Large-scale preparation method of covalent organic framework membrane for CO2 separation
Large-area COF membranes were prepared by interfacial polymerization and roll-to-roll coating technology, which solved the problems of limited area and high cost in the preparation of traditional COF membranes, and achieved efficient and environmentally friendly CO2 separation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-03-24
AI Technical Summary
Existing COF membrane preparation methods are limited by the size of the reaction vessel, resulting in an area limited to the square centimeter level. Furthermore, the high cost and high solvent usage violate the principles of green chemistry, making it difficult to achieve large-scale application.
COF nanosheet dispersions were synthesized in an aqueous phase using interfacial polymerization and combined with roll-to-roll coating technology to prepare large-area COF films. PAN-based films were modified with PEI solution, and ethanol solvent was added to prepare defect-free COF films through a blade coating process.
It has achieved the preparation of large-area COF membranes with high permeability and high selectivity, which are suitable for industrial applications, reduce costs, and comply with the principles of green chemical engineering.
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Figure CN121715069A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of gas separation materials and membrane preparation technology, and relates to a method for the large-scale preparation of a covalent organic framework membrane for CO2 separation. Background Technology
[0002] Global climate change has become a major challenge facing humanity, making the transition of energy systems towards low-carbon energy an urgent priority. Capturing CO2 from flue gas from large stationary emission sources (such as coal-fired power plants, steel mills, and cement kilns) is one of the key technological pathways. Currently, while the mainstream amine liquid chemical absorption method is technically mature, it suffers from inherent drawbacks such as high regeneration energy consumption, equipment corrosion, and solvent loss, resulting in high carbon capture costs. In contrast, membrane separation technology, due to its simple process, low energy consumption, modular equipment, and lack of phase change requirement, is widely considered a highly promising next-generation carbon capture technology. Developing separation membranes with high permeation flux and high selectivity is crucial for reducing the energy consumption and cost of carbon capture.
[0003] Compared to traditional amine liquid chemical absorption methods, membrane technology for CO2 separation consumes less energy and offers a more compact and modular system, eliminating the need for bulky absorption and regeneration towers, thus requiring less floor space and producing no waste amine liquid, making it more environmentally friendly. In existing membrane technologies, traditional polymer membranes are limited by the "trade-off" effect (selectivity and permeability are inversely related); furthermore, water vapor can cause plasticization (structural relaxation) in polymer membranes, leading to permanent selectivity degradation. While inorganic membranes such as zeolite membranes and carbon molecular sieve (CMS) membranes possess high thermal stability, their rigid structure makes large-area, defect-free fabrication difficult, limiting their further application. Additionally, the highly hydrophilic zeolite membrane's rigid pores, when exposed to wet CO2, strongly adsorb water molecules, causing pore blockage and a sharp drop in flux. CMS membrane separation performance is heavily dependent on the precursor polymer and the stringent carbonization process, resulting in poor performance reproducibility. Most critically, CMS membranes are inherently hydrophobic, and their amorphous carbon structure is prone to physical aging in humid environments, leading to performance degradation over time. Hybrid matrix membranes (MMMs) aim to combine polymer processability with high-performance fillers, but they are consistently hampered by interfacial defects between the filler and the polymer matrix (such as pores and rigid interfaces). These non-selective defects significantly reduce the actual selectivity of the membrane. Furthermore, the issues of uniform dispersion of high-proportion fillers and membrane plasticization remain unresolved.
[0004] Covalent organic frameworks (COFs) are an ideal class of gas separation membranes, but the preparation of traditional COF membranes relies on in-situ solvothermal synthesis. This method is limited by the size of the reaction vessel, resulting in membrane areas typically limited to the square centimeter scale. Furthermore, this reaction involves the use of large amounts of organic solvents, requiring high solvent tolerance in the base membrane, which leads to high preparation costs and violates green chemical principles. Another mainstream approach is to first prepare a COF nanosheet dispersion, followed by film deposition on a support using methods such as drop coating, spin coating, or vacuum filtration. These methods are only suitable for preparing small-area samples (below the centimeter scale), limiting their large-scale industrial application. Summary of the Invention
[0005] This invention addresses the significant performance degradation issues encountered during the mass production of traditional COF membranes by proposing a method for the large-scale preparation of covalent organic framework membranes for CO2 separation. Compared to the high-temperature hydrothermal synthesis of zeolite membranes, the dependence of CMS membranes on the size of the carbonization furnace, and the challenges of solution processing and interface control for MMMs, this invention, based on interfacial polymerization, first synthesizes a COF nanosheet dispersion in the aqueous phase and then combines it with roll-to-roll coating technology to prepare a large-area COF membrane with both high permeability and high selectivity. This provides a green, efficient, and highly compatible continuous scale-up pathway with existing chemical equipment.
[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: A method for large-scale preparation of a covalent organic framework membrane for CO2 separation, comprising the following steps: (1) Add the aldehyde monomer to octanoic acid and mix evenly to obtain the oil phase; add the amino monomer and sodium carbonate to deionized water and mix evenly to obtain the aqueous phase; slowly inject the oil phase into the aqueous phase at multiple points through a syringe to obtain the reaction solution for reaction; after the reaction is completed, remove the oil phase and dialyze the aqueous phase to obtain the COF nanosheet dispersion.
[0007] (2) The polyacrylonitrile base film is placed in a polyethyleneimine aqueous solution, immersed and then washed, and left to stand and dry to obtain a flexible PAN base film.
[0008] (3) Mix the COF nanosheet dispersion and ethanol evenly to obtain mixture A. Use a Mayer rod to coat mixture A onto the surface of a flexible PAN base film, heat and dry to obtain a COF film.
[0009] Preferably, in step (1), the aldehyde monomer is 1,3,5-trimethylaldehyde-resorcinol or 2,5-dihydroxyterephthalaldehyde, the concentration of the aldehyde monomer in the oil phase is 0.001-0.1 mol / L, and the amino monomer is any one of 4,4'-diamino-3,3'-biphenyl disulfonic acid, 2,5-diaminobenzenesulfonic acid, ethidium bromide, triaminoguanidine hydrochloride, and 5,5'-diamino-2,2'-bipyridine; the volume ratio of the oil phase to the aqueous phase is 2:(2.5-3.5), and the molar ratio of amino monomer: aldehyde monomer: sodium carbonate in the reaction solution is 1:1:2.
[0010] Preferably, in step (1), dialysis is performed using a dialysis bag with a molecular weight cutoff of 300,000, in deionized water for 2-4 days, with fresh deionized water replaced every 7-15 hours during the dialysis process.
[0011] Preferably, in step (2), the concentration of the polyethyleneimine aqueous solution is 0.1-1 mg / mL, and the immersion time of the polyacrylonitrile-based film in the polyethyleneimine aqueous solution is 2-10 min.
[0012] Preferably, in step (3), the concentration of the COF nanosheet dispersion is 3-6 mg / mL, and the volume ratio of the COF nanosheet dispersion to ethanol is (0.3-15):1.
[0013] Preferably, in step (3), the Mayer rod is set to a temperature of 35-45℃ and a heating rate of 3-6℃ / min.
[0014] This invention proposes the application of the above method in the preparation process of large-area covalent organic framework membranes, wherein the covalent organic framework membrane has a width of 0.1-0.5 m and a length of 0.5-1.0 m.
[0015] This invention proposes the application of the covalent organic framework membrane prepared by the above method in CO2 / N2 separation.
[0016] The large-area COF membrane prepared by this invention is uniform and has stable performance. Firstly, the PAN-based membrane is pretreated and modified using a PEI solution rich in amino groups. This transforms the PAN-based membrane from an inert support into a hydrophilic substrate rich in active sites, ensuring that the COF nanosheets are effectively captured and immobilized upon reaching the substrate surface, preventing them from re-aggregating or migrating with solvent flow. However, the PEI concentration cannot be too low, otherwise the hydrophilic modification of the substrate will be insufficient. If the PEI concentration is too high, the PEI will strongly aggregate due to the strong hydrogen bonding between its segments, clogging the substrate's pores and causing a sharp decrease in gas flux. Furthermore, the appropriate pretreatment time of the PAN substrate in the PEI solution ensures that the water contact angle of the substrate meets the hydrophilicity requirements.
[0017] However, PEI is a chain polymer rich in active groups, so its chain segments will more or less aggregate due to hydrogen bonding. This can lead to incomplete hydrophilic modification at the steps of some uneven areas of the PAN substrate. Therefore, this invention further adds a certain proportion of environmentally friendly, volatile, and polar ethanol solvent to the COF nanosheet dispersion. On the one hand, this ensures thorough hydrophilic modification of the PAN substrate; on the other hand, because ethanol evaporates quickly, it enables the rapid preparation of large-area defect-free COF films. If the proportion of ethanol added is too high, it will reduce the concentration of the COF nanosheet dispersion, resulting in a thinner COF film and exposing more nanoscale or even microscale defects. Similarly, if the concentration of the COF nanosheet dispersion is too high, due to the π-π stacking and electrostatic interaction between the nanosheets, thicker COF microsheets will form, or even agglomerate, which is not conducive to the preparation of large-area defect-free COF films. Therefore, it is necessary to first pretreat and modify the PAN substrate with a certain concentration of PEI solution, and then add an appropriate proportion of ethanol to the COF nanosheet dispersion at an appropriate concentration as a coating fluid. This is a necessary condition for the rapid preparation of large-area defect-free COF films.
[0018] Furthermore, the blade coating process is simple to operate and easily scaled up. The shear force applied during the blade coating process drives the COF nanosheets to align in the liquid layer, fixing them in an ordered state during drying. This results in a dense and uniform film formed through face-to-face stacking. Therefore, this method essentially combines the convenience of "solution-based processing of large-area films" with the precision of "layer-by-layer ordered assembly of two-dimensional materials." Simultaneously, interfacial chemical engineering provides the thermodynamic driving force and kinetic stability for the entire assembly process, thus successfully preparing large-area uniform COF films.
[0019] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The process proposed in this invention can prepare covalent organic framework membranes with a width of 0.1-0.5 m and a length of 0.5-1.0 m. The preparation process is simple and controllable, and the separation performance of the membrane fully meets the requirements of industrial separation of CO2 / N2 mixed gases, making it suitable for large-scale industrial market promotion and application. Attached Figure Description
[0020] Figure 1 This is a photograph of the COF membrane prepared in Example 1.
[0021] Figure 2 The image shows a surface SEM image of the COF membrane prepared in Example 1.
[0022] Figure 3 This is a cross-sectional SEM image of the COF membrane prepared in Example 1. Detailed Implementation
[0023] 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.
[0024] 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.
[0025] Example 1 0.2 mmol of 1,3,5-trimethylaldehyde phloroglucinol (Tp, CAS: 34374-88-4, Jilin Zhongke Science & Technology Co., Ltd.) was dissolved in 20 mL of octanoic acid (C8H4O). 16 In O2 (CAS: 124-07-2, Shanghai Aladdin Biochemical Technology Co., Ltd.), the oil phase was obtained by sonication at 25℃ for 20 min. 0.2 mmol of 4,4'-diamino-3,3'-biphenyl disulfonic acid (BD-(SO3H)2, (CAS: 117-61-3, Jilin Zhongke Science & Technology Co., Ltd.) and 0.4 mmol of sodium carbonate were added to 30 mL of deionized water. The mixture was sonicated at 25°C for 20 min to obtain the aqueous phase. The aqueous phase was added to an 8 cm diameter beaker using a pipette. Then, the oil phase was slowly injected along the beaker wall using a syringe pump (taken 30 min). During the injection process, the syringe pump was moved approximately 90° along the beaker every 5 min. The beaker was then placed in a 25°C incubator and allowed to react in the dark for 7 days. After the reaction, the upper octanoic acid phase was removed using a dropper. The lower aqueous COF nanosheet dispersion was dialyzed for 3 days in a beaker containing 1 L of deionized water using a dialysis bag with a molecular weight cutoff of 300,000. The dialysis bag was boiled in deionized water for 10 minutes before use. The dialysis bags were thoroughly cleaned, disinfected, and activated to remove any chemical contaminants and glycerin that may have been introduced during the production process. During dialysis, the deionized water was changed every 8 hours on the first day and every 12 hours on the last two days to obtain the post-dialysis COF nanosheet dispersion. 5 mL of the post-dialysis COF nanosheet dispersion was dried in a forced-air oven to determine the concentration of the COF nanosheet solids. The calculated concentration of the post-dialysis COF nanosheet dispersion was 5 mg / mL.
[0026] A polyacrylonitrile-based membrane (PAN, molecular weight cutoff 100,000, length 1.0 m, width 0.35 m, Taian Lanjing Trading Co., Ltd.) was laid flat and immersed in approximately 150 L of a 0.5 mg / mL aqueous solution of polyethyleneimine (PEI, molecular weight 70,000, Tianjin Xiens Biochemical Technology Co., Ltd.) for 5 min. Then it was transferred to deionized water and immersed flat for 2 min to remove excess PEI from the PAN surface. Finally, it was left to stand in a clean bench to air dry at room temperature for 2 h.
[0027] 20 mL of the dialyzed COF nanosheet dispersion was mixed with 20 mL of ethanol and magnetically stirred at 600 rpm for 5 min. The pretreated and dried PAN substrate membrane was fixed to both ends of the coating machine platform with tape. An automatic linear feeding mode was used (COF dispersion was added every 2 seconds, the outlet orifice diameter was 1.2 mm, and the feeding motion module was driven by a 5 bar gauge pressure). The coating machine, equipped with a Mayer rod, coated the flexible PAN substrate membrane at a speed of 30 mm / s. Then, the heating platform of the coating machine was turned on, with a heating rate of 5℃ / min, raising the temperature to 40℃ for 2 min to dry the COF membrane. This promoted the tight and orderly stacking of the COF nanosheets, forming a complete and defect-free separation layer, thus preparing a large-area ultrathin uniform COF membrane with a width of 0.35 m and a length of 1.0 m. (See attached image). Figure 1 As shown. After cutting out the COF, surface and cross-sectional SEM images were taken, as shown. Figure 2 and Figure 3 As shown, from Figure 1-3 As can be seen, the COF membrane prepared in this embodiment has a uniform surface and no obvious defects.
[0028] The COF membrane obtained in this embodiment was used in a CO2 / N2 (volume ratio of 15 / 85) separation system. Under the conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 2031 GPU and the selectivity was 59.
[0029] Example 2 Unless otherwise specified, the embodiments described in this example and the following examples are consistent with Example 1. 2 mmol of 1,3,5-triformaldehyde-based phloroglucinol was dissolved in 20 mL of octanoic acid and sonicated at 25°C for 20 min to obtain the oil phase. 0.2 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO3H, CAS: 88-45-9, Jilin Zhongke Science & Technology Co., Ltd.) and 0.4 mmol of sodium carbonate were added to 35 mL of deionized water and sonicated at 25°C for 20 min to obtain the aqueous phase. The aqueous phase was added to an 8 cm diameter beaker using a pipette, and then the oil phase was slowly injected along the beaker wall using a syringe pump (taken 30 min). During the injection process, the syringe pump was moved approximately 90° along the beaker every 5 min. The beaker was then placed in a 25°C incubator and allowed to react in the dark for 7 days. After the reaction, the upper octanoic acid phase was removed using a dropper. The lower aqueous COF nanosheet dispersion was dialyzed for 4 days in a beaker containing 1L of deionized water using a dialysis bag with a molecular weight cutoff of 300,000. Before use, the dialysis bag was boiled in deionized water for 10 minutes to thoroughly clean, disinfect, and activate it, while also removing any chemical contaminants and glycerol that might have been introduced during the production process. During the dialysis process, the deionized water was changed every 7 hours on the first day and every 15 hours for the last three days, resulting in a dialyzed COF nanosheet dispersion. 5mL of the dialyzed COF nanosheet dispersion was dried in a forced-air oven to determine the concentration of the COF nanosheet solids. The calculated concentration of the dialyzed COF nanosheet dispersion was 6mg / mL.
[0030] The polyacrylonitrile-based membrane (PAN, molecular weight cutoff of 100,000, length of 0.8 m and width of 0.5 m) was immersed in a 0.1 mg / mL aqueous solution of polyethyleneimine (PEI, molecular weight of 70,000) for 10 min, then transferred to deionized water for 2 min to remove excess PEI from the PAN surface, and finally left to stand in a clean bench to air dry at room temperature for 2 h.
[0031] 6 mL of the dialyzed COF nanosheet dispersion was mixed with 20 mL of ethanol and magnetically stirred at 600 rpm for 5 min. The two ends of the pretreated and dried PAN base film were fixed to the coating machine platform with tape. An automatic linear feeding mode was adopted (COF dispersion was added every 2 s, the outlet orifice diameter was 1.2 mm, and the feeding motion module was driven by a pressure of 5 bar). The coating machine was equipped with a Mayer rod to coat the flexible PAN base film at a speed of 30 mm / s. Then the heating platform of the coating machine was turned on, and the heating rate was 3℃ / min. The COF film was heated to 35℃ for 2 min for drying treatment, which promoted the tight and orderly stacking of COF nanosheets to form a complete and defect-free separation layer, thus preparing a large-area ultrathin uniform COF film with a width of 0.5 m and a length of 0.8 m.
[0032] The COF membrane obtained in this embodiment was used in a CO2 / N2 (volume ratio of 15 / 85) separation system. Under the conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 2300 GPU and the selectivity was 29.
[0033] Example 3 0.02 mmol of 1,3,5-trimethylaldehyde phloroglucinol was dissolved in 20 mL of octanoic acid and sonicated at 25 °C for 20 min to obtain the oil phase. 0.2 mmol of ethidium bromide (EB, CAS: 1239-45-8, Jilin Zhongke Science & Technology Co., Ltd.) and 0.4 mmol of sodium carbonate were added to 25 mL of deionized water and sonicated at 25 °C for 20 min to obtain the aqueous phase. The aqueous phase was added to an 8 cm diameter beaker using a pipette, and then the oil phase was slowly injected along the beaker wall using a syringe pump (taken 30 min). During the injection process, the syringe pump was moved approximately 90° along the beaker every 5 min. The beaker was then placed in a 25 °C incubator and allowed to react in the dark for 7 days. After the reaction, the upper octanoic acid phase was removed using a dropper. The lower aqueous COF nanosheet dispersion was dialyzed for two days in a beaker containing 1L of deionized water using a dialysis bag with a molecular weight cutoff of 300,000. Before use, the dialysis bag was boiled in deionized water for 10 minutes to thoroughly clean, disinfect, and activate it, while also removing any chemical contaminants and glycerol that might have been introduced during the production process. During the dialysis process, the deionized water was changed every 9 hours on the first day and every 14 hours on the last day, resulting in a dialyzed COF nanosheet dispersion. 5mL of the dialyzed COF nanosheet dispersion was dried in a forced-air oven to determine the concentration of the COF nanosheet solids. The calculated concentration of the dialyzed COF nanosheet dispersion was 4mg / mL.
[0034] The polyacrylonitrile-based membrane (PAN, molecular weight cutoff of 100,000, length of 0.5 m and width of 0.1 m) was immersed in a 1.0 mg / mL aqueous solution of polyethyleneimine (PEI, molecular weight of 70,000) for 2 min, then transferred to deionized water for 2 min to remove excess PEI from the PAN surface, and finally left to stand in a clean bench to air dry at room temperature for 2 h.
[0035] 20 mL of the dialyzed COF nanosheet dispersion was mixed with 1.33 mL of ethanol and magnetically stirred at 600 rpm for 5 min. The two ends of the pretreated and dried PAN base film were fixed to the coating machine platform with tape. An automatic linear feeding mode was adopted (COF dispersion was added every 2 s, the outlet orifice diameter was 1.2 mm, and the feeding motion module was driven by a pressure of 5 bar). The coating machine was equipped with a Mayer rod to coat the flexible PAN base film at a speed of 30 mm / s. Then the heating platform of the coating machine was turned on, and the heating rate was 6℃ / min. The temperature was raised to 45℃ and the COF film was heated for 2 min for drying treatment, which promoted the tight and orderly stacking of COF nanosheets to form a complete and defect-free separation layer, thus preparing a large-area ultrathin uniform COF film with a width of 0.1 m and a length of 0.5 m.
[0036] The COF membrane obtained in this embodiment was used in a CO2 / N2 (volume ratio of 15 / 85) separation system. Under the conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 1809 GPU and the selectivity was 35.
[0037] Example 4 0.2 mmol of 2,5-dihydroxyterephthalaldehyde (Dha, CAS: 1951-36-6, Jilin Zhongke Science & Technology Co., Ltd.) was dissolved in 20 mL of octanoic acid and sonicated at 25 °C for 20 min to obtain the oil phase. 0.2 mmol of triaminoguanidine hydrochloride (TGCl, CAS: 5329-29-3, Jilin Zhongke Science & Technology Co., Ltd.) and 0.4 mmol of sodium carbonate were added to 30 mL of deionized water and sonicated at 25 °C for 20 min to obtain the aqueous phase. The aqueous phase was added to an 8 cm diameter beaker using a pipette, and then the oil phase was slowly injected along the beaker wall using a syringe pump (taken 30 min). During the injection process, the syringe pump was moved approximately 90° along the beaker every 5 min. The beaker was then placed in a 25 °C incubator and allowed to react in the dark for 7 days. After the reaction, the upper octanoic acid phase was removed using a dropper. The lower aqueous COF nanosheet dispersion was dialyzed for 3 days in a beaker containing 1L of deionized water using a dialysis bag with a molecular weight cutoff of 300,000. Before use, the dialysis bag was boiled in deionized water for 10 minutes to thoroughly clean, disinfect, and activate it, while also removing any chemical contaminants and glycerol that might have been introduced during the production process. During the dialysis process, the deionized water was changed every 10 hours on the first day and every 12 hours on the last two days, resulting in a dialyzed COF nanosheet dispersion. 5mL of the dialyzed COF nanosheet dispersion was dried in a forced-air oven to determine the concentration of the COF nanosheet solids. The calculated concentration of the dialyzed COF nanosheet dispersion was 5mg / mL.
[0038] The polyacrylonitrile-based membrane (PAN, molecular weight cutoff of 100,000, length of 0.8 m and width of 0.35 m) was immersed in a 0.25 mg / mL aqueous solution of polyethyleneimine (PEI, molecular weight of 70,000) for 8 min, then transferred to deionized water for 2 min to remove excess PEI from the PAN surface, and finally left to stand in a clean bench to air dry at room temperature for 2 h.
[0039] 20 mL of the dialyzed COF nanosheet dispersion was mixed with 1.33 mL of ethanol and magnetically stirred at 600 rpm for 5 min. The two ends of the pretreated and dried PAN base film were fixed to the coating machine platform with tape. An automatic linear feeding mode was adopted (COF dispersion was added every 2 seconds, the outlet orifice diameter was 1.2 mm, and the feeding motion module was driven by a pressure of 5 bar). The coating machine was equipped with a Mayer rod to coat the flexible PAN base film at a speed of 30 mm / s. Then the heating platform of the coating machine was turned on, and the heating rate was 4℃ / min. The temperature was raised to 35℃ and the COF film was heated for 2 min for drying treatment, which promoted the tight and orderly stacking of COF nanosheets to form a complete and defect-free separation layer, thus preparing a large-area ultrathin uniform COF film with a width of 0.35 m and a length of 0.8 m.
[0040] The COF membrane obtained in this embodiment was used in a CO2 / N2 (volume ratio of 15 / 85) separation system. Under the conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 2197 GPU and the selectivity was 41.
[0041] Example 5 1.0 mmol of 1,3,5-trimethylaldehyde phloroglucinol was dissolved in 20 mL of octanoic acid and sonicated at 25 °C for 20 min to obtain the oil phase. 0.2 mmol of 5,5'-diamino-2,2'-bipyridine (Bpy, CAS: 52382-48-6, Jilin Zhongke Science & Technology Co., Ltd.) and 0.4 mmol of sodium carbonate were added to 25 mL of deionized water and sonicated at 25 °C for 20 min to obtain the aqueous phase. The aqueous phase was added to an 8 cm diameter beaker using a pipette, and then the oil phase was slowly injected along the beaker wall using a syringe pump (taken 30 min). During the injection process, the syringe pump was moved approximately 90° along the beaker every 5 min. The beaker was then placed in a 25 °C incubator and allowed to react in the dark for 7 days. After the reaction, the upper octanoic acid phase was removed using a dropper. The lower aqueous COF nanosheet dispersion was dialyzed for 4 days in a beaker containing 1L of deionized water using a dialysis bag with a molecular weight cutoff of 300,000. Before use, the dialysis bag was boiled in deionized water for 10 minutes to thoroughly clean, disinfect, and activate it, while also removing any chemical contaminants and glycerol that might have been introduced during the production process. During the dialysis process, the deionized water was changed every 8 hours on the first day and every 12 hours on the last 3 days, resulting in a dialyzed COF nanosheet dispersion. 5mL of the dialyzed COF nanosheet dispersion was dried in a forced-air oven to determine the concentration of the COF nanosheet solids. The calculated concentration of the dialyzed COF nanosheet dispersion was 3mg / mL.
[0042] The polyacrylonitrile-based membrane (PAN, molecular weight cutoff of 100,000, length of 0.9 m and width of 0.4 m) was immersed in a 0.75 mg / mL aqueous solution of polyethyleneimine (PEI, molecular weight of 70,000) for 3 min, then transferred to deionized water for 2 min to remove excess PEI from the PAN surface, and finally left to stand in a clean bench to air dry at room temperature for 2 h.
[0043] 20 mL of the dialyzed COF nanosheet dispersion was mixed with 4 mL of ethanol and magnetically stirred at 600 rpm for 5 min. The two ends of the pretreated and dried PAN base film were fixed to the coating machine platform with tape. An automatic linear feeding mode was adopted (COF dispersion was added every 2 s, the outlet orifice diameter was 1.2 mm, and the feeding motion module was driven by a pressure of 5 bar). The coating machine was equipped with a Mayer rod to coat the flexible PAN base film at a speed of 30 mm / s. Then the heating platform of the coating machine was turned on, and the heating rate was 3℃ / min. The temperature was raised to 40℃ and the COF film was heated for 2 min for drying treatment, which promoted the tight and orderly stacking of COF nanosheets to form a complete and defect-free separation layer, thus preparing a large-area ultrathin uniform COF film with a width of 0.4 m and a length of 0.9 m.
[0044] The COF membrane obtained in this embodiment was used in a CO2 / N2 (volume ratio of 15 / 85) separation system. Under the conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 2231 GPU and the selectivity was 33.
[0045] Comparative Example 1 The difference between this comparative example and Example 1 is that the PEI concentration is 0.01 mg / mL, while the amounts of other substances and preparation conditions remain the same as in Example 1. The COF membrane obtained in this comparative example was used in a CO2 / N2 (volume ratio 15 / 85) separation system. Under conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 3400 GPU, and the selectivity was 5.
[0046] Comparative Example 2 The difference between this comparative example and Example 1 is that the PEI concentration is 3 mg / mL, while the amounts of other substances and preparation conditions remain the same as in Example 1. The COF membrane obtained in this comparative example was used in a CO2 / N2 (volume ratio 15 / 85) separation system. Under conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 236 GPU, and the selectivity was 16.
[0047] Comparative Example 3 The difference between this comparative example and Example 1 is that 20 mL of COF nanosheet dispersion was mixed with 0.133 mL of ethanol, while the amounts of other substances and preparation conditions remained the same as in Example 1. The COF membrane obtained in this comparative example was used in a CO2 / N2 (volume ratio 15 / 85) separation system. Under conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 2909 GPU, and the selectivity was 7.
[0048] Comparative Example 4 The difference between this comparative example and Example 1 is that 20 mL of COF nanosheet dispersion was mixed with 200 mL of ethanol, while the amounts of other substances and preparation conditions remained the same as in Example 1. The COF membrane obtained in this comparative example was used in a CO2 / N2 (volume ratio 15 / 85) separation system. Under conditions of 25°C, feed gas pressure of 2 bar, and 100% relative humidity, the CO2 permeation flux was 3631 GPU, and the selectivity was 3.
[0049] 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 for large-scale preparation of a covalent organic framework membrane for CO2 separation, characterized in that, The steps are as follows: (1) Add the aldehyde monomer to octanoic acid and mix evenly to obtain the oil phase; add the amino monomer and sodium carbonate to deionized water and mix evenly to obtain the aqueous phase; slowly inject the oil phase into the aqueous phase at multiple points through a syringe to obtain the reaction solution for reaction; after the reaction is completed, remove the oil phase and dialyze the aqueous phase to obtain the COF nanosheet dispersion. (2) The polyacrylonitrile-based film is placed in a polyethyleneimine aqueous solution, immersed and then washed, and left to stand and dry to obtain a flexible PAN-based film. (3) Mix the COF nanosheet dispersion and ethanol evenly to obtain mixture A. Use a Mayer rod to coat mixture A onto the surface of a flexible PAN base film, heat and dry to obtain a COF film.
2. The method for large-scale preparation of the covalent organic framework membrane for CO2 separation according to claim 1, characterized in that, In step (1), the aldehyde monomer is 1,3,5-trimethylaldehyde-resorcinol or 2,5-dihydroxyterephthalaldehyde, the concentration of the aldehyde monomer in the oil phase is 0.001-0.1 mol / L, and the amino monomer is any one of 4,4'-diamino-3,3'-biphenyl disulfonic acid, 2,5-diaminobenzenesulfonic acid, ethidium bromide, triaminoguanidine hydrochloride, and 5,5'-diamino-2,2'-bipyridine; the volume ratio of the oil phase to the aqueous phase is 2:(2.5-3.5), and the molar ratio of amino monomer: aldehyde monomer: sodium carbonate in the reaction solution is 1:1:
2.
3. The method for large-scale preparation of the covalent organic framework membrane for CO2 separation according to claim 1, characterized in that, In step (1), dialysis is performed using a dialysis bag with a molecular weight cutoff of 300,000 in deionized water for 2-4 days, with fresh deionized water replaced every 7-15 hours during the dialysis process.
4. The method for large-scale preparation of the covalent organic framework membrane for CO2 separation according to claim 1, characterized in that, In step (2), the concentration of the polyethyleneimine aqueous solution is 0.1-1 mg / mL, and the immersion time of the polyacrylonitrile-based film in the polyethyleneimine aqueous solution is 2-10 min.
5. The method for large-scale preparation of a covalent organic framework membrane for CO2 separation according to claim 1, characterized in that, In step (3), the concentration of COF nanosheet dispersion is 3-6 mg / mL, and the volume ratio of COF nanosheet dispersion to ethanol is (0.3-15):
1.
6. The method for large-scale preparation of a covalent organic framework membrane for CO2 separation according to claim 1, characterized in that, In step (3), the Mayer rod is set to a temperature of 35-45℃ and a heating rate of 3-6℃ / min.
7. The application of the method of any one of claims 1-6 in the preparation process of large-area covalent organic framework membranes, wherein the covalent organic framework membrane has a width of 0.1-0.5 m and a length of 0.5-1.0 m.
8. The application of the covalent organic framework membrane prepared by any one of claims 1-6 in CO2 / N2 separation.