Performance change analysis method for composite semipermeable membrane, performance change analysis program for composite semipermeable membrane, and recording medium

Abstract

The purpose of the present invention is to provide a highly accurate analysis method eliminating the influence of deposits when analyzing the contribution of change factors to a performance change in a composite semipermeable membrane. The present invention relates to a method for analyzing a performance change caused by a change factor of a composite semipermeable membrane made of a separation function layer and a support membrane. The performance change analysis of the composite semipermeable membrane is characterized in that the support membrane obtained by removing the separation function layer from the composite semipermeable membrane is analyzed or measured.

Description

Method for analyzing changes in performance of composite semipermeable membranes, program for analyzing changes in performance of composite semipermeable membranes, and recording medium

[0001] The present invention relates to a method for analyzing changes in the performance of a composite semipermeable membrane used for selective separation of a liquid mixture.

[0002] Regarding the separation of liquid mixtures, there are various technologies for removing substances (e.g., salts) dissolved in a solvent (e.g., water), but membrane separation, which is characterized by its energy-saving, space-saving, and high separation performance, is increasingly being used. Membranes used in membrane separation include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes, and separation membrane elements using these membranes are used in a variety of applications, such as desalination of seawater or brackish water, production of ultrapure water, reuse of wastewater, and recovery of valuable resources.

[0003] Most reverse osmosis membranes 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. Among them, composite semipermeable membranes obtained by coating a support membrane with a separation functional layer made of a 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] The performance of separation membranes changes during operation, although the degree of this change varies depending on the type of separation membrane, the composition of the liquid being treated, and the operating conditions. Therefore, to ensure stable operation of liquid treatment equipment, it is necessary to understand the causes of changes in separation membrane performance and manage operation to reduce their impact.

[0005] There are many factors that can cause changes in separation membrane performance, such as physical damage due to contact with inflowing foreign matter, chemical degradation due to contact with chemicals such as pharmaceuticals, and irreversible compaction caused by high-pressure operation. In reality, performance changes in liquid treatment equipment are usually caused by multiple factors, and in order to identify the main cause, a technique is required to analyze the contribution of each factor to the performance change. The following examples are known as techniques for investigating the causes of changes in separation membrane performance.

[0006] Patent Document 1 discloses a method for checking for the presence or absence of physical damage to a composite semipermeable membrane, in which a composite semipermeable membrane element is disassembled, membrane pieces are collected, a dyeing solution is passed through the membrane pieces under pressure, and the stained areas of the membrane pieces are visually observed.

[0007] Non-Patent Document 1 describes the Fujiwara Test, a method for checking whether or not a composite semipermeable membrane has chemically deteriorated, in which a composite semipermeable membrane element is disassembled, a membrane piece is collected, and the membrane piece is reacted with an alkaline pyridine solution to check whether or not coloration occurs.

[0008] However, since all of the above-mentioned known techniques are aimed at analyzing composite semipermeable membranes, it is difficult to eliminate the influence of dirt (fouling) that has adhered during operation. In other words, since the adhesions affect the above-mentioned staining state and color reaction, it is not possible to selectively analyze and measure only the composite semipermeable membrane, resulting in a problem of low accuracy of the analysis results. Furthermore, although methods for physically or chemically cleaning fouled composite semipermeable membranes are known, it is difficult to remove the fouling.

[0009] Furthermore, Non-Patent Document 2 describes that the change in separation membrane performance over time due to compaction depends on the membrane material and specifications, operating time, temperature of the treated liquid, and pressure of the treated liquid. Non-Patent Document 3 describes a method for expressing the change in separation membrane performance over time due to compaction using the compaction coefficient (m value). The empirical formula described in Non-Patent Document 3 treats the m value as constant if the operating conditions are constant, but in actual liquid treatment devices, the water temperature of the treated liquid changes with the seasons and the accompanying pressure changes of the treated liquid occur, so the m value is not necessarily constant. Non-Patent Document 4 describes a method for more accurately estimating the m value after a predetermined time has elapsed by sequential calculation based on the changes in the temperature and pressure of the treated liquid over time.

[0010] These known techniques for compaction all estimate the change in separation membrane performance due to compaction based on operating condition information, and require the acquisition of this operating condition information. However, in liquid treatment devices that are not equipped with sufficient instruments, it may be impossible to acquire this operating condition information. In such cases, it is necessary to estimate the change in separation membrane performance due to compaction by examining the structure and performance of the separation membrane after operation.

[0011] However, as mentioned above, the separation membrane after operation contains the effects of fouling that occurred during operation. Since the effects of fouling appear only in the separation functional layer that comes into contact with the liquid to be treated, by examining the support membrane with the separation functional layer removed, it is possible to estimate changes in separation membrane performance while eliminating the effects of fouling. Patent Document 2 describes a method for analyzing the surface layer elastic modulus and surface roughness of the support membrane obtained by removing the separation functional layer of a composite semipermeable membrane.

[0012] International Publication No. 2015 / 063975 Japanese Patent No. 7343075

[0013] Journal of Membrane Science, 2010, Vol. 347, pp. 159-164; Bernard Baum, Stanley A. Margosiak, and William H. Holley, Jr., Ind. Eng. Chem. Prod. Res. Dev., vol. 11, No. 2, 195 (1972); Naohiko UKAWA, Ikuo NAKATANI, and Hideo IWAHASHI, Journal of the Society of Seawater Science of Japan, Vol. 43, No. 4, 218 (1989).

[0014] According to conventional methods, in an investigation of the causes of performance changes of a composite semipermeable membrane, it is possible to grasp whether or not each change factor is involved, but the accuracy of the analysis is low due to the influence of deposits. The present invention has been made in view of the above, and an object of the present invention is to provide a highly accurate analysis method that eliminates the influence of deposits when analyzing the contribution of each change factor to performance changes of a composite semipermeable membrane.

[0015] In order to solve the above problems, the present invention has the following configurations (1) to (11).

[0016] (1) A method for quantitatively analyzing the causes of performance changes in a composite semipermeable membrane consisting of a separation functional layer and a support membrane, characterized in that the performance change index of the support membrane obtained by removing the separation functional layer from the composite semipermeable membrane is analyzed or measured.

[0017] (2) A method for quantitatively analyzing the cause of a change in performance of a composite semipermeable membrane consisting of a separating functional layer and a support membrane, comprising the following steps A to C: Step A: A step of removing the separating functional layer from the composite semipermeable membrane to obtain the support membrane. Step B: A step of analyzing or measuring a performance change index of the support membrane. Step C: A step of calculating the performance change due to a change factor of the composite semipermeable membrane using a previously obtained relational expression between the performance change index of the support membrane and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane, and the analysis or measurement results of the performance change index of the support membrane obtained in step B.

[0018] (3) In the step C, instead of the relational expression between the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane, a relational expression between the ratio or difference of the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane is used, and instead of the measured value of the performance change index obtained in the step B, the ratio or difference of the performance change index of the support membrane obtained in the step B is used to calculate the performance change due to the change factor of the composite semipermeable membrane.

[0019] (4) The method for analyzing changes in performance of a composite semipermeable membrane according to (2) or (3), characterized in that the method for removing the separation functional layer in the step A is a method for contacting the composite semipermeable membrane with an oxidizing agent.

[0020] (5) The method for analyzing changes in performance of a composite semipermeable membrane according to any one of (2) to (4), characterized in that the change factor is at least one selected from the group consisting of physical damage, chemical deterioration, and compaction.

[0021] (6) The method for analyzing changes in performance of a composite semipermeable membrane according to any one of (2) to (5), wherein the change factor is compaction.

[0022] (7) The method for analyzing a change in performance of a composite semipermeable membrane according to any one of (2) to (6), wherein the performance change index in the step B is the water permeability of the support membrane.

[0023] (8) The method for analyzing a performance change of a composite semipermeable membrane according to any one of (2) to (7), wherein the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane in the step C is a ratio or difference of at least one performance index selected from the group consisting of a solute rejection rate, a solute permeability rate, a solute permeability coefficient, a membrane permeation flux, a pure water permeability coefficient, a water production rate, and a pressure drop before and after the performance change of the composite semipermeable membrane. (9) A program for analyzing a performance change of a composite semipermeable membrane, causing a computer to function as: a relational expression input means for inputting a relational expression between a performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane, a relational expression storage means for storing the relational expression, and a performance change calculation means for calculating a performance change due to a change factor before and after the performance change of the composite semipermeable membrane based on the relational expression in response to an input of a measurement value of the performance change index.

[0024] (10) The performance change analysis program for a composite semipermeable membrane according to (9) above, wherein the performance change index is the water permeability of the support membrane.

[0025] (11) A recording medium having recorded thereon a program for analyzing changes in performance of the composite semipermeable membrane according to either (9) or (10).

[0026] According to the performance change analysis method of the present invention, it is possible to quantitatively grasp the contribution of change factors to the changed performance of a composite semipermeable membrane, and therefore it is expected that the operation of a water treatment plant will be reliably improved based on the identification of the cause of the performance change.

[0027] 1 is a graph showing the relationship between the pure water permeability coefficient of a support membrane after compaction and the permeation flux ratio of a composite semipermeable membrane before and after compaction.

[0028] 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.

[0029] The present invention analyzes performance changes due to change factors of the composite semipermeable membrane by analyzing or measuring the performance change index of the support membrane obtained by removing the separation functional layer from the composite semipermeable membrane. That is, without measuring the change over time in separation membrane performance that occurs during operation of the water treatment plant, the contribution of change factors to separation membrane performance that changes during operation of the water treatment plant can be quantitatively analyzed from the performance change index of the support membrane obtained by removing the separation functional layer. Note that the performance change of the composite semipermeable membrane in the present invention refers to changes in membrane permeation flux, pure water permeability coefficient, water production rate, pressure drop, etc.

[0030] (Object of Analysis) The composite semipermeable membrane to be analyzed in the performance change analysis method of the present invention is not particularly limited in shape or material, but an example is a composite material in which a separation functional layer is formed on a support membrane. In particular, a crosslinked polyamide composite semipermeable membrane, which is currently widely used in various applications, is the main object of analysis.

[0031] The crosslinked polyamide composite semipermeable membrane is a composite membrane consisting of three layers: a substrate, a porous support layer, and a separation functional layer made of crosslinked polyamide. The support membrane consisting of the substrate and the porous support layer does not actually exhibit any separation performance for ions, etc., but serves to provide strength to the separation functional layer, which is responsible for the separation performance.

[0032] The material and shape of the substrate are not particularly limited, but examples include fabrics or nonwoven fabrics whose main component is at least one selected from polyester, polyamide, and polyolefin. Polyester is preferred because of its high mechanical and thermal stability. The thickness of the substrate is generally within the range of 10 to 200 μm to ensure dimensional stability.

[0033] 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. Various 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. Polysulfone, which has high chemical, mechanical, and thermal stability and is easy to mold, is commonly used.

[0034] A variety of materials and structures have been developed for the separation functional layer that essentially exhibits the separation performance of ions, etc. in a composite semipermeable membrane, and examples thereof include thin films made of materials such as polyamide, cellulose acetate, graphene, polystyrene sulfonic acid, polyallylamine, and siloxane derivatives. Although not particularly limited, a crosslinked polyamide thin film, which has excellent water permeability and selective separation properties, is preferably used. The crosslinked polyamide separation functional layer is formed by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide, and typically has a thickness of about 0.01 to 1 μm.

[0035] The change factor that is the subject of the performance change analysis method of the present invention is not particularly limited, but is preferably at least one selected from the group consisting of physical damage, chemical deterioration, and compaction.

[0036] Physical damage refers to a state in which a composite semipermeable membrane is damaged by a physical external stimulus, causing a portion of the raw water to leak through to the permeate side of the separation membrane. An example of physical damage is abrasion caused by contact with the inflowing material.

[0037] Chemical degradation refers to a decrease in the performance of the separation membrane due to changes in the chemical structure of the composite semipermeable membrane caused by chemical reactions. Examples of chemical degradation include oxidative degradation caused by contact with disinfectants that flow in due to a malfunction in the pretreatment process, and changes in the higher-order structure of the separation membrane polymer caused by chemical cleaning under excessive conditions.

[0038] Compaction refers to irreversible deformation of the composite semipermeable membrane due to high pressure operation.

[0039] The method for analyzing changes in performance of the composite semipermeable membrane of the present invention includes the following steps A to C.

[0040] (Step A) In the performance change analysis method of the present invention, it is necessary to remove the separation functional layer from the composite semipermeable membrane to obtain a support membrane. The method for removing the separation functional layer is not particularly limited, but a method of chemically decomposing the separation functional layer is preferred in order to maintain the structure of the support membrane. Furthermore, from the viewpoint of ease of operation, a method of chemically decomposing the separation functional layer is more preferably a method of contacting the separation functional layer with an oxidizing agent. A specific example is a method of immersing the composite semipermeable membrane in an aqueous sodium hypochlorite solution.

[0041] (Step B) In the performance change analysis method of the present invention, the support membrane obtained in step A is analyzed or measured for a performance change index. The performance change index for the support membrane is not particularly limited as long as it is a value of the structure or performance of the support membrane that changes with deterioration of the composite semipermeable membrane, and examples include the thickness, pore size, porosity, density, molecular weight, chemical structure, elemental composition, molecular weight cutoff, air permeability, and water permeability of the porous support layer. Among these, the water permeability of the support membrane is preferably used because it is easy to measure and analyze.

[0042] When physical damage is included in the change factors, examples of performance change indicators of physical damage include the molecular weight cutoff and air permeability of the support membrane. Various methods for measuring the molecular weight cutoff of a support membrane are known, including, for example, a method in which raw water containing polyethylene glycols of different molecular weights as solutes is supplied to the support membrane and the relationship between molecular weight and removal rate is derived from the concentrations of the raw water and permeated water. The air permeability of the support membrane can be measured by known methods such as the Frazier method, differential pressure method, and gas permeation test.

[0043] When the change factor includes chemical degradation, examples of performance change indicators due to chemical degradation include the molecular weight of the porous support layer, the chemical structure of the porous support layer, and the elemental composition of the porous support layer. The molecular weight of the porous support layer can be measured by known methods such as gel permeation chromatography, light scattering, and viscosity analysis. The chemical structure of the porous support layer can be analyzed by known methods such as infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, and Rutherford backscattering spectroscopy. The elemental composition of the porous support layer can be analyzed by known methods such as energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray fluorescence analysis, and combustion analysis.

[0044] When the change factor includes compaction, examples of performance change indicators of compaction include the thickness, pore size, porosity, density, and water permeability of the porous support layer. The thickness of the porous support layer can be measured by known methods such as a film thickness meter, air microsensor, optical interferometer, and ellipsometry, or by microscopic observation of a cross section obtained by fracturing a frozen support membrane. The pore size of the porous support layer can be measured by known methods such as mercury intrusion, gas adsorption, bubble point, and microscopic image analysis. The porosity of the porous support layer can be measured by known methods such as CT scan image analysis and water evaporation. The density of the porous support layer can be measured by known methods such as the Archimedes method, pycnometer method, and gas displacement method. The water permeability of the support membrane can be determined by measuring the amount of pure water passing through it over a certain period of time. Conventionally, in order to estimate a change in separation membrane performance due to compaction, it was necessary to use operating condition information, but according to one embodiment of the present invention, it is possible to quantitatively analyze the compaction of a composite semipermeable membrane based on a performance change index of compaction of a support membrane obtained by removing a separation functional layer from a composite semipermeable membrane after operation. Therefore, even when a composite semipermeable membrane with an unclear operating history is used, reliable improvements in the operation of a water treatment plant can be implemented.

[0045] More specifically, the water permeability of the support membrane is calculated as the pure water permeability coefficient based on the following formula after supplying pure water to the support membrane at a constant pressure and measuring the amount of pure water permeated over a certain period of time: Pure water permeability coefficient = pure water permeability / (membrane area x water sampling time x supply pressure)

[0046] (Step C) In the performance change analysis method of the present invention, the performance change due to the change factor of the composite semipermeable membrane to be analyzed is calculated from the analysis result or measurement result of the performance change index of the support membrane to be analyzed obtained in step B, using the "relational formula between the performance change index of the support membrane and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane" obtained in advance.

[0047] The method for creating the relational equation is explained below. Using composite semipermeable membranes manufactured by the same manufacturing method as the composite semipermeable membrane to be analyzed, a plurality of composite semipermeable membrane samples are degraded under different conditions, and the membrane performance before and after degradation is evaluated to determine the performance ratio or performance difference as a composite semipermeable membrane. In this case, the form of the composite semipermeable membrane to be performance-evaluated is not limited to a flat membrane, but may also be an element processed in combination with components such as a flow path material or a permeate pipe. A performance change index value of the support membrane obtained by removing the separation functional layer from each composite semipermeable membrane after performance evaluation is obtained. A relational equation is created based on the correlation between the performance change index value of the support membrane obtained above and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane.

[0048] A method for pre-changing the performance of a composite semipermeable membrane will be described below.

[0049] The composite semipermeable membrane that has been physically damaged in advance can be prepared by arbitrarily controlling the abrasion conditions in a known method such as a DIN abrasion test or a Tabar abrasion test.

[0050] The pre-chemically deteriorated composite semipermeable membrane can be prepared by supplying or allowing to come into static contact with a flat membrane or an element-shaped composite semipermeable membrane under any conditions with a chemical such as a disinfectant or a detergent used in a water treatment plant.

[0051] The pre-compacted composite semipermeable membrane can be prepared by applying water pressure under any conditions (pressure, temperature, time, etc.) to a flat membrane or element of the composite semipermeable membrane in a pressure-resistant vessel.

[0052] Furthermore, in the performance change analysis method of the present invention, in step C, instead of "the relationship formula between the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane," the relationship formula between the ratio or difference of the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane is used, and instead of the measured value of the performance change index obtained in step B, the ratio or difference of the performance change index before and after the performance change obtained in step B can be used to calculate the performance change due to the change factor of the composite semipermeable membrane. That is, the performance change due to the change factor of the composite semipermeable membrane can be calculated using the relationship formula between the ratio or difference of the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane and the ratio or difference of the performance change index before and after the performance change of the composite semipermeable membrane obtained in step B.

[0053] The performance ratio or difference before and after the performance change of the composite semipermeable membrane is preferably the ratio or difference of at least one performance index showing the performance of the composite semipermeable membrane selected from the group consisting of solute rejection rate, solute permeability, solute permeability coefficient, membrane permeation flux, pure water permeability coefficient, water production rate, and pressure drop. Among these, an index related to water permeability, which is easy to measure and analyze, is particularly preferred.

[0054] (Performance change analysis program for composite semipermeable membrane, recording medium) Another embodiment of the present invention is a performance change analysis program for composite semipermeable membranes, which causes a computer to function as a relational expression input means for inputting a relational expression between a performance change index of a support membrane acquired in advance and a performance ratio or performance difference before and after the performance change of the composite semipermeable membrane, a relational expression storage means for storing the relational expression, and a performance change calculation means for calculating the performance change due to a change factor before and after the performance change of the composite semipermeable membrane based on the relational expression in response to an input of a measured value of the performance change index. This embodiment causes a computer having each means to function to diagnose the deterioration state of a separation membrane. The program of this embodiment can be recorded in a recording device such as a computer memory or a hard disk, and the recording format is not particularly limited. Another embodiment of the present invention is a recording medium on which the performance change analysis program for composite semipermeable membranes is stored.

[0055] The performance change index to be input into the computer is not particularly limited as long as it is a value of the structure or performance of the support membrane that changes with the change in performance of the composite semipermeable membrane, and examples include the thickness, pore size, porosity, chemical structure, elemental composition of the porous support layer, the water permeability of the support membrane, etc. Among these, the water permeability of the support membrane is preferably used because it is easy to measure and analyze.

[0056] 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.

[0057] (Evaluation Method) Water permeability was evaluated using a flat membrane testing device.

[0058] Reference Example 1 An unused reverse osmosis membrane element for seawater desalination was disassembled, and multiple composite semipermeable membrane samples were cut out. A sodium chloride aqueous solution with a concentration of 32,000 mg / L, pH 6.5, and temperature of 25°C was supplied at a pressure of 5.5 MPa and a concentrate flow rate of 3.5 L / min, and the membrane permeation flux of each composite semipermeable membrane sample was measured. Each composite semipermeable membrane sample was consolidated by supplying a sodium chloride aqueous solution with a concentration of 32,000 mg / L, pH 6.5, and temperature of 35°C at a pressure of 7.0 MPa and a concentrate flow rate of 3.5 L / min for a time period ranging from 5 minutes to 6 hours. Then, a sodium chloride aqueous solution with a concentration of 32,000 mg / L, pH 6.5, and temperature of 25°C was supplied at a pressure of 5.5 MPa and a concentrated water flow rate of 3.5 L / min, and the membrane permeation flux of each consolidated composite semipermeable membrane sample was measured, and the membrane permeation flux ratio of each composite semipermeable membrane sample before and after consolidation was determined. Next, each consolidated composite semipermeable membrane sample was immersed in a 2.0 weight percent sodium hypochlorite aqueous solution at 20°C for 24 hours to remove the separation functional layer and obtain a support membrane sample. Pure water at 25°C was supplied to each support membrane sample at a pressure of 0.2 MPa, and the amount of pure water permeated over a certain period of time was measured to determine the pure water permeability coefficient.

[0059] The pure water permeability coefficient of the support membrane for each sample and the membrane permeation flux ratio of the composite semipermeable membrane before and after compaction were plotted as shown in Figure 1, and the relationship was expressed mathematically to obtain the following equation: Membrane permeation flux ratio of composite semipermeable membrane = 0.051 × ln (pure water permeability coefficient of support membrane) + 1.02

[0060] Example 1 A reverse osmosis membrane element of the same type as that used in Reference Example 1, which had been used for seawater desalination for one year, was disassembled, and composite semipermeable membranes were cut out. A sodium chloride aqueous solution with a concentration of 32,000 mg / L, pH 6.5, and temperature of 25°C was supplied to each composite semipermeable membrane at a pressure of 5.5 MPa and a concentrated water flow rate of 3.5 L / min, and the performance was evaluated. As a result, the membrane permeation flux ratio relative to that during production was calculated to be 0.86.

[0061] After the performance evaluation, the composite semipermeable membrane was immersed in a 2.0 weight percent sodium hypochlorite aqueous solution at 20°C for 24 hours, and the separating functional layer was removed to obtain a support membrane. Pure water at 25°C was supplied to the support membrane at a pressure of 0.2 MPa, and the amount of pure water permeated over a certain period of time was measured. As a result, the pure water permeability coefficient was 0.3 × 10 －９ m ３ / m ２ / s / Pa.

[0062] The membrane permeation flux ratio of the composite semipermeable membrane due to compaction alone was calculated based on the relational expression previously obtained in Reference Example 1 and the measured value of the pure water permeability coefficient, and was found to be 0.96, which was greater than the membrane permeation flux ratio of 0.86 measured for the composite semipermeable membrane. It is presumed that the measured membrane permeation flux ratio includes contributions from performance change factors other than compaction, such as fouling.

[0063] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0064] This application is based on a Japanese patent application (Patent Application No. 2023-202424) filed on November 30, 2023, the contents of which are incorporated herein by reference.

[0065] The present invention makes it possible to analyze the contribution of one change factor in a change in the performance of a composite semipermeable membrane while distinguishing it from the influence of other change factors, and is therefore useful for elucidating the cause of performance changes and improving operation in water treatment plants.

Claims

1. A method for quantitatively analyzing the cause of performance changes in a composite semipermeable membrane consisting of a separation functional layer and a support membrane, characterized in that a performance change index of the support membrane obtained by removing the separation functional layer from the composite semipermeable membrane is analyzed or measured.

2. A method for quantitatively analyzing the cause of a performance change of a composite semipermeable membrane consisting of a separation functional layer and a support membrane, comprising the following steps A to C. Step A: A step of removing the separation functional layer from the composite semipermeable membrane to obtain the support membrane. Step B: A step of analyzing or measuring a performance change index of the support membrane. Step C: A step of calculating the performance change due to the change factor of the composite semipermeable membrane using a relational equation between the performance change index of the support membrane and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane obtained in advance, and the analysis or measurement results of the performance change index of the support membrane obtained in step B.

3. The method for analyzing changes in performance of a composite semipermeable membrane described in claim 2, characterized in that in step C, instead of the relational expression between the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane, a relational expression between the ratio or difference of the performance change index of the support membrane obtained in advance and the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane is used, and instead of the measured value of the performance change index obtained in step B, the ratio or difference of the performance change index before and after the performance change obtained in step B is used to calculate the performance change due to the change factor of the composite semipermeable membrane.

4. A method for analyzing changes in the performance of a composite semipermeable membrane as described in claim 2 or 3, characterized in that the method for removing the separation functional layer in step A is a method for contacting the composite semipermeable membrane with an oxidizing agent.

5. A method for analyzing changes in performance of a composite semipermeable membrane according to any one of claims 2 to 4, characterized in that the change factor is at least one selected from the group consisting of physical damage, chemical deterioration and compaction.

6. The method for analyzing changes in performance of a composite semipermeable membrane according to any one of claims 2 to 5, wherein the change factor is compaction.

7. A method for analyzing changes in performance of a composite semipermeable membrane described in any one of claims 2 to 6, characterized in that the performance change index in step B is the water permeability of the support membrane.

8. A method for analyzing a change in performance of a composite semipermeable membrane according to any one of claims 2 to 7, characterized in that the performance ratio or performance difference before and after the performance change of the composite semipermeable membrane in step C is a ratio or difference before and after the performance change of the composite semipermeable membrane of at least one performance index selected from the group consisting of a solute rejection rate, a solute permeability, a solute permeability coefficient, a membrane permeation flux, a pure water permeability coefficient, a water production amount, and a pressure drop.

9. A performance change analysis program for a composite semipermeable membrane consisting of a separation functional layer and a support membrane, which causes a computer to function as: a relational equation input means for inputting a relational equation between a performance change index of the support membrane obtained in advance and a performance ratio or performance difference before and after the performance change of the composite semipermeable membrane; a relational equation storage means for storing the relational equation; and a performance change calculation means for calculating the performance change due to a change factor before and after the performance change of the composite semipermeable membrane based on the relational equation in response to an input of a measurement value of the performance change index.

10. The performance change analysis program for a composite semipermeable membrane according to claim 9, wherein the performance change index is the water permeability of the support membrane.

11. A recording medium having recorded thereon a program for analyzing changes in the performance of the composite semipermeable membrane according to claim 9 or 10.

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