Method for preparing chlorine-resistant polyesteramide nanofiltration membrane from high-activity aqueous phase monomer

Abstract

The invention discloses a method for preparing a chlorine-resistant polyesteramide nanofiltration membrane from a high-activity water-phase monomer. The method comprises the following steps: cutting a base membrane; performing ultrasonic cleaning; fixing the membrane; preparing a polymerization water phase solution; and carrying out intermittent interfacial polymerization reaction. According to the preparation method, a traditional piperazine monomer is replaced with a high-activity aqueous-phase monomer N2Hyd, and a certain amount of APG is introduced, so that the hydrophilicity of the membrane is effectively improved, a hydrophilic glycoside layer is formed on the surface of the membrane, and the lipophilicity of the membrane is remarkably reduced; the N2Hyd and the APG have high activity and contain a plurality of hydroxyl groups, so that the prepared polyesteramide nanofiltration membrane has better reaction activity. Finally, due to the fact that the membrane contains a large number of ester bonds and a thin active layer, the mass transfer resistance is greatly reduced, and therefore the membrane shows high water flux, the excellent desalting characteristic and the excellent anti-chlorine effect. The implementation of the method not only promotes the technical progress of the membrane material, but also provides a new thought and direction for research and application in related fields.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental science and engineering materials, and particularly to a method for preparing a chlorine-resistant polyester amide nanofiltration membrane from highly active aqueous monomers. Background Art

[0002] With the continuous exacerbation of the global water shortage problem, the application of seawater desalination technology has become increasingly important. Seawater desalination can not only effectively solve the problem of freshwater shortage, but also provide a reliable water source for arid regions. However, traditional seawater desalination methods, such as multi-stage flash evaporation, reverse osmosis, etc., still face many challenges in practical applications, especially in terms of the performance, durability, and cost of membrane materials. Membrane separation technology, especially reverse osmosis membranes and nanofiltration membranes, has become a research hotspot in the field of seawater desalination due to its high efficiency, energy conservation, and environmental friendliness.

[0003] Currently, reverse osmosis membranes are widely used in seawater desalination, and their main raw materials are polyamide and polyester materials. However, as the membrane is used for a longer time, problems such as membrane fouling and degradation gradually emerge, resulting in a decrease in membrane flux and salt rejection rate. Membrane fouling mainly comes from suspended solids, bacteria, and organic matter in water, and during seawater desalination, chlorinating agents are usually added to inhibit the growth of microorganisms. Although these chlorinating agents can effectively control biological fouling, they also cause certain damage to the membrane material, affecting the long-term stability and economy of the membrane. Therefore, how to improve the chlorine resistance of membrane materials and extend the service life of membranes is an urgent problem to be solved in current seawater desalination technology.

[0004] Polyester amide materials have become an important research direction for membrane materials due to their excellent mechanical strength, thermal stability, and chemical tolerance. The molecular structure of polyester amide endows it with good chemical stability and superior separation performance, and can effectively filter dissolved salts and impurities in water. In addition, polyester amide membranes also show excellent heat resistance and pressure resistance, and are suitable for application in the harsh environment of seawater desalination.

[0005] However, in the prior art, there has not yet been a method that can prepare a chlorine-resistant polyester amide nanofiltration membrane with stronger negative charges, greater hydrophilicity, larger membrane pores, and a smoother surface, and that has better water permeability at the optimal concentration of the co-monomer combination, while having a good Na2SO4 rejection rate and obvious Na2SO4 / NaCl separation ability.

[0006] Therefore, it is necessary to propose a method for preparing a chlorine-resistant polyester amide nanofiltration membrane from highly active aqueous monomers to solve the above problems. Summary of the Invention

[0007] Aiming at the application limitation problems of high pollution tendency and weak chlorine resistance of traditional nanofiltration membranes in the field of seawater desalination, the present invention proposes a method for preparing chlorine-resistant polyesteramide nanofiltration membrane with high-activity water-phase monomers.

[0008] The method for preparing chlorine-resistant polyesteramide nanofiltration membrane with high-activity aqueous phase monomer comprises: S1. Cut the PES-UF commercial base film to obtain a certain size and shape of the base film; S2, ultrasonically cleaning the PES-UF commercial base membrane twice with an ethanol solution to remove the glycerol protective agent and impurity pollutants on the membrane surface to obtain a spare PES ultrafiltration base membrane; S3, fixing the PES ultrafiltration base membrane cleaned in S2 on a polytetrafluoroethylene (PTFE) frame, with the membrane selection layer facing upward, for subsequent treatment and reaction; S4. Mix appropriate amounts of alkyl polyglucosides (APG) and N-(2-hydroxyethyl)ethylenediamine (N2Hyd) in deionized water to form a uniform (monomer / surfactant) aqueous polymerization solution, and control its alkaline solution environment; contact the aqueous polymerization solution with the surface of the PES ultrafiltration base membrane for a certain period of time, then gently pour out the remaining solution, gently wipe the residual liquid on the membrane surface with filter paper, blow it evenly with an air pump gun and dry it naturally to ensure that there is no residual liquid on the membrane surface; S5. Gently pour a n-hexane organic phase solution containing a certain concentration of trimesoyl chloride (TMC) onto the membrane surface, and intermittently initiate an interfacial polymerization (IP) reaction to obtain the prepared polyester amide composite nanofiltration membrane.

[0009] In a preferred embodiment of the present scheme, the PES-UF commercial base membrane in S1 is a polyethersulfone ultrafiltration membrane with a molecular weight cutoff (MWCO) of 30 kDa (provided by Microdyn-Nadir); the size of the base membrane obtained after cutting is 11 cm*11 cm.

[0010] In a preferred embodiment of the present scheme, the concentration of the ethanol solution in S2 is 1%-5% (v / v); the ultrasonic cleaning time is 1-3 min each time; and the obtained spare PES ultrafiltration base membrane is stored in pure water for standby use.

[0011] Furthermore, the specific steps of fixing the PES ultrafiltration base membrane on the PTFE frame in S3 are: taking out the PES ultrafiltration base membrane from the pure water, and using filter paper to dry the membrane surface until there are no obvious water droplets, and then fixing the ultrafiltration base membrane on the polytetrafluoroethylene (PTFE) frame with the membrane selection layer facing up, and drying it for 2-5 minutes. During this period, it is evenly blown with an air pump gun for 1-3 minutes to provide evenly distributed base membrane pores for the mixed water phase.

[0012] In a preferred embodiment of this solution, the uniform aqueous polymerization solution in S4 is an aqueous solution of 0.05 - 0.15 % (v / v) N2Hyd and 5% - 15% APG.

[0013] Furthermore, the specific operation to control its slightly alkaline solution environment is as follows: Mix an appropriate amount of APG and N2Hyd in deionized water to form a uniform aqueous polymerization solution. During this period, test the pH of its alkaline environment within the range of 8 - 10.5 to prevent the deprotonation of its subsequent side reaction products from having an impact.

[0014] Furthermore, the contact time between the aqueous polymerization solution and the surface of the PES ultrafiltration base membrane is 5 - 8 min.

[0015] Furthermore, the specific operation to gently dry the liquid remaining on the membrane surface with filter paper is as follows: Use filter paper to blot the membrane surface until there are no obvious water droplets; the specific operation to evenly blow air on it with an air pump gun and let it dry naturally is as follows: Evenly blow air on it with an air pump gun for an operation time of 30S, and then refix the PES ultrafiltration base membrane soaked in the aqueous solution to the PTFE frame and let it dry naturally for 2 - 5 min.

[0016] In a preferred embodiment of this solution, the specific operation to intermittently initiate the interfacial polymerization reaction in S5 is as follows: Gently pour the n - hexane organic phase solution containing 0.05 - 0.2 % (w / v) TMC onto the membrane surface and soak for 20 - 50S to initiate the first step of the intermittent interfacial polymerization reaction. Subsequently, pour off the organic phase solution and rinse it twice with n - hexane solution; After an interval of 10S, immediately invert the n - hexane organic phase solution containing 0.05 - 0.2 % (w / v) TMC on its surface for 30S to maintain a sufficient organic phase concentration to carry out the remaining reaction of the remaining aqueous phase monomers at the same diffusion rate, achieving a complete and uniform regulation characteristic. Then, put it into an oven for heat treatment for 5 - 10 min to enhance its mechanical properties of the thermally stable active layer. After taking it out and cooling it to room temperature, the prepared polyester amide composite nanofiltration membrane is obtained and soaked in pure water for storage for later use.

[0017] According to the method for preparing a chlorine - resistant polyester amide nanofiltration membrane using the above - mentioned highly active aqueous monomer, the prepared novel chlorine - resistant polyester amide nanofiltration membrane using the highly active aqueous monomer is applied in the fields of seawater desalination, wastewater treatment, and membrane separation technology.

[0018] The mechanism of the technical solution of the present invention: In the process of using the surfactant APG and the highly active aqueous monomer N2Hyd to carry out an interfacial polymerization reaction with TMC to prepare a polyester amide nanofiltration membrane, it is crucial to understand the chemical attraction or chemical synergy between the two in the aqueous solution. This effect can affect the reaction rate and thus contribute to the preparation of a uniform active layer.

[0019] Properties of surfactant alkyl polyglycoside (APG): (1) Surfactant properties: APG is a non-ionic surfactant with good wettability and foaming properties, capable of reducing the surface tension at the liquid interface.

[0020] (2) Molecular structure: Its molecule contains a hydrophobic alkyl chain and a hydrophilic glycosyl part. This amphiphilic structure enables APG to form micelles in the aqueous phase, facilitating the increase in the solubility of reactants and the mass transfer rate.

[0021] Properties of N2Hyd: (1) Highly active aqueous monomer: N2Hyd has two amino groups and one hydroxyl group. Its amino groups have strong nucleophilicity and can undergo a rapid chemical reaction with TMC to form polyester amide chains.

[0022] (2) Aqueous solubility: Due to its polarity, N2Hyd has a relatively high solubility in the aqueous phase, providing a good premise for the reaction with TMC.

[0023] Mechanism of chemical synergy: I. Mutual attraction and stability (1) Hydrogen bond formation: The hydroxyl groups in APG can form hydrogen bonds with the amino and hydroxyl groups in N2Hyd, enhancing the interaction between the two. This hydrogen bond interaction can stabilize the mixture of APG and N2Hyd, slowing down their diffusion rate in the aqueous phase, thereby regulating the reaction rate.

[0024] (2) Micelle effect: When APG forms micelles, N2Hyd can be "encapsulated" in the micelles, increasing the effective concentration of N2Hyd and promoting its reaction with TMC.

[0025] II. Kinetics regulation (1) Reaction interface characteristics: As a surfactant, APG can reduce the interfacial tension between the aqueous phase and the organic phase, thereby affecting the rate of interfacial polymerization reaction. The reduced interfacial tension can make N2Hyd and TMC more easily contact, increasing the probability of reaction.

[0026] (2) Reaction rate regulation: By adjusting the concentration of APG, effective regulation of the reaction rate can be achieved, promoting the formation of a uniform active layer. For example, an appropriate amount of APG can increase the concentration of reactants at the interface, thus accelerating the polymerization reaction; while an excessive amount of APG may lead to dilution of the reactants and slow down the reaction rate.

[0027] In summary, by reasonably blending APG and N2Hyd, the chemical attraction and synergistic effect between the two in the aqueous solution can be optimized. This optimization not only helps to improve the rate of interfacial polymerization reaction, but also forms a uniform active layer during the preparation of poly(ester amide) nanofiltration membrane, providing a theoretical basis and practical reference for improving the membrane performance. Through further experimental verification, the specific reaction mechanism can be explored and reference for industrial applications can be provided.

[0028] Implementing the present invention has the following beneficial effects: The method for preparing a chlorine-resistant poly(ester amide) nanofiltration membrane with a highly active aqueous monomer of the present invention constructs a crosslinked polymerization network structure of a PEA nanofiltration membrane using N-(2-hydroxyethyl)ethylenediamine (N2Hyd) as the main reaction monomer, which is mainly connected by amide bonds formed by the hydrolysis reaction of hydrazine-based bis(primary amine, secondary amine) amino groups and acyl chloride groups, and the hydroxyl groups contained in the monomer also react to form ester bonds to become part of the crosslinked network structure. This is also the first time that N2Hyd aqueous monomer is applied to the preparation of poly(ester amide) nanofiltration membrane.

[0029] The surface activity characteristics of APG contribute to the cleaning and regeneration of the membrane surface; during the separation process, dirt molecules are easily washed off the membrane surface, thereby reducing membrane fouling and flux decline; the present invention first uses it and N2Hyd water-soluble monomer as co-soluble aqueous polymerization monomers, combines the characteristics of the two, and successfully prepares the target poly(ester amide) composite nanofiltration membrane.

[0030] The poly(ester amide) nanofiltration membrane prepared by the present invention uses a hydrazine-based diamine reaction monomer with high activity, combines with the polyhydroxy surfactant APG for intermittent interfacial polymerization reaction, fully maintains the reaction intensity, forms a uniform, complete and relatively thin poly(ester amide) active layer, reduces the mass transfer resistance, effectively increases the water flux of the nanofiltration membrane, and enhances its anti-fouling property.

[0031] The poly(ester amide) nanofiltration membrane prepared by the present invention has stronger negative charges, higher hydrophilicity, larger membrane pores and a smoother surface, making it have better water permeability at the optimal co-soluble monomer combination concentration, and at the same time having a good Na2SO4 rejection rate and obvious Na2SO4 / NaCl separation ability.

[0032] The poly(ester amide) nanofiltration membrane prepared by the present invention has a significant anti-chlorine effect due to the uniform distribution of its multi-ester bond crosslinked structure, which is beneficial to alleviating the influence of membrane oxidation and hydrolysis by chlorine, thereby increasing the service life of the membrane. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 (a, b, c) are respectively the SEM surface morphologies of the ultrafiltration base membrane (PES-UF) required for the nanofiltration membranes prepared in Examples 1-5, the polyester amide nanofiltration membrane prepared in the optimal ratio in Example 3, and the optimal nanofiltration membrane after being immersed in sodium hypochlorite. Figure 2 (a, b, c) are respectively the AFM surface morphologies of the ultrafiltration base membrane (PES-UF) required for the nanofiltration membranes prepared in Examples 1-5, the polyester amide nanofiltration membrane prepared in the optimal ratio in Example 3, and the optimal nanofiltration membrane after being immersed in sodium hypochlorite.

[0035] Figure 3 It is the test of the water flux of the polyester amide nanofiltration membranes prepared in Examples 1-5 and the rejection rates of four conventional salts (Na2SO4, MgSO4, NaCl, MgCl2). Figure 4 It is the stability test diagram of the optimal polyester amide nanofiltration membrane prepared in Example 3 after being immersed in sodium hypochlorite for 24 hours. Detailed implementation manners

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] The method for preparing a chlorine-resistant polyester amide nanofiltration membrane with a high-activity aqueous monomer includes the following steps: S1. Cut a polyethersulfone ultrafiltration membrane with a molecular weight cut-off (MWCO) of 30 kDa to obtain a square base membrane with a size of 11 cm * 11 cm.

[0038] S2. Ultrasonically clean the PES-UF commercial base membrane twice with an ethanol solution with a concentration of 1% - 5% (v / v), each time for 1 - 3 minutes, to remove the glycerol protective agent and impurity pollutants on the membrane surface, and obtain a standby PES ultrafiltration base membrane, which is stored in pure water for standby.

[0039] S3. Fix the cleaned PES ultrafiltration base membrane in step S2 on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing upward for subsequent treatment and reaction. The specific steps are as follows: Take out the PES ultrafiltration base membrane from pure water, and use filter paper to blot the surface of the membrane until there are no obvious water droplets. Then fix the ultrafiltration base membrane on the polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing upward, and air-dry it for 2 - 5 minutes. During this period, use an air pump gun to blow it evenly for 1 - 3 minutes to provide a uniformly distributed pore channel of the base membrane for the mixed aqueous phase.

[0040] S4. Mix an appropriate amount of alkyl polyglycoside (APG) and N-(2-hydroxyethyl)ethylenediamine (N2Hyd) in deionized water to form a homogeneous (monomer / surfactant) aqueous polymerization solution, and control its slightly alkaline solution environment. The aqueous polymerization solution is a 0.05 - 0.15 % (v / v) N2Hyd and a 5% - 15% APG aqueous solution. The specific operation to control its slightly alkaline solution environment is as follows: Mix an appropriate amount of APG and N2Hyd in deionized water to form a homogeneous aqueous polymerization solution. During this period, test its alkaline environment pH within the range of 8 - 10.5 to prevent the deprotonation of its subsequent side reaction products from having an impact.

[0041] Contact the aqueous polymerization solution with the surface of the PES ultrafiltration base membrane for 5 - 8 minutes. Then gently pour out the remaining solution, use filter paper to gently dry the liquid remaining on the surface of the membrane, use an air pump gun to blow it evenly and let it air-dry naturally to ensure that there is no residual liquid on the membrane surface. The specific operation of using filter paper to gently dry the liquid remaining on the surface of the membrane is as follows: Use filter paper to blot the surface of the membrane until there are no obvious water droplets. The specific operation of using an air pump gun to blow it evenly and let it air-dry naturally is as follows: Use an air pump gun to blow it evenly for 30 seconds, and refix the PES ultrafiltration base membrane soaked in the aqueous solution to the PTFE frame, and then let it air-dry naturally for 2 - 5 minutes.

[0042] S5. Gently pour a n-hexane organic phase solution containing a certain concentration of trimesoyl chloride (TMC) on the membrane surface, and start the interfacial polymerization (IP) reaction intermittently to obtain the prepared polyester amide composite nanofiltration membrane.

[0043] The specific operation of the intermittent start-up interfacial polymerization reaction is as follows: Gently pour the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) TMC onto the membrane surface, and soak for 20 - 50 s to initiate the first step of the intermittent interfacial polymerization reaction. Subsequently, pour off the organic phase solution and rinse it twice with n-hexane solution; after an interval of 10 s, immediately invert the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) TMC on its surface for 30 s to maintain a sufficient organic phase concentration for the remaining reaction of the remaining aqueous phase monomers at the same diffusion rate, achieving complete and uniform regulation characteristics. Then, place it in an oven for heat treatment for 5 - 10 min to enhance the mechanical properties of the thermally stable active layer. After taking it out and cooling it to room temperature, the prepared polyester amide composite nanofiltration membrane is obtained and soaked in pure water for storage for later use.

[0044] According to the method for preparing a chlorine-resistant polyester amide nanofiltration membrane with the above-mentioned highly active aqueous monomer, the prepared novel chlorine-resistant polyester amide nanofiltration membrane with a highly active aqueous monomer is applied in the fields of seawater desalination, wastewater treatment, and membrane separation technology. Example 1

[0045] Under the condition of room temperature 25°C, a PEA-TFC-NF membrane was prepared on a PES ultrafiltration substrate by the IP technique. Before the IP reaction, the PES-UF substrate membrane was ultrasonically cleaned twice for 1 - 3 minutes (1 - 3 min) with an ethanol solution with a concentration of 1% (v / v) to remove the glycerol protective agent on the commercial ultrafiltration membrane and stored it in pure water for later use. The IP reaction steps are as follows: (a) Fix the cleaned ultrafiltration substrate membrane on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing up. (b) Contact the aqueous solution of the co-dissolved monomers of 0.05% (v / v) N-(2-hydroxyethyl)ethylenediamine (N2Hyd) and 5% (v / v) alkyl polyglycoside (APG) with the surface of the substrate membrane for 5 - 8 minutes (5 - 8 min). (c) After pouring out the aqueous phase, gently dry the liquid remaining on the membrane surface with filter paper and air dry it for 2 - 5 minutes (2 - 5 min). (d) Gently pour the organic phase containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) onto the membrane surface to initiate the intermittent interfacial polymerization (IP) reaction for 20 - 50 seconds (20 - 50 s), then remove the residual solution and rinse it twice with hexane and after an interval of 10 s, immediately invert the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) on its surface for 30 s to initiate the reaction again. (e) The obtained TFC membrane was further heat-treated in an oven at 60°C for 5 - 10 minutes (5 - 10 min), taken out and cooled to room temperature, and then transferred to ultrapure water at 4°C, and thus the polyester amide nanofiltration membrane prepared from the highly active aqueous monomer combined with a surfactant was obtained. Example 2

[0046] The difference between this example and Example 1 lies in the changed concentrations of the newly added aqueous monomer and the surfactant, while the remaining raw materials and preparation methods are the same. The specific steps are as follows: Under the condition of room temperature (25 °C), a PEA-TFC-NF membrane was prepared on a PES ultrafiltration substrate using the IP technique. Before the IP reaction, the PES-UF substrate membrane was ultrasonically cleaned twice for 1 - 3 minutes (1 - 3 min) with an ethanol solution at a concentration of 1% (v / v) to remove the glycerol protective agent on the commercial ultrafiltration membrane, and it was stored in pure water for later use. The IP reaction steps are as follows: (a) Fix the cleaned ultrafiltration substrate membrane on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing upwards. (b) Contact the co-solvent aqueous solution of 0.075% (v / v) N-(2-hydroxyethyl)ethylenediamine (N2Hyd) and 7.5% (v / v) alkyl polyglycoside (APG) with the surface of the substrate membrane for 5 - 8 minutes (5 - 8 min). (c) After pouring out the aqueous phase, gently dry the residual liquid on the membrane surface with filter paper and let it dry naturally for 2 - 5 minutes (2 - 5 min). (d) Gently pour the organic phase containing 0.05 - 0.2% (w / v) trimellitic acid trichloride (TMC) onto the membrane surface, initiate the batch interfacial polymerization (IP) reaction for 20 - 50 seconds (20 - 50 S), then remove the residual solution and rinse it twice with hexane and pause for 10 S, and immediately invert the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) trimellitic acid trichloride (TMC) on its surface for 30 S to initiate the reaction again. (e) The obtained TFC membrane was further heat-treated in an oven at 60 °C for 5 - 10 minutes (5 - 10 min), taken out, cooled to room temperature, and then transferred to ultrapure water at 4 °C, thus obtaining a polyester amide nanofiltration membrane prepared from a highly active aqueous monomer combined with a surfactant. Example 3

[0047] The difference between Example 3 and Example 1 lies in the changed concentrations of the newly added aqueous monomer and the surfactant, while the remaining raw materials and preparation methods are the same. The specific steps are as follows: Under the condition of room temperature (25 °C), a PEA-TFC-NF membrane was prepared on a PES ultrafiltration substrate using the IP technique. Before the IP reaction, the PES-UF substrate membrane was ultrasonically cleaned twice for 1 - 3 minutes (1 - 3 min) with an ethanol solution at a concentration of 1% (v / v) to remove the glycerol protective agent on the commercial ultrafiltration membrane and stored in pure water for later use. The IP reaction steps are as follows: (a) The cleaned ultrafiltration substrate membrane was fixed on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing upwards. (b) An aqueous solution of a co-monomer of 0.1% (v / v) N-(2-hydroxyethyl)ethylenediamine (N2Hyd) and 10% (v / v) alkyl polyglycoside (APG) was brought into contact with the surface of the substrate membrane for 5 - 8 minutes (5 - 8 min). (c) After pouring out the aqueous phase, the residual liquid on the membrane surface was gently blotted dry with filter paper and air-dried for 2 - 5 minutes (2 - 5 min). (d) An organic phase containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) was gently poured onto the membrane surface to initiate an interfacial polymerization (IP) reaction for 20 - 50 seconds (20 - 50 S), then the residual solution was removed and rinsed twice with hexane with an interval of 10 S, and immediately the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) was inverted on its surface for 30 S to initiate the reaction again. (e) The obtained TFC membrane was further heat-treated in an oven at 60 °C for 5 - 10 minutes (5 - 10 min), taken out, cooled to room temperature, and then transferred to ultrapure water at 4 °C, thus obtaining a polyester amide nanofiltration membrane prepared from a highly active aqueous monomer combined with a surfactant. Example 4

[0048] The difference between Example 4 and Example 1 lies in the change in the concentration of the newly added aqueous monomer and the concentration of the surfactant, while the other raw materials and preparation methods are the same. The specific steps are as follows: Under the condition of room temperature of 25 °C, the PEA-TFC-NF membrane was prepared on the PES ultrafiltration substrate by IP technology. Before the IP reaction, the PES-UF substrate membrane was ultrasonically cleaned twice for 1 - 3 minutes (1 - 3 min) with an ethanol solution with a concentration of 1% (v / v) to remove the glycerol protective agent on the commercial ultrafiltration membrane and stored it in pure water for later use. The IP reaction steps are as follows: (a) Fix the cleaned ultrafiltration substrate membrane on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing up. (b) Contact the aqueous solution of the co-monomer of 0.125% (v / v) N-(2-hydroxyethyl)ethylenediamine (N2Hyd) and 12.5% (v / v) alkyl polyglycoside (APG) with the surface of the substrate membrane for 5 - 8 minutes (5 - 8 min). (c) After pouring out the aqueous phase, gently dry the residual liquid on the membrane surface with filter paper and air dry for 2 - 5 minutes (2 - 5 min). (d) Gently pour the organic phase containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) onto the membrane surface, initiate the interfacial polymerization (IP) reaction for 20 - 50 seconds (20 - 50 S), then remove the residual solution and rinse it twice with hexane and pause for 10 S, and immediately invert the n-hexane organic phase solution containing 0.05 - 0.2% (w / v) trimesoyl chloride (TMC) on its surface for 30 S to initiate the reaction again. (e) The obtained TFC membrane was further heat-treated in an oven at 60 °C for 5 - 10 minutes (5 - 10 min), taken out, cooled to room temperature, and then transferred to ultrapure water at 4 °C to obtain the polyester amide nanofiltration membrane prepared from highly active aqueous phase monomers combined with surfactants. Example 5

[0049] The difference between Example 5 and Example 1 is that the concentrations of the added new aqueous phase monomers and surfactants have changed, and the remaining raw materials and preparation methods are the same. The specific steps are as follows: Under the condition of room temperature of 25 °C, the PEA-TFC-NF membrane was prepared on a PES ultrafiltration substrate using IP technology. Before the IP reaction, the PES-UF substrate membrane was ultrasonically cleaned twice for 1 - 3 minutes (1 - 3 min) with an ethanol solution at a concentration of 1% (v / v) to remove the glycerol protective agent on the commercial ultrafiltration membrane and stored in pure water for later use. The IP reaction steps are as follows: (a) Fix the cleaned ultrafiltration substrate membrane on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing up. (b) Contact the aqueous solution of the co-monomer of 0.15% (v / v) N-(2-hydroxyethyl)ethylenediamine (N2Hyd) and 15% (v / v) alkyl polyglycoside (APG) with the surface of the substrate membrane for 5 - 8 minutes (5 - 8 min). (c) After pouring out the aqueous phase, gently dry the residual liquid on the membrane surface with filter paper and air-dry for 2 - 5 minutes (2 - 5 min). (d) Gently pour the organic phase containing 0.05 - 0.2% (w / v) trimellitic acid trichloride (TMC) onto the membrane surface, initiate the batch interfacial polymerization (IP) reaction for 20 - 50 seconds (20 - 50 S), then remove the residual solution and rinse twice with hexane and pause for 10 S, and immediately invert the hexane organic phase solution containing 0.05 - 0.2% (w / v) trimellitic acid trichloride (TMC) on its surface for 30 S to initiate the reaction again. (e) The obtained TFC membrane was further heat-treated in an oven at 60 °C for 5 - 10 minutes (5 - 10 min), taken out, cooled to room temperature, and then transferred to ultrapure water at 4 °C to obtain a polyester amide nanofiltration membrane prepared from a highly active aqueous monomer combined with a surfactant.

[0050] The performance tests were carried out on the polyester amide nanofiltration membranes prepared in Examples 1 - 5 above: 1. Scanning electron microscopy (SEM) analysis Please refer to Figure 1 , Figure 1 (a, b, c) are respectively the ultrafiltration substrate membranes (PES-UF) required for the nanofiltration membranes prepared in Examples 1 - 5, the polyester amide nanofiltration membrane prepared with the optimal ratio in Example 3, and the SEM surface morphology of the optimal nanofiltration membrane after immersion in sodium hypochlorite. It can be seen from the scanning electron microscopy that the new monomer combined with the surfactant was successfully prepared into a polyester amide nanofiltration membrane, covering the membrane pores of the substrate membrane and having a relatively uniform and rough surface morphology, which is beneficial to improving hydrophilicity, and still maintains a relatively complete surface morphology after treatment with sodium hypochlorite, indicating that the polyester amide membrane has good anti-chlorine effect.

[0051] 2. Atomic force microscopy (AFM) analysis Please refer to Figure 2 , Figure 2(a, b, c) are respectively the ultrafiltration base membrane (PES-UF) required for the nanofiltration membranes prepared in Examples 1-5, the poly(ester amide) nanofiltration membrane prepared in the optimal ratio in Example 3, and the AFM surface morphology of the optimal nanofiltration membrane after being soaked in sodium hypochlorite. It can be seen from the observation by atomic force microscope that the poly(ester amide) nanofiltration membrane successfully prepared by combining the new monomer with the surfactant has a rougher surface compared with the ultrafiltration base membrane (PES-UF), corresponding to the SEM image, and still maintains a relatively rough surface morphology after being treated with sodium hypochlorite, which further proves that the poly(ester amide) nanofiltration membrane prepared by this invention has chlorine resistance.

[0052] 3. Water Flux and Desalination Test Please refer to Figure 3 , Figure 3 This is the test of the water flux and the rejection rate of four conventional salts of the poly(ester amide) nanofiltration membranes prepared in Examples 1-5. The water flux of the poly(ester amide) nanofiltration membranes prepared in Examples 1-5 was tested by cross-flow filtration under a pressure of 5 bar. To obtain stable pure water permeability, each membrane was pre-pressed with deionized water at 5 bar for at least 30 minutes. To avoid contingency, each measurement was repeated three times and the average value was taken as the final result. The water flux was calculated using the formula F = J / A*t (where F is the membrane flux; J is the sampling volume; A is the effective membrane area; t is the time). At the same time, in the same way, the nanofiltration membranes prepared in Examples 1-5 were used to conduct desalination tests on 1 g / L Na2SO4, MgSO4, NaCl, and MgCl2 salt solutions under a pressure of 4 bar. The test results were measured by an electrical conductivity meter for the electrical conductivity of the salt solutions before and after filtration, and the desalination efficiency was obtained according to the ratio of the difference before and after to the inlet water conductivity. The measurement results were all tested three times and the average value was taken, and the results are shown in Table 1.

[0053] Table 1 Water Flux Test Results and Desalination Test Results

[0054] It can be seen from Table 1 and Figure 3 the results that, compared with the commercially available NF270 nanofiltration membrane with better performance, the optimal poly(ester amide) nanofiltration membrane prepared in Example 3 of this invention has a greater water flux than NF270 and retains a higher Na2SO4 rejection rate. In contrast, the poly(ester amide) nanofiltration membrane prepared by this invention has better monovalent / divalent salt separation performance. It can be seen that the novel poly(ester amide) nanofiltration membrane prepared by combining the new monomer with the surfactant in the technical solution of this invention has the advantages of high flux, high separation performance, and simple operation. And in order to further prove its advantages, this invention conducted a chlorine resistance test.

[0055] 4. Chlorine Resistance Test The optimal poly(ester amide) nanofiltration membrane prepared in Example 3 was immersed in a sodium hypochlorite solution (pH = 8, available chlorine content = 2000 ppm) for 24 hours and stored in the dark and sealed. Subsequently, a performance test was carried out for 120 h continuously. The physicochemical stability of the poly(ester amide) nanofiltration membrane prepared in the present invention was judged by the ratio of the water flux to the initial water flux and the rejection rate of sodium sulfate (Na2SO4). Please refer to Figure 4 , Figure 4 which is the test chart for chlorine resistance performance. The results show that after the optimal poly(ester amide) nanofiltration membrane was immersed in the sodium hypochlorite solution for 24 h, the loss of sodium sulfate was only within 10%, and it had certain stability after continuous operation for 120 h, thus confirming its chlorine resistance effect.

[0056] The present invention provides a method and application for preparing a chlorine-resistant polyester amide nanofiltration membrane by combining a novel highly active aqueous monomer with a surfactant, aiming to solve the application limitation problems of high fouling tendency and weak chlorine resistance in the field of seawater desalination of traditional nanofiltration membranes. By using a highly active water-soluble monomer N-(2-hydroxyethyl)ethylenediamine (N2Hyd) with hydrazine diamine groups and hydroxyl groups as the aqueous monomer, and specifying a natural surfactant alkyl polyglycoside (APG) as the co-solvent polymerization monomer, and using an intermittent interfacial polymerization (IP) reaction to prepare the chlorine-resistant polyester amide nanofiltration membrane. The chlorine resistance of the membrane material is enhanced by the selection of specific co-solvent monomers, which helps to clean and regenerate the membrane surface. During the separation process, dirt molecules are easily washed off the membrane surface, thereby reducing membrane fouling and flux decline. The introduction of the N2Hyd / APG co-solvent aqueous polymerization solution containing polyhydroxy new monomers and specific surfactants makes the structure of the polyester amide more complete and stable due to the excessive exposure of the highly reactive structure of hydrazine diamine and special hydroxyl functional groups it contains, and the uniform distribution of ester bonds in the cross-linked structure improves the chlorine resistance of the membrane. And an intermittent interfacial polymerization reaction is proposed in the polymerization reaction. Through the intermittent regulation process of "reaction - short pause - re-reaction" within a short time, the reaction intensity is reasonably maintained, which helps to control the uniformity of the active layer and the problem of large diffusion rate differences during formation. This novel polyester amide membrane can not only maintain good separation performance in a chlorinated environment due to its rich ester bonds and activated special cross-linked polymerization structure, but also effectively reduce the membrane fouling risk. The preparation process of the membrane is optimized to ensure uniform pore size distribution and dense membrane layer of the membrane, thereby improving the water flux and salt rejection rate, and greatly enhancing the stability and economy of the membrane during the seawater desalination process. With the continuous development of seawater desalination technology, the market demand for high-performance membrane materials will continue to grow. The polyester amide membrane of the present invention can be widely applied to seawater desalination, wastewater treatment and other membrane separation technology fields, providing a feasible technical path for solving the problem of water resource shortage. This membrane material not only improves the economy and practicability of seawater desalination technology, but also lays a foundation for the further development of membrane separation technology. In the future, with the continuous progress of technology and the expansion of applications, the polyester amide nanofiltration membrane is expected to play a greater role in seawater desalination and other related fields, providing new solutions for the sustainable utilization of global water resources.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer, characterized in that, It includes the following steps: S1. Cut the PES-UF commercial base membrane to obtain the determined size and shape of the base membrane; S2. Ultrasonically clean the PES-UF commercial base membrane twice with an ethanol solution to remove the glycerol protective agent and impurity contaminants on the membrane surface, and obtain a spare PES ultrafiltration base membrane; S3. Fix the PES ultrafiltration base membrane cleaned in S2 on a PTFE frame with the membrane selective layer facing up for subsequent treatment and reaction; S4. Mix an appropriate amount of APG and N2Hyd in deionized water to form a uniform aqueous polymerization solution, and control its slightly alkaline solution environment; Contact the aqueous polymerization solution with the surface of the PES ultrafiltration base membrane for a certain period of time, then gently pour out the remaining solution, gently dry the residual liquid on the membrane surface with filter paper, uniformly blow it with an air pump gun and let it dry naturally to ensure that there is no residual liquid on the membrane surface; S5. Gently pour a hexane organic phase solution containing a certain concentration of TMC on the membrane surface, and intermittently initiate an interfacial polymerization reaction to obtain the prepared polyester amide composite nanofiltration membrane.

2. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 1, characterized in that, In S1, the PES-UF commercial base membrane is a polyethersulfone ultrafiltration membrane with a molecular weight cut-off of 30 kDa; the size of the base membrane obtained after cutting is 11 cm * 11 cm.

3. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 1, characterized in that, In S2, the concentration of the ethanol solution is 1% - 5% v / v; the ultrasonic cleaning time is 1 - 3 min each time; the obtained spare PES ultrafiltration base membrane is stored in pure water for later use.

4. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 3, characterized in that, The specific steps for fixing the PES ultrafiltration base membrane on the PTFE frame in S3 are as follows: Take out the PES ultrafiltration base membrane from pure water, and blot the membrane surface dry with filter paper until there are no obvious water droplets. Then fix the ultrafiltration base membrane on a polytetrafluoroethylene (PTFE) frame with the membrane selective layer facing up, and let it dry for 2 - 5 min. During this period, uniformly blow it with an air pump gun for 1 - 3 min to provide a uniformly distributed pore channel of the base membrane for the mixed aqueous phase.

5. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 1, characterized in that, In S4, the uniform aqueous polymerization solution is an aqueous solution of 0.05 - 0.15% v / v of N2Hyd and 5% - 15% of APG.

6. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 5, characterized in that, The specific operation for controlling its slightly alkaline solution environment is as follows: Mix an appropriate amount of APG and N2Hyd in deionized water to form a uniform aqueous polymerization solution. During this period, test its alkaline environment pH within the range of 8 - 10.5 to prevent the deprotonation of its subsequent side reaction products from having an impact.

7. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 6, characterized in that, The contact time of the aqueous polymerization solution with the surface of the PES ultrafiltration base membrane for a certain period of time is 5 - 8 min.

8. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 7, characterized in that, The specific operation for gently drying the residual liquid on the membrane surface with filter paper is as follows: Blot the membrane surface dry with filter paper until there are no obvious water droplets; the specific operation for uniformly blowing it with an air pump gun and letting it dry naturally is as follows: Uniformly blow it with an air pump gun for 30 s, and refix the PES ultrafiltration base membrane soaked in the aqueous phase solution to the PTFE frame, and then let it dry naturally for 2 - 5 min.

9. The method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to claim 1, characterized in that, The specific operation of the intermittent interfacial polymerization reaction in S5 is as follows: Gently pour the n-hexane organic phase solution containing 0.05 - 0.2% w / v TMC onto the membrane surface, and soak for 20 - 50 s to initiate the first step of the intermittent interfacial polymerization reaction. Subsequently, pour off the organic phase solution and rinse twice with n-hexane solution; after an interval of 10 s, immediately invert the n-hexane organic phase solution containing 0.05 - 0.2% w / v TMC on its surface for 30 s to maintain a sufficient organic phase concentration for the remaining reaction of the remaining aqueous monomers at the same diffusion rate, achieving complete and uniform regulation characteristics. Then, place it in an oven for heat treatment for 5 - 10 min to enhance the mechanical properties of the thermally stable active layer. After taking it out and cooling to room temperature, the prepared polyesteramide composite nanofiltration membrane is obtained and soaked in pure water for storage and standby.

10. A method for preparing a chlorine-resistant polyester amide nanofiltration membrane from a highly active aqueous monomer according to any one of claims 1-9, characterized in that, Application of the prepared novel high-activity aqueous monomer in preparing chlorine-resistant polyesteramide nanofiltration membranes in the fields of seawater desalination, wastewater treatment, and membrane separation technology.

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