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

Abstract

The application provides a monovalent selective cation exchange membrane and a preparation method thereof, and the preparation method comprises the following steps: mixing a polymer monomer, a coordination complex and a cation exchange base film to form a modified layer on the surface of the cation exchange base film; using a crosslinking agent and a reducing agent to stabilize the modified layer, and then using a detergent to elute, so as to obtain the monovalent selective cation exchange membrane; the coordination complex comprises a mixture of a functional monomer and a template agent; and the template agent comprises a metal salt. The preparation method provided by the application introduces the polymer monomer before eluting the template agent, and polymerizes the polymer monomer in the modified layer, so that the stability and compactness of the modified layer are enhanced, a monovalent selective cation exchange membrane with specific ion channels is constructed, the monovalent selective cation exchange membrane has high selectivity, high flux and high stability to monovalent cations, and the separation capacity for monovalent and multivalent cations is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology, and relates to a cation exchange membrane, in particular to a monovalent selective cation exchange membrane and a preparation method thereof. BACKGROUND

[0002] The monovalent cation exchange membrane can selectively pass monovalent cations and effectively block high-valence cations. When the monovalent cation exchange membrane is used in an electrodialysis process, the separation of monovalent and multivalent cations can be realized, and the concentration of monovalent cations can be realized. At present, monovalent selective electrodialysis is applied to the extraction of lithium from salt lakes, the development of seawater resources, the separation and recovery of waste acid / heavy metal ions and the like. Therefore, the research on the monovalent selective cation exchange membrane has received more attention.

[0003] The preparation method of the monovalent selective cation exchange membrane is divided into surface modification and membrane matrix modification according to different modification objects. The surface modification can introduce specific functional groups or modification layers on the surface of the membrane without changing the basic structure of the original membrane material, so as to significantly improve the selectivity and separation performance of the membrane. Compared with the membrane matrix modification, the surface modification is usually more flexible and controllable, and different modification strategies can be designed according to the needs to adapt to different application scenarios.

[0004] CN102935389A discloses a preparation method of a cation exchange membrane with monovalent selective separation function. First, chitosan is attached to the surface of a conventional cation exchange membrane through an inlaid dip-coating method. After draining in the dark, the chitosan azide derivative needs to be irradiated by ultraviolet light to initiate the bond insertion reaction of the azine, so as to complete the covalent bond fixation of chitosan on the surface of the base membrane. Finally, crosslinking treatment or amination treatment is used to realize the adjustment of the compactness of the functional layer matrix, the charge density and the fixation on the surface of the base membrane, so as to form a dense and uniform positively charged membrane layer on the surface of the conventional cation exchange membrane. However, the cation exchange membrane obtained by this method has the problem of flux decline.

[0005] By using the pore size screening mechanism, a modified membrane with a specific ion pore size is formed on the surface of the membrane by the surface modification method, which can ensure the selective separation of monovalent and multivalent ions and reduce the adverse effect on the flux. CN116531975A discloses a preparation method and application of a high-selectivity lithium ion-imprinted channel polyelectrolyte composite membrane. In this method, Li + Pb 2+ ions with a hydration radius between Li + and interfering ions are selected as templates to construct a polyelectrolyte layer by layer-by-layer self-assembly. The ion imprinting technology is used to improve the polyelectrolyte layer to form an ion-imprinted channel for selective screening of target Li

[0006] In view of the deficiencies in the prior art, for the electrodialysis process, how to improve the preparation process of the monovalent selective cation exchange membrane, and develop a monovalent selective cation exchange membrane with high selectivity, high flux and high stability is a technical problem to be solved in the field. SUMMARY

[0007] In view of the deficiencies in the prior art, the purpose of the present application is to provide a monovalent selective cation exchange membrane and a preparation method thereof, which can construct a monovalent selective cation exchange membrane with specific ion channels, so that it has high selectivity, high flux and high stability to monovalent cations, and improves the separation ability of monovalent and multivalent cations.

[0008] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0009] In a first aspect, the present application provides a preparation method of a monovalent selective cation exchange membrane, which comprises the following steps:

[0010] Mixing polymer monomers, coordination complexes and cation exchange base films to form a modified layer on the surface of the cation exchange base film; using a crosslinking agent and a reducing agent to stabilize the modified layer, and then using a detergent for elution to obtain the monovalent selective cation exchange membrane;

[0011] The coordination complex comprises a mixture of functional monomers and template agents;

[0012] The template agent comprises a metal salt.

[0013] The preparation method provided by the present application constructs specific ion channels on the cation exchange base film, that is, the polymer monomers are polymerized in the modified layer before eluting the template agent, and a monovalent selective cation exchange membrane with pore size screening as the dominant separation mechanism is prepared. The present application introduces polymer monomers before eluting the template agent, and polymerizes them in the modified layer, which enhances the stability and density of the modified layer, constructs a monovalent selective cation exchange membrane with specific ion channels, so that it has high selectivity, high flux and high stability to monovalent cations, and improves the separation ability of monovalent and multivalent cations.

[0014] The template agent used in the present application is a metal salt, and the type of metal ions affects the size of the ion channels. Selecting appropriate types of metal ions can improve the pore size screening effect of the obtained monovalent selective cation exchange membrane.

[0015] In the preparation method provided by the present application, the solvent used is water unless otherwise specified.

[0016] Preferably, the template agent comprises any one or a combination of at least two of a lithium salt, a nickel salt, a copper salt, a zinc salt, a calcium salt, or a magnesium salt, typically but not limitedly including a combination of a lithium salt and a nickel salt, a combination of a copper salt and a zinc salt, a combination of a calcium salt and a magnesium salt, a combination of a lithium salt, a copper salt, and a calcium salt, a combination of a nickel salt, a zinc salt, and a magnesium salt, or a combination of a lithium salt, a nickel salt, a copper salt, a zinc salt, a calcium salt, and a magnesium salt.

[0017] Illustratively, the lithium salt comprises any one or a combination of at least two of lithium chloride, lithium sulfate, or lithium nitrate, typically but not limitedly including a combination of lithium chloride and nickel sulfate, a combination of lithium sulfate and lithium nitrate, a combination of lithium chloride and lithium nitrate, or a combination of lithium chloride, lithium sulfate, and lithium nitrate.

[0018] Illustratively, the nickel salt comprises any one or a combination of at least two of nickel chloride, nickel sulfate, or nickel nitrate, typically but not limitedly including a combination of nickel chloride and nickel sulfate, a combination of nickel sulfate and nickel nitrate, a combination of nickel chloride and nickel nitrate, or a combination of nickel chloride, nickel sulfate, and nickel nitrate.

[0019] Illustratively, the copper salt comprises any one or a combination of at least two of copper chloride, copper sulfate, or copper nitrate, typically but not limitedly including a combination of copper chloride and copper sulfate, a combination of copper sulfate and copper nitrate, a combination of copper chloride and copper nitrate, or a combination of copper chloride, copper sulfate, and copper nitrate.

[0020] Illustratively, the zinc salt comprises any one or a combination of at least two of zinc chloride, zinc sulfate, or zinc nitrate, typically but not limitedly including a combination of zinc chloride and zinc sulfate, a combination of zinc sulfate and zinc nitrate, a combination of zinc chloride and zinc nitrate, or a combination of zinc chloride, zinc sulfate, and zinc nitrate.

[0021] Illustratively, the calcium salt comprises any one or a combination of at least two of calcium chloride, calcium sulfate, or calcium nitrate, typically but not limitedly including a combination of calcium chloride and calcium sulfate, a combination of calcium sulfate and calcium nitrate, a combination of calcium chloride and calcium nitrate, or a combination of calcium chloride, calcium sulfate, and calcium nitrate.

[0022] Illustratively, the magnesium salt comprises any one or a combination of at least two of magnesium chloride, magnesium sulfate, or magnesium nitrate, typically but not limitedly including a combination of magnesium chloride and magnesium sulfate, a combination of magnesium sulfate and magnesium nitrate, a combination of magnesium chloride and magnesium nitrate, or a combination of magnesium chloride, magnesium sulfate, and magnesium nitrate.

[0023] Preferably, the functional monomer comprises any one of methacrylic acid, N-isopropyl acrylamide (NIPAM), acrylic acid (AA), polyethylene imine (PEI), polyallylamine (PAAM), acrylamide ethyl dimethyl amine (AEDM), polyetherimide, or vinyl amine (VA), or a combination of at least two of them, typical but non-limiting combinations include a combination of methacrylic acid and NIPAM, a combination of AA and PEI, a combination of PAAM and AEDM, a combination of AEDM and VA, a combination of methacrylic acid, NIPAM and AA, a combination of PEI, PAAM, AEDM and VA, or a combination of methacrylic acid, NIPAM, AA, PEI, PAAM, AEDM, polyetherimide and VA.

[0024] The template agent used in the present application is a metal salt, wherein the amount of metal ions affects the number of ion channels, and selecting a suitable amount of metal ions can improve the pore size screening effect of the obtained monovalent selective cation exchange membrane.

[0025] Preferably, the molar ratio of metal ions to functional monomers in the template agent is 1:1 to 1:25, for example, it can be 1:1, 1:5, 1:10, 1:15, 1:20 or 1:25, but is not limited to the listed values, and the remaining values within the value range are also applicable.

[0026] Preferably, the concentration of the functional monomer in the coordination complex is 0.5 g / L to 10 g / L, for example, it can be 0.5 g / L, 1 g / L, 3 g / L, 5 g / L, 8 g / L or 10 g / L, but is not limited to the listed values, and the remaining values within the value range are also applicable.

[0027] Preferably, the solvent in the coordination complex is water, and also includes a 0.4 mol / L to 0.6 mol / L sodium chloride solution.

[0028] Preferably, the polymer monomer comprises any one of vinyl sulfonic acid (VSA), vinyl ether (VE), styrene (St), dopamine hydrochloride (DA·HCl), pyrrole (Py), chitosan (CS), acrylamide ethyl dimethyl amine (AEDM), or acrylamide (AM), or a combination of at least two of them, typical but non-limiting combinations include a combination of VSA and VE, a combination of St and DA·HCl, a combination of Py and Cs, a combination of AEDM and AM, a combination of VSA, VE and St, a combination of DA·HCl, Py, Cs and AEDM, or a combination of VSA, VE, St, DA·HCl, Py, CS, AEDM and AM.

[0029] The concentration of the polymer monomer in the system affects the formation of specific ion channels on the cation exchange base film, and the present application reduces the formation of non-specific ion channels by polymerizing the polymer monomer in the modified layer. As a preferred technical solution, controlling the concentration of the polymer monomer in the system can make the modified layer denser and the membrane separation performance better.

[0030] Preferably, after the polymer monomer is mixed with the coordination complex, the concentration of the polymer monomer is 0.5 g / L to 8 g / L, for example, it can be 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L or 8 g / L, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0031] In the present application, the temperature and time of mixing affect the deposition quality of the modified layer. For example, if the mixing time is too short, the deposition amount of the modified layer is too small, resulting in no obvious separation effect; if the mixing time is too long, the deposition amount of the modified layer is too much, which is easy to cause the decline of the membrane flux.

[0032] Preferably, the mixing temperature is 20℃ to 40℃, for example, it can be 20℃, 25℃, 30℃, 35℃ or 40℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0033] Preferably, the mixing time is 0.5h to 10h, for example, it can be 0.5h, 1h, 3h, 5h, 6h, 8h or 10h, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0034] Preferably, the cation exchange base film is a modified cation exchange base film modified by soaking with an oxidizing agent.

[0035] Preferably, the oxidizing agent includes any one or a combination of at least two of potassium permanganate, ferric chloride, benzoyl peroxide, ammonium persulfate, sodium persulfate or hydrogen peroxide. Typical but non-limiting combinations include a combination of potassium permanganate and ferric chloride, a combination of ferric chloride and benzoyl peroxide, a combination of ammonium persulfate and sodium persulfate, a combination of sodium persulfate and hydrogen peroxide, a combination of potassium permanganate, benzoyl peroxide and sodium persulfate, or a combination of potassium permanganate, ferric chloride, benzoyl peroxide, ammonium persulfate, sodium persulfate and hydrogen peroxide.

[0036] Preferably, during the soaking modification, the concentration of the oxidizing agent is 0.1 mol / L to 1 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L or 1 mol / L, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0037] Preferably, the time for the soaking modification is 5 min to 30 min, such as can be 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min, but is not limited to the listed values, and the remaining unlisted values within the range of values are equally applicable.

[0038] Preferably, the crosslinking agent comprises any one or a combination of at least two of ethylene glycol dimethacrylate (EGDMA), methyl methacrylate (MMA), ethyl vinyl acrylate, glutaraldehyde (GA), epichlorohydrin (ECH), ethylene oxide (EO), or dimethylol propyl (DMP), typically but not limited to combinations including EGDMA and MMA, ethyl vinyl acrylate and GA, ECH, EO and DMP, or a combination of EGDMA, MMA, ethyl vinyl acrylate, GA, ECH, EO and DMP.

[0039] Preferably, the reducing agent comprises any one or a combination of at least two of sodium borohydride, triethylamine, sodium bisulfite, ferrous sulfate, sodium cyanoborohydride, sodium iodide, or potassium iodide, typically but not limited to combinations including sodium borohydride and triethylamine, sodium bisulfite and ferrous sulfate, sodium cyanoborohydride, sodium iodide and potassium iodide, or a combination of sodium borohydride, triethylamine, sodium bisulfite, ferrous sulfate, sodium cyanoborohydride, sodium iodide and potassium iodide.

[0040] Preferably, the stabilization modification layer comprises a crosslinking soak using a crosslinking agent, followed by a reducing soak using a reducing agent.

[0041] Preferably, the concentration of the crosslinking agent in the system during the crosslinking soak is 1 wt% to 5 wt%, such as can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, but is not limited to the listed values, and the remaining unlisted values within the range of values are equally applicable.

[0042] Preferably, the temperature of the crosslinking soak is 20 °C to 40 °C, such as can be 20 °C, 25 °C, 30 °C, 35 °C, or 40 °C, but is not limited to the listed values, and the remaining unlisted values within the range of values are equally applicable.

[0043] Preferably, the time for the crosslinking soak is 10 min to 60 min, such as can be 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, but is not limited to the listed values, and the remaining unlisted values within the range of values are equally applicable.

[0044] Preferably, the concentration of the reducing agent in the system during the reducing soaking is 0.01 mol / L to 1 mol / L, for example, it can be 0.01 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L or 1 mol / L, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0045] Preferably, the temperature of the reducing soaking is 20℃ to 30℃, for example, it can be 20℃, 22℃, 25℃, 28℃ or 30℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0046] Preferably, the time of the reducing soaking is 10 min to 60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0047] Preferably, the washing agent includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, citric acid, disodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, acetonitrile, methanol, ammonia water or sodium hydroxide.

[0048] Preferably, the concentration of the washing agent is 0.05 mol / L to 0.5 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0049] Preferably, the number of times of elution is at least 3, and the time of each elution is more than 10 min.

[0050] As a preferred technical solution of the preparation method of the first aspect of the present application, the preparation method comprises the following steps:

[0051] (1) mixing sodium chloride and functional monomers to obtain a solution with a sodium chloride concentration of 0.4 mol / L to 0.6 mol / L and a functional monomer concentration of 0.5 g / L to 10 g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to functional monomers of 1:1 to 1:25 to obtain a coordination complex;

[0052] The template agent includes a metal salt.

[0053] (2) adding a polymer monomer into the coordination complex to make the concentration of the polymer monomer in the mixed system be 0.5 g / L to 8 g / L; then immersing the cation exchange-based membrane in the mixed system of the coordination complex and the polymer monomer to form a modified layer on the surface of the cation exchange-based membrane;

[0054] wherein the temperature of the immersion is 20℃ to 40℃, and the time is 0.5h to 10h;

[0055] (3) using a crosslinking agent with a concentration of 1wt% to 5wt% to perform crosslinking immersion on the cation exchange-based membrane with the modified layer formed;

[0056] wherein the temperature of the crosslinking immersion is 20℃ to 40℃, and the time is 10min to 60min;

[0057] (4) using a reducing agent with a concentration of 0.01mol / L to 1mol / L to perform reducing immersion, wherein the reducing immersion is performed under oscillation conditions, the temperature is 20℃ to 30℃, and the time is 10min to 60min;

[0058] (5) using a detergent with a concentration of 0.05mol / L to 0.5mol / L to perform oscillation elution, wherein the elution is performed at least 3 times, each time for more than 10min, to obtain a monovalent selective cation exchange membrane.

[0059] As a further preferred technical solution of the preparation method of the first aspect of the present application, the preparation method comprises the following steps:

[0060] (1) mixing sodium chloride and a functional monomer to obtain a solution with a sodium chloride concentration of 0.4mol / L to 0.6mol / L and a functional monomer concentration of 0.5g / L to 10g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to the functional monomer of 1:1 to 1:25 to obtain a coordination complex;

[0061] The template agent comprises a metal salt;

[0062] (2) adding a polymer monomer into the coordination complex to make the concentration of the polymer monomer in the mixed system be 0.5 g / L to 8 g / L; then immersing the cation exchange-based membrane in the mixed system of the coordination complex and the polymer monomer to form a modified layer on the surface of the cation exchange-based membrane;

[0063] wherein the temperature of the immersion is 20℃ to 40℃, and the time is 0.5h to 10h;

[0064] wherein the immersion modification is performed by using an oxidizing agent with a concentration of 0.1mol / L to 1mol / L for 5min to 30min;

[0065] (3) The cation exchange base membrane forming the modified layer is crosslinked and soaked with a crosslinking agent at a concentration of 1 wt% to 5 wt%;

[0066] The cross-linking soaking temperature is 20℃ to 40℃, and the time is 10 min to 60 min;

[0067] (4) Use a reducing agent with a concentration of 0.01 mol / L to 1 mol / L for reduction soaking. The reduction soaking is carried out under shaking conditions, with a temperature of 20℃ to 30℃ and a time of 10 min to 60 min.

[0068] (5) Use a detergent with a concentration of 0.05 mol / L to 0.5 mol / L to perform elution by shaking. The number of elutions should be at least 3 times, and the elution time should be more than 10 minutes each time to obtain a monovalent selective cation exchange membrane.

[0069] In a second aspect, the present invention provides a monovalent selective cation exchange membrane, which is prepared by the preparation method described in the first aspect.

[0070] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0071] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0072] The preparation method provided by this invention constructs specific ion channels on a cation exchange base membrane, introduces polymer monomers before eluting the template agent, and polymerizes them on a modified layer. This enhances the stability and density of the modified layer while reducing the formation of non-specific ion channels. Moreover, the monovalent selective cation exchange membrane prepared by this invention is based on the principle of pore size sieving, taking into account both high selectivity and high flux for monovalent cations. Furthermore, the use of polymer monomers and crosslinking agents improves the stability of the monovalent selective cation exchange membrane, effectively improving the membrane's separation performance. Detailed Implementation

[0073] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0074] In a specific embodiment of the present invention, the test is conducted in a conventional electrodialysis apparatus under the following conditions: a current density of 8 mA / cm². 2The constant current mode is used, the solution in the concentrating chamber and the diluting chamber is a mixed solution of 0.05 mol / L potassium chloride and 0.05 mol / L magnesium chloride, the solution in the electrode chamber is a 0.1 mol / L sodium sulfate solution, and the solutions in the chambers are circulated by using a peristaltic pump, the flow rate of the peristaltic pump is 150 mL / min, and the ambient temperature is 20℃.

[0075] The ion flux is defined as: J=(C t -C0)·V / (A·t), wherein J is the ion flux, C0 is the ion concentration (mol / L) of the concentrating chamber at the initial moment, C t is the ion concentration (mol / L) of the concentrating chamber at t, A is the effective area of the membrane, V is the solution volume (L) of the concentrating chamber, and t is the test time, the test time in the specific embodiment of the application is 1 h;

[0076] The selective separation coefficient is defined as: P=J M + ·C N 2+ / (J N 2+ ·C M + ), wherein P is the selective separation coefficient, J M + is the flux of monovalent cations, J N 2+ is the flux of divalent cations, C M + is the monovalent cation concentration (mol / L) of the diluting chamber at the initial moment, C N 2+ is the divalent cation concentration (mol / L) of the diluting chamber at the initial moment. The cation concentration is detected by using atomic absorption spectrophotometry, and the detection instrument is AA320CRT.

[0077] The membrane resistance is the low intersection point of the high-frequency semicircle and the Re(z) axis on the complex impedance plane in the Nyquist plot.

[0078] The cation exchange membrane used in the specific embodiment of the application is TRJCM II, which is purchased from Beijing Tingrun Membrane Technology Development Co., Ltd. When the membrane is used to test the fluxes of potassium ions and magnesium ions, the selective separation coefficient and the membrane resistance by electrodialysis, the potassium ion flux is 0.445 mmol / (m 2 ·s), the magnesium ion flux is 0.230 mmol / (m 2 ·s), the selective separation coefficient is 1.63, and the membrane resistance is 2.98 Ω·cm 2 .

[0079] Example 1

[0080] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and comprises the following steps:

[0081] (1) mixing sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w is 10000) to obtain a solution with a sodium chloride concentration of 0.5 mol / L and a functional monomer concentration of 4 g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to the functional monomer of 1:15 to obtain a coordination complex;

[0082] The template agent is lithium chloride.

[0083] (2) adding a polymer monomer (pyrrole) to the coordination complex to make the polymer monomer concentration in the mixed system 8 g / L; and then immersing the modified cation exchange base membrane in the mixed system by using an oxidizing agent to form a modified layer on the surface of the cation exchange base membrane;

[0084] The temperature of the immersion is 30 DEG C, and the time is 4 h.

[0085] The immersion modification is immersion modification for 10 min by using a FeCl3 solution with a concentration of 0.5 mol / L.

[0086] (3) cross-linking immersion of the cation exchange base membrane with the formed modified layer by using a cross-linking agent (glutaraldehyde) with a concentration of 2 wt%;

[0087] The temperature of the cross-linking immersion is 30 DEG C, and the time is 30 min.

[0088] (4) reduction immersion by using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1 mol / L, and the reduction immersion is carried out under oscillation conditions, the temperature is 25 DEG C, and the time is 30 min.

[0089] (5) oscillation elution by using a detergent (ethylenediaminetetraacetic acid disodium salt) with a concentration of 0.1 mol / L, the elution is performed for 3 times, the time of each elution is 10 min, and a monovalent selective cation exchange membrane is obtained.

[0090] Embodiment 2

[0091] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and except that the template agent is replaced by nickel chloride with an equimolar amount, the rest is the same as in embodiment 1.

[0092] Embodiment 3

[0093] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and except that the template agent is replaced by copper chloride with an equimolar amount, the rest is the same as in embodiment 1.

[0094] Embodiment 4

[0095] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and comprises the following steps:

[0096] (1) mixing sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w The concentration of the sodium chloride is 0.5 mol / L, and the concentration of the functional monomer is 4 g / L, and then a coordination complex is obtained by mixing a template agent at a molar ratio of metal ions in the template agent to the functional monomer of 1:25;

[0097] The template agent is nickel chloride;

[0098] (2) adding a polymer monomer (dopamine hydrochloride) into the coordination complex, so that the concentration of the polymer monomer in the mixed system is 4 g / L; and then immersing the modified cation exchange base membrane in the mixed system by using an oxidizing agent, so that a modified layer is formed on the surface of the cation exchange base membrane;

[0099] The temperature of the immersion is 30 DEG C, and the time is 4 h;

[0100] The modified layer is modified by immersing in a 0.5 mol / L FeCl3 solution for 10 min;

[0101] (3) cross-linking the cation exchange base membrane with the modified layer by using a cross-linking agent (glutaraldehyde) with a concentration of 2 wt%;

[0102] The temperature of the cross-linking immersion is 30 DEG C, and the time is 30 min;

[0103] (4) reducing immersion is performed by using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1 mol / L, and the reducing immersion is performed under oscillation conditions, the temperature is 25 DEG C, and the time is 30 min;

[0104] (5) oscillation elution is performed by using a washing agent (ethylenediaminetetraacetic acid disodium salt) with a concentration of 0.1 mol / L, the elution is performed for 3 times, the time of each elution is 10 min, and a monovalent selective cation exchange membrane is obtained.

[0105] Example 5

[0106] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and except that the amount of the template agent is changed, so that the molar ratio of metal ions in the template agent to the functional monomer is 1:15, the rest is the same as in the embodiment 4.

[0107] Example 6

[0108] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, in addition to changing the amount of a template agent, the molar ratio of metal ions in the template agent to functional monomers is 1:5, and the rest is the same as in Embodiment 4.

[0109] Embodiment 7

[0110] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0111] (1) mixing sodium chloride and functional monomers (polyethyleneimine with a weight average molecular weight M w of 10000) to obtain a solution with a sodium chloride concentration of 0.5 mol / L and a functional monomer concentration of 4 g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to functional monomers of 1:15 to obtain a coordination complex;

[0112] The template agent is nickel chloride;

[0113] (2) adding a polymer monomer (chitosan, McLean Biochemical Technology Co., Ltd., CAS: 9012-76-4; Lot#E2414152, degree of deacetylation≥95%, viscosity 150 mpa.s) to the coordination complex to obtain a mixed system with a polymer monomer concentration of 5 g / L; and then immersing the modified cation exchange base film in the mixed system to form a modified layer on the surface of the cation exchange base film;

[0114] The temperature of the immersion is 30 DEG C, and the time is 4 h.

[0115] The immersion modification is immersion modification for 10 min by using a FeCl3 solution with a concentration of 0.5 mol / L.

[0116] (3) crosslinking immersion of the cation exchange base film on which the modified layer is formed by using a crosslinking agent (glutaraldehyde) with a concentration of 2 wt%;

[0117] The temperature of the crosslinking immersion is 30 DEG C, and the time is 30 min.

[0118] (4) reduction immersion by using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1 mol / L, wherein the reduction immersion is carried out under oscillation conditions, the temperature is 25 DEG C, and the time is 30 min.

[0119] (5) oscillation elution by using a detergent (ethylenediaminetetraacetic acid disodium salt) with a concentration of 0.1 mol / L, wherein the elution is performed for 3 times, and the time of each elution is 10 min, to obtain a monovalent selective cation exchange membrane.

[0120] Embodiment 8

[0121] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and comprises the following steps:

[0122] (1) mixing sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w is 10000) to obtain a solution with a sodium chloride concentration of 0.5 mol / L and a functional monomer concentration of 4 g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to the functional monomer of 1:15 to obtain a coordination complex;

[0123] The template agent is nickel chloride;

[0124] (2) adding a polymer monomer (dopamine hydrochloride) into the coordination complex, so that the concentration of the polymer monomer in the mixed system is 3 g / L; and then immersing the modified cation exchange base membrane in the mixed system by using an oxidizing agent, so that a modified layer is formed on the surface of the cation exchange base membrane;

[0125] The temperature of the immersion is 30 DEG C, and the time is 4 h.

[0126] The immersion modification is immersion modification for 10 min by using a FeCl3 solution with a concentration of 0.5 mol / L.

[0127] (3) cross-linking immersion of the cation exchange base membrane with the modified layer formed thereon by using a cross-linking agent (glutaraldehyde) with a concentration of 2 wt%;

[0128] The temperature of the cross-linking immersion is 30 DEG C, and the time is 30 min.

[0129] (4) reduction immersion by using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1 mol / L, and the reduction immersion is carried out under oscillation conditions, the temperature is 25 DEG C, and the time is 30 min.

[0130] (5) oscillation elution by using a detergent (ethylenediaminetetraacetic acid disodium salt) with a concentration of 0.1 mol / L, the elution is performed for 3 times, the time of each elution is 10 min, and a monovalent selective cation exchange membrane is obtained.

[0131] Embodiment 9

[0132] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, and except that the concentration of the polymer monomer (dopamine hydrochloride) in the mixed system is 5 g / L in step (2), the rest is the same as in embodiment 8.

[0133] Embodiment 10

[0134] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, except that the concentration of the polymer monomer (dopamine hydrochloride) in the mixed system is 0.5 g / L in step (2), the rest is the same as in the embodiment 8.

[0135] Embodiment 11

[0136] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, except that the molar ratio of metal ions to functional monomers in the template agent is changed to 1:5, the rest is the same as in the embodiment 8.

[0137] Embodiment 12

[0138] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, except that the molar ratio of metal ions to functional monomers in the template agent is changed to 1:1, the rest is the same as in the embodiment 8.

[0139] Embodiment 13

[0140] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, except that the concentration of the functional monomer in the coordination complex is 0.5 g / L, the rest is the same as in the embodiment 8.

[0141] Embodiment 14

[0142] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, wherein, except that the concentration of the functional monomer in the coordination complex is 10 g / L, the rest is the same as in the embodiment 8.

[0143] Embodiment 15

[0144] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0145] (1) mixing sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w 10000) to obtain a solution with a sodium chloride concentration of 0.5 mol / L and a functional monomer concentration of 4 g / L, and then mixing a template agent according to a molar ratio of metal ions to functional monomers in the template agent of 1:15 to obtain a coordination complex;

[0146] The template agent is nickel chloride;

[0147] (2) adding a polymer monomer (dopamine hydrochloride) into the coordination complex to make the concentration of the polymer monomer in the mixed system be 3 g / L; and then immersing the modified cation exchange base film in the mixed system by using an oxidizing agent to form a modified layer on the surface of the cation exchange base film;

[0148] The temperature of the soaking is 20℃, and the time is 10h.

[0149] The soaking modification is using FeCl3 solution with a concentration of 0.1 mol / L to soak for 30min.

[0150] (3) Cross-linking agent (glutaraldehyde) with a concentration of 1wt% is used to soak the cation exchange base film for forming a modified layer;

[0151] The temperature of the cross-linking soaking is 20℃, and the time is 60min.

[0152] (4) Reducing agent (sodium cyanoborohydride) with a concentration of 0.01mol / L is used for reducing soaking, and the reducing soaking is carried out under oscillation conditions, the temperature is 20℃, and the time is 60min.

[0153] (5) Detergent (ethylenediaminetetraacetic acid disodium salt) with a concentration of 0.05mol / L is used for oscillation elution, the elution is carried out for 3 times, and the time of each elution is 10min, to obtain a monovalent selective cation exchange membrane.

[0154] Example 16

[0155] The embodiment provides a preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0156] (1) sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w 10000) are mixed to obtain a solution with a sodium chloride concentration of 0.5mol / L and a functional monomer concentration of 4g / L, and then a template agent is mixed according to a molar ratio of metal ions in the template agent to the functional monomer of 1:15 to obtain a coordination complex;

[0157] The template agent is nickel chloride;

[0158] (2) a polymer monomer (dopamine hydrochloride) is added to the coordination complex, so that the concentration of the polymer monomer in the mixed system is 3g / L; and then the cation exchange base film soaked by the oxidizing agent is soaked in the mixed system to form a modified layer on the surface of the cation exchange base film;

[0159] The concentration of the polymer monomer in the mixed system is 3g / L.

[0160] The temperature of the soaking is 40℃, and the time is 0.5h.

[0161] The soaking modification is using FeCl3 solution with a concentration of 1mol / L to soak for 5min.

[0162] (3) cross-linking soaking the cation exchange base film forming the modified layer using a cross-linking agent (glutaraldehyde) with a concentration of 5wt%;

[0163] wherein the temperature of the cross-linking soaking is 40℃ and the time is 10min;

[0164] (4) reduction soaking using a reducing agent (sodium cyanoborohydride) with a concentration of 1mol / L, the reduction soaking being performed under oscillation conditions, the temperature being 30℃ and the time being 10min;

[0165] (5) oscillation elution using a detergent (disodium ethylenediaminetetraacetate) with a concentration of 0.5mol / L, the elution being performed 3 times, each time for 10min, to obtain a monovalent selective cation exchange membrane.

[0166] Comparative Example 1

[0167] The present comparative example provides a preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0168] (1) mixing sodium chloride and a functional monomer (polyethyleneimine with a weight average molecular weight M w of 10000) to obtain a solution with a sodium chloride concentration of 0.5mol / L and a functional monomer concentration of 4g / L, to obtain a mixed solution;

[0169] (2) adding a polymer monomer (dopamine hydrochloride) to the coordination complex to make the concentration of the polymer monomer in the mixed system 3g / L; then soaking the modified cation exchange base film in the mixed system using an oxidizing agent to form a modified layer on the surface of the cation exchange base film;

[0170] wherein the temperature of the soaking is 30℃ and the time is 4h;

[0171] wherein the soaking modification is soaking modification using a FeCl3 solution with a concentration of 0.5mol / L for 10min;

[0172] (3) cross-linking soaking the cation exchange base film forming the modified layer using a cross-linking agent (glutaraldehyde) with a concentration of 2wt%;

[0173] wherein the temperature of the cross-linking soaking is 30℃ and the time is 30min;

[0174] (4) reduction soaking using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1mol / L, the reduction soaking being performed under oscillation conditions, the temperature being 25℃ and the time being 30min;

[0175] (5) using a detergent (disodium ethylenediaminetetraacetate) with a concentration of 0.1 mol / L for oscillation elution, the elution being performed 3 times, each time for 10 min, to obtain a monovalent selective cation exchange membrane.

[0176] Comparative Example 2

[0177] The present comparative example provides a preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0178] (1) mixing sodium chloride with a functional monomer (a polyethyleneimine with a weight average molecular weight M w of 10000) to obtain a solution with a sodium chloride concentration of 0.5 mol / L and a functional monomer concentration of 4 g / L, and then mixing a template agent according to a molar ratio of metal ions in the template agent to the functional monomer of 1:15 to obtain a coordination complex;

[0179] The template agent is nickel chloride;

[0180] (2) soaking the modified cation exchange base membrane in the coordination complex to form a modified layer on the surface of the cation exchange base membrane;

[0181] The soaking temperature is 30°C, and the soaking time is 4 h;

[0182] The soaking modification is soaking modification for 10 min using a FeCl3 solution with a concentration of 0.5 mol / L;

[0183] (3) cross-linking soaking of the cation exchange base membrane with the formed modified layer using a cross-linking agent (glutaraldehyde) with a concentration of 2 wt%;

[0184] The cross-linking soaking temperature is 30°C, and the cross-linking soaking time is 30 min;

[0185] (4) reduction soaking using a reducing agent (sodium cyanoborohydride) with a concentration of 0.1 mol / L, the reduction soaking being performed under oscillation conditions, at a temperature of 25°C, for 30 min;

[0186] (5) oscillation elution using a detergent (disodium ethylenediaminetetraacetate) with a concentration of 0.1 mol / L, the elution being performed 3 times, each time for 10 min, to obtain a monovalent selective cation exchange membrane.

[0187] Performance test

[0188] The fluxes of magnesium ions and potassium ions, the selectivity coefficients and the membrane resistances of the monovalent selective cation exchange membranes obtained in the above examples and comparative examples were tested, wherein a cation exchange base membrane without modification was used as a control example, and the obtained results are shown in Table 1.

[0189] Table 1

[0190]

[0191] As can be seen from Examples 1 to 3 in Table 1, the type of cation in the template determines the size of the specific ion channel, and the ion channels with different pore sizes have different blocking effects on monovalent ions and divalent ions. Meanwhile, as can be seen from the comparison of Examples 8, 11 and 12, the content of cation in the template determines how many specific ion channels are formed, and by selecting appropriate types and contents of templates, regular specific ion channels can be formed in the modified layer, thereby realizing selective separation of different ions.

[0192] As can be seen from the comparison of Example 2 and Examples 7 and 8, the type of polymer monomer provided by the application can assist in regulating the structure of the modified layer containing specific ion channels. By polymerizing in the modified layer before forming specific ion channels, the formation of non-specific ion channels can be reduced, thereby realizing precise regulation of specific ion channels, and also improving the firmness of the monovalent cation exchange membrane and enhancing the durability and selectivity of the monovalent cation exchange membrane.

[0193] As can be seen from the comparison of Examples 8, 9, 10 and Comparative Example 2, the content of polymer monomer has an important influence on ion flux and selectivity. The introduction of an appropriate amount of polymer monomer can make the modified layer of the membrane containing specific ion channels more dense, and further enhance the interception ability of other ions outside the specific ions, thereby realizing efficient and selective separation of different ions.

[0194] As can be seen from the comparison of Examples 8, 13 and 14, the content of functional monomer determines the deposition amount of the modified layer on the membrane surface, thereby affecting ion flux and selectivity. Meanwhile, as can be seen from the comparison of Examples 8, 15 and 16, experimental conditions such as soaking time and soaking temperature also play a decisive role in the formation of the modified layer, and reasonable determination of experimental conditions is crucial for the preparation of a monovalent and multivalent selective ion exchange membrane with high selectivity, high flux and low resistance.

[0195] In summary, the preparation method provided by the application constructs specific ion channels on a cation exchange base membrane, introduces polymer monomers before eluting the template, and polymerizes them in the modified layer, thereby enhancing the stability of the modified layer while improving the density of the modified layer and reducing the formation of non-specific ion channels. Moreover, the monovalent selective cation exchange membrane prepared by the application is mainly based on the principle of pore size screening, and has high selectivity for monovalent cations and high flux. Furthermore, the use of polymer monomers and cross-linking agents improves the stability of the monovalent selective cation exchange membrane, and effectively improves the separation performance of the membrane.

[0196] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a monovalent selective cation exchange membrane, characterized in that, The preparation method includes the following steps: (1) Mix sodium chloride and functional monomer to obtain a solution with sodium chloride concentration of 0.4 mol / L to 0.6 mol / L and functional monomer concentration of 0.5 g / L to 10 g / L. Then mix the template agent according to the molar ratio of metal ions to functional monomers in the template agent of 1:1 to 1:25 to obtain a coordination complex. The template agent includes any one or a combination of at least two of lithium salts, nickel salts, copper salts, zinc salts, calcium salts, or magnesium salts; The functional monomers include any one or a combination of at least two of the following: methacrylic acid, N-isopropylacrylamide, acrylic acid, polyethyleneimine, polyallylamine, acrylamide ethyl dimethylamine, polyetherimide, or vinylamine; (2) Add polymer monomers to the coordination complex to make the concentration of polymer monomers in the mixed system from 0.5 g / L to 8 g / L; then immerse the oxidant-modified cation exchange membrane in the mixed system of coordination complex and polymer monomers to form a modified layer on the surface of the cation exchange membrane. The polymer monomers include any one or a combination of at least two of vinyl sulfonic acid, vinyl ether, styrene, dopamine hydrochloride, pyrrole, chitosan, acrylamide ethyl dimethylamine, or acrylamide; (3) The cation exchange base membrane forming the modified layer is crosslinked and soaked with a crosslinking agent at a concentration of 1 wt% to 5 wt%; (4) Use a reducing agent with a concentration of 0.01 mol / L to 1 mol / L for reduction soaking, and carry out the reduction soaking under shaking conditions; (5) Use a detergent with a concentration of 0.05 mol / L to 0.5 mol / L to perform shaking elution to obtain a monovalent selective cation exchange membrane.

2. The preparation method according to claim 1, characterized in that, Step (2) The oxidant-modified cation exchange membrane is immersed in a mixture of coordination complex and polymer monomer at a temperature of 20°C to 40°C.

3. The preparation method according to claim 1, characterized in that, Step (2) involves immersing the oxidant-modified cation exchange membrane in a mixture of coordination complex and polymer monomer for 0.5 h to 10 h.

4. The preparation method according to claim 1, characterized in that, The oxidant includes any one or a combination of at least two of potassium permanganate, ferric chloride, benzoyl peroxide, ammonium persulfate, sodium persulfate, or hydrogen peroxide.

5. The preparation method according to claim 1, characterized in that, During the soaking modification, the concentration of the oxidant is from 0.1 mol / L to 1 mol / L.

6. The preparation method according to claim 1, characterized in that, The soaking modification time is 5 to 30 minutes.

7. The preparation method according to claim 1, characterized in that, The crosslinking agent includes any one or a combination of at least two of ethylene glycol dimethacrylate, methyl methacrylate, vinyl acrylate, glutaraldehyde, epichlorohydrin, ethylene oxide, or dimethylolpropane.

8. The preparation method according to claim 1, characterized in that, The reducing agent includes any one or a combination of at least two of sodium borohydride, triethylamine, sodium bisulfite, ferrous sulfate, sodium cyanoborohydride, sodium iodide, or potassium iodide.

9. The preparation method according to claim 1, characterized in that, The cross-linking soaking temperature is 20°C to 40°C.

10. The preparation method according to claim 1, characterized in that, The cross-linking soaking time is 10 min to 60 min.

11. The preparation method according to claim 1, characterized in that, The temperature of the reduction soaking is 20°C to 30°C.

12. The preparation method according to claim 1, characterized in that, The reduction soaking time is 10 min to 60 min.

13. The preparation method according to claim 1, characterized in that, The detergent comprises any one or a combination of at least two of the following: hydrochloric acid, sulfuric acid, citric acid, disodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, acetonitrile, methanol, ammonia, or sodium hydroxide.

14. The preparation method according to claim 1, characterized in that, The elution process is repeated at least three times, with each elution lasting at least 10 minutes.

15. A monovalent selective cation exchange membrane, characterized in that, The monovalent selective cation exchange membrane is prepared by the preparation method according to any one of claims 1 to 14.

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