Anion exchange membrane and method for manufacturing the same

Abstract

Provided is a cation exchange membrane having excellent selectivity for monovalent anions, which has a small electrical resistance when electrodialysis is performed and does not have an increased manufacturing cost, and a method for producing the same. The cation exchange membrane used is a cation exchange membrane having a tertiary amino group and a quaternary ammonium group as functional groups, and the intensity ratio of the tertiary amino group to the quaternary ammonium group when the surface of the cation exchange membrane having a tertiary amino group and a quaternary ammonium group as functional groups is measured by X-ray photoelectron spectroscopy is 1.0 or greater.

Description

Technical Field

[0001] This invention relates to anion exchange membranes and their manufacturing methods. The anion exchange membrane is an anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups, and has more tertiary amino groups than quaternary ammonium groups on its surface. Background Technology

[0002] Ion exchange membranes are selectively permeable membranes for ions, and are broadly classified into cation exchange membranes and anion exchange membranes. Anion exchange membranes have a structure in which positively charged exchange groups are fixed on the membrane surface. Therefore, anions can easily pass through, while cations are repelled by the positive charge and thus have difficulty passing through.

[0003] As anion exchange membranes, it is known that anion exchange membranes without quaternary ammonium groups as functional groups on their surface are effective against monovalent chloride ions (Cl). - The permeation of ) significantly reduces the divalent sulfate ions (SO4) 2- The permeability of monovalent anions is excellent (see Patent Document 1).

[0004] However, when the aforementioned anion exchange membrane is used for desalination and concentration of electrolyte solutions such as seawater in electrodialysis, the resistance is high, which makes it difficult to reduce the power consumption of the electrodialysis device.

[0005] Furthermore, regarding the structure of the membrane surface, it is known that a multilayer anion exchange membrane has a first layer on the substrate with tertiary amino groups as functional groups and a second layer thereon with quaternary ammonium groups as functional groups, relative to divalent sulfate ions (SO4). 2- The permeability of ) and a significant reduction in the divalent iron ion (Fe) 2+ The selective permeability of anions is excellent, and compared to monovalent chloride ions (Cl), the permeability of anions is relatively high. - The permeation of ) significantly reduces the divalent sulfate ions (SO4) 2- The transmittance of monovalent anions is excellent, and the selective transmittance of monovalent anions is superior (see Patent Document 2).

[0006] Compared to the case where anion exchange membranes consisting of single layers constitute a multilayer membrane, the aforementioned multilayer anion exchange membrane exhibits superior selective permeability for anions and monovalent anions. However, due to the need for two membrane formation processes, the manufacturing cost is increased compared to single-layer anion exchange membranes.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 48-034999

[0010] Patent Document 2: Japanese Patent Application Publication No. 3-115439 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] The present invention is made in view of such matters, and its object is to provide an anion exchange membrane with low resistance and low manufacturing cost during electrodialysis, and excellent selective permeability to monovalent anions, and a method thereof.

[0013] Solution for solving the problem

[0014] The present invention provides an anion exchange membrane, characterized in that it is an anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups, and the intensity ratio of tertiary amino to quaternary ammonium groups when the surface of the anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups is 1.0 or higher when measured by X-ray photoelectron spectroscopy.

[0015] Preferably, the strength ratio of the aforementioned tertiary amino group to the quaternary ammonium group is 1.0 or more and 7.0 or less.

[0016] Preferably, the range in which the strength ratio of the aforementioned tertiary amino group to the quaternary ammonium group is 1.0 or more is a depth of 25 nm or less from the membrane surface inward.

[0017] The aforementioned tertiary amino group is preferably dimethylamino.

[0018] A method for manufacturing anion exchange membrane is provided, characterized in that the anion exchange membrane is anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups, and the intensity ratio of tertiary amino groups to quaternary ammonium groups when the surface of the anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups is measured by X-ray photoelectron spectroscopy is 1.0 or higher. The manufacturing method includes the following steps:

[0019] (I) A process of introducing a polymeric composition for introducing ion exchange groups into the original membrane into a substrate;

[0020] (II) A process of heating the aforementioned substrate to polymerize the aforementioned polymeric composition, thereby producing an ion exchange group introduced into the original membrane;

[0021] (III) The process of introducing tertiary amino groups into the original membrane by introducing the aforementioned ion exchange groups;

[0022] (IV) The process of treating the original membrane with the tertiary amino ion exchange group introduced by the above-mentioned process using an alkaline aqueous solution at 50-70°C.

[0023] (V) The process of introducing quaternary ammonium groups into the original membrane after the ion exchange groups treated with the alkaline aqueous solution.

[0024] Preferably, the pH of the alkaline aqueous solution in the aforementioned (IV) process is 10 to 14 at 25°C.

[0025] Preferably, the treatment time of the alkaline aqueous solution in the aforementioned step (IV) is 4 to 24 hours.

[0026] X-ray photoelectron spectroscopy (XPS) is a known method for analyzing the chemical bonding states of various elements at a depth of several nm from the outermost surface of a sample. Therefore, in this specification, the "surface" of anion exchange membrane includes a depth of several nm from the outermost surface inwards. In this invention, XPS is used to measure the N1s spectrum to analyze the chemical bonding state of nitrogen on the surface of the anion exchange membrane. Tertiary amines and quaternary ammonium groups have peaks at 400.0 eV and 402.5 eV, respectively. Therefore, by using the integrated intensity of each peak area obtained through waveform separation, the intensity ratio of the tertiary amine to the quaternary ammonium group (integrated intensity of tertiary amine / integrated intensity of quaternary ammonium group = intensity ratio) is calculated. When the aforementioned intensity ratio is 1.0 or higher, the effect of introducing tertiary amines into the functional groups is achieved. Furthermore, a strength ratio of 1.0 or higher and 7.0 or lower is preferred, and a strength ratio of 2.0 or higher and 6.5 or lower is more preferred. If the strength ratio is too high, the selectivity is higher, but the resistance is too high.

[0027] Furthermore, it is known that in the aforementioned XPS, depth analysis is performed by etching the surface layer with an ion beam to analyze the interior in the depth direction. For example, after ion etching to a certain depth, the aforementioned N1s spectrum is measured. If the intensity ratio is less than 1.0, it can be determined that no tertiary amines have been introduced into the interior above that depth because the ratio of tertiary amines to quaternary ammonium groups is small. This analysis can be used to determine the thickness of the area where tertiary amines have been introduced.

[0028] The effects of the invention

[0029] When using the anion exchange membrane of the present invention for electrodialysis, the power consumption of the electrodialysis apparatus can be reduced due to its low resistance. Furthermore, although the manufacturing cost of the anion exchange membrane is roughly the same, the desalination and concentration efficiency of the electrolyte solution is high, thus enabling desalination and concentration in a shorter time, or even if the same amount of time is required, a larger volume of desalination and concentration can be performed. In addition, due to the high ion selectivity, a concentrated solution with fewer impurities can be obtained. Attached Figure Description

[0030] Figure 1The flowchart shows the important treatment steps on the surface of the anion exchange membrane of the present invention, which is (a) representing the surface chemical structure of the original membrane with ion exchange groups introduced into it and (b) representing the surface chemical structure of the anion exchange membrane of the present invention.

[0031] Figure 2 XPS spectra at various times for alkaline aqueous solutions.

[0032] Figure 3 The XPS spectra have undergone in-depth analysis.

[0033] Figure 4 The images show XPS spectra before and after the quaternary ammonium group introduction process in Example 1.

[0034] Figure 5 XPS spectra before and after the quaternary ammonium group introduction process in Comparative Example 1. Detailed Implementation

[0035] The preferred embodiments for carrying out the present invention will be described below. It should be noted that the present invention is not limited to the following content.

[0036] Figure 1 This describes the process flow of an important surface treatment step for the anion exchange membrane of the present invention. Here, Figure 1 (a) represents the surface chemical structure of the original membrane with ion exchange groups introduced. Figure 1 (b) represents the surface chemical structure of the anion exchange membrane of the present invention, wherein the chlorine of the chloromethylstyrene on the surface of the aforementioned original membrane is replaced by dimethylamine as a tertiary amino group. Additionally, in Figure 1 (b) is not illustrated, but the chlorine in chloromethylstyrene is replaced with a quaternary ammonium group by the introduction of a tertiary amino group in the direction of depth from the surface inward.

[0037] Figure 1 The ion exchange groups of (a) are introduced into the original membrane and manufactured through the following processes (I) to (II).

[0038] <(I) Process of introducing a polymeric composition for introducing ion exchange groups into a substrate>

[0039] The polymeric composition for introducing ion exchange groups into the original membrane is a polymeric composition containing aromatic polymeric monomers having halogenated alkyl groups.

[0040] The aforementioned aromatic polymerizable monomers having halogenated alkyl groups can be any known compounds without limitation. The alkyl group preferably has 1 to 8 carbon atoms, and examples of halogen atoms that can be substituted include chlorine, bromine, and iodine. Examples of such halogenated alkyl groups include chloromethyl, bromomethyl, iodomethyl, chloroethyl, bromoethyl, iodoethyl, chloropropyl, bromopropyl, iodopropyl, chlorobutyl, bromobutyl, iodobutyl, chloropentyl, bromopentyl, iodopentyl, chlorohexyl, bromohexyl, and iodohexyl. Specific examples of aromatic polymerizable monomers having such haloalkyl groups include chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, chloroethylstyrene, bromoethylstyrene, iodoethylstyrene, chloropropylstyrene, bromopropylstyrene, iodopropylstyrene, chlorobutylstyrene, bromobutylstyrene, iodobutylstyrene, chloropentylstyrene, bromopentylstyrene, iodopentylstyrene, chlorohexylstyrene, bromohexylstyrene, and iodohexylstyrene, among which chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, chloroethylstyrene, bromoethylstyrene, iodoethylstyrene, chloropropylstyrene, bromopropylstyrene, iodopropylstyrene, chlorobutylstyrene, bromobutylstyrene, and iodobutylstyrene are particularly preferred.

[0041] For the original membrane for introducing anion exchange groups obtained by polymerizing the aforementioned polymeric composition, the aromatic polymeric monomers having haloalkyl groups in the membrane are transformed into anion exchange groups, namely tertiary amino or quaternary ammonium groups, as described below. The aforementioned tertiary amino groups are weakly basic groups, and quaternary ammonium groups are strong basic groups, making them excellent as anion exchange groups. However, it is also desirable to have other anion exchange groups. In addition to the aforementioned aromatic polymeric monomers having haloalkyl groups, polymeric compositions can also use polymeric monomers having other anion exchange groups, or polymeric monomers having functional groups capable of introducing other anion exchange groups. As for such anion exchange groups other than tertiary amino or quaternary ammonium groups, there are no particular limitations on functional groups capable of forming negative or positive charges in aqueous solutions; examples include primary to secondary amino groups, pyridyl groups, imidazoyl groups, and quaternary pyridinium groups. The aforementioned aromatic polymerizable monomers having halogenated alkyl groups are preferably blended in a mixture of 30 to 98 parts by mass relative to 100 parts by mass of the polymerizable monomer component in the aforementioned polymerizable composition, and more preferably in a mixture of 50 to 95 parts by mass.

[0042] To increase the density and strength of the resulting anion exchange membrane, a crosslinking polymerizable monomer is preferably used in the polymerizable composition. This crosslinking polymerizable monomer can also be any monomer conventionally known for the manufacture of ion exchange membranes, without particular limitation. Specifically, for example, m-, p-, or o-divinylbenzene, divinylbiphenyl, divinyl sulfone, butadiene, chloroprene, isoprene, trivinylbenzene, divinylnaphthalene, diallylamine, triallylamine, divinylpyridine, or other functional vinylbenzyl compounds having three or more vinylbenzyl groups disclosed in Japanese Patent Application Publication No. 62-205153, etc.

[0043] If too many of these crosslinking polymerizable monomers are blended relative to the aromatic polymerizable monomers containing alkyl halogens, not only will the ion exchange capacity of the anion exchange membrane decrease, but the membrane resistance will also increase due to excessive crosslinking, potentially leading to higher power consumption per unit area. Conversely, if the blending ratio of crosslinking polymerizable monomers is too low, not only will the membrane strength decrease, but the difference in swelling ratio in the aqueous state due to the different degree of crosslinking between the crosslinking monomers and the tertiary amine-containing layer disposed on the membrane surface may cause the tertiary amine-containing layer to be on the inside, resulting in significant warping and making operation difficult. Therefore, relative to 100 parts by mass of the total polymerizable monomer composition including the aromatic polymerizable monomers containing alkyl halogens and the other polymerizable monomers described above for use in combination as needed, the crosslinking polymerizable monomers are preferably blended in a ratio of 3 to 40 parts by mass, appropriately 5 to 30 parts by mass, and more preferably 7 to 15 parts by mass.

[0044] In addition to aromatic polymerizable monomers and crosslinking polymerizable monomers having halogenated alkyl groups, other monomers may be used as needed. Specific examples include styrene, vinyltoluene, vinylxylene, ethylvinylbenzene, α-methylstyrene, vinylnaphthalene, acrylonitrile, acrolein, methyl vinyl ketone, etc.

[0045] Polymerization initiators are typically compounded into polymeric compositions. There are no particular restrictions on the use of conventionally known polymerization initiators; appropriate selection can be made taking into account factors such as the substrate and molding conditions. Specific examples include p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, α,α'-bis(tert-butylperoxide-m-isopropyl)benzene, di-tert-butyl peroxide, tert-butyl hydroperoxide, di-tert-pentyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexyn-3, cumene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethyl-2,5-dihydrohexane peroxide, 2,5-dimethyl-2,5-dihydrohexyn-3, benzoyl peroxide, methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, cyclohexane peroxide, methylcyclohexane peroxide, isobutyl peroxide, and 2,4-dichlorobenzoyl peroxide. Examples of peroxides include o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, p-chlorobenzoyl peroxide, 1,1-di-tert-butylperoxy-trimethylcyclohexane, 1,1-di-tert-butylperoxy-cyclohexane, 2,2-di-(tert-butylperoxy)-butane, 4,4-di-tert-butylperoxypentanoate-n-butyl ester, 2,4,4-trimethylpentanoate-peroxyphenoxyacetate, α-cumyl peroxyneodecanate, tert-butyl peroxyneodecanate, tert-butyl peroxyneodecanate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-isobutyrate, di-tert-butyl peroxy-hexahydroterephthalate, di-tert-butyl peroxyazelate, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peroxyacetate, and tert-butyl peroxybenzoate. They are added individually or in combination of two or more to the monomer paste.

[0046] The amount of the polymerization initiator described above is usually preferably 0.1 to 30 parts by mass, more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the aforementioned polymerizable monomer component.

[0047] In addition, a matrix resin can be blended into the polymeric composition as a viscosity modifier. By blending in this matrix resin, the coatability of the polymeric composition can be improved, and sagging can be prevented when it is applied to a high-porosity substrate.

[0048] Examples of matrix resins that can be used include polyvinyl chloride (PVC), chlorinated PVC, ethylene-vinyl chloride copolymers, vinyl chloride elastomers, chlorinated polyethylene, chlorosulfonated polyethylene, ethylene-propylene copolymers, saturated aliphatic hydrocarbon polymers such as polybutene, styrene-butadiene copolymers, and matrix resins made from styrene monomers such as polyvinyltoluene, vinylxylene, chlorostyrene, chloromethylstyrene, α-methylstyrene, α-halostyrene, and α,β,β'-trihalostyrene, monoolefins such as ethylene and butene, and conjugated dienes such as butadiene and isoprene. Additionally, styrene-butadiene rubber or its hydrogenated rubber, nitrile rubber or its hydrogenated nitrile rubber, pyridine rubber or its hydrogenated rubber, and styrene-based thermoplastic elastomers may also be suitable.

[0049] Here, styrene-based thermoplastic elastomers refer to polystyrene polymers and alternating copolymers of styrene with polybutadiene, polyisoprene, vinyl polyisoprene, ethylene-butene, and ethylene-propylene. Examples include polystyrene-hydrogenated polybutadiene-polystyrene copolymers, polystyrene-(polyethylene / butene rubber)-polystyrene copolymers, polystyrene-hydrogenated polyisoprene rubber-polystyrene copolymers, polystyrene-(polyethylene / propylene rubber)-polystyrene copolymers, polystyrene-polyethylene-(polyethylene / propylene rubber)-polystyrene copolymers, and polystyrene-vinyl polyisoprene-polystyrene copolymers. The molecular weight of the aforementioned matrix resins is not particularly limited, but is typically in the range of 1,000 to 1,000,000, and particularly preferably in the range of 50,000 to 500,000.

[0050] In addition, the matrix resin is mixed into the polymeric composition in an amount that ensures appropriate viscosity, based on the molecular weight. For example, this amount is preferably 1 to 50 parts by mass, more preferably 3 to 15 parts by mass, relative to 100 parts by mass of the aforementioned polymeric monomer component.

[0051] It should be noted that, in addition to the above-mentioned components, the polymerizable composition may also contain plasticizers such as dioctyl phthalate, dibutyl phthalate, tributyl phosphate, or alcohol esters of fatty acids and aromatic acids, as well as organic solvents, as needed.

[0052] In addition, in the above-mentioned polymerizable composition, it is also preferable to add compounds with one or more epoxy groups, such as styrene oxide and diethylene glycol diglycidyl ether, to supplement the halogen gas and hydrogen halide gas generated by the thermal decomposition of the aforementioned aromatic polymerizable monomers having alkyl haloside.

[0053] The polymeric composition comprising the above-mentioned components is polymerized after being introduced into the pores of a substrate to obtain a primary membrane for introducing anion exchange groups. As this substrate, any substrate known as a substrate for ion exchange membranes can be used, typically a support material with a porosity of 20-90%, preferably 40-80%, more preferably 45-55%. Examples include woven fabrics, nonwoven fabrics, porous films, and meshes formed from polyvinyl chloride, polyolefins, etc. The use of porous films is particularly preferred from the viewpoint of avoiding an extreme increase in membrane resistance and achieving monovalent anion selectivity. An average pore diameter of 0.05-0.20 μm is preferred from the viewpoint of balancing the stretching and resistance of the ion exchange membrane. The thickness of the substrate is typically selected from the range of 5-300 μm, and is preferably 70-250 μm from the viewpoint of maintaining membrane resistance and strength.

[0054] There are no particular limitations on the method of introducing the polymeric composition into the substrate. Examples include coating or spraying the polymeric composition onto the substrate, or impregnating the substrate with the polymeric composition. When the polymeric composition is in paste form, coating is preferred. Introducing the composition into the substrate by coating can be performed using known methods such as roller coaters, flow coaters, doctor blade coaters, comma coaters, spraying, and impregnation.

[0055] <(II) The process of heating the aforementioned substrate to polymerize the aforementioned polymeric composition, thereby producing an ion-exchange group-introduced membrane>

[0056] As described above, after introducing the polymerizable composition into the substrate, the substrate is layered together with a release material having release properties in a manner that prevents the substrates from adhering to each other, and then wound onto a roller and heated to polymerize.

[0057] As the aforementioned release material, a release material with heat resistance capable of withstanding polymerization and easy to release after polymerization is used. Examples include films formed from any of the following resins: polyolefins such as random or block copolymers of α-olefins such as polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene; ethylene-vinyl compound copolymers such as ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, and ethylene-vinyl chloride copolymers; polyvinyl compounds such as polymethyl acrylate and polymethyl methacrylate; polyamides such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, and nylon 12; thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polycarbonate; polyphenylene ether; biodegradable resins such as polylactic acid; or mixtures thereof; and films that can be biaxially stretched.

[0058] That is, a suitable film can be selected from the above-mentioned films according to the type of monomer component in the polymeric composition to be used as a release material. In particular, from the viewpoint of heat resistance and mold release properties, polyester films such as polyethylene terephthalate (PET) are most preferred.

[0059] The pressure during polymerization can be either atmospheric pressure or pressurized pressure, typically around 0.1 to 1.0 MPa.

[0060] The polymerization temperature can be lower than the melting point of the substrate, typically in the range of 40–130°C. That is, by heating to the above temperature range for polymerization, a portion of the substrate dissolves in the polymerizable composition. Polymerization under these conditions can improve the bonding strength between the ion exchange resin and the substrate, and further improve membrane strength and current efficiency.

[0061] It should be noted that the polymerization time varies depending on factors such as polymerization temperature, and is usually around 3 to 20 hours.

[0062] <(III) Step of introducing tertiary amino groups into the original membrane via the aforementioned ion exchange groups>

[0063] Figure 1 In example (a), an ion exchange group of chloromethylstyrene is used as the aforementioned aromatic polymerizable monomer having a haloalkyl group to introduce the ion exchange group into the original membrane. A secondary amine compound is used as the ion exchange group to introduce the tertiary amine group into the original membrane (tertiary amine introduction step). Examples of secondary amine compounds include dimethylamine, diethylamine, dipropylamine, dibutylamine, and diethanolamine. From the viewpoint of balancing electrical resistance and monovalent anion selectivity, a short substituent is preferable, and dimethylamine is preferred.

[0064] By contacting an aqueous solution of a secondary amine compound with the tertiary amino group, not only are the halogenated alkyl groups introduced onto the surface of the original membrane replaced by the tertiary amino group, but a cross-linking reaction also occurs on a portion of the aforementioned halogenated alkyl groups. In cases where diffusion into the aqueous solution is too slow or solubility is poor, a portion of the water can be replaced with an organic solvent to adjust the diffusion rate and improve solubility. Hydrophilic solvents such as methanol, ethanol, 1-propanol, 2-propanol, and acetone can be used as the organic solvent replacing the water. Its content relative to water is preferably 30% by mass or less, particularly preferably 5-15% by mass.

[0065] When the secondary amine compound is dissolved in water for the reaction, the preferred concentration is 0.01 mol / L to 2 mol / L, and particularly preferred is 0.03 mol / L to 1 mol / L. If the concentration is too dilute, the substitution reactivity with the haloalkyl group decreases; if the concentration is too concentrated, the diffusion into the interior of the original membrane is enhanced, making it easier for substitution reactions to occur in the deeper layers of the membrane.

[0066] It should be noted that the reaction temperature for introducing the tertiary amine is 20–50°C, and the reaction time is 1–24 hours. If the reaction temperature is below 20°C and / or the reaction time is less than 1 hour, the substitution reaction with the haloalkyl group cannot proceed sufficiently. If the reaction temperature exceeds 50°C and / or the reaction time exceeds 24 hours, diffusion into the interior of the original membrane for introducing the anion exchange group is enhanced, easily leading to substitution reactions deep within the membrane. After the original membrane for introducing the anion exchange group reacts with the secondary amine compound, it can be washed to remove excess secondary amine compound that was not used in the reaction.

[0067] <(IV) The process of treating the original membrane with the tertiary amino group introduced by using an alkaline aqueous solution at 50-70°C>

[0068] like Figure 1 As shown, a process of treatment with an alkaline aqueous solution (alkaline aqueous solution treatment process) is performed after the tertiary amine introduction process. By performing this process, the amount of tertiary amines on the surface of the original membrane with the aforementioned ion exchange groups increases. The detailed reaction is not understood, but it is presumed that some of the cross-linked structures generated in the aforementioned tertiary amine introduction process undergo hydrolysis. However, this hydrolysis does not occur until the tertiary amines are freed from the surface; rather, it is a degree of hydrolysis where one of the bonds in the aforementioned cross-linked structure breaks, causing the cross-linked structure to disappear. As a result, the amount of tertiary amines increases. Therefore, most of the haloalkyl groups on the surface of the original membrane with ion exchange groups are replaced with tertiary amines.

[0069] As an alkaline aqueous solution, known alkaline aqueous solutions such as sodium hydroxide solution, potassium hydroxide solution, barium hydroxide solution, and ammonia solution can be used. From the viewpoint of more efficient treatment, strongly alkaline sodium hydroxide solution or potassium hydroxide solution is preferred.

[0070] The aforementioned alkaline aqueous solution has a pH of 8-14 at 25°C. However, from the viewpoint of more efficient processing, a pH of 10-14 at 25°C is preferred. It should be noted that the processing temperature is preferably 50-70°C, more preferably 55-65°C. Below 50°C, processing requires a longer time, thus reducing productivity. Above 70°C, processing becomes harsh and may result in the release of tertiary amine groups.

[0071] The treatment time for the alkaline aqueous solution in step (IV) described above is 4 to 24 hours, preferably 6 to 12 hours, and more preferably 6 to 10 hours. If the treatment time is less than 4 hours, the treatment may become insufficient. If the treatment time exceeds 24 hours, the treatment becomes harsh and the resistance increases.

[0072] <(V) Step of introducing quaternary ammonium groups into the original membrane after treatment with alkaline aqueous solution>

[0073] like Figure 1 As shown, a process is performed to introduce residual haloalkyl groups into the original membrane after the alkaline aqueous solution treatment step, and a quaternary ammonium group is introduced using a tertiary amine compound (quaternary ammonium group introduction step). Examples of tertiary amine compounds include trimethylamine, triethylamine, N,N-dimethylpropylamine, and N-ethyl-N-methylbutylamine. From the viewpoint of electrical resistance, trimethylamine is preferred.

[0074] By contacting an aqueous solution of a tertiary amine compound to introduce quaternary ammonium groups, the surface of the membrane already incorporating tertiary amines is not affected, and residual haloalkyl groups present in the interior of the membrane are replaced compared to the surface. This method can be performed using conventional methods for introducing quaternary ammonium groups in the manufacture of anion exchange membranes.

[0075] The above methods can be used to manufacture Figure 1 The anion exchange membrane surface of the present invention described in (b). The present invention is a multilayer anion exchange membrane comprising layers having tertiary amino groups and layers having quaternary ammonium groups, but it can be manufactured without forming each membrane, thus reducing manufacturing costs.

[0076] <Anion exchange membrane of the present invention>

[0077] The anion exchange membrane of the present invention can be manufactured by the above-described method. The anion exchange membrane is an anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups. When the surface of the anion exchange membrane having tertiary amino and quaternary ammonium groups as functional groups is measured by X-ray photoelectron spectroscopy, the intensity ratio of tertiary amino to quaternary ammonium groups is 1.0 or higher.

[0078] Furthermore, the resistance of the anion exchange membrane of this invention is 1.5 Ω·cm. 2 Above and 3.0Ω·cm 2 The following is preferred: 1.8Ω·cm 2 Above and 2.5Ω·cm 2 Below, more preferably 2.1Ω·cm 2 Above and 2.4Ω·cm 2 The following is an example of chloride ions (Cl) in seawater concentration experiments. -The concentration of sulfate ions (SO4) is above 3.2 mol / L, preferably above 3.8 mol / L. 2- The concentration of ) is 20×10 -3 N below, preferably 15×10 -3 Below N.

[0079] That is, the anion exchange membrane of the present invention has high selectivity by forming a surface layer containing tertiary amino groups, and also has the property of low resistance by making the surface layer containing tertiary amino groups an ultrathin layer.

[0080] Example

[0081] The present invention will be described in detail below through embodiments, but the present invention is not limited to these embodiments.

[0082] (Example 1)

[0083] 85 parts by weight of chloromethylstyrene, 5.7 parts by weight of divinylbenzene, 4.3 parts by weight of ethylvinylbenzene, 4 parts by weight of di-tert-butylperoxide as a free radical polymerization initiator, and 3 parts by weight of styrene oxide as a supplement for hydrogen chloride gas were added to obtain a paste-like polymerizable composition.

[0084] Next, the above-mentioned polymeric composition is coated onto a biaxially stretched porous polyethylene film (100 μm thick, 46% porosity, and 0.13 μm average pore diameter) as a substrate, and the process of introducing the polymeric composition into the substrate is carried out.

[0085] Next, the substrate with the polymerizable composition introduced is covered on both sides with a release material made of polyester film and then wound onto a roller for polymerization. The polymerization temperature is set as follows: the temperature is increased from 20°C to 50°C in 30 minutes, held at 50°C for 20 minutes, then increased to 130°C in 80 minutes and held at 130°C for 4 hours to produce the original membrane for introducing anion exchange groups.

[0086] Next, the original membrane for introducing anion exchange groups is peeled off. However, at this point, the peeling material is not completely removed from both sides of the original membrane; some peeling material remains on one side. This original membrane for introducing anion exchange groups, with only one side covered by peeling material, is immersed in a 0.05 mol / L dimethylamine aqueous solution for 8 hours at 34°C. The chloromethyl chloride on the surface of the side not covered by peeling material is replaced by dimethylamine, thereby performing the tertiary amine introduction process. Then, the original membrane after tertiary amine introduction is washed with a 1.0 mol / L hydrochloric acid aqueous solution and pure water.

[0087] Next, after removing the polyester film covering one side, the anion exchange groups are introduced into the original membrane, which is then wound back onto a roller and immersed in a 0.01 mol / L sodium hydroxide aqueous solution at 60°C for 10 hours, performing a process of treatment with an alkaline aqueous solution. The original membrane treated with the alkaline aqueous solution is then washed with pure water.

[0088] Next, a quaternization reaction was carried out using an aqueous solution containing 5% by mass of trimethylamine and 25% by mass of acetone at 30°C for 16 hours to replace the residual chloromethyl chloride in the membrane with trimethylamine, thereby implementing the quaternary ammonium group introduction process. The original membrane after quaternary ammonium group introduction was then washed with a 1.0 mol / L aqueous hydrochloric acid solution and pure water.

[0089] (Examples 2-4 and Comparative Example 1)

[0090] The treatment time in the process of using alkaline aqueous solution in Example 1 was changed to 0 minutes (untreated), 10 minutes, 1 hour and 6 hours. Otherwise, the anion exchange membrane was manufactured in the same manner as in Example 1, and they were respectively referred to as Comparative Example 1, Example 2, Example 3 and Example 4.

[0091] Figure 2 The N1s spectra (hereinafter referred to as "XPS spectra") of the anion exchange membranes of Examples 1-4 and Comparative Example 1, measured by X-ray photoelectron spectroscopy (XPS), are shown for each time the membranes were treated with an alkaline aqueous solution. XPS was measured using a ULVAC-PHI, Inc. XPS measuring apparatus, "PHI5000 VersaProbe III". Monochromatic Al-Kα rays were used as the X-ray source, and the photoelectron emission angle was set to 45°.

[0092] The peaks at 400 eV and 402.5 eV in the XPS spectra originate from tertiary amine and quaternary ammonium groups, respectively, and the integrated intensity of the peak area reflects their respective intensities. As the treatment time with the alkaline aqueous solution increases, the intensity near 400 eV of the peak originating from the tertiary amine increases, while the intensity near 402.5 eV of the peak originating from the quaternary ammonium group decreases. Here, the aforementioned intensity ratio in Example 2, where the alkaline aqueous solution treatment time is 10 minutes, is 1.0 or higher. Specifically, the alkaline aqueous solution treatment times for Examples 4 and 1 are the same as those for Examples 6 and 8 described later. As shown in Table 1, the aforementioned intensity ratio for Example 4 (Example 6) is 3.8, and for Example 1 (Example 8) it is 6.5. The aforementioned intensity ratio for Comparative Example 1, where the alkaline aqueous solution treatment is untreated, is 0.4.

[0093] Figure 3XPS spectra of the anion exchange membrane of Example 1 are shown, obtained from analysis of the outermost surface without etching, and at etching depths of 3 nm and 24 nm. XPS was performed using an XPS measurement apparatus, Thermo Fisher Scientific Inc., "ESCALAB220iXL". Monochromatic Al-Kα rays were used as the X-ray source, and the photoelectron emission angle was set to 90°. It should be noted that Ar gas cluster ions were used as the etching ions, and the etching rate was set to 2.7 nm / min (LDPE conversion). The intensity ratio of tertiary amines to quaternary ammonium groups at the outermost surface and at an etching depth of 3 nm was greater than 1.0, while the intensity ratio of tertiary amines to quaternary ammonium groups at an etching depth of 24 nm was less than 1.0. Therefore, it can be seen that for the anion exchange membrane of Example 1, almost no tertiary amines are introduced at depths greater than 24 nm from the outermost surface inwards.

[0094] Figure 4 The XPS spectra of the anion exchange membrane surface in Example 5 described later, before and after the quaternary ammonium group introduction process, are shown. Each value represents the cumulative peak area reflecting intensity. (Before the quaternary ammonium group introduction process...) Figure 4 In (a), the strength ratio of the tertiary amino group to the quaternary ammonium group is 2.7 (3.0 / 1.1 = 2.7). The quaternary ammonium group is introduced after the process... Figure 4 The aforementioned intensity ratio in (b) is 1.8 (2.7 / 1.5 = 1.8). Therefore, it is believed that a portion of quaternary ammonium groups are introduced onto the surface of the anion exchange membrane in Example 1 through the quaternary ammonium group introduction process, but the tertiary amino group is rarely replaced by a quaternary ammonium group.

[0095] Figure 5 The XPS spectra of the anion exchange membrane of Comparative Example 1 before and after the quaternary ammonium group introduction process are shown. Each value represents the cumulative peak area reflecting intensity. (Before the quaternary ammonium group introduction process...) Figure 5 In (a), the strength ratio of the tertiary amino group to the quaternary ammonium group is 1.5 (1.6 / 1.1 = 1.5), while the quaternary ammonium group is introduced after the process. Figure 5 The aforementioned strength ratio in (b) is 0.4 (1.1 / 2.5 = 0.4). Therefore, it can be seen that without the process of treatment using an alkaline aqueous solution, most of the tertiary amino groups are replaced with quaternary ammonium groups.

[0096] (Examples 5-11 and Comparative Example 1)

[0097] The treatment time in the process of using alkaline aqueous solution in Example 1 was changed to 0 minutes (untreated), 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 16 hours and 24 hours. Otherwise, the anion exchange membrane was manufactured in the same way as in Example 1, and they were respectively used as Comparative Example 1, Example 5, Example 6 (same as Example 4), Example 7, Example 8 (same as Example 1), Example 9, Example 10 and Example 11.

[0098] The following resistance test and seawater concentration test were conducted using the anion exchange membranes of Examples 5-11 and Comparative Example 1.

[0099] <Resistance Test>

[0100] An ion-exchange membrane is sandwiched in a two-chamber tank with platinum black electrodes. The membrane is filled with 0.5 mol / L NaCl aqueous solution on both sides. The resistance between the electrodes at 25°C is measured using an AC bridge (frequency 1000 cycles / second). The membrane resistance (Ω·cm) is calculated by comparing this resistance with the resistance without the ion-exchange membrane. 2 It should be noted that the ion exchange membrane used in the above determination was a membrane that had been pre-equilibrated in a 0.5 mol / L NaCl aqueous solution.

[0101] <Seawater Concentration Experiment>

[0102] Small-scale electrodialysis device (electrolyte membrane area 100cm²) 2 The cation exchange membrane CIMS (manufactured by ASTOM Corporation) was used in pairs, assembled with the side of the anion exchange membrane containing tertiary amines facing the desalination chamber. Operating conditions were as follows: seawater at 25°C was flowed into the desalination chamber at a flow rate of 6 cm / s; the concentration chamber was filled with a 3.5 mol / L NaCl aqueous solution; and the current density was 3 A / dm³. 2 Electrodialysis was performed for at least 5 hours (until the concentration change in the concentration chamber disappeared) to determine the chloride ion concentration (Cl) in the concentration chamber. - ) and sulfate ions (SO4) 2- The concentration of ).

[0103] Table 1 shows the results of resistance tests and seawater concentration tests for the treatment times of each alkaline aqueous solution in Examples 5-11 and Comparative Example 1. Additionally, the results of the strength ratio of tertiary amines to quaternary ammonium groups are also shown.

[0104] For resistance, it remained between 2.0 and 2.6 Ω·cm until the treatment time with the alkaline aqueous solution was 4 to 24 hours (Examples 5 to 11). 2 ), and 2.0 (Ω·cm) of Comparative Example 1 2The resistance is roughly the same. Although not shown in Table 1, the resistance increases with further increases in the aforementioned processing time.

[0105] For concentration experiments using seawater, monovalent chloride ions (Cl...) - The concentration of sulfate ions (SO42-) was 3.78-3.85 mol / L when treated with alkaline aqueous solution for 4-24 hours (Examples 5-11), which was approximately the same as 3.70 mol / L in Comparative Example 1, without significant changes due to the aforementioned treatment time. 2- The concentration of sulfate ions was even lower in the alkaline aqueous solution. The treatment time was 4 hours (Example 5). Compared with Comparative Example 1, the concentration was reduced by 43% (16.3 / 38.3 = 0.43). Furthermore, the concentration of sulfate ions decreased as the treatment time increased. The concentration was 14% (5.5 / 38.3 = 0.14) when the treatment time was 16 hours (Example 10), 13% (5.0 / 38.3 = 0.13) when the treatment time was 24 hours (Example 11), and remained approximately constant when the treatment time was 24 hours.

[0106] Therefore, it can be seen that the anion exchange membrane of the present invention, when treated with alkaline aqueous solution for 4 to 24 hours, has a higher efficiency relative to monovalent chloride ions (Cl). - The permeation of ) significantly reduces the divalent sulfate ions (SO4) 2- The transmittance of monovalent anions is excellent, and the selective transmittance of monovalent anions is also excellent.

[0107] [Table 1]

[0108] Results of resistance tests and seawater concentration tests for various alkaline aqueous solution treatment times

[0109]

Claims

1. An anion exchange membrane, characterized in that, It is an anion exchange membrane with tertiary amino and quaternary ammonium groups as functional groups. When the surface of the anion exchange membrane with tertiary amino and quaternary ammonium groups as functional groups is measured by X-ray photoelectron spectroscopy, the intensity ratio of tertiary amino groups to quaternary ammonium groups at a depth of less than 3 nm from the membrane surface is greater than 1.0, and the intensity ratio of tertiary amino groups to quaternary ammonium groups at a depth of more than 24 nm from the membrane surface is less than 1.

0.

2. The anion exchange membrane according to claim 1, wherein, The tertiary amino group is dimethylamino.

3. A method for manufacturing an anion exchange membrane, characterized in that, The anion exchange membrane is an anion exchange membrane with tertiary amino and quaternary ammonium groups as functional groups. When the surface of the anion exchange membrane with tertiary amino and quaternary ammonium groups is measured by X-ray photoelectron spectroscopy, the intensity ratio of tertiary amino groups to quaternary ammonium groups at a depth of less than 3 nm from the membrane surface is greater than 1.0, and the intensity ratio of tertiary amino groups to quaternary ammonium groups at a depth of more than 24 nm from the membrane surface is less than 1.

0. The manufacturing method includes the following steps: (I) A process of introducing a polymeric composition for introducing ion exchange groups into the original membrane into a substrate; (II) A process of heating the substrate to polymerize the polymeric composition, thereby producing an ion-exchange group-introduced membrane; (III) The step of introducing the tertiary amino group into the original membrane; (IV) The step of treating the original membrane with the tertiary amino ion exchange group introduced by using an alkaline aqueous solution at 50~70°C; (V) The process of introducing quaternary ammonium groups into the original membrane after treatment with alkaline aqueous solution.

4. The method for manufacturing anion exchange membrane according to claim 3, wherein, The pH of the alkaline aqueous solution in step (IV) at 25°C is 10-14.

5. The method for manufacturing anion exchange membrane according to claim 3 or 4, wherein, The alkaline aqueous solution treatment time in step (IV) is 4 to 24 hours.

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