MOF (Metal Organic Framework) membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, in particular to an MOF (Metal Organic Framework) membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: uniformly mixing an organic ligand, metal salt and a solvent to obtain a synthetic solution; in the synthetic liquid, the molar concentration of the organic ligand is CL, the molar concentration of the metal salt is CM, and CL and CM meet the following relations: CL / CM is greater than or equal to 10, and CL * CM is greater than or equal to 0.01; immersing a substrate into the synthetic liquid, and reacting for a period of time under the conditions that the temperature is T DEG C and the pressure is P bar, so as to form an MOF (Metal Organic Framework) film on the substrate; wherein 20 < = T < = 40, and 0.8 < = P < = 1.2. The MOF membrane can be rapidly prepared at normal temperature and normal pressure by dissolving the organic ligand and the metal salt in the solvent according to a specific ratio, the problem that the preparation conditions of the existing MOF membrane are harsh can be solved, and the obtained MOF membrane has good gas permeability and particularly has high propylene / propane separation selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to a MOF membrane and a preparation method and application thereof. Background Art

[0002] The gas separation process is of great significance in modern energy and chemical production. Membrane separation technology has the advantages of low energy consumption, high efficiency, and continuous operation, and has broad application prospects. Membrane materials are the core of membrane separation technology. A class of metal organic framework materials (MOF) that have emerged in recent years is a class of crystalline materials with periodic pore structures formed by the orderly assembly of metal nodes and organic ligands. Because of its rich adjustability in window size, pore shape and chemical environment, it has unique advantages in constructing high-performance gas separation membranes. Therefore, polycrystalline MOF membranes can be prepared on porous support substrates to allow gas molecules to penetrate across the membrane through the pores of MOF, thereby achieving strict screening of target gases.

[0003] Currently, the preparation of MOF membranes is mainly based on the solvothermal method, which requires high temperature and high pressure conditions to complete the ligand deprotonation process. The reaction time is usually as long as several days, which greatly reduces the controllability of the MOFs film formation process and limits the large-scale application of MOF membranes. Summary of the invention

[0004] The present invention provides a MOF membrane and a preparation method and application thereof, so as to solve the problems of harsh conditions and long reaction time in the existing MOF membrane preparation method.

[0005] According to a first aspect of the present invention, the present invention provides a method for preparing a MOF film, comprising the following steps: The organic ligand, the metal salt and the solvent are mixed uniformly to obtain a synthetic solution; in the synthetic solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L With C M Satisfies the following relationship: C L / C M ≥10, C L *C M ≥0.01; The substrate is immersed in the synthetic solution, and reacted for a period of time under the conditions of temperature T°C and pressure P bar to form a MOF film on the substrate; 20≤T≤40, 0.8≤P≤1.2.

[0006] MOF is a new type of porous molecular sieve material, a type of porous material formed by self-assembly of metal ions or metal clusters and organic ligands. MOF has a highly regular crystal structure and can create materials with adjustable porosity and specific surface area at the nanoscale, making it show a wide range of application potential in many fields. MOF has a high specific surface area, which makes them very effective in applications such as gas storage and separation; MOF has adjustable porosity, and can be designed with a specific pore size and structure by selecting different metal centers and organic ligands to meet specific application requirements; MOF has good chemical stability and thermal stability, allowing it to maintain its performance in a variety of environments. The present invention found that by dissolving organic ligands and metal salts in a solvent in a specific proportion, a MOF membrane can be quickly prepared at room temperature and pressure, which can solve the problem of harsh preparation conditions of existing MOF membranes, and the resulting MOF membrane has good gas permeability, especially a high propylene / propane separation selectivity.

[0007] Preferably, 20≤T≤25.

[0008] Among them, T, P and t satisfy the following relationship: t=k*T 2 *P 2 , wherein k is 0.002-0.352; preferably, 5≤t≤90, more preferably 30≤t≤50, and in some specific embodiments, t=40.

[0009] Preferably, k is 0.06-0.1.

[0010] Furthermore, in the synthetic solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L With C M Satisfies the following relationship: C L / C M ≥13, C L *C M ≥0.012, preferably, 13≤C L / C M ≤25.

[0011] Furthermore, the relationship between the average pore size S of the substrate and the thickness D of the MOF film satisfies: D=N*S 1.5 , N is 0.17-2.26, D is 100-800nm ​​(preferably 150-200nm), and S is 50-70nm. The selection of substrate pore size is very important for the synthesis of MOF membranes, providing effective nucleus sites for the growth of MOF, thereby forming a MOF membrane with stable structure and excellent performance.

[0012] Furthermore, the material of the substrate is selected from one of anodized aluminum, polyethersulfone or polyacrylonitrile. Selecting a suitable type of substrate can optimize the performance of the MOF membrane.

[0013] Furthermore, the types of the MOF membrane include ZIF-8, ZIF-67, ZIF-L, ZIF-7, ZIF-7-8 or ZIF-90.

[0014] Furthermore, the organic ligand is selected from one or more of 2-methylimidazole, benzimidazole, imidazole and imidazole-2-carboxaldehyde. Organic ligands play a key role in the formation of MOF membranes. They form coordination bonds with metal ions or metal clusters to construct crystalline porous materials with a periodic network structure. Selecting suitable types of organic ligands to combine with metal ions is conducive to improving the performance of MOF membranes.

[0015] Furthermore, the metal salt is selected from one or both of zinc acetate dihydrate and cobalt acetate. By selecting the appropriate type of metal salt, the morphology, structure and performance of the MOF membrane can be significantly improved.

[0016] Further, the solvent is selected from one or more of water, methanol and N, N-dimethylformamide. By selecting a suitable type of solvent, the morphology, structure and performance of the MOF membrane can be improved.

[0017] According to the second aspect of the present invention, the present invention also provides a MOF membrane synthesized by the above-mentioned preparation method.

[0018] According to the third aspect of the present invention, the present invention further provides an application of a MOF membrane in gas separation, wherein the MOF membrane is a MOF membrane synthesized by the above-mentioned preparation method or the above-mentioned MOF membrane.

[0019] The MOF membrane of the present invention can be used to achieve efficient propylene / propane separation, hydrogen / carbon dioxide separation, carbon dioxide / methane separation, etc. The MOF membrane of the present invention has high propylene / propane separation selectivity. The separation of propylene and propane is a crucial process in modern chemical production, which is related to the production of chemicals, energy utilization, environmental protection and other tasks.

[0020] Beneficial effects of the present invention: The present invention provides a method for preparing a MOF membrane by dissolving an organic ligand and a metal salt in a solvent in a specific ratio, so that a MOF membrane can be quickly prepared at room temperature and pressure, which can solve the problem of harsh preparation conditions of existing MOF membranes, and the obtained MOF membrane has good gas permeability, especially high propylene / propane separation selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a scanning electron microscope image of the cross section of the MOF membrane obtained in Example 1 of the present invention.

[0023] Figure 2 This is a surface scanning electron microscope image of the MOF film obtained in Example 1 of the present invention.

[0024] Figure 3 This is the X-ray diffraction pattern of the MOF film obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1 This embodiment provides a method for preparing a MOF film, comprising the following steps: Mix the formulated amount of organic ligand, metal salt and solvent, and after they are completely dissolved, stir evenly to obtain a synthetic liquid; pour the obtained synthetic liquid into a beaker, put a substrate in it, and react for t=20min at T=30℃ and P=1.1bar; take out the substrate, put it in a vacuum oven to dry for later use.

[0027] Among them, organic ligand: 2-methylimidazole, concentration C L 0.5M; Metal salt: Zinc acetate dihydrate, concentration C M 0.03M; C L / C M =16.7, C L *C M =0.015; solvent: water; substrate: anodized aluminum substrate, pore size 50 nm, diameter 12 mm.

[0028] The MOF membrane obtained in this example is ZIF-8, and the thickness of the membrane is 200 nm. The cross-sectional scanning electron microscope image is shown in FIG. Figure 1As shown, it can be seen that the ZIF-8 grains grow continuously without obvious defects, and it is a dense ZIF-8 membrane. The scanning electron microscope image of the membrane surface is shown in Figure 2 As shown, it can be seen that ZIF-8 is tightly bonded to the substrate without any defects. Its X-ray diffraction pattern is as follows Figure 3 As shown, it can be seen that the crystallinity of the ZIF-8 membrane is very high, which confirms that this method can prepare a dense and continuous ZIF-8 membrane.

[0029] Embodiment 2-9 This embodiment provides a method for preparing a MOF membrane, which is different from Embodiment 1 in that T, P, and t of the reaction are different, and the specific differences are shown in Table 1 below.

[0030] Embodiment 10-11 This embodiment provides a method for preparing a MOF membrane, which is different from that of embodiment 1 in that C M and C L There are differences, and the specific differences are shown in Table 1 below.

[0031] Comparative Example 1 This comparative example provides a method for preparing a MOF membrane, which differs from Example 1 in that the ratio of the metal salt to the organic ligand in the synthetic solution does not satisfy: L / C M <10, specifically, metal salt C M is 0.25M, ligand C L The other organic ligands, solvents, substrates and synthesis conditions remained unchanged.

[0032] Comparative Example 2 This comparative example provides a method for preparing a MOF membrane, which differs from Example 1 in that the temperature, pressure and time in the synthesis conditions do not satisfy: t=k*T 2 *P 2 Specifically, the synthesis time t is 200 min, T is 80 °C, P is 5 bar, and the other organic ligands, solvents, substrates, and synthesis conditions remain unchanged.

[0033] Performance Testing The gas permeability of the MOF membranes obtained in each embodiment and comparative example was tested respectively.

[0034] The test method is as follows: Gas separation performance: The prepared MOF membrane was placed in a customized membrane cell and both sides of the membrane were sealed with silicone gaskets. The volume flow rate of the feed gas was 50 ml min -1 The air was introduced into the outlet, and the permeate side of the membrane was heated to 50 ml min -1The membrane is purged with Ar gas to quickly remove the gas that permeates through the membrane, so as to ensure that the transmembrane partial pressure difference of the gas to be separated is one atmosphere. The purge gas outlet is connected to a gas chromatograph to test the concentration of the separated components on the permeation side. Before passing into the gas chromatograph, a soap bubble flowmeter is used to measure the total outlet flow on the outlet side. The gas content is analyzed by gas chromatography, and the gas permeation rate P is calculated using formula (1): i (1) Where N is the flow rate of gas through the membrane, ∆P is the transmembrane pressure difference of component i on both sides of the membrane, and A is the effective test membrane area. The ideal selectivity S of the membrane C3H6 / C3H8 , can be calculated based on the permeation ratio of the two components through the membrane, as shown in formula (2): (2) The test results are shown in Table 1 below: Table 1

[0035] From the results in Table 1 above, it can be seen that the MOF membrane prepared in the examples of the present invention has good propylene permeability and propylene / propane selectivity, among which the conditions in Example 1 are better.

[0036] Example 12 This embodiment provides a method for rapidly synthesizing a MOF membrane at room temperature and pressure, comprising the following steps: Mix the formulated amount of organic ligand, metal salt and solvent, and after they are completely dissolved, stir evenly to obtain a synthetic liquid; pour the obtained synthetic liquid into a beaker, put a substrate in it, and react for 20 minutes at 30°C and 1.1 bar; take out the substrate, put it in a vacuum oven and dry it for later use.

[0037] Among them, organic ligand: 2-methylimidazole, concentration is 0.4M; metal salt: cobalt acetate, concentration is 0.01M; solvent: water + methanol; substrate: anodized aluminum substrate, pore size 50 nm, diameter 12 mm.

[0038] The MOF film obtained in this example is ZIF-67, and the thickness of the film is 400 nm.

[0039] Embodiment 13 This embodiment provides a method for rapidly synthesizing a MOF membrane at room temperature and pressure, comprising the following steps: Mix the formulated amount of organic ligand, metal salt and solvent, and after they are completely dissolved, stir evenly to obtain a synthetic liquid; pour the obtained synthetic liquid into a beaker, put a substrate in it, and react for 90 minutes at 40°C and 1.2 bar; take out the substrate, put it in a vacuum oven and dry it for later use.

[0040] Among them, the organic ligand is benzimidazole, with a concentration of 0.5M; the metal salt is zinc acetate dihydrate, with a concentration of 0.02M; the solvent is methanol + N, N-dimethylformamide; the substrate is polyacrylonitrile, with a pore size of 70 nm.

[0041] The MOF obtained in this example is ZIF-67, and the thickness of the film is 800 nm.

[0042] Embodiment 14 This embodiment provides a method for rapidly synthesizing a MOF membrane at room temperature and pressure, comprising the following steps: Mix the formulated amount of organic ligand, metal salt and solvent, and after they are completely dissolved, stir evenly to obtain a synthetic liquid; pour the obtained synthetic liquid into a beaker, put a substrate in it, and react for 5 minutes at 20°C and 0.8 bar; take out the substrate, put it in a vacuum oven and dry it for later use.

[0043] Among them, the organic ligand is imidazole-2-carboxaldehyde, with a concentration of 0.33M; the metal salt is zinc acetate dihydrate, with a concentration of 0.033M; the solvent is methanol + water; and the substrate is polyethersulfone, with a pore size of 60 nm.

[0044] The thickness of the MOF film obtained in this example is 100 nm.

[0045] The performance test results of the MOF membranes obtained in Examples 12-14 are shown in Table 2 below: Table 2

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a MOF membrane, characterized in that: The steps include: The organic ligand, the metal salt and the solvent are mixed uniformly to obtain a synthetic solution; in the synthetic solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L With C M Satisfies the following relationship: C L / C M ≥10, C L *C M ≥0.01; The substrate is immersed in the synthetic solution, and reacted for a period of time under the conditions of temperature T°C and pressure P bar to form a MOF film on the substrate; wherein 20≤T≤40, 0.8≤P≤1.

2.

2. The preparation method according to claim 1, characterized in that: The reaction time is t min , and T, P and t satisfy the following relationship: t=k*T 2 *P 2 , wherein k is 0.002-0.352; preferably, 5≤t≤90.

3. The preparation method according to claim 1, characterized in that: C L With C M Satisfies the following relationship: C L / C M ≥13, C L *C M ≥0.

012.

4. The preparation method according to claim 1, characterized in that: The relationship between the average pore size S of the substrate and the thickness D of the MOF film satisfies: D=N*S 1.5 , N is 0.17-2.26, D is 100-800nm, S is 50-70nm; And / or, the material of the substrate is selected from one of anodized aluminum, polyethersulfone or polyacrylonitrile.

5. The preparation method according to claim 1, characterized in that: The types of the MOF membrane include ZIF-8, ZIF-67, ZIF-L, ZIF-7, ZIF-7-8 or ZIF-90.

6. The preparation method according to claim 1 or 5, characterized in that: The organic ligand is selected from one or more of 2-methylimidazole, benzimidazole, imidazole and imidazole-2-carboxaldehyde.

7. The preparation method according to claim 1 or 5, characterized in that: The metal salt is selected from one or both of zinc acetate dihydrate and cobalt acetate.

8. The preparation method according to claim 1 or 5, characterized in that: The solvent is selected from one or more of water, methanol and N, N-dimethylformamide.

9. A MOF membrane, characterized in that: The preparation method according to any one of claims 1 to 8 is used for synthesis.

10. Application of a MOF membrane in gas separation, characterized in that: The MOF membrane is synthesized by the preparation method described in any one of claims 1 to 8.

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