A zeolite imidazolate skeleton polycrystalline membrane and preparation method thereof

Abstract

The present invention provides a zeolite imidazolate skeleton polycrystalline membrane and a preparation method thereof, comprising: S1: preparing a precursor solution containing metal ions and organic ligands, coating the precursor solution on a carrier, and heating and cooling the carrier coated with the precursor solution to prepare an amorphous film; the precursor solution includes a metal salt, an organic ligand, and a solvent; the zeolite imidazolate skeleton material is composed of a metal node, an organic ligand A, and an organic ligand B; the organic ligand A is imidazole-2-formaldehyde or 2-methylimidazole, and the organic ligand B is selected from 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, and 4-methylimidazole-5-formaldehyde; and the solvent is methanol. S2: treating the amorphous film with steam generated by heating a polar solvent to form a crystalline film; S3: activating the crystalline film with a volatile solvent; and the present invention prepares a continuous, dense, defect-free zeolite imidazolate skeleton membrane with strong carrier binding and gas separation performance.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, and in particular to a zeolite imidazolate skeleton polycrystalline membrane and a preparation method thereof. Background Art

[0002] Gas separation is a very challenging process in industrial production. Most industrial gas separations are typically accomplished through cryogenic distillation, an energy-intensive process that requires precise control of pressure and temperature. Reducing the energy consumption of gas separation has long been a major challenge facing industrial production. New membrane separation technology, with its advantages of no phase change, low energy consumption, high efficiency, low pollution, simple process, and easy operation, offers a new, energy-efficient approach to gas separation.

[0003] Metal-organic frameworks (MOFs) materials are composed of inorganic metal centers (metal ions or metal clusters) coordinated with organic ligands. They have rich topological structures and can achieve precise control of pore size and physicochemical properties. Their designability for specific separation systems is extremely attractive for constructing high-performance molecular sieve membranes. Zeolitic-imidazolate frameworks (ZIFs) materials are a class of MOFs materials with a zeolite skeleton structure. Compared with other types of MOFs materials, ZIFs materials have a pore size close to the kinetic diameter of gas molecules and exhibit higher thermal stability and hydrothermal stability. When converted into separation membranes, they can achieve high selectivity and high stability separation of gas mixtures.

[0004] However, conventional methods for preparing zeolitic imidazolate framework polycrystalline membranes currently suffer from complex operations and poor economic efficiency. Furthermore, the resulting zeolitic imidazolate framework polycrystalline membranes exhibit surface defects and weak binding to the support. In the development of ZIF membranes, the most commonly used synthesis methods include in situ synthesis and secondary growth. The in situ synthesis method involves directly placing the support into a reaction solution and hydrothermally synthesizing the ZIF membrane under a specific temperature and pressure. However, due to compatibility issues between organic ligands and inorganic supports, as well as the poor heterogeneous nucleation ability of ZIFs materials, the preparation of dense ZIF membranes is generally difficult. The secondary growth method involves pre-introducing a layer of uniformly dispersed ZIF seeds onto the support surface, followed by secondary growth of the seeds to synthesize ZIF membranes. While this secondary growth method can significantly improve the quality of synthesized ZIF membranes, its versatility and reproducibility require further improvement due to factors such as seed size, seed layer thickness, and binding strength between the seed layer and the support. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a zeolite imidazolate skeleton polycrystalline membrane to solve the problems of complex operation and poor economy of conventional preparation methods.

[0006] To solve the above problems, the present invention provides a method for preparing a zeolite imidazolate skeleton polycrystalline membrane, comprising the following steps:

[0007] S1: preparing a precursor solution containing metal ions and organic ligands, coating the precursor solution on a support, and heating and cooling the support coated with the precursor solution to prepare an amorphous thin film;

[0008] The precursor solution includes a metal salt, an organic ligand and a solvent; the zeolite imidazolate framework material is composed of a metal node, an organic ligand A and an organic ligand B;

[0009] The organic ligand A is imidazole-2-carboxaldehyde or 2-methylimidazole, and the organic ligand B is selected from one of 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, and 4-methylimidazole-5-carboxaldehyde; and the solvent is methanol.

[0010] In the technical solution of the present invention,

[0011] S2: treating the amorphous film obtained in step S1 with steam generated by heating a polar solvent to form a crystalline film;

[0012] S3: activating the obtained crystalline film using a volatile solvent to obtain a zeolite imidazolate skeleton polycrystalline film;

[0013] The volatile solvent is selected from one of methanol, ethanol, chloroform, acetone and acetonitrile.

[0014] In the reaction of step S1 above, the precursor solution can maintain a state without generating crystal particles. After being heated at a low temperature, a large amount of reaction raw materials are evenly covered on the surface of the carrier to form an amorphous layer.

[0015] In the above-mentioned preparation method of the present invention, the nucleation of the precursor liquid is suppressed by a single solvent system, the precursor liquid is coated on the carrier, and the carrier coated with the precursor liquid is heated and cooled to prepare an amorphous film layer without grains; the amorphous film layer obtained in the step S1 is treated with steam generated by a volatile solvent (polar solvent) to form a zeolite imidazolate skeleton polycrystalline film.

[0016] As a preferred solution, in step S1, the carrier is selected from α-Al2O3 carrier, γ-Al2O3 carrier, TiO2 carrier or polymer carrier.

[0017] As a preferred solution, in step S1, the metal node is zinc nitrate hexahydrate, zinc acetate dihydrate or cobalt acetate tetrahydrate.

[0018] As a preferred solution, in step S1, the precursor solution comprises, by mole, 1 part of Zn, 1-8 parts of organic ligand A, 0-8 parts of organic ligand B, and 50-500 parts of methanol.

[0019] As a preferred solution, in step S1, the precursor solution comprises, by mole fraction, 1 part of Zn, 1-4 parts of organic ligand A, 0-4 parts of organic ligand B, and 50-300 parts of methanol.

[0020] As a preferred solution, in step S1, the metal salt is zinc acetate dihydrate; the organic ligand A is imidazole-2-carboxaldehyde, and the ligand B is 2-methylimidazole.

[0021] As a preferred solution, in step S1, the heating temperature is 30-120° C. and the heating time is 5-60 min.

[0022] As a preferred solution, in step S2, the polar solvent is NN dimethylformamide or NN dimethylacetamide.

[0023] As a preferred solution, in step S2, the temperature of the steam treatment is 25-160° C., and the time is 4-36 hours.

[0024] As a preferred solution, in step S2, the temperature of the steam treatment process is 80-120° C. and the time is 8-12 hours.

[0025] As a preferred solution, in step S1, the carrier is selected from α-Al2O3 carrier, γ-Al2O3 carrier, TiO2 carrier or polymer carrier.

[0026] Another technical problem to be solved by the present invention is to provide a zeolite imidazolate skeleton polycrystalline membrane to solve the problems that the zeolite imidazolate skeleton polycrystalline membrane prepared by conventional methods has a non-dense surface and defects and poor binding ability with the carrier.

[0027] The zeolite imidazolate skeleton polycrystalline membrane prepared by the present invention can obtain zeolite imidazolate skeleton polycrystalline membranes with different pore sizes according to the types of added organic ligands and their different combinations. It is suitable for various gas separation systems and has the advantages of short synthesis cycle, simple process, wide controllable range of synthesis conditions, strong economy and low energy consumption.

[0028] In order to solve the above problems, the present invention provides a zeolite imidazolate skeleton polycrystalline membrane, which is prepared by the above preparation method.

[0029] Compared with the prior art, the present invention has the following improvements:

[0030] The present invention discloses a method for preparing a zeolite imidazolate skeleton polycrystalline membrane. In a traditional membrane-making method, the solvent and solute characteristics are utilized to effectively suppress the nucleation of the precursor solution, thereby avoiding the problems such as the film defects caused by the Odvals ripening effect. The viscosity of the precursor solution gradually increases during heating, which can effectively enhance the bonding force between the film layer and the carrier. Subsequently, mild steam treatment conditions are used to crystallize the amorphous layer, which not only reduces the use of organic solvents, but also effectively avoids the generation of film defects in the secondary treatment process. The preparation method of the present invention has the advantages of simple operation, high repeatability, wide versatility, energy saving and environmental protection, and successfully prepares a continuous, dense, defect-free zeolite imidazolate skeleton membrane with strong bonding force to the carrier. The membrane has good separation performance in various gas separation systems. In addition, the preparation method of the present invention can directly introduce two organic ligands to prepare the zeolite imidazolate skeleton polycrystalline membrane, which can effectively adjust the pore size of the porous material, thereby achieving the purpose of changing its effective separation pore size. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the X-ray diffraction characterization result diagram of the amorphous film A1 and the ZIF-90 (zeolite imidazolate framework) crystalline film M1;

[0032] Figure 2 This is the scanning electron microscope characterization result of the amorphous film A1;

[0033] Figure 3 This is the scanning electron microscope characterization result of ZIF-90 crystalline film M1;

[0034] Figure 4 This is the single-component gas permeation test result diagram of product M1;

[0035] Figure 5 It is product M 13 -M 15 X-ray diffraction characterization results. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing a zeolite imidazolate skeleton polycrystalline film, comprising the following steps:

[0038] S1: preparing a precursor solution containing metal ions and organic ligands, coating the precursor solution on a support, and heating and cooling the support coated with the precursor solution to prepare an amorphous thin film;

[0039] The precursor solution includes a metal salt, an organic ligand and a solvent; the zeolite imidazolate framework material is composed of a metal node, an organic ligand A and an organic ligand B;

[0040] The organic ligand A is imidazole-2-carboxaldehyde or 2-methylimidazole, and the organic ligand B is selected from one of 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, and 4-methylimidazole-5-carboxaldehyde; and the solvent is methanol.

[0041] S2: treating the amorphous film obtained in step S1 with steam generated by heating a polar solvent to form a crystalline film;

[0042] S3: activating the obtained crystalline film using a volatile solvent to obtain a zeolite imidazolate skeleton polycrystalline film;

[0043] As a preferred solution, in step S1, the carrier is selected from α-Al2O3 carrier, γ-Al2O3 carrier, TiO2 carrier or polymer carrier.

[0044] Preferably, in step S1, the metal node is zinc nitrate hexahydrate, zinc acetate dihydrate or cobalt acetate tetrahydrate.

[0045] As a preferred solution, in step S1, the precursor solution comprises, by mole, 1 part of Zn, 1-8 parts of organic ligand A, 0-8 parts of organic ligand B, and 50-500 parts of methanol.

[0046] As a preferred solution, in step S1, the precursor solution comprises, by mole fraction, 1 part of Zn, 1-4 parts of organic ligand A, 0-4 parts of organic ligand B, and 50-300 parts of methanol.

[0047] Preferably, in step S1, the metal salt is zinc acetate dihydrate; the organic ligand A is imidazole-2-carboxaldehyde, and the ligand B is 2-methylimidazole.

[0048] Preferably, in step S1, the heating temperature is 30-120° C. and the heating time is 5-60 min.

[0049] Preferably, in step S2, the polar solvent is N—N dimethylformamide or N—N dimethylacetamide.

[0050] Preferably, in step S2, the steam treatment is performed at a temperature of 25-160° C. for a time of 4-36 hours.

[0051] Preferably, in step S2, the temperature of the steam treatment process is 80-120° C., and the time is 8-12 hours.

[0052] The present invention provides a method for preparing a zeolite imidazolate framework polycrystalline membrane. A polar solvent is heated and vaporized, and then brought into contact with a support covered with an amorphous layer, thereby causing the amorphous layer to crystallize and form a ZIF-90 polycrystalline membrane. Specific polar solvents include, but are not limited to, N-dimethylformamide (DMF), N-dimethylacetamide (DMAc), and n-heptane. The heating temperature can be set between 80°C and 120°C, preferably 80°C, and the heating time is between 8 and 12 hours, preferably 12 hours.

[0053] The product after steam treatment and crystallization needs to be solvent activated. In a preferred embodiment of the present invention, methanol is used as an activator to activate the crystallized film. Unless otherwise specified, the activation described in this specification is understood in accordance with conventional knowledge, that is, the product to be activated is immersed in the activator for a period of time. As mentioned in this article, methanol activation refers to immersing the product to be activated in methanol for a specified time. The specified time is 0.5-6 hours, preferably 2 hours. Therefore, for the system of the present invention, a suitable activation time can achieve the purpose of removing residual polar solvents without destroying product performance.

[0054] Preferably, in step S1, the carrier is selected from α-Al2O3 carrier, γ-Al2O3 carrier, TiO2 carrier or polymer carrier.

[0055] The application of the above preferred technical means is helpful to establish a preferred embodiment of the method of the present invention. As an example, a more preferred specific embodiment of the method of the present invention is provided here: the zeolite imidazole organic framework precursor liquid is coated on the surface of the carrier, and then dried at a temperature of 50°C for 30 minutes. After naturally cooling to room temperature, the obtained product is steam-treated with N-dimethylformamide (DMF) vapor at a temperature of 80°C for 12 hours. After naturally cooling to room temperature, the obtained product is activated with methanol for 2 hours, and the ZIF-90 membrane product can be obtained after drying. The precursor solution is a mixed solution containing 1 part of Zn, 2 parts of imidazole-2-carboxaldehyde, and 124 parts of N,N-dimethylformamide according to a molar ratio.

[0056] The present invention also provides a zeolite imidazolate skeleton polycrystalline membrane prepared by the method.

[0057] The above technical solution of the present invention will be further described below with reference to the accompanying drawings, embodiments and specific data.

[0058] Unless otherwise specified, the separation selectivity of the two-component mixed gas mentioned in the present invention refers to the ratio of the permeabilities of the two gases; the gas permeability is the permeability of the gas per unit time (s) and unit pressure (Pa) per unit membrane area (m2). 2 The above two parameters in this specification are measured according to the method in J. Membr. Sci. (2010, 354, 48-54.).

[0059] Example 1:

[0060] Zeolite imidazolate skeleton polycrystalline membrane and preparation method thereof:

[0061] S1: Preparation of a zeolitic imidazolate framework (ZIF-90) precursor solution: Dissolve imidazole-2-carboxaldehyde in methanol to form a ligand solution. Slowly add zinc acetate dihydrate to the ligand solution and stir at 25°C until the solution becomes clear. The molar ratio of Zn, imidazole-2-carboxaldehyde, and methanol in the precursor solution is 1:2:124.

[0062] Amorphous films were prepared by immersing three identical α-Al2O3 alumina supports (pore size 70 nm) in the precursor solution for 30 seconds. The supports were then quickly transferred to a 50°C forced air oven and heated for 30 minutes, followed by natural cooling to room temperature. The resulting amorphous films were designated A1, A2, and A3.

[0063] S2: Preparation of a crystalline zeolitic imidazole organic framework membrane: A1, A2, and A3 membranes were suspended using a stand. 10 mL of DMF was added to the reactor, with the amorphous membrane layer facing the DMF to ensure direct vapor contact with the membrane surface. After sealing, the membrane was placed in an 80°C forced air oven and heated for 12 hours, followed by natural cooling to room temperature. The steam-treated ZIF-90 membrane was activated with methanol for 2 hours to remove any residual high-boiling-point DMF.

[0064] Characterization of ZIF-90 membranes: X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the amorphous films A1, A2, A3 and ZIF-90 crystalline films M1, M2, M3 prepared above, as well as the single-component gas permeability and the separation selectivity and permeability of two-component gases. The XRD characterization results of the amorphous film A1 and the ZIF-90 crystalline film M1 are shown in Figure 2. Figure 1 As shown; SEM characterization of amorphous film A1 is shown Figure 2 As shown; SEM characterization of ZIF-90 crystalline film M1 is as follows Figure 3 shown.

[0065] from Figure 1From the XRD characterization results of A1 and M1, it can be seen that the amorphous film A1 was successfully transformed into the ZIF-90 crystalline film M1 after DMF vapor treatment. Figure 2 ) and M1( Figure 3 ) showed that the morphology of the film layer changed significantly after treatment with DMF vapor, and the grains were cross-linked and intergrowth occurred after crystallization. Figure 4 The single-component gas permeabilities showed that the obtained ZIF-90 membrane had obvious retention regions between propylene / propane and n- / isobutane, which indicated that the obtained membrane was suitable for these two separation systems.

[0066] The permeability and separation selectivity of amorphous films A1, A2, A3 and ZIF-90 crystalline membranes M1, M2, M3 for equimolar propylene / propane mixtures are shown in Table 1.

[0067] Table 1

[0068]

[0069] The test results in Table 1 show that amorphous films A1, A2, and A3 all have extremely low propylene permeabilities and no propylene / propane separation selectivity. Crystalline ZIF-90 membranes M1, M2, and M3, obtained after treatment with the polar solvent DMF vapor, all exhibit excellent propylene / propane separation performance, with propylene / propane selectivities around 40. Furthermore, products M1-M3, synthesized from the same batch, exhibit high propylene / propane separation performance and excellent intra-batch reproducibility.

[0070] The results of n-butane / isobutane separation selectivity and permeability test for products M1-M3 are shown in Table 2. While this product has a certain separation selectivity for propylene / propane, it still has good n-butane / isobutane separation selectivity, and the synthesis repeatability between batches is good.

[0071] Table 2

[0072]

[0073] Example 2:

[0074] Preparation of ZIF-90 membranes at different steam treatment temperatures

[0075] Preparation of ZIF-90 membranes: A precursor solution was prepared according to the method in Example 1. Five identical alumina supports were immersed in the precursor solution for 30 seconds. The five supports coated with the ZIF-90 precursor solution were placed in a 50°C environment to dry. After cooling naturally to room temperature, the five prepared amorphous membranes were treated with DMF vapor according to the method in Example 1. They were heated at 40, 60, 80, 100, and 120°C for 12 hours and then cooled naturally to room temperature. The steam-treated ZIF-90 membranes were activated using methanol solvent for 2 hours. The resulting ZIF-90 polycrystalline membranes after drying were labeled M4, M5, M6, M7, and M8, respectively.

[0076] Characterization of ZIF-90 Membranes: Propylene / propane separation selectivity and permeability were measured for products M4 to M8. The results in Table 3 show that the temperature during polar steam treatment significantly affects the ZIF-90 membranes. The optimal performance of the ZIF-90 membrane was achieved at a steam treatment temperature of 80°C. Lower temperatures resulted in lower permeability due to incomplete crystallization of the precursor. At higher temperatures, the membranes lacked propylene / propane separation capability due to excessive crystallization and the thermal stability of the ligand.

[0077] Table 3

[0078]

[0079] Example 3:

[0080] Effect of polar solvent treatment time on ZIF-90 membrane

[0081] Preparation of ZIF-90 membrane: Prepare the precursor solution according to the method in Example 1, immerse four identical alumina supports in the precursor solution for 30 seconds, and place three supports coated with the ZIF-90 precursor solution in a 50°C environment to dry for 30 minutes. After naturally cooling to room temperature, the four prepared amorphous membranes were treated with DMF steam according to the method in Example 1, heated at 80°C for 6, 12, 24 and 36 hours, and then naturally cooled to room temperature. The steam-treated ZIF-90 membrane was activated with methanol solvent for 2 hours, and the ZIF-90 polycrystalline membranes obtained after drying were marked as M9, M 10 , M 11 , M 12 .

[0082] Characterization of ZIF-90 membrane: Product M9-M 12 The propylene / propane separation selectivity and permeability were determined. As shown in Table 4, when the DMF treatment time was 12 hours, the synthesized product M 10 It has high propylene / propane separation selectivity.

[0083] Table 4

[0084]

[0085] Example 4:

[0086] Preparation of ZIF-90 membranes by vapor treatment with solvents of different polarities

[0087] Preparation of ZIF-90 membrane: Prepare the precursor solution according to the method in Example 1, immerse three identical alumina supports in the precursor solution for 30 seconds respectively, and place the three supports coated with the ZIF-90 precursor solution in a 50°C environment to dry for 30 minutes. After naturally cooling to room temperature, the four prepared amorphous membranes were treated with polar solvent vapor according to the method in Example 1, wherein the polar solvents were NN dimethylacetamide, NN dimethylformamide and n-heptane respectively. After heating at 80°C for 12 hours, the membrane was naturally cooled to room temperature. The steam-treated ZIF-90 membrane was activated with methanol solvent for 2 hours, and the ZIF-90 polycrystalline membranes obtained after drying were marked as M 13 , M 14 , M 15 .

[0088] Characterization of ZIF-90 membranes, the above M 13 , M 14 , M 15 XRD characterization was performed respectively, and the product M 13 -M 15 The propylene / propane separation selectivity and permeability were measured.

[0089] from Figure 5 XRD characterization results show that all three polar solvents can cause the amorphous layer to undergo crystallization. Table 5 shows that the products after DMF and DMAc crystallization have a certain degree of propylene / propane selectivity and high flux. The product treated with N-dimethylformamide vapor exhibits the best propylene / propane separation selectivity; however, the membrane treated with n-heptane exhibits no propylene / propane separation selectivity.

[0090] Table 5

[0091]

[0092] Example 5:

[0093] Activation of zeolite imidazolate skeleton membranes by different solvents

[0094] Methanol, ethanol, chloroform, acetone, or acetonitrile

[0095] Preparation of ZIF-90 membrane: Prepare the precursor solution according to the method in Example 1, immerse 6 identical alumina supports in the precursor solution for 30 seconds, and place three supports coated with the ZIF-90 precursor solution in a 50°C environment to dry for 30 minutes. After cooling naturally to room temperature, the 6 prepared amorphous membranes were treated with DMF steam according to the method in Example 1, heated at 80°C for 12 hours, and then cooled naturally to room temperature. The steam-treated ZIF-90 membranes were marked as M 26 , M 27 , M 28 , M 29 , M 30 , M 31 . M 26 No. membrane is not activated, M 27 , M 28 , M 29 , M 30 , M 31 The membrane was soaked in 20 mL of methanol, ethanol, chloroform, acetone and acetonitrile for 2 hours respectively, and then dried to obtain the ZIF-90 polycrystalline membrane product.

[0096] Characterization of ZIF-90 membrane: 26 -M 31 The C3H6 / C3H8 separation selectivity and permeability were measured. The results in Table 8 show that the permeability and separation factor of the activated ZIF-90 membranes were improved to varying degrees, with the methanol-activated product having the highest C3H6 / C3H8 separation selectivity and permeability.

[0097] Table 6

[0098]

[0099] Example 6:

[0100] Preparation of Bi-ligand Zeolite Imidazolyl Skeleton Membrane (ZIF-8-90)

[0101] Preparation of a dual-ligand zeolite imidazolate skeleton membrane: Following the method described in Case 1, a fixed ratio of imidazole-2-carboxaldehyde and 2-methylimidazole was dissolved in methanol to form a ligand solution. Zinc acetate dihydrate was then slowly added to the ligand solution and stirred at 25°C for 30 minutes to obtain a precursor solution. The molar ratio of Zn, imidazole-2-carboxaldehyde, 2-methylimidazole, and methanol in the precursor solution was 1:X1:(2-X1):124.

[0102] Five identical alumina supports were immersed in the precursor solution for 30 seconds, and then the supports coated with the ZIF-8-90 precursor solution were placed in a 50°C environment to dry for 30 minutes. After cooling naturally to room temperature, the five prepared amorphous films were treated with DMF vapor according to the method of Example 1, heated at 80°C for 12 hours, and then cooled to room temperature. The synthesized polycrystalline film was activated with methanol for 2 hours to obtain product M. 16 , M 17 , M 18 , M 19 , M 20 .

[0103] Characterization of ZIF-8-90 membrane: Product M 16 , M 17 , M 18 , M 19 , M 20 The propylene / propane separation selectivity and permeability were measured. From the results in Table 6, it can be seen that as the imidazole-2-carboxaldehyde content increases, the propylene permeability gradually increases, while the propylene / propane separation selectivity decreases.

[0104] Table 7

[0105]

[0106] Example 7:

[0107] Preparation of dual-ligand zeolite imidazolate skeleton membrane (ZIF-8-7):

[0108] Preparation of a dual-ligand zeolite imidazolate skeleton membrane: Following the method described in Case 1, a fixed ratio of 2-methylimidazole and benzimidazole was dissolved in methanol to form a ligand solution. Zinc acetate dihydrate was then slowly added to the ligand solution and stirred at 25°C for 30 minutes to obtain a precursor solution. The molar ratio of Zn, 2-methylimidazole, benzimidazole, and methanol in the precursor solution was 1:Y1:(2-Y1):124.

[0109] Five identical alumina supports were immersed in the precursor solution for 30 seconds, and then the supports coated with the ZIF-8-7 precursor solution were placed in a 50°C environment to dry for 30 minutes. After cooling naturally to room temperature, the five prepared amorphous films were treated with DMF vapor according to the method of Example 1, heated at 80°C for 12 hours, and then cooled to room temperature. The synthesized polycrystalline film was activated with methanol for 2 hours to obtain product M. 21 , M 22 , M 23 , M 24 , M 25 .

[0110] Characterization of ZIF-8-7 membrane: Product M 21 -M25 H2 / CO2 separation selectivity and permeability were measured. The results in Table 7 show that as the benzimidazole content increases, the H2 permeability gradually decreases and the H2 / CO2 separation selectivity increases; while as the 2-methylimidazole content increases, the H2 permeability increases and the H2 / CO2 separation selectivity decreases.

[0111] Table 8

[0112]

[0113] Through the experiments and analysis of the above embodiments, it is further proved that the preparation method of the zeolite imidazolate skeleton polycrystalline membrane of the present invention is simple to operate and has good economy, and the prepared zeolite imidazolate skeleton polycrystalline membrane effectively avoids the defects generated in the process of preparing the membrane. The preparation method of the present invention can directly introduce two organic ligands to prepare the zeolite imidazolate skeleton membrane, and can effectively adjust the pore size of the porous material, thereby achieving the purpose of changing its effective separation pore size. The prepared zeolite imidazolate skeleton membrane has good separation performance in a variety of gas separation systems, and at the same time has the advantages of short synthesis cycle, simple process, wide controllable range of synthesis conditions, strong economy and low energy consumption.

[0114] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for preparing a zeolite imidazolate skeleton polycrystalline film, characterized in that: The following steps are involved: S1: preparing a precursor solution containing metal ions and organic ligands, coating the precursor solution on a support, and heating and cooling the support coated with the precursor solution to prepare an amorphous thin film; The precursor solution includes a metal salt, an organic ligand and a solvent; the zeolite imidazolate framework material is composed of a metal node, an organic ligand A and an organic ligand B; The organic ligand A is imidazole-2-carboxaldehyde or 2-methylimidazole, and the organic ligand B is selected from one of 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, and 4-methylimidazole-5-carboxaldehyde; and the solvent is methanol. S2: treating the amorphous film obtained in step S1 with steam generated by heating a polar solvent to form a crystalline film; S3: activating the obtained crystalline film using a volatile solvent to obtain a zeolite imidazolate skeleton polycrystalline film; The volatile solvent is selected from one of methanol, ethanol, chloroform, acetone and acetonitrile.

2. The method for preparing a zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In the step S1, the carrier is an α-Al2O3 carrier, a γ-Al2O3 carrier, a TiO2 carrier or a polymer carrier.

3. The method for preparing a zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In step S1, the metal node is zinc nitrate hexahydrate, zinc acetate dihydrate or cobalt acetate tetrahydrate.

4. The method for preparing a zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In step S1, the precursor solution comprises, by mole fraction, 1 part of Zn, 1-8 parts of organic ligand A, 0-8 parts of organic ligand B, and 50-500 parts of methanol.

5. The method for preparing the zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In step S1, the metal salt is zinc acetate dihydrate; and the organic ligand B is 2-methylimidazole or benzimidazole.

6. The method for preparing the zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In the step S1, the heating temperature is 30-120° C. and the heating time is 5-60 minutes.

7. The method for preparing the zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In the step S2, the polar solvent is N-N dimethylformamide or N-N dimethylacetamide.

8. The method for preparing the zeolite imidazolate skeleton polycrystalline film according to claim 1, wherein: In step S2, the steam treatment is performed at a temperature of 25-160° C. for a time of 4-36 hours.

9. The method for preparing the zeolite imidazolate skeleton polycrystalline film according to claim 8, wherein: In step S2, the temperature of the steam treatment process is 80-120° C. and the time is 8-12 hours.

10. A zeolite imidazolate skeleton polycrystalline membrane, characterized in that: The zeolite imidazolate skeleton polycrystalline membrane is prepared by the preparation method according to any one of claims 1 to 9.

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