Preparation and application of zwitterionic vinyl covalent organic framework mixed matrix membrane
By preparing a zwitterionic vinyl covalent organic framework hybrid matrix membrane, the azeotropic and poor stability problems in the ethanol and water separation process were solved, achieving efficient ethanol and water separation and improving the membrane's stability and selectivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-05
- Publication Date
- 2026-03-31
AI Technical Summary
Existing polymer membranes suffer from azeotropic and poor stability issues during ethanol and water separation, which limits their large-scale industrial application.
A zwitterionic vinyl covalent organic framework hybrid matrix membrane was prepared by reacting aldehyde monomers, methyl monomers and 4-dimethylaminopyridine in deionized water with ultrasound, followed by the addition of sodium alginate for crosslinking, to form a hybrid matrix membrane with high charge density and strong hydration capacity. The hydrophilicity and stability were improved by utilizing electrostatic interactions.
It improves the water mass transfer rate and permeation selectivity, enhances membrane stability, and achieves efficient ethanol and water separation, making it suitable for ethanol/water mixed systems.
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Figure CN121755050A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of pervaporation membrane preparation technology, and relates to the preparation and application of a zwitterionic vinyl covalent organic framework mixed matrix membrane for the separation of ethanol and water. Background Technology
[0002] Bioethanol, as a sustainable alternative to fossil fuels, can offset carbon emissions through carbon absorption during its production process, aligning with the concept of carbon neutrality. However, fuel-grade bioethanol requires a purity >99.5 wt%, and the presence of ethanol-water azeotropes makes traditional separation methods difficult to achieve. Common alcohol-water separation methods include adsorption separation, azeotropic distillation, extractive distillation, and membrane separation. Among these, pervaporation membrane technology has become a more promising method for bioethanol dehydration due to its advantages such as high separation efficiency, environmental friendliness, low energy consumption, and the ability to utilize low-grade heat energy to drive the separation process. However, existing polymer membranes are prone to swelling-induced plasticization, resulting in poor membrane stability, which limits their large-scale industrial application. Currently, no ideal technical solution to this problem has been reported. Summary of the Invention
[0003] This invention addresses the azeotropic problem in traditional ethanol and water separation processes and the low stability of traditional separation membranes by proposing a method for preparing and applying a zwitterionic vinyl covalent organic framework hybrid matrix membrane for ethanol and water separation.
[0004] To achieve the above objectives, the present invention is implemented using the following technical solution: A method for preparing a zwitterionic vinyl covalent organic framework hybrid matrix membrane, comprising the following steps: (1) Add aldehyde monomer, methyl monomer and 4-dimethylaminopyridine to deionized water, sonicate to obtain a suspension, freeze and seal, then heat to carry out the reaction, collect the solid product after the reaction is completed, centrifuge and wash, vacuum dry to obtain yellow powder; (2) Take the yellow powder and add it to deionized water and mix it evenly to obtain a dispersion. Add sodium alginate and stir to react. After the reaction is complete, filter and let stand to obtain a homogeneous liquid. (3) Spin-coat the homogenized liquid onto the polyacrylonitrile substrate, crosslink it with Ca2+ solution, and dry it to obtain a mixed matrix membrane.
[0005] Preferably, in step (1), the aldehyde monomer is 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, the methyl monomer is 3-(2,4,6-trimethylpyridin-1-onth-1-yl)propane-1-sulfonate, and the molar ratio of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 3-(2,4,6-trimethylpyridin-1-onth-1-yl)propane-1-sulfonate and 4-dimethylaminopyridine is (0.9-1.1):(0.9-1.1):(5.5-6.5); the concentration of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine in the suspension is 0.1 mol / L.
[0006] Preferably, the reaction temperature in step (1) is 155-165℃, the reaction time is 72 h, and the centrifugation washing method is as follows: centrifugation washing three times each with deionized water, N,N-dimethylformamide, tetrahydrofuran and ethanol.
[0007] Preferably, the concentration of the dispersion in step (2) is 0.4-0.8 g / L, and the mass ratio of yellow powder to sodium alginate is 1:(20-33).
[0008] Preferably, in step (3), the spin coating process is performed at 400-600 rpm for 15-25 seconds, followed by spin coating at 700-900 rpm for 35-50 seconds, wherein the Ca 2+ The solution is a CaCl2 solution with a concentration of 0.4-0.6 mol / L.
[0009] This invention proposes the application of zwitterionic vinyl covalent organic framework mixed matrix membranes prepared by the above method in the separation of ethanol / water mixed systems.
[0010] Amphoteric groups can significantly enhance the interaction with water molecules through electrostatic interactions, thereby greatly improving the hydrophilicity of the mixed matrix membrane and thus increasing water molecule mass transfer. On the other hand, the pyridine nitrogen on the COF and the sodium alginate segments with hydroxyl groups can be tightly bound through electrostatic interactions, eliminating membrane defects and increasing both permeation flux and selectivity. Furthermore, the electrostatic interaction between pyridine nitrogen and sodium alginate segments can restrict polymer chain movement and suppress free volume relaxation, thus reducing swelling. The methyl group of the methyl monomer and the aldehyde group of the aldehyde monomer undergo a condensation reaction to form an irreversible covalent bond, resulting in higher stability and maintaining structural integrity under strong acid, strong base, and various organic solvent conditions. During preparation, the amount of COF filler needs to be precisely controlled; too little will prevent the filler from functioning fully, while too much will cause COF aggregation, creating non-selective pores within the membrane and reducing selectivity.
[0011] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The mixed matrix membrane provided by this invention has a simple and controllable preparation process, good stability, and the high charge density and strong hydration capacity of zwitterionic groups can greatly improve the mass transfer rate of water and enhance the pervaporation performance. When applied to ethanol / water systems, it has high permeability and high selectivity, providing new possibilities for efficient separation processes of ethanol and water. Attached Figure Description
[0012] Figure 1 The image shows the surface SEM characterization of the hybrid matrix film prepared in Example 1.
[0013] Figure 2 The image shows a cross-sectional SEM image of the hybrid matrix membrane prepared in Example 1. Detailed Implementation
[0014] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.
[0015] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification. Example 1
[0016] 0.1 mmol of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine (CAS No. 443922-06-3), 0.1 mmol of 3-(2,4,6-trimethylpyridin-1-onthiol-1-yl)propane-1-sulfonate (Jilin Yansheng, 1140-67-6), and 0.6 mmol of 4-dimethylaminopyridine were added to 1 mL of deionized water and sonicated for 30 min to obtain a milky white suspension. The suspension was then placed in ampoules, evacuated with liquid nitrogen for 2 min, circulated three times, flame-sealed, and then placed in a 160 °C oven for three days of constant temperature reaction. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, then centrifuged at 10,000 rpm for 5 min. The supernatant was discarded, and the solid product obtained by centrifugation was collected. The solid product was washed sequentially with 25 mL of deionized water, N,N-dimethylformamide, tetrahydrofuran, and ethanol at 10,000 rpm for 5 min, and the washing process was repeated three times. The product was then dried overnight in a vacuum drying oven at 120℃ to obtain 51 mg of yellow solid powder. 22.85 mg of the yellow solid powder was weighed and added to 30 mL of deionized water. The mixture was stirred at 300 rpm for 10 min to disperse it evenly, obtaining a dispersion. 0.457 g of sodium alginate powder was added, and the mixture was stirred at 300 rpm for 5 h at room temperature to obtain a viscous homogeneous solution. The homogeneous solution was filtered through a 60-mesh nylon filter cloth, and the filtered solution was allowed to stand for 1 h to remove air bubbles formed by vigorous stirring, yielding a casting solution. A polyacrylonitrile substrate with a molecular weight cutoff of 100,000 was cut into 5*5 cm squares, attached to a glass plate, and fixed on a spin coater. 5 mL of casting solution was poured onto a PAN substrate and spin-coated at 500 rpm for 20 s, followed by spin-coating at 800 rpm for 40 s. The resulting mixed matrix membrane was allowed to stand overnight to allow the solvent to evaporate and form a dense membrane. The mixed matrix membrane was then added to 50 mL of a 0.5 mol / L CaCl2 solution and manually shaken for 10 min to crosslink. After crosslinking, the surface of the mixed matrix membrane was rinsed with deionized water for at least 5 min to remove excess CaCl2. The membrane was dried overnight at room temperature to obtain the mixed matrix membrane. The surface of the membrane was then examined. Figure 1 ) and cross-section ( Figure 2 The mixture was characterized by SEM. As can be seen from the figure, the mixed matrix membrane prepared in this embodiment has good homogeneity, no defects, and a dense separation layer.
[0017] The membrane prepared in this embodiment was used in an ethanol / water separation system. During the separation of an ethanol solution at 70 °C and an ethanol:water ratio of 9:1 (mass ratio), the membrane's water permeation flux was 2130 g / (m³). 2The permeation flux was 1021 g / (m²·h). During the long-term operation of up to 120 h, the permeation flux remained above 2000 g / (m²·h), and the mass fraction of permeate water remained above 99%. Example 2
[0018] 0.11 mmol of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 0.11 mmol of 3-(2,4,6-trimethylpyridin-1-onthiol-1-yl)propane-1-sulfonate, and 0.65 mmol of 4-dimethylaminopyridine were added to 1 mL of deionized water and sonicated for 30 min to obtain a milky white suspension. The suspension was then transferred to ampoules, evacuated with liquid nitrogen for 2 min, and circulated three times. The ampoules were then flame-sealed and placed in an oven at 155 °C for three days. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, then centrifuged at 10,000 rpm for 5 min. The supernatant was discarded, and the solid product obtained by centrifugation was collected and washed successively with 25 mL of deionized water, N,N-dimethylformamide, tetrahydrofuran, and ethanol, each centrifuged at 10,000 rpm for 5 min. The washing and centrifugation were repeated three times. The product was then dried overnight in a vacuum drying oven at 120 °C to obtain a yellow solid powder. Weigh 13.71 mg of yellow solid powder and add it to 30 mL of deionized water. Stir at 300 rpm for 10 min to disperse it evenly, obtaining a dispersion. Add 0.457 g of sodium alginate powder, and then stir at 300 rpm for 5 h at room temperature to obtain a viscous homogeneous solution. Filter the homogeneous solution through a 60-mesh nylon filter cloth and let the filtered solution stand for 1 h to obtain a casting solution. Pour 5 mL of the casting solution onto a PAN substrate, spin coat at 400 rpm for 25 s, and then spin coat at 900 rpm for 50 s. Let it stand overnight, then add the mixed matrix membrane to 50 mL of 0.5 mol / L CaCl2 solution, manually shake for 10 min, and rinse the surface of the mixed matrix membrane with deionized water for at least 5 min to remove excess CaCl2 from the membrane surface. Dry at room temperature overnight to obtain the mixed matrix membrane. The membrane prepared in this embodiment was used in an ethanol / water separation system. During the separation of an ethanol solution at 70 °C and an ethanol:water ratio of 9:1 (mass ratio), the membrane's water permeation flux was 1905 g / (m³). 2 ·h), the pervaporation selectivity is 899. Example 3
[0019] 0.09 mmol of 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 0.09 mmol of 3-(2,4,6-trimethylpyridin-1-onthiol-1-yl)propane-1-sulfonate, and 0.55 mmol of 4-dimethylaminopyridine were added to 1 mL of deionized water and sonicated for 30 min to obtain a milky white suspension. The suspension was then transferred to ampoules, evacuated with liquid nitrogen for 2 min, and circulated three times. The ampoules were then flame-sealed and placed in an oven at 165 °C for three days. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, then centrifuged at 10,000 rpm for 5 min. The supernatant was discarded, and the solid product obtained by centrifugation was collected and washed successively with 25 mL of deionized water, N,N-dimethylformamide, tetrahydrofuran, and ethanol, each centrifuged at 10,000 rpm for 5 min. This washing and centrifugation process was repeated three times. The product was then dried overnight in a vacuum drying oven at 120 °C to obtain a yellow solid powder. Weigh 34.4 mg of yellow solid powder and add it to 30 mL of deionized water. Stir at 300 rpm for 10 min to disperse it evenly, obtaining a dispersion. Add 0.457 g of sodium alginate powder, and then stir at 300 rpm for 5 h at room temperature to obtain a viscous homogeneous solution. Filter the homogeneous solution through a 60-mesh nylon filter cloth and let the filtered solution stand for 1 h to obtain a casting solution. Pour 5 mL of the casting solution onto a PAN substrate, spin coat at 600 rpm for 15 s, and then spin coat at 700 rpm for 35 s. Let it stand overnight, then add the mixed matrix membrane to 50 mL of 0.5 mol / L CaCl2 solution, manually shake for 10 min, and rinse the surface of the mixed matrix membrane with deionized water for at least 5 min to remove excess CaCl2 from the membrane surface. Dry at room temperature overnight to obtain the mixed matrix membrane. The membrane prepared in this embodiment was used in an ethanol / water separation system. During the separation of an ethanol solution at 70 °C and an ethanol:water ratio of 9:1 (mass ratio), the membrane's water permeation flux was 2208 g / (m³). 2 ·h), the pervaporation selectivity is 901.
[0020] Comparative Example 1 The difference between this comparative example and Example 1 is that the mass of the yellow solid powder weighed is 4.57 mg, while the rest of the preparation process and the amount of substances used are the same as in Example 1. Under the same detection conditions as in Example 1, the permeation flux of the membrane to water is 1433 g / (m²). 2 ·h), the pervaporation selectivity is 361.
[0021] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass of the yellow solid powder weighed is 45.7 mg, while the rest of the preparation process and the amount of substances used are the same as in Example 1. Under the same detection conditions as in Example 1, the permeation flux of the membrane to water is 2726 g / (m²). 2·h), the pervaporation selectivity is 271.
[0022] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A method of preparing a zwitterionic vinyl covalent organic framework mixed matrix membrane, characterized in that, The steps are as follows: (1) the aldehyde monomer, methyl monomer and 4-dimethylaminopyridine are added into deionized water, ultrasonic, to obtain a suspension, which is sealed after freezing, and then heated for reaction, and the solid product is collected after the reaction, centrifuged and washed, and vacuum dried to obtain a yellow powder; (2) the yellow powder is added into deionized water and mixed uniformly to obtain a dispersion, and sodium alginate is added for stirring reaction, and the homogeneous liquid is obtained after filtration and standing; (3) The homogeneous solution was spin-coated onto a polyacrylonitrile substrate, and Ca 2+ solution cross-linking treatment, drying, to obtain a mixed matrix membrane.
2. The method for preparing the zwitterionic vinyl covalent organic framework hybrid matrix membrane according to claim 1, characterized in that, The aldehyde monomer in step (1) is 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, the methyl monomer is 3-(2,4,6-trimethylpyridine-1-1-yl) propane-1-sulfonate, and the molar ratio of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 3-(2,4,6-trimethylpyridine-1-1-yl) propane-1-sulfonate and 4-dimethylaminopyridine is (0.9-1.1):(0.9-1.1):(5.5-6.5); the concentration of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine in the suspension is 0.1 mol / L.
3. The method for preparing the zwitterionic vinyl covalent organic framework hybrid matrix membrane according to claim 2, characterized in that, The reaction temperature in step (1) is 155-165℃, the reaction time is 72 h, and the centrifugal washing mode is: deionized water, N,N-dimethylformamide, tetrahydrofuran and ethanol are used for centrifugal washing for three times respectively.
4. The method for preparing the zwitterionic vinyl covalent organic framework hybrid matrix membrane according to claim 2, characterized in that, The concentration of the dispersion in step (2) is 0.4-0.8 g / L, and the mass ratio of the yellow powder to sodium alginate is 1:(20-33).
5. The method for preparing the zwitterionic vinyl covalent organic framework hybrid matrix membrane according to claim 2, characterized in that, The spin coating process in step (3) is 400-600 rpm for 15-25 s, then 700-900 rpm for 35-50 s, and the Ca 2+ The solution is a CaCl2solution with a concentration of 0.4-0.6 mol / L.
6. Application of the zwitterionic vinyl covalent organic framework mixed matrix membrane prepared by the method of any one of claims 1-5 in separation in an ethanol / water mixed system.