A high-flux nanofiltration membrane element for drinking water purification and a preparation method thereof

Abstract

The application discloses a high-flux nanofiltration membrane element for drinking water purification and a preparation method thereof, and belongs to the technical field of water treatment membrane separation. The method comprises the following specific steps: a membrane piece prepared by interface polymerization of a piperazine-benzene tricarboxylic acid chloride system is rolled into a 1812 type assembly, a water solution containing specific ions is introduced by using a peristaltic pump, and the circulation treatment is carried out at 30-90 DEG C for 1-30 minutes. The ion-dipole interaction between ions and polyamide segments is used to induce controllable expansion of the segments, so that a loose structure with a pore size of 0.8-1.5 nm is formed; meanwhile, the water bath and the weak alkaline environment promote the hydrolysis of residual acyl chloride into carboxyl, and the negative electric property of the membrane surface is improved; the prepared assembly has a rejection rate of new pollutants with a molecular weight of 200-500 Da of greater than or equal to 95%, a rejection rate of Ca 2+ , Mg 2+ of less than or equal to 30%, a pure water flux of greater than or equal to 20 L·m ‑2 ·h ‑1 ·bar ‑1 (0.4 MPa), and a running flux attenuation of less than 5% in 120 hours. The method does not need to disassemble the assembly and does not need organic solvents, and is simple, green and environment-friendly, and is suitable for industrialized batch treatment, and provides a reference for high-quality drinking water deep purification by using the nanofiltration membrane method.

Description

Technical Field

[0001] This invention belongs to the field of water treatment membrane separation technology, specifically relating to a high-flux nanofiltration membrane element for drinking water purification and its preparation method. Background Technology

[0002] With the continuous development of society and the economy, people have placed higher demands on drinking water quality. High-quality drinking water must meet the following requirements: it must be free from pollution, pathogens, heavy metals, and harmful chemicals; its hardness must be moderate, and it must contain natural minerals and trace elements needed by the human body. Trace organic pollutants such as endocrine disruptors, antibiotics, perfluorinated compounds, and disinfection byproducts in water bodies are receiving increasing attention due to their variety, difficulty in degradation, and teratogenic and carcinogenic hazards. For high-quality drinking water, the presence of hardness ions (…) in the water body… Mg 2+ Low levels of organic pollutants and total dissolved solids (TDS) are detrimental to the taste and health of drinking water. Healthy and safe drinking water should remove as many organic micro-pollutants as possible while retaining a certain concentration of organic pollutants. Mg 2+ Ions and other mineral elements. However, achieving high pollutant removal and low... Mg 2+ The goal of ion retention poses a serious challenge to conventional advanced drinking water treatment processes that rely primarily on degradation and adsorption. There is an urgent need to develop safe and efficient selective separation technologies that offer high levels of decontamination and low levels of hardness removal to ensure the demand for high-quality drinking water treatment.

[0003] Nanofiltration is an emerging drinking water treatment technology that shows promising application prospects in areas such as micro-pollutant removal and ion separation. As the core of nanofiltration technology, the nanofiltration membrane has a pore size of approximately 1 nm and a charged surface. It achieves selective separation of target precipitates through pore size sieving caused by physical pores and the Dornan effect generated by membrane surface charge. Currently, many commercial nanofiltration membranes (such as Dow NF90 and NF270) exhibit good removal efficiency (>80%) for micro-pollutants with higher molecular weights (>400 Da), but their effectiveness in removing water-borne micro-pollutants remains limited. Mg 2+ The ion removal rate is also high (>80%). This poses many problems for nanofiltration in drinking water treatment. Besides affecting drinking water health, the hardness ion content is also closely related to the chemical stability of water. Too low a hardness ion concentration can lead to increased corrosivity of the water. To maintain the health and chemical stability of nanofiltration permeate, remineralization is usually required, thus increasing investment and operating costs. Furthermore, nanofiltration membranes... Mg 2+The high efficiency of ion retention also increases the risk of fouling from sparingly soluble salts on the membrane surface, thereby increasing operating energy consumption and membrane fouling control costs. Therefore, developing high-flux nanofiltration membranes with "high decontamination and low hardness removal" is of great significance for promoting the application of nanofiltration technology in the field of advanced drinking water treatment.

[0004] To overcome this technological bottleneck, researchers have conducted extensive studies on membrane structure design, monomer modification, and interfacial polymerization process optimization. Regarding membrane structure design, CN119075715A introduces a hydrophobic interlayer between the porous base membrane and the filter layer to prevent skin collapse; CN118615865A further constructs a composite layer containing metal compounds and polyphenol monomers on a polyamide layer; and CN118320619B uses a hydrophilic polymerized layer and metal nanoparticles to construct a hydrophilic modified layer. In terms of monomer modification, CN120268258A adds tryptophan to a piperazine aqueous solution to adjust the monomer diffusion rate; and CN121130675A uses polyphenol monomers and polyamine monomers with rigid twisted structures for interfacial polymerization to achieve a narrow pore size distribution. Regarding interfacial polymerization process optimization, CN119701671A optimizes the active layer structure by adding cyclodextrin compounds to the aqueous phase and combining it with secondary interfacial polymerization technology. The above-mentioned research has made some progress in improving the retention performance of nanofiltration membranes for new pollutants.

[0005] However, the aforementioned methods generally suffer from problems such as complex processes, difficulty in dispersing nanomaterials, and the inability to balance flux and selectivity. For example, methods that introduce hydrophobic interlayers, nanomaterial composite layers, or multilayer structures generally involve complex processes, multi-step reactions, and difficulties in dispersing nanomaterials. Furthermore, the introduction of interlayers or composite layers increases membrane thickness and mass transfer resistance, leading to a decrease in water flux. In addition, while process optimization methods such as secondary interfacial polymerization can improve selectivity, they increase process complexity and production cycle, which is not conducive to industrial scale-up. Moreover, most of these existing technologies focus on the membrane fabrication stage, making it difficult to directly process membrane modules, thus lacking simple and effective post-processing methods at the module scale.

[0006] In conclusion, developing a novel nanofiltration technology that is simple to implement, allows for precise control of component dimensions, and can balance high throughput with "high decontamination and low hardening" is of significant engineering value for promoting the application of nanofiltration in the field of advanced drinking water treatment. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a high-flux nanofiltration membrane element for drinking water purification and its preparation method. Performance regulation is achieved through a one-step post-treatment cycle of the pre-formed membrane module. Specifically, this invention uses an ion-soluble aqueous solution that strongly interacts with the membrane to treat the nanofiltration membrane module under mild conditions. On one hand, the ion-dipole interaction between ions and polyamide segments induces controlled expansion and structural relaxation of the segments, forming a loose separation layer with increased pore size and reduced cross-linking density, thereby significantly improving the membrane element flux and reducing the hardness ion rejection rate. On the other hand, the water bath heating and the weakly alkaline environment (pH 7.5~9.0) provided by the ion-soluble aqueous solution synergistically promote the hydrolysis of residual acyl chloride groups on the membrane surface into carboxyl groups, increasing the negative charge of the membrane surface and enhancing the electrostatic repulsion of negatively charged new pollutants. Through this dual mechanism, this invention achieves a synergistic improvement in nanofiltration membrane element flux, new pollutant rejection rate, and salt ion selectivity, effectively solving the technical challenges of balancing flux and selectivity, complex processes, and limited controllability of membrane elements in existing technologies.

[0008] To solve the above-mentioned technical problems, the present invention specifically adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a high-flux nanofiltration membrane element for drinking water purification, comprising the following steps:

[0010] S1: The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module (2).

[0011] S2: A peristaltic pump (1) is used to introduce an aqueous solution (4) of ions that strongly interact with the membrane into the spiral wound nanofiltration membrane module. The module is then circulated under heating conditions to obtain a circulated nanofiltration membrane module. The ions that strongly interact with the membrane include inorganic anions, organic anions, and cations. The inorganic anions are selected from... , , , , Any one of the following; the organic anion is selected from any one of trifluoroacetate, benzoate, and p-toluenesulfonate; the organic cation is selected from any one of tetramethylammonium, tetraethylammonium, and tetrabutylammonium;

[0012] S3: Clean the nanofiltration membrane module after the recycling process to obtain the high-flux nanofiltration membrane element.

[0013] Further, in step S1, the polyamide composite nanofiltration membrane is prepared by the following method: immersing the base membrane in an aqueous solution containing amine monomers, then immersing it in an oil solution containing acyl chloride monomers, and after the reaction is completed, removing it and air-drying it to obtain the polyamide nanofiltration membrane.

[0014] Further, the base membrane is selected from polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, or polyvinylidene fluoride ultrafiltration membrane; the amine monomer is selected from piperazine, polyethyleneimine, or m-phenylenediamine, with a concentration of 0.2 wt% to 0.4 wt%; the acyl chloride monomer is selected from pyromellitic acid tricarboxylate chloride or isophthaloyl chloride, with a concentration of 0.1 wt% to 0.3 wt%.

[0015] Furthermore, in step S2, the heating conditions are at a temperature of 30~90℃ and a time of 1~30 minutes.

[0016] Furthermore, in step S2, the concentration of the ions that have a strong interaction with the membrane is 0.01~3 mol / L.

[0017] Furthermore, in step S2, the ionic aqueous solution that strongly interacts with the membrane is weakly alkaline, which, while inducing the loosening of chain segments, promotes the hydrolysis of residual acyl chloride groups on the membrane surface into carboxyl groups.

[0018] Secondly, the present invention provides a high-throughput nanofiltration membrane element prepared according to the above method.

[0019] Furthermore, the prepared nanofiltration membrane element exhibits selective separation characteristics of high decontamination and low hardness removal:

[0020] (a) Retention rate of ≥95% for new pollutants with molecular weight in the range of 200–500 Da;

[0021] (b) Hardness ions The retention rate is ≤30%.

[0022] Furthermore, the prepared nanofiltration membrane module has an average pore size of 0.8–1.5 nm and a pure water flux ≥80. .

[0023] Thirdly, the present invention also provides an application of the high-throughput nanofiltration membrane element in the field of selective separation of new pollutants and salt ions.

[0024] Compared with the prior art, the present invention has the following outstanding advantages:

[0025] (1) The present invention has the advantages of being extremely simple and environmentally friendly. By selecting different ion types and concentrations, the membrane pore size can be precisely controlled in the range of 0.6~1.8 nm. Moreover, only one recycling process is required after the component is rolled up. There is no need to disassemble the component or introduce organic solvents or nanomaterials, which makes it easy to process in batches for industrial use.

[0026] (2) The high-flux nanofiltration membrane element prepared can efficiently retain new pollutants while allowing hardness ions to pass through. The retention rate of new pollutants with molecular weight in the range of 200~500 Da is ≥95%, and the retention rate of hardness ions Ca2+ is ≥95%. 2+ Mg 2+ With a retention rate of ≤30%, the selective separation target of "high decontamination and low hardness removal" has been achieved.

[0027] (3) The flux of the high-flux nanofiltration membrane element prepared is 50-100% higher than that of the traditional nanofiltration membrane element, and the pure water flux is ≥80 L·m -2 ·h -1 . Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the use of an ion-rich aqueous solution with strong interactions with the membrane to regulate the performance of a nanofiltration membrane element;

[0029] Figure 2 This is a graph showing the effect of different post-processing methods and ion types on the flux of nanofiltration membrane elements.

[0030] Figure 3 This is a graph showing the effect of different post-treatment methods and ion types on the tetracycline rejection rate and calcium ion rejection rate of nanofiltration membrane elements.

[0031] Figure 4 This is a graph showing the effect of different NaI concentrations on the flux of nanofiltration membrane elements;

[0032] Figure 5 This is a graph showing the effect of different NaI concentrations on the tetracycline rejection rate and calcium ion rejection rate of nanofiltration membrane elements.

[0033] Figure 6 This is a graph showing the effect of different heat treatment temperatures on the flux of nanofiltration membrane elements;

[0034] Figure 7 This is a graph showing the effect of different heat treatment temperatures on the tetracycline rejection rate and calcium ion rejection rate of nanofiltration membrane elements.

[0035] Figure reference numerals: 1-peristaltic pump, 2-spiral wound nanofiltration membrane module, 3-heater, 4-ionic aqueous solution that strongly interacts with the membrane. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that, unless otherwise specified, the features in the following embodiments and implementation methods can be combined with each other.

[0038] In a first aspect, the present invention proposes a method for preparing a high-flux nanofiltration membrane element for drinking water purification, and a schematic diagram of the performance regulation of the high-flux nanofiltration membrane element is shown below. Figure 1 As shown, performance regulation is achieved by performing a one-step cyclic post-treatment on the polyamide composite nanofiltration membrane. The high-flux nanofiltration membrane element can efficiently retain trace organic pollutants in water while allowing hardness ions to pass through.

[0039] The control principle employed in this invention is as follows: By treating the polyamide composite nanofiltration membrane with an ion-water solution that strongly interacts with the membrane under mild conditions, on the one hand, the ion-dipole interaction between the ions interacting strongly with the membrane and the polyamide segments induces controlled expansion and structural relaxation of the polymer segments. This physical modification process effectively controls the crosslinking network of the separation layer, transforming it into a loose structure, thereby forming a loose separation layer with increased pore size and reduced crosslinking density. Using the above method, the pore size of the loose separation layer can be precisely controlled within the range of 0.6 nm to 1.8 nm, significantly improving the flux of the high-flux nanofiltration membrane element and reducing the rejection rate of hardness ions. On the other hand, the water bath heating and the weakly alkaline environment (pH 7.5 to 9.0) provided by the ion-water solution synergistically promote the hydrolysis of residual acyl chloride groups on the membrane surface into carboxyl groups. This chemical modification significantly improves the negative charge on the membrane surface and enhances the electrostatic repulsion and rejection capacity for negatively charged new pollutants. In summary, this invention achieves a synergistic improvement in nanofiltration membrane element flux, new pollutant rejection rate, and salt ion selectivity through the dual mechanism of structural fine-tuning and potential enhancement.

[0040] The method for preparing the high-flux nanofiltration membrane element for drinking water purification specifically includes the following steps:

[0041] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module 2;

[0042] (2) An aqueous solution 4 containing ions that strongly interact with the membrane is introduced into the spiral wound nanofiltration membrane module using a peristaltic pump 1 and circulated under heating conditions to obtain a circulated nanofiltration membrane module; wherein, the ions that strongly interact with the membrane include inorganic anions, organic anions, and cations; the inorganic anions are selected from... , , , , Any one of the following; the organic anion is selected from trifluoroacetate (CF3COO) - ), Benzoate (C6H5COO)- p-Toluenesulfonate (CH3C6H4) Any one of the following; the organic cation is selected from tetramethylammonium ( ), tetraethylammonium ( ), tetrabutylammonium ( Any one of the following;

[0043] (3) The high-throughput nanofiltration membrane element can be obtained by cleaning the nanofiltration membrane assembly after the recycling process.

[0044] The polyamide composite nanofiltration membrane is prepared by the following method: immersing the base membrane in an aqueous solution for 2 minutes to remove excess droplets from the surface, then immersing it in an oil solution for 100 seconds. After the reaction, it is removed and air-dried to obtain the polyamide nanofiltration membrane. The base membrane is selected from polysulfone ultrafiltration membranes, polyethersulfone ultrafiltration membranes, polyacrylonitrile ultrafiltration membranes, or polyvinylidene fluoride ultrafiltration membranes; the amine monomers are selected from piperazine, polyethyleneimine, and m-phenylenediamine, with a concentration of 0.2 wt%~0.4 wt%; the acyl chloride monomers are selected from trimesoyl chloride and isophthaloyl chloride, with a concentration of 0.1 wt%~0.3 wt%.

[0045] The heating conditions are as follows: the temperature is 30-90℃, and the time is 1-30 minutes. The aqueous ion solution that strongly interacts with the membrane is weakly alkaline, with a pH of 7.5-9.0. The concentration of ions in the aqueous ion solution that strongly interacts with the membrane is 0.01-3 mol / L, preferably 0.1-1 mol / L. By adjusting the type and concentration of ions, the effective pore size of the membrane can be precisely controlled within the range of 0.6-1.8 nm to meet the removal requirements of new pollutants of different sizes.

[0046] Furthermore, since the inorganic anions, organic anions, and organic cations described in this invention all have strong interactions with the polyamide membrane and possess similar membrane performance regulation capabilities, they can all be used to prepare the high-flux nanofiltration membrane module described in this invention. The base membrane, amine monomers, and acyl chloride monomers are all conventional materials in the art and can all be used to prepare the polyamide nanofiltration membrane. Only a portion of the ion types were selected for actual testing in the embodiments of this invention. The scope of protection of this invention is not limited to the examples in the embodiments; it includes all ion types mentioned in the above steps.

[0047] Secondly, the present invention provides a high-throughput nanofiltration membrane element obtained by the above preparation method.

[0048] Thirdly, the present invention provides an application of the high-throughput nanofiltration membrane element in the field of selective separation of new pollutants and salt ions.

[0049] Comparative Example 1

[0050] This comparative example uses a conventional polyamide nanofiltration membrane element.

[0051] Polyamide composite nanofiltration membrane elements were prepared according to the following steps: A polysulfone ultrafiltration membrane (molecular weight cut to 50,000 Da) was used as the base membrane. A 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution were prepared. The base membrane was immersed in the aqueous solution for 2 min to remove excess droplets from the surface, and then immersed in the oil solution for 100 s. Subsequently, it was heat-treated in an oven at 60°C for 10 min to obtain the polyamide nanofiltration membrane sheet. The membrane sheet was then rolled into an 1812-type spiral wound assembly, denoted as NF-1.

[0052] Comparative Example 2

[0053] This comparative example only uses pure water bath heat treatment.

[0054] A polysulfone ultrafiltration membrane (molecular weight cut to 50,000 Da) was used as the base membrane. A 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution were prepared. The base membrane was immersed in the aqueous solution for 2 min to remove excess droplets, then immersed in the oil solution for 100 s, and finally air-dried. The membrane was then rolled into an 1812-type spiral wound assembly. The assembly was placed in a circulation pipeline, and 60°C deionized water was circulated using a peristaltic pump for 10 min at a flow rate of 1 L / min and a volume of 5 L of deionized water. After treatment, the membrane was rinsed with deionized water and labeled NF-2.

[0055] Example 1

[0056] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an inorganic anion NaI aqueous solution.

[0057] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0058] (2) A 0.5 mol / L NaI aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the NaI aqueous solution was 5 L and the flow rate of the peristaltic pump was 1 L / min. The module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0059] (3) The nanofiltration membrane module after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-3.

[0060] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0061] Example 2

[0062] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an inorganic anion NaNO3 aqueous solution.

[0063] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0064] (2) A 0.5 mol / L NaNO3 aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the NaNO3 aqueous solution was 5 L, the flow rate of the peristaltic pump was 1 L / min, and the module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0065] (3) The nanofiltration membrane module after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-4.

[0066] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0067] Example 3

[0068] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an inorganic anion NaBr aqueous solution.

[0069] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0070] (2) A 0.5 mol / L NaBr aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the NaBr aqueous solution was 5 L, the flow rate of the peristaltic pump was 1 L / min, and the module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0071] (3) The nanofiltration membrane assembly after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-5.

[0072] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0073] Example 4

[0074] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an organic anionic sodium trifluoroacetate (CF3COONa) aqueous solution.

[0075] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0076] (2) A 0.5 mol / L sodium trifluoroacetate (CF3COONa) aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the sodium trifluoroacetate (CF3COONa) aqueous solution was 5 L, the flow rate of the peristaltic pump was 1 L / min, and the nanofiltration membrane module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0077] (3) The nanofiltration membrane assembly after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-6.

[0078] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0079] Example 5

[0080] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an organic anionic sodium benzoate (C6H5COONa) aqueous solution.

[0081] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0082] (2) A 0.5 mol / L sodium benzoate (C6H5COONa) aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the sodium benzoate (C6H5COONa) aqueous solution was 5 L, the flow rate of the peristaltic pump was 1 L / min, and the nanofiltration membrane module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0083] (3) The nanofiltration membrane assembly after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-7.

[0084] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0085] Example 6

[0086] In this embodiment, the ionic aqueous solution that strongly interacts with the membrane is treated with an organic anionic tetrabutylammonium bromide (TBAB) aqueous solution.

[0087] (1) The polyamide composite nanofiltration membrane sheet is made into a spiral wound nanofiltration membrane module;

[0088] (2) A 0.5 mol / L tetrabutylammonium bromide (TBAB) aqueous solution was introduced into the spiral wound nanofiltration membrane module using a peristaltic pump. The volume of the tetrabutylammonium bromide (TBAB) aqueous solution was 5 L, the flow rate of the peristaltic pump was 1 L / min, and the module was circulated at 60℃ for 10 min to obtain the circulated nanofiltration membrane module.

[0089] (3) The nanofiltration membrane module after the recycling process is washed with deionized water to obtain the target nanofiltration membrane, denoted as NF-8.

[0090] The polyamide composite nanofiltration membrane is prepared by the following method: a 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution are prepared. A polysulfone ultrafiltration membrane (with a molecular weight cut of 50,000 Da) is immersed in the piperazine aqueous solution for 2 min to remove excess droplets from the surface. Then, it is immersed in the trimesoyl chloride oil solution for 100 s and removed and air-dried to obtain the polyamide composite nanofiltration membrane.

[0091] Example 7

[0092] This example is a concentration optimization experiment.

[0093] A polysulfone ultrafiltration membrane (molecular weight cut to 50,000 Da) was used as the base membrane. A 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution were prepared. The base membrane was immersed in the aqueous solution for 2 min to remove excess droplets, then immersed in the oil solution for 100 s. After air drying, a polyamide composite nanofiltration membrane was obtained. The polyamide composite nanofiltration membrane was then rolled into an 1812 type spiral wound assembly.

[0094] The 1812-type spiral wound assembly obtained by the winding process was then placed in a circulation pipeline, and NaI aqueous solutions with concentrations of 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 1.0 mol / L, and 2.0 mol / L were prepared respectively. These solutions were circulated using a peristaltic pump and treated at 60°C for 10 min at a flow rate of 1 L / min, with a volume of 5 L of ion-soluble aqueous solution. After treatment, the membrane was washed with deionized water to obtain the high-flux nanofiltration membrane element. The effect of ion concentration on the performance of the high-flux nanofiltration membrane element was then investigated.

[0095] Example 8

[0096] This example is a temperature optimization experiment.

[0097] A polysulfone ultrafiltration membrane (molecular weight cut to 50,000 Da) was used as the base membrane. A 0.3 wt% piperazine aqueous solution and a 0.15 wt% trimesoyl chloride oil solution were prepared. The base membrane was immersed in the aqueous solution for 2 min to remove excess droplets, then immersed in the oil solution for 100 s. After air drying, a polyamide composite nanofiltration membrane was obtained. The polyamide composite nanofiltration membrane was then rolled into an 1812 type spiral wound assembly.

[0098] The 1812 spiral wound assembly obtained by winding was then placed in a circulation pipeline, and NaI aqueous solutions with a concentration of 0.5 mol / L were prepared. The solutions were introduced by a peristaltic pump and heat-treated for 10 min at different temperatures (30℃, 50℃, 70℃, 90℃) with a flow rate of 1 L / min and a volume of 5 L of ion-soluble aqueous solution. After treatment, the membrane was washed with deionized water to obtain a high-flux nanofiltration membrane element. The effect of temperature on membrane performance was then investigated.

[0099] Example 9

[0100] This embodiment verifies the retention performance of different new pollutants.

[0101] The NF-3 membrane element prepared by treatment with NaI solution in Example 1 was used to test the retention performance of different new pollutants at 0.4 MPa and 25°C. The new pollutants included tetracycline (molecular weight 444 Da), sulfamethoxazole (molecular weight 253 Da), perfluorooctanoic acid (molecular weight 414.07 Da), perfluorobutyric acid (molecular weight 214.04 Da), ofloxacin (molecular weight 361.373 Da), and ciprofloxacin (molecular weight 331.347 Da).

[0102] Example 10

[0103] This example is a long-term operational stability test.

[0104] The NF-3 membrane element prepared in Example 1 after treatment with NaI solution was continuously operated for 120 h at 0.4 MPa and 25°C (feed containing 200 ppb tetracycline and 100 ppm Ca). 2+ (Aqueous solution), monitoring its tetracycline rejection rate and Ca2+. 2+ Retention rate and flux changes.

[0105] Membrane performance characterization methods:

[0106] The high-throughput nanofiltration membrane elements prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0107] Pure water flux: measured at 0.4 MPa pressure and 25℃, unit is L·m -2 ·h -1 express.

[0108] New pollutant retention performance: A 200 ppb solution of new pollutants (tetracycline, sulfamethoxazole, perfluorooctanoic acid, perfluorobutyric acid, ofloxacin, ciprofloxacin, etc.) was prepared. The concentrations of the feed liquid and permeate were determined using high-performance liquid chromatography (HPLC), and the retention rate was calculated. .

[0109] Salt rejection performance: The rejection rate of 2000 ppm CaCl2 was determined by measuring the conductivity of the feed liquid and the permeate using a conductivity meter.

[0110] Pore ​​size distribution: The average effective pore size and pore size distribution of the membrane were determined using BET nitrogen adsorption experiments.

[0111] Table 1. Effects of different ion types on the performance of high-flux nanofiltration membrane elements

[0112]

[0113] From Table 1, Figure 2 , 3It is evident that treating the polyamide nanofiltration membrane element with an ionic solution that strongly interacts with the membrane significantly increases the average pore size (from 0.45 nm to 0.95–1.25 nm) and substantially improves the pure water flux (from 42.5 LMH to 78.5–105.2 LMH), which is significantly superior to traditional oven heat treatment and simple water bath heating. Regarding separation performance, this invention increases the rejection rate of tetracycline (molecular weight 444 Da) to 96.2% and the rejection rate of Ca... 2+ The retention rate dropped significantly from 85.2% to 26.5-42.5%. The results indicate that I - CF3COO - Ions with large hydration radii and high polarizability can penetrate into the polyamide network more effectively, shielding interchain hydrogen bonds through ion-dipole interactions and inducing more significant and controllable expansion and structural relaxation of chain segments. Among them, CF3COO... - The treatment (NF-6) showed the best results, achieving a pure water flux of 105.2 LMH, a 147.5% increase compared to Comparative Example 1 (e.g., Figure 2 (As shown); the tetracycline rejection rate was 91.2%. The retention rate dropped to 26.5%, a decrease of 58.7% (e.g., Figure 3 As shown). NaI treatment (NF-3) and TBAB treatment (NF-8) also exhibited excellent overall performance. In contrast, Br - Treatment (NF-5) was relatively weak, while benzoate ( Due to strong hydrophobic interactions, the effect was moderate. Compared with Comparative Example 1, Comparative Example 2 showed a slight increase in flux (48.2 LMH). The retention rate decreased slightly (83.5%), indicating that simple heat treatment can only cause water molecules to swell and cannot achieve precise control of membrane structure loosening.

[0114] The above results fully demonstrate that the weakly alkaline environment (pH 7.8~8.5) provided by the ion-soluble aqueous solution with strong interaction with the membrane synergistically promotes the hydrolysis of acyl chloride to carboxyl groups, increases the negative charge on the membrane surface, and enhances the electrostatic repulsion and retention of negatively charged new pollutants; at the same time, the ion-induced loosening of the chain segments increases the pore size and reduces the Dowson repulsion and retention of divalent ions.

[0115] Table 2 Results of Example 7 (NaI Concentration Optimization)

[0116]

[0117] From Table 2, Figure 4 , 5 It can be seen that as the NaI concentration increases from 0 to 0.5 mol / L, the membrane flux and tetracycline rejection rate increase simultaneously, while the Ca... 2+The rejection rate decreases and the pore size increases (e.g.) Figure 4 (As shown). When the concentration reaches 0.5 mol / L, the tetracycline rejection rate reaches a peak of 96.2%, Ca... 2+ The retention rate dropped to 28.5% (e.g.) Figure 5 As shown in the figure, the pore size reaches 1.18 nm. When the concentration exceeds 0.5 mol / L, the flux continues to increase slightly, but the tetracycline rejection rate begins to decrease, indicating that excessive looseness leads to a decrease in the screening accuracy of the target pollutant. Therefore, 0.1~1.0 mol / L is the preferred concentration range, and 0.3~0.5 mol / L is the optimal concentration range. This trend reflects the two-stage characteristic of ion-induced membrane structure loosening: in the low concentration stage, ions mainly destroy some inter-chain hydrogen bonds through the shielding effect, making the membrane structure moderately loose, and the flux and rejection rate increase simultaneously; in the high concentration stage, excessive ions lead to excessive destruction of inter-chain crosslinking points, and the membrane structure becomes too loose. Although the flux continues to increase, the ability to screen the target pollutant by size decreases.

[0118] Table 3 Results of Example 8 (Optimization of Heat Treatment Temperature)

[0119]

[0120] From Table 3, Figure 6 , 7 It is known that the optimal overall performance can be obtained within the heat treatment temperature range of 50~70℃. As the temperature rises from 30℃ to 70℃, the thermal motion of the chain segments gradually intensifies, I - The induced loosening effect is more complete, and the membrane flux and tetracycline rejection rate are increased simultaneously. 2+ The rejection rate decreased. When the temperature reached 70℃, the tetracycline rejection rate reached 95.8%, Ca... 2+ The retention rate dropped to 26.5% (e.g.) Figure 6 and 7 (As shown). When the temperature rises to 90℃, the thermal motion of the chain segments becomes too strong, which may destroy the ion-induced ordered loose structure, causing the tetracycline rejection rate to drop to 92.2%. Therefore, the preferred heat treatment temperature is 50~70℃.

[0121] Table 4 Results of Example 9 (Retention Performance of Different New Pollutants)

[0122]

[0123] As shown in Table 4, the NF-3 membrane element prepared in Example 1 after treatment with NaI solution exhibited excellent retention efficiency (90.2%–96.2%) for various novel pollutants with molecular weights ranging from 200 to 500 Da. Specifically, the retention rates for tetracycline (444.44 Da), ofloxacin (361.37 Da), ciprofloxacin (331.35 Da), and perfluorooctanoic acid (414.07 Da) all exceeded 94%. Retention rates for the smaller molecular weights of sulfamethoxazole (253.28 Da) and perfluorobutyric acid (214.04 Da) also reached 94.5% and 90.2%, respectively.

[0124] Table 5 Results of Example 10 (Long-term operational stability)

[0125]

[0126] As shown in Table 5, the NF-3 membrane element prepared in Example 1 after treatment with NaI solution maintained a tetracycline rejection rate of over 94.8% after continuous operation at 0.4 MPa for 120 h. The rejection rate remained stable at around 30%, and the pure water flux decline rate was less than 5%, demonstrating excellent operational stability. This result verifies that the loose separation layer constructed by the method of this invention has good structural stability, and the ion-induced loosening structure will not undergo significant relaxation or destruction during long-term operation.

[0127] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only.

[0128] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method for preparing a high-flux nanofiltration membrane element for drinking water purification, characterized in that, Includes the following steps: S1: The polyamide composite nanofiltration membrane is fabricated into a spiral-wound nanofiltration membrane assembly (2); the polyamide composite nanofiltration membrane is prepared by the following method: the base membrane is immersed in an aqueous solution containing amine monomers, and then immersed in an oil solution containing acyl chloride monomers. After the reaction is completed, it is taken out and air-dried to obtain the polyamide composite nanofiltration membrane; the amine monomers are selected from piperazine, polyethyleneimine, and m-phenylenediamine, with a concentration of 0.2 wt%~0.4 wt%; the acyl chloride monomers are selected from trimesoyl chloride and isophthaloyl chloride, with a concentration of 0.1 wt%~0.3 wt%; S2: An aqueous solution (4) containing ions that strongly interact with the membrane is introduced into the spiral wound nanofiltration membrane module using a peristaltic pump (1), and the module is circulated under heating conditions to obtain a circulated nanofiltration membrane module; wherein, the ions that strongly interact with the membrane include inorganic anions and organic anions; the inorganic anions are selected from... , , Any one of the following; the organic anion is selected from trifluoroacetate; the heating conditions are at a temperature of 30~90℃ and a time of 1~30 minutes; the concentration of the ion that strongly interacts with the membrane is 0.01~3 mol / L; the aqueous solution of the ion that strongly interacts with the membrane is sodium nitrate solution, sodium iodide solution, sodium bromide solution, or sodium trifluoroacetate solution; S3: Clean the nanofiltration membrane module after the recycling process to obtain the high-flux nanofiltration membrane element.

2. The method according to claim 1, characterized in that, The base membrane is selected from polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane or polyvinylidene fluoride ultrafiltration membrane.

3. A high-throughput nanofiltration membrane element prepared according to any one of claims 1-2.

4. The high-flux nanofiltration membrane element according to claim 3, characterized in that, The prepared nanofiltration membrane element exhibits selective separation characteristics of high decontamination and low hardness removal: (a) Retention rate of ≥95% for pollutants with molecular weight in the range of 200-500 Da; (b) Hardness ions The retention rate is ≤30%.

5. The high-flux nanofiltration membrane element according to claim 3, characterized in that, The prepared nanofiltration membrane elements have an average pore size of 0.8–1.5 nm and a pure water flux ≥80. .

6. The application of a high-throughput nanofiltration membrane element according to any one of claims 3 to 5 in the field of selective separation of novel pollutants and salt ions, characterized in that, The molecular weight of the new pollutant is in the range of 200 to 500 Da.

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