JP2008255351A - Anion exchange membrane for salt production and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an anion exchange membrane that is useful for salt production and improves concentration performance and mechanical strength without increasing electric resistance in comparison with a conventionally used membrane. <P>SOLUTION: The anion exchange membrane for salt production is obtained by irradiating an ultra high molecular weight polyethylene film with ionizing radiation to generate a radical in an ultra high molecular weight polyethylene and then carrying out graft polymerization using a polymerizable monomer alone containing a functional group into which a cation-exchange group is introduced or a polymerizable mixture of the polymerizable monomer and a crosslinkable monomer. When the graft polymerization is carried out by using the monomer alone or the polymerizable mixture of the polymerizable monomer and the crosslinking monomer, preferably a swelling solvent is used. The method for producing the anion exchange membrane for salt production is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an anion exchange membrane used for salt production and a method for producing the same.

  An electrodialysis tank using positive and anion 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). However, 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, the ion exchange membrane obtained by this method is difficult to improve the concentration performance without increasing the electrical resistance of the membrane, and the mechanical strength is not satisfactory.

  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, partial polymerization is performed with ionizing radiation, followed by heating in the presence of a polymerization initiator to complete the polymerization and obtain an ion exchange membrane (for example, Patent Documents 4 to 6). reference).

However, although either method can improve the mechanical strength of the membrane, no satisfactory result has been found in the concentration performance of the membrane.
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 JP-A-6-271687

  An object of the present invention is to improve the concentration performance and mechanical strength of an anion exchange membrane used for salt production without increasing the electric resistance as compared with a conventionally used membrane. Is.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors irradiate an ultrahigh molecular weight polyethylene film with ionizing radiation, graft polymerize a styrene monomer, and then form an anion on a graft side chain formed. By introducing an exchange group, it is possible to provide a membrane having an increased concentration performance and an improved mechanical strength, without increasing the electrical resistance, as compared with conventionally used ion exchange membranes for salt production. I found it.

That is, the present invention has achieved the above object by adopting the following configuration.
(1) A polymerizable monomer having a functional group capable of introducing an anion exchange group alone after generating radicals in ultrahigh molecular weight polyethylene by irradiating ionizing radiation to the ultrahigh molecular weight polyethylene film, or An anion exchange membrane for salt production, which is obtained by performing graft polymerization using a polymerizable mixture of a polymerizable monomer and a crosslinkable monomer.
(2) The said (1) description characterized by using a swelling solvent when graft-polymerizing using the said monomer alone or the polymeric mixture of the said polymerizable monomer and a crosslinkable monomer. Anion exchange membrane for salt production.
(3) In the case where the functional group capable of introducing an anion exchange group is not an anion exchange group, the functional group is treated with a compound capable of providing an anion exchange group after the graft polymerization (1) or (2) ) The anion exchange membrane for salt production as described.
(4) A polymerizable monomer having a functional group capable of introducing an anion exchange group alone after generating radicals in ultrahigh molecular weight polyethylene by irradiating ionizing radiation to the ultrahigh molecular weight polyethylene film, or A method for producing an anion exchange membrane for salt production, wherein graft polymerization is carried out using a polymerizable mixture of a polymerizable monomer and a crosslinkable monomer.
(5) The above (4), wherein a swelling solvent is used when graft polymerization is performed using the monomer alone or a polymerizable mixture of the polymerizable monomer and the crosslinkable monomer. Of producing an anion exchange membrane for salt production. (6) When the functional group itself capable of introducing the anion exchange group is not a cation exchange group, it is treated with a compound capable of imparting an anion exchange group after the graft polymerization (4) or (5) ) A method for producing an anion exchange membrane for salt production as described in the above.

As is clear from the above, the gist of the present invention resides in the following (a) and (b).
(A) A polymerizable monomer having a functional group capable of introducing an anion exchange group after generating radicals by irradiating ultrahigh molecular weight polyethylene with ionizing radiation, or the polymerizable monomer and a crosslink It is a method for producing an anion exchange membrane in which an anion exchange group is introduced by graft polymerization in a polymerizable mixture containing an ionic monomer.
(B) An anion exchange membrane obtained by the method described in (1) above.

  According to the present invention, an anion exchange membrane having an increased concentration performance and an improved mechanical strength can be provided without increasing the electric resistance as compared with the anion exchange membrane currently used for salt production. , Can contribute to reducing salt production costs.

  The method for producing an anion exchange membrane of the present invention comprises a polymerizable monomer having a functional group capable of introducing an anion exchange group after generating radicals by irradiating a film made of ultrahigh molecular weight polyethylene with ionizing radiation. Body and swelling solvent, or graft polymerization in a polymerizable mixture containing the polymerizable monomer, the crosslinkable monomer, and the swelling solvent, and the functional group of the polymerizable monomer is trimethylamine or the like It is characterized by introducing an anion exchange group.

Hereinafter, embodiments of the present invention will be described in detail.
As the polymer film substrate that can be used in the present invention, ultrahigh molecular weight polyethylene having a molecular weight of 300,000 or more, which improves the durability of the obtained ion exchange membrane and suppresses swelling, can be used. In particular, it is preferable to use those having a molecular weight of 1,000,000 to 6,300,000 and a thickness of 20 to 100 μm.
The form of the polymer substrate 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.
The type of the ultrahigh molecular weight polyethylene film according to the production method is not particularly limited, and any film such as an inflation film or a skive film can be used. Examples of the inflation film include Saxin New Light Film Innovate (product name) manufactured by Sakushin Kogyo Co., Ltd. Examples of the skive film include Saxin New Light Film (product name) manufactured by Sakushin Kogyo Co., Ltd.

  As the polymerizable monomer having a functional group capable of introducing an anion exchange group used in the present invention, chloromethylstyrene is generally used, but conventionally known anion exchange resins and anions are known. Monomers used in the production of the exchange membrane are not particularly limited and are used. Specifically, styrene, vinyl toluene, vinyl xylene, α-methyl styrene, acenaphthylene, vinyl naphthalene, α-halogenated styrene, α, β, β'-trihalogenated styrene, chlorostyrene, vinyl pyridine, methyl vinyl Pyridine, ethyl vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, vinyl imidazole, amino styrene, alkyl amino styrene, trialkyl amino styrene, acrylic amide, acrylamide, oxium, and the like are used.

  Examples of the crosslinkable monomer that can be used in the present invention include the monomers listed below. A monomer capable of introducing a crosslinked structure. That is, one having at least two vinyl groups. For example, divinylbenzene (DVB), trivinylbenzene, divinyltoluene, divinylnaphthalene, ethylene glycol dimethacrylate.

  In the present invention, the above-described polymerizable monomer having a functional group capable of introducing an ion exchange group, or the polymerizable monomer and the crosslinkable monomer are copolymerized with these monomers as necessary. Possible monomers may be used. Examples of such other monomers include styrene, acrylonitrile, methyl styrene, vinyl chloride, acrolein, methyl vinyl ketone, maleic anhydride, maleic acid, salts or esters thereof, itaconic acid, salts or esters thereof, and the like. Used.

  Further, the swelling solvent that can be used in the present invention is not particularly limited, but hydrocarbons such as benzene, xylene, toluene and hexane, alcohols such as methanol, ethanol and isopropyl alcohol, acetone, methyl isopropyl ketone and cyclohexane. And solvents such as ketones such as dioxane and tetrahydrofuran, esters such as ethyl acetate and butyl acetate, nitrogen-containing compounds such as isopropylamine, diethanolamine, N-methylformamide and N, N-dimethylformamide. These can be used by appropriately selecting at least one or more of them.

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

An example of the pre-irradiation method will be described below.
First, after inserting the polymer base material 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, at −10 to 80 ° C., preferably near room temperature, at 25 to 400 kGy. Next, after the irradiated base material is taken out in the atmosphere and transferred to a glass container, the container is filled with a monomer solution or a monomer solution (solvent dilution). As the monomer liquid or monomer solution, one obtained by removing oxygen gas in advance by bubbling or freeze degassing with an inert gas free of 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 25 to 70 ° C.

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

The introduction of an anion exchange group into a polymer substrate into which a graft chain has been introduced can be carried out without any limitation using a wide range of conventional methods.
Examples of agents that introduce anion exchange groups include ammonia, methylamine, and dimethylamine that can introduce weakly basic ion exchange groups, such as trimethylamine, dimethylamine ethanol, and triethanol that can introduce strong basic ion exchange groups. Examples include, but are not limited to, amines.

  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 1
After inserting an ultra-high molecular weight polyethylene base material (manufactured by Sakushin Kogyo Co., Ltd., Saxin New Light Film Innovate (product name)) with a molecular weight of 1.6 million and a film thickness of 30 μm into an oxygen-impermeable plastic bag, The inside of the bag is purged with nitrogen to remove oxygen in the bag. Subsequently, the bag containing this substrate was irradiated with an electron beam at 25 ° C., an acceleration voltage of 250 keV, and an electron beam current of 32.7 mA at 50 kGy. Next, the irradiated base material is taken out in the air, transferred to a glass container, bubbled with high-purity nitrogen, and a polymerization ratio of chloromethylstyrene, divinylbenzene and cyclohexane from which oxygen gas has been removed in advance is 15: 1: 4. The solution mixed in was filled. After filling, graft polymerization was performed at 50 ° C. for 180 minutes, and then the membrane was taken out of the glass container, washed with methanol, and air-dried. The graft rate was 109%.

  The polymer substrate after the graft reaction was immersed in a 30% by mass trimethylamine aqueous solution in an autoclave at 50 ° C. for 2 hours, and then allowed to stand at room temperature for 48 hours. The obtained anion exchange membrane was thoroughly washed with water and stored in a 0.5N-NaCl aqueous solution. The film thickness of the synthesized film was 71 μm. The burst strength was measured with a Murren burst strength tester.

Further, the anion exchange membrane and a commercially available cation exchange membrane (Asahi Glass Co., Ltd. CSO) were mounted on a small electrodialysis apparatus (membrane area 8 cm ² ), and a concentration test was performed. 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 .

(Examples 2-26, Comparative Examples 1-2)
Membranes synthesized by different base materials and methods from Example 1 were used as Examples 2 to 26, and membranes currently used as anion exchange membranes for salt production were set as Comparative Examples 1 and 2, and together with Example 1, synthesis conditions and The film properties are shown in Table 1.

  The monomer ratio indicates the mass ratio of chloromethylstyrene: divinylbenzene: swelling solvent in the solution used for polymerization. Example 15 is an example not containing a swelling solvent, and Example 16 is an example not containing divinylbenzene. Example 26 is an example in which neither divinylbenzene nor swelling solvent is contained.

Further, FIG. 1 shows the relationship between the membrane resistance and the concentration of sodium chloride in the concentrated solution as a result of the concentration test.
All of the membranes produced as shown in Table 1 showed high burst strength compared to the commercially available anion exchange membrane for salt production.
Further, the membrane resistance was almost the same as or lower than that of the commercially available membrane.
As shown in FIG. 1, any anion exchange membrane produced according to the present invention showed high concentration performance as compared with a commercially available anion exchange membrane. In addition, the straight line shown in FIG. 1 is a straight line which shows the concentration performance equivalent to a commercially available ion exchange membrane, and it can be said that all the membrane performance shown above a straight line is higher concentration performance than a commercial membrane.

It is a graph showing the relationship between the resistance of the anion exchange membrane in the Example and comparative example of this invention, and the sodium chloride density | concentration of a concentrate.

Claims (6)

  By irradiating the ultrahigh molecular weight polyethylene film with ionizing radiation, radicals are generated in the ultra high molecular weight polyethylene, and then the polymerizable monomer having a functional group capable of introducing an anion exchange group alone or the polymerizable monomer alone. An anion exchange membrane for salt production, which is obtained by graft polymerization using a polymerizable mixture of a monomer and a crosslinkable monomer.   The salt-forming shade according to claim 1, wherein a swelling solvent is used when graft polymerization is performed using the monomer alone or a polymerizable mixture of the polymerizable monomer and the crosslinkable monomer. Ion exchange membrane.   The salt production according to claim 1 or 2, wherein when the functional group capable of introducing an anion exchange group itself is not an anion exchange group, the functional group is treated with a compound capable of providing an anion exchange group after graft polymerization. Anion exchange membrane.   By irradiating the ultrahigh molecular weight polyethylene film with ionizing radiation, radicals are generated in the ultra high molecular weight polyethylene, and then the polymerizable monomer having a functional group capable of introducing an anion exchange group alone or the polymerizable monomer alone. A method for producing an anion exchange membrane for salt production, wherein graft polymerization is carried out using a polymerizable mixture of a monomer and a crosslinkable monomer.   The salt-forming shade according to claim 4, wherein a swelling solvent is used when graft polymerization is performed using the monomer alone or a polymerizable mixture of the polymerizable monomer and the crosslinkable monomer. A method for producing an ion exchange membrane.   6. The salt production according to claim 4 or 5, wherein when the functional group capable of introducing an anion exchange group is not a cation exchange group, the functional group is treated with a compound capable of providing an anion exchange group after graft polymerization. Of manufacturing anion exchange membranes.

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