Flexible metal-organic framework material for separating C2H2 and CO2 mixture as well as preparation method and application of flexible metal-organic framework material

Abstract

The invention belongs to the technical field of porous material preparation, and relates to a flexible metal-organic framework material (MOFs) for separating a mixture of C2H2 and CO2 as well as a preparation method and application of the flexible metal-organic framework material. The preparation method comprises the following steps: 1, dissolving a metal salt and an organic ligand in a solvent, and continuously stirring at room temperature; step 2, putting the solution into a high-pressure kettle, reacting for a certain time at a certain temperature, taking out and cooling to room temperature; and step 3, centrifuging the sample by using a solvent, and drying the obtained solid sample in a vacuum drying oven at a certain temperature for a certain time to obtain the flexible metal-organic framework material for separating the C2H2 and CO2 mixture. The flexible metal-organic framework material has the characteristics of high adsorption capacity, high selectivity, capability of keeping performance under a relatively high temperature condition and the like; the preparation method has the advantages of cheap and easily available raw materials, simple preparation, mild preparation conditions, suitability for industrial production and the like, and has great practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous material preparation, and in particular relates to a flexible metal-organic framework material (MOFs) for separating a mixture of C2H2 and CO2, and a preparation method and application thereof. Background Art

[0002] Acetylene (C2H2), the simplest alkyne, is widely used in the production of several commercial fine chemicals, such as methyl acrylate, butynediol, ethylene derivatives, acetylene alcohol, and electronic devices. It is one of the most critical raw materials in the petrochemical industry. Furthermore, acetylene is used as a gaseous fuel in oxyacetylene flames for welding and metal cutting. Acetylene production processes (such as methane oxidative coupling and petroleum cracking) inevitably produce carbon dioxide as an impurity. Therefore, removing carbon dioxide from the C2H2 product is a crucial industrial separation requirement. However, separation is challenging due to the linear shape of C2H2 and CO2 molecules, which share the same kinetic diameter, similar molecular size, and similar boiling points (189.3 K for C2H2 and 194.7 K for CO2, respectively). Traditional separation technologies mainly rely on solvent extraction and low-temperature distillation. These methods are inefficient and energy-intensive. The explosive properties of C2H2 also make it pose huge risks in transportation and storage, and have a significant impact on the environment. Therefore, adsorption separation technology will be an important technology for C2H2 / CO2 separation in the future. Among them, the use of porous materials for gas storage and separation has become one of the most useful technologies.

[0003] Traditional porous materials, such as zeolites, clays, and activated carbon, typically exhibit low selectivity and adsorption capacity at ambient temperature and pressure. The separation performance of an adsorbent depends on its pore structure and surface properties, as well as the physicochemical properties of the adsorbed gas. Metal-organic frameworks (MOFs), porous crystalline materials composed of metal nodes and bridging organic ligands, offer advantages such as extremely high specific surface area and pore volume, low density, and high designability. They hold great promise for application in gas separation.

[0004] The application of metal-organic frameworks in acetylene-carbon dioxide separation is attracting increasing attention from researchers. OMS MOFs have improved the separation of C2H2 and CO2 due to their powerful functional sites within ultra-microporous MOFs. In addition, some MOFs, such as NKMOF-1-Ni and Cul@Ui0-66-(COOH)2, show strong C2H2 binding sites and pore confinement, but they exhibit low adsorption capacity under high adsorption heat. MOFs with large pore sizes, such as FJU-90, have higher adsorption capacity but lower selectivity.

[0005] Currently, most metal-organic frameworks (MOFs) exhibit a rigid pore structure with a fixed lattice structure and uniform porosity, but lack flexibility and are prone to structural damage during gas adsorption or desorption. They have high gas adsorption capacity but low selectivity and poor stability, and are particularly prone to decomposition in acidic or high-temperature environments. Flexible MOFs exhibit superior performance in gas separation due to their ability to dynamically change porosity. At low pressures, the pores remain closed, and the gas adsorption capacity is extremely low. When the pressure reaches a certain threshold, the pores suddenly open, and the gas absorption capacity increases dramatically. Selective separation can be achieved by using different opening pressures for different gas molecules. However, the preparation of flexible MOFs still faces challenges, such as high synthesis costs, complex synthesis steps, harsh synthesis conditions, and structural collapse of the metal-organic framework material. Some studies have reported the flexibility of flexible MOFs in gas separation, such as [Cu2(dicarboxylate)2(amine)] n 、 X-pcu-3-Zn-3i and X-pcu-1-Zn-3i, but there are limited reports on the application of flexible MOFs in C2H2 / CO2 separation.

[0006] In summary, traditional C2H2 / CO2 separation methods are energy-intensive, inefficient, and environmentally unfriendly. The adsorption capacity and selectivity of rigid MOFs in C2H2 / CO2 separation need to be improved. There is currently little research on flexible MOFs in C2H2 / CO2 separation. How to prepare new metal-organic framework materials with high stability, high adsorption capacity, and adsorption separation selectivity for C2H2 / CO2 separation at low cost has become a technical problem that needs to be solved urgently. Summary of the Invention

[0007] In light of the problems existing in the prior art, the present invention aims to provide a flexible metal-organic framework (MOF) for separating C2H2 and CO2 mixtures, as well as its preparation method and application. This flexible MOF exhibits high adsorption capacity, high selectivity, and performance retention at elevated temperatures. The preparation method, featuring readily available, inexpensive raw materials, simple preparation, mild conditions, and suitability for industrial production, offers significant practical value.

[0008] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0009] A method for preparing a flexible metal-organic framework material (MOFs) for separating a mixture of C2H2 and CO2 comprises the following steps: Step 1: dissolving the metal salt and the organic ligand in a solvent and stirring continuously at room temperature; Step 2: Place the above solution in an autoclave, react at a certain temperature for a certain time, take it out and cool it to room temperature; Step 3: Centrifuge the sample using a solvent, place the obtained solid sample in a vacuum drying oven at a certain temperature and dry it for a certain period of time to obtain block crystals, i.e., a flexible metal-organic framework material for separating a mixture of C2H2 and CO2.

[0010] Furthermore, in step 1, the metal salt is one of nitrates, sulfates, chlorides or acetates of Zn, Co, Ni, Fe, Zr, Cu, Al, Cr or Mn.

[0011] Furthermore, in step 1, the organic ligand is one of imidazole, 2-methylimidazole, 2-nitroimidazole, isonicotinic acid, fumaric acid, terephthalic acid, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, trimesic acid, thiophene-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid or 1H-pyrrole-2,5-dicarboxylic acid.

[0012] Furthermore, in step 1, the molar ratio of the metal salt to the organic ligand is 0.2-1.0:1.

[0013] Furthermore, in steps 1 and 3, the solvent is one or more combinations of water, methanol, ethanol, N,N-dimethylacetamide, N,N-diethylformamide, N,N-dimethylformamide, dichloromethane, xylene or dimethyl sulfoxide.

[0014] Furthermore, in step 1, the stirring time is 3h~10h.

[0015] Furthermore, in step 2, the reaction temperature is 80°C to 300°C.

[0016] Furthermore, in step 2, the reaction time is 20h~40h.

[0017] Furthermore, in step 3, the temperature of the vacuum drying oven is 60°C to 200°C.

[0018] Furthermore, in step 3, the drying time is 4 to 10 hours.

[0019] On the other hand, the present invention provides the use of the flexible metal-organic framework material (MOFs) in separation and purification reactions. The gas separation and purification reaction is to separate and purify a mixture of C2H2 and CO2. The specific operation is as follows: Step 1: MOFs are degassed at a certain temperature and cooled to room temperature. In a fixed-bed reactor, they are fully activated under a flow of inert gas at a certain temperature and then cooled to room temperature through a temperature control program. Step 2: Fixed bed helium purge, using a 1:1 mixture of test gas and inert gas as carrier gas, setting the flow rate, and measuring the adsorption data of MOFs at the test temperature.

[0020] Furthermore, in step 1, the degassing temperature is 100°C to 250°C.

[0021] Furthermore, in step 1, the degassing time is 10h~30h.

[0022] Furthermore, in step 1, the activation temperature is 100°C to 250°C.

[0023] Furthermore, in step 1, the activated inert gas is one of nitrogen, argon or helium.

[0024] In a preferred embodiment of the present invention, the activation time in step 1 is 8 h to 20 h.

[0025] Compared with the prior art, the present invention has the following beneficial effects.

[0026] 1. The flexible metal-organic framework material provided by the present invention has the advantages of cheap and readily available raw materials, simple preparation, mild preparation conditions and suitability for industrial production.

[0027] 2. The flexible metal-organic framework material provided by the present invention has the characteristics of high adsorption capacity, high selectivity, and maintaining performance under high temperature conditions, and has great practical value.

[0028] 3. The present invention provides a flexible metal-organic framework material with a flexible ligand skeleton. Compared with carbon dioxide, the skeleton selectively adsorbs acetylene molecules through hydrogen bonds and van der Waals forces, and can open pores at a relatively low partial pressure line, forming excellent selective acetylene adsorption performance, showing superior performance in gas separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Adsorption isotherms of C2H2 and CO2 of Example 1 and Example 2.

[0030] Figure 2 The penetration test results of the C2H2 / CO2 mixed gas in Example 1. DETAILED DESCRIPTION

[0031] The following further describes the claims of the present invention in detail with reference to specific embodiments, but does not constitute any limitation to the present invention. Any limited number of modifications made by anyone within the scope of protection of the claims of the present invention are still within the scope of protection of the claims of the present invention.

[0032] A method for preparing a flexible metal-organic framework material (MOFs) for separating a mixture of C2H2 and CO2 comprises the following steps: Step 1: dissolving the metal salt and the organic ligand in a solvent and stirring continuously at room temperature; Step 2: Place the above solution in an autoclave, react at a certain temperature for a certain time, take it out and cool it to room temperature; Step 3: Centrifuge the sample using a solvent, place the obtained solid sample in a vacuum drying oven at a certain temperature and dry it for a certain period of time to obtain block crystals, i.e., a flexible metal-organic framework material for separating a mixture of C2H2 and CO2.

[0033] Furthermore, in step 1, the metal salt is one of the nitrates, sulfates, chlorides or acetates of Zn, Co, Ni, Fe, Zr, Cu, Al, Cr or Mn; preferably, Co(NO3)2, Cu(NO3)2 or Mn(NO3)2.

[0034] Furthermore, in step 1, the organic ligand is one of imidazole, 2-methylimidazole, 2-nitroimidazole, isonicotinic acid, fumaric acid, terephthalic acid, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, trimesic acid, thiophene-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid or 1H-pyrrole-2,5-dicarboxylic acid; preferably, isonicotinic acid.

[0035] Furthermore, in step 1, the molar ratio of the metal salt to the organic ligand is 0.2-1.0:1; preferably, 0.2-0.5:1.

[0036] Furthermore, in steps 1 and 3, the solvent is one or more of water, methanol, ethanol, N,N-dimethylacetamide, N,N-diethylformamide, N,N-dimethylformamide, dichloromethane, xylene or dimethyl sulfoxide; preferably, ethanol.

[0037] Furthermore, in step 1, the stirring time is 3 h to 10 h; preferably 3 h to 5 h.

[0038] Furthermore, in step 2, the reaction temperature is 80°C to 300°C; preferably 100°C to 150°C.

[0039] Furthermore, in step 2, the reaction time is 20 h to 40 h, preferably 20 h to 30 h.

[0040] Furthermore, in step 3, the temperature of the vacuum drying oven is 60°C to 200°C; preferably 60°C to 100°C.

[0041] Furthermore, in step 3, the drying time is 4 to 10 hours, preferably 5 to 7 hours.

[0042] On the other hand, the present invention provides the use of the flexible metal-organic framework material (MOFs) in separation and purification reactions. The gas separation and purification reaction is to separate and purify a mixture of C2H2 and CO2. The specific operation is as follows: Step 1: MOFs are degassed at a certain temperature and cooled to room temperature. In a fixed-bed reactor, they are fully activated under a flow of inert gas at a certain temperature and then cooled to room temperature through a temperature control program. Step 2: Fixed bed helium purge, using a 1:1 mixture of test gas and inert gas as carrier gas, setting the flow rate, and measuring the adsorption data of MOFs at the test temperature.

[0043] Furthermore, in step 1, the degassing temperature is 100°C to 250°C; preferably 100°C to 150°C.

[0044] Furthermore, in step 1, the degassing time is 10 h to 30 h, preferably 10 h to 15 h.

[0045] Furthermore, in step 1, the activation temperature is 100°C to 250°C; preferably 130°C to 180°C.

[0046] Furthermore, in step 1, the activated inert gas is one of nitrogen, argon or helium; preferably helium.

[0047] In a preferred embodiment of the present invention, the activation time in step 1 is 8 h to 20 h, preferably 10 h to 15 h.

[0048] Example 1.

[0049] A flexible metal-organic framework material (MOFs) Mn(INA)2 is prepared as follows: 0.03 g of Mn(NO3)2.6H20 and 0.034 g of isonicotinic acid were dissolved in ethanol and stirred at room temperature for 3 h. The resulting solution was then placed in a polytetrafluoroethylene-lined steel autoclave and reacted at 120°C for 24 h. After cooling to room temperature, the resulting solution was centrifuged with ethanol and the resulting solid was dried in a vacuum drying oven at 80°C for 6 h to obtain blocky crystalline Mn(INA)2.

[0050] Example 2.

[0051] Referring to the preparation method in Example 1, Mn(NO3)2.6H2O was replaced with an equal mole of Cu(NO3)2.6H2O to obtain a flexible metal-organic framework material (MOFs) Cu(INA)2.

[0052] Example 3.

[0053] According to the preparation method in Example 1, Mn(NO3)2.6H2O was replaced by an equal mole of Co(NO3)2.6H2O to obtain a flexible metal-organic framework material (MOFs) Co(INA)2.

[0054] Comparative Example 1.

[0055] Comparative Example 1 UTSA-300 is a material prepared according to the document Journal of the American Chemical Society 139(23) (2017) 8022-8028.

[0056] Comparative Example 2.

[0057] Comparative Example 2 CPL-1-NH2 is a material prepared according to the document Angewandte Chemie 133(9) (2021) 4620-4624.

[0058] Comparative Example 3.

[0059] Comparative Example 3 ZJU-196 is a material prepared according to the document Chemical Communications 54(38) (2018) 4846-4849.

[0060] Comparative Example 4.

[0061] Comparative Example 4 ZNU-3 is a material prepared according to the document Chemical Engineering Journal 439 (2022) 135745.

[0062] Comparative Example 5.

[0063] Comparative Example 5 Co(4-DPDS)2WO4 is a material prepared according to the document Advanced Science 10(9) (2023) 2207127.

[0064] Comparative Example 6.

[0065] Comparative Example 6 Co(4-DPDS)2MoO4 is a material prepared according to the document Advanced Science 10(9) (2023) 2207127.

[0066] Comparative Example 7.

[0067] Comparative Example 7 Co(4-DPDS)2CrO4 is a material prepared according to the document Advanced Science 10(9) (2023) 2207127.

[0068] Comparative Example 8.

[0069] Comparative Example 8 ZNU-5 is a material prepared according to the document Nano Research 16(2) (2023) 3536–3541.

[0070] Comparative Example 9.

[0071] Comparative Example 9 NTU-65 is a material prepared according to the document Angewandte Chemie International Edition 59(50) (2020) 22756–22762.

[0072] Comparative Example 10.

[0073] Comparative Example 10 NCU-100 is a material prepared according to the document Nature communications 13(1) (2022) 200.

[0074] Comparative Example 11.

[0075] Comparative Example 11 ATC-Cu is a material prepared according to the document Angewandte Chemie 133(10) (2021) 5343–5348.

[0076] Comparative Example 12.

[0077] Comparative Example 12 Co2a is a material prepared according to the document Inorganic Chemistry 63 (2024) 6033-6041.

[0078] test 1. Stability test: Mn(INA)2, Cu(INA)2 and Co(INA)2 were exposed to air and water with a relative humidity of 60%, respectively. Crystal structure analysis was performed after 7 days. All solid structures still maintained a good crystal form.

[0079] 2. Adsorption performance test: MOFs were degassed at 120°C and cooled to room temperature. They were then activated in a fixed-bed reactor at 160°C under a helium flow for 12 h, cooled to room temperature through a temperature control program, and purged with helium in the fixed bed. A 1:1 mixture of test gas (C2H2:CO2=1:1) and inert gas was used as the carrier gas, and the adsorption data of MOFs were measured at different test temperatures. During the measurement, the adsorption pressure was varied from 0 to 1 bar, and the adsorption temperature was maintained by changing the water temperature in the water bath. The single-component adsorption isotherm was tested. The adsorption isotherm of Mn(INA)2C2H2 was as follows: Figure 1As shown in a, the CO2 adsorption isotherm is as follows Figure 1 As shown in b, the Cu(INA)2C2H2 adsorption isotherm is as follows Figure 1 As shown in c, the CO2 adsorption isotherm is as follows Figure 1 As shown in d.

[0080] The adsorption isotherm of Mn(INA)2 shows that the opening pressure of C2H2 is about 0.2 bar, and the opening pressure increases slightly with increasing temperature. At 0.2 bar, the adsorption amount of C2H2 is 1.75 mmol / g, while that of CO2 is only 0.15 mmol / g, with high selectivity for C2H2 / CO2. At 273K, the opening pressure of CO2 is about 0.3 bar, and the opening pressure increases significantly with increasing temperature. However, at 308K, the adsorption isotherm of CO2 shows a linear trend. The adsorption isotherm of Cu(INA)2 shows that the CO2 adsorption isotherm is close to linear at several temperatures, which indicates that Mn(INA)2 has higher structural flexibility than Cu(INA)2.

[0081] 3. Penetration test: The penetration test of C2H2 / CO2 mixed gas was carried out on Mn(INA)2. The volume ratio of C2H2 and CO2 was 1:1, the flow rate was 2mL / min, and the pressure was 1MPa. The experiments were carried out at 25℃, 35℃, and 45℃ respectively. The results are shown in the figure. Figure 2 a (25°C), b (35°C) and c (45°C) are shown.

[0082] Figure 2 The chromatographic results show that when the test temperature is 25°C, C2H2 reaches saturation within 50s and CO2 elutes rapidly in 45s. When the test temperature is 35°C, C2H2 reaches saturation within 50s and CO2 elutes rapidly in 30s. When the test temperature is 45°C, C2H2 begins to slowly elute in 20s and elutes rapidly in 75s, and CO2 elutes rapidly in 20s.

[0083] 4. Comparison of opening pressure and adsorption capacity: The opening pressure and C2H2 adsorption capacity at 0.1 bar of Mn(INA)2 and different comparative MOFs were tested, and the results are shown in Table 1.

[0084] Table 1 Opening pressure and C2H2 adsorption capacity at 0.1 bar of Mn(INA)2 and different comparative MOFs.

[0085] From the results in Table 1, it can be seen that the C2H2 adsorption capacity of Mn(INA)2 at 0.1 bar is much higher than that of the comparative MOFs, and the opening pressure is lower than that of general MOFs, and only slightly higher than that of CPL-1-NH2, ZJU-196, Co(4-DPDS)2WO4 and GeFSIX-dps-Cu.

Claims

1. A method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2, characterized in that: The following steps are involved: Step 1: dissolving the metal salt and the organic ligand in a solvent and stirring continuously at room temperature; Step 2: Place the above solution in an autoclave, react at a certain temperature for a certain time, take it out and cool it to room temperature; Step 3: Centrifuge the sample using a solvent, place the obtained solid sample in a vacuum drying oven at a certain temperature and dry it for a certain period of time to obtain block crystals, i.e., a flexible metal-organic framework material for separating a mixture of C2H2 and CO2.

2. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In step 1, the metal salt is one of nitrates, sulfates, chlorides or acetates of Zn, Co, Ni, Fe, Zr, Cu, Al, Cr or Mn.

3. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In step 1, the organic ligand is one of imidazole, 2-methylimidazole, 2-nitroimidazole, isonicotinic acid, fumaric acid, terephthalic acid, 2-hydroxyterephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, trimesic acid, thiophene-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid or 1H-pyrrole-2,5-dicarboxylic acid.

4. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In the step 1, the molar ratio of the metal salt to the organic ligand is 0.2-1.0:

1.

5. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In steps 1 and 3, the solvent is one or more combinations of water, methanol, ethanol, N,N-dimethylacetamide, N,N-diethylformamide, N,N-dimethylformamide, dichloromethane, xylene or dimethyl sulfoxide.

6. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In the step 1, the stirring time is 3h~10h.

7. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In the step 2, the reaction temperature is 80° C. to 300° C.; and the reaction time is 20 h to 40 h.

8. The method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 1, characterized in that: In step 3, the temperature of the vacuum drying oven is 60° C. to 200° C., and the drying time is 4 to 10 hours.

9. A flexible metal-organic framework material for separating a mixture of C2H2 and CO2 is prepared by the method for preparing a flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to any one of claims 1 to 8.

10. The flexible metal-organic framework material for separating a mixture of C2H2 and CO2 according to claim 9, characterized in that The application of the flexible metal-organic framework material in separation and purification reactions is specifically performed as follows: Step 1: MOFs are degassed at a certain temperature and cooled to room temperature. In a fixed-bed reactor, they are fully activated under a flow of inert gas at a certain temperature and then cooled to room temperature through a temperature control program. Step 2: Fixed bed helium purge, using a 1:1 mixture of test gas and inert gas as carrier gas, setting the flow rate, and measuring the adsorption data of MOFs at the test temperature.

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