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 includes a cross-linked polyamide that is obtained by polymerizing a multifunctional amine compound and a multifunctional acid halide compound, and a structural parameter of the support layer as measured using the composite semipermeable membrane is smaller than the thickness of the support layer.

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 conservation. 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 having a separation functional layer containing a crosslinked polyamide obtained by interfacial polycondensation in which an aqueous solution of a polyfunctional amine and an organic solvent solution of a polyfunctional acid halide are brought into contact on a porous support membrane and carried out 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 describes 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 the thermosetting resin porous sheet has an average pore diameter of 0.01 to 0.4 μm. 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 properties 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, in which the average surface pore diameter of the microporous support membrane is 30 nm or more and 40 nm or less. According to Patent Document 4, it is disclosed that a composite semipermeable membrane having practical desalination ability and high permeation flux can be obtained even when an additive for expressing 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 is a composite semipermeable membrane comprising a semipermeable membrane layer and a porous support layer, wherein the semipermeable membrane layer contains a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound, and a ratio of a structural parameter of the support layer to a thickness of the support layer, which is measured using the composite semipermeable membrane by a forward osmosis method, is 1.5 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

Figure 6

Embodiments 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 performed 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 in, for example, 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] The forward osmosis method is a separation method in which two solutions with different solute concentrations are brought into contact through a semipermeable membrane, and a solvent such as water is permeated from a dilute solution with a low solute concentration to a concentrated solution with a high solute concentration by using the osmotic pressure difference generated from these concentration differences as a driving force. 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 a driving force is not the osmotic pressure difference generated from the solute concentration difference of the solutions existing across the composite semipermeable membrane, but the osmotic pressure difference generated from the solute concentration difference of 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 a driving force becomes small. For this reason, 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. Therefore, a composite semipermeable membrane having such a support layer is not only required 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, it is required to be able to sufficiently exhibit high water permeation performance 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 separation by the semipermeable membrane layer from being inhibited 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 pores formed on the inside and surface of the support layer so that the penetrating voids inside the support layer are easily permeated by the solute and a solvent such as water, for example, so that the internal concentration polarization phenomenon hardly occurs.

[0018] However, it has been considered that if only the pores formed in the support layer, particularly the pores formed on the surface of the support layer on the side in contact with the semipermeable membrane layer, are simply enlarged, 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 on a support layer that is less likely to inhibit separation by the semipermeable membrane layer, the present inventors have found that the above object of providing a composite semipermeable membrane capable of suitably performing 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 contains a crosslinked polyamide obtained by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The ratio (S / d) of the structural parameter S of the support layer to the thickness d of the support layer, measured using the composite semipermeable membrane by the forward osmosis method, is 1.5 or less. That is, the structural parameter S of the support layer is 1.5 times or less with respect to the thickness d of the support layer.

[0022] Such a composite semipermeable membrane can suitably perform separation by the semipermeable membrane layer. This is considered to be due to the following reasons. First, when the support layer is used, a semipermeable membrane layer containing a crosslinked polyamide obtained by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound can be suitably formed on its surface. Further, since the structural parameter of the support layer is small with respect to the thickness of the support layer, it is possible to sufficiently suppress inhibiting the separation by the semipermeable membrane layer. From these facts, a suitable semipermeable membrane layer is formed on the support layer where the inhibition of separation by the semipermeable membrane layer is sufficiently suppressed, so it is considered that the obtained composite semipermeable membrane can suitably perform separation by the semipermeable membrane layer.

[0023] When the composite semipermeable membrane is used, for example, in the forward osmosis method, by bringing two solutions with different solute concentrations into contact 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 (hollow fiber-shaped support layer) or a flat membrane (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, the composite semipermeable membrane is formed, 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 a hollow fiber membrane is preferable in terms of, for example, 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. Also, 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. Also, FIGS. 2 and 3 are enlarged views of a part A of the composite hollow fiber membrane 11 shown in FIG. 1, showing the layer structure of the composite hollow fiber membrane 11. Note that FIGS. 2 and 3 are schematic views that represent the positional relationship of the layers and do not particularly represent the relationship of the layer thicknesses.

[0027] The semipermeable membrane layer 13 contains a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound. The support layer 12 is a support layer in which the ratio (S / d) of the structural parameter S of the support layer 12 to the thickness d of the support layer 12, measured using the forward osmosis method for the composite hollow fiber membrane, is 1.5 or less. Such a composite hollow fiber membrane 11 can preferably perform separation by the semipermeable membrane layer, as in the case of the composite semipermeable membrane described above.

[0028] As shown in FIG. 2, the composite hollow fiber membrane 11 may be such that the semipermeable membrane layer 13 is 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, the composite hollow fiber membrane 11 may be such that the semipermeable membrane layer 13 is provided on both surfaces of the support layer 12.

[0029] (Support layer) For the support layer 12, the ratio (S / d) of the structural parameter S of the support layer 12 to the thickness d of the support layer 12 is 1.5 or less, more preferably 1 or less, and even more preferably 0.9 or less. Also, although the smaller this ratio (S / d) is, the more preferable it is, in practice, about 0.1 is the limit. Therefore, the ratio (S / d) is 1.5 or less, preferably 0.1 to 1, and more preferably 0.2 to 0.9.

[0030] The structural parameter S of the support layer is generally affected by the porosity, thickness d, and refractive curvature of the support layer. Specifically, the structural parameter S of the support layer decreases as the porosity of the support layer is higher, the thickness of the support layer is smaller, and the refractive curvature is smaller. And the smaller the structural parameter S of the support layer, the higher the flux of water or the like passing through the support layer, and the easier the diffusion of salts or the like inside the support layer, so that the internal concentration polarization phenomenon is less likely to occur. From this, the structural parameter S of the support layer is preferably smaller from the viewpoint of suppressing the occurrence of the internal concentration polarization phenomenon in the support layer. Therefore, if the ratio (S / d) is too large, the occurrence of the internal concentration polarization phenomenon in the support layer cannot be sufficiently suppressed, and the separation by the semipermeable membrane layer tends to be inhibited by the support layer. Also, since the structural parameter S depends on the thickness d of the support layer, it is considered that there is a limit to reducing the ratio (S / d) as described above. Further, as described above, the support layer 12 provided in the composite hollow fiber membrane 11 according to the present embodiment has a structural parameter S that is 1.5 times or less with respect to the thickness d of the support layer 12. From this, it is considered that the support layer 12 appropriately adjusts the porosity and refractive curvature of the support layer 12, rather than reducing the structural parameter S only by reducing the thickness d of the support layer 12.

[0031] The structural parameter S of the support layer 12 is the structural parameter measured using the forward osmosis method for the composite hollow fiber membrane (composite semipermeable membrane) 11. Specifically, as the structural parameter S of the support layer 12, there may be mentioned the structural parameter calculated by the method described in Alberto Tiraferri et al., ”Journal of Membrane Science”, 444, 523 - 538 (2013), etc. More specifically, as the structural parameter S of the support layer 12, there may be mentioned the structural parameter calculated using the values measured using the forward osmosis method for the composite hollow fiber membrane and the formulas (1) to (5) below, etc. Regarding the forward osmosis (FO) method, the case where the feed solution (FS) is arranged on the semipermeable membrane layer (active layer) 13 side and the draw solution (DS) having an osmotic pressure higher than that of the FS is arranged on the support layer 12 side, that is, the case measured under the so-called AL - FS conditions will be described.

[0032] First, the water flux J in AL - FS W Calc is represented by the formula (1). Also, the salt flux (reverse diffusion flux of salt) J in AL - FS S Calc is represented by the formula (2).

[0033]

Number

[0034]

Number

[0035] Also, the water permeability coefficient A and the salt permeability coefficient B have the relationship represented by the formula (3).

[0036]

Number

[0037] On the other hand, by using the composite hollow fiber membrane in the forward osmosis method under the conditions of AL-FS and substituting the conditional values and the obtained values in the experiments into Formula (4) and Formula (5), the water flux J W EXP and the salt flux (reverse diffusion flux of salt) J S EXP are respectively calculated. The obtained water flux J W EXP and the salt flux (reverse diffusion flux of salt) J S EXP and the water flux J W Calc calculated from Formula (1) and the salt flux (reverse diffusion flux of salt) J S Calc calculated from Formula (1), the water permeability coefficient A and the structural parameter S are calculated by using the least squares method or the like so that the error therebetween becomes the smallest, and the salt permeability coefficient B is calculated from Formula (3).

[0038]

Number

[0039]

Number

[0040] In Formulas (1) to (5), A represents the water permeability coefficient [LMH / bar]. S represents the structural parameter [μm]. B represents the salt permeability coefficient [LMH]. R represents the gas constant [L·bar / mol·K]. π FS represents the osmotic pressure [MPa] of FS. π DS represents the osmotic pressure [MPa] of DS. D represents the diffusion coefficient of salt [m 2 / s]. Note that when the salt is NaCl, D is 1.48×10 -9 m 2 / s. J W Calc represents the calculated value [LMH (=L / m 2 / hour)] of the water flux (water permeation rate). J W EXP represents the experimental value [LMH] of the water flux (water permeation rate).S Calc shows the calculated value of the salt flux (salt reverse flow velocity) [molMH (= mol / m 2 / h)]. J S EXP shows the experimental value of the salt flux (salt reverse flow velocity) [molMH]. β shows the van't Hoff coefficient [-]. T shows the temperature [K]. C DS shows the DS concentration [M]. C FS shows the FS concentration [M]. C0 shows the FS concentration [M] at the start of the experiment. C t shows the FS concentration [M] at the end of the experiment. m shows the amount of permeated water [g]. ρ shows the density of water [g / L]. Am shows the effective membrane area [m 2 . t shows the measurement time [h].

[0041] As an experiment using the composite hollow fiber membrane in the forward osmosis method under the conditions of AL-FS, for example, the following experiments and the like can be mentioned.

[0042] Through the composite hollow fiber membrane, an aqueous NaCl solution with respective concentrations of 0.6M, 1.0M, 1.5M, and 2.0M as a simulated driving solution (simulated DS) and ion-exchanged water as a simulated feed solution (simulated FS) are arranged for filtration. At that time, the simulated FS is arranged on the semipermeable membrane layer side of the composite hollow fiber membrane, and the simulated DS is arranged on the support layer side of the composite hollow fiber membrane. The amount of permeated water from the simulated FS to the simulated DS is calculated from the respective weight changes of the simulated FS and the simulated DS. Then, from this calculated amount of permeated water, it is converted to the amount of permeated water per unit membrane area, per unit time, and per unit pressure to obtain the water flux (water permeation velocity) (L / m 2 / h: LMH). Also, the change in the salt concentration of the simulated FS is measured. From this change in the salt concentration, the salt flux (salt reverse flow velocity) (mol / m 2 / h: molMH) is obtained.

[0043] And actually, the structural parameter S is obtained by inputting the conditional values and the obtained values in the above experiment using Fitting Soft etc. cited from the above-mentioned paper (Journal of Membrane Science).

[0044] The support layer 12 is not particularly limited as long as it is a porous support layer with a ratio (S / d) of 1.5 or less. In the case of the support layer provided in the composite hollow fiber membrane, it is in the form of a hollow fiber. And it is preferable that the pores of the support layer 12 have an inclined structure in which the pores gradually become larger from one of the inner peripheral surface and the outer peripheral surface toward the other. As this inclined structure, the pores of the support layer 12 may have an inclined structure in which the pores gradually become larger from the inner peripheral surface toward the outer peripheral surface, or may have an inclined structure in which the pores gradually become larger from the outer peripheral surface toward the inner peripheral surface. Further, the support layer 12 may have an inclined structure in which the pores of the support layer 12 gradually become larger from the inner peripheral surface toward the central portion and gradually become smaller from the central portion toward the outer peripheral surface.

[0045] When the support layer 12 has the inclined structure, it is preferable that the contact surface 14 with the semipermeable membrane layer 13 is a dense surface which is the surface on the side where the pores of the support layer 12 are small. That is, it is preferable that the semipermeable membrane layer 13 is 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.

[0046] It is preferable that the average diameter of the pores existing in the region (surface vicinity region) from the surface 14 (for example, the dense surface 14 of the support layer 12) in contact with the semipermeable membrane layer 13 to 40 μm of the support layer 12 is 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. Also, the average diameter of the pores existing in the surface vicinity region is preferably 10 μm or less, and more preferably 5 μm or less.

[0047] 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. 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 becomes 90% can be mentioned.

[0048] 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, it tends to be difficult to obtain sufficient desalination performance. Further, if the average diameter of the pores present in the surface vicinity region is too large, the fractional particle diameter of the support layer 12 tends to increase, and there is a tendency similar to the case where the fractional particle diameter of the support layer 12 is too large. On the other hand, if the fractional particle diameter of the support layer 12 or the average diameter of the pores present in the surface vicinity region 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 and the average diameter of the pores present in the surface vicinity region are within the above ranges, respectively, separation by the semipermeable membrane layer and permeability can be made compatible. Further, it is considered that the pore diameter of the pores present in the vicinity of the surface of the support layer 12 on the semipermeable membrane layer 13 side is more greatly affected by the internal concentration polarization phenomenon than the pore diameter of the pores present in other portions. From this, by making the fractional particle diameter of the support layer 12 and the average diameter of the pores present in the surface vicinity region within the above ranges, respectively, it is considered that the support layer can be suppressed from inhibiting the separation by the semipermeable membrane layer, and the separation by the semipermeable membrane layer can be suitably performed.

[0049] 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. Note that 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 and 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 and 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. Although the higher the pressure resistance strength is, the better, a pressure resistance strength that is too high may be unnecessary in practice.

[0050] 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 a portion of the support layer 12 other than the dense surface 14.

[0051] 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. It is considered that hydrophilicity imparting by a hydrophilic resin is easier for these resins, and it is easier to form a support layer containing these resins into a suitable inclined structure. Therefore, a composite hollow fiber membrane including a support layer containing these resins can perform separation by a semipermeable membrane layer more suitably, and can provide a composite hollow fiber membrane with more excellent durability. 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 kinds.

[0052] The hydrophilic resin is not particularly limited as long as it can hydrophilize the support layer 12 by being contained 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 polyvinylpyrrolidone-based polymers such as polyvinylpyrrolidone. Among these, vinyl alcohol-based polymers and polyvinylpyrrolidone-based polymers are preferred, and polyvinyl alcohol and polyvinylpyrrolidone are more preferred. Polyvinyl alcohol and polyvinylpyrrolidone 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 polyvinylpyrrolidone is used as the hydrophilic resin used when hydrophilizing the support layer, these resins are considered to be easily crosslinked and can 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 the crosslinked hydrophilic resin being contained in the support layer. From these, the semipermeable membrane layer can be preferably formed on the dense surface of the support layer, and it is considered that the formed semipermeable membrane layer can be sufficiently prevented from being peeled off from the support layer. From these, 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 having more excellent durability. Further, as the hydrophilic resin, the resins exemplified above may be used alone or in combination of two or more. 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.

[0053] 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, an acetalization reaction using glutaraldehyde, etc. can be mentioned. Also, when polyvinylpyrrolidone is used as the hydrophilic resin, for example, a reaction with hydrogen peroxide water can be mentioned. It is considered that when 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.

[0054] It is more preferable that the entire support layer is hydrophilized because the hydrophilization of the support layer is carried out more preferably. For this reason, the semipermeable membrane layer is more preferably 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.

[0055] 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, outer peripheral surface, and the inner surface of the support layer cut out, it can be known whether a hydrophilic resin exists at each position. And if it seems that a hydrophilic resin exists over the entire support layer, it can be known that the entire support layer is hydrophilized. That is, if the presence of the hydrophilic resin can be confirmed on all of the inner peripheral surface, outer peripheral surface, and inside of the support layer, it can be known that the entire support layer is hydrophilized.

[0056] 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 cross-linked 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 measured on the surface of the side contacting the semipermeable membrane layer is 1.2 times or more the ratio in the case where the hydrophilic resin is not included. 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 of the support layer on the side contacting the semipermeable membrane 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 the oxygen atoms in the support layer becomes 1.2 times that of the support layer in the case where the resin composition is not included, 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 fact that a more suitable semipermeable membrane layer is provided on the support layer. That is, it is considered to be due to the fact that the semipermeable membrane layer is more suitably formed on the support layer.

[0057] 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, the spectrum obtained by this surface X-ray analysis is analyzed with a predetermined analysis software to calculate the peak area and peak intensity derived from each atom. Then, the obtained peak area and peak intensity are analyzed with a predetermined analysis software to calculate the ratio of the oxygen atomic weight to the total atomic weight measured by this XPS. 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 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 they are conditions under which 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.

[0058] 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 it, 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 be in contact with 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, in such a case where the 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.

[0059] 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, and 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 draw 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 draw solution, which are aqueous solutions, efficiently diffuse in the support layer, so-called internal concentration polarization is suppressed, and separation by the semipermeable membrane layer can be carried out more suitably.

[0060] Further, 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.

[0061] 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 for 24 hours or more in a forced-air constant-temperature dryer at 60°C can be mentioned. One end of the support layer in this dry state 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 amount per minute. From this measured water permeation amount, it is converted into the water permeation amount per unit membrane area, per unit time, and per unit pressure to obtain the permeation rate of pure water (L / m 2 / h: LMH).

[0062] 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 brought into a wet state. 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 bringing it into a wet state is not particularly limited as long as the support layer can be suitably brought into a wet state. 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 hollow fiber membrane in this wet state instead of the hollow fiber membrane in the dry state, by the same method as the measurement method of the permeation rate in the dry state above, the permeation rate of pure water at a transmembrane differential pressure of 98 kPa and 25°C (L / m 2 / hour: LMH).

[0063] The support layer 12 preferably 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 still 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 carried out more suitably.

[0064] The support layer 12 preferably has an average pore diameter (opposite-side pore diameter) of the pores formed on the surface opposite to the dense surface 14 of 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 of 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.

[0065] 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 such a method of manufacturing a porous hollow fiber membrane, a method using phase separation is known. Examples of the method of manufacturing a hollow fiber membrane using this phase separation include, for example, the nonsolvent induced phase separation method (NIPS method) and the thermally induced phase separation method (TIPS method).

[0066] The NIPS method is a method that causes a phase separation phenomenon by substituting the solvent and non-solvent of a polymer stock solution, with 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.

[0067] 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. Since the heat exchange rate is generally faster than the solvent exchange rate in the NIPS method and it is difficult to control the rate, the TIPS method tends to form uniform pores in the membrane thickness direction.

[0068] 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 solidifying the extruded hollow fiber-shaped membrane-forming stock solution to form a hollow fiber membrane (formation step), and the like.

[0069] (Semipermeable membrane layer) The semipermeable membrane layer 13 is not particularly limited as long as it is a layer that exhibits the function of a semipermeable membrane and contains 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 that are generated during the polymerization of the polyfunctional amine compound and the polyfunctional acid halide compound. The semipermeable membrane layer 13 may include, for example, 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 may be stacked so as to cover at least one surface of the support layer 12. Further, the semipermeable membrane layer 13 may be a layer that includes the plurality of sheet-like bodies and further includes a crosslinked polyamide that does not constitute the sheet-like bodies.

[0070] The semipermeable membrane layer 13 preferably covers all of at least one surface of the support layer 12, and more specifically, all of the region of the support layer 12 that is used for permeation and the like (the region of the support layer 12 corresponding to the region of the composite hollow fiber membrane 11 that is used for permeation and the like). 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 a smaller pore diameter among the main surfaces of the support layer 12.

[0071] 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 backflow rate. This is considered to be due to the fact that the semipermeable membrane layer is too thin to fully exhibit the function of the semipermeable membrane layer, or the semipermeable membrane layer cannot sufficiently cover the support layer. Further, if the semipermeable membrane layer is too thick, the permeability tends to decrease. This is considered to be due to the fact that the semipermeable membrane layer is too thick, resulting in a high water permeation resistance and making it difficult for water to permeate.

[0072] 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 compound 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 compound include ethylenediamine, propylenediamine, and tris(2-aminoethyl)amine. Examples of the alicyclic polyfunctional amine compound 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.

[0073] 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 have been removed. The polyfunctional acid halide compound may have a valence of 2 or more, and 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 are most easily obtained and have high reactivity, but are not limited thereto. Further, polyfunctional acid chlorides will be exemplified below, and examples of polyfunctional acid halides other than polyfunctional acid chlorides include those obtained by changing the chlorides exemplified below to other halides.

[0074] 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.

[0075] (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.

[0076] 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 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 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.

[0077] 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, the composite hollow fiber membrane can preferably perform separation by a semipermeable membrane that has sufficient strength and excellent permeability.

[0078] In addition, the membrane 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 membrane 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. In addition, if the membrane thickness is too thick, the permeability tends to decrease. Also, if the membrane 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 membrane 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.

[0079] The membrane thickness of the support layer 12 is the difference between the membrane thickness of the composite hollow fiber membrane and the membrane 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 membrane thickness of the support layer is almost the same as the membrane thickness of the composite hollow fiber membrane because the semipermeable membrane layer is very thin compared to the support layer. If the membrane 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. In addition, if the membrane thickness is too thick, the permeability tends to decrease. Also, if the membrane 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 membrane 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.

[0080] The composite hollow fiber membrane is applicable to the 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, or the like. Among these, the composite hollow fiber membrane is preferably an FO membrane used in the FO method.

[0081] Generally, in the case of 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 separation by the FO membrane in the FO method is easily affected by internal concentration polarization. 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.

[0082] [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-described 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).

[0083] 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.

[0084] 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, 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.

[0085] 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.

[0086] 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 the 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.

[0087] 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, 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.

[0088] The organic solvent solution of the polyfunctional acid halide compound is a solution obtained by dissolving the polyfunctional acid halide compound in an organic solvent. The organic solvent is not particularly limited as long as it can dissolve the polyfunctional acid halide compound and is insoluble 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.

[0089] 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 contacting the aqueous solution of the polyfunctional amine compound with 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.

[0090] For the drying, as long as the formed crosslinked polyamide is dried, the temperature and the like are not particularly limited. The drying temperature is preferably, for example, 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. The drying time is preferably, for example, 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.

[0091] 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.

[0092] As described above, this specification discloses various aspects of technology, and the main technologies are summarized below.

[0093] One aspect of the present invention is a composite semipermeable membrane including a semipermeable membrane layer and a porous support layer, wherein the semipermeable membrane layer includes a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound, and a ratio of a structural parameter of the support layer to a thickness of the support layer, which is measured using the composite semipermeable membrane by a forward osmosis method, is 1.5 or less.

[0094] According to such a configuration, a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer can be provided. This is considered to be due to the following.

[0095] When the support layer is used, a semipermeable membrane layer containing a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound can be suitably formed on the surface thereof. Furthermore, since the structural parameter of the support layer is 1.5 times or less with respect to the thickness of the support layer and is small, it is possible to sufficiently suppress inhibiting separation by the semipermeable membrane layer. From these facts, since a suitable semipermeable membrane layer is formed on the support layer where inhibition of separation by the semipermeable membrane layer is sufficiently suppressed, it is considered that a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer can be obtained.

[0096] Also, in the composite semipermeable membrane, it is preferable that the support layer contacts the semipermeable membrane layer and an average diameter of pores existing in a region from a surface of the support layer where the semipermeable membrane layer contacts to 40 μm is 0.3 μm or more.

[0097] According to such a configuration, it is possible to provide a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer. This is considered to be due to the following. According to the study by the present inventors, it has been found that the pore diameter of the pores existing in the vicinity of the surface of the support layer on the semipermeable membrane layer side is more greatly affected by the internal concentration polarization phenomenon than the pore diameter of the pores existing in other portions. From this, when the support layer contacts the semipermeable membrane layer and the average diameter of the pores existing in the region from the surface where the semipermeable membrane layer contacts the support layer to 40 μm is within the above range, it is considered that the occurrence of the internal concentration polarization phenomenon in the support layer can be more suppressed. Therefore, it is considered that the support layer can be prevented from inhibiting the separation by the semipermeable membrane layer, and the separation by the semipermeable membrane layer can be suitably performed.

[0098] Further, in the composite semipermeable membrane, the support layer preferably has a pure water permeation rate at a transmembrane differential pressure of 98 kPa of 5000 L / m 2 / hour or more and less than 100000 L / m 2 / hour.

[0099] According to such a configuration, it is possible to provide a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer. This is considered to be because the water permeability of the support layer is excellent, and the occurrence of the internal concentration polarization phenomenon in the support layer can be more suppressed.

[0100] Further, in the composite semipermeable membrane, the fractional particle diameter of the support layer is preferably 0.1 μm or more and 10 μm or less.

[0101] According to such a configuration, it is possible to provide a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer. This is considered to be due to the following reasons. As described above, it is considered that the pore diameter of the pores existing near the surface of the support layer on the semipermeable membrane layer side is more greatly affected by the internal concentration polarization phenomenon than the pore diameter of the pores existing in other portions. The fraction particle diameter of the support layer is considered to be affected by the pores existing on the surface of the support layer on the semipermeable membrane layer side. From these facts, by setting the fraction particle diameter of the support layer within the above range, it is considered possible to suppress the support layer from inhibiting the separation by the semipermeable membrane layer and to suitably perform the separation by the semipermeable membrane layer.

[0102] Further, in the composite semipermeable membrane, the semipermeable membrane layer is in contact with the support layer, and the support layer is hydrophilized by including a crosslinked hydrophilic resin so that the ratio of the oxygen atomic weight to the total atomic weight in the X-ray photoelectron spectroscopy measured on the surface on the side in contact with the semipermeable membrane layer is 1.2 times or more the ratio in the case of not including the hydrophilic resin.

[0103] According to such a configuration, it is possible to provide a composite semipermeable membrane capable of more suitably performing separation by the semipermeable membrane layer. 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.

[0104] Further, in the composite semipermeable membrane, the support layer preferably contains at least one of polyvinylidene fluoride and polysulfone.

[0105] According to such a configuration, it is possible to suitably perform separation by the semipermeable membrane layer and to provide a composite semipermeable membrane excellent in durability and the like.

[0106] Further, in the composite semipermeable membrane, it is preferably a forward osmosis membrane used in the forward osmosis method.

[0107] According to such a configuration, it can be suitably used as a forward osmosis membrane used in the forward osmosis method.

[0108] It is known that the forward osmosis method is easily affected by the internal concentration polarization phenomenon in the separation by the forward osmosis membrane. In the case of the composite semipermeable membrane, the occurrence of the internal concentration polarization phenomenon can be sufficiently suppressed, so that 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.

[0109] In the composite semipermeable membrane, the support layer is preferably a hollow fiber membrane or a flat membrane.

[0110] 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, in the case of 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.

[0111] According to the present invention, a composite semipermeable membrane capable of suitably performing separation by the semipermeable membrane layer can be provided.

[0112] 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

[0113] [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.

[0114] 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, γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation) as a solvent, silica (Fine Seal X-45 manufactured by Tokuyama Corporation) as inorganic particles, and glycerin (purified glycerin manufactured by Kao Corporation) as a flocculant were used to prepare a mixture so that the weight ratio was 36:47:18:19. By dissolving this mixture, a casting dope was obtained. The materials of this casting dope (membrane material and the hydrophilic resin described later) are shown in Table 1.

[0115] The obtained casting dope 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 an internal coagulation liquid containing the hydrophilic resin and injected into the hollow part of the extrudate, and the casting dope was discharged together with this internal coagulation liquid.

[0116] The spinning dope extruded together with this internal coagulating liquid (the extruded product extruded from the spinneret into the air) was passed through an air travel distance of 3 cm and then put into an external coagulating 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, with most of the solvent, aggregating agent, and inorganic particles remaining in the hollow fiber-like material, stretching treatment was performed in hot water at 90 °C so that the length in the fiber direction became about 1.5 times the original length. After that, the obtained hollow fiber-like material was heat-treated in flowing water at 95 °C for 180 minutes, and the solvent (γ-butyrolactone), aggregating agent (glycerin), internal coagulating liquid (dimethylacetamide, glycerin), and excess polyvinyl alcohol were extracted and removed. At this time, the extraction and 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.

[0117] (Fractionation particle size) Next, the fractionation particle size (= pore size) of the obtained hollow fiber membrane (support layer) was measured by the following method.

[0118] 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 taken as the fractionation particle size.

[0119] 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.

[0120] The fractionation particle size obtained by the above measurement method was 2.0 μm.

[0121] (Permeation rate of pure water) The permeation rate of pure water at a transmembrane differential pressure of 98 kPa for the obtained support layer (hollow fiber membrane) was calculated from the amount of filtrate per unit time in the following operation using the hollow fiber membrane and the obtained amount and the membrane area.

[0122] First, a membrane filtration device 31 as shown in Fig. 4 was fabricated using this hollow fiber membrane. The membrane module 32 loaded in the membrane filtration device 31 has an effective membrane length of 20 cm and consists of 20 hollow fibers, and the upper end 33 is sealed with an epoxy resin. The hollow part of the hollow fiber membrane is open at the upper end 33, and the hollow part of the hollow fiber membrane is sealed with an epoxy resin at the lower end 34. This membrane filtration device 31 filtered pure water from the outer peripheral surface side of the hollow fiber membrane through the inlet 35 and obtained filtered water from the outlet 36 on the inner peripheral surface side of the upper end. At this time, it was adjusted so that the transmembrane differential pressure became 98 kPa. Fig. 4 is a schematic diagram showing an example of a membrane filtration device for measuring the water permeation rate of the support layer. Also, the air introduced into the membrane filtration device 31 is discharged from the air vent 37.

[0123] By dividing the amount of filtrate per unit time obtained by this measurement method by the membrane area, the permeation rate of pure water at a transmembrane differential pressure of 98 kPa can be calculated. The water permeation rate obtained in this way at a transmembrane differential pressure of 98 kPa was 20000 L / m 2 / h (LMH).

[0124] This support layer had a dense outer peripheral surface and a gradient structure in which the internal pores gradually became larger from the dense surface toward the inner peripheral surface. The presence of this gradient structure was also found from observations with a scanning electron microscope.

[0125] 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 is a hollow fiber membrane having a gradient structure in which the pores present on the outer peripheral surface are smaller than the pores present on the inner peripheral surface.

[0126] As the composite semipermeable membrane, as the semipermeable membrane layer, a layer containing crosslinked polyamide described later was used, and as the support layer, the hollow fiber membrane was used. Further, 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.

[0127] (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 a counter cathode of Al. Then, by analyzing the spectrum obtained by this surface X-ray analysis with Multipak software (data processing software using MAT_LAB software), the peak area and peak intensity derived from each atom were calculated. And from analyzing the obtained peak area and peak intensity with the Multipak software (data processing software using MAT_LAB software), the ratio of the oxygen atomic weight to the total atomic weight measured by this XPS [abundance of oxygen atoms (atomic %)] was calculated.

[0128] On the other hand, except for not using the hydrophilic resin, a hollow fiber membrane without the hydrophilic resin was manufactured in the same manner as the hollow fiber membrane. The abundance of oxygen atoms (atomic %) in the hollow fiber membrane without the hydrophilic resin was calculated.

[0129] Then, the ratio (oxygen atom abundance ratio) of the abundance of oxygen atoms (atomic %) in the support layer used in this example to the abundance of oxygen atoms (atomic %) in the hollow fiber membrane without the hydrophilic resin was calculated. As a result, the oxygen atom abundance ratio was 1.25.

[0130] (Fabrication of the semipermeable membrane layer) A semipermeable membrane layer was formed on the outer peripheral surface (dense surface) side of the support layer.

[0131] Specifically, first, the support layer was immersed in a 50% by mass aqueous solution of ethanol for 20 minutes, and then washed with pure water for 20 minutes to perform a wetting treatment. The wet 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 allowed to penetrate 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 penetrate into the support layer was removed.

[0132] 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 that had penetrated 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.

[0133] 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. The formed semipermeable membrane layer had a thickness of 1.2 μm. Also, the thickness of the support layer was 0.2 mm. The membrane thickness of the composite semipermeable membrane and the membrane thickness of the support layer were substantially the same. This is because the semipermeable membrane layer is very thin compared to the support layer, so its thickness is within the error range.

[0134] (Average pore diameter of the cross-section) First, for any three locations in the longitudinal direction of the support layer, cross-sections perpendicular to the longitudinal direction were photographed at a magnification of 2000 using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). By analyzing, using Image-J, the images (40 μm × 40 μm images) of any of the support layers in each cross-sectional photograph from the contact surface with the semipermeable membrane layer up to 40 μm, the average pore diameter of the cross-section (the average diameter of the pores existing in the region of the support layer from the surface in contact with the semipermeable membrane layer up to 40 μm) was determined. Specifically, the pore portions of the images (for example, the images shown in FIGS. 5 and 6) were recognized, and their respective areas were calculated using image processing software or the like, and from this, the average value of the equivalent pore diameter (the diameter when the area is regarded as a circle) was obtained. This average value was taken as the average pore diameter of the cross-section (the average diameter of the pores existing in the region of the support layer from the surface in contact with the semipermeable membrane layer up to 40 μm). Note that FIG. 5 is a diagram showing a scanning electron micrograph near the outer peripheral surface in the cross-section of the support layer (hollow fiber membrane) provided in the composite semipermeable membrane (composite hollow fiber membrane) according to Example 1. FIG. 6 is a diagram showing a scanning electron micrograph near the outer peripheral surface in the cross-section of the support layer (hollow fiber membrane) provided in the composite semipermeable membrane (composite hollow fiber membrane) according to Comparative Example 1 described later.

[0135] (S / d) Through the composite hollow fiber membrane, an aqueous NaCl solution with each concentration of 0.6 M, 1.0 M, 1.5 M, and 2.0 M 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 filtration conditions were the AL-FS conditions. That is, 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 amount of water permeated 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 water flux (water permeation rate) (L / m 2 / h: LMH). Also, the change in the salt concentration of the simulated FS was measured. From this change in the salt concentration, the salt flux (salt backflow rate) (mol / m 2 / h: molMH) was obtained.

[0136] Then, by inputting the conditional values and the obtained values in the above experiment using Fitting Soft et al. cited from the above-mentioned paper (Journal of Membrane Science), the structural parameter S was obtained. By dividing this structural parameter S by the thickness d of the semipermeable membrane layer, S / d was obtained.

[0137] The S / d obtained by the above measurement method was 0.5.

[0138] [Evaluation] The obtained composite hollow fiber membrane was used in the forward osmosis (FO) method, and the water permeability and desalination performance were measured.

[0139] (Water permeability) 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 permeability.

[0140] (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, from the following formula, the desalination rate (%) was calculated. Note that the desalination performance can be evaluated from this desalination rate.

[0141] R s = [1 - J s / (J w × C D )] × 100 In the above formula, R s represents the desalination rate (%), J s represents the salt backflow rate (gMH), Jw indicates the water permeation rate (LMH), and C D indicates the salt concentration of DS (g / L) [in this case, the NaCl concentration of the simulated DS is (0.6 M), which is approximately 35 g / L.].

[0142] These results are shown in Table 1.

[0143] [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 (hollow fiber membrane made of polysulfone with a fractional particle size of 2.0 μm) obtained by the following method was used as the support layer.

[0144] (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 prepared into a mixture so that the mass ratio was 20:54:20:6. The 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.

[0145] The film-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 film-forming stock solution was solidified, and a hollow fiber membrane was obtained. The obtained hollow fibers were 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 immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica), and dried to obtain hollow fibers.

[0146] When the fractionation particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 2.0 μm.

[0147] The composite semipermeable membrane (composite hollow fiber membrane) according to Example 2 was produced in the same manner as in Example 1 except that this hollow fiber membrane was used as the support layer. And the same evaluation as in Example 1 was carried out. The results are shown in Table 1.

[0148] [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.

[0149] (Fabrication 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 became 20:64:12:4. By dissolving this mixture in a dissolution tank at a constant temperature of 60°C, a casting solution was obtained. The obtained casting 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 - 89 mol%), and water were adjusted to a solution with a mass ratio of 80:1:19, and this solution was used as the internal coagulation liquid containing the hydrophilic resin and injected into the hollow part of the extrudate, and together with this internal coagulation liquid, the casting solution was discharged.

[0150] The casting 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 casting solution was solidified and a hollow fiber membrane was obtained. The obtained hollow fiber was washed with hot water to remove the solvent, the 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 then dried to obtain a hollow fiber.

[0151] When the fractionation particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 0.85 μm.

[0152] The composite semipermeable membrane (composite hollow fiber membrane) according to Example 3 was manufactured by the same method as in Example 1 except that this hollow fiber membrane was used as the support layer. And the same evaluation as in Example 1 was carried out. The results are shown in Table 1.

[0153] [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 (a polysulfone hollow fiber membrane with a fractional particle size of 0.45 μm) obtained by the following method was used as the support layer.

[0154] (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: 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 prepared into a mixture so that the mass ratio was 20:64:15:1. 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 45°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-205, average degree of polymerization: 500, saponification degree 87 to 89 mol%, manufactured by Kuraray Co., Ltd.), and water were adjusted to a solution so that the mass ratio was 80:3:17, and this solution 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 membrane-forming stock solution was discharged.

[0155] The membrane-forming stock solution extruded together with this internal coagulation liquid was immersed in water at 40°C as the external coagulation liquid after passing through an air travel distance of 4 cm. 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, the aggregating agent, and the excessive 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 then dried to obtain a hollow fiber.

[0156] When the fractional particle size of the obtained hollow fiber membrane was measured by the above measurement method, it was 0.45 μm.

[0157] 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. And the same evaluation as in Example 1 was conducted. The results are shown in Table 1.

[0158] [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 (hollow fiber membrane made of polyvinylidene fluoride with a fractional particle size of 0.02 μm) obtained by the following method was used as the support layer.

[0159] 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, 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.

[0160] The obtained mixture was supplied to a twin-screw extruder and heat-kneaded (temperature: 155°C) in this twin-screw extruder. The obtained film-forming stock solution (spinning stock solution) was extruded from 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 - 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 injected into the hollow part of the extrudate as an internal coagulation liquid containing the hydrophilic resin, and the film-forming stock solution at 155°C was discharged together with this internal coagulation liquid.

[0161] The film-forming stock solution extruded together with this internal coagulating liquid was passed through an air travel distance of 3 cm and then put into an external coagulation bath composed of a 20 wt% aqueous sodium sulfate solution (temperature 80 °C) for cooling and solidification. The obtained hollow fibers were washed with hot water to remove the solvent, the coagulant, and excessive polyvinyl alcohol. Subsequently, polyvinyl alcohol was acetalized to make it insoluble, and then immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica), followed by drying to obtain hollow fibers.

[0162] When the fractionation particle diameter of the obtained hollow fiber membrane was measured by the above measurement method, it was 0.02 μm.

[0163] The composite semipermeable membrane (composite hollow fiber membrane) according to Comparative Example 1 was produced in the same manner as in Example 1 except that this hollow fiber membrane was used as the support layer. And the same evaluation as in Example 1 was carried out. The results are shown in Table 1.

[0164] [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 with a fractionation particle diameter of 0.02 μm) obtained by the following method was used as the support layer.

[0165] 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., Inc.), 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., Inc.), 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.

[0166] 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.

[0167] The fractionation particle diameter of the obtained hollow fiber membrane was 0.02 μm as measured by the above measurement method.

[0168] 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. And the same evaluation as in Example 1 was carried out. The results are shown in Table 1.

[0169] [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.

[0170] As a result, in Comparative Example 3, the semipermeable membrane layer was not suitably formed on the support layer. For this reason, in Table 1, the column of S / d is indicated as "-". Further, since the semipermeable membrane layer was not suitably formed in the membrane obtained in Comparative Example 3, the evaluation could not be suitably performed, and the evaluation in Table 1 is indicated as "-".

[0171] [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.

[0172] As a result, in Comparative Example 4, the semipermeable membrane layer was not suitably formed on the support layer. For this reason, in Table 1, the column of S / d is indicated as "-". Further, since the semipermeable membrane layer was not suitably formed in the membrane obtained in Comparative Example 4, the evaluation could not be suitably performed, and the evaluation in Table 1 is indicated as "-".

[0173] [Table 1]

[0174] As can be seen from Table 1, the composite semipermeable membrane (Examples 1 to 4) in which the ratio (S / d) of the structural parameters of the support layer to the thickness of the support layer, measured using the forward osmosis method, is 1.5 or less was excellent in water permeability performance and desalination performance. The composite semipermeable membranes according to Examples 1 to 4 had a semipermeable membrane layer containing the crosslinked polyamide, and were excellent in water permeability performance and desalination performance, and particularly excellent in water permeability performance, even when compared with the case where S / d exceeded 1.5 (Comparative Examples 1 and 2). This is presumably because by using a support layer such that the ratio (S / d) is 1.5 or less, the fluidity of the solution present in the support layer was dramatically increased, and the occurrence of internal concentration polarization was suppressed. Also, what made this possible is presumably that the support layer contains a hydrophilic resin, is hydrophilized such that the abundance ratio of the oxygen atoms is 1.2 times or more, and is hydrophilized such that the contact angle of water with respect to the contact surface of the support layer that contacts the semipermeable membrane layer is, for example, 90° or less. This can also be understood from the fact that, for example, in the case of not containing a hydrophilic resin (Comparative Examples 3 and 4), a suitable semipermeable membrane layer could not be formed even though the average pore diameter of the cross section of the support layer was comparable to that of Examples 1 and 2.

[0175] From the above, it can be seen that the composite semipermeable membrane in which the ratio (S / d) is 1.5 or less is excellent in water permeability performance and desalination performance, and can suitably perform separation by the semipermeable membrane layer.

[0176] This application is based on Japanese Patent Application No. 2020-148358 filed on September 3, 2020, the content of which is incorporated herein.

[0177] In order to describe the present invention, the present invention has been appropriately and fully described through the embodiments above, but it should be recognized that those skilled in the art can easily make changes and / or improvements to the above embodiments. Therefore, as long as the changes or improvements implemented by those skilled in the art do not depart from the scope of the claims described in the claims, such changes or such improvements are construed to be included in the scope of the claims of the claims.

Industrial Applicability

[0178] According to the present invention, there is provided a composite semipermeable membrane capable of suitably performing separation by a semipermeable membrane layer.

Claims

1. A composite semipermeable membrane comprising a semipermeable membrane layer and a porous support layer, wherein the semipermeable membrane layer contains a crosslinked polyamide formed by polymerizing a polyfunctional amine compound and a polyfunctional acid halide compound, and a ratio of a structural parameter of the support layer to a thickness of the support layer, measured using the composite semipermeable membrane by a forward osmosis method, is 0.1 to 1. The composite semipermeable membrane is characterized by this.

2. The support layer contacts the semipermeable membrane layer, The composite semipermeable membrane according to claim 1, wherein an average diameter of pores existing in a region from a surface of the support layer in contact with the semipermeable membrane layer to 40 μm is 0.3 μm or more.

3. The support layer has a pure water permeation rate at a transmembrane differential pressure of 98 kPa of 5,000 L / m ２ / hour or more and less than 100,000 L / m ２ / hour, and the composite semipermeable membrane according to claim 1 or claim 2.

4. The composite semipermeable membrane according to any one of claims 1 to 3, wherein a fractional particle diameter of the support layer is 0.1 μm or more and 10 μm or less.

5. The semipermeable membrane layer is in contact with the support layer, By including a crosslinked hydrophilic resin in the support layer, a ratio of an oxygen atomic weight to a total atomic weight in X-ray photoelectron spectroscopy measured on a surface of the support layer in contact with the semipermeable membrane layer is 1.2 times or more the ratio when the hydrophilic resin is not included. The composite semipermeable membrane according to any one of claims 1 to 4 is hydrophilized in this way.

6. The composite semipermeable membrane according to any one of claims 1 to 5, wherein the support layer contains at least one of polyvinylidene fluoride and polysulfone.

7. The composite semipermeable membrane according to any one of claims 1 to 6, which is a forward osmosis membrane used in a forward osmosis method.

8. The composite semipermeable membrane according to any one of claims 1 to 7, wherein the support layer is a hollow fiber membrane or a flat membrane.

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