A metal-organic framework material suitable for propylene-propane adsorptive separation and a preparation method thereof

Abstract

The application discloses a metal-organic framework material suitable for propylene propane adsorption separation and a preparation method thereof, and belongs to the technical field of adsorption separation materials. The metal-organic framework material NKU-601-Y for C3H6 / C3H8 separation has a chemical formula of [Y6(mu3-OH)8(mdip)3(H2O)6(DMA)2] n , and a cell parameter of alpha=90.0°, beta=90.0° and gamma=90.0°. The NKU-601-Y adsorbent material provided by the application is synthesized by a solvothermal method, and is simple to prepare. The NKU-601-Y has a high-connection six-core secondary building unit, and has high structural stability. The NKU-601-Y can realize C3H6 / C3H8 separation through a molecular sieving effect, and simultaneously has high C3H6 adsorption capacity and high C3H6 / C3H8 separation selectivity.

Description

Technical Field

[0001] This invention belongs to the field of adsorption separation materials technology, specifically relating to a metal-organic framework material and its preparation method, and its application in propylene / propane adsorption separation. Technical Background

[0002] Propylene (C3H6) is a key petrochemical feedstock for the production of polypropylene, primarily obtained through naphtha steam cracking and propane dehydrogenation. However, impurities such as propane (C3H8) are inevitably generated during the production process. Therefore, removing C3H8 from C3H6 is a crucial step in the production of polymer-grade (>99.5%) propylene. Currently, industrially, C3H6 / C3H8 separation is mainly achieved through traditional distillation. Due to the similarity of C3H6 and C3H8 in properties such as boiling point (difference of 5.3K) and relative volatility (1.14), the distillation process requires low temperature, high pressure, and more than 100 tray stages, resulting in very high energy consumption and cost.

[0003] Adsorption separation based on porous materials is considered a promising alternative to traditional cryogenic distillation due to its high efficiency, energy saving, and economical separation capabilities. The design and selection of porous materials are the most critical factors determining adsorption separation performance. Metal-organic frameworks (MOFs) exhibit great potential in gas adsorption separation and purification due to their high porosity, large specific surface area, tunable pore chemistry, and pore size. (See X. Cui, K. Chen, H. Xing, Q. Yang, R. Krishna, Z. Bao, H. Wu, W. Zhou, X. Dong, Y. Han, B. Li, Q. Ren, M.J. Zaworotko and B. Chen, Science, 2016, 353, 141-144. J. Cui, Z. Zhang, L. Yang, J. Hu, A. Jin, Z. Yang, Y. Zhao, B. Meng, Y. Zhou, J. Wang, Y. Su, J. Wang, X. Cui and H. Xing, Science, 2024, 383, 179-183. H. Zeng, M. Xie, T. Wang, R.-J. Wei, X.-J. Xie, Y. Zhao, W. Lu and D.Li,Nature,2021,595,542-548.)

[0004] Existing metal-organic framework (MOF) materials used for the adsorption and separation of propylene / propane suffer from a trade-off between adsorption capacity and separation selectivity; that is, they cannot simultaneously possess high C3H6 adsorption capacity and high C3H6 / C3H8 separation selectivity. Although some reported MOF materials exhibit excellent C3H6 / C3H8 separation performance, they suffer from poor stability (chemical stability, thermal stability, and water / humidity stability), limiting their practical industrial applications. Therefore, designing and constructing a highly stable MOF material that combines high C3H6 adsorption capacity and high C3H6 / C3H8 separation selectivity is a crucial technical challenge. Summary of the Invention

[0005] The first aspect of this invention aims to provide a metal-organic framework material. The metal-organic framework material (named NKU-601-Y) synthesized by a solvothermal method is a three-dimensional (3D) porous framework with small windows and large cubic cages. The windows, with sizes between those of C3H6 and C3H8 molecules, enable efficient adsorption and separation of C3H6 / C3H8 at room temperature through molecular sieving effects, while the large cubic cages ensure a high adsorption capacity for C3H6. Furthermore, the NKU-601-Y framework possesses a high-connection-number hexanuclear secondary building unit (SBU) and binds high-valence M... 3+ The M–O bonds exhibit high chemical stability, thermal stability, and water / humidity stability.

[0006] The chemical formula of NKU-601-Y in this invention is [Y6(μ3-OH)8(mdip)3(H2O)6(DMA)2] n In this invention, H4mdip is 5,5'-methylenediisophthalic acid, mdip is obtained by losing four protons from H4mdip, and DMA is a dimethylamine ion. The NKU-601-Y in this invention crystallizes in the cubic crystal system, space group Im-3, and has an ftw topological network structure with cell parameters of... α=90.0°, β=90.0°, γ=90.0°.

[0007] The crystal structure of NKU-601-Y in this invention is described as follows: it consists of six Y atoms. 3+ Assembled into an octahedron, μ3-OH - Occupying all eight faces of the octahedron, each Y 3+ The ions are all nine-coordinate, connected by four oxygen atoms from four different carboxylate ligands of H4mdip, and four bridging μ3-OH groups. - An anion and a terminal water molecule constitute a twelve-linked SBU([Y6(OH)8(H2O)6(COO)) 12 ]2- Each SBU consists of twelve mdips. 4- Organic ligands connect and extend along axes a, b, and c respectively to form a three-dimensional organic framework structure with small windows and cubic cages.

[0008] In this invention, NKU-601-Y has a small window and a large cubic cage. The window, which is between the molecular sizes of C3H6 and C3H8, can achieve efficient adsorption and separation of C3H6 / C3H8 at room temperature through molecular sieving effect, while the large cubic cage ensures high adsorption capacity of C3H6.

[0009] A second aspect of this invention aims to provide a method for preparing NKU-601-Y material for C3H6 / C3H8 separation, comprising the following steps:

[0010] (1) Organic ligand H4mdip, metal salt Y(NO3)3·6H2O, and template agent o-fluorobenzoic acid were added to a mixed solvent of N,N-dimethylformamide (DMF) and water. The mixture was heated in an oven at 120°C for 72 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain colorless cubic crystals. The material was washed with DMF and dried to obtain the crystalline material. The molar ratio of H4mdip, Y(NO3)3·6H2O, and o-fluorobenzoic acid was 1:2:41; the volume ratio of DMF to water was 5:4.

[0011] (2) Obtaining activated NKU-601-Y: The MOF material obtained in step (1) was transferred to acetone solvent and soaked, and then activated at 300℃ for 12h to obtain activated NKU-601-Y.

[0012] Compared with the prior art, the advantages of the present invention are as follows:

[0013] (1) The NKU-601-Y adsorbent material is synthesized by a solvothermal method, which is simple to prepare;

[0014] (2) The NKU-601-Y adsorbent material has a high number of hexa-core SBUs, exhibiting high chemical stability, thermal stability and water stability.

[0015] (3) The NKU-601-Y adsorbent material can achieve C3H6 / C3H8 separation through molecular sieving effect, and at the same time has both high C3H6 adsorption capacity and high C3H6 / C3H8 separation selectivity. Attached Figure Description

[0016] Figure 1 This is a crystal structure diagram of the NKU-601-Y material.

[0017] Figure 2These are the prepared NKU-601-Y material and its PXRD patterns before and after activation treatment.

[0018] Figure 3 The images show the PXRD patterns of the prepared NKU-601-Y material after immersion in common chemical reagents (DMA represents N,N-dimethylacetamide, DCM represents dichloromethane, ACE represents acetone, ACN represents acetonitrile, MeOH represents methanol, and EtOH represents ethanol) and exposure to air for 72 hours.

[0019] Figure 4 The image shows the PXRD pattern of the prepared NKU-601-Y material after immersion in aqueous solutions with different pH values ​​for 72 hours.

[0020] Figure 5 The images show the prepared NKU-601-Y material and its thermogravimetric curves before and after activation treatment.

[0021] Figure 6 These are single-component adsorption isotherm curves of C3H6 and C3H8 on the activated NKU-601-Y material at different temperatures.

[0022] Figure 7 This is an adsorption-separation selectivity diagram of C3H6 / C3H8 (50 / 50, 90 / 10, v / v) binary gas mixtures on the activated NKU-601-Y material at different temperatures.

[0023] Figure 8 It is the fixed-bed breakthrough curve of C3H6 / C3H8 (50 / 50, v / v) on activated NKU-601-Y material at 298K. Detailed Implementation

[0024] Example 1:

[0025] (1) Synthesis of NKU-601-Y material

[0026] 9.0 mg H₄mdip, 38.3 mg Y(NO₃)₃·6H₂O, 1.0 g o-fluorobenzoic acid, 5 mL DMF, and 4 mL deionized water were added to a 20 mL glass vial and mixed thoroughly. The vial was sealed and heated in a 120 °C oven for 72 h. After the reaction was complete, the mixture was cooled to room temperature to obtain colorless cubic crystals. These crystals were washed with DMF and dried to obtain the preliminary crystalline material.

[0027] (2) Preparation of activated NKU-601-Y

[0028] The MOF material obtained in step (1) was transferred to acetone solvent for solvent exchange for 3 days, with 3 exchanges per day, and then activated at 300℃ for 12 hours to obtain activated NKU-601-Y.

[0029] The present invention uses the following instruments or methods to characterize and test the properties of materials.

[0030] Single-crystal X-ray diffraction (SCXRD) data of the NKU-601-Y material prepared in this invention were collected on a Rigaku XtaLABSynergy X-ray single-crystal diffractometer at 100 K and Cu Kα radiation. Multi-scan mode is employed. The structure of the NKU-601-Y material is as follows: Figure 1 As shown (analyzed using Olex2 software, plotted using Diamond software). Single-crystal data shows that NKU-601-Y crystallizes in the cubic crystal system, space group Im-3. The single-crystal structure reveals that NKU-601-Y belongs to the ftw topological network structure, possessing small windows between the molecular sizes of C3H6 and C3H8, and large cubic cages. The cages are connected to each other through small windows.

[0031] The powder X-ray diffraction (PXRD) pattern of the NKU-601-Y material prepared in this invention was collected on a Rigaku MiniFlex 600 X-ray instrument using Cu-Kα rays. Voltage 40kV, current 15mA, scanning speed 8° / min, step size 0.02. X-ray diffraction pattern as follows: Figure 2-4 As shown (drawn using Origin software, simulated using Mercury software). From Figure 2-4 It can be seen that before and after activation, in common solvents and aqueous solutions with pH 3-11, the PXRD characteristic peaks of the NKU-601-Y material prepared in this invention are not significantly different from the PXRD peaks simulated by single crystal structure, indicating that NKU-601-Y has excellent chemical stability and pH stability.

[0032] The thermogravimetric (TG) curves of the NKU-601-Y material prepared in this invention and its thermogravimetric (TG) curves before and after activation treatment were collected using a Rigaku TG-DTA analyzer (TG-8122). Heating was performed in air atmosphere, from room temperature to 800°C at a rate of 10°C / min, using an Al₂O₃ crucible as a reference. The TG curve of the NKU-601-Y material is shown below. Figure 5 As shown (drawn using Origin software). Figure 5 The results show that the thermal stability temperature of the NKU-601-Y material prepared by this invention is around 550℃.

[0033] The single-component adsorption isotherms of C3H6 and C3H8 at different temperatures after activation of the NKU-601-Y material prepared in this invention were collected using a Micrometrics ASAP 2020 gas adsorption analyzer. Approximately 100 mg of the activated NKU-601-Y sample was used for single-component adsorption curve measurements of C3H6 and C3H8. The single-component adsorption isotherms of C3H6 and C3H8 on the activated NKU-601-Y material at 273 K and 298 K are shown below. Figure 6 As shown (drawn using Origin software). By Figure 6 (b) It can be seen that at 298 K and 1 bar, the adsorption capacities of NKU-601-Y for C3H6 and C3H8 are 40.1 cm⁻¹, respectively. 3 / g and 7.2cm 3 / g, the adsorption curve shows that NKU-601-Y exhibits a molecular sieving effect on C3H6 and C3H8.

[0034] The adsorption-separation selectivity of the C3H6 / C3H8 (50 / 50, 90 / 10, v / v) binary gas mixture on the activated NKU-601-Y material at different temperatures was calculated using the ideal adsorbed solution theory (IAST). The adsorption isotherms of the single-component gases C3H6 and C3H8 were fitted using a two-site Langmuir-Freundlich model, and the selectivity was calculated using IAST (fitting and plotting were performed using Origin software). The adsorption-separation selectivity of the C3H6 / C3H8 (50 / 50, 90 / 10, v / v) binary gas mixture on the activated NKU-601-Y material at different temperatures is shown below. Figure 7 As shown, the NKU-601-Y material exhibits separation selectivity of 106.5 and 110.8 for C3H6 / C3H8 (50 / 50, 90 / 10, v / v) at 298 K and 100 kPa, respectively.

[0035] The two-site Langmuir-Freundlich (DSLF) model can be defined as follows:

[0036]

[0037] q A,sat and q B,sat : Saturated adsorption capacity of adsorption sites A and B, in mmol / g;

[0038] b A and b B : Affinity coefficient of adsorption site to sites A and B, in kPa;

[0039] vA and v B : Deviation from an ideal uniform surface;

[0040] p, the pressure of the gas phase and the adsorbed phase at equilibrium, in kPa;

[0041] q represents the amount of adsorbent adsorbed per unit mass, expressed in mmol / g.

[0042] The adsorption selectivity of IAST is defined as:

[0043]

[0044] S: Ideal selectivity of component 1 relative to component 2;

[0045] q i : Adsorption amount of component i (i=1,2);

[0046] p i : Partial pressure of component i.

[0047] The fixed-bed breakthrough experiment of the activated NKU-601-Y material prepared in this invention was conducted in a self-assembled experimental setup. The flow rates of all gases were regulated by a mass flow controller, and the gas flow from the column was monitored by gas chromatography (Nexis GC-2030). The weight of NKU-601-Y packed in the column was 0.6 g. The total flow rate of the C3H6 / C3H8 (50 / 50, v / v) mixed gas was 2 mL / min. The fixed-bed breakthrough curve of C3H6 / C3H8 (50 / 50, v / v) on the activated NKU-601-Y material at 298 K is shown below. Figure 8 As shown in the figure. The test results show that C3H6 exits the penetration column after 16.7 min / g, while C3H8 is not detected until 33.4 min / g. This means that the NKU-601-Y material has practical separation performance for the mixture of C3H6 and C3H8.

Claims

1. A metal-organic framework material suitable for the adsorption and separation of propylene and propane, characterized in that: This material belongs to the metal-organic framework, crystallizes in the cubic crystal system, Im-3 space group, and has an FTW topological network structure. Its cell parameters are a = 25.0636(3) Å, b = 25.0636(3) Å, c = 25.0636(3) Å, α = 90.0°, β = 90.0°, γ = 90.0°. Its composition is represented by the chemical formula [Y6(μ3-OH)8(mdip)3(H2O)6(DMA)2]. n Named NKU-601-Y, where H4mdip is 5,5'-methylene isophthalic acid, mdip is obtained by losing four protons from H4mdip, DMA is a dimethylamine ion, and the smallest asymmetric unit contains three mdips. 4- Organic ligands, six Y 3+ It contains eight µ3-OH groups, six coordinated water groups, and two counteracting dimethylamine ions.

2. The metal-organic framework material suitable for the adsorption and separation of propylene and propane as described in claim 1, characterized in that: Composed of six Y 3+ Assembled into an octahedron, µ3-OH − Occupying all eight faces of the octahedron, each Y 3+ All are nine-coordinate, connecting four oxygen atoms from different carboxylate groups of four H4mdip ligands, and four bridging µ3-OH groups. − An anion and a terminal water molecule constitute a twelve-linked SBU ([Y6(OH)8(H2O)6(COO)). 12 ] 2− Each SBU consists of twelve mdip 4− Organic ligands connect and extend along axes a, b, and c respectively to form a three-dimensional organic framework structure with small windows and cubic cages.

3. The metal-organic framework material suitable for the adsorption and separation of propylene and propane as described in claim 1, characterized in that: It features a small window and a large cubic cage. The window, which is between the molecular sizes of C3H6 and C3H8, can achieve efficient adsorption and separation of C3H6 / C3H8 at room temperature through molecular sieving effect, while the large cubic cage ensures high adsorption capacity of C3H6.

4. A method for preparing a metal-organic framework material suitable for the adsorption and separation of propylene and propane according to any one of claims 1-3, comprising the following steps: (1) Organic ligand H4mdip, metal salt Y(NO3)3·6H2O and template agent o-fluorobenzoic acid were added to a mixed solvent of N,N-dimethylformamide (DMF) and water. The mixture was placed in an oven at 120 °C and heated at a constant temperature for 72 h. After the reaction was completed, it was cooled to room temperature to obtain colorless cubic crystals. The material was washed with DMF and dried to obtain the crystal material. The molar ratio of H4mdip, Y(NO3)3·6H2O and o-fluorobenzoic acid was 1:2:41; the volume ratio of DMF and water was 5:

4. (2) Obtaining activated NKU-601-Y: The MOF material obtained in step (1) was transferred to acetone solvent and soaked, and then activated at 300 °C for 12 h to obtain activated NKU-601-Y.

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