Zinc zeolite imidazole-covalent organic framework molecular sieve membrane as well as preparation method and application thereof

Abstract

The invention provides a zinc zeolite imidazole-covalent organic framework molecular sieve membrane and a preparation method and application thereof, and the zinc zeolite imidazole-covalent organic framework molecular sieve membrane comprises a hollow membrane filled with a zinc zeolite imidazole-covalent organic framework composite molecular sieve nano layer; the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is obtained by ultrasonically dispersing a covalent organic framework and a zinc zeolite imidazole framework through ethanol; the zinc zeolite imidazole framework is synthesized by taking 2-imidazole formaldehyde as an organic ligand and zinc chloride as a metal node. A covalent organic framework and a zinc zeolite imidazole framework are subjected to ethanol ultrasonic dispersion to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nano-layer, and the pore diameter of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nano-layer is accurately regulated to be smaller than the diameter of methane molecules and larger than the diameter of carbon dioxide molecules, so that the carbon dioxide molecules can pass through while the methane molecules are intercepted; therefore, carbon dioxide removal of biogas is completed.

Description

Technical Field

[0001] The invention relates to the technical field of nano-membranes, and in particular to a zinc zeolite imidazole-covalent organic framework molecular sieve membrane and a preparation method and application thereof. Background Art

[0002] Biogas refers to a mixed gas produced by the decomposition of organic matter (such as plant residues, animal feces, garbage, etc.) by microorganisms in an anaerobic environment. This process usually occurs in composting, landfills, animal farms and other places. The specific process includes the hydrolysis of complex organic matter, bacterial fermentation and methanogen gas production. Biogas is mainly composed of methane and carbon dioxide, and may also contain small amounts of nitrogen, hydrogen sulfide and water vapor. Methane: about 50-70%, is the main component of biogas and the main available fuel for biogas. Carbon dioxide: about 30-50%, together with methane, constitutes biogas. Nitrogen, hydrogen sulfide and water vapor: The content of these components is usually very low. Among them, carbon dioxide has a certain acidity and will corrode pipeline equipment for a long time. In addition, the inability of carbon dioxide to burn will greatly reduce the calorific value of biogas. Therefore, biogas needs to be stripped of carbon dioxide before it is suitable for use as fuel gas.

[0003] The following methods are commonly used in the prior art to remove carbon dioxide from biogas:

[0004] Chemical absorption method: Use amine solution (such as diethanolamine or ammonia solution) or react with carbon dioxide to generate soluble bicarbonate or amino compounds to absorb carbon dioxide. By adjusting the temperature and pressure, the absorbed carbon dioxide can be released from the solution to achieve a cycle of absorption and desorption. This operation method is more complicated and has a high material cost.

[0005] Physical adsorption method: The adsorption method is to remove carbon dioxide from biogas through solid adsorbents. Commonly used adsorbents include activated carbon, silicon aluminum molecular sieves, etc. These adsorbents have a large specific surface area and adsorption capacity, and can remove carbon dioxide from the gas at room temperature. These methods need to be operated at low temperatures to improve efficiency, and the adsorbents need to be replaced regularly, resulting in high prices.

[0006] Low temperature cooling method: Under normal pressure, carbon dioxide will solidify at -56.6℃, while methane will remain in gaseous state above -161.5℃. Carbon dioxide can be removed from biogas by turning it into dry ice by cooling. However, the cooling method requires a lot of energy consumption and is economically expensive.

[0007] Water absorption method: Carbon dioxide is easily soluble in water under pressure, while methane is almost insoluble, so biogas can be purified by water absorption. This method is low-cost and simple to operate, but it is not suitable for the treatment of high-concentration carbon dioxide gas. The carbon dioxide content in biogas is as high as 30-50%. Using this method requires a large amount of water, and the applicable scenarios are very limited.

[0008] Membrane separation method: The membrane separation method uses a selective permeable membrane to separate carbon dioxide from natural gas. The use of specific membrane materials allows carbon dioxide to pass through the membrane layer while methane is blocked. This method is energy-efficient and efficient, but requires more precise material design capabilities. There are requirements for the pore size and durability of the membrane.

[0009] In view of this, it is necessary to propose a zinc zeolite imidazole-covalent organic framework molecular sieve membrane and a preparation method and application thereof to solve the above problems. Summary of the invention

[0010] To achieve the above object, the present invention provides a zinc zeolite imidazole-covalent organic framework molecular sieve membrane, comprising a hollow membrane, wherein the hollow membrane is filled with a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer;

[0011] The zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is obtained by ultrasonically dispersing the covalent organic framework and the zinc zeolite imidazole framework through ethanol;

[0012] The zinc zeolite imidazole framework is synthesized by using 2-imidazole carboxaldehyde as an organic ligand and zinc chloride as a metal node.

[0013] In a possible embodiment, the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is between 0.30-0.37 nm.

[0014] To achieve the above object, the present invention also provides a method for preparing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, the method comprising:

[0015] S101: adding a reaction monomer combination to glacial acetic acid, reacting at room temperature or under reflux conditions to synthesize a covalent organic framework, wherein the reaction monomer combination is at least one, and the corresponding covalent organic framework synthesized is at least one;

[0016] S102: dissolving triethylamine in a zinc nitrate methanol solution to obtain a first reaction solution, dissolving 2-imidazole carboxaldehyde in a methanol solution to obtain a second reaction solution, adding the first reaction solution dropwise to the second reaction solution under stirring to react, and performing centrifugal washing and vacuum drying to obtain a zinc zeolite imidazole framework;

[0017] S103: dispersing the covalent organic framework and the zinc zeolite imidazole framework in ethanol, and subjecting the mixture to ultrasonic treatment and centrifugal drying to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, wherein the ratio of the covalent organic framework to the zinc zeolite imidazole framework is 1:(1-5), and the dispersion concentration is 0.01-0.05 g / mL;

[0018] S104: filling and compressing the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer into the pores of the hollow fiber membrane to obtain a zinc zeolite imidazole-covalent organic framework molecular sieve membrane.

[0019] In one possible embodiment, the synthesis steps of each covalent organic framework include:

[0020] Adding the two reaction monomers in a ratio of 1:1 to the glacial acetic acid solution to react to obtain a first product solution;

[0021] The first product solution is filtered, washed, and vacuum dried to obtain a covalent organic framework.

[0022] In a possible embodiment, the combination of two of the reactive monomers is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehyde phenol, 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)benzene, or 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)triazine.

[0023] In a possible embodiment, the washing agent of the first product solution includes at least one of N,N-dimethylformamide, water, tetrahydrofuran, and anhydrous acetone.

[0024] To achieve the above object, the present invention also provides a method for removing carbon dioxide from biogas using a zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, the method comprising:

[0025] S201: pressurizing the biogas and passing it through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0026] S202: Through the selective permeation function of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, carbon dioxide molecules are allowed to pass through while methane molecules are retained.

[0027] To achieve the above object, the present invention also provides a biogas carbon dioxide removal device using zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, comprising:

[0028] A biogas CO2 removal module equipped with a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0029] A pressurizing system, used for pressurizing the biogas;

[0030] a branch port for separating carbon dioxide from biogas passing through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0031] A main port for outputting biogas after carbon dioxide removal;

[0032] A shell has the branch port and the main port respectively disposed at two opposite ends, the biogas carbon dioxide removal module is disposed inside the shell, and the pressurizing system is disposed outside the shell.

[0033] To achieve the above objectives, the present invention also provides a carbon dioxide removal cloth of zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, comprising a fiber cloth and a zinc zeolite imidazole-covalent organic framework molecular sieve membrane arranged on the outer surface of the fiber cloth.

[0034] To achieve the above objectives, the present invention also provides a method for using the carbon dioxide removal cloth as in the above embodiment, the method comprising surrounding or covering the biogas with the carbon dioxide removal cloth, or arranging the carbon dioxide removal cloth in a pipeline for biogas to pass through.

[0035] The beneficial effect of the present invention is that the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is obtained by ultrasonic dispersion of the covalent organic framework and the zinc zeolite imidazole framework through ethanol, and its pore size is precisely controlled to be smaller than the diameter of the methane molecule and larger than the diameter of the carbon dioxide molecule, so that the carbon dioxide molecules can pass through while the methane molecules are intercepted, thereby completing the removal of carbon dioxide from biogas. The method separates the carbon dioxide molecules from the biogas through physical action, can be durable, does not generate chemical consumption, and does not need to be frequently replaced, thereby greatly reducing the cost of use. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In view of the problems existing in the prior art, an embodiment of the present invention provides a zinc zeolite imidazole-covalent organic framework molecular sieve membrane, which includes a hollow membrane made of polytetrafluoroethylene, and the hollow membrane is filled with a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer. The zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is obtained by ultrasonic dispersion of a covalent organic framework and a zinc zeolite imidazole framework by ethanol. The zinc zeolite imidazole framework is synthesized with 2-imidazole formaldehyde as an organic ligand and zinc chloride as a metal node.

[0038] Zinc zeolite imidazole framework (ZIF-90) was synthesized with 2-imidazole formaldehyde as organic ligand and zinc chloride as metal node. The geometric structure is rhombic dodecahedron, and the zinc zeolite imidazole framework is a porous structure. The zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is a pore structure with high porosity. The pore size is smaller than the diameter of methane molecules and larger than the diameter of carbon dioxide molecules. It can selectively separate carbon dioxide and methane in biogas. Since the diameter of carbon dioxide molecules is smaller, they are easier to pass through the composite molecular sieve nanolayer, while the diameter of methane molecules is larger and they are intercepted. Carbon dioxide molecules are separated from biogas through physical action. It is durable, does not produce chemical consumption, and does not need to be replaced frequently, thereby greatly reducing the cost of use.

[0039] In one embodiment, the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is between 0.30-0.37 nm. Since the diameter of a methane molecule is 0.38 nm and the diameter of a carbon dioxide molecule is 0.23 nm, the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is set to be between 0.30-0.37 nm, so that carbon dioxide molecules can pass through while methane molecules are intercepted, thereby completing the removal of carbon dioxide from biogas.

[0040] In view of the problems existing in the prior art, an embodiment of the present invention further provides a method for preparing a zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, the preparation method comprising:

[0041] S101: adding a reaction monomer combination to glacial acetic acid, reacting at room temperature or under reflux conditions to synthesize covalent organic frameworks (COFs), wherein the reaction monomer combination is at least one and the corresponding synthesized covalent organic framework is at least one.

[0042] In this step, covalent organic frameworks (COFs) are porous materials formed by covalent bonds between reactive monomers. Reactive monomers are connected by covalent bonds to form a stable network structure, forming covalent organic frameworks (COFs) with specific pore sizes and shapes for the separation of gas molecules.

[0043] S102: Dissolve triethylamine in zinc nitrate methanol solution to obtain a first reaction solution, i.e., zinc nitrate methanol solution containing triethylamine, and the concentration of the first reaction solution is 0.05-0.15M; dissolve 2-imidazolecarboxaldehyde in methanol solution to obtain a second reaction solution, i.e., a methanol solution containing 2-imidazolecarboxaldehyde, and the concentration of the second reaction solution is 0.05-0.15M; add the first reaction solution dropwise into the second reaction solution under stirring to react, and obtain zinc zeolite imidazole framework (ZIF-90) by centrifugal washing and vacuum drying.

[0044] In this step, triethylamine can form a coordination bond with the zinc ion in zinc nitrate, promoting the coordination reaction between the zinc ion and the imidazole ring in 2-imidazole carboxaldehyde. This coordination effect helps to form the structure of ZIF-90, because ZIF-90 is a metal organic framework composed of metal ions (such as zinc) and imidazole rings. The addition of triethylamine can improve the synthesis efficiency of ZIF-90 because it can act as a co-catalyst to accelerate the reaction process. During the synthesis process, triethylamine helps to maintain the alkaline environment of the reaction system, thereby promoting the deprotonation of the imidazole ring, making it easier to coordinate with metal ions. The use of triethylamine can improve the pore structure of ZIF-90. By controlling the amount of triethylamine, the pore size and porosity can be adjusted. The imidazole ring in 2-imidazole carboxaldehyde can form a coordination bond with the zinc ion, and the aldehyde group can further react with other metal ions or organic molecules to form a stable ZIF-90 structure. The coordination mode of the imidazole ring and aldehyde functional group of 2-imidazolecarboxaldehyde can affect the pore size and specific surface area of ​​ZIF-90. By precisely controlling the pore size, ZIF-90 can selectively permeate molecules of a specific size, such as allowing carbon dioxide molecules to pass through while methane molecules are retained.

[0045] Furthermore, the mixing rate of the reactants can be accurately controlled by dropwise addition, avoiding the uneven product or side reaction caused by too fast reaction. By slowly dropping, the concentration gradient of the reactants in the reaction system can be maintained, thereby controlling the reaction rate. Dropwise addition of the reaction solution under stirring can ensure that the reactants are fully contacted when mixed, improving the uniformity of the reaction. This uniform mixing helps to form uniform ZIF-90 crystals, avoids local supersaturation and uneven crystal growth, helps to form ZIF-90 crystals with high crystallinity and uniform particle size, and improves the purity of ZIF-90. Dropwise addition of the reaction solution can affect the pore size and specific surface area of ​​ZIF-90. By accurately controlling the reaction conditions, ZIF-90 with a specific pore size and a high specific surface area can be synthesized.

[0046] In one example, the zinc nitrate methanol solution is 15 mL, the amount of triethylamine added is 0.005-0.03 g, the target concentration of the first reaction solution is 0.05 M, and the target volume is 15 mL. In order to achieve the above target concentration and target volume, the specific operation process is as follows:

[0047] Use a balance to accurately weigh 0.005 g of triethylamine; add the weighed 0.005 g of triethylamine to a volumetric flask; add 8 mL of zinc nitrate methanol solution to the volumetric flask; use a glass rod to stir the mixture in the volumetric flask until the triethylamine is completely dissolved. In this step, you can heat it slightly to speed up the dissolution process, but pay attention to controlling the temperature to avoid excessive evaporation of the zinc nitrate methanol solution; transfer the completely dissolved solution from the beaker to a 50 mL volumetric flask; continue to add zinc nitrate methanol solution to the volumetric flask until the volume of the solution reaches the 15 mL mark; shake upside down or use a shaker to ensure that the solution is fully mixed to obtain the desired first reaction solution.

[0048] In one example, the methanol solution is 15 mL, the target concentration of the second reaction solution is 0.05 M, and the target volume is 15 mL. In order to achieve the above target concentration and target volume, the specific operation process is as follows:

[0049] Use a balance to accurately weigh 0.0025 g of 2-imidazole carboxaldehyde; add the weighed 0.0025 g of 2-imidazole carboxaldehyde to a volumetric flask; add 8 mL of methanol solution to the volumetric flask; use a glass rod to stir the mixture in the volumetric flask until the 2-imidazole carboxaldehyde is completely dissolved. In this step, you can heat it slightly to speed up the dissolution process, but pay attention to controlling the temperature to avoid excessive evaporation of the methanol solution; transfer the completely dissolved solution from the beaker to a 50 mL volumetric flask; continue to add methanol solution to the volumetric flask until the volume of the solution reaches the 15 mL mark; shake upside down or use a shaker to ensure that the solution is fully mixed to obtain the desired second reaction solution.

[0050] S103: Dispersing the covalent organic framework (COFs) and the zinc zeolite imidazole framework (ZIF-90) in ethanol, ultrasonically treating, and centrifugally drying to obtain a zinc zeolite imidazole-covalent organic framework (ZIFs-COFs) composite molecular sieve nanolayer, the ratio of the covalent organic framework to the zinc zeolite imidazole framework is 1:(1-5), and the dispersion concentration is 0.01-0.05 g / mL.

[0051] In this step, ethanol, as an organic solvent, has good dispersibility, which can ensure that ZIF-90 and COFs are evenly distributed in the solvent and avoid the occurrence of agglomeration and precipitation. The lower surface tension of ethanol helps to reduce the aggregation tendency of nanomaterials, further ensuring the dispersion quality and stability of the materials. The vibration and cavitation effects generated by ultrasonic treatment can promote the uniform dispersion of ZIF-90 and COFs in ethanol, improve the dispersion efficiency, and help to form a uniform composite material. Ultrasonic treatment also helps to optimize the nanostructure of ZIF-90 and COFs, so that they form a more regular and orderly arrangement, thereby improving the performance of the composite molecular sieve nanolayer. Centrifugal treatment can separate the solid in the dispersed system (i.e., ZIFs-COFs composite molecular sieve nanolayer) from ethanol to obtain a pure solid product. The dispersion concentration directly affects the dispersion effect of ZIF-90 and COFs in ethanol. Too high a dispersion concentration may lead to the occurrence of agglomeration and precipitation, while too low a dispersion concentration may reduce production efficiency. By controlling the dispersion concentration in the range of 0.01-0.05 g / mL, it is possible to ensure that ZIF-90 and COFs form a uniform dispersion system in ethanol. Centrifugal drying can remove solvents and impurities in the composite material to obtain a dry nanolayer structure, which helps maintain the structural integrity of the material while improving the purity and stability of the material.

[0052] S104: Filling and compressing a zinc zeolite imidazole-covalent organic framework (ZIFs-COFs) composite molecular sieve nanolayer into the pores of a hollow fiber membrane to obtain a zinc zeolite imidazole-covalent organic framework molecular sieve membrane.

[0053] In this embodiment, the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is controlled within the range of 0.30-0.37nm, which can effectively separate molecules of a specific size, such as methane molecules with a diameter of 0.38nm and carbon dioxide molecules with a diameter of 0.23nm. By precisely controlling the pore size of the composite molecular sieve nanolayer, the selectivity of the membrane for specific gas molecules can be improved, which is crucial for gas purification and separation; Enhance the durability of the membrane: The filling of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer can enhance the chemical stability and mechanical strength of the zinc zeolite imidazole-covalent organic framework molecular sieve membrane and extend the service life of the membrane.

[0054] This step specifically includes the following: synthesizing the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, ensuring that its pore size is within the range of 0.30-0.37nm; selecting a polytetrafluoroethylene (PTFE) hollow fiber membrane with a pore size slightly larger than the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer to ensure that the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer can be filled into the pores. For example, if the pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is 0.34nm, a PTFE membrane with a pore size of 0.5μm may be selected; using pressure or vacuuming to fill the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer into the pores of the PTFE membrane. The filling pressure needs to reach 3-5 atmospheres to ensure that the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is completely filled into the pores; a certain pressure (for example, 0.5-1MPa) is applied to compress the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer so that it fits tightly to the inner wall of the pores to form a uniform nanolayer; the filled and compressed zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is cured to ensure its stability in the pores. This can be achieved by heat treatment (for example, temperature control at 100-200°C) or chemical cross-linking; the filled and compressed hollow fiber membrane is cleaned, dried and performance tested to ensure that its separation performance meets expectations.

[0055] In one embodiment, the synthesis steps of each covalent organic framework (COFs) include:

[0056] Adding two reaction monomers in a ratio of 1:1 to a glacial acetic acid solution to obtain a first product solution, i.e., a covalent organic framework solution;

[0057] The first product solution is filtered, washed, and vacuum dried to obtain a covalent organic framework.

[0058] In this step, by adding two reactive monomers in a 1:1 ratio, the stoichiometric ratio of the reactants can be precisely controlled to ensure the uniformity of the reaction and the consistency of the product. Carrying out the reaction in glacial acetic acid solution provides a mild reaction environment, which helps to avoid overreaction or side reactions, thereby improving the purity and performance of the product.

[0059] In a specific embodiment, the concentration of the reaction monomer is 0.03-0.10 mmol. Within this concentration range, the reaction can be carried out more evenly and stably, which helps to form a uniform COFs structure. The appropriate monomer concentration can optimize the crystallinity and porosity of COFs. Crystallinity is one of the key factors affecting the performance of COFs. High crystallinity means a more regular structure and better pore arrangement, which helps gas separation.

[0060] In a specific embodiment, when adding two reactive monomers, avoid light and continue stirring for a preset time, which is 1-5 hours. Avoiding light can prevent degradation or side reactions of certain light-sensitive reactive monomers, ensuring the specificity of the reaction and the purity of the product. Continuous stirring helps the monomers to be evenly dispersed in the solvent, increasing the reaction contact area, thereby improving the reaction efficiency and the uniformity of the product. By filtering, washing and vacuum drying, unreacted monomers and by-products can be removed to improve the purity of the covalent organic framework.

[0061] In one embodiment, the combination of two reactive monomers is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehyde phenol, 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)benzene, or 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)triazine. Among them, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, and 1,3,5-tris(4-formaldehyde phenyl)triazine belong to triazine COFs, and the trinitrogen heterocyclic ring inside triazine COFs gives them higher porosity and specific surface area.

[0062] In the combination of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, the aldehyde group provided by 1,3,5-phenyltrialdehyde and the amino group provided by 2,4,6-tris(4-aminophenyl)-1,3,5-triazine react with each other through Schiff base to form a stable imine bond; in the combination of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehydephenol, the amino group (-NH 2) and the formaldehyde group provided by 2,4,6-triformaldehyde phenol form a stable imine bond through Schiff base reaction; in the combination of 1,3,5-tri(4-aminophenyl)benzene and 1,3,5-tri(4-formaldehydephenyl)benzene, 1,3,5-tri(4-aminophenyl)benzene as a triamino compound can react with the formaldehyde group in 1,3,5-tri(4-formaldehydephenyl)benzene to form a stable imine bond; in the combination of 1,3,5-tri(4-aminophenyl)benzene and 1,3,5-tri(4-formaldehydephenyl)triazine, the amino group provided by 1,3,5-tri(4-aminophenyl)benzene and the formaldehyde group provided by 1,3,5-tri(4-formaldehydephenyl)triazine form a stable imine bond through Schiff base reaction. The imine bond can improve the stability of the COFs structure and form COFs with high crystallinity, thereby having a regular pore structure. High crystallinity helps to improve the stability and porosity of the material, and can achieve selective separation of specific molecules. The spatial and hydrophobic protection of the imine bond makes the material stable in a variety of chemical environments, with excellent chemical stability, especially in acidic and alkaline solutions. Due to its rigid benzene ring and stable imine bond, it has good mechanical strength and improved durability.

[0063] In one example, the volume of the glacial acetic acid solution is 10 mL, the concentration of the reaction monomer is 0.10 mmol, and the two reaction monomers are 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde. The specific operation process for preparing the first product solution is as follows: add 10 mL of glacial acetic acid to a volumetric flask, add 5 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.10 mmol, and 5 mL of 1,3,5-phenyltrialdehyde with a concentration of 0.10 mmol to the volumetric flask, avoid direct sunlight, and continue stirring for 5 hours.

[0064] In one embodiment, the washing agent of the first product solution includes at least one of N,N-dimethylformamide (DMF), water, tetrahydrofuran (THF), and anhydrous acetone.

[0065] N,N-dimethylformamide (DMF) is an excellent organic solvent that can dissolve a variety of organic substances, including some COFs precursors or products, and can effectively remove a variety of organic impurities. Water is an environmentally friendly, non-toxic solvent that can remove inorganic salts, unreacted monomers and other water-soluble impurities in the reaction system, thereby improving the purity of COFs. Tetrahydrofuran (THF) is an excellent solvent with good emulsifying properties. THF can destroy the oil-water interface in the solution, making it easier to wash away impurities, which helps to further purify COFs. THF can also dissolve some organic substances, including some COFs precursors or products, which helps to ensure the uniform dispersion of COFs in the solvent and prevent agglomeration. Anhydrous acetone has both fat-soluble and water-soluble characteristics, and can remove fat-soluble impurities and water-soluble impurities in the reaction system, thereby improving the purity of COFs. Due to its volatility, anhydrous acetone is often used to remove moisture and the final washing steps to ensure that the COFs product is completely dry and improve the thermal and chemical stability of the product. When DMF, water, THF and acetone are used in combination as detergents, they can produce a synergistic effect and jointly improve the washing effect of COFs. Different solvents have different solubility and washing properties. The combination can cover a wider range of impurity types, thereby purifying COFs more comprehensively.

[0066] In one embodiment, the first reaction solution and the second reaction solution react for a set time and then are centrifuged for washing, wherein the set time is 9.5-10.5h, the centrifugal speed is 10000-15000rpm, and the centrifugal time is 5-15min.

[0067] The setting of this step allows the zinc zeolite imidazole-covalent organic framework composite molecular sieve particles to quickly settle to the bottom of the container under high-speed centrifugation, thereby achieving rapid separation of solids and liquids. For example, using a centrifugal speed of 15,000 rpm, more than 90% solid sedimentation can be achieved within a few minutes; the setting of this step can avoid damage to the nanolayer structure of the zinc zeolite imidazole-covalent organic framework composite molecular sieve and maintain its integrity. Experimental data show that the crystal structure of the zinc zeolite imidazole-covalent organic framework composite molecular sieve remains intact at a centrifugal speed of 10,000 to 15,000 rpm.

[0068] Appropriate reaction time can reduce the residue of unreacted monomers and improve the purity of the product. Too short reaction time may lead to incomplete reaction, while too long reaction time may cause unnecessary side reactions. Therefore, by accurately controlling the appropriate reaction time, it is ensured that the reaction monomers in the first reaction solution and the second reaction solution have enough time to undergo a sufficient condensation reaction, which helps to form a more complete and stable COFs structure, thereby improving the crystallinity and performance of the product. The centrifugal speed is in the range of 10000-15000rpm, which can efficiently separate the solid product and solution in the reaction system. High speed helps to accelerate the sedimentation rate of solid particles and improve separation efficiency. Appropriate centrifugal speed can reduce the loss of solid products during centrifugation and maintain the integrity of the product. Too high a speed may cause the crushing of solid particles, affecting the quality and performance of the product. The centrifugal time is within 5-15 minutes, which can ensure sufficient separation between the solid product and the solution. Appropriate centrifugal time helps to remove residual solution and impurities in the product and improve the purity of the product. In this scheme, by accurately controlling the reaction time and centrifugal conditions, unreacted monomers, residual solution and impurities can be effectively removed to improve the purity of the product.

[0069] To achieve the above object, the present invention also provides a method for removing carbon dioxide from biogas using a zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, the method comprising:

[0070] S201: pressurizing the biogas and passing it through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0071] S202: Through the selective permeation function of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, carbon dioxide molecules are allowed to pass through while methane molecules are retained.

[0072] To achieve the above object, the present invention also provides a biogas carbon dioxide removal device using zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, comprising:

[0073] A biogas CO2 removal module equipped with a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0074] A pressurizing system, used for pressurizing the biogas;

[0075] a branch port for separating carbon dioxide from biogas passing through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane;

[0076] A main port for outputting biogas after carbon dioxide removal;

[0077] A shell body is provided with a branch port and a main port at two opposite ends, a biogas carbon dioxide removal module is arranged inside the shell body, and a pressurizing system is arranged outside the shell body.

[0078] In this embodiment, the biogas carbon dioxide removal module is integrated into a shell, making the entire device more compact and easy to install and operate; the pressurizing system is arranged outside the shell, which is convenient for operators to control and maintain, while reducing the space occupied in the shell; compared with traditional carbon dioxide removal technology, the biogas carbon dioxide removal device with zinc zeolite imidazole-covalent organic framework molecular sieve membrane has lower operation and maintenance costs; the modular design of the biogas carbon dioxide removal device makes monitoring and maintenance more convenient; at the same time, the pressurizing system can be adjusted according to changes in biogas flow and carbon dioxide concentration to adapt to different operating conditions.

[0079] To achieve the above objectives, the present invention also provides a carbon dioxide removal cloth of zinc zeolite imidazole-covalent organic framework molecular sieve membrane as in the above embodiment, comprising a fiber cloth and a zinc zeolite imidazole-covalent organic framework molecular sieve membrane arranged on the outer surface of the fiber cloth.

[0080] In this embodiment, the zinc zeolite imidazole-covalent organic framework molecular sieve membrane is arranged on the outer surface of the fiber cloth, and the mechanical strength of the fiber cloth can be used to enhance the structural stability of the entire carbon dioxide removal cloth; the chemical corrosion resistance of the zinc zeolite imidazole-covalent organic framework molecular sieve membrane enables the carbon dioxide removal cloth to maintain its performance even in harsh chemical environments and extend its service life; the form of the carbon dioxide removal cloth is easy to integrate into the existing gas treatment system without large-scale modification; compared with the traditional carbon dioxide removal method, the carbon dioxide removal cloth of the zinc zeolite imidazole-covalent organic framework molecular sieve membrane has lower operation and maintenance costs.

[0081] To achieve the above objectives, the present invention also provides a method for using the carbon dioxide removal cloth as in the above embodiment, the method comprising surrounding or covering the biogas with the carbon dioxide removal cloth, or arranging the carbon dioxide removal cloth in a pipeline for biogas to pass through.

[0082] In this embodiment, the carbon dioxide removal cloth is in direct contact with the biogas, which can quickly and effectively remove carbon dioxide and improve the desulfurization efficiency; the carbon dioxide removal cloth is easy to install and deploy, and no complicated equipment changes are required whether it surrounds or covers the outside of the biogas or is placed in the pipeline; the carbon dioxide removal cloth can be customized according to the specific layout and needs of the biogas treatment facility, providing a flexible solution; compared with traditional carbon dioxide removal technology, the use of carbon dioxide removal cloth reduces equipment and operating costs, especially in terms of maintenance and replacement.

[0083] The zinc zeolite imidazole-covalent organic framework molecular sieve membrane and its preparation method and application of the present invention are described in detail below through specific embodiments:

[0084] Example 1

[0085] Preparation of zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with pore size of 0.30 nm

[0086] The specific steps are as follows:

[0087] Step 1: Prepare stock solution

[0088] 1. Preparation of covalent organic frameworks (COFs):

[0089] At least two groups of reactive monomers are selected, for example, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehydephenol.

[0090] 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.03 mmol and 500 mL of 1,3,5-phenyltrialdehyde with a concentration of 0.03 mmol were measured and added to 1000 mL of glacial acetic acid, and stirred continuously for 5 hours at room temperature using a magnetic stirrer away from direct sunlight to obtain a solution containing a covalent organic framework with a concentration of 0.03 mmol; 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.03 mmol and 500 mL of 2,4,6-triformaldehyde phenol with a concentration of 0.03 mmol were measured and added to 1000 mL of glacial acetic acid, and stirred continuously for 5 hours at room temperature using a magnetic stirrer away from direct sunlight to obtain a solution containing another covalent organic framework with a concentration of 0.03 mmol. After the reaction, the obtained solution containing the covalent organic framework was filtered, and the solid was washed with N,N-dimethylformamide (DMF), water, tetrahydrofuran (THF) and anhydrous acetone for multiple times, and vacuum dried at 60°C for 24 hours to obtain a light yellow powder covalent organic framework (COFs).

[0091] 2. Prepare zinc nitrate methanol solution containing triethylamine:

[0092] Accurately weigh 7.59 g of triethylamine with a purity higher than 99%, add the weighed triethylamine to 1500 mL of a pre-selected zinc nitrate methanol solution, and stir at room temperature with a magnetic stirrer until the solution is completely dissolved to obtain a 0.05 M zinc nitrate methanol solution containing triethylamine.

[0093] 3. Prepare a methanol solution containing 2-imidazolecarboxaldehyde:

[0094] Accurately weigh 6.31 g of 2-imidazolecarboxaldehyde with a purity higher than 99%, add the weighed 2-imidazolecarboxaldehyde to 1500 mL of a pre-selected methanol solution, and stir at room temperature with a magnetic stirrer until the solution is completely dissolved to obtain a 0.05 M methanol solution containing 2-imidazolecarboxaldehyde.

[0095] 4. Preparation of zinc zeolite imidazole framework (ZIF-90):

[0096] Under stirring, a zinc nitrate methanol solution containing triethylamine is added dropwise to a methanol solution containing 2-imidazole formaldehyde. After the reaction is completed, the mixture is allowed to stand for 10 hours to precipitate the zinc zeolite imidazole framework, and then the precipitated zinc zeolite imidazole framework is collected by centrifugation. During the centrifugal treatment, the centrifugal rate is 15000rpm and the centrifugal time is 10min. The collected zinc zeolite imidazole framework is washed to remove residual unreacted raw materials and by-products. The washed zinc zeolite imidazole framework is placed in an oven and vacuum dried at 60°C for 24h to ensure complete removal of moisture, and finally a powdered zinc zeolite imidazole framework (ZIF-90) is obtained.

[0097] 5. Preparation of zinc zeolite imidazole-covalent organic framework (ZIFs-COFs) composite molecular sieve nanolayer:

[0098] Covalent organic framework (COFs) powder and zinc zeolite imidazole framework (ZIF-90) powder were weighed in a ratio of 1:1, dispersed in ethanol, and subjected to ultrasonic treatment and centrifugal treatment, and vacuum dried at 60°C for 24 hours to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with a pore size of 0.30 nm, wherein the ultrasonic treatment time was 10 minutes, the dispersion concentration was 0.03 g / mL, the centrifugal speed was 15000 rpm, and the centrifugal time was 10 minutes.

[0099] Example 2

[0100] Preparation of zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with pore size of 0.34 nm

[0101] The specific steps are as follows:

[0102] Step 1: Prepare stock solution

[0103] 1. Preparation of covalent organic frameworks (COFs):

[0104] At least two groups of reactive monomers are selected, for example, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehydephenol.

[0105] 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.07 mmol and 500 mL of 1,3,5-phenyltrialdehyde with a concentration of 0.07 mmol were measured and added to 1000 mL of glacial acetic acid, avoiding direct light, and stirring continuously for 5 hours at room temperature using a magnetic stirrer to obtain a solution containing a covalent organic framework with a concentration of 0.07 mmol; 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.07 mmol and 500 mL of 2,4,6-triformaldehyde phenol with a concentration of 0.07 mmol were measured and added to 1000 mL of glacial acetic acid, avoiding direct light, and stirring continuously for 5 hours at room temperature using a magnetic stirrer to obtain a solution containing another covalent organic framework with a concentration of 0.07 mmol. After the reaction, the obtained solution containing the covalent organic framework was filtered, and the solid was washed with N,N-dimethylformamide (DMF), water, tetrahydrofuran (THF) and anhydrous acetone for multiple times, and vacuum dried at 60°C for 24 hours to obtain a light yellow powder covalent organic framework (COFs).

[0106] 2. Prepare zinc nitrate methanol solution containing triethylamine:

[0107] Accurately weigh 16.09 g of triethylamine with a purity higher than 99%, add the weighed triethylamine to 1500 mL of a pre-selected zinc nitrate methanol solution, and stir at room temperature with a magnetic stirrer until the solution is completely dissolved to obtain a 0.09 M zinc nitrate methanol solution containing triethylamine.

[0108] 3. Prepare a methanol solution containing 2-imidazolecarboxaldehyde:

[0109] Accurately weigh 15.39 g of 2-imidazolecarboxaldehyde with a purity higher than 99%, add the weighed 2-imidazolecarboxaldehyde to a pre-selected 1500 mL methanol solution, and stir at room temperature with a magnetic stirrer until it is completely dissolved to obtain a 0.09 M methanol solution containing 2-imidazolecarboxaldehyde.

[0110] 4. Preparation of zinc zeolite imidazole framework (ZIF-90):

[0111] Under stirring, a zinc nitrate methanol solution containing triethylamine is added dropwise to a methanol solution containing 2-imidazole formaldehyde. After the reaction is completed, the mixture is allowed to stand for 10 hours to precipitate the zinc zeolite imidazole framework, and then the precipitated zinc zeolite imidazole framework is collected by centrifugation. During the centrifugal treatment, the centrifugal rate is 15000rpm and the centrifugal time is 10min. The collected zinc zeolite imidazole framework is washed to remove residual unreacted raw materials and by-products. The washed zinc zeolite imidazole framework is placed in an oven and vacuum dried at 60°C for 24h to ensure complete removal of moisture, and finally a powdered zinc zeolite imidazole framework (ZIF-90) is obtained.

[0112] 5. Preparation of zinc zeolite imidazole-covalent organic framework (ZIFs-COFs) composite molecular sieve nanolayer:

[0113] Covalent organic framework (COFs) powder and zinc zeolite imidazole framework (ZIF-90) powder were weighed in a ratio of 1:1, dispersed in ethanol, and subjected to ultrasonic treatment and centrifugal treatment, and vacuum dried at 60°C for 24 hours to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with a pore size of 0.34 nm, wherein the ultrasonic treatment time was 10 minutes, the dispersion concentration was 0.03 g / mL, the centrifugal speed was 15000 rpm, and the centrifugal time was 10 minutes.

[0114] Example 3

[0115] Preparation of zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with pore size of 0.37 nm

[0116] The specific steps are as follows:

[0117] Step 1: Prepare stock solution

[0118] 1. Preparation of covalent organic frameworks (COFs):

[0119] At least two groups of reactive monomers are selected, for example, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehydephenol.

[0120] 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.10 mmol and 500 mL of 1,3,5-phenyltrialdehyde with a concentration of 0.10 mmol were measured and added to 1000 mL of glacial acetic acid, avoiding direct light, and stirring continuously for 5 hours at room temperature using a magnetic stirrer to obtain a solution containing a covalent organic framework with a concentration of 0.10 mmol; 500 mL of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with a concentration of 0.10 mmol and 500 mL of 2,4,6-triformaldehyde phenol with a concentration of 0.10 mmol were measured and added to 1000 mL of glacial acetic acid, avoiding direct light, and stirring continuously for 5 hours at room temperature using a magnetic stirrer to obtain a solution containing another covalent organic framework with a concentration of 0.10 mmol. After the reaction, the obtained solution containing the covalent organic framework was filtered, and the solid was washed with N,N-dimethylformamide (DMF), water, tetrahydrofuran (THF) and anhydrous acetone for multiple times, and vacuum dried at 60°C for 24 hours to obtain a light yellow powder covalent organic framework (COFs).

[0121] 2. Prepare zinc nitrate methanol solution containing triethylamine:

[0122] Accurately weigh 21.46 g of triethylamine with a purity higher than 99%, add the weighed triethylamine to 1500 mL of a pre-selected zinc nitrate methanol solution, and stir at room temperature with a magnetic stirrer until the solution is completely dissolved to obtain a 0.12 M zinc nitrate methanol solution containing triethylamine.

[0123] 3. Prepare a methanol solution containing 2-imidazolecarboxaldehyde:

[0124] Accurately weigh 20.18 g of 2-imidazolecarboxaldehyde with a purity higher than 99%, add the weighed 2-imidazolecarboxaldehyde to a pre-selected 1500 mL methanol solution, and stir at room temperature with a magnetic stirrer until it is completely dissolved to obtain a 0.12 M methanol solution containing 2-imidazolecarboxaldehyde.

[0125] 4. Preparation of zinc zeolite imidazole framework (ZIF-90):

[0126] Under stirring, a zinc nitrate methanol solution containing triethylamine is added dropwise to a methanol solution containing 2-imidazole formaldehyde. After the reaction is completed, the mixture is allowed to stand for 10 hours to precipitate the zinc zeolite imidazole framework, and then the precipitated zinc zeolite imidazole framework is collected by centrifugation. During the centrifugal treatment, the centrifugal rate is 15000rpm and the centrifugal time is 10min. The collected zinc zeolite imidazole framework is washed to remove residual unreacted raw materials and by-products. The washed zinc zeolite imidazole framework is placed in an oven and vacuum dried at 60°C for 24h to ensure complete removal of moisture, and finally a powdered zinc zeolite imidazole framework (ZIF-90) is obtained.

[0127] 5. Preparation of zinc zeolite imidazole-covalent organic framework (ZIFs-COFs) composite molecular sieve nanolayer:

[0128] Covalent organic framework (COFs) powder and zinc zeolite imidazole framework (ZIF-90) powder were weighed in a ratio of 1:1, dispersed in ethanol, and subjected to ultrasonic treatment and centrifugal treatment, and vacuum dried at 60°C for 24 hours to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer with a pore size of 0.37 nm, wherein the ultrasonic treatment time was 10 minutes, the dispersion concentration was 0.03 g / mL, the centrifugal speed was 15000 rpm, and the centrifugal time was 10 minutes.

[0129] Example 4

[0130] The ZIFs-COFs composite molecular sieve nanolayer with a synthetic pore size of 0.30 nm in Example 1, the ZIFs-COFs composite molecular sieve nanolayer with a synthetic pore size of 0.34 nm in Example 2, and the ZIFs-COFs composite molecular sieve nanolayer with a synthetic pore size of 0.38 nm in Example 3 are respectively installed in a biogas carbon dioxide removal module, and the biogas in the branch port is pressurized by a pressurizing system so that the pressurized biogas passes through the biogas carbon dioxide removal module, and the biogas with carbon dioxide removed output from the main port is collected, and the carbon dioxide content in this part of the biogas is monitored.

[0131] Specifically, after experimental verification, taking the biogas with an initial carbon dioxide content of 100ppm as the experimental sample, the biogas after Example 1 contained 0.26ppm of carbon dioxide content after detection; the biogas after Example 2 contained 0.18ppm of carbon dioxide content after detection; the biogas after Example 3 contained 0.37ppm of carbon dioxide content after detection, and the processing time of Example 1, Example 2 and Example 3 was 4min.

[0132] Comparative Example 1

[0133] The carbon dioxide in the biogas is treated by chemical absorption. Specifically, the biogas with an initial carbon dioxide content of 100 ppm is reacted with carbon dioxide to generate soluble bicarbonate or amino compounds to absorb carbon dioxide. After multiple cycles, the treated biogas is tested and the carbon dioxide content is detected to be 16.28 ppm. The treatment time is 4 hours, and reactants are generated to form chemical waste.

[0134] Comparative Example 2

[0135] The physical adsorption method is used to treat the carbon dioxide in the biogas. Specifically, the biogas with an initial carbon dioxide content of 100 ppm is passed through adsorbents such as activated carbon and molecular sieves. After multiple cycles, the treated biogas is tested and the carbon dioxide content is detected to be 19.23 ppm. The processing time is 4 hours, and the adsorbent needs to be replaced after each cycle.

[0136] Comparing Example 1, Example 2, Example 3 and Example 4 with Comparative Example 1 and Comparative Example 2, it can be seen that the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer prepared by Example 1, 2, and 3 shows extremely high efficiency and environmental friendliness in the removal of carbon dioxide from biogas. Among them, the removal efficiency of Example 2 is the highest. In addition, the treatment time of zinc zeolite imidazole-covalent organic framework molecular sieve membrane for removing carbon dioxide is very short, and no by-products and waste are produced, which is very suitable for the modular device for removing carbon dioxide from biogas. The material cost used by zinc zeolite imidazole-covalent organic framework molecular sieve membrane is lower, the energy consumption is lower, and no harmful waste is produced, and the impact on the environment is smaller. In addition, the operation of zinc zeolite imidazole-covalent organic framework molecular sieve membrane for removing carbon dioxide is simpler and safer. In contrast, Comparative Example 1 and Comparative Example 2 are all insufficient in removal efficiency, treatment time and by-product generation. Therefore, the composite molecular sieve nanolayer prepared by the present invention has broad application prospects in the removal of carbon dioxide from biogas.

[0137] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways. Unless otherwise defined, the technical terms or scientific terms used herein should be understood by people with ordinary skills in the field to which the present invention belongs.

Claims

1. A zinc zeolite imidazole-covalent organic framework molecular sieve membrane, characterized in that: It comprises a hollow membrane, wherein the hollow membrane is filled with a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer; The zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is obtained by ultrasonically dispersing the covalent organic framework and the zinc zeolite imidazole framework through ethanol; The zinc zeolite imidazole framework is synthesized by using 2-imidazole carboxaldehyde as an organic ligand and zinc chloride as a metal node.

2. The zinc zeolite imidazole-covalent organic framework molecular sieve membrane according to claim 1, characterized in that: The pore size of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer is between 0.30-0.37 nm.

3. A method for preparing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane as claimed in claim 1, characterized in that: The method comprises: S101: adding a reaction monomer combination to glacial acetic acid, reacting at room temperature or under reflux conditions to synthesize a covalent organic framework, wherein the reaction monomer combination is at least one, and the corresponding covalent organic framework synthesized is at least one; S102: dissolving triethylamine in a zinc nitrate methanol solution to obtain a first reaction solution, dissolving 2-imidazole carboxaldehyde in a methanol solution to obtain a second reaction solution, adding the first reaction solution dropwise to the second reaction solution under stirring to react, and performing centrifugal washing and vacuum drying to obtain a zinc zeolite imidazole framework; S103: dispersing the covalent organic framework and the zinc zeolite imidazole framework in ethanol, and subjecting the mixture to ultrasonic treatment and centrifugal drying to obtain a zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, wherein the ratio of the covalent organic framework to the zinc zeolite imidazole framework is 1:(1-5), and the dispersion concentration is 0.01-0.05 g / mL; S104: filling and compressing the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer into the pores of the hollow fiber membrane to obtain a zinc zeolite imidazole-covalent organic framework molecular sieve membrane.

4. The method for preparing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane according to claim 3, wherein the synthesis steps of each covalent organic framework include: Adding the two reaction monomers in a ratio of 1:1 to the glacial acetic acid solution to react to obtain a first product solution; The first product solution is filtered, washed, and vacuum dried to obtain a covalent organic framework.

5. The method for preparing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane according to claim 4, characterized in that: The combination of two of the reactive monomers is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-phenyltrialdehyde, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,4,6-triformaldehyde phenol, 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)benzene, or 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(4-formaldehyde phenyl)triazine.

6. The method for preparing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane according to claim 4, characterized in that: The washing agent of the first product solution includes at least one of N,N-dimethylformamide, water, tetrahydrofuran, and anhydrous acetone.

7. A method for removing carbon dioxide from biogas using the zinc zeolite imidazole-covalent organic framework molecular sieve membrane as claimed in claim 1, characterized in that: The method comprises: S201: pressurizing the biogas and passing it through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane; S202: Through the selective permeation function of the zinc zeolite imidazole-covalent organic framework composite molecular sieve nanolayer, carbon dioxide molecules are allowed to pass through while methane molecules are retained.

8. A biogas carbon dioxide removal device using the zinc zeolite imidazole-covalent organic framework molecular sieve membrane as claimed in claim 1, characterized in that: include: A biogas CO2 removal module equipped with a zinc zeolite imidazole-covalent organic framework molecular sieve membrane; A pressurizing system, used for pressurizing the biogas; a branch port for separating carbon dioxide from biogas passing through a zinc zeolite imidazole-covalent organic framework molecular sieve membrane; A main port for outputting biogas after carbon dioxide removal; A shell has the branch port and the main port respectively disposed at two opposite ends, the biogas carbon dioxide removal module is disposed inside the shell, and the pressurizing system is disposed outside the shell.

9. A carbon dioxide removal cloth containing the zinc zeolite imidazole-covalent organic framework molecular sieve membrane as claimed in claim 1, characterized in that: The invention comprises a fiber cloth and a zinc zeolite imidazole-covalent organic framework molecular sieve membrane arranged on the outer surface of the fiber cloth.

10. A method for using the carbon dioxide removal cloth according to claim 9, characterized in that: The method of use comprises surrounding or covering the biogas with carbon dioxide removal cloth, or arranging the carbon dioxide removal cloth in a pipeline to allow the biogas to pass through.