Positively charged separation membranes, methods of making and using the same

Abstract

The application relates to the field of membranes, and discloses a positively charged separation membrane and a preparation method and application thereof. The separation membrane comprises a bottom layer, a porous support layer, a polyurea separation layer and / or a polysulfamide separation layer and a positive charge modification layer arranged in sequence; wherein the polymer forming the positive charge modification layer comprises structural unit I provided by a polyphenol, structural unit II provided by a first polyamine and structural unit III provided by a quaternary ammonium salt monomer containing an epoxy group; and the structural unit I provided by the polyphenol in at least part of the positive charge modification layer is connected with the amino group of the polyurea separation layer and / or the polysulfamide separation layer through a phenolic hydroxyl group. The positively charged separation membrane comprises an acid-resistant separation layer and a positive charge modification layer with a specific composition, so that the surface of the separation membrane is positively charged, the magnesium ion retention effect of the separation membrane is improved, and when the separation membrane is used for magnesium-lithium separation, high acid resistance is achieved while high magnesium-lithium separation efficiency is ensured.

Description

Technical Field

[0001] This invention relates to the field of membranes, and more specifically, to a positively charged separation membrane, its preparation method, and its application. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles and communications industries, lithium energy has received unprecedented attention. Therefore, the development and recycling of lithium resources has become a research hotspot for scientists. In nature, lithium resources are mostly found in ores and salt lake water. More than 80% of my country's lithium resources are found in salt lake water. Besides lithium ions, salt lake water contains large amounts of sodium, magnesium, and calcium ions, posing considerable challenges to the extraction of high-purity lithium resources. Currently, lithium extraction from salt lakes includes precipitation, solar pond extraction, extraction, calcination, membrane separation, and adsorption methods. Considering extraction efficiency, cost, and the absence of secondary pollution, the combined extraction process using adsorbents and separation membranes yields the best results.

[0003] In the combined lithium extraction process of adsorbent and membrane separation, the ions precipitated from the adsorbent in the eluent contain not only lithium ions but also a certain amount of magnesium and calcium ions. The separation membrane selectively separates lithium ions from magnesium and calcium ions, resulting in a high-purity lithium-ion aqueous solution, laying the foundation for subsequent precipitation to obtain high-purity lithium carbonate or lithium hydroxide. Therefore, the separation efficiency of the membrane significantly impacts the final purity of the lithium resource, making the development of nanofiltration membrane materials with high magnesium-lithium separation coefficients a top priority. Currently, most nanofiltration membranes used in salt lake lithium extraction projects are polyamide composite nanofiltration membranes produced by DuPont and Koch, which have relatively low magnesium-lithium separation coefficients (less than 5). In recent years, numerous scientific studies have demonstrated that reducing the pore size of nanofiltration membranes and increasing the positive charge density on the surface of the separation layer can increase the membrane's magnesium ion rejection rate, thereby improving magnesium-lithium separation efficiency. However, most related research is still in the laboratory stage, and due to the complexity of the preparation process, large-scale continuous production is difficult to achieve. On the other hand, the high calcium and magnesium content in salt lakes leads to severe scaling on the membrane surface during operation, requiring regular acid washing. Acid washing usually reduces the separation performance of nanofiltration membranes.

[0004] Therefore, it is of great significance to develop an acid-resistant nanofiltration membrane with a simple production process and high magnesium-lithium separation efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing nanofiltration membranes, such as low magnesium-lithium separation efficiency and poor acid resistance, and to provide a positively charged separation membrane, its preparation method and application. The positively charged separation membrane includes an acid-resistant separation layer and a positively charged modification layer of a specific composition, so that the surface of the separation membrane is positively charged, which improves the retention effect of the separation membrane on magnesium ions. When used for magnesium-lithium separation, it has high magnesium-lithium separation efficiency and high acid resistance.

[0006] To achieve the above objectives, the present invention provides a positively charged separation membrane, wherein the separation membrane comprises a bottom layer, a porous support layer, a polyurea separation layer and / or a polysulfonamide separation layer, and a positively charged modification layer arranged sequentially.

[0007] The polymer forming the positively charged modified layer includes structural unit I provided by a polyphenol, structural unit II provided by a first polyamine, and structural unit III provided by a quaternary ammonium salt monomer containing an epoxy group; at least a portion of the structural unit I provided by the polyphenol in the positively charged modified layer is linked to the amino groups of the polyurea separation layer and / or the polysulfonamide separation layer through phenolic hydroxyl groups.

[0008] A second aspect of the present invention provides a method for preparing a positively charged separation membrane, characterized in that the preparation method includes the following steps:

[0009] (1) A porous support layer, a polyurea separation layer, and / or a polysulfonamide separation layer are sequentially prepared on the bottom layer;

[0010] (2) Under a first pressure, while the polyphenol solution is kept flowing, the product of step (1) is first contacted with the polyphenol solution, and then under a second pressure, while the first polyamine solution is kept flowing, it is second contacted with the polyamine solution.

[0011] (3) After the product obtained in step (2) is brought into a third contact with an aqueous solution of a quaternary ammonium salt monomer containing an epoxy group, it is taken out and dried to obtain the positively charged separation membrane.

[0012] A third aspect of the present invention provides a positively charged separation membrane prepared by the above-described preparation method.

[0013] The fourth aspect of this invention provides an application of the above-mentioned positively charged separation membrane in the field of lithium extraction from salt lakes.

[0014] Through the above technical solutions, the positively charged separation membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0015] The positively charged separation membrane provided in this invention includes an acid-resistant separation layer and a positively charged modification layer with a specific composition, which makes the surface of the separation membrane positively charged, thereby improving the retention effect of the separation membrane on magnesium ions. When used for magnesium-lithium separation, it can ensure high magnesium-lithium separation efficiency while having high acid resistance.

[0016] Furthermore, the positively charged modification layer and the separation layer are connected by chemical bonds, ensuring the stability of the separation membrane during long-term operation. In addition, the polyurea separation layer and the polysulfonamide separation layer have excellent acid resistance, ensuring that processes such as acid washing will not damage the membrane separation performance during actual operation.

[0017] In the method for preparing the positively charged separation membrane provided by the present invention, polyphenols react with the amino groups remaining in the polyurea separation layer and / or polysulfonamide separation layer under pressure, thereby reducing the intermolecular pores in the separation layer; at the same time, a positively charged modification layer is formed on the separation layer by reacting polyamines with quaternary ammonium salts containing epoxy groups on the membrane surface; the reduction of intermolecular pores and the repulsion effect between positive charges work together to improve the retention effect of the separation membrane on magnesium ions. Detailed Implementation

[0018] 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.

[0019] The first aspect of the present invention provides a positively charged separation membrane, characterized in that the separation membrane comprises a bottom layer, a porous support layer, a polyurea separation layer and / or a polysulfonamide separation layer, and a positively charged modification layer arranged sequentially.

[0020] The polymer forming the positively charged modified layer includes structural unit I provided by a polyphenol, structural unit II provided by a first polyamine, and structural unit III provided by a quaternary ammonium salt monomer containing an epoxy group; at least a portion of the structural unit I provided by the polyphenol in the positively charged modified layer is linked to the amino groups of the polyurea separation layer and / or the polysulfonamide separation layer through phenolic hydroxyl groups.

[0021] In this invention, the positively charged separation membrane includes an acid-resistant separation layer and a positively charged modification layer with a specific composition, so that the surface of the separation membrane is positively charged, which improves the retention effect of the separation membrane on magnesium ions. When used for magnesium-lithium separation, it has high acid resistance while ensuring high magnesium-lithium separation efficiency.

[0022] Furthermore, the positively charged modification layer and the separation layer are connected by chemical bonds, ensuring the stability of the separation membrane during long-term operation. In addition, the polyurea separation layer and the polysulfonamide separation layer have excellent acid resistance, ensuring that processes such as acid washing will not damage the membrane separation performance during actual operation.

[0023] According to the present invention, the average pore size of the positively charged separation membrane is 0.1-0.4 nm.

[0024] In this invention, when the average pore size of the positively charged separation membrane meets the above-mentioned range, it indicates that the separation membrane contains a pore structure with a narrow distribution and suitable size. When used for magnesium-lithium separation, it can improve the magnesium ion rejection rate while ensuring the lithium ion permeability.

[0025] Furthermore, the average pore size of the positively charged separation membrane is 0.15-0.3 nm.

[0026] According to the present invention, the surface Zeta potential of the positively charged separation membrane is 0-20mV.

[0027] In this invention, when the surface Zeta potential of the positively charged separation membrane meets the above-mentioned range, it indicates that the surface of the separation membrane has a high positive potential, which can further improve the magnesium ion retention capacity when used for magnesium-lithium separation.

[0028] Furthermore, the surface Zeta potential of the positively charged separation membrane is 10-20 mV.

[0029] According to the present invention, the contact angle of the positively charged separation membrane is 10-50°.

[0030] In this invention, when the contact angle of the positively charged separation membrane meets the above-mentioned range, it indicates that the separation membrane has excellent hydrophilicity, thereby significantly improving the water permeation flux of the separation membrane and improving the separation efficiency of magnesium and lithium.

[0031] Furthermore, the contact angle of the positively charged separation membrane is 15-30°.

[0032] According to the present invention, the content of structural unit I on the membrane surface is 1×10⁻⁶. -3 -5×10 -2 mg / cm 2 The content of structural unit II on the membrane surface is 1×10⁻⁶. -3 -2.5×10 -2 mg / cm 2 The content of structural unit III on the membrane surface is 0.5 × 10⁻⁶. -3 -1×10 -2 mg / cm 2 .

[0033] In this invention, when the content of each structural unit in the polymer in the positive charge modification layer meets the above range, the separation membrane can contain a pore structure with a narrow distribution and appropriate size, and the surface has a high positive potential. This makes the separation membrane have a high magnesium ion retention capacity and lithium ion permeability when used for magnesium-lithium separation, thereby improving the magnesium-lithium separation efficiency.

[0034] Furthermore, the content of structural unit I on the membrane surface is 2 × 10⁻⁶. -3 -2×10 -2 mg / cm 2 The content of structural unit II on the membrane surface is 2×10. -3 -2×10 -2 mg / cm 2 The content of structural unit III on the membrane surface is 1×10⁻⁶. -3 -1×10 -2 mg / cm 2 .

[0035] According to the present invention, the structural unit III has a structure shown in at least one of Formula 1, Formula 2 and Formula 3;

[0036]

[0037] Wherein, R1 is a C1-C10 alkylene group, R2, R3 and R4 are each independently a C1-C5 alkyl group, X is a halogen, and m is an integer from 1000 to 3000.

[0038] In this invention, when the structural unit III provided by the quaternary ammonium salt monomer containing epoxy groups in the polymer forming the positive charge modification layer has the above-mentioned specific structure, the positive potential and hydrophilicity of the separation membrane surface can be further improved, thereby further enhancing the separation membrane's ability to retain magnesium ions and its water permeation flux.

[0039] Furthermore, R1 is a C1-C5 alkylene group, R2, R3 and R4 are each independently a C1-C3 alkyl group, X is Br or Cl, and m is an integer from 5 to 1000.

[0040] According to the present invention, the content of X ions in the positively charged modification layer of the positively charged separation membrane is 0.5-5 at.%.

[0041] In this invention, when the content of X ions in the positively charged modification layer of the positively charged separation membrane meets the above-mentioned range, the surface of the separation membrane can be made to have a high positive potential, thereby further improving the separation membrane's ability to retain magnesium ions.

[0042] Furthermore, the content of X ions in the positively charged modification layer of the positively charged separation membrane is 2-5 at.%.

[0043] In this invention, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials with certain strength that can be used for nanofiltration and reverse osmosis membranes.

[0044] In this invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0045] In this invention, the porous support layer material can be at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0046] According to the present invention, the thickness of the bottom layer, the porous support layer, the polyurea separation layer and / or the polysulfonamide separation layer, and the positive charge modification layer are not particularly limited, and can be conventional choices in the art. However, in order to enable these four layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent magnesium-lithium separation coefficient and high water flux, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; the thickness of the polyurea separation layer and / or the polysulfonamide separation layer is 10-500 nm, preferably 50-300 nm; and the thickness of the positive charge modification layer is 10-100 nm, preferably 20-80 nm.

[0047] A second aspect of the present invention provides a method for preparing a positively charged separation membrane, characterized in that the preparation method includes the following steps:

[0048] (1) A porous support layer, a polyurea separation layer, and / or a polysulfonamide separation layer are sequentially prepared on the bottom layer;

[0049] (2) Under a first pressure, while the polyphenol solution is kept flowing, the product of step (1) is first contacted with the polyphenol solution, and then under a second pressure, while the first polyamine solution is kept flowing, it is second contacted with the polyamine solution.

[0050] (3) After the product obtained in step (2) is brought into a third contact with an aqueous solution of a quaternary ammonium salt monomer containing an epoxy group, it is taken out and dried to obtain the positively charged separation membrane.

[0051] In this invention, during the preparation of the positively charged separation membrane, polyphenols undergo a pressure-driven reaction with residual amino groups in the polyurea and / or polysulfonamide separation layers, reducing the intermolecular porosity in the separation layers. Simultaneously, a positively charged modification layer is formed on the separation layer through the reaction of polyamines with quaternary ammonium salts containing epoxy groups on the membrane surface. This dual effect of reduced intermolecular porosity and repulsion between positive charges enhances the membrane's retention efficiency for magnesium ions. Consequently, the resulting positively charged separation membrane exhibits high magnesium-lithium separation efficiency.

[0052] In this invention, there is no particular limitation on the method for preparing the porous support layer on the bottom layer. Conventional methods in the art can be used for preparation, with phase inversion method preferred. Specifically, a polymer solution of the porous support layer material is coated on one surface of the bottom layer, and the porous support layer is obtained through phase inversion.

[0053] In this invention, the phase inversion method is preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20% by weight, degassing at 20-40°C for 10-180 min; then coating the polymer solution onto the bottom layer to obtain an initial film, and then immersing it in water at a temperature of 10-30°C for 10-60 min, thus forming the support layer polymer porous membrane through the phase inversion layer.

[0054] The solvent may be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0055] According to the present invention, in step (2), the first pressure and the second pressure are each independently 0.1-2.5 MPa.

[0056] In this invention, when the first pressure and the second pressure are each independently controlled to meet the above-mentioned range, it can be ensured that the polyphenols, driven by the pressure, enter the intermolecular pores of the polyurea separation layer and / or the polysulfonamide separation layer, and react chemically with the amino groups remaining on the surface of the polyurea separation layer and / or the polysulfonamide separation layer. This promotes a more complete reaction between the polyphenols and the polyamines, further improving the density of the separation membrane. At the same time, it results in a higher content of structural units provided by the polyamines in the separation membrane, giving the separation membrane higher hydrophilicity. Ultimately, this results in the separation membrane having excellent magnesium-lithium separation performance and water permeability.

[0057] Furthermore, in step (2), the first pressure and the second pressure are each independently 0.5-2 MPa.

[0058] According to the present invention, the duration of the first contact and the second contact are each independently 1-120 min.

[0059] In this invention, when the temperatures of the first and second contacts are controlled to meet the above-mentioned range, it is possible to ensure sufficient reaction between polyphenols and polyamines, so that the resulting separation membrane has the pore size and surface Zeta potential required by this invention, thereby improving the magnesium chloride retention rate and magnesium-lithium separation efficiency of the separation membrane when used for magnesium-lithium separation.

[0060] Furthermore, the duration of the first contact and the second contact are each independently 10-60 minutes.

[0061] According to the present invention, the concentration of the polyphenol solution is 0.00001wt%-1wt%, preferably 0.0001wt%-0.1wt%.

[0062] According to the present invention, the concentration of the first polyamine solution is 0.00001wt%-1wt%, preferably 0.0001wt%-0.1wt%.

[0063] In this invention, controlling the concentrations of the polyphenol solution and the polyamine solution to independently meet the above-mentioned ranges ensures that the resulting separation membrane has the pore size, surface Zeta potential, and thickness required by this invention. This ensures that when the separation membrane is used for magnesium-lithium separation, it can improve the retention rate of magnesium chloride while maintaining good water permeability.

[0064] In this invention, step (2) can be performed in conventional equipment in the art, such as a cross-flow membrane tank. In this invention, in the cross-flow membrane tank, a pump continuously delivers solution to the tank; therefore, the total amount of polyphenols or polyamines in the solution generally exceeds the amount that can adhere to the membrane surface for reaction, ensuring the obtained modified layer required by this invention. In this invention, there is no particular limitation on the flow rate of the polyphenol solution and the polyamine solution, as long as the polyphenol solution and the polyamine solution remain in flow during step (2). For example, the flow rate of the polyphenol solution or the polyamine solution can be 0.5-5 L / min.

[0065] In this invention, the method further includes: before performing step (2), cutting the product of step (1) according to the effective area of ​​the cross-flow membrane tank to suit cross-flow membrane tanks with different effective areas. In one specific embodiment of this invention, the effective area of ​​the cross-flow membrane tank is 42 cm². 2 .

[0066] In this invention, the ratio of the volume of the polyphenol solution to the membrane area (i.e., the effective area of ​​the cross-flow membrane cell) of the product from step (1) is 5-100 mL / cm². 2 The preferred value is 10-50 mL / cm³. 2 .

[0067] In this invention, the ratio of the volume of the first polyamine solution to the membrane area (i.e., the effective area of ​​the cross-flow membrane cell) of the product from step (1) is 5-100 mL / cm². 2 The preferred value is 10-50 mL / cm³. 2 .

[0068] 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.

[0069] In this invention, when the mass ratio of polyphenol to first polyamine is controlled to meet the above-mentioned range, the resulting separation membrane contains a narrowly distributed and appropriately sized pore structure, which enables the separation membrane to have high magnesium ion retention capacity and lithium ion permeability when used for magnesium-lithium separation, thereby improving the magnesium-lithium separation efficiency.

[0070] Furthermore, 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 0.5-5:1.

[0071] According to the present invention, the polyphenols are selected from at least one of tannic acid, tea polyphenols, gallic acid, catechins, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein, preferably tannic acid and / or tea polyphenols.

[0072] According to the present invention, the first polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, piperazine, and N-aminoethylpiperazine.

[0073] According to the present invention, in step (3), the quaternary ammonium salt monomer containing an epoxy group is selected from at least one of diethyl-2,3-epoxypropyl-[3-(methylmethoxy)]silylpropylammonium chloride, N-2,3-epoxypropyldimethyldodecylammonium chloride, 1,2-epoxypropyldimethyldodecylammonium chloride and 2,3-epoxypropyltrimethylammonium chloride, preferably 1,2-epoxypropyldimethyldodecylammonium chloride and / or 2,3-epoxypropyltrimethylammonium chloride.

[0074] According to the present invention, the concentration of the aqueous solution of the quaternary ammonium salt monomer containing the epoxy group is 0.05wt%-30wt%.

[0075] In this invention, when the concentration of the aqueous solution of the quaternary ammonium salt monomer containing epoxy groups is controlled to meet the above range, it can ensure that the quaternary ammonium salt monomer containing epoxy groups and the product obtained in step (2) are in full contact, ensuring that the two can react fully and ensuring high reaction efficiency. Finally, a quaternary ammonium salt structure is introduced on the surface of the separation membrane, so that the surface of the separation membrane has a high positive potential.

[0076] Furthermore, the concentration of the aqueous solution of the quaternary ammonium salt monomer containing the epoxy group is 5wt%-20wt%.

[0077] In this invention, the ratio of the volume of the aqueous solution containing the quaternary ammonium salt monomer with epoxy groups to the membrane area (i.e., the effective area of ​​the cross-flow membrane cell) of the product of step (2) is 1-10 mL / cm². 2 Preferably 2-8 mL / cm 2 .

[0078] According to the present invention, the amount of the aqueous solution of the quaternary ammonium salt monomer containing epoxy groups is such that the mass ratio of the quaternary ammonium salt monomer containing epoxy groups to the first polyamine is 0.1-1000:1.

[0079] In this invention, when the mass ratio of the quaternary ammonium salt monomer containing epoxy groups to the first polyamine is controlled to meet the above range, it can be ensured that a sufficient number of structural units provided by the quaternary ammonium salt monomer containing epoxy groups are introduced into the product obtained in step (2), thereby increasing the grafting rate of the quaternary ammonium salt monomer containing epoxy groups, ensuring the introduction of a high positively charged quaternary ammonium salt structure on the separation membrane, and ultimately making the surface of the separation membrane have a high positive potential.

[0080] Furthermore, the amount of the aqueous solution of the quaternary ammonium salt monomer containing epoxy groups is such that the mass ratio of the quaternary ammonium salt monomer containing epoxy groups to the first polyamine is 1-100:1.

[0081] According to the present invention, the time of the third contact is 10s-10min.

[0082] In this invention, when the time of the third contact is controlled to meet the above range, it can ensure that the quaternary ammonium salt monomer containing epoxy groups and the product obtained in step (2) can fully contact and react, improve the reaction efficiency of the two, and ultimately make the surface of the separation membrane have a high positive potential.

[0083] Furthermore, the duration of the third contact is 20 seconds to 1 minute.

[0084] According to the present invention, the drying temperature is 40-100℃, preferably 50-70℃; the drying time is 0.5-10min, preferably 3-5min.

[0085] In this invention, the polyurea separation layer and / or polysulfonamide separation layer are generated by interfacial polymerization of a second polyamine with a polyisocyanate and / or a polysulfonyl chloride.

[0086] In one specific embodiment of the present invention, the steps for preparing a polyurea separation layer and / or a polysulfonamide separation layer on a porous support layer are as follows:

[0087] The surface of the porous support layer away from the bottom layer is sequentially contacted with an aqueous phase containing a second polyamine and an organic phase containing polyisocyanate and / or polysulfonyl chloride. After heat treatment, a polyurea separation layer and / or a polysulfonamide separation layer are obtained by polymerization at the interface of the porous support layer.

[0088] In this invention, the second polyamine is selected from one of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, piperazine, m-phenylenediamine, and p-phenylenediamine, preferably polyethyleneimine and / or piperazine.

[0089] In this invention, the polyisocyanate is selected from one or more of the following: 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, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl isophthalic diisocyanate, preferably 1,4-phenyl diisocyanate and / or 1,3-phenyl diisocyanate.

[0090] In this invention, the polysulfonyl chloride is selected from at least one of 1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 1,4-benzene disulfonyl chloride, 2,4-disulfonyl chloride methyltrimethylbenzene, biphenyl-4,4'-disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 2,6-naphthalene disulfonyl chloride, 1,3-naphthalene disulfonyl chloride, 2,7-naphthalene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride, and 1,3,6-naphthalene trisulfonyl chloride.

[0091] According to the present invention, the concentration of the second polyamine in the aqueous phase is 0.1wt%-10wt%, preferably 0.5wt%-2.5wt%.

[0092] According to the present invention, the concentration of polyisocyanate and / or polysulfonyl chloride in the organic phase is 0.01wt%-1wt%, preferably 0.1wt%-0.5wt%.

[0093] According to the present invention, the mass ratio of the second polyamine to the polyisocyanate and / or polysulfonyl chloride is 0.1-10:1, preferably 0.5-5:1.

[0094] In this invention, the type of solvent for the organic phase is not particularly limited, as long as it can dissolve the polyisocyanate or polysulfonyl chloride. Preferably, the solvent for the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M).

[0095] In this invention, the conditions for interfacial polymerization are not specifically limited and can be chosen according to conventional methods in the field. However, in order to enable the four layers to play a better synergistic role and to make the resulting separation membrane better combine excellent magnesium-lithium separation coefficient and high water flux, preferably, the contact time between the porous support layer and the aqueous phase containing polyamine is 5-100s, preferably 10-60s; the contact time between the porous support layer and the organic phase containing polyisocyanate and / or polysulfonyl chloride is 10-200s, preferably 20-120s; the temperature of the heat treatment is 40-150℃, preferably 50-120℃; and the heat treatment time is 0.5-10 minutes, preferably 1-5 minutes.

[0096] In this invention, the ratio of the volume of the aqueous phase containing the second polyamine to the membrane area of ​​the membrane layer including the bottom layer and the porous support layer is 0.05-1 mL / cm². 2 Preferably, it is 0.1-0.5 mL / cm 2 .

[0097] In this invention, the volume ratio of the organic phase containing polyisocyanates and / or polysulfonyl chlorides to the membrane area of ​​the membrane layer comprising the bottom layer and the porous support layer is 0.01-0.5 mL / cm². 2 Preferably, the concentration is 0.05-0.25 mL / cm³. 2 .

[0098] A third aspect of the present invention provides a positively charged separation membrane prepared by the above-described preparation method.

[0099] The fourth aspect of this invention is the application of the above-mentioned positively charged separation membrane in the field of lithium extraction from salt lakes.

[0100] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0101] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0102] In the following embodiments and comparative examples:

[0103] (1) The water flux of the separation membrane was tested by the following method: The separation membrane was placed in a membrane tank, and the water permeation rate of the separation membrane was measured over a certain period of time under conditions of 2 MPa and 25°C. The water flux was then calculated using the following formula:

[0104] 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 separation membrane (m²). 2 ), where t is time (h);

[0105] (2) The desalination rate of the separation membrane was tested using the following method: The separation membrane was loaded into the membrane tank, and the original aqueous solution was 2000 ppm magnesium chloride or 2000 ppm lithium chloride. After pre-pressurization at 0.2 MPa for 0.5 h, the permeate was obtained at a pressure of 0.6 MPa, and the desalination rate was calculated using the following formula:

[0106] 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 or lithium chloride in the original aqueous solution (measured by a conductivity meter). p The concentration of magnesium chloride or lithium chloride in the permeate (measured by a conductivity meter);

[0107] (3) The magnesium-lithium separation coefficient of the separation membrane was measured by the following method: The separation membrane was loaded into the membrane tank. The original aqueous solution was a mixture of 2000 ppm magnesium chloride and 100 ppm lithium chloride. After pre-pressurization at 0.2 MPa for 0.5 h, the permeate was obtained at a pressure of 2 MPa.

[0108] The magnesium-lithium separation coefficient is calculated using the following formula:

[0109] Where S is the magnesium-lithium separation coefficient, C Li，p and C Li，f The concentrations of lithium ions in the permeate and feed solutions, respectively (measured by ion chromatography); C Mg，p and C Mg，f The concentrations of magnesium ions in the permeate and feed solution are respectively (measured by ion chromatography).

[0110] (4) The content of X ions in the positively charged modified layer of the separation membrane was determined by the following method:

[0111] The measurements were performed using a Sigma Probe X-ray photoelectron spectrometer manufactured by Thermo VG, UK.

[0112] (5) Average pore size of the separation membrane: The average pore size was measured using the PEG solute transfer method, and the detailed steps are as follows:

[0113] (i) Test the retention rate of composite membranes for PEG of different molecular sizes;

[0114] (ii) Linearly fit the PEG size and the rejection rate in a log-probability coordinate system. The PEG size corresponding to a 50% rejection rate is the average pore size of the composite membrane.

[0115] (6) Surface Zeta potential test of composite membrane: The test was performed using a Surpass electric analyzer (Anton Paar), with the circulating solution being a dilute aqueous solution of KCl and the pH of the test solution being 7.

[0116] (7) The content of each structural unit in the polymer that forms the positively charged modified layer in the separation membrane was determined by mass weighing:

[0117] A membrane comprising a substrate layer, a porous support layer, and a polyurea or polysulfonamide layer is dried in a vacuum oven at 60°C for 24 hours, and its mass is measured as M (mg). The membrane is then placed in a membrane tank containing an aqueous solution of a certain concentration of polyphenols. After circulating under certain conditions for a certain time, the membrane is removed, its surface is rinsed with deionized water, and it is dried at 60°C for 24 hours. The mass of the membrane is measured as W (mg). The membrane is then placed in a membrane tank containing an aqueous solution of a certain concentration of a first polyamine. After circulating under certain conditions for a certain time, the membrane is removed, its surface is rinsed with deionized water, and it is dried at 60°C for 24 hours. The mass of the membrane is measured as N (mg). Finally, the obtained membrane is immersed in an aqueous solution of a quaternary ammonium salt monomer containing epoxy groups at a certain concentration. After removal and drying, excess monomers adsorbed on the membrane surface and back are rinsed with deionized water, and the membrane is dried at 60°C for 24 hours. The mass of the membrane is measured as Q (mg).

[0118] In the positively charged modified polymer that forms the separation membrane, the content (P) of the structural unit I provided by the polyphenol on the membrane surface is... 2 The content T (mg / cm³) of structural unit II provided by the first polyamine 2 The content R (mg / cm³) of structural units provided by quaternary ammonium salts containing epoxy groups. 2 The results are obtained using the following formulas:

[0119]

[0120] (8) Contact angle of the separation membrane: The surface contact angle of the composite membrane sample was tested by the static drop method using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany. 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 performed immediately. The final contact angle was determined by taking the average value after multiple measurements.

[0121] (9) The thickness of each layer in the separation membrane was measured by scanning electron microscopy (SEM), which was a Hitachi S-4800.

[0122] (10) The acid washing stability of the separation membrane was measured using the following method:

[0123] Add 2 wt% citric acid to the test system of the separation membrane and circulate it for 24 hours at 0.2 MPa. Drain the citric acid aqueous solution from the system and rinse the system repeatedly with deionized water until the pH of the water in the system is neutral. Add 2000 ppm MgCl2 aqueous solution to the system and obtain the permeate at a pressure of 0.6 MPa. Calculate the desalination rate of the membrane for MgCl2 using the formula described above.

[0124] Additionally, in the following embodiments and comparative examples:

[0125] Branched polyethyleneimine (weight average molecular weight 25000 g / mol), polyethylene polyamine, triethylenetetramine, tetraethylenepentamine, tannic acid, tea polyphenols, gallic acid, 1,2-epoxypropyl dimethyl dodecyl ammonium chloride, 2,3-epoxypropyl trimethyl ammonium chloride, 1,3-benzene disulfonyl chloride, 1,4-benzene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride, 1,4-benzene diisocyanate, and 1,3-benzene diisocyanate were all purchased from Bailingwei Technology Co., Ltd., and other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0126] The support layer is prepared using a phase transformation method, and the specific steps are as follows:

[0127] A certain amount of polysulfone (number average molecular weight of 80,000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18% by weight. The solution was degassed at 25°C for 120 min. Then, the polysulfone solution was coated onto a polyester nonwoven fabric (75 μm thick) using a doctor blade to obtain an initial film. The film was then immersed in water at 25°C for 60 min, which allowed the polysulfone layer on the surface of the polyester nonwoven fabric to undergo phase transformation into a porous film. Finally, after three water washes, a support layer with a total thickness of 115 μm was obtained.

[0128] Comparative Example 1

[0129] The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 2% polyethyleneimine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.2% 1,4-phenyl diisocyanate at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite nanofiltration membrane D1. The mass ratio of polyethyleneimine to 1,4-phenyl diisocyanate was 20:1.

[0130] Comparative Example 2

[0131] S1, the above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 2% polyethyleneimine by weight, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.2% 1,4-phenyl diisocyanate by weight, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane. The mass ratio of polyethyleneimine to 1,4-phenyl diisocyanate was 20:1.

[0132] S2. The above composite nanofiltration membrane (the area of ​​the nanofiltration membrane is equal to the effective area of ​​the cross-flow membrane cell, 42 cm²) 2 The membrane was loaded into a cross-flow membrane tank. The feed solution was 2000 mL of 0.01 wt% tannic acid aqueous solution. The flow rate was 1.5 L / min. After the test system was run at 2 MPa for 30 min, the liquid was drained and the membrane surface was repeatedly rinsed with deionized water to remove the residual tannic acid on the membrane surface, thus obtaining the tannic acid modified separation membrane D2.

[0133] Comparative Example 3

[0134] S1, the above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 2% polyethyleneimine by weight, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.2% 1,4-phenyl diisocyanate by weight, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane. The mass ratio of polyethyleneimine to 1,4-phenyl diisocyanate was 20:1.

[0135] S2. The above composite nanofiltration membrane is immersed in 200 mL of an aqueous solution containing 10% by weight of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride for 1 min. After 1 min, it is taken out and dried at 70 °C for 5 min to obtain separation membrane D3 modified with epoxy group quaternary ammonium salt.

[0136] Comparative Example 4

[0137] S1, the above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 2% polyethyleneimine by weight, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.2% 1,4-phenyl diisocyanate by weight, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane. The mass ratio of polyethyleneimine to 1,4-phenyl diisocyanate was 20:1.

[0138] S2. The above composite nanofiltration membrane (the area of ​​the nanofiltration membrane is equal to the effective area of ​​the cross-flow membrane cell, 42 cm²) 2 The feed solution was 2000 mL of 0.01 wt% tannic acid aqueous solution, with a flow rate of 1.5 L / min. After running the test system at 2 MPa for 30 min, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid. Then, 2000 mL of 0.01 wt% polyethyleneimine aqueous solution was added to the feed tank at a flow rate of 1.5 L / min. After running the test system at 2 MPa for 30 min, the solution was drained, and the membrane surface was repeatedly rinsed with deionized water to remove residual tannic acid and polyethyleneimine, resulting in the tannic acid and polyethyleneimine modified separation membrane D4. The mass ratio of tannic acid to polyethyleneimine was 1:1.

[0139] Example 1

[0140] S1, the above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 2% polyethyleneimine by weight, and the solution was drained after 60 s at 25 °C. Then, the upper surface of the support layer was contacted with 25 mL of an Isopar E solution containing 0.2% 1,4-phenyl diisocyanate by weight, and the solution was drained after 60 s at 25 °C. The membrane was then placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane. The mass ratio of polyethyleneimine to 1,4-phenyl diisocyanate was 20:1.

[0141] S2. The above composite nanofiltration membrane (the area of ​​the nanofiltration membrane is equal to the effective area of ​​the cross-flow membrane cell, 42 cm²) 2The feed solution was 2000 mL of 0.01 wt% tannic acid aqueous solution, with a flow rate of 1.5 L / min. After the test system was run at 2 MPa for 30 min, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid. 2000 mL of 0.01 wt% polyethyleneimine aqueous solution was added to the feed tank at a flow rate of 1.5 L / min. After the test system was run at 2 MPa for 30 min, the solution was drained, and the membrane surface was repeatedly rinsed with deionized water to remove residual tannic acid and polyethyleneimine, thus obtaining a nanofiltration membrane modified with tannic acid and polyethyleneimine. The mass ratio of tannic acid to polyethyleneimine was 1:1.

[0142] S3. The obtained nanofiltration membrane (the area of ​​the nanofiltration membrane is equal to the effective area of ​​the cross-flow membrane pool, 42 cm²) 2 The membrane was immersed in 200 mL of an aqueous solution containing 10% by weight of 1,2-epoxypropyldimethyldodecyl ammonium chloride for 1 min, then removed and dried at 70 °C for 5 min to obtain a positively charged separation membrane N1. The mass ratio of 1,2-epoxypropyldimethyldodecyl ammonium chloride to polyethyleneimine in step S2 was 100:1.

[0143] Example 2

[0144] S1 is the same as S1 in Example 1, except that an aqueous solution of piperazine of equal volume and concentration is used instead of an aqueous solution of polyethyleneimine.

[0145] S2 is the same as S2 in Example 1, except that: an equal volume of 0.001wt% tea polyphenol aqueous solution is used to replace 0.01wt% tannic acid aqueous solution; an equal volume of 0.001wt% polyethyleneimine aqueous solution is used to replace 0.01wt% polyethyleneimine aqueous solution; wherein the mass ratio of tea polyphenol to polyethyleneimine is 1:1.

[0146] S3 is the same as S3 in Example 1. A positively charged separation membrane N2 is obtained.

[0147] Example 3

[0148] S1 is the same as S1 in Example 1;

[0149] S2 is the same as S2 in Example 1, except that: gallic acid aqueous solution of the same concentration and volume is used to replace tannic acid aqueous solution; polyethyleneimine aqueous solution of the same concentration and volume is used to replace polyethyleneimine aqueous solution; wherein, the mass ratio of tea polyphenols to polyethyleneimine is 1:1.

[0150] S3 is the same as S3 in Example 1. A positively charged separation membrane N3 is obtained.

[0151] Example 4

[0152] S1 is the same as S1 in Example 1;

[0153] S2 is the same as S2 in Example 1;

[0154] S3 is similar to S3 in Example 1, except that an equal volume and concentration of diethyl-2,3-epoxypropyl-[3-(methylmethoxy)]silylpropylammonium chloride aqueous solution is used instead of 10% by weight of 1,2-epoxypropyldimethyldodecylammonium chloride aqueous solution. The mass ratio of diethyl-2,3-epoxypropyl-[3-(methylmethoxy)]silylpropylammonium chloride to polyethyleneimine in step S2 is 100:1, resulting in a positively charged separation membrane N4.

[0155] Example 5

[0156] S1 is the same as S1 in Example 1;

[0157] S2 is the same as S2 in Example 1;

[0158] S3 is similar to S3 in Example 1, except that an equal volume and concentration of 2,3-epoxypropyltrimethylammonium chloride aqueous solution is used instead of 10% by weight of 1,2-epoxypropyldimethyldodecylammonium chloride aqueous solution. The mass ratio of 2,3-epoxypropyltrimethylammonium chloride to polyethyleneimine in step S2 is 100:1, resulting in a positively charged separation membrane N5.

[0159] Example 6

[0160] S1 is the same as S1 in Example 1;

[0161] S2 is the same as S2 in Example 1;

[0162] S3 is similar to S3 in Example 1, except that an equal volume of 5% by weight of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride aqueous solution is used instead of 10% by weight of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride aqueous solution. The mass ratio of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride to polyethyleneimine in step S2 is 50:1, resulting in a positively charged separation membrane N6.

[0163] Example 7

[0164] S1 is the same as S1 in Example 1;

[0165] S2 is the same as S2 in Example 1;

[0166] S3 is similar to S3 in Example 1, except that an equal volume of 20% by weight of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride aqueous solution is used instead of 10% by weight of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride aqueous solution. The mass ratio of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride to polyethyleneimine in step S2 is 200:1, resulting in a positively charged separation membrane N7.

[0167] Example 8

[0168] S1 is similar to S1 in Example 1, except that an equal volume and concentration of 1,3-phenyl diisocyanate solution is used instead of 1,4-phenyl diisocyanate solution.

[0169] S2 is the same as S2 in Example 1;

[0170] S3 is the same as S3 in Example 1. A positively charged separation membrane N8 is obtained.

[0171] Example 9

[0172] S1 is similar to S1 in Example 1, except that an equal volume and concentration of 1,3,5-benzenetrisulfonyl chloride solution is used instead of 1,4-benzene diisocyanate solution.

[0173] S2 is the same as S2 in Example 1;

[0174] S3 is the same as S3 in Example 1. A positively charged separation membrane N9 is obtained.

[0175] Example 10

[0176] S1 is the same as S1 in Example 1;

[0177] S2 is similar to S2 in Example 1, except that the system circulating pressure is 1 MPa;

[0178] S3, the same as S3 in Example 1, yields a positively charged separation membrane N10.

[0179] Example 11

[0180] S1 is the same as S1 in Example 1;

[0181] S2 is the same as S2 in Example 1;

[0182] S3 is similar to S3 in Example 1, except that the concentration of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride is 0.05% by weight, and the mass ratio of 1,2-epoxypropyl dimethyl dodecyl ammonium chloride to polyethyleneimine in step S2 is 0.5:1, thus obtaining the positively charged separation membrane N11.

[0183] Example 12

[0184] S1 is the same as S1 in Example 1.

[0185] S2. The above composite nanofiltration membrane (the area of ​​the nanofiltration membrane is equal to the effective area of ​​the cross-flow membrane cell, 42 cm²) 2 The feed solution was 2000 mL of 0.01 wt% tannic acid aqueous solution, with a flow rate of 1.5 L / min. After the test system was run at 0 MPa for 30 min, the solution was drained, and the test system was repeatedly rinsed with deionized water to remove residual tannic acid. 2000 mL of 0.01 wt% polyethyleneimine aqueous solution was added to the feed tank at a flow rate of 1.5 L / min. After the test system was run at 0 MPa for 30 min, the solution was drained, and the membrane surface was repeatedly rinsed with deionized water to remove residual tannic acid and polyethyleneimine, thus obtaining a separation membrane modified with tannic acid and polyethyleneimine. The mass ratio of tannic acid to polyethyleneimine was 1:1.

[0186] S3, the same as S3 in Example 1, yields a positively charged separation membrane N12. The mass ratio of 1,2-epoxypropyldimethyldodecylammonium chloride to polyethyleneimine in step S2 is 100:1.

[0187] The thickness of each layer of the composite membrane, surface Zeta potential, average pore size, content of X ions in the positively charged modification layer of the positively charged separation membrane, contact angle, and content of each structural unit in the polymer in the examples and comparative examples are shown in Table 1.

[0188] Table 1

[0189]

[0190]

[0191] Table 1 (continued)

[0192]

[0193] The content of X ions refers to the content of X ions in the separation membrane.

[0194] As shown in Table 1, the separation membrane provided by the present invention includes a positively charged modification layer generated in situ from polyphenols, a first polyamine, and a quaternary ammonium salt monomer containing epoxy groups. The polyphenols can reduce the pore size of the polyurea separation layer and / or the polysulfonamide separation layer, thereby significantly reducing the average pore size of the separation membrane. The quaternary ammonium salt monomer containing epoxy groups is chemically bonded to the surface of the separation layer, which significantly improves the surface positive potential and hydrophilicity of the separation membrane. Ultimately, the separation membrane can significantly improve the rejection rate of divalent metal ions and improve the magnesium-lithium separation efficiency while maintaining good water permeation flux.

[0195] The water flux, MgCl2 desalination rate, LiCl desalination rate, and magnesium-lithium separation factor of the composite membranes in the examples and comparative examples were tested, and the results are shown in Table 2.

[0196] Table 2

[0197]

[0198] As shown in Table 2, under pressure, the polyphenols react with the residual amino groups in the polyurea or polysulfonamide layer, reducing the intermolecular porosity in the separation layer. Simultaneously, a positively charged modification layer is constructed on the membrane surface through the reaction of polyamines with quaternary ammonium salts containing epoxy groups. This dual effect of reduced intermolecular porosity and repulsion between positive charges improves the membrane's retention of magnesium ions. Furthermore, the positively charged modification layer bonds with the polyphenols in the separation layer through chemical reactions, ensuring the membrane's long-term operational stability. More importantly, repeated washing of the separation membrane with 2% citric acid did not significantly reduce the magnesium chloride retention rate, demonstrating extremely strong acid-washing resistance.

[0199] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positively charged separation membrane, characterized in that, The separation membrane comprises, in sequence, a bottom layer, a porous support layer, a polyurea separation layer and / or a polysulfamide separation layer, and a positive charge modification layer; The polymer forming the positive charge modification layer comprises structural unit I provided by a polyphenol, structural unit II provided by a first polyamine, and structural unit III provided by a quaternary ammonium salt monomer containing an epoxy group; at least part of the structural unit I provided by the polyphenol in the positive charge modification layer is connected to the amino group of the polyurea separation layer and / or the polysulfamide separation layer through the phenolic hydroxyl group; The polyphenol is selected from one or more of tannic acid, tea polyphenol, gallic acid, catechol, lignin, sodium lignosulfonate, apple polyphenol, grape polyphenol, rutin, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin, and genistein.

2. The positively charged separation membrane of claim 1, wherein, The average pore size of the positively charged separation membrane is 0.1-0.4 nm.

3. The positively charged separation membrane according to claim 1 or 2, wherein, The average pore size of the positively charged separation membrane is 0.15-0.3 nm.

4. The positively charged separation membrane according to claim 1 or 2, wherein, The surface Zeta potential of the positively charged separation membrane is 0-20 mV; And / or, the contact angle of the positively charged separation membrane is 10-50°.

5. The positively charged separation membrane of claim 4, wherein, The surface Zeta potential of the positively charged separation membrane is 10-20 mV; And / or, the contact angle of the positively charged separation membrane is 15-30°.

6. The positively charged separation membrane according to claim 1 or 2, wherein, said structural unit I is present in an amount of 1 x 10 -3 -5 x 10 -2 mg / cm 2 , said structural unit II is present in an amount of 1 x 10 -3 -2.5 x 10 -2 mg / cm 2 , and said structural unit III is present in an amount of 0.5 x 10 -3 -1 x 10 -2 mg / cm 2 .

7. The positively charged separation membrane of claim 6, wherein, the content of the structural unit I at the film surface is 2 x 10 -3 -2 x 10 -2 mg / cm 2 , the content of the structural unit II at the film surface is 2 x 10 -3 -2 x 10 -2 mg / cm 2 , and the content of the structural unit III at the film surface is 1 x 10 -3 -1 x 10 -2 mg / cm 2 .

8. The positively charged separation membrane of claim 1, wherein, The structural unit III has a structure represented by at least one of Formula 1, Formula 2, and Formula 3; Formula 1; Formula 2; Formula 3; wherein R1 is C1-C10 alkylene, R2, R3, and R4 are each independently C1-C5 alkyl, X is halogen, and m is an integer of 1000-3000; And / or, the content of X ions in the positive charge modification layer of the positively charged separation membrane is 0.5-5 at.%.

9. The positively charged separation membrane of claim 8, wherein, The content of X ions in the positive charge modification layer of the positively charged separation membrane is preferably 2-5 at.%.

10. The positively charged separation membrane according to claim 1 or 2, wherein, The thickness of the bottom layer is 30-150 μm; And / or, the thickness of the porous support layer is 10-100 μm; And / or, the thickness of the polyurea separation layer and / or the polysulfamide separation layer is 10-500 nm; And / or, the thickness of the positive charge modification layer is 10-100 nm.

11. The positively charged separation membrane of claim 10, wherein, The thickness of the bottom layer is 50-120 μm; And / or, the thickness of the porous support layer is 30-60 μm; And / or, the thickness of the polyurea separation layer and / or the polysulfamide separation layer is 50-300 nm; And / or, the thickness of the positive charge modification layer is 20-80 nm.

12. A method for producing the positively-charged separation membrane according to any one of claims 1 to 11, characterized by, The preparation method comprises the following steps: (1) sequentially preparing a porous support layer and a polyurea separation layer and / or a polysulfamide separation layer on a bottom layer; (2) under a first pressure, while the polyphenol solution is kept flowing, performing a first contact between the product of step (1) and the polyphenol solution, and then under a second pressure, while the first polyamine solution is kept flowing, performing a second contact between the product of the first contact and the polyamine solution; (3) performing a third contact between the product of step (2) and an aqueous solution of a quaternary ammonium salt monomer containing an epoxy group, and then taking out and drying to obtain the positively charged separation membrane.

13. The method of making according to claim 12, wherein, In step (2), the first pressure and the second pressure are each independently 0.1-2.5 MPa; and / or, the first contact and the second contact are each independently 1-120 min; and / or, the concentration of the polyphenol solution is 0.00001wt%-1wt%; and / or, the concentration of the first polyamine solution is 0.00001wt%-1wt%; and / or, the polyphenol solution and the first polyamine solution are used in an amount such that the mass ratio of polyphenol to first polyamine is 0.1-10:1; and / or, the polyphenol is selected from one or more of tannic acid, tea polyphenol, gallic acid, catechol, lignin, sodium lignosulfonate, apple polyphenol, grape polyphenol, rutin, naringenin, epicatechin, luteolin, apigenin, kanferol, myricetin and genistein; and / or, the first polyamine is selected from at least one of polyethyleneimine, polyvinylamine, polyethylene polyamine, piperazine and N-aminoethyl piperazine.

14. The production method according to claim 13, wherein In step (2), the first pressure and the second pressure are each independently 0.5-2MPa; and / or, the first contact and the second contact are each independently 10-60 min; and / or, the concentration of the polyphenol solution is 0.0001wt%-0.1wt%; and / or, the concentration of the first polyamine solution is 0.0001wt%-0.1wt%; and / or, the polyphenol solution and the first polyamine solution are used in an amount such that the mass ratio of polyphenol to first polyamine is 0.5-5:1; and / or, the polyphenol is selected from tannic acid and / or tea polyphenol; and / or, the polyethylene polyamine is selected from at least one of tetraethylenepentamine, triethylenetetramine and diethylenetriamine.

15. The production method according to claim 12 or 13, wherein, In step (3), the quaternary ammonium salt monomer containing an epoxy group is selected from at least one of diethyl-2,3-epoxypropyl-[3-(methyl methoxy)] silane propyl ammonium chloride, N-2,3-epoxypropyl dimethyl dodecyl ammonium chloride, 1,2-epoxypropyl dimethyl dodecyl ammonium chloride and 2,3-epoxypropyl trimethyl ammonium chloride; and / or, the concentration of the aqueous solution of the quaternary ammonium salt monomer containing an epoxy group is 0.05wt%-30wt%; and / or, the aqueous solution of the quaternary ammonium salt monomer containing an epoxy group is used in an amount such that the mass ratio of the quaternary ammonium salt monomer containing an epoxy group to the first polyamine is 0.1-1000:1; and / or, the third contact is for 10s-10min; and / or, the temperature of the drying is 40-100℃ and the time of the drying is 0.5-10min.

16. The method of manufacturing according to claim 15, wherein, In step (3), the quaternary ammonium salt monomer containing an epoxy group is 1,2-epoxypropyl dimethyl dodecyl ammonium chloride and / or 2,3-epoxypropyl trimethyl ammonium chloride; and / or, the concentration of the aqueous solution of the quaternary ammonium salt monomer containing an epoxy group is 5wt%-20wt%; and / or, the aqueous solution of the quaternary ammonium salt monomer containing an epoxy group is used in an amount such that the mass ratio of the quaternary ammonium salt monomer containing an epoxy group to the first polyamine is 1-100:1; and / or, the third contact is for 20s-1min; And / or, the drying temperature is 50-70℃, and the drying time is 3-5 min.

17. The method of making according to claim 13, wherein, The step of preparing the polyurea separation layer and / or the polysulfonamide separation layer on the porous support is as follows: The surface of the porous support layer away from the bottom layer is sequentially contacted with an aqueous phase containing a second polyamine and an organic phase containing a polyisocyanate and / or a polysulfonyl chloride, and after heat treatment, a polyurea separation layer and / or a polysulfonamide separation layer is obtained by interfacial polymerization on the surface of the porous support layer.

18. The method of making according to claim 17, wherein, The concentration of the second polyamine in the aqueous phase is 0.1wt%-10wt%; And / or, the concentration of the polyisocyanate and / or the polysulfonyl chloride in the organic phase is 0.01wt%-1wt%; And / or, the mass ratio of the second polyamine to the polyisocyanate and / or the polysulfonyl chloride is 0.1-10:1; And / or, the time for the porous support layer to contact the aqueous phase containing the polyamine is 5-100s; And / or, the time for the porous support layer to contact the organic phase containing the polyisocyanate and / or the polysulfonyl chloride is 10-200s; And / or, the heat treatment temperature is 40-150℃, and the heat treatment time is 0.5-10 min.

19. The method of making according to claim 18, wherein, The concentration of the second polyamine in the aqueous phase is 0.5wt%-2.5wt%; And / or, the concentration of the polyisocyanate and / or the polysulfonyl chloride in the organic phase is 0.1wt%-0.5wt%; And / or, the mass ratio of the second polyamine to the polyisocyanate and / or the polysulfonyl chloride is 0.5-5:1; And / or, the time for the porous support layer to contact the aqueous phase containing the polyamine is 10-60s; And / or, the time for the porous support layer to contact the organic phase containing the polyisocyanate and / or the polysulfonyl chloride is 20-120s; And / or, the heat treatment temperature is 50-120℃, and the heat treatment time is 1-5 min.

20. A positively charged separation membrane prepared by the method of any one of claims 13-19.

21. Use of the positively charged separation membrane of any one of claims 1-12 and 20 in the field of lithium extraction from salt lakes.

Images