Preparation method of Cu metal-organic framework material and gas separation application

Abstract

A preparation method and gas separation application of a Cu-based metal-organic framework material belongs to the technical field of crystalline materials. The chemical formula is [Cu2(H2O)2(BCBA)], wherein the organic ligand (H4BCBA) is 5-(3,6-bis(4-carboxyphenyl)-9H-carbazole-9-yl)isophthalic acid. The metal-organic framework is synthesized by a solvothermal reaction of the organic ligand H4BCBA and copper nitrate in a mixed solution of N,N-dimethylformamide and trifluoroacetic acid under closed conditions to obtain crystals of the metal-organic framework material. The metal-organic framework material has a high adsorption capacity for acetylene and carbon dioxide, and the interaction between the framework and acetylene gas molecules is stronger, enabling efficient separation of acetylene / carbon dioxide mixed gases.

Description

Technical Field

[0001] The present invention relates to metal-organic coordination polymer materials, belonging to the technical field of crystalline materials. Specifically, it relates to a method for preparing Cu metal-organic frameworks (MOFs). The MOF is characterized by its ability to efficiently separate acetylene and carbon dioxide gas mixtures. Background Art

[0002] Acetylene gas is a key raw material in the petrochemical and electronics industries, commonly used to manufacture products such as acetaldehyde, acetic acid, synthetic rubber, and synthetic fibers. Furthermore, acetylene gas can be used as a welding gas for welding and metal cutting. In the petrochemical industry, crude acetylene is produced by coupling methane in the presence of oxygen. This crude product often contains significant byproducts, including carbon dioxide (CO2). Efficient separation and purification of acetylene and CO2 are challenging due to their linear molecular shape, similar boiling points (-84°C and -78.5°C), similar three-dimensional dimensions, and identical kinetic diameters. Furthermore, acetylene is sensitive to physical factors such as heat and pressure. At room temperature and in the absence of oxygen, it explodes when compressed above 0.2 MPa, presenting numerous challenges in industrial acetylene purification. Traditionally, separation of acetylene / CO2 mixtures has primarily relied on energy-intensive cryogenic distillation, requiring significant investment and complex maintenance for separation equipment. Therefore, developing new acetylene / CO2 separation technologies and optimizing existing separation processes are crucial for the acetylene industry. Due to its advantages such as relatively low energy consumption, high separation selectivity and simple process, adsorption separation technology based on porous materials is expected to solve many problems in traditional separation processes and bring new opportunities for acetylene purification.

[0003] Traditional porous materials, such as zeolite molecular sieves, clay, activated carbon, etc., usually have low selectivity and low adsorption capacity under normal temperature and pressure conditions. The separation performance of the adsorbent depends on the pore structure and pore surface properties of the adsorbent and the physicochemical properties of the adsorbed gas. Metal organic frameworks (MOFs) are a new type of crystalline porous functional material. They are porous network skeleton structures formed by metal / metal cluster nodes and organic ligands based on coordination bonds. Due to their diverse structures, adjustable sizes, and large specific surface area, they have been widely used in gas storage and separation, drug release, fluorescence detection, catalysis and other fields. In recent years, many MOFs have been used in the adsorption and separation of low-carbon hydrocarbons, such as the purification of ethylene from ethane / ethylene and acetylene / ethylene, the purification of propylene from propane / propylene and propyne / propylene, and also the separation of acetylene and carbon dioxide. Although numerous research results have shown that MOFs have unique advantages as adsorbent materials for separating low-carbon hydrocarbon mixtures and have achieved good results, how to balance high separation selectivity, relatively low preparation cost, and fast synthesis efficiency is still one of the difficulties faced in the screening and preparation of acetylene / carbon dioxide adsorption separation materials. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a Cu-based metal organic framework material constructed with a carbazole carboxylic acid ligand. The MOF material can be prepared in a relatively short time, is convenient for large-scale synthesis, and can be used for the efficient separation of acetylene / carbon dioxide mixtures.

[0005] The present invention discloses a novel carbazole-carboxylic acid Cu metal-organic framework material, characterized in that the copper-based metal-organic framework material is a crystalline material prepared by a solvent thermal reaction of an organic ligand and a copper salt. The chemical formula is [Cu2(H2O)2(BCBA)], wherein the organic ligand is 5-(3,6-bis(4-carboxyphenyl)-9H-carbazole-9-yl)isophthalic acid (H4BCBA), and the molecular formula is C 34 H 21 NO8, the structural formula is as follows:

[0006]

[0007] From the perspective of crystal structure, the crystal structure of the metal-organic framework belongs to the hexagonal system, the space group is P21 / n, and the unit cell parameters are: α=90°, β=102.697(5)°, γ=90°.

[0008] From a topological perspective, each BCBA 4-The ligands can be viewed as 4-connected nodes with a tetrahedral configuration, while the Cu2 clusters can be viewed as 4-connected vertices. These two types of structural units are alternately connected to form a (4,4)-connected network with nou topology, whose Schläfli symbol ( symbol) is {4.6 5}2{4 2 .8 4}{6 4 .8 2}.

[0009] The metal-organic framework material has a size of The pentagonal pores (the smallest pore size in the two vertical directions) make the metal-organic framework suitable for gas storage.

[0010] The method for synthesizing the metal-organic framework material of the present invention comprises the following steps:

[0011] Ligand synthesis: First, 4-methyl borate (molecular formula C8H9BO4), 3,6-dibromo-9H-carbazole (molecular formula C 12 H7Br2N), potassium carbonate, tetrakis(triphenylphosphine)palladium (molecular formula Pd[P(C6H5)3]4) and 1,4-dioxane were added into the reactor, sealed, evacuated, protected by nitrogen, and heated to react to obtain dimethyl 4,4'-(9H-carbazole-3,6-diyl)dibenzoate (molecular formula C 28 H 21 NO4). The above-synthesized product and dimethyl 5-iodoisophthalate (molecular formula C 10 H9IO4), potassium carbonate and N, N-dimethylformamide (DMF) were added to the reactor, sealed, vacuumed, protected by nitrogen, and heated for reaction. After the reaction, deionized water was added and filtered and dried to obtain 5-(3,6-bis(4-(methoxycarbonyl)phenyl)-9H-carbazol-9-yl)isophthalate (molecular formula C 38 H 29 NO8). Finally, 5-(3,6-bis(4-(methoxycarbonyl)phenyl)-9H-carbazol-9-yl)isophthalate was reacted in 2M sodium hydroxide, 1,4-dioxane and tetrahydrofuran (THF). After the reaction, the organic solvent was removed by distillation under reduced pressure, deionized water was added, and the pH was adjusted with 2M hydrochloric acid aqueous solution until the precipitation was complete. After filtration, washing and drying, 5-(3,6-bis(4-carboxyphenyl)-9H-carbazol-9-yl)isophthalic acid (H4BCBA) was obtained. The ligand synthesis scheme is shown in the attached figure. Figure 1 .

[0012] Cu-MOF Synthesis: Under sealed conditions, the organic ligand 5-(3,6-bis(4-carboxyphenyl)-9H-carbazol-9-yl)isophthalic acid (H4BCBA) and copper nitrate (Cu(NO3)2) were reacted in a mixture of N,N-dimethylformamide (DMF) and trifluoroacetic acid (TFA) via a solvothermal reaction to obtain crystals of the metal-organic framework. The molar ratio of 5-(3,6-bis(4-carboxyphenyl)-9H-carbazol-9-yl)isophthalic acid (H4BCBA) to Cu(NO3)2 was 1:2-6, with 1-4 mL of DMF and 0.01-0.1 mL of TFA per 0.04 mmol of Cu(NO3)2. The thermal reaction temperature was 80°C-135°C, and the reaction time was 12-48 hours.

[0013] The metal-organic framework of the present invention has a novel structure, a stable framework, a large pore size, and a large specific surface area, and has potential applications in gas storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the synthetic route of the carbazole-carboxylic acid ligand.

[0015] Figure 2 For the carbazole-carboxylic acid ligand 1 H NMR spectrum.

[0016] Figure 3 Figure 2 is the coordination pattern diagram of the ligand and metal ion of the metal-organic framework.

[0017] Figure 4 Schematic diagram of the three-dimensional structure of the metal-organic framework.

[0018] Figure 5 This is the N2 adsorption and desorption curve of the metal-organic framework material at 77K.

[0019] Figure 6 This is the single-component adsorption curve of acetylene and carbon dioxide of the metal-organic framework material at 298K.

[0020] Figure 7 Schematic diagram of the IAST selectivity of the metal-organic framework material for separating acetylene / carbon dioxide (50 / 50) mixture at 298K. DETAILED DESCRIPTION

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

[0022] Example 1

[0023] The organic ligand H4BCBA (0.04 mmol) and Cu(NO3)2 (0.04 mmol) were mixed in 2.0 mL of N,N-dimethylformamide, 0.01 mL of trifluoroacetic acid was added, and the mixture was sealed in a vial. A thermal reaction at 100°C for 48 hours yielded the metal-organic framework crystals.

[0024] Example 2

[0025] The organic ligand H4BCBA (0.04 mmol) and Cu(NO3)2 (0.04 mmol) were mixed in 2.0 mL of N,N-dimethylformamide, 0.01 mL of trifluoroacetic acid was added, and the mixture was sealed in a vial. The metal-organic framework crystals were obtained by thermal reaction at 90°C for 48 hours.

[0026] The test results of the products obtained in the above examples are the same, as shown below:

[0027] Determination of crystal structure:

[0028] Single crystals of suitable size were selected and data were collected at room temperature using an Agilent Technologies SuperNova X-ray single crystal diffractometer. Data were collected using a Cu-Kα (λ = 0.05) monochromated filter monochromator. ) target radiation. Absorption correction of the data was performed using SCALE3ABSPACK software. The crystal structure was solved by direct method using SHELXTL-97 program. The coordinates of all non-hydrogen atoms were first determined using the difference function method and least squares method, and the positions of hydrogen atoms were obtained using the theoretical hydrogenation method. The crystal structure was then refined using SHELXTL-97. Figure 2 and Figure 3 The crystallographic data are shown in Table 1.

[0029] Table 1 Crystallographic data of metal-organic framework materials

[0030]

[0031]

[0032] Figure 1 The synthetic route of the carbazole-carboxylic acid ligand is demonstrated.

[0033] Figure 2 ligand 1 The H NMR spectrum showed that 5-(3,6-bis(4-(methoxycarbonylphenyl)-9H-carbazole-9-yl)isophthalic acid was obtained by removing the protecting group of 5-(3,6-bis(4-(methoxycarbonylphenyl)-9H-carbazole-9-yl)isophthalic acid and hydrolyzing the ester group.

[0034] Figure 3 The coordination environment diagram shows that from a topological point of view, each BCBA 4- The ligands can be viewed as 4-connected nodes with a tetrahedral configuration, while the Cu2 clusters can be viewed as 4-connected vertices. These two types of structural units are alternately connected to form a (4,4)-connected network with nou topology, whose Schläfli symbol ( symbol) is {4.6 5}2{4 2 .8 4}{6 4 .8 2}.

[0035] Figure 4 The structural diagram shows that the metal-organic framework material has a size of (the smallest dimension of the channel in the two vertical directions) pentagonal channel.

[0036] Figure 5 The nitrogen adsorption curve in Figure 2 shows that the Cu-MOF exhibits a classic Type I N adsorption curve at 77 K. Using a commercially available physical or chemical adsorption instrument, the adsorbent is first thoroughly degassed at a specific temperature using a vacuum or purge gas. Then, at a constant temperature, the partial pressures of the adsorbate and carrier gas are controlled to gradually allow the adsorption system to reach equilibrium. This experimental curve, obtained by controlling the relationship between the adsorbate partial pressure and the corresponding equilibrium adsorption capacity, is known as the adsorption isotherm. Conventionally, isotherms derived from experimental adsorption and desorption processes are collectively referred to as adsorption isotherms. A Type I isotherm, the Langmuir isotherm, corresponds to the reversible adsorption process of the Langmuir monolayer. Adsorption occurs in narrow pores, while for micropores, it can be considered volume filling. The surface area of ​​the sample is much smaller than the internal pore surface area, and the adsorption capacity is controlled by the pore volume. The plateau inflection point corresponds to the complete filling of the adsorbent's pores with the condensate. When this type of isotherm approaches saturated vapor pressure, adsorption similar to that in macropores occurs due to the interstices between the particles, resulting in a rapid rise in the isotherm. The classic type I isotherm of N2 adsorption of this MOF material corresponds to the microporous channels in the structure, further confirming the structural basis of the material for gas adsorption.

[0037] Figure 6 The gas adsorption isotherm of the metal-organic framework material at 298K. As can be seen from the figure, the maximum adsorption capacity of the material for C2H2 and CO2 at 298K is 65.92cm 3 ·g -1 and 22.187cm 3 ·g -1The Cu-MOF exhibits high adsorption capacity for both gases, and the framework interacts more strongly with acetylene molecules. Specifically, at 298K, the acetylene adsorption capacity is higher at low pressures. This phenomenon paves the way for the material to be used in the separation and purification of acetylene / CO2 mixtures.

[0038] Figure 7 This is the IAST selectivity plot for CO2 and C2H2 (50:50) at 298K. Ideal Adsorption Solution Theory (IAST) is a thermodynamic theory that can predict the selectivity of mixed gases based on a series of adsorption isotherms for a single gas, greatly reducing the difficulty of testing mixed gas selectivity in experiments. Based on IAST, the adsorption selectivity of the MOF was calculated, and the separation performance of the CO2 / C2H2 mixture was quantitatively obtained.

Claims

1. A Cu-based microporous metal-organic framework material, characterized in that: The chemical formula is [Cu2(H2O)2(BCBA)], H4BCBA is an organic ligand 5-(3,6-bis(4-carboxyphenyl)-9 H -carbazol-9-yl)isophthalic acid, molecular formula C 34 H 21 The chemical structure of NO8, H4BCBA is: From the perspective of framework connection construction, the crystal structure of the metal-organic framework belongs to the monoclinic system, and the space group is P twenty one / n , the unit cell parameters are a =16.5594(8) Å, b =30.2399(11) Å, c =18.2574(12) Å; α = 90 o , β= 102.697(5) o , γ =90 o ; From a topological perspective, each BCBA 4- The ligands are all 4-connected nodes with a tetrahedral configuration, while the Cu2 clusters are 4-connected vertices. These two types of structural units are connected alternately to form a (4,4)-connected network with nou topology, whose Schläfli symbol is {4.6 5 }2{4 2 .8 4 }{6 4 .8 2 }; This metal-organic framework material has pentagonal channels with a size of 9.3 Å×17.4 Å along the a-axis; the larger pore structure makes this metal-organic framework suitable for gas storage.

2. The method for preparing the Cu-based microporous metal-organic framework material according to claim 1, characterized in that: Under sealed conditions, the organic ligand 5-(3,6-bis(4-carboxyphenyl)-9 H -carbazol-9-yl)isophthalic acid H4BCBA, with copper nitrate Cu(NO3)2 N , N In a mixed solution of dimethylformamide (DMF) and trifluoroacetic acid (TFA), the metal-organic framework crystal was obtained through a solvothermal reaction; the organic ligand 5-(3,6-bis(4-carboxyphenyl)-9 H The molar ratio of H4BCBA (9-carbazole-1-yl) isophthalic acid to Cu(NO3)2 is 1: (2-6); the thermal reaction temperature is 80°C-135°C, and the reaction time is 12-48 hours.

3. The method according to claim 2, characterized in that Every 0.04 mmol of Cu(NO3)2 corresponds to 1 mL~4 mL of DMF and 0.01 mL~0.1 mL of TFA.

4. The use of the Cu-based microporous metal-organic framework material according to claim 1, characterized in that: Used for selective separation of acetylene and carbon dioxide mixture.

5. The use according to claim 4, characterized in that The Cu-MOF material is washed with DMF, and then solvent exchanged and vacuum-removed to remove guest molecules to obtain a final separation material for selectively separating acetylene / carbon dioxide mixtures, preferentially adsorbing acetylene during the separation process. The solvent used for the exchange is characterized by its small size and low boiling point.

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