Composite hollow fiber membrane and method for manufacturing the same

Abstract

The present invention aims to provide a composite hollow fiber membrane and a method for producing the same that achieve a high level of both organic solvent permeability and solute inhibition performance in an organic solvent-based treated liquid. [Solution] The composite hollow fiber membrane of the present invention comprises an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, wherein the separation functional layer is provided on the surface of the dense layer, and the burst pressure measured under the following conditions is 2.25 MPa or higher. <Burst Pressure> A module fabricated using a composite hollow fiber membrane is subjected to a 0.25 MPa pressure increase at 10-minute intervals while N-methyl-2-pyrrolidone is passed through it, and the pressure (MPa) at which the composite hollow fiber membrane ruptures is measured.

Description

[Technical Field]

[0001] The present invention relates to a composite hollow fiber membrane having an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, and a method for producing the same. [Background technology]

[0002] In recent years, from the perspective of building a sustainable society and achieving carbon neutrality, the chemical industry has also been required to adopt more energy-efficient processes. In particular, since distillation processes account for a large proportion of the energy consumed by the chemical industry as a whole, there is a need to switch to more energy-efficient processes, and a shift to membrane separation processes, which are energy-efficient, is being considered.

[0003] Membrane separation processes are used in water purification, seawater desalination, and the manufacturing processes of various industrial products that use water as a solvent, and have become an industrially established technology. Polymer materials are the mainstream material for separation membranes used in membrane separation processes because they are relatively easy to mold and process, making it easy to establish inexpensive mass production processes, and they are lightweight, flexible, and easy to handle.

[0004] On the other hand, in the chemical industry, organic solvents are mainly used, so for the introduction of membrane separation processes, the separation membrane material must have sufficient durability against organic solvents. In particular, high-boiling-point aprotic polar solvents have recently been in high demand and consumption is increasing for applications such as media used in solution reactions in chemical synthesis, extraction media used in purification, solvents for polymer materials that take advantage of their high solubility, and cleaning agents. Representative aprotic polar solvents include dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene carbonate, and tetrahydrofuran, and the separation membrane must be durable against these solvents. However, these solvents have the property of dissolving and eroding separation membrane materials such as polysulfone, polyvinylidene fluoride, and cellulose acetate, which have been widely used in the water treatment field, and it is impossible to repurpose these separation membranes developed for water treatment for organic solvent membrane separation processes. In addition, a limited number of polymer materials such as polyethylene and tetrafluoroethylene have been used in organic solvent membrane separation processes for some time. However, separation membranes made of these polymer materials have been put into practical use as flat membranes of the dead-end filtration (total filtration) type, with pore sizes ranging from approximately 0.1 μm to several μm, and cannot be used for the purpose of separating polymer substances or low molecular weight solutes dissolved in organic solvents. Furthermore, they have not been put into practical use as hollow fiber membranes suitable for the cross-flow method, which is an effective operation method for concentrating the solute to be recovered. Hollow fiber filtration modules have significant advantages in terms of use and manufacturing, such as a simple flow path design and the elimination of parts such as spacer members and O-ring members required for flat membrane filtration modules.

[0005] Currently, distillation is used to purify and recover aprotic polar solvents or separate them from the solutes they contain. However, typical aprotic polar solvents have relatively high boiling points (around 150-200°C) and are susceptible to denaturation such as oxidation. Therefore, separating and purifying them from solutes by distillation requires not only energy consumption but also techniques to suppress denaturation. Furthermore, if the solute to be separated and recovered is heat-sensitive, distillation may not be applicable at all, presenting several challenges.

[0006] To address these challenges, membrane separation processes do not involve phase changes such as solvent evaporation, thus enabling the construction of energy-saving processes. Furthermore, they are unaffected by solvent oxidation and thermal denaturation, making them useful for separating solutions containing heat-sensitive solutes. Additionally, if nanofiltration membranes capable of efficiently separating low-molecular-weight solutes (molecular weight approximately 200-1000) from solvents (molecular weight approximately 100) can be provided, it is expected that the range of separation targets will expand beyond the limitations of existing microfiltration membranes. This field of separation membranes is called OSN (organic solvent nanofiltration).

[0007] OSN membranes have been under development in recent years, with several trials and practical applications being implemented. One approach involves using membranes made from inorganic materials such as ceramics, which have high solvent resistance due to their material properties. However, production costs and scale-up issues are hindering their widespread adoption. On the other hand, regarding the application of polymer materials, a representative method being considered is to fabricate polymer membranes using the non-solvent-induced layer separation (NIPS) process, which is used when fabricating conventional water treatment membranes. This process involves crosslinking the polymer membrane as a post-treatment to impart organic solvent resistance and make the polymer membrane insoluble in organic solvents. The NIPS method uses a film-forming stock solution in which polymers are dissolved in the aforementioned polar solvents, and since polymers themselves have low solvent resistance, a strong crosslinking treatment is required as a post-processing step.

[0008] For example, Non-Patent Document 1 proposes a nanofiltration membrane in which solvent resistance is imparted by crosslinking a polyimide flat membrane fabricated by the NIPS method. However, this nanofiltration membrane cannot be said to have sufficient resistance to aprotic polar solvents.

[0009] Furthermore, Non-Patent Document 2 proposes a reverse osmosis membrane for desalination (seawater desalination) in an aqueous system, using a polysulfone hollow fiber membrane fabricated by the NIPS method as a base material, with an interfacial polymerization film formed on the inner surface of the hollow fiber membrane. However, this polysulfone hollow fiber membrane has absolutely no resistance to organic solvents, especially aprotic polar solvents.

[0010] Furthermore, to improve the permeability of membranes with extremely small pore sizes, such as OSN membranes, it is necessary to make the separation active layer as thin as possible. In asymmetric membranes fabricated by the NIPS method, the separation active layer is generally thin, only a few μm thick, and can be thinned to about 0.5 μm with more advanced asymmetry (formation of a dense surface layer), allowing for the formation of membranes with superior permeability through asymmetric structure formation. In addition, for membranes that are intended for high-pressure operation exceeding 10 bar, such as OSN, mechanical strength in solvents is also important. Since membranes fabricated by the NIPS method are almost always made of amorphous polymers, their mechanical strength is not necessarily high, and especially in solvents where they are subject to solvent swelling, a decrease in elastic modulus occurs. Therefore, in order to maintain the strength of the membrane, it is necessary to adopt a method of forming the membrane on a separate backing carrier that is responsible for maintaining the membrane's strength. The same applies to the polyimide membranes mentioned above, where polyester or polyolefin nonwoven fabrics are used as the backing carrier.

[0011] On the other hand, another approach to OSN membrane fabrication is being investigated, using a method called thermally induced phase separation (TIPS) to obtain nanofiltration membranes. The TIPS method is a relatively new method in which a solvent that does not dissolve in a polymer material at low temperatures but dissolves at high temperatures is selected, and a homogeneous polymer solution dissolved at high temperatures is cooled to a temperature below the binodal line, which is the boundary between the one-phase and two-phase regions, thereby inducing phase separation and fixing the structure through polymer crystallization or glass transition. The TIPS method can be applied to polymers for which there are no solvents that dissolve at low temperatures, making it suitable for highly solvent-resistant crystalline polymers. Furthermore, it tends to produce a sponge-like homogeneous structure, resulting in a high-strength separation membrane, making it a suitable method for obtaining pressure-resistant OSN membranes, and is particularly suitable for fabricating hollow fiber type self-supporting membranes.

[0012] For example, Patent Document 1 describes a product produced by the TIPS method, with a fractional molecular weight of 200 to 1000 and a methanol permeate rate of 0.03 L / (m³). 2A nanofiltration hollow fiber membrane formed using a polyamide resin, which is (·bar·h) or more, has been proposed.

[0013] In addition, in Patent Document 2, a polyamide hollow fiber membrane used as an ultrafiltration membrane or a nanofiltration membrane, which is manufactured by applying the TIPS method, has a dense layer formed on at least one surface, and has linear concave portions extending in one direction on the surface of the dense layer, has been proposed.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0015]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0016] In order to use a membrane separation process as an alternative to a distillation process, a separation membrane having excellent permeate performance for organic solvents and excellent solute rejection performance in an organic solvent-based liquid to be treated is required. However, since the permeate performance and the rejection performance are conflicting performances, it is very difficult to achieve both the permeate performance and the rejection performance at a high level.

[0017] The polyamide hollow fiber membranes of Patent Documents 1 and 2 are in a shape suitable for cross-flow filtration and have high resistance to various organic solvents. However, since the mechanical strength in an organic solvent is not sufficient, it is difficult to increase the permeation rate of the organic solvent by increasing the pressure during operation. Also, the rejection performance of low-molecular solutes in an organic solvent-based liquid to be treated is not satisfactory, and there was room for improvement in terms of achieving both the permeation performance and the rejection performance at a high level.

[0018] An object of the present invention is to provide a composite hollow fiber membrane in which the permeation performance of an organic solvent and the rejection performance of solutes in an organic solvent-based liquid to be treated are achieved at a high level, and a method for producing the same.

Means for Solving the Problems

[0019] The present inventor conducted intensive studies to solve the above problems, and as a result, by providing a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of the dense layer of an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, it was found that a composite hollow fiber membrane capable of achieving both the permeation performance of an organic solvent and the rejection performance of solutes in an organic solvent-based liquid to be treated at a high level can be obtained. The present invention was completed by further studies based on such findings.

[0020] That is, the present invention provides an invention in the following aspects. Item 1. A composite hollow fiber membrane having an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, wherein the separation functional layer is provided on the surface of the dense layer, and the burst pressure measured under the following conditions is 2.25 MPa or more. <Burst Pressure> While passing N-methyl-2-pyrrolidone through a module prepared using the composite hollow fiber membrane, the pressure is increased by 0.25 MPa at 10-minute intervals, and the pressure (MPa) when the composite hollow fiber membrane breaks is measured. Item 2. The composite hollow fiber membrane according to Item 1, wherein the crosslinked resin is a crosslinked aromatic polyamide resin. Item 3. The supporting layer is a composite hollow fiber membrane according to item 1 or 2, wherein the porosity is 60-80%. Item 4. The dense layer is a composite hollow fiber membrane according to any one of items 1 to 3, with a thickness of 0.1 to 5 μm. Item 5. A composite hollow fiber membrane according to any one of items 1 to 4, wherein the dense layer is located on the luminal surface side of the aliphatic polyamide hollow fiber membrane. Item 6. The aliphatic polyamide hollow fiber membrane is a composite hollow fiber membrane according to any one of items 1 to 5, having a fractional molecular weight of 10,000 to 300,000. Item 7. The aliphatic polyamide hollow fiber membrane is a composite hollow fiber membrane according to any one of items 1 to 6, wherein the burst pressure measured under the following conditions is 2.1 MPa or higher. <Burst pressure> A module fabricated using aliphatic polyamide hollow fiber membranes is subjected to water pressure, and the pressure (MPa) at which the aliphatic polyamide hollow fiber membrane ruptures is measured. Item 8. A composite hollow fiber membrane according to any one of items 1 to 7, wherein the rejection rate of diphenyl sulfone when a solution in which the solvent is N-methyl-2-pyrrolidone and the solute is diphenyl sulfone is filtered is 30% or more. Item 9. The permeation rate of N-methyl-2-pyrrolidone at 25°C is 6 L / (m³). 2 • A composite hollow fiber membrane as described in any of items 1 to 8, wherein the above condition is met. Item 10. A filtration method for filtering a liquid to be treated, which contains an organic solvent and a solute, using a composite hollow fiber membrane as described in any of Items 1 to 9. Item 11. A hollow fiber membrane module comprising a module case containing a composite hollow fiber membrane as described in any of Items 1 to 9. Item 12. Method for producing a composite hollow fiber membrane, including the following steps 1 to 4: The first step involves preparing a film-forming stock solution by dissolving an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or higher and being immiscible with the aliphatic polyamide resin at temperatures below 100°C, at a temperature of 100°C or higher. A step of solidifying an aliphatic polyamide resin into a film by extruding the film-forming stock solution in a predetermined shape into a solidification bath at 100°C or lower, wherein in this step, a second step is to bring a solidification solution that is compatible with the organic solvent used in the film-forming stock solution and has low affinity for the aliphatic polyamide resin into contact with at least one surface of the film-forming stock solution extruded in the predetermined shape, thereby forming an aliphatic polyamide hollow fiber film having a dense layer on at least one surface. A third step involves removing the film-forming solvent and coagulation solution from the aliphatic polyamide hollow fiber membrane formed in the second step, and A fourth step involves forming a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of at least one dense layer of the aliphatic polyamide hollow fiber membrane obtained by the third step. [Effects of the Invention]

[0021] The composite hollow fiber membrane of the present invention has high mechanical strength in organic solvents (high burst pressure in pressure resistance tests in organic solvents), allowing for increased operating pressure and thus increased permeability of organic solvents. Furthermore, because the dense layer of the aliphatic polyamide hollow fiber membrane has a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, it can achieve a high level of both organic solvent permeability and solute blocking performance in organic solvent-based treated liquids (especially low molecular weight solutes with a molecular weight of approximately 200 to 1000). Moreover, because the composite hollow fiber membrane of the present invention is formed from a hollow fiber membrane containing aliphatic polyamide and a separation functional layer containing a crosslinked resin, it has excellent resistance to various types of organic solvents and can stably maintain membrane performance even when in contact with various types of organic solvents used industrially, making it suitable for use in membrane separation processes as an alternative to distillation processes. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram of an apparatus used to measure the molecular weight cutoff, burst pressure, permeability (Flux), and rejection rate of composite hollow fiber membranes or aliphatic polyamide hollow fiber membranes. [Figure 2]Figure a is a schematic diagram of the module used when measuring the burst pressure of an aliphatic polyamide hollow fiber membrane, and figure b is a schematic diagram of the apparatus used when measuring the burst pressure of an aliphatic polyamide hollow fiber membrane. [Figure 3] This is an image analysis diagram after binarization for calculating the porosity of the support layer of the aliphatic polyamide hollow fiber membrane in Example 1. [Figure 4] This is a scanning electron microscope image (magnification 10,000x) of the luminal surface of the aliphatic polyamide hollow fiber membrane (before separation functional layer formation) of Example 1. [Figure 5] This is a scanning electron microscope image (magnification 20,000x) of the luminal surface of the aliphatic polyamide hollow fiber membrane (before separation functional layer formation) of Example 1. [Figure 6] This is a scanning electron microscope image (magnification 10,000x) of the luminal cross-section of the aliphatic polyamide hollow fiber membrane (before separation functional layer formation) of Example 1. [Figure 7] This is a scanning electron microscope image (magnification 10,000x) of the luminal cross-section of the composite hollow fiber membrane of Example 1. [Figure 8] This is a scanning electron microscope image (magnification 20,000x) of the luminal cross-section of the composite hollow fiber membrane of Example 1. [Figure 9] This is a scanning electron microscope image (magnification 10,000x) of the luminal surface of the composite hollow fiber membrane of Example 1. [Figure 10] This is a scanning electron microscope image (magnification 20,000x) of the luminal surface of the composite hollow fiber membrane of Example 1. [Figure 11] This is a schematic diagram illustrating an example of calculating the porosity of the support layer of a composite hollow fiber membrane, and is a schematic cross-sectional view of an aliphatic polyamide hollow fiber membrane cut perpendicular to its longitudinal direction. [Figure 12] This is a magnified view of the area enclosed by the dotted line in Figure 11. [Figure 13] This is a magnified view of the area enclosed by the dotted line in Figure 11. [Modes for carrying out the invention]

[0023] 1.Definition In the present invention, when "ultrafiltration" or "ultrafiltration membrane" is used, it means filtration in which the molecular weight cutoff is set in the range of 1,000 to 1,000,000, or a filtration membrane in which the molecular weight cutoff is set in the range of 1,000 to 1,000,000. When "nanofiltration" or "nanofiltration membrane" is used, it means filtration in which the molecular weight cutoff is set in the range of 200 to 1,000, or a filtration membrane in which the molecular weight cutoff is set in the range of 200 to 1,000.

[0024] In the present invention, "aliphatic polyamide hollow fiber membrane" means a hollow fiber filtration membrane formed using an aliphatic polyamide resin, having a dense layer and a support layer.

[0025] In the present invention, "dense layer" refers to a region in an aliphatic polyamide hollow fiber membrane where dense micropores are aggregated, and where the presence of pores is substantially absent in scanning electron microscope (SEM) images at a magnification of 10,000x or higher.

[0026] In the present invention, the term "support layer" refers to a porous region in an aliphatic polyamide hollow fiber membrane that is other than the dense layer and has a continuous porous structure in which the presence of substantially pores can be observed in a scanning electron microscope (SEM) image at a magnification of 2000x.

[0027] In the present invention, the term "separation functional layer" means a layer provided on the surface of a dense layer of an aliphatic polyamide hollow fiber membrane and containing a crosslinked resin obtained by interfacial polycondensation.

[0028] 2.Composite hollow fiber membrane The composite hollow fiber membrane of the present invention comprises an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, wherein the separation functional layer is provided on the surface of the dense layer, and the burst pressure measured under the following conditions is 2.25 MPa or higher. The composite hollow fiber membrane of the present invention will be described in detail below. <Burst pressure> A module fabricated using a composite hollow fiber membrane is subjected to a 0.25 MPa pressure increase at 10-minute intervals while N-methyl-2-pyrrolidone is passed through it, and the pressure (MPa) at which the composite hollow fiber membrane ruptures is measured.

[0029] [Aliphatic polyamide hollow fiber membrane] The aliphatic polyamide hollow fiber membrane, which is the main component of the composite hollow fiber membrane of the present invention, has a dense layer and a support layer and is formed of an aliphatic polyamide resin. By using an aliphatic polyamide resin as the constituent resin of the hollow fiber membrane, the composite hollow fiber membrane of the present invention can be given not only resistance to a wide range of organic solvents but also high mechanical strength in organic solvents (it can increase the burst pressure in pressure resistance tests in organic solvents), so that the operating pressure can be increased and the amount of organic solvent permeable can be increased.

[0030] The type of aliphatic polyamide resin is not particularly limited, but examples include aliphatic polyamide homopolymers, aliphatic polyamide copolymers, or mixtures thereof. Specific examples of aliphatic polyamide homopolymers include polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, and polyamide 12. Specific examples of aliphatic polyamide copolymers include copolymers of aliphatic polyamide with polyethers such as polytetramethylene glycol and polyethylene glycol. The ratio of the aliphatic polyamide component in the aliphatic polyamide copolymer is not particularly limited, but for example, the proportion of the aliphatic polyamide component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. By satisfying the above range for the ratio of the aliphatic polyamide component in the aliphatic polyamide copolymer, the aliphatic polyamide hollow fiber membrane can be provided with even better organic solvent resistance and mechanical strength. Aliphatic polyamide resins may be used individually or in combination of two or more types.

[0031] Among these aliphatic polyamide resins, polyamide 6 is preferred as a resin for forming aliphatic polyamide hollow fiber films because it readily achieves a suitable balance of pressure resistance and solvent resistance, and also readily improves the permeability of organic solvents.

[0032] Aliphatic polyamide resins can be crosslinked or not, but from the viewpoint of reducing manufacturing costs, non-crosslinked resins are preferred.

[0033] The relative viscosity of the aliphatic polyamide resin is not particularly limited, but for example, it can be 2.0 to 7.0, preferably 2.5 to 6.0, and more preferably 3.0 to 5.0. By having such a relative viscosity, it is possible to improve moldability and controllability of phase separation during the production of aliphatic polyamide hollow fiber membranes, and to provide the aliphatic polyamide hollow fiber membranes with excellent dimensional stability. Here, relative viscosity refers to the value measured by an Ubbelohde viscometer at 25°C using a solution prepared by dissolving 1 g of aliphatic polyamide resin in 100 mL of 96% sulfuric acid.

[0034] The aliphatic polyamide hollow fiber membrane may contain fillers in addition to the aliphatic polyamide resin, as needed, to the extent that it does not impair the effects of the present invention. By including fillers, the strength, elongation, and modulus of elasticity of the aliphatic polyamide hollow fiber membrane can be improved. In particular, by including fillers, the aliphatic polyamide hollow fiber membrane becomes less prone to deformation even when high pressure is applied during filtration. There are no particular limitations on the type of filler to be added, but examples include fibrous fillers such as glass fibers, carbon fibers, potassium titanate whiskers, zinc oxide whiskers, calcium carbonate whiskers, wollastonite whiskers, aluminum borate whiskers, aramid fibers, alumina fibers, silicon carbide fibers, ceramic fibers, asbestos fibers, gypsum fibers, and metal fibers; talc, hydrotalcite, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, and asbestos fibers. Examples of fillers include silicates such as stratum and alumina silicate; metal compounds such as silicon dioxide, magnesium oxide, alumina, zirconium oxide, titanium dioxide, and iron oxide; carbonates such as calcium carbonate, magnesium carbonate, and dolomite; sulfates such as calcium sulfate and barium sulfate; metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; and inorganic materials such as glass beads, glass flakes, glass powder, ceramic beads, boron nitride, silicon carbide, carbon black, silica, and graphite as non-fiber fillers. These fillers may be used individually or in combination of two or more. Among these fillers, talc, hydrotalcite, silica, clay, and titanium dioxide are preferred, and talc and clay are more preferred. The filler content is not particularly limited, but for example, per 100 parts by weight of aliphatic polyamide resin, the filler may be 5 to 100 parts by weight, preferably 10 to 75 parts by weight, and more preferably 25 to 50 parts by weight. By including fillers in this quantity, it is possible to improve the strength, elongation, and elastic modulus of the aliphatic polyamide hollow fiber membrane.

[0035] Aliphatic polyamide hollow fiber membranes may contain additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants, as needed, to control pore size and improve membrane performance.

[0036] The outer diameter of the aliphatic polyamide hollow fiber membrane is appropriately set according to the application of the aliphatic polyamide hollow fiber membrane, the thickness of the dense layer and support layer, and the fluid permeability performance to be provided. However, considering the relationship between the effective membrane area when filled into a module, membrane strength, pressure loss of the fluid flowing through the hollow portion, and buckling pressure, the outer diameter of the hollow fiber membrane is 400 μm or more, preferably 450 to 4000 μm, and more preferably 500 to 3500 μm. The inner diameter of the aliphatic polyamide hollow fiber membrane is not particularly limited, but for example, it is 100 to 3000 μm, preferably 200 to 2500 μm, more preferably 300 to 2000 μm, and even more preferably 300 to 1500 μm. In this invention, the outer and inner diameters of the aliphatic polyamide hollow fiber membranes are determined by observing five hollow fiber membranes with an optical microscope at a magnification of 200x, measuring the outer and inner diameters (both at the point of maximum diameter) of each hollow fiber membrane, and calculating the average value of these values.

[0037] The thickness of the aliphatic polyamide hollow fiber membrane is appropriately set according to the application of the aliphatic polyamide hollow fiber membrane, the thickness of the dense layer and support layer, the liquid permeability performance to be provided, etc., but for example, 50 to 600 μm, preferably 100 to 350 μm is used. In the present invention, the thickness of the aliphatic polyamide hollow fiber membrane is a value calculated by dividing the value obtained by subtracting the inner diameter from the outer diameter by 2.

[0038] Here, filtration membranes (separation membranes) are classified in order of the size of the substances they separate, from largest to smallest: microfiltration (MF) membranes, ultrafiltration (UF) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes. For filtration membranes smaller than UF membranes, the molecular weight cutoff is used as an indicator of the size of the substance to be captured. The molecular weight cutoff is determined by a permeation test using a standard substance with a known molecular weight. The molecular weight cutoff is determined by the lower limit of molecular size (Dalton units: Da) at which 90% or more is retained by the permeation test. In this invention, the molecular weight cutoff of ultrafiltration membranes is 1,000 to 1,000,000, and the molecular weight cutoff of nanofiltration membranes is 200 to 1,000,000.

[0039] When forming a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of a dense layer of an aliphatic polyamide hollow fiber membrane, the fractionation performance of the aliphatic polyamide hollow fiber membrane, which is dominated by the dense layer, reflects the characteristics of the dense layer surface where the interfacial polycondensation reaction takes place. Therefore, the fractionation performance of the aliphatic polyamide hollow fiber membrane greatly affects the formation and characteristics of the separation functional layer. The fractionation molecular weight of the aliphatic polyamide hollow fiber membrane of the present invention is preferably within the range of an ultrafiltration membrane, more preferably 10,000 to 300,000, even more preferably 20,000 to 100,000, even more preferably 30,000 to 80,000, even more preferably 40,000 to 70,000, and particularly preferably 50,000 to 70,000, in order to form a separation functional layer on the surface of the dense layer that has excellent blocking performance for solutes (especially low molecular weight solutes with a molecular weight of about 200 to 1000) in an organic solvent-based liquid to be treated, and more preferably 10,000 to 300,000, even more preferably 20,000 to 100,000, even more preferably 30,000 to 80,000, even more preferably 40,000 to 70,000, and most preferably 50,000 to 70,000. If the molecular weight cutoff is within the above range, a uniform separation functional layer can be formed on the surface and surface layer (inside the layer close to the surface) of the dense layer, and a composite hollow fiber membrane of the present invention can be obtained that achieves a higher level of both organic solvent permeability and solute inhibition performance in organic solvent-based treated liquids. The molecular weight cutoff of the aliphatic polyamide hollow fiber membrane can be adjusted to the desired value by appropriately adjusting the thickness of the dense layer and the pore size of the support layer.

[0040] In this invention, the fractional molecular weight of the aliphatic polyamide hollow fiber membrane is determined when dextran is used as a standard substance and water as the solvent, if it is greater than 3000. Specifically, the fractional molecular weight of the aliphatic polyamide hollow fiber membrane (if it is greater than 3000) is determined when a cross-flow module is made using the aliphatic polyamide hollow fiber membrane, and aqueous solutions containing multiple known molecular weights of dextran at predetermined concentrations are used as circulating solutions (stock solutions) in an internal pressure cross-flow method. The dextran concentration in the permeate is measured by high-performance liquid chromatography, and the solute rejection rate at each molecular weight is calculated according to the following formula. The results are then plotted on a graph with molecular weight on the x-axis and rejection rate on the y-axis, and the molecular weight at the intersection of the resulting approximation curve and the 90% rejection rate is used. Solute rejection rate (%) = {(Dextran concentration in stock solution - Dextran concentration in permeate) / Dextran concentration in stock solution} × 100

[0041] Furthermore, in the present invention, the fractional molecular weight of the aliphatic polyamide hollow fiber membrane is a value determined when monodisperse polystyrene is used as a standard substance and N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") is used as the solvent, if the fractional molecular weight is 3000 or less. Specifically, the fractional molecular weight of the aliphatic polyamide hollow fiber membrane (if the fractional molecular weight is 3000 or less) is a value determined when a cross-flow module is made using an aliphatic polyamide hollow fiber membrane and an NMP solution containing multiple polystyrenes of known molecular weights at predetermined concentrations is used as the circulating liquid (stock solution) in an internal pressure cross-flow method. The polystyrene concentration in the permeate is measured by high-performance liquid chromatography, and the solute rejection rate at each molecular weight is calculated according to the following formula. The results are then plotted on a graph with molecular weight on the x-axis and rejection rate on the y-axis, and the molecular weight at the intersection of the resulting approximation curve and the 90% rejection rate is used. Solute rejection rate (%) = {(Polystyrene concentration in stock solution - Polystyrene concentration in permeate) / Polystyrene concentration in stock solution} × 100

[0042] The aliphatic polyamide hollow fiber membrane, which serves as the base material for the composite hollow fiber membrane, is responsible for the mechanical properties of the composite hollow fiber membrane, and the radial stress characteristics of the hollow fiber membrane, which are mainly related to pressure resistance, are important. Stress can be applied as internal pressure to the hollow portion, and the radial fracture stress can be evaluated by the burst pressure of the internal pressure. Furthermore, since the operating pressure during membrane filtration is related to the permeation rate, it is preferable that the pressure resistance of the aliphatic polyamide hollow fiber membrane is sufficiently high. The burst pressure of the aliphatic polyamide hollow fiber membrane of the present invention is not particularly limited and can be adjusted to the desired value by appropriately adjusting material properties such as the crystallinity and molecular weight of the aliphatic polyamide resin, the ratio of the inner diameter to the film thickness of the hollow fiber membrane, the thickness of the dense layer, the thickness and porosity of the support layer, and the pore size of the pores in the support layer. However, from the viewpoint of increasing the permeability by increasing the operating pressure during membrane filtration, it is preferably 2.1 MPa or higher, more preferably 2.5 MPa or higher, even more preferably 2.8 MPa or higher, and even more preferably 3.0 MPa or higher. The upper limit of the burst pressure of an aliphatic polyamide hollow fiber membrane is usually 4.0 MPa or less, preferably 3.8 MPa or less. Specifically, the burst pressure of an aliphatic polyamide hollow fiber membrane is preferably 2.1 to 4.0 MPa, more preferably 2.5 to 3.8 MPa, even more preferably 2.8 to 3.8 MPa, and even more preferably 3.0 to 3.8 MPa. In the present invention, the burst pressure of an aliphatic polyamide hollow fiber membrane is the pressure (MPa) at which the aliphatic polyamide hollow fiber membrane ruptures when water pressure is applied to a module made using the aliphatic polyamide hollow fiber membrane.

[0043] The burst pressure of the aliphatic polyamide hollow fiber membrane is measured by the following method. First, module 8 shown in Figure 2a is prepared. Specifically, ten hollow fiber membranes 8a are cut to a length of 30 cm and bundled together. Next, a nylon rigid tube 8b with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm is prepared, and a rubber stopper about 20 mm long is inserted into the opening at one end of the tube to seal the opening. Next, a two-part epoxy resin is injected into the opening of the tube opposite to the rubber stopper to fill the space inside the tube with the epoxy resin. After that, the bundle of hollow fiber membranes prepared is bent into a roughly U-shape, and both ends of the hollow fiber membranes are heat-sealed to prevent epoxy resin from entering the hollow part. These ends are then inserted into the tube filled with epoxy resin until they touch the rubber stopper, and the epoxy resin is allowed to harden in that state. Next, module 8 is created by cutting the rubber stopper side of the hardened epoxy resin portion together with the tube, thereby opening the hollow portions at both ends of the hollow fiber membrane. Next, module 8 is set in the apparatus shown in Figure 2b, and water pressure is applied to module 8 using a hand pump 9. The pressure (MPa) at which it ruptures is defined as the burst pressure.

[0044] The degree of crystallinity of the aliphatic polyamide hollow fiber membrane is not particularly limited, and is usually 25% or higher. From the viewpoint of improving solvent resistance and pressure resistance, it is preferably 30% or higher, more preferably 35% or higher, even more preferably 40% or higher, even more preferably 45% or higher, and particularly preferably 50% or higher. The degree of crystallinity of the aliphatic polyamide hollow fiber membrane can be adjusted to the desired value by, for example, annealing (heat treatment). Annealing can be performed by methods such as dry heat or autoclave.

[0045] In this invention, the degree of crystallinity of an aliphatic polyamide hollow fiber membrane is measured by X-ray diffraction (XRD). Specifically, multiple hollow fiber samples are arranged without gaps on a measurement stage, and the scattering pattern spectrum of scattering vectors and scattering intensities is obtained by scanning the scattering angle. The degree of crystallinity is determined by spectrally separating the obtained spectrum into crystalline components and amorphous components and quantifying them.

[0046] [Dense layer] The dense layer is a region in the aliphatic polyamide hollow fiber membrane where dense micropores are clustered together, and where the presence of pores is substantially absent in scanning electron microscope (SEM) images at a magnification of 10,000x or higher.

[0047] The dense layer may be formed on the inner surface of the aliphatic polyamide hollow fiber membrane, on the outer surface, or on both surfaces. However, from the viewpoint of achieving a higher level of balance between the permeability of organic solvents and the blocking performance of solutes in the organic solvent-based treated solution, it is preferable that the dense layer be formed on the inner surface. When observing the dense layer with a scanning electron microscope (SEM), if the dense layer is located on the outer surface of the aliphatic polyamide hollow fiber membrane, the aliphatic polyamide hollow fiber membrane can be cut to an appropriate size, placed on a sample stage, and then observed after vapor deposition of Pt, Au, Pd, etc. If the dense layer is located on the inner surface of the aliphatic polyamide hollow fiber membrane, the aliphatic polyamide hollow fiber membrane can be cut longitudinally with a sharp blade such as a scalpel to expose the inner surface, then cut to an appropriate size, placed on a sample stage, and then observed after vapor deposition of Pt, Au, Pd, etc.

[0048] The thickness of the dense layer is not particularly limited and can be adjusted to the desired value by appropriately adjusting the solvent, concentration, and temperature of the film-forming stock solution, the type and temperature of the coagulation solution, etc. However, from the viewpoint of improving the performance of blocking solutes in organic solvent-based treated liquids and from the viewpoint of stabilizing the separation function layer, it is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. Furthermore, from the viewpoint of improving the permeability of organic solvents, it is preferably 2.0 μm or less, more preferably 1.8 μm or less, even more preferably 1.5 μm or less, even more preferably 1.2 μm or less, and even more preferably 1.0 μm or less. Specifically, the thickness of the dense layer is preferably 0.1 to 2.0 μm, more preferably 0.2 to 1.8 μm, even more preferably 0.3 to 1.5 μm, even more preferably 0.3 to 1.2 μm, and even more preferably 0.3 to 1.0 μm. In this invention, the thickness of the dense layer is determined by measuring the distance (thickness) of the region where substantially no pores are observed in a scanning electron microscope (SEM) image of a cross-section of an aliphatic polyamide hollow fiber membrane at a magnification of 10,000x at 10 locations at regular intervals, and calculating the average value.

[0049] [Support layer] The support layer is a porous region in the aliphatic polyamide hollow fiber membrane that is other than the dense layer and has a continuous porous structure in which substantially pores are observed in scanning electron microscope (SEM) images at a magnification of 2000x.

[0050] The pore size of the support layer is not particularly limited, as long as it does not significantly hinder the strength required to hold the dense layer and the permeability of fluids.

[0051] The porosity of the support layer is not particularly limited and can be adjusted to the desired value by appropriately adjusting the solvent, concentration, and temperature of the film-forming stock solution, the type and temperature of the coagulation solution, etc., in the production of aliphatic polyamide hollow fiber membranes. However, from the viewpoint of ease of film formation and from the viewpoint of increasing membrane strength so that the operating pressure during membrane filtration can be increased to increase the permeability, it is preferably 60-80%, more preferably 63-78%, even more preferably 65-77%, and even more preferably 66-76%.

[0052] In this invention, the porosity of the support layer is calculated by the following method. Scanning electron microscope (SEM) images are taken at five equally spaced locations in the thickness direction of the support layer of the aliphatic polyamide hollow fiber membrane, in a cross section obtained by cutting the aliphatic polyamide hollow fiber membrane perpendicular to the longitudinal direction. Specifically, the images are taken as follows. Figure 11 is a schematic cross section obtained by cutting the aliphatic polyamide hollow fiber membrane perpendicular to the longitudinal direction, and Figures 12 and 13 are partially enlarged views of the area enclosed by the dotted line in Figure 11, showing an example of an aliphatic polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 11. Note that the description of the separation functional layer is omitted in Figures 11 to 13. As shown in Figure 12, a straight line is drawn from the center of the lumen of the aliphatic polyamide hollow fiber membrane 8a toward the outer surface, and this line is divided into five equal parts from the lumen side surface to the outer surface of the support layer 11. Then, as shown in Figure 12, the midpoint of the five divided line segments is determined. Then, as shown in Figure 13, the midpoint is positioned at the center of the captured image, and images are taken at a uniform magnification at five locations such that only the support layer 11 is included in the captured image and the number of pores is between 30 and 300. Image analysis of the five captured SEM images is performed using image analysis software (ImageJ) to analyze the region, and the pore portion and the polymer portion are distinguished by binarization. The area ratio (%) of the total pore area to the area of ​​the analysis region is then calculated for each, and the average value is calculated.

[0053] [Separation functional layer] The separation function layer is a layer provided on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane in order to improve the performance of blocking solutes in organic solvent-based treated liquids. The composite hollow fiber membrane of the present invention, which has a separation function layer on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane, shows a significant improvement in the performance of blocking solutes (especially low molecular weight solutes with a molecular weight of about 200 to 1000) in organic solvent-based treated liquids compared to an aliphatic polyamide hollow fiber membrane without a separation function layer, and can achieve a high level of both organic solvent permeability and solute blocking performance in organic solvent-based treated liquids.

[0054] The separation functional layer may be provided on the surface of the dense layer on the luminal side surface of the aliphatic polyamide hollow fiber membrane, or on the surface of the dense layer on the outer surface of the aliphatic polyamide hollow fiber membrane, but it is preferable that it be provided on the surface of the dense layer on the luminal side surface of the aliphatic polyamide hollow fiber membrane. The reason for this is that if the separation functional layer is provided on the surface of the dense layer on the outer surface of the aliphatic polyamide hollow fiber membrane, peeling of the separation functional layer due to contact between hollow fiber membranes during filtration, or peeling at the interface between both ends of the module and the sealant during module fabrication, may occur. Furthermore, if the aliphatic polyamide hollow fiber membrane has dense layers on both sides, the separation functional layer may be provided on the surface of only one of the dense layers, or on both dense layers, but for the reasons mentioned above, it is preferable that it be provided only on the surface of the dense layer on the luminal side surface.

[0055] The separation function layer is a layer mainly composed of a crosslinked resin obtained by interfacial polycondensation, and more specifically, a layer having a network structure formed of a crosslinked resin obtained by the interfacial polycondensation reaction of two or more polyfunctional monomers containing three or more monomers. Because the separation function layer is formed of a crosslinked resin, it has excellent resistance to various types of organic solvents and can stably maintain its film performance even when in contact with various types of organic solvents used industrially. The crosslinked resin is not particularly limited as long as it is a resin having a crosslinked structure obtained by interfacial polycondensation, and examples include crosslinked polyamide resins and crosslinked polyester resins. The crosslinked resin may contain one type or two or more types. In the case of crosslinked polyamide resins, typically two or more polyfunctional amines and two or more polyfunctional acyl halides are used as polyfunctional monomers. In the case of crosslinked polyester resins, typically two or more polyhydric alcohols and two or more polyfunctional acyl halides are used as polyfunctional monomers. By using highly reactive acyl halides, the interfacial polycondensation reaction can be easily and instantaneously carried out. In the present invention, from the viewpoint of improving the solvent resistance of the separation functional layer and obtaining a composite hollow fiber membrane that can achieve a higher level of both organic solvent permeability and solute inhibition performance in organic solvent-based treated liquids, the crosslinked resin constituting the separation functional layer is preferably a crosslinked polyamide resin, and more preferably a crosslinked aromatic polyamide resin. Below, as a representative example, the case in which the crosslinked resin constituting the separation functional layer is a crosslinked polyamide resin will be described.

[0056] The polyfunctional amines, which are raw material monomers for crosslinked polyamide resins, are amines having at least two amino groups in one molecule. For example, aromatic diamines such as phenylenediamine, xylylenediamine, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine, and compounds in which two hydrogen atoms of aromatic hydrocarbons are substituted with two amino groups, either directly or via functional groups, where two amino groups are bonded to the benzene ring at the ortho, meta, or para position; and compounds such as 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, biphenyl, and diphenylmethane, where two amino groups are bonded to the benzene ring at the ortho, meta, or para position. Examples include aromatic triamines, such as compounds in which three hydrogen atoms of an aromatic hydrocarbon directly or via a functional group are substituted with three amino groups; aromatic tetraamines, such as compounds in which four hydrogen atoms of an aromatic hydrocarbon whose benzene ring is directly or via a functional group are substituted with four amino groups (e.g., 3,3',4,4'-tetraaminobiphenyl); aliphatic polyfunctional amines such as ethylenediamine and propylenediamine; and alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, piperazine, and 4-aminoethylpiperazine. These polyfunctional amines may be further substituted with substituents such as halogen atoms, sulfo groups, alkyl groups, and fluoroalkyl groups. These polyfunctional amines may be used individually or in combination of two or more. Furthermore, among these polyfunctional amines, from the viewpoint of improving the performance of inhibiting solutes in organic solvent-based treatment solutions, reactivity, handling, and availability, aromatic polyfunctional amines are preferred, more preferably aromatic 2- to 4-functional amines, even more preferably at least one aromatic diamine selected from the group consisting of m-phenylenediamine, p-phenylenediamine, xylylenediamine, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine, and particularly preferably m-phenylenediamine.

[0057] The polyfunctional acyl halides used as raw material monomers for crosslinked polyamide resins are acyl halides having at least two halogenated carbonyl groups in one molecule. Examples include trifunctional acyl halides such as trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride; aromatic difunctional acyl halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic difunctional acyl halides such as adipoyl chloride and sebacoyl chloride; and difunctional acyl halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofrancicarboxylic acid dichloride. These polyfunctional acyl halides may be used individually or in combination of two or more. To obtain a crosslinked polyamide resin, it is necessary to use a polyfunctional amine and / or polyfunctional acyl halide with three or more functions. However, from the viewpoint of improving the solvent resistance of the separation functional layer, improving the performance of blocking solutes in organic solvent-based treatment liquids, reactivity, handling, and availability, it is preferable to use a trifunctional acyl halide, and more preferably trimesic acid chloride.

[0058] The separation functional layer may contain a non-crosslinked polyamide resin (a linear polyamide resin obtained by an interfacial polycondensation reaction between a diamine and a bifunctional acyl halide), but it is preferable not to include a non-crosslinked polyamide resin from the viewpoint of improving the solvent resistance of the separation functional layer. If the separation functional layer contains a non-crosslinked polyamide resin, the content of the non-crosslinked polyamide resin is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less.

[0059] The separation layer may contain additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants, as needed.

[0060] The thickness of the separation functional layer is not particularly limited, but because it is extremely thin (less than 0.1 μm), accurately measuring its thickness is very difficult even when observed at a scanning electron microscope (SEM) magnification of 10 to 200,000 times. Since the separation functional layer of the present invention is observed as a morphology completely integrated with the dense layer of the aliphatic polyamide hollow fiber membrane, it is difficult to determine the thickness of the separation functional layer. However, if the separation functional layer has a morphology with large irregularities, it will be observed as an irregular image different from that of the dense layer, and the presence of the separation functional layer can be determined from the SEM image. In this case as well, it is difficult to determine the thickness of the separation functional layer. On the other hand, the morphology in the SEM image of the surface on which the interfacial polycondensation reaction has been performed is different from the morphology in the SEM image of the surface of the dense layer of an aliphatic polyamide hollow fiber membrane on which the interfacial polycondensation reaction has not been performed (numerous circular protrusions, etc., that are not present on the surface of the dense layer can be seen), so the presence of the separation functional layer can be confirmed by comparing the SEM images.

[0061] Furthermore, the presence of the separation functional layer can also be confirmed by an air leak test of the composite hollow fiber membrane. The air leak test method involves applying an air pressure of approximately 0.2 MPa to the hollow portion of a dry composite hollow fiber membrane to seal in the pressurized air, and then evaluating the decrease in the containment pressure over time. If the aliphatic polyamide hollow fiber membrane has a pore size in the ultrafiltration membrane range, the aliphatic polyamide hollow fiber membrane cannot maintain the containment pressure at all. On the other hand, a composite hollow fiber membrane that is completely composited with a separation functional layer can maintain the containment pressure almost completely. Therefore, the presence of the separation functional layer can be confirmed by testing whether or not it can maintain the containment pressure. In addition, since the quality of the formation of the separation functional layer can be determined by quantifying the state of containment pressure retention, the air leak test method is effective in confirming defects in the separation functional layer. In one embodiment of the composite hollow fiber membrane of the present invention, when an air leak test is performed on a membrane area (S) and the total pressurized space volume (V) defined by the following formula 1, the amount of air leak (pressure drop) is preferably 0.05 MPa or less, more preferably 0.02 MPa or less, and even more preferably 0.005 MPa or less per 5 minutes. (Formula 1) V / S=0.0002×0.45 / R R is the inner diameter (mm) of the composite hollow fiber membrane. The error of V / S is within ±10%. When detecting air leakage through a hollow fiber membrane by pressure drop, it is necessary for quantitative accuracy that the membrane area S (leakage area) and the total pressurized space volume V remain relatively constant. In the case of a hollow fiber membrane, the hollow volume of the hollow fiber itself changes with changes in the inner diameter, and the ratio of volume to membrane area is proportional to the inner diameter. Furthermore, the module size and leak tester size also vary depending on the thickness of the hollow fiber membrane, so it is necessary to correct these as shown in Equation 1 above. In this invention, the inner diameter of the hollow fiber membrane is 0.45 mm and the length is 1 m. 2 0.0002m per unit 3 Based on air leak tests in the space, the optimal value was found, and for hollow fiber membranes with an inner diameter of 0.1 to 3 mm, which are suitable for the present invention, the conditions were standardized for hollow fiber membranes with different inner diameters based on this standard and the relationship described in Formula 1 above.

[0062] The amount of air leak (pressure drop) in a composite hollow fiber membrane is measured specifically by the following method. First, 20 composite hollow fiber membranes are cut to a length of 30 cm and bundled together. Next, a polybutylene terephthalate (PBT) tube with an outer diameter of 12.7 mm, an inner diameter of 9.5 mm, and a length of 53 mm is prepared. A silicone tube with an inner diameter of 12 mm and a length of approximately 50 mm is inserted about 15 mm into the opening at one end of the PBT tube to connect them. A rubber stopper about 20 mm long is inserted into the opposite end of the silicone tube from the end inserted into the PBT tube, sealing the opening at that end. Next, a two-part epoxy resin is injected into the opening of the connected tube on the opposite side from the rubber stopper to fill the space inside the tube with the epoxy resin. Subsequently, one end of the bundle of prepared composite hollow fiber membranes is heat-sealed to prevent epoxy resin from entering the hollow portion, and this end is inserted into a tube filled with epoxy resin until it touches a rubber stopper. The epoxy resin is then allowed to harden in this state. Next, the hardened epoxy resin portion on the rubber stopper side is cut along with the tube to open the hollow portion. The same operation is performed on the other end to create a cross-flow module with open hollow portions at both ends of the composite hollow fiber membrane. The membrane area of ​​the module is based on the inner area of ​​the hollow fibers and is calculated from the inner diameter, number of fibers, and effective length of the hollow fibers. One end of the outlet connecting to the hollow section of the fabricated module is sealed, and a valve and a pressure line with a pressure gauge between the valve and the module are attached to the other end. Air pressure of 0.2 MPa is applied to the hollow section, and the valve is closed to contain the pressure. Immediately thereafter, the pressure is monitored over time, and the change in pressure after 5 minutes is measured. The containment volume (total pressure space volume V) including the hollow fiber, module, and pressure line is estimated, and the length of the line etc. is controlled so that the ratio of the membrane area S to the total pressure space volume V is within ±10% of the relationship in Equation 1 above.

[0063] [Burst pressure of composite hollow fiber membranes] The composite hollow fiber membrane of the present invention has a burst pressure of 2.25 MPa or higher, as measured under the following conditions, and exhibits high mechanical strength (excellent pressure resistance) in organic solvents. Therefore, the operating pressure during membrane filtration can be increased to increase the permeability of the organic solvent. <Burst pressure> A module fabricated using a composite hollow fiber membrane is subjected to a 0.25 MPa pressure increase at 10-minute intervals while N-methyl-2-pyrrolidone is passed through it, and the pressure (MPa) at which the composite hollow fiber membrane ruptures is measured.

[0064] The burst pressure of the composite hollow fiber membrane is preferably 2.5 MPa or higher, more preferably 2.75 MPa or higher, from the viewpoint of increasing the operating pressure during membrane filtration and further increasing the permeability of the organic solvent. The upper limit of the burst pressure of the composite hollow fiber membrane is usually 4.0 MPa or lower. Specifically, the burst pressure of the composite hollow fiber membrane is preferably 2.5 to 4.0 MPa, more preferably 2.75 to 4.0 MPa. The burst pressure of the composite hollow fiber membrane can be adjusted to the desired value by appropriately adjusting the aliphatic polyamide hollow fiber membrane and the material forming the separation functional layer, the thickness of the dense layer, the thickness and porosity of the support layer, and the pore size of the pores in the support layer.

[0065] The burst pressure of the composite hollow fiber membrane is measured specifically by the following method. First, 20 composite hollow fiber membranes are cut to a length of 30 cm and bundled together. Next, a polybutylene terephthalate (PBT) tube with an outer diameter of 12.7 mm, an inner diameter of 9.5 mm, and a length of 53 mm is prepared. A silicone tube with an inner diameter of 12 mm and a length of approximately 50 mm is inserted about 15 mm into the opening at one end of the PBT tube to connect them. A rubber stopper about 20 mm in length is inserted into the opposite end of the silicone tube from the side inserted into the PBT tube to seal the opening at that end. Next, a two-part epoxy resin is injected into the opening of the connected tube on the opposite side from the rubber stopper to fill the space inside the tube with the epoxy resin. Subsequently, one end of the bundle of prepared composite hollow fiber membranes is heat-sealed to prevent epoxy resin from entering the hollow portion, and this end is inserted into the tube filled with epoxy resin until it touches the rubber stopper, and the epoxy resin is allowed to harden in this state. Next, the area of ​​the hardened epoxy resin on the rubber stopper side is cut along with the tube to open the hollow portion. The same operation is performed on the other end to create a cross-flow module with open hollow portions at both ends of the composite hollow fiber membrane. The fabricated cross-flow module 6 is connected to the internal pressure separation line shown in Figure 1, and NMP is continuously permeated through the cross-flow module 6 by the liquid circulation pump 2. In the module, the pressure of the primary pressure gauge 3 and the secondary pressure gauge 4 are adjusted by the regulator 5, and the arithmetic mean of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 is set as the applied pressure, which is increased by 0.25 MPa at 10-minute intervals. The burst pressure is defined as the pressure (MPa) at which the composite hollow fiber membrane ruptures, that is, when a rapid pressure drop occurs.

[0066] [Permeability of organic solvents and blocking performance of solutes] The composite hollow fiber membrane of the present invention, by having the separation function layer provided on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane, can achieve a high level of both organic solvent permeability and solute inhibition performance in organic solvent-based treated liquids, and has, for example, the following permeability and inhibition performance.

[0067] As one embodiment of the composite hollow fiber membrane of the present invention, the permeation rate of NMP at a pressure of 75% with respect to the burst pressure of the composite hollow fiber membrane at 25°C is preferably 6 L / (m 2 ·h) or more, more preferably 8 L / (m 2 ·h) or more, still more preferably 10 L / (m 2 ·h) or more, even more preferably 11 L / (m 2 ·h) or more, still more preferably 12 L / (m 2 ·h) or more, even more preferably 14 L / (m 2 ·h) or more. The upper limit value of the NMP permeation rate is usually 20 L / (m 2 ·h) or less. Specifically, the permeation rate of NMP at a pressure of 75% with respect to the burst pressure of the composite hollow fiber membrane at 25°C is preferably 6 to 20 L / (m 2 ·h), more preferably 8 to 20 L / (m 2 ·h), still more preferably 10 to 20 L / (m 2 ·h), even more preferably 11 to 20 L / (m 2 ·h), still more preferably 12 to 20 L / (m 2 ·h), even more preferably 14 to 20 L / (m 2 ·h). The NMP permeation rate can be adjusted to the target value by appropriately adjusting the fractional molecular weight of the aliphatic polyamide hollow fiber membrane, the thickness of the dense layer, the type of the forming material of the separation functional layer, etc.

[0068] The NMP permeation rate is a value measured by internal pressure filtration, and is measured using the following procedure. First, 20 composite hollow fiber membranes are cut to a length of 30 cm and bundled together. Next, a polybutylene terephthalate (PBT) tube with an outer diameter of 12.7 mm, an inner diameter of 9.5 mm, and a length of 53 mm is prepared. A silicone tube with an inner diameter of 12 mm and a length of approximately 50 mm is inserted about 15 mm into the opening at one end of the PBT tube to connect them. A rubber stopper about 20 mm in length is inserted into the opposite end of the silicone tube from the side inserted into the PBT tube, sealing the opening at that end. Next, a two-part epoxy resin is injected into the opening of the connected tube on the opposite side from the rubber stopper to fill the space inside the tube with the epoxy resin. Subsequently, one end of the bundle of prepared composite hollow fiber membranes is heat-sealed to prevent epoxy resin from entering the hollow portion, and this end is inserted into the tube filled with epoxy resin until it touches the rubber stopper, and the epoxy resin is allowed to harden in this state. Next, the area of ​​the hardened epoxy resin on the rubber stopper side is cut along with the tube to open the hollow portion. The same operation is performed on the other end to create a cross-flow module with open hollow portions at both ends of the composite hollow fiber membrane. The fabricated cross-flow module 6 is connected to the internal pressure separation line shown in Figure 1, and the fluid is continuously permeated through the cross-flow module 6 by the fluid circulation pump 2. NMP is used as the fluid. In the module, the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 are adjusted by the regulator 5 so that the arithmetic mean of the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 is 75% of the burst pressure of the composite hollow fiber membrane. Of the fluid that permeates through the module, the fluid that has permeated through the pores of the composite hollow fiber membrane is collected as permeate separated from the fluid, and the remainder is circulated back to the separation line. The permeate that flows out of the cross-flow module 6 between 2 and 4 hours after the start of circulation is collected in the receiving tray 7, and the NMP permeate amount (L / (m)) is calculated according to the following formula. 2 Calculate h)). NMP permeation volume = Volume of NMP that permeates to the outside of the composite hollow fiber membrane (L) / [Inner diameter of composite hollow fiber membrane (m) × 3.14 × Effective filtration length of composite hollow fiber membrane (m) × 20 (fibers) × Time (h)] Effective filtration length of composite hollow fiber membrane: In a cross-flow module, this is the length of the portion of the outer surface of the composite hollow fiber membrane that is not coated with epoxy resin.

[0069] The composite hollow fiber membrane of the present invention is preferably an ultrafiltration membrane or a nanofiltration membrane, more preferably a nanofiltration membrane, i.e., having a molecular weight cutoff of 200 to 1000. However, since the method for measuring molecular weight cutoff is complicated, a simple method for classifying filtration membranes was used to evaluate their blocking performance against specific substances. In this invention, the blocking rate of diphenyl sulfone (molecular weight: 218.27), which corresponds to the smallest molecular weight cutoff as an OSN, was used. Furthermore, the fact that the molecular weight cutoff is less than 1000 was confirmed using the blocking rate of monodisperse polystyrene (molecular weight: 1000). The composite hollow fiber membrane of the present invention had a blocking rate of 90% or more against polystyrene with a molecular weight of 1000, and a blocking rate of 30% or more against diphenyl sulfone, which is a low molecular weight, thus satisfying the performance requirements of a nanofiltration membrane.

[0070] In one embodiment of the composite hollow fiber membrane of the present invention, when a solution in which the solvent is NMP and the solute is diphenyl sulfone is filtered, the rejection rate of diphenyl sulfone is preferably 30% or more, more preferably 35% or more, even more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. The rejection rate of diphenyl sulfone can be adjusted to the desired value by appropriately selecting the type of material forming the separation functional layer.

[0071] The rejection rate of diphenylsulfone or polystyrene is measured by internal pressure filtration, and is measured using the same procedure as for measuring NMP permeability, except that an NMP solution containing 0.2% by weight of diphenylsulfone or polystyrene is used. The concentration of diphenylsulfone or polystyrene can be measured by liquid chromatography. The rejection rate of diphenylsulfone or polystyrene is calculated using the following formula. Rejection rate = 100 - (Concentration of permeate / Concentration of fluid) × 100

[0072] [Soil solvent resistance] The composite hollow fiber membrane of the present invention is mainly formed of an aliphatic polyamide resin and a crosslinked resin (preferably a crosslinked aromatic polyamide resin), and therefore possesses the property of maintaining a stable membrane structure by suppressing changes in strength and elongation even when in contact with various types of organic solvents (organic solvent resistance). More specifically, the composite hollow fiber membrane of the present invention has resistance to organic solvents such as alcohols, aprotic polar solvents, hydrocarbons, higher fatty acids, ketones, esters, and ethers. Examples of such organic solvents include the following. Alcohols: Primary alcohols such as methanol, ethanol, n-propanol, n-butanol, and benzyl alcohol; secondary alcohols such as isopropyl alcohol and isobutanol; tertiary alcohols such as tertiary butyl alcohol; and polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-butanediol, and glycerin. Ketones: Acetone, methyl ethyl ketone, cyclohexanone, diisopropyl ketone, etc. Ethers: 3-methoxybutanol, 3-methoxybutyl acetate, tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, etc. Aprotic polar solvents: N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, sulfolane, etc. Esters: Ethyl acetate, isobutyl acetate, ethyl lactate, dimethyl phthalate, diethyl phthalate, ethylene carbonate, propylene carbonate, etc. Hydrocarbons: Petroleum ether, pentane, hexane, heptane, benzene, toluene, xylene, liquid paraffin, gasoline, and mineral oil. Higher fatty acids: Fatty acids with 4 or more carbon atoms (preferably 4 to 30) other than the carboxyl group, such as oleic acid, linoleic acid, and linolenic acid.

[0073] [Application] The composite hollow fiber membrane of the present invention is suitably used, for example, as an ultrafiltration membrane or nanofiltration membrane in fields such as the semiconductor industry, chemical industry, food industry, pharmaceutical industry, and medical product industry. In particular, the composite hollow fiber membrane of the present invention has high resistance to aprotic polar solvents and is suitably used for filtration of liquids containing such solvents and solutes in industrial fields that use such solvents.

[0074] Furthermore, since the composite hollow fiber membrane of the present invention has resistance to various organic solvents, it is suitably used in membrane separation processes that treat a liquid containing an organic solvent and a solute.

[0075] 3. Method for manufacturing composite hollow fiber membranes The method for producing the composite hollow fiber membrane of the present invention is not particularly limited as long as a composite hollow fiber membrane having the above structure can be obtained, but a preferred example is a manufacturing method including the following steps 1 to 4. Step 1: Prepare a film-forming stock solution by dissolving an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or higher and being immiscible with the aliphatic polyamide resin at temperatures below 100°C, at a temperature of 100°C or higher. Step 2: A step in which the film-forming stock solution is extruded in a predetermined shape into a solidification bath at 100°C or lower to solidify an aliphatic polyamide resin into a film, wherein in this step, a solidification solution that is compatible with the organic solvent used in the film-forming stock solution and has low affinity for the aliphatic polyamide resin is brought into contact with at least one surface of the film-forming stock solution extruded in the predetermined shape to form an aliphatic polyamide hollow fiber film having a dense layer on at least one surface. Step 3: Remove the film-forming solvent and coagulation solution from the aliphatic polyamide hollow fiber membrane formed in Step 2. Step 4: A separation functional layer containing a crosslinked resin obtained by interfacial polycondensation is formed on the surface of at least one dense layer of the aliphatic polyamide hollow fiber membrane obtained by the Step 3.

[0076] [Formation of aliphatic polyamide hollow fiber membranes] The following describes in detail the first to third steps for forming the aliphatic polyamide hollow fiber membrane.

[0077] [1st step] In the first step, a film-forming stock solution is prepared by dissolving an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or higher and being immiscible with the aliphatic polyamide resin at temperatures below 100°C, at a temperature of 100°C or higher.

[0078] Organic solvents having a boiling point of 150°C or higher and being incompatible with aliphatic polyamide resins at temperatures below 100°C include, for example, aprotic polar solvents, glycerin ethers, polyhydric alcohols, organic acids and organic acid esters, and higher alcohols. Specific examples of aprotic polar solvents include sulfolane, dimethyl sulfone, dimethyl sulfoxide, γ-butyrolactone, δ-valerolactone, ε-caprolactone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, ethylene carbonate, and propylene carbonate. Specific examples of glycerin ethers include diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, and tetraethylene glycol dimethyl ether. Examples of polyhydric alcohols include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, hexylene glycol, 1,3-butanediol, and polyethylene glycol (molecular weight 100 to 10000). Examples of organic acids and organic acid esters include dimethyl phthalate, diethyl phthalate, diisopropyl phthalate, dibutyl phthalate, butyl benzyl phthalate, methyl salicylate, oleic acid, palmitic acid, stearic acid, and lauric acid. Among these organic solvents, from the viewpoint of obtaining aliphatic polyamide hollow fiber membranes with higher strength, preferred are aprotic polar solvents and polyhydric alcohols; more preferably sulfolane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, propylene glycol, hexylene glycol, 1,3-butanediol, and polyethylene glycol (molecular weight 100-600); even more preferably sulfolane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone; and even more preferably dimethyl sulfone. These organic solvents may be used individually or in combination of two or more.While sufficient effects can be obtained by using one of these organic solvents individually, mixing two or more can sometimes lead to the creation of even more effective aliphatic polyamide hollow fiber membranes due to differences in the order and structure of phase separation.

[0079] The concentration of the aliphatic polyamide resin in the film-forming stock solution should be 20% by weight or more, preferably 23-50% by weight, more preferably 25-38% by weight, and even more preferably 28-35% by weight. By satisfying the above range for the concentration of the aliphatic polyamide resin in the film-forming stock solution, a support layer with a porosity of 60-80% can be obtained, providing the aliphatic polyamide hollow fiber membrane with excellent pressure resistance. As a result, the composite hollow fiber membrane of the present invention can be provided with excellent pressure resistance and organic solvent permeability.

[0080] Furthermore, in the first step, when dissolving the aliphatic polyamide resin in the organic solvent, it is necessary to maintain the solvent temperature at 100°C or higher. Specifically, it is desirable to dissolve the resin at a temperature 10 to 50°C higher, preferably 20 to 40°C higher, than the phase separation temperature of the prepared film-forming stock solution. The phase separation temperature of the film-forming stock solution refers to the temperature at which liquid-liquid phase separation or solid-liquid phase separation by crystal precipitation occurs when a mixture of the aliphatic polyamide resin and the organic solvent at a sufficiently high temperature is gradually cooled. The phase separation temperature can be measured using a microscope equipped with a hot stage or the like.

[0081] In the first step, the temperature conditions for dissolving the aliphatic polyamide resin in the organic solvent can be appropriately set in a temperature range of 100°C or higher according to the indicators described above, depending on the type of aliphatic polyamide resin and the type of organic solvent used, but preferably 120 to 250°C, more preferably 140 to 220°C, and even more preferably 160 to 200°C.

[0082] Furthermore, fillers, thickeners, antioxidants, surface modifiers, lubricants, surfactants, etc., may be added to the film-forming stock solution as needed to control the pore size and improve the performance of the aliphatic polyamide hollow fiber membrane.

[0083] The film-forming stock solution prepared in the first step is subjected to the second step at the same temperature (i.e., above 100°C).

[0084] [Second process] In the second step, the film-forming stock solution prepared in the first step is extruded in a predetermined shape into a solidification bath at 100°C or lower to solidify the aliphatic polyamide resin into a film, wherein in this step, a solidification solution (hereinafter sometimes referred to as "solidification solution for forming a dense layer") which is compatible with the organic solvent used in the film-forming stock solution and has low affinity for the aliphatic polyamide resin is brought into contact with at least one surface of the film-forming stock solution extruded in the predetermined shape, thereby forming an aliphatic polyamide hollow fiber film having a dense layer on at least one surface.

[0085] In the second step, the film-forming stock solution extruded in a predetermined shape in the coagulation bath forms a dense layer on the surface that comes into contact with the coagulation solution for forming a dense layer. Near the surface where the film-forming stock solution comes into contact with the coagulation solution for forming a dense layer, non-solvent phase separation due to solvent exchange proceeds more favorably than thermal phase separation due to cooling, resulting in the formation of a denser structure on the surface than in the conventional TIPS method, and as a result, an aliphatic polyamide hollow fiber film having the aforementioned molecular weight cutoff is obtained.

[0086] When forming a dense layer on only one surface of an aliphatic polyamide hollow fiber membrane, in the second step, one surface of the film-forming stock solution extruded in a predetermined shape is brought into contact with the dense layer-forming coagulation solution, and the other surface is brought into contact with a coagulation solution that is compatible with the organic solvent used in the film-forming stock solution and has high affinity for the aliphatic polyamide resin (hereinafter sometimes referred to as the "support layer-forming coagulation solution"). Alternatively, when forming a dense layer on both surfaces of an aliphatic polyamide hollow fiber membrane, in the second step, both surfaces of the film-forming stock solution extruded in a predetermined shape are brought into contact with the dense layer-forming coagulation solution.

[0087] The solidifying solution for forming a dense layer is specifically a solvent that is compatible with the organic solvent used in the film-forming stock solution at a temperature of 25°C or lower, but does not dissolve the aliphatic polyamide resin at a temperature below its boiling point or below 200°C. Specific examples of solidifying solutions for forming a dense layer include aqueous solvents such as water and aqueous solutions with a water content of 80% by weight or more; monohydric alcohols such as 1-propanol, 2-propanol, and isobutanol; glycol ethers such as polyethylene glycol with an average molecular weight of 300 or more, polypropylene glycol with an average molecular weight of 400 or more, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and glycol acetates such as triacetin and propylene glycol monoethyl ether acetate. Among these, polyethylene glycol, triacetin, and triethylene glycol monomethyl ether with an average molecular weight of 300 to 600 are preferred; more preferably polyethylene glycol 300, polyethylene glycol 400, and polyethylene glycol 600; and even more preferably polyethylene glycol 300 and polyethylene glycol 400. These solvents may be used individually or in combination of two or more. In the present invention, the average molecular weights of polyethylene glycol and polypropylene glycol are number-average molecular weights calculated based on the hydroxyl value measured in accordance with JIS K 1557-6:2009 "Plastics - Polyurethane raw material polyols - Test methods - Part 6: Method for determining hydroxyl value by near-infrared (NIR) spectroscopy".

[0088] Furthermore, the solidifying solution for forming the dense layer may contain a solvent used in the solidifying solution for forming the support layer, such as glycerin (a solvent that is compatible with the organic solvent used in the film-forming stock solution at a temperature of 25°C or lower and dissolves the aliphatic polyamide resin at a temperature below its boiling point), to the extent that it is capable of forming a dense layer. When the solidifying solution for forming the dense layer contains a solvent used in the solidifying solution for forming the support layer (preferably at least one selected from the group consisting of glycerin, diglycerin, 1,3-butanediol, 1,4-butanediol, diethylene glycol, tetraethylene glycol, and polyethylene glycol 200), the content of the solvent is preferably 5 to 38% by weight, more preferably 10 to 35% by weight, even more preferably 15 to 32% by weight, and even more preferably 15 to 30% by weight, from the viewpoint of forming a dense layer of a suitable thickness and obtaining an aliphatic polyamide hollow fiber film having the aforementioned molecular weight cutoff.

[0089] The coagulation solution for forming the support layer can be any solvent that is compatible with the organic solvent used in the film-forming stock solution at a temperature of 25°C or lower, and that dissolves the aliphatic polyamide resin at a temperature below its boiling point. Specific examples of the coagulation solution for forming the support layer include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 200, propylene glycol, 1,3-butanediol, 1,4-butanediol, sulfolane, N-methyl-2-pyrrolidone, γ-butyrolactone, δ-valerolactone, and aqueous solutions containing 20% ​​or more of these by weight. Among these, from the viewpoint of obtaining a support layer having the aforementioned porosity, preferably, is an aqueous solution containing at least one selected from the group consisting of 1,4-butanediol, 1,3-butanediol, glycerin, propylene glycol, diethylene glycol, tetraethylene glycol, and polyethylene glycol 200, and at least one of these in a proportion of 25 to 75% by weight; more preferably, is an aqueous solution containing at least one selected from the group consisting of 1,4-butanediol, glycerin, propylene glycol, diethylene glycol, and tetraethylene glycol, and at least one of these in a proportion of 40 to 80% by weight (preferably 40 to 60% by weight).

[0090] To form an aliphatic polyamide hollow fiber membrane, the second step involves using a double-tube nozzle for hollow fiber production, discharging the film-forming raw material from the outer annular nozzle and the internal coagulation solution from the inner nozzle, and immersing the membrane in a coagulation bath. In this case, at least one of the internal coagulation solution and the coagulation bath should be a coagulation solution for forming a dense layer. When a coagulation solution for forming a dense layer is used for both the internal coagulation solution and the coagulation bath, a dense layer is formed on both the inner and outer surfaces, resulting in an aliphatic polyamide hollow fiber membrane with a support layer inside. Furthermore, when a coagulation solution for forming a dense layer is used as the internal coagulation solution and a coagulation solution for forming a support layer is used as the coagulation bath, a dense layer is formed on the inner surface, and an aliphatic polyamide hollow fiber membrane with support layers on both the inner and outer surfaces is obtained. Furthermore, when a coagulation solution for forming a support layer is used as the internal coagulation solution, and a coagulation solution for forming a dense layer is used as the coagulation bath, an aliphatic polyamide hollow fiber membrane is obtained in which a dense layer is formed on the outer surface and the inner surface and interior are support layers. It is preferable that the internal coagulation solution used when forming the aliphatic polyamide hollow fiber membrane does not contain water, whose boiling point is below the temperature of the double annular nozzle, since it passes through the double annular nozzle.

[0091] As a double-tubular nozzle for hollow fiber production, a nozzle having a double-tubular structure, similar to those used in melt spinning to produce core-sheath type composite fibers, can be used. The diameters of the outer annular nozzle and the inner nozzle of the double-tubular nozzle for hollow fiber production can be appropriately set according to the inner and outer diameters of the aliphatic polyamide hollow fiber membrane.

[0092] Furthermore, the flow rate when discharging the film-forming stock solution from the annular nozzle on the outside of the double-tubular nozzle for hollow fiber production is not particularly limited as it depends on the slit width, but for example, it can be 2 to 30 g / min, preferably 3 to 20 g / min, and more preferably 5 to 15 g / min. The flow rate of the internal coagulation solution is set appropriately considering the diameter of the inner nozzle of the double-tubular nozzle for hollow fiber production, the type of internal solution used, the flow rate of the film-forming stock solution, etc., but it can be 0.1 to 2 times, preferably 0.2 to 1 time, and more preferably 0.4 to 0.7 times the flow rate of the film-forming stock solution.

[0093] In the second step, the temperature of the coagulation bath should be 100°C or lower, but preferably -20 to 100°C, more preferably 0 to 60°C, even more preferably 2 to 20°C, and particularly preferably 2 to 10°C. The suitable temperature of the coagulation bath may vary depending on the organic solvent used in the film-forming stock solution, the composition of the coagulation solution, etc. Generally, lower temperatures tend to favor thermally induced phase separation, while higher temperatures tend to favor non-solvent phase separation. That is, when producing an aliphatic polyamide hollow fiber membrane in which a dense layer is formed on the luminal surface, it is preferable to set the coagulation bath to a low temperature in order to increase the pore size of the dense layer on the luminal surface, and it is preferable to set the coagulation bath to a high temperature in order to make the dense layer on the luminal surface more dense and to make the internal structure coarser.

[0094] Furthermore, the temperature of the internal coagulation solution should be approximately the set temperature of the double-tube nozzle, for example, 120 to 250°C, preferably 160 to 230°C, and more preferably 180 to 220°C.

[0095] Thus, by carrying out the second step, the film-forming stock solution solidifies in the solidification bath, and an aliphatic polyamide hollow fiber film is formed with a dense layer on at least one surface.

[0096] [3rd step] In the third step, the film-forming solvent and coagulation solution are removed from the aliphatic polyamide hollow fiber membrane formed in the second step.

[0097] The method for removing the film-forming solvent and coagulation solution from the aliphatic polyamide hollow fiber membrane is not particularly limited, but a method of immersing the aliphatic polyamide hollow fiber membrane formed in the second step in an extraction solvent for extraction and removal is preferred.

[0098] The extraction solvent used for extraction and removal is preferably inexpensive, has a low boiling point, and can be easily separated after extraction by the difference in boiling point, etc. Examples include water, glycerin, methanol, ethanol, isopropanol, acetone, diethyl ether, hexane, petroleum ether, and toluene. Among these, water, methanol, ethanol, isopropanol, and acetone are preferred; more preferably, water, methanol, and isopropanol. In particular, when extracting film-forming stock solvents and coagulation solutions that are soluble in water, winding while showering with water allows for simultaneous solvent extraction, which is efficient. Furthermore, when extracting water-insoluble organic solvents such as phthalates and fatty acids, isopropyl alcohol, petroleum ether, etc., can be suitably used.

[0099] When extracting and removing the film-forming solvent and coagulation solution by immersing an aliphatic polyamide hollow fiber membrane in an extraction solvent, there are no particular restrictions on the immersion time of the aliphatic polyamide hollow fiber membrane in the extraction solvent, but for example, 0.2 hours to 2 months, preferably 0.5 hours to 1 month, and more preferably 2 hours to 10 days. To effectively extract and remove the coagulation solution and other substances remaining on the aliphatic polyamide hollow fiber membrane, the extraction solvent may be replaced or stirred.

[0100] Thus, by carrying out the third step, an aliphatic polyamide hollow fiber membrane is obtained, having a dense layer on at least one surface, from which the film-forming solvent and coagulation solution have been removed.

[0101] After the third step, it is preferable to dry and remove the extraction solvent from the aliphatic polyamide hollow fiber membrane. The extraction solvent can be dried and removed by known drying treatments such as natural drying, hot air drying, reduced pressure drying, or vacuum drying.

[0102] Furthermore, in order to increase the strength of the aliphatic polyamide hollow fiber membrane and provide it with excellent pressure resistance, the aliphatic polyamide hollow fiber membrane may be stretched uniaxially (longitudinally) at the same time as drying or after drying.

[0103] To perform uniaxial stretching simultaneously with drying, the aliphatic polyamide hollow fiber membrane should be dried while tension for stretching is applied. The temperature conditions for uniaxial stretching simultaneously with drying are not particularly limited, as long as both drying and stretching are possible, but examples include 40°C or higher, preferably 40 to 160°C, more preferably 50 to 140°C, and even more preferably 120 to 140°C.

[0104] Furthermore, when stretching uniaxially after drying, the temperature conditions during drying are not particularly limited, as long as the adhering extraction solvent can be volatilized. For example, temperatures of 40°C or higher, preferably 40 to 160°C, more preferably 50 to 140°C, and even more preferably 120 to 140°C are recommended. Also, when stretching uniaxially after drying, the temperature conditions during stretching are not particularly limited, and -10 to 140°C, preferably 0 to 120°C is acceptable. However, from the viewpoint of further improving liquid permeability, it is desirable that the temperature be above the glass transition temperature of the aliphatic polyamide resin used (more preferably 50 to 120°C, and even more preferably 60 to 100°C).

[0105] Uniaxial stretching can be performed by known methods, for example, by winding from a low-speed roll to a high-speed roll continuously. Alternatively, the aliphatic polyamide hollow fiber membrane may be cut to a certain length, and stretched using a tensile testing machine or the like by grasping both ends, or manual stretching may be used.

[0106] Examples of stretching ratios include 1.2 to 5 times, preferably 1.2 to 3 times. From the viewpoint of increasing the strength of the aliphatic polyamide hollow fiber membrane and providing excellent pressure resistance, the stretching ratio is preferably 1.2 to 2.4 times, more preferably 1.2 to 2.0 times.

[0107] [Formation of the separation functional layer] The fourth step, which involves forming a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of at least one dense layer of the aliphatic polyamide hollow fiber membrane obtained by the third step, will be described in detail below.

[0108] The crosslinked resin constituting the separation functional layer is as described in the [Separation Functional Layer] section of "2. Composite Hollow Fiber Membrane" above. Below, as a representative example, we will explain the case where the crosslinked resin is a crosslinked polyamide resin.

[0109] Crosslinked polyamide resins are obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acyl halide. In order to obtain a crosslinked polyamide resin, at least one of the polyfunctional amine or polyfunctional acyl halide must contain a trifunctional or greater compound.

[0110] In the separation functional layer formation process, for example, a separation functional layer can be formed on the surface of the dense layer by performing interfacial polycondensation on the surface of the dense layer using a solution containing a polyfunctional amine (hereinafter also referred to as the polyfunctional amine solution) and an organic solution containing a polyfunctional acyl halide that is immiscible with the solvent of the polyfunctional amine solution (hereinafter also referred to as the polyfunctional acyl halide solution). Water is usually used as the solvent for the polyfunctional amine solution. However, if the polyfunctional amine is water-insoluble, an organic solvent such as dimethylformamide can be used instead of water, or a mixed solvent of water and an organic solvent such as dimethylformamide may be used. When m-phenylenediamine is used as the polyfunctional amine, it is preferable to use water as the solvent. When an organic solvent such as dimethylformamide is used instead of water, it is necessary that the organic solvent does not dissolve the hollow fiber membrane and is immiscible with the organic solvent of the polyfunctional acyl halide solution. The aliphatic polyamide hollow fiber membrane of the present invention has excellent resistance to a wide variety of organic solvents. Therefore, in the present invention, even organic solvents such as dimethylformamide, which conventionally dissolve hollow fiber membranes, can be used as solvents for the polyfunctional amine solution.

[0111] The concentration of the polyfunctional amine in the aqueous solution of the polyfunctional amine is not particularly limited, but is usually about 0.01 to 10% by weight, preferably 0.1 to 5% by weight, more preferably 0.5 to 4% by weight, and even more preferably 1 to 3% by weight.

[0112] The polyfunctional amine aqueous solution may contain surfactants and phase transfer catalysts, to the extent that they do not inhibit the interfacial polycondensation reaction. Surfactants have the function of improving the wettability of the dense layer surface and reducing the interfacial tension between the polyfunctional amine solution and the polyfunctional acyl halide solution. Examples of surfactants include sodium dodecyl sulfate and sodium dodecylbenzenesulfonate. Phase transfer catalysts have the function of promoting the reaction between the immiscible solutions, the polyfunctional amine solution and the polyfunctional acyl halide solution. Examples of phase transfer catalysts include tertiary amines such as triethylamine and quaternary ammonium salts such as trioctylmethylammonium chloride. When the above additives are added, the total content of the additives is preferably 0.5 to 20% by weight, and more preferably 1 to 10% by weight. Within this range, the effects of each additive can be effectively obtained.

[0113] To carry out interfacial polycondensation on the dense layer, it is preferable to first bring the polyfunctional amine solution into contact with the surface of the dense layer. It is preferable that the contact be uniform and gapless on the dense layer. Examples of contact methods include immersing an aliphatic polyamide hollow fiber membrane in the polyfunctional amine solution, and passing the polyfunctional amine solution through the interior of the aliphatic polyamide hollow fiber membrane. The contact time between the dense layer and the polyfunctional amine solution is not particularly limited, but is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. By keeping the time within this range, the polyfunctional amine solution can be sufficiently impregnated into the dense layer, and excessive impregnation into the support layer can be suppressed. In addition, the aliphatic polyamide hollow fiber membrane may be wetted with a solvent such as water before contact with the polyfunctional amine solution. This can promote the impregnation of the polyfunctional amine solution.

[0114] It is preferable to remove any excess polyfunctional amine solution after bringing the polyfunctional amine solution into contact with the dense layer. This improves the uniformity of the interface and reduces the likelihood of defects in the separation functional layer. Examples of removal methods include blowing off the excess polyfunctional amine remaining on the surface of the dense layer with an airflow, or passing air through the hollow portion of the aliphatic polyamide hollow fiber membrane. The time for blowing or passing air is not particularly limited, but is preferably 5 seconds to 3 minutes, more preferably 10 seconds to 2 minutes. If the time is too short, sufficient liquid removal will not be possible, and if the time is too long, the polyfunctional amine solution may be excessively removed or the contact surface may dry out, which can easily inhibit the optimal interfacial polycondensation reaction. Alternatively, a liquid that is immiscible with the solvent of the polyfunctional amine solution may be flowed onto the surface of the dense layer. In this case, the same effect as with airflow can be obtained. In this case, it is preferable to use the solvent of the polyfunctional acyl halide solution described later. When an immiscible liquid is passed through the hollow portion of an aliphatic polyamide hollow fiber membrane, the liquid can be passed either before or after the airflow dewatering, and the amount of liquid passed through is approximately 5 to 50 times the volume inside the hollow fiber.

[0115] Next, a polyfunctional acyl halide solution is brought into contact with the dense layer after contact with the polyfunctional amine solution, and a separation functional layer containing a crosslinked polyamide resin is formed on the surface of the dense layer by interfacial polycondensation.

[0116] The organic solvent in the polyfunctional acyl halide solution should be immiscible with the solvent in the polyfunctional amine solution, dissolve the polyfunctional acyl halide without dissolving the aliphatic polyamide hollow fiber membrane, and be inert to both the polyfunctional amine and the polyfunctional acyl halide. Examples of such organic solvents include hydrocarbon solvents, chlorinated solvents, and fluorinated solvents. These may be used individually or in combination of two or more. Of these, hydrocarbon solvents are preferred from the viewpoint of ease of handling and environmental impact. Examples of hydrocarbon solvents include aliphatic hydrocarbons and aromatic hydrocarbons. Examples of aliphatic hydrocarbons include linear aliphatic hydrocarbons such as hexane and octane, and branched aliphatic hydrocarbons such as isooctane. Examples of aromatic hydrocarbons include toluene and xylene.

[0117] The concentration of the polyfunctional acyl halide in the polyfunctional acyl halide solution is not particularly limited, but is usually around 0.01 to 5% by weight, preferably 0.01 to 1% by weight, and more preferably 0.05 to 0.5% by weight. Within this range, a uniform separation functional layer with sufficient thickness can be formed on the surface of the dense layer.

[0118] Contact between the polyfunctional acyl halide solution and the surface of the dense layer coated with the polyfunctional amine solution can be carried out in the same manner as the method for contacting the dense layer surface with the polyfunctional amine solution described above. The contact time is not particularly limited, and should be sufficient to allow the interfacial polycondensation reaction between the polyfunctional amine and the polyfunctional acyl halide to proceed sufficiently and for the separation functional layer to be formed on the surface of the dense layer. Typically, this is about 5 seconds to 10 minutes, preferably 10 seconds to 5 minutes, and more preferably 30 seconds to 3 minutes.

[0119] Next, it is preferable to remove the excess polyfunctional acyl halide solution using the same method as described above for removing the excess polyfunctional amine solution. Alternatively, washing and replacing only the contact surface with the solvent of the polyfunctional acyl halide solution, followed by deliquing, is also effective in removing the excess polyfunctional acyl halide solution. When passing the solvent of the polyfunctional acyl halide solution through the hollow portion of the aliphatic polyamide hollow fiber membrane, the passage can be done either before or after deliquing with airflow, and the amount of liquid passed through is approximately 5 to 50 times the volume inside the hollow fiber.

[0120] It is preferable to remove any excess polyfunctional acyl halide solution and then dry the contact surface. This allows the separation functional layer to be strongly immobilized on the dense layer. Examples of drying methods include placing the composite hollow fiber membrane in a dryer, or applying or ventilating only the surface where the separation functional layer is formed. The temperature during drying or ventilation is not particularly limited, but is preferably 50 to 120°C, more preferably 80 to 100°C. The drying time should be set appropriately to allow sufficient removal of the solvent from the polyfunctional acyl halide solution, but is usually about 0.5 to 60 minutes, preferably 0.5 to 30 minutes, more preferably 1 to 20 minutes, and even more preferably 1 to 10 minutes.

[0121] The dried composite hollow fiber membrane may be used as is, or it may be further washed. Unreacted polyfunctional amines and polyfunctional acyl halides may remain in the membrane, and if these remain, they may leach out when the composite hollow fiber membrane is used, so it is preferable to remove them by washing. It is preferable to use water for washing. Examples of washing methods include immersion in water and passing water through the hollow parts of the composite hollow fiber membrane. There are no particular restrictions on the temperature during washing, but it is usually around room temperature to 70°C. The washing time can be adjusted as appropriate according to the water temperature, and when immersing at room temperature, it is preferable to leave it for 12 hours or more.

[0122] The composite hollow fiber membrane that has undergone the washing treatment may be used as is, or it may be dried again. The composite hollow fiber membrane is more advantageous in subsequent processes such as modularization when it is in a dried state. The drying conditions should be such that the moisture is substantially removed, but the drying temperature is preferably 25 to 100°C, more preferably 40 to 70°C.

[0123] Below, as a preferred example of the fourth step, a method for forming a separation functional layer on the surface of the dense layer on the luminal side of an aliphatic polyamide hollow fiber membrane will be described in detail.

[0124] One method for forming a separation functional layer on the surface of the dense layer on the luminal side of an aliphatic polyamide hollow fiber membrane is to inject a polyfunctional amine solution into the hollow portion of the aliphatic polyamide hollow fiber membrane, and then inject a polyfunctional acyl halide solution into the hollow portion, thereby causing interfacial polycondensation of the polyfunctional amine and polyfunctional acyl halide on the dense layer to form a separation functional layer on the surface of the dense layer.

[0125] The method for injecting a polyfunctional amine solution and a polyfunctional acyl halide solution into the hollow portion of an aliphatic polyamide hollow fiber membrane is not particularly limited as long as the polyfunctional amine solution and the polyfunctional acyl halide solution can be uniformly coated onto the surface of the dense layer. However, a preferred method involves forming a module using aliphatic polyamide hollow fiber membranes, injecting the polyfunctional amine solution into the hollow portion of the aliphatic polyamide hollow fiber membrane of the module, and then injecting the polyfunctional acyl halide solution. Specifically, this injection method is carried out by the following procedure. First, a bundle of a desired number of aliphatic polyamide hollow fiber membranes of the desired length is prepared. Next, a rigid tube is prepared, and a rubber stopper of appropriate length is inserted into the opening at one end of the tube to seal the opening. Next, a two-component thermosetting resin is injected from the opening at the end opposite to the sealed end of the tube to fill the inner space of the tube with the resin. Subsequently, one end of the prepared bundled aliphatic polyamide hollow fiber membrane is heat-sealed to seal it, and the end is inserted into the tube filled with the thermosetting resin until it touches the stopper, and the thermosetting resin is allowed to cure in that state. Next, the tube is cut along with the stopper-side portion of the cured resin to open the hollow part of the aliphatic polyamide hollow fiber membrane. Then, a suitable jig is attached to the open end of the tube and a polyfunctional amine solution is injected, followed by a polyfunctional acyl halide solution. Alternatively, a wetting solution may be injected before the injection of the polyfunctional amine solution.

[0126] The injection method is not particularly limited and includes, for example, injection methods using a syringe, pumping methods using pressurized gas, and injection methods using pumps such as peristaltic pumps, plunger pumps, diaphragm pumps, and gear pumps.

[0127] The injection speed of the polyfunctional amine solution and the polyfunctional acyl halide solution is not particularly limited, but the linear velocity is, for example, about 0.01 to 2 m / second, and is preferably 0.05 to 1 m / second from the viewpoint of suppressing uneven wetting, ensuring uniform coating, and manufacturing efficiency. The injection of the polyfunctional amine solution and the polyfunctional acyl halide solution is preferably carried out continuously to ensure a predetermined contact time. The contact time is as described above.

[0128] As described above, in order to remove excess polyfunctional amine solution and polyfunctional acyl halide solution, it is preferable to pass gas through the hollow portion of the aliphatic polyamide hollow fiber membrane after the injection of the polyfunctional amine solution and after the injection of the polyfunctional acyl halide solution. The gas used for ventilation is not particularly limited, but from the viewpoint of preventing side reactions and safety, dry air or nitrogen is preferred.

[0129] The gas aeration rate is not particularly limited, but as a linear velocity, it is preferably about 1 to 100 m / s, and is preferably 2.5 to 70 m / s, more preferably 10 to 50 m / s, from the viewpoint of suppressing defects in the separation functional layer caused by poor interfacial polycondensation due to the removal of excess reaction liquid, from the viewpoint of preventing the formed separation functional layer from peeling off, and from the viewpoint of manufacturing efficiency. The aeration is preferably carried out continuously for a predetermined time, and although the aeration time is not particularly limited, it is preferably 5 seconds to 5 minutes, more preferably 20 seconds to 2 minutes.

[0130] After injecting the polyfunctional acyl halide solution, it is preferable to heat-treat and dry the film surface to promote the interfacial polycondensation reaction, fix the separation functional layer to the dense layer surface, and remove solvents, etc. The heating temperature and heating time are as described above.

[0131] After the interfacial polycondensation reaction is complete, it is preferable to wash the composite hollow fiber membrane to remove unreacted and by-reacting materials. The washing method and washing conditions are as described above.

[0132] The tubing used during the injection of the polyfunctional amine solution and the polyfunctional acyl halide solution should be cut and removed at an appropriate time, for example, before or after the heat treatment of the composite hollow fiber membrane.

[0133] Furthermore, as a method for forming a separation functional layer on the surface of the dense outer layer of an aliphatic polyamide hollow fiber membrane, for example, one could sequentially immerse the aliphatic polyamide hollow fiber membrane in baths of a polyfunctional amine solution and a polyfunctional acyl halide solution, or sequentially apply the polyfunctional amine solution and the polyfunctional acyl halide solution to the surface of the dense outer layer of the aliphatic polyamide hollow fiber membrane, and repeat the process of removing excess liquid by draining and blowing gas as needed. These processes may be carried out as batch processing of hollow fiber bundles or as continuous roll-to-roll processing. Even when a separation functional layer is formed on the surface of the dense outer layer of an aliphatic polyamide hollow fiber membrane by this method, it is preferable to carry out post-treatment with heat treatment and washing.

[0134] Furthermore, as a method for forming separation functional layers on the luminal and outer dense layers of the aliphatic polyamide hollow fiber membrane, for example, a method of forming a separation functional layer on the luminal dense layer surface of the aliphatic polyamide hollow fiber membrane and a method of forming a separation functional layer on the outer dense layer surface of the aliphatic polyamide hollow fiber membrane can be performed in any order or in combination.

[0135] Furthermore, it is preferable that the composite hollow fiber membrane be dry, as this facilitates adaptation to the potting process for immobilizing the composite hollow fiber membrane onto modules. Moreover, a dry composite hollow fiber membrane is preferable because it can also withstand the aforementioned air leak test. The composite hollow fiber membrane of the present invention can exhibit desired performance even when it is a dry membrane. Normally, when limit filtration membranes and reverse osmosis membranes are dried, the pores often shrink or become blocked due to surface tension caused by the evaporation of water, resulting in a loss of permeability. However, the composite hollow fiber membrane of the present invention can exhibit desired properties even when it is a dry membrane before the processing liquid is passed through it. The drying conditions are not particularly limited, but preferably it is air-dried at a temperature of 25 to 100°C, more preferably 40 to 70°C.

[0136] Thus, by carrying out the fourth step, a composite hollow fiber membrane of the present invention is obtained having a separation functional layer on the surface of at least one dense layer of the aliphatic polyamide hollow fiber membrane.

[0137] 4. Hollow fiber membrane module The composite hollow fiber membrane of the present invention is housed in a module case equipped with a liquid to be treated inlet and a permeate outlet, and is used as a hollow fiber membrane module.

[0138] Specifically, the hollow fiber membrane module may have a structure in which the composite hollow fiber membranes of the present invention are bundled together, housed in a module case, and one or both ends of the composite hollow fiber membranes are sealed and fixed with a potting agent. The hollow fiber membrane module may have an opening connected to a flow path passing through the outer wall surface of the composite hollow fiber membrane, and an opening connected to the hollow portion of the composite hollow fiber membrane, which serve as an inlet for the liquid to be treated or an outlet for the filtrate.

[0139] The shape of the hollow fiber membrane module is not particularly limited and may be a dead-end type module or a cross-flow type module. Specifically, examples include: a dead-end type module in which a bundle of hollow fiber membranes is bent into a U-shape and packed, and the ends of the bundle are sealed and then cut to create an opening; a dead-end type module in which a bundle of hollow fiber membranes with one end of the hollow opening sealed by heat sealing or the like is packed straight, and the end of the open end of the bundle is sealed and then cut to create an opening; a dead-end module in which a bundle of hollow fiber membranes is packed straight, both ends of the bundle are sealed, and only one end is cut to expose the opening; and a cross-flow type module in which a bundle of hollow fiber membranes is packed straight, both ends of the bundle are sealed, the sealed parts at both ends of the bundle are cut, and two flow paths are created on the side of the filter case.

[0140] The packing ratio of the composite hollow fiber membrane inserted into the module case is not particularly limited, but for example, the volume of the composite hollow fiber membrane including the volume of the hollow portion relative to the volume inside the module case is preferably 15 to 75 volume%, more preferably 25 to 65 volume%, and even more preferably 35 to 55 volume%. By satisfying such a packing ratio, a sufficient filtration area can be secured, the packing work of the composite hollow fiber membrane into the module case can be facilitated, and the potting agent can be easily flowed between the composite hollow fiber membranes.

[0141] The potting agent used in the manufacture of hollow fiber membrane modules is not particularly limited, but if the hollow fiber membrane modules are to be treated with organic solvents, it is desirable that the potting agent has resistance to organic solvents. Examples of such potting agents include polyamide, silicone resin, epoxy resin, melamine resin, polyethylene, polypropylene, phenolic resin, polyimide, and polyurea resin. Among these potting agents, those that exhibit little shrinkage or swelling upon curing and are not excessively hard are preferred, and suitable examples include polyamide, silicone resin, epoxy resin, and polyethylene. These potting agents may be used individually or in combination of two or more.

[0142] The material of the module case used in the hollow fiber membrane module is not particularly limited as long as it is durable to the solvent used. In addition to metal materials, polymer materials include, for example, polyamide, polyester, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polysulfone, polyethersulfone, polycarbonate, polyarylate, and polyphenylene sulfide. Among these, polyamide, polyethylene, polypropylene, polytetrafluoroethylene, polycarbonate, polysulfone, and polyethersulfone are preferred, and more preferably polyamide, polyethylene, polypropylene, and polytetrafluoroethylene.

[0143] The hollow fiber membrane module utilizing the composite hollow fiber membrane of the present invention is used in ultrafiltration or nanofiltration applications for removing foreign substances from solvents, concentrating useful components from solvents, and recovering solvents in fields such as the semiconductor industry, chemical industry, food industry, pharmaceutical industry, and medical product industry. [Examples]

[0144] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0145] 1.Measurement method [Outer and inner diameters of aliphatic polyamide hollow fiber membranes] Five aliphatic polyamide hollow fiber membranes were observed under an optical microscope at a magnification of 200x. The outer and inner diameters (at the point of maximum diameter) of each hollow fiber membrane were measured, and the average values ​​were calculated.

[0146] [Void ratio of the supporting layer] In a cross-section of the composite hollow fiber membrane cut perpendicular to its longitudinal direction, scanning electron microscope (SEM) images were taken at five equally spaced locations in the thickness direction of the support layer of the aliphatic polyamide hollow fiber membrane. Specifically, the images were taken as follows. Figure 11 is a schematic cross-sectional view of the aliphatic polyamide hollow fiber membrane cut perpendicular to its longitudinal direction, and Figures 12 and 13 are magnified views of the area enclosed by the dotted line in Figure 11, showing an example of an aliphatic polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 11. Note that the separation functional layer is omitted in Figures 11-13. As shown in Figure 11, a straight line was drawn from the center of the lumen of the aliphatic polyamide hollow fiber membrane 8a toward the outer surface, and this line was divided into five equal parts from the lumen side surface to the outer surface of the support layer 11. Then, as shown in Figure 12, the midpoints of the five divided line segments were determined. Then, as shown in Figure 13, images were taken at five locations at a uniform magnification such that the midpoint was at the center of the captured image, the image included only the support layer 11, and the number of pores was between 30 and 300. Image analysis of the five captured SEM images was performed using image analysis software (ImageJ), and the pore portion and the polymer portion were distinguished by binarization. The area ratio (%) of the total pore area to the area of ​​the analysis region was calculated for each, and the average value was calculated. The specific operations in ImageJ are as follows: The image to be analyzed was imported into ImageJ, the analysis range was specified, and the brightness value at which the peak of the histogram obtained by the operation "Analyze>Histogram" was set as the threshold (i.e., the Lower threshold level was set to the brightness value at which the peak of the histogram was highest, and the Upper threshold level was set to 255). The image was then binarized using "Image>Adjust>Threshold". Next, "Analyze>Set measurements" was used to check "Area", and the total area of ​​the analysis range was obtained by the operation "Analyze>Measure". After that, "Analyze>Set measurements" was used again to check "Area" and "Limit to threshold", and the operation "Analyze>Measure" was performed again to calculate the area of ​​the polymer portion and the pore portion, and the area ratio (%) of the total pore area to the area of ​​the analysis region was calculated.

[0147] [Thickness of the dense layer] A cross-section of an aliphatic polyamide hollow fiber membrane, cut perpendicular to its longitudinal direction, was observed at a scanning electron microscope (SEM) at a magnification of 10,000x. In the resulting SEM images, the distance (thickness) of the region where virtually no pores were observed was measured at 10 points at regular intervals, and the average value was calculated.

[0148] [Crystallization of aliphatic polyamide hollow fiber membranes] The crystallinity of aliphatic polyamide hollow fiber membranes was measured by X-ray diffraction (XRD). Multiple hollow fiber samples were arranged closely together on the measurement stage, and the scattering pattern spectrum, consisting of scattering vectors and scattering intensities, was obtained by scanning the scattering angle. The obtained spectra were spectrally separated into crystalline and amorphous components, and the crystallinity was determined by quantification.

[0149] [Fractional molecular weight of aliphatic polyamide hollow fiber membranes (when greater than 3000)] Ten aliphatic polyamide hollow fiber membranes were cut to a length of 30 cm and bundled together. Next, a nylon rigid tube with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm was prepared. A rubber stopper approximately 20 mm long was inserted into the opening at one end of the tube to seal the end opening. Next, a two-part epoxy resin was injected into the opening of the connecting tube opposite to the rubber stoppered end to fill the space inside the tube with the epoxy resin. After that, one end of the bundle of aliphatic polyamide hollow fiber membranes was heat-sealed to prevent epoxy resin from entering the hollow portion, and this end was inserted into the epoxy resin-filled tube until the tip touched the rubber stopper. The epoxy resin was then allowed to harden in this state. Next, the rubber stoppered portion of the hardened epoxy resin was cut along with the tube to open the hollow portion. The same procedure was performed on the other end to create a cross-flow module 6 with open hollow portions at both ends of the aliphatic polyamide hollow fiber membrane. The fabricated cross-flow module 6 was connected to the internal pressure separation line shown in Figure 1, and a fluid (undiluted solution) was continuously permeated through the cross-flow module 6 by the fluid circulation pump 2. The fluid was an aqueous solution containing 0.5% by weight, 0.5% by weight, 0.2% by weight, 0.2% by weight, and 0.4% by weight of five types of dextran with molecular weights of 5000, 10000, 40000, 70000, and 500000, respectively. The pressure of the primary pressure gauge 3 and the secondary pressure gauge 4 were adjusted by the regulator 5 so that the arithmetic mean of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 was 1 bar. Of the fluid permeating through the module, the portion that permeated through the pores of the polyamide hollow fiber membrane was collected as a permeate separated from the fluid, and the remainder was circulated back to the separation line. Two hours after the start of circulation, the permeate flowing out of the cross-flow module 6 was collected in a tray 7, and the dextran concentration in the permeate was measured by high-performance liquid chromatography. The rejection rate for each molecular weight was calculated according to the following formula. Based on the rejection rate results for each molecular weight of dextran, a graph was created with the molecular weight of the dextran used on the x-axis and the rejection rate on the y-axis. The molecular weight at the intersection of the resulting approximation curve and the point where the rejection rate was 90% was defined as the fractional molecular weight. Solute rejection rate (%) = {(Dextran concentration in stock solution - Dextran concentration in permeate) / Dextran concentration in stock solution} × 100

[0150] [Fractional molecular weight of aliphatic polyamide hollow fiber membranes (for those with a molecular weight of 3000 or less)] As the fluid, an NMP solution containing 0.05 wt% each of four types of polystyrene with molecular weights of 370, 1000, 2000, or 3000 was used. The arithmetic mean of the pressures on the primary pressure gauge 3 and the secondary pressure gauge 4 was set to 15 bar, and the fractional molecular weight was determined in the same manner as described above, except that the rejection rate was calculated according to the following formula. Solute rejection rate (%) = {(Polystyrene concentration in stock solution - Polystyrene concentration in permeate) / Polystyrene concentration in stock solution} × 100

[0151] [Burst pressure of aliphatic polyamide hollow fiber membranes] Module 8, shown in Figure 2a, was fabricated. First, ten aliphatic polyamide hollow fiber membranes 8a were cut to a length of 30 cm and bundled together. Next, a nylon rigid tube 8b with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm was prepared. A rubber stopper approximately 20 mm in length was inserted into the opening at one end of the tube to seal the end. Next, a two-part epoxy resin was injected into the opening on the opposite side of the tube from the rubber stopper to fill the internal space of the tube with the epoxy resin. After that, the bundle of aliphatic polyamide hollow fiber membranes prepared was bent into a roughly U-shape, and both ends of the aliphatic polyamide hollow fiber membranes were heat-sealed to prevent epoxy resin from entering the hollow portion. These ends were then inserted into the tube filled with epoxy resin until they touched the rubber stopper, and the epoxy resin was allowed to harden in that state. Next, module 8 was fabricated by cutting the rubber stopper side of the hardened epoxy resin portion together with the tube, thereby creating open hollow sections at both ends of the aliphatic polyamide hollow fiber membrane. Next, module 8 was placed in the apparatus shown in Figure 2b, and water pressure was applied to module 8 using a hand pump 9. The pressure at which module 8 ruptured (burst pressure, in MPa) was measured.

[0152] [Observation of the separation function layer] In cross-sections of composite hollow fiber membranes cut perpendicular to their longitudinal direction, the area near the composite surface was observed using a scanning electron microscope (SEM) at magnifications of 10,000x or 20,000x. Furthermore, the composite surface was observed from above using an SEM at magnifications of 10,000x or 20,000x, either on the inner or outer surface.

[0153] [Air leak rate (pressure drop) of composite hollow fiber membrane] Twenty composite hollow fiber membranes were cut to a length of 30 cm and bundled together. Next, a polybutylene terephthalate (PBT) tube with an outer diameter of 12.7 mm, an inner diameter of 9.5 mm, and a length of 53 mm was prepared. A silicone tube with an inner diameter of 12 mm and a length of approximately 50 mm was inserted about 15 mm into the opening at one end of the PBT tube to connect them. A rubber stopper about 20 mm long was inserted into the opposite end of the silicone tube from the end inserted into the PBT tube, sealing the opening at that end. Next, a two-part epoxy resin was injected into the opening of the connected tube on the opposite side from the rubber stopper to fill the space inside the tube with the epoxy resin. After that, one end of the bundle of composite hollow fiber membranes was heat-sealed to prevent epoxy resin from entering the hollow part, and this end was inserted into the tube filled with epoxy resin until the tip touched the rubber stopper, and the epoxy resin was allowed to harden in that state. Next, the hardened epoxy resin portion on the rubber stopper side was cut along with the tube to create a hollow section. The same procedure was performed on the other end to create a cross-flow module with hollow sections open at both ends of the composite hollow fiber membrane. The membrane area of ​​the module was calculated based on the inner area of ​​the hollow fibers, using the inner diameter, number of fibers, and effective length of the hollow fibers. One end of the outlet connecting to the hollow section of the fabricated module was sealed, and a valve and a pressure line with a pressure gauge between the valve and the module were attached to the other end. The hollow section was pressurized with 0.2 MPa of air, and the pressure was contained by closing the valve. Immediately thereafter, the pressure was monitored over time, and the change in pressure after 5 minutes was measured. In addition, the containment volume (total pressurized space volume V) including the hollow fiber, module, and pressure line was estimated, and the length of the line was adjusted so that the ratio of the membrane area S to the total pressurized space volume V was within ±10% of the relationship given by the following formula. V / S = 0.0002 × 0.45 / R R is the inner diameter (mm) of the composite hollow fiber membrane.

[0154] [Burst pressure of composite hollow fiber membranes] The cross-flow module 6 fabricated as described above was connected to the internal pressure separation processing line shown in Figure 1, and NMP was continuously permeated through the cross-flow module 6 by the liquid circulation pump 2. In the module, the pressure of the primary pressure gauge 3 and the secondary pressure gauge 4 were adjusted by the regulator 5, and the arithmetic mean of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 was set as the applied pressure, which was increased by 0.25 MPa at 10-minute intervals. The burst pressure was defined as the pressure (MPa) at which the composite hollow fiber membrane ruptured, that is, when a rapid pressure drop occurred.

[0155] [NMP permeation amount] The cross-flow module 6 fabricated as described above was connected to the internal pressure separation treatment line shown in Figure 1, and a fluid was continuously permeated through the cross-flow module 6 by the fluid circulation pump 2. NMP was used as the fluid. In the module, the pressure of the primary pressure gauge 3 and the secondary pressure gauge 4 were adjusted by the regulator 5 so that the arithmetic mean of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 was 75% of the burst pressure of the composite hollow fiber membrane. Of the fluid permeating through the module, the fluid that permeated through the pores of the composite hollow fiber membrane was collected as permeate separated from the fluid, and the remainder was circulated back to the separation treatment line. The permeate that flowed out of the cross-flow module 6 between 2 and 4 hours after the start of circulation was collected in a tray 7, and the amount of NMP permeate (L / (m2·h)) was calculated according to the following formula. NMP permeation volume = Volume of NMP that permeates to the outside of the composite hollow fiber membrane (L) / [Inner diameter of composite hollow fiber membrane (m) × 3.14 × Effective filtration length of composite hollow fiber membrane (m) × 20 (fibers) × Time (h)] Effective filtration length of composite hollow fiber membrane: In a cross-flow module, this is the length of the portion of the outer surface of the composite hollow fiber membrane that is not coated with epoxy resin.

[0156] [Rejection rate of polystyrene and diphenyl sulfone] The rejection rates of polystyrene and diphenyl sulfone were measured using the same procedure as for the measurement of [NMP permeate], except that an NMP solution containing 0.2% by weight of polystyrene or diphenyl sulfone was used. The concentrations of the obtained permeate and fluid were measured using the RI detection values ​​of each component separated by liquid chromatography (SEC mode, mobile phase: DMF), and the rejection rates (%) of polystyrene and diphenyl sulfone were calculated from the following formula. Rejection rate % = 100 - (Concentration of permeate / Concentration of fluid) × 100

[0157] 2. Example Test [Example 1] 350g of polyamide 6 chips (manufactured by Unitika Ltd., A1030BRT, relative viscosity 3.53) and 650g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were stirred at 180°C for 1.5 hours to dissolve, and the stirring speed was reduced and degassed for 1 hour to prepare a film-forming stock solution. The film-forming stock solution was delivered via a metering pump to a spinneret kept warm at 200°C, and a mixture of 70% by weight polyethylene glycol 300 (PEG300) and 30% by weight glycerin was passed through as an internal coagulation solution. The extruded film-forming stock solution was placed in a coagulation bath consisting of a 60% by weight 1,4-butylene glycol (1,4BG) aqueous solution at 5°C and cooled and solidified to form an aliphatic polyamide porous film. The wound aliphatic polyamide porous membrane was immersed in water for 24 hours for solvent extraction (washing), and then dried by passing it through a hot air dryer (internal temperature 130°C) without stretching to obtain an aliphatic polyamide hollow fiber membrane. The measurement results for the outer diameter, inner diameter, porosity of the support layer, thickness of the dense layer, molecular weight cutoff, burst pressure, and crystallinity of the obtained aliphatic polyamide hollow fiber membrane are shown in Table 1. Figure 3 is an image analysis diagram after binarization to calculate the porosity of the support layer of the obtained aliphatic polyamide hollow fiber membrane. Figure 4 is a scanning electron microscope image (magnification 10,000x) of the luminal surface of the obtained aliphatic polyamide hollow fiber membrane. Figure 5 is a scanning electron microscope image (magnification 20,000x) of the luminal surface of the obtained aliphatic polyamide hollow fiber membrane. Figure 6 is a scanning electron microscope image (magnification 10,000x) of the luminal cross-section of the obtained aliphatic polyamide hollow fiber membrane. A bundle of 20 aliphatic polyamide hollow fiber membranes, each 40 cm long, was prepared. A rigid nylon tube with an inner diameter of 8 mm and a length of 50 mm was prepared, and a rubber stopper approximately 20 mm long was inserted into the opening at one end of the tube to seal the end. Next, a two-part epoxy resin was injected into the tube from the opening opposite the rubber stopper, filling the internal space of the tube with the epoxy resin. Then, one end of the prepared aliphatic polyamide hollow fiber membrane was heat-sealed to seal it, and the end was inserted into the tube filled with epoxy resin until it touched the rubber stopper, and the epoxy resin was allowed to harden in that state. Subsequently, the rubber stopper side of the hardened epoxy resin portion was cut along with the tube to open the hollow portion of the aliphatic polyamide hollow fiber membrane, obtaining a module for injecting the interfacial polymerization solution. Water was filled into the resin-fixed open end of the module and immersed in the water for one hour to wet the entire membrane. Next, the module was removed from the water and gently shaken to remove any adhering water. Then, nitrogen was blown in through the open end to drain all remaining water from the hollow section and perform a wetting treatment. After that, a PP connector with a three-way stopcock was connected to the open end of the module, and a circuit device for injecting an interfacial polymerization solution and nitrogen gas for ventilation was connected to the inside of the hollow fiber membrane. Then, an aqueous solution containing 2% by weight of m-phenylenediamine (MPD) was passed through the open end of the module at a linear velocity of 0.12 m / s for 1 minute. Subsequently, the flow path was switched to an airflow, and nitrogen gas was flowed at a linear velocity of 20 m / s for 1 minute. Next, a hexane solution containing 0.1% by weight of trimesinate chloride (TMC) was passed through at a linear velocity of 0.12 m / s for 1 minute. Subsequently, the flow path was switched to an airflow, and nitrogen gas was flowed at a linear velocity of 20 m / s for 1 minute. After that, the module was removed from the circuit device and dried in a 100°C oven for 5 minutes. The dried module was immersed in pure water and washed for 24 hours with several water changes. After that, the washed module was dried in a convection dryer at 50°C. After that, the hollow fiber membrane was cut on the epoxy resin side of the dried module to obtain 20 composite hollow fiber membrane bundles. Modules were fabricated using the obtained composite hollow fiber membranes, and air leak tests and filtration tests were performed. Table 1 shows the measurement results for each of the above measurements. Figure 7 is a scanning electron microscope image (magnification 10,000x) of the inner cross-section of the obtained composite hollow fiber membrane. Figure 8 is a scanning electron microscope image (magnification 20,000x) of the inner cross-section of the obtained composite hollow fiber membrane. Figure 9 is a scanning electron microscope image (magnification 10,000x) of the inner surface of the obtained composite hollow fiber membrane. Figure 10 is a scanning electron microscope image (magnification 20,000x) of the inner surface of the obtained composite hollow fiber membrane.

[0158] [Example 2] The following interfacial polymerization was carried out using the aliphatic polyamide hollow fiber membrane prepared in Example 1. First, a module for injecting the interfacial polymerization solution was prepared in the same manner as in Example 1, and it was similarly wetted and connected to a circuit device for liquid passage. Next, a dimethylformamide solution containing 2% by weight of 3,3',4,4'-tetraaminobiphenyl (TAB) was passed through the open end of the module at a linear velocity of 0.12 m / s for 1 minute. Then, the flow path was switched to an airflow, and nitrogen gas was flowed at a linear velocity of 20 m / s for 1 minute. Subsequently, a hexane solution containing 0.1% by weight of trimesinate chloride (TMC) was passed through at a linear velocity of 0.12 m / s for 1 minute. Then, the flow path was switched to an airflow, and nitrogen gas was flowed at a linear velocity of 20 m / s for 1 minute. After that, the module was removed from the circuit device and dried in a 100°C oven for 1 minute. The dried module was immersed in pure water and washed for 24 hours with several water changes. After that, the washed module was dried in a convection dryer at 50°C. After that, the hollow fiber membrane was cut on the epoxy resin side of the dried module to obtain 20 composite hollow fiber membrane bundles. Modules were fabricated using the obtained composite hollow fiber membranes, and air leak tests and filtration tests were performed. Table 1 shows the measurement results for each of the above measurements.

[0159] [Comparative Example 1] In preparing the film-forming stock solution, a composite hollow fiber membrane was manufactured in the same manner as in Example 1, except that 280 g of polyamide 6 chips (manufactured by Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720 g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were stirred at 190°C for 1.5 hours to dissolve, and then the stirring speed was reduced and degassed for 1 hour to prepare the film-forming stock solution. Table 1 shows the measurement results for each of the above measurements.

[0160] [Comparative Example 2] In preparing the film-forming stock solution, a composite hollow fiber membrane was manufactured in the same manner as in Example 1, except that 250 g of polyamide 6 chips (manufactured by Unitika Ltd., A1030BRT, relative viscosity 3.53) and 750 g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were stirred at 180°C for 1.5 hours to dissolve, and then the stirring speed was reduced and degassed for 1 hour to prepare the film-forming stock solution. Table 1 shows the measurement results for each of the above measurements.

[0161] [Comparative Example 3] In preparing the film-forming stock solution, a composite hollow fiber membrane was manufactured in the same manner as in Example 1, except that 230 g of polyamide 6 tips (manufactured by Unitika Ltd., A1030BRT, relative viscosity 3.53) and 770 g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were stirred at 180°C for 1.5 hours to dissolve, and then the stirring speed was reduced and degassed for 1 hour to prepare the film-forming stock solution. Table 1 shows the measurement results for each of the above measurements.

[0162] [Comparative Example 4] In preparing the film-forming stock solution, 280g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720g of dimethyl sulfone (Tokyo Chemical Industries, Ltd.) were stirred at 180°C for 1.5 hours to dissolve, and then the stirring speed was reduced and degassed for 1 hour to prepare the film-forming stock solution. Furthermore, a mixture of 60% by weight polyethylene glycol 300 (PEG300) and 40% by weight glycerin was used as the internal coagulation solution. A composite hollow fiber membrane was produced in the same manner as in Example 1. No dense layer was observed in the aliphatic polyamide hollow fiber membrane before interfacial polymerization. The estimated pore size by the bubble point method was approximately 5 nm. Table 1 shows the measurement results for each of the above measurements.

[0163] [Comparative Example 5] In preparing the film-forming stock solution, 280g of polyamide 6 chips (manufactured by Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were stirred at 180°C for 1.5 hours to dissolve, and then the stirring speed was reduced and degassed for 1 hour to prepare the film-forming stock solution. Polyethylene glycol 400 (PEG400) was used as the internal coagulation solution, and the obtained aliphatic polyamide hollow fiber film was stretched 1.3 times by passing it between rolls at different speeds. The aliphatic polyamide hollow fiber film was produced in the same manner as in Example 1. The produced hollow fiber film was subjected to each measurement without interfacial polymerization. Table 1 shows the measurement results for each of the above measurements.

[0164] [Table 1]

[0165] The composite hollow fiber membranes of Examples 1 and 2 have a separation functional layer containing a crosslinked aromatic polyamide resin on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane, and the NMP burst pressure is 2.25 MPa or higher, so the NMP permeation rate is 6 L / (m³). 2 The pressure was very high, exceeding h), and the rejection rate of diphenyl sulfone in the NMP solution was over 30%, and the rejection rate of polystyrene with a molecular weight of 1000 was over 90%. This demonstrated extremely high rejection performance at the nanofiltration level, achieving a high level of both NMP permeability and diphenyl sulfone rejection. On the other hand, the composite hollow fiber membranes of Comparative Examples 1-4 and the aliphatic polyamide hollow fiber membrane of Comparative Example 5 had low NMP burst pressure, resulting in low NMP permeability and inferior NMP permeability. [Explanation of Symbols]

[0166] 1. Fluidized liquid tank 2. Liquid transfer pump 3. Primary pressure gauge 4. Secondary pressure gauge 5. Regulator 6. Cross-flow module 7. Drip tray 8. Burst pressure evaluation module 8a Aliphatic polyamide hollow fiber membrane 8b Nylon rigid tubing 9. Hand pump 10 compact layer 11 Support layer

Claims

1. A composite hollow fiber membrane comprising an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, wherein the separation functional layer is provided on the surface of the dense layer, and the burst pressure measured under the following conditions is 2.25 MPa or higher. <Burst pressure> A module fabricated using a composite hollow fiber membrane is subjected to a 0.25 MPa pressure increase at 10-minute intervals while N-methyl-2-pyrrolidone is passed through it, and the pressure (MPa) at which the composite hollow fiber membrane ruptures is measured.

2. The composite hollow fiber membrane according to claim 1, wherein the crosslinked resin is a crosslinked aromatic polyamide resin.

3. The composite hollow fiber membrane according to claim 1, wherein the support layer has a porosity of 60 to 80%.

4. The composite hollow fiber membrane according to claim 1, wherein the dense layer has a thickness of 0.1 to 5 μm.

5. The composite hollow fiber membrane according to claim 1, wherein the dense layer is located on the luminal surface side of the aliphatic polyamide hollow fiber membrane.

6. The aliphatic polyamide hollow fiber membrane is a composite hollow fiber membrane according to claim 1, wherein the fractional molecular weight is 10,000 to 300,000.

7. The aliphatic polyamide hollow fiber membrane is a composite hollow fiber membrane according to claim 1, wherein the burst pressure measured under the following conditions is 2.1 MPa or higher. <Burst pressure> A module fabricated using aliphatic polyamide hollow fiber membranes is subjected to water pressure, and the pressure (MPa) at which the aliphatic polyamide hollow fiber membrane ruptures is measured.

8. The composite hollow fiber membrane according to claim 1, wherein the rejection rate of diphenyl sulfone when a solution in which the solvent is N-methyl-2-pyrrolidone and the solute is diphenyl sulfone is filtered is 30% or more.

9. The permeation rate of N-methyl-2-pyrrolidone at 25°C is 6 L / (m³). 2 - The composite hollow fiber membrane according to claim 1, wherein h) is greater than or equal to h.

10. A filtration method for filtering a liquid to be treated, which contains an organic solvent and a solute, using a composite hollow fiber membrane according to any one of claims 1 to 9.

11. A hollow fiber membrane module comprising a module case containing a composite hollow fiber membrane according to any one of claims 1 to 9.

12. A method for manufacturing a composite hollow fiber membrane, including the following steps 1 to 4: The first step involves preparing a film-forming stock solution by dissolving an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or higher and being immiscible with the aliphatic polyamide resin at temperatures below 100°C, at a temperature of 100°C or higher. A step of solidifying an aliphatic polyamide resin into a film by extruding the film-forming stock solution in a predetermined shape into a solidification bath at 100°C or lower, wherein in the first step, a solidification solution that is compatible with the organic solvent used in the film-forming stock solution and has low affinity for the aliphatic polyamide resin is brought into contact with at least one surface of the film-forming stock solution extruded in the predetermined shape, thereby forming an aliphatic polyamide hollow fiber film having a dense layer on at least one surface. A third step involves removing the film-forming solvent and coagulation solution from the aliphatic polyamide hollow fiber membrane formed in the second step, and A fourth step involves forming a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of at least one dense layer of the aliphatic polyamide hollow fiber membrane obtained by the third step.

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