A cleaning and repairing agent for waste nanofiltration membranes in a brine system and a cleaning and repairing method

Abstract

The application discloses a kind of cleaning repair agent and method of waste nanofiltration membrane in brine system, belong to nanofiltration membrane cleaning regeneration repair technical field.Through three-step method, first cleaning, then repair, again strengthen the mode of repair protection, the performance of calcium ion rejection rate of waste nanofiltration membrane after repair reaches more than 79.6% of new membrane performance, magnesium ion rejection rate reaches more than 70.4% of new membrane, sulfate radical rejection rate reaches more than 95.5% of new membrane, online cleaning cycle is more than 60 days, offline cleaning cycle is more than 150 days, reaches the performance comparable to new membrane.The cleaning repair agent and cleaning repair method of the application are suitable for waste nanofiltration membrane of various materials, also suitable for waste nanofiltration membrane of concentrated seawater or higher brine system, the method is simple and effective, easy for industrial application, can reduce the purchase of new nanofiltration membrane, prolong cleaning cycle, reduce the replacement frequency of nanofiltration membrane, save cost.

Description

Technical Field

[0001] This invention relates to a cleaning and repair agent for used nanofiltration membranes in brine systems and a method for cleaning and repairing them, belonging to the field of nanofiltration membrane cleaning, regeneration and repair technology. Background Technology

[0002] Because the brine system contains abundant minerals and microorganisms, the fouling of nanofiltration membranes is mainly due to microbial fouling and inorganic fouling, with microbial fouling having the greatest impact on nanofiltration membranes.

[0003] Nanofiltration membranes typically have a lifespan of 3-5 years. After multiple cleanings, they may even be nearing the end of their lifespan in just 2 years. Therefore, the efficient reuse of waste nanofiltration membranes has become a hot research topic.

[0004] The reuse of spent nanofiltration membranes includes three methods: direct reuse, conversion regeneration, and remediation regeneration. Direct reuse has certain requirements on the performance of the spent membrane and the quality of the produced water in the reuse scenario. Conversion regeneration involves converting the membrane into a nanofiltration or ultrafiltration membrane for reuse or even other materials through oxidation treatment, although the fouling resistance of the converted membrane is reduced. Remediation treatment through physical or chemical modification can restore the separation performance of nanofiltration membranes and improve their chlorine resistance and fouling resistance to a certain extent, making it the best way to treat spent nanofiltration membranes.

[0005] Most research on the recycling of spent nanofiltration membranes is limited to polyamide-based membranes (organic nanofiltration membranes). While there is considerable research on restoring the performance of nanofiltration membranes through chemical cleaning and on hydrophilic modification of new membranes, research on further repairing spent nanofiltration membranes after cleaning is scarce. Furthermore, the performance degradation cycle of long-term used spent nanofiltration membranes differs from that of new membranes, making it difficult to restore them using a single chemical cleaning and repair agent. Therefore, there is an urgent need to develop a cleaning and repair agent and method with a certain capacity for regenerating and repairing spent nanofiltration membranes.

[0006] Chinese invention patent document CN109289539A discloses a cleaning agent for nanofiltration membranes used in brine refining and its preparation method. The method utilizes a cleaning agent containing components such as acids, alkalis, bactericides, and surfactants to clean used nanofiltration membranes (that have suffered membrane fouling), and the pH of this cleaning agent is 2-8. Therefore, this method essentially uses acidic or alkaline components to clean the membrane. After cleaning, the performance of the nanofiltration membrane recovers by a maximum of about 10% compared to before cleaning. However, it is difficult to restore the membrane's performance using only acidic and alkaline cleaning agents. Furthermore, long-term chemical cleaning gradually damages the hydrophilic functional groups on the membrane surface, further reducing the nanofiltration membrane's lifespan.

[0007] Chinese invention patent document CN111729515A discloses a nanofiltration membrane repair agent and its preparation method for brine refining. The method involves "repairing" the nanofiltration membrane using a nanofiltration membrane activator / repair agent A and a nanofiltration membrane curing / maintenance agent B. The activator / repair agent A is mixed with an acidic regulator (citric acid) to adjust the pH to 2-4 for further "repairing," while the curing / maintenance agent B is mixed with an alkaline regulator (sodium carbonate or sodium bicarbonate) to adjust the pH to 7-9 for the same purpose. Therefore, the essence of this patent is to remove contaminants from the nanofiltration membrane using acidic and alkaline cleaning solutions, representing an optimization and improvement of the acidic and alkaline cleaning solution formulations. While this method improves the calcium and magnesium rejection rate, it reduces the membrane flux, and with prolonged cleaning, the membrane flux further decreases, resulting in no improvement in the membrane's operating cycle; in fact, it may even reduce it. Meanwhile, this method introduces repair components, but the method used is to add the repair components to acidic and alkaline cleaning agents, which repairs the membrane while cleaning. Since the repair is carried out before the contaminants are removed, the repair effect of the repair components will be reduced.

[0008] Chinese invention patent document CN115105963A discloses a repair agent and method for used reverse osmosis membrane elements. This method involves repairing the membrane after acidic and alkaline chemical cleaning with a repair agent. First, a repair component A modifies the surface membrane groups, followed by a repair component B that modifies the surface membrane groups again. The surface modification by these two components results in a membrane performance improvement of no more than 7% (compared to the desalination rate of the used membrane, which is 90.4%). Therefore, relying solely on surface modification for membrane repair has limited effectiveness. This suggests that repairing reverse osmosis membranes is not very meaningful. Since reverse osmosis membranes are mostly used downstream of ultrafiltration and nanofiltration systems, the degree of membrane fouling is very low. Simple chemical cleaning or backwashing of the device itself is sufficient, or even proper pre-treatment of the reverse osmosis water source can eliminate the need for a separate repair step.

[0009] Chinese invention patent document with publication number CN114130204A discloses an anti-attenuation agent for forward osmosis, reverse osmosis and nanofiltration membranes and its preparation method. This anti-fading agent is composed of a reducing agent, a bactericide, a surfactant, a surface-modifying protective agent, and water. The surface-modifying protective agent is one or a mixture of several of the following: trimesoyl chloride, polyphenylene diamine, and polyvinyl alcohol. This method utilizes the principle of interfacial polymerization to generate a protective layer on the membrane surface. However, acyl chlorides such as trimesoyl chloride are organic phase monomers that require an organic phase and a certain reaction temperature (generally 50°C) to undergo interfacial polymerization and form a protective layer. Under the conditions of this method, it is difficult to achieve interfacial polymerization and form a protective layer. The principle of the surface-modifying protective agent in this method is essentially surface coating rather than interfacial polymerization, and it repairs the pores on the membrane surface. In this method, we found that the agent components mainly target microbial sterilization (organic pollution), achieving the purpose by reducing organic pollution, but it does not alleviate the problem of inorganic scaling. At the same time, although the anti-fading agent improves the antifouling resistance of the nanofiltration membrane with long-term addition, it also affects the cost of long-term addition of the agent and the quality of subsequent products. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a cleaning and repair agent for used nanofiltration membranes in brine systems and a method for cleaning and repairing them, so as to achieve the repair and regeneration of used nanofiltration membranes and extend the service life of nanofiltration membranes.

[0011] To address the above problems, the present invention provides a cleaning and repair agent for used nanofiltration membranes in a brine system, comprising the following components:

[0012] (a) Alkaline cleaning solution, which is composed of alkaline cleaning agent, alkaline additives, and non-oxidizing bactericide mixed with water;

[0013] (b) An acidic cleaning solution, composed of an acidic cleaning agent and an acidic additive mixed with water;

[0014] (c) Repair solution A, which is composed of a repair agent and a repair aid mixed with an alcoholic organic solvent;

[0015] (d) Repair solution B is composed of a glutaraldehyde solution containing surfactant and water;

[0016] (e) The repair and enhancement solution is composed of a mixture of surfactants and hydroxyimidazolium ionic liquids with water;

[0017] In component (a), the alkaline cleaning agent is sodium hydroxide or sodium carbonate, the alkaline cleaning aid is a combination of sodium tripolyphosphate or tetrasodium ethylenediaminetetraacetate in any mass ratio, and the non-oxidizing bactericide is a combination of organic bromine compounds and amphoteric bactericides.

[0018] In component (b), the acidic cleaning agent is one or more of citric acid, oxalic acid, aminosulfonic acid, and acetic acid, and the pickling aid is a combination of sodium metabisulfite or sodium dithionite in any mass ratio.

[0019] In component (c), the repair agent is two of piperazine and pyromellitic methyl chloride, the auxiliary repair agent is two or more of tannic acid, triethanolamine, polyetheramine, and 2,2'-oxodiethylamine in any mass ratio, and the alcoholic organic solvent is methanol or ethanol.

[0020] In component (d), the surfactant is a combination of two or more of the following in any mass ratio: hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, sodium butanediol bis(succinate) monochlorohydroxypropyl quaternary ammonium salt diester sulfonate, and polyvinylpyridinium ketone.

[0021] In component (e), the surfactant is a combination of two or more of the following in any mass ratio: hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, sodium butanediol bis(succinate) monochlorohydroxypropyl quaternary ammonium salt diester sulfonate, and polyvinylpyridinium ketone; and the hydroxyimidazole ionic liquid is one of 2-hydroxybenzimidazole, tetrahydroxyethylimidazole, and hydroxytolueneimidazole.

[0022] In component (a), the organic bromine compound is a combination of 2,2-dibromo-3-azolidinamide and 2-bromo-2-nitro-1,3-propanediol in any mass ratio, and the amphoteric bactericide is a combination of dodecyl betaine and hexadecyl dimethyl (2-sulfite) ethylammonium in any mass ratio; in component (a), the mass fraction of alkaline cleaning agent is 0.1%-0.3%, the mass fraction of alkaline auxiliary agent is 0.01%-0.05%, the mass fraction of non-oxidizing bactericide is 0.05%-0.1%, and the balance is water;

[0023] In component (a), the mass ratio of organic bromine compounds to amphoteric fungicides in the non-oxidizing fungicide is 1.5-6:1;

[0024] In component (b), the mass fraction of acidic cleaning agent is 1%-3%, the mass fraction of acidic additive is 0.5%-1%, and the balance is water;

[0025] In component (c), the concentration of the repair agent in the alcohol-based organic solvent is 1000 mg / L-3000 mg / L, and the concentration of the auxiliary repair agent in the organic solvent is 100 mg / L-500 mg / L;

[0026] In component (d), the concentration of the surfactant in the glutaraldehyde solution is 500 mg / L-1000 mg / L, and the mass fraction of the glutaraldehyde solution in water is 0.2-0.5%.

[0027] In component (e), the concentration of the hydroxyimidazolium ionic liquid is 500-800 mg / L, and the concentration of the surfactant is 200-500 mg / L.

[0028] Another objective of this invention is a method for cleaning and repairing used nanofiltration membranes in a brine system, characterized by comprising the following steps:

[0029] (1) Rinse the used nanofiltration membrane element with clean water for 1-3 hours at the rated operating flow rate;

[0030] (2) After cleaning in step (1), the waste nanofiltration membrane element is soaked and rinsed with component (a) alkaline cleaning solution at the rated operating flow rate for 1-3 hours. Then, the operating flow rate of component (a) alkaline cleaning solution is increased to 1.5 times the rated operating flow rate and circulated for 30-60 minutes. Then, the alkaline cleaning solution is rinsed off with water.

[0031] (3) After the alkaline cleaning in step (2), the waste nanofiltration membrane element is soaked and rinsed with component (b) acidic cleaning solution at the rated operating flow rate for 1-3 hours. Then, the operating flow rate of component (b) acidic cleaning solution is increased to 1.5 times the rated operating flow rate, and the solution is circulated for 30-60 minutes. Then, the acidic cleaning solution is rinsed off with water.

[0032] (4) After the acid cleaning in step (3), the waste nanofiltration membrane element is immersed and rinsed with component (c) repair solution A at 50℃-70℃ and rated operating flow rate for 1-3 hours, and then the repair solution A is rinsed off with water.

[0033] (5) After the waste nanofiltration membrane element is repaired by repair solution A in step (4), it is soaked and rinsed with component (d) repair solution B at 30-40℃ and rated operating flow rate for 1-5 hours. Then, the repair solution B is washed away with water to obtain the repaired nanofiltration membrane element.

[0034] (6) After the waste nanofiltration membrane element is repaired by the repair solution B in step (5), it is soaked and rinsed with component (e) repair and enhancement solution at the rated operating flow rate for 2-5 hours, and then the repair and enhancement solution is washed away with water to obtain the repaired nanofiltration membrane element.

[0035] In step (1), the rated operating flow rate is 20-60 m³ / h;

[0036] The steps (1)-(6) involve cleaning and repairing the nanofiltration membrane on the nanofiltration membrane cleaning and repair test device;

[0037] In steps (2)-(6), the soaking and rinsing conditions are 1.2-3.0 MPa; the rated operating flow rate is 20-60 m³ / h.

[0038] In steps (2)-(6), the meaning of cyclic soaking and rinsing is: the cleaning solution or repair solution is sent from its respective storage tank into the nanofiltration membrane cleaning device, flows out and then returns to its respective storage tank, thereby realizing the cyclic soaking and rinsing of the decommissioned nanofiltration membrane by the cleaning solution or repair solution.

[0039] The acidic cleaning solution composed of acidic cleaning agent and acidic additive in this invention is mainly used to remove inorganic scale (calcium carbonate, calcium sulfate, etc.), metal oxides, and inorganic colloids. The combination of the two has a synergistic effect.

[0040] The non-oxidizing bactericide in this invention has a good bactericidal effect on algae, plankton, halophilic bacteria and other organisms. Its bactericidal principle is to stop the redox behavior inside the cell by penetrating the cell membrane of microorganisms (inhibiting respiration), thus causing the microorganisms to die.

[0041] The organic bromine compound non-oxidizing bactericide in this invention has excellent bactericidal effects against halophilic bacteria and sulfate-reducing bacteria. 2,2-Dibromo-3-azapropanamide is characterized by low dosage, rapid bactericidal speed, good compatibility with other bactericides, low toxicity, and easy degradation. 2-Bromo-2-nitro-1,3-propanediol has good water solubility and compatibility; when combined with 2,2-dibromo-3-azapropanamide, it exhibits a broad-spectrum and highly effective bactericidal effect, and the two have an excellent synergistic effect.

[0042] The amphoteric bactericide of this invention is a non-oxidizing bactericide with high resistance to organic matter and slow-release capability, low toxicity, sensitivity to halophilic bacteria and sulfate-reducing bacteria, good compatibility, and good degradability. The combination of organic bromine compounds and the amphoteric bactericide exhibits excellent synergistic effects.

[0043] In this invention, the surfactant not only has the function of emulsifying pollutants in water, but also has the function of killing pollutants in water and improving the hydrophilicity of nanofiltration membrane surface; the compounding of surfactants not only enhances water solubility, but also enhances bactericidal properties.

[0044] The repair agent in this invention is a main nanofiltration membrane manufacturing and repair aqueous phase (piperazine) and oil phase (trimethylammonium chloride) monomer, which repairs the damaged membrane surface through a surface coating reaction.

[0045] In this invention, the repair agent further repairs the membrane by removing pore blockages, and the hydroxyl and amino functional groups in the repair agent impart hydrophilicity to the repaired waste nanofiltration membrane, which has a synergistic effect with the repair agent.

[0046] In this invention, glutaraldehyde can be used to solidify the pores repaired by the repair solution.

[0047] In this invention, the hydroxyimidazolium ionic liquid reacts with the residual acyl chloride groups after repair by the repair agent, enhancing the positive charge effect of the membrane and improving the divalent rejection rate and permeability (flux). Compared with the prior art, this invention has the following beneficial effects after adopting the above technical solution:

[0048] This invention relates to a cleaning and repair agent for the repair and regeneration of spent nanofiltration membranes that have reached the end of their lifespan after 3-5 years of operation in a nanofiltration unit. An alkaline cleaning solution, a composite of alkaline cleaning agents and alkaline additives, is used to remove organic pollutants and reduce membrane fouling. An acidic cleaning solution, a composite of acidic cleaning agents and acidic additives, is used to remove inorganic scale. Repair solution A is used for physical repair (internal membrane damage) and to improve hydrophilicity. Repair solution B not only solidifies the pores but also further improves hydrophilicity; the hydrophilicity of the repaired spent nanofiltration membrane is increased by more than 10%, improving its antifouling properties. A repair enhancement solution, a composite of hydroxyimidazolium ionic liquid, surfactant, and pH adjuster, reacts with and permeates the membrane. Through compounding and pH adjustment, the antifouling capacity, flux, and rejection rate of the repaired spent nanofiltration membrane are improved, reducing the risk of membrane fouling, reducing the frequency of membrane cleaning, reducing the purchase of new membranes, and lowering costs.

[0049] (2) The cleaning and repair method of the present invention is aimed at membrane fouling (microbial and inorganic salt scaling) and membrane damage leading to Ca in high-salt complex brine systems. 2+ Mg 2+ SO4 2- The decline in retention rate, flux, and service life was addressed through a three-step process: cleaning, repair, and enhanced repair and protection. This method resolved the incomplete cleaning issues caused by the original coarse cleaning method, improved the membrane's antifouling properties, and extended its service life. The repaired waste nanofiltration membrane achieved a calcium ion retention rate of over 79.6%, a magnesium ion retention rate of over 70.4%, and a sulfate retention rate of over 95.5%, comparable to that of a new membrane. The online cleaning cycle was over 60 days, and the offline cleaning cycle was over 150 days, achieving performance comparable to that of a new membrane.

[0050] (3) The cleaning and repair method of the present invention is suitable for waste nanofiltration membranes of various materials in brine and concentrated seawater or high salinity systems. The method is simple and effective and easy to apply in industrial applications. Attached Figure Description

[0051] Figure 1 Diagram of nanofiltration membrane cleaning and repair test device.

[0052] In the diagram: 1. Clean water / test solution tank; 2. Alkali solution tank; 3. Acid solution tank; 4. Repair solution A tank; 5. Repair solution B tank; 6. Repair and enhancement solution tank; 7. Water outlet valve of clean water / test solution tank; 8. Plate and frame filter; 9. Inlet turbidity meter; 10. Booster pump; 11. Security filter; 12. Inlet pressure gauge; 13. Inlet flow meter; 14. Inlet pipeline; 15. Nanofiltration membrane; 16. Membrane element; 17. Permeate pipeline; 18. Concentrate pipeline; 19. Permeate flow meter; 20. Permeate pressure gauge; 21. Permeate main valve; 22. Permeate inlet valve of clean water / test solution tank; 23. Concentrate inlet valve of clean water / test solution tank; 25. Drain valve of clean water / test solution tank; 26. Water outlet valve of alkali solution tank; 27. Alkali solution pH meter; 28. Permeate inlet valve of alkali solution tank; 29. ​​Concentrate inlet valve of alkali solution tank; 30. Drain valve of alkali solution tank; 31. Acid solution. 32. pH meter; 33. Acid tank product water inlet valve; 34. Acid tank concentrate inlet valve; 35. Acid tank drain valve; 36. Repair solution A tank outlet valve; 37. Repair solution A tank product water inlet valve; 38. Repair solution A tank concentrate inlet valve; 39. Repair solution A tank drain valve; 40. Repair solution B tank outlet valve; 41. Repair solution B tank product water inlet valve; 42. Repair solution B tank concentrate inlet valve; 43. Repair and enhancement solution tank outlet valve; 44. Repair and enhancement solution tank product water inlet valve; 45. Repair and enhancement solution tank concentrate inlet valve; 46. Repair and enhancement solution tank drain valve; 47. Clean water / test solution tank temperature control system; 48. Alkali tank temperature control system; 49. Acid tank temperature control system; 50. Repair solution A tank temperature control system; 51. Repair solution B tank temperature control system; 52. Repair and enhancement solution temperature control system; 53. Product water turbidity meter. Detailed Implementation

[0053] The present invention will be further described below through examples, but the scope of protection of the present invention is not limited thereto. In the following examples, unless otherwise specified, all raw materials used are commercially available.

[0054] The nanofiltration membrane cleaning and repair testing device described herein has the following structure (see attached instruction manual). Figure 1 :

[0055] The equipment mainly consists of a shut-off valve, flow meter, pH meter, pressure gauge, booster pump 10, temperature control system, membrane element 16, nanofiltration membrane 15, plate and frame filter 8, turbidity meter, security filter 9, and cleaning and repair water tank. The shut-off valve comprises a clean water / test solution tank outlet valve 7, a product water main valve 21, a clean water / test solution tank product water inlet valve 22, a concentrate main valve 23, a clean water / test solution tank concentrate inlet valve 24, a clean water / test solution tank drain valve 25, and an alkali solution tank outlet valve. 26. Alkali tank product water inlet valve; 28. Alkali tank concentrated water inlet valve; 29. ​​Alkali tank drain valve; 30. Acid tank outlet valve; 31. Acid tank product water inlet valve; 33. Acid tank concentrated water inlet valve; 34. Acid tank drain valve; 35. Repair solution A tank outlet valve; 36. Repair solution A product water inlet valve; 37. Repair solution A concentrated water inlet valve; 38. Repair solution A drain valve; 39. Repair solution B tank outlet valve; 40. Repair solution B product water inlet valve; 41. Repair solution B concentrated water inlet valve; 42. Repair The system comprises: a drain valve 43 for the reconstituted liquid B, a water outlet valve 44 for the repair and enhancement liquid tank, a product water inlet valve 45 for the repair and enhancement liquid tank, a concentrated water product valve 46 for the repair and enhancement liquid tank, and a drain valve 47 for the repair and enhancement liquid; the flow meters consist of an inlet flow meter 13 and a product water flow meter 19; the pH meters consist of an alkaline pH meter 27 and an acidic pH meter 32; the pressure gauges consist of an inlet pressure gauge 12 and a product water pressure gauge 20; and the temperature control system is a clear water / test liquid tank temperature control system 48. The temperature control system includes an alkali tank (49), an acid tank (50), a repair solution A tank (51), a repair solution B tank (52), and a repair and enhancement solution tank (53). The temperature control system is controlled by a jacketed heater. The turbidity meters are an inlet water turbidity meter (9) and a product water turbidity meter (54). The cleaning and repair water tanks include a clean water / test solution tank (1), an alkali tank (2), an acid tank (3), a repair solution A tank (4), a repair solution B tank (5), and a repair and enhancement solution tank (6). All cleaning and repair water tanks are equipped with drain lines.

[0056] The purified water / test solution tank 1 is connected in series with the plate and frame filter 8, the inlet turbidity meter 9, the booster pump 10, the security filter 11, the inlet pressure gauge 12, and the inlet flow meter 13 via the outlet valve 7 of the purified water / test solution tank 1. Then, it is connected to the inlet pipeline 14 and enters the membrane element 16. The concentrate from the membrane element 16 returns to the purified water / test solution tank 1 via the concentrate pipeline 18, the main concentrate valve 23, and the purified water / test solution tank concentrate inlet valve 24. The permeate from the membrane element 16 returns to the purified water / test solution tank 1 via the permeate pipeline 17, the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, and the purified water / test solution tank permeate inlet valve 22.

[0057] The alkaline solution tank 2 is connected in series with the alkaline solution tank outlet valve 26, alkaline solution pH meter 27, plate and frame filter 8, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to the inlet pipeline 14 to enter the membrane element 16. The concentrate from the membrane element 16 returns to the alkaline solution tank 2 via the concentrate pipeline 18, the concentrate main valve 23, and the alkaline solution tank concentrate inlet valve 29. The permeate from the membrane element 16 returns to the alkaline solution tank 2 via the permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and the alkaline solution tank permeate inlet valve 28.

[0058] The acid tank 3 is connected in series with the acid tank outlet valve 31, acid pH meter 32, plate and frame filter 8, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to the inlet pipeline 14 to enter the membrane element 16. The concentrate from the membrane element 16 returns to the acid tank 2 via the concentrate pipeline 18, the concentrate main valve 23, and the acid tank concentrate inlet valve 34. The permeate from the membrane element 16 returns to the acid tank 3 via the permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and the acid tank permeate inlet valve 33.

[0059] Repair fluid tank 4 is connected in series with repair fluid tank A outlet valve 36, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to inlet pipeline 14 to enter membrane element 16. The concentrate from membrane element 16 returns to repair fluid tank A 4 via concentrate pipeline 18, concentrate main valve 23, and repair fluid tank A concentrate inlet valve 38. The permeate from membrane element 16 returns to repair fluid tank A 4 via permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and repair fluid tank A permeate inlet valve 37.

[0060] Repair solution tank 5 is connected in series with repair solution tank B outlet valve 40, inlet turbidity meter 9, booster pump 10, security filter 11, inlet pressure gauge 12, and inlet flow meter 13, and then connected to inlet pipeline 14 to enter membrane element 16. The concentrate from membrane element 16 returns to repair solution tank B 5 via concentrate pipeline 18, concentrate main valve 23, and repair solution tank B concentrate inlet valve 42; the permeate from membrane element 16 returns to repair solution tank B 5 via permeate pipeline 17, permeate turbidity meter 54, permeate flow meter 19, permeate pressure gauge 20, and repair solution tank B permeate inlet valve 41.

[0061] The repair and enhancement liquid tank 6 is connected in series with the repair and enhancement liquid tank outlet valve 44, the inlet turbidity meter 9, the booster pump 10, the security filter 11, the inlet pressure gauge 12, and the inlet flow meter 13. Then, it is connected to the inlet pipeline 14 and enters the membrane element 16. The concentrate from the membrane element 16 returns to the repair and enhancement liquid tank 6 via the concentrate pipeline 18, the concentrate main valve 23, and the repair and enhancement liquid tank concentrate inlet valve 46. The permeate from the membrane element 16 returns to the repair and enhancement liquid tank 6 via the permeate pipeline 17, the permeate turbidity meter 54, the permeate flow meter 19, the permeate pressure gauge 20, and the repair and enhancement liquid tank permeate inlet valve 45.

[0062] By adopting the above technical solution, the alkaline cleaning solution in this invention is mainly used to remove organic pollution. Alkaline cleaning agents alone cause membrane pore swelling after alkaline cleaning, allowing hydrophobic small molecules to more easily enter the membrane pores, clogging them and reducing their diameter. With increasing cleaning cycles, the cleaning effect becomes increasingly poor. The addition of alkaline additives can improve the membrane's hydrophilicity and negative charge, filling the swollen pores and rapidly eliminating the alkali-induced membrane pore swelling effect, preventing the accumulation of pollutants in the membrane pores. It also enhances the flotation, solubilization, and dispersion effects of the alkaline cleaning agent on organic matter and sludge. Example 1

[0063] A cleaning and repair agent for used nanofiltration membranes in a brine system comprises the following components:

[0064] (a) Alkaline cleaning solution:

[0065] Add 3.0 kg sodium hydroxide (0.2%), 0.15 kg sodium tripolyphosphate (0.01%), 0.3 kg tetrasodium ethylenediaminetetraacetate (0.02%), 0.6 kg 2,2-dibromo-3-azapropanamide (0.04%), 0.3 kg 2-bromo-2-nitro-1,3-propanediol (0.02%), and 0.15 kg dodecyl betaine (0.01%) to 1.49 m³. 3 Mix thoroughly with water (99.7%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0066] (b) Acidic cleaning solution:

[0067] Add 30 kg of acetic acid (2%), 7.5 kg of citric acid (0.5%), 4.5 kg of sodium metabisulfite (0.3%), and 4.5 kg of sodium disulfite (0.3%) to a 1.45 m³ solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0068] (c) Repair solution A:

[0069] Dissolve 1.5 kg piperazine, 1.5 kg trimesoyl chloride, 0.3 kg tannic acid, and 0.15 kg 2,2'-oxodiethylamine in 1.5 mL of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 2000 mg / L, auxiliary repair agent: 300 mg / L).

[0070] (d) Repair solution B:

[0071] Dissolve 1.8 g of hexadecyl dimethyl allyl ammonium chloride and 2.0 g of sodium trichloroethyl dodecyl ether sulfate in 4.5 kg of glutaraldehyde (4.75 L) (surfactant: 800 mg / L), then dissolve in 1.495 mL of water. 3 Prepare repair solution B by stirring thoroughly in water.

[0072] (e) Repair and enhancement solution:

[0073] Dissolve 1.05 kg of 2-hydroxybenzimidazole, 0.325 kg of sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate, and 0.2 kg of polyvinylpyridinium ketone (3%) in 1.5 mL of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 700 mg / L, surfactant: 350 mg / L).

[0074] The method for cleaning and repairing used nanofiltration membranes in brine systems, using the aforementioned cleaning and repair agent, includes the following steps:

[0075] (1) For commercially available waste nanofiltration membrane elements made of polyamide that have been in use for 3 years, the waste nanofiltration membrane is first rinsed with clean water on the nanofiltration membrane cleaning test device for 2 hours, with a rated operating flow rate of 60 m³ / h. 3 / h.

[0076] (2) After cleaning in step (1), the waste nanofiltration membrane element is subjected to a pressure of 2.5 MPa and a rated operating flow rate of 60 m³ / h. 3 Use an alkaline cleaning solution to circulate and soak for 2 hours at a flow rate of / h, then adjust the operating flow rate to 75m³ / h. 3 Rinse at / h for 50 minutes, and then rinse with clean water to remove the alkaline cleaning solution.

[0077] (3) After the alkaline cleaning in step (2), the waste nanofiltration membrane element is subjected to a pressure of 2.5 MPa and a rated operating flow rate of 60 m³ / h. 3 Use an acidic cleaning solution to circulate and soak for 2 hours at a flow rate of / h, then adjust the operating flow rate to 75m³ / h. 3 Rinse at / h for 50 minutes, and then rinse with clean water to remove the acidic cleaning solution.

[0078] (4) Heat the repair solution A to 60°C, and then apply the waste nanofiltration membrane element cleaned in step (3) with the repair solution A at 2.5 MPa and a rated operating flow rate of 60 m³ / h. 3 Soak and rinse for 2 hours at / h, then rinse off repair solution A with clean water.

[0079] (5) Heat the repair solution B to 35°C, and then apply the repair solution B to the waste nanofiltration membrane element after the repair solution A in step (4) at 2.5 MPa and a rated operating flow rate of 60 m³ / h. 3 Soak and rinse for 5 hours at / h, then rinse off the repair solution B with clean water.

[0080] (6) After the waste nanofiltration membrane element has been repaired by repair solution B in step (5), apply the repair and enhancement solution to it at 2.5 MPa and a rated operating flow rate of 60 m³ / h. 3 Soak and rinse for 5 hours at / h, then rinse off the repair and enhancement solution with clean water.

[0081] The physical cleaning effect and hydrophilicity of static contact angle were tested by using brine at 1.5 MPa in step (1) to obtain data on calcium, magnesium, sulfate, turbidity, flux and contact angle. Then, the product was rinsed multiple times with pure water to ensure that it would not affect subsequent steps.

[0082] In step (2), the alkaline cleaning solution was calibrated with brine at 1.5 MPa and the hydrophilicity of the static contact angle was tested to obtain data on calcium, magnesium, sulfate, permeate turbidity, flux and contact angle. Then, the solution was rinsed multiple times with pure water to ensure that it would not affect subsequent steps.

[0083] The effect of calibrating the acidic cleaning solution with brine at 1.5 MPa in step (3) and the hydrophilicity test of the static contact angle were tested to obtain data on calcium, magnesium, sulfate, product water turbidity, flux and contact angle. Then, the solution was rinsed multiple times with pure water so as not to affect subsequent steps.

[0084] In step (4), the repair effect test of repair solution A was performed by calibrating the brine at 1.5 MPa and the hydrophilicity test of the static contact angle. Data on calcium, magnesium, sulfate, turbidity of the product water, flux and contact angle were obtained. Then, the solution was rinsed multiple times with pure water so as not to affect the subsequent steps.

[0085] For step (5), the repair effect of brine calibration repair solution B was tested at 1.5 MPa and the hydrophilicity of static contact angle was tested to obtain data on calcium, magnesium, sulfate, product water turbidity, flux and contact angle. Then, the solution was rinsed multiple times with pure water so as not to affect subsequent steps.

[0086] The repair effect of the brine calibration and repair enhancement solution in step (6) at 1.5 MPa and the hydrophilicity test of the static contact angle were tested. The turbidity change of the brine before and after the test and the data of the produced water (flux and calcium, magnesium and sulfate ion rejection rate) were tested by turbidity meter and ion detector (ICP) respectively to determine the cleaning cycle.

[0087] The test results are shown in Table 1. Under the same conditions, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the membrane after repair were 56.6-65.3%, 66.9-73.8%, 94.6-98.5%, and 13-15 L / m³, respectively. 2 • h, 0.06-0.15 NTU, 63.6°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2 •h, 60.3°, the calcium, magnesium, and sulfate rejection rates and fluxes of the repaired nanofiltration membrane reached 93.3-94.3%, 86.8-89.2%, 99.5-99.6%, and 83.3-86.7% of the performance of a new membrane, respectively. The hydrophilicity was improved by 17.2% compared to the unwashed waste nanofiltration membrane, and the permeate turbidity was improved by 70%. The cleaning cycle for the repaired nanofiltration membrane was 80 / 170 days, approaching the performance of a new membrane.

[0088] Example 2

[0089] A cleaning and repair agent for used nanofiltration membranes in a brine system comprises the following components:

[0090] (a) Alkaline cleaning solution

[0091] Add 1.5 kg sodium carbonate (0.1%), 0.15 kg sodium tripolyphosphate (0.01%), 0.45 kg 2,2-dibromo-3-azine propionamide (0.03%), and 0.3 kg dodecyl betaine (0.02%) to 1.498 m³. 3 Mix thoroughly with water (99.84%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0092] (b) Acidic cleaning solution

[0093] Add 15 kg of acetic acid (1%) and 7.5 kg of sodium metabisulfite (0.5%) to 1.45 m³. 3 Mix thoroughly with water (98.5%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0094] (c) Repair solution A

[0095] Dissolve 1.5 kg piperazine and 0.15 kg tannic acid in 1.5 ml of water. 3 Prepare repair solution A by stirring thoroughly in ethanol (total repair agent: 1000 mg / L, auxiliary repair agent: 100 mg / L).

[0096] (d) Repair solution B

[0097] Dissolve 0.634 g of hexadecyl dimethyl allyl ammonium chloride in 3.0 kg of glutaraldehyde (3.17 L) (surfactant: 200 mg / L), then dissolve in 1.497 mL of water. 3 Prepare repair solution B by stirring thoroughly in water.

[0098] (e) Repair and enhancement solution

[0099] Dissolve 0.75 kg of tetrahydroxyethylimidazolium and 0.3 kg of hexadecyl dimethyl allyl ammonium chloride in 1.5 ml of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 500 mg / L, surfactant: 200 mg / L).

[0100] A method for cleaning and repairing spent nanofiltration membranes in a brine system, using the aforementioned cleaning and repair agent, includes the following steps:

[0101] (1) For commercially used nanofiltration membranes made of polyamide that have been in use for 5 years, the used nanofiltration membranes are thoroughly cleaned with clean water on a nanofiltration membrane cleaning test device. The rinsing time is 1 hour and the rated operating flow rate is 20 m³ / h. 3 / h.

[0102] (2) After cleaning in step (1), the waste nanofiltration membrane element is subjected to a pressure of 1.2 MPa and a rated operating flow rate of 20 m³ / h. 3 Circulate and soak for 1 hour at a flow rate of / h, then adjust the flow rate to 30m³ / h. 3 Rinse at / h for 30 minutes, and then rinse with clean water to remove the alkaline cleaning solution.

[0103] (3) After the alkaline cleaning in step (2), the waste nanofiltration membrane element is subjected to a pressure of 1.2 MPa and a rated operating flow rate of 20 m³ / h. 3 Use an acidic cleaning solution to circulate and soak for 1 hour at a flow rate of / h, then adjust the operating flow rate to 30m³ / h. 3 Rinse at / h for 30 minutes, and then rinse with clean water to remove the acidic cleaning solution.

[0104] (4) Heat the repair solution A to 50°C, and then use the waste nanofiltration membrane element after cleaning in step (3) at 1.2 MPa and a rated operating flow rate of 20 m³ / h. 3Soak and rinse for 1 hour at / h, then rinse off repair solution A with clean water.

[0105] (5) Heat the repair solution B to 30°C, and then apply the repair solution B to the waste nanofiltration membrane element after the repair solution A in step (4) at 1.2 MPa and a rated operating flow rate of 20 m³ / h. 3 Soak and rinse for 1 hour at / h, then rinse off the repair solution B with clean water.

[0106] (6) After the waste nanofiltration membrane element has been repaired by the repair solution B in step (5), apply the repair and enhancement solution to it at 1.2 MPa and a rated operating flow rate of 20 m³ / h. 3 Soak and rinse for 2 hours at / h, then rinse off the repair and enhancement solution with clean water.

[0107] The testing and detection methods for steps (1)-(6) are the same as in Example 1.

[0108] The performance test results are shown in Table 2. Under the same conditions, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the membrane after repair were 47.0-55.7%, 61.1-69.3%, 90.7-94.7%, and 12-13 L / m³, respectively. 2 • h, 0.1-0.2 NTU, 65.6°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2 • h, 60.3°, the calcium, magnesium, and sulfate rejection rates and fluxes of the repaired nanofiltration membrane reached 79.6-98.5%, 70.4-81.5%, 95.5-95.7%, and 72.2-80.0% of the performance of a new membrane, respectively. The hydrophilicity was improved by 14.6% compared to the untreated waste nanofiltration membrane, and the turbidity was improved by 50-60%. The cleaning cycle for the repaired nanofiltration membrane was 60 / 150 days, approaching the level of a new membrane.

[0109] Example 3

[0110] A cleaning and repair agent for used nanofiltration membranes in a brine system comprises the following components:

[0111] (a) Alkaline cleaning solution:

[0112] 4.5 kg sodium hydroxide (0.3%), 0.75 kg sodium tripolyphosphate (0.05%), 1.2 kg 2,2-dibromo-3-azolidinyl propionamide (0.08%), 0.15 kg dodecyl betaine (0.01%), and 0.15 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.01%) were added to 1.493 m³ of solution. 3Mix thoroughly with water (99.55%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0113] (b) Acidic cleaning solution:

[0114] Add 15 kg of citric acid (1%), 15 kg of oxalic acid (1%), 15 kg of sulfamic acid (1%), and 15 kg of sodium metabisulfite (1%) to a 1.44 m³ solution. 3 Mix thoroughly with water (96.0%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0115] (c) Repair solution A:

[0116] Dissolve 4.5 kg of trimesoyl chloride, 0.75 kg of triethanolamine, and 0.75 kg of polyetheramine in 1.5 ml of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 3000 mg / L, auxiliary repair agent: 1000 mg / L).

[0117] (d) Repair solution B:

[0118] Dissolve 0.99 g of hexadecyl dimethyl allyl ammonium chloride, 0.99 g of sodium trichloroethyl dodecyl ether sulfate, 0.99 g of sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate, and 0.99 g of polyvinylpyridinium ketone in 7.5 kg of glutaraldehyde (7.92 L) (surfactant: 500 mg / L), then dissolve in 1.492 m... 3 Prepare repair solution B by stirring thoroughly in water.

[0119] (e) Repair and enhancement solution:

[0120] Dissolve 1.2 kg of 2-hydroxymethylimidazolium, 0.25 kg of hexadecyl dimethyl allyl ammonium chloride, 0.2 kg of sodium trichloroethyl dodecyl ether sulfate, 0.2 kg of sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate, and 0.1 kg of polyvinylpyridine ketone in 1.5 mL of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 800 mg / L, surfactant: 500 mg / L).

[0121] A method for cleaning and repairing spent nanofiltration membranes in a brine system, using the aforementioned cleaning and repair agent, includes the following steps:

[0122] (1) For commercially available waste ceramic nanofiltration membranes made of alumina that have been in use for 4 years, the waste nanofiltration membranes were rinsed with clean water in the nanofiltration membrane cleaning test device for 3 hours, with a rated operating flow rate of 40 m³ / h. 3 / h.

[0123] (2) After cleaning in step (1), the waste nanofiltration membrane element is subjected to a pressure of 3.0 MPa and a rated operating flow rate of 40 m³ / h. 3 Circulate and soak for 3 hours at a flow rate of / h, then adjust the flow rate to 60m³ / h. 3 Rinse at / h for 60 minutes, and then rinse with clean water to remove the alkaline cleaning solution.

[0124] (3) After the alkaline cleaning in step (2), the waste nanofiltration membrane element is subjected to a pressure of 3.0 MPa and a rated operating flow rate of 40 m³ / h. 3 Circulate and soak for 3 hours at a flow rate of / h, then adjust the flow rate to 60m³ / h. 3 Rinse at / h for 60 minutes, and then rinse with clean water to remove the acidic cleaning solution.

[0125] (4) Heat the repair solution A to 70°C, and then apply the waste nanofiltration membrane element cleaned in step (3) with the repair solution A at 3.0 MPa and a rated operating flow rate of 40 m³ / h. 3 Soak and rinse for 3 hours at / h, then rinse off repair solution A with clean water.

[0126] (5) Heat the repair solution B to 40°C, and then apply the repair solution B to the waste nanofiltration membrane element after the repair solution A in step (4) at 3.0 MPa and a rated operating flow rate of 40 m³ / h. 3 Soak and rinse for 3 hours at / h, then rinse off the repair solution B with clean water.

[0127] (6) After the waste nanofiltration membrane element has been repaired by repair solution B in step (5), apply the repair and enhancement solution to it at 3.0 MPa and a rated operating flow rate of 40 m³ / h. 3 Soak and rinse for 3 hours at / h, then rinse off the repair and enhancement solution with clean water.

[0128] The testing and detection methods for steps (1)-(6) are the same as in Example 1.

[0129] The test results are shown in Table 3. Under the same conditions, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the membrane after repair were 54.5-64.4%, 66.0-71.7%, 93.8-97.4%, and 13-15 L / m³, respectively. 2 • h, 0.09-0.18 NTU, 65.1°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2• h, 0.05-0.1 NTU, 60.3°, calcium, magnesium, and sulfate rejection rates and fluxes reached 90.8-92%, 84.3-88.0%, 98.4-98.7%, and 83.3-86.7% of the performance of a new membrane, respectively. Hydrophilicity was improved by 15.2% compared to an unwashed waste nanofiltration membrane, and permeate turbidity was improved by 55-64%. The cleaning cycle for the repaired nanofiltration membrane was 68 / 175, approaching the level of a new membrane.

[0130] Example 4

[0131] The difference from Example 1 is that the test solution for calibrating the physical cleaning effect is replaced with a mixture of seawater and brine (brine:seawater = 3:1). The seawater-brine mixture is used to simulate concentrated seawater or high seawater concentration, and the water to be filtered is a mixture of seawater and brine.

[0132] The test results are shown in Table 4. Under the same conditions, after replacing the brine with simulated concentrated seawater or seawater with a higher concentration, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the membrane after repair were 60.6-65.3%, 66.4-78.5%, 97.1-97.9%, and 17-18 L / m³, respectively. 2 • h, 0.07-0.13 NTU, 63.6°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 62-73%, 73-83%, 98-99.5%, and 20-25 L / m, respectively. 2 •h, 60.3°. The calcium, magnesium, and sulfate rejection rates and fluxes of the repaired nanofiltration membrane reached 89.5-97.7%, 90.1-94.6%, 98.4-99.1%, and 72-85% of the performance of a new membrane, respectively. The hydrophilicity was improved by 17.2% compared to the unwashed spent nanofiltration membrane, and the permeate turbidity was improved by 65-74%. However, its performance in brine was worse than in simulated seawater. The cleaning cycle for the spent nanofiltration membrane in simulated seawater was 85 / 175 days, reaching the performance degradation cycle of a new membrane.

[0133] Example 5

[0134] The steps for cleaning and repairing the waste nanofiltration membrane in this embodiment are the same as in Embodiment 2. The difference lies in the different alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution. The alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution in this embodiment are prepared as follows.

[0135] (a) Alkaline cleaning solution

[0136] Add 1.5 kg sodium hydroxide (0.1%), 0.15 kg tetrasodium ethylenediaminetetraacetate (0.01%), 0.6 kg 2-bromo-2-nitro-1,3-propanediol (0.04%), and 0.15 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.01%) to 1.498 m 3 Mix thoroughly with water (99.84%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0137] (b) Acidic cleaning solution

[0138] Add 15 kg of citric acid (1%) and 7.5 kg of sodium dithionite (0.5%) to 1.45 m³. 3 Mix thoroughly with water (98.5%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0139] (c) Repair solution A

[0140] Dissolve 1.5 kg of trimesoyl chloride and 0.15 kg of triethanolamine in 1.5 ml of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 1000 mg / L, auxiliary repair agent: 100 mg / L).

[0141] (d) Repair solution B

[0142] Dissolve 2.5g of sodium trichloroethyl dodecyl ether sulfate in 6.0kg of glutaraldehyde (6.33L) (surfactant: 400mg / L), then dissolve in 1.494m 3 Prepare repair solution B by stirring thoroughly in water.

[0143] (e) Repair and enhancement solution

[0144] Dissolve 0.9 kg of 1-hydroxybenzimidazole and 0.45 kg of sodium trichloroethyl dodecyl ether sulfate in 1.5 mL of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 600 mg / L, surfactant: 300 mg / L).

[0145] After repair, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the nanofiltration membrane were 49.0-57.7%, 62.1-68.3%, 91.7-95.7%, and 12-13 L / m³, respectively. 2 • h, 0.1-0.2 NTU, 65.1°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2•h、60.3°, the cleaning cycle of the repaired nanofiltration membrane is 65 / 160 days, which is close to the level of a new membrane, thus achieving the purpose of the invention. Example 6

[0146] The steps for cleaning and repairing the waste nanofiltration membrane in this embodiment are the same as in embodiment 5. The difference lies in the different acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution. The acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution are prepared as follows in this embodiment.

[0147] (b) Acidic cleaning solution

[0148] Add 15 kg of oxalic acid (1%) and 7.5 kg of sodium dithionite (0.5%) to 1.45 m³. 3 Mix thoroughly with water (98.5%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0149] (c) Repair solution A

[0150] Dissolve 1.5 kg of trimesoyl chloride and 0.15 kg of polyetheramine in 1.5 ml of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 1000 mg / L, auxiliary repair agent: 100 mg / L).

[0151] (d) Repair solution B

[0152] Dissolve 2.5g of sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate in 6.0kg of glutaraldehyde (6.33L) (surfactant: 400mg / L), then dissolve in 1.494m 3 Prepare repair solution B by stirring thoroughly in water.

[0153] (e) Repair and enhancement solution

[0154] Dissolve 0.9 kg of hydroxytoluene imidazolium and 0.45 kg of butanediol disuccinate monochlorohydroxypropyl quaternary ammonium diester sulfonate in 1.5 ml of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 600 mg / L, surfactant: 300 mg / L).

[0155] After repair, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the nanofiltration membrane were 48.8-57.5%, 62.0-68.2%, 91.5-95.5%, and 12-13 L / m³, respectively. 2 • h, 0.1-0.2 NTU, 65.1°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively.2 •h、60.3°, the cleaning cycle of the repaired nanofiltration membrane is 65 / 160 days, which is close to the level of a new membrane, thus achieving the purpose of the invention. Example 7

[0156] The steps for cleaning and repairing the waste nanofiltration membrane in this embodiment are the same as in embodiment 5. The difference lies in the different acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution. The acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution are prepared as follows in this embodiment.

[0157] (b) Acidic cleaning solution

[0158] Add 15 kg of sulfamic acid (1%) and 7.5 kg of sodium metabisulfite (0.5%) to 1.45 m³. 3 Mix thoroughly with water (98.5%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0159] (c) Repair solution A

[0160] Dissolve 1.5 kg piperazine and 0.15 kg 2,2'-oxodiethylamine in 1.5 mL of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 1000 mg / L, auxiliary repair agent: 100 mg / L).

[0161] (d) Repair solution B

[0162] Dissolve 2.5g of polyvinylpyridine ketone in 6.0kg of glutaraldehyde (6.33L) (surfactant: 400mg / L), then dissolve in 1.494m... 3 Prepare repair solution B by stirring thoroughly in water.

[0163] (e) Repair and enhancement solution

[0164] Dissolve 0.9 kg of hydroxytoluene imidazolium and 0.45 kg of polyvinylpyridine ketone in 1.5 ml of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 600 mg / L, surfactant: 300 mg / L).

[0165] After repair, the calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the nanofiltration membrane were 48.9-57.6%, 62.1-68.3%, 91.6-95.4%, and 12-13 L / m³, respectively. 2 • h, 0.1-0.2 NTU, 65.1°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2•h、60.3°, the cleaning cycle of the repaired nanofiltration membrane is 64 / 161 days, which is close to the level of a new membrane, thus achieving the purpose of the invention. Example 8

[0166] The steps for cleaning and repairing the waste nanofiltration membrane in this embodiment are the same as in Embodiment 1. The difference lies in the different alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution. The alkaline cleaning solution, acidic cleaning solution, repair solution A, repair solution B, and repair enhancement solution in this embodiment are prepared as follows.

[0167] (a) Alkaline cleaning solution:

[0168] Add 3.0 kg sodium hydroxide (0.2%), 0.15 kg sodium tripolyphosphate (0.01%), 0.3 kg tetrasodium ethylenediaminetetraacetate (0.02%), 0.45 kg 2,2-dibromo-3-azolidinyl propionamide (0.03%), 0.3 kg 2-bromo-2-nitro-1,3-propanediol (0.02%), 0.15 kg dodecyl betaine (0.01%), and 0.15 kg hexadecyl dimethyl (2-sulfite) ethylammonium (0.01%) to 1.49 m³. 3 Mix thoroughly with water (99.7%) to prepare a 1.5m solution. 3 Alkaline cleaning solution.

[0169] (b) Acidic cleaning solution:

[0170] Add 22.5 kg of acetic acid (1.5%), 7.5 kg of citric acid (0.5%), 7.5 kg of oxalic acid (0.5%), 4.5 kg of sodium metabisulfite (0.3%), and 4.5 kg of sodium disulfite (0.3%) to a 1.45 m³ solution. 3 Mix thoroughly with water (96.9%) to prepare a 1.5m solution. 3 Acidic cleaning solution.

[0171] (c) Repair solution A:

[0172] Dissolve 1.5 kg piperazine, 1.5 kg trimesoyl chloride, 0.15 kg tannic acid, 0.15 kg 2,2'-oxodiethylamine, and 0.15 kg polyetheramine in 1.5 mL of water. 3 Prepare repair solution A by stirring in methanol until homogeneous (total repair agent: 2000 mg / L, auxiliary repair agent: 300 mg / L).

[0173] (d) Repair solution B:

[0174] Dissolve 1.3 g cetyldimethylallyl ammonium chloride, 1.5 g sodium trichloroethyl dodecyl ether sulfate, and 1.0 g polyvinylpyridinium ketone in 4.5 kg glutaraldehyde (4.75 L) (surfactant: 800 mg / L), then dissolve in 1.495 mL of water. 3 Prepare repair solution B by stirring thoroughly in water.

[0175] (e) Repair and enhancement solution:

[0176] Dissolve 1.0 kg of 2-hydroxybenzimidazole, 0.2 kg of butanediol disuccinate monochlorohydroxypropyl quaternary ammonium salt diester sodium salt, 0.2 kg of polyvinylpyridinium ketone, and 0.13 kg of hexadecyl dimethyl allyl ammonium chloride in 1.5 mL of water. 3 Prepare a repair and enhancement solution by stirring in water until homogeneous (hydroxyimidazole ionic liquid: 700 mg / L, surfactant: 350 mg / L).

[0177] The calcium, magnesium, and sulfate rejection rates, flux, permeate turbidity, and hydrophilicity of the repaired nanofiltration membrane were 56.4-65.1%, 66.7-73.6%, 94.4-98.3%, and 13-15 L / m³, respectively. 2 • h, 0.06-0.15 NTU, 63.6°, the calcium, magnesium, and sulfate rejection rates, flux, and hydrophilicity of the new membrane are 60-70%, 75-85%, 95-99%, and 15-18 L / m, respectively. 2 •h、60.3°, the cleaning cycle of the repaired nanofiltration membrane is 70 / 180 days, which is similar to the performance of the new membrane, thus achieving the purpose of the invention. Comparative Example 1

[0178] The difference between Comparative Example 1 and Example 1 is that the cleaning and repair method only includes steps (1) and (2), which involves cleaning the waste nanofiltration membrane with an alkaline cleaning solution. Comparative Example 2

[0179] The difference between Comparative Example 3 and Example 1 is that only steps (1) to (3) are performed, in which the waste nanofiltration membrane is cleaned with alkaline cleaning solution and acidic cleaning solution. Comparative Example 3

[0180] The difference between Comparative Example 3 and Example 1 is that only steps (1) to (4) are performed, in which the membrane is cleaned with acidic and alkaline cleaning solutions and then repaired with repair solution A. Comparative Example 4

[0181] The difference between Comparative Example 4 and Example 1 is that only steps (1) to (5) are performed, in which the membrane is cleaned with acidic and alkaline cleaning solutions and then repaired with repair solution A and repair solution B. Comparative Example 5

[0182] The difference between Comparative Example 5 and Example 1 is that the repair solution B in step (5) does not contain surfactant components. Comparative Example 6

[0183] The difference between Comparative Example 6 and Example 1 is that the repair and enhancement solution in step (6) does not contain surfactant components. Comparative Example 7

[0184] The difference between Comparative Example 7 and Example 1 is that the repair and enhancement solution in step (6) is a hydroxyl-based ionic liquid. Comparative Example 8

[0185] The difference between Comparative Example 8 and Example 1 is that the alkaline cleaning solution, acidic cleaning solution and repair solution are replaced with repair and enhancement solution in steps (1) to (5). Comparative Example 9

[0186] The difference between Comparative Example 9 and Comparative Example 3 is that Comparative Example 9 was cleaned with an acidic cleaning solution first and then with an alkaline cleaning solution. Comparative Example 10

[0187] The difference between Comparative Example 10 and Comparative Example 5 is that the repair solution B in step (5) has no surfactant component, and the temperature of the repair solution B in step (5) is increased to 80°C.

[0188]

[0189] As can be seen from the comparison of Examples 1-8, concentration and time affect the cleaning and repair effect; the change of components in a single-component cleaning agent has little effect on the cleaning and repair effect; the cleaning and repair effect of a single-component cleaning and repair agent (non-combined) is not as good as that of a cleaning and repair agent with two or more components. Considering the cost issue, a single-component cleaning and repair agent can also achieve the purpose of the invention.

[0190] Comparing Comparative Examples 1-10 with Example 1, it can be seen that the alkaline cleaning solution mainly removes organic matter, primarily affecting the rejection rate, turbidity, flux, and service life; the acidic cleaning solution mainly removes inorganic scale, primarily affecting turbidity and service life, with a smaller impact on the rejection rate; repair solution A mainly repairs damaged pores in the membrane, primarily affecting the membrane's service life; repair solution B mainly improves the membrane's hydrophilicity and, in the presence of surfactants, requires a lower temperature to solidify the pores, improving antifouling properties, thereby increasing flux and service life; the surfactants in the repair and enhancement solution mainly improve hydrophilicity and rejection rate, and have a synergistic effect with hydroxyimidazole liquids, which can modify the membrane to improve its antifouling ability and extend its service life. However, surfactants are beneficial components. Not a key component; hydroxyl-based ionic liquids are the key component in the repair and enhancement solution, mainly affecting service life and hydrophilicity; with a simple cleaning and repair agent (repair and enhancement solution), it is difficult to clean the contaminants of the waste membrane and restore its performance without a process of cleaning before repair. Cleaning before repair and then enhancement repair is the best way to treat waste membranes for reuse; the effect of alkaline washing followed by acid washing has little effect on the rejection rate and flux of calcium, magnesium, and sulfate ions, as well as turbidity, but has a great impact on the membrane's service life. Alkaline washing followed by acid washing helps to extend the membrane's service life, which may be related to the fact that the outermost layer of the membrane surface is contaminated with organic matter, and organic matter contamination is the key factor affecting service life; repair solution B has no surfactant and requires a higher temperature to achieve the effect of Example 1.

[0191] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent variations and modifications described in the scope of the present invention and the description should fall within the scope of the present invention.

Claims

1. A cleaning and repair agent for used nanofiltration membranes in a brine system, characterized in that, The cleaning and repair agent comprises the following components: (a) Alkaline cleaning solution, which is composed of alkaline cleaning agent, alkaline additives, and non-oxidizing bactericide mixed with water; (b) An acidic cleaning solution, which is a mixture of an acidic cleaning agent and an acidic additive with water; (c) Repair solution A, which is a mixture of repair agent and auxiliary repair agent with alcohol organic solvent; (d) Repair solution B is a mixture of glutaraldehyde solution containing surfactant and water; (e) The repair and enhancement solution is composed of a mixture of surfactants and hydroxyimidazolium ionic liquids with water; In component (a), the alkaline cleaning agent is sodium hydroxide or sodium carbonate, the alkaline cleaning aid is a combination of sodium tripolyphosphate or tetrasodium ethylenediaminetetraacetate in any mass ratio, and the non-oxidizing bactericide is a combination of an organic bromine compound and an amphoteric bactericide; in component (b), the acidic cleaning agent is a combination of two or more of citric acid, oxalic acid, sulfamic acid, and acetic acid, and the pickling aid is a combination of sodium metabisulfite or sodium dithionite in any mass ratio; in component (c), the repair agent is a combination of piperazine and trimesoyl chloride in any mass ratio, and the repair aid is two or more of tannic acid, triethanolamine, polyetheramine, and 2,2'-oxodiethylamine in any mass ratio. The combination includes an alcoholic organic solvent of methanol or ethanol; in component (d), the surfactant is a combination of two or more of the following in any mass ratio: hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium salt diester sulfonate, and polyvinylpyridinium ketone; in component (e), the surfactant is a combination of two or more of the following in any mass ratio: hexadecyl dimethyl allyl ammonium chloride, sodium trichloroethyl dodecyl ether sulfate, sodium butanediol disuccinate monochlorohydroxypropyl quaternary ammonium salt diester sulfonate, and polyvinylpyridinium ketone, and the hydroxyimidazole ionic liquid is one of 2-hydroxybenzimidazole, tetrahydroxyethylimidazole, and hydroxytolueneimidazole. In component (a), the organic bromine compound is a combination of two of the following in any mass ratio: 2,2-dibromo-3-azolidinamide and 2-bromo-2-nitro-1,3-propanediol, and the amphoteric bactericide is a combination of two or more of the following in any mass ratio: dodecyl betaine and hexadecyl dimethyl (2-sulfite) ethylammonium.

2. The cleaning and repair agent for used nanofiltration membranes in a brine system according to claim 1, characterized in that, In component (a), the mass fraction of alkaline cleaning agent is 0.1%-0.3%, the mass fraction of alkaline auxiliary agent is 0.01%-0.05%, the mass fraction of non-oxidizing bactericide is 0.05%-0.1%, and the balance is water; the mass ratio of organic bromine compounds to amphoteric bactericides in the non-oxidizing bactericide is 1.5-6:1; in component (b), the mass fraction of acidic cleaning agent is 1%-3%, the mass fraction of acidic auxiliary agent is 0.5%-1%, and the balance is water; in component (c), the repair agent... The concentration of the alcohol-based organic solvent is 1000 mg / L-3000 mg / L, and the concentration of the repair agent in the organic solvent is 100 mg / L-500 mg / L; in component (d), the concentration of the surfactant in the glutaraldehyde solution is 500 mg / L-1000 mg / L, and the mass fraction of the glutaraldehyde solution in water is 0.2-0.5%; in component (e), the concentration of the hydroxyimidazolium ionic liquid is 500-800 mg / L, and the concentration of the surfactant is 200-500 mg / L.

3. A method for cleaning and repairing spent nanofiltration membranes in a brine system, comprising using the cleaning and repair agent for spent nanofiltration membranes in a brine system as described in claim 1 or 2, characterized in that... Includes the following steps: (1) Rinse the used nanofiltration membrane element with clean water for 1-3 hours at the rated operating flow rate; (2) After cleaning in step (1), the waste nanofiltration membrane element is soaked and rinsed with component (a) alkaline cleaning solution at the rated operating flow rate for 1-3 hours. Then, the operating flow rate of component (a) alkaline cleaning solution is increased to 1.5 times the rated operating flow rate and circulated for 30-60 minutes. Then, the alkaline cleaning solution is rinsed off with water. (3) After the alkaline cleaning in step (2), the waste nanofiltration membrane element is soaked and rinsed with component (b) acidic cleaning solution at the rated operating flow rate for 1-3 hours. Then, the operating flow rate of component (b) acidic cleaning solution is increased to 1.5 times the rated operating flow rate, and the solution is circulated for 30-60 minutes. Then, the acidic cleaning solution is rinsed off with water. (4) After the acid cleaning in step (3), the waste nanofiltration membrane element is immersed and rinsed with component (c) repair solution A at 50℃-70℃ and rated operating flow rate for 1-3 hours, and then the repair solution A is rinsed off with water. (5) After the waste nanofiltration membrane element is repaired by repair solution A in step (4), it is soaked and rinsed with component (d) repair solution B at 30-40℃ and rated operating flow rate for 1-5 hours. Then, the repair solution B is washed away with water to obtain the waste nanofiltration membrane element after repair by repair solution B. (6) After the waste nanofiltration membrane element is repaired by the repair solution B in step (5), it is soaked and rinsed with component (e) repair and enhancement solution at the rated operating flow rate for 2-5 hours, and then the repair and enhancement solution is washed away with water to obtain the repaired nanofiltration membrane element. The steps (1)-(6) involve cleaning and repairing the nanofiltration membrane on the nanofiltration membrane cleaning and repair test device; In step (1), the rated operating flow rate is 20-60 m³ / h.

4. The method for cleaning, repairing, and using spent nanofiltration membranes in a brine system according to claim 3, characterized in that, In steps (2)-(6), the soaking and rinsing conditions are 1.2-3.0 MPa; the rated operating flow rate is 20-60 m³ / h.

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