Negatively charged composite nanofiltration membrane, preparation method therefor, and application thereof

Abstract

The present invention relates to the technical field of membrane separation. Disclosed are a negatively charged composite nanofiltration membrane, a preparation method therefor, and an application thereof. The negatively charged composite nanofiltration membrane sequentially comprises a bottom layer, a porous support layer, and a polyamide separation layer; a sulfonic acid group and / or a sulfonate group represented by formula I are grafted to the polyamide separation layer by means of N atoms; formula I, where M is H, Li, Na, or K, and R1 and R2 are each independently H or C1-C6 alkyl or phenyl; (aa) is the position at which the group represented by formula I and the polyamide separation layer are linked to form a bond; and Ar is derived from a post-reaction residue of a compound containing an electron-withdrawing group. In the composite nanofiltration membrane, a sulfonic acid group and / or a sulfonate group of a specific structure are grafted to the polyamide separation layer such that the surface of the composite nanofiltration membrane is negatively charged, thereby improving selectivity with respect to monovalent ions / divalent ions while maintaining a high water flux.

Description

Negatively charged composite nanofiltration membranes, their preparation methods and applications

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202411596852.1, filed on November 8, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of membrane separation technology, specifically to a negatively charged composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0004] Nanofiltration membranes are separation membrane materials with pore sizes ranging from 0.1 to 1 nanometer, and an average molecular weight cutoff (MWCO) of 200-1000 Da. They can effectively separate divalent and monovalent inorganic salts. Due to their advantages such as low operating pressure and high separation precision, nanofiltration technology has been widely used in seawater desalination, zero discharge of industrial wastewater, and resource recovery.

[0005] In industrial wastewater zero-discharge and resource recovery processes, sodium sulfate and sodium chloride need to be separated to obtain sodium sulfate products with high purity. Currently, the separation efficiency of commercially available nanofiltration membranes and those reported in literature and patents for sodium sulfate and sodium chloride needs further improvement. J. Tannenen et al. systematically investigated the ion selectivity of five commercial nanofiltration membranes—Desal-5 DK, NF-270, NF(Dow), NF-20, and ESNA-1-LF—in single-salt solutions (NaCl) and mixed-salt solutions (NaCl / Na2SO4, molar ratio 1:1) under constant permeate flux conditions (Journal of Membrane Science 283(2006)57-64). They found that commercial nanofiltration membranes struggle to simultaneously achieve high Na2SO4 rejection and high NaCl permeability, thus hindering efficient separation and resource recovery of both.

[0006] Introducing negatively charged groups onto the membrane surface is an effective way to achieve high sodium sulfate rejection rates. The separation principle of negatively charged nanofiltration membranes is based on two factors: physical sieving based on pore size and electrostatic adsorption and repulsion based on the Donnan effect. Furthermore, by introducing charged groups, the membrane's hydrophilicity is enhanced, operating pressure is reduced, and it offers advantages in terms of antifouling resistance and selective permeability.

[0007] Most charge modification methods will significantly reduce membrane water flux. Although they improve the separation efficiency of monovalent and divalent salts, they do not offer an advantage in overall water treatment efficiency.

[0008] Therefore, there is an urgent need to provide a charged nanofiltration membrane with high water flux and high efficiency in separating monovalent / divalent salts. Summary of the Invention

[0009] The purpose of this invention is to overcome the limitations of existing composite nanofiltration membranes, which cannot simultaneously maintain high monovalent / divalent anion selectivity and high water flux. This invention provides a negatively charged composite nanofiltration membrane, its preparation method, and its application. This negatively charged composite nanofiltration membrane has sulfonic acid groups and / or sulfonate groups of a specific structure grafted into the polyamide separation layer, enabling the composite nanofiltration membrane surface to be negatively charged, thus improving monovalent / divalent anion selectivity while maintaining high water flux.

[0010] The first aspect of the present invention provides a negatively charged composite nanofiltration membrane, wherein the negatively charged composite nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer and a polyamide separation layer;

[0011] The polyamide separation layer is grafted with N atoms to form sulfonic acid groups and / or sulfonate groups as shown in Formula I;

[0012] Wherein, M is H, Li, Na or K, and R1 and R2 are each independently H, C1-C6 alkyl or phenyl;

[0013] The location where the group shown in Formula I is bonded to the polyamide separation layer;

[0014] Ar comes from the residues following the reaction of compounds containing electron-withdrawing groups.

[0015] A second aspect of the present invention provides a method for preparing a negatively charged composite nanofiltration membrane, wherein the preparation method includes the following steps:

[0016] S1. Prepare a porous support layer and a polyamide separation layer on the bottom layer to obtain a composite membrane;

[0017] S2. The composite membrane is contacted with an aqueous solution containing an aldehyde compound of Formula 1, an electron-withdrawing sulfonate and / or an electron-withdrawing sulfonic acid compound and an acid catalyst, and then dried to obtain the negatively charged composite nanofiltration membrane.

[0018] R1 and R2 are each independently H, C1-C6 alkyl or phenyl.

[0019] A third aspect of the present invention provides a negatively charged composite nanofiltration membrane prepared by the above-described preparation method.

[0020] The fourth aspect of the present invention provides an application of the above-mentioned negatively charged composite nanofiltration membrane in water treatment.

[0021] Through the above technical solutions, the negatively charged composite nanofiltration membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0022] The negatively charged composite nanofiltration membrane provided by this invention grafts sulfonic acid groups and / or sulfonate groups of a specific structure into the polyamide separation layer, which enables the composite nanofiltration membrane to exhibit a negative charge, thereby improving the selectivity of monovalent / divalent anions while maintaining a high water flux.

[0023] In this invention, the Mannnich reaction mechanism is used to modify the composite nanofiltration membrane. Sulfonates and / or sulfonic acid compounds containing electron-withdrawing groups react with primary and / or secondary amine groups in the polyamide separation layer. This allows sulfonic acid groups and / or sulfonate groups with specific structures to be grafted onto the polyamide separation layer, significantly increasing the negative charge density on the surface of the composite nanofiltration membrane. The repulsion effect between negative charges enhances the membrane's retention efficiency for sulfate ions. Furthermore, the sulfonic acid / sulfonate groups are strongly hydrophilic, and this modification method creates a relatively loose structure. Therefore, while maintaining a high water flux, the separation efficiency for monovalent / divalent anions is improved.

[0024] Furthermore, in the present invention, during the preparation of the polyamide separation layer by interfacial polymerization, a first organic solvent is added to the first liquid phase containing polyamines. In particular, by controlling the concentration of the first organic solvent in the first liquid phase, the interfacial polymerization reaction process can be regulated, thereby preparing a composite nanofiltration membrane with high water flux, which provides a basis for the high water flux of the charged nanofiltration membrane. Attached Figure Description

[0025] Figure 1 shows the surface infrared spectra of the composite nanofiltration membranes obtained in Example 1 and Comparative Example 1.

[0026] Figure 2 shows the surface SEM image (left) and AFM image (right) of the composite nanofiltration membrane obtained in Example 1. Detailed Implementation

[0027] The first aspect of the present invention provides a negatively charged composite nanofiltration membrane, wherein the negatively charged composite nanofiltration membrane comprises, in sequence, a bottom layer, a support layer and a polyamide separation layer;

[0028] The polyamide separation layer is grafted with N atoms to form sulfonic acid groups and / or sulfonate groups as shown in Formula I;

[0029] Wherein, M is H, Li, Na or K, and R1 and R2 are each independently H, C1-C6 alkyl or phenyl;

[0030] The location where the group shown in Formula I is bonded to the polyamide separation layer;

[0031] Ar comes from the residues following the reaction of compounds containing electron-withdrawing groups.

[0032] In this invention, the negatively charged composite separation membrane has sulfonic acid groups and / or sulfonate groups of a specific structure grafted into the polyamide separation layer, which makes the surface of the composite nanofiltration membrane negatively charged, thereby improving the selectivity of monovalent / divalent anions while maintaining a high water flux.

[0033] Furthermore, the inventors discovered that the negatively charged composite separation membrane provided by this invention is rich in sulfonic acid or sulfonate groups (-SO3M), which can weaken the interaction with common metal ions or metal oxides that cause fouling on the membrane surface, effectively reducing various fouling ions, especially Ca. 2+ The adsorption on the membrane surface during heterogeneous nucleation reduces the adhesion and growth of crystal nuclei on the membrane surface, thus giving the negatively charged composite separation membrane provided by this invention excellent anti-fouling performance.

[0034] In this invention, The groups represented by Formula I and the -NH- or -NH- in the polyamide separation layer The location where the connection forms a bond.

[0035] Furthermore, M is H or Na.

[0036] In this invention, the "C1-C6 alkyl group" can be a straight-chain alkyl group or a branched alkyl group of C1-C6, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isopentyl, n-hexyl or isohexyl.

[0037] Furthermore, R1 and R2 are each independently selected from H or C1-C5 alkyl groups.

[0038] Furthermore, the electron-withdrawing group is selected from one of carbonyl, carboxyl, ester, alkynyl, cyano, or phenolic hydroxyl groups.

[0039] According to the present invention, *-Ar-SO3M is selected from at least one of the following groups:

[0040] R3, R4, R5 and R6 are each independently H, C1-C3 alkyl, NH2 or -SO3M, and at least one of R3, R4, R5 and R6 is -SO3M;

[0041] Wherein, R7 is H, methyl, or ethyl; R8 and R9 are each independently an H or a C1-C3 alkyl group;

[0042] Among them, R10 It can be an alkynyl or carboxyl group, where m is an integer between 0 and 3;

[0043] Where z is an integer from 1 to 3;

[0044] Among them, R 16 It is a C1-C3 alkylene group, R 17 and R 18 Each is independently a C1-C8 straight-chain alkyl or branched alkyl.

[0045] In this invention, the "C1-C3 alkylene group" can be -CH2-, -CH2CH2-, -CH2CH2CH2- or -CH2(CH3)2-.

[0046] In this invention, when *Ar-SO3M has the above-mentioned specific structure, it can impart negative electrical properties to the surface of the nanofiltration membrane, improve the sieving efficiency for monovalent / divalent anions, and cause very little loss to the flux, thus meeting the requirements of high sieving efficiency and high flux of nanofiltration membrane.

[0047] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0048] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0049] In one specific embodiment of the present invention, *——Ar——SO3M is In this configuration, any two of R3, R4, R5, and R6 are H, any one of R3, R4, R5, and R6 is a methyl group, and any one of R3, R4, R5, and R6 is -SO3M, where M is H or Na.

[0050] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0051] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0052] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0053] In one specific embodiment of the present invention, *——Ar——SO3M is Where M is H or Na.

[0054] In one specific embodiment of the present invention, *——Ar——SO3M is Among them, R 16 Methylene, R 17 and R 18 Each is an independent C8 straight-chain alkyl group, and M is H or Na.

[0055] According to the present invention, the sulfur atom content in the polyamide separation layer of the negatively charged composite nanofiltration membrane is 0.1-5 at.%.

[0056] In this invention, when the content of sulfur atoms in the polyamide separation layer of the negatively charged composite nanofiltration membrane meets the above-mentioned range, the content of sulfonic acid groups and / or sulfonate groups in the separation layer is relatively high, which makes the nanofiltration membrane have strong hydrophilicity and surface negative charge.

[0057] In this invention, the sulfur atom content in the polyamide separation layer of the negatively charged composite nanofiltration membrane is 0.1-5 at.%, for example, it can be 0.1 at.%, 0.2 at.%, 0.3 at.%, 0.4 at.%, 0.5 at.%, 0.6 at.%, 0.7 at.%, 0.8 at.%, 0.9 at.%, 1.1 at.%, 1.2 at.%, 1.3 at.%, 1.4 at.%, 1.5 at.%, 1.6 at.%, 1.7 at.%, 1.8 at.%, 1.9 at.%, 2.0 at.%, 2.1 at.%, 2.2 at.%, 2.3 at.%, 2.4 at.%. 2.5 at.%, 2.6 at.%, 2.7 at.%, 2.8 at.%, 2.9 at.%, 3 at.%, 3.1 at.%, 3.2 at.%, 3.3 at.%, 3.4 at.%, 3.5 at.%, 3.6 at.%, 3.7 at.%, 3.8 at.%, 3.9 at.%, 4 at.%, 4.1 at.%, 4.2 at.%, 4.3 at.%, 4.4 at.%, 4.5 at.%, 4.6 at.%, 4.7 at.%, 4.8 at.%, 4.9 at.%, 5 at.%, and any range consisting of two values, preferably 0.5-3 at.%.

[0058] According to the present invention, at pH=7, the surface Zeta potential of the negatively charged composite nanofiltration membrane is -50mV to -30mV.

[0059] In this invention, when the surface Zeta potential of the negatively charged composite nanofiltration membrane meets the above range at pH=7, it indicates that the surface negative charge density of the negatively charged composite nanofiltration membrane is high, which can improve the rejection rate of divalent and high-valence anions of the nanofiltration membrane.

[0060] In this invention, at pH=7, the surface Zeta potential of the negatively charged composite nanofiltration membrane is -50mV to -30mV, for example, it can be -50mV, -49mV, -48mV, -47mV, -46mV, -45mV, -44mV, -43mV, -42mV, -41mV, -40mV, -39mV, -38mV, -37mV, -36mV, -35mV, -34mV, -33mV, -32mV, -31mV, -30mV, or any range of two values.

[0061] Furthermore, at pH=7, the surface Zeta potential of the negatively charged composite nanofiltration membrane is -45mV to -35mV.

[0062] According to the present invention, the average pore size of the negatively charged composite nanofiltration membrane is 0.1-0.5 nm.

[0063] In this invention, when the average pore size of the negatively charged composite nanofiltration membrane meets the above-mentioned range, the pore size of the separation layer of the composite nanofiltration membrane is small and the pore size distribution is narrow, which can significantly improve the retention capacity of the composite nanofiltration membrane for divalent anions.

[0064] In this invention, the average pore size of the negatively charged composite nanofiltration membrane is 0.1-0.5 nm, for example, it can be 0.1 nm, 0.11 nm, 0.12 nm, 0.13 nm, 0.14 nm, 0.15 nm, 0.16 nm, 0.17 nm, 0.18 nm, 0.19 nm, 0.2 nm, 0.21 nm, 0.22 nm, 0.23 nm, 0.24 nm, 0.25 nm, 0.26 nm, 0.27 nm, or 0.28 nm. 0.29nm, 0.3nm, 0.31nm, 0.32nm, 0.33nm, 0.34nm, 0.35nm, 0.36nm, 0.37nm, 0.38nm, 0.39nm, 0.4nm, 0.41nm, 0.42nm, 0.43nm, 0.44nm, 0.45nm, 0.46nm, 0.47nm, 0.48nm, 0.49nm, 0.50nm, and any range of two values.

[0065] Furthermore, the average pore size of the negatively charged composite nanofiltration membrane is 0.15-0.35 nm, more preferably 0.20 nm-0.35 nm.

[0066] According to the present invention, the contact angle of the negatively charged composite nanofiltration membrane is 20-80°.

[0067] In this invention, when the contact angle of the negatively charged composite nanofiltration membrane meets the above-mentioned range, the surface of the composite nanofiltration membrane has strong hydrophilicity and good water wetting ability, which is beneficial to obtaining a higher water flux.

[0068] In this invention, the contact angle of the negatively charged composite nanofiltration membrane is 20-80°, for example, it can be 20°, 22°, 24°, 26°, 28°, 30°, 32°, 34°, 36°, 38°, 40°, 42°, 44°, 46°, 48°, 50°, or any range of two values.

[0069] Furthermore, the contact angle of the negatively charged composite nanofiltration membrane is 30-50°.

[0070] In this invention, there is no specific limitation on the materials of the bottom layer and the porous support layer. They can be made of various existing materials that have a certain strength and can be used for nanofiltration and reverse osmosis membranes.

[0071] In this invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyolefin.

[0072] In this invention, the porous support layer material can be at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0073] According to the present invention, the thickness of the bottom layer, the porous support layer, and the separation layer is not particularly limited, and can be a conventional choice in the art. However, in order to enable these three layers to play a better synergistic role and to enable the resulting composite nanofiltration membrane to better combine excellent separation efficiency for divalent anions (e.g., sulfate ions) and monovalent anions (e.g., chloride ions) and high water flux, the thickness of the bottom layer is preferably 30-150 μm, for example, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or 55 μm. The thickness of the porous support layer is 10-100 μm, for example, it can be 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, or any two values ​​within a range, preferably 50-120 μm; The thickness of the separation layer is 10-500 nm, for example, it can be 10 nm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or any two values ​​in the range, preferably 30-70 μm; the thickness of the separation layer is 10-500 nm, for example, it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm. The range is 120nm, 125nm, 130nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 175nm, 180nm, 185nm, 190nm, 195nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, and any range of two values, preferably 30-300nm.

[0074] A second aspect of the present invention provides a method for preparing a negatively charged composite nanofiltration membrane, characterized in that the preparation method includes the following steps:

[0075] S1. Prepare a porous support layer and a polyamide separation layer on the bottom layer to obtain a composite membrane;

[0076] S2. The composite membrane is contacted with an aqueous solution containing an aldehyde compound of Formula 1, an electron-withdrawing sulfonate and / or an electron-withdrawing sulfonic acid compound and an acid catalyst, and then dried to obtain the negatively charged composite nanofiltration membrane.

[0077] R1 and R2 are each independently H, C1-C6 alkyl or phenyl.

[0078] In this invention, an electron-withdrawing sulfonate and / or electron-withdrawing sulfonic acid compound reacts with primary and / or secondary amine groups in the polyamide separation layer via the Mannich reaction. This allows for the grafting of sulfonic acid and / or sulfonate groups with specific structures onto the polyamide separation layer, significantly increasing the negative charge density on the surface of the composite nanofiltration membrane. The repulsive effect between negative charges enhances the membrane's retention of sulfate ions. Simultaneously, the specific sulfonic acid and / or sulfonate groups possess a loose molecular structure, preventing a decrease in flux after nanofiltration membrane modification. This improves the separation efficiency for monovalent / divalent anions while maintaining high water flux in the nanofiltration membrane.

[0079] The present invention does not particularly limit the method for preparing a porous support layer on the substrate. Conventional methods in the art can be used for preparation, with phase inversion being preferred. Specifically, a polymer solution of a porous support layer material is coated on one surface of the substrate, and a porous support layer is obtained through phase inversion.

[0080] In this invention, the sulfonate containing electron-withdrawing groups can be a conventional salt in the art, such as sodium sulfonate, potassium sulfonate, or lithium sulfonate.

[0081] In this invention, the phase inversion method is preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20% by weight, degassing at 20-40°C for 10-180 min; then coating the polymer solution onto the substrate to obtain an initial film, and then immersing it in water at a temperature of 10-30°C for 10-60 min, thereby obtaining the support layer polymer porous membrane through phase inversion.

[0082] The solvent may be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0083] In this invention, there are no particular limitations on the method for preparing the polyamide separation layer on the porous support layer; conventional methods in the art can be used.

[0084] In a preferred embodiment of the present invention, the composite membrane is prepared according to the following steps:

[0085] (1) Prepare a porous intermediate layer on the bottom layer;

[0086] (2) The membrane obtained in step (1) is brought into first contact with a first liquid phase; wherein the first liquid phase includes a polyamine, a first organic solvent and water;

[0087] (3) The membrane obtained in step (2) is brought into a second contact with the second liquid phase, and after heat treatment, the composite membrane is obtained; wherein, the second liquid phase includes polyacrylamide chloride and a second organic solvent;

[0088] According to the present invention, the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, ethanol and methanol.

[0089] In this invention, the polyamine is selected from at least one of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylene polyamine, piperazine, m-phenylenediamine, and p-phenylenediamine, preferably selected from polyethyleneimine and / or polyethylene polyamine.

[0090] In this invention, the polyacryl chloride is selected from at least one of 1,3,5-benzenetricarboxyl chloride, 1,2-benzenedicarboxyl chloride, 1,3-benzenedicarboxyl chloride, 1,4-benzenedicarboxyl chloride, and adipyl chloride, preferably selected from 1,3,5-benzenetricarboxyl chloride and / or 1,4-benzenedicarboxyl chloride.

[0091] According to the present invention, the concentration of the first organic solvent in the first liquid phase is 0.05-6 wt%.

[0092] In this invention, during the preparation of the polyamide separation layer by interfacial polymerization, the first organic solvent in the first liquid phase containing the polyamine, and particularly by controlling the concentration of the first organic solvent in the first liquid phase, can achieve the regulation of the interfacial polymerization reaction process, and further prepare a composite nanofiltration membrane with high water flux, providing a basis for the high water flux of the charged nanofiltration membrane.

[0093] In this invention, the concentration of the first organic solvent in the first liquid phase is 0.05-6 wt%, for example, it can be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%. 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3wt%, and any range of two values.

[0094] Furthermore, in the first liquid phase, the concentration of the first organic solvent is 0.1-3 wt%.

[0095] In this invention, the concentration of the polyamine in the aqueous phase is 0.05wt%-5wt%, for example, it can be 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.75wt%, 0.8wt%, 0.85wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, or any two of these values, preferably 0.2wt%-2wt%.

[0096] In this invention, the concentration of polyacrylamide chloride in the second liquid phase is 0.01wt%-1wt%, for example, it can be 0.01wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, or any two of these values, preferably 0.1wt%-0.5wt%.

[0097] In this invention, the amounts of the first liquid phase and the second liquid phase are such that the mass ratio of polyamine to polyacrylamide chloride is 1-50:1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 30:1, 32:1, 34:1, 36:1, 38:1, 40:1, 42:1, 44:1, 46:1, 50:1, or any range of two values, preferably 2-20:1.

[0098] In this invention, when preparing the polyamide separation layer on the porous support layer, the ratio of the volume of the first liquid phase to the membrane area of ​​the porous support layer is 0.05-1 mL / cm². 2 For example, it can be 0.05 mL / cm 2 0.1 mL / cm 2 0.2 mL / cm 2 0.3 mL / cm 2 0.4 mL / cm 2 0.5 mL / cm 2 0.6 mL / cm 2 0.7 mL / cm 2 0.8 mL / cm2 0.9 mL / cm 2 1mL / cm 2 The ratio of the volume of the second liquid phase to the membrane area of ​​the porous support layer is 0.01-0.5 mL / cm², and any two values ​​within a range. 2 For example, it can be 0.05 mL / cm 2 0.1 mL / cm 2 0.2 mL / cm 2 0.3 mL / cm 2 0.4 mL / cm 2 0.5 mL / cm 2 , and the range of any two values.

[0099] In this invention, there is no particular limitation on the type of the second organic solvent, as long as it can dissolve the polyacrylamide chloride. Preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0100] In this invention, the conditions for the interfacial polymerization of the polyamine and the polyacrylamide chloride are not particularly limited and can be carried out according to conventional conditions in the art. Preferably, in order to enable the composite nanofiltration membrane to better combine high water flux and excellent separation selectivity of divalent anions (e.g., sulfate) and monovalent anions (e.g., chloride), the contact time between the porous support layer and the first liquid phase is preferably 5-240 s, for example, 5 s, 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, or 110 s. The time between the porous support layer and the second liquid phase is 10-200 s, for example, 10 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, 220 s, 230 s, 240 s, or any two values ​​within a range, preferably 10-180 s; the time between the porous support layer and the second liquid phase is 10-200 s, for example, 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s. The heat treatment temperature is 40-60℃, for example, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, for example, 45-55℃; the heat treatment time is 0.5-20min, for example, 0.5min, 1min... n, 1.5min, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 7.5min, 8min, 8.5min, 9min, 9.5min, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min, 20min, and any range of two values, preferably 1-10min.

[0101] In one specific embodiment of the present invention, R1 and R2 are each independently selected from alkyl groups that are H or C1-C5.

[0102] In this invention, the aldehyde compounds represented by Formula 1 include, but are not limited to, at least one of acyclic aliphatic aldehydes such as formaldehyde, acetaldehyde, pentanal, octanal, nonanal, decanal, and undecaldehyde, or aromatic aldehydes such as benzaldehyde, phenylacetaldehyde, and phenylpropanal.

[0103] In one specific embodiment of the present invention, the electron-withdrawing group is selected from one of carbonyl, carboxyl, ester, alkynyl, cyano, or phenolic hydroxyl groups.

[0104] According to the present invention, the sulfonate containing an electron-withdrawing group and / or the sulfonic acid compound containing an electron-withdrawing group are selected from at least one of the following:

[0105] R3, R4, R5 and R6 are each independently H, C1-C3 alkyl, NH2 or -SO3M, and at least one of R3, R4, R5 and R6 is -SO3M;

[0106] Wherein, R7 is H, methyl, or ethyl; R 11 R 12 R 13 R 14 R 15 Each is independently H or -SO3M, and R 11 and R 12 At least one of them is H;

[0107] R8 and R9 are each independently an H or a C1-C3 alkyl group;

[0108] Among them, R 10 It can be an alkynyl or carboxyl group, where m is an integer between 0 and 3;

[0109] Where z is an integer from 1 to 3;

[0110] Among them, R 16 It is a C1-C3 alkylene group, R 17 and R 18 Each is independently a C1-C8 straight-chain alkyl or branched alkyl, and M is H, Li, Na or K.

[0111] In this invention, the sulfonates containing electron-withdrawing groups and / or sulfonic acid compounds containing electron-withdrawing groups include, but are not limited to, camphor sulfonic acid, sodium camphor sulfonate, o-hydroxybenzene sulfonic acid, m-hydroxybenzene sulfonic acid, p-hydroxybenzene sulfonic acid, sodium o-hydroxybenzene sulfonate, sodium m-hydroxybenzene sulfonate, sodium p-hydroxybenzene sulfonate, 2-aminophenol-4-sulfonic acid, o-cresol sulfonic acid, m-cresol sulfonic acid, p-cresol sulfonic acid, sodium 2-acetylbenzene sulfonate, sodium 3-acetylbenzene sulfonate, sodium 4-acetylbenzene sulfonate, sodium 1-acetylindoline-2-sulfonate, sodium propargyl sulfonate, sulfonic acid acetic acid, sulfonic acid propionic acid, sodium dioctyl succinate sulfonate, sodium diisobutyl succinate sulfonate, and D-2-amino-4-sulfobutyric acid.

[0112] In one specific embodiment of the present invention, the acid catalyst is selected from hydrochloric acid and / or sulfuric acid.

[0113] According to the present invention, in step S2, the concentration of the aldehyde compound in the aqueous solution is 0.05-5 wt%, for example, it can be 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, 5 wt%, or any range of two values; the concentration of the sulfonate containing an electron-withdrawing group and / or the sulfonic acid compound containing an electron-withdrawing group is 0.05-5 wt%, for example, it can be 0.05 wt%. The concentrations of the acid catalyst are 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, 5 wt%, and any two of these values; the concentration of the acid catalyst is 0.01%-0.15 wt%, for example, 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.07 wt%, 0.09 wt%, 0.11 wt%, 0.13 wt%, 0.15 wt%, and any two of these values.

[0114] In this invention, when the concentrations of aldehyde compounds, sulfonates containing electron-withdrawing groups, and / or sulfonic acid compounds containing electron-withdrawing groups in the aqueous solution meet the above-mentioned ranges, the resulting composite nanofiltration membrane can better combine high water flux with excellent separation selectivity for divalent anions (e.g., sulfate ions) and monovalent anions (e.g., chloride ions).

[0115] Further, in step S2, the concentration of the aldehyde compound in the aqueous solution is 0.1-4 wt%; the concentration of the sulfonate containing electron-withdrawing groups and / or the sulfonic acid compound containing electron-withdrawing groups is 0.1-4 wt%; and the concentration of the acid catalyst is 0.03 wt%-0.12 wt%.

[0116] In this invention, there are no particular limitations on the contact conditions between the composite membrane and the aqueous solution containing aldehyde compounds, sulfonates containing electron-withdrawing groups and / or sulfonic acid compounds containing electron-withdrawing groups, and acid catalysts in step S2. Preferably, in order to enable the composite nanofiltration membrane to better combine high water flux and excellent separation selectivity of divalent anions (e.g., sulfate ions) and monovalent anions (e.g., chloride ions), the contact conditions include: a contact time of 5-240 s, for example, 5 s, 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, 220 s, 230 s, 240 s, and any two of these values, preferably 10-180 s. More preferably, the drying conditions include: a drying temperature of 20-80℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, and any range of two values, preferably 30-70℃; and a drying time of 0.5-120 min, for example, 0.5 min, 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, 120 min, and any range of two values, preferably 1-60 min.

[0117] In this invention, when the composite membrane comes into contact with an aqueous solution containing aldehyde compounds, active sulfonic acid or sulfonate compounds, and an acid catalyst, the ratio of the volume of the aqueous solution to the membrane area of ​​the composite membrane is 0.1-5 mL / cm². 2 For example, it can be 0.1 mL / cm 2 0.2 mL / cm 2 0.3 mL / cm 2 0.4 mL / cm 2 0.5 mL / cm 2 0.6 mL / cm 2 0.7 mL / cm 2 0.8 mL / cm 2 0.9 mL / cm 2 1mL / cm 2 1.2 mL / cm 2 1.4 mL / cm 2 1.6 mL / cm 21.8 mL / cm 2 2mL / cm 2 2.2 mL / cm 2 2.4 mL / cm 2 2.6 mL / cm 2 2.8 mL / cm 2 3mL / cm 2 3.2 mL / cm 2 3.4 mL / cm 2 3.6 mL / cm 2 3.8 mL / cm 2 4mL / cm 2 4.2 mL / cm 2 4.4 mL / cm 2 4.6 mL / cm 2 4.8 mL / cm 2 5mL / cm 2 And the range of any two values, preferably 0.5-3 mL / cm 2 .

[0118] A third aspect of the present invention provides a negatively charged composite nanofiltration membrane prepared by the above-described preparation method.

[0119] A fourth aspect of the present invention provides an application of the above-mentioned negatively charged composite nanofiltration membrane in the field of water treatment.

[0120] The present invention will be described in detail below through embodiments.

[0121] In the following embodiments and comparative examples:

[0122] (1) The water flux of the separation membrane was obtained by testing it using the following method: The separation membrane was installed in the membrane tank, and the water permeation rate of the separation membrane was measured over a certain period of time under the conditions of 0.5 MPa and 25°C. The water flux was then calculated using the following formula: J=Q / (A·t) (1)

[0123] Where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the separation membrane (m²). 2 ), where t is time (h);

[0124] (2) The rejection rate of the separation membrane for a single salt was tested using the following method: The composite separation membrane was loaded into a membrane tank. The original aqueous solution was sodium chloride or sodium sulfate with a concentration of 2000 ppm. After pre-pressurization at 0.5 MPa for 0.5 h, the permeate was obtained at a pressure of 0.5 MPa, and the desalination rate was calculated using the following formula: R = (Cf -C p ) / C f ×100% (2)

[0125] Where R is the desalination rate, C f The concentration of sodium chloride or sodium sulfate in the original aqueous solution (measured by conductivity method), ppm, C p The concentration of sodium chloride or sodium sulfate in the permeate (measured by conductivity), in ppm;

[0126] (3) Measurement of contact angle of nanofiltration membrane surface

[0127] The surface contact angle of the composite film sample was tested using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany, via the static drop method. Before the test, the sample was dried in a vacuum oven at 60°C for 30 minutes to remove surface and internal moisture. The dried film was then attached to a flat glass slide with double-sided tape. The volume of the water droplet was 4 μL each time during the test. The image was captured immediately 3 seconds after the water droplet landed on the film surface. The final contact angle was determined by taking the average value after multiple measurements.

[0128] (4) Determination of sulfur atom content on the surface of nanofiltration membrane:

[0129] Before measurement, the samples were dried to constant weight in an oven, and the elemental composition of the composite film sample surface was determined using a Sigma Probe X-ray photoelectron spectrometer manufactured by Thermo VG, UK.

[0130] (5) Total reflectance infrared spectroscopy characterization of nanofiltration membrane surface (ATR-FTIR)

[0131] Before testing, the samples were dried to constant weight in an oven, and attenuated total reflectance infrared spectroscopy was used. The infrared spectrum of the nanofiltration membrane was determined using a Fourier transform infrared spectrometer (Nicolet 6700, USA).

[0132] (6) Zeta potential test of membrane surface: The test was performed using a Surpass electric analyzer (Anton Paar), the circulating solution was a dilute aqueous solution of KCl, and the pH of the test solution was 7.

[0133] (7) Membrane surface morphology test: The surface morphology was tested using a Hitachi S-4800 scanning electron microscope.

[0134] (8) Membrane surface roughness test: The surface roughness was tested using an atomic force microscope (AFM) of Park Systems, South Korea, model Park FX-40.

[0135] (9) Anti-scaling performance test:

[0136] A gypsum solution with a saturation index (SI) of 1.0 was used as the model system to test the anti-fouling performance of the membrane. The test solution was a mixed solution of CaCl2 and Na2SO4, with a CaCl2 concentration of 1905 mg / L and a Na2SO4 concentration of 6683 mg / L. The above process was a continuous test, with the feed system maintained at 25°C to eliminate the influence of temperature on membrane flux changes and fouling. The test lasted for 40 hours. After the fouling test, a 1 cm sample was taken from the membrane. 2 The sample was placed in 20 mL of deionized water and sonicated for 30 min, then stirred for 24 hours to fully dissolve the calcium sulfate crystals deposited on the membrane surface, yielding the test solution S. A standard curve (ρconductivity) was established to predict the conductivity versus concentration of the calcium sulfate standard solution. CaSO4 ~σ curve), determine the conductivity of the test solution S, based on ρ CaSO4 The concentration ρ of calcium sulfate in the test solution S was calculated using the σ curve. CaSO4 Based on the volume L of the solution to be tested, the mass m of calcium sulfate in the solution to be tested is calculated.

[0137] Additionally, in the following embodiments and comparative examples:

[0138] Polyethyleneimine (weight average molecular weight of 25000 g / mol), 1,3,5-benzenetricarboxyl chloride, formaldehyde, acetaldehyde, propionaldehyde, camphor sulfonic acid, p-hydroxybenzene sulfonic acid, sodium 3-acetylbenzene sulfonate, sodium dioctyl succinate sulfonate, hydrochloric acid, etc. were all purchased from Bailingwei Technology Co., Ltd., and other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0139] The support layer is prepared using a phase transformation method, and the specific steps are as follows:

[0140] A certain amount of polyethersulfone (number average molecular weight of 80,000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polyethersulfone solution with a concentration of 18 wt%. The solution was degassed at 25 °C for 120 min. Then, the polyethersulfone solution was coated onto a polyester nonwoven fabric (75 μm thick) using a doctor blade to obtain an initial film. The film was then immersed in water at 25 °C for 60 min, which allowed the polyethersulfone layer on the surface of the polyester nonwoven fabric to undergo phase transformation into a porous film. Finally, after three water washes, a support layer with a total thickness of 115 μm was obtained.

[0141] Example 1

[0142] S1, with an area of ​​400cm² 2 The upper surface of the polysulfone support layer is in contact with 50 mL of a first liquid phase containing 0.5 wt% polyethyleneimine, 0.2 wt% N-methylpyrrolidone, and water (the volume ratio of the first liquid phase to the film area of ​​the support layer is 0.125 mL / cm²). 2After contacting at 25°C for 120 seconds, the liquid was drained; then, the upper surface of the support layer was contacted again with 50 mL of a second liquid phase containing 0.1 wt% 1,3,5-benzenetriformyl chloride and Isopar E solution (the volume ratio of the second liquid phase to the membrane area of ​​the support layer was 0.125 mL / cm²). 2 The membrane was contacted at 25°C for 120 seconds, and then drained. The membrane was placed in an oven and heated at 50°C for 10 minutes to obtain a composite membrane. The mass ratio of polyethyleneimine to 1,3,5-benzenetricarboxylic acid chloride was 5:1.

[0143] S2. Immerse the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid (the volume ratio of the aqueous solution to the membrane area of ​​the composite membrane is 1.25 mL / cm²). 2 After 1 minute, the membrane is removed and dried at 50°C for 5 minutes to obtain composite nanofiltration membrane N1.

[0144] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0145] As shown in Figure 1, characteristic peaks of sulfonic acid groups can be detected on the surface of the composite nanofiltration membrane N1, indicating that the Mannich reaction was successfully carried out and sulfonic acid groups with a specific structure were introduced onto the composite nanofiltration membrane.

[0146] Figure 2 (left) is a SEM image of the composite nanofiltration membrane N1 prepared in Example 1. As can be seen from Figure 2 (left), the membrane surface of the composite nanofiltration membrane N1 is dense, uniform and smooth. Figure 2 (right) is an AFM image of the composite nanofiltration membrane N1 prepared in Example 1. As can be seen from Figure 2 (right), the Ra value of the membrane surface of the composite nanofiltration membrane N1 is only 5.6 nm, which is very flat.

[0147] Example 2

[0148] Step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% acetaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N2.

[0149] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0150] Example 3

[0151] Step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% propionaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", to obtain composite nanofiltration membrane N3.

[0152] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0153] Example 4

[0154] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% p-hydroxybenzenesulfonic acid, and 0.04 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N4.

[0155] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0156] Example 5

[0157] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% sodium 3-acetylbenzenesulfonate, and 0.04 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N5.

[0158] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0159] Example 6

[0160] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% sodium dioctyl succinate, and 0.04 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N6.

[0161] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0162] Example 7

[0163] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 1 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid" to obtain the composite nanofiltration membrane N7.

[0164] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0165] Example 8

[0166] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.15 wt% formaldehyde, 1 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N8.

[0167] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0168] Example 9

[0169] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.1 wt% hydrochloric acid", to obtain the composite nanofiltration membrane N9.

[0170] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0171] Example 10

[0172] In step S1, "the area is 400cm²" 2 The upper surface of the polysulfone support layer is in contact with 50 mL of a first liquid phase containing 0.5 wt% polyethyleneimine, 0.2 wt% N-methylpyrrolidone, and water (the volume ratio of the first liquid phase to the film area of ​​the support layer is 0.125 mL / cm²). 2 ")" is changed to "the area is 400cm" 2 The upper surface of the polysulfone support layer is in contact with 50 mL of a first liquid phase containing 0.5 wt% polyethyleneimine and water (the volume ratio of the first liquid phase to the film area of ​​the support layer is 0.125 mL / cm²). 2 )”, to obtain the composite nanofiltration membrane N10.

[0173] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0174] Example 11

[0175] In step S1, "the area is 400cm²" 2 The upper surface of the polysulfone support layer is in contact with 50 mL of a first liquid phase containing 0.5 wt% polyethyleneimine, 0.2 wt% N-methylpyrrolidone, and water (the volume ratio of the first liquid phase to the film area of ​​the support layer is 0.125 mL / cm²). 2 ")" is changed to "the area is 400cm" 2 The upper surface of the polysulfone support layer is in contact with 50 mL of a first liquid phase containing 0.5 wt% polyethyleneimine, 1 wt% N-methylpyrrolidone, and water (the volume ratio of the first liquid phase to the film area of ​​the support layer is 0.125 mL / cm²). 2 )”, to obtain the composite nanofiltration membrane N11.

[0176] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0177] Comparative Example 1

[0178] The area is 400cm 2 The upper surface of the polysulfone support layer is contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethyleneimine and 0.2 wt% N-methylpyrrolidone (the volume ratio of the aqueous solution to the film area of ​​the support layer is 0.125 mL / cm²). 2 After contacting at 25°C for 120 seconds, the solution was drained; then, the upper surface of the support layer was contacted again with 50 mL of Isopar E solution containing 0.1 wt% 1,3,5-benzenetriformyl chloride (the ratio of the volume of the organic phase to the membrane area of ​​the support layer was 0.125 mL / cm²). 2 After contacting at 25℃ for 120s, the liquid was drained; the membrane was placed in an oven and heated at 50℃ for 10min to obtain a composite membrane. The mass ratio of polyethyleneimine to 1,3,5-benzenetricarboxylic acid chloride was 5:1, resulting in composite membrane D1.

[0179] Comparative Example 2

[0180] The step S2, "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 0.26 wt% formaldehyde, 2 wt% camphor sulfonic acid, and 0.04 wt% hydrochloric acid", is changed to "immersing the composite membrane obtained in step S1 in 500 mL of an aqueous solution containing 2 wt% camphor sulfonic acid and 0.04 wt% hydrochloric acid", to obtain composite nanofiltration membrane D2.

[0181] The physicochemical properties of the composite nanofiltration membrane were characterized and analyzed, and the results are shown in Table 1.

[0182] The thickness, surface zeta potential, average pore size, sulfur atom content in the polyamide separation layer, and contact angle of each layer of the composite membrane in the examples and comparative examples are shown in Table 1.

[0183] Table 1

[0184] The water flux and desalination rate of the composite nanofiltration membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 2.

[0185] Table 2

[0186] Compared with Comparative Examples 1 and 2, in Examples 1-11 of the present invention, the Mannich reaction mechanism is utilized to react sulfonates and / or sulfonic acid compounds containing electron-withdrawing groups with amino groups in the polyamide separation layer in the presence of aldehyde compounds. This introduces sulfonic acid groups and / or sulfonate groups with specific structures into the polyamide separation layer, which can significantly reduce the Zeta potential on the surface of the composite nanofiltration membrane, enhance the negative charge on the membrane surface, reduce the average pore size of the composite nanofiltration membrane, and improve the hydrophilicity of the composite nanofiltration membrane. When used for water treatment, it can improve the rejection rate of divalent sulfate ions while having high permeability to monovalent chloride ions. At the same time, the water flux of the composite nanofiltration membrane remains at a high level, thereby achieving efficient separation of salts and minerals.

[0187] As can be seen from Examples 1, 10 and 11, adding a certain concentration of organic solvent to the first liquid phase during the interfacial polymerization process can further improve the water flux of the composite nanofiltration membrane.

[0188] Comparative Example 1, Comparative Example 1, and commercially available DuPont products TM FilmTec TM The anti-fouling performance of the NF270 nanofiltration membrane was tested, and the results are shown in Table 3.

[0189] Table 3

[0190] Compared to the composite nanofiltration membrane D1 obtained in Comparative Example 1, the composite nanofiltration membrane N1 obtained in Example 1 showed significantly enhanced resistance to calcium sulfate scaling. This is because Ca... 2+ The primary interaction with the membrane surface is not electrostatic force, but rather the chelation effect between it and the -COOH groups on the membrane surface. The N1 surface of the composite nanofiltration membrane is rich in sulfonic acid groups, which interact with Ca... 2+The interaction between them is significantly weakened, which effectively reduces the adsorption of scaling ions on the membrane surface during heterogeneous nucleation, enhances the nucleation energy barrier, reduces the adhesion and growth of crystal nuclei on the membrane surface, and thus significantly improves the anti-fouling performance of nanofiltration membranes.

[0191] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A negatively charged composite nanofiltration membrane, characterized in that, The negatively charged composite nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer, and a polyamide separation layer; The polyamide separation layer is grafted with N atoms to form sulfonic acid groups and / or sulfonate groups as shown in Formula I; Wherein, M is H, Li, Na or K, and R1 and R2 are each independently H, C1-C6 alkyl or phenyl; The location where the group shown in Formula I is bonded to the polyamide separation layer; Ar comes from the residues following the reaction of compounds containing electron-withdrawing groups.

2. The negatively charged composite nanofiltration membrane according to claim 1, wherein, R1 and R2 are each independently selected from H or C1-C5 alkyl groups; And / or, the electron-withdrawing group is selected from one of carbonyl, carboxyl, ester, alkynyl, cyano, or phenolic hydroxyl groups.

3. The negatively charged composite nanofiltration membrane according to claim 1 or 2, wherein, *Ar-SO3M is selected from at least one of the following groups: R3, R4, R5 and R6 are each independently H, C1-C3 alkyl, -NH2 or -SO3M, and at least one of R3, R4, R5 and R6 is -SO3M; Wherein, R7 is H, methyl, or ethyl; R8 and R9 are each independently H or C1-C3 alkyl; Among them, R 10 It can be an alkynyl or carboxyl group, where m is an integer between 0 and 3; Where z is an integer from 1 to 3; Among them, R 16 It is a C1-C3 alkylene group, R 17 and R 18 Each is independently a C1-C8 straight-chain alkyl or branched alkyl.

4. The negatively charged composite nanofiltration membrane according to any one of claims 1-3, wherein, The sulfur atom content in the polyamide separation layer of the negatively charged composite nanofiltration membrane is 0.1-5 at.%, preferably 0.5-3 at.%.

5. The negatively charged composite nanofiltration membrane according to any one of claims 1-4, wherein, At pH=7, the surface Zeta potential of the composite nanofiltration membrane is -50mV to -30mV, preferably -45mV to -35mV.

6. The negatively charged composite nanofiltration membrane according to any one of claims 1-5, wherein, The average pore size of the composite nanofiltration membrane is 0.1-0.5 nm, preferably 0.15-0.35 nm.

7. The negatively charged composite nanofiltration membrane according to any one of claims 1-6, wherein, The contact angle of the composite nanofiltration membrane is 20-80°, preferably 30-50°.

8. A method for preparing a negatively charged composite nanofiltration membrane, characterized in that, The preparation method includes the following steps: S1. A porous support layer and a polyamide separation layer are sequentially prepared on the bottom layer to obtain a composite membrane; S2. The composite membrane is contacted with an aqueous solution containing an aldehyde compound of Formula 1, an electron-withdrawing sulfonate and / or an electron-withdrawing sulfonic acid compound and an acid catalyst, and then dried to obtain the negatively charged composite nanofiltration membrane. R1 and R2 are each independently H, C1-C6 alkyl or phenyl.

9. The preparation method according to claim 8, wherein, The electron-withdrawing group is selected from one of carbonyl, carboxyl, ester, alkynyl, cyano, or phenolic hydroxyl groups; And / or, the acid catalyst is selected from hydrochloric acid and / or sulfuric acid.

10. The preparation method according to claim 8 or 9, wherein, The method for preparing the composite membrane includes: (1) Prepare a porous support layer on the bottom layer; (2) The membrane obtained in step (1) is brought into first contact with a first liquid phase; wherein the first liquid phase includes a polyamine, a first organic solvent and water; (3) The membrane obtained in step (2) is brought into a second contact with the second liquid phase, and after heat treatment, the composite membrane is obtained; wherein, the second liquid phase includes polyacrylamide chloride and a second organic solvent; Preferably, the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, ethanol, and methanol; Preferably, the concentration of the first organic solvent in the first liquid phase is 0.05-6 wt%, more preferably 0.1-3 wt%. Preferably, the concentration of polyamine in the first liquid phase is 0.05wt%-5wt%, more preferably 0.2wt%-2wt%.

11. The preparation method according to any one of claims 8-10, wherein, The sulfonate containing an electron-withdrawing group and / or the sulfonic acid compound containing an electron-withdrawing group are selected from at least one of the following groups: R3, R4, R5 and R6 are each independently H, C1-C3 alkyl, -NH2 or -SO3M, and at least one of R3, R4, R5 and R6 is -SO3M; Wherein, R7 is H, methyl, or ethyl; R 11 R 12 R 13 R 14 R 15 Each is independently H or -SO3M, and R 11 and R 12 At least one of them is H; R8 and R9 are each independently an H or a C1-C3 alkyl group; Among them, R 10 It can be an alkynyl or carboxyl group, where m is an integer between 0 and 3; Where z is an integer from 1 to 3; Among them, R 16 It is a C1-C3 alkylene group, R 17 and R 18 Each is independently a C1-C8 straight-chain alkyl or branched alkyl; M is H, Li, Na or K; Preferably, the sulfonate containing an electron-withdrawing group and / or the sulfonic acid compound containing an electron-withdrawing group are selected from at least one of camphor sulfonic acid, sodium camphor sulfonate, o-hydroxybenzene sulfonic acid, m-hydroxybenzene sulfonic acid, p-hydroxybenzene sulfonic acid, sodium o-hydroxybenzene sulfonate, sodium m-hydroxybenzene sulfonate, sodium p-hydroxybenzene sulfonate, o-cresol sulfonic acid, m-cresol sulfonic acid, p-cresol sulfonic acid, sodium 2-acetylbenzene sulfonate, sodium 3-acetylbenzene sulfonate, sodium 4-acetylbenzene sulfonate, sodium 1-acetylindoline-2-sulfonate, sodium propargyl sulfonate, sulfonic acid acetic acid, sulfonic acid propionic acid, sodium dioctyl dibutyrate sulfonate, sodium diisobutyl succinate sulfonate, and D-2-amino-4-sulfobutyric acid.

12. The preparation method according to any one of claims 8-11, wherein, In step S2, the concentration of the aldehyde compound in the aqueous solution is 0.05-5 wt%, preferably 0.1-4 wt%; the concentration of the sulfonate containing electron-withdrawing groups and / or the sulfonic acid compound containing electron-withdrawing groups is 0.05-5 wt%, preferably 0.1-4 wt%; and the concentration of the acid catalyst is 0.01%-0.15 wt%, preferably 0.03%-0.12%. And / or, in step S2, the ratio of the volume of the aqueous solution to the area of ​​the composite membrane is 0.1-5 mL / cm². 2 Preferably 0.5-3 mL / cm 2 .

13. The preparation method according to any one of claims 8-12, wherein, In step S2, the contact time is 5s-240s, preferably 10s-180s; And / or, in step S2, the drying temperature is 20-80℃, preferably 30-70℃; the drying time is 0.5-120min, preferably 1-60min.

14. A negatively charged composite nanofiltration membrane prepared by the preparation method according to any one of claims 8-13.

15. The application of the negatively charged composite nanofiltration membrane according to any one of claims 1-7 and 14 in the field of water treatment.

Images