JP2899352B2 - Porous hollow fiber membrane - Google Patents

Description

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 about.

(Prior Art) In recent years, a technique using a hollow fiber membrane having selective permeability in a separation operation has been remarkably advanced, and has been put to practical use in various fields. As a material for such a hollow fiber membrane, a resin such as a cellulose-based, polyamide-based, polyacrylonitrile-based, polyvinyl alcohol-based, or polysulfone-based resin is 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 a film.

However, a drawback of a hollow fiber membrane made of a hydrophobic polymer such as a polysulfone-based resin is that when the hollow fiber membrane is dried, the permeation rate is significantly reduced. As a method of solving this drawback, for example, JP-A-58-104940 and JP-A-61-93801 describe that a hydrophilic polyvinylpyrrolidone is contained in a membrane to make a polysulfone membrane hydrophilic. ing. Further, JP-A-61-238306 and JP-A-61-238834 disclose polysulfone resins,
A highly water-permeable hydrophilized polysulfone membrane having pores having an average pore diameter of 500 ° or more on both surfaces of a membrane using a spinning solution composed of polyvinylpyrrolidone, a swelling agent, and a solvent is described.

(Problems to be Solved by the Invention) However, the former polysulfone membrane has a pore size of 0.001 to 0.0.
Since the membrane has a skin layer having fine pores of 5 μm, there is a problem that water permeability is extremely low.

The latter polysulfone membrane has an average of 50 micropores on the membrane surface.
Since it is 0 mm or more, the water permeability is high, but there is a problem that the fractionation is large and FLUX is greatly reduced due to excess.

Accordingly, an object of the present invention is to provide a porous hollow fiber membrane having high water permeability and excellent fractionation properties, and having a hydrophilic property that does not cause a decrease in FLUX during use.

(Means for Solving the Problems) The present invention relates to a porous hollow fiber membrane containing 0.5 to 10% of a hydrophilic polymer with respect to a hydrophobic polymer, wherein the porous hollow fiber membrane is 0.5 to 5μ thickness, having irregular fine pores with an average pore diameter of 500mm or less on the inner surface at a porosity of 10 to 50%
m and a network structure formed integrally and continuously with the dense layer, and the outer surface has a maximum pore diameter of 0.5 to 5 μm formed by partially opening the network. It has a hole, the pure water permeation rate at 25 ° C. is ^{800l / m 2 · hr · kg} /
It is a porous hollow fiber membrane characterized by having a size of not less than cm ² .

The shape of the micropores formed on the inner surface of the hollow fiber membrane of the present invention is not particularly limited, and examples thereof include a single micropore, a porous micropore in which pores are continuously connected, a slit micropore, and a network micropore. Can be The average pore size of such micropores is 500 ° or less. Here, the average pore diameter is a value obtained by measuring and summing the diameters of the largest inscribed circles of all the amorphous fine pores present from the electron micrograph of the surface and dividing the sum by the total number of pores.
The opening rate of the irregular micropores is present at a rate of 10 to 50%,
A dense layer having a thickness of 0.5 to 5 μm is formed. The porosity referred to in the present invention is a percentage of the total pore area of the fine pores formed on the inner surface to the outer surface area.
If the porosity is less than 10%, the water permeability decreases, and if the porosity exceeds 50%, the surface strength decreases and the handling of the hollow fiber membrane becomes poor, which is not preferable. It is preferable that the porosity is 10 to 30% in terms of the balance between the permeability and the mechanical strength of the hollow fiber membrane. Further, the distribution density of the micropores is preferably as uniform as possible, but may be nonuniform.

In the hollow fiber membrane of the present invention, a porous structure of a network is continuously formed integrally with a dense layer formed on the inner surface, and the outer surface has a maximum pore diameter of 0.1 formed by partially opening the network. ~ 5
It has a hole of μm. The network formed inside the hollow fiber membrane has a large number of continuous pores having an average of 1 to 5 μm,
And there is no huge cavity of 10 μm or more. For this reason, the consolidation property during long-term use is excellent, and the strength is also excellent. The shape and porosity of the pores on the outer surface of the hollow fiber membrane are not particularly limited, but are usually circular and elliptical, and the porosity is preferably 10 to 50%, which is almost the same as that of the inner surface. When the pore size of the outer surface is 5 μm or more, not only does it pose a problem in terms of pressure resistance, but when the external pressure is exceeded, residues easily accumulate inside the hollow fiber membrane, so that the permeation rate decreases quickly, and Also, there is a tendency that regeneration of the film by backwashing is not sufficiently performed, which is not preferable. Conversely, if the maximum pore diameter is smaller than 0.1 μm, the water permeability is undesirably small.

The hollow fiber membrane of the present invention is constituted by a dense layer having irregular fine pores on the inner surface and a porous structure composed of a network structure.
And since the thickness of the dense layer is as thin as 0.5 to 5 μm, for example, despite the fact that 135%
Pure water permeation rate at 5 ° C is 800 l / m ² · hr · kg / cm ² or more, indicating high water permeability. In addition, when water is actually passed, when the external pressure is exceeded, particles of submicron order or more are captured on the outer surface and substances of submicron or less such as dissolved polymer are captured on the hollow fiber membrane wall or the dense layer on the inner surface. . That is, since the outer surface and the hollow fiber membrane wall play a role of a pre-filter, a decrease in the permeation rate is small and a high permeation rate can be maintained. Conversely, when the internal pressure is too high, a dense layer is formed on the inner surface of the hollow fiber membrane, which is effective for the cross flow method.

Further, the hollow fiber membrane of the present invention has a dense layer and a porous structure integrated, and the problem of pinholes in the dense layer and separation of the dense layer from the support layer as in a composite hollow fiber membrane obtained by a coating method or the like. I don't wanna

Furthermore, the hollow fiber membrane of the present invention has a
Contains ~ 10% hydrophilic polymer. Therefore, it is excellent in hydrophilicity, has little adsorption of proteins and the like, and has little decrease in permeation performance due to excess. Further, there is no substantial decrease in water permeability or dimensional change of the hollow fiber membrane due to drying, and a completely dry hollow fiber membrane can be produced. This is advantageous in many aspects such as handling of the hollow fiber membrane, modularization, and transport of the module, and can improve workability and productivity.

Next, a method for producing the porous hollow fiber membrane of the present invention will be described.

The spinning solution for producing the hollow fiber membrane of the present invention comprises a hydrophobic polymer, a hydrophilic polymer, a micropore-forming agent, and a polar solvent dissolving these.

Examples of the hydrophobic polymer include polysulfone, polyethersulfone, polyvinylidene fluoride, polyethylene, and vinyl chloride. Among them, polysulfone and polyether sulfone are excellent in heat resistance, chemical resistance, oxidizing agent resistance, strength, and strong in intermolecular cohesion, so that spinning is easy and suitable.

As the hydrophilic polymer, for example, polyvinylpyrrolidone, polyethylene glycol having an average molecular weight of 20,000 or more,
Examples include, but are not limited to, polyvinyl alcohol, ethylene / vinyl alcohol copolymer, and modified polymers thereof. Desirably, such a hydrophilic polymer has excellent compatibility with a hydrophobic polymer in a solvent, and a water-soluble polymer such as polyvinylpyrrolidone, which can be easily insolubilized by crosslinking or the like, is desirable. The higher the molecular weight, the less the amount of the hydrophilic polymer added. In particular, in the case of a water-soluble polymer, it is preferably used since it is likely to remain in the hollow fiber membrane and is less likely to be eluted during washing with water, hot water treatment or use of the hollow fiber membrane. The type of these hydrophilic polymers can be selected in consideration of the manufacturing process, suitability for the intended use, and the like.

In the hollow fiber membrane of the present invention, micropores are formed by Miuro phase separation, and a micropore forming agent is added for the purpose of easily causing the microphase separation. Conventionally, alcohols such as methanol and ethanol, ethylene glycol, propylene glycol, and an average molecular weight of 400 to 2
Glycols such as polyethylene glycol having a low molecular weight of 0,000, LiCl, inorganic salts ZnCl ₂ or the like, water and the like have been used, the above fine pore-forming agent in the present invention can be used.
The amount of the micropore-forming agent needs to be kept within a range that keeps the spinning dope uniform and transparent, but it is desirable that the addition amount be as large as possible because the micropore-forming agent is assumed to be the core of the pores.
Among them, low molecular weight polyethylene glycol having a molecular weight of 400 to 20,000 is preferable because the amount of addition to the spinning dope can be increased. This low-molecular-weight polyethylene glycol is excellent in forming micropores and has a thickening effect of a stock solution for spinning, and therefore has an advantage of improving spinning stability.

The polar solvent is not particularly limited as long as it dissolves a hydrophobic polymer, a hydrophilic polymer, and a micropore-forming agent. Examples thereof include N, N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethylsulfoxide. Is mentioned.

These four types of compositions can be selected at an arbitrary ratio. However, in order to produce the hollow fiber membrane of the present invention, the spinning solution is subjected to phase separation at a certain temperature or lower (low-temperature phase separation type). Alternatively, it is preferable to prepare so as to cause phase separation at a certain temperature or higher (high temperature phase separation type).

The hollow fiber membrane of the present invention is produced by a known dry-wet method using the above spinning stock solution. As the internal coagulation liquid discharged from the center of the nozzle together with the spinning solution, water, a mixture of water and a polar solvent, alcohols, glycols, or the like alone or a mixture of two or more of these are used.
By changing the composition of the internal coagulation liquid, the structure near the inner surface of the hollow fiber membrane, such as the shape of the fine pores on the inner surface of the hollow fiber membrane, the average pore diameter, the porosity, and the thickness of the dense layer, is controlled.

In order to form irregular micropores on the inner surface, water or a mixture of water and a solvent is usually used as the internal coagulating liquid. The concentration (solvent / water) of the internal coagulation liquid is 0/100 to 85 /
15 is preferred. A solvent / water ratio of 0/100 to 75/25 is particularly preferred in terms of the balance between spinnability and membrane performance.

The spinning solution discharged from the nozzle travels in the air (dry zone) and is then immersed in an external coagulation solution containing water as a main component. In the present invention, by controlling the length of the dry zone, the atmospheric humidity and the temperature in the dry zone, the amount of a small amount of water present in the dry zone is adjusted, and the pore structure on the outer surface is controlled. The length of this dry zone is a balance between spinning stability and hollow fiber membrane performance.
A suitable size is 0.1 to 200 cm, usually 1 to 500 cm. In the atmosphere of the dry zone, larger holes are more likely to be formed as the humidity becomes higher, and the opening ratio increases.

The hollow fiber membrane formed with the coagulation liquid is then washed with water in order to extract a solvent and a pore-forming agent. In addition, if necessary, in order to extract the micropore-forming agent and to improve the pressure resistance of the hollow fiber membrane, a wet heat treatment is performed in a bath containing water as a main component. When a water-soluble polymer is used as the hydrophilic polymer, extraction of the hydrophilic polymer excessively remaining in the hollow fiber membrane can be simultaneously performed by washing with water or moist heat treatment. However, since this extraction effect differs depending on the type and molecular weight of the hydrophilic polymer, another extraction operation may be performed in some cases to adjust the amount of the hydrophilic polymer finally remaining in the hollow fiber membrane. Is preferred. Usually, the hydrophilic polymer remaining in the hollow fiber membrane hardly elutes during use, but depending on the special use such as medical use, the hydrophilic polymer is physically or chemically insolubilized, It is preferable to completely prevent elution of the hydrophilic polymer during use. The determination of the hydrophilic polymer can be easily performed by a suitable means such as a gravimetric method or elemental analysis.

The hollow fiber membrane obtained by the above method contains 0.5 to 10% of a hydrophilic polymer with respect to a hydrophobic polymer. If the content of the hydrophilic polymer exceeds 10%, the properties of the hydrophobic polymer may be inhibited by the hydrophilic polymer.
If it is less than 5%, the hydrophilic effect cannot be obtained. The content of the hydrophilic polymer is preferably a minimum amount that can impart hydrophilicity to the hollow fiber membrane. The dispersion state of the hydrophilic polymer in the hollow fiber membrane is not particularly limited, but it is preferable to disperse the hydrophilic polymer as uniformly as possible in order to impart hydrophilicity to the hollow fiber membrane.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples. The measurement of the pure water permeation rate and the fractionation was performed by the following methods.

(I) Pure permeation speed A 25 cm hollow fiber membrane with an effective length of 20 cm is prepared from 25 hollow fiber membranes, and pure water at 25 ° C is supplied to the outside of the hollow fiber membrane at an overpressure of 1 kg / cm ^2. The amount of pure water transmitted through the hollow fiber membrane was measured.

(Ii) Fractionability A 1% dispersion of colloidal silica (Catalyst Kasei Kogyo Co., Ltd. SI-30) of 135 と し て was prepared as a measuring solution, and overpressure was 0.5 kg / c.
An external pressure was applied at m ² and a circulation linear velocity of 0.3 m / sec, and the weight of the collected permeate and the evaporation residue of the measurement liquid was measured to calculate the removal rate.

Example 1 19 parts by weight of a polysulfone resin (UDEL P-1700 manufactured by Amoco), 1.9 parts by weight of polyvinylpyrrolidone having an average molecular weight of 1.2 million (K-90 manufactured by GAF), and polyethylene glycol having an average molecular weight of 600 (PEG # manufactured by Sanyo Chemical Co., Ltd.) 600) 30.4 parts by weight and dimethylformamide 48.7 parts by weight were heated and dissolved at 120 ° C. for 6 hours. This spinning stock solution was a stock solution that caused phase separation at 75 ° C or higher and 29 ° C or lower. This spinning solution was kept at 45 ° C, and dimethylformamide / water (78/22) kept at the same temperature as the internal coagulating solution was simultaneously discharged from the double annular nozzle at a length of 1
After passing through a dry zone of 0 cm, ambient temperature of 45 ° C, and relative humidity of 85%, it was immersed in 45 ° C water to obtain an outer diameter of 0.6 mm.
A hollow fiber membrane having an inner diameter of 0.4 mm was obtained. This hollow fiber membrane was subjected to wet heat treatment with 90 ° C. warm water for 2 hours, washed, and dried at 60 ° C. for 8 hours. The resulting hollow fiber membrane had a pure water permeation rate of 1900 l / m ² · hr · kg / cm ² and a removal rate of colloidal silica of 135 ° was 90%. There are heterogeneous pores on the inner surface determined from the scanning electron micrograph, and the average pore diameter is 300
Å, the porosity was 20%, the thickness of the dense layer was 1.0 μm, the maximum pore diameter on the outer surface was 1.5 μm, and the hollow fiber membrane wall had a reticulated porous structure with an average pore size of 1 μm. Further, when the amount of polyvinylpyrrolidone in the hollow fiber membrane was measured by elemental analysis, it was 4% based on polysulfone. After passing the water through the hollow fiber membrane, it was dried again and the water permeability was measured again. As a result, no change in the water permeability was observed. FIGS. 1 to 5 show photographs of the hollow fiber membrane taken by a scanning electron microscope. 1 shows the outer surface of the hollow fiber membrane, FIG. 2 shows the inner surface, FIG. 3 shows the cross section of the outer surface side, FIG. 4 shows the cross section of the substantially central portion, and FIG. 5 shows the cross section of the inner surface side. I have.

Examples 2 to 5 Using the same polysulfone resin, polyvinylpyrrolidone and polyethylene glycol as in Example 1, a hollow fiber membrane was prepared by changing the composition of the spinning dope and the spinning conditions, and pure water permeation of the obtained hollow fiber membrane was performed. Table 1 shows the speed and the removal rate of the colloidal silica at 135 °.

Example 6 18 parts by weight of polysulfone, 2 parts by weight of polyvinylpyrrolidone, 1 part by weight of anhydrous lithium chloride, dimethylformamide
79 parts by weight were heated and dissolved at 60 ° C. for 8 hours to prepare a spinning dope. This stock solution was a high temperature separation type stock solution that phase-separated at 45 ° C.
The pure water permeation rate of the hollow fiber membrane obtained in the same manner as in Example 1 was 1800 l / m ² · hr · kg / cm ² , and the removal rate of colloidal silica at 135 ° was 96%. The average pore diameter of the inner surface determined from the scanning electron micrograph is 2000 mm, the porosity is 15%, the thickness of the dense layer is 3 μm, the maximum pore diameter of the outer surface is 1.5 μm, and the inside of the membrane is a reticulated porous structure with an average pore diameter of 3 μm. It was. The amount of polyvinylpyrrolidone in the membrane measured by elemental analysis was 4.5% with respect to polysulfone.

Comparative Example 1 A hollow fiber membrane was obtained in the same manner as in Example 1 except that the dry zone was 0 cm (wet spinning). The pure water permeation rate of this hollow fiber membrane was as low as 400 l / m ² · hr · kg / cm ² . From the scanning electron micrograph, the outer surface had a pore size of 0.1.
No pores of more than μm were present, and a dense layer was recognized on both the inner surface and the outer surface.

Example 7 Using the hollow fiber membranes of Example 1 and Comparative Example 1, an external pressure type module having an effective membrane area of 1 m ² was produced. Tap water was subjected to an external pressure of 0.5 kg / cm ² at an external pressure of 0.5 kg / cm ² , and the excess amount when the permeation rate was reduced by half was measured. In contrast, the module containing the hollow fiber membrane of Comparative Example 1 was 25 m ³ . The module containing the hollow fiber membrane of Example 1 was 60 m ³ .

(Effect of the Invention) The porous hollow fiber membrane of the present invention has a specific structure, so that it has excellent water permeability, fractionation properties, and stain resistance, and is hydrophilic, so that it can be used for a long time. Suitable for and economical. Therefore, it can be applied to a wide range of fields such as industrial uses and medical uses such as blood and ascites.

[Brief description of the drawings]

FIG. 1 shows the structure of the outer surface of the polysulfone hollow fiber membrane obtained in Example 1, FIG. 2 shows the structure of the inner surface, FIG. 3 shows the cross-sectional structure on the outer surface side, and FIG. Structure and Fifth
The figure is a scanning electron micrograph (5,000 times magnification) showing the cross-sectional structure on the inner surface side.

Continuation of the front page (56) References JP-A-3-267128 (JP, A) JP-A-3-258330 (JP, A) JP-A-63-99325 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) B01D 69/08 B01D 71/68 D01D 5/24 D01F 6/76 B01D 69/02

Claims (1)

(57) [Claims] 1. A porous hollow fiber membrane containing 0.5 to 10% of a hydrophilic polymer with respect to a hydrophobic polymer, wherein the porous hollow fiber membrane has an average pore diameter of 500 mm or less on its inner surface. 0.5 to 5μ thick with irregular micropores at a porosity of 10 to 50%
m and a network structure formed integrally and continuously with the dense layer, and the outer surface has a maximum pore diameter of 0.5 to 5 μm formed by partially opening the network. It has a hole, the pure water permeation rate at 25 ° C. is ^{800l / m 2 · hr · kg} /
A porous hollow fiber membrane having a size of not less than ² cm ² .