A method for improving the CO2 separation performance of mixed matrix membranes by using γ-cyclodextrin

Abstract

The present invention discloses a method for improving the CO2 separation performance of mixed matrix membranes by using γ-cyclodextrin (γ-CD). In the present invention, pebax-1657 is used as the matrix material of the mixed matrix membrane, and ZIF-8 synthesized by coordination with cyclodextrin is used as the filler material. A high-performance mixed matrix membrane is prepared by blending. ZIF-8 has an appropriate pore cage size in the CO2 / N2 separation system, thereby creating a large number of directional transport channels for CO2 permeation in the membrane. To further improve the selectivity of this material for CO2, γ-cyclodextrin is combined with ZIF-8. Utilizing its self-mesoporous structure, the original pore cage size of ZIF-8 is increased, and the permeation is increased. At the same time, the presence of hydroxyl groups increases the adsorption of CO2, thereby achieving the purpose of improving the CO2 separation performance of the mixed matrix membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation materials, and in particular to a method for improving the CO2 separation performance of mixed matrix membranes by using γ-cyclodextrin. Background Art

[0002] CO2 is a major contributor to global climate change, and the current global CO2 emissions have reached 33 billion tons. CO2 is mainly produced by the combustion of fossil fuels and is also a component of natural gas, biogas, and landfill gas. At the same time, as an important feed gas for chemical production, CO2 has a wide range of applications in industries such as chemicals and food. Therefore, in order to achieve the goals of "carbon neutrality" and "carbon peak", it is imperative to research and develop efficient gas separation technologies.

[0003] Compared with traditional gas separation technologies, membrane separation technology has the advantages of convenient operation, low energy consumption, and no pollution. It is considered the most promising third-generation separation technology and has received extensive attention from all sectors of society. Among many membrane materials, polymer materials have been widely studied due to their advantages such as low cost, easy availability, and the ability to form large-area membranes. However, it is difficult for these materials to overcome the mutual restriction between permeability and selectivity (trade-off effect), and the performance of the membrane is usually limited below the Robeson upper bound. Inorganic membranes have excellent separation performance, thermal stability, and chemical stability, and have always been a research hotspot in membrane technology. However, high cost and difficulty in large-scale preparation have hindered the further development of inorganic membranes. To solve these problems, researchers have tried to combine the advantages of low-cost and easy film-forming of polymer membranes with the advantages of high-performance of inorganic membranes to prepare mixed matrix membranes with more excellent performance.

[0004] Polyether block amide (Pebax) is copolymerized from a rigid polyamide (PA) segment that provides mechanical strength and a flexible polyether (PE) segment that provides free volume. The flexible PE segment has extremely excellent preferential adsorption properties for the polar gas CO2. Therefore, Pebax has extremely excellent performance in separating polar and non-polar mixed gases. In this patent, Pebax-1657 is selected as the membrane matrix. Pebax-1657 is copolymerized from 40 wt% PA and 60 wt% PE. This model is selected because the membrane needs to have a certain mechanical strength and good CO2 adsorption performance. Compared with other models, the mechanical strength and adsorption performance are relatively balanced. If a model with a higher PE content is selected, agglomeration is very likely to occur on the membrane surface. If a model with a higher PA content is selected, the CO2 adsorption performance of the membrane will be weak. At the same time, if some metal-organic frameworks with special carbon dioxide adsorption functions are introduced into the polyether block amide to prepare mixed matrix membranes, the separation performance of the membrane material can be further improved, thus solving the problem of low permeability of organic polymer gas separation membranes. Summary of the Invention

[0005] [Object of the Invention]

[0006] The object of the present invention is to introduce metal-organic frameworks with CO2 adsorption performance by blending to solve the problem of low CO2 / N2 permeability and selectivity of membrane materials, and to provide a method for improving the CO2 separation performance of mixed matrix membranes using γ-cyclodextrin.

[0007] [Technical Solution]

[0008] To solve the above technical problems, the present invention provides a method for improving the CO2 separation performance of mixed matrix membranes using γ-cyclodextrin, and the method is as follows:

[0009] An ethanol solution containing ZIF-8 nanoparticles synthesized by coordinating with γ-cyclodextrin is mixed with a Pebax-1657 solution to prepare a casting solution required for casting membranes, and finally a mixed matrix membrane is prepared by the solvent evaporation method.

[0010] Based on the above technical solution, the specific steps are as follows:

[0011] Step 1: Mix absolute ethanol and deionized water, heat it to 80 - 85 °C under stirring conditions in an oil bath, then add Pebax-1657 and keep stirring at 80 - 85 °C for 4 - 5 hours to completely dissolve it, obtaining a Pebax-1657 solution;

[0012] Step 2: Add ZIF-8 nanoparticles coordinated with γ-cyclodextrin to 15 - 20 parts of the Pebax1657 solution prepared in Step 1, and ultrasonically stir and mix to obtain a casting solution containing fillers;

[0013] Step 3: Ultrasonically degas the casting solution obtained in Step 2 for 10 - 30 min, and let it stand for 4 - 10 min. Then pour it onto a clean polytetrafluoroethylene plate, place it in a constant temperature oven at 60 - 80 °C and dry for 18 - 24 h, and then place it in a vacuum oven to evacuate and continue to remove the solvent for 18 - 24 h to obtain a ZIF-8@CD modified mixed matrix membrane.

[0014] Based on the above technical solution, modified γ-cyclodextrin can also be used for coordination, and the specific steps are as follows:

[0015] Step 1: Mix absolute ethanol and deionized water, heat it to 80 - 85 °C under stirring conditions in an oil bath, then add Pebax-1657 and keep stirring at 80 - 85 °C for 4 - 5 hours to completely dissolve it, obtaining a Pebax-1657 solution;

[0016] Step 2: Add the ZIF-8 nanoparticles coordinated with modified γ-cyclodextrin into 15 - 20 parts of the Pebax-1657 solution prepared in Step 1, and ultrasonically stir and mix to obtain a casting solution containing fillers.

[0017] Step 3: Ultrasonically degas the casting solution obtained in Step 2 for 10 - 30 min, and let it stand for 4 - 10 min. Then pour it onto a clean polytetrafluoroethylene plate, place it in a constant temperature oven at 60 - 80 °C and dry for 18 - 24 h. Subsequently, place it in a vacuum oven to evacuate and continue to remove the solvent for 18 - 24 h to obtain the ZIF-8@CD modified mixed matrix membrane.

[0018] Based on the above technical solution, the method for modifying γ-cyclodextrin also includes:

[0019] By weight, add 20 - 30 parts of γ-cyclodextrin and 200 - 300 parts of DMF, stir until completely dissolved, place the system in an ice bath with a constant temperature of 0 - 5 °C, weigh 0.5 - 3.4 parts of 4-vinylbenzene-1-sulfonyl chloride, add it, keep stirring, react at room temperature for 2 - 5 h, then add 0.2 - 2.2 parts of vinylguanamine, 0.1 - 0.4 parts of benzoyl peroxide, stir and react at 40 - 50 °C for 30 - 100 minutes, remove DMF by reduced pressure distillation, wash with acetone, and dry to obtain modified γ-cyclodextrin.

[0020] Based on the above technical solution, the preparation method of the filler pure ZIF-8 also includes:

[0021] By mass, weigh 0.5 - 2 parts of Zn(NO3)2·6H2O and 10 - 25 parts of 2-methylimidazole and dissolve them in 10 - 15 parts and 90 - 95 parts of solvent respectively. Under stirring, mix the Zn(NO3)2 solution and the 2-methylimidazole solution. After stirring at room temperature for 1 - 1.5 hours, the product is collected by centrifugation and washed three times by "methanol washing - centrifugal recovery". Then dry it in the air until there is no obvious liquid, and activate it at 130 - 180 °C in a vacuum drying oven for 12 - 24 h to obtain the dried nano ZIF-8 filler.

[0022] Based on the above technical solution, the preparation method of the filler ZIF-8 coordinated with γ-cyclodextrin also includes:

[0023] Weigh 0.5 - 5 parts by weight of Zn(NO3)2·6H2O and 0.09 - 0.5 parts of γ-CD, add them to 10 - 15 parts of a solvent, and stir well for 1.5 - 2.5 hours. The purpose is to chelate cyclodextrin with metal ions. Subsequently, dissolve 10 - 40 parts of 2-methylimidazole in 90 - 95 parts of the solvent, and then mix the two and stir for 1 - 1.5 h. The product is collected by centrifugation and washed three times by "methanol washing - centrifugal recovery", and activated at 130 - 180 °C for 12 - 24 h in a vacuum drying oven to obtain dry nano-ZIF-8@CD filler.

[0024] Based on the above technical solution, preferably, the solvent is one of methanol, deionized water, ethanol, chloroform, N,N-dimethylformamide, and N,N-diethylformamide.

[0025] Based on the above technical solution, preferably, the mass fraction of Zn(NO3)2·6H2O is 1 - 7 parts.

[0026] Based on the above technical solution, preferably, the mass fraction of 2-methylimidazole is 20 - 65 parts.

[0027] Based on the above technical solution, preferably, the molar ratio of Zn 2+ :γ-CD is 20 - 36:1 - 3.

[0028] Based on the above technical solution, preferably, the rotation speed of the centrifuge is 7000 - 10000, and the centrifugation time is 5 - 10 min.

[0029] Based on the above technical solution, preferably, the mass ratio of ethanol to water is 6 - 9:1 - 4.

[0030] Based on the above technical solution, preferably, the solid content of the Pebax-1657 solution is 1 - 5%.

[0031] Based on the above technical solution, preferably, the mass fraction of pure ZIF-8 nanoparticles in the casting solution is 1 - 20 wt%.

[0032] Based on the above technical solution, preferably, the mass fraction of ZIF-8@CD nanoparticles in the casting solution is 1 - 20 wt%.

[0033] Based on the above technical solution, preferably, the ultrasonic stirring and mixing method: ultrasonic dispersion for 15 - 45 min, and then stirring at a rotation speed of 500 - 1000 rpm for 30 - 60 min at room temperature.

[0034] Based on the above technical solution, preferably, the drying time in the oven and the vacuum drying time are both 18 - 24 h.

[0035] Based on the above technical solution, the mixed matrix membrane prepared by the present invention is used for CO2 / N2 gas separation.

[0036] Based on the above technical solution, the structural formulas of the various substances mentioned above are as follows:

[0037] The structural formula of ZIF-8 is:

[0038] The structural formula of γ-cyclodextrin (γ-CD) is:

[0039] The structural formula of pebax-1657 is:

[0040] [Beneficial Effects]

[0041] In the present invention, pebax-1657 is used as the polymer matrix material of the mixed matrix membrane. This polymer is composed of polyamide (PA) and polyether (PE). The hardness and crystal structure of PA can provide good mechanical properties, and there is a strong adsorption effect between the ether oxygen groups in PE and polar molecules. The porous ZIF-8 metal-organic framework filler prepared by blending and participating in coordination with γ-cyclodextrin has a suitable pore size structure, so that a large number of directional transport channels for CO2 permeation can be created in the membrane. In addition, the presence of hydroxyl groups in the synthesized filler further improves the sieving and adsorption properties of the membrane material for carbon dioxide. Using deionized water as a solvent in the method for preparing the filler conforms to the current concept of environmental protection development. The whole preparation process is mild and simple, and the cost is relatively low, providing method support for the large-scale separation of CO2 by mixed matrix membranes in future green development. The CO2 permeation performance PCO2 of the mixed matrix membrane can reach 109.02 - 173.41 Barrer, and the selectivity of CO2 / N2 is 58.37 - 82.08. Description of the Drawings

[0042] Figure 1 Scanning electron micrographs of the mixed matrix membranes obtained in Examples 1 - 4.

[0043] Figure 2 Fourier transform infrared test spectra of the mixed matrix membranes obtained in Examples 1 - 4.

[0044] Figure 3 X-ray diffraction patterns of the mixed matrix membranes obtained in Examples 1 - 4. Among them, corresponding to the mixed matrix membranes of Example 1, Example 2, Example 3, and Example 4 respectively from low to high peak height. Detailed Embodiments

[0045] The following illustrates the technical solutions in the present invention by listing some specific embodiments, but the protection scope of the present invention is not limited to the listed embodiments:

[0046] The materials used in the following embodiments were all purchased from the market. Among them, Pebaxs-1657 was purchased from Arkema France; 2-methylimidazole was purchased from Shanghai Macklin Biochemical Co., Ltd.; γ-cyclodextrin (γ-CD) was purchased from Shanghai Macklin Biochemical Co., Ltd.; Zn(NO3)2·6H2O was purchased from Aladdin US Co., Ltd.

[0047] Comparative example:

[0048] 1) Preparation of casting solution: Weigh 64.55 g of ethanol and 25.55 g of distilled water and mix them. Heat the mixture to 80 °C under stirring, and then add 1.21 g of Pebax-1657 thereto and keep stirring at 80 °C for 5 hours to completely dissolve it to obtain a Pebax-1657 casting solution.

[0049] 2) After ultrasonic degassing the above casting solution for 15 min, let it stand for 5 minutes, pour it into a clean polytetrafluoroethylene mold, and then put the film into a constant temperature oven and dry it at 60 °C for 24 hours, and then continue to dry it in a vacuum oven under vacuum for 24 hours to obtain a Pebax-1657 organic polymer film. The thickness of the prepared organic polymer film is 51.12 μm. After testing, the separation performance of the above mixed matrix membrane is PCO2 = 55.98 Barrer, and the CO2 / N2 selectivity is 39.73.

[0050] Example 1

[0051] 1) Preparation of pure ZIF-8: Weigh 1.488 g of Zn(NO3)2.6H2O and 12.3 g of 2-methylimidazole and dissolve them in 10 ml and 90 ml of deionized water respectively. Mix the Zn(NO3)2 solution and the 2-methylimidazole solution under stirring. After stirring at room temperature for 1 hour, the product was collected by centrifugation and washed three times by "methanol washing - centrifugal recovery". Then, after drying in air until there is no obvious liquid, it was activated at 150 °C in a vacuum drying oven for 12 h to obtain dry nano-ZIF-8 filler.

[0052] 2) Preparation of casting solution: Weigh 18.0395 g of ethanol and 9.7932 g of distilled water and mix them. Heat the mixture to 80 °C under stirring, and then add 1.0096 g of Pebax-1657 thereto and keep stirring at 80 °C for 5 hours to completely dissolve it. Then, after removing impurities by centrifugation, take 6.67 g of the Pebax-1657 solution and add 0.035 g of ZIF-8 nanoparticles thereto, ultrasonically treat it for 10 min and vigorously stir it for 30 min to make it evenly dispersed to obtain a casting solution.

[0053] 3) After ultrasonic degassing the above casting solution for 15 min, let it stand for another 5 minutes, then pour it into a clean polytetrafluoroethylene mold. After that, place the membrane in a constant-temperature oven and dry it at 60 °C for 24 h. Finally, continue to dry it under vacuum in a vacuum oven for 24 h to obtain a mixed matrix membrane modified by pure ZIF-8. The thickness of the prepared mixed matrix membrane is 61.85 μm.

[0054] The separation performance of the above mixed matrix membrane was tested and found to be PCO2 = 109.02 Barrer and CO2 / N2 selectivity of 58.37. It can be clearly seen that by introducing pure ZIF-8, both the gas permeability and gas selectivity of the mixed matrix membrane have been improved.

[0055] Example 2

[0056] 1) Prepare ZIF-8@CD (Zn 2+ : The molar ratio of CD is: 24:1): 0.744 g of Zn(NO3)2·6H2O and 0.1351 g of γ-CD were added to 10 ml of deionized water and stirred well for 2 hours to chelate cyclodextrin with metal Zn ions. Subsequently, 12.3 g of 2-methylimidazole was dissolved in 90 ml of deionized water, and then the two were mixed and stirred for 1 hour. The product was collected by centrifugation and washed three times by "methanol washing - centrifugal recovery". Then, after drying in air until there was no obvious liquid, it was activated at 150 °C in a vacuum drying oven for 12 hours to obtain dry nano-ZIF-8@CD filler.

[0057] 2) Prepare the casting solution: Weigh 18.0395 g of ethanol and 9.7932 g of distilled water and mix them. Heat the mixture to 80 °C under stirring, then add 1.0096 g of Pebax-1657 and keep stirring at 80 °C for 5 hours until it is completely dissolved. After removing impurities by centrifugation, take 6.67 g of the Pebax-1657 solution and add 0.035 g of ZIF-8@CD nanoparticles, then perform ultrasonic treatment for 10 min and stir vigorously for 30 min to make it disperse evenly to obtain the casting solution.

[0058] 3) After ultrasonic degassing the above casting solution for 15 min, let it stand for another 5 minutes, then pour it into a clean polytetrafluoroethylene mold. After that, place the membrane in a constant-temperature oven and dry it at 60 °C for 24 h. Finally, continue to dry it under vacuum in a vacuum oven for 24 h to obtain a ZIF-8@CD composite modified mixed matrix membrane. The thickness of the prepared mixed matrix membrane is 65.43 μm.

[0059] The separation performance of the above mixed matrix membrane was tested and found to be PCO2 = 110.58 Barrer and CO2 / N2 selectivity of 82.08.

[0060] Example 3

[0061] 1) Preparation of ZIF-8@CD(Zn 2+ : The molar ratio of CD is: 30:1): 0.744 g of Zn(NO3)2·6H2O and 0.1081 g of modified γ-cyclodextrin are added to 10 ml of deionized water and stirred well for 2 hours. The purpose is to chelate cyclodextrin with metal Zn ions. Subsequently, 12.3 g of 2-methylimidazole is dissolved in 90 ml of deionized water, and then the two are mixed and stirred for 1 hour. The product is collected by centrifugation and washed three times by "methanol washing - centrifugal recovery". Then it is dried in air until there is no obvious liquid, and then activated at 150 °C in a vacuum drying oven for 12 hours to obtain the dried nano ZIF-8@CD filler.

[0062] The method for the modified γ-cyclodextrin is as follows:

[0063] 2 g of γ-cyclodextrin and 20 g of DMF are stirred until completely dissolved. The system is placed in an ice bath with a constant temperature of 0 °C. 0.15 g of 4-vinylbenzene-1-sulfonyl chloride is weighed and added. After addition, stirring is maintained, and the reaction is carried out at room temperature for 2 h. Then 0.02 g of vinylguanamine and 0.01 g of benzoyl peroxide are added, and the reaction is stirred at 40 °C for 100 minutes. DMF is removed by reduced pressure distillation, washed with acetone, and dried to obtain the modified γ-cyclodextrin.

[0064] 2) Preparation of the casting solution: Weigh 36.3542 g of ethanol and 19.7357 g of distilled water and mix them. Under stirring conditions, it is heated to 80 °C, and then 2.0346 g of Pebax-1657 is added thereto and stirred at 80 °C for 5 hours to completely dissolve it. After removing impurities by centrifugation, 6.67 g of the Pebax-1657 solution is taken, and 0.035 g of ZIF-8 nanoparticles are added thereto. It is ultrasonicated for 10 min and vigorously stirred for 30 min to make it uniformly dispersed, obtaining the casting solution.

[0065] 3) After ultrasonic degassing the above casting solution for 15 min, it is then allowed to stand for 5 minutes, and then poured into a clean polytetrafluoroethylene mold. Then the membrane is placed in a constant temperature oven and dried at 60 °C for 24 h, and finally dried in a vacuum oven under vacuum for another 24 h to obtain the ZIF-8@CD composite modified mixed matrix membrane. The thickness of the prepared mixed matrix membrane is 76.5 μm.

[0066] After testing, the separation performance of the above mixed matrix membrane is PCO2 = 160.48 Barrer, and the CO2 / N2 selectivity is 77.69.

[0067] Example 4

[0068] 1) Preparation of ZIF-8@CD(Zn 2+: The CD molar ratio is: 36:1): 0.744 g of Zn(NO3)2·6H2O and 0.0901 g of modified γ-cyclodextrin were added to 10 ml of deionized water and stirred well for 2 hours. The purpose was to chelate cyclodextrin with metal Zn ions. Subsequently, 12.3 g of 2-methylimidazole was dissolved in 90 ml of deionized water, and then the two were mixed and stirred for 1 hour. The product was collected by centrifugation and washed three times by "methanol washing - centrifugal recovery". Then, after drying in air until there was no obvious liquid, it was activated at 150 °C in a vacuum drying oven for 12 hours to obtain the dried nano-ZIF-8@CD filler.

[0069] The method for the modified γ-cyclodextrin is as follows:

[0070] 3 g of γ-cyclodextrin and 30 g of DMF were stirred until completely dissolved. The system was placed in an ice bath with a constant temperature of 5 °C. 0.34 g of 4-vinylbenzene-1-sulfonyl chloride was weighed and added. After the addition, stirring was maintained, and the reaction was carried out at room temperature for 5 h. Then, 0.22 g of vinylguanamine and 0.04 g of benzoyl peroxide were added, and the reaction was stirred at 50 °C for 30 minutes. DMF was removed by vacuum distillation, washed with acetone, and dried to obtain the modified γ-cyclodextrin.

[0071] 2) Preparation of the casting solution: 36.3542 g of ethanol and 19.7357 g of distilled water were weighed and mixed. Under stirring conditions, it was heated to 80 °C, and then 2.0346 g of Pebax-1657 was added thereto. Stirring was maintained at 80 °C for 5 hours to completely dissolve it. After removing impurities by centrifugation, 6.67 g of the Pebax-1657 solution was taken, and 0.035 g of ZIF-8 nanoparticles was added thereto. It was ultrasonically treated for 10 min and vigorously stirred for 30 min to make it disperse evenly to obtain the casting solution.

[0072] 3) After the above casting solution was ultrasonically degassed for 15 min, it was then left standing for 5 minutes, and then poured into a clean polytetrafluoroethylene mold. Then, the membrane was placed in a constant-temperature oven and dried at 60 °C for 24 h. Finally, it was further dried in a vacuum oven under vacuum for 24 h to obtain the ZIF-8@CD composite modified mixed matrix membrane. The thickness of the prepared mixed matrix membrane is 83 μm.

[0073] After testing, the separation performance of the above mixed matrix membrane is PCO2 = 173.41 Barrer, and the CO2 / N2 selectivity is 77.01.

[0074] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments described herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the CO2 separation performance of mixed matrix membranes using γ-cyclodextrin, comprising the following steps: Step 1: Mix absolute ethanol and deionized water, heat the mixture to 80-85 °C under stirring in an oil bath, then add Pebax-1657 and keep stirring at 80-85 °C for 4-5 hours until it is completely dissolved to obtain a Pebax-1657 solution; Step 2: Add ZIF-8 nanoparticles coordinated with modified γ-cyclodextrin to 15-20 parts of the Pebax-1657 solution prepared in Step 1, and ultrasonically stir and mix to obtain a casting solution containing fillers; Step 3: Subject the casting solution obtained in Step 2 to ultrasonic degassing treatment for 10-30 min, and let it stand for 4-10 min. Then pour it onto a clean polytetrafluoroethylene plate, place it in a constant temperature oven at 60-80 °C and dry it for 18-24 h. Subsequently, place it in a vacuum oven to evacuate and continue to remove the solvent for 18-24 h to obtain a ZIF-8@CD modified mixed matrix membrane; The method for the modified γ-cyclodextrin is as follows: By weight, mix 20-30 parts of γ-cyclodextrin and 200-300 parts of DMF, stir until completely dissolved, place the system in an ice bath with a constant temperature of 0-5 °C, weigh 0.5-3.4 parts of 4-vinylbenzenesulfonyl chloride, add it, keep stirring, react at room temperature for 2-5 h, then add 0.2-2.2 parts of vinylguanamine and 0.1-0.4 parts of benzoyl peroxide, stir and react at 40-50 °C for 30-100 minutes, distill off DMF under reduced pressure, wash with acetone, and dry to obtain modified γ-cyclodextrin.

2. The method for improving the CO2 separation performance of a mixed matrix membrane by using γ-cyclodextrin as claimed in claim 1, wherein: The preparation method of ZIF-8 nanoparticles coordinated with the modified γ-cyclodextrin: Weigh 0.5 to 5 parts of Zn(NO3)2·6H2O and 0.09 to 0.5 parts of modified γ-cyclodextrin by weight and add them to 10 to 15 parts of a solvent. Zn 2+ : The molar ratio of modified γ-cyclodextrin is 20 to 36:1 to 3. Stir well for 1.5 to 2.5 hours to chelate cyclodextrin with metal ions. Subsequently, dissolve 10 to 40 parts of 2-methylimidazole in 90 to 95 parts of the solvent, and then mix the two and stir for 1 to 1.5 h. The product is collected by centrifugation and washed three times with "methanol wash - centrifugal recovery". The rotational speed of the centrifuge is 7000 to 10000, and the centrifugation time is 5 to 10 min. Activate at 130 to 180 °C in a vacuum drying oven for 12 to 24 h to obtain ZIF-8 nanoparticles coordinated with dried modified γ-cyclodextrin.

3. The method for improving the CO2 separation performance of a mixed matrix membrane by using γ-cyclodextrin according to claim 2, characterized in that: The solvent is one of methanol, deionized water, ethanol, chloroform, N,N-dimethylformamide, and N,N-diethylformamide.

4. A method for improving the performance of a mixed matrix membrane in separating CO2 by using γ-cyclodextrin as claimed in claim 1, characterized in that: The mass ratio of the ethanol to the deionized water is 6-9:1-4.

5. A method for improving the performance of a mixed matrix membrane in separating CO2 by using γ-cyclodextrin, as claimed in claim 1, wherein: The solid content of the Pebax-1657 solution is 1-5%.

6. A method for improving the CO2 separation performance of a mixed matrix membrane by using γ-cyclodextrin as claimed in claim 1, characterized in that: The ultrasonic stirring and mixing method: Ultrasonically disperse for 15-45 min, and then stir at a speed of 500-1000 rpm / min at room temperature for 30-60 min.

7. A method for improving the CO2 separation performance of a mixed matrix membrane by using γ-cyclodextrin, as described in any one of claims 1-6, characterized in that: The prepared mixed matrix membrane is used for CO2 / N2 gas separation.

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