Polyamide nanofiltration composite membrane and method for preparing the same

Abstract

The application provides a kind of polyamide nanofiltration composite membrane and its preparation method, belong to nanofiltration membrane technical field.The preparation method of the nanofiltration composite membrane includes the following steps: after polyimide casting solution is prepared into film, it is immersed in water to carry out phase inversion, and polyimide ultrafiltration support film is obtained;Polyimide ultrafiltration support film is immersed in crosslinking agent solution to carry out crosslinking reaction, and crosslinking support film is obtained;Crosslinking support film is immersed in aqueous solution of organic amine type water phase reaction monomer, and support film containing saturated water phase monomer is obtained;Support film containing saturated water phase monomer is placed in acyl chloride type organic phase reaction monomer solution, and interfacial polymerization reaction is carried out, and nanofiltration membrane precursor is obtained;Nanofiltration membrane precursor is immersed in activation solution to carry out activation treatment, and target membrane is obtained;Wherein casting solution includes polyimide and pore former, and pore former is low eutectic solvent.The nanofiltration composite membrane is modified by ultrafiltration support base layer to improve solvent permeation flux and ensure high solute rejection rate.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, and in particular to a polyamide nanofiltration composite membrane and its preparation method. Background Technology

[0002] With the continuous advancement of manufacturing technology in modern chemical industry and the increasing scale of various enterprises, the large amounts of waste generated during their production processes, such as waste solvents and wastewater, have had a significant adverse impact on the environment. Therefore, various separation technologies have emerged, among which membrane separation technology has become a research hotspot due to its advantages such as high efficiency, energy saving, and small footprint. As the core component of membrane separation technology, the separation membrane itself needs to possess good chemical stability, permeability, and mechanical strength. Based on the pore size, separation membranes can be broadly classified into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. Nanofiltration membranes have pore sizes between 1 and 2 nm and an average molecular weight cutoff of 200–1000 Da, effectively separating divalent and higher ions, large organic molecular weight solutes, etc. In the field of nanofiltration membranes, polyamide composite membranes (TFC) have attracted much attention due to their unique resistance to organic solvents. The structure of the composite membrane consists of a lower ultrafiltration support substrate and a surface polyamide separation layer. However, due to the trade-off effect, increasing the solvent permeation flux will reduce the solute rejection rate. Therefore, how to ensure a high rejection rate while increasing the flux is currently a key research focus.

[0003] SK Lim et al. (SK Lim, L. Setiawan, TH Bae, et al. Journal of Membrane Science, 2016, 501: 152-160.) used APTMS to prepare cross-linked polyamide-imide (PAI) hollow fiber membranes, which improved the hydrophilicity of the membrane, achieving an IPA permeation flux of 6.4 L / m³. -2 h -1 bar -1 S. Amiri et al. (S. Amiri, A. Asghari, AR Hariff-Mood, et al. Chemosphere, 2022, 308: 136323.) used polyvinyl alcohol and sodium alginate to prepare a hydrogel coating, which improved the membrane's permeability and antifouling properties. The membrane's highest pure water flux reached 11.2 L / m³. -2 h -1 bar -1Carlos EG et al. (Carlos EG, Yolanda AM, Marta N., et al. ACS Appl. Mater. Interfaces, 2021, 13: 7773-7783.) synthesized polyamide-MIL-101(Cr) nanocomposite films on porous polysulfone hollow fibers, achieving a rejection rate of 87.4% for acridine orange and a water flux of 2.8 L / m³. -2 h -1 bar -1 The polyamide composite membranes studied in the above literature are still limited by the trade-off effect, and cannot simultaneously achieve solvent permeation flux and high solute rejection rate. Moreover, the experimental operation is difficult, the steps are complex, and it is not easy to prepare them. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a polyamide nanofiltration composite membrane and its preparation method. The polyamide nanofiltration composite membrane provided by this invention improves solvent permeation flux and ensures high solute retention rate by modifying the ultrafiltration support substrate layer.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is a method for preparing a polyamide nanofiltration composite membrane, comprising the following steps: After preparing a membrane from a polyimide casting solution, the membrane is immersed in water for phase inversion to obtain a polyimide ultrafiltration supported membrane. The polyimide ultrafiltration support membrane is immersed in a crosslinking agent solution to carry out a crosslinking reaction, thereby obtaining a crosslinked support membrane; The cross-linked support membrane is immersed in an aqueous solution of an organic amine aqueous reactive monomer to obtain a support membrane containing saturated aqueous monomer. The supported membrane containing the saturated aqueous monomer is placed in an acyl chloride organic phase reaction monomer solution to carry out an interfacial polymerization reaction to form a polyamide separation layer, thereby obtaining a nanofiltration membrane precursor. The nanofiltration membrane precursor is immersed in an activation solution for activation treatment to obtain the polyamide nanofiltration composite membrane; The casting solution includes polyimide and a pore-forming agent; the pore-forming agent is a eutectic solvent.

[0006] The second technical solution of the present invention is a polyamide nanofiltration composite membrane prepared by the above preparation method.

[0007] The present invention discloses the following technical effects: This invention improves the solvent resistance of nanofiltration membranes by crosslinking polyimide ultrafiltration support membranes with crosslinking liquids. By replacing traditional macromolecular polymer pore-forming agents with DES pore-forming agents, the formation rate of ultrafiltration support membranes is directly affected, changing the density and pore size distribution of ultrafiltration membranes, effectively improving the overall permeation flux of polyamide nanofiltration membranes, while ensuring good separation performance.

[0008] The preparation method of this invention is simple, requires little equipment, consumes little energy, and is suitable for large-scale industrial production. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in 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 effort.

[0010] Figure 1 DES Fourier transform infrared spectra of choline chloride and 1,4-butanediol. Figure 2 The figures show the water contact angle test results of the polyamide nanofiltration composite membranes prepared in Examples 1-4 and Comparative Example 1. Figure 3 The images show scanning electron microscope (SEM) top and cross-sectional views of the polyamide nanofiltration composite membranes prepared in Examples 1-4 and Comparative Example 1, where (a) and (b) are the SEM top and cross-sectional views of the nanofiltration membrane (M0 membrane) obtained in Comparative Example 1, respectively; (c) and (d) are the SEM top and cross-sectional views of the nanofiltration membrane (M-DES-1 membrane) obtained in Example 1, respectively; (e) and (f) are the SEM top and cross-sectional views of the nanofiltration membrane (M-DES-2 membrane) obtained in Example 2, respectively; (g) and (h) are the SEM top and cross-sectional views of the nanofiltration membrane (M-DES-4 membrane) obtained in Example 3, respectively; and (i) and (j) are the SEM top and cross-sectional views of the nanofiltration membrane (M-DES-6 membrane) obtained in Example 4, respectively. Figure 4 The graph shows the test results of methanol permeation flux and Rhodamine B (RDB) dye rejection rate of the polyamide nanofiltration composite membranes prepared in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0011] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0012] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0013] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0014] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0015] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0016] The first aspect of this invention provides a method for preparing a polyamide nanofiltration composite membrane, comprising the following steps: After preparing a membrane from a polyimide casting solution, the membrane is immersed in water for phase inversion to obtain a polyimide ultrafiltration supported membrane. The polyimide ultrafiltration support membrane is immersed in a crosslinking agent solution to carry out a crosslinking reaction, thereby obtaining a crosslinked support membrane; The cross-linked support membrane is immersed in an aqueous solution of an organic amine aqueous reactive monomer to obtain a support membrane containing saturated aqueous monomer. The supported membrane containing the saturated aqueous monomer is placed in an acyl chloride organic phase reaction monomer solution to carry out an interfacial polymerization reaction to form a polyamide separation layer, thereby obtaining a nanofiltration membrane precursor. The nanofiltration membrane precursor is immersed in an activation solution for activation treatment to obtain the polyamide nanofiltration composite membrane; The casting solution includes polyimide and a pore-forming agent; the pore-forming agent is a eutectic solvent.

[0017] In a preferred embodiment of the present invention, the eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor; the hydrogen bond donor is choline chloride, betaine, tetrabutylammonium fluoride, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrabutylammonium hydrogen sulfate, tetrabutylphosphine fluoride, or tetrabutylphosphine chloride; the hydrogen bond acceptor is butanediol, ethylene glycol, glycerol, urea, citric acid, phenylacetic acid, malic acid, sulfamic acid, lactic acid, formic acid, acetic acid, or acetamide; the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:1 to 4.

[0018] More preferably, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:1, 1:2, 1:3 or 1:4.

[0019] In this invention, the butanediol is 1,2-butanediol, 1,3-butanediol, or 1,4-butanediol.

[0020] In a preferred embodiment of the present invention, the polyimide casting solution further includes an organic solvent; the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0021] In a preferred embodiment of the present invention, the mass ratio of the polyimide to the pore-forming agent is 3 to 20:1.

[0022] More preferably, the mass ratio of the polyimide to the pore-forming agent is 3:1, 5:1, 7:1, 9:1, 12:1, 14:1, 16:1, 18:1 or 20:1.

[0023] In a preferred embodiment of the present invention, the mass fraction of polyimide in the polyimide casting solution is 18wt%~22wt%.

[0024] More preferably, the mass fraction of polyimide in the polyimide casting solution is 18wt%, 19wt%, 20wt%, 21wt%, or 22wt%.

[0025] The present invention provides a method for preparing a polyimide casting solution, comprising the following steps: mixing a pore-forming agent, polyimide, and an organic solvent uniformly, then allowing the mixture to stand to remove air bubbles and improve the uniformity of the polyimide ultrafiltration support membrane, thereby obtaining the polyimide casting solution. The mixing temperature is 50-60°C, the mixing time is 24-48 hours (more preferably 24-30 hours), the standing temperature is room temperature, and the standing time is 1-4 hours (more preferably 2 hours).

[0026] In this invention, the method for preparing a film from a polyimide casting solution includes the following steps: casting the polyimide casting solution onto a carrier to form a film.

[0027] In this invention, the carrier is a nonwoven fabric, and the material of the nonwoven fabric is polyethylene terephthalate, nylon, polyethylene, polypropylene, acrylic, or chlorofiber; the pore size of the carrier is 10~150μm, preferably 50~100μm; in this invention, the casting is preferably performed using a casting knife, the size of which is 100~350μm, preferably 200~250μm; the casting speed is 0.025~0.05m / s, preferably 0.025~0.035m / s. The purpose of casting the polyimide casting solution onto the carrier in this invention is to ensure that the polyamide nanofiltration membrane can maintain sufficient support strength under high-pressure filtration.

[0028] In a preferred embodiment of the present invention, when the polyimide casting solution is prepared into a film and then immersed in water for phase transformation, the phase transformation includes a first phase transformation and a second phase transformation; the temperature of the first phase transformation is room temperature and the time is 0.5~1.5h; the temperature of the second phase transformation is room temperature and the time is 24~72h.

[0029] In this invention, after the phase inversion is completed, the process further includes washing the polyimide ultrafiltration support membrane with an alcohol solvent; the alcohol solvent is isopropanol, and the washing is performed 2 to 4 times, with each washing lasting 1 to 2 hours. The purpose of washing is to remove residual solvent and moisture from the polyimide ultrafiltration membrane.

[0030] In a preferred embodiment of the present invention, the crosslinking agent in the crosslinking agent solution is an organic fatty amine compound; the concentration of the crosslinking agent solution is 100~150g / L.

[0031] More preferably, the organic fatty amine compound is at least one selected from hexamethylenediamine, ethylenediamine, m-phenylenediamine, cyclohexamethylenediamine, and polyetheramine.

[0032] In a preferred embodiment of the present invention, the crosslinking agent solution solvent is at least one of n-butanol, isopropanol, and ethanol.

[0033] In a preferred embodiment of the present invention, the crosslinking reaction is carried out at a temperature of 20-35°C for 16-24 hours. The present invention enhances the solvent resistance and mechanical strength of the nanofiltration membrane through a crosslinking reaction.

[0034] In this invention, after the crosslinking reaction is completed, the crosslinking support membrane is further washed with an alcohol solvent; the alcohol solvent is isopropanol; the washing is performed 2 to 4 times, and each washing lasts 1 to 2 hours. This invention removes residual crosslinking solution from the crosslinking support membrane through the washing step.

[0035] In a preferred embodiment of the present invention, the organic amine aqueous reaction monomer is selected from at least one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2,2'-biphenylenediamine, 4,4'-biphenylenediamine, 1,5'-naphthylenediamine and 2,6'-naphthylenediamine; the concentration of the aqueous solution of the organic amine aqueous reaction monomer is 2wt% to 4wt%.

[0036] In a preferred embodiment of the present invention, the crosslinked support membrane is immersed in an aqueous solution of organic amine aqueous reactants for 2-10 minutes. After immersion, the crosslinked support membrane is further subjected to a step of removing excess solution from its surface using a rubber roller, followed by natural air drying. The purpose of immersing the crosslinked support membrane in the aqueous solution of organic amine aqueous reactants is to ensure that the organic amine aqueous reactants fully penetrate the pores within the crosslinked support membrane, thus providing conditions for subsequent reactions.

[0037] In a preferred embodiment of the present invention, the concentration of the acyl chloride organic phase reaction monomer solution is 0.1wt%~0.15wt%; the acyl chloride organic phase reaction monomer in the acyl chloride organic phase reaction monomer solution is selected from at least one of 4,4'-biphenyldicarboxylic acid chloride, 2,2'-biphenyldicarboxylic acid chloride, 3,3'-biphenyldicarboxylic acid chloride, 2,3'-biphenyldicarboxylic acid chloride, 2,4'-biphenyldicarboxylic acid chloride, 3,4',5-biphenyltricarboxylic acid chloride, 3,3',5,5'-biphenyltetracarboxylic acid chloride, 2,2',4,4'-biphenyltetracarboxylic acid chloride, 2,2',5,5'-biphenyltetracarboxylic acid chloride, 2,4,4',6-biphenyltetracarboxylic acid chloride, phthaloyl chloride, terephthaloyl chloride, isophthaloyl chloride, trimellitic acid chloride, and pyromellitic acid chloride; the temperature of the interfacial polymerization reaction is 20~25℃, and the time is 1~1.5min.

[0038] In this invention, the solvent for the monomer solution of the acyl chloride organic phase reaction is at least one of n-hexane, n-pentane, and toluene.

[0039] In this invention, after the interfacial polymerization reaction is completed, the process further includes a settling and washing step; the solvent used for washing is at least one of n-hexane, n-pentane, and toluene; the number of washings is 2-3 times, and the settling time is 1-6 minutes, preferably 3-5 minutes. In this invention, the purpose of washing is to remove unreacted acyl chloride organic phase reactants from the surface of the polyamide separation layer.

[0040] In a preferred embodiment of the present invention, the activation solvent is an amide solvent, a pyrrolidone solvent, or dimethyl sulfoxide; the activation treatment temperature is 70-90°C, and the time is 20-40 min. The purpose of solvent activation in this invention is to reduce the thickness of the polyamide separation layer, decrease solvent transport resistance, and improve the overall permeation flux of the nanofiltration membrane.

[0041] More preferably, the amide solvent is N,N-dimethylformamide (DMF).

[0042] In a preferred embodiment of the present invention, after the activation treatment is completed, a solute exchange treatment is further included to remove the residual activation solvent in the activated nanofiltration composite membrane. In the present invention, the solvent used for solute exchange is methanol, the temperature of solute exchange is 20~25℃, and the time is 15~25min.

[0043] After obtaining the polyamide nanofiltration composite membrane, the present invention stores the polyamide nanofiltration composite membrane in an alcohol solvent. The alcohol solvent is at least one selected from methanol, ethanol, isopropanol, and n-butanol.

[0044] A second aspect of the present invention provides a polyamide nanofiltration composite membrane prepared by the above-described preparation method.

[0045] The polyamide nanofiltration composite membrane of the present invention comprises a polyimide ultrafiltration support membrane and a polyamide separation layer located on the surface of the polyimide ultrafiltration support membrane; the thickness of the polyimide ultrafiltration support membrane is 50-300 μm (preferably 100-250 μm), and the thickness of the polyamide separation layer is 50-300 nm (preferably 100-250 nm); the polyimide ultrafiltration support membrane includes a polyimide substrate and a DES porogen added to the polyimide substrate. DES adjusts the stacking pattern of the polyimide segments, forming transport channels inside the ultrafiltration support membrane that facilitate the passage of organic solvent molecules, resulting in a more porous overall structure; simultaneously, the DES porogen slows down the exchange rate between solvent and non-solvent during phase inversion, making the pore size distribution of the polyimide ultrafiltration support membrane more uniform, which is beneficial for improving sieving efficiency.

[0046] The present invention also provides the application of the polyamide nanofiltration composite membrane in dye separation, organic solvent separation or drug separation.

[0047] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0048] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0049] Example 1 The preparation method of polyamide nanofiltration composite membrane includes the following steps: (1) 1,4-Butanediol and choline chloride were mixed and stirred at 90°C for 2 hours in a molar ratio of 3:1 to obtain DES; (2) Polyimide P84 was completely dissolved in N,N-dimethylformamide (DMF), and then DES was added. The mixture was stirred at 60°C for 24 h, and the resulting liquid was allowed to stand at 25°C for 2 h to obtain a polyimide casting solution (in which the mass fraction of P84 was 20 wt% and the mass fraction of DES was 1 wt%). The polyimide casting solution was uniformly poured onto a polyethylene terephthalate (PET) nonwoven fabric substrate with a pore size of 23.31 μm using a 200 μm casting tool at a speed of 0.025 m / s. The substrate was then quickly transferred to deionized water for immersion and phase inversion at 25°C for 60 min. The substrate was then transferred to fresh deionized water for another 24 h of phase inversion. The substrate was then washed three times in isopropanol to remove DMF and water from the polymer. Each wash lasted for 1 h to obtain a polyimide support film.

[0050] (3) The polyimide support membrane was immersed in an isopropanol solution of 1,6-hexanediamine (the concentration of 1,6-hexanediamine was 120 g / L), crosslinked at 25 °C for 16 h, and then immersed in isopropanol for washing 3 times to remove excess crosslinking solution from the support membrane. Each washing time was 1 h, and the crosslinked support membrane was obtained and stored in a water bath.

[0051] (4) After sonicating m-phenylenediamine and deionized water at room temperature for 15 min, 25 ml of a mixed aqueous solution of m-phenylenediamine (where the mass fraction of m-phenylenediamine is 2 wt%) is obtained. The cross-linked support membrane is immersed in the mixed aqueous solution of m-phenylenediamine at 20 °C for 2 min, and then the excess mixed aqueous solution on the surface of the cross-linked support membrane is removed with a rubber roller. After air drying, a support membrane containing saturated aqueous reactive monomers is obtained.

[0052] (5) The support membrane containing the saturated aqueous reactive monomer was immersed in a hexane solution of trimesoyl chloride at 20°C for 1 min (where the mass fraction of trimesoyl chloride was 0.15 wt%) to carry out interfacial polymerization. Then it was rinsed 3 times with hexane and allowed to stand for 3 min. The support membrane containing the saturated aqueous reactive monomer formed a polyamide separation layer (thickness of 200~300 nm), thus obtaining the nanofiltration membrane precursor.

[0053] The nanofiltration membrane precursor was activated by immersing it in DMF at 80°C for 30 min, and then transferred to methanol and immersed at room temperature for 15 min to perform solute exchange, thereby obtaining a solvent-resistant nanofiltration composite membrane (named M-DES-1 membrane), which was stored in methanol for later use.

[0054] Example 2 The only difference from Example 1 is that the mass fraction of DES in the polyimide casting solution is 2 wt%, resulting in a polyamide nanofiltration composite membrane (named M-DES-2 membrane). All other steps and parameters are the same as in Example 1.

[0055] Example 3 The only difference from Example 1 is that the mass fraction of DES in the polyimide casting solution is 4 wt%, resulting in a polyamide nanofiltration composite membrane (named M-DES-4 membrane). All other steps and parameters are the same as in Example 1.

[0056] Example 4 The only difference from Example 1 is that the mass fraction of DES in the polyimide casting solution is 6 wt%, resulting in a polyamide nanofiltration composite membrane (named M-DES-6 membrane). All other steps and parameters are the same as in Example 1.

[0057] Example 5 The only difference from Example 3 is that 1,4-butanediol is replaced with ethylene glycol, and the molar ratio of ethylene glycol to choline chloride is 2:1, resulting in a polyamide nanofiltration composite membrane (named M-DES). EG -4 membrane). Other steps and parameters are the same as in Example 3.

[0058] Example 6 The only difference from Example 3 is that 1,4-butanediol is replaced with glycerol, and the molar ratio of glycerol to choline chloride is 1.5:1, resulting in a polyamide nanofiltration composite membrane (named M-DES). GLY -4 membrane). Other steps and parameters are the same as in Example 3.

[0059] Example 7 The only difference from Example 3 is that 1,4-butanediol is replaced with urea, and the molar ratio of urea to choline chloride is 2:1, resulting in a polyamide nanofiltration composite membrane (named M-DES). UR -4 membrane). Other steps and parameters are the same as in Example 3.

[0060] Example 8 The only difference from Example 3 is that 1,4-butanediol is replaced with phenylacetic acid, and the molar ratio of phenylacetic acid to choline chloride is 2:1, resulting in a polyamide nanofiltration composite membrane (named M-DES). PLA -4 membrane). Other steps and parameters are the same as in Example 3.

[0061] Comparative Example 1 The only difference from Example 1 is that 1 wt% of DES in the polyimide casting solution is replaced with 1 wt% polyvinylpyrrolidone (PVP) to obtain a polyamide nanofiltration composite membrane (named MO membrane). All other steps and parameters are the same as in Example 1.

[0062] Figure 1This is the DES infrared spectrum prepared from choline chloride and 1,4-butanediol, from... Figure 1 It can be seen that at 3334cm -1 A broad hydroxyl (-OH) stretching vibration peak appeared at 3386 cm⁻¹, compared to the usual 3386 cm⁻¹. -1 The hydroxyl absorption peak showed a significant red shift, indicating the formation of strong intermolecular hydrogen bonds in the DES system. Furthermore, in... Figure 1 It can be seen that at 2940cm -1 The stretching vibration peak of CH appeared at 1052 cm⁻¹, and at 1052 cm⁻¹... -1 The appearance of CO stretching vibration peaks indicates the successful preparation of DES.

[0063] Figure 2 The figures show the water contact angle test results for membranes M0, M-DES-1, M-DES-2, M-DES-4, and M-DES-6. The figures show that the water contact angle is lowest when the mass fraction of DES porogen reaches 4 wt%, indicating the best hydrophilicity of the membrane surface at this concentration. This is likely because a 4 wt% DES concentration provides the optimal porogen effect, resulting in a uniformly sized, loosely porous structure on the prepared ultrafiltration support substrate. Ultimately, this leads to a ridge-valve morphology in the topmost polyamide separation layer, increasing roughness and thus improving hydrophilicity.

[0064] Figure 3 Scanning electron microscope (SEM) top and cross-sectional views of polyamide nanofiltration composite membranes prepared using DES as a pore-forming agent with different mass fractions are shown. (a)-(b) are SEM top and cross-sectional views of the nanofiltration membrane obtained in the comparative example (M0 membrane); (c)-(d) are SEM top and cross-sectional views of the nanofiltration membrane obtained in Example 1 (M-DES-1 membrane); (e)-(f) are SEM top and cross-sectional views of the nanofiltration membrane obtained in Example 2 (M-DES-2 membrane); (g)-(h) are SEM top and cross-sectional views of the nanofiltration membrane obtained in Example 3 (M-DES-4 membrane); and (i)-(j) are SEM top and cross-sectional views of the nanofiltration membrane obtained in Example 4 (M-DES-6 membrane). Figure 2The top-view electron microscope image shows that as the amount of DES porogen increases, the polyamide membrane surface changes from a nodular shape to a distinct ridge-valve shape. When the mass fraction reaches 6 wt%, a dense agglomerated structure gradually appears on the membrane surface. This may be because the porogen effect of 6 wt% DES is uneven, causing excessive aggregation of m-phenylenediamine on the ultrafiltration substrate surface, thus forming dense clusters on the polyamide surface. The cross-sectional image also shows that as the mass fraction of DES porogen increases, the pores of the ultrafiltration support substrate gradually increase, the structure becomes looser, and the separation layer thickness gradually decreases. When the mass fraction of DES reaches 6 wt%, the separation layer thickness is increased compared to the MO membrane, which is also related to the formation of denser clusters on its surface.

[0065] Permeation performance test of polyamide nanofiltration composite membrane: The nanofiltration performance of the polyamide nanofiltration composite membranes prepared in Examples 1-8 and Comparative Example 1 was tested using a methanol solution of 20 mg / L Rhodamine B (RDB). The test operating pressure was 10 bar. The permeation flux was calculated according to Equation (1), and the rejection rate was calculated according to Equation (2). Equations (1) and (2) are as follows: Equation (1); Equation (2); In equation (1), A is the effective membrane area (m²). 2 ), where Δt is the operating time (h), ΔV is the volume of permeate during the operating time (L), and ΔP is the operating pressure (bar); In equation (2), C f C represents the concentration of the dye in the raw material solution. p The concentration of the dye in the permeate is denoted as R. The rejection rate R is between 0 and 100%. The larger the value of R, the less dye permeates and the better the separation performance.

[0066] The test results are shown in Table 1 and Figure 4 As shown.

[0067] Table 1. Methanol permeation flux and Rhodamine B rejection rate of polyamide nanofiltration composite membrane

[0068] From Table 1 and Figure 4 The results show that the methanol permeation flux of the MO membrane with 1 wt% PVP as a pore-forming agent is 8.87 L·m. - 2 h -1 bar -1 The rejection rate for Rhodamine B dye reached 97.3%. In contrast, the methanol permeation flux of the M-DES-1 membrane using 1 wt% DES as a porogen was only 6.70 L·m⁻¹. -2 h-1 bar -1 However, as the mass fraction of DES porogen continued to increase, the methanol permeation flux of the M-DES-4 membrane reached its maximum of 12.9 L·m⁻¹ at 4 wt%. -2 h -1 bar -1 Compared to the MO membrane, the efficiency was improved by 45.4%, while the rejection rate of Rhodamine B dye remained at a high level of 97.1%. As the mass fraction of DES porogen increased to 6 wt%, the methanol permeation flux of the membrane decreased sharply, but the rejection rate of Rhodamine B did not change significantly.

[0069] As can be seen from Table 1, the M-DES-4 membrane, compared to other membranes such as M-DES... EG -4 membrane, M-DES GLY Examples of the -4 membrane and the M0 membrane, among others, demonstrated the best permeation performance for methanol solvent, while the rejection rate of Rhodamine B remained above 97%.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polyamide nanofiltration composite membrane, characterized in that, Includes the following steps: After preparing a membrane from a polyimide casting solution, the membrane is immersed in water for phase inversion to obtain a polyimide ultrafiltration supported membrane. The polyimide ultrafiltration support membrane is immersed in a crosslinking agent solution to carry out a crosslinking reaction, thereby obtaining a crosslinked support membrane; The cross-linked support membrane is immersed in an aqueous solution of an organic amine aqueous reactive monomer to obtain a support membrane containing saturated aqueous monomer. The supported membrane containing the saturated aqueous monomer is placed in an acyl chloride organic phase reaction monomer solution to carry out an interfacial polymerization reaction to form a polyamide separation layer, thereby obtaining a nanofiltration membrane precursor. The nanofiltration membrane precursor is immersed in an activation solution for activation treatment to obtain the polyamide nanofiltration composite membrane; The casting solution includes polyimide and a pore-forming agent; the pore-forming agent is a eutectic solvent.

2. The preparation method according to claim 1, characterized in that, The eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor; the hydrogen bond donor is choline chloride, betaine, tetrabutylammonium fluoride, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrabutylammonium hydrogen sulfate, tetrabutylphosphine fluoride, or tetrabutylphosphine chloride; the hydrogen bond acceptor is butanediol, ethylene glycol, glycerol, urea, citric acid, phenylacetic acid, malic acid, sulfamic acid, lactic acid, formic acid, acetic acid, or acetamide; the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:1 to 4.

3. The preparation method according to claim 1, characterized in that, The polyimide casting solution also includes an organic solvent; the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

4. The preparation method according to claim 1, characterized in that, The mass ratio of polyimide to porogen is 3~20:

1.

5. The preparation method according to claim 1, characterized in that, The crosslinking agent in the crosslinking agent solution is an organic fatty amine compound; the concentration of the crosslinking agent solution is 100~150g / L.

6. The preparation method according to claim 1, characterized in that, The cross-linking reaction is carried out at a temperature of 20-35°C for 16-24 hours.

7. The preparation method according to claim 1, characterized in that, The organic amine aqueous phase reaction monomer is selected from at least one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2,2'-biphenylenediamine, 4,4'-biphenylenediamine, 1,5'-naphthylenediamine and 2,6'-naphthylenediamine; the concentration of the aqueous solution of the organic amine aqueous phase reaction monomer is 2wt% to 4wt%.

8. The preparation method according to claim 1, characterized in that, The concentration of the acyl chloride organic phase reaction monomer solution is 0.1wt%~0.15wt%; the acyl chloride organic phase reaction monomer in the solution is selected from at least one of 4,4'-biphenyldicarboxylic acid chloride, 2,2'-biphenyldicarboxylic acid chloride, 3,3'-biphenyldicarboxylic acid chloride, 2,3'-biphenyldicarboxylic acid chloride, 2,4'-biphenyldicarboxylic acid chloride, 3,4',5-biphenyltricarboxylic acid chloride, 3,3',5,5'-biphenyltetracarboxylic acid chloride, 2,2',4,4'-biphenyltetracarboxylic acid chloride, 2,2',5,5'-biphenyltetracarboxylic acid chloride, 2,4,4',6-biphenyltetracarboxylic acid chloride, phthaloyl chloride, terephthaloyl chloride, isophthaloyl chloride, trimellitic acid chloride, and pyromellitic acid chloride; the interfacial polymerization reaction is carried out at a temperature of 20~25℃ for 1~1.5min.

9. The preparation method according to claim 1, characterized in that, The activation solvent is an amide solvent, a pyrrolidone solvent, or a dimethyl sulfoxide; the activation treatment temperature is 70~90℃ and the time is 20~40min.

10. A polyamide nanofiltration composite membrane prepared by the preparation method according to any one of claims 1-9.

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