Method for analyzing change in performance of composite semipermeable membrane, program for analyzing change in performance of composite semipermeable membrane, and recording medium

Abstract

The purpose of this invention is to provide a high-precision analytical method that eliminates the influence of deposits in the analysis of the contribution of various variation factors in the performance changes of composite semipermeable membranes. The method relates to a performance change analysis method for composite semipermeable membranes, specifically a method for analyzing the performance changes of a composite semipermeable membrane comprising a separation functional layer and a support membrane caused by variation factors. Its characteristic feature is that the support membrane obtained by removing the separation functional layer from the composite semipermeable membrane is analyzed or measured.

Description

Technical Field

[0001] This invention relates to a method for analyzing performance changes of composite semipermeable membranes used for the selective separation of liquid mixtures. Background Technology

[0002] Regarding the separation of liquid mixtures, various techniques exist for removing substances (such as salts) dissolved in solvents (such as water). Membrane separation, with its advantages of energy saving, space saving, and high separation performance, is seeing increasing applications. Membranes used in membrane separation include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. Separation membrane elements utilizing these membranes are applied to various uses, such as desalination of seawater and brackish water, production of ultrapure water, wastewater reuse, and recovery of valuable substances.

[0003] Most of the reverse osmosis and nanofiltration membranes that have been put into practical use are composite semi-permeable membranes. There are two types of composite semi-permeable membranes: composite semi-permeable membranes with a gel layer and a separation functional layer obtained by cross-linking a polymer on a support membrane; and composite semi-permeable membranes with a separation functional layer obtained by polycondensation of monomers on a support membrane. Among them, composite semi-permeable membranes obtained by coating a support membrane with a separation functional layer formed from cross-linked polyamide (which is obtained by polycondensation reaction between polyfunctional amines and polyfunctional acyl halides) have been widely used as high-performance separation membranes with excellent solvent permeability and selective separation properties.

[0004] Although the degree of change varies depending on the type of membrane, the composition of the liquid being processed, and the operating conditions, the performance of the membrane will change during operation. Therefore, for the stable operation of the liquid processing unit, it is necessary to understand the causes of the changes in the membrane performance and to minimize their impact through operational management.

[0005] Factors contributing to changes in membrane performance include physical damage from contact with incoming foreign matter, chemical degradation from contact with chemicals such as pharmaceuticals, and irreversible compaction due to high-pressure operation. Typically, performance changes in real-world liquid handling systems are related to multiple factors, and techniques for analyzing the contribution of each factor to the performance change are needed to determine the primary cause. The following examples are known techniques for investigating the causes of membrane performance changes.

[0006] Patent document 1 discloses a method for investigating whether there is physical damage to a composite semipermeable membrane, which involves pressurizing a dyeing solution, disassembling the composite semipermeable membrane element to collect a membrane sheet, and visually observing the dyeing position of the membrane sheet.

[0007] In Non-Patent Literature 1, as a method for investigating whether a composite semipermeable membrane has chemical deterioration, the Fujiwaratest test is described, which involves reacting a membrane sample collected by disassembling the composite semipermeable membrane element with an alkaline pyridine solution to confirm whether a color development occurs.

[0008] However, the aforementioned known techniques all use composite semi-permeable membranes as the analytical object, making it difficult to exclude the influence of contaminants (scaling) that adhere during operation. That is, since the deposits affect the staining state and colorimetric reaction, it is impossible to selectively analyze and measure only the composite semi-permeable membrane, leading to reduced accuracy of the analytical results. Furthermore, although methods for washing the scaled composite semi-permeable membrane using physical or chemical methods are known, these methods are difficult to completely remove the scale.

[0009] Furthermore, Non-Patent Document 2 describes that the time-dependent change in the performance of the separation membrane caused by compaction depends on the membrane's raw material, specifications, operating time, temperature of the liquid being treated, and pressure of the liquid being treated. Non-Patent Document 3 describes a method for expressing the time-dependent change in the performance of the separation membrane caused by compaction using a compaction coefficient (m-value). In the empirical formula described in Non-Patent Document 3, the m-value is set to be constant if the operating conditions are constant. However, in actual liquid treatment devices, seasonal changes in the water temperature of the liquid being treated, along with accompanying changes in the pressure of the liquid being treated, will occur; therefore, the m-value may not be constant. Non-Patent Document 4 describes a method for more accurately estimating the m-value after a specified time by successive calculations based on the time-dependent changes in the temperature and pressure of the liquid being treated.

[0010] The aforementioned known techniques related to compaction all estimate the changes in separation membrane performance caused by compaction based on operating condition information. This requires obtaining the aforementioned operating condition information, but for liquid handling devices lacking sufficient instrumentation, there are situations where this information cannot be obtained. In such cases, it is necessary to investigate the structure and performance of the separation membrane after operation to infer the changes in separation membrane performance caused by compaction.

[0011] However, as mentioned above, the separation membrane after operation is affected by scaling that occurs during operation. The effect of scaling is only manifested in the separation functional layer that comes into contact with the liquid being treated. Therefore, by investigating the support membrane obtained after removing the separation functional layer, the effect of scaling can be eliminated and the changes in the performance of the separation membrane can be estimated. Patent Document 2 describes a method for analyzing the surface elastic modulus and surface roughness of the support membrane obtained after removing the separation functional layer of the composite semi-permeable membrane.

[0012] Existing technical documents Patent documents Patent Document 1: International Publication No. 2015 / 063975 Patent Document 2: Japanese Patent No. 7343075 Non-patent literature Non-patent literature 1: Journal of Membrane Science, 2010, Vol.347, pp.159-164 Non-patent literature 2: Bernard Baum, Stanley A. Margosiak, and William H. Holley, Jr., Ind. Eng. Chem. Prod. Res. Dev., vol. 11, No. 2, 195 (1972). Non-patent literature 3: Takashi Kimura, Membranes, Vol. 6, No. 3, 83 (1981) Non-patent literature 4: Naohiko UKAWA, Ikuo NAKATANI and Hideo IWAHASHI, Journal of the Japan Marine Science Society, Vol. 43, No. 4, 218 (1989) Summary of the Invention

[0013] The problem that the invention aims to solve While conventional methods can identify the involvement of various factors in investigating performance changes in composite semipermeable membranes, the influence of deposits reduces analytical precision. This invention addresses this issue by providing a high-precision analytical method that eliminates the influence of deposits when analyzing the contributions of different factors to the performance changes of composite semipermeable membranes.

[0014] Methods for solving problems In order to solve the above-mentioned problems, the present invention has the following (1) to (11) configurations.

[0015] (1) A method for analyzing the performance changes of a composite semipermeable membrane, which is a method for quantitatively analyzing the causes of performance changes of a composite semipermeable membrane containing 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.

[0016] (2) The performance change analysis method of the composite semipermeable membrane described in (1) above is a method for quantitatively analyzing the causes of performance changes of a composite semipermeable membrane containing a separation functional layer and a support membrane, wherein the performance change analysis method includes the following steps A to C.

[0017] Step A: The process of removing the aforementioned separation functional layer from the aforementioned composite semipermeable membrane to obtain the aforementioned support membrane.

[0018] Process B: The process of analyzing or measuring the performance change indicators of the aforementioned support membrane.

[0019] Step C: Using the previously obtained performance change index of the aforementioned support membrane and the relationship between the performance ratio or performance difference of the aforementioned composite semipermeable membrane before and after the performance change, as well as the analysis or measurement results of the performance change index of the aforementioned support membrane obtained in Step B, the process of calculating the performance change of the aforementioned composite semipermeable membrane caused by the change factor.

[0020] (3) The composite semipermeable membrane performance change analysis method as described in (2) above is characterized in that, in the aforementioned step C, instead of the previously obtained performance change index of the aforementioned support membrane and the performance ratio or performance difference of the aforementioned composite semipermeable membrane before and after the performance change, the previously obtained ratio or difference of the performance change index of the aforementioned support membrane before and after the performance change and the performance ratio or performance difference of the aforementioned composite semipermeable membrane before and after the performance change are used; and instead of the measured value of the performance change index obtained in the aforementioned step B, the ratio or difference of the performance change index of the aforementioned support membrane before and after the performance change is used to calculate the performance change of the aforementioned composite semipermeable membrane caused by the change factor.

[0021] (4) The performance change analysis method of the composite semipermeable membrane as described in (2) or (3) above, characterized in that the method of removing the aforementioned separation functional layer in the aforementioned process A is a method of contacting the aforementioned composite semipermeable membrane with the oxidant.

[0022] (5) The performance change analysis method of the composite semipermeable membrane as described in any one of (2) to (4) above, characterized in that the aforementioned change factor is selected from at least one of the group consisting of physical damage, chemical degradation and compaction.

[0023] (6) The performance change analysis method of the composite semipermeable membrane as described in any one of (2) to (5) above, characterized in that the aforementioned change factor is compaction.

[0024] (7) The performance change analysis method of the composite semipermeable membrane as described in any one of (2) to (6) above, characterized in that the aforementioned performance change index in the aforementioned step B is the water permeability of the aforementioned support membrane.

[0025] (8) The performance change analysis method of the composite semipermeable membrane as described in any one of (2) to (7) above, characterized in that the performance ratio or performance difference of the composite semipermeable membrane before and after the performance change in the aforementioned step C is the ratio or difference of at least one performance index selected from the group consisting of solute removal rate, solute permeability, solute permeability coefficient, membrane permeation flux, pure water permeability coefficient, water production capacity and pressure loss before and after the performance change of the aforementioned composite semipermeable membrane.

[0026] (9) A performance change analysis program for composite semipermeable membranes, which is used to enable a computer to function as a mechanism for analyzing the performance changes of composite semipermeable membranes: The relational input mechanism inputs the pre-obtained relational formula between the performance change index of the aforementioned support membrane and the performance ratio or performance difference of the aforementioned composite semipermeable membrane before and after the performance change. A relational storage mechanism that stores the aforementioned relational expressions; The performance change calculation mechanism calculates the performance change of the composite semipermeable membrane before and after the performance change caused by the change factor based on the aforementioned relationship, using the measured values ​​of the aforementioned performance change indicators as input.

[0027] (10) The performance change analysis procedure of the composite semipermeable membrane as described in (9) above, characterized in that the aforementioned performance change index is the water permeability of the aforementioned support membrane.

[0028] (11) A recording medium that records the performance change analysis program of the composite semipermeable membrane described in any one of (9) or (10) above.

[0029] Invention Effects According to the performance change analysis method of the present invention, the contribution of the change factors in the performance of the composite semipermeable membrane can be quantitatively grasped. Therefore, it is expected that the operation of water treatment equipment can be effectively improved based on the determination of the cause of performance change. Attached Figure Description

[0030] [ Figure 1 This is a graph showing the relationship between the pure water permeability coefficient of the compacted support membrane and the permeation flux ratio of the composite semipermeable membrane before and after compaction. Detailed Implementation

[0031] The present invention will now be described in detail, but these descriptions are examples of preferred embodiments and the present invention is not limited thereto.

[0032] This invention analyzes or measures the performance changes of the support membrane obtained after removing the separation functional layer from a composite semi-permeable membrane, and analyzes the performance changes of the composite semi-permeable membrane caused by changing factors. That is, without measuring the time-dependent changes in the performance of the separation membrane during the operation of the water treatment equipment, it is possible to quantitatively analyze the contribution of changing factors to the performance changes of the separation membrane during the operation of the water treatment equipment based on the performance change indicators of the support membrane obtained after removing the separation functional layer. It should be noted that the performance changes of the composite semi-permeable membrane in this invention refer to changes in membrane permeation flux, pure water permeation coefficient, water production capacity, pressure loss, etc.

[0033] (Object of analysis) In the performance change analysis method of this invention, the shape and material of the composite semipermeable membrane being analyzed are not particularly limited; for example, a composite material with a separation functional layer formed on a support membrane can be used. In particular, cross-linked polyamide composite semipermeable membranes, which are currently widely used in various applications, are the main objects of analysis.

[0034] Cross-linked polyamide composite semi-permeable membranes are composite membranes comprising three layers: a substrate, a porous support layer, and a separation functional layer formed from cross-linked polyamide. The support membrane, including the substrate and the porous support layer, does not actually exhibit separation properties such as ion separation; rather, it is used to impart strength to the separation functional layer responsible for separation performance.

[0035] The raw materials and shape of the substrate are not particularly limited, and examples include fabrics or nonwovens with at least one of polyester, polyamide, and polyolefin as the main component. Polyester with high mechanical and thermal stability is preferred. In terms of substrate thickness, to ensure dimensional stability, it is typically in the range of 10 to 200 μm.

[0036] The raw material and shape of the porous support layer disposed between the substrate and the separation functional layer are not particularly limited. It is typically a porous structure with micropores of approximately 0.1 nm to 100 nm on the surface of the side where the separation functional layer is formed. This can be obtained, for example, by phase separation of a polymer cast on the substrate. For the raw material of the porous support layer, various polymeric materials such as polysulfone, polyethersulfone, polyphenylene sulfide sulfone, polyphenylene sulfone, and cellulose acetate can be used alone or in mixtures. Polysulfone, which has high chemical stability, mechanical stability, thermal stability, and is easy to mold, is commonly used.

[0037] As the separation functional layer in a composite semi-permeable membrane that substantially performs the separation of ions, various raw materials and structures have been developed. Examples of membranes using raw materials such as polyamide, cellulose acetate, graphene, polystyrene sulfonic acid, polyallylamine, and siloxane derivatives are not particularly limited, but cross-linked polyamide membranes with excellent water permeability and selective separation properties are preferred. The cross-linked polyamide separation functional layer is formed through the polycondensation reaction of polyfunctional amines and polyfunctional acyl halides, and typically has a thickness of about 0.01–1 μm.

[0038] While there is no particular limitation on the change factors that are the object of the performance change analysis method of the present invention, it is preferred to select at least one of the group consisting of physical damage, chemical degradation and compaction.

[0039] Physical damage refers to a defect that occurs in a composite semipermeable membrane due to external physical stimuli, causing some of the raw water to leak into the permeate side of the separation membrane. An example of physical damage is abrasion caused by contact with influent.

[0040] Chemical degradation refers to the change in the chemical structure of a composite semipermeable membrane due to chemical reactions, resulting in a decrease in membrane performance. Examples of chemical degradation include oxidative degradation caused by contact with bactericides that flow in due to defects in the pretreatment process, and changes in the higher-order structure of the membrane polymer caused by excessive washing with chemicals under excessive conditions.

[0041] Compactionization refers to the irreversible deformation of a composite semipermeable membrane due to high-pressure operation.

[0042] As a method for analyzing the performance changes of the composite semipermeable membrane of the present invention, a method comprising the following steps A to C can be cited.

[0043] (Process A) In the performance change analysis method of the present invention, a support membrane is obtained by removing the separation functional layer from the composite semipermeable membrane. The method for removing the separation functional layer is not particularly limited, but a method of chemically decomposing the separation functional layer to maintain the structure of the support membrane is preferred. Furthermore, from the viewpoint of ease of operation, a method of contacting the separation functional layer with an oxidant is more preferred as a method of chemically decomposing the separation functional layer. As a specific example, immersing the composite semipermeable membrane in an aqueous sodium hypochlorite solution can be cited.

[0044] (Process B) In the performance change analysis method of this invention, the performance change indicators are analyzed or measured using the support membrane obtained in step A as the object. As for the performance change indicators of the support membrane, there are no particular limitations as long as they are values ​​of the structure and properties of the support membrane that change along with the deterioration of the composite semi-permeable membrane. Examples include the thickness, pore size, porosity, density, molecular weight, chemical structure, elemental composition of the porous support layer, the molecular weight cutoff of the support membrane, air permeability, and water permeability. Preferably, the water permeability of the support membrane, which is easy to measure and analyze, is used.

[0045] When the changing factors include physical damage, performance indicators of physical damage can include, for example, the molecular weight cutoff and air permeability of the support membrane. Various methods are known for determining the molecular weight cutoff of the support membrane. For instance, one method involves supplying raw water with polyethylene glycol of different molecular weights as solutes to the support membrane and deriving the relationship between molecular weight and removal rate from the concentrations of the raw water and permeated water. The air permeability of the support membrane can be determined using known methods such as the Frazer method, differential pressure method, and gas permeation test.

[0046] When chemical degradation is a factor of change, performance changes due to chemical degradation can be exemplified by the molecular weight, chemical structure, and elemental composition of the porous support layer. The molecular weight of the porous support layer can be determined using known methods such as gel permeation chromatography, light scattering, and viscometry. The chemical structure of the porous support layer can be analyzed using 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 using known methods such as energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, fluorescence X-ray analysis, and combustion analysis.

[0047] When compaction is involved, performance indicators of the compressibility can include the thickness, pore size, porosity, density, and permeability of the porous support layer. The thickness of the porous support layer can be measured using known methods such as film thickness gauges, air microsensors, optical interferometers, and ellipsometry, or by microscopic observation of cross-sections obtained from cutting frozen support layers. The pore size of the porous support layer can be measured using known methods such as mercury intrusion porosimetry, gas adsorption, bubble point analysis, and microscopic image analysis. The porosity of the porous support layer can be measured using known methods such as CT scan image analysis and water evaporation methods. The density of the porous support layer can be measured using known methods such as the Archimedes method, specific gravity bottle method, and gas displacement method. The permeability of the support membrane can be determined by measuring the amount of pure water that permeates over a certain period of time. Previously, estimating changes in the performance of separation membranes caused by compaction required operating condition information. However, according to an embodiment of the present invention, the compaction of the composite semi-permeable membrane can be quantitatively analyzed based on performance changes in the support membrane obtained by removing the separation functional layer from the composite semi-permeable membrane after operation. Therefore, even when using composite semi-permeable membranes with unclear operating histories, it is possible to implement tangible improvements in the operation of water treatment equipment.

[0048] More specifically, the permeability of the support membrane is calculated in the form of a pure water permeation coefficient based on the following formula, after supplying pure water to the aforementioned support membrane under a certain pressure and measuring the amount of pure water permeation over a certain period of time.

[0049] Pure water permeability coefficient = Pure water permeation rate ÷ (Membrane area × Water sampling time × Supply pressure) (Process C) In the performance change analysis method of the present invention, the "relationship between the performance change index of the support membrane and the performance ratio or performance difference of the composite semipermeable membrane before and after the performance change" obtained in advance is used. Based on the analysis results or measurement results of the performance change index of the support membrane as the analysis object obtained in step B, the performance change of the composite semipermeable membrane as the analysis object caused by the change factor is calculated.

[0050] The method for generating the aforementioned relationship is explained below. Using a composite semi-permeable membrane manufactured using the same method as the composite semi-permeable membrane being analyzed, multiple composite semi-permeable membrane samples were degraded under their respective conditions. The membrane performance before and after the degradation was evaluated, and the performance ratio or performance difference of the composite semi-permeable membrane was determined. The form of the composite semi-permeable membrane used for performance evaluation is not limited to a flat membrane; it can also be an element obtained by combining it with components such as flow path materials and permeable water pipes and then processing it. The performance change index value of the support membrane obtained after removing the separation functional layer from each composite semi-permeable membrane after performance evaluation was obtained. A relationship was generated based on the correlation between the performance change index value of the support membrane obtained above and the performance ratio or performance difference of the composite semi-permeable membrane before and after the performance change.

[0051] The method for pre-changing the properties of the composite semipermeable membrane is described below.

[0052] The pre-damaged composite semipermeable membrane can be prepared by arbitrarily controlling the wear conditions using known methods such as the DIN wear test and the Tiber wear test.

[0053] The pre-chemically degraded composite semipermeable membrane can be prepared by supplying or allowing the bactericides, detergents, and other chemicals used in water treatment equipment to contact the flat or element-shaped composite semipermeable membrane under any conditions.

[0054] The pre-compacted composite semipermeable membrane can be prepared by applying water pressure (pressure, temperature, time, etc.) to the flat membrane or element of the composite semipermeable membrane in a pressure vessel.

[0055] Furthermore, in the performance change analysis method of the present invention, in step C, instead of "the pre-obtained relationship between the performance change index of the support membrane and the performance ratio or difference of the composite semi-permeable membrane before and after the performance change", the pre-obtained relationship between the ratio or difference of the performance change index of the support membrane before and after the performance change and the performance ratio or difference of the composite semi-permeable membrane before and after the performance change can be 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 obtained in step B can be used to calculate the performance change of the composite semi-permeable membrane caused by the change factor. That is, the performance change of the composite semi-permeable membrane caused by the change factor can be calculated using the pre-obtained relationship between the ratio or difference of the performance change index of the support membrane before and after the performance change and the performance ratio or difference of the composite semi-permeable membrane before and after the performance change, as well as the ratio or difference of the performance change index obtained in step B.

[0056] The ratio or difference in performance of the aforementioned composite semi-permeable membrane before and after the performance change is preferably a ratio or difference selected from at least one of the following performance indicators representing the performance of the composite semi-permeable membrane: solute removal rate, solute permeability, solute permeation coefficient, membrane permeation flux, pure water permeation coefficient, water production capacity, and pressure loss. Among these, indicators related to permeability, which are easily measured and analyzed, are particularly preferred.

[0057] (Performance change analysis program and recording medium for composite semi-permeable membrane) As another aspect of the present invention, a performance change analysis program for composite semi-permeable membranes can be provided. This program enables a computer to function as a performance change analysis mechanism, which inputs a pre-obtained relationship between the performance change index of the support membrane and the performance ratio or difference of the composite semi-permeable membrane before and after the performance change; a relationship storage mechanism stores the relationship; and a performance change calculation mechanism calculates the performance change of the composite semi-permeable membrane caused by the change factor before and after the performance change based on the relationship, using the measured value of the performance change index as input. This method enables a computer with each mechanism to function for the purpose of diagnosing the deterioration state of the separation membrane. The program of this method can be stored in a computer's memory, hard disk, or other recording device, and the recording method is not particularly limited. Furthermore, as another aspect of the present invention, a recording medium storing the aforementioned performance change analysis program for composite semi-permeable membranes can be provided.

[0058] The performance change indicators input into the computer are not particularly limited as long as they are values ​​of the structure and performance of the support membrane that change together with the performance change of the composite semi-permeable membrane. Examples include the thickness, pore size, porosity, chemical structure, elemental composition of the porous support layer, and the water permeability of the support membrane. Among these, the water permeability of the support membrane, which is easy to measure and analyze, is preferred.

[0059] Example The present invention will now be described in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0060] (Evaluation Method) The permeability was evaluated using a flat membrane testing device.

[0061] <Reference Example 1> Unused reverse osmosis membrane elements for seawater desalination were disassembled, and multiple composite semi-permeable membrane samples were cut out. A sodium chloride aqueous solution with a concentration of 32000 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 semi-permeable membrane sample was measured. For each composite semi-permeable membrane sample, a sodium chloride aqueous solution with a concentration of 32000 mg / L, pH 6.5, and temperature of 35°C was supplied at a pressure of 7.0 MPa and a concentrate flow rate of 3.5 L / min for varying time conditions from 5 minutes to 6 hours, thereby compacting the composite semi-permeable membrane samples. Then, a sodium chloride aqueous solution with a concentration of 32000 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 compacted composite semi-permeable membrane sample was measured, and the membrane permeation flux ratio before and after compaction was determined. Next, each compacted composite semipermeable membrane sample was immersed in a 2.0% by weight sodium hypochlorite aqueous solution at 20°C for 24 hours to remove the separation functional layer, thus obtaining the support membrane sample. Pure water at 25°C was supplied to each support membrane sample at a pressure of 0.2 MPa, and the pure water permeation rate was measured over a certain period of time to determine the pure water permeation coefficient.

[0062] The pure water permeation coefficient of the supporting membrane and the membrane permeation flux of the composite semi-permeable membrane before and after compaction in each sample, as calculated above, are used as examples. Figure 1 By drawing the diagram in that way and converting the relationship into a formula, we obtain the following expression.

[0063] The membrane permeation flux ratio of the composite semi-permeable membrane = 0.051 × ln(pure water permeation coefficient of the supporting membrane) + 1.02 <Example 1> A reverse osmosis membrane element of the same model as that in Reference Example 1, which had been used for seawater desalination for one year, was disassembled, and composite semi-permeable membranes were cut out. Each composite semi-permeable membrane was fed a sodium chloride aqueous solution with a concentration of 32000 mg / L, pH 6.5, and temperature of 25°C at a pressure of 5.5 MPa, a concentrate flow rate of 3.5 L / min, to evaluate its performance. The results showed that the ratio of the membrane permeation flux to that at production was 0.86.

[0064] The composite semi-permeable membrane, after performance evaluation, was immersed in a 2.0% (w / w) sodium hypochlorite aqueous solution at 20°C for 24 hours. The separation functional layer was then removed, and pure water at 25°C was supplied to the resulting support membrane at a pressure of 0.2 MPa. The pure water permeation rate was measured over a certain period, and the pure water permeation coefficient was calculated to be 0.3 × 10⁻⁶. -9 m 3 / m 2 / s / Pa.

[0065] Based on the pre-obtained relationship in Reference Example 1 and the measured value of the pure water permeability coefficient, the membrane permeation flux ratio of the composite semipermeable membrane caused solely by compaction was calculated to be 0.96. This result is larger than the measured membrane permeation flux ratio of 0.86 obtained for the composite semipermeable membrane. It is speculated that the measured membrane permeation flux ratio includes the contribution of performance change factors other than compaction, such as scaling.

[0066] The various embodiments have been described above, but the present invention is not limited to these examples. Obviously, those skilled in the art will be able to conceive of various variations or modifications within the scope of the patent claims, and these should also be understood to fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

[0067] It should be noted that this application is based on Japanese patent application (Japanese Patent Application No. 2023-202424) filed on November 30, 2023, the contents of which are incorporated herein by reference.

[0068] Industrial availability This invention enables the analysis of the contribution of one variable factor in the performance variation of a composite semipermeable membrane, distinguishing it from the influence of other variable factors. Therefore, it is useful for elucidating the causes of performance variations in water treatment equipment and improving its operation.

Claims

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

2. The method for analyzing the change in performance of a composite semipermeable membrane according to claim 1, which is a method for quantitatively analyzing the cause of the change in performance of a composite semipermeable membrane comprising a separation functional layer and a support membrane, wherein The performance change analysis method includes the following steps A to C. Step A: The step of removing the separation functional layer from the composite semipermeable membrane to obtain the support membrane; Process B: The process of analyzing or measuring the performance change indicators of the support membrane; Step C: Using the pre-obtained relationship between the performance change index of the support membrane and the performance ratio or difference of the composite semipermeable membrane before and after the performance change, as well as the analysis or measurement results of the performance change index of the support membrane obtained in Step B, the performance change of the composite semipermeable membrane caused by the change factor is calculated.

3. The method of claim 2, wherein the composite semipermeable membrane is a hollow fiber membrane. In step C, instead of the previously obtained relationship between the performance change index of the support membrane and the performance ratio or difference of the composite semipermeable membrane before and after the performance change, the previously obtained relationship between the ratio or difference of the performance change index of the support membrane before and after the performance change and the performance ratio or difference of the composite semipermeable membrane before and after the performance change is used. Furthermore, instead of the measured value of the performance change index obtained in step B, the ratio or difference of the performance change index obtained in step B is used to calculate the performance change of the composite semipermeable membrane caused by the change factor.

4. The method for analyzing the performance change of a composite semipermeable membrane according to claim 2 or 3, characterized in that, The method for removing the separation functional layer in step A is to bring the composite semi-permeable membrane into contact with an oxidant.

5. The method for analyzing the performance change of a composite semipermeable membrane according to any one of claims 2 to 4, wherein The change factor is selected from at least one of the group consisting of physical damage, chemical degradation, and compaction.

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

7. The method for analyzing the performance change of a composite semipermeable membrane according to any one of claims 2 to 6, wherein The performance change index in process B is the water permeability of the support membrane.

8. The method for analyzing the performance change of a composite semipermeable membrane according to any one of claims 2 to 7, wherein The performance ratio or difference of the composite semi-permeable membrane before and after the performance change in step C is the ratio or difference of at least one performance index selected from the group consisting of solute removal rate, solute permeability, solute permeability coefficient, membrane permeation flux, pure water permeability coefficient, water production capacity, and pressure loss before and after the performance change of the composite semi-permeable membrane.

9. A program for analyzing a change in performance of a composite semipermeable membrane, which is a program for analyzing a change in performance of a composite semipermeable membrane comprising a separation functional layer and a support membrane, wherein, The performance change analysis program is used to enable the computer to function as a mechanism for: The relational input mechanism inputs the pre-obtained relational formula between the performance change index of the support membrane and the performance ratio or performance difference of the composite semipermeable membrane before and after the performance change. A relational storage mechanism that stores the relation; The performance change calculation mechanism calculates the performance change of the composite semipermeable membrane before and after the performance change caused by the change factor based on the measured value input of the performance change index and the relationship.

10. The program for analyzing the performance change of 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 that records a performance change analysis program for the composite semipermeable membrane according to any one of claims 9 or 10.

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