JPH11172024A - Anion-exchange membrane and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anion-exchange membrane which has a good selective permeability against monovalent anions or specific ions among the monovalent anions and gives a small amount of percolating water at an elevated temperature. SOLUTION: A monomer mixture comprising a monomer having a functional group into which an anion-exchange group may be introduced or an anion- exchange group, N-isopropyl acrylamide, a crosslinking agent and a polymerization initiator, is applied onto a substrate, molded and polymerized and, if required, introduced with an anion-exchange group to produced an anion- exchange membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anion exchange membrane and a method for producing the same, and more particularly, to an anion exchange membrane having good permselectivity for monovalent anions and a small amount of permeated water at high temperatures. And its manufacturing method.

[0002]

2. Description of the Related Art At present, the electrochemical performance of anion exchange membranes is extremely excellent, and is widely used in various fields. Conventionally, these anion exchange membranes are, for example, a mixture of a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group, a cross-linking agent and a polymerization initiator, and optionally other copolymerization. It is produced by mixing possible monomers, adhering them to a substrate, polymerizing and molding, and then introducing an anion exchange group as necessary.
Here, various other copolymerizable monomers are used, but no examples using N-isopropylacrylamide are known at all.

An important property when using such an anion exchange membrane is permselectivity between anions. That is, the permselectivity between anions affects the yield when a specific salt is concentrated or desalted from a mixed solution. For example, in seawater concentration, etc., good permselectivity for monovalent cations is required. And
Further, desalting of nitrate ions in groundwater requires good permeation of the nitrate ions even in the same monovalent anion. Therefore, it is desired to develop an anion exchange membrane having a good permselectivity for such specific anions.

[0004] These anion exchange membranes are generally
The amount of permeated water is large, and the amount of permeated water increases proportionally with an increase in temperature. On the other hand, in the electrodialysis of concentration and desalination, it is advantageous to perform electrodialysis at a relatively high temperature of about 50 ° C. in order to increase the electric conductivity of the treated water and reduce the energy consumption. As described above, there is a problem that the amount of permeated water into the anion exchange membrane becomes considerably large. That is, when the amount of infiltrated water is large, for example, in the case of seawater concentration, low-concentration brine is obtained and the energy consumption in the concentration step is increased. Will drop.

[0005]

SUMMARY OF THE INVENTION From the above background, the present invention provides a selective permeation of monovalent anions and a better permeation of specific monovalent anions such as nitrate ions. It is an object of the present invention to develop an anion exchange membrane having a small amount of permeated water at a high temperature.

[0006]

Means for Solving the Problems The present inventors have intensively studied in view of the above problems. As a result, they have found that an anion exchange membrane containing polymerized units based on N-isopropylacrylamide satisfies the above object, and have completed the present invention.

[0007] That is, the present invention is an anion exchange membrane comprising a polymer having an anion exchange group, which contains polymerized units based on N-isopropylacrylamide.

Further, the present invention relates to a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group,
The above-mentioned anion exchange characterized in that a monomer mixture comprising isopropylacrylamide, a crosslinking agent, and a polymerization initiator is adhered to a substrate and molded and polymerized, and then, if necessary, an anion exchange group is introduced. A method of making the membrane is also provided.

The ion exchange resin constituting the anion exchange membrane of the present invention comprises an ion exchange polymer containing a unit based on N-isopropylacrylamide as a polymerization unit. Here, a polymer obtained by polymerizing N-isopropylacrylamide as a monomer component exhibits a unique property of undergoing a phase transition at about 32 ° C. In the present invention, by using N-isopropylacrylamide having such a unique property as a monomer component for producing a polymer constituting an anion exchange membrane, excellent ion selective permeability at high temperature is obtained. And an anion exchange membrane having a small amount of permeated water can be obtained.

In the above ion-exchangeable polymer, the content of the polymerized unit based on N-isopropylacrylamide is not particularly limited. Suitably, it is 50% by weight, more preferably 10 to 40% by weight.

As the anion exchange group to be bound to the polymer, any functional group capable of becoming positively charged in an aqueous solution can be used without any limitation. Specific examples include primary, secondary, and tertiary amino groups, quaternary ammonium bases, and phosphonium groups. Of these, tertiary amino groups,
Strongly basic anion exchange groups such as quaternary ammonium bases are preferred.

In the anion exchange membrane of the present invention prepared by using these polymers as an ion exchange resin, the amount of anion exchange groups is not particularly limited, but usually, the ion exchange capacity is 0.1 to 5 mm. Amount / g-dry film, preferably 0.5-3 milliequivalent / g-dry film. In addition, the thickness of the anion exchange membrane is related to desired electrical resistance, mechanical strength, transport number, durability, and the like, but is generally in the range of 10 to 500 μm, preferably 40 to 300 μm. is there.

Further, in the anion exchange membrane, the N
The amount of the polymerized unit based on -isopropylacrylamide is 0.01 to 1.5 with respect to 1 mol of the anion exchange group.
Mol / mol-anion exchange group, preferably from 0.03 to
The amount is preferably 1.0 mol / mol-anion exchange group, more preferably 0.1 to 1.0 mol / mol-anion exchange group.

The anion exchange membrane of the present invention may be any membrane as long as it is formed into a membrane using the above polymer as an ion exchange resin. The production method is not particularly limited, and for example, a known casting method, a monomer coating method, a paste method, a bulk polymerization method, an impregnation method and the like can be appropriately adopted. In addition, in order to reinforce the film, a substrate may be used if necessary. Of these, it is preferable to use a substrate and produce it by a monomer coating method or a paste method.

In particular, a monomer mixture comprising a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group, N-isopropylacrylamide, a crosslinking agent, and a polymerization initiator is attached to a substrate. After the polymerization polymerization
It is preferable to produce it by a method of introducing an anion exchange group as needed.

In this production method, as the functional group capable of introducing an anion exchange group or the monomer having an anion exchange group, a monomer used in the production of a conventionally known anion exchange membrane is particularly limited. Used without. Specifically, examples of the monomer having a functional group capable of introducing an anion exchange group include styrene, chloromethylstyrene, bromomethylstyrene, and glycidyl methacrylate.

The monomers having an anion exchange group include 4-vinylpyridine, 2-vinylpyridine, methylvinylpyridine, ethylvinylpyridine, vinylpyrrolidone, N, N-dimethylaminoethyl methacrylate,
N, N dimethylaminopropylacrylamide, vinylcarbazole, vinylimidazole, aminostyrene,
Methylaminostyrene, dimethylaminostyrene, trimethylaminostyrene and the like can be mentioned. These monomers having an anion exchange group are also monomers having a functional group capable of introducing a quaternary ammonium base by quaternization. Also, quaternized monomers of these monomers can be used as monomers having an anion exchange group.

As the cross-linking agent, a conventionally known monomer used in the production of an ion exchange membrane is used without any particular limitation. Specifically, for example, m-, p-, o-divinylbenzene, ethylene glycol bis (methacrylate), divinylsulfone, butadiene, chloroprene, isoprene, trivinylbenzenes, divinylnaphthalene, diallylamine, triallylamine, divinylpyridines and the like And the like.

As the polymerization initiator, conventionally known polymerization initiators are used without any particular limitation, and may be appropriately selected according to the base material of the ion exchange membrane to be used and the molding conditions. For example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butylperoxy-2-ethylhexanoate, lauryl peroxide, stearyl peroxide, methyl isobutyl ketone peroxide, cyclohexane peroxide, o-methylbenzoyl oxide 2,4,4-trimethylpentylperoxy-phenoxyacetate, α-cumylperoxyneodecanoate, di-t-butylperoxyhexahydroterephthalate, t-butylperoxybenzoate, diisopropylbenzene hydroperoxide, di-t- Butyl peroxide, 1,1-bis-t
-Butylperoxy-3,3,5-trimethylcyclohexane and the like are used.

In the present invention, the above-mentioned mixture of a functional group capable of introducing an ion-exchange group or a monomer having an ion-exchange group, N-isopropylacrylamide, a crosslinking agent and a polymerization initiator may be used, if necessary. Other monomers copolymerizable with these monomers may be used as a mixture. Examples of such a monomer include styrene, acrylonitrile, ethylstyrene, vinyl chloride, acrolein, methyl vinyl ketone, methyl acrylate, and the like. In addition, a thickener and a plasticizer may be mixed for the purpose of enhancing film forming properties. Specifically, as the thickener, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer or a hydrogenated product thereof can be used,
As the plasticizer, dioctyl phthalate, dibutyl phthalate, tributyl phosphate, styrene oxide, or a fatty acid or an alcohol ester of an aromatic acid can be used. Further, a solvent or the like for diluting the monomer may be appropriately added.

The mixing ratio of each of the above components is not particularly limited, but generally, a functional group capable of introducing an ion exchange group or a monomer having an ion exchange group is used in an amount of 10 to 10%.
93% by weight, preferably 20 to 85% by weight, N-isopropylacrylamide 5 to 50% by weight, preferably 10 to 10%
40% by weight, 2-40% by weight of crosslinking agent, preferably 5-3%
0% by weight, and other monomers copolymerizable with these monomers are preferably blended in the range of 0 to 40% by weight, preferably 0 to 30% by weight. Further, the polymerization initiator is preferably blended in an amount of 0.1 to 15 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the total of the respective monomers. Further, the thickener is preferably compounded in the range of 0.1 to 15 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of each of the above monomers. 5 plasticizers
It is preferable to mix in an amount of 40 parts by weight, preferably 10 to 30 parts by weight.

The monomer mixture obtained as described above is usually attached to a substrate and molded and polymerized. Here, as the base material, those which use polyvinyl chloride, polyolefin or the like as a material resin, which has been conventionally used as a base material for an ion exchange membrane, are used without any limitation. As the base material made of polyolefin, a woven fabric made of polyethylene, polypropylene, polybutene, a copolymer thereof, a blend of these polymers, or the like is preferable. In addition, a nonwoven fabric, a net, a porous sheet, or the like can be used without limitation. The single yarn of such a woven fabric may be either a monofilament or a multifilament. Further, the smaller the basis weight of the warp and the weft, the smaller the electrical resistance of the obtained ion exchange membrane can be.
The range of -500 is preferable. A woven fabric having a small number of stitches can be reduced to 1 by a method such as partial fusion at the intersection of single yarns.
A woven fabric having a small number of stitches can be used by fusing the polyethylene portion at the intersection with a composite filament having a core portion of polypropylene and a sheath portion of polyethylene, for example. The thickness of these substrates is not particularly limited, but is preferably in the range of 10 to 500 μm.

When the monomer mixture is adhered to the above-mentioned base material and then subjected to molding polymerization, the temperature is generally raised from normal temperature under pressure, but the rate of temperature rise is not particularly limited. Instead, it may be appropriately selected. These polymerization conditions also depend on the type of polymerization initiator involved, the composition of the monomer mixture, and the type of base material, and cannot be determined unequivocally; It may be appropriately selected in consideration of mechanical properties.

As a method of attaching the monomer mixture to the cloth-like substrate, a known method such as coating, impregnation, immersion, etc. may be appropriately adopted. Further, a so-called paste method in which the above monomer mixture is mixed with a powder of polyvinyl chloride or the like and applied as a paste may be appropriately adopted according to a conventional method.

The film-like polymer obtained by the above polymerization can be used, if necessary, by subjecting it to a desired shade by a known treatment such as chloromethylation and amination, quaternary ammonium basification, and phosphonium formation. An anion exchange membrane can be obtained by introducing an ion exchange group.

[0026]

The anion exchange membrane of the present invention comprises an ion exchange resin containing a polymer unit based on N-isopropylacrylamide as an ion exchange resin. It changes greatly, and has properties useful as a diaphragm in electrodialysis. That is, at a temperature higher than the above-mentioned temperature, it has good permselectivity for monovalent anions, and among monovalent anions, it has a very good permselectivity for bromide ions and nitrate ions. Become. Further, as the temperature rises up to the temperature, the amount of permeated water decreases, and when the temperature is higher than the temperature, the amount of permeated water has a peculiar property that it is almost constant at an extremely small value. The reason why the anion exchange membrane of the present invention exhibits such characteristic properties is not clear, but is about 3 times.
At 2 ° C. or higher, it is speculated that the isopropyl groups of N-isopropylacrylamide aggregate and the membrane structure becomes dense, and at the same time, the degree of hydrophilicity of the anion exchange membrane decreases.

The anion exchange membrane of the present invention can be used in high-temperature electrodialysis at a temperature of about 32 ° C. or more, preferably 35 ° C. or more by utilizing the above-mentioned properties, and the above-mentioned condition can be obtained with little permeated water. Selective concentration and desalting of specific anions can be performed. Therefore, it can be used very effectively in seawater concentration and desalination of nitrate ions in groundwater.

[0028]

Hereinafter, Examples and Comparative Examples of the present invention will be described.
The present invention is not limited to these examples.

In the following Examples and Comparative Examples,
The permselectivity of various anions to chloride ions and the amount of permeated water were measured by the following methods.

1) Selective permeability of various anions to chloride ions The following four-chamber cell: Ag-AgCl electrode / 0.2 mol NaCl aqueous solution / C membrane / 0.2 mol NaCl aqueous solution / A membrane / 0.2 mol NaX containing 0.2 mol NaCl aqueous solution / C film / 0.2 mol
NaCl aqueous solution / Ag-AgCl C membrane: Cation exchange membrane A membrane: Anion exchange membrane The selective permeability of various anions to chloride ions in an anion exchange membrane was measured by the following formula.

P ^X _Cl = (t _x / t _Cl ) / (C _x / C _Cl ) X: Various anions t _x : Transfer amount of X ion t _Cl : Transfer amount of Cl ion C _x : Desalination side X ion concentration C _Cl : Cl ion concentration on the desalination side 2) Permeation water amount A two-chamber cell is set up using an anion exchange membrane as a diaphragm, 4N-NaCl is supplied to one chamber, and water is supplied to the other chamber. Supply and agitate each room. The amount of water transferred from the water supply chamber to the saline solution supply chamber for a certain period of time was measured, and the amount of permeated water (Wo) was determined from the following equation.

W _o = ΔM _w / (CA · Δt) [mol-H ₂ O /
Sec (mol / l) cm ² ] ΔM _w : amount of water transferred / 18 (mol-H ₂ O) C: salt concentration before diffusion (4 mol / l) A: effective membrane area (10 cm ² ) Δt: diffusion Time (6 hours) Example 1 50% by weight of N, N dimethylaminoethyl methacrylate, 25% by weight of N-isopropylacrylamide, 25% by weight of ethylene glycol bis (methacrylate), and 100 parts by weight of these monomers in total Then, 0.5 parts by weight of benzoyl peroxide was mixed to obtain a monomer mixture.

Next, the above-mentioned monomer mixture was applied to a woven fabric made of polyvinyl chloride, coated with a polyester film as a release material, and then subjected to molding polymerization at a polymerization temperature of 85 ° C. Then, the obtained film-like polymer was converted to 1N HCl.
For 24 hours to obtain an anion exchange membrane. Table 1 shows the properties of the anion exchange membrane. In this anion exchange membrane, the amount of the polymerized unit based on N-isopropylacrylamide was 0.63 mol / mol-anion exchange group with respect to 1 mol of the anion exchange group.

About this anion exchange membrane, 25, 3
The selective permeabilities of sulfate, fluorine, bromine and nitrate with respect to chloride at 0, 32, 35 and 40 ° C. were measured. The results are shown in FIGS.
It was shown to.

Example 2 50% by weight of glycidyl methacrylate, 25% by weight of N-isopropylacrylamide, 25% by weight of ethylene glycol bis (methacrylate), and 0.5 parts of benzoyl peroxide based on 100 parts by weight of these monomers in total The parts by weight were mixed to obtain a monomer mixture.

Next, the above-mentioned monomer mixture was applied to a woven fabric made of polyvinyl chloride, coated with a polyester film as a release material, and then subjected to molding polymerization at a polymerization temperature of 85 ° C. Then, the obtained membrane polymer was subjected to an amination reaction at 30 ° C. for 48 hours using an aqueous solution of 10% by weight of trimethylamine and 20% by weight of acetone to obtain an anion exchange membrane. Table 1 shows the properties of the anion exchange membrane. In this anion exchange membrane, the amount of the polymerized unit based on N-isopropylacrylamide was 0.57 mol / mol-anion exchange group with respect to 1 mol of the anion exchange group.

About this anion exchange membrane, 25, 3
The selective permeabilities of sulfate, fluorine, bromine and nitrate with respect to chloride at 0, 32, 35 and 40 ° C. were measured. The results are shown in FIGS.
It was shown to. Further, the amount of permeated water at each of the above temperatures was measured and is shown in Table 3. The result is shown in FIG.

Example 3 An anion exchange membrane obtained in the same manner as in Example 1 was treated at 25 ° C. with a hexane solution containing 50% by weight of methyl iodide.
It was subjected to a quaternization reaction for 24 hours. Table 1 shows the properties of the obtained anion exchange membrane.

About this anion exchange membrane, 25, 3
The selective permeabilities of sulfate, fluorine, bromine and nitrate with respect to chloride at 0, 32, 35 and 40 ° C. were measured. The results are shown in FIGS.
It was shown to.

Comparative Example 1 Commercially available membrane "NEOSEPTA AM-1" (manufactured by Tokuyama Corporation)
The permselectivity of sulfate, fluorine, bromine, and nitrate ions to chloride ions at 25, 30, 32, 35, and 40 ° C. was measured, and the results are shown in Table 2.
The results are shown in FIGS. Further, the amount of permeated water at each of the above temperatures was measured and is shown in Table 3. The result is shown in FIG.
It was shown to.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[Brief description of the drawings]

FIG. 1 is a graph showing the selective permeability of sulfate ions to chloride ions at various temperatures of an anion exchange membrane. In the figure,-○-is the anion exchange membrane obtained in Example 1,-●-is the anion exchange membrane obtained in Example 2,-□.
-Indicates the anion exchange membrane obtained in Example 3, and-■-indicates the anion exchange membrane used in Comparative Example 1.

FIG. 2 is a graph showing the selective permeability of fluorine ions to chloride ions at various temperatures of an anion exchange membrane. In the figure,-○-is the anion exchange membrane obtained in Example 1,-●-is the anion exchange membrane obtained in Example 2,-□.
-Indicates the anion exchange membrane obtained in Example 3, and-■-indicates the anion exchange membrane used in Comparative Example 1.

FIG. 3 is a graph showing the selective permeability of bromide ions to chloride ions at various temperatures of an anion exchange membrane. In the figure,-○-is the anion exchange membrane obtained in Example 1,-●-is the anion exchange membrane obtained in Example 2,-□.
-Indicates the anion exchange membrane obtained in Example 3, and-■-indicates the anion exchange membrane used in Comparative Example 1.

FIG. 4 is a graph showing the selective permeability of nitrate ions to chloride ions at various temperatures of an anion exchange membrane. In the figure,-○-is the anion exchange membrane obtained in Example 1,-●-is the anion exchange membrane obtained in Example 2,-□.
-Indicates the anion exchange membrane obtained in Example 3, and-■-indicates the anion exchange membrane used in Comparative Example 1.

FIG. 5 is a graph showing the amount of permeated water at each temperature of the anion exchange membrane. In the figure,-●-indicates the anion exchange membrane obtained in Example 2, and-■-indicates the anion exchange membrane used in Comparative Example 1.

Claims (2)

[Claims] 1. An anion exchange membrane comprising a polymer having an anion exchange group, comprising polymer units based on N-isopropylacrylamide. 2. Adhering a monomer mixture comprising a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group, N-isopropylacrylamide, a crosslinking agent, and a polymerization initiator to a substrate. The method for producing an anion-exchange membrane according to claim 1, wherein an anion-exchange group is introduced as necessary after the formation and polymerization.