Microporous copper-based wheel paddle dual-core metal organic framework material and application thereof in gas separation

Abstract

The invention discloses a preparation method of a novel microporous copper-based metal organic framework material (Cu-MOF) and gas separation application of the novel microporous copper-based metal organic framework material (Cu-MOF). The Cu metal center is in a four-coordination mode, each independent Cu atom at the coordination position is coordinated with one oxygen atom on four BODC ligands, carboxyl O atoms on the BODC ligands participate in coordination, and a Cu-MOF wheel paddle binuclear coordination geometric configuration is formed. Wherein each BODC ligand serves as four connection nodes and is respectively connected with four crystallographically independent Cu centers, carboxyl groups on the BODC ligands participate in connection and support, bridge rings of middle segments of the BODC ligands contain rich methylene groups, and rich H atoms of the BODC ligands can serve as potential action sites. BODC ligands which are regularly arranged in a pore channel of the Cu-MOF provide a hydrogen bond acceptor, so that the acting force between low-carbon hydrocarbon gas molecules and a framework is enhanced, and the effect of preferentially adsorbing acetylene, ethane, propylene, propyne and sulfur hexafluoride gas in mixed gas such as acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen and the like is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline porous material preparation and gas separation, and specifically relates to a method for preparing a microporous copper-based paddle binuclear metal organic framework (MOF) material. The MOF material is characterized in that it has unique hydrogen-rich adsorption sites and a stable paddle binuclear coordination mode, and can preferentially capture acetylene, ethane, propylene, propyne, and sulfur hexafluoride, thereby achieving efficient separation and purification of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases. Background Art

[0002] With the rapid development of industry, the purity requirements for low-carbon hydrocarbons in various industries are getting higher and higher, and the petrochemical industry is the main source of these low-carbon hydrocarbon gases. Therefore, the requirements for the purification and separation of low-carbon hydrocarbons in the chemical industry are also getting higher and higher, that is, the separation of important industrial raw materials such as methane, acetylene, and propylene. Acetylene gas is an important basic raw material and fuel for the electronics and petrochemical industries. As the simplest unsaturated hydrocarbon compound, its unique and very active C≡C can participate in the production of various value-added compounds. The industrial preparation of acetylene is mainly produced by hydrocarbon cracking or partial combustion of natural gas, and carbon dioxide needs to be removed as the main impurity. Since the physical and chemical properties of acetylene and carbon dioxide (molecular size, boiling point, relative polarizability, etc.) are very similar, the separation of the two faces many challenges. The industry mainly uses high-energy-consuming low-temperature distillation, partial hydrogenation or solvent extraction, which are usually energy-intensive or polluting technologies, resulting in high production costs of acetylene. Therefore, optimizing the separation process and developing new separation technologies are of great significance to the acetylene industry. Propylene is a major raw material for the production of value-added chemicals, but the molecular structure and size of propylene and propyne are very similar (C3H4: 4.4 × 6.8 Å 2 , C3H6: 5.4 × 6.8 Å 2), which makes the separation of the two face many challenges. In industry, propyne catalytic hydrogenation is mainly used to purify propylene, but this technology usually has problems such as high energy consumption, frequent catalyst regeneration, and secondary pollution caused by excessive hydrogenation to generate C3H8. Therefore, optimizing the separation process and developing new separation technologies are of great significance to the propylene industry. In addition to the urgent need to solve the separation and purification needs of low-carbon hydrocarbons, the separation and purification needs of fluorine-containing gases also need to be improved, especially the purification of sulfur hexafluoride gas. Sulfur hexafluoride (SF6) is a chemically stable, non-flammable, colorless and odorless gas. Due to its excellent insulation and arc extinguishing properties, SF6 plays a key role as an insulator in the power and semiconductor industries. At the same time, SF6 is an ideal plasma etching electronic etchant, so high-purity SF6 is a key material for the manufacture of micro-electromechanical systems and photovoltaic devices. However, the large-scale use of sulfur hexafluoride has also brought more serious environmental problems, such as global warming. In the past 25 years, the average global concentration of sulfur hexafluoride has increased threefold. SF6 is a potent greenhouse gas with a global warming potential 23,900 times greater than that of CO2 and remains stable in the atmosphere for about 3,200 years. Therefore, in the Kyoto Protocol adopted in 1997, SF6 was listed as a greenhouse gas along with N2O, CH4, and CO2. Since SF6 / N2 mixtures containing only a small amount of SF6 have similar insulating capabilities to high-purity SF6, pressurized gas mixtures have been used to reduce the use of SF6. Therefore, it is crucial to find an effective method to separate SF6 / N2, especially from mixtures with low SF6 concentrations. Therefore, research on SF6 / N2 mixture separation technology has attracted much attention. Adsorption separation based on porous materials, as a relatively energy-saving and highly selective separation method, is expected to solve many problems in the traditional separation process and bring new opportunities for the purification of gases such as acetylene, propylene, and sulfur hexafluoride. The core of adsorption separation is to develop and prepare efficient porous separation materials to selectively capture gases such as acetylene, propyne, and sulfur hexafluoride.

[0003] Metal organic frameworks (MOFs) are a new type of crystalline porous functional material. They are porous network skeleton materials formed by metal ions or metal clusters and organic ligands based on coordination bonds. Due to their high porosity, large specific surface area, and adjustable pore size and physical and chemical environment, MOFs have potential application value in adsorption separation, gas storage, drug sustained release and catalysis. In recent years, many MOFs have been developed as low-carbon hydrocarbon separation materials and have achieved good results. At the same time, based on the open metal sites and pore screening effects in MOFs, a large number of acetylene and propylene preferential adsorbent materials have been discovered, and they have shown certain separation performance for acetylene / carbon dioxide, acetylene / ethylene, acetylene / ethane, and propyne / propylene mixed gases. However, in general, a large number of acetylene and propylene preferential MOFs adsorbents with high selectivity and high adsorption capacity have been discovered, but their preparation process is generally complicated and the raw material price is also high. Therefore, we urgently need to develop cheap and easy-to-prepare MOF materials to solve the problems encountered. The present invention adopts a relatively cheap bridged ring dicarboxylic acid ligand, a pseudo-three-dimensional dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and copper nitrate to self-assemble under solvent thermal conditions to form a copper-based wheel-paddle binuclear MOF material. The MOF crystal structure has a high porosity, and at the same time has a unique hydrogen-rich adsorption site and a stable wheel-paddle binuclear coordination mode, which provides an action site and place for the adsorption of gas molecules. The material shows preferential adsorption of acetylene, ethane, propylene, propyne, and sulfur hexafluoride gases in the adsorption of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases, thereby achieving efficient purification of acetylene, ethylene, propylene, and sulfur hexafluoride in one adsorption and desorption cycle. Summary of the invention

[0004] The purpose of the present invention is to provide a novel method for preparing a copper-based paddle dual-core MOF material (Cu-MOF), which can be used for the efficient separation of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen and is a preferential adsorbent for acetylene, ethylene, and propylene sulfur hexafluoride.

[0005] A copper-based paddle dual-core MOF material, characterized in that an organic ligand and a copper source are reacted by a solvothermal method to prepare a dark green block crystalline material, whose chemical formula is C8H 12 CuO4, molecular formula is [Cu(BODC)].

[0006] From the perspective of crystal structure, the Cu-MOF material belongs to the cubic system, and the space group is Pm 3 m, the unit cell parameters are: a ≈ 10.4526(3), b ≈ 10.4526(3), c ≈ 10.4526(3), α ≈ β ≈ γ ≈ 90°, V ≈ 1142.02(10). The main peak positions of XRD powder diffraction peaks are θ ° ≈ 8.45°, 11.91°, 16.94°, 18.93°.

[0007] The Cu metal centers in this Cu-MOF are all in a four-coordinate mode. At the coordination site, each independent Cu atom is coordinated with an oxygen atom on four BODC ligands, and the carboxyl O atoms on the BODC ligands all participate in the coordination, forming the paddle binuclear coordination geometry of the Cu-MOF. Each BODC ligand acts as a four-connected node, connected to four crystallographically independent Cu centers respectively. In addition to participating in connection and support, the carboxyl groups on the BODC ligands contain abundant methylene groups on the bridge ring in the middle segment, and their abundant H atoms can serve as potential action sites.

[0008] The synthesis method of the above-mentioned Cu-MOF material of the present invention mainly includes the following steps: dissolving the organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and copper nitrate Cu(NO3)2 in a mixed solvent of N,N-dimethylacetamide, water and nitric acid, and then obtaining the Cu-MOF product through a solvothermal reaction under closed conditions.

[0009] The ratio of organic ligand to metal salt (mass ratio) in the above technical scheme is 1: (1-4); the volume ratio of water to DMA in the mixed solvent is 1: (2-5); the solvent thermal reaction temperature is 80 ℃~110 ℃, and the reaction time is 24 h~72 h. The volume concentration of nitric acid is 50%, which acts as an acid-base regulator and template agent.

[0010] The Cu-MOF material obtained above is washed with DMA, and then exchanged with methanol or dichloromethane solvent and the organic molecules are removed in vacuo (the above process is called activation). The obtained material is used as the final separation material for the efficient and selective separation of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases. During the separation process, acetylene, ethane, propylene, propyne, and sulfur hexafluoride are preferentially adsorbed.

[0011] The present invention prepares a copper-based wheel-paddle dual-core MOF material based on a bridged ring-configured dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and a metal copper source. The specific beneficial effects of the material are as follows: The organic ligand BODC used in material synthesis has a simple structure and is relatively cheap. The Cu metal centers in the Cu-MOF are all in a four-coordinate mode. At the coordination site, each independent Cu atom is coordinated with an oxygen atom on four BODC ligands, and the carboxyl O atoms on the BODC ligands are all involved in the coordination, forming the paddle binuclear coordination geometry of the Cu-MOF; each BODC ligand acts as a four-connected node, connected to four crystallographically independent Cu centers, and the carboxyl groups on the BODC ligands not only participate in connection and support, but also contain abundant methylene groups on the bridge ring in the middle segment, and their abundant H atoms can serve as potential action sites.

[0012] The final Cu-MOF material forms a three-dimensional network structure that can accommodate gas molecules. There are a large number of methylene groups in the structure, which can contribute high-density hydrogen-containing sites, which is beneficial to strengthening the host-guest interaction between gas molecules and the framework.

[0013] The regularly arranged carboxyl oxygen groups in the Cu-MOF pores also provide potential action sites, which are beneficial to strengthening the interaction between acetylene, ethylene, propyne, propylene, and sulfur hexafluoride gas molecules and the framework, thereby achieving the effect of preferentially adsorbing acetylene, ethane, propylene, propyne, and sulfur hexafluoride gases in acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases, so that the purification task of acetylene, ethylene, propylene, and sulfur hexafluoride can be completed within one adsorption and desorption cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the three-dimensional crystal structure of Cu-MOF in the present invention.

[0015] Figure 2 These are the powder diffraction patterns of Cu-MOF in the present invention based on single crystal data simulation, freshly synthesized samples, and freshly synthesized samples after grinding.

[0016] Figure 3 This is the N2 adsorption and desorption curve of Cu-MOF at 77 K in the present invention.

[0017] Figure 4 This is the single-component adsorption curve of acetylene and carbon dioxide of Cu-MOF at 298 K in the present invention.

[0018] Figure 5 This is the single-component adsorption curve of ethane and ethylene of Cu-MOF at 298 K in the present invention.

[0019] Figure 6 This is the single-component adsorption curve of propylene and ethylene of Cu-MOF at 298 K in the present invention.

[0020] Figure 7This is the single-component adsorption curve of propyne and propylene of Cu-MOF at 298 K in the present invention.

[0021] Figure 8 This is a single-component adsorption curve of sulfur hexafluoride and nitrogen on Cu-MOF at 298 K in the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0023] Example 1 Step 1: Weigh 15.0 mg of bicyclo[2.2.2]octane-1,4-dicarboxylic acid organic ligand and 45 mg of copper nitrate trihydrate and dissolve them in 2.3 ml N,N -dimethylacetamide (DMA), 20 μl nitric acid (pH ≈ 5.50 solution after dilution of concentrated nitric acid) and 0.5 ml deionized water. After ultrasonication and obtaining a homogeneous solution, it was transferred into a 20 ml glass reaction bottle and heated at 100 o The Cu-MOF crystalline sample (15 mg) was obtained by constant temperature reaction at 400 °C for 36 h, with a yield of 33.3% (calculated based on metal salt). The Cu-MOF can be synthesized on a large scale, that is, according to the reaction dosage of the vial, the ligand, metal source, and solvent are all increased by 15, 30, 60, and 150 times and then placed in 50 ml, 100 ml, 200 ml, and 500 ml reaction bottles to prepare the Cu-MOF.

[0024] Step 2: Select a single crystal sample of suitable size and good crystallization, collect diffraction data using a single crystal diffractometer at 293 K, and then use the relevant structure analysis software Olex2 to refine the crystal structure. The specific structure is shown in the figure in the specification. The purity of the overall prepared sample is confirmed by X-ray powder diffraction technology.

[0025] Step 3: In order to remove the solvent molecules in the pores of the material, the crystalline sample obtained above was washed with DMA and then immersed in anhydrous methanol solvent. The solvent exchange process lasted for 5 times, and finally dichloromethane was used as the exchange solvent for 2 times. The exchanged sample was degassed at 80°C under vacuum conditions for 6 h to prepare the material for testing gas adsorption.

[0026] Step 4: Before the single-component static adsorption test, the above materials were loaded into the adsorption tube, and the test materials were degassed again at 80°C for 2 h (the above process is called activation), and then the single-component adsorption curve data of acetylene, carbon dioxide, ethylene, ethane, sulfur hexafluoride, propyne, and propylene at 25°C were collected on the gas adsorption instrument. The Cu-MOF material can efficiently and selectively separate acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases, and preferentially adsorbs acetylene, ethane, propylene, propyne, and sulfur hexafluoride during the separation process.

[0027] Figure 1 The crystal structure in shows that the Cu metal centers in the Cu-MOF are all in a four-coordinate mode. At the coordination site, each independent Cu atom is coordinated with an oxygen atom on four BODC ligands, and the carboxyl O atoms on the BODC ligands all participate in the coordination, forming the paddle binuclear coordination geometry of the Cu-MOF. Each BODC ligand acts as a four-connected node, connected to four crystallographically independent Cu centers respectively. In addition to participating in connection and support, the carboxyl groups on the BODC ligands contain abundant methylene groups on the bridge ring in the middle segment, and their abundant H atoms can serve as potential action sites.

[0028] Figure 2 The powder diffraction spectrum in the figure shows that the freshly prepared Cu-MOF sample is well crystallized and has good purity. The main peak positions of the XRD powder diffraction peaks are θ ° ≈ 8.45°, 11.91°, 16.94°, 18.93°.

[0029] Figure 3 The nitrogen adsorption curve in Figure 2 shows that the N2 adsorption of Cu-MOF at 77 K exhibits a classic Ӏ-shaped curve, corresponding to the microporous channels in the structure, further confirming the structural basis of the separation.

[0030] Figure 4 The single-component adsorption curves of acetylene / carbon dioxide show that Cu-MOF has a relatively high adsorption capacity for the two gases, and the interaction between the framework and acetylene gas molecules is stronger. This phenomenon is that Cu-MOF preferentially captures acetylene gas in the acetylene / carbon dioxide mixture.

[0031] Figure 5 The single component adsorption curves of acetylene / ethylene show that Cu-MOF has a relatively high adsorption capacity for the two gases, and the interaction between the framework and ethane gas molecules is stronger. This phenomenon is that Cu-MOF preferentially captures ethane gas in the ethane / ethylene mixture.

[0032] Figure 6The single-component adsorption curves of propylene / ethylene show that Cu-MOF has a higher adsorption capacity for the two gases, and the interaction between the framework and propylene gas molecules is stronger. This phenomenon is that Cu-MOF preferentially captures propylene gas in a propylene / ethylene mixture.

[0033] Figure 7 The propyne / propylene single component adsorption curves show that Cu-MOF has a higher adsorption capacity for the two gases, and the interaction between the framework and propyne gas molecules is stronger. This phenomenon is that Cu-MOF preferentially captures propyne gas in the propyne / propylene mixture.

[0034] Figure 8 The single-component adsorption curves of sulfur hexafluoride / nitrogen in the graph show that Cu-MOF has a high adsorption capacity for the two gases, and the interaction between the framework and sulfur hexafluoride gas molecules is stronger. This phenomenon is that Cu-MOF preferentially captures sulfur hexafluoride gas in a sulfur hexafluoride / nitrogen mixture.

[0035] The above results show that the microporous paddle binuclear Cu-MOF material has a unique hydrogen-rich adsorption site and a stable paddle binuclear coordination mode, and has a high adsorption capacity and good separation performance for acetylene / carbon dioxide, acetylene / ethylene, acetylene / ethane, acetylene / methane, and propyne / propylene gases. At the same time, the invention provides a useful reference for the correlation between the structural design and gas separation performance of metal organic framework materials, and can realize the application of such materials in the field of low-carbon hydrocarbon gas separation. That is, after the Cu-MOF material obtained above is washed with DMA, after being exchanged with methanol or dichloromethane solvent and vacuum-removed organic molecules (the above process is called activation), the material obtained is used for the final separation material of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gas with high efficiency and selectivity, and acetylene, ethane, propylene, propyne, and sulfur hexafluoride are preferentially adsorbed during the separation process.

[0036] The above contents are only preferred examples of the present invention, but the present invention should not be limited to the contents disclosed in the examples. Therefore, any equivalent or modified contents completed without departing from the spirit disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A microporous copper-based paddle dual-core metal organic framework material, characterized in that: Its chemical formula is C8H 12 CuO4, the molecular formula is [Cu(BODC)], BODC is bicyclo[2.2.2]octane-1,4-dicarboxylic acid.

2. The copper-based wheel-paddle dual-core metal organic framework material according to claim 1, characterized in that: The unit cell parameters are: V ≈ 1142.02(10), a ≈ 10.4526(3), b ≈ 10.4526(3), c ≈ 10.4526(3), α ≈ β≈ γ ≈ 90°; the main peak positions of the prepared XRD powder diffraction peaks are θ ° Including about 8.45°, about 11.91°, about 16.94°, and about 18.93°.

3. The copper-based wheel-paddle dual-core metal organic framework material according to claim 1, characterized in that: The Cu metal centers in this Cu-MOF are all in a four-coordinated mode. At the coordination site, each independent Cu atom is coordinated with an oxygen atom on four BODC ligands, and the carboxyl O atoms on the BODC ligands all participate in the coordination, forming the paddle binuclear coordination geometry of the Cu-MOF.

4. A method for preparing the copper-based wheel-paddle dual-core metal organic framework material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Preparation of Cu-MOF: The organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and copper nitrate Cu(NO3)2 are dissolved in a mixed solvent of N,N-dimethylacetamide, water and acid-base regulator, and then the Cu-MOF product is obtained through solvothermal reaction under closed conditions.

5. The method according to claim 4, characterized in that In the step, the solvent thermal reaction conditions are 80°C ~110°C, the reaction time is 24 h ~72 h, and the mass ratio of the organic ligand to copper nitrate is 1: (1~4), preferably 1:

2.

6. The method according to claim 4, characterized in that The copper source used includes copper chloride, copper nitrate, copper sulfate, copper perchlorate and cuprous iodide, preferably copper nitrate; the acid-base regulator used includes nitric acid, hydrochloric acid, fluoroboric acid and acetic acid, preferably with a volume concentration of 40-50% nitric acid.

7. The method according to claim 4, characterized in that The volume ratio of water to DMA in the mixed solvent is 1:(2-5), preferably 1:

3.

8. Use of the copper-based paddle dual-core metal organic framework material according to any one of claims 1 to 3 for selectively separating any one of the mixed gases of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, or sulfur hexafluoride / nitrogen.

9. The use according to claim 8, wherein the Cu-MOF material is washed with DMA, exchanged with methanol or dichloromethane solvent and vacuum-removed organic molecules to obtain a final separation material for selectively separating acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene or sulfur hexafluoride / nitrogen mixed gases, and preferentially adsorbs acetylene, ethane, propylene, propyne and sulfur hexafluoride gases during the separation process.

10. The use according to claim 8 or 9, characterized in that: The separation conditions are 0~25°C and standard atmospheric pressure; preferably 25°C.

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