Monovalent selective cation exchange membrane and preparation method thereof

Abstract

The invention relates to a monovalent selective cation exchange membrane and a preparation method thereof, and the preparation method of the monovalent selective cation exchange membrane comprises the following steps: blade-coating a nonmetallic ion initiator solution containing a surfactant on the surface of a cation exchange membrane, then spraying a mixed aqueous solution of a catechol compound and an amine compound for reaction, thermally curing the obtained modified membrane layer, and then placing the modified membrane layer in a cross-linking agent solution for cross-linking reaction to obtain the monovalent selective cation exchange membrane. The nonmetal ion initiator is adopted to initiate the catechol compound and the amine compound to react on the surface of the base membrane, so that good ion flux is maintained while membrane modification is guaranteed; the modified layer is stably fixed on the surface of the membrane through good adsorbability of catechol groups; the obtained monovalent selective cation exchange membrane has high ion flux and shows good monovalent selectivity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of ion exchange membranes, and in particular to a monovalent selective cation exchange membrane and a preparation method thereof. Background Art

[0002] Lithium extraction from salt lakes has become one of the important ways to obtain lithium resources due to its rich resources and low cost. + In addition, it usually contains a lot of Mg 2+ , Ca 2+ These ions have similar physical and chemical properties to Li+, which results in low efficiency and high cost of traditional separation methods. Therefore, it is crucial to develop efficient and stable lithium ion selective separation technology.

[0003] Electrodialysis has shown good application prospects in lithium extraction from salt lakes due to its low energy consumption, high selectivity, and easy scale-up. Electrodialysis drives ion directional migration through an external electric field and uses ion exchange membranes to achieve ion separation. If an ion exchange membrane with monovalent selectivity is used, it can further achieve the separation of Li+ and Mg while separating anions and cations. 2+ , Ca 2+ The separation mechanism of monovalent selective membranes is primarily electrostatic repulsion, pore size screening, and hydration energy differences. Their preparation methods can be categorized into matrix modification and surface modification. Matrix modification achieves selective separation by manipulating the overall membrane structure, but this can easily lead to increased membrane resistance. Surface modification, on the other hand, involves introducing a positively charged modified layer onto the membrane surface, improving selectivity while maintaining low resistance.

[0004] At present, the common methods of 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, which contacts a homemade negatively charged base membrane with an aqueous solution of an amine compound and an oil phase solution respectively for a first interfacial polymerization, and then contacts the aqueous phase solution for a second time to obtain a monovalent selective cation exchange membrane. CN105655616A discloses a method for preparing a monovalent selective cation exchange membrane by electrodeposition, which deposits a polymer of aniline and chitosan on the membrane surface by electrodeposition, and then increases the density by cross-linking to obtain a monovalent selective cation exchange membrane. However, the above method has the problems of complex modification process and long time consumption, and the modified layer is mainly combined by electrostatic adsorption, easily falls off, resulting in poor stability and low load. In recent years, scraping or spraying methods have attracted attention due to their simple operation and quantitative load, but if the modified substance does not react with the base membrane, they still face the problems of weak binding force and easy falling off.

[0005] In order to improve the stability of the modified layer, researchers borrowed the adhesion mechanism of mussels and introduced dopamine as a "biological glue". Its catechol group can firmly adhere to the basement membrane through a variety of interactions and serve as an intermediate layer to bridge amine-modified substances. For example, CN112007526A uses an immersion method to make dopamine self-polymerize on the polysulfone membrane, but it takes 12-30 hours. In order to reduce the reaction time, some experiments added initiators to the co-deposition solution. Although the reaction speed was increased to a certain extent, the reaction occurred more in the solution, which was not conducive to the reaction and deposition of the modified layer on the membrane. In CN114377731A, Fe 3+ As an initiator, the cation exchange membrane is pre-soaked in Fe 3+ The solution was soaked for 0.5-2 hours, and then soaked in a buffer solution of dopamine and polyethyleneimine. Although the reaction speed was increased, the use of Cu 2+ or Fe 3+ As an initiator, there is a risk of occupying the ion exchange channels of the cation exchange membrane, resulting in a significant reduction in ion flux. 2+ or Fe 3+ It is easily 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 the reaction to occur more in the solution.

[0006] In view of this, there is an urgent need to develop a preparation method for a cation exchange membrane with a controllable reaction process and the ability to achieve rapid and stable loading of modified substances on the membrane surface. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a monovalent selective cation exchange membrane and its preparation method, which adopts a non-metallic ion initiator and adds a surfactant to enhance its dispersibility at the liquid-solid interface, thereby avoiding clogging of the membrane pores while achieving rapid and stable loading of the modified substance on the membrane surface.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

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

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

[0011] The present invention uses a non-metallic ion initiator to initiate the oxidation of catechol groups to oxidized quinones, promotes the reaction of catechol compounds and amine compounds on the surface of the base membrane, avoids the use of initiators containing metal ions, and therefore does not cause metal ions to occupy ion exchange channels and block membrane pores, thereby ensuring that the membrane surface is modified while maintaining good ion flux; in order to increase the compatibility of the non-metallic ion initiator with water-soluble modifiers (catechol compounds and amine compounds), the present invention adds a surfactant to enable the initiator to more effectively initiate the reaction of the modifier at the solid-liquid contact interface on the membrane surface to generate a modified layer, and the non-water solubility of the non-metallic ion initiator also avoids its large-scale diffusion into the solution, causing the reaction to occur in the solution, making the reaction more accurate and effective, and avoiding pollution and waste of the modifier solution. The initiator and modifier solution are quantitatively introduced step by step on the membrane surface using the scraping and spraying process, which reduces the adsorption time required for traditional dipping, ensures that the content of the modifier on the membrane surface is fixed, has strong controllability, and high reproducibility; by regulating the scraping thickness and spraying amount, the performance of the subsequent modified membrane layer can be accurately controlled. The good adsorption properties of the catechol group are utilized to stably fix the modified substance on the membrane surface, and the cross-linking degree and positive charge density of the modified membrane layer on the membrane surface are further regulated through thermal curing and cross-linking reactions, ultimately producing 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, and other values ​​not listed within the numerical 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, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, the surfactant includes at least one of sodium lauryl sulfate, sodium dodecylbenzene sulfonate and polysorbate surfactants.

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

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

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

[0019] Preferably, the specific steps of the scraping include: vacuum adsorbing the cation exchange membrane on the surface of the scraping equipment, scraping the non-metallic ion initiator solution containing a surfactant on the surface of the cation exchange membrane with a scraper, and then drying it.

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

[0021] The thickness of the scraping is 0.1-10 μm, for example, 0.1 μm, 1 μm, 3 μm, 5 μm, 8 μm or 10 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] The speed of the scraping is 10-2000 mm / s, for example, 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, and other values ​​not listed within the numerical range are also applicable.

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

[0024] The mass percentage of the catechol compound is 0.01%-5%, for example, 0.01%, 0.1%, 2%, 3% or 5%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0026] Preferably, in the mixed aqueous solution of the catechol compound and the amine compound, the mass ratio of the catechol compound to the amine compound 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, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the solvent in the mixed aqueous solution of the catechol compound and the amine compound is a Tris-HCl buffer solution with a pH value of 7-9, for example, 7, 7.5, 8, 8.5 or 9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the catechol compound includes at least one of catechol, catechin, epigallocatechin, epigallocatechin gallate, dopamine, 3,4-dihydroxyphenylalanine, pyrogallol and protocatechuic acid.

[0029] Preferably, the amine compound includes at least one of 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 600-100,000 Da, for example, 600 Da, 1,000 Da, 5,000 Da, 10,000 Da, 50,000 Da or 100,000 Da, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the spraying amount is 0.1-1L / m 2 , for example, it can be 0.1L / m 2 , 0.3L / m 2 , 0.5L / m 2 , 0.8L / m 2 or 1L / m 2 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

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

[0033] The reaction temperature is 60-120°C, for example, 60°C, 70°C, 80°C, 100°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] The reaction environment humidity is 60%-90%, for example, 60%, 65%, 75%, 80% or 90%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0036] Preferably, the thermal curing temperature is 40-90°C, for example, 40°C, 50°C, 60°C, 80°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0038] Preferably, the mass percentage of the crosslinker in the crosslinker solution is 0.001%-2%, for example, 0.001%, 0.01%, 0.1%, 1% or 2%, but is not limited to the listed values, and other values ​​not listed within the numerical 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 cross-linking agent solution includes water.

[0041] Preferably, the cross-linking reaction temperature is 25-60° C., and the time is 5-120 min.

[0042] The temperature of the cross-linking reaction is 25-60°C, for example, 25°C, 30°C, 40°C, 50°C or 60°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] The cross-linking reaction time is 5-120 min, for example, 5 min, 15 min, 30 min, 50 min, 80 min, 100 min or 120 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] In a second aspect, the present invention provides a monovalent selective cation exchange membrane, which is prepared by the method for preparing the monovalent selective cation exchange membrane according to the first aspect.

[0045] The monovalent selective cation exchange membrane provided by the present invention has high monovalent ion selectivity and stability and can be used for separating monovalent cations from divalent and / or multivalent cations in electrodialysis.

[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 a reaction between 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 of the non-metallic ion initiator with the water-soluble modifying substance by adding a surfactant, so that the initiator can more effectively initiate the reaction of the modifying substance at the solid-liquid contact interface on the membrane surface to form a modified layer, and the non-water solubility of the non-metallic ion initiator also avoids its large-scale diffusion into the solution, causing the reaction to occur in the solution, making the reaction more accurate and effective, and avoiding pollution and waste of the modifying substance solution.

[0048] (2) The present invention uses a scraping and spraying process to quantitatively introduce the initiator and the modifying substance solution onto the membrane surface in steps, reducing the adsorption time required for traditional dipping and ensuring a fixed content of the modifying substance on the membrane surface. This method is highly controllable and reproducible. By regulating 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 cross-linking reactions can further increase the density of the modified layer, improve its pore size screening performance and the stability of the modified membrane, and ultimately produce a monovalent selective cation exchange membrane with good stability and separation performance.

[0049] (3) The method for preparing a monovalent selective cation exchange membrane provided by the present invention is highly efficient, repeatable, controllable, and conveniently adjustable. It requires minimal reagents, produces minimal wastewater, and is low in cost. During the preparation process, the separation performance of the modified layer can be optimized by adjusting the scraping and spraying parameters. This provides a more flexible optimization process, facilitates the large-scale preparation of monovalent selective cation exchange membranes, and offers a higher degree of adaptability to different substrates. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0054] Figure 53. It is an infrared spectrum of the monovalent selective cation exchange membrane provided by Example 1 of the present invention and the cation exchange membrane provided by Comparative Example 1. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0056] The cation exchange membrane used in the examples and comparative examples of the present invention is produced by Hangzhou Lanran Technology Co., Ltd., and its model 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 comprises the following steps:

[0059] The cation exchange membrane was vacuum-adsorbed on the surface of a coating device, and a mixed benzene solution containing 0.1% (w / v) polysorbate 80 and 0.5% (w / v) dibenzoyl peroxide was coated on the surface of the cation exchange membrane 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% by mass of epigallocatechin gallate and 2% by mass of polyethyleneimine with a molecular weight of 10,000 Da was sprayed on the membrane for reaction. The pH value of the Tris-HCl buffer solution was 8, and the spraying amount was 0.8 L / m 2 The reaction temperature is 80°C, the reaction humidity is 75%, and the reaction time is 30 minutes. The modified membrane layer is thermally cured at 60°C for 20 minutes and then placed in a 1% by mass glutaraldehyde aqueous solution. The cross-linking reaction is carried out at 50°C for 15 minutes 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 comprises the following steps:

[0062] The cation exchange membrane was vacuum-adsorbed on the surface of a coating device, and a mixed ethanol solution containing 0.001% (w / v) sodium lauryl sulfate and 0.001% (w / v) di-tert-butyl peroxide was coated on the surface of the cation exchange 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% by mass of dopamine and 0.1% by mass of tris(2-aminoethyl)amine was sprayed for reaction. The pH value of the Tris-HCl buffer solution was 7, and the spraying amount was 0.1 L / m2 The reaction temperature is 60°C, the reaction ambient humidity is 90%, and the reaction time is 60 minutes. The modified membrane layer is thermally cured at 40°C for 30 minutes and then placed in a 0.001% by mass triethanolamine aqueous solution, and cross-linked at 25°C for 120 minutes 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 comprises the following steps:

[0065] The cation exchange membrane was vacuum-adsorbed on the surface of a coating device, and a mixed acetone solution containing 2% (w / v) sodium dodecylbenzenesulfonate and 1% (w / v) dibenzoyl peroxide was coated on the surface of the cation exchange membrane 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% by weight of catechin and 1% by weight of dicyandiamide was sprayed on the membrane for reaction. The pH value of the Tris-HCl buffer solution was 9, and the spraying amount was 1 L / m 2 The reaction temperature is 120°C, the reaction environment humidity is 60%, and the reaction time is 5 minutes. The modified membrane layer is thermally cured at 90°C for 5 minutes and then placed in a 2% by mass carbodiimide aqueous solution, and cross-linked at 60°C for 5 minutes to obtain the monovalent selective cation exchange membrane.

[0066] Example 4

[0067] 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 Example 1 is that, except that the thickness of the scraping is adjusted to 0.05 μm, the rest is the same as that of Example 1.

[0068] Example 5

[0069] 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 Example 1 is that, except that the thickness of the scraping is adjusted to 12 μm, the rest is the same as that of Example 1.

[0070] Example 6

[0071] 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 Example 1 is that, except that the coating speed is adjusted to 5 mm / s, the rest is the same as that of Example 1.

[0072] Example 7

[0073] 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 Example 1 is that, except that the coating speed is adjusted to 2050 mm / s, the rest is the same as that of Example 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 Example 1 is that, in addition to adjusting the spraying amount to 0.05 L / m 2 Except for this, the rest are 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 Example 1 is that, in addition to adjusting the spraying amount to 1.2 L / m 2 Except for this, the rest are the same as in Example 1.

[0078] Example 10

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

[0080] Example 11

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

[0082] Comparative Example 1

[0083] This comparative example provides a cation exchange membrane, which 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 difference between the preparation method of the monovalent selective cation exchange membrane and that of Example 1 is that polysorbate 80 is not added to the mixed benzene solution. The rest is the same as that of Example 1.

[0086] Comparative Example 3

[0087] This comparative example provides a monovalent selective cation exchange membrane. The difference between the preparation method of the monovalent selective cation exchange membrane and that of Example 1 is that the scraping is adjusted to the first immersion, and the time of the first immersion is 30 minutes; the spraying is adjusted to the second immersion, the temperature of the second immersion is 80°C, the ambient humidity is 75%, and the time is 30 minutes. The rest is the same as in Example 1.

[0088] Comparative Example 4

[0089] This comparative example provides a monovalent selective cation exchange membrane. The method for preparing the monovalent selective cation exchange membrane differs from that in Example 1 in that the scraping step is not provided, i.e., a mixed benzene solution of polysorbate 80 and dibenzoyl peroxide is not introduced. The rest is the same as in Example 1.

[0090] Comparative Example 5

[0091] This comparative example provides a monovalent selective cation exchange membrane. The method for preparing the monovalent selective cation exchange membrane differs from that in Example 1 in that no dibenzoyl peroxide is added to the mixed benzene solution, and no epigallocatechin gallate is added to the mixed Tris-HCl buffer solution. The remaining steps are the same as in Example 1.

[0092] Comparative Example 6

[0093] This comparative example provides a monovalent selective cation exchange membrane. The difference between the preparation method of the monovalent selective cation exchange membrane and that of Example 1 is that the obtained modified membrane layer is no longer placed in a glutaraldehyde aqueous solution for cross-linking reaction after being heat-cured at 60°C for 20 minutes, and the monovalent selective cation exchange membrane is directly obtained. The rest is the same as that of Example 1.

[0094] Comparative Example 7

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

[0096] Performance Testing

[0097] The optical image of the monovalent selective cation exchange membrane provided in Example 1 is as follows: Figure 1 As shown, the optical image of the cation exchange membrane provided in Comparative Example 1 is as shown Figure 2 As shown in the figure, it can be seen that the surface color of the modified monovalent selective cation exchange membrane is darker than that of the base membrane, 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 as follows: Figure 3 As shown, the SEM image of the cation exchange membrane provided in Comparative Example 1 is as shown Figure 4 As shown in the figure, it can be seen from the comparison that a uniform and dense modified layer is generated 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 as follows: Figure 5 As shown, compared with the base membrane of Comparative Example 1, the monovalent selective cation exchange membrane has a -1 -3600cm -1 The stretching vibration peaks of OH and NH in the region are enhanced, indicating that a modified layer rich in OH and NH is formed on the surface of the base membrane. -1 The absorption peaks on the left and right are also significantly enhanced, which is attributed to the quinone structure formed by the oxidation of the catechol group and the enhancement of the bending vibration peak of the C=N bond generated by the reaction of catechol with the amino group, indicating 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-chamber electrodialysis device. The cathode chamber contains a 0.5 mol / L NaCl solution, the concentrated chamber contains a mixed solution of LiCl and MgCl2, with LiCl and MgCl2 concentrations of 0.1 mol / L and 0.5 mol / L, respectively (simulating the lithium-magnesium ratio in brine), and the dilute chamber contains a 0.01 mol / L LiCl solution. The applied current is 10 mA / cm 2 After running for 2 hours, the Li + Mg 2+ concentration, Li-Mg selectivity coefficient and ion flux J i Calculate according to the following formula and the results are shown in Table 1.

[0101]

[0102] In formula (1): J i is the ion flux, in mol / m 2 h; t is the test time, unit is h; A m To test the effective membrane area, the unit is m 2 ; C tis 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 recorded as The measured magnesium ion flux is recorded as

[0103] In formula (2): C t Li is the Li in the concentration chamber after 2 hours of operation + Concentration, unit is mol / L; C0 Li is the Li of the concentration chamber before operation + Concentration, unit is mol / L; C t Mg is the Mg content in the concentration chamber after 2 hours of operation 2+ Concentration, unit is mol / L; C0 Mg is the Mg content of the concentration chamber before operation 2+ Concentration, unit is mol / L; C Li + is the initial Li of the light room + Concentration, unit is mol / L, C Mg 2+ is the initial Mg in the dilute chamber 2+ Concentration, unit is mol / L.

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

[0105]

[0106] In formula (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 + valence, i.e. +1; F is the Faraday constant, which is 26.801A·h / mol; V0 is the initial volume of the concentrated solution, in L; V t It is the volume of the concentration chamber solution after running for 2 hours, in L.

[0107] Table 1

[0108]

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

[0110] (1) From the comparison of Examples 1-3, it can be seen that using different initiators and surfactants and controlling various reaction parameters within a limited range can also effectively promote the reaction and make the obtained modified membranes have good selectivity.

[0111] (2) By comparing Example 1 with Examples 4, 5, 8, and 9, it can be seen that the separation performance of the modified membrane obtained varies depending on the thickness of the initiator scraping and the amount of the modifying solution sprayed. If the thickness of the initiator scraping is too small or the amount of the modifying solution sprayed is too low, the modification is insufficient or the modified layer is discontinuous, which will cause magnesium ions to pass preferentially and reduce selectivity. If the thickness of the initiator scraping is too large or the amount of the modifying solution sprayed is too high, the reaction degree and thickness of the modified layer will be enhanced, the pore size screening of the modified layer will be improved, and the selectivity will be higher, but at the same time the ion flux will also be reduced.

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

[0113] (4) It can be seen from Examples 1, 10 and 11 that the mass ratio of catechol compounds to amine compounds needs to be controlled within a reasonable range. If the mass ratio of amine substances is too high, most of the polyethyleneimine that does not participate in the reaction on the membrane will fall off, while if the mass ratio is too low, more negatively charged catechol polymer layers will appear on the membrane, resulting in poor lithium-magnesium separation.

[0114] (5) From the comparison between Example 1 and Comparative Examples 1 and 2, it can be seen that the modified membrane prepared by adding a 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 modifying substance, enhances the degree of modification of the membrane, and at the same time, the surfactant can improve the hydrophilicity of the modified membrane to a certain extent, making the ion flux of the membrane higher.

[0115] (6) From the comparison between Example 1 and Comparative Example 3, it can be seen that compared with impregnation, the use of scraping and spraying can quickly and efficiently introduce the initiator and the modifying substance into the membrane surface, 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) Comparison of Example 1 with Comparative Example 4 shows that the modified membrane without an initiator has poor separation properties. This is because the initiator can significantly increase the reaction rate of catechol compounds and amine compounds in a short period of time, allowing the modified layer to be deposited on the membrane surface more quickly and effectively, resulting in the modified membrane having good selectivity and good ion flux.

[0117] (8) Comparison between Example 1 and Comparative Example 5 shows that after crosslinking and quaternization of the membrane surface with a simple amine compound, the modified membrane exhibits certain separation performance. However, the separation performance is limited, and due to the lack of the dispersing effect of the catechol compound, the crosslinking effect between the amine and the crosslinking agent is relatively strong, resulting in a relatively low ion flux through the modified membrane.

[0118] (9) From the comparison between Example 6 and Comparative Example 6, it can be seen that the separation effect of the modified membrane is the synergistic effect of pore size screening 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) From the comparison between Example 6 and Comparative Example 7, it can be seen that the use of a water-soluble initiator will cause it to diffuse into the solution in large quantities, thereby causing the reaction to occur in the solution and occupying the ion exchange channel, resulting in a significant reduction in the ion flux and the inability of the modified substance to be effectively deposited on the membrane surface.

[0120] In summary, the method for preparing a monovalent selective cation exchange membrane provided by the present invention enhances the diffusion efficiency of the non-metallic ion initiator and the water-soluble modifier at the membrane interface by adding a surfactant to the non-metallic ion initiator. The initiator induces the oxidation of the catechol group to oxidized quinone, promoting the reaction of catechol compounds and amine compounds on the surface of the base membrane. The non-water solubility of the non-metallic ion initiator also prevents its large-scale diffusion into the solution, causing the reaction to occur in the solution, making the reaction more accurate and effective, and avoiding contamination and waste of the modifier solution. At the same time, the non-metallic ion initiator does not occupy the ion exchange channel, and the surfactant can also increase the hydrophilicity of the modified membrane, so that it has a higher ion flux.

[0121] The present invention uses a doctor blade and spray coating process to quantitatively introduce initiator and modifier solutions onto the membrane surface in a step-by-step manner. This reduces the adsorption time required by traditional dipping methods, ensures a constant content of the modifier on the membrane surface, and offers strong controllability and high reproducibility. By regulating the doctor blade coating thickness and spraying amount, the performance of the subsequent modified membrane layer can be precisely controlled. Thermal initiation induces a surface reaction to form an adherent and stable modified membrane layer. Subsequent thermal curing and cross-linking reactions further increase the density of the modified layer, improving its pore size screening performance and the stability of the modified membrane, ultimately yielding a monovalent selective cation exchange membrane with excellent stability and separation performance.

[0122] The method for preparing a monovalent selective cation exchange membrane provided by the present invention is highly efficient, repeatable, controllable, and easily adjustable. It requires minimal reagents, produces minimal waste, and is low in cost. During the preparation process, the separation performance of the modified layer can be optimized by adjusting the doctor blade and spray coating parameters. This provides a more flexible optimization process, facilitates the large-scale production of monovalent selective cation exchange membranes, and offers a higher degree of adaptability to different substrates.

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

Claims

1. A method for preparing a monovalent selective cation exchange membrane, characterized in that: The preparation method comprises the following steps: A non-metallic ion initiator solution containing a surfactant is scraped onto the surface of the cation exchange membrane, and then a mixed aqueous solution of a catechol compound and an amine compound is sprayed for reaction. The resulting modified membrane layer is thermally cured and then placed in a crosslinker solution for a crosslinking reaction to obtain the monovalent selective cation exchange membrane.

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 or 2, characterized in that The surfactant includes at least one of sodium lauryl sulfate, sodium dodecylbenzene sulfonate and polysorbate surfactant; Preferably, the non-metallic ion initiator in the non-metallic ion initiator solution comprises dibenzoyl peroxide and / or di-tert-butyl peroxide; Preferably, the solvent in the non-metal ion initiator solution includes at least one of ethanol, benzene, toluene and acetone.

4. The preparation method according to any one of claims 1 to 3, characterized in that The specific steps of the scraping coating include: vacuum adsorbing the cation exchange membrane on the surface of the scraping equipment, scraping the non-metallic ion initiator solution containing a surfactant on the surface of the cation exchange membrane with a scraper, and then drying; Preferably, the coating thickness is 0.1-10 μm, and the speed is 10-2000 mm / s.

5. The preparation method according to any one of claims 1 to 4, characterized in that In the mixed aqueous solution of the catechol compound and the amine compound, the mass percentage of the catechol compound is 0.01%-5%, and the mass percentage of the amine compound is 0.01%-5%; Preferably, in the mixed aqueous solution of the catechol compound and the amine compound, the mass ratio of the catechol compound to the amine compound is (0.1-5):

1.

6. The preparation method according to any one of claims 1 to 5, characterized in that The solvent in the mixed aqueous solution of the catechol compound and the amine compound is a Tris-HCl buffer solution with a pH value of 7-9; Preferably, the catechol compound includes at least one of catechol, catechin, epigallocatechin, epigallocatechin gallate, dopamine, 3,4-dihydroxyphenylalanine, pyrogallol and protocatechuic acid; Preferably, the amine compound includes at least one of piperazine, pyrrole, aniline, diisopropylamine, polyethyleneimine, dicyandiamide, m-phenylenediamine, melamine, tris(2-aminoethyl)amine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine.

7. The preparation method according to any one of claims 1 to 6, characterized in that The spraying amount is 0.1-1L / m 2 ; Preferably, the reaction temperature is 60-120° C., the reaction environment humidity is 60%-90%, and the reaction time is 5-60 minutes.

8. The preparation method according to any one of claims 1 to 7, characterized in that The temperature of the thermal curing is 40-90°C; Preferably, the thermal curing time is 5-30 minutes.

9. The preparation method according to any one of claims 1 to 8, characterized in that In the cross-linking agent solution, the mass percentage of the cross-linking agent is 0.001%-2%; Preferably, the crosslinking agent in the crosslinking agent solution includes at least one of epichlorohydrin, carbodiimide, triethanolamine, glyoxal and glutaraldehyde; Preferably, the solvent in the cross-linker solution comprises water; Preferably, the cross-linking reaction temperature is 25-60° C., and the time is 5-120 min.

10. A monovalent selective cation exchange membrane, characterized in that The monovalent selective cation exchange membrane is prepared by the method for preparing the monovalent selective cation exchange membrane according to any one of claims 1 to 9.

Images