Preparation method of novel microporous flexible metal organic framework material and gas separation application of novel microporous flexible metal organic framework material

Abstract

The invention relates to a preparation method of a novel microporous flexible metal organic framework material and gas separation application of the novel microporous flexible metal organic framework material. A Cu metal center is in a hexa-coordination mode, each independent Cu atom at the coordination position is coordinated with four O atoms on two BODC ligands, carboxyl O atoms on the BODC ligands participate in coordination, and two nitrogen-containing auxiliary bis-imidazole butane also participate in the hexa-coordination geometrical configuration of the metal center; the BODC ligand and the BIB ligand both participate in connection and contain rich methylene groups, rich H atoms of the BODC ligand and the BIB ligand can serve as potential action sites, and N atoms on the nitrogen-containing ligand bis-imidazole butane can also serve as potential action sites to act with gas. BODC ligands which are regularly arranged in a Cu-MOF pore channel provide a hydrogen bond donor, so that the acting force between low-carbon hydrocarbon gas molecules and a framework is enhanced; the straight-chain n-butane configuration at the middle end of the nitrogen-containing auxiliary BIB has certain flexibility, so that the frame structure is converted in the gas adsorption process. According to the Cu-MOF, the effect of preferentially adsorbing acetylene, propyne and sulfur hexafluoride gas from mixed gas such as acetylene / carbon dioxide, propyne / propylene and sulfur hexafluoride / nitrogen can be achieved, the structure of the Cu-MOF is changed in the propyne gas adsorption process, and the Cu-MOF shows a flexible adsorption behavior.

Description

Technical Field

[0001] The present invention belongs to the technical fields of the preparation of crystalline porous materials and gas separation, and particularly relates to a preparation method of a microporous copper-based flexible metal organic framework material (Metal organic frameworks, MOF). The feature is that the MOF material has unique hydrogen-rich adsorption sites and can induce the framework to generate flexible adsorption behavior under a certain pressure for gases such as acetylene, propyne, and sulfur hexafluoride, and can preferentially capture acetylene, propyne, and sulfur hexafluoride, thereby realizing the efficient separation and purification of acetylene / carbon dioxide, 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 all walks of life are getting higher and higher. 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 material gases such as methane, acetylene, and propylene. Propylene is the main raw material for producing value-added chemicals, but the molecular structures and sizes of propylene and propyne are extremely similar (C3H4: 4.4×6.8 Å 2 , C3H6: 5.4×6.8 Å 2), making the separation between the two face numerous challenges. Industrially, propylene is mainly purified by catalytic hydrogenation of propyne. However, this technology usually has problems such as high energy consumption, frequent catalyst regeneration, and secondary pollution caused by over-hydrogenation to produce C3H8. Therefore, optimizing the separation process and developing new separation technologies are of great significance for the propylene industry. In addition to the urgent need to solve the separation and purification requirements of light hydrocarbons, the separation and purification requirements of fluorine-containing gases also need to be improved, especially the purification of sulfur hexafluoride gas. Sulfur hexafluoride (SF6) is a gas with stable chemical properties, non-flammable, colorless, and odorless. Due to the excellent insulation and arc extinguishing properties of SF6, 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 electron etchant. Therefore, high-purity SF6 is a key material for manufacturing microelectromechanical 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 in the world has tripled. 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 together with N2O, CH4, and CO2. Since the SF6 / N2 mixture containing only a small amount of SF6 has similar insulating capabilities to high-purity SF6, pressurized gas mixtures have been used to reduce the use of SF6. Therefore, finding an effective method to separate SF6 / N2 is crucial, especially from mixtures with low SF6 concentrations. Therefore, the research on SF6 / N2 mixture separation technology has attracted much attention. Adsorptive separation based on porous materials, as a relatively energy-efficient and highly selective separation method, is expected to solve many problems in traditional separation processes. However, most porous materials are relatively rigid, and very few flexible MOF materials have been reported so far. In this patent, this flexible material brings new opportunities for the purification of gases such as acetylene, propylene, and sulfur hexafluoride.

[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 bonds. Due to its high porosity, large specific surface area, and adjustable pore size and physicochemical environment, MOFs have potential application values in the fields of adsorption separation, gas storage, drug slow release, and catalysis. In recent years, many MOFs have been developed into low-carbon hydrocarbon separation materials and achieved good results. At the same time, based on the open metal sites and pore sieving effects in MOFs, a large number of preferential adsorbent materials for acetylene and propylene have been discovered. However, there is less research on the separation of these energy gases by flexible MOF materials, and flexible materials may have unique advantages in the separation of energy gases. In this invention, a cheap bridged dicarboxylic acid ligand, the three-dimensional structure of the dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC), and a cheap nitrogen-containing co-ligand bisimidazole butane are self-assembled with copper nitrate under solvothermal conditions to form a microporous copper-based flexible MOF material. The crystal structure of this MOF has a high porosity, and at the same time has unique hydrogen-rich adsorption sites and can induce the framework to produce flexible deformation under a certain pressure for gases such as acetylene, propyne, and sulfur hexafluoride, providing action sites and places for gas molecule adsorption. This material shows preferential adsorption of acetylene, propyne, and sulfur hexafluoride gases in the adsorption of acetylene / carbon dioxide, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases, thus realizing the efficient purification of acetylene, propylene, and sulfur hexafluoride in one adsorption / desorption cycle. Summary of the Invention

[0004] The purpose of this invention is to provide a preparation method of a new type of microporous copper-based flexible MOF material (Cu-MOF), which can be used for the efficient separation of acetylene / carbon dioxide, propyne / propylene, and sulfur hexafluoride / nitrogen and is a preferential adsorbent for acetylene, propylene, and sulfur hexafluoride.

[0005] A microporous copper-based flexible MOF material, characterized in that an organic ligand and a copper source are reacted by a solvothermal method to prepare a dark blue block crystal material, and its chemical formula is C 20 H 26 CuN4O4, and the molecular formula is [Cu(BODC)(BIB)].

[0006] Analyzed from the perspective of crystal structure, this Cu-MOF material belongs to the orthorhombic system, the space group is Pbca , and the unit cell parameters are: V ≈ 5149.6(2), a ≈ 19.9765(4), b ≈ 13.7509(4), c ≈ 18.7465(4), α ≈ β ≈ γ ≈ 90°. The main peak positions of the PXRD powder diffraction peaks of the freshly prepared sampleθ ° Including approximately 8.60°, approximately 9.75°, approximately 13.97°, and approximately 18.23°.

[0007] The Cu metal centers in this Cu-MOF are all in a six-coordination mode. At the coordination site, each independent Cu atom coordinates with four O atoms on two BODC ligands. The carboxyl O atoms on the BODC ligands all participate in coordination, and two nitrogen-containing auxiliary ligands, bis(imidazolyl)butane, also participate in the six-coordination geometry of the metal center; both BODC and BIB ligands participate in addition to connection, and their ligands contain rich methylene groups, and their abundant H atoms can all act as potential action sites. The N atoms on the nitrogen-containing ligand bis(imidazolyl)butane can also act as potential action sites to interact with gases.

[0008] The synthesis method of the above-mentioned Cu-MOF material of the present invention mainly includes the following steps: Dissolve the organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC), the nitrogen-containing auxiliary ligand bis(imidazolyl)butane, and copper nitrate Cu(NO3)2 into a mixed solvent of N,N-dimethylformamide, water, and nitric acid, and then obtain the Cu-MOF product through a solvothermal reaction under closed conditions.

[0009] In the above technical solution, the ratio of the organic ligand to the metal salt (mass ratio) 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 °C - 110 °C, and the reaction time is 24 h - 36 h. The volume concentration of nitric acid is 30 - 50%, acting as an acid-base regulator and a template agent.

[0010] The obtained Cu-MOF material is washed with DMF, and then after solvent exchange with methanol or dichloromethane and vacuum removal of organic molecules (the above process is called activation), the obtained material is used as the final separation material for the efficient selective separation of acetylene / carbon dioxide, propyne / propylene, sulfur hexafluoride / nitrogen mixed gas, and preferentially adsorbs acetylene, propyne, and sulfur hexafluoride during the separation process.

[0011] The present invention prepares a microporous copper-based flexible MOF material based on a bridged-ring configuration dicarboxylic acid organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid (BODC), a nitrogen-containing auxiliary ligand bis(imidazolyl)butane, and a copper metal source. The specific beneficial effects of this material are as follows: The organic ligand BODC and the nitrogen-containing co-ligand bis(imidazolyl)butane used in the material synthesis have simple structures and relatively low prices. The Cu metal centers in this Cu-MOF are all in a six-coordination mode. At the coordination site, each independent Cu atom coordinates with four O atoms on two BODC ligands. The carboxyl O atoms on the BODC ligand all participate in the coordination, and two nitrogen-containing co-ligands bis(imidazolyl)butane also participate in the six-coordination geometry of the metal center; in addition to both participating in the connection, the BODC and BIB ligands both contain rich methylene groups on their ligands, and their rich H atoms can all act as potential action sites, and the N atoms on the nitrogen-containing ligand bis(imidazolyl)butane can also act as potential action sites to interact with gases.

[0012] The finally obtained Cu-MOF material has a three-dimensional network structure, can accommodate gas molecules, and there are a large number of methylene groups in the structure, which can contribute to high-density hydrogen-containing sites, facilitating the strengthening of the host-guest interaction between gas molecules and the framework.

[0013] The regularly arranged carboxyl O in the pores of this Cu-MOF also provides potential action sites, facilitating the strengthening of the interaction between acetylene, propyne, propylene, sulfur hexafluoride gas molecules and the framework; the N atoms on the nitrogen-containing ligand bis(imidazolyl)butane can also act as potential action sites to interact with gases, thus achieving the effect of preferentially adsorbing acetylene, propyne, and sulfur hexafluoride gases in the acetylene / carbon dioxide, propyne / propylene, sulfur hexafluoride / nitrogen mixed gases, enabling the purification tasks of acetylene, propylene, and sulfur hexafluoride to be completed within one adsorption-desorption cycle. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the three-dimensional crystal structure of Cu-MOF in the present invention.

[0015] Figure 2 It is the powder diffraction pattern of Cu-MOF in the present invention based on single crystal data simulation, fresh synthesized sample, and fresh synthesized sample after grinding.

[0016] Figure 3 It is the N2 adsorption-desorption curve of Cu-MOF in the present invention under the condition of 77 K.

[0017] Figure 4 It is the CO2 adsorption-desorption curve of Cu-MOF in the present invention under the condition of 195 K.

[0018] Figure 5 It is the single-component adsorption curve of acetylene and carbon dioxide of Cu-MOF in the present invention under the condition of 298 K.

[0019] Figure 6 It is the single-component adsorption curve of propyne and propylene of Cu-MOF in the present invention under the condition of 298 K.

[0020] Figure 7 This is the single-component adsorption curve of sulfur hexafluoride and nitrogen of Cu-MOF in the present invention under the condition of 298 K. Specific Embodiments

[0021] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0022] Example 1 First step: Weigh 30.0 mg of the organic ligand bicyclo[2.2.2]octane-1,4-dicarboxylic acid, 30.0 mg of the nitrogen-containing co-ligand bis(imidazolyl)butane, and 45 mg of copper nitrate trihydrate, and dissolve them in 2.3 mL N,N of N,N-dimethylformamide (DMF), 20 μL of nitric acid (a solution with pH ≈ 5.00 after dilution of concentrated nitric acid), and 0.5 mL of deionized water. After ultrasonic treatment to obtain a homogeneous solution, transfer it into a 20 mL glass reaction flask, and react at a constant temperature of 90 o °C for 36 h to obtain the Cu-MOF crystalline sample (30 mg), with a yield of 66.7% (calculated based on the metal salt).

[0023] Second step: Select a single crystal sample with appropriate size and good crystallization, collect diffraction data using a single crystal diffractometer at 293 K, and then refine the crystal structure using the relevant structure analysis software Olex2. The specific structure is shown in the attached drawings of the specification. The purity of the overall prepared sample is confirmed by X-ray powder diffraction technology.

[0024] Third step: In order to remove the solvent molecules in the pores of this material, the obtained crystalline sample is washed with DMF and then soaked in anhydrous methanol solvent. The solvent exchange process is carried out 5 times, and finally dichloromethane is used as the exchange solvent for treatment 2 times. The exchanged sample is degassed under vacuum at 80 o °C for 6 h to prepare the material for gas adsorption testing.

[0025] Fourth step: Before the single-component static adsorption test, load the above material into the adsorption tube, degas the test material again at 80 °C for 2 h (the above process is called activation), and then collect the single-component adsorption curve data of acetylene, carbon dioxide, sulfur hexafluoride, nitrogen, propyne, and propylene of this material at 25 o °C on the gas adsorption instrument. This Cu-MOF material can efficiently and selectively separate the mixed gases of acetylene / carbon dioxide, propyne / propylene, and sulfur hexafluoride / nitrogen, and preferentially adsorb acetylene, propyne, and sulfur hexafluoride during the separation process.

[0026] Figure 1The crystal structure in it shows that the Cu metal centers in this Cu-MOF are all in a six-coordination mode. At the coordination site, each independent Cu atom coordinates with four oxygen atoms on two BODC ligands. The carboxyl O atoms on the BODC ligands all participate in the coordination, and two nitrogen-containing auxiliary ligands, bis(imidazolyl)butane, also participate in the six-coordination geometry of the metal center; both BODC and BIB ligands participate in addition to connection, and their ligands all contain rich methylene groups, and their rich H atoms can all act as potential action sites, and the N atoms on the nitrogen-containing ligand bis(imidazolyl)butane can also act as potential action sites to interact with gases.

[0027] Figure 2 The powder diffraction pattern in it shows that the freshly prepared Cu-MOF sample has good crystallinity and good purity. The main peak positions of the PXRD powder diffraction peaks are θ ° ≈ 8.60°, about 9.75°, about 13.97°, about 18.23°.

[0028] Figure 3 The nitrogen adsorption curve in it shows that the N2 adsorption of Cu-MOF at 77 K shows a classic type I curve, corresponding to the microporous channels in the structure, further confirming the structural basis for separation.

[0029] Figure 4 The 195K carbon dioxide adsorption curve in it shows that Cu-MOF adsorbs carbon dioxide at 195K, which is the basic manifestation of the flexible segmental adsorption of the MOF framework. This phenomenon further confirms the structural basis for Cu-MOF to separate gases.

[0030] Figure 5 The acetylene / carbon dioxide single-component adsorption curve in it shows that Cu-MOF has a certain adsorption capacity for the two gases, and at the same time, the interaction between the framework and acetylene gas molecules is stronger. This phenomenon enables Cu-MOF to preferentially capture acetylene gas in the acetylene / carbon dioxide mixture.

[0031] Figure 6 The propyne / propylene single-component adsorption curve in it shows that Cu-MOF has a high adsorption capacity for the two gases, and at the same time, the interaction between the framework and propyne gas molecules is stronger. This phenomenon enables Cu-MOF to preferentially capture propyne gas in the propyne / propylene mixture.

[0032] Figure 7 The sulfur hexafluoride / nitrogen single-component adsorption curve in it shows that Cu-MOF has a high adsorption capacity for sulfur hexafluoride gas, and the interaction between the framework and sulfur hexafluoride gas molecules is stronger. This phenomenon enables Cu-MOF to preferentially capture sulfur hexafluoride gas in the sulfur hexafluoride / nitrogen mixture.

[0033] The above results indicate that the microporous flexible Cu-MOF material in this example has unique hydrogen-rich adsorption sites and that gases such as acetylene, propyne, and sulfur hexafluoride can cause certain deformations to the framework under a certain pressure, and it has a high adsorption capacity and good separation performance for acetylene / carbon dioxide, propyne / propylene, and sulfur hexafluoride / nitrogen gases. At the same time, this 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 this type of material in the fields of low-carbon hydrocarbon gas and fluorine-containing gas separation. That is, the obtained Cu-MOF material is washed with DMF, and then used as the final separation material for the efficient selective separation of acetylene / carbon dioxide, propyne / propylene, and sulfur hexafluoride / nitrogen mixed gases after solvent exchange with methanol or dichloromethane and vacuum removal of organic molecules (the above process is called activation). During the separation process, acetylene, propyne, and sulfur hexafluoride are preferentially adsorbed.

[0034] 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 microporous copper-based flexible metal organic framework material, characterized in that: Its chemical formula is C 20 H 26 CuN4O4, the molecular formula is [Cu(BODC)(BIB)], BODC is bicyclo[2.2.2]octane-1,4-dicarboxylic acid, and BIB is bisimidazobutane.

2. The microporous copper-based flexible metal organic framework material according to claim 1, characterized in that: The unit cell parameters are: V ≈ 5149.6(2), a ≈ 19.9765(4), b ≈ 13.7509(4), c ≈ 18.7465(4), α ≈ β≈ γ ≈ 90°. The main peak position of the PXRD powder diffraction peak of the freshly prepared sample is θ ° Including about 8.60°, about 9.75°, about 13.97°, and about 18.23°.

3. The microporous copper-based flexible metal organic framework material according to claim 1, characterized in that: The Cu metal centers in this Cu-MOF are all in a hexacoordinated mode. At the coordination site, each independent Cu atom is coordinated with four O atoms on two BODC ligands. The carboxyl O atoms on the BODC ligands all participate in the coordination, and the two nitrogen-containing auxiliary bisimidazolidinyl butanes also participate in the hexacoordinated geometric configuration of the metal center.

4. A method for preparing the microporous copper-based flexible 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), the nitrogen-containing auxiliary ligand bisimidazolidinone and copper nitrate Cu(NO3)2 are dissolved in a mixed solvent of N,N-dimethylformamide, water and nitric acid, 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 80-110°C, the reaction time is 24-36 hours, 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 is copper chloride, copper nitrate, copper sulfate, copper perchlorate and cuprous iodide, preferably copper nitrate; the acid-base regulator used is 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 microporous copper-based flexible metal organic framework material according to any one of claims 1 to 2 for selective separation of any one of acetylene / carbon dioxide, propyne / propylene or sulfur hexafluoride / nitrogen mixed gases.

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