A MOF film, its preparation method and application

Abstract

The application relates to the field of membrane separation technology, in particular to a MOF membrane and a preparation method and application thereof. The preparation method comprises the following steps: uniformly mixing an organic ligand, a metal salt and a solvent to obtain a synthesis solution; in the synthesis solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L and C M satisfy the following relationship: C L / C M >=10, C L *C M >=0.01; a substrate is taken and immersed into the synthesis solution, and a MOF membrane is formed on the substrate under the condition of a temperature T (unit: DEG C) and a pressure P (unit: bar) for a period of time; wherein 20<=T<=40 and 0.8<=P<=1.2. According to the application, the organic ligand and the metal salt are dissolved in the solvent at a specific proportion, so that the MOF membrane can be prepared quickly under normal temperature and pressure, the problem of harsh preparation conditions of the existing MOF membrane can be solved, and the obtained MOF membrane has good gas permeability and high propylene / propane separation selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a MOF membrane and a preparation method and application thereof. BACKGROUND

[0002] 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, continuous operation, etc., and has wide application prospect. Membrane material is the core of membrane separation technology. In recent years, a kind of metal organic framework material (MOF) is a kind of crystal material with periodic pore structure formed by orderly assembling metal nodes and organic ligands. Because its window size, pore shape and chemical environment have rich adjustability, it has unique advantages in constructing high-performance gas separation membrane. Therefore, polycrystalline MOF membrane can be prepared on porous support substrate, so that gas molecules pass through the pores of MOF for transmembrane permeation, thereby realizing strict screening of target gas.

[0003] At present, the preparation of MOF membrane is mainly based on solvothermal method, but the solvothermal method needs to complete the deprotonation process of ligand under high temperature and high pressure conditions, and the reaction time is usually as long as several days, which greatly reduces the controllability of MOF membrane forming process and limits the large-scale application of MOF membrane. SUMMARY

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

[0005] According to the first aspect of the present application, the present application provides a preparation method of a MOF membrane, comprising the following steps:

[0006] Mixing the organic ligand, metal salt and solvent uniformly to obtain a synthesis solution; in the synthesis solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L and C M satisfy the following relationship: C L / C M ≥10, C L *C M ≥0.01;

[0007] Immerse the substrate in the synthesis solution, react for a period of time under the condition of temperature T℃ and pressure P bar, and form a MOF membrane on the substrate; 20≤T≤40, 0.8≤P≤1.2.

[0008] MOF is a new type of porous molecular sieve material, which is a kind of porous material formed by self-assembly of metal ions or metal clusters and organic ligands. MOF has a highly regular crystal structure, which can create materials with adjustable porosity and specific surface area at the nanoscale, showing a wide application potential in many fields. MOF has a high specific surface area, which makes it very effective in gas storage and separation applications; MOF has adjustable porosity, which can be designed by selecting different metal centers and organic ligands to design MOFs with specific pore size and structure to meet specific application requirements; MOF has good chemical stability and thermal stability, which can maintain performance in various environments. The present application found that by dissolving organic ligands and metal salts in a solvent at a specific ratio, MOF membranes can be quickly prepared at room temperature and normal pressure, which can solve the problem of harsh preparation conditions of existing MOF membranes, and the obtained MOF membranes have good gas permeability, especially high propylene / propane separation selectivity.

[0009] Preferably, 20≤T≤25.

[0010] wherein 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.

[0011] Preferably, k is 0.06-0.1.

[0012] Further, in the synthesis solution, the molar concentration of the organic ligand is C L , the molar concentration of the metal salt is C M , C L and C M satisfy the following relationship: C L / C M ≥13, C L *C M ≥0.012, preferably, 13≤C L / C M ≤25.

[0013] Further, the relationship between the average pore size S of the substrate and the thickness D of the MOF membrane 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 the pore size of the substrate is important for the synthesis of the MOF membrane, which provides effective nucleation sites for the growth of MOF, thereby forming a MOF membrane with stable structure and excellent performance.

[0014] Further, the material of the substrate is selected from one of anodized aluminum, polyether sulfone or polyacrylonitrile. Selecting a proper kind of substrate can optimize the performance of the MOF membrane.

[0015] Further, the kind of the MOF membrane includes ZIF-8, ZIF-67, ZIF-L, ZIF-7, ZIF-7-8 or ZIF-90.

[0016] Further, the organic ligand is selected from one or more of 2-methylimidazole, benzimidazole, imidazole and imidazole-2-carboxaldehyde. The organic ligand plays a key role in the formation of the MOF membrane. They form coordination bonds with metal ions or metal clusters, thereby constructing a crystalline porous material with a periodic network structure. Selecting a proper kind of organic ligand in combination with metal ions is conducive to improving the performance of the MOF membrane.

[0017] Further, the metal salt is selected from one or both of zinc acetate dihydrate and cobalt acetate. By selecting a proper kind of metal salt, the morphology, structure and performance of the MOF membrane can be significantly improved.

[0018] Further, the solvent is selected from one or more of water, methanol and N, N-dimethylformamide. By selecting a proper kind of solvent, the morphology, structure and performance of the MOF membrane can be improved.

[0019] According to a second aspect of the present application, the present application further provides a MOF membrane synthesized by the above preparation method.

[0020] According to a third aspect of the present application, the present application further provides an application of a MOF membrane in gas separation, wherein the MOF membrane is a MOF membrane synthesized by the above preparation method or the above MOF membrane.

[0021] The MOF membrane of the present application can be used to realize efficient propylene / propane separation, hydrogen / carbon dioxide separation, carbon dioxide / methane separation, etc. The MOF membrane of the present application has high propylene / propane separation selectivity. The separation of propylene and propane is a crucial process in modern chemical production, which is related to chemical production, energy utilization and environmental protection and other tasks.

[0022] The present application has the following beneficial effects:

[0023] The preparation method of the MOF membrane provided by the present application can quickly prepare the MOF membrane at normal temperature and pressure by dissolving the organic ligand and the metal salt in the solvent at a specific ratio, which can solve the problem of harsh preparation conditions of the existing MOF membrane, and the obtained MOF membrane has good gas permeability, especially high propylene / propane separation selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0024] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a cross-sectional scanning electron microscope image of the MOF film obtained in Example 1 of the present invention.

[0026] Figure 2 This is a scanning electron microscope image of the surface of the MOF film obtained in Example 1 of the present invention.

[0027] Figure 3 The X-ray diffraction pattern of the MOF film obtained in Example 1 of this invention is shown. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] Example 1

[0030] This embodiment provides a method for preparing a MOF membrane, including the following steps:

[0031] Mix the formulated amounts of organic ligand, metal salt, and solvent. After complete dissolution, stir until homogeneous to obtain a synthesis solution. Pour the obtained synthesis solution into a beaker, place the substrate inside, and react at T=30℃ and P=1.1 bar for t=20 min. Remove the substrate and place it in a vacuum oven to dry for later use.

[0032] Among them, the organic ligand is 2-methylimidazole, with a concentration of C. L 0.5M; Metal salt: Zinc acetate dihydrate, concentration C M It is 0.03M; C L / C M =16.7, C L *C M =0.015; Solvent: water; Substrate: anodic aluminum oxide substrate, pore size 50 nm, diameter 12 mm.

[0033] The MOF film obtained in this embodiment is ZIF-8, with a thickness of 200 nm. Its cross-sectional scanning electron microscope image is shown below. Figure 1As shown, it can be seen that the ZIF-8 crystal grains grow continuously without obvious defects, and the ZIF-8 film is dense. The surface scanning electron microscope image of the film is as shown in Figure 2. Figure 2 As shown, it can be seen that the ZIF-8 and the substrate are closely combined without defects. The X-ray diffraction pattern thereof is as shown in Figure 3. Figure 3 As shown, it can be seen that the crystallinity of the ZIF-8 film is very high, which proves that the method can prepare a dense and continuous ZIF-8 film.

[0034] Examples 2-9

[0035] This example provides a method for preparing a MOF film, which is different from Example 1 in that the T, P, and t of the reaction are different, as shown in Table 1.

[0036] Examples 10-11

[0037] This example provides a method for preparing a MOF film, which is different from Example 1 in that the C M and C L are different, as shown in Table 1.

[0038] Comparative Example 1

[0039] This comparative example provides a method for preparing a MOF film, which is different from Example 1 in that the ratio of the metal salt and the organic ligand in the synthesis solution does not satisfy: C L / C M <10. Specifically, the metal salt C M is 0.25M, the ligand C L is 0.5M, and the rest of the organic ligand, the solvent, the substrate, and the synthesis conditions remain unchanged.

[0040] Comparative Example 2

[0041] This comparative example provides a method for preparing a MOF film, which is different 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℃, and P is 5 bar, and the rest of the organic ligand, the solvent, the substrate, and the synthesis conditions remain unchanged.

[0042] Performance Test

[0043] The MOF films obtained in each example and comparative example were tested for gas permeability.

[0044] The test method is as follows:

[0045] Gas separation performance: Put the prepared MOF membrane into a custom-made membrane cell, and seal the two sides of the membrane with silica gel gaskets. The volumetric flow rate of the feed gas is 50 ml / min -1 , the outlet is connected to air, and the permeation side of the membrane is purged with 50 ml / min -1 of Ar gas to quickly remove the gas permeated through the membrane 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 in the permeation side. Before connecting to the gas chromatograph, the total outlet flow rate on the outlet side is measured using a soap bubble flowmeter. The content of the gas is analyzed by gas chromatography, and the permeation P i

[0046] (1)

[0047] Where N represents the flow rate of the gas permeating through the membrane, ΔP represents the transmembrane pressure difference of component i on both sides of the membrane, and A represents the effective test membrane area. The ideal selectivity S C3H6 / C3H8 of the membrane can be calculated according to the ratio of the permeation of the two components through the membrane, as shown in formula (2):

[0048] (2)

[0049] The test results are shown in Table 1 below:

[0050] Table 1

[0051]

[0052] From the results in Table 1 above, it can be seen that the MOF membrane prepared in the embodiments of the present application has good propylene permeability and propylene / propane selectivity, and the condition of Example 1 is more optimal.

[0053] Example 12

[0054] The present embodiment provides a method for rapidly synthesizing a MOF membrane at room temperature and normal pressure, comprising the following steps:

[0055] Mix the formula amount of organic ligand, metal salt, and solvent, and after complete dissolution, stir uniformly to obtain a synthesis liquid; pour the obtained synthesis liquid into a beaker, place it in a substrate, and react at 30℃ and 1.1bar for 20min; take out the substrate and place it in a vacuum oven for drying.

[0056] Wherein the organic ligand is 2-methylimidazole with a concentration of 0.4M; the metal salt is cobalt acetate with a concentration of 0.01M; the solvent is water + methanol; and the substrate is an anodized aluminum substrate with a pore size of 50nm and a diameter of 12mm.

[0057] The MOF film obtained in this example is ZIF-67, and the thickness of the film is 400 nm.

[0058] Example 13

[0059] This example provides a method for rapidly synthesizing a MOF film at room temperature and normal pressure, comprising the following steps:

[0060] The formula amount of organic ligand, metal salt and solvent are mixed, and after complete dissolution, the mixture is stirred uniformly to obtain a synthesis solution; the obtained synthesis solution is poured into a beaker, placed in a substrate, and reacted at 40℃ and 1.2bar for 90min; the substrate is taken out and placed in a vacuum oven for drying.

[0061] 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; and the substrate is polyacrylonitrile with a pore size of 70nm.

[0062] The MOF obtained in this example is ZIF-67, and the thickness of the film is 800 nm.

[0063] Example 14

[0064] This example provides a method for rapidly synthesizing a MOF film at room temperature and normal pressure, comprising the following steps:

[0065] The formula amount of organic ligand, metal salt and solvent are mixed, and after complete dissolution, the mixture is stirred uniformly to obtain a synthesis solution; the obtained synthesis solution is poured into a beaker, placed in a substrate, and reacted at 20℃ and 0.8bar for 5min; the substrate is taken out and placed in a vacuum oven for drying.

[0066] 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 polyether sulfone with a pore size of 60nm.

[0067] The thickness of the MOF film obtained in this example is 100 nm.

[0068] The performance test results of the MOF films obtained in Examples 12-14 are shown in Table 2 below:

[0069] Table 2

[0070]

[0071] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a MOF membrane, characterized in that, Includes the following steps: An organic ligand, a metal salt, and a solvent are mixed uniformly to obtain a synthesis solution; in the synthesis 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 Satisfy the following relationship: C L / C M ≥10, C L *C M ≥0.01; The substrate is immersed in the synthesis solution and reacted for a period of time under the conditions of temperature T℃ and pressure P bar to form an MOF film on the substrate; wherein, 20≤T≤40, 0.8≤P≤1.2; The reaction time is t min, and T, P, and t satisfy the following relationship: t = k * T 2 *P 2 Where k is 0.002-0.352; 5≤t≤90; The types of MOF membranes include ZIF-8, ZIF-67, ZIF-L, ZIF-7, ZIF-7-8, or ZIF-90.

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

012.

3. 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, and S is 50-70nm; And / or, the material of the substrate is selected from one of anodized aluminum oxide, polyethersulfone, or polyacrylonitrile.

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

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

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

7. A MOF membrane, characterized in that, It is synthesized using the preparation method described in any one of claims 1-6.

8. An application of a MOF membrane in gas separation, characterized in that, The MOF membrane is synthesized using the preparation method described in any one of claims 1-6.

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