A fluorine-containing metal organic framework material for methane and nitrogen separation, and its preparation method and application

Abstract

The present invention discloses a fluorinated metal organic framework material for methane and nitrogen separation, and its preparation method and application. The porous metal organic framework material is a compound with a supramolecular porous network structure formed by self-assembly of metal ions and fluorinated organic ligands in a solvent through coordination and complexation; the metal ions are one or more metal ions of Mg(II), Al(III), Ni(II), Cu(II), and Co(II), preferably Cu(II), and the organic ligands are monodentate or multidentate organic compounds of fluorinated carboxylic acids or their derivatives. The fluorinated metal organic framework material of the present invention has a large specific surface area, and has a suitable pore size and a fluorinated porous environment. A strong C-H...F interaction force is generated by F atoms and CH4, which can enhance the recognition of methane, has a high CH4 adsorption capacity and CH4 / N2 selectivity, and can achieve efficient separation of CH4 / N2 at room temperature, low methane content, and low methane partial pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of gas adsorption separation, and in particular to a fluorine-containing metal organic framework material for methane and nitrogen separation and a preparation method thereof. Background Art

[0002] Methane is a low-carbon, clean energy source. However, due to natural generation or subsequent mining, this energy gas contains other impurities besides CH4, such as N2, CO2, H2S, and H2O. The presence of these impurities not only reduces the calorific value of natural gas but also limits its application. Therefore, efficient separation of CH4 and impurities is a prerequisite for its efficient utilization. Currently, the main methods being developed and researched for CH4 / N2 separation in unconventional natural gas include cryogenic distillation, membrane separation, hydrate separation, and adsorption separation. Cryogenic distillation utilizes the 34K difference in boiling points between CH4 and N2 at atmospheric pressure to separate them through gas compression, liquefaction, and re-distillation. While cryogenic distillation offers high product purity and methane recovery, it suffers from complex equipment, high investment, and high energy consumption. Membrane separation offers advantages such as simple equipment, no phase changes, and continuous operation. However, limited by low methane / nitrogen separation selectivity, poor permeability, and the need for efficient membrane materials and membrane fabrication technologies, membrane separation of CH₄ / N₂ remains in the research and development stage. Hydrate gas separation technology offers advantages such as simple operation, no pretreatment requirements, wide applicability, and low separation costs. However, further development is needed in identifying efficient hydrate promoters and controlling optimal operating conditions. Pressure swing adsorption technology can effectively separate low-concentration gases at room temperature, thus addressing the high energy consumption of traditional methods.

[0003] Porous materials have been widely studied as solid adsorbents commonly used in pressure swing adsorption technology. Currently, porous solid adsorbents for separating CH4 / N2 mixtures can be divided into three categories, including zeolites, carbon materials and metal organic framework materials (MOFs). Zeolites are usually defined as aluminum oxide (AlO4) and silicon oxide (SiO4) tetrahedrons connected to each other by covalent bonds to form a structurally stable inorganic porous material. The separation performance of conventional zeolites for CH4 / N2 mixtures has been improved by optimizing the molding method, ion exchange, adjusting the silicon-aluminum ratio or composite modified zeolites. For example, the adsorption capacity of zeolite-5A particles without binder for CH4 can reach 15.7cm 3 (STP)g -1, 20% higher than binder-containing zeolite-5A particles (Ind. Eng. Chem. Res, 2015, 54: 6390-9639). The CH4 / N2 separation selectivity of alkaline earth metal ion exchange zeolite-X increases with cation size. In particular, the CH4 / N2 separation selectivity of Cs-NaX material is greatly improved, reaching a value of 3.8 (Chem. Asian J, 2018, 13: 3222-3230). Patent CN102219235A reports a Naβ molecular sieve modified with acids or acidic salts of varying strengths. While increasing the CH4 gas adsorption capacity, it also reduces the molecular sieve's adsorption capacity for N2, thereby increasing the CH4 and N2 separation factor from 1.63 to 2.66, achieving separation and enrichment of both CH4 and N2 gases. Although molecular sieves play a certain role in the adsorption and separation of CH4 / N2, there is still a contradiction between the highly polarized surface of zeolite molecular sieves preferentially adsorbing CH4 and their diffusion kinetics preferentially selecting N2. Carbon-based materials are traditional porous materials and have good performance in the adsorption and separation of CH4 / N2 mixtures. Patent CN117942942A reports a coal-based carbon nanotube / activated carbon composite material for CH4 / N2 adsorption and separation. Nitrogen doping under hydrothermal conditions promotes the formation of microporous structure at the nanoscale. The interlayer stacking space of the formed carbon nanotubes has a narrow pore size distribution, has good selectivity for CH4 / N2 adsorption and separation, and reduces the cost of materials. Li et al. used rice as the carbon source to prepare a series of PRCs carbon materials. The CH4 adsorption capacity and CH4 / N2 adsorption selectivity at 298K and 1 bar reached 25.1 cm 3 (STP)g -1 and 5.7, which are better than most reported carbon materials (Chem. Eng. J, 2020, 384: 123388). Although carbon materials have been widely used in the separation of CH4 / N2 mixtures. However, most of the carbon materials reported so far are mesoporous materials, and the pore size distribution is uneven, and the adsorption separation performance shown in the separation system is still relatively low. Therefore, there is a need to further develop microporous or even ultramicroporous materials with uniform pore size distribution.

[0004] MOFs are new porous crystalline materials formed by the coordination of metal ions / metal clusters with organic bridging ligands. Compared with traditional inorganic porous materials, MOFs have ultra-high specific surface area and porosity, highly modular composition and structure, and customizable pore chemical properties, which have made them widely studied in many fields. In recent years, MOFs have shown excellent CH4 adsorption capacity and CH4 / N2 separation selectivity for the separation of CH4 / N2 mixtures. Sun reported a [Ni3(HCOO)6] framework constructed by the smallest and shortest monodentate ligand HCOO-. The adsorption capacity of this material for CH4 and the CH4 / N2 separation selectivity were 16.8 cm 3 (STP)g -1 and 6.5 (Microporous Mesoporous Mat, 2014, 186, 1387-1811). Hu et al. successfully synthesized the nanoporous material Cu(INA)2 by hydrothermal reaction using isonicotinic acid organic ligands and copper ions, and found that ultramicropores can be used to improve separation efficiency. In addition, the weakly polar surface also promotes the separation of methane and nitrogen. Under the conditions of 298K and 100KPa, the separation selectivity of Cu(INA)2 for CH4 / N2 is as high as 8.34 (Rsc Advances, 2016, 68, 64039-64046). Patent CN102962036A dissolves cobalt metal salts or mixtures of cobalt metal salts and other metal salts and organic ligands in a solvent in a certain proportion to prepare a metal organic framework material based on transition metal cobalt. It has excellent selectivity for methane in the separation of methane and nitrogen, and its methane equilibrium selectivity reaches more than 7. Patent CN111298771B adopts SiF6 2- 、GeF6 2- 、ZrF6 2- 、SnF6 2-Layered fluorinated metal-organic framework materials are synthesized by coordinating inorganic fluorinated anions with organic ligands. These materials have high selectivity and high capacity for acetylene and are particularly suitable for the adsorption and separation of trace acetylene. Patent CN117586514A uses fluorinated reagents to in situ fluorinate tetravalent metal MOFs adsorbents, which have good chemical stability and water resistance and can be used for hydrogen storage, C2H6 / C2H4 adsorption and separation. Patent CN115678024A introduces a fluorinated metal salt copper hexafluorosilicate and an organic ligand tetrakis(4-pyridyl)porphine under heating conditions to obtain a unit structure Cu(TPyP)(SiF6). Through the hydrogen bonds and strong interactions between the anion column and the porphyrin and acetylene, the material's recognition of acetylene is enhanced, resulting in an acetylene adsorption capacity higher than that of carbon dioxide. The above studies mainly focus on the introduction of fluorinated metal anions or the fluorination modification of MOFs with fluorinated reagents, but there are fewer reports on the introduction of fluorinated organic ligands, especially in the field of CH4 / N2 adsorption separation. Therefore, based on the above phenomenon, this paper proposes a fluorinated metal organic framework material for methane and nitrogen separation and its preparation method. By in situ introducing F atoms at different positions on the pyridine ring, not only can the pore size be adjusted, but the strong interaction with CH4 is enhanced by fluorinated pore surface, achieving preferential adsorption of low-concentration methane in a large amount of nitrogen. Summary of the Invention

[0005] Based on this, in order to solve the problems of low coalbed methane utilization, environmental pollution, low adsorption capacity of CH4 and N2 in coalbed methane, and poor separation effect in the existing technology, the present invention provides a fluorine-containing metal organic framework material for methane and nitrogen separation, as well as its preparation method and application.

[0006] The technical solution adopted in the present invention is as follows:

[0007] The fluorinated metal organic framework material for methane and nitrogen separation is a porous metal organic framework material which is a compound having a supramolecular porous network structure formed by self-assembly of metal ions and fluorinated organic ligands in a solvent through coordination and complexation.

[0008] The metal ion is one or more metal ions of Mg(II), Al(III), Ni(II), Cu(II), Co(II), preferably Cu(II), and the organic ligand is a monodentate or multidentate organic compound of a fluorinated carboxylic acid or its derivative.

[0009] Furthermore, the fluorine-containing organic ligand is one or more of 2-fluoroisonicotinic acid, 3-fluoroisonicotinic acid, 3,5-difluoroisonicotinic acid, 2,3-difluoroisonicotinic acid, and 2,6-difluoroisonicotinic acid, preferably 3,5-difluoroisonicotinic acid.

[0010] The present invention also provides a method for preparing the fluorine-containing metal organic framework material for methane and nitrogen separation, comprising the following steps:

[0011] 1) dissolving the metal salt and the fluorine-containing organic ligand in a solvent and stirring to form a mixture;

[0012] 2) placing the mixture from step 1) in a sealed reactor, and then transferring the reactor to an oven for a solvothermal synthesis reaction to form a precipitate;

[0013] 3) After cooling, the precipitate is centrifuged, washed, and soaked with acetone, and then dried to obtain the fluorine-containing metal organic framework material product.

[0014] Furthermore, the specific operation of step 1) includes the following steps: dissolving the metal salt in water to prepare solution A, dissolving the fluorinated organic ligand in an organic solvent to prepare solution B, and adding solution A dropwise to solution B, with the volume ratio of solution A to solution B being 1:0.5-2; wherein the organic solvent is one or a mixed solvent of two or more selected from DMF, DEF, NMP, methanol, ethanol, and acetonitrile.

[0015] Furthermore, the metal compound in step 1) is any one of chloride, nitrate, sulfate, acetate, basic carbonate, methoxide, and ethanolate corresponding to the metal ion, or a mixture thereof.

[0016] Furthermore, the molar ratio of the metal salt to the fluorine-containing organic ligand is 1:5 to 4:1, preferably 1:1.5-2.

[0017] Furthermore, in the step 2), the temperature of the solvent thermal synthesis reaction is 100° C.±20° C., and the time of the solvent thermal synthesis reaction is 24 h to 72 h.

[0018] Furthermore, the precipitate obtained in step 3) is collected in a centrifuge tube, washed with N,N-dimethylformamide, centrifuged and replaced with fresh solvent 2-4 times a day, and then circulated for 2-3 days to dissolve and remove unreacted fluorinated organic ligands.

[0019] Furthermore, the acetone soaking time in step 3) is 2-3 days, and the mixture is centrifuged and replaced with fresh solvent 2-4 times every day to replace the high-boiling-point solvent of N,N-dimethylformamide.

[0020] The present invention also provides an application of a fluorine-containing metal organic framework material for the adsorption separation of a mixed gas of CH4 and N2.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The fluorine-containing metal organic framework material of the present invention introduces F atoms on the pyridine ring, so that it can produce better adsorption and separation effects on CH4 at different positions. In particular, when using 3,5-difluoroisonicotinic acid as a ligand to coordinate with metal copper ions, the F atoms on the pyridine ring can successfully point to the interior of the pore, thereby generating a strong CH...F interaction force with CH4. It has certain structural innovation and potential adsorption and separation application capabilities.

[0023] (2) The fluorinated metal organic framework material in the present invention has a suitable pore size and fluorinated functional sites. By introducing F atoms at different positions on the ligand to modify the pores, not only the polar environment of the pore surface is regulated, but also the pore size can be reduced, thereby enhancing the material's recognition of methane, making the adsorption amount of methane higher than that of nitrogen, and having the ability to separate CH4 / N2 mixed gases, with high separation selectivity and large adsorption capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the N2 adsorption-desorption isotherm of the novel fluorinated metal organic framework material prepared in Example 1 at 77K;

[0025] Figure 2 is the adsorption isotherm of methane and nitrogen of the novel fluorine-containing metal organic framework material prepared in Example 1 at 298K;

[0026] Figure 3 Adsorption isotherms of methane and nitrogen of the novel fluorinated metal organic framework material prepared in Example 1 at 288K;

[0027] Figure 4 This is the CH4 / N2 adsorption selectivity curve of the new fluorine-containing metal organic framework material prepared in Example 1;

[0028] Figure 5 The novel fluorinated metal organic framework material prepared in Example 1 is used for CH4 / N2 (v:v=10:90, total flow rate is 4cm 3 / min) breakthrough curve of mixed gas (298K, 1bar);

[0029] Figure 6 is the N2 adsorption-desorption isotherm of the novel fluorinated metal organic framework material prepared in Example 4 at 77K;

[0030] Figure 7 is the N2 adsorption-desorption isotherm of the novel fluorinated metal organic framework material prepared in Example 5 at 77K;

[0031] Figure 8 is the N2 adsorption-desorption isotherm of the novel fluorinated metal organic framework material prepared in Example 6 at 77K;

[0032] Figure 9 The metal organic framework material prepared in Comparative Example 1 was used for CH4 / N2 (v:v=10:90, with a total flow rate of 4 cm 3 / min) breakthrough curve of mixed gas (298K, 1bar);

[0033] Figure 10 The novel fluorinated metal organic framework material prepared in Example 2 is subjected to CH4 / N2 (v:v=10:90, with a total flow rate of 4 cm 3 / min) breakthrough curve of mixed gas (298K, 1bar); DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example 1

[0036] Prepare Solution A: Dissolve copper nitrate trihydrate (242 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 3,5-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min and allow static crystallization at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Cu(3,5-FINA)2.

[0037] The permanent porosity of the above-mentioned synthetic material Cu(3,5-FINA)2 was determined by measuring the nitrogen adsorption-desorption isotherm at 77K, as shown in Figure 1 As shown, the pore size of the material is approximately distributed at 0.52 nm, and its specific surface area is measured to be 390 m 2 / g, and the temperature is maintained at 77K by liquid nitrogen. The metal organic framework material provided by the present invention contains fluorine adsorption sites, and combined with the appropriate pore size and specific surface area of ​​the metal organic framework material, it can selectively adsorb methane.

[0038] The fluorinated metal organic framework material prepared in this embodiment is used to adsorb methane or nitrogen gas. The gas adsorption isotherm of the sample is measured on the adsorption instrument 3Flex of Micromeritics. The adsorbed gases are methane (99.99%) and nitrogen (99.99%). In order to study the effect of the fluorinated metal organic framework material on the methane adsorption effect, the above material is dehydrated in 3Flex to avoid the influence of physically adsorbed water in the material on the gas adsorption effect. Under low vacuum conditions (below 0.005 mmHg), it is heated to 150°C at a heating rate of 5°C / min and maintained at 150°C for 6 hours. The sample tube is then loaded into the 3Flex adsorption device and the static adsorption curve is tested (0-1 bar). The temperature in the gas adsorption sample tube is controlled by a constant temperature water bath (accuracy 0.01°C), and the adsorption temperature is 298K.

[0039] The adsorption isotherm test results of the novel fluorine-containing metal organic framework material prepared in Example 1 of the present invention for methane and nitrogen at 298K and 288K are as follows: Figure 2 and Figure 3 As shown. Figure 2 The results show that at 298K and 1 bar, the adsorption capacity of methane is as high as 38.97 cm 3 / g, and the adsorption capacity of nitrogen is 5.61cm 3 / g.

[0040] like Figure 4 As shown in Figure 2, the IAST selectivity of CH4 / N2 (50 / 50, v / v) is 16.3 at 298K and 1 bar, indicating that the novel fluorinated metal organic framework exhibits excellent CH4 adsorption capacity and CH4 / N2 separation selectivity for the separation of CH4 / N2 mixtures.

[0041] The methane and nitrogen gas adsorption penetration curve of the sample was measured on an Agilent 8860 series gas chromatograph. The adsorbed mixed gas composition was methane: nitrogen = 1:9 (volume ratio), the total flow rate of the mixed gas was 4 ml / min, and the adsorbent mass was 1.5 g. The peaks of each pure gas component molecule in the detector were first tested. After the peak area error of each component was within 1%, the valve was switched to allow the raw mixed gas to pass into the reaction tube. The outlet of the reaction tube was connected to the automatic injection port of the gas chromatograph, and the gas chromatograph was started for testing. After obtaining the test results, the gas phase penetration curve of methane-nitrogen was obtained by comparing the peak areas of each component at the outlet mixer of the reaction tube with those of the pure gas components. The schematic diagram is shown as follows. Figure 5 As shown in Table 1, the dynamic adsorption capacity and dynamic adsorption selectivity of Cu(3,5-FINA)2 adsorbent for methane and nitrogen gases at a partial pressure of 0.1 bar are shown.

[0042] The static adsorption capacity of the adsorbent is obtained from the adsorption isotherm of the pure component gas at normal pressure; the dynamic adsorption capacity is obtained from the breakthrough curve of the mixed component gas collected experimentally according to the following formula:

[0043]

[0044] Among them, Q t is the dynamic adsorption capacity of gas, v is the total flow rate of feed gas, in mL / min; m is the mass of adsorbent sample, in g; t is the adsorption time, in minutes; C0 and C are the gas concentrations at the inlet and outlet, respectively, in mmol / mL.

[0045] The dynamic adsorption selectivity is calculated as follows:

[0046] Among them S ads is the selectivity of CH4 relative to N2. q1 and q2 are the dynamic adsorption amounts of component 1 (CH4) and component 2 (N2) in the adsorption phase, respectively. P1 and P2 are the partial pressures of component 1 (CH4) and component 2 (N2) in the gas phase, respectively.

[0047] Example 2

[0048] Prepare Solution A: Dissolve magnesium nitrate hexahydrate (256 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 3,5-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min. Allow to crystallize statically at this temperature for 40 hours, then cool naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled as Mg(3,5-FINA)2.

[0049] The above Mg(3,5-FINA)2 was subjected to dynamic adsorption of methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Mg(3,5-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0050] Example 3

[0051] Prepare Solution A: Dissolve aluminum nitrate nonahydrate (375 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 3,5-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min. Allow to crystallize statically at this temperature for 40 hours, then cool naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Al(3,5-FINA)2.

[0052] The above Al(3,5-FINA)2 was subjected to dynamic adsorption of methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Al(3,5-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0053] Example 4

[0054] Prepare Solution A: Dissolve copper nitrate trihydrate (242 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 2,3-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min and allow static crystallization at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Cu(2,3-FINA)2.

[0055] The permanent porosity of the Cu(2,3-FINA)2 material was determined by measuring the nitrogen adsorption-desorption isotherm at 77K, as shown in Figure 6 As shown, the pore size of the material is approximately distributed at 0.61 nm, and its specific surface area is measured to be 462 m 2 / g, and the temperature of 77K was maintained by liquid nitrogen.

[0056] The above Cu(2,3-FINA)2 was subjected to dynamic adsorption of methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Cu(2,3-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0057] Example 5

[0058] Prepare Solution A: Dissolve copper nitrate trihydrate (242 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 2,6-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min and allow static crystallization at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Cu(2,6-FINA)2.

[0059] The permanent porosity of the Cu(2,6-FINA)2 material was determined by measuring the nitrogen adsorption-desorption isotherm at 77K, as shown in Figure 1 As shown, the pore size of the material is approximately distributed at 0.58 nm, and its specific surface area is measured to be 437 m 2 / g, and the temperature of 77K was maintained by liquid nitrogen.

[0060] The above Cu(2,6-FINA)2 was subjected to dynamic adsorption of methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Cu(2,6-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0061] Example 6

[0062] Prepare Solution A: Dissolve copper nitrate trihydrate (2.42 g, 10 mmol) in 20 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 2-fluoroisonicotinic acid (2.12 g, 15 mmol) in 20 ml of anhydrous ethanol and stir at 60°C for 1 hour. Add Solution A dropwise to Solution B at 60°C with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, heat it to 100°C at 10°C / min in a reaction oven, and allow it to crystallize statically at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Cu(2-FINA)2.

[0063] The permanent porosity of the Cu(2-FINA)2 material was determined by measuring the nitrogen adsorption-desorption isotherm at 77K, as shown in Figure 1 As shown, the pore size of the material is approximately distributed at 0.65 nm, and its specific surface area is measured to be 489 m 2 / g, and the temperature of 77K was maintained by liquid nitrogen.

[0064] The above Cu(2-FINA)2 was used to dynamically adsorb methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Cu(2-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0065] Example 7

[0066] Prepare Solution A: Dissolve copper nitrate trihydrate (2.42 g, 10 mmol) in 20 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 3-fluoroisonicotinic acid (2.12 g, 15 mmol) in 20 ml of anhydrous ethanol and stir at 60°C for 1 hour. Add Solution A dropwise to Solution B at 60°C with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, heat it to 100°C at 10°C / min in a reaction oven, and allow it to crystallize statically at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder, that is, a fluorine-containing metal organic framework material, which was labeled Cu(3-FINA)2.

[0067] The above Cu(3-FINA)2 was used to dynamically adsorb methane and nitrogen gases. The adsorption test conditions were repeated in Example 1. The dynamic adsorption capacity and dynamic adsorption selectivity of Cu(3-FINA)2 for methane and nitrogen gases are shown in Table 1.

[0068] Comparative Example 1

[0069] Prepare Solution A: Dissolve copper nitrate trihydrate (2.42 g, 10 mmol) in 50 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve isonicotinic acid (2.46 g, 20 mmol) in 50 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark blue. Place the reaction mixture in a sealed stainless steel autoclave, then heat to 100°C in a reaction oven at 10°C / min and allow static crystallization at this temperature for 40 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a blue powder. The product was labeled Cu(INA)2.

[0070] The methane and nitrogen gas adsorption penetration curve of the sample was measured on an Agilent 8860 series gas chromatograph. The adsorbed mixed gas composition was methane: nitrogen = 1:9 (volume ratio), the total flow rate of the mixed gas was 4 ml / min, and the adsorbent mass was 1.5 g. The peaks of each pure gas component molecule in the detector were first tested. After the peak area error of each component was within 1%, the valve was switched to allow the raw mixed gas to pass into the reaction tube. The outlet of the reaction tube was connected to the automatic injection port of the gas chromatograph, and the gas chromatograph was started for testing. After obtaining the test results, the gas phase penetration curve of methane-nitrogen was obtained by comparing the peak areas of each component at the outlet mixer of the reaction tube with those of the pure gas components. The schematic diagram is shown as follows. Figure 6 As shown in Table 1, the dynamic adsorption capacity and dynamic adsorption selectivity of Cu(INA)2 adsorbent for methane and nitrogen gases at a partial pressure of 0.1 bar are shown.

[0071] Comparative Example 2

[0072] Prepare Solution A: Dissolve nickel nitrate hexahydrate (291 mg, 1 mmol) in 6 ml of deionized water and mix thoroughly. Prepare Solution B: Dissolve 3,5-difluoroisonicotinic acid (318 mg, 2 mmol) in 6 ml of anhydrous ethanol and mix thoroughly. Add Solution A dropwise to Solution B with continuous stirring until the solution turns dark green. Place the reaction mixture in a sealed stainless steel autoclave, heat it to 100°C at 10°C / min in a reaction oven, and allow it to crystallize statically at this temperature for 48 hours before cooling naturally to room temperature. After cooling to room temperature, the obtained product was collected in a centrifuge tube, first centrifuged three times with deionized water, then washed with N,N-dimethylformamide (DMF), centrifuged and replaced with fresh solvent three times a day and then cycled for two days to dissolve and remove unreacted organic ligands. Next, the DMF-treated sample was placed in an acetone solvent for soaking and replacement for two days, centrifuged and replaced with fresh solvent three times a day to replace the high-boiling point DMF in the pores, and then dried at 100°C for 12 hours to obtain a green powder. The product was labeled Ni(3,5-FINA)2.

[0073] The methane and nitrogen gas adsorption penetration curve of the sample was measured on an Agilent 8860 series gas chromatograph. The adsorbed mixed gas composition was methane: nitrogen = 1:9 (volume ratio), the total flow rate of the mixed gas was 4 ml / min, and the adsorbent mass was 1.5 g. The peaks of each pure gas component molecule in the detector were first tested. After the peak area error of each component was within 1%, the valve was switched to allow the raw mixed gas to pass into the reaction tube. The outlet of the reaction tube was connected to the automatic injection port of the gas chromatograph, and the gas chromatograph was started for testing. After obtaining the test results, the gas phase penetration curve of methane-nitrogen was obtained by comparing the peak areas of each component at the outlet mixer of the reaction tube with those of the pure gas components. The schematic diagram is shown as follows. Figure 7As shown in Table 1, the dynamic adsorption capacity and dynamic adsorption selectivity of Ni(3,5-FINA)2 adsorbent for methane and nitrogen gases at a partial pressure of 0.1 bar are shown.

[0074] Table 1 Dynamic adsorption capacity and dynamic adsorption selectivity of methane and nitrogen gases for Cu(3,5-FINA)2, Mg(3,5-FINA)2, Al(3,5-FINA)2, Ni(3,5-FINA)2, Cu(2,3-FINA)2, Cu(2,6-FINA)2, Cu(2-FINA)2, Cu(3-FINA)2 and Cu(INA)2 at 298K

[0075]

[0076] From the adsorption data results of the adsorbents of Examples 1 and 4-5 in Table 1, it can be seen that 3,5-difluoroisonicotinic acid, 2,3-difluoroisonicotinic acid, and 2,6-difluoroisonicotinic acid only differ in the position of the F atom substitution. The choice of different fluorine-containing organic ligands has a great influence on the adsorption performance results. This is because: after 3,5-difluoroisonicotinic acid coordinates with copper ions to form a channel, the F atoms at these two positions on the pyridine ring can successfully point to the interior of the channel, closer to the center of the gas molecule, and have a stronger interaction force. However, after the other two ligands coordinate with copper ions, some of the F atoms will be parallel to the channel, and the interaction force between them and the gas is weaker.

[0077] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A fluorinated metal organic framework material for methane and nitrogen separation, characterized by: The porous metal organic framework material is a compound with a supramolecular porous network structure formed by self-assembly of metal ions and fluorine-containing organic ligands in a solvent through coordination and complexation. The metal ion is one or more metal ions of Mg(II), Al(III), Ni(II), and Co(II), and the fluorine-containing organic ligand is one or more of 2-fluoroisonicotinic acid, 3-fluoroisonicotinic acid, 3,5-difluoroisonicotinic acid, 2,3-difluoroisonicotinic acid, and 2,6-difluoroisonicotinic acid.

2. A fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 1, characterized in that The fluorine-containing organic ligand is 3,5-difluoroisonicotinic acid.

3. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 1, characterized in that The following steps are involved: 1) Dissolve the metal salt and the fluorine-containing organic ligand in a solvent and stir to form a mixture; 2) placing the mixture from step 1) in a sealed reactor, and then transferring the reactor to an oven for a solvothermal synthesis reaction to form a precipitate; 3) After cooling, the precipitate is centrifuged, washed, and soaked with acetone, and then dried to obtain the fluorine-containing metal organic framework material product.

4. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 3, characterized in that The specific operation of step 1) includes the following steps: dissolving the metal salt in water to prepare solution A, dissolving the fluorinated organic ligand in an organic solvent to prepare solution B, and adding solution A dropwise to solution B, with the volume ratio of solution A to solution B being 1:0.5-2; wherein the organic solvent is one or a mixed solvent of two or more selected from the group consisting of DMF, DEF, NMP, methanol, ethanol, and acetonitrile.

5. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 3, characterized in that The metal compound in step 1) is any one of chloride, nitrate, sulfate, acetate, basic carbonate, methoxide, and ethanolate corresponding to the metal ion, or a mixture thereof.

6. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 3, characterized in that The molar ratio of the metal salt to the fluorine-containing organic ligand is 1:5 to 4:

1.

7. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 6, characterized in that The molar ratio of the metal salt to the fluorine-containing organic ligand is 1:1.5-2.

8. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 3, characterized in that In the step 2), the temperature of the solvent thermal synthesis reaction is 100° C.±20° C., and the time of the solvent thermal synthesis reaction is 24 h to 72 h.

9. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 3, characterized in that The precipitate obtained in step 3) is collected in a centrifuge tube, washed with N,N-dimethylformamide, centrifuged and replaced with fresh solvent 2-4 times a day, and then circulated for 2-3 days to dissolve and remove unreacted fluorinated organic ligands.

10. The method for preparing a fluorine-containing metal organic framework material for methane and nitrogen separation according to claim 9, characterized in that The acetone soaking time in step 3) is 2-3 days, and the mixture is centrifuged and replaced with fresh solvent 2-4 times every day to replace the high-boiling-point solvent of N,N-dimethylformamide.

11. The use of a fluorinated metal organic framework material for methane and nitrogen separation according to claim 1, characterized in that Used for adsorption separation of CH4 and N2 mixed gases.

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