Composite semipermeable membrane

Abstract

One aspect of the present invention is a composite semipermeable membrane comprising a semipermeable membrane layer and a porous support layer, wherein the semipermeable membrane layer is provided with a plurality of flakes that include a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound, the plurality of flakes are in a stacked state such that at least one surface of the support layer is covered by the plurality of flakes, the thickness of the semipermeable membrane layer is 0.1-10 μm, and the fractional particle size of the support layer is 0.1-10 μm.

Description

Technical Field

[0001] The present invention relates to a composite semipermeable membrane.

Background Art

[0002] Membrane separation technology using semipermeable membranes has attracted attention from the viewpoints of energy saving, resource saving, and environmental protection. In this membrane separation technology using semipermeable membranes, for example, membranes having a semipermeable membrane layer having the function of a semipermeable membrane, such as a nanofiltration (NF) membrane, a reverse osmosis (RO) membrane, and a forward osmosis (FO) membrane, are used. Examples of the membrane used in such a membrane separation technology using a semipermeable membrane include a composite semipermeable membrane having not only the semipermeable membrane layer but also a support layer that supports the semipermeable membrane layer. Examples of such a composite semipermeable membrane include the membranes described in Patent Documents 1 to 4.

[0003] Patent Document 1 describes a composite semipermeable membrane including a separation functional layer containing a crosslinked polyamide obtained by interfacial polycondensation performed by bringing an aqueous solution of a polyfunctional amine into contact with an organic solvent solution of a polyfunctional acid halide on a porous support membrane in the presence of a predetermined aliphatic carboxylic acid ester. According to Patent Document 1, it is disclosed that a composite semipermeable membrane having high water permeability that can be operated at a lower operating pressure can be obtained.

[0004] Further, Patent Document 2 describes a forward osmosis membrane including a hydrophilic porous support layer and a first polyamide barrier layer, wherein the support layer and the barrier layer are incorporated into a thin film composite membrane and are adjacent to each other in the thin film composite membrane. According to Patent Document 2, it is disclosed that the performance of forward osmosis and osmotic pressure power generation can be improved.

[0005] In addition, Patent Document 3 discloses a composite semipermeable membrane in which a skin layer is formed on the surface of a porous support. The porous support includes a thermosetting resin porous sheet having pores communicating with a three-dimensional network skeleton, and a composite semipermeable membrane having an average pore diameter of 0.01 to 0.4 μm is described for the thermosetting resin porous sheet. According to Patent Document 3, it is disclosed that a composite semiconductor membrane excellent in chemical resistance and having practical water permeability and salt rejection can be obtained.

[0006] In addition, Patent Document 4 describes a composite semipermeable membrane composed of a microporous support membrane and a crosslinked aromatic polyamide, and a composite semipermeable membrane in which the average surface pore diameter of the microporous support membrane is 30 nm or more and 40 nm or less is described. According to Patent Document 4, it is disclosed that a composite semipermeable membrane having practical desalination and a high permeation flux can be obtained even when an additive for expressing a high permeation flux is not used.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0008] An object of the present invention is to provide a composite semipermeable membrane capable of suitably performing separation by a semipermeable membrane layer.

[0009] One aspect of the present invention provides a composite semipermeable membrane comprising a semipermeable membrane layer and a porous support layer. The semipermeable membrane layer includes a plurality of sheet-like bodies containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The plurality of sheet-like bodies are stacked so as to cover at least one surface of the support layer. The thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less, and the fractional particle diameter of the support layer is 0.1 μm or more and 10 μm or less.

[0010] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0012] In the membrane separation technology using a composite semipermeable membrane comprising a semipermeable membrane layer and a support layer, separation is carried out using a semipermeable membrane layer that allows a solvent such as water to permeate more easily than a solute. That is, when the composite semipermeable membrane is used in the membrane separation technology, the separation is mainly contributed by the semipermeable membrane layer. From this, the present inventors have focused on the fact that the support layer is required not only to suitably support the semipermeable membrane, such as enhancing the strength and durability of the composite semipermeable membrane, but also not to more inhibit the separation by the semipermeable membrane layer.

[0013] In addition, as described above, the composite semipermeable membrane can be used for various applications. Among these, when used as a forward osmosis membrane, since the driving force for membrane separation is the natural osmotic pressure difference, a reduction in energy consumption is expected. Furthermore, it is expected that the membrane separation technology using a forward osmosis membrane will be applied in various fields such as, for example, osmotic pressure power generation technology and concentration technology, and has attracted attention.

[0014] When the composite semipermeable membrane is used, for example, in such a forward osmosis method, that is, when used as a forward osmosis membrane, the present inventors have focused on the following requirements for the composite semipermeable membrane.

[0015] Forward osmosis is a method of separation by allowing a solvent such as water to permeate from a dilute solution with a low solute concentration to a concentrated solution with a high solute concentration, using the osmotic pressure difference resulting from the concentration difference between two solutions with different solute concentrations as the driving force, by bringing the two solutions into contact through a semipermeable membrane. When a composite semipermeable membrane comprising a semipermeable membrane layer and a support layer is used instead of this semipermeable membrane, the osmotic pressure difference as the driving force is not the osmotic pressure difference resulting from the solute concentration difference between the solutions existing across the composite semipermeable membrane, but the osmotic pressure difference resulting from the solute concentration difference between the solutions existing across the semipermeable membrane layer provided in the composite semipermeable membrane. From this, if a solute concentration bias, that is, an internal concentration polarization phenomenon, occurs in the solution existing in the support layer due to reasons such as low fluidity of the solution in the support layer, it is considered that the osmotic pressure difference as the driving force will become smaller. Therefore, the support layer provided in the composite semipermeable membrane is required to enhance the fluidity of the solution in the support layer and to make it difficult for the internal concentration polarization phenomenon to occur. Thus, a composite semipermeable membrane having such a support layer is required not only to preferably support the semipermeable membrane such as enhancing the strength and durability of the composite semipermeable membrane, but also to be able to preferably perform the separation by the semipermeable membrane layer, for example, to be able to sufficiently exhibit high water permeability while maintaining high desalination performance.

[0016] From the above, it is required that the composite semipermeable membrane comprising a semipermeable membrane layer and a support layer can preferably perform the separation by the semipermeable membrane layer by suppressing the inhibition of the separation by the semipermeable membrane layer by the support layer.

[0017] In order to obtain a support layer that is difficult to inhibit the separation by the semipermeable membrane layer, it is conceivable to increase the size of the pores formed inside and on the surface of the support layer so that the solvent such as solute and water can easily pass through the through-holes inside the support layer, for example, so that the internal concentration polarization phenomenon is difficult to occur.

[0018] However, if the pores formed in the support layer, particularly the pores formed on the surface of the support layer in contact with the semipermeable membrane layer, are too large, it has been considered that the support layer cannot be preferably covered with the semipermeable membrane layer and the separation by the semipermeable membrane layer cannot be preferably performed.

[0019] Therefore, as a result of various studies, the inventors of the present invention have found that by enlarging the pores formed in the support layer, it becomes difficult for the support layer to inhibit the separation by the semipermeable membrane layer. Further, even if the pores formed on the surface on the side in contact with the semipermeable membrane layer are of a certain size, by examining the structure of the semipermeable membrane layer and the like, it is possible to suitably perform the separation by the semipermeable membrane layer. That is, as a result of various studies, the inventors of the present invention have found that the above object of providing a composite semipermeable membrane capable of suitably performing the separation by the semipermeable membrane layer is achieved by the following present invention.

[0020] Hereinafter, embodiments according to the present invention will be described, but the present invention is not limited thereto.

[0021] [Composite semipermeable membrane] The composite semipermeable membrane according to an embodiment of the present invention includes a semipermeable membrane layer and a porous support layer. The semipermeable membrane layer includes a plurality of sheet-like bodies containing a crosslinked polyamide obtained by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The plurality of sheet-like bodies are stacked so as to cover at least one surface of the support layer. That is, the semipermeable membrane layer is in a state where the plurality of sheet-like bodies are stacked so as to cover at least one surface of the support layer by the plurality of sheet-like bodies. The thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less. Further, the fractional particle diameter of the support layer is 0.1 μm or more and 10 μm or less.

[0022] Such a composite semipermeable membrane can preferably perform separation by the semipermeable membrane layer. This is considered to be due to the following reasons. First, when the fractional particle diameter of the support layer is 0.1 μm or more, it is possible to sufficiently suppress the support layer from inhibiting the separation by the semipermeable membrane layer. In order to form the semipermeable membrane layer on such a support layer, when a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound is formed on the support layer, a plurality of sheet-like bodies containing the crosslinked polyamide can be formed. And if the fractional particle diameter of the support layer is 10 μm or less, such a plurality of sheet-like bodies can be stacked so that the thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less to form the semipermeable membrane layer. For such a semipermeable membrane layer, the semipermeable membrane layer is preferably in a state of covering at least one surface of the support layer. From these facts, since a suitable semipermeable membrane layer is formed on the support layer where the inhibition of separation by the semipermeable membrane layer is sufficiently suppressed, it is considered that the obtained composite semipermeable membrane can preferably perform separation by the semipermeable membrane layer.

[0023] In the case where the composite semipermeable membrane is used, for example, in the forward osmosis method, by bringing two solutions with different solute concentrations into contact with each other through the composite semipermeable membrane, using the osmotic pressure difference generated from the solute concentration difference as the driving force, water can be preferably permeated from a dilute solution with a low solute concentration to a concentrated solution with a high solute concentration. When the composite semipermeable membrane is used in the forward osmosis method, for example, it can exhibit high water permeation performance while maintaining high desalination performance.

[0024] In the composite semipermeable membrane, the support layer may be a hollow fiber membrane (a hollow fiber-shaped support layer) or a flat membrane (a flat membrane-shaped support layer). That is, whether the support layer is a hollow fiber membrane or a flat membrane, by providing the semipermeable membrane layer on the support layer, it becomes the composite semipermeable membrane, and this composite semipermeable membrane can preferably perform separation by the semipermeable membrane layer. Also, the support layer may be a hollow fiber membrane or a flat membrane, but the hollow fiber membrane is preferable in terms of being able to increase the membrane area compared to the case of using a flat membrane.

[0025] Hereinafter, a composite hollow fiber membrane, which is a composite semipermeable membrane using a hollow fiber membrane as the support layer, will be described as an example.

[0026] [Composite hollow fiber membrane] As shown in FIG. 1, the composite hollow fiber membrane 11 according to an embodiment of the present invention is a hollow fiber-shaped membrane. Further, as shown in FIGS. 2 and 3, the composite hollow fiber membrane 11 includes a hollow fiber-shaped porous support layer 12 and a semipermeable membrane layer 13. Note that FIG. 1 is a partial perspective view showing the composite hollow fiber membrane 11 according to an embodiment of the present invention. FIGS. 2 and 3 are enlarged views of a part A of the composite hollow fiber membrane 11 shown in FIG. 1 and show the layer structure of the composite hollow fiber membrane 11. Note that FIGS. 2 and 3 are schematic views showing the positional relationship between the layers and not particularly showing the relationship between the layer thicknesses.

[0027] As shown in FIGS. 2 and 3, the semipermeable membrane layer 13 includes a plurality of sheet-like bodies 21 containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. And the semipermeable membrane layer 13 is in a state where the plurality of sheet-like bodies 21 are stacked so as to cover at least one surface of the support layer 12 by the plurality of sheet-like bodies 21. The thickness of the semipermeable membrane layer 13 is 0.1 μm or more and 10 μm or less. Also, the fractional particle diameter of the support layer 12 is 0.1 μm or more and 10 μm or less. As described above, such a composite hollow fiber membrane 11 can preferably perform separation by the semipermeable membrane layer, similar to the case of the composite semipermeable membrane described above.

[0028] As shown in FIG. 2, the semipermeable membrane layer 13 of the composite hollow fiber membrane 11 may be provided on the outer peripheral surface of the support layer 12, or as shown in FIG. 3, the semipermeable membrane layer 13 may be provided on the inner peripheral surface of the support layer 12. Further, in the composite hollow fiber membrane 11, the semipermeable membrane layer 13 may be provided on both surfaces of the support layer 12.

[0029] (Semipermeable membrane layer) The semipermeable membrane layer 13 includes a plurality of sheet bodies 21 containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The crosslinked polyamide is composed of a polyfunctional amine compound and a polyfunctional acid halide compound, and may contain other components other than the polyfunctional amine compound and the polyfunctional acid halide compound generated during the polymerization of the polyfunctional amine compound and the polyfunctional acid halide compound.

[0030] The semipermeable membrane layer 13 is in a state where the plurality of sheet bodies 21 are stacked so as to cover at least one surface of the support layer 12 with the plurality of sheet bodies 21. Further, the semipermeable membrane layer 13 may include a crosslinked polyamide that includes the plurality of sheet bodies 21 and does not constitute the sheet bodies 21. The semipermeable membrane layer 13 preferably covers all of at least one surface of the support layer 12, more specifically, the entire region of the support layer 12 that is used for permeation or the like (the region of the support layer 12 corresponding to the region used for permeation or the like in the composite hollow fiber membrane 11). When the semipermeable membrane layer 13 is provided on one surface of the support layer 12, it is preferably provided on the dense surface 14 which is the surface with the smaller pore diameter among the main surfaces of the support layer 12.

[0031] The sheet body 21 is not particularly limited as long as it contains the crosslinked polyamide and can constitute the semipermeable membrane layer 13. Further, the size of the sheet body 21 is not particularly limited as long as a plurality of sheet bodies 21 can be stacked to cover at least one surface of the support layer 12. For example, the area of the sheet body 21 is preferably 0.0001 to 20 μm 2 and more preferably 0.01 to 5 μm 2It is more preferable that it is so. Also, the thickness of the thin sheet body 21 is preferably 0.01 to 1 μm, and more preferably 0.01 to 0.3 μm. If the thin sheet body 21 is too small, the support layer 12 cannot be suitably covered, and the semipermeable membrane layer 13 cannot be suitably formed. Also, although the larger the thin sheet body 21 is, the more preferable it is, when the crosslinked polyamide is formed on the support layer 12, the size of the obtained thin sheet body 21 becomes the size as described above. On the other hand, it is difficult to cover the entire surface of the support layer 12 with one thin sheet body, but a plurality of thin sheet bodies 21 having the size as described above can be stacked to cover at least one surface of the support layer 12.

[0032] The thickness of the semipermeable membrane layer 13 is 0.1 μm or more and 10 μm or less, preferably 0.25 μm or more and 5 μm or less, and more preferably 0.45 μm or more and 2 μm or less. If the semipermeable membrane layer is too thin, there is a tendency that separation by the semipermeable membrane layer cannot be suitably performed. For example, when the composite semipermeable membrane is used as a forward osmosis membrane, sufficient desalination performance cannot be exhibited, and there is a tendency that separation by the semipermeable membrane layer cannot be suitably performed, such as an increase in the salt reverse flow rate. This is considered to be due to the fact that the semipermeable membrane layer is too thin and the function of the semipermeable membrane layer cannot be sufficiently exerted, or even when the plurality of thin sheet bodies 21 are stacked, the semipermeable membrane layer cannot sufficiently cover the support layer. Also, if the semipermeable membrane layer is too thick, the permeability tends to decrease. This is considered to be because the semipermeable membrane layer is too thick and the water permeation resistance becomes high, making it difficult for water to permeate.

[0033] The polyfunctional amine compound is not particularly limited as long as it has two or more amino groups in the molecule. Examples of the polyfunctional amine compound include aromatic polyfunctional amine compounds, aliphatic polyfunctional amine compounds, and alicyclic polyfunctional amine compounds. Examples of the aromatic polyfunctional amine compounds include phenylenediamines such as m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine; triaminobenzenes such as 1,3,5-triaminobenzene and 1,3,4-triaminobenzene; diaminotoluenes such as 2,4-diaminotoluene and 2,6-diaminotoluene; 3,5-diaminobenzoic acid; xylylenediamine; and 2,4-diaminophenol dihydrochloride (amidol). Examples of the aliphatic polyfunctional amine compounds include ethylenediamine, propylenediamine, and tris(2-aminoethyl)amine. Examples of the alicyclic polyfunctional amine compounds include 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, and 4-aminomethylpiperazine. Among these, aromatic polyfunctional amine compounds are preferred, and phenylenediamines are more preferred. Further, as the polyfunctional amine compound, the compounds exemplified above may be used alone or in combination of two or more kinds.

[0034] The polyfunctional acid halide compound (polyfunctional acid halide) is not particularly limited as long as it is a compound in which two or more hydroxyl groups are removed from the acids contained in a polyfunctional organic acid compound having two or more acids such as carboxylic acid in the molecule, and a halogen is bonded to the acid from which the hydroxyl groups are removed. The polyfunctional acid halide compound may have a valence of 2 or more, preferably 3 or more. Examples of the polyfunctional acid halide compound include polyfunctional acid fluorides, polyfunctional acid chlorides, polyfunctional acid bromides, and polyfunctional acid iodides. Among these, polyfunctional acid chlorides (polyfunctional acid chloride compounds) are preferably used because they can be obtained most easily and have high reactivity, but the present invention is not limited thereto. Hereinafter, polyfunctional acid chlorides will be exemplified, but examples of polyfunctional acid halides other than polyfunctional acid chlorides include those obtained by changing the chlorides exemplified below to other halides, and the like.

[0035] Examples of the polyfunctional acid chloride compound include aromatic polyfunctional acid chloride compounds, aliphatic polyfunctional acid chloride compounds, and alicyclic polyfunctional chloride compounds. Examples of the aromatic polyfunctional acid chloride compounds include trimesic acid trichloride, terephthalic acid dichloride, isophthalic acid dichloride, biphenyldicarboxylic acid dichloride, naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid trichloride, and benzenedisulfonic acid dichloride. Examples of the aliphatic polyfunctional acid chloride compounds include propanedicarboxylic acid dichloride, butanedicarboxylic acid dichloride, pentanedicarboxylic acid dichloride, propanetricarboxylic acid trichloride, butanetricarboxylic acid trichloride, pentanetricarboxylic acid trichloride, glutaryl chloride, and adipoyl chloride. Examples of the alicyclic polyfunctional chloride compounds include cyclopropanetricarboxylic acid trichloride, cyclobutanetetracarboxylic acid tetrachloride, cyclopentanetricarboxylic acid trichloride, cyclopentanetetracarboxylic acid tetrachloride, cyclohexanetricarboxylic acid trichloride, tetrahydrofuran tetracarboxylic acid tetrachloride, cyclopentanedicarboxylic acid dichloride, cyclobutanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride. Among these, aromatic polyfunctional acid chloride compounds are preferred, and trimesic acid trichloride is more preferred. Further, as the polyfunctional acid halide compound, the compounds exemplified above may be used alone or in combination of two or more kinds.

[0036] (Support layer) The support layer 12 is not particularly limited as long as it is a porous support layer. In the case of the support layer provided in the composite hollow fiber membrane, it is in the form of a hollow fiber and is porous. And the support layer 12 preferably has an inclined structure in which the pores of the support layer 12 gradually increase from one of the inner peripheral surface and the outer peripheral surface toward the other. As this inclined structure, the inclined structure in which the pores of the support layer 12 gradually increase from the inner peripheral surface toward the outer peripheral surface may be used, or the inclined structure in which the pores gradually increase from the outer peripheral surface toward the inner peripheral surface may be used. Further, the support layer 12 may have an inclined structure in which the pores of the support layer 12 gradually increase from the inner peripheral surface toward the central portion and gradually decrease from the central portion toward the outer peripheral surface.

[0037] When the support layer 12 has the inclined structure, the contact surface 14 with the semipermeable membrane layer 13 is preferably a dense surface which is the surface on the side where the pores of the support layer 12 are small. That is, the semipermeable membrane layer 13 is preferably provided in contact with the dense surface 14 which is the surface on the side where the pores of the support layer 12 are small. For example, when the outer peripheral surface of the support layer 12 is the dense surface 14, as shown in FIG. 2, the semipermeable membrane layer 13 is preferably provided on the outer peripheral surface. Also, when the inner peripheral surface of the support layer 12 is the dense surface 14, as shown in FIG. 3, the semipermeable membrane layer 13 is preferably provided on the inner peripheral surface.

[0038] The fractional particle diameter of the support layer 12 is 0.1 μm or more and 10 μm or less, preferably 0.25 μm or more and 5 μm or less, and more preferably 0.45 μm or more and 2 μm or less. That is, the pores present on the surface 14 (for example, the dense surface 14 of the support layer 12) of the support layer 12 on the semipermeable membrane layer 13 side are preferably pores such that the fractional particle diameter of the support layer 12 is within the above range. In the case of the composite semipermeable membrane (composite hollow fiber membrane) according to the present embodiment, even if the fractional particle diameter of the support layer 12 is relatively large as in the above range, a suitable semipermeable membrane layer is formed on the support layer 12 by stacking the thin sheets. Even so, if the fractional particle diameter of the support layer 12 is too large, the pores present on the surface of the support layer 12 on the semipermeable membrane layer 13 side, for example, the dense surface, become too large, and there is a tendency that a semipermeable membrane cannot be suitably formed on the support layer 12. That is, the entire support layer 12 cannot be covered with the semipermeable membrane layer 13, and there is a tendency that separation by the semipermeable membrane layer cannot be suitably performed. When the composite hollow fiber membrane is used as, for example, a forward osmosis (FO) membrane, there is a tendency that sufficient desalination performance cannot be obtained. On the other hand, if the fractional particle diameter of the support layer 12 is too small, separation by the semipermeable membrane layer can be suitably performed. For example, although desalination performance can be sufficiently exhibited, the permeation flux tends to decrease. Therefore, when the fractional particle diameter of the support layer 12 is within the above range, both separation by the semipermeable membrane layer and permeability can be achieved. The fractional particle diameter refers to the particle diameter of the smallest particle that can block the passage of the support layer. Specifically, for example, the diameter of the particle when the blocking rate (blocking rate by the support layer) by the support layer is 90% can be mentioned.

[0039] The support layer 12 preferably has a pressure resistance strength of 0.3 MPa or more and less than 5 MPa, more preferably 0.3 MPa or more and less than 4 MPa, and even more preferably 0.3 MPa or more and less than 3 MPa. This pressure resistance strength is the lower of the maximum pressure that can maintain the shape of the support layer when pressure is applied from the outside of the support layer and the maximum pressure that can maintain the shape of the support layer when pressure is applied from the inside of the support layer. Here, the maximum pressure that can maintain the shape of the support layer when pressure is applied from the outside of the support layer is, for example, the pressure when pressure is applied from the outside of the support layer until the support layer collapses. Also, the maximum pressure that can maintain the shape of the support layer when pressure is applied from the inside of the support layer is, for example, the pressure when pressure is applied from the inside of the support layer until the support layer ruptures. If the pressure resistance strength is too low, the durability of the composite hollow fiber membrane tends to be insufficient in practical operation using the composite hollow fiber membrane. Although the higher the pressure resistance strength is, the more preferable it is, a pressure resistance strength that is too high may be unnecessary in practice.

[0040] The support layer 12 is preferably hydrophilized by containing a hydrophilic resin. Further, the hydrophilic resin contained in the support layer 12 is preferably crosslinked. Therefore, the support layer 12 preferably contains a crosslinked hydrophilic resin in a hollow fiber-shaped porous substrate. In this case, it is sufficient that at least the crosslinked hydrophilic resin is contained in the dense surface 14, and the crosslinked hydrophilic resin may also be contained in portions of the support layer 12 other than the dense surface 14.

[0041] The hollow fiber-shaped porous base material is not particularly limited as long as it is a base material made of a material capable of forming a hollow fiber membrane. Examples of the components included in the support layer 12 (components constituting the hollow fiber-shaped porous base material) include acrylic resin, polyacrylonitrile, polystyrene, polyamide, polyacetal, polycarbonate, polyphenylene ether, polyphenylene sulfide, polyethylene terephthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyetherimide, polyamideimide, polychloroethylene, polyethylene, polypropylene, crystalline cellulose, polysulfone, polyphenylsulfone, polyethersulfone, acrylonitrile-butadiene-styrene (ABS) resin, and acrylonitrile-styrene (AS) resin. Among these, polyvinylidene fluoride, polysulfone, and polyethersulfone are preferred, and polyvinylidene fluoride and polysulfone are more preferred. These resins are more easily imparted with hydrophilicity by a hydrophilic resin, and it is considered that the support layer containing these resins can be more easily made into a suitable inclined structure. Therefore, the composite hollow fiber membrane provided with a support layer containing these resins can more suitably perform separation by the semipermeable membrane layer, and a composite hollow fiber membrane having more excellent durability can be provided. Further, as the components included in the support layer 12 (components constituting the hollow fiber-shaped porous base material), the resins exemplified above may be used alone or in combination of two or more.

[0042] The hydrophilic resin is not particularly limited as long as it can hydrophilize the support layer 12 by being included in the hollow fiber-shaped porous base material. Examples of the hydrophilic resin include cellulose acetate-based polymers such as cellulose, cellulose acetate, and cellulose triacetate; vinyl alcohol-based polymers such as polyvinyl alcohol and polyethylene vinyl alcohol; polyethylene glycol-based polymers such as polyethylene glycol and polyethylene oxide; acrylic acid-based polymers such as sodium polyacrylate; and polyvinyl pyrrolidone-based polymers such as polyvinyl pyrrolidone. Among these, vinyl alcohol-based polymers and polyvinyl pyrrolidone-based polymers are preferred, and polyvinyl alcohol and polyvinyl pyrrolidone are more preferred. Polyvinyl alcohol and polyvinyl pyrrolidone are considered to be more easily crosslinked and can enhance the adhesiveness with the semipermeable membrane layer. That is, when at least one of polyvinyl alcohol and polyvinyl pyrrolidone is used as the hydrophilic resin used when hydrophilizing the support layer, these resins are easily crosslinked and are considered to easily impart appropriate hydrophilicity to the support layer. And it is considered that the adhesiveness with the semipermeable membrane layer containing the crosslinked polyamide polymer can be enhanced by including the crosslinked hydrophilic resin in the support layer. From these facts, it is considered that the semipermeable membrane layer can be preferably formed on the dense surface of the support layer, and the formed semipermeable membrane layer can be sufficiently prevented from being peeled off from the support layer. From these facts, a composite hollow fiber membrane provided with a support layer containing these resins as hydrophilic resins can perform separation by the semipermeable membrane layer more preferably and can provide a composite hollow fiber membrane with more excellent durability. Further, as the hydrophilic resin, the resins exemplified above may be used alone, or two or more kinds may be used in combination. Further, the hydrophilic resin may contain hydrophilic monomolecules such as glycerin and ethylene glycol, may be these polymers, or may contain these as copolymerization components with the above resins.

[0043] The crosslinking of the hydrophilic resin only needs to crosslink the hydrophilic resin so that the solubility of the hydrophilic resin in water decreases. For example, crosslinking that insolubilizes it so that it does not dissolve in water can be mentioned. As the crosslinking of the hydrophilic resin, when polyvinyl alcohol is used as the hydrophilic resin, for example, an acetalization reaction using formaldehyde or an acetalization reaction using glutaraldehyde can be mentioned. Further, when polyvinylpyrrolidone is used as the hydrophilic resin, for example, a reaction with hydrogen peroxide water can be mentioned. It is considered that if the crosslinking degree of the hydrophilic resin is high, elution of the hydrophilic resin from the composite hollow fiber membrane can be suppressed even when the composite hollow fiber membrane is used for a long period of time. For this reason, it is considered that peeling between the semipermeable membrane layer and the support layer can be suppressed over a long period of time.

[0044] It is more preferable that the entire support layer is hydrophilized because the hydrophilization of the support layer is more suitably performed. For this reason, the semipermeable membrane layer is more suitably formed on the support layer, and a highly durable composite hollow fiber membrane with less peeling between the semipermeable membrane layer and the support layer is obtained.

[0045] Whether or not the support layer is hydrophilized can be determined by performing IR (Infrared Spectroscopy) analysis and X-ray Photoelectron Spectroscopy (XPS) analysis on the support layer. For example, by performing the above analysis on each of the inner peripheral surface, the outer peripheral surface, and the inner surface of the support layer cut out, it can be determined whether or not a hydrophilic resin is present at each position. And if it seems that the hydrophilic resin exists over the whole support layer, it turns out that the whole support layer is hydrophilized. That is, if the presence of the hydrophilic resin can be confirmed on all of the inner peripheral surface, the outer peripheral surface, and the inside of the support layer, it can be seen that the entire support layer is hydrophilized.

[0046] As described above, it is preferable that the entire support layer is hydrophilized, and it is more preferable that the hydrophilic resin is uniformly diffused and dispersed throughout the support layer. The state of diffusion and dispersion of the hydrophilic resin can be confirmed by IR analysis, XPS analysis, etc., as described above. Specifically, the support layer is hydrophilized by containing a crosslinked hydrophilic resin such that the ratio of the oxygen atomic weight to the total atomic weight (abundance ratio of oxygen atoms) in the X-ray photoelectron spectroscopy measurement of the surface on the side contacting the semipermeable membrane layer is 1.2 times or more the ratio in the case where the hydrophilic resin is not contained. It is preferable that the ratio of the abundance ratio of oxygen atoms in the case of containing the hydrophilic resin to the abundance ratio of oxygen atoms in the case of not containing the hydrophilic resin is 1.2 times or more, and more preferably 1.5 to 4 times. Further, the abundance ratio of oxygen atoms is the ratio (atomic %) of the oxygen atomic weight to the total atomic weight calculated from the spectrum obtained by measuring the surface on the side contacting the semipermeable membrane layer of the support layer by XPS. A high abundance ratio of oxygen atoms indicates a high abundance ratio of oxygen (O), and the fact that the abundance ratio of this oxygen atom is increased by 1.2 times or more by the hydrophilization (including the hydrophilic resin) indicates that the hydrophilic resin is suitably contained in the support layer, that is, the support layer is suitably hydrophilized. As described above, by making the support layer (support layer containing the resin composition) contain the hydrophilic resin so that the abundance ratio of oxygen atoms in the support layer becomes 1.2 times that of the support layer in the case where the resin composition is not contained, and hydrophilizing it, a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer can be provided. This is considered to be due to the more suitable semipermeable membrane layer being provided on the support layer. That is, it is considered to be due to the more suitable formation of the semipermeable membrane layer on the support layer.

[0047] Incidentally, the abundance ratio of the oxygen atoms can be measured, for example, as follows. The surface of the support layer on the side in contact with the semipermeable membrane layer is subjected to surface X-ray analysis using an X-ray photoelectron spectrometer. Then, by analyzing the spectrum obtained by this surface X-ray analysis with a predetermined analysis software, the peak area and peak intensity derived from each atom are calculated. And by analyzing the obtained peak area and peak intensity with a predetermined analysis software, the ratio of the oxygen atomic weight to the total atomic weight measured by this XPS is calculated. The X-ray photoelectron spectrometer is not particularly limited as long as it can perform measurement by X-ray photoelectron spectroscopy. For example, a scanning type X-ray photoelectron spectrometer (PHI Quantera SXM manufactured by ULVAC-PHI, Inc.) etc. may be mentioned. The measurement conditions for the surface X-ray analysis are not particularly limited as long as the abundance ratio of the oxygen atoms can be measured. For example, X-ray excitation conditions of 100 μm - 25 W - 15 kV, conditions of the counter cathode Al etc. may be mentioned. Also, the analysis software is not particularly limited as long as it can calculate the abundance ratio of the oxygen atoms. For example, Multipak software (data processing software using MAT_LAB software) etc. may be mentioned.

[0048] The support layer 12 preferably has a water contact angle with respect to the dense surface 14 of 90° or less, more preferably 65° or less, and even more preferably 10 to 65°. If the contact angle is too large, the hydrophilization of the support layer is insufficient, and there is a tendency that the semipermeable membrane layer cannot be suitably formed on the support layer. This is considered to be due to the following reasons. When forming the semipermeable membrane layer, first, an aqueous solution of a polyfunctional amine compound, which is a raw material of the crosslinked polyamide polymer constituting the semipermeable membrane layer, is brought into contact with the dense surface side of the support layer. At this time, if the water contact angle with respect to the dense surface 14 is 90° or less, the aqueous solution of the polyfunctional amine compound sufficiently penetrates into the dense surface side of the support layer. In this state, after bringing an organic solvent of a polyfunctional acid halide compound, which is a raw material of the crosslinked polyamide polymer, into contact with the dense surface side of the support layer and then drying, the polyfunctional amine compound and the polyfunctional acid halide compound undergo interfacial polymerization, and a semipermeable membrane layer containing the crosslinked polyamide polymer is formed so as to contact the dense surface of the support layer. On the other hand, if the water contact angle with respect to the dense surface 14 is too large, the aqueous solution of the polyfunctional amine compound cannot sufficiently penetrate into the dense surface side of the support layer, and there is a tendency that the above interfacial polymerization cannot be suitably carried out. For this reason, there is a tendency that the semipermeable membrane layer cannot be suitably formed on the support layer. Further, when such a water contact angle with respect to the dense surface 14 is too large, even if the semipermeable membrane layer is formed, the semipermeable membrane layer also tends to be easily peeled off from the support layer.

[0049] As described above, the support layer 12 preferably is hydrophilized so that the water contact angle with respect to the dense surface 14 is 90° or less. More preferably, the entire support layer 12 is hydrophilized. For example, when the composite hollow fiber membrane is used for water treatment by the FO method, it is preferable that two aqueous solutions as a feed solution and a driving solution are efficiently brought into contact through the semipermeable membrane layer of the composite hollow fiber membrane used as the FO membrane. For this reason, when the entire support layer is hydrophilized, the feed solution and the driving solution, which are aqueous solutions, efficiently diffuse within the support layer, so-called internal concentration polarization is suppressed, and separation by the semipermeable membrane layer can be more suitably carried out.

[0050] In addition, whether the entire support layer is hydrophilized can also be understood from the water permeability. Specifically, if the transmembrane differential pressure in the wet state is 98 kPa and the permeation rate of pure water at 25°C is equivalent to that in the dry state with a transmembrane differential pressure of 98 kPa and 25°C, it can be understood that the entire support layer is hydrophilized. Specifically, it is preferable that the permeation rate of pure water at a transmembrane differential pressure of 98 kPa and 25°C in the wet state is 0.9 to 2 times that in the dry state with a transmembrane differential pressure of 98 kPa and 25°C.

[0051] Examples of the permeation rate of pure water at a transmembrane differential pressure of 98 kPa and 25°C in the dry state include the permeation rate measured by the following method. First, the support layer (hollow fiber membrane) to be measured is dried. This drying is not particularly limited as long as the support layer can be dried. For example, drying in a forced-air constant-temperature dryer at 60°C for 24 hours or more can be mentioned. One end of the dried support layer is sealed, and using a single hollow fiber membrane module with an effective length of 20 cm, pure water is used as the raw water, and external pressure filtration is performed under the conditions of a filtration pressure of 98 kPa and a temperature of 25°C to measure the water permeation volume per minute. From this measured water permeation volume, it is converted to the water permeation rate (L / m 2 / h: LMH) of pure water.

[0052] Examples of the permeation rate of pure water at a transmembrane differential pressure of 98 kPa and 25°C in the wet state include the permeation rate measured by the following method. First, the support layer (hollow fiber membrane) to be measured is made wet. In the case of the support layer according to this embodiment, the hydrophilic resin contained in the support layer is wetted. This wetting treatment for making it wet is not particularly limited as long as the support layer can be suitably made wet. Specifically, a wetting treatment such as immersing the support layer in a 50% by mass aqueous solution of ethanol for 20 minutes and then washing it with pure water for 20 minutes is performed. Except for using the wet hollow fiber membrane instead of the dry hollow fiber membrane, the permeation rate of pure water at a transmembrane differential pressure of 98 kPa and 25°C is measured by the same method as the above-mentioned measurement method for the permeation rate in the dry state (L / m 2 / hour: LMH).

[0053] Preferably, the support layer 12 has a water permeation rate at a transmembrane differential pressure of 98 kPa of 5000 LMH or more and 100000 LMH or less, more preferably 7000 LMH or more and 90000 LMH or less, and even more preferably 8000 LMH or more and 80000 LMH or less. If the support layer 12 has such a water permeation rate, since the water permeability of the support layer is excellent, the occurrence of the internal concentration polarization phenomenon in the support layer can be further suppressed, and the separation by the semipermeable membrane layer can be more suitably performed.

[0054] Preferably, the average pore diameter (opposite side pore diameter) of the pores formed on the surface of the support layer 12 opposite to the dense surface 14 is 1 to 50 μm, more preferably 1 to 30 μm, and still more preferably 1 to 20 μm. If this average diameter is too small, the degree of increase in the pores of the support layer in the inclined structure of the support layer from one of the inner peripheral surface and the outer peripheral surface to the other is too low, and the permeability tends to be insufficient. Also, if this average diameter is too large, the strength of the support layer tends to be insufficient.

[0055] The manufacturing method of the support layer 12 is not particularly limited as long as a hollow fiber membrane having the above-described configuration can be manufactured. Examples of the manufacturing method of the hollow fiber membrane include a method of manufacturing a porous hollow fiber membrane. As a method of manufacturing such a porous hollow fiber membrane, a method using phase separation is known. Examples of the manufacturing method of the hollow fiber membrane using phase separation include, for example, the nonsolvent induced phase separation method (NIPS method) and the thermally induced phase separation method (TIPS method).

[0056] The NIPS method is a method that causes a phase separation phenomenon by substituting the solvent and non-solvent of a polymer stock solution using the concentration difference between the polymer stock solution and the non-solvent as the driving force, by bringing a uniform polymer stock solution in which the polymer is dissolved in a solvent into contact with a non-solvent that does not dissolve the polymer. In the NIPS method, generally, the pore diameter of the formed pores changes depending on the solvent exchange rate. Specifically, the slower the solvent exchange rate, the more likely the pores are to coarsen. Also, in the production of hollow fiber membranes, the solvent exchange rate is fastest at the contact surface with the non-solvent and becomes slower toward the inside of the membrane. For this reason, a hollow fiber membrane produced by the NIPS method has a dense structure near the contact surface with the non-solvent and has an asymmetric structure in which the pores gradually coarsen toward the inside of the membrane.

[0057] Also, the TIPS method is a method that causes a phase separation phenomenon by dissolving a polymer in a poor solvent that can dissolve the polymer at high temperatures but cannot dissolve it when the temperature decreases, and then cooling the solution. The heat exchange rate is generally faster than the solvent exchange rate in the NIPS method and is difficult to control. Therefore, in the TIPS method, uniform pores are likely to be formed in the membrane thickness direction.

[0058] Also, the method for producing the hollow fiber membrane is not particularly limited as long as the hollow fiber membrane can be produced. Specifically, examples of this production method include the following production methods. This production method includes a step of preparing a membrane-forming stock solution containing a resin and a solvent that constitute the hollow fiber membrane (preparation step), a step of extruding the membrane-forming stock solution into a hollow fiber shape (extrusion step), and a step of coagulating the extruded hollow fiber-shaped membrane-forming stock solution to form a hollow fiber membrane (formation step), and the like.

[0059] (Composite hollow fiber membrane) The composite hollow fiber membrane 11 according to this embodiment is not particularly limited as long as it includes the semipermeable membrane layer 13 and the support layer 12 that supports the semipermeable membrane layer 13. The shape of the composite hollow fiber membrane is not particularly limited. The composite hollow fiber membrane is in the shape of a hollow fiber, with one side in the longitudinal direction open, and the other side may be open or closed. Examples of the shape of the open side of the composite hollow fiber membrane include the shape shown in FIG. 1.

[0060] The outer diameter R1 of the composite hollow fiber membrane is preferably 0.1 to 2 mm, more preferably 0.2 to 1.5 mm, and even more preferably 0.3 to 1.5 mm. If the outer diameter is too small, the inner diameter of the composite hollow fiber membrane may also become too small. In this case, the liquid flow resistance in the hollow part increases, and there is a tendency that a sufficient flow rate cannot be ensured. When the composite hollow fiber membrane is used as a forward osmosis membrane or the like, there is a tendency that the driving solution cannot be flowed at a sufficient flow rate. Also, if the outer diameter is too small, the pressure resistance against the pressure applied to the outside also tends to decrease. Furthermore, if the outer diameter is too small, the membrane thickness of the composite hollow fiber membrane may become too thin. In this case, the strength of the composite hollow fiber membrane tends to be insufficient. That is, there is a tendency that a suitable pressure resistance cannot be realized. Also, if the outer diameter is too large, when constructing a hollow fiber membrane module in which a plurality of composite hollow fiber membranes are housed in a casing, the number of hollow fiber membranes housed in the casing decreases, so the membrane area of the hollow fiber membrane decreases, and as a hollow fiber membrane module, there is a tendency that a sufficient flow rate cannot be ensured practically. If the outer diameter is too large, the pressure resistance against the pressure applied from the inside tends to decrease. Therefore, if the outer diameter of the composite hollow fiber membrane is within the above range, the composite hollow fiber membrane can preferably perform separation by a semipermeable membrane with excellent permeability while having sufficient strength.

[0061] The inner diameter R2 of the composite hollow fiber membrane is preferably 0.05 to 1.5 mm, more preferably 0.1 to 1 mm, and even more preferably 0.2 to 1 mm. If the inner diameter is too small, the liquid flow resistance in the hollow part increases, and there is a tendency that a sufficient flow rate cannot be ensured. When the composite hollow fiber membrane is used as a forward osmosis membrane or the like, there is a tendency that the driving solution cannot be flowed at a sufficient flow rate. Further, if the inner diameter is too small, the outer diameter of the composite hollow fiber membrane may become too small. In this case, the pressure resistance against the pressure applied to the outside tends to decrease. Further, if the inner diameter is too large, the outer diameter of the composite hollow fiber membrane may become too large. In this case, when a hollow fiber membrane module in which a plurality of composite hollow fiber membranes are housed in a housing is configured, the number of hollow fiber membranes housed in the housing is not small, so the membrane area of the hollow fiber membrane decreases, and as a hollow fiber membrane module, there is a tendency that a sufficient flow rate cannot be ensured practically. And, if the inner diameter is too large, the outer diameter of the composite hollow fiber membrane may become too large. In this case, the pressure resistance against the pressure applied from the inside tends to decrease. Further, if the inner diameter is too large, the membrane thickness of the composite hollow fiber membrane may become too thin. In this case, the strength of the composite hollow fiber membrane tends to be insufficient. That is, there is a tendency that a suitable pressure resistance cannot be realized. Therefore, if the inner diameter of the composite hollow fiber membrane is within the above range, separation by a semipermeable membrane with excellent permeability while the composite hollow fiber membrane has sufficient strength can be suitably performed.

[0062] Also, the film thickness T of the composite hollow fiber membrane is preferably 0.02 to 0.3 mm, more preferably 0.05 to 0.3 mm, and even more preferably 0.05 to 0.28 mm. If the film thickness is too thin, the strength of the composite hollow fiber membrane tends to be insufficient. That is, there is a tendency that a suitable pressure resistance cannot be achieved. Also, if the film thickness is too thick, the permeability tends to decrease. Also, if the film thickness is too thick, internal concentration polarization in the support layer is likely to occur, and there is also a tendency to inhibit separation by the semipermeable membrane. That is, when the composite hollow fiber membrane is used as a forward osmosis membrane or the like, the contact resistance between the driving solution and the supply solution increases, so the permeability tends to decrease. Therefore, if the film thickness of the composite hollow fiber membrane is within the above range, the composite hollow fiber membrane has sufficient strength, excellent permeability, and separation by the semipermeable membrane can also be suitably performed.

[0063] The film thickness of the support layer 12 is the difference between the film thickness of the composite hollow fiber membrane and the film thickness of the semipermeable membrane layer 13. Specifically, it is 0.02 to 0.3 mm, more preferably 0.05 to 0.3 mm, and even more preferably 0.05 to 0.25 mm. Note that the film thickness of the support layer is almost the same as the film thickness of the composite hollow fiber membrane because the semipermeable membrane layer is very thin compared to the support layer. If the film thickness is too thin, the strength of the composite hollow fiber membrane tends to be insufficient. That is, there is a tendency that a suitable pressure resistance cannot be achieved. Also, if the film thickness is too thick, the permeability tends to decrease. Also, if the film thickness is too thick, internal concentration polarization in the support layer is likely to occur, and there is also a tendency to inhibit separation by the semipermeable membrane. That is, when the composite hollow fiber membrane is used as a forward osmosis membrane or the like, the contact resistance between the driving solution and the supply solution increases, so the permeability tends to decrease. Therefore, if the film thickness of the composite hollow fiber membrane is within the above range, the composite hollow fiber membrane has sufficient strength, excellent permeability, and separation by the semipermeable membrane can also be suitably performed.

[0064] The composite hollow fiber membrane is applicable to membrane separation technology using a semipermeable membrane. That is, the composite hollow fiber membrane can be used, for example, as an NF membrane, an RO membrane, an FO membrane, etc. Among these, the composite hollow fiber membrane is preferably an FO membrane used in the FO method.

[0065] Generally, if it is an RO membrane, since it exhibits the function of a semipermeable membrane, it can also be used as an FO membrane. However, when a conventional RO membrane is directly used as an FO membrane, it may be affected by internal concentration polarization and may not be able to perform separation by the semipermeable membrane suitably. That is, it is known that the FO method is easily affected by internal concentration polarization in the separation by the FO membrane. For the composite hollow fiber membrane according to this embodiment, as described above, the occurrence of internal concentration polarization can be sufficiently suppressed, so it can also be suitably used as an FO membrane used in the FO method.

[0066] [Method for manufacturing a composite hollow fiber membrane] The method for manufacturing the composite hollow fiber membrane according to this embodiment is not particularly limited as long as the above-mentioned composite hollow fiber membrane can be manufactured. Examples of the manufacturing method include the following. The manufacturing method includes a step of bringing an aqueous solution of the polyfunctional amine compound into contact with the dense surface side of the support layer (first contact step), a step of further bringing an organic solvent solution of the polyfunctional acid halide compound into contact with the dense surface side of the support layer that has been brought into contact with the aqueous solution of the polyfunctional amine compound (second contact step), and a step of drying the support layer that has been brought into contact with the aqueous solution of the polyfunctional amine compound and the organic solvent solution of the polyfunctional acid halide compound (drying step).

[0067] In the first contact step, an aqueous solution of the polyfunctional amine compound is brought into contact with the dense surface side of the support layer. By doing so, the aqueous solution of the polyfunctional amine compound penetrates into the support layer from the dense surface side.

[0068] The aqueous solution of the polyfunctional amine compound preferably has a concentration of the polyfunctional amine compound of 0.1 to 5% by mass, more preferably 0.1 to 3% by mass. If the concentration of the polyfunctional amine compound is too low, a suitable semipermeable membrane layer tends not to be formed, such as pinholes being formed in the formed semipermeable membrane layer. For this reason, the separation by the semipermeable membrane layer tends to be insufficient. Also, if the concentration of the polyfunctional amine compound is too high, the semipermeable membrane layer tends to become too thick. And when the semipermeable membrane layer becomes too thick, the permeability of the obtained composite hollow fiber membrane tends to decrease.

[0069] The aqueous solution of the polyfunctional amine compound is a solution in which the polyfunctional amine compound is dissolved in water, and additives such as salts, surfactants, and polymers may be added as necessary.

[0070] In the second contact step, an organic solvent solution of the polyfunctional acid halide compound is further brought into contact with the dense surface side of the support layer that has been brought into contact with the aqueous solution of the polyfunctional amine compound. By doing so, an interface is formed between the aqueous solution of the polyfunctional amine compound that has penetrated into the dense surface side of the support layer and the organic solvent solution of the polyfunctional acid halide compound. And at this interface, the reaction between the polyfunctional amine compound and the polyfunctional acid halide compound proceeds. That is, interfacial polymerization of the polyfunctional amine compound and the polyfunctional acid halide compound occurs. By this interfacial polymerization, a crosslinked polyamide is formed. When the support layer having a fractional particle diameter of 0.1 μm or more and 10 μm or less is used, even if a crosslinked polyamide is formed by the interfacial polymerization, the entire surface of the support layer cannot be covered with a single crosslinked polyamide membrane, and a plurality of thin sheet bodies containing the crosslinked polyamide are provided, and the support layer can be covered with a layer in a state where the plurality of thin sheet bodies are stacked. This is because the pores present on the surface of the support layer are large, so even if a crosslinked polyamide is formed to cover the support layer, the layer of the crosslinked polyamide will crack, but even if the layer of the crosslinked polyamide cracks, it is considered that a plurality of the thin sheet bodies can be formed by further forming the crosslinked polyamide.

[0071] The organic solvent solution of the polyfunctional acid halide compound preferably has a concentration of the polyfunctional acid halide compound of 0.01 to 5% by mass, more preferably 0.01 to 3% by mass. If the concentration of the polyfunctional acid halide compound is too low, a suitable semipermeable membrane layer tends not to be formed, such as pinholes being formed in the formed semipermeable membrane layer. For this reason, separation by the semipermeable membrane layer, for example, the desalination performance tends to be insufficient. Also, if the concentration of the polyfunctional acid halide compound is too high, the semipermeable membrane layer tends to become too thick. And when the semipermeable membrane layer becomes too thick, the permeability of the obtained composite hollow fiber membrane tends to decrease.

[0072] The organic solvent solution of the polyfunctional acid halide compound is a solution in which the polyfunctional acid halide compound is dissolved in an organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyfunctional acid halide compound and does not dissolve in water. Examples of the organic solvent include alkane-based saturated hydrocarbons such as cyclohexane, heptane, octane, and nonane. Additives such as salts, surfactants, and polymers may be added to the organic solvent as necessary.

[0073] In the drying step, the support layer obtained by bringing the aqueous solution of the polyfunctional amine compound into contact with the organic solvent solution of the polyfunctional acid halide compound is dried. In the second contact step, a crosslinked polyamide obtained by interfacial polymerization by the contact of the aqueous solution of the polyfunctional amine compound and the organic solvent solution of the polyfunctional acid halide compound is formed so as to cover the dense surface of the support layer. By drying this support layer, the formed crosslinked polyamide is dried, and a semipermeable membrane layer containing the crosslinked polyamide is formed.

[0074] For the drying, once the formed crosslinked polyamide polymer is dried, its temperature and the like are not particularly limited. As the drying temperature, for example, it is preferably 50 to 150°C, more preferably 80 to 130°C. If the drying temperature is too low, not only does the drying tend to be insufficient, but the drying time becomes too long and the production efficiency tends to decrease. Also, if the drying temperature is too high, the formed semipermeable membrane layer undergoes thermal degradation, and it tends to be difficult to suitably perform separation by the semipermeable membrane. For example, the desalination performance tends to decrease or the water permeability tends to decrease. Also, as the drying time, for example, it is preferably 1 to 30 minutes, more preferably 1 to 20 minutes. If the drying time is too short, the drying tends to be insufficient. Also, if the drying time is too long, the production efficiency tends to decrease. There is also a tendency for the formed semipermeable membrane layer to undergo thermal degradation, making it difficult to suitably perform separation by the semipermeable membrane. For example, the desalination performance tends to decrease or the water permeability tends to decrease.

[0075] The method for producing the composite hollow fiber membrane is carried out by appropriately adjusting various conditions so that the semipermeable membrane layer (a semipermeable membrane layer in a state where the plurality of thin sheet bodies are stacked so as to cover at least one surface of the support layer) is formed on the support layer. Specifically, it is adjusted by changing the support layer, changing the thickness of the semipermeable membrane layer to be formed, and the like. More specifically, methods such as adjusting the fractional particle diameter of the support layer to be used within a range of, for example, 0.1 μm or more and 10 μm or less, hydrophilizing the support layer so that the abundance ratio of the oxygen atoms in the support layer is within a range of 1.2 times or more with respect to the abundance ratio of the oxygen atoms in the support layer in a state where the hydrophilic resin is not included, and adjusting the contact angle of water with respect to the surface of the support layer (the surface on the side in contact with the semipermeable membrane layer) within a range of, for example, 90° or less can be mentioned. Also, methods such as adjusting the thickness of the semipermeable membrane layer to be formed within a range of, for example, 0.1 μm or more and 10 μm or less can be mentioned. The method for producing the composite hollow fiber membrane is a method capable of forming the semipermeable membrane layer on the support layer by appropriately adjusting various conditions including these.

[0076] According to the manufacturing method as described above, separation by the semipermeable membrane layer can be suitably performed, and furthermore, a composite hollow fiber membrane excellent in durability can be suitably manufactured.

[0077] As described above, this specification discloses various aspects of technology, and the main technologies among them are summarized below.

[0078] One aspect of the present invention includes a semipermeable membrane layer and a porous support layer. The semipermeable membrane layer includes a plurality of sheet-like bodies containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The plurality of sheet-like bodies are stacked so as to cover at least one surface of the support layer. The thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less, and the fractional particle diameter of the support layer is 0.1 μm or more and 10 μm or less. It is a composite semipermeable membrane characterized by this.

[0079] According to such a configuration, it is possible to provide a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer. This is considered to be due to the following.

[0080] First, when the fractional particle diameter of the support layer is 0.1 μm or more, it is possible to sufficiently suppress the support layer from inhibiting the separation by the semipermeable membrane layer. On the other hand, with such a support layer, it was considered that the semipermeable membrane layer could not be suitably formed. That is, it was considered that the semipermeable membrane layer could not be formed so as to cover at least one surface of the support layer. According to the study by the present inventors, in order to form the semipermeable membrane layer, when a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound is formed on the support layer, a plurality of sheet-like bodies containing the crosslinked polyamide can be formed. More specifically, since the pores present on the surface of the support layer are large, even if the crosslinked polyamide is formed so as to cover the support layer, the layer of the crosslinked polyamide cracks. Even if the layer of the crosslinked polyamide cracks, a plurality of the sheet-like bodies can be formed by further forming the crosslinked polyamide. And if the fractional particle diameter of the support layer is 10 μm or less, such a plurality of sheet-like bodies can be stacked in a state where the thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less to form the semipermeable membrane layer. Even if there is only one of the sheet-like bodies and it cannot cover at least one surface of the support layer, by forming a plurality of the sheet-like bodies and stacking the plurality of sheet-like bodies so that the thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less, the at least one surface of the support layer can be covered by the plurality of sheet-like bodies. That is, with such a semipermeable membrane layer, the semipermeable membrane layer is in a state of suitably covering at least one surface of the support layer. From these facts, it is considered that a composite semipermeable membrane capable of suitably performing the separation by the semipermeable membrane layer can be obtained because a suitable semipermeable membrane layer is formed on the support layer in which the inhibition of the separation by the semipermeable membrane layer is sufficiently suppressed.

[0081] Further, in the composite semipermeable membrane, the semipermeable membrane layer is in contact with the support layer, and the support layer is hydrophilized by containing a crosslinked hydrophilic resin so that the ratio of the oxygen atomic weight to the total atomic weight in the X-ray photoelectron spectroscopy measurement of the surface on the side in contact with the semipermeable membrane layer is 1.2 times or more the ratio when the hydrophilic resin is not contained.

[0082] According to such a configuration, a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer can be provided. This is considered to be due to the more suitable semipermeable membrane layer being provided on the support layer. That is, it is considered to be due to the semipermeable membrane layer being more suitably formed on the support layer.

[0083] Further, in the composite semipermeable membrane, it is preferable that the support layer contains at least one of polyvinylidene fluoride and polysulfone.

[0084] According to such a configuration, separation by the semipermeable membrane layer can be suitably performed, and a composite semipermeable membrane excellent in durability and the like can be provided.

[0085] Further, in the composite semipermeable membrane, it is preferable that it is a forward osmosis membrane used in the forward osmosis method.

[0086] According to such a configuration, it can be suitably used as a forward osmosis membrane used in the forward osmosis method.

[0087] It is known that in the forward osmosis method, separation by the forward osmosis membrane is easily affected by the internal concentration polarization phenomenon. For such a composite semipermeable membrane, the occurrence of the internal concentration polarization phenomenon can be sufficiently suppressed, so it can be suitably used as a forward osmosis membrane used in the forward osmosis method. When the composite semipermeable membrane is used in the forward osmosis method, for example, it can exhibit high water permeation performance while maintaining high desalination performance.

[0088] Further, in the composite semipermeable membrane, it is preferable that the support layer is a hollow fiber membrane or a flat membrane.

[0089] According to such a configuration, a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer can be provided, and a composite semipermeable membrane in the form of a hollow fiber membrane or a flat membrane can be provided. That is, for the composite semipermeable membrane, whether the support layer is a hollow fiber membrane or a flat membrane, by providing the semipermeable membrane layer on the support layer, separation by the semipermeable membrane layer can be suitably performed.

[0090] According to the present invention, a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer can be provided.

[0091] Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited thereto.

Examples

[0092] [Example 1] (Production of support layer) As the support layer of the composite semipermeable membrane (composite hollow fiber membrane), a hollow fiber membrane obtained by the following method was used.

[0093] First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polyvinylidene fluoride (PVDF: SOLEF6010 manufactured by Solvay Specialty Polymers Japan Co., Ltd.), which is a vinylidene fluoride-based resin, as the solvent, γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation), as the inorganic particles, silica (Fine Seal X-45 manufactured by Tokuyama Corporation), and as the aggregating agent, glycerin (purified glycerin manufactured by Kao Corporation) were mixed so that the weight ratio was 36:47:18:19. By dissolving this mixture, a membrane-forming stock solution was obtained. The materials of this membrane-forming stock solution (membrane material and the hydrophilic resin described later) are shown in Table 1.

[0094] The obtained film-forming stock solution was heat-kneaded in a twin-screw kneading extruder (temperature: 150°C), and extruded using an extruder (150°C) equipped with a nozzle having a double-ring structure with an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At this time, as the hydrophilic resin, a solution composed of polyvinyl alcohol (PVA, PVA-205 manufactured by Kuraray Co., Ltd., average degree of polymerization: 500, saponification degree: 87 to 89 mol%), dimethylacetamide (DMAc manufactured by Mitsubishi Gas Chemical Company, Inc.), and glycerin (purified glycerin manufactured by Kao Corporation) in a weight ratio of 2:58.8:39.2 was used as the internal coagulation liquid containing the hydrophilic resin, and was injected into the hollow part of the extrudate. Together with this internal coagulation liquid, the film-forming stock solution was discharged.

[0095] The film-forming stock solution extruded together with this internal coagulation liquid (the extrusion molding product extruded from the spinneret into the air) passed through an air travel distance of 3 cm and was put into an external coagulation liquid composed of a 20 wt% aqueous sodium sulfate solution (temperature: 60°C), and passed through a water bath of about 100 cm to be cooled and solidified. Next, in a state where most of the solvent, flocculant, and inorganic particles remained in the hollow fiber-like material, after stretching treatment in hot water at 90°C so as to be about 1.5 times the original length in the fiber direction, the obtained hollow fiber-like material was heat-treated in flowing water at 95°C for 180 minutes, and the solvent (γ-butyrolactone), flocculant (glycerin), internal coagulation liquid (dimethylacetamide, glycerin), and excess polyvinyl alcohol were extracted and removed. At this time, the extraction removal rate of polyvinyl alcohol was 70%. 30% of polyvinyl alcohol remained in the hollow fiber-like material, and a hollow fiber membrane containing polyvinyl alcohol could be formed. Then, polyvinyl alcohol was acetalized to make it insoluble. Subsequently, it was immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica), and dried to obtain hollow fibers.

[0096] (Fractionation particle size) Next, the fractionation particle size (= pore size) of the obtained hollow fiber membrane (support layer) was measured by the following method.

[0097] The rejection rates of at least two types of particles having different particle sizes were measured, and based on the measured values, in the following approximate formula, the value of S at which R becomes 90 was obtained, and this was taken as the fractionation particle size.

[0098] R = 100 / (1 - m×exp(-a×log(S))) In the above formula, a and m are constants determined by the hollow fiber membrane, and are calculated based on the measured values of two or more rejection rates.

[0099] The fraction particle size obtained by the above measurement method was 2.0 μm.

[0100] This support layer had a dense outer peripheral surface and had a gradient structure in which the internal pores gradually became larger from this dense surface toward the inner peripheral surface. The presence of this gradient structure was also found from observations with a scanning electron microscope.

[0101] Specifically, the inner peripheral surface and the outer peripheral surface of the support layer were observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). From the obtained images, it was found that the support layer was a hollow fiber membrane having a gradient structure in which the pores present on the outer peripheral surface were smaller than the pores present on the inner peripheral surface.

[0102] As a composite semipermeable membrane, a layer containing crosslinked polyamide described below was used as the semipermeable membrane layer, the above hollow fiber membrane was used as the support layer, and a composite hollow fiber membrane with an outer diameter of 1000 μm and an inner diameter of 600 μm, having the semipermeable membrane layer on the outer peripheral surface side and the support layer on the inner peripheral surface side, was prepared.

[0103] (Oxygen atom abundance ratio) First, the surface of the obtained hollow fiber membrane (support layer) on the side where the semipermeable membrane layer described later is to be formed was subjected to surface X-ray analysis using a scanning X-ray photoelectron spectrometer (PHI Quantera SXM manufactured by ULVAC-PHI, Inc.) under the X-ray excitation conditions of 100 μm - 25 W - 15 kV and with a counter cathode Al. Then, the spectrum obtained by this surface X-ray analysis was analyzed using Multipak software (data processing software utilizing MAT_LAB software) to calculate the peak area and peak intensity derived from each atom. And by analyzing the obtained peak area and peak intensity using the Multipak software (data processing software utilizing MAT_LAB software), the ratio of the oxygen atomic weight to the total atomic weight measured by this XPS [abundance ratio of oxygen atoms (atomic %)] was calculated.

[0104] On the other hand, except for not using the hydrophilic resin, a hollow fiber membrane without the hydrophilic resin was produced in the same manner as the hollow fiber membrane. The abundance ratio of oxygen atoms (atomic %) of the hollow fiber membrane without the hydrophilic resin was calculated.

[0105] And the ratio of the abundance ratio of oxygen atoms (atomic %) of the support layer used in this example to the abundance ratio of oxygen atoms (atomic %) of the hollow fiber membrane without the hydrophilic resin (abundance ratio of oxygen atoms) was calculated. As a result, the abundance ratio of oxygen atoms was 1.25.

[0106] (Fabrication of semipermeable membrane layer) A semipermeable membrane layer was formed on the outer peripheral surface side of the support layer.

[0107] Specifically, first, the support layer was immersed in a 50% by mass aqueous ethanol solution for 20 minutes, and then washed with pure water for 20 minutes to perform a wetting treatment. The wetted support layer after this wetting treatment was fixed to a frame so as not to come into contact with other support layers. Then, the support layer was immersed in a 2% by mass aqueous solution of m-phenylenediamine, which is an aromatic polyfunctional amine compound, for 2 minutes so that the 2% by mass aqueous solution of m-phenylenediamine contacted the outer peripheral surface side of the support layer. By doing so, the 2% by mass aqueous solution of m-phenylenediamine was infiltrated from the outer peripheral surface (dense surface) side of the support layer. Then, the excess 2% by mass aqueous solution of m-phenylenediamine that did not infiltrate into the support layer was removed.

[0108] Then, the support layer was immersed in a 0.2% by mass hexane solution of trimesic acid chloride, which is an aromatic acid halide compound, for 1 minute so that the 0.2% by mass hexane solution of trimesic acid chloride contacted the outer peripheral surface side of the support layer. By doing so, an interface was formed between the aqueous m-phenylenediamine solution infiltrated into the outer peripheral surface side of the support layer and the hexane solution of trimesic acid chloride. At this interface, interfacial polymerization between m-phenylenediamine and trimesic acid chloride proceeded, and a crosslinked polyamide was formed.

[0109] After that, the support layer on which the crosslinked polyamide was formed was dried in a dryer at 120 °C. By doing so, a semipermeable membrane layer was formed on the outer peripheral surface side of the support layer so as to be in contact therewith. When the vicinity of the outer peripheral surface in the cross section of this semipermeable membrane layer was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.), as shown in FIG. 4, this semipermeable membrane layer included a plurality of thin sheet bodies containing the crosslinked polyamide, and the plurality of thin sheet bodies were stacked so as to cover at least one surface of the support layer. Note that FIG. 4 is a diagram showing a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the composite semipermeable membrane (composite hollow fiber membrane) according to Example 1.

[0110] (Measurement of the thickness of the semipermeable membrane layer) For any three points in the longitudinal direction of the composite hollow fiber membrane (composite semipermeable membrane), cross-sections perpendicular to the longitudinal direction were photographed at 5000 times magnification using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.), and the thicknesses of the semipermeable membrane layers at any two points in each cross-section were measured. The thickness of the semipermeable membrane layer was measured from the surface of the support layer to the semipermeable membrane layer farthest from the surface of the support layer, and was taken as the sum of the laminated semipermeable membrane layers. The thickness of the semipermeable membrane layer measured by this measurement was 1.20 μm. Incidentally, the thickness of the support layer was 200 μm. Also, the membrane thickness of the composite semipermeable membrane and the membrane thickness of the support layer were almost the same. This is because the semipermeable membrane layer is very thin compared to the support layer, and its thickness is within the error range.

[0111] [Evaluation] The obtained composite hollow fiber membrane was used in the forward osmosis (FO) method to measure the water permeation performance and desalination performance.

[0112] (Water permeation performance) Specifically, through the obtained composite hollow fiber membrane, a 0.6 M aqueous NaCl solution as a simulated driving solution (simulated DS) and ion-exchanged water as a simulated feed solution (simulated FS) were arranged for filtration. At that time, the simulated FS was arranged on the semipermeable membrane layer side of the composite hollow fiber membrane, and the simulated DS was arranged on the support layer side of the composite hollow fiber membrane. The water permeation amount from the simulated FS to the simulated DS was calculated from the respective weight changes of the simulated FS and the simulated DS. Then, from this calculated water permeation amount, it was converted to the water permeation amount per unit membrane area, per unit time, and per unit pressure to obtain the pure water permeation rate (L / m 2 / h: LMH). This permeation rate was evaluated as the water permeation performance.

[0113] (Desalination performance) Also, the change in the salt concentration of the simulated FS was measured. From this change in the salt concentration, the salt backflow rate (g / m 2 / h: gMH) was obtained. Then, the desalination rate (%) was calculated from the following formula. Incidentally, the desalination performance can be evaluated from this desalination rate.

[0114] R s =[1 - J s / (J w ×CD )]×100 In the above formula, R s represents the desalination rate (%), J s represents the salt countercurrent velocity (gMH), J w represents the water permeation rate (LMH), C D represents the salt concentration of DS (g / L) [in this case, the NaCl concentration of the simulated DS is (0.6M), which is approximately 35 g / L.].

[0115] These results are shown in Table 1.

[0116] [Example 2] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1, except that a hollow fiber membrane (a polysulfone hollow fiber membrane with a fractional particle size of 2.0 μm) obtained by the following method was used as the support layer.

[0117] (Preparation of the support layer) First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polysulfone (PSF: Ultrason S3010 manufactured by BASF Japan Ltd.), as the solvent, dimethylacetamide (DMAc manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the inorganic particles, silica (Fine Seal X-30 manufactured by Tokuyama Corporation), and as the additive, ethylene glycol (manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used to prepare a mixture so that the mass ratio was 20:54:20:6. This mixture was dissolved in a dissolution tank at a constant temperature of 50 °C to obtain a membrane-forming stock solution. The obtained membrane-forming stock solution at 50 °C was extruded into a hollow shape. At this time, a solution prepared by adjusting dimethylformamide (DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the hydrophilic resin, polyvinyl alcohol (PVA: PVA-205 manufactured by Kuraray Co., Ltd., average degree of polymerization: 500, saponification degree 87 to 89 mol%), and water so that the mass ratio was 78:1:21 was used as the internal coagulation liquid containing the hydrophilic resin and was injected into the hollow part of the extrudate, and the membrane-forming stock solution was discharged together with this internal coagulation liquid.

[0118] The membrane-forming stock solution extruded together with this internal coagulating liquid was immersed in water at 50°C as the external coagulating liquid after passing through an air travel distance of 8 cm. By doing so, the membrane-forming stock solution was solidified, and a hollow fiber membrane was obtained. The resulting hollow fiber was washed with hot water to remove the solvent, coagulant, and excess polyvinyl alcohol. Subsequently, the polyvinyl alcohol was acetalized to make it insoluble, and then it was immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica), and dried to obtain a hollow fiber.

[0119] When the fractionation particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 2.0 μm.

[0120] The composite semipermeable membrane (composite hollow fiber membrane) according to Example 2 was produced by the same method as in Example 1 except that this hollow fiber membrane was used as the support layer. The vicinity of the outer peripheral surface in the cross section of the semipermeable membrane layer provided in the obtained composite semipermeable membrane (composite hollow fiber membrane) was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). This semipermeable membrane layer included a plurality of thin sheet bodies containing the crosslinked polyamide, and the plurality of thin sheet bodies were stacked so as to cover at least one surface of the support layer. Then, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0121] [Example 3] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1 except that a hollow fiber membrane (a polysulfone hollow fiber membrane with a fractionation particle diameter of 0.85 μm) obtained by the following method was used as the support layer.

[0122] (Preparation of the support layer) First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polysulfone (PSF: Ultrason S3010 manufactured by BASF Japan Ltd.), as the solvent, dimethylformamide (DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the inorganic particles, silica (Fine Seal F-80 manufactured by Tokuyama Corporation), and as the additive, ethylene glycol (manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used to prepare a mixture so that the mass ratio was 20:64:12:4. By dissolving this mixture in a dissolution tank at a constant temperature of 60°C, a membrane-forming stock solution was obtained. The obtained membrane-forming stock solution at 40°C was extruded in a hollow shape. At this time, dimethylformamide (DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the hydrophilic resin, polyvinyl alcohol (PVA: PVA-205 manufactured by Kuraray Co., Ltd., average degree of polymerization: 500, saponification degree 87 to 89 mol%), and water were adjusted to a solution with a mass ratio of 80:1:19 and injected into the hollow part of the extrudate as the internal coagulation liquid containing the hydrophilic resin, and together with this internal coagulation liquid, the membrane-forming stock solution was discharged.

[0123] The membrane-forming stock solution extruded together with this internal coagulation liquid passed through an air travel distance of 8 cm and was immersed in water at 50°C as the external coagulation liquid. By doing so, the membrane-forming stock solution was solidified and a hollow fiber membrane was obtained. The obtained hollow fiber was washed with hot water to remove the solvent, coagulant, and excess polyvinyl alcohol. Then, polyvinyl alcohol was acetalized to make it insoluble, and subsequently, it was immersed in an aqueous sodium hydroxide solution to extract and remove the inorganic particles (silica), and dried to obtain a hollow fiber.

[0124] When the fractionation particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 0.85 μm.

[0125] The composite semipermeable membrane (composite hollow fiber membrane) according to Example 3 was produced in the same manner as in Example 1, except that this hollow fiber membrane was used as the support layer. The vicinity of the outer peripheral surface in the cross section of the semipermeable membrane layer provided in the obtained composite semipermeable membrane (composite hollow fiber membrane) was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). This semipermeable membrane layer included a plurality of thin sheet bodies containing the crosslinked polyamide, and the plurality of thin sheet bodies were stacked so as to cover at least one surface of the support layer. Then, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0126] [Example 4] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1, except that a hollow fiber membrane (polysulfone hollow fiber membrane with a fractional particle size of 0.45 μm) obtained by the following method was used as the support layer.

[0127] (Production of the support layer) First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polysulfone (Ultrason S3010 manufactured by BASF Japan Ltd.), as the solvent, dimethylformamide (DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the inorganic particles, silica (Fine Seal B manufactured by Tokuyama Corporation), and as the additive, water were mixed to prepare a mixture so that the mass ratio was 20:64:15:1. The mixture was dissolved in a dissolution tank at a constant temperature of 60 °C to obtain a membrane-forming stock solution. The obtained membrane-forming stock solution at 45 °C was extruded in a hollow shape. At this time, a solution adjusted so that the mass ratio of dimethylformamide (DMF: manufactured by Mitsubishi Gas Chemical Co., Ltd.), as the hydrophilic resin, polyvinyl alcohol (PVA-205, average degree of polymerization: 500, saponification degree 87 to 89 mol%, manufactured by Kuraray Co., Ltd.), and water was 80:3:17 was used as the internal coagulation liquid containing the hydrophilic resin and was injected into the hollow portion of the extrudate, and the membrane-forming stock solution was discharged together with this internal coagulation liquid.

[0128] The film-forming stock solution extruded together with this internal coagulant was immersed in water at 40 °C as an external coagulant after traveling a distance of 4 cm in the air. By doing so, the film-forming stock solution was solidified, and a hollow fiber membrane was obtained. The obtained hollow fiber was washed with hot water to remove the solvent, the aggregating agent, and the excess polyvinyl alcohol. Subsequently, the polyvinyl alcohol was acetalized to make it insoluble, and then it was immersed in an aqueous sodium hydroxide solution to extract and remove the inorganic particles (silica), and dried to obtain a hollow fiber.

[0129] The fractionation particle diameter of the obtained hollow fiber membrane was 0.45 μm as measured by the above measurement method.

[0130] The composite semipermeable membrane (composite hollow fiber membrane) according to Example 4 was produced in the same manner as in Example 1, except that this hollow fiber membrane was used as the support layer. The vicinity of the outer peripheral surface in the cross section of the semipermeable membrane layer provided in the obtained composite semipermeable membrane (composite hollow fiber membrane) was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). This semipermeable membrane layer included a plurality of thin sheet bodies containing the crosslinked polyamide, and the plurality of thin sheet bodies were stacked so as to cover at least one surface of the support layer. Then, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0131] [Comparative Example 1] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1, except that a hollow fiber membrane (a polyvinylidene fluoride hollow fiber membrane with a fractionation particle diameter of 0.02 μm) obtained by the following method was used as the support layer.

[0132] First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polyvinylidene fluoride (PVDF: SOLEF 6010 manufactured by Solvay Specialty Polymers Japan Co., Ltd.), which is a polyvinylidene fluoride-based resin, γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation) as a solvent, silica (Aerosil 50 manufactured by Nippon Aerosil Co., Ltd.) as inorganic particles, and polyethylene glycol (PEG200 manufactured by Sanyo Chemical Industries, Ltd.) as a flocculant were mixed so that the weight ratio was 34:21:25:20.

[0133] The obtained mixture was supplied to a twin-screw extruder and heat-kneaded (at a temperature of 155°C) in the twin-screw extruder to obtain a membrane-forming stock solution (spinning stock solution), which was extruded from a nozzle with a double-ring structure having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At this time, as the hydrophilic resin, a solution composed of polyvinyl alcohol (PVA: PVA-205 manufactured by Kuraray Co., Ltd., average degree of polymerization: 500, saponification degree 87 to 89 mol%), dimethylacetamide (DMAc manufactured by Mitsubishi Gas Chemical Company, Inc.), and glycerin (purified glycerin manufactured by Kao Corporation) in a weight ratio of 2:58.8:39.2 was used as an internal coagulation liquid containing the hydrophilic resin and was injected into the hollow part of the extrudate, and the membrane-forming stock solution at 155°C was discharged together with this internal coagulation liquid.

[0134] The membrane-forming stock solution extruded together with this internal coagulation liquid passed through an air travel distance of 3 cm and was put into an external coagulation bath (temperature 80°C) composed of a 20 wt% aqueous sodium sulfate solution, cooled and solidified, and then centrifuged. The obtained hollow fiber was washed with hot water to extract and remove the solvent (γ-butyrolactone), flocculant (PEG200), injection liquid (DMAc, glycerin), and excess polyvinyl alcohol. At this time, the extraction removal rate of polyvinyl alcohol was 70%. 30% of polyvinyl alcohol remained in the hollow fiber-like material, and a hollow fiber membrane containing polyvinyl alcohol could be formed. Then, polyvinyl alcohol was acetalized to make it insoluble. Subsequently, it was immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica) and dried to obtain hollow fibers.

[0135] The fractional particle diameter of the obtained hollow fiber membrane was 0.02 μm as measured by the above measurement method.

[0136] The composite semipermeable membrane (composite hollow fiber membrane) according to Comparative Example 1 was produced by the same method as in Example 1 except that this hollow fiber membrane was used as the support layer. The vicinity of the outer peripheral surface in the cross section of the semipermeable membrane layer provided in the obtained composite semipermeable membrane (composite hollow fiber membrane) was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). As shown in FIG. 5, this semipermeable membrane layer included a plurality of thin sheet bodies containing the crosslinked polyamide, and the plurality of thin sheet bodies did not overlap so as to cover at least one surface of the support layer. Note that FIG. 5 is a diagram showing a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the composite semipermeable membrane (composite hollow fiber membrane) according to Comparative Example 1. Then, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0137] [Comparative Example 2] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1, except that a hollow fiber membrane (a polysulfone hollow fiber membrane having a fractional particle diameter of 0.02 μm) obtained by the following method was used as the support layer.

[0138] First, as the resin (membrane material) constituting the hollow fiber membrane (support layer), polysulfone (PSF: Ultrason S3010 manufactured by BASF Japan Ltd.), as the solvent, dimethylformamide (DMF: DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), and as the additive, polyethylene glycol (PEG-600 manufactured by Sanyo Chemical Industries, Ltd.) were used to prepare a mixture so that the mass ratio was 20:44:36. By dissolving this mixture in a dissolution tank at a constant temperature of 25°C, a casting solution was obtained. The obtained casting solution at 25°C was extruded in a hollow shape. At this time, dimethylformamide (DMF: DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.), polyvinyl alcohol (PVA: PVA-205 manufactured by Kuraray Co., Ltd., average degree of polymerization: 500, saponification degree 87 to 89 mol%) as a hydrophilic resin, and water were adjusted to a solution with a mass ratio of 85:2:13 and injected into the hollow part of the extrudate as an internal coagulation liquid containing the hydrophilic resin, and the casting solution was discharged together with this internal coagulation liquid.

[0139] The casting solution extruded together with this internal coagulation liquid was immersed in water at 60°C as an external coagulation liquid after passing through an air travel distance of 5 cm. By doing so, the casting solution was solidified and a hollow fiber membrane was obtained. The obtained hollow fiber was washed with hot water to remove the solvent, aggregating agent, and excessive polyvinyl alcohol. Then, polyvinyl alcohol was acetalized to make it insoluble and dried to obtain a hollow fiber.

[0140] When the fractional particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 0.02 μm.

[0141] The composite semipermeable membrane (composite hollow fiber membrane) according to Comparative Example 2 was produced by the same method as in Example 1, except that this hollow fiber membrane was used as the support layer. The vicinity of the outer peripheral surface in the cross section of the semipermeable membrane layer provided in the obtained composite semipermeable membrane (composite hollow fiber membrane) was observed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). This semipermeable membrane layer included a plurality of sheet-like bodies containing the crosslinked polyamide, and the plurality of sheet-like bodies were not stacked so as to cover at least one surface of the support layer. Then, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0142] [Comparative Example 3] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1, except that a hollow fiber membrane produced in the same manner as in Example 1 was used, except that the internal coagulation liquid did not contain a hydrophilic resin as the support layer.

[0143] As a result, in Comparative Example 3, the semipermeable membrane layer was not suitably formed on the support layer. Therefore, in Table 1, the column for the thickness of the semipermeable membrane layer is indicated as "-". Further, since the semipermeable membrane layer was not suitably formed in the membrane obtained in Comparative Example 3, the above evaluation could not be suitably performed, and the evaluation in Table 1 is indicated as "-".

[0144] [Comparative Example 4] A composite semipermeable membrane (composite hollow fiber membrane) was produced in the same manner as in Example 1 (Example 2), except that a hollow fiber membrane produced in the same manner as in Example 2 was used, except that the internal coagulation liquid did not contain a hydrophilic resin as the support layer.

[0145] As a result, in Comparative Example 4, the semipermeable membrane layer was not suitably formed on the support layer. Therefore, in Table 1, the column for the thickness of the semipermeable membrane layer is indicated as "-". Further, since the semipermeable membrane layer was not suitably formed in the membrane obtained in Comparative Example 4, the above evaluation could not be suitably performed, and the evaluation in Table 1 is indicated as "-".

[0146]

Table 1

[0147] As can be seen from the above description such as Table 1, by forming a semipermeable membrane layer on a support layer having a fractional particle diameter of 0.1 μm or more and 10 μm or less so that the thickness is 0.1 μm or more and 10 μm or less, like the composite semipermeable membranes (composite hollow fiber membranes) according to Examples 1 to 4, a plurality of sheet-like bodies containing a crosslinked polyamide obtained by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound are provided, and by the plurality of sheet-like bodies, a semipermeable membrane layer in a state where the plurality of sheet-like bodies are stacked is formed so as to cover at least one surface of the support layer, and it was found that a composite semipermeable membrane (composite hollow fiber membrane) can be obtained. And the composite semipermeable membranes (composite hollow fiber membranes) according to Examples 1 to 4 were excellent in water permeation performance and desalination performance. Specifically, the composite semipermeable membranes (composite hollow fiber membranes) according to Examples 1 to 4 were excellent in water permeation performance and desalination performance, and particularly excellent in water permeation performance, even when compared with the case where a support layer having a small fractional particle diameter was used (Comparative Examples 1 and 2). Also, when not containing a hydrophilic resin (Comparative Examples 3 and 4), although the fractional particle diameter of the support layer was about the same as that in Examples 1 and 2, a suitable semipermeable membrane layer could not be formed.

[0148] From the above, it can be seen that a composite semipermeable membrane in which a semipermeable membrane layer is formed on a support layer having a fractional particle diameter of 0.1 μm or more and 10 μm or less so that the thickness is 0.1 μm or more and 10 μm or less, and a semipermeable membrane layer in a state where the plurality of sheet-like bodies containing the crosslinked polyamide are stacked so as to cover at least one surface of the support layer is excellent in water permeation performance and desalination performance, and can suitably perform separation by the semipermeable membrane layer.

[0149] This application is based on Japanese Patent Application No. 2020-148357 filed on September 3, 2020, the content of which is incorporated herein.

[0150] In order to represent the present invention, the present invention has been appropriately and sufficiently described through the embodiments above. However, those skilled in the art should recognize that it is easy to make changes and / or improvements to the above embodiments. Therefore, as long as the changes or improvements made by those skilled in the art do not depart from the scope of the claims described in the claims, the changes or the improvements are construed to be included in the scope of the claims of the claims.

Industrial Applicability

[0151] According to the present invention, a composite semipermeable membrane capable of suitably performing separation by a semipermeable membrane layer is provided.

Claims

1. comprising a semipermeable membrane layer and a porous support layer; the semipermeable membrane layer includes a plurality of sheet-like bodies containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound, and the plurality of sheet-like bodies are stacked so as to cover at least one surface of the support layer; the semipermeable membrane layer is in contact with the support layer; by including a crosslinked hydrophilic resin, the support layer is hydrophilized such that the ratio of the oxygen atomic weight to the total atomic weight in X-ray photoelectron spectroscopy measured on the surface in contact with the semipermeable membrane layer is 1.2 times or more the ratio when the hydrophilic resin is not included; the thickness of the semipermeable membrane layer is 0.1 μm or more and 10 μm or less; A composite semipermeable membrane, characterized in that the fractional particle diameter of the support layer is 0.45 μm or more and 10 μm or less.

2. The composite semipermeable membrane according to claim 1, wherein the support layer contains at least one of polyvinylidene fluoride and polysulfone.

3. The composite semipermeable membrane according to claim 1 or claim 2, which is a forward osmosis membrane used in the forward osmosis method.

4. The composite semipermeable membrane according to any one of claims 1 to 3, wherein the support layer is a hollow fiber membrane or a flat membrane.

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