Application of pyrazole-cobalt-based metal organic framework material with dynamic pore size in trapping sulfur hexafluoride

Abstract

The invention relates to application of a pyrazole-cobalt-based metal organic framework material with a dynamic pore size to capture sulfur hexafluoride, and belongs to the technical field of preparation of crystal porous materials. Co-DPB is synthesized from an organic ligand (H2DPB) [H2DPB = 1, 3-di (1-H-pyrazolyl) benzene] and cobalt acetate tetrahydrate under a solvothermal condition. The MOF has a dynamic pore size due to the vibration of a ligand benzene ring, and the acting force on sulfur hexafluoride molecules can be improved. Based on the strong acting force of Co-DPB on sulfur hexafluoride, the Co-DPB has excellent sulfur hexafluoride / nitrogen separation capacity. In addition, Co-DPB also has high thermal stability and moisture resistance, and has a potential application prospect in trapping sulfur hexafluoride in real industrial tail gas.

Description

Technical Field

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

[0002] Sulfur hexafluoride (SF 6 ) is widely used as a protective gas in the power industry due to its excellent dielectric and arc extinguishing properties. However, it also has an extremely strong greenhouse effect, with a unit warming capacity about 23,900 times that of carbon dioxide, and is considered the gas with the highest current warming capacity. Therefore, in order to protect the environment and mitigate the greenhouse effect, it is necessary to control the emission of sulfur hexafluoride as much as possible. Industrially, the mainstream method for treating sulfur hexafluoride-containing waste gas is incineration, that is, calcining and degrading SF 6 . However, other gases that may be harmful to the environment, such as hydrofluoric acid (HF), sulfur dioxide (SO 6 ), etc., will be produced after the degradation of SF 2 , which is likely to cause secondary pollution. Another more preferable treatment method is to separate sulfur hexafluoride in the waste gas from the main impurity nitrogen (N 2 ), and after purification, it can be reused. This method can not only effectively mitigate the greenhouse effect but also realize the recycling value of SF 6 gas, thereby reducing the use cost of SF 6 .

[0003] Existing technologies for separating SF 6 / N 2 include cryogenic distillation, liquefaction, and cryogenic freezing, etc. However, due to the low concentration of SF 6 in industrial waste gas (less than 10%), these separation technologies usually have inevitable drawbacks such as high energy consumption and low purification efficiency.

[0004] In contrast, the 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 core of the adsorption separation technology lies in the research and development of adsorbents. Traditional porous materials such as zeolites and porous carbons have made preliminary progress as adsorbents in the field of sulfur hexafluoride capture, promoting the development of this field. However, it is quite challenging to precisely control the pore size and pore environment 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 the self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. The advantages of precise regulation of pore size and pore environment in MOFs materials make them one of the ideal candidate materials in the field of adsorption separation. Based on the above characteristics, MOFs show unique advantages in selective molecular recognition and separation. In this invention, a cobalt-based MOF (Co-DPB) constructed with a bidentate pyrazole ligand (H 2 DPB)[H 2 DPB = 1,3-bis(1-H-pyrazolyl)benzene] is used to achieve efficient SF 6 trapping. Due to the vibrational flexibility of the benzene ring structure of the MOF ligand, Co-DPB presents a molecular trap structure with dynamic size which is beneficial to recognize and capture sulfur hexafluoride molecules of corresponding size In terms of performance, Co-DPB shows excellent sulfur hexafluoride adsorption capacity (2.82 mmol / g) and excellent sulfur hexafluoride / nitrogen selectivity at room temperature (25 °C) and even under low pressure (0.1 bar) conditions. In addition, from the dynamic breakthrough separation experiment, 10% concentration of SF 6 can be purified to a concentration higher than 99.9% by Co-DPB adsorbent through one adsorption-desorption cycle. At the same time, its efficient SF 6 / N 2 separation ability can also maintain multiple rounds of breakthrough adsorption-desorption cycles without attenuation at RH = 90% humidity. Summary of the Invention

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

[0007] A Co(II)-based metal-organic framework material Co-DPB constructed with a pyrazole ligand is a purple block crystal material prepared by a solvothermal reaction of an organic ligand H 2 DPB and a cobalt source, with the chemical formula CoC 12 H 8 N 4 , where H 2 DPB is 1,3-bis(1-H-pyrazolyl)benzene, and the molecular formula is C 12 H 10 N 4 .

[0008] From the perspective of crystal structure analysis, Co-DPB belongs to the tetragonal system, the space group is I4 1 / amd, and the unit cell parameters are α = 90°, β = 90°, γ = 90°. 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 the pyrazole groups of four different ligands. The N atoms on two pyrazoles in each ligand in the framework participate in coordination, and adjacent metal atoms form a zigzag metal chain secondary building unit (SBU) through the bridging pyrazole groups. The ligands and the metal chain SBUs are alternately connected to form a three-dimensional framework structure; Co-DPB has pores with dynamically changing sizes, and the dynamic pore size is

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

[0010] (1) Dissolve the organic ligand H 2 DPB and Co(CH 3 COO) 2 in a mixed solution of N,N-dimethylformamide (DMF), acetic acid and water;

[0011] (2) After ultrasonic oscillation and stirring of the mixed solution in step (1), carry out solvothermal treatment to obtain bulk single crystals, and wash them successively with DMF and methanol;

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

[0013] The obtained Co-DPB material is washed with DMF, subjected to methanol solvent exchange and vacuum heated at 120 °C to remove solvent molecules, and is used for the adsorption of SF 6 , especially for the adsorption separation of SF 6 / N 2 .

[0014] The further above-mentioned application is at room temperature (such as 25 degrees Celsius) and a pressure of 0.1 bar - 1.0 bar.

[0015] It also has good water resistance and can maintain multiple rounds of penetration adsorption and desorption cycles without attenuation at a humidity of RH = 0 - 90%.

[0016] The Co-DPB material adsorbed with SF 6 is desorbed by helium purging, so as to carry out cyclic application. Description of the Drawings

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

[0018] Figure 2 It 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 It is a thermal analysis diagram of the metal-organic framework material.

[0020] Figure 4 It is a powder diffraction diagram of the freshly synthesized sample of the metal-organic framework material and the sample after adsorption / penetration test.

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

[0022] Figure 6 It is a breakthrough adsorption diagram of sulfur hexafluoride / nitrogen mixed gas (volume ratio 1:9) of the metal-organic framework material at room temperature.

[0023] Figure 7 It is a breakthrough 5-cycle diagram of sulfur hexafluoride / nitrogen mixed gas (volume ratio 1:9) of the metal-organic framework material under the condition of 90% humidity. Detailed Embodiments

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

[0025] Example: (Co-DPB)

[0026] First step: Weigh 15.0 mg of H 2 DPB 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, then put them into a 20 mL glass bottle, add 50 μL of acetic acid, seal the glass bottle with a plastic bottle cap and ultrasonicate for 20 minutes.

[0027] Finally, remove the lid of the glass bottle, place it open in a 50 mL stainless steel autoclave, transfer it to an oven at 150 °C and react for 12 hours to obtain a Co-DPB crystal sample.

[0028] Second step: Select a single crystal sample with appropriate size and high crystallinity, collect diffraction data using a single crystal diffractometer at 298 K, and then refine the crystal structure using the structure analysis software Olex2. The specific structural features can be seen in the attached drawings of the specification.

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

[0030] Step 4: Before the adsorption test, the methanol suspension of the sample in Step 3 was centrifuged at 5000 rpm for 5 minutes, the supernatant was discarded, and the sample was degassed at 120 °C for 8 hours to obtain a dry sample of the desolvated material. 100 - 150 mg of this powder was loaded into an adsorption tube and connected to an adsorption instrument for adsorption isotherm testing.

[0031] Step 5: Before the breakthrough test, the methanol suspension of the sample in Step 3 was centrifuged at 5000 rpm for 5 minutes, the supernatant was discarded, and the sample was degassed at 120 °C for 8 hours to obtain a dry sample of the desolvated material. 800 - 1000 mg of this powder was loaded into a breakthrough tube and connected to a breakthrough device for testing.

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

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

[0034]

[0035] Figure 1 The structure diagram of the ligand shows that the ligand of Co-DPB is pyrazolyl, and two coordinating pyrazole groups are located at the 1, 3 substitution positions of the benzene ring respectively.

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

[0037] Figure 3 The thermogram of the activated metal-organic framework proves that Co-DPB has high thermal stability. Before 570 °C, no obvious collapse of the MOF framework structure is observed. (The mass loss before 200 °C is presumably due to the removal of guest molecules in the pores.)

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

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

[0040] Figure 6 The breakthrough schematic 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 breakthrough schematic diagram at 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 indicate that Co-DPB has dynamic pores that can be used to capture sulfur hexafluoride molecules. Based on the molecular trap structure of the dynamic pores, Co-DPB exhibits high-performance sulfur hexafluoride capture ability. In addition, Co-DPB has high thermal stability and moisture resistance, laying a foundation for meeting 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, all equivalent or modified completions made without departing from the spirit disclosed by the present invention fall within the protection scope of the present invention.

Claims

1. A Co(II)-based metal-organic framework material Co-DPB constructed with a pyrazole ligand, characterized in that: It is a purple block crystalline material prepared by solvent thermal reaction of organic ligand H2DPB and cobalt source, with the chemical formula of CoC 12 H8N4, where H2DPB is 1,3-di(1-H-pyrazolyl)benzene, with the molecular formula C 12 H 10 N4; From the perspective of crystal structure, Co-DPB belongs to the tetragonal system, the space group is I41 / amd, and the unit cell parameters are 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 metal chain SBUs are alternately connected to form a three-dimensional framework structure; Co-DPB has pores with dynamically changing sizes, and the pore size dynamics is 2. The method for synthesizing Co-DPB according to claim 1, characterized in that The main steps include: (1) dissolving 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 thermal treatment to obtain bulk single crystals, which are then washed with DMF and methanol.

3. The method according to claim 2, characterized in that The molar ratio of H2DPB to 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 each millimole of organic ligand H2DPB to the amount of solvent is 1:120-130.

4. The method according to claim 2, characterized in that The solvent thermal reaction temperature is 130-160° C., and the reaction time is 8-16 hours.

5. Use of the Co-DPB according to claim 1 for adsorption of SF6.

6. The use as claimed in claim 5, wherein the Co-DPB is washed with DMF, exchanged with methanol solvent and heated at 120°C in vacuum to remove solvent molecules, and then used for the adsorption of SF6.

7. The use according to claim 5 for adsorption separation of SF6 / N2.

8. The use according to claim 5, wherein the application conditions are: room temperature and pressure of 0.1 bar to 1.0 bar.

9. The use according to claim 5, wherein the use is performed under the condition of humidity RH = 0-90%.

10. The use according to claim 5, wherein the Co-DPB material adsorbing SF6 is desorbed by helium purging, thereby being recycled.

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