Metal organic framework membrane capable of efficiently separating carbon dioxide as well as preparation method and application of metal organic framework membrane

Abstract

The invention discloses a metal organic framework membrane capable of efficiently separating carbon dioxide as well as a preparation method and application of the metal organic framework membrane, and belongs to the technical field of membrane separation. According to the membrane material, Al < 3 + > serves as a central metal node, dicarboxylic acid serves as a ligand, and efficient screening of carbon dioxide / methane is achieved by constructing a polycrystalline aluminum-based metal organic framework membrane of an angstrom-scale hole window structure. The preparation method comprises the following steps: adopting a strategy of inducing secondary solvothermal growth by a low-crystalline nanocrystalline seed, modifying the nanocrystalline seed to the surface of a support body through a dip-coating method, and then self-assembling in a synthetic solution to form a compact defect-free polycrystalline film. When the membrane is used for separating equimolar carbon dioxide / methane mixed gas, the carbon dioxide / methane selectivity is up to 185, the methane loss rate is lower than 0.2%, and the membrane has the characteristics of high permeation rate and low methane escape. The excellent stability and separation performance can be applied to the fields of natural gas decarburization, biogas purification and industrial carbon capture.

Description

Technical Field

[0001] The present invention belongs to the field of membrane preparation technology, and specifically relates to a metal organic framework membrane capable of efficiently separating carbon dioxide, a preparation method and application thereof, and in particular to an aluminum-based metal organic framework membrane capable of efficiently separating carbon dioxide / methane, a preparation method and application thereof. Background Art

[0002] Methane, as an effective, safe and clean fuel and chemical raw material, has two main sources: one is the associated gas released during oil extraction, and the other is biogas generated by anaerobic fermentation of sewage and organic waste. The methane produced by these two pathways generally contains 5%-50% carbon dioxide. This type of mixed gas faces a dual challenge in practical applications - carbon dioxide, as an inert component, will not only further reduce the calorific value of methane and significantly weaken its combustion economy, but will also cause electrochemical corrosion of pipelines in high-pressure transmission and storage systems, increasing maintenance costs and safety risks. Traditional heat-driven separation technologies (such as ammonia absorption, water washing, adsorption, and deep cooling) are widely used, but these technologies are usually accompanied by high energy consumption. Membrane separation technology has the advantages of no phase change, low energy consumption, simple operation, small footprint and continuous operation. It is a new type of gas separation method with high efficiency and low energy consumption.

[0003] To ensure that the gas meets pipeline specifications for a carbon dioxide content of less than 2%, most plants use ammonia absorption technology, which can achieve almost complete separation of carbon dioxide and lose less than 1% of the feed methane in the separated carbon dioxide stream. Traditional polymer membranes represented by cellulose acetate (carbon dioxide / methane selectivity of approximately 15) can achieve a carbon dioxide removal rate of 60%-80%, but are accompanied by a 2%-4% methane escape loss, and the membrane plasticization effect caused by C2-C6+ hydrocarbons and water vapor seriously restricts its long-term stability. Inorganic microporous membranes, due to their excellent stability and highly defined sub-nanometer pore structure, can achieve precise recognition of molecules such as carbon dioxide and methane, and their permeation rate is much higher than that of traditional polymer membranes. CHA topology zeolite molecular sieves exhibit good permeability and selectivity, but existing separation systems still face the bottleneck of methane loss rates exceeding 5%. For example, the document (Chemical Engineering Science, 2024, 284, 119452) discloses a zeolite membrane. When the feed flow rate is 12 SLPM, membrane separation is performed at 1.4 MPa, and the methane purity can be increased to 98.4 mol%, which meets the standard of pipeline gas, but the methane loss reaches ~24.5%.

[0004] Metal-Organic Framework (MOF) materials, with their unique organic-inorganic hybrid structure, have demonstrated revolutionary potential in the field of gas separation. As a representative of the third generation of porous materials, MOFs construct a three-dimensional network structure through the precise coordination of metal nodes and organic ligands, combining characteristics such as ultra-large specific surface area, adjustable pore size (0.3-2nm), and surface functionalization. Although MOF membranes have made great progress in carbon dioxide separation, traditional MOF membranes face three major technical bottlenecks in the field of carbon dioxide / methane separation: first, the molecular sieving efficiency of existing metal-organic framework membrane materials is limited and lacks precise structural design; second, under high pressure differential conditions (0.7-2MPa), the membrane structure is prone to deformation, resulting in performance degradation; third, there is a significant "trade-off effect" between permeation flux and selectivity, making it difficult to achieve both high separation efficiency and low methane loss rate.

[0005] The above technical problems are common in the currently developed metal-organic framework gas separation membranes. Therefore, it is necessary to develop a metal-organic framework separation membrane with stronger selectivity and matching permeability compared to traditional carbon dioxide separation membranes, and it is necessary to take into account both high separation efficiency and low methane loss rate. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings and deficiencies of the existing technology and provide a method for preparing a metal organic framework membrane. The membrane material prepared by this preparation method has excellent carbon dioxide, especially carbon dioxide / methane separation performance, and can take into account high separation efficiency and low methane loss rate.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing an aluminum-based metal-organic framework membrane, characterized in that the preparation method comprises the following steps:

[0009] 1) Solvothermal reaction of aluminum salt, carboxylic acid ligand and modifier in a solvent to obtain low-crystalline nanocrystal seeds, wherein the specific surface area of ​​the low-crystalline nanocrystal seeds measured by nitrogen adsorption at 77K is 1-20m 2 / g, and there is no obvious sharp diffraction peak in XRD, only diffuse peak;

[0010] 2) dispersing the low-crystalline nanocrystal seeds in a solvent to obtain a dispersion, and immersing a support in the dispersion to obtain a support modified with the low-crystalline nanocrystal seeds;

[0011] 3) placing the support modified with low-crystalline nanocrystal seeds in a synthesis solution for secondary solvent thermal growth to obtain the aluminum-based metal organic framework membrane; the synthesis solution includes an aluminum salt, a carboxylic acid ligand, a regulator and a solvent; the carboxylic acid ligand is selected from isophthalic acid or pyridine-3,5-dicarboxylic acid.

[0012] The preparation method of the present invention includes the steps of synthesizing low-crystalline nanocrystals. Prior to growing an aluminum-based metal-organic framework membrane, the low-crystalline nanocrystals are introduced onto the surface of a support by an impregnation method. Subsequently, a secondary solvothermal method is used to allow the aluminum-based metal-organic framework crystals in the synthesis solution to self-assemble and grow on the modified support surface, ultimately yielding a dense and continuous polycrystalline membrane. During the secondary solvothermal growth, the use of specific carboxylic acid ligands in the synthesis solution can control the pore size of the final membrane material, thereby achieving excellent separation performance.

[0013] The type of the carboxylic acid ligand in step 1) may be the same as or different from that in step 3).

[0014] The specific surface area of ​​low-crystalline nanocrystals measured by nitrogen adsorption at 77K is 1-20m 2 / g, for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20m 2 / g.

[0015] In some embodiments, in step 1), the aluminum salt is selected from a combination of one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminum sulfate 18hydrate.

[0016] In some embodiments, in step 1), the carboxylic acid ligand is selected from isophthalic acid, pyridine-3,5-dicarboxylic acid, or 1H-pyrrole-2,5-dicarboxylic acid.

[0017] In some embodiments, in step 1), the regulator is selected from sodium hydroxide or potassium hydroxide.

[0018] In some embodiments, in step 1), the solvent is methanol. Methanol is more conducive to the synthesis of low-crystalline nanocrystal seeds. In the prior art, water is usually used for synthesis, and the resulting nanocrystal seeds are highly crystalline.

[0019] In some embodiments, in step 1), the molar ratio of the aluminum salt, carboxylic acid ligand, modifier, and solvent is 1:1:1-1.5:200-8000, preferably 1:1:1-1.5:600-5000. For example, the molar ratio may be 1:1:1-1.5:700, 1:1:1-1.5:1700, 1:1:1-1.5:2700, 1:1:1-1.5:3700, 1:1:1-1.5:4700, etc.

[0020] In some embodiments, in step 1), the temperature of the solvothermal reaction is 100-120°C.

[0021] In some embodiments, the size of the low-crystalline nanocrystal seeds is 40-540 nm, preferably 42-530 nm, and more preferably 80 nm-120 nm.

[0022] In some embodiments, the mass percent concentration of the dispersion is 0.05%-0.1%.

[0023] In some embodiments, in step 2), the solvent is selected from a combination of one or more of methanol, ethanol, and isopropanol.

[0024] In some embodiments, the impregnation is achieved by an immersion-pulling method, wherein the support is subjected to immersion-pulling to modify the nanocrystals and provide nucleation sites.

[0025] In some embodiments, the dipping is performed 1-3 times, and the duration of each dipping is 5-15 seconds.

[0026] In some embodiments, the preparation method further comprises the step of pre-treating the support, wherein the pre-treatment comprises ultrasonic cleaning and drying. The ultrasonic cleaning time is 10-30 minutes. The drying can be performed by heating in an oven at 120° C. for 0.5-2 hours.

[0027] In some embodiments, in step 3), the temperature of the secondary solvothermal growth is 90-150°C.

[0028] In some embodiments, in step 3), the secondary solvothermal growth time is 2-24 hours.

[0029] In some embodiments, in step 3), in the synthesis solution, the molar ratio of the aluminum salt, the carboxylic acid ligand, the regulator and the solvent is 1:1:1-1.5:1000-5000.

[0030] In some embodiments, in step 3), the aluminum salt is selected from a combination of one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminum sulfate 18hydrate.

[0031] In some embodiments, in step 3), the regulator is selected from sodium hydroxide or potassium hydroxide.

[0032] In some embodiments, in step 3), the solvent is water.

[0033] The steps of secondary solvent thermal growth synthesis include adding the secondary synthesis liquid into a reaction kettle, placing the support of the modified low-crystalline nanocrystal seed on a polytetrafluoroethylene bracket, and placing the bracket in the reaction kettle for reaction.

[0034] In some embodiments, the support is an α-Al2O3 porous support.

[0035] In some embodiments, the support body is a porous aluminum-containing ceramic disk.

[0036] In some embodiments, the α-Al 2 O 3 porous support is a porous ceramic disc material.

[0037] In some embodiments, the disk material has a diameter of 1.8-3.0 cm.

[0038] In some embodiments, the disc material has a thickness of 1-5 mm.

[0039] The present invention also provides an aluminum-based metal-organic skeleton membrane prepared by the above-mentioned method for preparing the aluminum-based metal-organic skeleton membrane.

[0040] Furthermore, the aluminum-based metal organic framework membrane has an angstrom-level pore structure with a pore size of about 0.4-0.45 nm, which can preferentially adsorb and diffuse carbon dioxide and block the penetration of methane.

[0041] The present invention also provides use of the aluminum-based metal organic framework membrane material for separating mixed gases containing carbon dioxide.

[0042] Furthermore, the mixed gas also contains a combination of one or more selected from methane, nitrogen, and carbon monoxide.

[0043] Furthermore, the mixed gas is carbon dioxide and methane.

[0044] Furthermore, when used for separation of carbon dioxide / methane mixed gas, at a pressure of 0-0.7 MPa, the carbon dioxide / methane selectivity is ≥200, and the methane loss rate is ≤0.2%.

[0045] Furthermore, the use is applicable to the fields of natural gas decarbonization, biogas purification or industrial carbon capture.

[0046] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0047] The membrane material of the present invention has a precisely controlled pore size at the angstrom level by selecting a specific carboxylic acid ligand, and can achieve effective separation of carbon dioxide and methane.

[0048] The present invention first modifies low-crystalline nanocrystals on a support, which exhibit high reactivity and can well induce the formation of high-quality aluminum-based metal organic framework membranes, thereby ensuring the separation performance of the membrane material.

[0049] Compared with traditional membrane materials, when the membrane material of the present invention is used for carbon dioxide / methane separation, the methane loss rate is very low even under high pressure. The membrane material can achieve both high separation efficiency and low methane loss rate.

[0050] The membrane material of the present invention shows broad application potential in scenarios such as natural gas decarbonization, low-concentration biogas purification and industrial carbon capture, and is expected to become a potential separation technology to replace ammonia decarbonization.

[0051] By constructing an aluminum-based metal-organic framework membrane with angstrom-scale pore sizes, this new membrane achieves preferential adsorption and rapid permeation of carbon dioxide molecules while effectively blocking methane permeation, achieving both high gas permeation rates and low methane losses. In tests with equimolar carbon dioxide / methane mixtures (at a separation pressure of 0-0.7 MPa), the carbon dioxide / methane selectivity reached as high as 180, with methane losses below 0.2%, significantly outperforming both traditional polymer membranes and existing inorganic membrane materials.

[0052] The present invention uses low-crystalline nanocrystal seeds to induce the formation of high-quality membranes by inducing a heterogeneous nucleation mechanism, significantly optimizing the crystal density of metal-organic framework membranes during secondary synthesis. The present invention employs a secondary solvothermal growth strategy induced by small-sized low-crystalline nanocrystal seeds. These small-sized low-crystalline nanocrystal seeds exhibit both high reactivity and dispersibility, effectively improving membrane uniformity and density while avoiding common interfacial cracks and defects. The resulting membranes exhibit a continuous, defect-free surface, facilitating long-term stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 : SEM and size distribution diagram of low-crystalline nanocrystals prepared in Preparation Example 1.

[0054] Figure 2 : 77K nitrogen adsorption diagram of low-crystalline nanocrystals prepared in Preparation Example 1.

[0055] Figure 3 : XRD spectrum of the low-crystalline nanocrystals prepared in Preparation Example 1.

[0056] Figure 4 : TG spectrum of the low-crystalline nanocrystals prepared in Preparation Example 1.

[0057] Figure 5 : Surface SEM image of the aluminum-based metal-organic framework membrane prepared in Example 1.

[0058] Figure 6 : Cross-sectional SEM image of the aluminum-based metal-organic framework membrane prepared in Example 1.

[0059] Figure 7 : XRD spectrum of the aluminum-based metal-organic framework membrane prepared in Example 1.

[0060] Figure 8 : Single-component permeability performance diagram of the aluminum-based metal-organic framework membrane prepared in Example 1 to common gases.

[0061] Figure 9 : The separation performance of the aluminum-based metal organic framework membrane prepared in Example 1 for carbon dioxide / methane gas mixture under high pressure.

[0062] Figure 10 : The loss rate of methane gas during separation under high pressure by the aluminum-based metal-organic framework membrane prepared in Example 1.

[0063] Figure 11 : Surface SEM image of the aluminum-based metal-organic framework membrane prepared in Example 2.

[0064] Figure 12 : Cross-sectional SEM image of the aluminum-based metal-organic framework membrane prepared in Example 2.

[0065] Figure 13 : Single-component permeability performance diagram of the aluminum-based metal-organic framework membrane prepared in Example 2 to common gases.

[0066] Figure 14 : XRD spectrum of the highly crystalline submicron seed crystals prepared in Comparative Preparation Example 1.

[0067] Figure 15 : SEM of the aluminum-based metal organic framework membrane prepared in Comparative Example 1 after coating the seed crystal and growing.

[0068] Figure 16 : Surface SEM image of the aluminum-based metal-organic framework membrane prepared in Comparative Example 2.

[0069] Figure 17 : Cross-sectional SEM image of the aluminum-based metal-organic framework membrane prepared in Comparative Example 2.

[0070] Figure 18 : Single-component permeability performance diagram of the aluminum-based metal-organic framework membrane prepared in Comparative Example 2 to common gases.

[0071] Figure 19 : Comparison chart of the crystallographically predicted limit pore diameter of the aluminum-based metal organic framework membrane prepared in Comparative Example 2 with that of Examples 2 and 3.

[0072] Figure 20 : The separation performance of the aluminum-based metal organic framework membrane prepared in Comparative Example 2 for carbon dioxide / methane gas mixture under high pressure.

[0073] Figure 21 : The loss rate of methane gas during separation under high pressure by the aluminum-based metal organic framework membrane prepared in Comparative Example 2. DETAILED DESCRIPTION

[0074] The innovation of the preparation method of the present invention lies in the modification of low-crystalline nanocrystals on the surface of the support, which have high reactivity and uniformity. During the secondary synthesis process, the formation of high-quality aluminum-based metal organic framework membranes is effectively promoted, the uniformity and density of the membrane layer are improved, common interface defect problems are avoided, and long-term stable operation is facilitated. In the prior art, in the seed secondary growth method, highly crystalline seeds are usually used as the growth substrate. However, the inventors of this application have found through research that the use of low-crystalline seeds can better achieve the density and integrity of the membrane compared to the use of traditional highly crystalline seeds, thereby further improving the gas separation performance.

[0075] Another innovation of the preparation method of the present invention lies in the selection of specific carboxylic acid ligands to construct an aluminum-based complex MOF membrane material with a specific pore size. This results in a membrane material with a pore size at a specific angstrom level, thereby achieving precise angstrom-level control of the pore size in the membrane structure. This specific small pore size can prevent the passage of methane molecules, thereby intercepting methane during gas separation, significantly enhancing the aluminum-based metal-organic framework membrane's ability to recognize and exclude methane molecules. This design significantly suppresses methane permeation, achieving high carbon dioxide selectivity while minimizing methane loss, thereby helping to retain the economic value of methane in the upstream feed gas and improving the overall efficiency of the separation process.

[0076] The aluminum-based metal organic skeleton membrane material of the present invention is Al3 +The metal-based metal organic framework (MOF) is a central metal node. By regulating the geometry and connection of carboxylic acid ligands, the pore size can be precisely controlled from 0.3 nm to 2.5 nm. This type of material has significant advantages in CO2 / methane separation: first, the aluminum oxide cluster (Al-O) of the MOF strongly interacts with the polar quadrupole moment of CO2, enabling preferential CO2 adsorption; second, the hard acid-hard base coordination imparts excellent hydrothermal stability and a robust framework to the membrane material. The key to achieving CO2 / methane separation in polycrystalline aluminum-based MOF membranes is the precise design of the window size. By utilizing the bond angles of bidentate ligands and variations in ligand volume, the MOF window size is limited to the angstrom range, resulting in a membrane pore system with suitable molecular sieving capabilities. This allows for CO2 separation while retaining methane, while maintaining methane loss rates at the same level as in amine plants under high-pressure separation. The selected aluminum-based metal-organic framework crystallographic pore size is slightly larger than the kinetic diameter of the methane molecule, and the carbon dioxide and methane molecules are separated by utilizing the diffusion differences in the pores. The metal-organic framework exhibits a stronger adsorption affinity for carbon dioxide, and thus can achieve both high separation efficiency and low methane loss rate during carbon dioxide / methane separation.

[0077] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples.

[0078] Preparation Example 1

[0079] This preparation example provides a low-crystalline nanocrystal, and the preparation method thereof is as follows:

[0080] 1) A certain amount of aluminum chloride hexahydrate and isophthalic acid were dissolved in 20 mL of methanol, and a certain amount of sodium hydroxide was dissolved in 10 mL of methanol. The mixture was stirred at room temperature for 15 minutes to fully dissolve. The molar ratios of aluminum chloride hexahydrate, isophthalic acid, sodium hydroxide, and methanol were varied to perform five experiments. The detailed mass ratios are shown in Table 1 below.

[0081] Table 1 Synthesis formula of low-crystalline nanometal salt organic framework particles

[0082]

[0083] 2) Mixing a methanol solution of a metal salt, a methanol solution of a carboxylic acid, and a methanol solution of sodium hydroxide to form a precursor solution, stirring for 5 minutes, and then transferring the solution to a polytetrafluoroethylene reactor;

[0084] 3) Place the reactor in a convection oven and heat to 110°C for 12 hours;

[0085] 4) After the reaction is completed, the precipitate is collected by centrifugation, washed 2-3 times with methanol, and dried in a convection oven at 60°C.

[0086] The results showed that nano-scale aluminum-based metal organic framework crystals were successfully synthesized under the conditions of the metal salt aluminum chloride hexahydrate, the ligand isophthalic acid, the regulator sodium hydroxide and the solvent methanol in a molar ratio range of 1:1:1:4667 to 1:1:1:667. The scanning electron microscope (SEM) image of the obtained product is shown below. Figure 1 As shown in Figure 2, the crystal morphology is uniform and presents a regular nanostructure. The particle size analysis results are also shown in Figure 2. Figure 1 As shown, it can be seen that the average size distribution range of the prepared crystals is about 40nm to 530nm, indicating that the synthesis system has good nanoscale control capabilities.

[0087] Comparative Preparation Example 1

[0088] This comparative preparation example provides a comparative high-crystalline nanocrystal, and its preparation method is as follows:

[0089] 1) 0.3017 g of aluminum chloride hexahydrate and 0.2076 g of isophthalic acid were dissolved in 20 mL of water, and 0.1500 g of sodium hydroxide was dissolved in 10 mL of water. The mixture was stirred at room temperature for 15 minutes to fully dissolve. The molar ratio of aluminum chloride hexahydrate, isophthalic acid ligand, sodium hydroxide modifier, and water solvent was 1:1:3:2667 (when water is used as the solvent, the amount of sodium hydroxide needs to be adjusted accordingly to better synthesize highly crystalline nanocrystals).

[0090] 2) Mixing the aqueous solution of the metal salt, the aqueous solution of the carboxylic acid, and the aqueous solution of sodium hydroxide to form a precursor solution, stirring for 5 minutes, and then transferring the solution to a polytetrafluoroethylene reactor;

[0091] 3) Place the reactor in a convection oven and heat to 110°C for 12 hours;

[0092] 4) After the reaction is completed, the precipitate is collected by centrifugation, washed with water 2-3 times, and dried in a convection oven at 60° C. to obtain nanocrystals.

[0093] Figure 2 The figure shows the nitrogen adsorption behavior of the nano-scale aluminum-based metal organic framework crystals of Preparation Example 1 and Comparative Preparation Example 1 at 77K. It can be seen that the specific surface areas of the samples in Preparation Example 1 range from 3.2 to 19 m 2 / g, which is significantly lower than the specific surface area of ​​the submicron aluminum-based metal organic framework crystals in Comparative Preparation Example 1 (which is 970m 2 / g).

[0094] The nano-crystals synthesized in Preparation Example 1 were further detected by X-ray powder diffraction (XRD) pattern. Figure 3 As shown in Figure 1, each product does not show obvious sharp diffraction peaks, but only shows broad and blunt diffuse peaks, indicating that its crystallinity is low and belongs to a low crystalline structure. Figure 14 As shown, it has sharp and obvious diffraction peaks, which shows that it has high crystallinity. When the crystallinity is high, the formed seeds have regular channels and pore sizes, and therefore have a significantly higher specific surface area. The low-crystalline seeds in Preparation Example 1 have a low specific surface area, and the low surface area is a characterization of low crystallinity.

[0095] The thermogravimetric analysis (TGA) curve of the low crystalline crystal was further compared with the TGA curve of the high crystalline submicron crystal obtained in Comparative Preparation Example 1 ( Figure 4 ), it can be observed that the residual masses of the two in the high temperature region are basically the same, indicating that the coordination mode of the framework is consistent; but the low crystalline crystal undergoes faster ligand decomposition and structural collapse in the lower temperature region, further confirming the low order of its crystal structure, that is, low crystalline.

[0096] Based on the nitrogen adsorption, XRD and TGA results at 77K, it can be seen that low-crystalline aluminum-based metal-organic framework nanocrystals are obtained under the synthesis conditions of Preparation Example 1.

[0097] Example 1

[0098] This embodiment provides a highly dense metal organic framework membrane - CAU-10-PDC membrane material (chemical formula is Al(OH)(3,5-PDC), where PDC is pyridine-3,5-dicarboxylic acid (3,5-PDC)). The preparation method is as follows:

[0099] 1) Synthesis of low-crystalline nanocrystals was the same as in Preparation Example 1, with the molar ratio of the precursor solution being 1:1:1:2667;

[0100] 2) 0.05 g of dried low-crystalline nanocrystals were dispersed in 100 g of methanol, and ultrasonicated and stirred for 30 min to obtain a uniform dispersion to obtain a seed solution;

[0101] 3) Using an immersion-coating method, the seed solution was applied to the surface of a porous α-Al2O3 support (a ceramic disc with a diameter of 2.2 cm and a thickness of 2 mm) for 10 seconds. After coating, the support was dried in a convection oven at 60°C for 10 minutes. This process was repeated twice.

[0102] 4) Take 0.3018 g of aluminum chloride hexahydrate, 0.2089 g of pyridine-3,5-dicarboxylic acid, and 0.075 g of sodium hydroxide, dissolve them in 60 mL of water to prepare a synthetic solution, transfer the synthetic solution to a polytetrafluoroethylene liner, place the pretreated support therein, and then react at 150°C for 4 hours to form a dense and defect-free CAU-10-PDC membrane material.

[0103] The surface of the support after modification of low-crystalline nanocrystals obtained in step 3) was observed by SEM. Figure 5 As shown in the upper right panel, the nanocrystals are evenly distributed on the surface of the support, and no exposed support is found. The surface morphology of the CAU-10-PDC membrane prepared by secondary growth is then observed, as shown in the figure below. Figure 5 As shown in the figure, the crystals on the membrane surface are closely arranged and interlaced, and the overall structure is uniform and dense, with no obvious cracks or defects, showing good membrane density and continuity. Figure 6 As shown, the film thickness is about 9 μm. The entire film covers the surface of the alumina support and is tightly bonded to the interface of the support. No delamination, voids or cracks are observed, indicating that the film material has good mechanical adhesion and integrity.

[0104] The XRD pattern of the obtained CAU-10-PDC film is shown in Figure 7 As shown in the figure, the diffraction peak position is in good agreement with the standard CAU-10-PDC crystal data, indicating that the structure formed in the film is the target crystal structure. At the same time, the diffraction peak of the alumina support can also be observed in the spectrum, and its intensity is comparable to the main peak intensity of CAU-10-PDC, further confirming that the film crystals are orderly arranged and have a high degree of crystalline characteristics.

[0105] The single-component gas permeability test of the prepared CAU-10-PDC membrane was carried out. Figure 8 The test results show that the membrane exhibits a high permeation rate of approximately 280 GPU for carbon dioxide. In contrast, the permeation rate for gases with larger molecular sizes, such as methane, ethane, and propane, is significantly lower, with a difference of more than an order of magnitude. This indicates that the membrane material has good selective separation capabilities for carbon dioxide, with a carbon dioxide / methane selectivity of approximately 185.

[0106] The separation performance of the membrane at different operating pressures was further evaluated under an 80 SCCM equimolar carbon dioxide / methane feed flow. Figure 9 As shown in the figure, the prepared CAU-10-PDC membrane still maintains stable gas selectivity under high pressure conditions, indicating that the membrane has excellent structural stability and pressure-resistant mass transfer performance.

[0107] In addition, in order to evaluate the economic feasibility of the membrane material in practical applications, the methane loss rate during the separation process was calculated using the following formula:

[0108] CH4,loss (methane, loss rate) = V (methane, permeate side) / V (methane, feed side)

[0109] like Figure 10 As shown, the methane loss rate of the membrane during the carbon dioxide / methane separation process at 0-0.8 MPa is between 0.026-0.164%, both lower than 0.2%, which is significantly better than the loss level in traditional ammonia washing technology, further highlighting the application potential and practical value of the membrane material of the present invention in industrial scenarios such as natural gas decarbonization.

[0110] Example 2

[0111] This embodiment provides a highly dense metal organic framework membrane - CAU-10-H membrane material, the preparation method of which is as follows:

[0112] 1) Synthesis of low-crystalline nanocrystals was the same as in Preparation Example 1, with the molar ratio of the precursor solution being 1:1:1:2667;

[0113] 2) 0.05 g of dried low-crystalline nanocrystals were dispersed in 100 g of methanol, and ultrasonicated and stirred for 30 min to obtain a uniform dispersion to obtain a seed solution;

[0114] 3) Using an immersion-coating method, the seed solution was applied to the surface of a porous α-Al2O3 support (a ceramic disc with a diameter of 2.2 cm and a thickness of 2 mm) for 10 seconds. After coating, the support was dried in a convection oven at 60°C for 10 minutes. This process was repeated twice.

[0115] 4) 0.1811 g of aluminum chloride hexahydrate, 0.1246 g of isophthalic acid, and 0.045 g of sodium hydroxide were dissolved in 60 mL of water to prepare a synthetic solution, which was transferred to a polytetrafluoroethylene liner and the pretreated support was placed therein. The solution was then reacted at 90°C for 24 h to form a dense, defect-free CAU-10-H membrane material.

[0116] The surface morphology and cross-sectional structure of the prepared CAU-10-H membrane were characterized by SEM. Figure 11 and Figure 12 The images show that the crystals on the membrane surface are densely and evenly arranged, and the membrane structure is intact, with no obvious cracks or holes. Furthermore, the interface between the membrane and the underlying inorganic support is tightly bonded, with no obvious delamination or shedding observed, indicating good membrane structural continuity, high mechanical stability, and high film quality.

[0117] The permeability test of single-component gas was carried out on the prepared CAU-10-H membrane. Figure 13 As shown. The test results show that the membrane has a high permeation rate for carbon dioxide gas, while gas molecules with larger molecular sizes can hardly pass through the membrane layer and have an extremely low permeation rate. This indicates that the prepared membrane material exhibits excellent permeation selectivity for carbon dioxide gas under the molecular sieving effect, with a carbon dioxide / methane selectivity of approximately 178. Compared with Example 1, although the aluminum-based metal organic framework membrane provided in this example has a slightly lower permeation rate, this is because the window size (membrane crystal pore size) is further reduced, and the rate of molecular permeation is reduced. However, this does not prevent the prepared CAU-10-H from having good carbon dioxide separation potential. At the same time, the carbon dioxide permeation rate is about 35GPU at normal pressure, and the methane loss rate is about 0.045%.

[0118] Comparative Example 1

[0119] This comparative example provides a submicron-sized highly crystalline seed-induced aluminum-based metal organic framework membrane, CAU-10-PDC membrane material, the preparation method of which is as follows:

[0120] 1) 0.05 g of the dried high-crystalline nanocrystals prepared in Comparative Preparation Example 1 was dispersed in 100 g of methanol, and ultrasonicated and stirred for 30 minutes to uniformly disperse the nanocrystals to obtain a seed solution;

[0121] 2) Using an immersion-coating method, the seed solution was applied to the surface of a porous α-Al2O3 support (a ceramic disc with a diameter of 2.2 cm and a thickness of 2 mm) for 10 seconds. After coating, the support was dried in a convection oven at 60°C for 10 minutes. This process was repeated twice.

[0122] 3) 0.3018 g of aluminum chloride hexahydrate, 0.2089 g of pyridine-3,5-dicarboxylic acid, and 0.075 g of sodium hydroxide were dissolved in 60 mL of water to prepare a synthetic solution, which was transferred to a polytetrafluoroethylene liner and the pretreated support was placed therein. The solution was then reacted at 150° C. for 4 h to form a CAU-10-PDC membrane material.

[0123] The support of the impregnation and pulling modified seed crystal in step 2) was characterized by SEM, as shown in FIG. Figure 15 As shown in the upper right panel, it can be seen that the submicron-sized high-crystalline crystals are unevenly dispersed on the surface of the support, forming obvious agglomerations, which leads to the film layer (such as Figure 15 The coverage is incomplete and the support body is obviously partially exposed. This discontinuous membrane structure seriously affects the density and integrity of the membrane and significantly reduces the gas separation performance. Due to the partial exposure, this membrane cannot be used for gas separation.

[0124] Comparative Example 2

[0125] This comparative example provides a highly dense metal organic framework membrane - KMF-1 material, the preparation method of which is basically the same as that of Example 1, except that there is a slight difference in step 4), as follows:

[0126] 4) 0.4824g of aluminum chloride hexahydrate, 0.3102g of 1H-pyrrole-2,5-dicarboxylic acid, and 0.12g of sodium hydroxide were dissolved in 60mL of water to prepare a synthetic solution. The synthetic solution was transferred to a polytetrafluoroethylene liner, and the pretreated support was placed therein. The reaction was then carried out at 110°C for 12 hours to form a dense, defect-free KMF-1 membrane material. That is, during the secondary growth, the type of ligand was changed, and the amounts of aluminum salt, ligand, and modifier, as well as the reaction temperature and time, were adjusted. In addition to the change in the type of ligand, the other adjusted conditions were to obtain the KMF-1 membrane material. This membrane material differed from the membrane material in Example 1, and the growth conditions of the two were also different. Using the conditions of Example 1 alone would not have been sufficient to obtain the KMF-1 material.

[0127] The surface and cross-sectional SEM images of the KMF-1 membrane prepared in Comparative Example 2 are shown in FIG. Figure 16-17 As shown, it can be observed that the surface of the membrane is composed of a large number of tightly arranged crystals. These crystals show obvious polygonal or interlocking structures. It can be seen that the membrane layer is a continuous and dense structure with a uniform thickness of about 9-10μm. The membrane is well bonded to the support, and no obvious stratification, voids or cracks are observed, indicating that the membrane structure is stable and firmly attached.

[0128] like Figure 18 As shown in Figure 2, the single-component gas permeation test results of the KMF-1 membrane show that it still exhibits a significantly higher permeability to carbon dioxide, and the overall permeability gradually decreases with the increase of the gas dynamic diameter, showing a clear size screening effect. However, the carbon dioxide / methane selectivity of the KMF-1 membrane is relatively low, only about 30. This phenomenon is mainly attributed to the larger opening angle of the ligand (1H-pyrrole-2,5-dicarboxylic acid) in the KMF-1 membrane. According to the crystallographic simulation results, its limiting pore diameter is about (like Figure 19 ), which is slightly larger than the pore size of the CAU-10-PDC membrane and the CAU-10-H membrane used in Examples 1 and 2.

[0129] Although the larger pore size is conducive to the rapid flux transmission of carbon dioxide, its ability to retain methane is significantly weakened. Further testing in the feed pressure range of 0-0.8MPa under an equimolar feed flow of 80SCCM found that the selectivity of the KMF-1 membrane decreased significantly with increasing pressure, from 30 to 15 ( Figure 20); At the same time, the loss rate of methane also increased significantly, from 0.34% to a higher level ( Figure 21 ), the overall performance is inferior to that of the CAU-10-PDC membrane in Example 1.

[0130] This comparative result further verifies the key role of precise pore size control in improving gas separation performance, especially in achieving high carbon dioxide selectivity while effectively reducing methane loss. The CAU-10-PDC membrane exhibits better separation efficiency.

[0131] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum-based metal organic framework membrane, characterized in that: The preparation method comprises the following steps: 1) Solvothermal reaction of aluminum salt, carboxylic acid ligand and modifier in a solvent to obtain low-crystalline nanocrystal seeds, wherein the specific surface area of ​​the low-crystalline nanocrystal seeds measured by nitrogen adsorption at 77K is 1-20m 2 / g, and XRD has no obvious sharp diffraction peaks, only diffuse peaks; 2) dispersing the low-crystalline nanocrystal seeds in a solvent to obtain a dispersion, and immersing a support in the dispersion to obtain a support modified with the low-crystalline nanocrystal seeds; 3) placing the support modified with low-crystalline nanocrystal seeds in a synthesis solution for secondary solvent thermal growth to obtain the aluminum-based metal organic framework membrane; the synthesis solution includes an aluminum salt, a carboxylic acid ligand, a regulator and a solvent; the carboxylic acid ligand is selected from isophthalic acid or pyridine-3,5-dicarboxylic acid.

2. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: In step 1), the aluminum salt is selected from a combination of one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate or aluminum sulfate 18hydrate; and / or, in step 1), the carboxylic acid ligand is selected from isophthalic acid or pyridine-3,5-dicarboxylic acid or 1H-pyrrole-2,5-dicarboxylic acid; and / or, in step 1), the regulator is selected from sodium hydroxide or potassium hydroxide; and / or, in step 1), the solvent is methanol.

3. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: In step 1), the molar ratio of the aluminum salt, carboxylic acid ligand, regulator and solvent is 1:1:1-1.5:200-8000; and / or, in step 1), the temperature of the solvent thermal reaction is 100-120°C; and / or, the size of the low-crystalline nanocrystal seeds is 40-540nm.

4. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: The mass percentage concentration of the dispersion is 0.05%-0.1%; and / or, in step 2), the solvent is selected from a combination of one or more of methanol, ethanol and isopropanol; and / or, the impregnation is achieved by an immersion pulling method; and / or, the number of impregnations is 1-3 times, and the time of each impregnation is 5-15 seconds.

5. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: In step 3), the temperature of the secondary solvent thermal growth is 90-150° C.; and / or, in step 3), in the synthesis solution, the molar ratio of the aluminum salt, carboxylic acid ligand, regulator and solvent is 1:1:1-1.5:1000-5000.

6. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: In step 3), the aluminum salt is selected from a combination of one or more of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminum sulfate 18hydrate; and / or, in step 3), the regulator is selected from sodium hydroxide or potassium hydroxide; and / or, in step 3), the solvent is water.

7. The method for preparing an aluminum-based metal-organic framework membrane according to claim 1, wherein: The support body is an α-Al2O3 porous support body; preferably, the α-Al2O3 porous support body is a porous ceramic disc material with a diameter of 1.8-3.0 cm and a thickness of 1-5 mm.

8. An aluminum-based metal-organic framework membrane prepared by the method for preparing an aluminum-based metal-organic framework membrane according to any one of claims 1 to 7.

9. Use of the aluminum-based metal-organic framework membrane according to claim 8 for separating a mixed gas containing carbon dioxide, wherein the mixed gas further contains a combination of one or more selected from methane, nitrogen, and carbon monoxide.

10. The use according to claim 9, characterized in that: The application is applicable to the fields of natural gas decarbonization, biogas purification or industrial carbon capture.

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