JPH05214125A - Anion exchange membrane excellent in selectivity between anion - Google Patents

Abstract

PURPOSE:To obtain an anion exchange membrane low in electric resistance and excellent in selective permeability of a monovalent ion between anions. CONSTITUTION:The objective anionic ion exchange membrane is characterized in that an ion exchange group of an anion exchange membrane is crosslinked with an aliphatic hydrocarbon and a thin film of a high polymer having a cation exchange group is formed on the surface of the membrane. The membrane is an anion exchange membrane extremely low in electric resistance and having practical monovalent anion-selective permeability and reduces electric power cost of electric dialysis in a salt producing technique for sea water concentration by electric diagnosis.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to anion selective permeability between anions, more specifically, an anion exchange having a property of selectively passing anions having a small charge to anions having different charges. Regarding the membrane.

[0002]

2. Description of the Related Art Anion exchange membranes are used in a wide range of fields such as electrodialysis, diaphragms for electrode reactions, and diffusion dialysis. In electrodialysis of seawater concentration, there are problems of scale generation such as gypsum and power loss due to permeation of polyvalent anions, and it is not possible to have selective permeability of monovalent ions between ions of the same sign in the ion exchange membrane. It is an essential technique in seawater-concentrated electrodialysis and many proposals have been made. For example, formation of a dense layer of condensed crosslinks on the surface of an anion exchange membrane (Japanese Patent Publication No. 36-15258) and crosslinking of haloalkyl groups on the surface of anion exchange membrane (Japanese Patent Publication No. 56-80).
49), formation of a thin layer having a cation exchange group on the surface of an anion exchange membrane (Japanese Patent Publication No. 45-19980), oxidation treatment of the surface layer portion of the anion exchange membrane (Japanese Patent Publication No. 40-34649).
No.), an alkyl group is provided on the exchange group of the anion exchange membrane (JP-A-55-78021), and the like.

[0003]

The characteristics required for anion exchange membranes for electrodialysis for seawater concentration are that they have high seawater concentration performance, that polyvalent anions are difficult to permeate, and monovalent anions are It has a property of easily transmitting selectively and has a low electric resistance. Therefore, it is important to improve the selectivity between anions to a practical level without increasing the electric resistance of the film. For example, by performing crosslinking with a hydrocarbon compound or introducing an alkyl group into the exchange group of the anion exchange membrane, the selective permeability between the anions is improved, and the practical level of selectivity is secured. In any of the methods of cross-linking with a hydrocarbon compound and introducing an alkyl group, the carbon number must be increased, and as a result, the electric resistance of the membrane increases, which results in a selective permeation of monovalent ions. An excellent low electric resistance film has not been put to practical use. Further, even a film having a thin layer having a cation exchange group formed on the surface of an anion exchange film to impart selective permeability, a film having a low electric resistance has not been obtained. In particular, in recent years, in salt production by ion exchange membrane electrodialysis, pursuit of cost reduction to counter imported raw material salt has been made. From this point as well, a membrane having low electric resistance is strongly desired. The direction of the membrane's low electrical resistance is the direction of the membrane's high exchange capacity without impairing the compactness of the membrane, and in such a membrane of high exchange capacity, a thin layer having a cation exchange group on the surface of the anion exchange membrane. In order to improve the selective permeation between anions, the membrane still has an excellent selective permeation of anions, that is, a monovalent anion selective permeation with low electrical resistance (high exchange capacity). A film satisfying both of the excellent properties has not yet been obtained.

As described above, for practical use of the low electric resistance film,
In the prior art, the relationship with the selective permeability between anions has been a serious problem.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors of the present invention have used an anion exchange membrane as a membrane matrix and a polymer having a cation exchange group formed as a thin layer on the surface thereof. As a result of intensive investigations focusing on the points of adsorption and binding, it was found that cross-linking the exchange groups of the anion exchange membrane having a high exchange capacity with an appropriate aliphatic hydrocarbon satisfies the above object, and the present invention Came to make.

That is, in the present invention, the ion-exchange groups of the anion-exchange membrane are crosslinked by the aliphatic hydrocarbon, and a thin layer of a polymer having a cation-exchange group is formed on the surface of the membrane. It is an anion exchange membrane that is characterized. The present inventors have examined the selectivity between anions of a low electric resistance film, that is, a high exchange capacity film, and the higher the exchange capacity film, the smaller the amount of the polymer having cation exchange groups on the surface of the film becomes. I confirmed that.

It was confirmed that the increase in the hydrophobicity of the ion exchange membrane matrix increased the adsorption amount of the polymer having a cation exchange group. Furthermore, we found that the structure in which the exchange groups of the anion-exchange membrane were cross-linked by appropriate aliphatic hydrocarbons increased the hydrophobicity of the membrane matrix while suppressing the increase in membrane resistance to a minimum. Invented. The reason why the increase in the hydrophobicity of the ion exchange membrane matrix is effective in increasing the adsorption amount is as follows.
It is considered that the hydrophobic bond is dominant in this adsorption.

Further, since the structure in which the exchange group is crosslinked by the aliphatic hydrocarbon is crosslinked, it is dense and has a characteristic that the performance of the anion exchange membrane is not deteriorated. The number of bonded carbon atoms of the aliphatic hydrocarbon depends on the structure of the anion exchange membrane matrix, the degree of crosslinking, the hydrophobicity of the exchange group species, and the hydrophobicity of the polymer having cation exchange groups on the membrane surface. Suitable carbon numbers are different, but preferably ── (CH ₂ )
_n = 4-1 among the aliphatic hydrocarbons represented by the formula _n ──
It is 0. More preferably, n = 4-8. For example, when the carbon number is small, if the carbon number is too small, the hydrophobicity of the membrane matrix does not increase, and the adsorption amount of the thin layer having the cation exchange group on the membrane surface is small, which results in the selective permeation of monovalent ions between anions. The sex has not been improved to the point where sufficient satisfaction is obtained. On the other hand, when the carbon number is large, when the carbon number is too large, the hydrophobicity of the membrane matrix increases but the membrane electric resistance increases. Therefore, it is necessary to select an aliphatic hydrocarbon having an appropriate number of carbon atoms.

The present invention will be specifically described below. Each composition of the anion exchange membrane of the present invention includes a conventionally known and usually used copolymerizable monomer, or a monomer having a group capable of being converted into an ion exchange group having polymerization ability, a crosslinking agent, and radical polymerization. A catalyst, a plasticizer, and, depending on other cases, a linear polymer soluble in the monomer mixture may be used. Also, it can be combined with a base material if necessary.

Among the respective compositions of the anion exchange membrane, the copolymerizable monomer or the monomer having a group having a polymerization ability and capable of being converted into an ion exchange group includes styrene, acrylonitrile, ethylstyrene and vinyl. Chloride,
It can be appropriately selected from acrolein, methyl vinyl ketone, maleic anhydride, maleic acid and its salts or esters, itaconic acid and its salts or esters, methyl vinyl ketone, vinyl pyridine and its derivatives, acrylonitrile and chloromethyl styrene.

As the crosslinking agent, polyvinyl compounds such as m-, p-, o-divinylbenzene, divinylsulfone, butadiene, chloroprene, trivinylbenzenes, divinylnaphthalene and trivinylnaphthalene are used. As the radical polymerization catalyst, known radical polymerization initiators such as benzoyl peroxide, azoisobutyronitrile and dicumyl peroxide are used.

As the plasticizer, phthalic acid esters such as dimethyl phthalate and dioctyl phthalate, and alcohol esters of aliphatic acids and aromatic acids are used. Examples of soluble linear polymer substances that are optionally used in the monomer mixture include polystyrenes, polybutadienes, polyisobutylenes, polybutylenes, styrene-
Butydiene copolymer, ethylene-propylene copolymer,
Polyhalogenated olefins, polyvinyl chloride fine powder,
Polyethylene fine powder and polypropylene fine powder are used.

The base material can be appropriately selected from polyolefins such as polyethylene and polypropylene, polyhalogenated olefins such as polyvinyl chloride and polyvinylidene chloride, nylon and the like, and these polymers can be used alone or in combination. And a woven cloth, a non-woven cloth, a net, a sheet made of them, or a porous material thereof can be used as the base material without any limitation.

Next, regarding the introduction of the exchange group,
Suitable for a monomer having an exchange group, for example, JP-A-58-93
The exchange group may be crosslinked with an aliphatic hydrocarbon and quaternized simultaneously by a conventionally known means such as No. 729. Examples of the polymer having a cation exchange group used in the present invention include those disclosed in JP-B-45-19980.
Examples thereof include a polymer electrolyte having a cation exchange group and a molecular weight of 500 or more, a linear polymer electrolyte, and an insoluble polymer having a cation exchange group shown in JP-B-58-12901. Specifically, among sulfonates such as lignin sulfonates and phosphate ester salts such as higher alcohol phosphates, polyelectrolytes having a cation exchange group having a molecular weight of 500 or more, methacrylic acid, styrene sulfonic acid Such as linear polyelectrolytes containing a large number of monomer units having carboxylic acid groups or sulfonic acid groups, insoluble with cation exchange groups such as those obtained by condensing phenols and aldehydes containing cation exchange groups Polymer, with exchange capacity of 0.5 meq / g (dry) or more, particle size of 100 μm
The following can be listed.

The method for forming a thin layer of the above-mentioned polymer is, for example, a method of immersing the anion-exchange membrane of the matrix in an aqueous solution of the polymer or a mixture with an organic substance, an anion-exchange membrane of the matrix. Method of applying or spraying an aqueous solution of the polymer or a mixture of the polymer and the anion / cation exchange membrane in an electrodialysis tank, and then removing the aqueous solution of the polymer with or without electricity. It can be performed by contact such as a method of passing the solution to the salt chamber side.

The temperature at that time is 0 to 120 ° C., but depending on the properties of the anion exchange membrane matrix and the polymer having a cation exchange group, the temperature, the electrolyte concentration, and the P
H and time are appropriately selected. The thickness of the thin film of the present invention is
The thickness must be less than the thickness that causes water to be decomposed in the membrane, but the upper limit depends on various factors such as the material of the anion-exchange resin membrane as a base and the state of the surface. However, an example of the standard is considered as follows. That is, 2A / 0.5N electrolyte solution is placed on both sides of the membrane.
When a direct current of dm ² is applied from the anion exchange membrane side to the thin layer membrane side and the current efficiency of hydrolysis exceeds 3%, this membrane is not suitable for the purpose of the present invention. Therefore, the thickness of the thin film must be smaller than that.

[0017]

EXAMPLES Examples will be given below to explain the present invention in detail, but the present invention is not limited by the description of the following examples. The symbols and measurement methods used in the examples will be described below. (1) R: resistance of the ion exchange membrane (Ω · cm ² ), 0.5
Measured value at an alternating current of 1000 HZ and a temperature of 25 ° C. in normal saline.

(2) FSO ₄ : A value indicating the specific selective permeability of sulfate radicals to chlorine ions in the anion exchange membrane. (Value according to the following formula 1: Smaller value is better)

[0019]

[Chemical 1]

Measurement method: Silver-silver chloride electrodes were installed at both ends of the electrodialysis tank, and an ordinary cation exchange membrane having an effective current-carrying area of 4 cm × 4 cm from the anode side between both electrodes, the present invention. The anion exchange membrane and the ordinary cation exchange membrane are alternately arranged side by side, and the electrodialysis tank is divided into five chambers of an anode chamber, a dilution chamber, a concentration chamber, a dilution chamber and a cathode chamber. Chloride ion 0.3632 normal, sulfate radical 0.0368 normal, sodium ion 0.3179 normal, magnesium ion 0.
A mixed salt aqueous solution of 0691 N and calcium ion 0.0130 N was passed at a linear velocity of 5 cm per second, the concentration chamber was filled with the mixed salt aqueous solution having the same composition as the dilution chamber, and the anode chamber and the cathode chamber were filled with A 0.4 N saline solution was passed through each, and electrodialysis was performed at a temperature of 25 ° C. and a current density of 3.0 A / dm ² .

After applying electricity for 4 hours, the newly overflowing concentrated solution is analyzed, and FSO ₄ is calculated from the analytical value of the obtained concentrated solution and the composition of the diluted solution. (3) NOS: Normality of chloride ion in the concentrated solution in the electrodialysis. (4) Exchange capacity: meq / g-dry membrane.

[0022]

Example 1 and Comparative Example 1 Production of Ion Exchange Membrane Base; Divinylbenzene (Purity 56
%) 11 parts, 4-vinylpyridine 45 parts, styrene 44
Part, dioctyl phthalate 15 parts, and azobisisobutyl nitrile 0.2 parts were soaked in a pre-electron-beam-irradiated polypropylene plain weave cloth, and then two polyesters were used to prevent air from entering. Sandwiched between sheets, 40
Polymerization was performed by heating at 20 ° C. for 20 hours, 60 ° C. for 10 hours, and further at 95 ° C. for 10 hours to obtain a membrane-shaped ion exchange membrane matrix.

[0023]

Example 1 Introduction and cross-linking of ion exchange groups with aliphatic hydrocarbons: The above ion exchange membrane matrix was immersed in a 10% dibromohexane / acetone solution at 40 ° C. for 4 days and equilibrated with brine, A pre-selection treatment membrane A was obtained. Membrane selection by a polymer having a cation exchange group (giving selective permeability); on the other hand, benzoyl peroxide 1 to 100 parts of styrene
Parts and 400 parts of methanol were sealed in an ampoule purged with nitrogen, shaken at 100 ° C. for 48 hours for polymerization, and the polymer obtained was washed with methanol, dried, and concentrated with sulfuric acid to 100%.
It was treated at 24 ° C. for 24 hours for sulfonation. 200 this
Dissolve in water twice the weight and neutralize with caustic soda solution,
A treatment solution was prepared by adding dibenzyl alcohol so that the sodium sulfonate had a concentration of 5%. The pre-selection film A was immersed in this treatment liquid at 90 ° C. for 20 hours. After the treatment, the membrane was brought into contact with a large amount of salt water to remove organic substances in the membrane, and then a treated membrane A was obtained. The performance of the obtained treated film is as shown in Table 1.

As shown in Table 1 and Example 1, when the number of crosslinked carbons of the present invention is large (6), the FSO is high even with a high exchange capacity.
₄ , good electrical resistance.

[0025]

[Comparative Example 1] Introduction and cross-linking of ion exchange groups with aliphatic hydrocarbons: The above ion exchange membrane matrix was immersed in a 10% dibromopropane / acetone solution at 40 ° C for 4 days, equilibrated with brine, and then selected. A pre-chemical treatment film B was obtained. Membrane selection with a polymer having a cation exchange group (giving selective permeability): The same procedure as in Example 1 was carried out to obtain a treated membrane B. The performance of the obtained treated film is as shown in Table 1.

As shown in Table 1 and Comparative Example 1, when the number of crosslinked carbon atoms is small (less than 4), the electric resistance is good but FSO ₄
Becomes larger and the monovalent ion selectivity deteriorates.

[0027]

[Table 1]

[0028]

As described above, the anion exchange membrane of the present invention is an anion exchange membrane having extremely low electric resistance and practical monovalent anion selective permeability. In the salt-making technology of seawater concentration by electrodialysis using the anion exchange membrane of the present invention, electric power cost is reduced.

Claims (1)

[Claims] 1. An anion exchange membrane, wherein ion exchange groups are cross-linked by an aliphatic hydrocarbon, and a thin layer of a polymer having a cation exchange group is formed on the surface of the membrane. Anion exchange membrane to do.