JPH0759644B2 - Method for producing modified anion exchange membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to ion selective permeability between anions, more specifically, it is easy to selectively permeate anions having a small valence with respect to anions having different valences. A method for producing a modified anion exchange membrane having properties.

[Prior art]

In Japan, in particular, because of the necessity of establishing salt-making technology for seawater concentration by electrodialysis, many studies have been conducted to impart ion-selective permeability to the ion-exchange membrane with the same sign, and it has been carried out over many years and has also been carried out industrially. ing. Among these, for the production of the anion permselective membrane, for example, a method of forming a dense thin layer of condensation type crosslinks on the surface of the anion exchange membrane (Japanese Patent Publication No. 36-15258), the surface layer of the basic anion exchange membrane. Partial oxidative decomposition (Japanese Patent Publication No. 40-34649), and a method of forming an anionic thin layer on the surface of an anion exchange membrane (Japanese Patent Publication No. 45
-30693), a method of inactivating the surface layer part of the anion exchange membrane (Japanese Patent Publication No. 34-9994, 53-1071), of an anion exchange membrane in which only the surface layer part is cross-linked with a haloalkyl group by treatment with a Lewis acid. A manufacturing method (Japanese Patent Publication Sho 56-8049) and the like have been proposed.

[Problems to be solved by the invention]

However, in the anion exchange membrane whose surface is treated as described above, it is difficult to permeate a polyvalent anion, and in particular, it is possible to selectively permeate a monovalent anion to a practically necessary degree. Therefore, the problem that electric resistance increases at the same time cannot be avoided. Incidentally, in the case of producing a monovalent anion-selective anion exchange membrane which can be put to practical use by the conventional method, it is generally difficult to avoid an increase in its electrical resistance to the order of 0.3 to 3 Ω-cm ² . Therefore, in the production of such a selectively permeable anion exchange membrane, it is required to improve the anion selective permeability and to keep the increase in electrical resistance as small as possible. Especially in recent years, in salt production technology by ion exchange membrane electrodialysis, in order to pursue low prices against imported raw material salts, the development of monovalent ion selective permeable anion exchange membranes with lower electrical resistance has been developed. This is where it is required.

[Means for solving problems]

As a result of earnest research in view of the above-mentioned problems and desires, the present inventors have obtained an anion exchange membrane having a desired increase in electric resistance and a favorable monovalent anion selective permeability by the following production method. The inventors of the present invention have found out that and have proposed the present invention. That is, the present invention is a modified anion exchange membrane characterized by irradiating the surface of an ion exchange membrane matrix having a haloalkyl group with ionizing radiation and then introducing an anion exchange group into the anion exchange membrane matrix. Is a manufacturing method.

The ion-exchange membrane matrix having a haloalkyl group in the present invention is generally suitable for a method of preliminarily polymerizing a monomer having a haloalkyl group by homopolymerization or copolymerization with another monomer copolymerizable therewith, or for introducing a haloalkyl group. It can be obtained by a method of introducing a haloalkyl group into a polymer of a monomer or a copolymer thereof by post-treatment. A typical example obtained by the former method is a polymer of halomethylstyrene or a copolymer of this with styrene or divinylbenzene. Further, a typical example obtained by the latter method is a method in which a polymer such as styrene or vinyltoluene or a copolymer thereof with divinylbenzene or divinylsulfone is haloalkylated with a haloalkyl ether solution in the presence of a Lewis acid. Obtained by conventional haloalkylation, especially halomethylation, such as haloalkylation with hydrogen and aldehydes.

Furthermore, the method for producing the anion exchange membrane matrix having a haloalkyl group according to the present invention will be described in detail. A suitable linear polymer is dissolved or not dissolved in styrene-divinylbenzene to obtain a film, a cloth or a net. A method of coating or impregnating a film-like substrate such as, and polymerizing, and then haloalkylating by a conventional method; a fine powdery polymer compound suitable for a monomer such as styrene-divinylbenzene, for example, polyethylene, polypropylene, polyvinyl chloride, fluorine resin Etc. to make a suspension, and if necessary, a paste-like mixture in which a linear polymer is dissolved is applied to a substrate and then polymerized, or the mixture is polymerized as it is and then cut, or polymerized between two flat plates. Method to introduce a haloalkyl group after obtaining a film-like product by attaching a styrene-butadiene latex to the film-like substrate Preparation of intermediates used without particular limitation in a conventional anion exchange membrane and a method of haloalkylated brought partially crosslinked after drying Te. Further, for example, a method in which a linear polymer of a haloalkyl monomer such as chloromethylstyrene and another inert linear polymer are dissolved in a common solvent and cast into a film, and then the solvent is scattered, a haloalkyl monomer is used. A method of polymerizing after preparing a base material by preparing a paste mixture in the same manner as described above,
A method of cutting after forming a bulk polymer, a method of polymerizing between flat plates, a method of impregnating and polymerizing a film, and the like are adopted. In this case, in addition to the haloalkyl monomer, a crosslinking agent such as divinylbenzene, divinylsulfone or butadiene may be used together, or another copolymerizable monomer may be used.

In the present invention, it is preferable to treat the surface of the ion-exchange membrane matrix having a haloalkyl group obtained by the method as described above by irradiating it with ionizing radiation, which is particularly good in monovalent anion while keeping the increase in electric resistance small. It is extremely important to obtain anion exchange membranes that are permselective. That is, according to the present invention, by a simple method of only irradiating the surface of the ion exchange membrane matrix having a haloalkyl group with ionizing radiation, the increase in electrical resistance is generally maintained in the range of 0.5 Ω-cm ² or less. Thus, an anion exchange membrane having a desired practical monovalent anion selective permeability can be obtained.

Examples of the ionizing radiation used in the present invention include radiation sources such as plasma, ultraviolet rays, X-rays, gamma rays, and electron beams, but it is preferable to use plasma, ultraviolet rays by a mercury lamp, electron beams, or the like. . Irradiation with ionizing radiation may be carried out in vacuum, in air, or in an inert gas such as nitrogen helium or argon as an atmosphere, and may be carried out in a continuous line or intermittently.
In the present invention, when the dose of such ionizing radiation is too large, the electric resistance of the obtained anion exchange membrane increases. Therefore, the irradiation amount and irradiation time of the ionizing radiation in the present invention, depending on the radiation source and its intensity, may be determined in consideration of the increase in the group resistance of the anion exchange membrane obtained in advance by experiments, Generally, the object of the present invention can be achieved with an irradiation time of several minutes to several tens of minutes.

Next, in the present invention, by introducing an anion exchange group into the ion exchange membrane matrix in which the haloalkyl group that has been treated by irradiation with the ionizing radiation remains, the desired monovalent anion selective permeability is obtained. The anion exchange membrane can be obtained. For introducing such an anion exchange group, a conventionally known anion exchange group is introduced by using a known method.
That is, as the anion exchange group, for example, —NH ₂ , ═NH, ≡
Examples include amino groups or imino groups such as N, quaternary ammonium bases, tertiary sulfonium bases, quaternary phosphonium bases, arsonium bases, and stibonium bases, provided that they have a positive charge in an aqueous solution. There is no particular limitation. Further, the introduction of such anion exchange group, for example, by immersing in an aqueous solution of ammonia or primary to tertiary amine of the ion exchange membrane matrix,
An amino group, an imino group, or a quaternary ammonium base can be introduced, and the former can be converted to a quaternary ammonium by a quaternizing agent. Similarly, the sulfonium base can be introduced by immersing the ion exchange membrane matrix in a solution of triphenylphosphine, and the sulfonium base can be easily introduced by reacting with methyl sulfide.

[Action]

Although the mechanism of action of the present invention is not yet sufficiently clear, in the extremely thin surface layer portion of the anion-exchange membrane matrix upon irradiation with ionizing radiation, the existing haloalkyl group is decomposed and a part is crosslinked to the surface layer portion. It is speculated that a dense structure is formed. As a result, it is recognized that the obtained ion exchange membrane maintains a small increase in electric resistance and exhibits desired monovalent anion selective permeability.

〔effect〕

As explained above, according to the production method of the present invention, it is possible to easily obtain a practical modified anion exchange membrane having extremely low electric resistance and particularly having a monovalent anion selective permeability. Therefore, in the salt-making technique of seawater concentration by electrodialysis using the modified anion exchange membrane of the present invention,
This contributes to the effect that the power consumption of electrodialysis can be greatly reduced.

〔Example〕

Examples will be given below for illustrating the present invention further in detail, but the present invention is not limited to the description of the examples below.

Regarding the anion exchange membranes obtained in the examples, the selective permeability of sulfate ion to chlorine ion was measured. That is, in a two-chamber acrylic cell equipped with silver and silver chloride in each chamber, 0.5N-NaCl was used for the anode chamber and 0.25 for the cathode chamber.
N-NaCl and 0.25N-Na ₂ SO ₄ were put in 1: 1 and electrodialyzed at a current density of ² A / dm ² for 1 hour with stirring at 1500 rpm of the stirrer and permeated into the anode chamber. Select the permeation coefficient by determining the ratio of sulfate ion and chloride ion Is given by

tSO ₄ ^-2: SO ₄ wheel rate in the anion exchange membrane ^-2 Tcl ^-: Cl ^- wheel index TSO ₄ in anionic membrane of ^-2: SO ₄ cathode layer ^- the concentration (eq) CCl ^-: Concentration (equivalent) of Cl ⁻ in the cathode layer The electric resistance of the film was measured by 1000 cycle AC in 0.5 N NaCl (25 ° C.).

Example 1 100 parts of polyvinyl chloride fine powder, 500 parts of vinylbenzyl chloride, 100 parts of divinylbenzene having a purity of 50% and 10 parts of benzoyl peroxide were mixed with a viscous pasty mixture on a polyvinyl chloride cloth while degassing. After uniform coating, both sides were covered with slophane and polymerized at 80 ° C. for 16 hours to obtain a film-like polymer.

The film-shaped polymer was irradiated with ultraviolet rays from a low-pressure mercury lamp of 20 W for each predetermined time shown in Table 1. Next, these film materials were immersed in a 30% aqueous solution of trimethylamine 2 and methanol 1 (volume ratio) for 16 hours to carry out a quaternary amination reaction.

The results of measuring the electric resistance and the selective permeability of each of the obtained anion exchange membranes are shown in Table 1.

Example 2 The film-like polymer obtained in Example 1 was irradiated with ultraviolet rays from a 3 kW high-pressure mercury lamp for each predetermined time shown in Table 2.

Then, a quaternary amination reaction was carried out under the same conditions as in Example 1. The electric resistance and selective permeability of the obtained anion exchange membrane were measured and the results are shown in Table 2.

Example 3 In Example 1, a plasma treatment of 100 W was performed at 1.0 Torr (air) instead of UV irradiation for a predetermined time shown in Table 3. Table 3 shows the measurement results of the anion exchange membrane obtained by the same procedure as in Example 1 except for the above.

Claims (1)

[Claims] 1. A modified anion exchange membrane, characterized in that the surface of an ion exchange membrane matrix having a haloalkyl group is irradiated with ionizing radiation, and then an anion exchange group is introduced into the ion exchange membrane matrix. Method