JPH073051A - Bipolar membrane - Google Patents

Abstract

PURPOSE:To obtain a bipolar membrane having small lowering of voltage, having high dissociation efficiency in water and exhibiting stable performance over a long period. CONSTITUTION:The bipolar membrane 1 has an inorganic ion exchanger layer 3 between a cation-exchange membrane 2 and an anion-exchange membrane 4 whose either one surface or both surfaces are coarsened.

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 current is applied between the electrodes with the anion-exchange membrane side of the bipolar membrane facing the anode side and the cation-exchange membrane side facing the cathode side, the water splits and hydrogen ions and water Dissociation into acid ions was reported by Frilette in 1956 and is widely known.

A bipolar membrane is useful because it has this ability, and by using an anion exchange membrane and / or a cation exchange membrane in appropriate combination, a neutral salt such as Glauber's salt is used as a raw material to produce sulfuric acid and an acid such as caustic soda. It is known that alkali can be produced. Considering the production costs of acids and alkalis, it is necessary to have a bipolar membrane that has a small voltage drop across the membrane and at the same time has high water dissociation efficiency, and these performances must be exhibited for a long period of time.

Several bipolar films and their manufacturing methods have already been reported. For example, styrene-
A bipolar membrane in which one side of a film based on a divinylbenzene copolymer is introduced with a cation exchange group by a treatment such as sulfonation and the other side is introduced with an anion exchange group of a quaternized ammonium group is formed. Japanese Patent Sho 60-31
860 and JP-A-63-95235. In addition, a method of producing by previously fusing an anion exchange membrane and a cation exchange membrane by heat and pressure is disclosed in US Pat. No. 3,372,101, which uses polyvinylamine as an adhesive agent. The method to do this is JP-A-61-1
No. 207444.

However, since these bipolar membranes have a cation exchange group and an anion exchange group in the same membrane, these oppositely charged groups invade each other and are ionically bound to each other, resulting in neutralization. It has the disadvantage of forming layers and causing a large voltage drop.

To avoid this, US Pat.
No. 53,900 and JP-B No. 60-35936 disclose a bipolar membrane in which an ion exchange resin having a high cross-linking structure is introduced between a cation exchange layer and an anion exchange layer to prevent mutual intrusion of groups having opposite charges. ing. Further, there is a method for producing a bipolar film by post-pressing with an inorganic compound interposed at the stacking interface, as disclosed in JP-A-59-47235.
And Japanese Patent Publication No. 3-505894.

However, each of the bipolar films has the following drawbacks. That is, when a highly crosslinked ion exchange resin is interposed at the interface, even if highly crosslinked, an organic substance cannot prevent mutual intrusion of ion exchange groups, resulting in an increase in voltage drop over time. Further, even when an inorganic compound is interposed at the interface, those substances are gradually eluted out of the film, which also causes an increase in voltage drop over time.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks in the bipolar film, has a small voltage drop,
It is intended to provide a bipolar membrane having high water dissociation efficiency and stable performance over a long period of time.

[0009]

The above object is a bipolar membrane in which an inorganic ion exchange layer is present between a cation exchange membrane and an anion exchange membrane, which is in contact with the inorganic ion exchange layer. This is achieved by a bipolar membrane characterized in that the surface of the ion exchange membrane and / or the anion exchange membrane is roughened.

Various types of inorganic ion exchangers are used in the present invention. For example, there are aluminosilicate type inorganic ion exchangers, hydrous oxide type inorganic ion exchangers, acidic salt type inorganic ion exchangers, basic salt type inorganic ion exchangers, heteropolyacid type inorganic ion exchangers, etc.,
Any of a cation exchanger, an anion exchanger and an amphoteric ion exchanger can be used as the inorganic ion exchanger layer of the bipolar membrane. Representative examples of the inorganic ion exchanger used in the present invention include hydrous zirconium oxide, hydrous titanium oxide, hydrous bismuth oxide, hydrous manganese oxide, antimonic acid, zirconium phosphate, titanium phosphate, aluminosilicate,
Zeolite, tobermorite, ammonium molybdophosphate, hexacyanoferrate (III) cobalt (II) potassium,
Examples thereof include potassium titanate. If the inorganic ion exchanger is crystalline, it has a low solubility and is more preferable.

The thickness of the inorganic ion exchanger layer is from 0.01 to
100 μm, particularly 0.1 to 10 μm is preferable. If the inorganic ion exchanger layer is thinner than this, it elutes out of the membrane over time and the voltage drop of the bipolar membrane gradually increases, while if it is thicker than this, the bonding strength between the anion exchange membrane and the cation exchange membrane decreases. However, it is not preferable.

The particle size of the inorganic ion exchanger is preferably 1 μm or less. If the particle size is larger than this, the bonding strength between the anion exchange membrane and the cation exchange membrane is lowered, and bubbles are formed at the bonding interface during bonding. Is not preferable. Among them, the particle diameter of 0.01 to 0.5 μm is particularly preferable.

Various methods can be adopted as the method of allowing the inorganic ion exchanger layer to exist between the anion exchange membrane and the cation exchange membrane, but the following method is preferably employed.
A liquid or paste prepared by dispersing an inorganic ion exchanger in a solvent is applied to the surface of the cation exchange membrane or the anion exchange membrane,
A method can be used in which the particles are attached by using casting, spraying, screen printing, thermal transfer, etc., and then an ion exchange membrane having a charge opposite to that of the initial ion exchange membrane is cast, or bonded by thermocompression bonding. Further, it is more preferable to add a polymer compound soluble in a solvent as a binder because the bonding strength is increased.

When the inorganic ion exchange layer is introduced between the anion exchange membrane and the cation exchange membrane, the surface of the ion exchange membrane which is in contact with the inorganic ion exchange layer is roughened in advance to further improve the bonding strength. As well as increasing the voltage drop, the voltage drop of the bipolar film can be reduced. As a roughening method, various methods can be adopted depending on the size of the unevenness, and are preferably used depending on the size of the inorganic ion exchanger. For example, sandblasting, sandpaper polishing, wire brush brushing, woven cloth,
Thermal transfer of a non-woven fabric, an embossed film or an embossing roll, plasma surface treatment, removal of a particle layer provided on the film surface, etc. are used.

The rough surface of the ion exchange membrane is determined by the fine irregularities formed on the membrane surface. The fine irregularities have an average depth or height from the membrane surface of 0.01 to 50 μm, preferably 0. 1 to ²⁰ μm, average 1 per cm ^{2 of} film surface
0 ³ to 10 ¹⁵ pieces, particularly 10 ⁵ to 10 ¹² pieces on average are preferable. As the surface or cross-sectional shape of the unevenness, a suitable shape such as a circle or a rectangle is selected.

As the cation exchange membrane which constitutes the bipolar membrane of the present invention, a cation exchange membrane which has a large permeability for hydrogen ions generated in the bipolar membrane and which is difficult for anions to permeate can be used, and preferably a sulfone. An example is a cation exchange membrane containing an acid group. As such a strongly acidic cation exchange membrane, a styrene-divinylbenzene-based polymer film, a styrene-butadiene-based polymer film, polysulfone, polyphenylene oxide, a sulfonic acid group is introduced into a polymer film having an aromatic ring such as polyethersulfone. Examples of the film include a film obtained by graft-polymerizing a monomer such as styrene onto an olefin-based or fluorine-containing polymer, woven fabric, non-woven fabric or the like and introducing a sulfonic acid group.

Further, the cation exchange membrane formed of the perfluoro cation exchange polymer composed of the repeating unit represented by the chemical formula 2 has a current efficiency and a sulfuric acid,
Since it is excellent in acid resistance to nitric acid, hydrofluoric acid, etc., it was found to be a polymer which forms a preferable cation exchange layer.

[0018]

[Chemical 2]

In Chemical formula 2, m is 0 or 1, and n is 1.
To 5, x / y is 2 to 16, X is SO ₃ M or COOM.
M represents hydrogen, an alkali metal, an alkaline earth metal or ammonium.

Since the cation exchange membrane is formed of a perfluoropolymer, it has excellent acid resistance and heat resistance against hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and the like. Also,
Since the ion exchange group forms a cluster structure, it has a high anion-excluding property, and can exhibit a high water dissociation efficiency in a bipolar membrane.

The thickness of the cation exchange membrane is 5 μm to 300 μm.
It is usually used in the range of m, but from the viewpoint of membrane resistance and strength, the range of 20 μm to 150 μm is preferably used. The ion exchange capacity is preferably 0.5 to 2.0 meq / g dry resin, more preferably 0.8 to 1.5 meq / g dry resin from the viewpoint of membrane resistance and transport number.

As the anion exchange membrane constituting the bipolar membrane of the present invention, an anion exchange membrane having a large permeability of hydroxyl 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. A base material such as a body, a woven cloth, a non-woven cloth or a film, and an anion exchange membrane obtained by graft polymerization can be used.

Of these, a woven fabric of polyolefin such as polypropylene or polyethylene is preferably used because of its excellent alkali resistance and chemical resistance, and the woven fabric is a copolymer of styrene and divinylbenzene, or further It is desirable to use an anion exchange membrane having a quaternary ammonium group in which a part of the copolymer added with vinylbenzyl chloride is graft-polymerized to the above-mentioned polyolefin by radiation or the like.

The thickness of the anion exchange membrane constituting the bipolar membrane is usually in the range of 5 μm to 300 μm, but preferably 20 μm to 1 from the viewpoint of membrane resistance and strength.
Those in the range of 50 μm are used. Regarding the ion exchange capacity, it is preferably 0.5 to 4.0 meq / g dry resin, particularly 0.8 to 3.0 meq / g dry resin.

[0025]

The bipolar film of the present invention retains a low voltage drop for a long period of time as described above, but the mechanism is presumed as follows. That is, since the inorganic ion exchanger has a solid structure, each ion-exchange group in contact with the inorganic ion-exchange layer in the bipolar membrane cannot enter the inorganic ion-exchange layer, and therefore,
It is difficult to form an ionic bond to form a neutral layer. Further, the inorganic ion exchanger has a larger ion exchange capacity per volume than the organic ion exchange resin, and because of the structure capable of holding a large amount of water, the electric resistance of the inorganic ion exchanger layer is small and the voltage drop of the bipolar membrane is suppressed. It seems that it can be kept small. Further, it is considered that by roughening the surface of the ion exchange membrane that is in contact with the inorganic ion exchanger layer, the contact area between the inorganic ion exchanger and the ion exchange membrane is increased and the voltage drop is reduced.

[0026]

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

[Example 1] 4 made of a styrene-divinylbenzene copolymer and reinforced with a polypropylene woven fabric
An anion exchange membrane having a primary ammonium group (ion exchange capacity 3.0 meq / g dry resin, film thickness 120 μm) was polished with sandpaper. Membrane surface has an average depth of 0.2μ
m, and a fine recess having an average width of 0.8 μm was formed over the entire surface. The membrane was thoroughly washed with water and dried, and then 10% by weight of a crystalline zirconium phosphate dispersion was applied and dried at 60 ° C. to form an inorganic ion exchange layer having a thickness of 5 μm.

In addition to this, CF ₂ = CF ₂ and CF ₂ = CFOC
A cation exchange membrane (ion exchange capacity 1.1 meq / g dry resin, thickness 80 μm) made of a copolymer with F ₂ CFCF ₃ OCF ₂ CF ₂ SO ₃ H was used at 190 ° C., 70 kg /
The bipolar film was manufactured by pressing in cm. After storing the bipolar membrane in 0.5N sodium chloride solution,
The performance was evaluated in the electrodialysis tank shown in.

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

The cation exchange membrane is a styrene-divinylbenzene copolymer type sulfonic acid membrane (ion exchange capacity 3.3).
Milli-equivalent / g dry resin, thickness 140 μm) is used, and the anion exchange membrane is a styrene-divinylbenzene copolymer system weakly basic anion-exchange membrane (ion exchange capacity 2.0 meq / g dry resin, thickness 120 μm) was used. When electrodialysis at a current density of 10 A / dm ² was performed at 60 ° C.,
The voltage drop due to the bipolar membrane was 1.0 V, and the dissociation efficiency of water was 95% or more. This performance did not change after 3 months, and no peeling of the film was observed.

[Embodiment 2] The anion exchange membrane used in Embodiment 1 was thermally transferred to an embossed film to form a rough surface by forming an average depth of 3 μm and an average of 10 ⁸ irregularities per cm ² on the membrane surface. Then, a crystalline antimonic acid layer having a thickness of 1 μm was formed thereon by screen printing. Thereafter, the cation exchange membrane used in Example 1 was replaced with 19
A bipolar film was manufactured by pressing at 0 ° C. and 70 kg / cm. When the performance of this bipolar film was measured by the same method as in Example 1, the voltage drop was 1.2 V and the water dissociation efficiency was 95% or more. This performance did not change after 3 months, and no peeling of the film was observed.

[0032]

The bipolar membrane of the present invention has a smaller voltage drop than the conventional method, a high water dissociation efficiency, and 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 Codes] 1: Bipolar membrane 2: Cation exchange membrane 3: Inorganic ion exchanger layer 4: Anion exchange membrane 5: Alkali production chamber 6: Acid production 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 (5)

[Claims] 1. A bipolar membrane in which an inorganic ion exchange layer is present between a cation exchange membrane and an anion exchange membrane, wherein the cation exchange membrane and / or anion exchange membrane is in contact with the inorganic ion exchange layer. Is a bipolar film having a roughened surface. 2. The bipolar membrane according to claim 1, wherein the inorganic ion exchanger is a crystalline inorganic ion exchanger. 3. The inorganic ion exchanger layer has a thickness of 0.01 to 1.
The bipolar film according to claim 1, which has a thickness of 00 μm. 4. The bipolar membrane according to claim 1, 2 or 3, wherein the cation exchange membrane is made of a polymer having a repeating unit represented by Chemical formula 1. [Chemical 1] In Chemical formula 1, m is 0 or 1, n is 1 to 5, x / y
Is 2 to 16, and X is SO ₃ M or COOM. M represents hydrogen, an alkali metal, an alkaline earth metal or an ammonium group. 5. An anion exchange membrane comprising a styrene polymer or a copolymer of styrene and divinylbenzene supported on a polyolefin film substrate, and having a quaternary ammonium group as an anion exchange group. 2, 3 or 4 bipolar membranes.