Method for preparing a nanofiltration membrane and nanofiltration membrane prepared thereby

Abstract

This invention relates to a method for preparing a nanofiltration membrane and the nanofiltration membrane prepared therefrom. The preparation method includes: preparing a casting solution; solidifying the casting solution on a reinforcing material to form a base membrane, wherein the casting solution comprises a polymer, a solvent, and optionally a hydrophilic nanofiller; sequentially contacting the base membrane with an aqueous solution and an oil solution to form a functional layer on the base membrane via interfacial polymerization, wherein the aqueous solution comprises an aqueous monomer, an acid-binding agent, and a positive charge modifier, and the oil solution comprises an oil monomer, a solvent, and a pore size modifier; and obtaining the nanofiltration membrane through post-treatment. The nanofiltration membrane prepared by the method of this invention has a mixed-charge Janus structure in its functional layer, ensuring a high removal rate of divalent cations and divalent anions through the synergistic effect of mixed charge and pore size regulation. Furthermore, the nanofiltration membrane has a smooth surface and high hydrophilicity, effectively mitigating the membrane flux decline problem caused by oil and organic matter contamination.

Description

Technical Field

[0001] This invention relates to the technical field of water treatment membranes, and more particularly to a method for preparing nanofiltration membranes and nanofiltration membranes prepared therefrom. Background Technology

[0002] Petroleum products are a crucial pillar industry of the current national economy. With the intensification of oil and gas exploration and development, the proportion of reserves and production from low-grade oil and gas fields is increasing year by year. Maintaining reservoir pressure through artificial water injection for secondary and tertiary oil recovery has become an important means of improving crude oil recovery rates. Oilfield wastewater carries not only petroleum, dissolved salts, suspended solids, harmful gases, organic matter, and chemical agents, but also a large number of microorganisms and bacteria. As national and local governments impose increasingly stringent requirements on environmental protection and governance, oilfield produced water reinjection has become an important way to ensure the sustainable use of water resources and protect the ecological environment. However, traditional water treatment processes are insufficient to meet the water quality requirements of oilfield reinjection water. When reinjection water is incompatible with reservoir fluids, it can cause reservoir damage, directly affecting water recovery rates and even reservoir life.

[0003] Currently, upstream treatment technologies such as ultrafiltration and microfiltration can effectively remove oil, suspended solids, and bacteria from water, and the effluent quality can meet reuse standards. However, this type of produced water has high mineralization and still contains scaling ions such as calcium, magnesium, and sulfate. It also contains residual components of crude oil, humic acid, and other organic matter. Severe corrosion and scaling still occur, making it difficult to achieve a virtuous cycle of water injection development in low-permeability oil reservoirs.

[0004] Nanofiltration membrane desalination technology has a high rejection rate for divalent ions and can remove most of the total dissolved solids (TDS) and divalent scaling ions such as Ba from oilfield water. 2+ Ca 2+ Mg 2+ SO4 2- CO3 2- These technologies effectively reduce the mineralization and residual organic matter in oilfield water while meeting the requirements for oilfield water reuse. Therefore, integrating nanofiltration membrane separation technology with other technologies, leveraging their respective strengths, has broad application prospects in the field of oilfield wastewater treatment, reinjection, and reuse.

[0005] Patent document CN103601314A discloses a treatment system and process for producing oilfield reinjection water using seawater. It uses an ultrafiltration membrane for pretreatment and a nanofiltration membrane for desalination of seawater to obtain qualified oilfield reinjection water. This solves the problems of corrosion and scaling in oil wells in the prior art, achieves high oil recovery rate of oil well platforms and reduces oil production costs.

[0006] In the non-patent literature “Produced water treatment by nanofiltration and reverse osmosis membranes, Journal of Membrane Science, 2008, 322(1), pp. 162-170”, Mondal et al. disclosed the use of different nanofiltration membranes to treat produced water from the Colorado oilfield. With a high recovery rate (>62%), the NF270 nanofiltration membrane can effectively reduce the salinity of the produced water to below 1000 mg / L. Several different nanofiltration membranes showed high removal rates for total organic carbon (TOC), suspended solids, salt and oil, verifying the feasibility of using nanofiltration membranes to treat oilfield produced water.

[0007] Jin Limei et al. reported a method for preparing a negatively charged nanofiltration membrane using PAMAM / TMC as a monomer in the non-patent literature “Preparation of composite nanofiltration membrane with PAMAM / TMC as monomer and its application in oilfield produced water treatment, Membrane Science and Technology, 37(4), pp. 100-106”, and applied it to oilfield produced water treatment. However, the membrane has poor retention capacity for divalent cations and a removal rate of only 68% for MgCl2. Pollutants are prone to form a gel layer and cause partial membrane pore blockage. The poor antifouling ability leads to a rapid decline in membrane flux.

[0008] Liu et al. proposed a method for preparing Janus-structured polyamide membranes with opposite charges in the non-patent literature "One-step constructed ultrathin Janus polyamide nanofilms with opposite charges for highly efficient nanofiltration, J. Mater. Chem. A, 2017(5), pp. 22988–22996". By controlling the aqueous phase temperature at 70℃ and the organic phase temperature at -5℃, and due to the self-inhibition of interfacial polymerization, the ratio of amine to carboxyl groups in the membrane can be adjusted by controlling the concentration of piperazine near the reaction zone, thereby preparing a polyamide functional layer with opposite charges on the surface and back. The prepared membrane material achieved a Na2SO4 removal rate of 82%–96.5% and a MgCl2 removal rate of 97%–99%. However, this method has excessively high requirements for equipment and technology, making large-scale preparation difficult.

[0009] Patent document CN109200833A discloses a method for preparing a nanofiltration membrane that removes divalent cations and positively charged PPCPs. The prepared nanofiltration membrane exhibits a high removal rate for high-valent cation salt solutions, but the removal rate for sulfate is only 78.13%.

[0010] In the process of applying nanofiltration technology to oilfield reinjection water, the following problems still need to be solved: (1) Nanofiltration membranes are difficult to simultaneously and efficiently retain divalent cations and divalent anions; (2) Commercially available nanofiltration membranes widely use polyamide composite nanofiltration membranes, with a maximum operating temperature of only 45℃, while the temperature of the oilfield wastewater after pretreatment is still above 30℃, which may cause irreversible damage to the membrane structure; (3) Severe membrane fouling problems lead to reduced flux, deterioration of water quality, and shortened membrane life. Unfortunately, there are not many relevant research and application reports on the application of deep treatment for oilfield reinjection water, and the development of nanofiltration membrane materials that simultaneously have high removal rates for divalent ions, good stability, and effective removal of oil and organic pollutants still faces challenges. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] To address the aforementioned technical problems of existing nanofiltration membranes used for oilfield reinjection water, the present invention aims to provide a nanofiltration membrane whose functional layer has a mixed-charge Janus structure, thereby improving the nanofiltration membrane's ability to filter Mg from oilfield wastewater. 2+ Ca 2+ and SO4 2- It achieves the same removal rate of divalent cations and divalent anions, while simultaneously addressing the flux decline issues caused by membrane fouling, oil contamination, and organic pollution.

[0013] Solution for solving the problem

[0014] To achieve the above objectives, the inventors of this invention, through dedicated research, discovered that during the formation of the functional layer, adding a positive charge regulator loads a positive charge on the back side of the functional layer, while the surface of the functional layer itself is loaded with -COOH. This allows the formation of a functional layer with a mixed-charge Janus structure. While the functional layer is loaded with a positive charge, the polymer network structure may become more porous. Simultaneously, adding a pore size regulator ensures a highly cross-linked polymer network structure. The synergistic effect of mixed charge and pore size regulation ensures a high removal rate for divalent cations and anions. The positive charge on the back side of the functional layer and the -COOH on the surface give the nanofiltration membrane stronger hydrophilicity. The addition of the positive charge regulator restricts the diffusion of aqueous monomers, and the reduction of nodular material on the surface of the functional layer improves membrane surface smoothness, effectively mitigating contamination caused by oils and organic matter.

[0015] This invention provides a method for preparing a nanofiltration membrane, characterized by comprising the following steps:

[0016] A casting solution is prepared and solidified on a reinforcing material to form a base film, wherein the casting solution comprises a polymer, a solvent, and an optional hydrophilic nanofiller;

[0017] The base film is sequentially contacted with an aqueous solution and an oil solution to form a functional layer on the base film through an interfacial polymerization reaction, wherein the aqueous solution contains an aqueous monomer, an acid-binding agent and a positive charge modifier, and the oil solution contains an oil monomer, a solvent and a pore size modifier;

[0018] The nanofiltration membrane is obtained after post-processing.

[0019] According to the preparation method of the present invention, the positive charge regulator is at least one selected from octaaminopropyl polyhedral oligomeric silsesquioxane hydrochloride, amino-functionalized mesoporous silica, amino-functionalized multi-arm carbon nanotubes, quaternized cellulose nanofibers and branched-chain amino acids. Preferably, the mass percentage concentration of the positive charge regulator is 0.5 wt% to 5.0 wt% based on the total mass of the aqueous solution.

[0020] According to the preparation method of the present invention, the polymer is at least one selected from bisphenol A type polysulfone, polyethersulfone, sulfonated polyethersulfone, polyarylsulfone, polyetherimide, polyetheretherketone, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride and polystyrene. Preferably, the mass percentage concentration of the polymer is 15wt% to 25wt% based on the total mass of the casting solution.

[0021] According to the preparation method of the present invention, the hydrophilic nanofiller is at least one selected from bentonite, graphene oxide, dopamine, hydrotalcite, nano-attapulgite, cellulose nanocrystals, functionalized carbon nanotubes, carbon nitride quantum dots and nano-metal-organic framework materials. Preferably, based on the total mass of the casting solution, the mass percentage concentration of the hydrophilic nanofiller is 0.5wt% to 5.0wt%.

[0022] According to the preparation method of the present invention, the aqueous monomer is at least one selected from polyamide amine, polyethyleneimine, piperazine and m-phenylenediamine; preferably, the mass percentage concentration of the aqueous monomer is 1.0 to 5.0 wt% based on the total mass of the aqueous solution.

[0023] According to the preparation method of the present invention, the acid-binding agent is at least one selected from sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, triethylamine, sodium camphor sulfonate, and triethylamine hydrochloride. Preferably, the mass percentage concentration of the acid-binding agent is 0.1 to 2.0 wt% based on the total mass of the aqueous solution.

[0024] According to the preparation method of the present invention, the oil phase monomer is at least one selected from pyromellitic methyl chloride, 1,3,5-benzenetrisulfonyl chloride, 3,4,5-biphenyltriacyl chloride and 3,3',5,5'-biphenyltetraacyl chloride. Preferably, the mass percentage concentration of the oil phase monomer is 0.1 to 1.0 wt% based on the total mass of the oil phase solution.

[0025] According to the preparation method of the present invention, the pore size regulator is at least one selected from terephthaloyl chloride, isophthaloyl chloride, 2,6-pyridinedicarboxyl chloride, 2,5-bis(chloroformyl)thiophene, 2,5-furandicarboxyl chloride, 4,4'-biphenyldicarboxyl chloride, 4,4'-biphenyldiacetyl chloride, glutaryl chloride, adipicoyl chloride, pimecroyl chloride, octanoyl chloride, azeloyl chloride, sebacic acid chloride, 1,4-cyclohexadiacyl chloride, and 1,3-adamantanedicarboxyl chloride. Preferably, the mass percentage concentration of the pore size regulator is 0.05 wt% to 0.5 wt% based on the total mass of the oil phase solution.

[0026] The present invention also provides a nanofiltration membrane prepared by the preparation method described in the present invention.

[0027] The effects of the invention

[0028] The nanofiltration membrane prepared by the method of the present invention has a mixed-charge Janus structure in its functional layer. The nanofiltration membrane has a high removal rate for both divalent cations and divalent anions. The nanofiltration membrane has a smooth surface and high hydrophilicity, which can effectively alleviate the fouling of the membrane surface caused by oil and organic matter, thereby alleviating the problem of flux decline. Attached Figure Description

[0029] Figure 1 The results show the comparison of the antifouling performance of the nanofiltration membranes prepared in Comparative Example 1 and Example 1. Detailed Implementation

[0030] This invention provides a method for preparing a nanofiltration membrane, which includes the following steps:

[0031] A casting solution is prepared and solidified on a reinforcing material to form a base film, wherein the casting solution comprises a polymer, a solvent, and an optional hydrophilic nanofiller;

[0032] The base film is sequentially contacted with an aqueous solution and an oil solution to form a functional layer on the base film through an interfacial polymerization reaction, wherein the aqueous solution contains an aqueous monomer, an acid-binding agent and a positive charge modifier, and the oil solution contains an oil monomer, a solvent and a pore size modifier;

[0033] The nanofiltration membrane is obtained after post-processing.

[0034] The technical concept of this invention lies in the following: During the formation of the functional layer, a positive charge regulator is added to load a positive charge on the back side of the functional layer, while the surface of the functional layer itself is loaded with -COOH. Therefore, a functional layer with a mixed-charge Janus structure can be formed. After adding the positive charge regulator, the polymer network structure may become looser while the functional layer is loaded with a positive charge. At the same time, the addition of a pore size regulator can ensure a highly cross-linked structure of the polymer network. The synergistic effect of mixed charge and pore size regulation ensures a high removal rate for divalent cations and divalent anions. The positive charge loaded on the back side of the functional layer and the -COOH loaded on the surface endow the nanofiltration membrane with stronger hydrophilicity, which can promote the improvement of the water flux of the nanofiltration membrane. The addition of the positive charge regulator restricts the diffusion of aqueous monomers, reduces the nodular substances on the surface of the functional layer obtained by interfacial polymerization, thereby improving the surface smoothness of the membrane and effectively mitigating pollution caused by oil and organic matter.

[0035] The preparation method of the present invention uses a positive charge regulator selected from at least one of octaaminopropyl polyhedral oligomeric silsesquioxane hydrochloride (POSS-NH3Cl), amino-functionalized mesoporous silica, amino-modified multi-arm carbon nanotubes, quaternized cellulose nanofibers, and branched-chain amino acids. Preferably, the positive charge regulator is octaaminopropyl polyhedral oligomeric silsesquioxane hydrochloride (POSS-NH3Cl).

[0036] Preferably, the mass percentage concentration of the positive charge regulator is 0.5 wt% to 5.0 wt% based on the total mass of the aqueous solution.

[0037] The preparation method of the present invention uses a polymer selected from at least one of bisphenol A type polysulfone, polyethersulfone, sulfonated polyethersulfone, polyarylsulfone, polyetherimide, polyetheretherketone, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and polystyrene. The polyarylsulfone includes, for example, polyphenylene sulfone and polyphenylene sulfone, and the polyethersulfone includes, for example, polyphenylene sulfide sulfone. Preferably, the polymer is bisphenol A type polysulfone or polyethersulfone.

[0038] Preferably, the polymer has a mass percentage concentration of 15 wt% to 25 wt% based on the total mass of the casting solution.

[0039] The solvent in the casting solution is not particularly limited, as long as it can fully dissolve the polymer. Preferably, the solvent is at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and imidazolinone.

[0040] The reinforcing material used in this invention can be polypropylene (PP) nonwoven fabric, nylon (PA) nonwoven fabric, or polyethylene (HDPE) nonwoven fabric, preferably polypropylene (PP) nonwoven fabric.

[0041] There are no particular limitations on the method for coating the casting solution onto the nonwoven fabric. Coating methods commonly used in nanofiltration membrane preparation, such as casting, dip coating, blade coating, and spin coating, are acceptable, with blade coating being more preferred. After coating onto the nonwoven fabric, it is then immersed in a coagulation bath to allow the casting solution to solidify into a film.

[0042] Optionally, the casting solution contains a non-solvent. Preferably, the non-solvent is at least one selected from alcohols having 1 to 6 carbon atoms, polyethylene glycol, polyvinylpyrrolidone, polypropylene glycol, and polybutanediol. Examples of alcohols having 1 to 6 carbon atoms include at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, and hexanol. The non-solvent is preferably at least one selected from ethanol, n-propanol, isopropanol, n-butanol, polyethylene glycol, polypropylene glycol, polybutanediol, and polyvinylpyrrolidone. Preferably, the mass percentage concentration of the non-solvent is 0.5 wt% to 5.0 wt% based on the total mass of the casting solution.

[0043] In the preparation method described in this invention, the thermodynamic stability of the components used to form the base film is a key factor affecting the formation of the film structure during the liquid-solid phase transformation process. Preferably, by introducing hydrophilic nanofillers, the thermodynamic and kinetic parameters during the phase transformation process can be affected, thereby controlling the pore structure and hydrophilicity / hydrophobicity of the base film. This further provides a good reaction site for the interfacial polymerization used to form the functional layer (also known as the desalination layer). The hydrophilic nanofiller is selected from at least one of bentonite, graphene oxide, dopamine, hydrotalcite, nano-attapulgite, cellulose nanocrystals, functionalized carbon nanotubes, carbon nitride quantum dots, and nano-metal-organic framework materials. Preferably, the hydrophilic nanofiller is bentonite.

[0044] Preferably, the mass percentage concentration of the hydrophilic nanofiller is 0.5 wt% to 5.0 wt% based on the total mass of the casting solution.

[0045] In the preparation method of the present invention, the aqueous monomer is at least one selected from polyamide amine, polyethyleneimine, piperazine, and m-phenylenediamine. Preferably, the aqueous monomer is polyamide amine.

[0046] Preferably, the mass percentage concentration of the aqueous monomer is 1.0 to 5.0 wt% based on the total mass of the aqueous solution.

[0047] In the preparation method of the present invention, preferably, the acid-binding agent is at least one selected from sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, triethylamine, sodium camphor sulfonate, and triethylamine hydrochloride. Preferably, the mass percentage concentration of the acid-binding agent is 0.1 to 2.0 wt% based on the total mass of the aqueous solution. By adding the acid-binding agent, the pH value of the aqueous solution can be adjusted to the range of 9 to 10.

[0048] In the preparation method of the present invention, the oil phase monomer is at least one selected from pyromellitic methyl methacrylate chloride, 1,3,5-benzenetrisulfonyl chloride, 3,4,5-biphenyltriacyl chloride, and 3,3',5,5'-biphenyltetraacyl chloride. Preferably, the oil phase monomer is pyromellitic methyl methacrylate chloride.

[0049] Preferably, the mass percentage concentration of the oil phase monomer is 0.1 to 1.0 wt% based on the total mass of the oil phase solution.

[0050] In the preparation method described in this invention, a positive charge regulator expands the pore size of the polymer network, and the pore size is adjusted by adding a pore size regulator. A pore size regulator with less steric hindrance is more easily stretched into the formed polymer network structure, thereby polymerizing with the aqueous monomer primary amine that has not participated in the interfacial polymerization reaction to produce a relatively dense functional layer, thereby reducing the pore size of the polymer network, that is, reducing the pore size of the obtained nanofiltration membrane, and changing the aggregated state structure of the nanofiltration membrane. The pore size regulator is selected from at least one of terephthaloyl chloride, isophthaloyl chloride, 2,6-pyridinedicarboxylic acid chloride, 2,5-bis(chloroformyl)thiophene, 2,5-furandicarboxylic acid chloride, 4,4'-biphenyldicarboxylic acid chloride, 4,4'-biphenyldiacetyl chloride, glutaryl chloride, adipic acid chloride, pimecroyl chloride, octanoyl chloride, azeloyl chloride, sebacic acid chloride, 1,4-cyclohexadiacyl chloride, and 1,3-adamantanedicarboxylic acid chloride.

[0051] Preferably, the mass percentage concentration of the pore size regulator is 0.05 wt% to 0.5 wt% based on the total mass of the oil phase solution.

[0052] The following are non-limiting examples of the method for preparing the nanofiltration membrane of the present invention:

[0053] Bisphenol A type polysulfone or polyethersulfone (15-25 wt%) was dissolved in dimethylformamide (DMF) or dimethylacetamide (DMAC) as a polymer. Bentonite (0.5-5.0 wt%) and polyvinylpyrrolidone (0.5-5.0 wt%) were added, and the mixture was stirred at 100-150°C for 2-6 hours until the polymer was completely dissolved and the bentonite was evenly dispersed. The mixture was then allowed to stand under vacuum to remove bubbles. The casting solution was then used to form a base film on a nonwoven fabric via a liquid-solid phase inversion method. The prepared base film was stored in deionized water for later use.

[0054] The prepared base film was immersed in an aqueous solution containing polyamide amine (1.0–5.0 wt%), a positive charge control agent (such as octaaminopropyl polyhedral silsesquioxane oligomer hydrochloride (POSS-NH3Cl), 0.5–5.0 wt%), and sodium hydroxide (0.1–2.0 wt%) for 0.5–2 min, and the surface water droplets were drained off.

[0055] Then, it is immersed in an organic solvent (n-hexane, cyclohexane, ethylcyclohexane, n-octane, n-heptane, etc.) containing pyromellitic terephthaloyl chloride (0.1-1.0 wt%) and a pore size modifier (such as terephthaloyl chloride, 0.05-0.5 wt%) and reacted for 0.5-2 min.

[0056] Next, it is immersed in an aqueous solution containing 5 wt% N,N-dimethylformamide (DMF) for 0.5–1 min for post-treatment. After removal, it is washed with ultrapure water, then heat-treated in hot water at 70–80 °C for 1–3 min, washed with pure water, and then immersed in an aqueous solution containing glycerol for 1–3 min. Finally, it is dried to obtain a nanofiltration membrane with a desalination layer having a mixed charged Janus structure.

[0057] This invention also provides a nanofiltration membrane prepared by the preparation method described in this invention. The functional layer of the nanofiltration membrane prepared by the above-described preparation method of this invention has a mixed-charge Janus structure. The nanofiltration membrane has a high removal rate for both divalent cations and divalent anions. The nanofiltration membrane has high hydrophilicity and a smooth surface, which can effectively alleviate the fouling of the membrane surface caused by oils and organic matter, thereby alleviating the problem of flux decline.

[0058] Example

[0059] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but this should not be construed as limiting the present invention. It should be noted that, unless otherwise specified, the reagents and raw materials used in the embodiments of the present invention are all commercially available conventional products.

[0060] Comparative Example 1

[0061] (1) Dissolve bisphenol A polysulfone in DMAC to make the concentration of bisphenol A polysulfone 20wt%, add 0.5wt% polyvinylpyrrolidone, stir at 120℃ for 2h until bisphenol A polysulfone is completely dissolved, and let the resulting solution stand under vacuum to remove bubbles to obtain casting solution.

[0062] (2) The casting solution obtained in step (1) was used to prepare a porous polymer support layer on nonwoven fabric by liquid-solid phase conversion method. The phase conversion time was 0.5 min, the water bath temperature was 18℃, the thermosetting water bath temperature was 80℃, and the film thickness was controlled at 5.3 mil. The prepared base film was stored in deionized water.

[0063] (3) Add piperazine and sodium phosphate to ultrapure water to make their concentrations 2.0wt% and 0.2wt% respectively, stir and dissolve completely to obtain an aqueous solution; immerse the base membrane prepared in step (2) in the aqueous solution for 2 minutes and drain the water droplets on the membrane surface.

[0064] (4) Dissolve pyromellitic chloride in n-hexane to make the concentration of pyromellitic chloride 0.1wt%, stir to dissolve and obtain an oil phase solution; immerse the base membrane soaked in the aqueous phase solution in step (3) in the oil phase solution for 1 min to obtain the nascent nanofiltration membrane;

[0065] (5) The nascent nanofiltration membrane was immersed in an aqueous solution containing 5 wt% dimethylformamide (DMF) for 0.5 min, then washed with ultrapure water, then heat-treated in hot water at 75°C for 2 min, washed with pure water, then soaked in an aqueous solution containing glycerol for 2 min, and dried to obtain nanofiltration membrane NF-J1.

[0066] Comparative Example 2

[0067] (1) Dissolve bisphenol A polysulfone in DMAC to make the concentration of bisphenol A polysulfone 20wt%, add 0.5wt% polyvinylpyrrolidone, stir at 120℃ for 2h until the polymer is completely dissolved, and let the resulting solution stand under vacuum to remove bubbles to obtain casting solution.

[0068] (2) The casting solution obtained in step (1) was used to prepare a porous polymer support layer on nonwoven fabric by liquid-solid phase conversion method. The phase conversion time was 0.5 min, the water bath temperature was 18℃, the thermosetting water bath temperature was 80℃, and the film thickness was controlled at 5.2 mil. The prepared base film was stored in deionized water.

[0069] (3) Add polyamide amine, POSS-NH3Cl and sodium phosphate to ultrapure water so that the concentrations of the three are 2.0wt%, 0.5wt% and 0.2wt% respectively. Stir and dissolve completely to obtain an aqueous solution. Soak the base membrane prepared in step (2) in the aqueous solution for 2 minutes and drain the water droplets on the membrane surface.

[0070] (4) Dissolve pyromellitic chloride in n-hexane to make the concentration of pyromellitic chloride 0.1wt%, stir to dissolve and obtain an oil phase solution; immerse the base membrane soaked in the aqueous phase solution in step (3) in the oil phase solution for 1 min to obtain the nascent nanofiltration membrane;

[0071] (5) The nascent nanofiltration membrane was immersed in an aqueous solution containing 5 wt% dimethylformamide (DMF) for 0.5 min, then washed with ultrapure water, then heat-treated in hot water at 75°C for 2 min, washed with pure water, then soaked in an aqueous solution containing glycerol for 2 min, and dried to obtain nanofiltration membrane NF-J2.

[0072] Comparative Example 3

[0073] (1) Dissolve bisphenol A polysulfone in DMAC to make the concentration of bisphenol A polysulfone 20wt%, add 2wt% bentonite and 1wt% polyvinylpyrrolidone, stir at 120℃ for 3h until the polymer is completely dissolved, and let the resulting solution stand under vacuum to remove bubbles to obtain casting solution.

[0074] (2) The casting solution obtained in step (1) was used to prepare a porous polymer support layer on nonwoven fabric by liquid-solid phase conversion method. The phase conversion time was 0.5 min, the water bath temperature was 18℃, the thermosetting water bath temperature was 80℃, and the film thickness was controlled at 5.2 mil. The prepared base film was stored in deionized water.

[0075] (3) Add polyamide amine, POSS-NH3Cl and sodium phosphate to ultrapure water so that the concentrations of the three are 2.0wt%, 0.5wt% and 0.2wt% respectively. Stir and dissolve completely to obtain an aqueous solution. Soak the base membrane prepared in step (2) in the aqueous solution for 2 minutes and drain the water droplets on the membrane surface.

[0076] (4) Dissolve pyromellitic chloride in n-hexane to make the concentration of pyromellitic chloride 0.1wt%, stir to dissolve and obtain an oil phase solution; immerse the base membrane soaked in the aqueous phase solution in step (3) in the oil phase solution for 1 min to obtain the nascent nanofiltration membrane;

[0077] (5) The nascent nanofiltration membrane was immersed in an aqueous solution containing 5 wt% dimethylformamide (DMF) for 0.5 min, then washed with ultrapure water, then heat-treated in hot water at 75°C for 2 min, washed with pure water, then soaked in an aqueous solution containing glycerol for 2 min, and dried to obtain nanofiltration membrane NF-J3.

[0078] Example 1

[0079] (1) Dissolve bisphenol A polysulfone in DMAC to make the concentration of bisphenol A polysulfone 20wt%, add 2wt% bentonite and 1wt% polyvinylpyrrolidone, stir at 120℃ for 3h until the polymer is completely dissolved, and let the resulting solution stand under vacuum to remove bubbles to obtain casting solution.

[0080] (2) The casting solution from step (1) was used to prepare a porous polymer support layer on nonwoven fabric by liquid-solid phase conversion method. The phase conversion time was 0.5 min, the water bath temperature was 18℃, the thermosetting water bath temperature was 80℃, the film thickness was controlled at 5.2 mil, and the prepared base film was stored in deionized water.

[0081] (3) Add the aqueous monomer polyamide amine, the positive charge regulator POSS-NH3Cl and the acid-binding agent sodium phosphate to ultrapure water so that the concentrations of the three are 2.0wt%, 0.5wt%, and 0.2wt%, respectively. Stir and dissolve completely to obtain an aqueous solution. Soak the base membrane prepared in step (2) in the aqueous solution for 2 minutes and drain the water droplets on the membrane surface.

[0082] (4) Dissolve the oil phase monomer pyromellitic acid chloride and the pore size regulator terephthaloyl chloride in n-hexane so that their concentrations are 0.1wt% and 0.05wt% respectively, and stir to dissolve to obtain an oil phase solution; immerse the base membrane soaked in the aqueous phase solution in step (3) in the oil phase solution for 1 min to obtain the nascent nanofiltration membrane;

[0083] (5) The nascent nanofiltration membrane was immersed in an aqueous solution containing 5 wt% dimethylformamide (DMF) for 0.5 min, then washed with ultrapure water, then heat-treated in hot water at 75°C for 2 min, washed with pure water, then soaked in an aqueous solution containing glycerol for 2 min, and dried to obtain nanofiltration membrane NF-J4.

[0084] Examples 2 to 6

[0085] Except for the changes made according to Table 1 below, Examples 2 to 6 are performed in the same manner as Example 1.

[0086] Table 1

[0087]

[0088] Performance characterization and test results

[0089] (1) Contact angle and roughness

[0090] The roughness and hydrophilicity of the nanofiltration membranes prepared in Comparative Examples 1 to 3 and Example 1 were characterized, and the results are shown in Table 2 below. The data in the table show that adding a positive charge modifier can improve the hydrophilicity and surface smoothness of the membrane.

[0091] Table 2

[0092] NF-J1 43.6 4.35 NF-J2 29.5 3.82 NF-J3 28.7 3.77 NF-J4 27.5 3.63

[0093] (2) Ion removal performance

[0094] The nanofiltration membranes prepared in Comparative Examples 1 to 3 and Example 1 were tested for membrane performance on a cross-flow membrane testing platform. 2000 ppm solutions of Na₂SO₄, MgSO₄, MgCl₂, CaCl₂, and NaCl were prepared using deionized water. The test conditions were: operating pressure 100 psi, solution temperature 25°C, and pH 6.5–7.5. The water flux and rejection rate were measured after 30 minutes of membrane operation, and the results are shown in Table 3 below.

[0095] From Table 3 below, the membrane rejection rate order is MgSO4≈Na2SO4>MgCl2>CaCl2>NaCl, where for SO4... 2- The retention capacity of nanofiltration membranes is generally higher than that of other anions and cations. After adding a positive charge regulator to form a Janus mixed charge structure, the retention capacity of nanofiltration membranes for divalent cations is improved, and the flux is increased. After further adding a pore size regulator, the retention capacity of nanofiltration membranes is further significantly improved, while the flux is slightly reduced.

[0096] Table 3

[0097]

[0098] (3) Anti-pollution performance

[0099] Bovine serum albumin was selected as the contaminant to determine and compare the antifouling performance of the nanofiltration membranes prepared in Comparative Example 1 and Example 1. The determination steps are as follows:

[0100] (a) After running in pure water for 0.5 hours, the pure water flux J of the membrane was tested. w (b) After running the contaminant solution (2000 ppm MgSO4 + 50 ppm BSA) for 12 h, the flux J of the membrane after fouling was measured. p (c) Rinse the membrane surface with 2000ppm NaOH for 1 hour, and measure the pure water flux J of the membrane after rinsing. e .

[0101] The calculation method for pollution resistance parameters is as follows:

[0102] Flux decay rate: 100×(1-J) p / J w Formula 1

[0103] Flux recovery rate: 100×(1-J) e / J w Equation 2

[0104] The flux decay rate of NF-J0 was measured to be 58.1%, and the flux recovery rate was 86.6%; the flux decay rate of NF-J3 was 76.9%, and the flux recovery rate was 99.6%.

[0105] By comparing Comparative Example 1 and Example 1, it can be seen that the overall anti-fouling performance of NF-J4 is better than that of NF-J1, such as... Figure 1 As shown. This result corroborates the hydrophilicity and roughness test results, confirming that the nanofiltration membrane obtained by the method according to the present invention has superior antifouling performance. Furthermore, due to the higher smoothness of the NF-J4 membrane surface, the cleaning effect after fouling is better, and the flux recovery is better.

[0106] Industrial availability

[0107] This invention provides a method for preparing a nanofiltration membrane. The nanofiltration membrane prepared by this method has a mixed charged Janus structure in its functional layer and a controllable polymer pore size structure. It exhibits high removal rates for both divalent cations and divalent anions. Furthermore, the high hydrophilicity and high flatness of the membrane surface can effectively alleviate membrane fouling caused by oils and organic matter, which is beneficial for mitigating flux decline and improving the long-term operational stability of the nanofiltration membrane. It can be widely applied in industries such as oilfield reinjection water treatment, water softening, material concentration and purification, and wastewater (liquid) decolorization treatment in the dye, pigment, printing and dyeing, textile, chemical, and pharmaceutical industries.

Claims

1. A method for producing a nanofiltration membrane, characterized by, Includes the following steps: A casting solution is prepared and then cured on a reinforcing material to form a base film. The casting solution comprises a polymer, a solvent, and a hydrophilic nanofiller. The polymer is at least one selected from bisphenol A polysulfone, polyethersulfone, sulfonated polyethersulfone, polyarylsulfone, polyetherimide, polyetheretherketone, and polyvinylidene fluoride. The hydrophilic nanofiller is at least one selected from bentonite, graphene oxide, dopamine, nano-attapulgite, functionalized carbon nanotubes, and carbon nitride quantum dots. The base film is sequentially contacted with an aqueous phase solution and an oil phase solution to form a functional layer on the base film via interfacial polymerization. The aqueous phase solution comprises an aqueous monomer, an acid-binding agent, and a positive charge modifier. The mass percentage concentration of the aqueous monomer is 1.0–5.0 wt% based on the total mass of the aqueous phase solution. The positive charge modifier is selected from at least one of octaaminopropyl polyhedral oligomeric silsesquioxane hydrochloride, amino-functionalized mesoporous silica, aminated multi-arm carbon nanotubes, quaternized cellulose nanofibers, and branched-chain amino acids. The mass percentage concentration of the positive charge modifier is 0.5% based on the total mass of the aqueous phase solution. The oil phase solution comprises oil phase monomers, solvents, and pore size modifiers, with a mass percentage concentration of 0.1-1.0 wt% based on the total mass of the oil phase solution. The pore size modifier is selected from at least one of terephthaloyl chloride, isophthaloyl chloride, 2,6-pyridinedicarboxyl chloride, 2,5-bis(chloroformyl)thiophene, 2,5-furandicarboxyl chloride, 4,4'-biphenyldicarboxyl chloride, 4,4'-biphenyldiacetyl chloride, glutaryl chloride, adipicoyl chloride, pimecroyl chloride, octanoyl chloride, azeloyl chloride, sebacic acid chloride, 1,4-cyclohexadiyl chloride, and 1,3-adamantanedicarboxyl chloride. The nanofiltration membrane is obtained after post-processing.

2. The preparation method according to claim 1, wherein the mass percentage concentration of the positive charge regulator is 0.5wt%~4wt% based on the total mass of the aqueous solution.

3. The preparation method according to claim 1 or 2, wherein the mass percentage concentration of the polymer is 15wt% to 25wt% based on the total mass of the casting solution.

4. The preparation method according to claim 1 or 2, wherein the mass percentage concentration of the hydrophilic nanofiller is 0.5wt% to 5.0wt% based on the total mass of the casting solution.

5. The preparation method according to claim 1 or 2, wherein the aqueous monomer is at least one selected from polyamide amine, polyethyleneimine, piperazine and m-phenylenediamine.

6. The preparation method according to claim 1 or 2, wherein the mass percentage concentration of the acid-binding agent is 0.1~2.0 wt% based on the total mass of the aqueous solution.

7. The preparation method according to claim 1 or 2, wherein the oil phase monomer is at least one selected from pyromellitic methyl chloride, 1,3,5-benzenetrisulfonyl chloride, 3,4,5-biphenyltriacyl chloride and 3,3',5,5'-biphenyltetraacyl chloride.

8. The preparation method according to claim 1 or 2, wherein the mass percentage concentration of the pore size regulator is 0.05wt% to 0.5wt% based on the total mass of the oil phase solution.

9. A nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

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