A novel high-flux, high-selectivity organic solvent nanofiltration membrane and its preparation method

Abstract

This invention provides a novel high-throughput, high-selectivity organic solvent nanofiltration membrane and its preparation method, belonging to the field of membrane separation technology. β-Cyclodextrin (β-CD) is added as a segregating agent to a casting bath containing 3,3'-di(4-aminophenyl)-teregol base monomer (DAPTB), trifluoroacetic acid, and polyimide. A polyimide substrate rich in DAPTB is prepared via a phase inversion reaction. Then, an initial nanofiltration membrane is obtained by interfacial polymerization with trimesoyl chloride. Subsequently, it is further crosslinked with 1,6-hexanediamine to improve the membrane's polar solvent resistance. Finally, the membrane's permeability is improved by activation with N,N'-dimethylformamide solvent, ultimately yielding a high-throughput, high-selectivity organic solvent nanofiltration membrane. Utilizing the hydrogen bonding between β-CD and DAPTB monomers and the hydrophilicity of β-CD, the migration of DAPTB monomers to the surface of the polyimide substrate membrane can be promoted faster, more abundantly, and more uniformly during the phase inversion process, thereby improving the crosslinking degree and separation selectivity of the nanofiltration membrane separation layer.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a novel high-throughput, high-selectivity organic solvent nanofiltration membrane and its preparation method. Background Technology

[0002] Nanofiltration is an emerging low-energy separation technology that lies between ultrafiltration and reverse osmosis. It can retain organic molecules with molecular weights of 200 to 1000 Da, with high separation precision, wide separation range, energy saving and high efficiency. It has great application potential in the separation and concentration of feed liquids, product refining and purification, and solvent concentration and recovery.

[0003] However, currently mainstream nanofiltration membranes on the market mainly consist of a polysulfone support layer and an active polypiperazine amide separation layer. The polysulfone layer is poorly resistant to organic solvents, while the polypiperazine amide separation layer exhibits low permeation selectivity in organic solvent systems. Although polyimide (PI) is a polymer material with excellent thermal stability, mechanical strength, and chemical stability, nanofiltration membranes made from it show good stability in common organic solvents such as ethyl acetate, methanol, ethanol, and acetone. However, they are not resistant to aprotic strongly polar solvents such as N,N-dimethylformamide (DMSO), N,N-dimethylacetamide (DMF), and N-methylpyrrolidone (NMP). Therefore, currently commercially available nanofiltration membranes cannot meet the practical requirements of organic solvent systems, greatly limiting the separation applications of nanofiltration technology in pharmaceuticals, petrochemicals, and food industries. There is an urgent need to develop high-performance organic solvent nanofiltration membranes (OSN).

[0004] Researchers have introduced various additives into nanofiltration membranes to improve the permeation flux of the membrane. For example, Li et al. (ACS Appl. Mater. Interfaces, 2019, 11: 6527-6540) introduced graphene quantum dots into the selective layer, which significantly improved the water flux without affecting the retention. Li et al. (J. Membr. Sci., 2019, 572: 520-531) added covalent organic framework (COF) nanoparticles into the selective layer, which increased the ethanol flux by 46.7% compared with the membrane without COFs. Some researchers have also introduced molecules with cavity structures into the polyamide layer. For example, Li et al. (Surfaces and Interfaces, 2025, 72) successfully prepared a (PA-TFC) OSN membrane with both high permeability and high selectivity by incorporating cucurbita[6]urea (CB[6]) into the PA layer. However, the above-mentioned process membrane products have poor dispersibility in strongly polar solvent systems, poor compatibility with polymers, and do not solve the fundamental problem of insufficient enrichment of amine groups on the bottom film surface.

[0005] Therefore, there is an urgent need to develop an organic solvent nanofiltration membrane and its preparation method that takes into account high permeation flux, high retention selectivity and long-term tolerance to strong polar solvents. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of conventional commercial polypiperazine amide nanofiltration membranes and polyamide imide nanofiltration membranes, such as poor tolerance to organic solvents, narrow tolerance range, and low permeation selectivity, and to develop a novel high-pass, high-selectivity organic solvent nanofiltration membrane and its preparation method. The nanofiltration membrane is prepared by first adding a self-made functional monomer—3,3'-di(4-aminophenyl)-teregol base (DAPTB), a protective agent trifluoroacetic acid (TFA), a segregating agent β-cyclodextrin (β-CD), and polyimide (PI) to an organic solvent to prepare a casting solution. After stirring evenly and allowing it to stand to remove bubbles, the solution is coated onto a nonwoven fabric to form a liquid film. Then, it is placed in a coagulation bath to prepare a polyimide porous support substrate rich in DAPTB through non-solvent-induced phase inversion (NIPs). The substrate is then subjected to interfacial polymerization by contacting one side with an organic phase solution containing acyl chloride monomers. After the reaction is completed, the remaining organic phase solution is removed and the substrate is air-dried. Finally, it is crosslinked with 1,6-hexanediamine (HDA) and activated with N,N-dimethylformamide (DMF) to obtain the final product.

[0007] The self-production process of 3,3'-bis(4-aminophenyl)-teleg base (abbreviated as DAPTB) in this invention is as follows: (1) 4-Bromoaniline (25.905 g, 150.6 mmol) and paraformaldehyde (9.18 g, 306 mmol) were added to trifluoroacetic acid (300 mL) at -15 °C. After stirring for 20 min, the mixture was brought to room temperature and stirred for 48 h. Dichloromethane (DCM) was added to quench the reaction, and ammonia was added dropwise until the color of the mixture changed from purple-red to yellow. The mixture was extracted with DCM (20 mL × 3), and the organic phase was collected and dried with anhydrous sodium sulfate. The mixture was then purified by column chromatography to obtain white crystalline 3,3'-dibromo-teleglerin. Then, 3.34 g (8.78 mmol) of 3,3'-dibromo-teleglerin was dissolved in 35 mL of dry tetrahydrofuran and cooled to -78 °C. A solution containing 2.5 mol / L n-hexane was slowly added dropwise under nitrogen. n -BuLi (8.4 mL, 21 mmol) solution was stirred for 45 min, and then trimethyl borate (3.75 mL, 33.63 mmol) was slowly added dropwise. The reaction was then stirred at room temperature for 1.5 h. After the reaction was completed, H2O was added to the reaction solution and stirred for 5 min to quench the reaction. Then DCM was added for extraction and the aqueous phase solution was collected. 6 mol / L HCl solution was added to the aqueous phase solution to acidify it. After the reaction was carried out at room temperature, the solution was filtered and dried to obtain a white solid product, namely the intermediate 3,3'-diboronic acid-terleg base.

[0008] (2) Add intermediate 3,3'-diboronic acid-teleg base (0.5 g, 1.6 mmol), p-nitroiodobenzene (0.956 g, 3.84 mmol), CsF (1.8295 g, 12 mmol) and H2O (10 mL) to a three-necked flask with stirring. Then add tris(dibenzylideneacetone)dipalladium (0.0293 g, 0.032 mmol), tri-tert-butylphosphine (0.14 mL, 0.596 mmol) and 1,4-dioxane (20 mL) under nitrogen protection. After stirring the system at 95 °C for 6 hours under sealed conditions, add H2O to the reaction solution to quench the reaction. Extract the mixed solution with DCM and collect the organic phase. After drying with anhydrous sodium sulfate, filter out the filtrate and separate the yellow intermediate 3,3'-di(4-nitrophenyl)-teleg base by column chromatography.

[0009] (3) Under stirring, the intermediate 3,3'-bis(4-nitrophenyl)-teleg base (1 g, 2.15 mmol) and ethanol (30 mL) were added to a 100 mL three-necked flask, and 10% palladium on carbon (0.3 g, 0.14 mmol) was added under nitrogen. Then, 80% hydrazine hydrate (8 mL) was slowly added dropwise at 65 °C. The system was heated to 78 °C and stirred under reflux for 10 hours. After the reaction was completed, the mixed solution was filtered while hot. The filtrate was concentrated by rotary evaporation until the product was slightly precipitated. H2O was added to crystallize the product. Finally, the product was vacuum filtered and dried to obtain a white solid product, namely 3,3'-bis(4-aminophenyl)-teleg base.

[0010] Since β-CD is a hydrophilic molecule rich in hydroxyl groups, it can bind to the amino groups in DAPTB molecules through hydrogen bonds. This invention utilizes the hydrogen bonds formed between the hydroxyl groups in β-CD and the amino groups in DAPTB molecules. β-Cyclodextrin has strong hydrophilicity and migrates rapidly to the coagulation bath interface during non-solvent-induced phase inversions (NIPs), promoting faster, more abundant, and more uniform segregation of DAPTB molecules to the polyimide substrate surface during phase inversion. This increases the crosslinking degree and selectivity of the separation layer, ultimately forming a high density of amino active sites on the membrane surface, laying the foundation for the subsequent preparation of high-performance composite nanofiltration membranes. Simultaneously, the DAPTB molecule contains a unique V-shaped rigid twisted structure, which endows the separation layer with excellent solvent resistance and permeability. Furthermore, the polyimide-supported substrate, after HDA crosslinking, can withstand aprotic strongly polar solvents, while moderate activation with DMF can further enhance the permeation flux of the nanofiltration membrane.

[0011] This invention proposes to dissolve DAPTB monomer, protective agent trifluoroacetic acid, segregating agent β-CD, and polyimide together in a polar solution to obtain a casting solution. Then, through a non-solvent-induced phase transformation, DAPTB is uniformly segregated and enriched onto the surface of the polyimide substrate membrane. Subsequently, a novel high-flux and high-selectivity organic solvent nanofiltration membrane is prepared by in-situ interfacial polymerization, HDA crosslinking, and DMF activation.

[0012] On the one hand, this invention proposes a novel method for preparing a high-flux, high-selectivity organic solvent nanofiltration membrane, comprising the following process steps: (1) A certain amount of DAPTB monomer and protective agent trifluoroacetic acid are added to a polar solvent and stirred at low temperature for 1 to 2 hours to form a homogeneous solution. Then, polyimide and the remaining polar solvent are added to the homogeneous solution and stirred at room temperature for 3 to 6 hours. β-CD is added and stirred until uniform and clear. Then, the solution is allowed to stand to remove bubbles and obtain a uniform and bubble-free polyimide casting solution. (2) The casting solution obtained in step (1) is scraped onto the surface of the nonwoven fabric and the nonwoven fabric with the casting solution attached is quickly immersed in the coagulation bath for non-solvent-water induced phase transformation. Then, the membrane surface is rinsed with deionized water to remove impurities and then air-dried to obtain a polyimide support substrate with DAPTB monomer on the surface. (3) Pour the organic phase solution containing polyacryl chloride monomer evenly onto the surface of the polyimide support substrate membrane that was air-dried in step (2) and carry out the interfacial polymerization reaction. After reacting for a period of time, remove the remaining organic phase solution and then soak and wash it in anhydrous ethanol to obtain the initial nanofiltration membrane. (4) The initial nanofiltration membrane obtained in step (3) is immersed in a 1,6-hexanediamine / alcohol solution at 60°C for crosslinking reaction, and then immersed in DMF solution for activation, and finally a high-flux Teleg base polyamide solvent-resistant nanofiltration membrane is obtained.

[0013] Wherein, the polar solvent in step (1) is one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; the polyacrylamide monomer in step (3) is one of isophthaloyl chloride, biphenyltetracarboxylic chloride, pyromellitic tricarboxylic chloride or phthaloyl chloride; the organic solvent in the organic phase solution of the polyacrylamide monomer in step (3) is one of solvent oil Isopar G, cyclohexane, n-hexane or n-heptane.

[0014] Furthermore, in step (1), the low temperature is -10 to -20°C, the stirring temperature is 20 to 60°C, the stirring time after adding β-cyclodextrin is 6 to 12 hours, and the standing degassing time is 6 to 24 hours.

[0015] Further, in step (1), the content of DAPTB monomer in the casting solution is 0.5-2 wt%, the content of trifluoroacetic acid is 0.85-3.4 wt%, and the content of β-cyclodextrin is 0.05-0.19 wt%.

[0016] Furthermore, in step (2), the volume of the coagulation bath aqueous solution is 1.2 to 2 L, and the time for the non-solvent-water induced phase transition is 30 to 300 seconds; Furthermore, in step (2), the air-drying time is 5 to 20 minutes; Furthermore, in step (3), the concentration of polyacryl chloride monomer in the organic phase solution containing polyacryl chloride monomer is 0.01 to 0.35 wt%. Furthermore, in step (3), the reaction time in the polyacrylamide chloride monomer solution is 5 to 60 seconds; Further, in step (4), the reaction time in the 1,6-hexanediamine / alcohol solution is 10–40 minutes, and the concentration of the 1,6-hexanediamine / alcohol solution is 2.5–12.5 wt%. The crosslinking reaction is carried out at 40–80 °C; the activation time of the N,N-dimethylformamide solvent is 2–10 minutes; and the alcohol in the 1,6-hexanediamine / alcohol solution is any one of isopropanol, ethanol, or methanol.

[0017] The present invention also proposes a novel high-flux, high-selectivity organic solvent nanofiltration membrane prepared by the preparation method described above, comprising a polyimide porous support layer and a telage-containing polyamide separation layer bonded to its surface. The polyimide support layer is crosslinked and modified by a 1,6-hexanediamine / alcohol solution, and the separation layer is incorporating a rigid V-shaped network structure formed by the polymerization of DAPTB monomers enriched by β-cyclodextrin segregation.

[0018] The core technical principle of this invention lies in: First, the segregating agent effect of β-cyclodextrin. β-cyclodextrin is a hydrophilic macrocyclic molecule containing multiple hydroxyl groups, which can form hydrogen bonds with the amino groups in the DAPTB molecule. During solvent-induced phase inversion, due to the strong hydrophilicity of β-CD, it tends to migrate towards the water coagulation bath interface, and through hydrogen bonding, it drives the DAPTB monomers bound to it to segregate to the polyimide substrate surface more quickly, in greater quantity, and more uniformly. This mechanism results in a high density of amino active sites on the substrate surface, providing sufficient reaction sites for subsequent interfacial polymerization reactions, thereby improving the crosslinking degree and selectivity of the separation layer.

[0019] Second, the V-shaped rigid twisted structure of the DAPTB monomer. The DAPTB monomer contains the unique V-shaped rigid twisted structure of the telreg base. Introducing this structure into the polyamide separation layer endows the separation layer with a rigid molecular chain structure and a large free volume, which facilitates the rapid permeation of solvent molecules, thereby increasing the membrane flux. Simultaneously, the hydrogen bonding interaction between the hydrogen atoms of the amide group and the nitrogen atoms of the telreg base enhances the interchain interactions, giving the membrane precise molecular sieving selectivity for organic solutes.

[0020] Third, crosslinking modification of the polyimide substrate. This invention utilizes 1,6-hexanediamine to undergo a crosslinking reaction with the imide groups in polyimide, enabling the polyimide-supported substrate to form a three-dimensional network structure. This significantly improves the membrane's resistance to aprotic strong polar solvents (such as DMF, DMAc, NMP, DMSO, etc.), overcoming the defect of traditional polyimide membranes being intolerant to strong polar solvents.

[0021] Fourth, moderate activation with DMF. This invention moderately activates the cross-linked nanofiltration membrane with DMF, further improving the membrane's permeation flux without significantly affecting its selectivity.

[0022] The synergistic effect of the above four aspects enables the organic solvent nanofiltration membrane prepared by the present invention to simultaneously possess high flux, high selectivity, and excellent solvent resistance.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High flux. The present invention uses β-CD-assisted segregation to enrich DAPTB monomers at a high density on the bottom membrane surface, combined with the V-shaped rigid twisted structure of DAPTB to give the separation layer a large free volume, and the appropriate activation treatment of DMF, so that the prepared nanofiltration membrane has a significantly higher flux than the membrane without β-CD and conventional polypiperazine amide nanofiltration membrane.

[0024] (2) High selectivity. This invention uses β-CD-assisted segregation to uniformly enrich DAPTB on the bottom membrane surface, increasing the density and uniformity of interfacial polymerization reaction sites, thereby improving the crosslinking degree of the separation layer. At the same time, the hydrogen bonding interaction between H and N in the amide group of the Teleg base structure enhances the interchain interaction, giving the membrane precise molecular sieving properties.

[0025] (3) Excellent solvent resistance. The present invention modifies the polyimide substrate by crosslinking with 1,6-hexanediamine, so that the film can withstand aprotic strong polar solvents such as DMF, DMAc, NMP, and DMSO.

[0026] (4) Wide range of applications. The nanofiltration membrane prepared by this invention has good flux and stability in a variety of organic solvents such as methanol, ethanol, acetonitrile, tetrahydrofuran, ethyl acetate, DMAc, DMF, DMSO, NMP, and isopropanol. It can be widely used in the separation of feed and liquid, product purification and solvent recovery in the fields of medicine, petrochemicals and food.

[0027] In summary, this invention adds a segregating agent β-CD to the casting solution, which, through hydrogen bonding with the amino groups in DAPTB molecules, promotes faster, more abundant, and more uniform segregation of DAPTB molecules to the polyimide substrate surface, thereby improving the crosslinking degree and selectivity of the separation layer. Simultaneously, a special V-shaped rigid twisted structure is introduced into the separation layer using a self-made DAPTB monomer, thereby increasing the free volume and permeation flux of the separation layer. Furthermore, the crosslinking of 1,6-hexanediamine with polyimide enhances the membrane's tolerance in aprotic, highly polar solvents. Ultimately, a high-flux, high-selectivity organic solvent nanofiltration membrane is obtained, which can be effectively used for the separation and purification of products (such as dyes, pharmaceuticals, catalysts, etc.) and solvent concentration and recovery in highly polar solvent systems, showing broad application prospects. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the mechanism by which the segregating agent β-CD described in this invention promotes the segregation of 3,3'-bis(4-aminophenyl)-teregol base (DAPTB) monomer during phase transformation.

[0029] Figure 2 The invention comprises a base film S PI (M0), S PI-DAPTB (M1), nanofiltration membrane OSN DAPTB-TMC (M2), and the nanofiltration membrane OSN before and after the addition of β-CD. DAPTB-TMC@HDA@DMF Fourier attenuated total reflectance infrared (ATR-FTIR) spectra of (M3 and M4) and polypiperazine amide nanofiltration membrane M5.

[0030] Figure 3 The images are SEM images of organic solvent nanofiltration membranes M3 and M4 and polypiperazine amide nanofiltration membrane before and after immersion in DMF for 30 days, as described in this invention, before and after the addition of β-CD. Detailed Implementation

[0031] The following detailed description, in conjunction with specific embodiments, further clarifies the invention. However, the scope and content of this patent are not limited to the following embodiments. Any variations or implementations that do not depart from the scope and content of this invention should be included within the technical scope of this invention.

[0032] Example 1 ① Preparation of casting solution 1.0 wt% DAPTB, 1.7 wt% trifluoroacetic acid, and 10 mL N-methylpyrrolidone were added to a round-bottom flask. The mixture was stirred at -15°C for 1 hour, then stirred at room temperature. 17 wt% polyimide and the remaining N-methylpyrrolidone were then added. After stirring at room temperature for 4 hours, β-CD(n) was added. β-CD :n DAPTB =1:30), stir for 12 hours and let stand for 12 hours to remove bubbles, and a uniform casting solution without bubbles is obtained.

[0033] ② Non-solvent-induced phase transformation The casting solution was poured evenly and quickly onto the nonwoven fabric, and then scraped into a uniform liquid film with a 200-micron doctor blade. The nonwoven fabric coated with the liquid film was then immersed in a 2L coagulation bath aqueous solution for a non-solvent-induced phase transformation for 60 seconds to obtain a base film containing DAPTB monomer.

[0034] ③ In-situ interface aggregation A hexane solution containing 0.05 w / v pyromellitic methyl chloride was uniformly and rapidly poured onto the surface of an air-dried PI porous support membrane for in-situ interfacial polymerization for 5 seconds. After removing excess organic phase solution from the membrane surface, it was stored in anhydrous ethanol. The resulting polyamide nanofiltration membrane containing telage bases was designated OSN. DAPTB-TMC Membrane (M2).

[0035] ④ Crosslinking activation OSN DAPTB-TMC The membrane was crosslinked for 30 minutes by immersing it in a 7.5 wt% 1,6-hexanediamine / isopropanol solution at 60°C, and then activated by immersion in DMF at 80°C for 15 minutes. The resulting polyamide nanofiltration membrane containing telage bases is denoted as OSN. DAPTB-TMC@HDA@DMF Membrane (M3).

[0036] Example 2

[0037] In step ①, n β-CD :n DAPTB =1:30 was changed to 0 (i.e., no β-CD was added), and other operations were the same as in Example 1. The membrane performance data are listed in Table 1.

[0038] Example 3

[0039] In step ①, n β-CD :n DAPTB =1:30 was changed to 1:120, and other operations were the same as in Example 1. The membrane performance data are listed in Table 1.

[0040] Example 4

[0041] In step ①, n β-CD :n DAPTB=1:30 was changed to 1:90, and other operations were the same as in Example 1. The membrane performance data are listed in Table 1.

[0042] Example 5

[0043] In step ①, n β-CD :n DAPTB = 1:30 was changed to 1:60, and other operations were the same as in Example 1. The membrane performance data are listed in Table 1.

[0044] Example 6

[0045] In step ①, n β-CD :n DAPTB =1:30 was changed to 1:1, and other operations were the same as in Example 1. The membrane performance data are listed in Table 1.

[0046] Example 7

[0047] The TMC concentration in step ③ was changed from 0.05 w / v% to 0.075 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0048] Example 8

[0049] The TMC concentration in step ③ was changed from 0.05 w / v% to 0.01 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0050] Example 9

[0051] The TMC concentration in step ③ was changed from 0.05 w / v% to 0.125 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0052] Example 10 The TMC concentration in step ③ was changed from 0.05 w / v% to 0.15 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0053] Example 11 The TMC concentration in step ③ was changed from 0.05 w / v% to 0.175 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0054] Example 12 The TMC concentration in step ③ was changed from 0.05 w / v% to 0.2 w / v%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 2.

[0055] Example 13 Change the interface polymerization time in step ③ from 5 seconds to 10 seconds, and perform the other operations as in Example 1. The membrane performance data are listed in Table 3.

[0056] Example 14 Change the interface polymerization time in step ③ from 5 seconds to 15 seconds, and perform the other operations as in Example 1. The membrane performance data are listed in Table 3.

[0057] Example 15 Change the interface polymerization time in step ③ from 5 seconds to 20 seconds, and perform the other operations as in Example 1. The membrane performance data are listed in Table 3.

[0058] Example 16 The interfacial polymerization time in step ③ was changed from 5 seconds to 25 seconds, and other operations were the same as in Example 1. The membrane performance data are listed in Table 3.

[0059] Example 17 Change the interface polymerization time in step ③ from 5 seconds to 30 seconds, and perform the other operations as in Example 1. The membrane performance data are listed in Table 3.

[0060] Example 18 The interfacial polymerization time in step ③ was changed from 5 seconds to 35 seconds, and other operations were the same as in Example 1. The membrane performance data are listed in Table 3.

[0061] Example 19 Change the interface polymerization time in step ③ from 5 seconds to 40 seconds, and perform the other operations as in Example 1. The membrane performance data are listed in Table 3.

[0062] Example 20 The concentration of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 7.5 wt% to 2.5 wt%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 4.

[0063] Example 21 The concentration of the 1,6-hexanediamine / isopropanol solution in step ④ was changed to 5 wt%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 4.

[0064] Example 22 The concentration of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 7.5 wt% to 10 wt%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 4.

[0065] Example 23 The concentration of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 7.5 wt% to 12.5 wt%, and other operations were the same as in Example 1. The membrane performance data are listed in Table 4.

[0066] Example 24 The crosslinking time of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 30 minutes to 10 minutes. Other operations were the same as in Example 1. The membrane performance data are listed in Table 5.

[0067] Example 25 The crosslinking time of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 30 minutes to 20 minutes. Other operations were the same as in Example 1. The membrane performance data are listed in Table 5.

[0068] Example 26 The crosslinking time of the 1,6-hexanediamine / isopropanol solution in step ④ was changed from 30 minutes to 40 minutes. Other operations were the same as in Example 1. The membrane performance data are listed in Table 5.

[0069] Comparative Example 1 Replace the mixed monomers DAPTB and β-CD in step ① with pure monomer DAPTB, and follow the same preparation steps as in Example 1. The resulting membrane is designated as M4 and used for comparative testing. The performance data are listed in Tables 2-4.

[0070] Comparative Example 2 In Comparative Example 1, the pure monomer DAPTB was replaced with pure piperazine, and the mixture was placed in an aqueous solution. Other procedures were the same as in Example 1. The resulting membrane was denoted as OSN. PIP-TMC@HDA@DMF The membranes were prepared and used for comparative testing; the performance data are listed in Tables 7 and 8.

[0071] Table 1: Comparison of separation performance of nanofiltration membranes prepared in Examples 1-6

[0072] As shown in Table 1, when the molar ratio of β-CD to DAPTB is 1:30 (Example 1), the membrane flux reaches the optimal value of 8.55 μm. -2 h -1 bar -1 While maintaining a high rejection rate of 99.7%, the flux in Example 2 without β-CD addition was significantly reduced to 6.99 Lm. -2 h -1 bar -1 This indicates that the addition of β-CD has a significant effect on improving membrane flux. However, when the β-CD ratio is too high (Example 6, 1:1), the flux actually decreases to 4.71 Lm. -2 h -1 bar -1 This indicates that the amount of β-CD added needs to be controlled within an appropriate range.

[0073] Table 2: Comparison of separation performance of nanofiltration membranes prepared in Examples 7-12

[0074] As shown in Table 2, when the TMC concentration is 0.075 w / v% (Example 7), the membrane flux reaches the optimal value of 12.41 Lm. -2 h- 1 bar -1 Too low a TMC concentration (Example 8) or too high a concentration (Examples 11, 12) will result in a decrease in flux.

[0075] Table 3: Comparison of separation performance of nanofiltration membranes prepared in Examples 13-19

[0076] As shown in Table 3, when the interfacial polymerization time is 10–20 seconds (Examples 13–15), the membrane flux is relatively high (8.15–8.29 μm). -2 h -1 bar -1 While maintaining a high retention rate of over 99.7%, throughput gradually decreases as the interface aggregation time increases.

[0077] Table 4: Comparison of separation performance of nanofiltration membranes prepared in Examples 20-23

[0078] As shown in Table 4, the membrane flux was highest (14.87 Lm) when the HDA concentration was 2.5 wt% (Example 20). -2 h -1 bar -1 The retention rate also remained at a high level of 99.3%.

[0079] Table 5: Comparison of separation performance of nanofiltration membranes prepared in Examples 24-26

[0080] As shown in Table 5, the membrane flux was highest (16.35 μm) when the crosslinking time was 10 minutes (Example 24). -2 h -1 bar -1 However, the retention rate was relatively low (97.8%). As the crosslinking time increased, the retention rate improved.

[0081] The solvent flux performance of the membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested. The solvents tested were methanol, ethanol, acetonitrile, tetrahydrofuran, ethyl acetate, DMAc, DMF, DMSO, NMP, and IPA, respectively. The test conditions were 25°C and 0.6 MPa. The test results are shown in Table 6.

[0082] Table 6: Comparison of solvent flux prepared in Example 1, Comparative Example 1, and Comparative Example 2

[0083] As shown in Table 6, the nanofiltration membrane prepared in Example 1 of this invention exhibited significantly higher fluxes in all tested solvents than Comparative Example 1 (without β-CD) and Comparative Example 2 (conventional polypiperazine amide nanofiltration membrane). Particularly in aprotic strongly polar solvents such as DMAc, DMF, DMSO, and NMP, the flux of Comparative Example 2 was zero (completely intolerable), while Example 1 maintained a high flux (5.95 μm in DMF). -2 h -1 bar -1 4.88Lm in DMAc -2 h -1 bar -1 This indicates that the membrane prepared by the present invention has excellent resistance to strong polar solvents.

[0084] Solvent resistance tests were conducted using two membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2. The membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were immersed in DMF for 30 days, and then the methanol flux and chrome black T retention performance were tested at 25°C and 0.6 MPa. The test results are shown in Table 7.

[0085] Table 7: Changes in methanol flux and Eriochrome Black T rejection rate of nanofiltration membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 after immersion in DMF solvent for 30 days.

[0086] As shown in Table 7, the methanol flux of the membrane prepared in Example 1 of this invention remained at 16.41 Lm after immersion in DMF for 30 days. -2 h -1 bar -1 The high level of chrome black T rejection was 89.8%. Comparative Example 1 (without β-CD) membrane also exhibited some DMF tolerance (attributed to HDA ​​crosslinking), but its flux (7.35 Lm) was significantly lower. -2 h -1 bar -1 The flux was significantly lower than that of Example 1. Comparative Example 2 (conventional polypiperazine amide nanofiltration membrane) maintained a high rejection rate, but its flux was extremely low (4.73 μm). -2 h -1 bar -1 Furthermore, as shown in Table 6, its initial flux in the DMF is zero.

[0087] Based on the above results, it can be seen that the polyimide solvent-resistant nanofiltration membrane M3 prepared in this invention significantly improves the flux of various solvents while maintaining a relatively small reduction in dye rejection rate compared to the membrane M4 without the addition of β-CD and conventional polypiperazine amide nanofiltration membrane. It also has high separation selectivity and solvent tolerance, and exhibits excellent stability in conventional polar solvents, aprotic strong polar solvents, and non-polar solvents.

[0088] The above results demonstrate that the present invention successfully prepared an organic solvent nanofiltration membrane with high throughput, high selectivity, and excellent solvent resistance through the synergistic effect of β-CD-assisted segregation, the V-shaped rigid structure of DAPTB, HDA crosslinking, and DMF activation.

[0089] Figure 1 This is a schematic diagram illustrating the mechanism by which the segregating agent β-cyclodextrin (β-CD) promotes the segregation and enrichment of 3,3′-di(4-aminophenyl)-teregol base (DAPTB) monomers onto the membrane surface during solvent-inducible phase inversions (NIPs) according to this invention. The explanation is as follows: In the casting solution, β-CD forms intermolecular hydrogen bonds with the amino groups in the DAPTB molecule through its abundant hydroxyl groups. Upon immersion in the coagulation bath, due to the strong hydrophilicity of β-CD, this complex preferentially migrates to the water / solvent interface, thereby driving the high-density and uniform enrichment of DAPTB monomers on the substrate surface, providing sufficient active sites for subsequent interfacial polymerization. 。

[0090] Figure 2 This is a comparison of the Fourier attenuated total reflectance infrared spectra (ATR-FTIR) of the substrate membrane and nanofiltration membrane involved in this invention. By comparing the infrared absorption peaks of the polyimide substrate membrane (M0), the DAPTB-rich substrate membrane (M1), the interfacial polymerization nascent membrane (M2), the cross-linked activated membrane after adding β-CD (M3), the cross-linked activated membrane without adding β-CD (M4), and the conventional polypiperazine amide membrane (M5), it is demonstrated that the DAPTB monomer was successfully introduced and participated in the interfacial polymerization reaction, and the evolution of the chemical structure during the cross-linking and activation process is verified.

[0091] The vertical lines in the figure mark two key characteristic absorption peaks, located at approximately 1662 cm⁻¹. -1 and 1587cm -1 Place.

[0092] 1662 cm -1 The nearby peaks usually correspond to the amide I band (C=O stretching vibration).

[0093] 1587 cm -1 The nearby peaks typically correspond to the amide II band (coupled NH bending vibration and CN stretching vibration).

[0094] These two peaks are a sign of successful formation of the polyamide (PA) separation layer.

[0095] The spectra of M1 through M5 are all at 1662 cm⁻¹. -1 and 1587 cm -1 The presence of a distinct amide characteristic peak strongly demonstrates that the present invention successfully generated a polyamide separation layer on a polyimide substrate through interfacial polymerization.

[0096] By comparing the spectra of M3 (with β-CD) and M4 (without β-CD), differences in the intensity or shape of the amide peak can be observed. This indirectly indicates that the addition of β-CD affects the enrichment degree of DAPTB on the membrane surface, thereby changing the chemical structure or crosslinking density of the final polyamide separation layer, confirming the mechanism of this invention, "using β-CD to promote DAPTB segregation".

[0097] Figure 3 The images show a comparison of the surface morphology of the organic solvent nanofiltration membrane prepared in this embodiment of the invention before and after immersion in DMF (N,N-dimethylformamide) for 30 days using scanning electron microscopy (SEM).

[0098] By comparing the membrane of the present invention with added β-CD (M3, corresponding to...) Figure 3 (a1, a2) and the comparative sample membrane without β-CD (M4, corresponding to...) Figure 3 (b1, b2) and conventional polypiperazine amide membrane (M5, corresponding to b ... Figure 3 The surface morphology changes of c1 and c2 after immersion in a strongly polar solvent directly verify that the membrane prepared by this invention has superior dimensional stability and swelling resistance in aprotic strongly polar solvents, proving its structural stability during long-term operation. It also further illustrates that the introduction of β-CD helps to form a separation layer with a better structure and more stable structure, thereby further improving the long-term stability of the membrane.

[0099] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a novel high-flux, high-selectivity organic solvent nanofiltration membrane, characterized in that, Includes the following steps: (1) Mix 3,3'-bis(4-aminophenyl)-Tellerg base monomer, trifluoroacetic acid and polar solvent, and stir at low temperature to form a homogeneous solution; (2) Add polyimide and the remaining polar solvent to the homogeneous solution in step (1), stir at room temperature, add β-cyclodextrin, and continue stirring until the solution is uniform and clear. Then let it stand to remove bubbles and obtain the casting solution. (3) The casting solution from step (2) is scraped onto a nonwoven fabric and then immersed in a water coagulation bath for non-solvent-induced phase transformation. After that, the film surface is rinsed with deionized water to remove impurities and then air-dried to obtain a polyimide-supported substrate film with a surface rich in 3,3'-bis(4-aminophenyl)-Tellerg base monomer. (4) Pour the organic phase solution containing polyacryl chloride monomers evenly onto the polyimide support substrate obtained in step (3) with a surface rich in 3,3'-bis(4-aminophenyl)-Tellerg base monomers, and carry out interfacial polymerization reaction. After the reaction, remove the excess organic phase solution, and then soak and wash it in anhydrous ethanol to obtain the initial nanofiltration membrane. (5) The initial nanofiltration membrane obtained in step (4) is immersed in a 1,6-hexanediamine / alcohol solution for crosslinking reaction, and then immersed in an N,N-dimethylformamide solution for activation, and finally a novel high-flux and high-selectivity organic solvent nanofiltration membrane is obtained.

2. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: In steps (1) and (2), the weight percentages of 3,3'-bis(4-aminophenyl)-teleg base monomer, trifluoroacetic acid, β-cyclodextrin, polyimide, and polar solvent in the casting solution are calculated as 100% by weight: 0.5–2 wt% of 3,3'-bis(4-aminophenyl)-teleg base monomer; Trifluoroacetic acid 0.85–3.4 wt%; β-Cyclodextrin 0.05–0.19 wt%; 15-20 wt% polyimide; Balance of polar solvent.

3. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: The molar ratio of the 3,3'-bis(4-aminophenyl)-teleg base monomer to trifluoroacetic acid is 1:4 to 1:

8.

4. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: The polar solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone.

5. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: The low temperature mentioned in step (1) is -10 to -20°C, and the stirring time is 1 to 2 hours; the stirring time after adding β-cyclodextrin in step (2) is 6 to 12 hours; the standing degassing time is 6 to 24 hours.

6. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: In step (3), the air-drying time after phase transformation is 5 to 20 minutes; the time for non-solvent-induced phase transformation is 30 to 300 seconds; and the air-drying time is 5 to 20 minutes.

7. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: In step (4), the polyacrylamide chloride monomer is one or any combination of two of isophthaloyl chloride, biphenyltetracarboxylic chloride, trimesoyl chloride or phthaloyl chloride, and the concentration of polyacrylamide chloride monomer in the organic phase solution containing the polyacrylamide chloride monomer is 0.05 to 0.35 w / v.

8. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: In step (4), the organic solvent in the organic phase solution of the polyacrylamide chloride monomer is one or any combination of two of the solvent oil Isopar G, cyclohexane, n-hexane or n-heptane, and the reaction time of the interfacial polymerization reaction is 5 to 60 seconds.

9. The method for preparing the novel high-flux, high-selectivity organic solvent nanofiltration membrane as described in claim 1, characterized in that: In step (5), the concentration of the 1,6-hexanediamine / alcohol solution is 2.5 to 12.5 wt%, the crosslinking reaction time in the 1,6-hexanediamine / alcohol solution is 10 to 40 minutes, and the crosslinking reaction is carried out at 40 to 80°C; the activation time of the N,N-dimethylformamide solvent is 2 to 10 minutes; in step (5), the alcohol is any one of isopropanol, ethanol, or methanol.

10. The novel high-flux, high-selectivity organic solvent nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 9, characterized in that, It includes a porous polyimide support layer and a telage-containing polyamide separation layer bonded to its surface. The polyimide support layer is crosslinked and modified with a 1,6-hexanediamine / alcohol solution, and the separation layer is incorporating a rigid V-shaped network structure formed by the polymerization of DAPTB monomers enriched by β-cyclodextrin segregation.

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