Defect analysis method for desalination rate performance of reverse osmosis membrane

Abstract

The invention relates to the technical field of reverse osmosis, in particular to a desalination rate performance defect analysis method of a reverse osmosis membrane. According to the method, membrane damage is diagnosed step by step by adopting three steps of exclusion, positioning and qualification: firstly, non-damage problems such as dirt blockage and leakage are eliminated through performance testing, O-shaped ring inspection and chemical cleaning; dyeing with 0.3 MPa low pressure + 480-520 ppm gentian violet (avoiding secondary damage, and converting desalination rate reduction into line, block and point atlas) to locate irreversible damage; and finally, detecting N-X bonds (halogen oxidized'biomarkers') on a polyamide chain of the membrane through chemical color development and qualitative oxidative damage (which is more pathological than that of pure detection of elements). According to the method, the composite damage (such as oxidation and physical wear) can be analyzed through a dyeing form (such as dense distribution points suggest oxidation and discrete lines suggest physical wear), the process is simple, and the method can be operated without a standard laboratory.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis technology, and more specifically to a method for analyzing the desalination performance defects of reverse osmosis membranes. Background Technology

[0002] Reverse osmosis technology, as one of the key technologies in membrane water treatment, has been widely used in many fields such as chemical engineering, environmental protection, papermaking, and semiconductors due to its excellent filtration, separation, and purification performance. The principle of this technology is to overcome the osmotic pressure of the solution by applying high pressure equivalent to 4 to 20 times the osmotic pressure of the solution, thereby achieving the separation of the solute and water, and ultimately achieving the purpose of separation and purification.

[0003] Reverse osmosis technology has seen its application rate increase year by year in various fields of water treatment due to its many advantages, such as ease of operation, low cost, no phase change, and no chemical reaction. However, during the use of reverse osmosis membranes, problems in system design, system operation, usage, cleaning, and maintenance can damage the desalination layer of the reverse osmosis membrane, leading to a serious decline in the desalination performance of the membrane element. This can result in a series of problems, including reduced project production efficiency, equipment downtime, membrane module replacement, increased operating costs, and increased equipment maintenance difficulty.

[0004] The existing solutions mainly fall into two categories of detection methods: 1. Conventional methods for analyzing the desalination performance defects of reverse osmosis membranes primarily involve conducting basic performance tests on the flux and desalination rate of membrane elements to determine the damage status of the reverse osmosis membrane desalination layer. However, these conventional methods lack a complete and easily operable analytical workflow, resulting in insufficient depth of failure diagnosis. This leads to the recurrence of the same type of membrane performance defects within the same system or across different projects, creating a vicious cycle of "damage - analysis (unknown cause) - replacement - recurring damage," which fails to improve the overall level of system design and operation maintenance.

[0005] 2. In addition, advanced scientific and technological methods can be used, such as X-ray photoelectron spectroscopy and ATR-FTIR infrared spectroscopy, to observe the microstructure of the reverse osmosis desalination layer, clarify the damage to the desalination layer, and ultimately determine the damage status of the reverse osmosis surface.

[0006] The two methods mentioned above can only determine the extent of damage to the desalination layer of the membrane element and the degree of damage to the membrane element itself. However, they cannot pinpoint the cause of the damage, making it difficult to implement targeted and effective prevention or improvement measures in practical applications. Furthermore, existing technologies cannot effectively determine the specific reasons for the decline in desalination performance of the membrane element during operation, thereby reducing the efficiency of reverse osmosis membranes under complex operating conditions and the service life of the membrane element.

[0007] Currently, China's reverse osmosis membrane technology lags behind internationally renowned brands such as Dow, and analytical methods for addressing performance defects in reverse osmosis desalination rates are relatively scarce.

[0008] CN109884076A describes a method for analyzing the desalination performance of reverse osmosis membranes. The method includes a detection procedure for abnormal desalination in reverse osmosis membranes, which involves staining the membrane element with a dye and determining the cause of the abnormality by observing the morphology of the stained area. However, this method can only preliminarily confirm that the membrane element is damaged, but it cannot identify the specific cause of the abnormality.

[0009] CN110538581A introduces a method for determining the oxidation of reverse osmosis membranes. The method describes an analysis of the damage to the desalination layer of the membrane using X-ray photoelectron spectroscopy or ATR-FTIR infrared spectroscopy. However, this method has a complicated operation process and may require the commissioning of a professional testing agency to carry out the testing, which will increase the time and production costs. It is not suitable for routine analysis and it is difficult to specifically analyze the cause of the damage.

[0010] Therefore, it is urgent to explore a conventional analytical method for the desalination performance defects of reverse osmosis membranes, so as to achieve a rapid response to the post-sales analysis of the desalination performance defects of the project system, identify the problem, explore solutions, and ensure the long-term stable operation of the system. Summary of the Invention

[0011] This invention aims to provide a method for analyzing the performance defects of reverse osmosis membranes in terms of desalination rate. This method is particularly suitable for the qualitative analysis of reverse osmosis membrane oxidation. The specific scheme is as follows: A method for analyzing the desalination performance defects of a reverse osmosis membrane, comprising the following steps: (1) Observe whether the fiberglass of the reverse osmosis membrane element to be analyzed and its two end faces are clean, tidy and undamaged; (2) Weigh the membrane element to be analyzed; (3) Test the flux and desalination rate of the membrane element to be analyzed under national standard conditions; if the desalination rate is normal, check whether there is O-ring leakage in the system; if the desalination rate exceeds the normal range, determine that the desalination rate is abnormal and proceed to the next step of analysis. (4) After acid and alkali chemical cleaning, the membrane element to be analyzed is tested again according to national standards. If the desalination rate of the membrane element is restored, it indicates that the membrane element is seriously contaminated; if the desalination rate is not restored, the next test is carried out. (5) The membrane element to be analyzed is subjected to a low-pressure operation staining test using a staining agent, namely gentian violet; the membrane element to be analyzed is disassembled and the staining of the reverse osmosis membrane surface and the staining of the reverse osmosis membrane non-woven support layer are observed; if the membrane staining shows discrete lines, it indicates that the membrane surface is physically worn; if the membrane staining shows a regular pattern, it indicates that the membrane itself is abnormal; if the membrane staining is concentrated in a certain area and a large area of ​​staining occurs, it indicates that the membrane desalination layer adheres to the scale during the cleaning process after the membrane element has scaled, and the desalination layer falls off along with the scale during cleaning; if the membrane staining shows a large area of ​​dense scattered spots, it indicates that the membrane has been oxidized and damaged, and the type of oxidation of the membrane needs to be further determined. (6) Cut the membrane that has been dyed into dense red dot areas, and soak the membrane with a surfactant to remove the dye from the surface of the membrane; (7) Soak the soaked and cleaned membrane in clean water for later use, and prepare the halogen element oxidation qualitative detection solution; soak the soaked and cleaned membrane in the uniformly mixed halogen element oxidation qualitative detection solution, let it stand, and observe the color change of the reaction system.

[0012] In step (5), the concentration of gentian violet is 480-520 ppm, and the low-pressure operating pressure is 0.3 MPa.

[0013] The staining test in step (5) takes 30-40 minutes to run.

[0014] The surfactant used in step (6) is 0.1% SDBS.

[0015] The soaking process in step (6) requires stirring, and the soaking time is based on the absence of purple dye on the surface of the membrane.

[0016] In step (6), the halogen element oxidation qualitative detection solution is a mixture of potassium hydroxide and pyridine solution.

[0017] The potassium hydroxide solution has a concentration of 168.33 g / L, the pyridine solution has a concentration of 79.1 g / L (standard solution), and the mixture of potassium hydroxide and pyridine solution has a volume ratio of 1:3.

[0018] In step (6), the single-use volume of the halogen element oxidation qualitative detection solution is 200 mL.

[0019] In step (7), the color change depends on the degree of oxidation damage to the membrane. If the reaction system is red, orange, or pink, it indicates that the membrane has been oxidized and damaged by halogens. If the reaction system does not change color, the membrane may be damaged by other oxidizing substances.

[0020] This invention has the following advantages: 1. This invention employs a step-by-step elimination approach. Specifically, the overall approach consists of three steps: ① Elimination: Through performance testing → O-ring inspection → chemical cleaning, the most common and reversible "non-destructive" problems (such as fouling and leakage) are first eliminated. This step ensures that subsequent analysis targets the "irreversible damage" to the membrane itself. ② Localization: Irreversible damage is initially classified through low-pressure staining-morphology analysis. The apparent "decreased desalination rate" is transformed into a concrete "staining pattern" (lines, blocks, dots), which realizes the mapping from performance parameters to physical morphology and is a crucial step in diagnosis. ③ Qualitative Analysis: For the "pattern" initially determined to be oxidative damage, final chemical colorimetric qualitative analysis is performed. This step delves into the chemical causes of failure, moving beyond physical morphology.

[0021] 2. The parameters are not conventional choices in this field; specifically: The effects of using a low pressure of 0.3 MPa and a medium concentration of 480-520 ppm gentian violet solution are as follows: Traditional staining may require higher pressure to ensure clear staining. However, this invention uses low pressure to achieve "minimally invasive diagnosis." Excessive pressure forces the staining agent to forcefully pass through tiny initial defects and amplifies them, or even causes secondary damage, leading to erroneous analysis. A pressure of 0.3 MPa allows the staining agent to slowly penetrate only through existing defect points without damaging the membrane structure, thus accurately restoring the original size and distribution of defects and ensuring the accuracy of staining morphology judgment. This specific concentration is matched with the low pressure parameter; excessively high concentrations at low pressure can easily lead to non-specific adsorption, causing background color interference; excessively low concentrations result in unclear staining. This combination ensures optimal signal-to-noise ratio and clear defect boundaries. The colorimetric reaction of halogens with pyridine under alkaline conditions is known. However, the innovation of this invention lies in its successful application from the realm of solution chemistry to the detection of trace components in solid phases (aromatic polyamide membrane surfaces).

[0022] The staining agent on the membrane surface was removed using a 0.1% SDBS solution, which eliminated the interference of the gentian violet solution's own color on the final colorimetric reaction and ensured the accuracy of the result interpretation.

[0023] This invention moves from "detecting halogens in solution" to "detecting active groups generated by halogens on a membrane": the essence of the method is not to detect whether the membrane contains halogen elements (XPS can also do this), but rather to detect whether stable NX bonds have formed on the polyamide molecular chains of the membrane after damage. In an alkaline detection solution, this bond can release hypohalite ions, thereby triggering a colorimetric reaction. Therefore, it detects "biomarkers" of halogen oxidative damage, which is more pathologically significant than simply detecting elemental content, directly proving that "halogens are the cause of disease."

[0024] 3. In practical applications, damage to membrane elements is often the result of multiple factors (e.g., initial slight oxidation, which then leads to increased scaling, and finally, failure during cleaning). Existing technologies struggle to analyze this sequential or complex damage.

[0025] This method's hierarchical design enables the resolution of complex damage. For example, during the staining process, if both "dense scattered dots" (indicating oxidation) and "discrete lines" (indicating physical wear) are observed on the membrane surface, analysts can determine that this may be a composite damage that occurred sequentially. Furthermore, samples can be taken separately from different stained areas for qualitative analysis of halogen elements. If only the scattered dot areas show positive colorimetry, while the line areas show negative colorimetry, it can be concluded that the membrane first suffered halogen oxidation, followed by material weakening, and then physical wear occurred during operation or cleaning. This "stepwise resolution" capability is difficult to achieve even with advanced spectroscopic analysis because it not only identifies components but also spatially correlates chemical components with physical forms. This is crucial for tracing accident chains under complex operating conditions and determining responsibility (such as whether it's due to influent water quality issues or operational errors).

[0026] 4. This invention clarifies that the appearance of "discrete lines", "regular patterns", "large-area staining" and "dense scattered dots" in membrane staining has established a strong correlation with specific causes of damage.

[0027] 5. This invention is highly operable, with simple and easy-to-operate procedures, and can be carried out even outside of a standard laboratory. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for analyzing the desalination performance defects of a reverse osmosis membrane according to the present invention; Figure 2 This is a schematic diagram illustrating different morphological variations of gentian violet staining according to the present invention; Figure 3 This is a schematic diagram showing different color development states of the membrane oxidation detection according to the present invention. Detailed Implementation

[0029] A method for analyzing the desalination performance defects of a reverse osmosis membrane, the specific steps of which are as follows: 1. Observe whether the fiberglass of the reverse osmosis membrane element to be analyzed and its two end faces are clean, tidy, and undamaged; 2. Weigh and measure the membrane element to be analyzed.

[0030] 3. Test the flux and desalination rate of the membrane element to be analyzed under national standard conditions.

[0031] 4. If the desalination rate is normal, check if there is an O-ring leak in the system. If the desalination rate exceeds the normal range, it is determined to be abnormal and further analysis should be performed.

[0032] 5. After acid and alkali chemical cleaning, the membrane element to be analyzed is tested again according to national standards. If the desalination rate of the membrane element recovers, it indicates that the membrane element is severely contaminated and the excessive operating pressure difference of the membrane element causes defects in the desalination performance. If the desalination rate does not recover, proceed to the next test.

[0033] 6. A low-pressure operation staining test is performed on the membrane element to be analyzed using a staining agent, wherein the staining agent is gentian violet, the concentration of the staining agent is 480-520 ppm, the low-pressure operation pressure is 0.3 MPa, and the staining test operation time is 30-40 min.

[0034] 7. Disassemble the membrane element to be analyzed and observe the staining of the reverse osmosis membrane surface and the staining of the nonwoven support layer of the reverse osmosis membrane.

[0035] 8. If the membrane staining shows discrete lines, it indicates physical wear on the membrane surface; if the membrane staining shows a regular pattern, it indicates an abnormality in the membrane itself; if the membrane staining is concentrated in a large area, it may be due to the desalination layer adhering to the scale during cleaning after fouling, and the desalination layer falling off along with the scale during cleaning; if the membrane staining shows large areas of dense, scattered spots, it indicates that the membrane has been oxidized and damaged, requiring further qualitative analysis of the type of oxidation. Figure 2 As shown.

[0036] 9. Cut the membrane sheet with densely reddish areas into 10*10mm pieces. Soak the membrane sheet in a surfactant solution to remove the dye from the membrane surface. The surfactant solution is 0.1% SDBS. Stirring is required during the soaking process. The soaking time is until no purple dye remains on the membrane surface.

[0037] 10. After soaking and cleaning, immerse the membrane in clean water for later use. Prepare the halogen oxidation qualitative detection solution. The halogen oxidation qualitative detection solution is a mixture of potassium hydroxide and pyridine solution. The concentration of the potassium hydroxide solution is 168.33 g / L, and the concentration of the pyridine solution is 79.1 g / L standard solution. The volume ratio of the potassium hydroxide and pyridine solution mixture is 1:3, and the single-use volume of the potassium hydroxide and pyridine solution mixture is 200 mL.

[0038] 11. Immerse the cleaned membrane in a uniformly mixed halogen oxidation qualitative detection solution, let it stand for 2 hours, and observe the color change of the reaction system. The color change depends on the degree of oxidation damage to the membrane. If the reaction system turns red, orange, or pink, it indicates that the membrane has been oxidized and damaged by halogens. If there is no color change, the membrane may have been damaged by other oxidizing substances, such as iron or manganese. Figure 3 As shown.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for analyzing the desalination performance defects of a reverse osmosis membrane, characterized in that, Includes the following steps: (1) Observe whether the fiberglass of the reverse osmosis membrane element to be analyzed and its two end faces are clean, tidy and undamaged; (2) Weigh the membrane element to be analyzed; (3) Test the flux and desalination rate of the membrane element to be analyzed under national standard conditions; if the desalination rate is normal, check whether there is O-ring leakage in the system; if the desalination rate exceeds the normal range, determine that the desalination rate is abnormal and proceed to the next step of analysis. (4) After acid and alkali chemical cleaning, the membrane element to be analyzed is tested again according to national standards. If the desalination rate of the membrane element is restored, it indicates that the membrane element is seriously contaminated; if the desalination rate is not restored, the next test is carried out. (5) The membrane element to be analyzed is subjected to a low-pressure operation staining test using a staining agent, namely gentian violet; the membrane element to be analyzed is disassembled and the staining of the reverse osmosis membrane surface and the staining of the reverse osmosis membrane non-woven support layer are observed; if the membrane staining shows discrete lines, it indicates that the membrane surface is physically worn; if the membrane staining shows a regular pattern, it indicates that the membrane itself is abnormal; if the membrane staining is concentrated in a certain area and a large area of ​​staining occurs, it indicates that the membrane desalination layer adheres to the scale during the cleaning process after the membrane element has scaled, and the desalination layer falls off along with the scale during cleaning; if the membrane staining shows a large area of ​​dense scattered spots, it indicates that the membrane has been oxidized and damaged, and the type of oxidation of the membrane needs to be further determined. (6) Cut the membrane that has been dyed into dense red dot areas, and soak the membrane with a surfactant to remove the dye from the surface of the membrane; (7) Soak the soaked and cleaned membrane in clean water for later use, and prepare the halogen element oxidation qualitative detection solution; soak the soaked and cleaned membrane in the uniformly mixed halogen element oxidation qualitative detection solution, let it stand, and observe the color change of the reaction system.

2. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 1, characterized in that: In step (5), the concentration of gentian violet is 480-520 ppm, and the low-pressure operating pressure is 0.3 MPa.

3. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in any one of claims 1-2, characterized in that: The staining test in step (5) takes 30-40 minutes to run.

4. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 1, characterized in that: The surfactant used in step (6) is 0.1% SDBS.

5. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 1, characterized in that: The soaking process in step (6) requires stirring, and the soaking time is based on the absence of purple dye on the surface of the membrane.

6. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 1, characterized in that: In step (6), the halogen element oxidation qualitative detection solution is a mixture of potassium hydroxide and pyridine solution.

7. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 6, characterized in that: The potassium hydroxide solution has a concentration of 168.33 g / L, the pyridine solution has a concentration of 79.1 g / L (standard solution), and the mixture of potassium hydroxide and pyridine solution has a volume ratio of 1:

3.

8. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 7, characterized in that: In step (6), the single-use volume of the halogen element oxidation qualitative detection solution is 200 mL.

9. The method for analyzing the desalination performance defects of a reverse osmosis membrane as described in claim 1, characterized in that: In step (7), the color change depends on the degree of oxidation damage to the membrane. If the reaction system is red, orange, or pink, it indicates that the membrane has been oxidized and damaged by halogens. If the reaction system does not change color, the membrane may be damaged by other oxidizing substances.

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