Composite semipermeable membrane, method for producing same, separation membrane element, and fluid separation device

Abstract

The present invention relates to: a composite semipermeable membrane which comprises a base material, a porous layer that is provided on the base material, and a separation function layer that is provided on the porous layer, wherein the molecular weight cut-off of the porous layer is 10 kDa to 60 kDa, and the specific surface area is 20 to 50 m2 / g; or a composite semipermeable membrane which comprises a base material, a porous layer that is provided on the base material, and a separation function layer that is provided on the porous layer, wherein the molecular weight cut-off of the porous layer is 10 kDa to 60 kDa, and the tortuosity after supplying the composite semipermeable membrane with an aqueous solution that has an NaCl concentration of 3.5 mass% and a pH of 6.5 for 2 hours under the conditions of 5.5 MPa and 25°C is 1.5 to 7.0.

Description

Composite semipermeable membrane and its manufacturing method, separation membrane element, and fluid separation device

[0001] The present invention relates to a composite semipermeable membrane useful in high-pressure operation and a method for producing the same, and also to a separation membrane element comprising the composite semipermeable membrane, and a fluid separation device comprising the separation membrane element.

[0002] Composite semipermeable membranes, which are generally obtained by coating a porous layer with a separation functional layer made of crosslinked polyamide obtained by the polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide, are used in reverse osmosis processes to remove solutes from raw water, such as seawater desalination, because they have high water permeability and salt rejection properties.

[0003] In reverse osmosis, a pressure equal to or greater than the difference between the osmotic pressures of the feed water and the permeate water is applied to the feed water side of the composite semipermeable membrane. In recent years, reverse osmosis has been used for zero liquid discharge (ZLD) and for concentration in valuable resource recovery processes, and there has been an increase in cases where the process is operated at higher pressures than before depending on the solute concentration.

[0004] Such high-pressure operation of reverse osmosis treatment can reduce the permeability of the composite semipermeable membrane. In the absence of a pressure history, the permeability of the porous layer is approximately 100 times or more that of the separation functional layer, so the separation functional layer is dominant in the permeability of the composite semipermeable membrane. However, Patent Documents 1 to 3 point out that compaction of the porous layer caused by high-pressure operation reduces the permeability of the porous layer, thereby reducing the permeability of the composite semipermeable membrane.

[0005] In Patent Document 1, a pressure of 5.5 MPa is applied in the film thickness direction for 3 hours, and then the average film thickness t of the support film after the pressure is released is ０ [μm] and pure water permeability coefficient p ０ [g / (cm ２ s MPa)], and the average thickness t of the support film after applying a pressure of 10 MPa in the film thickness direction for 3 hours and then releasing it. １ [μm] and pure water permeability coefficient p １ [g / (cm ２ s MPa)], t １ / t ０ and p １ / p ０A composite reverse osmosis membrane is disclosed in which compaction is suppressed by satisfying a specific numerical range.

[0006] Patent Document 2 discloses a composite semipermeable membrane in which a porous support includes a dense layer in contact with a separation functional layer and a macrovoid layer located between the dense layer and the substrate. In particular, it discloses that when the number of macrovoids per unit length in the membrane surface direction in the macrovoid layer is within a specific range, the thickness of the porous support is maintained even under high pressure operation.

[0007] Patent Document 3 discloses a porous layer structure that focuses on the surface layer elastic modulus and dense layer thickness to suppress collapse during high-temperature and high-pressure operation based on the relationship between the porosity and compressive strength of the porous layer.

[0008] Japanese Patent Publication No. 2001-252538 Japanese Patent Publication No. 2018-039003 International Publication No. 2023 / 145845

[0009] In processes operating under high pressure, such as ZLD, there is a concern that the permeability of the composite semipermeable membrane may decrease. Furthermore, for example, in a seawater desalination system, the system may be temporarily stopped, and therefore start-stop operation is performed under high pressure, and the composite semipermeable membrane is subjected to pressure and released from the pressure. As a result, the composite semipermeable membrane is damaged multiple times, and the permeability and salt rejection of the composite semipermeable membrane decrease.

[0010] As disclosed in Patent Documents 1 to 3, it has become clear that the decrease in water permeability is caused by compaction of the porous layer, and this problem has been solved by techniques for suppressing compaction of the porous layer. However, the suppression of compaction of the porous layer under harsh operating conditions such as start-stop operation under high temperature and high pressure has been insufficient. Furthermore, conventional techniques for suppressing compaction of the porous layer involve changes in the surface structure of the porous layer, which also cause structural changes at the interface between the crosslinked polyamide and the porous layer or at the crosslinked polyamide itself, and it has not been possible to obtain a composite semipermeable membrane that can maintain its salt rejection properties under harsh operating conditions involving start-stop operation.

[0011] An object of the present invention is to provide a composite semipermeable membrane that exhibits high retention of water permeability and salt rejection and high salt rejection even during start-stop operation at high temperatures and high pressures. Another object of the present invention is to provide a method for producing the composite semipermeable membrane. A further object of the present invention is to provide a separation membrane element comprising the composite semipermeable membrane, and a fluid separation device comprising the separation membrane element.

[0012] In order to solve the above problems, the composite semipermeable membrane of the present invention includes the following configurations [1] to

[11] . [1] A composite semipermeable membrane having a substrate, a porous layer provided on the substrate, and a separation functional layer provided on the porous layer, wherein the molecular weight cutoff of the porous layer is 10 kDa to 60 kDa and the specific surface area is 20 to 50 m ２ / g. [2] A composite semipermeable membrane having a substrate, a porous layer provided on the substrate, and a separation functional layer provided on the porous layer, wherein the porous layer has a molecular weight cut-off of 10 kDa to 60 kDa, and the tortuosity after supplying an aqueous solution having a NaCl concentration of 3.5 mass % and a pH of 6.5 to the composite semipermeable membrane for 2 hours under conditions of 5.5 MPa and 25°C is 1.5 to 7.0. [3] The composite semipermeable membrane according to [1] or [2] above, wherein the surface of the porous layer opposite to the surface on which the separation functional layer is provided has an uneven shape, and the average circle equivalent diameter of the pores present in the recesses is 0.30 to 0.60 μm. [4] The porous layer has a mass per unit area of ​​10 to 17 g / m ２ [5] The composite semipermeable membrane according to any one of the above [1] to [3], wherein the specific surface area of ​​the porous layer is 22 to 40 m ２ / g. [6] The composite semipermeable membrane according to any one of [1] to [5] above, wherein the molecular weight cutoff of the porous layer is 30 kDa to 45 kDa. [7] The composite semipermeable membrane according to any one of [1] to [6] above, wherein the thickness of the porous layer is 10 to 20 μm after supplying the composite semipermeable membrane with an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 for 24 hours under conditions of 7.0 MPa and 45°C. [8] The composite semipermeable membrane according to any one of [1] to [7] above, wherein the substrate is a long-fiber nonwoven fabric having a thickness of 80 to 100 μm, and the long-fiber nonwoven fabric has a tensile strength in the longitudinal direction of 400 to 900 N / 5 cm. [9] A separation membrane element comprising the composite semipermeable membrane according to any one of [1] to [8] above.

[10] A fluid separation device comprising the separation membrane element according to [9] above.

[11] A method for producing a composite semipermeable membrane, comprising the following steps (a) to (c): step (a): a step of disposing a polymer solution obtained by dissolving a thermoplastic polymer in a good solvent on a substrate; step (b): a step of contacting the polymer solution disposed on the substrate with a first coagulation liquid containing a non-solvent and a good solvent for the thermoplastic polymer to form a porous layer on the substrate, and step (c): a step of forming a porous layer on the substrate such that the amount of the good solvent in the porous support comprising the substrate and the porous layer is 10 to 60 g / m ２ Step (c): A step of immersing the porous support in a second coagulation liquid.

[0013] According to the present invention, a composite semipermeable membrane can be obtained which has high retention of water permeability and salt rejection properties even after high-temperature and high-pressure operation, and also has high salt rejection properties.

[0014] Fig. 1 is a cross-sectional view of a composite semipermeable membrane in one embodiment of the present invention. Fig. 2 is a development view of a separation membrane element in one embodiment of the present invention. Fig. 3 is an image of the substrate-side surface of the porous layer of the composite semipermeable membrane of Example 1 observed at 500x magnification with a scanning electron microscope. White parts in the image are convex parts, and gray parts around them are concave parts.

[0015] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these in any way.

[0016] In this specification, the term "to" in a numerical range means a range including the preceding and following numerical values. For example, "0% by mass to 100% by mass" means a range of 0% by mass or more and 100% by mass or less.

[0017] 1. Composite Semipermeable Membrane As one embodiment of the present invention, a composite semipermeable membrane 1 having a substrate 2, a porous layer 3 provided on the substrate 2, and a separation functional layer 4 provided on the porous layer 3, as shown in Figure 1, will be described below. The composite of the substrate and the porous layer is referred to as a porous support.

[0018] 1.1 Substrate The substrate provides physical strength to the composite semipermeable membrane. Examples of the substrate include fabrics made of polymers such as polyester, polyamide, polyolefin, and mixtures or copolymers thereof.

[0019] As the fabric used for the substrate, a nonwoven fabric is preferably used from the viewpoints of strength, ability to form irregularities, and fluid permeability. As the nonwoven fabric, either a long fiber nonwoven fabric or a short fiber nonwoven fabric can be preferably used.

[0020] Furthermore, long-fiber nonwoven fabrics made of thermoplastic continuous filaments are less likely to fluff. Therefore, using a long-fiber nonwoven fabric as a substrate can suppress membrane defects. Furthermore, in the continuous production of composite semipermeable membranes, tension is applied to the substrate in the film production direction, so it is preferable to use a long-fiber nonwoven fabric, which has excellent dimensional stability, as a substrate.

[0021] 1.1.1 Average Single Fiber Diameter of Substrate When the substrate is a nonwoven fabric, the average single fiber diameter of the fibers constituting the nonwoven fabric is preferably 8 to 14 μm, more preferably 10 to 13 μm, and even more preferably 11 to 12 μm. When the average single fiber diameter is 8 μm or more, internal voids are maintained throughout the substrate. By maintaining voids in this manner, the polymer solution can quickly penetrate into the substrate during porous layer formation, resulting in strong adhesion between the substrate and the porous layer and a composite semipermeable membrane with excellent membrane peel strength. On the other hand, when the average single fiber diameter is 14 μm or less, a substrate and porous layer with excellent uniformity can be obtained.

[0022] The average single fiber diameter is determined by randomly selecting 10 single fibers from a nonwoven fabric substrate, measuring the diameter of each single fiber at a randomly selected position, and calculating the arithmetic mean of the obtained values.

[0023] 1.1.2 Basis Weight of Substrate The basis weight of the substrate used in the composite semipermeable membrane according to this embodiment is 60 to 120 g / m ２ is preferred, and 60 to 100 g / m ２ More preferably, 70 to 90 g / m ２ By setting the basis weight of the substrate within the above range, the composite semipermeable membrane has high mechanical strength capable of withstanding high-pressure operation, and the thickness of the composite semipermeable membrane can be reduced, thereby increasing the membrane area per separation membrane element.

[0024] 1.1.3 Density of the substrate The density of the substrate used in the composite semipermeable membrane according to this embodiment is 0.70 to 0.95 g / cm ３ is preferred, and 0.75 to 0.95 g / cm ３ More preferably, 0.80 to 0.95 g / cm ３ is more preferable. By setting the density of the substrate within the above range, deformation of the porous layer and the separating functional layer caused by sagging of the substrate due to high-pressure operation can be suppressed. In addition, since there are voids that allow the polymer solution to quickly penetrate into the substrate during porous layer formation, the substrate and the porous layer are firmly bonded, and a composite semipermeable membrane with excellent membrane peel strength can be obtained.

[0025] 1.1.4 Thickness of the Substrate The thickness of the substrate in the composite semipermeable membrane according to this embodiment is preferably 80 to 100 μm. By setting the thickness of the substrate within this range, the composite semipermeable membrane has high mechanical strength capable of withstanding high-pressure operation, and the thickness of the composite semipermeable membrane can be reduced, allowing the membrane area per separation membrane element to be increased.

[0026] The thickness of the substrate can be measured using a dial thickness gauge or a digital thickness gauge. As the dial thickness gauge or digital thickness gauge, products such as PEACOCK from Ozaki Manufacturing Co., Ltd. and TECLOCK Corporation can be used. When using a dial thickness gauge or a digital thickness gauge, the thickness is measured at 20 randomly selected locations, and the arithmetic average is calculated to determine the thickness of the substrate.

[0027] 1.1.5 Tensile Strength of the Substrate The substrate of the composite semipermeable membrane according to this embodiment is preferably a long-fiber nonwoven fabric made of thermoplastic continuous filaments. Long-fiber nonwoven fabrics made of thermoplastic continuous filaments have higher mechanical strength than short-fiber nonwoven fabrics, particularly short-fiber papermaking nonwoven fabrics. Composite semipermeable membranes using long-fiber nonwoven fabrics as a substrate can exhibit excellent durability, especially under conditions of high pressure during use. Furthermore, composite semipermeable membranes using long-fiber nonwoven fabrics as a substrate can suppress a decrease in water production rate due to the composite semipermeable membrane sinking into depressions in the feedwater flow path material when operated as a separation membrane element, or the resulting membrane damage.

[0028] Furthermore, the tensile strength of the long-fiber nonwoven fabric in the machine direction (MD) of the nonwoven fabric is preferably 400 to 900 N / 5 cm. By setting the tensile strength within this range, the composite semipermeable membrane can exhibit excellent durability even under conditions where high pressure is applied during use. Furthermore, the tensile strength aspect ratio of the long-fiber nonwoven fabric is preferably 1.0 to 3.0. Here, the "tensile strength aspect ratio" refers to the ratio of the tensile strength in the machine direction (MD) of the nonwoven fabric to the tensile strength in the cross direction (CD) of the nonwoven fabric (tensile strength in MD / tensile strength in CD).

[0029] One method for controlling the tensile strength and aspect ratio of tensile strength of a long-fiber nonwoven fabric is to apply heat or pressure to the long-fiber nonwoven fabric to form a laminate with multiple calender rolls or the like. The number of layers of long-fiber nonwoven fabric is preferably 2 to 5. If the number of layers of nonwoven fabric is 2 or more, the strength is improved compared to a single layer, and if the number of layers is 5 or less, wrinkling during lamination and peeling between layers can be suppressed.

[0030] 1.2 Porous Layer The porous layer of the composite semipermeable membrane according to this embodiment is preferably formed from a thermoplastic polymer. Here, the term "thermoplastic polymer" refers to a polymer made of a chain polymer substance that exhibits the property of deforming or flowing when heated by an external force.

[0031] Examples of thermoplastic polymers include polysulfone (hereinafter referred to as "PSf"), polyethersulfone, polyphenylene sulfide sulfone, and polyphenylene sulfone. Among these, PSf is generally used because it has high chemical, mechanical, and thermal stability and is easy to mold. The porous layer preferably contains these listed compounds as its main component. Here, "main component" means a component that accounts for 50% by mass or more of the components that make up the porous layer.

[0032] When the thermoplastic polymer is PSf, the weight average molecular weight (hereinafter "Mw") of the PSf, as measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard, is preferably 10,000 to 200,000, more preferably 15,000 to 100,000. When the Mw of PSf is 10,000 or more, the porous layer can have desirable mechanical strength and heat resistance. Furthermore, when the Mw is 200,000 or less, the viscosity of the solution falls within an appropriate range, enabling good moldability to be achieved.

[0033] 1.2.1 Specific Surface Area and Molecular Weight Cutoff of Porous Layer In the first embodiment of the composite semipermeable membrane of the present invention, the molecular weight cutoff of the porous layer is 10 kDa to 60 kDa and the specific surface area S is 20 to 50 m ２ / g. In this specification, the molecular weight cutoff and specific surface area S of the porous layer may be measured using a composite semipermeable membrane either before or after use. For example, the molecular weight cutoff and specific surface area S of the porous layer may be measured after supplying an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 to the composite semipermeable membrane under conditions of 7.0 MPa and 45°C for 24 hours, or after supplying an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 under conditions of 5.5 MPa and 25°C for 2 hours.

[0034] The specific surface area S represents the degree of three-dimensional network structure in the porous layer. A large value of the specific surface area S means that the porous layer has a dense three-dimensional network structure with many small voids. The three-dimensional network structure acts as a resistance to the water permeation path, but it can also disperse pressure, which has the effect of increasing the pressure resistance of the porous layer. A specific surface area S of 20 m ２ When the porous layer has a three-dimensional network structure, the pressure can be sufficiently dispersed, and therefore, compaction can be suppressed even in high-pressure operation. ２ / g or less, the proportion of the three-dimensional mesh structure that acts as a resistance to the water permeation path can be reduced, and sufficient water permeability can be ensured. That is, when the specific surface area S of the porous layer of the composite semipermeable membrane satisfies the above range, the three-dimensional mesh structure suppresses compaction of the porous layer during high-pressure operation. Therefore, when the specific surface area S of the porous layer of the composite semipermeable membrane after use satisfies the above range, the specific surface area S of the composite semipermeable membrane before use also satisfies the above range.

[0035] From the viewpoint of suppressing compaction of the porous layer and ensuring water permeability, the specific surface area S is 20 to 40 m ２ / g is preferred, and 22 to 40m ２ / g is more preferable, and 28 to 35m ２ / g is more preferred.

[0036] A method for controlling the specific surface area S within the above range includes, for example, a method in which, in the process of forming a porous layer, the porous support, on which a porous layer has been formed by immersing it in a first coagulation liquid, is brought into contact with a second coagulation liquid in a state containing a good solvent for the polymer that forms the porous layer. The specific surface area S can be controlled by the contact time with the first and second coagulation liquids and the temperatures of the respective coagulation liquids.

[0037] Furthermore, maintaining salt removal performance is also an issue during high-pressure operation that involves starts and stops. The main cause of the decline in salt removal performance is structural changes at the interface between the crosslinked polyamide and the porous layer or at the crosslinked polyamide itself, and the structure of the porous layer surface that forms the crosslinked polyamide is important. However, when attempting to control the specific surface area within the above range, the structure of the porous layer surface also changes, making it difficult to achieve the desired salt removal performance.

[0038] As a result of extensive research into the above-mentioned problems, the present inventors have discovered a porous layer having a molecular weight cutoff of 10 kDa to 60 kDa and a specific surface area of ​​20 to 50 m ２ / g can maintain water permeability and salt rejection properties while maintaining high salt rejection properties during start-stop operation at high temperatures and high pressures.

[0039] In other words, by achieving both the above-mentioned fractionation ability and specific surface area, it is possible to suppress compaction of the porous layer of the composite semipermeable membrane due to high-pressure operation, and to suppress a decrease in water permeability and salt rejection. A composite semipermeable membrane that achieves both fractionation ability and specific surface area like this has not been obtained in the prior art.

[0040] The "molecular weight cutoff" refers to the dextran molecular weight at which the removal rate of linear dextran is 90%, and can be measured by the method described in "7. Molecular weight cutoff of porous layer" in the Examples below. The molecular weight cutoff of the porous layer is more preferably 30 kDa to 50 kDa, and even more preferably 30 kDa to 45 kDa.

[0041] By setting the molecular weight cutoff of the porous layer within the above range, a composite semipermeable membrane can be obtained that can maintain salt rejection even during start-stop operation. If the molecular weight cutoff of the porous layer is greater than 60 kDa, the separation functional layer will collapse onto the surface of the porous layer during start-stop operation under high pressure, causing deformation of the separation functional layer and resulting in a decrease in salt rejection. Furthermore, if the molecular weight cutoff of the porous layer is less than 10 kDa, the amine aqueous solution will not be sufficiently supplied from the porous layer to the interface during the formation of the polyamide separation functional layer by interfacial polymerization, resulting in a decrease in the permeability of the composite semipermeable membrane and the formation of low-strength polyamide, making it impossible to maintain salt rejection during high-pressure operation. Methods for controlling the molecular weight cutoff of the porous layer within the above range include, for example, adjusting the temperature of the coagulation solution when forming the porous layer and adjusting the polymer concentration of the polymer solution used to form the porous layer.

[0042] 1.2.2 Tortuosity of Porous Layer In a second embodiment of the composite semipermeable membrane of the present invention, the porous layer has a molecular weight cutoff of 10 kDa to 60 kDa, and the tortuosity is 1.5 to 7.0 after supplying the composite semipermeable membrane with an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 for 2 hours under conditions of 5.5 MPa and 25° C. The molecular weight cutoff is as described above.

[0043] The "tortuosity," also known as the degree of bending, refers to the degree to which the flow path through which the permeate passes is bent. In other words, the lower the tortuosity, the more linear the flow path and the more interconnected the structure. From the perspective of pressure resistance, it is preferable that the porous layer has a three-dimensional network structure formed by non-solvent-induced phase separation. As described above, a three-dimensional network structure acts as a resistance to the water permeation path, but it can also disperse pressure, thereby enhancing pressure resistance. That is, a tortuosity of the porous layer of a composite semipermeable membrane after operation at a pressure of 5.5 MPa of 1.5 to 7.0 means that the porous layer has a highly interconnected three-dimensional network structure even after high-pressure operation. In other words, similar to the specific surface area S described above, the three-dimensional network structure can suppress consolidation of the porous layer due to high-pressure operation. When the tortuosity of the porous layer is greater than 7.0, the degree of bending of the flow path within the porous layer is high, making it more likely that the flow path will be blocked due to consolidation caused by high-pressure operation, resulting in reduced water permeability. On the other hand, if the tortuosity is less than 1.5, the proportion of the three-dimensional network structure in the porous layer is small and pressure cannot be dispersed, so consolidation is likely to occur during high-pressure operation exceeding 5.5 MPa.

[0044] The "tortuosity" can generally be calculated based on the Kozeny-Carman formula, and is described, for example, in Journal of the Japanese Association for Petroleum Technology (Vol. 75, No. 2 (March, 2010) pp. 164-176). The tortuosity of the porous layer is preferably 1.5 to 5.5, more preferably 1.5 to 4.0, from the viewpoint of suppressing compaction of the porous layer. A tortuosity of 1.0 means that the pores are linear cylindrical pores. It is more preferable that the tortuosity after supplying an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 for 24 hours under conditions of 7.0 MPa and 45°C satisfies the above range.

[0045] A method for controlling the tortuosity of the porous layer within the above range includes, for example, a method in which, during the process of forming the porous layer, the porous support, on which the porous layer has been formed by immersing it in a first coagulation liquid, is brought into contact with a second coagulation liquid in a state containing a good solvent for the polymer that forms the porous layer. The tortuosity can be controlled by the contact time with the first and second coagulation liquids and the temperature of each coagulation liquid.

[0046] In this specification, the tortuosity is calculated using the following formula (1): Tortuosity = (ε / 2k) １／２ (V / S) ... Equation (1) ε: Porosity of the porous layer after operation at 5.5 MPa [-] k: Permeability coefficient of the porous layer after operation at 5.5 MPa [m ２ ] V: Pore volume of the porous layer after operation at 5.5 MPa [m ３ / g] S: specific surface area of ​​the porous layer after operation at 5.5 MPa [m ２ / g]

[0047] Here, "after operation at 5.5 MPa" means after a membrane filtration operation in which an aqueous solution with a NaCl concentration of 3.5 mass% and a pH of 6.5 is supplied to the composite semipermeable membrane for 2 hours under conditions of 5.5 MPa and 25°C. The porosity ε of the porous layer after operation at 5.5 MPa is calculated based on the density ρ [g / cm 3] of the thermoplastic polymer forming the porous layer. ３] and the porous layer mass, and the porous layer volume calculated from the porous layer thickness. Specifically, it is calculated by the methods described in "3. Thickness of porous layer and substrate" and "4. Porosity ε of porous layer" in the examples below.

[0048] Pore ​​volume V [m of the porous layer after operation at 5.5 MPa ３ / g] is the density ρ [g / cm 3 ] of the thermoplastic polymer forming the porous layer ３ ] and the porosity ε of the porous layer after operation at 5.5 MPa. Specifically, it is calculated by the method described in "5. Pore volume V of porous layer" in the examples below.

[0049] Permeability coefficient k [m ２ ] is the porous layer thickness L [m], membrane area A [m] at 25 ° C. and pressure P [Pa]. ２ ] pure water permeability Q [m ３ / s] and the viscosity of pure water μ [Pa·s], and specifically, it is measured by the method described in "1. Permeability coefficient k of porous layer" in the examples below.

[0050] The permeability coefficient k is set to 0.35×10 from the viewpoint of stably obtaining good characteristics of the porous membrane. －１７ ~5.0 x 10 －１７ m ２ is preferable, and 0.70 × 10 －１７ ~5.0 x 10 －１７ m ２ More preferably, 1.0 × 10 －１７ ~5.0 x 10 －１７ m ２ When the permeability coefficient k is within the above range, sufficient water permeability of the porous layer can be obtained, and compaction of the porous layer can be suppressed even during high-temperature and high-pressure operation at, for example, 7.0 MPa and 45°C.

[0051] For measuring the above-mentioned properties, a method for removing the separation functional layer from the composite semipermeable membrane includes, for example, immersing the composite semipermeable membrane in an aqueous sodium hypochlorite solution to decompose and remove the separation functional layer when the separation functional layer is made of polyamide. Specifically, the separation functional layer is removed by the method described in "1. Permeability coefficient k of porous layer" in the examples below.

[0052] 1.2.2 Pore size on the back surface of the porous layer From the viewpoint of improving adhesion to the substrate, the composite semipermeable membrane according to this embodiment preferably has an uneven shape on the surface of the porous layer opposite to the surface on which the separation functional layer is provided (hereinafter referred to as the "back surface"). The uneven shape on the back surface of the porous layer is formed by transferring the uneven shape on the surface of the substrate. The "uneven shape" refers to a shape in which convex portions and concave portions are alternately continuous. The uneven shape can be observed using a scanning electron microscope (hereinafter referred to as "SEM").

[0053] In the composite semipermeable membrane according to this embodiment, the average equivalent circle diameter of the pores present in the recesses on the back surface of the porous layer is preferably 0.30 to 0.60 μm, more preferably 0.30 to 0.50 μm, and even more preferably 0.30 to 0.40 μm. When the average equivalent circle diameter is within the above range, clogging of the pores on the porous layer substrate side due to high-pressure operation can be suppressed, and water permeability can be easily ensured.

[0054] In the composite semipermeable membrane according to this embodiment, the number of pores present in the recessed portion on the back surface of the porous layer is 25 μm ２ Preferably, the number of pores per recess is 15 to 35. The pores present in the recesses on the back surface of the porous layer are flow paths through which the filtrate passes, so the greater the number of pores on the back surface, the more interconnected the inner layer structure of the porous layer will be, which is more resistant to compaction. The number of pores present in the recesses on the back surface of the porous layer can be measured by observing the surface using an SEM. Specifically, the number of pores is measured by the method described in "8. Uneven shape, number of pores, and average circle equivalent diameter on the back surface of the porous layer" in the Examples below.

[0055] The number of pores present in the recesses on the back surface of the porous layer and the average equivalent circle diameter of the pores can be controlled, for example, by the coating thickness of the polymer solution on the substrate and the amount of good solvent in the thermoplastic polymer immediately before entering step (c) described in "2.1 Porous layer formation step" below.

[0056] 1.2.3 Mass per unit area of ​​porous layer The mass per unit area of ​​the porous layer according to this embodiment is 10 to 17 g / m ２ is preferred, and 10 to 15 g / m ２ More preferably, 11 to 15 g / m ２When the mass per unit area of ​​the porous layer is within the above range, it is easy to achieve both high mechanical strength that can withstand high-pressure operation and interconnectivity (low tortuosity). The mass per unit area of ​​the porous layer can be controlled, for example, by the polymer concentration in the polymer solution, the coating thickness of the polymer solution on the substrate, the temperature of the coagulation liquid, etc.

[0057] 1.2.4 Thickness of the Porous Layer After supplying an aqueous solution with a NaCl concentration of 3.5% by mass and a pH of 6.5 to the composite semipermeable membrane according to this embodiment for 24 hours at 7.0 MPa and 45°C, the thickness of the porous layer is preferably 10 to 20 μm, more preferably 10 to 18 μm, and even more preferably 10 to 15 μm. When the thickness of the porous layer is within the above range, sufficient strength is maintained to obtain pressure resistance, the tortuosity can be easily designed to be small, and changes in water permeability due to high-pressure operation can be suppressed. Furthermore, the thickness of the porous support after the high-pressure operation is preferably 90 to 120 μm, more preferably 100 to 115 μm. The thickness of the porous layer can be controlled, for example, by the thickness of the polymer solution applied to the substrate and the temperature of the coagulation liquid.

[0058] 1.3 Separation Functional Layer The separation functional layer of the composite semipermeable membrane according to this embodiment preferably contains a crosslinked polyamide, more preferably contains a crosslinked polyamide as the main component. Furthermore, the separation functional layer more preferably contains a crosslinked aromatic polyamide as the crosslinked polyamide. The main component refers to a component that accounts for 50% by mass or more of the components of the separation functional layer. When the separation functional layer contains 50% by mass or more of crosslinked polyamide, it can exhibit higher removal performance. Furthermore, the content of crosslinked polyamide in the separation functional layer is more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0059] Crosslinked polyamides can be formed by chemically reacting a polyfunctional amine with a polyfunctional acid halide. Preferably, at least one of the polyfunctional amine and the polyfunctional acid halide contains a trifunctional or higher functional compound. This results in rigid molecular chains and a pore structure suitable for removing fine solutes such as hydrated ions and boron. Among these, crosslinked aromatic polyamides are preferably formed as the separation layer by chemically reacting a polyfunctional aromatic amine with a polyfunctional aromatic acid halide.

[0060] The term "polyfunctional amine" refers to an amine having at least two primary and / or secondary amino groups in one molecule. Examples of polyfunctional amines include polyfunctional aromatic amines in which two amino groups are bonded to an aromatic ring at the ortho, meta, or para positions, such as o-phenylenediamine, m-phenylenediamine (hereinafter referred to as "m-PDA"), p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, and p-diaminopyridine; 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. Examples of suitable amines include polyfunctional aromatic amines such as diaminomethane, aliphatic amines such as ethylenediamine and propylenediamine, and alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2-n-propylpiperazine, 2,5-di-n-butylpiperazine, 1,3-bispiperidylpropane, and 4-aminomethylpiperazine. These polyfunctional amines may be used alone or in combination.

[0061] In particular, m-PDA, p-phenylenediamine, and 1,3,5-triaminobenzene are preferred in consideration of the selectivity, permeability, and heat resistance of the membrane. Of these, m-PDA is more preferred due to its availability and ease of handling. These polyfunctional aromatic amines may be used alone or in combination of two or more.

[0062] The term "polyfunctional acid halide" refers to an acid halide or polyfunctional acid anhydride halide having at least two halocarbonyl groups in one molecule, and is not particularly limited as long as it forms a crosslinked polyamide separation functional layer upon reaction with the polyfunctional amine. Examples of trifunctional acid halides include trimesoyl chloride (hereinafter referred to as "TMC"), 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride. Examples of the bifunctional acid halides include aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, biphenylenecarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride, aliphatic bifunctional acid halides such as adipoyl chloride and sebacoyl chloride, and alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride. These polyfunctional acid halides may be used alone or in combination.

[0063] In consideration of the selectivity and heat resistance of the membrane, polyfunctional aromatic acid chlorides having 2 to 4 carbonyl chloride groups in one molecule are more preferred.

[0064] 1.4 Separation Membrane Element The separation membrane element according to this embodiment includes the composite semipermeable membrane according to this embodiment. An example of the configuration of the separation membrane element will be described with reference to FIG.

[0065] As shown in FIG. 2, the separation membrane element 5 includes a composite semipermeable membrane 1, a feed-side channel material 8, a permeate-side channel material 9, a water collection pipe 10, and end plates 6 and 7.

[0066] The feed-side passage material 8 is disposed so as to face the feed side of the composite semipermeable membrane 1, and is wrapped around the water collection pipe 10 together with the composite semipermeable membrane 1. The feed-side passage material 8 is preferably, for example, a net.

[0067] The permeate-side channel material 9 is disposed so as to face the permeate side of the composite semipermeable membrane 1, and is wrapped around the water collection pipe 10 together with the composite semipermeable membrane 1. As the permeate-side channel material 9, for example, tricot or a projection-fixed sheet can be used.

[0068] The water collection pipe 10 is a hollow cylindrical member having a plurality of holes on the side surface.

[0069] The end plates 6 and 7 are disk-shaped members each having a plurality of supply ports (or discharge ports).

[0070] Fluid separation by the separation membrane element 5 will now be described. Feed water 11 is supplied to the separation membrane element 5 through multiple supply ports in the end plate 6. The feed water 11 moves through a feed-side flow channel formed by a feed-side flow channel material 8 on the supply side of the composite semipermeable membrane 1. The fluid that has permeated the composite semipermeable membrane 1 (shown as permeate 12 in the figure) moves through a permeate-side flow channel formed by a permeate-side flow channel material 9. The permeate 12 that has reached the water collection pipe 10 enters the inside of the water collection pipe 10 through holes in the water collection pipe 10. The permeate 12 that has flowed through the water collection pipe 10 is discharged to the outside from the end plate 7. On the other hand, the fluid that has not permeated the composite semipermeable membrane 1 (shown as concentrate 13 in the figure) moves through the feed-side flow channel and is discharged to the outside from the end plate 7. In this way, the feed water 11 is separated into permeate 12 and concentrate 13.

[0071] 2. Method for Producing Composite Semipermeable Membrane 2.1 Porous Layer Forming Step The porous layer forming step in the method for producing a composite semipermeable membrane of the present invention includes the following steps (a) to (c): Step (a): A step of disposing a polymer solution obtained by dissolving a thermoplastic polymer in a good solvent on a substrate. Step (b): A step of contacting the polymer solution disposed on the substrate with a first coagulation liquid containing a non-solvent and a good solvent for the thermoplastic polymer to form a porous layer on the substrate, and forming a porous support comprising the substrate and the porous layer such that the amount of the good solvent in the porous support is 10 to 60 g / m. ２Step (c): A step of immersing the porous support in a second coagulation liquid.

[0072] In the step (a), a polymer solution is applied onto a substrate, and then in the step (b), the polymer solution is brought into contact with a first coagulation liquid containing a non-solvent and a good solvent for the polymer, thereby initiating phase separation from the surface of the polymer solution and forming a porous layer.

[0073] In conventional methods for forming porous layers, the surface of the polymer solution comes into contact with a large amount of coagulating liquid, which is a non-solvent for the polymer, causing it to coagulate instantly and form a dense three-dimensional network structure. Meanwhile, the dense three-dimensional network structure formed on the surface of the polymer solution inhibits the inflow of the coagulating liquid and the outflow of the good solvent in the polymer solution, causing the interior of the polymer solution to coagulate relatively slowly compared to the surface of the polymer solution. Therefore, in conventional methods for forming porous layers, phase separation progresses within the polymer solution, forming a network structure with larger voids inside the porous layer compared to the surface. A network structure with larger voids is less pressure-resistant and is disadvantageous for high-pressure operation.

[0074] As a result of extensive research, the present inventors have found that the amount of good solvent in the porous support in step (b) is 10 to 60 g / m ２ The inventors have found that by completely solidifying the interior of the porous layer by immersing the porous support obtained in step (b) in a second coagulation liquid in step (c), a dense three-dimensional network structure is formed inside the porous layer as well, and a composite semipermeable membrane having a small pore size at the surface of the porous layer can be obtained. In step (c), by contacting the inner layer with the second coagulation liquid while the porous support contains a certain amount of good solvent, the inner layer of the porous layer is dissolved, forming a dense three-dimensional network structure with high interconnectivity in the inner layer, and improving pressure resistance. In other words, it is possible to control the molecular weight cutoff and specific surface area S or the molecular weight cutoff and tortuosity after high-temperature, high-pressure operation within appropriate ranges.

[0075] The term "polymer" refers to a thermoplastic polymer that is the main component of the porous layer, and is specifically as described above.

[0076] A "good solvent" refers to a solvent that dissolves a polymer. By selecting the good solvent, the rate at which the good solvent flows out of the polymer solution in step (b) can be adjusted. As a result, the pore size on the back surface of the porous layer and the flow paths on the back surface of the porous layer can be controlled. As the good solvent, for example, at least one solvent selected from the group consisting of amides such as N-methyl-2-pyrrolidone, tetrahydrofuran, dimethyl sulfoxide, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide (hereinafter referred to as "DMF"), N,N-dimethylisobutyramide, N,N-diisopropylisobutyramide, and N,N-bis(2-ethylhexyl)isobutyramide, acetone, lower alkyl ketones such as methyl ethyl ketone, esters such as trimethyl phosphate, and lactones such as γ-butyrolactone is preferably used. Among these, it is more preferable to use DMF as the good solvent.

[0077] Step (a) can be carried out by applying the polymer solution to the substrate or by immersing the substrate in the polymer solution.

[0078] The polymer solution can be applied to the substrate by various coating methods. Among these, pre-metered coating methods such as die coating, slide coating, and curtain coating, which can supply a precise amount of polymer solution, are preferred. Among these, the slit die method for applying the polymer solution is particularly preferred for forming a porous layer. The thickness of the polymer solution applied to the substrate is preferably 50 to 150 μm, and more preferably 80 to 120 μm. By setting the coating thickness within the above range, the thickness of the porous layer and the pore size on the back surface of the porous layer can be controlled within suitable ranges.

[0079] For example, when the polymer solution contains PSf, the PSf concentration (ie, solid content concentration) is preferably 17 to 24 mass %.

[0080] By setting the PSf concentration within the above range, a certain amount of good solvent can be contained in the step (c), and as a result, the specific surface area S or the tortuosity after high-temperature, high-pressure operation can be controlled within a preferred range.

[0081] When PSf is used as the polymer, the temperature of the polymer solution during application is preferably within a range of 10 to 40°C. Within this range, application can be performed without PSf precipitating. The preferred temperature range of the polymer solution may be adjusted as appropriate depending on the viscosity of the polymer solution used, etc.

[0082] The thermoplastic polymer contained in the polymer solution may be appropriately changed in consideration of various properties such as strength, permeability, and surface properties of the porous layer.

[0083] The solvent contained in the polymer solution may be a single solvent or a mixture of multiple good solvents as long as it is a good solvent for the polymer. The solvent content can be adjusted appropriately taking into consideration the strength characteristics of the porous layer to be produced and the impregnation of the substrate with the polymer solution.

[0084] In step (b), the polymer solution disposed on the substrate is brought into contact with a first coagulation liquid mainly composed of a non-solvent in which the polymer has a lower solubility than the good solvent in the polymer solution, thereby coagulating the polymer, thereby forming a porous layer having a dense three-dimensional network structure.

[0085] The contacting can be performed by immersing the substrate having the polymer solution disposed thereon into the first coagulation liquid.

[0086] The first coagulation liquid is a mixed solution of a non-solvent and a good solvent for the polymer, and the non-solvent is the main component. Here, "main component" means a component that accounts for 50% by mass or more of the components that make up the first coagulation liquid. The concentration of the good solvent in the first coagulation liquid is preferably 10 to 40% by mass.

[0087] The contact time between the polymer solution and the first coagulation liquid is preferably 3 to 60 seconds, more preferably 3 to 30 seconds. When the contact time between the polymer solution and the first coagulation liquid is within the above range, the replacement of the good solvent in the polymer solution with the coagulation liquid can be controlled.

[0088] Furthermore, the temperature of the first coagulation liquid is preferably 10 to 45°C. When the temperature of the first coagulation liquid is 45°C or lower, the vibration of the coagulation liquid surface due to thermal motion is not intensified, and the surface smoothness of the porous layer is increased. Furthermore, when the temperature of the first coagulation liquid is 10°C or higher, a sufficient coagulation rate is obtained, resulting in good membrane formability. When the temperature of the coagulation liquid is within the above range, the molecular weight cutoff of the porous layer can be controlled in the range of 10k to 60kDa, and a separation functional layer with excellent salt removal properties can be formed.

[0089] Examples of the non-solvent used in the first coagulation liquid include aliphatic hydrocarbons such as water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, and low-molecular-weight polyethylene glycol, aromatic hydrocarbons, aliphatic alcohols, and mixed solvents thereof.

[0090] In step (c), a second coagulation liquid is brought into contact with the inner layer of the porous layer while the porous support obtained in step (b) contains a good solvent, and the inner layer of the porous layer is dissolved, thereby forming a dense three-dimensional network structure in the inner layer of the porous layer, and the specific surface area S or the tortuosity after a specified operation can be controlled.

[0091] An important control factor in the method for producing a composite semipermeable membrane according to this embodiment is the amount of good solvent in the porous support. The amount of good solvent in the porous support when immersed in the second coagulation liquid is 10 to 60 g / m ２ and 20 to 50 g / m ２ is preferred, and 30 to 40 g / m ２ It is more preferable that the amount of the good solvent in the porous support is 10 g / m ２ On the other hand, when the amount of the good solvent in the porous support is 60 g / m or more, the amount of the good solvent is sufficient to dissolve the polymer. ２ The amount of the good solvent in the porous support when immersed in the second coagulation liquid can be controlled by, for example, the concentration of the good solvent in the first coagulation liquid used in step (b), the temperature, the contact time between the polymer solution and the first coagulation liquid, etc.

[0092] The temperature of the second coagulation liquid used in step (c) is preferably 20 to 90° C., more preferably 50 to 85° C. If the temperature of the coagulation liquid is 20° C. or higher, the inner layer of the porous layer can be sufficiently dissolved and the tortuosity can be controlled, and if the temperature is 90° C. or lower, changes in the surface structure of the porous layer due to thermal shrinkage can be suppressed.

[0093] The second coagulation liquid used in step (c) may contain a non-solvent for the polymer, and is preferably a mixed solution of a non-solvent for the polymer and a good solvent. The concentration of the good solvent in the second coagulation liquid is preferably 0.1 to 10 mass %, more preferably 1 to 10 mass %. When the concentration of the good solvent in the second coagulation liquid is 0.1 mass % or more, the inner layer of the porous layer can be sufficiently dissolved, and when it is 10 mass % or less, changes in the surface structure of the porous layer can be suppressed.

[0094] Furthermore, since phase separation progresses with time, it is preferable that the time from step (b) to step (c) is short. The interval between obtaining the porous support in step (b) and carrying out step (c) is preferably within 10 seconds, more preferably within 7 seconds, and even more preferably within 5 seconds.

[0095] Next, the porous support obtained in step (c) is preferably washed with hot water or the like to remove the solvent remaining in the porous support. The temperature of the hot water used for washing is preferably 50 to 100°C, more preferably 60 to 95°C. If the hot water temperature is 100°C or less, the degree of shrinkage of the porous support can be kept small. Furthermore, if the hot water temperature is 50°C or higher, a high washing effect can be obtained.

[0096] 2.2 Step of Forming Separation Functional Layer Next, a method of forming the separation functional layer will be described.

[0097] The separation functional layer can be obtained, for example, by chemically reacting a polyfunctional amine with a polyfunctional acid halide to form a crosslinked polyamide, as described above. As a chemical reaction method, interfacial polymerization is the most preferred from the standpoint of productivity and performance. That is, the separation functional layer is preferably formed by performing interfacial polycondensation on the surface of the porous layer using an aqueous solution containing a polyfunctional amine and an organic solvent solution containing a polyfunctional acid halide. This process results in the formation of a crosslinked polyamide. Below, we will specifically explain the process of forming a crosslinked aromatic polyamide using a polyfunctional aromatic amine as the polyfunctional amine and a polyfunctional acid chloride as the polyfunctional acid halide, but the present invention is not limited thereto.

[0098] The interfacial polymerization includes the following steps (d) and (e): step (d): contacting an aqueous solution containing a polyfunctional aromatic amine with the porous layer, and step (e): after step (d), contacting a solution in which a polyfunctional aromatic acid chloride is dissolved with the porous layer.

[0099] In step (d), the concentration of the polyfunctional aromatic amine in the aqueous polyfunctional aromatic amine solution is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass. When the concentration of the polyfunctional aromatic amine is within this range, sufficient solute removal performance and water permeability can be obtained.

[0100] The contact of the aqueous polyfunctional aromatic amine solution with the porous layer is preferably carried out uniformly and continuously. Specific examples include a method of coating the porous layer with the aqueous polyfunctional aromatic amine solution and a method of immersing the porous layer in the aqueous polyfunctional aromatic amine solution. The contact time between the porous layer and the aqueous polyfunctional aromatic amine solution is preferably 1 second to 10 minutes, and more preferably 10 seconds to 3 minutes.

[0101] After contacting the polyfunctional aromatic amine aqueous solution with the porous layer, it is preferable to drain the solution so that no droplets remain on the surface of the porous support. This draining can prevent defects in the separation function layer. For example, methods for draining the solution include vertically holding the porous support after contact with the polyfunctional aromatic amine aqueous solution to allow excess aqueous solution to flow naturally, or blowing an air current such as nitrogen from an air nozzle to forcibly drain the solution. After draining the solution, the membrane surface can also be dried to remove some of the water content of the aqueous solution.

[0102] The concentration of the polyfunctional aromatic acid chloride in the solution is preferably 0.01 to 10% by mass, more preferably 0.02 to 2.0% by mass. When the concentration of the polyfunctional aromatic acid chloride in the solution is 0.01% by mass or more, a sufficient reaction rate can be obtained. Furthermore, when the concentration of the polyfunctional aromatic acid chloride in the solution is 10% by mass or less, the occurrence of side reactions can be suppressed.

[0103] The solvent used for the solution in which the polyfunctional aromatic acid chloride is dissolved is preferably an organic solvent that is immiscible with water, dissolves the polyfunctional aromatic acid chloride, and does not destroy the porous support, and is inert to the polyfunctional aromatic amine and the polyfunctional aromatic acid chloride. Preferred examples of the organic solvent include hydrocarbon compounds such as n-nonane, n-decane, n-undecane, n-dodecane, isooctane, isodecane, and isododecane, and mixtures thereof.

[0104] The method of contacting the organic solvent solution of the polyfunctional aromatic acid chloride with the porous layer that has been brought into contact with the aqueous polyfunctional aromatic amine solution may be carried out in the same manner as the method of coating the aqueous polyfunctional aromatic amine solution on the porous layer.

[0105] After the interfacial polymerization reaction, the organic solvent is removed from the membrane surface by, for example, holding the porous support vertically and allowing the excess organic solvent to flow down by gravity, blowing air onto the support with a fan to dry and remove the organic solvent, or using a water-air mixture to remove the excess organic solvent.

[0106] Furthermore, depending on the performance of the intended composite semipermeable membrane, a crosslinked aliphatic polyamide or a crosslinked alicyclic polyamide may be formed by using an aliphatic amine or an alicyclic polyfunctional amine instead of a polyfunctional aromatic amine, and an aliphatic bifunctional acid halide or an alicyclic bifunctional acid halide instead of a polyfunctional aromatic acid chloride.

[0107] 3. Method of Using the Composite Semipermeable Membrane The composite semipermeable membrane according to this embodiment is suitably used as a spiral composite semipermeable membrane element by being wound around a cylindrical water collection pipe having many holes, together with a feed water flow path material such as a plastic net, a permeate water flow path material such as tricot, and, if necessary, a film for increasing pressure resistance. Furthermore, this element can also be connected in series or in parallel and housed in a pressure vessel to form a composite semipermeable membrane module.

[0108] Furthermore, the composite semipermeable membranes, their elements, and modules can be combined with a pump that supplies feed water to them, a device that pretreats the feed water, etc. to form a fluid separation device. By using this fluid separation device, feed water can be separated into permeated water such as drinking water and concentrated water that has not permeated the membrane, thereby obtaining water suitable for the intended purpose.

[0109] The feed water to be treated by the composite semipermeable membrane according to this embodiment includes liquid mixtures containing 500 mg / L to 100 g / L of TDS (Total Dissolved Solids), such as seawater, brine, and wastewater. Generally, TDS is expressed as "mass / volume" or "mass ratio." According to the definition, TDS can be calculated from the mass of the residue obtained by evaporating a solution filtered through a 0.45 micron filter at a temperature of 39.5 to 40.5°C, but it can be more simply calculated from the practical salinity (S).

[0110] The higher the operating pressure when permeating feed water through the composite semipermeable membrane, the higher the solute removal rate. However, taking into consideration the increased energy required for operation and the durability of the composite semipermeable membrane, the operating pressure when permeating feed water through the composite semipermeable membrane is preferably 0.5 to 12 MPa. As the temperature of the feed water increases, the solute removal rate decreases, and as the temperature decreases, the membrane permeation flux decreases. Therefore, the temperature of the feed water is preferably 5 to 55°C.

[0111] In the composite semipermeable membrane according to this embodiment, the water production rate change ratio calculated by the method described in "12. High-pressure test" in the examples described later is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and particularly preferably 0.94 or more. Furthermore, the rejection rate change ratio calculated by the above method is preferably 1.30 or less, more preferably 1.20 or less, and even more preferably 1.10 or less. Furthermore, it is preferable that the water production rate change ratio and the rejection rate change ratio simultaneously satisfy the above ranges.

[0112] With a typical composite semipermeable membrane, when operated at 35°C or higher with a TSD of 40,000 mg / L or higher and with on-off operation, the amount of water produced decreases significantly due to compaction of the porous layer. Therefore, in order to maintain a constant amount of water produced by the fluid separation device, it is necessary to increase the operating pressure, which increases the energy required for operation.

[0113] In the fresh water production method using the composite semipermeable membrane according to this embodiment, consolidation of the porous layer does not progress even during operation with on-off operation at a TSD of 40,000 mg / L or more at 35° C. or higher. This prevents a decrease in the amount of fresh water produced by the composite semipermeable membrane, reduces the increase in operating pressure required to maintain a constant amount of fresh water produced by the fluid separation device, and reduces the increase in energy required for operation.

[0114] Furthermore, if the pH of the feed water is high, there is a risk of magnesium scale formation in the case of feed water with a high solute concentration, such as seawater. Furthermore, there is a concern that membrane deterioration may occur due to filtering of high-pH feed water. Therefore, it is preferable that the pH of the feed water is neutral.

[0115] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited thereto. Unless otherwise specified, the porous support used in each measurement was obtained by immersing a composite semipermeable membrane in a 2% by mass aqueous solution of sodium hypochlorite for 48 hours and removing the separation functional layer.

[0116] 1. Permeability coefficient k of porous layer A 5.5 MPa operation was performed in which an aqueous solution with a NaCl concentration of 3.5% by mass and a pH of 6.5 was supplied to the composite semipermeable membrane for 2 hours under conditions of 5.5 MPa and 25 ° C. The composite semipermeable membrane after the 5.5 MPa operation was immersed in a 2% by mass aqueous sodium hypochlorite solution for 48 hours, the separation function layer was removed, and a porous support was obtained. The porous support was cut into a circle with a diameter of 4.3 cm and set in a stirring type ultra holder (UHP-43K manufactured by Advantec Toyo Co., Ltd.) (effective filtration area: 10.9 cm ２ ) Pure water at 25°C was placed in the cell of the Ultra Holder, and the cap was attached. The pressure was increased to 0.2 MPa with nitrogen, and the pure water permeation rate Q [m ３ / s] was measured. At 25°C, the porous layer thickness L [m] and the membrane area A [m ２ ] pure water permeability Q [m ３ The permeability coefficient k of the porous layer after operation at 5.5 MPa was calculated from the viscosity μ [Pa·s] of the porous layer and the permeability coefficient μ [m ２ ]=Q×μ×L / (A×P) ...Equation (2) Here, a porous support is used for the measurement, but the water permeability resistance of the base material in the porous support is negligibly small compared to the porous layer, so the permeability coefficient k obtained by the above equation (2) is regarded as the permeability coefficient of the porous layer.

[0117] 2. Mass per unit area of ​​porous layer The porous support was cut into a rectangle of 0.11 m x 0.19 m, dried at 120°C for 2 hours, and the mass of the porous support was measured. In addition, the porous layer was peeled off from the porous support with tape, and the mass of the substrate was measured. The mass per unit area of ​​the porous layer was calculated using the following formula (3). Mass per unit area of ​​the porous layer [g / m ２ ]=(mass of porous support−mass of substrate) / (0.11×0.19) Equation (3)

[0118] 3. Thickness of Porous Layer and Substrate The thickness of the porous layer after supplying an aqueous solution with a NaCl concentration of 3.5 mass% and a pH of 6.5 to the composite semipermeable membrane for 24 hours under conditions of 7.0 MPa and 45°C (thickness of the porous layer after high-temperature and high-pressure operation) was measured using a dial thickness gauge (constant-pressure thickness gauge PG-01A, manufactured by Teclock Corporation) using the composite semipermeable membrane after operation under these conditions. First, because the separation functional layer is very thin, the sum of the thicknesses of the substrate and porous layer was considered to be the thickness of the composite semipermeable membrane, and the thickness of the composite semipermeable membrane was measured. Then, the substrate was peeled from the composite semipermeable membrane with tape, and the thickness of the peeled substrate was measured with the above-mentioned dial thickness gauge PG-01A. The difference between the thickness of the composite semipermeable membrane and the thickness of the substrate was taken as the thickness of the porous layer. Note that for each thickness measurement, the arithmetic mean value of measurements at 20 points randomly selected on the same membrane surface was used. Furthermore, the thickness of the substrate of the composite semipermeable membrane was measured by the same method using the composite semipermeable membrane before operation under the above conditions.

[0119] 4. Porosity ε of the porous layer For the porous support obtained by the method described in "1. Permeability coefficient k of the porous layer" above after operation at 5.5 MPa, the porosity was calculated using the following formulas (4), (5), and (6). ３ ] is the density of the thermoplastic polymer that forms the porous layer, and when the porous layer is a mixture of multiple types of thermoplastic polymers, the mixed density is used. ３ ] = mass per unit area of ​​porous layer × (0.11 × 0.19) / polymer density ... formula (4) Apparent volume [m ３ ]=thickness of porous layer×(0.11×0.19) Equation (5) Porosity of porous layer ε[−]=1−(volume of polymer / apparent volume of porous layer) Equation (6)

[0120] 5. Pore volume V of the porous layer The pore volume V of the porous layer after operation at 5.5 MPa was calculated from the following formula (7) based on the relationship of pore volume: (1 / polymer density) = porosity: (1 - porosity). Pore volume V [cm ３ / g]=porosity×(1-porosity) / polymer density...Equation (7)

[0121] 6. Specific Surface Area S and Tortuosity of Porous Layer The specific surface area S of the porous layer was measured from the porous support by nitrogen adsorption measurement. Furthermore, the tortuosity after operation at 5.5 MPa was calculated using the above-mentioned formula (1) from the porosity ε, permeability coefficient k, pore volume V, and specific surface area S of the porous layer after operation at 5.5 MPa. The porous layer was peeled off from the porous support, and only the peeled porous layer was cut into 5 mm squares with a single-edged blade to obtain 0.1 to 0.3 g of measurement samples. The measurement samples were dried in a vacuum at 45°C for 4 hours. The specific surface area S of the dried samples was measured by the BET method using a nitrogen adsorption measurement device (Microtrackbell; BELSORP-mini II). A leak check was performed before measurement, and after confirming that the leak was less than 5 Pa / min, measurement was started under the following conditions. [Adsorbate Setting] The adsorbate was N ２ The gas and adsorption temperature were set to 77 K. [Thermal transpiration settings] The molecular diameter was set to 0.364 mm, the sample tube inner diameter was set to 7.0 mm, and the glass rod outer diameter was set to 6.0 mm. [Measurement device settings] "Dewar flask" was selected. [Saturated vapor pressure settings] "Actual measurement" was selected. [Adsorbed gas non-ideality correction] The second virial coefficient was -4.264 x 10 －７ Pa －１ [Purge settings] The sample tube disposal rate was set to "slow" and the purge gas was set to Ads (V2). [nth-order adsorption settings] The degassing time was set to 120 minutes, and the third-order isotherm was selected. [Adsorbate introduction pressure settings] "Relative pressure display" was selected. [Measurement method] The simple method was selected, and the upper limit of the adsorption relative pressure was set to 0.35, desorption measurement, and measurement relative pressure specification were set.

[0122] 7. Molecular Weight Cutoff of Porous Layer Aldrich dextran with Mw 1500 (product number: 31394), Mw 6000 (product number: 31388), Mw 15000-20000 (product number: 31387), Mw up to 40000 (product number: 31389), Mw up to 60000 (product number: 31397), and Mw up to 200000 (product number: 31398) was each dissolved in distilled water to a concentration of 500 ppm to prepare an aqueous dextran solution, which was used as raw water.

[0123] The porous support was cut into a circle with a diameter of 4.3 cm, and the cut sample was set in a stirring type ultra holder (UHP-43K manufactured by Advantec Toyo Co., Ltd.) (effective filtration area: 10.9 cm ２ The dextran solution at 25°C was placed in the cell of the Ultra Holder, and the cap was attached. The amount of water produced was adjusted to 0.2 to 0.8 [m ３ / m ２ The pressure was increased to [1 / day], and filtration was initiated. The first 5 g of the permeate was discarded as a preliminary permeate, and the next 5 g was collected as a filtration sample. The dextran concentrations in the raw water and the filtrate sample were measured by GPC.

[0124] The concentration was measured by GPC as follows: The sampled solution was filtered through a filter with a pore size of 0.45 microns, and the obtained filtrate was analyzed using a GPC column (TSK-gel-G4000PWXL, manufactured by Tosoh Corporation) at a column temperature of 40°C, a mobile phase of distilled water for liquid chromatography at a flow rate of 1 mL / min, and a sample injection volume of 100 μl. The measurement was performed using a differential refractive index system (RI-8020, manufactured by Tosoh Corporation) with a slice time of 0.02 min and a base-line range of 4.5 to 11.0 min.

[0125] A calibration curve showing the relationship between retention time in GPC and the molecular weight of dextran was calculated as follows: A solution of monodispersed dextran was analyzed by GPC, and each retention time was measured. The retention time of each peak top was plotted against the measured molecular weight of the monodispersed dextran, and a calibration curve of retention time and molecular weight was obtained from an exponential approximation curve. Furthermore, the retention time at which 90% dextran removal was achieved was calculated from the difference in refractive index between the raw water and the filtered sample, and the dextran molecular weight cutoff at which 90% dextran removal was achieved was determined from the calibration curve.

[0126] 8. Concave and convex shape of the back surface of the porous layer and average circular equivalent diameter of the pores The concave and convex shape of the back surface of the porous layer and the average circular equivalent diameter of the pores present in the recesses were measured by surface observation using SEM and image analysis using analysis software (ImageJ). First, the composite semipermeable membrane was air-dried at room temperature, and the substrate was peeled from the porous layer in a 180-degree direction at a peeling speed of 50 mm / min. The back surface of the porous layer exposed by the peeling was thinly coated with platinum, and observed at 500x magnification using an SEM (Hitachi High-Technologies Corporation S-5500 model) at an acceleration voltage of 5 kV and images were taken. In the obtained image, the contrast of the image confirmed the presence of convex portions 14 (white portions) on the back surface of the porous layer and the surrounding concave portions 15 (gray portions) on the back surface of the porous layer. The concave portions (gray portions) were further observed at 10,000x magnification and images were taken. In the obtained image, 25 μm ２ The pore area within the area of ​​5 μm × 5 μm was binarized using the mean method in analysis software (Image-j), and the pore contours were extracted using the Find Edge function, after which the circle-equivalent diameter was calculated. The same procedure was performed on five samples, and the arithmetic mean of the circle-equivalent diameter data for all five samples was calculated, which was used as the average circle-equivalent diameter of the pores present in the recesses on the back surface of the porous layer.

[0127] 9. Tensile Strength of Substrate Based on JIS L 1906:2000 5.3.1, a 5 cm × 30 cm substrate obtained by peeling from the composite semipermeable membrane was used as a sample, and measurements were carried out at five points in the longitudinal direction under conditions of a gripping distance of 20 cm and a pulling speed of 10 cm / min. The value was read from the obtained strength-elongation curve, and rounded to the first decimal place, to obtain the tensile strength of the substrate in the longitudinal direction.

[0128] 10. Amount of Good Solvent in Porous Support In the process of producing a composite semipermeable membrane, a porous support having a porous layer formed on a substrate, obtained by immersion in the first coagulation liquid in step (b), was cut into a 0.11 m x 0.19 m rectangle together with the substrate in a wet state, and immersed in a polytetrafluoroethylene container containing 500 g of pure water at 90°C for 1 hour. After immersion, 10 mL of the extract in which the porous support was immersed was collected. GC-MS measurement was performed on the collected extract. The good solvent concentration [ppm] of the extract was calculated from the previously prepared calibration curve of the peak area and the good solvent concentration of the polymer solution. The amount of good solvent in the porous support was calculated from the calculated good solvent concentration of the extract using the following formula (8): Amount of good solvent in the porous support [g / m ２ ] = 500 × (concentration of good solvent in solution / 1000) / 1000 / (0.11 × 0.19) ... Equation (8)

[0129] 11. NaCl Rejection Rate and Water Production Amount of Composite Semipermeable Membrane Raw water (NaCl concentration 3.2% by mass) adjusted to 25°C and pH 6.5 was supplied to a composite semipermeable membrane at an operating pressure of 5.5 MPa, and membrane filtration was carried out for 24 hours. Thereafter, the electrical conductivity of the feed water and permeate was measured using a multi-purpose water quality meter (MM60R) manufactured by DKK-TOA Corporation. Next, using a calibration curve prepared in advance, this electrical conductivity was converted to calculate the NaCl concentration. From the obtained NaCl concentration, the initial salt removal performance, i.e., the initial NaCl rejection rate, was calculated using the following formula (9): NaCl rejection rate [%] = 100 × {1 - (NaCl concentration in permeate water / NaCl concentration in feed water)} ... formula (9)

[0130] After the membrane filtration treatment was carried out for 24 hours, the amount of water passing through the membrane for 30 minutes was measured, and the initial water production amount [m ３ / m ２ / day] was calculated.

[0131] 12. High-Pressure Test Raw water (NaCl concentration 3.2% by mass) adjusted to 45°C and pH 6.5 was supplied to the composite semipermeable membrane whose performance was evaluated in the above "11. NaCl Rejection Rate and Water Production Amount of Composite Semipermeable Membrane" at an operating pressure of 7.0 MPa, and the membrane filtration process was stopped and started every hour, for a total of 24 hours of operation. Thereafter, membrane performance was evaluated in the same manner as in "11. NaCl Rejection Rate and Water Production Amount of Composite Semipermeable Membrane," and the NaCl rejection rate and water production amount after high-temperature, high-pressure operation were determined. The quality of the membrane performance was determined by the water production rate change ratio and the removal rate change ratio calculated by the following formulas (10) and (11). Water production rate change ratio = water production rate after high-pressure operation / initial water production rate ... formula (10) Removal rate change ratio = (100 - NaCl removal rate after high-pressure operation) / (100 - initial NaCl removal rate) ... formula (11)

[0132] [Example 1] A 20 mass % DMF solution of PSf was applied as a polymer solution onto a long-fiber polyester nonwoven fabric (average thickness 90 μm, tensile strength in the machine direction 420 N / 5 cm) as a substrate at 25°C until the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 20 g / m ２ The substrate coated with the polymer solution was then immersed in a first coagulation liquid consisting of an aqueous DMF solution at 20°C for 15 seconds, producing a porous support with a porous layer formed on the substrate. The porous support was then immersed in a second coagulation liquid consisting of an aqueous DMF solution, left for 5 minutes, and then washed with hot water at 90°C for 2 minutes. The washed porous support was then immersed in a 3% by mass aqueous solution of m-PDA for 2 minutes. The support was slowly pulled up vertically, and excess aqueous solution was removed from the surface of the porous support by spraying nitrogen with an air nozzle. A decane solution containing 0.165% by mass of TMC was then applied so that the surface was completely wet, and the mixture was allowed to stand for 1 minute. The membrane was then turned vertically, and excess solution was drained off and removed, followed by washing with pure water to obtain a composite semipermeable membrane with a crosslinked polyamide separation function layer.

[0133] [Reference Example 1] The composite semipermeable membrane obtained in Example 1 was supplied with an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 at 7.0 MPa and 45°C for 24 hours, and then immersed in a 2 mass% aqueous sodium hypochlorite solution for 48 hours to remove the separation functional layer, thereby obtaining a porous support.

[0134] [Example 2] A composite semipermeable membrane having a crosslinked polyamide separating function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed in the first coagulation liquid at 40°C for 15 seconds.

[0135] [Example 3] A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that an 18% by mass solution of PSf in DMF was used as the polymer solution and the substrate coated with the polymer solution was immersed in the first coagulation liquid at 20°C for 25 seconds.

[0136] [Example 4] The mass per unit area of ​​the porous layer in the composite semipermeable membrane was 18 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 25°C for 25 seconds.

[0137] [Example 5] A 21% by mass DMF solution of PSf was used as the polymer solution, and the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 10 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of a DMF aqueous solution at 30°C for 15 seconds.

[0138] [Example 6] A composite semipermeable membrane having a porous layer with a mass per unit area of ​​12 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of a DMF aqueous solution at 30°C for 12 seconds.

[0139] [Example 7] A composite semipermeable membrane having a porous layer with a mass per unit area of ​​14 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 25°C for 15 seconds.

[0140] [Example 8] The mass per unit area of ​​the porous layer in the composite semipermeable membrane was 11 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 25°C for 15 seconds.

[0141] [Example 9] A composite semipermeable membrane having a crosslinked polyamide separating function layer was obtained in the same manner as in Example 1, except that a long-fiber polyester nonwoven fabric (average thickness 95 μm, longitudinal tensile strength 350 N / 5 cm) was used as the substrate.

[0142] Comparative Example 1 A 15.7 mass % DMF solution of PSf was used as the polymer solution, and the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 25 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 30°C for 5 minutes.

[0143] [Comparative Example 2] A polymer solution was added to a composite semipermeable membrane having a porous layer with a mass per unit area of ​​23 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Comparative Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed for 20 seconds in a first coagulation liquid consisting of an aqueous DMF solution at 25°C.

[0144] Comparative Example 3 A 18% by mass DMF solution of PSf as a polymer solution was applied to the same substrate as in Example 1 under the condition of 25°C until the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 20 g / m ２ The polymer solution was applied so that the thickness of the polymer solution was 100 μm. Thereafter, within 1.0 second of immersing the substrate coated with the polymer solution in pure water, pure water was pressed against the substrate from the side at a pressure of 1 kPa for about 3 seconds, and the substrate was then left in the pure water for 5 minutes to prepare a porous support. A crosslinked polyamide was formed on the obtained porous support in the same manner as in Example 1, and a composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained.

[0145] [Comparative Example 4] A 18 mass % solution of PSf in a mixed solvent of DMF and DMSO in a ratio of 90:10 was used as the polymer solution, and the mass of the porous layer per unit area of ​​the composite semipermeable membrane was 25 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 25°C for 5 minutes.

[0146] Comparative Example 5: A 18.3 mass % DMF solution of PSf was used as the polymer solution, and the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 12 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed for 2 seconds in a first coagulation liquid consisting of an aqueous DMF solution at 25°C.

[0147] Comparative Example 6: A 28% by mass DMF solution of PSf was used as the polymer solution, and the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 15 g / m ２ A composite semipermeable membrane having a crosslinked polyamide separation function layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution so that the polymer solution was immersed in a first coagulation liquid consisting of an aqueous DMF solution at 5°C for 15 seconds.

[0148] Tables 1 to 3 show the structures of the porous layers of the composite semipermeable membranes obtained in the Examples and Comparative Examples, the characteristics of the substrates, and the results of measuring the membrane performance.

[0149]

[0150]

[0151]

[0152] As is clear from the results shown in Tables 1, 2, and 3, the composite semipermeable membranes of Examples 1 to 9 according to the present embodiment have sufficient water production ability and salt removal ability, and are able to suppress a decrease in the amount of water produced even after high-pressure operation.

[0153] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-068770) filed on April 22, 2024, the entire contents of which are incorporated by reference.

[0154] The composite semipermeable membrane of the present invention is used for seawater desalination, brackish water desalination, drinking water production, industrial ultrapure water production, wastewater treatment, valuable resource recovery, and the like.

[0155] REFERENCE SIGNS LIST 1 composite semipermeable membrane 2 substrate 3 porous layer 4 separation function layer 5 separation membrane element 6 end plate 7 end plate 8 feed side channel material 9 permeate side channel material 10 water collection pipe 11 feed water 12 permeated water 13 concentrated water 14 convex portion on back surface of porous layer 15 concave portion on back surface of porous layer

Claims

1. A composite semipermeable membrane having a substrate, a porous layer provided on the substrate, and a separation functional layer provided on the porous layer, wherein the molecular weight cutoff of the porous layer is 10 kDa to 60 kDa and the specific surface area is 20 to 50 m ２ / g.

2. A composite semipermeable membrane having a substrate, a porous layer provided on the substrate, and a separation functional layer provided on the porous layer, wherein the molecular weight cutoff of the porous layer is 10 kDa to 60 kDa, and the tortuosity after supplying an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 to the composite semipermeable membrane for 2 hours under conditions of 5.5 MPa and 25°C is 1.5 to 7.

0.

3. The composite semipermeable membrane according to claim 1 or 2, wherein the surface of the porous layer opposite to the surface on which the separation functional layer is provided has an uneven shape, and the average equivalent circle diameter of the pores present in the recesses is 0.30 to 0.60 μm.

4. The mass per unit area of ​​the porous layer is 10 to 17 g / m ２ The composite semipermeable membrane according to claim 1 or 2, 5. The specific surface area of ​​the porous layer is 22 to 40 m ２ The composite semipermeable membrane according to claim 1 or 2, wherein the tensile strength is 1 / g.

6. The composite semipermeable membrane according to claim 1 or 2, wherein the molecular weight cutoff of the porous layer is 30 kDa to 45 kDa.

7. The composite semipermeable membrane according to claim 1 or 2, wherein the thickness of the porous layer is 10 to 20 μm after supplying an aqueous solution having a NaCl concentration of 3.5 mass% and a pH of 6.5 to the composite semipermeable membrane under conditions of 7.0 MPa and 45°C for 24 hours.

8. The composite semipermeable membrane according to claim 1 or 2, wherein the substrate is a long-fiber nonwoven fabric having a thickness of 80 to 100 μm, and the long-fiber nonwoven fabric has a tensile strength in the machine direction of 400 to 900 N / 5 cm.

9. A separation membrane element comprising the composite semipermeable membrane according to claim 1 or 2.

10. A fluid separation device comprising the separation membrane element according to claim 9.

11. A method for producing a composite semipermeable membrane, comprising the following steps (a) to (c): Step (a): A step of disposing a polymer solution obtained by dissolving a thermoplastic polymer in a good solvent on a substrate. Step (b): A step of contacting the polymer solution disposed on the substrate with a first coagulation liquid containing a non-solvent and a good solvent for the thermoplastic polymer to form a porous layer on the substrate, and forming the porous layer so that the amount of the good solvent in the porous support consisting of the substrate and the porous layer is 10 to 60 g / m. ２ Step (c): A step of immersing the porous support in a second coagulation liquid.

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