Preparation method of ternary copolymerized cation selective separation membrane

Abstract

The invention discloses a preparation method of a ternary copolymerized cation selective separation membrane, which comprises the following steps: selecting an own microporous polymer PN as a membrane base polymer material, introducing a monomer containing a flexible chain on a main chain, and carrying out ternary polymerization, so that the mechanical property of the membrane is improved, the transmission difference of different ions in the membrane is realized, and the ion selectivity is constructed. The industrial production difficulty is remarkably reduced through a membrane synthesis preparation route of a one-pot reaction, the prepared membrane material can achieve high-performance electrodialysis ion flux, the selectivity superior to that of a current commercial cation selective separation membrane is finally achieved, and large-scale application is expected to be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and specifically relates to a method for preparing a ternary copolymer cation selective separation membrane. The cation selective separation membrane can be applied to many fields such as seawater desalination, lithium extraction from salt lakes, and liquid flow batteries. Background Art

[0002] Ion-selective separation technology holds broad application prospects in seawater desalination, lithium extraction from salt lakes, the chlor-alkali industry, waste acid (alkali) recovery, and flow batteries. It involves key chemical processes such as energy conversion and storage, environmental pollution and monitoring, and resource recovery and reuse. Traditional separation methods primarily include nanofiltration, reverse osmosis, solvent extraction, and chromatography. However, due to inherent technical limitations, these processes suffer from high costs, low recovery rates, and high energy consumption. In recent years, electrodialysis technology, which uses ion-selective separation membranes as key materials, has garnered widespread attention due to its high efficiency, low energy consumption, and environmentally friendly cleanliness. With the continuous development of various industries, higher performance requirements have been placed on membrane materials, including cation-selective separation membranes. However, current ion-selective separation membranes suffer from insufficient performance and high costs. Therefore, further research and development of cation-selective separation membranes is needed to improve their performance to meet application requirements, optimize preparation routes to enable industrial production, and control membrane production costs to achieve cost reduction and efficiency improvement.

[0003] Based on the physicochemical properties of ions with different valence states, research on cation-selective separation membranes has mainly focused on three aspects: utilizing the pore size screening effect to increase the density of the membrane to separate ions of different sizes; utilizing the electrostatic repulsion effect to graft charged groups to separate ions of different charge sizes; and utilizing specific interactions to graft functional side chains to separate target ions. However, most current methods for preparing polymer ion exchange membranes improve the cation selectivity of the membrane through surface modification or blending. Surface modification methods usually modify a dense layer on the membrane surface, which often increases the membrane resistance and leads to increased energy consumption during actual application. At the same time, the problem of surface layer shedding also greatly reduces the stability of the membrane during operation. Although the method of preparing mixed matrix membranes by blending avoids the introduction of a surface modification layer, it increases the complexity of the process and is difficult to adapt to the mature production process of existing membrane material production lines, making it difficult to achieve large-scale preparation. Summary of the Invention

[0004] In light of this, the present invention aims to provide a method for preparing a homogeneous, stable, and simple-to-prepare ternary copolymeric cationic selective separation membrane with high ion selectivity. The selected matrix polymer possesses both a self-polymerizing microporous structure and flexible alkyl chains, which can effectively utilize intermolecular interactions to achieve regular alignment between polymer molecules, thereby regulating micropore size and improving ion selectivity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A method for preparing a ternary copolymerized cationic selective separation membrane comprises the following steps:

[0007] Step 1: copolymerizing 1,1-bi(2-naphthol), isatin and a compound having a structural formula (1) by a superacid catalysis method to obtain a BPN polymer;

[0008]

[0009] In formula (1), R is an electron-rich aromatic ring and n is an integer;

[0010] Step 2: reacting and grafting the BPN polymer with the sulfonated monomer to obtain the SBPN polymer with cation exchange groups;

[0011] Step 3: dissolving the SBPN polymer in an organic solvent to prepare a membrane solution, pouring the membrane solution onto a glass plate and drying it to prepare a ternary copolymer cation selective separation membrane.

[0012] Furthermore, in step 1, the compound with the structural formula shown in formula (1) is 1,2-diphenylethane, 1,2-di(1-naphthyl)ethane, biphenyl, 1,3-diphenylpropane, 1,3-diphenylbutane or 1,4-diphenylbutane.

[0013] Furthermore, in step 1, the molar ratio of 1,1-bi(2-naphthol), isatin and the compound having the structural formula (1) is x:1:1-x, wherein 0.1≤x<1; the super acid used for the super acid catalysis is trifluoroacetic acid and trifluoromethanesulfonic acid, and the volume ratio of the two is 5:1; the reaction temperature of the copolymerization is -10°C to 10°C.

[0014] Further, in step 2, the sulfonated monomer is Wherein, l and m are each independently selected from any integer between 1 and 5.

[0015] Furthermore, in step 2, the molar ratio of the BPN polymer to the sulfonated monomer is 1:0.1-2.

[0016] Furthermore, in step 2, the sites of reactive grafting on the BPN polymer are some -OH sites or -NH- sites. The reaction temperature for reactive grafting of the sulfonated monomer is 50°C-100°C, and the reaction time is 12 hours-48 hours. A hydrogenation reagent is added during the reaction, and the molar ratio of the hydrogenation reagent to the sulfonated monomer is 1-1.5:1. The hydrogenation reagent includes sodium hydroxide, potassium hydroxide, potassium carbonate, sodium tert-butoxide, etc. The solvent used in the reaction is N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, etc.

[0017] Furthermore, in step 3, the drying temperature is between 40°C and 100°C.

[0018] The method for preparing a cation-selective separation membrane provided by the present invention is fully compatible with the existing homogeneous membrane casting process. The membrane preparation process is simple and the selectivity of the membrane is greatly improved. The beneficial effects are specifically reflected in the following aspects:

[0019] (1) The molecular structure of binaphthol in the polymer backbone facilitates the formation of a self-polymerized microporous structure. Its confined pores facilitate the construction of selective ion transport channels, avoiding the problem of random distribution and uncontrollable ion transport channels in traditional polymers due to the random arrangement of molecular chains. Furthermore, the polymer prepared from binaphthol has a certain rigidity, which ensures that the prepared cation exchange membrane has minimal swelling in water, ensures the dimensional stability of the formed ion transport channels, and prolongs the service life of the membrane.

[0020] (2) The active functional groups -OH and -NH- on binaphthol and isatin are conducive to further grafting modification of the polymer, and the hydrogen bond interaction formed between the two functional groups promotes the formation of confined channels. At the same time, the strong π-π interaction formed by binaphthol promotes the regularity of the channels within the membrane. The regular channels reduce the resistance to the transmission of target ions, and the limited channel size increases the energy barrier for the transmission of other ions across the membrane, which is conducive to the efficient and rapid separation of target ions. At the same time, the membrane can be regulated by changing the membrane preparation temperature, binaphthol content, and other methods to form channels suitable for the transmission of target ions, thereby achieving selective separation of different target ions.

[0021] (3) The flexible chain connecting two electron-rich monomers can enhance the toughness of the membrane, solving the problem of fragile membranes made from rigid binaphthol polymers. In addition, the flexible alkyl chain reduces steric hindrance, which is conducive to the self-assembly of binaphthol to form more regular channels, enhancing the orientation of the confined channels formed, thereby reducing the energy barrier for the transport of target ions across the membrane and further improving the flux of target ions.

[0022] (4) The grafting modification of the polymer by sulfonated monomers forms hydrophilic regions in the membrane. By controlling the grafting ratio of the sulfonated monomers, the microphase separation structure is regulated, thereby changing the size of the ion transmission channel, improving the membrane's ion screening ability, and thus improving ion selectivity.

[0023] (5) The synthesis process of the present invention is simple and easy to industrialize. The polymer obtained can be formed into a film by solvent evaporation, which is easy to mass-produce. In addition, the obtained membrane is a homogeneous membrane with regular confined channels and low membrane resistance, avoiding the problems of high energy consumption and poor stability caused by surface modification methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a photograph of the cation selective separation membrane prepared in Example 1 of the present invention.

[0025] Figure 2 These are the NMR results of the SBPN polymers prepared in various examples and comparative examples of the present invention.

[0026] Figure 3 2 is a diagram of an ion selectivity testing device used in a specific embodiment of the present invention.

[0027] Figure 4 The cation selective separation membranes in the embodiments and comparative examples of the present invention are -2 Graph of ion separation performance at different current densities.

[0028] Figure 5 The cation selective separation membranes in the embodiments and comparative examples of the present invention are -2 Graph of ion separation performance at different current densities.

[0029] Figure 6 is the IEC value of the cation selective separation membrane in each embodiment and comparative example of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions of the present invention are further illustrated by examples below. These technical solutions are only intended to make the present invention easier to understand by researchers in the field, and are not intended to limit the scope of protection of the present invention. All variations and extensions made using the present invention are within the scope of protection of the present invention.

[0031] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0032] 1. Preparation of ternary copolymer cation selective separation membrane

[0033] Example 1

[0034] The preparation steps of the ternary copolymer cation selective separation membrane provided in this embodiment are as follows:

[0035] 1. Preparation of BPN polymer: Measure 0.09 mol of 1,1-bi(2-naphthol) and 0.01 mol of 1,2-diphenylethane in a round-bottom three-necked flask, then add 15 mL of dichloromethane, place the three-necked flask in an ice bath circulation system, add a magnetic rod, start stirring until all the solids are dissolved, add 0.1 mol of indigo, then add 15 mL of trifluoroacetic acid dropwise, continue stirring until all the indigo is dissolved to form a light red uniform solution, set the condensation circulation temperature to -10 ° C, and after the temperature stabilizes, slowly add 3 mL of trifluoromethanesulfonic acid dropwise to the three-necked flask. After reacting for 48 hours, the viscosity of the system rises sharply. Slowly pour the reactant into pure water to obtain a crude BPN product. After drying this product, dissolve it in the organic solvent DMSO, and pour the dissolved solution into pure water again to precipitate. Repeat this operation three times, and then dry the precipitated polymer to obtain the final BPN polymer:

[0036]

[0037] 2. Preparation of SBPN-17.5 polymer: Weigh 1 mol of BPN polymer and place it in a single-necked round-bottom flask. Place the round-bottom flask in an oil bath and add a magnet. Add the organic solvent DMSO and stir to dissolve. After dissolution is complete, add 0.175 mol of propanesulfonic acid lactone and 0.175 mol of sodium tert-butoxide as a hydrogen extraction agent. Raise the oil bath temperature to 70°C and react for 48 hours. Then, precipitate the reactant and dry it to obtain a crude SBPN product. Dissolve the crude SBPN product in the organic solvent DMSO and precipitate it again. Repeat this process three times to obtain a high-purity SBPN polymer, designated as SBPN-17.5 polymer:

[0038]

[0039] 3. Membrane Preparation: Weigh 0.25 g of SBPN polymer into a 20 mL glass vial. Add 2.5 g of the organic solvent DMSO to the vial. Stir on a magnetic stirrer until dissolved to obtain a membrane solution. This membrane solution was evenly cast onto a glass plate and dried at 90°C for 12 hours to form a membrane. This membrane produced a cation-selective membrane with high monovalent / divalent selectivity.

[0040] The prepared membrane materials are Figure 1 The H NMR analysis results of the obtained SBPN-17.5 polymer are shown in Figure 2 shown.

[0041] Example 2

[0042] The preparation steps of the ternary copolymer cation selective separation membrane provided in this embodiment are as follows:

[0043] Preparation of BPN polymer: The same preparation method as in Example 1 was used.

[0044] Preparation of SBPN-25 polymer: The same preparation method as in Example 1 was used, except that 0.25 mol of propane sultone and 0.25 mol of sodium tert-butoxide were added during the reaction. The obtained product was designated as SBPN-25 polymer.

[0045] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0046] The H NMR analysis results of the obtained SBPN-25 polymer are as follows: Figure 2 shown.

[0047] Example 3

[0048] The preparation steps of the ternary copolymer cation selective separation membrane provided in this embodiment are as follows:

[0049] Preparation of BPN polymer: The same preparation method as in Example 1 was used.

[0050] Preparation of SBPN-12.5 polymer: The same preparation method as in Example 1 was used, except that 0.125 mol of propane sultone was added during the reaction. The obtained product was designated as SBPN-12.5 polymer.

[0051] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0052] The H NMR analysis results of the obtained SBPN-12.5 polymer are as follows: Figure 2 shown.

[0053] Example 4

[0054] The preparation steps of the ternary copolymer cation selective separation membrane provided in this embodiment are as follows:

[0055] Preparation of 15BPN polymer: The same preparation method as in Example 1 was used, except that 0.085 mol of 1-bi(2-naphthol) and 0.015 mol of 1,2-diphenylethane were added during the reaction.

[0056] Preparation of 15SBPN-17.5 polymer: The same preparation method as in Example 1 was used, and the obtained product was recorded as 15SBPN-17.5 polymer.

[0057] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0058] The H NMR analysis results of the obtained 15SBPN-17.5 polymer are as follows: Figure 2 shown.

[0059] Example 5

[0060] The preparation steps of the ternary copolymer cation selective separation membrane provided in this embodiment are as follows:

[0061] Preparation of 20BPN polymer: The same preparation method as in Example 1 was used, except that 0.08 mol of 1-bi(2-naphthol) and 0.02 mol of 1,2-diphenylethane were added during the reaction.

[0062] Preparation of 20SBPN-17.5 polymer: The same preparation method as in Example 1 was used, and the obtained product was recorded as 20SBPN-17.5 polymer.

[0063] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0064] The H NMR analysis results of the obtained 20SBPN-17.5 polymer are as follows: Figure 2 shown.

[0065] Comparative Example 1

[0066] The commercial cation selective separation membrane CIMS was used as a comparison.

[0067] Comparative Example 2

[0068] The amounts of 1,1-bi(2-naphthol) and 1,2-diphenylethane in step 1 of Example 1 were adjusted to 0.1 mol and 0 mol to obtain a PN polymer, which was then used to replace the BPN polymer in step 2 of Example 1 for sulfonation to obtain an SPN-17.5 polymer, which was then formed into a film according to the method of step 3 of Example 1.

[0069] Comparative Example 3

[0070] The preparation steps of the ternary copolymer cationic selective separation membrane provided in this comparative example are as follows:

[0071] Preparation of 20BPN polymer: The same preparation method as in Example 5 was adopted.

[0072] Preparation of 20SBPN-24 polymer: The same preparation method as in Example 5 was used, except that 0.24 mol of propane sultone and 0.24 mol of sodium tert-butoxide were added during the reaction. The obtained product was designated as 20SBPN-24 polymer.

[0073] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0074] The H NMR analysis results of the obtained 20SBPN-24 polymer are as follows: Figure 2shown.

[0075] Comparative Example 4

[0076] The preparation steps of the ternary copolymer cationic selective separation membrane provided in this comparative example are as follows:

[0077] Preparation of 5BPN polymer: The same preparation method as in Example 1 was used, except that 0.095 mol of 1-bi(2-naphthol) and 0.005 mol of 1,2-diphenylethane were added during the reaction.

[0078] Preparation of 5SBPN-17.5 polymer: The same preparation method as in Example 1 was used, and the obtained product was recorded as 5SBPN-17.5 polymer.

[0079] Preparation of the membrane: The same preparation method as in Example 1 was adopted.

[0080] The HNMR analysis results of the obtained 5SBPN-17.5 polymer are as follows: Figure 2 shown.

[0081] 2. Membrane flux and ion selectivity test

[0082] Use Figure 3 The device shown is at 5 mA cm -2 or 2mAcm -2 The current density of the cation selective separation membranes obtained in Examples 1 to 5 and Comparative Examples 1 to 4 was tested. + / Mg 2+ Ion selectivity (commercial monovalent / divalent selective cation exchange membrane CIMS tested under the same conditions was used as a control), the specific method is as follows:

[0083] The device is divided into four chambers by three membranes: (cathode) pole chamber | concentration chamber | desalination chamber | pole chamber (anode). The membranes between the cathode and concentration chamber, and between the anode and desalination chamber are commercial common anion exchange membranes AGU, whose main purpose is to separate the pole chamber solution from the internal chamber solution. The membrane to be tested is between the desalination chamber and the concentration chamber. A 0.3M sodium sulfate solution circulates in the pole chamber, a 0.01M KCl solution circulates in the concentration chamber, and a 0.1M LiCl and 0.1M MgCl2 mixed solution circulates in the desalination chamber. After the device circulates the corresponding solutions, voltage is applied on both sides. The cations in the desalination chamber migrate from the desalination chamber to the concentration chamber under the action of the electric field. Due to the ion selectivity of the membrane, a large amount of lithium ions pass through, while a small amount of magnesium ions pass through. Finally, the concentrations of lithium ions and magnesium ions in the concentration chamber are measured, and the ion flux is calculated based on the concentration:

[0084]

[0085] Where C tis the ion concentration after the concentration chamber has been running for t hours, C0 is the initial ion concentration of the concentration chamber, and A m is the effective area of the membrane in the test, t is the operating time, V is the final volume of the concentration chamber, and the final flux ratio of lithium ions to magnesium ions is the selectivity value.

[0086] Li of all cation selective separation membranes in Examples 1 to 5 and Comparative Examples 1 to 4 + / Mg 2+ Ion selection test results are as follows Figure 4 、 5 As shown, the IEC value is as follows Figure 6 As shown, it can be seen that the BPN polymer prepared by the present invention shows a higher lithium ion flux and a higher lithium magnesium selectivity only after sulfonation, and the preparation method is simple. The degree of sulfonation of the SBPN polymer obtained in Example 1 is 17.5%. Even though the IEC value of the membrane is only 0.41, the flux and selectivity it exhibits are higher than those of the commercial membrane CIMS and the pure SPN membrane, which illustrates the effectiveness of the membrane prepared by the present invention in the selective construction of mono / divalent selective cation exchange membranes. A small amount of 1,2-diphenylethane in the main chain can promote the self-assembly of binaphthol through its own flexible chain, making the channel more regular and improving the lithium ion flux, as shown in Example 4. Reducing the content of 1,2-diphenylethane, such as in Comparative Example 4, due to the low content of 1,2-diphenylethane, its ability to promote polymer self-assembly is weakened, and the selectivity is not greatly improved compared with the pure SPN membrane. When the content of 1,2-diphenylethane is increased, such as in Example 5, the π-π interaction in the polymer is weakened, resulting in a widening of the pores, thereby reducing the selectivity, but its content at 2mAcm -2 The selectivity is still greater than that of commercial membrane CIMS.

[0087] In summary, the preparation method of the ternary copolymer cationic selective separation membrane provided by the present invention has a simple process, superior performance, and is extremely easy to achieve industrial preparation. It has great application potential in the fields of chemical precision separation, seawater desalination, and lithium extraction from salt lakes.

Claims

1. A method for preparing a ternary copolymer cation selective separation membrane, characterized in that: The steps include: Step 1: copolymerizing 1,1-bi(2-naphthol), isatin and a compound having a structural formula (1) by a superacid catalysis method to obtain a BPN polymer; In formula (1), R is an electron-rich aromatic ring and n is an integer; Step 2: reacting and grafting the BPN polymer with the sulfonated monomer to obtain the SBPN polymer with cation exchange groups; Step 3: dissolving the SBPN polymer in an organic solvent to prepare a membrane solution, pouring the membrane solution onto a glass plate and drying it to prepare a ternary copolymer cation selective separation membrane.

2. The preparation method according to claim 1, wherein: In step 1, the compound having the structural formula shown in formula (1) is 1,2-diphenylethane, 1,2-di(1-naphthyl)ethane, biphenyl, 1,3-diphenylpropane, 1,3-diphenylbutane or 1,4-diphenylbutane.

3. The preparation method according to claim 1, characterized in that In step 1, the molar ratio of 1,1-bi(2-naphthol), isatin and the compound represented by the structural formula (1) is x:1:1-x, wherein 0.1≤x<1; the super acid used in the super acid catalysis is trifluoroacetic acid and trifluoromethanesulfonic acid, and the volume ratio of the two is 5:1; the reaction temperature of the copolymerization is -10°C to 10°C.

4. The preparation method according to claim 1, characterized in that In step 2, the sulfonated monomer is or Wherein, l and m are each independently selected from any integer between 1 and 5.

5. The preparation method according to claim 1 or 4, characterized in that: In step 2, the molar ratio of the BPN polymer to the sulfonated monomer is 1:0.1-2.

6. The preparation method according to claim 1, wherein: In step 2, the reactive grafting site on the BPN polymer is the -OH site or the -NH- site.

7. The preparation method according to claim 1, wherein: In step 2, the reaction temperature of the grafting reaction is 50° C.-100° C., the reaction time is 12 h-48 h, a hydrogenation reagent is added during the reaction, and the molar ratio of the hydrogenation reagent to the sulfonated monomer is 1 to 1.5:

1.

8. The preparation method according to claim 1, wherein: In step 3, the drying temperature is between 40°C and 100°C.

9. A ternary copolymer cation selective separation membrane prepared by the preparation method according to any one of claims 1 to 8.

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