Process for the preparation of polyvinylamine modified schiff base framework materials for the preparation of high performance carbon dioxide separation mixed matrix membranes

Abstract

The application relates to a preparation method of a polyvinylamine modified Schiff base framework material for preparing a high-performance carbon dioxide separation mixed matrix membrane; a polyvinylamine aqueous solution is poured into acetone to obtain polyvinylamine precipitation without new white precipitate being generated, and white polyvinylamine solid is obtained after drying; the solid is dissolved in ethanol to obtain a polyvinylamine ethanol solution; the polyvinylamine ethanol solution and a Schiff base framework are mixed, zeolite molecular sieves are added, and stirring reaction is carried out at 70-80 DEG C for 2-8 h; after centrifugation, the precipitate is washed with deionized water and anhydrous ethanol, and the precipitate is placed in a vacuum drying box for heating and drying until the solvent is removed, so that the polyvinylamine modified Schiff base framework material is obtained. Compared with a pure PVAm membrane, the CO2 permeation rate is increased by 292%-425%, and the CO2 / N2 separation factor is increased by 233%-294%. The polyvinylamine modified Schiff base framework material has a strong application prospect.

Description

Technical Field

[0001] This invention belongs to the field of gas separation mixed matrix membrane packing preparation; it relates to a polyvinylamine (PVAm) modified Schiff base framework material (SNW-1) with improved dispersibility for preparing CO2 separation mixed matrix membranes; by controlling the time of polyvinylamine modification of the Schiff base framework, polyvinylamine modified Schiff base frameworks with different dispersibility are obtained. In particular, it relates to mixed matrix membranes using polyvinylamine modified Schiff base frameworks with excellent CO2 separation performance as packing materials. It is a method for preparing high-performance CO2 separation mixed matrix membranes using polyvinylamine modified Schiff base framework materials. Background Technology

[0002] Membrane separation technology has gained increasing attention due to its lower energy consumption, more flexible operating conditions, and environmental friendliness compared to traditional separation methods. Mixed matrix membranes (MMMs) typically consist of a continuous polymer phase and a dispersed nanofiller phase, combining the advantages of both polymers and fillers, and hold promise for overcoming the permeability-selectivity trade-off commonly found in polymer membranes. Currently, nanofillers, such as porous zeolites and metal-organic frameworks (MOFs), as well as some porous organic materials, such as covalent organic frameworks (COFs) and some amorphous porous organic frameworks (POFs), have been used as MMM fillers, showing good improvements in membrane performance. Ideally, membrane performance should continuously improve with increasing filler loading. However, in reality, the increase in nanofiller content and the performance improvement of MMMs are generally found to be unrelated. At lower filler loadings, membrane performance improves with increasing filler content. But at higher filler loadings, the selectivity of MMMs decreases significantly. This is due to interfacial incompatibility issues related to particle aggregation and differences in the physicochemical properties between nanofillers and polymers, leading to (polymer / nanofiller and nanofiller / nanofiller) nonselective defects in MMMs.

[0003] Many strategies have been proven to overcome defect formation to some extent, among which nanoparticle modification is one of the most widely used. Adding polymers to the surface of nanofillers is an effective modification method. Polymers containing a large number of functional groups such as -NH2, -OH, and -COOH are selected and modified onto the surface of nanofillers. The abundance of polar groups on the nanoparticle surface enhances its surface charge and generates more hydrogen bonds between polymers, thereby improving its dispersibility. Most reported polymer-modified fillers are based on MOFs and COFs.

[0004] Schiff base frameworks are covalent triazine frameworks obtained by reacting terephthalaldehyde with melamine to form CN bonds, exhibiting good thermal stability. Studies show that they have a nitrogen content as high as 40%, indicating a large number of CO2 adsorption sites within the framework. The secondary amine groups in the framework can act as immobilization supports, allowing CO2 to pass through the internal channels in a way that promotes transport. The inexpensive raw materials mean that it holds promise for large-scale applications. Currently, Schiff base frameworks have been reported as packing materials for MMMs (Medium-to-Metal Mixtures) for CO2 separation. Gao et al. prepared 15 μm thick MMMs by mixing Schiff base frameworks with PSf and solvent evaporation. With a packing loading of 12%, they achieved an increase in CO2 permeability from 11 barrer to 22 barrer and an increase in the CO2 / N2 separation factor from 18 to 40. Wu et al. prepared an MMM with a thickness of approximately 100 μm using an intrinsic microporous polymer (PIM-1) as the continuous phase and a Schiff base framework as the dispersed phase. With a 10% filler loading, the CO2 permeability reached 7954 barrer, an improvement of 116.6% compared to the PIM membrane, and the CO2 / N2 separation factor increased from 16 to 22. The introduction of the Schiff base framework resulted in a relatively superior performance improvement for the mixed matrix membrane. The application potential of the Schiff base framework in mixed matrix membranes is enormous.

[0005] Currently, all reported Schiff base framework-based CO2 separation mixed matrix membranes have thicknesses exceeding 10 μm. Although the introduction of the Schiff base framework improves CO2 permeability, they still exhibit relatively low CO2 permeability. Furthermore, at high filler loadings (above 15 wt%), particle aggregation significantly reduces the membrane's CO2 selectivity. This is detrimental to further improving membrane performance. Especially for ultrathin mixed matrix membranes, improving membrane performance by increasing filler loading is even more difficult. Moreover, existing research lacks exploration of modifications to the Schiff base framework.

[0006] Therefore, modifying Schiff base framework materials to enhance their dispersibility in order to prepare high-throughput CO2 separation mixed matrix membranes is a key issue that needs to be studied. Summary of the Invention

[0007] To address the shortcomings of existing technologies, we conducted in-depth research, recognizing that the dispersibility of nanoparticles can be improved through surface modification. Schiff base frameworks contain both -NH2 and C=O groups on their surface. Therefore, we selected polyvinylamine (PVA), a polymer containing both -NH2 and C=O groups in its chain segments, as the modifying polymer. The surface of the Schiff base framework was modified via a Schiff base reaction. With increasing modification time, the content of PVA-modified Schiff base framework grafted onto its surface increased. The alkaline PVA increases the surface charge of the PVA-modified Schiff base framework when dispersed in water, thereby enhancing its dispersibility. The dispersibility of the PVA-modified Schiff base framework gradually increases with modification time, thus enabling higher loading within the membrane, increasing CO2 selective channels, and simultaneously improving CO2 permeability and selectivity. However, short modification times with PVA do not significantly improve particle dispersibility, while long modification times lead to a significant decrease in nanoparticle pore size and specific surface area, resulting in minimal improvement in membrane performance. Furthermore, prolonged modification times also result in high energy consumption. Based on this, the present invention proposes the following technical solution:

[0008] The preparation method of polyvinylamine modified Schiff base framework material for preparing high-performance carbon dioxide separation mixed matrix membranes includes the following steps:

[0009] 1) Pour an aqueous solution of polyvinylamine into acetone until no new white precipitate is formed, and obtain a polyvinylamine precipitate. After drying the polyvinylamine precipitate, obtain a white polyvinylamine solid.

[0010] 2) Dissolve white polyvinylamine solid in ethanol to obtain an ethanol solution of polyvinylamine;

[0011] 3) Mix the ethanol solution of polyvinylamine with the Schiff base framework, add zeolite molecular sieve to the mixture, stir and react at 70-80℃ for 2-8 hours, centrifuge to obtain polyvinylamine modified Schiff base framework precipitate, wash the precipitate with deionized water and anhydrous ethanol, and place the precipitate in a vacuum drying oven to heat and dry until the solvent is removed to obtain polyvinylamine modified Schiff base framework material.

[0012] In step 1), the concentration of polyvinylamine is 5-10 wt%.

[0013] In step 3), the ethanol solution of polyvinylamine and the Schiff base framework are prepared in a mass ratio of polyvinylamine:Schiff base framework of 0.2-3:1.

[0014] In step 3), the zeolite molecular sieve has a mass concentration of 1-2 wt% in the mixed solution.

[0015] The zeolite molecular sieves in step 3) include, but are not limited to, 5A molecular sieves, 4A molecular sieves, or 13X type molecular sieves.

[0016] The polyvinylamine-modified Schiff base framework material prepared by this invention is used to prepare a high-performance carbon dioxide separation mixed matrix membrane. The feature is that the powder of the polyvinylamine-modified Schiff base framework is ultrasonically dispersed in deionized water, and a coating solution is prepared by mixing the polyvinylamine-modified Schiff base framework and polyvinylamine in a mass ratio of 0.5-3:7. The coating solution is then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane.

[0017] The specific explanation is as follows:

[0018] The preparation method of the polyvinylamine aqueous solution in step 1) is described in the invention patent "Preparation method of polyvinylamine with a degree of hydrolysis of 40-70% for preparing carbon dioxide separation composite membrane", patent application number: 2019110647491.

[0019] The preparation method of the Schiff base framework in step 3) is referenced in: "Catalyst-free Preparation of Melamine-Based Microporous Polymer Networks through Schiff Base Chemistry", DOI: 10.1021 / ja902116f. Other published methods for preparing Schiff base frameworks are also included for reference.

[0020] The main reaction of this invention is illustrated below:

[0021]

[0022] This invention obtains a series of polyvinylamine-modified Schiff base frames with varying degrees of enhanced dispersibility by controlling the surface modification time of polyvinylamine to 2-8 hours. The dispersibility of nanoparticles is analyzed by examining the average dispersed particle size in water and SEM images of the membrane surface. Within the modification time specified in this invention, the dispersibility of the nanofiller within the membrane continuously improves with increasing modification time. This improved dispersibility increases the filler loading of the mixed matrix membrane while reducing membrane defects, thereby enhancing the CO2 permeability and CO2 / N2 separation factor of the mixed matrix membrane. The key steps are steps 2 and 3 of the aforementioned technical method, with the key parameter being the reaction time in step 3. Modification times exceeding 8 hours lead to a significant decrease in the pore size of the nanofiller, which is detrimental to gas transfer and separation and increases energy consumption; modification times below 2 hours do not significantly improve the dispersibility of the nanofiller. The prepared polyvinylamine-modified Schiff base frame is used as the dispersed phase, blended with a polyvinylamine aqueous solution, and coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to prepare a high-flux CO2 separation mixed matrix membrane. The prepared CO2 separation mixed matrix composite membrane was tested with a mixed gas (CO2 / N2 15 / 85). The results showed that the membrane had ultra-high CO2 permeability and good CO2 / N2 separation factor. The experimental conditions of this invention are easy to control, and the obtained materials have high reproducibility.

[0023] The prepared CO2 separation mixed matrix composite membranes were tested with mixed gases (CO2 / N2 15 / 85). The results showed that the mixed matrix composite membrane with a polyvinylamine-modified Schiff base framework modified for 2 hours exhibited the highest CO2 permeation rate (2123.58 GPU) and the highest CO2 / N2 separation factor (149.06). The mixed matrix composite membrane with a polyvinylamine-modified Schiff base framework modified for 4 hours showed the best performance, with a highest CO2 permeation rate (3092 GPU) and a highest CO2 / N2 separation factor (184). The mixed matrix composite membrane with a polyvinylamine-modified Schiff base framework modified for 8 hours exhibited the highest CO2 permeation rate (2809.68 GPU) and the highest CO2 / N2 separation factor (188.09). Due to enhanced dispersibility, the mixed matrix membranes with polyvinylamine-modified Schiff base frameworks achieved excellent CO2 / N2 separation performance. Table 1 compares the separation performance of several mixed matrix membranes. Compared with the hybrid matrix membranes reported in the literature, this material leads in both CO2 permeation rate and CO2 / N2 selectivity. Compared with the pure PVAm membranes in previous work, the CO2 permeation rate is increased by 292%-425%, and the CO2 / N2 separation factor is increased by 233%-294%. Polyvinylamine-modified Schiff base framework materials have strong application prospects.

[0024] Table 1 Comparison of membrane performance with literature reports

[0025] Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image corresponding to the time of the polyvinylamine-modified Schiff base framework;

[0027] Scanning electron microscope (SEM) images of (a) Schiff base framework, (b) polyvinylamine-modified Schiff base framework with a modification time of 2 h, (c) polyvinylamine-modified Schiff base framework with a modification time of 4 h, and (d) polyvinylamine-modified Schiff base framework with a modification time of 8 h.

[0028] Figure 2 Scanning electron microscope image of the surface of the CO2 separation mixed matrix membrane:

[0029] Among them: Figures (a), (b), and (c) show mixed matrix membranes with different loads, using polyvinylamine-modified Schiff base frameworks modified for 2 hours as fillers, with filler loads of 10 wt%, 20 wt%, and 30 wt%, respectively.

[0030] Figures (d), (e), and (f) show mixed matrix membranes with different loads, using polyvinylamine-modified Schiff base frameworks modified for 4 hours as fillers, with filler loads of 10 wt%, 20 wt%, and 30 wt%, respectively.

[0031] Figures (g), (h), and (i) show mixed matrix membranes with different loads, using polyvinylamine-modified Schiff base frameworks modified for 8 hours as fillers, with filler loads of 10 wt%, 20 wt%, and 30 wt%, respectively. Detailed Implementation

[0032] The Schiff base framework was prepared by referring to the reference "Catalyst-free Preparation of Melamine-Based Microporous Polymer Networks through Schiff Base Chemistry" (DOI:10.1021 / ja902116f); the preparation of the polyvinylamine aqueous solution was referred to the invention patent "Preparation Method of Polyvinylamine with a Degree of Hydrolysis of 40-70% for Preparing Carbon Dioxide Separation Composite Membrane", patent application number: 2019110647491.

[0033] 1) After concentrating the aqueous solution of polyvinylamine by rotary evaporation under reduced pressure, a large amount of acetone was added to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 40-90℃ for 10-24 hours to obtain white polyvinylamine solid.

[0034] 2) Dissolve polyvinylamine in ethanol to obtain an ethanol solution of polyvinylamine;

[0035] 3) Mix excess polyvinylamine in ethanol and a Schiff base framework, add zeolite molecular sieves, and stir the reaction at 80℃ for 2-8 hours. After centrifugation, obtain a polyvinylamine-modified Schiff base framework precipitate. Wash the precipitate with deionized water and anhydrous ethanol, and dry it in a vacuum drying oven until the solvent is removed to obtain polyvinylamine-modified Schiff base framework powder. SEM images of the Schiff base framework and the polyvinylamine-modified Schiff base framework are shown below. Figure 1 Before and after modification, the morphology of the nanoparticles did not change significantly, indicating that the modification of polyvinylamine does not affect the morphology of the nanoparticles.

[0036] The polyvinylamine-modified Schiff base framework obtained in the above steps is ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion is mixed with 1 wt% polyvinylamine aqueous solution in a certain proportion and diluted to obtain a coating solution. The coating solution is then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. Figure 2 The images show scanning electron microscopy (SEM) images of the CO2 separation mixed matrix composite membrane. The images show that, compared to the Schiff base framework, the dispersibility of the polyvinylamine-modified Schiff base framework in the mixed matrix membrane is improved to varying degrees with different modification times.

[0037] The synthesis of the Schiff base framework in the following examples and comparative examples was carried out according to the method described in the literature "Catalyst-free Preparation of Melamine-Based Microporous Polymer Networks through SchiffBase Chemistry" (DOI:10.1021 / ja902116f). The preparation of the polyvinylamine aqueous solution was carried out according to the invention patent "Preparation Method of Polyvinylamine with a Degree of Hydrolysis of 40-70% for Preparing Carbon Dioxide Separation Composite Membranes", patent application number: 2019110647491.

[0038] Example 1

[0039] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0040] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0041] 3) Mix 10g of 1wt% polyvinylamine ethanol solution with 100mg of Schiff base framework, add 5 5A molecular sieves, and stir the reaction at 80℃ for 2h. Wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 2h. SEM image as follows. Figure 1 As shown in b, the particle size is approximately 40 nm.

[0042] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. Dynamic light scattering analysis was used to analyze the average dispersed particle size of the polyvinylamine-modified Schiff base framework in water after a modification time of 2 h; the results are shown in Table 2. The dispersion was mixed with a 1 wt% aqueous polyvinylamine solution at a mass ratio of 2:9 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. This coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown in [Table 2]. Figure 2 a. The separation membrane was then tested in a mixed gas system (CO2 / N2 15 / 85). The test results are shown in Table 3.

[0043] Example 2

[0044] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0045] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0046] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 2h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 2h.

[0047] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 4:8 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 b. Then, the separation membrane was tested in a mixed gas system (CO2 / N2 15 / 85). The test results are shown in Table 3.

[0048] Example 3

[0049] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0050] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0051] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 2h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 2h.

[0052] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 6:7 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 c. The separation membrane was then tested in a mixed gas (CO2 / N2 15 / 85) system. The test results are shown in Table 3.

[0053] Example 4

[0054] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0055] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0056] 3) Mix 10g of 1wt% polyvinylamine ethanol solution with 100mg of Schiff base framework, add 5 5A molecular sieves, and stir the reaction at 80℃ for 4h. Wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 4h. SEM image as follows. Figure 1 As shown in c, the particle size is approximately 40 nm.

[0057] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. Dynamic light scattering analysis was used to analyze the average dispersed particle size of the polyvinylamine-modified Schiff base framework in water after a modification time of 4 h; the results are shown in Table 2. The dispersion was mixed with a 1 wt% aqueous polyvinylamine solution at a mass ratio of 2:9 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. This coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown in [Table 2]. Figure 2 d. The separation membrane was then tested in a mixed gas system (CO2 / N2 15 / 85). The test results are shown in Table 3.

[0058] Example 5

[0059] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0060] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0061] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 4h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 4h.

[0062] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 4:8 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 e. Then the separation membrane was tested in a mixed gas (CO2 / N2 15 / 85) system. The test results are shown in Table 3.

[0063] Example 6

[0064] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0065] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0066] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 4h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 4h.

[0067] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 6:7 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 f. The separation membrane was then tested in a mixed gas (CO2 / N2 15 / 85) system. The test results are shown in Table 3.

[0068] Example 7

[0069] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0070] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0071] 3) Mix 10g of 1wt% polyvinylamine ethanol solution with 100mg of Schiff base framework, add 5 5A molecular sieves, and stir the reaction at 80℃ for 8h. Wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 8h. SEM image as follows. Figure 1 As shown in d, the particle size is approximately 40 nm.

[0072] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. Dynamic light scattering analysis was used to determine the average dispersed particle size of the polyvinylamine-modified Schiff base framework in water after 8 hours of modification; the results are shown in Table 2. The dispersion was mixed with a 1 wt% aqueous polyvinylamine solution at a mass ratio of 2:9 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. This coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown in [Table 2]. Figure 2 g. The separation membrane was then tested under a mixed gas system (CO2 / N2 15 / 85). The test results are shown in Table 3.

[0073] Example 8

[0074] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0075] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0076] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 8h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 8h.

[0077] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 4:8 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 h. The separation membrane was then tested in a mixed gas (CO2 / N2 15 / 85) system. The test results are shown in Table 3.

[0078] Example 9

[0079] 1) 1000g of 1wt% polyvinylamine aqueous solution was concentrated to 5wt% by rotary evaporation under reduced pressure and then poured into 1L of acetone to obtain polyvinylamine precipitate. The polyvinylamine precipitate was dried in a vacuum drying oven at 80℃ for 24h to obtain white polyvinylamine solid.

[0080] 2) Dissolve solid polyvinylamine in ethanol to obtain a 1 wt% polyvinylamine ethanol solution;

[0081] 3) Mix 10g of 1wt% polyvinylamine ethanol solution and 100mg of Schiff base framework, add 5 5A molecular sieves, stir and react at 80℃ for 8h, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry the precipitate in a vacuum drying oven at 80℃ for 24h to obtain polyvinylamine modified Schiff base framework powder with a modification time of 8h.

[0082] The powder obtained in the above steps was ultrasonically dispersed in deionized water to form a dispersion with a concentration of 0.5 wt%. The dispersion was mixed with a 1 wt% polyvinylamine aqueous solution at a mass ratio of 6:7 and diluted to a polyvinylamine concentration of 0.05 wt% to obtain a coating solution. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane. The surface SEM image of the membrane is shown below. Figure 2 i. The separation membrane was then tested in a mixed gas (CO2 / N2 15 / 85) system. The test results are shown in Table 3.

[0083] The performance of hybrid matrix membranes using Schiff base frameworks as fillers, as reported in the literature, is presented as a comparative example below.

[0084] Comparative Example 1

[0085] The best performance of the membrane with PSf as polymer matrix and Schiff base framework as filler reported in the literature "Highly selective and permeable porous organic framework membrane for CO2 capture" (DOI:10.1002 / adma.201400020) is used as Comparative Example 1, and the data are listed in Table 3.

[0086] Comparative Example 2

[0087] The best performance of the membrane with PIM-1 as polymer matrix and Schiff base framework as filler reported in the literature "Mixed matrix membranes comprising polymers of intrinsic microporosity and covalent organic framework for gas separation" (DOI:10.1016 / j.memsci.2017.01.042) is used as Comparative Example 1, and the data are listed in Table 3.

[0088] Test data and conclusions

[0089] The average dispersed particle size of Schiff base frameworks and polyvinylamine-modified Schiff base frameworks with different modification times in water was tested, and the results are shown in Table 2.

[0090] Table 2. CO2 / N2 separation performance of mixed matrix membranes prepared using Schiff base frameworks and polyvinylamine-modified Schiff base frameworks with different modification times as packing materials.

[0091]

[0092] According to Table 2 and Figure 2It can be seen that with the increase of modification time, the average dispersed particle size of the nanofiller in water decreases, and the degree of aggregation of the nanofiller on the membrane surface also decreases. This indicates that polyvinylamine-modified Schiff base frameworks with different modification times have different dispersibility, and the modified nanofiller has enhanced dispersibility. With the increase of modification time, the dispersibility of the nanofiller also increases.

[0093] A mixed matrix membrane was prepared using polyvinylamine-modified Schiff base frameworks with different modification times as fillers. The CO2 permeation rate and CO2 / N2 separation factor in the CO2 / N2 mixed gas system are shown in Table 3.

[0094] Table 3. CO2 / N2 separation performance of mixed matrix membranes prepared using Schiff base frameworks and polyvinylamine-modified Schiff base frameworks with different modification times as packing materials.

[0095] <![CDATA[CO2 Permeability (GPU)]]> <![CDATA[CO2 / N2 separation factor]]> Example 1 2123.58 149.06 Example 2 2492.71 94.81 Example 3 3661.55 81.79 Example 4 1814.12 153.07 Example 5 2134.82 154.21 Example 6 3092.02 183.78 Example 7 1674.33 158.36 Example 8 1865.08 170.49 Example 9 2809.68 188.09 Comparative Example 1 1.5 40 Comparative Example 2 75 22.1

[0096] Table 3 shows that, in the CO2 / N2 system, the CO2 separation mixed matrix membrane using a polyvinylamine-modified Schiff base framework as packing material can achieve superior performance at higher packing loads. Figure 2 It can be seen that the dispersion of the polyvinylamine-modified Schiff base framework within the membrane improves with increasing modification time. Membranes using a polyvinylamine-modified Schiff base framework modified for 2 hours as packing material achieved significantly higher CO2 / N2 separation factors than membranes using the Schiff base framework as packing material at 20 wt% and 30 wt% loadings. Membranes using polyvinylamine-modified Schiff base frameworks modified for 4 hours and 8 hours as packing material maintained extremely high CO2 / N2 separation factors even at a 30 wt% packing material loading. Membranes using a polyvinylamine-modified Schiff base framework as packing material exhibit excellent membrane performance, far exceeding the reported performance of membranes using the Schiff base framework as packing material. Furthermore, the method of this invention is simple, low-cost, and highly reproducible, showing promising application prospects.

[0097] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A method for preparing a polyvinylamine-modified Schiff base framework material for preparing a high-performance carbon dioxide separation mixed matrix membrane, characterized in that: Includes the following steps: 1) Pour an aqueous solution of polyvinylamine into acetone until no new white precipitate forms, obtaining a polyvinylamine precipitate. Dry the polyvinylamine precipitate to obtain a white polyvinylamine solid. The preparation method of the polyvinylamine aqueous solution is as follows: prepare a solution of poly(N-vinylformamide), then add hydrochloric acid to the solution until the concentration of hydrochloric acid in the reaction solution is 8~12wt%; stir and hydrolyze at a constant temperature of 65~75 ℃ under N2 protection to obtain polyvinylamine hydrochloride PVAm·HCl; add the PVAm·HCl solution to excess ethanol to precipitate, obtaining a white PVAm·HCl solid; dissolve the obtained PVAm·HCl solid in deionized water; add excess anion exchange resin to the solution and stir until the pH of the solution is 12.0~13.0, filter, and obtain a PVAm aqueous solution with a degree of hydrolysis of 40~70%. 2) Dissolve white polyvinylamine solid in ethanol to obtain an ethanol solution of polyvinylamine; 3) Mix the ethanol solution of polyvinylamine with the Schiff base framework material, add zeolite molecular sieve to the mixture, stir and react at 70-80℃ for 2-8 h, centrifuge to obtain polyvinylamine modified Schiff base framework precipitate, wash the precipitate with deionized water and anhydrous ethanol, and place the precipitate in a vacuum drying oven to heat and dry until the solvent is removed to obtain polyvinylamine modified Schiff base framework material; The preparation method of Schiff base framework material is as follows: melamine and terephthalaldehyde are heated in dimethyl sulfoxide at 180 ℃ for 72 h under an inert atmosphere to carry out a condensation reaction; finally, it is washed with acetone, tetrahydrofuran and dichloromethane in sequence to obtain grayish-white powdery Schiff base framework material.

2. The preparation method according to claim 1, characterized in that, In step 1), the concentration of polyvinylamine is 5-10 wt%.

3. The preparation method according to claim 1, characterized in that, In step 3), the ethanol solution of polyvinylamine and the Schiff base framework are prepared in a mass ratio of polyvinylamine:Schiff base framework of 0.2-3:

1.

4. The preparation method according to claim 1, characterized in that, In step 3), the mass concentration of zeolite molecular sieve in the mixed solution is 1-2 wt%.

5. The preparation method according to claim 1, characterized in that, In step 3), the zeolite molecular sieve is 5A molecular sieve, 4A molecular sieve or 13X type molecular sieve.

6. The polyvinylamine-modified Schiff base framework material prepared according to claim 1 is used to prepare a high-performance carbon dioxide separation mixed matrix membrane, characterized in that, The powder of polyvinylamine modified Schiff base framework was ultrasonically dispersed in deionized water, and a coating solution was prepared by mixing polyvinylamine modified Schiff base framework and polyvinylamine in a mass ratio of 0.5-3:

7. The coating solution was then coated onto a polysulfone ultrafiltration membrane containing a silicone rubber interlayer to obtain a CO2 separation mixed matrix composite membrane.

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