Preparation method of in-situ cross-linked monovalent / divalent selective cation exchange membrane
By introducing crosslinking agents with -NCO groups at both ends into the polymer film, chemical bonding of the polymer backbone is achieved, which solves the problems of poor selectivity and stability of existing membranes, and significantly improves the selectivity and mechanical strength of primary/divalent cation separation.
Patent Information
- Application Number
- CN202510469896.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-15
- Publication Date
- 2025-05-30
AI Technical Summary
The existing polymer films have problems of poor selectivity and poor stability in the field of mono/divalent cation separation, and it is difficult to effectively separate similar cations.
By introducing crosslinking agents with -NCO groups at both ends, the polymer backbone is connected by chemical bonds, the membrane pore size is divided, the interaction between ions and membrane pore walls is enhanced, and the ion transport path is optimized, thereby improving the selectivity of one/divalent ion.
It significantly improves the density of the film and selectivity of ion separation, enhances the mechanical strength, extends the service life of the film, and is adapted to the existing homogeneous film casting production process.
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Figure CN120054246A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of membrane technology, and in particular relates to a method for preparing an in-situ cross-linked monovalent / divalent selective cation exchange membrane. Background Art
[0002] The development of ion exchange membranes for the separation of monovalent and divalent cations can be traced back to the 1950s. In the early days, homogeneous membranes such as sulfonated polystyrene and resin-based heterogeneous membranes were mainly used in the field of electrodialysis. The emergence of perfluorosulfonic acid membranes (such as Nafion) in the 1960s significantly improved chemical stability and selectivity, and promoted the innovation of the chlor-alkali industry. Entering the 21st century, various technological breakthroughs have given rise to composite membranes, multilayer membranes, and advanced membrane materials containing specific functional groups, further optimizing ion selectivity and separation efficiency. The importance of this technology is particularly prominent in the field of resources and environment. For example, the separation of lithium and magnesium in salt lake brine is the core challenge of the lithium extraction process in the new energy industry, while the separation of sodium and calcium is directly related to the softening of industrial water and the efficiency of seawater desalination. By reducing the concentration of divalent ions, membrane pollution can be reduced and the life of the equipment can be extended. In the field of metallurgy and chemical industry, the selective interception of heavy metal ions can greatly improve the recycling rate of wastewater or reduce the cost of sewage treatment.
[0003] The technological development of ion exchange membranes in the field of monovalent / divalent cation separation is essentially a precise control project of multiple physical and chemical forces in the process of ion transport. The core challenge of monovalent / divalent ion separation stems from their similar hydration radius (such as Li+0.38nm and Mg2+0.43nm, with a difference of only 13%) and the same charge sign, which requires the separation material to have sub-nanometer structural accuracy and ion recognition capabilities. To achieve efficient separation, modern ion exchange membranes mainly rely on multiple synergistic mechanisms: first, by regulating the sub-nanometer pore size (such as <1nm), the size screening effect is used to preferentially screen monovalent ions with a smaller hydration radius; second, the charged groups on the membrane surface are used to suppress divalent ions with higher charge density (such as Ca) through electrostatic repulsion. 2 +) transmembrane migration; third, the introduction of bionic ion channel design, such as the introduction of specific ligands such as crown ethers, can utilize their interaction with specific ions to achieve selective separation of ions.
[0004] Emerging membrane materials such as MOFs and COFs have achieved extremely high monovalent / divalent ion selectivity due to their easy-to-regulate pores and high structural regularity. However, in practical applications, the selectivity and service life of membrane materials need to be comprehensively considered. Therefore, homogeneous polymer membrane materials are still the best choice for industrial applications. However, current polymer membranes still have problems such as poor selectivity and poor stability, which need to be solved urgently. Summary of the invention
[0005] Based on the above background, the present invention proposes a method for preparing an in-situ crosslinked monovalent / divalent selective cation exchange membrane. By introducing a crosslinking agent with -NCO groups at both ends, the polymer main chains can be connected by chemical bonds, effectively dividing the membrane pore size, improving the membrane density, and facilitating the pore size screening effect of the membrane. At the same time, the crosslinking agent with hydrophilic ends and hydrophobic middle promotes ion transport along the polymer main chain, enhances the interaction between ions and the membrane pore wall, optimizes the ion transport path, and greatly improves the ion separation selectivity.
[0006] To achieve the above object, the present invention adopts the following technical solutions:
[0007] A method for preparing an in-situ crosslinked monovalent / divalent selective cation exchange membrane, comprising the following steps:
[0008] Step 1: Use the PN polymer shown in the structural formula (1) as a precursor;
[0009]
[0010] Step 2: React and graft the PN polymer with a sulfonated monomer to obtain an SPN polymer with ion exchange groups;
[0011] Step 3: Dissolve the SPN polymer and an appropriate amount of acid in an organic solvent, and add a crosslinking agent for reaction;
[0012] Step 4: Directly coat the reaction solution on a glass plate, and dry it to obtain a monovalent / divalent selective cation exchange membrane.
[0013] Further, in formula (1), R is from a bisphenol monomer, and the structural formula of R is shown as any one of formula (2), where * is the connection position:
[0014]
[0015] Further, the PN polymer used in the present invention is prepared by reacting a bisphenol monomer (such as 1,1-bi(2-naphthol), 2,2'-dihydroxybiphenyl, 3,3,3,3-tetramethyl-1,1-spirobi(indane)-6,6-diol) with a keto monomer (such as isatin). The specific reaction method can refer to the literature "One-step synthesis of hydroxyl-functionalized fully carbon main chain PIMs via a Friedel-Crafts reaction for efficient gas separation" (Separation and Purification Technology 262(2021)118313).
[0016] Further, in step 2, the sulfonated monomer is wherein x is any integer with a value of 1 - 5 and can be commercially available.
[0017] Further, in step 2, the molar ratio of the PN polymer to the sulfonated monomer is 1:0.1 - 2.
[0018] Further, in step 2, the grafting sites on the PN polymer are -OH sites or -NH- sites.
[0019] Further, in step 2, the reaction temperature for grafting is 50°C - 120°C, the reaction time is 12h - 48h, and a hydrogen abstraction reagent (such as NaH, potassium carbonate, or sodium tert-butoxide, etc.) is added during the reaction. The molar ratio of the added hydrogen abstraction reagent to the PN polymer is 0.1 - 2:1.
[0020] Further, in step 3, the acid is trifluoroacetic acid, and the addition amount is 0.1% of the mass of the dissolved SPN polymer.
[0021] Further, in step 3, the cross-linking agent is wherein n takes any integer from 2 to 6 and can be commercially available.
[0022] Further, in step 3, the molar ratio of the -OH sites of the SPN polymer to the cross-linking agent is 1:0.05 - 0.5.
[0023] Further, in step 3, the reaction time of the reaction is 0.5h - 4h, the reaction temperature is 25°C - 80°C, and the reaction solvent is dimethyl sulfoxide.
[0024] Further, in step 4, the drying temperature is 60°C - 80°C, and the drying duration is 24h - 48h.
[0025] The method for preparing a divalent and monovalent selective cation exchange membrane provided by the present invention is fully compatible with the existing homogeneous membrane casting production process, greatly improving various performance indicators of the membrane. Its beneficial effects are specifically reflected in the following aspects:
[0026] 1. The precursor polymer PN of the present invention is a self-integrated microporous polymer. Its ether-free structure ensures the chemical stability of the polymer, and the rigid skeleton avoids structural collapse, endowing the membrane with swelling resistance and ensuring the movement space of the sulfonic acid side chains, thereby making ion transport faster and more stable.
[0027] 2. Based on the π-π interaction of the PN polymer, it promotes self-assembly between molecular chains, enhances the long-range order of the structure, and effectively constructs ion transport channels.
[0028] 3. In this experiment, the crosslinking reaction occurs very rapidly, which is very unfavorable for industrial production. By adding an appropriate amount of acid to the reaction solvent, the hydroxyl reaction sites of the SPN polymer can be preferentially occupied to protect the hydroxyl groups, thereby delaying the reaction time and preventing gelation before film coating due to too fast reaction rate, making the entire film-forming process more conducive to industrial production.
[0029] 4. The introduction of the crosslinking agent divides the pores of the self-intrinsic microporous polymer, increasing the density of the membrane. The narrowed pores are beneficial for the sieving between ions of different radii. At the same time, the hydrophobic structure in the middle adjusts the microenvironment of the ion transport channels, promoting the ion transport along the polymer main chain. The sulfonic acid groups in the polymer structure can provide ion hopping sites, and the carbonyl groups generated after in-situ crosslinking, as well as the -OH, -NH- and other sites existing in the polymer itself, can have dipole interactions with ions, which can assist the transport of smaller monovalent ions in the narrowed pore structure, further enhancing the selectivity between monovalent / divalent ions.
[0030] 5. By introducing side chains with -NCO groups at both ends, the molecular chains can be connected by chemical bonds, greatly improving the mechanical strength of the membrane and enhancing the application potential of the membrane in actual scenarios. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 is the ion selectivity test device diagram used in the present invention.
[0032] Figure 2 is the membrane material prepared in Example 4 of the present invention.
[0033] Figure 3 is the ATR-FTIR characterization result of the separation membranes obtained in Examples 1-5 of the present invention.
[0034] Figure 4 is the Li + / Mg 2+ separation test result of the present invention.
[0035] Figure 5 is the Na + / Ca 2+ separation test result of the separation membranes obtained in Examples 1-5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0036] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following detailed description of the specific embodiments of the present invention will be provided in conjunction with the accompanying drawings. The following content is merely an example and explanation of the concept of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, they should fall within the protection scope of the present invention.
[0037] The following examples use the device as Figure 1 shown to perform electrodialysis tests on the obtained polymer membranes: The test device includes a cathode plate and an anode plate. An anion exchange membrane (AGU), the polymer membrane to be tested, and an anion exchange membrane (AGU) are arranged in sequence between the two electrode plates to form a cathode chamber, a concentration chamber, a desalination chamber, and an anode chamber. The cathode chamber is connected to the anode chamber, and the effective area of the membrane is 7.07 cm 2 . The specific test conditions are as follows:
[0038] NaCl-CaCl 2 system: In the desalination chamber, there is 100 mL of 0.1 mol L -1 NaCl and 0.1 mol L -1 CaCl 2 mixed solution. In the concentration chamber, there is 100 mL of 0.01 mol L -1 NaCl solution. In the electrode chamber, there is 0.3 mol L -1 Na 2 SO 4 solution, the current density is 2 mA cm -2 , and the test time is 1 h.
[0039] LiCl-MgCl 2 system: In the desalination chamber, there is 100 mL of 0.1 mol L -1 LiCl and 0.1 mol L -1 MgCl 2 mixed solution. In the concentration chamber, there is 100 mL of 0.01 mol L -1 LiCl solution. In the polarization chamber, there is 0.3 mol L -1 Na 2 SO 4 solution, the current density is 2 mA cm -2 , and the test time is 1 h.
[0040] The calculation method of ion flux is shown in the following formula:
[0041]
[0042] J represents the flux, C 0 represents the initial concentration of cations in the concentration chamber, Ct represents the cation concentration in the concentration chamber when the electrodialysis has been carried out for t hours, V represents the volume of the solution in the concentration chamber, A represents the effective area of the membrane, and t represents the test duration.
[0043] The calculation method of the osmotic selectivity is shown as follows:
[0044]
[0045] P represents the osmotic selectivity, J M + represents the flux of monovalent ions, represents the initial concentration of monovalent ions in the concentration chamber, J D 2+ represents the flux of divalent ions, represents the initial concentration of divalent ions in the concentration chamber.
[0046] Example 1
[0047] Preparation of PN polymer: Measure 28.6 g of 1,1 - bi(2 - naphthol) into a three - necked round - bottom flask, then add 150 mL of dichloromethane. Place the three - necked flask in an ice - bath circulation system, insert a stirring paddle, and start stirring until all the solid medicine bottles are completely dissolved. Add 18.6 g of isatin, then dropwise add 15 mL of trifluoroacetic acid, and continue stirring until isatin is completely dissolved to form a light - red homogeneous solution. Set the condensation circulation temperature to - 10 °C. After the temperature is stable, slowly dropwise add 150 mL of trifluoromethanesulfonic acid to the three - necked flask. After reacting for 48 h, the viscosity of the system rises sharply. Slowly pour the reactant into pure water to obtain the PN crude product. After drying this product, dissolve it with an organic solvent, and pour the obtained solution into pure water again to precipitate. After repeating this operation three times, dry the precipitated polymer to obtain the final polymer PN.
[0048] Preparation of SPN polymer: Weigh 2.5 g of PN polymer and place it in a single - necked round - bottom flask. Put the round - bottom flask into an oil - bath pot, add a magnetic stirrer into the round - bottom flask, add the organic solvent DMSO and stir to dissolve. After dissolution is complete, add 0.1 g of propanesultone, and at the same time add 0.13 g of NaH as a hydrogen - abstracting reagent. Raise the temperature of the oil - bath pot to 70 °C. After reacting for 12 h, precipitate the reactant and dry it to obtain the SPN crude product. Dissolve the SPN crude product with an organic solvent and precipitate it again. After repeating this three times, obtain the high - purity SPN polymer.
[0049] Preparation of the membrane: Take 0.3 g of SPN polymer, dissolve it in 3 g of DMSO, coat the solution on a glass plate, and heat and dry it at 80 °C for 2 h to form a membrane.
[0050] Example 2
[0051] Preparation of PN polymer: same as Example 1.
[0052] Preparation of SPN polymer: same as Example 1.
[0053] Preparation of the membrane: Take 3 g of SPN polymer, dissolve it in 30 g of DMSO, then add 0.003 g of trifluoroacetic acid, and then add 0.157 g of hexamethylene diisocyanobutyrate. After thoroughly mixing for 1 h, apply the reaction solution onto a glass plate and dry it at 80 °C for 12 h to form a membrane, denoted as HCSPN-7, where 7 represents that the molar amount of the cross-linking agent is 7% of the -OH sites in the SPN polymer.
[0054] Example 3
[0055] Preparation of PN polymer: same as Example 1.
[0056] Preparation of SPN polymer: same as Example 1.
[0057] Preparation of the membrane: Take 3 g of SPN polymer, dissolve it in 30 g of DMSO, then add 0.003 g of trifluoroacetic acid, and then add 0.313 g of hexamethylene diisocyanobutyrate. After thoroughly mixing for 1 h, apply the reaction solution onto a glass plate and dry it at 80 °C for 12 h to form a membrane, denoted as HCSPN-14, where 14 represents that the molar amount of the cross-linking agent is 14% of the -OH sites in the SPN polymer.
[0058] Example 4
[0059] Preparation of PN polymer: same as Example 1.
[0060] Preparation of SPN polymer: same as Example 1.
[0061] Preparation of the membrane: Take 0.3 g of SPN polymer, dissolve it in 30 g of DMSO, then add 0.003 g of trifluoroacetic acid, and then add 0.4694 g of hexamethylene diisocyanobutyrate. After thoroughly mixing for 1 h, apply the reaction solution onto a glass plate and dry it at 80 °C for 12 h to form a membrane, denoted as HCSPN-21, where 21 represents that the molar amount of the cross-linking agent is 21% of the -OH sites in the SPN polymer.
[0062] Example 5
[0063] Preparation of PN polymer: same as Example 1.
[0064] Preparation of SPN polymer: same as Example 1.
[0065] Preparation of membrane: Take 0.3g of SPN polymer, dissolve it in 30g of DMSO, then add 0.003g of trifluoroacetic acid, then add 0.939g of hexamethylene diisobutyl cyanate, mix thoroughly for 1h, apply the reaction solution on a glass plate, heat and dry at 80℃ for 12h to form a film, recorded as HCSPN-42, where 42 represents the molar amount of the cross-linking agent is 42% of the -OH sites in the SPN polymer.
[0066] Figure 3 The ATR-FTIR characterization results of the separation membranes obtained in Examples 1-5 are shown in the figure. As the amount of cross-linking agent added increases, the proportion of ether bonds contained in the membrane gradually increases, indicating an increase in the degree of cross-linking. This increase in the degree of cross-linking will divide the membrane pores and have a direct impact on the pore size of the membrane, so that the pore size screening effect can be used to improve the separation effect of monovalent and divalent ions with different hydration radii. At the same time, since the cross-linking agent is hydrophobic in the middle and hydrophilic at both ends, it can promote the transmission of ions along the polymer main chain, and the isocyanate groups at both ends of the cross-linking agent can react with the main chain structure to form carbonyl groups, providing sites for the interaction between ions and the main chain, thereby adjusting the ion transmission path and energy barrier, greatly enhancing the monovalent / divalent ion selectivity of the membrane material.
[0067] Li of the separation membrane obtained in Example 1 to Example 5 + / Mg 2+ The separation test results are as follows Figure 4 As the cross-linking agent content increases, the flux of the membrane to magnesium ions gradually decreases, the flux to lithium ions gradually increases, and the lithium-magnesium selectivity is greatly improved, up to 1067.
[0068] Na of the separation membrane obtained in Example 1-Example 5 + / Ca 2+ The separation test results are as follows Figure 5 As the cross-linking agent content increases, the flux of the membrane to calcium ions gradually decreases, the flux to sodium ions gradually increases, and the sodium-calcium selectivity is greatly improved, up to 132.
[0069] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing an in-situ cross-linked monovalent / divalent selective cation exchange membrane, characterized in that: The steps include: Step 1: using a PN polymer having a structural formula as shown in formula (1) as a precursor; Step 2: reacting and grafting the PN polymer with the sulfonated monomer to obtain the SPN polymer with ion exchange groups; Step 3: dissolving the SPN polymer and an appropriate amount of acid in an organic solvent, and adding a cross-linking agent to react; Step 4: directly apply the reaction solution onto a glass plate and prepare a monovalent / divalent selective cation exchange membrane after drying.
2. The preparation method according to claim 1, characterized in that: In formula (1), the structural formula of R is shown in any one of formulas (2), where * is the connection position:
3. The preparation method according to claim 1, characterized in that: In step 2, the sulfonated monomer is Here, x is any integer between 1 and 5.
4. The preparation method according to claim 1, characterized in that: In step 2, the molar ratio of the PN polymer to the sulfonated monomer is 1:0.1-2.
5. The preparation method according to claim 1, characterized in that: In step 2, the site of reactive grafting on the PN polymer is -OH site or -NH- site, the reaction temperature of reactive grafting is 50°C-120°C, the reaction time is 12h-48h, and a hydrogenation reagent is added during the reaction, and the molar ratio of the amount of hydrogenation reagent added to the PN polymer is 0.1-2:
1.
6. The preparation method according to claim 1, characterized in that: In step 3, the acid is trifluoroacetic acid, and the amount added is 0.1% of the mass of the dissolved SPN polymer.
7. The preparation method according to claim 1, characterized in that: In step 3, the cross-linking agent is Wherein, n is any integer between 2 and 6, and the molar ratio of -OH sites of the SPN polymer to the crosslinking agent is 1:0.05 to 0.
5.
8. The preparation method according to claim 1, characterized in that: In step 3, the reaction time is 0.5h-4h, and the reaction temperature is 25°C-80°C.
9. The preparation method according to claim 1, characterized in that: In step 4, the drying temperature is 60° C.-80° C., and the drying time is 24 h-48 h.
10. A monovalent / divalent selective cation exchange membrane prepared by the preparation method according to any one of claims 1 to 9.