An iron-based metal-organic framework material, its preparation method and application in separating methane and propane

Abstract

The present invention provides an iron-based metal-organic framework material, a preparation method thereof, and an application thereof in separating methane and propane, belonging to the technical field of gas separation. The organic ligands of the iron-based metal-organic framework material of the present invention are 5-(3-pyridyl)isophthalic acid and formic acid, and the coordination metal is Fe<supgt;3+< / supgt>. This material is a microporous material with a new topological structure, belonging to the trigonal crystal system. In its structure, every 3 Fe<supgt;3+< / supgt> are coordinated with 4 carboxylic acids from 5-(3-pyridyl)isophthalic acid, 2 formic acids, and 2 pyridine N from 5-(3-pyridyl)isophthalic acid to form a secondary structure unit with six connections. The secondary structure unit is connected with 5-(3-pyridyl)isophthalic acid to form a three-dimensional network structure with a curved pore channel having unidirectional connectivity. The iron-based metal-organic framework material of the present invention has a relatively high specific surface area and a relatively high propane adsorption capacity, and can well separate propane from methane.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation, and particularly relates to an iron-based metal-organic framework material, a preparation method thereof, and an application thereof in separating methane and propane. Background Art

[0002] With the rapid development of the global economy, environmental problems caused by the consumption of fossil energy have attracted serious attention from the public. Therefore, the demand for clean energy is increasing continuously. Compared with traditional fuels such as coal, diesel, and petroleum, natural gas is a clean energy source with broad prospects, having advantages such as safety, high heat energy, and high efficiency. Natural gas is mainly composed of methane and contains a small amount of impurities such as propane. The presence of propane will reduce the cyclic steady state and utilization efficiency of natural gas. Therefore, in order to improve economic efficiency, it is very meaningful to separate propane from methane in natural gas. At present, the traditional method of separating mixed gases by low-temperature distillation in industry not only consumes huge energy, but also the operating conditions of the machine are very harsh. Developing microporous materials with good gas separation ability for efficiently and energy-savingly separating propane from methane is very important in industrial production.

[0003] Metal-organic framework materials are inorganic-organic hybrid crystal materials composed of organic ligands and metal ions / clusters. In recent years, they have received extensive attention due to their diverse structures, large specific surface areas, precisely adjustable pore structures, and functionalization characteristics. Gas adsorption and separation are properties that can most fully utilize the pore characteristics and permanent porosity advantages of metal-organic framework materials. Since methane and propane are non-polar molecules, it is difficult for these gas molecules to be separated by the enhanced electrostatic interaction through functional group modification. Therefore, it is very meaningful to design and synthesize metal-organic framework materials with novel pore structures that can generate stronger van der Waals interactions with propane gas. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an iron-based metal-organic framework material, a preparation method thereof, and an application thereof in separating methane and propane. The iron-based metal-organic framework material of the present invention has a good separation effect on methane and propane.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides an iron-based metal-organic framework material, wherein the organic ligands of the iron-based metal-organic framework material are 5-(3-pyridyl)isophthalic acid and formic acid, and the coordinating metal is Fe 3+ .

[0007] Preferably, the topological node symbol of the iron-based metal-organic framework material is {4 2 .6}2{44 .6 7 .8 4};

[0008] The iron-based metal-organic framework material has space group.

[0009] Preferably, the chemical formula of the iron-based metal-organic framework material is C 35 H 35 Fe3N4O 19 .

[0010] Preferably, in the structure of the iron-based metal-organic framework material, each Fe 3+ center coordinates with 4 carboxyl groups from 5-(3-pyridyl)isophthalic acid, 2 formic acids, and 2 pyridine N atoms from 5-(3-pyridyl)isophthalic acid to form a secondary structure unit with six-connectivity. The secondary structure units are connected with 5-(3-pyridyl)isophthalic acid to form a three-dimensional network structure with a curved pore channel having unidirectional connectivity.

[0011] The present invention provides a preparation method of the above iron-based metal-organic framework material, including the following steps:

[0012] Mix 5-(3-pyridyl)isophthalic acid, soluble ferric salt, formic acid, and an organic solvent, and carry out a solvothermal reaction to obtain the iron-based metal-organic framework material.

[0013] Preferably, the organic solvent is one or more of N,N-dimethylformamide, N-methylformamide, and N,N-diethylformamide.

[0014] Preferably, the molar ratio of the soluble ferric salt to 5-(3-pyridyl)isophthalic acid is 1:(0.2 - 1);

[0015] The molar ratio of the soluble ferric salt to formic acid is 1:(300 - 1500);

[0016] The molar ratio of the soluble ferric salt to the organic solvent is 1:(100 - 600).

[0017] Preferably, the temperature of the solvothermal reaction is 80 - 200 °C, and the time is 10 - 48 h.

[0018] The present invention provides the application of the above iron-based metal-organic framework material in separating methane and propane.

[0019] The present invention provides an iron-based metal-organic framework material, wherein the organic ligands of the iron-based metal-organic framework material are 5-(3-pyridyl)isophthalic acid and formic acid, and the coordination metal is Fe 3+。The iron-based metal-organic framework material provided by the present invention is a microporous material with a new topological structure, belonging to the trigonal crystal system. In its structure, each Fe 3+ center coordinates with 4 carboxylic acids from 5-(3-pyridyl) isophthalic acid, 2 formic acids, and 2 pyridine N from 5-(3-pyridyl) isophthalic acid to form a six-connected secondary structure unit. The secondary structure unit is connected with the organic ligand 5-(3-pyridyl) isophthalic acid to form a three-dimensional network structure with a curved pore channel having unidirectional connectivity. The iron-based metal-organic framework material provided by the present invention uses Fe 3+ as the coordination metal. Fe 3+ is a strong Lewis acid and is prone to forming MOFs with relatively strong water stability and thermal stability. 5-(3-pyridyl) isophthalic acid has carboxylic acid and pyridine groups, and the resulting metal-organic framework material after coordination with Fe 3+ has a relatively high specific surface area; since the pore channels are filled with formic acid participating in coordination, it increases the specific surface area of the pore channels and the interaction force with non-polar gas molecules, making the pore channels have a higher interaction force with propane. Therefore, it has a relatively high propane adsorption capacity and can well separate propane from methane. The results of the examples show that its C3H8 adsorption capacity can be 120-140 cm 3 ·g -1 (298K and 1 bar), and its separation ratio of C3H8 / CH4 (50:50, v / v) can reach 80-360.

[0020] The present invention provides a preparation method for the above iron-based metal-organic framework material. This method is simple in operation, low in cost, and easy to realize industrial mass production. Brief Description of the Drawings

[0021] Figure 1 is the crystal structure diagram of the iron-based metal-organic framework material;

[0022] Figure 2 is the powder X-ray diffraction spectrum and the structure-simulated XRD spectrum of the iron-based metal-organic framework material prepared in Example 1;

[0023] Figure 3 is the photo of the crystal morphology of the iron-based metal-organic framework material prepared in Example 1;

[0024] Figure 4 is the X-ray diffraction spectrum and the structure-simulated XRD spectrum of the iron-based metal-organic framework materials prepared in Examples 2-3;

[0025] Figure 5 is the single-component adsorption isotherm of propane and methane of the iron-based metal-organic framework material prepared in Example 3;

[0026] Figure 6The adsorption selectivity curve of propane / methane for the iron-based metal-organic framework material prepared in Example 3 was calculated by IAST. Detailed implementation mode

[0027] The present invention provides an iron-based metal-organic framework material, characterized in that the organic ligand of the iron-based metal-organic framework material is 5-(3-pyridyl)isophthalic acid and formic acid, and the coordination metal is Fe 3+ .

[0028] The chemical formula of the iron-based metal-organic framework material is C 35 H 35 Fe3N4O 19 .

[0029] In the present invention, the molar ratio of 5-(3-pyridyl)isophthalic acid to formic acid is 1:1.5.

[0030] In the present invention, the chemical formula of the iron-based metal-organic framework material is C 35 H 35 Fe3N4O 19 .

[0031] In the present invention, the topological node symbol of the iron-based metal-organic framework material is {4 2 .6}2{4 4 .6 7 .8 4}. In the present invention, the iron-based metal-organic framework material has space group.

[0032] In the present invention, in the structure of the iron-based metal-organic framework material, each Fe 3+ center coordinates with 4 carboxylic acids from 5-(3-pyridyl)isophthalic acid, 2 formic acids and 2 pyridine Ns from 5-(3-pyridyl)isophthalic acid to form a secondary structure unit with six connections. The secondary structure units are connected with 5-(3-pyridyl)isophthalic acid to form a three-dimensional network structure with a curved pore channel having unidirectional connectivity. In the present invention, the crystal structure diagram of the iron-based metal-organic framework material is as Figure 1 shown.

[0033] In the present invention, the specific surface area of the iron-based metal-organic framework material is preferably 800-1600 m 2 / g, more preferably 1000-1500 m 2 / g; the pore size is preferably more preferably

[0034] The present invention provides a method for preparing the above-mentioned iron-based metal-organic framework material, comprising the following steps:

[0035] Mix 5-(3-pyridyl)isophthalic acid, a soluble ferric salt, formic acid and an organic solvent, and carry out a solvothermal reaction to obtain the iron-based metal-organic framework material.

[0036] In the present invention, the soluble ferric salt is preferably one or more of ferric nitrate, ferric sulfate and ferric chloride.

[0037] In the present invention, the organic solvent is preferably one or more of N,N-dimethylformamide, N-methylformamide and N,N-diethylformamide, and more preferably N,N-dimethylformamide.

[0038] In the present invention, the molar ratio of the soluble ferric salt to 5-(3-pyridyl)isophthalic acid is preferably 1:(0.2-1), more preferably 1:(0.2-0.6), and further preferably 1:(0.2-0.4); the molar ratio of the soluble ferric salt to formic acid is preferably 1:(300-1500), more preferably 1:(400-1300), and further preferably 1:(500-1100); a part of the formic acid added in the present invention participates in the coordination of the iron-based metal-organic framework material, and a part acts as an acidic regulator to promote the reaction.

[0039] In the present invention, the molar ratio of the soluble ferric salt to the organic solvent is 1:(100-600), and more preferably 1:(200-500).

[0040] In the present invention, the preferred mixing method is: first mix the soluble ferric salt into the organic solvent, then add 5-(3-pyridyl)isophthalic acid for the second mixing, and then add formic acid for the third mixing; there is no special limitation on the mixing method in the present invention, and a mixing method well-known to those skilled in the art can be used, such as the ultrasonic mixing method. There is no special limitation on the frequency and temperature of the ultrasonic mixing in the present invention, as long as the raw materials can be mixed evenly; there is no special limitation on the time of the first mixing in the present invention, and the first mixing is until the iron source is dissolved in the organic solvent; there is no special limitation on the time of the second mixing and the third mixing in the present invention, and it is sufficient to mix evenly.

[0041] In the present invention, the temperature of the solvothermal reaction is preferably 80-200 °C, more preferably 130-160 °C, and further preferably 150 °C; the time of the solvothermal reaction is preferably 10-48 h, and more preferably 24-36 h. In the present invention, the solvothermal reaction is a crystallization process, and the solvothermal reaction is preferably carried out under static conditions.

[0042] In the present invention, the solvothermal reaction is preferably carried out in a transparent glass bottle with a sealing gasket made of polytetrafluoroethylene, and the glass vial is preferably placed in an oven for the solvothermal reaction. In the present invention, the atmosphere of the solvothermal reaction is preferably air.

[0043] In the present invention, the crystal length of the iron-based metal-organic framework material prepared after the solvothermal reaction is preferably 40 - 800 μm, more preferably 100 - 500 μm; the width is preferably 20 - 400 μm, more preferably 50 - 200 μm; the thickness is preferably 20 - 400 μm, more preferably 50 - 200 μm.

[0044] In the present invention, after the solvothermal reaction, the present invention preferably performs post-treatment on the obtained solvothermal reaction product, and the post-treatment preferably includes the following steps:

[0045] Cool the solvothermal reaction product and perform solid-liquid separation. The obtained solid product is successively subjected to amide solvent exchange, small molecule solvent exchange, and drying to obtain an iron-based metal-organic framework material.

[0046] The present invention has no special limitation on the cooling method, and any well-known cooling method in the art can be used, such as natural cooling. The present invention has no special limitation on the solid-liquid separation method, and any well-known solid-liquid separation method in the art can be used, such as centrifugal separation.

[0047] In the present invention, the amide solvent is preferably N,N-dimethylformamide; the present invention has no special limitation on the temperature of the amide solvent exchange, and the time of the amide solvent exchange is preferably 1 day.

[0048] In the present invention, the temperature of the small molecule solvent exchange is room temperature, the small molecule solvent for the exchange is preferably one or more of methanol, acetonitrile, and ethanol, most preferably ethanol, and the time of the small molecule solvent exchange is preferably 2 days.

[0049] In the present invention, the drying is preferably vacuum drying; in the present invention, the temperature of the vacuum drying environment is preferably 100 - 180 °C, most preferably 150 °C, the time of the vacuum drying is preferably 10 - 48 h, most preferably 10 h, and the vacuum drying is preferably carried out in a vacuum oven.

[0050] The present invention provides the application of the above iron-based metal-organic framework material in separating methane and propane. In the present invention, in the mixed gas of methane and propane, the volume ratio of methane to propane is preferably (0.95 - 0.5):(0.5 - 0.15).

[0051] In the present invention, when separating methane and propane, the temperature of the mixed gas is preferably 0 - 25 °C.

[0052] The iron-based metal-organic framework material provided by the present invention, its preparation method, and its application in separating methane and propane will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0053] Example 1

[0054] At room temperature, 20 mg of iron(III) nitrate nonahydrate was dissolved in 0.5 mL of N,N-dimethylformamide, and 3 mg of 5-(3-pyridyl)isophthalic acid was also dissolved in 0.5 mL of N,N-dimethylformamide. Then, the two were mixed, and 0.4 mL of formic acid was added. After ultrasonic mixing for 40 s, the mixed solution was transferred into a 10 mL glass vial with a polytetrafluoroethylene sealing gasket. The glass vial was placed in an oven at 150 °C, and a solvothermal reaction was carried out for 24 h under the pressure naturally generated in the glass vial. Then, the vial was taken out and naturally cooled to room temperature. After washing with N,N-dimethylformamide and drying to constant weight, an iron-based metal-organic framework material with the chemical formula C 35 H 35 Fe3N4O 19 was obtained, with a grain size of 600 - 800 μm in length, 200 - 300 μm in width, and 200 - 300 μm in thickness.

[0055] Figure 2 are the powder X-ray diffraction pattern and the simulated XRD pattern of the single crystal structure of the iron-based metal-organic framework material prepared in this example. As can be seen from Figure 2 , the iron-based metal-organic framework material prepared by the present invention has characteristic diffraction peaks of a simulated single crystal structure, indicating that the iron-based metal-organic framework material prepared by the present invention has the same crystal structure as that obtained by actual single crystal X-ray diffraction and has high crystallinity.

[0056] Figure 3 are the photos of the iron-based metal-organic framework material prepared in this example under an electron microscope. As can be seen from Figure 3 , the morphology of the iron-based metal-organic framework material prepared by the present invention is hexagonal columnar crystals.

[0057] Example 2

[0058] At room temperature, 16 mg of iron(III) nitrate nonahydrate and 3 mg of 5-(3-pyridyl) isophthalic acid were dissolved in 1 mL of N,N-dimethylformamide. After adding 1.6 mL of formic acid and sonicating for 120 s, the mixed solution was transferred into a 10 mL glass vial with a polytetrafluoroethylene sealing gasket. The glass vial was placed in an oven at 160 °C and subjected to solvothermal reaction for 16 h under the pressure naturally generated in the glass vial. Then the vial was taken out and naturally cooled to room temperature. After washing with N,N-dimethylformamide and drying to a constant weight, the iron-based metal-organic framework material with smaller grain size and higher yield was obtained. The grain size had a length of 40 - 80 μm, a width of 20 - 40 μm, and a thickness of 20 - 40 μm.

[0059] Example 3

[0060] At room temperature, 10 mg of iron(III) chloride and 3 mg of 5-(3-pyridyl) isophthalic acid were dissolved in 1 mL of N,N-diethylformamide. After adding 0.8 mL of formic acid and sonicating for 120 s, the mixed solution was transferred into a 10 mL glass vial with a polytetrafluoroethylene sealing gasket. The glass vial was placed in an oven at 150 °C and subjected to solvothermal reaction for 48 h under the pressure naturally generated in the glass vial. Then the vial was taken out and naturally cooled to room temperature. After washing with N,N-dimethylformamide and drying to a constant weight, the iron-based metal-organic framework material with moderate grain size, higher yield, and good crystallinity was obtained. The grain size had a length of 200 - 400 μm, a width of 80 - 120 μm, and a thickness of 80 - 120 μm.

[0061] Figure 4 Powder X-ray diffraction patterns and simulated XRD patterns of single crystal structures for the iron-based metal-organic framework materials prepared in Examples 2 - 3. From Figure 4 it can be seen that the iron-based metal-organic framework materials prepared in Examples 2 - 3 have characteristic diffraction peaks of the simulated single crystal structure, and the iron-based metal-organic framework materials prepared in Examples 2 - 3 have a crystal structure consistent with that obtained from actual single crystal X-ray diffraction and high crystallinity.

[0062] Application Example 1

[0063] 100 mg of the iron-based metal-organic framework material prepared in Example 3 was subjected to ethanol exchange for 48 h and vacuum dried at 150 °C for 10 h in a vacuum drying oven to obtain an iron-based metal-organic framework material for propane-methane adsorption separation. The single-component adsorption isotherm of propane and methane was measured using the above iron-based metal-organic framework material, and the adsorption test temperature was 25 °C.

[0064] Figure 5 The single-component adsorption isotherm of propane and methane for the iron-based metal-organic framework material prepared in Example 3 at 1 bar and 298 K.

[0065] Figure 6 For the iron-based metal-organic framework material prepared in Example 3, when the propane / methane volume ratio is 50:50, the adsorption selectivity curves of this adsorbent for the two gases under 1 bar condition are shown in .

[0066] After testing, at 25 °C and 1 bar, the adsorption amount of propane reaches 128 cm 3 ·g -1 , while the adsorption amount of methane is only 8 cm 3 ·g -1 . After IAST calculation, when the propane / methane volume ratio is 50:50, the adsorption selectivity of this adsorbent for the two gases under 1 bar condition can reach 354, which is higher than that of many other existing MOF materials, such as BSF-1 (353) [1] , FJI-C4 (293) [2] , UPC-100-In (186) [3] .

[0067] [1] Zhang Y B, Yang L F, Xing H B, et al. A Microporous Metal-Organic Framework Supramolecularly Assembled from a Cu(II) Dodecaborate Cluster Complex for Selective Gas Separation. [J]. Angew. Chem. Int. Ed., 2019, 58, 8145 - 8150.

[0068] [2] Li L, Wang X, Liang J, et al. Water-Stable Anionic Metal-Organic Framework for Highly Selective Separation of Methane from Natural Gas and Pyrolysis Gas [J]. ACS Appl. Mater. Interfaces, 2016, 8, 9777 - 9781.

[0069] [3]Fan W,Wang X,Xu B,et al.Amino-functionalized MOFs with highphysicochemical stability for efficient gas storage / separation,dye adsorptionand catalytic performance[J].Journal ofMaterials ChemistryA,2018,6,24486-24495.

[0070] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of an iron-based metal-organic framework material in separating methane and propane, characterized in that, The organic ligands of the iron-based metal-organic framework material are 5-(3-pyridyl) isophthalic acid and formic acid, and the coordinating metal is Fe 3+ ; The molar ratio of the 5-(3-pyridyl) isophthalic acid to formic acid is 1:1.

5.

2. The application according to claim 1, wherein The topological node symbol of the iron-based metal-organic framework material is {4 2 .6}2{4 4 .6 7 .8 4}; The iron-based metal-organic framework material has space group.

3. The application according to claim 1, wherein The chemical formula of the iron-based metal-organic framework material is C 35 H 35 Fe3N4O 19 .

4. The application according to claim 1, characterized in that In the structure of the iron-based metal-organic framework material, each Fe 3+ center coordinates with 4 carboxylic acids from 5-(3-pyridyl)isophthalic acid, 2 formic acids, and 2 pyridine N from 5-(3-pyridyl)isophthalic acid to form a six-connected secondary structure unit. The secondary structure units are connected with 5-(3-pyridyl)isophthalic acid to form a three-dimensional network structure with a curved pore channel having unidirectional connectivity.

5. The application according to claim 1, characterized in that, The preparation method of the iron-based metal-organic framework material comprises the following steps: Mix 5-(3-pyridyl) isophthalic acid, soluble ferric salt, formic acid and an organic solvent, and carry out a solvothermal reaction to obtain the iron-based metal-organic framework material.

6. The application according to claim 5, characterized in that, The organic solvent is one or more of N,N-dimethylformamide, N-methylformamide and N,N-diethylformamide.

7. The application according to claim 5, characterized in that, The molar ratio of the soluble ferric salt to 5-(3-pyridyl) isophthalic acid is 1:(0.2 - 1); The molar ratio of the soluble ferric salt to formic acid is 1:(300 - 1500); The molar ratio of the soluble ferric salt to the organic solvent is 1:(100 - 600).

8. The application according to claim 5, characterized in that The temperature of the solvothermal reaction is 80 - 200 °C, and the time is 10 - 48 h.

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