JPH11179176A - Composite porous polysulfone membrane and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve pollution resistance without remarkable deterioration of the permeation and separation performance of an original porous polysulfone membrane. SOLUTION: A solution of 0.05-2 wt.% of a hydrophilic organic polymer like polyvinyl butyral having a molecular weight smaller than the fractional molecular weight of a porous polysulfone membrane is applied on the polysulfone membrane, and thereafter, the solution is heated and dried, the hydrophilic organic polymer is adhered to the surfaces of pores to be held to produce a composite porous polysulfone membrane the surface zeta potential of which is at the lowest -20 mV at pH 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polysulfone composite porous membrane and a method for producing the same. More specifically, the present invention relates to a polysulfone composite porous membrane which is preferably used as an ultrafiltration membrane, a microfiltration membrane, a support membrane of a reverse osmosis composite membrane, etc., and which is not easily contaminated by a membrane surface, and a method for producing the same.

[0002]

2. Description of the Related Art Porous polysulfone membranes are excellent in heat resistance and chemical resistance. Therefore, ultrapure water production, purification, concentration and disinfection in the pharmaceutical and food industries, and treatment of industrial wastewater and domestic wastewater. It is used in various fields. But,
Although the polysulfone porous membrane has the above excellent properties, it is hydrophobic, so that organic substances are easily adsorbed on the membrane and contaminated, and the permeation performance may be rapidly lowered.

Various methods for modifying the surface of a polysulfone membrane, ie, a hydrophilization method, have been proposed to improve the contamination resistance of the porous polysulfone membrane. For example, a method in which a water-soluble polymer such as polyethylene glycol, polyvinylpyrrolidone, or polyvinyl alcohol is attached to a porous polysulfone membrane and crosslinked (JP-A-61-268302, JP-A-6-268302).
JP-A-2-125802, JP-A-63-31501, etc.), a method of introducing a sulfone group into a polysulfone porous membrane (JP-A-63-54452, etc.), a method in which a hydrophilic polyphenol is added to the surface of a polysulfone porous membrane. A method of attaching (JP-A-5-301036), a method of hydrophilizing the film surface by plasma treatment or sputter etching (JP-A-54-95982, JP-A-59-186)
604) and a method of attaching a water-insoluble hydrophilic polymer such as an ethylene-vinyl alcohol copolymer (JP-A-8-131794, JP-A-6-170193).
And the like are known.

[0004]

However, these methods have the following disadvantages. (1) The hydrophilizing agent is eluted and the effect of preventing the contamination of the membrane surface is lacking. (2) The effect of preventing film surface contamination is insufficient. (3) The fractionation performance of the membrane is significantly changed by the hydrophilization treatment, and the permeation performance is significantly reduced. (4) Even if the effect of the hydrophilic treatment is sufficient, the treatment operation is complicated or the treatment cost is high, which is not suitable for industrial implementation. However, it is not always a practical and effective method for preventing film surface contamination.

[0005] The present invention has been made in view of the above problems, and a polysulfone composite porous membrane having improved contamination resistance without significantly lowering the original permeation performance and separation performance of the polysulfone porous membrane. It is an object of the present invention to provide a manufacturing method thereof.

[0006]

In order to achieve the above object, the polysulfone composite porous membrane of the present invention has a hydrophilic organic polymer adhered and held on the pore surface of the polysulfone porous membrane and has a pH of 6 Surface zeta potential is -20mV
It is characterized by the above. By using such a polysulfone porous membrane, it becomes possible to improve the contamination resistance without greatly reducing the original permeation performance and separation performance of the polysulfone porous membrane.

In the polysulfone porous membrane, it is preferable that the organic polymer is a polyvinyl alcohol polymer.

Further, the degree of saponification of the polyvinyl alcohol-based polymer is preferably at least 90 mol%. According to this preferred example, the crystallization of the polyvinyl alcohol-based polymer proceeds easily, and the polyvinyl alcohol-based polymer is easily insolubilized in water or an aqueous solution.

Further, the method for producing a polysulfone composite porous membrane of the present invention is a method for producing a polysulfone composite porous membrane, which comprises a step of applying a solution containing a hydrophilic organic polymer to the polysulfone porous membrane. The average molecular weight of the organic polymer is smaller than the cut-off molecular weight of the polysulfone porous membrane, and the concentration of the organic polymer in the solution is 0.0
5 to 2% by weight. According to such a production method, a hydrophilic organic polymer is adhered and held on the surface of the pores, and the surface zeta potential at pH 6 is -20 m
The polysulfone composite porous membrane having a V or more can be easily and rationally manufactured.

Here, the molecular weight cutoff of the polysulfone porous membrane can be determined by using polyethylene oxide (PEO) as a standard substance. This fractional molecular weight is
Specifically, PEO aqueous solutions having various average molecular weights with a concentration of 500 ppm were filtered under the conditions of an operating pressure of 1 kgf / cm ² and a linear velocity of the membrane surface of 2 m / sec, and the rejection corresponding to each average molecular weight was measured. The average molecular weight of PEO when the rejection obtained by plotting the results on a graph is 90%. Here, the rejection rate (%) = 1− (concentration of permeate / concentration of stock solution) × 100.

In the method for producing a polysulfone composite porous membrane, the organic polymer is preferably a polyvinyl alcohol-based polymer.

Further, in the method for producing a polysulfone composite porous membrane, a step of drying the polysulfone porous membrane at 100 to 180 ° C. is performed after the step of applying the solution to the polysulfone porous membrane. Is preferred. By setting the temperature in the drying treatment to 100 ° C. or higher, crystallization can be sufficiently advanced, and the elution of the attached organic polymer into water or the like can be suppressed for a long time.
On the other hand, by setting the temperature to 180 ° C. or lower, melting and thermal decomposition of the organic polymer can be suppressed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a porous polysulfone membrane used as a substrate is made of, for example, a polysulfone resin having a repeating unit represented by the following general formulas (I) to (IV).

[0014]

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[0015]

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[0016]

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[0017]

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The structure of the polysulfone porous membrane has an asymmetric structure composed of a dense layer on the membrane surface and a porous layer formed integrally with this layer, and a homogeneous structure in which substantially uniform microporosity exists in the thickness direction of the membrane. Any of the structures may be used. Further, the shape of the polysulfone porous membrane is not particularly limited,
It is preferable to use a sheet-like membrane supported by a reinforcing material such as a nonwoven fabric because the production of a polysulfone composite porous membrane can be relatively easily continuous.

The polysulfone porous membrane is preferably a membrane having a molecular weight cut-off of 20,000 or more, more preferably 100,000 or more.
This is because, when a polysulfone composite porous membrane is used, it is easy to use the porous polysulfone membrane that is the base material while basically maintaining the permeation performance.

In the present invention, the hydrophilic organic polymer introduced into the pores of the polysulfone porous membrane serving as the base material and adhered and retained on the surface of the pores is polyethylene glycol-based.
, Polyethyleneimine, polyacrylic acid, polyvinylpyrrolidone, etc., but a polyvinyl alcohol polymer is preferred. Here, the polyvinyl alcohol-based polymer is a polymer having vinyl alcohol as a main monomer, and includes polyvinyl alcohol and a copolymer of polyvinyl alcohol and another vinyl monomer. The vinyl monomer mentioned here includes, for example, ethylene, vinylpyrrolidone, acrylonitrile, and vinyl chloride. The polyvinyl alcohol copolymer preferably contains such a vinyl monomer in less than 50 mol%.

As the polyvinyl alcohol-based polymer,
Polyvinyl alcohol is preferred. Polyvinyl alcohol has, for example, an average degree of polymerization of 200 to 3500 and a degree of saponification of 1
Although 0 to 100 mol% can be used, it preferably has a saponification degree of 90 mol% or more, more preferably 99 to 100 mol%. Such polyvinyl alcohol having a high degree of saponification is soluble in hot water due to the influence of intermolecular hydrogen bonds, but shows water insolubility at around room temperature.

When polyvinyl alcohol having a degree of saponification of 90 mol% or more (more preferably 99 to 100 mol%) is used, a sufficient crystal structure is formed without remaining vinyl acetate groups hindering crystallization. Is done. Therefore, as described above, the polyvinyl alcohol becomes insoluble in water or an aqueous solution in a normal use temperature range of the polysulfone composite porous membrane, and the polyvinyl alcohol can be stably held in the pores. When polyvinyl alcohol that satisfies such a condition for the degree of saponification is used, the hydrophilicity increases due to the large number of hydroxyl groups (OH groups) on the surface of the film in contact with the treated water, so that the stain resistance (organic Resistance to contaminants). Further, a decrease in the amount of permeated water due to the compounding is suppressed, and very good membrane performance can be realized.

It is also preferable to add a saponifier during the production process in order to achieve the preferred conditions for the degree of saponification. When a saponifying agent is used, the same advantageous effects as described above can be obtained even when the degree of saponification of the polyvinyl alcohol used is low, but sufficient saponification occurs within a practical film-forming time. Preferably, the degree of saponification of polyvinyl alcohol is 10 mol% or more. The saponifying agent is not particularly limited, but sodium hydroxide, potassium hydroxide and the like are preferably used.

The polysulfone composite porous membrane of the present invention is a hydrophilic organic polymer solution (preferably a polyvinyl alcohol polymer solution) dissolved in a polysulfone porous membrane, for example, in a mixed solvent of lower alcohol and water. And then drying the porous membrane.
The lower alcohol / water mixed solvent is used to make the membrane easy to wet and to allow the polyvinyl alcohol-based polymer solution to penetrate into the inside of the membrane. The proportion of the lower alcohol is 20 to 70% by weight, and more preferably 30 to 30% by weight. ~ 50% by weight
Is preferred. In addition, as lower alcohol, methanol, ethanol, and isopropanol are preferably used.

The concentration of the organic polymer solution is 0.05 to 2% by weight as described above, and preferably 0.1 to 1% by weight. By making the concentration 0.05% or more,
It is easy to secure the amount of the organic polymer adhering to the membrane and make the surface zeta potential at pH 6 equal to or higher than -20 mV. On the other hand, by setting the concentration to 2% or less, the solution can be easily permeated into the pores of the membrane. If the concentration is too high and the viscous resistance is too large, a barrier layer of an organic polymer is formed on the surface of the membrane, and the permeability of the membrane may be impaired.

In order to prevent the formation of a barrier layer on the membrane surface, as described above, an organic polymer having an average molecular weight smaller than the fractional molecular weight of the polysulfone porous membrane is selected. Specifically, the average molecular weight of polyvinyl alcohol is preferably from 20,000 to 200,000, although it depends on the molecular weight cut-off of the porous membrane used.

The method for applying the organic polymer solution to the polysulfone porous membrane is not particularly limited, and examples thereof include an immersion method, a transfer method, and a spraying method. In particular, when the polysulfone porous membrane is in the form of a sheet, , A roll coater, a gravure coater, a bar coater, a die coater and the like are preferable.

The polysulfone composite porous membrane of the present invention is obtained by heating and drying the polysulfone porous membrane coated with the organic polymer solution at a temperature of 100 to 180 ° C., preferably 130 to 160 ° C. as described above. be able to.
By drying in this temperature range, the organic polymer is firmly adhered and retained on the pore surface of the membrane without thermal decomposition and crystallized, and becomes insoluble in water or a lower alcohol / water mixed solvent. .

In the polysulfone porous membrane obtained by the above-described method, a polymer such as a polyvinyl alcohol-based polymer is adhered and held almost uniformly on the pore surface. Such a polysulfone composite porous membrane preferably has no apparent polymer-adhered layer on its surface even when observed at a magnification of about 20,000 with a scanning electron microscope.

However, this polysulfone composite porous membrane can be distinguished from an untreated membrane by, for example, measuring the surface zeta potential. The surface zeta potential at pH 6 is -20 mV or more, and more preferably As shown in the examples, values of -18 mV to -8 mV are shown.
The polysulfone composite porous membrane preferably has a thickness of 5 μm.
Permeated water volume of m ³ / m ² · day · kgf / cm ² or more (measuring temperature 25 ° C)
To enable practical solution processing.

[0031]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these examples. (Examples 1 to 3 and Comparative Examples 1 to 3) Polyvinyl alcohol (PVA) having a degree of saponification of 99 mol% and a degree of polymerization of 1700 (average molecular weight of about 75,000) was added to isopropanol /
Dissolved in a mixed solvent of water = 3/7 (weight ratio),
PV at each concentration of 2, 0.1, 0.5, 1, 2.5% by weight
A solution was prepared.

Each of these solutions was subjected to a molecular weight cut off of 750,000, 25
The surface of a sheet-like polysulfone porous membrane (NTU-3175M, manufactured by Nitto Denko Corporation) reinforced with a nonwoven fabric having a permeated water amount of 50 m ³ / m ² · day · kgf / cm ² at ℃ was coated with a bar coater. After one minute, it was dried in a drying oven at 130 ° C. for 5 minutes.

After the obtained membrane was wetted with 30% by weight of isopropanol, the amount of permeated water, the amount of adsorbed protein at pH 7 and the surface zeta potential were measured. Note that γ-globulin as a standard protein was used for the adsorption amount measurement.

The zeta potential was measured using an electrophoretic light scattering device ELS-800 manufactured by Otsuka Electronics Co., Ltd., and the composite porous membrane sufficiently washed with water was subjected to electrophoretic measurement in a NaCl solution having a pH of 6.0. It was calculated from the electrical mobility using the Smoluchouski equation shown below.

U = εζ / 4πη where U is the electric mobility, ε is the dielectric constant of the solution, and η is the viscosity of the solution (the zeta potential is determined by ζ = 4πηU / ε).

Specifically, the zeta potential was measured using a membrane sample having a size of 30 × 60 mm, and standard particles for electrophoresis were polystyrene particles (particle diameter: 520 nm) whose surfaces were coated with hydroxypropylcellulose.
What was dispersed in a 0 mM NaCl solution was used.

From the results of the measurements shown in Table 1, Examples 1 to 5 in which the PVA concentrations were 0.1, 0.5 and 1% by weight, respectively.
The polysulfone composite porous membrane of No. 3 has a surface zeta potential of −
It is more than 20 mV and is more hydrophilic than the membrane of Comparative Example 1 to which PVA is not attached (untreated membrane). As a result, the amount of adsorbed protein is about 1/2 or less than that of the untreated membrane. It was confirmed that: On the other hand, it was also confirmed that the permeated water amount was 80% or more of the untreated membrane, and a practical solution processing ability was maintained.

In the membrane of Comparative Example 2 treated with a PVA solution having a low concentration of 0.02% by weight, both the surface zeta potential and the amount of adsorbed protein were almost the same as those of the untreated membrane, and the stain resistance was improved. I couldn't. On the other hand, in the membrane of Comparative Example 3 treated with the PVA solution having a high concentration of 2.5% by weight, the stain resistance was remarkably improved, but the permeation performance was completely lost. When a cross section of this film was observed with a scanning electron microscope at a magnification of 4,000 times, a dense layer having a thickness of about 1 μm considered to be a PVA layer was observed.

[0039]

[Table 1]

Example 4 PVA having a degree of saponification of 99 mol% and a degree of polymerization of 700 (average molecular weight of about 30,000) was dissolved in a mixed solvent of isopropanol / water = 3/7 (weight ratio). A weight percent PVA solution was prepared. The solution fractional molecular weight of 50,000, and permeate flow 10m ³ / m ² · da at 25 ° C.
It is applied to the surface of a sheet-like polysulfone porous membrane (NTU-3150, manufactured by Nitto Denko Corporation) reinforced with a nonwoven fabric of y · kgf / cm ^{2 using} a bar coater, and after 1 minute, dried in a drying oven at 130 ° C. Dried for minutes.

When the surface zeta potential and the amount of adsorbed protein of this membrane were measured, they were -15 mV and 100 μg / c, respectively.
m ² . The amount of permeated water at 25 ° C. is 9.5 m
³ / m ² · day · kgf / cm ² , showing a retention of 95% as compared with the untreated membrane. Furthermore, after this membrane was immersed in pure water at 50 ° C. for one month, the surface zeta potential and the amount of adsorbed protein were measured. As a result, PVA was eluted at -15 mV and 95 μg / cm ² , respectively, with almost no change. It was confirmed that the film adhered firmly to the film without any problem.

(Example 5) The drying conditions in Example 4 were changed.
Same as Example 4 except for 30 minutes at room temperature (25 ° C.)
Then, PVA was attached to the polysulfone porous membrane. This
Of the surface zeta potential and the amount of protein adsorbed on the membrane
Roller, each -14mV, 100μg / cm ^TwoAnd both
The characteristics were almost the same as those of Example 4. However, 5
Surface zeta potential after immersion in pure water at 0 ° C for one month and
When the protein adsorption amount was measured, each was -30 mV, 18
0 μg / cm^TwoMet. This change is caused by PV
It is estimated that A was eluted from the membrane.
When the temperature is about room temperature, the drying temperature is about 100-180 ° C.
In the longer term than the case where
Was confirmed.

Comparative Example 4 A saponification degree of 9 in Example 4.
9 mol%, degree of polymerization 2600 (average molecular weight about 114,0
PVA was adhered to the membrane in the same manner as in Example 4 except that the PVA of (00) was used to obtain a polysulfone composite porous membrane. When the surface zeta potential and the amount of adsorbed protein of this membrane were measured, they were -5 mV and 20 μg / cm ² , respectively. However, the amount of permeated water at 25 ° C. is 0.5 m ³
/ m ² · day · kgf / cm ² . When a cross section of this film was observed with a scanning electron microscope at a magnification of 4,000 times, P
A dense layer having a thickness of about 1 μm, which is considered to be a VA layer, was observed.

Example 6 Film of Example 1 and Comparative Example 1
Using the film (film not to adhere the PVA), respectively to produce a spiral module with a membrane area of about 5 m ^2, permeate flow industrial water as raw water 1.3m ³ / m ² · day, 95% recovery The operation was performed for one month by the quantitative filtration method under the following conditions. As a result, the operation pressure required for the quantitative filtration was 0.2 kgf / cm ² in any of the membranes at the initial stage, but 3.4 kgf / c in the membrane of Comparative Example 1 after one month.
m ² , indicating the progress of membrane surface contamination. On the other hand, in the membrane of Example 1, the operation pressure was 0.8 kgf / cm ² even after one month, and the effect of preventing the membrane surface from being adhered by PVA was confirmed.

[0045]

As described above, according to the present invention,
By making a polysulfone composite porous membrane in which a hydrophilic organic polymer is adhered and held on the pore surface of the polysulfone porous membrane and the surface zeta potential at pH 6 is -20 mV or more, the permeation performance of the polysulfone porous membrane is improved. It can be suitably used as an ultrafiltration membrane, a microfiltration membrane, or a reverse osmosis composite membrane having improved stain resistance while being retained. Further, according to the present invention, there is provided a method for producing a polysulfone composite porous membrane comprising a step of applying a solution containing a hydrophilic organic polymer to a polysulfone porous membrane, wherein the average molecular weight of the organic polymer is Smaller than the molecular weight cutoff of the porous membrane, the concentration of the organic polymer in the solution is 0.05
By using the method for producing a polysulfone composite porous membrane having a content of about 2% by weight, the polysulfone composite porous membrane of the present invention can be easily and rationally produced.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisao Hachisuka 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Kenichi Ikeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (6)

[Claims] 1. A polysulfone composite porous membrane, characterized in that a hydrophilic organic polymer is adhered and held on the pore surface of the polysulfone porous membrane, and that the surface zeta potential at pH 6 is -20 mV or more. 2. The polysulfone composite porous membrane according to claim 1, wherein the organic polymer is a polyvinyl alcohol-based polymer. 3. The polysulfone composite porous membrane according to claim 2, wherein the degree of saponification of the polyvinyl alcohol-based polymer is 90 mol% or more. 4. A method for producing a polysulfone composite porous membrane, comprising a step of applying a solution containing a hydrophilic organic polymer to a polysulfone porous membrane, wherein the organic polymer has an average molecular weight of the polysulfone porous membrane. The molecular weight of the organic polymer in the solution is less than 0.0
A method for producing a polysulfone composite porous membrane, which comprises 5 to 2% by weight. 5. The method according to claim 4, wherein the organic polymer is a polyvinyl alcohol-based polymer. 6. After the step of applying the solution to the polysulfone porous membrane, the polysulfone porous membrane is
The method for producing a polysulfone composite porous membrane according to claim 4 or 5, wherein a step of drying at 0 to 180 ° C is performed.