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

Abstract

The present invention relates to 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 10k to 60kDa and the specific surface area is 20 to 50m². 2 The present invention relates to a composite semipermeable membrane having a molecular weight of / g, or 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 fractional molecular weight of the porous layer is 10k to 60kDa, and the curve ratio after supplying an aqueous solution with an NaCl concentration of 3.5 mass% and pH 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.

Description

Technical Field

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

Background Art

[0002] Generally, a composite semipermeable membrane obtained by coating a porous layer with a separation functional layer made of a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide is used for reverse osmosis treatment for removing solutes from raw water, such as seawater desalination, because of its high water permeability and salt removal property.

[0003] In reverse osmosis treatment, a pressure greater than the difference between the osmotic pressure on the feed water side and the osmotic pressure on the permeate water side is applied to the feed water side of the composite semipermeable membrane. In recent years, reverse osmosis treatment has been used for zero liquid discharge (ZLD) to achieve zero drainage and for concentration in a valuable substance recovery process. Depending on the solute concentration, the number of cases where the operation is carried out at a higher pressure than in the past has been increasing.

[0004] In such high-pressure operation of reverse osmosis treatment, the water permeability of the composite semipermeable membrane may decrease. When there is no pressure history, the water permeability of the porous layer is about 100 times or more that of the separation functional layer. Therefore, the water permeability of the composite semipermeable membrane is dominated by the separation functional layer. However, it has been pointed out in Patent Documents 1 to 3 that the compaction of the porous layer caused by high-pressure operation reduces the water permeability of the porous layer and thus reduces the water permeability of the composite semipermeable membrane.

[0005] In Patent Document 1, the average membrane thickness t0 [μm] of the support membrane after applying a pressure of 5.5 MPa in the membrane thickness direction for 3 hours and then releasing the pressure and the pure water permeation coefficient p [g / (cm 2 , 2 ·s·MPa)], the average membrane thickness t1 [μm] of the support membrane after applying a pressure of 10 MPa in the membrane thickness direction for 3 hours and then releasing the pressure, and the pure water permeation coefficient p1 [g / (cm 2In the (s·MPa) setting, a reverse osmosis composite membrane is disclosed in which compaction is suppressed by satisfying specific numerical ranges for t1 / t0 and p1 / p0.

[0006] Patent Document 2 discloses a composite semipermeable membrane in which the porous support comprises 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 is disclosed that if the number of macrovoids per unit length in the membrane plane direction in the macrovoid layer is within a specific range, the thickness of the porous support can be maintained even under high-pressure operation.

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

[0008] [Patent Document 1] Japanese Patent Publication No. 2001-252538 [Patent Document 2] Japanese Patent Application Publication No. 2018-039003 [Patent Document 3] International Publication No. 2023 / 145845 [Overview of the project] [Problems that the invention aims to solve]

[0009] In processes operating at high pressure, such as ZLD (Zero-Layer Dehydration), there is concern about a decrease in the permeability of composite semipermeable membranes. Furthermore, in seawater desalination systems, for example, the system may be temporarily shut down, resulting in start-stop operations under high pressure, during which the composite semipermeable membrane is subjected to and released from pressure. As a result, the composite semipermeable membrane is damaged multiple times, leading to a decrease in its permeability and salt removal capabilities.

[0010] It has become clear that the decrease in water permeability is caused by the compaction of the porous layer, as disclosed in Patent Documents 1 to 3, and this has been solved by techniques to suppress the 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 to suppress the compaction of the porous layer involve changes in the surface structure of the porous layer, causing structural changes at the interface between the cross-linked polyamide and the porous layer or the cross-linked polyamide itself, and thus a composite semipermeable membrane that can maintain salt removal properties under harsh operation involving start-stop operation has not been obtained.

[0011] The present invention aims to provide a composite semipermeable membrane that maintains high water permeability and salt removal properties, and has high salt removal properties, even during operation involving on / off cycles at high temperatures and high pressures. The present invention also aims to provide a method for manufacturing the above composite semipermeable membrane. Furthermore, the present invention also aims to provide a separation membrane element comprising the above composite semipermeable membrane, and a fluid separation device comprising the above separation membrane element. [Means for solving the problem]

[0012] To solve the above problems, the composite semipermeable membrane in 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 10k to 60kDa and the specific surface area is 20 to 50m². 2 A composite semipermeable membrane with a density of / 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 10k to 60kDa, and the curve ratio after supplying an aqueous solution with an NaCl concentration of 3.5 mass% and pH 6.5 to the composite semipermeable membrane at 5.5 MPa and 25°C for 2 hours is 1.5 to 7.0. [3] The composite semipermeable membrane according to [1] or [2], wherein the surface of the porous layer opposite to the side on which the separation functional layer is provided has an uneven shape, and the average circle equivalent diameter of the pores 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 A composite semipermeable membrane as described in any one of the above [1] to [3]. [5] The specific surface area of ​​the porous layer is 22 to 40 m² 2 A composite semipermeable membrane according to any one of the above [1] to [4], wherein the density is / g. [6] A composite semipermeable membrane according to any one of [1] to [5] above, wherein the molecular weight cutoff of the porous layer is 30k to 45kDa. [7] The composite semipermeable membrane according to any one of [1] to [6] above, wherein the thickness of the porous layer after supplying the composite semipermeable membrane with an aqueous solution of 3.5% by mass and pH 6.5 to the composite semipermeable membrane under conditions of 7.0 MPa and 45°C for 24 hours is 10 to 20 μm. [8] The composite semipermeable membrane according to any one of [1] to [7] above, wherein the base material is a long-fiber nonwoven fabric with a thickness of 80 to 100 μm, and the tensile strength of the long-fiber nonwoven fabric in the longitudinal direction is 400 to 900 N / 5 cm. [9] A separation membrane element comprising a composite semipermeable membrane as described in any one of [1] to [8] above.

[10] A fluid separation device comprising the separation membrane element described in [9] above.

[11] A method for producing a composite semipermeable membrane, comprising the following steps (a) to (c). Step (a): A step of placing a polymer solution, obtained by dissolving a thermoplastic polymer in a good solvent, onto a substrate. Step (b): The polymer solution placed on the substrate is brought into contact with a first coagulation solution containing a non-solvent and a good solvent for the thermoplastic polymer to form a porous layer on the substrate, and the amount of the good solvent in the porous support consisting of the substrate and the porous layer is 10 to 60 g / m². 2 A process to obtain a porous support. Step (c): Step of immersing the porous support in a second solidification solution. [Effects of the Invention]

[0013] According to the present invention, a composite semipermeable membrane can be obtained that maintains high water permeability and salt removal properties after high-temperature and high-pressure operation, and also has high salt removal properties. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a cross-sectional view of a composite semipermeable membrane in one embodiment of the present invention. [Figure 2] Figure 2 is an unfolded view of a separation membrane element in one embodiment of the present invention. [Figure 3] Figure 3 shows an image of the substrate-side surface of the porous layer of the composite semipermeable membrane of Example 1, observed at 500x magnification using a scanning electron microscope. The white areas in the image are convex, and the surrounding gray areas are concave. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described in detail below, but the present invention is not limited thereto.

[0016] In this specification, the "~" in a numerical range means a range that includes the numbers before and after it. For example, "0 mass%~100 mass%" means a range that is 0 mass% or greater and 100 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 will be described below, as shown in Figure 1. The composite of the substrate and the porous layer will be referred to as a porous support.

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

[0019] As the fabric used as the base material, it is preferable to use a nonwoven fabric from the viewpoint of strength, ability to form irregularities, and fluid permeability. As the nonwoven fabric, both long-fiber nonwoven fabrics and short-fiber nonwoven fabrics can be preferably used.

[0020] In addition, the long-fiber non-woven fabric composed of thermoplastic continuous filaments is less likely to have lint. Therefore, by using the long-fiber non-woven fabric as a base material, film defects can be suppressed. Further, in the continuous film formation of the composite semi-permeable membrane, since tension is applied to the base material in the film formation direction, it is preferable to use a long-fiber non-woven fabric having excellent dimensional stability as the base material.

[0021] 1.1.1 Average single fiber diameter of the base material When the base material is a non-woven fabric, the average single fiber diameter of the fibers constituting the non-woven 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 base material. By maintaining the voids in this way, the polymer solution can quickly penetrate into the base material during the formation of the porous layer, so that the base material and the porous layer are firmly adhered, and a composite semi-permeable membrane with excellent film peeling strength can be obtained. On the other hand, when the average single fiber diameter is 14 μm or less, a base material and a porous layer with excellent uniformity can be obtained.

[0022] The average single fiber diameter is obtained by randomly selecting 10 single fibers from the base material which is a non-woven fabric, measuring the diameters at randomly selected positions of each single fiber, and calculating the arithmetic mean of the obtained values as the average single fiber diameter.

[0023] 1.1.2 Basis weight of the base material The basis weight of the base material used for the composite semi-permeable membrane according to the present embodiment is preferably 60 to 120 g / m 2 is more preferably 60 to 100 g / m 2 is even more preferably 70 to 90 g / m 2 By setting the basis weight of the base material within the above range, it has high mechanical strength that can withstand high-pressure operation, and can reduce the thickness of the composite semi-permeable membrane and increase the membrane area per separation membrane element.

[0024] 1.1.3 Density of the base material The density of the base material used for the composite semi-permeable membrane according to the present embodiment is 0.70 to 0.95 g / cm 3Preferably, 0.75-0.95 g / cm³ 3 More preferably, 0.80-0.95 g / cm³ 3 This is even more preferable. By setting the density of the substrate within the above range, deformation of the porous layer and separation functional layer caused by the material sinking into the substrate due to high-pressure operation can be suppressed. Furthermore, because there are voids that allow the polymer solution to quickly penetrate into the substrate during porous layer formation, the substrate and the porous layer adhere firmly, and a composite semipermeable membrane with excellent peel strength can be obtained.

[0025] 1.1.4 Thickness of the base material In this embodiment, the substrate thickness of the composite semipermeable membrane is preferably 80 to 100 μm. By setting the substrate thickness within this range, it is possible to have high mechanical strength that can withstand high-pressure operation, reduce the thickness of the composite semipermeable membrane, and increase the membrane area per separation membrane element.

[0026] The thickness of the substrate can be measured using a dial thickness gauge or a digital thickness gauge. Suitable dial thickness gauges and digital thickness gauges include those from Ozaki Seisakusho Co., Ltd. (PEACOCK) and Teclock Co., Ltd. When using a dial thickness gauge or digital thickness gauge, measure the thickness at 20 randomly selected locations, calculate the arithmetic mean, and use this as the substrate thickness.

[0027] 1.1.5 Tensile strength of the base material In this embodiment, it is preferable to use a long-fiber nonwoven fabric made of thermoplastic continuous filaments as the substrate for the composite semipermeable membrane. Long-fiber nonwoven fabrics made of thermoplastic continuous filaments have higher mechanical strength than short-fiber nonwoven fabrics, especially papermaking nonwoven fabrics with short fiber lengths, and composite semipermeable membranes using long-fiber nonwoven fabrics as a substrate can exhibit excellent durability even under conditions where high pressure is applied during use. Furthermore, composite semipermeable membranes using long-fiber nonwoven fabrics as a substrate can suppress a decrease in water production volume or membrane damage caused by the composite semipermeable membrane falling into the recess of the supply water channel material when operated as a separation membrane element.

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

[0029] One method for controlling the tensile strength and tensile strength-to-width ratio of a long-fiber nonwoven fabric is to apply heat or pressure to form a laminate of the long-fiber nonwoven fabric into a structure with multiple calender rolls or the like. The number of layers of the long-fiber nonwoven fabric is preferably 2 to 5. If the number of layers is 2 or more, the strength is improved compared to a single layer, and if it is 5 or less, wrinkles during lamination and delamination 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 of a thermoplastic polymer. Here, "thermoplastic polymer" refers to a polymer made of chain-like polymer material 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 components. Here, "main component" means a component that accounts for 50% or more by mass of the components constituting the porous layer.

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

[0033] 1.2.1 Specific surface area and molecular weight cutoff of porous layers The first embodiment of the composite semipermeable membrane of the present invention has a porous layer with a molecular weight cutoff of 10k to 60kDa and a specific surface area S of 20 to 50m². 2 The value is / g. In this specification, the fractional molecular weight and specific surface area S of the porous layer may be measured using either the composite semipermeable membrane before use or after use. For example, the fractional molecular weight and specific surface area S of the porous layer may be measured after supplying an aqueous solution of 3.5% by mass and pH 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 of 3.5% by mass and pH 6.5 to the composite semipermeable membrane under conditions of 5.5 MPa and 25°C for 2 hours.

[0034] The specific surface area S represents the degree of the three-dimensional network structure within the porous layer. A large specific surface area S indicates a dense three-dimensional network structure with numerous small voids. While this three-dimensional network structure resists water permeability, it can also distribute pressure, thus increasing the pressure resistance of the porous layer. A specific surface area S of 20 m² represents the degree of the three-dimensional network structure. 2 When the pressure is 50m or higher, the porous layer can sufficiently distribute the pressure due to its three-dimensional network structure, thus suppressing consolidation even under high-pressure operation. 2If the value is less than / g, the proportion of the three-dimensional network structure that acts as resistance to the water permeability path can be suppressed, and sufficient water permeability can be ensured. In other words, if the specific surface area S of the porous layer of the composite semipermeable membrane satisfies the above range, the compaction of the porous layer during high-pressure operation is suppressed by the three-dimensional network structure. Therefore, if 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 will also satisfy the above range.

[0035] From the perspective of suppressing compaction of the porous layer and ensuring water permeability, the specific surface area S is 20-40 m². 2 / g is preferred, 22-40m 2 / g is more preferable at 28-35m 2 / g is even more preferable.

[0036] One method for controlling the specific surface area S within the above range is to bring a porous support, which has been immersed in a first coagulation solution to form a porous layer, into contact with a second coagulation solution containing a good solvent for the polymer forming the porous layer during the process of forming the porous layer. The specific surface area S can be controlled by the contact time between the first and second coagulation solutions and the temperature of each coagulation solution.

[0037] Furthermore, maintaining salt removal performance is a challenge during high-pressure operation involving on / off cycles. The decrease in salt removal performance is mainly due to structural changes at the interface between the cross-linked polyamide and the porous layer, or the cross-linked polyamide itself, and the structure of the porous layer surface forming the cross-linked 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 obtain the desired salt removal performance.

[0038] As a result of diligent research into the above-mentioned problems, the inventors have found that the molecular weight cutoff of the porous layer is 10k to 60kDa, and the specific surface area is 20 to 50m². 2 We found that a composite semipermeable membrane with a density of / g can achieve both water permeability, retention of salt removal properties, and high salt removal performance during operation involving on-stop and off cycles at high temperatures and high pressures.

[0039] In other words, by achieving both the aforementioned fractionation properties and specific surface area, it is possible to suppress the consolidation of the porous layer of the composite semipermeable membrane due to high-pressure operation, thereby suppressing the decrease in water permeability and salt removal performance. Such a composite semipermeable membrane that achieves both fractionation properties and specific surface area has not been obtained with conventional technology.

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

[0041] By keeping the molecular weight cutoff of the porous layer within the above range, a composite semipermeable membrane can be obtained that maintains salt removal performance even during operation involving on-stop cycles. If the molecular weight cutoff of the porous layer is greater than 60 kDa, the separation functional layer will sink into the surface of the porous layer during high-pressure on-stop operation, causing deformation of the separation functional layer and a decrease in salt removal performance. 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. This not only reduces the water permeability of the composite semipermeable membrane but also forms a low-strength polyamide, making it impossible to maintain salt removal performance during high-pressure operation. Methods for controlling the molecular weight cutoff of the porous layer within the above range include, for example, adjusting the coagulation solution temperature when forming the porous layer and adjusting the polymer concentration of the polymer solution used to form the porous layer.

[0042] 1.2.2 Curvature of porous layers A second embodiment of the composite semipermeable membrane of the present invention is characterized in which the molecular weight cutoff of the porous layer is 10k to 60kDa, and the curve ratio 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 for 2 hours under conditions of 5.5 MPa and 25°C is 1.5 to 7.0. The molecular weight cutoff is as described above.

[0043] "Curvature ratio," also known as the degree of curvature, refers to the degree to which the flow path through which the permeate passes is curved. In other words, the lower the curvature ratio, the closer the flow path is to a straight line, resulting in a highly interconnected structure. From the viewpoint of pressure resistance, it is preferable for the porous layer to have a three-dimensional network structure formed by non-solvent-induced phase separation. As mentioned above, the three-dimensional network structure provides resistance to the permeable pathway, but it can also disperse pressure, thus increasing pressure resistance. That is, a curvature ratio of 1.5 to 7.0 for the porous layer of a composite semipermeable membrane after operation at a pressure of 5.5 MPa means that even after high-pressure operation, the porous layer has a highly interconnected three-dimensional network structure, meaning that, similar to the specific surface area S mentioned above, the three-dimensional network structure can suppress the consolidation of the porous layer due to high-pressure operation. If the curvature ratio of the porous layer is greater than 7.0, the degree of curvature of the flow path within the porous layer is large, making it easier for the flow path to become blocked due to consolidation caused by high-pressure operation, resulting in reduced water permeability. On the other hand, if the curvature ratio is less than 1.5, the proportion of the three-dimensional network structure in the porous layer is small, making it difficult to distribute the pressure, and thus consolidation is likely to occur during high-pressure operation exceeding 5.5 MPa.

[0044] The "curvature ratio" can generally be calculated based on the Kozeny-Carman formula, and is described, for example, in the Journal of the Japanese Association for Petroleum Technology (Vol.75, No.2 (March, 2010) pp.164~176). From the viewpoint of suppressing the compaction of the porous layer, the curvature ratio of the porous layer is preferably 1.5 to 5.5, and more preferably 1.5 to 4.0. A curvature ratio of 1.0 means that the pores are cylindrical in shape and in a straight line. Furthermore, it is more preferable that the curvature ratio after supplying an aqueous solution with an 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] One method for controlling the curvature of the porous layer within the above range is to bring a porous support, which has been immersed in a first coagulation solution to form a porous layer, into contact with a second coagulation solution containing a good solvent for the polymer forming the porous layer. This can be controlled by the contact time between the first and second coagulation solutions and the temperature of each coagulation solution.

[0046] In this specification, the curvature ratio is determined using the following formula (1). Curvature rate=(ε / 2k) 1 / 2 ·(V / S) ···Formula (1) ε: Porosity of the porous layer after 5.5 MPa operation [-] k: Permeability coefficient of the porous layer after operation at 5.5 MPa [m 2 ] V: Pore volume of the porous layer after 5.5 MPa operation [m³ 3 / g] S: Specific surface area of ​​the porous layer after operation at 5.5 MPa [m²] 2 / g]

[0047] Here, "after 5.5 MPa operation" refers to the period after 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. Furthermore, the porosity ε of the porous layer after 5.5 MPa operation is the density ρ [g / cm³] of the thermoplastic polymer forming the porous layer. 3 It can be calculated by the ratio of the volume of the porous layer, which is determined from the mass of the porous layer, to the volume of the porous layer, which is determined from the thickness of the porous layer. Specifically, it is calculated by the method described in "3. Thickness of the porous layer and substrate" and "4. Porosity ε of the porous layer" in the examples described later.

[0048] Pore ​​volume V[m³] of the porous layer after 5.5 MPa operation 3 [ / g] is the density ρ[g / cm³] of the thermoplastic polymer that forms the porous layer. 3 It can be calculated using the porosity ε of the porous layer after 5.5 MPa operation. Specifically, it is calculated using the method described in "5. Pore Volume V of the Porous Layer" in the examples described later.

[0049] Permeability coefficient k[m] of the porous layer after 5.5 MPa operation 2 ] is calculated at 25℃, pressure P[Pa], porous layer thickness L[m], membrane area A[m] 2 The pure water permeability Q[m] 3 It can be calculated from the viscosity of pure water μ[Pa·s], and specifically measured by the method described in "1. Permeability coefficient k of porous layer" in the examples described later.

[0050] Furthermore, the permeability coefficient k is set to 0.35 × 10⁻⁶ from the viewpoint of stably obtaining good properties of the porous membrane. -17 ~5.0×10 -17 m 2 Preferably, 0.70 × 10 -17 ~5.0×10 -17 m 2 More preferably, 1.0 × 10 -17 ~5.0×10 -17 m 2 This is even more preferable. 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 such as 7.0 MPa and 45°C.

[0051] To measure the above physical properties, a method for removing the separation functional layer from the composite semipermeable membrane is, for example, if the separation functional layer is composed of polyamide, to immerse the composite semipermeable membrane in an aqueous sodium hypochlorite solution to decompose and remove it. Specifically, it is removed by the method described in "1. Permeability coefficient k of the porous layer" in the examples described later.

[0052] 1.2.2 Pore diameter on the back surface of the porous layer In this embodiment, from the viewpoint of improving adhesion to the substrate, it is preferable that the composite semipermeable membrane has an uneven surface on the side opposite to the side of the porous layer on which the separation functional layer is provided (hereinafter referred to as the "back surface"). The uneven surface on the back surface of the porous layer is formed by transferring the uneven surface of the substrate surface, etc. "Uneven surface" means a shape in which convex and concave portions are alternately continuous. The uneven surface can be observed with a scanning electron microscope (hereinafter referred to as "SEM").

[0053] In the composite semipermeable membrane according to this embodiment, the average circle equivalent diameter of the pores 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 circle equivalent diameter is within the above range, blockage of 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 in the recesses on the back surface of the porous layer is 25 μm. 2 A number of pores per unit area of ​​15 to 35 is preferable. The pores in the recesses on the back surface of the porous layer serve as channels through which the filtrate permeates. Therefore, the more pores there are on the back surface, the more interconnected the inner structure of the porous layer becomes, allowing it to withstand compaction. The number of pores in the recesses on the back surface of the porous layer can be measured by surface observation using a scanning electron microscope (SEM). Specifically, it is measured by the method described in "8. Unevenness shape, number of pores, and average circle equivalent diameter of the back surface of the porous layer" in the examples described later.

[0055] The number of pores and the average diameter of the pores in the recesses on the back surface of the porous layer can be controlled, for example, by the thickness of the polymer solution applied to the substrate and the amount of good solvent in the thermoplastic polymer immediately before proceeding to step (c) described in "2.1 Porous Layer Formation Process" 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 / m². 2 Preferably, 10-15 g / m 2 More preferably, 11-15 g / m 2 This is even more preferable. When the mass per unit area of ​​the porous layer is within the above range, it is easier to achieve both high mechanical strength capable of withstanding high-pressure operation and good interoperability (low curvature). 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, and the temperature of the coagulation solution.

[0057] 1.2.4 Thickness of the porous layer The 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 under conditions of 7.0 MPa and 45°C 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 curvature 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, and 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, the temperature of the coagulation solution, etc.

[0058] 1.3 Separation functional layer The separation functional layer of the composite semipermeable membrane according to this embodiment preferably contains a crosslinked polyamide, and more preferably contains a crosslinked polyamide as the main component. Furthermore, it is even more preferable that the separation functional layer contains a crosslinked aromatic polyamide as the crosslinked polyamide. The main component refers to the component that accounts for 50% by mass or more of the components of the separation functional layer. If the separation functional layer contains 50% by mass or more of crosslinked polyamide, it can exhibit higher removal performance. Furthermore, the crosslinked polyamide content 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 compound or higher. This results in rigid molecular chains and a pore structure suitable for the removal of fine solutes such as hydrated ions and boron. In particular, it is preferable to form a crosslinked aromatic polyamide as a separation functional layer by chemically reacting a polyfunctional aromatic amine with a polyfunctional aromatic acid halide.

[0060] A "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 the aromatic ring in an ortho, meta, or para position, 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, as well as 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. Examples include polyfunctional aromatic amines such as sylamine, 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 individually or in combination.

[0061] In particular, considering the selective separation, permeability, and heat resistance of the membrane, m-PDA, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, m-PDA is more preferable due to its availability and ease of handling. These polyfunctional aromatic amines may be used individually or in combination of two or more.

[0062] "Polyfunctional acid halides" refer to acid halides or polyfunctional acid anhydride halides having at least two halogenated carbonyl groups in one molecule, and are not particularly limited as long as they form a separation functional layer of crosslinked polyamide through reaction with the above-mentioned polyfunctional amine. For example, trifunctional acid halides include trimesic acid chloride (hereinafter referred to as "TMC"), 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride. Examples of difunctional acid halides include aromatic difunctional acid halides such as biphenyldicarboxylic acid dichloride, biphenylenecarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic difunctional acid halides such as adipoyl chloride and sebacoyl chloride; and alicyclic difunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofrancicarboxylic acid dichloride. These polyfunctional acid halides may be used individually or in combination.

[0063] Considering the selective separation properties and heat resistance of the membrane, a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule is more preferable.

[0064] 1.4 Separation membrane element The separation membrane element according to this embodiment comprises a composite semipermeable membrane according to this embodiment. An example of the configuration of the separation membrane element will be described with reference to Figure 2.

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

[0066] The supply-side flow channel material 8 is positioned opposite the supply side of the composite semipermeable membrane 1 and is wrapped around the water collection pipe 10 together with the composite semipermeable membrane 1. A net is preferred as the supply-side flow channel material 8.

[0067] The permeable channel material 9 is positioned opposite the permeable side of the composite semipermeable membrane 1 and is wrapped around the water collection pipe 10 together with the composite semipermeable membrane 1. For the permeable channel material 9, for example, tricot or a sheet with protrusions can be used.

[0068] The water collection pipe 10 is a hollow cylindrical member having multiple holes on its side.

[0069] The end plates 6 and 7 are disc-shaped members equipped with multiple supply ports (or discharge ports).

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

[0071] 2. Method for manufacturing composite semipermeable membranes 2.1 Process for forming a porous layer The porous layer formation 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 placing a polymer solution, obtained by dissolving a thermoplastic polymer in a good solvent, onto a substrate. Step (b): The polymer solution placed on the substrate is brought into contact with a first coagulation solution containing the non-solvent and good solvent of the thermoplastic polymer to form a porous layer on the substrate, and the amount of the good solvent in the porous support consisting of the substrate and the porous layer is 10 to 60 g / m². 2 A process to obtain a porous support. Step (c): Step of immersing the porous support in a second solidification solution.

[0072] In step (a) above, a polymer solution is applied to the substrate. Subsequently, in step (b) above, the polymer solution is brought into contact with a first coagulation solution containing a polymer non-solvent and a good solvent, 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 large contact with the coagulation solution, which is composed of the polymer's non-solvent, causing it to solidify immediately and form a dense three-dimensional network structure. On the other hand, the interior of the polymer solution solidifies relatively slowly compared to the surface because the dense three-dimensional network structure formed on the surface of the polymer solution inhibits the inflow of the coagulation solution and the outflow of good solvents from the polymer solution. Therefore, in conventional methods for forming porous layers, phase separation progresses inside the polymer solution, and the interior of the porous layer forms a network structure with larger voids compared to the surface. This network structure with large voids has poor pressure resistance and is unfavorable for high-pressure operation.

[0074] After diligent research, the inventors determined that in step (b), the amount of good solvent in the porous support is 10 to 60 g / m². 2 By setting the porous support obtained in step (b) to a state and immersing it in a second solidification solution in step (c), the interior of the porous layer is completely solidified, forming a dense three-dimensional network structure inside the porous layer, and a composite semipermeable membrane with a small pore size on the surface of the porous layer is obtained. In step (c), by bringing the inner layer of the porous support into contact with the second solidification solution while the porous support contains a certain amount of good solvent, the inner layer of the porous layer dissolves, forming a dense three-dimensional network structure with high communication in the inner layer, thereby improving pressure resistance. In other words, it becomes possible to control the molecular weight cutoff and specific surface area S or the molecular weight cutoff and the curvature ratio after high-temperature and high-pressure operation within an appropriate range.

[0075] "Polymer" refers to thermoplastic polymers that are the main components of porous layers, and specifically as described above.

[0076] A "good solvent" refers to a solvent that dissolves polymers. By selecting a 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 path on the back surface of the porous layer can be controlled. As a good solvent, 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-dimethylisobutylamide, N,N-diisopropylisobutylamide, and N,N-bis(2-ethylhexyl)isobutylamide, 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, the use of DMF as the good solvent is more preferable.

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

[0078] The application of polymer solutions to substrates can be carried out by various coating methods. Among these, pre-metering coating methods such as die coating, slide coating, and curtain coating, which can supply an accurate amount of polymer solution, are preferred. In particular, the slit die method for applying polymer solutions is preferred for forming porous layers. The coating thickness of the polymer solution on the substrate is preferably 50 to 150 μm, and more preferably 80 to 120 μm. By keeping 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 to a suitable range.

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

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

[0081] When applying a polymer solution, if PSf is used as the polymer, it is preferable to apply the solution within the range of 10 to 40°C. Within this range, the PSf can be applied without precipitation. The preferred temperature range of the polymer solution can be adjusted as appropriate depending on the viscosity of the polymer solution used.

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

[0083] The solvent contained in the polymer solution may be a single good solvent for polymers, or a mixture of several good solvents may be used. The solvent can be adjusted as appropriate, taking into account the strength characteristics of the porous layer to be manufactured and the impregnation of the polymer solution into the substrate.

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

[0085] The above contact can be performed by immersing the substrate on which the polymer solution is placed in the first coagulation solution.

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

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

[0088] Furthermore, the temperature of the first coagulation solution is preferably 10 to 45°C. If the temperature of the first coagulation solution is 45°C or lower, the vibration of the coagulation solution surface due to thermal motion does not intensify, and the surface smoothness of the porous layer is improved. Also, if the temperature of the first coagulation solution is 10°C or higher, a sufficient coagulation rate is obtained, and film-forming properties are good. When the temperature of the coagulation solution is within the above range, the molecular weight cutoff of the porous layer can be controlled to the range of 10k to 60kDa, and a separation functional layer with excellent salt removal properties can be formed.

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

[0090] In step (c), the porous support obtained in step (b) is brought into contact with the inner layer of the porous layer with a second coagulation solution while containing a good solvent. By dissolving the inner layer of the porous layer, a dense three-dimensional network structure is formed in the inner layer of the porous layer, allowing control of the specific surface area S or the curvature ratio after a predetermined operation.

[0091] In the method for producing a composite semipermeable membrane according to this embodiment, an important control factor 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 solution is 10 to 60 g / m². 2 It is 20-50 g / m 2 Preferably, 30-40 g / m 2 A more preferable amount of good solvent in the porous support is 10 g / m². 2 If the amount is above this, the amount of good solvent is sufficient to dissolve the polymer. On the other hand, the amount of good solvent in the porous support is 60 g / m². 2The following conditions can suppress structural changes in the surface layer of the porous layer. The amount of good solvent in the porous support when immersed in the second coagulation solution can be controlled, for example, by the concentration of the good solvent in the first coagulation solution used in step (b), the temperature, and the contact time between the polymer solution and the first coagulation solution.

[0092] The temperature of the second coagulation solution used in step (c) is preferably 20 to 90°C, and more preferably 50 to 85°C. If the temperature of the coagulation solution is 20°C or higher, the inner layer of the porous layer can be sufficiently dissolved and the curvature can be controlled, and if it 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 solution used in step (c) only needs to contain a polymeric non-solvent, and is preferably a mixed solution of a polymeric non-solvent and a good solvent. The concentration of the good solvent in the second coagulation solution is preferably 0.1 to 10% by mass, and more preferably 1 to 10% by mass. If the concentration of the good solvent in the second coagulation solution is 0.1% by mass or more, the inner layer of the porous layer can be sufficiently dissolved, and if it is 10% by mass or less, changes in the surface structure of the porous layer can be suppressed.

[0094] Furthermore, since phase separation progresses moment by moment, it is preferable that the time between step (b) and step (c) be as short as possible. The interval between obtaining the porous support in step (b) and carrying out step (c) is preferably 10 seconds or less, more preferably 7 seconds or less, and even more preferably 5 seconds or less.

[0095] Next, it is preferable to wash the porous support obtained in step (c) with hot water or the like to remove any remaining solvent in the porous support. The temperature of the hot water used for washing is preferably 50 to 100°C, and more preferably 60 to 95°C. If the hot water temperature is 100°C or lower, the degree of shrinkage of the porous support can be kept to a minimum. Also, if the hot water temperature is 50°C or higher, a high cleaning effect can be obtained.

[0096] 2.2 Process for forming the separation functional layer Next, we will explain the method for forming the separation functional layer.

[0097] The separation functional layer can be obtained, for example, by forming a crosslinked polyamide by chemically reacting a polyfunctional amine with a polyfunctional acid halide, as described above. Interfacial polymerization is the most preferred method of chemical reaction from the viewpoint of productivity and performance. Specifically, 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 forms a crosslinked polyamide. The following describes a specific process for 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] Interfacial polymerization includes steps (d) and (e) below. Step (d): A step of bringing an aqueous solution containing a polyfunctional aromatic amine into contact with a porous layer. Step (e): A step in which, after step (d), a solution containing a polyfunctional aromatic acid chloride is brought into contact with the porous layer.

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

[0100] It is preferable to apply the polyfunctional aromatic amine aqueous solution uniformly and continuously to the porous layer. Specifically, examples include coating the porous layer with the polyfunctional aromatic amine aqueous solution or immersing the porous layer in the polyfunctional aromatic amine aqueous solution. The contact time between the porous layer and the polyfunctional aromatic amine aqueous solution is preferably 1 second to 10 minutes, and more preferably 10 seconds to 3 minutes.

[0101] After contacting the porous layer with the polyfunctional aromatic amine aqueous solution, it is preferable to remove any remaining liquid droplets from the surface of the porous support. Removing the liquid can suppress the occurrence of defects in the separation functional layer. Methods for removing the liquid include, for example, holding the porous support vertically after contact with the polyfunctional aromatic amine aqueous solution to allow excess solution to flow naturally, or forcibly removing the liquid by blowing a stream of air such as nitrogen from an air nozzle. After removing the liquid, the film surface can also be dried to remove some of the water from the aqueous solution.

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

[0103] The solvent used in the solution for dissolving the polyfunctional aromatic acid chloride is preferably an organic solvent that is immiscible with water, dissolves the polyfunctional aromatic acid chloride without destroying the porous support, and is inert to the polyfunctional aromatic amine and the polyfunctional aromatic acid chloride. Preferred examples of organic solvents include hydrocarbon compounds such as n-nonane, n-decane, n-undecane, n-dodecane, isooctane, isodecane, and isododecane, or mixtures thereof.

[0104] The method for contacting the porous layer with the organic solvent solution of the polyfunctional aromatic acid chloride with the aqueous solution of the polyfunctional aromatic amine can be the same as the method for coating the porous layer with the aqueous solution of the polyfunctional aromatic amine.

[0105] After the interfacial polymerization reaction, the organic solvent is removed from the film surface. Methods for removing the organic solvent include, for example, vertically gripping the porous support and allowing excess organic solvent to flow naturally; drying the organic solvent by blowing air with a fan; or removing excess organic solvent with a mixed fluid of water and air.

[0106] Furthermore, depending on the desired performance of the composite semipermeable membrane, aliphatic amines or alicyclic polyfunctional amines may be used instead of polyfunctional aromatic amines, and aliphatic difunctional acid halides or alicyclic difunctional acid halides may be used instead of polyfunctional aromatic acid chlorides to form crosslinked aliphatic polyamides or crosslinked alicyclic polyamides.

[0107] 3. Methods of using composite semipermeable membranes The composite semipermeable membrane according to this embodiment is preferably used as a spiral-type composite semipermeable membrane element, wound around a cylindrical water collection pipe with numerous holes, together with a water supply channel material such as a plastic net, a permeable water channel material such as tricot, and a film to enhance pressure resistance as needed. Furthermore, a composite semipermeable membrane module can be formed by connecting these elements in series or parallel and housing them in a pressure vessel.

[0108] Furthermore, the composite semipermeable membranes, their elements, and modules can be combined with pumps that supply water to them, and devices that pre-treat the water, to form a fluid separation system. By using this fluid separation system, the water can be separated into permeate (such as drinking water) and concentrated water that did not permeate the membrane, thereby obtaining water suitable for the purpose.

[0109] Examples of feedwater treated by the composite semipermeable membrane according to this embodiment include 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, it can be calculated from the mass of the residue after evaporating a solution filtered through a 0.45 micron filter at a temperature of 39.5 to 40.5°C, but a simpler method is to convert it from the practical salinity (S).

[0110] A higher operating pressure when permeating feedwater through the composite semipermeable membrane improves the solute removal rate. However, considering the increased energy required for operation and the durability of the composite semipermeable membrane, an operating pressure of 0.5 to 12 MPa is preferable. As the feedwater temperature increases, the solute removal rate decreases, and as it decreases, the membrane permeation flux decreases. Therefore, a feedwater temperature of 5 to 55°C is preferable.

[0111] In this embodiment, the composite semipermeable membrane preferably has a water production volume change ratio calculated by the method described in "12. High-Pressure Test" in the examples described later, which is 0.80 or higher, more preferably 0.85 or higher, even more preferably 0.90 or higher, and particularly preferably 0.94 or higher. Furthermore, the removal rate change ratio calculated by the above method is preferably 1.30 or lower, more preferably 1.20 or lower, and even more preferably 1.10 or lower. Moreover, it is preferable that both the water production volume change ratio and the removal rate change ratio simultaneously satisfy the above ranges.

[0112] In typical composite semipermeable membranes, during operation at temperatures above 35°C with a TSD of 40,000 mg / L or higher, involving on-and-off cycles, the water production rate decreases significantly due to the compaction of the porous layer. Therefore, to maintain a constant water production rate in the fluid separation unit, the operating pressure must be increased, which increases the energy required for operation.

[0113] In the water production method using the composite semipermeable membrane according to this embodiment, compaction of the porous layer does not progress even during operation at 35°C or above with a TSD of 40,000 mg / L or more, accompanied by start-stop operation. As a result, the decrease in water production volume of the composite semipermeable membrane is suppressed, the increase in operating pressure required to maintain a constant water production volume of the fluid separation device can be reduced, and the increase in energy required for operation can be reduced.

[0114] Furthermore, if the pH of the supply water is high, there is a risk of scale formation, such as magnesium, in the case of supply water with high solute concentrations, such as seawater. There is also concern about membrane degradation due to filtering high-pH supply water. Therefore, it is preferable for the supply water to have a neutral pH. [Examples]

[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 for each measurement was obtained by immersing a composite semipermeable membrane in a 2% by mass sodium hypochlorite aqueous solution for 48 hours and removing the separation functional layer.

[0116] 1. Permeability coefficient k of the porous layer A composite semipermeable membrane was subjected to a 5.5 MPa operation, where an aqueous solution with a NaCl concentration of 3.5% by mass and a pH of 6.5 was supplied for 2 hours at 5.5 MPa and 25°C. After the 5.5 MPa operation, the composite semipermeable membrane was immersed in a 2% by mass sodium hypochlorite aqueous solution for 48 hours to remove the separation functional layer and obtain a porous support. 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 cm²). 2 ). Pure water at 25°C was placed inside 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 permeability Q[m] over a certain period of time was measured. 3 The measurement was taken at 25°C, pressure P[Pa], porous layer thickness L[m], and membrane area A[m]. 2 The pure water permeability Q[m] 3 The permeability coefficient k of the porous layer after 5.5 MPa operation was calculated from the [s] and pure water viscosity μ[Pa·s] using the following formula (2). Two significant figures were used. k[m 2 ]=Q×μ×L / (A×P)...Equation (2) Here, a porous support is used for the measurement, but since the water permeability resistance of the substrate in the porous support is negligibly small compared to that of the porous layer, the permeability coefficient k obtained in equation (2) above is considered to be the permeability coefficient of the porous layer.

[0117] 2. Mass per unit area of ​​the porous layer A porous support was cut into a rectangle measuring 0.11 m × 0.19 m, dried at 120°C for 2 hours, and its mass was measured. The porous layer was then peeled off the support using 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 ​​porous layer [g / m²] 2 ] = (mass of porous support - mass of substrate) / (0.11 × 0.19) ... Equation (3)

[0118] 3. Thickness of the porous layer and substrate The thickness of the porous layer (thickness of the porous layer after high-temperature, high-pressure operation) after supplying an aqueous solution with a NaCl concentration of 3.5 mass and a pH of 6.5 to a composite semipermeable membrane under conditions of 7.0 MPa and 45°C for 24 hours was measured using a dial thickness gauge (TECLOCK Corporation, constant-pressure thickness measuring instrument PG-01A) on the composite semipermeable membrane after operation under these conditions. First, since the separation functional layer is very thin, the sum of the thickness of the substrate and the porous layer was considered as the thickness of the composite semipermeable membrane, and the thickness of the composite semipermeable membrane was measured. Then, the substrate was peeled off the composite semipermeable membrane with tape, and the thickness of the peeled substrate was measured with the above 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. For each thickness measurement, the arithmetic mean of 20 randomly selected measurement points on the same membrane surface was used. The thickness of the substrate of the composite semipermeable membrane was measured using the same method on the composite semipermeable membrane before operation under the above conditions.

[0119] 4. Porosity ε of the porous layer For the porous support obtained after operation at 5.5 MPa using the method described in "1. Permeability coefficient k of the porous layer" above, the porosity was calculated using the following equations (4), (5), and (6). Note that polymer density [g / m³] 3 ] is the density of the thermoplastic polymer that forms the porous layer; if the porous layer is a mixture of multiple types of thermoplastic polymers, the mixed density is used. Polymer volume [m³] 3 ] = Mass per unit area of ​​porous layer × (0.11 × 0.19) / Polymer density ... Equation (4) Apparent volume of porous layer [m³] 3 ] = thickness of porous layer × (0.11 × 0.19) ... Equation (5) Porosity of the porous layer ε[-] = 1 - (Volume of polymer / Apparent volume of the 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 using the following formula (7), based on the relationship: pore volume : (1 / polymer density) = porosity : (1 - porosity). Pore ​​volume V [cm³] of porous layer 3 / g]=porosity×(1-porosity) / polymer density...Equation (7)

[0121] 6. Specific surface area S and curvature ratio of the porous layer The specific surface area S of the porous layer was measured from the porous support by nitrogen adsorption measurement. Furthermore, the curvature ratio after 5.5 MPa operation was calculated using equation (1) above from the porosity ε, permeability coefficient k, pore volume V, and specific surface area S of the porous layer after 5.5 MPa operation. The porous layer was peeled from the porous support, and only the peeled porous layer was cut into 5 mm squares using a single blade to obtain 0.1 to 0.3 g of measurement sample. The measurement sample was dried in a vacuum at 45°C for 4 hours. The specific surface area S of the dried sample was measured by the BET method using a nitrogen adsorption analyzer (Microtrac Bell; BELSORP-miniII). Before measurement, a leak check was performed to confirm that the leak was less than 5 Pa / min, and then the measurement was started under the following conditions. [Adsorbent setting] The adsorbate was set to N2 gas, and the adsorption temperature was set to 77K. [Thermal Transpilation Settings] The molecular diameter was set to 0.364 mm, the inner diameter of the sample tube to 7.0 mm, and the outer diameter of the glass rod to 6.0 mm. [Measurement device settings] I chose "Dewar flask". [Saturated vapor pressure setting] I selected "Actual Measurement". [Adsorbed gas non-ideality correction] The second virial coefficient is -4.264 × 10⁻⁶ -7 Pa -1 I set it to that. [Purge settings] The sample tube discard rate was set to "slow," and the purge gas was set to Ads(V2). [Nth adsorption setting] The degassing time was set to 120 minutes, and a third-order isotherm was selected. [Adsorbate introduction pressure setting] I selected "Relative pressure display". [Measurement method] I selected the simplified method, set the upper limit of the adsorption relative pressure to 0.35, and configured desorption measurement and measurement relative pressure specification.

[0122] 7. Molecular weight of the porous layer Aldrich's dextran Mw1500 (product number: 31394), Mw6000 (product number: 31388), Mw15000~20000 (product number: 31387), Mw~40000 (product number: 31389), Mw~60000 (product number: 31397), and Mw~200000 (product number: 31398) were each dissolved in distilled water to a concentration of 500 ppm to prepare dextran aqueous solutions, which were used as the raw water.

[0123] A porous support was cut into a 4.3 cm diameter circle, and the cut-out sample was placed in a stirring-type ultra-holder (UHP-43K, manufactured by Advantec Toyo Co., Ltd.) (effective filtration area: 10.9 cm²). 2 ). A 25°C dextran solution was placed in the cell of the Ultra Holder and the cap was attached. While stirring at 1000 rpm, the water production volume was increased to 0.2~0.8 [m³]. 3 / m 2 The pressure was increased to [ / day] and filtration was started. The first 5g of the permeate was discarded as preliminary permeate, and the next 5g was taken as the filtration sample. The dextran concentration of the raw water and the filtration sample was measured by GPC.

[0124] Concentration measurements using GPC were performed as follows: The sampled solution was filtered through a 0.45 micron pore size filter, and the resulting filtrate was analyzed using a GPC column (Tosoh Corporation; TSK-gel-G4000PWXL), at a column temperature of 40°C, with distilled water for liquid chromatography as the mobile phase at 1 mL / min, and a sample input volume of 100 μl. The results were measured using a suggestive refractive index system (Tosoh Corporation; RI-8020) with a slice time of 0.02 min and a baseline range of 4.5 to 11.0 min.

[0125] The calibration curve showing the relationship between retention time and dextran molecular weight in GPC was calculated as follows: A monodisperse dextran solution was analyzed using GPC, and the retention time for each was measured. The retention time at the peak top of each solution was plotted against the measured molecular weight of monodisperse dextran, and the calibration curve between retention time and molecular weight was obtained from the exponential approximation curve. In addition, the retention time at which the dextran removal rate reached 90% was calculated from the difference in suggested refractive index between the raw water and the filtered sample, and the molecular weight of the dextran fraction at which the dextran removal rate reached 90% was determined from the calibration curve.

[0126] 8. Irregular shape of the back surface of the porous layer, and average circle diameter of the pores. The uneven surface shape on the back of the porous layer and the average equivalent diameter of the pores in the depressions were measured by surface observation using a scanning electron microscope (SEM) and image analysis using ImageJ software. First, the composite semipermeable membrane was air-dried at room temperature, and the substrate was peeled from the porous layer at a peeling speed of 50 mm / min in a 180-degree direction. A thin layer of platinum was coated onto the back of the porous layer exposed by peeling, and an SEM (Hitachi High-Technologies S-5500) was used to observe it at 500x magnification with an accelerating voltage of 5 kV, and images were captured. In the obtained images, as shown in Figure 3, the contrast of the images confirmed the presence of convex parts 14 (white parts) on the back of the porous layer and the depressions 15 (gray parts) on the back of the surrounding porous layer. The depressions (gray parts) were further observed at 10,000x magnification, and images were captured. In the obtained images, 25 μm 2 The pore areas within a (5μm × 5μm) area were binarized using the mean method in analysis software (image-j), and the pore contours were extracted using the Find Edge function. After that, the equivalent circle diameter was calculated. The same procedure was performed on five samples, and the arithmetic mean of the equivalent circle diameter data for all five samples was calculated to determine the average equivalent circle diameter of the pores located in the recesses on the back surface of the porous layer.

[0127] 9. Tensile strength of the base material Based on JIS L 1906:2000 5.3.1, a 5cm × 30cm sample of substrate obtained by peeling from a composite semipermeable membrane was used. Measurements were taken at five points in the longitudinal direction under conditions of a gripping interval of 20cm and a tensile speed of 10cm / min. The values ​​were read from the resulting strength-elongation curve and rounded to the first decimal place to represent the longitudinal tensile strength of the substrate.

[0128] 10. Amount of good solvent in porous support In the process of fabricating the composite semipermeable membrane, the porous support, which had a porous layer formed on the substrate after being immersed in the first coagulation solution in step (b), was cut into a 0.11 m × 0.19 m rectangle while still wet, 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 a calibration curve of peak area and good solvent concentration of polymer solution prepared in advance. From the calculated good solvent concentration of the extract, the amount of good solvent in the porous support was determined using the following formula (8). Amount of good solvent in porous support [g / m³] 2 ] = 500 × (concentration of good solvent in the solution / 1000) / 1000 / (0.11 × 0.19) ... Equation (8)

[0129] 11. NaCl removal rate and water production volume of composite semipermeable membranes 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 for 24 hours of membrane filtration. Subsequently, the electrical conductivity of the feedwater and permeate was measured using a multi-water quality meter (MM60R) manufactured by Toa DKK Corporation. Next, the NaCl concentration was calculated by converting this conductivity using a calibration curve prepared in advance. From the obtained NaCl concentration, the initial salt removal performance, i.e., the initial NaCl removal rate, was determined using the following formula (9). NaCl removal rate [%] = 100 × {1 - (NaCl concentration in permeate / NaCl concentration in feedwater)} ... Equation (9)

[0130] Furthermore, after performing the above membrane filtration treatment for 24 hours, the membrane permeate rate was measured over 30 minutes and converted to the daily permeate rate (cubic meters) per square meter of membrane surface, which represents the initial water production volume [m³]. 3 / m 2 The calculation for [ / day] was performed.

[0131] 12. High-pressure test The composite semipermeable membrane, whose performance was evaluated in "11. NaCl removal rate and water production volume of composite semipermeable membrane" described above, was supplied with raw water (NaCl concentration 3.2 mass%) adjusted to 45°C and pH 6.5 at an operating pressure of 7.0 MPa. The membrane filtration process was stopped and restarted every hour, and the operation was repeated for a total of 24 hours. Subsequently, the membrane performance was evaluated using the same method as in "11. NaCl removal rate and water production volume of composite semipermeable membrane," and the NaCl removal rate and water production volume after high-temperature and high-pressure operation were determined. Furthermore, the quality of the membrane performance was judged by the ratio of change in water production volume and the ratio of change in removal rate calculated by the following equations (10) and (11). Water production volume change ratio = Water production volume after high-pressure operation / Initial water production volume ... Equation (10) Removal rate change ratio = (100 - NaCl removal rate after high-pressure operation) / (100 - initial NaCl removal rate) ... Equation (11)

[0132] [Example 1] On a long-fiber polyester nonwoven fabric base material (average thickness 90 μm, longitudinal tensile strength 420 N / 5 cm), a 20% by mass DMF solution of PSf was applied as a polymer solution. Under conditions of 25°C, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 20 g / m². 2The polymer solution was applied in this manner. Subsequently, the substrate coated with the polymer solution was immersed for 15 seconds in a first solidification solution consisting of a 20°C DMF aqueous solution to create a porous support with a porous layer formed on the substrate. Next, the porous support was immersed in a second solidification solution consisting of a DMF aqueous solution, left for 5 minutes, and then washed with 90°C hot water for 2 minutes. The washed porous support was immersed for 2 minutes in a 3 mass% aqueous solution of m-PDA. The support was slowly lifted vertically, and excess aqueous solution was removed from the surface of the porous support by blowing nitrogen with an air nozzle. Then, a decane solution containing 0.165 mass% TMC was applied to the surface until it was completely wet, and it was left to stand for 1 minute. Furthermore, the film was held vertically to drain and remove excess solution, and washed with pure water to obtain a composite semipermeable film having a cross-linked polyamide separation functional layer.

[0133] [Reference example 1] The composite semipermeable membrane obtained in Example 1 was subjected to a 7.0 MPa, 45°C, 3.5% by mass NaCl aqueous solution, and pH 6.5 for 24 hours. After that, it was immersed in a 2% by mass sodium hypochlorite aqueous solution for 48 hours to remove the separation functional layer and obtain a porous support.

[0134] [Example 2] A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed in a first coagulation solution 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 DMF solution of PSf was used as the polymer solution, and the substrate coated with the polymer solution was immersed in a first coagulation solution at 20°C for 25 seconds.

[0136] [Example 4] The mass per unit area of ​​the porous layer in the composite semipermeable membrane is 18 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution was immersed for 25 seconds in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0137] [Example 5] Using a 21% by mass DMF solution of PSf as the polymer solution, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 10 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 15 seconds in a first coagulation solution consisting of a 30°C DMF aqueous solution.

[0138] [Example 6] The mass per unit area of ​​the porous layer in the composite semipermeable membrane is 12 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 12 seconds in a first coagulation solution consisting of a 30°C DMF aqueous solution.

[0139] [Example 7] The mass per unit area of ​​the porous layer in the composite semipermeable membrane is 14 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution was immersed for 15 seconds in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0140] [Example 8] The mass per unit area of ​​the porous layer in the composite semipermeable membrane is 11 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 3, except that the substrate coated with the polymer solution was immersed for 15 seconds in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0141] [Example 9] A composite semipermeable membrane having a cross-linked polyamide separation functional layer was obtained by the same method 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 base material.

[0142] [Comparative Example 1] Using a 15.7% by mass DMF solution of PSf as the polymer solution, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 25 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 5 minutes in a first coagulation solution consisting of a 30°C DMF aqueous solution.

[0143] [Comparative Example 2] The mass per unit area of ​​the porous layer in the composite semipermeable membrane of the polymer solution is 23 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Comparative Example 1, except that the substrate coated with the polymer solution was immersed for 20 seconds in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0144] [Comparative Example 3] On a substrate similar to that in Example 1, an 18% by mass DMF solution of PSf was added as the polymer solution, and under conditions of 25°C, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 20 g / m². 2 The substrate was coated in such a manner. Subsequently, the substrate coated with the polymer solution was immersed in pure water, and within 1.0 second, pure water was pressed against the substrate from the substrate side at a pressure of 1 kPa for about 3 seconds, and then left in pure water for 5 minutes to prepare a porous support. A cross-linked polyamide was formed on the obtained porous support in the same manner as in Example 1 to obtain a composite semipermeable membrane having a cross-linked polyamide separation functional layer.

[0145] [Comparative Example 4] As the polymer solution, an 18% by mass solution of PSf was used, prepared by mixing DMF and DMSO in a 90:10 ratio. The mass of the porous layer per unit area in the composite semipermeable membrane was 25 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 5 minutes in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0146] [Comparative Example 5] Using an 18.3% by mass DMF solution of PSf as the polymer solution, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 12 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 2 seconds in a first coagulation solution consisting of a DMF aqueous solution at 25°C.

[0147] [Comparative Example 6] Using a 28% by mass DMF solution of PSf as the polymer solution, the mass per unit area of ​​the porous layer in the composite semipermeable membrane was 15 g / m². 2 A composite semipermeable membrane having a crosslinked polyamide separation functional layer was obtained in the same manner as in Example 1, except that the substrate coated with the polymer solution was immersed for 15 seconds in a first coagulation solution consisting of a DMF aqueous solution at 5°C.

[0148] Tables 1-3 show the structure of the porous layer, the properties of the substrate, and the measurement results of the membrane performance of the composite semipermeable membranes obtained in the examples and comparative examples.

[0149] [Table 1]

[0150] [Table 2]

[0151] [Table 3]

[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 this embodiment possess sufficient water production capacity and salt removal capacity, and can suppress the decrease in water production 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 are possible without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-068770, filed on April 22, 2024, which is incorporated herein by reference in its entirety. [Industrial applicability]

[0154] The composite semipermeable membrane of the present invention can be used for seawater desalination, brine desalination, drinking water production, industrial ultrapure water production, wastewater treatment, and recovery of valuable materials. [Explanation of Symbols]

[0155] 1 Composite semipermeable membrane 2 Base material 3. Porous layer 4 Separation functional layer 5 Separation membrane element 6 End plate 7 End plate 8 Supply side channel material 9 Permeate side channel material 10 Water collection pipe 11 Supply water 12 Permeated water 13 Concentrated water 14. Protrusions on the back surface of the porous layer 15. Recesses on the back surface of the 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 fractional molecular weight of the porous layer is 10 k to 60 kDa and the specific surface area is 20 to 50 m². ２ A composite semipermeable membrane with a density of / 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 k to 60 kDa, and the curve ratio after supplying an aqueous solution with an NaCl concentration of 3.5 mass% and pH 6.5 to the composite semipermeable membrane at 5.5 MPa and 25°C for 2 hours 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 side on which the separation functional layer is provided has an uneven shape, and the average circular diameter of the pores 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 / m². ２ The composite semipermeable membrane according to claim 1 or 2.

5. The specific surface area of ​​the porous layer is 22 to 40 m² ２ A composite semipermeable membrane according to claim 1 or 2, wherein the density is / g.

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

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

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

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

10. A fluid separation apparatus comprising the separation membrane element described in claim 9.

11. A method for producing a composite semipermeable membrane, comprising the following steps (a) to (c). Step (a): A step of placing a polymer solution, obtained by dissolving a thermoplastic polymer in a good solvent, onto a substrate. Step (b): The polymer solution placed on the substrate is brought into contact with a first coagulation solution containing the non-solvent and good solvent of the thermoplastic polymer to form a porous layer on the substrate, wherein the amount of the good solvent in the porous support consisting of the substrate and the porous layer is 10 to 60 g / m². ２ A process to obtain a porous support. Step (c): Step of immersing the porous support in a second solidification solution.

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