Composite semipermeable membrane

Abstract

Providing a composite semipermeable membrane having superior permeability while maintaining high desalination properties. The composite semipermeable membrane (1) comprises a porous support layer (10) and a separation functional layer (20) formed on the porous support layer (10) and comprising an aromatic polyamide, wherein the separation functional layer (20) has a plurality of hollow cells (21), and in cross-sectional observation using a transmission electron microscope at a magnification of 8000x, the sum of the areas of each cell (21) with a cross-sectional area of ​​1000 nm² to 8000 nm² is 1.8 × 10⁵ nm² to 1.0 × 10⁷ nm² in two different regions of 2.8 μm × 2.8 μm.

Description

Technology Field

[0001] The present disclosure relates to a composite semipermeable membrane. Background Technology

[0002] Conventionally, composite semipermeable membranes are used for purifying tap water, desalination of seawater or brine, and production of industrial ultrapure water. For example, Patent Document 1 describes a technology of this type. Patent Document 1 describes a composite separation membrane having a separation functional layer which is a polyamide layer having a first layer portion having a plurality of protrusions and a second layer portion covering at least a portion of the plurality of protrusions. Prior art literature

[0003] Patent Document 1: Japanese Published Patent Application No. 2011-189340 The problem to be solved

[0004] However, in purification systems that purify tap water, etc., there is a requirement for a composite semipermeable membrane that possesses high desalination properties along with high permeability. Since conventional composite semipermeable membranes have low permeability, there have been cases where a pressurized pump or the like was provided in the purification system. The composite separation membrane of Patent Document 1 has excellent desalination properties and permeability, but there was room for further improvement in terms of improving permeability under low-pressure conditions.

[0005] The present disclosure is made in light of the above and aims to provide a composite semipermeable membrane having superior permeability while maintaining high desalination properties. means of solving the problem

[0006] The present disclosure comprises a porous support layer and a separation functional layer formed on the porous support layer and comprising an aromatic polyamide, wherein the separation functional layer has a plurality of hollow cells and, upon cross-sectional observation at a magnification of 8000x using a transmission electron microscope, has a cross-sectional area of ​​1000 nm 2 ~8000 nm 2The sum of the areas of each of the above cells is 1.8 × 10⁻⁶ as a sum from two different regions of 2.8 μm × 2.8 μm. 5 nm 2 ~1.0×10 7 nm 2 This concerns a composite semipermeable membrane.

[0007] Additionally, the present disclosure comprises a porous support layer and a separation functional layer formed on the porous support layer and comprising an aromatic polyamide, wherein the separation functional layer has a plurality of hollow cells and, upon cross-sectional observation at a magnification of 8000x using a transmission electron microscope, has a cross-sectional area of ​​1000 nm 2 ~8000 nm 2 The present invention relates to a composite semipermeable membrane containing a total of 60 to 3500 of the above-mentioned cells in two different regions of 2.8 μm × 2.8 μm. Brief explanation of the drawing

[0008] FIG. 1 is a drawing showing a membrane element including a composite semipermeable membrane according to one embodiment of the present disclosure. FIG. 2 is a drawing showing a composite semipermeable membrane according to one embodiment of the present disclosure. FIG. 3 is a drawing showing a method for manufacturing a composite semipermeable membrane according to one embodiment of the present disclosure. FIG. 4 is a diagram showing the cross-sectional area of ​​the cumulative cell of Example 1, Example 2 and Comparative Example 1 of the present disclosure. FIG. 5 is a diagram showing the distribution of the cross-sectional areas of cells in Example 1, Example 2 and Comparative Example 1 of the present disclosure. FIG. 6 is a diagram showing the distribution of the cross-sectional areas of cells in Example 1, Example 2 and Comparative Example 1 of the present disclosure. Specific details for implementing the invention

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments.

[0010] The composite semipermeable membrane (1) according to the present embodiment is a membrane that removes impurities, such as salts, from water to be treated. The composite semipermeable membrane (1) is used in the membrane element (2) of a water purification device that purifies water to be treated, such as tap water, for example. The membrane element (2) is filled into the pressure vessel of the water purification device.

[0011] [Mask Element]

[0012] As shown in FIG. 1, the membrane element (2) comprises a water collection pipe (3), a composite semipermeable membrane (1), and a mesh-shaped spacer (4). The membrane element (2) is formed by winding a composite semipermeable membrane (1), sandwiched between two spacers (4), around the water collection pipe (3) in a spiral shape.

[0013] Water to be treated supplied from one end of the membrane element (2) is supplied to the composite semipermeable membrane (1) through a flow path formed by a spacer (4). As shown in FIG. 1, a portion of the water to be treated passes through the composite semipermeable membrane (1), is collected in the collection pipe (3), and is recovered as permeate water from the other end of the membrane element (2). Water to be treated that does not pass through the composite semipermeable membrane (1) is discharged as wastewater from the other end of the membrane element (2).

[0014] [Composite Semipermeable Membrane]

[0015] Next, a composite semipermeable membrane (1) according to the present embodiment will be described with reference to FIG. 2. The composite semipermeable membrane (1) includes a porous support layer (10) and a separation functional layer (20).

[0016] The porous support layer (10) has a substrate (11) and a porous support (12) formed on the substrate (11).

[0017] The substrate (11) is a sheet-type member such as a nonwoven fabric. For example, materials for the nonwoven fabric may include polyethylene, polyester, etc. The thickness of the substrate (11) is preferably 30 μm to 120 μm. In this embodiment, the thickness of the substrate (11) is about 90 μm.

[0018] The porous support (12) is a membrane having a pore structure. The size of the pores of the porous support (12) is not particularly limited, but, for example, it is preferably 300 nm or less, and more preferably 30 nm or less.

[0019] The thickness of the porous support (12) is preferably 20 μm to 100 μm. In this embodiment, the thickness of the porous support (12) is about 50 μm.

[0020] As a material for the porous support (12), examples include polysulfone, polyethersulfone, cellulose acetate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, polyimide, polyvinylidene fluoride, etc. Among these, polysulfone is particularly preferred in that it has high chemical stability, mechanical stability, and thermal stability.

[0021] The separation functional layer (20) is formed on the porous support layer (10) and is a layer having a plurality of hollow cells (21). The separation functional layer (20) is composed mainly of aromatic polyamide. The aromatic polyamide can be synthesized, for example, by an interfacial polycondensation reaction between a polyfunctional aromatic amine and a polyfunctional halogen oxide.

[0022] As a polyfunctional aromatic amine, at least one polyfunctional aromatic amine selected from the group consisting of m-phenylenediamine (MPD), p-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, amidol, xylylenediamine, N-methyl-m-phenylenediamine, and N-methyl-p-phenylenediamine is preferred, and these may be used alone or in combination of two or more types.

[0023] Examples of polyfunctional acid halides include trifunctional acid halides such as trimethic acid chloride (TMC), 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride, and examples of difunctional acid halides such as biphenyldicarboxylic acid dichloride, terephthalic acid chloride, naphthalenedicarboxylic acid chloride, and cyclohexanedicarboxylic acid chloride.

[0024] The separation functional layer (20) may include cellulose nanofibers (CNF) in addition to aromatic polyamide. The content of CNF in the separation functional layer (20) is preferably 0.001 mass% to 1 mass% relative to the aromatic polyamide, more preferably 0.03 mass% to 0.5 mass%, and even more preferably 0.05 mass% to 0.35 mass%. By the separation functional layer (20) containing 0.05 mass% to 0.35 mass% of CNF relative to the aromatic polyamide, the chlorine resistance and fouling resistance of the composite semipermeable membrane (1) are further improved. The CNF content (C) is determined using FTIR data of the membrane surface, 1237 cm -1 Nearby (P1) and 1486 cm -1 It is calculated by the ratio of peak intensities in the vicinity (P2) (R=P1 / P2) and the equation C=5.3-5.34R.

[0025] The separation functional layer (20) has a plurality of hollow cells (21). As shown in FIG. 2, the plurality of cells (21) overlap in the thickness direction of the separation functional layer (20), thereby forming a wrinkled structure in which irregularities are continuously repeated. The thickness of the separation functional layer (20) is preferably 100 nm to 2000 nm, and more preferably 500 nm to 1000 nm.

[0026] The cell (21) of this embodiment has a cross-sectional area of ​​1000 nm when observed in cross-sectional view using a transmission electron microscope (TEM). 2 ~8000 nm 2In cells (21) are contained in a total of 60 to 3500 in two different regions of 2.8 μm × 2.8 μm. Additionally, the cross-sectional area is 1000 nm 2 ~8000 nm 2 The sum of the areas of each cell (21) is 1.8 × 10⁻¹⁰, which is the sum of two different areas of 2.8 μm × 2.8 μm. 5 nm 2 ~1.0×10 7 nm 2 In addition, the "cross-sectional area of ​​the cell (21)" referred to in this specification is the cross-sectional area of ​​each hollow portion formed in the separation functional layer (20).

[0027] As the water to be treated passes through the separation functional layer (20), impurities such as salts contained in the water to be treated are removed. When there are many cells (21) having a small cell cross-sectional area in the separation functional layer (20), the water to be treated passes through many cells (21), so the desalination ability increases but the permeability decreases. On the other hand, when there are many cells (21) having a large cell cross-sectional area, the water to be treated does not pass through a sufficient number of cells (21), so the permeability increases but the desalination ability decreases.

[0028] In this embodiment, high desalination and water permeability are achieved by adjusting the cross-sectional area and number of cells (21) included in the separation functional layer (20). Specifically, in cross-sectional observation using TEM, the cross-sectional area is 1000 nm 2 ~8000 nm 2 The in-cell (21) is configured to include a total of 60 to 3500 cells in two different regions of 2.8 μm × 2.8 μm of the separation functional layer (20). Additionally, the cross-sectional area is 1000 nm 2 ~8000 nm 2 The sum of the areas of each in cell (21) is 1.8 × 10 in two different regions of 2.8 μm × 2.8 μm. 5 nm 2 ~1.0×10 7 nm 2It was configured with this composition. Through this composition, high desalination and high permeability under low pressure conditions of the composite semipermeable membrane (1) are realized. In order to exhibit even higher desalination and permeability, the cross-sectional area is 1000 nm 2 ~8000 nm 2 It is preferable that the in-cell (21) be configured to include a total of 70 to 1750 cells in two different regions of 2.8 μm × 2.8 μm of the separation functional layer (20). Additionally, the cross-sectional area is 1000 nm 2 ~8000 nm 2 The sum of the areas of each in cell (21) is 2.0 × 10 in two different regions of 2.8 μm × 2.8 μm of the separation functional layer (20). 5 nm 2 ~5.0×10 6 nm 2 It is desirable to make it a human composition.

[0029] [Method for measuring the separated functional layer using TEM]

[0030] Next, details of the measurement method of the separation functional layer (20) using TEM will be explained.

[0031] First, the composite semipermeable membrane (1) is sliced ​​in the thickness direction by the freeze-thin sectioning method. Additionally, during the sectioning process, the thickness is set to 40 nm to 45 nm using an ultramicrotome (a product of Leica Microsystems). Then, carbon is deposited on the obtained slice of the composite semipermeable membrane (1) to prepare a sample for TEM observation.

[0032] Next, a sample of the prepared separation functional layer (20) is measured using a TEM to capture an image. For the TEM, for example, a transmission electron microscope (HT-7700, Hitachi High-Tech Corporation product) can be used. The measurement conditions of the TEM are appropriately determined according to the measurement target. For example, the following conditions can be selected.

[0033] Resolution: 0.204 nm

[0034] Acceleration voltage: 100 kV

[0035] Magnification: 8000x

[0036] In addition, the magnification referred to herein is the magnification set on the device of a transmission electron microscope (hereinafter the same).

[0037] Next, the image obtained by measurement using TEM is analyzed using WinROOF (manufactured by Mitani Shoji Co., Ltd.). Then, the analysis range of the image is set to an area of ​​2.8 μm × 2.8 μm, and a predetermined parameter is measured. At this time, the predetermined parameter is measured in a state where at least one of the four sides determining the analysis range is approximately parallel to the extending direction of the separation functional layer (20) within the image, and at least the area from the interface between the porous support layer (10) and the separation functional layer (20) to the outermost surface of the separation functional layer (20) falls within the analysis range. Then, the predetermined parameter is measured at two different locations, and the sum of the values ​​is evaluated.

[0038] As parameters, the cross-sectional area of ​​each cell (21) included in the separation functional layer (20), the total number of cells (21), and the total sum of the cross-sectional areas of the cells (21) may be used. When measuring the cross-sectional area of ​​each cell (21), the total number of cells (21), or the total sum of the cross-sectional areas of the cells (21), the cross-sectional area is 100 nm 2 Cell (21) less than 10000 nm 2 Cells (21) exceeding the limit are deleted from the measurement data.

[0039] [Method for manufacturing a composite semipermeable membrane]

[0040] Next, a method for manufacturing a composite semipermeable membrane (1) according to the present disclosure is described using FIG. 3. In the following description, an example of a method for manufacturing a composite semipermeable membrane (1) is described using a polyethylene nonwoven fabric as the substrate (11), polysulfone as the material of the porous support (12), and an MPD solution containing MPD, which is a polyfunctional aromatic amine, as a raw material for the aromatic polyamide. The manufacturing method according to the present embodiment includes a porous support layer fabrication process, an immersion process, a polymerization process, and a post-treatment process.

[0041] First, in the porous support layer manufacturing process, polysulfone is applied to the surface of a polyethylene nonwoven fabric to produce a porous support layer (10) containing a porous support (12) with a thickness of about 50 μm.

[0042] Next, in the immersion process, an MPD solution containing a predetermined amount of polyfunctional aromatic amine and an additive is immersed in a porous support (12) of polysulfone. The MPD solution is an aqueous solution containing distilled water as a solvent, 0.5 mass% to 2.0 mass% of MPD, 0.15 mass% of sodium lauryl sulfate (SLS), 0.5 mass% to 2.0 mass% of triethylamine (TEA), 1.0 mass% to 4.0 mass% of campersulfonic acid (CSA), and 6.0 mass% to 15 mass% of isopropyl alcohol (IPA) as an additive. As an additive other than IPA, CNF may be used. In the immersion process, the MPD solution is immersed in the skin layer of the porous support (12) and left for 1 to 60 seconds. Then, remove the excess MPD solution applied to the surface of the porous support (12), remove droplets of MPD solution from the surface using an air knife or squeegee, and leave it for 10 to 60 seconds.

[0043] Next, in the polymerization process, a polyfunctional acid halide solution is immersed on the surface of a porous support (12) coated with an MPD solution and left for 120 seconds to promote an interfacial polycondensation reaction. As for the polyfunctional acid halide solution, for example, a TMC solution in which TMC is dissolved in an amphiphilic solvent such as ethyl acetate in an appropriate amount of isoparaffinic hydrocarbon to obtain a TMC solution with a TMC concentration of 0.05 mass% to 0.1 mass% may be used.

[0044] Finally, in the post-processing step, the TMC solution is removed, and after drying in a drying oven at 120°C for 3 minutes, a composite semipermeable membrane (1) having a separation functional layer (20) is formed by washing in water.

[0045] Examples

[0046] Next, embodiments of the present disclosure will be described. The present disclosure is not limited to these embodiments.

[0047] [Method for manufacturing a composite semipermeable membrane]

[0048] <Example 1>

[0049] In Example 1, as the porous support layer (10), a layer was used in which a porous support (12) of polysulfone with a thickness of about 50 nm was formed on a polyethylene nonwoven fabric. First, an MPD solution was poured onto the surface of the porous support (12) of polysulfone surrounding the four sides and left for 10 seconds. As the MPD solution, a solution containing 0.8 mass% MPD, 0.15 mass% SLS, 0.8 mass% TEA, 1.6 mass% CSA, and 10 mass% IPA in distilled water as the solvent was used. After that, the excess MPD aqueous solution applied to the surface of the porous support (12) was removed, the MPD solution adhering to the membrane was removed with a squeegee, and left for 60 seconds. Then, a TMC solution was poured onto the surface of the porous support (12) coated with the MPD solution and left for 120 seconds. As the TMC solution, a solution in which 0.1 mass% of TMC and 2 mass% of ethyl acetate were dissolved in IP solvent 1016, an isoparaffinic hydrocarbon, was used. Afterward, the TMC solution was removed and dried in a drying oven at 120°C for 3 minutes. Then, after removing from the drying oven, it was washed in water.

[0050] <Example 2>

[0051] In Example 2, a composite semipermeable membrane was prepared in the same manner as in Example 1, except for the composition of the MPD solution. The MPD solution of Example 2 had a composition comprising distilled water as a solvent, 0.75 mass% MPD, 0.15 mass% SLS, 1.5 mass% CSA, 0.75 mass% TEA, 6 mass% IPA, and 0.03 mass% CNF. The CNF content was 0.12 mass% relative to the aromatic polyamide. When comparing the MPD solutions of Example 1 and Example 2, the main difference is that in Example 2, CNF was used along with IPA as an additive.

[0052] <Comparative Example 1>

[0053] In Comparative Example 1, a composite semipermeable membrane was prepared without using IPA. The method of preparing the composite semipermeable membrane in Comparative Example 1 is under all conditions identical to the method of Example 1, except that the MPD solution does not contain IPA.

[0054] [evaluation]

[0055] <Measurement of Cross-sectional Shape>

[0056] For the composite semipermeable membranes of Example 1, Example 2 and Comparative Example 1, the composite semipermeable membranes were thinned by the freeze-ultrathin sectioning method, and the cross-sectional shape was measured using TEM. The measurement of the cross-sectional shape of the composite semipermeable membranes was performed according to the measurement conditions described above, except for changing the magnification. The measurement magnifications were 2000x, 8000x, and 20000x.

[0057] In all three composite semipermeable membranes, it was confirmed that a separation functional layer with a wrinkled structure having multiple cells was formed on a porous support layer. Furthermore, while in Comparative Example 1, the portion where cells overlapped in the thickness direction was formed only in a part of the separation functional layer, in Examples 1 and 2, a multilayer wrinkled structure with multiple cells overlapping in the thickness direction was formed over the entire surface of the separation functional layer. In addition, the cross-sectional area of ​​the cells in Examples 1 and 2 was formed to be larger than that of Comparative Example 1. These trends were the same in two different measurement regions. From the above, it can be confirmed that the separation functional layer prepared by adding 10 mass% of IPA or 0.03 mass% of CNF to the MPD solution has a larger cross-sectional area of ​​cells and a multilayer wrinkled structure formed over the entire surface compared to the separation functional layer without added additives.

[0058] Distribution of cell cross-sectional area

[0059] For the composite semipermeable membranes of Example 1, Example 2, and Comparative Example 1, images measured using TEM under the measurement conditions of the above-described embodiment were analyzed using the method of the above-described embodiment. Figures 4 to 6 show the distribution of the cross-sectional areas of cells formed in the separation functional layers of the three composite semipermeable membranes. In addition, the vertical axis of Figures 4 to 6 represents the total number of cells or the sum of the total areas in two different regions of 2.8 μm × 2.8 μm. The horizontal axis of Figure 4 represents the cross-sectional area per cell, and the vertical axis represents the cumulative cross-sectional area of ​​cells smaller than the cross-sectional area shown on the horizontal axis. As shown in Figure 4, 8000 nm 2 When the cumulative cross-sectional area of ​​the cells below is calculated, it can be confirmed that the cross-sectional area of ​​the cells in the separation functional layer of Example 1 and Example 2 is about twice as large as the cross-sectional area of ​​the cells in the separation functional layer of Comparative Example 1.

[0060] The horizontal axis of Fig. 5 represents the range of cross-sectional areas per cell, and the vertical axis represents the sum of the cross-sectional areas of all cells whose cross-sectional areas fall within the range indicated by the horizontal axis. The horizontal axis of Fig. 6 represents the range of cross-sectional areas per cell, and the vertical axis represents the total number of all cells whose cross-sectional areas fall within the range indicated by the horizontal axis. As shown in Figs. 5 and 6, the cross-sectional area is 1000 nm 2 ~8000 nm 2 Within this range, it can be confirmed that the total number of cells in the separation functional layer of Examples 1 and 2 is greater and the total area is larger than that of the separation functional layer of Comparative Example 1. Specifically, in Example 1, the cross-sectional area is 1000 nm 2 ~8000 nm 2 The total number of cells is approximately 80, and the total area of ​​the cells is approximately 2.47 × 10⁻⁶ 5 nm 2 was. In Example 2, the cross-sectional area was 1000 nm 2 ~8000 nm 2 The total number of cells is approximately 79, and the total area of ​​the cells is approximately 2.15 × 10⁻⁶5 nm 2 was. In Comparative Example 1, the cross-sectional area was 1000 nm 2 ~8000 nm 2 The total number of cells is approximately 41, and the total area of ​​the cells is 1.02 × 10⁻⁶ 5 nm 2 was.

[0061] <Measurement of Desalination and Permeability>

[0062] For the composite semipermeable membranes of Example 1, Example 2 and Comparative Example 1, the desalination rate and permeability were measured by the following method.

[0063] Desalination

[0064] An aqueous NaCl solution with a concentration of 0.05% at a temperature of 25°C was supplied to a composite semipermeable membrane at a flow rate of 300 ml / min and an operating pressure of 0.75 MPa using a cross-flow device. Desalination performance was determined by measuring the salt concentrations of the supply solution and the permeate solution 2 hours after the supply of the aqueous NaCl solution began, and by calculating the desalination rate using the following formula.

[0065] Desalination rate (%) = (1 - Salt concentration of permeate solution / Salt concentration of feed solution) × 100

[0066] <Permeability>

[0067] Permeability was measured by measuring the amount of water permeation for 30 minutes from 1 hour 30 minutes after the supply of the NaCl aqueous solution began to 2 hours after the start of supply, and was calculated as the permeation velocity using the following formula.

[0068] Permeation velocity (m 3 / m 2 / d)=(pitch volume over 30 minutes(m 3 ) / 30)×60×24) / effective membrane area(m 2 )

[0069] Amount of IPA added to MPD solution (mass%) Amount of CNF added to MPD solution (mass%) Desalination rate (%) Permeation velocity (m 3 / m 2 / d) Example 1 10 - 96.77 2.289 Example 2 6 0.03 98.27 2.234 Comparative Example 1 - - 98.59 1.165

[0070] As shown in Table 1, the desalination rate in Comparative Example 1 exceeded 98%. The permeate flow velocity was approximately 1.2 m 3 / m 2It was less than / d. In contrast, in Example 1, where the IPA content in the MPD solution was 10 mass%, the desalination rate was maintained at 96% or higher, and the permeate flow rate was approximately twice that of Comparative Example 1. In Example 2, where the CNF content in the MPD solution was 0.03 mass%, the desalination rate exceeded 98%, and the permeate flow rate was approximately twice that of Comparative Example 1, similar to Example 1. From these results, the cross-sectional area is 1000 nm 2 ~8000 nm 2 There are about 80 cells (21) in two different areas of 2.8 μm × 2.8 μm (total area is about 2.47 × 10⁻⁶ 5 nm 2 Example 1 including ) and about 79 (total area is about 2.15 × 10 5 nm 2 In the composite semipermeable membrane (1) of Example 2 including ), the cross-sectional area is 2000 nm 2 ~8000 nm 2 There are about 41 cells (21) in an area of ​​2.8 μm × 2.8 μm (total area is about 1.02 × 10⁻⁶ 5 nm 2 It was confirmed that permeability increased by about 2 times compared to the comparative example including ). Explanation of the symbols

[0071] 1: Composite semipermeable membrane 10: Porous support layer 20: Separation functional layer 21: Cell

Claims

Claim 1 A porous support layer and a separation functional layer formed on the porous support layer and comprising an aromatic polyamide, wherein the separation functional layer has a plurality of hollow cells and, upon cross-sectional observation at a magnification of 8000x using a transmission electron microscope, has a cross-sectional area of ​​1000 nm 2 ~8000 nm 2 The sum of the areas of each of the above cells is 1.8 × 10⁻⁶ as a sum from two different regions of 2.8 μm × 2.8 μm. 5 nm 2 ~1.0×10 7 nm 2 A composite semipermeable membrane having a separation functional layer thickness of 100 nm to 2000 nm. Claim 2 A porous support layer and a separation functional layer formed on the porous support layer and comprising an aromatic polyamide, wherein the separation functional layer has a plurality of hollow cells and, upon cross-sectional observation at a magnification of 8000x using a transmission electron microscope, has a cross-sectional area of ​​1000 nm 2 ~8000 nm 2 A composite semipermeable membrane comprising a total of 60 to 3500 cells in two different regions of 2.8 μm × 2.8 μm, wherein the thickness of the separation functional layer is 100 nm to 2000 nm. Claim 3 A composite semipermeable membrane according to claim 1 or 2, wherein the separation functional layer comprises 0.001 mass% to 1 mass% of cellulose nanofibers with respect to aromatic polyamide.

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