Chloropolyamide-resistant composite nanofiltration membrane and preparation method thereof

Abstract

The invention discloses a chlorine-resistant polyamide composite nanofiltration membrane and a preparation method thereof. The composite nanofiltration membrane is composed of a polysulfone-based membrane, and a catechol intermediate layer and a polyamide desalination layer which are sequentially arranged on the polysulfone-based membrane, wherein the catechol middle layer comprises a plurality of catechol self-polymerization layers, and catechol is subjected to oxidation self-polymerization and then is constructed on the polysulfone base membrane layer by layer to obtain the catechol self-polymerization layers; and the polyamide desalination layer is constructed on the catechol intermediate layer through an interfacial polymerization reaction. The chlorine-resistant polyamide composite nanofiltration membrane comprises a polysulfone base membrane, a catechol middle layer and a polyamide desalination layer, the catechol self-polymerization middle layer is formed through a layer-by-layer construction technology, certain chlorine resistance is provided, meanwhile, the possibility that the middle layer falls off is reduced, and the stability of the composite nanofiltration membrane is enhanced; the tannic acid is added into a water-phase solution, so that the performance of the polyamide composite nanofiltration membrane is adjusted, and the polyamide composite nanofiltration membrane is endowed with relatively high chlorine resistance.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment separation membranes, and in particular to a chlorine-resistant polyamide composite nanofiltration membrane and a preparation method thereof. Background Art

[0002] Nanofiltration membrane is a membrane separation technology between reverse osmosis and ultrafiltration. It has excellent selective filtration ability and can effectively remove divalent ions, organic matter and some monovalent ions (such as nitrates, etc.) in water. This nanofiltration membrane is usually made of polymer materials and has a specific pore size distribution and charge characteristics. It allows water molecules to pass smoothly while effectively blocking pollutants with larger molecular weights, making it an ideal choice for treating surface water, groundwater and industrial wastewater.

[0003] At present, composite nanofiltration membranes based on polyamide are still the main application materials in the commercial market. However, these membranes are easily contaminated during actual use, especially from the adsorption and deposition of organic pollutants such as fungi and microorganisms. The accumulation of such pollutants will not only destroy the structure of the active layer, but also significantly affect the separation performance of the membrane and shorten the service life of the membrane.

[0004] To prevent microbial contamination, active chlorine (such as Cl2, HClO, ClO - The active chlorine is highly reactive to polyamide materials and can attack the unreacted amino groups in polyamide, thus causing changes in the cross-linked network of polyamide and even breaking of the molecular chains, which will eventually cause irreversible damage to the reverse osmosis membrane and affect its performance and life.

[0005] Therefore, developing polyamide composite nanofiltration membranes with good chlorine resistance is crucial to extending the service life of the membrane. Summary of the invention

[0006] The purpose of the present invention is to propose a chlorine-resistant polyamide composite nanofiltration membrane and a preparation method thereof to address the problem that the polyamide layer of the existing composite nanofiltration membrane is easily destroyed by residual chlorine, thereby affecting the membrane separation performance and service life, thereby avoiding the nanofiltration membrane separation performance being reduced and the service life being shortened due to residual chlorine destruction.

[0007] To achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The invention provides a chlorine-resistant polyamide composite nanofiltration membrane, which is composed of a polysulfone-based membrane, and a catechol intermediate layer and a polyamide desalination layer which are sequentially arranged on the polysulfone-based membrane; wherein the catechol intermediate layer comprises a plurality of catechol self-polymerized layers, which are obtained by constructing catechol layer by layer on the polysulfone-based membrane after oxidative self-polymerization; and the polyamide desalination layer is constructed on the catechol intermediate layer by interfacial polymerization reaction.

[0009] Further, a chlorine-resistant polyamide composite nanofiltration membrane: the catechol self-polymerization layer is 3 to 7 layers. Specifically, in order to ensure that the intermediate layer structure can completely cover the base membrane, the catechol self-polymerization layer is preferably 3 to 7 layers.

[0010] The present invention also provides a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane, the method comprising the following steps:

[0011] S1. Preparation of a casting solution: dissolving polysulfone in N,N-dimethylformamide to prepare a casting solution;

[0012] S2, preparation of polysulfone-based membrane: coating the casting solution on a non-woven fabric, immersing the non-woven fabric in water to form a membrane through phase conversion, and washing the non-woven fabric with water to obtain a polysulfone-based membrane;

[0013] S3. Preparation of catechol solution: dissolving catechol in water to prepare a catechol solution;

[0014] S4. Preparation of oxidation solution: preparing oxidation solution for oxidative self-polymerization of catechol;

[0015] S5, modification of a single layer of a polysulfone-based membrane: applying the catechol solution to the surface of the polysulfone-based membrane, allowing it to stand, removing the residual solution on the membrane surface, and then applying the oxidizing solution to the surface of the polysulfone-based membrane, allowing it to stand, drying the oxidizing solution on the membrane surface, and obtaining a single-layer catechol self-polymerization layer through oxidative self-polymerization;

[0016] S6, constructing the catechol intermediate layer layer by layer: repeating the process of step S5 several times to obtain a catechol intermediate layer constructed layer by layer;

[0017] Specifically, after repeating step S5 several times, a layered intermediate layer can be obtained, and the number and thickness of the intermediate layer can be controlled by controlling the number of times step S5 is repeated;

[0018] S7, preparing an aqueous phase liquid: dissolving piperazine and tannic acid in water to obtain an aqueous phase liquid;

[0019] S8, preparing an oil phase liquid: dissolving the acyl chloride monomer in an organic solvent to obtain an oil phase liquid;

[0020] S9, preparation of polyamide desalination layer: the polysulfone-based membrane covered with the catechol intermediate layer prepared in step S6 is first immersed in the aqueous phase liquid, the liquid on the membrane surface is removed, and then immersed in the oil phase liquid to perform interfacial polymerization reaction to form a polyamide desalination layer, and the liquid on the membrane surface is removed to obtain a chlorine-resistant polyamide composite nanofiltration membrane.

[0021] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane: Step S1, preparation of a casting solution: dissolving polysulfone in N,N-dimethylformamide to prepare a casting solution with a polysulfone concentration of 15.0-22.0 wt%.

[0022] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane is provided: Step S2, preparation of a polysulfone-based membrane: coating the casting liquid on a non-woven fabric with a coating thickness of 100.0 to 500.0 μm, immersing the non-woven fabric in water at 20 to 70°C for 20 to 60 seconds to form a membrane through phase conversion, and washing the non-woven fabric with water to obtain a polysulfone-based membrane.

[0023] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane: Step S3, preparation of a catechol solution: dissolving catechol in water to prepare a catechol solution with a concentration of 0.1 to 2.0 wt%.

[0024] Further, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane: Step S4, preparation of an oxidizing solution: dissolving sodium periodate in a sodium acetate solution, thereby preparing a sodium periodate solution for oxidative self-polymerization of catechol;

[0025] The concentration of the sodium acetate solution is 0.2-2.0 wt %, and the concentration of the sodium periodate in the sodium periodate solution is 0.2-2.0 wt %.

[0026] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane: Step S7, preparing an aqueous phase liquid: dissolving piperazine and tannic acid in water to obtain an aqueous phase liquid with a piperazine concentration of 0.25-1.5wt% and a tannic acid concentration of 0.001-0.01wt%.

[0027] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane: step S8, preparing an oil phase liquid: dissolving an acyl chloride monomer in an organic solvent to obtain an oil phase liquid with a concentration of 0.02 to 0.3 wt%; wherein the acyl chloride is trimesoyl chloride, and the organic solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, and isoparaffin solvents.

[0028] Furthermore, a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane is provided: Step S9, preparation of a polyamide desalting layer: the polysulfone-based membrane covered with the catechol intermediate layer prepared in step S6 is first immersed in the aqueous phase liquid for 20 to 60 seconds to remove the liquid on the membrane surface, and then immersed in the oil phase liquid for 20 to 60 seconds to carry out an interfacial polymerization reaction to form a polyamide desalting layer, and the liquid on the membrane surface is blown away with an air knife to obtain a chlorine-resistant polyamide composite nanofiltration membrane.

[0029] Specifically, the chlorine-resistant polyamide composite nanofiltration membrane constructed based on piperazine and trimesoyl chloride of the present invention usually has chlorination occurring on the amine side; specifically, the amidation reaction between piperazine and trimesoyl chloride has a high steric hindrance, thus leaving a large number of unreacted NH bonds, and these residual NH bonds will be replaced or oxidized by active chlorine when the membrane contacts active chlorine, causing the structure of the polyamide desalting layer to change, thereby affecting its separation performance. At present, there are relatively few studies on this chlorination damage mechanism, but the more recognized mechanisms include the chlorine substitution reaction of the amine group and the conversion of the amine group into hydroxylamine imine. This structural change not only reduces the stability of the membrane, but also weakens its separation effect. The specific chlorination mechanism is shown below.

[0030]

[0031] In addition, the regulator tannic acid added in the aqueous phase liquid of the present invention is a polyphenol compound, and its molecule contains a large amount of phenolic hydroxyl groups, which can not only participate in interfacial polymerization and acyl chloride reaction to form more stable polyester bonds that are not attacked by chlorine free radicals, thereby ensuring that the polyamide desalination layer has a certain chlorine resistance; and the phenolic hydroxyl groups in the tannic acid can also react with active chlorine to capture chlorine free radicals, thereby protecting the amide bonds in the polyamide membrane from being attacked by chlorine free radicals. In addition, tannic acid can also be used as a modifier of the membrane, which can not only increase the hydrophilicity of the polyamide desalination layer, but also provide more hydrogen bonding sites, enhance the interaction between the membrane and water molecules, thereby reducing the adsorption of organic pollutants and improving the anti-pollution performance of the membrane. The present invention can make the chlorine-resistant nanofiltration membrane obtain better chlorine resistance on the basis of maintaining the original separation performance by adding tannic acid.

[0032] The monomer catechol of the middle layer of the present invention is a simple dihydric phenol, which is easily oxidized to quinone and can undergo secondary reaction with electrophilic groups. Due to the above characteristics, catechol can undergo self-polymerization reaction, and sodium periodate with strong oxidizing property can break the benzene ring in catechol to form carboxyl groups, and finally spontaneously polymerize to form a hydrophilic surface with multiple carboxyl groups, which can improve the surface hydrophilicity of the hydrophobic polysulfone-based membrane. The process of catechol oxidation self-polymerization is shown as follows.

[0033]

[0034] Beneficial effects of the present invention:

[0035] (1) The present invention uses tannic acid as a regulator and constructs a polyamide composite nanofiltration membrane through the self-polymerization of catechol to construct an intermediate layer. The chlorine resistance of the nanofiltration membrane is improved through the synergistic effect of the tannic acid and catechol intermediate layer, while the hydrophilicity of the nanofiltration membrane is improved and its permeation flux and separation performance are guaranteed.

[0036] (2) The present invention uses tannic acid as a regulator added to the aqueous phase liquid. Tannic acid has multiple phenolic hydroxyl groups that can react with acyl chloride groups, and the polyester bonds formed are beneficial to improving the chlorine resistance of the nanofiltration membrane. In addition, the phenolic hydroxyl group also has a strong free radical capture ability, which can protect the amide bond from the attack of chlorine free radicals, so that the selective layer of the nanofiltration membrane has considerable chlorine resistance. In addition, introducing tannic acid molecules containing rich hydroxyl groups into the selective layer of the nanofiltration membrane can enhance the hydrophilicity of the nanofiltration membrane and improve the surface charge of the nanofiltration membrane. At the same time, the electrostatic attraction on the membrane surface and the hydrogen bonds introduced by tannic acid can form a hydration layer on the membrane surface, acting as a barrier between it and the dirt, thereby reducing the adsorption of dirt, improving the anti-pollution performance of the composite nanofiltration membrane, and to a certain extent, blocking some chlorine-containing compounds from damaging the polyamide layer, further improving its chlorine resistance.

[0037] (3) The chlorine-resistant polyamide composite nanofiltration membrane of the present invention includes a polysulfone base membrane, a catechol intermediate layer and a polyamide desalination layer. The complete catechol self-polymerization intermediate layer formed by the layer-by-layer construction technology provides a certain chlorine resistance, while reducing the possibility of the intermediate layer falling off, thereby enhancing the stability of the composite nanofiltration membrane; by adding tannic acid to the aqueous solution, the performance of the polyamide composite nanofiltration membrane is adjusted, giving the polyamide composite nanofiltration membrane a stronger chlorine resistance.

[0038] (4) In the preparation method of the chlorine-resistant polyamide composite nanofiltration membrane provided by the present invention, the catechol self-polymerization technology is used to construct the intermediate layer, which not only gives the composite nanofiltration membrane higher stability and reduces the possibility of the intermediate layer falling off, but also realizes the precise regulation of the thickness and performance of the intermediate layer, effectively avoiding the performance fluctuation problem caused by the uneven thickness of the intermediate layer. In addition, the surface of the catechol intermediate layer is rich in a large number of carboxyl groups, which also significantly improves the hydrophilicity of the polysulfone-based membrane and promotes the uniform dispersion of piperazine monomers on its surface, thereby providing a guarantee for the preparation of a chlorine-resistant polyamide composite nanofiltration membrane with high permeation flux and retention performance.

[0039] (5) The chlorine-resistant polyamide composite nanofiltration membrane of the present invention greatly improves its long-term chlorine resistance while ensuring good permeation flux and retention rate. The chlorine-resistant polyamide composite nanofiltration membrane of the present invention exhibits excellent permeation flux, retention rate and long-term chlorine resistance, and the preparation process is simple, safe and environmentally friendly, the modified materials used are low in cost, and have good commercial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 This is a water contact angle diagram of the chlorine-resistant polyamide composite nanofiltration membrane prepared in Example 1;

[0042] Figure 2 This is the water contact angle diagram of the polyamide composite nanofiltration membrane prepared in Comparative Example 1. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] This embodiment 1 provides a chlorine-resistant polyamide composite nanofiltration membrane, which is composed of a polysulfone-based membrane, and a catechol intermediate layer and a polyamide desalination layer sequentially arranged on the polysulfone-based membrane;

[0046] The catechol intermediate layer includes four catechol self-polymerized layers, which are constructed layer by layer on the polysulfone-based membrane after oxidative self-polymerization of catechol; the polyamide desalination layer is constructed on the catechol intermediate layer by interfacial polymerization reaction;

[0047] The preparation method of the chlorine-resistant polyamide composite nanofiltration membrane comprises the following specific steps:

[0048] S1. Preparation of a casting solution: dissolving polysulfone in N,N-dimethylformamide to prepare a casting solution having a polysulfone concentration of 18.0 wt %;

[0049] S2. Preparation of polysulfone-based membrane: coating the above-mentioned casting solution on non-woven fabric with a coating thickness of 150.0 μm, immersing in 25° C. water for 30 seconds to form a membrane through phase conversion, and washing with water to obtain a polysulfone-based membrane;

[0050] S3, preparation of catechol solution: dissolving catechol in water to prepare a catechol aqueous solution with a concentration of 0.2 wt %;

[0051] S4, preparation of oxidation solution: dissolving sodium periodate (SP) in a sodium acetate solution with a concentration of 0.2 wt %, thereby preparing a sodium periodate solution with a concentration of 0.2 wt %, which is used for the oxidative self-polymerization of catechol;

[0052] S5, modification of a single layer of a polysulfone-based membrane: applying the catechol solution to the surface of the polysulfone-based membrane, leaving it to stand for 10 minutes, removing the residual solution on the membrane surface, and then pouring the sodium periodate oxidation solution on the surface of the polysulfone-based membrane, leaving it to stand for 5 minutes, drying the oxidation solution on the membrane surface, and obtaining a single-layer catechol self-polymerization layer after oxidation self-polymerization;

[0053] S6, constructing the catechol intermediate layer layer by layer: repeating the process of step S5 three times, thereby obtaining four layers of catechol intermediate layers constructed layer by layer;

[0054] S7, preparing an aqueous phase liquid: dissolving piperazine and tannic acid in water to obtain an aqueous phase liquid with a piperazine concentration of 1.0 wt % and a tannic acid concentration of 0.005 wt %;

[0055] S8, preparing an oil phase liquid: dissolving trimesoyl chloride in an isoparaffin organic solvent whose main component is n-hexane to obtain an oil phase liquid with a concentration of 0.15 wt %;

[0056] S9, preparation of polyamide desalination layer: the polysulfone-based membrane covered with a single-layer catechol intermediate layer prepared in step S6 is first immersed in an aqueous phase liquid for 35 seconds, and then the liquid on the membrane surface is removed, and then immersed in an oil phase liquid for 25 seconds to perform an interfacial polymerization reaction to form a polyamide desalination layer, and then the liquid on the membrane surface is blown away with an air knife to obtain a chlorine-resistant polyamide composite nanofiltration membrane. The preparation process of the chlorine-resistant polyamide composite nanofiltration membrane in the above embodiment 1 is as follows:

[0057]

[0058] Example 2

[0059] The difference between Example 2 and Example 1 is that in Example 2, step S5 is repeated twice to obtain three layers of catechol intermediate layers constructed layer by layer, and the rest is the same as Example 1.

[0060] Example 3

[0061] The difference between Example 3 and Example 1 is that in Example 3, step S5 is repeated 4 times to obtain 5 layers of catechol intermediate layers constructed layer by layer, and the rest is the same as Example 1.

[0062] Example 4

[0063] The difference between Example 4 and Example 1 is that the concentration of tannic acid in the aqueous phase of Example 4 is 0.001 wt %, and the rest is the same as Example 1.

[0064] Example 5

[0065] The difference between Example 5 and Example 1 is that the concentration of tannic acid in the aqueous phase of Example 5 is 0.01 wt %, and the rest is the same as Example 1.

[0066] Example 6

[0067] The difference between Example 6 and Example 1 is that the concentration of the catechol aqueous solution in Example 6 is 0.1 wt %, and the rest is the same as Example 1.

[0068] Example 7

[0069] The difference between Example 7 and Example 1 is that the concentration of the catechol aqueous solution in Example 7 is 0.4 wt %, and the rest is the same as Example 1.

[0070] Comparative Example 1

[0071] Comparative Example 1 provides a method for preparing a polyamide composite nanofiltration membrane, comprising the following steps:

[0072] (1) Preparation of a casting solution: polysulfone is dissolved in N,N-dimethylformamide to prepare a casting solution having a polysulfone concentration of 18.0 wt %;

[0073] (2) Preparation of polysulfone-based membrane: The above-mentioned casting solution was coated on a non-woven fabric with a coating thickness of 150.0 μm, and then immersed in 25° C. water for 30 seconds to form a membrane through phase inversion reaction, and then washed with water and taken out to obtain a polysulfone-based membrane;

[0074] (3) Preparation of polyamide layer: The polysulfone-based membrane obtained above was immersed in an aqueous solution containing 1.0 wt% piperazine (NaOH adjusted pH ≥ 10) for 35 seconds, and then the liquid on the membrane surface was removed with a rubber roller. The membrane was then immersed in an oil phase liquid containing 0.15 wt% trimesoyl chloride for interfacial polymerization for 25 seconds, and then the liquid on the membrane surface was blown away with an air knife to obtain a polyamide composite nanofiltration membrane.

[0075] The difference between the comparative example 1 and the example 1 is that the comparative example 1 does not construct a catechol intermediate layer and does not introduce tannic acid, and the rest is the same as the example 1.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Comparative Example 1 is that the concentration of piperazine in the aqueous phase liquid of Comparative Example 2 is 1.5 wt %, and the rest is the same as Comparative Example 1.

[0078] Comparative Example 3

[0079] The difference between Comparative Example 3 and Comparative Example 1 is that the concentration of piperazine in the aqueous phase liquid of Comparative Example 3 is 0.5 wt %, and the rest is the same as Comparative Example 1.

[0080] Comparative Example 4

[0081] The difference between Comparative Example 4 and Comparative Example 1 is that the concentration of trimesoyl chloride in the oil phase liquid of Comparative Example 4 is 0.3 wt %, and the rest is the same as Comparative Example 1.

[0082] test:

[0083] 1. Separation performance and chlorine resistance test of composite nanofiltration membrane:

[0084] (1) The separation performance of the polyamide composite nanofiltration membranes prepared in Examples 1 to 7 and Comparative Examples 1 to 4 was tested. The performance was mainly characterized by two characteristic parameters, namely, the water flux and the salt rejection rate of the membrane. The test results are shown in Table 1 below.

[0085] ① Water flux: refers to the volume of water passing through the effective unit area membrane per unit time under certain test conditions;

[0086] ②Desalination rate R, the calculation formula is: R = (1-C p / C f )*100%, where R is the interception rate or desalination rate, C p is the influent salt concentration, C f is the salt concentration of produced water.

[0087] The test conditions for the above water flux and desalination rate are as follows: the feed liquid is a 2000 ppm magnesium sulfate aqueous solution, the feed liquid temperature is 25° C., and the operating pressure is 70 psi (0.483 MPa).

[0088] (2) The chlorine resistance of the polyamide composite nanofiltration membranes prepared in the above Examples 1 to 7 and Comparative Examples 1 to 4 was tested. The test conditions were as follows: the composite nanofiltration membranes that had completed the above separation performance test were placed in a sodium hypochlorite aqueous solution (pH=7.5±0.5) containing 500 ppm active chlorine and immersed at room temperature 25°C±0.5°C for 24 hours, then part of the membrane was taken out, and then the chlorinated membrane was rinsed with deionized water to remove residual active chlorine. Finally, the water flux and desalination rate of the membrane treated with the sodium hypochlorite aqueous solution were further tested under the above water flux and desalination rate test conditions. The chlorine resistance of the composite nanofiltration membranes of Examples 1 to 7 and Comparative Examples 1 to 4 was investigated by the water flux change rate and desalination rate change rate. The specific test results are shown in Table 1 below.

[0089] Table 1 shows the performance test results of the composite nanofiltration membranes of Examples 1 to 7 and Comparative Examples 1 to 4

[0090]

[0091] It can be seen from the test results in Table 1 that compared with the polyamide composite nanofiltration membranes prepared in Comparative Examples 1 to 4, the chlorine-resistant polyamide composite nanofiltration membranes prepared in Examples 1 to 7 of the present invention and containing a catechol intermediate layer modified with tannic acid prepared in Examples 1 to 7 have relatively small changes in water flux after sodium hypochlorite chlorination treatment, and the decrease in salt rejection rate is also significantly lower than that of the polyamide composite nanofiltration membranes of Comparative Examples 1 to 4, which indicates that the introduction of tannic acid, an aqueous phase additive, and the constructed catechol intermediate layer in the present invention can significantly improve the chlorine resistance of the nanofiltration membrane.

[0092] 2. Contact angle test:

[0093] The contact angle tests were performed on the polyamide composite nanofiltration membranes prepared in Example 1 and Comparative Example 1. The test results showed that the contact angle of the chlorine-resistant polyamide composite nanofiltration membrane prepared in Example 1 was as follows: Figure 1 As shown, the contact angle of the polyamide composite nanofiltration membrane prepared in Comparative Example 1 is as shown Figure 2 As shown; it can be seen from the figure that the chlorine-resistant polyamide composite nanofiltration membrane prepared in Example 1 of the present invention has better hydrophilicity. This result verifies that the introduction of tannic acid can effectively enhance the hydrophilicity of the membrane surface, which improves the chlorine resistance of the nanofiltration membrane to a certain extent.

[0094] The above are preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A chlorine-resistant polyamide composite nanofiltration membrane, characterized in that: The composite nanofiltration membrane is composed of a polysulfone-based membrane, and a catechol intermediate layer and a polyamide desalination layer sequentially arranged on the polysulfone-based membrane; The catechol intermediate layer comprises a plurality of catechol self-polymerized layers, which are constructed layer by layer on the polysulfone-based membrane after oxidative self-polymerization of catechol; and the polyamide desalination layer is constructed on the catechol intermediate layer by interfacial polymerization reaction.

2. The chlorine-resistant polyamide composite nanofiltration membrane according to claim 1, characterized in that: The catechol self-polymerization layer is 3 to 7 layers.

3. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 1 or 2, characterized in that: The method comprises the following steps: S1. Preparation of a casting solution: dissolving polysulfone in N,N-dimethylformamide to prepare a casting solution; S2, preparation of polysulfone-based membrane: coating the casting solution on a non-woven fabric, immersing the non-woven fabric in water to form a membrane through phase conversion, and washing the non-woven fabric with water to obtain a polysulfone-based membrane; S3, preparation of catechol solution: dissolving catechol in water to prepare a catechol solution; S4. Preparation of oxidation solution: preparing oxidation solution for oxidative self-polymerization of catechol; S5, modification of a single layer of a polysulfone-based membrane: applying the catechol solution to the surface of the polysulfone-based membrane, allowing it to stand, removing the residual solution on the membrane surface, and then applying the oxidizing solution to the surface of the polysulfone-based membrane, allowing it to stand, drying the oxidizing solution on the membrane surface, and obtaining a single-layer catechol self-polymerization layer through oxidative self-polymerization; S6, constructing the catechol intermediate layer layer by layer: repeating the process of step S5 several times to obtain a catechol intermediate layer constructed layer by layer; S7, preparing an aqueous phase liquid: dissolving piperazine and tannic acid in water to obtain an aqueous phase liquid; S8, preparing an oil phase liquid: dissolving the acyl chloride monomer in an organic solvent to obtain an oil phase liquid; S9, preparation of polyamide desalination layer: the polysulfone-based membrane covered with the catechol intermediate layer prepared in step S6 is first immersed in the aqueous phase liquid, the liquid on the membrane surface is removed, and then immersed in the oil phase liquid to perform interfacial polymerization reaction to form a polyamide desalination layer, and the liquid on the membrane surface is removed to obtain a chlorine-resistant polyamide composite nanofiltration membrane.

4. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S1, preparation of a casting solution: dissolving polysulfone in N,N-dimethylformamide to prepare a casting solution with a polysulfone concentration of 15.0-22.0 wt%.

5. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S2, preparation of polysulfone-based membrane: coating the casting solution on non-woven fabric with a coating thickness of 100.0-500.0 μm, immersing in 20-70° C. water to form a membrane for 20-60 seconds through phase conversion, and washing with water to obtain a polysulfone-based membrane.

6. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S3, preparation of catechol solution: dissolving catechol in water to prepare a catechol solution with a concentration of 0.1-2.0 wt %.

7. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S4, preparation of oxidation solution: dissolving sodium periodate in sodium acetate solution, thereby preparing a sodium periodate solution for oxidative self-polymerization of catechol; The concentration of the sodium acetate solution is 0.2-2.0 wt %, and the concentration of the sodium periodate in the sodium periodate solution is 0.2-2.0 wt %.

8. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S7, preparing an aqueous phase liquid: dissolving piperazine and tannic acid in water to obtain an aqueous phase liquid with a piperazine concentration of 0.25-1.5 wt % and a tannic acid concentration of 0.001-0.01 wt %.

9. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S8, preparing an oil phase liquid: dissolving the acyl chloride monomer in an organic solvent to obtain an oil phase liquid with a concentration of 0.02-0.3 wt %; Wherein, the acyl chloride is trimesoyl chloride, and the organic solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, and isoparaffin solvents.

10. The method for preparing a chlorine-resistant polyamide composite nanofiltration membrane according to claim 3, characterized in that: Step S9, preparation of a polyamide desalination layer: the polysulfone-based membrane covered with the catechol intermediate layer prepared in step S6 is first immersed in the aqueous phase liquid for 20 to 60 seconds to remove the liquid on the membrane surface, and then immersed in the oil phase liquid for 20 to 60 seconds to perform an interfacial polymerization reaction to form a polyamide desalination layer, and the liquid on the membrane surface is blown away with an air knife to obtain a chlorine-resistant polyamide composite nanofiltration membrane.

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