A fluorinated modified MOF glass membrane and its preparation method and application

Abstract

The present invention provides a fluorinated modified MOF glass membrane and its preparation method and application, which belongs to the field of membrane material technology. The fluorinated modified MOF glass membrane provided by the present invention contains organic ligands and fluorine element ligands, wherein the molar ratio of the organic ligands to the fluorine element ligands is (25-80): (20-75). The present invention is modified on the basis of the existing metal organic skeleton membrane. Unlike the metal organic skeleton membrane in the prior art, the fluorinated modified MOF glass membrane provided by the present invention is an amorphous MOF glass structure. Since the fluorine element is introduced into the MOF membrane, the pore size of the fluorinated modified MOF glass membrane provided by the present invention is smaller, and it has higher selectivity in gas separation. At the same time, because the present invention introduces the fluorine element into the MOF membrane, the hydrophobicity of the membrane is greatly improved, which greatly improves the separation stability of the membrane.

Description

Technical Field

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

[0002] Membrane separation offers advantages such as high energy efficiency, low operating costs, a small footprint, and the ability to operate continuously. Compared to traditional, energy-intensive separation methods, membrane separation holds great promise for widespread adoption in gas separation. MOFs are a novel class of nanoporous organic-inorganic hybrids with a regular lattice structure and a rigid pore structure. MOFs consist of metal nodes interconnected by multi-toothed organic linkers, resulting in diverse structures and chemical functions, with well-defined pores, channels, and cavities at the molecular scale. MOF glass is a newly developed MOF material. MOF glass membranes offer advantages such as the absence of intercrystalline defects, permanent porosity, and ease of processing. Furthermore, MOF glass exhibits structural diversity and tunability unattainable with traditional inorganic and organic glass. Currently, MOF glass membranes are primarily prepared through a melt-quenching method, where a polycrystalline membrane is melted at high temperature to form a glass membrane. However, this method requires multiple steps, including the preparation of the polycrystalline membrane and the high-temperature melting in a tube furnace. It would be highly desirable to be able to produce high-performance MOF glass membranes through a simple method. Summary of the Invention

[0003] The object of the present invention is to provide a MOF membrane with high selectivity and simple preparation method. To achieve the above purpose, the first aspect of the present invention provides a fluorinated modified MOF glass membrane, in which organic ligands and fluorine element ligands are present, wherein the molar ratio of organic ligands to fluorine element ligands is (25~80): (20~75).

[0004] Preferably, the organic ligand is selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, 4-methylimidazole-5-carboxaldehyde.

[0005] Preferably, the metal element framework of the fluorinated modified MOF glass membrane is zinc and / or cobalt.

[0006] Compared to the prior art, the fluorinated MOF glass membrane provided by the present invention has the following advantages: The present invention modifies existing metal-organic framework membranes. Unlike the prior art metal-organic framework membranes, the fluorinated MOF glass membrane provided by the present invention has an amorphous MOF glass structure. Due to the introduction of fluorine into the MOF membrane, the fluorinated MOF glass membrane provided by the present invention has a smaller pore size and higher selectivity in gas separation. Furthermore, the introduction of fluorine into the MOF membrane significantly enhances the membrane's hydrophobicity and water contact angle, significantly increasing the separation stability of the MOF membrane in high humidity environments.

[0007] Furthermore, the second aspect of the present invention provides a method for preparing the fluorinated modified MOF glass film according to the first aspect, comprising the following steps:

[0008] S1: Preparation of MOF membrane;

[0009] S2: heating the fluorine-containing imidazole ligand to generate fluorine-containing vapor, which contacts the MOF membrane to form a MOF-F glass membrane;

[0010] S3: activating the MOF-F glass film in an activator to obtain a fluorinated modified MOF glass film.

[0011] Preferably, in step S1, the carrier used to prepare the MOF membrane is selected from one of α-Al2O3 carrier, γ-Al2O3 carrier, anodic aluminum oxide carrier, TiO2 carrier, PVDF carrier, PAN carrier, PES carrier, PTFE carrier, and PEI carrier.

[0012] Preferably, in step S2, the fluorine-containing ligand is selected from any one or more of monofluoromethylimidazole, difluoromethylimidazole, trifluoromethylimidazole, and 2-methyl-4-fluoroimidazole.

[0013] Preferably, in step S2, the heating temperature for heating the fluorine-containing imidazole ligand to generate fluorine-containing steam is 60-100°C.

[0014] Preferably, in step S2, the contact time between the fluorine-containing steam and the MOF membrane is 6 to 48 hours.

[0015] Preferably, in step S3, the activating agent is selected from any one or more of dichloromethane, chloroform, dimethylformamide, methanol, ethanol, chloroform, acetone, acetonitrile, chloroform, acetone, and dimethylformamide.

[0016] Preferably, in step S3, the activation time is 0.5 to 24 hours.

[0017] The preparation method of the fluorinated modified MOF glass film provided by the present invention has the advantage of simple processing technology, and the fluorinated imidazole ligand therein can be used multiple times, which has the advantage of high economy and practicality.

[0018] Furthermore, the third aspect of the present invention provides an application of the fluorinated modified MOF glass membrane described in the first aspect, specifically, separating the fluorinated modified MOF glass membrane using a mixed gas.

[0019] Preferably, the mixed gas is selected from any one of a hydrogen-helium mixed gas, a helium-nitrogen mixed gas, a helium-methane mixed gas, a carbon dioxide-methane mixed gas, a carbon dioxide-nitrogen mixed gas, and a propylene-propane mixed gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an X-ray diffraction characterization result diagram of product M1 in Example 1 of the specific embodiment of the present invention;

[0021] Figure 2 This is a scanning electron microscope cross-sectional view of the product C1 obtained in Example 1 of the specific embodiment of the present invention;

[0022] Figure 3 This is a scanning electron microscope surface characterization result diagram of product M1 in Example 1 of the specific embodiment of the present invention;

[0023] Figure 4 This is a scanning electron microscope cross-sectional view of the product M1 in Example 1 of the specific embodiment of the present invention;

[0024] Figure 5 This is a water contact angle diagram of products M1, M4, and C1 in Example 1 of the specific embodiment of the present invention;

[0025] Figure 6 This is a graph showing the carbon dioxide / methane gas separation performance of product M1 in a wet environment in Example 2 of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0026] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only intended to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter ranges described in the present invention. Reasonable variations derived therefrom are still within the scope of protection of the claims of the present invention.

[0027] It should be noted that the endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0028] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventional understandings are defined herein for the purpose of illustrating or facilitating reference, and such definitions herein should not be construed as representing significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments is carried out in accordance with the protocols and parameters given by the manufacturers.

[0029] In the prior art, MOF membranes often have the disadvantages of being difficult to prepare and unsuitable for gas separation. Based on this, a specific embodiment of the present invention provides a fluorinated modified MOF glass membrane suitable for gas separation and having a simple preparation method.

[0030] The fluorinated modified MOF glass film provided in a specific embodiment of the present invention contains organic ligands and fluorine ligands, wherein the molar ratio of the organic ligands to the fluorine ligands is (25-80): (20-75).

[0031] In the above embodiment, the fluorine-containing ligand can be replaced by a halogen-containing ligand with similar properties, such as a chlorine-containing ligand, 4-chloroimidazole, 5-chloro-1-methylimidazole, etc., or replaced by a bromine-containing ligand, 2-bromobenzimidazole, 4-bromo-1-H-imidazole, etc.

[0032] In the fluorinated modified MOF glass film provided in the above embodiment, the organic ligand is selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, 4-methylimidazole-5-carboxaldehyde.

[0033] In the fluorinated modified MOF glass film provided in a specific embodiment of the present invention, the metal frame is zinc and / or cobalt.

[0034] The specific embodiment of the present invention also provides a method for preparing the aforementioned fluorinated modified MOF, which specifically comprises the following steps:

[0035] S1: Preparation of MOF membrane;

[0036] S2: heating the fluorine-containing imidazole ligand to generate fluorine-containing vapor, which contacts the MOF membrane to form a MOF-F glass membrane;

[0037] S3: activating the MOF-F modified membrane in an activator to obtain a fluorinated modified MOF glass membrane.

[0038] In step S1 of the above embodiment, the MOF film can be prepared by a conventional MOF preparation method.

[0039] Specifically, in step S1 of the above embodiment, the MOF membrane is preferably any one of ZIF-8, high-flux ZIF-8, ZIF-7, ZIF-93, ZIF-67, and ZIF-90, and more preferably any one of ZIF-8, high-flux ZIF-8, and ZIF-90.

[0040] ZIF-8 membranes are prepared by dip-coating thermal conversion (patent CN 111841333 B). This method is simple to synthesize, highly reproducible, and has excellent separation selectivity for macromolecular gases such as propylene and propane. By further reducing the precursor concentration, high-throughput ZIF-8 membranes can be prepared (J.Membr.Sci. 643 (2022)).

[0041] 120055). A high-throughput ZIF-8 membrane was prepared by controlling the precursor concentration. Fluorine ligand vapor treatment and conversion were performed under the high-throughput ZIF-8 membrane, thereby improving the gas permeability.

[0042] Furthermore, the ZIF-90 membrane preparation method specifically includes the following steps: dissolving 0.577g of imidazole-2-carboxaldehyde in 15ml of methanol at 80°C, cooling to room temperature, adding 0.66g of zinc acetate dihydrate, and stirring in an ice bath for 8 minutes to obtain a ZIF-90 precursor solution; dipping the support in the precursor solution for 30 seconds, removing it, absorbing the water, and reacting it in a 50°C forced air oven for 30 minutes. After natural cooling, a ZIF-90 amorphous layer is obtained; and the ZIF-90 amorphous layer is steam-treated in a DMF solution at 80°C for 12 hours to obtain a ZIF-90 membrane. The ZIF-90 membrane is prepared by a steam conversion method (Chem. Eng. J. 496 (2024) 153737). The ZIF-90 membrane prepared by this method has excellent separation performance for n-isobutane and propylene and propane. In step S2 of the above embodiment, the fluorine-containing ligand is selected from any one or more of monofluoromethylimidazole, difluoromethylimidazole, trifluoromethylimidazole, and 2-methyl-4-fluoroimidazole.

[0043] In step S2 of the above embodiment, the heating temperature for heating the fluorinated imidazole ligand to generate fluorinated vapor is 60-100°C, and the contact time between the fluorinated vapor and the MOF membrane is 6-48 hours. Preferred heating temperatures include 60°C, 80°C, and 100°C. The optimal heating temperature is 80°C. Heating methods include heating in a reactor, heating in air, and heating in a vacuum environment. Heating in a reactor is most preferred.

[0044] In step S3 of the above embodiment, the activating agent is selected from any one or more of dichloromethane, chloroform, dimethylformamide, methanol, ethanol, chloroform, acetone and acetonitrile. Unless otherwise specified, the activation described in the specific embodiment of the present invention is based on conventional understanding, that is, the product to be activated is immersed in the activating agent for a period of time. The activation time is 0.5 to 24 hours, preferably 1 to 12 hours, and most preferably 3 to 6 hours.

[0045] The fluorinated modified MOF glass membrane provided in the specific embodiment of the present invention is improved based on the MOF membrane in the prior art. Even after the MOF membrane comes into contact with fluorine-containing vapor, fluorine element is incorporated into the MOF membrane, which reduces the pore size of the MOF membrane and greatly improves the gas selectivity of the MOF membrane. At the same time, the incorporation of fluorine element increases the water contact angle of the MOF membrane, which makes the fluorinated modified MOF glass membrane provided in the specific embodiment of the present invention still have good stability even in an environment with high humidity.

[0046] The technical solution of the present invention is further described below through specific embodiments.

[0047] Example 1

[0048] Preparation of fluorinated ZIF-8 glass membrane

[0049] 1.32 g (15 mmol) of Zn(OAc)2·2H2O and 1 g of 2-methylimidazole (30 mmol) were added to 15 ml of H2O / DMAC (2 / 1) solution, respectively, marked as solution A and solution B. After stirring in an ice bath for 8 minutes, solution B was added to solution A within 90 s. After stirring for 30 s, the precursor solution of ZIF-8 membrane was obtained. The Al2O3 support was dipped in the precursor solution for 30 s, taken out and dried, and reacted in a forced air oven at 200°C for 15 min. After natural cooling, ZIF-8 polycrystalline membranes were obtained, which were marked as C1 to C6 respectively.

[0050] Take 0.2g of 4-trifluoromethylimidazole and place it in a small bottle. Invert the surface of the C1-C3 membrane (not in direct contact with the ligand) and react in a 70℃ forced air oven for 12h. C3-C6 react in an 80℃ forced air oven for 12h.

[0051] C1 to C6 were taken out, activated in 10 ml of chloroform for 2 h, and then vacuum activated in a vacuum oven at 100° C. for 12 h. They were respectively recorded as products M1 to M6.

[0052] Characterization of fluorinated ZIF-8 glass membrane: XRD and SEM characterizations of the products M1 to M3 prepared above were carried out, and the separation selectivity and permeability were measured. The XRD characterization results of product M4 are shown in the figure below. Figure 1 As shown in Figure 2, after fluorination modification, the polycrystalline structure of ZIF-8 disappears and becomes an amorphous MOF glass structure; the SEM characterization results of product M1 are shown in Figure 2. Figure 3 As shown; the SEM characterization results of the product and M4 are shown in Figure 4 As shown in the figure, after fluorination modification, the regular polyhedral structure of the ZIF-8 surface disappears and transforms into an amorphous glass structure; the water contact angles of products M1 and M4 are shown in the figure. Figure 5 As shown, the water contact angle increases with increasing fluorine content, indicating that fluorine incorporation enhances the membrane's hydrophobicity. H-NMR spectroscopy revealed that the fluorine ligand incorporation in product M1 was 22%. The ratio of 2-methylimidazole to 4-trifluoromethylimidazole in the unmodified ZIF-8 ligands was 78:22, and the incorporation level in M4 was 58%.

[0053] The results of the CO2 / methane and CO2 / nitrogen separation selectivity and permeability tests for products C1-C3 and M1-M3 are shown in Tables 1-1, 1-2, and 1-3. Table 1-4 shows that when the doping level is low, the fluorinated ZIF-8 glass membrane exhibits excellent CO2 / methane and CO2 / nitrogen separation performance. Further increasing the volatilization temperature of the fluorinated imidazole ligand and when the doping level is high, the separation selectivity and permeability of the fluorinated ZIF-8 glass membrane for hydrogen / methane and helium / nitrogen are shown in Tables 1-5, 1-6, 1-7, and 1-8. Highly doped fluorinated ZIF-8 glass membranes exhibit excellent hydrogen / methane and helium / nitrogen separation performance.

[0054] Table 1-1: Test results of carbon dioxide / methane separation selectivity and permeability for C1 to C3

[0055]

[0056] Table 1-2: Test results of carbon dioxide / methane separation selectivity and permeability of products M1 to M3

[0057]

[0058] Table 2-3: Carbon dioxide / nitrogen separation selectivity and permeability test results for C1 to C3

[0059]

[0060] Table 1-4: Carbon dioxide / nitrogen separation selectivity and permeability test results of products M1 to M3

[0061]

[0062] Table 3-5: Hydrogen / methane separation selectivity and permeability test results for C4 to C6

[0063]

[0064] Table 4-6: Hydrogen / methane separation selectivity and permeability test results of M4~M6

[0065]

[0066] Table 5-7: Helium / nitrogen separation selectivity and permeability test results for C4 to C6

[0067]

[0068]

[0069] Table 6-8: Helium / nitrogen separation selectivity and permeability test results for M4 to M6

[0070]

[0071] Example 2

[0072] Fluorinated ZIF-8 glass film tested in humidity environment

[0073] M1 to M3 in Example 1 were tested under a wet environment. A mixed gas of carbon dioxide and methane was introduced into water, and the mixed gas carrying water vapor was separated and tested when passing through the membrane surfaces of M1 to M3.

[0074] The carbon dioxide-methane separation selectivity and permeability of products M1 to M3 were tested under a humid environment. The separation selectivity and permeability test results of M1 to M3 under a humid environment are shown in Table 2 and the attached Figure 6 As shown in Table 2, the permeability of the fluorinated ZIF-8 glass membrane is slightly reduced under humidity conditions, but it still maintains good separation selectivity.

[0075] Table 2: Test results of carbon dioxide / methane separation selectivity and permeability of M1-M3 under humidity environment

[0076]

[0077] Example 3

[0078] Preparation of high-throughput fluorinated ZIF-8 glass membrane

[0079] 0.33 g Zn(OAc)2·2H2O and 0.25 g 2-methylimidazole were added to 15 ml of H2O / DMAC (2 / 1) solution, respectively, marked as solution A and solution B. After stirring in an ice bath for 8 minutes, solution B was added to solution A within 90 seconds. After stirring for 30 seconds, a high-flux ZIF-8 membrane precursor solution was obtained. The Al2O3 support was dipped in the precursor solution for 30 seconds, taken out and dried, and reacted in a forced air oven at 200°C for 15 minutes. After natural cooling, high-flux fluorinated ZIF-8 glass membranes were obtained, marked as C7, C8, and C9, respectively.

[0080] 0.2 g of 4-trifluoromethylimidazole was placed in a small bottle, and the surfaces of the C7, C8, and C9 membranes were inverted (not in direct contact with the ligands), and the mixture was reacted in a forced air oven at 80° C. for 12 h.

[0081] C7 to C9 were taken out, activated in 10 ml of chloroform for 2 h, and then vacuum activated in a vacuum oven at 100° C. for 12 h. They were respectively recorded as product M7, product M8, and product M9.

[0082] The results of the carbon dioxide / methane separation selectivity and permeability test of products M7 to M9 are shown in Table 3. It can be seen that the high-flux ZIF-8 glass membrane after fluorination modification has excellent carbon dioxide / methane separation performance.

[0083] Table 3-1: Test results of carbon dioxide / methane separation selectivity and permeability for C7-C9

[0084]

[0085] Table 3-2: Test results of carbon dioxide / methane separation selectivity and permeability of products M7 to M9

[0086]

[0087] Example 4

[0088] Preparation of fluorinated ZIF-90 glass membrane

[0089] 0.577g of imidazole-2-carboxaldehyde was dissolved in 15ml of methanol at 80℃, cooled to room temperature, added with 0.66g of zinc acetate dihydrate, and stirred in an ice bath for 8min to obtain a ZIF-90 precursor solution. The Al2O3 support was dip-coated in the precursor solution for 30s, removed and dried, and reacted in a 50℃ forced air oven for 30min. After natural cooling, the ZIF-90 amorphous layer was obtained. The ZIF-90 amorphous layer was steam-treated in DMF solution at 80℃ for 12h to obtain a ZIF-90 polycrystalline film, marked as C. 10 , C11 and C 12 .

[0090] Take 0.2g of 4-trifluoromethylimidazole and place it in a small bottle. 10 , C 11 , C 12 The membrane surface was inverted (not in direct contact with the ligand) and reacted in a forced air oven at 80°C for 12 h.

[0091] C 10 ~C 12 Take it out, activate it in 10 ml of chloroform for 2 h, and activate it in a vacuum oven at 100 ° C for 12 h, and record it as product M 10 , Product M 11 and product M 12 .

[0092] The propylene / propane separation selectivity and permeability test results of products M4 to M6 are shown in Table 2. After fluorination modification, the propylene / propane separation performance of the fluorinated ZIF-90 glass membrane is significantly improved.

[0093] Table 4-1: C 10 ~C 12 Propylene / propane separation selectivity and permeability test results table

[0094]

[0095] Table 4-2: Product M 10 ~M 12 Propylene / propane separation selectivity and permeability test results table

[0096]

[0097] It can be seen from the experimental results of Examples 1 to 4 that the fluorinated modified MOF glass membrane provided by the specific embodiment of the present invention has a smaller pore size than the pure MOF membrane, thereby achieving the separation of specific gases.

[0098] 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 fluorinated MOF glass film, characterized in that: The fluorinated modified MOF glass film has an amorphous MOF glass structure, and contains organic ligands and fluorinated imidazole ligands, wherein: The organic ligand is selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 4,5-dichloroimidazole, 2-nitroimidazole, and 4-methylimidazole-5-carboxaldehyde; The fluorinated imidazole ligand is selected from any one or more of monofluoromethylimidazole, difluoromethylimidazole, trifluoromethylimidazole, and 2-methyl-4-fluoroimidazole; The molar ratio of the organic ligand to the fluorine-containing imidazole ligand is 25-80:20-75.

2. A method for preparing the fluorinated MOF glass film according to claim 1, characterized in that: The following steps are involved: S1: Preparation of MOF membrane; S2: heating the fluorine-containing imidazole ligand to generate fluorine-containing vapor, which contacts the MOF membrane to form a MOF-F glass membrane; S3: activating the MOF-F glass film in an activator to obtain a fluorinated modified MOF glass film.

3. The preparation method according to claim 2, wherein In step S2, the heating temperature for heating the fluorine-containing imidazole ligand to generate fluorine-containing steam is 60-100°C.

4. The preparation method according to claim 2, wherein In step S2, the contact time between the fluorine-containing steam and the MOF membrane is 6 to 48 hours.

5. The preparation method according to claim 2, wherein In step S3, the activating agent is selected from any one or more of dichloromethane, chloroform, dimethylformamide, methanol, ethanol, acetone, and acetonitrile.

6. The preparation method according to claim 2, wherein In step S3, the activation time is 0.5 to 24 hours.

7. An application of the fluorinated modified MOF glass film according to claim 1, characterized in that: Fluorinated MOF glass membranes were used for mixed gas separation.

8. The use according to claim 7, characterized in that The mixed gas is selected from any one of hydrogen-helium mixed gas, helium-nitrogen mixed gas, helium-methane mixed gas, carbon dioxide-methane mixed gas, carbon dioxide-nitrogen mixed gas, and propylene-propane mixed gas.

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