Application of a pyrazole-cobalt-based metal-organic framework material with dynamic pore size to capture sulfur hexafluoride

Abstract

A pyrazole-cobalt-based metal-organic framework material with dynamic pore size is used to capture sulfur hexafluoride, belonging to the technical field of preparation of crystalline porous materials. Co-DPB is synthesized by organic ligand (H2DPB) [H2DPB = 1,3-di(1-H-pyrazolyl)benzene] and cobalt acetate tetrahydrate under solvent thermal conditions. The vibration of the ligand benzene ring gives the MOF a dynamic pore size, which is beneficial to enhance the force on the sulfur hexafluoride molecule. Based on the strong force of Co-DPB on sulfur hexafluoride, it exhibits excellent sulfur hexafluoride / nitrogen separation ability. In addition, Co-DPB also has high thermal stability and moisture resistance, and has potential application prospects for the capture of sulfur hexafluoride in real industrial tail gas.

Description

Technical Field

[0001] The present invention relates to metal-organic coordination polymer materials, belonging to the technical field of crystalline materials. It is characterized by a cobalt-based metal-organic framework material for the efficient capture of sulfur hexafluoride, belonging to the technical field of crystalline porous material preparation and gas adsorption. Background Art

[0002] Sulfur hexafluoride (SF6) is widely used as a shielding gas in the power industry due to its excellent dielectric and arc-extinguishing properties. However, it also has a strong greenhouse effect, with a unit temperature rise approximately 23,900 times that of carbon dioxide, making it considered the gas with the highest temperature rise. Therefore, to protect the environment and mitigate the greenhouse effect, sulfur hexafluoride emissions must be controlled as much as possible. In industry, the mainstream method for treating waste gas containing sulfur hexafluoride is incineration, which involves calcining and degrading SF6. However, degradation of SF6 produces other potentially harmful gases, such as hydrofluoric acid (HF) and sulfur dioxide (SO2), which can easily cause secondary pollution. A more desirable treatment method is to separate the sulfur hexafluoride from the primary impurity, nitrogen (N2), and purify it for reuse. This method not only effectively mitigates the greenhouse effect but also allows for the recycling of SF6 gas, thereby reducing the cost of using SF6.

[0003] Existing technologies for separating SF6 / N2 include cryogenic distillation, liquefaction, and cryogenic freezing. However, due to the low concentration of SF6 in industrial waste gas (less than 10%), these separation technologies often have unavoidable drawbacks such as high energy consumption and low purification efficiency.

[0004] In contrast, adsorption separation technology based on porous adsorbents is an efficient and energy-saving purification method. This technology has shown great potential in the field of gas separation. The technical core of adsorption separation lies in the research and development of adsorbents. Traditional porous materials such as zeolites and porous carbon have made initial progress in the field of sulfur hexafluoride capture as adsorbents, promoting the development of this field. However, fine control of pore size and pore environment is quite challenging for these materials, thus limiting further breakthroughs in separation performance (adsorption capacity and separation selectivity).

[0005] Metal-organic frameworks (MOFs) materials are crystalline porous materials with a periodic network structure formed by self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. The advantage of its precise control of pore size and pore environment makes MOFs materials one of the ideal candidate materials in the field of adsorption separation. It is precisely based on the above characteristics that MOFs have shown unique advantages in selective molecular recognition and separation. The present invention uses cobalt-based MOFs (Co-DPB) constructed with bidentate pyrazole ligands (H2DPB) [H2DPB = 1,3-di(1-H-pyrazolyl)benzene] to achieve efficient SF6 capture. Since the benzene ring structure of the MOFs ligand has vibrational flexibility, Co-DPB presents a molecular trap structure with dynamic size. It is helpful to identify and capture sulfur hexafluoride molecules of corresponding size In terms of performance, Co-DPB exhibited excellent sulfur hexafluoride adsorption capacity (2.82 mmol / g) and excellent sulfur hexafluoride / nitrogen selectivity at room temperature (25 degrees Celsius) and even at low pressure (0.1 bar). Furthermore, dynamic permeation separation experiments showed that a 10% concentration of SF6 could be purified to a concentration exceeding 99.9% by the Co-DPB adsorbent in a single adsorption-desorption cycle. Furthermore, its high SF6 / N2 separation capability was maintained without degradation over multiple permeation adsorption-desorption cycles even at RH = 90%. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing a Co(II)-based metal organic framework material constructed with a pyrazole ligand, which can be used for the capture of low-concentration sulfur hexafluoride.

[0007] A pyrazole ligand-based Co(II)-based metal-organic framework material Co-DPB is a purple bulk crystalline material prepared by solvent thermal reaction of organic ligand H2DPB and cobalt source. The chemical formula is CoC 12 H8N4, where H2DPB is 1,3-di(1-H-pyrazolyl)benzene, with the molecular formula C 12 H 10 N4.

[0008] From the perspective of crystal structure, Co-DPB belongs to the tetragonal system with space group I41 / amd and unit cell parameters α=90°,β=90°,γ=90°. In the Co-DPB framework, all Co atoms are coordinated with four N atoms in a tetrahedral configuration. These coordinated N atoms come from the pyrazole groups of four different ligands. The N atoms on the two pyrazoles in each ligand in the framework participate in the coordination, and the adjacent metal atoms form a zigzag metal chain secondary building unit (SBU) through the bridging pyrazole groups. The ligands and the metal chain SBU are alternately connected to form a three-dimensional framework structure; Co-DPB has pores with dynamically changing sizes, and the pore size dynamics is

[0009] The synthesis method of the above-mentioned Co-DPB of the present invention mainly comprises the following steps:

[0010] (1) Dissolve the organic ligands H2DPB and Co(CH3COO)2 in a mixed solution of N,N-dimethylformamide (DMF), acetic acid, and water;

[0011] (2) ultrasonically vibrating and stirring the mixed solution in step (1), and then performing solvent heating to obtain bulk single crystals, which were washed with DMF and methanol successively;

[0012] (3) The molar ratio of H2DPB to Co(CH3COO)2 in the above-mentioned Co-DPB technical solution is 1:1-2; the volume ratio of DMF, water and acetic acid in the mixed solvent is 100:80-90:1-3; the volume ratio (mL) of the solvent used per millimole of the organic ligand H2DPB is 1:120-130; the solvothermal reaction temperature is 130-160°C, and the reaction time is 8-16 hours;

[0013] The Co-DPB material obtained above is washed with DMF, exchanged with methanol solvent and heated at 120°C in vacuum to remove solvent molecules, and is used for SF6 adsorption, especially for SF6 / N2 adsorption separation.

[0014] Further, the above application is room temperature (such as 25 degrees Celsius) and pressure is 0.1 bar-1.0 bar.

[0015] At the same time, it also has good water resistance and can maintain multiple rounds of penetrating adsorption and desorption cycles without attenuation at a humidity of RH = 0-90%.

[0016] The Co-DPB material adsorbed with SF6 is desorbed by helium purging for recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Figure 3 is the structural diagram of the bidentate pyrazole ligand used to construct the cobalt-based metal-organic framework.

[0018] Figure 2This is a schematic diagram of the dynamic pores of the metal-organic framework material and the pores after adsorbing sulfur hexafluoride molecules.

[0019] Figure 3 This is the thermal analysis diagram of the metal-organic framework material.

[0020] Figure 4 These are the powder diffraction patterns of the freshly synthesized sample of the metal-organic framework material and the sample after adsorption / penetration test.

[0021] Figure 5 This is the adsorption isotherm diagram of sulfur hexafluoride and nitrogen on the metal-organic framework material at room temperature.

[0022] Figure 6 This is the penetration adsorption diagram of the metal-organic framework material in sulfur hexafluoride / nitrogen mixture (volume ratio of 1:9) at room temperature.

[0023] Figure 7 This is a graph of the metal-organic framework material penetrating five cycles of sulfur hexafluoride / nitrogen mixture (volume ratio of 1:9) under 90% humidity conditions. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0025] Example: (Co-DPB)

[0026] Step 1: Weigh 15.0 mg of H2DPB organic ligand and 30.0 mg of copper acetate tetrahydrate, dissolve them in 5 mL of N,N-dimethylformamide (DMF) and 4 mL of deionized water, and then place them in a 20 mL glass bottle. After adding 50 μL of acetic acid, seal the glass bottle with a plastic bottle cap and sonicate for 20 minutes.

[0027] Finally, the lid of the glass bottle was removed, and the exposed bottle was placed in a 50 mL stainless steel high-pressure reactor, and then transferred to a 150°C oven for reaction for 12 hours to obtain a Co-DPB crystal sample.

[0028] Step 2: Select a single crystal sample of appropriate size and high crystallinity, collect diffraction data using a single crystal diffractometer at 298K, and then use the structure analysis software Olex2 to refine the crystal structure. The specific structural features are shown in the attached figure of the manual.

[0029] Step 3: To remove the solvent molecules in the pores of the material, the crystalline sample obtained above was washed with DMF solvent and then immersed in methanol solvent. The solvent exchange was repeated 6-8 times. The exchanged crystalline sample was transferred to fresh methanol solvent.

[0030] Step 4: Prior to adsorption testing, centrifuge the methanol suspension of the sample from Step 3 at 5000 rpm for 5 minutes, discard the supernatant, and degas at 120°C for 8 hours to obtain a dry sample of the material. Place 100-150 mg of this powder in an adsorption tube and connect it to the adsorption instrument for adsorption isotherm testing.

[0031] Step 5: Before conducting the penetration test, centrifuge the methanol suspension of the sample from Step 3 at 5000 rpm for 5 minutes, discard the supernatant, and degas at 120°C for 8 hours to obtain a dry sample of the material. Place 800-1000 mg of this powder in a penetration tube and connect it to the penetration apparatus for testing.

[0032] The synthesis steps of the organic ligand HDPB are referred to the following literature: (Nature Materials 2022, 21, 689-695)

[0033] Co-DPB crystal data are as follows:

[0034]

[0035] Figure 1 The structural diagram of the ligand shows that the ligand of Co-DPB is pyrazolyl, and the two pyrazol groups with coordination ability are located at the 1 and 3 substitution positions of the benzene ring respectively.

[0036] Figure 2 The schematic diagram of the pores of the metal-organic framework material shows that the pore size of Co-DPB is dynamic. After adsorption of sulfur hexafluoride, the pore size is fixed to about.

[0037] Figure 3 Thermal analysis of the activated metal-organic framework demonstrates the high thermal stability of Co-DPB, with no significant collapse of the MOF framework observed before 570°C. (The mass loss before 200°C is presumably due to the removal of guest molecules from the pores.)

[0038] Figure 4 The powder diffraction pattern of the metal-organic framework material shows that the Co-DPB structure has good stability, maintains good crystallinity after adsorption / penetration test, and the structure does not collapse significantly.

[0039] Figure 5 The steep adsorption isotherm of this metal-organic framework for sulfur hexafluoride at room temperature indicates that Co-DPB has a high affinity for sulfur hexafluoride and a strong interaction with it. Its low adsorption capacity for nitrogen indicates a weak interaction between Co-DPB and nitrogen.

[0040] Figure 6 The breakthrough diagram at room temperature shows that Co-DPB has the potential to truly separate sulfur hexafluoride and nitrogen, and the sulfur hexafluoride adsorbed in the framework can be desorbed by helium purging.

[0041] Figure 7 The penetration diagram of 90% humidity at room temperature shows that Co-DPB can maintain the ability to efficiently separate sulfur hexafluoride and nitrogen under multiple humidity conditions, demonstrating its excellent moisture resistance.

[0042] The above results show that Co-DPB has dynamic channels that can be used to capture sulfur hexafluoride molecules. Based on the molecular trap structure of the dynamic channels, Co-DPB exhibits high-performance sulfur hexafluoride capture ability. In addition, Co-DPB has high thermal stability and moisture resistance, which lays the foundation for separation applications under complex working conditions. The above content is only a preferred example of the present invention, but the present invention should not be limited to the content disclosed in this example. Therefore, any equivalent or modification that does not deviate from the spirit disclosed in the present invention falls within the scope of protection of the present invention.

Claims

1. Application of a Co(II)-based metal-organic framework material constructed with a pyrazole ligand in the separation of SF6 / N2, characterized in that: The metal organic framework material is a purple block crystal material prepared by solvent thermal reaction of organic ligand H2DPB and cobalt source, and its chemical formula is CoC 12 H8N4, where H2DPB is 1,3-di(1-H-pyrazolyl)benzene, with the molecular formula C 12 H 10 N4, named Co-DPB; From the perspective of crystal structure, Co-DPB belongs to the tetragonal system with a space group of I41 / amd, The unit cell parameter is V = 6546.9(3) Å 3 , a = 22.9279(5) Å, b = 22.9279(5) Å, c = 12.4539(3) Å, α = 90 o , β = 90 o , γ =90 o ; In the Co-DPB framework, all Co atoms are coordinated with four N atoms in a tetrahedral configuration, and these coordinated N atoms come from pyrazole groups of four different ligands; The two nitrogen atoms on the pyrazoles in each ligand in the framework participate in coordination, and adjacent metal atoms form zigzag metal chain secondary building units (SBUs) through bridging pyrazole groups. The ligands and metal chain SBUs are alternately connected to form a three-dimensional framework structure. Co-DPB has pores with dynamically changing sizes, ranging from 4 to 8 Å. The separation of SF6 / N2 is carried out under the condition of humidity RH = 0-90%; The Co-DPB material adsorbed with SF6 is desorbed by helium purging for recycling.

2. Use of the Co(II)-based metal-organic framework material constructed with a pyrazole ligand according to claim 1 in the separation of SF6 / N2, characterized in that: The synthetic method of Co-DPB comprises the following steps: (1) Dissolve the organic ligands H2DPB and Co(CH3COO)2 in a mixed solution of N,N-dimethylformamide (DMF), acetic acid, and water; (2) The mixed solution in step (1) is ultrasonically shaken and stirred, and then subjected to solvent heating to obtain bulk single crystals, which are then washed with DMF and methanol.

3. Use of the Co(II)-based metal-organic framework material constructed with pyrazole ligands according to claim 2 in the separation of SF6 / N2, characterized in that: The molar ratio of H2DPB and Co(CH3COO)2 is 1:1~2; the volume ratio of DMF, water and acetic acid in the mixed solvent is 100:80~90:1~3; the volume ratio of the solvent used per millimole of organic ligand H2DPB is 1:120~130.

4. Use of the Co(II)-based metal-organic framework material constructed with pyrazole ligands according to claim 2 in the separation of SF6 / N2, characterized in that: The solvent thermal reaction temperature is 130~160℃, and the reaction time is 8~16 hours.

5. Use of the Co(II)-based metal-organic framework material constructed with a pyrazole ligand according to claim 1 in the separation of SF6 / N2, characterized in that: Co-DPB is used for the adsorption of SF6.

6. Use of the Co(II)-based metal-organic framework material constructed with pyrazole ligands according to claim 5 in the separation of SF6 / N2, characterized in that: Co-DPB was washed with DMF, exchanged with methanol solvent, and heated at 120 °C in vacuum to remove solvent molecules for SF6 adsorption.

7. Use of the Co(II)-based metal-organic framework material constructed with pyrazole ligands according to claim 1 in the separation of SF6 / N2, characterized in that: The separation application conditions are room temperature and pressure of 0.1 bar-1.0 bar.

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