Composite semipermeable membrane and spiral membrane element

Abstract

The present invention provides: a composite semipermeable membrane that makes it possible to obtain desired rejection performance and that achieves both antifouling properties and high water-permeability; and a spiral membrane element using the same. The present invention provides a composite semipermeable membrane comprising a porous support, a separation functional layer that is formed of a polyamide-based resin on the porous support, and a coating layer that coats the separation functional layer and that contains a hydrophilic polymer, said composite semipermeable membrane characterized in that: the polyamide-based resin contains constituent components derived from m-phenylenediamine (MPD) and trimesic acid chloride (TMC); the molar ratio (TMC / MPD) of TMC to MPD is within the range of 0.65-1.00; and the separation functional layer, when in the state of being coated with the coating layer, has a surface roughness Ra1 of not less than 60 nm when a region of 5 μm × 5 μm is measured with an atomic force microscope (AFM) in water, and has a surface zeta potential of not less than -20 mV at a pH of 7.

Description

Composite semipermeable membrane and spiral membrane element

[0001] The present invention relates to a composite semipermeable membrane comprising a porous support and a separation functional layer, and a spiral-wound membrane element (hereinafter sometimes abbreviated as "membrane element") using the same.

[0002] RO (reverse osmosis) membranes use pressure as the driving force for separation and are used in a very wide range of fields, such as seawater desalination, the production of ultrapure water, pure water, and sterile water, wastewater treatment and recovery from factories and buildings, and the separation, concentration, and purification of products from various processes in the food and pharmaceutical industries, etc. Reverse osmosis is a technology that works by applying a pressure greater than the osmotic pressure of the liquid to be treated, so high-pressure operation is necessarily required.

[0003] Therefore, in recent years, there has been a demand for composite semipermeable membranes with improved water permeability in order to reduce running costs and environmental loads. However, there is generally a trade-off between blocking performance and water permeability, and it is difficult to obtain a composite semipermeable membrane that achieves both blocking performance and water permeability.

[0004] Conventionally, a known method for increasing the permeation flux (Flux) of a composite semipermeable membrane and reducing the operating pressure is to increase the effective membrane area of ​​the membrane by controlling the surface irregularities of the separation functional layer, as described in Patent Document 1. In addition, since the permeation flux of a composite semipermeable membrane shows a negative correlation with desalination performance, it is also possible to reduce operating energy by adjusting the desalination performance.

[0005] Furthermore, since the operating energy of the membrane element and the frequency of chemical cleaning also have a large impact on the environmental load, the development of membranes with fouling resistance is also desired from the perspective of reducing the environmental load. As a method for imparting fouling resistance to RO membranes, for example, as described in Patent Document 2, a method of coating the surface of the separation functional layer with a polymer such as polyvinyl alcohol (PVA) is known.

[0006] However, when a coating is applied to the membrane surface to impart fouling resistance, the flux tends to decrease, and therefore, the reality is that no composite semipermeable membrane that combines fouling resistance and high water permeability has been reported to date.

[0007] International Publication No. WO2024 / 122107 Japanese Patent Application Laid-Open No. 11-47566

[0008] According to the studies of the present inventors, it was found that in the case of conventional composite semipermeable membranes, the unevenness of the surface of the separation functional layer is not large enough, so that the concave portions are easily filled with the polymer coating (see Figure 4), which causes a decrease in flux. Furthermore, it was found that even in the case of composite semipermeable membranes in which the unevenness of the surface of the separation functional layer is made larger, the flux may decrease depending on the state of the coating, and that non-uniform coating may result in insufficient contamination resistance.

[0009] Therefore, an object of the present invention is to provide a composite semipermeable membrane that can obtain the desired blocking performance while simultaneously achieving both contamination resistance and high water permeability, and a spiral membrane element using the same.

[0010] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that by using a composite semipermeable membrane in which a separation functional layer is formed at a specific composition ratio and whose surface roughness is greater than that of conventional membranes, and by controlling the coating state using the surface roughness in water after coating as an indicator, it is possible to achieve both contamination resistance and high water permeability while maintaining the desired blocking performance, and have completed the present invention. That is, the present invention includes the following aspects.

[0011] [1] A composite semipermeable membrane comprising a porous support, a separation functional layer formed on the porous support from a polyamide resin, and a coating layer covering the separation functional layer and containing a hydrophilic polymer, wherein the polyamide resin contains components derived from m-phenylenediamine (MPD) and trimesoyl chloride (TMC), and the molar ratio of TMC to MPD (TMC / MPD) is in the range of 0.65 to 1.00, and the separation functional layer in a state covered with the coating layer has a surface roughness Ra1 of 60 nm or more when measured in a 5 μm × 5 μm area in water with an atomic force microscope (AFM), and a surface zeta potential at pH 7 of -20 mV or more.

[0012] The composite semipermeable membrane of the present invention can achieve the desired blocking performance while simultaneously achieving both contamination resistance and high water permeability. While the details of the reasons for this are unclear, it is believed to be as follows: Because the molar ratio of TMC to MPD (TMC / MPD) constituting the polyamide resin forming the separation functional layer is 0.65 to 1.00, the crosslinked structure can be loosened while maintaining the desired blocking performance. This loose crosslinked structure is thought to contribute to increasing the surface roughness of the separation functional layer while improving the permeability performance of the material. Furthermore, because the surface roughness in water after coating is 60 nm or more, the increased membrane area due to the increased roughness can be maintained, thereby increasing water permeability. Furthermore, by achieving a surface zeta potential of -20 mV or more at pH 7, it is thought that adsorption of cationic contaminants in particular can be suppressed.

[0013] [2] The composite semipermeable membrane according to [1], which has a rejection of 95% or more at an operating pressure of 2.0 MPa and an NaCl concentration of 500 ppm.

[0014] With this configuration, the rejection rate of NaCl is set lower than that of conventional RO membranes, which improves the permeability of the material and enables it to be used in a wide range of applications. Furthermore, by reducing the operating energy, it can contribute to reducing the environmental load.

[0015] [3] Flux is 3.0 m at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm. ３ / m ２ / d or more.

[0016] Assuming blocking performance as in [2], the flux is 3.0 m ３ / m ２ When the ratio is 1 / d or more, blocking performance and permeability, which are in a trade-off relationship, are both achieved, and the higher permeability allows for further reduction in operating energy.

[0017] [4] The composite semipermeable membrane according to any one of [1] to [3], wherein the flux maintenance rate after exposure to an aqueous solution of a nonionic surfactant having a concentration of 500 ppm by volume for 30 minutes is 50% or more.

[0018] According to this configuration, the stain resistance against nonionic surfactants is improved, and it becomes easier to obtain sufficient stain resistance against other charged substances.

[0019] [5] The composite semipermeable membrane according to any one of [1] to [4], wherein the separation functional layer before being coated with the coating layer has a surface roughness Ra0 of 90 nm or more when measured in an area of ​​5 μm × 5 μm in water with an atomic force microscope (AFM).

[0020] According to this configuration, the surface roughness of the separation functional layer before coating is sufficiently large, so that even after coating, it is easy to make the surface roughness Ra1 60 nm or more, and water permeability can be more reliably increased.

[0021] [6] A spiral membrane element having the composite semipermeable membrane according to any one of [1] to [5].

[0022] The spiral wound membrane element of the present invention has the composite semipermeable membrane of the present invention as described above, and therefore can provide a spiral wound membrane element that not only has the desired blocking performance but also has good fouling resistance and high water permeability.

[0023] According to the present invention, it is possible to provide a composite semipermeable membrane that not only has the desired blocking performance but also has good fouling resistance and high water permeability, and a spiral membrane element using the same.

[0024] 1 is a conceptual diagram schematically illustrating the difference between a separation functional layer of a composite semipermeable membrane in air and a separation functional layer of a composite semipermeable membrane in water. 2 is a partially cutaway perspective view showing an example of a spiral membrane element. 3 is a scanning electron microscope (SEM) photograph showing the composite semipermeable membrane obtained in Example 1, where the photograph on the left shows the state before a coating layer is formed (two locations), and the photograph on the right shows the state after formation (two locations). 4 is a scanning electron microscope (SEM) photograph showing the composite semipermeable membrane obtained in Comparative Example 3, where the photograph on the left shows the state before a coating layer is formed (two locations), and the photograph on the right shows the state after formation (two locations).

[0025] Hereinafter, an embodiment of the present invention will be described.

[0026] (Composite semipermeable membrane) The composite semipermeable membrane of the present invention comprises a porous support, a separation functional layer formed on the porous support from a polyamide resin, and a coating layer covering the separation functional layer and containing a hydrophilic polymer. The polyamide resin forming the separation functional layer contains components derived from m-phenylenediamine (MPD) and trimesoyl chloride (TMC).

[0027] The separation functional layer can be formed by interfacial polymerization of a polyamide resin, and is particularly preferably a separation functional layer containing a polyamide resin obtained by polymerizing a polyfunctional amine component and a polyfunctional acid halogen component. In the present invention, the polyfunctional amine component contains m-phenylenediamine, and the polyfunctional acid halogen component contains trimesoyl chloride, but other polyfunctional amine components or other polyfunctional acid halogen components may also be used.

[0028] The polyfunctional amine component is a polyfunctional amine having two or more reactive amino groups, and examples thereof include aromatic, aliphatic, and alicyclic polyfunctional amines. In the present invention, at least a divalent polyfunctional amine is used as the polyfunctional amine component.

[0029] Examples of aromatic polyfunctional amines other than m-phenylenediamine (MPD) include p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, N,N'-dimethyl-m-phenylenediamine, 2,4-diaminoanisole, amidol, and xylylenediamine.

[0030] Examples of the aliphatic polyfunctional amine include ethylenediamine, propylenediamine, tris(2-aminoethyl)amine, and n-phenyl-ethylenediamine.

[0031] Examples of the alicyclic polyfunctional amine include 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, and 4-aminomethylpiperazine.

[0032] These polyfunctional amines may be used alone or in combination of two or more. In order to obtain a separating functional layer with the desired blocking performance, it is preferable to use an aromatic polyfunctional amine.

[0033] In particular, from the viewpoint of achieving a rejection rate of 95% or more at an operating pressure of 2.0 MPa and an NaCl concentration of 500 ppm, it is preferable to use m-phenylenediamine in an amount of 20 to 100 mol %, more preferably 50 to 100 mol %, and most preferably 100 mol % in the polyfunctional amine component. This allows the separation functional layer to be formed from a polyamide-based resin containing a component derived from m-phenylenediamine.

[0034] The polyfunctional acid halide component is a polyfunctional acid halide having two or more reactive carbonyl groups. Examples of the polyfunctional acid halide include aromatic, aliphatic, and alicyclic polyfunctional acid halides. In the present invention, at least trimesoyl chloride (TMC) is used as the polyfunctional acid halide component.

[0035] Examples of aromatic polyfunctional acid halides other than TMC include terephthalic acid dichloride, isophthalic acid dichloride, biphenyldicarboxylic acid dichloride, naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid trichloride, benzenedisulfonic acid dichloride, and chlorosulfonylbenzenedicarboxylic acid dichloride.

[0036] Examples of the aliphatic polyfunctional acid halides include propanedicarboxylic acid dichloride, butanedicarboxylic acid dichloride, pentanedicarboxylic acid dichloride, propanetricarboxylic acid trichloride, butanetricarboxylic acid trichloride, pentanetricarboxylic acid trichloride, glutaryl halide, and adipoyl halide.

[0037] Examples of alicyclic polyfunctional acid halides include cyclopropanetricarboxylic acid trichloride, cyclobutanetetracarboxylic acid tetrachloride, cyclopentanetricarboxylic acid trichloride, cyclopentanetetracarboxylic acid tetrachloride, cyclohexanetricarboxylic acid trichloride, tetrahydrofurantetracarboxylic acid tetrachloride, cyclopentanedicarboxylic acid dichloride, cyclobutanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride.

[0038] These polyfunctional acid halides may be used alone or in combination of two or more. To obtain a separation functional layer with high salt rejection performance, it is preferable to use an aromatic polyfunctional acid halide. It is also preferable to use a trivalent or higher polyfunctional acid halide as at least a part of the polyfunctional acid halide component to form a crosslinked structure, and it is preferable to use at least trimesoyl chloride (TMC).

[0039] In particular, from the viewpoint of achieving a rejection rate of 95% or more at an operating pressure of 2.0 MPa and an NaCl concentration of 500 ppm, trimesoyl chloride (TMC) is preferably used in an amount of 20 to 100 mol %, more preferably 50 to 100 mol %, and most preferably 100 mol % in the polyfunctional acid halide component. This allows the separation functional layer to be formed from a polyamide-based resin containing a component derived from trimesoyl chloride.

[0040] In the present invention, from the viewpoint of achieving a rejection rate of 95% or more at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm, the molar ratio of TMC to MPD (TMC / MPD) is preferably 0.65 or more, more preferably 0.7 or more, and even more preferably 0.8 or more. ３ / m ２From the viewpoint of achieving a TMC / MPD ratio of 1.00 or more, the molar ratio of TMC to MPD (TMC / MPD) is preferably 1.00 or less, more preferably 0.95 or less, and even more preferably 0.9 or less. Such a molar ratio can be adjusted by increasing or decreasing the concentration or amount of each component.

[0041] The molar ratio of TMC to MPD (TMC / MPD) can be calculated from the peak area value by removing the substrate and porous resin layer from the composite semipermeable membrane, hydrolyzing the resulting separation functional layer in a strong alkaline heavy water solution, filtering the hydrolyzed heavy water solution, and measuring it by 1H-NMR, and analyzing the data obtained by the measurement.

[0042] It was found that when the molar ratio of the trivalent or higher polyfunctional acid halide to the divalent polyfunctional amine is less than 1.5, unreacted terminal carboxylic acids are present, but when the molar ratio is 1.0 or less, the crosslinked structure becomes loose and water permeability is improved.

[0043] In order to improve the performance of the separating functional layer containing a polyamide resin, it may be copolymerized with polymers such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, and polyhydric alcohols such as sorbitol and glycerin.

[0044] The porous support supporting the separation functional layer may be any one having a porous resin layer, and may be formed only from a porous resin layer, but is preferably one that is reinforced by a backing made of a substrate such as a woven fabric, a nonwoven fabric, etc. The porous support having a porous resin layer is not particularly limited as long as it can support the separation functional layer on its upper surface, and typically, an ultrafiltration membrane with an average pore size of about 10 to 500 Å is preferably used.

[0045] Examples of materials for forming the porous resin layer include polysulfone-based resins such as polysulfone, polyethersulfone, and polyphenylsulfone, polyimide, polyetherimide, and polyvinylidene fluoride, but polysulfone-based resins are preferably used because they are particularly chemically, mechanically, and thermally stable.

[0046] The total thickness of the porous support having the porous resin layer is, for example, about 50 to 200 μm, preferably about 80 to 150 μm. The thickness of the porous resin layer is, for example, 10 to 50 μm, preferably 20 to 40 μm. The porosity of the porous resin layer is, for example, 50 to 80%, preferably 60 to 70%.

[0047] Preferred methods for forming a separation functional layer containing a polyamide resin on the surface of a porous support include interfacial condensation. Specifically, the interfacial condensation method involves contacting an aqueous amine solution containing a polyfunctional amine component with an organic solution containing a polyfunctional acid halide component to form a separation functional layer by interfacial polymerization, and then placing the separation functional layer on a porous support. Alternatively, the interfacial polymerization on the porous support is used to directly form a separation functional layer of a polyamide resin on the porous support. Details of the conditions for such interfacial condensation methods are described in JP-A-58-24303 and JP-A-1-180208, and known techniques from these methods can be used as appropriate.

[0048] The separation functional layer formed on the porous support has fine irregularities, and the size of the irregularities can be measured using the surface roughness Ra as an index when a 5 μm × 5 μm area is measured in water with an atomic force microscope (AFM). In this specification, the surface roughness of the separation functional layer before being coated with the coating layer is defined as Ra0, and the surface roughness of the separation functional layer after being coated with the coating layer is defined as Ra1.

[0049] In the present invention, from the viewpoint of making the surface roughness Ra1 of the separation functional layer after being coated with the coating layer 60 nm or more, the surface roughness Ra0 of the separation functional layer before being coated with the coating layer is preferably 90 nm or more, more preferably 95 nm or more, even more preferably 100 nm or more, and particularly preferably 105 nm or more.

[0050] Furthermore, from the viewpoint of preventing defects in the separation functional layer and durability, the surface roughness Ra0 is preferably 150 nm or less, more preferably 140 nm or less, even more preferably 130 nm or less, and particularly preferably 125 nm or less.

[0051] The degree of the fine irregularities of the separation functional layer can be known to some extent from the surface roughness Ra when a 5 μm x 5 μm area is measured in air using an atomic force microscope (AFM). However, compared to this case, using the surface roughnesses Ra0 and Ra1 measured in water as indicators allows for a more appropriate measurement of the fine irregularities of the separation functional layer under conditions closer to those actually used in membrane separation.

[0052] In other words, as shown in Figure 1, the separation function layer 1a formed on the porous support 1b of the composite semipermeable membrane 1 in the atmosphere tends to be observed in a collapsed or crushed state with fine irregularities in the separation function layer 1a compared to the state in which it is actually used for membrane separation, and by using the surface roughness Ra measured in water as an indicator, it becomes possible to more accurately measure the size of the fine irregularities in the separation function layer in a state close to the state in which it is actually used for membrane separation.

[0053] In this specification, the surface roughnesses Ra0 and Ra1 measured in water refer to the planar surface roughness Ra defined by the following formula (Mathematical Formula 1).

[0054]

[0055] Planar surface roughness can be calculated using values ​​measured using an atomic force microscope (AFM). The average surface roughness (Ra) is a three-dimensional extension of the centerline average roughness Ra defined in JIS B0601 so that it can be applied to measurement surfaces, and is the average value of the absolute values ​​of the deviations from the reference surface to the specified surface. Here, the measurement surface refers to the surface indicated by all measurement data, the specified surface refers to the surface that is the target of roughness measurement, and refers to a specific portion of the measurement surface designated by a clip (designated area is 5 μm × 5 μm), and the reference surface refers to the average height of the designated surface, calculated by Z ０ Then, Z = Z ０ This refers to a plane represented by

[0056] Methods for producing composite semipermeable membranes capable of adjusting the surface roughness Ra measured in air are described in, for example, Japanese Patent Application Laid-Open Nos. 9-85068 and 7-8770. In accordance with such production methods, the present invention also makes it possible to adjust the surface roughness Ra while checking the surface roughness Ra measured in water.

[0057] In particular, in a method for producing a composite semipermeable membrane by forming a polyamide-based skin layer (separation functional layer) by a means including a step of coating a porous support with a solution A containing a polyfunctional amine component and a step of contacting the solution A phase with a solution B containing a polyfunctional acid halide component, it is preferable to add an interfacial conditioner such as an alkanolamine compound, an alkyl ketone compound, or an alkyl ester compound to the solution A.

[0058] Examples of the alkanolamine compound include ethanolamine, methanolamine, propanolamine, butanolamine, etc., and may be any of monoalkanolamine, dialkanolamine, and trialkanolamine. In addition, the hydrogen atom bonded to the nitrogen atom of the alkanolamine compound may be substituted with an alkyl group, an alkenyl group, an alkynyl group, a phenyl group, etc. Among these, monoethanolamine, diethanolamine, and triethanolamine are preferred, and monoethanolamine and triethanolamine are more preferred.

[0059] Examples of the alkyl ketone compound include acetone, diisopropyl ketone, and cyclohexanone, and examples of the alkyl ester compound include ethyl acetate, propyl acetate, and butyl acetate.

[0060] The concentration of the interfacial conditioner in the solution A is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 5.0% by mass, from the viewpoint of producing a composite semipermeable membrane having the above-mentioned surface roughness Ra0.

[0061] The surface roughness Ra0 can also be adjusted by the difference in solubility parameter between the solution A and the solution B, or the solubility parameter of a compound added to the solution A and / or the solution B. When producing a composite semipermeable membrane having the above-mentioned surface roughness Ra0, it is preferable to add a compound having a solubility parameter of 8 to 17 (cal / cm) to at least one selected from the solution A, the solution B, and the microporous support. ３ ) １／２ It is preferred that a compound of the formula:

[0062] Examples of the solubility parameter adjuster include alcohols such as ethanol, propanol, butanol, and pentanol, and nitrogen compounds such as ethylamine, triethylamine, and n-butylamine. The solubility parameter can also be adjusted by the type and concentration of the polyfunctional amine component or polyfunctional acid halogen component used.

[0063] In order to improve the salt blocking property, water permeability, and fouling resistance of the composite semipermeable membrane, various conventionally known treatments may be carried out before forming the coating layer.

[0064] (Coating Layer) The composite semipermeable membrane of the present invention is provided with a coating layer that coats the separation functional layer and contains a hydrophilic polymer, and the separation functional layer in a coated state is characterized in that the surface roughness Ra1, when measured in a 5 μm × 5 μm area in water with an atomic force microscope (AFM), is 60 nm or more, and the surface zeta potential at pH 7 is −20 mV or more.

[0065] The hydrophilic polymer contained in the coating layer may be a polymer having a cationic group or a nonionic hydrophilic group, but from the viewpoint of suppressing charged adsorption, a polymer having a nonionic hydrophilic group is preferred. Examples of nonionic hydrophilic groups include -OH, -NHCO-, -O-, and organic groups represented by the following structural formulas:

[0066]

[0067] Examples of such polymers having electrically neutral hydrophilic groups include polyvinyl alcohol, saponified polyethylene-vinyl acetate copolymer, polyvinylpyrrolidone, hydroxypropyl cellulose, polyethylene glycol, etc. A more preferred hydrophilic polymer is an organic polymer having a nonionic hydrophilic group that is insoluble in water at 25°C and soluble in hot water, such as polyvinyl alcohol. Such solubility can be adjusted by the degree of saponification, weight average molecular weight, etc. of the polyvinyl alcohol.

[0068] When using polyvinyl alcohol, a saponification degree of 95% or higher, preferably 99-100%, is recommended. In this case, polyvinyl alcohol is insoluble in water at 25°C due to intermolecular hydrogen bonding, but is soluble in hot water. Meeting these conditions is advantageous because the increased hydrophilicity due to the high number of -OH groups on the membrane surface in contact with the treated water enhances the ability to inhibit contaminant adsorption and increases the amount of permeated water, thereby providing excellent membrane performance. Furthermore, polymers containing cationic groups are preferably polymers containing quaternary ammonium groups, such as diallylamine hydrochloride polymer, diallylamine hydrochloride-maleic acid copolymer, allylamine amide sulfate polymer, allylamine hydrochloride polymer, and cationized cellulose. Coating the surface of the separation functional layer with these hydrophilic polymers allows for control of the surface charge of the separation functional layer. Surface zeta potential is a suitable measure of surface charge analysis. The coating layer may also contain a crosslinking agent, surfactant, or the like for crosslinking the hydrophilic polymer.

[0069] A method for forming a coating layer containing a hydrophilic polymer on a composite semipermeable membrane involves applying a solution of the hydrophilic polymer to the composite semipermeable membrane and then drying it to obtain a composite semipermeable membrane with a controlled surface charge. The hydrophilic polymer is used by dissolving it in a solvent that does little damage to the separating functional layer of the composite semipermeable membrane, such as water, a lower alcohol, a halogenated hydrocarbon, an aliphatic hydrocarbon, acetone, acetonitrile, or a mixed solution of at least two of these.

[0070] Among these solvents, preferred examples include aliphatic alcohols such as methanol, ethanol, propanol, and butanol, halogenated aliphatic alcohols such as ethylene chlorohydrin, methoxymethanol, methoxyethanol, and mixed solvents of at least one of these lower alcohols with water.

[0071] In the case of a mixed solvent, the ratio of lower alcohol to water is not particularly limited, but the ratio of water is preferably 0% to 90%. When water is used as a solvent, it is also preferable to add a surfactant to improve wettability with the film.

[0072] The concentration of the hydrophilic polymer solution prepared using the above solvent is, for example, 0.01 to 20% by weight, preferably 0.05 to 5% by weight, and more preferably 0.1 to 2% by weight. The coating method is not particularly limited, but dipping, transfer, spraying, and the like are preferably used. The drying method and drying temperature after coating are also not particularly limited, but are in the range of 20°C to 200°C, preferably 50°C to 170°C, and more preferably 100°C to 150°C.

[0073] The separation functional layer when coated with the coating layer has a surface zeta potential of −20 mV or more at pH 7, but from the viewpoint of further improving contamination resistance, the surface zeta potential at pH 7 is preferably −15 to 15 mV, and more preferably −10 to 10 mV.

[0074] The surface zeta potential at pH 7 can be adjusted by the type of hydrophilic polymer, the concentration of the hydrophilic polymer in the solution, the method of applying the solution, the amount of the solution applied, the uniformity of the applied state of the hydrophilic polymer, etc. When the hydrophilic polymer is applied non-uniformly, the surface zeta potential tends to be less than −20 mV.

[0075] On the other hand, the separation functional layer in a state coated with the coating layer has a surface roughness Ra1 of 60 nm or more when measured in a 5 μm × 5 μm area with an atomic force microscope (AFM) in water, but from the viewpoint of obtaining high water permeability while obtaining the desired blocking performance, the surface roughness Ra1 is preferably 70 nm or more, more preferably 75 nm or more, and even more preferably 80 nm or more. Furthermore, from the viewpoint of preventing defects in the separation functional layer, durability, etc., the surface roughness Ra1 is preferably 150 nm or less, more preferably 140 nm or less, and even more preferably 130 nm or less.

[0076] The surface roughness Ra1 of the separation functional layer in a state coated with the coating layer can be adjusted by adjusting the surface roughness Ra0 of the separation functional layer before the coating layer is coated, but it can also be adjusted by the amount of coating layer and the coating state. For example, if a composite semipermeable membrane having a relatively large surface roughness Ra0 is used and as little coating layer as possible is applied within a range in which the surface zeta potential is −20 mV or more, the surface roughness Ra1 becomes relatively large compared to the surface roughness Ra0, which is preferable from the viewpoint of obtaining high water permeability while obtaining the desired blocking performance.

[0077] Therefore, the larger the ratio R = Ra1 / Ra0, the more advantageous it is for obtaining high water permeability while maintaining the desired blocking performance. Therefore, from the viewpoint of obtaining high water permeability while maintaining the desired blocking performance, the ratio R = Ra1 / Ra0 is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. This is more effective in controlling the surface roughness after coating and the amount of coating layer coverage using the surface roughness Ra1 as an index in the present invention. If the ratio R = Ra1 / Ra0 is too large, the coating state of the coating layer is likely to become non-uniform. Therefore, the ratio R = Ra1 / Ra0 is preferably 0.95 or less, more preferably 0.9 or less.

[0078] The composite semipermeable membrane of the present invention preferably has a rejection of 95% or more at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm, but the rejection can also be set to 97% or more, 98% or more, or 99% or more depending on the application.

[0079] In particular, when the rejection rate is 95% or more at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm, the composite semipermeable membrane of the present invention has a flux of 3.0 m at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm. ３ / m ２ / d or more, and preferably the flux is 3.2 m ３ / m ２ / d or more, and more preferably, the flux is 3.4 m ３ / m ２ / d or more, and more preferably, the flux is 3.5 m ３ / m ２ / d or more.

[0080] The composite semipermeable membrane of the present invention preferably has a flux retention rate of 50% or more after 30 minutes of exposure to an aqueous solution of a nonionic surfactant with a concentration of 500 ppm by volume, but from the viewpoint of making it easier to obtain higher contamination resistance against other charged substances, the flux retention rate is more preferably 70% or more, and even more preferably 90% or more. As described above, the composite semipermeable membrane of the present invention is one in which the separation functional layer is formed at a specific composition ratio, and by using a composite semipermeable membrane whose surface roughness is greater than that of conventional ones, and by controlling the coating state using the surface roughness in water after coating and the surface zeta potential as indicators, it is possible to achieve both contamination resistance and high water permeability while maintaining the desired blocking performance.

[0081] (Spiral-type membrane element) The spiral-type membrane element of the present invention is characterized by having the composite semipermeable membrane as described above, and any of the conventional membrane element configurations can be adopted for the parts other than the composite semipermeable membrane.

[0082] The spiral membrane element of the present invention comprises, for example, a perforated central tube 5 and a wound body R wound around the central tube 5 and including a separation membrane 1, as shown in FIG.

[0083] 2 , the device includes a plurality of membrane leaves L, each having a permeate-side channel material 3 interposed between opposing separation membranes 1, a feed-side channel material 2 interposed between the membrane leaves L, a perforated central tube 5 around which the membrane leaves L and the feed-side channel material 2 are wound, and a sealing portion 12 that prevents mixing of the feed-side channel and the permeate-side channel. In this case, the permeate-side channel within the membrane leaf L can be formed by the permeate-side channel material 3 (also referred to as a permeate-side spacer).

[0084] It is also possible to form the feed-side flow path and / or the permeate-side flow path in the separation membrane 1 itself by providing irregularities or grooves on the surface of the separation membrane 1, and in this case, it is possible to omit the feed-side flow path material 2 and / or the permeate-side flow path material 3.

[0085] 2 shows an example in which the sealed portion includes both end sealed portions and an outer peripheral sealed portion 12. Of the sealed portions, the both end sealed portions are formed by sealing two edge portions on both sides of the membrane leaf L in the axial direction A1 with an adhesive. The outer peripheral sealed portion 12 is formed by sealing the edge portion at the outer peripheral tip of the membrane leaf L with an adhesive. The region surrounded by the opposing separation membranes 1, the both end sealed portions, and the outer peripheral sealed portion 12 forms a permeate-side flow path, which is structured to communicate with the openings 5a of the central tube 5.

[0086] It is also preferable to have a central sealing portion in which the perforated central tube 5 and the base end sides of both end sealing portions of the membrane leaf L are sealed with an adhesive. The membrane leaf L and the feed-side channel material 2 are wound around the central tube 5 via such a central sealing portion to form a wound body R. The adhesive is not particularly limited, and any conventionally known adhesive such as a urethane adhesive or an epoxy adhesive can be used.

[0087] A first end member 10 having a function such as a seal carrier may be provided on the upstream side of the membrane element wound body R, and a second end member 20 having a function such as an anti-telescope material may be provided on the downstream side.

[0088] In a typical 8-inch diameter spiral membrane element, about 15 to 30 sets of membrane leaves L are wound. When the membrane element is in use, it is housed in a pressure vessel, and a feed liquid 7 is supplied from one end face of the membrane element. The supplied feed liquid 7 flows along the feed-side flow path material 2 in a direction parallel to the axial direction A1 of the central tube 5, and is discharged from the other end face of the membrane element as a concentrated liquid 9. In addition, permeated liquid 8, which has permeated through the separation membrane 1 while the feed liquid 7 flows along the permeation-side flow path material 3, flows through the permeation-side flow path material 3, and then flows into the central tube 5 through the openings 5a and is discharged from the end of the central tube 5.

[0089] The feed-side channel material 2 generally serves to ensure gaps for uniformly supplying the fluid to the membrane surface. For example, nets, knitted fabrics, textured sheets, etc. can be used as such feed-side channel material 2, and those with a maximum thickness of approximately 0.1 to 3 mm can be used as needed. Furthermore, when channel materials are installed on both sides of the separation membrane 1, different channel materials are generally used as the feed-side channel material 2 on the feed liquid side and the permeate-side channel material 3 on the permeate side. It is preferable to use a thick, coarse-mesh net-like channel material for the feed-side channel material 2, while using a fine-mesh woven or knitted channel material for the permeate-side channel material 3.

[0090] When RO membranes or NF membranes are used in applications such as seawater desalination and wastewater treatment, the permeate-side channel material 3 is provided so as to be interposed between opposing separation membranes 1 in the membrane leaf L. This permeate-side channel material 3 is required to support the pressure applied to the membrane from the back side of the membrane and to ensure a channel for the permeate 8.

[0091] In order to ensure such a function, the permeate side channel material 3 is preferably formed of a tricot knit fabric, and more preferably, the tricot knit fabric is subjected to a resin impregnation reinforcement or fusion treatment after the knit fabric is formed.

[0092] The composite semipermeable membrane of the present invention described above is used as separation membrane 1. That is, the spiral membrane element of the present invention is a composite semipermeable membrane comprising a porous support, a separation functional layer formed on the porous support from a polyamide resin, and a coating layer containing a hydrophilic polymer and covering the separation functional layer, wherein the polyamide resin contains components derived from m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the molar ratio of TMC to MPD (TMC / MPD) is in the range of 0.65 to 1.00, and the separation functional layer in a state coated with the coating layer has a surface roughness Ra1 of 60 nm or more when measured in a 5 μm × 5 μm area in water with an atomic force microscope (AFM), and a surface zeta potential at pH 7 of −20 mV or more.

[0093] In the case of a typical spiral membrane element, an outer periphery of the wound body R is provided with an exterior material 15. The exterior material 15 is not particularly limited, and examples thereof include various sheets, films, tapes, etc., and, if necessary, a fiber-reinforced resin (FRP) or the like is used for reinforcement. A preferred method for forming the fiber-reinforced resin is to use roving, in which fibers are impregnated with a curable resin, and wrap this around the outer periphery of the wound body R.

[0094] (Applications) The composite semipermeable membrane and spiral-wound separation membrane element of the present invention can reduce the environmental load, which has been in increasing demand in recent years, particularly by reducing the operating pressure and the number of cleaning operations, and can therefore be widely used in various membrane separation applications such as the production of drinking water, the treatment of wastewater, and the recovery of valuable resources.

[0095] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, physical properties were measured or evaluated by the following methods. The physical properties in the present invention are specifically values ​​measured by the following methods.

[0096] (1) Molar ratio (TMC / MPD) The prepared composite semipermeable membrane was immersed in cyclohexanone, and the polyamide resin in the skin layer was recovered. The recovered polyamide resin was then collected in a stainless steel tube, and methanol and an alkali were added thereto. The mixture was heated at 240°C for 1 hour to decompose the polyamide resin. After that, the mixture was allowed to cool to room temperature, and the decomposition liquid was collected. １ H-NMR measurement (measurement conditions: apparatus BRUKER Biospin, AVANCE III-600, measurement solvent: DMSO-d6, chemical shift reference: 2.50 ppm (deuterated DMSO), integration 64 times, chemical shifts: metaphenylenediamine (7.56 ppm), trimesoyl chloride (8.60 ppm) was performed. The data obtained by the measurement was analyzed, and the molar ratio of trimesoyl chloride (TMC) to m-phenylenediamine (MPD) (TMC / MPD) was calculated from the peak area values.

[0097] (2) Surface Roughness Ra1 Measured by AFM in Water In this specification, the surface roughness Ra means the roughness of a flat surface, and is defined by the following equation (Equation 2).

[0098]

[0099] The surface roughness Ra defined by the above formula was calculated using values ​​measured using an atomic force microscope (AFM) (AFM5300E, manufactured by Hitachi High-Tech Science Corporation). The average surface roughness (Ra) is a three-dimensional extension of the centerline average roughness Ra defined in JIS B0601 so that it can be applied to the measurement surface, and is the average value of the absolute value of the deviation from the reference surface to the designated surface. Here, the measurement surface refers to the surface indicated by all measurement data, the designated surface refers to a specific portion of the measurement surface that is the target of roughness measurement and is designated by a clip (designated area is 5 μm × 5 μm), and the reference surface refers to the average height of the designated surface, Z ０ Then, Z = Z ０ This refers to a plane represented by

[0100] For the prepared composite semipermeable membranes, measurements were performed with the composite semipermeable membranes on which a coating layer was formed immersed in ultrapure water. For commercially available products, measurements were performed using a composite semipermeable membrane that was purchased as a dry membrane, a coating layer was formed, and then immersed in ultrapure water. The sample immersed in ultrapure water was placed in a holder for liquid measurement while maintaining the wet state, and the liquid holder was filled with ultrapure water to perform AFM measurements. AFM measurements in water were performed on three samples each, and the average value of the surface roughness Ra1 was calculated.

[0101] (3) Surface roughness Ra0 before coating The surface roughness Ra0 of the composite semipermeable membrane before coating with a coating layer was measured by AFM in water in the same manner as in (2) above, except that the measurement sample was changed. That is, for the prepared composite semipermeable membrane, the measurement sample was a composite semipermeable membrane obtained after the drying step before the formation of the coating layer, which was temporarily hydrophilized by passing water under pressure, and stored immersed in ultrapure water to be in a wet state, and the measurement was performed using this. For commercially available products, a dried membrane was purchased, temporarily hydrophilized by passing water under pressure, and then immersed in ultrapure water, and the measurement was performed using this composite semipermeable membrane.

[0102] The ratio (-) of the surface roughness Ra1 after coating with the coating layer to the surface roughness Ra0 before coating with the coating layer was calculated by Ra1 / Ra0.

[0103] (4) Surface Zeta Potential After thoroughly washing the obtained composite semipermeable membrane, the electrical mobility of the surface of the composite semipermeable membrane was measured using an electrophoretic light scattering device (ELS-800; manufactured by Otsuka Electronics Co., Ltd.). The surface zeta potential was calculated from the obtained electrical mobility according to the following formula: U = εζ / 4πη (where U: electrical mobility, ε: dielectric constant of the solution, ζ: surface zeta potential, η: viscosity of the solution). More specifically, the composite semipermeable membrane was cut to approximately 30 x 60 mm and placed in a flat sample cell attached to the above-mentioned measuring device. The standard particles used for electrophoresis were polystyrene particles (520 nm) with their surfaces coated with hydroxypropyl cellulose dispersed in a 10 mM NaCl solution (pH 7).

[0104] (5) Flux and Rejection of NaCl Aqueous Solution An aqueous solution of NaCl was prepared by dissolving NaCl in RO water at a concentration of 500 ppm. The flat composite semipermeable membrane was cut to a predetermined shape and size and placed in a cell (effective membrane surface area: 44.2 cm) of a cross-flow test system for flat membrane evaluation. ２ ) was set. An aqueous NaCl solution (temperature: 25°C) was allowed to permeate through the composite semipermeable membrane at an operating pressure of 2.0 MPa for 30 minutes. Thereafter, a membrane separation operation was carried out, and the permeation rate of the permeated water was measured, and the permeation flux (m ３ / m ２ / d) was calculated.

[0105] After 2 minutes had elapsed, the permeated liquid, the concentrated liquid, and the feed liquid were subjected to conductivity measurement using a conductivity measuring device, and the NaCl rejection rate was calculated from the results and the calibration curve (concentration - conductivity) according to the following formula: NaCl rejection rate (%) = (1 - (NaCl concentration in permeated liquid / (NaCl concentration in feed liquid + NaCl concentration in concentrated liquid) / 2)) x 100

[0106] (6) Evaluation of anti-fouling properties by nonionic surfactants The permeation flux of the obtained composite semipermeable membrane was measured as follows. First, a flat composite semipermeable membrane was cut into a predetermined shape and size, and placed in a cell (effective membrane surface area: 44.2 cm) of a cross-flow test system for flat membrane evaluation. ２ ) The pressure was set to 1.5 MPa. RO water (temperature 25°C) was allowed to permeate through the composite semipermeable membrane for 30 minutes. The permeation rate of the permeated water obtained by this operation for 30 minutes was measured, and the permeation flux was calculated.

[0107] Next, an aqueous solution (temperature 25°C) containing 500 ppm by volume of a nonionic surfactant (manufactured by Fujifilm Electronic Materials Co., Ltd., NCW1002) was subjected to membrane separation at an operating pressure of 1.5 MPa, and the aqueous solution was contacted with the composite semipermeable membrane for 30 minutes. Then, RO water (temperature 25°C) was subjected to membrane separation at an operating pressure of 1.5 MPa for 30 minutes. The permeation rate of the permeated water obtained by this operation for 30 minutes was measured, and the permeation flux was calculated. The permeation flux maintenance rate was calculated using the following formula. The results are shown in Table 1.

[0108] Flux maintenance rate (%) = 100 × (flux of RO water after contact with nonionic surfactant) / (flux of RO water before contact with nonionic surfactant). When the flux maintenance rate is 50% or more, the contamination resistance against various contaminants is sufficient.

[0109] Example 1: An aqueous amine solution containing 2.5% by mass of m-phenylenediamine (MPD), 0.1% by mass of sodium dodecyl sulfate, 2.6% by mass of triethylamine, 1.7% by mass of monoethanolamine, 0.03% by mass of sodium hydroxide, 6% by mass of camphorsulfonic acid, 1.5% by mass of magnesium nitrate, and 4% by mass of isopropyl alcohol was applied to a polysulfone porous support formed on a polyester nonwoven fabric, and then excess amine aqueous solution was removed to form an aqueous solution coating layer. Next, the surface of the aqueous solution coating layer was immersed for 7 seconds in an acid chloride solution prepared by dissolving 0.2% by mass of trimesoyl chloride (TMC) and 0.2% by mass of 2-methyl-2-butanol in a naphthenic solvent (Exxsol D40, manufactured by ExxonMobil Corporation). Thereafter, excess solution on the surface of the aqueous solution coating layer was removed, followed by air drying for 20 seconds and then holding in a hot air dryer at 140°C for 3 minutes to form a separating function layer containing a polyamide resin on the porous polysulfone support layer, thereby forming a composite semipermeable membrane having a nonwoven fabric substrate, a polysulfone porous support layer, and a polyamide separating function layer arranged in this order. The surface roughness Ra0 of this composite semipermeable membrane before the formation of the coating layer was as shown in Table 1.

[0110] Next, 0.1 mass% of polyvinyl alcohol (PVA) (JC-25 manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree ≧99%, viscosity (4%, 20°C) 62.0 to 72.0 mPa·s), 10 mass% of isopropyl alcohol (IPA), and 89.9 mass% of water were uniformly mixed and dissolved to obtain a coating solution. The surface of the separation functional layer of the composite semipermeable membrane produced above was immersed in this coating solution for 10 seconds. Thereafter, the separation functional layer was air-dried for 30 seconds and further held in a hot air dryer at 120°C for 2 minutes to form a coating layer. The evaluation results of the composite semipermeable membrane on which the coating layer was formed are shown in Table 1, along with the coating conditions. A scanning electron microscope (SEM) photograph of the obtained composite semipermeable membrane is shown in Figure 3. From this photograph, it can be seen that in the composite semipermeable membrane of the present invention, the fine irregularities of the separation functional layer before the coating layer is applied are sufficiently large, and by forming the coating layer on top of this in an appropriate application state, the fine irregularities of the separation functional layer are sufficiently maintained.

[0111] (Example 2) A composite semipermeable membrane was produced under the same conditions as in Example 1, except that the interfacial conditioner used in Example 1 was changed from 1.7% by mass of monoethanolamine to 1.7% by mass of diethanolamine. The evaluation results are shown in Table 1.

[0112] (Example 3) A composite semipermeable membrane was produced under the same conditions as in Example 1, except that the interfacial conditioner in Example 1 was changed from 1.7% by mass of monoethanolamine to 2.0% by mass of triethanolamine. The evaluation results are shown in Table 1.

[0113] Example 4 A composite semipermeable membrane was prepared under the same conditions as in Example 1, except that the concentration of PVA in Example 1 was changed to the concentration shown in Table 1. The evaluation results are shown in Table 1.

[0114] (Example 5) A composite semipermeable membrane was prepared under the same conditions as in Example 1, except that 0.1% by mass of poly(2-ethyl-2-oxazoline) (PEOX) (Sigma-Aldrich, weight-average molecular weight: 50,000 g / mol) was used instead of PVA. The evaluation results are shown in Table 1.

[0115] Comparative Example 1 A composite semipermeable membrane was produced under the same conditions as in Example 1, except that monoethanolamine was not used as an interfacial conditioner and an amine aqueous solution was prepared so that the other components had the same concentrations. The evaluation results are shown in Table 1.

[0116] Comparative Example 2 A composite semipermeable membrane was produced under the same conditions as in Example 1, except that the amount of monoethanolamine used as the interface conditioner was changed from 1.7% by mass to 4.0% by mass. The evaluation results are shown in Table 1.

[0117] (Comparative Example 3) A composite semipermeable membrane was produced under the same conditions as in Example 1, except that a coating layer was formed under the same conditions using a commercially available dried NF membrane (NF90-400, manufactured by DuPont). The evaluation results are shown in Table 1. A scanning electron microscope (SEM) photograph of the obtained composite semipermeable membrane is shown in Figure 4. This photograph shows that in the composite semipermeable membrane of Comparative Example 3, the fine irregularities in the separation functional layer before the coating layer was applied were small, and the fine recesses in the separation functional layer were easily filled when the coating layer was applied.

[0118] Comparative Example 4 A commercially available dried NF membrane (NF90-400, manufactured by DuPont) was used without forming a coating layer. The evaluation results are shown in Table 1.

[0119] Comparative Example 5 A composite semipermeable membrane was prepared under the same conditions as in Example 1, except that the concentration of PVA in Example 1 was changed to the concentration shown in Table 1. The evaluation results are shown in Table 1.

[0120]

[0121] As shown in the results in Table 1, in Examples 1 to 5, the desired blocking performance was obtained, and composite semipermeable membranes that were both anti-fouling and had high water permeability were obtained.

[0122] In contrast, Comparative Example 1, in which the surface roughness Ra1 after the formation of the coating layer was small, had insufficient water permeability. Furthermore, Comparative Example 2, in which the molar ratio (TMC / MPD) was too high, had a surface zeta potential of -20 mV or less, and thus had insufficient fouling resistance. Comparative Example 3, in which a commercially available NF membrane was used to form a coating layer, had a small surface roughness Ra1, a small molar ratio (TMC / MPD), and therefore insufficient water permeability. Comparative Example 4, in which a commercially available NF membrane was used without forming a coating layer, had low water permeability relative to the rejection rate, a surface zeta potential of -20 mV or less, and therefore also had insufficient fouling resistance.

[0123] In Comparative Example 5, in which the concentration was low when forming the coating layer, uniform coating could not be achieved, the surface zeta potential was −20 mV or less, and the stain resistance was insufficient.

[0124] According to the present invention, it is possible to provide a composite semipermeable membrane that not only achieves the desired blocking performance but also combines fouling resistance with high water permeability, and a spiral membrane element using the same.

[0125] In recent years, there has been a tendency for the requirements for blocking performance to change depending on the application of composite semipermeable membranes, and new requirements include the reduction of environmental load (CO ２ The composite semipermeable membrane of the present invention is particularly effective as a technology for reducing such environmental loads.

[0126] 1: Separation membrane 1a: Separation functional layer 1b: Porous support 5: Center tube A1: Axial direction R: Wound body

Claims

1. A composite semipermeable membrane comprising a porous support, a separation functional layer formed on the porous support from a polyamide resin, and a coating layer covering the separation functional layer and containing a hydrophilic polymer, wherein the polyamide resin contains components derived from m-phenylenediamine (MPD) and trimesoyl chloride (TMC), and the molar ratio of TMC to MPD (TMC / MPD) is in the range of 0.65 to 1.00, and the separation functional layer in a state covered with the coating layer has a surface roughness Ra1 of 60 nm or more when measured in a 5 μm x 5 μm area in water with an atomic force microscope (AFM), and a surface zeta potential at pH 7 of -20 mV or more.

2. The composite semipermeable membrane according to claim 1, which has a rejection of 95% or more at an operating pressure of 2.0 MPa and an NaCl concentration of 500 ppm.

3. Flux is 3.0 m at an operating pressure of 2.0 MPa and a NaCl concentration of 500 ppm. ３ / m ２ The composite semipermeable membrane according to claim 2, wherein the ρ is 0.1 / d or more.

4. The composite semipermeable membrane according to claim 1, which has a flux retention rate of 50% or more after being exposed to an aqueous solution of a nonionic surfactant having a concentration of 500 ppm by volume for 30 minutes.

5. The composite semipermeable membrane according to claim 1, wherein the separation functional layer before being coated with the coating layer has a surface roughness Ra0 of 90 nm or more when measured in an area of ​​5 μm × 5 μm in water with an atomic force microscope (AFM).

6. A spiral-wound membrane element having the composite semipermeable membrane according to any one of claims 1 to 5.

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