JPH0747654B2 - Multilayered ion exchange membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multilayered ion exchange membrane that permeates and separates a specific component from a mixed liquid.

More specifically, ultra-low resistance multi-layered ion-exchange membranes useful for electrodialysis such as seawater concentration and battery separators, or acid discharged from all industries including plating waste liquid and metal refining industry. The present invention relates to a multi-layered ion exchange membrane that is useful when recovering an acid or separating and purifying a valuable compound contained in an acid solution.

[Conventional technology]

A system for permeating and separating a specific component from a mixed liquid using an ion exchange membrane has already been used in a wide field.

Many documents and patents have been reported as conventional ion exchange membranes, but the most practical and useful ones are the amination (or quaternary pyridium) of chloromethylated styrene (or vinylpyridine) -divinylbenzene copolymer. There is an anion exchange membrane or a sulfonated cation exchange membrane of a styrene-divinylbenzene copolymer. In addition to chemical resistance, heat resistance, and ion exchangeability, these change the content of divinylbenzene, which is a cross-linking agent,
Since it is possible to control the ion exchange characteristics and the selective permeability, various varieties have been synthesized and developed for all purposes.

However, new applications include, for example, phosphoric acid recovery from phosphoric acid waste liquids such as in the aluminum industry, recovery of sulfuric acid from sulfuric acid waste liquids such as in the titanium industry, seawater concentration for producing inexpensive salt comparable to industrial salt, and redox flow. The conventional styrene-divinylbenzene system has a drawback that it cannot meet the demand for an ion exchange membrane having low resistance, durability and heat resistance such as a separator for batteries and methanol batteries. That is, it is necessary to reduce the film thickness in order to obtain a film having low resistance and high permeability. However, since styrene-divinylbenzene resin has mechanical strength, particularly brittleness, it is an ion exchange film with a thickness of 100 μm or less. Can't get

Furthermore, styrene-divinylbenzene-based membranes have poor mechanical properties in addition to mechanical properties, and hollow fiber-type membranes used in other separation systems such as reverse osmosis, ultrafiltration, microfiltration and gas separation can be obtained. There are drawbacks that cannot be avoided.

On the other hand, engineering plastics having excellent mechanical strength and processability are used in separation membranes such as ultrafiltration membranes, 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, if the repeating unit is Anion exchange resin synthesized by chlormethylation / quaternary amination reaction of polysulfone and cation exchange resin synthesized by sulfonation reaction of polysulfone are Polymeric Amines and Ammonium Salts, Pergamon, New
York, 1980, p.37, Polmer Preprints, Am.Chem.Soc., Di
v. Polym. Chem., 20 (1), 835 (1979). And USP 3,709,8
41, the polymer is dissolved in a solvent to obtain a thin film of these polymers, it is possible to obtain an asymmetric structure ion exchange membrane by aggregating in water after cast membrane formation
USP3,709,841, USP3,855,122, Desalination, 46,327 (1
983), J. Membrane Sci., 22, 1 (1985). , J. Membrane
Sci., 22,325 (1985). , Desalination, 70,191 (198
8). Etc. However, polysulfone ion exchange membranes with these asymmetric structures have a large dimensional change during aggregation and are prone to defects, and when the ion exchange capacity increases, the affinity for water increases, making aggregation difficult and sufficient mechanical strength. There is a defect that a film having a stickiness cannot be obtained.

In addition, an ion exchange thin film in which a polysulfone type ion exchange resin is coated on a polysulfone porous membrane having an asymmetric structure has been reported (Japanese Patent Laid-Open Nos. 61-4505 and 61-4506,
61-146303, 62-79811, Textile and Industry, 44,1, P-11
(1988). ), The polysulfone porous membrane as a supporting membrane has a low surface porosity of 10 to 30%, and therefore has a high resistance, and there is a drawback that sufficient mechanical strength cannot be obtained if the surface porosity is increased.

An example in which a polysulfone ion exchange resin is embedded in a highly porous polytetrafluoroethylene (PTFE) membrane has also been reported (AICHE Symposium Series 248,82,70 (1
986). ), Since the surface free energy of the PTFE porous film is low, it is difficult to obtain a defect-free film by solution coating or dipping, and the film thickness becomes large, so that a film with low resistance cannot be obtained. Furthermore, since the ion exchange resin is embedded in the intricate pores of the porous membrane, the resistance is further increased.

[Problems to be Solved by the Invention]

An object of the present invention is to solve the above-mentioned drawbacks of the conventional techniques, and an object thereof is to provide a novel multilayer ion exchange membrane having an ultralow resistance.

[Means for solving problems]

The above object of the present invention is to have a pore size of 0.01 to 5 μm and a porosity of 30 to 90.
%, 10 to 200 μm in thickness of the inner wall of the porous membrane having hydrophilicity, and an ion exchange comprising a sulfonated product of an aromatic polysulfone block copolymer having the following general formula (1) or a quaternary ammonium salt group introduced product This can be achieved by forming a thin film of a functional polymer into a multilayer.

Examples of the porous film used in the present invention include polyethylene, polypropylene, polyhydrocarbon olefins such as poly-4-methylpentene-1, polyvinylidene fluoride, polytetrofluoroethylene, hexafluoropropylene / tetrafluoroethylene copolymer, Examples thereof include polyfluoroolefins such as fluoroolefin-based monomers / olefin-based monomer copolymers.

Although there are various methods for producing the porous membrane, the stretching and opening method is used as a preferable method. Stretching and opening method is a method in which a crystalline polymer is molded into a hollow fiber or a film, and then the crystalline lamellae are cleaved by stretching, and then a heat treatment is performed to form a porous structure. It is preferable to be used in the present invention because a quality film can be obtained, there is no problem of residual solvent, etc., and a film having high porosity and high mechanical strength is obtained. On the other hand, in the wet phase inversion method, the obtained pore structure is an asymmetric structure, and the porosity of the surface is small, so that the resistance becomes high when the ion exchange membrane is made into a multilayer, which is not preferable.

In the present invention, the pore size is 0.01 to 5 μm, preferably 0.02 to 2 μm.
m, porosity 30-90%, especially 40-70%, thickness 10-200μ
m, in particular 25-150 μm porous membranes are used. If the pore diameter is larger than 5 μm, the ion-exchange resin penetrates into the inside of the complicated pores of the porous membrane when the ion-exchange membrane is made into a multi-layer structure, resulting in high resistance, which is not preferable. 30% porosity
If it is lower than 90%, the resistance becomes high, and if it is higher than 90%, the mechanical strength decreases, which is not preferable. When the thickness is 200 μm or more, concentration polarization occurs in the porous body and the permeability is lowered, which is not preferable.

As a method for forming a multi-layered ion-exchange resin on such a porous membrane, a method of melt-laminating a polymer, a polymer solution coating method, a method of applying a monomer and then polymerizing or grafting it, and the like can be considered. The method is a preferable method for use in the present invention because a dense thin film can be easily obtained. However,
Since the porous membrane used in the present invention has a low surface free energy and a small pore size, the solution is repelled during the solvent evaporation process, and it is difficult to obtain a homogeneous thin film.

As a method for hydrophilizing the inner wall of the pores of the porous membrane, that is, the inner wall of the large number of pores of the porous membrane, a method of adsorbing a low molecular weight substance or a high molecular weight substance having hydrophilicity to the porous membrane or after impregnating the low molecular weight substance Method of reacting with electron beam or ultraviolet ray, fuming sulfuric acid,
Method of sulfonation of porous membrane surface with chlorosulfonic acid, method of oxidization with chromic acid, method of surface treatment with exciting gas or active gas such as plasma gas and ozone gas, further impregnated with ionic surfactant Examples of the method include a method of treating with a polymer having a reverse charge in the main chain, and a method of treating with a polymer having a reverse charge in the main chain after impregnation with an ionic surfactant is a porous membrane substrate. It is preferable because permanent hydrophilicity can be obtained even on the inner wall of the pores of the porous membrane having a small pore diameter of 5 μm or less without damaging the surface.

Examples of the thin film of the ion-exchangeable polymer that forms a multi-layer on the hydrophilized porous film include a sulfonated product of an aromatic polysulfone block copolymer having the following general formula (1):
Alternatively, an introduced product of a quaternary ammonium base can be used.

(However, Ar in the formula is Or R ^{1 to} R ⁹ are the same or different hydrocarbon groups having 1 to 8 carbon atoms. a to d are 0 to 4, e is 0 to 3, and f + g is 0.
7, h + i is 0 to 5, R ^{10 to} R ¹¹ are hydrogen, and a hydrocarbon group having 1 to 6 carbon atoms. X is -O- or -S-, m / n = 100
/ 1 to 1/10 and Z = 1 to 100 are shown. ) In the above aromatic polysulfone block copolymer, when the ion exchange group is introduced by sulfonation or halomethylation / quaternary amination, it is easy to control the ion exchange group capacity, and the obtained membrane has ion selective permeability. Is preferable, and the mechanical strength and the forming processability are excellent, which is preferable. Such a copolymer is described in JP-A-61-168629 by the applicant of the present invention.

As a solvent for dissolving the ion exchange resin composed of such an aromatic polysulfone block copolymer, N, N,-
Dimethylformamide, N, N-dimethylacetamide,
Dimethyl sulfoxide, N-methylpyrrolidone, 1,1,2
-Trichloroethane, 1,1,2,2-tetrachloroethane,
In addition to a single solvent of triethyl phosphate, a mixed solvent such as a water / acetone mixed solution or a methanol / tetrahydrofuran mixed solution is used. The polymer solution concentration is 1 to
20% by weight, especially 5 to 15% is preferred. 20% by weight
If it exceeds, it is difficult to obtain a thin film.

After coating with the polymer solution, the multi-layer membrane is dried with hot air at a temperature not higher than the crystal melting temperature of the porous membrane material, thus obtaining a low-resistance multi-layered ion exchange membrane. The thickness of the multilayered ion-exchange membrane on the hydrophilized porous membrane is 0.1.
.About.50 .mu.m, particularly preferably 1 to 30 .mu.m. 50 μm thickness
If it is more than the above value, resistance becomes high, and if it is 0.1 μm or less, defects are likely to occur, which is not preferable.

Also, when the inner wall of the pores of the porous membrane is not hydrophilized,
It is made hydrophilic at this stage.

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, 4,
4'-diphenol and dihalodiphenyl sulfone are reacted to form an aromatic polysulfone unit m =
10 precursors were synthesized, and then the precursor was reacted with dihalodiphenyl sulfone and sodium sulfide,
An aromatic polysulfone / polythioether sulfone copolymer A represented by the following formula was obtained.

Next, the copolymer A was dissolved in 1,1,2,2, -tetrachloroethane, chloromethyl methyl ether and anhydrous tin chloride were added, and the mixture was reacted at 101 ° C. for 4 hours, then methyl alcohol was added. And washed with chloromethylated copolymer B
Got

The copolymer B thus obtained was dissolved in N, N-dimethylformamide to obtain a 10% by weight solution. Then in the solution
A predetermined amount of N, N-dimethylformamide solution of 1.2N trimethylamine was added to prepare a solution of quaternary aminated polymer C having an ion exchange capacity of 2.0 meq / g.

On the other hand, a polypropylene porous film having a pore size of 0.04 μm, a porosity of 45% and a film thickness of 25 μm was impregnated with ethyl alcohol, then immersed in water, and further immersed in a 1% by weight aqueous solution of sodium isopropylnaphthalenesulfonate at room temperature for 3 minutes, 60 Anion surfactant-impregnated porous membrane was prepared by drying at 0 ° C for 10 minutes. This membrane was immersed in a 0.5 wt% aqueous solution of poly (2-hydroxy-3-dimethylaminopropyl chloride) for 1 minute at room temperature and dried at 60 ° C for 10 minutes to obtain a hydrophilic polypropylene porous membrane.

The N, N, -dimethylformamide solution of the quaternary aminated polymer C described above was coated on a hydrophilic polypropylene porous membrane and dried at 50 ° C for 2 hours to form an ion exchange membrane layer having a thickness of 10 µm. The obtained ion exchange membrane was obtained. 0.5 N-NaCl aqueous solution of the resulting ion exchange membrane, and 0.5M-H ₂
Table 1 shows the measurement results of the effective resistance in the SO ₄ aqueous solution. The value of the effective resistance was sufficiently lower than that of the conventional styrene-divinylbenzene-based anion exchange membrane.

COMPARATIVE EXAMPLE 1 Three kinds of monomer mixed liquids having different compositions of chloromethylstyrene-divinylbenzene and styrene monomer were used.
A monomer syrup solution was prepared by dissolving nitrile rubber in a weight percentage and further dissolving benzoyl peroxide as a polymerization initiator. The monomer syrup solution was applied to a polyvinyl chloride cloth, and then sandwiched between Mylar films for polymerization. The polymerized membrane thus obtained was aminated in a trimethylamine solution to obtain an anion exchange membrane having a thickness of 120 μm. As in Example 1, 0.5 N- of the ion exchange membrane was used.
The effective resistances in the NaCl aqueous solution and the 0.5M-H ₂ SO ₄ aqueous solution were measured, and the results are summarized in Table-1.

Example 2 The multilayer membrane obtained in the same manner as in Example 1 was sandwiched between small batch type acid diffusion dialysis cells and placed on one side. The static permeation rate and selectivity of sulfuric acid were evaluated from the sulfuric acid concentration on the ion-exchanged water side and the concentration of Zn ions after 2 hours from the addition of constant-concentration sulfuric acid and ZnSO ₄ aqueous solution to the other. The results are shown in Table-2. The value of the permeation rate U decreases with an increase in the concentration of sulfuric acid, but the rate of decrease is small as compared with the conventional styrene-divinylbenzene ion exchange membrane, and a high permeation rate, which was unprecedented, was obtained especially at a high concentration. . In addition, it was found that the selectivity R _S (U Zn / UH ₂ SO ₄ ) was also sufficiently low and had high selective permeation performance.

Comparative Example 2 Using the chloromethylstyrene-divinylbenzene anion exchange membrane obtained in Comparative Example 1-3, the diffusion dialysis performance of a sulfuric acid-zinc sulfate solution was obtained in the same manner as in Example 2.
It shows in Table-2.

Example 3 A multilayer membrane obtained in the same manner as in Example 1 was sandwiched between small batch type acid diffusion dialysis cells, and 0.84 N phosphoric acid and 0.0
Put 75N AlPO ₄ aqueous solution and ion-exchanged water into the other 2
The static permeation rate and selectivity of phosphoric acid were evaluated from the concentration of phosphoric acid on the ion-exchanged water side and the concentration of Al ions after a lapse of time.
As a result, it was found that the permeation rate U was 4.2 mol / m ² · h · Δc and the selectivity R _S (U Al / UH ₃ PO ₄ ) was 0.02, indicating high dialysis performance.

Comparative Example 3 The diffusion dialysis performance of a phosphoric acid-aluminum phosphate solution was determined in the same manner as in Example 3 using the chloromethylstyrene-divirbenzene-based anion exchange membrane obtained in Comparative Example 1-3. . As a result, the value of permeation rate U is 0.8 mol / m ² · h
The values of Δc and selectivity R _S (U Al / UH ₃ PO ₄ ) were 0.02.

Example 4 Outer diameter 250 μm, inner diameter 200 μm, pore diameter 0.02 μm, porosity 45
%, And a 25 μm-thick polypropylene hollow fiber porous membrane was hydrophilized in the same manner as in Example 1. On the obtained hydrophilized hollow fiber porous membrane, the quaternary aminated polymer solution obtained by the same method as in Example 1 was applied and dried.
A 10 μm multi-layer hollow fiber membrane was obtained. This hollow fiber is 60 cm long,
A bundle of 1000 pieces was fixed to a separator made of heat-resistant vinyl chloride with epoxy resin at both ends, and an acid recovery device as shown in Fig. 1 was created.

The acid solution containing 10 mol / l sulfuric acid and 0.1 mol / l zinc sulfate was added to the inside of the hollow fiber of the acid recovery device thus obtained from the bottom at 0.5 l / mi.
Feed at a rate of n. On the other hand, add 0.5 l / m of pure water outside the hollow fiber.
When supplied at a rate of in. from above, a 7.5 mol / l sulfuric acid, 0.001 mol / l zinc sulfate solution was obtained. The recovery rate of sulfuric acid was 80%.

Example 5 An aromatic polysulfone / polythioether sulfone copolymer A was obtained in the same manner as in Example 1.

Next, 56 g of triethyl phosphate was mixed with 400 ml of 1,1,2-trichloroethane, and 82 g of fuming sulfuric acid was gently added dropwise at 0 ° C. to prepare a sulfonation solution. The sulfonation solution and 1060 g of a 9 wt% 1,2,2-trichloroethane solution of copolymer A were added dropwise to 700 ml of 1,1,2-trichloroethane with vigorous stirring. After dropping, the mixture was stirred at room temperature for 97 hours, filtered and washed to obtain a sulfonated product D of copolymer A.

The sulfonated polymer D thus obtained was dissolved in N-methylpyrrolidone to obtain a 10% by weight solution.

On the other hand, a hydrophilic polypropylene porous membrane was obtained in the same manner as in Example 1.

The N-methylpyrrolidone solution of the sulfonated polymer D was coated on a hydrophilic polypropylene porous membrane and dried at 50 ° C. for 2 hours to form a multilayer ion exchange membrane having an ion exchange membrane layer thickness of 10 μm. Got The effective resistance of the obtained ion-exchange membrane in 0.5N-NaCl aqueous solution is 0.4Ω.
· M ² illustrates a conventional styrene - was sufficiently low in comparison with divinylbenzene based cation exchange membrane.

Claims (3)

[Claims] 1. A polyhydrocarbon olefin or polyfluoroolefin porous membrane having a pore diameter of 0.01 to 5 μm, a porosity of 30 to 90% and a thickness of 10 to 200 μm having hydrophilic inner walls, and the following general formula (1): A multi-layered ion-exchange membrane, characterized in that the sulfonated aromatic polysulfone-based block copolymer or a thin film of an ion-exchangeable polymer formed by introducing a quaternary ammonium salt group is multi-layered. (However, Ar in the formula is Or R ^{1 to} R ⁹ are the same or different hydrocarbon groups having 1 to 8 carbon atoms. a to d are 0 to 4, e is 0 to 3, and f + g is 0.
7, h + i is 0 to 5, R ^{10 to} R ¹¹ are hydrogen, and a hydrocarbon group having 1 to 6 carbon atoms. X is -O- or -S-, m / n = 100/1
.About.1 / 10 and Z = 100 are shown. ) 2. The thin film of the ion-exchange polymer has a thickness of 0.1.
The multi-layered ion exchange membrane according to claim 1, wherein the ion exchange membrane has a thickness of ˜50 μm. 3. A porous membrane comprising hollow fibers having an inner diameter of 0.1 to 1 mm,
The multilayer ion exchange membrane according to claim (1) or (2), wherein the entire ion exchange membrane has a hollow fiber shape.