Composite semipermeable membrane and method for producing the same

Abstract

To provide a composite semipermeable membrane excellent in permeability retention of raw water containing various contaminants during operation.SOLUTION: In a composite semipermeable membrane having a separation function layer positioned on a porous support layer: the separation function layer has a thin film where a cross-linked polyamide is a main component and includes two or more kinds of hydrophilic polymers being a polymer of a monomer having an ethylenic unsaturated group; functional group density Dw having a positive charge and functional group density Db having a negative charge from the surface of the separation function layer to 200 nm are satisfied with (a)-(c) (where, (a) Dw>0.30×10-9 mol / cm2; (b) Db>0.30×10-9 mol / cm2; and (c) 0.9<Dw / Db<1.1); and a zeta potential of the surface of the separation function layer at pH7 and NaCl 10 mM is -10 mV or more and 10 mV or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composite semipermeable membrane useful for the selective separation of liquid mixtures. The composite semipermeable membrane obtained by the present invention can be suitably used, for example, for the desalination of seawater or brackish water.

Background Art

[0002] Regarding the separation of mixtures, there are various techniques for removing substances (such as salts) dissolved in a solvent (such as water). In recent years, the use of membrane separation methods has been expanding as an energy-saving and resource-saving process.

[0003] The membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, and the like. These membranes are used, for example, to obtain drinking water from seawater, brackish water, water containing harmful substances, etc., or for the production of industrial ultrapure water, wastewater treatment, recovery of valuable substances, and the like.

[0004] Most of the currently commercially available reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes, and there are two types: those having an active layer in which a gel layer and a polymer are crosslinked on a microporous support membrane, and those having an active layer in which a monomer is polycondensed on a microporous support membrane.

[0005] Among them, a composite semipermeable membrane (Patent Document 1) obtained by coating a porous support membrane with a separation functional layer made of a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide is widely used as a separation membrane with high water permeability and removability.

[0006] On the other hand, these membranes have a problem that foulant components in the raw water adhere to the membrane surface by continuously permeating the raw water, reducing the permeate water volume and the selective separation performance.

[0007] As a membrane with improved fouling resistance (anti-fouling property) of the composite semipermeable membrane, a method (Patent Document 2) of introducing a hydrophilic polymer containing an acidic group onto the surface of the separation functional layer by an amide bond is disclosed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, when filtering raw water with an extremely high turbidity concentration or raw water containing various contaminants using these membranes, there is a problem that the hydration amount of the hydrophilic polymer tends to decrease, resulting in a decrease in fouling resistance.

Means for Solving the Problems

[0010] The present invention for solving the above problems includes the following configurations 1 to 7. 1. A composite semipermeable membrane comprising a separation functional layer located on a porous support layer, wherein the separation functional layer has a thin film mainly composed of crosslinked polyamide, the separation functional layer contains two or more hydrophilic polymers that are polymers of monomers having ethylenically unsaturated groups, a composite semipermeable membrane in which the positive charge functional group density Dw and the negative charge functional group density Db from the surface of the separation functional layer to 200 nm satisfy the following (a) to (c), and the zeta potential at pH 7 and 10 mM NaCl on the surface of the separation functional layer is -10 mV or more and 10 mV or less. (a) Dw > 0.30×10 -9 mol / cm 2 (b) Db > 0.30×10 -9 mol / cm 2 (c) 0.9 < Dw / Db < 1.1 2. The composite semipermeable membrane according to 1 above, wherein the hydrophilic polymer comprises a total of two or more kinds, including one or more kinds of hydrophilic polymers having a positively charged functional group and one or more kinds of hydrophilic polymers having a negatively charged functional group. 3. The composite semipermeable membrane according to 1 or 2 above, wherein the zeta potential at pH 3 and 10 mM NaCl on the surface of the separation functional layer is 30 mV or more. 4. The composite semipermeable membrane according to any one of 1 to 3 above, wherein the zeta potential at pH 11 and 10 mM NaCl on the surface of the separation functional layer is -30 mV or less. 5. The composite semipermeable membrane according to any one of 1 to 4 above, wherein the positively charged functional group contains an amino group and the negatively charged functional group contains a carboxyl group. 6. A method for producing a composite semipermeable membrane comprising a separation functional layer provided on a porous support layer, a step of forming a layer containing crosslinked polyamide by interfacial polymerization on the porous support layer; a step of bonding the layer containing crosslinked polyamide and a hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group; a step of bonding a nanoparticle body mainly composed of a hydrophilic polymer B which is a polymer of a monomer having a type of ethylenically unsaturated group different from that of the hydrophilic polymer A to the hydrophilic polymer A; A method for producing a composite semipermeable membrane, comprising the above steps. 7. The method for producing a composite semipermeable membrane according to 6 above, wherein the hydrophilic polymer A and the hydrophilic polymer B have mutually opposite charged groups.

Advantages of the Invention

[0011] In the composite semipermeable membrane of the present invention, since the density of the positively charged functional groups and the density of the negatively charged functional groups on the separation functional layer are appropriately controlled, for example, it can exhibit excellent fouling resistance against various foulants such as nonionic, anionic, and cationic foulants.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0013] (1) Composite semipermeable membrane The composite semipermeable membrane described below includes a porous support layer and a separation functional layer located on the porous support layer.

[0014] (1-1) Separation functional layer (1-1-1) Composition In the composite semipermeable membrane according to the embodiment of the present invention, it is the separation functional layer that substantially has separation performance for ions and the like.

[0015] The separation functional layer in the embodiment of the present invention contains a thin film mainly composed of crosslinked polyamide. The main component refers to a component that occupies 50% by weight or more among the components of the separation functional layer. By containing 50% by weight or more of crosslinked polyamide, the separation functional layer can exhibit high removal performance. Further, the content of crosslinked polyamide in the separation functional layer is preferably 80% by weight or more, and more preferably 90% by weight or more.

[0016] The crosslinked polyamide constituting the separation functional layer can be formed, for example, by an interfacial polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide. Here, it is preferable that at least one of the polyfunctional amine or the polyfunctional acid halide contains a compound having three or more functional groups.

[0017] The thickness of the separation functional layer is, for example, in the range of 0.01 to 1 μm, preferably in the range of 0.1 to 0.5 μm in order to obtain sufficient separation performance and water permeation amount. The thickness of the separation functional layer can be measured by photographing a cross-section of the fold structure with a transmission electron microscope (TEM) and reading the cross-sectional photograph into image analysis software for analysis. Specifically, five convex portions of the separation functional layer are selected, and for each convex portion, the thickness of the convex portion of the separation functional layer at 10 points is measured from the upper part of the convex portion height to 90% of the range, and the arithmetic mean value of 50 points can be obtained for measurement.

[0018] Here, the convex portion of the separation functional layer refers to a convex portion having a height of 1 / 5 or more of the 10-point average surface roughness. The 10-point average surface roughness is a value obtained by the following calculation method. First, a cross-section in the direction perpendicular to the film surface is observed with an electron microscope. The observation magnification is preferably 10,000 to 100,000 times. In the obtained cross-sectional image, as shown in FIG. 1, the surface of the separation functional layer 1 appears as a curve of a pleated structure in which convex portions and concave portions are continuously repeated. For this curve, a roughness curve defined based on ISO4287:1997 is obtained. A cross-sectional image is extracted with a width of 2.0 μm in the direction of the average line X of the roughness curve. Note that the average line is a straight line defined based on ISO4287:1997, and is a straight line drawn so that the total area of the region surrounded by the average line and the roughness curve is equal above and below the average line in the measurement length.

[0019] Here, the polyfunctional amine refers to an amine having at least two primary amino groups and / or secondary amino groups in one molecule, and at least one of the amino groups is a primary amino group. Examples of the polyfunctional amine include polyfunctional aromatic amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine, etc. in which two amino groups are bonded to a benzene ring in any of the ortho, meta, and para positional relationships, aliphatic amines such as ethylenediamine and propylenediamine, and alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, 4-aminoethylpiperazine, etc.

[0020] Among them, considering the selective separation property, permeability, and heat resistance of the membrane, the polyfunctional amine is preferably a polyfunctional aromatic amine having 2 to 4 primary amino groups and / or secondary amino groups in one molecule. As such a polyfunctional aromatic amine, for example, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, etc. are preferably used. Among them, from the viewpoint of easy availability or ease of handling, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA).

[0021] These polyfunctional amines may be used alone or two or more of them may be used simultaneously. When two or more of them are used simultaneously, the above amines may be combined with each other, or the above amine may be combined with an amine having at least two secondary amino groups in one molecule. Examples of the amine having at least two secondary amino groups in one molecule include piperazine, 1,3-bispiperidylpropane, etc.

[0022] The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule. For example, as a trifunctional acid halide, for example, trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, etc. can be mentioned.

[0023] Examples of the bifunctional acid halide include aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalenedicarboxylic acid chloride, aliphatic bifunctional acid halides such as adipoyl chloride, sebacoyl chloride, and alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, tetrahydrofuran dicarboxylic acid dichloride, etc.

[0024] Considering the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride. Further, considering the selective separability and heat resistance of the membrane, it is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Among them, from the viewpoint of easy availability or ease of handling, it is even more preferable to use trimesic acid chloride. These polyfunctional acid halides may be used alone or two or more of them may be used simultaneously.

[0025] In these separation functional layers, by bonding a hydrophilic polymer, which is a polymer of a monomer having an ethylenically unsaturated group, to a thin film mainly composed of a crosslinked polyamide, the amount of hydration water in water of the separation functional layer can be increased. Thereby, it is known that it is possible to suppress a decrease in water permeability due to the adhesion of contaminants (foulants) in raw water to the separation functional layer (fouling), that is, to improve fouling resistance. Here, the fouling resistance may include either suppressing fouling or suppressing a small decrease in performance even if fouling occurs.

[0026] As a result of intensive studies, the present inventors have found that when the separation functional layer contains two or more hydrophilic polymers, which are polymers of monomers having ethylenically unsaturated groups, and the positive charge functional group density Dw and the negative charge functional group density Db from the surface of the separation functional layer up to 200 nm satisfy the following (a) to (c), and the zeta potential at pH 7 and 10 mM NaCl on the surface of the separation functional layer is -10 mV or more and 10 mV or less, excellent fouling resistance can be imparted to various types of foulants. (a) Dw > 0.30×10 -9 mol / cm 2 (b) Db > 0.30×10 -9 mol / cm 2 (c) 0.9 < Dw / Db < 1.1

[0027] When the above positive charge functional group density Dw (hereinafter, also referred to as positive charge group density) is 0.30×10 -9 mol / cm2 By being larger, it indicates that the separation functional layer contains a hydrophilic polymer having a positively charged functional group (hereinafter also referred to as a positively charged group) capable of retaining a sufficient amount of hydration water for imparting stable fouling resistance, and the above negative charge functional group density Db (hereinafter also referred to as the negative charge group density) is 0.30×10 -9 mol / cm 2 By being larger, it indicates that the separation functional layer contains a hydrophilic polymer having a negatively charged functional group (hereinafter also referred to as a negatively charged group) capable of retaining a sufficient amount of hydration water for imparting stable fouling resistance.

[0028] And, by the ratio of the densities of these opposite charge groups being greater than 0.9 and less than 1.1, it is possible to effectively exhibit fouling resistance against foulants in various ionic states. And the inventors have clarified that the zeta potential at pH 7 and 10 mM NaCl on the surface of the separation functional layer at that time is -10 mV or more and 10 mV or less.

[0029] The hydrophilic polymer that is a polymer of the monomer having the ethylenically unsaturated group preferably contains two or more kinds in total, including one or more kinds of a hydrophilic polymer having a positively charged group and a hydrophilic polymer having a negatively charged group respectively.

[0030] Examples of the hydrophilic polymer having a positively charged group include polyethyleneimine, polyallylamine, polyvinylamine, polyamidoamine dendrimer, polyamino acid, polydialkylaminoalkyl (meth) acrylate, polydialkylaminoalkyl (meth) acrylamide, polydiallylalkylamine, polydiallylamine and chitosan, and salts thereof. Among these, particularly from the viewpoints of versatility and ease of synthesis, polyethyleneimine, polyallylamine, polyvinylamine, polydialkylaminoalkyl (meth) acrylate, polydialkylaminoalkyl (meth) acrylamide, polydiallylalkylamine, polydiallylamine and chitosan, and salts thereof are preferable.

[0031] Examples of the hydrophilic polymer having a negatively charged group include hydrophilic polymers composed of monomers having a negatively charged group. Examples of the negatively charged group include a carboxy group, a phosphonic acid group, a sulfonic acid group, etc. Examples of the monomer having a carboxy group include the following. Maleic acid, maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, 2-(hydroxymethyl)acrylic acid, 4-(meth)acryloyloxyethyl trimellitic acid and the corresponding anhydride, 10-methacryloyloxydecyl malonic acid, N-(2-hydroxy-3-methacryloyloxypropyl)-N-phenylglycine, 4-vinylbenzoic acid, etc. Among them, from the viewpoints of versatility and copolymerizability, acrylic acid, methacrylic acid, and maleic acid are preferable.

[0032] Examples of the monomer having a phosphonic acid group include vinylphosphonic acid, 4-vinylphenylphosphonic acid, 4-vinylbenzylphosphonic acid, 2-methacryloyloxyethylphosphonic acid, 2-methacrylamidoethylphosphonic acid, 4-methacrylamido-4-methyl-phenyl-phosphonic acid, 2-[4-(dihydroxyphosphoryl)-2-oxa-butyl]-acrylic acid, and 2-[2-dihydroxyphosphoryl)-ethoxymethyl]-acrylic acid 2,4,6-trimethyl-phenyl ester, etc.

[0033] Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, 4-vinylphenylsulfonic acid, 3-(methacrylamide)propylsulfonic acid, etc.

[0034] Among them, from the viewpoints of versatility and copolymerizability, the hydrophilic polymer having a negatively charged group preferably contains a monomer having a carboxy group, and particularly preferably contains a monomer unit derived from at least one compound selected from acrylic acid, methacrylic acid, and maleic acid.

[0035] The separation functional layer obtained using these hydrophilic polymers preferably contains an amino group as a positively charged functional group and a carboxy group as a negatively charged functional group.

[0036] It is desirable that the weight average molecular weight of these hydrophilic polymers is 500 or more. When the weight average molecular weight is 500 or more, the separation functional layer can contain a sufficient amount of hydration water for imparting stable fouling resistance. The weight average molecular weight is more preferably 2,000 or more. The upper limit of the weight average molecular weight is not particularly limited, but from the viewpoint of ease of handling of the polymer solution, it is preferably 2,000,000 or less.

[0037] The hydrophilic polymer, which is a polymer of a monomer having an ethylenically unsaturated group, is preferably contained in the surface layer of the separation functional layer. For example, the separation functional layer preferably has a configuration in which a layer containing a hydrophilic polymer is provided on a thin film mainly composed of crosslinked polyamide. The fact that the separation functional layer has a layer containing a hydrophilic polymer on a thin film mainly composed of crosslinked polyamide can be confirmed, for example, from the fact that the contact angle between the separation functional layer and water is 40 degrees or less. The contact angle here refers to the static contact angle, which means the wettability and hydrophilicity of the surface of the separation functional layer. The smaller the contact angle, the higher the hydrophilicity.

[0038] The method for measuring the contact angle between the separation functional layer and water will be schematically described with reference to FIG. 2. The state when water 2 is dropped onto the surface of the separation functional layer 1 is as shown in FIG. 2. When water is dropped onto the surface of the separation functional layer, the following formula called "Young's formula" holds. γ S =γ L cosθ+γ SL Here, γ S is the surface tension of the separation functional layer, γ L is the surface tension of water, and γ SL is the interfacial tension between the separation functional layer and water. The angle θ formed between the tangent of water 2 when this formula is satisfied and the surface of the separation functional layer 1 is called the contact angle. The contact angle gradually changes to a smaller value with the passage of time. The time from the dropping of water onto the surface of the separation functional layer to the measurement of the contact angle is within 25 seconds, preferably within 15 seconds.

[0039] Among the hydrophilic polymers that are polymers of monomers having ethylenically unsaturated groups, at least one kind is preferably chemically bonded to a thin film mainly composed of crosslinked polyamide. By this, the hydrophilic polymer is more stably fixed to the thin film mainly composed of crosslinked polyamide. The chemical bond between the hydrophilic polymer and the thin film mainly composed of crosslinked polyamide is preferably a covalent bond, and more preferably an amide bond. The amide bond can use the functional groups possessed by the polymers constituting each layer.

[0040] Also, it is preferable that different kinds of hydrophilic polymers are chemically bonded to each other, and a covalent bond, particularly an amide bond, is preferable.

[0041] Among the hydrophilic polymers that are polymers of monomers having ethylenically unsaturated groups and are contained in two or more kinds in the separation functional layer, one or more hydrophilic polymers not bonded to the thin film mainly composed of crosslinked polyamide preferably form nanoparticle bodies. This is because by forming nanoparticle bodies, it is possible to suppress intrusion into the polymer chains of the hydrophilic polymer bonded to the separation functional layer, and it is possible to maximally suppress a decrease in the amount of hydrated water due to ionic bonding between the respective hydrophilic polymers.

[0042] If the average particle diameter of the nanoparticle bodies is 5 nm or more, it is effective in suppressing a decrease in the amount of hydrated water due to ionic bonding between the hydrophilic polymers, and preferably in the range of 5 nm or more and 50 nm. When the average particle diameter becomes 100 nm or more, it may affect the decrease in water permeability of the composite semipermeable membrane, so the average particle diameter is preferably 100 nm or less.

[0043] The nanoparticle can be prepared, for example, by copolymerizing one kind of hydrophilic polymer with another kind of polymer in advance. The average particle diameter of the nanoparticle bodies at that time can be measured with a particle size distribution analyzer. Here, the average particle diameter means the median diameter (D 50 ) in the volume-based particle size distribution measured by the particle size distribution analyzer.

[0044] (1-1-2) Characteristics The composite semipermeable membrane according to the embodiment of the present invention satisfies the following (a) to (c) for the positive charge functional group density Dw and the negative charge functional group density Db from the surface of the separation functional layer to 200 nm, and the zeta potential at pH 7 on the surface of the separation functional layer is -10 mV or more and 10 mV or less. (a) Dw > 0.30×10 -9 mol / cm 2 (b) Db > 0.30×10 -9 mol / cm 2 (c) 0.9 < Dw / Db < 1.1

[0045] (i) The positive charge functional group density Dw and the negative charge functional group density Db In the embodiment of the present invention, the positive charge functional group density Dw and the negative charge functional group density Db can be quantified, for example, by Rutherford backscattering (RBS) measurement. RBS is a measurement method in which a sample is irradiated with high-speed ions, and the elemental composition in the sample depth direction is read from the scattered ion energy and yield of elastic scattering received from the atomic nuclei in the sample.

[0046] As a method for reading the positive charge functional group density Dw using RBS measurement, the following method can be used. First, a 5 cm square sample is washed with hot water at 95°C for 30 minutes. Further, the sample is immersed in a 1×10 -4 M aqueous solution of sodium tungstate adjusted to pH 3 for 30 minutes. Then, in order to remove free tungstic acid, it is immersed and washed with pure water for 5 minutes each time.

[0047] Tungstate ions become counterions of positive charge functional groups. Therefore, for the areal density of surface-attached tungsten (unit: 10 15 atoms / cm 2 ) in the RBS measurement of the obtained sample, the positive charge group density can be derived by converting the number of atoms to mol.

[0048] As a method for reading the density Db of negatively charged functional groups using RBS measurement, the following method can be used. First, a 5 cm square sample is washed with hot water at 95 °C for 30 minutes. Subsequently, the sample is immersed in a 50% aqueous methanol solution for 16 hours, and then the sample is immersed in a 1×10 -4 M aqueous solution of barium nitrate adjusted to pH 10 for 30 minutes. Thereafter, in order to remove free barium, it is immersed and washed with methanol for 5 minutes each time.

[0049] Barium ions serve as counterions for negatively charged functional groups. Therefore, regarding the areal density of surface-attached barium (unit: 10 15 atoms / cm 2 ) in the RBS measurement of the obtained sample, the density of negatively charged groups can be derived by converting the number of atoms to moles.

[0050] (ii) Zeta potential of the surface of the separation functional layer The zeta potential is a measure of the net fixed charge on the surface of the ultra-thin film layer. In the embodiments of the present invention, the zeta potential of the surface of the thin film layer can be obtained from the electrophoretic mobility by the Helmholtz-Smoluchowski equation shown in the following formula (1). Zeta potential ζ = 4πηU / ε (1) (In formula (1), U is the electrophoretic mobility, ε is the dielectric constant of the solution, and η is the viscosity of the solution). Here, as the dielectric constant and viscosity of the solution, literature values at the measurement temperature can be used.

[0051] Usually, for the measurement of the zeta potential, a film sample with a size of 20 mm × 30 mm is used, and as standard particles for electrophoresis, polystyrene particles (particle size 520 nm) coated with hydroxypropyl cellulose on the surface are dispersed in an aqueous NaCl solution adjusted to a predetermined concentration. As the measuring device, for example, an electrophoretic light scattering photometer ELS-8000 manufactured by Otsuka Electronics Co., Ltd. can be used.

[0052] The composite semipermeable membrane according to an embodiment of the present invention is controlled such that the surface zeta potential of the separation functional layer is -10 mV or more and 10 mV or less when measured under the conditions of pH 7 and 10 mM NaCl. Under the conditions satisfying both (a) and (b) above, the zeta potential within the above range means that the charge groups opposite to each other are present in a well-balanced manner on the surface of the separation functional layer. Thereby, fouling resistance can be effectively exhibited against foulants in various ionic states.

[0053] Further, in the composite semipermeable membrane according to an embodiment of the present invention, the zeta potential at pH 3 and 10 mM NaCl is preferably 30 mV or more, and the zeta potential at pH 11 and 10 mM NaCl is preferably -30 mV or less.

[0054] The surface zeta potential of the separation functional layer in the composite semipermeable membrane according to an embodiment of the present invention is governed by the composition of the hydrophilic polymer. In the composition of the hydrophilic polymer where the zeta potential at pH 3 and 10 mM NaCl is 30 mV or more, it means that the positive charge group density is sufficient to improve fouling resistance. Also, in the composition of the hydrophilic polymer where the zeta potential at pH 11 and 10 mM NaCl is -30 mV or less, it means that the negative charge group density is sufficient to improve fouling resistance.

[0055] (1-2) Porous support layer The porous support layer serves as a scaffold for forming the separation functional layer and itself has substantially no separation performance for ions and the like. The size and distribution of the pores in the porous support layer are not particularly limited. For example, a porous support layer having uniform and fine pores, or gradually larger fine pores from the surface on the side where the separation functional layer is formed to the other side, and the size of the fine pores on the surface where the separation functional layer is formed being 0.1 nm or more and 100 nm or less is preferred.

[0056] The porous support layer can be obtained by casting a polymer on a substrate which is a fabric made of at least one selected from, for example, polyester and aromatic polyamide. Hereinafter, the structure in which the porous support layer is formed on the substrate may be referred to as a "support film".

[0057] As the material of the porous support layer, homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose-based polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide can be used alone or in blend. Here, as the cellulose-based polymer, cellulose acetate, cellulose nitrate, etc. can be used, and as the vinyl polymer, polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, etc. can be used. Among them, as the material of the porous support layer, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferable. As the material of the porous support layer, more preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone can be mentioned. Further, among these materials, polysulfone is generally preferably used because it has high chemical, mechanical, and thermal stability and is easy to mold.

[0058] For example, a solution of polysulfone in N,N-dimethylformamide (hereinafter referred to as DMF) is cast to a certain thickness on a tightly woven polyester fabric or a polyester non-woven fabric, and it is wet-solidified in water, whereby a support film having most of its surface with fine pores having a diameter of several tens of nm or less can be obtained.

[0059] The thickness of the above-mentioned support film affects the strength of the resulting composite semipermeable membrane and the packing density when it is used as an element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support film is preferably in the range of 30 μm or more and 300 μm or less, more preferably in the range of 100 μm or more and 220 μm or less.

[0060] The morphology of the porous support layer can be observed by a scanning electron microscope, a transmission electron microscope, or an atomic force microscope. For example, if observed with a scanning electron microscope, after peeling the porous support layer from the substrate, it is cut by a freeze-fracture method to prepare a sample for cross-sectional observation. This sample is thinly coated with platinum or platinum-palladium or ruthenium tetrachloride, preferably ruthenium tetrachloride, and observed by a high-resolution field emission scanning electron microscope (UHR-FE-SEM) at an acceleration voltage of 3 to 15 kV. As the high-resolution field emission scanning electron microscope, an S-900 type electron microscope manufactured by Hitachi, Ltd. can be used.

[0061] The thickness of the porous support layer is preferably in the range of 20 μm or more and 100 μm or less. When the thickness of the porous support layer is 20 μm or more, good pressure resistance can be obtained and a uniform support film without defects can be obtained. Therefore, a composite semipermeable membrane provided with such a porous support layer can exhibit good salt removal performance. When the thickness of the porous support layer exceeds 100 μm, the residual amount of unreacted substances during manufacturing increases, thereby reducing the water permeation amount and possibly reducing the chemical resistance.

[0062] (2) Manufacturing method (2-1) Formation step of the porous support layer The formation step of the porous support layer includes a step of applying a polymer solution to a substrate and a step of immersing the substrate coated with the solution in a coagulation bath to coagulate the polymer.

[0063] In the step of applying a polymer solution to a substrate, the polymer solution is prepared by dissolving a polymer, which is a component of the porous support layer, in a good solvent for the polymer.

[0064] When applying the polymer solution, the temperature of the polymer solution is preferably 10°C or higher and 60°C or lower when using polysulfone as the polymer. If the temperature of the polymer solution is within this range, the polymer will not precipitate, and after the polymer solution has sufficiently impregnated between the fibers of the substrate, it will solidify. As a result, due to the anchor effect, the porous support layer will be firmly bonded to the substrate, and a good support membrane can be obtained. Note that the preferred temperature range of the polymer solution can be appropriately adjusted according to the type of polymer used, the desired solution viscosity, etc.

[0065] After applying the polymer solution on the substrate, the time until it is immersed in the coagulation bath is preferably 0.1 second or longer and 5 seconds or shorter. If the time until immersion in the coagulation bath is within this range, the organic solvent solution containing the polymer will solidify after sufficiently impregnating between the fibers of the substrate. Note that the preferred range of the time until immersion in the coagulation bath can be appropriately adjusted according to the type of polymer solution used, the desired solution viscosity, etc.

[0066] As the coagulation bath, generally water is used, but it is not particularly limited as long as it does not dissolve the polymer that is a component of the porous support layer. The membrane morphology of the support membrane obtained depends on the composition of the coagulation bath, and the composite semipermeable membrane obtained thereby also changes. The temperature of the coagulation bath is preferably -20°C or higher and 100°C or lower, more preferably 10°C or higher and 50°C or lower. If the temperature of the coagulation bath is within this range, the vibration of the coagulation bath surface due to thermal motion will not become intense, and the smoothness of the membrane surface after membrane formation will be maintained. Also, if the temperature is within this range, the coagulation rate is appropriate and the film-forming property is good.

[0067] Next, the support membrane thus obtained is washed with hot water to remove the solvent remaining in the membrane. The temperature of the hot water at this time is preferably 40°C or higher and 100°C or lower, more preferably 60°C or higher and 95°C or lower. If it is within this range, the shrinkage degree of the support membrane will not increase, and the water permeation amount is good. Also, if the temperature is within this range, the washing effect is sufficient.

[0068] (2-2) Formation process of the separation functional layer Next, the formation process of the separation functional layer constituting the composite semipermeable membrane will be described. The formation process of the separation functional layer includes the following steps (A), (B), and (C). The formation process of the separation functional layer is preferably carried out in the order of (A), (B), and (C). (A) A step of forming a layer containing crosslinked polyamide by interfacial polymerization on a porous support layer. (B) A step of bonding the layer containing the crosslinked polyamide with a hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group. (C) A step of bonding a nanoparticle body mainly composed of a hydrophilic polymer B which is a polymer of a monomer having a different type of ethylenically unsaturated group from the hydrophilic polymer A to the hydrophilic polymer A.

[0069] (2-2-1) Step (A) of forming a layer containing crosslinked polyamide by interfacial polymerization on a porous support layer In step (A), for example, a layer containing crosslinked polyamide can be formed by an interfacial polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide. Preferred embodiments of the polyfunctional amine and the polyfunctional acid halide are the same as described above. Hereinafter, step (A) will be described by taking the case where a polyfunctional aromatic amine is used as the polyfunctional amine and a polyfunctional aromatic acid chloride is used as the polyfunctional acid halide as an example.

[0070] As the organic solvent for dissolving the polyfunctional aromatic acid chloride, any solvent that is immiscible with water, does not destroy the support membrane, and does not inhibit the formation reaction of the crosslinked aromatic polyamide may be used. Representative examples include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. Considering that it does not destroy the ozone layer, is easily available, easy to handle, and safe to handle, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, etc., alone or a mixture thereof, are preferably used.

[0071] In an aqueous solution containing a polyfunctional aromatic amine (polyfunctional aromatic amine aqueous solution) or an organic solvent solution containing a polyfunctional aromatic acid chloride (polyfunctional aromatic acid chloride-containing solution), compounds such as an acylation catalyst, a polar solvent, an acid scavenger, a surfactant, and an antioxidant may be contained as necessary, as long as they do not interfere with the reaction between the two components.

[0072] In order to perform interfacial polycondensation on the support membrane, first, the surface of the support membrane is coated with the polyfunctional aromatic amine aqueous solution. Here, the concentration of the aqueous solution containing the polyfunctional aromatic amine is preferably 0.1% by weight or more and 20% by weight or less, more preferably 0.5% by weight or more and 15% by weight or less.

[0073] As a method for coating the surface of the support membrane with the polyfunctional aromatic amine aqueous solution, it is only necessary that the surface of the support membrane is uniformly and continuously coated with this aqueous solution, and it may be carried out by known coating means, for example, a method of coating the aqueous solution on the surface of the support membrane, a method of immersing the support membrane in the aqueous solution, etc. The contact time between the support membrane and the polyfunctional aromatic amine aqueous solution is preferably in the range of 5 seconds or more and 10 minutes or less, more preferably in the range of 10 seconds or more and 3 minutes or less. Next, it is preferable to remove the excessively coated aqueous solution by a liquid draining step. As a method of draining the liquid, for example, there is a method of holding the membrane surface in the vertical direction and allowing it to flow down naturally. After draining the liquid, the membrane surface may be dried to remove all or part of the water in the aqueous solution.

[0074] Thereafter, the above-mentioned polyfunctional aromatic acid chloride-containing solution is applied to the support membrane coated with the polyfunctional aromatic amine aqueous solution, and a crosslinked aromatic polyamide is formed by interfacial polycondensation. The time for carrying out the interfacial polycondensation is preferably 0.1 second or more and 3 minutes or less, more preferably 0.1 second or more and 1 minute or less.

[0075] The concentration of the polyfunctional aromatic acid chloride in the polyfunctional aromatic acid chloride-containing solution is not particularly limited, but if it is too low, the formation of the first layer, which is the active layer, may be insufficient and may become a drawback, and if it is too high, it will be disadvantageous in terms of cost. Therefore, for example, about 0.01% by weight or more and 1.0% by weight or less is preferable.

[0076] Next, it is preferable to remove the organic solvent remaining after the reaction by a liquid draining step. For removing the organic solvent, for example, a method can be used in which the membrane is held vertically and the excess organic solvent is allowed to flow down naturally for removal. In this case, the time for holding vertically is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. When the holding time is 1 minute or more, it is easy to obtain a crosslinked aromatic polyamide having the desired function, and when it is 3 minutes or less, the occurrence of drawbacks due to over-drying of the organic solvent can be suppressed, so that a performance degradation can be suppressed.

[0077] (2-2-2) Step (B) of bonding the layer containing the crosslinked polyamide and a hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group In step (B), the hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group used may be either one having a positively charged group or one having a negatively charged group. Note that, as long as the effects of the present invention are not inhibited, the hydrophilic polymer A may have both a positively charged group and a negatively charged group.

[0078] The hydrophilic polymer A is preferably used as an aqueous solution having a weight concentration of 0.001% by weight or more and 1% by weight or less. When the concentration is 0.001% by weight or more, it can be efficiently bonded to the layer containing the crosslinked polyamide in a relatively short time. Further, when the concentration of the hydrophilic polymer A is 1% by weight or less, a moderately thin hydrophilic polymer A layer is formed, so that a decrease in the water permeation amount is suppressed.

[0079] The bonding between the layer containing the crosslinked polyamide and the hydrophilic polymer A is not limited to the method as long as the layer containing the crosslinked polyamide and the aqueous solution of the hydrophilic polymer A are in contact, and examples thereof include a method of immersing a membrane having a layer containing the crosslinked polyamide on a porous support layer in an aqueous solution and a method of applying an aqueous solution to the surface of the layer containing the crosslinked polyamide.

[0080] Here, various reaction aids (condensation accelerators) can be used to promote the reaction between the layer containing the crosslinked polyamide and the hydrophilic polymer A, that is, to make it easier to bond the two. As the condensation accelerator, sulfuric acid, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, N,N'-carbonyldiimidazole, 1,1'-carbonyldi(1,2,4-triazole), 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, (7-azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, chlorotripyrrolidinophosphonium hexafluorophosphate, bromotris(dimethylamino)phosphonium hexafluorophosphate, 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(N-succinimidyl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(N-succinimidyl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(3,4-dihydro-4-oxo-1,2,3-benzotriazin-3-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, trifluoromethanesulfonic acid (4,6-dimethoxy-1,3,5-triazin-2-yl)-(2-octyloxy-2-oxoethyl)dimethylammonium, S-(1-oxide-2-pyridyl)-N,N,N',N'-tetramethylthiuronium tetrafluoroborate, O-[2-oxo-1(2H)-pyridyl]-N,N,N',N'-tetramethyluronium tetrafluoroborate, {{[(1-cyano-2-ethoxy-2-oxoethylidene)amino]oxy}-4-morpholinomethylene}dimethylammonium hexafluorophosphate, 2-chloro-1,3-dimethylimidazolinium hexafluorophosphate, 1-(chloro-1-pyrrolidinylmethylene)pyrrolidinium hexafluorophosphate, 2-fluoro-1,3-dimethylimidazolinium hexafluorophosphate, fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate, etc. are given as examples.,

[0081] The reaction time between the layer containing the crosslinked polyamide and the hydrophilic polymer A and the concentration of the compound can be appropriately adjusted according to the solvent, condensation accelerator, and chemical structure of the compound used. From the viewpoint of productivity, the reaction time is preferably within 24 hours, more preferably within 12 hours, still more preferably within 6 hours, and particularly preferably within 1 hour.,

[0082] After the reaction, the obtained membrane may be washed with hot water, an aqueous acid solution, or an aqueous alkali solution to remove the residue.,

[0083] (2-2-3) Step (C) of bonding a nanoparticle body mainly composed of a hydrophilic polymer B, which is a polymer of a monomer having an ethylenically unsaturated group different from that of the hydrophilic polymer A, to the hydrophilic polymer A

[0084] Examples of the method for preparing in advance a nanoparticle body mainly composed of the hydrophilic polymer B in step (C) are shown. Note that the hydrophilic polymer B needs to be of a different type from the hydrophilic polymer A. Furthermore, it is preferable that the hydrophilic polymer A and the hydrophilic polymer B have mutually opposite charge groups.,

[0085] First, a solution is prepared by mixing the hydrophilic polymer B and a hydrophilic polymer C that is further different. As the type of the solvent, for example, water is preferable., Here, the hydrophilic polymer C may be of the same type as the hydrophilic polymer A or different.,

[0086] The concentrations of hydrophilic polymer B and hydrophilic polymer C in the aqueous solution are preferably 0.001% by weight or more and 0.1% by weight or less, more preferably 0.005% by weight or more and 0.05% by weight or less. By having the concentrations within this range, nanoscale particle bodies of appropriate size can be prepared.

[0087] Also, the weight concentration ratio of hydrophilic polymer B to hydrophilic polymer C is preferably 1.2 times or more and 10 times or less, more preferably 1.5 times or more and 3 times or less. Thereby, nanoscale particle bodies mainly composed of hydrophilic polymer B can be prepared.

[0088] It is preferable that hydrophilic polymer B and hydrophilic polymer C are chemically bonded. Thereby, the structure of the nanoscale particle body can be stabilized. The chemical bond between hydrophilic polymer B and hydrophilic polymer C is preferably a covalent bond, more preferably an amide bond.

[0089] Various reaction aids (condensation accelerators) can be used to promote the reaction between hydrophilic polymer B and hydrophilic polymer C, that is, to make it easier for the two to bond. Specific examples include those described above in step (B).

[0090] The reaction time between hydrophilic polymer B and hydrophilic polymer C can be appropriately adjusted according to the solvent used, the condensation accelerator, and the chemical structure of the compound. From the viewpoint of productivity, the reaction time is preferably within 24 hours, more preferably within 12 hours, even more preferably within 6 hours, and particularly preferably within 1 hour.

[0091] As a method for binding the nanoparticle body mainly composed of the hydrophilic polymer B thus obtained to the hydrophilic polymer A, for the separation functional layer of the membrane obtained after step (B), that is, the layer containing crosslinked polyamide to which the hydrophilic polymer A is bound, a solution containing the nanoparticle body mainly composed of the hydrophilic polymer B may be used to perform the same treatment as in step (B). That is, any method may be used as long as the separation functional layer of the membrane obtained after step (B) comes into contact with the solution containing the nanoparticle body mainly composed of the hydrophilic polymer B. Specifically, methods include immersing the membrane obtained after step (B) in the solution containing the nanoparticle body, and applying the solution containing the nanoparticle body to the surface of the separation functional layer of the membrane obtained after step (B). The nanoparticle body mainly composed of the hydrophilic polymer B can be used in the state of the reaction solution with the hydrophilic polymer C.

[0092] (2-2-4) Other steps Furthermore, a step of converting the amino group of the crosslinked polyamide into another functional group may be provided thereafter. In particular, it is preferable to contact with a reagent that reacts with the amino group to generate a diazonium salt or its derivative to perform the conversion of the functional group. Examples of the reagent that reacts with the amino group to generate a diazonium salt or its derivative include aqueous solutions of nitrous acid and its salts, nitrosyl compounds, etc. Since aqueous solutions of nitrous acid and nitrosyl compounds have the property of decomposing by generating gas, it is preferable to sequentially generate nitrous acid by the reaction of a nitrite with an acidic solution. Generally, nitrite reacts with hydrogen ions to generate nitrous acid (HNO 2 )), but it is efficiently generated when the pH of the aqueous solution is 7 or less, preferably 5 or less, more preferably 4 or less. Among them, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferable from the viewpoint of ease of handling.

[0093] The concentration of nitrous acid or nitrite in the reagent that reacts with an amino group to produce a diazonium salt or its derivative is preferably in the range of 0.01% by weight or more and 1% by weight or less, more preferably in the range of 0.05% by weight or more and 0.5% by weight or less. If the concentration is 0.01% by weight or more, a sufficient effect can be obtained, and if the concentration is 1% by weight 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 can be obtained, and if it is 45°C or lower, decomposition of nitrous acid hardly occurs, so it is easy to handle.

[0095] The contact time with the aqueous nitrous acid solution may be the time when at least one of the diazonium salt and its derivative is generated. At high concentrations, the treatment can be carried out in a short time, but at low concentrations, a long time is required. Therefore, in the solution of the above concentration, it is preferably within 10 minutes, more preferably within 3 minutes. Also, the method of contact is not particularly limited, and the solution of the reagent may be applied, or the composite semipermeable membrane may be immersed in the solution of the reagent. Any solvent can be used as long as the reagent dissolves and the composite semipermeable membrane is not eroded. Further, the solution may contain a surfactant, an acidic compound, an alkaline compound, etc., as long as they do not interfere with the reaction between the amino group and the reagent.

[0096] Next, a part of the generated diazonium salt or its derivative is converted into a different functional group. A part of the diazonium salt or its derivative is converted into a phenolic hydroxyl group, for example, by reacting with water. Also, when it is brought into contact with a solution containing chloride ion, bromide ion, cyanide ion, iodide ion, fluoroboric acid, hypophosphorous acid, sodium bisulfite, sulfite ion, aromatic amine, hydrogen sulfide, thiocyanic acid, etc., it is converted into the corresponding functional group. Also, a diazo coupling reaction occurs by contacting with an aromatic amine, and it becomes possible to introduce an aromatic group onto the membrane surface. These reagents may be used singly, mixed in plural, or contacted with different reagents a plurality of times.

[0097] Examples of the reagent in which the diazo coupling reaction occurs include compounds having an electron-rich aromatic ring or heteroaromatic ring. Examples of the compounds having an electron-rich aromatic ring or heteroaromatic ring include unsubstituted heteroaromatic compounds, aromatic compounds having an electron-donating substituent, and heteroaromatic compounds having an electron-donating substituent. Examples of the electron-donating substituent include an amino group, an ether group, a thioether group, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, and the like. Specific examples of the above compounds include, for example, aniline, methoxyaniline bonded to a benzene ring in any of ortho, meta, and para positional relationships, phenylenediamine having two amino groups bonded to a benzene ring in any of ortho, meta, and para positional relationships, 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, or N-alkylated products of these compounds.

[0098] The composite semipermeable membrane obtained by at least steps (a), (b), and (c) can preferably improve the solute rejection performance and the permeate water amount of the composite semipermeable membrane by washing with hot water in the range of 25°C or higher and 90°C or lower for 1 minute or longer and 60 minutes or shorter. This washing treatment may be performed any number of times as long as it is after step (a). However, when the temperature of the hot water is too high, the chemical resistance decreases when it is rapidly cooled after the hot water washing treatment. Therefore, it is preferable to perform the hot water washing in the range of 25°C or higher and 60°C or lower. Further, when performing the hot water washing treatment at a high temperature of 61°C or higher and 90°C or lower, it is preferable to cool it gently after the hot water washing treatment. For example, there is a method of contacting with hot water at gradually lower temperatures and cooling to room temperature.

[0099] In addition, in the above-described step of hot water washing, acid or alcohol may be contained in the hot water. By containing acid or alcohol, it becomes easier to control the formation of hydrogen bonds in the crosslinked aromatic polyamide. Examples of the acid include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as citric acid and oxalic acid. The concentration of the acid is preferably adjusted to a pH of 2 or less, and more preferably a pH of 1 or less. Examples of the alcohol include monohydric alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and polyhydric alcohols such as ethylene glycol and glycerin. The concentration of the alcohol is preferably 10% by weight or more and 100% by weight or less, and more preferably 10% by weight or more and 50% by weight or less.

[0100] In the composite semipermeable membrane obtained by the production method exemplified above, the separation functional layer includes a thin film mainly composed of crosslinked polyamide, a hydrophilic polymer A is bonded to such a thin film, and a nanoparticle body mainly composed of a hydrophilic polymer B is bonded to the hydrophilic polymer A bonded to the thin film. In other words, the separation functional layer has a structure in which a layer containing a hydrophilic polymer is formed on a thin film mainly composed of crosslinked polyamide, and the layer containing the hydrophilic polymer is considered to include a hydrophilic polymer A bonded to the thin film mainly composed of crosslinked polyamide and a nanoparticle body mainly composed of a hydrophilic polymer B bonded to the hydrophilic polymer A.

[0101] Since the separation functional layer has a layer containing such a hydrophilic polymer, it is considered that each charge density from the surface of the separation functional layer to 200 nm satisfies the above (a) to (c), and the zeta potential at pH 7 and 10 mM of NaCl is -10 mV or more and 10 mV or less. Generally, when oppositely charged groups form an ionic bond, the respective charge groups cancel each other out and the charge is neutralized. That is, simply mixing oppositely charged groups in the surface layer of the separation functional layer makes them easily form an ionic bond and become neutralized. In this case, it is considered difficult to make both the positive charge density and the negative charge density equal to or greater than a predetermined value, particularly to achieve (a) and (b) simultaneously. However, in the present invention, by having a configuration including one or more hydrophilic polymers bonded to a thin film mainly composed of a crosslinked polyamide and a nanoparticle body mainly composed of one or more other hydrophilic polymers, it is considered possible to suppress the neutralization of the charge groups contained in the hydrophilic polymer bonded to the thin film and the hydrophilic polymer that is the nanoparticle body. As a result, it is presumed that a composite semipermeable membrane with the positive charge functional group density and the negative charge functional group density on the separation functional layer appropriately controlled as described above can be obtained.

[0102] (3) Use of the composite semipermeable membrane The composite semipermeable membrane according to the embodiment of the present invention is wound around a cylindrical water collection pipe with a large number of holes together with a raw water flow path material such as a plastic net, a permeated water flow path material such as a tricot, and a film for enhancing pressure resistance as needed, and is suitably used as a spiral type composite semipermeable membrane element. Further, a composite semipermeable membrane module can be formed by connecting these elements in series or in parallel and housing them in a pressure vessel.

[0103] In addition, the above composite semipermeable membrane, its element, and module can be combined with a pump for supplying raw water thereto, a device for pretreating the raw water, etc. to constitute a fluid separation device. By using this separation device, raw water can be separated into permeated water such as drinking water and concentrated water that did not permeate through the membrane, and water suitable for the purpose can be obtained.

[0104] The operating pressure of the fluid separation device is preferably high to improve the salt rejection rate, but the energy required for operation also increases. Considering the durability of the composite semipermeable membrane, the operating pressure when the water to be treated permeates the composite semipermeable membrane is preferably 0.1 MPa or more and 10 MPa or less. When the feed water temperature increases, the salt rejection rate decreases, but as the temperature decreases, the membrane permeation flux also decreases. Therefore, a temperature range of 5°C or more and 45°C or less is preferred. Also, when the feed water pH is high, in the case of high-salt-concentration feed water such as seawater, there is a risk of scale formation such as magnesium, and there is concern about membrane deterioration due to high-pH operation. Therefore, operation in the neutral region is preferred.

[0105] Examples of the raw water treated by the composite semipermeable membrane according to the embodiment of the present invention include liquid mixtures containing 500 mg / L to 100 g / L of TDS (Total Dissolved Solids) such as seawater, brackish water, and wastewater. Generally, TDS refers to the total amount of dissolved solids and is expressed as "weight ÷ volume" or "weight ratio". According to the definition, it can be calculated from the weight of the residue obtained by evaporating the solution filtered through a 0.45-micron filter at a temperature of 39.5 to 40.5°C, but more simply, it can be converted from the practical salinity (S).

Examples

[0106] The present invention will be described below with reference to examples, but the present invention is not limited to these examples in any way.

[0107] [1. Measurement of properties] (NaCl rejection rate) Evaluation water adjusted to a temperature of 25°C, pH 7, and sodium chloride concentration of 2,000 ppm was supplied to the composite semipermeable membrane at an operating pressure of 1.55 MPa for membrane filtration treatment. The electrical conductivities of the feed water and the permeate water were measured with a conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. to obtain the respective practical salinities, that is, the NaCl concentrations. Based on the NaCl concentrations thus obtained and the following formula, the NaCl rejection rate was calculated. Here, the sodium chloride concentration (ppm) means the concentration on a mass basis. NaCl rejection rate (%) = 100 × {1 - (NaCl concentration in permeate water / NaCl concentration in feed water)}

[0108] (Water permeation amount) In the above test, the amount of water permeated through the membrane of the feed water (NaCl aqueous solution) was measured, and the value converted to the amount of water permeated per day (cubic meters) per square meter of the membrane surface was defined as the membrane permeation flux (m 3 / m 2 / day). The measurement of the membrane performance was conducted as follows.

[0109] First, the amount of water permeated when an aqueous solution with a temperature of 25°C, pH 7, and NaCl concentration of 2,000 mg / L was filtered under a pressure of 1.55 MPa for 2 hours was measured and defined as the initial water permeation amount (F1). Subsequently, polyoxyethylene (10) octyl phenyl ether (POEOPE) was added to the aqueous solution to a concentration of 150 mg / L and filtered for 2 hours, and the amount of water permeated at this time was F2. Sodium dodecyl sulfate (DSS) was added to the aqueous solution to a concentration of 50 mg / L and filtered for 2 hours, and the amount of water permeated at this time was F3. Dodecyl trimethyl ammonium bromide (DTAB) was added to the aqueous solution to a concentration of 10 mg / L and filtered for 2 hours, and the amount of water permeated at this time was F4. Then, F2 / F1, F3 / F1, and F4 / F1 were calculated as the water permeation amount retention rates, respectively.

[0110] (RBS) (Preparation of positively charged group quantitative sample) A 5 cm square sample was washed with hot water at 95°C for 30 minutes. Subsequently, the sample was immersed in a 1×10 -4 M aqueous solution of sodium tungstate adjusted to pH 3 for 30 minutes. Then, in order to remove the free tungstic acid, the sample was immersed and washed with pure water for 5 minutes each time to prepare the sample.

[0111] (Preparation of negatively charged group quantitative sample) A 5 cm square sample was washed with hot water at 95°C for 30 minutes. Subsequently, the sample was immersed in a 50% aqueous methanol solution for 16 hours, and further immersed in a 1×10 -4 M aqueous solution of barium nitrate adjusted to pH 10 for 30 minutes. Then, in order to remove the free barium, the sample was immersed and washed with methanol for 5 minutes each time to prepare the sample.

[0112] The obtained sample was measured under the following conditions. · Apparatus: Pelletron 3SDH manufactured by National Electrostatics Corporation · Incident ion: 4 He ++ · Incident energy: 2300 keV · Incident angle: 0 deg · Scattering angle: 160 deg · Sample current: 4 nA · Beam diameter: 2 mm in diameter · In-plane rotation: None · Irradiation dose: 100 μC (4 μC × 25 locations)

[0113] The average composition (atomic %) of each element from the surface layer of the sample (composite semipermeable membrane), that is, up to 200 nm from the surface of the separation functional layer, was calculated. Assuming that the tungsten content corresponds to the amount of positively charged groups and the barium content corresponds to the amount of negatively charged groups, the obtained surface density of the deposited elements (10 -9 mol / cm 2 ) was defined as the positively charged group density Dw and the negatively charged group density Db, respectively.

[0114] (Zeta potential) The composite semipermeable membrane as the sample was washed with ultrapure water and set in a cell for flat samples such that the separation functional layer surface of the composite semipermeable membrane was in contact with the monitor particle solution, and measured with an electrophoresis light scattering photometer (ELS-8000) manufactured by Otsuka Electronics Co., Ltd. As the monitor particle solution, a measurement solution in which monitor particles of polystyrene latex were dispersed in a 10 mM aqueous NaCl solution adjusted to pH 3, 7, and 11, respectively, was used.

[0115] Using the above measurement solution, the surface zeta potential α (pH 7, NaCl 10 mM), surface zeta potential β (pH 3, NaCl 10 mM), and surface zeta potential γ (pH 11, NaCl 10 mM) of the separation functional layer were measured, respectively.

[0116] [2. Preparation of Composite Semipermeable Membrane] (2-1. Preparation of Aqueous Nanoparticle Solution Mainly Composed of Hydrophilic Polymer B) (Synthesis Example 1) An aqueous solution containing 0.02 wt% of polyethyleneimine (PEI) with a weight average molecular weight of 25,000 as hydrophilic polymer B, 0.01 wt% of polyacrylic acid (PAA) with a weight average molecular weight of 2,000 as hydrophilic polymer C, and 0.1 wt% of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PEI as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 20 nm.

[0117] (Synthesis Example 2) An aqueous solution containing 0.02 wt% of polyallylamine (PAAm) with a weight average molecular weight of 5,000 as hydrophilic polymer B, 0.01 wt% of PAA with a weight average molecular weight of 2,000 as hydrophilic polymer C, and 0.1 wt% of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PAAm as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 30 nm.

[0118] (Synthesis Example 3) An aqueous solution containing 0.02 wt% of PAA with a weight average molecular weight of 2,000 as hydrophilic polymer B, 0.01 wt% of PEI with a weight average molecular weight of 25,000 as hydrophilic polymer C, and 0.1 wt% of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PAA as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 25 nm.

[0119] (Synthesis Example 4) An aqueous solution containing 0.02 wt% of PAA with a weight average molecular weight of 2,000 as hydrophilic polymer B, 0.01 wt% of PAAm with a weight average molecular weight of 5,000 as hydrophilic polymer C, and 0.1 wt% of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PAA as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 28 nm.

[0120] (Synthesis Example 5) An aqueous solution containing 0.02% by weight of polymethacrylic acid (PMA) with a weight average molecular weight of 5,400 as hydrophilic polymer B, 0.01% by weight of PEI with a weight average molecular weight of 25,000 as hydrophilic polymer C, and 0.1% by weight of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PMA as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 30 nm.

[0121] (Synthesis Example 6) An aqueous solution containing 0.02% by weight of polyethyleneimine (PEI) with a weight average molecular weight of 25,000 as hydrophilic polymer B, 0.01% by weight of PMA with a weight average molecular weight of 5,400 as hydrophilic polymer C, and 0.1% by weight of DMT-MM was stirred at 20 °C for 1 hour to prepare an aqueous solution of nanoparticle bodies mainly composed of PEI as hydrophilic polymer B. The average particle size of the nanoparticle bodies was 25 nm.

[0122] (Preparation of Composite Semipermeable Membrane 2-2) (Comparative Example 1) A 15.0% by weight DMF solution of polysulfone was cast on a polyester nonwoven fabric made of long fibers (air permeability 2.0 cc / cm 2 / sec) under the condition of 25 °C, immediately immersed in pure water, and left for 5 minutes to prepare a support membrane with a thickness of the porous support layer of 40 μm. Next, this support membrane was immersed in a 3.5% by weight aqueous solution of m-PDA, then the excess aqueous solution was removed, and further a n-decane solution in which TMC was dissolved to a concentration of 0.14% by weight was applied so that the surface of the porous support layer was completely wetted. Next, in order to remove the excess solution from the membrane, the membrane was made vertical for liquid drainage, dried by blowing air at 25 °C using a blower, and then washed with pure water at 40 °C to obtain the composite semipermeable membrane of Comparative Example 1.

[0123] (Comparative Example 2) The composite semipermeable membrane obtained in Comparative Example 1 was immersed in a 0.3% by weight aqueous solution of sodium nitrite adjusted to pH 3 and 35 °C for 1 minute. The pH of sodium nitrite was adjusted with sulfuric acid. Next, it was washed with pure water at 20 °C to obtain the composite semipermeable membrane of Comparative Example 2.

[0124] (Comparative Example 3) On the composite semipermeable membrane obtained in Comparative Example 1, a solution in which polyvinyl alcohol (PVA) with a saponification degree of 99% and a weight average molecular weight of 2,000 was dissolved in a 3:7 solution of isopropyl alcohol and water to a concentration of 0.25% by weight was applied, dried at 130°C for 5 minutes, and a composite semipermeable membrane of Comparative Example 3 in which PVA was disposed on the crosslinked aromatic polyamide was obtained.

[0125] (Comparative Example 4) The composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with an aqueous solution containing 0.01% by weight of PEI with a weight average molecular weight of 25,000 and 0.1% by weight of DMT-MM as hydrophilic polymer A at 20°C for 1 hour, and then washed with water to obtain a composite semipermeable membrane of Comparative Example 4.

[0126] (Comparative Example 5) The composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with an aqueous solution containing 0.01% by weight of PAA with a weight average molecular weight of 2,000 and 0.1% by weight of DMT-MM as hydrophilic polymer A at 20°C for 1 hour, and then washed with water to obtain a composite semipermeable membrane of Comparative Example 5.

[0127] (Comparative Example 6) The composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with the solution obtained in Synthesis Example 1 at 20°C for 1 hour, and then washed with water to obtain a composite semipermeable membrane of Comparative Example 6.

[0128] (Comparative Example 7) The composite semipermeable membrane obtained in Comparative Example 1 was brought into contact with the solution obtained in Synthesis Example 3 at 20°C for 1 hour, and then washed with water to obtain a composite semipermeable membrane of Comparative Example 7.

[0129] (Comparative Example 8) The composite semipermeable membrane obtained in Comparative Example 4 was brought into contact with an aqueous solution containing 0.01% by weight of PAA with a weight average molecular weight of 2,000 and 0.1% by weight of DMT-MM as hydrophilic polymer B at 20°C for 1 hour, and then washed with water to obtain a composite semipermeable membrane of Comparative Example 8.

[0130] (Comparative Example 9) The composite semipermeable membrane obtained in Comparative Example 5 was brought into contact with an aqueous solution containing 0.01% by weight of PEI with a weight average molecular weight of 25,000 and 0.1% by weight of DMT-MM as hydrophilic polymer B at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Comparative Example 9.

[0131] (Comparative Example 10) The composite semipermeable membrane obtained in Comparative Example 4 was brought into contact with the solution obtained in Synthesis Example 1 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Comparative Example 10.

[0132] (Comparative Example 11) The composite semipermeable membrane obtained in Comparative Example 5 was brought into contact with the solution obtained in Synthesis Example 3 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Comparative Example 11.

[0133] (Example 1) The composite semipermeable membrane obtained in Comparative Example 4 was brought into contact with an aqueous solution of nanoparticles mainly composed of PAA obtained in Synthesis Example 3 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 1.

[0134] (Example 2) The composite semipermeable membrane obtained in Comparative Example 4 was brought into contact with an aqueous solution of nanoparticles mainly composed of PAA obtained in Synthesis Example 4 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 2.

[0135] (Example 3) The composite semipermeable membrane obtained in Comparative Example 5 was brought into contact with an aqueous solution of nanoparticles mainly composed of PEI obtained in Synthesis Example 1 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 3.

[0136] (Example 4) The composite semipermeable membrane obtained in Comparative Example 5 was brought into contact with an aqueous solution of nanoparticles mainly composed of PAAm obtained in Synthesis Example 2 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 4.

[0137] (Example 5) The composite semipermeable membrane obtained in Comparative Example 4 was brought into contact with an aqueous solution of nanoparticles mainly composed of PMA obtained in Synthesis Example 5 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 5.

[0138] (Example 6) The composite semipermeable membrane obtained in Comparative Example 5 was brought into contact with an aqueous solution of nanoparticles mainly composed of PEI obtained in Synthesis Example 6 at 20°C for 1 hour, and then washed with water to obtain the composite semipermeable membrane of Example 6.

[0139] The characteristics and performance values of the separation functional layer of the composite semipermeable membrane obtained as described above are shown in Table 1 and Table 2, respectively.

[0140]

Table 1

[0141]

Table 2

[0142] As described above, the composite semipermeable membrane of the present invention has high fouling resistance against various membrane contaminants and can stably maintain high performance.

Claims

1. A composite semipermeable membrane comprising a separation functional layer located on a porous support layer, wherein the separation functional layer has a thin film mainly composed of crosslinked polyamide, the separation functional layer contains two or more hydrophilic polymers which are polymers of monomers having ethylenically unsaturated groups, a composite semipermeable membrane in which the density Dw of positively charged functional groups and the density Db of negatively charged functional groups from the surface of the separation functional layer up to 200 nm satisfy the following (a) to (c), and the zeta potential at pH 7 and 10 mM NaCl on the surface of the separation functional layer is -10 mV or more and 10 mV or less. (a) Dw > 0.30 × 10 －９ mol / cm ２ (b) Db > 0.30 × 10 －９ mol / cm ２ (c) 0.9 < Dw / Db < 1.1

2. The composite semipermeable membrane according to claim 1, wherein the hydrophilic polymer is a total of two or more kinds including one or more hydrophilic polymers having positively charged functional groups and one or more hydrophilic polymers having negatively charged functional groups.

3. The composite semipermeable membrane according to claim 1 or 2, wherein the zeta potential at pH 3 and 10 mM NaCl on the surface of the separation functional layer is 30 mV or more.

4. The composite semipermeable membrane according to any one of claims 1 to 3, wherein the zeta potential at pH 11 and 10 mM NaCl on the surface of the separation functional layer is -30 mV or less.

5. The composite semipermeable membrane according to any one of claims 1 to 4, wherein the positively charged functional group contains an amino group and the negatively charged functional group contains a carboxy group.

6. A method for producing a composite semipermeable membrane comprising a separation functional layer provided on a porous support layer, a step of forming a layer containing crosslinked polyamide by interfacial polymerization on the porous support layer, a step of bonding the layer containing crosslinked polyamide and a hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group, a step of bonding a nanoparticle body mainly composed of a hydrophilic polymer B which is a polymer of a monomer having an ethylenically unsaturated group different from that of the hydrophilic polymer A to the hydrophilic polymer A, A method for producing a composite semipermeable membrane, including.

7. The method for producing a composite semipermeable membrane according to claim 6, wherein one of the hydrophilic polymer A and the hydrophilic polymer B has a positively charged functional group and the other has a negatively charged functional group.

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