A monovalent selective cation exchange membrane and a method for preparing the same

Abstract

The application relates to the technical field of ion exchange membranes, and discloses a monovalent selective cation exchange membrane and a preparation method thereof, which comprises the following steps: taking a thin film casting solution as a solvent; adding a functional additive and a positively charged compound into the solvent to obtain a modified solution; coating the modified solution on the surface of a commercial cation exchange membrane, and performing heat treatment and solidification to form a modified layer; and after the heat treatment and solidification are completed, performing secondary crosslinking in a crosslinking agent solution to obtain the monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane uses a thin film casting solution as a solvent to replace a traditional single solvent (such as water or an organic solvent), and uses polymer matrix solidification to firmly fix modified substances on the surface of the membrane to form a stable modified layer, wherein a pore-forming agent can optimize the pore structure of the membrane and improve ion flux.

Description

Technical Field

[0001] This application relates to the field of ion exchange membrane technology, and mainly to a monovalent selective cation exchange membrane and its preparation method. Background Technology

[0002] Monovalent selective cation exchange membranes (M-CEMs) are core components of electrodialysis technology and are widely used in seawater desalination, resource recovery, and environmental protection for monovalent cations (such as Li₂). + Na + ) and polyvalent cations (such as Mg 2+ Ca 2+ The separation of ions and membrane structures is a challenge. Existing modification methods mostly focus on membrane surface treatment or bulk modification, but they suffer from drawbacks such as insufficient monovalent selectivity, low ion flux, and poor stability of the modified layer. For example, while chemical modification can improve monovalent selectivity, the modified material is prone to detachment; conventional deposition or electrodeposition methods are highly efficient in high-concentration systems, but they struggle to maintain membrane mechanical strength and can easily lead to a significant increase in membrane surface resistance, limiting industrial applications. Furthermore, conventional preparation methods use a single solvent system, mostly aqueous solutions, lacking innovative utilization of solvent systems, resulting in poor stability and difficulty in simultaneously optimizing membrane structure selectivity and ion flux.

[0003] Therefore, existing technologies still need to be improved and developed. It is urgent to develop a method for preparing a monovalent selective cation exchange membrane that is easy to operate, highly stable, and can significantly improve monovalent selectivity and flux. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a monovalent selective cation exchange membrane and its preparation method. This application uses a thin film casting solution as a solvent and prepares a monovalent selective cation exchange membrane and product through an innovative modification process, aiming to solve the problem of poor stability of the modified layer in existing modification methods.

[0005] The technical solution of this application is as follows: A method for preparing a monovalent selective cation exchange membrane, comprising the following steps: Thin film casting solution is used as the solvent; A modified solution is obtained by adding functional additives and positively charged compounds to the solvent. The modified solution was coated onto the surface of a commercial cation exchange membrane and cured by heat treatment to form a modified layer; After heat treatment and curing, the membrane is placed in a crosslinking agent solution for secondary crosslinking to obtain the monovalent selective cation exchange membrane.

[0006] The method for preparing a monovalent selective cation exchange membrane, wherein the thin film casting solution is composed of a polymer matrix, a thin film casting solution solvent, and a pore-forming agent; The polymer matrix in the thin film casting solution has a mass fraction of 5% to 40%; The solvent in the thin film casting solution has a mass fraction of 50% to 85%. The pore-forming agent has a mass fraction of 1% to 20% in the thin film casting solution.

[0007] The method for preparing the monovalent selective cation exchange membrane, wherein the polymer matrix includes one of polyetheretherketone, polysulfone, polyetherketone, polyvinylidene fluoride, polystyrene, and polyethersulfone; The solvent of the thin film casting solution includes one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dichloromethane, and pure water; The pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, β-cyclodextrin, and lithium chloride.

[0008] The method for preparing the monovalent selective cation exchange membrane, wherein the functional additive has a mass fraction of 0.01% to 5% in the modified solution; The positively charged compound has a mass fraction of 0.01% to 10% in the modified solution; And / or, in the modified solution, the mass ratio of the functional additive to the positively charged compound is (0.01~5):1.

[0009] The method for preparing the monovalent selective cation exchange membrane, wherein the functional additive includes one or more of a sulfonating agent or an amination agent; The positively charged compound includes at least one of piperazine, pyrrole, chitosan, aniline, diisopropylamine, polyethyleneimine of different molecular weights, polyquaternium-7, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or a homologue of any of the foregoing compounds.

[0010] The method for preparing the monovalent selective cation exchange membrane, wherein the sulfonating agent is chlorosulfonic acid; The amination reagent is dopamine, tannic acid, gallic acid, or catechol.

[0011] The method for preparing the monovalent selective cation exchange membrane, wherein the coating method is blade coating; The coating process involves vacuum adsorption fixing of the commercial cation exchange membrane onto a coating device, and then using a scraper to coat the modified solution onto the surface of the commercial cation exchange membrane. The coating thickness of the doctor blade is 0.1μm~10μm, the coating speed is 10~2000mm / s, and the coating amount is 10~500mL / m. 2 .

[0012] The method for preparing the monovalent selective cation exchange membrane, wherein the heat treatment curing temperature is 50~150℃ and the time is 5~60min.

[0013] The method for preparing the monovalent selective cation exchange membrane, wherein the crosslinking agent is at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal, glutaraldehyde, or a homologue of any of the aforementioned compounds; The mass fraction of the crosslinking agent in the crosslinking agent solution is 0.001%~2%; The solvent for the crosslinking agent solution is water; The secondary crosslinking temperature is 15~80℃, and the reaction time is 5min~120min.

[0014] A monovalent selective cation exchange membrane is prepared using the method described above.

[0015] Beneficial effects: The method for preparing a monovalent selective cation exchange membrane in this application uses a thin film casting solution as a solvent to replace traditional single solvents (such as water or organic solvents). The modified material is firmly fixed on the membrane surface by the solidification of the polymer matrix to form a stable modified layer. The pore-forming agent can optimize the membrane pore structure and improve the ion flux. Attached Figure Description

[0017] Figure 1 The image shows the surface morphology of the base film in Comparative Example 1 using SEM.

[0018] Figure 2 The image shows the surface morphology of the monovalent selective cation exchange membrane prepared in Comparative Example 2 using SEM.

[0019] Figure 3 The image shows the surface morphology of the monovalent selective cation exchange membrane prepared in Example 1 using SEM.

[0020] Figure 4 The image shows the surface morphology of the monovalent selective cation exchange membrane prepared in Example 2 using SEM. Detailed Implementation

[0021] This application provides a monovalent selective cation exchange membrane and a method for preparing the same. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] This application provides a method for preparing a monovalent selective cation exchange membrane, improving the solvent to provide an effective method for preparing a monovalent selective cation exchange membrane. Specifically, it includes the following steps: (1) The thin film casting solution, which consists of a polymer matrix, a solvent, and a pore-forming agent, is used as the solvent; (2) Add functional additives and positively charged compounds to the solvent to obtain a modified solution; (3) The modified solution is uniformly coated on the surface of a commercial cation exchange membrane, heat-treated and cured, and polymerized to generate a positively charged and strong modified layer; (4) After heat treatment and curing, the membrane is placed in a crosslinking agent solution for secondary crosslinking to obtain a monovalent selective cation exchange membrane with stable ion selectivity and high throughput.

[0023] The method for preparing a monovalent selective cation exchange membrane disclosed in this application uses a thin-film casting solution as a solvent system to construct a modified solution. A stable, effective, and high-throughput monovalent selective cation exchange membrane is then prepared through a coating-curing-crosslinking process. This monovalent selective cation exchange membrane utilizes electrostatic repulsion and secondary crosslinking to improve the density of the modified layer, achieving selective separation of monovalent ions. Simultaneously, the addition of a pore-forming agent in the thin-film casting solution ensures the hydrophilicity of the monovalent selective cation exchange membrane and the target ion flux. This preparation process for the monovalent selective cation exchange membrane is short, significantly improves the stability and selectivity of the membrane while ensuring high target ion flux, making it suitable for large-scale membrane production.

[0024] In optional embodiments, the polymer matrix includes one of polyetheretherketone (PEEK), polysulfone (PSF), polyetherketone (S-PEK-C), polyvinylidene fluoride (S-PVDF), polystyrene, and polyethersulfone (PES). The polymer matrix has a mass fraction of 5% to 40% in the thin film casting solution. The polymer matrix is ​​used to provide the framework for the modified layer.

[0025] In optional embodiments, the thin-film casting solution solvent includes one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dichloromethane, and pure water. The mass fraction of the thin-film casting solution solvent in the thin-film casting solution is 50% to 85%. The thin-film casting solution solvent is used to dissolve the polymer and ensure the homogeneity of the modified solution.

[0026] In optional embodiments, the pore-forming agent includes one or more of the following: low molecular weight polyvinylpyrrolidone (PVP) (Mw=8000-10000 Da), polyethylene glycol (PEG) (Mw=200-4000 Da), β-cyclodextrin, and lithium chloride (LiCl). The mass fraction of the pore-forming agent in the thin film casting solution is 1%~20%. The pore-forming agent is used to control the density of the modified layer.

[0027] In optional embodiments, the functional additive includes one or more of a sulfonating agent or an amination agent. The sulfonating agent may be chlorosulfonic acid, etc., and the amination agent may be dopamine, tannic acid, gallic acid, or catechol, etc. The functional additive is used for subsequent modification.

[0028] In an optional embodiment, the positively charged compound includes at least one of piperazine, pyrrole, chitosan, aniline, diisopropylamine, polyethyleneimine (PEI) (Mw=600-10w Da), polyquaternium-7, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or homologues of the foregoing.

[0029] In an optional embodiment, the functional additive has a mass fraction of 0.01% to 5% in the modified solution, and the positively charged compound has a mass fraction of 0.01% to 10% in the modified solution; and / or, the mass ratio of the functional additive to the positively charged compound in the modified solution is (0.01 to 5): 1.

[0030] In an optional embodiment, the coating method is blade coating. The blade coating process involves vacuum adsorption fixing of a commercial cation exchange membrane onto the surface of a blade coating device, and then using a blade to coat the surface with a modified solution of a certain thickness and concentration. The coating thickness is 0.1 μm to 10 μm, the coating speed is 10 to 2000 mm / s, and the coating volume is 10 to 500 mL / m. 2 .

[0031] In an optional embodiment, the heat treatment curing temperature is 50~150℃, preferably 60~120℃, and the time is 5~60min.

[0032] In an optional embodiment, the crosslinking agent is at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal, glutaraldehyde, or a homologue thereof.

[0033] In an optional embodiment, the mass fraction of the crosslinking agent in the crosslinking agent solution is 0.001% to 2%.

[0034] In an optional embodiment, the solvent for the crosslinking agent solution is water.

[0035] In an optional embodiment, the temperature for secondary crosslinking is 15~80℃, preferably 25~60℃, and the reaction time is 5min~120min.

[0036] The method for preparing the monovalent selective cation exchange membrane of this application has the following advantages: 1. Innovative solvent system: Using thin film casting solution as a solvent to replace traditional single solvents (such as water or organic solvents), the modified material is firmly fixed on the membrane surface by the polymer matrix curing to form a stable modified layer. The pore-forming agent can optimize the membrane pore structure and improve ion flux.

[0037] 2. High-efficiency modified combination: By leveraging the synergistic effect of multi-component modified solutions, the limitations of single modification methods are overcome. Simultaneously, chemical stability, monovalent ion selectivity, and ion flux are enhanced, endowing monovalent selective cation exchange membranes with excellent separation performance.

[0038] 3. Simple process flow: The film is made by using the "coating-curing-crosslinking" modification process, which is fast, requires simple equipment, and is easy to industrialize.

[0039] The present application will be further described below through specific embodiments.

[0040] Example 1 A thin-film casting solution was prepared by mass fraction of 15% PES (average molecular weight 3w Da) + 3% PEG (Mw = 400 Da) + 82% NMP. Using the thin-film casting solution as a solvent, 0.2% tannic acid was added and mixed thoroughly, followed by 1% triethylenetetramine and 0.3% pyrrole, dissolved evenly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above modified solution was coated onto the surface of the commercial cation exchange membrane (Hangzhou Lanran, CT-5-CEM) using a 3μm coating blade at a speed of 1000mm / s, with a coating volume of 50mL / m. 2 The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0041] Example 2 A thin-film casting solution was prepared by mass fraction of 10% PVDP (average molecular weight 40 w Da) + 5% PVP (Mw = 1 w Da) + 85% DMF. Using the thin-film casting solution as a solvent, 0.5% tannic acid was added and mixed thoroughly, followed by 1% triethylenetetramine and 0.3% pyrrole, dissolved evenly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was then coated onto the surface of the commercial cation exchange membrane using a 3 μm coating blade at a speed of 1000 mm / s, with a coating volume of 50 mL / m. 2 The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0042] Example 3 A thin-film casting solution was prepared by mass fraction of 20% PEEK (average molecular weight 5w Da), 6% PVP (Mw=1w Da), and 74% NMP. Using the casting solution as a solvent, 0.5% dopamine was added as a functional additive for subsequent modification, along with 2% polyethyleneimine (7w) and 0.5% diethylenetriamine, which were then mixed thoroughly as a modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the modified solution was then coated onto the surface of the commercial cation exchange membrane using a 5μm coating blade at a speed of 1500mm / s, with a coating volume of 10mL / m. 2 The membrane is then placed in a 90℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, it is removed, the surface residue is washed off, and it is then immersed in a 2% glutaraldehyde aqueous solution and crosslinked at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0043] Example 4 A thin-film casting solution was prepared by mass fraction of 13% PES (average molecular weight 3w Da), 5% PEG (Mw=400 Da), and 82% NMP. Using the thin-film casting solution as a solvent, 0.2% tannic acid was added and mixed thoroughly, followed by 1% triethylenetetramine and 0.3% pyrrole, dissolved evenly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was coated onto the surface of the commercial cation exchange membrane using a 3μm coating blade at a speed of 1000mm / s, with a coating volume of 50mL / m. 2The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0044] Example 5 A thin-film casting solution was prepared by mass fraction of 10% PVDP (average molecular weight 40 w Da), 5% PVP (Mw = 1 w Da), and 85% DMF. Using the thin-film casting solution as a solvent, 0.5% gallic acid, 1% PEI (7 w), and 0.5% chitosan were added and mixed thoroughly as a modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was coated onto the surface of the commercial cation exchange membrane using a 10 μm coating blade at a speed of 800 mm / s, with a coating volume of 50 mL / m. 2 The membrane is then placed in an 80℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, it is removed, the surface residue is washed off, and it is then immersed in a 1% glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0045] Example 6 A thin-film casting solution was prepared by mass fraction of 10% PVDP (average molecular weight 40 w Da) + 5% PVP (Mw = 1 w Da) + 85% DMF. Using the thin-film casting solution as a solvent, 0.1% chlorosulfonic acid was added as a functional additive for subsequent modification, along with 2% quaternary ammonium salt and 1% Hoffmann reagent, which were then mixed thoroughly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was then coated onto the surface of the commercial cation exchange membrane using a 5 μm coating blade at a speed of 1200 mm / s, with a coating volume of 60 mL / m. 2 The membrane is then placed in a 90℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, it is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0046] Example 7 A thin-film casting solution was prepared by mass fraction of 20% PEEK (average molecular weight 5w Da), 6% PVP (Mw=1w Da), and 74% NMP. Using the casting solution as a solvent, 0.5% dopamine was added as a functional additive for subsequent modification, along with 2% polyethyleneimine (7w) and 0.5% diethylenetriamine, which were then mixed thoroughly as a modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was then coated onto the surface of the commercial cation exchange membrane using a 10μm thickness doctor blade at a speed of 1000mm / s, with a coating volume of 10mL / m. 2 The membrane is then placed in a 90℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, it is removed, the surface residue is washed off, and it is then immersed in a 2% glutaraldehyde aqueous solution and crosslinked at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0047] Comparative Example 1 This comparative example provides a base membrane that has not been treated by the preparation method provided in this application, namely the commercial cation exchange membrane used in Example 1.

[0048] Comparative Example 2 This comparative example is basically the same as Example 1, except that pure water is used as the solvent for the modifying agent in this comparative example, and the specific steps include the following: Based on mass fraction, using pure water as the solvent, 0.2% tannic acid was added and mixed thoroughly. Then, 1% triethylenetetramine and 0.3% pyrrole were added and dissolved thoroughly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was then coated onto the surface of the commercial cation exchange membrane using a doctor blade with a coating thickness of 3 μm at a speed of 1000 mm / s, with a coating volume of 50 mL / m. 2 The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0049] Comparative Example 3 This comparative example is basically the same as Example 1, except that no pore-forming agent was added in this comparative example. The specific steps include the following: A 15% PES + 85% NMP thin-film casting solution was prepared as the solvent by mass fraction. Using the thin-film casting solution as the solvent, 0.2% tannic acid was added and mixed thoroughly, followed by 1% triethylenetetramine and 0.3% pyrrole, dissolved evenly to serve as the modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was coated onto the surface of the commercial cation exchange membrane using a 3μm coating blade at a speed of 1000mm / s, with a coating volume of 50mL / m. 2 The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0050] Comparative Example 4 This comparative example is basically the same as Example 1, except that tannic acid was not added as a functional additive in this comparative example. The specific steps include the following: A thin-film casting solution of 15% PES + 3% PEG + 82% NMP was prepared by mass fraction. Using the thin-film casting solution as a solvent, 1% triethylenetetramine and 0.3% pyrrole were added and dissolved uniformly as a modifying agent. A commercial cation exchange membrane was vacuum-adsorbed and fixed onto the surface of a coating device. A layer of the above-mentioned modified solution was coated onto the surface of the commercial cation exchange membrane using a 3μm coating blade at a speed of 1000mm / s, with a coating volume of 50mL / m. 2 The membrane is then placed in a 70℃ oven for heat treatment and curing for 30 minutes. After the reaction is complete, the membrane is removed, the surface residue is washed off, and it is then immersed in a 1% (w / w) glutaraldehyde aqueous solution for crosslinking at 40℃ for 10 minutes. After removal and washing, a monovalent selective cation exchange membrane is obtained.

[0051] Figures 1 to 4 The images show the surface electron microscope (SEM) morphology of the base membrane of Comparative Example 1, and the monovalent selective cation exchange membranes prepared in Comparative Example 2, Example 1, and Example 2, respectively. By comparison... Figure 1-4 As can be seen, compared with the base membrane and the monovalent selective cation exchange membrane modified with water as the solvent, the monovalent selective cation exchange membrane modified with thin film casting solution as the solvent forms a continuous modified layer on its surface, which is more dense and uniform.

[0052] The monovalent selective cation exchange membranes prepared in Examples 1-7, the base membrane of Comparative Example 1, and the monovalent selective cation exchange membranes prepared in Comparative Examples 2-4 were subjected to selectivity tests, and the results are shown in Table 1. Meanwhile, the long-term separation effects of Example 1 and Comparative Example 2 were compared, and the results are shown in Table 2.

[0053] The selectivity coefficient of Li-Mg ( The test method includes: alternating arrangement of the monovalent selective cation exchange membrane to be tested and two anion exchange membranes to form a four-compartment electrodialysis unit. The electrode compartment contains a 0.5 mol / L NaCl solution, the concentration compartment contains a mixed solution of LiCl and MgCl2 with concentrations of 0.1 mol / L and 0.5 mol / L (simulating the lithium-magnesium ratio in brine), and the dilute compartment contains a 0.01 mol / L LiCl solution. The applied current is 10 mA / cm². 2 The concentrations of Li and Mg were calculated after 2 hours. The calculation method is as follows:

[0054]

[0055] J i Ion flux, in mol / m 2 •h, where t is the test time, in hours. A m C represents the effective membrane area used for permeation. t C0 represents the ion concentration in the concentration chamber after the test time, while C0 represents the ion concentration in the concentration chamber before energization.

[0056] C t Li The concentration of Li in the concentration chamber after 2 hours is expressed in mol / L, CO. Li The concentration of Li in the concentration chamber before energization is given, in mol / L.

[0057] C t Mg The concentration of Mg in the concentration chamber after 2 hours is expressed in mol / L, CO. Mg The concentration of Mg in the concentration chamber before energization is given, in mol / L.

[0058] C Li + The initial Li concentration in the dilute chamber is expressed in mol / L. (C) Mg 2+ The initial Mg concentration in the dilute chamber is expressed in mol / L.

[0059] Table 1. Selectivity test results of monovalent selective cation exchange membranes in Examples 1-7 and Comparative Examples 1-4

[0060] Table 2. Long-term selectivity test results of monovalent selective cation exchange membranes in Example 1 and Comparative Example 2.

[0061] The following conclusions can be drawn from Table 1: (1) As can be seen from Comparative Example 1 and Examples 1-7, the modification scheme of this application has good feasibility, and the monovalent selective cation exchange membranes obtained by the modification in Examples 1-7 of this application all have good separation effect.

[0062] (2) As can be seen from Examples 1-3, the separation performance of monovalent selective cation exchange membranes obtained by coating different thin film casting solutions and modified components on the base membrane varies to a certain extent, but all of them have good separation effect. This shows that the preparation of monovalent selective cation exchange membranes by the present application is feasible.

[0063] (3) As can be seen from Examples 1, 4 and Comparative Example 3, the addition of the pore-forming agent significantly increased the ion flux of the monovalent selective cation exchange membrane. As the content of the polymer in the thin film casting solution decreased, the concentration of the pore-forming agent increased, the modified layer structure became loose, and the ion flux also increased.

[0064] (4) As can be seen from Example 1 and Comparative Example 4, the introduction of functional additives can effectively promote the occurrence of subsequent reactions and make the modified layer more dense and effective.

[0065] (5) As can be seen from Examples 2, 5 and 6, when the composition of the thin film casting solution and the coating parameters are the same, the modified components have a significant impact on the separation mode and separation effect of the monovalent selective cation exchange membrane. For example, the modified components in Examples 2 and 5 mainly affect the density of the modified layer after reaction, with good selectivity but relatively low ion flux. The modified layer formed in Example 6 mainly relies on electrostatic repulsion for separation, with a large ion flux but relatively low selectivity.

[0066] (6) As can be seen from Examples 3 and 7, when the thin film casting solution and the modified components are the same, and the initial amount of coating is kept the same, the separation performance of the final monovalent selective cation exchange membrane can be significantly changed by adjusting the coating parameters. Increasing the coating thickness and decreasing the coating speed results in a thicker modified layer and better selectivity of the modified membrane, but the ion flux is relatively reduced.

[0067] (7) Based on the long-term selectivity test results of Example 1 and Comparative Example 2, the monovalent selective cation exchange membrane prepared by coating with water as the solution gradually showed a decrease in selectivity during the long-term test, indicating that the modified layer was gradually damaged and detached. However, the modified layer obtained by coating with thin film casting solution as the solvent of the modified component was stable and did not easily detach. It maintained good selectivity and surface morphology even after long-term testing, which shows that the method has good stability.

[0068] Compared to other modification schemes, the modification scheme of this application uses thin film casting solution as the solvent of the modification component, and the modified film obtained by scraping is more stable and has a significant effect on lithium-magnesium separation.

[0069] In summary, the monovalent selective cation exchange membrane prepared by the method provided in this application has better selective permeability to monovalent ions, and the preparation method is simple and easy to operate.

[0070] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for preparing a monovalent selective cation exchange membrane, characterized in that, Includes the following steps: Thin film casting solution is used as the solvent; A modified solution is obtained by adding functional additives and positively charged compounds to the solvent. The modified solution was coated onto the surface of a commercial cation exchange membrane and cured by heat treatment to form a modified layer; After heat treatment and curing, the membrane is placed in a crosslinking agent solution for secondary crosslinking to obtain the monovalent selective cation exchange membrane.

2. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The thin film casting solution is composed of a polymer matrix, a thin film casting solution solvent, and a pore-forming agent; The polymer matrix in the thin film casting solution has a mass fraction of 5% to 40%; The solvent in the thin film casting solution has a mass fraction of 50% to 85%. The pore-forming agent has a mass fraction of 1% to 20% in the thin film casting solution.

3. The method for preparing a monovalent selective cation exchange membrane according to claim 2, characterized in that, The polymer matrix includes one of polyetheretherketone, polysulfone, polyetherketone, polyvinylidene fluoride, polystyrene, and polyethersulfone; The solvent of the thin film casting solution includes one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dichloromethane, and pure water; The pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, β-cyclodextrin, and lithium chloride.

4. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The functional additive has a mass fraction of 0.01% to 5% in the modified solution; The positively charged compound has a mass fraction of 0.01% to 10% in the modified solution; And / or, in the modified solution, the mass ratio of the functional additive to the positively charged compound is (0.01~5):

1.

5. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The functional additives include one or more of sulfonating agents or amination agents; The positively charged compound includes at least one of piperazine, pyrrole, chitosan, aniline, diisopropylamine, polyethyleneimine of different molecular weights, polyquaternium-7, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or a homologue of any of the foregoing compounds.

6. The method for preparing a monovalent selective cation exchange membrane according to claim 5, characterized in that, The sulfonating agent is chlorosulfonic acid; The amination reagent is dopamine, tannic acid, gallic acid, or catechol.

7. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The coating method is scraping; The coating process involves vacuum adsorption fixing of the commercial cation exchange membrane onto a coating device, and then using a scraper to coat the modified solution onto the surface of the commercial cation exchange membrane. The coating thickness of the doctor blade is 0.1μm~10μm, the coating speed is 10~2000mm / s, and the coating amount is 10~500mL / m. 2 .

8. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The heat treatment curing temperature is 50~150℃, and the time is 5~60min.

9. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that, The crosslinking agent in the crosslinking agent solution is at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal, glutaraldehyde, or a homologue of any of the aforementioned compounds; The mass fraction of the crosslinking agent in the crosslinking agent solution is 0.001%~2%; The solvent for the crosslinking agent solution is water; The secondary crosslinking temperature is 15~80℃, and the reaction time is 5min~120min.

10. A monovalent selective cation exchange membrane, characterized in that, It is prepared by the method for preparing a monovalent selective cation exchange membrane as described in any one of claims 1-9.

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