JPH0722710B2 - Anion exchanger - 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 quaternary pyridation)
There is an anion exchanger. These are chemical resistance, heat resistance,
In addition to the ion exchange property, the ion exchange property and the selective permeability can be controlled by changing the content of divinylbenzene which is a cross-linking agent. Therefore, various kinds of products have been synthesized and developed for all purposes.

However, new needs, such as seawater concentration for producing inexpensive salt equivalent to industrial salt, separator for redox flow batteries and other batteries, and ultra-low resistance ion exchange such as recovery of phosphoric acid from phosphoric acid etching waste liquid in the aluminum industry. There is a drawback that the conventional styrene-divinylbenzene copolymer type cannot meet the demand for the membrane.
That is, in order to reduce the resistance, the content of chloromethylated styrene (or vinyl pyridine) is increased, the amount of divinylbenzene in the cross-linking agent is decreased, and the ion exchange capacity is increased.
Although it is necessary to increase the water content, the required membrane cannot be obtained because the mechanical strength is lowered and the selective permeability is lowered. Further, as another means for reducing the resistance, it is necessary to reduce the film thickness, but the styrene-divinylbenzene copolymer has a mechanical strength, especially 100% because it has brittleness.
An ion exchange membrane with a thickness of 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 for separation membranes such as ultrafiltration, reverse osmosis membranes and gas separation membranes. In particular, polysulfonic acid, 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. Membranl. Sciense, 22 (1
985) 325 to 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-selective permeability is increased. Then, the resistance rises sharply. As an optimal anion exchange membrane, it is necessary to synthesize an ion exchange capacity within a narrow range of 1.25 to 1.35,
In addition, comparing the conventional styrene-divinylbenzene-based anion exchange membrane with the negative substance is insufficient and cannot be replaced.

[Problems to be Solved by the Present Invention] The present invention is intended to solve the above-mentioned drawbacks of the prior art and is a novel anion having excellent processability and large ion selective permeability. The purpose is to provide a exchanger.

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

[Means for Solving the Problems] The above object of the present invention is to provide a segment substantially composed of an aromatic nucleus and a linking group, in which a segment into which an anion exchange group is easily introduced and an anion exchange group are A segment which is a block copolymer composed of at least two types of repetitive segments that are difficult to be introduced, and in which an anion exchange group is easily introduced is represented by the general formula (1) —O—Ar—O— (1) (however, Medium Ar Or X is a single bond, -O-, -S- or Indicates. R _{1 to} R ₅ are the same or different hydrocarbon groups having 1 to 8 carbon atoms, a is 0 to 3 and b + c is 0 to
7, d + e is 0-5, R ₆ and R ₇ are hydrogen or 1-carbon
6 shows a hydrocarbon group of 6. And an anion exchange group is introduced into the aromatic ring of the block copolymer.

The anion exchanger of the present invention basically has the above-mentioned specific —O.
A skeleton is a heat-resistant block copolymer composed of a linking group and an aromatic nucleus of a unit having a -Ar-O- unit and a unit not having a -O-Ar-O- unit. It is based on a novel idea and knowledge that does not exist, and as a result, it is possible to provide an anion exchanger having characteristics significantly superior to conventional anion exchangers.

That is, as a conventional polysulfone-based anion exchanger, J.
As described in Memb. Sci. 22 (1985) 325-332. The ion exchange capacity exceeds 1.7 meq / g, which increases the water absorption, leading to a decrease in ion selectivity, or an ion exchange capacity of 1.1 m.
Below eq / g, the water absorption is small and the resistance increases.

The present inventor has conducted earnest research on an anion exchanger made of so-called engineering plastic having excellent mechanical strength and heat resistance. As a result, a segment in which an ion exchange group is easily introduced into a molecule and an ion exchange group is introduced. By using a block copolymer composed of an aromatic nucleus having a segment that is difficult to be blocked and a linking group, the capacity of the ion-exchange group can be controlled, the ion selective permeability is excellent, and the mechanical strength. It was found that an anion exchanger having excellent moldability can be obtained, and the present invention was completed.

The reason why the block copolymer composed of the aromatic nucleus and the linking group effectively acts on the ion selective permeability and the mechanical properties has not always been elucidated, but it is probably because of the following reasons.

That is, the permeation rate of ions (inversely proportional to the membrane resistance) increases as the water absorption in the membrane increases, and the selective permeability of ions (transport number and current efficiency) depends on the fixed ion concentration in the membrane (water content in the membrane). The higher the amount of ion-exchange groups per unit), 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.

Further, in the anion exchanger using the polysulfone homopolymer, when the ion exchange capacity is small, water is not introduced into the ion exchange group due to the cohesive force of the polysulfone skeleton, the membrane resistance is high, and the ion exchange capacity is constant. As a result, the effect of suppressing the water absorption of the ion-exchange group due to the cohesive force of the polysulfone skeleton is lost, resulting in a rapid increase in water absorption and a decrease in fixed ion concentration, leading to a decrease in ion selective permeability and mechanical properties. .

On the other hand, in the aromatic block copolymer of the present invention, the ion-exchange groups are distributed at a high density in the segments where they are easily introduced. Therefore, even if the ion exchange capacity is low, water is sufficiently supplied to the ion exchange group, resulting in lower membrane resistance compared to the homopolymer system, and even if the ion exchange capacity is increased, the ion exchange group is difficult to be introduced. The rigid aromatic nuclei connecting segment acts as a pseudo bridge, suppressing a sharp increase in water absorption, reducing the fixed ion concentration, increasing ion selective permeability, and lowering mechanical strength. Explained to be difficult. However, such description is provided for the purpose of understanding the present invention and does not limit the present invention in any way.

Explaining the present invention in more detail below, the block copolymer composed of an aromatic nucleus and a linking group used in the anion exchanger of the present invention is a block composed of repeating units having different ion-exchange group introduction reactivity. Any copolymer can be used without any limitation, but the aromatic nucleus is preferably -O.
A segment having -O-Ar-O- linked with-,
A block copolymer with a segment not containing it is used.

As such a segment having —O—Ar—O—, And as a segment not containing -O-Ar-O-, And a block copolymer thereof is exemplified.

Among them, as a block copolymer with excellent chemical resistance, especially hydrolysis resistance, (However, in the formula, Ar is the same as the general formula (1). Y is -SO _2- ,
Indicates -S- or -O-. R _{8 to} R ₁₁ are the same or different hydrocarbon groups having 1 to 8 carbon atoms, and f to i are 0.
˜4, m, n are integers of 2 to 200, and m / n is 100/1 to 1/10. ) The aromatic polysulfone-based block copolymer represented by In the general formula (2), when the ratio of the segment number m containing -Ar- in which a chloromethyl group is easily introduced and the segment number n containing -Y- in which a chloromethyl group is difficult to be introduced is 100/1 or more, -Y- is contained. The pseudo-crosslinking effect due to the cohesive force of the segment is reduced, which leads to a decrease in the ion selective permeability due to a decrease in the fixed ion concentration, and the ion exchange capacity is not large at 1/10 or less, which causes an increase in the membrane resistance, and preferably m / n = 10/1 to 2/10 is used.

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. Is likely to occur, therefore,
A block copolymer having m = 2 to 200, n = 2 to 200 and an intrinsic viscosity of 0.3 or more is used. Among them, the aromatic polysulfone / aromatic thioether sulfone in which Y in the general formula (2) is —S— gives a high molecular weight copolymer, and the number of segments m, n and the segment ratio m / n are controlled. It can be exemplified as a preferable block copolymer because it is easy to process and has molding processability, mechanical properties and chemical resistance. These block copolymers are exemplified in JP-A-61-72020, JP-A-61-76523 and JP-A-61-168629 by the present applicant.

As a method for obtaining the anion exchanger in the present invention, (1) a method of molding the block copolymer and then chlormethylating and aminating it. (2) a method of molding the block copolymer after chlormethylating and (3) Chloromethylation and amination of the block copolymer, followed by molding into a desired shape can be used.
(2) and (3), which can easily control the chloromethylation reaction, are preferably used.

As the chloromethylation method of the block copolymer, a method of contacting a solid polymer with a chloromethylating agent can be used, but in order to selectively introduce a chloromethyl group into segments having different reactivity, preferably, chloromethyl is used. It is preferable to dissolve the block copolymer in a solvent that is stable to the agent and dissolve the block copolymer, and then react in a liquid state. Halogenated hydrocarbons such as trichloroethane and tetrachloroethane are used as such a solvent.

As chloromethylating agents, limit nucleophilic chloromethylating agents such as chloromethyl methyl ether, 1.4 bis (chloromethoxy) butane, 1-chloromethoxy-4chlorobutane, formalin-hydrogen chloride system, paraformaldehyde-hydrogen chloride system. Can be used without.

Thus, a chloromethylating polysulfone block copolymer having a desired chloromethyl group content can be obtained by adding a chloromethylating agent and a catalyst such as tin chloride to the polysulfone block copolymer solution and selecting the reaction temperature and the reaction time conveniently. can get. Type of aminating agent that follows,
For example, ammonia or primary to tertiary amines, monoamines,
Depending on the diamine, polyamine, etc., the types of membranes obtained differ, so the preferred chloromethyl group content differs, but usually the ion exchange group capacity is 0.5 to 3.5 meq / g,
It is preferably selected to be 0.8 to 3.5 meq / g, particularly 1.0 to 2.5 meq / g.

The chloromethylated block copolymer thus obtained is
Preferably, the anion exchanger can be prepared by the following method.

(1) After solubilizing the chloromethylated copolymer, casting it, casting it on a flat membrane, hollow fiber, or porous support membrane, and then immersing it in an amination solution to obtain 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.

Such a solution is 0.1 to 30% by weight, preferably 1 to 2
A 0 wt% solution is used, and the solvent is trichloroethane, tetrachloroethane, dimethylacetamide,
Dimethylformide, dimethylsulfoxide, triethylphosphate, N-methylpyrrolidone as a single solvent, water-acetone mixed solution, methanol-tetrahydrofuran mixed solution and the like are used.

The chloromethylated copolymer thus obtained or its aminated copolymer 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. A molded article having a porous structure can be produced by immersing it in a solution containing a solvent.

As the aminating agent for the chloromethylated copolymer in the present invention, any conventionally known one can be used without any limitation, and ammonia and its alkyl-substituted products, alkyl-substituted products, aromatic-substituted products, benzyl group-substituted products, etc. 1 to 3 primary amines, monoamines such as pyridine ring compounds, and polyamines thereof are exemplified.

The molded product of the aminated copolymer thus obtained is immersed in a convenient solution, for example, a saline solution to hydrate the anion-exchange groups, and then separated into a diaphragm for electrodialysis, a separator for batteries, a diaphragm for diffusion dialysis and the like. It can be used as a membrane.

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

Example 1 An aromatic polythioether sulfone copolymer was produced in the same manner as in the synthesis method described in JP-A-61-168629. That is, 4,4'-diphenol and dichlorodiphenyl sulfone were put in a solvent N-methylpyrrolidone, and the mixture was mixed at 190 ° C. for 3 times.
A condensation reaction was carried out for a time to synthesize a precursor m = 10 composed of an aromatic polysulfone unit. Then, the precursor, dichlorodiphenyl 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, after casting the polymer solution on a glass plate, heat-dry at 50 ° C. for 2 hours,
A cast film having a film thickness of 25 μm was obtained.

Then, the cast film of the copolymer B was immersed in a 1.2N methanol-water mixed solution of trimethylamine at 40 ° C. for 16 hours to obtain an anion exchange film.

The anion exchange membrane thus obtained has an ion exchange capacity of 2.
2 meq / g resin, after immersion in 0.5 N NaCl aqueous solution, AC resistance were determined the transport number of Na ions by membrane potential method, AC resistance ^{(0.5N NaCl1000Hz) 0.35Ω · cm 2} Cl - transport number (0.5
M NaCl / 1M NaCl) 0.95.

Example 2 An anion exchange membrane was obtained in exactly the same manner as in Example 1 except that the chloromethyl reaction in Example 1 was carried out at 60 ° C for 4 hours.

The ion exchange capacity was 1.5 meq / g resin AC resistance 0.8 Ω · cm ² Cl ⁻ transport number 0.96.

Example 3 The chloromethylated copolymer B obtained in Example 1 was dissolved in dimethylformaldehyde to obtain a 10% by weight solution. Then, a predetermined amount of 1.2N trimethylamine dimethylformamide solution was added to the solution.

The aminated polymer solution thus obtained was cast on a glass plate, dried at 50 ° C. for 2 hours and then immersed in a 0.5N NaCl aqueous solution. Table 1 shows the amount of trimethylamine added and the properties of the obtained film.

Comparative Example 1 A membrane was prepared in the same manner as in Example 1 except that the homopolymers of polysulfone polymer C and polymer D were used instead of the copolymer of Example 1.

Polymer C Intrinsic viscosity 0.6 Polymer D When the chloromethylated polymer membrane was dipped in an amination solution, the intrinsic viscosity 0.4 polymer C swelled in the form of jelly and an anion exchange membrane could not be obtained.

On the other hand, the polymer D after the amination treatment had a membrane resistance of 1000 kΩ or higher.

Example 4 The procedure of Example 1 was repeated, except that bisphenol A was used instead of 4,4′-diphenol. That is, a precursor of m = 10 was synthesized by reacting bisphenol A with dichlorodiphenyl sulfone, and then the precursor, dichlorodiphenyl sulfone and sodium sulfide were reacted to obtain an aromatic polysulfone-polythioether sulfone copolymer represented by the following formula. It was

m / n = 1 Intrinsic viscosity 0.51 Next, the copolymer E was treated in the same manner as in Example 1 to obtain a chloromethylated copolymer. The chloromethylated copolymer F thus obtained was dissolved in N, N ', dimethylformamide in the same manner as in Example 3 and trimethylamine was added to prepare an aminated polymer solution, which was then placed on a glass plate. Anion exchange membrane was obtained by casting and heating.

The anion exchange membrane thus obtained has an ion exchange capacity of 2.1 meq / g resin, an AC resistance of 0.4 Ω · cm ² , Cl ^{− and a} transport number of 0.95.
Met. The anion exchange membrane was insoluble in methanol.

Comparative Example 2 An anion exchange membrane was produced in the same manner as in Example 4 except that the polymer G represented by the following formula was used instead of the copolymer E of Example 4.

Intrinsic viscosity 0.53 The anion exchange membrane was significantly swollen and damaged when immersed in a 0.5N NaCl aqueous solution, and the resistance and transport number could not be measured.

Comparative Example 3 The polymer G used in Comparative Example 2 was used, and the reaction conditions of chloromethylation were changed to obtain polymers having different chloromethyl group contents.

An anion exchange membrane was prepared from the thus obtained chloromethylated polymer in the same manner as in Example 1. The anion exchange membrane having an ion exchange capacity of 1.6 meq / g resin or more swelled in a dissolved or jelly-like form, No anion exchange membrane was obtained.

Comparative Example 4 An anion exchange membrane was obtained in the same manner as in Example 4, except that the chloromethylated polymer prepared in Comparative Example 3 and having a chloromethyl group content of 1.8 meq / g resin was obtained.

The anion exchange membrane thus obtained had an ion exchange capacity of 1.63 meq / g resin, a resistance of 0.3 Ω · cm ² and a Cl ⁻ transport number of 0.92. The anion exchange membrane was dissolved when immersed in methanol.

Example 5 A copolymer H was obtained in the same manner as in Example 4 except that hydroquinone was used instead of bisphenol A.

m / n = 1 Intrinsic viscosity 0.64 The copolymer H thus obtained was treated in the same manner as in Example 4 to obtain an anion exchange membrane.

The anion exchange membrane thus obtained had an ion exchange capacity of 1.50 meq / g resin, a resistance of 1.5 Ω · cm ² and a Cl ⁻ transport number of 0.97.

Example 6 In the synthesis of the copolymer A of Example 1, potassium carbonate was used instead of sodium sulfide to obtain a polysulfone-polyethersulfone copolymer I.

m / n = 1 intrinsic viscosity 0.50 An anion exchange membrane was obtained in the same manner as in Example 4 from the copolymer I thus obtained.

The anion exchange membrane thus obtained has an ion exchange capacity of 2.
2 meq / g resin, resistance was 0.35Ω · cm ² , Cl ^- transport number was 0.96.

EFFECTS OF THE INVENTION The anion exchanger of the present invention is characterized by comprising an engineering plastic block copolymer having excellent mechanical properties and heat resistance. Therefore, by using the segment into which the ion exchange group is easily introduced and the segment into which the ion exchange group is difficult to be introduced, and changing the block copolymerization ratio, the ion exchange capacity can be controlled. In addition, since the hydrophobic and rigid segment where no ion-exchange group is introduced acts as a pseudo bridge, the fixed ion concentration does not decrease even if the ion-exchange capacity is large, so an anion with low resistance and high selective permeability is obtained. An exchange membrane is obtained.

In particular, since the polysulfone-based block copolymer has excellent chemical resistance, it is possible to obtain an anion exchange membrane that can be used for various purposes.

Furthermore, since these copolymers can be cast from a solution, a thin anion exchange membrane can be obtained, and by coating and drying on a porous substrate or other polymer membrane,
The feature is that a multilayer ion exchange membrane having a new function can be obtained.

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Claims (6)

[Claims] 1. A segment consisting essentially of an aromatic nucleus and a linking group, which is composed of at least two types of repeating segments, a segment into which an anion exchange group is easily introduced and a segment into which an anion exchange group is difficult to be introduced. Which is a block copolymer having the following general formula (1) —O—Ar—O— (1) (where Ar is Or X is a single bond, -O-, -S- or Indicates. R _{1 to} R ₅ are the same or different hydrocarbon groups having 1 to 8 carbon atoms, a is 0 to 3 and b + c is 0 to
7, d + e is 0-5, R ₆ and R ₇ are hydrogen or 1-carbon
6 shows a hydrocarbon group of 6. ), And an anion exchange group is introduced into the aromatic ring of the block copolymer. 2. A block copolymer having the general formula (2) (However, in the formula, Ar is the same as the general formula (1). Y is -SO _2- ,
Indicates -S- or -O-. Further, R _{8 to} R ₁₁ are the same or different hydrocarbon groups having 1 to 8 carbon atoms, f to i are 0 to 4, m and n are integers of 2 to 200, and m / n is 100/1 to Indicates 1/10. The anion exchanger according to claim 1, which comprises an aromatic polysulfone-based block copolymer represented by the formula (1) and has an anion exchange group introduced into the aromatic ring. 3. The anion exchange group is a primary to tertiary amine or a quaternary ammonium salt, and the anion exchanger is
Ion exchange capacity 0.5-4.5 meq / g dry resin, thickness 0.01
The anion exchanger according to claim (1) or (2), which is an anion exchange membrane having a thickness of 100 μm. 4. The anion exchanger according to claim 1, wherein the introduction of the ion exchange group is carried out after the introduction of the chloromethyl group, followed by an amination treatment. 5. An anion exchanger is cast from a solution of a chloromethylated copolymer and heat-treated to form a membrane having a thickness of 100 μm or less, and then ammonia or at least one or more first membranes is formed.
The anion exchange membrane according to any one of claims (1) to (4), which is an anion exchange membrane aminated with a primary to tertiary amine. 6. An anion exchanger comprising a solution of chloromethylated copolymer, ammonia or at least one or more first
The anion exchange membrane having a thickness of 100 μm or less cast and heat-treated from an aminated copolymer which is a reaction product with a primary to tertiary amine. One anion exchanger.