Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
  • B01D63/02—Hollow fibre modules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/08—Hollow fibre membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/12—Composite membranes; Ultra-thin membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/56—Polyamides, e.g. polyester-amides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out

Definitions

• the present invention relates to a composite hollow fiber membrane having an aliphatic polyamide hollow fiber membrane with a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, and a method for producing the same.
• Membrane separation processes are used in the fields of water purification and seawater desalination, as well as 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.
• Representative aprotic polar solvents include dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, ⁇ -butyrolactone, propylene carbonate, and tetrahydrofuran, and separation membranes are required to be durable against these solvents.
• these solvents have the property of dissolving and corroding separation membrane materials such as polysulfone, polyvinylidene fluoride, and cellulose acetate, which have been widely used in the water treatment field, and these separation membranes developed for water treatment cannot be used in membrane separation processes for organic solvents.
• limited polymer materials such as polyethylene and polyethylene tetrafluoride have been used in membrane separation processes for organic solvents.
• aprotic polar solvents are purified and recovered, or separated from dissolved solutes, by distillation.
• typical aprotic polar solvents have relatively high boiling points of around 150-200°C and are susceptible to denaturation such as oxidation. Therefore, in order to separate and purify solutes by distillation, technology is required that not only consumes energy but also suppresses denaturation. Furthermore, if the solute to be separated and recovered is sensitive to heat, distillation cannot be applied in the first place, which is an issue.
• membrane separation processes do not involve phase changes such as evaporation of the solvent, making it possible to develop energy-saving processes, and are not affected by oxidation or thermal denaturation of the solvent, making them useful for separating solutions containing heat-sensitive solutes.
• OSN organic solvent nanofiltration
• OSN membranes have been developed in recent years, and several attempts and practical applications have been implemented.
• One approach is to use a membrane made of inorganic materials such as ceramics, which have high solvent resistance in terms of material properties, but production costs and scale-up issues have prevented this from becoming widespread.
• a representative method is to produce a polymer membrane using the non-solvent induced phase separation (NIPS) process used to produce conventional water treatment membranes, and then perform a cross-linking process in a post-process to give the polymer membrane organic solvent resistance and make it insoluble in organic solvents.
• NIPS non-solvent induced phase separation
• the NIPS method uses a membrane-making solution in which a polymer is dissolved in the aforementioned polar solvent, and since the polymer itself has low solvent resistance, a strong cross-linking process is required as a post-process.
• Non-Patent Document 1 proposes a nanofiltration membrane that is made solvent-resistant by crosslinking a polyimide flat membrane produced by the NIPS method.
• this nanofiltration membrane cannot be said to have sufficient resistance to aprotic polar solvents.
• Non-Patent Document 2 proposes a reverse osmosis membrane for desalination (seawater desalination) in aqueous systems, in which a polysulfone hollow fiber membrane produced by the NIPS method is used as a substrate and an interfacially polymerized membrane is formed on the inner surface of the hollow fiber membrane.
• this polysulfone hollow fiber membrane has no resistance to organic solvents, particularly aprotic polar solvents.
• the separation active layer is generally as thin as a few ⁇ m, and it is possible to make it as thin as about 0.5 ⁇ m by more advanced asymmetricization (formation of a dense surface layer), and a membrane with superior permeability can be formed by asymmetric structure membrane formation.
• mechanical strength in a solvent is also important.
• membranes formed by the NIPS method are mostly made of amorphous polymers, their mechanical strength is not necessarily high, and especially when they are subjected to solvent swelling, such as in a solvent, their elastic modulus decreases. Therefore, in order to maintain the strength of the membrane, it is necessary to adopt a method of forming the membrane on a separate backing carrier that is responsible for maintaining the strength of the membrane. The same is true for the polyimide membrane mentioned above, and nonwoven fabrics of polyester or polyolefin are used as the backing carrier.
• TIPS thermally induced phase separation
• the TIPS method is a relatively new method in which a solvent that does not dissolve the polymer material at low temperatures but does dissolve it at high temperatures is selected, and the homogeneous polymer solution dissolved at high temperatures is cooled to a temperature below the binodal line, which is the boundary between the one-phase and two-phase regions, to induce phase separation and fix the structure through polymer crystallization and glass transition.
• the TIPS method can be applied to polymers that do not dissolve in solvents at low temperatures, so it can be applied to crystalline polymers with high solvent resistance.
• the TIPS method tends to have a sponge-like homogeneous structure, which results in a high-strength separation membrane. Therefore, it is a suitable method for obtaining pressure-resistant OSN membranes, and is particularly suitable for producing hollow fiber-type freestanding membranes.
• Patent Document 1 proposes a nanofiltration hollow fiber membrane formed using a polyamide resin produced by the TIPS method, having a molecular weight cutoff of 200 to 1000 and a methanol permeation rate of 0.03 L/( m2 ⁇ bar ⁇ h) or more.
• Patent Document 2 proposes a polyamide hollow fiber membrane manufactured by applying the TIPS method, which 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, and which is used as an ultrafiltration membrane or nanofiltration membrane.
• a separation membrane 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 being treated.
• liquid permeability and blocking performance are contradictory properties, it is very difficult to achieve both high levels of liquid permeability and blocking performance.
• the polyamide hollow fiber membranes of Patent Documents 1 and 2 have a shape suitable for cross-flow filtration and have high resistance to various organic solvents, but because their mechanical strength in organic solvents is insufficient, it is difficult to increase the amount of organic solvent permeation by increasing the operating pressure, and the blocking performance of low molecular weight solutes in organic solvent-based treated liquids is not satisfactory, leaving room for improvement in terms of achieving both high levels of permeability and blocking performance.
• the objective 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 blocking performance for solutes in organic solvent-based treated liquids, and a method for producing the same.
• the inventors conducted extensive research to solve the above problems and discovered that by providing a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of a dense layer of an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, it is possible to obtain a composite hollow fiber membrane that can achieve both high levels of organic solvent permeability and high levels of blocking performance for solutes in an organic solvent-based treated liquid.
• the present invention was completed through further research based on this knowledge.
• a composite hollow fiber membrane comprising an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, the separation functional layer being provided on the surface of the dense layer, and having a burst pressure of 2.25 MPa or more measured under the following conditions: ⁇ Burst pressure> While passing N-methyl-2-pyrrolidone through a module prepared using the composite hollow fiber membrane, the pressure is increased by 0.25 MPa at 10-minute intervals, and the pressure (MPa) at which the composite hollow fiber membrane breaks is measured.
• Item 1 A composite hollow fiber membrane comprising an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, the separation functional layer being provided on the surface of the dense layer, and having a burst pressure of 2.25 MPa or more measured under the following conditions: ⁇ Burst pressure> While passing
• the composite hollow fiber membrane according to Item 1 wherein the crosslinked resin is a crosslinked aromatic polyamide resin.
• Item 3 The composite hollow fiber membrane according to Item 1 or 2, wherein the support layer has a porosity of 60 to 80%.
• Item 4. The composite hollow fiber membrane according to any one of Items 1 to 3, wherein the dense layer has a thickness of 0.1 to 5 ⁇ m.
• Item 5. The composite hollow fiber membrane according to any one of Items 1 to 4, wherein the dense layer is provided on the inner lumen surface side of the aliphatic polyamide hollow fiber membrane.
• Item 6. The composite hollow fiber membrane according to any one of Items 1 to 5, wherein the aliphatic polyamide hollow fiber membrane has a molecular weight cutoff of 10,000 to 300,000. Item 7.
• Item 8 The composite hollow fiber membrane according to any one of Items 1 to 7, wherein when a solution in which the solvent is N-methyl-2-pyrrolidone and the solute is diphenyl sulfone is filtered, the rejection rate of diphenyl sulfone is 30% or more.
• Item 10 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 9.
• Item 11 A hollow fiber membrane module comprising a module case and the composite hollow fiber membrane according to any one of Items 1 to 9 housed in the module case.
• 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 an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150° C. or more and being incompatible with the aliphatic polyamide resin at a temperature of less than 100° C. at a temperature of 100° C. or more; a second step of extruding the membrane-forming solution in a predetermined shape into a coagulation bath at 100° C.
• a coagulating liquid having compatibility with the organic solvent used in the membrane-forming solution but low affinity with the aliphatic polyamide resin is brought into contact with at least one surface of the membrane-forming solution extruded in the predetermined shape, thereby forming an aliphatic 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 aliphatic polyamide hollow fiber membrane formed in the second step; and a fourth step of forming a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation on the surface of at least one of the dense layers of the aliphatic polyamide hollow fiber membrane obtained by carrying out the third step.
• the composite hollow fiber membrane of the present invention has high mechanical strength in organic solvents (high burst pressure in pressure resistance tests in organic solvents), so the pressure during operation can be increased to increase the amount of organic solvent permeation.
• the surface of the dense layer of the aliphatic polyamide hollow fiber membrane has a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, it is possible to achieve both high levels of organic solvent permeability and high levels of blocking performance for solutes in the organic solvent-based treated liquid (especially low molecular weight solutes with a molecular weight of about 200 to 1000).
• the composite hollow fiber membrane of the present invention is formed of a hollow fiber membrane containing aliphatic polyamide and a separation functional layer containing a crosslinked resin, it has excellent resistance to various types of organic solvents and can stably maintain membrane performance even when in contact with various types of organic solvents used industrially, so it can be suitably used in membrane separation processes that are alternatives to distillation processes.
• FIG. 1 is a schematic diagram of an apparatus used for measuring the molecular weight cutoff, burst pressure, permeation rate (Flux), and rejection rate of a composite hollow fiber membrane or an aliphatic polyamide hollow fiber membrane.
• FIG. 2A is a schematic diagram of a module used when measuring the burst pressure of an aliphatic polyamide hollow fiber membrane
• FIG. 2B is a schematic diagram of an apparatus used for measuring the burst pressure of an aliphatic polyamide hollow fiber membrane.
• FIG. 2 is an image analysis diagram after binarization processing for calculating the porosity of the support layer of the aliphatic polyamide hollow fiber membrane of Example 1.
• 1 is a scanning electron microscope image (magnification 10,000 times) of the lumen side surface of the aliphatic polyamide hollow fiber membrane of Example 1 (before the formation of a separation functional layer).
• 1 is a scanning electron microscope image (magnification 20,000 times) of the lumen side surface of the aliphatic polyamide hollow fiber membrane of Example 1 (before the formation of a separation functional layer).
• 1 is a scanning electron microscope image (magnification 10,000 times) of the lumen side cross section of the aliphatic polyamide hollow fiber membrane of Example 1 (before the formation of a separation functional layer).
• 1 is a scanning electron microscope image (magnification 10,000 times) of the lumen side cross section of the composite hollow fiber membrane of Example 1.
• FIG. 1 is a scanning electron microscope image (magnification: 20,000 times) of the lumen side cross section of the composite hollow fiber membrane of Example 1.
• 1 is a scanning electron microscope image (magnification 10,000 times) of the lumen side surface of the composite hollow fiber membrane of Example 1.
• 1 is a scanning electron microscope image (magnification: 20,000 times) of the lumen side surface of the composite hollow fiber membrane of Example 1.
• FIG. 2 is a schematic diagram for explaining an example of calculating the porosity of a support layer of a composite hollow fiber membrane, and is a schematic cross-sectional view of an aliphatic polyamide hollow fiber membrane cut in a direction perpendicular to the longitudinal direction.
• FIG. 12 is a partial enlarged view of the area surrounded by the dotted line in FIG. 11 .
• FIG. 12 is a partial enlarged view of the area surrounded by the dotted line in FIG. 11 .
• ultrafiltration or “ultrafiltration membrane” refers to 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
• nanofiltration or “nanofiltration membrane” refers to 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.
• aliphatic polyamide hollow fiber membrane refers to a filtration membrane in the form of hollow fibers that is formed using an aliphatic polyamide resin and has a dense layer and a support layer.
• the term "dense layer” refers to a region in an aliphatic polyamide hollow fiber membrane where dense micropores are concentrated, and where the presence of pores is substantially not observed in a scanning electron microscope (SEM) photograph at a magnification of 10,000 times or more.
• the "support layer” refers to a region of an aliphatic polyamide hollow fiber membrane other than the dense layer, which is a porous region having a continuous pore structure in which the presence of pores is substantially evident in a scanning electron microscope (SEM) photograph at a magnification of 2000 times.
• SEM scanning electron microscope
• separation functional layer refers to a layer that is provided on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane and contains a crosslinked resin obtained by interfacial polycondensation.
• the composite hollow fiber membrane of the present invention comprises an aliphatic polyamide hollow fiber membrane having a dense layer and a support layer, and a separation functional layer containing a crosslinked resin obtained by interfacial polycondensation, the separation functional layer being provided on the surface of the dense layer, and characterized in that the burst pressure measured under the following conditions is 2.25 MPa or more.
• the composite hollow fiber membrane of the present invention will be described in detail below. ⁇ Burst pressure> While passing N-methyl-2-pyrrolidone through a module prepared using the composite hollow fiber membrane, the pressure is increased by 0.25 MPa at 10-minute intervals, and the pressure (MPa) at which the composite hollow fiber membrane breaks is measured.
• the aliphatic 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 an aliphatic polyamide resin.
• an aliphatic polyamide resin as a constituent resin of the hollow fiber membrane, the composite hollow fiber membrane of the present invention can be endowed with resistance to a wide range of organic solvents, as well as with high mechanical strength in organic solvents (the burst pressure in a pressure resistance test in an organic solvent can be increased), and therefore the pressure during operation can be increased to increase the amount of organic solvent permeation.
• the type of aliphatic polyamide resin is not particularly limited, but examples thereof include homopolymers of aliphatic polyamides, copolymers of aliphatic polyamides, and mixtures thereof.
• specific examples of homopolymers of aliphatic polyamides include polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, and polyamide 12.
• Specific examples of copolymers of aliphatic polyamides include copolymers of aliphatic polyamides and polyethers such as polytetramethylene glycol and polyethylene glycol.
• the ratio of the aliphatic polyamide component in the copolymer of aliphatic polyamides is not particularly limited, but examples thereof include a ratio of the aliphatic polyamide component of 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.
• the aliphatic polyamide hollow fiber membrane can be provided with even better organic solvent resistance and mechanical strength.
• the aliphatic polyamide resins may be used alone or in combination of two or more.
• polyamide 6 is preferred as a resin for forming aliphatic polyamide hollow fiber membranes because it is easy to achieve both good pressure resistance and solvent resistance and also easy to improve the liquid permeability of organic solvents.
• the aliphatic polyamide resin may or may not be crosslinked, but from the standpoint of reducing manufacturing costs, non-crosslinked resins are preferred.
• the relative viscosity of the aliphatic 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. By having such a relative viscosity, the moldability and controllability of phase separation during the production of the aliphatic polyamide hollow fiber membrane are improved, and it is possible to provide the aliphatic polyamide hollow fiber membrane with excellent shape stability.
• the relative viscosity here refers to the value measured with an Ubbelohde viscometer at 25°C using a solution in which 1 g of aliphatic polyamide resin is dissolved in 100 mL of 96% sulfuric acid.
• the aliphatic polyamide hollow fiber membrane may contain a filler as necessary within a range that does not impair the effects of the present invention.
• a filler By containing a filler, the strength, elongation, and elastic modulus of the aliphatic polyamide hollow fiber membrane can be improved.
• the aliphatic polyamide hollow fiber membrane is less likely to deform even when high pressure is applied during filtration.
• filler there are no particular limitations on the type of filler to be added, but examples of such fillers include fibrous fillers such as glass fiber, carbon fiber, potassium titanate whiskers, zinc oxide whiskers, calcium carbonate whiskers, wollastonite whiskers, aluminum borate whiskers, 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.
• fibrous fillers such as glass fiber, carbon fiber, potassium titanate whiskers, zinc oxide whiskers, calcium carbonate whiskers, wollastonite whiskers, aluminum borate whiskers, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, gypsum fiber, and metal fiber; talc, hydrotalcite, wollastonite, zeolite, sericite, mica, kaolin,
• the filler examples include silicates such as sulphur oxide 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.
• silicates such as sulphur oxide 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
• fillers preferred are talc, hydrotalcite, silica, clay, and titanium oxide, and more preferred are talc and clay.
• the content of the filler 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 of the filler per 100 parts by weight of the aliphatic polyamide resin. By including filler in this amount, it is possible to improve the strength, elongation, and elastic modulus of the aliphatic polyamide hollow fiber membrane.
• the aliphatic polyamide hollow fiber membrane may contain additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants as necessary to control pore size and improve membrane performance.
• the outer diameter of the aliphatic polyamide hollow fiber membrane is set appropriately depending on the application of the aliphatic polyamide hollow fiber membrane, the thickness of the dense layer and the support layer, the liquid permeability to be provided, etc., but in consideration of the relationship between the effective membrane area when packed in a module, the membrane strength, the pressure loss of the fluid flowing through the hollow portion, and the buckling pressure, the outer diameter of the hollow fiber membrane is 400 ⁇ m or more, preferably 450 to 4000 ⁇ m, and more preferably 500 to 3500 ⁇ m.
• the inner diameter of the aliphatic polyamide hollow fiber membrane is not particularly limited, but may be, for example, 100 to 3000 ⁇ m, preferably 200 to 2500 ⁇ m, more preferably 300 to 2000 ⁇ m, and even more preferably 300 to 1500 ⁇ m.
• the outer and inner diameters of the aliphatic polyamide hollow fiber membranes are determined by observing five hollow fiber membranes with an optical microscope at a magnification of 200 times, measuring the outer and inner diameters of each hollow fiber membrane (both at the point where they are maximum), and calculating the average value of each.
• the thickness of the aliphatic polyamide hollow fiber membrane is set appropriately depending on the application of the aliphatic 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 ⁇ m, preferably 100 to 350 ⁇ m.
• the thickness of the aliphatic polyamide hollow fiber membrane is a value calculated by subtracting the inner diameter from the outer diameter and dividing the value by 2.
• filtration membranes are classified in order of the size of the substances to be separated into microfiltration (MF) membranes, ultrafiltration (UF) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes, from largest to smallest.
• MF microfiltration
• UF ultrafiltration
• NF nanofiltration
• RO reverse osmosis
• the molecular weight cutoff is used as an indicator of the size of the substances 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 (Daltons: Da) that is retained by 90% or more in the permeation test.
• the molecular weight cutoff of ultrafiltration membranes is 1,000 to 1,000,000
• the molecular weight cutoff of nanofiltration membranes is 200 to 1,000.
• the fractionation performance of the aliphatic polyamide hollow fiber membrane which is dominated by the dense layer, reflects the characteristics of the dense layer surface where the interfacial polycondensation reaction takes place, so the fractionation performance of the aliphatic polyamide hollow fiber membrane has a significant impact on the formation and characteristics of the separation functional layer.
• the molecular weight fractionation of the aliphatic polyamide hollow fiber membrane of the present invention is preferably in the range of an ultrafiltration membrane, more preferably 10,000 to 300,000, even more preferably 20,000 to 100,000, even more preferably 30,000 to 80,000, even more preferably 40,000 to 70,000, and particularly preferably 50,000 to 70,000, in order to form a separation functional layer on the surface of the dense layer that has excellent blocking performance for solutes (especially low molecular weight solutes with a molecular weight of about 200 to 1000) in the organic solvent-based treated liquid.
• the molecular weight cutoff is within the above range, a uniform separation functional layer can be formed on the surface and the surface layer (inside the layer close to the surface) of the dense layer to form a composite, and the composite hollow fiber membrane of the present invention can be obtained that has a higher level of both organic solvent permeability and blocking performance for solutes in the organic solvent-based treated liquid.
• the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane can be adjusted to the desired value by appropriately adjusting the thickness of the dense layer and the pore size of the support layer.
• the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane when greater than 3000, it is a value determined when dextran is used as a standard substance and water is used as a solvent.
• the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane (when greater than 3000) is a value determined when a crossflow module is prepared using the aliphatic polyamide hollow fiber membrane, and an aqueous solution containing a plurality of dextrans of known molecular weights at a predetermined concentration is used as a circulating liquid (raw solution) in an internal pressure crossflow system, and the dextran concentration in the permeate is measured by high performance liquid chromatography, and the solute rejection rate at each molecular weight is calculated according to the following formula, and each result is plotted on a graph showing molecular weight on the horizontal axis and rejection rate on the vertical axis, and the molecular weight is the molecular weight at the intersection of the obtained approximation curve and
• the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane is a value determined when monodisperse polystyrene is used as a standard substance and N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") is used as a solvent when the molecular weight cutoff is 3000 or less.
• NMP N-methyl-2-pyrrolidone
• the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane (when the molecular weight cutoff is 3000 or less) is a value determined when a crossflow module is produced using the aliphatic polyamide hollow fiber membrane and an NMP solution containing a plurality of polystyrenes of known molecular weights at predetermined concentrations is used as a circulating liquid (raw liquid) in an internal pressure crossflow system, and the polystyrene concentration in the permeate is measured by high performance liquid chromatography, the solute rejection rate at each molecular weight is calculated according to the following formula, and each result is plotted on a graph showing molecular weight on the horizontal axis and rejection rate on the vertical axis, and the molecular weight is the molecular weight at the intersection of the obtained approximation curve and a rejection rate of 90%.
• Solute rejection rate (%) ⁇ (polystyrene concentration in original solution - polystyrene concentration in permeate) / polyst
• the aliphatic polyamide hollow fiber membrane which is the base material of the composite hollow fiber membrane, is responsible for the mechanical properties of the composite hollow fiber membrane, and the radial stress characteristics of the hollow fiber membrane, which are mainly related to pressure resistance, are important. Stress can be applied as an internal pressure to the hollow part, and the radial breaking stress can be evaluated by the burst pressure of the internal pressure. In addition, since the operating pressure during membrane filtration is also related to the permeation rate, it is preferable that the pressure resistance of the aliphatic polyamide hollow fiber membrane is sufficiently high.
• the burst pressure of the aliphatic polyamide hollow fiber membrane of the present invention is not particularly limited, and can be adjusted to the desired value by appropriately adjusting the material properties such as the crystallinity and molecular weight of the aliphatic polyamide resin, the ratio of the inner diameter and membrane thickness of the hollow fiber membrane, the thickness of the dense layer, the thickness and porosity of the support layer, and the pore size of the pores in the support layer, etc., but from the viewpoint of increasing the operating pressure during membrane filtration to increase the amount of liquid permeation, it is preferably 2.1 MPa or more, more preferably 2.5 MPa or more, even more preferably 2.8 MPa or more, and even more preferably 3.0 MPa or more.
• the upper limit of the burst pressure of the aliphatic polyamide hollow fiber membrane is usually 4.0 MPa or less, preferably 3.8 MPa or less.
• the burst pressure of the aliphatic polyamide hollow fiber membrane is preferably 2.1 to 4.0 MPa, more preferably 2.5 to 3.8 MPa, even more preferably 2.8 to 3.8 MPa, and even more preferably 3.0 to 3.8 MPa.
• the burst pressure of the aliphatic polyamide hollow fiber membrane is the pressure (MPa) at which the aliphatic polyamide hollow fiber membrane breaks when hydraulic pressure is applied to a module made using the aliphatic polyamide hollow fiber membrane.
• the burst pressure of the aliphatic polyamide hollow fiber membrane is measured by the following method.
• a module 8 shown in FIG. 2a is prepared. Specifically, ten hollow fiber membranes 8a are cut to a length of 30 cm, and bundled together.
• 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, and a rubber plug with a length of about 20 mm is inserted from one end opening of the tube to plug the one end opening.
• a two-liquid mixed epoxy resin is injected from the opening of the tube opposite to the rubber plug to fill the inner space of the tube with the epoxy resin.
• the bundle of hollow fiber membranes prepared is bent into an approximately U-shape, and both ends of the hollow fiber membrane are heat-sealed to seal the holes so that the epoxy resin does not penetrate into the hollow part, and the end tip is inserted into the tube filled with the epoxy resin until it touches the rubber plug, and the epoxy resin is cured in this state.
• the region of the hardened epoxy resin on the rubber plug side is cut together with the tube to produce a module 8 having open hollow portions at both ends of the hollow fiber membrane.
• the module 8 is set in the device shown in FIG. 2b, and water pressure is applied to the module 8 by a hand pump 9.
• the pressure (MPa) at which the module 8 breaks is defined as the burst pressure.
• the crystallinity of the aliphatic polyamide hollow fiber membrane is not particularly limited and is usually 25% or more, and from the viewpoint of improving the solvent resistance and pressure resistance, it is preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more.
• the crystallinity of the aliphatic polyamide hollow fiber membrane can be adjusted to a desired value, for example, by annealing (heat treatment). Annealing can be performed by, for example, a dry heat method or an autoclave method.
• the crystallinity of an aliphatic polyamide hollow fiber membrane is a value measured by X-ray diffraction (XRD). Specifically, multiple hollow fiber samples are arranged closely together on a measurement stage, and a spectrum of the scattering pattern of scattering vectors and scattering intensity is obtained by scanning measurement of the scattering angle. The obtained spectrum is spectrally separated into components derived from crystals and components derived from amorphous phases, and the crystallinity is determined by quantifying them.
• XRD X-ray diffraction
• the dense layer is a region in the aliphatic polyamide hollow fiber membrane where dense micropores are concentrated, and where the presence of pores is substantially not observed in a scanning electron microscope (SEM) photograph at a magnification of 10,000 times or more.
• the dense layer may be formed on the inner surface of the aliphatic polyamide hollow fiber membrane, on the outer surface, or on both surfaces. However, it is preferable to form it on the inner surface from the viewpoint of achieving a higher level of both the liquid permeability of the organic solvent and the blocking performance of the solute in the organic solvent-based liquid to be treated.
• SEM scanning electron microscope
• the aliphatic polyamide hollow fiber membrane may be cut in the longitudinal direction with a sharp blade such as a scalpel to expose the inner surface, cut to an appropriate size, placed on a sample stage, and then vapor-deposited with Pt, Au, Pd, etc. before observation.
• a sharp blade such as a scalpel
• 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 raw 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 and from the viewpoint of stabilizing the separation functional layer, it is preferably 0.1 ⁇ m or more, more preferably 0.2 ⁇ m or more, and even more preferably 0.3 ⁇ m or more, and from the viewpoint of improving the liquid permeability of the organic solvent, it is preferably 2.0 ⁇ m or less, more preferably 1.8 ⁇ m or less, even more preferably 1.5 ⁇ m or less, even more preferably 1.2 ⁇ m or less, and even more preferably 1.0 ⁇ m or less.
• the thickness of the dense layer is preferably 0.1 to 2.0 ⁇ m, more preferably 0.2 to 1.8 ⁇ m, even more preferably 0.3 to 1.5 ⁇ m, even more preferably 0.3 to 1.2 ⁇ m, and even more preferably 0.3 to 1.0 ⁇ m.
• the thickness of the dense layer is a value that is determined by measuring the distance (thickness) of an area where substantially no pores are present at 10 points at regular intervals in a scanning electron microscope (SEM) photograph of the cross section of an aliphatic polyamide hollow fiber membrane at a magnification of 10,000 times, and calculating the average value.
• the support layer is a region of the aliphatic polyamide hollow fiber membrane other than the dense layer, and is a porous region having a continuous pore structure in which the presence of substantial pores is recognized in a scanning electron microscope (SEM) photograph at a magnification of 2000 times.
• SEM scanning electron microscope
• the porosity of the support layer is not particularly limited, and can be adjusted to a desired value by appropriately adjusting the solvent, concentration, and temperature of the membrane-forming raw solution, the type and temperature of the coagulation liquid, etc., in the production of the aliphatic polyamide hollow fiber membrane.
• 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%.
• the porosity of the support layer is calculated by the following method.
• a cross section of an aliphatic polyamide hollow fiber membrane or a composite hollow fiber membrane cut perpendicular to the longitudinal direction five scanning electron microscope (SEM) photographs are taken at equal intervals in the thickness direction of the support layer of the aliphatic polyamide hollow fiber membrane. Specifically, the photographs are taken as follows.
• FIG. 11 is a schematic cross-sectional view of an aliphatic polyamide hollow fiber membrane cut perpendicular to the longitudinal direction
• FIG. 12 and FIG. 13 are partial enlarged views of the area surrounded by dotted lines in FIG. 11, showing an example of an aliphatic polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 11.
• FIGS. 11 to 13 the separation function layer is omitted in FIGS. 11 to 13.
• a straight line is drawn from the center of the lumen of the aliphatic polyamide hollow fiber membrane 8a to the outer surface, and the straight line is divided into five equal parts from the lumen side surface of the support layer 11 to the outer surface.
• the midpoint of the five equal parts is determined.
• five locations are photographed at a uniform magnification so that the midpoint is at the center of the photographed image, the photographed image includes only the support layer 11 portion, and the number of pores is 30 to 300.
• 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, and the average value is calculated.
• ImageJ image analysis software
• the separation functional layer is a layer provided on the surface of the dense layer of the aliphatic 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 having a separation functional layer on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane has a significantly improved blocking performance of solutes in the organic solvent-based liquid to be treated (especially low molecular weight solutes with a molecular weight of about 200 to 1000) compared to an aliphatic polyamide hollow fiber membrane not having a separation functional layer, and can achieve both high levels of organic solvent permeability and blocking performance of solutes in the organic solvent-based liquid to be treated.
• the separation functional layer may be provided on the surface of the dense layer on the inner surface of the aliphatic polyamide hollow fiber membrane, or on the surface of the dense layer on the outer surface of the aliphatic polyamide hollow fiber membrane, but is preferably provided on the surface of the dense layer on the inner surface of the aliphatic polyamide hollow fiber membrane. This is because providing a separation functional layer on the surface of the dense layer on the outer surface of the aliphatic polyamide hollow fiber membrane may cause peeling of the separation functional layer due to contact between the hollow fiber membranes during filtration, or peeling may easily occur at the interface between both ends of the module and the sealant during module production.
• the separation functional layer may be provided only on the surface of one of the dense layers, or may be provided on the surfaces of both dense layers, but for the above reasons, it is preferable that the separation functional layer is provided only on the surface of the dense layer on the inner surface.
• the separation functional layer is a layer containing a crosslinked resin obtained by interfacial polycondensation as a main component, and more specifically, a layer having a mesh-like structure formed of a crosslinked resin obtained by an interfacial polycondensation reaction of two or more polyfunctional monomers including a monomer having three or more functionalities. Since the separation functional layer is formed of a crosslinked resin, it has excellent resistance to various types of organic solvents, and can stably maintain membrane performance even when in contact with various types of organic solvents used industrially.
• the crosslinked resin is not particularly limited as long as it is a resin having a crosslinked structure obtained by interfacial polycondensation, and examples thereof include crosslinked polyamide resins and crosslinked polyester resins.
• One type of crosslinked resin may be contained, or two or more types may be contained.
• a crosslinked polyamide resin a polyfunctional amine having two or more functionalities and a polyfunctional acyl halide having two or more functionalities are usually used as the polyfunctional monomer.
• a polyhydric alcohol having two or more functionalities and a polyfunctional acyl halide having two or more functionalities are usually used as the polyfunctional monomer.
• the crosslinked resin constituting the separation functional layer is preferably a crosslinked polyamide resin, more preferably a crosslinked aromatic polyamide resin.
• Polyfunctional amines which are raw material monomers for crosslinked polyamide resins, are amines that have at least two amino groups in one molecule, and examples of such polyfunctional amines include phenylenediamines in which two amino groups are bonded to a benzene ring at the ortho, meta, or para positions, xylylenediamine, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine, aromatic diamines such as biphenyl and diphenylmethane, in which two hydrogen atoms of an aromatic hydrocarbon to which a benzene ring is bonded directly or via a functional group are replaced with two amino groups, and benzene rings such as 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, biphenyl, and diphenylmethane.
• aromatic polyfunctional amines include aromatic triamines such as compounds in which three hydrogen atoms of an aromatic hydrocarbon to which a benzene ring such as biphenyl or diphenylmethane is bonded directly or via a functional group are substituted with three amino groups, aromatic tetraamines such as compounds in which four hydrogen atoms of an aromatic hydrocarbon to which a benzene ring such as biphenyl or diphenylmethane is bonded directly or via a functional group are substituted with four amino groups (e.g., 3,3',4,4'-tetraaminobiphenyl, etc.); aliphatic polyfunctional amines such as ethylenediamine and propylenediamine; alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, piperazine, and 4-aminoethylpiperazine.
• aromatic triamines such as
• the polyfunctional amines may be further substituted with substituents such as halogen atoms, sulfo groups, alkyl groups, and fluoroalkyl groups. These polyfunctional amines may be used alone or in combination of two or more.
• aromatic polyfunctional amines more preferably, aromatic di- to tetrafunctional amines, even more preferably, at least one aromatic diamine selected from the group consisting of m-phenylenediamine, p-phenylenediamine, xylylenediamine, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine, and particularly preferably, m-phenylenediamine.
• the polyfunctional acyl halide which is a raw material monomer for crosslinked polyamide resins, is an acyl halide having at least two halogenated carbonyl groups in one molecule, and examples thereof include trifunctional acyl halides such as trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride; aromatic bifunctional acyl halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic bifunctional acyl halides such as adipoyl chloride and sebacoyl chloride; and alicyclic bifunctional acyl halides such as cyclopentanedicarboxylic acid dichloride, cyclohex
• polyfunctional acyl halides may be used alone or in combination of two or more.
• a polyfunctional amine having three or more functionalities and/or a polyfunctional acyl halide it is necessary to use a trifunctional acyl halide, and more preferably trimesic acid chloride.
• the separation functional layer may contain a non-crosslinked polyamide resin (a linear polyamide resin obtained by an interfacial polycondensation reaction between a diamine and a bifunctional acyl halide), but from the viewpoint of improving the solvent resistance of the separation functional layer, it is preferable that it does not contain a non-crosslinked polyamide resin.
• the separation functional layer contains a non-crosslinked polyamide resin
• the content of the non-crosslinked polyamide resin is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less.
• the separation functional layer may contain additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants, as necessary.
• the thickness of the separation functional layer is not particularly limited, but since it is extremely thin (less than 0.1 ⁇ m), it is very difficult to accurately measure the thickness even when observed with a scanning electron microscope (SEM) at a magnification of 100,000 to 200,000 times. Since the separation functional layer of the present invention is observed as a form completely integrated with the dense layer of the aliphatic polyamide hollow fiber membrane, it is difficult to specify the thickness of the separation functional layer. However, if the separation functional layer has a form with large irregularities, it is observed as an uneven image different from the dense layer, and the presence of the separation functional layer can be determined from the SEM image. In this case, it is also difficult to specify the thickness of the separation functional layer.
• the morphology in the SEM image of the surface where the interfacial polycondensation reaction has been performed is different from the morphology in the SEM image of the surface of the dense layer of the aliphatic polyamide hollow fiber membrane where the interfacial polycondensation reaction has not been performed (numerous circular protrusions that are not on the surface of the dense layer can be seen), so the presence of the separation functional layer can be confirmed by comparing the SEM images.
• the presence of the separation functional layer can also be confirmed by an air leak test of the composite hollow fiber membrane.
• the air leak test method is a method in which air pressure of about 0.2 MPa is applied to the hollow part of a composite hollow fiber membrane in a dry state to seal in the pressurized air, and the decrease in the containment pressure over time is evaluated.
• an aliphatic polyamide hollow fiber membrane has a pore size in the range of an ultrafiltration membrane, the aliphatic polyamide hollow fiber membrane cannot hold the containment pressure at all.
• a composite hollow fiber membrane completely composited with a separation functional layer can almost completely hold the containment pressure. Therefore, the presence of the separation functional layer can be confirmed by testing whether the containment pressure can be held.
• the quality of the formation state of the separation functional layer can be judged by quantifying the state of holding the containment pressure, so the air leak test method is effective in confirming defects in the separation functional layer.
• the air leak amount (pressure drop amount) per 5 minutes is preferably 0.05 MPa or less, more preferably 0.02 MPa or less, and even more preferably 0.005 MPa or less.
• V/S 0.0002 ⁇ 0.45/R R is the inner diameter (mm) of the composite hollow fiber membrane. The error of V/S is within ⁇ 10%.
• the membrane area S (the leaking portion) and the total pressurized space volume V are constant to a certain extent.
• the hollow volume of the hollow fiber itself varies with the change in the inner diameter, and the ratio of the volume to the membrane area is proportional to the inner diameter.
• the module size and the leak tester size also vary depending on the thickness of the hollow fiber membrane, so they need to be corrected as shown in the above formula 1.
• the optimal value is found based on an air leak test in a space of 0.0002 m3 per m2 with an inner diameter of 0.45 mm for the hollow fiber membrane, and for hollow fiber membranes with inner diameters of 0.1 to 3 mm, which are suitable in the present invention, the conditions are standardized for hollow fiber membranes with different inner diameters based on the relationship described in the above formula 1.
• the air leak amount (pressure drop amount) of the composite hollow fiber membrane is measured by the following method. 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, and a silicone tube with an inner diameter of 12 mm and a length of about 50 mm is inserted about 15 mm into one end opening of the tube to connect it, and a rubber plug with a length of about 20 mm is inserted on the side of the silicone tube opposite to the side inserted into the PBT tube to plug the one end opening.
• PBT polybutylene terephthalate
• a two-liquid mixed epoxy resin is injected from the opening on the opposite side of the connecting tube from the side where the rubber plug is inserted, and the space inside the tube is filled with the epoxy resin.
• one end of the bundle of composite hollow fiber membranes prepared above is heat sealed to prevent the epoxy resin from penetrating into the hollow portion, and the end is inserted into the 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.
• the region of the cured epoxy resin part on the rubber stopper side is cut together with the tube to open the hollow portion. The same operation is performed on the other end to prepare a crossflow module in which the hollow portions at both ends of the composite hollow fiber membrane are open.
• the membrane area of the module is calculated based on the internal area of the hollow fibers, and from the internal diameter, number, and effective length of the hollow fibers.
• One end of the outlet connected to the hollow part of the prepared module is sealed, and a valve and a pressure line having a pressure gauge between the valve and the module are attached to the other end.
• Air is pressurized to 0.2 MPa in the hollow part, and the valve is closed to contain the pressure.
• the pressure is checked over time, and the change in pressure after 5 minutes is measured.
• the containment volume (total pressurized space volume V) including the hollow fiber, module, pressurized line, etc. is estimated, and the length of the line is controlled so that the ratio of the membrane area S to the total pressurized space volume V is within ⁇ 10% of the relationship in formula 1 above.
• the composite hollow fiber membrane of the present invention has a burst pressure of 2.25 MPa or more as measured under the conditions described below, and has high mechanical strength in organic solvents (excellent pressure resistance), so that the operating pressure during membrane filtration can be increased to increase the amount of organic solvent passing through.
• ⁇ Burst pressure> While passing N-methyl-2-pyrrolidone through a module prepared using the composite hollow fiber membrane, the pressure is increased by 0.25 MPa at 10-minute intervals, and the pressure (MPa) at which the composite hollow fiber membrane breaks is measured.
• the burst pressure of the composite hollow fiber membrane is preferably 2.5 MPa or more, more preferably 2.75 MPa or more, from the viewpoint of increasing the operating pressure during membrane filtration and further increasing the amount of organic solvent permeation.
• the upper limit of the burst pressure of the composite hollow fiber membrane is usually 4.0 MPa or less.
• the burst pressure of the composite hollow fiber membrane is preferably 2.5 to 4.0 MPa, more preferably 2.75 to 4.0 MPa.
• the burst pressure of the composite hollow fiber membrane can be adjusted to a desired value by appropriately adjusting the materials for forming the aliphatic polyamide hollow fiber membrane and the separation functional layer, the thickness of the dense layer, the thickness and porosity of the support layer, and the pore size of the pores in the support layer, etc.
• the burst pressure of the composite hollow fiber membrane is measured by the following method. 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, and a silicone tube with an inner diameter of 12 mm and a length of about 50 mm is inserted about 15 mm into one end opening of the tube to connect it, and a rubber plug with a length of about 20 mm is inserted on the side of the silicone tube opposite to the side inserted into the PBT tube to plug the one end opening.
• PBT polybutylene terephthalate
• a two-liquid mixed epoxy resin is injected from the opening on the opposite side of the connecting tube from the side where the rubber plug is inserted, and the space inside the tube is filled with the epoxy resin.
• one end of the bundle of composite hollow fiber membranes prepared above is heat sealed to prevent the epoxy resin from penetrating into the hollow portion, and the end is inserted into the 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.
• 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 operation is performed on the other end to prepare a crossflow module with open hollow portions at both ends of the composite hollow fiber membrane.
• the prepared cross-flow module 6 is connected to the internal pressure separation treatment line shown in Figure 1, and NMP is continuously permeated through the cross-flow module 6 by the liquid supply circulation pump 2.
• the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 are adjusted by the regulator 5, the arithmetic mean value of the pressures of the primary pressure gauge 3 and the secondary pressure gauge 4 is taken as the applied pressure, and the pressure is increased by 0.25 MPa at 10-minute intervals.
• the pressure (MPa) at which the composite hollow fiber membrane breaks, that is, when a sudden pressure drop occurs, is taken as the burst pressure.
• the composite hollow fiber membrane of the present invention has a separation functional layer provided on the surface of the dense layer of the aliphatic 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 the organic solvent-based treated liquid, and has, for example, the following liquid permeability and blocking performance.
• the NMP permeation amount at 25° C. and a pressure of 75% of the burst pressure of the composite hollow fiber membrane is preferably 6 L/( m2 ⁇ h) or more, more preferably 8 L/( m2 ⁇ h) or more, even more preferably 10 L/( m2 ⁇ h) or more, still more preferably 11 L/( m2 ⁇ h) or more, even more preferably 12 L/( m2 ⁇ h) or more, and even more preferably 14 L/( m2 ⁇ h) or more.
• the upper limit of the NMP permeation amount is usually 20 L/( m2 ⁇ h) or less.
• the NMP permeation rate at 25° C. and a pressure of 75% of the burst pressure of the composite hollow fiber membrane is preferably 6 to 20 L/( m2 ⁇ h), more preferably 8 to 20 L/( m2 ⁇ h), even more preferably 10 to 20 L/( m2 ⁇ h), still more preferably 11 to 20 L/( m2 ⁇ h), even more preferably 12 to 20 L/( m2 ⁇ h), and even more preferably 14 to 20 L/( m2 ⁇ h).
• the NMP permeation rate can be adjusted to a desired value by appropriately adjusting the molecular weight cutoff of the aliphatic polyamide hollow fiber membrane, the thickness of the dense layer, the type of material forming the separation functional layer, and the like.
• the NMP permeation amount is a value measured by internal pressure filtration, and is a value measured by the following procedure.
• 20 composite hollow fiber membranes are cut into a length of 30 cm, and prepared by arranging and bundling them.
• 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, and a silicone tube with an inner diameter of 12 mm and a length of about 50 mm is inserted about 15 mm into one end opening of the tube to connect it, and a rubber plug with a length of about 20 mm is inserted on the side of the silicone tube opposite to the side inserted into the PBT tube to plug the one end opening.
• a two-liquid mixed epoxy resin is injected from the opening on the opposite side of the connecting tube from the side where the rubber plug is inserted, and the space inside the tube is filled with the epoxy resin.
• one end of the bundle of composite hollow fiber membranes prepared above is heat sealed to prevent the epoxy resin from penetrating into the hollow portion, and the end is inserted into the 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.
• 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 operation is performed on the other end to prepare a crossflow module with open hollow portions at both ends of the composite hollow fiber membrane.
• the prepared cross-flow module 6 is connected to the internal pressure separation processing line shown in FIG. 1, and the flowing liquid is continuously passed through the cross-flow module 6 by the liquid supply circulation pump 2. NMP is used as the flowing liquid.
• the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 are adjusted by the regulator 5 so that the arithmetic mean value of the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 is 75% of the burst pressure of the composite hollow fiber membrane.
• the one that has passed through the pores of the composite hollow fiber membrane is collected as a permeated liquid separated from the flowing liquid, and the remainder is circulated again to the separation processing line.
• NMP permeation amount volume (L) of NMP permeated to the outside of the composite hollow fiber membrane/[inner diameter (m) of the composite hollow fiber membrane ⁇ 3.14 ⁇ effective filtration length (m) of the composite hollow fiber membrane ⁇ 20 (pieces) ⁇ time (h)]
• Effective filtration length of composite hollow fiber membrane This is the length of the portion of the outer surface of the composite hollow fiber membrane that is not covered with epoxy resin in the crossflow module.
• 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., has a molecular weight cutoff of 200 to 1000.
• a molecular weight cutoff of 200 to 1000.
• the blocking rate of diphenyl sulfone (molecular weight: 218.27), which is equivalent to the minimum molecular weight of the molecular weight cutoff as OSN, was used.
• the composite hollow fiber membrane of the present invention has a blocking rate of 90% or more for polystyrene with a molecular weight of 1000, and a blocking rate of 30% or more for diphenyl sulfone, which is a low molecular weight, and therefore satisfies the performance as a nanofiltration membrane.
• the rejection rate of diphenyl sulfone when a solution in which the solvent is NMP and the solute is diphenyl sulfone is filtered is preferably 30% or more, more preferably 35% or more, even more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more.
• the rejection rate of diphenyl sulfone can be adjusted to a desired value by appropriately selecting the type of material forming the separation functional layer, etc.
• the rejection rate of diphenyl sulfone or polystyrene is a value measured by internal pressure filtration, and is a value measured by the same measurement procedure as the measurement of the NMP permeation rate, except that an NMP solution containing 0.2 wt% of diphenyl sulfone or polystyrene is used.
• the concentration of diphenyl sulfone or polystyrene can be measured by liquid chromatography.
• the composite hollow fiber membrane of the present invention is mainly formed of an aliphatic polyamide resin and a crosslinked resin (preferably a crosslinked aromatic polyamide resin), and therefore 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.
• organic solvents such as alcohols, aprotic polar solvents, hydrocarbons, higher fatty acids, ketones, esters, and ethers.
• 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, dimethylsulfoxide, N-methyl-2-pyrrolidone, sulfolane, and the like.
• Esters ethyl acetate, isobutyl acetate, ethyl lactate, dimethyl phthalate, diethyl phthalate, ethylene carbonate, propylene carbonate, and the like.
• Hydrocarbons petroleum ether, pentane, hexane, heptane, benzene, toluene, xylene, liquid paraffin, gasoline, and mineral oil.
• Higher fatty acid A fatty acid having 4 or more carbon atoms (preferably 4 to 30 carbon atoms) other than the carboxy group, such as oleic acid, linoleic acid, and linolenic acid.
• the composite hollow fiber membrane of the present invention is preferably used, for example, as an ultrafiltration membrane or nanofiltration membrane in the fields of semiconductor industry, chemical industry, food industry, pharmaceutical industry, medical product industry, etc.
• the composite hollow fiber membrane of the present invention has high resistance to aprotic polar solvents, and is preferably used in filtration of a liquid to be treated that contains the solvent and a solute in industrial fields that use the solvent.
• the composite hollow fiber membrane of the present invention is resistant to various organic solvents, making it suitable for use in membrane separation processes that treat liquids containing organic solvents and solutes.
• 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-described structure.
• a suitable example includes a production method including the following first to fourth steps.
• Second step A step of coagulating the aliphatic polyamide resin into a membrane by extruding the membrane-forming solution in a predetermined shape into a coagulation bath at 100°C or less.
• a coagulation liquid that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the aliphatic polyamide resin is brought into contact with at least one surface of the membrane-forming solution extruded in the predetermined shape, thereby forming an aliphatic 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 aliphatic polyamide hollow fiber membrane formed in the second step.
• a membrane-forming stock solution is prepared by dissolving an aliphatic polyamide resin at a concentration of 20% by weight or more in an organic solvent having a boiling point of 150°C or more and being incompatible with the aliphatic polyamide resin at a temperature below 100°C at a temperature of 100°C or more.
• aprotic polar solvents include sulfolane, dimethyl sulfone, dimethyl sulfoxide, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -caprolactone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, etc.
• glycerin ethers include diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, etc.
• 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.
• 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.
• organic solvents from the viewpoint of obtaining an aliphatic polyamide hollow fiber membrane with higher strength, preferably, aprotic polar solvents and polyhydric alcohols; more preferably, sulfolane, dimethyl sulfone, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -caprolactone, propylene glycol, hexylene glycol, 1,3-butanediol, polyethylene glycol (molecular weight 100 to 600); even more preferably, sulfolane, dimethyl sulfone, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -caprolactone; even more preferably, dimethyl sulfone.
• aprotic polar solvents and polyhydric alcohols more preferably, sulfolane, dimethyl sulfone, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -caprolactone, propylene glycol, hexy
• 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, by using two or more of them in combination, a more effective aliphatic polyamide hollow fiber membrane may be produced due to the difference in the order of phase separation and structure.
• the concentration of the aliphatic 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.
• the temperature of the solvent when dissolving the aliphatic polyamide resin in the organic solvent, it is necessary to keep the temperature of the solvent at 100°C or higher. Specifically, it is desirable to dissolve the resin at a temperature 10 to 50°C higher than the phase separation temperature of the membrane-forming solution to be prepared, and preferably 20 to 40°C higher.
• 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 aliphatic polyamide resin and the organic solvent at a sufficiently high temperature is gradually cooled.
• the phase separation temperature can be measured using a microscope equipped with a hot stage, etc.
• the temperature conditions for dissolving the aliphatic polyamide resin in the organic solvent may be appropriately set in the temperature range of 100°C or higher according to the above-mentioned index depending on the type of aliphatic 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.
• fillers, thickeners, antioxidants, surface modifiers, lubricants, surfactants, etc. may be added to the membrane-forming solution as necessary to control the pore size of the aliphatic polyamide hollow fiber membrane and improve its performance.
• the film-forming solution prepared in the first step is sent to the second step while still at that temperature (i.e., at or above 100°C).
• the membrane-forming solution prepared in the first step is extruded in a predetermined shape into a coagulation bath at 100°C or less to coagulate the aliphatic polyamide resin into a membrane.
• a coagulation liquid (hereinafter sometimes referred to as "coagulation liquid for forming a dense layer") that is compatible with the organic solvent used in the membrane-forming solution but has low affinity for the aliphatic polyamide resin is contacted with at least one surface of the membrane-forming solution extruded in the predetermined shape to form an aliphatic polyamide hollow fiber membrane having a dense layer on at least one surface.
• the membrane-forming stock solution extruded into a predetermined shape into the coagulation bath forms a dense layer on the surface that 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, resulting in an aliphatic polyamide hollow fiber membrane having the above molecular weight cutoff.
• a dense layer is formed on only one surface of the aliphatic polyamide hollow fiber membrane
• one surface of the membrane-forming stock solution extruded in a predetermined shape is contacted with a dense layer-forming coagulating liquid, and the other surface is contacted with a coagulating liquid (hereinafter sometimes referred to as "support layer-forming coagulating liquid") that is compatible with the organic solvent used in the membrane-forming stock solution and has a high affinity with the aliphatic polyamide resin.
• support layer-forming coagulating liquid a coagulating liquid that is compatible with the organic solvent used in the membrane-forming stock solution and has a high affinity with the aliphatic polyamide resin.
• the dense layer forming solidifying liquid is a solvent that is compatible with the organic solvent used in the film forming solution at a temperature of 25°C or less, but does not dissolve the aliphatic polyamide resin at a temperature below the boiling point or below 200°C.
• the dense layer forming solidifying 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; glycol ethers such as polyethylene glycol with an average molecular weight of 300 or more, polypropylene glycol with an average molecular weight of 400 or more, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and propylene glycol monoethyl ether; glycol acetates such as triacetin and propylene glycol monoethyl ether acetate.
• aqueous solvents such as water and aqueous solutions with a water content of 80% by weight or more
• monohydric alcohols such as 1-propanol, 2-propanol, and isobutanol
• glycol ethers such as polyethylene glycol with an average molecular weight of 300 or more, polypropylene
• the average molecular weight of polyethylene glycol and polypropylene glycol is a number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS K 1557-6:2009 "Plastics - Polyurethane raw material polyol test method - Part 6: Determination of hydroxyl value by near infrared (NIR) spectroscopy.”
• the dense layer forming coagulation liquid may contain a solvent used in the support layer forming coagulation liquid, such as glycerin, to the extent that a dense layer can be formed (a solvent that is compatible with the organic solvent used in the membrane forming solution at a temperature of 25°C or less and dissolves the aliphatic polyamide resin at a temperature of the boiling point or less).
• a solvent used in the support layer forming coagulation liquid such as glycerin
• the dense layer forming coagulation liquid contains a 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% by weight, more preferably 10 to 35% by weight, even more preferably 15 to 32% by weight, and even more preferably 15 to 30% by weight, from the viewpoint of forming a dense layer of suitable thickness and obtaining an aliphatic polyamide hollow fiber membrane having the above molecular weight cutoff.
• a 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 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 aliphatic 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, ⁇ -butyrolactone, ⁇ -valerolactone, and aqueous solutions containing 20% or more by weight of these.
• a double-tube nozzle for hollow fiber production having a double tube structure is used, the membrane raw solution is discharged from the outer annular nozzle and the internal coagulation liquid is discharged from the inner nozzle, and the membrane is immersed in a coagulation bath.
• a dense layer forming coagulation liquid is used for at least one of the internal coagulation liquid and the coagulation bath.
• a dense layer forming coagulation liquid is used as the internal coagulation liquid and a support layer forming coagulation liquid is used as the coagulation bath, a dense layer is formed on the inner surface, and an aliphatic polyamide hollow fiber membrane with a support layer on the inside and the outer surfaces is obtained.
• the coagulation liquid for forming the support layer is used as the coagulation liquid for the inside and the coagulation liquid for forming the dense layer is used as the coagulation bath, a dense layer is formed on the outer surface, and an aliphatic polyamide hollow fiber membrane in which the inner surface and the inside are the support layer is obtained.
• the coagulation liquid for the inside used in forming the aliphatic polyamide hollow fiber membrane passes through a double annular nozzle, it is preferable that it does not contain water whose boiling point is equal to or lower than the temperature of the double annular nozzle.
• a die having a double tubular structure such as that used for producing core-sheath composite fibers in melt spinning can be used.
• the diameter of the outer annular nozzle and the diameter of the inner nozzle of the double tubular nozzle for producing hollow fibers can be appropriately set according to the inner and outer diameters of the aliphatic polyamide hollow fiber membrane.
• the flow rate of the membrane stock solution discharged from the outer annular nozzle of the hollow fiber manufacturing 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 set appropriately taking into consideration the diameter of the inner nozzle of the hollow fiber manufacturing double tubular nozzle, the type of internal liquid used, the flow rate of the membrane stock solution, etc., and may be 0.1 to 2 times, preferably 0.2 to 1 times, and more preferably 0.4 to 0.7 times the flow rate of the membrane stock solution.
• the temperature of the coagulation bath may be 100°C or less, preferably -20 to 100°C, more preferably 0 to 60°C, even more preferably 2 to 20°C, and particularly preferably 2 to 10°C.
• the suitable temperature of the coagulation bath may vary depending on the organic solvent used in the membrane-forming solution, the composition of the coagulation solution, etc., but generally, a lower temperature tends to favor thermally induced phase separation, while a higher temperature tends to favor non-solvent phase separation.
• the coagulation bath when producing an aliphatic polyamide hollow fiber membrane with 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.
• the temperature of the internal coagulation liquid may be approximately 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.
• the membrane-forming solution coagulates in the coagulation bath, and an aliphatic polyamide hollow fiber membrane is formed with a dense layer on at least one surface.
• 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 the difference in boiling points, for example, water, glycerin, methanol, ethanol, isopropanol, acetone, diethyl ether, hexane, petroleum ether, toluene, etc.
• water, methanol, ethanol, isopropanol, and acetone are preferred; water, methanol, and isopropanol are more preferred.
• isopropyl alcohol, petroleum ether, etc. can be suitably used when extracting water-insoluble organic solvents such as phthalic acid esters and fatty acids.
• the time for which the aliphatic polyamide hollow fiber membrane is immersed 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.
• the extraction solvent may be replaced or stirred to effectively extract and remove the coagulation liquid remaining in the aliphatic polyamide hollow fiber membrane.
• an aliphatic polyamide hollow fiber membrane is obtained from which the membrane forming solution solvent and the coagulation liquid have been removed and which has a dense layer on at least one surface.
• drying and removal of the extraction solvent can be performed by known drying processes such as natural drying, hot air drying, reduced pressure drying, and vacuum drying.
• the aliphatic polyamide hollow fiber membrane may be stretched in one axis direction (longitudinal direction) simultaneously with or after drying.
• the aliphatic polyamide hollow fiber membrane may be dried while tension for stretching is applied to the membrane.
• temperature conditions include temperatures of 40°C or higher, preferably 40 to 160°C, more preferably 50°C to 140°C, and even more preferably 120 to 140°C.
• the temperature conditions during drying are not particularly limited as long as the adhering extraction solvent can be evaporated, but examples include 40°C or higher, preferably 40 to 160°C, more preferably 50°C to 140°C, and even more preferably 120 to 140°C.
• the temperature conditions during stretching are not particularly limited, and may be -10 to 140°C, preferably 0 to 120°C, but from the viewpoint of further improving the liquid permeability, it is desirable for the temperature to be equal to or higher than the glass transition point of the aliphatic polyamide resin used (more preferably 50 to 120°C, and even more preferably 60 to 100°C).
• the stretching in the uniaxial direction may be performed by a known method, for example, continuously by winding from a low-speed roll to a high-speed roll.
• the aliphatic polyamide hollow fiber membrane cut to a certain length may be stretched by holding both ends of the membrane using a tensile tester or the like, or by manual stretching.
• the stretching ratio is, for example, 1.2 to 5 times, and preferably 1.2 to 3 times. From the viewpoint of increasing the strength of the aliphatic polyamide hollow fiber membrane and providing it with excellent pressure resistance, the stretching ratio is preferably 1.2 to 2.4 times, and more preferably 1.2 to 2.0 times.
• the cross-linked resin constituting the separation functional layer is as described in the [Separation functional layer] section of "2. Composite hollow fiber membrane" above. Below, as a representative example, we will explain the case where the cross-linked resin is a cross-linked polyamide resin.
• Crosslinked polyamide resins are obtained by interfacial polycondensation of polyfunctional amines and polyfunctional acyl halides.
• at least one of the polyfunctional amines or polyfunctional acyl halides must contain a compound with three or more functionalities.
• a solution containing a polyfunctional amine hereinafter also referred to as a polyfunctional amine solution
• an organic solution containing a polyfunctional acyl halide that is immiscible with the solvent of the polyfunctional amine solution hereinafter also referred to as a polyfunctional acyl halide solution
• a separation functional layer can be formed on the surface of the dense layer by performing interfacial polycondensation on the surface of the dense layer.
• Water is usually used as the solvent for the polyfunctional amine solution.
• an organic solvent such as dimethylformamide can be used instead of water, or a mixed solvent of water and an organic solvent such as dimethylformamide can be used.
• m-phenylenediamine is used as the polyfunctional amine, it is preferable to use water as the solvent.
• an organic solvent such as dimethylformamide is used instead of water, it is necessary that the organic solvent does not dissolve the hollow fiber membrane and is immiscible with the organic solvent of the polyfunctional acyl halide solution.
• the aliphatic polyamide hollow fiber membrane of the present invention has excellent resistance to a wide variety of organic solvents. Therefore, in the present invention, even organic solvents such as dimethylformamide, which dissolve conventional hollow fiber membranes, can be used as the solvent for the polyfunctional amine solution.
• the concentration of the polyfunctional amine in the aqueous polyfunctional amine solution is not particularly limited, but is usually about 0.01 to 10% by weight, preferably 0.1 to 5% by weight, more preferably 0.5 to 4% by weight, and even more preferably 1 to 3% by weight.
• the polyfunctional amine aqueous solution may contain a surfactant and a phase transfer catalyst, etc., to the extent that the interfacial polycondensation reaction is not inhibited.
• the surfactant has the function of improving the wettability of the dense layer surface and reducing the interfacial tension between the polyfunctional amine solution and the polyfunctional acyl halide solution.
• Examples of the surfactant include sodium dodecyl sulfate and sodium dodecylbenzenesulfonate.
• the phase transfer catalyst has the function of promoting the reaction between the immiscible solutions of the polyfunctional amine solution and the polyfunctional acyl halide solution.
• phase transfer catalyst examples include tertiary amines such as triethylamine, and quaternary ammonium salts such as trioctylmethylammonium chloride.
• tertiary amines such as triethylamine
• quaternary ammonium salts such as trioctylmethylammonium chloride.
• the contact is preferably carried out uniformly and without gaps on the dense layer.
• Examples of the contact method include a method of immersing the aliphatic polyamide hollow fiber membrane in the polyfunctional amine solution and a method of passing the polyfunctional amine solution through the inside of the aliphatic polyamide hollow fiber membrane.
• the contact time between the dense layer and the polyfunctional amine solution is not particularly limited, but is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes.
• the polyfunctional amine solution can be sufficiently impregnated into the dense layer and excessive impregnation into the support layer can be suppressed.
• the aliphatic polyamide hollow fiber membrane may be wetted with a solvent such as water before contact with the polyfunctional amine solution. This can promote impregnation of the polyfunctional amine solution.
• the removal method include a method of blowing off the excess polyfunctional amine remaining on the dense layer surface with an airflow such as air, and a method of ventilating air or the like into the hollow part of the aliphatic polyamide hollow fiber membrane.
• the time for blowing or ventilating air or the like is not particularly limited, but is preferably 5 seconds to 3 minutes, more preferably 10 seconds to 2 minutes.
• the time is too short, the liquid cannot be sufficiently removed, and if the time is too long, the polyfunctional amine solution is excessively removed or the contact surface dries out, which makes it easy to inhibit the optimal interfacial polycondensation reaction.
• a liquid that is immiscible with the solvent of the polyfunctional amine solution may be flowed on the dense layer surface. In this case, the same effect as the airflow can be obtained.
• the liquid When passing an immiscible liquid through the hollow portion of an aliphatic polyamide hollow fiber membrane, the liquid may be passed either before or after the liquid is drained off with an airflow, and the amount of liquid passed is about 5 to 50 times the volume inside the hollow fiber.
• the dense layer that has been in contact with the polyfunctional amine solution is contacted with a polyfunctional acyl halide solution, and a separation functional layer containing a cross-linked polyamide resin is formed on the surface of the dense layer by interfacial polycondensation.
• the organic solvent of the polyfunctional acyl halide solution may be any solvent that is immiscible with the solvent of the polyfunctional amine solution, dissolves the polyfunctional acyl halide, does not dissolve the aliphatic polyamide hollow fiber membrane, and is inactive against the polyfunctional amine and the polyfunctional acyl halide.
• the organic solvent include hydrocarbon solvents, chlorine-based solvents, and fluorine-based solvents. These may be used alone or in combination of two or more. Of these, hydrocarbon solvents are preferred from the viewpoints of ease of handling and environmental impact.
• the hydrocarbon solvent include aliphatic hydrocarbons and aromatic hydrocarbons.
• aliphatic hydrocarbons examples include linear aliphatic hydrocarbons such as hexane and octane, and branched aliphatic hydrocarbons such as isooctane.
• aromatic hydrocarbons examples include toluene and xylene.
• the concentration of the polyfunctional acyl halide in the polyfunctional acyl halide solution is not particularly limited, but is usually about 0.01 to 5% by weight, preferably 0.01 to 1% by weight, and more preferably 0.05 to 0.5% by weight. If it is within this range, a separation functional layer with a uniform and sufficient thickness can be formed on the surface of the dense layer.
• the contact between the polyfunctional acyl halide solution and the dense layer surface coated with the polyfunctional amine solution may be carried out in the same manner as the above-mentioned contact method of the polyfunctional amine solution with the dense layer surface.
• the solution may be passed either before or after draining with an airflow, and the amount of solution passed is about 5 to 50 times the volume inside the hollow fiber.
• drying methods include placing the composite hollow fiber membrane in a dryer, or applying or ventilating hot air only to the surface on which the separation functional layer is formed.
• the temperature during drying or ventilating is not particularly limited, and is preferably 50 to 120°C, more preferably 80 to 100°C.
• the drying time can be set appropriately so that the solvent of the polyfunctional acyl halide solution can be sufficiently removed, but is usually about 0.5 to 60 minutes, preferably 0.5 to 30 minutes, more preferably 1 to 20 minutes, and even more preferably 1 to 10 minutes.
• the composite hollow fiber membrane that has been dried may be used as is, or may be further washed. Unreacted polyfunctional amines and polyfunctional acyl halides may remain in the membrane. If these remain in the membrane, they may dissolve during use of the composite hollow fiber membrane, so it is preferable to remove them by washing. It is preferable to use water for the washing. Examples of the washing method include immersing the membrane in water and passing water through the hollow part of the composite hollow fiber membrane. The temperature during the washing is not particularly limited, but is usually room temperature to about 70°C. The washing time can be adjusted appropriately depending on the water temperature, and if immersing the membrane at room temperature, it is preferable to leave it for 12 hours or more.
• the composite hollow fiber membrane that has been washed may be used as is, or may be dried again.
• a dried composite hollow fiber membrane is more advantageous for subsequent processes such as modularization. Drying should be performed under conditions that substantially eliminate moisture, and the drying temperature is preferably 25 to 100°C, more preferably 40 to 70°C.
• a method for forming a separation functional layer on the surface of the dense layer on the inner side of the aliphatic polyamide hollow fiber membrane for example, a method is given in which a polyfunctional amine solution is injected into the hollow portion of the aliphatic polyamide hollow fiber membrane, and then a polyfunctional acyl halide solution is injected into the hollow portion to cause interfacial polycondensation of the polyfunctional amine and the polyfunctional acyl halide on the dense layer, thereby forming a separation functional layer on the surface of the dense layer.
• the method of injecting the polyfunctional amine solution and the polyfunctional acyl halide solution into the hollow part of the aliphatic polyamide hollow fiber membrane is not particularly limited as long as the surface of the dense layer can be uniformly coated with the polyfunctional amine solution and the polyfunctional acyl halide solution.
• a preferred method is to form a module using the aliphatic polyamide hollow fiber membrane, inject the polyfunctional amine solution into the hollow part of the aliphatic polyamide hollow fiber membrane of the module, and then inject the polyfunctional acyl halide solution.
• the injection method is as follows. First, a desired number of aliphatic polyamide hollow fiber membranes of the desired length are prepared and bundled.
• a hard tube is prepared, and a rubber plug or the like of an appropriate length is inserted into one end opening of the tube to plug the one end opening.
• a two-liquid mixed type thermosetting resin is injected from the end opening opposite the plugged end of the tube, and the space inside the tube is filled with the resin.
• one end of the bundled aliphatic polyamide hollow fiber membrane is heat sealed to seal the openings, and the end is inserted into the tube filled with the thermosetting resin until the tip of the end touches the plug, and the thermosetting resin is cured in this state.
• the plug side area of the cured resin is cut together with the tube to open the hollow part of the aliphatic polyamide hollow fiber membrane.
• a suitable tool is attached to the tube on the opening side, and a polyfunctional amine solution is injected, and then a polyfunctional acyl halide solution is injected. Note that a wetting solution may be injected before the injection of the polyfunctional amine solution.
• the injection method is not particularly limited, and examples 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.
• a pump such as a peristaltic pump, a plunger pump, a diaphragm pump, or a gear pump.
• the speed at which the polyfunctional amine solution and the polyfunctional acyl halide solution are injected is not particularly limited, but the linear speed is, for example, about 0.01 to 2 m/sec, and from the viewpoint of suppressing uneven wetting and achieving uniform coating, and from the viewpoint of manufacturing efficiency, it is preferably 0.05 to 1 m/sec.
• the polyfunctional amine solution and the polyfunctional acyl halide solution are preferably injected continuously so as to ensure a predetermined contact time. The contact time is as described above.
• the gas aeration speed is not particularly limited, but is, for example, about 1 to 100 m/sec as a linear velocity. From the viewpoint of preventing defects in the separation functional layer due to poor interfacial polycondensation caused by removal of excess reaction liquid, from the viewpoint of preventing peeling of the formed separation functional layer, and from the viewpoint of production efficiency, it is preferably 2.5 to 70 m/sec, more preferably 10 to 50 m/sec. Aeration is preferably performed continuously for a predetermined period of time, and the aeration time is not particularly limited, but is preferably 5 seconds to 5 minutes, more preferably 20 seconds to 2 minutes.
• the membrane surface After injecting the polyfunctional acyl halide solution, it is preferable to heat-treat and dry the membrane surface in order to promote the interfacial polycondensation reaction, fix the separation functional layer to the dense layer surface, and remove the solvent, etc.
• the heating temperature and heating time are as described above.
• the interfacial polycondensation reaction After the interfacial polycondensation reaction is completed, it is preferable to wash the composite hollow fiber membrane to remove unreacted materials and by-products.
• the washing method and conditions are as described above.
• the tube sections used when injecting the polyfunctional amine solution and the polyfunctional acyl halide solution are cut and removed at the appropriate time, for example, before or after the composite hollow fiber membrane is heat-treated.
• the aliphatic polyamide hollow fiber membrane may be successively immersed in a bath of a polyfunctional amine solution and a polyfunctional acyl halide solution, or a polyfunctional amine solution and a polyfunctional acyl halide solution may be successively applied to the surface of the outer dense layer of an aliphatic polyamide hollow fiber membrane, and if necessary, the liquid may be drained off and excess liquid may be removed by blowing gas, and the process may be repeated.
• These processes may be performed as a batch process of a hollow fiber bundle, or may be performed continuously as a roll-to-roll process. Even when a separation functional layer is formed on the surface of the outer dense layer of an aliphatic polyamide hollow fiber membrane by this method, it is preferable to perform post-treatments such as heat treatment and washing.
• examples of methods for forming a separation functional layer on the surface of the dense layer on the inner lumen side and the outer lumen side of the aliphatic polyamide hollow fiber membrane include a method for forming a separation functional layer on the surface of the dense layer on the inner lumen side of the aliphatic polyamide hollow fiber membrane and a method for forming a separation functional layer on the surface of the dense layer on the outer lumen side of the aliphatic polyamide hollow fiber membrane, in any order or in combination.
• the composite hollow fiber membrane is dried, since this makes it easier to apply the composite hollow fiber membrane to the potting process for fixing the composite hollow fiber membrane to the module. Furthermore, a dried composite hollow fiber membrane is preferable because it can also be used in the air leak test.
• the composite hollow fiber membrane of the present invention can exhibit the desired performance even when it is a dried membrane. Normally, when ultrafiltration membranes and reverse osmosis membranes are dried, the pores shrink or become blocked due to the surface tension caused by the evaporation of water, and permeability is often lost. However, the composite hollow fiber membrane of the present invention can exhibit the desired characteristics even if it is a dry membrane before the processing liquid is passed through it. There are no particular limitations on the drying conditions, but ventilation drying at a temperature of 25 to 100°C is preferable, and more preferably 40 to 70°C is more preferable.
• a composite hollow fiber membrane of the present invention having a separation functional layer on the surface of at least one of the dense layers of the aliphatic polyamide hollow fiber membrane is obtained.
• 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.
• 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.
• the shape of the hollow fiber membrane module is not particularly limited, and may be a dead-end type module or a cross-flow type module.
• examples include a dead-end type module in which a hollow fiber membrane bundle is folded into a U-shape and filled, and the ends of the hollow fiber membrane bundle are sealed and then cut to open; a dead-end type module in which a hollow fiber membrane bundle is filled straight with one end of the hollow fiber membrane bundle closed by heat sealing or the like, 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 filled 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 type module in which a hollow fiber membrane bundle is filled straight, both ends of the hollow fiber membrane bundle are sealed, and the sealed parts at both ends of the hollow fiber membrane bundle are cut to create two flow paths on the side of the filter case.
• the filling rate of the composite hollow fiber membrane inserted into the module case is not particularly limited, but for example, the volume of the composite hollow fiber membrane including the volume of the hollow portion relative to the volume inside the module case is preferably 15 to 75 volume %, more preferably 25 to 65 volume %, and even more preferably 35 to 55 volume %. By satisfying such a filling rate, it is possible to ensure a sufficient filtration area while facilitating the filling of the composite hollow fiber membrane into the module case and allowing the potting agent to flow easily between the composite hollow fiber membranes.
• the potting agent used in the manufacture of the hollow fiber membrane module there are no particular limitations on the potting agent used in the manufacture of the hollow fiber membrane module, but when the hollow fiber membrane module is used to treat organic solvents, it is desirable that the potting agent has organic solvent resistance.
• examples of such potting agents include polyamide, silicone resin, epoxy resin, melamine resin, polyethylene, polypropylene, phenolic resin, polyimide, polyurea resin, etc.
• suitable examples include polyamide, silicone resin, epoxy resin, and polyethylene. These potting agents may be used alone or in combination of two or more types.
• the material of the module case used in the hollow fiber membrane module is not particularly limited as long as it is durable against the solvent used, and in addition to metal materials, examples of polymeric materials include polyamide, polyester, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polysulfone, polyethersulfone, polycarbonate, polyarylate, polyphenylene sulfide, etc.
• polyamide, polyethylene, polypropylene, polytetrafluoroethylene, polycarbonate, polysulfone, polyethersulfone, and more preferably polyamide, polyethylene, polypropylene, and polytetrafluoroethylene are preferred.
• the hollow fiber membrane module using the composite hollow fiber membrane of the present invention is used in ultrafiltration or nanofiltration applications for removing foreign matter from solvents, concentrating useful components in solvents, recovering solvents, etc. in the fields of semiconductor industry, chemical industry, food industry, pharmaceutical industry, medical product industry, etc.
• FIG. 11 is a schematic cross-sectional view of an aliphatic polyamide hollow fiber membrane cut in a direction perpendicular to the longitudinal direction
• FIG. 12 and FIG. 13 are partial enlarged views of the area surrounded by a dotted line in FIG. 11, which are diagrams showing an example of an aliphatic polyamide hollow fiber membrane 8a having a dense layer 10 and a support layer 11. Note that the separation function layer is omitted in FIG.
• FIG. 13 As shown in FIG. 11, a straight line was drawn from the center of the lumen of the aliphatic polyamide hollow fiber membrane 8a to the outer surface, and the straight line was divided into five equal parts from the lumen side surface of the support layer 11 to the outer surface. Then, as shown in FIG. 12, the midpoint of the five equal parts was determined. 13, five locations were photographed at a uniform magnification such that the midpoint was the center of the photographed image, the photographed image included only the support layer 11 portion, and the number of pores was 30 to 300.
• ImageJ The specific operations in ImageJ are as follows: The image to be analyzed is imported into ImageJ, the analysis range is specified, and the luminance value at which the peak of the histogram obtained by the "Analyze>Histogram” operation is the highest is set as the threshold value (i.e., the Lower threshold level is set as the luminance value at which the peak of the histogram is the highest, and the Upper threshold level is set as 255), and the image is binarized by "Image>Adjust>Threshold”. Next, "Area” was checked under “Analyze>Set measurements” and the total area of the analysis range was calculated by the "Analyze>Measure” operation.
• Crystallinity of the aliphatic polyamide hollow fiber membrane was measured by X-ray diffraction (XRD). A plurality of hollow fiber samples were arranged on a measurement stage without gaps, and a scattering pattern spectrum of scattering vector and scattering intensity was obtained by scanning measurement of the scattering angle. The obtained spectrum was separated into crystal-derived components and amorphous-derived components, and the crystallinity was calculated by quantifying them.
• one end of the bundle of aliphatic polyamide hollow fiber membranes prepared as above was heat sealed to prevent the epoxy resin from penetrating into the hollow portion, and the end tip was inserted into the tube filled with the epoxy resin until it touched the rubber stopper, and the epoxy resin was cured in this state.
• the region of the rubber stopper side of the cured epoxy resin part was cut together with the tube to open the hollow portion.
• the same operation was performed on the other end to prepare a crossflow module 6 in which the hollow portions at both ends of the aliphatic polyamide hollow fiber membrane were opened.
• the prepared cross-flow module 6 was connected to the internal pressure separation processing line shown in FIG. 1, and the flowing liquid (raw liquid) was continuously passed through the cross-flow module 6 by the liquid sending circulation pump 2.
• the flowing liquid was an aqueous solution containing 0.5 wt%, 0.5 wt%, 0.2 wt%, 0.2 wt%, or 0.4 wt% of five types of dextran with molecular weights of 5000, 10000, 40000, 70000, or 500000.
• 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 1 bar.
• the flowing liquid passing through the module the one that passed through the pores of the polyamide hollow fiber membrane was collected as a permeated liquid separated from the flowing liquid, and the remainder was circulated again to the separation processing line.
• the module 8 shown in FIG. 2a was prepared. First, 10 aliphatic 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, and a rubber plug with a length of about 20 mm was inserted into one end opening of the tube to plug the one end opening. Next, a two-liquid mixed epoxy resin was injected from the opening of the tube opposite to the rubber plug, and the inner space of the tube was filled with the epoxy resin.
• the bundle of aliphatic polyamide hollow fiber membranes prepared as above was bent into an approximately U-shape, and both ends of the aliphatic polyamide hollow fiber membrane were heat-sealed to seal the holes so that the epoxy resin would not penetrate into the hollow part, and the end tip was inserted into the tube filled with the epoxy resin until it touched the rubber plug, and the epoxy resin was cured in this state.
• the region of the hardened epoxy resin on the rubber plug side was cut together with the tube to produce a module 8 having open hollow portions at both ends of the aliphatic polyamide hollow fiber membrane.
• the module 8 was set in the device shown in FIG. 2b, and water pressure was applied to the module 8 by a hand pump 9, and the pressure (burst pressure, unit: MPa) at which the module 8 broke was measured.
• the membrane area of the module was calculated based on the inner area of the hollow fibers, and the inner diameter, number, and effective length of the hollow fibers.
• One end of the outlet connected to the hollow part of the produced module was sealed, and a valve and a pressure line having a pressure gauge between the valve and the module were attached to one end. Air was pressurized to 0.2 MPa in the hollow part, and the pressure was contained by closing the valve. Immediately after that, the pressure was checked over time, and the change in pressure after 5 minutes was measured.
• the cross-flow module 6 prepared above was connected to the internal pressure separation treatment line shown in FIG. 1, and the flowing liquid was continuously permeated through the cross-flow module 6 by the liquid supply circulation pump 2. NMP was used as the flowing liquid.
• the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 were adjusted by the regulator 5 so that the arithmetic mean value of the pressure of the primary pressure gauge 3 and the pressure of the secondary pressure gauge 4 was 75% of the burst pressure of the composite hollow fiber membrane.
• the one that permeated the pores of the composite hollow fiber membrane was collected as a permeated liquid separated from the flowing liquid, and the remainder was circulated again to the separation treatment line.
• NMP permeation amount volume (L) of NMP permeated to the outside of the composite hollow fiber membrane/[inner diameter (m) of the composite hollow fiber membrane ⁇ 3.14 ⁇ effective filtration length (m) of the composite hollow fiber membrane ⁇ 20 (pieces) ⁇ time (h)]
• Effective filtration length of composite hollow fiber membrane This is the length of the portion of the outer surface of the composite hollow fiber membrane that is not covered with epoxy resin in the crossflow module.
• Test Example 1 350 g of polyamide 6 chips (Unitika Co., Ltd., A1030BRT, relative viscosity 3.53) and 650 g of dimethyl sulfone (Tokyo Chemical Industry Co., Ltd.) were stirred and dissolved at 180 ° C. for 1.5 hours, and the stirring speed was reduced and degassed for 1 hour to prepare a membrane-forming stock solution.
• the membrane-forming stock solution was sent to a spinneret kept at 200 ° C. via a metering pump, and a mixture of 70 wt % polyethylene glycol 300 (PEG300) and 30 wt % glycerin was passed as an internal coagulation liquid.
• the extruded membrane-forming stock solution was poured into a coagulation bath consisting of a 60 wt % 1,4-butylene glycol (1,4BG) aqueous solution at 5 ° C. and cooled and solidified to form an aliphatic polyamide porous membrane.
• the wound aliphatic polyamide porous membrane was immersed in water for 24 hours to perform solvent extraction (washing), and then dried by passing through a hot air dryer (temperature inside the oven: 130° C.) without stretching to obtain an aliphatic polyamide hollow fiber membrane.
• FIG. 3 is an image analysis diagram after binarization processing for calculating the porosity of the support layer of the obtained aliphatic polyamide hollow fiber membrane.
• FIG. 4 is a scanning electron microscope image (magnification: 10,000 times) of the inner surface of the obtained aliphatic polyamide hollow fiber membrane.
• FIG. 5 is a scanning electron microscope image (magnification: 20,000 times) of the inner surface of the obtained aliphatic polyamide hollow fiber membrane.
• FIG. 6 is a scanning electron microscope image (magnification: 10,000 times) of the inner cross section of the obtained aliphatic polyamide hollow fiber membrane.
• a membrane bundle was prepared by arranging the obtained aliphatic polyamide hollow fiber membranes into 20 pieces each having a length of 40 cm.
• a nylon hard tube with an inner diameter of 8 mm and a length of 50 mm was prepared, and a rubber plug having a length of about 20 mm was inserted into one end opening of the tube to plug the one end opening.
• a two-liquid mixed epoxy resin was injected from the opening of the tube opposite to the rubber plugged end to fill the inner space of the tube with the epoxy resin.
• one end of the prepared aliphatic polyamide hollow fiber membrane was heat sealed to seal the opening, and the end tip was inserted into the tube filled with the epoxy resin until it touched the rubber plug, and the epoxy resin was cured in this state.
• the region of the rubber plug side of the cured epoxy resin part was cut together with the tube to open the hollow part of the aliphatic polyamide hollow fiber membrane, and a module for injecting an interfacial polymerization solution was obtained. Water was filled into the resin-fixed open end of the module, and the module was immersed in water for 1 hour to wet the entire membrane.
• the module was then taken out of the water and gently shaken to remove the adhering water, and nitrogen was blown in from the open end to drain all the water remaining in the hollow portion, for wet treatment.
• a PP connector with a three-way cock was then connected to the open end of the module, and a circuit device was connected to inject the interfacial polymerization solution and nitrogen gas for aeration into the hollow fiber membrane.
• an aqueous solution containing 2% by weight of m-phenylenediamine (MPD) was passed through the open end of the module at a linear speed of 0.12 m/sec for 1 minute, then the flow path was switched to an air flow, and nitrogen gas was passed through at a linear speed of 20 m/sec for 1 minute.
• MPD m-phenylenediamine
• trimesic acid chloride TMC
• the module was removed from the circuit device and placed in an oven at 100°C for 5 minutes to dry.
• the dried module was immersed in pure water and washed for 24 hours while exchanging the water several times.
• the washed module was placed in a convection dryer at 50°C to dry it.
• the hollow fiber membrane was cut on the side of the epoxy resin part of the dried module, and 20 composite hollow fiber membrane bundles were obtained.
• FIG. 7 is a scanning electron microscope image (magnification 10,000 times) of the inner cavity side cross section of the obtained composite hollow fiber membrane.
• FIG. 8 is a scanning electron microscope image (magnification 20,000 times) of the inner cavity side cross section of the obtained composite hollow fiber membrane.
• FIG. 9 is a scanning electron microscope image (magnification 10,000 times) of the inner cavity side surface of the obtained composite hollow fiber membrane.
• FIG. 10 is a scanning electron microscope image (magnification 20,000 times) of the inner cavity side surface of the obtained composite hollow fiber membrane.
• Example 2 The following interfacial polymerization was carried out using the aliphatic polyamide hollow fiber membrane prepared in Example 1.
• a module for injecting the interfacial polymerization solution was prepared in the same manner as in Example 1, and the module was subjected to a wetting treatment in the same manner, followed by connection to a circuit device for liquid passage.
• a dimethylformamide solution containing 2% by weight of 3,3',4,4'-tetraaminobiphenyl (TAB) was passed through the open end of the module at a linear speed of 0.12 m/sec for 1 minute, then the flow path was switched to an air flow, and nitrogen gas was passed through at a linear speed of 20 m/sec for 1 minute.
• TAB 3,3',4,4'-tetraaminobiphenyl
• TMC trimesic acid chloride
• Example 1 A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in the preparation of the membrane forming stock solution, 280 g of polyamide 6 chips (A1030BRT, manufactured by Unitika Ltd., relative viscosity 3.53) and 720 g of dimethyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved by stirring at 190° C. for 1.5 hours, and the stirring speed was reduced to degas for 1 hour to prepare the membrane forming stock solution. Table 1 shows the measurement results for each of the above measurements.
• Example 2 A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in the preparation of the membrane forming stock solution, 250 g of polyamide 6 chips (Unitika Ltd., A1030BRT, relative viscosity 3.53) and 750 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 stock solution. Table 1 shows the measurement results for each of the above measurements.
• polyamide 6 chips Unitika Ltd., A1030BRT, relative viscosity 3.53
• dimethyl sulfone Tokyo Chemical Industry Co., Ltd.
• Example 3 A composite hollow fiber membrane was produced in the same manner as in Example 1, except that in the preparation of the membrane forming stock 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 stock solution. Table 1 shows the measurement results for each of the above measurements.
• polyamide 6 chips Unitika Ltd., A1030BRT, relative viscosity 3.53
• dimethyl sulfone Tokyo Chemical Industry Co., Ltd.
• the composite hollow fiber membranes of Examples 1 and 2 have a separation functional layer containing a crosslinked aromatic polyamide resin on the surface of the dense layer of the aliphatic polyamide hollow fiber membrane, and have an NMP burst pressure of 2.25 MPa or more, so that the NMP permeation rate is very high at 6 L/( m2 ⁇ h) or more, and the rejection rate of diphenyl sulfone in the NMP solution is 30% or more, and the rejection rate of polystyrene with a molecular weight of 1000 is 90% or more, so that they have extremely high rejection performance at the nanofiltration level, and can achieve both NMP permeation performance and diphenyl sulfone rejection performance at a high level.
• the composite hollow fiber membranes of Comparative Examples 1 to 4 and the aliphatic polyamide hollow fiber membrane of Comparative Example 5 have a low NMP burst pressure, so that the NMP permeation rate is low and the NMP permeation performance is inferior.
• Reference Signs List 1 Flowing liquid tank 2 Liquid delivery pump 3 Primary pressure gauge 4 Secondary pressure gauge 5 Regulator 6 Cross flow module 7 Receiver 8 Burst pressure evaluation module 8a Aliphatic polyamide hollow fiber membrane 8b Nylon hard tube 9 Hand pump 10 Dense layer 11 Support layer

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