A covalent organic framework for krypton-xenon gas separation and its preparation method

Abstract

This invention discloses a covalent organic framework for the separation of krypton and xenon gases and its preparation method. Using tetrahedral symmetric aldehyde ligands with four sites and amino ligands with different side group substitution sites as raw materials, o-dichlorobenzene and n-butanol as solvents, and glacial acetic acid as catalyst, a covalent organic framework compound with a 7-fold interpenetrating PTS topological network structure is synthesized through pre-ultrasonic treatment, high-temperature reaction process, and purification steps such as filtration and extraction. The synthesized covalent organic framework compound can selectively adsorb and separate xenon-krypton mixed gases.

Description

Technical Field

[0001] This invention relates to the field of gas separation technology, specifically to a novel covalent organic framework material and its preparation method, as well as its application in the field of krypton-xenon gas separation. Background Technology

[0002] Xenon (Xe) and krypton (Ke) gases have important applications in nuclear energy, semiconductor manufacturing, medical devices, and space technology. However, these two rare gases exist in the air at extremely low concentrations (0.087 ppm V xenon, 1.14 ppm V krypton), and the separation of their mixtures is a crucial industrial process. Industrially, high-purity xenon and krypton are produced as byproducts of cryogenic air fractionation, yielding a mixture of 20% xenon and 80% krypton, which can then be purified through further fractionation. On the other hand, xenon and krypton are also present in radioactive waste gases from nuclear power plants. Separating them using specific technologies provides another source of high-purity xenon and krypton. Given the significant damage that radioactive xenon and krypton waste gases cause to the atmosphere and living organisms, the reuse of xenon and krypton gases from nuclear power plant waste gases holds immense importance and has promising applications.

[0003] Although cryogenic distillation is a feasible gas separation technology, its complex working environment and high energy consumption necessitate the search for alternative methods. Physical adsorption is considered a promising method for selective adsorption and separation of gases. However, traditional physical adsorbents, such as activated carbon, zeolite, and clay, often exhibit low selectivity and adsorption capacity. In recent years, covalent organic frameworks (COFs), as emerging porous materials, possess abundant pores and a large specific surface area, showing great potential for development in the field of selective adsorption and separation of gases.

[0004] In view of this, the present invention designs a novel covalent organic framework that can effectively and selectively separate xenon-krypton mixed gases. Summary of the Invention

[0005] This invention provides a novel covalent organic framework, its preparation method, and its application. This covalent organic framework can effectively selectively adsorb and separate xenon-krypton mixed gases.

[0006] The technical solution of the present invention is as follows:

[0007] A covalent organic framework material is synthesized from aldehyde ligands with tetrahedral symmetry at four sites and amino ligands with different side group substitutions at four sites, and has a seven-fold interpenetrating PTS topological three-dimensional network structure.

[0008] The structural formula of the aldehyde ligand with tetrahedral symmetry at four sites is selected from one of the following:

[0009]

[0010] The structural formulas of amino ligands with different side group substitution sites at four sites are selected from one of the following:

[0011]

[0012] The preparation method of the covalent organic framework material of the present invention is as follows:

[0013] The aldehyde ligand with four tetrahedral symmetric sites, the amino ligand with four sites having different side group substitutions, and the organic solvent were mixed, and the catalyst acetic acid was added. The mixture was ultrasonically mixed (10 min), and then cyclically frozen and vacuumed (to remove air from the system). The mixture was then reacted at 120°C for three days in a sealed state. After post-treatment, the covalent organic framework material was obtained.

[0014] The preferred molar ratio of an aldehyde ligand with four sites of tetrahedral symmetry to an amino ligand with four sites of different side group substitution is 1:1.

[0015] The preferred organic solvent is a mixture of o-dichlorobenzene and n-butanol in a volume ratio of 1:1;

[0016] The preferred catalyst is fed in the form of 6 mol / L acetic acid, with a volume ratio of 6 mol / L acetic acid to organic solvent of 1:10;

[0017] The specific post-processing method is as follows: After the reaction is completed, the mixture is cooled to room temperature and filtered to obtain the crude product. The crude product is purified by extraction with tetrahydrofuran and acetone, respectively. After extraction, the product is placed in a vacuum oven and dried at 80°C for 12 hours to obtain the final purified covalent organic framework solid powder.

[0018] The covalent organic framework material described in this invention can be applied to the field of gas separation, especially to the effective selective adsorption and separation of xenon-krypton mixed gases.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] (1) The novel covalent organic framework material prepared by this invention has high crystallinity and good thermal stability. Due to its characteristic pores and high specific surface area, it has important development potential and application prospects in the field of gas separation.

[0021] (2) The novel covalent organic framework material prepared by this invention has high selectivity, large adsorption capacity and fast separation effect in the xenon-krypton mixed gas separation experiment. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a covalent organic framework with a seven-fold interpenetrating PTS topology.

[0023] Figure 2 The experimental PXRD and refined PXRD spectra of COF-1 in Example 1 of this invention are shown.

[0024] Figure 3 The image shows the FT-IR spectra of COF-1 and its corresponding ligands in Example 1 of this invention.

[0025] Figure 4 This is the single-component adsorption isotherm of xenon and krypton in COF-1 in Example 1 of the present invention.

[0026] Figure 5 The experimental PXRD and refined PXRD spectra of COF-2 in Example 2 of this invention are shown.

[0027] Figure 6 The image shows the FT-IR spectra of COF-2 and its corresponding ligands in Example 2 of this invention.

[0028] Figure 7 This is the single-component adsorption isotherm of xenon and krypton in COF-2 in Example 2 of the present invention.

[0029] Figure 8 This is a diagram of the COF-2 penetration experiment in a xenon-krypton (20 / 80) mixture in Example 2 of the present invention. Detailed Implementation

[0030] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1

[0032] Preparation of COF-1 and its application in the separation of xenon-krypton mixed gases:

[0033]

[0034] 0.02 mmol of a four-site aldehyde ligand (Formula 1) and 0.02 mmol of a four-site amino ligand (Formula 2a) were added to a Schlenk tube, along with 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol as a mixed solvent. After thorough mixing, 100 μL of 6M AA was added as a catalyst. The mixture was sonicated for 10 minutes, and then the air in the system was removed by three cycles of freezing and vacuuming. The sealed Schlenk tube was then heated in an oven at 120 °C for 72 h. After the reaction was completed and cooled to room temperature, the crude product was collected by filtration. The precipitate was extracted with tetrahydrofuran and acetone for 24 h using a Soxhlet extractor, and finally dried in a vacuum oven at 80 °C for 12 h to obtain purified powdered COF-1.

[0035] The obtained COFs material has a seven-fold interlocked PTS topology, and the specific structural information is as follows: Figure 1 As shown.

[0036] See Figure 2 Powder X-ray diffraction measurements showed that COF-1 exhibited three strong peaks at 4.74°, 6.24°, and 9.50°, which corresponded well with the PXRD pattern simulated by the PTS topology with seven interlocks, proving the successful synthesis of COF-1 material.

[0037] See Figure 3 Fourier transform infrared (FT-IR) spectroscopy was used to analyze the infrared spectra of the required ligand and the corresponding product COF-1. The product was found to be 1618 cm⁻¹. -1 The presence of characteristic stretching vibrations of C=N bonds and the significant reduction in characteristic peaks corresponding to amino and aldehyde groups also demonstrate the successful synthesis of COF-1.

[0038] See Figure 4 Single-component adsorption isotherms of xenon and krypton were measured at 273 K and 298 K, respectively. The results showed that COF-1 exhibited a higher adsorption capacity for xenon than krypton, reaching 1.4 mmol / g under optimal conditions (273 K), which is relatively high among known covalent organic frameworks, indicating its potential application in the field of selective adsorption and separation of gases.

[0039] Example 2

[0040] Preparation of COF-2 and its application in the separation of xenon-krypton mixed gases:

[0041]

[0042] 0.02 mmol of a four-site aldehyde ligand (Formula 1) and 0.02 mmol of a four-site amino ligand (Formula 2b) were added to a Schlenk tube, along with 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol as a mixed solvent. After thorough mixing, 100 μL of 6M AA was added as a catalyst. The mixture was sonicated for 10 minutes, and then the air in the system was removed by three cycles of freezing and vacuuming. The sealed Schlenk tube was then placed in an oven at 120 °C and heated for 72 h. After the reaction was completed and cooled to room temperature, the crude product was collected by filtration. The precipitate was extracted with tetrahydrofuran and acetone for 24 h using a Soxhlet extractor, and finally dried in a vacuum oven at 80 °C for 12 h to obtain purified powdered COF-2.

[0043] The obtained COFs material has a seven-fold interlocked PTS topology, and the specific structural information is as follows: Figure 1 As shown.

[0044] See Figure 5 Powder X-ray diffraction measurements showed that the three strong peaks of COF-2 at 4.6°, 6.2°, and 9.5° corresponded well with the PXRD pattern simulated by the PTS topology with seven interlocks, proving the successful synthesis of COF-2 material.

[0045] See Figure 6 Fourier transform infrared (FT-IR) spectroscopy was used to analyze the infrared spectra of the required ligand and the corresponding product COF-2. The product was found to have a wavelength of 1624 cm⁻¹. -1 The presence of characteristic stretching vibrations of C=N bonds and the significant reduction in characteristic peaks corresponding to amino and aldehyde groups also demonstrate the successful synthesis of COF-2.

[0046] See Figure 7 The single-component adsorption isotherms of xenon and krypton were measured at 273 K and 298 K, respectively. The results showed that COF-2 exhibited a higher adsorption capacity for xenon than krypton, reaching 4.3 mmol / g under optimal conditions (273 K), which is in a leading position in the field of gas adsorption and has great application prospects in the selective adsorption of xenon.

[0047] See Figure 8 Gas penetration experiments at room temperature and in a xenon and krypton (20 / 80) mixture showed that COF-2 can achieve efficient separation of this mixture.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. For those skilled in the art, several modifications and changes can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. Application of a covalent organic framework material in selective adsorption and separation of xenon-krypton mixed gas. The covalent organic framework material is synthesized by tetrahedral symmetry four-site aldehyde ligand and amino ligand with different side group substitution four-site, and has seven-fold interpenetrating pts topology three-dimensional network structure. wherein The structural formula of the tetrahedral symmetry four-site aldehyde ligand is selected from one of the following: The structural formula of the amino ligand with different side group substitution four-site is selected from one of the following: 。 2. Use according to claim 1, wherein The preparation method of the covalent organic framework material is: The tetrahedral symmetry four-site aldehyde ligand, the amino ligand with different side group substitution four-site and the organic solvent are mixed, the catalyst acetic acid is added, ultrasonic mixing is carried out, and then the cycle freezing and vacuumizing is carried out. The reaction is carried out at 120 DEG C for three days in a sealed state, and then the post-treatment is carried out to obtain the covalent organic framework material.

3. Use according to claim 2, wherein the compound is ###0002### The molar ratio of the tetrahedral symmetry four-site aldehyde ligand to the amino ligand with different side group substitution four-site is 1:

1.

4. The use according to claim 2, wherein The organic solvent is a mixed solvent of o-dichlorobenzene and n-butanol with a volume ratio of 1:

1.

5. The use according to claim 2, wherein the compound is ###0002### The catalyst is fed in the form of 6 mol / L acetic acid, and the volume ratio of 6 mol / L acetic acid to organic solvent is 1:

10.

6. The use according to claim 2, wherein The post-treatment method is as follows: after the reaction is completed, the reaction system is cooled to room temperature, the crude product is obtained by filtration, the crude product is subjected to Soxhlet purification with tetrahydrofuran and acetone respectively, and then the Soxhlet purification is completed. The vacuum oven is placed at 80 DEG C for 12 h to obtain the final purified covalent organic framework solid powder.

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