Zr-MOF Materials for One-Step Purification of Ethylene and Propylene and Their Preparation Methods

Abstract

The present invention discloses a Zr-MOF material for one-step purification of ethylene and propylene and a preparation method thereof. This material can purify olefins in a one-step manner from a C2 or C3 three-component mixed gas, and has two mutually perpendicular one-dimensional pore channels in the shapes of "pear" and rhombus, with a structural general formula of ZrO(C 34 H 24 O 16 S2). This MOF material exhibits a high alkane adsorption capacity and a high separation selectivity for olefins. This material can purify ethylene in a one-step manner from a C2 three-component mixed gas (ethane / ethylene / acetylene) and purify propylene in a one-step manner from a C3 three-component mixed gas (propane / propylene / propyne) in a dynamic breakthrough experiment. The novel Zr-MOF material constructed in the present invention (named NKU-301) not only has high stability and can purify olefins in a one-step manner from a three-component mixed gas in an industrial environment, but also provides a new design strategy and theoretical guidance for the design and synthesis of adsorbent materials for highly efficient one-step separation of olefins.

Description

Technical Field

[0001] The present invention relates to the technical field of MOF material preparation, and specifically relates to a preparation method of a hexanuclear cluster-based Zr-MOF material and its gas separation application for one-step purification of olefins in a C2, C3 three-component mixed gas. Background Art

[0002] Ethylene and propylene are one of the most important chemical raw materials in the petrochemical field. Crude olefin products can be obtained by industrial petroleum cracking or fractionation of hydrocarbon mixtures, and are mixed with a small amount of impurities, mainly including alkanes (ethane and propane) and alkynes (acetylene and propyne). Since olefins are raw materials for manufacturing high-value chemical products, it is a major and difficult task to remove these impurities by an energy-saving and environment-friendly approach to obtain polymer-grade olefins. So far, the most commonly used olefin purification methods are low-temperature distillation to remove alkanes and solvent extraction of alkynes or noble metal-catalyzed hydrogenation. As is well known, traditional industrial purification technologies are costly and energy-intensive, and will cause serious energy losses in industrial separation. The separation of alkanes and olefins, as one of the seven key chemical separations, accounts for about 0.3% of the global energy consumption. Therefore, the development of new energy-saving separation methods and the design and synthesis of green, environment-friendly and sustainable high-performance adsorbent materials have great research significance.

[0003] Zirconium-based metal-organic frameworks (Zr-MOFs) are considered to be one of the ideal platforms for constructing efficient, green and economical adsorbent materials due to their inherent crystalline characteristics, designable pore structures and topological networks. However, in fact, most Zr-MOF materials have low alkane / olefin selectivity, so their performance is not outstanding. With the different types and increasing amounts of competing components, the alkane / olefin selectivity is further reduced. Therefore, it is a challenging scientific problem to adopt appropriate design strategies to design and synthesize new Zr-MOF materials with excellent adsorption and separation advantages oriented by functions. Summary of the Invention

[0004] The purpose of the present invention is to provide an adsorbent material based on a hexanuclear cluster-based Zr-MOF, its preparation method and application for simultaneously separating and purifying olefins in a C2, C3 three-component mixed gas in one step, aiming at the shortage of the number and performance of existing one-step purification olefin adsorbent materials. This adsorbent can not only separate ethylene in one step in a C2 three-component system, but also separate propylene in one step in a C3 three-component system with greater separation difficulty. It not only preferentially adsorbs alkanes and alkynes and has a high adsorption capacity, but also has the advantages of recyclability and a long separation time.

[0005] Technical Solution of the Present Invention

[0006] A Zr-MOF material for one-step purification of ethylene and propylene. The material is an adsorbent material of a hexanuclear cluster-based zirconium metal-organic framework, which is a framework material with an sqc topological network structure. The structural general formula is ZrO(C 34 H 24 O 16 S2), named NKU-301. The terminal coordinated water on the equatorial plane of the hexanuclear zirconium cluster in this material can serve as a hydrogen bond donor, exposing a large number of adsorption sites pointing to the pores. The polar thiophene S atoms can serve as electron donors, thus realizing the one-step separation and purification of olefins. It is worth mentioning that the special topological network enables this material to have two mutually perpendicular one-dimensional pores running through each other. One is a "pear-shaped" pore, and the other is a rhombic pore, making it have a high adsorption capacity and appropriate pore size, making it more suitable for the one-step separation and purification of three components of propylene.

[0007] A preparation method of the Zr-MOF material for one-step separation and purification of ethylene and propylene includes the following steps:

[0008] (1) Mix an organic ligand 2,3,5,6-tetrakis(4-carboxyphenyl)thieno[3,2-b]thiophene (H4TCPTT), a metal salt, a templating agent trifluoroacetic acid, and a solvent in a certain proportion, and carry out a hydrothermal reaction. After the synthesis is completed, filter, wash, and dry to initially obtain the adsorbent material NKU-301 crystal of the hexanuclear cluster-based zirconium metal-organic framework with the structural general formula ZrO(C 34 H 24 O 16 S2). The molar ratio of the organic ligand to the metal salt is 1:(6-10);

[0009] (2) Exchange the initially obtained crystal material with an ethanol solution, and perform heat degassing treatment to obtain the final adsorbent material NKU-301.

[0010] Furthermore, the metal salt is a zirconium salt, specifically zirconium oxychloride octahydrate or zirconium tetrachloride;

[0011] Furthermore, the solvent is N,N-dimethylformamide (DMF);

[0012] Furthermore, the temperature of the hydrothermal reaction is 100-130 °C; the reaction time is 48-96 h, preferably the reaction temperature is 110-120 °C, and preferably the reaction time is 48 h-72 h.

[0013] The Zr-MOF material provided by the present invention can be applied to the one-step separation and purification of olefins. It can separate and purify olefins from a C2, C3 three-component mixed gas in one step. It can not only separate ethylene from the C2 three-component system in one step, but also separate propylene from the C3 three-component system with greater separation difficulty in one step.

[0014] Advantages and beneficial effects of the present invention:

[0015] (1) The preparation process of the Zr-MOF material is simple and its structure is stable.

[0016] (2) The Zr-MOF material has a large porosity, a high specific surface area, and good cycle stability and recyclability.

[0017] (3) The MOF material has a high selectivity for separating alkanes / alkenes, can be recycled, and is promising for use in practical industrial applications such as petrochemical industry to achieve one-step separation of propylene. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the crystal structure of the material in Example 1. (a) is a diagram of the secondary building unit, including a hexanuclear zirconium cluster as an inorganic building block and 2,3,5,6-tetrakis(4-carboxyphenyl)thieno[3,2-b]thiophene with four connections as an organic building block. (b) is an electrostatic potential map of the pores of NKU-301. (c) is the three-dimensional network structure and topological structure of NKU-301.

[0019] Figure 2 It is a diagram of the crystal interpenetrating pores of the material in Example 1.

[0020] Figure 3 It is the PXRD diffraction pattern of the material in Example 1 in different solvents.

[0021] Figure 4 It is the PXRD diffraction pattern of the material in Example 1 in aqueous solutions with different pH values.

[0022] Figure 5 It is the nitrogen adsorption isotherm curve and pore size distribution diagram measured for the material in Example 1 at 77K.

[0023] Figure 6 It is the adsorption isotherm diagram of the material in Example 1. Among them, (a) is the adsorption isotherm of ethane, ethylene, and acetylene of NKU-301 at 298K. (b) is the adsorption isotherm of propane, propylene, and propyne of NKU-301 at 298K. (c) is the adsorption isotherm of ethane, ethylene, and acetylene of NKU-301 at 308K. (d) is the adsorption isotherm of propane, propylene, and propyne of NKU-301 at 308K.

[0024] Figure 7 It is the C2 three-component density distribution diagram of the material in Example 1 simulated by grand canonical Monte Carlo. (a) is at 1 kPa, (b) is at 10 kPa, and (c) is at 100 kPa.

[0025] Figure 8 C3 three-component density distribution diagrams of the materials in Example 1 obtained by grand canonical Monte Carlo simulation. (a) is at 1 kPa, (b) is at 10 kPa, and (c) is at 100 kPa.

[0026] Figure 9 Analysis diagrams of the interactions of C2 three-component and C3 three-component of the materials in Example 1 obtained by grand canonical Monte Carlo simulation. (a) is for ethane, the interaction is between the gas molecule and the bithiophene ring, and the distance is between the gas molecule and the S atom, and the distance is The binding energy is 26.79 kJ / mol; (b) is for ethylene, the interaction is between the gas molecule and the bithiophene ring, and the distance is between the gas molecule and the benzene ring, and the distance is The binding energy is 25.28 kJ / mol; (c) is for acetylene, the interaction is between the gas molecule and the S atom, and the distance is between the gas molecule and the benzene ring, and the distance is The binding energy is 26.42 kJ / mol, (d) is for propane, the interaction is between the gas molecule and the bithiophene ring, and the distance is between the gas molecule and the S atom, and the distance is The acting binding energy is 31.27 kJ / mol, (e) is for propylene, the interaction is between the gas molecule and the bithiophene ring, and the distance is between the gas molecule and the S atom, and the distance is The binding energy is 28.85 kJ / mol, (f) is for propyne, the interaction is between the gas molecule and the S atom, and the distance is between the gas molecule and the benzene ring, and the distance is between the gas molecule and the O atom, and the distance is The binding energy is 32.78 kJ / mol.

[0027] Figure 10 Schematic diagram of the experimental device for the dynamic breakthrough experiment of the materials in Example 1.

[0028] Figure 11It is the experimental diagram of the dynamic breakthrough of materials in Example 1. (a) is the breakthrough curve of two components of ethane / ethylene (10 / 90, v / v) of NKU-301 at 298K, (b) is the breakthrough curve of two components of propane / propylene (10 / 90, v / v) of NKU-301 at 298K, (c) is the breakthrough curve of three components of ethane / ethylene / acetylene (9 / 90 / 1, v / v / v) of NKU-301 at 298K, (d) is the breakthrough curve of three components of propane / propylene / propyne (9 / 90 / 1, v / v / v) of NKU-301 at 298K, (e) is the breakthrough curve of three components of propane / propylene / propyne (9 / 90 / 1, v / v / v) of NKU-301 at 308K, (f) is the cyclic breakthrough curve of three components of propane / propylene / propyne (9 / 90 / 1, v / v / v) of NKU-301 at 298K. Detailed implementation mode

[0029] To make the purpose, technical solutions and advantages of the present invention clearer, the content of the present invention will be further clarified below in conjunction with the drawings and embodiments. However, these examples do not limit the protection scope of the present invention. Based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.

[0030] Example 1

[0031] Synthesis of NKU-301 material

[0032] Dissolve 10 mg of organic ligand H4TCPTT, 20 mg of zirconium oxychloride octahydrate, and 0.30 mL of trifluoroacetic acid in 3 mL of DMF, ultrasonicate for 15 min, and react at 120 °C for 48 h. After the reaction, slowly cool to room temperature in air. Rinse 3 times with DMF during suction filtration, and obtain a relatively pure Zr-MOF material after drying, named NKU-301. The schematic diagram of the microscopic crystal structure is shown in Figure 1 . The obtained crystal material was exchanged in ethanol for three days, three times a day using the solvent exchange method, and then vacuum dried at 120 °C for 12 h to obtain purified NKU-301.

[0033] To test the solvent stability and pH stability of NKU-301, the synthesized fresh sample was soaked in common organic solvents and aqueous solutions with different pH values for 72 h, and then the PXRD data of the sample was measured ( Figure 2 and Figure 3 ). It can be seen from the figure that the material still maintains good structural integrity, indicating that it has good solvent stability and pH stability.

[0034] To test the specific surface area of NKU-301, a 77K nitrogen isothermal adsorption test was carried out. The results are shown in Figure 4, the BET specific surface area is 1200 m 2 ·g –1 .

[0035] To test the adsorption capacity of NKU-301, the adsorption curve test of the material was carried out ( Figure 5 ), and the results showed that at room temperature and one atmosphere, the ethane adsorption capacity of the material was 68.3 cm 3 g –1 , the propane adsorption capacity was 124.6 cm 3 g –1 , and the separation selectivity of propane / propylene reached more than 2 under 0.1 atm. Therefore, the material as a whole showed excellent olefin separation performance and was an adsorbent material for one-step separation and purification of ethylene and propylene in a ternary component at the same time.

[0036] To further analyze the action mechanism of NKU-301 on C2 and C3 gas molecules, the adsorption behavior of NKU-301 and different gas molecules from low pressure to high pressure was simulated by grand canonical Monte Carlo simulation (GCMC). The results showed that the gas molecules were mainly distributed at the top of the special "pear-shaped" pores in the sqc network, that is, in the confined space "clamped" by two ligands ( Figure 7 and Figure 8 ). Olefins and alkynes mainly have van der Waals interactions with the bithiophene ring, benzene ring and polar S atoms on the ligand, while alkanes can have more van der Waals interactions than alkynes and olefins. Therefore, the force is the most and the binding energy is the strongest ( Figure 9 ). According to the different binding energies of the adsorbent framework and gas molecules, NKU-301 can be applied to the separation field of olefins in C2 and C3.

[0037] To detect the one-step separation and purification effect of NKU-301 on ethylene and propylene, a dynamic breakthrough experiment was carried out according to the device shown in Figure 10 as shown in Figure 11As shown in the figure, (a) is the breakthrough curve of the two-component of ethane / ethylene (10 / 90, v / v) on NKU-301 at 298K, (b) is the breakthrough curve of the two-component of propane / propylene (10 / 90, v / v) on NKU-301 at 298K, (c) is the breakthrough curve of the three-component of ethane / ethylene / acetylene (9 / 90 / 1, v / v / v) on NKU-301 at 298K, (d) is the breakthrough curve of the three-component of propane / propylene / propyne (9 / 90 / 1, v / v / v) on NKU-301 at 298K, (e) is the breakthrough curve of the three-component of propane / propylene / propyne (9 / 90 / 1, v / v / v) on NKU-301 at 308K, and (f) is the cyclic breakthrough curve of the three-component of propane / propylene / propyne (9 / 90 / 1, v / v / v) on NKU-301 at 298K. The results show that NKU-301 can achieve the one-step separation and purification of ethylene in the C2 three-component and ethylene and propylene in the C3 three-component (separation time interval > 4 minutes). The adsorbent material has good recyclability. More notably, this MOF adsorbent material is the first example that can purify ethylene in the C2 three-component in one step and also purify propylene in the C3 three-component in one step.

[0038] Example 2

[0039] Synthesis of NKU-301 Material

[0040] Dissolve 10 mg of the organic ligand H4TCPTT, 30 mg of zirconium oxychloride octahydrate, and 2 mL of formic acid (trifluoroacetic acid as the template agent is replaced by formic acid) in 5 mL of DMF, ultrasonicate for 15 min, and react at 120 °C for 48 h. The remaining operations and conditions are the same as in Example 1.

Claims

1. A Zr-MOF material for one-step purification of ethylene and propylene. The material is a hexanuclear cluster-based zirconium metal-organic framework adsorbent material with two mutually perpendicular one-dimensional pores. One is a "pear-shaped" pore, and the other is a rhombic pore. The structural general formula is ZrO(C 34 H 24 O 16 S2), with an sqc topological network structure, named NKU-301; The preparation method of the Zr-MOF material comprises the following steps: (1) Mix the organic ligand 2,3,5,6-tetrakis(4-carboxyphenyl)thieno[3,2- b thiophene, metal salt, templating agent trifluoroacetic acid and solvent in proportion, carry out hydrothermal reaction. After synthesis is completed, carry out suction filtration, washing and drying to preliminarily obtain the hexanuclear cluster-based zirconium metal-organic framework adsorbent material with the structural general formula ZrO(C 34 H 24 O 16 S2); the molar ratio of the organic ligand to the metal salt is 1:(6~10); (2) The preliminarily obtained crystal adsorbent material is exchanged with an ethanol solution and subjected to heat degassing treatment to finally obtain the adsorbent material NKU-301.

2. The Zr-MOF material for one-step purification of ethylene and propylene according to claim 1, wherein The metal salt is a zirconium salt, which is zirconium oxychloride octahydrate or zirconium tetrachloride.

3. The Zr-MOF material for one-step purification of ethylene and propylene according to claim 1, wherein The solvent is N,N-dimethylformamide.

4. The Zr-MOF material for one-step purification of ethylene and propylene according to claim 1, wherein The temperature of the hydrothermal reaction is 100 °C to 130 °C; the reaction time is 48–96 h.

5. The Zr-MOF material for one-step purification of ethylene and propylene according to claim 4, characterized in that, The temperature of the hydrothermal reaction is 110 °C - 120 °C, and the reaction time is 48 h to 72 h.

6. Use of the Zr-MOF material according to claim 1 in the one-step separation and purification of olefins.

7. The application according to claim 6, wherein The use is the one-step separation and purification of olefins from a C2, C3 three-component mixed gas. The Zr-MOF material can not only separate ethylene in one step in the C2 three-component system, but also separate propylene in one step in the C3 three-component system with greater separation difficulty.

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