Microporous copper-based wheel paddle binuclear metal-organic framework material and its application in gas separation

Abstract

The application relates to a preparation method of a novel microporous copper-based metal organic framework material (Cu-MOF) and gas separation application thereof. Cu metal centers are all in a four-coordination mode, each independent Cu atom is coordinated with one oxygen atom on a BODC ligand, carboxyl O atoms on the BODC ligand all participate in coordination, and a propeller binuclear coordination geometry of the Cu-MOF is formed; wherein each BODC ligand acts as a four-connected node and is connected with four crystallographically independent Cu centers, and the carboxyl on the BODC ligand is connected and supported, and the bridge ring in the middle section contains rich methylene groups, and the rich H atoms can all act as potential action sites. The regularly arranged BODC ligands in the Cu-MOF channel provide hydrogen bond acceptors, which are favorable for strengthening the action force between low-carbon hydrocarbon gas molecules and the framework, so that the effects of preferentially adsorbing acetylene, ethane, propylene, propyne and sulfur hexafluoride gas in acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen and other mixed gases are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of crystalline porous materials and gas separation, and particularly relates to a preparation method of microporous copper-based paddle-wheel binuclear metal organic framework (MOF) material, characterized in that the MOF material has unique hydrogen-rich adsorption sites and stable paddle-wheel binuclear coordination mode, can preferentially capture acetylene, ethane, propylene, propyne and sulfur hexafluoride, and thus realizes efficient separation and purification of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene and sulfur hexafluoride / nitrogen mixed gas. BACKGROUND

[0002] With the rapid development of industry, the purity requirements of low-carbon hydrocarbons are becoming higher and higher in various industries, and the petroleum chemical industry is the main source of producing these low-carbon hydrocarbon gases, so the purification and separation requirements of low-carbon hydrocarbons are also becoming higher and higher in the chemical industry, that is, the separation of important industrial raw gas such as methane, acetylene and propylene. Acetylene gas is an important basic raw material and fuel for 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. Industrial acetylene is mainly produced by hydrocarbon cracking or partial combustion of natural gas, and carbon dioxide as the main impurity needs to be removed. Due to the extremely similar physicochemical properties (molecular size, boiling point, relative polarizability, etc.) of acetylene and carbon dioxide, the separation of the two faces many challenges. Industrially, high-energy consumption low-temperature distillation, partial hydrogenation or solvent extraction are mainly used, which are usually energy-intensive or polluting technologies, resulting in high production cost of acetylene. Therefore, optimizing the separation process and developing new separation technology are of great significance to the acetylene industry. Propylene is a main raw material for producing value-added chemicals, but the molecular structure and size of propylene and propyne are extremely similar (C3H4: 4.4 x 6.8 Å 2 , C3H6: 5.4 x 6.8 Å 2), making their separation a challenge. The main industrial purification process for propylene is the catalytic hydrogenation of propyne, but this technology usually has high energy consumption, frequent catalyst regeneration, and excessive hydrogenation to generate C3H8, causing secondary pollution. 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 separate and purify low-carbon hydrocarbons, the separation and purification of fluorine-containing gases also needs to be improved, especially the purification of sulfur hexafluoride gas. Sulfur hexafluoride (SF6) is a stable, non-flammable, colorless, and odorless gas. Due to its excellent insulation and arc-extinguishing properties, it plays a key role as an insulating agent in the power and semiconductor industries. At the same time, SF6 is an ideal plasma etching electronic corrosion agent, so high-purity SF6 is a key material for manufacturing micro-electromechanical systems and photovoltaic devices. However, the extensive use of sulfur hexafluoride has also brought more serious environmental problems, such as global warming. In the past 25 years, the average concentration of sulfur hexafluoride has increased by three times. SF6 is a potent greenhouse gas, with a global warming potential 23,900 times 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 insulation capabilities to high-purity SF6, pressurized gas mixtures have been used to reduce SF6 use. Therefore, it is crucial to find an effective method to separate SF6 / N2, especially from mixtures with low SF6 concentrations. Therefore, the separation technology of SF6 / N2 mixtures has attracted much attention. As a relatively energy-efficient and highly selective separation method, adsorption separation based on porous materials is expected to solve many problems in traditional separation processes and bring new opportunities for the purification of acetylene, propylene, and sulfur hexafluoride. The core of adsorption separation is to develop efficient porous separation materials to selectively capture acetylene, propyne, sulfur hexafluoride, and other gases.

[0003] Metal organic frameworks (MOFs) are a new type of crystalline porous functional material, which is a porous network framework material formed by metal ions or metal clusters and organic ligands based on coordination bond. Due to its high porosity, large specific surface area and adjustable pore size and physicochemical environment, MOFs have potential application value in the fields of adsorption separation, gas storage, drug 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 size effect in MOFs, a large number of acetylene, propylene preferential adsorbent materials have been explored, and they show certain separation performance for acetylene / carbon dioxide, acetylene / ethylene, acetylene / ethane, propyne / propylene mixed gas. However, in general, a large number of acetylene, propylene preferential MOF adsorbents with high selectivity and high adsorption capacity have been found, but their preparation process is generally complex, and the price of raw materials is also high, so we urgently need to develop cheap and simple MOF materials to solve the problems. The present application uses a relatively cheap bridged dicarboxylic acid ligand, a quasi-three-dimensional dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and copper nitrate under solvothermal conditions to form a copper-based paddle double-core MOF material. The crystal structure of the MOF has high porosity, and has unique hydrogen-rich adsorption sites and stable paddle double-core coordination mode, providing sites and places for gas molecule adsorption. The material shows preferential adsorption of acetylene, ethane, propylene, propyne and sulfur hexafluoride gas in acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen mixed gas adsorption, thereby realizing efficient purification of acetylene, ethylene, propylene and sulfur hexafluoride in one adsorption / desorption cycle. SUMMARY

[0004] The present application aims to provide a new preparation method of a copper-based paddle double-core MOF material (Cu-MOF), which can be used for efficient separation of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene and sulfur hexafluoride / nitrogen, and is an acetylene, ethylene, propylene and sulfur hexafluoride preferential adsorbent.

[0005] A copper-based paddle double-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 crystal material, which has a chemical formula C8H 12 CuO4, and a molecular formula [Cu(BODC)].

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

[0007] The Cu metal centers in the Cu-MOF are all in a four-coordinated mode, and each independent Cu atom is coordinated with one oxygen atom on the BODC ligand at the coordination site, and the carboxyl O atoms on the BODC ligand all participate in coordination, forming a propeller binuclear coordination geometry of the Cu-MOF; wherein each BODC ligand acts as a four-connected node and is connected to four crystallographically independent Cu centers, and the carboxyl on the BODC ligand participates in connection and support, and the bridge ring in the middle section contains rich methylene groups, and the rich H atoms can all act as potential active sites.

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

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

[0010] The Cu-MOF material obtained above is washed with DMA, and then exchanged with a methanol or dichloromethane solvent and removed of organic molecules under vacuum (the above process is called activation) to obtain a final separation material for high-efficiency selective separation of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene and sulfur hexafluoride / nitrogen mixed gas, which preferentially adsorbs acetylene, ethane, propylene, propyne and sulfur hexafluoride in the separation process.

[0011] The application prepares a copper-based propeller binuclear MOF material based on a bridged ring configuration dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC) and a copper source.

[0012] The organic ligand BODC used in the material synthesis has a simple structure and a relatively low price. The Cu metal centers in the Cu-MOF are in a four-coordinated mode, each independent Cu atom is coordinated with one oxygen atom of the four BODC ligands, and the carboxyl O atoms of the BODC ligands are all involved in the coordination, forming a propeller binuclear coordination geometry of the Cu-MOF; each BODC ligand acts as a four-connected node and is connected to four crystallographically independent Cu centers, and the methylene groups on the bridge ring of the middle section of the BODC ligand contain rich H atoms which can all act as potential active sites.

[0013] The finally obtained Cu-MOF material forms a three-dimensional network structure, can accommodate gas molecules, and a large number of methylene groups exist in the structure, which can contribute to a high density of hydrogen-containing sites, thereby facilitating the strengthening of the host-guest interaction between the gas molecules and the framework.

[0014] The regularly arranged carboxyl oxygen in the channel of the Cu-MOF also provides potential active sites, which is conducive to the strengthening of the force between the acetylene, ethylene, propyne, propylene, sulfur hexafluoride gas molecules and the framework, thereby realizing the effect of preferentially adsorbing acetylene, ethane, propylene, propyne, sulfur hexafluoride gas in the acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen mixed gas, so that the purification task of acetylene, ethylene, propylene, sulfur hexafluoride is completed in one adsorption / desorption cycle. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a schematic diagram of the three-dimensional crystal structure of the Cu-MOF in the application.

[0016] Figure 2 It is a powder diffraction pattern of the Cu-MOF in the application based on single crystal data simulation, a freshly synthesized sample and a ground powder of the freshly synthesized sample.

[0017] Figure 3 It is an N2 adsorption / desorption curve of the Cu-MOF in the application under the condition of 77 K.

[0018] Figure 4 It is an acetylene and carbon dioxide single-component adsorption curve of the Cu-MOF in the application under the condition of 298 K.

[0019] Figure 5 It is an ethane and ethylene single-component adsorption curve of the Cu-MOF in the application under the condition of 298 K.

[0020] Figure 6 It is a propylene and ethylene single-component adsorption curve of the Cu-MOF in the application under the condition of 298 K.

[0021] Figure 7This is a single-component adsorption curve of propyne and propylene using Cu-MOF at 298 K in this invention.

[0022] Figure 8 This is a single-component adsorption curve of Cu-MOF for sulfur hexafluoride and nitrogen at 298 K in this invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0024] Example 1

[0025] 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 of water. N,N - Dimethylacetamide (DMA), 20 μl nitric acid (a solution diluted with concentrated nitric acid to pH ≈ 5.50), and 0.5 ml deionized water. After sonicating to obtain a homogeneous solution, the mixture was then transferred to a 20 ml glass reaction flask and incubated at 100 °C. o The Cu-MOF crystalline sample (15 mg) was obtained by isothermal reaction at C for 36 h, with a yield of 33.3% (based on metal salt calculation). This Cu-MOF can be synthesized on a scale-up basis; that is, by increasing the reaction dosage in vials by 15, 30, 60, and 150 times, and then placing the samples in reaction flasks of 50 ml, 100 ml, 200 ml, and 500 ml, Cu-MOF can be prepared.

[0026] Step 2: Select a single-crystal sample of suitable size and good crystallinity. Collect diffraction data using a single-crystal diffractometer at 293 K, and then refine the crystal structure using the relevant structural analysis software Olex2. See the attached diagram in the instruction manual for the specific structure. The purity of the overall prepared sample was confirmed using X-ray powder diffraction.

[0027] Step 3: To remove solvent molecules from 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 was repeated 5 times, and finally, dichloromethane was used as the exchange solvent for 2 treatments. The exchanged sample was then degassed at 80°C under vacuum for 6 h to prepare the material for testing gas adsorption.

[0028] Fourth step: before the single-component static adsorption test, the above material is loaded into the adsorption tube, and the test material is degassed again at 80℃ for 2 hours (the above process is called activation), and then the single-component adsorption curve data of the material at 25℃ for acetylene, carbon dioxide, ethylene, ethane, sulfur hexafluoride, propyne, propylene are collected on the gas adsorption instrument. The Cu-MOF material can selectively separate acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen mixed gas, and preferentially adsorb acetylene, ethane, propylene, propyne, sulfur hexafluoride in the separation process.

[0029] Figure 1 The crystal structure in the formula (I) shows that the Cu metal center in the Cu-MOF is in a four-coordinated mode, and each independent Cu atom is coordinated with one oxygen atom on the BODC ligand at the coordination site. The carboxyl O atom on the BODC ligand is involved in coordination, forming a propeller binuclear coordination geometry of the Cu-MOF. Each BODC ligand acts as a four-connected node and is connected to four crystallographically independent Cu centers. In addition to participating in connection and support, the bridge ring on the middle section of the BODC ligand contains rich methylene groups, and the rich H atoms can all act as potential active sites.

[0030] Figure 2 The powder diffraction spectrum in the formula (II) shows that the freshly prepared Cu-MOF sample has good crystallinity and good purity. The XRD powder diffraction peaks mainly appear at θ ° ≈ 8.45°, 11.91°, 16.94°, 18.93°.

[0031] Figure 3 The nitrogen adsorption curve in the formula (III) shows that the Cu-MOF exhibits a classic Ӏ type curve under N2 adsorption at 77 K, corresponding to the microporous channel in the structure, further confirming the structural basis for separation.

[0032] Figure 4 The acetylene / carbon dioxide single-component adsorption curve in the formula (IV) shows that the Cu-MOF has a relatively high adsorption capacity for the two gases, and the framework has a stronger interaction with the acetylene gas molecules. This phenomenon enables the Cu-MOF to preferentially capture acetylene gas in the acetylene / carbon dioxide mixed gas.

[0033] Figure 5 The acetylene / ethylene single-component adsorption curve in the formula (V) shows that the Cu-MOF has a relatively high adsorption capacity for the two gases, and the framework has a stronger interaction with the ethane gas molecules. This phenomenon enables the Cu-MOF to preferentially capture ethane gas in the ethane / ethylene mixed gas.

[0034] Figure 6The propylene / ethylene single-component adsorption curve in the above table shows that the Cu-MOF has a higher adsorption capacity for the two kinds of gases, and the framework has a stronger interaction with propylene gas molecules. This phenomenon enables the Cu-MOF to preferentially capture propylene gas in a propylene / ethylene mixed gas.

[0035] Figure 7 The propyne / propylene single-component adsorption curve in the above table shows that the Cu-MOF has a higher adsorption capacity for the two kinds of gases, and the framework has a stronger interaction with propyne gas molecules. This phenomenon enables the Cu-MOF to preferentially capture propyne gas in a propyne / propylene mixed gas.

[0036] Figure 8 The sulfur hexafluoride / nitrogen single-component adsorption curve in the above table shows that the Cu-MOF has a higher adsorption capacity for the two kinds of gases, and the framework has a stronger interaction with sulfur hexafluoride gas molecules. This phenomenon enables the Cu-MOF to preferentially capture sulfur hexafluoride gas in a sulfur hexafluoride / nitrogen mixed gas.

[0037] The above results show that the microporous wheel paddle binuclear Cu-MOF material has unique hydrogen-rich adsorption sites and a stable wheel paddle binuclear coordination mode, and has a higher adsorption capacity and good separation performance for acetylene / carbon dioxide, acetylene / ethylene, acetylene / ethane, acetylene / methane, propyne / propylene gas. At the same time, the present application provides a beneficial 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, the Cu-MOF material obtained above is subjected to DMA washing, and then exchanged with methanol or dichloromethane solvent and vacuumed to remove the organic molecules (the above process is referred to as activation) to obtain a final separation material for efficiently and selectively separating acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, sulfur hexafluoride / nitrogen mixed gas, which preferentially adsorbs acetylene, ethane, propylene, propyne, and sulfur hexafluoride in the separation process.

[0038] The above is a preferred example of the present application, but the present application should not be limited to the disclosed content of the example. Therefore, equivalents or modifications made without departing from the spirit of the present application fall within the scope of the present application.

Claims

1. A microporous copper-based wheel paddle dual-core metal-organic framework material, characterized in that, Cell parameters: V = 1142.02(10), a = 10.4526(3), b = 10.4526(3), c = 10.4526(3), a = b = g = 90°; the prepared XRD powder diffraction peak mainly appears at the peak position of θ ° about 8.45°, about 11.91°, about 16.94°, about 18.93°, and the molecular formula is [Cu(BODC)], and BODC is bicyclo[2.2.2]octane-1,4-dicarboxylic acid.

2. The copper-based wheel paddle dual-core metal-organic framework material of claim 1, wherein The Cu metal centers in Cu-MOF are all in tetrahedral coordination mode, each independent Cu atom is coordinated with one oxygen atom on four BODC ligands, and the carboxyl O atoms on BODC ligands are all involved in coordination, forming the propeller dinuclear coordination geometry of Cu-MOF.

3. Process for the preparation of a copper-based wheel-shaped dinuclear metal-organic framework material according to any one of claims 1 to 2, characterized in that, The method comprises the following steps: Preparation of Cu-MOF: dissolve 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 and water, an acid-base regulator, and then obtain the Cu-MOF product through a solvothermal reaction under a closed condition.

4. The method of claim 3, wherein, In the step, the solvothermal reaction condition is 80 ℃-110 ℃, the reaction time is 24 h-72 h, and the mass ratio of the organic ligand to copper nitrate is 1: (1-4).

5. The method of claim 3, wherein, The copper sources used include copper chloride, copper nitrate, copper sulfate, copper perchlorate, and cuprous iodide; the acid-base regulators used include nitric acid, hydrochloric acid, fluoroboric acid, and acetic acid.

6. The method of claim 3, wherein, The volume ratio of water to DMA in the mixed solvent is 1: (2-5).

7. Use of the copper-based propeller dinuclear metal organic framework material according to any one of claims 1-2 for selectively separating any one of acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, or sulfur hexafluoride / nitrogen mixed gas.

8. The use according to claim 7, wherein the final separation material for selectively separating acetylene / carbon dioxide, ethane / ethylene, propylene / ethylene, propyne / propylene, or sulfur hexafluoride / nitrogen mixed gas is obtained by washing the Cu-MOF material with DMA, then exchanging the solvent with methanol or dichloromethane and removing the organic molecules under vacuum, and in the separation process, the acetylene, ethane, propylene, propyne, and sulfur hexafluoride gases are preferentially adsorbed.

9. Use according to claim 7 or 8, characterized in that, The separation condition is 0-25 ℃ under one standard atmosphere.

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