A method for protecting and repairing oxidatively damaged seawater desalination membranes

Abstract

The present invention belongs to the field of preparation of seawater desalination separation membranes, and specifically refers to a method for in-situ repairing of oxidative defects of reverse osmosis membranes and constructing an antioxidant protective layer. The present invention is to first soak the waste reverse osmosis membrane in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean it in deionized water, and dry it for use. Then, the reverse osmosis membrane is immersed in a cross-linking solution and a repair solution in turn for treatment, and finally the membrane is soaked in deionized water. The advantages of the present invention are: using a special polymer material with a flexible molecular chain of an ether bond and an oxidative sacrificial structure of an amide bond / amine group, the repair of oxidative defects of the reverse osmosis membrane and the antioxidant protection function are simultaneously achieved. The constructed repair layer has good affinity with the surface of the reverse osmosis membrane and can operate in cross-flow for a long time without failure. In addition, a stable chemical bond is constructed between the repair layer and the surface of the reverse osmosis membrane, further improving the stability of the repair layer.

Description

Technical Field

[0001] The present invention relates to a technology that can be used to repair oxidative damage to reverse osmosis membranes and improve the membrane's antioxidant capacity. Specifically, it refers to a method for in-situ repairing oxidative defects of reverse osmosis membranes and constructing an antioxidant protective layer. The method belongs to the field of seawater desalination separation membrane preparation. The method can achieve performance recovery and reuse of discarded reverse osmosis membranes, enhance their antioxidant lifespan, and reduce the cost of reverse osmosis membrane use. Background Art

[0002] Desalination-based water supply technologies can significantly improve water resource utilization efficiency. Reverse osmosis membrane technology, with its high energy efficiency and environmental friendliness, is a key technology for ensuring the efficient operation of desalination systems. However, reverse osmosis membranes face severe performance degradation in seawater. This is primarily due to the high doses of active chlorine fungicides (10-15 mg / L) required during the pretreatment of seawater to inhibit microbial growth. However, active chlorine (HClO, ClO-) readily undergoes chlorination substitution reactions with the amide bonds in the RO membrane separation layer. This chlorination reaction significantly disrupts the strong hydrogen bonding of the amide bonds, causing hydrolysis and cleavage of the molecular chains, leading to a decrease in separation performance. Therefore, repairing and regenerating degraded membrane elements is crucial to restore membrane performance to a certain extent, and even further improve the membrane's antioxidant capacity and extend its service life.

[0003] At present, when repairing the performance of reverse osmosis membranes at home and abroad, surface modification methods (including coating and chemical grafting) are mainly used to plug defects on the membrane surface and construct a physical protective barrier. The repair functional reagents involved are mainly hydrophilic polymer materials, such as polyols (CN202110302656.9), polyacrylamides (such as CN202011413824.3), polyphenols (CN202011564702.4) and natural polymers (proteins, polysaccharides, humic acid) (CN202110218966.2, CN202111169981.9). Although the membrane performance is restored to a certain extent, the permeation resistance is also increased, resulting in membrane permeability loss. In particular, most of the repair polymer materials and the polyamide separation layer of the reverse osmosis membrane body are in an obvious two-phase separation structure, and the mutual binding force is weak. After long-term cross-flow treatment, mutual delamination may still occur. To this end, it is necessary to develop a repair material that is more compatible with the surface of the polyamide reverse osmosis membrane and to build a stable chemical bond between the membrane surface and the repair material.

[0004] Polyether block polyamide (trade name Pebax) is a type of regular linear polymer currently used in food packaging, sporting goods, medical devices, and other fields. Composed of rigid polyamide segments interlocked with flexible polyether segments, it was previously explored as an anti-fouling coating for reverse osmosis membranes (JS Louie, Journal of Membrane Science, 280 (2006) 762-770). Due to its high affinity for the reverse osmosis polyamide separation layer, Pebax exhibits excellent stability as a protective coating during long-term cross-flow operation.

[0005] Unlike commonly used polyol-based (hydroxyl-rich) repair agents, Pebax polymers are rich in ether and amide bonds. The amide segments not only enhance hydrogen bonding interactions with the polyamide separation layer but also function as a "sacrificial layer," preferentially consuming oxidants in the water and protecting the amide bonds in the reverse osmosis membrane. Therefore, this material is an ideal membrane repair agent. Furthermore, polyetheramine polymers, which have a similar structure to Pebax and similarly possess primary amine groups that preferentially consume oxidants, are also ideal membrane repair agents. Given the abundance of amino, hydroxyl, and carboxyl groups remaining on the surface of reverse osmosis membranes after oxidative damage, these surface grafting sites can be fully utilized. Through cross-linking and curing, a stable chemical bond can be established between the repair layer and the membrane surface, further enhancing the long-term effectiveness of the repair layer. Summary of the Invention

[0006] The present invention addresses the problem of reverse osmosis membrane performance degradation caused by oxidative damage and provides a simple method for repairing reverse osmosis membrane oxidative defects and further improving the oxidation resistance of membrane materials. The method is based on the characteristics of polyether block polyamide and polyetheramine polymer materials, which have both flexible molecular chains of ether bonds and oxidation-sacrificial structures of amide bonds / amine groups. When used as a repair agent, it can quickly and fully embed into the surface molecular layer of the polyamide reverse osmosis membrane, not only blocking the damaged points on the membrane surface, but also constructing a stable antioxidant sacrificial protective layer, preferentially consuming oxidants in the water body, inhibiting their attack on the amide bonds of the polyamide membrane body, and having the dual functions of repairing existing membrane damage and preventing the membrane material from being oxidized and degraded again. When repairing / protecting the reverse osmosis membrane, the present invention only requires the membrane separation layer to be simply contacted with a cross-linking solution containing a cross-linking agent and a repair solution containing a repair polymer in sequence. No complex post-processing process is required, which can greatly reduce the operating cost of the reverse osmosis membrane water treatment system and reduce the burden of solid waste treatment of discarded membrane elements. The repaired and regenerated membrane material can be further reused to further play its use value, effectively promoting the high-quality development of the green circular economy.

[0007] The technical solution of the present invention is as follows: A method for protecting and repairing a seawater desalination membrane damaged by oxidation, comprising the following steps:

[0008] (1) Cleaning of waste reverse osmosis membranes: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0009] As an illustration, due to the serious organic pollution on the membrane surface in the seawater desalination system, sodium hypochlorite is used here to degrade the organic pollutants on the membrane surface, fully clean the membrane surface, and provide strong conditions for subsequent repair treatment.

[0010] (2) Immerse the reverse osmosis membrane treated in step (1) in the cross-linking solution for 10-20 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 30-120 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 2-8 hours. Then immerse it in deionized water for 10 minutes. Repeat the washing three times. Finally, immerse the membrane in deionized water for testing.

[0011] The cross-linking solution is prepared by dissolving cross-linking agent molecules in an alkane organic solvent, wherein the cross-linking agent concentration is controlled at 0.1-0.5% (mass percentage), wherein the cross-linking agent can be one or a mixture of polyvalent epoxy or polyvalent isocyanate compounds, wherein the polyvalent epoxy compound can be one of glycerol tri(1,2-epoxy)propyl ether, diglycidyl ether, ethylene glycol diglycidyl ether, and pentaerythritol glycidyl ether, and the polyvalent isocyanate can be one or a mixture of m-phenylene diisocyanate, p-phenylene diisocyanate, and toluene diisocyanate; and the alkane organic solvent can be one of pentane, hexane, cyclohexane, and heptane.

[0012] The repair solution is: one of two polymer materials, polyether block polyamide or polyether amine, or a mixture thereof, is dissolved in an alcohol-alkane mixed solvent (the volume fraction of the alcohol solvent is 10%-30%), with the mass fraction of the polymer material being 0.2%-2% (mass percentage), wherein the relative molecular weight of the polyether block polyamide can be 50,000 to 300,000, and the ratio of polyether repeating units to polyamide repeating units in the molecular structure can be 2:1, 3:1 or 1:2; the relative molecular weight of the polyether amine can be 200 to 4000; the alcohol solvent can be one of ethanol, isopropanol, butanol or isobutanol, or a mixture thereof; the alkane organic solvent can be one of pentane, hexane, cyclohexane and heptane;

[0013] Preferably, the cross-linking agent in step (2) is an isocyanate compound, because its cross-linking reaction activity is higher than that of epoxy compounds;

[0014] Preferably, the concentration of the cross-linking agent in the above step (2) is preferably 0.2-0.4%;

[0015] Preferably, the repair polymer material in step (2) above is polyether block polyamide, because its molecular weight is higher than that of polyether amine, and it has a better filling effect on membrane surface defects; further, the preferred ratio of polyether repeating units to polyamide repeating units in the polyether block polyamide structure is 2:1 or 3:1; the relative molecular weight is preferably 100,000 or 250,000;

[0016] Preferably, the polymer mass fraction of the repair solution in the above step (2) is 0.5-1%;

[0017] Preferably, the alcohol solvent system fraction of the alcohol-alkane organic solvent in the above step (2) is 15-20%;

[0018] Preferably, the immersion time of the cross-linking solution in the above step (2) is 10-15 minutes;

[0019] Preferably, the immersion time of the repair solution in the above step (2) is 60-90 minutes;

[0020] Preferably, the drying time of the film in the above step (2) is 15-25 minutes;

[0021] As an explanation, the purpose of drying the reverse osmosis membrane is to promote the further progress of the cross-linking reaction, but too long a drying time can easily lead to irreversible dehydration of the reverse osmosis membrane and reduce the membrane permeability.

[0022] Compared with existing membrane repair technologies, the present invention has the following advantages:

[0023] (1) A special polymer material with a flexible molecular chain of ether bond and an oxidative sacrificial structure of amide bond / amine group is used to simultaneously achieve the repair of oxidative defects of reverse osmosis membrane and anti-oxidation protection function. The constructed repair layer has good affinity with the surface of reverse osmosis membrane and can operate in cross-flow for a long time without failure.

[0024] (2) The surface of the reverse osmosis membrane is pretreated with a crosslinker. The epoxy or isocyanate groups in the crosslinking solution can react with the hydroxyl, amine and carboxyl groups on the surface of the reverse osmosis membrane at the same time, and then react with the hydroxyl and carboxyl groups at the end of the polyether block polyamide molecular chain in the repair solution, or with the amino groups at the end of the polyetheramine molecular chain to undergo crosslinking reaction, thereby building a stable chemical bond between the repair layer and the reverse osmosis membrane surface, further improving the stability of the repair layer.

[0025] (3) Existing repair treatment technologies generally use aqueous solution treatment, while the cross-linking solution and the repair solution in the present invention both use organic solvents. Since organic solvents have better wettability for polyamide reverse osmosis membrane materials, the cross-linking agent and the repair agent can more fully contact the membrane surface, resulting in better repair and protection effects. DETAILED DESCRIPTION

[0026] In order to better understand the present invention, the present invention is further described below with reference to specific examples:

[0027] The test method for the water flux and salt rejection of the reverse osmosis membrane of the present invention is as follows:

[0028] The reverse osmosis membrane to be tested was pre-pressed with a 0.2% (mass percentage) NaCl electrolyte aqueous solution at 1.55 MPa for half an hour to test the desalination performance and water flux of the reverse osmosis membrane.

[0029] The calculation formula for water flux is as follows:

[0030] (1)

[0031] Where A is the effective membrane area, in m 2 ; t—the time required to collect Q volume of produced liquid, in h; Q—the volume of produced liquid collected within t time, in L.

[0032] The calculation method of membrane desalination is shown in (2):

[0033] (2)

[0034] Among them, R is the membrane rejection rate, C f —Conductivity of the stock solution, in μS / cm; C p - Conductivity of produced water, in μS / cm.

[0035] After testing the membrane's separation performance using the aforementioned method, to further evaluate the repaired layer's antioxidant capacity, 0.05% (mass percentage) sodium hypochlorite was added to a standard NaCl test solution and the membrane was operated for an additional 12 hours. The changes in the membrane's salt rejection were examined to assess the repaired layer's enhanced antioxidant properties. As a control, a parallel test was conducted using an unrepaired reverse osmosis membrane.

[0036] In order to demonstrate the long-term stability of the repair layer, the repaired reverse osmosis membrane was immersed in ethanol solution for 48 hours to promote the dissociation of the repair layer from the reverse osmosis membrane surface, and to evaluate the effect of cross-linking treatment on the structural stability of the repair layer. Example 1

[0037] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0038] Repair recipe modulation:

[0039] (1) Cross-linking solution: dissolve isocyanate in pentane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.1% (mass percentage).

[0040] (2) Repair solution: dissolve polyether block polyamide with a relative molecular weight of 250,000 and a ratio of polyether repeating units to polyamide repeating units of 2:1 in an ethanol-pentane mixed solvent (alcohol solvent volume fraction of 10%), with a high molecular weight fraction of 0.2% (mass percentage).

[0041] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 10 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 30 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 2 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 2

[0042] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0043] Repair recipe modulation:

[0044] (1) Cross-linking solution: dissolve p-phenylene diisocyanate in hexane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.2% (mass percentage).

[0045] (2) Repair solution: dissolve polyether block polyamide with a relative molecular weight of 50,000 and a ratio of polyether repeating units to polyamide repeating units of 3:1 in an ethanol-hexane mixed solvent (alcohol solvent volume fraction 20%), with a high molecular weight fraction of 0.5% (mass percentage).

[0046] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 15 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 60 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 5 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 3

[0047] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0048] Repair recipe modulation:

[0049] (1) Cross-linking solution: toluene diisocyanate is dissolved in cyclohexane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.3% (mass percentage).

[0050] (2) Repair solution: dissolve polyether block polyamide with a relative molecular weight of 100,000 and a ratio of polyether repeating units to polyamide repeating units of 1:2 in an isopropanol-cyclohexane mixed solvent (alcohol solvent volume fraction 30%), with a high molecular weight fraction of 1% (mass percentage).

[0051] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 20 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 100 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 6 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 4

[0052] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0053] Repair recipe modulation:

[0054] (1) Cross-linking solution: dissolve glycerol tri(1,2-epoxy)propyl ether in heptane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.4% (mass percentage).

[0055] (2) Repair solution: dissolve polyether block polyamide with a relative molecular weight of 300,000 and a ratio of polyether repeating units to polyamide repeating units of 2:1 in a butanol-heptane mixed solvent (alcohol solvent volume fraction 10%), with a high molecular weight fraction of 1.5% (mass percentage).

[0056] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 10 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 120 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 8 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 5

[0057] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0058] Repair recipe modulation:

[0059] (1) Cross-linking solution: diglycidyl ether was dissolved in pentane solvent as a cross-linking solution, and the cross-linking agent concentration was 0.5% (mass percentage).

[0060] (2) Repair solution: dissolve polyetheramine with a relative molecular weight of 200 in an isobutanol-pentane mixed solvent (alcohol solvent volume fraction 20%), with a high molecular weight fraction of 2% (mass percentage).

[0061] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 15 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 60 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 2 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 6

[0062] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0063] Repair recipe modulation:

[0064] (1) Cross-linking solution: dissolve ethylene glycol diglycidyl ether in hexane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.1% (mass percentage).

[0065] (2) Repair solution: dissolve polyetheramine with a relative molecular weight of 2000 in an ethanol-hexane mixed solvent (alcohol solvent volume fraction 20%), with a high molecular weight fraction of 0.2% (mass percentage).

[0066] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 20 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 80 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 4 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 7

[0067] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0068] Repair recipe modulation:

[0069] (1) Cross-linking solution: dissolve pentaerythritol glycidyl ether in cyclohexane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.2% (mass percentage).

[0070] (2) Repair solution: dissolve polyetheramine with a relative molecular weight of 4000 in an isopropyl alcohol-cyclohexane mixed solvent (alcohol solvent volume fraction 30%), with a high molecular weight fraction of 0.5% (mass percentage).

[0071] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 10 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 120 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 6 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing. Example 8

[0072] Waste membrane cleaning: Collect the discarded reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution (pH adjusted to 10) for 12 hours, then soak and clean them in deionized water for 1 hour. Repeat the cleaning three times, then take them out and dry them for use.

[0073] Repair recipe modulation:

[0074] (1) Cross-linking solution: dissolve isocyanate in heptane solvent as a cross-linking solution, and the cross-linking agent concentration is 0.5% (mass percentage).

[0075] (2) Repair solution: dissolve polyether block polyamide with a relative molecular weight of 250,000 and a ratio of polyether repeating units to polyamide repeating units of 2:1 in a butanol-heptane mixed solvent (alcohol solvent volume fraction 20%), with a high molecular weight fraction of 1% (mass percentage).

[0076] Membrane repair treatment: Immerse the cleaned waste reverse osmosis membrane in the cross-linking solution for 20 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then immerse it in the repair solution for 120 minutes. After taking it out, blow the membrane surface with high-pressure air until there is no obvious trace of liquid. Then keep the membrane dry for 8 hours, then immerse it in deionized water for 10 minutes, repeat the cleaning 3 times, and finally soak the membrane in deionized water for testing.

[0077]

[0078] It can be proved from the above table that after repair, the desalination rate of the waste reverse osmosis membrane is significantly improved.

[0079]

[0080] Blank control: The unrepaired waste reverse osmosis membrane was oxidized again

[0081] The above table shows that when the repaired reverse osmosis membrane is exposed to hypochlorous acid oxidant for a long time again, it can maintain relatively stable separation performance and its antioxidant performance is significantly enhanced.

[0082]

[0083] It can be proved from the table that the repair layer still maintains basically stable membrane performance after 48 hours of ethanol immersion.

Claims

1. A method for protecting and repairing oxidatively damaged seawater desalination membranes, characterized in that: The steps include: (1) Cleaning of waste reverse osmosis membranes: Collect the waste reverse osmosis membranes from the seawater desalination system, soak the membranes in 0.2% sodium hypochlorite solution with a pH of 10 for 12 hours, then soak them in deionized water for 1 hour, repeat the washing three times, take them out, and dry them for later use; (2) Immerse the reverse osmosis membrane treated in step (1) in the cross-linking solution for 10-20 minutes, blow the membrane surface with high-pressure air until there is no obvious trace of liquid, and then immerse it in the repair solution for 30-120 minutes. Blow the membrane surface with high-pressure air until there is no obvious trace of liquid, then keep the membrane dry for 2-8 hours, and then immerse it in deionized water for 10 minutes. Repeat the washing three times, and finally immerse the membrane in deionized water for testing; The cross-linking solution is prepared by dissolving cross-linking agent molecules in an alkane organic solvent, wherein the cross-linking agent concentration is controlled at 0.1-0.5% by mass, wherein the cross-linking agent is one or a mixture of polyvalent epoxy or polyvalent isocyanate compounds, wherein the polyvalent epoxy is one of glycerol tri(1,2-epoxy)propyl ether, diglycidyl ether, ethylene glycol diglycidyl ether, or pentaerythritol glycidyl ether, and the polyvalent isocyanate is one or a mixture of m-phenylene diisocyanate, p-phenylene diisocyanate, or toluene diisocyanate; and the alkane organic solvent is one of pentane, hexane, cyclohexane, and heptane. The repair solution refers to: dissolving one of the two polymer materials, polyether block polyamide or polyether amine, or a mixture thereof into an alcohol-alkane mixed solvent, with the volume fraction of the alcohol solvent being 10%-30% and the mass fraction of the polymer material being 0.2%-2%, wherein the relative molecular weight of the polyether block polyamide is 50,000 to 300,000, and the relative molecular weight of the polyether amine is 200 to 4,000; the alcohol solvent is one of ethanol, isopropanol, butanol or isobutanol or a mixture thereof; the alkane organic solvent is one of pentane, hexane, cyclohexane and heptane.

2. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that: In step (2), the cross-linking agent is a polyisocyanate compound.

3. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The mass concentration of the cross-linking agent in step (2) is 0.2-0.4%.

4. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The polymer material in the repair solution in step (2) is polyether block polyamide; the ratio of polyether repeating units to polyamide repeating units in the polyether block polyamide structure is 2:1, 3:1, or 1:2; and the relative molecular weight is 100,000 to 250,000.

5. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The polymer mass fraction of the repair solution in step (2) is 0.5-1%.

6. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The alcohol solvent system fraction of the alcohol-alkane organic solvent in step (2) is 15-20%.

7. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The immersion time of the cross-linking solution in step (2) is 10-15 minutes.

8. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The immersion time of the repair solution in step (2) is 60-90 minutes.

9. The method for protecting and repairing oxidatively damaged seawater desalination membrane according to claim 1, characterized in that The drying time of the film in step (2) is 15-25 minutes.

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