JP2002191947A - Ultrafiltration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultrafiltration membrane with high water permeability and soil resistance. SOLUTION: The ultrafiltration membrane consisting of a hydrophilic polymer and a hydrophobic polymer and in which both polymers are under a phase- separated condition and the hydrophilic polymer is a polyvinyl alcohol with a degree of saponification of 5-50% is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly hydrophilic membrane excellent in stain resistance and water permeability.

[0002]

2. Description of the Related Art From the viewpoint of environmental protection in recent years, ultrafiltration membranes in the form of flat membranes or hollow fibers have been used for various water treatment / reuse applications. These membrane materials include, for example, cellulose, polyacrylonitrile, polysulfone, and the like.

When performing water treatment using various ultrafiltration membranes, it is necessary to prevent a decrease in the amount of permeated water due to contamination of the membrane surface. Therefore, conventionally, a method of adding polyvinylpyrrolidone (PVP) has been used for the purpose of adding hydrophilic properties.
However, since PVP is soluble in water, the membrane performance is not stable, and there has been a problem that the eluted PVP contaminates a reverse osmosis membrane at a later stage. For the purpose of preventing this problem, thermal crosslinking and radiation treatment (Japanese Patent Application Laid-Open No. Hei 6-339620) are also performed. However, when a crosslinked structure is introduced, the hydrophilic portion is reduced by the introduction of the crosslinked structure, and the stain resistance is impaired, so that the essential problem has not been solved.

[0004]

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrafiltration membrane having high permeate and high contamination. The present inventors can solve the above problem by forming an ultrafiltration membrane in which both materials are in a phase-separated state using a hydrophobic polymer and a polyvinyl alcohol having a specific hydrophilicity and a specific degree of saponification. As a result, the present invention has been completed. Further, in the ultrafiltration membrane of the present invention, a hydrophilic polymer can be easily extracted using alcohols, and the amount of permeated water can be improved.

The present invention relates to an ultrafiltration membrane comprising a hydrophilic polymer and a hydrophobic polymer, wherein both polymers are in a phase-separated state, wherein the hydrophilic polymer has a saponification degree of 5 to 50%. An object of the present invention is to provide an ultrafiltration membrane using polyvinyl alcohol. The ultrafiltration membrane of the present invention has both a high amount of permeated water and contamination resistance. Its water permeability is 100 l / m ² / hr
(Measurement pressure: 0.1 MPa, measurement temperature: 25 ° C.) or more, and a membrane having a molecular weight cut off of 100,000 (based on polyethylene glycol) or more is preferable.

[0006] The content of the hydrophilic polymer is 5 in the ultrafiltration membrane.
It is preferable that the content is not less than 50% by weight and not less than 50% by weight. In the ultrafiltration membrane of the present invention, it is preferable to partially extract and remove the hydrophilic polymer in the membrane using alcohols.

(Hydrophobic polymer) Examples of the hydrophobic polymer used in the ultrafiltration membrane of the present invention include polysulfone-based and polyimide-based polymers. Of these, heat resistance,
Polysulfone-based polymers are preferred as having excellent acid / alkali resistance, oxidation resistance and the like. Specific examples of such polysulfone polymers include polysulfone, polyether sulfone (PES), and polyphenyl ether sulfone. The molecular weight of these hydrophobic polymers is 2 to 10
And more preferably 30,000 to 80,000. If the molecular weight of the hydrophobic polymer is larger than 100,000, the cohesive force at the time of gelation is too strong and the pore size becomes small, so that a sufficient water permeability cannot be obtained. When the molecular weight is less than 20,000, the mechanical strength of the obtained ultrafiltration membrane is impaired.

(Hydrophilic polymer) In the ultrafiltration membrane of the present invention, a hydrophilic polymer is used to impart stain resistance to the hydrophobic polymer. Such a hydrophilic polymer is required to form a phase-separable state with the hydrophobic polymer. This phase separation structure
It is suitable for improving the amount of permeated water by extracting a hydrophilic polymer component with alcohols. Since the hydrophilic polymer is insoluble in water, polyvinyl alcohol (PVA) having a saponification degree of 5 to 50% is preferable. When the degree of saponification of PVA is less than 5%, the amount of hydrophilic OH groups is small, so that sufficient stain resistance cannot be obtained and the stain is easily caused. On the other hand, if the degree of saponification is higher than 50%, it becomes easy to dissolve in water, and PVA dissolves into the gelled phase at the time of film formation, and sufficient hydrophilicity cannot be imparted to the ultrafiltration membrane.

The amount of the hydrophilic high molecular weight used is preferably 5% by weight or more and less than 50% by weight in the ultrafiltration membrane. If the amount of the hydrophilic polymer is more than this, the strength of the hydrophobic polymer is reduced.

(Preparation of membrane forming solution)

In preparing a film-forming solution using the above-mentioned polymer compound, any of known solvents that dissolve both of these polymers may be used. Examples of such a solvent include nitrogen-containing compounds such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide, pyridine, diethylene glycol, diethylene glycol dimethyl ether,
Examples thereof include polyhydric alcohols such as diethylene glycol diethyl ether and diethylene glycol dibutyl ether and derivatives thereof, ether-acetals such as 1,4-dioxane, tetrahydrofuran, and ethyl butyl ether, and sulfolane. These solvents may be used alone or as a mixture of two or more. Furthermore,
Poor solvents such as water, alcohols such as methanol, ethanol and isopropanol and glycerin may be added in a blending amount of 30% by weight or less.

In preparing the film-forming solution, a polymer solution having a concentration of 5 to 50% by weight, preferably 10 to 30% by weight is prepared using the above-mentioned solvent. The polymer concentration of the film forming solution is 5
If the amount is less than 10% by weight, a uniform film cannot be formed due to low solution viscosity. On the other hand, when the solution concentration is higher than 50% by weight, the film is difficult to form because the viscosity is too high, and the film is dense and the desired film structure cannot be formed.
The temperature of these film forming solutions is preferably adjusted to 0 to 95 ° C, preferably 0 to 80 ° C.

(Membraning) In order to produce the ultrafiltration membrane of the present invention, various methods known in the art can be used by using the above membrane-forming solution. Among them, the method using the wet phase inversion film forming method will be described below.

As the membrane shape, any of conventionally known shapes such as a hollow fiber shape, a flat membrane shape, and a tube shape can be adopted. A known method can be used for film formation.

In the case of a flat film, for example, the solution is applied to a nonwoven fabric substrate by a casting or dipping method and then immersed in a coagulating liquid. The coating thickness of the solution on these substrates is 25 to 400 μm, preferably 30 to 250 μm.
It is.

In order to produce a hollow fiber spinning solution, the membrane forming solution is discharged together with an injection liquid from a double annular nozzle and then immersed in a coagulation liquid to obtain a hollow fiber membrane. As the injection liquid, water, alcohols such as methanol, ethanol and isopropyl alcohol, polyhydric alcohols such as glycerin, and a mixed solution containing at least two of these are used. Further, a solvent for dissolving the film material, for example, N-
Nitrogen-containing compounds such as methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide, and pyridine; polyhydric alcohols such as diethylene glycol, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether; and derivatives thereof. ,
Mixing ether-acetals such as 1,4-dioxane, tetrahydrofuran, and ethyl butyl ether and sulfolane at a ratio of 50% by weight or less is also suitable for increasing the water permeability. Of these solvents, N-methyl-2
-Pyrrolidone, N, N-dimethylacetamide, N, N-
Nitrogen-containing compounds such as dimethylformamide, dimethylsulfoxide and pyridine are preferably used.

The coagulating solution used for forming a flat membrane or a hollow fiber membrane is not particularly limited as long as it is miscible with the solvent for preparing the membrane forming solution and does not dissolve the hydrophobic polymer. And alcohols such as methanol, ethanol, isopropyl alcohol and the like, and a mixed solution comprising two or more thereof.

The temperature of these coagulating liquids is 0 to 100 ° C., preferably 20 to 95 ° C. 100 ° C. is a limit value when water is used, and if it is 20 ° C. or less, the membrane becomes too dense and causes a decrease in the amount of permeated water.

As described above, the ultrafiltration membrane of the present invention can take various forms, but a hollow fiber membrane is most preferred.

The ultrafiltration membrane of the present invention has a water permeability of 100 l /
m ² / hr (measuring pressure: 0.1 MPa, measuring temperature: 25
C) or more, and the molecular weight cut off is preferably 100,000 (based on polyethylene glycol) or more. The amount of permeated water is 100 l /
When it is smaller than m ² / hr and / or when the molecular weight cut off is less than 100,000, practical problems occur. That is, when the permeated water amount is low, the system for increasing the membrane area when processing a predetermined water amount becomes large. Also, when the molecular weight cut off is small,
Clogging (fouling) due to small organic substances and the like makes stable operation impossible.

Further, the ratio of the hydrophilic polymer in the obtained ultrafiltration membrane is preferably 5% by weight or more and less than 50% by weight. If it is 50% by weight or more, the strength of the hydrophobic polymer is reduced due to the influence of the hydrophilic polymer. On the other hand, if it is less than 5% by weight, sufficient stain resistance cannot be obtained.

In order to further improve the amount of water permeated through the obtained membrane, the membrane may be extracted and removed with a solvent that dissolves the hydrophilic polymer (PVA) but does not dissolve the hydrophobic polymer. Alcohols are suitably used for the extraction of such a hydrophilic polymer (PVA). As such alcohols, methanol, ethanol, isopropyl alcohol and the like are used. These may be used as a mixture, or may be further diluted with water for safety considerations.

The ratio of the remaining hydrophilic polymer in the ultrafiltration membrane subjected to the extraction treatment is preferably 5% by weight or more and less than 50% by weight. Therefore, when performing the treatment, the ratio of the hydrophilic polymer in the base film needs to be more than 5% by weight. Further, as described above, the content is preferably less than 50% by weight from the viewpoint of mechanical problems.
The definition of this range is the same as the reason described above.

That is, when focusing on giving the mechanical strength of the hollow fiber membrane, if the PVA content is 50% or more before the PVA extraction and removal, the mechanical strength dependent on the hydrophobic polymer PES decreases. Would. That is, the hollow fiber membrane of the present invention forms a phase-separated structure (sea-island structure, in which PES exists in a PVA site island shape in a main skeleton) before PVA removal, and its basic skeleton (PES site) is PVA. Must be formed before removal.

The mechanical strength and stain resistance are characteristics of the membrane of the present invention. In order to maintain the mechanical strength, the content of the hydrophobic polymer PES contributing to the mechanical strength must be 50% before removing PVA.
% Or more.

[0026]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 Polyethersulfone (Ultrason ^™ E6020P) using N-methyl 2-pyrrolidone as a solvent
A solution of 18% by weight (manufactured by BASF, average molecular weight: 58,000) and 4% by weight of polyvinyl alcohol (PVA-L-7514 (manufactured by Nippon Gohsei), saponification degree: about 40%) was prepared (solution temperature: 65).
° C). The obtained solution was extruded together with the injection liquid from a double annular nozzle and spinning was performed. At this time, a 1/1 solution of water / dimethylformamide (temperature: 65 ° C.) was used as the injection solution. Water at 85 ° C. was used as the coagulating liquid.

The amount of pure water permeated through the obtained hollow fiber membrane was 246 l / m ² / hr at a pressure of 0.1 MPa and a temperature of 25 ° C. In addition, it was confirmed that the molecular weight cut off was 300,000 based on polyethylene glycol. The PVA content was 18% by weight.

Alb of 500 ppm as a stain resistance evaluation
Min solution at 1kgf / cm for 30 minutes ²Before and after
As a result of measuring the retention of the amount of pure water permeated water, the retention was 40
%Met.

Example 2 The hollow fiber membrane obtained in Example 1 was immersed in an isopropyl alcohol (IPA) solution for 15 hours to extract PVA. PVA content after extraction is 1
5% by weight (3 points reduced by extraction). The amount of permeated pure water obtained was 320 l / m ² / hr at a pressure of 0.1 MPa and a temperature of 25 ° C. (320 l / m ² / hr / 246 l / m ² /hr=1.3 by extraction).
0, or 30% increase). 50 as contamination resistance evaluation
As a result of measuring the retention of the amount of pure water permeated before and after passing the 0 pp albumin solution at 1 kgf / cm ² for 30 minutes, the retention was 35%.

Comparative Example 1 Spinning / evaluation was carried out in the same manner as in Example 1, except that PVA was not used. The amount of pure water permeated through the hollow fiber membrane was 0.1 MPa,
80 l / m ² / hr at a temperature of 25 ° C. The molecular weight cut off was 50,000 based on polyethylene glycol. As a result of measuring the retention of pure water permeated water before and after passing a 500 pp albumin solution at 0.1 MPa for 30 minutes as a stain resistance evaluation, the retention was 8%.

[0032]

The ultrafiltration membrane of the present invention has high permeation water and high contamination.

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Claims (4)

[Claims] 1. A method comprising: a hydrophilic polymer and a hydrophobic polymer;
And an ultrafiltration membrane in which both polymers are in a phase separated state,
An ultrafiltration membrane comprising polyvinyl alcohol having a saponification degree of 5 to 50% as the hydrophilic polymer. 2. The method according to claim 1, wherein the water permeability is 100 l / m ² / hr (measuring pressure: 0.1 MPa, measuring temperature: 25 ° C.) or more, and the molecular weight cut off is 100,000 (based on polyethylene glycol). Filtration membrane. 3. The ultrafiltration membrane according to claim 1, wherein the content of the hydrophilic polymer in the ultrafiltration membrane is 5% by weight or more and less than 50% by weight. 4. The ultrafiltration membrane according to claim 1, wherein the membrane structure is a hollow fiber.