Polysulfone-based hollow fiber membranes and hollow fiber membrane modules

Abstract

For example, to provide a novel hollow fiber membrane with high air discharge performance, and a hollow fiber membrane module equipped with it. [Solution] For example, a hollow fiber membrane module comprising a polysulfone-based hollow fiber membrane (30b) containing a polysulfone-based resin and having a total content of hydrophilic components of 3.5% by mass or less; a case (50); and a hollow fiber membrane bundle (30) housed in the case (50), wherein the hollow fiber membrane bundle (30) has a polysulfone-based hollow fiber membrane (30b) and a hydrophilic polysulfone-based hollow fiber membrane (30a).

Description

[Technical Field]

[0001] This invention relates to polysulfone-based hollow fiber membranes and hollow fiber membrane modules. [Background technology]

[0002] Because membrane separation methods using hollow fiber membranes offer a high processing capacity per unit volume, they are used in a wide range of applications, including membrane modules for household and industrial water purifiers, membrane modules for hemodialysis machines, humidifying membrane modules, and dehumidifying membrane modules.

[0003] In particular, hydrophilic hollow fiber membranes are often used as water purifier membrane modules. For example, polysulfone-based hollow fiber membranes with added hydrophilic components are sometimes used. However, if only such hydrophilic hollow fiber membranes are used in a hollow fiber membrane module, there is a possibility that air will accumulate inside the module and reduce its water permeability if air is mixed into the module due to reasons such as the water being treated containing air.

[0004] Therefore, a hollow fiber membrane module has been proposed that includes hydrophilic hollow fiber membranes mixed with hydrophobic hollow fiber membranes for air discharge. For example, Patent Document 1 describes a module containing a polysulfone resin with a water permeability of 1 ml / (h·cm) under a pressure of 100 kPa. 2 ) or less, and the air permeability under a pressurized 100kPa is 1000ml / (h·cm 2 A polysulfone-based hollow fiber membrane having a specific molecular weight () or higher, and a hollow fiber membrane module comprising the same are disclosed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-169058 [Overview of the project] [Problems that the invention aims to solve]

[0006] Even with hydrophobic hollow fiber membranes, when exposed to conditions that make them prone to wetting, such as during operation under high water pressure, water can be incorporated into the porous structure of the membrane, temporarily impairing its air permeability. In such cases, applying air at a certain pressure or higher for a predetermined time can expel the water from the porous structure and restore air permeability. However, with conventional hydrophobic hollow fiber membranes, high pressure and long processing times were required to restore air permeability.

[0007] The present invention provides, for example, a novel hollow fiber membrane with excellent air discharge performance, and a hollow fiber membrane module equipped therewith. [Means for solving the problem]

[0008] The polysulfone-based hollow fiber membrane of the present invention, for example, contains a polysulfone-based resin, and the total content of hydrophilic components is 3.5% by mass or less.

[0009] Furthermore, the hollow fiber membrane module of the present invention comprises a case and a bundle of hollow fiber membranes housed within the case, wherein the bundle of hollow fiber membranes comprises the polysulfone-based hollow fiber membrane and a hydrophilic polysulfone-based hollow fiber membrane. [Effects of the Invention]

[0010] According to the present invention, for example, a novel hollow fiber membrane with excellent air discharge performance and a hollow fiber membrane module equipped therewith are provided. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a hollow fiber membrane module according to one embodiment. [Modes for carrying out the invention]

[0012] Examples of each aspect of the present invention are listed below. [1] A polysulfone-based hollow fiber membrane containing a polysulfone-based resin, wherein the total content of hydrophilic components is 3.5% by mass or less. [2] The polysulfone hollow fiber membrane according to [1] above, containing 95% by mass or more of a polysulfone resin. [3] The polysulfone hollow fiber membrane according to [1] or [2] above, in which the total content of an alkylene glycol and a water-soluble polymer is 3.5% by mass or less. [4] The polysulfone hollow fiber membrane according to any one of [1] to [3] above, which is for air discharge. [5] A method for producing a polysulfone hollow fiber membrane, using a casting dope containing a polysulfone resin, a solvent, and an additive, and having a total content of hydrophilic components of 5% by mass or less. [6] A hollow fiber membrane module including a case and a hollow fiber membrane bundle housed in the case, the hollow fiber membrane bundle having the polysulfone hollow fiber membrane according to any one of [1] to [4] above and a hydrophilic polysulfone hollow fiber membrane.

[0013] [Polysulfone hollow fiber membrane] Hereinafter, the polysulfone hollow fiber membrane will be described in detail. The polysulfone hollow fiber membrane disclosed in this specification contains a polysulfone resin and has a total content of hydrophilic components of 5% by mass or less. Such a polysulfone hollow fiber membrane with a low content of hydrophilic components has not been obtained conventionally and has excellent performance as a hollow fiber membrane for air discharge.

[0014] The polysulfone resin contained in the polysulfone hollow fiber membrane means a polymer containing a sulfonyl group (-SO2-) in the repeating unit. Examples of the polysulfone resin include polysulfone, polyethersulfone, polyphenylsulfone, and the like.

[0015] Polysulfone is a polymer having the following repeating unit.

[0016] [Chemical formula]

[0017] Polyethersulfone is a polymer having the following repeating unit.

[0018] [ka]

[0019] Polyphenylsulfone is a polymer having the following repeating units.

[0020] [ka]

[0021] Polysulfone-based hollow fiber membranes preferably contain polysulfone among polysulfone-based resins, and more preferably consist of polysulfone.

[0022] The polysulfone-based hollow fiber membranes disclosed herein have a total hydrophilic component content of 3.5% by mass or less. The total hydrophilic component content may be 3% by mass or less, 2.5% by mass or less, 2% by mass or less, 1.5% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. Furthermore, the polysulfone-based hollow fiber membranes may contain substantially no hydrophilic components or none at all. Here, "substantially no hydrophilic components" means that the hydrophilic components are not present in the final obtained hollow fiber membrane to an extent detectable by conventional detection methods.

[0023] In this specification, "hydrophilic component" refers to a component conventionally known in the field of hollow fiber membrane technology to enhance the hydrophilicity of polysulfone resins. The hydrophilic component as used herein does not include water. A hydrophilic component is, for example, a water-soluble compound. Examples of hydrophilic components include polyhydric alcohols and water-soluble polymers. Here, a polyhydric alcohol is a compound having two or more hydroxyl groups, and includes, for example, ethylene glycol, propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0024] Examples of water-soluble polymers include polymers having multiple structures selected from the group consisting of ether bonds, hydroxyl groups, carboxyl groups, ester groups, amide groups, amino groups, and pyrrolidonyl groups in a single molecule (excluding polysulfone resins). Specific examples of water-soluble polymers include polyalkylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, polyhydroxyethyl (meth)acrylate, polyacrylamide, and polyethyleneimine. Examples of polyalkylene glycols include polyethylene glycol and polypropylene glycol.

[0025] In other words, the polysulfone-based hollow fiber membrane preferably has a total content of polyhydric alcohols and water-soluble polymers of 3.5% by mass or less. The total content of polyhydric alcohols and water-soluble polymers may be 3% by mass or less, 2.5% by mass or less, 2% by mass or less, 1.5% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. Furthermore, the polysulfone-based hollow fiber membrane may be substantially free of polyhydric alcohols and water-soluble polymers, or completely free of them. Here, "substantially free of polyhydric alcohols and water-soluble polymers" means that the final hollow fiber membrane does not contain polyhydric alcohols and water-soluble polymers to an extent that is detectable by conventional detection methods.

[0026] The polysulfone-based hollow fiber membrane preferably contains 95% by mass or more of polysulfone-based resin. The polysulfone-based resin content may be 95.5% by mass or more, 96% by mass or more, 96.5% by mass or more, 97% by mass or more, 97.5% by mass or more, 98% by mass or more, 98.5% by mass or more, 99% by mass or more, 99.5% by mass or more, or 99.9% by mass or more. The polysulfone-based resin may contain 100% by mass of polysulfone-based resin.

[0027] Polysulfone-based hollow fiber membranes can be manufactured, for example, by nonsolvent-induced phase separation (NIPS) or thermally-induced phase separation (TIPS). Preferably, polysulfone-based hollow fiber membranes are manufactured by nonsolvent-induced phase separation (NIPS), such as wet spinning or wet-dry spinning. More specifically, a film-forming stock solution is prepared first, then the stock solution is extruded into a coagulation bath directly or by air from the outer tube of a double-ring structured hollow fiber spinning nozzle, and at the same time, the core liquid is extruded from the inner tube of the hollow fiber spinning nozzle to form a film. The polysulfone-based hollow fiber membrane thus obtained is washed with water as needed and then dried.

[0028] The film-forming stock solution contains a polysulfone resin, a solvent capable of dissolving the polysulfone resin, and additives, with a total hydrophilic component content of 5% by mass or less. However, the hydrophilic component referred to here does not include water or the aforementioned solvent. Commercially available polysulfone resins can be used, such as Ultrason® S3010, S6010, E1010, E2010, E3010, E3010P, E6020P, P3010 (all manufactured by BASF), Udel® P-1700, P-3500, Veradel® 3100P, 3000P, 3000MP, and RADEL® R-5000, R-5500 (all manufactured by SOLVAY). The solvent is not particularly limited as long as it can dissolve the polysulfone resin, but examples include tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and triethyl phosphate. Preferably, aprotic polar solvents with high solubility, such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone, can be used.

[0029] If the film-forming stock solution contains a large amount (e.g., more than 5% by mass) of hydrophilic components such as polyhydric alcohols or water-soluble polymers, these hydrophilic components remain in the hydrophobic polysulfone hollow fiber membrane after film formation. As a result, water incorporated into the porous structure is retained by the hydrophilic components remaining in the hollow fiber membrane, requiring high pressure and long exposure times when air is applied to restore the air permeability of the hydrophobic polysulfone hollow fiber membrane. This problem persists even when relatively low molecular weight hydrophilic components such as ethylene glycol are used. On the other hand, if the amount of these hydrophilic components used is below a predetermined amount, the question arises as to how to make the membrane porous. The inventors have for the first time discovered that by increasing the amount of water in the film-forming stock solution as much as possible without causing phase separation of the film-forming stock solution, it is possible to produce a porous membrane even when the amount of hydrophilic components used is below a predetermined amount.

[0030] In the film-forming stock solution, the content of polysulfone resin may be, for example, in the range of 10% to 20% by mass, or in the range of 12% to 16% by mass. The water content may also be, for example, in the range of 0.1% to 3% by mass, or in the range of 1% to 2% by mass. However, it is preferable to have as much water as possible without causing phase separation in the film-forming stock solution.

[0031] In the film-forming stock solution, the total content of hydrophilic components is 5% by mass or less, may be 4.5% by mass or less, 4% by mass or less, 3.5% by mass or less, 3% by mass or less, 2.5% by mass or less, 2% by mass or less, 1.5% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.1% by mass or less, or 0% by mass.

[0032] The core solution and coagulation bath can be, for example, dimethylformamide, ethylene glycol, water, etc. The temperature of the core solution and coagulation bath is not particularly limited, but to ensure stable film formation, it is preferably -20°C to 60°C, more preferably 0°C to 30°C. The viscosity of the film-forming stock solution at room temperature is preferably 300 mPa·s or higher to enhance film-forming stability. The drying conditions for the polysulfone-based hollow fiber film after film formation are not particularly limited as long as the polysulfone-based hollow fiber film is sufficiently dried, but for example, it may be carried out at 20°C to 80°C, preferably 25°C to 60°C, for 0.5 hours to 4 hours.

[0033] The pore size of polysulfone-based hollow fiber membranes can be controlled to a desired range by adjusting the polymer concentration in the spinning solution, the additive concentration, and the spinning conditions. Depending on the pore size of the polysulfone-based hollow fiber membrane, it can be used for a variety of applications, from microfiltration to ultrafiltration.

[0034] [Hollow fiber membrane module] The hollow fiber membrane module will now be described in detail. The hollow fiber membrane module disclosed herein comprises a case and a bundle of hollow fiber membranes housed within the case, wherein the bundle of hollow fiber membranes comprises the polysulfone-based hollow fiber membrane described above and a hydrophilic polysulfone-based hollow fiber membrane.

[0035] Such hollow fiber membrane modules, having both hydrophobic and hydrophilic polysulfone-based hollow fiber membranes, can achieve excellent water and air permeability and processing capacity simultaneously. Since the hollow fiber membrane bundle can be obtained by simultaneously forming both polysulfone-based and hydrophilic polysulfone-based hollow fiber membranes, the manufacturing cost of the hollow fiber membrane module can be reduced. By adjusting the composition of the film-forming solution and spinning conditions, the polysulfone-based hollow fiber membrane can have a pore size comparable to that of the hydrophilic polysulfone-based hollow fiber membrane. Therefore, when fixing the hollow fiber membrane bundle within a case using a potting agent, the potting agent can be suitably impregnated into the polysulfone-based and hydrophilic polysulfone-based hollow fiber membranes, resulting in good adhesion between the hollow fiber membranes and between the hollow fiber membrane bundle and the inner wall of the case due to the anchoring effect. Furthermore, by adjusting the composition of the film-forming solution and spinning conditions, hydrophobic polysulfone-based hollow fiber membranes can be made to have mechanical strength comparable to that of hydrophilic polysulfone-based hollow fiber membranes. Therefore, when producing hollow fiber membrane bundles, it is possible to effectively prevent hydrophobic polysulfone-based hollow fiber membranes from damaging hydrophilic polysulfone-based hollow fiber membranes.

[0036] The following describes a hollow fiber membrane module according to one embodiment, with reference to Figure 1. Note that the following embodiment represents an example of the hollow fiber membrane module of the present invention, and the hollow fiber membrane module of the present invention is not limited to that shown in Figure 1. Figure 1 is a schematic cross-sectional view of a hollow fiber membrane module according to one embodiment. Note that Figure 1 is a cross-sectional view obtained by cutting the hollow fiber membrane module in a plane containing the central axis of the hollow fiber membrane module.

[0037] The hollow fiber membrane module 100 in Figure 1 comprises a bottomed cylindrical case 50, a hollow fiber membrane bundle 30 housed inside the case 50, and a piping member 20 fitted and fixed to one end of the case 50. The hollow fiber membrane bundle 30 is housed inside the case 50 in a state where both ends are bent so that they face the opening side, which is one end of the case 50. More specifically, the hollow fiber membrane bundle 30, which is a bundle of multiple hollow fiber membranes, is housed inside the case 50 in a state where its central part is bent in a curved shape (approximately U-shape). The hollow fiber membrane bundle 30 is composed of, for example, one hydrophobic polysulfone-based hollow fiber membrane 30b and multiple hydrophilic polysulfone-based hollow fiber membranes 30a.

[0038] The hydrophobic polysulfone-based hollow fiber membrane 30b contains a polysulfone-based resin, and the total content of hydrophilic components is 3.5% by mass or less. Furthermore, a sealing and fixing portion 40 is provided inside the case 50, which fixes both ends of the hollow fiber membrane bundle 30 to the case 50 at one end of the case 50 while leaving the hollow interior of each hollow fiber membrane open. More specifically, the hollow fiber membrane bundle 30 is fixed to the case 50 with the opening of the case 50 sealed by the sealing and fixing portion 40, while the hollow interior of each hollow fiber membrane is open. The sealing and fixing portion 40 is made of a sealing material (potting material) such as cured epoxy resin.

[0039] The hollow fiber membrane module 100, as configured as shown in Figure 1, is placed, for example, inside a water purifier body (not shown). In this configuration, the case 50 is positioned with its opening facing downward in the vertical direction. Foreign matter contained in the liquid (such as tap water) flowing in through the inlet 21 on the other end of the case 50 is removed by membrane separation treatment using the hollow fiber membrane. The liquid, after membrane separation treatment using the hollow fiber membrane, flows out through the outlet 22 provided on the piping member 20.

[0040] In the hollow fiber membrane module 100 shown in Figure 1, the hollow fiber membrane bundle 30 comprises, for example, one hydrophobic polysulfone-based hollow fiber membrane 30b and multiple hydrophilic polysulfone-based hollow fiber membranes 30a. Therefore, the hollow fiber membrane module 100 can achieve both excellent water permeability, air permeability, and processing capacity. As the hydrophilic polysulfone-based hollow fiber membrane 30a, known polysulfone-based hollow fiber membranes containing polyvinylpyrrolidone or the like as a hydrophilic component can be used.

[0041] Furthermore, a hollow fiber membrane module of one embodiment can be used for a wide variety of applications in various technical fields. The applications of the hollow fiber membrane module are not particularly limited, but for example, it can be used as a water purifier membrane module, an industrial membrane module, an artificial dialysis membrane module, a humidifier membrane module, a dehumidifier membrane module, and so on.

[0042] Although embodiments of the present invention have been described above with examples, the present invention is not limited to the embodiments described above, but includes all aspects included in the concept and claims of the present invention, and can be modified in various ways within the scope of the present invention. [Examples]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0044] [Manufacturing of hollow fiber membranes] (Example 1) A film-forming stock solution was prepared containing 14.5% by mass of polysulfone resin (Ultrason® S3010; manufactured by BASF), 1.4% by mass of water, and 84.1% by mass of dimethylformamide, and was homogenized at room temperature. A polysulfone hollow fiber film was formed by wet-dry spinning by extruding the film-forming stock solution from the outer tube and the dimethylformamide core solution from the inner tube of a double-ring hollow fiber spinning nozzle into a water coagulation bath by air-running. The formed polysulfone hollow fiber film was then washed in water at room temperature for 12 hours and dried at 60°C to obtain a porous polysulfone hollow fiber film.

[0045] (Comparative Example 1) Regarding the composition of the casting dope solution, except that it was 14.65% by mass of polysulfone resin (Ultrason® S3010; manufactured by BASF), 19.49% by mass of polyethylene glycol (PEG-600), 0.40% by mass of water, and 65.45% by mass of dimethylformamide, a polysulfone hollow fiber membrane was obtained in the same manner as in Example 1.

[0046] [Analysis of the content of hydrophilic components] Regarding the hollow fiber membranes obtained in Example 1 and Comparative Example 1, 1 Using 1H NMR, the content of hydrophilic components was measured under the following conditions and methods.

[0047] (Measurement conditions) Software: TopSpin 3.1 (manufactured by Bruker) Nucleus: 1 H Solvent: Deuterated chloroform Pulse angle: 90° Number of integrations: 64 times Excitation center frequency: 6.174 ppm Waiting time: 5 seconds

[0048] For each hollow fiber membrane obtained, 1 In the 1H NMR spectrum, by comparing with the 1H NMR spectra of pure polysulfone (PSU) and polyethylene glycol (PEG), the presence or absence of peaks derived from these was examined. For PEG, the integrated value S of the peak at 3.45 to 4.20 ppm [[ID=�9]] 1 was used. However, the peak of PSU also exists in this range. Therefore, the integrated value of 3.45 to 4.20 ppm derived from these was obtained from the 1H NMR spectrum of pure PSU, and subtracted from S as follows. <o000007>was used. However, the peak of PSU also exists in this range. Therefore, the integrated value of 3.45 to 4.20 ppm derived from these was obtained from the 1H NMR spectrum of pure PSU, and subtracted from S as follows. 1 H NMR spectrum of pure PSU to obtain the integrated value of 3.45 to 4.20 ppm derived from these, and subtracted from S as follows. 3.45~4.20ppm was subtracted.

[0049] Integrated value of PEG = S 3.45~4.20ppm -(S 6.70~7.12ppm ×5.1×10 -3 [[ID=?6]]

[0050] From the integral values ​​obtained as described above, the content of each component in each hollow fiber membrane was determined. As a result, the hollow fiber membrane obtained in Example 1 contained 100% by mass of PSU. In Comparative Example 1, the hollow fiber membrane contained 96.0% by mass of PSU and 4.0% by mass of PEG.

[0051] [Air permeability test] The hollow fiber membranes obtained in Example 1 and Comparative Example 1 were subjected to air permeability tests as described in paragraphs

[0018] and

[0019] of Japanese Patent Application Publication No. 2021-169058. However, the amount of air permeation after wetting was obtained in two stages: immediately after air permeation and after air permeation for 1 minute.

[0052] (Get initial values) A single polysulfone-based hollow fiber membrane was placed in a U-shape inside one end of a cylindrical container and then sealed and fixed with a potting agent. The other end of the cylindrical container was then sealed with a resin head. Next, a tube was installed that penetrated the resin head and reached into the cylindrical container. The tube branched into two; one branch connected to a pressure gauge, and the other to a supply tube for deionized water and air. Air was then supplied into the cylindrical container from the supply tube for one minute to pressurize the container until the pressure gauge reading reached 100 kPaG. During this time, the volume of air leaking from the sealed end of the cylindrical container was measured. The volume of air was then divided by the lateral surface area of ​​the polysulfone-based hollow fiber membrane (diameter of the polysulfone-based hollow fiber membrane × 3.14 × length of the polysulfone-based hollow fiber membrane) and time (1 / 60) to determine the air permeability (ml / (h·cm)). 2 The initial value of )) was obtained.

[0053] (Acquisition of air permeability) Next, after returning the pressure inside the cylindrical container to atmospheric pressure, deionized water was supplied into the cylindrical container from the supply pipe for 1 minute, pressurizing the inside of the cylindrical container to a pressure gauge reading of 200 kPaG. Then, immediately after removing the water that had filled cylindrical container 1, air was supplied into the cylindrical container from the supply pipe, pressurizing the inside of the cylindrical container to a pressure gauge reading of 100 kPaG. The air permeability immediately after that was (ml / (h·cm). 2 The amount of air permeation (ml / (h·cm)) was obtained first. Next, the amount of air permeation (ml / (h·cm)) when air supply was continued for 1 minute was obtained. 2 )) was measured.

[0054] The results are shown in the table below.

[0055] [Table 1]

[0056] In Comparative Example 1, the air permeability of the hollow fiber membrane recovered after wetting and the application of air pressure for 1 minute, whereas in Example 1, the hollow fiber membrane already showed high air permeability immediately after air pressurization. For example, in the actual use of a water purifier, air can be discharged even with the hollow fiber membrane of Comparative Example 1 by leaving the water tap open for a predetermined time, but considering that a single use of water in daily life is generally within 1 minute, the effect of incorporating the hollow fiber membrane of the present invention as a hydrophobic hollow fiber membrane is significant. [Industrial applicability]

[0057] The hollow fiber membranes and hollow fiber membrane modules of the present invention can be used in a wide variety of applications in various technical fields. The applications of the hollow fiber membrane modules are not particularly limited, but they can be used, for example, as water purifier membrane modules, industrial membrane modules, hemodialysis membrane modules, humidifying membrane modules, dehumidifying membrane modules, etc. [Explanation of symbols]

[0058] 20...Piping component, 21...Inlet, 22...Outlet, 30...Hollow fiber membrane bundle, 30a...Hydrophilic polysulfone-based hollow fiber membrane, 30b...Polysulfone-based hollow fiber membrane, 40...Sealing and fixing part, 50...Case, 100...Hollow fiber membrane module.

Claims

1. Contains polysulfone resin, A polysulfone-based hollow fiber membrane having a total hydrophilic component content of 3.5% by mass or less.

2. A polysulfone-based hollow fiber membrane according to claim 1, comprising 95% by mass or more of a polysulfone-based resin.

3. The polysulfone-based hollow fiber membrane according to claim 1 or 2, wherein the total content of polyhydric alcohols and water-soluble polymers is 3.5% by mass or less.

4. A polysulfone-based hollow fiber membrane according to claim 1 or 2, for use in air discharge.

5. A method for producing a polysulfone-based hollow fiber membrane, using a film-forming stock solution containing a polysulfone-based resin, a solvent, and additives, wherein the total content of hydrophilic components is 5% by mass or less.

6. The case and, A bundle of hollow fiber membranes housed in the aforementioned case, Equipped with, The hollow fiber membrane module comprises a polysulfone-based hollow fiber membrane according to claim 1 or 2 and a hydrophilic polysulfone-based hollow fiber membrane.

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