JPH02294338A - Novel multi-layered ion exchange membrane - Google Patents

Abstract

PURPOSE:To obtain the subject ion exchange membrane having large permeability and selectivity and hardly generating increase of electric resistance in highly concentrated electrolyte solution comprising multi-layered membrane of ionic conductive semipermeable membrane not containing ion exchange group and ion exchange layer thinner than the semipermeable membrane. CONSTITUTION:The aimed ion exchange membrane is composed of multi-layered membrane of an ionic conductive semipermeable membrane substantially not containing ion exchange group and an ion exchange layer thinner than the semipermeable membrane (preferably anion exchanger composed of reaction product of haloalkylated polysulfone resin with ammonia or primary-tertiary amine and having 0.5-3.5m equiv./g dry resin and 0.01-50mum membrane thickness).

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an ion exchange membrane that adsorbs or permeates and separates specific components from a mixed fluid. More details relate to ion exchange membranes with low resistance useful for electrodialysis such as seawater concentration, diffusion dialysis of acids or alkalis, or battery separators, and ion exchange membranes with high permeability to organic ions useful in the bioindustry. [Prior Art] Numerous documents and patents have been reported regarding ion exchange membranes, but the most practical and useful ones include sulfonated cation exchange membranes made of styrene-divinylbenzene copolymers and chloromethylated polymers. There is an aminated anion exchange membrane. In addition to their chemical resistance and heat resistance, ion exchange properties and selective permselectivity can be controlled by changing the content of divinylbenzene, a crosslinking agent, so a wide variety of products have been synthesized and developed for various uses. Ta. However, new applications, such as seawater concentration to produce inexpensive common salt equivalent to industrial salt, and ultra-low resistance ion exchange membranes such as redoc flow batteries and separators for methanol batteries, are being developed.
However, there are drawbacks that conventional styrene-divinylbenzene systems cannot deal with. In other words, in order to lower the resistance, it is necessary to reduce the film thickness, but styrene-divinylbenzene resin has mechanical strength, especially brittleness, so
Ion exchange membranes with a thickness of 0 μm or less cannot be obtained. Furthermore, in addition to mechanical properties, styrene-divinylbenzene resins have poor processability and have the disadvantage that processed membranes such as hollow fiber type or porous ion exchange membranes cannot be obtained. On the other hand, in separation membranes such as ultrafiltration membranes, reverse osmosis membranes, and gas separation membranes, Embra-based plastics, which have excellent mechanical strength and processability, are used. Polysulfone membranes, which have particularly excellent chemical resistance, have ion exchange groups introduced into the membrane to improve permeability in ultrafiltration and reverse osmosis, as well as impart selective ion permeability, making them suitable for ion exchange membranes. It is being considered. For example, a sulfonated polysulfone whose repeating unit is 1'LL and
3709841, published in Japanese Unexamined Patent Application Publication No. 50-1999.
73. JP-A-51-146379, JP-A-Sho BL-4
505, such sulfonated polysulfone,
Ultrafiltration membranes and reverse osmosis membranes laminated on anisotropic ultrafiltration membranes are described. In addition, a cation exchange membrane or anion exchange membrane synthesized from the sulfone polymer or chloromethylated polymer of the above polysulfone is disclosed in J. Membrane Science
ce, 22 (1985) 325-332. However, these polysulfone-based ion exchange membranes are non-crosslinked, and when attempts are made to increase the ion exchange capacity and lower the resistance, the water absorption rate increases rapidly, leading to a decrease in fixed ion concentration, and ion selective permeation. The resistance rapidly decreases, and when an attempt is made to increase the ion selectivity, the resistance rapidly increases. As a way to overcome these drawbacks, an asymmetric multilayer membrane has been proposed, which consists of a dense layer with ion-selective permeability of several lθμm and a thicker porous layer. Comparing membrane performance is insufficient and cannot be used as a substitute. [Problems to be Solved by the Invention] The present invention attempts to solve the above-mentioned drawbacks of the prior art, and provides a novel multilayer ion exchange membrane with high ion selective permeability and low resistance. The purpose is to provide the following. The purpose of the present invention is to provide an ion exchange membrane that can be used in energy-saving electrodialysis methods, battery separators, and hollow fiber dialysis modules that are compact and easy to maintain, which cannot be achieved using conventional techniques.
[Means for Solving the Problems] The above object of the present invention is characterized in that it consists of a composite membrane consisting of an ion conductive semipermeable membrane containing substantially no ion exchange groups and a thinner ion exchange layer. This is achieved by using an ion exchange membrane. The ion exchange membrane of the present invention is basically a combination of a base membrane consisting of an ion conductive semipermeable membrane that does not have ion exchange properties and a specific ion exchange layer, which is unprecedented. It is based on new ideas and knowledge. That is, conventional multilayer ion exchange membranes include a thin ion exchanger layer with high ion-selective permeability and low ion exchange capacity, and a thick ion exchanger layer with low resistance and high ion exchange capacity. Used as a diaphragm for salt electrolysis. It is also known that for the purpose of imparting selective permeability to specific ions, an ion exchanger layer with a dense structure or a thin layer of an ion exchanger layer with an opposite charge is multilayered with a thick ion exchanger layer. ing. In order to further improve the strength of the membrane,
A multilayer membrane consisting of an ion exchanger layer and a porous support membrane has been proposed. In any case, conventional multilayer ion exchange membranes
The idea and structure is that the ion exchanger layer is in direct contact with the external liquid and selectivity is developed at the interface. On the other hand, in the multilayer membrane of the present invention, the selective ion permeability exhibited depends on the ion exchanger layer layered on at least one side of the semipermeable membrane that does not contain an ion exchange group,
Ion conductive semipermeable membranes are basically based on the idea of supporting and reinforcing the ion exchanger layer. In this way, the ion exchange layer, which has high electrical resistance, has the minimum thickness necessary to exhibit ion selective permeability, and the ion exchange layer has low electrical resistance, and has ion conductivity, which has high mechanical strength. The multilayer membrane of the present invention is composed of a semipermeable membrane layer. To explain the present invention in more detail below, the ion exchanger layer of the present invention can be used with a wide range of types of ion exchange groups, ion exchange capacities, and base resins. Sulfonated cation exchangers such as Jun-based cation exchangers, aminated anion exchangers of haloalkylated resins, ethylene-acrylic acid-based cation exchangers, vinylpyridine-based anion exchangers, perfluorinated cation exchangers. Examples include fluorine-containing anion exchange resins. However, an ion exchanger derived from an aromatic Embla resin is preferred from the viewpoint of adhesion to the semipermeable membrane, thin film-forming properties of the ion exchanger layer, and its mechanical strength. In particular, an ion exchanger layer made of aromatic polysulfone resin is used because of its chemical resistance. The polysulfone polymer used in the ion exchanger of the present invention has the general formula R1 to R, are hydrocarbon groups having 1 to 8 carbon atoms that are the same or different from each other, a% d is θ~4, and e is O~3. ．． (f+
g) is O~7. (h+i) is 0 to 5, R,. +RIl is hydrogen, a hydrocarbon group having 1 to 6 carbon atoms, and 100/. 0
〜l/100 is shown. An example is an aromatic polysulfone polymer represented by: Such polysulfone polymers include, in addition to polysulfone polymers such as 1"L, the above polysulfone units and units different from them,
For example, block copolymers with are used. According to the present invention, a multilayer ion exchange membrane with unprecedented high performance can be obtained by using polysulfone, but preferably, the ion exchange capacity can be easily controlled and the ion exchanger to be obtained can be selected. Polysulfone block copolymers are used because of their permeability, mechanical properties, and chemical resistance. Although it is not necessarily clear why the block copolymer is excellent as an ion exchange membrane in the present invention, it is explained as follows. In other words, the rate of ion permeation (membrane resistance) increases as the water absorption rate within the membrane increases, and the selective permeability (transportation number, current efficiency) of ions increases with the concentration of fixed ions within the membrane (per water content in the membrane). The higher the amount of ion exchange groups), the thicker it becomes. Therefore, in order to obtain an ion exchanger with excellent ion permselectivity, 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-based ion exchange resins, crosslinking with divinylbenzene is used to prevent an excessive increase in water absorption. However, an increase in the number of ion exchange groups and a commensurate increase in the amount of crosslinking agent lead to embrittlement of the resin, so the balance between selective ion permeability and mechanical strength naturally hits a certain level. In addition, in anion exchangers using polysulfone homopolymer, when the ion exchange capacity is small, water is not introduced into the ion exchange groups due to the cohesive force of the polysulfone skeleton, resulting in high membrane resistance; Above a certain level, the cohesive force of the polysulfone skeleton loses its effect of suppressing the water absorption of ion exchange groups, resulting in a rapid increase in water absorption and a decrease in fixed ion concentration, resulting in a decrease in ion selective perms and mechanical properties. invite On the other hand, in polysulfone block copolymers, ion-exchange groups are distributed with high density in segments where they are easily introduced. Therefore, even if the ion exchange capacity is low, water is sufficiently introduced into the ion exchange groups, resulting in a lower membrane resistance compared to a homobolymer series, and even if the ion exchange capacity is high, the ion exchange groups are difficult to introduce. The cohesive force between the segments acts as a pseudo-crosslink, suppressing a rapid increase in water absorption, resulting in a high ion selective permeability without a decrease in fixed ion concentration, and a decrease in mechanical strength.
It is explained that Thus, the preferred polysulfone polymer used in the ion exchanger layer of the present invention has the general formula: Pa, -o-, -
s-, -so■- R1 to R'' are mutually the same or different hydrocarbon groups having 1 to 8 carbon atoms, a to d are O to 4,
e is O~3, (f+g) is 0~7, (h+i) is 0~5
, R1. +Rll is hydrogen, a hydrocarbon group having 1 to 6 carbon atoms,
Indicates m/n = 100/1 to 1/10. ) is used in aromatic polysulfone block copolymers represented by
In particular, the aromatic polysulfone/borithioethersulfone copolymer in which Z in the general formula is represented by -S-,
It is preferably used because a high molecular weight copolymer can be obtained, the copolymer composition can be easily controlled, and it is moldable and processable, mechanical strength, and chemical resistance. Thus, as an anion exchanger layer synthesized from polysulfone resin, after haloalkylation of polysulfone resin,
An ion exchange layer consisting of ammonia or a reactant with a primary to tertiary amine and having an ion exchange capacity of 0.5 to 3.5 milliequivalents/g and a resin film thickness of 0.01 to 50 μm is used. Examples of the haloalkyl group include -(CL). Cl. −
(CH.). %Br, -(CL). ! , − (C
I. ). Examples include CI.
Cl group, -CHJr group, and chloromethyl group are preferred from the viewpoint of mass production.
It can be obtained by contacting 4-bis(chloromethoxy)butane, 1-chloromethoxy-4chlorobutane and a nucleophilic chloromethylating agent such as formalin-hydrogen chloride or paraformaldehyde hydrogen chloride in the presence of a catalyst. The above polysulfone polymer has one CH. As a method for introducing Cl groups, a method of contacting a granular polymer or a film-like molded product with the above-mentioned chloromethylating agent can also be used, but it is possible to obtain a polymer with good reaction uniformity and thin film molding processability. Therefore, it is preferable to dissolve the polysulfone-based polymer in a solvent that is stable to the chloromethylating agent and to react in a liquid state. As such a solvent, halogenated hydrocarbons such as trichloroethane, tetrachloroethane, etc. are used. In this way, 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 a polysulfone polymer solution and appropriately selecting the reaction temperature and reaction time. The thus obtained chloromethylated polysulfone polymer contains trichloroethane, tetrachlorethane, dimethylacetamide, dimethylformide, dimethylsulfoxide,
In addition to triethyl phosphate and N-methylpyrrolidone as a single solvent, they are dissolved in a mixture of water and acetone, a mixture of methanol and tetrahydrofuran, etc., and then cast onto an ion-conductive semipermeable membrane to be multilayered, dried, and molded. Add an amine, preferably a tertiary amine, to the solution of the aminated or chloromethylated polysulfone polymer due to the stability of the aminated polysulfone solution, and cast the solution onto a semipermeable membrane to double layer the aminated polysulfone polymer. By doing so, S*θ. The anion exchanger layer has a thickness of Ql to 50 μm, preferably 0.1 to 20 μm. As a method for obtaining the cation exchange membrane of the present invention, a method can also be used in which a polysulfone polymer is cast into a multi-layered ion conductive semipermeable membrane and then sulfonated. It is preferable to cast a polymer solution onto the semipermeable membrane because the semipermeable membrane will not be deteriorated by the sulfonating agent. As a method for sulfonating a polysulfone polymer, a method in which a solid polysulfone polymer is brought into contact with a sulfonating agent can also be used, but it is preferable to dissolve the polysulfone polymer in a solvent that is stable to the sulfonating agent and dissolves polysulfone. It is preferable to carry out the reaction, and halogenated hydrocarbons such as trichloroethane, tetrachloroethane, etc. are used as such a solvent. As the sulfonating agent, concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, sulfuric anhydride, and sulfuric anhydride-triethyl phosphate complex can be used without limitation. Thus, by adding a sulfonating agent to a polysulfone solution and appropriately selecting the reaction temperature and reaction time, a sulfonated polysulfone polymer having a desired ion exchange capacity can be obtained. However, the ion exchange capacity is 0.
．． Below 5 milliequivalents/g resin, the membrane resistance is extremely high;
Furthermore, at 3.5 milliequivalents/gtl fat or higher, the water absorption of the polymer is extremely high. Therefore, in order to reduce the water absorption, it is necessary to cure the polymer, and as a result, the ion exchange capacity of the cured membrane is reduced. The ion exchange capacity is preferably 0.5 to 3.5 millimeters per 1 t/g of resin, particularly 0.8 to 3. React to give 0 meq/g resin. The sulfonated polysulfone thus obtained can be used as it is by molding it into a flat membrane shape, hollow fiber shape, etc., but if necessary, it is possible to add a curing agent to improve the water absorption rate and mechanical strength of the molded product. This is preferable for obtaining an ion exchange membrane with excellent ion permselectivity and chemical resistance. Such a curing method can be used without any problem as long as it reacts with the functional group contained in polysulfone and has a stable crosslinked structure. Coalescence and the use of polysulfone polymers containing a Yaguchi methyl group, preferably a chloromethyl group, are preferred because a polymerized or crosslinked cured product can be obtained without impairing the mechanical properties of the polysulfone resin. Such curing agents include, for polysulfone polymers containing one SH group, epoxy compounds having two or more epoxy groups, aminoblast resins, metal acetylacetonates, compounds having two or more isocyanate groups, group Examples include Group I-B metal halides and polyfunctional maleimide compounds containing two or more maleimide groups. Thus, the obtained sulfonated polysulfone polymer is
If necessary, add 0.1-100 parts of curing agent to 100 parts by weight.
Parts by weight, preferably 0.5 to 50 parts by weight, are added and mixed. As for the mixing method, dissolving the polymer and the curing agent in a common solvent is preferably used from the viewpoint of obtaining a homogeneous mixture and the subsequent molding process. As such a solution, a solution containing 0.1 to 30% by weight, preferably 1 to 20% by weight of the sulfonated polysulfone polymer is used, and as a solvent, dimethylacetamide, dimethylformide, dimethylsulfone is used. Polar solvents such as phoxide, triethyl phosphate, and N-methylpyrrolidone are used. After the polymer solution is cast on the multi-layered semipermeable membrane having an appropriate shape, the solvent is removed to obtain a molded article such as a composite membrane in the form of a flat membrane or a hollow fiber. Also, when the solvent is removed by heat treatment,
On the other hand, when a molded article with a dense structure is immersed in a solution that extracts the solvent while the solvent remains, particularly preferably a solution using a poor solvent for the polymer, the ions of the porous structure can be removed. Composite membranes with exchanger layers can be produced. The composite membrane thus obtained is heated at 50 to 350°C, preferably 100 to 250°C, to react the polymer and the curing agent and convert it into a cured molded product insoluble in the solvent. After that, the ion exchange group is hydrated with a convenient solution, such as a saline solution, and then used as a separation membrane such as a diaphragm for electrodialysis, a separator for batteries, and a diaphragm for diffusion dialysis. The ion-conducting semipermeable membranes that do not contain ion-exchange groups and which constitute the present invention include hydrated cellulose membranes represented by cellophane, cubrohan membranes made of cellulose regenerated by the cuprammonium method, cellulose acetate membranes, and polyvinyl alcohol membranes represented by vinylon. , poly(hydroxymethylene) membrane, which is a hydrolyzate of poly(vinyl carbonate), and other hydrous polymer membranes can be used. Among them, a cellophane film or a vinylon film having a film thickness of 20 to 100 μm, which has a large area and is available at low cost, is preferable in that the multilayer film of the present invention can be provided to the market in large quantities. Thus, the multilayer membrane of the present invention is obtained by laminating 0.01 to 50μ, preferably 0.1 to 20μ, of the aforementioned polysulfone ion exchange resin on at least one side of a semipermeable membrane such as cellophane or vinylon film. be able to. The thus obtained multilayer membrane of the present invention consisting of an ion conductive semipermeable membrane containing no ion exchange group and a thin layer of an ion exchanger layer has excellent properties not found in conventional multilayer membranes consisting of an ion exchanger layer. have. For example, when used in a highly concentrated electrolyte solution, the water content of the ion exchanger layer decreases and the resistance increases significantly, but the multilayer membrane of the present invention has a very thin ion exchanger layer, so the resistance There is little increase in Such applications include alkaline batteries, especially silver oxide batteries, etc.
It is useful as a sebarator in a 40wt% alkaline solution. Another excellent feature of the present invention is that fouling due to organic ions in the ion exchanger layer is less likely to occur in the separation of solutions containing organic ions, making it an excellent property for bio-related separation applications. Be expected. In particular, the multilayer membrane of the present invention can be used as a diffusion dialysis membrane with excellent permselectivity in a separation method in which acid or alkali is recovered by diffusion dialysis from a solution containing acid or alkali. Next, the present invention will be explained by examples, but the present invention is not limited to these examples.

【Example】

Example 1 4,4°-diphenol and dihalodiphenylsulfone were reacted in the same manner as the synthesis method described in JP-A-61-168629 to synthesize a Bricaser with m = 10 consisting of aromatic polysulfone units. Then, the bricasser, dihalodiphenylsulfone, and sodium sulfide were reacted to obtain an aromatic polysulfone-polythioethersulfone copolymer A represented by the following formula. m/n=l/l+intrinsic viscosity 0.65 Next, the copolymer A has 1.1.2.2. After dissolving in tetrachloroethane, chloromethyl methyl ether and anhydrous tin chloride were added, and the mixture was reacted at 110° C. for 4 hours, followed by precipitation and washing with methyl alcohol to obtain chloromethylated copolymer B. After dissolving the thus obtained copolymer B in dimethylformamide, 2.0 milliequivalents of trimethylamine was added to the chloromethylated copolymer B Ig to obtain an aminated copolymer solution. The thus obtained aminated copolymer solution was cast onto a 50 μl thick cellophane film, and then heated and dried at 50° C. for 2 hours to prepare five types of composite membranes with different ion exchanger thicknesses. AC resistance of 0.5N NaCl and 0.5M NaCl of the thus obtained composite membrane.1. Table 1 shows the transport numbers of Cl- ions determined from the membrane potential of OM NaCl. The ion exchange capacity of the anion exchange membrane obtained by casting the aminated copolymer solution on a glass plate was 1.9 milliequivalent to 7 g of resin. Table 1 Table 2 Example 2 In one chamber on the ion exchanger layer side of the dialysis cell, which was divided into two chambers by the anion exchange membrane obtained in Example 1, 1 mol/l of sulfuric acid and 1 mol/l of sulfuric acid were added. filled with a solution containing zinc sulfate,
The chamber on the cellophane membrane side was filled with pure water, and the permeation rate of sulfuric acid and zinc sulfate permeated to the pure water side was determined. The results are shown in Table 2. Example 3 Aromatic polysulfone-polythioethersulfone copolymer A obtained in Example 1 was prepared by l. 1.2 After dissolving in 1-lichloroethane, the copolymer A was brought into contact with a trichloroethane solution containing a complex of 271 molar ratio of sulfuric anhydride/triethyl phosphate in an amount of 2 equivalents per unit of copolymer A. , 25°C for 43 hours to obtain a sulfonated copolymer C having an ion exchange capacity of 1.85 meq/g resin. The thus obtained copolymer C was dissolved in N-methylpyrrolidone to obtain a sulfonated copolymer solution. The sulfonated copolymer solution thus obtained was cast onto a 50 μm thick cellophane film, and then heated and dried at 100°C for 2 hours to prepare composite membranes with different cation exchanger layer thicknesses. 0.5N Na of the thus obtained composite membrane
25°C AC resistance in C1 and 40wt% koH,
The transport numbers of Na'' ions determined from the membrane potentials of 0.5M NaCl and 1.0M NaCl are shown in Table 3. Table 3 [Effects of the Invention] The ion exchange membrane of the present invention does not contain ion exchange groups. It is characterized by a multilayer structure consisting of an ion-conductive semipermeable membrane and an ion exchanger layer with ion selective permeability.Therefore, a hole-free ion exchanger layer is formed on the semipermeable membrane. Therefore, the ion exchanger layer can be made as thin as possible, resulting in a membrane with high permeability and high selectivity.In particular, ion exchangers synthesized from polysulfone block copolymers are Since it consists of a segment into which a group has been introduced and a hydrophobic segment in which no ion exchange group has been introduced, the cohesive force of the hydrophobic segment acts as a pseudo crosslink, so even if the ion exchange capacity is large, the fixed ion concentration does not decrease. Therefore, it exhibits high selective permeability and good film forming properties, making it possible to obtain excellent multilayer ion exchange membranes.Also, these multilayer ion exchange membranes have the characteristics that the ion exchanger layer is extremely thin. Because it is thin,
The drawbacks of ion exchangers are that, for example, increases in resistance in highly concentrated electrolyte solutions and increases in resistance due to adsorption of fouling substances are less likely to occur. Furthermore, by using cellophane or vinylon as the neutral membrane, it is possible to provide users with inexpensive multilayer membranes in large quantities, which has the advantage of reducing investment efficiency and allowing it to be used in applications where conventional membranes cannot be used. .

Claims (5)

[Claims] (1) A multilayer ion exchange membrane characterized by being composed of a multilayer membrane consisting of an ion conductive semipermeable membrane that does not substantially contain ion exchange groups and a thinner ion exchanger layer. (2) The ion exchanger layer is composed of a haloalkylated polysulfone resin reacted with ammonia or a primary amine to a tertiary amine and has an ion exchange capacity of 0.5 to 3.5 milliequivalents/g dry resin, membrane The multilayer ion exchange membrane according to claim (1), which is an anion exchanger layer with a thickness of 0.01 to 50 μm. (3) The ion exchanger layer is a cation exchanger layer made of a sulfonation reaction product of polysulfone resin with an ion exchange capacity of 0.5 to 3.5 milliequivalents/g dry resin and a film thickness of 0.01 to 50 μm. Multilayer ion exchange membrane according to patent claim (1) (4) The polysulfone resin that forms the ion exchanger layer has the general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. There is▼
, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, Y is a single bond, -O-, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, Z is -O-, -S- or -SO_2-. R^1 to R^9 are the same or different carbon atoms from 1 to
8 hydrocarbon group, a to d are 0 to 4, e is 0 to 3, (f+
g) is 0 to 7, (h+i) is 0 to 5, R_1_0, R_
1_1 is hydrogen, a hydrocarbon group having 1 to 6 carbon atoms, m/n: 1
Shows 00/1 to 1/10. ) The multilayer ion exchange membrane according to claim (1), (2) or (3), which is an aromatic polysulfone copolymer represented by (5) Claim (1), (2), (3) or (4), wherein the ion conductive semipermeable membrane containing substantially no ion exchange group is a cellophane or vinylon film with a thickness of 10 to 100 μm. Multilayer ion exchange membrane