Preparation method of monovalent selective cross-linked anion exchange membrane and application of monovalent selective cross-linked anion exchange membrane in rectification mixed salt separation

Abstract

The invention relates to the field of polymer materials, and discloses a preparation method of a monovalent selective cross-linked anion exchange membrane and an application of the monovalent selective cross-linked anion exchange membrane in rectification mixed salt separation, the preparation method comprises the following steps: step 1, preparing a synthetic monomer; 2, preparation of a structure main chain; and step 3, preparing the cross-linked anionic membrane. The monovalent selective cross-linked anion exchange membrane prepared by the method has the advantages of good ionic conductivity, good dimensional stability, higher monovalent anion permeation selectivity and the like, and particularly has a wide application prospect in the field of electrodialysis application.

Description

Technical Field

[0001] The present invention relates to the field of polymer macromolecular materials, and specifically relates to a preparation method of a monovalent selective cross-linked anionic exchange membrane and its application in the separation of rectification mixed salts, belonging to the field of membrane technology. Background Art

[0002] In the fields of chemical production, mineral processing, seawater desalination, and industrial wastewater treatment, the separation and resource utilization of mixed salt solutions (such as multi-component salts containing sodium chloride, sodium sulfate, potassium nitrate, etc.) are long-standing technical problems. Traditional separation processes such as evaporation crystallization, chemical precipitation, and ion exchange methods have significant limitations: evaporation crystallization has extremely high energy consumption (the energy consumption can reach more than 1000 kWh / ton when treating high-concentration salt solutions), and it is difficult to selectively separate specific salt components; the chemical precipitation method requires the addition of a large amount of chemical agents (such as sodium carbonate, barium chloride), which is easy to cause secondary pollution and resource waste; while the conventional ion exchange resin method can achieve partial ion separation, but it has frequent regeneration, discontinuous operation, and poor applicability to high-salt systems. With the tightening of environmental protection regulations and the upgrading of the demand for resource recycling economy, the development of efficient, low-consumption, and green mixed salt separation technologies has become an urgent need in the industry.

[0003] Electrodialysis technology provides an innovative solution for the separation of mixed salts due to its unique ion selective migration characteristics. Based on the membrane stack structure with alternating anion and cation exchange membranes, this technology realizes the directional migration and enrichment of target ions under the drive of a direct current electric field, and has the advantages of no phase change, no chemical additives, and continuous operation. In recent years, with the research and development breakthroughs of monovalent selective ion exchange membranes (such as CSV) and bipolar membranes, the application potential of electrodialysis in the separation of mixed salts has been further expanded. For example, monovalent selective membranes can preferentially permeate monovalent ions (such as Na + , Cl - ), while retaining polyvalent ions (such as Ca 2+ , SO4 2- ), thereby realizing the fine fractionation of salt components; bipolar membrane electrodialysis can directly convert mixed salts (such as Na2SO4) into acid (H2SO4) and base (NaOH), greatly enhancing the resource value. In addition, the successful application of electrodialysis technology in scenarios such as lithium extraction from salt lakes and zero liquid discharge (ZLD) of industrial wastewater has verified its technical feasibility in the separation of complex salt systems.

[0004] However, the existing electrodialysis technology still faces multiple challenges in the separation of mixed salts: firstly, high-salt concentration or mixed systems containing polyvalent ions are prone to cause membrane fouling and concentration polarization, resulting in membrane flux decay and increased energy consumption; secondly, traditional homogeneous membranes have similar charge density ions (such as K + and Na +)Insufficient selectivity makes it difficult to achieve precise separation of high-purity salt components. Thirdly, the chemical corrosion resistance and mechanical stability of membrane materials during long-term operation still need to be improved. To address the above problems, this patent proposes an optimized electrodialysis process based on gradient electric field regulation and composite membrane stack design. By introducing a series of measures such as multi-stage membrane stack in series, pulsed electric field mode, and functionalized membrane surface modification, it effectively inhibits concentration polarization, enhances ion selectivity, and improves the long-term operation stability of the system, providing an innovative technical path for the efficient separation and resource utilization of mixed salts. Therefore, it is expected to promote the large-scale application of electrodialysis technology in fields such as salt chemical industry, wastewater reuse, and strategic resource extraction (such as lithium and boron), contributing to the transformation of clean production and circular economy under the "dual carbon" goal. Summary of the Invention

[0005] To solve the above technical problems existing in the prior art, the present invention discloses a method for preparing a monovalent-selective crosslinked anion exchange membrane, which includes the following steps:

[0006] Step 1: Preparation of the monomer

[0007] In a three-necked flask, 1-(3-aminopropyl)imidazole and 3,3-bis(4-hydroxyphenyl)-3H-isobenzofuranone (phenolphthalein) are reacted at a certain molar ratio under a nitrogen atmosphere at 150 - 200 °C for 10 - 60 h by reflux reaction to prepare PPH-Im.

[0008] Step 2: Preparation of the main chain structure

[0009] The PPH-Im monomer and the DFBP (4,4'-difluorodiphenyl sulfone) monomer are co-polycondensed in a polar aprotic solvent at a certain temperature for a certain time according to a molar ratio of 1:1 to obtain a poly(arylene ether sulfone) with imidazole side chains (PAES-Im). The number average molecular weight Mn of the poly(arylene ether sulfone) with imidazole side chains is 10,000 - 150,000.

[0010] Step 3: Preparation of the crosslinked anion membrane

[0011] A certain mass of the poly(arylene ether sulfone) with imidazole side chains (PAES-Im) is dissolved in an organic solvent, and then Br-6C-IM and Br-3C-3OCH3 are added respectively in a certain proportion. After stirring for a certain time at a certain temperature, it is left to stand and defoamed to obtain a casting solution. The mass-volume concentration of the poly(arylene ether sulfone) with imidazole side chains in the casting solution is 3 - 8%. The obtained casting solution is poured onto a glass plate and maintained at 40 - 200 °C for 12 - 96 h to achieve in-situ reaction and drying. After cooling, the film is peeled off from the glass plate in water to obtain the crosslinked anion exchange membrane cPAES-2Im-SiO with a thickness of 70 - 150 μm.

[0012] Furthermore, the molar ratio of the feed in Step 1 is 2.5 - 3.5:1, and the most preferred is 3:1.

[0013] Furthermore, the reflux reaction temperature in Step 1 is 150 - 200 °C.

[0014] Furthermore, the certain temperature and certain time in Step 2 are 150 - 200 °C respectively, the reaction time is 5 - 24 h, and more preferably 180 °C and 18 h.

[0015] Furthermore, the polar aprotic solvent in Step 2 is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide, and N-methylpyrrolidone.

[0016] Furthermore, the molar ratio of PAES-Im to the sum of Br-6C-IM and Br-3C-3OCH3 in Step 3 is 0.4 - 1.00:1. Preferably, the molar ratio of PAES-Im to the sum of Br-6C-IM and Br-3C-3OCH3 is 0.6 - 1.00:1.

[0017] Furthermore, the molar ratio of Br-6C-IM to Br-3C-3OCH3 in Step 3 is 1 - 5:1, and the most preferred is 4:1.

[0018] Furthermore, the in-situ reaction temperature in Step 3 is preferably 170 °C for 16 h.

[0019] Application of the monovalent selective cross-linked anion exchange membrane prepared by the described preparation method in the separation of rectified mixed salts.

[0020] The monovalent selective cross-linked anion exchange membrane prepared by the present invention has advantages such as good ionic conductivity, good dimensional stability, and high monovalent anion permeation selectivity. In particular, it has broad application prospects in the field of electrodialysis applications.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] (1) Due to its rigid and twisted structure containing N-ring QA cations, it hinders the stacking of molecular chains to a certain extent, thus generating free volumes, and further forming unique sub-nanoscale ion transport channels with high monovalent anion permeation and selectivity.

[0023] (2) Introducing a hydrophilic siloxane network structure in the membrane reduces the water absorption rate and swelling rate of the ion membrane and enhances the mechanical strength and tolerance; on the other hand, it can achieve high conductivity at a low exchange capacity, making the membrane have a low surface resistance. Description of the Drawings

[0024] Figure 1It is a physical picture of the cross-linked anion exchange membrane prepared in Example 1;

[0025] Figure 2 It is a schematic diagram of the electrodialysis ion membrane distillation structure. Detailed implementation manners

[0026] To further illustrate the technical solution of the present invention, the preferred implementation manners of the present invention are described below in conjunction with specific embodiments.

[0027] The preparation method of the monovalent selective cross-linked anion exchange membrane of the present invention includes the following steps:

[0028] Step 1: Preparation of the synthetic monomer

[0029] In a three-necked flask, 1-(3-aminopropyl)imidazole and 3,3-bis(4-hydroxyphenyl)-3H-isobenzofuranone (phenolphthalein) are reacted at a certain molar ratio (3:1) under a nitrogen atmosphere at 150-200 °C for 10-60 h by reflux reaction to prepare PPH-Im shown in formula (I);

[0030]

[0031] Step 2: Preparation of the main structure chain

[0032] The PPH-Im monomer shown in formula (I) and the DFBP (4,4'-difluorodiphenyl sulfone monomer) monomer shown in formula (II) are subjected to co-polycondensation in a polar aprotic solvent at a certain temperature for a certain time in a molar ratio of 1:1 of the feed to obtain a poly(arylene ether sulfone) with imidazole in the side chain (PAES-Im) as shown in formula (IV). The number average molecular weight Mn of the poly(arylene ether sulfone) is 10,000-150,000.

[0033]

[0034] Step 3: Preparation of the cross-linked anion membrane

[0035] A certain mass of the poly(arylene ether sulfone) with imidazole in the side chain PAES-Im shown in formula (IV) is dissolved in an organic solvent, and then Br-6C-IM shown in formula (III) and Br-3C-3OCH3 shown in formula (IV) are added respectively in a certain proportion, and stirred at a certain temperature for a certain time, and then left to stand for defoaming to obtain a casting solution. The mass volume concentration of the poly(arylene ether sulfone) with imidazole in the side chain in the casting solution is 3-8%; the obtained casting solution is poured onto a glass plate and kept at 40-200 °C for 12-96 h to achieve in-situ reaction and drying. After cooling, the film is peeled off from the glass plate in water to obtain the cross-linked anion exchange membrane cPAES-2Im-SiO, the structural formula of which is shown in formula (V), and the thickness is 70-150 μm.

[0036]

[0037] The molar ratio of the raw materials in Step 1 is 2.5 - 3.5:1, and the most preferred is 3:1.

[0038] The reaction temperature in Step 1 is 150 - 200 °C, and the reaction time is 10 - 60 h. Further preferably, it is 180 °C for 48 h.

[0039] The certain temperature and certain time in Step 2 are 150 - 200 °C and 5 - 24 h respectively. Further preferably, it is 180 °C and 18 h.

[0040] The polar aprotic solvent in Step 2 is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide, and N-methylpyrrolidone.

[0041] The molar ratio of PAES-Im, Br-6C-IM, and Br-3C-3OCH3 in Step 3 is 0.4 - 1.00:1. As a further preference, the molar ratio of PAES-Im, Br-6C-IM, and Br-3C-3OCH3 is 0.6 - 1.00:1; the reaction temperature is 20 - 100 °C, and the reaction time is 24 h. Further preferably, it is 80 °C.

[0042] The ratio of the two small molecule modifiers Br-6C-IM and Br-3C-3OCH3 in Step 3 is 1 - 5:1, and the most preferred is 4:1.

[0043] The polar aprotic solvent in Step 3 is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide, and N-methylpyrrolidone.

[0044] The drying (in-situ reaction) temperature of the casting solution on the glass plate in Step 3 is 40 - 200 °C and the time is 12 - 96 h. Further preferably, it is 170 °C for 16 h.

[0045] Example 1

[0046] Preparation of synthetic monomers:

[0047] In a three-necked flask, 1-(3-aminopropyl)imidazole and 3,3-bis(4-hydroxyphenyl)-3H-isobenzofuran-1-one (phenolphthalein) were refluxed at 180 °C for 48 h under a nitrogen atmosphere in a molar ratio of 3:1 to prepare PPH-Im.

[0048] Preparation of the structural backbone:

[0049] The poly(arylene ether sulfone) with imidazole groups in the side chain (PAES-Im) was obtained by the copolymerization of PPH-Im monomer and DFBP monomer in a molar ratio of 1:1 in the polar aprotic solvent N-methylpyrrolidone at 180 °C for 18 h. Its number-average molecular weight is 121,200.

[0050] Preparation of crosslinked ion exchange membrane:

[0051] A certain mass of the poly(arylene ether sulfone) main chain PAES-Im was dissolved in N-methylpyrrolidone, and then Br-6C-IM and Br-3C-3OCH3 (with a molar ratio of 1:1 between the two) were added in a molar ratio of 0.8:1. The mixture was stirred at 80 °C for 24 h and then left to stand for defoaming to obtain a casting solution. The mass-volume concentration of poly(arylene ether sulfone) in the casting solution was 5%. The obtained casting solution was poured onto a glass plate and kept at 170 °C for 16 h for in-situ reaction and drying. After cooling, the film was peeled off from the glass plate in water to obtain the crosslinked anion exchange membrane cPAES-2Im-SiO with a thickness of 120 μm, as Figure 1 shown.

[0052] The thickness, ion exchange capacity, tensile strength, and swelling ratio of the prepared crosslinked anion-selective anion exchange membrane were tested by the national standard method; as Figure 2 shown, the surface resistance, transference number, permselectivity (NaCl / Na2SO4), ion flux, and the purity of refined salt of the ion exchange membrane were tested using a self-made device (electrodialysis ion membrane distillation device). The results are shown in Table 1. (For the specific test methods, please refer to the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Science Advances 9,eadh0207(2023); AIChE J.2022; 68:e17710)

[0053] Example 2

[0054] Preparation of synthetic monomers:

[0055] The same preparation process as in Example 1 was used.

[0056] Preparation of the main chain:

[0057] The same preparation process as in Example 1 was used.

[0058] Preparation of crosslinked ion exchange membrane:

[0059] The same preparation process as in Example 1 was used, except that the molar ratio of Br-6C-IM and Br-3C-3OCH3 was 2:1.

[0060] The thickness, ion exchange capacity, tensile strength, and swelling ratio of the prepared cross-linked anionic selective anion exchange membrane were experimentally tested using national standard methods; as Figure 2 shown, a self-made device (electrodialysis ion membrane rectification device) was used to test the surface resistance, transference number, permeation selectivity (NaCl / Na2SO4), ion flux, and the purity of refined salt of the ion exchange membrane. The results are shown in Table 1. (For the specific test methods, see the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Science Advances 9, eadh0207(2023); AIChE J. 2022; 68:e17710)

[0061] Example 3

[0062] Preparation of the synthetic monomer:

[0063] The same preparation process as in Example 1 was adopted.

[0064] Preparation of the structural main chain:

[0065] The same preparation process as in Example 1 was adopted.

[0066] Preparation of the cross-linked ion membrane:

[0067] The same preparation process as in Example 1 was adopted, except that the molar ratio of Br-6C-IM to Br-3C-3OCH3 was 3:1.

[0068] The thickness, ion exchange capacity, tensile strength, and swelling ratio of the prepared cross-linked anionic selective anion exchange membrane were experimentally tested using national standard methods; as Figure 2 shown, a self-made device (electrodialysis ion membrane rectification device) was used to test the surface resistance, transference number, permeation selectivity (NaCl / Na2SO4), ion flux, and the purity of refined salt of the ion exchange membrane. The results are shown in Table 1. (For the specific test methods, see the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Science Advances 9, eadh0207(2023); AIChE J. 2022; 68:e17710)

[0069] Example 4

[0070] Preparation of synthetic monomers:

[0071] The same preparation process as in Example 1 was adopted.

[0072] Preparation of the main chain structure:

[0073] The same preparation process as in Example 1 was adopted.

[0074] Preparation of the crosslinked ion membrane:

[0075] The same preparation process as in Example 1 was adopted, except that the molar ratio of Br-6C-IM to Br-3C-3OCH3 was 4:1.

[0076] The thickness, ion exchange capacity, tensile strength, and swelling ratio of the prepared crosslinked anionic selective anion exchange membrane were experimentally tested using the national standard method; as Figure 2 shown, the surface resistance, transference number, permeation selectivity (NaCl / Na2SO4), ion flux, and purity of refined salt of the ion exchange membrane were tested using a self-made device (electrodialysis ion membrane rectification device). The results are shown in Table 1. (For the specific test method, see the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Science Advances 9, eadh0207(2023); AIChE J.2022; 68:e17710)

[0077] Example 5

[0078] Preparation of synthetic monomers:

[0079] The same preparation process as in Example 1 was adopted.

[0080] Preparation of the main chain structure:

[0081] The same preparation process as in Example 1 was adopted.

[0082] Preparation of the crosslinked ion membrane:

[0083] The same preparation process as in Example 1 was adopted, except that the molar ratio of Br-6C-IM to Br-3C-3OCH3 was 5:1.

[0084] The thickness, ion exchange capacity, tensile strength, and swelling ratio of the prepared crosslinked anionic selective anion exchange membrane were experimentally tested using the national standard method; as Figure 2As shown, a self-made device (electrodialysis ion membrane distillation device) was used to test the surface resistance, transference number, permeation selectivity (NaCl / Na2SO4), ion flux of the ion exchange membrane, and the purity of refined salt. The results are shown in Table 1. (For the specific test method, see the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Science Advances 9, eadh0207(2023); AIChE J. 2022; 68: e17710)

[0085]

[0086] Table 1.

Claims

1. Preparation method of monovalent selective cross-linked anion exchange membrane, comprising the following steps: Step 1: Preparation of monomer In a three-necked flask, 1-(3-aminopropyl)imidazole and 3,3-bis(4-hydroxyphenyl)-3H-isobenzofuranone (phenolphthalein) are refluxed at 150-200 °C for 10-60 h under a nitrogen atmosphere in a certain molar ratio to prepare PPH-Im; Step 2: Preparation of main structure chain PPH-Im monomer and DFBP (4,4'-difluorodiphenyl sulfone) monomer are co-polycondensed in a polar aprotic solvent at a certain temperature for a certain time in a feed molar ratio of 1:1 to obtain poly(arylene ether sulfone) with imidazole side chains (PAES-Im); the number average molecular weight Mn of the poly(arylene ether sulfone) with imidazole side chains is 10,000-150,000; Step 3: Preparation of cross-linked anion membrane A certain mass of poly(arylene ether sulfone) with imidazole side chains (PAES-Im) is dissolved in an organic solvent, and then Br-6C-IM and Br-3C-3OCH3 are added respectively in a certain proportion, stirred at a certain temperature for a certain time, and left to stand for defoaming to obtain a casting solution. The mass-volume concentration of the poly(arylene ether sulfone) with imidazole side chains in the casting solution is 3-8%; the obtained casting solution is poured onto a glass plate and in-situ reaction and drying are carried out at 40-200 °C for 12-96 h. After cooling, the film is peeled off from the glass plate in water to obtain a cross-linked anion exchange membrane cPAES-2Im-SiO with a thickness of 70-150 μm.

2. The preparation method of the monovalent selective cross-linked anion exchange membrane according to claim 1, characterized in that: The feed molar ratio in Step 1 is 2.5-3.5:1, and most preferably 3:

1.

3. The preparation method of the monovalent selective cross-linking type anion exchange membrane according to claim 1, characterized in that: The reflux reaction temperature in Step 1 is 150-200 °C.

4. The preparation method of the monovalent selective cross-linking type anion exchange membrane according to claim 1, characterized in that: The certain temperature and certain time in Step 2 are 150-200 °C respectively, and the reaction time is 5-24 h, and more preferably 180 °C and 18 h.

5. The preparation method of the monovalent selective cross-linked anion exchange membrane according to claim 1, characterized in that: The polar aprotic solvent in Step 2 is at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide and N-methylpyrrolidone.

6. The preparation method of the monovalent selective cross-linking type anion exchange membrane according to claim 1, characterized in that: The molar ratio of PAES-Im to the sum of Br-6C-IM and Br-3C-3OCH3 in Step 3 is 0.4-1.00:

1. Preferably, the molar ratio of PAES-Im to the sum of Br-6C-IM and Br-3C-3OCH3 is 0.6-1.00:

1.

7. The preparation method of the monovalent selective cross-linked anion exchange membrane according to claim 1, characterized in that: The molar ratio of Br-6C-IM to Br-3C-3OCH3 in Step 3 is 1-5:1, and most preferably 4:

1.

8. The preparation method of the monovalent selective crosslinking type anion exchange membrane according to claim 1, characterized in that: The in-situ reaction temperature in Step 3 is preferably 170 °C for 16 h.

9. Application of the monovalent selective cross-linked anion exchange membrane prepared by the preparation method according to any one of claims 1-8 in the separation of mixed salts by rectification.

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