Composite hollow fiber membrane and its manufacturing method

Abstract

The purpose of the present invention is to provide: a composite hollow fiber membrane, in which the liquid permeability of an organic solvent and the blocking performance of a solute in an organic solvent-based liquid to be treated are both achieved to a great extent; and a method for manufacturing the same. This composite hollow fiber membrane includes: a polyamide hollow fiber membrane having a dense layer and a support layer; and a silicone layer. The silicone layer is provided on the surface of the dense layer.

Description

[Technical Field]

[0001] The present invention relates to a composite hollow fiber membrane having a polyamide hollow fiber membrane having a dense layer and a support layer, and a silicone layer, and a method for producing the same. [Background technology]

[0002] In recent years, the chemical industry has been seeking more energy-efficient processes in order to build a sustainable society and achieve carbon neutrality. In particular, the distillation process accounts for a large proportion of the energy consumed by the entire chemical industry, so there is a need to switch to more energy-efficient processes, and a switch to an energy-efficient membrane separation process is being considered.

[0003] Membrane separation processes are used in the fields of water purification and in the manufacturing processes of various industrial products that use water as a solvent, and are an industrially established technology. Polymer membranes are the mainstream material for the separation membranes used in membrane separation processes because they are relatively easy to mold, an inexpensive mass-production process can be easily established, and they are lightweight, flexible, and easy to handle.

[0004] On the other hand, in the chemical industry, organic solvents are the primary solvent used, so separation membrane materials must be solvent-resistant. For example, in the manufacture of semiconductors and liquid crystal panels, the photoresist solutions, cleaning solutions, and stripping solutions used to form wiring patterns include glycol ether solvents such as propylene glycol monomethyl ether, 3-methoxybutanol, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate, dipropylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; cyclic ketones such as cyclohexanenone; and aprotic polar solvents such as dimethyl sulfoxide and N-methylpyrrolidone. To use membrane separation processes as an alternative to distillation processes, separation membrane materials must be resistant to these organic solvents.

[0005] Furthermore, in order to use the membrane separation process as an alternative to the distillation process, a separation membrane with nanofiltration-level separation performance is required that can separate solutes in organic solvent-based liquids to be treated, particularly solutes with molecular weights of approximately 200 to 1000.

[0006] Under these circumstances, attempts have been made to obtain nanofiltration membranes using polyamide resins, which are highly resistant to various organic solvents. The TIPS method is a relatively new technique. The polymer material is dissolved in a solvent that is insoluble at high temperatures but not at low temperatures. The resulting homogeneous polymer solution is then cooled below the binodal line, which is the boundary between the one-phase and two-phase regions, to induce phase separation and fix the structure through polymer crystallization and glass transition. The TIPS method is applicable to polymers that do not dissolve in solvents at low temperatures, making it suitable for solvent-resistant resins. Furthermore, the TIPS method tends to produce a homogeneous, sponge-like structure, resulting in high-strength separation membranes. This allows for the application of high pressure, which is the driving force for liquid permeation, to nanofiltration membranes with small pore sizes, which typically result in low liquid permeation rates. Therefore, it is a suitable method for obtaining solvent-resistant nanofiltration membranes.

[0007] For example, Patent Document 1 describes a polymer produced by the TIPS method, which has a molecular weight cutoff of 200 to 1000 and a methanol permeation rate of 0.03 L / (m 2 A nanofiltration hollow fiber membrane formed using a polyamide resin has been proposed, which has a resistance of at least 100 MPa (100 MPa).

[0008] Furthermore, Patent Document 2 proposes a polyamide hollow fiber membrane for use as an ultrafiltration membrane or nanofiltration membrane, which is manufactured by applying the TIPS method and has a dense layer formed on at least one surface, and has streak-like recesses extending in one direction on the surface of the dense layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2022 / 071123 [Patent Document 2] International Publication No. 2022 / 071122 Summary of the Invention [Problem to be solved by the invention]

[0010] In order to use the membrane separation process as an alternative to the distillation process, a separation membrane is required that has excellent liquid permeability for organic solvents and excellent blocking performance for solutes in the organic solvent-based liquid to be treated. However, since the liquid permeability and blocking performance are contradictory properties, it is very difficult to achieve both high levels of liquid permeability and blocking performance.

[0011] The polyamide hollow fiber membranes of Patent Documents 1 and 2 have high resistance to various organic solvents, but there is room for improvement in terms of achieving both high levels of liquid permeability and high levels of blocking performance.

[0012] An object of the present invention is to provide a composite hollow fiber membrane that achieves both high levels of organic solvent permeability and high levels of rejection of solutes in organic solvent-based treated liquids, and a method for producing the same. [Means for solving the problem]

[0013] The present inventors have conducted extensive research to solve the above problems and have found that by providing a silicone layer on the surface of the dense layer of a polyamide hollow fiber membrane, a composite hollow fiber membrane can be obtained that can achieve high levels of both organic solvent permeability and high levels of solute rejection in organic solvent-based treated liquids.The present invention was completed through further research based on this finding.

[0014] That is, the present invention provides the following aspects. Item 1. A polyamide hollow fiber membrane having a dense layer and a support layer, and a silicone layer, The silicone layer is provided on the surface of the dense layer. Item 2. The composite hollow fiber membrane according to Item 1, wherein the support layer has a porosity of 60 to 80%. Item 3. The composite hollow fiber membrane according to Item 1 or 2, wherein the dense layer has a thickness of 0.1 μm or more. Item 4. The composite hollow fiber membrane according to any one of Items 1 to 3, wherein the dense layer is provided on the lumen surface side of the polyamide hollow fiber membrane. Item 5. The composite hollow fiber membrane according to any one of Items 1 to 4, wherein the silicone layer has a thickness of 0.2 to 10 μm. Item 6. The composite hollow fiber membrane according to any one of Items 1 to 5, wherein the silicone layer is formed of silicone rubber. Item 7. A filtration method, comprising filtering a liquid to be treated, which contains an organic solvent and a solute, using the composite hollow fiber membrane according to any one of Items 1 to 6. Item 8. A hollow fiber membrane module comprising a module case and the composite hollow fiber membrane according to any one of Items 1 to 6 housed in the module case. Item 9. A method for producing a composite hollow fiber membrane, comprising the following steps 1 to 4: A first step of preparing a film-forming solution by dissolving a polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or more and being incompatible with the polyamide resin at a temperature below 100°C at a temperature of 100°C or more; a second step in which the membrane-forming solution is extruded into a coagulation bath at 100°C or less in a predetermined shape to coagulate the polyamide resin into a membrane, in which a coagulation liquid that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the polyamide resin is brought into contact with at least one surface of the membrane-forming solution extruded into the predetermined shape, thereby forming a polyamide hollow fiber membrane having a dense layer on at least one surface; A third step of removing the membrane forming solution solvent and the coagulation solution from the polyamide hollow fiber membrane formed in the second step; and A fourth step of forming a silicone layer on the surface of at least one of the dense layers of the polyamide hollow fiber membrane obtained by carrying out the third step. [Effects of the Invention]

[0015] The composite hollow fiber membrane of the present invention can achieve both high levels of organic solvent permeability and high levels of solute rejection in organic solvent-based treated liquids. Furthermore, since the composite hollow fiber membrane of the present invention is formed from a polyamide resin and silicone, 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. Therefore, the composite hollow fiber membrane of the present invention can be suitably used in membrane separation processes that can replace distillation processes. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of an apparatus used to measure the molecular weight cutoff, permeation rate (Flux), and rejection rate of a composite hollow fiber membrane or a polyamide hollow fiber membrane. [Figure 2] FIG. 1A is a schematic diagram of a module used when measuring the burst pressure of a composite hollow fiber membrane or a polyamide hollow fiber membrane, and FIG. 1B is a schematic diagram of an apparatus used to measure the burst pressure of a composite hollow fiber membrane or a polyamide hollow fiber membrane. [Figure 3] FIG. 10 is an image analysis diagram after binarization processing for calculating the porosity of the support layer of the composite hollow fiber membrane of Example 3. [Figure 4] 1 is a scanning electron microscope image (magnification: 5000 times) of the lumen side cross section of the composite hollow fiber membrane of Example 3. [Figure 5] FIG. 1 is a schematic diagram illustrating an example of calculating the porosity of the support layer of a composite hollow fiber membrane, and is a cross-sectional schematic diagram of a polyamide hollow fiber membrane cut in a direction perpendicular to the longitudinal direction. [Figure 6] FIG. 6 is a partial enlarged view of the area surrounded by the dotted line in FIG. 5. [Figure 7] FIG. 6 is a partial enlarged view of the area surrounded by the dotted line in FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1.Definition In the present invention, when the term "ultrafiltration" or "ultrafiltration membrane" is used, it means a filtration having a molecular weight cutoff set within a range of 1,000 to 1,000,000 or a filtration membrane having a molecular weight cutoff within a range of 1,000 to 1,000,000, and when the term "nanofiltration" or "nanofiltration membrane" is used, it means a filtration having a molecular weight cutoff set within a range of 200 to 1,000 or a filtration membrane having a molecular weight cutoff within a range of 200 to 1,000.

[0018] In the present invention, the term "polyamide hollow fiber membrane" refers to a filtration membrane in the form of hollow fibers formed using a polyamide resin and having a dense layer and a support layer.

[0019] In the present invention, the term "dense layer" refers to a region in a polyamide hollow fiber membrane where dense micropores are concentrated, and in which the presence of substantially no pores is observed in a scanning electron microscope (SEM) photograph at a magnification of 10,000 times.

[0020] In the present invention, the "support layer" refers to a region other than the dense layer in a polyamide hollow fiber membrane, which is a porous region having a continuous porous structure in which the presence of pores is substantially evident in a scanning electron microscope (SEM) photograph at 2000x magnification.

[0021] In the present invention, the term "silicone layer" refers to a layer formed using silicone and provided on the surface of the dense layer of a polyamide hollow fiber membrane.

[0022] 2.Composite hollow fiber membrane The composite hollow fiber membrane of the present invention comprises a polyamide hollow fiber membrane having a dense layer and a support layer, and a silicone layer, the silicone layer being provided on the surface of the dense layer. The composite hollow fiber membrane of the present invention is described in detail below.

[0023] [Polyamide hollow fiber membrane] The polyamide hollow fiber membrane, which is a main component of the composite hollow fiber membrane of the present invention, has a dense layer and a support layer and is formed of a polyamide resin. By using a polyamide resin as a constituent resin of the polyamide hollow fiber membrane, the composite hollow fiber membrane of the present invention can be endowed with resistance to a wide range of organic solvents.

[0024] The type of polyamide resin is not particularly limited, and examples thereof include polyamide homopolymers, polyamide copolymers, and mixtures thereof. Specific examples of polyamide homopolymers include polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide MXD6, polyamide 4T, polyamide 6T, polyamide 9T, and polyamide 10T. Specific examples of polyamide copolymers include copolymers of polyamide with polyethers such as polytetramethylene glycol or polyethylene glycol. The proportion of the polyamide component in the polyamide copolymer is not particularly limited, and examples of the proportion of the polyamide component include 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 ensuring that the proportion of the polyamide component in the polyamide copolymer satisfies the above range, the polyamide hollow fiber membrane can be provided with even better organic solvent resistance. The polyamide resins may be used singly or in combination of two or more.

[0025] Among these polyamide resins, polyamide 6 is preferably used as a resin for forming polyamide hollow fiber membranes because it easily achieves both good pressure resistance and solvent resistance and also easily improves the liquid permeability of organic solvents.

[0026] The polyamide resin may be crosslinked or not, but from the viewpoint of reducing production costs, it is preferable that the polyamide resin is not crosslinked.

[0027] The relative viscosity of the polyamide resin is not particularly limited, but may be, for example, 2.0 to 7.0, preferably 2.5 to 6.0, and more preferably 3.0 to 5.0. Having such a relative viscosity improves moldability and controllability of phase separation during the production of polyamide hollow fiber membranes, and makes it possible to provide the polyamide hollow fiber membrane with excellent shape stability. Here, the relative viscosity refers to the value measured with an Ubbelohde viscometer at 25°C using a solution in which 1 g of polyamide resin is dissolved in 100 mL of 96% sulfuric acid.

[0028] In addition to the polyamide resin, the polyamide hollow fiber membrane may contain a filler, if necessary, to the extent that the effects of the present invention are not impaired. The inclusion of a filler can improve the strength, elongation, and elastic modulus of the polyamide hollow fiber membrane. In particular, the inclusion of a filler has the effect of making the polyamide hollow fiber membrane less likely to deform even when high pressure is applied during filtration. The type of filler to be added is not particularly limited, and examples thereof include fibrous fillers such as glass fiber, carbon fiber, potassium titanate whisker, zinc oxide whisker, calcium carbonate whisker, wollastonite whisker, aluminum borate whisker, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, gypsum fiber, and metal fiber; talc, hydrotalcite, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, and the like. Examples of fillers include silicates such as sintered silicate and alumina silicate; metal compounds such as silicon oxide, magnesium oxide, alumina, zirconium oxide, titanium oxide, 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 non-fibrous fillers such as glass beads, glass flakes, glass powder, ceramic beads, boron nitride, silicon carbide, carbon black, silica, and graphite. These fillers may be used alone or in combination of two or more. Among these fillers, preferred are talc, hydrotalcite, silica, clay, and titanium oxide, and more preferred are talc and clay. The filler content is not particularly limited, but may be, for example, 5 to 100 parts by weight, preferably 10 to 75 parts by weight, and more preferably 25 to 50 parts by weight per 100 parts by weight of polyamide resin. By including the filler in such an amount, the strength, elongation, and elastic modulus of the polyamide hollow fiber membrane can be improved.

[0029] The polyamide hollow fiber membrane may contain additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants, as needed, for the purpose of pore size control and improving membrane performance.

[0030] The outer diameter of the polyamide hollow fiber membrane is appropriately set depending on the application of the polyamide hollow fiber membrane, the thickness of the dense layer and the support layer, the desired liquid permeability, etc., but in consideration of the relationship between the effective membrane area when packed in a module, the membrane strength, the pressure drop of the fluid flowing through the hollow portion, and the 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 polyamide hollow fiber membrane is not particularly limited, but may be, for example, 100 to 3000 μm, preferably 200 to 2500 μm, more preferably 300 to 2000 μm, and even more preferably 300 to 1500 μm. In the present invention, the outer diameter and inner diameter of the polyamide hollow fiber membrane are values ​​that can be determined by observing five composite hollow fiber membranes with an optical microscope at a magnification of 200x, measuring the outer diameter and inner diameter (both at the point where they are maximum diameter) of the polyamide hollow fiber membranes that make up each composite hollow fiber membrane, and calculating the average value of each.

[0031] The thickness of the polyamide hollow fiber membrane is appropriately set depending on the application of the polyamide hollow fiber membrane, the thickness of the dense layer and the support layer, the liquid permeability to be provided, etc., and is, for example, 50 to 600 μm, preferably 100 to 350 μm. In the present invention, the thickness of the polyamide hollow fiber membrane is a value calculated by subtracting the inner diameter from the outer diameter and dividing the value by 2.

[0032] Here, filtration membranes (separation membranes) are classified into microfiltration (MF) membranes, ultrafiltration (UF) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes in order of the size of the substance to be separated. For filtration membranes below UF membranes, the molecular weight cutoff is used as an index of the size of the substance to be captured. The molecular weight cutoff is determined by a permeation test using a standard substance of known molecular weight. The molecular weight cutoff is determined by the lower limit molecular size (Dalton unit: Da) that is retained by 90% or more in the permeation test. In the present invention, the molecular weight cutoff of an ultrafiltration membrane is 1,000 to 1,000,000, and the molecular weight cutoff of a nanofiltration membrane is 200 to 1,000.

[0033] The polyamide hollow fiber membrane is preferably an ultrafiltration membrane or a nanofiltration membrane from the viewpoint of obtaining a composite hollow fiber membrane of the present invention that can achieve both high levels of organic solvent permeability and high levels of rejection of solutes in the organic solvent-based liquid to be treated. The molecular weight cutoff of the polyamide hollow fiber membrane is not particularly limited and can be adjusted to the desired value by appropriately adjusting the thickness of the dense layer and the pore size of the support layer. However, from the viewpoint of obtaining a composite hollow fiber membrane of the present invention that can achieve both high levels of organic solvent permeability and high levels of rejection of solutes in the organic solvent-based liquid to be treated, the molecular weight cutoff of the polyamide hollow fiber membrane is preferably 1000 to 120,000, more preferably 1000 to 100,000, even more preferably 1000 to 60,000, and even more preferably 1000 to 50,000 in the case of an ultrafiltration membrane, and is preferably 200 to 1000, more preferably 400 to 1000, and even more preferably 600 to 1000.

[0034] In the present invention, when the molecular weight cutoff of a polyamide hollow fiber membrane is greater than 3000, it is a value determined using dextran as the standard substance and water as the solvent. Specifically, the molecular weight cutoff of a polyamide hollow fiber membrane (when greater than 3000) is a value determined when a crossflow module is fabricated using the polyamide hollow fiber membrane and an aqueous solution containing a plurality of dextrans of known molecular weights at predetermined concentrations is used as the circulating liquid (raw solution) in an internal pressure crossflow system. The dextran concentrations in the permeate are measured by high-performance liquid chromatography, and the solute rejection at each molecular weight is calculated according to the following formula. The results are then plotted on a graph with molecular weight on the horizontal axis and rejection on the vertical axis, and the molecular weight is the molecular weight at the intersection of the obtained approximation curve and a rejection of 90%. Solute rejection rate (%) = {(dextran concentration in the original solution - dextran concentration in the permeate) / dextran concentration in the original solution} x 100

[0035] In the present invention, when the molecular weight cutoff of a polyamide hollow fiber membrane is 3000 or less, it is a value determined using monodisperse polystyrene as a standard substance and N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") as a solvent. Specifically, the molecular weight cutoff of a polyamide hollow fiber membrane (when 3000 or less) is a value determined when a crossflow module is fabricated using polyamide hollow fiber membranes and an NMP solution containing polystyrenes of known molecular weights at predetermined concentrations is used as the circulating liquid (raw solution) in an internal pressure crossflow system. The polystyrene concentrations in the permeate are measured by high performance liquid chromatography, and the solute rejection at each molecular weight is calculated according to the following formula. The results are then plotted on a graph with molecular weight on the horizontal axis and rejection on the vertical axis, and the molecular weight is the molecular weight at the intersection of the obtained approximation curve and a rejection of 90%. Solute rejection rate (%) = {(Polystyrene concentration in raw solution - Polystyrene concentration in permeate) / Polystyrene concentration in raw solution} x 100

[0036] The burst pressure of a polyamide hollow fiber membrane is not particularly limited and can be adjusted to a desired value by appropriately adjusting the thickness of the dense layer, the thickness of the support layer, the pore size of the support layer, etc. However, from the viewpoint of increasing the operating pressure during membrane filtration to increase the amount of liquid permeated, it is preferably 10 bar or more, more preferably 15 bar or more, even more preferably 20 bar or more, and even more preferably 25 bar or more. The upper limit of the burst pressure of a polyamide hollow fiber membrane is usually 40 bar or less, preferably 35 bar or less. In the present invention, the burst pressure of a polyamide hollow fiber membrane refers to the pressure (bar) at which a hollow fiber membrane breaks when hydraulic pressure is applied to a module prepared using the polyamide hollow fiber membrane. Specifically, the burst pressure of a polyamide hollow fiber membrane is preferably 10 to 40 bar, more preferably 15 to 35 bar, even more preferably 20 to 35 bar, and even more preferably 25 to 35 bar.

[0037] The burst pressure of polyamide hollow fiber membranes is measured by the following method. First, a module 8 shown in Figure 2a is prepared. Specifically, ten hollow fiber membranes 8a are cut to 30 cm lengths and bundled together. Next, a nylon hard tube 8b with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm is prepared. A rubber stopper approximately 20 mm long is inserted into one end opening of the tube to plug the end opening. Next, a two-component epoxy resin is injected into the opening opposite the rubber stopper to fill the inner space of the tube. The bundle of hollow fiber membranes is then bent into an approximately U-shape, and both ends of the hollow fiber membranes are heat-sealed to prevent the epoxy resin from penetrating the hollow space. The end tip is then inserted into the tube filled with epoxy resin until it touches the rubber stopper, and the epoxy resin is cured in this state. Next, the region of the hardened epoxy resin on the rubber stopper side is cut off together with the tube, thereby producing a module 8 in which the hollow portions at both ends of the hollow fiber membrane are open. Next, the module 8 is set in the device shown in FIG. 2b, and water pressure is applied to the module 8 using a hand pump 9. The pressure (bar) at which the module 8 breaks is taken as the burst pressure.

[0038] [Dense layer] The dense layer is a region in the polyamide hollow fiber membrane where dense micropores are concentrated, and is a region in which the presence of pores is substantially not observed in a scanning electron microscope (SEM) photograph at 10,000x magnification.

[0039] The dense layer may be formed on the lumen-side surface of the polyamide hollow fiber membrane, on the outer surface, or on both surfaces, but is preferably formed on the lumen-side surface from the viewpoint of achieving both higher levels of organic solvent permeability and higher levels of blocking performance for solutes in the organic solvent-based treated liquid. When observing the dense layer with a scanning electron microscope (SEM), if the dense layer is present on the outer surface of the polyamide hollow fiber membrane, the polyamide hollow fiber membrane can be cut to an appropriate size, mounted on a sample stage, and then vapor-deposited with Pt, Au, Pd, or the like before observation. If the dense layer is present on the lumen-side surface of the polyamide hollow fiber membrane, the polyamide hollow fiber membrane can be cut longitudinally with a sharp blade such as a scalpel to expose the lumen-side surface, cut to an appropriate size, mounted on a sample stage, and then vapor-deposited with Pt, Au, Pd, or the like before observation.

[0040] 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 membrane-forming solution, the type and temperature of the coagulation solution, etc., but from the viewpoint of improving the blocking performance of solutes in the organic solvent-based treated solution, it is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more, and from the viewpoint of improving the liquid permeability of the organic solvent, it is preferably 2.0 μm or less, more preferably 1.8 μm or less, even more preferably 1.5 μm or less, still 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, still more preferably 0.3 to 1.2 μm, and even more preferably 0.3 to 1.0 μm. In the present invention, the thickness of the dense layer is a value obtained by measuring the distance (thickness) of an area where substantially no pores are found in the polyamide hollow fiber membrane constituting the composite hollow fiber membrane at 10,000x magnification in a scanning electron microscope (SEM) photograph, and calculating the average value.

[0041] [Support layer] The support layer is a region of the polyamide hollow fiber membrane other than the dense layer, and is a porous region having a continuous porous structure in which the presence of substantial pores can be seen in a scanning electron microscope (SEM) photograph at 2000x magnification.

[0042] The pore size of the support layer is not particularly limited as long as it has a strength sufficient to support the dense layer and does not significantly impede fluid permeation.

[0043] 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 membrane-forming solution, the type and temperature of the coagulation solution, etc., in the production of a polyamide hollow fiber membrane. From the viewpoint of ease of membrane production and from the viewpoint of increasing membrane strength so that the operating pressure during membrane filtration can be increased to increase the amount of liquid permeated, the porosity is preferably 60 to 80%, more preferably 63 to 78%, even more preferably 65 to 77%, and even more preferably 66 to 76%.

[0044] In the present invention, the porosity of the support layer is calculated by the following method. Scanning electron microscope (SEM) photographs are taken at five locations equidistantly spaced in the thickness direction of the support layer of the polyamide hollow fiber membrane in a cross section obtained by cutting the composite hollow fiber membrane perpendicular to the longitudinal direction. Specifically, the photographs are taken as follows. Fig. 5 is a schematic cross-sectional view of a polyamide hollow fiber membrane cut perpendicular to the longitudinal direction, and Figs. 6 and 7 are partial enlarged views of the area surrounded by the dotted line in Fig. 5, illustrating an example of a polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 12. Note that the silicone layer is omitted in Figs. 5 to 7. As shown in Fig. 6, a straight line is drawn from the center of the lumen of the polyamide hollow fiber membrane 8a toward the outer surface, and the line is divided into five equal parts from the lumen-side surface of the support layer 12 to the outer surface. Then, the midpoints of the five equal parts are determined as shown in Fig. 6. 7, the midpoint is positioned at the center of the captured image, and five locations are photographed at a uniform magnification such that only the support layer 12 portion is included in the captured image and the number of pores is 30 to 300. For the five SEM photographs taken, image analysis of the above-mentioned regions is performed using image analysis software (ImageJ), and the pore portion and the polymer portion are distinguished by binarization processing, and the area ratio (%) of the total pore area to the area of ​​the analyzed region is calculated for each, and the average value is calculated.

[0045] [Silicone layer] The silicone layer is a non-porous region layer provided on the surface of the dense layer of the polyamide hollow fiber membrane in order to improve the blocking performance of solutes in the organic solvent-based liquid to be treated. The composite hollow fiber membrane of the present invention, which has a silicone layer on the surface of the dense layer of the polyamide hollow fiber membrane, has significantly improved blocking performance of solutes in the organic solvent-based liquid to be treated compared to polyamide hollow fiber membranes not having a silicone layer, and can achieve both high levels of organic solvent permeability and high levels of blocking performance of solutes in the organic solvent-based liquid to be treated.

[0046] The silicone layer may be provided on the surface of the dense layer on the lumen side surface of the polyamide hollow fiber membrane or on the surface of the dense layer on the outer surface of the polyamide hollow fiber membrane, but is preferably provided on the surface of the dense layer on the lumen side surface of the polyamide hollow fiber membrane. This is because providing a silicone layer on the surface of the dense layer on the outer surface of the polyamide hollow fiber membrane may cause peeling of the silicone layer due to contact between the hollow fiber membranes during filtration, or peeling at the interfaces between both ends of the module and the sealant during module fabrication. Furthermore, when the polyamide hollow fiber membrane has dense layers on both sides, the silicone layer may be provided on the surface of only one of the dense layers or on the surfaces of both dense layers, but for the above reasons, it is preferably provided only on the surface of the dense layer on the lumen side surface.

[0047] The silicone that is the material for forming the silicone layer is not particularly limited as long as it does not significantly inhibit the liquid permeability of the organic solvent and can improve the blocking performance of solutes in the organic solvent-based liquid to be treated, and may be a silicone resin or a silicone rubber. However, from the viewpoint of imparting elasticity and flexibility to the silicone layer and obtaining a silicone layer with excellent shape stability, silicone rubber is preferred.

[0048] Silicone rubber is a rubbery cured product having a polyorganosiloxane structure obtained by curing polyorganosiloxane. Polyorganosiloxane is a linear, branched, or network-like compound having an Si-O bond (siloxane bond). The substituent bonded to the silicon atom is not particularly limited, and examples thereof include alkyl groups having 1 to 10 carbon atoms such as methyl, ethyl, propyl, and butyl; alkenyl groups having 2 to 10 carbon atoms such as vinyl, allyl, and butenyl; aryl groups having 6 to 20 carbon atoms such as phenyl, tolyl, and naphthyl; and cycloalkyl groups having 3 to 10 carbon atoms such as cyclopentyl and cyclohexyl. These substituents may be contained alone or in combination.

[0049] Examples of polyorganosiloxanes include polydialkylsiloxanes (e.g., polydiC such as polydimethylsiloxane). 1-10 alkylsiloxanes), polyalkylalkenylsiloxanes (e.g., polyC such as polymethylvinylsiloxane, 1-10 Alkyl C 2-10 alkenylsiloxane), polyalkylarylsiloxane (e.g., polyC such as polymethylphenylsiloxane) 1-10 Alkyl C 6-20 arylsiloxane), polydiarylsiloxane (e.g., polydiphenylsiloxane, etc.) 6-20 arylsiloxane), dialkylsiloxane-alkylalkenylsiloxane copolymer (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane copolymer) 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 alkenylsiloxane copolymer), dialkylsiloxane-alkylarylsiloxane copolymer (e.g., di-C such as dimethylsiloxane-methylphenylsiloxane copolymer) 1-10 Alkylsiloxane-C 1-10 Alkyl C 6-20 arylsiloxane copolymer), dialkylsiloxane-alkylalkenylsiloxane-alkylarylsiloxane copolymer (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer) 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 Alkenylsiloxane-C 1-10 Alkyl C 6-20 arylsiloxane copolymers). The alkyl group of the polyorganosiloxane may be a fluorinated alkyl group. The polyorganosiloxane may be used singly or in combination of two or more. Among these polyorganosiloxanes, polyalkylalkenylsiloxanes (e.g., polyC such as polymethylvinylsiloxane) are preferred from the viewpoint of obtaining a silicone layer that does not significantly inhibit the liquid permeability of organic solvents and has excellent blocking performance for solutes in the organic solvent-based liquid to be treated. 1-10Alkyl C 2-10 Alkenylsiloxane), dialkylsiloxane-alkylalkenylsiloxane copolymer (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane copolymer) 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 alkenylsiloxane copolymers), and dialkylsiloxane-alkylalkenylsiloxane-alkylarylsiloxane copolymers (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 Alkenylsiloxane-C 1-10 Alkyl C 6-20 aryl siloxane copolymers).

[0050] The polyorganosiloxane may have a substituent such as an epoxy group, a hydroxy group, an alkoxy group, a carboxy group, an amino group, an ether group, an acryloyl group, or a methacryloyl group at the molecular end or the main chain. The terminal of the polyorganosiloxane is not particularly limited, and may be, for example, a trialkylsilyl group (e.g., a tri-C group such as a trimethylsilyl group). 1-10 alkylsilyl groups), dialkylalkenylsilyl groups (e.g., di-C such as dimethylvinylsilyl groups) 1-10 Alkyl C 2-10 alkenylsilyl group), silanol group, trialkoxysilyl group (e.g., tri-C such as trimethoxysilyl group) 1-10 Alkoxysilyl groups) may also be used.

[0051] The polyorganosiloxane structure forming the silicone rubber may be linear, branched, or network-like, but is preferably linear from the viewpoint of elasticity and flexibility.

[0052] The silicone rubber may be either a one-component curing type (a type that cures by reacting with moisture in the air) or a two-component curing type (a type that cures by mixing a crosslinking agent), but the two-component curing type is preferred from the viewpoints of easy control of reaction time and excellent storage stability. Also, the silicone rubber may be either a room temperature curing type (condensation type) or a thermosetting type (addition type), but the thermosetting type (addition type) is preferred from the viewpoint of easy reaction control.

[0053] The thermosetting (addition) two-component curing silicone rubber is not particularly limited, but from the viewpoint of obtaining a silicone layer that does not significantly inhibit the liquid permeability of organic solvents and has excellent blocking performance for solutes in the organic solvent-based liquid to be treated, a two-component curing silicone rubber utilizing a hydrosilylation reaction is preferred, more preferably a cured product of a polyorganosiloxane having alkenyl groups as a base polymer and an organohydrogenpolysiloxane (e.g., polydialkylsiloxane, polyalkylarylsiloxane, and polydiarylsiloxane having multiple hydrogen atoms bonded to silicon atoms) as a crosslinking agent, and even more preferably a polyalkylalkenylsiloxane (e.g., polyC such as polymethylvinylsiloxane). 1-10 Alkyl C 2-10 Alkenylsiloxane), dialkylsiloxane-alkylalkenylsiloxane copolymer (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane copolymer) 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 alkenylsiloxane copolymers), and dialkylsiloxane-alkylalkenylsiloxane-alkylarylsiloxane copolymers (e.g., di-C such as dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers 1-10 Alkylsiloxane-C 1-10 Alkyl C 2-10 Alkenylsiloxane-C 1-10 Alkyl C 6-20 The cured product is a mixture of at least one base polymer selected from the group consisting of organohydrogenpolysiloxanes and arylsiloxane copolymers.

[0054] The silicone rubber may contain a curing catalyst. The curing catalyst must be appropriately selected depending on the type of silicone rubber, but examples thereof include organic peroxides (e.g., diacyl peroxide, peroxy ester, dialkyl peroxide, etc.), tin salts (e.g., tin soap, etc.), platinum group metal compounds (e.g., platinum catalysts such as platinum fine powder, platinum black, chloroplatinic acid, alcohol solutions of chloroplatinic acid, platinum-olefin complexes, platinum-alkenylsiloxane complexes, and platinum-phosphorus complexes; palladium-based catalysts and rhodium-based catalysts corresponding to these platinum-based catalysts), etc.

[0055] The silicone layer may contain additives such as a cure retarder, a thickener, an antioxidant, a surface modifier, a lubricant, and a surfactant, as required.

[0056] The thickness of the silicone layer is not particularly limited, but from the viewpoint of suppressing the occurrence of defects and improving the blocking performance of solutes in the organic solvent-based liquid to be treated, and from the viewpoint of suppressing a decrease in the liquid permeability of the organic solvent, it is preferably 0.2 to 10 μm, more preferably 0.5 to 8 μm, even more preferably 0.8 to 5 μm, still more preferably 1 to 5 μm, even more preferably 1.5 to 5 μm, and even more preferably 2 to 5 μm. In the present invention, the thickness of the silicone layer is a value determined by measuring the distance (thickness) of the non-porous region present on the surface of the dense layer at 10 regularly spaced points in a scanning electron microscope (SEM) photograph of the cross section of the composite hollow fiber membrane at a magnification of 5000 times, and calculating the average value.

[0057] [Permeability of organic solvents and solute rejection] The composite hollow fiber membrane of the present invention has the silicone layer provided on the surface of the dense layer of the polyamide hollow fiber membrane, and therefore can achieve both high levels of liquid permeability for organic solvents and high levels of blocking performance for solutes in organic solvent-based treated liquids, and has, for example, the following liquid permeability and blocking performance.

[0058] In one embodiment of the composite hollow fiber membrane of the present invention, the NMP permeation rate at 25°C and a pressure that is 90% of the burst pressure of the composite hollow fiber membrane is preferably 0.5 L / (m 2 ·h), more preferably 1.0 L / (m 2 ·h), more preferably 1.2 L / (m 2 ·h) or more, and even more preferably 1.5 L / (m 2 ·h), more preferably 2.0 L / (m 2 ·h) or more, and even more preferably 3.0 L / (m 2 The upper limit of the NMP permeation amount is usually 20 L / (m 2 ·h) or less, and preferably 15 L / (m 2 ·h), more preferably 10 L / (m 2 ·h) or less, and even more preferably 6.0 L / (m 2 Specifically, the permeation amount of NMP at 25°C and a pressure of 90% of the burst pressure of the composite hollow fiber membrane is preferably 0.5 to 20 L / (m 2 ·h), more preferably 1.0 to 15 L / (m 2 ·h), more preferably 1.2 to 10 L / (m 2 ·h), more preferably 2.0 to 10 L / (m 2 ·h), and more preferably 3.0 to 6.0 L / (m 2 The NMP permeation rate can be adjusted to a desired value by appropriately adjusting the type of polyamide resin that is the material for forming the polyamide hollow fiber membrane, the molecular weight cutoff of the polyamide hollow fiber membrane, the thickness of the dense layer, the type of silicone that is the material for forming the silicone layer, the thickness of the silicone layer, etc.

[0059] In one embodiment of the composite hollow fiber membrane of the present invention, the permeation rate of a mixture of 30% by weight of propylene glycol monomethyl ether acetate and 70% by weight of propylene glycol monomethyl ether (hereinafter also referred to as "thinner") at 25°C and a pressure that is 90% of the burst pressure of the composite hollow fiber membrane is preferably 0.5 L / (m 2 ·h), more preferably 0.8L / (m 2·h), more preferably 1.0 L / (m 2 ·h) or more, and even more preferably 1.7 L / (m 2 ·h), more preferably 2.3 L / (m 2 ·h) or more, and even more preferably 3.0 L / (m 2 ·h), and particularly preferably 4.0 L / (m 2 The upper limit of the amount of thinner permeation is usually 20 L / (m 2 ·h) or less, and preferably 15 L / (m 2 ·h), more preferably 10 L / (m 2 ·h) or less, more preferably 7 L / (m 2 Specifically, the permeation amount of thinner at 25°C and a pressure that is 90% of the burst pressure of the composite hollow fiber membrane is preferably 0.5 to 20 L / (m 2 ·h), more preferably 0.8 to 15 L / (m 2 ·h), more preferably 1.0 to 10 L / (m 2 ·h), and even more preferably 1.7 to 10 L / (m 2 ·h), more preferably 2.3 to 10 L / (m 2 ·h), and more preferably 3.0 to 7.0 L / (m 2 ·h), particularly preferably 4.0 to 7.0 L / (m 2 The thinner permeation amount can be adjusted to a desired value by appropriately adjusting the type of polyamide resin that is the material for forming the polyamide hollow fiber membrane, the molecular weight cutoff of the polyamide hollow fiber membrane, the thickness of the dense layer, the type of silicone that is the material for forming the silicone layer, the thickness of the silicone layer, etc.

[0060] The NMP permeation rate and the thinner permeation rate are values ​​measured by internal pressure filtration and are measured by the following procedure. First, 20 composite hollow fiber membranes are cut into 30 cm lengths 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 approximately 15 mm into one end opening of the tube to connect the two. A rubber stopper approximately 20 mm long is inserted into the end of the silicone tube opposite the end inserted into the PBT tube to plug the one end opening. Next, a two-component epoxy resin mixture is injected into the opening of the connecting tube opposite the end with the rubber stopper, filling the space inside the tube with the epoxy resin. One end of the bundle of composite hollow fiber membranes prepared above is then heat-sealed to prevent the epoxy resin from penetrating the hollow portion, and the end is inserted into a tube filled with the epoxy resin until the tip of the end touches the rubber stopper, and the epoxy resin is cured in this state. Next, the region of the cured epoxy resin on the rubber stopper side is cut together with the tube to open the hollow portion. The same procedure is performed on the other end to produce a cross-flow module with open hollow portions at both ends of the composite hollow fiber membrane. The fabricated crossflow module 6 is connected to the internal pressure separation treatment line shown in Figure 1, and the flowing liquid is continuously passed through the crossflow module 6 by the liquid circulation pump 2. NMP or thinner is used as the flowing liquid. In the module, the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 are adjusted by the regulator 5 so that the arithmetic mean value of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 is 90% of the burst pressure of the composite hollow fiber membrane. Of the flowing liquid passing through the module, that which has passed through the pores of the composite hollow fiber membrane is recovered as permeated liquid separated from the flowing liquid, and the remainder is circulated again to the separation treatment line. The permeated liquid that flows out of the crossflow module 6 between 2 and 4 hours after the start of circulation is recovered in a receiver 7, and the NMP permeation amount or thinner permeation amount (L / (m)) is calculated according to the following formula: 2 Calculate h). NMP permeation rate = volume of NMP permeated 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 (membranes) × time (h)] Amount of thinner permeated = Volume of thinner permeated 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 (membranes) × Time (h)] Effective filtration length of composite hollow fiber membrane: This is the length of the outer surface of the composite hollow fiber membrane in the crossflow module that is not coated with epoxy resin.

[0061] The burst pressure of the composite hollow fiber membrane of the present invention is not particularly limited and can be adjusted to a desired value by appropriately adjusting the thickness of the dense layer, the thickness of the support layer, the pore size of the pores in the support layer, etc. From the viewpoint of increasing the operating pressure during membrane filtration to increase the amount of liquid permeated, the burst pressure is preferably 10 bar or more, more preferably 15 bar or more, even more preferably 20 bar or more, and even more preferably 25 bar or more. The upper limit of the burst pressure of the composite hollow fiber membrane is usually 40 bar or less, preferably 35 bar or less. Specifically, the burst pressure of the composite hollow fiber membrane of the present invention is preferably 10 to 40 bar, more preferably 15 to 35 bar, even more preferably 20 to 35 bar, and even more preferably 25 to 35 bar. In the present invention, the burst pressure of the composite hollow fiber membrane is the pressure (bar) at which the composite hollow fiber membrane ruptures when hydraulic pressure is applied to a module produced using the composite hollow fiber membrane.

[0062] The burst pressure of the composite hollow fiber membrane is measured as follows. First, a module 8 shown in Figure 2a is prepared. Specifically, ten composite hollow fiber membranes 8a are cut to a length of 30 cm and bundled together. Next, a nylon hard tube 8b with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm is prepared. A rubber stopper approximately 20 mm long is inserted into one end opening of the tube to plug the end opening. Next, a two-component epoxy resin is injected into the opening opposite the rubber stopper to fill the inner space of the tube. The bundle of composite hollow fiber membranes prepared is then bent into an approximately U-shape, and both ends of the composite hollow fiber membrane are heat-sealed to prevent the epoxy resin from penetrating the hollow portion. The end tip is then inserted into the tube filled with epoxy resin until it touches the rubber stopper, and the epoxy resin is cured in this state. Next, the region of the cured epoxy resin on the rubber stopper side is cut off together with the tube to produce a module 8 in which the hollow portions at both ends of the composite hollow fiber membrane are open. Next, the module 8 is set in the device shown in FIG. 2b, and water pressure is applied to the module 8 using a hand pump 9. The pressure (bar) at which the module 8 breaks is taken as the burst pressure.

[0063] 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., a membrane with a molecular weight cutoff of 200 to 1000. However, since the method for measuring the molecular weight cutoff is complicated, a simple method for identifying the classification of filtration membranes is to measure the molecular weight of a vitamin B 12 The composite hollow fiber membrane of the present invention having a molecular weight cutoff of 1000 is preferably used to reject vitamin B 12 The inventor's test confirmed that the inhibition rate of vitamin B 12 If the rejection rate of vitamin B is 90% or more, the composite hollow fiber membrane of the present invention can be determined to be a nanofiltration membrane. 12 The rejection rate is preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more.

[0064] In one embodiment of the composite hollow fiber membrane of the present invention, the solvent is NMP or thinner, and the solute is vitamin B 12 Vitamin B when filtered 12 The inhibition rate of vitamin B is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, and even more preferably 99% or more. 12 The rejection rate can be adjusted to a desired value by appropriately adjusting the type of polyamide resin that is the material for forming the polyamide hollow fiber membrane, the molecular weight cutoff of the polyamide hollow fiber membrane, the thickness of the dense layer, the type of silicone that is the material for forming the silicone layer, the thickness of the silicone layer, etc.

[0065] Vitamin B 12 The rejection rate is a value measured by internal pressure filtration using the same procedure as in the measurement of the NMP permeation amount and the thinner permeation amount. The absorbance of the resulting permeate and flow-through liquid at a wavelength of 550 nm was measured using an absorption spectrometer, and the rejection rate of vitamin B was calculated from the following formula: 12 The blocking rate of the fluid was calculated. 12 (500 ppm) NMP solution or thinner solution is used. Vitamin B 12 Rejection rate = 100 - (absorbance of permeate / absorbance of flow-through) x 100

[0066] [Organic solvent resistance] The composite hollow fiber membrane of the present invention is formed mainly from polyamide resin and silicone, and therefore has the property of suppressing changes in strength and elongation and stably maintaining the membrane structure even when it comes into contact with various types of organic solvents (organic solvent resistance). More specifically, the composite hollow fiber membrane of the present invention is resistant to organic solvents such as alcohols, aprotic polar solvents, hydrocarbons, higher fatty acids, ketones, esters, and ethers. Specific examples of such organic solvents include the following: Alcohols: primary alcohols such as methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, etc.; secondary alcohols such as isopropyl alcohol, isobutanol, etc.; tertiary alcohols such as tertiary butyl alcohol, etc.; polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-butanediol, glycerin, etc. 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, and the like. Aprotic polar solvents: N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, sulfolane, and the like. 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 having 4 or more carbon atoms (preferably 4 to 30 carbon atoms) other than the carboxyl group, such as oleic acid, linoleic acid, and linolenic acid.

[0067] [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, medical product industry, etc. In particular, the composite hollow fiber membrane of the present invention is suitably used for filtration of a liquid to be treated that contains an organic solvent and a solute and is used in the electronics industry, such as in the production of semiconductors and liquid crystal panels.

[0068] Furthermore, the composite hollow fiber membrane of the present invention is resistant to various organic solvents and is therefore suitable for use in membrane separation processes in which a liquid to be treated containing an organic solvent and a solute is to be treated.

[0069] 3. Manufacturing method of composite hollow fiber membrane The method for producing the composite hollow fiber membrane of the present invention is not particularly limited as long as it can produce a composite hollow fiber membrane having the above structure, but a suitable example is a production method including the following first to fourth steps. First step: A membrane-forming solution is prepared by dissolving polyamide resin at a concentration of 20% by weight or more in an organic solvent that has a boiling point of 150°C or higher and is incompatible with polyamide resin at temperatures below 100°C, at a temperature of 100°C or higher. Second step: A step of solidifying the polyamide resin into a membrane by extruding the membrane-forming solution in a predetermined shape into a coagulation bath at 100°C or less. In this step, a coagulation liquid that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the polyamide resin is brought into contact with at least one surface of the membrane-forming solution extruded in the predetermined shape, thereby forming a polyamide hollow fiber membrane having a dense layer on at least one surface. Third step: The membrane forming solution solvent and the coagulation solution are removed from the polyamide hollow fiber membrane formed in the second step. Fourth step: A silicone layer is formed on the surface of at least one of the dense layers of the polyamide hollow fiber membrane obtained by carrying out the third step.

[0070] [Formation of polyamide hollow fiber membrane] Hereinafter, the first to third steps for forming the polyamide hollow fiber membrane will be described in detail for each step.

[0071] [1st step] In the first step, a film-forming solution is prepared by dissolving 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 which is incompatible with polyamide resin at temperatures below 100°C at a temperature of 100°C or higher.

[0072] Examples of organic solvents that have a boiling point of 150°C or higher and are incompatible with polyamide resins at temperatures below 100°C include 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. Specific examples of polyhydric alcohols include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, hexylene glycol, 1,3-butanediol, polyethylene glycol (molecular weight 100 to 10,000), etc. Specific 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, lauric acid, etc. Among these organic solvents, from the viewpoint of obtaining a polyamide hollow fiber membrane with higher strength, preferred are aprotic polar solvents and polyhydric alcohols; more preferred are sulfolane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, propylene glycol, hexylene glycol, 1,3-butanediol, and polyethylene glycol (molecular weight 100 to 600); even more preferred are sulfolane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone; and even more preferred are dimethyl sulfone. These organic solvents may be used alone or in combination of two or more.Although sufficient effects can be obtained by using one of these organic solvents alone, a more effective polyamide hollow fiber membrane can sometimes be produced by mixing two or more of them due to differences in the order and structure of phase separation.

[0073] The concentration of the polyamide resin in the membrane-forming solution may be 20% by weight or more, preferably 23 to 50% by weight, more preferably 25 to 38% by weight, and even more preferably 28 to 35% by weight. By ensuring that the concentration of the polyamide resin in the membrane-forming solution satisfies the above range, a support layer with a porosity of 60 to 80% can be obtained, and the polyamide hollow fiber membrane can be provided with excellent pressure resistance, and as a result, the composite hollow fiber membrane of the present invention can be provided with excellent pressure resistance and organic solvent permeability.

[0074] Furthermore, in the first step, when dissolving the polyamide resin in the organic solvent, it is necessary to maintain the temperature of the solvent at 100°C or higher. Specifically, it is desirable to dissolve the polyamide resin at a temperature 10 to 50°C higher, preferably 20 to 40°C higher, than the phase separation temperature of the membrane-forming solution to be prepared. The phase separation temperature of the membrane-forming solution refers to the temperature at which liquid-liquid phase separation or solid-liquid phase separation due to crystal precipitation occurs when a mixture of the 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, etc.

[0075] In the first step, the temperature conditions for dissolving the polyamide resin in the organic solvent may be appropriately set in the temperature range of 100°C or higher in accordance with the above-mentioned index depending on the type of polyamide resin and the type of organic solvent used, but are preferably 120 to 250°C, more preferably 140 to 220°C, and even more preferably 160 to 200°C.

[0076] Furthermore, the membrane-forming solution may contain, as necessary, fillers, thickeners, antioxidants, surface modifiers, lubricants, surfactants, etc., in order to control the pore size of the polyamide hollow fiber membrane or improve its performance.

[0077] The membrane-forming solution prepared in the first step is supplied to the second step at the same temperature (ie, at 100° C. or higher).

[0078] [Second process] In the second step, the membrane-forming solution prepared in the first step is extruded into a predetermined shape into a coagulation bath at 100°C or less, thereby coagulating the polyamide resin into a membrane. In this step, a coagulation liquid (hereinafter sometimes referred to as a "dense layer-forming coagulation liquid") that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the polyamide resin is contacted with at least one surface of the membrane-forming solution extruded into a predetermined shape, thereby forming a polyamide hollow fiber membrane having a dense layer on at least one surface.

[0079] In the second step, the membrane-forming solution is extruded into a coagulation bath in a predetermined shape, and a dense layer is formed on the surface where the solution comes into contact with the dense-layer-forming coagulation liquid. Near the surface where the membrane-forming solution comes into contact with the dense-layer-forming coagulation liquid, non-solvent phase separation due to solvent exchange proceeds more predominantly than thermally induced phase separation due to cooling, and a denser structure is formed on the surface than in the conventional TIPS method. As a result, a polyamide hollow fiber membrane having the above-mentioned molecular weight cutoff is obtained.

[0080] When a dense layer is to be formed on only one surface of the polyamide hollow fiber membrane, in the second step, one surface of the membrane-forming solution extruded into a predetermined shape is contacted with a coagulating liquid for forming a dense layer, and the other surface is contacted with a coagulating liquid that is compatible with the organic solvent used in the membrane-forming solution and has a high affinity for the polyamide resin (hereinafter, sometimes referred to as a "coagulating liquid for forming a support layer"). When a dense layer is to be formed on both surfaces of the polyamide hollow fiber membrane, in the second step, both surfaces of the membrane-forming solution extruded into a predetermined shape are contacted with a coagulating liquid for forming a dense layer.

[0081] Specifically, the dense layer-forming coagulation liquid is a solvent that is compatible with the organic solvent used in the membrane-forming solution at temperatures below 25°C, but does not dissolve the polyamide resin at temperatures below the boiling point or below 200°C. Specific examples of the dense layer-forming coagulation liquid 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; polyethylene glycols with an average molecular weight of 300 or more, polypropylene glycols with an average molecular weight of 400 or more, glycol ethers such as 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, preferred are polyethylene glycols, triacetin, and triethylene glycol monomethyl ethers with an average molecular weight of 300 to 600; more preferred are polyethylene glycol 300, polyethylene glycol 400, and polyethylene glycol 600; and even more preferred are polyethylene glycol 300 and polyethylene glycol 400. These solvents may be used alone 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 polyols - Test methods - Part 6: Determination of hydroxyl value by near-infrared (NIR) spectroscopy."

[0082] Furthermore, the dense layer-forming coagulation liquid may contain, to the extent that a dense layer can be formed, a solvent used in the support layer-forming coagulation liquid, such as glycerin (a solvent that is compatible with the organic solvent used in the membrane-forming solution at temperatures below 25°C and dissolves the polyamide resin at temperatures below its boiling point. When the dense layer-forming coagulation liquid contains the solvent used in the support layer-forming coagulation liquid (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 wt%, more preferably 10 to 35 wt%, even more preferably 15 to 32 wt%, and even more preferably 15 to 30 wt%, from the viewpoint of forming a dense layer of suitable thickness and obtaining a polyamide hollow fiber membrane having the aforementioned molecular weight cutoff.

[0083] The solidifying liquid for forming the support layer may be any solvent that is compatible with the organic solvent used in the film-forming solution at a temperature of 25° C. or less and dissolves the polyamide resin at a temperature of the boiling point or less. Specific examples of the solidifying liquid 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% ​​by weight or more of these. Among these, from the viewpoint of obtaining a support layer having the above-mentioned porosity, preferred are 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 an aqueous solution containing at least one of these in a proportion of 25 to 75% by weight; and more preferred are at least one selected from the group consisting of 1,4-butanediol, glycerin, propylene glycol, diethylene glycol, and tetraethylene glycol, and an aqueous solution containing at least one of these in a proportion of 40 to 80% by weight (preferably 40 to 60% by weight).

[0084] To form a polyamide hollow fiber membrane, the second step involves using a double-tube nozzle for hollow fiber production with a double-tube structure, discharging the membrane forming solution from the outer annular nozzle and the inner coagulation liquid from the inner nozzle, and immersing the membrane in a coagulation bath. In this case, a dense layer-forming coagulation liquid may be used for at least one of the inner coagulation liquid and the coagulation bath. When a dense layer-forming coagulation liquid is used for both the inner coagulation liquid and the coagulation bath, a dense layer is formed on both the lumen-side surface and the outer surface, resulting in a polyamide hollow fiber membrane with a support layer as the interior. When a dense layer-forming coagulation liquid is used as the inner coagulation liquid and a support layer-forming coagulation liquid is used as the coagulation bath, a dense layer is formed on the lumen-side surface, and the interior and outer surfaces are support layers. When a support layer-forming coagulation liquid is used as the inner coagulation liquid and a dense layer-forming coagulation liquid is used as the coagulation bath, a polyamide hollow fiber membrane with a dense layer formed on the outer surface and a support layer as the interior is obtained. Since the internal coagulation liquid used in forming the polyamide hollow fiber membrane passes through the double annular nozzle, it is preferable that the liquid does not contain water whose boiling point is equal to or lower than the temperature of the double annular nozzle.

[0085] The double-tubular nozzle for producing hollow fibers may be a spinneret having a double-tubular structure such as that used for producing core-sheath composite fibers in melt spinning. The diameters of the outer annular nozzle and the inner nozzle of the double-tubular nozzle for producing hollow fibers may be appropriately set depending on the inner and outer diameters of the polyamide hollow fiber membrane.

[0086] The flow rate of the membrane-forming solution discharged from the outer annular nozzle of the hollow fiber production double-tubular nozzle is not particularly limited because it depends on the slit width, but may be, for example, 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 liquid is appropriately set taking into consideration the diameter of the inner nozzle of the hollow fiber production double-tubular nozzle, the type of internal liquid used, the flow rate of the membrane-forming solution, etc., but may 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 membrane-forming solution.

[0087] In the second step, the temperature of the coagulation bath may be 100°C or lower, 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 varies depending on the organic solvent used in the membrane-forming solution, the composition of the coagulation solution, etc., but generally, lower temperatures tend to favor thermally induced phase separation, while higher temperatures tend to favor non-solvent phase separation. That is, when producing a polyamide hollow fiber membrane having a dense layer formed on the lumen-side surface, it is preferable to set the coagulation bath at a low temperature to increase the pore size of the dense layer on the lumen-side surface, and it is preferable to set the coagulation bath at a high temperature to make the dense layer on the lumen-side surface denser and the internal structure coarser.

[0088] The temperature of the internal coagulation liquid may be about the set temperature of the double tubular nozzle, for example, 120 to 250°C, preferably 160 to 230°C, and more preferably 180 to 220°C.

[0089] By carrying out the second step in this manner, the membrane-forming solution is coagulated in the coagulation bath, and a polyamide hollow fiber membrane having a dense layer formed on at least one surface is formed.

[0090] [3rd step] In the third step, the membrane forming solution solvent and the coagulation solution are removed from the polyamide hollow fiber membrane formed in the second step.

[0091] The method for removing the membrane-forming solution solvent and the coagulation solution from the polyamide hollow fiber membrane is not particularly limited, but a method in which the polyamide hollow fiber membrane formed in the second step is immersed in an extraction solvent to extract and remove them is preferred.

[0092] The extraction solvent used for extraction and removal is preferably one that is inexpensive, has a low boiling point, and can be easily separated after extraction due to differences in boiling points, such as water, glycerin, methanol, ethanol, isopropanol, acetone, diethyl ether, hexane, petroleum ether, and toluene. Among these, water, methanol, ethanol, isopropanol, and acetone are preferred; water, methanol, and isopropanol are more preferred. In particular, when extracting a water-soluble membrane-forming solution solvent and a coagulation solution, winding the solution while showering it with water allows for simultaneous solvent extraction, which is efficient. Furthermore, isopropyl alcohol, petroleum ether, and the like are suitable for extracting water-insoluble organic solvents such as phthalate esters and fatty acids.

[0093] When the membrane-forming solution solvent and the coagulation solution are extracted and removed by immersing the polyamide hollow fiber membrane in the extraction solvent, the time for immersing the polyamide hollow fiber membrane in the extraction solvent is not particularly limited, but may be, for example, 0.2 hours to 2 months, preferably 0.5 hours to 1 month, and more preferably 2 hours to 10 days. In order to effectively extract and remove the coagulation solution remaining in the polyamide hollow fiber membrane, the extraction solvent may be replaced or stirred.

[0094] By carrying out the third step in this manner, a polyamide hollow fiber membrane is obtained from which the membrane-forming solution solvent and the coagulation solution have been removed and which has a dense layer on at least one surface.

[0095] After the third step, it is preferable to dry and remove the extraction solvent from the polyamide hollow fiber membrane, which can be done by known drying methods such as natural drying, hot air drying, reduced pressure drying, and vacuum drying.

[0096] In order to increase the strength of the polyamide hollow fiber membrane and provide it with excellent pressure resistance, the polyamide hollow fiber membrane may be stretched in one axial direction (longitudinal direction) simultaneously with or after drying.

[0097] To simultaneously dry and stretch the polyamide hollow fiber membrane in the uniaxial direction, the membrane may be dried while tension for stretching is applied to the membrane. The temperature conditions for simultaneously drying and stretching the membrane in the uniaxial direction are not particularly limited as long as both drying and stretching are possible, and may be, for example, 40°C or higher, preferably 40 to 160°C, more preferably 50 to 140°C, and even more preferably 120 to 140°C.

[0098] Furthermore, when stretching in the uniaxial direction after drying, the temperature conditions during drying are not particularly limited as long as the adhering extraction solvent can be evaporated, and 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. Furthermore, when stretching in the uniaxial direction after drying, the temperature conditions during stretching are not particularly limited as long as it is −10 to 140° C., preferably 0 to 120° C., but from the viewpoint of further improving the liquid permeability, it is desirable that the temperature be above the glass transition point of the polyamide resin used (more preferably 50 to 120° C., and even more preferably 60 to 100° C.).

[0099] The uniaxial stretching may be carried out by a known method, for example, by continuously winding the membrane from a low-speed roll to a high-speed roll. Alternatively, the membrane may be cut to a predetermined length and stretched by holding both ends of the membrane using a tensile tester or the like, or by manual stretching.

[0100] The stretching ratio is, for example, 1.2 to 5, preferably 1.2 to 3. From the viewpoint of increasing the strength of the polyamide hollow fiber membrane and imparting excellent pressure resistance, the stretching ratio is preferably 1.2 to 2.4, more preferably 1.2 to 2.0.

[0101] [Formation of silicone layer] The fourth step for forming a silicone layer on the surface of at least one dense layer of the polyamide hollow fiber membrane obtained by carrying out the third step will be described in detail below.

[0102] The method for forming the silicone layer is not particularly limited as long as it can provide a silicone layer having the above-described structure and properties. A suitable example is the following formation method.

[0103] A method for forming a silicone layer on the surface of the dense layer on the lumen side surface of a polyamide hollow fiber membrane includes, for example, injecting a silicone coating liquid into the hollow portion of the polyamide hollow fiber membrane to form a silicone coating film on the surface of the dense layer, and then curing the silicone coating film to form a silicone layer.

[0104] The silicone coating liquid is a liquid composition containing a precursor (uncured product) of the silicone (e.g., silicone rubber) described in the section "Silicone Layer" of "2. Composite Hollow Fiber Membrane." As a representative example, the case where the silicone that forms the silicone layer is a two-component curing silicone rubber will be described below.

[0105] The silicone coating liquid contains at least a precursor of two-component curing silicone rubber (a polyorganosiloxane base polymer and a crosslinking agent), and can be prepared by, for example, mixing a first component (main component) containing polyorganosiloxane and a curing catalyst with a second component (curing agent) containing a crosslinking agent. Commercially available two-component curing silicone rubber kits that combine a main component and a curing agent include, for example, SYLGARD from Toray Dow Co., Ltd. TM 184, 527, DOWSIL TM Examples include EG-3100, CY52-276, YE5822, TSE3032, 3033, and 3070 manufactured by Momentive Performance Materials Japan, LLC, and KE-109E, KE-106F, KE-1012, KE-1051, and FE-77 manufactured by Shin-Etsu Chemical Co., Ltd.

[0106] The silicone coating liquid preferably contains a diluent solvent from the viewpoints of forming a thin and uniform silicone layer on the surface of the dense layer, facilitating control of the addition reaction, and improving workability. The diluent solvent may be added to either or both of the base agent and the curing agent before mixing them, or may be added to the mixture obtained by mixing the base agent and the curing agent.

[0107] The dilution solvent is not particularly limited as long as it dissolves the polyorganosiloxane and the crosslinking agent, and examples thereof include linear alkanes such as hexane and pentane; aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and cyclic ethers such as tetrahydrofuran.

[0108] The amount of dilution solvent to be added needs to be adjusted appropriately depending on the viscosity of the polyorganosiloxane. From the viewpoint of maintaining a silicone coating film of the desired thickness on the surface of the dense layer, preventing the silicone layer from becoming too thin and causing defects in the silicone layer, preventing unevenness in the thickness of the silicone layer, and workability, the amount of dilution solvent is preferably such that the concentration of polyorganosiloxane in the silicone coating liquid is 2 to 40% by weight, more preferably 5 to 30% by weight, and even more preferably 10 to 20% by weight.

[0109] In the silicone coating liquid, the blending ratio of the crosslinking agent needs to be adjusted appropriately depending on the types of polyorganosiloxane and crosslinking agent, but is usually 1 to 30 parts by weight, preferably 3 to 25 parts by weight, and more preferably 5 to 20 parts by weight, calculated as solid content per 100 parts by weight of polyorganosiloxane.

[0110] The method for injecting the silicone coating liquid into the hollow portion of the polyamide hollow fiber membrane is not particularly limited as long as it can form a silicone coating membrane of the desired thickness on the surface of the dense layer. However, a preferred method is to form a module using polyamide hollow fiber membranes and inject the silicone coating liquid into the hollow portion of the polyamide hollow fiber membrane of the module. Specifically, this injection method is performed as follows: First, a desired number of polyamide hollow fiber membranes of the desired length are bundled together. Next, a hard tube is prepared, and a rubber stopper or the like of an appropriate length is inserted into one end opening of the tube to plug the end opening. Next, a two-component thermosetting resin is injected through the end opening opposite the plugged end of the tube to fill the inner space of the tube with the resin. One end of the bundled polyamide hollow fiber membranes is then heat-sealed to seal the opening, and the end is inserted into the tube filled with the thermosetting resin until the tip of the end touches the plug. The thermosetting resin is cured in this state. Next, the area of ​​the hardened resin on the plug side is cut together with the tube to open the hollow part of the polyamide hollow fiber membrane. After that, an appropriate jig is attached to the tube on the open side and a silicone coating liquid is injected.

[0111] The injection method is not particularly limited, and examples thereof include an injection method using a syringe, a pressure-feeding method using pressurized gas, and an injection method using a pump such as a peristaltic pump, a plunger pump, a diaphragm pump, or a gear pump.

[0112] The speed at which the silicone coating liquid is injected is not particularly limited, but is, for example, about 0.04 to 2.5 m / sec as a linear velocity, and from the viewpoints of suppressing defects in the silicone layer, suppressing unevenness in the thickness of the silicone layer, and manufacturing efficiency, it is preferably 0.1 to 1.0 m / sec, and more preferably 0.1 to 0.5 m / sec.

[0113] In order to form a silicone coating film of uniform thickness on the surface of the dense layer, it is preferable to blow a gas into the hollow part of the polyamide hollow fiber membrane after injecting the silicone coating liquid. The gas used for blowing is not particularly limited, but dry air or nitrogen is preferred from the viewpoint of preventing reaction with the silicone coating liquid and from the viewpoint of safety.

[0114] The blowing speed is not particularly limited, but is, for example, about 1 to 50 m / s as a linear speed, and from the viewpoints of suppressing defects in the silicone layer, suppressing unevenness in the thickness of the silicone layer, and producing efficiency, is preferably 2.5 to 20 m / s, and more preferably 5 to 10 m / s.

[0115] To accelerate the curing (addition reaction) of the silicone-coated membrane formed on the surface of the dense layer, the silicone-coated membrane is preferably heat-treated. The heating temperature is not particularly limited, but from the viewpoint of further accelerating the curing (addition reaction) and suppressing deterioration of the physical properties of the polyamide hollow fiber membrane due to heat, it is preferably 40 to 160°C, more preferably 60 to 140°C, and even more preferably 80 to 120°C. The heating time is not particularly limited, but from the above viewpoints, it is preferably 10 minutes to 24 hours, more preferably 15 minutes to 16 hours, even more preferably 30 minutes to 8 hours, and even more preferably 1 to 5 hours.

[0116] The portion of the tube used for injecting the silicone coating liquid is cut and removed at an appropriate time, for example, before or after the silicone coating film is heat treated.

[0117] Furthermore, examples of methods for forming a silicone layer on the surface of the dense layer on the outer surface of a polyamide hollow fiber membrane include immersing the polyamide hollow fiber membrane in a bath of the silicone coating liquid, or applying the silicone coating liquid to the outer surface of the polyamide hollow fiber membrane to form a silicone coating film on the surface of the dense layer, and then curing the silicone coating film to form a silicone layer. To form a silicone coating film with a uniform thickness on the surface of the dense layer, the gas may be blown onto the outer surface of the polyamide hollow fiber membrane. Furthermore, to promote curing (addition reaction) of the silicone coating film formed on the surface of the dense layer, the silicone coating film may be heat-treated under the above conditions.

[0118] Furthermore, examples of methods for forming silicone layers on the surface of the dense layer on the lumen side surface and the outer surface of the polyamide hollow fiber membrane include a method for forming a silicone layer on the surface of the dense layer on the lumen side surface of the polyamide hollow fiber membrane and a method for forming a silicone layer on the surface of the dense layer on the outer surface of the polyamide hollow fiber membrane, performed in any order or in combination.

[0119] By carrying out the fourth step in this manner, the composite hollow fiber membrane of the present invention having a silicone layer on the surface of at least one of the dense layers of the polyamide hollow fiber membrane can be obtained.

[0120] 4. Hollow fiber membrane module The composite hollow fiber membrane of the present invention is housed in a module case equipped with an inlet for the liquid to be treated, an outlet for the permeated liquid, etc., and used as a hollow fiber membrane module.

[0121] Specifically, the hollow fiber membrane module may have a structure in which the composite hollow fiber membranes of the present invention are bundled and 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 side of the composite hollow fiber membrane and an opening connected to the hollow portion of the composite hollow fiber membrane, as an inlet for the liquid to be treated or an outlet for the filtrate.

[0122] The shape of the hollow fiber membrane module is not particularly limited and may be a dead-end module or a cross-flow module. Specific examples include a dead-end module in which a hollow fiber membrane bundle is bent into a U-shape and packed, and the ends of the hollow fiber membrane bundle are sealed and then cut to open; a dead-end module in which a hollow fiber membrane bundle with the hollow opening at one end closed by heat sealing or the like is packed straight, and the open end of the hollow fiber membrane bundle is sealed and then cut to open; a dead-end module in which a hollow fiber membrane bundle is packed straight, both ends of the hollow fiber membrane bundle are sealed, and only one end is cut to expose the opening; and a cross-flow module in which a hollow fiber membrane bundle is packed straight, both ends of the hollow fiber membrane bundle are sealed, and the sealed ends at both ends of the hollow fiber membrane bundle are cut to create two flow paths on the side of the filter case.

[0123] The packing rate of the composite hollow fiber membranes inserted into the module case is not particularly limited, but for example, the volume of the composite hollow fiber membranes, including the volume of the hollow portions, relative to the internal volume of 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 rate, a sufficient filtration area can be ensured, and the operation of packing the composite hollow fiber membranes into the module case can be facilitated, allowing the potting agent to easily flow between the composite hollow fiber membranes.

[0124] The potting agent used in the manufacture of the hollow fiber membrane module is not particularly limited, but when the hollow fiber membrane module is used to treat organic solvents, it is desirable to provide an organic solvent. Examples of such potting agents include polyamide, silicone resin, epoxy resin, melamine resin, polyethylene, polypropylene, phenolic resin, polyimide, polyurea resin, etc. Among these potting agents, those that shrink or swell little when cured and are not too hard are preferred, and suitable examples include polyamide, silicone resin, epoxy resin, and polyethylene. These potting agents may be used alone or in combination of two or more.

[0125] The material of the module case used in the hollow fiber membrane module is not particularly limited, and examples thereof include polyamide, polyester, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polysulfone, polyethersulfone, polycarbonate, polyarylate, polyphenylene sulfide, etc. Among these, preferred are polyamide, polyethylene, polypropylene, polytetrafluoroethylene, polycarbonate, polysulfone, and polyethersulfone, and more preferred are polyamide, polyethylene, polypropylene, and polytetrafluoroethylene.

[0126] Hollow fiber membrane modules using the composite hollow fiber membrane of the present invention are used in ultrafiltration or nanofiltration applications for removing contaminants from solvents, concentrating useful components in solvents, and recovering solvents in fields such as the semiconductor, chemical, food, pharmaceutical, and medical product industries. In particular, one embodiment of a hollow fiber membrane module using the composite hollow fiber membrane of the present invention is suitable for filtration of a liquid to be treated containing a solute and an organic solvent used in the electronics industry, such as semiconductor and liquid crystal panel manufacturing. Examples of the organic solvent include glycol ether solvents such as propylene glycol monomethyl ether, 3-methoxybutanol, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate, dipropylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; cyclic ketones such as cyclohexanenone; and aprotic polar solvents such as dimethyl sulfoxide and N-methylpyrrolidone. These organic solvents may be contained alone or in combination. [Example]

[0127] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0128] 1.Measurement method [Outer and inner diameters of polyamide hollow fiber membrane] The five composite hollow fiber membranes were observed under an optical microscope at a magnification of 200x, and the outer and inner diameters (both at the maximum diameter points) of the polyamide hollow fiber membranes constituting the composite hollow fiber membrane were measured, and the average values ​​were calculated.

[0129] [Porosity of supporting layer] Scanning electron microscope (SEM) photographs were taken at five locations equidistantly spaced in the thickness direction of the support layer of the polyamide hollow fiber membrane in a cross section obtained by cutting a composite hollow fiber membrane perpendicular to the longitudinal direction. Specifically, the photographs were taken as follows. Fig. 5 is a schematic cross-sectional view of a polyamide hollow fiber membrane cut perpendicular to the longitudinal direction, and Figs. 6 and 7 are partial enlarged views of the area surrounded by the dotted line in Fig. 5, showing an example of a polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 12. Note that the silicone layer is omitted in Figs. 5 to 7. As shown in Fig. 6, a straight line was drawn from the center of the lumen of the polyamide hollow fiber membrane 8a to the outer surface, and this line was divided into five equal parts from the lumen-side surface of the support layer 12 to the outer surface. Then, the midpoints of the five equal parts were determined as shown in Fig. 6. 7, the midpoint was positioned at the center of the captured image, and five locations were photographed at a uniform magnification such that only the support layer 12 portion was included in the captured image and the number of pores was 30 to 300. For the five SEM photographs taken, image analysis of the above-mentioned regions was performed using image analysis software (ImageJ), and the pore portion and the polymer portion were distinguished by binarization processing.The area ratio (%) of the total pore area to the area of ​​the analyzed region was then calculated, and the average value was calculated. The specific procedures for 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 histogram peak, obtained by the "Analyze > Histogram" operation, was set as the threshold (i.e., the lower threshold level was set to the brightness value at which the histogram peak 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 checked, and the total area of ​​the analysis range was calculated using the "Analyze > Measure" operation. Then, "Analyze > Set measurements" was checked, and "Area" and "Limit to threshold" were checked, and the "Analyze > Measure" operation was performed again to calculate the areas of the polymer and pore portions, and the area ratio (%) of the total pore area to the analysis region area was calculated.

[0130] [Dense layer thickness] A cross section of the composite hollow fiber membrane cut perpendicular to the longitudinal direction was observed with a scanning electron microscope (SEM) at a magnification of 10,000. In the obtained SEM photograph, the distance (thickness) of the region where the polyamide hollow fiber membrane constituting the composite hollow fiber membrane was substantially free of pores was measured at 10 equally spaced locations, and the average value was calculated.

[0131] [Molecular weight cutoff of polyamide hollow fiber membrane (greater than 3000)] Ten polyamide hollow fiber membranes were cut to 30 cm lengths and bundled together. Next, a nylon hard 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 one end opening of the tube to plug the opening. Next, a two-component epoxy resin was injected into the opening opposite the rubber stopper to fill the inner space of the tube. One end of the bundle of polyamide hollow fiber membranes was then heat-sealed to prevent the epoxy resin from penetrating the hollow space. The end was then inserted into the tube filled with the epoxy resin until its tip touched the rubber stopper, and the epoxy resin was allowed to cure in this state. Next, the region of the cured epoxy resin facing the rubber stopper was cut along with the tube to open the hollow space. The same procedure was performed on the other end to produce a cross-flow module 6 with open hollow spaces at both ends of the polyamide hollow fiber membranes. The fabricated crossflow module 6 was connected to the internal pressure separation treatment line shown in Figure 1, and the flowing liquid (raw liquid) was continuously passed through the crossflow module 6 by the liquid circulation pump 2. The flowing liquid was an aqueous solution containing five types of dextrans with molecular weights of 5,000, 10,000, 40,000, 70,000, and 500,000 at concentrations of 0.5 wt%, 0.5 wt%, 0.2 wt%, 0.2 wt%, or 0.4 wt%, respectively. The pressures measured by the primary pressure gauge 3 and the secondary pressure gauge 4 were adjusted by the regulator 5 so that the arithmetic mean value of the pressures measured by the primary pressure gauge 3 and the secondary pressure gauge 4 was 1 bar. Of the flowing liquid passing through the module, that which permeated the pores of the polyamide hollow fiber membrane was separated from the flowing liquid and collected as permeate, while the remainder was circulated back to the separation treatment line. Two hours after the start of circulation, the permeate flowing out of the cross-flow module 6 was collected in a receiver 7, and the dextran concentration in each 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 dextran of each molecular weight, a graph was created with the molecular weight of the dextran used on the horizontal axis and the rejection rate on the vertical axis, and the molecular weight at the intersection of the resulting approximation curve and the 90% rejection rate was taken as the molecular weight cutoff. Solute rejection rate (%) = {(dextran concentration in the original solution - dextran concentration in the permeate) / dextran concentration in the original solution} x 100

[0132] [Molecular weight cutoff of polyamide hollow fiber membrane (3000 or less)] The molecular weight cutoff was determined in the same manner as above, except that an NMP solution containing 0.05% by weight of each of four types of polystyrene having molecular weights of 370, 1000, 2000, or 3000 was used as the flowing liquid, the arithmetic mean value of the pressure measured by the primary pressure gauge 3 and the pressure measured by the secondary pressure gauge 4 was set to 15 bar, and the rejection rate was calculated according to the following formula. Solute rejection rate (%) = {(Polystyrene concentration in raw solution - Polystyrene concentration in permeate) / Polystyrene concentration in raw solution} x 100

[0133] [Burst pressure of composite hollow fiber membrane or polyamide hollow fiber membrane] The module 8 shown in Figure 2a was fabricated. First, ten composite hollow fiber membranes or polyamide hollow fiber membranes 8a were cut to a length of 30 cm and bundled together. Next, a nylon hard 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 long was inserted into one end opening of the tube to plug the end opening. Next, a two-component epoxy resin was injected into the opening opposite the rubber stopper to fill the inner space of the tube. The bundle of composite hollow fiber membranes or polyamide hollow fiber membranes prepared above was then bent into an approximately U-shape, and both ends of the composite hollow fiber membranes or polyamide hollow fiber membranes were heat-sealed to prevent the epoxy resin from penetrating the hollow space. The end tip was inserted into the tube filled with epoxy resin until it touched the rubber stopper, and the epoxy resin was allowed to harden in this state. Next, the region of the cured epoxy resin on the rubber stopper side was cut together with the tube to produce a module 8 in which the hollow portions at both ends of the composite hollow fiber membrane or polyamide hollow fiber membrane were opened. Next, the module 8 was set in the device shown in Figure 2b, and water pressure was applied to the module 8 using a hand pump 9, and the pressure (burst pressure, unit: bar) at which the module 8 ruptured was measured.

[0134] [Silicone layer thickness] The cross section of the composite hollow fiber membrane cut perpendicular to the longitudinal direction was observed with a scanning electron microscope (SEM) at a magnification of 10,000. In the obtained SEM photograph, the distance (thickness) of the nonporous region present on the surface of the dense layer was measured at 10 equally spaced locations, and the average value was calculated.

[0135] [NMP permeation amount and thinner permeation amount] Twenty composite hollow fiber membranes were cut into 30 cm lengths 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 approximately 15 mm into one end opening of the tube to connect the two. A rubber stopper approximately 20 mm long was inserted into the end of the silicone tube opposite the end inserted into the PBT tube to plug the one end opening. Next, a two-component epoxy resin was injected through the opening opposite the rubber stopper to fill the inner space of the tube. One end of the bundle of composite hollow fiber membranes prepared above was then heat-sealed to prevent the epoxy resin from penetrating the hollow space. The end tip was then inserted into the epoxy resin-filled tube until it touched the rubber stopper, and the epoxy resin was allowed to harden in this state. Next, the region of the cured epoxy resin on the rubber stopper side of the tube was cut to open the hollow portion. The same procedure was repeated on the other end to prepare a cross-flow module with open hollow portions at both ends of the composite hollow fiber membrane. The fabricated crossflow module 6 was connected to the internal pressure separation treatment line shown in Figure 1, and the flowing liquid was continuously passed through the crossflow module 6 by the liquid circulation pump 2. NMP or thinner (a mixture of 30 wt% propylene glycol monomethyl ether acetate and 70 wt% propylene glycol monomethyl ether) was used as the flowing liquid. In the module, the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 were adjusted by the regulator 5 so that the arithmetic mean value of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 was 90% of the burst pressure of the composite hollow fiber membrane. Of the flowing liquid passing through the module, that which had permeated the pores of the composite hollow fiber membrane was collected as permeated liquid separated from the flowing liquid, and the remainder was circulated back to the separation treatment line. The permeated liquid flowing out of the crossflow module 6 between 2 and 4 hours after the start of circulation was collected in the receiver 7, and the NMP permeation amount or thinner permeation amount (L / (m)) was calculated according to the following formula: 2 ·h)) was calculated. NMP permeation rate = volume of NMP permeated 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 (membranes) × time (h)] Amount of thinner permeated = Volume of thinner permeated 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 (membranes) × Time (h)] Effective filtration length of composite hollow fiber membrane: This is the length of the outer surface of the composite hollow fiber membrane in the crossflow module that is not coated with epoxy resin.

[0136] [Vitamin B 12 Rejection rate] Vitamin B 12 The inhibition rate of vitamin B 12 The measurement was performed in the same manner as in the measurement of the above [NMP permeation amount and thinner permeation amount] except that an NMP solution or thinner solution containing 500 ppm of vitamin B was used. The absorbance of the resulting permeate and flow-through liquid was measured at a wavelength of 550 nm using an absorption spectrometer, and the amount of vitamin B was calculated from the following formula: 12 The inhibition rate (%) was calculated. Vitamin B12 Rejection rate = 100 - (absorbance of permeate / absorbance of flow-through) x 100

[0137] 2. Test Example [Example 1] 280 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) were dissolved by stirring at 190 °C for 1.5 hours, then the stirring speed was reduced and degassed for 1 hour to prepare a membrane-forming solution. The membrane-forming solution was pumped via a metering pump to a spinneret maintained at 200 °C, and a mixture of 70 wt% polyethylene glycol 300 (PEG300) and 30 wt% glycerin was added as the internal coagulation solution. The extruded membrane-forming solution was poured into a coagulation bath containing a 60 wt% aqueous solution of 1,4-butylene glycol (1,4BG) at 5 °C and cooled to solidify, forming a polyamide porous membrane. The wound polyamide porous membrane was immersed in water for 24 hours for solvent extraction (washing), and then dried in a hot air dryer (internal temperature 130 °C) without stretching to obtain a polyamide hollow fiber membrane. The burst pressure and molecular weight cutoff of the polyamide hollow fiber membrane were evaluated using the polyamide hollow fiber membrane. A membrane bundle of 20 polyamide hollow fiber membranes, each 40 cm long, was prepared. A nylon hard 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 one end opening of the tube to plug the opening. Next, a two-component epoxy resin was injected into the opening opposite the rubber stopper, filling the inner space of the tube with the epoxy resin. One end of the prepared polyamide hollow fiber membrane was then heat-sealed to seal the opening, and the membrane was inserted into the epoxy resin-filled tube until the tip of the membrane touched the rubber stopper. The epoxy resin was then cured in this state. The cured epoxy resin was then cut along the rubber stopper side of the tube, opening the hollow portion of the polyamide hollow fiber membrane, to obtain a module for injecting silicone coating liquid. The base component of a commercially available two-component silicone (manufactured by Momentive, product name: TSE3033) was diluted 10-fold with ethyl acetate, and then an equal amount of curing agent was added to prepare a silicone coating solution. The silicone coating solution was then filled into a plastic syringe. The syringe and the silicone coating solution injection module were connected with a silicone tube, and the silicone coating solution was extruded into the hollow portion of the polyamide hollow fiber membrane at a linear velocity of 0.16 m / s, i.e., 0.25 L / min. Next, the syringe was removed, and nitrogen was blown at a linear velocity of 6.6 m / s, i.e., 10 L / min, followed by a curing treatment at 120 °C for 3 hours. The hollow fiber membrane was then cut near the epoxy resin portion of the injection module to obtain a composite hollow fiber membrane. The outer and inner diameters of the polyamide hollow fiber membrane, the porosity of the support layer, the thickness of the dense layer, the burst pressure of the composite hollow fiber membrane, the thickness of the silicone layer, the NMP permeation rate, and the thinner permeation rate were evaluated using the composite hollow fiber membrane. Table 1 shows the results of each of the measurements.

[0138] [Example 2] A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in preparing the membrane-forming solution, 250 g of polyamide 6 chips (A1030BRT, manufactured by Unitika Ltd., relative viscosity 3.53) and 750 g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved by stirring at 180°C for 1.5 hours, and the stirring speed was reduced to degas for 1 hour to prepare the membrane-forming solution. Table 1 shows the measurement results for each of the above measurements.

[0139] [Example 3] A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in preparing the membrane-forming solution, 350 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 650 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) were dissolved by stirring at 180°C for 1.5 hours, and then the stirring speed was reduced and the mixture was degassed for 1 hour to prepare a membrane-forming solution. Figure 3 is an image analysis diagram after binarization processing to calculate the porosity of the support layer of the obtained composite hollow fiber membrane. Figure 4 is a scanning electron microscope image (magnification 5000x) of the lumen side cross section of the obtained composite hollow fiber membrane. Table 1 shows the measurement results for each of the above measurements.

[0140] [Example 4] A composite hollow fiber membrane was produced in the same manner as in Example 1, except that the membrane-forming solution was prepared by stirring and dissolving 280 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) at 180°C for 1.5 hours, then reducing the stirring speed and degassing for 1 hour, polyethylene glycol 400 (PEG400) was used as the internal coagulation liquid, and the resulting polyamide hollow fiber membrane was stretched 1.5 times by passing it between rolls moving at different speeds. Table 1 shows the measurement results for each of the above measurements.

[0141] [Example 5] A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in preparing the membrane-forming solution, 230 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 770 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) were dissolved by stirring at 180°C for 1.5 hours, and the stirring speed was reduced to degas for 1 hour to prepare the membrane-forming solution. Table 1 shows the measurement results for each of the above measurements.

[0142] [Comparative Example 1] A polyamide hollow fiber membrane (without a silicone layer) was produced in the same manner as in Example 3. Table 1 shows the results of each of the measurements described above.

[0143] Comparative Example 2 A polyamide hollow fiber membrane (without a silicone layer) was produced in the same manner as in Example 4. Table 1 shows the results of each of the measurements.

[0144] Comparative Example 3 Polyamide hollow fiber membranes (without a silicone layer) were produced in the same manner as in Example 1, except that the membrane-forming solution was prepared by stirring 280 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 720 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) at 180 °C for 1.5 hours, followed by degassing for 1 hour at a reduced stirring speed. The internal coagulation solution was a mixture of 60 wt% polyethylene glycol 300 (PEG300) and 40 wt% glycerin. No dense layer was observed in the resulting polyamide hollow fiber membranes, and the molecular weight cutoff could not be measured because it did not achieve a 90% rejection rate at any molecular weight. The estimated pore size by bubble point analysis was equivalent to 5 nm. Then, a silicone coating liquid was injected into the hollow portion of the obtained polyamide hollow fiber membrane and a curing treatment was carried out in the same manner as in Example 1, but no clear silicone layer was observed. It is presumed that the silicone coating liquid penetrated into the support layer of the polyamide hollow fiber membrane, preventing the formation of a silicone layer. Table 1 shows the measurement results for each of the above measurements.

[0145] [Table 1]

[0146] In the composite hollow fiber membranes of Examples 1 to 5, a silicone layer is provided on the surface of the dense layer of the polyamide hollow fiber membrane, and therefore, vitamin B 12 The rejection rate is 99%, which is extremely high at the nanofiltration level, and it has excellent liquid permeability for thinner and NMP and vitamin B 12 On the other hand, the polyamide hollow fiber membranes of Comparative Examples 1 to 3 did not have a silicone layer, and therefore were able to achieve a high level of vitamin B blocking performance. 12 The rejection rate was 0% or in the 80% range, and these membranes could not be used as nanofiltration level filtration membranes. [Explanation of symbols]

[0147] 1. Fluid tank 2. Liquid transfer pump 3 Primary pressure gauge 4 Secondary pressure gauge 5. Regulator 6 Crossflow Module 7 saucers 8 Burst pressure evaluation module 8a Polyamide hollow fiber membrane 8b Nylon Hard Tube 9. Hand Pump 10 compact layer 11 Silicone layer 12 Support layer

Claims

1. A polyamide hollow fiber membrane having a dense layer and a support layer, and a silicone layer, the silicone layer is provided on a surface of the dense layer, A composite hollow fiber membrane, wherein the polyamide resin constituting the polyamide hollow fiber membrane is at least one selected from the group consisting of polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide MXD6, polyamide 4T, polyamide 6T, polyamide 9T, and polyamide 10T.

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

3. 2. The composite hollow fiber membrane according to claim 1, wherein the dense layer has a thickness of 0.1 μm or more.

4. 2. The composite hollow fiber membrane according to claim 1, wherein the dense layer is provided on the lumen side of the polyamide hollow fiber membrane.

5. 2. The composite hollow fiber membrane according to claim 1, wherein the silicone layer has a thickness of 0.2 to 10 μm.

6. The composite hollow fiber membrane according to claim 1 , wherein the silicone layer is formed of silicone rubber.

7. The NMP permeation rate at 25°C and a pressure of 90% of the burst pressure of the composite hollow fiber membrane is 0.5 L / (m 2 ·h) or more; 2. The composite hollow fiber membrane according to claim 1, which has a rejection rate of vitamin B 12 of 90% or more when a solution containing NMP as a solvent and vitamin B 12 as a solute is filtered.

8. A filtration method for filtering a liquid to be treated, which contains an organic solvent and a solute, using the composite hollow fiber membrane according to any one of claims 1 to 7.

9. A hollow fiber membrane module comprising a module case containing the composite hollow fiber membrane according to any one of claims 1 to 7.

10. A method for producing a composite hollow fiber membrane, comprising the following first to fourth steps: a first step of preparing a membrane-forming solution by dissolving a polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or more and being incompatible with the polyamide resin at a temperature below 100°C at a temperature of 100°C or more; a second step in which the membrane-forming solution is extruded into a coagulation bath at 100°C or less in a predetermined shape to coagulate the polyamide resin into a membrane, in which a coagulation liquid that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the polyamide resin is brought into contact with at least one surface of the membrane-forming solution extruded into the predetermined shape, thereby forming a polyamide hollow fiber membrane having a dense layer on at least one surface; A third step of removing the membrane forming solution solvent and the coagulation solution from the polyamide hollow fiber membrane formed in the second step; and A fourth step of forming a silicone layer on the surface of at least one of the dense layers of the polyamide hollow fiber membrane obtained by carrying out the third step.

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