A cobalt-based metal organic framework compound, a preparation method and application thereof

Abstract

The application provides a cobalt-based metal organic framework compound, a preparation method and application; the chemical formula of the cobalt-based metal organic framework compound is [Co2(F-tzba)2(bpy)2]·DMF·0.5C2H5OH. The application also relates to a preparation method of the compound, under solvent thermal reaction conditions, a cobalt-based metal organic framework compound is prepared by using a benzoic acid containing fluorine and a tetrazole group and a 4,4'-bipyridine mixed ligand. The preparation process is simple, the reaction condition is mild, mixed ligands are used, the ligands contain fluorine and a tetrazole functional group, finally, a constructed metal organic framework compound is obtained, and the compound can be applied to selective separation of ethyne / ethylene and ethane / ethylene as a potential adsorption and separation material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of inorganic chemistry and materials chemistry; in particular, it relates to a cobalt-based metal organic framework compound, a preparation method and application. BACKGROUND

[0002] Acetylene is one of the most important raw materials in chemical production. The crude acetylene produced by pyrolysis contains various by-products, among which the volume ratio of acetylene / ethylene can reach 3-15. In order to meet safety and quality requirements, acetylene must be purified.

[0003] On the other hand, the by-product ethylene is the largest basic chemical in the petrochemical industry, so recovering ethylene from crude acetylene is also of great value. Ethylene is an important petrochemical raw material, and the global production capacity exceeded 200 million tons in 2023. Industrially, ethylene is mainly produced by water vapor cracking of ethane, which inevitably leaves a certain amount of ethane in the obtained crude product ethylene, thereby reducing the purity below the level required for ethylene polymerization. Traditional separation methods require extremely high energy consumption and cause serious environmental pollution. Adsorption separation using porous materials is considered a more energy-efficient method. However, traditional porous materials such as zeolites and activated carbons have limitations in structure and are difficult to meet the actual separation requirements. Therefore, the development of new adsorption separation materials is crucial for petrochemical production.

[0004] Due to high specific surface area, tunable pore size, and modifiable pore surface, metal organic framework compounds, as a new class of crystalline porous materials, have attracted attention in the field of adsorption separation. Inorganic and organic building units are two important components of metal organic framework compounds, and designing organic ligands is a key factor in determining the structure and function of the compounds. Carboxylic acids and nitrogen heterocyclic ligands (such as pyridine, triazole, and tetrazole) are two of the most representative and widely used ligands. Carboxylic acids can provide a rich coordination mode, and nitrogen heterocyclic ligands can form strong coordination bonds, and the uncoordinated nitrogen atoms with lone pairs of electrons enhance the polarity of the pores, resulting in stronger interaction between the framework and gas molecules. In addition, due to the high electronegativity of fluorine atoms, they can interact with positively charged hydrogen atoms in gas molecules, which is more conducive to gas adsorption. However, there are few metal organic framework compounds containing fluorine sites used for ethylene adsorption separation research. SUMMARY

[0005] The purpose of the present application is to provide a cobalt-based metal organic framework compound, a preparation method and application.

[0006] The present application is realized by the following technical solutions:

[0007] The present application relates to a kind of cobalt-based metal organic framework compounds, the chemical formula of the cobalt-based metal organic framework compound is [Co2 (F-tzba) 2 (bpy) 2]·DMF·0.5C2H5OH;

[0008] Wherein, F-tzba in formula is deprotonated 2-F-4-(1H-tetrazole-5-yl) benzoic acid, its structural formula is as shown in (I), bpy is 4,4'-bipyridine, its structural formula is as shown in (II), and DMF is N,N-dimethylformamide;

[0009]

[0010] Preferably, the cobalt-based metal organic framework compound is a three-dimensional porous structure containing doubly interpenetrated quadrilateral channels, and the surface of the channels contains exposed nitrogen, oxygen and fluorine active sites.

[0011] Preferably, the cobalt-based metal organic framework compound has an adsorption capacity of 50.7 cm 3 g -1 , 35.5 cm 3 g -1 and 35.5 cm 3 g -1 for acetylene, ethylene and ethane respectively at 298 K and 1 atm.

[0012] Preferably, the cobalt-based metal organic framework compound has an adsorption selectivity ratio of 2.9 and 1.9 for equimolar acetylene / ethylene and ethane / ethylene mixtures, respectively.

[0013] The present application also relates to a preparation method of the aforementioned cobalt-based metal organic framework compound, comprising the following steps:

[0014] Step 1, 0.09-0.11 mmol of cobalt nitrate hexahydrate metal salt, 0.09-0.11 mmol of 4,4'-bipyridine (organic ligand) and 0.07-0.09 mmol of 2-F-4-(1H-tetrazole-5-yl) benzoic acid (organic ligand) are dissolved in a mixed solution of 10.4-15.6 mmol of N,N-dimethylformamide, 30.8-37.7 mmol of ethanol, 211.1-233.3 mmol of water and 1.3-1.9 mmol of HBF4 (fluoroboric acid), and stirred uniformly to obtain a mixture;

[0015] Step 2, the mixture is sealed in a 15 mL polytetrafluoroethylene reactor, heated and thermostated, and cooled to room temperature;

[0016] Step 3, after taking out the reaction product, pink flaky crystals are obtained;

[0017] Step 4, the pink flaky crystals are exchanged with methanol, and activated under vacuum heating to obtain the cobalt-based metal organic framework compound.

[0018] Preferably, in step 2, the heating temperature is 100-110 DEG C, and the constant temperature time is 64-80 hours.

[0019] Preferably, in step 2, the cooling speed is 0.1-0.2 DEG C / min.

[0020] Preferably, in step 4, the exchange time is 48-60 hours or more.

[0021] Preferably, in step 4, the activation temperature is 100-110 DEG C, and the time is 4-6 hours.

[0022] The application also relates to the application of the aforementioned cobalt-based metal organic framework compound in separating acetylene / ethylene and ethane / ethylene mixtures.

[0023] The preparation principle of the application is that a cobalt salt and an organic ligand are added into a solvent to perform a synthesis reaction, wherein the organic ligand is 4,4'-dipyridyl and 2-F-4-(1H-tetrazole-5-yl) benzoic acid; the cobalt salt is nitrate; and the solvent is a mixed solvent of N,N-dimethylformamide, water, ethanol and fluoroboric acid.

[0024] The application has the following advantages:

[0025] (1) The application uses a benzoic acid containing fluorine and tetrazole groups and a mixed ligand of 4,4'-dipyridyl to prepare a cobalt-based metal organic framework compound under a solvothermal reaction condition, the compound has nitrogen, oxygen and fluorine site modified channels, and shows high acetylene / ethylene and ethane / ethylene selective adsorption and separation functions.

[0026] (2) The application relates to a cobalt-based metal organic framework compound for adsorbing and separating ethylene, the preparation process is simple, the reaction condition is mild, a mixed ligand is used, the ligand contains fluorine and tetrazole functional groups, and finally a constructed metal organic framework compound is obtained, and the compound can be applied to acetylene / ethylene and ethane / ethylene selective separation as a potential adsorption and separation material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a coordination environment diagram of Co 2+ ions in the metal organic framework compound;

[0028] Figure 2 is a three-dimensional structure diagram of the metal organic framework compound;

[0029] Figure 3is a comparison chart of adsorption isotherms of ethyne, ethylene and ethane at 273 K for the metal organic framework compound described in the present disclosure;

[0030] Figure 4 is a comparison chart of adsorption isotherms of ethyne, ethylene and ethane at 298 K for the metal organic framework compound described in the present disclosure;

[0031] Figure 5 is a comparison chart of adsorption selectivity curves of ethyne / ethylene and ethane / ethylene at 273 K at an equimolar ratio (50:50) for the metal organic framework compound calculated by ideal adsorbed solution theory;

[0032] Figure 6 is a comparison chart of adsorption selectivity curves of ethyne / ethylene and ethane / ethylene at 298 K at an equimolar ratio (50:50) for the metal organic framework compound calculated by ideal adsorbed solution theory. DETAILED DESCRIPTION

[0033] The present disclosure will be described in detail below with specific embodiments. It should be noted that the following implementation examples are only further illustrations of the present disclosure, and the protection scope of the present disclosure is not limited to the following examples.

[0034] EMBODIMENT

[0035] This embodiment relates to a preparation method of a cobalt-based metal organic framework compound, comprising the following steps:

[0036] Cobalt nitrate hexahydrate (0.029 g, 0.10 mmol), 4,4'-dipyridyl (0.016 g, 0.10 mmol) and 2-F-4-(1H-tetrazol-5-yl)benzoic acid (0.016 g, 0.08 mmol) were added to a mixed solvent of N,N-dimethylformamide (12.9 mmol)-ethanol (34.3 mmol)-water (222.2 mmol)-fluoroboric acid (1.6 mmol) to obtain a mixture;

[0037] Step 2, the mixed solution was placed in a 15 mL high-pressure reaction kettle, heated to 105°C and kept for 72 hours, and then cooled to room temperature at a speed of 0.2°C per minute;

[0038] Step 3, after taking out, pink flaky crystals were obtained;

[0039] Step 4, the pink flaky crystals were exchanged with methanol for 70 hours, and activated at 110°C under vacuum for 6 hours to obtain the cobalt-based metal organic framework compound.

[0040] The cobalt-based metal organic framework compound prepared in the embodiment has a chemical formula of [Co2(F-tzba)2(bpy)2]·DMF·0.5C2H5OH.

[0041] In the formula, F-tzba is deprotonated 2-F-4-(1H-tetrazol-5-yl)benzoic acid, the structural formula of which is shown as (I), bpy is 4,4'-bipyridine, the structural formula of which is shown as (II), and DMF is N,N-dimethylformamide.

[0042]

[0043]

[0044] Structure description: The crystal of the cobalt-based metal organic framework compound prepared by the method of the embodiment is subjected to structure characterization and analysis, and the unit cell and space structure thereof are determined. The compound has a monoclinic P21 / c space group. The asymmetric unit of the compound is composed of two Co 2+ ions, two bpy ligands, and two F-tzba ligands. It contains a binuclear cluster composed of Co 2+ ions and tetrazoles, and two Co 2+ ions have the same coordination environment. Each Co 2+ ion is coordinated by two N atoms and two chelating carboxyl O atoms in the F-tzba and bpy organic ligands, as shown in Figure 1 .

[0045] In the cobalt-based metal organic framework compound, the binuclear cluster is connected to form a two-dimensional layer, and different layers are connected by the bpy ligand to form a three-dimensional framework with a porosity of 23.8%. Two parallel bpy ligands are connected between two adjacent clusters and form π…π interactions between the pyridine rings, resulting in good stability of the framework. In the three-dimensional structure, two identical frameworks are interpenetrated, as shown in Figure 2 . This feature makes the framework form a small pore size, which is beneficial for gas adsorption and separation. The pore wall of the cobalt-based metal organic framework compound contains active sites such as exposed nitrogen, oxygen, and fluorine atoms, which will play an important role in gas adsorption and separation.

[0046] Adsorption test: The obtained cobalt-based metal organic framework compound is subjected to solvent exchange with methanol, the solvent is exchanged every 12 hours, and the exchange is performed 6 times. The activated metal organic framework compound is obtained by activating the compound under vacuum at 100-110°C for 4-6 hours. The ASAP 2020M specific surface area tester of American Micromeritics is used for gas adsorption test. The compound is subjected to adsorption isotherm test of acetylene, ethylene, and ethane at 273K and 298K, respectively. As shown in Figure 3As shown in Figure 2, at 273 K, the maximum adsorption capacities of acetylene, ethylene, and ethane are 61.6 cm 3 g -1 、44.9cm 3 g -1 and 40.7cm 3 g -1 .like Figure 4 As shown, the maximum adsorption capacity at 298K is 50.7cm 3 g -1 、35.5cm 3 g -1 and 35.5cm 3 g -1 . For the desorption curve of acetylene, there is a hysteresis behavior, which means that there is a strong interaction between the framework and the acetylene molecule; at the same time, the slope of the ethane adsorption curve in the low-pressure region is significantly higher than that of ethylene. Based on the differences in the above adsorption curves, the selective adsorption of the compound to acetylene / ethylene and ethane / ethylene was further investigated. For equimolar amounts of acetylene / ethylene and ethane / ethylene, the selectivities were 3.3 and 1.4, respectively, at 273K. Figure 5 As shown; at 298K, the selectivities are 2.9 and 1.9 respectively, as shown Figure 6 The excellent selectivity indicates that the compound can be used as a good adsorbent for selective separation of acetylene / ethylene and ethane / ethylene.

[0047] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An application of a cobalt-based metal organic framework compound, characterized in that: Application in separation of ethane / ethylene mixtures; The chemical formula of the cobalt-based metal organic framework compound is [Co2(F-tzba)2(bpy)2]·DMF·0.5C2H5OH; Wherein, F-tzba is deprotonated 2-F-4-(1H-tetrazol-5-yl)benzoic acid, whose structural formula is shown in (I); bpy is 4,4'-bipyridine, whose structural formula is shown in (II); DMF is N,N-dimethylformamide; （I）, (II); The cobalt-based metal organic framework compound is a three-dimensional porous structure containing doubly interpenetrating quadrilateral channels, and the surface of the channels contains exposed nitrogen, oxygen, and fluorine active sites; The adsorption capacities of the cobalt-based metal organic framework compound for acetylene, ethylene, and ethane at 298 K and 1 atm are 50.7 cm 3 g -1 、35.5 cm 3 g -1 and 35.5 cm 3 g -1 ; The cobalt-based metal organic framework compound has an adsorption selectivity ratio of 2.9 and 1.9 for equimolar mixtures of acetylene / ethylene and ethane / ethylene, respectively; The preparation method of the cobalt-based metal organic framework compound comprises the following steps: Step 1: dissolving 0.09-0.11 mmol of cobalt nitrate hexahydrate, 0.09-0.11 mmol of 4,4'-bipyridine, and 0.07-0.09 mmol of 2-F-4-(1H-tetrazol-5-yl)benzoic acid in a mixed solution of 10.4-15.6 mmol of N,N-dimethylformamide, 30.8-37.7 mmol of ethanol, 211.1-233.3 mmol of water, and 1.3-1.9 mmol of HBF4, and stirring the mixture to obtain a mixture; Step 2: The mixture was sealed in a 15 mL polytetrafluoroethylene reactor, heated and kept at a constant temperature, and then cooled to room temperature; Step 3, after taking out the reaction product, pink flaky crystals are obtained; Step 4, exchanging the pink flaky crystals with methanol and activating them under vacuum heating to obtain a cobalt-based metal organic framework compound; In step 2, the heating temperature is 100-110°C, the constant temperature time is 64-80 hours, and the cooling rate is 0.1-0.2°C / min; In step 4, the exchange time is more than 48 to 60 hours, and the activation temperature is 100 to 110° C. for 4 to 6 hours.

Images