Preparation method and application of COF-polyamide composite membrane loaded with ionic liquid

Abstract

The present invention discloses a preparation method and application of a COF-polyamide composite membrane loaded with an ionic liquid, which belongs to the field of gas separation membranes. The separation layer of the COF-polyamide composite membrane loaded with an ionic liquid includes a COF-polyamide layer and a spin-coated ionic liquid, and the supporting layer is a porous base membrane, wherein the COF-polyamide layer is prepared by an interfacial polymerization method, and the embedded amide bonds can effectively make up for the defects in the COF layer and improve its stability; the ionic liquid is loaded onto the surface of the COF-polyamide layer by spin coating, and the electrostatic interaction between the two causes it to enter the COF pores, reduce the pore size of the COF, and enhance the affinity of the composite membrane for CO2. The method of the present invention is simple to operate, has a short process flow, and the composite membrane obtained has a high permeability selectivity for CO2.

Description

[0001] Technical field: The present invention relates to a preparation method and application of a COF-polyamide composite membrane loaded with ionic liquid, which belongs to the field of gas separation membranes. Background technology: The extensive use of fossil fuels has led to a continuous increase in the concentration of CO2 in the atmosphere, triggering a series of climate crises such as sea level rise and greenhouse effect, which has placed a huge burden on the ecological environment. At present, the main methods for capturing CO2 are low-temperature distillation and absorption, but both face huge energy consumption and environmental pollution problems. Membrane separation technology has gradually shown its unique advantages in the field of CO2 separation. Compared with traditional processes, membrane separation technology has low energy consumption, an environmentally friendly operation process, and good separation effect. Therefore, membrane separation technology is expected to become an important development direction in the field of CO2 separation in the future.

[0002] Covalent organic frameworks (COFs) are an emerging class of porous materials formed by covalently linking organic monomers. They possess inherent pores, adjustable pore size, low density, high thermal stability, and chemical stability. These properties make COFs useful in the manufacture of efficient gas separation membranes. The traditional interfacial polymerization process is an important method for preparing COFs membranes, characterized by mild reaction conditions, simple operation, automated membrane formation, and ease of scalability. Compared with the solvothermal method, the COFs membranes synthesized by this process are often structurally disordered and have defects. Furthermore, the inherent large pore size of COFs membranes makes it difficult to achieve precise screening of specific gas molecules, limiting their application in the field of gas separation.

[0003] Therefore, the present invention devised a method to repair defects in pure COF membranes by introducing trimesoyl chloride (TMC) to compensate for the disordered pores generated during interfacial polymerization. Simultaneously, the COF-polyamide composite membrane was post-modified with an imidazole ionic liquid (IL) to reduce the COF pore size and enhance its affinity for CO₂, thereby achieving efficient CO₂ separation.

[0004] SUMMARY OF THE INVENTION: The present invention provides a method for preparing a COF-polyamide composite membrane loaded with ionic liquid. The method is not only simple to operate and has a short process flow, but also can effectively separate CO2.

[0005] The technical solutions of the present invention are as follows:

[0006] (1) Preparation of precursor solution

[0007] Aqueous Solution: Weigh a certain amount of p-phenylenediamine and dissolve it in deionized water. Stir thoroughly to prepare an aqueous solution with a certain mass fraction. Then, add a certain amount of glacial acetic acid to the solution to promote interfacial polymerization. Ultrasonic treatment can be performed during the dissolution process to ensure that the amine monomer is evenly dispersed in the deionized water.

[0008] Oil Phase Solution: Weigh a certain amount of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and trimesoyl chloride monomers and dissolve them in n-hexane organic solvent and stir until uniform. The aldehyde and acyl chloride are weighed in a specific mass ratio to prepare an oil phase solution with a certain total mass fraction of aldehyde and acyl chloride. Ultrasonic treatment can be performed during the dissolution process to ensure that the two monomers are evenly dispersed in the n-hexane.

[0009] (2) Interfacial Polymerization Reaction (2.1) The aqueous solution prepared in step (1) is poured onto the surface of the porous support. The aqueous solution is allowed to remain on the polysulfone porous substrate for a certain period of time, and then the aqueous solution on the substrate surface is rolled dry using a rubber roller. The time the aqueous solution remains on the porous substrate surface is the aqueous contact time.

[0010] (2.2) Pour the oil phase solution prepared in step (1) onto the surface of the polysulfone substrate treated in step (2.1), allowing the polysulfone substrate saturated with the amine solution to contact the oil phase solution for a certain period of time, thereby forming a COF-polyamide layer on the porous support surface. Excess oil phase solution is then poured out, and the membrane is washed several times with n-hexane to obtain a COF-polyamide composite membrane. The trimesoyl chloride in the oil phase undergoes an amidation reaction with p-phenylenediamine. The embedded amide bonds can repair defects in the COF layer and effectively improve its stability. The contact time between the oil phase solution and the porous support surface is the reaction time.

[0011] (3) Heat treatment

[0012] The COF-polyamide composite membrane prepared in step (2) is heat-treated at an appropriate temperature for a certain period of time to enhance the binding force between the COF-polyamide separation layer and the polysulfone, and to facilitate the reversibility of the ketoamine condensation reaction, promote the error correction process in the cross-linked network, and compensate for the dangling bonds in the 2D COF network to improve the crystallinity.

[0013] (4) Loaded ionic liquid

[0014] A certain amount of ionic liquid ethanol solution is spin-coated onto the composite membrane obtained in step (3) to obtain a COF-polyamide composite membrane loaded with ionic liquid. The ionic liquid is introduced into the COF pores to reduce the pore size of the COF and enhance the affinity for CO2.

[0015] The mass fraction of the amine aqueous solution in the above step (1) is 0.05 wt% to 1 wt%, preferably 0.1 wt%.

[0016] The volume fraction of the acid catalyst in the above step (1) is 1 v / v%.

[0017] The mass ratios of the aldehyde and the acyl chloride in the above step (1) are 9:1, 7:3, 5:5, and 3:7.

[0018] The mass fraction of the aldehyde and acyl chloride oil phase solution in the above step (1) is 0.00125 wt% to 0.025 wt%, preferably 0.0025 wt%.

[0019] The pore size of the polysulfone described in the above step (2) is 20 nm.

[0020] The water phase contact time in the above step (2) is 30 seconds, and the reaction time is 5 to 40 seconds.

[0021] The heat treatment temperature in the above step (3) is 60° C. and the heat treatment time is 5 min.

[0022] The ionic liquid described in the above step (4) is 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), preferably 1-butyl-3-methylimidazolium tetrafluoroborate.

[0023] The mass percent concentration of the ionic liquid solution in the above step (4) is 5 wt%.

[0024] The amount of the spin-coated ionic liquid solution in step (4) is 300 μL, 500 μL, 1000 μL, preferably 500 μL. The spin-coating speed in step (4) is 1000 r / min.

[0025] The method of the present invention uses direct interfacial polymerization on a porous substrate, followed by spin coating to introduce the ionic liquid into the COF pores, resulting in an ionic liquid-loaded COF-polyamide composite membrane. Compared with existing technologies, the present invention has the following advantages:

[0026] 1) This method is simple to operate, has a short process flow, mild operating conditions, and high film production efficiency;

[0027] 2) Ionic liquids are green and pollution-free, and have high CO2 solubility. Loading ionic liquids on COF membranes can effectively enhance CO2 capture capacity;

[0028] Description of the drawings: Figure 1 It is a preparation flow chart of Examples 1 to 10.

[0029] Figure 2 This is a surface scanning electron microscope image of the COF-polyamide composite membrane prepared in Example 9 without loading ionic liquid.

[0030] Figure 3 Surface and cross-sectional scanning electron microscopy images of the ionic liquid-loaded COF-polyamide composite membrane prepared in Example 9.

[0031] Figure 4This is the element distribution energy spectrum of the ionic liquid-loaded COF-polyamide composite membrane prepared in Example 9.

[0032] Specific implementation: The technical solution of the present invention is further described in detail below in combination with specific examples based on the accompanying drawings.

[0033] Examples 1 to 3

[0034] 1) Weigh 0.025g of p-phenylenediamine (Pa) and dissolve it in 50mL of deionized water, then ultrasonically disperse it to obtain a 0.05wt% aqueous p-phenylenediamine solution. Furthermore, prepare 0.5wt% and 1wt% aqueous p-phenylenediamine solutions. Simultaneously, add 0.5mL of 99.5wt% glacial acetic acid as a catalyst to each aqueous solution, with the volume fraction of glacial acetic acid in the aqueous solution being 1v / v%. Separately, weigh 0.005g of 2,4,6-trihydroxybenzene-1,3,5-triformaldehyde (Tp) and 0.005g of trimesoyl chloride (TMC), i.e., a 5:5 mass ratio of Tp to TMC, for a total mass of 0.01g. Furthermore, weigh 9.99g of n-hexane to obtain an oily solution of aldehyde and acyl chloride with a total mass fraction of 0.1wt%, which serves as the oily mother liquor.

[0035] 0.5g of the mother liquor was removed and diluted 80-fold with 39.5g of n-hexane, yielding an oil-phase solution containing 0.00125wt% of the aldehyde and acyl chloride. Separately, a 0.0125wt% oil-phase solution containing 0.025wt% of the aldehyde and acyl chloride was prepared. Separately, 0.5g of 1-butyl-3-methylimidazolium tetrafluoroborate was weighed and added to 9.5g of anhydrous ethanol to prepare a 5wt% ionic liquid ethanol solution.

[0036] 2) Remove excess water from the surface of the polysulfone (PSF) porous substrate and fix it in an interfacial polymerization device. PSF is soaked in deionized water overnight before use. Pour 4.5mL of the aqueous solution on the PSF surface and keep it for 30s to allow the aqueous solution to fully infiltrate the substrate. Subsequently, pour out the aqueous solution and remove the residual aqueous solution on the surface of the porous substrate to prevent subsequent interfacial polymerization from causing defects on the membrane surface. Specifically, use a dry and clean rubber roller to roll the p-phenylenediamine solution on the membrane surface dry.

[0037] Then, 4.5 mL of the aldehyde and acyl chloride oil phase solution was poured into the PSF substrate saturated with the above-mentioned p-phenylenediamine solution and allowed to react for 10 seconds. The amine monomer inside the porous substrate diffused to the water / oil interface and underwent Schiff base reaction and amidation reaction with the aldehyde and acyl chloride in the oil phase, respectively, to form a COF-polyamide separation layer on the surface of the PSF substrate; then, the excess oil phase solution was poured out and washed several times with n-hexane.

[0038] 3) heat treating the composite membrane prepared above at 60° C. for 5 min without air blowing;

[0039] 4) The composite membrane obtained by the above heat treatment was spin-coated with 500 μL of ionic liquid ethanol solution, wherein the rotation speed of the spin coater was 1000 r / min, to obtain a COF-polyamide composite membrane loaded with ionic liquid.

[0040] The composite membrane prepared in this example was subjected to gas permeation tests and CO2 and N2 separation performance tests, wherein the volume ratio of CO2 to N2 was 15 / 85, the inlet pressure was 1 bar, and the test temperature was 35°C. The test results are shown in Table 1.

[0041] Table 1 Separation performance of composite membranes of Examples 1 to 3

[0042]

[0043] Examples 4 to 6

[0044] 1) Weigh 0.05 g of p-phenylenediamine (Pa) and dissolve it in 50 mL of deionized water, then ultrasonically disperse it to obtain a 0.1 wt% aqueous solution of p-phenylenediamine. Simultaneously, add 0.5 mL of 99.5 wt% glacial acetic acid as a catalyst to the aqueous solution, with the volume fraction of glacial acetic acid in the aqueous solution being 1 v / v%. Separately, weigh 0.005 g of 2,4,6-trihydroxybenzene-1,3,5-triformaldehyde (Tp) and 0.005 g of trimesoyl chloride (TMC), i.e., a Tp:TMC mass ratio of 5:5, for a total mass of 0.01 g. Add 9.99 g of n-hexane to obtain a 0.1 wt% oily solution of the aldehyde and acyl chloride, which serves as the oily mother liquor. 1g of the mother liquor was taken and diluted 40-fold with 39g of n-hexane to obtain a 0.0025wt% oil-phase solution of aldehyde and acyl chloride. Separately, 0.5g of 1-butyl-3-methylimidazolium tetrafluoroborate was weighed and added to 9.5g of anhydrous ethanol to prepare a 5wt% ionic liquid ethanol solution.

[0045] 2) The operation steps were the same as step 2) in Examples 1 to 4, wherein the water phase contact time was 30 s, and the reaction time was 5 s, 20 s, and 40 s.

[0046] 3) heat treating the composite membrane prepared above at 60° C. for 5 min without air blowing;

[0047] 4) The composite membrane obtained by the above heat treatment was spin-coated with 500 μL of ionic liquid ethanol solution, wherein the rotation speed of the spin coater was 1000 r / min, to obtain a COF-polyamide composite membrane loaded with ionic liquid.

[0048] The composite membrane prepared in this example was subjected to gas permeation tests and CO2 and N2 separation performance tests, wherein the volume ratio of CO2 to N2 was 15 / 85, the inlet pressure was 1 bar, and the test temperature was 35°C. The test results are shown in Table 2.

[0049] Table 2 Separation performance of composite membranes of Examples 4 to 6

[0050]

[0051] Examples 7 to 10

[0052] 1) Weigh 0.05 g of p-phenylenediamine (Pa) and dissolve it in 50 mL of deionized water, then ultrasonically disperse it to obtain a 0.1 wt% aqueous solution of p-phenylenediamine. Simultaneously, add 0.5 mL of 99.5 wt% glacial acetic acid as a catalyst to the aqueous solution, with the volume fraction of glacial acetic acid in the aqueous solution being 1 v / v%. Separately, weigh 0.005 g of 2,4,6-trihydroxybenzene-1,3,5-triformaldehyde (Tp) and 0.005 g of trimesoyl chloride (TMC), i.e., a Tp:TMC mass ratio of 5:5, for a total mass of 0.01 g. Add 9.99 g of n-hexane to obtain a 0.1 wt% oily solution of the aldehyde and acyl chloride, which serves as the oily mother liquor. 1g of the mother liquor was taken and diluted 40-fold with 39g of n-hexane, yielding a 0.0025wt% oil-phase solution of aldehyde and acyl chloride. Separately, 0.0025wt% oil-phase solutions were prepared with Tp:TMC ratios of 9:1, 7:3, and 3:7. Separately, 0.5g of 1-butyl-3-methylimidazolium tetrafluoroborate was weighed and added to 9.5g of anhydrous ethanol to prepare a 5wt% ionic liquid ethanol solution.

[0053] 2) The operation steps are the same as step 2) in Examples 1-2, wherein the water phase contact time is 30 s and the reaction time is 10 s.

[0054] 3) heat treating the composite membrane prepared above at 60° C. for 5 min without air blowing;

[0055] 4) The composite membrane obtained by the above heat treatment was spin-coated with 500 μL of ionic liquid ethanol solution, wherein the rotation speed of the spin coater was 1000 r / min, to obtain a COF-polyamide composite membrane loaded with ionic liquid.

[0056] The composite membrane prepared in this example was subjected to gas permeation tests and CO2 and N2 separation performance tests, wherein the volume ratio of CO2 to N2 was 15 / 85, the inlet pressure was 1 bar, and the test temperature was 35°C. The test results are shown in Table 3.

[0057] Table 3 Separation performance of composite membranes of Examples 7 to 10

[0058]

[0059]

[0060] Comparative Example 1

[0061] 1) Weigh 0.5 g of 1-butyl-3-methylimidazolium tetrafluoroborate and add 9.5 g of anhydrous ethanol to prepare a 5 wt % ionic liquid ethanol solution.

[0062] 2) Soak the polysulfone (PSF) in deionized water overnight before use. Remove excess water from the membrane surface before spin coating. Spin coat 500 μL of the ionic liquid ethanol solution onto the base film at a spin coater speed of 1000 rpm.

[0063] The membrane prepared in this comparative example was subjected to gas permeation tests and its CO2 and N2 separation performance was tested, with a CO2 to N2 volume ratio of 15 / 85, an inlet pressure of 1 bar, and a test temperature of 35°C. The test results showed a CO2 flux of 49.7 GPU, an N2 flux of 2 GPU, and a CO2 / N2 separation selectivity of 24.5.

[0064] Figure 1 The following is a flow chart of the preparation of Examples 1 to 10. The entire preparation process is simple and fast, the interfacial polymerization process only takes tens of seconds, and the spin coating process takes less than 1 minute, which greatly saves preparation time.

[0065] Figure 2 This is a surface scanning electron micrograph of the COF-polyamide composite membrane prepared in Example 9 without loading ionic liquid. Figure 2 It can be seen that there are no obvious defects on the membrane surface, proving that the amide structure is embedded into the COFs layer through the cross-linking of COF by TMC monomer, making the COF layer more dense and stable.

[0066] Figure 3 The surface and cross-sectional scanning electron micrographs of the COF-polyamide composite membrane loaded with ionic liquid prepared in Example 9 are shown. Figure 3 (a) It can be seen that the IL forms a film on the COF-polyamide separation layer without obvious defects. Figure 3 (b) It can be seen that the prepared composite membrane is only 276 nm, which can greatly reduce the gas mass transfer resistance.

[0067] Figure 4 : is the element distribution spectrum of the COF-polyamide composite membrane loaded with ionic liquid prepared in Example 9. Figure 4 (b) It can be seen that the F element is evenly distributed, proving that the ionic liquid is evenly loaded on the COF-polyamide separation layer and can effectively improve the separation of CO2.

Claims

1. A method for preparing a COF-polyamide composite membrane loaded with ionic liquid, characterized in that: The following steps are involved: (1) Preparation of precursor solution dissolving p-phenylenediamine monomer in deionized water to prepare an aqueous solution with a mass fraction of 0.05 wt% to 1 wt%, and then adding 1 v / v% glacial acetic acid to the aqueous solution to obtain an aqueous phase solution containing the amine monomer; A certain mass ratio of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and trimesoyl chloride monomers are dissolved in n-hexane organic solvent to prepare an organic phase solution of aldehyde and acyl chloride with a total mass fraction of 0.00125wt% to 0.025wt%; (2) Interfacial polymerization reaction (2.1) Pour the aqueous solution prepared in step (1) onto the surface of the polysulfone porous substrate, keep the aqueous solution on the substrate for 30 seconds, and then use a rubber roller to roll the aqueous solution on the substrate surface dry; (2.2) Pour the organic phase solution prepared in step (1) onto the surface of the polysulfone porous substrate treated in step (2.1) for 5 to 40 seconds to form a COF-polyamide layer on the surface of the polysulfone substrate, then pour out the excess organic phase solution, and finally wash with n-hexane several times to obtain a COF-polyamide composite membrane; (3) Heat treatment The COF-polyamide composite membrane prepared in step (2) was heat-treated at 60 °C for 5 min; (4) Loaded ionic liquid A certain amount of ionic liquid ethanol solution is spin-coated onto the composite membrane obtained in step (3) to obtain a COF-polyamide composite membrane loaded with ionic liquid.

2. The method according to claim 1, wherein: The mass ratios of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and trimesoyl chloride described in step (1) are 9:1, 7:3, 5:5, and 3:

7.

3. The method according to claim 1, wherein: The pore size of the polysulfone porous substrate described in step (2.1) is 20 nm.

4. The method according to claim 1, wherein: The ionic liquid described in step (4) is 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

5. The method according to claim 1, wherein: The mass percent concentration of the ionic liquid solution described in step (4) is 5 wt%.

6. The method according to claim 1, wherein: The amount of ionic liquid described in step (4) is 300 μL, 500 μL, and 1000 μL.

7. The method according to claim 1, wherein: The spin coating speed described in step (4) is 1000 r / min.

8. A COF-polyamide composite membrane loaded with ionic liquid, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 7 and is used for CO2 / N2 separation.

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