Composite semipermeable membrane, composite semipermeable membrane module, fluid separation device, and method for manufacturing composite semipermeable membrane

Abstract

Provided is a composite semipermeable membrane having excellent oxidation resistance, acid resistance, and alkali resistance, while having excellent fouling resistance. This composite semipermeable membrane is provided with: a support membrane; a separation function layer that is arranged on the support membrane and contains a crosslinked polyamide; and a coating layer that is arranged on the separation function layer and contains a vinyl alcohol copolymer having a structure represented by general formula (1). [In general formula (1), X represents a divalent hydrocarbon group having 2-6 carbon atoms, and l, m and n represent the number of repeating units]. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a composite semipermeable membrane useful for selective separation of liquid mixtures, a composite semipermeable membrane module, a fluid separation device, and a method for producing the composite semipermeable membrane. Background Art

[0002] There are various technologies for removing substances (e.g., salts) dissolved in solvents (e.g., water), but in recent years, the use of membrane separation methods using semipermeable membranes such as reverse osmosis membranes and nanofiltration membranes has been expanding as a process for saving energy and resources.

[0003] Currently available reverse osmosis membranes and nanofiltration membranes are generally composite semipermeable membranes comprising a support membrane and a separation functional layer laminated on the support membrane. As the separation functional layer, crosslinked polyamides obtained by the polycondensation reaction of polyfunctional amines and polyfunctional acyl halides are known.

[0004] One of the challenges in membrane separation is scaling. Scaling occurs when substances contained in the treated water adsorb onto the surface or pores of a semipermeable membrane, hindering the passage of the solution and reducing the water permeability of the composite semipermeable membrane. Scaling is categorized by the type of adsorbed substance, including chemical scaling (based on organic adsorption) and biological scaling (based on microbial adsorption).

[0005] As a method for suppressing these fouling phenomena, a method of coating the semipermeable membrane surface with a hydrophilic substance is known. For example, Patent Document 1 proposes a method for suppressing fouling by introducing a hydrophilic polymer having an acidic group onto the surface of a separation functional layer via an amide bond.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent document: International Publication No. 2015 / 046582 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] In various water treatment facilities such as fresh water generators, ultrafiltration and other methods are sometimes used for pretreatment before reverse osmosis filtration or nanofiltration. If oxidants used for cleaning ultrafiltration membranes used in pretreatment leak and come into contact with the reverse osmosis membrane or nanofiltration membrane, these membranes may sometimes undergo oxidative degradation. Furthermore, reverse osmosis membranes and nanofiltration membranes are typically cleaned with acid and alkali solutions, so it is important that these membranes have acid and alkali resistance.

[0011] Therefore, an object of the present invention is to provide a composite semipermeable membrane having excellent anti-fouling properties as well as good oxidation resistance, acid resistance, and alkali resistance.

[0012] Means for solving problems

[0013] In order to solve the above-mentioned problems, the present invention provides the following composite semipermeable membrane, composite semipermeable membrane module, fluid separation device, and method for producing a composite semipermeable membrane.

[0014] [1] A composite semipermeable membrane comprising a supporting membrane, a separation functional layer disposed on the supporting membrane and comprising a cross-linked polyamide, and a coating layer disposed on the separation functional layer and comprising a vinyl alcohol copolymer having a structure represented by the following general formula (1).

[0015] [Chemical Formula 1]

[0016]

[0017] [In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, and l, m, and n are the numbers of repeating units.]

[0018] [2] The composite semipermeable membrane according to [1] above, wherein X in the general formula (1) is a divalent hydrocarbon group having 2 carbon atoms.

[0019] [3] The composite semipermeable membrane according to [2] above, wherein X in the general formula (1) is 1,2-ethylene.

[0020] [4] The composite semipermeable membrane according to any one of [1] to [3] above, wherein the copolymerization ratio of the vinyl alcohol copolymer: n / (l+m+n) is 0.035 to 0.16.

[0021] [5] The composite semipermeable membrane according to any one of [1] to [4] above, wherein the degree of polymerization of the vinyl alcohol copolymer is 100 to 1,500.

[0022] [6] The composite semipermeable membrane according to any one of [1] to [5] above, wherein the degree of saponification of the vinyl alcohol copolymer is 96 mol% or more.

[0023] [7] The composite semipermeable membrane according to any one of [1] to [6] above, wherein the total thickness of the separation functional layer and the coating layer is 10 to 100 nm.

[0024] [8] The composite semipermeable membrane according to any one of [1] to [7] above, wherein the ratio of the water permeability to the helium permeability of the composite semipermeable membrane is 0.0105 to 0.0400.

[0025] [9] The composite semipermeable membrane according to any one of [1] to [8] above, wherein the He / O2 selectivity of the composite semipermeable membrane is 7.5 to 10.4.

[0026]

[10] The composite semipermeable membrane according to any one of [1] to [9] above, wherein the bonding strength when the covering layers of two composite semipermeable membranes are bonded together is 0.9 to 5.0 N / 25 mm.

[0027]

[11] A composite semipermeable membrane module comprising the composite semipermeable membrane according to any one of [1] to

[10] above.

[0028]

[12] A fluid separation device comprising the composite semipermeable membrane assembly described in

[11] above.

[0029]

[13] The method for producing a composite semipermeable membrane according to any one of [1] to

[10] , comprising the following steps (i) and (ii):

[0030] (i) forming a separation functional layer comprising a cross-linked polyamide by interfacial polymerization of a polyfunctional amine and a polyfunctional acid chloride on a supporting membrane;

[0031] (ii) A step of contacting a solution containing a vinyl alcohol copolymer represented by the following general formula (1) on the separation functional layer to insolubilize the copolymer and forming a coating layer containing the vinyl alcohol copolymer.

[0032] [Chemical Formula 2]

[0033]

[0034] [In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, and l, m, and n are the numbers of repeating units.]

[0035] Effects of the Invention

[0036] According to the present invention, it is possible to provide a composite semipermeable membrane having excellent anti-fouling properties as well as good oxidation resistance, acid resistance, and alkali resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] [ Figure 1 ] Figure 1 Schematic diagram showing the cross-sectional structure of a composite semipermeable membrane.

[0038] [ Figure 2 ] Figure 2 Schematic diagram showing the structure of a composite semipermeable membrane having a pleated separation functional layer and a coating layer, (a) is a partial enlarged view, and (b) is an enlarged view of Y in (a). DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these examples.

[0040] It should be noted that, in this specification, “mass” and “weight” have the same meaning.

[0041] 1. Composite semipermeable membrane

[0042] Figure 1 A first embodiment of the structure of the composite semipermeable membrane 1 in this embodiment is shown. The composite semipermeable membrane 1 of the present invention includes a supporting membrane 2 , a separation functional layer 3 , and a coating layer 4 .

[0043] (1-1) Support membrane

[0044] The supporting membrane included in the composite semipermeable membrane according to this embodiment includes at least a porous supporting layer. The supporting membrane is used to impart strength to the composite semipermeable membrane, and does not substantially have solute separation performance itself.

[0045] The porous supporting layer has a large number of interconnected pores. The pore diameter and pore size distribution are not particularly limited. For example, a porous supporting layer having a symmetrical structure with uniform pore diameter or an asymmetrical structure with gradually increasing pore diameter from one surface to the other surface, with the pore diameter on the surface with smaller pore diameter being 0.1 to 100 nm, is preferred.

[0046] As the raw material of the porous supporting layer, homopolymers or copolymers such as polysulfone (hereinafter also referred to as "PSf"), polyethersulfone, polyamide, polyester, cellulose-based polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene ether can be used alone or in combination. Here, examples of the cellulose-based polymer include cellulose acetate and cellulose nitrate, and examples of the vinyl polymer include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile. Among them, homopolymers or copolymers such as PSf, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferred, and cellulose acetate, PSf, polyphenylene sulfide sulfone, or polyphenylene sulfone is more preferred. PSf is particularly preferred from the perspectives of high chemical stability, mechanical stability, thermal stability, and ease of molding.

[0047] The weight-average molecular weight (hereinafter referred to as "Mw") of PSf is preferably 10,000 to 200,000, and more preferably 15,000 to 100,000. A PSf Mw of 10,000 or greater provides mechanical strength and heat resistance suitable for a porous supporting layer. On the other hand, a PSf Mw of 200,000 or less maintains an appropriate viscosity within the porous supporting layer stock solution, achieving excellent moldability.

[0048] Furthermore, the supporting membrane may have a substrate in addition to the porous supporting layer.

[0049] Examples of the base material include fabrics made from polyester polymers, polyamide polymers, polyolefin polymers, and mixtures or copolymers thereof. Among these, fabrics made from polyester polymers with high mechanical and thermal stability are preferred. The fabric may be in the form of long-fiber nonwoven fabrics or short-fiber nonwoven fabrics, with woven knitted fabrics being more preferred.

[0050] The thickness of the supporting membrane affects the strength of the composite semipermeable membrane and the packing density when it is made into an element. In order to obtain good mechanical strength and packing density, the thickness of the supporting membrane is preferably 50 to 300 μm, more preferably 100 to 250 μm. In addition, when the supporting membrane is composed of a porous supporting layer and a substrate, the thickness of the porous supporting layer is preferably 20 to 100 μm. It should be noted that the thickness of the supporting membrane can be obtained as follows: by cross-sectional observation, measurement is performed at intervals of 20 μm in a direction perpendicular to the thickness direction (the surface direction of the membrane), and the average value of the thickness of 20 points is calculated.

[0051] (1-2) Separation functional layer

[0052] The separation functional layer is disposed on the supporting membrane. The separation functional layer of the composite semipermeable membrane according to this embodiment is a layer that performs the solute separation function and comprises a cross-linked polyamide. The proportion of the cross-linked polyamide in the separation functional layer is preferably 50% by mass or greater, more preferably 80% by mass or greater, and even more preferably 90% by mass or greater. The content of the cross-linked polyamide in the separation functional layer can generally be calculated by analysis using nuclear magnetic resonance.

[0053] The crosslinked polyamide is preferably a condensation polymer of a polyfunctional amine and a polyfunctional acid chloride. Preferably, at least one of the polyfunctional amine and the polyfunctional acid chloride comprises a trifunctional or higher compound. This provides a rigid molecular chain and a good pore structure for removing fine solutes such as hydrated ions and silica.

[0054] A polyfunctional amine is an amine having at least two primary and / or secondary amino groups in one molecule. Examples include aromatic trifunctional amines such as 1,3,5-triaminobenzene and 1,2,4-triaminobenzene; aromatic difunctional amines such as o-phenylenediamine, m-phenylenediamine (hereinafter also referred to as "m-PDA"), p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-diaminopyridine, m-diaminopyridine, p-diaminopyridine, 3,5-diaminobenzoic acid, 2,4-diaminobenzenesulfonic acid, 3-aminobenzylamine, and 4-aminobenzylamine; and aliphatic difunctional amines such as ethylenediamine, propylenediamine, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, 4-aminopiperidine, and aminoethylpiperazine. These polyfunctional amines may be used alone or in combination of two or more.

[0055] From the perspectives of separation performance, water permeability, and heat resistance of the composite semipermeable membrane, the polyfunctional amine is preferably m-PDA, p-phenylenediamine, or 1,3,5-triaminobenzene. Among them, m-PDA is particularly preferred from the perspectives of ease of availability and handling.

[0056] The so-called polyfunctional acid chloride refers to an acid chloride having at least two chlorocarbonyl groups in one molecule. For example, there can be mentioned aromatic trifunctional acid chlorides such as trimesoyl chloride (hereinafter also referred to as "TMC") and trimellitic trifunctional acid chlorides, aliphatic trifunctional acid chlorides such as 1,3,5-cyclohexanetricarboxylic acid chloride, aromatic difunctional acid chlorides such as biphenyl dicarboxylic acid chloride, azophthaloyl dicarboxylic acid chloride, terephthaloyl dicarboxylic acid chloride, isophthaloyl dicarboxylic acid chloride, and 2,6-naphthalene dicarboxylic acid chloride, and aliphatic difunctional acid chlorides such as adipoyl chloride, sebacoyl chloride, and 1,4-cyclohexane dicarboxylic acid chloride. These polyfunctional acid chlorides can be used alone or in combination of two or more.

[0057] From the viewpoint of separation performance and heat resistance of the composite semipermeable membrane, the polyfunctional acid chloride is preferably a polyfunctional aromatic acid chloride having 2 to 4 chlorocarbonyl groups in one molecule. Among them, TMC is particularly preferred from the viewpoint of easy availability and handling.

[0058] (1-3) Coating layer

[0059] The coating layer of the composite semipermeable membrane according to this embodiment is a layer responsible for protecting the separation functional layer and is disposed on the separation functional layer. The coating layer comprises a vinyl alcohol copolymer having a structure represented by the following general formula (1) (hereinafter also referred to as "vinyl alcohol copolymer").

[0060] [Chemical Formula 3]

[0061]

[0062] In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, and l, m, and n are the numbers of repeating units.

[0063] The vinyl alcohol copolymer may contain any other structure as long as it contains the structure represented by the general formula (1). The proportion of the structure represented by the general formula (1) in the vinyl alcohol copolymer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. It is particularly preferred that the copolymer be composed solely of the structure represented by the general formula (1). The proportion of the structure represented by the general formula (1) in the vinyl alcohol copolymer can usually be calculated by analysis using nuclear magnetic resonance.

[0064] The vinyl alcohol copolymer having the structure represented by the general formula (1) above shows hydrophobic interactions between hydrocarbons in addition to the intermolecular hydrogen bonds between hydroxyl groups shown by polyvinyl alcohol (hereinafter also referred to as "PVA") having only hydroxyl groups and acetyl groups as functional groups. Therefore, compared with PVA, the intermolecular interactions of the vinyl alcohol copolymer are stronger, and when cleaning with acid or alkali, the higher-order structure formed by the intermolecular interactions of the vinyl alcohol copolymer is not easily changed. Therefore, by having a coating layer containing the vinyl alcohol copolymer, a composite semipermeable membrane with good acid and alkali resistance can be obtained. In addition, as disclosed in "Journal of Membrane Science", vol. 501, 2016, p. 209-219 or "Desalination", vol. 367, 2015, p. 11-20, the hydroxyl groups of PVA form hydrogen bonds with the amino groups at the ends of the cross-linked polyamide of the separation functional layer and the amide groups of the skeleton, thereby inhibiting the oxidation of the cross-linked polyamide. Furthermore, as mentioned above, the higher-order structure of vinyl alcohol copolymers is less susceptible to change compared to PVA, making it easier to maintain these hydrogen bonds. Therefore, by using vinyl alcohol copolymers in the coating layer, a composite semipermeable membrane with a low risk of oxidative degradation due to oxidant leakage and excellent oxidation resistance can be obtained.

[0065] By coating a composite semipermeable membrane with a vinyl alcohol copolymer, a composite semipermeable membrane that is less susceptible to chemical fouling can be obtained. Furthermore, by inhibiting chemical fouling, the growth of microorganisms that feed on organic matter can be prevented, thereby achieving a composite semipermeable membrane that is less susceptible to biological fouling. Furthermore, because the vinyl alcohol copolymer is hydrophilic, the coating layer minimizes the reduction in water permeability, resulting in a composite semipermeable membrane with sufficient water permeability.

[0066] In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, for example, 1,2-ethylene (-CH2CH2-), 1,1-ethylene (-CH(CH3)-), 1,2-vinylene (-CH=CH-), trimethylene (-CH2CH2CH2-), 1,2-propylene (-CH(CH3)CH2-), tetramethylene (-CH2(CH2)2CH2-), cyclopentyl, hexamethylene (-CH2(CH2(CH2)4), etc. X in the general formula (1) is preferably a divalent hydrocarbon group having 2 carbon atoms. The general formula When X in (1) is a divalent hydrocarbon group having 2 carbon atoms, the vinyl alcohol copolymer has sufficient water solubility, and a coating layer can be easily formed on the separation functional layer using an aqueous solution of the vinyl alcohol copolymer in the "(2-3) Coating Layer Formation Step" described later. In addition, X in the general formula (1) is preferably a divalent saturated hydrocarbon group having 2 to 6 carbon atoms. When X in the general formula (1) is a divalent saturated hydrocarbon group having 2 to 6 carbon atoms, a coating layer that is not easily degraded by oxidation or the like can be formed. Among them, from the viewpoint of ease of acquisition, X in the general formula (1) is particularly preferably 1,2-ethylene.

[0067] The copolymerization ratio of the vinyl alcohol copolymer containing the structure represented by the above-mentioned general formula (1) contained in the coating layer of the composite semipermeable membrane involved in this embodiment: n / (l+m+n) is preferably 0.035 to 0.16, more preferably 0.040 to 0.11, and further preferably 0.042 to 0.095. When the copolymerization ratio is 0.035 or more, the vinyl alcohol copolymer shows a strong intermolecular interaction through sufficient hydrophobic interaction, and a composite semipermeable membrane with good oxidation resistance, acid resistance and alkali resistance can be obtained. On the other hand, when the copolymerization ratio is 0.16 or less, the vinyl alcohol copolymer has sufficient water solubility and can be used in the "(2-3) coating layer formation step" described later to simply form a coating layer on the separation functional layer using a vinyl alcohol copolymer aqueous solution. The copolymerization ratio can usually be calculated by analysis using a nuclear magnetic resonance method.

[0068] The coating layer may contain a hydrophilic polymer such as PVA or polyacrylic acid (hereinafter also referred to as "PAA") in addition to the vinyl alcohol copolymer.

[0069] The proportion of the vinyl alcohol copolymer in the coating layer of the composite semipermeable membrane according to this embodiment is preferably 50% by mass or greater, more preferably 60% by mass or greater, and even more preferably 70% by mass or greater. When the proportion of the vinyl alcohol copolymer in the coating layer is 50% by mass or greater, a composite semipermeable membrane having excellent oxidation resistance, acid resistance, and alkali resistance can be obtained.

[0070] In addition, the ratio of the vinyl alcohol copolymer in the coating layer can usually be calculated by analysis using a nuclear magnetic resonance method.

[0071] The degree of saponification {m / (l+m)×100} of the vinyl alcohol copolymer is preferably 96 mol% or greater, more preferably 98 mol% or greater. By increasing the degree of saponification of the vinyl alcohol copolymer to 96 mol% or greater, i.e., by increasing the number of hydroxyl groups in the vinyl alcohol copolymer, the intermolecular hydrogen bonds of the vinyl alcohol copolymer and the hydrogen bonds with the cross-linked polyamide become stronger, thereby providing a composite semipermeable membrane with excellent oxidation resistance, acid resistance, and alkali resistance.

[0072] The degree of polymerization of the vinyl alcohol copolymer: l+m+n is preferably 100 to 1,500, more preferably 200 to 1,200. When the degree of polymerization of the vinyl alcohol copolymer is 100 or more, a coating layer having a sufficient thickness can be provided, and a composite semipermeable membrane exhibiting excellent anti-fouling properties can be obtained. On the other hand, when the degree of polymerization of the vinyl alcohol copolymer is 1,500 or less, the permeation resistance caused by the thickness of the coating layer can be suppressed, and a composite semipermeable membrane having sufficient water permeability can be obtained. In addition, when the degree of polymerization is within the above range, the vinyl alcohol copolymer has sufficient water solubility, and a coating layer can be simply formed on the separation functional layer using an aqueous solution of the vinyl alcohol copolymer in the "(2-3) Coating Layer Formation Step" described later.

[0073] The coating layer is preferably insolubilized to prevent dissolution during use of the composite semipermeable membrane. Examples of methods for insolubilizing the coating layer include methods in which the coating layer is fixed to the separation functional layer by forming non-covalent bonds such as hydrogen bonds or ionic bonds with the cross-linked polyamide; methods in which the coating layer is fixed to the separation functional layer by forming covalent bonds with the cross-linked polyamide using a cross-linking agent; and methods in which the coating layer is insolubilized by forming covalent bonds with each other using a cross-linking agent to form a three-dimensional structure. Of these, methods in which the coating layer is fixed to the separation functional layer by forming covalent bonds with the cross-linked polyamide using a cross-linking agent are more preferred for long-term, stable operation.

[0074] The shape and thickness of the separation functional layer and the coating layer affect the separation performance and water permeability. Figure 2 A second embodiment of the structure of the composite semipermeable membrane 1 in this embodiment is shown. Figure 2 As shown in (a) and (b), the separation functional layer 3 preferably has a corrugated shape with multiple convex portions. In addition, it is more preferred that the interior 5 of the convex portion (between the separation functional layer 3 and the supporting membrane 2) is a gap. When the separation functional layer 3 has a corrugated shape, it is possible to obtain a larger surface area than when it has a flat shape, so that a high water permeability can be achieved while maintaining separation performance. It should be noted that the coating layer 4 can also be formed thinly on the separation functional layer 3 to form a corrugated shape together with the separation functional layer 3, or have a relatively large thickness such as the corrugated shape of the separation functional layer 3.

[0075] The root mean square height (hereinafter referred to as "Sq") of the coating layer side surface of the composite semipermeable membrane is preferably 60 to 300 nm, more preferably 100 to 280 nm, and even more preferably 140 to 260 nm. When Sq is 60 nm or greater, the surface area of ​​the separation functional layer increases, and a composite semipermeable membrane with good water permeability can be obtained. On the other hand, when Sq is 300 nm or less, the pleated shape can be maintained even under high-pressure operating conditions such as those used in seawater desalination applications, and a composite semipermeable membrane with good water permeability can be obtained.

[0076] The total thickness T of the separation functional layer and the coating layer is preferably 10 to 100 nm, more preferably 11 to 70 nm, and further preferably 11 to 20 nm. When the total thickness T of the separation functional layer and the coating layer is 10 nm or more, a composite semipermeable membrane with good separation performance can be obtained. On the other hand, when the total thickness T of the separation functional layer and the coating layer is 100 nm or less, a composite semipermeable membrane with good water permeability can be obtained. Figure 2 As shown in (b), the so-called "total thickness T" refers to the thickness from the inside 5 of the convex portion to the outside when the separation functional layer 3 and the coating layer 4 are overlapped into one and form a wrinkled shape with multiple hollow convex portions in the separation functional layer and the coating layer.

[0077] In order to prevent the separation target substance from penetrating into the composite semipermeable membrane, the separation functional layer and the coating layer are preferably disposed on the surface side of the composite semipermeable membrane. The surface side of the composite semipermeable membrane on which the separation functional layer is disposed is preferably used as the primary filtration side.

[0078] The helium permeability of the composite semipermeable membrane involved in this embodiment is affected by the crystallinity of the vinyl alcohol copolymer contained in the coating layer and the intermolecular interaction of the amorphous portion. Insofar as the helium permeability of the composite semipermeable membrane is low, that is, the coating layer has excellent gas barrier properties, it means that the crystallinity of the vinyl alcohol copolymer contained in the coating layer is high and the intermolecular interaction of the amorphous portion is strong. The higher the crystallinity of the vinyl alcohol copolymer contained in the coating layer and the stronger the intermolecular interaction of the amorphous portion, the less likely the higher-order structure of the coating layer will change when cleaning with acid or alkali. As a result, a composite semipermeable membrane with good oxidation resistance, acid resistance and alkali resistance can be obtained. On the other hand, when the helium permeability of the composite semipermeable membrane is extremely low, the water permeability of the composite semipermeable membrane also becomes low.

[0079] Specifically, the ratio of the water permeability (m / d / MPa) to the helium permeability (m / d / MPa) of the composite semipermeable membrane (hereinafter also referred to as "water permeability / helium permeability") is preferably 0.0105 to 0.0400, more preferably 0.0106 to 0.0300, and even more preferably 0.0108 to 0.0250. Here, "water permeability" and "helium permeability" refer to values ​​measured by the methods described in "(1) Water Permeability" and "(8) Gas Permeability and Selectivity" below.

[0080] When the water permeability / helium permeability ratio of the composite semipermeable membrane is 0.0105 or higher, a composite semipermeable membrane having both excellent water permeability and good acid resistance, alkali resistance, and oxidation resistance can be obtained. On the other hand, when the water permeability / helium permeability ratio of the composite semipermeable membrane is 0.0400 or lower, a composite semipermeable membrane having sufficient water permeability can be obtained.

[0081] The He / O2 selectivity of the composite semipermeable membrane according to this embodiment is preferably 7.5 to 10.4, more preferably 7.8 to 10.2, and even more preferably 8.0 to 10.0. Here, "He / O2 selectivity" refers to the helium permeability relative to the oxygen permeability of the composite semipermeable membrane as measured by the method described in "(8) Gas Permeability and Selectivity" below.

[0082] The He / O2 selectivity of a composite semipermeable membrane is correlated with its separation performance and water permeability. A composite semipermeable membrane with a He / O2 selectivity of 7.5 or greater exhibits excellent separation performance. On the other hand, a composite semipermeable membrane with a He / O2 selectivity of 10.4 or less exhibits sufficient water permeability.

[0083] For the composite semipermeable membrane involved in this embodiment, the bonding strength when the covering layers of two composite semipermeable membranes are attached to each other (hereinafter also referred to as "bonding strength between the covering layers") is preferably 0.9 to 5.0 N / 25 mm, more preferably 1.4 to 4.0 N / 25 mm, and further preferably 2.0 to 3.5 N / 25 mm.

[0084] The bonding strength between the coating layers is affected by the intermolecular interactions of the vinyl alcohol copolymer contained in the coating layers. High bonding strength between the coating layers means that the vinyl alcohol copolymer contained in the coating layers forms strong intermolecular interactions. The stronger the intermolecular interactions of the vinyl alcohol copolymer contained in the coating layers, the less likely the higher-order structure of the coating layers will change when cleaned with acid or alkali. As a result, a composite semipermeable membrane with good oxidation resistance, acid resistance, and alkali resistance can be obtained. On the other hand, when the bonding strength between the coating layers is too strong, the permeation resistance of the coating layers increases, and thus the water permeability of the composite semipermeable membrane decreases. When the bonding strength between the coating layers is 0.9 N / 25 mm or more, a composite semipermeable membrane with good oxidation resistance, acid resistance, and alkali resistance can be obtained. On the other hand, when the bonding strength between the coating layers is 5.0 N / 25 mm or less, a composite semipermeable membrane with sufficient water permeability can be obtained. The conditions for measuring bonding strength are described in "(9) Bonding Strength" described later.

[0085] (1-4) NaCl removal rate and water permeability

[0086] The composite semipermeable membrane of this embodiment preferably has a NaCl removal rate of 99.55% or greater, more preferably 99.65% or greater, and even more preferably 99.75% or greater. Furthermore, the composite semipermeable membrane preferably has a water permeability F0 of 0.65 m / d / MPa or greater, more preferably 0.75 m / d / MPa or greater, and even more preferably 0.85 m / d / MPa or greater. By ensuring that the composite semipermeable membrane has membrane performance within the above range, it can be preferably used as a separation membrane for separating salts and the like.

[0087] The composite semipermeable membrane preferably has a water permeability F1 after scaling of 0.50 m / d / MPa or greater, more preferably 0.60 m / d / MPa or greater, and even more preferably 0.70 m / d / MPa or greater. Furthermore, the composite semipermeable membrane preferably has a water permeability F1 after scaling relative to the water permeability F0 (hereinafter also referred to as "F1 / F0") of 0.7 or greater, more preferably 0.8 or greater.

[0088] By setting the membrane performance of the composite semipermeable membrane after fouling treatment within the above range, it can be preferably used as a composite semipermeable membrane having excellent fouling resistance. The fouling conditions are as described in "(3) Water permeability after fouling" described later.

[0089] The NaCl removal rate of the composite semipermeable membrane according to this embodiment after contact with an oxidant is preferably 99.50% or greater, more preferably 99.60% or greater, and even more preferably 99.70% or greater. By ensuring that the membrane performance of the composite semipermeable membrane after contact with an oxidant is within the above range, it can be preferably used as a composite semipermeable membrane with a low risk of oxidative degradation due to oxidant leakage. The conditions for contact with an oxidant are as described in "(6) Contact with an Oxidant" below.

[0090] The NaCl removal rate of the composite semipermeable membrane according to this embodiment after acid or alkali contact is preferably 99.40% or higher, more preferably 99.50% or higher, and even more preferably 99.60% or higher. By ensuring that the membrane performance of the composite semipermeable membrane after acid or alkali contact is within the above range, it can be preferably used as a composite semipermeable membrane that maintains separation performance even after repeated chemical cleaning. The conditions for acid or alkali contact are as described in "(4) Alkali Contact" or "(5) Acid Contact" described below.

[0091] Furthermore, the NaCl removal rate of the composite semipermeable membrane according to this embodiment after the membrane degradation test is preferably 99.15% or more, more preferably 99.30% or more, and even more preferably 99.40% or more. By ensuring that the membrane performance of the composite semipermeable membrane after the membrane degradation test is within the above range, it can be preferably used as a composite semipermeable membrane with a low risk of composite degradation caused by alkali, acid, and oxidant. The conditions of the membrane degradation test are as described in "(7) Membrane Degradation Test" described later.

[0092] 2. Method for manufacturing composite semipermeable membrane

[0093] The method for producing the composite semipermeable membrane according to the present embodiment is not particularly limited as long as a composite semipermeable membrane satisfying the above-mentioned desired characteristics can be obtained. For example, the composite semipermeable membrane can be produced by the following method.

[0094] (2-1) Formation of Supporting Film

[0095] As a method for forming the supporting membrane, a known method can be appropriately used. Hereinafter, a case where PSf is used as a raw material for the porous supporting layer will be described as an example.

[0096] First, PSf is dissolved in a good solvent for PSf to prepare a porous supporting layer stock solution. As a good solvent for PSf, for example, N,N-dimethylformamide (hereinafter also referred to as "DMF") is preferred.

[0097] The PSf concentration in the porous supporting layer stock solution is preferably 10-25% by mass, more preferably 12-20% by mass. By adjusting the PSf concentration in the porous supporting layer stock solution within this range, both the strength and water permeability of the resulting porous supporting layer can be achieved. The preferred range of the raw material concentration in the porous supporting layer stock solution can be appropriately adjusted depending on the raw materials, good solvent, etc. used.

[0098] Next, the obtained porous supporting layer stock solution was applied to the surface of the substrate, and then immersed in a coagulation bath containing a PSf non-solvent.

[0099] The non-solvent for PSf contained in the coagulation bath is preferably water, for example. By contacting the porous supporting layer stock solution coated on the substrate surface with the coagulation bath containing the non-solvent for PSf, the porous supporting layer stock solution is coagulated due to non-solvent-induced phase separation, thereby obtaining a supporting membrane having a porous supporting layer formed on the substrate surface.

[0100] The coagulation bath may consist solely of a non-solvent for PSf, or may contain a good solvent for PSf within a range capable of coagulating the porous supporting layer stock solution.

[0101] The solvent remaining in the supporting membrane can be removed by washing the obtained supporting membrane before forming the separation functional layer.

[0102] (2-2) Separation Functional Layer Polymerization Step

[0103] Next, a separation functional layer comprising cross-linked polyamide is formed on the supporting membrane.

[0104] The method for forming a separation functional layer comprising a cross-linked polyamide is described below, using as an example a method for polymerizing and curing a polyfunctional amine and a polyfunctional acid chloride on the supporting membrane obtained in "(2-1) Formation of Support Membrane." Interfacial polymerization is the most preferred polymerization method from the perspectives of productivity and performance. The interfacial polymerization process is described below.

[0105] The interfacial polymerization process comprises: (a) a process of bringing an aqueous solution containing a polyfunctional amine into contact with a supporting membrane; (b) a process of bringing an organic solvent solution containing a polyfunctional acid chloride into contact with the supporting membrane after contact with the aqueous solution containing the polyfunctional amine; (c) a process of dehydrating the organic solvent solution after contact; and (d) a process of washing the composite semipermeable membrane from which the organic solvent solution has been dehydrated with hot water.

[0106] In step (a), the aqueous solution contains at least a polyfunctional amine. Examples of the polyfunctional amine include the polyfunctional amines exemplified in "(1-2) Separation functional layer".

[0107] The concentration of the polyfunctional amine in the aqueous solution is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 1.0 to 10% by mass. When the concentration of the polyfunctional amine is 0.1% by mass or greater, a separation functional layer with solute separation performance can be formed. On the other hand, when the concentration of the polyfunctional amine is 20% by mass or less, a separation functional layer with good water permeability can be formed.

[0108] Furthermore, the aqueous solution may contain compounds such as a surfactant and an antioxidant as needed, as long as they do not inhibit polymerization.

[0109] The aqueous solution is preferably brought into uniform and continuous contact with the supporting membrane. Specifically, examples include coating the supporting membrane with the aqueous solution of a polyfunctional amine or immersing the supporting membrane in the aqueous solution. The contact time between the supporting membrane and the aqueous solution is preferably 1 second to 10 minutes, more preferably 3 seconds to 3 minutes.

[0110] After the aqueous solution is brought into contact with the supporting membrane, it is preferably thoroughly dehydrated to prevent any droplets from remaining on the supporting membrane. This thorough dehydration prevents residual droplets from forming membrane defects after the separation functional layer is formed, potentially reducing separation performance. Examples of dehydration methods include holding the supporting membrane vertically after contact with the aqueous solution to allow excess solution to flow naturally downward, and forcibly dehydrating the membrane by blowing a stream of nitrogen or other substances through an air nozzle. Alternatively, the membrane surface can be dried after dehydration to remove some of the water from the aqueous solution.

[0111] In step (b), examples of the polyfunctional acid chloride include the polyfunctional acid chlorides exemplified in "(1-2) Separation functional layer".

[0112] The organic solvent is preferably immiscible with water, capable of dissolving the polyfunctional acid chloride, non-corrosive to the supporting membrane, and inactive toward polyfunctional amines and polyfunctional acid chlorides. Examples of the organic solvent include hydrocarbon compounds such as n-nonane, n-decane, n-undecane, n-dodecane, isooctane, isodecane, and isododecane, and mixed solvents thereof.

[0113] The concentration of the polyfunctional acyl chloride in the organic solvent solution is preferably 0.01 to 10 mass %, more preferably 0.02 to 4 mass %, further preferably 0.03 to 2 mass %. When the concentration of the polyfunctional acyl chloride is 0.01 mass % or more, polymerization can be carried out with sufficient reaction speed. On the other hand, when the concentration of the polyfunctional acyl chloride is 10 mass % or less, the generation of the side reaction in the polymerization can be suppressed. In addition, in the organic solvent solution, as long as it does not hinder polymerization, compounds such as surfactants can be included as needed.

[0114] The organic solvent solution of the polyfunctional acid chloride is preferably brought into uniform and continuous contact with the supporting membrane after contact with the aqueous polyfunctional amine solution. Specifically, for example, a method can be employed in which the organic solvent solution of the polyfunctional acid chloride is coated onto the supporting membrane after contact with the aqueous polyfunctional amine solution. The contact time between the supporting membrane after contact with the aqueous polyfunctional amine solution and the organic solvent solution of the polyfunctional acid chloride is preferably 3 seconds to 10 minutes, more preferably 5 seconds to 3 minutes.

[0115] If necessary, the supporting membrane may be heat-treated after contact with the organic solvent solution of the polyfunctional acid chloride. When heat-treated, the heating temperature is preferably 35-180°C, more preferably 50-160°C, and even more preferably 60-150°C. The optimal heating time varies depending on the temperature of the membrane surface, which serves as the reaction site, but is preferably 5 seconds or longer, and more preferably 10 seconds or longer.

[0116] In step (c), the organic solvent solution on the composite semipermeable membrane after the polymerization reaction is removed by degassing. Examples of degassing methods include a method in which the membrane is held vertically and excess organic solvent solution is allowed to flow down and be removed naturally; a method in which the organic solvent is dried and removed by blowing air with a blower; and a method in which excess organic solvent solution is removed using a mixed fluid of water and air.

[0117] In step (d), the composite semipermeable membrane from which the organic solvent has been removed is cleaned with hot water. The temperature of the hot water is preferably 40 to 95°C, more preferably 60 to 95°C. When the temperature of the hot water is 40°C or above, the unreacted products and oligomers remaining in the membrane can be fully removed. On the other hand, when the temperature of the hot water is 95°C or below, the shrinkage of the composite semipermeable membrane does not increase, and good water permeability can be maintained. It should be noted that the preferred range of the temperature of the hot water can be appropriately adjusted according to the polyfunctional amine or polyfunctional acid chloride used.

[0118] (2-3) Coating Layer Formation Step

[0119] Next, a coating layer containing a vinyl alcohol copolymer is formed on the separation functional layer.

[0120] The method for forming the covering layer containing a vinyl alcohol copolymer will be described by taking as an example a method of bringing a solution containing a vinyl alcohol copolymer into contact with the separation functional layer obtained in "(2-2) Separation functional layer polymerization step" to insolubilize the vinyl alcohol copolymer.

[0121] The process of forming the coating layer includes: (e) a process of bringing a solution containing a vinyl alcohol copolymer and a cross-linking agent into contact with the separation functional layer; (f) a process of cross-linking the vinyl alcohol copolymer and the cross-linked polyamide and fixing them on the separation functional layer; (g) a process of removing excess solution; and (h) a process of cleaning the composite semipermeable membrane.

[0122] In step (e), the solution contains at least a vinyl alcohol copolymer and a cross-linking agent. From the perspective of suppressing modification of the separation functional layer and the supporting membrane during contact with the solution, water is preferably used as the solution for dissolving the vinyl alcohol copolymer and the cross-linking agent. Furthermore, additives may be used to improve the solubility of the vinyl alcohol copolymer.

[0123] The concentration of the vinyl alcohol copolymer in the solution is preferably 0.05 to 10% by mass, more preferably 0.1 to 8% by mass, and even more preferably 0.2 to 5% by mass. When the concentration of the vinyl alcohol copolymer is 0.05% by mass or more, a coating layer having a sufficient thickness can be provided, and a composite semipermeable membrane exhibiting excellent anti-fouling properties can be obtained. On the other hand, when the concentration of the vinyl alcohol copolymer is 10% by mass or less, the decrease in water permeability caused by the coating layer can be suppressed, and a composite semipermeable membrane having sufficient water permeability can be obtained.

[0124] Furthermore, the solution may contain components forming the coating layer other than the vinyl alcohol copolymer, such as PVA and PAA.

[0125] The term "crosslinking agent" refers to a compound that reacts with the functional groups of the vinyl alcohol copolymer and the functional groups of the crosslinked polyamide to form covalent bonds therewith. Examples of the crosslinking agent include polyaldehydes such as succinaldehyde, glutaraldehyde, and terephthalaldehyde.

[0126] The concentration of the crosslinking agent in the solution is preferably 0.01 to 5% by mass, more preferably 0.02 to 1% by mass, and even more preferably 0.05 to 0.5% by mass. When the concentration of the crosslinking agent is 0.01% by mass or greater, the vinyl alcohol copolymer and the crosslinked polyamide form covalent bonds, thereby insolubilizing the vinyl alcohol copolymer. On the other hand, when the concentration of the crosslinking agent is 5% by mass or less, the rapid crosslinking reaction is suppressed, allowing for the formation of a uniform coating layer.

[0127] Furthermore, the solution may contain compounds such as catalysts as needed. When a vinyl alcohol copolymer is used and a polyaldehyde is used as a crosslinking agent, examples of the catalyst include inorganic acids such as hydrochloric acid and sulfuric acid.

[0128] The solution is preferably brought into uniform and continuous contact with the separation functional layer. Specifically, for example, the solution may be applied to the separation functional layer. The contact time between the separation functional layer and the solution is preferably 5 seconds to 10 hours, more preferably 10 seconds to 1 hour.

[0129] In step (f), the vinyl alcohol copolymer and the cross-linked polyamide of the separation functional layer are cross-linked to be insolubilized. The cross-linking method can be appropriately selected according to the cross-linking agent used. When a polyaldehyde is used as a cross-linking agent, thermal cross-linking is preferably used as the cross-linking method. As a method of thermal cross-linking, for example, a method of heating the aqueous solution and the composite semipermeable membrane by blowing hot air with a blower can be cited. The temperature of the hot air is preferably 30 to 120°C, more preferably 40 to 80°C. When the temperature of the hot air is above 30°C, the vinyl alcohol copolymer and the cross-linked polyamide form a covalent bond and the vinyl alcohol copolymer can be insolubilized. On the other hand, when the temperature of the hot air is below 120°C, the rapid cross-linking reaction can be suppressed to form a uniform coating layer, and the shrinkage of the composite semipermeable membrane will not increase, and good water permeability can be maintained.

[0130] In step (g), the solution on the composite semipermeable membrane after the cross-linking reaction is removed by desolvation. Examples of the desolvation method include a method in which the membrane is held vertically to allow the excess solution to flow down and be removed naturally; and a method in which the solvent is dried and removed by blowing air with a blower.

[0131] In step (h), the composite semipermeable membrane from which the solution has been removed is washed with water. The temperature of the water used for washing is preferably 15 to 70° C., more preferably 20 to 50° C. When the temperature of the water is above 15° C., the unreacted substances, catalysts, etc. remaining in the composite semipermeable membrane can be fully removed. On the other hand, when the temperature of the water is below 70° C., the shrinkage of the composite semipermeable membrane will not increase, and good water permeability can be maintained. It should be noted that the preferred range of the water temperature can be appropriately adjusted according to the type of vinyl alcohol copolymer and cross-linking agent used.

[0132] In addition, as required, the composite semipermeable membrane may be subjected to a hydrophilic treatment. Examples of the hydrophilic treatment method include contacting the composite semipermeable membrane with an aqueous surfactant solution such as polyoxyethylene octylphenyl ether, sodium n-dodecylbenzenesulfonate, or an aqueous alcohol solution such as methanol, ethanol, isopropyl alcohol, or glycerol.

[0133] 3. Application of composite semipermeable membrane

[0134] The composite semipermeable membrane of this embodiment is suitable for use as a spiral composite semipermeable membrane element, wound around a cylindrical water collection pipe having multiple holes therethrough, along with a feed water flow path material such as a plastic mesh, a permeate water flow path material such as a tricot fabric, and, if necessary, a membrane for improving pressure resistance. Furthermore, a composite semipermeable membrane module can be constructed by connecting these elements in series or in parallel and housing them in a pressure vessel.

[0135] Furthermore, the composite semipermeable membrane, its elements, and modules can be combined with a pump to supply feed water, a device to pre-treat the feed water, and the like to form a fluid separation device. This fluid separation device can separate the feed water into permeate water, such as drinking water, and concentrated water that has not permeated the membrane, thereby obtaining target water.

[0136] Examples of the supply water to be treated using the composite semipermeable membrane involved in this embodiment include liquid mixtures containing 500 mg / L to 100 g / L of total dissolved solids (Total Dissolved Solids: hereinafter also referred to as "TDS"), such as seawater, brackish water, and wastewater. Generally, TDS refers to the total dissolved solids content and is expressed as "mass / volume" or "mass ratio." By definition, it is calculated based on the weight 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 it is more convenient to convert it based on the practical salinity (S).

[0137] When the operating pressure of the fluid separation device is high, the solute removal rate is improved, but the energy required for operation is also increased. In addition, if the durability of the composite semipermeable membrane is taken into consideration, the operating pressure when the treated water passes through the composite semipermeable membrane is preferably 0.5 to 10 MPa. When the supply water temperature becomes higher, the solute removal rate decreases, but as the supply water temperature decreases, the water permeability also decreases. Therefore, the supply water temperature is preferably 5 to 45°C. In addition, in the case of supply water with a high solute concentration such as seawater, when the pH of the supply water becomes high, scale such as magnesium may be generated. In addition, since operation under high pH conditions may cause degradation of the composite semipermeable membrane, it is preferably operated in the neutral region.

[0138] Example

[0139] The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.

[0140] The physical properties of the composite semipermeable membrane of the present invention were measured by the following methods.

[0141] (1) Water permeability

[0142] Evaluation water (hereinafter referred to as "evaluation water") prepared at a NaCl concentration of 2,000 mg / L, 25°C, and pH 7 was supplied to a composite semipermeable membrane with a diameter of 75 mm at an operating pressure of 1.55 MPa. After 2 hours of operation, permeate water was collected for 15 minutes. The permeate water volume (m 3 ) and converted into per unit membrane area (m 2 ), unit time (d) and unit pressure (MPa), and calculate the water permeability F0 (m / d / MPa).

[0143] (2) NaCl removal rate

[0144] In the membrane filtration test of "(1) Water Permeability," the conductivity of the evaluation water and the permeate were measured using a multifunctional water quality meter (MM-60R, manufactured by DKK Toa Co., Ltd.), and the NaCl concentration (practical salinity) of each was measured. The NaCl removal rate (%) was calculated based on the obtained NaCl concentration using the following formula (1). Note that the value obtained by rounding off to the third decimal place was used.

[0145] NaCl removal rate (%) = 100 × {1-(NaCl concentration in permeate water / NaCl concentration in evaluation water)} ···Formula (1)

[0146] (3) Water permeability after scaling

[0147] Evaluation water to which polyoxyethylene (10) octylphenyl ether was added to a concentration of 50 mg / L was supplied to the composite semipermeable membrane under the conditions described in "(1) Water Permeability". After 30 minutes of operation, permeate was collected for 15 minutes. The water permeability F1 (m / d / MPa) after scaling was calculated from the permeate obtained using the same calculation method as in "(1) Water Permeability".

[0148] (4) Alkali contact

[0149] The composite semipermeable membrane was immersed in a sodium hydroxide aqueous solution adjusted to 25° C. and pH 12.5 for 72 hours, and then washed with distilled water.

[0150] (5) Acid contact

[0151] The composite semipermeable membrane was immersed in sulfuric acid adjusted to 25° C. and pH 2.0 for 3 hours, and then washed with distilled water.

[0152] (6) Oxidant contact

[0153] The composite semipermeable membrane was immersed in a 5 mg / L sodium hypochlorite aqueous solution adjusted to 25°C and pH 7.0 for a total of 96 hours, with the aqueous solution replaced every 24 hours. It was then immersed in a 1000 mg / L sodium bisulfite aqueous solution for 10 minutes and washed with distilled water.

[0154] (7) Membrane degradation test

[0155] For the composite semipermeable membrane, "(4) alkali contact", "(5) acid contact", "(6) oxidant contact", "(4) alkali contact", "(5) acid contact" were carried out in sequence, and the NaCl removal rate (%) was calculated by the method described in "(2) NaCl removal rate" at each stage.

[0156] (8) Gas permeability and selectivity

[0157] The composite semipermeable membrane is cut out and dried to a moisture content of 0.5% or less. In a test unit having a supply side unit and a permeation side unit, the composite semipermeable membrane is maintained between the supply side unit and the permeation side unit in such a way that the separation functional layer and the coating layer become the supply side. Helium and oxygen are used as supply gases, and the pressure change of the permeation side of helium and oxygen per unit time is measured at a measuring temperature of 25°C according to the pressure sensor method of ISO15105-1 (2007). Here, the supply side is set to 100kPa, the permeation side is set to 0kPa, and the pressure difference between the supply side and the permeation side is set to 100kPa. Then, based on the following formula (2), the permeability of helium and oxygen (m / d / MPa) is calculated. It should be noted that STP represents standard conditions.

[0158] Helium or oxygen permeability (m / d / Mpa) = [Helium or oxygen permeability (m 3 ·STP)] / [Effective membrane area of ​​composite semipermeable membrane (m 2 )×time (d)×pressure difference (MPa)]…Formula (2)

[0159] In addition, the He / O2 selectivity was calculated by dividing the helium permeability by the oxygen permeability.

[0160] The details of the measurement conditions are shown below.

[0161] Effective membrane area of ​​composite semipermeable membrane: 25cm 2

[0162] Unit temperature: 25°C

[0163] Supply gas: Helium and oxygen mixture (volume ratio 1:1), 0% RH

[0164] (9) Bonding strength

[0165] The composite semipermeable membrane was cut into 2 pieces with a width of 25 mm and a length of 300 mm, and washed with 90° C. hot water for 5 minutes, and then immersed in distilled water at 20° C. for 10 minutes. The two composite semipermeable membranes obtained were bonded to a length of 220 mm from each end in a manner that the coating layers overlap each other to make a test piece (hereinafter also referred to as a "T-shaped test piece"). After blowing hot air at 120° C. for 20 minutes to the T-shaped test piece, it was immersed in water at 20° C. for 1 hour. Then, according to JIS K 6854-3 (1999), the two unbonded ends of the T-shaped test piece were each fixed with a clamp of a tensile testing machine (made by A&D Co., Ltd.; RTG-1210), and a T-shaped peel test was performed under the following conditions.

[0166] Peeling speed: 200mm / min

[0167] Peeling distance: 200mm

[0168] Measurement room temperature: 25℃

[0169] Calculate the average strength (N / 25mm) for a peel distance of 50 to 150 mm. Repeat the same measurement 10 times with a different T-shaped test piece. The average of the obtained average strengths is used as the adhesive strength (N / 25mm). However, if the supporting film has a substrate and the substrate peels while the coating layers remain bonded, such as in the case where the coating layers peel before the peel distance reaches 150 mm, the maximum strength at the time of peeling is used as the average strength for calculating the adhesive strength.

[0170] (10) Total thickness of the separation functional layer and the coating layer T

[0171] The composite semipermeable membrane was cut into 3 cm × 3 cm squares and immersed in distilled water at 25°C for 24 hours. After the impregnation, the composite semipermeable membrane was embedded in epoxy resin, stained with osmium tetroxide, and extremely thin slices were cut out using a microtome as measurement samples. For the obtained sample, the cross section of the composite semipermeable membrane was used as the observation surface and observed using a scanning transmission electron microscope (made by Hitachi, Ltd.; HD2700). Using an image acquired at a magnification of 1 million times, the shortest distance from a certain point on the external surface of the separation functional layer or the coating layer to the internal surface was measured. For 10 randomly selected protrusions, 5 points were measured on one protrusion, and the average value was taken as the total thickness T (nm) of the separation functional layer and the coating layer.

[0172] (11) Root mean square height Sq of the separation functional layer

[0173] The composite semipermeable membrane was cut into 3 cm x 3 cm squares and immersed in distilled water at 25°C for 24 hours. The immersed composite semipermeable membrane was observed using an atomic force microscope (Bruker; Dimension FastScan) with the separation functional layer as the measurement surface, while wet with distilled water, under the following conditions. The root mean square height (RMS) of 10 randomly selected locations was calculated according to ISO 25178:2014 (Surface Roughness Measurement), and the average value was used as the RMS height (nm).

[0174] Scanning Mode: Nanomechanical Mapping in Water

[0175] Probe: Silicon cantilever (Bruker; Scan Asyst-Fluid)

[0176] Maximum load: 5nN

[0177] Scanning range: 10μm×10μm

[0178] Scan speed: 1Hz

[0179] Number of pixels: 512×512

[0180] Measurement environment: distilled water

[0181] Measurement temperature: 25°C

[0182] (12) Weight average molecular weight

[0183] The weight average molecular weight (in terms of polystyrene) of PSf was measured using gel permeation chromatography (manufactured by Tosoh Corporation; HLC-8022). Specific measurement conditions are as follows.

[0184] Chromatographic columns: 2 TSK gel SuperHM-H (manufactured by Tosoh Corporation; inner diameter 6.0 mm, length 15 cm)

[0185] Eluent: LiBr / N-methylpyrrolidone solution (10 mM)

[0186] Sample concentration: 0.1 mass%

[0187] Flow rate: 0.5mL / min

[0188] Temperature: 40℃

[0189] The raw materials of the composite semipermeable membranes used in the Examples and Comparative Examples are summarized below.

[0190] PSf (manufactured by Solvay Specialty Polymers Japan Co., Ltd.; Udel P-3500, Mw80,000)

[0191] DMF (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0192] Polyester long fiber nonwoven fabric (thickness 90 μm; density 0.42 g / cm 3 )

[0193] m-PDA (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0194] TMC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0195] n-Decane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0196] Sodium nitrite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0197] Sodium sulfite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0198] Polyoxyethylene (10) octylphenyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0199] Sodium hypochlorite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0200] Sodium bisulfite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0201] Sulfuric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0202] Sodium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0203] PAA (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; Mw 25,000)

[0204] 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholine chloride (hereinafter also referred to as "DMT-MM") (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0205] PVA1 (manufactured by Sigma-Aldrich; saponification degree 99.5 mol%, polymerization degree 2,600)

[0206] PVA2 (manufactured by Sigma-Aldrich; saponification degree 98.0-99.0 mol%, polymerization degree 900)

[0207] PVA3 (manufactured by Sigma-Aldrich; saponification degree 87.0-89.0 mol%, polymerization degree 900)

[0208] Vinyl alcohol copolymer 1 (manufactured by Kuraray Co., Ltd.; EXCEVAL RS-2117, saponification degree 97.5-99.0 mol%, polymerization degree 1,700, ethylene copolymerization ratio 0.030)

[0209] Vinyl alcohol copolymer 2 (manufactured by Kuraray Co., Ltd.; EXCEVAL RS-1717, saponification degree 92.0-94.0 mol%, polymerization degree 1,700, ethylene copolymerization ratio 0.028)

[0210] Vinyl alcohol copolymer 3 (manufactured by Kuraray Co., Ltd.; EXCEVAL AQ-4104, saponification degree 98.0-99.0 mol%, polymerization degree 400, ethylene copolymerization ratio 0.059)

[0211] Vinyl alcohol copolymer 4 (manufactured by Kuraray Co., Ltd.; EXCEVAL HR-3010, saponification degree 99.0-99.4 mol%, polymerization degree 1,000, ethylene copolymerization ratio 0.045)

[0212] Glutaraldehyde (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0213] Isopropyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0214] Hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0215] (Comparative Example 1)

[0216] A porous supporting layer stock solution was prepared by dissolving 15% by mass of PSf and 85% by mass of DMF at 100°C. This porous supporting layer stock solution was applied to the surface of a polyester long-fiber nonwoven fabric at 25°C. After 3 seconds, the fabric was coagulated by immersion in a coagulation bath of 25°C distilled water for 30 seconds. The fabric was then rinsed with 80°C hot water for 2 minutes. This produced a supporting membrane in which a porous supporting layer made of PSf was formed on the surface of the polyester long-fiber nonwoven fabric serving as a substrate. The thickness of the porous supporting layer in the resulting supporting membrane was 30 μm.

[0217] Next, the obtained supporting membrane was immersed in a 3% by mass aqueous solution of m-PDA for 2 minutes, the supporting membrane was slowly pulled up in the vertical direction, and nitrogen was blown from the air nozzle to remove excess aqueous solution from the surface of the supporting membrane. Under an environment controlled at 25°C, 20 ml of a 25°C n-decane solution containing 0.12% by mass of TMC was applied so as to completely wet the surface of the supporting membrane and allowed to stand for 1 minute to form a separation functional layer by interfacial polymerization. Then, the obtained membrane was kept vertically for 30 seconds, the excess solution was dehydrated and removed, and then washed with hot water at 80°C for 2 minutes. Furthermore, the washed membrane was immersed in a 0.3% by mass aqueous solution of sodium nitrite at 35°C and pH 3 for 1 minute, and then immersed in a 0.1% by mass aqueous solution of sodium sulfite for 2 minutes to obtain a composite semipermeable membrane.

[0218] (Comparative Example 2)

[0219] The composite semipermeable membrane obtained in Comparative Example 1 was immersed in an aqueous solution containing 0.01% by mass of PAA and 0.1% by mass of DMT-MM for 6 hours at a controlled temperature of 20°C to form a coating layer on the separation functional layer. The composite semipermeable membrane was then held vertically, and the excess aqueous solution was drained and removed, followed by rinsing with 40°C water for 2 minutes.

[0220] (Comparative Example 3)

[0221] The surface of the separation functional layer of the composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with the entire surface under an environment controlled at 20°C, containing a solution (isopropyl alcohol / water = 3 / 7) of 0.25% by mass of PVA1 (99.5% by mole of saponification degree, 2,600 degree of polymerization). In a state where the aqueous solution remained on the surface of the separation functional layer, it was kept at 100°C for 5 minutes, and the solution was brought into contact again and kept at 130°C for 5 minutes to form a coating layer on the separation functional layer. Then, it was washed with water at 20°C for 2 minutes. Finally, the composite semipermeable membrane was immersed in a 14% by mass aqueous solution of isopropyl alcohol at 20°C for 5 minutes to perform a hydrophilic treatment.

[0222] (Comparative Example 4)

[0223] The surface of the separation functional layer of the composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with the entire surface by an aqueous solution containing 2.0% by mass of PVA3 (degree of saponification 87.0-89.0 mol%, degree of polymerization 900), 0.5% by mass of glutaraldehyde, and 0.1% by mass of sulfuric acid under an environment controlled at 20°C. In a state where an aqueous solution remained on the surface of the separation functional layer, hot air at 70°C was blown toward the composite semipermeable membrane for 3 minutes, thereby forming a coating layer on the separation functional layer. Then, the composite semipermeable membrane was made vertical, the excess aqueous solution was dehydrated and removed, and washed with water at 20°C for 2 minutes. Finally, the composite semipermeable membrane was immersed in a 14% by mass aqueous solution of isopropyl alcohol at 20°C for 5 minutes for hydrophilization.

[0224] (Comparative Example 5)

[0225] A coating layer was formed on the separation functional layer and hydrophilic treatment was performed in the same manner as in Comparative Example 4 except that an aqueous solution containing 2.0 mass % of PVA2 (saponification degree 98.0-99.0 mol %, polymerization degree 900), 0.5 mass % of glutaraldehyde, and 0.1 mass % of sulfuric acid was used.

[0226] (Example 1)

[0227] A coating layer was formed on the separation functional layer to perform a hydrophilic treatment in the same manner as in Comparative Example 4, except that an aqueous solution containing 0.5% by mass of vinyl alcohol copolymer 3 (EXCEVAL AQ-4104), 0.3% by mass of glutaraldehyde, and 0.1% by mass of sulfuric acid was used and the blowing time of hot air at 70°C was set to 1 minute.

[0228] (Example 2)

[0229] A coating layer was formed on the separation functional layer and hydrophilic treatment was performed in the same manner as in Example 1 except that an aqueous solution containing 0.8 mass % of vinyl alcohol copolymer 4 (EXCEVAL HR-3010), 0.4 mass % of glutaraldehyde, and 0.1 mass % of sulfuric acid was used.

[0230] (Example 3)

[0231] A coating layer was formed on the separation functional layer and hydrophilic treatment was performed in the same manner as in Example 1 except that an aqueous solution containing 0.35 mass % of vinyl alcohol copolymer 1 (EXCEVAL RS-2117), 0.15 mass % of glutaraldehyde, and 0.1 mass % of sulfuric acid was used.

[0232] (Example 4)

[0233] A coating layer was formed on the separation functional layer and hydrophilic treatment was performed in the same manner as in Example 1 except that an aqueous solution containing 0.4 mass % of vinyl alcohol copolymer 2 (EXCEVAL RS-1717), 0.2 mass % of glutaraldehyde, and 0.1 mass % of sulfuric acid was used.

[0234] (Example 5)

[0235] A coating layer was formed on the separation functional layer and hydrophilic treatment was performed by the same method as in Example 1, except that an aqueous solution containing 0.7 mass% of PVA2 (saponification degree 98.0-99.0 mol%, polymerization degree 900), 0.3 mass% of vinyl alcohol copolymer 4 (EXCEVAL HR-3010), 0.4 mass% of glutaraldehyde, and 0.1 mass% of sulfuric acid was used.

[0236] (Example 6)

[0237] The surface of the separation functional layer of the composite semipermeable membrane obtained in Comparative Example 2 was brought into contact with an aqueous solution containing 0.3% by mass of vinyl alcohol copolymer 4 (EXCEVAL HR-3010), 0.2% by mass of glutaraldehyde, and 0.1% by mass of sulfuric acid in an environment controlled at 20°C. While the aqueous solution remained on the surface of the separation functional layer, hot air at 70°C was blown onto the composite semipermeable membrane for 3 minutes, thereby forming a coating layer on the separation functional layer. Thereafter, the composite semipermeable membrane was held vertically, and the excess aqueous solution was dehydrated and removed, followed by washing with water at 20°C for 2 minutes. Finally, the composite semipermeable membrane was immersed in a 14% by mass aqueous solution of isopropyl alcohol at 20°C for 5 minutes to perform a hydrophilic treatment.

[0238] (Example 7)

[0239] The surface of the separation functional layer of the composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with the entire surface of an aqueous solution containing 0.4% by mass of vinyl alcohol copolymer 4 (EXCEVAL HR-3010), 0.2% by mass of glutaraldehyde, and 0.04 mol / l of hydrochloric acid under an environment controlled at 20°C. While the aqueous solution remained on the surface of the separation functional layer, it was maintained at 100°C for 5 minutes, and the solution was again brought into contact with the entire surface and maintained at 130°C for 5 minutes, thereby forming a coating layer on the separation functional layer. Then, it was washed with water at 20°C for 2 minutes. Finally, the composite semipermeable membrane was immersed in a 14% by mass aqueous solution of isopropyl alcohol at 20°C for 5 minutes to perform a hydrophilic treatment.

[0240] The structures of the composite semipermeable membranes obtained in Comparative Examples 1 to 5 and Examples 1 to 7 are shown in Table 1, and their performance is shown in Tables 2 and 3. The membrane obtained in Comparative Example 1 did not have a coating layer, so the adhesive strength was not measured.

[0241] [Table 1]

[0242] Table 1

[0243]

[0244] [Table 2] Table 2

[0245]

[0246] [Table 3]

[0247] Table 3

[0248]

[0249] As shown in Table 3, the composite semipermeable membranes of Examples 1 to 7 having a coating layer containing a vinyl alcohol copolymer had high chemical resistance and exhibited sufficient water permeability even after fouling.

[0250] Furthermore, the results of Examples 1 to 4 show that when the copolymerization ratio of ethylene in the vinyl alcohol copolymer is higher, the membrane performance of the composite semipermeable membrane after the membrane degradation test tends to be better. Furthermore, a comparison between Examples 3 and 4 shows that increasing the saponification degree of the vinyl alcohol copolymer improves the membrane performance of the composite semipermeable membrane after the membrane degradation test.

[0251] The present invention is described in detail using specific embodiments, but it is obvious to those skilled in the art that various changes and modifications can be made without departing from the intention and scope of the present invention. It should be noted that this application is based on Japanese patent applications (Special Application Nos. 2023-015302, 2023-015303, and 2023-015304) filed on February 3, 2023, and is incorporated herein by reference in its entirety.

[0252] Reference numerals

[0253] 1 Composite semipermeable membrane

[0254] 2 Support membrane

[0255] 3 Separation functional layer

[0256] 4 Coating layer

[0257] 5 Inside the convex part

Claims

1. A composite semipermeable membrane comprising a supporting membrane, a separation functional layer disposed on the supporting membrane and comprising a cross-linked polyamide, and a coating layer disposed on the separation functional layer and comprising a vinyl alcohol copolymer having a structure represented by the following general formula (1). [Chemical Formula 1] In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, and l, m, and n are the numbers of repeating units.

2. The composite semipermeable membrane according to claim 1, wherein X in the general formula (1) is a divalent hydrocarbon group having 2 carbon atoms.

3. The composite semipermeable membrane according to claim 2, wherein X in the general formula (1) is 1,2-ethylene.

4. The composite semipermeable membrane according to claim 1 or 2, wherein The copolymerization ratio of the vinyl alcohol copolymer: n / (l+m+n) is 0.035 to 0.

16.

5. The composite semipermeable membrane according to claim 1 or 2, wherein The polymerization degree of the vinyl alcohol copolymer is 100 to 1,500.

6. The composite semipermeable membrane according to claim 1 or 2, wherein The saponification degree of the vinyl alcohol copolymer is 96 mol % or more.

7. The composite semipermeable membrane according to claim 1 or 2, wherein The total thickness of the separation functional layer and the covering layer is 10 to 100 nm.

8. The composite semipermeable membrane according to claim 1, wherein The ratio of the water permeability to the helium permeability of the composite semipermeable membrane is 0.0105 to 0.0400.

9. The composite semipermeable membrane according to claim 1 or 2, wherein The He / O2 selectivity of the composite semipermeable membrane is 7.5 to 10.

4.

10. The composite semipermeable membrane according to claim 1 or 2, wherein The bonding strength when the covering layers of two composite semipermeable membranes are bonded together is 0.9 to 5.0 N / 25 mm. A composite semipermeable membrane module comprising the composite semipermeable membrane according to claim 1 or 8.

12. A fluid separation device comprising the composite semipermeable membrane module according to claim 11.

13. The method for producing a composite semipermeable membrane according to claim 1 or 8, comprising the following steps (i) and (ii): (i) forming a separation functional layer comprising a cross-linked polyamide by interfacial polymerization of a polyfunctional amine and a polyfunctional acid chloride on a supporting membrane; (ii) a step of contacting a solution containing a vinyl alcohol copolymer represented by the following general formula (1) on the separation functional layer to insolubilize the vinyl alcohol copolymer and forming a coating layer containing the vinyl alcohol copolymer; [Chemical Formula 2] In the general formula (1), X is a divalent hydrocarbon group having 2 to 6 carbon atoms, and l, m, and n are the numbers of repeating units.

Images