JP2910138B2 - Method for producing ultrafiltration membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polymer molded product (fiber, film, structural material, separation membrane, various types) used in a field requiring durability such as heat resistance and solvent resistance. Parts).

[Prior art] Conventionally, as a polymer having excellent durability, Teflon (PTF
E), polyimide (PI), polyetheretherketone (PEEK), polyphenylenesulfone (PPS),
Polymers called various engineering plastics are known. However, the higher the durability of these polymers, the worse the processability becomes, and it becomes difficult to form a molded product having a fine structure. In order to solve this problem, a method has been devised in which a polymer containing a sulfide bond, which is relatively workable, is first molded and then subjected to an oxidation treatment to impart durability (JP-A-63-225636). Issue, International Publication 90/3210
issue). Oxidizing agents include hydrogen peroxide, hypochlorite, sulfuric acid, chlorine, sulfuryl chloride, nitrogen dioxide, chromium trioxide, alkali permanganate, nitric acid, and organic peroxides (eg, peracetic acid, perbutylic acid, perbenzoic acid). Acids and chlorobenzoic acid) are known (US Pat. No. 3,948,865, German Patent No. 1938806, JP-A-63-225636).

[Problems to be Solved by the Invention] However, these oxidizing agents have many problems such as insufficient oxidizing power, oxidization accompanied by decomposition and side reaction of a polymer, and oxidizing agents being explosive.

The present invention is intended to solve the disadvantages of the prior art, and to provide a method for producing a polymer molded product using an oxidizing agent having both mild oxidation and excellent oxidation ability and selective reactivity. With the goal.

[Means for Solving the Problems] To achieve the above object, the present invention has the following constitution.

"A method for producing a ultrafiltration membrane, comprising oxidizing a polymer having a sulfide bond in the main chain with a solution containing potassium hydrogen persulfate." In the present invention, a polymer having a sulfide bond in the main chain Is represented by the following general formula.

R ₁ -S _m R ₂ -X _{n In the} formula, R ₁ and R ₂ are selected from aromatic, aliphatic and heterocyclic rings, and are preferably aromatic and heterocyclic rings in consideration of mechanical strength and heat resistance. In consideration of the above, aliphatic is preferable. X is selected from a single bond, a sulfone, a ketone, and an ether,
When R ₁ and / or R ₂ are aromatic, an electron-withdrawing sulfone or ketone bond is preferable in order to improve the chemical stability of the ring. m and n represent an integer of 0 or more. m
Is small, the effect of imparting durability by the oxidizing agent is small.
When the number increases, the crystallinity improves, so that the solubility decreases or the penetration of the oxidizing agent is inhibited.
/(M+n)<0.9, more preferably 0.3 <m (m + n)
<0.7. The higher the degree of polymerization, the higher the durability of the polymer. The polymer exhibits desirable properties as a molded product, but it is difficult to process. Therefore, the molecular weight is preferably from 100,000 to 100,000. These polymers can be made into a target molded product by melt molding, wet solidification molding, pressure molding, sintering molding or a combination thereof.

In the present invention, the persulfate compound refers to a compound having a chemical structure represented by SO ₅ or S ₂ O ₈ and generally has a strong oxidizing power. Specific examples include persulfuric acid (peroxomonosulfuric acid, peroxodisulfuric acid), alkali persulfate, alkali hydrogen persulfate, ammonium persulfate and the like. In the present invention, potassium hydrogen persulfate is used. Here, the alkali is not particularly limited, and in some cases, a plurality of types may be combined.Alkali metal elements such as potassium and sodium are preferable, and particularly those using potassium have good solubility, preferable. Among them, potassium hydrogen persulfate is combined with potassium hydrogen sulfate and potassium sulfate:
It is known that a 1: 1 (molar ratio) mixture improves the stability, which is particularly preferred, but is not limited thereto. The solution containing the persulfate compound is preferably an aqueous solution in view of its solubility, but is not limited to an aqueous solution because it has a sufficient oxidizing power even in a suspended state in a water-organic solvent. However, when oxidizing the polymer molded product, it is preferable to mix a small amount of an organic solvent since the reactivity is improved when the molecular motion of the polymer is activated. For example, a mixture of potassium hydrogen persulfate: potassium hydrogen sulfate: potassium sulfate = 2: 1: 1 (molar ratio) is water / acetic acid, water / methanol, water / ethanol, water / isopropyl alcohol, water / N-methylpyrrolidone, The polymer is efficiently oxidized in a water / ethanol / acetic acid system.

The concentration of the oxidizing solution is not particularly limited as long as it does not decompose the polymer. For example, potassium hydrogen persulfate:
In the case of a mixture aqueous solution of potassium hydrogen sulfate: potassium sulfate = 2: 1: 1 (molar ratio), it can be arbitrarily selected from 0 to 25.6% by weight at 20 ° C. and from 0 to 33.5% by weight at 71 ° C. From the viewpoint of efficiency, 15 to 22% by weight is particularly preferable.

The pH of the oxidizing solution is not particularly limited as long as it does not decompose the polymer. For example, in the case of a mixture aqueous solution of potassium hydrogen persulfate: potassium hydrogen sulfate: potassium sulfate = 2: 1: 1 (molar ratio), the pH becomes 2.0 in a 3.0% by weight aqueous solution, but the stability becomes higher when the pH becomes 5 or more. It is preferable to maintain the pH at 5 or less during the oxidation treatment since the pH rapidly decreases.

Oxidation treatment methods include a) a method of immersing a polymer molded article in an oxidizing solution and heating if necessary, b) a method of applying or impregnating an oxidizing solution to the molded article and heating if necessary, c) oxidizing. There is a method of spraying a liquid (heated if necessary), and it is desirable to select a treatment method according to the form and purpose of the molded product.

In the case of the polymer immersion method, the oxidation temperature is preferably from 50 to 95 ° C in consideration of the molecular motion, and is preferably from 50 to 80 ° C in consideration of the stability of the oxidizing agent solution. Heating up to 170 ° C. is possible in the coating method and the spraying method, but heating at about 50 to 120 ° C. is preferably used in consideration of the stability of the oxidizing agent.

The oxidation treatment time can be any time according to the required required characteristics. The oxidation rate increases linearly with the treatment time, but the oxidation rate does not increase beyond a certain value because diffusion of the oxidizing agent into the polymer does not occur more than a certain amount. This depends on the thickness of the molded product. For example, a porous membrane which is considered to be an aggregate of fine particles depends on the particle size. The oxidation treatment time also depends on the concentration of the oxidizing agent and the treatment temperature. As the concentration is higher and the temperature is higher, a higher oxidation rate can be obtained even if the treatment time is shorter.

The form of the polymer molded product is not particularly limited, but due to the nature of the treatment method, relatively thin molded products such as fibers, films, and porous materials must be modified as a whole, and thick molded products such as structures and parts must be modified. become. From the viewpoint of the durability of the molded product, it is preferable that the entire polymer is oxidized. However, in many cases, sufficient durability can be imparted even in surface modification, and the degree of oxidation is not particularly limited.

When the polymer molding is a microporous membrane, the oxidation method according to the present invention results in a separation membrane having excellent heat resistance and solvent resistance. Heat resistance and solvent resistance refer to small changes in solute (eg, polyethylene glycol) rejection and water permeability after exposure of a microporous membrane to high temperature or a solvent for a certain period of time. It has been difficult to suppress the change in pore size at the angstrom level with conventional polymers having resistance to steam sterilization used in the production process.

The oxidation rate is preferably all oxidized, but a sufficient durability can be imparted with an oxidation rate of about 40%. This oxidation rate is important not only for the oxidizing power of the oxidizing agent but also for the swelling of the polymer, and it is important to select swelling conditions that do not disturb the form of the molded product and allow the oxidizing agent to react efficiently.

Examples will be described below, but the present invention is not limited to these examples.

Example Reference Example 1 Poly (phenylene sulfide sulfone) (PPSS) was synthesized by the method described in JP-A-63-270736.

That is, in one autoclave equipped with a temperature and pressure measuring device, a stirrer and a heating device, a screw (4-
Chlorophenyl) sulfone 154.7 g, sodium carbonate 56.5
g, sodium acetate 43.7 g, sodium hydrogen sulfide (NaSH 59.
50.7 g of N-methyl-2-pyrrolidone (NMP) and 14.4 g of deionized water.
The mixture was stirred with stirring at 25 ° C to 200 ° C for 3 hours. Then a mixture of 160 ml of NMP and 26.7 ml of deionized water was injected. Stirring was continued until about 150 ° C. The reaction mixture was removed from the reaction vessel as solid particulate matter and the liquid was aspirated. The solid substance is deionized water boiling water (about 90
C., about 600 ml), filtered and rinsed once on the filter. This step was repeated twice, then the final washing procedure was completed with cold deionized water to remove water-soluble impurities. Stirrer,
About 1 equipped with a heating / cooling machine, thermometer and pressure gauge
In an autoclave, 40 g of the purified and recovered polymer described above, 400 g of deionized water, and 4.0 g of zinc acetate [Zn (C ₂ H ₃ O ₂ .2H ₂ O)]
Was put. The polymer / aqueous zinc acetate aqueous mixture is heated to 185 ° C. with stirring and then brought to that temperature with stirring.
Hold for hours. The mixture was then cooled to room temperature, and the recovered polymer was washed once with boiling water (about 90 ° C., about 400 ml) while stirring. The recovered polymer was dried under reduced pressure at a temperature of 160 ° C. The weight average molecular weight of the polymer obtained by gel permeation chromatography was 31600 (in terms of polystyrene).

Hereinafter, this polymer is abbreviated as PPSS (polyphenylene sulfide sulfone). This PPSS It is represented by the following chemical formula.

REFERENCE EXAMPLE 2 16 g of the PPSS polymer obtained in Reference Example 1 was added to 84 g of dry dimethylimidazolidinone (DMI), and the container storing the polymer mixture was placed under a nitrogen atmosphere and then heated to 180 ° C. To dissolve the polymer. Then, insoluble components were filtered off with a polytetrafluoroethylene membrane filter having a pore diameter of 10 μm. Taffeta made of polyester fiber of 30cm length and 20cm width (multi-filament yarn of 150 denier for both warp and weft, 90 / inch in weaving density, 67 / width)
(Inch, 160 μm thick) was fixed on a glass plate, and the polymer solution was cast on a taffeta with an average thickness of 150 μm, and immediately immersed in water (25 ° C.) to obtain a porous material.

When the obtained membrane was evaluated using 1000 ppm polyethylene glycol (molecular weight 100,000) as raw water at a pressure of 1 kg / cm ² and a temperature of 25 ° C., the rejection rate was 89.9%, and the water permeability was 2.03 m ³ / m ² · day (30
(Min value).

Example 1 In a 500 ml separable flask, potassium hydrogen persulfate /
75 g of a mixture of potassium hydrogen sulfate / potassium sulfate (molar ratio) (“OXONE”, Aldrich), 75 g of water, and 50 g of acetic acid were added and dissolved, followed by heating to 70 ° C.

The film obtained in Reference Example 2 was immersed in this solution for 100 minutes and washed with water.

The obtained membrane was evaluated using 1000 ppm polyethylene glycol (molecular weight 100,000) as raw water at a pressure of 1 kg / cm ² and a temperature of 25 ° C. When the rejection was 89.6% and the water permeability was 2.03 m ³ / m ² · day (30
(Min value).

Example 2 The membrane obtained in Example 1 was treated with dimethylformamide (DM
F) After immersion in water for 24 hours, washed with water, using 1000 ppm polyethylene glycol (molecular weight 100,000) as raw water, pressure 1 kg / cm ² , temperature 2
When evaluated at 5 ° C, rejection = 94.9%, water permeability = 1.64m ³
/ M ² · day (30 minutes value).

Example 3 In Example 2, the immersion solvent was methyl ethyl ketone (ME
K) was evaluated under the same conditions except that
The rejection was 92.4%, and the water permeability was 1.87 m ³ / m ² · day (30 minutes).

Example 4 Evaluation was performed under the same conditions as in Example 2 except that the immersion solvent was N-methylpyrrolidone (NMP). The inhibition rate was 92.4%, and the water permeability was 2.05 m ³ / m ² · day (30 days). (Min value).

Example 5 In Example 2, the immersion solvent was tetrahydrofuran (TH
F), the evaluation was performed under the same conditions except that
The rejection was 92.7%, and the water permeability was 2.05 m ³ / m ² · day (30 minutes value).

Example 6 Evaluation was performed under the same conditions as in Example 2 except that the immersion solvent was ethanol, and the rejection was 92.4%.
Permeability = 1.71 m ³ / m ² · day (30 minute value).

Example 7 Evaluation was performed under the same conditions as in Example 2 except that the immersion solvent was pyridine, and the rejection was 95.1% and the water permeability was 1.65 m ³ / m ² · day (30 minutes value). there were.

Example 8 The film obtained in Example 1 was immersed in ethanol for 30 minutes, immersed in benzene for 24 hours, immersed again in ethanol for 30 minutes, and washed with water. Evaluated at a pressure of 1 kg / cm ² and a temperature of 25 ° C. using 1000 ppm polyethylene glycol (molecular weight 100,000) as raw water, the rejection = 92.2%, the water permeability = 1.94 m ³ / m ² · day (30
(Min value).

Example 9 Evaluation was performed under the same conditions as in Example 8 except that methylene chloride was used instead of benzene. The rejection was 94.0%, and the water permeability was 1.34 m ³ / m ² · day (30-minute value). Performance.

Example 10 The membrane obtained in Example 1 was placed in a 300 ml beaker containing distilled water, and heated in an autoclave at 120 ° C. and 1 kg / cm ² for 8 hours. When this membrane was evaluated using 1000 ppm polyethylene glycol (molecular weight 100,000) as raw water at a pressure of 1 kg / cm ² and a temperature of 25 ° C., the rejection was 88.4%, and the water permeability was 1.92 m ³ / m ^2.
It was the performance of the day (30 minutes value).

Comparative Example 1 When the membrane obtained in Reference Example 2 was evaluated under the same conditions as in Example 10, the performance was as follows: rejection = 76.0%, water permeability = 1.87 m ³ / m ² · day (30 minutes value). .

Example 11 A DMI solution of the PPSS polymer obtained in Reference Example 2 was thinly applied on a glass plate, and the solvent was evaporated and dried in an oven at 120 ° C. for 15 minutes. After cooling to room temperature, the glass plate on which the polymer thin film was formed was immersed in water to peel the thin film. The thickness of the obtained thin film was about 1 to 3 μm. When this thin film was subjected to oxidation treatment for 4 hours under the same conditions as in Example 1, it was possible to obtain a thin film that did not change its form when dipped in methylene chloride.

Comparative Example 2 A thin film obtained in the same manner as in Example 11 except that the oxidation treatment was not performed was immersed in methylene chloride. As a result, rapid shrinkage occurred and the shape of the thin film could not be maintained.

[Effects of the Invention] By using the method of the present invention, a polymer molded product having excellent durability such as heat resistance and solvent resistance could be produced. In particular, according to the present invention, it has become possible to efficiently supply an ultrafiltration membrane having extremely excellent heat resistance and solvent resistance under safe and mild conditions.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 1-259037 (JP, A) JP-A 63-225636 (JP, A) JP-A 63-22835 (JP, A) JP-A 59-1990 196322 (JP, A) JP-A-60-25513 (JP, A) US Patent 3,948,865 (US, A)

Claims (4)

(57) [Claims] 1. A method for producing an ultrafiltration membrane, comprising oxidizing a molded polymer having a sulfide bond in the main chain with a solution containing potassium hydrogen persulfate. 2. The ultrafiltration membrane according to claim 1, wherein the solution containing potassium hydrogen persulfate is an aqueous solution further containing potassium hydrogen sulfate or potassium sulfate. Method. 3. The method for producing an ultrafiltration membrane according to claim 1, wherein the oxidation treatment temperature is 50 to 95 ° C. 4. The method for producing an ultrafiltration membrane according to any one of claims (1) to (3), wherein the molded polymer is a microporous membrane.