Covalent organic framework materials with three-dimensional pts topology and methods of making and using the same

Abstract

This invention discloses a covalent organic framework material with a three-dimensional interpenetrating polymorphic structure (PTS) topology, its preparation method, and its applications. The covalent organic framework material is synthesized from tetrahedral symmetrical four-site aldehyde ligands and four-site amino ligands with different side group substitutions as raw materials, anisole and n-butanol as solvents, and glacial acetic acid as a catalyst. The process involves pre-treatment with ultrasound, a high-temperature reaction, and purification steps such as filtration and extraction to synthesize a three-dimensional network structure with a seven-fold interpenetrating PTS topology. Through specific monomer combinations and reaction conditions, this material forms a unique highly interpenetrating framework, exhibiting preferential adsorption characteristics for ethane molecules. The material has a high adsorption capacity for ethane and excellent selective separation capability for ethylene / ethane mixtures. This invention also provides a simple and mild preparation method for this material. This material can be used for energy-saving separation of ethylene and ethane in petrochemical industries, replacing traditional high-energy-consuming distillation processes, and has great application potential.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, specifically relating to a covalent organic framework material, particularly a covalent organic framework material with a seven-fold interpenetrating PTS topological three-dimensional network structure, its preparation method, and its application in the selective separation of ethylene / ethane mixed gases. Background Technology

[0002] Ethylene (C2H4) is the most produced basic organic chemical in the petrochemical industry, widely used in the production of polyethylene, synthetic rubber, and other products. Industrially, ethylene mainly originates from petroleum steam cracking, and ethane (C2H6) often coexists in the cracked gas. To obtain polymerization-grade ethylene (purity >99.5%), ethylene and ethane must be efficiently separated.

[0003] However, ethylene and ethane have extremely similar molecular sizes, polarities, and boiling points, meaning that traditional separation methods—low-temperature high-pressure distillation—must be achieved under harsh conditions of approximately 240 K and 2.4 MPa, requiring hundreds of distillation columns and resulting in extremely high energy consumption. Statistics show that the annual energy consumption of olefin / alkane distillation accounts for approximately 0.3% of global energy consumption. Therefore, the development of energy-efficient and novel separation technologies is urgently needed.

[0004] Physical adsorption separation technology has attracted much attention due to its low energy consumption and simple operation. However, traditional porous adsorbents such as activated carbon and zeolite exhibit poor selectivity and low adsorption capacity for ethylene / ethane. In recent years, covalent organic frameworks (COFs), as an emerging crystalline porous material, have shown great potential in the field of gas adsorption separation due to their advantages such as designable structure, regular pores, and large specific surface area. Therefore, developing a novel COF material with high ethane selectivity, high adsorption capacity, and stable structure can effectively and selectively separate ethylene / ethane mixtures, which has significant scientific and industrial value. Summary of the Invention

[0005] To address the aforementioned issues and solve the problems of high energy consumption in ethylene / ethane separation and insufficient selectivity and adsorption capacity of traditional adsorbents and existing COF materials in the prior art, this invention provides a covalent organic framework material with a three-dimensional PTS topology, its preparation method, and its application. This novel covalent organic framework material achieves preferential and efficient adsorption of ethane through specific monomer design and a highly interpenetrating network structure, and can be applied to the energy-saving separation of ethylene / ethane mixed gases.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention proposes a covalent organic framework material with a three-dimensional PTS topology. The covalent organic framework material is obtained by condensation of a tetrahedral symmetric four-site aldehyde ligand and a four-site amino ligand with different side group substitutions. The covalent organic framework material has a seven-fold interpenetrating PTS topology three-dimensional network structure. The structure of the tetrahedral symmetric four-site aldehyde ligand is as follows: ; The structure of the four-site amino ligand with different side group substitutions is selected from one of the following formulas: .

[0007] The combination of a tetrahedral symmetrical four-site aldehyde ligand with four-site amino ligands having different side group substitutions can form an unprecedented seven-fold interpenetrating polarimetric (PTS) topological network structure under solvothermal conditions. This highly interpenetrating structure endows the material with a unique nano-confined space, which has a significantly stronger affinity for ethane molecules than for ethylene molecules, thereby achieving preferential adsorption of ethane.

[0008] Furthermore, the side groups (such as methyl and methoxy) on the four-site amino ligands with different side group substitutions can further regulate the adsorption selectivity of the material for ethane / ethylene by changing the pore microenvironment.

[0009] Furthermore, the specific surface area of ​​the material is 800~1500 m². 2 / g, pore size distribution is concentrated in 1.2~1.8 nm; under 298K and 1 bar conditions, the ethane adsorption capacity is ≥3.6 mmol / g, and the ethane / ethylene single component adsorption capacity ratio is ≥1.3.

[0010] This invention also provides a method for preparing the covalent organic framework material, comprising the following steps: Tetrahedral symmetrical four-site aldehyde ligands and four-site amino ligands with side group substitutions are added to an organic solvent, followed by the addition of acetic acid catalyst. After ultrasonic dispersion, the mixture is cyclically frozen and vacuumed to remove oxygen. After sealing, the mixture is reacted at 110~130℃ for 60~84h. After the reaction is completed, post-treatment is performed to obtain the covalent organic framework material.

[0011] Furthermore, the molar ratio of the tetrahedral symmetrical four-site aldehyde ligand to the four-site amino ligand with side group substitution is 1:(0.9~1.1); the organic solvent is a mixed solvent of anisole and n-butanol in a volume ratio of 1:(0.8~1.2).

[0012] Furthermore, the concentration of the acetic acid catalyst is 5-7 mol / L, and the volume ratio of the catalyst to the organic solvent is 1:(8-12).

[0013] Furthermore, the post-processing includes: cooling to room temperature after the reaction, filtering and collecting the crude product; then purifying the crude product by Soxhlet extraction with tetrahydrofuran and acetone respectively; finally, vacuum drying at 80-100℃ for 10-14h under vacuum conditions to obtain the purified covalent organic framework material.

[0014] This invention also proposes the application of covalent organic framework materials with three-dimensional PTS topology as described above in the field of gas separation. Specifically, it proposes an application for the selective adsorption of ethane in ethylene / ethane mixed gases to achieve the separation of ethylene and ethane.

[0015] The volume percentage of ethylene in the mixed gas is 10% to 90%. Experiments show that, under the conditions of 298 K and 1 bar, the adsorption capacity of the material of the present invention for ethane can reach 4.56 mmol / g (methyl-substituted side groups), which is significantly higher than that for ethylene, and it exhibits excellent dynamic separation performance in the mixed gas breakthrough experiment.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a combination of a tetrahedral aldehyde ligand with a specific side group substituted four-site amino ligand to successfully construct a novel COF material with a seven-fold interpenetrating PTS topology. This material has high crystallinity, good thermal stability, and due to its characteristic pores and high specific surface area, it has important development potential and application prospects in the field of gas separation.

[0017] (2) The material of the present invention achieves preferential and efficient adsorption of ethane in the COF system, which breaks through the conventional understanding that most porous materials preferentially adsorb ethylene. It belongs to reverse selective adsorption, which provides a new path for ethylene / ethane separation (i.e., directly obtaining pure ethylene, rather than first adsorbing ethylene and then desorbing it). It has outstanding substantive features and significant progress.

[0018] (3) The material of the present invention has a high adsorption capacity for ethane (up to 4.56 mmol / g), excellent ethylene / ethane selectivity, good thermal stability, high crystallinity, and can be reused, which is superior to activated carbon, zeolite and most COF materials in the prior art.

[0019] (4) The preparation method of the present invention is stable, has mild conditions, is easy to scale up, and is suitable for industrial production. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the seven-fold interpenetrating PTS topology of the covalent organic framework material of the present invention.

[0021] Figure 2The experimental PXRD pattern and the refined PXRD pattern of the 3D-TAPB-Me-COF prepared in Example 1 of this invention are compared.

[0022] Figure 3 The FT-IR spectra of 3D-TAPB-Me-COF and its corresponding ligand prepared in Example 1 of this invention are shown.

[0023] Figure 4 The single-component adsorption isotherms of ethylene and ethane at 298 K for the 3D-TAPB-Me-COF prepared in Example 1 of this invention are shown.

[0024] Figure 5 The experimental PXRD pattern and the refined PXRD pattern of the 3D-TAPB-OMe-COF prepared in Example 2 of this invention are compared.

[0025] Figure 6 The FT-IR spectra of 3D-TAPB-OMe-COF and its corresponding ligand prepared in Example 2 of this invention are shown.

[0026] Figure 7 The single-component adsorption isotherms of ethylene and ethane at 298 K for the 3D-TAPB-OMe-COF prepared in Example 2 of this invention are shown.

[0027] Figure 8 The breakthrough test curve of 3D-TAPB-Me-COF prepared in Example 1 of this invention for ethylene / ethane (50 / 50) mixture at room temperature. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Example 1: Preparation and performance testing of 3D-TAPB-Me-COF

[0030] 1. Material synthesis 0.02 mmol of a tetrahedral symmetrical four-site aldehyde ligand (structure shown in Formula 1) and 0.02 mmol of a methyl-substituted four-site amino ligand (structure shown in Formula 2b) were added to a Schlenk tube, followed by 0.5 mL of anisole and 0.5 mL of n-butanol as a mixed solvent. After thorough mixing, 100 μL of 6 M acetic acid aqueous solution was added as a catalyst. The Schlenk tube was ultrasonically treated for 10 minutes to ensure complete dispersion of the reactants. Subsequently, air was thoroughly removed from the system through three cycles of "freezing-vacuuming-thawing" (i.e., cyclic freezing-vacuuming). The sealed Schlenk tube was placed in an oven at 120 °C and allowed to react for 72 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the crude product was collected by filtration. The crude product was purified by Soxhlet extraction for 24 hours, using tetrahydrofuran and acetone as solvents, respectively. Finally, the purified product was placed in a vacuum oven and dried at 80°C for 12 hours to obtain a light yellow powder 3D-TAPB-Me-COF.

[0031] The obtained COFs material has a seven-fold interpenetrating PTS topology, and the specific structural information is as follows: Figure 1 As shown.

[0032] 2. Structural Characterization PXRD characterization: such as Figure 2 As shown, powder X-ray diffraction (PXRD) measurements revealed a strong diffraction peak at 6.34°, attributed to the (202) crystal plane. Simultaneously, significant diffraction peaks appeared at 4.20°, 4.78°, 9.52°, 10.35°, 12.67°, and 17.52°, corresponding to the (200), (002), (004), (402), (404), and (800) crystal planes, respectively. This pattern closely matches the PXRD pattern of the seven-fold interpenetrating PTS topology simulated using Materials Studio, confirming that the synthesized material possesses the target three-dimensional network structure, and the 3D-TAPB-Me-COF material was successfully synthesized.

[0033] FT-IR characterization: such as Figure 3 As shown, Fourier transform infrared (FT-IR) spectroscopy was used to compare the infrared spectra of the corresponding ligand and the corresponding product COF-1. The product was found to have a wavelength of 1622 cm⁻¹. -1 A distinct new absorption peak appears at this point, attributed to the characteristic stretching vibration of the C=N bond, while the aldehyde group (~1700 cm⁻¹) shows a similar peak. -1 ) and amino (~3300-3500 cm) -1 The significant decrease in the characteristic peaks of ) indicates that the Schiff base condensation reaction was successfully carried out, and also proves the successful synthesis of 3D-TAPB-Me-COF.

[0034] 3. Gas adsorption performance test The single-component adsorption isotherms of pure ethylene and ethane on 3D-TAPB-Me-COF were tested using a gravimetric gas adsorption analyzer at 298 K and 1 bar. The results are as follows: Figure 4 As shown, the material's adsorption capacity for ethane reaches 4.56 mmol / g, which is relatively high among known covalent organic frameworks, while its adsorption capacity for ethylene is significantly lower. This indicates that the material has preferential adsorption capacity for ethane, and its ethane / ethylene adsorption selectivity is superior to most porous materials reported to date.

[0035] 4. Dynamic separation performance test At room temperature, 3D-TAPB-Me-COF was packed into a fixed-bed adsorption column, and an ethylene / ethane mixture with a volume ratio of 50 / 50 was introduced. Figure 8 The breakthrough curves show that ethane preferentially exits from the adsorption column outlet (ethane breakthrough time is earlier), while ethylene breakthrough occurs after a longer period. This result directly proves that the material can efficiently separate ethylene / ethane mixtures under actual dynamic conditions, and that ethane, as the preferential adsorption component, allows for the initial acquisition of high-purity ethylene in the outlet gas.

[0036] Example 2: Preparation and performance testing of 3D-TAPB-OMe-COF

[0037] 1. Material synthesis 0.02 mmol of a tetrahedral symmetric four-site aldehyde ligand (structure shown in Formula 1) and 0.02 mmol of a methoxy-substituted four-site amino ligand (structure shown in Formula 2d) were added to a Schlenk tube, and the remaining synthesis steps and post-treatment conditions were the same as in Example 1. The final product was a pale yellow powder, 3D-TAPB-OMe-COF.

[0038] 2. Structural Characterization PXRD characterization: such as Figure 5 As shown, the PXRD pattern of the product shows a main peak at 6.43°, which belongs to the (202) crystal plane. Meanwhile, the diffraction peaks at 4.79°, 9.53°, 10.60°, 12.86°, and 17.93° correspond to the (200), (400), (402), (404), and (800) crystal planes, respectively. The PXRD pattern is well-corresponding to the simulated PXRD pattern of the PTS topology with seven-fold interpenetration, proving the successful synthesis of the 3D-TAPB-OMe-COF material.

[0039] FT-IR characterization: such as Figure 6As shown, the infrared spectra of the corresponding ligand and the corresponding product 3D-TAPB-OMe-COF were compared by Fourier transform infrared (FT-IR) spectroscopy. The product's infrared spectrum was at 1630 cm⁻¹. -1 The presence of a characteristic absorption peak for the C=N bond and a significant decrease in the amino and aldehyde peaks of the ligand indicate successful condensation.

[0040] 3. Gas adsorption performance test Single-component adsorption isotherms of ethylene and ethane for 3D-TAPB-OMe-COF were tested at 298 K and 1 bar. The results are as follows: Figure 7 As shown, the adsorption capacity of the material for ethane is 3.64 mmol / g, which is still higher than that for ethylene, but slightly lower than that of the methyl-substituted material in Example 1. This indicates that the adsorption capacity and selectivity of the material can be adjusted within a certain range by changing the side groups (methyl, methoxy).

[0041] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A covalent organic framework material with a three-dimensional PTS topology, characterized in that, The covalent organic framework material is obtained by condensation of a tetrahedral symmetric four-site aldehyde ligand and a four-site amino ligand with different side group substitutions, and the covalent organic framework material has a seven-fold interpenetrating PTS topological three-dimensional network structure. The structure of the tetrahedral symmetric four-site aldehyde ligand is as follows: ； The structure of the four-site amino ligand with different side group substitutions is selected from one of the following formulas: 。 2. The method for preparing a covalent organic framework material with a three-dimensional PTS topology as described in claim 1, characterized in that, Includes the following steps: Tetrahedral symmetrical four-site aldehyde ligands and four-site amino ligands with side group substitutions are added to an organic solvent, followed by the addition of acetic acid catalyst. After ultrasonic dispersion, the mixture is cyclically frozen and vacuumed to remove oxygen. After sealing, the mixture is reacted at 110~130℃ for 60~84h. After the reaction is completed, post-treatment is performed to obtain the covalent organic framework material.

3. The method for preparing a covalent organic framework material with a three-dimensional PTS topology according to claim 1, characterized in that, The molar ratio of the tetrahedral symmetrical four-site aldehyde ligand to the four-site amino ligand with side group substitution is 1:(0.9~1.1); the organic solvent is a mixed solvent of anisole and n-butanol in a volume ratio of 1:(0.8~1.2).

4. The method for preparing a covalent organic framework material with a three-dimensional PTS topology according to claim 1, characterized in that, The concentration of the acetic acid catalyst is 5-7 mol / L, and the volume ratio of the catalyst to the organic solvent is 1:(8-12).

5. The method for preparing a covalent organic framework material with a three-dimensional PTS topology according to claim 1, characterized in that, The post-processing includes: cooling to room temperature after the reaction, filtering and collecting the crude product; then purifying the crude product by Soxhlet extraction with tetrahydrofuran and acetone, respectively; and finally drying under vacuum at 80-100℃ for 10-14 hours to obtain the purified covalent organic framework material.

6. The application of the covalent organic framework material with three-dimensional PTS topology as described in claim 1 in the field of gas separation.

7. The application according to claim 6, characterized in that: The covalent organic framework material is used to selectively adsorb ethane in an ethylene / ethane mixture, thereby achieving the separation of ethylene and ethane.

8. The application according to claim 7, characterized in that, The volume percentage of ethylene in the mixed gas is 10% to 90%; the adsorption capacity of the covalent organic framework material for ethane is greater than that for ethylene, and the adsorption capacity for ethane is not less than 3.6 mmol / g under the conditions of 298 K and 1 bar.

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