The bipolar membrane according to claim 1 or 2, wherein the anion exchange membrane is an anion exchange membrane that has been immersed in an aqueous solution containing metal ions. 6. The bipolar membrane according to claim 1 or 2, wherein the anion exchange membrane is an anion exchange membrane which has been subjected to an immersion treatment with a metal ion-containing aqueous solution and then with an alkali.