A flexible metal-organic framework material with molecular sieve-like performance and a preparation method and application thereof

Abstract

The application discloses a flexible metal organic framework material with molecular sieve-like separation performance and a preparation method and application thereof, and preparation of the flexible metal organic framework material comprises the following steps: a copper hexafluorosilicate solution is added drop by drop into a 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution in an ice water environment, after dropping, the reaction is stirred for 10-15 hours in the ice water environment, and the obtained reaction solution is subjected to post-treatment to obtain the flexible metal organic framework material [Cu(bpz)(SiF6)] with molecular sieve-like separation performance. The framework material has a great adsorption difference for C2H2 and CO2, can be used for separating C2H2 / CO2 mixed gas, has very high separation selectivity, has a large adsorption capacity for C2H2, and is a solid physical adsorbent with both characteristics.

Description

Technical Field

[0001] This invention relates to the field of petrochemical gas separation and purification technology, and in particular to a flexible metal-organic framework material with molecular sieving properties, its preparation method, and its application. Background Technology

[0002] Acetylene is an important chemical raw material, serving as a fundamental feedstock for acetaldehyde, acetic acid, benzene, synthetic rubber, and synthetic fibers. High purity is typically required, making separation and purification crucial for improving its utilization. Industrially, acetylene (C2H2) is primarily produced by methane combustion and thermal hydrocarbon cracking. The resulting C2H2 inevitably contains trace amounts of CO2 impurities. Therefore, separating high-purity C2H2 (>99%) from C2H2 / CO2 mixtures is of significant industrial importance. Current separation processes mostly employ energy-intensive solvent extraction and cryogenic distillation to separate acetylene and carbon dioxide mixtures. However, due to their very close boiling points (acetylene 189.3 K; carbon dioxide 194.7 K), separation is extremely difficult, these methods are energy inefficient, and they are very environmentally unfriendly. Therefore, it is necessary to develop novel separation technologies at ambient temperature and pressure for the efficient separation of acetylene and carbon dioxide.

[0003] In recent years, the use of adsorbent separation technology for gas separation and purification has attracted great attention from both academia and industry. This suggests that future separation technologies may shift from traditional energy-intensive low-temperature distillation methods to energy-efficient adsorbent separation methods. Adsorption separation, as an energy-efficient and highly effective separation technology, features low energy consumption, simple operation, and high separation selectivity. With the development of adsorption separation materials such as carbon materials, molecular sieves, and porous polymers, adsorption separation technology has made significant progress in the field of gas separation.

[0004] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with defined compositions and structures, formed by the self-assembly of metal nodes and organic ligands. Due to their tunable pore size, high specific surface area, and ease of functionalization, they have experienced rapid development and have become highly promising adsorbent materials in the field of low-carbon hydrocarbon gas separation and purification.

[0005] When metal-organic frameworks (MOFs) are used for gas separation and purification, achieving a high adsorption capacity and selectivity is often a challenging task that is difficult to balance. The SIFSIX series of anion-supported materials, with their one-dimensional, regular, linear channels, can effectively aggregate target gases during adsorption. Furthermore, by replacing the metal ion centers or selecting organic linkers with specific functional units, the framework can form hydrogen bonds, coordination bonds, or van der Waals forces with target gas molecules, effectively improving the framework's ability to recognize target gases. Therefore, the SIFSIX series of materials holds promise for solving the trade-off effect that has not yet been addressed in ordinary MOFs. Summary of the Invention

[0006] To overcome the shortcomings of traditional C2H2 / CO2 separation methods, this invention provides a flexible metal-organic framework material with molecular sieving properties, its preparation method, and its applications. The flexible metal-organic framework material of this invention has a large adsorption capacity for acetylene and extremely high selectivity for C2H2 / CO2 separation at room temperature and pressure.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a flexible metal-organic framework material with molecular sieving properties includes the following steps: copper hexafluorosilicate solution is added dropwise to 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution under ice-water conditions. After the addition is complete, the mixture is stirred and reacted under ice-water conditions for 10-15 hours. The resulting reaction solution is then post-treated to obtain the flexible metal-organic framework material [Cu(bpz)(SiF6)] with molecular sieving properties, thus completing the preparation.

[0009] Further, the molar ratio of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole to copper hexafluorosilicate is 1.5-2.5:1, preferably 2-2.5:1.

[0010] Furthermore, the solvent for the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution is methanol, and the volume of the solvent, based on the amount of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole, is 10-15 L / mol, preferably 13.5-14 L / mol.

[0011] Furthermore, the solvent of the copper hexafluorosilicate solution is water, and the volume of the solvent, based on the amount of copper hexafluorosilicate, is 20-40 L / mol, preferably 28-32 L / mol.

[0012] Furthermore, the dropping rate of the copper hexafluorosilicate solution is 0.01-0.15 mL / s.

[0013] Specifically, this invention recommends that both solutions be pre-cooled at 0°C before adding the copper hexafluorosilicate solution dropwise to the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution. Generally, 50-60 minutes is sufficient; in the embodiments of this invention, the pre-cooling time is 50 minutes. This invention also recommends that the copper hexafluorosilicate solution be continuously stirred during the dropwise addition process to prevent sedimentation before addition.

[0014] Furthermore, the reaction temperature is 0°C.

[0015] Further, the post-processing is as follows: the reaction solution is filtered, the resulting filter cake is washed several times with anhydrous methanol and dried to obtain the metal-organic framework material [Cu(bpz)(SiF6)].

[0016] The present invention also provides the application of the flexible metal-organic framework material with molecular sieving properties in the adsorption and separation of C2H2 / CO2 in mixed gases.

[0017] The flexible metal-organic framework material of this invention uses copper hexafluorosilicate as the metal salt and 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole as the organic ligand. Due to its suitable pore size and fluorinated functional sites, the material enhances its recognition of acetylene through strong hydrogen bonding between the anion column and the pyrazole ligand with C2H2. However, the presence of the methyl group lowers the binding energy of CO2, preventing CO2 molecules from opening the framework channels and resulting in a macroscopically non-adsorbed effect, thus exhibiting a sieving effect similar to a molecular sieve. The significant adsorption difference between C2H2 and CO2 in this framework material can be used to separate C2H2 / CO2 mixed gases, exhibiting extremely high separation selectivity and a large adsorption capacity for C2H2. It is a superior solid physical adsorbent possessing both characteristics.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The metal-organic framework material of the present invention is based on inorganic metal ions Cu 2+ Inorganic anion SiF6 2-The ultramicroporous metal-organic framework material [Cu(bpz)(SiF6)] was obtained by stirring the organic ligand 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole in an ice-water environment. The metal-organic framework material of this invention enhances acetylene capture through hydrogen bonding, and the presence of methyl groups lowers the binding energy of CO2, preventing CO2 molecules from opening the flexible framework channels. This results in extremely low, negligible, adsorption of carbon dioxide by the metal-organic framework material, exhibiting a molecular sieving effect. The rotation of the methyl group on the pyrazole ring causes the opening and closing of the pore windows, giving the material complete flexibility.

[0020] (2) The flexible metal-organic framework material of the present invention, which has molecular sieving properties, can be used to separate C2H2 / CO2 mixed gases due to the large adsorption difference between C2H2 and CO2, and has virtually no absorption of CO2, thus exhibiting molecular sieving properties. This material can be reused after multiple desorption / adsorption cycles, showing great potential in industrial applications. Attached Figure Description

[0021] Figure 1 The image shows the XRD pattern of the flexible MOF material with molecular sieving properties prepared in Example 1.

[0022] Figure 2 These are the nitrogen adsorption-desorption isotherms and CO2 adsorption isotherms of the flexible MOF material with molecular sieving properties prepared in Example 1.

[0023] Figure 3 This is the C2H2 / CO2 adsorption curve of the flexible MOF material with molecular sieving properties prepared in Example 1.

[0024] Figure 4 This is the IAST selectivity diagram of the MOF material with molecular sieve-like properties prepared in Example 1 at 296K for a C2H2 / CO2 mixed gas.

[0025] Figure 5 This is the Qst curve of C2H2 gas at 296K in Example 1. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0028] Example 1

[0029] 0.29 mmol of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole was dispersed in 4 mL of methanol by shaking, and this solution was designated as solution A. 0.13 mmol of copper hexafluorosilicate was dissolved in 4 mL of deionized water, and this solution was designated as solution B. Solutions A and B were simultaneously pre-cooled in an ice-water mixture for 50 min. Under 0 °C, solution B was slowly added dropwise to solution A with stirring, maintaining a dropping rate between 0.01 and 0.15 mL / s. The mixed solution was stirred in an ice-water environment at 0 °C for 12 h. After the reaction was complete, the mixture was filtered to obtain a blue-purple powder, which was washed three times with anhydrous methanol and dried under vacuum at 50 °C to obtain a novel flexible MOF material with molecular sieve-like properties.

[0030] The purity of the flexible MOF material prepared in Example 1 was first verified by powder X-ray diffraction. The XRD pattern of the flexible MOF material is shown below. Figure 1 As shown, the XRD characterization results of the flexible MOF material are consistent with the simulation.

[0031] The process of obtaining the fitted XRD pattern of MOF material is as follows:

[0032] 1) Cultivating Single Crystals: The lower layer solution, transition layer solution, and upper layer solution were sequentially added dropwise to a test tube. The lower layer solution was an ethylene glycol solution containing 0.005 g of copper hexafluorosilicate (1 mL). The transition layer solution was a methanol / ethylene glycol mixture with a volume ratio of 1:1 (0.75 mL each of methanol and ethylene glycol). The upper layer solution was a methanol solution containing 0.0058 g of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole (1 mL). The test tube was then placed in a constant temperature incubator at 27°C and allowed to stand for 3 months to obtain blue-purple crystals, which constitute the single crystal.

[0033] 2) Fitted XRD pattern of MOF material: Perform XRD analysis on the single crystal obtained in step 1) to obtain the fitted XRD result.

[0034] Then, the specific surface area of ​​the flexible MOF material prepared in Example 1 was characterized using an N2 adsorption-desorption isotherm at 77 K. However, even at low temperatures, N2 was still blocked outside the pores, resulting in almost no N2 adsorption at 77 K. Therefore, the characterization gas was changed, and the specific surface area of ​​[Cu(bpz)(SiF6)] was characterized using a CO2 adsorption-desorption isotherm at 195 K. Figure 2 As shown, under conditions of 195 K and 1 bar, the material's CO2 adsorption capacity reaches 116.12 (cm³). 3 / g STP), the curve is a type I adsorption isotherm, showing the characteristics of microporous materials, and the calculated BET specific surface area is 180.237m². 2 / g.

[0035] pass Figure 1 and Figure 2 As a result, it can be seen that the flexible MOF material synthesized in Example 1 is [Cu(bpz)(SiF6)].

[0036] To test the gas separation capability of the flexible MOF material in Example 1, the guest solvent in the framework needs to be removed by activation treatment before gas adsorption and separation capability testing: First, the freshly synthesized flexible MOF material product powder sample with molecular sieving properties is exchanged with dry methanol at least 8 times in one day. Then, on a Micromeritics ASAP 2020 instrument, the temperature is raised to 50°C at a heating rate of 1°C / min and vacuumed for 24 hours until the exhaust rate before measurement is 4 mm Hg / min.

[0037] The gases used for gas separation capability testing are C2H2 and CO2, and the temperature is 296K. The gas separation can be stabilized in a low-temperature thermostat. The test pressure is 0-1 bar. The gases used and their purities include: N2 (>99.999%), He (99.999%), C2H2 (99.99%), and CO2 (99.99%). The dry methanol used for exchange is HPLC-grade methanol produced by Alfa Aesar.

[0038] Gas adsorption tests were performed using a Micromeritics ASAP 2020 fully automated adsorption analyzer, and the resulting adsorption isotherms are shown below. Figure 3 As shown, the adsorption capacity for acetylene is as high as 92.1 cm⁻¹ at 296 K and 1 bar. 3 / g, adsorption capacity for carbon dioxide 2cm 3 / g.

[0039] The pure component isotherm data of C2H2 and CO2 at 296K were fitted and calculated in Origin using the two-site Langmuir-Frendrick isotherm model, and the results are as follows: Figure 4 As shown. IAST calculations indicate that at 296 K and 1 bar, the IAST selectivity for C2H2 / CO2 (50 / 50, v / v) is approximately 1*10-1. 5 Therefore, it can be seen that this novel MOF material with molecular sieving properties has excellent gas adsorption capacity and extremely excellent separation selectivity.

[0040] To further investigate the magnitude of the interaction forces between metal-organic framework materials and C2H2 and CO2 gas molecules, the equivalent heat of adsorption (Q) generated by the interaction between the framework and gas molecules was calculated through simulation. st To explain, such as Figure 5As shown in the figure. Since this MOF material basically does not adsorb CO2, the corresponding heat of adsorption is not calculated. As can be seen from the figure, Q st The value is 40.5 kJ / mol. As the acetylene loading increases, Q... st The value decreased slightly, which may be due to the acetylene molecule entering the skeleton and occupying adsorption sites, thus reducing the number of interaction sites.

[0041] Example 2

[0042] Example 2: Preparation of Flexible MOF Material. Example 1 was repeated, except that the reaction temperature was changed to room temperature, i.e., the mixed solution was stirred at room temperature for 12 hours. All other conditions remained unchanged, and the flexible MOF material was finally obtained. The MOF material prepared in Example 2 was characterized by XRD. Its XRD curve was consistent with the simulation, but at 296 K and 1 bar, the adsorption capacity for acetylene was only 24 cm³. 3 / g.

[0043] Example 2: The adsorption performance of the flexible MOF material is not ideal. The reason is that room temperature reduces the coordination between copper ions and organic ligands, thus affecting the material performance.

[0044] Example 3 (The ratio of reaction ligand to salt differs from that in Example 1)

[0045] Example 3: Preparation of Flexible MOF Material. Example 1 was repeated, except that the amount of copper hexafluorosilicate was replaced with 0.29 mmol. All other conditions remained unchanged, and the flexible MOF material was finally obtained. XRD characterization of the MOF material prepared in Example 3 revealed numerous impurity peaks around 20°, indicating that the flexible MOF material in Example 3 was impure. This may be due to incomplete reaction between the ligand and the salt.

[0046] Comparative Example 1

[0047] Comparative Example 1: Preparation of Flexible MOF Material Example 1 was repeated, except that instead of dissolving 0.13 mmol copper hexafluorosilicate in 4 mL of deionized water (referred to as Solution B), 0.13 mmol copper hexafluorosilicate was dissolved in 4 mL of N,N-dimethylformamide (referred to as Solution B). All other conditions remained the same. After filtration and drying, a blue-purple product was obtained. XRD analysis showed that the desired material was not synthesized. The reason for this may be that copper ions and ligands cannot coordinate in the DMF and methanol environment.

[0048] Comparative Example 2

[0049] 0.29 mmol of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole was dispersed and dissolved in 4 mL of methanol, denoted as solution A; 0.13 mmol of copper hexafluorozirconate was dissolved in 4 mL of deionized water, denoted as solution B. Solutions A and B were simultaneously pre-cooled in an ice-water mixture for 50 min. Under 0 °C, solution B was slowly added dropwise to solution A with stirring, maintaining a dropping rate between 0.01 and 0.15 mL / s. The mixed solution was stirred at 0 °C in an ice-water environment for 12 h. After the reaction was complete, the solid product was obtained by filtration, washed three times with anhydrous methanol, and dried under vacuum at 50 °C to obtain the final product.

[0050] The product of Comparative Example 2 was found to have impurity peaks by XRD characterization. It is considered that the atomic radius of zirconium is much larger than that of silicon atoms, so it cannot coordinate to form MOF.

[0051] Comparative Example 3

[0052] 0.29 mmol of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole was dispersed in 4 mL of chloroform, and 0.13 mmol of copper hexafluorosilicate was dissolved in 2 mL of deionized water. The two were mixed, and the mixture was heated under reflux at 50 °C for 12 hours. After filtration, washing, and drying, the product was characterized. XRD characterization of the product showed many impurity peaks and insufficient purity, which may be due to the ligand not coordinating well with copper ions in the chloroform and water system.

[0053] Comparative Example 4

[0054] Comparative Example 4: Preparation of Flexible MOF Material. Example 1 was repeated, except that "copper hexafluorosilicate was replaced with an equal molar amount of zinc hexafluorosilicate". All other conditions remained the same, and MOF material was finally obtained.

[0055] The XRD curves of the comparative 4MOF material were consistent with the simulations, but the adsorption capacity for acetylene at 296 K and 1 bar was too low, at 37 cm⁻¹. 3 The reason for the / g is likely that the radius of zinc atoms is larger than that of copper atoms, resulting in larger pores in the MOF material. However, the hydrogen bonding forces are reduced, thus significantly decreasing the amount of acetylene absorbed.

[0056] Comparative Example 5

[0057] Comparative Example 5: Preparation of Flexible MOF Material. Example 1 was repeated, except that the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole ligand was replaced with an equal molar amount of tetraethylbipyrazole (92494-09-2). All other conditions remained the same, and the MOF material was finally obtained.

[0058] The XRD pattern of the comparative 5MOF material is consistent with the simulation, but the adsorption capacity for acetylene at 296 K and 1 bar is too low, at 12 cm⁻¹.3 The reason for the / g is that the structure of the tetraethylbipyrazole ligand is too long, which makes it difficult for the prepared MOF material to form a certain adsorption channel.

[0059] Comparative Example 6

[0060] The preparation of the flexible MOF material in Comparative Example 6 was repeated in Example 1, except that the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole ligand was replaced with an equal molar amount of bipyrazole (16227-15-9), and all other conditions remained the same. The MOF material was finally obtained.

[0061] The comparative example 6MOF material product showed many impurity peaks when characterized by XRD, indicating insufficient purity. This was likely due to Cu not being properly coupled to the ligand.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a flexible metal-organic framework material with molecular sieving properties, characterized in that... Includes the following steps: Copper hexafluorosilicate solution was added dropwise to 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution under ice-water conditions. After the addition was complete, the reaction was stirred under ice-water conditions for 10-15 hours. The resulting reaction solution was post-treated to obtain the flexible metal-organic framework material [Cu(bpz)(SiF6)] with molecular sieving properties, thus completing the preparation. The molar ratio of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole to copper hexafluorosilicate is 1.5-2.5:1; The solvent for the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution is methanol; the solvent for the copper hexafluorosilicate solution is water.

2. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that... The molar ratio of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole to copper hexafluorosilicate is 2-2.5:

1.

3. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that... The volume of solvent in the 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole solution, expressed as the molar amount of 3,5,3,5-tetramethyl-1H,1H-[4,4]bipyrazole, is 10-15 L / mol.

4. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that... The volume of the solvent in the copper hexafluorosilicate solution, expressed as the amount of copper hexafluorosilicate, is 20-40 L / mol.

5. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that... The dropping rate of the copper hexafluorosilicate solution is 0.01-0.15 mL / s.

6. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that: The reaction temperature is 0°C.

7. The method for preparing a flexible metal-organic framework material with molecular sieving properties as described in claim 1, characterized in that... The post-processing is as follows: the reaction solution is filtered, the resulting filter cake is washed several times with anhydrous methanol and dried to obtain the metal-organic framework material [Cu (bpz)(SiF6)].

8. A flexible metal-organic framework material with molecular sieving properties prepared by the method described in any one of claims 1-7.

9. The application of the flexible metal-organic framework material with molecular sieving properties as described in claim 8 in the adsorption and separation of C2H2 / CO2 mixed gases.

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