Acid- and alkali-resistant separation membrane and its preparation method and application

Abstract

This invention relates to the field of membranes, and discloses an acid and alkali resistant separation membrane, its preparation method, and its application. The acid and alkali resistant separation membrane sequentially comprises a substrate layer, a porous support layer, a poly(triazineamine-urea) layer, and a modification layer. The crosslinked polymer forming the modification layer comprises structural units provided by polyphenols and structural units provided by a first polyamine. At least some of the structural units provided by the polyphenols are also connected to the poly(triazineamine-urea) layer through the ortho-position of phenolic hydroxyl groups. The pore size of the separation membrane is 0.1-0.5 nm, and the surface Zeta potential of the acid and alkali resistant separation membrane is 0-30 mV. When used for magnesium-lithium separation, it can maintain a high water flux and possess a high magnesium-lithium separation coefficient, and can be used for magnesium-lithium separation under acidic / alkaline environments.

Description

Technical Field

[0001] This invention relates to the field of membranes, and more specifically, to an acid and alkali resistant separation membrane, its preparation method, and its application. Background Technology

[0002] Lithium resources, as a new energy source and strategic resource, are widely used in lithium batteries, aerospace, pharmaceuticals, and the glass and ceramics industries. In recent years, with the rapid development of new energy vehicles, the demand for lithium, as a core raw material, has been increasing year by year. Salt lake lithium resources account for approximately 70% of global lithium reserves. Compared to mining lithium ore, lithium extraction from brine has a large available reserve, lower cost, and simpler process, making it a global trend in lithium extraction. Typically, lithium resources in salt lake brines exist in the form of lithium chloride; however, a large amount of magnesium chloride often coexists with it. The lithium ion radius (7.4 × 10⁻⁶) is... -13 m) is very close to that of magnesium ions (7.2 × 10⁻⁶). -13 Furthermore, lithium ions and magnesium ions have similar chemical properties, making them difficult to separate and posing significant challenges to lithium extraction from salt lake brines. my country's salt lake brines suffer from a high magnesium-to-lithium ratio, making the effective separation of magnesium and lithium ions in brine resources crucial for the development of lithium resources in my country's salt lakes.

[0003] Typically, the specific process for lithium extraction from salt lakes varies depending on the lake's specific conditions, with each lake employing its own unique approach. Precipitation involves concentrating the brine, then removing impurity ions through acidification or extraction, followed by the addition of Na₂CO₃ to precipitate Li₂CO₃. This process is cumbersome, energy-intensive, and unsuitable for China's high magnesium-to-lithium ratio brine. Solvent extraction utilizes the difference in solubility between magnesium and lithium ions in the extractant to achieve separation; however, the extractant is expensive and corrosive to equipment. Lithium extraction via calcination generates large amounts of hydrogen chloride gas, posing corrosion and energy consumption problems. Considering both technical feasibility and economic benefits, the adsorption-membrane lithium extraction process has become the mainstream choice for my country's high magnesium-to-lithium ratio salt lakes, contributing 93% of my country's salt lake lithium production capacity in 2020.

[0004] Specifically, the adsorption-membrane lithium extraction process utilizes a selective adsorbent to adsorb lithium ions and a small amount of other ions. The adsorbent is then desorbed, and the eluent is filtered using a nanofiltration membrane to further separate lithium ions from other ions. The filtrate is then concentrated, and finally, industrial-grade lithium carbonate is precipitated. The problem lies in the fact that the desorption process requires acidic conditions, making the initial solution for nanofiltration acidic. However, commercially available nanofiltration membrane materials are primarily polyamides, and under acidic conditions, the C=O bonds are easily affected by H+. +Nucleophilic electron attack causes hydrolysis of the amide bonds, damaging the membrane separation layer structure and reducing retention performance. Furthermore, commercial nanofiltration membranes suffer from low magnesium-lithium separation efficiency and short lifespan, necessitating the development of nanofiltration membranes with positively charged surfaces, good acid resistance, and high magnesium-lithium separation efficiency to meet the application requirements of magnesium-lithium separation. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low magnesium-lithium separation efficiency and poor acid and alkali resistance in the prior art, and to provide an acid and alkali resistant separation membrane, its preparation method and application. The poly(triazineamine-urea) contains inert chemical groups, which makes the acid and alkali resistant separation membrane have high acid / alkali resistance. The modification layer includes a cross-linked polymer, which makes the acid and alkali resistant separation membrane have high density and high surface electrode potential (Zeta potential). When used for magnesium-lithium separation, it can maintain a high water flux and has a high magnesium-lithium separation coefficient, which can be used in the field of water treatment separation.

[0006] To achieve the above objectives, the first aspect of the present invention provides an acid and alkali resistant separation membrane, wherein the separation layer sequentially comprises a substrate layer, a porous support layer, a poly(triazineamine-urea) layer, and a modification layer;

[0007] The crosslinked polymer forming the modified layer includes structural units provided by polyphenols and structural units provided by a first polyamine, and at least some of the structural units provided by polyphenols are also connected to the poly(triazineamine-urea) layer through the ortho position of phenolic hydroxyl groups;

[0008] The pore size of the separation membrane is 0.1-0.5 nm, and the surface Zeta potential of the separation membrane is 0-30 mV.

[0009] A second aspect of the present invention provides a method for preparing an acid and alkali resistant separation membrane, wherein the preparation method includes the following steps: sequentially preparing a porous support layer, a poly(triazineamine-urea) layer and a modification layer on a substrate layer;

[0010] The method for preparing the modified layer includes: under a first pressure, while the polyphenol solution is kept flowing, making a first contact between one side of the poly(triazineamine-urea) layer of the material, which includes a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer of the material, while the first polyamine solution is kept flowing, making a second contact between one side of the poly(triazineamine-urea) layer of the material and the first polyamine solution, thereby completing the self-assembly reaction.

[0011] A third aspect of the present invention provides an acid and alkali resistant separation membrane prepared by the above-described preparation method.

[0012] The fourth aspect of this invention provides the application of the above-mentioned acid and alkali resistant separation membrane in the field of water treatment.

[0013] Through the above technical solutions, the separation membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0014] The poly(triazineamine-urea) layer in the separation membrane provided by this invention improves the acid and alkali resistance of the separation membrane, enabling it to be used for magnesium-lithium separation even in acidic / alkaline environments. The modification layer includes a cross-linked polymer, which gives the separation membrane a smaller pore size and improves the membrane's density. The high positive charge density in the cross-linked polymer allows the separation membrane to maintain a high water flux while possessing a high magnesium-lithium separation coefficient, making it suitable for use in water treatment separation applications.

[0015] The separation membrane preparation method provided by this invention allows polyphenols and a first polyamine to undergo a Michael addition reaction on the surface of a poly(triazineamine-urea) layer to form a cross-linked structure. Furthermore, some of the structural units provided by the polyphenols are connected to the poly(triazineamine-urea) layer through carbon atoms at the adjacent positions of the phenolic hydroxyl groups, resulting in a more compact stack. The poly(triazineamine-urea) layer enables the separation membrane to have acid / alkali resistance. The cross-linked polymer in the modification layer increases the density of the separation membrane and the positive charge density on the surface of the separation membrane, enabling the separation membrane to maintain a high water flux while having a high magnesium-lithium separation coefficient. Attached Figure Description

[0016] Figure 1 This is the N atom spectrum of XPS on the surface of the acid and alkali resistant separation membrane N1 prepared in Example 1. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] The first aspect of the present invention provides an acid and alkali resistant separation membrane, wherein the separation layer comprises, in sequence, a substrate layer, a porous support layer, a poly(triazineamine-urea) layer, and a modification layer;

[0019] The crosslinked polymer forming the modified layer includes structural units provided by polyphenols and structural units provided by a first polyamine, and at least some of the structural units provided by polyphenols are also connected to the poly(triazineamine-urea) layer through the ortho position of phenolic hydroxyl groups;

[0020] The pore size of the separation membrane is 0.1-0.5 nm, and the surface Zeta potential of the separation membrane is 0-30 mV.

[0021] The inventors of this invention discovered in their research that the acid- and alkali-resistant separation membrane, comprising the layers described above, enables the membrane to possess the pore size range and surface Zeta potential range described in this invention. This indicates that the separation membrane exhibits high density and a high surface Zeta electrode potential. When used for magnesium-lithium separation in acid / alkali environments, it can repel divalent magnesium ions while allowing monovalent lithium ions to pass through as much as possible, resulting in a high magnesium-lithium separation coefficient. Simultaneously, the synergistic effect of the several membrane layers enables the separation membrane to achieve a high water flux. When used in water treatment, it allows for the passage of larger flow rates, thereby improving treatment efficiency.

[0022] In this invention, the pore size of the acid and alkali resistant separation membrane is measured using the polyethylene glycol (PEG) solute transfer method, and the detailed steps are as follows:

[0023] (1) Test the retention rate of the separation membrane for PEG of different molecular sizes;

[0024] (2) Linear fitting of PEG size and retention rate in log-probability coordinate system, the PEG size corresponding to 50% retention rate is the average pore size of the separation membrane.

[0025] In this invention, the surface zeta potential of the acid and alkali resistant separation membrane is measured using a potential analyzer.

[0026] Furthermore, the pore size of the acid and alkali resistant separation membrane is 0.15-0.3 nm, and the surface zeta potential of the separation membrane is 5 mV to 20 mV.

[0027] According to the present invention, the modification layer includes the structural unit shown in Formula I;

[0028]

[0029] In this invention, the inventors discovered through research that when the nitrogen element in the modified layer of the separation membrane is tested by XPS, the modified layer of the acid and alkali resistant separation membrane provided by this invention contains the structural unit shown in Formula I, that is, the modified layer contains π-π formed by benzene ring-nitrogen atom-benzene ring. * The electronic conjugated structural unit further illustrates that at least some of the structural units from polyphenols in the modified layer undergo cross-linking reactions with structural units from the first polyamine and / or nitrogen atoms from the poly(triazineamine-urea) layer through the ortho position of the phenolic hydroxyl groups, thereby further reducing the pore size of the acid and alkali resistant separation membrane containing the modified layer and further improving the density of the acid and alkali resistant separation membrane, thereby improving the magnesium and lithium separation efficiency of the acid and alkali resistant separation membrane when used for magnesium and lithium separation.

[0030] According to the present invention, the content of the structural units provided by the polyphenols on the membrane surface is 2 × 10⁻⁶. -3 -5×10 -2mg / cm 2 The content of the structural units provided by the first polyamine on the membrane surface is 1×10. -3 -2.5×10 -2 mg / cm 2 .

[0031] In this invention, the content of structural units provided by polyphenols and structural units provided by the first polyamine on the surface of the acid- and alkali-resistant separation membrane is determined according to the following steps:

[0032] The membrane, comprising a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, was dried in a vacuum oven at 60°C for 24 hours. The mass of the membrane was then measured and denoted as M. n mg; The membrane was placed in a membrane tank, and the feed tank contained an aqueous solution of polyphenols of a certain concentration. After circulating for a certain period of time under certain conditions, the membrane was removed, the surface of the membrane was rinsed with deionized water, and then dried at 60℃ for 24 hours. The mass of the membrane was then measured as W. n mg; then the membrane is placed in the membrane tank, and the feed tank contains an aqueous solution of the first polyamine of a certain concentration. After circulating for a certain period of time under certain conditions, the membrane is removed, the surface of the membrane is rinsed with deionized water, and then dried at 60℃ for 24 hours. The mass of the membrane is then weighed as N. n mg; the content of polyphenols P on the membrane surface each time the membrane is modified. n and the content of polyamines T n The results are obtained using the following formulas:

[0033]

[0034] Where, when n is greater than 1, M n =N n-1 When n=1, M n This refers to the mass of the original poly(triazineamine-urea) membrane;

[0035]

[0036] After self-assembly, the total content of polyphenols on the surface of the separation membrane is ΣPn, n≥1, and the total content of the first polyamine on the surface is ΣTn, n≥1.

[0037] Where n is the number of self-assemblies, and S is the effective membrane area in cm². 2 .

[0038] In this invention, the inventors discovered through research that when the content of structural units provided by polyphenols and structural units provided by the first polyamine on the membrane surface meets the above-mentioned range, the separation membrane has a suitable degree of compactness and thickness, thereby ensuring that the acid and alkali resistant separation membrane has a high magnesium-lithium separation coefficient and water flux.

[0039] Furthermore, the content of the structural units provided by the polyphenols on the membrane surface is 1×10⁻⁶. -2 -3×10 -2 mg / cm 2 The content of the structural units provided by the first polyamine on the membrane surface is 5 × 10⁻⁶. -3 -2×10 -2 mg / cm 2 .

[0040] According to the present invention, the content of N atoms in the modified layer is 10-20 at.%.

[0041] In this invention, the content of N atoms in the modified layer is measured by X-ray photoelectron spectroscopy.

[0042] In this invention, when the content of N atoms in the modified layer meets the above-mentioned range, the separation membrane can have a high surface electrode potential and excellent hydrophilicity. When used for magnesium-lithium separation, it has high magnesium-lithium separation efficiency and high water flux.

[0043] Furthermore, the N atom content in the modified layer is 14-18 at.%.

[0044] According to the present invention, the contact angle of the separation membrane is 20-60°.

[0045] In this invention, the contact angle of the separation membrane is measured using the following method: The surface contact angle of the composite membrane sample is tested using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany, via the static drop method. Before the test, the sample is dried in a vacuum oven at 60°C for 30 minutes to remove surface and internal moisture. Then, the dried membrane is attached to a flat glass slide with double-sided tape. During the test, the volume of each water droplet is 2 μL. The water droplet is placed on the membrane surface for 3 seconds and the test is performed immediately. The final contact angle is determined by taking the average value after multiple measurements.

[0046] In this invention, the separation membrane has a contact angle within the range described in this invention, thereby indicating that the separation membrane has excellent hydrophilicity and can enable the separation membrane to have excellent water flux.

[0047] Furthermore, the contact angle of the separation membrane is 20-50°.

[0048] According to the present invention, the thickness of the separation membrane is 100-200 μm.

[0049] According to the present invention, the thickness of the substrate layer is 30-150 μm, preferably 50-120 μm.

[0050] According to the present invention, the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm.

[0051] According to the present invention, the thickness of the poly(triazineamine-urea) layer is 10-500 nm, preferably 50-200 nm.

[0052] According to the present invention, the thickness of the modified layer is 10-200 nm, preferably 10-60 nm.

[0053] In this invention, the thicknesses of the separation membrane, porous support layer, and poly(triazineamine-urea) layer are measured using a micrometer and a scanning electron microscope. The thickness of the modified layer is obtained by subtracting the thicknesses of the substrate layer, porous support layer, and poly(triazineamine-urea) layer from the thickness of the separation membrane. The thickness of the substrate layer is the thickness measured before coating the porous support layer material solution.

[0054] The inventors of this invention discovered in their research that when the thickness range of each layer is met, the layers can work together better, resulting in a separation membrane with small pore size and high Zeta potential. When used for magnesium-lithium separation in acidic or alkaline environments, it can achieve both higher magnesium-lithium separation efficiency and water flux.

[0055] According to the present invention, the material of the substrate layer is not particularly limited and can be any material commonly used in the art that has a certain strength and is suitable for nanofiltration or reverse osmosis, and can serve as a support. However, preferably, the material of the substrate layer is selected from polyester nonwoven fabric and / or polyethylene nonwoven fabric.

[0056] According to the present invention, the poly(triazineamine-urea) layer is synthesized from a second polyamine, a triazine compound containing at least two C-Cl bonds, and a polyisocyanate.

[0057] In this invention, the poly(triazineamine-urea) layer described above contains inert chemical groups, which enables the final acid and alkali resistant separation membrane to adapt to acid / alkali environments, while having a suitable cross-linking structure. In conjunction with the amino groups therein, it can achieve a better retention effect on divalent magnesium ions.

[0058] Furthermore, the second polyamine is selected from at least one of triethylenetetramine, tetraethylenepentamine, polyethylene polyamine, polyethyleneimine, and polyetheramine, preferably polyethyleneimine and / or polyethylene polyamine.

[0059] Furthermore, the triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine, and 2,4-dichloro-6-phenyl-1,3,5-triazine, preferably cyanuric chloride.

[0060] Further, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, and 1,4-cyclohexyl diisocyanate, preferably 1,3-phenyl diisocyanate.

[0061] According to the present invention, the modified layer is obtained by a self-assembly reaction of a polyphenol and a first polyamine on a poly(triazineamine-urea) layer.

[0062] According to the present invention, the polyphenols are selected from at least one of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, gallic acid, protocatechuic acid, apigenin, calciferol, myricetin, and genistein, preferably tannic acid and / or tea polyphenols.

[0063] According to the present invention, the first polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, polyethylene polyamine, piperazine, and N-aminoethylpiperazine, preferably at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, and polyethylene polyamine.

[0064] A second aspect of the present invention provides a method for preparing an acid and alkali resistant separation membrane, wherein the preparation method includes the following steps: sequentially preparing a porous support layer, a poly(triazineamine-urea) layer and a modification layer on a substrate layer;

[0065] The method for preparing the modified layer includes: under a first pressure, while the polyphenol solution is kept flowing, making a first contact between one side of the poly(triazineamine-urea) layer of the material, which includes a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer of the material, while the first polyamine solution is kept flowing, making a second contact between one side of the poly(triazineamine-urea) layer of the material and the first polyamine solution, thereby completing the self-assembly reaction.

[0066] According to the present invention, the first pressure and the second pressure are each independently 1-3 MPa.

[0067] In this invention, when the pressure applied during the preparation of the modified layer meets the above-mentioned range, it can ensure that the prepared acid and alkali resistant separation membrane has a high density, while also ensuring a high content of structural units provided by the first polyamine in the separation membrane, thus giving the separation membrane higher hydrophilicity, and ultimately giving the separation membrane excellent magnesium-lithium separation performance and water permeability.

[0068] Furthermore, the first pressure and the second pressure are each independently 1.5-2 MPa.

[0069] According to the present invention, the amounts of the polyphenol solution and the first polyamine solution are such that the mass ratio of the polyphenol to the first polyamine is 0.1-10:1.

[0070] In this invention, controlling the mass ratio of polyphenols to the first polyamine to meet the above-mentioned range not only ensures that the polyphenols and polyamines can react fully and that the resulting separation membrane has the pore size required by this invention, but also ensures that the surface of the separation membrane contains more residual amino groups, so that the acid and alkali resistant separation membrane has the high surface Zeta potential and hydrophilicity required by this invention. When this acid and alkali resistant separation membrane is used for magnesium-lithium separation, the acid and alkali resistant separation membrane has a higher divalent magnesium ion rejection rate and water flux.

[0071] Furthermore, the amounts of the polyphenol solution and the first polyamine solution are such that the mass ratio of polyphenol to first polyamine is 0.25-6:1.

[0072] According to the present invention, the concentration of the polyphenol is 0.00001 wt%-1 wt%.

[0073] According to the present invention, the concentration of the first polyamine is 0.00001 wt% - 1 wt%.

[0074] In this invention, by controlling the concentrations of the polyphenol solution and the first polyamine solution to independently satisfy the above-mentioned ranges, we can ensure that the acid and alkali resistant separation membrane prepared thereby has the pore size, surface Zeta potential and thickness required by this invention, and can ensure that when the acid and alkali resistant separation membrane is used for magnesium-lithium separation in acid / alkali environments, it has both a high magnesium-lithium separation coefficient and a high water flux.

[0075] Furthermore, the concentration of the polyphenol is 0.0001 wt% - 0.1 wt%.

[0076] Furthermore, the concentration of the first polyamine is 0.0001 wt% - 0.1 wt%.

[0077] According to the present invention, the temperatures of the first contact and the second contact are each independently 10-30°C.

[0078] In this invention, when the temperatures of the first contact and the second contact are controlled to meet the above-mentioned range, it is possible to ensure that the polyphenol and the first polyamine react fully, so that the prepared separation membrane has the required pore size and surface Zeta potential, thereby enabling the acid and alkali resistant separation membrane to have high magnesium-lithium separation efficiency and high rejection rate.

[0079] According to the present invention, in a single self-assembly reaction, the duration of the first contact is 1-120 min.

[0080] According to the present invention, in a single self-assembly reaction, the second contact time is 1-120 min.

[0081] In this invention, during a single self-assembly reaction, the timing of the first and second contacts is controlled to satisfy the above-mentioned range formula. While ensuring sufficient reaction, the density and thickness of the final acid-alkali resistant separation membrane can be controlled, resulting in a high water permeability and magnesium-lithium separation rate of the acid-alkali resistant separation membrane.

[0082] Furthermore, in a single self-assembly reaction, the duration of the first contact is 10-60 min.

[0083] Furthermore, in a single self-assembly reaction, the second contact time is 10-60 min.

[0084] According to the present invention, the number of self-assembly reactions is 1-10.

[0085] In this invention, the inventors further discovered that by preparing a modification layer on a poly(triazineamine-urea) layer made of a material including a matrix layer, a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, and repeating the following steps to complete multiple self-assemblies, it is possible to further ensure that the separation membrane has a higher surface zeta potential and a smaller pore size, thereby further ensuring a higher magnesium-lithium separation efficiency.

[0086] Furthermore, the self-assembly reaction is performed 2-5 times.

[0087] According to the present invention, the conditions for preparing the modified layer include making the thickness of the modified layer in the separation membrane 10-200 nm.

[0088] In this invention, the separation membrane that meets the thickness of the above-mentioned modified layer has a small pore size and a high Zeta potential. When used for magnesium-lithium separation in acidic or alkaline environments, it can achieve both higher magnesium-lithium separation efficiency and water flux.

[0089] Furthermore, the conditions for preparing the modified layer include making the thickness of the modified layer in the separation membrane 20-100 nm.

[0090] According to the present invention, the polyphenols in the polyphenol solution are selected from at least one of tannic acid, tea polyphenols, gallic acid, catechin, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein, preferably tannic acid and / or tea polyphenols.

[0091] According to the present invention, the first polyamine in the first polyamine solution is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, polyethylene polyamine, piperazine, and N-aminoethylpiperazine, preferably at least one of polyethyleneimine, tetraethylenepentamine, triethylenetetramine, and polyethylene polyamine.

[0092] In this invention, the method for preparing the porous support layer on the substrate layer can be a method commonly used in the art. However, preferably, the method for preparing the porous support layer includes: coating a solution containing the porous support layer material onto the substrate layer, performing a phase transformation, and obtaining a material containing the substrate layer and the porous support layer.

[0093] According to the present invention, the conditions for the phase transformation include: soaking in water at 10-30°C for 10-60 minutes.

[0094] In this invention, when the porous support layer is prepared using the method described above, the solvent in the solution containing the porous support layer material gradually leaves the porous support layer during immersion in water. This phase transformation method further ensures that a support layer with a porous structure is obtained.

[0095] According to the present invention, the thickness of the substrate layer is 30-150 μm, preferably 50-120 μm.

[0096] The thickness of the substrate layer remains essentially unchanged before and after preparation.

[0097] According to the present invention, the material of the substrate layer is not particularly limited and can be any material commonly used in the art that has a certain strength and is suitable for nanofiltration or reverse osmosis, and can serve as a support. However, preferably, the material of the substrate layer is selected from polyester nonwoven fabric and / or polyethylene nonwoven fabric.

[0098] According to the present invention, the conditions for preparing the porous support layer include making the thickness of the porous support layer in the separation membrane 10-100 μm, more preferably 30-60 μm.

[0099] It is understandable that the thickness can be controlled by adjusting the amount of coating applied. However, due to thickness collapse after coating, the thickness set during coating will differ somewhat from the thickness of the porous support layer in the final separation membrane. Generally, the thickness set during coating should be approximately 40-60 μm greater than the desired porous support layer thickness in the separation membrane.

[0100] According to the present invention, the concentration of the solution containing the porous support layer material is 10wt%-20wt%.

[0101] According to the present invention, the porous support layer material is selected from at least one of polyethersulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride and polyaryletherketone.

[0102] According to the present invention, the solvent in the solution containing the porous support layer material is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0103] In this invention, there is no particular limitation on the preparation method of the solution containing the porous support layer material. Conventional methods in the art can be used for preparation. For example, the porous support layer material is first dissolved in a solvent and degassed (degassed at 20-40°C for 10-180 min) to obtain a solution containing the porous support layer material.

[0104] In this invention, after the porous support layer is prepared, the material can be washed, such as by multiple water washes.

[0105] According to the present invention, the method for preparing the poly(triazineamine-urea) layer includes: sequentially contacting the surface of a porous support layer of a material comprising a substrate layer and a porous support layer with an aqueous phase containing a second polyamine and an organic phase containing a triazine compound and a polyisocyanate containing at least two C-Cl bonds, and then subjecting it to heat treatment.

[0106] In this invention, the poly(triazineamine-urea) layer prepared by the above method contains inert chemical groups and is suitable for acidic / alkaline environments; the surface modification layer can enhance the positive charge of the membrane surface, ensuring that the membrane has high magnesium-lithium separation efficiency and water flux.

[0107] According to the present invention, the conditions for preparing the poly(triazineamine-urea) layer include making the thickness of the poly(triazineamine-urea) layer in the separation membrane 10-500 nm, more preferably 50-200 nm.

[0108] In this invention, the poly(triazineamine-urea) layer is not only dense but also very thin, further ensuring high magnesium-lithium separation efficiency and water flux.

[0109] According to the present invention, the contact time between the porous support layer and the aqueous phase containing the second polyamine is 5-100 s.

[0110] According to the present invention, the contact time between the porous support layer and the organic phase containing at least two C-Cl bonds of triazine compounds and polyisocyanates is 10-200 s.

[0111] In this invention, the contact time between the porous support layer and the organic phase of the second polyamine, the triazine compound containing at least two C-Cl bonds, and the polyisocyanate allows the reaction to proceed fully. The resulting poly(triazineamine-urea) layer has a high water flux and magnesium-lithium separation coefficient, while the reaction rate is fast and the process is simple.

[0112] Furthermore, the porous support layer is in contact with the aqueous phase containing the second polyamine for 10-60 seconds.

[0113] Furthermore, the contact time between the porous support layer and the organic phase containing at least two C-Cl bonds (triazine compounds and polyisocyanates) is 20-120 s.

[0114] According to the present invention, the amounts of the aqueous phase containing the second polyamine, the triazine compound containing at least two C-Cl bonds, and the organic phase containing the polyisocyanate are such that the mass ratio of the second polyamine to the triazine compound containing at least two C-Cl bonds and the polyisocyanate is 10-80:1-8:1.

[0115] The inventors of this invention have discovered that when the mass ratio of the second polyamine, the triazine compound containing at least two C-Cl bonds, and the polyisocyanate is controlled to meet the above-mentioned ratio, the prepared poly(triazineamine-urea) layer has a suitable pore size, ensuring that the poly(triazineamine-urea) layer has excellent lithium chloride permeability while having a good magnesium chloride rejection rate.

[0116] Meanwhile, by modifying the poly(triazineamine-urea) layer with polyphenols and a first polyamine, the pore size of the poly(triazineamine-urea) layer can be further reduced and the surface Zeta potential can be further increased, ultimately obtaining an acid and alkali resistant separation membrane with a specific pore size and surface Zeta potential as defined in the first aspect of the present invention. When this separation membrane is used for magnesium-lithium separation, it can significantly improve the magnesium-lithium separation efficiency.

[0117] Furthermore, the amounts of the aqueous phase containing the second polyamine, the triazine compound containing at least two C-Cl bonds, and the organic phase containing the polyisocyanate are such that the mass ratio of the polyamine to the triazine compound containing at least two C-Cl bonds and the polyisocyanate is 20-70:1-5:1.

[0118] According to the present invention, the concentration of the aqueous phase containing the second polyamine is 0.2 wt% to 10 wt%.

[0119] According to the present invention, the concentration of the organic phase of the triazine compound containing at least two C-Cl bonds is 0.05 wt% to 2 wt%.

[0120] According to the present invention, the concentration of the organic phase containing the polyisocyanate is 0.001 wt% to 0.5 wt%.

[0121] In this invention, the specific concentrations of the second polyamine, the triazine compound containing at least two C-Cl bonds, and the polyisocyanate enable a more complete reaction, resulting in an acid- and alkali-resistant separation membrane with appropriate density and thickness, thereby ensuring that the acid- and alkali-resistant separation membrane has a high magnesium-lithium separation coefficient and water flux.

[0122] Furthermore, the concentration of the aqueous phase containing the second polyamine is 0.5 wt% to 5 wt%.

[0123] Furthermore, the concentration of the organic phase of the triazine compound containing at least two C-Cl bonds is 0.1 wt% to 1 wt%.

[0124] Furthermore, the concentration of the organic phase containing the polyisocyanate is 0.01wt%-0.2wt%.

[0125] According to the present invention, the second polyamine is selected from at least one of triethylenetetramine, tetraethylenepentamine, polyethylene polyamine, polyethyleneimine and polyetheramine, preferably polyethyleneimine and / or polyethylene polyamine.

[0126] According to the present invention, the triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine and 2,4-dichloro-6-phenyl-1,3,5-triazine, preferably cyanuric chloride.

[0127] According to the present invention, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, and 1,4-cyclohexyl diisocyanate, preferably 1,3-phenyl diisocyanate.

[0128] According to the present invention, the temperature of the heat treatment is 40-150°C; the time of the heat treatment is 0.5-10 min.

[0129] In this invention, specific heat treatment conditions enable a more complete reaction and make the final acid and alkali resistant separation membrane suitable for acid and alkali environments, with a denser surface, and both high water flux and magnesium-lithium separation rate.

[0130] Furthermore, the heat treatment temperature is 50-120℃; the heat treatment time is 1-5 minutes.

[0131] In this invention, the ratio of the polyphenol solution to the film area of ​​the poly(triazineamine-urea) layer comprising the substrate layer, the porous support layer, and the poly(triazineamine-urea) layer is 5-30 mL / cm². 2 .

[0132] In this invention, the ratio of the area of ​​the first polyamine solution to the area of ​​the poly(triazineamine-urea) layer comprising the substrate layer, the porous support layer, and the poly(triazineamine-urea) layer is 10-20 mL / cm². 2 .

[0133] A third aspect of the present invention provides a separation membrane prepared by the above-described preparation method.

[0134] The fourth aspect of this invention provides the application of the above-mentioned acid and alkali resistant separation membrane in the field of water treatment.

[0135] The present invention will be described in detail below through embodiments, wherein,

[0136] In the following embodiments, when the material including the substrate layer, the porous support layer, and the poly(triazineamine-urea) layer comes into contact with the solution in the cross-flow membrane tank, water is pumped into the membrane tank by a water pump to keep the polyphenol solution and the first polyamine solution in the membrane tank in a flowing state.

[0137] The pore size of the acid and alkali resistant separation membrane was determined using the PEG solute transfer method, the detailed steps of which are as follows:

[0138] (1) Test the retention rate of the separation membrane for PEG of different molecular sizes;

[0139] (2) Linear fitting of PEG size and retention rate in log-probability coordinate system, the PEG size corresponding to 50% retention rate is the average pore size of the separation membrane.

[0140] Surface Zeta potential of acid and alkali resistant separation membrane: The surface Zeta potential was determined in accordance with GB / T 37617-2019.

[0141] The nitrogen atom content in the modified layer of the acid and alkali resistant separation membrane was determined by X-ray photoelectron spectroscopy (XPS) using Al-Kα X-ray irradiation on an ESCALAB250 X-ray photoelectron spectrometer.

[0142] The content of structural units provided by polyphenols and the first polyamine in the acid and alkali resistant separation membrane:

[0143] The membrane, comprising a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, was dried in a vacuum oven at 60°C for 24 hours. The mass of the membrane was then measured as M. n mg; The membrane was placed in a membrane tank, and the feed tank contained an aqueous solution of polyphenols of a certain concentration. After circulating for a certain period of time under certain conditions, the membrane was removed, the surface of the membrane was rinsed with deionized water, and then dried at 60℃ for 24 hours. The mass of the membrane was then measured as W. n mg; then the membrane is placed in the membrane tank, and the feed tank contains an aqueous solution of the first polyamine of a certain concentration. After circulating for a certain period of time under certain conditions, the membrane is removed, the surface of the membrane is rinsed with deionized water, and then dried at 60℃ for 24 hours. The mass of the membrane is then weighed as N. n mg; the content of polyphenols P on the membrane surface each time the membrane is modified. n and the content of polyamines T n The results are obtained using the following formulas:

[0144]

[0145] Where, when n is greater than 1, M n =N n-1 When n=1, M n This refers to the mass of the original poly(triazineamine-urea) film.

[0146]

[0147] After self-assembly, the total content of polyphenols on the surface of the separation membrane is ΣPn, n≥1, and the total content of polyamines on the surface is ΣTn, n≥1.

[0148] Where n is the number of self-assemblies, and S is the effective membrane area in cm². 2 .

[0149] The contact conditions between the membrane and the aqueous solutions of polyphenols and the first polyamine correspond to the first pressure, second pressure, first contact temperature and time, and second contact temperature and time of the self-assembly process in the examples and comparative examples, respectively.

[0150] Contact angle of acid and alkali resistant separation membrane: The surface contact angle of the composite membrane sample was tested using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany, by the static drop method. Before the test, the sample was dried in a vacuum oven at 60℃ for 30 minutes to remove surface and internal moisture. Then, the dried membrane was attached to a flat glass slide with double-sided tape. The volume of water droplets was 2μL each time during the test. The water droplets were dropped onto the membrane surface for 3 seconds and the test was conducted immediately. The final contact angle was determined by taking the average value after multiple measurements.

[0151] The thickness of the acid and alkali resistant separation membrane and its layers: The thicknesses of the separation membrane, porous support layer, and poly(triazineamine-urea) layer were measured using a micrometer and scanning electron microscope. The thickness of the modification layer was obtained by subtracting the thicknesses of the substrate layer, porous support layer, and poly(triazineamine-urea) layer from the thickness of the separation membrane. The thickness of the substrate layer was the same as the thickness measured before coating the porous support layer material solution.

[0152] Test method for water flux of acid and alkali resistant separation membrane: The acid and alkali resistant separation membrane is loaded into the membrane tank and pre-pressurized at 1.5 MPa for 1 hour. Then, the water permeation rate of the acid and alkali resistant separation membrane is measured over a certain period of time under a pressure of 2 MPa and a temperature of 25℃. The water flux is calculated using the following formula: J = Q / (A·t), where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the acid and alkali resistant separation membrane (m²). 2 ), where t is time (h).

[0153] Test method for desalination rate of acid and alkali resistant separation membrane: The acid and alkali resistant separation membrane is loaded into the membrane tank and pre-pressurized at 1.5 MPa for 1 hour. Then, under the conditions of 2 MPa pressure and 25℃, the concentration change of magnesium chloride in the initial aqueous solution of magnesium chloride (2000 ppm) and the magnesium chloride in the permeate is measured within 1 hour. The desalination rate is calculated using the following formula: R = (C f -C p ) / C f ×100%, where R is the desalination rate, and C is the desalination rate. f C represents the concentration of magnesium chloride in the original solution. p This represents the concentration of magnesium chloride in the permeate.

[0154] Test method for magnesium-lithium separation coefficient of acid and alkali resistant separation membrane: The acid and alkali resistant separation membrane is loaded into a membrane tank. The original aqueous solution is a mixture of 2000 ppm magnesium chloride and 100 ppm lithium chloride. The mixture is pre-pressurized at 1.5 MPa for 1 hour, followed by permeate at 2 MPa and 25°C. The mass concentrations of magnesium and lithium ions in the original solution and permeate are determined by ion chromatography. The lithium-magnesium separation coefficient is calculated using the following formula:

[0155]

[0156] Where S is the lithium-magnesium separation coefficient, C Mg,f and C Li,f These represent the mass concentrations of magnesium and lithium ions in the raw water (measured by ion chromatography); C Mg,p and C Li,p These represent the mass concentrations of magnesium ions and lithium ions in the permeate (measured by ion chromatography).

[0157] Test method for acid and alkali resistant separation membrane: Immerse the membrane sheet of the acid and alkali resistant separation membrane in a 5 wt% HCl solution for 7 days, and test the changes in magnesium-lithium separation coefficient and water flux of the acid and alkali resistant separation membrane.

[0158] Branched polyethyleneimine (weight average molecular weight of 25000 g / mol), polyethylene polyamine, tetraethylenepentamine, cyanuric chloride, 2,4-dichloro-6-phenyl-1,3,5-triazine, 1,3-phenyl diisocyanate, toluene-2,4-diisocyanate, tannic acid, gallic acid, tea polyphenols, etc. were all purchased from Bailingwei Technology Co., Ltd., and other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0159] The porous support layer was prepared using a phase transformation method, and the specific steps are as follows:

[0160] Polysulfone (number-average molecular weight 80,000 g / mol) was dissolved in N,N-dimethylformamide to prepare an 18 wt% polysulfone solution, which was then degassed at 25 °C for 120 min. The polysulfone solution was then coated onto a 75 μm thick polyester nonwoven fabric (substrate layer) using a doctor blade, and subsequently immersed in water at 25 °C for 60 min. This allowed the polysulfone layer on the surface of the polyester nonwoven fabric to undergo phase inversion, forming a porous membrane. Finally, after three water washes, a material with a total thickness of 115 μm, including the substrate layer and a porous support layer (40 μm), and an area of ​​400 cm² was obtained. 2 .

[0161] Example 1

[0162] (1) The surface of the porous support layer, which includes the substrate layer and the porous support layer, is contacted with 50 mL of an aqueous solution containing 2 wt% polyethyleneimine at 25 °C for 60 s and then drained. Then, the upper surface of the support layer is contacted with 30 mL of an Isopar E solution containing 0.15 wt% cyanuric chloride and 0.05 wt% 1,3-phenyl diisocyanate at 25 °C for 60 s and then drained. Then, the membrane is placed in an oven and heated at 70 °C for 3 min.

[0163] (2) The heat-treated product was loaded into a cross-flow test system, so that the poly(triazineamine-urea) layer of the material made first contact with a 0.001 wt% tannic acid aqueous solution in the cross-flow membrane pool. The volume of the tannic acid aqueous solution was 5 L. After the test system was run at 2 MPa and 25 °C for 30 min, the liquid was drained and the test system was repeatedly rinsed with deionized water to remove the residual tannic acid in the system. 5 L of a 0.004 wt% polyethyleneimine aqueous solution was added to the cross-flow test system for second contact. The test system was run at 2 MPa and 25 °C for 30 min, the liquid was drained and the test system was repeatedly rinsed with deionized water to remove the residual polyethyleneimine in the system. This completed one self-assembly process. The above operation was repeated to perform another self-assembly process to obtain the acid and alkali resistant separation membrane N1.

[0164] Figure 1 In the figure, the characteristic peak at 407 eV corresponds to the structural unit shown in Equation I, which is the signal peak generated by the π-π* electron conjugation formed by the benzene ring-nitrogen atom-benzene ring. In this structural unit, one nitrogen atom undergoes a cross-linking reaction with two benzene rings, which further reduces the pore size of the separation membrane, improves the density of the separation membrane, and enables the separation membrane to have a high magnesium-lithium separation coefficient.

[0165] Example 2

[0166] The method of Example 1 was implemented, except that in step (2), 5L of 0.01wt% tea polyphenols were added to replace tannic acid, and 5L of 0.04wt% polyethyleneimine aqueous solution was added to replace 0.004wt% polyethyleneimine aqueous solution, so as to obtain acid and alkali resistant separation membrane N2.

[0167] Example 3

[0168] The method of Example 1 was implemented, except that in step (2), 5L of 0.1wt% gallic acid was added to replace tannic acid, and 5L of 0.04wt% polyethyleneimine aqueous solution was added to replace 0.004wt% polyethyleneimine aqueous solution, so as to obtain acid and alkali resistant separation membrane N3.

[0169] Example 4

[0170] The method was carried out according to Example 1, except that in step (1), 30 mL of Isopar E solution containing 0.15 wt% 2,4-dichloro-6-phenyl-1,3,5-triazine and 0.05 wt% toluene-2,4-diisocyanate was added instead of 30 mL of Isopar E solution containing 0.15 wt% cyanuric chloride and 0.05 wt% 1,3-phenyl diisocyanate to obtain acid and alkali resistant separation membrane N4.

[0171] Example 5

[0172] The method of Example 1 was followed, except that in step (1), the surface of the porous support layer, which includes a substrate layer and a porous support layer, was contacted with 60 mL of an aqueous solution containing 2 wt% polyethyleneimine at 25°C for 60 s and then drained; then, the upper surface of the support layer was contacted with 30 mL of an Isopar E solution containing 0.3 wt% cyanuric chloride and 0.05 wt% 1,3-phenyl diisocyanate at 25°C for 60 s and then drained; then, the membrane was placed in an oven and heated at 70°C for 3 min; then step (2) was carried out according to the method of Example 1 to obtain the acid and alkali resistant separation membrane N5.

[0173] Example 6

[0174] The method of Example 1 was implemented, except that in step (2), polyethyleneimine was replaced with polyethyleneimine during the self-assembly process to obtain acid and alkali resistant separation membrane N6.

[0175] Example 7

[0176] The method of Example 1 was implemented, except that in step (2), tetraethylenepentamine was used to replace polyethyleneimine during the self-assembly process to obtain acid and alkali resistant separation membrane N7.

[0177] Example 8

[0178] The method was implemented according to Example 1, except that the self-assembly was performed once to obtain the acid and alkali resistant separation membrane N8.

[0179] Example 9

[0180] The method was implemented according to Example 1, except that the self-assembly was performed 5 times to obtain the acid and alkali resistant separation membrane N9.

[0181] Example 10

[0182] The method of Example 1 was implemented, except that in step (1), triethylenetetramine was used to replace polyethyleneimine to obtain acid and alkali resistant separation membrane N10.

[0183] Example 11

[0184] The method was implemented according to Example 1, except that the first pressure was 1.5 MPa and the second pressure was 1.5 MPa, resulting in an acid and alkali resistant separation membrane N11.

[0185] Example 12

[0186] The method was implemented according to Example 1, except that the first pressure was 1.5 MPa and the second pressure was 3 MPa, resulting in an acid and alkali resistant separation membrane N12.

[0187] Example 13

[0188] The method was implemented according to Example 1, except that the first pressure was 1 MPa and the second pressure was 1.5 MPa, resulting in an acid and alkali resistant separation membrane N13.

[0189] Comparative Example 1

[0190] The method of Example 1 was carried out, except that no polyphenols and the first polyamine were added, resulting in an acid and alkali resistant separation membrane D1.

[0191] Comparative Example 2

[0192] The method of Example 1 was carried out, except that the first polyamine was not added, and acid and alkali resistant separation membrane D2 was obtained.

[0193] Comparative Example 3

[0194] The method was implemented according to Example 1, except that immersion was used instead of the first contact and immersion was used instead of the second contact to obtain the acid and alkali resistant separation membrane D3.

[0195] The results of the structure-related performance tests on the acid and alkali resistant separation membrane are shown in Tables 1 and 2.

[0196] Table 1

[0197]

[0198] Table 2

[0199]

[0200] The water flux, desalination rate of magnesium chloride and lithium chloride, and magnesium-lithium separation coefficient of the acid-alkali resistant separation membranes prepared in the examples and comparative examples were tested. After acid treatment, the magnesium-lithium separation coefficient and water flux of the acid-alkali resistant separation membranes in the examples and comparative examples were tested, and the results are shown in Table 3.

[0201] Table 3

[0202]

[0203]

[0204] The results in Tables 1, 2, and 3 show that, compared with the comparative examples, the Zeta potential in the examples is higher. When used for magnesium-lithium separation, it can allow monovalent lithium ions to pass through while repelling divalent magnesium ions, resulting in a higher magnesium-lithium separation coefficient. The data in Table 3, "after treatment with 5 wt% HCl for 7 days", shows that the separation membrane still has a high separation coefficient after acid treatment. Therefore, the separation membrane of the present invention can be used for magnesium-lithium separation under acidic conditions.

[0205] A comparison of Examples 1-3 shows that the types and amounts of polyphenols and the first polyamine have a synergistic effect, jointly affecting the water flux and magnesium-lithium separation coefficient of the prepared acid and alkali resistant separation membrane.

[0206] Compared with Examples 1 and 8, the assembly that satisfies the technical solution of the present invention can achieve better water flux and magnesium-lithium separation coefficient.

[0207] Compared to using polyethyleneimine with abundant amino groups in the aqueous phase, when small molecule amine monomers are selected, the poly(triazineamine-urea) separation layer obtained by interfacial polymerization has a larger pore size, and the separation membrane obtained after surface self-assembly has a lower rejection rate for magnesium chloride, thus the magnesium-lithium separation coefficient is also lower.

[0208] 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. An acid- and alkali-resistant separation membrane, characterized in that, The acid and alkali resistant separation membrane comprises, in sequence, a substrate layer, a porous support layer, a poly(triazineamine-urea) layer, and a modification layer; The crosslinked polymer forming the modified layer includes structural units provided by polyphenols and structural units provided by a first polyamine, and at least some of the structural units provided by polyphenols are also connected to the poly(triazineamine-urea) layer through the ortho position of phenolic hydroxyl groups; The pore size of the separation membrane is 0.1-0.5 nm, and the surface Zeta potential of the acid and alkali resistant separation membrane is 0-30 mV.

2. The acid and alkali resistant separation membrane according to claim 1, wherein, The separation membrane has a pore size of 0.15-0.3 nm and a surface zeta potential of 5 mV to 20 mV.

3. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The modification layer contains the structural unit shown in Formula I; Formula I.

4. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The structural units provided by the polyphenols have an abundance of 2 × 10⁻⁶ on the membrane surface. -3 -5×10 -2 mg / cm 2 The content of the structural units provided by the first polyamine on the membrane surface is 1×10. -3 -2.5×10 -2 mg / cm 2 .

5. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The structural units provided by the polyphenols have an abundance of 1×10 on the membrane surface. -2 -3×10 -2 mg / cm 2 The content of the structural units provided by the first polyamine on the membrane surface is 5 × 10⁻⁶. -3 -2×10 -2 mg / cm 2 .

6. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The content of N atoms in the modified layer is 10-20 at.%.

7. The acid and alkali resistant separation membrane according to claim 6, wherein, The content of N atoms in the modified layer is 14-18 at.%.

8. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The contact angle of the separation membrane is 20-60°.

9. The acid and alkali resistant separation membrane according to claim 8, wherein, The contact angle of the separation membrane is 20-50°.

10. The acid- and alkali-resistant separation membrane according to claim 1 or 2, wherein, The thickness of the separation membrane is 100-200 μm; And / or, the thickness of the substrate layer is 30-150 μm; And / or, the thickness of the porous support layer is 10-100 μm; And / or, the thickness of the poly(triazineamine-urea) layer is 10-500 nm; And / or, the thickness of the modification layer is 10-200 nm.

11. The acid and alkali resistant separation membrane according to claim 10, wherein, The thickness of the substrate layer is 50-120 μm; And / or, the thickness of the porous support layer is 30-60 μm; And / or, the thickness of the poly(triazineamine-urea) layer is 50-200 nm; And / or, the thickness of the modification layer is 10-60 nm.

12. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The material of the substrate layer is selected from polyester nonwoven fabric and / or polyethylene nonwoven fabric; And / or, the material of the porous support layer is selected from at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride and polyaryl etherketone.

13. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The poly(triazineamine-urea) layer is synthesized from a second polyamine, a triazine compound containing at least two C-Cl bonds, and a polyisocyanate. And / or, the second polyamine is selected from at least one of polyethylene polyamine, polyethyleneimine, and polyetheramine; And / or, the triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine and 2,4-dichloro-6-phenyl-1,3,5-triazine; And / or, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, and 1,4-cyclohexyl diisocyanate.

14. The acid and alkali resistant separation membrane according to claim 13, wherein, The second polyamine is polyethyleneimine and / or polyethylene polyamine; And / or, the triazine compound containing at least two C-Cl bonds, cyanuric chloride; And / or, the polyisocyanate is 1,3-phenyl diisocyanate.

15. The acid and alkali resistant separation membrane according to claim 14, wherein, The polyethylene polyamine is triethylenetetramine and / or tetraethylenepentamine.

16. The acid and alkali resistant separation membrane according to claim 1 or 2, wherein, The modified layer is obtained by a self-assembly reaction of a polyphenol and a first polyamine on a poly(triazineamine-urea) layer; And / or, the polyphenols are selected from at least one of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, gallic acid, protocatechuic acid, apigenin, calciferol, myricetin, and genistein. And / or, the first polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, piperazine, and N-aminoethylpiperazine.

17. The acid and alkali resistant separation membrane according to claim 16, wherein, The polyphenols are tannic acid and / or tea polyphenols; And / or, the first polyamine is polyethyleneimine and / or polyethylene polyamine.

18. The acid and alkali resistant separation membrane according to claim 17, wherein, The polyethylene polyamine is selected from at least one of tetraethylenepentamine, triethylenetetramine, and diethylenetriamine.

19. A method for preparing an acid- and alkali-resistant separation membrane, characterized in that, The preparation method includes the following steps: sequentially preparing a porous support layer, a poly(triazineamine-urea) layer, and a modification layer on a substrate layer; The method for preparing the modified layer includes: under a first pressure, while the polyphenol solution is kept flowing, making a first contact between one side of the poly(triazineamine-urea) layer of the material, which includes a substrate layer, a porous support layer, and a poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer, and the poly(triazineamine-urea) layer of the material, while the first polyamine solution is kept flowing, making a second contact between one side of the poly(triazineamine-urea) layer of the material and the first polyamine solution, thereby completing the self-assembly reaction.

20. The preparation method according to claim 19, wherein, The first pressure and the second pressure are each independently 1-3 MPa; And / or, the amounts of the polyphenol solution and the first polyamine solution are such that the mass ratio of polyphenol to first polyamine is 0.1-10:1; And / or, the concentration of the polyphenol is 0.0001wt%-1wt%; And / or, the concentration of the first polyamine is 0.0001wt%-1wt%.

21. The preparation method according to claim 20, wherein, The first pressure and the second pressure are each independently 1.5-2 MPa; And / or, the amounts of the polyphenol solution and the first polyamine solution are such that the mass ratio of polyphenol to first polyamine is 0.25-6:1; And / or, the concentration of the polyphenol is 0.0001wt%-0.1wt%; And / or, the concentration of the first polyamine is 0.0001wt%-0.1wt%.

22. The preparation method according to claim 19 or 20, wherein, The temperatures of the first contact and the second contact are each independently 10-30°C; And / or, in a single self-assembly reaction, the duration of the first contact is 1-120 min; And / or, in a single self-assembly reaction, the duration of the second contact is 1-120 min; And / or, the number of self-assembly reactions is 1-10; And / or, the conditions for preparing the modified layer include making the thickness of the modified layer in the separation membrane 10-200 nm.

23. The preparation method according to claim 22, wherein, In a single self-assembly reaction, the duration of the first contact is 10-60 min; And / or, in a single self-assembly reaction, the duration of the second contact is 10-60 min; And / or, the number of self-assembly reactions is 2-5 times; And / or, the conditions for preparing the modified layer include making the thickness of the modified layer in the separation membrane 20-100 nm.

24. The preparation method according to claim 19 or 20, wherein, The polyphenols in the polyphenol solution are selected from at least one of tannic acid, tea polyphenols, gallic acid, catechin, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein. And / or, the first polyamine in the first polyamine solution is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, piperazine, and N-aminoethylpiperazine.

25. The preparation method according to claim 24, wherein, The polyphenols in the polyphenol solution are selected from tannic acid and / or tea polyphenols; And / or, the first polyamine in the first polyamine solution is polyethyleneimine and / or polyethylene polyamine.

26. The preparation method according to claim 25, wherein, The polyethylene polyamine in the first polyamine solution is selected from at least one of tetraethylenepentamine, triethylenetetramine, and diethylenetriamine.

27. The preparation method according to claim 19 or 20, wherein, The method for preparing the porous support layer includes: A solution containing a porous support layer material is coated onto a substrate layer, and a phase transformation is performed to obtain a material containing a substrate layer and a porous support layer.

28. The preparation method according to claim 27, wherein, The conditions for the phase transformation include: soaking in water at 10-30°C for 10-60 minutes; And / or, the thickness of the substrate layer is 30-150 μm; And / or, the material of the substrate layer is selected from polyester nonwoven fabric and / or polyethylene nonwoven fabric; And / or, the conditions for preparing the porous support layer include making the thickness of the porous support layer in the separation membrane 10-100 μm; And / or, the concentration of the solution containing the porous support layer material is 10wt%-20wt%; And / or, the porous support layer material is selected from at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride and polyaryl etherketone; And / or, the solvent in the solution containing the porous support layer material is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

29. The preparation method according to claim 28, wherein, The thickness of the substrate layer is 50-120 μm; And / or, the conditions for preparing the porous support layer include making the thickness of the porous support layer in the separation membrane 30-60 μm.

30. The preparation method according to claim 19 or 20, wherein, The method for preparing the poly(triazineamine-urea) layer includes: sequentially contacting the surface of a porous support layer, comprising a substrate layer and a porous support layer, with an aqueous phase containing a second polyamine and an organic phase containing a triazine compound and a polyisocyanate containing at least two C-Cl bonds, followed by heat treatment.

31. The preparation method according to claim 30, wherein, The conditions for preparing the poly(triazineamine-urea) layer include making the thickness of the poly(triazineamine-urea) layer in the separation membrane 10-500 nm; And / or, the contact time between the porous support layer surface and the aqueous phase containing the second polyamine is 5-100 s; And / or, the contact time between the porous support layer surface and the organic phase containing at least two C-Cl bonds, triazine compounds, and polyisocyanates is 10-200 s; And / or, the amounts of the aqueous phase containing the second polyamine, the triazine compound containing at least two C-Cl bonds, and the organic phase containing the polyisocyanate are such that the mass ratio of the second polyamine to the triazine compound containing at least two C-Cl bonds and the polyisocyanate is 10-80:1-8:1; And / or, the concentration of the aqueous phase containing the second polyamine is 0.2wt%-10wt%; And / or, the concentration of the organic phase of the triazine compound containing at least two C-Cl bonds is 0.05 wt%-2 wt%; And / or, the concentration of the organic phase containing the polyisocyanate is 0.001 wt% to 0.5 wt%; And / or, the second polyamine is selected from at least one of polyethylene polyamine, polyethyleneimine, and polyetheramine; And / or, the triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine and 2,4-dichloro-6-phenyl-1,3,5-triazine; And / or, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, and 1,4-cyclohexyl diisocyanate; And / or, the temperature of the heat treatment is 40-150℃; the time of the heat treatment is 0.5-10min.

32. The preparation method according to claim 31, wherein, The conditions for preparing the poly(triazineamine-urea) layer include making the thickness of the poly(triazineamine-urea) layer in the separation membrane 50-200 nm; And / or, the contact time between the porous support layer surface and the aqueous phase containing the second polyamine is 10-60 s; And / or, the contact time between the porous support layer surface and the organic phase containing at least two C-Cl bonds (triazine compounds and polyisocyanates) is 20-120 s; And / or, the amounts of the aqueous phase containing the second polyamine, the triazine compound containing at least two C-Cl bonds, and the organic phase containing the polyisocyanate are such that the mass ratio of the second polyamine to the triazine compound containing at least two C-Cl bonds and the polyisocyanate is 20-70:1-5:1; And / or, the concentration of the aqueous phase containing the second polyamine is 0.5wt%-5wt%; And / or, the concentration of the organic phase of the triazine compound containing at least two C-Cl bonds is 0.1 wt% - 1 wt%; And / or, the concentration of the organic phase containing the polyisocyanate is 0.01wt%-0.2wt%; And / or, the second polyamine, polyethyleneimine and / or polyethylene polyammonium; And / or, the triazine compound containing at least two C-Cl bonds is cyanuric chloride; And / or, the polyisocyanate 1,3-phenyl diisocyanate; And / or, the temperature of the heat treatment is 50-120°C; the time of the heat treatment is 1-5 min.

33. The preparation method according to claim 32, wherein, The polyethylene polyamine is triethylenetetramine and / or tetraethylenepentamine.

34. An acid- and alkali-resistant separation membrane prepared by the method according to any one of claims 19-33.

35. The application of the acid and alkali resistant separation membrane according to any one of claims 1-18 and 34 in magnesium-lithium separation.

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