JP2855233B2 - Method for producing aromatic polysulfone semipermeable membrane having excellent water permeability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aromatic polysulfone semipermeable membrane having excellent water permeability.

2. Description of the Related Art Since polysulfone is excellent in heat resistance and chemical resistance, a large number of semipermeable membranes using the same as a material have been conventionally proposed and have been put to practical use in various industrial fields. However, since polysulfone is hydrophobic and has low hydrophilicity, a semi-permeable membrane made of polysulfone has significantly lower water permeability than a semi-permeable membrane made of a hydrophilic material.

Therefore, conventionally, various attempts to improve the water permeability of a semi-permeable membrane made of polysulfone have been proposed. Among them, a film forming solution from polysulfone and a hydrophilic resin, that is,
Attention has been paid to a method of preparing a dope and forming a film from the dope to obtain a semipermeable membrane. For example, J. Applied Polymer Sci., 2
0, 2377-2394 (1976) proposes to use polyvinylpyrrolidone having an average molecular weight of 10,000 to 40,000 as the hydrophilic resin.

However, since polyvinylpyrrolidone is an aqueous solution, when a semipermeable membrane containing such a resin as a part of the material polymer component is used for water treatment over a long period of time, elution is inevitable, and thus the semipermeable membrane is used. Decrease in water permeability over time.

In order to solve such a problem, it has been proposed to prepare a semipermeable membrane containing polyvinylpyrrolidone as a polymer material for the membrane material and then insolubilize the polyvinylpyrrolidone with water. For example, Japanese Patent Application Laid-Open No. 62-38205 proposes a method in which a polysulfone semipermeable membrane containing polyvinylpyrrolidone is immersed in an aqueous solution of a strong base or persulfate and heat-treated at 90 to 100 ° C. Also, Japanese Patent Application Laid-Open No. 63-97205 proposes a method of heat treating a film for a long time.

Problems to be Solved by the Invention The present invention is to produce a semipermeable membrane comprising a hydrophilic resin and an aromatic polysulfone, which has excellent water permeability and suppresses elution of the hydrophilic resin, under a simple and mild condition. The purpose is to provide a way to:

Means for Solving the Problems The semipermeable membrane of aromatic polysulfone having excellent water permeability according to the present invention is obtained by converting a semipermeable membrane produced from a membrane forming solution containing aromatic polysulfone and a hydrophilic resin to α, β-unsaturated carboxylic acid. After immersion in an aqueous solution of a polycarboxylic acid containing an acid as a main monomer component, heat treatment is performed.

The polysulfone used in the present invention usually has a repeating unit represented by formulas (I) to (V).

However, the polysulfone used in the present invention is not particularly limited to the above, and for example, in the above formula, the aromatic ring may have a substituent.

In the present invention, the hydrophilic resin includes polyvinylpyrrolidone having compatibility with aromatic polysulfone, an alkyl-substituted vinylpyrrolidone polymer, a vinylpyrrolidone-vinyl acetate copolymer, polyethylene glycol, and polyvinyl alcohol. And polyvinylpyrrolidone are most preferably used.

The hydrophilic resin is usually used in the dope in a concentration range of 0.1 to 20% by weight. Generally, when a low molecular weight compound is used, a large amount is preferably used, and when a high molecular weight compound is used, a relatively small amount may be used. For example, commercially available K-90 (average molecular weight 360,000,
When Wako Pure Chemical Industries, Ltd. is used, the range is preferably 2 to 10% by weight based on the aromatic polysulfone.

The polysulfone semipermeable membrane according to the present invention is preferably prepared by dissolving a polysulfone in an organic solvent in which an additive is previously dissolved, and then dissolving a hydrophilic resin to form a membrane forming solution.
That is, it can be obtained by preparing a dope and forming the film by a conventional phase inversion method.

The additive is dissolved in an organic solvent and water to be used, and is a good solvent for the hydrophilic resin to be used, and refers to a substance that is a poor solvent for polysulfone. Usually, water, methanol, ethanol, isopropanol, hexanol, 1 , 4-butanediol, ethylene glycol, diethylene glycol, propylene glycol, and the like, but are not limited thereto. These additives are usually used by dissolving them in a concentration of 0.1 to 10% by weight based on the solvent.

Further, as an organic solvent for preparing a film forming solvent,
It is appropriately selected according to the polysulfone, hydrophilic resin, additives and the like to be used, but usually dimethylformaldehyde, dimethylacetamide, N-methyl-2-pyrrolidone and the like are preferably used.

The concentration of polysulfone in the dope is usually 5-20
A range of% by weight is good. If it is less than 5% by weight, the viscosity of the dope is too low, resulting in difficulty in film formation. On the other hand, if it exceeds 20% by weight, the resulting semipermeable membrane is not sufficiently water-permeable.

If a flat dope is cast on a support and immersed in a coagulation bath, a plate-like film can be obtained.In addition, the dope is extruded from the outer tube of the double tube type nozzle, and solidified from the inner tube. By discharging the liquid and holding the extruded dope in the form of a hollow fiber and then immersing it in a coagulating liquid, a hollow fiber-like membrane can be obtained. Such a film formation method by the phase change method is already well known.

According to the present invention, the semipermeable membrane made of the aromatic polysulfone containing the hydrophilic resin thus obtained is immersed in an aqueous solution of a polycarboxylic acid containing α, β-unsaturated carboxylic acid as a main monomer component. Then, heat treatment is performed to make the hydrophilic resin insoluble in water. Examples of the polycarboxylic acid containing the α, β-unsaturated carboxylic acid as a main monomer component include, for example, polyacrylic acid and polyitaconic acid.

The concentration of the polycarboxylic acid aqueous solution used is usually in the range of 0.001 to 10% by weight, though it depends on the temperature and the time for immersing the semipermeable membrane in it. The immersion temperature is usually in the range of 20 to 100 ° C. When the concentration of the polycarboxylic acid is less than 0.01% by weight, there is no effect on water insolubilization of the hydrophilic resin.
If it exceeds 10% by weight, an excess of polycarboxylic acid may be eluted. The polycarboxylic acid crosslinks between molecules of a hydrophilic resin, for example, polyvinylpyrrolidone. Therefore, when the amount of the polycarboxylic acid is excessive relative to the hydrophilic resin, the polycarboxylic acid not involved in the crosslinking may elute. Furthermore, it is not preferable from the viewpoint of manufacturing cost.
The time for immersing the semipermeable membrane in the aqueous solution of polycarboxylic acid may usually be in the range of 10 minutes to 2 hours.

The heat treatment temperature after immersing the semipermeable membrane in the aqueous polycarboxylic acid solution is 80 to 180 ° C, preferably 130 to 170 ° C.
Usually, it is sufficient to perform the heat treatment for 1 hour or more. For such heat treatment, for example, the film may be placed in a hot-air dryer.

Effect of the Invention The polysulfone semipermeable membrane according to the present invention contains a hydrophilic resin as a membrane material component, has high water permeability, and since the hydrophilic resin is insoluble in water, it can be eluted. In addition, even when used for water treatment for a long period of time, the initially high water permeability is maintained.

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

In the following, the water permeability of the obtained semipermeable membrane and the dissolution property of polyvinylpyrrolidone from the membrane were evaluated by the following methods.

Water Permeation Rate With respect to the flat membrane, a permeation test was performed at 25 ° C. for a certain period of time using a plastic stirring cell type permeation tester to determine the water permeation rate.

One end of the hollow fiber membrane was plugged, inserted into a plastic tube, a small module was prepared using a commercially available potting agent, and measured simultaneously.

Solubility of polyvinylpyrrolidone 0.5 g of membrane was immersed in 50 ml of water and heated at 70 ° C for 1 hour.
Water containing the eluted resin was measured for its ultraviolet absorption spectrum at a wavelength of 350 to 220 nm.

Example 1 15 parts by weight of polysulfone (Udel P-3500), 5 parts by weight of polyvinylpyrrolidone (K-90) and 3 parts by weight of water were added to 77 parts by weight of dimethylacetamide, and heated to 80 ° C to prepare a uniform dope. .

This dope was cast on a glass plate at 25 ° C., immersed in water at 20 ° C. for coagulation, and further washed with running water at 20 ° C. for 1 hour to obtain a plate-like semi-permeable polysulfone membrane. Hereinafter, this film is referred to as a precursor film.

Next, this precursor film was treated with an aqueous solution of polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd .;
It has a viscosity of 000 centipoise. ) At 80 ° C. for 1 hour and then heated at 150 ° C. for 1 hour.

The obtained semi-permeable membrane has a water permeability of 3970 / m ²・ hr ・ kgf / c
m ² , the maximum value of the ultraviolet absorption spectrum of the eluate was 0.078.

Example 2 The precursor film obtained in Example 1 was immersed in a 0.01% by weight aqueous solution of polyitaconic acid at 90 ° C. for 1 hour, and then heat-treated at 170 ° C. for 1 hour.

The obtained semi-permeable membrane has a water permeability of 7480 / m ²・ h ・ kgf / c
m ² , the maximum value of the ultraviolet absorption spectrum of the eluate was 0.094.

Example 3 The precursor film obtained in Example 1 was immersed in a 1% by weight aqueous solution of polyitaconic acid at 20 ° C. for 10 minutes, and then heat-treated at 150 ° C. for 1 hour.

The resulting semi-permeable membrane, at water permeation rate ^{4750 / m 2 · · kgf /} c
m ² , the maximum value of the ultraviolet absorption spectrum of the eluate was 0.048.

Example 4 17 parts by weight of polysulfone (Udel P-3500), 4 parts by weight of polyvinylpyrrolidone (K-90) and 3 parts by weight of water were added to 76 parts by weight of dimethylacetamide, and heated to 80 ° C. to prepare a uniform dope. .

The dope was extruded from the outer tube of the double tube type nozzle, dimethyl sulfoxide / water mixed solvent (70/30) was discharged from the inner tube, and immersed and passed through 70 cm of coagulated water 30 cm below the nozzle. After washing with running water at a temperature of 1 ° C. for 1 hour and removing the solvent, a hollow fiber precursor membrane having an inner diameter of 0.3 mm and an outer diameter of 0.5 mm was obtained.

Next, the precursor film was immersed in a 0.01% by weight aqueous solution of polyitaconic acid at 85 ° C. for 1 hour, and then heated at 150 ° C. for 1 hour.

The obtained hollow fiber-shaped semipermeable membrane has a water permeability of 8760 / m ²・ hr ・ kgf / cm ² , and the maximum value of the ultraviolet absorption spectrum of the eluate is
It was 0.085.

Example 5 The precursor film obtained in Example 4 was immersed in a 0.1% by weight aqueous solution of polyitaconic acid at 20 ° C. for 30 minutes, and then heat-treated at 170 ° C. for 1 hour.

The obtained hollow fiber-shaped semipermeable membrane has a water permeability of 1091 / m ²・ h ・ kgf / cm ² , and the maximum value of the ultraviolet absorption spectrum of the eluate is
It was 0.097.

Comparative Example 1 The precursor membrane obtained in Example 1 had a water permeability of 120 / m ² · h · kgf / cm ² , and the maximum value of the ultraviolet absorption spectrum of the eluate was
It was 1.776.

Comparative Example 2 The precursor film obtained in Example 1 was heat-treated at 150 ° C. for 1 hour without immersion in an aqueous solution of polyacrylic acid.

The obtained semi-permeable membrane has a water permeability of 950 / m ²・ hour ・ kgf / c
m ² , the maximum value of the ultraviolet absorption spectrum of the eluate was 1.060.

Claims (1)

(57) [Claims] 1. A semi-permeable membrane produced from a membrane forming solution containing an aromatic polysulfone and a hydrophilic resin is immersed in an aqueous solution of a polycarboxylic acid containing α, β-unsaturated carboxylic acid as a main monomer component. A method of producing a semipermeable aromatic polysulfone membrane having excellent water permeability, characterized by heat-treating.