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

Abstract

The present application relates to a kind of monovalent selective cation exchange membrane and its preparation method, the preparation method of the monovalent selective cation exchange membrane includes the following steps: the non-metallic ion initiator solution containing surfactant is scraped on the surface of cation exchange membrane, then the mixed aqueous solution of catechol compound and amine compound is sprayed to carry out reaction, the obtained modified membrane layer is cured by heat and placed in crosslinking agent solution to carry out crosslinking reaction, obtain the monovalent selective cation exchange membrane.The present application uses non-metallic ion initiator to initiate catechol compound and amine compound to occur on the surface of base film reaction, to ensure that membrane modification maintains good ion flux simultaneously;Through the good adsorption of catechol group, the modified layer is stably fixed on the membrane surface;The obtained monovalent selective cation exchange membrane has high ion flux, and shows good monovalent selectivity and stability.

Description

Technical Field

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

[0002] Lithium extraction from salt lakes has become an important method for obtaining lithium resources due to their abundant resources and low cost. However, in addition to Li, salt lake brine also contains other minerals. + In addition, it usually contains a large amount of Mg 2+ Ca 2+ Divalent ions, such as those in the lithium group, have similar physicochemical properties to Li+, leading to low efficiency and high cost in traditional separation methods. Therefore, developing efficient and stable lithium-ion selective separation technology is crucial.

[0003] Electrodialysis has shown promising application prospects in lithium extraction from salt lakes due to its advantages such as low energy consumption, high selectivity, and ease of scaling up. Electrodialysis drives the directional migration of ions through an external electric field and achieves ion separation using ion exchange membranes. If ion exchange membranes with monovalent selectivity are used, Li+ and Mg+ can be further separated simultaneously with anions and cations. 2+ Ca 2+ Efficient separation of divalent ions. The separation mechanism of monovalent selective membranes mainly involves electrostatic repulsion, pore size sieving, and differences in hydration energy. Their preparation methods can be divided into matrix modification and surface modification. Matrix modification achieves selective separation by controlling the overall membrane structure, but this easily leads to increased membrane resistance. Surface modification, on the other hand, introduces a positively charged modified layer on the membrane surface, improving selectivity while maintaining low resistance.

[0004] Currently, common methods for surface modification include impregnation, interfacial polymerization, electrodeposition, and layer-by-layer self-assembly. CN114713295A discloses a monovalent selective cation exchange membrane and its preparation method and application. This method involves contacting a self-made negatively charged base membrane with an aqueous solution of an amine compound and an oil phase solution for interfacial polymerization, followed by a second contact with an aqueous phase solution to obtain a monovalent selective cation exchange membrane. CN105655616A discloses a method for preparing a monovalent selective cation exchange membrane by electrodeposition. This method involves depositing a polymer of aniline and chitosan onto the membrane surface via electrodeposition, followed by crosslinking to increase density, thus obtaining a monovalent selective cation exchange membrane. However, the above methods suffer from complex modification processes and long processing times. Furthermore, the modified layer is mainly bonded through electrostatic adsorption, making it prone to detachment, resulting in poor stability and low loading capacity. In recent years, blade coating or spray coating methods have attracted attention due to their ease of operation and quantitative loading capability. However, if the modified material does not react with the base membrane, the problem of weak adhesion and easy detachment still exists.

[0005] To improve the stability of the modified layer, researchers borrowed the adhesion mechanism of mussels and introduced dopamine as a "bio-glue." Its catechol groups can firmly adhere to the base film through various interactions and act as an intermediate layer bridging amine-based modified materials. For example, CN112007526A uses an immersion method to allow dopamine to self-polymerize on a polysulfone film, but this requires 12-30 hours. To reduce reaction time, some experiments added initiators to the co-deposition solution. While this increased the reaction rate to some extent, the reaction occurred more within the solution, which was detrimental to the deposition of the modified layer on the film. In CN114377731A, Fe... 3+ As an initiator, the cation exchange membrane was pre-soaked in Fe... 3+ Soak in the solution for 0.5-2 hours, then soak in a buffer solution of dopamine and polyethyleneimine. While this increases the reaction rate, the use of Cu... 2+ or Fe 3+ As an initiator, Cu poses a risk of occupying ion exchange channels in the cation exchange membrane, leading to a significant reduction in ion flux. Meanwhile, Cu... 2+ or Fe 3+ It is readily soluble in water and reacts upon contact with the modified substance solution. The process is uncontrollable and it easily diffuses into the modified substance solution, causing more of the reaction to occur in the solution.

[0006] Therefore, there is an urgent need to develop a method for preparing cation exchange membranes with a controllable reaction process that enables rapid and stable loading of modified substances on the membrane surface. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a monovalent selective cation exchange membrane and its preparation method. The method employs a non-metallic ion initiator and adds a surfactant to enhance its dispersibility at the liquid-solid interface, thereby achieving rapid and stable loading of modified substances onto the membrane surface while avoiding membrane pore blockage.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a monovalent selective cation exchange membrane, the method comprising the following steps:

[0010] A solution of non-metallic ion initiator containing surfactant is scraped onto the surface of a cation exchange membrane, and then a mixed aqueous solution of catechol and amine compounds is sprayed on to react. The resulting modified membrane layer is then thermo-cured and placed in a crosslinking agent solution for crosslinking reaction to obtain the monovalent selective cation exchange membrane.

[0011] This invention employs a non-metallic ion initiator to oxidize catechol groups to quinone oxide, promoting the reaction of catechol and amine compounds on the base membrane surface. This avoids the use of initiators containing metal ions, thus preventing metal ions from occupying ion exchange channels and clogging membrane pores, thereby ensuring good ion flux while modifying the membrane surface. To increase the compatibility between the non-metallic ion initiator and water-soluble modifying substances (catechins and amines), a surfactant is added. This allows the initiator to more effectively initiate the reaction at the solid-liquid interface on the membrane surface, forming the modified layer. The non-water-insoluble nature of the non-metallic ion initiator also prevents its excessive diffusion into the solution, ensuring the reaction occurs in solution and making the reaction more accurate and efficient, avoiding contamination and waste of the modified substance solution. Using a blade coating and spray coating process, the initiator and modified substance solution are introduced stepwise and quantitatively onto the membrane surface, reducing the adsorption time required for traditional impregnation, ensuring a fixed content of modified substances on the membrane surface, strong controllability, and high reproducibility. By adjusting the blade coating thickness and spray coating amount, the performance of the subsequent modified membrane layer can be precisely controlled. By utilizing the good adsorption properties of catechol groups, modified substances can be stably fixed on the membrane surface. Furthermore, the degree of crosslinking and positive charge density of the modified membrane layer on the membrane surface can be controlled through thermosetting and crosslinking reactions, ultimately resulting in a monovalent selective cation exchange membrane with good stability and separation performance.

[0012] Preferably, in the non-metallic ion initiator solution, the concentration of the non-metallic ion initiator is 0.001%-1% (w / v), and the concentration of the surfactant is 0.001%-2% (w / v).

[0013] The concentration of the non-metallic ion initiator is 0.001%-1% (w / v), for example, it can be 0.001% (w / v), 0.01% (w / v), 0.1% (w / v), 0.5% (w / v) or 1% (w / v), but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] The concentration of the surfactant is 0.001%-2% (w / v), for example, it can be 0.001% (w / v), 0.01% (w / v), 0.1% (w / v), 1% (w / v) or 2% (w / v), but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the surfactant comprises at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polysorbate surfactant.

[0016] Preferably, the polysorbate surfactant includes at least one of polysorbate 20, polysorbate 40, and polysorbate 80.

[0017] Preferably, the non-metallic ion initiator in the non-metallic ion initiator solution includes benzoyl peroxide and / or di-tert-butyl peroxide.

[0018] Preferably, the solvent in the non-metallic ion initiator solution includes at least one of ethanol, benzene, toluene, and acetone.

[0019] Preferably, the specific steps of the coating process include: vacuum adsorbing the cation exchange membrane onto the surface of the coating equipment, using a scraper to coat the surface of the cation exchange membrane with the non-metallic ion initiator solution containing surfactant, and then drying.

[0020] Preferably, the thickness of the coating is 0.1-10 μm and the speed is 10-2000 mm / s.

[0021] The thickness of the coating is 0.1-10μm, for example, it can be 0.1μm, 1μm, 3μm, 5μm, 8μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The scraping speed is 10-2000 mm / s, for example, it can be 10 mm / s, 100 mm / s, 600 mm / s, 1000 mm / s, 1500 mm / s or 2000 mm / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, in the mixed aqueous solution of the catechol compounds and amine compounds, the mass percentage of the catechol compounds is 0.01%-5% and the mass percentage of the amine compounds is 0.01%-5%.

[0024] The mass percentage of the catechins is 0.01%-5%, for example, it can be 0.01%, 0.1%, 2%, 3% or 5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] The mass percentage of the amine compound is 0.01%-5%, for example, it can be 0.01%, 0.1%, 2%, 3% or 5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, in the mixed aqueous solution of the catechol compounds and amine compounds, the mass ratio of the catechol compounds to the amine compounds is (0.1-5):1, for example, it can be 0.1:1, 1:1, 2:1, 3:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the solvent in the mixed aqueous solution of the catechol and amine compounds is a Tris-HCl buffer solution with a pH of 7-9, such as 7, 7.5, 8, 8.5 or 9, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the catechin compounds include at least one selected from catechin, catechin, epigallocatechin, epigallocatechin gallate, dopamine, 3,4-dihydroxyphenylalanine, pyrogallol, and protocatechuic acid.

[0029] Preferably, the amine compound includes at least one selected from piperazine, pyrrole, aniline, diisopropylamine, polyethyleneimine, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

[0030] Preferably, the molecular weight of the polyethyleneimine is 600-100000 Da, for example, it can be 600 Da, 1000 Da, 5000 Da, 10000 Da, 50000 Da or 100000 Da, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the amount of the spray coating is 0.1-1 L / m³. 2 For example, it could be 0.1 L / m 2 0.3L / m 2 0.5L / m 2 0.8L / m 2 or 1L / m 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0032] Preferably, the reaction temperature is 60-120℃, the ambient humidity is 60%-90%, and the reaction time is 5-60 minutes.

[0033] The reaction temperature is 60-120℃, for example, it can be 60℃, 70℃, 80℃, 100℃ or 120℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] The ambient humidity for the reaction is 60%-90%, for example, it can be 60%, 65%, 75%, 80% or 90%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] The reaction time is 5-60 min, for example, it can be 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the thermosetting temperature is 40-90℃, for example, it can be 40℃, 50℃, 60℃, 80℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heat curing time is 5-30 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the mass percentage of the crosslinking agent in the crosslinking agent solution is 0.001%-2%, for example, it can be 0.001%, 0.01%, 0.1%, 1% or 2%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the crosslinking agent in the crosslinking agent solution includes at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal, and glutaraldehyde.

[0040] Preferably, the solvent in the crosslinking agent solution includes water.

[0041] Preferably, the crosslinking reaction is carried out at a temperature of 25-60°C for a time of 5-120 minutes.

[0042] The temperature of the crosslinking reaction is 25-60℃, for example, it can be 25℃, 30℃, 40℃, 50℃ or 60℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] The crosslinking reaction time is 5-120 min, for example, it can be 5 min, 15 min, 30 min, 50 min, 80 min, 100 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Secondly, the present invention provides a monovalent selective cation exchange membrane, which is prepared by the method for preparing the monovalent selective cation exchange membrane described in the first aspect.

[0045] The monovalent selective cation exchange membrane provided by this invention has high monovalent ion selectivity and stability, and can be used in electrodialysis to separate monovalent and divalent and / or polyvalent cations.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The method for preparing a monovalent selective cation exchange membrane provided by the present invention uses a non-metallic ion initiator to initiate the reaction of catechol compounds and amine compounds on the surface of the base membrane, thereby ensuring membrane modification while maintaining good ion flux. The present invention increases the compatibility between the non-metallic ion initiator and the water-soluble modified material by adding a surfactant, so that the initiator can more effectively initiate the reaction of the modified material at the solid-liquid interface on the membrane surface to generate a modified layer. The non-water-soluble nature of the non-metallic ion initiator also avoids its large-scale diffusion into the solution, which would cause the reaction to occur in the solution, making the reaction more accurate and effective, and avoiding contamination and waste of the modified material solution.

[0048] (2) This invention uses a combination of scraping and spraying processes to introduce initiator and modifier solutions onto the membrane surface in a stepwise and quantitative manner, reducing the adsorption time required for traditional impregnation, ensuring a fixed content of modifiers on the membrane surface, strong controllability, and high reproducibility; by adjusting the scraping thickness and spraying amount, the performance of the subsequent modified membrane layer can be precisely controlled. Thermal initiation induces a reaction on the membrane surface to generate an adhesive and stable modified membrane layer. Subsequent thermal curing and crosslinking reactions can further improve the density of the modified layer, enhance its pore size sieving performance and the stability of the modified membrane, ultimately resulting in a monovalent selective cation exchange membrane with good stability and separation performance.

[0049] (3) The preparation method of the monovalent selective cation exchange membrane provided by the present invention is highly efficient and repeatable, with controllable operation, convenient adjustment of variables, low reagent consumption, low waste liquid production, and low cost. During the preparation process, the separation performance of the modified layer can be optimized directly by adjusting the scraping and spraying parameters, making the optimization process more flexible and more conducive to the large-scale preparation of monovalent selective cation exchange membranes, and with a higher degree of adaptability to different base membranes. Attached Figure Description

[0050] Figure 1 This is an optical image of the monovalent selective cation exchange membrane provided in Embodiment 1 of the present invention;

[0051] Figure 2 This is an optical image of the cation exchange membrane provided in Comparative Example 1 of the present invention;

[0052] Figure 3 This is a SEM image of the monovalent selective cation exchange membrane provided in Embodiment 1 of the present invention;

[0053] Figure 4 This is a SEM image of the cation exchange membrane provided in Comparative Example 1 of the present invention;

[0054] Figure 5These are the infrared spectra of the monovalent selective cation exchange membrane provided in Embodiment 1 of the present invention and the cation exchange membrane provided in Comparative Example 1. Detailed Implementation

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0056] The cation exchange membrane used in the embodiments and comparative examples of this invention was manufactured by Hangzhou Lanran Technology Co., Ltd., and its model number is CT-4.

[0057] Example 1

[0058] This embodiment provides a monovalent selective cation exchange membrane, and the preparation method of the monovalent selective cation exchange membrane includes the following steps:

[0059] A cation exchange membrane was vacuum-adsorbed onto the surface of a coating device. A mixed benzene solution containing 0.1% (w / v) polysorbate 80 and 0.5% (w / v) benzoyl peroxide was then coated onto the membrane surface using a scraper. The coating thickness was 3 μm, and the speed was 600 mm / s. The membrane was then air-dried. A mixed Tris-HCl buffer solution containing 2% epigallocatechin gallate and 2% polyethyleneimine (molecular weight 10000 Da) was then sprayed onto the membrane for reaction. The pH of the Tris-HCl buffer solution was 8, and the spraying volume was 0.8 L / m³. 2 The reaction temperature was 80℃, the ambient humidity was 75%, and the reaction time was 30 min. After the modified membrane was heat-cured at 60℃ for 20 min, it was placed in a 1% (w / w) glutaraldehyde aqueous solution and crosslinked at 50℃ for 15 min to obtain the monovalent selective cation exchange membrane.

[0060] Example 2

[0061] This embodiment provides a monovalent selective cation exchange membrane, and the preparation method of the monovalent selective cation exchange membrane includes the following steps:

[0062] A cation exchange membrane was vacuum-adsorbed onto the surface of a coating device. A mixed ethanol solution containing 0.001% (w / v) sodium dodecyl sulfate and 0.001% (w / v) di-tert-butyl peroxide was then coated onto the membrane using a scraper. The coating thickness was 0.1 μm, and the speed was 10 mm / s. The membrane was then air-dried. A mixed Tris-HCl buffer solution containing 0.01% dopamine and 0.1% tris-(2-aminoethyl)amine was then sprayed onto the membrane for reaction. The pH of the Tris-HCl buffer solution was 7, and the spraying volume was 0.1 L / m³.2 The reaction temperature was 60℃, the ambient humidity was 90%, and the reaction time was 60 min. After the modified membrane was heat-cured at 40℃ for 30 min, it was placed in a 0.001% triethanolamine aqueous solution and crosslinked at 25℃ for 120 min to obtain the monovalent selective cation exchange membrane.

[0063] Example 3

[0064] This embodiment provides a monovalent selective cation exchange membrane, and the preparation method of the monovalent selective cation exchange membrane includes the following steps:

[0065] A cation exchange membrane was vacuum-adsorbed onto the surface of a coating device. A mixed acetone solution containing 2% (w / v) sodium dodecylbenzenesulfonate and 1% (w / v) benzoyl peroxide was then coated onto the membrane surface using a scraper. The coating thickness was 10 μm, and the speed was 2000 mm / s. The membrane was then air-dried. A mixed Tris-HCl buffer solution containing 5% (w / v) catechin and 1% (w / v) dicyandiamide was then sprayed onto the membrane for reaction. The pH of the Tris-HCl buffer solution was 9, and the spraying volume was 1 L / m³. 2 The reaction temperature was 120℃, the ambient humidity was 60%, and the reaction time was 5 min. After the modified membrane was heat-cured at 90℃ for 5 min, it was placed in a 2% (w / w) carbodiimide aqueous solution and subjected to a crosslinking reaction at 60℃ for 5 min to obtain the monovalent selective cation exchange membrane.

[0066] Example 4

[0067] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Embodiment 1 in that, except that the thickness of the coating is adjusted to 0.05 μm, the rest is the same as that of Embodiment 1.

[0068] Example 5

[0069] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Embodiment 1 in that, except for adjusting the thickness of the coating to 12 μm, the rest is the same as that of Embodiment 1.

[0070] Example 6

[0071] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Embodiment 1 in that, except for adjusting the coating speed to 5 mm / s, the rest is the same as that of Embodiment 1.

[0072] Example 7

[0073] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Embodiment 1 in that, except for adjusting the coating speed to 2050 mm / s, all other aspects are the same as those of Embodiment 1.

[0074] Example 8

[0075] This embodiment provides a monovalent selective cation exchange membrane. The difference between the preparation method of the monovalent selective cation exchange membrane and that of Embodiment 1 is that the amount of coating is adjusted to 0.05 L / m. 2 Except for the above, everything else is the same as in Example 1.

[0076] Example 9

[0077] This embodiment provides a monovalent selective cation exchange membrane. The difference between the preparation method of the monovalent selective cation exchange membrane and that of Embodiment 1 is that the amount of coating is adjusted to 1.2 L / m. 2 Except for the above, everything else is the same as in Example 1.

[0078] Example 10

[0079] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that, except that the mass percentage of epigallocatechin gallate in the mixed Tris-HCl buffer solution is adjusted to 0.1% and the mass percentage of polyethyleneimine is adjusted to 5%, the rest are the same as in Example 1.

[0080] Example 11

[0081] This embodiment provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that, except that the mass percentage of epigallocatechin gallate in the mixed Tris-HCl buffer solution is adjusted to 0.1% and the mass percentage of polyethyleneimine is adjusted to 0.01%, the rest are the same as in Example 1.

[0082] Comparative Example 1

[0083] This comparative example provides a cation exchange membrane that is the same as the cation exchange membrane in Example 1.

[0084] Comparative Example 2

[0085] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that polysorbate 80 is not added to the mixed benzene solution, while the rest is the same as in Example 1.

[0086] Comparative Example 3

[0087] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that the scraping coating is changed to a first immersion, and the first immersion time is 30 min; the spraying coating is changed to a second immersion, and the second immersion temperature is 80°C, the ambient humidity is 75%, and the time is 30 min. All other aspects are the same as in Example 1.

[0088] Comparative Example 4

[0089] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that the coating step is omitted, i.e., the mixed benzene solution of polysorbate 80 and benzoyl peroxide is not introduced. All other steps are the same as in Example 1.

[0090] Comparative Example 5

[0091] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that benzoyl peroxide is not added to the mixed benzene solution, and epigallocatechin gallate is not added to the mixed Tris-HCl buffer solution. All other aspects are the same as in Example 1.

[0092] Comparative Example 6

[0093] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that the modified membrane layer is not placed in a glutaraldehyde aqueous solution for crosslinking reaction after being heat-cured at 60°C for 20 min, and the monovalent selective cation exchange membrane is obtained directly. All other aspects are the same as those in Example 1.

[0094] Comparative Example 7

[0095] This comparative example provides a monovalent selective cation exchange membrane. The preparation method of the monovalent selective cation exchange membrane differs from that of Example 1 in that, except that the mixed benzene solution containing 0.1% (w / v) polysorbate 80 and 0.5% (w / v) benzoyl peroxide is replaced with a mixed aqueous solution containing 0.1% (w / v) polysorbate 80 and 0.5% (w / v) FeCl3·6H2O, the rest is the same as in Example 1.

[0096] Performance testing

[0097] The optical image of the monovalent selective cation exchange membrane provided in Example 1 is shown below. Figure 1 As shown, the optical image of the cation exchange membrane provided in Comparative Example 1 is as follows. Figure 2 As shown in the figure, compared with the base membrane, the surface color of the modified monovalent selective cation exchange membrane is darker, which is attributed to the oxidation of catechol compounds.

[0098] The SEM image of the monovalent selective cation exchange membrane provided in Example 1 is shown below. Figure 3 As shown, the SEM image of the cation exchange membrane provided in Comparative Example 1 is as follows. Figure 4 As shown in the figure, the comparison reveals that a uniform and dense modified layer is formed on the surface of the modified monovalent selective cation exchange membrane.

[0099] The infrared spectra of the monovalent selective cation exchange membrane provided in Example 1 and the cation exchange membrane provided in Comparative Example 1 are shown below. Figure 5 As shown, compared to the base membrane of Comparative Example 1, the monovalent selective cation exchange membrane at 3100 cm⁻¹... -1 -3600cm -1 The enhanced stretching vibration peaks of OH and NH in the region indicate the formation of a modified layer rich in OH and NH on the base membrane surface. The monovalent selective cation exchange membrane exhibits enhanced performance at 1640 cm⁻¹. -1 The absorption peaks on the left and right sides were also significantly enhanced, which is attributed to the enhanced bending vibration peaks of the quinone structure formed by the oxidation of catechol groups and the C=N bond generated by the reaction of catechol with amino groups. This indicates that a modified layer has been formed on the surface of the base film.

[0100] Monovalent cation selectivity test: The cation exchange membrane to be tested is alternately arranged with two anion exchange membranes to form a four-compartment electrodialysis device. 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 After running for 2 hours, Li was detected using an atomic absorption spectrometer. + Mg 2+ Concentration, Li-Mg selectivity coefficient ion flux J i The calculations were performed using the following formulas, and the results are shown in Table 1.

[0101]

[0102] In equation (1): J i Ion flux, in mol / m 2 ·h; t is the test time, in hours; A m To test the effective membrane area, the unit is m. 2 C tC0 is the ion concentration in the concentration chamber after 2 hours of operation, in mol / L; C0 is the ion concentration in the concentration chamber before operation, in mol / L; the measured lithium-ion flux is denoted as . The measured magnesium ion flux is denoted as

[0103] In equation (2): C t Li For the Li in the concentration chamber after 2 hours of operation + Concentration, in mol / L; CO Li For the Li in the concentration chamber before operation + Concentration, in units of mol / L; C t Mg For Mg in the concentration chamber after 2 hours of operation 2+ Concentration, in mol / L; CO Mg Mg in the concentration chamber before operation 2+ Concentration, in units of mol / L; C Li + For the initial Li in the dilute chamber + Concentration, in units of mol / L, C Mg 2+ Initial Mg for dilute chamber 2+ Concentration, in mol / L.

[0104] The lithium current efficiency was calculated using the following formula, and the results are shown in Table 1.

[0105]

[0106] In equation (3): η is the lithium current efficiency, in %; N is the number of membrane pairs in the electrodialysis device; I is the electrodialysis test current, in A; Z is the Li-C-C-E ratio. + Valence, i.e., +1; F is the Faraday constant, 26.801 A·h / mol; V0 is the initial volume of the concentrated solution in the chamber, in L; V t The volume of the concentrated solution after 2 hours of operation is expressed in L.

[0107] Table 1

[0108]

[0109] The following conclusions can be drawn from Table 1:

[0110] (1) As can be seen from the comparison of Examples 1-3, different initiators and surfactants can be used to effectively promote the reaction by controlling the reaction parameters within the specified range, so that the modified films obtained have good selectivity.

[0111] (2) A comparison of Examples 1 with Examples 4, 5, 8, and 9 shows that the separation performance of the modified membrane varies depending on the thickness of the initiator coating and the amount of modified substance solution sprayed. If the initiator coating thickness is too small or the amount of modified substance solution sprayed is too low, the modification will be insufficient or the modified layer will be discontinuous, which will cause magnesium ions to pass through preferentially and reduce selectivity. If the initiator coating thickness is too large or the amount of modified substance solution sprayed is too high, the degree of reaction and thickness of the modified layer will be enhanced, which will improve the pore size sieving of the modified layer and result in higher selectivity, but at the same time the ion flux will also be reduced.

[0112] (3) As can be seen from Examples 1 and 6 and 7, adjusting the coating speed can effectively control the separation performance of the modified membrane. If the coating speed is too low, a certain amount of initiator will be adsorbed or retained on the membrane surface, resulting in a relatively high initiator dosage and a thicker modified layer. Although it has high selectivity, the ion flux is reduced. If the coating speed is too high, the adsorption of initiator by the membrane itself will be reduced, and the initiator content on the membrane will be reduced.

[0113] (4) As can be seen from Examples 1 and 10 and 11, the mass ratio of catechol compounds and amine compounds needs to be controlled within a reasonable range. If the amine content is too high, most of the unreacted polyethyleneimine on the membrane will fall off, while if it is too low, more negatively charged catechol polymer layers will be on the membrane, resulting in poor lithium-magnesium separation.

[0114] (5) As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, the modified membrane prepared by adding surfactant to the initiator has higher lithium ion flux and selectivity. This is because the surfactant improves the contact efficiency between the initiator and the modified substance, enhances the degree of membrane modification, and at the same time, the surfactant can improve the hydrophilicity of the modified membrane to a certain extent, making the membrane have higher ion flux.

[0115] (6) As can be seen from the comparison between Example 1 and Comparative Example 3, compared with impregnation, the initiator and modifier can be introduced to the membrane surface quickly and efficiently by scraping and spraying. The modification effect is faster and more effective, and the separation effect is significantly higher than that of the base membrane and the monovalent selective cation exchange membrane prepared by impregnation modification.

[0116] (7) As can be seen from the comparison between Example 1 and Comparative Example 4, the modified membrane without initiator has poor separation performance. This is because in a short time, the initiator can significantly increase the reaction rate of catechol and amine compounds, allowing the modified layer to be deposited on the membrane surface more quickly and effectively, so that the modified membrane has both good selectivity and good ion flux.

[0117] (8) As can be seen from the comparison between Example 1 and Comparative Example 5, the modified membrane has certain separation performance after the simple amine compounds are cross-linked and quaternized on the membrane surface. However, the separation performance is limited, and due to the lack of the dispersing effect of catechol compounds, the cross-linking effect of amines and cross-linking agents is strong, resulting in a relatively low ion flux of the modified membrane.

[0118] (9) As can be seen from the comparison between Example 6 and Comparative Example 6, the separation effect of the modified membrane is the synergistic effect of pore size sieving and electrostatic repulsion. Without cross-linking and quaternization, the density and positive charge density of the modified membrane are relatively low, and the selectivity of the modified membrane is poor.

[0119] (10) As can be seen from the comparison between Example 6 and Comparative Example 7, the use of water-soluble initiators will cause them to diffuse into the solution in large quantities, which will lead to the reaction occurring in the solution. At the same time, they will occupy the ion exchange channels, resulting in a significant reduction in ion flux and the inability of the modified material to be effectively deposited on the membrane surface.

[0120] In summary, the method for preparing a monovalent selective cation exchange membrane provided by this invention enhances the diffusion efficiency of the non-metallic ion initiator and water-soluble modifier at the membrane interface by adding a surfactant to the non-metallic ion initiator. The initiator oxidizes catechol groups to oxyquinone, promoting the reaction of catechol and amine compounds on the base membrane surface. The non-water-insoluble nature of the non-metallic ion initiator also prevents its extensive diffusion into the solution, thus ensuring the reaction occurs in solution and making the reaction more accurate and efficient, avoiding contamination and waste of the modifier solution. Simultaneously, the non-metallic ion initiator does not occupy ion exchange channels, and the surfactant also improves the hydrophilicity of the modified membrane, giving it a higher ion flux.

[0121] This invention utilizes a combination of blade coating and spray coating processes to introduce initiator and modifier solutions onto the membrane surface in a stepwise and quantitative manner. This reduces the adsorption time required for traditional impregnation, ensuring a fixed content of modifiers on the membrane surface, strong controllability, and high reproducibility. By adjusting the blade coating thickness and spray coating amount, the performance of the subsequent modified membrane layer can be precisely controlled. Thermal initiation induces a reaction on the membrane surface to generate an adhesive and stable modified membrane layer. Subsequent thermal curing and cross-linking reactions can further improve the density of the modified layer, enhance its pore size sieving performance, and improve the stability of the modified membrane. Ultimately, a monovalent selective cation exchange membrane with good stability and separation performance can be obtained.

[0122] The method for preparing monovalent selective cation exchange membranes provided by this invention is highly efficient, repeatable, controllable, and easy to adjust variables. It requires less reagent, produces less waste liquid, and is low in cost. During the preparation process, the separation performance of the modified layer can be optimized directly by adjusting the coating and spraying parameters, making the optimization process more flexible and more conducive to the large-scale preparation of monovalent selective cation exchange membranes. It also offers greater adaptability to different base membranes.

[0123] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a monovalent selective cation exchange membrane, characterized in that, The preparation method includes the following steps: A solution of non-metallic ion initiator containing surfactant is scraped onto the surface of a cation exchange membrane, and then a mixed aqueous solution of catechol and amine compounds is sprayed on to react. The resulting modified membrane layer is then thermo-cured and placed in a crosslinking agent solution for crosslinking reaction to obtain the monovalent selective cation exchange membrane. The surfactant includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polysorbate surfactant; The non-metallic ion initiator in the non-metallic ion initiator solution includes benzoyl peroxide and / or di-tert-butyl peroxide; The solvent in the non-metallic ion initiator solution includes at least one of ethanol, benzene, toluene, and acetone.

2. The preparation method according to claim 1, characterized in that, In the non-metallic ion initiator solution, the concentration of the non-metallic ion initiator is 0.001%-1% (w / v), and the concentration of the surfactant is 0.001%-2% (w / v).

3. The preparation method according to claim 1, characterized in that, The specific steps of the coating process include: vacuum adsorbing the cation exchange membrane onto the surface of the coating equipment, using a scraper to coat the surface of the cation exchange membrane with the non-metallic ion initiator solution containing surfactant, and then drying it.

4. The preparation method according to claim 1, characterized in that, The thickness of the coating is 0.1-10 μm, and the speed is 10-2000 mm / s.

5. The preparation method according to claim 1, characterized in that, In the mixed aqueous solution of the catechols and amines, the mass percentage of the catechols is 0.01%-5% and the mass percentage of the amines is 0.01%-5%.

6. The preparation method according to claim 5, characterized in that, In the mixed aqueous solution of the catechols and amines, the mass ratio of the catechols to the amines is (0.1-5):

1.

7. The preparation method according to claim 1, characterized in that, The solvent in the mixed aqueous solution of the catechol and amine compounds is a Tris-HCl buffer solution with a pH of 7-9.

8. The preparation method according to claim 1, characterized in that, The catechin compounds include at least one of catechin, catechin, epigallocatechin, epigallocatechin gallate, dopamine, 3,4-dihydroxyphenylalanine, pyrogallol, and protocatechuic acid.

9. The preparation method according to claim 1, characterized in that, The amine compounds include at least one of piperazine, pyrrole, aniline, diisopropylamine, polyethyleneimine, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

10. The preparation method according to claim 1, characterized in that, The amount of the spray coating is 0.1-1 L / m. 2 .

11. The preparation method according to claim 1, characterized in that, The reaction temperature is 60-120℃, the ambient humidity is 60%-90%, and the reaction time is 5-60 minutes.

12. The preparation method according to claim 1, characterized in that, The thermosetting temperature is 40-90℃.

13. The preparation method according to claim 1, characterized in that, The thermosetting time is 5-30 minutes.

14. The preparation method according to claim 1, characterized in that, The crosslinking agent solution contains a crosslinking agent mass percentage of 0.001%-2%.

15. The preparation method according to claim 1, characterized in that, The crosslinking agent in the crosslinking agent solution includes at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal, and glutaraldehyde.

16. The preparation method according to claim 1, characterized in that, The solvent in the crosslinking agent solution includes water.

17. The preparation method according to claim 1, characterized in that, The cross-linking reaction is carried out at a temperature of 25-60℃ for a time of 5-120 min.

18. A monovalent selective cation exchange membrane, characterized in that, The monovalent selective cation exchange membrane is prepared by the method for preparing a monovalent selective cation exchange membrane according to any one of claims 1-17.

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