Composite semipermeable membrane, separation membrane element, and liquid separation device

Abstract

The purpose of the present invention is to provide a composite semipermeable membrane having both high chemical resistance and high scratch resistance. The present invention relates to a composite semipermeable membrane comprising a porous support layer and a separation function layer on the porous support layer, the separation function layer containing a polyamide, wherein the composite semipermeable membrane has, on a surface of the separation function layer, a structure having three or more consecutive repeating units, each of which is represented by general formula (I) or general formula (II) described in the specification, with at least one repeating unit containing a nitrogen atom.

Description

Composite semipermeable membranes, separation membrane elements, and liquid separation devices

[0001] The present invention relates to a composite semipermeable membrane comprising a separation functional layer containing polyamide, a separation membrane element comprising the composite semipermeable membrane, and a liquid separation apparatus comprising the separation membrane element.

[0002] Semipermeable membranes used for separating liquid mixtures include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These semipermeable membranes are used, for example, in the production of drinking water from water containing salt or harmful substances, the production of industrial ultrapure water, wastewater treatment, or the recovery of valuable materials.

[0003] Most reverse osmosis and nanofiltration membranes currently on the market are composite semipermeable membranes. A typical example of a composite semipermeable membrane is a polyamide semipermeable membrane, which comprises a porous support layer and a separation functional layer made of polyamide obtained by the polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide, covering the porous support layer. It exhibits high water permeability and selective separation capabilities.

[0004] However, if oxidizing agents such as chlorine, supplied for cleaning pipes and other equipment, become mixed into the liquid supplied to the composite semipermeable membrane, the oxidizing agent may degrade the membrane, reducing its removal performance. Furthermore, alkalis may be supplied to enhance the cleaning effect of oxidizing agents such as chlorine, or acids may be supplied to clean fouling caused by metal compounds that are difficult to decompose with oxidizing agents. These alkalis and acids can similarly reduce the removal performance of the composite semipermeable membrane.

[0005] Furthermore, salts concentrated and precipitated on the surface of the composite semipermeable membrane, as well as friction with the supply-side flow channel material in contact with the composite semipermeable membrane, can cause scratches, which can reduce the removal performance of the composite semipermeable membrane.

[0006] Patent Document 1 discloses a composite semipermeable membrane having both low fouling properties and high chemical resistance, comprising a separation functional layer made of crosslinked aromatic polyamide and a coating layer containing aliphatic polyamide.

[0007] International Publication No. 2018 / 198679

[0008] However, the coating layer of the composite semipermeable membrane described in Patent Document 1 has insufficient chemical resistance because the sites that interact with the amide bonds of the separation functional layer are not densely located. Furthermore, there are issues with abrasion resistance. Therefore, the present invention aims to provide a composite semipermeable membrane that combines high chemical resistance and abrasion resistance.

[0009] To solve the above problems, the present invention includes the following configurations [1] to [9]. [1] A composite semipermeable membrane comprising a porous support layer and a separation functional layer containing polyamide on the porous support layer, wherein three or more repeating units represented by the following general formula (I) and repeating units represented by the following general formula (II) are adjacent to each other on the surface of the separation functional layer, and at least one repeating unit contains a nitrogen atom.

[0010] [In general formulas (I) and (II), X is a hydrogen bond donor, Y is a hydrogen bond acceptor, l and m are integers of 1 or more, the sum of l and m is 3 or more, and n in each repeating unit is independently 0 or 1.] [2] The composite semipermeable membrane according to [1], wherein the surface of the separation functional layer is a polymer compound containing the above structure. [3] The composite semipermeable membrane according to [1] or [2], wherein the structure has four or more adjacent repeating units represented by general formula (I) and repeating units represented by general formula (II). [4] The composite semipermeable membrane according to [1] or [2], wherein the structure is a urea structure and / or a urethane structure. [5] The composite semipermeable membrane according to [3], wherein the structure is a ureidopyrimidinone structure. [6] The composite semipermeable membrane according to [2], wherein the polymer compound contains a polyalkylene glycol structure. [7] The composite semipermeable membrane according to [6], wherein the structure is at least one structure selected from a urea structure, a urethane structure, and a ureidopyrimidinone structure. [8] A separation membrane element comprising the composite semipermeable membrane according to any one of [1] to [7] above. [9] A liquid separation apparatus comprising the separation membrane element according to [8] above.

[0011] According to the present invention, it is possible to provide a composite semipermeable film that combines high chemical resistance and abrasion resistance.

[0012] <Composite Semipermeable Membrane> The composite semipermeable membrane of the present invention is a composite semipermeable membrane (hereinafter also referred to as a "polyamide-based semipermeable membrane") comprising a porous support layer and a separation functional layer containing polyamide on the porous support layer. From the viewpoint of increasing the strength of the composite semipermeable membrane, the porous support layer may be formed on a substrate. In this specification, the form in which the porous support layer is formed on a substrate is also referred to as a support.

[0013] A "separation function layer" refers to a layer that has the function of separating the substances to be removed contained in the liquid being treated.

[0014] A "porous support layer" refers to a porous layer with a dense structure. The pore size on the surface of the porous support layer that forms the separation function layer is, for example, between 0.1 nm and 100 nm.

[0015] Examples of materials that constitute the porous support layer include polysulfone, polyethersulfone, polyamide, polyester, cellulose polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide. Examples of cellulose polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile.

[0016] The separation functional layer of a polyamide-based semipermeable membrane preferably contains polyamide as its main component. The main component refers to the component that accounts for 50% or more by mass of the components constituting the separation functional layer. The polyamide content in the separation functional layer is preferably 80% or more by mass, and more preferably 90% or more by mass.

[0017] "Polyamide" refers to a polymer of a polyfunctional amine and a polyfunctional acid halide. In particular, the polyamide is preferably an aromatic polyamide, which is a polymer of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide. Furthermore, the polyamide is preferably a crosslinked polyamide in which at least one of the polyfunctional amine and polyfunctional acid halide described later is trifunctional or higher, and it is even more preferably a crosslinked aromatic polyamide in which at least one of the polyfunctional aromatic amine and polyfunctional aromatic acid halide is trifunctional or higher.

[0018] Examples of polyfunctional amines include polyfunctional aromatic amines and polyfunctional aliphatic amines.

[0019] A "polyfunctional aromatic amine" refers to an aromatic amine that has two or more amino groups, at least one of either a primary amino group or a secondary amino group, in a single molecule, and at least one of the amino groups is a primary amino group. Examples of polyfunctional aromatic amines include compounds in which two amino groups are bonded to an aromatic ring in an ortho, meta, or para position, such as o-phenylenediamine, m-phenylenediamine (hereinafter referred to as "m-PDA"), p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, and p-diaminopyridine; 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. In particular, from the viewpoint of obtaining a semipermeable membrane with excellent selective separation properties, membrane permeation flow rate, and heat resistance, m-PDA, p-phenylenediamine, or 1,3,5-triaminobenzene are preferably used.

[0020] A "polyfunctional aliphatic amine" refers to an aliphatic amine having two or more amino groups in a single molecule. Examples of polyfunctional aliphatic amines include piperazine derivatives represented by the following general formula (III) and ethylenediamines.

[0021] In general formula (III), R １ , R ２Each of these is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0022] Specific examples of piperazine derivatives include piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, and 2,5-diethylpiperazine. In particular, it is preferable to use piperazine or dimethylpiperazine.

[0023] When forming the separation functional layer, at least one polyfunctional amine is required, and two or more compounds may be selected from polyfunctional aromatic amines and polyfunctional aliphatic amines. In particular, from the viewpoint of easily improving the performance of the polyamide semipermeable membrane, it is preferable to use a polyfunctional aromatic amine as the polyfunctional amine.

[0024] A "polyfunctional acid halide" refers to an acid halide that has two or more halogenated carbonyl groups in a single molecule. Polyfunctional acid halides can form amide bonds through reaction with terminal amino groups.

[0025] Examples of polyfunctional acid halides that can be used include oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, trimesic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, and 1,4-benzenedicarboxylic acid. Polyfunctional aromatic acid halides are preferred. Among acid halides, acid chlorides are preferred.

[0026] Specifically, "polyfunctional aromatic acid chloride" refers to an aromatic acid chloride having at least two, preferably two to four, carbonyl chloride groups in one molecule (i.e., a polyfunctional aromatic acid chloride). For example, trifunctional acid chlorides include trimesic acid chloride, and difunctional acid chlorides include biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride. These polyfunctional aromatic acid halides may be used individually or in combination of two or more.

[0027] The composite semipermeable membrane of the present invention has a structure in which three or more repeating units represented by the following general formula (I) and three or more repeating units represented by the following general formula (II) are adjacent to each other on the surface of the separation functional layer, and at least one repeating unit contains a nitrogen atom. As long as any of the repeating units contains a nitrogen atom, X and Y in each repeating unit in the structure may be the same or different, and the order and position of each repeating unit do not matter. That is, when the repeating unit represented by general formula (I) is A and the repeating unit represented by the following general formula (II) is B, when there are three adjacent units, they may be A-A-B, A-B-A, A-B-B, B-A-A, B-A-B, B-B-A, and the same applies when there are four or more adjacent units. Furthermore, adjacent repeating units may form a cyclic structure.

[0028] In general formulas (I) and (II), X is a hydrogen bond donor, Y is a hydrogen bond acceptor, l and m are integers of 1 or greater, the sum of l and m is 3 or greater, and n in each repeating unit is independently 0 or 1. Specifically, C where n is 0. ０ This means that X or Y are continuously bonded without a carbon atom in between, and n is 1. １ This refers to a methylene group that may or may not be substituted.

[0029] When a structure exists on the surface of the separation functional layer in which three or more repeating units represented by general formula (I) and general formula (II) are adjacent to each other, and at least one repeating unit contains a nitrogen atom, the amide bond sites, which are the starting points for degradation of polyamide by chemicals such as chlorine, alkalis, and acids, form hydrogen bonds with hydrogen bond donors and hydrogen bond acceptors. This formation of hydrogen bonds protects the amide bond sites from chemicals such as chlorine, alkalis, and acids, thus providing a composite semipermeable membrane with excellent chemical resistance. Furthermore, the structure in which three or more repeating units represented by general formula (I) and general formula (II) are adjacent to each other facilitates the formation of intramolecular and intermolecular hydrogen bonds between hydrogen bond donors and hydrogen bond acceptors, providing robustness to the surface of the separation functional layer and providing a composite semipermeable membrane with excellent abrasion resistance. Moreover, the presence of at least one repeating unit containing a nitrogen atom facilitates the rearrangement of hydrogen bonds between hydrogen bond donors and hydrogen bond acceptors, making it possible to form a stable structure against external stimuli.

[0030] A hydrogen bond donor is a structure having a hydrogen atom that forms a covalent bond with an atom with relatively high electronegativity. Examples of X include a primary or secondary amine, a primary or secondary amide structure having a hydrogen atom bonded to a nitrogen atom, an NH moiety, or a hydroxyl group.

[0031] Examples of hydrogen bond acceptors include structures having an electronegative atom such as a fluorine atom, oxygen atom, nitrogen atom, or sulfur atom, and examples of Y include tertiary amines, imines, carbonyl groups, thiocarbonyl groups, ether groups, and thioether groups. Therefore, any structure in which at least one repeating unit contains a nitrogen atom will contain a nitrogen atom in either the hydrogen bond donor or the hydrogen bond acceptor.

[0032] In this embodiment, the composite semipermeable membrane preferably has a structure on the surface of the separation functional layer in which four or more repeating units represented by the general formula (I) and the general formula (II) are adjacent, and more preferably has a structure in which five or more repeating units are adjacent. That is, when the sum of l and m is 4 or more, the above-mentioned characteristics can be expressed more prominently. Furthermore, the inventors have found that a function of spontaneously repairing itself (hereinafter referred to as "self-repair function") can also be obtained when the composite semipermeable membrane deteriorates due to chemicals or abrasion. The presence of a self-repair function against abrasion can be confirmed by confirming the disappearance of abrasion marks using the method described in "Self-Repair Function" below. It is presumed that the self-repair function against abrasion is due to the hydrogen bonds between the structures in the separation functional layer that have been cleaved by abrasion and in which four or more repeating units represented by the general formula (I) and the general formula (II) are adjacent, forming hydrogen bonds again. Furthermore, the presence of a self-repair function against deterioration due to chemicals can be confirmed by calculating the self-repair rate using the method described in "Self-Repair Rate" below. The self-repair function against chemical degradation is presumed to be due to the formation of hydrogen bonds between structures where four or more repeating units represented by general formula (I) and general formula (II) are adjacent, and where the amide bonds broken by the chemicals originally interacted with each other.

[0033] The presence of a structure on the surface of the separation functional layer in which three or more repeating units represented by the above general formula (I) and the above general formula (II) are adjacent to each other can be determined by measuring solid-state nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and X-ray electron spectroscopy (XPS).

[0034] From the perspective of protecting the separation functional layer, the composite semipermeable membrane according to this embodiment preferably includes a polymer compound having a structure in which three or more repeating units represented by the above general formula (I) and three or more repeating units represented by the above general formula (II) are adjacent to each other, and at least one repeating unit contains a nitrogen atom. The structure in which three or more repeating units represented by the general formula (I) and three or more repeating units represented by the general formula (II) are adjacent to each other, and at least one repeating unit contains a nitrogen atom may be included in either the main chain or the side chain of the polymer compound.

[0035] In the composite semipermeable membrane according to this embodiment, the mass fraction of the polymer compound (hereinafter referred to as "polymer compound") having a structure in which three or more repeating units represented by the above general formula (I) and three or more repeating units represented by the above general formula (II) are adjacent to each other, and at least one repeating unit contains a nitrogen atom is preferably 0.005% by mass or more and 6.0% by mass or less, more preferably 0.008% by mass or more and 5.0% by mass or less, still more preferably 0.01% by mass or more and 3.0% by mass or less, and particularly preferably 0.1% by mass or more and 1.0% by mass or less. When the mass fraction of the polymer compound is 0.005% by mass or more, it is easy to exhibit excellent chemical resistance and abrasion resistance. On the other hand, when the mass fraction of the polymer compound is 6.0% by mass or less, a decrease in the membrane permeation flux can be suppressed. The mass fraction is measured by the method described in the example "mass fraction of polymer compound" described later.

[0036] Examples of the structure in which three or more repeating units represented by the above general formula (I) and three or more repeating units represented by the above general formula (II) are adjacent to each other, and at least one repeating unit contains a nitrogen atom include a urea structure represented by the following formula (IV), a urethane structure represented by the following formula (V), a ureidopyrimidinone structure represented by the following general formula (VI), and the like. In the chemical formula, the wavy line represents the bonding site with other structures, and when it is at the end, it may be a hydrogen atom.

[0037] In general formula (VI), R ３ is an optionally substituted hydrocarbon group having 1 to 4 carbon atoms, a methoxy group, a carboxyl group, an amino group, a hydroxyl group or a hydrogen atom.

[0038] The urea structure corresponds to the case where there are two repeating units in the general formula (I) where X is a secondary amide (NH) and n is 0 (l = 2), and in the general formula (II) where Y is a carbonyl group (CO) and there is one repeating unit where n is 0 (m = 1).

[0039] The urethane structure corresponds to the case where there is one repeating unit in the general formula (I) where X is a secondary amide (NH) and n is 0 (l = 1), and in the general formula (II) where Y is an ether group (–O–), there is one repeating unit where n is 0 and one repeating unit where Y is a carbonyl group (CO) and n is 0 (m = 2).

[0040] The ureidopyrimidinone structure corresponds to the case where there is one repeating unit where n is 0 and one repeating unit where n is 1 in the general formula (I) where X is a secondary amide (NH) (l = 2), and in the general formula (II) where Y is a carbonyl group (CO), there are two repeating units where n is 0 and one repeating unit where Y is an imine (=N–) and n is 0 (m = 3).

[0041] The composite semipermeable membrane according to this embodiment preferably has at least one structure selected from a urea structure, a urethane structure, and a ureidopyrimidinone structure on the surface of the separation functional layer. Among them, the surface of the separation functional layer preferably has a ureidopyrimidinone structure represented by the above general formula (VI) in which the sum of the values of l and m is 4 or more. Also, R in the general formula (VI) ３ is preferably a hydrocarbon group having 1 to 4 carbon atoms, and more preferably a methyl group.

[0042] As a method for introducing a structure in which three or more repeating units represented by the general formula (I) and repeating units represented by the general formula (II) are adjacent to each other on the surface of the separation functional layer and at least one repeating unit contains a nitrogen atom, for example, a method of dissolving a polymer compound in a solvent that is non-invasive to polyamide such as water or ethanol and coating it on the surface of the separation functional layer can be mentioned.

[0043] In this embodiment, the composite semipermeable membrane preferably has a polyalkylene glycol structure in which three or more repeating units represented by the general formula (I) and the general formula (II) are adjacent to each other on the surface of the separation functional layer, and at least one repeating unit contains a nitrogen atom. The polyalkylene glycol structure may be included in either the main chain or the side chain of the polymer compound. Having a polyalkylene glycol structure, which is a hydrophilic part, can increase solubility in water and ethanol, and can be easily coated onto the surface of the separation functional layer. Furthermore, it can suppress the decrease in membrane permeation flux that occurs when the polymer compound is applied to the surface of the separation functional layer.

[0044] Examples of polyalkylene glycol structures include polyethylene glycol and polypropylene glycol. Examples of polymer compounds having a polyalkylene glycol structure include copolymers of polyethylene glycol and polyurea, copolymers of polyethylene glycol and polyurethane, and copolymers of polyethylene glycol and monomers having a ureidopyrimidinone structure.

[0045] When a polyalkylene glycol structure is included in the main chain of a polymer compound, the average degree of polymerization of the polyalkylene glycol structure is preferably 2 to 400, and more preferably 20 to 75.

[0046] <Method for Manufacturing a Composite Semipermeable Membrane> The method for manufacturing a composite semipermeable membrane according to this embodiment is a method for manufacturing a composite semipermeable membrane comprising a porous support layer and a separation functional layer containing polyamide on the porous support layer, comprising the steps of contacting the separation functional layer with a polyfunctional amine solution and contacting the separation functional layer with an organic solvent solution containing a polyfunctional halide.

[0047] In this embodiment, the separation functional layer of the composite semipermeable membrane is preferably formed by interfacial polymerization using an aqueous solution containing a polyfunctional amine and an organic solvent solution containing a polyfunctional acid halide. In particular, it is preferable to use a polyfunctional aromatic amine as the polyfunctional amine and a polyfunctional aromatic acid halide as the polyfunctional acid halide, and to form a crosslinked aromatic polyamide as the separation functional layer. Examples using a polyfunctional aromatic amine and a polyfunctional aromatic acid halide will be described below.

[0048] The interfacial polymerization step comprises (i) applying an aqueous solution containing a polyfunctional aromatic amine to a porous support layer, and (ii) applying an organic solvent solution containing a polyfunctional aromatic acid halogen to the porous support layer after step (i).

[0049] In steps (i) and (ii), means for applying the solution include, for example, immersion, showering, and coating.

[0050] The organic solvent used to dissolve the polyfunctional aromatic acid halide in step (ii) is one that is immiscible with water and has a solubility parameter of 15.2 (MPa). １／２ It is preferable to use an organic solvent that is 3.0% or higher and has an octanol / water partition coefficient of 3.2 or higher. Furthermore, it is preferable that the organic solvent does not damage the support, especially the porous support layer.

[0051] Typical examples of organic solvents that satisfy the above requirements include octane, nonane, decane, undecane, dodecane, isododecane, tridecane, tetradecane, heptadecane, hexadecane, isodecane, cyclooctane, isooctane, ethylcyclohexane, 1-octene, and 1-decene, either individually or in mixtures thereof.

[0052] Furthermore, a polymer compound solution containing a structure in which three or more repeating units represented by general formula (I) and general formula (II) are adjacent to each other may be applied to the separation functional layer. The polymer compound containing a structure in which three or more repeating units represented by general formula (I) and general formula (II) are adjacent to each other may be, for example, a commercially available polyurea, or it may be synthesized as described later.

[0053] The concentration of the polymer compound solution having a structure in which three or more repeating units represented by general formula (I) and three or more repeating units represented by general formula (II) are adjacent, and at least one repeating unit contains a nitrogen atom, is preferably 0.05% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less. The temperature of the polymer solution is preferably 10°C or more and 75°C or less, and more preferably 30°C or more and 60°C or less.

[0054] In this embodiment, the salt permeability ratio of the composite semipermeable membrane after chemical degradation treatment, calculated by the method described in the examples later, is preferably 2.00 or less, more preferably 1.50 or less, and even more preferably 1.25 or less. Furthermore, the boron permeability ratio of the composite semipermeable membrane, calculated by the method described in the examples later, is preferably 3.00 or less, more preferably 2.00 or less, and even more preferably 1.75 or less.

[0055] In this embodiment, the area ratio of the stained portion of the composite semipermeable membrane, calculated by the method described later in the "scratches test," is preferably 5.0% or less, and more preferably 2.5% or less. When the area ratio of the stained portion is 5.0% or less, the deterioration of the performance of the composite semipermeable membrane due to scraping can be sufficiently suppressed.

[0056] <Separation Membrane Element> The composite semipermeable membrane according to this embodiment is wound around a cylindrical water collection pipe with numerous holes, together with a supply-side flow channel material such as a plastic net, a permeable-side flow channel material such as tricot, and a film to enhance pressure resistance as needed, and is suitably used as a spiral-type separation membrane element. Furthermore, these elements can be connected in series or parallel and housed in a pressure vessel to form a separation membrane module.

[0057] Furthermore, the composite semipermeable membrane, separation membrane element, and separation membrane module can be combined with a pump to supply water to them, and a device to pre-treat the supply water, to constitute a liquid separation apparatus. By using this liquid separation apparatus, the supply water can be separated into permeate water such as drinking water and concentrated water that did not permeate the membrane, thereby obtaining water suitable for the purpose.

[0058] <Liquid Separation Device>The liquid separation device using the separation membrane element according to this embodiment includes a tank for storing the water to be treated, an element mounting part for mounting a separation membrane element incorporating at least one composite semi-permeable membrane according to this embodiment, a pipe connecting the tank and the element mounting part, and a pump between the tank and the element mounting part, in order to perform the liquid passing process of the separation membrane element.

[0059] More specifically, the liquid separation device using the separation membrane element according to this embodiment includes an element mounting part including a container for mounting the separation membrane element, a pipe connecting the element mounting part and the tank, and a pump connected to the pipe.

[0060] The liquid separation device may further include a tank for the cleaning solution, a pump, a pipe, etc.

[0061] Hereinafter, the present invention will be described more specifically with examples. However, the present invention is not limited thereto.

[0062] <Membrane Permeation Flux>Evaluation water (NaCl concentration 3.5% by mass, boron concentration about 5 ppm) adjusted to pH 6.5 was supplied to the composite semi-permeable membrane at an operating pressure of 5.5 MPa and a concentrated water flow rate of 3.5 L / min, and the membrane permeation water volume after performing cross-flow membrane filtration treatment for 2 hours was measured. It was converted to the water permeation volume (m ３ ) per square meter of the membrane surface per day, and the membrane permeation flux (m ３ / m ２ / day) was calculated.

[0063] <Salt Permeation Rate> For the feed water and permeated water when evaluation water (NaCl concentration 3.5% by mass, boron concentration about 5 ppm) adjusted to pH 6.5 was supplied to the composite semi-permeable membrane at an operating pressure of 5.5 MPa and a concentrated water flow rate of 3.5 L / min and cross-flow membrane filtration treatment was performed for 2 hours, the salt concentration was determined by a stationary-type electrical conductivity composite pH meter (WM-50G manufactured by Toa Denpa Kogyo Co., Ltd.), and the salt permeation rate was calculated from the following formula. Salt permeation rate (%) = 100 × (salt concentration of permeated water / salt concentration of evaluation water)

[0064] <Boron Permeability> Evaluation water (NaCl concentration 3.5% by mass, boron concentration approximately 5 ppm), adjusted to pH 6.5, was supplied to a composite semipermeable membrane at an operating pressure of 5.5 MPa and a concentrated water flow rate of 3.5 L / min. After 2 hours of membrane filtration, the boron concentration in the supplied water and permeate was determined using an ICP emission spectrometer (Agilent Technologies 5110 ICP-OES). The boron permeability was then calculated using the following formula: Boron Permeability (%) = 100 × (Boron concentration in permeate / Boron concentration in evaluation water)

[0065] <Chemical Degradation Treatment> The composite semipermeable membrane was subjected to the following treatments in sequence: chlorine degradation treatment by immersing it in a sodium hypochlorite aqueous solution (100 ppm) prepared to pH 8 using monopotassium phosphate at 25°C for 24 hours; alkali degradation treatment by immersing it in a sodium hydroxide aqueous solution with pH 13.0 at 25°C for 24 hours; and acid degradation treatment by immersing it in sulfuric acid with pH 1.0 at 25°C for 24 hours. After the chemical degradation treatment and after storage in pure water at 25°C for 3 days after the chemical degradation treatment (hereinafter referred to as "after pure water storage"), the membrane permeation flux, salt permeability, and boron permeability were measured for the composite semipermeable membrane using the methods described above for "membrane permeation flux," "salt permeability," and "boron permeability," and the membrane permeation flux ratio, salt permeability ratio, and boron permeability ratio were calculated from the following formulas. Membrane permeation flux ratio = (Membrane permeation flux after chemical degradation treatment or storage in pure water) / (Membrane permeation flux before chemical degradation treatment) Salt permeation ratio = (Salt permeation rate after chemical degradation treatment or storage in pure water) / (Salt permeation rate before chemical degradation treatment) Boron permeation ratio = (Boron permeation rate after chemical degradation treatment or storage in pure water) / (Boron permeation rate before chemical degradation treatment)

[0066] <Self-repair rate> Using the "membrane permeation flux ratio," "salt permeability ratio," and "boron permeability ratio" calculated by the method described in the "chemical degradation treatment" above, the self-repair rates of membrane permeation flux, salt permeability, and boron permeability were calculated from the following formulas. Self-repair rate of membrane permeation flux (%) = 100 × (membrane permeation flux ratio after chemical degradation treatment - membrane permeation flux ratio after 3 days of storage after chemical degradation treatment) / (membrane permeation flux ratio after chemical degradation treatment - 1) Self-repair rate of salt permeability (%) = 100 × (salt permeability ratio after chemical degradation treatment - salt permeability ratio after 3 days of storage after chemical degradation treatment) / (salt permeability ratio after chemical degradation treatment - 1) Self-repair rate of boron permeability (%) = 100 × (boron permeability ratio after chemical degradation treatment - boron permeability ratio after 3 days of storage after chemical degradation treatment) / (boron permeability ratio after chemical degradation treatment - 1) If any of the membrane permeation flux ratio, salt permeability ratio, or boron permeability ratio after chemical degradation treatment is less than 1.05, it is assumed that no degradation by the chemical has occurred, and the self-repair rate is not calculated. If the self-repair rate is 30% or higher, it is considered to have a self-repair function.

[0067] <Abrasion Test> A waterproof sandpaper with a grit size of #40, manufactured by TRUSCO Nakayama Co., Ltd., was brought into contact with the surface of the separation functional layer of the composite semipermeable membrane, and a load of 2.1 kg was applied while abrading was performed over a distance of 30 mm at a speed of 100 mm / min. After that, a 100 ppm methyl violet aqueous solution was applied to the abraded surface of the composite semipermeable membrane, left to stand for 10 minutes, and then washed with pure water for 1 minute. After washing, the abraded surface of the composite semipermeable membrane was photographed with a microscope at 10x magnification, and the area percentage (%) of the stained area by methyl violet was calculated using the image analysis software ImageJ.

[0068] <Self-healing function> On the surface of the separation functional layer of the composite semipermeable membrane, a scratch approximately 50 μm wide was created using a polypropylene net while observing it at 150x magnification with a microscope. After that, the membrane was stored in pure water at 25°C for 3 hours, and the scratch was observed again with a microscope to observe the change in the scratch. If the scratch has disappeared even slightly, it is considered to have a self-healing function.

[0069] <Synthesis of Polymer Compound A> 2-acetylbutyrolactone (2 mL) and guanidine carbonate (3.3 g) were refluxed in ethanol (20 mL) in the presence of triethylamine (5.2 mL) for 20 hours, then filtered, washed with ethanol, and suspended in water. After adjusting the pH to 7 with hydrochloric acid, the mixture was filtered again, washed with water and ethanol, and compound 1 represented by the following formula (VII) was obtained.

[0070] The obtained compound 1 (12 g) was suspended in isophorone diisocyanate (150 mL), stirred at 90°C for 20 hours under an argon atmosphere, then the solution was cooled and precipitated in hexane. The precipitate was filtered and washed with hexane to obtain compound 2, represented by the following formula (VIII).

[0071] A solution of Telechelic PEO-1500 (5.83 g) dissolved in toluene (30 mL) was mixed with a solution of Compound 2 (2.39 g) dissolved in toluene (14 mL) and to which dibutyltin dilaurate was added. The mixture was heated at 120°C for 20 hours under an argon atmosphere, and the reaction product was added to diethyl ether to obtain polymer compound A (weight-average molecular weight 7,000) represented by the following formula (IX) as a precipitate. In formula (IX), p and q indicate the number of repeating units.

[0072]

[0073] <Synthesis of Polymer Compound B> 1,1'-Carbonyldiimidazole (4.86 g) was added to a solution of 1,2-bis(2-aminoethoxy)ethane (4.62 g) in N-methylpyrrolidone (15 mL), stirred at 60°C for 24 hours, cooled to room temperature, and the reaction mixture was placed in acetone. The precipitate was washed with methanol and thoroughly dried to obtain polymer compound B (weight-average molecular weight 13,900) represented by the following formula (X). In formula (X), r indicates the number of repeating units.

[0074]

[0075] <Mass fraction of polymer compounds> 5m ２The composite semipermeable membrane, which had been cut out, was thoroughly dried, and its dry mass was measured. Then, the substrate was peeled off by hand, the porous support layer was dissolved using dichloromethane, and the remaining separation functional layer was filtered. The obtained separation functional layer was dissolved using a 12% by mass sodium hypochlorite aqueous solution. After thoroughly drying the remaining undissolved substance, the mass of the remaining substance was measured, and the mass fraction was calculated using the following formula: Mass fraction (%) = 100 × Mass of remaining substance / Dry mass of composite semipermeable membrane

[0076] [Reference Example 1] A reverse osmosis membrane element TSW-400LE for seawater desalination manufactured by Toray Industries was disassembled to obtain a composite semipermeable membrane.

[0077] [Example 1] A composite semipermeable membrane obtained by disassembling a Toray Industries TSW-400LE reverse osmosis membrane element for seawater desalination was contacted with an ethanol solution containing 1% by mass of polymer compound A at 25°C for 2 minutes. The composite semipermeable membrane was then immersed in pure water and washed to produce a composite semipermeable membrane.

[0078] [Example 2] A composite semipermeable membrane was prepared in the same manner as in Example 1, except that the concentration of polymer compound A was changed to 0.1% by mass.

[0079] [Example 3] A composite semipermeable membrane was prepared in the same manner as in Example 1, except that the concentration of polymer compound A was changed to 5% by mass and the contact time to 20 minutes.

[0080] [Example 4] A composite semipermeable membrane was prepared in the same manner as in Example 1, except that polymer compound A was replaced with polymer compound B.

[0081] [Comparative Example 1] A composite semipermeable membrane was prepared in the same manner as in Example 1, except that polymer compound A was changed to poly(2-ethyl-2-oxazoline), a polymer compound having a tertiary amide structure of hydrogen bond acceptors.

[0082] Table 1 shows the evaluation results of the composite semipermeable membranes obtained in Reference Example 1, Examples 1-4, and Comparative Example 1.

[0083]

[0084] The composite semipermeable membrane of the present invention can be particularly suitable for use in desalination of brine and seawater, and as a water purifier.

Claims

1. A composite semipermeable membrane comprising a porous support layer and a separation functional layer containing polyamide on the porous support layer, wherein three or more repeating units represented by the following general formula (I) and repeating units represented by the following general formula (II) are adjacent to each other on the surface of the separation functional layer, and at least one repeating unit has a structure in which a nitrogen atom is contained. [In general formulas (I) and (II), X is a hydrogen bond donor, Y is a hydrogen bond acceptor, l and m are integers of 1 or greater, the sum of l and m is 3 or greater, and n in each repeating unit is independently 0 or 1.] 2. The composite semipermeable membrane according to claim 1, wherein the surface of the separation functional layer has a polymer compound containing the above structure.

3. The composite semipermeable membrane according to claim 1 or 2, wherein the structure has a structure in which four or more repeating units represented by the general formula (I) and the repeating units represented by the general formula (II) are adjacent to each other.

4. The composite semipermeable membrane according to claim 1 or 2, wherein the structure is a urea structure and / or a urethane structure.

5. The composite semipermeable membrane according to claim 3, wherein the structure is a ureidopyrimidinone structure.

6. The composite semipermeable membrane according to claim 2, wherein the polymer compound comprises a polyalkylene glycol structure.

7. The composite semipermeable membrane according to claim 6, wherein the structure is at least one structure selected from a urea structure, a urethane structure, and a ureidopyrimidinone structure.

8. A separation membrane element comprising a composite semipermeable membrane according to claim 1 or 2.

9. A liquid separation apparatus comprising the separation membrane element described in claim 8.

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