A pillared metal organic framework material, and a preparation method and application thereof

Abstract

The application belongs to the technical field of chemical separation, and particularly relates to a pillared metal organic framework material and a preparation method and application thereof. A polycyclic alkane dicarboxylic acid and (E)-1,2-bis (pyridine-4-yl) diazene are used as ligands; the polycyclic alkane dicarboxylic acid provides a carboxyl group, the (E)-1,2-bis (pyridine-4-yl) diazene provides a nitrogen coordination site, and a transition metal ion is used as a construction center for coordination to obtain the pillared metal organic framework material. The pillared metal organic framework material in the application can preferentially adsorb acetylene gas in a mixture, and high-purity acetylene can be efficiently separated from an acetylene / carbon dioxide mixture, thereby providing a new solution for efficiently separating and purifying C2H2 in a C2H2 / CO2 mixed gas system.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation technology, specifically relating to a pillar-supported metal-organic framework material, its preparation method, and its application. Background Technology

[0002] Acetylene (C2H2) is the simplest alkyne and one of the most important raw materials in the petrochemical industry. It is widely used in the production of fine chemicals such as methyl acrylate, butynediol, vinyl derivatives, and acetylenol. In addition, acetylene can be used as a gaseous fuel for welding and metal cutting. Industrial C2H2 is generally produced by coupling methane in the presence of oxygen or by hydrocarbon cracking. However, trace amounts (<3%) of carbon dioxide (CO2) impurities are inevitably generated during its production. Both C2H2 and CO2 are nonpolar linear molecules with similar sizes and highly similar physical properties, such as boiling point and polarizability. Therefore, the highly selective separation of C2H2 and CO2 is extremely challenging.

[0003] Currently, the main methods for separating C2H2 and CO2 mixtures are solvent extraction or cryogenic distillation, which are energy-intensive, costly, and environmentally polluting. Adsorption separation technology based on porous materials is economically feasible, energy-efficient, and environmentally friendly, making it a highly promising alternative technology for gas separation. The key lies in the design and development of highly efficient adsorbents. Metal-organic frameworks (MOFs) are a class of porous crystalline materials constructed from metal nodes and bridging organic ligands. They possess advantages such as large specific surface area, high porosity, tunable structure, and easily functionalized pore surfaces. Therefore, MOFs have broad application prospects in the separation of gas mixtures with similar structural properties.

[0004] Currently, many MOF adsorbents have been designed and developed for separating C2H2 and CO2 mixtures. Most MOF materials exhibit a seesaw effect: small-pore MOFs have high separation selectivity but limit C2H2 adsorption capacity; macroporous MOFs have high C2H2 adsorption capacity but lower selectivity. To overcome this limitation of balancing selectivity and adsorption capacity, the C2H2 adsorption capacity of small-pore MOFs can be increased, or the separation selectivity of macroporous MOFs can be improved. Due to their high specific surface area, suitable pore / cage size, and abundant open metal sites (OMSs), most MOF materials with metal impeller structures exhibit extremely high C2H2 adsorption capacity. However, the OMSs, as the main binding sites, exhibit strong electrostatic interactions with CO2, failing to effectively distinguish between C2H2 and CO2 gas molecules, resulting in low C2H2 and CO2 separation selectivity for these materials. Summary of the Invention

[0005] To address the above problems, this invention provides a pillar-supported metal-organic framework material, its preparation method, and its application.

[0006] The first aspect of the present invention provides a pillared metal-organic framework material, using polycyclic alkane dicarboxylic acid and (E)-1,2-bis(pyridin-4-yl)diazepine as ligands; the polycyclic alkane dicarboxylic acid provides a carboxyl group, and (E)-1,2-bis(pyridin-4-yl)diazepine provides a nitrogen coordination site, with a transition metal ion as the building center for coordination, to obtain the pillared metal-organic framework material; The pillar-supported metal-organic framework material is used for the selective adsorption of acetylene.

[0007] Using (E)-1,2-bis(pyridin-4-yl)diazene as a pillar results in a more uniform pore size in the MOF (Metal-Oxide-Foil) structure. Furthermore, the stretching / bending of the azo intermediate significantly alters the pore size (cavity) along the pillar direction, further shrinking the pore size to achieve a suitable window for C2H2 entry. Simultaneously, the torsion of (E)-1,2-bis(pyridin-4-yl)diazene in a certain direction further modulates the interlayer sliding distance of the planar layers, making it more closely aligned with the kinetic diameter of C2H2. Polycyclic alkane dicarboxylic acids possess greater rigidity, enabling the formation of a more stable pore structure and fixed pore windows. The increased ring number and group volume in the ligand significantly reduce the pore size in specific directions, forming a contoured pore surface rich in alkyl sites. This structural design simultaneously enhances the van der Waals forces and hydrogen bond / dipole interactions of the material, thereby achieving highly efficient and selective adsorption of C2H2 molecules.

[0008] When the pillar-supported metal-organic framework material of this invention comes into contact with a gas mixture containing acetylene / carbon dioxide, it can selectively adsorb acetylene in the gas mixture and has a high acetylene adsorption capacity at 0 bar to 1 bar (the commonly used temperatures in existing separation systems are 298 K and 1 bar), thereby enabling efficient separation of acetylene.

[0009] In another preferred embodiment, the polycyclic alkane dicarboxylic acid is any one of bicyclic [2,2,2]octane-1,4-dicarboxylic acid, 1,3-bicyclic [1,1,1]pentane dicarboxylic acid, 1,4-cubicane dicarboxylic acid, and trans-1,4-cyclohexane dicarboxylic acid; In another preferred embodiment, the transition metal ion is any one of Zn, Cu, Ni, and Co.

[0010] In another preferred embodiment, the columnar metal-organic framework material has a pore size of 0.5 nm to 0.65 nm and a pore volume of 0.12 cm³. 3 / g~0.15cm 3 / g, with a specific surface area of ​​260m² 2 / g~320m 2 / g.

[0011] A second aspect of this invention provides a method for preparing the aforementioned pillar-supported metal-organic framework material, comprising the following steps: Polycyclic alkane dicarboxylic acid ligands, (E)-1,2-bis(pyridin-4-yl)diazeline and transition metal salts were dissolved in an organic solvent, and after a solvothermal reaction under closed conditions, the solid was separated and then activated under vacuum to obtain the pillared metal-organic framework material. The mass ratio of polycyclic alkane dicarboxylic acid ligands to transition metal salts is 1:1~4; The mass ratio of (E)-1,2-bis(pyridin-4-yl)diazeline to transition metal salt is 1:1.5~3.5.

[0012] In another preferred embodiment, the transition metal salt is a transition metal acetate or a transition metal nitrate.

[0013] In another preferred embodiment, the temperature of the solvothermal reaction is 90°C to 130°C, and the reaction time is 6h to 120h.

[0014] In another preferred embodiment, the organic solvent is a mixture of solvent A and solvent B in a volume ratio of 1:0.2~1.2; Solvent A is one of N',N-dimethylformamide, acetonitrile, ethanol, and N',N-dimethylacetamide.

[0015] In another preferred embodiment, the activation refers to drying under vacuum conditions at 60°C to 100°C for 6 to 12 hours.

[0016] A third aspect of the present invention provides the application of the aforementioned pillar-supported metal-organic framework material in the preparation of an adsorbent, wherein the adsorbent is used to separate a mixture of acetylene and carbon dioxide and to selectively adsorb acetylene.

[0017] Specifically, the metal-organic framework material is used as an adsorbent and loaded into an adsorption column. At 298 K and 1 bar, a gas mixture containing acetylene and carbon dioxide is introduced into the adsorption column at a flow rate of 2 ml / min to 8 ml / min to contact the adsorbent. The adsorbent is used to selectively adsorb acetylene.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention uses a transition metal as the building center, with a polycyclic alkane dicarboxylic acid ligand and (E)-1,2-bis(pyridin-4-yl)diazene bridging the metal building center to ensure high stability. The (E)-1,2-bis(pyridin-4-yl)diazene acts as a pillar, resulting in a more uniform pore size in the formed MOF. Furthermore, the stretching / bending of the azo intermediate significantly alters the pore size along the pillar direction of the MOF, facilitating the entry of C2H2. The polycyclic alkane dicarboxylic acid ligand possesses a unique quasi-three-dimensional rigid framework, enabling precise control of pore size and achieving highly selective separation based on molecular dynamics diameter through kinetic diffusion restriction or molecular sieving mechanisms. Its surface is rich in non-aromatic aliphatic CH groups, providing potential adsorption sites for multiple CH…O / N hydrogen bonding interactions with guest molecules. The pillared metal-organic framework material of this invention has a pore surface rich in non-aromatic aliphatic CH groups, serving as binding sites for acetylene, and the pore size is suitable, exhibiting a high acetylene adsorption capacity.

[0019] The pillared metal-organic framework material of this invention exhibits excellent thermal, chemical, and cyclic stability, maintaining a certain separation effect even in breakthrough experiments, thus reducing economic costs and environmental burden caused by material depletion. With its highly efficient separation capability, the pillared metal-organic framework material can purify acetylene from acetylene / carbon dioxide mixtures, achieving efficient resource utilization. Compared with traditional methods such as solvent extraction or cryogenic distillation, it is more environmentally friendly and economical. Attached Figure Description

[0020] Figure 1 The image shows the pillar-supported metal-organic framework material prepared in Example 1 and its simulated X-ray diffraction pattern.

[0021] Figure 2 This is a crystal structure diagram of the pillar-supported metal-organic framework material prepared in Example 1.

[0022] Figure 3 The figure shows the thermal stability analysis results of the pillared metal-organic framework material prepared in Example 1, where Zn-bcp-dpd represents the pillared metal-organic framework material.

[0023] Figure 4 The figure shows the specific surface area of ​​the pillared metal-organic framework material prepared in Example 1, with the inset showing the pore size distribution.

[0024] Figure 5 The graph shows the adsorption performance analysis results of the pillared metal-organic framework material prepared in Example 1.

[0025] Figure 6This is a diagram showing the dynamic separation effect of the pillar-supported metal-organic framework material prepared in Example 1 on a fixed bed of acetylene / carbon dioxide mixture.

[0026] Figure 7 This is a graph showing the adsorption cycle performance of the pillared metal-organic framework material prepared in Example 1.

[0027] Figure 8 The images show the adsorption cycle and simulated X-ray diffraction patterns of the pillared metal-organic framework material prepared in Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Bicyclic [2,2,2]octane-1,4-dicarboxylic acid (bodc), 1,3-bicyclic [1,1,1]pentane-dicarboxylic acid (bcp), 1,4-cubicane-dicarboxylic acid (bgc), and trans-1,4-cyclohexane-dicarboxylic acid (boc) in polycyclic alkane dicarboxylic acid ligands H2L possess unique quasi-three-dimensional rigid frameworks, enabling precise control of pore size. Through kinetic diffusion restriction or molecular sieving mechanisms, they achieve highly selective separation based on molecular dynamics diameters. Furthermore, their non-planar, highly symmetrical "cage-like" structure effectively inhibits local rotation of the ligands. Their surfaces are rich in non-aromatic aliphatic CH groups, providing potential adsorption sites for multiple CH…O / N hydrogen bonding interactions with guest molecules. These ligands hold promise as highly selective adsorbents for the separation of C2H2 / CO2 mixtures.

[0031] Existing technologies include the construction of columnar MOFs using dicarboxylic acid ligands and bipyridine-based bridging ligands. However, most developed metal-organic framework (MOF) materials primarily employ planar ligands, such as aromatic polycarboxylic acids. However, these ligands often exhibit structural flexibility and dynamic pore changes due to the lack of free rotation of the linking groups and steric hindrance, thus affecting their separation performance for specific components.

[0032] This invention employs polycyclic alkane aliphatic dicarboxylic acids as linkers, enabling precise control of pore size and achieving highly selective separation based on molecular dynamics diameter through kinetic diffusion restriction or molecular sieving mechanisms. The three-dimensional configuration of the polycyclic alkane bridging ligand, while restricting local linker rotation (physical factor), possesses unique steric effects and provides a non-aromatic olefin-rich surface (chemical factor), enhancing the orthogonal steric hindrance effect and promoting specific interactions between the adsorbate and the pore surface. This provides new opportunities to fabricate adsorbents with ideal pore size / geometry and site distribution by selecting appropriate column modules. Compared to aromatic carboxylic acids, the polycyclic alkane dicarboxylic acid used in this invention exhibits greater rigidity, forming a more stable pore structure and fixed pore windows. The increased ring number and group volume in the ligand significantly reduce the pore size in specific directions and form a contoured pore surface rich in alkyl sites. This structural design simultaneously enhances the van der Waals forces and hydrogen bond / dipole interactions of the material, thereby achieving highly efficient and selective adsorption of C2H2 molecules.

[0033] The MOF synthesized in this invention has three-dimensional through-pores. Compared with the 4,4'-bipyridine used as the pillar in the prior art, (E)-1,2-bis(pyridin-4-yl)diazepine (dpd) produces a MOF with more uniform pore size. Furthermore, the stretching / bending of the azo intermediate significantly alters the pore size (cavity) in the pillar direction of the MOF, further shrinking the pore size to achieve a window suitable for C2H2 entry. Simultaneously, the torsion of (E)-1,2-bis(pyridin-4-yl)diazepine in a certain direction further regulates the interlayer sliding distance of the planar layers, making it more closely aligned with the kinetic diameter of C2H2.

[0034] Bicyclo[2,2,2]octane-1,4-dicarboxylic acid (bodc), 1,3-bicyclo[1,1,1]pentanedicarboxylic acid (bcp), 1,4-cubicanedicarboxylic acid (bgc), trans-1,4-cyclohexanedicarboxylic acid (boc), and (E)-1,2-bis(pyridin-4-yl)diazepine were all purchased from Shanghai Haohong Biomedical Technology Co., Ltd.

[0035] Example 1 A method for preparing a pillar-supported metal-organic framework material includes the following steps: S1. Add 0.15g zinc nitrate, 0.1g bcp and 0.12g dpd to a mixed solvent of 30mL N',N dimethylformamide and 20mL methanol. After ultrasonic dissolution, add the solution to a 100mL polytetrafluoroethylene reactor and react at 100℃ for 12h to obtain a solid sample.

[0036] S2. The solid sample was collected by vacuum filtration, washed three times with methanol, and dried under vacuum at 60°C for 12 hours to obtain Zn4C. 48 H 40 N 16 O6 powder is a pillar-supported metal-organic framework material.

[0037] Example 2 A method for preparing a pillar-supported metal-organic framework material includes the following steps: S1. Add 0.15g zinc nitrate, 0.1g bodc and 0.12g dpd to a mixed solvent of 30mL N',N dimethylformamide and 20mL methanol. After ultrasonic dissolution, add the solution to a 100mL polytetrafluoroethylene reactor and react at 120℃ for 72h to obtain a solid sample.

[0038] S2. The solid sample was collected by vacuum filtration, washed three times with methanol, and dried under vacuum at 80°C for 8 hours to obtain Zn4C. 48 H 40 N 16 O6 powder is a pillar-supported metal-organic framework material.

[0039] Example 3 A method for preparing a pillar-supported metal-organic framework material includes the following steps: S1. Add 0.17g zinc nitrate, 0.1g bcp and 0.05g dpd to a mixed solvent of 15mL N',N dimethylformamide and 5mL methanol. After ultrasonic dissolution, add the solution to a 100mL polytetrafluoroethylene reactor and react at 110℃ for 48h to obtain a solid sample.

[0040] S2. The solid sample was collected by vacuum filtration, washed three times with methanol, and dried under vacuum at 70°C for 10 hours to obtain Zn4C. 48 H 40 N 16 O6 powder is a pillar-supported metal-organic framework material.

[0041] All three examples above, from Example 1 to Example 3, prepared a pillared metal-organic framework material with comparable results. The following experiment uses the pillared metal-organic framework material from Example 1 as an example.

[0042] Synthesis and simulated X-ray diffraction of pillar-supported metal-organic framework materials Figure 1 As shown.

[0043] By acquiring X-ray diffraction (PXRD) data of pillared metal-organic framework materials, a single crystal sample of suitable size and good crystallinity was selected. Diffraction data were collected using a single-crystal diffractometer at 298 K, and the crystal structure was obtained using the relevant structure analysis software Olex2. The results are as follows: Figure 2 As shown, in the metal-organic framework material, Zn coordinates with four oxygen atoms from two carboxylic acids, exhibiting a stable propeller-like coordination mode, and Zn coordinates with two nitrogen atoms from two different nitrogen-containing ligands. This coordination mode exhibits extremely high stability to meet the needs of practical and complex environmental applications. The pore surface is rich in non-aromatic aliphatic CH groups, enabling preferential adsorption of acetylene. The pore size is 6.5 Å.

[0044] Furthermore, the thermal stability of the material was verified by TGA testing, and the results are as follows: Figure 3 As shown, Zn4C synthesized in Example 1 48 H 40 N 16 The O6 material completely removes solvent molecules from the framework at 100℃, and only begins to show significant weight loss after 294℃, indicating that the material has good thermal stability.

[0045] To characterize Zn4C 48 H 40 N 16 The specific surface area and pore size of O6 were used to conduct CO2 adsorption tests at 195 K, and the results are as follows: Figure 4 As shown, the specific surface area is calculated to be 290 m² based on CO2 adsorption at 195 K. 2 / g, pore volume is 0.12cm³ 3 / g. Zn₄C was calculated based on CO₂ adsorption at 195K and the Horvath-Kawazoe model. 48 H 40 N 16 The pore size distribution of O6 is concentrated at 6.5 Å.

[0046] To further verify Zn4C 48 H 40 N 16 The actual adsorption performance of O6 material for acetylene and carbon dioxide was tested under adsorption isotherms at 298 K and 1 bar for these two gases. Figure 5 As shown, Zn4C 48 H 40 N 16 The adsorption capacities of O6 material for acetylene and carbon dioxide were 3.05 mmol / g and 0.65 mmol / g, respectively.

[0047] To verify Zn4C 48 H 40 N16 The actual separation capability of O6 for a mixture of acetylene and carbon dioxide was demonstrated by placing the sample in a sample tube and activating it at 100℃ for 12 hours in a vacuum degassing station. The activated sample was then loaded into a fixed-bed adsorption column with an inner diameter of 4.6 mm and a length of 10 cm, with a packing mass of 0.9048 g. At 298 K and 1 bar, an equal volume ratio mixture of acetylene and carbon dioxide was flowed through a Zn4C metal-organic framework material at a fixed flow rate of 4.0 ml / min. 48 H 40 N 16 The concentration of the gas was detected by gas chromatography-mass spectrometry using an O6 fixed-bed adsorption column. Figure 6 This indicates that Zn4C 48 H 40 N 16 O6 can be used to obtain high-purity acetylene (≥99%) in a mixture of acetylene and carbon dioxide.

[0048] To verify Zn4C 48 H 40 N 16 The adsorption cycle stability of O6 for carbon dioxide gas was assessed by loading activated samples (0.08–0.1 g) into an ASAP 2460 mass adsorption analyzer and performing five adsorption isothermal cycles at 298 K and 1 bar. The results are as follows: Figure 7 As shown, the sample maintained the same adsorption capacity for acetylene throughout the five adsorption cycles. To verify the stability of the material framework after adsorption cycles, the samples that had completed the adsorption cycles were tested using powder X-ray diffraction (PXRD) and compared with the samples before the tests, as shown in the figure. Figure 8 As shown, the sample after 5 adsorption cycles still maintains the same diffraction peak intensity as before adsorption, indicating that Zn4C 48 H 40 N 16 O6 exhibits strong adsorption cycle stability.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A column-supported metal-organic framework material, characterized in that, Polycyclic alkane dicarboxylic acid and (E)-1,2-bis(pyridin-4-yl)diazepine are used as ligands; wherein the polycyclic alkane dicarboxylic acid provides a carboxyl group and (E)-1,2-bis(pyridin-4-yl)diazepine provides a nitrogen coordination site, and a transition metal ion is used as the building center for coordination to obtain the pillared metal-organic framework material. The pillar-supported metal-organic framework material is used for the selective adsorption of acetylene.

2. The column-supported metal-organic framework material according to claim 1, characterized in that, The polycyclic alkane dicarboxylic acid is any one of bicyclic [2,2,2]octane-1,4-dicarboxylic acid, 1,3-bicyclic [1,1,1]pentane dicarboxylic acid, 1,4-cubicane dicarboxylic acid, and trans-1,4-cyclohexane dicarboxylic acid.

3. The column-supported metal-organic framework material according to claim 1, characterized in that, The transition metal ion is any one of Zn, Cu, Ni, and Co.

4. The column-supported metal-organic framework material according to claim 1, characterized in that, The pillared metal-organic framework material has a pore size of 0.5 nm to 0.65 nm and a pore volume of 0.12 cm³. 3 / g~0.15cm 3 / g, specific surface area 260m² 2 / g~320m 2 / g.

5. A method for preparing a pillar-supported metal-organic framework material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Polycyclic alkane dicarboxylic acid ligand, (E)-1,2-bis(pyridin-4-yl)diazeline and transition metal ions are dissolved in an organic solvent, and after a solvothermal reaction under closed conditions, the solid is separated and then activated under vacuum to obtain the pillared metal-organic framework material. The mass ratio of polycyclic alkane dicarboxylic acid ligands to transition metal ions is 1:1~4; The mass ratio of (E)-1,2-bis(pyridin-4-yl)diazeline to transition metal ions is 1:1.5~3.

5.

6. The method for preparing the pillar-supported metal-organic framework material according to claim 5, characterized in that, Transition metal ions originate from transition metal acetates or transition metal nitrates.

7. The method for preparing the pillar-supported metal-organic framework material according to claim 5, characterized in that, The temperature of the solvothermal reaction is 90℃~130℃, and the reaction time is 6h~120h.

8. The method for preparing the pillar-supported metal-organic framework material according to claim 5, characterized in that, The organic solvent is a mixture of solvent A and solvent B in a volume ratio of 1:0.2~1.2; Solvent A is one of N',N-dimethylformamide, acetonitrile, ethanol, and N',N-dimethylacetamide.

9. The method for preparing the pillar-supported metal-organic framework material according to claim 5, characterized in that, The activation refers to drying under vacuum conditions at 60℃~100℃ for 6h~12h.

10. The application of a pillar-type metal-organic framework material as described in any one of claims 1 to 4 in the preparation of adsorbents, characterized in that, The adsorbent is used to ionize a mixture of acetylene and carbon dioxide, and selectively adsorbs acetylene.

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