JP2522356B2 - Anion exchanger having a novel crosslinked structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ion exchanger that adsorbs or permeates and separates a specific component from a mixed fluid.

More specifically, a low resistance anion exchange thin film useful for electrodialysis such as seawater concentration and a separator for redox flow batteries, a hollow fiber type anion exchange membrane useful for dialysis, and high permeability for polymer anions. The present invention relates to a method for producing an anion exchanger having excellent workability such as a porous anion exchange membrane.

[Prior Art] Although many documents and patents have been reported as anion exchangers, the most practical and useful one is the amination of chloromethylated styrene (or vinylpyridine) -divinylbenzene copolymer ( Or there is a quaternary pyridated anion exchanger. In addition to chemical resistance, heat resistance, and ion exchange properties, these can control ion exchange characteristics and selective permeability by changing the content of divinylbenzene, which is a cross-linking agent. Has been synthesized and developed.

However, new needs such as ultra-low resistance anions such as seawater concentration for manufacturing cheap salt as industrial salt, separator for redox flow battery and other batteries, and phosphoric acid recovery from phosphoric acid etching waste liquid in aluminum industry. There is a drawback that the conventional styrene-divinylbenzene copolymer membrane type cannot meet the demand for the exchange membrane. That is, in order to reduce the resistance, it is necessary to increase the content of chloromethylated styrene (or vinyl pyridine), decrease the amount of divinylbenzene in the cross-linking agent, increase the ion exchange capacity, and increase the water content. The required membrane cannot be obtained because the selective permeability is lowered in addition to the reduction in the mechanical strength. Further, as another means for reducing the resistance, it is necessary to reduce the film thickness, but the styrene-divinylbenzene copolymer has mechanical strength, especially brittleness.
An ion exchange membrane with a thickness of 100 μm or less cannot be obtained.

Furthermore, the styrene-divinylbenzene copolymer has poor mechanical processability as well as processability, and thus has a drawback that a modified ion exchange membrane such as a hollow fiber type or a porous anion exchange membrane cannot be obtained.

On the other hand, engineering plastics having excellent mechanical strength and processability are used in ultrafiltration, separation membranes such as reverse osmosis membranes and gas separation membranes. In particular, the polysulfone membrane, which has excellent chemical resistance, has ion exchange groups introduced into the membrane to improve permeability in ultrafiltration and reverse osmosis, and to impart ion selective permeability, making it suitable for ion exchange membranes. Is being considered.

For example, the repeating unit is An anion exchange membrane synthesized from a chloromethylated copolymer of polysulfone consisting of: J, Membrane Science, 22 (1
985) 325-332.

However, these polysulfone-based ion exchange membranes are non-crosslinked, and when the ion exchange capacity is increased and the resistance is lowered, the ion selective permeability is sharply reduced, and the ion selectivity is increased. , Resistance rises sharply. As an optimal anion exchange membrane, it is necessary to synthesize ion exchange capacity within a narrow range of 1.25 to 1.35. Furthermore, the above-mentioned polysulfone-based anion exchange membrane is cast by casting from a polymer solution such as dimethylformide or dimethylsulfoxide, and the obtained anion exchange membrane is formed by these dimethylformide or dimethylsulfoxide. Since it dissolves in a polar hydrophilic solvent or swells remarkably, it has a drawback that it cannot be used in a solution containing these organic solvents, and it can be replaced by comparing the membrane properties with conventional styrene-divinylbenzene anion exchange membranes. Not a thing.

[Problems to be Solved by the Present Invention] The present invention is intended to solve the above-mentioned drawbacks of the prior art, and has excellent processability, large ion selective permeability, and chemical resistance. It is an object of the present invention to provide an anion exchanger having a novel and excellent cross-linking structure.

An object of the present invention is to provide an anion exchanger that can not be reached by conventional techniques and can be used in an energy-saving electrodialysis method, a battery separator, and a compact and easy-to-maintain hollow fiber dialysis module. To do.

[Means for Solving Problems] The above object of the present invention is to provide at least a repeating unit. It comprises a cross-linked product of a chloromethylated aromatic polysulfone-based polymer containing a polyamine and preferably has an ion exchange capacity of 0.5 to 4.5 meq / g dry resin anion exchanger.

Here, the polyamine represents an aliphatic or aromatic amine having at least two 1-3 primary amino groups in at least one molecule.

The anion exchanger of the present invention comprises a cross-linked product of the chloromethylated product of the above-mentioned specific polysulfone polymer with a polyamine, which is an anion exchanger having a significantly superior specificity to the conventional anion exchanger. Can be provided.

That is, as a conventional polysulfone-based anion exchanger, as described in J. Membrane. Sci. 22 (1985) pages 325 to 332, It consists of a cationic polymer of repeating units of, and when the ion exchange capacity exceeds 1.7 meq / g, the water absorption rate increases,
Ion selectivity is reduced, and the ion exchange capacity is 1.1 m.
Below eq / g, the water absorption rate is small and the resistance increases significantly.
Further, since these anion exchangers are soluble in hydrophilic polar solvents such as dimethylformide and dimethylsulfoxide, they have the advantage that various molded products can be obtained from these polymer solutions, but on the other hand, they can be used as molded anions. Ion exchanger
It has the drawback of being dissolved or remarkably swollen in organic solvents and solutions containing them.

As a result of earnest research on a polysulfone-based anion exchange membrane having significantly excellent ion selectivity and solvent resistance, the present inventor has found that a polyamine having at least two or more primary to tertiary amines is a solution of a chloromethylated polysulfone polymer. The ion-exchange group introduction and cross-linking introduction reaction occur simultaneously by contacting with the molded product processed from, resulting in a decrease in the water content per ion-exchange group, resulting in an increase in the concentration of fixed ions in the membrane, resulting in ion selection. The inventors have completed the present invention by finding that an anion exchanger having improved permeability and excellent chemical resistance and mechanical properties can be obtained.

The present invention will be described in more detail below. As the anion exchanger of the present invention, a polymer having an aromatic ring into which a chloromethyl group is introduced can be used without any trouble, but in a thin film of several 10 μm or less. Aromatic engineering plastics that have practical strength and excellent mechanical strength are also preferable, and because the polymer does not deteriorate during the ion-exchange group introduction reaction, and the chemical resistance when used as an ion-exchanger, it is aromatic. A polysulfone polymer is preferably used.

As such a polysulfone-based polymer, Is exemplified.

Furthermore, as the polymer used for the polysulfone-based anion exchanger, by using a block copolymer having a segment in which an ion exchange group is easily introduced in the molecule and a segment in which an ion exchange group is difficult to be introduced, It is particularly preferably used because an anion exchanger having excellent ion selective permeability and excellent mechanical properties and molding processability can be obtained while controlling the capacity of the exchanger.

The reason why the polysulfone-based block copolymer effectively acts on the ion-selective permeability and mechanical properties has not always been elucidated, but it is considered to be probably due to the following reasons.

That is, the permeation rate of ions (membrane resistance) is higher as the water absorption rate in the membrane is higher, and the selective permeability of ions (transport number, current efficiency) is fixed ion concentration in the membrane (per water content in the membrane). The higher the amount of ion-exchange groups, the larger the property.
Therefore, in order to obtain an ion exchanger having excellent ion selective permeability, it is necessary to increase the ion exchange capacity and prevent an increase in water absorption so that the fixed ion concentration does not decrease. In conventional styrene ion exchange resins, a method of crosslinking with divinylbenzene is used to prevent an excessive increase in water absorption. However, an increase in the number of ion-exchange groups and an increase in the amount of a cross-linking agent corresponding thereto cause embrittlement of the resin. Therefore, the ion-selective permeability and the mechanical strength are naturally struck against a certain level of wall.

In addition, in the present invention, when a polysulfone homopolymer is used and, after chlormethylation, it is aminated with a polyamine, compared with a conventional monoamine-treated ion exchanger such as trimethylamine, a parallel cross-linking structure with amination is obtained. As a result, the water absorption rate per ion-exchange group decreases, the fixed ion concentration increases, and the effect of improving the ion selective permeability is recognized, but when the chloromethyl group content increases, the crosslinking density remarkably increases. However, the mechanical properties of the polysulfone skeleton, particularly the toughness, may be impaired and the polysulfone skeleton may become brittle.

On the other hand, in the present invention, when polysulfone block copolymers having different chloromethylation reactivity are used,
The ion exchange group and the crosslinked structure are distributed at high density in the segment where the chloromethyl group is easily introduced. Therefore, even if the content of chloromethyl group is large, the toughness of the polymer in the segment where the ion exchange group or the crosslinked structure is difficult to be introduced is not lost, so that the ion selective permeability is higher than that of the homopolymer system and the mechanical strength is high. It is described that an ion exchanger having excellent dynamic strength can be obtained. However,
This description is given for the sake of understanding the present invention and is not intended to limit the present invention in any way.

Examples of the polysulfone block copolymers having different chloromethylation reactivity preferable in the present invention include: Such as polyether sulfone / polyarylene sulfone copolymer, aromatic polysulfone-aromatic polyether sulfone copolymer, aromatic polysulfone-aromatic thioether sulfone copolymer, and aromatic polysulfone-
Examples thereof include a polyphenylene sulfide copolymer, an aromatic polysulfone-polyphenylene sulfide ketone copolymer, an aromatic polysulfone-polyphenylene oxide copolymer, an aromatic polysulfone-acrylate copolymer, and an aromatic polysulfone-polycarbonate copolymer.

Among them, the general formula (a) and the general formula (b) are excellent block copolymers having excellent chemical resistance, particularly hydrolysis resistance and different chloromethylation reactivity. (Ar is Y is a single bond, -O-, X is, -O -, - S -, - SO 2.

Particularly preferred is a polysulfone-based block copolymer consisting of

These block copolymers have the following general formula (c): A block copolymer having m / n = 100/1 to 1/10 and Z = 1 to 100 is used. In the general formula (1), when the ratio of the segment number m containing -Ar- in which a chloromethyl group is easily introduced and the segment number n containing -X- in which a chloromethyl group is difficult to be introduced is 100/1 or more, -X- is contained. The pseudo-crosslinking effect due to the cohesive force of the segment is reduced, leading to a reduction in the ion selective permeability due to a fixed ion concentration reduction, and at 1/10 or less, the ion exchange capacity is not large, which causes an increase in the membrane resistance, and preferably, Used by m / n = 10/1 to 2/10.

Further, the alternating copolymer of m or n = 1 has a short segment length, so that the action of each segment is not sufficiently exerted, and a high molecular weight copolymer cannot be obtained and mechanical strength is insufficient. A block copolymer having m = 2 to 200, n = 2 to 200, and an intrinsic viscosity of 0.3 or more is preferably used because defects are likely to occur. Among them, aromatic polysulfone / aromatic thioether sulfone can be obtained as a high molecular weight copolymer, and the number of segments m, n and segment ratio m / n
Can be easily controlled and can be exemplified as a preferable block copolymer from the viewpoints of molding processability, mechanical properties and chemical resistance, and is disclosed by the present applicant in Japanese Patent Laid-Open Nos. 61-72020, 61-76523 and 61-76523. It can be obtained by the method described in 61-168629.

As a method for obtaining the anion exchanger in the present invention, (1) a method of molding a polysulfone-based polymer and then chlormethylating and aminating it (2) a method of chlormethylating the polysulfone-based polymer, and then molding and aminating Method (3) A method in which a polysulfone-based polymer is chloromethylated and aminated and then molded into a desired shape can be used. However, in the present invention, a crosslinking reaction is generated during amination. Preformed (1) and (2) are preferably used.

As the chlormethylation method of the polysulfone-based polymer, a method of contacting a solid polymer and a chloromethylating agent can be used, but in the case of selectively introducing a chloromethyl group into a segment having different reactivity, preferably,
In many cases, it is preferable to dissolve the block copolymer in a solvent that is stable against the chloromethylating agent and to make it react in a liquid state. As such a solvent, a halogenated hydrocarbon such as trichloroethane or tetrachloroethane is used.

Further, as the chloromethylating agent, chloromethyl methyl methyl ether, 1,4-bis (chloromethoxy) butane, 1
-Nucleophilic chloromethylating agents such as chloromethoxy-4-chlorobutane, formalin-hydrogen chloride system and paraformaldehyde-hydrogen chloride system can be used without limitation.

Thus, a chloromethylated polysulfone polymer having a desired chloromethyl group content can be obtained by adding a chloromethylating agent and a catalyst such as tin chloride to the polysulfone polymer solution and selecting the reaction temperature and the reaction time for convenience. .

The chloromethyl group content of the chloromethylated polysulfone-based copolymer varies depending on the type of the subsequent aminating agent and the application used as an anion exchanger,
Usually, the ion exchange capacity is selected to be about 0.5 to 4.5 meq / g resin, preferably 1.0 to 3.5 meq / g resin.

In the present invention, the chloromethylated polymer thus obtained is reacted with a polyamine compound having at least two 1-3 primary amino groups in at least one molecule.

As the amination method, (1) a chloromethylated copolymer is made into a solution, then cast, and formed into a flat membrane, a hollow fiber shape, or a porous support membrane, and then immersed in an amination solution. , As an anion exchanger.

(2) After solubilizing the chloromethylated copolymer, adding an aminating agent to form an anion exchange resin solution, and then casting and molding on a flat membrane, hollow fiber shape, or porous support membrane. Use as an anion exchanger.

(3) After amination treatment of the chloromethylated copolymer,
The anion exchange resin is made into a solution and molded into a desired shape.

Is used, but when using a polyamine compound,
(2) and (3) are cases in which the viscosity of the solution increases over time and gels, or a solution cannot be obtained, or even if a solution is obtained, only a very thin solution with a polymer concentration of several% or less is obtained. Therefore, it is usually aminated by the method (1).

As the solution of the chloromethylated polysulfone polymer, a solution of 0.1 to 30% by weight, preferably 1 to 20% by weight is used, and the solvent is trichloroethane, tetrachloroethane, dimethylacetamide, dimethylformamide, dimethylsulfuric acid. In addition to a single solvent of foxoxide, triethyl phosphate and N-methylpyrrolidone, a water-acetone mixed solution, a methanol-tetrahydrofuran mixed solution and the like are used.

As another preferred production method, a partially aminated polymer containing a chloromethyl group obtained by reacting a small amount of a monoamine with a chloromethylated polysulfone polymer may be molded and then reacted with a polyamine.

The chloromethylated polymer thus obtained or its partially aminated polymer solution is cast into a convenient shape, and then the solvent is removed. When the removal of the solvent is carried out by a heat treatment, a molded article having a dense structure is usually used, while a solvent for extracting the solvent in the state where the solvent remains, particularly preferably, a poor polymer is used. By immersing the solution in a used solution, a molded article having a porous structure can be produced.

Examples of the polyamine compound for aminating the chloromethylated polymer used in the present invention or the polymer containing a partially aminated chloromethyl group include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine and phenylene. Polyamine compounds composed of primary and secondary amines such as diamines, NNN'N 'tetramethyldiaminomethane, NNN'N' tetramethyl1.2 diaminoethane, NNN '
N'tetramethyl 1.3 diaminopropane, NNN'N 'tetramethyl 1.6 diaminohexane, NNN'N' tetramethylbenzidine, PP 'tetramethyldiaminodiphenylmethane, polyvinyl pyridine, polychloromethylstyrene primary and secondary aminated compounds are used. To be done. General formula A diamine having two tertiary amines consisting of is easily available, has a high amination reaction, and can easily control the physical properties of the film by changing the number of methylene groups. Can be used as a particularly preferred polyamine compound.

The molded product of the aminated polymer thus obtained is immersed in a convenient solution, for example, an aqueous solution of sodium chloride to hydrate the anion-exchange group, and then separated into a membrane for electrodialysis, a separator for batteries, a membrane for diffusion dialysis and the like. It is possible to obtain an anion exchange membrane having high ion selective permeability and excellent solvent resistance as compared with an anion exchanger aminated with a monoamine.

Next, the present invention will be described with reference to examples, but the present invention is not limited to the examples.

[Example] Example 1 In the same manner as in the synthesis method described in JP-A-61-168629,
The reaction of 4,4'-diphenol and dihalodiphenyl sulfone was carried out to form an aromatic polysulfone unit m =
Ten brikers were synthesized, and then the bricarcers, dihalodiphenyl sulfone and sodium sulfide were reacted to obtain an aromatic polysulfone-polythioether sulfone copolymer A represented by the following formula.

m / n = 1/1, intrinsic viscosity 0.65 Next, the copolymer A was dissolved in 1,1,2,2-tetrachloroethane, and then chloromethyl methyl ether and anhydrous tin chloride were added. After reacting at 4 ° C. for 4 hours, precipitation with methyl alcohol and washing were performed to obtain a chloromethylated copolymer B.

The copolymer B thus obtained was dissolved in tetrachloroethane to obtain a 10% by weight solution. Then, the polymer solution was cast on a glass plate and then dried by heating at 50 ° C. for 2 hours to obtain a cast film having a film thickness of 25 μm.

Then, the cast film of the copolymer B is 1.2 mol / 1
Was immersed in a mixed solution of NNN'N 'tetramethyl1.3-diaminopropane in methanol-dimethylsulfoxide at 40 ° C for 16 hours to obtain an anion exchange membrane.

The anion exchange membrane thus obtained had an ion exchange capacity of 2.6 meq / g resin, and was immersed in a 0.5N NaCl aqueous solution, and then the Cl ^- ion transport number was determined by the AC resistance membrane potential method. The resistance (0.5N NaCl 1000Hz) was 0.5Ω · cm ² Cl ^- Transportation (0.5M NaCl / 1.0M NaCl membrane potential) was 0.97. Further, the obtained anion exchange membrane was immersed in dimethyl sulfoxide or dimethylformamide, but it was not dissolved in any solvent.

Comparative Example 1 An anion exchange membrane was obtained in the same manner as in Example 1 except that trimethylamine was used instead of NNN′N ′ tetramethyl1.3-diaminopropane. The ion exchange capacity was 2.2 meq / g resin, AC resistance is 0.2Ω · cm ² , Na ⁺
The transfer rate was 0.82. Further, when the obtained anion exchange membrane was dipped in dimethyl sulfoxide or dimethylformamide, it was dissolved in any solvent.

Example 2 The chloromethylation reaction in Example 1 was carried out at 60 ° C. for 4 hours to obtain a chloromethylated copolymer C. Copolymer C was dissolved in tetrachloroethane in the same manner as in Example 1, cast on a glass plate, dried, and 25 μm thick of copolymer C.
A film was obtained. The copolymer C membrane was aminated with a mixed solution of NNN'N 'tetramethyl 1.2 diaminoethane in methanol-dimethyl sulfoxide to obtain an anion exchange membrane.

The film is insoluble in dimethylformamide and has an AC resistance of 1.
The 2 Ω · cm ² and Cl ⁻ transport number was 0.97.

Comparative Example 2 An anion exchange membrane was obtained in the same manner as in Example 2 except that trimethylamine was used instead of NNN'N 'tetramethyl1.2-diaminoethane, and the ion exchange capacity was 1.
5 meq / g resin, AC resistance 0.9Ω · cm ² , Na ⁺ transport number 0.95
Met. When the membrane was immersed in dimethylformamide, it dissolved.

Example 3 The 25 μm thick copolymer C film obtained in Example 2 was treated with NNN ′.
It was dipped in a mixed amination solution with N'tetramethyldiaminomethane or trimethylamine to determine the resistance and transport number. The results are shown in Table 1.

Example 4 The 25 μm thick copolymer C film obtained in Example 2 was treated with NNN ′.
Immerse in N'tetramethyl 1.6-diaminohexane or its mixed amination solution with trimethylamine,
Resistance and transport numbers were calculated. The results are shown in Table-1.

Example 5 The chloromethylated copolymer B obtained in Example 1 was dissolved in dimethylformamide. Next, to the solution, toemethylamine was added in an amount of 1.5 milliequivalent to 1 g of the chloromethylated copolymer B. The partially aminated copolymer solution thus obtained was cast on a glass plate and dried. The membrane was then aminated with NNN'N 'tetramethyldiaminomethane solution. The obtained anion-exchange membrane is insoluble in dimethylforimamide and has AC resistance of 0.5 Ω ・ cm ² and Cl ^- transport number of 0.97.
Met.

Comparative Example 3 In Example 5, the partially aminated copolymer film was
The AC resistance was 1.5 Ω · cm ² , and the Cl ⁻ transport number was 0.96. Also NNN ′
Anion film aminated with trimethylamine solution instead of N'tetramethyldiaminomethane has an AC resistance of 0.4Ω.
・ Cm ² , Cl ^- Transportation rate was 0.94. Both the partially aminated film and the trimethylamine-treated film were dissolved when immersed in dimethylformide.

Example 6 Instead of the copolymer A of Example 2, After chloromethylating a polymer consisting of
In the same manner as above, a 25 μm thick chloromethylated polymer film was
It was aminated with N'N 'tetramethyl1.3-diaminopropane solution.

The obtained anion exchange membrane has an AC resistance of 0.2 Ω ・ cm ² , Cl
^- transport number was 0.90.

Comparative Example 4 Example 6, the NNN'N 'tetramethyl 1,3-diaminopropane, except that the trimethylamine, was prepared anion exchanger in the same manner, swollen jelly, film resistance, Cl ^- transportation The rate could not be measured.

EFFECTS OF THE INVENTION The anion exchanger of the present invention is characterized by reacting a chloromethyl group-introduced polymer of a polysulfone polymer having excellent chemical resistance and mechanical properties with a polyamine compound. Therefore, along with the introduction of the ion-exchange group by the amination reaction, a cross-linked structure is formed, excellent solvent resistance, An anion exchanger having excellent ion selective permeability can be obtained.

In particular, in the present invention, by using a polysulfone-based block copolymer composed of a segment where a chloromethyl group is easily introduced and a segment where a chloromethyl group is difficult to be introduced, by changing the block copolymerization ratio,
It has a feature that the ion exchange capacity can be controlled. In addition, the segment into which the chloromethyl group is not introduced retains the mechanical properties inherent to the polysulfone resin, so there is no deterioration of mechanical properties due to the introduction of ion-exchange groups, especially no embrittlement, and sufficient strength even in thin films. An anion exchange membrane can be obtained.

Furthermore, since these anion exchangers can be cast from a solution to form a film, an anion exchange film having a small film thickness and low resistance can be obtained, and the anion exchanger is coated on a porous substrate or another polymer film and dried. As a result, a multilayer ion exchange membrane having a new function can be obtained.

Claims (5)

(57) [Claims] 1. At least a repeating unit Anion exchanger characterized by comprising a cross-linked product of a chloromethylated aromatic polysulfone-based polymer containing a polyamine 2. Anion exchanger according to claim 1, wherein the ion exchange capacity is 0.5 to 4.5 meq / g dry resin. 3. An aromatic polysulfone-based polymer is represented by the general formula (a): (However, Ar in the formula is Y is a single bond, -O -, - S -, - SO 2 -, R _{1 to} R ₇ are the same or different hydrocarbons having 1 to 8 carbon atoms, a and b are 0 to 4, c is 0 to 3, d + e is 0 to 7, and f + g is 0.
~ 5. R _{8 to} R ₉ are hydrogen, a hydrocarbon having 1 to 6 carbon atoms) and the general formula (b) (However, in the formula, X is —O—, —S—, —SO ₂ —. R _{10 to} R ₁₁
Are hydrocarbons having 1 to 8 carbon atoms which are the same or different from each other.
h, i is a copolymer of m / n = 100/1 to 1/10 with 0 to 4) (1)
Or the anion exchanger of (2) 4. A polyamine having the general formula (c) (However, in the formula, R _{12 to} R ₁₅ are hydrogen, or hydrocarbons having 1 to 5 carbon atoms which are the same or different from each other. 1 is 1 to 10), (1), (2) or (3) ) Anion exchanger 5. The anion exchanger according to claim 1, which is not dissolved in dimethylformamide or dimethylsulfoxide.