Lithium-doped metal organic framework hydrogen separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a lithium-doped metal organic framework hydrogen separation membrane as well as a preparation method and application thereof, and belongs to the technical field of membrane separation. The preparation method of the hydrogen separation membrane containing the lithium-doped metal organic framework comprises the following steps: dissolving a zinc salt, a lithium salt and an organic ligand in an organic solvent I, and carrying out ultrasonic treatment, hydrothermal reaction and post-treatment to obtain the lithium-doped metal organic framework; mixing with a polybenzimidazole solution, stirring, and carrying out ultrasonic dispersion to obtain a uniform membrane casting solution; and carrying out film casting and drying. The gas separation membrane is prepared by mixing the lithium-doped metal organic framework and the polybenzimidazole, the lithium-doped metal organic framework is prepared by partially replacing zinc ions with lithium ions, and strong polar sites are introduced while the microporous structure of the metal organic framework is regulated, so that the H2 adsorption capacity is enhanced; the trade-off effect of permeability and selectivity in a polymer material is effectively broken, and meanwhile, the permeability and selectivity of hydrogen can be improved.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a lithium-doped metal-organic framework hydrogen separation membrane, its preparation method, and its application. Background Technology

[0002] Hydrogen, as one of the cleanest energy carriers, is strongly supporting the green economic transformation and driving the transition to a carbon-neutral environment. Common hydrogen production methods include coal gasification, steam reforming, methane pyrolysis, and water electrolysis. Different hydrogen production methods produce mixtures of hydrogen and other gases, with specific products varying depending on the method, typically including carbon dioxide, nitrogen, and methane. While traditional industrial technologies such as cryogenic distillation and pressure swing adsorption can separate hydrogen from other gas molecules, they generally suffer from high energy consumption and complex operation. Compared to traditional gas separation technologies, membrane separation technology, due to its advantages of low energy consumption, modularity, ease of scaling up or down, and ease of operation, has broad application prospects in natural gas purification, carbon dioxide capture, and hydrogen recovery.

[0003] Hybrid matrix membranes are hybrid membrane materials formed by dispersing microporous fillers within a polymer matrix. They combine the advantages of both microporous fillers and polymers, and their preparation methods are relatively simple and cost-effective. Commonly used microporous fillers include metal-organic frameworks (MOFs), zeolites, and coordination nanocages. MOFs are three-dimensional porous crystalline materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. Due to their high specific surface area, tunable pore size, and functionalized sites, they are considered ideal fillers for hybrid matrix membranes. MOF-based hybrid matrix membranes are widely used in gas separation research. However, most MOFs exhibit weak selective adsorption / diffusion capabilities for hydrogen and poor interfacial compatibility with the polymer matrix, easily forming non-selective defects, resulting in generally low hydrogen separation performance of existing hybrid matrix membranes. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a lithium-doped metal-organic framework (MOF) hydrogen separation membrane, its preparation method, and its applications. This invention utilizes a mixture of lithium-doped MOF and polybenzimidazole to prepare a gas separation membrane. The lithium-doped MOF is prepared by partially replacing zinc ions with lithium ions. This process modulates the microporous structure of the MOF while introducing strongly polar sites, enhancing the H2 gas adsorption capacity. This effectively overcomes the trade-off between permeability and selectivity in polymer materials, simultaneously improving both hydrogen permeability and selectivity.

[0005] The technical solution of the present invention is as follows: The first aspect of this invention protects a method for preparing a lithium-doped metal-organic framework hydrogen separation membrane, the method comprising the following steps: S1: Dissolve zinc salt, lithium salt and organic ligand in organic solvent I, sonicate, hydrothermal reaction, and after the reaction is completed, post-processing is performed to obtain lithium-doped metal-organic framework; S2: Add the lithium-doped metal-organic framework prepared in step S1 to the polybenzimidazole solution, stir and ultrasonically disperse to obtain a uniform casting solution; S3: Cast the casting solution from step S2 into a film, dry it, and obtain a hydrogen separation membrane containing a lithium-doped metal-organic framework.

[0006] Preferably, in step S1, the zinc salt includes at least one of zinc nitrate, zinc acetate, zinc chloride, and zinc perchlorate; The lithium salt includes at least one of lithium nitrate, lithium acetate, lithium chloride, and lithium perchlorate; The organic ligand includes at least one of terephthalic acid, 2-nitroterephthalic acid, biphenyl phthalic acid, and 2-hydroxyterephthalic acid; The organic solvent I includes at least one of N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone.

[0007] Preferably, in step S1, the molar ratio of the zinc salt, lithium salt, and organic ligand is 1:(0.5~2):2.

[0008] This invention prepares lithium-doped metal-organic frameworks by partially replacing zinc ions with lithium ions, thereby controlling the microporous structure of the metal-organic framework and introducing strongly polar sites to enhance the H2 gas adsorption capacity. The lithium-doped metal-organic framework can also control the interchain spacing and free volume of polybenzimidazole, thus achieving a simultaneous improvement in hydrogen permeability and selectivity. If the lithium salt content is too low, it cannot achieve good control; however, if the lithium salt content is too high, it will cause framework charge imbalance, decreased crystallinity, micropore collapse and the generation of impurity phases, which will reduce the H2 adsorption-separation performance.

[0009] The molar volume ratio of the organic ligand to the organic solvent I is 3~7.5 mmol: 20 mL.

[0010] Preferably, in step S1, the temperature of the ultrasound is 20~40℃ and the time is 15~25min; The hydrothermal reaction is carried out at a temperature of 120~150℃ for a time of 36~48h. The post-processing includes: cooling the reaction product, filtering the product, washing, and drying. The drying temperature is 60~90℃, and the time is 8~12h.

[0011] Preferably, in step S2, the polybenzimidazole solution is obtained by mixing polybenzimidazole with organic solvent II; Preferably, in step S2, the polybenzimidazole includes at least one of aryl ether polybenzimidazole and aromatic polybenzimidazole; The polybenzimidazole has a strength of 40,000 to 100,000 Daltons.

[0012] Preferably, in step S2, the mass ratio of the polybenzimidazole to the organic solvent II is 8.5~9.75:90.

[0013] The organic solvent II includes at least one of N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone.

[0014] Preferably, in step S2, the mass fraction of polybenzimidazole in the casting solution is 8.5~9.75%, and the mass fraction of lithium-doped metal-organic framework is 0.25~1.5%.

[0015] If the polybenzimidazole content in the casting solution is too high, the viscosity of the casting solution will be too high, making it difficult to process. If it is too low, the support will be insufficient, making it difficult to form a complete film structure. Similarly, lithium doping with metal-organic frameworks can adjust the microporous structure and the inter-chain spacing and free volume of polybenzimidazole. When there is too little lithium doping with metal-organic frameworks, it is not possible to effectively control the porosity and polymer inter-chain spacing. However, if the content of lithium doping with metal-organic frameworks is too high, it will exacerbate the agglomeration of fillers, which will easily form stress concentration points after film formation, and thus cause cracks or interface peeling.

[0016] Preferably, in step S3, the specific method of drying is as follows: the casting solution is dried at 50~90℃ for 12~24h, and then the temperature is raised to 120~150℃ and dried for 12~24h.

[0017] The second aspect of this invention protects a lithium-doped metal-organic framework hydrogen separation membrane prepared by the preparation method described in the first aspect above.

[0018] The third aspect of this invention protects the application of a hydrogen separation membrane with a lithium-doped metal-organic framework prepared by the preparation method described in the first aspect above, or the hydrogen separation membrane with a lithium-doped metal-organic framework described in the second aspect above, wherein the hydrogen separation membrane with a lithium-doped metal-organic framework is used for separating hydrogen from other gases. The other gases include at least one of carbon dioxide, methane, and nitrogen.

[0019] The beneficial technical effects of this invention are as follows: This invention utilizes a mixture of lithium-doped metal-organic frameworks (MOFs) and polybenzimidazole to prepare a gas separation membrane. Specifically, the lithium-doped MOF is prepared by partially replacing zinc ions with lithium ions, thereby controlling the microporous structure of the MOF and introducing strongly polar sites to enhance H2 gas adsorption capacity. Furthermore, the lithium-doped MOF can regulate the interchain spacing and free volume of the polybenzimidazole, resulting in a separation membrane that simultaneously improves hydrogen permeability and selectivity.

[0020] The method for preparing the lithium-doped metal-organic framework hydrogen separation membrane of the present invention is simple, requires no post-processing, can be continuously produced, and is suitable for various hydrogen recovery scenarios such as hydrogen / carbon dioxide, hydrogen / nitrogen, and hydrogen / methane. Attached Figure Description

[0021] Figure 1 The infrared spectra of the films prepared in Example 1 and Comparative Example 1 of this invention are shown.

[0022] Figure 2 The images show the X-ray diffraction patterns of the films prepared in Example 1 and Comparative Example 1 of this invention.

[0023] Figure 3 The XRD patterns are of the metal-organic framework MOF-5 prepared in step (1) of Comparative Example 2 and the lithium-doped MOF-5 prepared in step (1) of Example 1. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the embodiments.

[0025] To address the problems of existing gas separation membranes, this invention provides a lithium-doped metal-organic framework hydrogen separation membrane, its preparation method, and its applications.

[0026] This invention prepares lithium-doped metal-organic frameworks (MOFs) by partially replacing zinc ions with lithium ions. By controlling the microporous structure of the MOFs and introducing strongly polar sites, the hydrogen adsorption capacity is enhanced. Hydrogen separation membranes are prepared by incorporating the lithium-doped MOFs into polybenzimidazole. By utilizing the microporous structure and gas adsorption properties of the lithium-doped MOFs and their ability to regulate the polymer chain structure, both hydrogen permeability and selectivity can be improved.

[0027] The present invention will be further described below through examples and other means.

[0028] Example 1 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 1.5 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0029] (2) 0.975g of aryl ether polybenzimidazole was dissolved in 9.0g of N,N'-dimethylacetamide organic solvent to form a homogeneous solution. Then, 0.025g of lithium-doped metal-organic framework was added, stirred and ultrasonically dispersed to obtain a homogeneous casting solution. The aryl ether polybenzimidazole was poly[2,2'-(4,4'-oxybis(1,4-phenylene))-5,5'-bibenzimidazole] with a molecular weight of 40,000 Daltons, purchased from Zhongke Energy Materials Technology (Dalian) Co., Ltd.

[0030] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0031] Example 2 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 1.5 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0032] (2) Dissolve 0.950g of aryl ether polybenzimidazole in 9.0g of N,N-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.050g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0033] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0034] Example 3 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 1.5 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0035] (2) Dissolve 0.925g of aryl ether polybenzimidazole in 9.0g of N,N-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.075g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0036] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0037] Example 4 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 1.5 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0038] (2) Dissolve 0.90g of aryl ether polybenzimidazole in 9.0g of N,N-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.10g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0039] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0040] Example 5 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 1.5 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0041] (2) Dissolve 0.850g of aryl ether polybenzimidazole in 9.0g of N,N-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.150g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0042] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0043] Example 6 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) 1.5 mmol zinc acetate, 1.5 mmol lithium acetate and 3.0 mmol 2-nitroterephthalic acid were dissolved in 20 mL N,N′-dimethylformamide. After sonication at 20 °C for 20 minutes, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and reacted at 130 °C for 36 hours. After cooling and filtering the crystal product and washing it with ethanol, the product was dried in a vacuum oven at 90 °C for 8 hours to obtain a lithium-doped metal-organic framework.

[0044] (2) Dissolve 0.90g of aryl ether polybenzimidazole in 9.0g of N,N'-dimethylformamide organic solvent to form a homogeneous solution, then add 0.10g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0045] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 60°C for 20 hours, it is vacuum dried at 120°C for 20 hours to obtain a hydrogen separation membrane.

[0046] Example 7 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc chloride, 1.5 mmol lithium chloride and 3.0 mmol biphenyl dicarboxylic acid in 20 mL N-methylpyrrolidone, sonicate at 40 °C for 25 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 150 °C for 40 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 80 °C for 10 hours to obtain lithium-doped metal-organic framework.

[0047] (2) Dissolve 0.850g of aryl ether polybenzimidazole in 9.0g of N-methylpyrrolidone organic solvent to form a homogeneous solution, then add 0.150g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution, wherein the aryl ether polybenzimidazole is the same as in Example 1.

[0048] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 50°C for 12 hours, it is vacuum dried at 130°C for 12 hours to obtain a hydrogen separation membrane.

[0049] Comparative Example 1 The preparation method of the polybenzimidazole hydrogen separation membrane includes the following steps: (1) Dissolve 3.0 g of aryl ether polybenzimidazole in 24.0 g of N,N'-dimethylacetamide and dissolve at 90 °C for 24 h to form a homogeneous solution; stir and ultrasonically disperse to obtain a homogeneous casting solution. The aryl ether polybenzimidazole is the same as in Example 1.

[0050] (2) After degassing under vacuum, the membrane is cast and dried at 90°C for 24 hours, and then vacuum dried at 150°C for 24 hours to obtain a polybenzimidazole hydrogen separation membrane.

[0051] Comparative Example 2 A metal-organic framework hydrogen separation membrane is prepared by the following steps: (1) Dissolve 1.5 mmol zinc nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain a metal-organic framework.

[0052] (2) Dissolve 0.975 g of aryl ether polybenzimidazole (same as in Example 1) in 9.0 g of N,N'-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.025 g of metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution.

[0053] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0054] Comparative Example 3 A lithium-doped metal-organic framework hydrogen separation membrane, the preparation method of which includes the following steps: (1) Dissolve 1.5 mmol zinc nitrate, 0.75 mmol lithium nitrate and 3.0 mmol terephthalic acid in 20 mL N,N'-dimethylacetamide, sonicate at 25 °C for 15 minutes, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, react at 120 °C for 48 hours, cool and filter the crystal product and wash with ethanol, then dry in a vacuum oven at 60 °C for 12 hours to obtain lithium-doped metal-organic framework.

[0055] (2) Dissolve 0.99g of aryl ether polybenzimidazole (same as in Example 1) in 9.0g of N,N'-dimethylacetamide organic solvent to form a homogeneous solution, then add 0.01g of lithium-doped metal-organic framework, stir and ultrasonically disperse to obtain a homogeneous casting solution.

[0056] (3) After vacuum degassing the casting solution, it is cast onto a glass plate to form a film. After drying at 90°C for 24 hours, it is vacuum dried at 150°C for 24 hours to obtain a hydrogen separation membrane.

[0057] Test case (1) Membrane structure characterization Figure 1 This is a comparison of the infrared spectra of the lithium-doped metal-organic framework hydrogen separation membrane of Example 1 and the polybenzimidazole membrane of Comparative Example 1. Compared with the pure polybenzimidazole membrane, the C=N stretching vibration peak of the imidazole ring in the lithium-ion coordinated polybenzimidazole membrane is significantly enhanced and shifted to higher wavenumbers; the CN stretching vibration peak of the imidazole ring and the COC stretching vibration peak of the aromatic ether bond both show a blue shift. These phenomena confirm that the lithium-doped metal-organic framework has been successfully introduced into the polybenzimidazole membrane.

[0058] Figure 2 The X-ray diffraction (XRD) patterns of the lithium-doped metal-organic framework hydrogen separation membrane of Example 1 and the polybenzimidazole membrane of Comparative Example 1 are shown. The results show that the lithium-doped metal-organic framework hydrogen separation membrane exhibits obvious strong crystalline peaks, which are consistent with the XRD pattern characteristics of pure lithium-doped metal-organic framework particles, confirming that the lithium-doped metal-organic framework has been successfully incorporated into the polybenzimidazole membrane matrix.

[0059] Figure 3X-ray diffraction (XRD) patterns of the metal-organic framework MOF-5 prepared in step (1) of Comparative Example 2 and the lithium-doped MOF-5 (Li-MOF-5) prepared in step (1) of Example 1 are shown. The results indicate that the diffraction peak intensity is significantly enhanced when lithium ions are inserted into the MOF-5 cluster. This confirms that lithium-doped MOF-5 and undoped MOF-5 have the same cubic crystal structure, while the slight differences between the diffraction peaks indicate the formation of new crystal planes, attributed to the presence of the doping metal / metal sites. The experimental results demonstrate that lithium has been successfully doped into the metal-organic framework material.

[0060] (2) Gas performance determination The gas permeability (expressed as permeability coefficient P) and ideal selectivity α of the membranes prepared in the embodiments and comparative examples of the present invention were determined. i / j The specific method is as follows: The gas permeation test method is as follows: the gas separation membrane prepared in the examples or comparative examples is placed in a gas permeation cell, and the gas permeability of the membrane is measured using the constant volume pressure swing method. Under conditions of 35°C and 0.5 MPa, the gas permeability P and ideal selectivity α are determined using pure H2 and CO2. i / j .

[0061] The formula for calculating the gas permeability coefficient P is as follows: (1) In the formula: P Gas permeability coefficient ( ); Q For the gas to permeate from the beginning to t Cumulative osmosis at time (cm) 3 ); A The area of ​​the membrane (cm²) 2 ); l Film thickness (cm); ΔP t represents the pressure difference between the upstream and downstream sides (MPa); t represents the infiltration time (s).

[0062] Selective α i / j The calculation formula is shown below: (2) In the formula: α i / j This indicates the ideal selectivity of the membrane for gaseous components H2 and CO2; P i P represents the permeability coefficient (barrer) of H2. j This represents the permeability coefficient (barrer) of the gaseous component CO2.

[0063] The results are shown in Table 1.

[0064] Table 1. Gas separation performance tests of the membranes prepared in the examples and comparative examples.

[0065] As shown in Table 1, the lithium-ion-doped metal-organic framework hydrogen separation membrane prepared in the embodiments of the present invention exhibits higher H2 / CO2 selectivity compared to the separation membrane in the comparative example, thus achieving more efficient hydrogen separation, while also possessing a relatively high H2 permeability. Comparative Example 1, without the addition of a metal-organic framework, resulted in a membrane with low H2 / CO2 selectivity. Comparative Example 2, lacking the regulatory effect of lithium salt in its metal-organic framework, showed a significantly lower H2 / CO2 selectivity compared to the embodiments. Comparing Examples 1-5 and Comparative Example 3 reveals that when the lithium-doped organic framework content is too low or too high, both the H2 permeability and H2 / CO2 selectivity of the resulting membrane are affected. When the content is too low, the H2 / CO2 selectivity of the membrane decreases significantly, failing to meet the separation requirements.

[0066] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium-containing doped metal-organic framework hydrogen separation membrane, characterized in that, The method comprises the following steps: S1: Dissolve zinc salt, lithium salt and organic ligand in organic solvent I, after ultrasonic treatment, hydrothermal reaction, reaction is completed, post-processing, to obtain lithium doped metal organic framework; S2: Add lithium doped metal organic framework prepared in step S1 to polybenzimidazole solution, stir and ultrasonic dispersion to prepare uniform casting solution; S3: Cast the casting solution of step S2 into film, dry to obtain hydrogen separation membrane containing lithium doped metal organic framework.

2. The production method according to claim 1, characterized by, In step S1, the zinc salt includes at least one of zinc nitrate, zinc acetate, zinc chloride and zinc perchlorate; The lithium salt includes at least one of lithium nitrate, lithium acetate, lithium chloride and lithium perchlorate; The organic ligand includes at least one of terephthalic acid, 2-nitroterephthalic acid, diphenic acid and 2-hydroxyterephthalic acid; The organic solvent I includes at least one of N,N'-dimethylacetamide, N,N'-dimethylformamide and N-methylpyrrolidone.

3. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of zinc salt, lithium salt and organic ligand is 1:(0.5-2):2; The molar volume ratio of the organic ligand to the organic solvent I is 3-7.5 mmol:20 mL.

4. The method of claim 1, wherein, In step S1, the ultrasonic temperature is 20-40℃, and the time is 15-25 min; The temperature of the hydrothermal reaction is 120-150℃, and the time is 36-48 h; The post-processing includes cooling the reaction product, filtering the product, washing and drying; The drying temperature is 60-90℃, and the time is 8-12 h.

5. The preparation method according to claim 1, characterized in that, In step S2, the polybenzimidazole solution is obtained by mixing polybenzimidazole and organic solvent II; The polybenzimidazole includes at least one of aralkyl ether type polybenzimidazole and aromatic type polybenzimidazole; The polybenzimidazole is 40,000-100,000 Dalton.

6. The production method according to claim 5, wherein The mass ratio of the polybenzimidazole to the organic solvent II is 8.5-9.75:90; The organic solvent II includes at least one of N,N'-dimethylacetamide, N,N'-dimethylformamide and N-methylpyrrolidone.

7. The preparation method according to claim 1, characterized in that, In step S2, in the casting solution, the mass fraction of polybenzimidazole is 8.5-9.75%, and the mass fraction of lithium doped metal organic framework is 0.25-1.5%.

8. The method of claim 1, wherein, In step S3, the specific method of drying is: drying the casting solution at 50-90℃ for 12-24 h, then heating to 120-150℃, and drying for 12-24 h.

9. A hydrogen separation membrane containing lithium doped metal organic framework prepared by the preparation method of any one of claims 1-8.

10. A hydrogen separation membrane comprising a lithium-doped metal-organic framework prepared according to the method of any one of claims 1 to 8 or use of a hydrogen separation membrane comprising a lithium-doped metal-organic framework according to claim 9, characterized in that, The hydrogen separation membrane containing lithium doped metal organic framework is used for separating hydrogen from other gases; The other gases include at least one of carbon dioxide, methane and nitrogen.

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