JP5028661B2 - Cation exchange, anion exchange membrane and production method thereof - Google Patents

Description

  The present invention relates to cation exchange and anion exchange membranes used for salt production and methods for producing them.

  An electrodialysis tank using positive and negative ion exchange membranes is used in the seawater concentration step in the ion exchange membrane salt production method. What is required in terms of the performance of ion exchange membranes used in electrodialysis tanks is membrane electrical resistance, concentration performance, durability, etc. To reduce manufacturing costs, without increasing membrane electrical resistance. It is necessary to improve the concentration performance. In addition, it is necessary to improve durability, particularly mechanical strength.

  Many methods have been proposed for producing an ion exchange membrane for salt production (see, for example, Patent Documents 1 to 3). A monomer having a functional group or an ion exchange group into which an ion exchange group can be introduced, a crosslinking agent, and There is widely known a method in which a mixture containing a polymerization catalyst as a main component is applied to a woven fabric made of polyvinyl chloride and polymerized, and then ion exchange groups are introduced as necessary.

  However, it has been difficult to improve the concentration performance of the ion exchange membrane obtained by this method without increasing the electrical resistance of the membrane.

  In order to solve this problem, after impregnating and supporting a polymerizable monomer on a polypropylene fiber base material, etc., a method of obtaining an ion exchange membrane by graft polymerization with ionizing radiation, or impregnating and supporting a polymerizable monomer on an olefin base material, etc. Then, a method is proposed in which the polymerization is completed by partially polymerizing with ionizing radiation, followed by heating in the presence of a polymerization initiator to obtain an ion exchange membrane (for example, Patent Documents 4 to 4). 6).

However, none of the methods yielded satisfactory results in terms of membrane concentration performance.
Japanese Examined Patent Publication No. 39-27861 Japanese Patent Publication No.40-28951 Japanese Patent Publication No. 44-19253 JP-A-51-52489 JP 60-238327 A Japanese Patent Application Laid-Open No. 06-271687

  The object of the present invention is to improve the concentration performance of cation and anion exchange membranes used for salt production without increasing the electrical resistance as compared with conventionally used membranes.

  As a result of intensive studies to solve the above problems, the inventors of the present invention irradiate the polyamide film with ionizing radiation, for example, graft polymerization of a polymerizable monomer having a sulfonic acid group or a quaternary ammonium group. As a result, it has been found that a membrane having an increased concentration performance can be provided without increasing the electric resistance as compared with conventionally used ion exchange membranes for salt production.

That is, the present invention has achieved the above object by adopting the following configuration.
(1) Radiation is generated in polyamide by irradiating the polyamide film with ionizing radiation, and then at least one cation exchange group or quaternary ammonium group selected from a sulfonic acid group and a salt thereof and a halide thereof. A positive electrode suitable for salt production obtained by graft polymerization in a polymerizable mixture containing a polymerizable monomer having at least one anion exchange group selected from the group consisting of a crosslinkable monomer and a solvent. Ion exchange membrane or anion exchange membrane.
(2) After generating radicals in polyamide by irradiating the polyamide film with ionizing radiation, at least one cation exchange group or quaternary ammonium group selected from sulfonic acid groups and salts thereof and halides thereof A cation suitable for salt production comprising a step of graft polymerization in a polymerizable mixture containing a polymerizable monomer having at least one anion exchange group selected from the group consisting of a crosslinkable monomer and a swelling solvent A method for producing an exchange membrane or an anion exchange membrane.

As is clear from the above, the gist of the present invention resides in the following (1) and (2).
(1) After the radicals are generated by irradiating the polyamide with ionizing radiation, the above-described polymerizable monomer having a cation or anion exchange group, a crosslinkable monomer, and a solvent are used as main components. A method for producing a salt-forming cation and anion exchange membrane comprising a step of performing graft polymerization in a mixture.
(2) A salt-forming cation and anion exchange membrane obtained by the method described in (1) above.

  According to the present invention, it is possible to provide a cation or anion exchange membrane having an increased concentration performance without increasing the electric resistance as compared with the cation or anion exchange membrane currently used for salt production. Can contribute.

  The method for producing a cation and anion exchange membrane according to the present invention comprises a polymerizable unit having a cation or anion exchange group after generating radicals by irradiating a polyamide film such as nylon 6 film with ionizing radiation. It is characterized in that graft polymerization is carried out in a polymerizable mixture containing a monomer, a crosslinkable monomer, and a solvent as main components.

Hereinafter, embodiments of the present invention will be described in detail.
Polyamides obtained from polylactams such as nylon 6, nylon 11 and nylon 12 and polyamides obtained from dicarboxylic acids such as nylon 6,6, nylon 6,10 and nylon 6,12 and diamines as polyamide film substrates that can be used in the present invention It is preferable to use one having a thickness of 20 to 100 μm. Polylactams are included in the polyamide referred to in the present invention.
The form of the base material is a form of a membrane (film) from the viewpoint of utilization as an ion exchange membrane for salt production, and its size and thickness can be appropriately determined.
Examples of the polyamide film according to the present invention include Unitika Nylon Film Emblem (product name) manufactured by Unitika Corporation.

Examples of the monomer that can be used in the present invention include monomers listed below.
(1) A monomer having a cation exchange group. For example, styrene sulfonic acid, sulfopropyl methacrylate and the like.
(2) A monomer having an anion exchange group. For example, vinylbenzyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, methacryloylaminopropyltrimethylammonium chloride, and the like.
(3) A monomer capable of introducing a crosslinked structure (crosslinkable monomer). That is, one having at least two vinyl groups. For example, divinylbenzene (DVB), trivinylbenzene, divinyltoluene, divinylnaphthalene, ethylene glycol dimethacrylate, methylenebisacrylamide (MBAAm) and the like.
The proportion of the crosslinkable monomer used is 0.3 to 3% by mass, preferably 0.4 to 2% by mass, based on the monomer having a cation or anion exchange group.

  In the present invention, the polymerizable monomer, that is, the polymerizable monomer may be used by dissolving in a solvent, dispersing in a solvent, or diluting with a solvent. Examples of the dilution solvent include water, methanol, ethanol and the like, and at least one or more of them can be appropriately selected and used. When diluted in a solvent and used, the monomer concentration is not particularly limited, but it is usually preferably 10% by weight or more.

  Graft polymerization of the above-mentioned monomer onto the substrate is a so-called pre-irradiation method in which the substrate is irradiated with ionizing radiation and then the monomer is subjected to a polymerization reaction, or a so-called simultaneous irradiation method in which the substrate and the monomer are simultaneously irradiated and polymerized. Any of the above can be performed. The pre-irradiation method is preferably used because the amount of homopolymer that does not undergo graft polymerization on the substrate is small. There are two pre-irradiation methods, a polymer radical method in which the substrate is irradiated in an inert gas, and a peroxide method in which the substrate is irradiated in an oxygen-existing atmosphere, both of which are used in the present invention. be able to.

An example of the pre-irradiation method will be described below.
First, after the base material is inserted into an oxygen-impermeable plastic bag, the inside of the bag is purged with nitrogen to remove oxygen in the bag. Next, the bag containing the base material is irradiated with an electron beam, which is one of ionizing radiation, in the range from −80 ° C. to room temperature for 50 to 200 kGy. Next, the bag is filled with the monomer liquid or the monomer solution (solvent dilution liquid). As the monomer solution or monomer solution, one obtained by removing oxygen gas in advance by bubbling or freeze degassing with an inert gas containing no oxygen is used. Graft polymerization for introducing a polymer graft chain to an irradiated substrate is usually carried out at room temperature to 80 ° C, preferably 40 to 70 ° C.

  The graft ratio of the polymer thus obtained (that is, the weight percentage of the graft chain with respect to the substrate before polymerization) is 5 to 300% by weight, more preferably 50 to 200% by weight. The graft ratio can be appropriately changed depending on the irradiation dose, polymerization temperature, polymerization time and the like.

  Hereinafter, the cation exchange membrane of the present invention and the production method thereof will be described in more detail based on examples. In addition, this invention is not limited to this Example.

Example 1
After inserting a nylon 6 base material having a film thickness of 25 μm into an oxygen-impermeable plastic bag, the inside of the bag is purged with nitrogen to remove oxygen in the bag. Next, the bag containing the substrate was irradiated with an electron beam at −80 ° C., an acceleration voltage of 2.0 MeV, and an electron beam current of 20 mA at 200 kGy. The bag was then bubbled with nitrogen and filled with a 10% by weight aqueous solution of sodium styrenesulfonate from which oxygen gas had been removed in advance. After filling, the bag was immersed in a constant temperature bath at 40 ° C. for 8 hours. Thereafter, the membrane was taken out from the bag, washed with water, and air-dried. The graft rate was 125%. The obtained cation exchange membrane was thoroughly washed with water and stored in a 0.5 M sodium chloride aqueous solution.

Furthermore, the cation exchange membrane of the present invention and the membrane currently used as an anion exchange membrane for salt production (Asahi Glass Co., Ltd. ASA) were mounted on a small electrodialysis apparatus (membrane area 8 cm ² ), and a concentration test was carried out. . A 0.5 M sodium chloride aqueous solution was used as the feed solution under the concentration conditions of a desalting chamber flow rate of 6 cm / s and a current density of 3 A / dm ² .

The membrane synthesized by a method different from that in Example 1 is Example 2-6, the membrane currently used as a cation exchange membrane for salt production is Comparative Example 1, and together with Example 1, the synthesis conditions and membrane characteristics are shown in Table 1. Shown in The salt-forming cation exchange membrane used in Comparative Example 1 is Selemion CSO manufactured by Asahi Glass Co., Ltd. In Table 1, the crosslinking concentration is the weight ratio of the charge to the monomer having a cation exchange group. The membrane resistance was measured by calculating the electrical resistance of the membrane using an electrical resistance measurement cell (effective area 1.77 cm ² ) and an AC bridge circuit and multiplying the effective area of the cell by 1.77 cm ² . The electrical resistance of the membrane is measured by measuring the electrical resistance of the membrane and 0.5 M NaCl using an AC bridge circuit with the membrane sandwiched between cells for electrical resistance measurement and filling the cell with 0.5 M NaCl. The electric resistance of only 0.5 M NaCl was measured in a state where the film was not sandwiched, and the electric resistance of only 0.5 M NaCl was subtracted from the electric resistance of the film and 0.5 M NaCl to obtain the electric resistance of the film.

  Hereinafter, the anion exchange membrane of the present invention and the production method thereof will be described in more detail based on examples. In addition, this invention is not limited to this Example.

(Example 7)
After inserting a nylon 6 base material having a film thickness of 25 μm into an oxygen-impermeable plastic bag, the inside of the bag is purged with nitrogen to remove oxygen in the bag. Next, the bag containing the substrate was irradiated with an electron beam at 200 kGy in the range from −80 ° C. to room temperature at an acceleration voltage of 2.0 MeV and an electron beam current of 20 mA. The bag was then bubbled with nitrogen and filled with vinylbenzyltrimethylammonium chloride and DVB, 20 and 0.8 wt% aqueous solutions, respectively, excluding oxygen gas, in advance. After filling, the bag was immersed in a constant temperature bath at 40 ° C. for 48 hours. Thereafter, the membrane was taken out from the bag, washed with water, and air-dried. The graft ratio was 133%. The obtained anion exchange membrane was washed thoroughly with water and stored in a 0.5 M aqueous sodium chloride solution.

Furthermore, the anion exchange membrane of the present invention and a membrane (Asahi Glass Co., Ltd. CSO) currently used as a cation exchange membrane for salt production were mounted on a small electrodialysis apparatus (membrane area 8 cm ² ), and a concentration test was conducted. . A 0.5 M sodium chloride aqueous solution was used as the feed solution under the concentration conditions of a desalting chamber flow rate of 6 cm / s and a current density of 3 A / dm ² .

  A membrane synthesized by a method different from that in Example 7 was designated as Example 8-11, a membrane currently used as an anion exchange membrane for salt production was designated as Comparative Example 2, and together with Example 7, the synthesis conditions and membrane characteristics were shown in Table 2. Shown in The anion exchange membrane for salt production used in Comparative Example 2 is Selemion ASA manufactured by Asahi Glass Co., Ltd.

1 and 2 show the relationship between the membrane resistance and the concentration of sodium chloride in the concentrated liquid as a result of the concentration test.
As shown in Tables 1 and 2, for any of the films produced according to the present invention, the film resistance was almost equal to or lower than that of the commercially available film.
Furthermore, as shown in FIGS. 1 and 2, any cation or anion exchange membrane produced according to the present invention showed a concentration performance equal to or higher than that of a commercially available cation or anion exchange membrane. . The straight lines shown in FIGS. 1 and 2 are straight lines showing the same concentration performance as that of the current ion exchange membrane, and all the membrane performances shown above the straight line can be said to be higher than the current membrane. .

It is a graph showing the relationship between the sum of the membrane resistance of the cation exchange membrane of this invention in the Example and a comparative example, and the membrane resistance of the present anion exchange membrane, and a concentrate chloride ion concentration. It is a graph showing the relationship between the sum of the membrane resistance of the anion exchange membrane of this invention in the Example and a comparative example, and the membrane resistance of the present cation exchange membrane, and a concentrate chloride ion concentration.

Claims (8)

A polymerizable mixture containing a polymerizable monomer having at least one cation exchange group selected from sulfonic acid groups and salts thereof after generating radicals in polyamide by irradiating the polyamide film with ionizing radiation A cation exchange membrane for salt production obtained by graft polymerization in the inside. The cation exchange membrane for salt production according to claim 1, wherein the polymerizable mixture further contains a crosslinkable monomer. It contains a polymerizable monomer having at least one anion exchange group selected from a quaternary ammonium group and a halide thereof after generating a radical in the polyamide film by irradiating the polyamide film with ionizing radiation. An anion exchange membrane for salt production obtained by graft polymerization in a polymerizable mixture. The anion exchange membrane for salt production according to claim 3, wherein the polymerizable mixture further contains a crosslinkable monomer. A polymerizable mixture containing a polymerizable monomer having at least one cation exchange group selected from sulfonic acid groups and salts thereof after generating radicals in polyamide by irradiating the polyamide film with ionizing radiation The manufacturing method of the cation exchange membrane for salt manufacture including the process of performing graft polymerization in the inside. The method for producing a cation exchange membrane for salt production according to claim 5, wherein the polymerizable mixture further contains a crosslinkable monomer. It contains a polymerizable monomer having at least one anion exchange group selected from a quaternary ammonium group and a halide thereof after generating a radical in the polyamide film by irradiating the polyamide film with ionizing radiation. A method for producing an anion exchange membrane for salt production comprising a step of graft polymerization in a polymerizable mixture. The method for producing an anion exchange membrane for salt production according to claim 7, wherein the polymerizable mixture further contains a crosslinkable monomer.

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