JPH10235170A - Hollow fiber filtration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the filtration reliability and water permeation performance by forming a membrane of gradient structure in which pore diameters are varied continuously from the outer face of the membrane toward the inner face, forming dense layers on both faces of the membrane and also forming a plurality of pores running through the dense layer at least on one face. SOLUTION: This hollow fiber filtration membrane (hereinafter referred to as membrane) is composed of a polymer, for instance, a polysulfone polymer or the like, and formed into the hollow fiber shape having an inner face and an outer face, and also formed into a structure continuously integrated from one face of the membrane to the other face. Dense layers are formed on both faces of the membranes, and a continuos network structure is formed from one dense layer of the membrane to the other dense layer. The pores of the network structure are of the gradient structure in which the pores are formed larger or smaller concentrically as pores are closer to the surface of the membrane. Also a plurality of pores are opened running through the dense layer at least on one face of the membrane, and the average pore diameter of the pores opened on the inner face is preferably formed larger than the average pore diameter of the pores opened on the outer face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a hollow fiber microfiltration membrane having high water permeability and high reliability.

[0002]

2. Description of the Related Art A hollow fiber membrane can increase the effective membrane area per unit volume as compared with a flat membrane, so that the membrane filtration device can be downsized. In addition, when a hollow fiber membrane is used, it has excellent characteristics such as a uniform flow of fluid, and has been used in various fields.

[0003] As the structure of the hollow fiber membrane, there are two types of membranes, which are made with emphasis on membrane strength and have a uniform thickness as shown in Japanese Patent Publication No. 60-23130.
As shown in Japanese Patent Application Laid-Open No. 2-102722, it is roughly classified into a film having a gradient structure having a dense layer on the outer surface or in the vicinity of the outer surface, which has been developed with an emphasis on improving water permeability. However, in the above structure, the filtration resistance at the time of passing water is large, and as a result, the water permeability is insufficient. In the structure of the above, for example, rubbing between the membranes due to rapid pressure fluctuation during the filtration operation, or Hard solutes in the actual liquid during filtration from the surface to the inner surface may damage the outer surface or the dense layer near the outer surface that determines the membrane's fractionation performance, and the filtration reliability is not sufficient. I can't say.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable microfiltration membrane having high water permeability.

[0005]

The present invention has solved the above-mentioned problems. That is, the present invention provides (1) a film having a gradient structure in which the pore diameter changes continuously from the outer surface to the inner surface of the film, and has a dense layer on both surfaces of the film, and at least one surface has A hollow fiber filtration membrane having a plurality of holes opened through the dense layer, (2) having a slope structure in which the pore diameter increases from the outer surface to the inner surface of the membrane, and penetrating the dense layer on the inner surface; The hollow fiber filter membrane of (1) above, which has a plurality of open pores, and (3) the average of the number of pores which have a plurality of pores which are opened through the dense layer on both surfaces of the membrane and which are opened on the inner surface. The hollow fiber filter membrane according to the above (1) or (2), wherein the pore diameter is larger than the average pore diameter of the pores opened on the outer surface.

Hereinafter, the configuration of the hollow fiber membrane (hereinafter, also simply referred to as membrane) of the present invention will be described. The membrane is made of a polymer, for example, a polysulfone polymer, a vinylidene fluoride polymer, an acrylonitrile polymer,
Examples include methacrylic acid-based polymers, polyamide-based polymers, polyimide-based polymers, polyetherimide-based polymers, and cellulose-based polymers.

The membrane of the present invention has the shape of a hollow fiber having an inner surface and an outer surface, and is integrally formed from one surface (for example, the inner surface) to the other surface (for example, the outer surface) of the membrane. Consists of a continuous structure. The film has a dense layer on both surfaces and a continuous network structure from one dense layer to the other dense layer of the film. The pores of the network structure show an inclined structure that becomes concentrically larger or smaller as it goes to one surface in a cross section perpendicular to the length direction of the membrane. Further, the film of the present invention has a plurality of holes opened through the dense layer on at least one surface.

The through hole is preferably opened in the dense layer on the side where the hole of the inclined structure is large. For example, in the case of an inclined structure in which the hole diameter increases from the outer surface to the inner surface of the film, it is preferable that a hole penetrating through the dense layer is opened on the inner surface of the film. Further, in order to improve the water permeability of the membrane, through holes may be opened in the dense layers on both the inner and outer surfaces.
In this case, it is preferable that the average diameter of the holes opened on the inner surface is larger than the average diameter of the holes opened on the outer surface.

A typical example of the film of the present invention will be described in more detail with reference to the drawings. FIG. 1 is an electron micrograph of a cross section (part) perpendicular to the length direction of the hollow fiber membrane, and FIG. 2 is an electron micrograph showing the state of the inner surface of the membrane. As shown in FIG. 1, this membrane has layers on the outer surface and inner surface of the membrane where the structure is denser than the central part of the membrane. And has a network structure having anisotropy with respect to the pore diameter, which increases toward the inner surface. FIG. 2 shows a state in which a large number of holes penetrating the dense surface layer are opened on the dense inner surface. As another embodiment, in order to improve the water permeability of the membrane, the through holes may be opened not only in the dense layer on the inner surface but also in the dense layers on both the inner and outer surfaces.

[0010] In the present invention, the dense layer is a microscopic cross section perpendicular to the longitudinal direction of the hollow fiber membrane, in which the pores, ie, pores, of the polymer constituting the membrane are small, and the filtration reliability or A layer that contributes to fractionation performance. In FIG. 1, the inner surface has a pore size much smaller than the adjacent layer,
The outer surface following the smallest pore diameter layer of the inclined structure corresponds to this.
Further, the through-hole refers to a circular, elliptical or mesh-like hole of 0.01 μm or more penetrating the dense layer, preferably 0.05 μm to 50 μm in the case of the inner surface, and preferably in the case of the outer surface. A hole having a size of 0.01 μm to 1 μm.

Since the membrane of the present invention has a plurality of through holes in at least one of the dense layers on both surfaces, it can exhibit high water permeability while maintaining high filtration reliability. Further, in the present invention, by making the diameter of the through-holes of the dense layers on both surfaces smaller than the diameter of the solute to be prevented, even if the dense layer on one surface is damaged, the solute is formed by the other dense layer. It is possible to block things.

A typical example of the method for producing a hollow fiber membrane according to the present invention will be described below. The hollow fiber membrane of the present invention comprises a double annular nozzle comprising a membrane-forming stock solution consisting essentially of a film-forming polymer, a solvent for the polymer, and a specific additive, and an internal solution consisting of a high-concentration aqueous solution of a good solvent for the polymer. After passing through an air gap, and then coagulated in a coagulation bath.

The film-forming polymer used may be a polymer capable of forming a film by wet film-forming.
Examples include polysulfone-based polymers, vinylidene fluoride-based polymers, acrylonitrile-based polymers, methacrylic acid-based polymers, polyamide-based polymers, polyimide-based polymers, polyetherimide-based polymers, and cellulose-based polymers.

The additive may be any as long as it is compatible with the polymer. For example, in the case of a polysulfone polymer, tetraethylene glycol, triethylene glycol, nitrobenzene, tetrahydrofuran, dioxane, dimethyl carbonate, polyvinylpyrrolidone polymer,
Examples include polyethylene glycol polymers, isopropyl alcohol, methanol, ethanol, propanol, butanol, acetone, and methyl ethyl ketone.

The solvent used for dissolving the polymer and the additive dissolves both the polymer and the additive.
For example, when the polymer is a polysulfone-based polymer and the additive is a polyvinylpyrrolidone-based polymer, N-methyl-2-pyrrolidone, N, N-dimethylformamide,
N, N-dimethylacetamide and the like. The polymer concentration of the film-forming stock solution is not particularly limited as long as the film can be formed and the obtained film has a performance as a film in the range of 5 to 35% by weight, preferably 10 to 30% by weight. %. In order to achieve high water permeability or a high molecular weight cut-off, the lower the polymer concentration, the better the concentration of the polymer is 10 to 25% by weight.
Is preferred.

The concentration of the additive in the film forming solution depends on the type and molecular weight of the additive, but is 1 to 30% by weight, preferably 1% by weight or more and 25% by weight or less. Also,
For the purpose of controlling the viscosity of the stock solution and the dissolution state, it is possible to add a fourth component such as water or a salt, and the type and the amount of addition may be determined as needed depending on the combination. The internal liquid forms the hollow portion and the inner surface of the hollow fiber membrane, and in order to obtain a dense layer having through holes as shown in FIG. 1, the internal liquid induces phase separation from the stock solution for film formation. A liquid having the ability to form a liquid and having a viscosity of 15 cp (centipoise) or more at 20 ° C. is preferable, for example, ethylene glycol, propylene glycol, trimethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, −
Butyne-1,4-diol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, glycerin, tetraethylene glycol, polyethylene glycol 200, polyethylene glycol 30
0, polyethylene glycol 400 and the like. It also has the ability to induce phase separation and at 20 ° C.
As long as the liquid has a viscosity of cp (centipoise) or more, a mixed solution with water or a mixed solution with a polymer solvent may be used.

The hollow fiber filtration membrane of the present invention can be formed using a known tube-in-orifice type double annular nozzle. More specifically, it can be obtained by simultaneously discharging a film forming stock solution and an internal solution from the double annular nozzle, passing through a slight air gap, and immersing in a coagulation bath to coagulate. 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.
In addition, as one method of opening a through hole in the dense layer on the outer surface of the membrane, a non-solvent vapor of the used polymer may be caused to flow through the air gap, and the membrane forming stock solution may be phase-separated and opened.

Examples of the coagulation bath include water; methanol,
Liquids that do not dissolve polymers, such as alcohols such as ethanol; ethers; aliphatic hydrocarbons such as n-hexane and n-heptane, are used, but water is preferred. Also,
It is also possible to control the coagulation rate by adding a small amount of a solvent that dissolves the polymer to the coagulation bath. By coagulation in a coagulation bath, a dense layer is formed on the outer surface of the film.

The temperature of the coagulation bath is from -30 ° C to 90 ° C, preferably from 0 ° C to 90 ° C, more preferably from 0 ° C to 80 ° C. When the temperature of the coagulation bath exceeds 90 ° C. or is lower than −30 ° C., the state of the surface of the hollow fiber membrane in the coagulation bath is not easily stabilized.

[0020]

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. The hollow fiber filtration membranes used as measurement samples were all completely impregnated with water.

The amount of water permeated through the hollow fiber membrane is determined by passing 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 of water per liter / hr ·
It was expressed in m ² · atm. However, the effective film area was converted to the inner surface. The film strength was measured using an autograph AGS-5D manufactured by Shimadzu Corporation at a sample length of 30 mm and a pulling speed of 50 mm / min.

The breaking strength is expressed by the load at the time of breaking per hollow fiber filter membrane calculated by the membrane cross-sectional area before pulling (kgf / cm ² ), and the elongation (elongation) is expressed by the original length. And the length (%) extended until the fracture. The fractionation performance was determined by adding a 0.605 μm Uniform Latex Par to a 0.2 wt% aqueous solution of sodium dodecyl sulfate.
The rejection after 40 minutes when the stock solution prepared so that the particles had a volume of 0.02% by volume was filtered against the hollow fiber membrane at an average pressure of the input pressure and the output pressure of 0.5 kgf / cm ^2. Show.

The removal of the dense layer on the outer surface was carried out by shaving with a razor while using a stereoscopic microscope so as not to damage other layers. The size of the pores on the inner and outer surfaces of the membrane was measured by electron micrograph. The average pore diameter on the inner surface and the outer surface is a value represented by the following formula.

[0024]

(Equation 1)

[0025]

Example 1 Polysulfone (AMOCO Co. P-
3500) 19% by weight, polyethylene glycol having a weight average molecular weight of about 8,000 (PEG600 manufactured by Kanto Chemical Co., Ltd.)
0) 25% by weight was dissolved in 56% by weight of N-methyl-2-pyrrolidone to obtain a uniform solution. This was kept at 40 ° C., and polyethylene glycol (PEG2 manufactured by Kanto Chemical Co., Ltd.) was used.
00) A mixed solution of 95% by weight and 5% by weight of water (6% at 20 ° C.)
1 cp) together with the internal liquid, which was discharged from a spinneret (double annular nozzle 0.5 mm-0.7 mm-1.3 mm), passed through a 30 mm air gap, and immersed in a coagulation bath composed of 50 ° C. water. .

At this time, the space from the spinneret to the coagulation bath was surrounded by a cylindrical tube, and the humidity was controlled at 100% and the temperature was controlled at 30 ° C. while flowing nitrogen gas containing water vapor into the tube. The spinning speed was fixed at 10 m / min. Table 1 shows the structure and performance of this film.

[0027]

Example 2 Instead of the polysulfone used in Example 1, polyetherimide (GENERAL) was used as a polymer.
ELECTRIC Co. A membrane forming stock solution was prepared with the same composition ratio and conditions as in Example 1 except that Ultem 1010) was used, and spinning was performed under the same conditions as in Example 1 to obtain a hollow fiber filter membrane. Table 1 shows the structure and performance of the obtained hollow fiber membrane.

[0028]

COMPARATIVE EXAMPLE 1 Except for using the same membrane-forming stock solution as in Example 1 and a mixed solution of N-methyl-2-pyrrolidone 95% by weight and water 5% by weight (4 cp at 20 ° C.) as an internal coagulating liquid, Spinning was performed under the same conditions as in Example 1 to obtain a hollow fiber membrane.
Table 1 shows the structure and performance of the obtained hollow fiber filtration membrane.

[0029]

[Table 1]

[0030]

According to the present invention, a hollow fiber microfiltration membrane having a large water permeability and high filtration reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (350 times magnification) showing a cross section (part) of one embodiment of the hollow fiber filtration membrane of the present invention.

FIG. 2 is an electron micrograph (× 1,000) of the inner surface of the hollow fiber filtration membrane shown in FIG. 1.

[Procedure amendment]

[Submission date] March 7, 1997

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[Procedure amendment]

[Submission date] March 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

A typical example of the method for producing a hollow fiber membrane according to the present invention will be described below. Hollow fiber membranes of the present invention, the film-forming polymer, ejected solvent of the polymer, and the film-forming solution consisting essentially of certain additives together with the inner part liquid from a double annular nozzle, after passing through an air gap Manufactured by coagulation in a coagulation bath.

Claims (3)

[Claims] 1. A film having a gradient structure in which the pore size changes continuously from the outer surface to the inner surface of the film, wherein the film has a dense layer on both surfaces and a dense layer on at least one surface. A hollow fiber-shaped filtration membrane having a plurality of holes opened therethrough. 2. The film according to claim 1, wherein the film has an inclined structure in which the hole diameter increases from the outer surface to the inner surface, and the inner surface has a plurality of holes opened through the dense layer. Hollow fiber filtration membrane. 3. A membrane having a plurality of holes opened through the dense layer on both surfaces of the membrane, wherein the average diameter of the holes opened on the inner surface is larger than the average diameter of the holes opened on the outer surface. The hollow fiber filtration membrane according to claim 1 or 2, wherein