JP7687175B2 - Composite semipermeable membrane and method for producing same - Google Patents

Description

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

Regarding the separation of mixtures, there are various techniques for removing substances (e.g. salts) dissolved in a solvent (e.g. water). In recent years, the use of membrane separation has expanded as an energy- and resource-saving process.

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, brackish water, and water containing harmful substances, as well as to produce ultrapure water for industrial use, treat wastewater, and recover valuable materials.

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 in which a gel layer and a polymer are crosslinked on a microporous support membrane, and those with an active layer in which a monomer is polycondensed on a microporous support membrane.

Among these, 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 removal properties.

However, as raw water continuously passes through these membranes, foulants in the raw water adhere to the membrane surface, reducing the amount of water passing through and selective separation.

As a method for improving the dirt resistance (fouling resistance) of a composite semipermeable membrane, a method for introducing a hydrophilic polymer containing an acidic group into the surface of the separation functional layer via an amide bond (Patent Document 2) has been disclosed.

Japanese Patent Application Publication No. 2001-79372 International Publication No. WO 2015/46582

However, when these membranes are used to filter raw water with extremely high turbidity concentrations or raw water containing a variety of pollutants, the amount of hydration of the hydrophilic polymer is likely to decrease, which poses the problem of reduced fouling resistance.

In order to solve the above problems, the present invention includes the following configurations 1 to 7.
1. A composite semipermeable membrane comprising a separation functional layer located on a porous support layer,
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 an ethylenically unsaturated group,
A composite semipermeable membrane, wherein the density of positively charged functional groups Dw and the density of negatively charged functional groups Db within 200 nm from the surface of the separation functional layer satisfy the following (a) to (c), and the zeta potential of the surface of the separation functional layer at pH 7 and NaCl 10 mM 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 is a total of two or more types including one or more types of hydrophilic polymers having a positively charged functional group and one or more types of hydrophilic polymers having a negatively charged functional group.
3. The composite semipermeable membrane according to 1 or 2 above, wherein the surface of the separation functional layer has a zeta potential of 30 mV or more at pH 3 and 10 mM NaCl.
4. The composite semipermeable membrane according to any one of 1 to 3 above, wherein the zeta potential of the surface of the separation functional layer at pH 11 and NaCl 10 mM 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 comprises an amino group, and the negatively charged functional group comprises a carboxy group.
6. A method for producing a composite semipermeable membrane having a separation functional layer provided on a porous support layer, comprising the steps of:
forming a layer comprising a crosslinked polyamide on the porous support layer by interfacial polymerization;
a step of bonding the layer containing the crosslinked polyamide to 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, comprising:
7. The method for producing a composite semipermeable membrane according to 6 above, wherein the hydrophilic polymer A and the hydrophilic polymer B have oppositely charged groups.

The composite semipermeable membrane of the present invention has an appropriately controlled density of positively charged functional groups and negatively charged functional groups on the separation functional layer, and therefore exhibits excellent fouling resistance against a variety of foulants, such as nonionic, anionic, and cationic foulants.

FIG. 1 is a diagram showing a schematic diagram of a method for measuring the thickness of a separation functional layer. FIG. 2 is a diagram showing a schematic diagram of a method for measuring the contact angle between the separation functional layer and water.

(1) Composite Semipermeable Membrane The composite semipermeable membrane described below comprises a porous support layer and a separation functional layer located on the porous support layer.

(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 the performance of separating ions and the like.

The separation functional layer in an embodiment of the present invention contains a thin film whose main component is crosslinked polyamide. The main component refers to a component that accounts for 50% or more by weight of the components of the separation functional layer. By containing 50% or more by weight of crosslinked polyamide, the separation functional layer can exhibit high removal performance. In addition, 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.

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 and the polyfunctional acid halide contains a compound having three or more functionalities.

In order to obtain sufficient separation performance and permeate volume, the thickness of the separation functional layer is, for example, within the range of 0.01 to 1 μm, and preferably within the range of 0.1 to 0.5 μm. The thickness of the separation functional layer can be analyzed by photographing the cross section of the pleated structure with a transmission electron microscope (TEM) and loading the cross section photograph into image analysis software. Specifically, five convex parts of the separation functional layer are selected, and the thickness of the separation functional layer at the convex parts is measured at 10 points for each convex part within a range of 90% from the top of the convex part height, and the arithmetic mean value of a total of 50 points is calculated.

Here, the convex portion of the separation functional layer refers to a convex portion having a height equal to or greater than one-fifth 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 perpendicular to the film surface is observed using 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 curved pleated structure in which convex portions and concave portions are continuously repeated. For this curve, a roughness curve defined based on ISO 4287:1997 is obtained. A cross-sectional image is taken with a width of 2.0 μm in the direction of the average line X of the roughness curve.
The mean line is a straight line defined based on ISO 4287:1997, and is a straight line drawn so that the total area of the region enclosed by the mean line and the roughness curve over the measurement length is equal above and below the mean line.

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

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

These polyfunctional amines may be used alone or in combination of two or more. When two or more are used in combination, 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 amines having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidylpropane.

A polyfunctional acid halide is an acid halide that has at least two halogenated carbonyl groups in one molecule. For example, trifunctional acid halides include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride.

Examples of bifunctional acid halides include aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic bifunctional acid halides such as adipoyl chloride and sebacoyl chloride; and alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride.

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

In these separation functional layers, the amount of hydration water in water of the separation functional layer can be increased by bonding a hydrophilic polymer, which is a polymer of a monomer having an ethylenically unsaturated group, to a thin film mainly composed of crosslinked polyamide. This is known to make it possible to suppress the decrease in water permeability caused by the adhesion of contaminants (foulants) in the raw water to the separation functional layer (fouling), i.e., to improve fouling resistance. Here, fouling resistance can include both suppressing fouling and minimizing the decrease in performance even if fouling occurs.

As a result of extensive research, the inventors have found that when a separation functional layer contains two or more hydrophilic polymers which are polymers of monomers having ethylenically unsaturated groups, the positively charged functional group density Dw and the negatively charged functional group density Db within 200 nm from the surface of the separation functional layer satisfy the following (a) to (c), and the zeta potential of the surface of the separation functional layer at pH 7 and NaCl 10 mM is -10 mV or more and 10 mV or less, it is possible to impart excellent fouling resistance against 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

The positively charged functional group density Dw (hereinafter also referred to as the positively charged group density) being greater than 0.30×10 ⁻⁹ mol/cm ² indicates that the separation functional layer contains a hydrophilic polymer having a positively charged functional group (hereinafter also referred to as the positively charged group) sufficient to retain a sufficient amount of hydration water to impart stable fouling resistance, and the negatively charged functional group density Db (hereinafter also referred to as the negatively charged group density) being greater than 0.30×10 ⁻⁹ mol/cm ² indicates that the separation functional layer contains a hydrophilic polymer having a negatively charged functional group (hereinafter also referred to as the negatively charged group) sufficient to retain a sufficient amount of hydration water to impart stable fouling resistance.

In addition, by making the density ratio of these opposing charged groups greater than 0.9 and less than 1.1, it is possible to effectively exhibit fouling resistance against foulants in a variety of ionic states. The inventors have also clarified that in this case, the zeta potential of the surface of the separation functional layer at pH 7 and NaCl 10 mM is between -10 mV and 10 mV.

The hydrophilic polymer, which is a polymer of a monomer having an ethylenically unsaturated group, is preferably a total of two or more types, including at least one hydrophilic polymer having a positively charged group and at least one hydrophilic polymer having a negatively charged group.

Preferred examples of hydrophilic polymers having positively charged groups include polyethyleneimine, polyallylamine, polyvinylamine, polyamidoamine dendrimers, polyamino acids, polydialkylaminoalkyl(meth)acrylates, polydialkylaminoalkyl(meth)acrylamides, polydiallylalkylamines, polydiallylamine, and chitosan, as well as salts thereof. Among these, polyethyleneimine, polyallylamine, polyvinylamine, polydialkylaminoalkyl(meth)acrylates, polydialkylaminoalkyl(meth)acrylamides, polydiallylalkylamines, polydiallylamine, and chitosan, as well as salts thereof, are particularly preferred from the standpoint of versatility and ease of synthesis.

Examples of hydrophilic polymers having negatively charged groups include hydrophilic polymers that contain monomers having negatively charged groups. Examples of negatively charged groups include carboxy groups, phosphonic acid groups, and sulfonic acid groups. Examples of monomers having carboxy groups include the following: maleic acid, maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, 2-(hydroxymethyl)acrylic acid, 4-(meth)acryloyloxyethyl trimellitic acid and corresponding anhydrides, 10-methacryloyloxydecylmalonic acid, N-(2-hydroxy-3-methacryloyloxypropyl)-N-phenylglycine, and 4-vinylbenzoic acid. Among these, acrylic acid, methacrylic acid, and maleic acid are preferred from the viewpoints of versatility and copolymerizability.

Examples of monomers having a phosphonic acid group include vinyl phosphonic acid, 4-vinylphenyl phosphonic acid, 4-vinylbenzyl phosphonic acid, 2-methacryloyloxyethyl phosphonic acid, 2-methacrylamidoethyl phosphonic 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.

Examples of monomers having a sulfonic acid group include vinyl sulfonic acid, 4-vinylphenyl sulfonic acid, and 3-(methacrylamide)propyl sulfonic acid.

Among these, from the viewpoints of versatility and copolymerizability, it is preferable that the hydrophilic polymer having a negatively charged group is composed of a monomer having a carboxy group, and it is particularly preferable that it contains a monomer unit derived from at least one compound selected from acrylic acid, methacrylic acid, and maleic acid.

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

The weight-average molecular weight of each of these hydrophilic polymers is desirably 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 to provide stable anti-fouling properties. The weight-average molecular weight is more preferably 2,000 or more. There is no particular upper limit to the weight-average molecular weight, but from the viewpoint of ease of handling of the polymer solution, it is preferably 2,000,000 or less.

A 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 is preferably configured to have a layer containing a hydrophilic polymer 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, by the contact angle between the separation functional layer and water being 40 degrees or less. The contact angle here refers to the static contact angle, and means the wettability and hydrophilicity of the surface of the separation functional layer, and the smaller the contact angle, the higher the hydrophilicity.

A method for measuring the contact angle between the separation functional layer and water will be explained using 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 equation, called "Young's equation", holds true.
γ _S = γ _L cosθ+γ _SL
Here, _γS is the surface tension of the separation functional layer, _γL is the surface tension of water, and _γSL is the interfacial tension between the separation functional layer and water. The angle θ between the tangent of the water 2 and the surface of the separation functional layer 1 when this formula is satisfied is called the contact angle. The contact angle gradually decreases over time. The time from when the water lands on the surface of the separation functional layer to when the contact angle is measured is within 25 seconds, and preferably within 15 seconds.

At least one of the hydrophilic polymers, which are polymers of monomers having ethylenically unsaturated groups, is preferably chemically bonded to the thin film mainly composed of crosslinked polyamide. This allows the hydrophilic polymer to be 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 a functional group possessed by the polymer constituting each layer.

It is also preferable that different types of hydrophilic polymers are chemically bonded to each other, preferably by covalent bonds, particularly amide bonds.

Of the two or more hydrophilic polymers contained in the separation functional layer, which are polymers of monomers having ethylenically unsaturated groups, it is preferable that one or more hydrophilic polymers that are not bonded to the thin film mainly composed of crosslinked polyamide form nanoparticles. This is because forming nanoparticles prevents the hydrophilic polymers from penetrating into the polymer chains of the hydrophilic polymers bonded to the separation functional layer, and minimizes the reduction in the amount of water of hydration caused by ionic bonds between the hydrophilic polymers.

If the average particle size of the nanoparticles is 5 nm or more, it is effective in suppressing the decrease in the amount of water of hydration due to ionic bonds between hydrophilic polymers, and is preferably in the range of 5 nm to 50 nm. If the average particle size is 100 nm or more, it may affect the decrease in water permeability of the composite semipermeable membrane, so the average particle size is preferably 100 nm or less.

The nanoparticles can be prepared, for example, by copolymerizing one hydrophilic polymer with another type of polymer in advance. The average particle size of the nanoparticles can be measured with a particle size distribution meter. Here, the average particle size means the median diameter ( _D50 ) in the volume-based particle size distribution measured with a particle size distribution meter.

(1-1-2) Characteristics In the composite semipermeable membrane according to an embodiment of the present invention, the positively charged functional group density Dw and the negatively charged functional group density Db within 200 nm from the surface of the separation functional layer satisfy the following (a) to (c), and the zeta potential at pH 7 of 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

(i) Positively charged functional group density Dw and negatively charged functional group density Db
In an embodiment of the present invention, the positively charged functional group density Dw and the negatively charged 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 fast ions, and the elemental composition in the sample depth direction is read from the scattered ion energy and yield of elastic scattering from atomic nuclei in the sample.

The following method can be used to read the positively charged functional group density Dw using RBS measurement. First, a 5 cm square sample is washed with hot water at 95° C. for 30 minutes. The sample is then immersed in a 1×10 ⁻⁴ M aqueous solution of sodium tungstate adjusted to pH 3 for 30 minutes. After that, in order to remove free tungstic acid, the sample is immersed and washed in pure water for 5 minutes each.

Tungstate ions serve as counter ions for positively charged functional groups. Therefore, the surface density of tungsten attached to the surface in RBS measurement of the obtained sample (unit: 10 ¹⁵ atoms/cm ² ) can be converted into the number of atoms per mole to derive the density of the positively charged groups.

The following method can be used to read the negatively charged functional group density Db using RBS measurement. First, a 5 cm square sample is washed with hot water at 95° C. for 30 minutes. The sample is then immersed in a 50% aqueous solution of methanol for 16 hours, and further immersed in a 1×10 ⁻⁴ M aqueous solution of barium nitrate adjusted to pH 10 for 30 minutes. After that, the sample is immersed and washed in methanol for 5 minutes each to remove free barium.

Barium ions serve as counter ions for negatively charged functional groups. Therefore, the surface density of barium attached to the surface in RBS measurement of the obtained sample (unit: 10 ¹⁵ atoms/cm ² ) can be converted into the number of atoms per mole to derive the density of negatively charged groups.

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

Zeta potential is usually measured using a membrane sample measuring 20 mm x 30 mm, and dispersing polystyrene particles (particle size 520 nm) with a hydroxypropyl cellulose surface coating as standard particles for electrophoresis in an aqueous NaCl solution adjusted to a specified concentration. A measuring device that can be used is, for example, an electrophoretic light scattering photometer ELS-8000 manufactured by Otsuka Electronics.

In the composite semipermeable membrane according to an embodiment of the present invention, the surface zeta potential of the separation functional layer is controlled to be between -10 mV and 10 mV when measured under conditions of pH 7 and 10 mM NaCl. Under conditions that satisfy both (a) and (b) above, the zeta potential being in the above range means that oppositely charged groups are present on the surface of the separation functional layer in a well-balanced manner. This makes it possible to effectively exhibit anti-fouling properties even against foulants in a variety of ionic states.

In addition, the composite semipermeable membrane according to an embodiment of the present invention preferably has a zeta potential of 30 mV or more at pH 3 and 10 mM NaCl, and preferably has a zeta potential of -30 mV or less at pH 11 and 10 mM NaCl.

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 a hydrophilic polymer composition in which the zeta potential is 30 mV or more at pH 3 and 10 mM NaCl, this means that the density of positively charged groups is sufficient to improve fouling resistance. In addition, in a hydrophilic polymer composition in which the zeta potential is -30 mV or less at pH 11 and 10 mM NaCl, this means that the density of negatively charged groups is sufficient to improve fouling resistance.

(1-2) Porous Support Layer The porous support layer serves as a base for forming a separation functional layer, and does not itself have substantial separation performance for ions, etc.
The size and distribution of the pores in the porous support layer are not particularly limited, but a preferred porous support layer has, for example, uniform, fine pores, or gradually larger fine pores from the surface on which the separation functional layer is formed to the other surface, and the size of the fine pores on the surface on which the separation functional layer is formed is 0.1 nm or more and 100 nm or less.

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

The material for the porous support layer may be a homopolymer or copolymer such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, or polyphenylene oxide, either alone or in a blend. Here, the cellulose polymer may be cellulose acetate or cellulose nitrate, and the vinyl polymer may be polyethylene, polypropylene, polyvinyl chloride, or polyacrylonitrile. Among these, the material for the porous support layer is preferably a homopolymer or copolymer such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, or polyphenylene sulfide sulfone. More preferably, the material for the porous support layer is cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone. Among these materials, polysulfone is generally preferred because it is chemically, mechanically, and thermally stable and easy to mold.

For example, a polysulfone solution in N,N-dimethylformamide (DMF) can be cast to a certain thickness onto a tightly woven polyester fabric or polyester nonwoven fabric, and then wet-coagulated in water to obtain a support membrane whose surface is mostly covered with fine pores with diameters of tens of nanometers or less.

The thickness of the support membrane affects the strength of the resulting composite semipermeable membrane and the packing density when it is made into an element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support membrane is preferably in the range of 30 μm to 300 μm, more preferably in the range of 100 μm to 220 μm.

The morphology of the porous support layer can be observed using a scanning electron microscope, a transmission electron microscope, or an atomic force microscope. 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 observed using a high-resolution field emission scanning electron microscope (UHR-FE-SEM) at an accelerating voltage of 3 to 15 kV. The high-resolution field emission scanning electron microscope that can be used is, for example, the S-900 type electron microscope manufactured by Hitachi, Ltd.

The thickness of the porous support layer is preferably in the range of 20 μm to 100 μm. A porous support layer having a thickness of 20 μm or more provides good pressure resistance and a uniform support membrane without defects, so that a composite semipermeable membrane equipped with such a porous support layer can exhibit good salt removal performance. If the thickness of the porous support layer exceeds 100 μm, the amount of unreacted substances remaining during production increases, which may reduce the amount of permeated water and reduce chemical resistance.

(2) Manufacturing Method (2-1) Porous Support Layer Forming Step The porous support layer forming step includes a step of applying a polymer solution to a substrate and a step of immersing the substrate to which the solution has been applied in a coagulation bath to coagulate the polymer.

In the process of applying a polymer solution to a 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.

When polysulfone is used as the polymer, the temperature of the polymer solution when applied is preferably 10°C or higher and 60°C or lower. If the temperature of the polymer solution is within this range, the polymer does not precipitate, and the polymer solution is sufficiently impregnated into the spaces between the fibers of the substrate and then solidified. As a result, the porous support layer is firmly bonded to the substrate due to the anchor effect, and a good support film 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, etc.

After the polymer solution is applied to the substrate, it is preferable that the time until the substrate is immersed in the coagulation bath is 0.1 seconds or more and 5 seconds or less. If the time until the substrate is immersed in the coagulation bath is within this range, the organic solvent solution containing the polymer will be sufficiently impregnated into the spaces between the fibers of the substrate and then solidified. The preferable range of the time until the substrate is immersed in the coagulation bath can be appropriately adjusted depending on the type of polymer solution used, the desired solution viscosity, etc.

Water is generally used as the coagulation bath, but there are no particular limitations as long as it does not dissolve the polymer that is a component of the porous support layer. The membrane form of the resulting support membrane changes depending on the composition of the coagulation bath, and therefore the resulting composite semipermeable membrane also changes. The temperature of the coagulation bath is preferably -20°C or higher and 100°C or lower, and 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 does not become intense, and the smoothness of the membrane surface after membrane formation is maintained. Furthermore, if the temperature is within this range, the coagulation speed is appropriate and membrane formability is good.

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 at this time is preferably 40°C or higher and 100°C or lower, and more preferably 60°C or higher and 95°C or lower. If it is within this range, the shrinkage of the support membrane will not increase and the amount of permeated water will be good. Also, if the temperature is within this range, the washing effect will be sufficient.

(2-2) Formation process of 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) forming a layer comprising a crosslinked polyamide on a porous support layer by interfacial polymerization;
(B) A step of bonding the layer containing the crosslinked polyamide to a hydrophilic polymer A which is a polymer of a monomer having an ethylenically unsaturated group.
(C) A step of bonding a nanoparticle 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.

(2-2-1) Step (A) of forming a layer containing a crosslinked polyamide on a porous support layer by interfacial polymerization
In step (A), for example, a layer containing crosslinked polyamide can be formed by interfacial polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide. The preferred embodiments of the polyfunctional amine and the polyfunctional acid halide are the same as those described above. Hereinafter, step (A) will be described using an example in which a polyfunctional aromatic amine is used as the polyfunctional amine and a polyfunctional aromatic acid chloride is used as the polyfunctional acid halide.

The organic solvent for dissolving the polyfunctional aromatic acid chloride may be any that is immiscible with water, does not destroy the support film, and does not inhibit the reaction for producing the crosslinked aromatic polyamide. Representative examples include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. Considering that they do not destroy the ozone layer, are readily available, are easy to handle, and are safe to handle, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, and the like, or mixtures thereof, are preferably used.

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

To perform interfacial polycondensation on a support film, the surface of the support film is first coated with an aqueous solution of a polyfunctional aromatic amine. 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, and more preferably 0.5% by weight or more and 15% by weight or less.

The method for coating the surface of the support membrane with the aqueous polyfunctional aromatic amine solution may be any method that can uniformly and continuously coat the surface of the support membrane with the aqueous solution, and may be carried out by a known coating method, such as a method of coating the surface of the support membrane with the aqueous solution or a method of immersing the support membrane in the aqueous solution. The contact time between the support membrane and the aqueous polyfunctional aromatic amine solution is preferably within a range of 5 seconds to 10 minutes, and more preferably within a range of 10 seconds to 3 minutes. Next, it is preferable to remove the excess aqueous solution by a draining process. As a method for draining, for example, a method of holding the membrane surface vertically and allowing it to flow naturally may be used. After draining, the membrane surface may be dried to remove all or part of the water in the aqueous solution.

Then, the above-mentioned polyfunctional aromatic acid chloride-containing solution is applied to the support film 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 seconds to 3 minutes, and more preferably 0.1 seconds to 1 minute.

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, which may result in a defect, and if it is too high, it will be disadvantageous in terms of cost, so for example, a concentration of 0.01% by weight or more and 1.0% by weight or less is preferable.

Next, the organic solvent remaining after the reaction is preferably removed by a draining process. For example, the organic solvent can be removed by a method in which the film is held vertically and the excess organic solvent is allowed to flow down by gravity. In this case, the time for holding vertically is preferably from 1 minute to 5 minutes, and more preferably from 1 minute to 3 minutes. Holding for 1 minute or more makes it easier to obtain a crosslinked aromatic polyamide having the desired function, while holding for 3 minutes or less can suppress the occurrence of defects due to over-drying of the organic solvent, thereby suppressing a decrease in performance.

(2-2-2) Step (B) of bonding the layer containing the crosslinked polyamide to 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, may have either a positively charged group or a negatively charged group. However, the hydrophilic polymer A may have both a positively charged group and a negatively charged group as long as the effects of the present invention are not impaired.

It is preferable to use hydrophilic polymer A as an aqueous solution with a weight concentration of 0.001% to 1% by weight. A concentration of 0.001% by weight or more allows it to be bonded to the layer containing crosslinked polyamide efficiently in a relatively short time. Furthermore, a concentration of hydrophilic polymer A of 1% by weight or less forms a moderately thin hydrophilic polymer A layer, suppressing a decrease in water permeability.

The method for bonding the layer containing crosslinked polyamide to the hydrophilic polymer A is not limited as long as the layer containing crosslinked polyamide comes into contact with an aqueous solution of the hydrophilic polymer A. Examples of the method include immersing a membrane having a layer containing crosslinked polyamide on a porous support layer in an aqueous solution, or applying an aqueous solution to the surface of the layer containing crosslinked polyamide.

Here, various reaction aids (condensation promoters) can be used to promote the reaction between the layer containing crosslinked polyamide and the hydrophilic polymer A, i.e., to facilitate bonding between the two. Examples of condensation promoters include 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, and 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate. phosphate, (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, (4,6-dimethoxy-1,3,5-triazin-2-yl)-(2-octoxy-2-oxoethyl)dimethylammonium trifluoromethanesulfonate, S-(1-oxido-2-pyridyl)-N,N,N',N'-tetramethylthiuronium tetrafluoroborate, O-[2-oxoethyl]-N,N,N',N'-tetramethylthiuronium tetrafluoroborate, Examples include 1-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, and fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate.

The reaction time and compound concentration of the layer containing crosslinked polyamide with hydrophilic polymer A can be adjusted as appropriate depending on the solvent, condensation promoter, and chemical structure of the compound used, but 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.

After the reaction, the resulting film may be washed with hot water, an aqueous acid solution, or an aqueous alkali solution to remove any residues.

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

The following is an example of a method for preparing nanoparticles in advance, the main component of which is hydrophilic polymer B in step (C). Note that hydrophilic polymer B must be of a different type from hydrophilic polymer A. Furthermore, it is preferable that hydrophilic polymer A and hydrophilic polymer B have oppositely charged groups.

First, a solution is prepared by mixing a hydrophilic polymer B with a further different hydrophilic polymer C. The type of solvent is preferably water, for example.
Here, the hydrophilic polymer C may be of the same type as the hydrophilic polymer A, or may be different.

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, and more preferably 0.005% by weight or more and 0.05% by weight or less. By keeping the concentrations in this range, nanoparticles of an appropriate size can be prepared.

The weight concentration ratio of hydrophilic polymer B is preferably 1.2 to 10 times that of hydrophilic polymer C, and more preferably 1.5 to 3 times. This makes it possible to prepare nanoparticles whose main component is hydrophilic polymer B.

Hydrophilic polymer B and hydrophilic polymer C are preferably chemically bonded. This makes it possible to stabilize the structure of the nanoparticle body. The chemical bond between hydrophilic polymer B and hydrophilic polymer C is preferably a covalent bond, and more preferably an amide bond.

In order to promote the reaction between hydrophilic polymer B and hydrophilic polymer C, i.e., to facilitate the bonding of the two, various reaction aids (condensation promoters) can be used, specific examples of which include those mentioned above in step (B).

The reaction time between hydrophilic polymer B and hydrophilic polymer C can be adjusted as appropriate depending on the solvent, condensation promoter, and chemical structure of the compound used, but 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.

The method of bonding the thus obtained nanoparticles mainly composed of hydrophilic polymer B with the hydrophilic polymer A may be to carry out the same treatment as in step (B) using a solution containing nanoparticles mainly composed of hydrophilic polymer B on the separation functional layer of the membrane obtained after step (B), i.e., the layer containing crosslinked polyamide in which hydrophilic polymer A is bonded. That is, any method may be used in which the separation functional layer of the membrane obtained after step (B) comes into contact with a solution containing nanoparticles mainly composed of hydrophilic polymer B. Specifically, the membrane obtained after step (B) may be immersed in a solution containing nanoparticles, or a solution containing nanoparticles may be applied to the surface of the separation functional layer of the membrane obtained after step (B). The nanoparticles mainly composed of hydrophilic polymer B may be used in the state of a reaction solution with the hydrophilic polymer C.

(2-2-4) Other Steps Further, a subsequent step of converting the amino groups of the crosslinked polyamide into other functional groups may be provided.
In particular, it is preferable to contact the functional group with a reagent that reacts with the amino group to generate a diazonium salt or a derivative thereof, and convert the functional group. Examples of reagents that react with the amino group to generate a diazonium salt or a derivative thereof 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 generating gas and decomposing, it is preferable to sequentially generate nitrous acid by reacting a nitrite with an acidic solution. In general, nitrite reacts with hydrogen ions to generate nitrous acid (HNO ₂ ), which is efficiently generated when the pH of the aqueous solution is 7 or less, preferably 5 or less, and 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.

The concentration of nitrous acid or nitrite in the reagent that reacts with amino groups to produce a diazonium salt or its derivative is preferably in the range of 0.01% to 1% by weight, more preferably 0.05% to 0.5% by weight. A concentration of 0.01% by weight or more provides sufficient effect, and a concentration of 1% by weight or less makes the solution easy to handle.

The temperature of the aqueous nitrous acid solution is preferably 15°C or higher and 45°C or lower. A temperature of 15°C or higher provides sufficient reaction time, while a temperature of 45°C or lower makes handling easy as decomposition of nitrous acid is unlikely to occur.

The contact time with the aqueous nitrous acid solution may be long enough to produce at least one of the diazonium salt and its derivatives. At high concentrations, the treatment can be completed in a short time, but at low concentrations, a long time is required. Therefore, with a solution of the above concentration, the contact time is preferably within 10 minutes, and more preferably within 3 minutes. The contact method 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 may be used to dissolve the reagent, as long as the reagent dissolves and the composite semipermeable membrane is not eroded. The solution may contain a surfactant, an acidic compound, an alkaline compound, or the like, as long as it does not interfere with the reaction between the amino group and the reagent.

Next, a part of the diazonium salt or its derivative is converted to a different functional group. A part of the diazonium salt or its derivative is converted to a phenolic hydroxyl group, for example, by reacting with water. In addition, when it is brought into contact with a solution containing chloride ions, bromide ions, cyanide ions, iodide ions, fluoroboric acid, hypophosphorous acid, sodium hydrogen sulfite, sulfite ions, aromatic amines, hydrogen sulfide, thiocyanic acid, or the like, it is converted to the corresponding functional group. In addition, when it is brought into contact with an aromatic amine, a diazo coupling reaction occurs, making it possible to introduce aromatic groups onto the film surface. These reagents may be used alone or in a mixture of multiple reagents, or may be brought into contact with different reagents multiple times.

Reagents that undergo diazo coupling reactions include compounds with electron-rich aromatic or heteroaromatic rings. Compounds with electron-rich aromatic or heteroaromatic rings include unsubstituted heteroaromatic ring compounds, aromatic compounds with electron-donating substituents, and heteroaromatic ring compounds with electron-donating substituents. Electron-donating substituents include amino groups, ether groups, thioether groups, alkyl groups, alkenyl groups, alkynyl groups, and aryl groups. Specific examples of the above compounds include aniline, methoxyaniline bonded to a benzene ring in the ortho, meta, or para position, phenylenediamine in which two amino groups are bonded to a benzene ring in the ortho, meta, or para position, 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.

The composite semipermeable membrane obtained by at least steps (a), (b), and (c) can be further improved in solute blocking performance and permeation amount by washing with hot water, preferably at a temperature in the range of 25°C to 90°C for 1 minute to 60 minutes. This washing treatment can be performed any number of times after step (a). However, if the temperature of the hot water is too high, the chemical resistance will decrease if the membrane is cooled rapidly after the hot water washing treatment. Therefore, hot water washing is preferably performed at a temperature in the range of 25°C to 60°C. In addition, when hot water washing is performed at a high temperature of 61°C to 90°C, it is preferable to cool the membrane slowly after the hot water washing treatment. For example, the membrane can be cooled to room temperature by contacting the membrane with hot water of lower temperatures in stages.

In the hot water washing step, the hot water may contain an acid or alcohol. By containing an 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 pH 2 or less, and more preferably pH 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.

In the composite semipermeable membrane obtained by the above-mentioned exemplary manufacturing method, the separation functional layer is considered to have a configuration including a thin film mainly composed of crosslinked polyamide, a hydrophilic polymer A is bonded to the thin film, and nanoparticles mainly composed of hydrophilic polymer B are bonded to the hydrophilic polymer A bonded to the thin film. In other words, the separation functional layer has a configuration in which a layer containing a hydrophilic polymer is formed on a thin film mainly composed of crosslinked polyamide, and the layer containing a hydrophilic polymer is considered to include a hydrophilic polymer A bonded to a thin film mainly composed of crosslinked polyamide, and nanoparticles mainly composed of hydrophilic polymer B bonded to the hydrophilic polymer A.

It is believed that the separation functional layer has a layer containing such a hydrophilic polymer, so that the density of each charged group from the surface of the separation functional layer to 200 nm satisfies the above-mentioned (a) to (c), and the zeta potential at pH 7 and NaCl 10 mM is -10 mV or more and 10 mV or less. In general, when oppositely charged groups are ionically bonded to each other, the respective charged groups cancel each other out and the charges are neutralized. In other words, simply mixing oppositely charged groups on the surface layer of the separation functional layer will result in ionically bonded groups that are easily neutralized. In this case, it is believed to be difficult to achieve both the positively charged group density and the negatively charged group density at or above a predetermined value, particularly to achieve (a) and (b) simultaneously. However, in the present invention, by including one or more hydrophilic polymers bonded to a thin film mainly composed of crosslinked polyamide and nanoparticles mainly composed of one or more other hydrophilic polymers, it is believed that neutralization of the charged groups contained in the hydrophilic polymers bonded to the thin film and the hydrophilic polymers that are nanoparticles can be suppressed. It is presumed that this makes it possible to obtain a composite semipermeable membrane in which the density of positively charged functional groups and the density of negatively charged functional groups on the separation functional layer are appropriately controlled, as described above.

(3) Use of the Composite Semipermeable Membrane The composite semipermeable membrane according to the embodiment of the present invention is preferably used as a spiral-type composite semipermeable membrane element by being wound around a cylindrical water collection pipe having a large number of 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, this element can be connected in series or in parallel and housed in a pressure vessel to form a composite semipermeable membrane module.

The above-mentioned composite semipermeable membranes and their elements and modules can be combined with a pump that supplies raw water to them and a device that pretreats the raw water to form 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 the membrane, allowing water suitable for the purpose to be obtained.

The higher the operating pressure of the fluid separation device, the higher the salt rejection rate, but the more energy required for operation. Also, taking into consideration the durability of the composite semipermeable membrane, the operating pressure when passing the treated water through the composite semipermeable membrane is preferably 0.1 MPa or more and 10 MPa or less. As the supply water temperature increases, the salt rejection rate decreases, but as the temperature decreases, the membrane permeation flux also decreases, so a temperature of 5°C or more and 45°C or less is preferable. In addition, if the supply water pH is high, there is a risk of magnesium scale formation in the case of supply water with a high salt concentration such as seawater, and there is also concern about membrane deterioration due to high pH operation, so operation in the neutral region is preferable.

Raw water to be treated by the composite semipermeable membrane according to the embodiment of the present invention includes liquid mixtures containing 500 mg/L to 100 g/L of TDS (Total Dissolved Solids), such as seawater, brackish water, and wastewater. In general, TDS refers to the total dissolved solids content and is expressed as "weight/volume" or "weight ratio". By definition, it can be calculated from the weight of the residue left after evaporating a solution filtered through a 0.45 micron filter at a temperature of 39.5 to 40.5°C, but it is more convenient to convert it from the practical salinity (S).

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

1. Measurement of Characteristics
(NaCl removal rate)
Water to be evaluated, adjusted to a temperature of 25° C., pH 7, and a sodium chloride concentration of 2,000 ppm, was supplied to the composite semipermeable membrane at an operating pressure of 1.55 MPa to perform membrane filtration. The electrical conductivity of the supply water and the permeated water was measured using an electrical conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. to obtain the practical salinity, i.e., NaCl concentration, of each. The NaCl removal rate was calculated based on the thus obtained NaCl concentration and the following formula. Here, the sodium chloride concentration (ppm) means the concentration based on mass.
NaCl removal rate (%)=100×{1-(NaCl concentration in permeate water/NaCl concentration in feed water)}

(permeated water amount)
In the test described above, the amount of water permeating the membrane of the feed water (NaCl aqueous solution) was measured, and the value converted into the amount of water permeating (cubic meters) per square meter of membrane surface per day was defined as the membrane permeation flux ( ^m3 / ^m2 /day). The membrane performance was measured as follows.

First, the amount of permeated water was measured when an aqueous solution with a pH of 7 and a NaCl concentration of 2,000 mg/L was filtered at a pressure of 1.55 MPa at 25°C for 2 hours, and this was designated as the initial amount of permeated water (F1). Next, polyoxyethylene (10) octylphenyl ether (POEOPE) was added to the aqueous solution to a concentration of 150 mg/L and filtered for 2 hours, and the amount of permeated water was designated as F2. The amount of permeated water was added to the aqueous solution to a concentration of 50 mg/L and filtered for 2 hours, and the amount of permeated water was designated as F3. The amount of permeated water was added to the aqueous solution to a concentration of 10 mg/L and filtered for 2 hours, and the amount of permeated water was designated as F4. F2/F1, F3/F1, and F4/F1 were calculated as the permeated water amount retention rates, respectively.

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

(Preparation of samples for quantitative determination of negatively charged groups)
A 5 cm square sample was washed for 30 minutes in hot water at 95° C. The sample was then immersed in a 50% aqueous solution of methanol for 16 hours, and further immersed for 30 minutes in a 1×10 ⁻⁴ M aqueous solution of barium nitrate adjusted to pH 10. After that, in order to remove free barium, the sample was immersed and washed for 5 minutes each in methanol, and the sample was prepared.

The obtained sample was measured under the following conditions.
Apparatus: Pelletron 3SDH manufactured by National Electrostatics Corporation
Incident ions: ^{4He ++}
Incident energy: 2300 keV
・Incidence angle: 0deg
・Scattering angle: 160deg
Specimen current: 4 nA
Beam diameter: 2 mm
In-plane rotation: None Irradiation amount: 100 μC (4 μC x 25 locations)

The average composition (atomic %) of each element in the surface layer of the sample (composite semipermeable membrane), i.e., from the surface of the separation functional layer to 200 nm, 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 attached element surface densities (10 ⁻⁹ mol/cm ² ) were defined as the positively charged group density Dw and the negatively charged group density Db, respectively.

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

Using the above-mentioned 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.

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

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

(Synthesis Example 3)
An aqueous solution containing 0.02 wt% of PAA having a weight-average molecular weight of 2,000 as hydrophilic polymer B, 0.01 wt% of PEI having 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 nanoparticle solution mainly composed of PAA as hydrophilic polymer B. The average particle size of the nanoparticles was 25 nm.

(Synthesis Example 4)
An aqueous solution containing 0.02 wt % of PAA having a weight-average molecular weight of 2,000 as hydrophilic polymer B, 0.01 wt % of PAAm having 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 nanoparticle solution mainly composed of PAA as hydrophilic polymer B. The average particle size of the nanoparticles was 28 nm.

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

(Synthesis Example 6)
An aqueous solution containing 0.02% by weight of polyethyleneimine (PEI) having a weight-average molecular weight of 25,000 as hydrophilic polymer B, 0.01% by weight of PMA having 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 nanoparticles mainly composed of PEI as hydrophilic polymer B. The average particle size of the nanoparticles was 25 nm.

(2-2. Preparation of composite semipermeable membrane)
(Comparative Example 1)
A 15.0 wt% DMF solution of polysulfone was cast on a polyester nonwoven fabric (air permeability 2.0 cc/cm ² /sec) made of long fibers under the condition of 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 wt% m-PDA aqueous solution, and then excess aqueous solution was removed, and a n-decane solution in which TMC was dissolved so that the concentration was 0.14 wt% was applied so that the surface of the porous support layer was completely wet. Next, in order to remove excess solution from the membrane, the membrane was vertically drained, and dried by blowing air at 25°C using a blower, and then washed with pure water at 40°C to obtain a composite semipermeable membrane of Comparative Example 1.

(Comparative Example 2)
The composite semipermeable membrane obtained in Comparative Example 1 was immersed for 1 minute in a 0.3 wt% aqueous sodium nitrite 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 2 was obtained by washing with pure water at 20° C.

(Comparative Example 3)
On the composite semipermeable membrane obtained in Comparative Example 1, a solution prepared by dissolving polyvinyl alcohol (PVA) having a saponification degree of 99% and a weight-average molecular weight of 2,000 as hydrophilic polymer A in a 3:7 solution of isopropyl alcohol and water to a concentration of 0.25% by weight was applied, and the mixture was dried at 130°C for 5 minutes to obtain a composite semipermeable membrane of Comparative Example 3 in which PVA was disposed on the crosslinked aromatic polyamide.

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

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

(Comparative Example 6)
The composite semipermeable membrane obtained in Comparative Example 1 was contacted 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.

(Comparative Example 7)
The composite semipermeable membrane obtained in Comparative Example 1 was contacted 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.

(Comparative Example 8)
The composite semipermeable membrane obtained in Comparative Example 4 was contacted with an aqueous solution containing 0.01 wt % of PAA having a weight-average molecular weight of 2,000 and 0.1 wt % 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.

(Comparative Example 9)
The composite semipermeable membrane obtained in Comparative Example 5 was contacted with an aqueous solution containing 0.01 wt % of PEI having a weight-average molecular weight of 25,000 and 0.1 wt % 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 9.

(Comparative Example 10)
The composite semipermeable membrane obtained in Comparative Example 4 was contacted 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 10.

(Comparative Example 11)
The composite semipermeable membrane obtained in Comparative Example 5 was contacted 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 11.

Example 1
The composite semipermeable membrane obtained in Comparative Example 4 was contacted with the aqueous solution of nanoparticles containing PAA as a main component 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.

Example 2
The composite semipermeable membrane obtained in Comparative Example 4 was contacted with the aqueous solution of nanoparticles containing PAA as a main component 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.

Example 3
The composite semipermeable membrane obtained in Comparative Example 5 was contacted with the aqueous solution of nanoparticles containing PEI as a main component 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.

Example 4
The composite semipermeable membrane obtained in Comparative Example 5 was contacted with the aqueous solution of nanoparticles containing PAAm as a main component 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.

Example 5
The composite semipermeable membrane obtained in Comparative Example 4 was contacted with the aqueous nanoparticle solution containing PMA as a main component 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.

Example 6
The composite semipermeable membrane obtained in Comparative Example 5 was contacted with the 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.

The characteristics and performance values of the separation functional layer of the composite semipermeable membrane obtained in the above manner are shown in Tables 1 and 2, respectively.

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

Claims (7)

A composite semipermeable membrane comprising a separation functional layer located on a porous support layer,
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 an ethylenically unsaturated group,
A composite semipermeable membrane, wherein the density of positively charged functional groups Dw and the density of negatively charged functional groups Db within 200 nm from the surface of the separation functional layer satisfy the following (a) to (c), and the zeta potential of the surface of the separation functional layer at pH 7 and NaCl 10 mM 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 The composite semipermeable membrane according to claim 1, wherein the hydrophilic polymer is a total of two or more types, including at least one hydrophilic polymer having a positively charged functional group and at least one hydrophilic polymer having a negatively charged functional group. The composite semipermeable membrane according to claim 1 or 2, wherein the zeta potential of the surface of the separation functional layer at pH 3 and NaCl 10 mM is 30 mV or more. The composite semipermeable membrane according to any one of claims 1 to 3, wherein the zeta potential of the surface of the separation functional layer at pH 11 and NaCl 10 mM is -30 mV or less. The composite semipermeable membrane according to any one of claims 1 to 4, wherein the positively charged functional group includes an amino group and the negatively charged functional group includes a carboxy group. A method for producing a composite semipermeable membrane having a separation functional layer provided on a porous support layer, comprising:
forming a layer comprising a crosslinked polyamide on the porous support layer by interfacial polymerization;
a step of bonding the layer containing the crosslinked polyamide to 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, comprising: 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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