JPH03258330A - Porous hollow fiber membrane - Google Patents

Abstract

PURPOSE:To obtain a hydrophilic hollow fiber membrane having high water permeability, excellent fractionating property and small reduction of flux by forming such a porous structure comprising a dense layer of the inner surface and a reticular structure in a manner that the reticular structure partially has openings to give pores to the outer surface, and specifying the permeation rate for pure water to a certain value or larger. CONSTITUTION:The porous hollow fiber membrane contains 0.5-10% hydrophilic polymers (e.g. polyvinylpyrrolidone) to hydrophobic polymers (preferably, polysulfone or polyethersulfone). This membrane has a porous structure comprising 0.5-5mum-thick dense layer having fine pores of various shapes with 10-50% porosity and a reticular structure formed continuously to the dense layer. The outer surface of the membrane has pores with the maximum pore diameter of 0.5-5mum which are formed by partial opening of the reticular structure. The permeation rate for pure water of the membrane at 25 deg.C is specified to >=800l/m<2>.hr.kg/cm<2>. The obtd. porous hollow fiber membrane is excellent in water permeability and fractionating property, and moreover, it is hydrophilic.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a porous hollow fiber membrane, particularly a porous hollow fiber membrane having high water permeability, excellent fractionation properties, and excellent hydrophilicity. It is.

(Prior Art) In recent years, the technology of using selectively permeable membranes in separation operations has made remarkable progress and has been put into practical use in various fields. In particular, hollow fiber-shaped membranes are industrially advantageous because they have a large membrane area per occupied volume and can be used in large quantities. Materials for hollow fiber membranes include cellulose, polyamide, polyacrylonitrile, and polyvinyl alcohol.

Resins such as polysulfone are used. Among them, polysulfone resins are used in various applications because they have excellent physical and chemical properties such as heat resistance, acid resistance, alkali resistance, and oxidizing agent resistance, and are easy to form into films.

However, a drawback of hollow fiber membranes made of hydrophobic polymers such as polysulfone resins is that the permeation rate decreases significantly when the hollow fiber membranes are dried. As a method to solve this drawback, for example, Japanese Patent Application Laid-Open No. 58-104940
Hydrophilized polysulfone membranes containing hydrophilic polyvinylpyrrolidone in the membrane are described in Japanese Patent Application Laid-Open No. 61-93801. Also, JP-A-61-2383
No. 06 and Jikai No. 61-238834 use a spinning dope consisting of polysulfone resin, polyvinylpyrrolidone, a swelling agent, and a solvent to form pores tV with an average pore diameter of 500 A or more on both moat surfaces of the membrane. A hydrophilic polysulfone membrane with high water permeability has been described.

(Problem to be solved by the invention) However, the former hydrophilized polysulfone membrane has a pore size of 0.0
01~0. Since it is an asymmetric membrane with a skin layer having micropores of O5l1m, it has a problem of extremely low water permeability.In addition, the latter hydrophilized polysulfone membrane has micropores on the membrane surface with an average size of 500λ or more, so it has low water permeability. However, there was a problem in that the FLUX decreased significantly due to filtration due to the high fractionability.

Therefore, an object of the present invention is to provide a hydrophilic hollow fiber membrane that has high water permeability and excellent fractionation properties and exhibits a small decrease in FLUX during use. The present invention is a porous hollow fiber membrane containing 0.5 to 10 of a hydrophilic polymer to a hydrophobic polymer, the porous hollow fiber membrane having irregularly shaped micropores on its inner surface. Porosity 10-50
It has a porous structure consisting of a dense layer with a thickness of 0.5 to 5p and a network structure integrally and continuously formed in the dense layer, and the outer surface is one part of the network structure. It has pores with a maximum pore diameter of 0.5 to 5-5, and the pure water permeation rate at 25°C is 800 t/♂・hr-kp/-.
This is a porous hollow fiber membrane characterized by the above.

The shape of the micropores formed on the inner surface of the hollow fiber membrane is not particularly limited, and examples thereof include individual micropores, porous micropores in which pores are continuously connected, slit-like micropores, network micropores, and the like. The average pore diameter of such micropores is preferably 0.2txn or less; a pore diameter larger than this is not preferred because the surface strength of the membrane becomes small. The average pore diameter here is the value obtained by dividing the sum of the diameters of the maximum inscribed circles of all missing micropores measured from an electron micrograph of the surface by the total number of pores. These irregularly shaped micropores are present at a ratio of 50 to 50 mm, forming a dense IM with a thickness of 0.5 to 5 inches. In the present invention, the porosity refers to the ratio of the total pore area of micropores formed on the inner surface to the outer surface area, expressed as a percentage. If the porosity is less than 10 m, the water permeability will be low, and if it exceeds 50 m, the surface strength will decrease and the membrane will be difficult to handle, which is not preferable. Open area ratio is 1
A range of 0 to 30 is preferable in terms of the balance between membrane permeability and mechanical strength. Further, although it is preferable that the distribution density of the micropores be as uniform as possible, it may be non-uniform.

In addition, the hollow fiber membrane of the present invention has a porous network structure formed integrally and continuously in the dense layer formed on the inner surface, and the outer surface has the largest pore structure formed by opening a part of the network structure. Pore diameter 0.
It has pores of 1 to 5 Pi.

The network formed inside such a membrane has a large number of continuous pores, on average 1 to 5 holes, and there are no large cavities of 10 or more. Therefore, it has excellent compactability during long-term use and also has excellent strength. There are no particular restrictions on the shape or porosity of the pores on the outer surface, but it is desirable that the porosity is about the same as that on the inner surface, 10-50. If the maximum pore diameter exceeds 5Ixn, not only will pressure resistance become a problem, but when filtration is performed under external pressure, residue will easily accumulate inside the membrane, resulting in a rapid decrease in permeation rate, and chemical washing and backwashing will be difficult. This is undesirable because it tends to result in insufficient regeneration of the membrane.

Conversely, if the maximum pore diameter is smaller than 0.11 inch, the water permeability will be reduced.

The hollow fiber 1[11[ of the present invention] has a porous structure consisting of a dense layer and a network structure. And the thickness of the dense layer is 0.
Because it is as thin as 5~5Afri, for example, the pure water permeation rate at 25°C is 8004/ra'-hr- even though it blocks more than 90 particles of 135A? /- or more, showing high water permeability. Furthermore, when water is actually filtered, in external pressure filtration, particles of submicron order or larger are captured on the outer surface, and submicron or smaller substances such as dissolved polymers are captured inside the membrane or in a dense layer on the inner surface. That is, since the outer surface and the inside of the membrane play the role of a blur filter, a high permeation rate can be maintained with little decrease in permeation rate. On the other hand, internal pressure filtration has a dense layer on the inner surface, so it is effective for cross-flow one-way filtration, and the substances that pass through the membrane are difficult to remain inside the membrane, so they are less likely to be contaminated. Thread membranes have a dense layer and a porous structure integrated, and unlike composite membranes obtained by coating methods, there are problems with pinholes in the dense layer and peeling between the dense layer and the support layer.
l″i, not at all.

Furthermore, the hollow fiber membrane of the present invention has a hydrophilic polymer of 0.5 to 10 times more than a hydrophobic polymer in the membrane. Therefore, it has excellent hydrophilicity and adsorption of proteins, etc. is small. There is little decrease in permeation performance due to offshore passage.

In addition, a completely dry membrane can be produced without any substantial decrease in water permeability or dimensional change of the hollow fiber membrane due to drying. This is advantageous in many aspects such as handling of hollow fiber membranes, modularization, and transportation of modules, and can improve workability and productivity.

Next, the method for producing the porous mid-wall fiber membrane of the present invention will be explained.○ The spinning stock solution for producing the hollow fiber membrane of the present invention includes a hydrophobic polymer, a hydrophilic polymer, a pore-forming agent, and It consists of a polar solvent that dissolves

Hydrophobic polymers include, for example, polysulfone, polyj-titsulfone, polyvinyritine fluoride, vol; ethylene,
Examples include vinyl chloride. The former also has excellent heat resistance, chemical resistance, oxidizing agent resistance, and strength compared to polysulfone and polyether sulfone. 1. Hydrophilic polymers are suitable because they have a strong intermolecular cohesive force and are therefore easy to form into films.
Examples include, but are not limited to, poly]dilene 11 co--not haholyl alcohol copolymers of 00 or more and vinyl alcohol copolymers and modified polymers thereof. I don't care. 〃Dashi, hydrophobic polymer・
It is desirable that the polymer has excellent compatibility with the polymer in the solvent, and in the case of water-soluble polymers such as polyvinylhydrolidone', it is desirable that the polymer can be easily made insolubilized by crosslinking or the like. The higher the molecular weight, the smaller the amount of hydrophilic polymer added. In the case of water-soluble polymers, I7 is more likely to remain in the membrane, and there is less elution during water washing, hot water treatment, or when the membrane is used, so 1 m is preferable.

stomach. These hydrophilic polymers can be selected taking into account the S manufacturing process, suitability for each application, and the like.

In the hollow fiber membrane of the present invention, micropores are formed by microphase separation, and the micropore-forming agent is added for the purpose of facilitating the microphase separation. Conventional Eri, pore-forming agent and 17 alcohols such as methanol and ethanol, ethylene glycol, phlopylene gelicol, average molecular f
Many glycols such as polyethylene glycol with a low molecular weight of i400 to 20,000, inorganic salts such as Liα and ZnO2, and water are used, and the above-mentioned pore-forming agents can also be used in the present invention. The addition i of the pore-forming agent must be kept within a range that allows the spinning dope to remain uniform and transparent, but since the pore-forming agent is presumed to form the core of the pores, it is desirable to add it as much as possible. Molecules @400~20,000
Low molecular weight polyethylene glycol is suitable because it can be added in a large amount to the spinning dope. In addition, this low molecular weight polyethylene glycol is excellent in forming micropores and has the effect of thickening the spinning dope, so it has the advantage of improving the stability of spinning.

There are no restrictions on polar solvents as long as they can dissolve hydrophobic polymers, hydrophilic polymers, and pore-forming agents.1. Examples include N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, and the like.

The compositions of these four groups can be selected in any proportion, but in order to produce the hollow fiber membrane of the present invention, the spinning stock solution is subjected to phase separation at a temperature below a certain temperature (
It is preferable to prepare the phase separation type (low-temperature phase separation type) or to cause phase separation at a certain temperature or higher (high-temperature phase separation type).

The hollow fiber membrane of the present invention is manufactured by a known dry-wet method using the above-mentioned spinning dope. The internal coagulating liquid discharged from the center of the nozzle together with the spinning dope may be, for example, water, a mixture of water and a polar solvent, alcohols, glycols, etc. alone,
Or use a mixture of two or more of them. By changing the composition of this internal coagulation liquid, the structure near the inner surface, such as the shape of the micropores on the inner surface, the average pore diameter, the porosity, and the thickness of the dense layer, can be controlled.

The spinning stock solution discharged from the nozzle travels in the air (dry zone), and then is immersed in an external coagulation liquid mainly composed of water. In the present invention, by changing the length of this dry zone and the atmospheric humidity and temperature in the dry zone, the amount of moisture present in the dry zone is adjusted, thereby reducing the formation of pores on the outer surface of the hollow fiber membrane. Perform control for The length of this dry zone is suitably 0.1 to 200 cM, usually 1 to 5,051 cM, from the viewpoint of the balance between spinning stability and membrane performance. Also, the higher the humidity in the dry zone atmosphere, the more large pores are likely to form, leading to open pores! There will also be more.

The hollow fiber membrane coated with the coagulating liquid is then subjected to a moist heat treatment in a water-based bath to remove the solvent. When a water-soluble polymer is used as the hydrophilic polymer, the excess hydrophilic polymer remaining in the membrane can be extracted at the same time by water washing or moist heat treatment.

However, since this extraction effect differs depending on the type and molecular weight of the hydrophilic polymer, it is preferable to perform another extraction operation in some cases to adjust the weight of the hydrophilic polymer ultimately remaining in the membrane. Hydrophilic polymers that remain in the membrane after extraction - They rarely elute during use, but depending on the application, such as medical applications, the hydrophilic polymers may be physically or chemically insolubilized to elute the hydrophilic polymers. It is desirable to completely prevent this. Quantification of this hydrophilic polymer can be easily carried out by appropriate means such as gravimetric method or elemental analysis.

The hollow fiber membrane obtained by the above method contains a hydrophilic polymer having a ratio of 05 to 10 relative to a hydrophobic polymer. If the content of the hydrophilic polymer exceeds 10%, the hydrophilic polymer may inhibit the properties of the hydrophobic polymer, and if the content is less than 0.5%, no hydrophilic effect can be obtained. . The content of the hydrophilic polymer is preferably the minimum amount that can impart hydrophilicity to the membrane. Further, although there is no particular restriction on the dispersion state of the hydrophilic polymer in the hollow fiber membrane, it is desirable to disperse it as uniformly as possible in order to impart hydrophilicity to the membrane.

(Example) The present invention will be explained in more detail with reference to Examples below. Note that the pure water permeation rate and fractionability were measured by the following method.

(1) Pure water permeation rate An external pressure filtration type lab module with an effective length of 20α was made using 25 hollow fibers, and pure water at 25°C was permeated from the outside of the membrane at a filtration pressure of 1 kf/- for a certain period of time. The amount of pure water coming out of the hollow part was measured.

(11) As a fractionation measurement liquid, a 1-ti dispersion of 135λ colloidal silica (catalyst chemical industry 5I-30) was prepared, and the filtration pressure was O15.
External pressure filtration was performed at kf/i and circulation linear velocity of 0.3 rrVsec, and the weight of the collected permeate and the evaporation residue of the measurement solution was measured to calculate the removal rate.

Example 1 Polysulfone resin (UDEL P-1700 manufactured by Amoco)
19 parts by weight, polyvinylpyrrolidone with an average molecular weight of 1.2 million (GAF K-90) 1.9 parts by weight, average molecular weight 6
00 polyethylene glycol (manufactured by Sanyo Chemical PEGφ
600) 30.4 parts by weight, dimethylformamide 48,
7 parts by weight were heated and dissolved at 120°C for 6 hours. This spinning stock solution caused phase separation at temperatures above 75°C and below 29°C. This spinning stock solution was kept at 45°C, and dimethylformamide/water: 80/20 kept at the same temperature was simultaneously discharged as an internal coagulation liquid from a double annular nozzle to a length of lOc.
! After passing through a dry zone at 1K, an ambient temperature of 45°C, and a relative humidity of 85%, it was immersed in water at 45°C to reduce the outer diameter to 0.
A hollow fiber membrane with a diameter of 6 mm and an inner diameter of 0.4 mm was obtained. After washing this hollow fiber membrane with water at 90°C for 2 hours through moist heat treatment,
It was dried at 60°C for 8 hours. The pure water permeation rate of the obtained hollow fiber membrane was 3500 t/d-hr-ke/cd, 1
The removal rate Fi of 35λ colloidal silica was 40chi. The average pore diameter on the inner surface determined from scanning electron micrographs is 600^, the porosity is 25, the thickness of the dense layer is 1.5, the maximum pore diameter on the outer surface is 1.5, and the inside of the membrane is average. This occurred due to the network-like porous structure of Cape 1. Further, when the amount of poly and nylpyrrolidone in the film was measured by elemental analysis, it was found to be 4% relative to polysulfone.

After passing water through this hollow fiber membrane, it was re-dried and the water permeability is shown in Figure 5. Figure 1 shows the outer surface of the hollow fiber membrane, Figure 2 shows the inner surface, Figure 3 shows the cross section of the outer surface, Figure 4 shows the cross section of the central part of the hollow fiber membrane, and Figure 5 shows the cross section of the inner surface. ing.

Examples 2 to 8 1. Same as Example 1 with different spinning conditions. A hollow fiber membrane was manufactured. As shown in Table 1, hollow fiber membranes with a wide range of performance from the ultrafiltration level to the precision filtration level were obtained.

Below, pallor Example 9 Polysulfone TS31111 parts, Polyvinyl vinyl 0917
2 parts by weight, 1 part by weight of anhydrous lithium chloride, and 79 parts by weight of dimethylformamide were dissolved by heating at 60° C. for 8 hours to obtain a spinning stock solution. This stock solution was a high temperature separation type stock solution that undergoes phase separation at 45°C. A hollow fiber membrane was produced using this stock solution under the same conditions as in Example 1.

The pure water permeation rate of the obtained hollow fiber membrane was t, 800t/n.
The removal rate of colloidal silica of i'-hr-'q/d, 135X was 964. The average pore diameter of the inner surface, determined from scanning electron micrographs, is 200λ, the porosity is 15cm, the thickness of the dense layer is t/'13Afn, and the maximum pore diameter on the outer surface is 1.5IIl'n1. It had a network-like porous structure with a pore diameter of 11n. In addition, the amount of polyvinylpyrrolidone in the membrane based on elemental analysis was 45 mm compared to polysulfone.

Comparative Example 1 Example 1 except that dry yarn fO (wet spinning) was used.
Hollow fiber membranes were manufactured under the same conditions. The pure water permeation rate of the obtained hollow fiber membrane was s 400 Z/a! -hr・kf1
It was as low as 51. In addition, scanning electron micrographs showed that it was not present on the outer surface or in pores with a pore diameter of 0.1 μm or more, and dense layers were observed on the inner and outer surfaces.

Example 10 Using the hollow fiber membranes of Example 1 and Comparative Example 1, the effective membrane area was 1rr! An external pressure filtration type module was fabricated. Using this module, tap water was subjected to external pressure total filtration at r overpressure Q and 5 m/d, and the filtration amount when the zero permeation rate was halved was measured. was 25ftIl''T: whereas the module containing the hollow fiber membrane of Example 1 had a capacity of 60rrl. It has excellent water permeability, fractionation, clogging and stain resistance, etc., and is hydrophilic, making it suitable for long-term use and economical. It can be used in a wide range of fields including medical applications such as filtration.

[Brief explanation of drawings]

Figures 1 to 5 are scanning electron micrographs of the polysulfone hollow fiber membrane obtained in Example 1. Figure 1 is the structure of the outer surface of the hollow fiber membrane (magnification: 5.000), and Figure 2 is a scanning electron micrograph of the polysulfone hollow fiber membrane obtained in Example 1. Figure 3 shows the structure of the inner surface of the hollow fiber membrane (magnification 5,000), Figure 3 shows the cross-sectional structure of the outer surface of the hollow fiber membrane (magnification 5,000), Figure 4
The figure shows the structure of the inside (center part) of the hollow fiber membrane (magnification: 5.0
00) and Figure 5 show the cross-sectional structure of the inner surface side of the hollow fiber membrane (
Magnification: 5,000).

Claims (1)

[Claims] (1) A porous hollow fiber membrane containing 0.5 to 10% of a hydrophilic polymer to a hydrophobic polymer, the porous hollow fiber membrane having irregularly shaped micropores on its inner surface. It has a porous structure consisting of a dense layer having a porosity of 10 to 50% and a thickness of 0.5 to 5 μm, and a network structure integrally and continuously formed in the dense layer, and the outer surface is It has pores with a maximum pore diameter of 0.5 to 5 μm created by opening a part of the network, and the pure water permeation rate at 25°C is 800 l/m^2・hr・kg/c.
A porous hollow fiber membrane characterized by having a porous hollow fiber membrane of m^2 or more.