A graphene-assisted MOF membrane material for extracting helium from natural gas, a preparation method and application thereof

Abstract

The application discloses a graphene-assisted MOF film material for extracting helium from natural gas, and further discloses a preparation method of the MOF film material. Two-dimensional porous graphene is selected as a base material, and the base material is cleaned with deionized water and acetone for several times, dried, calcined in air and then grafted and modified, so that a modified graphene base is obtained. Then, the modified graphene base is placed in a reaction kettle, zinc nitrate aqueous solution is added, and heating is carried out at 100-140 DEG C for 5-12 hours. Then, 2-methyl imidazole aqueous solution and benzene dimethyl imidazole aqueous solution are added, and stirring is continuously carried out for 12-24 hours. After methanol washing and drying, a graphene-assisted ZIF-8 film material is finally obtained. The application further discloses an application of the MOF film material. The novel graphene-assisted mixed ZIF-8 film material prepared by the application can effectively extract helium from natural gas. The material has good stability, and has good separation selectivity and permeability for helium in He / N2 and He / CH4. The synthesis method of the material is simple and feasible, and the material can be mass-produced.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary fields of nanomaterials, coordination chemistry and separation chemistry, and specifically relates to a graphene-assisted MOF membrane material for helium extraction from natural gas, its preparation method and application. Background Technology

[0002] Helium (He) is a rare strategic resource and an essential inert gas for many high-tech applications, such as leak detectors, coolants for operating superconducting magnets and manufacturing glass fibers, protective gases for welding and crystal growth, and carrier gases in chromatographs. Although helium (He) is abundant in the universe, its terrestrial sources are limited, and its shortage has adversely affected industry, medicine, and basic research. Primary production of helium involves extraction from natural gas via cryogenic distillation or pressure swing adsorption, but these methods are costly due to the low helium content of natural gas and therefore cannot be widely used. Summary of the Invention

[0003] The purpose of this invention is to provide a graphene-assisted MOF membrane material for helium extraction from natural gas, its preparation method, and its application. The novel graphene-assisted mixed ZIF-8 membrane material prepared by this invention can effectively extract helium from natural gas. This material has good stability and excellent separation selectivity and permeability for helium in He / N2 and He / CH4. The preparation method of this material is simple and feasible, and can be mass-produced. This material is a highly promising, safe, and reliable material for preparing helium extraction membrane materials from natural gas and separating helium from methane.

[0004] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas includes the following steps:

[0006] S1. Two-dimensional porous graphene is selected as the substrate material. It is washed several times with deionized water and acetone, dried, and then calcined in air at 250-350℃ for 8-16 hours to enhance the activated surface of porous graphene and increase surface functional groups, thereby obtaining an activated graphene substrate.

[0007] S2. Aromatic carboxylic acid derivative functional groups are grafted onto the surface of an activated graphene substrate to obtain a modified graphene substrate.

[0008] The structural formulas of the aromatic carboxylic acid derivatives are as follows:

[0009]

[0010] (R1, R2, and R3 may be the same or different, and R1, R2, and R3 may be independently selected from H, CH3, and OCH3)

[0011] The method for grafting aromatic carboxylic acid derivative functional groups onto the surface of an activated graphene substrate is as follows:

[0012] Weigh out activated graphene groups and add them to dichloromethane. Sonicate for 40 min, then add 4-dimethylaminopyridine, dicyclohexylcarbodiimide, and an aromatic carboxylic acid derivative, respectively. React in a water bath at 60°C under nitrogen protection with stirring for 12 h. Remove the supernatant, wash, then soak in sodium hypochlorite solution, wash again, filter, and freeze-dry to obtain the modified graphene substrate. The mass ratio of activated graphene substrate, dichloromethane, 4-dimethylaminopyridine, dicyclohexylcarbodiimide, and aromatic carboxylic acid derivative is 1:200:10:1:3.

[0013] S3. The modified graphene substrate obtained in S2 is placed in a reaction vessel, and zinc nitrate aqueous solution is added. The mixture is heated at 100-140℃ for 5-12 hours. Then, 2-methylimidazole aqueous solution and benzodimethylimidazole aqueous solution are added, and stirring is continued for 12-24 hours. This allows the functional groups of aromatic carboxylic acid derivatives on the activated surface of the two-dimensional porous graphene substrate to form MOF structures with metal ions in a self-assembly form on the graphene surface, thereby constructing a graphene-MOF nanocomposite material. This ensures the bonding strength between the mixed ZIF-8 and the substrate. After washing with methanol and drying, graphene-assisted ZIF-8 membrane material is finally obtained. The thickness of the well-co-existing mixed ZIF-8 membrane formed on the modified graphene substrate is about 10 μm.

[0014] Furthermore, the mass ratio of the two-dimensional porous graphene, 2-methylimidazole, benzodimethylimidazole, and zinc nitrate is 1:0.20-0.30:0.25-0.35:0.25-0.50.

[0015] Furthermore, the diameter of the two-dimensional porous graphene selected in S1 is 15-25 mm.

[0016] Furthermore, the zinc nitrate aqueous solution described in S2 is prepared by mixing 0.2–0.3 g of zinc nitrate with 1–3 mL of deionized water.

[0017] The 2-methylimidazole aqueous solution was prepared by mixing 0.20-0.30 g of 2-methylimidazole with 8-10 mL of deionized water.

[0018] The benzodimethylimidazol aqueous solution was prepared by mixing 0.25-0.35 benzodimethylimidazol with 8-10 mL of deionized water.

[0019] Furthermore, the drying described in S2 is vacuum drying, and the vacuum drying conditions are: vacuum degree -0.05 to -0.08 MPa, processing temperature 40 to 60°C, and processing time 1 to 3 hours.

[0020] This invention also provides a graphene-assisted ZIF-8 membrane material prepared according to the above-described method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas, wherein the pore size of the graphene-assisted ZIF-8 membrane material is approximately [missing information].

[0021] The present invention also provides the application of the graphene-assisted ZIF-8 membrane material prepared according to the above-described method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas in the extraction of helium from natural gas.

[0022] The present invention has at least the following beneficial effects:

[0023] 1. This invention is applied to the separation of helium from natural gas. The two-dimensional porous graphene substrate in this material has abundant functional groups on its surface, which can effectively capture and fix metal ions, ensuring the bonding strength between the mixed ZIF-8 and the substrate. The pore size of this novel graphene-assisted mixed ZIF-8 membrane is approximately [missing information]. Larger than the dynamic diameter of a helium molecule It can selectively pass through helium molecules, exhibiting good helium separation selectivity. This material has certain channels and specific surface area, which can further improve the permeability of helium molecules. Therefore, this material can efficiently and quickly separate helium from natural gas.

[0024] 2. The novel graphene-assisted mixed ZIF-8 membrane material prepared by this invention can effectively extract helium from natural gas. This material has good stability and excellent separation selectivity and permeability for helium in He / N2 and He / CH4. The synthesis method of this material is simple, feasible, and low in cost, thus enabling large-scale production. Therefore, this material is a highly promising, safe, and reliable material for preparing helium extraction membrane materials from natural gas and separating helium from methane.

[0025] 3. This invention constructs a graphene-MOF nanocomposite material by grafting functional groups of aromatic carboxylic acid derivatives onto the activated surface of a two-dimensional porous graphene substrate, and by forming MOF structures on the graphene surface through the self-assembly of the functional groups of aromatic carboxylic acid derivatives and metal ions. This ensures the bonding strength between the mixed ZIF-8 and the substrate and improves the stability of the composite material. Attached Figure Description

[0026] Figure 1 X-ray powder diffraction pattern of a ZIF-8 membrane mixed in an embodiment of a graphene-assisted MOF membrane material for helium extraction from natural gas according to the present invention.

[0027] Figure 2 Infrared spectrum of a ZIF-8 membrane mixed in an embodiment of a graphene-assisted MOF membrane material for helium extraction from natural gas according to the present invention;

[0028] Figure 3 The N2 adsorption curve of a mixed ZIF-8 membrane is shown in an example of a graphene-assisted MOF membrane material for helium extraction from natural gas according to the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Example 1

[0031] A method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas includes the following steps:

[0032] Graphene substrate preparation: 10g of two-dimensional porous graphene with a diameter of 15mm was selected as the substrate material, washed several times with deionized water and acetone, dried, and then calcined in air at 250℃ for 8h to enhance the activated surface of the porous graphene and increase the surface functional groups, thereby obtaining an activated graphene substrate.

[0033] Preparation of modified graphene substrate: 10g of activated graphene was weighed and added to 2kg of dichloromethane. The mixture was ultrasonically vibrated for 40min. Then, 100g of 4-dimethylaminopyridine, 10g of dicyclohexylcarbodiimide, and 30g of aromatic carboxylic acid derivative were added. The mixture was stirred in a water bath at a constant temperature of 60℃ under nitrogen protection for 12h. The supernatant was removed, the substrate was washed, and then soaked in sodium hypochlorite solution. After washing, the substrate was filtered and freeze-dried to obtain the modified graphene substrate.

[0034] Preparation of solutions: Dissolve 2g of zinc nitrate in 10mL of deionized water to prepare zinc nitrate aqueous solution; dissolve 2g of 2-methylimidazole in 80mL of deionized water to prepare 2-methylimidazole aqueous solution; dissolve 2.5g of benzodimethylimidazole in 80mL of deionized water to prepare benzodimethylimidazole aqueous solution.

[0035] Preparation of graphene-assisted ZIF-8 membrane: The modified graphene substrate was placed in a reaction vessel, and the above-mentioned zinc nitrate aqueous solution was added. The mixture was heated at 100°C for 5 hours. Then, the above-mentioned 2-methylimidazole aqueous solution and benzodimethylimidazole aqueous solution were added, and the mixture was stirred for 12 hours. After washing with methanol, the mixture was vacuum dried at -0.05 MPa and 40°C for 1 hour to obtain the graphene-assisted ZIF-8 membrane material.

[0036] Example 2

[0037] A method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas includes the following steps:

[0038] Graphene substrate preparation: 10g of two-dimensional porous graphene with a diameter of 20mm was selected as the substrate material, washed several times with deionized water and acetone, dried, and then calcined in air at 300℃ for 12h to enhance the activated surface of the porous graphene and increase the surface functional groups, thereby obtaining an activated graphene substrate.

[0039] Preparation of modified graphene substrate: 10g of activated graphene was weighed and added to 2kg of dichloromethane. The mixture was ultrasonically vibrated for 40min. Then, 100g of 4-dimethylaminopyridine, 10g of dicyclohexylcarbodiimide, and 30g of aromatic carboxylic acid derivative were added. The mixture was stirred in a water bath at a constant temperature of 60℃ under nitrogen protection for 12h. The supernatant was removed, the substrate was washed, and then soaked in sodium hypochlorite solution. After washing, the substrate was filtered and freeze-dried to obtain the modified graphene substrate.

[0040] Preparation of solutions: Dissolve 2.5g of zinc nitrate in 20mL of deionized water to prepare zinc nitrate aqueous solution; dissolve 2.5g of 2-methylimidazole in 90mL of deionized water to prepare 2-methylimidazole aqueous solution; dissolve 3-benzodimethylimidazole in 90mL of deionized water to prepare benzodimethylimidazole aqueous solution.

[0041] Preparation of graphene-assisted ZIF-8 membrane: The modified graphene substrate was placed in a reaction vessel, and the above-mentioned zinc nitrate aqueous solution was added. The mixture was heated at 120°C for 8 hours. Then, the above-mentioned 2-methylimidazole aqueous solution and benzodimethylimidazole aqueous solution were added, and the mixture was stirred for another 20 hours. After washing with methanol, the mixture was vacuum dried at -0.06 MPa and 50°C for 2 hours to obtain the graphene-assisted ZIF-8 membrane material.

[0042] Example 3

[0043] A method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas includes the following steps:

[0044] Preparation of graphene substrate: 10g of two-dimensional porous graphene with a diameter of 25mm was selected as the substrate material, washed several times with deionized water and acetone, dried, and then calcined in air at 350℃ for 8-16h to enhance the activated surface of the porous graphene and increase the surface functional groups, thereby obtaining an activated graphene substrate.

[0045] Preparation of modified graphene substrate: 10g of activated graphene was weighed and added to 2kg of dichloromethane. The mixture was ultrasonically vibrated for 40min. Then, 100g of 4-dimethylaminopyridine, 10g of dicyclohexylcarbodiimide, and 30g of aromatic carboxylic acid derivative were added. The mixture was stirred in a water bath at a constant temperature of 60℃ under nitrogen protection for 12h. The supernatant was removed, the substrate was washed, and then soaked in sodium hypochlorite solution. After washing, the substrate was filtered and freeze-dried to obtain the modified graphene substrate.

[0046] Preparation of solutions: Dissolve 3g of zinc nitrate in 30mL of deionized water to prepare zinc nitrate aqueous solution; dissolve 3g of 2-methylimidazole in 100mL of deionized water to prepare 2-methylimidazole aqueous solution; dissolve 3,5-benzodimethylimidazole in 100mL of deionized water to prepare benzodimethylimidazole aqueous solution.

[0047] Preparation of graphene-assisted ZIF-8 membrane: The modified graphene substrate was placed in a reaction vessel, and the above-mentioned zinc nitrate aqueous solution was added. The mixture was heated at 140°C for 12 hours. Then, the above-mentioned 2-methylimidazole aqueous solution and benzodimethylimidazole aqueous solution were added, and the mixture was stirred for another 24 hours. After washing with methanol, the mixture was vacuum dried at -0.08 MPa and 60°C for 3 hours to obtain the graphene-assisted ZIF-8 membrane material.

[0048] The MXene-assisted ZIF-67 film prepared in Example 2 was tested, and its X-ray powder diffraction pattern and infrared spectrum are shown below. Figure 1 , Figure 2 As shown.

[0049] The nitrogen adsorption performance of the product obtained in Example 2 was tested using a Micromeritics ASAP 2020 instrument. The nitrogen adsorption-desorption curves of the sample synthesized in Example 2 at 77 K were measured at 298 K, as shown below. Figure 3 As shown.

[0050] This invention is applied to the separation of helium from natural gas. In this material, the functional groups of aromatic carboxylic acid derivatives on the activated surface of a two-dimensional porous graphene substrate are self-assembled with metal ions to form a MOF structure on the graphene surface, thereby constructing a graphene-MOF nanocomposite material. This ensures the bonding strength between the mixed ZIF-8 and the substrate. The pore size of this novel graphene-assisted mixed ZIF-8 film is approximately [missing information - likely a number]. Larger than the dynamic diameter of a helium molecule However, it can still selectively allow helium molecules to pass through, exhibiting good helium separation selectivity. This material possesses certain pore size and specific surface area, which can further improve the permeability to helium molecules. Therefore, this material can efficiently and rapidly separate helium from natural gas. Graphene-assisted mixed ZIF-8 membrane gas separation performance test:

[0051] The graphene-assisted ZIF-8 membrane materials prepared in Examples 1 to 3 were placed in a gas permeation measurement device system to determine the selectivity and permeability of a single gas and a gas mixture, and to calculate the selectivity of A for B under Knudsen diffusion conditions for gases A and B.

[0052] In the case of Sen diffusion, the selectivity of A for B.

[0053] Table 1. Permeation rates of four single-component gases via MXene-assisted ZIF-67 membrane (0.1 MPa pressure drop, room temperature)

[0054]

[0055] Analysis of the test data in Table 1 shows that the He permeability of the graphene-assisted ZIF-8 membrane is higher than that of CO. 2、 The N2 and CH4 content is more than 14 times higher, which is superior to the MOF membranes currently reported for helium separation. It has shown great potential for application in the field of gas separation, i.e., the recovery of helium from natural gas.

[0056] Table 2. Selectivity of MOF separation membranes at room temperature (Si) of the present invention and published literature. permeance ) and penetration rate (P He) Comparison

[0057]

[0058] For comparison, the permeation rates of helium and the ideal selectivity of helium for methane, hydrogen, and carbon dioxide, as reported in published literature, are also listed in Table 2. The comparison of the test data in Table 2 shows that the graphene-assisted mixed ZIF-8 membrane exhibits selectivity greater than 14 for He / N2 and He / CH4, a selectivity greater than 7 for He / CO2, and a He permeability greater than 7.6 × 10⁻⁶. -6 mol / m 2 The permeability of sPa and He is more than 14 times higher than that of N2 and CH4. This performance is superior to that of MOF membranes currently reported for helium separation, and it shows great potential for application in the field of gas separation, i.e., the recovery of helium from natural gas.

[0059] The novel graphene-assisted mixed ZIF-8 membrane material prepared by this invention can effectively extract helium from natural gas. This material has good stability and excellent separation selectivity and permeability for helium in He / N2 and He / CH4. The synthesis method of this material is simple, feasible, and low in cost, thus enabling large-scale mass production. Therefore, this material is a highly promising, safe, and reliable material for preparing helium extraction membrane materials from natural gas and separating helium from methane.

[0060] Membrane separation of gases has very low energy costs (because it does not require phase change), smaller equipment footprint and lower mechanical complexity. A membrane-based method can modify existing processing infrastructure to separate helium from natural gas resources. For the extraction of helium from natural gas using membrane separation technology, the preparation and screening of membrane materials is an important research direction for membrane separation technology due to the influence of permeate flux.

[0061] Metal-organic frameworks (MOFs), as a novel family of microporous materials, are formed by transition metal networks linked by organic ligands. They possess a variety of tunable ordered structures, functional groups, pore sizes, and porosities, thus offering potential applications in gas separation and storage, catalysis, and membranes. With significant progress in the development of microporous and mesoporous inorganic membranes for gas-liquid separation, MOFs have recently attracted attention in the materials and membrane fields as thin films (on dense substrates) or membranes (on porous substrates). Graphene, a novel two-dimensional material, possesses abundant hydrophilic functional groups on its surface. Through graft modification, the activated surface of a two-dimensional porous graphene substrate can acquire functional groups of aromatic carboxylic acid derivatives. These aromatic carboxylic acid derivative functional groups can self-assemble with metal ions to form MOF structures on the graphene surface, thereby constructing graphene-MOF nanocomposites that ensure the bonding strength between the mixed ZIF-8 and the substrate.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas, characterized in that, Includes the following steps: S1. Two-dimensional porous graphene is selected as the substrate material. It is washed several times with deionized water and acetone, dried, and then calcined in air at 250-350℃ for 8-16 hours to enhance the activated surface of porous graphene and increase surface functional groups, thereby obtaining an activated graphene substrate. S2. Aromatic carboxylic acid derivative functional groups are grafted onto the surface of an activated graphene substrate to obtain a modified graphene substrate. The structural formulas of the aromatic carboxylic acid derivatives are as follows: R1, R2, and R3 may be the same or different, and R1, R2, and R3 may be independently selected from H, CH3, and OCH3; The method for grafting aromatic carboxylic acid derivative functional groups onto the surface of an activated graphene substrate is as follows: The activated graphene substrate is weighed and added to dichloromethane. The substrate is ultrasonically vibrated for 40 min. Then, 4-dimethylaminopyridine, dicyclohexylcarbodiimide, and the aromatic carboxylic acid derivative are added separately. The mixture is stirred and reacted for 12 h in a water bath at a constant temperature of 60°C under nitrogen protection. The supernatant is removed, the substrate is washed, then soaked in sodium hypochlorite solution, washed again, filtered, and freeze-dried to obtain the modified graphene substrate. The mass ratio of the activated graphene substrate, dichloromethane, 4-dimethylaminopyridine, dicyclohexylcarbodiimide, and aromatic carboxylic acid derivative is 1:200:10:1:

3. S3. The modified graphene substrate obtained in S2 is placed in a reaction vessel, and zinc nitrate aqueous solution is added. The mixture is heated at 100-140℃ for 5-12 hours. Then, 2-methylimidazole aqueous solution and benzodimethylimidazole aqueous solution are added, and stirring is continued for 12-24 hours. This allows the functional groups of aromatic carboxylic acid derivatives on the activated surface of the two-dimensional porous graphene substrate to form MOF structures with metal ions in a self-assembly form on the graphene surface, thereby constructing a graphene-MOF nanocomposite material. This ensures the bonding strength between the mixed ZIF-8 and the substrate. After washing with methanol and drying, graphene-assisted ZIF-8 membrane material is finally obtained. The mass ratio of the two-dimensional porous graphene, 2-methylimidazole, benzodimethylimidazole, and zinc nitrate is 1:0.20-0.30:0.25-0.35:0.25-0.

50. The zinc nitrate aqueous solution described in S3 is prepared by mixing 0.2-0.3g of zinc nitrate with 1-3mL of deionized water. The 2-methylimidazole aqueous solution was prepared by mixing 0.20-0.30 g of 2-methylimidazole with 8-10 mL of deionized water. The benzodimethylimidazol aqueous solution was prepared by mixing 0.25-0.35 mL of benzodimethylimidazol with 8-10 mL of deionized water. The graphene-assisted ZIF-8 membrane material has a pore size of 2.8-3.6 Å.

2. The graphene-assisted ZIF-8 membrane material prepared by the method for preparing a graphene-assisted MOF membrane material for helium extraction from natural gas as described in claim 1.

3. The application of the graphene-assisted ZIF-8 membrane material prepared by the method for preparing graphene-assisted MOF membrane material for helium extraction from natural gas as described in claim 1 in the extraction of helium from natural gas.

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