Method for analyzing polyamide composite semipermeable membrane, method for diagnosing condition, and method for diagnosing separation performance

Abstract

To provide a method that allows simple quantification of amino groups present in a composite semipermeable membrane irrespective of membrane color.SOLUTION: A method for analyzing a polyamide composite semipermeable membrane comprises bringing the composite semipermeable membrane into contact with a solution containing a fluorescent dye to cause a chemical reaction, then irradiating the composite semipermeable membrane with excitation light of a specific wavelength, and measuring fluorescence intensity at a specific wavelength to quantify a content of amino groups.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing, diagnosing the state, and diagnosing the separation performance of a composite semipermeable membrane used for selective separation of a liquid mixture. [Background technology]

[0002] There are various technologies for separating liquid mixtures to remove substances (e.g., salts) dissolved in solvents (e.g., water), but membrane separation, which is characterized by its energy-saving, space-saving, and high separation performance, is becoming increasingly popular. Separation membranes used in membrane separation, which filters liquid mixtures and separates them into concentrated water and filtrate, include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes, and separation membrane elements using these membranes are used in a variety of water treatment applications, such as desalination of seawater and brackish water, production of ultrapure water, reuse of wastewater, and recovery of valuable resources.

[0003] The majority of reverse osmosis and nanofiltration membranes in practical use are composite semipermeable membranes, and there are two types: those with a separation functional layer formed by crosslinking a gel layer and a polymer on a support membrane, and those with a separation functional layer formed by polycondensation of a monomer on a support membrane. Of these, composite semipermeable membranes obtained by coating a support membrane with a separation functional layer made of crosslinked polyamide obtained by the polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide are widely used as high-performance separation membranes with excellent solvent permeability and selective separation.

[0004] Many factors affect the permselectivity of composite semipermeable membranes, but the chemical structure of the separating functional layer is a particularly important factor. For example, cross-linked polyamide separating functional layers are cross-linked by amide bonds and contain amino and carboxyl groups as unreacted functional groups derived from the monomers. These functional groups affect the pore size and hydrophilicity of the composite semipermeable membrane, which in turn affects the permeability of the composite semipermeable membrane to water and impurities.

[0005] During the use of composite semipermeable membranes in water treatment, the amide bonds present in the separation functional layer made of crosslinked polyamide may be hydrolyzed, resulting in an increase in uncrosslinked amino groups. On the other hand, these amino groups may be oxidized by contact with oxidizing substances and converted into other functional groups. Therefore, methods for analyzing the amount of functional groups, such as amino groups, present in separation membranes have been investigated to analyze the characteristics of separation membranes and their changes before and after use.

[0006] As a method for analyzing the amount of functional groups contained in a composite semipermeable membrane, Non-Patent Document 1 discloses a method for determining the ratio of nitrogen and oxygen by X-ray photoelectron spectroscopy (XPS) to obtain an indication of the degree of crosslinking in a crosslinked polyamide separation functional layer. However, this method does not allow for direct and quantitative analysis of the amount of uncrosslinked amino groups, and accurate analysis is difficult. Non-Patent Document 1 also discloses a method for determining peak intensities corresponding to amide groups and carboxyl groups using infrared absorption spectroscopy (IR). However, the detected peak intensities of amino groups are relatively weak, and the background from the support layer overlaps, making it impractical to quantitatively analyze the amount of amino groups from the peak intensities. Patent Document 1 discloses a method for quantitatively analyzing the carboxyl groups contained in a composite polyamide membrane using Rutherford backscattering spectroscopy, which utilizes the formation of salts between silver ions and carboxyl groups. However, quantitative analysis of the amount of amino groups using this method is difficult. Patent Document 2 discloses a method for quantitatively analyzing functional groups by analyzing an analytical sample extracted from a separation functional layer using solid-state nuclear magnetic resonance spectroscopy (solid-state NMR). However, application of this method requires extraction of an analytical sample from the separation functional layer, and the amount of functional groups cannot be quantitatively analyzed in the composite semipermeable membrane state. Patent Document 3 discloses a method in which a composite semipermeable membrane is reacted with vanillin and the amino groups are quantitatively analyzed comparatively based on the change in yellowness. However, this method makes it difficult to quantitatively evaluate the change in the amount of amino groups when the separation membrane is colored or when the membrane becomes discolored or colored after use in water treatment, etc. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2014 / 0199483 [Patent Document 2] International Publication No. 2016 / 002819 [Patent Document 3] International Publication No. 2022 / 138975 [Non-patent literature]

[0008] [Non-Patent Document 1] Tang, CY, Kwon, YN & Leckie, JO Desalination 242, 149-167 (2009). Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, in the conventional techniques, it was difficult to simply and quantitatively analyze functional groups present in a composite semipermeable membrane while maintaining the membrane structure, such as unreacted functional groups derived from monomers that can affect the performance of the composite semipermeable membrane and uncrosslinked functional groups generated during use. In addition, when the composite semipermeable membrane to be analyzed is colored, there was a problem in that it was difficult to quantitatively analyze the change in the amount of amino groups contained in the composite semipermeable membrane.

[0010] The present invention has been made in view of the above, and aims to provide a method for quantitatively analyzing the amount of amino groups present on the surface of a composite semipermeable membrane per unit area in a simple and quantitative manner while maintaining the state of the chemical structure of the composite semipermeable membrane, regardless of the color of the membrane to be analyzed. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention has the following features (1) to (10). (1) A method for analyzing a polyamide composite semipermeable membrane, comprising: A solution containing a fluorescent dye is brought into contact with the polyamide composite semipermeable membrane to cause a chemical reaction, A method for analyzing a polyamide composite semipermeable membrane, comprising irradiating the composite semipermeable membrane with excitation light of a specific wavelength and measuring the fluorescence intensity at a specific fluorescence detection wavelength to quantitatively evaluate the amount of amino groups. (2) The method for analyzing a polyamide composite semipermeable membrane according to (1), wherein the polyamide composite semipermeable membrane comprises a separation functional layer, a porous support layer, and a substrate, and the separation functional layer contains a crosslinked wholly aromatic polyamide as a main component. (3) The method for analyzing the polyamide composite semipermeable membrane according to (2), wherein the separation functional layer is made of a crosslinked wholly aromatic polyamide obtained by condensing trimesoyl chloride and m-phenylenediamine. (4) The method for analyzing a polyamide composite semipermeable membrane according to any one of (1) to (3), wherein the fluorescent dye contains, as a reactive site, any one of isocyanate, isothiocyanate, acyl azide, NHS ester, sulfonyl chloride, aldehyde, epoxide, aryl halide, imide ester, carbodiimide, and acid anhydride. (5) The method for analyzing a polyamide composite semipermeable membrane according to (4), characterized in that the fluorescent dye contains any one of an NHS ester, an aldehyde, and an imide ester, and the solvent of the solution containing the fluorescent dye contains water in an amount of 90% by weight or more. (6) The method for analyzing a polyamide composite semipermeable membrane according to any one of (1) to (3), wherein the specific fluorescence detection wavelength is 650 nm or more and 1000 nm or less. (7) A method for diagnosing the state of a polyamide composite semipermeable membrane, characterized in that the method for analyzing a polyamide composite semipermeable membrane according to any one of (1) to (6) is used to obtain analytical results for a polyamide composite semipermeable membrane 1 and a polyamide composite semipermeable membrane 2, and the change in the amount of amino groups is determined based on the difference between the two analytical results. (8) A method for diagnosing the state of a polyamide composite semipermeable membrane according to (7), characterized in that, after a step of removing deposits from the membrane surface, an analysis result of the polyamide composite semipermeable membrane 1 and an analysis result of the polyamide composite semipermeable membrane 2 are obtained. (9) A method for diagnosing the state of a polyamide composite semipermeable membrane according to (7) or (8), characterized in that the analysis result of the polyamide composite semipermeable membrane 1 is at least either the analysis result of an unused polyamide composite semipermeable membrane or the analysis result according to the progress of oxidative degradation, the polyamide composite semipermeable membrane 2 is a target polyamide composite semipermeable membrane, and the method for diagnosing the state of a polyamide composite semipermeable membrane determines the change in the amount of amino groups on the surface of the target polyamide composite semipermeable membrane and the degree of oxidation of the amino groups. (10) A method for diagnosing the separation performance of a polyamide composite semipermeable membrane, which quantitatively evaluates the effect of the degree of oxidation of amino groups in the polyamide composite semipermeable membrane on separation membrane performance based on the judgment results obtained by the polyamide composite semipermeable membrane state diagnosis method described in (9). [Effects of the Invention]

[0012] According to the present invention, even in the case of a colored composite semipermeable membrane, it is possible to simply and quantitatively evaluate the amount of amino groups present on the surface of the composite semipermeable membrane while maintaining the chemical structure of the composite semipermeable membrane. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but these are examples of preferred embodiments, and the present invention is not limited to these details.

[0014] The method for analyzing a polyamide composite semipermeable membrane of the present invention is characterized by quantitatively evaluating the amount of amino groups present on the surface of the polyamide composite semipermeable membrane by contacting the polyamide composite semipermeable membrane with a solution containing a fluorescent dye and causing a chemical reaction. This analysis method makes it possible to simply and quantitatively analyze the amount of amino groups present on the surface of the polyamide composite semipermeable membrane while maintaining the membrane structure and chemical structure of the polyamide composite semipermeable membrane to be analyzed. Furthermore, even if the polyamide composite semipermeable membrane to be analyzed is colored or pigmented, quantitative analysis is possible by labeling the amino groups to be analyzed with a fluorescent dye.

[0015] The polyamide composite semipermeable membrane that is the subject of the analytical method of the present invention is not particularly limited, but examples include composite semipermeable membranes in which a separation functional layer is formed on a support membrane. Among these, polyamide composite semipermeable membranes that are preferably used are those that consist of three layers: a substrate, a porous support layer, and a separation functional layer containing crosslinked polyamide as the main component. In polyamide composite semipermeable membranes, the support membrane consisting of the substrate and the porous support layer does not substantially exhibit separation performance for ions, etc., but serves to provide strength to the separation functional layer that is responsible for the separation performance.

[0016] The material and shape of the substrate are not particularly limited, but examples include fabrics or nonwoven fabrics primarily composed of at least one selected from polyester, polyamide, and polyolefin. Of these, polyester, which has high mechanical and thermal stability, is preferred. The thickness of the substrate is generally within the range of 10 to 200 μm to ensure dimensional stability.

[0017] The material and shape of the porous support layer provided between the substrate and the separation functional layer are not particularly limited, but it generally has a porous structure with fine pores of approximately 0.1 nm to 100 nm on the surface on which the separation functional layer is formed, and is obtained, for example, by phase separation of a high molecular weight polymer cast onto the substrate. A variety of polymer materials, such as polysulfone, polyethersulfone, polyphenylene sulfide sulfone, polyphenylene sulfone, and cellulose acetate, are used alone or in combination as materials for the porous support layer. Of these, polysulfone is commonly used because of its high chemical, mechanical, and thermal stability and ease of molding.

[0018] The separating functional layer to be analyzed in the present invention contains a polyamide. The polyamide is not particularly limited, but a crosslinked polyamide thin film, which has excellent water permeability and selective separation, is preferably used. The crosslinked polyamide separating functional layer is formed by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide, and typically has a thickness of about 0.01 to 1 μm. Preferably, at least one of the polyfunctional amine and the polyfunctional halide contains a compound with three or more functional groups. Examples of polyfunctional amines include polyfunctional aromatic amines in which two amino groups are bonded to an aromatic ring at the ortho, meta, or para positions, such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, and p-diaminopyridine; 1,3,5-triaminobenzene; and 1,2,4-triaminobenzene. Examples of suitable polyfunctional aromatic amines include polyfunctional aromatic amines such as benzophenone, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine; and polyfunctional aliphatic amines such as piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2-n-propylpiperazine, and 2,5-di-n-butylpiperazine. Examples of suitable polyfunctional acid halides include polyfunctional aromatic acid halides such as trimesic acid chloride, biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; and polyfunctional aliphatic acid halides such as 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. In particular, in recent years, crosslinked aromatic polyamides obtained by condensing trimesoyl chloride or isophthaloyl chloride with m-phenylenediamine or piperazine have been preferably used as separation functional layers with excellent selective permeability, and crosslinked wholly aromatic polyamides obtained by condensing trimesoyl chloride with m-phenylenediamine are particularly preferably used for applications requiring high removability.Such crosslinked wholly aromatic polyamides have significant steric hindrance and the reaction rate of the amino groups is slower than that of aliphatic amines, so unreacted primary amino groups are likely to be produced, which is a feature that makes them easy to detect using the analytical method of the present invention.

[0019] In the present invention, amino groups in polyamide present on the surface of a composite semipermeable membrane are labeled with a fluorescent dye. The fluorescent dye preferably has a functional group (reactive site) capable of reacting with the amino group of the polyamide to form a covalent bond. The fluorescent dye used may have a carboxyl group capable of reacting with the amino group by adding a separate condensing agent. More preferably, the fluorescent dye has a site that spontaneously reacts with the amino group. The reactive site that spontaneously reacts with the amino group preferably includes any of isocyanate, isothiocyanate, acyl azide, NHS ester, sulfonyl chloride, aldehyde, epoxide, aryl halide, imide ester, carbodiimide, and acid anhydride moieties. It is more preferable that the fluorescent dye includes any of NHS ester, aldehyde, and imide ester, and that the solvent of the solution containing the fluorescent dye contains 90% or more by weight of water. By using a solution of a fluorescent dye containing a hydrolysis-resistant NHS ester, aldehyde, imide ester, or the like dissolved in a solvent containing 90% or more by weight of water, it is possible to prevent the porous support layer of the composite semipermeable membrane to be analyzed from dissolving or swelling due to the action of the organic solvent. Therefore, the fluorescent dye is preferably soluble in water or an aqueous solution containing a water-miscible organic solvent, and more preferably, is soluble in water. This is because many polymers used as the porous support layer of composite semipermeable membranes are materials that dissolve or swell in organic solvents other than alkanes and alcohols. If a fluorescent dye is dissolved in such an organic solvent and brought into contact with the membrane, the structure of the composite semipermeable membrane is likely to collapse.

[0020] Examples of commercially available compounds include AF430 carboxylic acid, AF488 carboxylic acid, AF555 carboxylic acid, AF568 carboxylic acid, AF594 carboxylic acid, AF647 carboxylic acid, BDP650 / 665, BDP FL carboxylic acid, BDP TMR carboxylic acid, Cyanine 3 carboxylic acid, Cyanine7.5 carboxylic acid, Cyanine7 carboxylic acid, sulfo-Cyanine3.5 carboxylic acid, sulfo-Cyanine3 carboxylic acid, sulfo-Cyanine5.5 carboxylic acid, sulfo-Cyanine5 bis-carboxylic acid, sulfo-Cyanine5 carboxylic acid, sulfo-Cyanine7.5 carboxylic acid, sulfo-Cyanine7 bis-carboxylic acid, sulfo-Cyanine7 carboxylic acid, Fluorescein, 5-ROX, Pyrene carboxylic acid, AF430 NHS ester, AF488 NHS ester, AF555 NHS ester, AF568 NHS ester, AF594 NHS ester, AF647 NHS ester, BDP650 / 665, BDP FL NHS ester, BDP TMR NHS ester, Cyanine 3 NHS ester, Cyanine7.5 NHS ester, Cyanine7 NHS ester, sulfo-Cyanine3.5 NHS ester, sulfo-Cyanine3 NHS ester, sulfo-Cyanine5.5 NHS ester, sulfo-Cyanine5 bis-NHS ester, sulfo-Cyanine5 NHS ester, sulfo-Cyanine7.Examples include 5-NHS ester, sulfo-Cyanine 7 bis-NHS ester, sulfo-Cyanine 7 NHS ester, Fluorescein NHS ester, and 5-ROX NHS ester.

[0021] The structure of the light-emitting site of the fluorescent dye is not particularly limited. However, when the composite semipermeable membrane is fluorescent, it is preferable to use a fluorescent dye with a fluorescence different from that of the composite semipermeable membrane to be analyzed from the viewpoint of accuracy. For example, a crosslinked wholly aromatic polyamide obtained by condensing trimesoyl chloride and m-phenylenediamine has a fluorescence that emits fluorescence around 580 nm when irradiated with excitation light of 300 to 500 nm. When a composite semipermeable membrane containing such a polyamide is to be analyzed, it is preferable to use a fluorescent dye that emits fluorescence at a longer wavelength, such as in the near-infrared region. For the above reasons, the fluorescence detection wavelength is preferably 650 nm or longer, and, in terms of the measurement wavelength range of a spectrofluorometer, it is preferably 1000 nm or shorter.

[0022] The method for analyzing a composite semipermeable membrane of the present invention includes a method comprising the following steps A to D. (Process A) In the analytical method of the present invention, the composite semipermeable membrane is analyzed as is, but it is preferable to remove any dirt or surfactants that may be present during use beforehand. For example, methods include washing the target composite semipermeable membrane in pure water at 80 to 95°C for several minutes or physically wiping it with absorbent cotton or the like. Note that if physical scratches are made on the membrane surface, some dyes may physically adsorb to the exposed support membrane due to the scratches, reducing the accuracy of quantification. Therefore, it is preferable to handle the membrane without scratching it. (Process B) Next, the composite semipermeable membrane is contacted with a solution of the fluorescent dye. The solution is preferably an aqueous solution, but a condensing agent, salt, pH adjuster, or organic solvent may be added separately, or an organic solvent may be added to promote dissolution of the fluorescent dye. The method for contacting the solution is not particularly limited, but immersion or coating is commonly used. Examples of coating methods that can be used include bar coating, spray coating, microgravure coating, and spray coating. To ensure quantitative application, it is preferable to apply the solution precisely so that the amount applied per area is uniform, or to use spacers or other devices after coating to maintain a constant amount of solution on the membrane surface. (Process C) Next, the solution containing the fluorescent dye is kept in contact with the membrane to be analyzed for a certain period of time, allowing the fluorescent dye to react with the composite semipermeable membrane. The reaction conditions, such as the reaction temperature and reaction time, can be appropriately set depending on the fluorescent dye. After the reaction is complete, the composite semipermeable membrane is thoroughly washed. Although washing with pure water is preferred, the temperature, pH, etc. may be changed as appropriate. (Process D) Next, the fluorescence spectrum of the dyed composite semipermeable membrane is measured using a spectrofluorometer. A certain area of ​​the composite semipermeable membrane is cut out, flattened, and irradiated with excitation light in the excitation wavelength range of the fluorescent dye, and the emitted fluorescence spectrum is measured. An integrating sphere unit may be used as the spectrofluorometer.

[0023] By comparing the fluorescence spectral intensities at the appropriate specific wavelengths obtained, the amount of amino groups on the membrane surface can be compared relative to one another among multiple samples. Furthermore, if a calibration curve is prepared using membranes or films whose amino group amounts have been determined by known analytical methods, the absolute value of the amount of amino groups can also be quantified. Furthermore, if the unstained composite semipermeable membrane is fluorescent, preparing a calibration curve allows the influence of the fluorescence from the composite semipermeable membrane on the analytical results to be subtracted, which is preferable from the viewpoint of quantitative analytical results.

[0024] One embodiment of the present invention is a method for diagnosing the state of a polyamide composite semipermeable membrane, characterized in that the method for analyzing a polyamide composite semipermeable membrane of the present invention is used to obtain analysis results for polyamide composite semipermeable membrane 1 and polyamide composite semipermeable membrane 2, and based on the difference between the two analysis results, a change in the amount of amino groups in the polyamide composite semipermeable membrane is determined.

[0025] In the above-mentioned method for diagnosing the condition of a polyamide composite semipermeable membrane, after the step of removing deposits on the surface of the polyamide composite semipermeable membrane, it is preferable to obtain the analysis results of the polyamide composite semipermeable membrane 1 and the polyamide composite semipermeable membrane 2. By removing the deposits attached to the membrane surface before contacting the polyamide composite semipermeable membrane with a solution containing a fluorescent dye, the amount of amino groups on the membrane surface can be compared more accurately.

[0026] Examples of the polyamide composite semipermeable membrane 1 include an unused polyamide composite semipermeable membrane and a polyamide composite semipermeable membrane that has been previously subjected to oxidative degradation using a chemical such as an oxidizing agent, and an example of the polyamide composite semipermeable membrane 2 is the target polyamide composite semipermeable membrane.

[0027] In the present invention, the above-mentioned unused membrane refers to a membrane having the same amount of amino groups as the membrane at the time of shipment or in a state equivalent thereto. For example, even if a separation membrane has been passed through pure water, water to be filtered, or the like, it is considered to be an unused membrane if no change in the amount of amino groups has occurred.

[0028] By using polyamide composite semipermeable membranes that have been oxidatively deteriorated to different degrees in advance by chemicals such as oxidizing agents as the polyamide composite semipermeable membrane 1, the analytical results of the target polyamide composite semipermeable membrane can be quantitatively evaluated from the analytical results according to the progress of oxidative deterioration.

[0029] The polyamide composite semipermeable membrane to be evaluated is a polyamide composite semipermeable membrane to be evaluated, such as a polyamide composite semipermeable membrane after use in water treatment applications.

[0030] The fluorescent dye used in this invention has a surface pore size larger than that of polyamide composite semipermeable membranes used in water treatment applications, and therefore rarely penetrates into the inner layer of the separation functional layer of the polyamide composite semipermeable membrane. However, the fluorescent dye allows for highly sensitive detection of the amount of amino groups on the surface of the separation functional layer. Quantitative comparison of the amount of amino groups on the surface of the polyamide composite semipermeable membrane allows for quantitative evaluation of the degree of oxidative degradation of the amino groups contained in the polyamide composite semipermeable membrane, which affect the performance of the separation membrane. For example, an increase in amino groups can be inferred to indicate that the amide bonds in the crosslinked portions have been cleaved by hydrolysis or other factors. A decrease in amino groups can be inferred to indicate that the amide bonds have not been cleaved, or that the amino groups have been converted to other functional groups through reaction with other chemicals. Furthermore, under severe hydrolysis conditions, the decrease in amino groups can also occur when polyamide is decomposed into monomer and oligomer units and released. Therefore, considering other results, such as membrane performance and electron micrographs, more accurate assessment of polyamide composite semipermeable membrane degradation can be achieved.

[0031] By creating an empirical formula for determining the deterioration of the polyamide composite semipermeable membrane, the effect of amino group oxidation on separation membrane performance can be quantitatively evaluated using the results of quantitatively evaluating the degree of oxidation of amino groups on the surface of the polyamide composite semipermeable membrane. [Example]

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0033] <Reference example 1> 50 mL of 1 mol / L aqueous sodium bicarbonate solution was prepared. 1 mg of the fluorescent dye 1-(6-((2,5-dioxopyrrolidin-1-yl)oxy)-6-oxohexyl)-3,3-dimethyl-2-(5-(1,3,3-trimethyl-5-sulfonatoindolin-2-ylidene)penta-1,3-dien-1-yl)-3H-indol-1-ium-5-sulfonate potassium salt (commonly known as Sulfo-Cy5 NHS ester) was dissolved in 2 mL of the above sodium bicarbonate solution to prepare a reaction solution.

[0034] An unused reverse osmosis membrane element for seawater desalination was disassembled, and a 2 cm square composite semipermeable membrane sample was cut out. After removing excess water from the composite semipermeable membrane to semi-dry it, it was attached to a glass slide with instant adhesive, and 0.6 mL of the above reaction solution was applied to the composite semipermeable membrane using a micropipette. A 1.1 mm thick glass slide was sandwiched between the membrane as a spacer, and another glass slide was placed on top to maintain a layer of reaction solution on the membrane. The reaction cell thus created was left to stand in an incubator set at 37°C for 2 hours. After the reaction, the cell was disassembled, and the removed composite semipermeable membrane was thoroughly washed with pure water to obtain a dyed membrane.

[0035] The stained membrane was set in a fluorescence spectrophotometer (Fluorolog 3-22, manufactured by Horiba Jobin Yvon). The light source was a xenon lamp, the detector was a PMT, the slit width was 3 nm on the excitation side and 5 nm on the observation side, the time constant was 0.1 s, and the measurement mode was Sc / Rc. The excitation light was incident perpendicular to the sample membrane surface, and fluorescence was observed at a 22.5° angle to the direction of the excitation light. A filter that cuts off light below 480 nm was inserted in the optical path on the excitation side to prevent second-order diffracted light in the spectrometer from irradiating the sample. The fluorescence spectrum was measured when excited at a wavelength of 646 nm. The fluorescence intensity at a fluorescence detection wavelength of 685 nm was measured twice and averaged to obtain an average of 1.91 x 10 6 The same measurement was performed on an unstained membrane, and the fluorescence intensity was 5.48 × 10 4 It was.

[0036] Example 1 A reverse osmosis membrane element of the same type as that of Reference Example 1, which had been used for seawater desalination for one year, was disassembled, and the composite semipermeable membrane was cut out. This composite semipermeable membrane was washed at 85°C for 5 minutes and measured in the same manner as Reference Example 1. The fluorescence intensity value was 1.85 × 10 6 Since the fluorescence intensity did not increase compared to the unused composite semipermeable membrane sample, it was estimated that the amino groups in the separating functional layer were not oxidized.

[0037] <Example 2> A reverse osmosis membrane element of the same type as Reference Example 1, which had been used for one year for seawater desalination purposes other than those in Example 1, was disassembled, and a composite semipermeable membrane was cut out. This composite semipermeable membrane was washed at 85°C for 5 minutes and measured in the same manner as in Reference Example 1. The fluorescence intensity value was 7.03 × 10 6 Since the fluorescence intensity increased compared to an unused composite semipermeable membrane sample, it was estimated that the separating functional layer had been hydrolyzed, resulting in an increase in amino groups. [Industrial Applicability]

[0038] The present invention makes it possible to easily analyze the amino groups in the separation functional layer of a composite semipermeable membrane while the membrane is in its intact state, which is useful for clarifying the cause of performance changes in separation membrane elements in water treatment plants and for improving their operation.

Claims

1. A method for analyzing a polyamide composite semipermeable membrane, comprising: A solution containing a fluorescent dye is brought into contact with the polyamide composite semipermeable membrane to cause a chemical reaction, A method for analyzing a polyamide composite semipermeable membrane, comprising irradiating the composite semipermeable membrane with excitation light of a specific wavelength and measuring the fluorescence intensity at a specific fluorescence detection wavelength to quantitatively evaluate the amount of amino groups.

2. 2. The method for analyzing a polyamide composite semipermeable membrane according to claim 1, wherein the polyamide composite semipermeable membrane comprises a separation functional layer, a porous support layer, and a substrate, and the separation functional layer contains a crosslinked wholly aromatic polyamide as a main component.

3. 3. The method for analyzing a polyamide composite semipermeable membrane according to claim 2, wherein the separating functional layer comprises a crosslinked wholly aromatic polyamide obtained by condensing trimesoyl chloride and m-phenylenediamine.

4. The method for analyzing a polyamide composite semipermeable membrane according to any one of claims 1 to 3, wherein the fluorescent dye contains, as a reactive site, any one of isocyanate, isothiocyanate, acyl azide, NHS ester, sulfonyl chloride, aldehyde, epoxide, aryl halide, imide ester, carbodiimide, and acid anhydride.

5. 5. The method for analyzing a polyamide composite semipermeable membrane according to claim 4, wherein the fluorescent dye contains any one of an NHS ester, an aldehyde, and an imide ester, and the solvent of the solution containing the fluorescent dye contains 90% by weight or more of water.

6. The method for analyzing a polyamide composite semipermeable membrane according to any one of claims 1 to 3, wherein the specific fluorescence detection wavelength is 650 nm or more and 1000 nm or less.

7. A method for diagnosing the state of a polyamide composite semipermeable membrane, characterized in that the analysis results of the polyamide composite semipermeable membrane 1 and the polyamide composite semipermeable membrane 2 are obtained using the method for analyzing a polyamide composite semipermeable membrane according to any one of claims 1 to 6, and the change in the amount of amino groups is determined based on the difference between the two analysis results.

8. 8. A method for diagnosing the state of a polyamide composite semipermeable membrane according to claim 7, characterized in that, after a step of removing deposits from the membrane surface, an analysis result of the polyamide composite semipermeable membrane 1 and an analysis result of the polyamide composite semipermeable membrane 2 are obtained.

9. 9. A method for diagnosing the state of a polyamide composite semipermeable membrane according to claim 7 or 8, characterized in that the analysis result of the polyamide composite semipermeable membrane 1 is at least one of the analysis result of an unused polyamide composite semipermeable membrane or the analysis result according to the progress of oxidative degradation, the polyamide composite semipermeable membrane 2 is a target polyamide composite semipermeable membrane, and a change in the amount of amino groups on the surface of the target polyamide composite semipermeable membrane and the degree of oxidation of the amino groups are determined.

10. A method for diagnosing the separation performance of a polyamide composite semipermeable membrane, which quantitatively evaluates the effect of the degree of oxidation of amino groups in the polyamide composite semipermeable membrane on separation membrane performance based on the judgment results obtained by the polyamide composite semipermeable membrane state diagnosis method according to claim 9.