An al-based metal-organic framework material, a preparation method thereof and application thereof in ethane-ethylene separation

Abstract

The application discloses an aluminum-based metal organic framework material, a preparation method thereof and application of the aluminum-based metal organic framework material in ethane-ethylene separation, and belongs to the technical field of metal organic framework materials. The preparation method comprises the following steps: 1) uniformly mixing a metal aluminum salt and an organic ligand in a solvent, and then adding alkali to adjust the pH value to 8-11 to obtain a precursor solution; wherein the solvent is a polar mixed solution of monohydric alcohol and acetonitrile; and 2) performing a hydrothermal reaction on the precursor solution at a temperature of 90-130 DEG C to obtain the aluminum-based metal organic framework material. The preparation method has the advantages of simple preparation process and low cost, and the obtained aluminum-based metal organic framework material has a suitable pore chemical surface environment and pore size, is beneficial to the selectivity and static adsorption capacity of ethane molecules, has a high ethane adsorption capacity, and also has excellent C2H6 / C2H4 separation selectivity, and therefore has an important application prospect.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework materials technology, specifically relating to an aluminum-based metal-organic framework material, its preparation method, and its application in ethane-ethylene separation. Background Technology

[0002] Ethylene (C2H4) is a crucial raw material for the petrochemical industry in manufacturing various high-value chemical products, with a global annual production exceeding 200 million tons, surpassing any other organic compound. Industrial production of C2H4 primarily involves steam cracking and ethane (C2H6) dehydrogenation, inevitably resulting in a certain amount of C2H6 impurities (6%). Therefore, further purification is necessary to obtain high-purity C2H4 products. However, due to similar petrochemical properties, such as boiling points (C2H6 184.55K, C2H4 169.42K) and kinetic diameters (C2H6...),... C2H4 The separation of C2H6-C2H4 mixtures has been listed as one of the seven world-changing chemical separation techniques. Currently, cryogenic distillation is the main technology for industrial separation of C2H6-C2H4 mixtures, but this energy-intensive, thermally driven process typically requires distillation columns at low temperatures (180-258 K) and high pressures (7-28 bar). Therefore, developing more energy-efficient alternative technologies and materials has become an urgent pursuit. Non-thermally driven physical separation technologies based on porous materials have advantages such as low energy consumption and high efficiency, and have broad application prospects in the separation of light hydrocarbons.

[0003] Metal-organic frameworks (MOFs), as unique porous materials, have been extensively studied in recent years for the separation of C2H6 / C2H4 due to their designable pore structures. Currently known separation systems are primarily C2H4-selective adsorbents, mainly based on two separation mechanisms. One is to enhance the selective interaction between C2H4 and the framework by introducing open metal sites (OMSs). The other is a molecular sieving effect based on MOF pore optimization, allowing small C2H4 molecules to pass through the channels while blocking C2H6 molecules. However, this system requires additional heating and / or multiple inert gas purgings to remove adsorbed C2H4 from the material, increasing the complexity and energy consumption of the process. In contrast, the less studied C2H6-selective MOFs can easily obtain pure C2H4 gas in a single step, significantly reducing energy consumption compared to C2H4-selective MOFs. Currently, research on C2H6-selective MOFs is relatively limited because C2H4 binding sites are easier to introduce into the framework than C2H6 binding sites. Summary of the Invention

[0004] The purpose of this invention is to provide an aluminum-based metal-organic framework material, its preparation method, and its application in ethane-ethylene separation. The obtained aluminum-based metal-organic framework material has a suitable pore chemistry surface environment and pore size, which is beneficial to the selectivity of ethane molecules and static adsorption capacity. While having a high ethane adsorption capacity, it also has excellent C2H6 / C2H4 separation selectivity.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing an aluminum-based metal-organic framework material for ethane-ethylene separation is provided, comprising the following steps:

[0007] 1) Add the aluminum salt and organic ligand to the solvent and mix them evenly. Then add alkali to adjust the pH to 8-11 to obtain the precursor solution. The solvent is a polar mixture of monohydric alcohol and acetonitrile.

[0008] 2) The precursor solution obtained in step 1) is subjected to a hydrothermal reaction at a temperature of 90-130℃ to obtain an aluminum-based metal-organic framework material.

[0009] According to the above scheme, in step 1), the aluminum salt is one of aluminum chloride hexahydrate and aluminum nitrate hexahydrate.

[0010] According to the above scheme, in step 1), the organic ligand is at least one of 2,5-dihydroxyterephthalic acid, 2-hydroxyterephthalic acid, 2-methylterephthalic acid, and 2-aminoterephthalic acid.

[0011] Preferably, the organic ligand is a mixture of 2-hydroxyterephthalic acid and 2-aminoterephthalic acid, or a mixture of 2-aminoterephthalic acid and 2-methylterephthalic acid. More preferably, the molar ratio of the two organic ligands in the mixture is 0.5-2:1.

[0012] According to the above scheme, in step 1), the molar ratio of the aluminum salt and the organic ligand is 1-5:1.

[0013] According to the above scheme, in step 1), the molar volume ratio of organic ligand to solvent is 1 mol: 5-20 L.

[0014] According to the above scheme, in step 1), the monohydric alcohol is methanol, ethanol or propanol.

[0015] According to the above scheme, in step 1), the volume ratio of alcohol to acetonitrile is 1-3:1.

[0016] According to the above scheme, in step 1), the alkali is sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide, or ammonia.

[0017] According to the above scheme, in step 2), the temperature of the hydrothermal reaction is 110-130℃.

[0018] According to the above scheme, in step 2), the reaction time of the hydrothermal reaction is 5-12 hours.

[0019] According to the above scheme, in step 2), after the hydrothermal reaction is completed, the product is cooled to room temperature, washed with water and purified with methanol. Fresh methanol is replaced every 10-15 hours, and the number of exchanges is 5-7 times. After drying, the aluminum-based metal-organic framework material is obtained.

[0020] An aluminum-based metal-organic framework material prepared by the above method is provided.

[0021] According to the above scheme, the pore size distribution of the aluminum-based metal-organic framework material is as follows:

[0022] According to the above scheme, the specific surface area of ​​the aluminum-based metal-organic framework material is 800-1100 m². 2 / g.

[0023] This invention provides an application of the aforementioned aluminum-based metal-organic framework material as an adsorbent in the separation of ethane / ethylene gases.

[0024] According to the above scheme, the aluminum-based metal-organic framework material is activated at 100-150℃ for 8-12 hours before ethane / ethylene gas separation.

[0025] According to the above scheme, the adsorption temperature is 0-100℃ and the adsorption pressure is 0-1 bar.

[0026] This invention provides a method for preparing aluminum-based metal-organic frameworks (MOFs) for ethane-ethylene separation. A polar mixed solution of alcohols and acetonitrile is used as the solvent, and the pH of the system is adjusted to 8-11. The MOF is then prepared by self-assembly of aluminum salts and ligands under hydrothermal reaction. On the one hand, the alkaline conditions allow the solvent to form hydrogen bonds or coordination bonds with the organic ligands during crystallization, thus affecting the growth mode of the MOF crystals and contributing to obtaining MOF crystals with high crystallinity and purity. On the other hand, it also helps to improve the crystallization efficiency of MOFs, shorten the synthesis time, and reduce production costs. Furthermore, this invention also achieves the regulation of the pore chemical environment of the MOF by changing the proportion and type of ligands, giving it suitable pore chemical surfaces and pore sizes. This is beneficial for the entry and diffusion of ethane molecules and for the interaction between gas molecules and pore walls, thereby improving ethane selectivity.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention provides a method for preparing an aluminum-based metal-organic framework material for ethane-ethylene separation. A polar mixed solution of alcohol and acetonitrile is used as the solvent, and the pH of the system is adjusted to 8-11. The aluminum-based metal-organic framework material is then prepared by self-assembly of aluminum salt and ligands under hydrothermal reaction. The obtained aluminum-based metal-organic framework material possesses a suitable pore chemistry surface environment and pore size, which is beneficial for ethane molecule selectivity and static adsorption capacity. While exhibiting high ethane adsorption capacity, it also demonstrates excellent C2H6 / C2H4 separation selectivity. Specifically, at 298 K and 1 bar, its IAST selectivity for C2H6 / C2H4 can reach 4.2, which is higher than most other ethane-selective materials, showing significant application potential.

[0029] 2. The preparation process of this invention is simple and low-cost, and it can be prepared in large quantities in a short time. In addition, it has excellent separation effect and is expected to be applied industrially. Attached Figure Description

[0030] Figure 1 The images show the XRD patterns of the metal-organic framework materials prepared in Examples 1-6.

[0031] Figure 2 The N2 adsorption-desorption curves (top) and pore size distribution diagrams (bottom) of the metal-organic framework materials prepared in Examples 1-6 are shown.

[0032] Figure 3 The adsorption curves of ethane / ethylene for the hierarchical porous single-crystal metal-organic framework materials prepared in Examples 1, 5 and 6 at 298 K; pressure: 0-1 bar.

[0033] Figure 4 The separation performance of the hierarchical porous single-crystal metal-organic framework materials prepared in Examples 1, 5 and 6 and other representative C2H6 selective MOFs are compared, and the C2H6 adsorption capacity is plotted.

[0034] Figure 5 The image shows the cyclic adsorption of ethane on the hierarchical porous single-crystal metal-organic framework material prepared in Example 5 at 298 K.

[0035] Figure 6 The breakthrough curve is shown for the ethane / ethylene (50 / 50, V / V) obtained in Example 5.

[0036] Figure 7 These are the preferred adsorption sites for (a) C2H4 and (b) C2H6 in the metal-organic framework obtained in Example 1. Detailed Implementation

[0037] To make the objectives, methods, and advantages of the present invention clearer, the present invention will now be further described in conjunction with embodiments, but is not limited thereto.

[0038] Example 1

[0039] A method for preparing an aluminum-based metal-organic framework material is provided, comprising the following steps:

[0040] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 609 mg (3.07 mmol) of 2,5-dihydroxyterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. A suitable amount of sodium hydroxide was then added to adjust the pH to 9.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, with fresh methanol replaced every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-(OH)₂.

[0041] like Figure 1 The PXRD pattern of Al-(OH)2 and the PXRD pattern simulated based on crystal data confirm that it has high crystallinity, and the two agree well, indicating excellent phase purity. Figure 2 The N2 adsorption-desorption curve of Al-(OH)2 shows a completely reversible type I microporous adsorption curve, and the obtained specific surface area is 935 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0042] Example 2

[0043] A method for preparing an aluminum-based metal-organic framework material is provided, comprising the following steps:

[0044] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 559 mg (3.07 mmol) of 2-hydroxyterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. Then, an appropriate amount of sodium hydroxide was added to adjust the pH to 10.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, replacing the methanol every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-OH.

[0045] like Figure 1 The PXRD patterns of Al-OH and those simulated based on crystal data confirm high crystallinity, showing good agreement and excellent phase purity. Figure 2 The N2 adsorption-desorption curve of Al-OH exhibits a completely reversible type I microporous adsorption curve, with a specific surface area of ​​1035 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0046] Example 3

[0047] A method for preparing an aluminum-based metal-organic framework material is provided, comprising the following steps:

[0048] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 553 mg (3.07 mmol) of 2-methylterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. A suitable amount of sodium hydroxide was then added to adjust the pH to 11.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and the mixture was cooled to room temperature, it was washed three times with water and then purified with methanol, with fresh methanol replaced every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-CH3.

[0049] like Figure 1 The PXRD pattern of Al-CH3 and the PXRD pattern simulated based on crystal data confirm its high crystallinity; the two patterns agree well, indicating excellent phase purity. Figure 2 The N2 adsorption-desorption curve of Al-CH3 exhibits a completely reversible type I microporous adsorption curve, with a obtained specific surface area of ​​962 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0050] Example 4

[0051] A method for preparing an aluminum-based metal-organic framework material is provided, comprising the following steps:

[0052] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 556 mg (3.07 mmol) of 2-aminoterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. Then, an appropriate amount of sodium hydroxide was added to adjust the pH to 9.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, replacing the methanol every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-NH2.

[0053] like Figure 1The PXRD pattern of Al-NH2 and the PXRD pattern simulated based on crystal data verified the phase purity, and the two showed good agreement, indicating high crystallinity. Figure 2 The N2 adsorption-desorption curve of Al-NH2 shows a completely reversible type I microporous adsorption curve, and the obtained specific surface area is 1021 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0054] Example 5

[0055] A method for preparing aluminum-based metal-organic framework materials is provided, comprising the following steps:

[0056] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate, 280 mg (1.54 mmol) of 2-hydroxyterephthalic acid, and 279 mg (1.54 mmol) of 2-aminoterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. A suitable amount of sodium hydroxide was then added to adjust the pH to 9.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, with fresh methanol replaced every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-(OH). 0.5 (NH2) 0.5 .

[0057] like Figure 1 Al-(OH) 0.5 (NH2) 0.5 The PXRD pattern and the PXRD pattern simulated based on crystal data confirm that it has high crystallinity, and the two match well, indicating excellent phase purity. Figure 2 Al-(OH) 0.5 (NH2) 0.5 The N2 adsorption-desorption curves exhibited completely reversible type I microporous adsorption curves, with a obtained specific surface area of ​​852 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0058] Example 6

[0059] A method for preparing aluminum-based metal-organic framework materials is provided, comprising the following steps:

[0060] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate, 279 mg (1.54 mmol) of 2-aminoterephthalic acid, and 277 mg (1.54 mmol) of 2-methylterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. A suitable amount of sodium hydroxide was then added to adjust the pH to 9.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, with fresh methanol replaced every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-(CH3). 0.5 (NH2) 0.5 .

[0061] like Figure 1 Al-(CH3) 0.5 (NH2) 0.5 The PXRD pattern and the PXRD pattern simulated based on crystal data confirm that it has high crystallinity, and the two match well, indicating excellent phase purity. Figure 2 Al-(CH3) 0.5 (NH2) 0.5 The N2 adsorption-desorption curves exhibited completely reversible type I microporous adsorption curves, with a obtained specific surface area of ​​839 m². 2 / g, pore size distribution is Small molecule gases are allowed to pass through freely.

[0062] Comparative Example 1

[0063] A method for preparing aluminum-based metal-organic framework materials is provided, comprising the following steps:

[0064] 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 556 mg (3.07 mmol) of 2-aminoterephthalic acid were weighed and added to 40 mL of a 1:1 methanol / acetonitrile mixture. The mixture was sonicated for 30 min to ensure homogeneity. Then, an appropriate amount of sodium hydroxide was added to adjust the pH to 12.0, followed by a hydrothermal reaction (125 °C, 5 h). After the reaction was complete and cooled to room temperature, the mixture was washed three times with water and purified with methanol, replacing the methanol every 12 h for a total of 6 exchanges. The mixture was then placed in a vacuum drying oven at 60 °C for 24 h to obtain an aluminum-based metal-organic framework material, denoted as Al-NH2 (pH = 12).

[0065] Adsorption separation tests were conducted using the aluminum-based metal-organic framework material obtained in Comparative Example 1, and it was found that it had virtually no ethane-ethylene separation performance.

[0066] The aluminum-based metal-organic framework materials prepared in Examples 1, 5, and 6 were used as adsorbents for the adsorption and separation of ethane / ethylene. The specific steps are as follows:

[0067] 100 mg of the obtained aluminum-based metal-organic framework material was weighed out and vacuum dried at 120 °C for about 12 h to obtain the activated adsorbent. Then, its single-component adsorption curves for ethane and ethylene were tested at 298 K.

[0068] Figure 3 The graphs show the adsorption curves of the aluminum-based metal-organic frameworks prepared in Examples 1, 5, and 6 for ethane / ethylene at 298 K. The adsorption capacity of C2H6 was consistently higher than that of C2H4 in all tests. Furthermore, at 298 K and 1 bar, the adsorption capacities of Al-(OH)2 for ethane and ethylene were 5.3 mmol / g and 3.2 mmol / g, respectively. The calculated IAST selectivity of Al-(OH)2 for ethane / ethylene (50 / 50, v / v) was 3.4. 0.5 (NH2) 0.5 The adsorption capacities for ethane and ethylene were 4.8 mmol / g and 2.4 mmol / g, respectively. The calculated Al-(OH)⁻... 0.5 (NH2) 0.5 The IAST selectivity for ethane / ethylene (50 / 50, v / v) was 4.1, and for Al-(CH3)... 0.5 (NH2) 0.5 The adsorption capacities for ethane and ethylene were 5.0 mmol / g and 2.4 mmol / g, respectively. The calculated Al-(CH3) adsorption values... 0.5 (NH2) 0.5 The IAST selectivity for ethane / ethylene (50 / 50, v / v) was 4.2. This is because the MOF pores contain abundant amino and hydroxyl or methyl groups, and lack OMS (unsaturated sites) (if metals have unsaturated sites, they will preferentially adsorb ethylene, leading to a decrease in ethane selectivity). This allows the CH bonds in the ethane molecule to form more and stronger interactions with the MOF framework than with ethylene molecules (e.g., CH…N, CH…O, CH…π, etc.), resulting in preferential adsorption of C2H6 over C2H4. Furthermore, its higher ethane adsorption capacity and separation performance surpass those of many other ethane-selective materials with excellent performance. Figure 4 ).

[0069] Adsorption cycle test ( Figure 5 This indicates that Al-(OH) 0.5 (NH2) 0.5It exhibits excellent reusability and regeneration performance. Thanks to the fully reversible adsorption and desorption process, C2H6 and C2H4 molecules can avoid aggregation, thus preventing channel blockage. This characteristic effectively avoids the inherent defects of MOF materials with strong adsorption sites (such as OMS).

[0070] A 50mm x 10mm stainless steel packed column was used, filled with 2g of degassed Al-(OH)₂. 0.5 (NH2) 0.5 A C2H4 / C2H6 (50:50, V / V) breakthrough experiment was conducted at 298 K and 1 bar, with a mixed gas flow rate of 2.0 mL / min. Figure 6 As can be seen from this, Al-(OH) 0.5 (NH2) 0.5 It can effectively separate C2H4 / C2H6 (50:50, V / V) gas mixtures. C2H6 breaks through after 15.6 minutes and quickly reaches saturation. C2H4 does not begin to break through until after 61.4 minutes, indicating that the aluminum-based metal-organic framework material has completely adsorbed the ethane component, thus ensuring the purity of ethylene (>99%).

[0071] The adsorption sites for ethylene and ethane were studied using quantum chemical theoretical calculations. Figure 7 As can be seen, the interaction force distance between ethylene molecules and the pores of the metal-organic framework material obtained in Example 1 is... Compared to ethane molecules Furthermore, this indicates that the metal-organic framework material obtained in Example 1 has a strong electrostatic interaction with ethane, exhibiting a strong force for ethane adsorption and the ability to preferentially adsorb ethane.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum-based metal-organic framework material, characterized in that, Includes the following steps: 1) Add the aluminum salt and organic ligand to a solvent and mix thoroughly. Then, adjust the pH to 8-11 with alkali to obtain a precursor solution. The solvent is a polar mixture of monohydric alcohol and acetonitrile. The organic ligand is a mixture of 2-hydroxyterephthalic acid and 2-aminoterephthalic acid or a mixture of 2-aminoterephthalic acid and 2-methylterephthalic acid, with a molar ratio of 0.5-2:

1. The volume ratio of monohydric alcohol to acetonitrile in the solvent is 1-3:

1. The molar ratio of aluminum salt to organic ligand is 1-5:

1. 2) hydrothermal reaction of the precursor solution obtained in step 1) at a temperature of 90-130°C for 5-12 h to obtain an aluminum-based metal organic framework material; wherein: the pore size distribution of the obtained aluminum-based metal organic framework material is 4.8-7Å; the specific surface area is 800-1100 m 2 / g.

2. The preparation method according to claim 1, characterized in that, In step 1), the aluminum salt is one of aluminum chloride hexahydrate or aluminum nitrate hexahydrate.

3. The preparation method according to claim 1, characterized in that, In step 1), the monohydric alcohol is methanol, ethanol, or propanol; in step 1), the alkali is sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide, or ammonia.

4. An aluminum-based metal-organic framework material prepared by the preparation method according to any one of claims 1-3.

5. The application of the aluminum-based metal-organic framework material of claim 4 as an adsorbent in the separation of ethane / ethylene gas.

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