JPH10314555A - Polyacrylonitrile-based membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyacrylonitrile based precision filter membrane superior in water permeability and mechanical strength. SOLUTION: In a polyacrylonitrile based membrane composed of a sponge structure having no deficiency part such as voids within the membrane, a minimum hole diameter layer is provided with an average hole diameter of more than 0.05 μm and not more than 1 μm. Then, a precision filter membrane having a high mechanical strength and a high water permeability, which is suitable for preparing water such as city water required to be heated in a large quantity and collecting an enzyme from fermentation broth, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyacrylonitrile-based microfiltration membrane having excellent water permeability and mechanical strength.

[0002]

2. Description of the Related Art In recent years, the technology of using a membrane having a selective filtration property in a separation operation has been remarkably advanced, and is currently used in fields such as food industry, pharmaceutical industry, electronics industry, medical treatment, drinking water, and nuclear power condensate treatment. Has been put to practical use. As the material of the membrane, cellulose-based, polyamide-based, polyacrylonitrile-based, polycarbonate-based, and polysulfone-based resins are used. It has the advantages of excellent heat resistance and water permeability and good mechanical properties. Polyacrylonitrile-based membranes have been developed with emphasis on separation performance, water permeation performance, or mechanical strength, and various membrane structures and chemical compositions have been proposed according to the purpose.

[0003] For example, Japanese Patent Publication No. 60-39404 discloses a film structure comprising a dense layer, a porous layer, and huge pores. The membrane of this structure has excellent fractionation performance but low water permeability, so in applications where large quantities of water, such as waterworks, are purified, a large number of membrane modules must be used. And the processing cost increases.

On the other hand, Japanese Patent Application Laid-Open No. 63-190012 discloses a structure using an acrylonitrile polymer having a very high degree of polymerization, having a dense layer only on the outer surface of the film, and having no defective portions such as voids. Although this membrane is excellent in mechanical strength, it has insufficient water permeability. Also,
JP-A-6-65809 similarly discloses a membrane structure comprising a dense layer and huge pores using an acrylonitrile polymer having a very high degree of polymerization. Low strength and elongation are not preferred.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high mechanical strength and water permeation suitable for purifying water such as waterworks and recovering enzymes from fermentation broth which require a large volume of treatment. It is to provide a high precision filtration membrane.

[0006]

The present invention has solved the above-mentioned problems. That is, the present invention is characterized in that (1) in a polyacrylonitrile-based film having a sponge structure that does not include a defect part such as a void inside the film, the average pore size of the minimum pore size layer of the film is larger than 0.05 μm and 1 μm or less. (2) the polyacrylonitrile-based membrane of (1) above, wherein the membrane is a hollow fiber membrane; and (3) the outermost layer of the membrane (3) having a minimum pore size layer.
A polyacrylonitrile-based film.

Hereinafter, the structure of the film of the present invention will be described. The film of the present invention has a sponge (mesh) structure which is integrally continuous from one surface to the other surface of the film and substantially does not contain a defect site such as a void (hole) inside the film.
The void referred to here is a cavity having a diameter of 5 μm or more, and more preferably 10 μm or more. The membrane has a structure in which the average pore size of the minimum pore size layer of the membrane is greater than 0.05 μm and 1 μm or less. By setting the average pore diameter of the minimum pore diameter layer of the membrane to be larger than 0.05 μm and 1 μm or less, the water permeability of the membrane can be improved. The shape of the membrane is not limited, but is preferably a hollow fiber shape. Since the hollow fiber membrane can increase the effective membrane area per unit volume as compared with the flat membrane, there is an advantage that the membrane filtration device can be downsized.

Further, in the case of a hollow fiber membrane, it is preferable that the outermost layer of the membrane has a minimum pore size layer. For example, when filtering a large volume of water, if a method of filtering water from the outer surface to the inner surface (called “external pressure filtration”) is used, the filtration membrane area in the module becomes the outer surface, The effective membrane area can be further increased as compared with internal pressure filtration. In the case of external pressure filtration, in order to reduce clogging of the membrane, it is preferable that the minimum pore size layer of the membrane is located at or near the outermost layer of the membrane.

A typical example of the film of the present invention will be described in more detail with reference to the drawings. 1 is an electron micrograph showing a cross section perpendicular to the length direction of the hollow fiber membrane, that is, a part of a cross section in the film thickness direction, and FIG. 2 is an electron micrograph showing a state of the outer surface of the membrane. It is. As shown in FIG. 1, the membrane has a sponge structure in which the entire thickness does not include voids, and the minimum pore size layer of the membrane is on the outer surface of the membrane.

The minimum pore size layer of the membrane referred to in the present invention is a layer which has small pores, ie, small pores, of the polymer constituting the membrane in a cross section in the thickness direction when viewed microscopically, and contributes to the fractionation performance of the membrane. The average pore size of the pores present in the minimum pore size layer of the membrane (hereinafter referred to as the average pore size of the minimum pore size layer) is 0.05
It is larger than μm and 1 μm or less. If the average pore size of the minimum pore size layer is 0.05 μm or less, the water permeability of the membrane tends to decrease, and if it is more than 1 μm, the performance of removing fine particles tends to decrease. The average pore size of the preferred minimum pore size layer is more than 0.05 μm and 0.5 μm or less. Further, the thickness of the minimum pore size layer is arbitrary, but if it is too thick, water permeability is reduced, so that it is usually 30 μm or less, preferably 10 μm or less.
μm or less.

Hereinafter, an example of the method for producing a film of the present invention will be described. The hollow fiber membrane is discharged from a double annular nozzle together with the internal liquid from a film forming stock solution obtained by dissolving a polyacrylonitrile-based polymer in a mixed solvent of propylene carbonate and another organic solvent, passes through an air gap, and then solidifies. Manufactured by coagulation in a bath. In the case of a flat film, the film-forming stock solution is uniformly cast into a thin film on a flat plate having a smooth surface, on an endless belt, or on a rotating drum using a knife edge or the like, and is coagulated in a coagulation bath. It is manufactured by

As the polyacrylonitrile polymer used in the present invention, at least 70% by weight, preferably 85% to 100% by weight of acrylonitrile and one or two kinds of vinyl compounds copolymerizable with acrylonitrile. These are 30% by weight or less, preferably 0% to 15% by weight or less of acrylonitrile homopolymer or acrylonitrile copolymer. The intrinsic viscosity of the acrylonitrile polymer is preferably 0.4 or more and less than 2.0. If the intrinsic viscosity is less than 0.4, the strength of the film tends to be low, and if it is 2.0 or more, the solubility tends to be poor.

The vinyl compound is not particularly limited as long as it is a known compound having copolymerizability with acrylonitrile. Preferred copolymerization components include acrylic acid, methyl acrylate, ethyl acrylate and itacone. Acid, vinyl acetate, sodium acrylsulfonate, sodium methallylsulfonate, sodium p (para) -styrenesulfonate, hydroxyethyl methacrylate,
Examples thereof include ethyl triethyl ammonium methacrylate, ethyl trimethyl ammonium methacrylate, and vinylpyrrolidone.

Examples of the organic solvent for dissolving the acrylonitrile polymer include propylene carbonate, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene carbonate, N-methyl-2-pyrrolidone, and 2-pyrrolidone. And hexamethylenephosphamide. The mixed solvent of propylene carbonate and another organic solvent, which is important for obtaining the film of the present invention, is a mixture of propylene carbonate and at least one organic solvent other than the solvent (propylene carbonate). It is. Further, unless propylene carbonate is used, the film of the present invention is difficult to obtain.

The concentration of the acrylonitrile-based polymer in the film-forming stock solution is not particularly limited as long as it can be formed into a film and the obtained film has a performance as a film.
It is 5% by weight, preferably 10 to 30% by weight. In order to achieve high water permeation performance or a high molecular weight cut-off, the lower the acrylonitrile-based polymer concentration, the better.
% By weight is preferred. Further, for the purpose of controlling the viscosity of the stock solution and the dissolution state, it is also possible to add a plurality of non-solvents such as water, salts, polyvinylpyrrolidone, glycols and the like, and the kind and the addition amount may be determined as needed depending on the combination.

The internal liquid used in the production of the hollow fiber membrane is used for forming a hollow portion of the hollow fiber membrane. When a minimum pore size layer is formed on the outer surface, acrylonitrile such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene carbonate, propylene carbonate, N-methyl-2-pyrrolidone is used as the internal solution. An aqueous solution of a good solvent that dissolves the polymer is used. When a minimum pore size layer is formed on the inner surface, those described in a coagulation bath described later are employed as the internal liquid.

The aqueous solution of a good solvent is preferably an aqueous solution containing 50% by weight or more of a good solvent, preferably 75% by weight or more of a good solvent. In order to further reduce the filtration resistance in the inner surface layer of the membrane, the content is preferably 90% by weight or more. It is also possible to add glycols such as tetraethylene glycol and polyethylene glycol and non-solvents such as glycerin for the purpose of controlling the viscosity of the internal liquid.

The hollow fiber membrane can be formed using a known tube-in-orifice type double annular nozzle. More specifically, the hollow fiber-like membrane of the present invention is obtained by simultaneously discharging the above-mentioned stock solution and the internal solution from the double annular nozzle, passing through an air gap, and coagulating in a coagulation bath. Can be. Here, the air gap means a gap between the nozzle and the coagulation bath. When the air gap is surrounded by a cylindrical tube or the like and a gas having a certain temperature and humidity flows through the air gap at a certain flow rate, the hollow fiber membrane can be manufactured in a more stable state.

As the coagulation bath, for example, a liquid that does not dissolve the polymer such as water; alcohols such as methanol and ethanol; ethers; and aliphatic hydrocarbons such as n-hexane and n-heptane is used. Preferably, it is used. The solidification rate can also be controlled by adding the good solvent to the coagulation bath. In the case of a planar membrane, a minimum pore size layer is formed on the membrane surface on the side contacting the coagulation bath.

The temperature of the coagulation bath is from -30 ° C to 90 ° C, preferably from 0 ° C to 90 ° C, and more preferably from 0 ° C to 80 ° C. The temperature of the coagulation bath exceeds 90 ° C or -30
If the temperature is lower than ℃, the state of the surface of the film in the coagulation bath is difficult to be stabilized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Each measuring method is as follows. In addition, the hollow fiber membrane and the planar membrane used as the measurement samples were all completely impregnated with water.

The amount of water permeation of the hollow fiber membrane is determined by permeating ultrafiltration water at 25 ° C. from the inner surface to the outer surface of the hollow fiber membrane sample having a length of 50 mm, and the amount is liter / hr · m ² · a.
tm. However, the effective film area was converted to the inner surface.
The water permeability of the flat membrane is 25 m in ultrafiltration water with a diameter of 25 m.
The sample was permeated through a sample of a flat membrane punched out to a diameter of m, and the amount was expressed in liter / hr · m ² · atm.

The film strength was measured using an Autograph AGS-5D manufactured by Shimadzu Corporation at a sample length of 50 mm and a pulling speed of 10 mm / min. The breaking strength is
The load at break per hollow fiber membrane is expressed as the calculation per kg of the cross-sectional area of the membrane before pulling (kgf / cm ² ), and the elongation (elongation) is the length of the original length up to the break. (%).

The fractionation performance (A) is as follows:
0.2% by weight of an aqueous solution of sodium dodecyl sulfate.
A stock solution prepared such that uniform latex particles having a particle size of 132 μm (PS particles, 0.132 μm, manufactured by Seradyne Co., Ltd.) were suspended at a concentration of 0.02% by volume was 70 mm
When the filtration from the outer surface to the inner surface is performed under the cross flow conditions of 0.5 kgf / cm ² and the fluid linear velocity of 1 m / sec with respect to the hollow fiber membrane,
The rejection after minutes is shown. The fluid linear velocity was calculated using the area (see FIG. 3) obtained by subtracting the cross-sectional area calculated from the outer diameter of the hollow fiber membrane from the cross-sectional area of the cylindrical container. The concentration of latex particles in the undiluted filtrate was measured at a wavelength of 260 nm using an ultraviolet-visible spectrometer. In the case of a flat membrane, the rejection after 2 minutes is shown when a flat membrane punched to a diameter of 25 mm is incorporated in a filter holder and the stock solution is supplied at a membrane differential pressure of 0.5 kgf / cm ² .

The fractionation performance (B) was determined by using 0.1% by weight of dextran T-2000 (Pharmacia Biotec).
The procedure was the same as that for the fractionation performance (A), except that an aqueous solution of Dextran T-2000 manufactured by Company h was used.
The concentration was measured by a refractometer at a temperature of 25 ° C. The intrinsic viscosity of acrylonitrile polymer is Jo
urnal of polymer science
(A-1) According to the measurement method described in Volume 6, 147 to 157 (1968), measurement was carried out at 30 ° C. using N, N-dimethylformamide as a solvent.

Regarding the average pore size of the minimum pore size layer, the average pore size of the film having the minimum pore size layer on the surface of the membrane was determined by observing the membrane surface with an electron microscope and analyzing the image. The average pore size is represented by the following equation.

[0027]

(Equation 1)

For the membrane having the minimum pore size layer inside the membrane, the average pore size of the minimum pore size layer was measured by the air flow method described in ASTM F316-86.

[0029]

Example 1 Copolymer 16 having 91.5% by weight of acrylonitrile, 8.0% by weight of methyl acrylate, 0.5% by weight of sodium methallylsulfonate and intrinsic viscosity [η] = 1.2
12% by weight of polyvinylpyrrolidone (K17, manufactured by BASF) having a weight% and a weight average molecular weight of 9,000 was dissolved in a mixed solvent of 54% by weight of N-methyl-2-pyrrolidone and 18% by weight of propylene carbonate to form a uniform solution. . This solution was maintained at 60 ° C., and a spinneret (a double annular nozzle 0.5 mm-0. 5 mm) was prepared together with an internal solution composed of a mixed solution of 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of water.
(7 mm-1.3 mm) and immersed in a coagulation bath made of water at 80 ° C. through an air gap of 20 mm to complete coagulation. At this time, the area from the spinneret to the coagulation bath is surrounded by a cylindrical tube, and the temperature of the air gap in the tube is adjusted to 60 ° C.
The temperature and humidity were controlled at 100%. The spinning speed was fixed at 10 m / min. The obtained hollow fiber membrane had a minimum pore size layer on the outer surface, had no void in the cross section in the film thickness direction, and had a sponge structure. Table 1 shows the structure and performance of this film.

[0030]

Example 2 The stock solution used in Example 1 was cast on a glass plate to a thickness of 400 μm, and a mixture of 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of water was used.
The casting surface was immersed in a solution at a temperature of ° C. and solidified to obtain a planar film. The water permeability of the obtained membrane is 3000 liter / hr · m
^{It was 2} · atm (measured at 25 ° C.), had no voids in the cross section in the film thickness direction, and had a structure having a minimum pore diameter layer on the casting surface side. The average pore size of the minimum pore size layer was 0.15 μm. The fractionation performance (A) was 100%, and the fractionation performance (B) was 0%.

[0031]

Comparative Example 1 16% by weight of the polymer used in Example 1 and polyvinylpyrrolidone 12 used in Example 1
% By weight was dissolved in 72% by weight of N-methyl-2-pyrrolidone to obtain a homogeneous solution. A hollow fiber membrane was obtained in the same manner as in Example 1 except that this stock solution was used. Table 1 shows the structure and performance of the obtained hollow fiber membrane.

[0032]

[Table 1]

[0033]

According to the present invention, a polyacrylonitrile-based film having excellent water permeability and mechanical strength can be obtained.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 200) showing a cross section (part) of one embodiment of the hollow fiber filtration membrane of the present invention.

FIG. 2 is an electron micrograph (magnification: 50,000) of the outer surface of the hollow fiber filtration membrane shown in FIG.

FIG. 3 is a cross-sectional view illustrating positioning of a hollow fiber membrane and a container when measuring a fluid linear velocity.

[Procedure amendment]

[Submission date] May 26, 1997

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[Procedure amendment 2]

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Claims (1)

[Claims] 1. A polyacrylonitrile-based film having a sponge structure which does not include a void or the like in the inside of the film, wherein the average pore size of the smallest pore size layer of the film is larger than 0.05 μm and 1 μm or less. Acrylonitrile film.