Monovalent selective ion exchange membrane as well as preparation method and application thereof

Abstract

The invention provides a monovalent selective ion exchange membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing a functional material; (2) preparing the functional material into an ion exchange membrane by adopting a solvent evaporation method; and (3) further performing secondary surface graft polymerization on the ion exchange membrane to prepare the monovalent selective ion exchange membrane. The monovalent selective ion exchange membrane prepared by the preparation method disclosed by the invention not only can effectively avoid the defects of high membrane resistance and mutual limitation between selectivity and flux of a homogeneity selective ion exchange membrane, but also can solve the problem of lack of stable chemical bonds between a modified layer and a base membrane when the selective ion exchange membrane is prepared by using a surface modification method.

Description

Technical Field

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

[0002] At present, homogeneous selective ion exchange membranes have the advantage of high stability, but have problems of high membrane resistance and poor separation performance. In contrast, asymmetric selective ion exchange membranes improve the selective separation performance of the membrane by constructing a separation skin layer, and have the advantages of low resistance and high selectivity. However, there is a lack of stable chemical bond connection between the surface modification layer and the base membrane of the membranes prepared by common surface modification methods (such as electrostatic deposition, electrodeposition and layer-by-layer self-assembly, etc.), resulting in weak stability. During long-term use, the rejection rate of multivalent ions will be significantly reduced, and the separation performance will also decline.

[0003] The sieving mechanism of monovalent selective ion exchange membranes mainly includes pore size sieving effect, electrostatic repulsion effect and hydration energy difference. At present, common preparation methods of monovalent selective ion exchange membranes include blending, covalent cross-linking and deposition method, layer-by-layer self-assembly method, surface grafting method, interfacial polymerization, etc. Among them, blending and covalent cross-linking methods mainly improve the separation performance of the membrane by regulating the overall structure of the membrane, increasing the density or hydrophilicity / hydrophobicity of the membrane. However, this process often significantly increases the resistance of the membrane. The deposition method forms a film on the substrate surface through the interaction between substances or between substances and fields, mainly including co-deposition and electrodeposition. However, since the modification layer is combined with the base membrane through electrostatic adsorption / physical force, the stability of the modification layer is poor and it is easy to fall off from the base membrane. The layer-by-layer assembly method forms an ultrathin modification layer by alternately adsorbing cation and anion layers on the surface of the ion exchange membrane. The modification layer can enhance the electrostatic interaction and the hydration radius repulsion of multivalent ions, thereby improving the selective permeability of the membrane. However, the disadvantage of this preparation method is that the relatively weak physical interaction between the polyelectrolyte and the ion exchange membrane easily causes poor stability, and the preparation of the multi-layer polyelectrolyte ion exchange membrane is a cumbersome process, and the thickness of each layer cannot be accurately adjusted, resulting in a decrease in the permeability of monovalent ions.

[0004] The surface grafting method refers to treating the membrane surface with chemical methods, high-energy rays or plasma to generate reactive sites and free radicals on the membrane surface, and then reacting them with modifier monomers with excellent properties to form a grafted layer in the form of covalent bonds. A stable covalent bond is formed between the modified layer and the membrane surface, which can effectively enhance the stability of the modified layer and extend the service life of the membrane. At the same time, grafting modification is carried out on the membrane surface, and the internal skeleton structure of the modified ion exchange membrane is not damaged. Among them, compared with the high-energy ray and plasma treatment methods, the chemical modification process has become a research focus because of its simple operation and strong operability. In addition, we found that the surface grafting of the membrane is only a reaction between chemical bonds. Although functional groups can be grafted onto the membrane surface through chemical bonds to effectively regulate the charge property of the membrane surface, if we want to further improve the separation performance, we still need to rely on the dense skin layer of the membrane.

[0005] As one of the commonly used membrane surface chemical modification methods, interfacial polymerization (IP) can also form a polymer thin film on the membrane surface through a polymerization reaction. It is a polymerization reaction that occurs at the solvent interface of two immiscible phases (aqueous phase, organic phase) to form a polyamide thin film. This method is mainly used to prepare separation membranes with high selectivity and density. The polymer membrane layer is thin and uniform. However, this dense skin layer is usually formed on the surface of the base membrane in the form of physical embedding, and its stability is relatively weak. If the dense polyimide layer is grafted onto the membrane surface by the surface grafting method, it is expected to obtain a dense polyamide layer with high stability bonded by chemical bonds.

[0006] Xiao et al. proposed a new "covalent bond triggered self-assembly" (CBTS) strategy to construct a chemically bonded carboxylic acid polymer layer containing quaternary amine groups and carboxyl groups to achieve high anion permeability and ionic charge permeability selectivity. The surface functional polymer layer is chemically bonded to the substrate by the Menshutkin reaction between the tertiary amine group in the graft copolymer and the bromomethyl group in the base membrane, and a polymer membrane with strong stability is obtained. The schematic diagram is shown in Figure 1.4. In the ED test, the DMC4 membrane with the highest carboxyl content has the highest Cl - / SO4 2- permeation selectivity (7.31) and high Cl - flux (5.18×10 - 8 mol·cm -2 ·s -1), almost twice higher than that of commercial NEOSETA ACS membranes. In addition, high limiting current density and excellent desalination performance are additional features of membranes fabricated for large-scale industrial processes, but their preparation... (Xiao X, Shehzad M A, Yasmin A, et al. Anion permselective membranes with chemically-bound carboxylic polymer layer for fast anion separation[J]. Journal of Membrane Science, 2020, 614:118553) However, the monovalent-selective membranes prepared in this prior art are purchased base membranes with bromomethyl groups, grafted with a layer of polymer, and their densification needs to be further improved.

[0007] Chen et al. developed a simple sequential interfacial polymerization (SIP) method to regulate the surface charge and pore size of electro-nanofiltration membranes (ENFMs). Due to the electrostatic repulsion and pore size sieving effects, ENFMs were endowed with excellent selectivity. As the molecular weight of PEI increased, the Zeta potential on the membrane surface changed from negative to positive, and the pore size of the membrane decreased. The optimal ENFM had excellent selectivity (16.55) and high lithium flux (3.08×10 -8 mol·cm -2 ·s -1 ). (Chen J, Wang J, Ji Z-Y, et al. Electro-nanofiltration membranes with high Li + / Mg 2+ selectivity prepared via sequential interfacial polymerization[J].

[0008] Desalination, 2023, 549:116312.) However, the method for preparing monovalent-selective membranes in this prior art is to construct a polyamide skin layer on the ultrafiltration membrane, and the connection between the modified layer and the base membrane is physical embedding, and its stability needs to be further improved.

[0009] Therefore, in the art, there is a desire to develop a monovalent-selective ion exchange membrane with low membrane resistance, high separation performance, and high stability. Summary of the Invention

[0010] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a monovalent-selective ion exchange membrane, its preparation method and application.

[0011] The present invention combines two methods, namely surface grafting method and interfacial polymerization method, and grafts a dense polyamide layer on the membrane surface by surface grafting. The dense polyamide cortex solves the limitation of the surface grafting method in further improving selectivity; the cortex and the base membrane are bonded by chemical bonds through surface grafting, improving the stability of the monovalent ion exchange membrane. To achieve such an effect, a functionalized membrane material is also required, which needs to meet two basic conditions: having cation exchange groups or anion exchange groups; having groups that can be activated for subsequent reaction with charged polyelectrolytes to form the cortex. Therefore, the present invention is an innovation in both the material and preparation method of the monovalent selective ion exchange membrane.

[0012] To achieve the purpose of this invention, the following technical solutions are adopted in the present invention:

[0013] In the first aspect, the present invention provides a preparation method of a monovalent selective ion exchange membrane, and the preparation method includes the following steps:

[0014] (1) Mix a first monomer, a second monomer, an alkaline substance, a solvent, and an azeotropic agent, react, raise the temperature, and continue the reaction to obtain a polymer product solution, and perform post-treatment to obtain a functionalized material;

[0015] (2) Mix the functionalized material obtained in step (1), an optional additive, and a solvent to obtain a casting solution, coat the casting solution on a substrate, and dry to obtain an ion exchange membrane;

[0016] (3) Dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS) in 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution to prepare an EDC / NHS carboxyl activation solution, soak the ion exchange membrane obtained in step (2) in the carboxyl activation solution for reaction, after the reaction is completed, wash the membrane surface, then perform a second reaction on the membrane with an aqueous monomer solution, then perform a third reaction on the membrane with an oil-phase monomer solution, then perform a fourth reaction on the membrane with an aqueous solution of the aqueous monomer, and perform heat treatment to obtain the monovalent selective ion exchange membrane;

[0017] Among them, the first monomer includes a compound having a structure shown in the following formula I or formula II:

[0018]

[0019] In formula I and formula II, R1 and R2 are halogens (such as -F, -Cl, or -Br, etc.);

[0020] R3 and R4 are each independently a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms (such as C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10), -SO3H (sulfonic acid group), -SO3M, or -COOH (carboxyl group), and M is Na or K;

[0021] m and n are each independently an integer from 0 to 4, such as 0, 1, 2, 3 or 4;

[0022] x and y are each independently an integer from 1 to 3, such as 1, 2 or 3;

[0023] The second monomer includes a compound having a structure shown in the following formula III or formula IV:

[0024]

[0025] In formula III and formula IV, R5, R6, R7, and R8 are each independently a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms, -SO3H, -SO3M, or -COOH, and M is Na or K;

[0026] a, b, p, and q are each independently an integer from 0 to 4, such as 0, 1, 2, 3 or 4;

[0027] Moreover, at least one of the first monomer and the second monomer contains -COOH.

[0028] What is obtained by the above method is a monovalent-selective cation exchange membrane. The preparation of the monovalent-selective cation exchange membrane in the present invention is mainly divided into three parts: (1) preparing a functionalized material; (2) preparing an ion exchange membrane from the functionalized material by the solvent evaporation method; (3) further performing EDC / NHS amidation and secondary surface graft polymerization on the ion exchange membrane to prepare a monovalent-selective cation exchange membrane.

[0029] In order to solve the problem of the lack of stable chemical bonds between the modified layer and the base membrane, the present invention adopts a preparation method combining a novel functional membrane material and surface grafting. First, a novel carboxyl, sulfonic acid or amino-functionalized membrane material is synthesized, and then a stable countercharge cortex is constructed by the reaction of the functional groups with a charged polymer, aiming to increase the chemical bond connection between the surface modified layer and the base membrane and develop a monovalent-selective ion exchange membrane with high stability, good mono- and polyvalent selectivity, excellent mechanical properties and low membrane resistance. Therefore, the advantages of the present invention are that it not only effectively avoids the disadvantages of high membrane resistance, mutual limitation between selectivity and flux of homogeneous selective exchange membranes, but also can solve the problem of the lack of stable chemical bonds between the modified layer and the base membrane when preparing a selective ion exchange membrane by the surface modification method.

[0030] Preferably, the first monomer comprises any one or a combination of at least two of the following compounds:

[0031]

[0032] Preferably, the first monomer comprises 4,4'-difluorobenzophenone (DFBP).

[0033] Preferably, the second monomer comprises any one or a combination of at least two of the following compounds:

[0034]

[0035] Preferably, the second monomer comprises 4,4-bis(4-hydroxyphenyl) valeric acid (BPVA) and / or potassium hydrogensulfate of hydroquinone (HSAP).

[0036] Preferably, the molar ratio of the first monomer to the second monomer is (0.8 - 1.2):1, such as 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, etc.

[0037] Preferably, the basic substance comprises potassium carbonate.

[0038] Preferably, the molar ratio of the first monomer to the basic substance is 1:(1.5 - 3), such as 1:1.5, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, etc.

[0039] Preferably, the solvent in step (1) comprises any one or a combination of at least two of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), sulfolane, N,N-dimethylacetamide (DMAc).

[0040] Preferably, the azeotropic agent in step (1) comprises benzene and / or toluene.

[0041] Preferably, the temperature of the reaction in step (1) is 130 - 150 °C, such as 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, etc., and the reaction time is 2 - 5 h, such as 2 h, 3 h, 4 h, 5 h, etc.

[0042] Preferably, the temperature increase in step (1) is to 160 - 170 °C, such as 160 °C, 165 °C, 170 °C, etc.

[0043] Preferably, the time for the continued reaction in step (1) is 5 - 8 h, such as 5 h, 6 h, 7 h, 8 h, etc.

[0044] Preferably, the post-treatment in step (1) includes precipitation, acidification, washing, and drying.

[0045] Preferably, the precipitant used for the precipitation includes isopropanol.

[0046] Preferably, the reagent used for the acidification includes dilute hydrochloric acid.

[0047] Preferably, the temperature for the drying is 70 - 90 °C, such as 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, etc., and the time for the drying is 20 - 30 h, such as 20 h, 22 h, 24 h, 25 h, 26 h, 28 h, 30 h, etc.

[0048] Preferably, step (1) is carried out under an inert atmosphere.

[0049] Preferably, the inert atmosphere includes nitrogen.

[0050] Preferably, the solvent in step (2) includes any one or a combination of at least two of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), sulfolane, and dimethylacetamide (DMAc).

[0051] Preferably, in the casting solution of step (2), the concentration of the functionalized material is 5 wt% - 20 wt%, such as 5 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 20 wt%, etc.

[0052] Preferably, the additive in step (2) includes a pore-forming agent.

[0053] Preferably, the pore-forming agent includes any one or a combination of at least two of polyvinylpyrrolidone (PVP K30 ), polyethylene glycol (PEG), sodium chloride (NaCl), and ionic liquids.

[0054] Preferably, in the casting solution of step (2), the concentration of the additive is 0 - 30 wt%, such as 0 (i.e., not added), 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.

[0055] Preferably, the coating in step (2) includes knife coating.

[0056] Preferably, the thickness of the knife used for the knife coating is 200 - 500 μm, such as 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc.

[0057] Preferably, the substrate in step (2) includes nylon mesh cloth.

[0058] Preferably, the temperature of the drying in step (2) is 60 - 80°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the drying time is 10 - 24h, such as 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc.

[0059] Preferably, the temperature of the reaction in step (3) is 30 - 50°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, etc., and the reaction time is 20 - 30h, such as 20h, 22h, 24h, 25h, 26h, 28h, 30h, etc.

[0060] Preferably, the aqueous monomers in the aqueous monomer solution in step (3) include any one or a combination of at least two of polyethyleneimine (PEI), piperazine, m - phenylenediamine, p - phenylenediamine, hexamethylenediamine, quaternized polyethyleneimine, quaternized diaminopyridine, and quaternized tetra - hydroxyethyl imidazole.

[0061] Preferably, the solvent in the aqueous monomer solution in step (3) includes PBS buffer solution.

[0062] Preferably, in the aqueous monomer solution in step (3), the concentration of the aqueous monomers is 1wt% - 3wt%, such as 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, etc.

[0063] Preferably, the temperature of the second reaction in step (3) is 40 - 60°C, such as 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the time of the second reaction is 40 - 60h, such as 40h, 42h, 44h, 45h, 46h, 48h, 50h, 52h, 54h, 55h, 56h, 58h, 60h, etc.

[0064] Preferably, the second reaction of the membrane with the aqueous monomer solution in step (3) specifically includes: soaking the membrane in the aqueous monomer solution for the second reaction, or, after fixing the membrane, bringing it into single - side contact with the aqueous monomer solution for the second reaction.

[0065] Preferably, after the second reaction in step (3), it further includes the step of scraping off the moisture on the membrane surface or heating to evaporate the moisture.

[0066] Preferably, the oil - phase monomers in the oil - phase monomer solution in step (3) include any one or a combination of at least two of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and tetracarbonyl chloride.

[0067] Preferably, the solvent in the oil - phase monomer solution in step (3) includes n - heptane.

[0068] Preferably, in the oil phase monomer solution in step (3), the concentration of the oil phase monomer is 0.1 wt% - 2 wt%, such as 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, etc.

[0069] Preferably, the time for the third reaction in step (3) is 0.5 - 5 min, such as 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.

[0070] Preferably, the third reaction of the membrane with the oil phase monomer solution in step (3) specifically includes:

[0071] Immersing the membrane in the oil phase monomer solution for the third reaction, or, after fixing the membrane, bringing it into single-sided contact with the oil phase monomer solution for the third reaction.

[0072] Preferably, the aqueous solution of the aqueous phase monomer in step (3) is prepared by the following method:

[0073] Mixing 2-bromoethylamine hydrobromide, the aqueous phase monomer, and deionized water, and heating to obtain the aqueous solution of the aqueous phase monomer.

[0074] Preferably, the mass ratio of 2-bromoethylamine hydrobromide, the aqueous phase monomer, and deionized water is 1:(8 - 12):(80 - 120), where 8 - 12 can be, for example, 8, 9, 10, 11, 12, etc., and 80 - 120 can be, for example, 80, 90, 100, 110, 120, etc.

[0075] Preferably, the heating temperature is 70 - 90 °C, such as 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, etc., and the heating time is 10 - 14 h, such as 10 h, 11 h, 12 h, 13 h, 14 h, etc.

[0076] Preferably, the temperature for the fourth reaction in step (3) is 10 - 30 °C, such as 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc., and the time for the fourth reaction is 2 - 10 min, such as 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0077] Preferably, the fourth reaction of the membrane with the aqueous solution of the aqueous phase monomer in step (3) specifically includes:

[0078] The fourth reaction is carried out by immersing the membrane in an aqueous solution of the aqueous monomer, or, after the membrane is fixed, the fourth reaction is carried out by bringing it into single-sided contact with the aqueous solution of the aqueous monomer.

[0079] Preferably, the temperature of the heat treatment in step (3) is 70-90 °C, such as 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, etc., and the time of the heat treatment is 8-12 min, such as 8 min, 9 min, 10 min, 11 min, 12 min, etc.

[0080] In a second aspect, the present invention provides another method for preparing a monovalent selective ion exchange membrane, and the preparation method includes the following steps:

[0081] (A) Mix a first monomer, a second monomer, a basic substance, a solvent, and an azeotropic agent, react, raise the temperature, continue to react to obtain a polymer product solution, and perform post-treatment to obtain a functional material;

[0082] Among them, the difference between the first monomer and the first monomer in claim 1 is only that R3 and R4 are each independently a linear or branched alkyl or amino group having 1 to 10 carbon atoms;

[0083] The difference between the second monomer and the second monomer in claim 1 is only that R5, R6, R7, and R8 are each independently a linear or branched alkyl or amino group having 1 to 10 carbon atoms;

[0084] And at least one of the first monomer and the second monomer contains an amino group;

[0085] (B) Mix the functional material obtained in step (1), an optional additive, and a solvent to obtain a casting solution, coat the casting solution on a substrate, and dry it to obtain an ion exchange membrane;

[0086] (C) Immerse the ion exchange membrane obtained in step (2) in an oil-phase monomer solution for the first reaction, then immerse the membrane in an aqueous monomer solution for the second reaction, then immerse the membrane in the oil-phase monomer solution for the third reaction, and perform heat treatment to obtain the monovalent selective ion exchange membrane.

[0087] What is obtained by using the preparation method of the second aspect is a monovalent selective anion ion exchange membrane. The preparation of the monovalent selective anion exchange membrane in the present invention is mainly divided into three parts: (1) preparing a functional material; (2) preparing an ion exchange membrane from the functional material by a solvent evaporation method; (3) further performing secondary surface graft polymerization on the ion exchange membrane to prepare a monovalent selective anion exchange membrane.

[0088] Preferably, the time of the first reaction in step (C) is 0.5 - 5 min, such as 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.

[0089] Preferably, the temperature of the second reaction in step (C) is 10 - 30 °C, such as 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc., and the time of the second reaction is 2 - 10 min, such as 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0090] Preferably, after the second reaction in step (C), it further includes the steps of scraping off the moisture on the surface of the film or heating to evaporate the moisture.

[0091] Preferably, the time of the third reaction in step (C) is 0.5 - 5 min, such as 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.

[0092] Preferably, the other parameters in steps (A) to (C) are the same as those in the first aspect.

[0093] In the third aspect, the present invention provides a monovalent selective ion exchange membrane, which is prepared by the preparation method as described in the first aspect or the preparation method as described in the second aspect.

[0094] In the fourth aspect, the present invention provides an application of the monovalent selective ion exchange membrane as described in the third aspect in monovalent and polyvalent ion exchange.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] The present invention adopts a preparation method combining a novel functional membrane material and surface grafting. First, a novel carboxyl, sulfonic acid or amino functionalized membrane material is synthesized, and then a stable countercharge skin layer is constructed by the reaction of functional groups and charged polymers, aiming to increase the chemical bond connection between the surface modification layer and the base membrane, and develop a monovalent selective ion exchange membrane with high stability, good monovalent and polyvalent selectivity, excellent mechanical properties and low membrane resistance. Therefore, the advantages of the present invention are not only effectively avoiding the disadvantages of high membrane resistance, mutual limitation between selectivity and flux of homogeneous selective exchange membranes, but also solving the problem of lack of stable chemical bonds between the modification layer and the base membrane when preparing selective ion exchange membranes by the surface modification method. Description of the Drawings

[0097] Figure 1It is the Fourier transform infrared spectrum of the carboxyl / sulfonated functionalized polyether ether ketone material obtained in step (1) of Examples 1-3 of the present invention.

[0098] Figure 2 It is the test result graph of the cation migration number of the cation exchange membrane obtained in step (2) of Examples 1-4 of the present invention and the commercial CGU.

[0099] Figure 3 It is the test result graph of the separation performance of the monovalent selective ion exchange membrane prepared in Examples 1-4 of the present invention.

[0100] Figure 4 It is the test result graph of the ion flux of the monovalent selective ion exchange membrane prepared in Examples 1-4 of the present invention. Detailed implementation manners

[0101] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0102] Example 1

[0103] In this example, a preparation method of a monovalent selective ion exchange membrane (specifically a polyether ether ketone monovalent selective cation exchange membrane) is provided. The preparation method includes the following steps:

[0104] (1) Synthesis of carboxyl / sulfonated functionalized polyether ether ketone (CPEEK 50 -S 50 ):

[0105] Under a nitrogen atmosphere, DFBP (11.35 g, 0.052 mol), BPVA (7.16 g, 0.025 mol), HSAP (5.71 g, 0.025 mol), K2CO3 (13.82 g, 0.1 mol), DMSO (180 mL) and toluene (20 mL) are added to a four-necked flask. The mixture is heated to 140 °C and reacted for 4 h until the water is completely separated. Subsequently, the temperature is raised to 165 °C and the reaction is continued for 6 h to obtain a polymer product solution. After cooling, the polymer product solution is poured into a mixed solution of isopropanol and dilute hydrochloric acid, allowed to stand for 12 h, and the adsorbed dilute hydrochloric acid is washed away with distilled water. Finally, it is placed in a vacuum oven and dried at 80 °C for 24 h to obtain a pure carboxyl / sulfonated functionalized polyether ether ketone material (denoted as CPEEK 50 -S 50 ).

[0106] The synthesis route is as follows:

[0107]

[0108] (2) Prepare the cation exchange membrane by the solvent evaporation method: Dissolve the CPEEK 50 -S 50 polymer material in N-methylpyrrolidone (NMP) at room temperature and stir for 24 h to obtain a uniform casting solution (where the concentration of the CPEEK 50 -S 50 polymer material is 10 wt%). After standing for 12 h to remove bubbles, use a 200-μm doctor blade to scrape the casting solution onto a nylon mesh cloth placed on the surface of a glass plate, and then dry it in a drying oven at 60 °C for 24 h to evaporate the solvent. Finally, peel the film off the glass plate to obtain the cation exchange membrane (denoted as MC 50 -S 50 ).

[0109] (3) Prepare the monovalent selective cation exchange membrane (MC 50 -S 50 ) based on the cation exchange membrane MC 50 -S 50 prepared in (2) by EDC / NHS amidation and secondary surface graft polymerization.

[0110] a. EDC / NHS amidation reaction: Dissolve 4 mmol·L -1 of EDC·HCl and 10 mmol·L -1 of NHS in 10 mmol·L -1 of MES buffer solution to prepare an EDC / NHS carboxyl activation solution. Immerse MC 50 -S 50 in the carboxyl activation solution and react at 40 °C for 24 h. After the reaction, wash the membrane surface 3 times with deionized water. Subsequently, immerse the membrane in a PBS buffer solution (pH = 7.5, 8 g NaCl, 0.2 g KCl, 1.44 g Na2HPO4, 0.24 g KH2PO4) containing 2 wt% PEI600 and react at 50 °C for 48 h to construct an amine layer on the membrane surface.

[0111] b. Membrane preparation: Fix the MC 50 -S 50 after EDC / NHS amidation on an acrylic plate and scrape off the excess water on the membrane surface. Immerse the membrane in an oil phase solution (a n-heptane solution containing 0.1 wt% TMC) for 1 min, and then pour 20 mL of the aqueous solution of QPEI onto the membrane surface and react for 2 min to construct a positively charged dense skin layer. Finally, heat-treat the prepared membrane at 80 °C for 10 min to obtain the monovalent selective ion exchange membrane (denoted as MC 50 -S 50-PA), and store it in deionized water for later use.

[0112] Among them, the preparation of the QPEI solution: Add 2-bromoethylamine hydrobromide, PEI750k, and deionized water (mass ratio 1:10:100) into a 50 mL beaker, place it on a magnetic stirrer at 80 °C and heat for 12 h to obtain the QPEI solution.

[0113] Example 2

[0114] The difference between this example and Example 1 is only that in step (1), the molar amount of BPVA is 0.0375 mol (the mass amount is adaptively changed), the molar amount of HSAP is 0.0125 mol (the mass amount is adaptively changed), and the products of steps (1)-(3) are respectively denoted as CPEEK 75 -S 25 、MC 75 -S 25 、MC 75 -S 25 -PA.

[0115] Example 3

[0116] The difference between this example and Example 1 is only that in step (1), the molar amount of BPVA is 0.0125 mol (the mass amount is adaptively changed), the molar amount of HSAP is 0.0375 mol (the mass amount is adaptively changed), and the products of steps (1)-(3) are respectively denoted as CPEEK 25 -S 75 、MC 25 -S 75 、MC 25 -S 75 -PA.

[0117] Example 4

[0118] In this example, a preparation method of a monovalent selective ion exchange membrane (specifically a polyether ether ketone monovalent selective cation exchange membrane) is provided, and the preparation method includes the following steps:

[0119] (1) Synthesis of carboxyl / sulfonated functionalized polyether ether ketone (CPEEK 100 -S0):

[0120] Under a nitrogen atmosphere, DFBP (11.35 g, 0.052 mol), BPVA (14.32 g, 0.05 mol), K2CO3 (13.82 g, 0.1 mol), DMSO (180 mL) and toluene (20 mL) were added to a four-necked flask. The mixture was heated to 140 °C and reacted for 4 h until the water was completely separated. Subsequently, the temperature was raised to 165 °C and the reaction was continued for 6 h to obtain a viscous polymer solution. After cooling, the upper liquid phase was removed from the solid precipitate, THF and dilute hydrochloric acid were added, and the mixture was vigorously stirred to completely dissolve the reaction precipitate. The dissolved solution was poured into isopropanol to precipitate a large amount of white precipitate, which was washed 3 times with deionized water and dried in a vacuum oven at 80 °C for 24 h to obtain a crude product. The crude product was dissolved in DMF and poured into deionized water to precipitate, obtaining a white flocculent substance, which was washed 3 times with deionized water and finally dried in a vacuum oven at 80 °C for 24 h to obtain a pure carboxyl-functionalized polyether ether ketone material (denoted as CPEEK 100 -S0).

[0121] The synthesis route is as follows:

[0122]

[0123] (2) Preparation of cation exchange membrane by solvent evaporation method: CPEEK 100 -S0 polymer material and polyvinylpyrrolidone (PVP K30 ) were dissolved in NMP at room temperature and stirred for 24 h to obtain a homogeneous casting solution (where the concentration of CPEEK 100 -S0 polymer material was 10 wt%, and the concentration of PVP K30 was 20 wt%). After standing for 12 h to remove bubbles, the casting solution was scraped onto a nylon mesh cloth placed on the surface of a glass plate with a 200 μm blade, and then dried in a drying oven at 60 °C for 24 h to evaporate the solvent. Finally, the film was peeled off from the glass plate to obtain a cation exchange membrane (denoted as MC 100 -S0).

[0124] (3) Preparation of monovalent selective cation exchange membrane by EDC / NHS amidation and secondary surface graft polymerization

[0125] (a) 4 mmol·L -1 of EDC·HCl and 10 mmol·L -1 of NHS were dissolved in 10 mmol·L -1In the MES buffer solution, it was formulated into an EDC / NHS carboxyl activation solution. The cation exchange membrane prepared in the previous step was immersed in the carboxyl activation solution and reacted at 40 °C for 24 h. After the reaction, the membrane surface was washed 3 times with deionized water. Subsequently, the membrane was immersed in a 10 mmol·L -1 PBS buffer solution (pH = 7.5, 8 g NaCl, 0.2 g KCl, 1.44 g Na2HPO4, 0.24 g KH2PO4), and reacted at 50 °C for 48 h to construct an amine layer on the membrane surface.

[0126] (b) Fix the cation exchange membrane with the constructed amine layer on the acrylic plate and scrape off the excess water on the membrane surface. Immerse the membrane in the oil phase solution (n-heptane solution containing 0.1 wt% of TMC), and the reaction time is 1 min. Subsequently, pour 20 mL of the aqueous solution of QPEI onto the membrane surface, and the reaction time is 2 min to construct a positively charged dense skin layer. Finally, the prepared membrane was heat-treated at 80 °C for 10 min to obtain the monovalent selective ion exchange membrane (denoted as MC 100 -S0-PA), and it was stored in deionized water for standby.

[0127] Among them, the preparation of the QPEI solution: Add 2-bromoethylamine hydrobromide, PEI750k, and deionized water (mass ratio of 1:10:100) into a 50 mL beaker, and place it on a magnetic stirrer at 80 °C and heat for 12 h to obtain the QPEI solution.

[0128] The carboxyl / sulfonated functionalized polyether ether ketone materials obtained in step (1) of Examples 1-3 of the present invention were characterized by Fourier transform infrared spectroscopy, and the test results are as Figure 1 shown. It can be seen that the characteristic absorption peak appearing at 1227 cm -1 corresponds to the stretching vibration peak of the ether bond (C-O-C). The appearance of the C-O-C structure proves that DFBP respectively undergoes nucleophilic substitution polycondensation reactions with BPVA and HSAP. The characteristic peak at 1719 cm -1 is the stretching vibration peak of the carboxyl group (O-C=O), and the characteristic peaks at 1012 cm -1 and 1310 cm -1 are the stretching vibration peaks of -SO3H, among which the peak at 1012 cm -1 is the stretching vibration peak of S-O, and the peak at 1310 cm -1This is the stretching vibration peak of S-O. The appearance of -COOH and -SO3H proves that the functional groups have been successfully introduced into the polymer main chain. At the same time, with the regulation of the carboxyl / sulfonic acid group content, the absorption peak intensity of the O-C=O peak weakens, while the absorption peak intensity of the -SO3H peak strengthens. This change in peak intensity is consistent with our expected results. The above conclusions preliminarily prove the successful synthesis of carboxylic acid / sulfonic acid functionalized polyether ether ketone materials with different proportion contents.

[0129] The cation transport numbers (the ion transport number is the number of ions passing through the ion exchange membrane per unit time) of the cation exchange membranes obtained in steps (2) of Examples 1-4 of the present invention and the commercial CGU were tested. The test method is as follows: Immerse the membrane to be tested in a 0.15 mol·L -1 KCl solution for 6 h and fix it on the test cell. The solution concentrations on both sides of the cell are 0.1 mol·L -1 and 0.2 mol·L -1 KCl solutions; Place the tips of the Ag / AgCl electrodes on both sides close to the membrane position, and connect both ends to a digital display voltmeter through wires to measure the potential difference across the membrane. The displayed value is the voltage E m across the membrane. The cation transport number can be calculated by the following formula:

[0130]

[0131] where E represents the measured potential of the membrane, E1 represents the absolute value of the potential measured for the first time, E2 represents the absolute value of the potential measured after swapping the electrodes, represents the transport number of cations in the membrane, and E0 represents the membrane potential under ideal conditions (at 25 °C, E0 = 16.1 mV).

[0132] Among them, the commercial CGU is a commercial cation exchange membrane (ASTOM Corporation), and the relevant parameters are as follows:

[0133]

[0134] X is the content of -COOH, Y is the content of -HSO3), the shows a trend of first increasing and then decreasing, among which MC 50 -S 50 of the reaches 0.96, which is the same as that of the commercial CGU (0.93) Comparable. This result indicates that an appropriate -SO3H ratio can effectively enhance the cation transport ability. However, when the -SO3H ratio increases to 75%, due to the overly large ion transport channels formed by the overly large hydrophilic domains, anion penetration may occur, thereby inhibiting the cation transport ability. Generally speaking, compared with the MC 100 -S0 membrane, the addition of -SO3H significantly improves the pore structure and physicochemical properties of the MC X -S Y membrane; with the increase of the -SO3H ratio, the degree of microphase separation increases significantly, further promoting the formation of ion transport channels. At the same time, the increase in the content of -SO3H with strong hydrophilicity and high dissociation also directly affects the negative charge density, IEC, and hydrophilicity of the membrane surface; the regulation of these membrane structures and physicochemical properties jointly affects the ion transport performance of the MC X -S Y membrane.

[0135] At a current density of 2 mA·cm -2 in a Li + / Mg 2+ binary mixed solution, the separation performance and ion flux of the monovalent selective ion exchange membranes prepared in Examples 1-4 were tested, and the test results are shown in Figure 3 and Figure 4 respectively. It can be seen that with the increase of the -SO3H ratio, the Li + flux first increases and then decreases, the Mg 2+ flux first decreases and then increases, and the changes in the Li + , Mg 2+ flux and separation performance mainly come from the dense positively charged cortex on the membrane surface. The number of reactive sites (carboxyl group content) on the surface of the MC X -S Y membrane affects the grafting amount of PEI grafted on the surface of the MC X -S Y -NH2 membrane, resulting in differences in the density and charge of the MC X -S Y -PA membrane. Therefore, with the increase of the -HSO3 ratio, the density and positive charge of the MC X -S Y -PA membrane increase accordingly. The synergistic effect of pore size and Donnan effect effectively inhibits the selective transport of Mg 2+ , reduces the Mg 2+ flux, and significantly improves the selectivity. However, when the content of -HSO3 increases to 75%, the Mg 25 -S 75 -PA membrane of the MC 2+The flux slightly increases again, which may be because the highly dissociable -HSO3 has a higher affinity for Mg than -COOH, thereby promoting the transport of Mg. 2+ 2+

[0136] The applicant declares that the present invention illustrates the monovalent selective ion exchange membrane of the present invention and its preparation method and application through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the raw materials selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.​​

Claims

1. A method for preparing a monovalent selective ion exchange membrane, characterized in that, The preparation method comprises the following steps: (1) Mix a first monomer, a second monomer, an alkaline substance, a solvent, and an azeotropic agent, react, raise the temperature, and continue the reaction to obtain a polymer product solution, and perform post-treatment to obtain a functionalized material; (2) Mix the functionalized material obtained in step (1), an optional additive, and a solvent to obtain a casting solution, coat the casting solution on a substrate, and dry to obtain an ion exchange membrane; (3) Dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in 2-morpholinoethanesulfonic acid buffer solution to prepare an EDC / NHS carboxyl activation solution, soak the ion exchange membrane obtained in step (2) in the carboxyl activation solution for reaction, after the reaction ends, wash the membrane surface, then perform a second reaction of the membrane with an aqueous monomer solution, then perform a third reaction of the membrane with an oil-phase monomer solution, then perform a fourth reaction of the membrane with an aqueous solution of the aqueous monomer, and perform heat treatment to obtain the monovalent selective ion exchange membrane; Wherein, the first monomer comprises a compound having a structure shown in the following formula I or formula II: In formula I and formula II, R1 and R2 are halogens; R3 and R4 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms, -SO3H, -SO3M, or -COOH, and M is Na or K; m and n are each independently an integer from 0 to 4; x and y are each independently an integer from 1 to 3; The second monomer comprises a compound having a structure shown in the following formula III or formula IV: In formula III and formula IV, R5, R6, R7, and R8 are each independently a linear or branched alkyl group having 1 to 10 carbon atoms, -SO3H, -SO3M, or -COOH, and M is Na or K; a, b, p, and q are each independently an integer from 0 to 4; And at least one of the first monomer and the second monomer contains -COOH.

2. The preparation method according to claim 1, characterized in that, The first monomer comprises any one or a combination of at least two of the following compounds: Preferably, the first monomer comprises 4,4'-difluorobenzophenone; Preferably, the second monomer comprises any one or a combination of at least two of the following compounds: Preferably, the molar ratio of the first monomer to the second monomer is (0.8 - 1.2):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The alkaline substance comprises potassium carbonate; Preferably, the molar ratio of the first monomer to the alkaline substance is 1:(1.5 - 3); Preferably, the solvent in step (1) comprises any one or a combination of at least two of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, sulfolane, and N,N-dimethylacetamide; Preferably, the azeotropic agent in step (1) comprises benzene and / or toluene.

4. The preparation method according to any one of claims 1-3, characterized in that, The temperature of the reaction in step (1) is 130 - 150 °C, and the reaction time is 2 - 5 h; Preferably, the temperature increase in step (1) is to 160 - 170 °C; Preferably, the time for the continued reaction in step (1) is 5 - 8 h; Preferably, the post-treatment in step (1) comprises precipitation, acidification, washing, and drying; Preferably, the precipitant used for the precipitation comprises isopropanol; Preferably, the reagent used for acidification includes dilute hydrochloric acid; Preferably, the temperature for drying is 70 - 90 °C, and the drying time is 20 - 30 h; Preferably, step (1) is carried out under an inert atmosphere; Preferably, the inert atmosphere includes nitrogen.

5. The preparation method according to any one of claims 1-4, characterized in that, The solvent in step (2) includes any one or a combination of at least two of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran, sulfolane, and dimethylacetamide; Preferably, in the casting solution of step (2), the concentration of the functionalized material is 5 wt% - 20 wt%; Preferably, the additive in step (2) includes a pore-forming agent; Preferably, the pore-forming agent includes any one or a combination of at least two of polyvinylpyrrolidone, polyethylene glycol, sodium chloride, and ionic liquid; Preferably, in the casting solution of step (2), the concentration of the additive is 0 - 30 wt%; Preferably, the coating in step (2) includes knife coating; Preferably, the thickness of the knife used for knife coating is 200 - 500 μm; Preferably, the substrate in step (2) includes nylon mesh; Preferably, the temperature for drying in step (2) is 60 - 80 °C, and the drying time is 10 - 24 h.

6. The preparation method according to any one of claims 1-5, characterized in that, The temperature of the reaction in step (3) is 30 - 50 °C, and the reaction time is 20 - 30 h; Preferably, the aqueous phase monomers in the aqueous phase monomer solution in step (3) include any one or a combination of at least two of polyethyleneimine, piperazine, m-phenylenediamine, p-phenylenediamine, hexamethylenediamine, quaternized polyethyleneimine, quaternized diaminopyridine, and quaternized tetra-hydroxyethylimidazole; Preferably, the solvent in the aqueous phase monomer solution in step (3) includes PBS buffer; Preferably, in the aqueous phase monomer solution in step (3), the concentration of the aqueous phase monomer is 1 wt% - 3 wt%; Preferably, the temperature of the second reaction in step (3) is 40 - 60 °C, and the second reaction time is 40 - 60 h; Preferably, the second reaction of the membrane with the aqueous phase monomer solution in step (3) specifically includes: soaking the membrane in the aqueous phase monomer solution for the second reaction, or, after fixing the membrane, bringing it into single-sided contact with the aqueous phase monomer solution for the second reaction; Preferably, after the second reaction in step (3), it further includes the step of scraping dry the moisture on the membrane surface or heating to evaporate the moisture.

7. The preparation method according to any one of claims 1-6, characterized in that, The oil phase monomers in the oil phase monomer solution in step (3) include any one or a combination of at least two of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, and tetracarbonyl chloride; Preferably, the solvent in the oil phase monomer solution in step (3) includes n-heptane; Preferably, in the oil phase monomer solution in step (3), the concentration of the oil phase monomer is 0.1 wt% - 2 wt%; Preferably, the time of the third reaction in step (3) is 0.5 - 5 min; Preferably, the third reaction of the membrane with the oil phase monomer solution in step (3) specifically includes: Soaking the membrane in the oil phase monomer solution for the third reaction, or, after fixing the membrane, bringing it into single-sided contact with the oil phase monomer solution for the third reaction; Preferably, the aqueous solution of the aqueous-phase monomer in step (3) is prepared by the following method: Mix 2-bromoethylamine hydrobromide, the aqueous-phase monomer, and deionized water, and heat to obtain the aqueous solution of the aqueous-phase monomer; Preferably, the mass ratio of 2-bromoethylamine hydrobromide, the aqueous-phase monomer, and deionized water is 1:(8-12):(80-120); Preferably, the heating temperature is 70-90 °C, and the heating time is 10-14 h; Preferably, the temperature of the fourth reaction in step (3) is 10-30 °C, and the time of the fourth reaction is 2-10 min; Preferably, the fourth reaction of the membrane with the aqueous solution of the aqueous-phase monomer in step (3) specifically includes: Immerse the membrane in the aqueous solution of the aqueous-phase monomer for the fourth reaction, or, after fixing the membrane, bring it into single-sided contact with the aqueous solution of the aqueous-phase monomer for the fourth reaction; Preferably, the heat treatment temperature in step (3) is 70-90 °C, and the heat treatment time is 8-12 min.

8. A method for preparing a monovalent selective ion exchange membrane, characterized in that, The preparation method includes the following steps: (A) Mix the first monomer, the second monomer, an alkaline substance, a solvent, and an azeotropic agent, react, raise the temperature, and continue to react to obtain a polymer product solution, and perform post-treatment to obtain a functionalized material; Among them, the difference between the first monomer and the first monomer in claim 1 is only that R3 and R4 are each independently a straight-chain or branched-chain alkyl or amino group with 1-10 carbon atoms; The difference between the second monomer and the second monomer in claim 1 is only that R5, R6, R7, and R8 are each independently a straight-chain or branched-chain alkyl or amino group with 1-10 carbon atoms; And at least one of the first monomer and the second monomer contains an amino group; (B) Mix the functionalized material obtained in step (1), an optional additive, and a solvent to obtain a casting solution, coat the casting solution on a substrate, and dry to obtain an ion exchange membrane; (C) Immerse the ion exchange membrane obtained in step (2) in an oil-phase monomer solution for the first reaction, then immerse the membrane in an aqueous-phase monomer solution for the second reaction, and then immerse the membrane in the oil-phase monomer solution for the third reaction, and perform heat treatment to obtain the monovalent selective ion exchange membrane; Preferably, the time of the first reaction in step (C) is 0.5-5 min; Preferably, the temperature of the second reaction in step (C) is 10-30 °C, and the time of the second reaction is 2-10 min; Preferably, after the second reaction in step (C), it further includes the step of scraping off the moisture on the membrane surface or heating to evaporate the moisture; Preferably, the time of the third reaction in step (C) is 0.5-5 min; Preferably, the other parameters in steps (A) to (C) are the same as those in claims 1-7.

9. A monovalent selective ion exchange membrane, characterized in that, The monovalent selective ion exchange membrane is prepared by the preparation method described in any one of claims 1-7 or by the preparation method described in claim 8.

10. Use of a monovalent selective ion exchange membrane as described in claim 9 in monovalent and polyvalent ion exchange.

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