A high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane and a preparation method thereof

Abstract

This invention belongs to the field of membrane material technology and discloses a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane and its preparation method. The method includes: (1) coating an aqueous solution containing cyclic tertiary nitrogen oligomers onto a porous support substrate membrane, wetting it, and then removing excess liquid; (2) subsequently coating the surface of the material obtained in step (1) with a hexane solution containing benzyl bromide, wetting it so that the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomers undergo a quaternization reaction with the benzyl bromide, gradually forming a dense separation membrane at the water-hexane interface; after the reaction is completed, it is dried to obtain the nanofiltration membrane. The nanofiltration membrane prepared by this invention overcomes the disadvantages of traditional polyquaternary ammonium membranes, which require several hours to prepare and have low permeability. A defect-free nanofiltration separation membrane can be prepared in just 1 minute. After soaking in 1M sulfuric acid for 30 days, it can still maintain high permeability and rejection rate, showing good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, and more specifically, relates to a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane and its preparation method. Background Technology

[0002] The rapid development of industries such as new energy and microelectronics has generated a large amount of waste acid, which is rich in precious metal ions such as cobalt, nickel, manganese, and lithium. This not only causes serious environmental pollution but also leads to the waste of valuable resources. Nanofiltration, as a pressure-driven membrane separation technology, has advantages such as being environmentally friendly, highly efficient, and without phase change, and has been widely used in ion separation processes such as lithium extraction from salt lakes and the chlor-alkali industry. However, traditional nanofiltration membranes are mostly polyamide structures, and their amide bonds are prone to hydrolysis in strong acid environments, resulting in poor membrane stability and a sharp decline in separation performance.

[0003] Polyquaternary ammonium membranes are formed by interfacial quaternization reactions of tertiary amines and halogen atoms, with CN as the base material. + The cross-linked network of bonds exhibits good acid resistance and high divalent cation rejection. However, the quaternization reaction rate is much lower than that of the traditional amidation reaction, typically requiring several hours to form a defect-free separation layer, severely restricting its industrial-scale production. More importantly, as the reaction time increases, the membrane thickness continuously increases, leading to a corresponding increase in mass transfer resistance and a significant decrease in membrane permeability. This is because the tertiary amines used in existing technologies are mostly small molecule compounds, each containing only 2–3 reaction sites, and the nitrogen atom is often surrounded by alkyl groups, resulting in significant steric hindrance. This makes the quaternization reaction kinetics slow, making it difficult to form a dense network in a short time. For example, the literature (Adv. Funct. Mater. 2023, 33, 2300183) reports a polyquaternary ammonium membrane prepared by interfacial polymerization of pentamethyldiethylenetriamine and 1,3,5-tribromomethylbenzene. Although it remained stable after being immersed in 1.5 M sulfuric acid for 28 days, the reaction time was as long as 24 hours. Patent CN120079267A discloses a method for preparing polyquaternary ammonium nanofiltration membranes based on the Menshutkin reaction interfacial polymerization. The method involves dissolving a surfactant in an aqueous solution of tris(2-dimethylaminoethyl)amine as the aqueous phase and using a heptane solution of 1,3,5-tris(bromomethyl)benzene as the oil phase to construct an ultrathin polyquaternary ammonium separation layer on the bottom membrane surface. Although the resulting membrane has good acid resistance, the reaction time still requires 4 hours.

[0004] In summary, the existing technology still lacks a rapid method for preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method for high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane, which solves the difficulties of long preparation time and low membrane permeability of traditional polyquaternary ammonium membranes.

[0006] To achieve the above objectives, in one aspect of the present invention, a method for rapidly preparing a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane is provided, comprising the following steps: (1) Coat the porous support substrate with an aqueous solution containing cyclic tertiary nitrogen oligomers, and after wetting, remove the excess liquid; (2) Subsequently, the surface of the material obtained in step (1) is coated with a hexane solution containing benzyl bromide compound, and the wetting causes the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomer to undergo a quaternization reaction with the benzyl bromide compound, and a dense separation membrane is gradually formed at the water-hexane interface; after the reaction is completed, it is dried to obtain a nanofiltration membrane. The structural formula of the cyclic tertiary nitrogen oligomer is shown in general formula (1): Equation (1); The cyclic tertiary nitrogen ring structure in the cyclic tertiary nitrogen oligomer is selected from one of imidazole, pyridine, quinoline, triazole, bipyridine, carbonyl diimidazole, triethylenediamine, and hexamethylenetetramine; wherein, the value of n is 15~50; The structure of the benzyl bromide-containing compound is shown in general formula (2): Equation (2); where m takes values ​​from 2 to 4.

[0007] Preferably, the cyclic tertiary nitrogen oligomer is one of formulas (3) to (10): Equation (3); Equation (4); Equation (5); , Equation (6); Equation (7); Equation (8); Equation (9); Equation (10).

[0008] Preferably, the benzyl bromide-containing compound is one of formulas (11) to (13): , Equation (11); Equation (12); Equation (13).

[0009] Preferably, in step (1), the mass concentration of the cyclic tertiary nitrogen oligomer in the aqueous solution of the cyclic tertiary nitrogen oligomer is 1-3 wt%, the pH is 5-7, and the soaking time is 1-10 min; the pH is preferably 5.

[0010] Preferably, in step (2), the mass concentration of the benzyl bromide compound in the hexane solution containing the benzyl bromide compound is 0.2 to 0.5 wt%.

[0011] Preferably, in step (2), the soaking time is 0.5 to 2 min.

[0012] Preferably, the preparation of the cyclic tertiary nitrogen oligomer includes the following steps: dissolving the substrate and azobisisobutyronitrile in dimethyl sulfoxide, reacting under vacuum, precipitating the product from ethyl acetate, filtering, washing, and vacuum drying to obtain the cyclic tertiary nitrogen oligomer; wherein the substrate is a cyclic tertiary nitrogen containing a double bond.

[0013] Preferably, the porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

[0014] In another aspect of the present invention, a polyquaternary ammonium nanofiltration membrane prepared according to the method described above is provided.

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. This invention designs cyclic tertiary nitrogen oligomers as aqueous monomers and uses interfacial polymerization to cause the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomers to undergo quaternization with benzyl bromide, gradually forming a dense separation membrane at the water-n-hexane interface. This can rapidly form a defect-free polyquaternary ammonium separation layer in about 1 minute, while traditional methods usually take several hours or even tens of hours, which is difficult to meet the efficiency requirements of industrial production.

[0016] 2. The polyquaternary ammonium nanofiltration membrane obtained by this invention has a permeation flux of 7.2~11.6 L / m³. -2 h -1 bar -1 For divalent ions (such as Mg) 2+ The rejection rate is 93.7%~98.1%. After soaking in 1 M sulfuric acid for 30 days, the rejection rate still remains above 94%, overcoming the bottleneck of existing polyquaternary ammonium membranes that cannot simultaneously achieve high throughput and high acid resistance.

[0017] 3. The preparation method is highly compatible with the interfacial polymerization process of existing commercial nanofiltration membranes and has good potential for large-scale production. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the mechanism of the quaternization reaction between the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomer and the benzyl bromide compound in this invention.

[0019] Figure 2 The diagram shows the synthesis of polyvinylimidazolium in Example 1 of this invention, along with its 1H NMR spectrum (a) and gel permeation chromatogram (b).

[0020] Figure 3 This invention, in Example 1, describes the changes in membrane permeability, magnesium chloride rejection rate, infrared spectroscopy, and surface morphology after immersion in 20wt% hydrochloric acid for 30 days; wherein, Figure 3 In the diagram, a represents membrane permeability data, b represents magnesium chloride rejection rate change data, c represents surface morphology at day 0, and d represents surface morphology at day 30. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] To achieve the above objectives, the technical solution of the present invention is as follows: First, this invention provides a method for preparing a high-flux acid-resistant nanofiltration membrane, comprising the following steps: (1) Coat the porous support membrane with an aqueous solution containing cyclic tertiary nitrogen oligomers, soak it for a period of time, remove the liquid and let it dry until there are no droplets visible to the naked eye.

[0023] (2) Subsequently, a hexane solution containing benzyl bromide is coated onto the surface of the material obtained in step (1). This wetting process causes the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomer to undergo a quaternization reaction with the benzyl bromide, gradually forming a dense separation film at the water-hexane interface. Excess liquid on the surface is then removed. At this point, as... Figure 1 As shown, the wetting process involves an interfacial polymerization reaction.

[0024] (3) Then the membrane obtained in step (2) is dried in an oven to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0025] Preferably, the cyclic tertiary nitrogen oligomer structure is as shown in general formula (1): Equation (1); The cyclic structure of the cyclic tertiary nitrogen in the cyclic tertiary nitrogen oligomer is selected from one of imidazole, pyridine, quinoline, triazole, bipyridine, carbonyl diimidazole, triethylenediamine, and hexamethylenetetramine; and the value of n is 15 to 50 (corresponding to a number average molecular weight of 1440 to 4800), with a preferred range of 20 to 30.

[0026] Preferably, the structure of the benzyl bromide compound is shown in general formula (2): Equation (2); where m is 2 to 4.

[0027] Preferably, the cyclic tertiary nitrogen oligomer is any one of formulas (3) to (10), wherein, Equation (3); Equation (4); Equation (5); , Equation (6); Equation (7); Equation (8); Equation (9); Equation (10).

[0028] Preferably, the benzyl bromide compound is any one of formulas (11) to (13), wherein, , Equation (11); Equation (12); Equation (13).

[0029] Preferably, the aqueous solution of the cyclic tertiary nitrogen oligomer has a mass concentration of 1–3 wt%, a soaking time of 1–10 min, and a pH of 5–7, preferably 5.

[0030] Preferably, the concentration of the hexane solution containing benzyl bromide is 0.2–0.5 wt%, and the soaking time is 0.5–2 min.

[0031] Preferably, the porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

[0032] Preferably, the drying temperature in the oven is 50–70 °C and the drying time is 10–20 min.

[0033] Preferably, the synthesis of the cyclic tertiary nitrogen oligomers used in this invention is shown in schematic diagram a. The substrate and azobisisobutyronitrile (AIBN) are dissolved in dimethyl sulfoxide and reacted under vacuum at 80°C for 12 h. The product is precipitated from ethyl acetate, filtered, washed, and dried under vacuum to obtain the oligomer. The substrate is a cyclic tertiary nitrogen containing a double bond, specifically 1-vinylimidazolium, 1-vinylpyridine, 5-vinylquinoline, 1-vinyltriazole, 1-vinylbipyridine, 1-vinylcarbonyldiimidazole, 1-vinyltriethylenediamine, or 1-vinylhexamethylenetetramine.

[0034] The present invention also provides a polyquaternary ammonium nanofiltration membrane prepared according to any one of the above methods.

[0035] The following specific embodiments further illustrate the preparation method of the high-throughput acid-resistant nanofiltration membrane of this application.

[0036] Example 1 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0037] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0038] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0039] The preparation of polyvinylimidazole is as follows: 1-vinylimidazole and AIBN are dissolved in DMSO, and the mixture is reacted under vacuum at 80°C for 12 h. The reaction solution is added dropwise to ethyl acetate, filtered, washed with ethyl acetate, and dried under vacuum to obtain polyvinylimidazole with a yield of 95%. Figure 2 The NMR spectrum and gel permeation chromatography of polyvinyl imidazole indicate that the product has been successfully synthesized, with a number-average molecular weight of 2770 Da.

[0040] .

[0041] Example 2 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinylpyridine aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0042] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0043] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0044] Example 3 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyltriazole aqueous solution was coated onto a polysulfone support membrane. The solution had a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0045] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0046] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0047] Example 4 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane. The solution had a mass fraction of 3 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was air-dried.

[0048] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0049] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0050] Example 5 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0051] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.5 wt%, and immerse for 1 min. Then remove the liquid.

[0052] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0053] Example 6 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0054] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 3 min. Then remove the liquid.

[0055] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0056] Example 7 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polyacrylonitrile support membrane. The solution had a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0057] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0058] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0059] Example 8 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0060] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0061] (3) The membrane was placed in an oven to dry at 80°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0062] Example 9 A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, the specific process of which is as follows: (1) A polyvinyl imidazole aqueous solution was coated onto a polysulfone support membrane with a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was dried.

[0063] (2) Coat the membrane surface with a hexane solution of 1,4-p-phenylenedibenzyl bromide, with a mass fraction of 0.2 wt%, and a wetting time of 1 min. Then remove the liquid.

[0064] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain a high-flux, acid-resistant polyquaternary ammonium nanofiltration membrane.

[0065] Comparative Example 1 (1) A pentamethyldiethylenetriamine aqueous solution was coated onto a polysulfone support membrane. The solution had a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was air-dried.

[0066] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and immerse for 1 min. Then remove the liquid.

[0067] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain control membrane 1.

[0068] Comparative Example 2 (1) A pentamethyldiethylenetriamine aqueous solution was coated onto a polysulfone support membrane. The solution had a mass fraction of 1 wt%, a pH of 5, and a wetting time of 3 min. The liquid was then removed and the membrane was air-dried.

[0069] (2) Coat the membrane surface with a hexane solution of 1,3,5-tribromomethylbenzene, with a mass fraction of 0.2 wt%, and soak for 8 hours. Then remove the liquid.

[0070] (3) The membrane was placed in an oven to dry at 50°C for 10 min to obtain control membrane 2.

[0071] The chemical structures of the aqueous and organic phase monomers in Examples 1-9 and Comparative Examples 1-2 are shown in Table 1. The formulations, including concentrations and reaction times, are shown in Table 2. The ion separation performance test results of the nanofiltration membranes prepared in the above examples and comparative examples are shown in Figures 3.

[0072] Table 1: Monomer structures of Examples 1-9 and Comparative Examples 1-2

[0073] The preparation methods of the cyclic tertiary nitrogen oligomers involved in Examples 2-9 are consistent with the method for preparing polyvinylimidazole in Example 1, except that the substrates are replaced with 1-vinylpyridine and 1-vinyltriazole, respectively. The successful preparation of the cyclic tertiary nitrogen oligomers involved in Examples 2-9 was verified by the same testing methods.

[0074] Table 2: Membrane preparation conditions of Examples 1-9 and Comparative Examples 1-2

[0075] Nanofiltration performance of the nanofiltration membranes prepared in Examples 1-9 and Comparative Examples 1-2 was tested. The test mode was cross-flow, and the shear flow rate was 0.5 L / min. Test conditions: 1000 ppm magnesium chloride solution, test pressure and temperature were 6 bar and 30°C, respectively. Permeability (J ), retention rate ( R The calculation formula is as follows:

[0076] in, S The effective test area of ​​the membrane (m²) 2 ), t The operation time is in seconds. V for t The volume of liquid permeating within a time interval (L) is given, and p is the instrument operating pressure (bar).

[0077]

[0078] in, C f and C p These are the solute concentrations of the feed liquid and the permeate, respectively.

[0079] Membrane acid resistance test: The membrane was immersed in 1M sulfuric acid solution, and the solution was changed every two days. After a certain period of time, the membrane was taken out and repeatedly washed with deionized water. Then the membrane was immersed in deionized water for 24 hours. After that, it was taken out and nanofiltration test was performed.

[0080] The test results are shown in Table 3 below.

[0081] Table 3: Test Results Table

[0082] Examples 1-3, using oligomers containing imidazole, pyridine, and triazole rings respectively, prepared polyquaternary ammonium membranes. All three formed a defect-free separation layer within 1 minute, demonstrating the good versatility of the cyclic tertiary nitrogen design of this invention. Among them, the polyvinylimidazolium containing the imidazole ring (Example 1) exhibited the best overall performance, with a permeation flux of 8.6 L / m³. -2 h -1 bar -1 The retention rate was 97.2%.

[0083] Examples 4-6 further optimized the preparation conditions: aqueous phase concentration (1-3 wt%), organic phase concentration (0.2-0.5 wt%), and reaction time (1-3 min), determining the optimal process window. Examples 7-8 verified the applicability of different substrate membrane types (polyacrylonitrile) and drying temperatures (80°C). In Example 9, when using the dibenzyl bromide monomer (1,4-p-dibenzyl bromide), the membrane rejection rate decreased slightly (93.7%), indicating that the tribenzyl bromide structure (1,3,5-tribromomethylbenzene) is more conducive to the formation of a dense network.

[0084] Table 3 shows that: Comparative Example 1, using a small molecule amine (pentamethyldiethylenetriamine), showed almost no separation performance (retention rate of only 0.7%) at the same reaction time (1 min), indicating that the small molecule amine cannot form an effective separation layer in a short time; Comparative Example 2, after extending the reaction time to 8 h, although the retention rate increased to 94.2%, the permeation flux decreased to 1.2 L m. - 2 h -1 bar -1 In contrast, Example 1 of this invention uses an oligomer containing an imidazole ring, which can achieve a high retention rate (97.2%) and a high permeation flux (8.6 L m) within 1 min. -2 h -1 bar -1 Significant technological progress has been made.

[0085] This is because the quaternization reaction is slow; when the reaction time is only 1 minute, the membrane is not yet fully formed. As the reaction time increases, the membrane thickness gradually increases, eventually leading to a dense and thick membrane with decreased permeability. This invention uses oligomers as the aqueous phase molecules and selects cyclic tertiary amines with low steric hindrance as reaction sites, significantly increasing the reaction probability between tertiary nitrogen and benzyl bromide. This results in the formation of a dense cross-linked network in a very short time, overcoming the technical bottleneck of traditional polyquaternary ammonium membrane preparation where efficiency and separation performance are difficult to achieve simultaneously.

[0086] The acid resistance stability of the film prepared in Example 1 was further investigated. Figure 3 As shown in Figure a, after the membrane was immersed in 1 M sulfuric acid for 30 days, its rejection rate for magnesium chloride remained above 95%, and the permeation flux remained at ~9 L / m². -2 h -1 bar -1 .like Figure 3 As shown in Figure bd, infrared spectroscopy reveals no significant change in the chemical structure of the membrane before and after immersion, while scanning electron microscopy indicates that the membrane surface remains smooth, dense, and free of obvious defects. These results demonstrate that the polyquaternary ammonium nanofiltration membrane prepared in this invention exhibits excellent acid resistance and is suitable for the separation and recovery of noble metal ions in strongly acidic environments.

[0087] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes, characterized in that, Includes the following steps: (1) Coat the porous support substrate with an aqueous solution containing cyclic tertiary nitrogen oligomers, and after wetting, remove the excess liquid; (2) Subsequently, the surface of the material obtained in step (1) is coated with a hexane solution containing benzyl bromide compound, and the wetting causes the tertiary nitrogen atoms on the cyclic tertiary nitrogen oligomer to undergo a quaternization reaction with the benzyl bromide compound, and a dense separation membrane is gradually formed at the water-hexane interface; after the reaction is completed, it is dried to obtain a nanofiltration membrane. The structural formula of the cyclic tertiary nitrogen oligomer is shown in general formula (1): Equation (1); The cyclic tertiary nitrogen ring structure in the cyclic tertiary nitrogen oligomer is selected from one of imidazole, pyridine, quinoline, triazole, bipyridine, carbonyl diimidazole, triethylenediamine, and hexamethylenetetramine; wherein, the value of n is 15~50; The structure of the benzyl bromide-containing compound is shown in general formula (2): Equation (2); where m takes values ​​from 2 to 4.

2. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, The cyclic tertiary nitrogen oligomer is one of formulas (3) to (10): Equation (3); Equation (4); Equation (5); , Equation (6); Equation (7); Equation (8); Equation (9); Equation (10).

3. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, The benzyl bromide compound is one of formulas (11) to (13): , Equation (11); Equation (12); Equation (13).

4. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, In step (1), the mass concentration of the cyclic tertiary nitrogen oligomer in the aqueous solution is 1-3 wt%, the pH is 5-7, and the soaking time is 1-10 min; the pH is preferably 5.

5. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, In step (2), the mass concentration of the benzyl bromide compound in the hexane solution containing the benzyl bromide compound is 0.2 to 0.5 wt%.

6. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, In step (2), the soaking time is 0.5 to 2 minutes.

7. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, In step (2), the drying film formation conditions are: drying temperature of 50-70℃ and time of 10-20 min.

8. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, The preparation of the cyclic tertiary nitrogen oligomer includes the following steps: dissolving the substrate and azobisisobutyronitrile in dimethyl sulfoxide, reacting under vacuum, precipitating the product from ethyl acetate, filtering, washing, and vacuum drying to obtain the cyclic tertiary nitrogen oligomer; wherein the substrate is a cyclic tertiary nitrogen containing a double bond.

9. The method for rapidly preparing high-flux, acid-resistant polyquaternary ammonium nanofiltration membranes according to claim 1, characterized in that, The porous support substrate is a polysulfone membrane, a polyethersulfone membrane, or a polyacrylonitrile membrane.

10. The polyquaternary ammonium nanofiltration membrane prepared by the method according to any one of claims 1-9.

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