A mixed matrix membrane of a methane purification MOF and a method of making the same

Abstract

The application relates to a methane purification MOF mixed matrix membrane and a preparation method thereof, and belongs to the technical field of separation membranes. The mixed matrix membrane adopts a mechanical chemical in-situ crystallization method to uniformly disperse metal organic framework material Ni(ina)2 in inherent microporous polymer PIM-1, and forms a composite membrane with a three-layer structure. The application realizes uniform distribution and strong interface combination of the MOF in the polymer matrix through a room-temperature ball milling process, and solves the technical problems of easy agglomeration of the MOF and many interface defects in the traditional mixed matrix membrane. The membrane has excellent performance in CH4 / N2 separation: the CH4 permeation rate reaches 8120 GPU, the CH4 / N2 selectivity reaches 6.52-7.11, and the membrane has excellent thermal stability, humidity stability and anti-aging performance; the performance attenuation is less than 11% after aging for 180 days under the condition of 60 DEG C / 85% humidity, and the performance is far superior to that of the traditional separation membrane.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane technology and relates to a MOF mixed matrix membrane for methane purification and its preparation method. Background Technology

[0002] Coalbed methane, commonly known as "gas," is an unconventional natural gas that coexists with coal and is stored in an adsorbed state within coal seams. Its main component is methane. my country has abundant coalbed methane reserves, with proven reserves of approximately 420 billion cubic meters in 2020. However, over 70% of coalbed methane is mixed with a large amount of air during extraction due to extraction techniques (underground extraction), resulting in low-concentration coalbed methane (methane concentration <30%) that cannot be effectively utilized. This low-concentration coalbed methane is generally directly released into the atmosphere, causing resource waste and contributing to the greenhouse effect.

[0003] Currently, the separation and enrichment technology of low-concentration coalbed methane has become a bottleneck problem in the development and utilization of coalbed methane. CH4 and N2 are the main components of low-concentration coalbed methane. Under normal temperature and pressure, their kinetic diameters and physical properties are similar (CH4 kinetic diameter 0.38 nm, N2 0.36 nm), making separation difficult. Traditional pressure swing adsorption (PSA) technology typically yields methane with a purity of 40-60% and a recovery rate of 50-70%, which is inefficient and costly.

[0004] Membrane separation, as a novel separation technology, boasts advantages such as simple process, convenient operation, low cost, and no secondary pollution. However, conventional separation membrane materials suffer from a trade-off effect, meaning that selectivity and permeability are mutually restrictive and difficult to improve simultaneously. Particularly for the CH4 / N2 system, when the membrane pore diameter is smaller than the mean free path of gas molecules, the collision frequency between molecules and the pore wall is greater than the intermolecular collision frequency. The gas transfer mechanism through the membrane pores is Knudsen diffusion. In this case, the ideal separation factor for CH4 / N2 is only 1.32, which is insufficient for effective separation.

[0005] Metal-organic frameworks (MOFs) are a new type of porous material with advantages such as large specific surface area and high porosity, showing great potential in gas adsorption and separation. The nickel-based MOF material Ni(ina)₂ developed by Professor Yang Qingyuan's research group at Xi'an Jiaotong University exhibits high methane / nitrogen selectivity (15.8) and large adsorption capacity (46.7 cm⁻¹). 3 The characteristics of MOF materials ( / g) are evident. However, when combining MOF materials with polymer matrices to prepare hybrid matrix membranes, problems such as MOF particle agglomeration and poor interfacial compatibility with the polymer matrix often occur, leading to a decline in membrane performance. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a methane-purified MOF mixed matrix membrane and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a methane-purified MOF mixed matrix membrane, the MOF mixed matrix membrane comprising a carrier layer, an intermediate layer and a surface skin layer, the carrier layer being a polytetrafluoroethylene porous membrane, the intermediate layer being a mixed matrix of Ni(ina)2MOF material crystallized in situ by mechanochemical processes and PIM-1 having microporous polymer, and the surface skin layer being a styrene-butadiene-styrene triblock polymer. Preferably, the pore size of the carrier layer is 0.5-1.0 μm and the thickness is 5-20 μm, the mass fraction of Ni(ina)2 in the intermediate layer is 30-40%, the thickness of the MOF hybrid matrix film is 15-30 μm, and the tensile strength is 23-35 MPa; Furthermore, the method for preparing the methane-purified MOF hybrid matrix membrane includes the following steps: S1: Carrier layer pretreatment A polytetrafluoroethylene porous membrane with an average pore size of 0.8 μm and a thickness of 15 μm was taken, immersed in a mixed solution of ethanol and water, and ultrasonically cleaned at a frequency of 40 kHz for 30 minutes. Then the membrane was taken out, immersed in sodium naphthalene tetrahydrofuran solution for 1 hour, rinsed thoroughly with deionized water, and dried in an oven at 50 ℃ for 4 hours. S2: Mechanochemical in-situ crystallization Nickel source, organic ligand ina and PIM-1 were added to a ball mill jar in a certain proportion, and zirconia grinding balls were added. The mixture was ball milled at 400-500 rpm for 2-4 hours at room temperature to obtain a uniform Ni(ina)2@PIM-1 mixed powder. S3: Intermediate layer molding The Ni(ina)2@PIM-1 mixed powder obtained in step S2 was dispersed in an appropriate amount of tetrahydrofuran to form a uniform slurry with a solid content of 10wt%. The slurry was uniformly coated on the pretreated polytetrafluoroethylene carrier layer and the solvent was evaporated at room temperature for 2 hours. S4: Surface Skin Preparation Prepare a 5 wt% styrene-butadiene-styrene triblock polymer toluene solution, immerse the composite membrane with the intermediate layer obtained in step S3 into the triblock polymer toluene solution, maintain it under a vacuum of 0.1 MPa for 20 minutes, then slowly pull out the membrane, and dry it at 50°C for 6 hours to obtain the MOF mixed matrix membrane. Preferably, in step S1, the volume ratio of ethanol to water is 1:1; Preferably, in step S2, the molar ratio of nickel source to organic ligand is 1:2; Preferably, in step S2, the mass fraction of Ni(ina)2 is 35%; Preferably, in step S3, the thickness of the slurry uniformly coated on the pretreated polytetrafluoroethylene carrier layer is 5-15 μm.

[0008] The beneficial effects of this invention are as follows: Compared with the prior art, the present invention has the following outstanding advantages: 1. Record-breaking separation performance: The MOF mixed matrix membrane prepared in this invention exhibits record-breaking performance in CH4 / N2 separation, with a CH4 permeability of 8120 Bar and a CH4 / N2 selectivity of 6.52-7.11, far exceeding that of conventional separation membranes (CH4 / N2 separation ratio is usually 3-6) and most reported mixed matrix membranes.

[0009] 2. Excellent anti-aging properties: The membrane has excellent thermal stability, humidity stability and long-term stability. After aging for 180 days at 60°C / 85% humidity, the performance degradation is less than 11%, which is far better than the value reported in the literature (usually >30%), making it suitable for harsh industrial environments.

[0010] 3. Innovative preparation process: The mechanochemical in-situ crystallization method achieves uniform dispersion and strong interfacial bonding of MOFs in the polymer matrix at room temperature, solving the technical problems of easy MOF agglomeration and numerous interfacial defects in traditional mixed matrix membranes. This "one-pot" green process requires no complex equipment and is suitable for large-scale production.

[0011] 4. High efficiency in purifying low-concentration coalbed methane: This membrane can purify low-concentration coalbed methane with a methane concentration of less than 30% to a methane concentration of more than 85%, with a methane recovery rate of more than 90%, which greatly improves the utilization efficiency of coalbed methane resources.

[0012] 5. Good mechanical properties: This composite membrane has both high separation performance and good mechanical strength. The tensile strength of the membrane is 23-35 MPa, which meets the requirements of industrial applications.

[0013] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1This is a schematic diagram of the three-layer structure of the MOF hybrid matrix membrane of the present invention; 1-upper surface skin layer; 2-middle MOF / PIM-1 hybrid matrix functional layer; 3-lower porous support layer.

[0015] Figure 2 The graph shows a comparison of the CH4 pure gas permeability of the MOF hybrid matrix membrane prepared in Example 1 and the conventional hybrid matrix membrane prepared in Comparative Example 1.

[0016] Figure 3 The graph shows a comparison of the N2 pure gas permeability of the MOF hybrid matrix membrane prepared in Example 1 and the conventional hybrid matrix membrane prepared in Comparative Example 1.

[0017] Figure 4 This is a comparison diagram of the CH4 / N2 selectivity of the MOF hybrid matrix membrane prepared in Example 1 and the conventional hybrid matrix membrane prepared in Comparative Example 1. Detailed Implementation

[0018] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0019] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0020] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0021] Example 1 1. Preparation method (1) Pretreatment of carrier layer A polytetrafluoroethylene porous membrane with an average pore size of 0.8 μm and a thickness of 15 μm was immersed in a 1:1 volume ratio of ethanol and water and ultrasonically cleaned at 40 kHz for 30 minutes. The membrane was then removed, immersed in sodium naphthalenete tetrahydrofuran solution for 1 hour, thoroughly rinsed with deionized water, and dried in a 50°C oven for 4 hours for later use.

[0022] (2) Mechanochemical in-situ crystallization Weigh 1.0 g of PIM-1 polymer, 0.745 g of nickel nitrate hexahydrate (nickel source), and 0.492 g of isonicotinic acid (organic ligand ina) into a 250 mL ball mill jar. The molar ratio is Ni². + The ratio of Ni(ina) to PIM-1 is 1:2. Add 100g of zirconia grinding balls (5mm in diameter) and seal the grinding jar. Fix the grinding jar on a planetary ball mill and ball mill at 450 rpm for 3 hours at room temperature. After ball milling, a uniform Ni(ina)2@PIM-1 mixed powder is obtained, in which the mass fraction of Ni(ina)2 is approximately 35%.

[0023] (3) Intermediate layer molding The Ni(ina)2@PIM-1 mixed powder obtained in step two was dispersed in an appropriate amount of tetrahydrofuran to form a uniform slurry with a solid content of 10 wt%. The slurry was uniformly coated onto the pretreated polytetrafluoroethylene carrier layer using a doctor blade coating method, with the wet film thickness controlled at 100 μm. The solvent was evaporated at room temperature for 2 hours to form an intermediate layer with a thickness of approximately 10 μm.

[0024] (4) Preparation of surface skin A 5 wt% solution of styrene-butadiene-styrene triblock polymer (SBS) in toluene was prepared. The composite membrane with the intermediate layer obtained in step three was immersed in the SBS solution and kept under a vacuum of 0.1 MPa for 20 minutes to allow the SBS solution to fully penetrate. The membrane was then slowly pulled out and dried at 50°C for 6 hours to form a surface skin. Finally, a complete three-layer MOF hybrid matrix membrane with a total thickness of approximately 25 μm was obtained.

[0025] 2. Performance Testing 1) Gas separation performance: The permeation performance of the membrane for CH4 and N2 was measured using a gas permeameter. The test conditions were: room temperature (25℃) and pressure difference of 0.1 MPa. The measured CH4 permeability was 8120 GPU, and the CH4 / N2 selectivity was 7.11.

[0026] 2) Mechanical properties: The tensile strength of the membrane was measured using a universal testing machine, and the result was 28 MPa.

[0027] 3) Stability test: The membrane sample was placed in a constant temperature and humidity chamber at 60°C and 85% relative humidity, and its gas separation performance was tested periodically. After 180 days, the CH4 permeability remained at 7260 GPU (89.4% retention rate), the CH4 / N2 selectivity remained at 6.52 (91.7% retention rate), and the overall performance degradation was less than 11%.

[0028] 4) Low-concentration coalbed methane separation experiment: Using simulated low-concentration coalbed methane with a methane concentration of 25% and a nitrogen concentration of 75% as raw material, the membrane separation performance was tested under a pressure of 0.5 MPa. The results showed that the methane concentration in the product gas increased to 88%, and the methane recovery rate reached 92%.

[0029] Example 2 1. Preparation method (1) Pretreatment of carrier layer Same as Example 1.

[0030] (2) Mechanochemical in-situ crystallization Weigh out 1.0 g of PIM-1 polymer, 0.497 g of nickel nitrate hexahydrate, and 0.328 g of isonicotinic acid, with a molar ratio of Ni... 2+ The ratio of Ni(ina)₂ to PIM-1 was 1:2. The ball milling conditions were the same as in Example 1, but the milling time was shortened to 2 hours. A Ni(ina)₂@PIM-1 mixed powder was obtained, wherein the mass fraction of Ni(ina)₂ was approximately 25%.

[0031] (3) Intermediate layer molding Same as Example 1.

[0032] (4) Preparation of surface skin Same as Example 1.

[0033] 2. Performance Testing The membrane's CH4 permeability was measured to be 5650 GPU, its CH4 / N2 selectivity to be 15.83, and its tensile strength to be 25 MPa. After 180 days of aging testing, its performance degraded by approximately 15%.

[0034] Comparative Example 1: Traditional Hybrid Matrix Membrane 1. Preparation method Pre-synthesized Ni(ina)₂MOF powder was directly mixed with PIM-1 polymer to prepare a mixed matrix membrane using a solution blending method. The MOF content was the same as in Example 1 (35 wt%).

[0035] 2. Performance Testing The measured CH4 permeability was 2850 GPUs, and the CH4 / N2 selectivity was 4.27, both lower than in Example 1. After 180 days of aging testing, performance degradation reached 32%.

[0036] Comparative Example 2: Different MOF Materials: ZIF-8 1. Preparation method (1) Pretreatment of carrier layer Same as Example 1.

[0037] (2) Mechanochemical in-situ crystallization (ZIF-8 system) Weigh 1.0 g of PIM-1 polymer, 0.594 g of zinc nitrate hexahydrate (zinc source), and 0.656 g of 2-methylimidazole (organic ligand), with a molar ratio of Zn². + The ratio of ZIF-8 to PIM-1 was 1:2. The mixture was placed in a 250 mL ball mill jar, and 100 g of zirconia grinding balls (5 mm in diameter) were added. The mixture was ball milled at 450 rpm for 3 hours at room temperature. After ball milling, a ZIF-8@PIM-1 mixed powder was obtained, in which the ZIF-8 mass fraction was approximately 35%.

[0038] (3) Intermediate layer molding Same as in Example 1, a ZIF-8@PIM-1 intermediate layer with a thickness of approximately 10 μm was obtained.

[0039] (4) Preparation of surface skin Same as Example 1.

[0040] 2. Performance Testing: CH4 penetration rate: 9560 GPU; CH4 / N2 selectivity: 2.83; Tensile strength: 24 MPa; Performance degradation after 180 days of aging at 60°C / 85% humidity: 28%.

[0041] Comparative Example 3: Different Polymer Matrices: Matrimid 1. Preparation method (1) Pretreatment of carrier layer Same as Example 1.

[0042] (2) Mechanochemical in-situ crystallization (Matrimid system) 1.0 g of Matrimid 5218 polyimide, 0.745 g of nickel nitrate hexahydrate, and 0.492 g of isonicotinic acid were placed in a ball mill jar, with a molar ratio of Ni... 2+ The ratio of ina to 1:2 was used. The ball milling conditions were the same as in Example 1, yielding a Ni(ina)₂@Matrimid mixed powder with a MOF mass fraction of approximately 35%.

[0043] (3) Intermediate layer molding The obtained powder was dispersed in N-methylpyrrolidone with a solid content of 10 wt%, and coated onto a carrier layer with a wet film thickness of 100 μm. The solvent was evaporated at 80 °C for 4 hours to form an intermediate layer with a thickness of about 10 μm.

[0044] (4) Preparation of surface skin Same as Example 1.

[0045] 2. Performance Testing: CH4 penetration rate: 1870 GPU; CH4 / N2 selectivity: 4.92; Tensile strength: 31 MPa; Performance degradation after 180 days of aging at 60°C / 85% humidity: 19%.

[0046] Comparative Example 4: Pure PIM-1 interlayer, without MOF filler 1. Preparation method (1) Pretreatment of carrier layer Same as Example 1.

[0047] (2) Preparation of intermediate layer 1.0 g of PIM-1 polymer was dissolved in tetrahydrofuran to prepare a 10 wt% solution, which was then directly coated onto the carrier layer with a wet film thickness of 100 μm. The solvent was allowed to evaporate at room temperature for 2 hours to form a pure PIM-1 intermediate layer with a thickness of approximately 10 μm.

[0048] (3) Preparation of surface skin Same as Example 1.

[0049] 2. Performance Testing: CH4 penetration rate: 11200 GPU; CH4 / N2 selectivity: 2.41; Tensile strength: 18 MPa; Performance degradation after 180 days of aging at 60°C / 85% humidity: 35%.

[0050] Comparative Example 5: Traditional solution blending method, different MOFs: HKUST-1 1. Preparation method (1) Pretreatment of carrier layer Same as Example 1.

[0051] (2) MOF synthesis and blending HKUST-1 (copper-based MOF) crystals were synthesized in advance via a hydrothermal method, ground, and passed through a 400-mesh sieve. 0.35 g of HKUST-1 and 0.65 g of PIM-1 were co-dissolved in tetrahydrofuran and ultrasonically dispersed for 2 hours to obtain a mixed slurry.

[0052] (3) Intermediate layer molding The slurry was coated onto the carrier layer, with a wet film thickness of 100 μm. The solvent was allowed to evaporate at room temperature for 2 hours to form an intermediate layer with a thickness of about 10 μm and an MOF mass fraction of 35%.

[0053] (4) Preparation of surface skin Same as Example 1.

[0054] 2. Performance Testing: CH4 penetration rate: 3120 GPU; CH4 / N2 selectivity: 3.65; Tensile strength: 21 MPa; Performance degradation after 180 days of aging at 60°C / 85% humidity: 30%.

[0055] Example 3 Performance Comparison Analysis The performance data of the above comparative examples and Example 1 of the present invention are compared in the following table:

[0056] Analysis conclusion: The effect of MOF materials: Although the permeability of Comparative Example 2 (ZIF-8) was slightly higher than that of Example 1, the selectivity decreased significantly (2.83 vs 7.11), indicating that the pore structure of ZIF-8 is not conducive to CH4 / N2 separation; the selectivity of Comparative Example 5 (HKUST-1) was also significantly lower than that of the present invention, indicating that the unique ultra-microporous structure of Ni(ina)2 is the key to achieving high selectivity.

[0057] Effect of polymer matrix: The permeability of Comparative Example 3 (Matrimid) was much lower than that of Example 1 (1870 vs 8120), which is attributed to the smaller free volume of Matrimid and the greater gas transport resistance, while the inherent microporosity of PIM-1 is conducive to increasing permeation flux.

[0058] Effect of preparation method: Comparative Examples 1 and 5 both used traditional solution blending. MOF agglomeration and interfacial defects led to a decrease in both permeability and selectivity, and poor aging stability. Although Comparative Examples 2 and 3 used mechanochemical in-situ crystallization, their performance was still not as good as Example 1 due to improper selection of MOF or polymer.

[0059] Comparative Example 4 without MOF filler: Although the pure PIM-1 membrane has extremely high permeability, it has extremely low selectivity and cannot meet the requirements for industrial concentration. In addition, its mechanical strength and stability are also poor.

[0060] As can be seen from the above examples and comparative examples, the MOF mixed matrix membrane prepared by the mechanochemical in-situ crystallization method provided by the present invention is significantly superior to mixed matrix membranes prepared by traditional methods in terms of gas separation performance, mechanical strength, and long-term stability. This indicates that the mechanochemical in-situ crystallization method effectively solves the dispersion problem and interfacial compatibility problem of MOF in the polymer matrix, forming a uniform mixed matrix structure with strong interfacial bonding.

[0061] The superior performance of the MOF hybrid matrix membrane of this invention mainly stems from the following aspects: 1. Uniform MOF dispersion: The mechanical force generated during the mechanochemical ball milling process can uniformly disperse the MOF precursor in the polymer matrix and crystallize in situ to form MOF particles of uniform size, avoiding the problem of MOF particle agglomeration in traditional methods.

[0062] 2. Strong interfacial bonding: The MOF particles formed by in-situ crystallization have strong interactions with the polymer molecular chains, which reduces interfacial defects and improves gas selectivity.

[0063] 3. Optimized pore structure: The ultra-microporous structure of Ni(ina)2MOF (pore size of about 0.5-0.8nm) and the inherent micropores of PIM-1 form a continuous sub-angstrom-level channel network, which enables the specific recognition and transport of CH4 molecules.

[0064] 4. Stable three-layer structure: The carrier layer provides mechanical support, the middle layer is the main separation functional layer, and the surface skin layer provides surface modification and selective separation functions. The three layers work together to achieve efficient and stable gas separation.

[0065] The MOF hybrid matrix membrane prepared by this invention can be widely used in fields such as low-concentration coalbed methane purification and natural gas denitrification. Based on the proven coalbed methane reserves in China (greater than 4 trillion cubic meters) and the current development scale (my country's coalbed methane production was 7.26 billion cubic meters in 2018, growing at a rate of 7% annually), this project has broad application prospects. This membrane can be integrated into mobile skid-mounted coalbed methane enrichment devices, making it particularly suitable for low-concentration coalbed methane extraction scenarios characterized by dispersed distribution and unstable gas supply.

[0066] In summary, the combination of Ni(ina)2MOF and PIM-1 polymer selected in this invention, combined with the mechanochemical in-situ crystallization method, achieves uniform dispersion and strong interfacial bonding of MOF, thereby obtaining high selectivity while maintaining high permeability, and endowing the membrane with excellent mechanical properties and long-term stability.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A methane-purified MOF hybrid matrix membrane, characterized in that: The MOF hybrid matrix membrane includes a carrier layer, an intermediate layer, and a surface skin layer. The carrier layer is a polytetrafluoroethylene porous membrane. The intermediate layer is a hybrid matrix of Ni(ina)2MOF material crystallized in situ by mechanochemical processes and PIM-1 with microporous polymer. The surface skin layer is a styrene-butadiene-styrene triblock polymer.

2. The methane-purified MOF mixed matrix membrane according to claim 1, characterized in that: The carrier layer has a pore size of 0.5-1.0 μm and a thickness of 5-20 μm. The mass fraction of Ni(ina)2 in the intermediate layer is 30-40%. The thickness of the MOF hybrid matrix film is 15-30 μm and the tensile strength is 23-35 MPa.

3. The method for preparing a methane-purified MOF mixed matrix membrane according to claim 1 or 2, characterized in that, Includes the following steps: S1: Carrier layer pretreatment A polytetrafluoroethylene porous membrane with an average pore size of 0.8 μm and a thickness of 15 μm was taken, immersed in a mixed solution of ethanol and water, and ultrasonically cleaned at a frequency of 40 kHz for 30 minutes. Then the membrane was taken out, immersed in sodium naphthalene tetrahydrofuran solution for 1 hour, rinsed thoroughly with deionized water, and dried in an oven at 50 ℃ for 4 hours. S2: Mechanochemical in-situ crystallization Nickel source, organic ligand ina and PIM-1 were added to a ball mill jar in a certain proportion, and zirconia grinding balls were added. The mixture was ball milled at 400-500 rpm for 2-4 hours at room temperature to obtain a uniform Ni(ina)2@PIM-1 mixed powder. S3: Intermediate layer molding The Ni(ina)2@PIM-1 mixed powder obtained in step S2 was dispersed in an appropriate amount of tetrahydrofuran to form a uniform slurry with a solid content of 10wt%. The slurry was uniformly coated on the pretreated polytetrafluoroethylene carrier layer and the solvent was evaporated at room temperature for 2 hours. S4: Surface Skin Preparation Prepare a 5 wt% styrene-butadiene-styrene triblock polymer toluene solution, immerse the composite membrane with the intermediate layer obtained in step S3 into the triblock polymer toluene solution, maintain it under a vacuum of 0.1 MPa for 20 minutes, then slowly pull out the membrane and dry it at 50°C for 6 hours to obtain the MOF mixed matrix membrane.

4. The preparation method according to claim 3, characterized in that: In step S1, the volume ratio of ethanol to water is 1:

1.

5. The preparation method according to claim 3, characterized in that: In step S2, the molar ratio of nickel source to organic ligand is 1:

2.

6. The preparation method according to claim 3, characterized in that: In step S2, the mass fraction of Ni(ina)2 is 35%.

7. The preparation method according to claim 3, characterized in that: In step S3, the slurry is uniformly coated on the pretreated polytetrafluoroethylene carrier layer with a thickness of 5-15 μm.

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