JPH0148933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to anion exchange membranes. More specifically, the present invention relates to an anion exchange membrane that can be effectively used as a diffusion dialysis membrane and a method for producing the same. Conventionally, anion exchange membranes used for diffusion dialysis are made by first introducing a chloromethyl group into a base polymer such as polystyrene, and then reacting it with a tertiary amine to form a quaternary ammonium salt. The anion exchange membrane itself consists of a nearly uniform microstructure.
In such anion exchange membranes, a method of thinning the membrane has traditionally been used as a means of increasing the diffusion dialysis rate. Because it is easy to use, the disadvantage of being difficult to handle cannot be avoided. The present inventor conducted various studies in search of an anion exchange membrane that has a membrane thickness sufficient to maintain the necessary strength and also has a high diffusion dialysis rate, and as a result, the present inventor developed a linear polymer having an aminatable group. Amines are mixed with a solution of the linear polymer dissolved in a solvent, and the mixed solution is cast onto a substrate flat plate.Then, the linear polymer is immersed in a non-solvent, and the surface of the formed film is densely coated. It has been found that this purpose can be satisfactorily achieved by the presence of a layer and a large number of pores in the interior and back side of the membrane. When such an anion exchange membrane is used for diffusion dialysis, both the acid or alkali dialysis rate and the acid/alkali dialysis rate ratio are high, and these preferable dialysis performances are not achieved by a thick membrane. However, it is fully demonstrated, and therefore
Although it cannot withstand 180° bending, its high strength reduces deformation of the membrane and makes it easier to handle. The production of an anion exchange membrane with a dense surface portion, which characterizes the present invention, is carried out as follows. First, a linear polymer that can be aminated, such as chloromethylated polystyrene, polychloromethylstyrene, chlorinated polyethylene, etc., is mixed with a solvent that can dissolve such a polymer, preferably a solvent that is also miscible with water, such as dimethylformamide. It is dissolved in dimethylacetamide, dioxane, tetrahydrofuran, morpholine, N-methylpyrrolidone, etc., and amines as an aminating agent are added to the formed solution. Examples of amines include primary amines such as monomethylamine and monoethylamine, secondary amines such as dimethylamine, diethylamine, and diethanolamine, trimethylamine, triethylamine, triethanolamine,
tertiary amines such as dimethylethanolamine,
Furthermore, ethylenediamine, diethylenetriamine,
Triethylenetetramine, N,N,N',N'-tetramethyl-p-phenylenediamine, N,N,
N′,N′-tetramethylethylenediamine, N,
Polyamines such as N,N',N'-tetramethyl-1,6-hexanediamine and 4,4'-bis(dimethylamino)diphenylmethane are used. A mixture of these amines is cast onto a flat substrate plate that is not affected by the solvent, such as a glass plate, SUS plate, or Teflon plate. After a short period of time, generally within 5 minutes, the substrate is placed in a non-solvent for the linear polymer, preferably water or a hydroxyl group-containing compound such as an alcohol such as methanol or ethanol, or a glycol such as ethylene glycol. Soak. Due to this immersion, non-solvents such as water penetrate into the cast film through the surface of the membrane, and the linear polymer gels and contracts to form a dense layer on the surface of the membrane, and the non-solvent that has penetrated into the film This portion forms a large number of pores from the inside of the membrane to the back surface. The film formed in this state is then peeled off from the substrate. The ion exchange membrane obtained in this way has both good dialysis performance and strength, but these properties can be further improved. It is extremely effective to treat the membrane again with aminos, and to further increase the strength, it is effective to use fibers made of other materials or fibrous reinforcing materials such as non-woven fabric during membrane formation and incorporate them into the membrane. . Next, the present invention will be explained with reference to examples. Reference Example 1 mole of polystyrene (Asahi Dow product No. 666), 5 moles of chloromethyl methyl ether, and 0.1 mole of anhydrous zinc chloride were charged into a reaction vessel equipped with a stirring device, and the reaction was carried out at 17° C. for 5 hours. The reaction mixture was poured into methanol to form a white precipitate. This was purified by repeating the acetone dissolution-sotanol precipitation operation several times, and then vacuum-dried at 20°C until a constant weight was reached, producing chloromethylated polystyrene. Comparative example Chloromethylated polystyrene obtained in reference example
80 parts by weight of dimethylformamide was added to 20 parts by weight, and the mixture was stirred and dissolved to form a uniform solution. To this solution, further add N,N,N',N'-tetramethyl-1,
8 parts by weight of 6-diaminohexane was added and similarly stirred and dissolved to obtain a uniform liquid mixture. The prepared mixture solution is 0.2mm thick,
It was cast onto a flat glass plate with 0.1 mm or 0.05 mm guides attached to both ends and left at room temperature (20°C) for 5 hours to form a transparent, uniform, and 0.15 mm thick plate.
Anion exchange membranes of 0.08 mm or 0.02 mm were obtained. The anion exchange capacity of these anion exchange membranes was all 0.57 meq/g dry membrane. Furthermore, the acid dialysis rate of these anion exchange membranes was measured by the following method. That is, 300 ml of sulfuric acid with a concentration of 1.90 molar temperature controlled at 30°C was placed in the first chamber of a two-chamber dialysis cell partitioned by the obtained anion exchange membrane.
The second chamber was filled with 300 ml of distilled water, which was also controlled at 30℃, and the entire cell was immersed in a constant temperature bath set at 30℃.The liquid in the two chambers was sampled as it changed over time. By titrating
The dialysis rate of each anion exchange membrane was determined.
Similarly, a 1.90 molar sodium hydroxide aqueous solution
Using 300 ml, the dialysis rate was determined. The results obtained are shown in Table 1 below.

[Table] From the above results, it can be seen that the anion exchange capacity is constant regardless of the membrane thickness, and the acid/alkali dialysis rate ratio increases as the membrane thickness becomes thinner. The membrane had extremely low strength and was inconvenient to handle. Example 1 The mixed solution prepared in Comparative Example was cast onto a glass flat plate with guide surfaces of 0.2 mm thick on both ends, left at room temperature (20°C) for 10 seconds, and then immediately poured.
An opaque, white anion exchange membrane was obtained by immersing the entire glass plate in distilled water at 20°C. The thickness of the anion exchange membrane obtained was 0.2 mm, and its anion exchange capacity was 0.17 meq/g dry membrane. Also, the dialysis rate of sulfuric acid and sodium hydroxide is
5.0×10 ^-4 (mol/hour・cm ² ) and 3.6×, respectively.
10 ⁻⁵ (mol/hour·cm ² ), and their dialysis rate ratio was 13.9. This anion exchange membrane has the same thickness as that obtained in the comparative example.
Compared to a 0.15 mm anion exchange membrane, despite the larger membrane thickness or much lower anion exchange capacity, it has similar performance in terms of acid dialysis rate and acid/alkali dialysis rate. The speed ratio also shows a larger value. Furthermore, since the film is thick and rigid, it has the advantage of being easy to handle other than bending. Example 2 The opaque and white anion exchange membrane (thickness 0.2 mm) obtained in Example 1 was treated with various concentrations of N, N, N',
Anion exchange membranes were obtained by immersing them in N'-tetramethyl-1,6-diaminohexane at 20°C for a predetermined period of time to further proceed with quaternary ammonium salt formation.
The anion exchange capacity and dialysis rate of sulfuric acid and sodium hydroxide were measured for these anion exchange membranes, and the results shown in Table 2 below were obtained.

[Table] Comparing the above results with the results of Example 1, it is found that not only the acid dialysis rate has increased significantly, but also the acid/alkali dialysis rate ratio has increased approximately twice. It can be seen that the performance of the anion exchange membrane as a membrane for diffusion dialysis against acids has been further improved. In addition, when compared with the anion exchange membrane with a thickness of 0.02 mm obtained in the comparative example, its acid/alkali dialysis rate ratio is approximately 1.5 times larger, and the membrane thickness is also sufficiently thick. Although it cannot withstand 180° bending, it has excellent shape retention and is easy to handle. Figures 1 to 3 show the membrane shape of the No. 1 ion exchange membrane on the front side (10000x) and back side (2000x), and the cut surface (200x, the left side is the front side and the right side is the back side. ) is an electron micrograph of the membrane structure, and as can be seen from these drawings, the surface side is dense,
It has a non-uniform membrane structure with almost no large pores and many large and small pores inside and on the back side.

[Brief explanation of drawings]

1 to 3 are electron micrographs of the membrane shape on the front side and back side of the anion exchange membrane obtained in No. 1 of Example 2, and the membrane structure of the cut surface, respectively.

Claims (1)

[Scope of Claims] 1. An anion exchange membrane in which a dense layer exists on the surface portion of the membrane and a large number of pores exist in the inside and back surface portion of the membrane. 2. An anion exchange membrane according to claim 1, which is used as a diffusion dialysis membrane. 3. The anion exchange membrane according to claim 1, wherein a fibrous reinforcing material is included in the membrane. 4 Mixing amines with a solution of a linear polymer having an aminatable group dissolved in a solvent, casting the mixture onto a flat substrate, and then immersing the linear polymer in a non-solvent. 1. A method for producing an anion exchange membrane in which a dense layer is present on the surface portion of the membrane and a large number of pores are present in the interior and back surface portion of the membrane. 5. The method for producing an anion exchange membrane according to claim 4, wherein a water-miscible solvent is used as the solvent for dissolving the linear polymer. 6. The method for producing an anion exchange membrane according to claim 4, wherein water or a hydroxyl group-containing compound is used as a non-solvent for the linear polymer. 7. The method for producing an anion exchange membrane according to claim 4, which comprises treating the formed anion exchange membrane again with amines.