A hybrid matrix membrane for CO2 separation and its preparation method

Abstract

This invention provides a method for preparing a mixed matrix membrane for CO2 separation, including the preparation of an electrospinning precursor solution and electrospinning, the preparation of hollow ZnO nanotubes, the preparation of ZIF-8 hollow nanotubes, the preparation of a modified IL@MOF composite material, the preparation of a casting precursor solution and coating, and the preparation of a mixed matrix membrane for CO2 separation. The mixed matrix membrane for CO2 separation prepared by this invention has high permeability and high adsorption selectivity, and has high promotion and commercialization value.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane technology, and more specifically, to a mixed matrix membrane for separating CO2 and a method for preparing the same. Background Technology

[0002] With the development of modern industry, global energy consumption has been increasing, especially the combustion of fossil fuels, which has led to a sharp increase in the concentration of carbon dioxide in the air. This has resulted in a series of serious phenomena, such as the greenhouse effect and water pollution. Therefore, effective capture and separation of CO2 is of great significance for improving the environment. Commonly used CO2 capture technologies include adsorption, adsorption, cryogenic distillation, and membrane separation. Membrane separation is a method of selective separation based on the different permeation rates of various gas components through the membrane. Compared with traditional cryogenic distillation, adsorption, and absorption methods, membrane separation is a new type of separation technology. Due to its many advantages such as low cost, low pollution, low energy consumption, and small footprint, it is widely used in the field of gas separation. To date, various CO2 separation membranes can be mainly classified into inorganic membranes, polymer membranes, and composite membranes according to the different membrane materials.

[0003] Inorganic membranes possess high permeability and strong stability, exhibiting excellent performance. However, their large-scale development is limited by high manufacturing costs and poor film-forming properties. Polymer membranes are dense membranes formed by polymerizing high-molecular materials. While their preparation cost is lower, their permeability and selectivity are limited by a trade-off effect. Composite membranes, which combine the advantages of both inorganic and polymer membranes, are currently a hot research topic. Composite membranes used for CO2 separation are mainly mixed-matrix hybrid membranes (MMMs). Mixed-matrix hybrid membranes are the most common and widely used type of metal-organic framework-organic polymer hybrid membrane. They are hybrid membranes formed using metal-organic framework nanocrystals as the filler and organic polymers as the continuous phase, hereinafter referred to as mixed-matrix membranes or MMMs. MMMs have attracted widespread attention due to their ability to overcome the shortcomings of polymer membranes and are recognized as one of the fastest-growing research areas; the development of single inorganic or polymer membranes is limited by their respective limitations. MMMs combine the density of polymer membranes with the high permeability of inorganic membranes, and are expected to break this trade-off effect. Advances in metal-organic framework (MMM) for gas separation have primarily focused on incorporating porous fillers into the continuous phase of a polymer matrix. However, the structure of the filler is considered a key factor influencing the diffusion rate of gas molecules within the MMM; simultaneously, the filler thickness, composition, and distribution within the matrix are crucial. Ultrathin nanofillers can significantly reduce the mass transfer resistance of gas molecules within the membrane, providing faster molecular mass transfer channels and improving gas permeability. Furthermore, recent studies have found that CO2 exhibits excellent solubility in ionic liquids. In mixed-matrix hybrid membranes, ionic liquids act as the matrix, forming the main body of the hybrid membrane. Metal-organic framework nanocrystals, as filler particles, are uniformly distributed within the matrix, providing new channels for the transport and separation of guest molecules.

[0004] Currently, there are no mature mixed matrix membranes for CO2 separation or their preparation methods, and conventional matrix membranes generally have relatively low permeability and adsorption selectivity. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a mixed matrix membrane for separating CO2, so as to solve the problem that the permeability and adsorption selectivity of mixed matrix membranes prepared by conventional methods are relatively general.

[0006] To address the above problems, this invention provides a method for preparing a mixed matrix membrane for CO2 separation, comprising the following steps:

[0007] S1: Prepare N-methylpyrrolidone solution of polyacrylonitrile and N-methylpyrrolidone solution of polyvinylpyrrolidone and zinc acetate dihydrate. Mix the two solutions and stir to obtain PAN / PVP+Zn(Ac)2 emulsion as electrospinning precursor solution.

[0008] S2: The precursor solution prepared in step S1 is electrospun to obtain PAN / PVP+Zn(Ac)2 composite nanofibers with core-shell structure. The composite nanofibers are dried and then calcined at high temperature to remove the polymer, resulting in ZnO nanotubes with hollow structure.

[0009] S3: Dissolve the ZnO nanotubes prepared in step S2 in N,N-dimethylformamide solution, stir and disperse, and add the organic ligand 2-methylimidazole during stirring. After hydrothermal reaction, ZIF-8 hollow nanotubes are obtained.

[0010] S4: Weigh the amino acid ionic liquid and place it in methanol and stir. Then add the dried ZIF-8 hollow nanotubes and continue stirring until the methanol is completely evaporated to obtain the loaded modified IL@MOF composite material.

[0011] S5: Prepare an N-methylpyrrolidone solution containing polymer particles; prepare an N-methylpyrrolidone solution of polyvinylpyrrolidone and IL@MOF composite material; mix and stir the above two solutions to obtain a casting precursor solution containing polymer particles / polyvinylpyrrolidone / hollow IL@MOF nanotubes; degas the casting precursor solution and then coat it on a flatbed coating machine;

[0012] S6: After mixing and stirring boric acid aqueous solution and ammonium fluorotitanate hexahydrate, a suspension of nano-TiO2 is obtained; after drying the membrane solution after coating in step S5 and evaporating the solvent, a mixed matrix membrane with gas transmission channels is obtained. The mixed matrix membrane is loaded into a membrane contactor and the suspension of nano-TiO2 is introduced. After drying the matrix membrane, a mixed matrix membrane for CO2 separation is obtained.

[0013] As a preferred embodiment, in step S1, the concentration of polyacrylonitrile in the N-methylpyrrolidone solution of polyacrylonitrile is 12%-15%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 10-12% and 3%, respectively, and the mass ratio of the two solutions is 1:2.

[0014] As a preferred embodiment, in step S2, the drying conditions are: drying in an oven at 60°C for 12 hours; the high-temperature calcination conditions are: heating to 650°C at a heating rate of 50°C / hour and holding at that temperature for 2 hours.

[0015] As a preferred embodiment, in step S3, the mass ratio of the ZnO nanotubes to the N,N-dimethylformamide solution is 0.5:99.5, the stirring and dispersion temperature is 100℃, the mass ratio of the organic ligands to the ZnO nanotubes is 2:1, and the hydrothermal reaction time is 4h.

[0016] As a preferred embodiment, in step S4, the drying process is performed overnight at a temperature of 150°C.

[0017] As a preferred embodiment, in step S4, the ionic liquid includes one of 1-ethyl-3-methylimidazolium glycinate, 1-butyl-3-methylimidazolium glutamate, 1-hydroxyethyl-3-butylimidazolium alanine, or 1-butyl-3-methylimidazolium tetrafluoroborate.

[0018] As a preferred embodiment, in step S5, the polymer particles are one of polyethersulfone, polyimide, polyethylene glycol, polyacrylonitrile, and polyvinylidene fluoride; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 12%-15% and 2%-5%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 12%-15%; and the mass of the IL@MOF composite material is 2%-8% of the casting precursor solution.

[0019] As a preferred embodiment, in step S5, the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 6% of the casting precursor solution.

[0020] As a preferred embodiment, in step S5, the degassing treatment conditions are as follows: the casting precursor solution is first ultrasonically degassed for 30 minutes, and then allowed to stand at room temperature for 24 hours for further degassing; the thickness of the coating film is 200 μm.

[0021] As a preferred embodiment, in step S6, the conditions for drying and evaporating the solvent are: drying in an oven at 60°C for 12 hours; the method of introducing the nano-TiO2 suspension is: introducing the nano-TiO2 suspension through a peristaltic pump; after introducing the nano-TiO2 suspension and before drying, the substrate membrane is further washed with water to remove unloaded TiO2 nanoparticles from the surface.

[0022] Another technical problem to be solved by the present invention is to provide a mixed matrix membrane for separating CO2, so as to fill the technical gap in this field and provide a mixed matrix membrane with high permeability and high adsorption selectivity.

[0023] To address the aforementioned problems, the present invention provides a mixed matrix membrane for separating CO2, wherein the mixed matrix membrane is prepared by the above-described preparation method.

[0024] The hollow IL@MOF nanotubes provided by this invention are a novel functional filler. The mixed matrix membrane for CO2 separation provided by this invention, compared with the pure polymer membrane without filler and the mixed matrix membrane with MOF particles, shows significantly improved hydrophobicity, CO2 permeability and selectivity.

[0025] The present invention has the following beneficial effects: The ionic liquid-supported MOF composite nanotubes prepared by the present invention are a novel filler material. They possess CO2 gas transport channels and selective MOF tube walls that facilitate gas adsorption and sieving, ensuring both the CO2 transport rate and the CO2 / N2 selectivity. Compared with pure polymer membranes without fillers and mixed matrix membranes with added MOF particles, both exhibit varying degrees of performance improvement, balancing permeability and selectivity. Attached Figure Description

[0026] Figure 1 The graph shows the CO2 / N2 pure gas permeation / selectivity performance of mixed matrix membranes of IL@MOF composites with different filler contents. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention provides a method for preparing a mixed matrix membrane for separating CO2, comprising the following steps:

[0029] S1: Prepare N-methylpyrrolidone solution of polyacrylonitrile and N-methylpyrrolidone solution of polyvinylpyrrolidone and zinc acetate dihydrate. Mix the two solutions and stir to obtain PAN / PVP+Zn(Ac)2 emulsion as electrospinning precursor solution.

[0030] S2: The precursor solution prepared in step S1 is electrospun to obtain PAN / PVP+Zn(Ac)2 composite nanofibers with core-shell structure. The composite nanofibers are dried and then calcined at high temperature to remove the polymer, resulting in ZnO nanotubes with hollow structure.

[0031] S3: Dissolve the ZnO nanotubes prepared in step S2 in N,N-dimethylformamide solution, stir and disperse, and add the organic ligand 2-methylimidazole during stirring. After hydrothermal reaction, ZIF-8 hollow nanotubes are obtained.

[0032] S4: Weigh the amino acid ionic liquid and place it in methanol and stir. Then add the dried ZIF-8 hollow nanotubes and continue stirring until the methanol is completely evaporated to obtain the loaded modified IL@MOF composite material.

[0033] S5: Prepare an N-methylpyrrolidone solution containing polymer particles; prepare an N-methylpyrrolidone solution of polyvinylpyrrolidone and IL@MOF composite material; mix and stir the above two solutions to obtain a casting precursor solution containing polymer particles / polyvinylpyrrolidone / hollow IL@MOF nanotubes; degas the casting precursor solution and then coat it on a flatbed coating machine;

[0034] S6: After mixing and stirring boric acid aqueous solution and ammonium fluorotitanate hexahydrate, a suspension of nano-TiO2 is obtained; after drying the membrane solution after coating in step S5 and evaporating the solvent, a mixed matrix membrane with gas transmission channels is obtained. The mixed matrix membrane is loaded into a membrane contactor and the suspension of nano-TiO2 is introduced. After drying the matrix membrane, a mixed matrix membrane for CO2 separation is obtained.

[0035] Preferably, in step S1, the concentration of polyacrylonitrile in the N-methylpyrrolidone solution of polyacrylonitrile is 12%-15%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 10-12% and 3%, respectively, and the mass ratio of the two solutions is 1:2.

[0036] Preferably, in step S2, the drying conditions are: drying in an oven at 60°C for 12 hours; the high-temperature calcination conditions are: heating to 650°C at a heating rate of 50°C / hour and holding at that temperature for 2 hours.

[0037] Preferably, in step S3, the mass ratio of the ZnO nanotubes to the N,N-dimethylformamide solution is 0.5:99.5, the stirring and dispersion temperature is 100°C, the mass ratio of the organic ligand to the ZnO nanotubes is 2:1, and the hydrothermal reaction time is 4 hours.

[0038] Preferably, in step S4, the drying process is carried out overnight at a temperature of 150°C.

[0039] Preferably, in step S4, the ionic liquid includes one of 1-ethyl-3-methylimidazolium glycine [Emim][Gly], 1-butyl-3-methylimidazolium glutamate [Bmim][Glu], 1-hydroxyethyl-3-butylimidazolium alanine [HEBim][Ala], and 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4].

[0040] Preferably, the polymer particles are one of polyethersulfone, polyimide, polyethylene glycol, polyacrylonitrile, and polyvinylidene fluoride; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 12%-15% and 2%-5%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 12%-15%; and the mass of the IL@MOF composite material is 2%-8% of the casting precursor solution.

[0041] Preferably, in step S5, the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 6% of the casting precursor solution.

[0042] Preferably, in step S5, the degassing treatment conditions are as follows: the casting precursor solution is first ultrasonically degassed for 30 minutes, and then allowed to stand at room temperature for 24 hours for further degassing; the thickness of the coating film is 200 μm.

[0043] Preferably, in step S6, the conditions for drying and evaporating the solvent are: drying in an oven at 60°C for 12 hours; the method of introducing the nano-TiO2 suspension is: introducing the nano-TiO2 suspension through a peristaltic pump; after introducing the nano-TiO2 suspension, the substrate membrane is further washed with water to remove unloaded TiO2 nanoparticles from the surface.

[0044] The present invention also provides a mixed matrix membrane for separating CO2, wherein the mixed matrix membrane is prepared by the above preparation method.

[0045] The following provides a detailed description of the above-mentioned technical solution of the present invention, incorporating specific embodiments and data:

[0046] Example 1:

[0047] This embodiment provides a method for preparing a mixed matrix membrane for separating CO2, including the following steps:

[0048] S1: Prepare N-methylpyrrolidone solution of polyacrylonitrile and N-methylpyrrolidone solution of polyvinylpyrrolidone and zinc acetate dihydrate. Mix the two solutions and stir to obtain PAN / PVP+Zn(Ac)2 emulsion as electrospinning precursor solution.

[0049] The concentration of polyacrylonitrile in the N-methylpyrrolidone solution is 13.5%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 11% and 3%, respectively, and the mass ratio of the two solutions is 1:2.

[0050] S2: The precursor solution prepared in step S1 is electrospun to obtain core-shell structured PAN / PVP+Zn(Ac)2 composite nanofibers. The composite nanofibers are dried and then calcined at high temperature to remove the polymer. The drying conditions are: drying in an oven at 60°C for 12 hours; the high-temperature calcination conditions are: heating to 650°C at a heating rate of 50°C / hour and holding at that temperature for 2 hours to obtain ZnO nanotubes with a hollow structure.

[0051] S3: Dissolve the ZnO nanotubes prepared in step S2 in an N,N-dimethylformamide solution, wherein the mass ratio of the ZnO nanotubes to the N,N-dimethylformamide solution is 0.5:99.5. Disperse the solution by stirring at 100°C, and add the organic ligand 2-methylimidazole during stirring, wherein the mass ratio of the organic ligand to the ZnO nanotubes is 2:1. After a hydrothermal reaction for 4 hours, ZIF-8 hollow nanotubes are obtained.

[0052] S4: Weigh the amino acid ionic liquid and place it in methanol and stir. Then add the dried ZIF-8 hollow nanotubes. The drying conditions are to dry overnight at 150°C. Continue stirring until the methanol is completely evaporated to obtain the loaded modified IL@MOF composite material.

[0053] In step S4, the ionic liquid is 1-ethyl-3-methylimidazolium glycinate [Emim][Gly].

[0054] S5: Prepare an N-methylpyrrolidone solution containing polymer particles; prepare an N-methylpyrrolidone solution of polyvinylpyrrolidone and IL@MOF composite material; mix and stir the above two solutions to obtain a casting precursor solution containing polymer particles / polyvinylpyrrolidone / hollow IL@MOF nanotubes; ultrasonically degas the casting precursor solution for 30 min, and then continue to stand at room temperature for 24 h to degas; then coat the film on a flatbed coating machine to a thickness of 200 μm;

[0055] The polymer particles are polyethersulfone; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 13.5% and 3.5%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 13.5%; and the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 5% of the casting precursor solution.

[0056] S6: A suspension of nano-TiO2 is obtained by mixing and stirring boric acid aqueous solution and ammonium fluorotitanate hexahydrate; the membrane solution after coating in step S5 is dried in an oven at 60°C for 12 hours to obtain a mixed matrix membrane with gas transmission channels; the mixed matrix membrane is loaded into a membrane contactor, and the nano-TiO2 suspension is introduced through a peristaltic pump; the matrix membrane is washed with water to remove unloaded TiO2 nanoparticles on the surface; the matrix membrane is dried to obtain a mixed matrix membrane for CO2 separation.

[0057] The present invention also provides a mixed matrix membrane for separating CO2, wherein the mixed matrix membrane is prepared by the above preparation method.

[0058] Example 2:

[0059] Example 2 is similar to Example 1, except that:

[0060] In step S1, the concentration of polyacrylonitrile in the N-methylpyrrolidone solution of polyacrylonitrile is 12%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 10% and 3%, respectively, and the mass ratio of the two solutions is 1:2.

[0061] In step S4, the ionic liquid is 1-butyl-3-methylimidazolium glutamate [Bmim][Glu].

[0062] In step S5, the polymer particles are polyimide; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 12% and 2%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 12%; and the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 2% of the casting precursor solution.

[0063] Example 3:

[0064] Example 3 is similar to Example 1, except that:

[0065] In step S1, the concentration of polyacrylonitrile in the N-methylpyrrolidone solution is 12%-15%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 10-12% and 3%, respectively, and the mass ratio of the two solutions is 1:2.

[0066] In step S4, the ionic liquid is 1-hydroxyethyl-3-butylimidazolium alanine salt [HEBim][Ala].

[0067] In step S5, the polymer particles are polyethylene glycol; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 15% and 5%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 15%; and the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 8% of the casting precursor solution.

[0068] The following provides a detailed description of the above-mentioned technical solution of the present invention, incorporating specific embodiments and data:

[0069] Example 4:

[0070] This embodiment provides a mixed matrix membrane for efficient CO2 separation and its preparation method:

[0071] Includes the following steps:

[0072] S1: Prepare a 13.5% N-methylpyrrolidone (NMP) solution of polyacrylonitrile (PAN) and an 11% N-methylpyrrolidone (PVP) and 3% zinc acetate dihydrate Zn(Ac)2·2(H2O) N-methylpyrrolidone (NMP) solution; mix the two solutions at a mass ratio of 1:2 and stir to obtain a PAN / PVP+Zn(Ac)2 emulsion as a precursor solution for electrospinning.

[0073] The specific procedure is as follows: Dissolve 1.5g of PAN in 10mL of NMP solution. In another beaker, add 2.8g of PVP and 0.96g of Zn(Ac)₂·2(H₂O) dissolved in 20mL of NMP solution. Then, stir each solution separately for 15 hours to ensure complete dissolution, resulting in clear and transparent solutions. Next, mix the two completely dissolved solutions in a sealed beaker and stir at medium speed (300 rpm) for 5 hours to obtain a PAN / PVP+Zn(Ac)₂ emulsion as a precursor solution for electrospinning. The emulsion is primarily composed of PVP+Zn(Ac)₂, with the PAN solution existing in the form of droplet spheres.

[0074] S2: The aforementioned precursor solution was slowly drawn into a 20ml syringe while expelling air bubbles, and the electrospinning needle was connected to the syringe. Then, the positive terminal of the variable high-voltage power supply of the electrospinning apparatus was connected to the needle tip of the syringe, and the negative terminal of the other end was connected to the aluminum foil receiving roller. The voltages applied to the positive and negative electrodes were set to +13kV and -1kV respectively, the distance between the positive electrode needle tip and the front end of the negative electrode roller was 21 cm, the air humidity was controlled at 40%, and the injection speed was finely adjusted to approximately 1mL / hour according to actual conditions to ensure no droplet spray at the needle tip. Finally, core-shell structured PAN / PVP+Zn(Ac)2 composite nanofibers were obtained on the negative electrode aluminum foil collecting paper and dried in a 60℃ oven for 12 hours. Afterward, the PAN / PVP+Zn(Ac)2 composite nanofibers were cut into small square pieces and placed in a crucible to ensure uniform heating. Subsequently, they were placed in a muffle furnace and calcined at high temperature in an air atmosphere to remove the polymer. The heating rate was set at 50℃ / hour, and the temperature was raised to 650℃ and held for 2 hours to ensure complete removal of the polymer. Finally, ZnO nanotubes with a hollow structure were obtained.

[0075] S3: Dissolve ZnO hollow nanotubes in N,N-dimethylformamide solution, controlling the mass fraction of ZnO hollow nanotubes to be about 0.5%; then slowly stir and disperse at 100℃, adding the organic ligand 2-methylimidazole corresponding to MOFs during the process, controlling the mass ratio of organic ligand to metal oxide hollow nanotubes to be 2:1; hydrothermal reaction for 4 h to obtain ZIF-8 hollow nanotubes;

[0076] S4: Hollow MOF nanotubes modified with ionic liquid (IL) were synthesized using a wet impregnation method, hereinafter referred to as hollow IL@MOF composite nanotubes. Before composite preparation, the ZIF-8 hollow nanotubes prepared in the above steps were dried overnight in an oven at 150℃ to ensure they were free of moisture or any other impurities. After the solid ZIF-8 was ready, the specific operation method was as follows: a certain mass of amino acid ionic liquid was weighed and placed in a round-bottom flask containing 15g of methanol. The ionic liquid was 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4]. The mixture was stirred for 30 minutes to fully dissolve the ionic liquid in the methanol. Then, the prepared ZIF-8 hollow nanotubes were added to the above mixed solution and stirred thoroughly at room temperature until the methanol was completely evaporated. The resulting powdered solid was the modified IL@MOF composite material.

[0077] S5: Prepare a polyvinylidene fluoride (PVF) N-methylpyrrolidone (NMP) solution with a mass fraction of 12%-15%; prepare a polyvinylidene fluoride (PVP) and hollow IL@MOF nanotube N-methylpyrrolidone solution, with mass fractions of 12%-15% for PVP and 2%-5% for IL@MOF nanotubes; mix the two solutions at a mass ratio of 3:1 and stir to obtain a casting precursor solution containing PVP / PVP / hollow IL@MOF nanotubes, wherein the mass of the IL@MOF composite material is 6% of the casting precursor solution; degas the solution by ultrasonication for 30 min, then continue to degas by standing at room temperature for 24 h, and then coat the film on a flatbed coating machine, scraping the casting solution onto a glass plate to a film thickness of 200 μm;

[0078] S6: Mix 90 ml of 3.3 wt% boric acid aqueous solution and 30 ml of 10 wt% ammonium fluorotitanate hexahydrate together and stir for five hours to obtain a suspension of nano-TiO2; dry the glass plate with the membrane solution in a 60°C oven for 12 hours to completely evaporate the solvent and obtain a mixed matrix membrane with gas transmission channels. Then, load the membrane into the prepared membrane contactor and pass the TiO2 suspension through a peristaltic pump. Utilize the filtration and adsorption effects to load TiO2 onto the surface of the mixed matrix membrane. Wash thoroughly with water three times to remove unloaded TiO2 nanoparticles from the surface.

[0079] The membrane was placed in a vacuum oven to remove solvent and moisture as a pretreatment before the gas permeation test. The gas permeation and separation performance were then tested, and the results are as follows: Figure 1 As shown, Figure 1The CO2 / N2 pure gas permeation / selectivity performance diagrams of the mixed matrix membranes of IL@MOF composite materials with different filler contents further demonstrate that the mixed matrix membrane for CO2 separation prepared by using the IL@MOF composite material added in this invention as a filler has a high CO2 transport rate and CO2 / N2 selectivity. Moreover, the overall performance of the mixed matrix membrane reaches its optimal level when the mass of the IL@MOF composite material is 6% of the casting precursor solution.

[0080] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing a mixed matrix membrane for separating CO2, characterized in that: Includes the following steps: S1: Prepare N-methylpyrrolidone solution of polyacrylonitrile and N-methylpyrrolidone solution of polyvinylpyrrolidone and zinc acetate dihydrate. Mix the two solutions and stir to obtain PAN / PVP+Zn(Ac)2 emulsion as electrospinning precursor solution. S2: The precursor solution prepared in step S1 is electrospun to obtain PAN / PVP+Zn(Ac)2 composite nanofibers with core-shell structure. The composite nanofibers are dried and then calcined at high temperature to remove the polymer, resulting in ZnO nanotubes with hollow structure. S3: Dissolve the ZnO nanotubes prepared in step S2 in N,N-dimethylformamide solution, stir and disperse, and add the organic ligand 2-methylimidazole during stirring. After hydrothermal reaction, ZIF-8 hollow nanotubes are obtained. S4: Weigh the amino acid ionic liquid and place it in methanol and stir. Then add the dried ZIF-8 hollow nanotubes and continue stirring until the methanol is completely evaporated to obtain the loaded modified IL@MOF composite material. S5: Prepare an N-methylpyrrolidone solution containing polymer particles; prepare an N-methylpyrrolidone solution of polyvinylpyrrolidone and IL@MOF composite material; mix and stir the above two solutions to obtain a casting precursor solution containing polymer particles / polyvinylpyrrolidone / hollow IL@MOF nanotubes; degas the casting precursor solution and then coat it on a flatbed coating machine; S6: After mixing and stirring boric acid aqueous solution and ammonium fluorotitanate hexahydrate, a suspension of nano-TiO2 is obtained; after drying the membrane solution after coating in step S5 and evaporating the solvent, a mixed matrix membrane with gas transmission channels is obtained. The mixed matrix membrane is loaded into a membrane contactor and the suspension of nano-TiO2 is introduced. After drying the matrix membrane, a mixed matrix membrane for CO2 separation is obtained.

2. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S1, the concentration of polyacrylonitrile in the N-methylpyrrolidone solution is 12%-15%, and the concentrations of polyvinylpyrrolidone and zinc acetate dihydrate in the N-methylpyrrolidone solution are 10-12% and 3%, respectively, and the mass ratio of the two solutions is 1:

2.

3. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S2, the drying conditions are: drying in an oven at 60°C for 12 hours; the high-temperature calcination conditions are: heating to 650°C at a heating rate of 50°C / hour and holding at that temperature for 2 hours.

4. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S3, the mass ratio of the ZnO nanotubes to the N,N-dimethylformamide solution is 0.5:99.5, the stirring and dispersion temperature is 100℃, the mass ratio of the organic ligands to the ZnO nanotubes is 2:1, and the hydrothermal reaction time is 4h.

5. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S4, the drying process is performed overnight at 150°C; the ionic liquid includes one of 1-ethyl-3-methylimidazolium glycinate, 1-butyl-3-methylimidazolium glutamate, 1-hydroxyethyl-3-butylimidazolium alanine, or 1-butyl-3-methylimidazolium tetrafluoroborate.

6. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S5, the polymer particles are one of polyethersulfone, polyimide, polyethylene glycol, polyacrylonitrile, and polyvinylidene fluoride; in the N-methylpyrrolidone solution of the polyvinylpyrrolidone and IL@MOF composite material, the concentrations of the polyvinylpyrrolidone and IL@MOF composite material are 12%-15% and 2%-5%, respectively; in the N-methylpyrrolidone solution containing polymer particles, the concentration of the polymer particles is 12%-15%; and the mass of the IL@MOF composite material is 2%-8% of the casting precursor solution.

7. The method for preparing a mixed matrix membrane for CO2 separation according to claim 6, characterized in that: In step S5, the mass ratio of the two solutions is 3:1, and the mass of the IL@MOF composite material is 6% of the casting precursor solution.

8. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S5, the degassing treatment conditions are as follows: the casting precursor solution is first ultrasonically degassed for 30 minutes, and then allowed to stand at room temperature for 24 hours for further degassing; the thickness of the coating film is 200 μm.

9. The method for preparing a mixed matrix membrane for CO2 separation according to claim 1, characterized in that: In step S6, the conditions for drying and evaporating the solvent are: drying in an oven at 60°C for 12 hours; the method of introducing the nano-TiO2 suspension is: introducing the nano-TiO2 suspension through a peristaltic pump; after introducing the nano-TiO2 suspension and before drying, the substrate membrane is washed with water to remove unloaded TiO2 nanoparticles from the surface.

10. A mixed matrix membrane for separating CO2, characterized in that, The hybrid matrix membrane is prepared by any one of the preparation methods of claims 1-9.

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