A method for cleaning the surface contamination of polyamide composite membranes and simultaneously repairing their water flux and salt rejection
By treating polyamide composite membranes with a repair solution containing methoxyamine salts and metal catalysts, the performance degradation caused by chlorine damage and contamination was resolved, restoring water flux and salt rejection rate, and reducing energy consumption and cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-04-21
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies are insufficient to effectively remove chlorine damage and contamination from polyamide composite membranes, leading to irreversible degradation of membrane performance. Furthermore, the cleaning process requires shutdown, increasing costs and energy consumption.
A remediation solution using methoxyamine salts and metal catalysts was used to treat polyamide composite membranes at room temperature. Contaminants were removed and membrane properties were restored through redox reactions, including the reaction of methoxyamine salts with chlorinated amino groups on the membrane surface, restoring hydrophilicity and the intramolecular and extramolecular hydrogen bond network.
It significantly improves the water flux and salt rejection rate of the membrane without requiring shutdown, reduces energy consumption, is simple to operate and low in cost, and is suitable for the repair of polyamide composite membranes treated with chlorine disinfectants.
Smart Images
Figure CN122164239A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polyamide composite membrane water treatment technology, and relates to a method for repairing polyamide composite membranes, specifically a method for repairing the water treatment performance of polyamide composite membranes with the function of cleaning membrane surface contaminants for energy saving in water treatment. Background Technology
[0002] With the large-scale application of reverse osmosis and nanofiltration technologies, the consumption of polyamide membrane composites continues to grow. A large number of membrane elements are discarded or scrapped before they fully fail, causing significant environmental and resource pressure. Chlorine damage has become one of the key issues limiting their stable operation and service life. Most actual water treatment processes use disinfectants containing active chlorine components, such as sodium hypochlorite, for raw water disinfection and system sterilization. However, polyamide membranes are highly sensitive to chlorine; even low concentrations of residual chlorine or short-term chlorine shocks can trigger irreversible degradation of membrane performance. On the other hand, during long-term operation, the membrane surface and pores inevitably experience reversible or irreversible fouling, such as inorganic scaling, organic fouling, biological fouling, and colloidal deposition, affecting membrane performance and potentially leading to irreversible performance decline in severe cases. Existing cleaning methods mostly use chemicals such as acids, alkalis, and surfactants, which can remove fouling to some extent and restore the performance of polyamide membranes. However, polyamide materials are sensitive to strong acids, strong alkalis, and oxidizing substances. Repeated cleaning easily causes amide bond hydrolysis, changes in surface charge and hydrophilicity, leading to a decrease in salt rejection and irreversible aging of the membrane structure. In addition, the cleaning process usually requires shutdown, which not only increases the system operating cost, but also causes additional consumption of energy and chemicals.
[0003] Therefore, there is a need to develop a simple method for treating damaged polyamide membranes that can restore membrane water flux and desalination rate to some extent while removing reversible fouling, thereby reducing energy consumption caused by subsequent cleaning or replacement of membrane elements. Summary of the Invention
[0004] To overcome the shortcomings of the prior art, the present invention provides a method for cleaning the surface fouling of polyamide composite membranes and simultaneously restoring their water flux and salt rejection rate. This method can clean and remove inorganic scale, organic matter and other pollutants from the membrane surface while restoring the water flux and salt rejection rate of polyamide membranes damaged by sodium hypochlorite oxidation.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] A method for cleaning surface contaminants of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate includes the following steps:
[0007] Step 1: Under normal temperature conditions, immerse the polyamide composite membrane damaged by oxidation from active chlorine substances in a repair solution, wherein: the active chlorine substances are one or a combination of two or more of sodium hypochlorite, hypochlorous acid, chlorine dioxide, and chlorine gas; the polyamide composite membrane is a polyamide composite nanofiltration membrane or a polyamide composite reverse osmosis membrane; the repair solution is composed of methoxyamine salt and a metal catalyst; the methoxyamine salt is one or a combination of two or more of methoxyamine hydrochloride, methoxyamine sulfate, methoxyamine phosphate, methoxyamine acetate, methoxyamine trifluoroacetate, methoxyamine formate, methoxyamine methanesulfonate, methoxyamine trifluoromethanesulfonate, and methoxyamine p-toluenesulfonate; the metal catalyst is Fe 2+ Co 2+ Ni 2+ Cu 2+ The metal ion is one or a combination of two or more metal ions, or is one or a combination of two or more elemental metals such as iron, aluminum, nickel, and copper; the concentration of the methoxyamine salt is 0.1–1.5 mmol / L, preferably 0.5–1 mmol / L; the concentration of the metal catalyst is 0.01–0.1 mmol / L, preferably 0.05–0.1 mol / L.
[0008] Step 2: After 2-5 hours of repair, remove the membrane and rinse off the residual repair solution with water. The repair time of the polyamide composite membrane in the repair solution is preferably 3-4 hours.
[0009] Compared with the prior art, the present invention has the following advantages:
[0010] 1) The membranes repaired by this invention, under the same operating conditions, can increase the rejection rates of sodium chloride and sodium sulfate to 95-100% of those of new membranes; for membranes with decreased water flux after damage, the water flux can be restored to 95-100% of that of new membranes after repair; for membranes damaged by sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), L-xylose, and Ca... 2+ Mg 2+ For membranes that have experienced a decrease in water flux due to contamination, the water flux can be restored to 80-100% after cleaning.
[0011] 2) The remediation method of this invention creatively utilizes a methoxyamine salt / metal catalytic system to chemically react with the chlorine-substituted polyamide separation layer. While maintaining the physical structure of the polyamide functional layer, the methoxyamine salt undergoes an oxime reaction on the membrane surface, achieving contaminant cleaning by altering the intermolecular interactions and electrostatic forces between the contaminants and the membrane. The reducing imine groups in the methoxyamine salt undergo a redox reaction with the chlorine-substituted amino groups on the membrane surface, removing chlorine and restoring the hydrophilicity of the separation layer. The intramolecular / intermolecular hydrogen bond network of the polyamide is also restored, increasing the desalination rate. Therefore, the methoxyamine salt / metal catalytic system of this invention can restore the membrane's water flux and desalination rate while cleaning contaminants on the membrane surface, thereby reducing reverse osmosis operating pressure and system energy consumption.
[0012] 3) The modification method of the present invention is simple to operate, has few process steps, low cost, and the repair solution can be recycled. It can be used for the performance repair and pollutant cleaning of polyamide composite reverse osmosis and nanofiltration membranes that use chlorine disinfectant at the front end. Attached Figure Description
[0013] Figure 1 The graph shows the test results of water flux and desalination rate of the polyamide composite membrane after chlorination and surface modification in Example 1.
[0014] Figure 2 The graph shows the test results of water flux and desalination rate of the polyamide composite membrane after chlorination and surface modification in Example 2.
[0015] Figure 3 The graph shows the test results of water flux and desalination rate of the polyamide composite membrane after chlorination and surface modification in Example 3.
[0016] Figure 4 The graph shows the test results of water flux and desalination rate of the polyamide composite membrane after chlorination and surface modification in Example 4. Detailed Implementation
[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.
[0018] Example 1
[0019] Three sets of 2000 ppm NaOCl solutions were prepared, using 200 ppm dodecyltrimethylammonium bromide (DTAB) and 200 ppm calcium chloride as contaminants. The pH of the solutions was adjusted to (1) 4.0 and (2) 7.0 with hydrochloric acid and sodium hydroxide, respectively. A polyamide composite reverse osmosis membrane (named M0) prepared by conventional interfacial polymerization of m-phenylenediamine and trimesoyl chloride was immersed in solutions (1) and (2) for 5 hours to achieve a chlorine treatment CT value of 10000 ppm h. After treatment, the membranes were removed and named membranes M1 and M2, and their water flux and NaCl rejection rate were tested respectively. After testing, membranes M1 and M2 were removed and treated with a remediation solution. The remediation solution contained: 0.5 mmol / L methoxyamine hydrochloride, 0.5 mmol / L methoxyamine sulfate, and 0.05 mM Ni 2+ and 0.05mM Cu 2+ After 3 hours of repair treatment, the membranes were removed, thoroughly rinsed with water, and named M1-2 and M2-2, respectively. Their water flux and NaCl rejection rate were then tested.
[0020] The test conditions for water flux and NaCl rejection were as follows: operating pressure 14 bar, flow rate 3 LPM. New membrane M0, damaged membranes M1 and M2, and repaired membranes M1-2 and M2-2 were pre-pressurized with ultrapure water at 25ºC for 6 h to stabilize membrane performance. The operating pressure was then adjusted to 10 bar, and the water flux of the repaired membrane and the control membrane was measured. A 0.05 mol / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 h of filtration to evaluate the membrane salt rejection.
[0021] Example 2
[0022] A polyamide composite nanofiltration membrane M0, prepared using piperazine and trimesoyl chloride via conventional interfacial polymerization, was immersed in a 5000 ppm NaOCl solution. Using 100 ppm sodium dodecyl sulfate (SDS), 100 ppm L-xylose, and 100 ppm magnesium sulfate as contaminants, accelerated oxidation was carried out at pH 4 and pH 7 for 10 h, respectively, to obtain membranes M1 and M2. Their water flux and salt rejection rates were then tested. After testing, membranes M1 and M2 were removed and treated with a remediation solution. The remediation solution contained: 1 mmol / L methoxyamine phosphate and 0.05 mM Fe. 2+ and 0.05 mM Co 2+ After 4 hours of repair treatment, the membranes were removed, thoroughly rinsed with water, and named M1-2 and M2-2, respectively. Their water flux and Na2SO4 rejection rate were then tested.
[0023] The test conditions for water flux and Na₂SO₄ rejection were as follows: operating pressure 6 bar, flow rate 3 LPM. New membrane M0, damaged membranes M1–M2, and repaired membranes M1-2–M2-2 were pre-pressurized with ultrapure water at 25ºC for 4 h to stabilize membrane performance. The operating pressure was then adjusted to 4 bar, and the water flux of the modified and control membranes was measured. A 1500 mg / L sodium sulfate solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 h of filtration to evaluate the membrane's salt rejection rate.
[0024] Example 3
[0025] A polyamide composite reverse osmosis membrane M0 from Dow Filmtec Corporation was selected, and damaged membranes M1 and M2 were obtained as described in Example 1. After repair, M1-2 and M2-2 were obtained. The repair solution contained: 0.5 mmol / L methoxyamine hydrochloride, 0.5 mmol / L methoxyamine sulfate, and 0.05 mM Ni. 2+ and 0.05 mM Cu 2+ Repair processing time: 3 hours.
[0026] The water flux and desalination rate testing methods are as described in Example 1.
[0027] Example 4
[0028] A polyamide composite nanofiltration membrane M0 from Dow Filmtech (USA) was selected, and damaged membranes M1 and M2 were obtained as described in Example 2. After repair, M1-2 and M2-2 were obtained. The repair solution contained: 1 mmol / L methoxyamine phosphate, 0.05 mM Fe 2+ and 0.05mM Co 2+ Repair processing time: 4 hours.
[0029] The water flux and desalination rate testing methods are as described in Example 2.
[0030] Example 5
[0031] The difference between this embodiment and embodiments 1-4 is that the active chlorine-containing substance is hypochlorous acid, and the metal catalyst is iron.
[0032] Example 6
[0033] The difference between this embodiment and embodiments 1-4 is that the active chlorine-containing substance is a combination of chlorine dioxide and chlorine gas, and the metal catalyst is a combination of nickel and copper.
[0034] Table 1 Performance test results of the new membrane, damaged membrane, and repaired membrane described in Examples 1-4
[0035]
[0036] from Figures 1-4 As shown in Table 1, firstly, the water flux and desalination rate of different polyamide composite membranes decreased significantly after treatment with NaOCl and pollutants, but after remediation treatment, the water flux and desalination rate recovered significantly. Overall, the modification method of this invention is applicable to different polyamide composite membranes and has significant cleaning and remediation effects on polyamide composite membranes.
Claims
1. A method for cleaning surface contaminants of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate, characterized in that... The method includes the following steps: Step 1: Under normal temperature conditions, immerse the polyamide composite membrane damaged by oxidation with active chlorine substances in a repair solution, wherein: the repair solution is composed of methoxyamine salt and a metal catalyst; the methoxyamine salt is one or a combination of two or more of methoxyamine hydrochloride, methoxyamine sulfate, methoxyamine phosphate, methoxyamine acetate, methoxyamine trifluoroacetate, methoxyamine formate, methoxyamine methanesulfonate, methoxyamine trifluoromethanesulfonate, and methoxyamine p-toluenesulfonate, with a concentration of 0.1–1.5 mmol / L; the metal catalyst is Fe 2+ Co 2+ Ni 2+ Cu 2+ One or more combinations of metal ions, or one or more combinations of elemental iron, aluminum, nickel, and copper, with a concentration of 0.01–0.1 mmol / L; Step 2: Remove the product after 2-5 hours of repair and rinse off any remaining repair solution with water.
2. The method for cleaning the surface contamination of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate according to claim 1, characterized in that... The active chlorine-containing substance is one or a combination of two or more of sodium hypochlorite, hypochlorous acid, chlorine dioxide, and chlorine gas.
3. The method for cleaning the surface contamination of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate according to claim 1, characterized in that... The polyamide composite membrane is a polyamide composite nanofiltration membrane or a polyamide composite reverse osmosis membrane.
4. The method for cleaning the surface contamination of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate according to claim 1, characterized in that... The concentration of the methoxyamine salt is 0.5–1 mmol / L.
5. The method for cleaning the surface contamination of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate according to claim 1, characterized in that... The concentration of the metal catalyst is 0.05–0.1 mol / L.
6. The method for cleaning the surface contamination of a polyamide composite membrane and simultaneously restoring its water flux and salt rejection rate according to claim 1, characterized in that... The repair time of the polyamide composite membrane in the repair solution is 3 to 4 hours.