Composite semipermeable membrane and composite semipermeable membrane element

Abstract

To provide a composite semipermeable membrane having both of fouling resistance and high salt removability and having acid / alkali resistance.SOLUTION: A composite semipermeable membrane comprising a porous support layer, a separation functional layer provided on one surface side of the support layer and containing a polyamide, and a coating layer provided on the separation functional layer, wherein the coating layer contains a copolymer containing a first monomer represented by the following general formula (I), a second monomer represented by the following general formula (II), and a hydrophilic third monomer: H2C = C (R1) CONR2R3 (1) H2C = C (R4) COOH (2) [In general formula (I), R1 is hydrogen or methyl, R2 and R3 are optionally substituted C1-6 aliphatic chains, and R2 and may be bonded directly or indirectly to form a ring structure.] R3. In general formula (II), R4 is hydrogen or methyl. ] SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite semipermeable membrane and a composite semipermeable membrane element used for liquid filtration and the like. [Background technology]

[0002] Regarding the separation of mixtures, there are various technologies for removing substances (e.g., salts) dissolved in a solvent (e.g., water). In recent years, the use of membrane separation has expanded as a process for saving energy and resources. Membranes used in membrane separation include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes are used, for example, to obtain drinking water from seawater, brine, or water containing harmful substances, to produce ultrapure water for industrial use, to treat wastewater, and to recover valuable resources.

[0003] The majority of reverse osmosis and nanofiltration membranes currently on the market are composite semipermeable membranes, and there are two types: those with an active layer made of a gel layer and a crosslinked polymer on a support membrane, and those with an active layer formed by polycondensation of monomers on a support membrane. Among these, composite semipermeable membranes obtained by coating a support membrane with a separation functional layer made of crosslinked polyamide obtained by the polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide are widely used as separation membranes with high permeability and selectivity.

[0004] One of the challenges in membrane separation technology using such separation membranes is fouling. Fouling occurs when substances contained in the water being treated adhere to the surface or inside the pores of the separation membrane, inhibiting the permeation of the solution and reducing the separation performance of the separation membrane. Fouling is classified according to the type of substance adsorbed, and includes chemical fouling caused by the adhesion of organic matter and biofouling caused by the adhesion of microorganisms.

[0005] Chemical fouling is a phenomenon in which organic matter such as humic substances and surfactants contained in the water being treated, such as wastewater, accumulates on the surface of a separation membrane or adheres to the inside of the pores of the membrane, causing the membrane to become clogged, reducing the amount of water passing through and degrading the solute separation performance.

[0006] On the other hand, biofouling is a phenomenon in which microorganisms contained in the water being treated multiply on the surface or inside the pores of the separation membrane, using organic matter that has adhered to the membrane due to chemical fouling as a nutrient source, causing the separation membrane to become clogged, reducing the amount of water passing through and deteriorating its separation performance.

[0007] As a method for improving the decrease in permeate flow rate due to fouling, a method for restoring permeate flow rate by cleaning a fouled reverse osmosis membrane with chemicals such as acid or alkali has been disclosed (Patent Document 1). Another method for suppressing fouling is to coat the surface of the separation functional layer with polyvinyl alcohol (Patent Documents 2 and 3). Another method for suppressing fouling is to introduce a hydrophilic polymer with acidic groups into the surface of the separation functional layer via an amide bond (Patent Document 4). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-66972 [Patent Document 2] International Publication No. 1997 / 34686 [Patent Document 3] International Publication No. 2014 / 133132 [Patent Document 4] International Publication No. 2015 / 46582 Summary of the Invention [Problem to be solved by the invention]

[0009] Thus, fouling resistance is an important function of separation membranes. In addition, achieving more efficient water treatment processes requires separation membranes with high salt rejection and acid and alkali resistance. However, with conventional technology, it has been difficult to achieve both fouling resistance and high salt rejection, as well as acid and alkali resistance. Therefore, an object of the present invention is to provide a composite semipermeable membrane that has both fouling resistance and high salt rejection, as well as acid and alkali resistance. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention includes the following configurations [1] to [5]. [1] A composite semipermeable membrane comprising a porous support layer, a separation functional layer containing a polyamide provided on one side of the porous support layer, and a coating layer provided on the separation functional layer, wherein the coating layer contains a copolymer including a first monomer represented by the following general formula (I), a second monomer represented by the following general formula (II), and a hydrophilic third monomer:

[0011] [ka]

[0012] [ka]

[0013] [In general formula (I), R 1 is a hydrogen atom or a methyl group, R 2 , R 3 is an optionally substituted aliphatic chain having 1 to 6 carbon atoms, and R 2 and R 3 may be bonded directly or indirectly to form a ring structure. 4 is a hydrogen atom or a methyl group. [2] The composite semipermeable membrane according to [1] above, wherein, when the molar ratio of the first monomer in the copolymer is X mol %, the molar ratio of the second monomer is Y mol %, and the molar ratio of the third monomer is Z mol %, X, Y, and Z satisfy the following formulas (1) to (4):

[0014] 50≦X≦90...Equation (1) 5≦Y≦20...Equation (2) 5≦Z≦40...Equation (3) X+Y+Z≦100 Equation (4) [3] The composite semipermeable membrane according to [1] or [2] above, wherein the third monomer is a zwitterionic monomer or a monomer containing a vinyl group and a tertiary amide group in the side chain. [4] The composite semipermeable membrane according to [3] above, wherein the third monomer is a zwitterionic monomer. [5] An element using the composite semipermeable membrane according to any one of [1] to [4] above. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a composite semipermeable membrane that has both fouling resistance and high salt rejection properties, and also has acid and alkali resistance. DETAILED DESCRIPTION OF THE INVENTION

[0016] (1) Composite semipermeable membrane The composite semipermeable membrane of the present invention comprises a porous support layer, a separation functional layer containing polyamide (hereinafter also simply referred to as a "polyamide separation functional layer" or "separation functional layer") provided on one side of the porous support layer, and a coating layer provided on the separation functional layer.

[0017] (1-1) Porous support layer The porous support layer of the composite semipermeable membrane of the present invention does not substantially have the ability to separate ions, etc., but serves to provide strength to the separation functional layer, which does substantially have separation performance. The size and distribution of the pores in the porous support layer are not particularly limited, but a preferred porous support layer is, for example, one having uniform fine pores, or pores that gradually increase in size from the surface on which the separation functional layer is formed to the other surface, and in which the size of the pores on the surface on which the separation functional layer is formed is 0.1 nm to 100 nm.

[0018] The material and shape of the porous support layer are not particularly limited, but an example is a composite semipermeable membrane having a substrate and a porous support layer formed thereon. Hereinafter, the structure having a substrate and a porous support layer formed thereon will also be referred to as a support membrane. Examples of the material for the substrate include fabrics mainly composed of polyester, aromatic polyamide, etc.

[0019] The fabric used for the substrate is preferably a long-fiber nonwoven fabric or a short-fiber nonwoven fabric, and more preferably a long-fiber nonwoven fabric from the viewpoint of suppressing the occurrence of defects such as strike-through of the solution due to excessive penetration when a solution of a high molecular weight polymer is cast onto the substrate, peeling between the substrate and the porous support layer, and non-uniformity of the film and pinholes due to fluffing of the substrate.

[0020] Examples of long-fiber nonwoven fabrics include long-fiber nonwoven fabrics made of thermoplastic continuous filaments. In addition, since tension is applied to the substrate in the film-forming direction during the process of continuously forming the composite semipermeable membrane, it is preferable to use a long-fiber nonwoven fabric, which has excellent dimensional stability, as the substrate.

[0021] In particular, the orientation of the fibers arranged on the opposite side of the substrate from the porous support layer is preferably longitudinal to the film-forming direction, since this maintains the strength of the substrate and prevents film breakage, etc. Here, longitudinal orientation means that the fiber orientation direction is parallel to the film-forming direction, and transverse orientation means that the fiber orientation direction is perpendicular to the film-forming direction.

[0022] When the substrate is a nonwoven fabric, the degree of fiber orientation of the nonwoven fabric on the side opposite the porous support layer is preferably 0° or more and 25° or less. Here, the degree of fiber orientation is an index showing the direction of the fibers of the nonwoven fabric constituting the substrate of the support film, and refers to the average angle of the fibers constituting the nonwoven fabric when the film-forming direction during continuous film production is set to 0° and the direction perpendicular to the film-forming direction, i.e., the width direction of the nonwoven fabric, is set to 90°. Therefore, the closer the fiber orientation degree is to 0°, the more longitudinally oriented it is, and the closer it is to 90°, the more transversely oriented it is.

[0023] The manufacturing process for composite semipermeable membranes and the manufacturing process for composite semipermeable membrane elements include a heating step, and heating can cause the support membrane or composite semipermeable membrane to shrink. In particular, in continuous membrane production, no tension is applied in the width direction, so the support membrane or composite semipermeable membrane is prone to shrinkage in the width direction. Shrinkage of the support membrane or composite semipermeable membrane can cause problems with dimensional stability, so a substrate with a small rate of thermal dimensional change is desirable.

[0024] In the nonwoven fabric used as the substrate, from the viewpoint of suppressing changes in the width direction due to heat, the difference in orientation between the fibers arranged on the side opposite the porous support layer and the fibers arranged on the porous support layer side is preferably 10° or more and 90° or less.

[0025] The base material has a permeability of 2.0cc / cm 2 / s or more is preferable. When the air permeability is in this range, the amount of water permeated through the composite semipermeable membrane increases. This is thought to be because, in the process of forming the support membrane, when a high molecular weight polymer is cast onto a substrate and immersed in a coagulation bath, the rate of non-solvent replacement from the substrate side increases, changing the internal structure of the porous support layer and affecting the amount of monomer retained and the diffusion rate in the subsequent process of forming the separation function layer.

[0026] Air permeability can be measured using a Frazier tester in accordance with JIS L1096 (2010). For example, a sample of 200mm x 200mm of substrate is cut out. This sample is attached to the Frazier tester, and the intake fan and air holes are adjusted so that the inclined barometer reads 125 Pa. The amount of air passing through the substrate, i.e., air permeability, can be calculated from the pressure indicated by the vertical barometer and the type of air hole used. A Frazier tester such as the KES-F8-AP1 manufactured by Kato Tech Co., Ltd. can be used.

[0027] The thickness of the substrate is preferably 10 μm or more and 200 μm or less, and more preferably 30 μm or more and 120 μm or less.

[0028] As the material for the porous support layer, homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose-based polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide can be used alone or in blends.

[0029] Examples of cellulose polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile. Among these, homopolymers or copolymers of polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferred as materials for the porous support layer. Furthermore, polysulfone, cellulose acetate, and polyvinyl chloride, or a mixture thereof, are more preferred, with polysulfone being particularly preferred due to its high chemical, mechanical, and thermal stability.

[0030] The thickness of the porous support layer is preferably 10 μm or more and 200 μm or less, and more preferably 20 μm or more and 100 μm or less. When the thickness of the porous support layer is 10 μm or more, good pressure resistance can be obtained, and a uniform support membrane without defects can be obtained, resulting in a composite semipermeable membrane that exhibits good salt rejection performance. When the thickness of the porous support layer is 200 μm or less, the amount of unreacted substances remaining during production does not increase, and a decrease in the amount of permeate water and a decrease in chemical resistance can be prevented.

[0031] The thickness of the support membrane, which is a substrate having a porous support layer formed thereon, affects the strength of the composite semipermeable membrane and the packing density when the composite semipermeable membrane is made into an element. From the viewpoint of obtaining sufficient mechanical strength of the composite semipermeable membrane and the packing density of the composite semipermeable membrane in the element, the thickness of the support membrane is preferably 30 μm or more and 300 μm or less, and more preferably 50 μm or more and 250 μm or less.

[0032] The morphology of the support membrane and porous support layer can be observed using a scanning electron microscope, a transmission electron microscope, an atomic force microscope, or the like. For example, when observing using a scanning electron microscope, the porous support layer is peeled off from the substrate and then cut by freeze-fracturing to obtain a sample for cross-sectional observation. This sample is thinly coated with platinum, platinum-palladium, or ruthenium tetrachloride, preferably ruthenium tetrachloride, and the cross-section is observed using a high-resolution field-emission scanning electron microscope (UHR-FE-SEM) at an accelerating voltage of 3 to 6 kV. A Hitachi S-900 electron microscope or the like can be used as the high-resolution field-emission scanning electron microscope.

[0033] The porous support layer used in the composite semipermeable membrane of this embodiment can be produced, for example, according to the method described in "Office of Saline Water Research and Development Progress Report" No. 359 (1968).

[0034] The thicknesses of the substrate, porous support layer, and composite semipermeable membrane can be measured using a digital thickness gauge. Furthermore, since the thickness of the separation functional layer is much thinner than that of the support membrane, in this specification, the thickness of the composite semipermeable membrane measured using a digital thickness gauge is considered to be the thickness of the support membrane. Therefore, the thickness of the composite semipermeable membrane can be measured using a digital thickness gauge, and the thickness of the porous support layer can be easily calculated by subtracting the thickness of the substrate from the thickness of the composite semipermeable membrane. Examples of digital thickness gauges that can be used include PEACOCK from Ozaki Seisakusho Co., Ltd. When using a digital thickness gauge, the thickness is measured at 20 randomly selected locations, and the average value is calculated.

[0035] The thickness of the substrate, porous support layer, and composite semipermeable membrane may be measured using the above-mentioned electron microscope. The thickness can be determined by measuring the thickness from electron microscope photographs of cross-sections observed at any five points on one sample and calculating the average value. In this specification, the thickness and pore size refer to average values.

[0036] (1-2) Separation functional layer The polyamide-containing separation functional layer of the composite semipermeable membrane of the present invention is a layer that performs the function of separating solutes in the composite semipermeable membrane. The composition, thickness, and other configurations of the separation functional layer are set according to the intended use of the composite semipermeable membrane. The separation functional layer preferably contains polyamide as a main component. "Main component" means a component that accounts for 50% by mass or more of the components that make up the separation functional layer. The polyamide content in the separation functional layer is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0037] Among these, the polyamide is preferably a crosslinked polyamide obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and more preferably a crosslinked aromatic polyamide.

[0038] The term "crosslinked polyamide" refers to a polyamide having a crosslinked structure, such as a form in which the crosslinked structure is formed via a crosslinking agent, or a form in which at least one of a polyfunctional amine and a polyfunctional acid halide is trifunctional or higher and the polyamide forms a network-like crosslinked structure.

[0039] The term "crosslinked aromatic polyamide" refers to a crosslinked polyamide made from a polyfunctional aromatic amine and a polyfunctional aromatic acid halide.

[0040] Whether the separating functional layer contains polyamide can be confirmed by, for example, ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy).

[0041] The polyfunctional amine preferably includes at least one of a polyfunctional aromatic amine and a polyfunctional aliphatic amine.

[0042] "Polyfunctional aromatic amine" refers to an aromatic amine having two or more amino groups in one molecule. Examples of polyfunctional aromatic amines include metaphenylenediamine, paraphenylenediamine, and 1,3,5-triaminobenzene. Examples of N-alkylated products of these amines include N,N-dimethyl metaphenylenediamine, N,N-diethyl metaphenylenediamine, N,N-dimethyl paraphenylenediamine, and N,N-diethyl paraphenylenediamine. From the perspective of stability in performance development, metaphenylenediamine (hereinafter referred to as "m-PDA") or 1,3,5-triaminobenzene is particularly preferred as the polyfunctional aromatic amine.

[0043] "Polyfunctional aliphatic amine" refers to an aliphatic amine having two or more amino groups per molecule. Examples of polyfunctional aliphatic amines include piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2-n-propylpiperazine, 2,5-di-n-butylpiperazine, and ethylenediamine. From the perspective of stability of performance expression, the polyfunctional aliphatic amine is preferably a piperazine-based amine or a derivative thereof, with piperazine, 2-methylpiperazine, or 2,5-dimethylpiperazine being more preferred. These polyfunctional amines may be used alone or in a mixture of two or more.

[0044] "Polyfunctional aliphatic acid halide" refers to an aliphatic acid halide having two or more halocarbonyl groups in one molecule. Examples of polyfunctional aliphatic acid halides include oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. In terms of the stability of performance development, 1,3,5-cyclohexanetricarboxylic acid is preferred as the polyfunctional aliphatic acid halide.

[0045] The term "polyfunctional aromatic acid halide" refers to an aromatic acid halide having two or more halocarbonyl groups in one molecule. Examples of polyfunctional aromatic acid halides include halides of 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, 1,4-benzenedicarboxylic acid, and the like. Among acid halides, acid chlorides are preferred, and trimesoyl chloride (hereinafter referred to as "TMC"), an acid halide of 1,3,5-benzenetricarboxylic acid, is particularly preferred from the standpoints of economy, availability, ease of handling, and ease of reactivity. The polyfunctional acid halides may be used singly or in combination of two or more.

[0046] The polyamide separation functional layer obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide contains amide groups derived from the polymerization of the polyfunctional amine and the polyfunctional acid halide, as well as amino and carboxy groups derived from unreacted functional groups. In addition to these, other functional groups possessed by the polyfunctional amine or polyfunctional acid halide are also present. Furthermore, chemical treatment can introduce new functional groups into the polyamide forming the separation functional layer, thereby improving the performance of the composite semipermeable membrane. Examples of new functional groups that can be introduced into the polyamide include alkyl groups, alkenyl groups, alkynyl groups, halogeno groups, hydroxyl groups, ether groups, thioether groups, ester groups, aldehyde groups, nitro groups, nitroso groups, nitrile groups, and azo groups. For example, chlorine groups (chloro groups) can be introduced into the polyamide skeleton terminals by treating the polyamide separation functional layer with an aqueous sodium hypochlorite solution. Alternatively, halogeno groups can be introduced by a Sandmeyer reaction via the formation of a diazonium salt. Furthermore, an azo group can be introduced by carrying out an azo coupling reaction via the generation of a diazonium salt.

[0047] (1-3 coating layer) The membrane performance can be improved by forming a coating layer on the separating functional layer of a composite semipermeable membrane. After extensive research, the inventors discovered that by incorporating a coating layer containing a copolymer containing three types of monomers each having a tertiary amide group, a carboxyl group, and a hydrophilic group in the side chain, salt rejection and fouling resistance are improved, and acid and alkali resistance is also achieved.

[0048] That is, the composite semipermeable membrane of the present invention comprises a porous support layer, a separation functional layer containing a polyamide provided on one side of the porous support layer, and a coating layer provided on the separation functional layer, the coating layer containing a copolymer containing a first monomer represented by the following general formula (I), a second monomer represented by the following general formula (II), and a hydrophilic third monomer. Hereinafter, the copolymer containing the first monomer, the second monomer, and the third monomer will also be simply referred to as a copolymer.

[0049] [ka]

[0050] [ka]

[0051] In general formula (I), R 1 is a hydrogen atom or a methyl group, R 2 , R 3 is an optionally substituted aliphatic chain having 1 to 6 carbon atoms, and R 2 and R 3 may be bonded directly or indirectly to form a ring structure. 4 is a hydrogen atom or a methyl group. 4 is a hydrogen atom or a methyl group.

[0052] That is, the copolymer contained in the coating layer has a first monomer that is an α,β-unsaturated amide having a tertiary amide moiety, a second monomer that is an α,β-unsaturated carboxylic acid, and a third monomer that is a hydrophilic monomer. Here, "hydrophilic monomer" means a monomer that dissolves in an amount of 1 g or more in 1 L of pure water at 25°C.

[0053] The first monomer contains a tertiary amide moiety, which gives the coating layer hydrogen bond-accepting ability and forms hydrogen bonds with the amide groups in the coarse pores of the polyamide separation layer. This reduces the apparent pore size of the coarse pores in the separation layer, thereby improving salt removal. Furthermore, the second monomer contains a carboxy group, which imparts a charge to the coating layer. Electrostatic repulsion with the charge of the coating layer can suppress the adhesion of charged foulants. Furthermore, the carboxy group of the second monomer can react with the amino group of the polyamide forming the separation layer to form an amide bond. Furthermore, the hydrophilicity of the third monomer increases the amount of hydration water on the surface of the coating layer, thereby suppressing the adhesion of foulants. The copolymer may contain other monomers as long as the effects of the present invention are not impaired, and the coating layer may contain components other than the copolymer. It is preferable that the coating layer contain the above polymer as the main component. The proportion of the copolymer in the coating layer is more preferably 80% by mass or more, even more preferably 90% by mass or more. It is particularly preferable that the coating layer be composed solely of the copolymer.

[0054] The first monomer is preferably a monomer having a (meth)acrylamide group from the viewpoint of ease of polymerization. Examples of the first monomer include N,N-dimethylacrylamide, N,N-diethylacrylamide, and acryloylmorpholine. Among them, N,N-dimethylacrylamide and N,N-diethylacrylamide are more preferred, and N,N-dimethylacrylamide is particularly preferred, from the viewpoint of ease of interaction with polyamide.

[0055] The second monomer is methacrylic acid or acrylic acid, and among them, acrylic acid is preferred from the viewpoint of ease of polymerization.

[0056] The third monomer is a hydrophilic monomer different from the first and second monomers, and examples of the third monomer include monomers having a hydrophilic functional group in the side chain, such as a hydroxyl group, a carboxyl group, a sulfate group, a phosphate group, an amino group, an amide group, or an ether group. Examples of such monomers include (meth)acrylic acid, vinylbenzoic acid, styrenesulfonic acid, vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-(2-hydroxyethyl)acrylamide, acryloylmorpholine, acrylamide, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethyl (meth)acrylamide, glycerol (meth)acrylate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, N-(4-hydroxyphenyl)maleimide, hydroxystyrene, and vinyl alcohol (a vinyl carboxylic acid ester precursor). Among these, it is preferable that the third monomer has an amide group in the side chain, as described below.

[0057] Furthermore, from the viewpoint of facilitating polymerization of the first and second monomers, the third monomer preferably has an allyl group, a vinyl group, or a (meth)acryloyl group, and more preferably a vinyl group or a (meth)acryloyl group. Specifically, from the viewpoint of improving acid and alkali resistance, a monomer having a vinyl group and a tertiary amide group in a side chain is more preferable, and N-vinylpyrrolidone is particularly preferable.

[0058] It is also preferable to use a zwitterionic monomer as the third monomer. The zwitterionic monomer prevents the crosslinked polyamide from swelling due to acid or alkali due to the charge of the zwitterion. This reduces the amount of chlorine that penetrates into the pores of the crosslinked polyamide, improving not only the acid and alkali resistance but also the chlorine resistance.

[0059] The term "zwitterionic monomer" refers to a monomer having both a cationic moiety and an anionic moiety in the same molecule, and is preferably a monomer having a zwitterion in the side chain. A representative example of a zwitterion is a betaine structure. Examples of zwitterionic monomers having a betaine structure include 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, N-(meth)acryloyloxyethyl-N,N-dimethylammonium-α-N-methylcarboxybetaine, and N-(meth)acryloylaminoethyl-N,N-dimethylammonium-α-N-methylcarboxybetaine.

[0060] "Fouling resistance" includes both the ability to suppress fouling and the ability to minimize performance degradation when fouling occurs.

[0061] The improvement of salt removal and the suppression of fouling will be explained in detail below.

[0062] First, we will explain how to improve salt rejection. To achieve a high salt rejection rate, two points are particularly important: reducing the size of the coarse pores and charging the membrane surface.

[0063] We explain how reducing the coarse pores improves salt rejection. The separation layer contains pores formed by polyamide, through which water and solutes pass. If the pore size is larger than the water molecule but smaller than the solute molecules, such as sodium ions and chloride ions (salts), only water passes through the pore, resulting in increased salt rejection. On the other hand, if the pore size is larger than the solute molecule, both water and solute pass through the pore, resulting in decreased salt rejection. The tertiary amide groups derived from the first monomer contained in the copolymer in the coating layer have high hydrogen-bond accepting capacity and can form hydrogen bonds with hydrogen-bond donors, such as amide groups and amino groups, derived from the polyamide present in the pores. Therefore, the pores where hydrogen bonds are formed are filled with the tertiary amide groups derived from the first monomer contained in the copolymer in the coating layer, reducing the apparent pore size and improving salt rejection. Furthermore, if the third monomer has an amide group in its side chain, it can fill pores that were not filled by the tertiary amide group structure derived from the first monomer, further improving salt rejection.

[0064] Next, we will explain how salt rejection can be improved by charging the membrane surface. Sodium chloride, the main solute, ionizes in water into sodium ions and chloride ions, each with a positive and negative charge. To maintain electrical neutrality, both ions must pass through the membrane in order for sodium chloride to pass through. Therefore, if the membrane surface is charged and one ion is prevented from passing through by electrostatic repulsion, sodium chloride permeation will be suppressed. Here, by using a carboxyl group, which has a negative charge in a neutral aqueous solution, or a zwitterionic monomer, which has both positive and negative charges, as the monomer that makes up the copolymer contained in the coating layer, the membrane surface can be charged, thereby improving salt rejection.

[0065] Next, we will explain how to suppress fouling. Two points are particularly important for suppressing fouling: the charge on the membrane surface and the hydration water on the membrane surface.

[0066] This section explains how fouling can be suppressed by the charge on the membrane surface. When contaminants have an electric charge, if the charge is the same as that of the membrane surface, electrostatic repulsion will suppress the adhesion of the contaminants. For example, by forming a copolymer containing a coating layer using a monomer with a carboxyl group that has a negative charge in a neutral aqueous solution, the coating layer will be negatively charged, and the adhesion of contaminants with the same negative charge can be suppressed. In addition, by using a monomer with a zwitterionic functional group that has both positive and negative charges as a hydrophilic monomer, the adhesion of contaminants with either charge can be suppressed.

[0067] Next, we will explain the fouling suppression by hydration water. It is known that water called hydration water exists on the surface of highly hydrophilic compounds in water, and it is believed that this hydration water layer suppresses the adhesion of contaminants. The greater the amount of hydration water on the membrane surface, i.e., the coating layer, the more difficult it is for contaminants to approach the membrane surface. By using a hydrophilic monomer as the monomer of the copolymer contained in the coating layer, the hydrophilicity of the coating layer is increased, and the amount of hydration water on the coating layer surface also increases, and this hydration water is thought to suppress the adhesion of contaminants. Furthermore, the increased mobility of the hydration water allows contaminants near the membrane surface to be pushed away by the hydration water. Because the copolymer contained in the coating layer has higher molecular mobility than rigid cross-linked polyamides, the mobility of the hydration water is also increased, which is thought to improve the ability to suppress the adhesion of contaminants.

[0068] When the molar ratio of the first monomer in the copolymer contained in the coating layer of the composite semipermeable membrane according to this embodiment is X mol %, the molar ratio of the second monomer is Y mol %, and the molar ratio of the third monomer is Z mol %, it is preferable that X, Y, and Z satisfy the formulas (1) to (4).

[0069] 50≦X≦90...Equation (1) 5≦Y≦20...Equation (2) 5≦Z≦40...Equation (3) X+Y+Z≦100 Equation (4) The molar ratio X of the first monomer is preferably 50 mol% to 90 mol%, more preferably 60 mol% to 85 mol%, and even more preferably 70 mol% to 80 mol%. When the molar ratio X is within the above range, a sufficient improvement in salt rejection is achieved and a decrease in the amount of water permeated through the membrane can be suppressed. The molar ratio Y of the second monomer is preferably 5 mol% to 20 mol%, more preferably 5 mol% to 15 mol%, and even more preferably 8 mol% to 10 mol%. When the molar ratio Y is within the above range, a covalent bond between the polyamide in the separation functional layer and the copolymer contained in the coating layer can be appropriately formed, making the coating layer less likely to peel off from the separation functional layer. Furthermore, the mobility of the copolymer contained in the coating layer is not reduced, making it easier to achieve anti-fouling properties. The molar ratio Z of the third monomer is preferably 5 mol% to 40 mol%, more preferably 8 mol% to 30 mol%, and even more preferably 10 mol% to 20 mol%. When the molar ratio Z is within the above range, the fouling resistance and salt removal rate are improved, and it is also advantageous in terms of cost. The molar ratios of these monomers are selected so that their sum is 100 mol % or less. Here, the molar ratio means the ratio of the number of moles of each monomer to the total number of moles of the monomers constituting the copolymer. The molar ratio of each monomer in the copolymer can be measured, for example, by dissolving the copolymer in heavy water. 1 It is calculated from the signal area ratio of 1 H NMR.

[0070] The molecular weight of the copolymer contained in the coating layer is preferably 2,000 to 1,500,000, more preferably 5,000 to 1,200,000, and even more preferably 10,000 to 1,000,000. In this specification, the molecular weight is the weight average molecular weight in terms of polyethylene glycol or polyethylene oxide measured by gel permeation chromatography (aqueous solvent).

[0071] In the composite semipermeable membrane according to this embodiment, a chemical bond is preferably formed between the copolymer contained in the coating layer and the polyamide in the separation functional layer. By forming a chemical bond between the coating layer and the polyamide in the separation functional layer, the coating layer is more stably fixed to the separation functional layer. The chemical bond between the copolymer and the polyamide is preferably a covalent bond, more preferably an amide bond. For example, an amide bond can be formed by condensing a carboxy group derived from the second monomer of the copolymer with a terminal amine of the polyamide in the separation functional layer.

[0072] A copolymer containing a first monomer, a second monomer, and a third monomer can be synthesized, for example, by a general radical polymerization reaction. The molar ratio of the first monomer, the second monomer, and the third monomer can be controlled by changing conditions such as the monomer ratio during the polymerization reaction.

[0073] The separating functional layer of the composite semipermeable membrane according to this embodiment preferably has a pleated structure having a plurality of convex portions, from the viewpoint of improving the amount of permeated water.

[0074] (2) Manufacturing of composite semipermeable membranes As one embodiment of the present invention, a method for producing a support membrane having a porous support layer formed on a substrate and a composite semipermeable membrane having a polyamide separating function layer and a coating layer on the support membrane will be described below.

[0075] (2-1) Support membrane formation process The support film forming step includes a step of applying a polymer solution to a substrate and a step of immersing the substrate, to which the polymer solution has been applied, in a coagulation liquid to coagulate the polymer.

[0076] In the step of applying the polymer solution to the substrate, the polymer solution is prepared by dissolving the polymer, which is a component of the porous support layer, in a good solvent for the polymer.

[0077] When polysulfone is used as the polymer, the temperature of the polymer solution during application is preferably 10°C or higher and 60°C or lower. When the temperature of the polymer solution is within the above range, the polymer does not precipitate, and the polymer solution is sufficiently impregnated into the spaces between the fibers of the substrate before solidifying. As a result, the porous support layer is firmly bonded to the substrate due to the anchoring effect, and a good support membrane can be obtained. The preferred temperature range of the polymer solution can be adjusted as appropriate depending on the type of polymer used, the desired solution viscosity, and other factors.

[0078] After the polymer solution is applied to the substrate, the time until the substrate is immersed in the coagulation liquid is preferably 0.1 seconds or more and 5 seconds or less. If the time until the substrate is immersed in the coagulation liquid is within the above range, the polymer solution will be sufficiently impregnated into the spaces between the fibers of the substrate and then solidified. The preferred range of the time until the substrate is immersed in the coagulation liquid can be appropriately adjusted depending on the type of polymer solution used, the desired solution viscosity, etc.

[0079] Water is usually used as the coagulation liquid, but any liquid that does not dissolve the polymers that are components of the porous support layer will suffice. The morphology of the resulting porous support layer and the resulting composite semipermeable membrane will vary depending on the composition of the coagulation liquid. The temperature of the coagulation liquid is preferably between -20°C and 100°C, and more preferably between 10°C and 50°C. When the temperature of the coagulation liquid is within the above range, the vibration of the coagulation bath surface due to thermal motion is not severe, and the smoothness of the support membrane surface after the porous support layer is formed is maintained. Furthermore, when the temperature of the coagulation bath is within the above range, the coagulation rate is appropriate and membrane formability is good.

[0080] Next, the support membrane thus obtained is washed with hot water to remove any remaining solvent in the membrane. The temperature of the hot water used for hot water washing is preferably 40°C to 100°C, more preferably 60°C to 95°C. When the hot water temperature is within the above range, the shrinkage of the support membrane is not large, the amount of permeated water is good, and a sufficient washing effect is obtained.

[0081] (2-2) Separation functional layer formation process The polyamide separating functional layer is formed by carrying out interfacial polycondensation on the surface of the porous support layer of the support membrane using an aqueous solution containing a polyfunctional amine and an organic solvent solution containing a polyfunctional acid halide.

[0082] The organic solvent for dissolving the polyfunctional acid halide is not particularly limited as long as it is immiscible with water, does not destroy the support film, and does not inhibit the polyamide production reaction. Examples of organic solvents for dissolving the polyfunctional acid halide include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. Among these, considering that they do not destroy the ozone layer, are readily available, easy to handle, and safe to handle, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, and the like, alone or in combination, are preferred.

[0083] The polyfunctional amine aqueous solution or the organic solvent solution containing the polyfunctional acid halide may contain compounds such as an acylation catalyst, a polar solvent, an acid scavenger, a surfactant, and an antioxidant, as needed, as long as they do not inhibit the reaction between the two components.

[0084] To carry out interfacial polycondensation on the support membrane, the surface of the porous support layer of the support membrane is first coated with an aqueous polyfunctional amine solution, the concentration of which is preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass.

[0085] The method for coating the surface of the porous support layer with the aqueous polyfunctional amine solution can be any method that uniformly and continuously coats the surface of the porous support layer with the aqueous solution, and can be carried out by known coating methods such as coating the surface of the porous support layer with the aqueous solution or immersing the support membrane in the aqueous solution. The contact time between the porous support layer and the aqueous polyfunctional amine solution is preferably 5 seconds to 10 minutes, more preferably 10 seconds to 3 minutes. Next, it is preferable to remove the excess aqueous solution by a draining process. Examples of draining methods include holding the membrane surface vertically and allowing it to flow naturally. After draining, the membrane surface may be dried to remove all or part of the water content of the aqueous solution.

[0086] Then, an organic solvent solution containing a polyfunctional acid halide is applied to the porous support layer coated with the polyfunctional amine aqueous solution to form a polyamide separation layer by interfacial polycondensation. The time for carrying out the interfacial polycondensation is preferably 0.1 seconds to 3 minutes, more preferably 0.1 seconds to 1 minute. The concentration of the polyfunctional acid halide in the organic solvent solution is preferably 0.01% by mass to 1.0% by mass, from the viewpoint of sufficient polyamide formation and cost.

[0087] Next, the organic solvent solution after the reaction is preferably removed by a draining step. For example, the organic solvent can be removed by holding the membrane vertically and allowing the excess organic solvent to flow down naturally. In this case, the vertical holding time is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. Holding the membrane for 1 minute or more makes it easier to obtain a polyamide having the desired functionality, while holding the membrane for 3 minutes or less can prevent defects caused by over-drying the organic solvent and suppress performance degradation.

[0088] Furthermore, it is preferable that the process for forming the separation functional layer further includes step (a) washing the obtained polyamide separation functional layer, step (b) contacting the separation functional layer with a reagent that reacts with the primary amino group to produce a diazonium salt or a derivative thereof, and step (c) contacting the separation functional layer with a reagent that reacts with the diazonium salt or a derivative thereof.

[0089] By carrying out step (c), the functional group of the polyamide can be converted or a new functional group can be introduced.

[0090] In step (a), the polyamide separating functional layer obtained by the above-mentioned method is washed with hot water. From the viewpoint of further improving the solute blocking performance and permeate volume of the composite semipermeable membrane, the hot water temperature is preferably 25°C or higher and 90°C or lower, and the washing time is preferably 1 minute or higher and 60 minutes or lower. From the viewpoint of preventing a decrease in chemical resistance due to rapid cooling after hot water washing, the hot water temperature is more preferably 25°C or higher and 60°C or lower. When using hot water of 61°C or higher and 90°C or lower, it is preferable to cool the layer slowly after hot water washing. For example, a method of cooling the layer to room temperature by contacting the layer with hot water of gradually lower temperatures can be used.

[0091] The hot water used for hot water washing may contain an acid or an alcohol. The inclusion of an acid or an alcohol makes it easier to control the formation of hydrogen bonds in the polyamide. Examples of acids include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as citric acid and oxalic acid. When an acid is added, the pH of the hot water is preferably 2 or less, more preferably 1 or less. Examples of alcohols include monohydric alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and polyhydric alcohols such as ethylene glycol and glycerin. The concentration of alcohol in the hot water is preferably 10% by mass or more and 100% by mass or less, more preferably 10% by mass or more and 50% by mass or less.

[0092] In step (b), the washed polyamide separating functional layer is contacted with a reagent that reacts with primary amino groups to produce a diazonium salt or its derivative, thereby converting the functional groups. Examples of reagents that react with primary amino groups to produce a diazonium salt or its derivative include aqueous solutions of nitrous acid and its salts, nitrosyl compounds, etc. Because aqueous solutions of nitrous acid and nitrosyl compounds decompose by generating gas, it is preferable to sequentially generate nitrous acid by reacting nitrite with an acidic solution. Generally, nitrite reacts with hydrogen ions to produce nitrous acid (HNO), which is efficiently generated when the aqueous solution has a pH of 7 or less, preferably 5 or less, and more preferably 4 or less. Among these, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferred for its ease of handling.

[0093] The concentration of nitrous acid or nitrite salt in the aqueous solution that reacts with a primary amino group to produce a diazonium salt or its derivative is preferably 0.01% by mass or more and 1% by mass or less, and more preferably 0.05% by mass or more and 0.5% by mass or less. When the concentration of nitrous acid in the aqueous solution is 0.01% by mass or more, a sufficient effect can be obtained, and when it is 1% by mass or less, the solution is easy to handle.

[0094] The temperature of the aqueous nitrous acid solution is preferably 15° C. or higher and 45° C. or lower. If the temperature is 15° C. or higher, a sufficient reaction time is obtained, and if the temperature is 45° C. or lower, decomposition of nitrous acid is unlikely to occur, making handling easy.

[0095] The contact time between the separation functional layer and the aqueous nitrous acid solution may be sufficient as long as it is long enough to produce at least one of a diazonium salt and its derivatives; the higher the concentration, the shorter the treatment time. Therefore, when using a solution of the above concentration, the contact time between the separation functional layer and the aqueous nitrous acid solution is preferably within 10 minutes, more preferably within 3 minutes. The contact method is not particularly limited; a solution of the reagent may be applied, or the composite semipermeable membrane may be immersed in a solution containing the reagent. Any solvent may be used to dissolve the reagent, as long as it dissolves the reagent and does not erode the composite semipermeable membrane. The solution may also contain surfactants, acidic compounds, alkaline compounds, etc., as long as they do not inhibit the reaction between the primary amino group and the reagent.

[0096] In step (c), a portion of the diazonium salt or its derivative produced in step (b) is converted to a different functional group. A portion of the diazonium salt or its derivative is converted to a phenolic hydroxyl group, for example, by reaction with water. Furthermore, contact with a solution containing chloride ions, bromide ions, cyanide ions, iodide ions, fluoroboric acid, hypophosphorous acid, sodium bisulfite, sulfite ions, aromatic amines, hydrogen sulfide, thiocyanic acid, or the like results in conversion to the corresponding functional group. Furthermore, contact with an aromatic amine causes a diazo coupling reaction, enabling the introduction of aromatic groups onto the membrane surface. These reagents may be used singly or in combination, or may be contacted multiple times with different reagents.

[0097] Examples of reagents that undergo diazo coupling reactions include compounds having electron-rich aromatic or heteroaromatic rings. Examples of compounds having electron-rich aromatic or heteroaromatic rings include unsubstituted heteroaromatic ring compounds, aromatic compounds having electron-donating substituents, and heteroaromatic ring compounds having electron-donating substituents. Examples of electron-donating substituents include amino groups, ether groups, thioether groups, alkyl groups, alkenyl groups, alkynyl groups, and aryl groups. Specific examples of the compound include aniline, methoxyaniline bonded to a benzene ring at the ortho, meta, or para positions, phenylenediamine in which two amino groups are bonded to a benzene ring at the ortho, meta, or para positions, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine, sulfanilic acid, 3,3′-dihydroxybenzidine, 1-aminonaphthalene, 2-aminonaphthalene, and N-alkylated products of these compounds.

[0098] Among these reagents, phenylenediamine and triaminobenzene, which have amino groups, are particularly preferred. This is because the amino groups necessary for bonding the separation functional layer to the coating layer in the coating layer formation process described below can be introduced into the separation functional layer through a diazo coupling reaction. The concentration and time when the separation functional layer is contacted with the reagent that reacts with these diazonium salts or their derivatives can be adjusted appropriately to achieve the desired effect. The temperature at which the separation functional layer is contacted with the reagent is preferably 10°C or higher and 90°C or lower. At a temperature of 10°C or higher, the diazo coupling reaction proceeds, suppressing the generation of phenolic hydroxyl groups due to side reactions with water. Furthermore, at a temperature of 90°C or lower, shrinkage of the separation functional layer is suppressed, thereby suppressing a decrease in the amount of permeated water.

[0099] (2-3) Coating layer formation process Finally, a coating layer containing a copolymer comprising the first monomer, the second monomer, and a hydrophilic third monomer is formed on the separation functional layer. The coating layer can be formed by any method that brings the copolymer into contact with the surface of the polyamide separation functional layer. Suitable methods include contacting the surface of the polyamide separation functional layer with an aqueous solution containing the copolymer, immersing the entire composite semipermeable membrane in an aqueous solution containing the copolymer, and spraying the composite semipermeable membrane surface with an aqueous solution containing the copolymer. Amide bonds are formed by a condensation reaction between the functional groups on the surface of the polyamide separation functional layer and the functional groups contained in the copolymer, forming a coating layer containing the copolymer on the separation functional layer.

[0100] The aqueous solution containing the copolymer that is brought into contact with the surface of the polyamide separating functional layer may contain other components within the range that does not impair the effects of the present invention.

[0101] The concentration of the copolymer-containing aqueous solution is preferably 0.001% by mass or more and 1% by mass or less. When the copolymer concentration is 0.001% by mass or more, the copolymer can be sufficiently reacted with the functional groups present in the polyamide. On the other hand, when the copolymer concentration is 1% by mass or less, the coating layer does not become too thick, and a decrease in the amount of permeated water can be suppressed.

[0102] Other compounds can also be mixed into the copolymer-containing aqueous solution as needed. For example, alkaline metal compounds such as sodium carbonate, sodium hydroxide, and sodium phosphate, or condensing agents, can be added to promote the reaction between the polyamide surface and the copolymer. It is also preferable to add surfactants such as sodium dodecyl sulfate and sodium benzenesulfonate to remove water-immiscible organic solvents, monomers such as polyfunctional acid halides and polyfunctional amine compounds, and oligomers produced by the reaction of these monomers remaining in the polyamide separation functional layer.

[0103] The term "condensing agent" refers to a compound that activates a carboxy group in water. Examples of condensing agents include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 1,3-bis(2,2-dimethyl-1,3-dioxolan-4-ylmethyl)carbodiimide, and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (hereinafter referred to as "DMT-MM"). Among these, DMT-MM is particularly preferred from the viewpoints of stability during the condensation reaction and low toxicity of by-products after the condensation reaction.

[0104] The concentration of the condensing agent in the aqueous solution containing the copolymer is not particularly limited as long as it is higher than the concentration of the carboxyl groups to be activated, and sufficient effect can be obtained in condensing with the reactive groups.

[0105] The pH of the aqueous solution containing the copolymer is preferably 2 or more and 6 or less. When the pH is 2 or more, the condensation reaction can proceed without deteriorating the composite semipermeable membrane. In addition, when the pH is 6 or less, ionization of the carboxyl group can be prevented, which prevents repulsion between the polyamide and the copolymer due to electrostatic interaction, and the condensation reaction can proceed more efficiently, which is preferable.

[0106] (3) Use of composite semipermeable membranes The composite semipermeable membrane according to this embodiment is preferably used as a spiral composite semipermeable membrane element, wound around a cylindrical water collection pipe with numerous holes, together with a raw water flow path material such as a plastic net, a permeate water flow path material such as tricot, and, if necessary, a film for increasing pressure resistance. Furthermore, such elements can be connected in series or parallel and housed in a pressure vessel to form a composite semipermeable membrane module. Furthermore, the above-described composite semipermeable membrane, its element, and module can be combined with a pump for supplying raw water to them and a device for pretreating the raw water to form a fluid separation device. By using this separation device, raw water can be separated into permeate, such as drinking water, and concentrated water that has not permeated the membrane, thereby obtaining water suitable for the intended purpose.

[0107] By using the composite semipermeable membrane according to this embodiment, for example, in a low pressure range where the operating pressure is 0.1 MPa or more and 6 MPa or less, more preferably 0.1 MPa or more and 1.55 MPa or less, high water permeation amount can be maintained while separating solutes. Since the operating pressure can be lowered, the capacity of pumps and the like to be used can be reduced, power consumption can be suppressed, and the cost of water production can be reduced. When the operating pressure is less than 0.1 MPa, the water permeation amount tends to decrease, and when it exceeds 6 MPa, the power consumption of pumps and the like increases, and membrane fouling is likely to occur.

Example

[0108] The present invention will be described in more detail by way of examples below, but the present invention is not limited to these examples in any way.

[0109] <NaCl removal rate> An aqueous solution with a temperature of 25 °C, a pH of 7, and a sodium chloride concentration of 2,000 mg / L was supplied as feed water to the composite semipermeable membrane at an operating pressure of 1.55 MPa, and membrane filtration treatment was performed for 2 hours by a cross-flow filtration method. The electrical conductivity of the feed water and the permeated water collected after 2 hours was measured with a conductivity meter (WM-50EG) manufactured by Toa Denpa Kogyo Co., Ltd., and the practical salinity, that is, the NaCl concentration, was calculated respectively. Based on the following formula from the obtained NaCl concentration, the NaCl removal rate was calculated. NaCl removal rate (%) = 100 × {1 - (NaCl concentration in permeated water / NaCl concentration in feed water)}.

[0110] <Water permeation amount> In the membrane filtration treatment described in the above-mentioned "NaCl removal rate", the water permeation amount after 2 hours was measured and converted to the water permeation amount (cubic meters) per square meter of the membrane surface per day (m 3 / m 2 / day).

[0111] <Acid / alkali degradation test> The composite semipermeable membrane was immersed in a sodium hydroxide aqueous solution of pH 12.4 at a constant temperature of 30°C for 24 hours, and then immersed in water for 5 minutes. Subsequently, the composite semipermeable membrane was immersed in dilute sulfuric acid of pH 2.0 at a constant temperature of 30°C for 1 hour, and then immersed in water for 5 minutes. The above constituted one cycle, and this was repeated three times. The NaCl rejection rate of the obtained composite semipermeable membrane was measured by the method described above in "NaCl rejection rate."

[0112] <Combined Degradation Test> The composite semipermeable membrane after the acid-alkali deterioration test was immersed in a 5 ppm sodium hypochlorite aqueous solution of pH 7 at a constant temperature of 25°C for 96 hours. The sodium hypochlorite aqueous solution was replaced with a new one every 24 hours. After 96 hours, the composite semipermeable membrane was immersed in a 0.1 mass % sodium hydrogen sulfite aqueous solution for 10 minutes. The acid-alkali deterioration test was carried out again on the obtained composite semipermeable membrane. The NaCl rejection rate of the obtained composite semipermeable membrane was measured by the method described above in "NaCl rejection rate".

[0113] <Fouling resistance> The permeate volume calculated in the above "permeate volume" was designated as the initial permeate volume (F1). Next, an aqueous solution containing polyoxyethylene (10) octylphenyl ether at a concentration of 150 mg / L, pH 7, and 2,000 mg / L of sodium chloride, was used as feed water. The aqueous solution was fed at an operating pressure of 1.55 MPa. After 2 hours of membrane filtration using a cross-flow filtration system, the permeate volume was designated as F2, and the value of F2 / F1 was calculated. Furthermore, RO water was fed at an operating pressure of 1.55 MPa as feed water. After 30 minutes of membrane filtration using a cross-flow filtration system, an aqueous solution containing 2,000 mg / L of NaCl at a temperature of 25 °C, pH 7, was used as feed water. The permeate volume after 2 hours of membrane filtration using a cross-flow filtration system at an operating pressure of 1.55 MPa was designated as F3, and the value of F3 / F1 was calculated.

[0114] <Breathability> Air permeability was measured using a Frazier tester in accordance with JISL1096 (2010). The substrate was cut into a piece measuring 200 mm x 200 mm and attached to the Frazier tester. The intake fan and air holes were adjusted so that the inclined barometer read 125 Pa, and the air permeability was calculated from the pressure indicated by the vertical barometer and the type of air hole used. The Frazier tester used was the KES-F8-AP1 manufactured by Kato Tech Co., Ltd.

[0115] <Molecular weight measurement> The weight average molecular weight of the copolymer was measured under the following conditions. Equipment: Shimadzu Prominence GPC system Pump: LC-20AD Autosampler: SIL-20AHT Column oven: CTO-20A RI detector: RID-10A Column: Tosoh GMPWXL (inner diameter 7.8 mm x 30 cm, particle size 13 μm) Solvent: Water / methanol = 1 / 1 (0.1N lithium nitrate added) Flow rate: 0.5mL / min Measurement time: 30 minutes Sample concentration: 0.1 to 0.3% by mass Sample injection volume: 100 μL Standard sample: Polyethylene oxide standard sample (0.1 kD to 1258 kD) manufactured by Agilent.

[0116] <Synthesis of copolymer> [Synthesis Example 1] 36.5 g of purified water, 36.5 g of t-butanol, 7.92 g of dimethylacrylamide, and 1.44 g of acrylic acid were weighed into a flask and thoroughly stirred with a stirring blade. The flask was equipped with a condenser and the atmosphere inside the flask was replaced with nitrogen three times while stirring. 20 g of purified water containing 0.088 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was slowly added dropwise using a syringe while stirring. The mixture was heated to reflux in a 90°C oil bath for 2 hours, and then cooled to obtain a dimethylacrylamide / acrylic acid copolymer. The resulting copolymer had a weight-average molecular weight of 800,000 and a molar ratio of 80% / 20%.

[0117] [Synthesis Example 2] A dimethylacrylamide / acrylic acid / 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid copolymer was obtained in the same manner as in Synthesis Example 1, except that 36.5 g of purified water, 36.5 g of t-butanol, 7.92 g of dimethylacrylamide, 0.72 g of acrylic acid, and 2.79 g of 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid were used. The weight-average molecular weight of the obtained copolymer was 500,000, and the molar ratio was 80% / 20% / 10%.

[0118] [Synthesis Example 3] A dimethylacrylamide / acrylic acid / N-vinylpyrrolidone copolymer was obtained in the same manner as in Synthesis Example 1, except that 36.5 g of purified water, 36.5 g of t-butanol, 7.92 g of dimethylacrylamide, 0.72 g of acrylic acid, and 1.11 g of N-vinylpyrrolidone were used. The weight-average molecular weight of the obtained copolymer was 500,000, and the molar ratio was 80% / 20% / 10%.

[0119] <Preparation of composite semipermeable membrane> [Comparative Example 1] Polyester nonwoven fabric made of long fibers (breathability 2.0cc / cm 2A 15.0 mass% DMF solution of polysulfone was cast onto the substrate at 25°C, and immediately immersed in pure water and left for 5 minutes to produce a support membrane with a porous support layer thickness of 40 μm. Next, this support membrane was immersed in a 3.5 mass% m-PDA aqueous solution, after which excess aqueous solution was removed. An n-decane solution containing 0.14 mass% TMC was then applied so that the surface of the porous support layer was completely wet. Next, to remove excess solution from the membrane, the membrane was vertically drained, dried by blowing air at 25°C using a fan, and then washed with pure water at 40°C. Next, this composite semipermeable membrane was immersed for 1 minute in a 0.3 mass% sodium nitrite aqueous solution adjusted to pH 3 and 35°C. The pH of the sodium nitrite was adjusted with sulfuric acid. Next, the composite semipermeable membrane of Comparative Example 1 was obtained by washing with pure water at 20°C.

[0120] Comparative Example 2 The composite semipermeable membrane obtained in Comparative Example 1 was contacted with an aqueous solution containing 0.02 mass% of the dimethylacrylamide / acrylic acid copolymer obtained in Synthesis Example 1 and 0.1 mass% DMT-MM at 25°C for 1 minute, and then washed at 70°C. Next, this composite semipermeable membrane was immersed for 1 minute in a 0.3 mass% aqueous sodium nitrite solution adjusted to pH 3 and 35°C. The pH of the sodium nitrite was adjusted with sulfuric acid. Next, by washing with pure water at 20°C, a composite semipermeable membrane of Comparative Example 2 was obtained.

[0121] [Example 1] The composite semipermeable membrane of Example 1 was obtained in the same manner as in Comparative Example 2, except that the dimethylacrylamide / acrylic acid / 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid copolymer obtained in Synthesis Example 2 was used instead of the dimethylacrylamide / acrylic acid copolymer.

[0122] [Example 2] A composite semipermeable membrane of Example 2 was obtained in the same manner as in Comparative Example 2, except that the dimethylacrylamide / acrylic acid / N-vinylpyrrolidone copolymer obtained in Synthesis Example 3 was used instead of the dimethylacrylamide / acrylic acid copolymer.

[0123] The performance evaluation results of each composite semipermeable membrane obtained are shown in Table 1.

[0124] [Table 1]

[0125] As described above, it is clear that the composite semipermeable membrane according to this embodiment has both fouling resistance and high salt rejection properties, and also has acid and alkali resistance. [Industrial Applicability]

[0126] The composite semipermeable membrane of the present invention can separate raw water into permeated water such as drinking water and concentrated water that has not permeated the membrane, thereby obtaining water suitable for the intended purpose, and can be particularly suitably used for desalinating brine or seawater.

Claims

1. A composite semipermeable membrane comprising: a porous support layer; a separation functional layer containing a polyamide provided on one side of the porous support layer; and a coating layer provided on the separation functional layer, wherein the coating layer contains a copolymer including a first monomer represented by the following general formula (I), a second monomer represented by the following general formula (II), and a hydrophilic third monomer: 【Chemistry 1】 【Chemistry 2】 [In general formula (I), R １ is a hydrogen atom or a methyl group, R ２ , R ３ is an optionally substituted aliphatic chain having 1 to 6 carbon atoms, and R ２ and R ３ may be bonded directly or indirectly to form a ring structure. ４ is a hydrogen atom or a methyl group.

2. 2. The composite semipermeable membrane according to claim 1, wherein X, Y, and Z satisfy the following formulas (1) to (4), where X is the molar ratio of the first monomer in the copolymer, Y is the molar ratio of the second monomer, and Z is the molar ratio of the third monomer: 50≦X≦90...Formula (1) 5≦Y≦20...Formula (2) 5≦Z≦40...Formula (3) X+Y+Z≦100 Equation (4)

3. 3. The composite semipermeable membrane according to claim 1, wherein the third monomer is a zwitterionic monomer or a monomer containing a vinyl group and a tertiary amide group in a side chain.

4. The composite semipermeable membrane according to claim 3 , wherein the third monomer is a zwitterionic monomer.

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

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