Composite nanofiltration membrane, method for preparing the same, and water treatment device

Abstract

The application relates to a composite nanofiltration membrane, a preparation method thereof and a water treatment device, wherein the preparation method of the composite nanofiltration membrane comprises the following steps: preparing an aqueous phase solution by mixing an alkaline ionic liquid, a cyclodextrin, a polyamine and water; sequentially placing the aqueous phase solution and an oil phase solution containing a polyacyl chloride on the same surface of a porous support membrane to form a separation layer through heat treatment, so as to obtain a preformed membrane; and cleaning the preformed membrane by using an acidic solution to obtain the composite nanofiltration membrane. The composite nanofiltration membrane prepared by the preparation method has the performances of high water flux and high retention rate when applied to water treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment membrane, in particular to a composite nanofiltration membrane, a preparation method thereof and a water treatment device. BACKGROUND

[0002] Nanofiltration membrane is one of the core separation membranes in the field of water treatment, and is widely used in the fields of drinking water purification, seawater desalination, material separation, wastewater reuse, etc. due to its nanoscale pore size. Interfacial polymerization is the core process for preparing nanofiltration membranes, and the process is to form a polyamide separation layer by polycondensation of polyamines and polyacyl chlorides on the surface of a porous support membrane. However, in the process of preparing nanofiltration membranes by using the traditional interfacial polymerization method, the reaction rate is usually extremely fast and difficult to control, and the generated by-product HCl will also accumulate at the reaction interface, inhibiting the further reaction of polyamines, resulting in the difficulty in forming a separation layer with ideal crosslinking degree and pore structure, so that the performance of the prepared nanofiltration membrane is generally limited by the "trade-off" effect between rejection rate and water flux, and it is difficult to simultaneously achieve high water flux and high rejection rate. SUMMARY

[0003] Therefore, it is necessary to provide a composite nanofiltration membrane, a preparation method thereof and a water treatment device, so that the composite nanofiltration membrane prepared by the preparation method has the performances of high water flux and high rejection rate when applied to water treatment.

[0004] A preparation method of a composite nanofiltration membrane, comprising the following steps:

[0005] Preparation of an aqueous phase solution by mixing an alkaline ionic liquid, a cyclodextrin, a polyamine and water;

[0006] Placing the aqueous phase solution and an oil phase solution containing polyacyl chloride on the same surface of a porous support membrane in sequence, and performing heat treatment to form a separation layer, thereby obtaining a preformed membrane;

[0007] Cleaning the preformed membrane with an acidic solution to obtain a composite nanofiltration membrane.

[0008] In one of the embodiments, the mass ratio of the alkaline ionic liquid to the cyclodextrin is 1:10-1:2;

[0009] And / or, the Coulomb force between the cation and the anion in the alkaline ionic liquid is 0.2nN-2nN;

[0010] And / or, the difference between the cavity size of the cyclodextrin and the size of the cation of the alkaline ionic liquid is less than 1 angstrom.

[0011] In one of the embodiments, the mass fraction of the alkaline ionic liquid in the aqueous phase solution is 0.1%-1%;

[0012] And / or, the basic ionic liquid is selected from at least one of imidazolium ionic liquid, quaternary phosphonium base ionic liquid or guanidine ionic liquid.

[0013] In one embodiment, the mass fraction of the cyclodextrin in the aqueous phase solution is 0.5%-5%;

[0014] And / or, the cyclodextrin is selected from at least one of α-cyclodextrin, α-cyclodextrin derivative, β-cyclodextrin, β-cyclodextrin derivative, γ-cyclodextrin or γ-cyclodextrin derivative.

[0015] In one embodiment, the mass fraction of the polyamine in the aqueous phase solution is 1%-5%;

[0016] And / or, the mass fraction of the polyacyl chloride in the oil phase solution containing polyacyl chloride is 0.1%-1%;

[0017] And / or, the polyamine is selected from at least one of piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethyl-m-phenylenediamine, murexide, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline or m-fluoroaniline;

[0018] And / or, the polyacyl chloride is selected from at least one of murexide chloride, p-phthaloyl chloride or m-phthaloyl chloride.

[0019] In one embodiment, the pH of the acidic solution is >2.

[0020] In one embodiment, in the step of heat treatment to form the separation layer, the heat treatment temperature is 60-80℃ and the heat treatment time is 3-10min.

[0021] In one embodiment, after the pre-made film is cleaned by the acidic solution, it is further rinsed.

[0022] A composite nanofiltration membrane prepared by the preparation method of the composite nanofiltration membrane.

[0023] The application of the composite nanofiltration membrane in a water treatment device.

[0024] The preparation method of the composite nanofiltration membrane of the application, by introducing basic ionic liquid and cyclodextrin as composite additives in the aqueous solution at the same time, in the process of interfacial polymerization reaction, the basic ionic liquid plays multiple roles due to its basicity and good solubility, on the one hand, it can form stable supramolecular inclusion complex with cyclodextrin, which not only significantly improves the solubility of cyclodextrin, but also the inclusion complex can diffuse to the water-oil interface with polyamine, thereby effectively controlling the mass transfer rate of polyamine, which is beneficial to the formation of a dense and uniform separation layer; on the other hand, it can provide a basic environment for the deprotonation of polyamine to enhance its reactivity, and as an acid absorbent to neutralize the byproduct hydrogen chloride, to promote the interfacial polymerization reaction to proceed in the positive direction, at the same time, the ionic liquid salt generated in the reaction can reduce the viscosity of the aqueous solution, ensuring the continuous diffusion and supply of polyamine, thereby further improving the density and uniformity of the separation layer. At the same time, the hydroxyl group of cyclodextrin will also undergo esterification reaction with polyacyl chloride to form a cross-linked structure interpenetrated with the polyamide network, together forming the separation layer, significantly enhancing the structural strength and integrity of the separation layer. After the reaction, an acidic solution is used for post-treatment to remove the residual basic components and part of the inclusion complex in the separation layer, effectively increasing the free volume of the separation layer and optimizing its pore structure. Finally, the prepared separation layer has both high cross-linking degree and optimized pore structure, successfully overcoming the "trade-off" limitation between rejection rate and water flux of traditional nanofiltration membranes, so that the prepared composite nanofiltration membrane can simultaneously achieve high water flux and high rejection rate.

[0025] Therefore, the composite nanofiltration membrane of the application has the performance of high water flux and high rejection rate when applied to water treatment. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments described in the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0027] Fig. 1 The electron microscope image of the composite nanofiltration membrane prepared in Example 1 of the application;

[0028] Fig. 2 The electron microscope image of the composite nanofiltration membrane prepared in Example 4 of the application;

[0029] Fig. 3 The electron microscope image of the composite nanofiltration membrane prepared in Comparative Example 1 of the application. DETAILED DESCRIPTION

[0030] For the purposes of promoting an understanding of the principles of the application, reference will now be made to the embodiments illustrated in the drawings. It is expressly understood that the drawings are presented for the purposes of illustration and teaching the disclosed embodiments and are not intended as a definition of the limits of the disclosed application. In the drawings, the same reference numbers identify elements in different views of the drawing:

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the application. As used in this description, the term "and / or" means any one of the items, optionally including any two or more of the items, and / or any one of the items individually. As used herein, the term "or" means any one of the items, optionally including any two or more of the items, and / or any one of the items individually.

[0032] The application provides a preparation method of a composite nanofiltration membrane, comprising the following steps:

[0033] An alkaline ionic liquid, a cyclodextrin, a polyamine and water are prepared into an aqueous phase solution;

[0034] The aqueous phase solution and an oil phase solution containing a polyacyl chloride are sequentially placed on the same surface of a porous support membrane, and a separation layer is formed by heat treatment to obtain a preformed membrane;

[0035] An acid solution is used to clean the preformed membrane, and then a composite nanofiltration membrane is obtained.

[0036] Specifically, when the aqueous solution and the oil phase solution containing the polybasic acid chloride are sequentially placed on the same surface of the porous support membrane, the polybasic amine in the aqueous solution and the polybasic acid chloride in the oil phase solution will undergo interfacial polymerization and form a polyamide layer, and in the process, due to the fact that the aqueous solution contains a basic ionic liquid and a cyclodextrin, the basic ionic liquid has both basicity and good solubility, and the cyclodextrin has a hydrophobic inner cavity and a hydrophilic outer cavity, and the two play a multiple synergistic effect, on the one hand, the basic ionic liquid and the cyclodextrin form a stable supramolecular inclusion complex through ion-dipole interaction, not only significantly improving the solubility of the cyclodextrin in the aqueous solution, but also the inclusion complex can diffuse to the water-oil interface with the polybasic amine, thereby effectively controlling the mass transfer rate of the polybasic amine, which is conducive to the formation of a dense and uniform separation layer; on the other hand, the basic ionic liquid can provide an alkaline environment for the deprotonation of the polybasic amine, enhancing its nucleophilicity and reactivity, and at the same time, as an acid absorbent, it neutralizes the reaction byproduct hydrogen chloride, promotes the interfacial polymerization reaction to proceed in the forward direction, avoids the protonation of amine groups and the hydrolysis of acid chlorides, and at the same time, the ionic liquid salt generated by the reaction of the basic ionic liquid and hydrogen chloride can reduce the viscosity of the aqueous solution, "unlock" the diffusion restriction of the polybasic amine, compensate for the concentration gradient decay caused by the reaction consumption, and then ensure the continuous diffusion and supply of the polybasic amine, further improving the density and uniformity of the separation layer. At the same time, the hydroxyl groups of the cyclodextrin will also undergo esterification with the polybasic acid chloride to form a crosslinked network interpenetrated with the polyamide network, together forming the separation layer, significantly enhancing the structural strength and integrity of the separation layer.

[0037] When the prepared membrane is cleaned with an acidic solution, the acidic solution can neutralize the residual basic components (such as basic ionic liquid, unreacted polybasic amine) to remove the residual basic components, and at the same time, part of the residual inclusion complex can also be removed, effectively increasing the free volume of the separation layer, and then optimizing the pore size structure of the separation layer. Finally, the prepared separation layer has high crosslinking degree and optimized pore size structure, successfully overcoming the "trade-off" limitation between rejection rate and water flux of traditional nanofiltration membranes, so that the prepared composite nanofiltration membrane can simultaneously realize high water flux and high rejection rate.

[0038] Therefore, the composite nanofiltration membrane of the present application has high water flux and high rejection rate when applied to water treatment.

[0039] It should be noted that in the present application, the acidic solution refers to a solution with a pH less than 7.

[0040] In an embodiment, in the step of preparing the aqueous solution, the basic ionic liquid and the cyclodextrin are first mixed with water, and then the polybasic amine is added to prepare the aqueous solution. In this way, it is beneficial to better form a stable supramolecular inclusion complex between the basic ionic liquid and the cyclodextrin, while improving the mixing uniformity of the components in the aqueous solution.

[0041] In the present application, the mass ratio of the basic ionic liquid to the cyclodextrin is 1:10-1:2; by setting the mass ratio of the basic ionic liquid to the cyclodextrin, the basic ionic liquid and the cyclodextrin can form a stable supramolecular inclusion complex, and at the same time, a sufficient basic environment is provided, the mass transfer rate of the polyamine is better controlled, and then the interface polymerization reaction process is controlled, so that a separation layer with high crosslinking degree and optimized pore size structure is better obtained, and then the synergistic improvement of high water flux and high retention rate of the composite nanofiltration membrane is better realized.

[0042] Optionally, the difference between the cavity size of the cyclodextrin and the cation size of the basic ionic liquid is less than 1 Å; by setting the difference, the cyclodextrin and the basic ionic liquid can form a more stable inclusion complex, and at the same time, each inclusion unit has a stable and predictable positive charge, so that a uniform and repeatable electrostatic potential barrier can be generated for the polyamine, and then the mass transfer rate of the polyamine is accurately controlled, and a separation layer with high crosslinking degree and optimized pore size structure is better obtained.

[0043] It should be noted that in the present application, the difference between the cavity size of the cyclodextrin and the cation size of the basic ionic liquid is calculated according to the following formula: wherein D1 is the cavity size of the cyclodextrin, In D1, n is the number of glucose units that make up the cyclodextrin, each unit contributes about 0.72 nm in circumference; d is the wall thickness, generally 0.15 nm-0.20 nm, so that the inner diameters of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin are about 0.49 nm, 0.62 nm and 0.79 nm, respectively; D2 is the cation size of the basic ionic liquid, In D2, V vdW is the van der Waals volume of the cation of the basic ionic liquid, and the unit is usually Å 3 or nm 3 .

[0044] Optionally, the mass fraction of the basic ionic liquid in the aqueous solution is 0.1%-1%, and the mass fraction of the cyclodextrin in the aqueous solution is 0.5%-5%; by controlling the mass fraction of the basic ionic liquid and the cyclodextrin in the aqueous solution within a suitable range, on the one hand, the basic ionic liquid and the cyclodextrin can form a stable supramolecular inclusion complex, a sufficient basic environment is provided, the mass transfer rate of the polyamine is better controlled, and then the interface polymerization reaction process is controlled; on the other hand, the basic ionic liquid and the cyclodextrin can fully react with the polyacyl chloride to form a crosslinked structure interpenetrated with a polyamide network, and the structural strength and integrity of the separation layer are better improved, so that a separation layer with high crosslinking degree and optimized pore size structure is better obtained, and then the synergistic improvement of high water flux and high retention rate of the composite nanofiltration membrane is better realized.

[0045] In the present application, the Coulomb force between the cation and the anion in the basic ionic liquid is 0.2 nN-2 nN; by setting it in this way, on the one hand, by controlling the Coulomb force between the cation and the anion in the basic ionic liquid within a suitable range, the inclusion driving force between the basic ionic liquid and the cyclodextrin can be improved, which promotes the cation to enter the cavity of the cyclodextrin to form a stable inclusion compound, and at the same time, it will not be 'locked' due to excessive action, hindering the hydrophobic interaction between the cation and the cyclodextrin; on the other hand, the inclusion compound formed has a positive charge, and a controllable Coulomb repulsion is generated between the positive polyamine added subsequently, which is a designed 'electrostatic potential barrier' that can accurately delay the diffusion rate of the polyamine molecules to the interface, thereby actively regulating the interface reaction kinetics, and then a separation layer with high cross-linking degree and optimized pore size structure can be better obtained, and then the synergistic improvement of high water flux and high retention rate of the composite nanofiltration membrane can be better realized.

[0046] It should be noted that in the present application, the calculation formula of the Coulomb force (F) between the cation and the anion in the basic ionic liquid is as follows: , wherein ε o is the vacuum dielectric constant 8.854×10 -12 F / m, ε r is the relative dielectric constant of the basic ionic liquid, q1=+e, q2=-e, e=1.602×10 -19 C, and r is the distance between the anion and the cation of the basic ionic liquid, in meters.

[0047] Alternatively, the basic ionic liquid is selected from at least one of imidazole ionic liquid, quaternary phosphonium base ionic liquid or guanidine ionic liquid, preferably imidazole ionic liquid, and the imidazole ionic liquid is selected from at least one of 1-butyl-3-methylimidazole bicarbonate, 1-butyl-3-methylimidazole hydroxide, 1-ethyl-3-methylimidazole acetate or 1-butyl-3-methylimidazole benzoate.

[0048] In the present application, the cyclodextrin is selected from at least one of α-cyclodextrin, α-cyclodextrin derivative, β-cyclodextrin, β-cyclodextrin derivative, γ-cyclodextrin or γ-cyclodextrin derivative, preferably β-cyclodextrin or β-cyclodextrin derivative, and the β-cyclodextrin derivative is preferably hydroxypropyl-β-cyclodextrin or carboxymethyl-β-cyclodextrin.

[0049] Optionally, the mass fraction of the polyamine in the aqueous phase solution is 1%-5%; the mass fraction of the polyacyl chloride in the oil phase solution containing polyacyl chloride is 0.1%-1%; in this way, the polyamine and the polyacyl chloride can be fully reacted to form a dense, uniform and structurally complete polyamide separation layer, and the composite nanofiltration membrane can have a high rejection rate.

[0050] Further, the polyamine is at least one of piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethyl-m-phenylenediamine, m-phenylendiamine, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline or m-fluoroaniline, and preferably is piperazine; and the polyacyl chloride is at least one of trimesoyl chloride, terephthaloyl chloride or isophthaloyl chloride, and preferably is trimesoyl chloride.

[0051] In an embodiment, the solvent in the oil phase solution containing polyacyl chloride is at least one of acetone, n-hexane, acetonitrile, ethyl acetate, methyl acetate, toluene, dichloromethane, 1,2-dichloroethane, cyclohexane, n-heptane, trichloromethane, mesitylene or isomeric alkanes, and the isomeric alkanes are at least one of Isopar-E, Isopar-G, Isopar-L, Isopar-H and Isopar-M.

[0052] In an embodiment, the porous support membrane is a high molecular ultrafiltration membrane, and preferably is any one of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, a polyvinylidene fluoride ultrafiltration membrane, a polyethylene ultrafiltration membrane, a polypropylene ultrafiltration membrane or a polyacrylonitrile ultrafiltration membrane, and further preferably is a polysulfone ultrafiltration membrane or a polyethersulfone ultrafiltration membrane.

[0053] In an embodiment, before the aqueous phase solution and the oil phase solution containing polyacyl chloride are sequentially placed on the same surface of the porous support membrane, the porous support membrane is subjected to a cleaning treatment to remove surface impurities and sufficiently wet the surface.

[0054] In the present application, the specific steps of sequentially placing the aqueous phase solution and the oil phase solution containing polyacyl chloride on the same surface of the porous support membrane are as follows: first, the aqueous phase solution is placed on any surface of the porous support membrane, and is left to stand for 2-10 minutes to remove excess aqueous phase solution on the surface; then, the oil phase solution containing polyacyl chloride is placed on the surface of the porous support membrane with the aqueous phase solution, and is left to stand for 10-120 seconds to remove excess oil phase solution on the surface.

[0055] In an embodiment, the way of sequentially placing the aqueous phase solution and the oil phase solution containing polyacyl chloride on the same surface of the porous support membrane can be soaking, dipping or coating, etc.

[0056] Optionally, the pH of the acidic solution is greater than 2, preferably 2 < pH ≤ 5, and more preferably a citric acid solution, an acetic acid solution, a tartaric acid solution or a malic acid solution with a mass fraction of 0.1% to 1%. It can be understood that, at this time, the acidic solution is a weak acid solution, and the use of the acidic solution can effectively neutralize and clean the residual alkaline components and partially remove the inclusion compound, while avoiding the hydrolysis of the main chain of the separation layer, the destruction of the structure or the damage to the porous support membrane that may be caused by too low pH (i.e., too strong acidity), so that the integrity and stability of the separation layer can be better ensured while optimizing the pore size structure, thereby simultaneously improving the water flux and the rejection rate of the composite nanofiltration membrane.

[0057] Optionally, in the step of forming the separation layer by heat treatment, the heat treatment temperature is 60°C to 80°C, and the heat treatment time is 3 min to 10 min; in this way, the integrity and uniformity of the cross-linking of the separation layer can be further ensured, and the rejection rate and water flux of the composite nanofiltration membrane can be further improved, while the residual solvent is removed.

[0058] In the present application, after the prepared membrane is cleaned with the acidic solution, the prepared membrane is further subjected to a rinsing treatment. In an embodiment, deionized water is used to rinse the prepared membrane after the cleaning treatment, so as to remove the residual acidic solution and salt.

[0059] It should be noted that, in the present application, the prepared composite nanofiltration membrane is stored in deionized water for use.

[0060] Meanwhile, the present application also provides a composite nanofiltration membrane prepared by using the preparation method of the composite nanofiltration membrane. The composite nanofiltration membrane has high water flux and high rejection rate when applied to water treatment.

[0061] In addition, the present application also provides an application of the composite nanofiltration membrane in a water treatment device.

[0062] In an embodiment, the water treatment device can be a hard water softening device. When the composite nanofiltration membrane is applied to the hard water softening device, the raw water to be softened can be driven by pressure to pass through the separation layer of the composite nanofiltration membrane from one side of the separation layer, wherein the hardening ions such as calcium ions (Ca 2+ ), magnesium ions (Mg 2+ ) in the hard water can be efficiently rejected, achieving excellent softening effect.

[0063] In an embodiment, the water treatment device can also be a purification machine, a rare earth concentration device or a seawater desalination device.

[0064] Hereinafter, the composite nanofiltration membrane, the preparation method thereof and the water treatment device will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. The specific conditions not indicated in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by purchase.

[0065] Example 1

[0066] 1-butyl-3-methylimidazolium hydroxide, β-cyclodextrin, piperazine and water were mixed to prepare an aqueous phase solution, wherein the mass fraction of 1-butyl-3-methylimidazolium hydroxide in the aqueous phase solution was 0.1%, the mass fraction of β-cyclodextrin was 0.5%, the mass fraction of piperazine was 1%, and the Coulomb force between the cation and the anion in 1-butyl-3-methylimidazolium hydroxide was about 0.3 nN, and the difference between the cavity size of β-cyclodextrin and the cation size of 1-butyl-3-methylimidazolium hydroxide was about 0.1 Å; trimesoyl chloride and n-hexane solvent were mixed to prepare an oil phase solution, wherein the mass fraction of trimesoyl chloride in the oil phase solution was 0.2%; citric acid and water were mixed to prepare a citric acid solution, wherein the mass fraction of citric acid in the citric acid solution was 0.5%, and the pH of the citric acid solution was 2.6.

[0067] After the cleaned polysulfone ultrafiltration membrane was soaked in the above-mentioned aqueous phase solution for 3 min, the excess aqueous phase solution on the surface was scraped off with a rubber roller; then the above-mentioned oil phase solution was applied to the surface of the polysulfone ultrafiltration membrane with the aqueous phase solution, and after standing for 60 s, the excess oil phase solution was poured off, and then it was placed in a 70°C oven for heat treatment for 5 min to form a separation layer, thereby obtaining a pre-membrane.

[0068] The pre-membrane was soaked in the above-mentioned citric acid solution for 2 min for cleaning treatment, and after being taken out, it was rinsed with deionized water to obtain a composite nanofiltration membrane as shown in Fig. 1 .

[0069] Example 2

[0070] The 1-butyl-3-methylimidazolium hydroxide, β-cyclodextrin, piperazine and water are mixed to prepare an aqueous solution, wherein the mass fraction of the 1-butyl-3-methylimidazolium hydroxide in the aqueous solution is 0.5%, the mass fraction of the β-cyclodextrin is 3%, the mass fraction of the piperazine is 3%, the Coulomb force between the cation and the anion in the 1-butyl-3-methylimidazolium hydroxide is about 0.3 nN, and the difference between the cavity size of the β-cyclodextrin and the cation size of the 1-butyl-3-methylimidazolium hydroxide is about 0.1 Å; the trimesoyl chloride and the n-hexane solvent are mixed to prepare an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 0.6%; the citric acid and water are mixed to prepare a citric acid solution, wherein the mass fraction of the citric acid in the citric acid solution is 0.1%, and the pH of the citric acid solution is 3.

[0071] The cleaned polysulfone ultrafiltration membrane is soaked in the aqueous solution for 3 min, and then the excess aqueous solution on the surface is removed by a rubber roller; then the oil phase solution is coated on the surface of the polysulfone ultrafiltration membrane with the aqueous solution, the excess oil phase solution is removed after 60 s, and then the polysulfone ultrafiltration membrane is placed in an oven at 80 ℃ for heat treatment for 3 min to form a separation layer, thereby obtaining a pre-membrane.

[0072] The pre-membrane is soaked in the citric acid solution for 2 min for cleaning treatment, and then is taken out and rinsed with deionized water, thereby obtaining a composite nanofiltration membrane.

[0073] Example 3

[0074] The 1-butyl-3-methylimidazolium hydroxide, β-cyclodextrin, piperazine and water are mixed to prepare an aqueous solution, wherein the mass fraction of the 1-butyl-3-methylimidazolium hydroxide in the aqueous solution is 1%, the mass fraction of the β-cyclodextrin is 5%, the mass fraction of the piperazine is 5%, the Coulomb force between the cation and the anion in the 1-butyl-3-methylimidazolium hydroxide is about 0.3 nN, and the difference between the cavity size of the β-cyclodextrin and the cation size of the 1-butyl-3-methylimidazolium hydroxide is about 0.1 Å; the trimesoyl chloride and the n-hexane solvent are mixed to prepare an oil phase solution, wherein the mass fraction of the trimesoyl chloride in the oil phase solution is 1%; the citric acid and water are mixed to prepare a citric acid solution, wherein the mass fraction of the citric acid in the citric acid solution is 1%, and the pH of the citric acid solution is 2.3.

[0075] The cleaned polysulfone ultrafiltration membrane is soaked in the aqueous solution for 3 min, and then the excess aqueous solution on the surface is removed by a rubber roller; then the oil phase solution is coated on the surface of the polysulfone ultrafiltration membrane with the aqueous solution, the excess oil phase solution is removed after 60 s, and then the polysulfone ultrafiltration membrane is placed in an oven at 60 ℃ for heat treatment for 10 min to form a separation layer, thereby obtaining a pre-membrane.

[0076] The prepared membrane was immersed in the above citric acid solution for 2 min for cleaning treatment, and then taken out and rinsed with deionized water to obtain a composite nanofiltration membrane.

[0077] Example 4

[0078] Example 4 differs from Example 1 only in that 1-octyl-3-methylimidazole bicarbonate is used instead of 1-butyl-3-methylimidazole hydroxide, and γ-cyclodextrin is used instead of β-cyclodextrin in the step of preparing the aqueous phase solution, wherein the mass fraction of 1-octyl-3-methylimidazole bicarbonate in the aqueous phase solution is 0.5%, the mass fraction of γ-cyclodextrin is 0.1%, and the Coulomb force between the cation and the anion in 1-octyl-3-methylimidazole bicarbonate is about 0.28 nN, and the difference between the cavity size of γ-cyclodextrin and the cation size of 1-octyl-3-methylimidazole bicarbonate is about 0.6 Å; the other conditions are the same, and a composite nanofiltration membrane as shown in Fig. 2 is obtained.

[0079] Example 5

[0080] Example 5 differs from Example 4 only in that acetic acid is used instead of citric acid, i.e., acetic acid and water are uniformly mixed to prepare an acetic acid solution, wherein the mass fraction of acetic acid in the acetic acid solution is 0.3%, and the pH of the acetic acid solution is 3.7; the other conditions are the same, and a composite nanofiltration membrane is obtained.

[0081] Example 6

[0082] Example 6 differs from Example 1 only in that the mass fraction of 1-butyl-3-methylimidazole hydroxide in the aqueous phase solution is 0.03% in the step of preparing the aqueous phase solution; the other conditions are the same, and a composite nanofiltration membrane is obtained.

[0083] Example 7

[0084] Example 7 differs from Example 1 only in that the mass fraction of 1-butyl-3-methylimidazole hydroxide in the aqueous phase solution is 1.5% in the step of preparing the aqueous phase solution; the other conditions are the same, and a composite nanofiltration membrane is obtained.

[0085] Example 8

[0086] Example 8 differs from Example 1 only in that the mass fraction of β-cyclodextrin in the aqueous phase solution is 0.1% in the step of preparing the aqueous phase solution; the other conditions are the same, and a composite nanofiltration membrane is obtained.

[0087] Example 9

[0088] Example 9 is the same as Example 1 except that the mass fraction of the β-cyclodextrin in the aqueous solution is 6% in the step of preparing the aqueous solution, and the rest conditions are the same, to obtain the composite nanofiltration membrane.

[0089] Example 10

[0090] Example 10 is the same as Example 1 except that hydrochloric acid is used instead of citric acid, i.e., hydrochloric acid and water are mixed uniformly to prepare a dilute hydrochloric acid solution, wherein the mass fraction of the dilute hydrochloric acid solution is 1%, and the pH of the dilute hydrochloric acid solution is 1; the rest conditions are the same, to obtain the composite nanofiltration membrane.

[0091] Example 11

[0092] Example 11 is the same as Example 1 except that 1-ethyl-3-methylimidazole acetate is used instead of 1-butyl-3-methylimidazole hydroxide, and hydroxypropyl-β-cyclodextrin is used instead of β-cyclodextrin in the step of preparing the aqueous solution, and the Coulomb force between the cation and the anion in the 1-ethyl-3-methylimidazole acetate is 0.28 nN, and the difference between the cavity size of the hydroxypropyl-β-cyclodextrin and the cation size of the 1-ethyl-3-methylimidazole acetate is 0.3 Å; the rest conditions are the same, to obtain the composite nanofiltration membrane.

[0093] Example 12

[0094] Example 12 is the same as Example 1 except that 1-butyl-3-methylimidazole bicarbonate is used instead of 1-butyl-3-methylimidazole hydroxide, and γ-cyclodextrin is used instead of β-cyclodextrin in the step of preparing the aqueous solution, wherein the mass fraction of the 1-butyl-3-methylimidazole bicarbonate in the aqueous solution is 0.5%, and the mass fraction of the γ-cyclodextrin is 0.1%, and the Coulomb force between the cation and the anion in the 1-butyl-3-methylimidazole bicarbonate is about 0.3 nN, and the difference between the cavity size of the γ-cyclodextrin and the cation size of the 1-butyl-3-methylimidazole bicarbonate is about 1.2 Å; the rest conditions are the same, to obtain the composite nanofiltration membrane.

[0095] Comparative Example 1

[0096] Comparative Example 1 is the same as Example 1 except that 1-butyl-3-methylimidazole hydroxide and β-cyclodextrin are not added in the step of preparing the aqueous solution; the rest conditions are the same, to obtain the composite nanofiltration membrane as shown in Fig. 3 .

[0097] Comparative Example 2

[0098] Comparative Example 2 is the same as Example 1 except that 1-butyl-3-methylimidazole hydroxide is not added in the step of preparing the aqueous solution; the rest conditions are the same, to obtain the composite nanofiltration membrane.

[0099] Comparative Example 3

[0100] Compared with Example 1, Comparative Example 3 differs only in that β-cyclodextrin is not added in the step of preparing the aqueous solution; all other conditions are the same, and a composite nanofiltration membrane is obtained.

[0101] Comparative Example 4

[0102] Compared with Example 1, Comparative Example 4 differs only in that deionized water (pH 7) is used instead of citric acid solution. That is, the pre-made membrane is soaked in deionized water for 2 minutes for cleaning and then taken out to obtain a composite nanofiltration membrane.

[0103] The composite nanofiltration membranes prepared in Examples 1 to 12 and Comparative Examples 1 to 4 were subjected to performance tests. The test conditions were as follows: test pressure was 0.4 MPa, concentrate flow rate was 1.0 GPM, ambient temperature was 25°C, concentrate pH was 6.5-7.5, and concentrate was 2000 mg of sodium sulfate aqueous solution, sodium chloride aqueous solution, or gadolinium trichloride aqueous solution. The test results are shown in Table 1.

[0104] Table 1

[0105]

[0106] It should be noted that in Table 1, the membrane water flux (F) is calculated from the volume of water passing through the composite nanofiltration membrane under a unit pressure within a certain time period, using the following formula: Where V is the volume of water passing through the composite nanofiltration membrane per unit time, A is the effective membrane area, T is the time, and P is the test pressure.

[0107] The rejection rate (R) is calculated using the concentrations of the feed solution and the permeate solution, and the formula is as follows: Where C1 is the concentration of the permeate and C0 is the concentration of the feed liquid.

[0108] from Figs. 1 to 3 As can be seen, compared with the composite nanofiltration membrane prepared in Comparative Example 1, the composite nanofiltration membrane prepared in Examples 1 and 4 has a vesicle structure on its surface due to the addition of alkaline ionic liquid and cyclodextrin as composite additives in the aqueous solution, which changes the surface morphology of the original nanofiltration membrane.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that, Includes the following steps: An aqueous solution was prepared by combining an alkaline ionic liquid, cyclodextrin, polyamine, and water. The aqueous solution and the oil solution containing polyacrylamide chloride are sequentially placed on the same surface of the porous support membrane, and a separation layer is formed by heat treatment to obtain the pre-formed membrane. The pre-fabricated membrane was cleaned with an acidic solution to obtain a composite nanofiltration membrane.

2. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, The mass ratio of the alkaline ionic liquid to the cyclodextrin is 1:10-1:2; And / or, the Coulomb force between cations and anions in the alkaline ionic liquid is 0.2nN-2nN; And / or, the difference between the cavity size of the cyclodextrin and the cation size of the basic ionic liquid is less than 1 Å.

3. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, The mass fraction of the alkaline ionic liquid in the aqueous solution is 0.1%-1%; And / or, the basic ionic liquid is selected from at least one of imidazole ionic liquids, quaternary phosphonium base ionic liquids, or guanidine ionic liquids.

4. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, The mass fraction of the cyclodextrin in the aqueous solution is 0.5%-5%; And / or, the cyclodextrin is selected from at least one of α-cyclodextrin, α-cyclodextrin derivatives, β-cyclodextrin, β-cyclodextrin derivatives, γ-cyclodextrin, or γ-cyclodextrin derivatives.

5. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, The mass fraction of the polyamine in the aqueous solution is 1%-5%; And / or, the mass fraction of the polyacrylamide chloride in the oil phase solution containing the polyacrylamide chloride is 0.1%-1%; And / or, the polyamine is selected from at least one of piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethylm-phenylenediamine, pyromellitic triamine, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline, or m-fluoroaniline; And / or, the polyacryl chloride is selected from at least one of pyromellitic chloroformyl chloride, terephthaloyl chloride, or isophthaloyl chloride.

6. The method for preparing the composite nanofiltration membrane according to claim 1, characterized in that, The pH of the acidic solution is greater than 2.

7. The method for preparing the composite nanofiltration membrane according to any one of claims 1 to 6, characterized in that, In the step of forming the separation layer by heat treatment, the heat treatment temperature is 60℃-80℃ and the heat treatment time is 3min-10min.

8. The method for preparing the composite nanofiltration membrane according to any one of claims 1 to 6, characterized in that, After cleaning the preformed membrane with an acidic solution, a rinsing process is also included.

9. A composite nanofiltration membrane prepared by the method described in any one of claims 1 to 8.

10. The application of the composite nanofiltration membrane as described in claim 9 in a water treatment device.

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