A zirconium-based MOF material for one-step purification of ethylene and recovery of propylene in MTO products and a method for preparing the same

Abstract

This application relates to the fields of crystalline porous materials and chemical separation technology, specifically, to a zirconium-based MOF material and its preparation method for one-step purification of ethylene and recovery of propylene from MTO products. The zirconium-based MOF material NKU-400 has a (4,4,12)-linked topology, belongs to the monoclinic crystal system, C2 / c space group, and exhibits extremely high chemical stability. It maintains the integrity of its framework structure after immersion in water, organic solvents, concentrated hydrochloric acid, and sodium hydroxide aqueous solution at pH=11 for 48 hours. This effectively solves the technical bottleneck of instability of existing MOF materials under harsh industrial environments and has important applications in the processing of methanol-to-olefins products.

Description

Technical Field

[0001] This application relates to the fields of crystalline porous materials and chemical separation technology, specifically, to a zirconium-based MOF material for one-step purification of ethylene and recovery of propylene from MTO products and its preparation method. Background Technology

[0002] Ethylene (C2H4) and propylene (C3H6) are cornerstones of the modern petrochemical industry and have wide applications. Methanol to olefins (MTO) process, as an important non-petroleum route, can effectively alleviate dependence on petroleum resources and has become a key alternative for sustainable olefin production. However, the product stream of the MTO process has a complex composition. Its typical products usually contain about 51.1% ethylene, about 20.9% propylene, and about 6%–10% ethane (C2H6) and other byproducts. In order to meet the high standard requirements of downstream polymerization reactions for raw materials, ethylene and propylene in the crude gas stream must be separated and purified to the polymer grade (purity ≥99.95%).

[0003] Currently, industrial separation mainly employs traditional cryogenic distillation techniques. However, due to the extreme similarity in size and physical properties of C2 / C3 hydrocarbon molecules, the molecular polarizability volumes of C3H6, C2H6, and C2H4 are 62.6 × 10⁻⁶. -25 cm 3 44.7×10 -25 cm 3 and 42.52×10 -25 cm 3 This leads to the need for a huge reflux ratio and number of trays in the distillation process, resulting in extremely high energy consumption and expensive equipment investment. In contrast, adsorption separation technology, especially adsorption separation based on porous materials such as metal-organic frameworks (MOFs), has the characteristics of high energy efficiency and structural tunability. However, existing adsorbents still face many severe challenges when dealing with complex MTO ternary mixture products, such as (1) it is difficult to achieve high selective separation while maintaining high adsorption capacity, and the separation efficiency is limited; (2) ethylene is preferentially adsorbed, which on the one hand increases desorption energy consumption, and on the other hand makes it difficult to achieve direct one-step purification of ethylene, and it is difficult to achieve reverse selectivity; (3) many MOF materials with excellent separation performance have insufficient chemical stability and the framework is prone to collapse under water vapor or acid-base conditions, making it difficult to meet the needs of long-term industrial operation; (4) the recovery rate of high-value components is low, resulting in resource waste.

[0004] Therefore, developing a novel adsorbent that possesses both ultra-high chemical stability and the ability to achieve a specific reverse adsorption sequence of C3H6>C2H6>C2H4 is of significant industrial application value and economic importance for the efficient recovery of propylene while purifying ethylene in one step. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a zirconium-based MOF material NKU-400 with high stability, high adsorption capacity and excellent selectivity, and to provide its preparation method and its application in the separation of methanol-to-olefins (MTO) products, so as to solve the technical problems of difficult one-step purification of ethylene, low propylene recovery rate and poor stability of adsorbent materials in existing technologies.

[0006] The primary objective of this application is to provide a zirconium-based MOF material for one-step purification of ethylene and recovery of propylene from MTO products. The zirconium-based MOF material has the chemical formula Zr6(μ3-O)4(μ3-OH)4(TCPPDA)3(H2O)2 and has a (4,4,12)-linked topology with the topological symbol {4 26 ·6 32 ·8 8}{4 6}3. Zirconium-based MOF materials belong to the monoclinic crystal system, space group C2 / c, and are named NKU-400.

[0007] Optionally, the zirconium-based MOF material has uniform one-dimensional rhombic channels with a pore size of 10.0 Å, and the surface of the channels is modified with abundant aromatic rings and functionalized nitrogen / oxygen adsorption sites.

[0008] The second objective of this application is to provide a method for preparing a zirconium-based MOF material, comprising the following steps: S1, dissolving a zirconium salt, an organic ligand N,N,N',N'-tetra(4-carboxyphenyl)-1,4-phenylenediamine, and a modifier in an amide-based organic solvent, and ultrasonically mixing them to obtain a precursor solution; S2, transferring the precursor solution to a sealed container and sealing it, and carrying out a solvothermal reaction at a temperature of 140℃-150℃; S3, after the reaction is completed, cooling to room temperature, collecting the product, and performing post-processing operations to obtain the zirconium-based MOF material NKU-400.

[0009] Optionally, step S1 shall satisfy at least one of the following: (1) the zircon salt is zirconium tetrachloride; (2) the modifier is benzoic acid; (3) the organic solvent is N,N-dimethylformamide.

[0010] Optionally, in step S1, the molar ratio of zirconium salt, regulator, and organic ligand is 5-10:400-500:1.

[0011] Optionally, the temperature of the solvothermal reaction in step S2 is 140°C and the reaction time is 48 hours.

[0012] Optionally, the post-processing operations in step S3 include washing and drying.

[0013] A third objective of this application is to provide the application of zirconium-based MOF materials in the treatment of methanol-to-olefins products.

[0014] Optionally, the adsorption affinity of zirconium-based MOF materials for the main components of MTO products follows the order: propylene > ethane > ethylene.

[0015] The fourth objective of this application is to provide a method for using zirconium-based MOF materials in the treatment of methanol-to-olefins products, including one of the following:

[0016] (1) A mixture of MTO products containing ethylene, propylene and ethane is passed into an adsorption bed filled with zirconium-based MOF material to adsorb propylene and ethane, so that the ethylene component is the first to pass through the adsorption bed as the outflow gas and is collected to obtain polymer grade ethylene with a purity ≥99.95%.

[0017] (2) The MTO product mixture containing ethylene, propylene and ethane is introduced into an adsorption bed filled with zirconium-based MOF material to adsorb propylene and ethane. After the adsorption bed is saturated, the propylene and ethane adsorbed in the pores are decomposed and collected to obtain high-purity propylene with a purity ≥99.5%.

[0018] Optionally, the desorption method for the propylene and ethane components in (2) is inert gas purging.

[0019] Compared with the prior art, this application has the following beneficial effects:

[0020] (1) This application provides a zirconium-based MOF material NKU-400, which has a unique (4,4,12)-connection topology, with the topology symbol {4 26 ·6 32 ·8 8}{4 6 3. Compared to existing adsorbents and other conventional zirconium-based MOF materials, this unique bonding method endows NKU-400 with superior chemical and thermal stability. Experiments have shown that NKU-400 can not only withstand water and common organic solvents, but also maintain its structural integrity after being immersed in 12M concentrated hydrochloric acid (extremely acidic environment) and a strong alkaline solution with pH=11 for 48 hours. In addition, NKU-400 has a thermal decomposition temperature as high as 450℃. This stability under extreme conditions enables this application to effectively solve the technical bottleneck of existing materials being prone to collapse in harsh industrial environments, and has a longer service life and industrial applicability.

[0021] (2) When the zirconium-based MOF material NKU-400 provided in this application is actually processed with ethylene / propylene mixed gas of equal molar ratio, its yield of polymer grade ethylene (purity ≥99.95%) is as high as 94.45 L / kg, which is at the leading level among the known MOF materials. First, while existing technologies can handle the separation of three components, they often face the challenge of balancing selectivity and capacity when processing ethylene / ethane / propylene ternary mixtures in methanol-to-olefins products. NKU-400, with its 10.0 Å one-dimensional rhombic channels, exhibits a significant synergistic effect through the steric hindrance of the channels and the multiple C–H···π / N / O weak interactions generated by the abundant aromatic rings and functionalized N / O sites on the pore walls. This mechanism enables NKU-400 to exhibit a unique reverse adsorption order of C3H6 > C2H6 > C2H4. Therefore, compared to existing technologies, NKU-400 can not only efficiently capture propylene but also utilize its stronger affinity for ethane (single-component adsorption capacity: C2H6 4.29 mmol / g vs C2H4 3.11 mmol / g) to simultaneously retain ethane and propylene as "dual impurities" within the channels, thereby achieving one-step direct purification of ethylene in complex ternary systems. Secondly, unlike traditional separation technologies that only focus on ethylene purification, NKU-400 utilizes its extremely strong adsorption affinity for propylene. During the desorption process after adsorption saturation, it can recover high-purity propylene with a purity ≥99.5%, achieving a recovery rate of 77.62 L / kg (59.72 L / kg in a ternary system). In summary, this unique "two-component high-efficiency purification and recovery" capability enables the simultaneous resource utilization of two high-value olefin components in the methanol-to-olefins process, greatly improving the economic efficiency of industrial separation while simplifying the process flow.

[0022] (3) The zirconium-based MOF material NKU-400 provided in this application exhibits excellent regeneration capability and cycle stability during dynamic separation. In dynamic breakthrough experiments conducted at 298 K on C3H6 / C2H4 (1 / 1, v / v) and C2H6 / C2H4 (1 / 9, v / v) mixed gases, the material maintained a high degree of consistency in breakthrough time, separation capacity, and breakthrough curve shape after five consecutive adsorption-desorption cycles, with no significant performance degradation observed. Notably, the regeneration process of NKU-400 is extremely simple and efficient, requiring only Ar gas purging under ambient conditions for complete regeneration. Furthermore, PXRD characterization results show that the crystal structure of NKU-400 remains intact after multiple gas adsorption, dynamic breakthrough, and water vapor adsorption tests, fully verifying the strength and toughness of its framework. Combined with its physicochemical stability under extremely acidic and alkaline environments, this demonstrates the high reliability of the material under long-term, continuous industrial operation and harsh regeneration conditions. Attached Figure Description

[0023] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0024] Figure 1 This is a schematic diagram of the crystal structure assembly and topology of the zirconium-based MOF material NKU-400 in Example 1 of this application; wherein (a) is the 12-linked Zr6 metal cluster structure, (b) is the ligand conformation, (c) is the three-dimensional framework structure formed by assembly, (d) is a simplified topological structure diagram, and (e) is a schematic diagram of a one-dimensional rhombic through-hole observed along the c-axis.

[0025] Figure 2 The image shows the powder X-ray diffraction (PXRD) pattern of NKU-400 in Example 1 of this application; from bottom to top, the images are the simulated pattern based on single crystal data, the experimental pattern of the synthesized sample, and the experimental pattern of the activated sample.

[0026] Figure 3 The N2 adsorption-desorption isotherm of NKU-400 at 77K is shown in the inset; the inset is a pore size distribution diagram.

[0027] Figure 4 Thermogravimetric analysis (TGA) curve of NKU-400 in Embodiment 1 of this application;

[0028] Figure 5 The following are PXRD spectra of NKU-400 of this application after treatment in different chemical environments for 48 hours; (a) is the spectrum after treatment in water and different organic solvents, and (b) is the spectrum after treatment in hydrochloric acid aqueous solution of different concentrations and alkaline solution of pH=11.

[0029] Figure 6 The adsorption isotherms of the NKU-400 of this application for single-component gases C3H6, C2H6 and C2H4 at 298K are shown.

[0030] Figure 7 The above are IAST selectivity prediction curves of the NKU-400 of this application for binary gas systems; where (a) is the selectivity curve of the C2H6 / C2H4 system and (b) is the selectivity curve of the C3H6 / C2H4 system.

[0031] Figure 8 The dynamic breakthrough curves of the NKU-400 of this application at 298K for C2H6 / C2H4 binary mixtures with different ratios are shown.

[0032] Figure 9The diagram shows the dynamic breakthrough and desorption curves of the NKU-400 of this application for a C3H6 / C2H4 binary gas mixture; where (a) corresponds to a gas mixture with a volume ratio of 1 / 1, (b) corresponds to a gas mixture with a volume ratio of 2 / 5, and (c) corresponds to a gas mixture with a volume ratio of 1 / 9.

[0033] Figure 10 The dynamic breakthrough curve and desorption curve of NKU-400 of this application for a ternary gas mixture of C3H6 / C2H6 / C2H4 with a volume ratio of 1 / 1 / 1 are shown.

[0034] Figure 11 The following are the cycle regeneration stability test diagrams of the NKU-400 of this application; wherein, (a) is a dynamic breakthrough cycle curve of 5 consecutive cycles conducted at 298 K for a C3H6 / C2H4 mixture with a volume ratio of 1 / 1, and (b) is a dynamic breakthrough cycle curve of 5 consecutive cycles conducted at 298 K for a C2H6 / C2H4 mixture with a volume ratio of 1 / 9.

[0035] Figure 12 The images show the powder X-ray diffraction (PXRD) spectra of NKU-400 before and after different test conditions. From bottom to top, the images show the simulated single-crystal spectrum of NKU-400, the spectrum after multiple single-component gas adsorption experiments, the spectrum after dynamic penetration experiments, and the spectrum after water vapor adsorption tests. Detailed Implementation

[0036] The present application will be further described below with reference to specific embodiments. These embodiments are only used to more clearly illustrate the technical solutions of the present application and should not be construed as limiting the scope of protection of the present application. Anything not described in detail in this patent application is considered common knowledge in the art.

[0037] The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized by conventional methods and are ready for use without further processing, as are the instruments used in the examples. All technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application and in its specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0038] Existing adsorbents face several severe challenges when treating complex MTO ternary mixtures (C3H6 / C2H6 / C2H4). (1) Trade-off effect between adsorption capacity and selectivity: Existing materials often struggle to achieve high selective separation while maintaining high adsorption capacity, limiting the separation efficiency of the mixture. (2) Difficulty in achieving reverse selectivity: Traditional MOF materials often utilize strongly polar sites such as open metal sites to enhance adsorption, but this usually results in the material having a stronger affinity for ethylene C2H4 than for ethane C2H6 / propylene C3H6, causing ethylene to be preferentially adsorbed. This not only increases desorption energy consumption but also makes it difficult to allow ethylene to elute first as a non-adsorbed component, achieving direct one-step purification of ethylene. (3) Insufficient chemical stability: The actual working environment in industry is very harsh, requiring adsorbents to have extremely high requirements for water resistance, acid and alkali resistance, and thermal stability. However, the framework of many MOF materials with excellent separation performance is prone to collapse under water vapor or acid and alkali conditions, making it difficult to meet the needs of long-term industrial operation. (4) Low recovery rate of high-value components: Existing technical routes often focus too much on the purification of ethylene, while neglecting the efficient recovery and utilization of propylene, a high-value byproduct in the mixed gas, resulting in a waste of resources.

[0039] To address the shortcomings of the aforementioned existing methods, the inventors have developed a zirconium-based MOF material for one-step purification of ethylene and recovery of propylene from MTO products. The chemical formula is Zr6(μ3-O)4(μ3-OH)4(TCPPDA)3(H2O)2, named NKU-400. This zirconium-based MOF material has a (4,4,12)-connected topology, with the topological symbol {4... 26 ·6 32 ·8 8}{4 6}3, belonging to the monoclinic crystal system, space group C2 / c, has uniform one-dimensional rhombic channels with a pore size of 10.0 Å and a surface modified with abundant aromatic rings and functionalized nitrogen / oxygen adsorption sites.

[0040] In some specific embodiments, the preparation method of zirconium-based MOF material NKU-400 includes the following steps: S1, dissolving zirconium salt, organic ligand N,N,N',N'-tetra(4-carboxyphenyl)-1,4-phenylenediamine (H4TCPPDA), and a modifier in an amide-based organic solvent at a molar ratio of 5-10:1:400-500, and ultrasonically mixing to obtain a precursor solution; wherein, the zirconium salt includes, but is not limited to, zirconium tetrachloride (ZrCl4); and the modifier is benzoic acid. Acid); organic solvents include, but are not limited to, N,N-dimethylformamide (DMF); S2, the precursor solution is transferred to a sealed container and sealed, and a solvothermal reaction is carried out at a temperature of 140℃-150℃; on the one hand, the self-generated pressure generated by the closed system at high temperature induces the reaction substrate to assemble in a specific conformation to form a unique topological structure; on the other hand, the zirconium salt in the precursor solution is easily affected by moisture in the air and undergoes side reactions. Carrying this step in a sealed environment can effectively isolate the negative impact of the components of the external environment of the reaction container on the crystallization process; S3, after the reaction is completed, the product is cooled to room temperature, collected, and after post-processing operations such as washing and drying, the zirconium-based MOF material NKU-400 is obtained.

[0041] In some specific embodiments, the zirconium-based MOF material NKU-400 is applied in the treatment of methanol-to-olefins (MTO) products. In some specific embodiments, after obtaining the zirconium-based MOF material NKU-400, it needs to be activated before application: first, NKU-400 is soaked in anhydrous acetone for 3 days, with the acetone replaced daily; then, NKU-400 is placed in a vacuum activation station and vacuum activated at 120°C for 12 hours to completely remove residual solvent from the pores, obtaining an activated material with a high specific surface area. In practical applications, the adsorption affinity of the zirconium-based MOF material NKU-400 for the main components of the ternary mixture product (C3H6 / C2H6 / C2H4) of methanol-to-olefins (MTO) follows the order: propylene (C3H6) > ethane (C2H6) > ethylene (C2H4).

[0042] In some specific embodiments, the method of using zirconium-based MOF materials in the treatment of methanol-to-olefins products includes a one-step high-yield purification of ethylene: a ternary gas mixture (volume ratio of 1:1:1) containing ethylene, propylene, and ethane is passed into an adsorption bed packed with 0.5 g of activated zirconium-based MOF material at a flow rate of 2.0 mL / min. Propylene and ethane are adsorbed, and the ethylene component is allowed to penetrate the adsorption bed first as the outflow gas. The adsorption bed is then collected to obtain polymer-grade ethylene with a purity ≥99.95%.

[0043] In some specific embodiments, the method of using zirconium-based MOF materials in the treatment of methanol-to-olefins products also includes the recovery of high-purity propylene: a mixed gas of MTO products containing ethylene, propylene and ethane is passed into an adsorption bed filled with zirconium-based MOF materials to adsorb propylene and ethane. After the adsorption bed is saturated, the propylene and ethane adsorbed in the pores are decomposed and collected by purging with an inert gas to obtain high-purity propylene with a purity ≥99.5%.

[0044] In some specific embodiments, the used zirconium-based MOF material NKU-400 is regenerated: complete regeneration can be achieved simply by purging with Ar gas under ambient conditions.

[0045] Example 1

[0046] This embodiment provides a zirconium-based MOF material NKU-400, and its crystal structure assembly and topology diagram are shown below. Figure 1 As shown, the preparation method is as follows: S1, ZrCl4 (0.9 mmol, 210 mg), H4TCPPDA (0.12 mmol, 70 mg) and benzoic acid (7.0 g) are dissolved in N,N-dimethylformamide (DMF, 14 mL), mixed in a 20 mL glass bottle, and sonicated to dissolve, to obtain a precursor solution; S2, the glass bottle is sealed and placed in an oven, and heated at 140 °C for 48 hours for a solvothermal reaction; S3, after the reaction is completed, it is cooled to room temperature, and the resulting pale yellow crystals are collected by centrifugation, washed with DMF, and dried in air to obtain zirconium-based MOF material NKU-400.

[0047] Example 2

[0048] This embodiment provides a zirconium-based MOF material NKU-400 with higher crystallinity than that in Example 1. The preparation method is basically the same as that in Example 1: S1, ZrCl4 (1.2 mmol, 280 mg), H4TCPPDA (0.12 mmol, 70 mg), and benzoic acid (7.3 g, about 60 mmol) are dissolved in N,N-dimethylformamide (DMF, 14 mL). At this time, the molar ratio of zirconium salt, regulator, and organic ligand is 10:500:1. The solution is mixed in a 20 mL glass bottle and sonicated for 20 minutes to ensure complete dissolution, thus obtaining a precursor solution; S2, the glass bottle is sealed and placed in an oven, and heated at 140 °C for 48 hours for a solvothermal reaction; S3, after the reaction is completed, the solution is cooled to room temperature, and the resulting pale yellow crystals are collected by centrifugation, washed with DMF, and dried in air to obtain the zirconium-based MOF material NKU-400.

[0049] Example 3

[0050] This embodiment provides a zirconium-based MOF material NKU-400, prepared by the following method: S1, ZrCl4 (0.6 mmol, 140 mg), H4TCPPDA (0.12 mmol, 70 mg), and benzoic acid (5.86 g, approximately 48 mmol) are dissolved in N,N-dimethylformamide (DMF, 14 mL). At this point, the molar ratio of zirconium salt, regulator, and organic ligand is 5:400:1. The solution is mixed in a 20 mL glass bottle and sonicated for 20 minutes to ensure complete dissolution, thus obtaining a precursor solution; S2, the glass bottle is sealed and placed in an oven, where it is heated at 140 °C for 48 hours for a solvothermal reaction; S3, after the reaction is complete, the solution is cooled to room temperature, and the resulting pale yellow crystals are collected by centrifugation, washed with DMF, and dried in air to obtain the zirconium-based MOF material NKU-400.

[0051] Comparative Example 1

[0052] To further verify the technical solution of this application and its beneficial effects, Example 1 was verified.

[0053] Experimental Example 1: Structure and Yield Identification

[0054] 1. An appropriate amount of NKU-400 prepared in Example 1 was selected, and the yield was calculated to be 60.1% based on the H4TCPPDA ligand. The measured elemental analysis values ​​(%) were: C 49.76, H 2.73, N 3.36; the theoretical calculated values ​​were: C 49.53, H 2.91, N 3.40, indicating that the purity of NKU-400 is high.

[0055] 2. Select an appropriate amount of NKU-400 prepared in Example 1 for crystal structure analysis and porosity characterization, such as... Figure 1 As shown, the NKU-400 framework is constructed from {Zr6(μ3-O)4(μ3-OH)4} clusters, each cluster being linked to 12 ligands to form a unique (4,4,12)-linked topological network. This framework has one-dimensional rhombic channels along the c-axis with a pore size of approximately 10.0 Å. The channel surface is modified with abundant aromatic rings and functionalized N / O adsorption sites. Crystallographic data obtained by single-crystal X-ray diffraction (SCXRD) indicate that NKU-400 crystallizes in a monoclinic system with space group C2 / c. The cell parameters are a=22.2447(2) Å, b=27.3434(3) Å, c=30.8176(2) Å, β=100.980(1)°.

[0056] 3. Powder X-ray diffraction (PXRD) was performed on the prepared NKU-400 crystal and the activated crystal. The results are as follows: Figure 2As shown, from bottom to top, the spectra simulated based on single crystal data, the spectra of the synthesized sample, and the spectra of the activated sample are shown. The diffraction peak positions of the synthesized sample are highly consistent with the simulated spectra, proving that Example 1 successfully prepared a high-purity NKU-400 phase. The spectra of the activated sample show that the skeleton remains intact after solvent removal.

[0057] 4. To characterize the porosity of NKU-400, N2 adsorption-desorption tests were performed on the activated sample at 77K. The results are as follows: Figure 3 As shown, the adsorption isotherm is a typical type I isotherm, indicating that the material has microporous properties. The interpolated pore size distribution map shows that the pore size is concentrated at approximately 10 Å, consistent with the crystal structure analysis results. The calculated BET specific surface area is 1174 m². 2 g −1 .

[0058] Experimental Example 2: Thermal and Chemical Stability Tests

[0059] To assess the industrial application potential of this material, thermogravimetric analysis and chemical stability tests were performed on NKU-400, and the results are as follows: Figure 4 and Figure 5 As shown.

[0060] Figure 4 The thermogravimetric curves showed that neither the synthesized nor the activated sample underwent significant skeletal decomposition before approximately 450°C, demonstrating that NKU-400 exhibits excellent thermal stability.

[0061] Figure 5 (a) indicates that after the NKU-400 sample was treated in pure water and common organic solvents such as methanol, ethanol, and acetone for 48 hours, its PXRD spectrum was consistent with the original sample, indicating that the skeleton structure was intact and did not collapse, and it had excellent water and organic solvent resistance. Figure 5 (b) The PXRD spectrum of NKU-400 samples remained intact after being immersed in HCl aqueous solutions of different concentrations from 1M to 12M and NaOH aqueous solution of pH=11 for 48 hours, which proves that NKU-400 has excellent acid and alkali resistance and can maintain the integrity of the skeleton structure under harsh industrial environment.

[0062] Experimental Example 3: Analysis of Gas Adsorption Performance and Selectivity

[0063] The single-component adsorption isotherms of NKU-400 for C3H6, C2H6, and C2H4 were measured at 298 K and 1 bar. The results are as follows: Figure 6 As shown, the adsorption capacities of NKU-400 for the three gases are: C3H6 (6.01 mmol g) −1 C2H6 (4.29 mmol g) > C2H6 (4.29 mmol g g) −1C2H4 (3.11 mmol g) > C2H4 (3.11 mmol g g) −1 It exhibits the obvious reverse adsorption characteristics of NKU-400.

[0064] The selectivity of binary gas mixtures can be calculated using the Ideal Adsorption Solution Theory (IAST), such as... Figure 7 As shown in (a), for the C3H6 / C2H4 system, NKU-400 exhibits preferential adsorption of ethane, with a selectivity of approximately 1.55–1.64; Figure 7 As shown in (b), NKU-400 exhibits excellent propylene selectivity for the C3H6 / C2H4 system, especially for the C3H6 / C2H4 (1 / 1, v / v) mixture, with a selectivity of up to 9.83, which is better than most similar materials.

[0065] Experimental Example 4: Dynamic Breakthrough Separation of Binary Gas Mixture and Recovery of High-Purity Propylene

[0066] At 298 K, the separation performance of NKU-400 for binary gas mixtures with different ratios (C2H6 / C2H4 and C3H6 / C2H4) was tested using a dynamic breakthrough device. The test conditions were: an adsorption column with a length of 200 mm, an inner diameter of 3 mm, and approximately 0.5 g of activated NKU-400.

[0067] For C2H6 / C2H4 mixtures, different proportions (1 / 1, 1 / 9, 1 / 15, v / v) were introduced into the adsorption column at a flow rate of 2 mL / min. Figure 8 As shown, in all proportions, ethylene (C2H4) was the first non-adsorbed component to efflux and was able to achieve polymerization-grade purity (≥99.95%).

[0068] For C3H6 / C2H4 mixed gases, the NKU-400 exhibits excellent "adsorption-capture-desorption-recovery" cycle performance. For example... Figure 9 As shown in (a), for a C3H6 / C2H4 (1 / 1, v / v) mixture, ethylene first penetrates the adsorption bed, achieving a yield of 94.45 L / kg of polymerization-grade ethylene (purity ≥99.95%). After adsorption saturation, in-situ purging with Ar gas at a flow rate of 6 mL / min is performed (see...). Figure 9 (The curve on the right) Propylene adsorbed within the pores is released in a concentrated manner, recovering high-purity propylene with a purity ≥99.5%, with a recovery rate as high as 77.62 L / kg. For a typical MTO product ratio of C3H6 / C2H4 (2 / 5, v / v), such as Figure 9As shown in b, NKU-400 also achieved one-step purification of ethylene. Under these conditions, the yield of polymerization-grade ethylene was significantly increased to 176.55 L / kg, with a corresponding propylene recovery of 66.1 L / kg. For lower propylene concentrations of C3H6 / C2H4 (1 / 9, v / v), such as Figure 9 As shown in c, NKU-400 exhibits an extremely long ethylene breakthrough time, with a polymerization-grade ethylene yield as high as 263.68 L / kg and a propylene recovery rate of 33.84 L / kg during the desorption stage.

[0069] Experimental Example 5: One-step purification of a ternary gas mixture

[0070] Further testing of the NKU-400's separation performance for C3H6 / C2H6 / C2H4 (1 / 1 / 1, v / v / v) ternary gas mixtures yielded the following results: Figure 10 As shown in the breakthrough curve, the gas efflux sequence strictly follows the order of C2H4, C2H6, and C3H6. Before the C2H6 breakthrough, ethylene of polymerization-grade purity (≥99.95%) can be directly collected, achieving one-step purification with an ethylene yield of 1.83 L / kg. −1 After adsorption saturation, Ar purging was performed. The weakly adsorbed C2H4 and C2H6 were purged first, followed by concentrated desorption of high-purity propylene (≥99.5%), with a recovery rate of 59.72 L / kg. −1 .

[0071] Test Example 6: Recycling Capacity Test

[0072] 1. Further test the regeneration capability and cycle stability of NKU-400 during dynamic separation, such as... Figure 11 As shown, dynamic breakthrough experiments were conducted at 298 K for C3H6 / C2H4 (1 / 1, v / v) and C2H6 / C2H4 (1 / 9, v / v) mixtures. The NKU-400 underwent five consecutive adsorption-desorption cycles to test its breakthrough time, separation capacity, and breakthrough curve shape. The results show that after cycling, its breakthrough time, separation capacity, and breakthrough curve shape remained highly consistent with the initial test results, with no significant performance degradation observed.

[0073] 2. Further structural changes in NKU-400 were observed through PXRD characterization experiments, such as... Figure 12 As shown, the results indicate that after undergoing multiple gas adsorption, dynamic penetration, and water vapor adsorption tests, the crystal structure of NKU-400 remains intact, fully verifying the strength and toughness of its framework and further demonstrating the high reliability of NKU-400 under long-term, continuous industrial operation and harsh regeneration conditions.

[0074] Based on the preferred embodiments of this application, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope is not limited to the contents of the specification.

Claims

1. A zirconium-based MOF material for one-step purification of ethylene and recovery of propylene from MTO products, characterized in that, The zirconium-based MOF material has the chemical formula Zr6(μ3-O)4(μ3-OH)4(TCPPDA)3(H2O)2 and has a (4,4,12)-connected topology with the topological symbol {4 26 ·6 32 ·8 8 }{4 6 }3, The zirconium-based MOF material belongs to the monoclinic crystal system, space group C2 / c, and is named NKU-400.

2. The zirconium-based MOF material according to claim 1, characterized in that, The zirconium-based MOF material has uniform one-dimensional rhombic channels with a pore size of 10.0 Å, and the surface of the channels is modified with abundant aromatic rings and functionalized nitrogen / oxygen adsorption sites.

3. The method for preparing the zirconium-based MOF material according to claim 1 or 2, characterized in that, Includes the following steps: S1. Dissolve zirconium salt, organic ligand N,N,N',N'-tetra(4-carboxyphenyl)-1,4-phenylenediamine and regulator in an amide organic solvent, and mix them evenly by ultrasonication to obtain a precursor solution. S2. Transfer the precursor solution to a sealed container and seal it, and carry out a solvothermal reaction at a temperature of 140℃-150℃. S3. After the reaction is complete, cool to room temperature, collect the product, and obtain the zirconium-based MOF material NKU-400 through post-processing.

4. The preparation method according to claim 3, characterized in that, Step S1 must satisfy at least one of the following: (1) The zircon salt is zirconium tetrachloride; (2) The regulator is benzoic acid; (3) The organic solvent is N,N-dimethylformamide.

5. The preparation method according to claim 3, characterized in that, In step S1, the molar ratio of zirconium salt, regulator, and organic ligand is 5-10:400-500:

1.

6. The preparation method according to claim 3, characterized in that, The temperature of the solvothermal reaction in step S2 is 140°C and the reaction time is 48 hours.

7. The preparation method according to claim 3, characterized in that, The post-processing operations in step S3 include washing and drying.

8. The application of the zirconium-based MOF material according to claim 1 or 2 in the treatment of methanol-to-olefins products.

9. The application according to claim 8, characterized in that, The adsorption affinity of the zirconium-based MOF material for the main components of MTO products follows the order: propylene > ethane > ethylene.

10. The method of using the zirconium-based MOF material of claim 8 in the treatment of methanol-to-olefins products, characterized in that, Including one of the following: (1) A mixture of MTO products containing ethylene, propylene and ethane is passed into an adsorption bed filled with the zirconium-based MOF material to adsorb propylene and ethane, so that the ethylene component is the first to penetrate the adsorption bed as the outflow gas and is collected to obtain polymer-grade ethylene with a purity ≥99.95%. (2) The MTO product mixture containing ethylene, propylene and ethane is introduced into the adsorption bed filled with the zirconium-based MOF material to adsorb propylene and ethane. After the adsorption bed is saturated, the propylene and ethane adsorbed in the pores are decomposed and collected to obtain high-purity propylene with a purity of ≥99.5%.

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