Aluminum-based metal organic framework material, preparation method thereof and application of aluminum-based metal organic framework material in ethane-ethylene separation

Abstract

The invention 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) adding a metal aluminum salt and an organic ligand into a solvent, uniformly mixing, 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) carrying out hydrothermal reaction on the precursor solution at 90-130 DEG C to obtain the aluminum-based metal organic framework material. The method is simple in preparation process and low in cost, and the obtained aluminum-based metal organic framework material has appropriate pore chemical surface environment and pore diameter, is beneficial to ethane molecular selectivity and static adsorption capacity, has high ethane adsorption capacity, also has excellent C2H6 / C2H4 separation selectivity and has important application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of metal organic framework materials, and in particular relates to an aluminum-based metal organic framework material and a preparation method thereof and application in ethane-ethylene separation. Background Art

[0002] Ethylene (C2H4) is one of the important raw materials for the manufacture of various high-value chemical products in the petrochemical industry, with an annual global production of more than 200 million tons, exceeding any other organic compound. The industrial production of C2H4 is mainly through steam cracking and dehydrogenation of ethane (C2H6), which inevitably contains a certain amount of C2H6 impurities (6%), so further purification is required to obtain high-purity C2H4 products. However, due to similar petrochemical properties, such as boiling point (C2H6 184.55K, C2H4 169.42K) and kinetic diameter (C2H6 C2H4 ), the separation of C2H6-C2H4 mixtures was listed as one of the seven chemical separations that changed the world. Currently, cryogenic distillation is the main technology for industrial separation of C2H6-C2H4 mixtures, but this energy-intensive heat-driven process usually requires a distillation tower with low temperature (180-258K) and high pressure (7-28bar). Therefore, the development of more energy-efficient alternative technologies and materials has become an urgent pursuit. Non-thermal driven physical separation technology based on porous materials has the advantages of low energy consumption and high efficiency, and has broad application prospects in the separation of light hydrocarbons.

[0003] Metal-organic frameworks (MOFs), as a unique porous material, have been widely studied in C2H6 / C2H4 separation in recent years due to their designable pore structure. The currently known separation systems are mainly C2H4-selective adsorbents, which are 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 the molecular sieving effect based on the optimization of MOF pores, which allows small C2H4 molecules to pass through the channel but prevents C2H6 molecules from passing through. However, for this system, additional heating and / or multiple inert gas purges are required to drive away the adsorbed C2H4 in the material, which increases the complexity and energy consumption of the process. In contrast, the less studied C2H6-selective MOF can easily obtain pure C2H4 gas in one step, and the energy consumption is greatly reduced compared with the C2H4-selective MOF. At present, C2H6-selective MOFs are relatively less studied because C2H4 binding sites in the framework are easier to introduce than C2H6 binding sites. Summary of the invention

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

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

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

[0007] 1) adding a metal aluminum salt and an organic ligand to a solvent and uniformly mixing them, then adding a base to adjust the pH to 8-11 to obtain a precursor solution; wherein the solvent is a polar mixed solution of a monohydric alcohol and acetonitrile;

[0008] 2) subjecting the precursor solution obtained in step 1) to a hydrothermal reaction at a temperature of 90-130° C. to obtain an aluminum-based metal organic framework material.

[0009] According to the above scheme, in step 1), the metal 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 metal aluminum salt to the organic ligand is 1-5:1.

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

[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 base is sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide or ammonia water.

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

[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, during which fresh methanol is replaced every 10-15 hours, the number of exchanges is 5-7 times, and the aluminum-based metal organic framework material is obtained by drying.

[0020] Provided is an aluminum-based metal organic framework material prepared by the method.

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

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

[0023] Provided is a use of the aluminum-based metal organic framework material as an adsorbent in ethane / ethylene gas separation.

[0024] According to the above scheme, the aluminum-based metal organic framework material is heat-activated at 100-150° C. for 8-12 hours and then ethane / ethylene gas separation is performed.

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

[0026] The present invention provides a method for preparing an aluminum-based metal organic framework material for ethane-ethylene separation, using a polar mixed solution of alcohols and acetonitrile as a solvent, adjusting the system pH to 8-11, and then preparing the aluminum-based metal organic framework material by self-assembly of metal aluminum salts and ligands under hydrothermal reaction; on the one hand, under alkaline conditions, the solvent can form hydrogen bonds or coordination bonds with organic ligands during the crystallization process, thereby affecting the growth mode of MOF crystals, which helps to obtain MOF crystals with high crystallinity and purity; on the other hand, it also helps to improve the crystallization efficiency of MOF, shorten the synthesis time, and reduce production costs. In addition, the present invention also achieves the regulation of the pore chemical environment of the metal organic framework material by changing the proportion and type of ligands, so that it has a suitable pore chemical surface and pore size, which is conducive to the entry and diffusion of ethane molecules, and is conducive to the interaction between gas molecules and pore walls, thereby improving the selectivity of ethane.

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

[0028] 1. The present invention provides a method for preparing an aluminum-based metal organic framework material for ethane-ethylene separation, wherein a polar mixed solution of alcohols and acetonitrile is used as a solvent, and the pH of the system is adjusted to 8-11, and then the aluminum-based metal organic framework material is prepared by self-assembly of a metal aluminum salt and a ligand under a hydrothermal reaction; the obtained aluminum-based metal organic framework material has a suitable pore chemical surface environment and pore size, which is beneficial to the ethane molecule selectivity and static adsorption capacity; while having a high ethane adsorption capacity, it also has excellent C2H6 / C2H4 separation selectivity, wherein at 298K and 1 bar, its C2H6 / C2H4IAST selectivity can reach 4.2, which is higher than most other ethane selective materials, and has important application prospects.

[0029] 2. The preparation process of the present invention is simple, low-cost, can be prepared in large quantities in a short time, and has excellent separation effect and is expected to be industrially applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the XRD pattern of the metal organic framework materials prepared in Examples 1-6.

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

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

[0033] Figure 4 Comparison of separation performance and C2H6 adsorption capacity of the hierarchical pore single crystal metal organic framework materials prepared in Example 1, Example 5 and Example 6 and other representative C2H6 selective MOFs.

[0034] Figure 5 This is the cyclic adsorption diagram of ethane on the hierarchical porous single crystal metal organic framework material prepared in Example 5 at 298K.

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

[0036] Figure 7 The preferential adsorption sites of (a) C2H4 and (b) C2H6 in the metal organic framework obtained in Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, method and advantages of the present invention more clear, the present invention is further described in conjunction with embodiments, but is not limited thereto.

[0038] Example 1

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

[0040] Weigh 2226 mg (9.22 mmol) of aluminum chloride hexahydrate and 609 mg (3.07 mmol) of 2,5-dihydroxyterephthalic acid and add them to 40 mL of a 1:1 methanol / acetonitrile mixed solution and mix them evenly by ultrasonication for 30 minutes. Then add an appropriate amount of sodium hydroxide to adjust the pH to 9.0, and then perform a hydrothermal reaction (125°C, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12 hours, and the number of exchanges is 6 times. Then put it in a 60°C vacuum drying oven for 24 hours to obtain an aluminum-based metal organic framework material, which is recorded as Al-(OH)2.

[0041] like Figure 1 The PXRD pattern of Al-(OH)2 and the PXRD pattern simulated based on crystal data verify that it has a high degree of crystallinity, and the two are in good agreement, with 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 specific surface area is 935m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0042] Example 2

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

[0044] Weigh 2226mg (9.22mmol) of aluminum chloride hexahydrate and 559mg (3.07mmol) of 2-hydroxyterephthalic acid and add them to 40mL of a 1:1 methanol / acetonitrile mixed solution and mix them evenly by ultrasonication for 30min. Then add an appropriate amount of sodium hydroxide to adjust the pH to 10.0, and then perform a hydrothermal reaction (125℃, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12h, and the number of exchanges is 6 times. Then put it in a 60℃ vacuum drying oven for 24h to obtain an aluminum-based metal organic framework material, which is recorded as Al-OH.

[0045] like Figure 1 The PXRD pattern of Al-OH and the PXRD pattern simulated based on crystal data verify that it has a high degree of crystallinity, and the two are in good agreement, with excellent phase purity. Figure 2 The N2 adsorption-desorption curve of Al-OH shows a completely reversible type I microporous adsorption curve, and the specific surface area is 1035m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0046] Example 3

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

[0048] Weigh 2226mg (9.22mmol) of aluminum chloride hexahydrate and 553mg (3.07mmol) of 2-methylterephthalic acid and add them to 40mL of a 1:1 methanol / acetonitrile mixed solution and mix them evenly by ultrasonication for 30min. Then add an appropriate amount of sodium hydroxide to adjust the pH to 11.0, and then perform a hydrothermal reaction (125℃, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12h, and the number of exchanges is 6 times. Then put it in a 60℃ vacuum drying oven for 24h to obtain an aluminum-based metal organic framework material, which is recorded as Al-CH3.

[0049] like Figure 1 The PXRD pattern of Al-CH3 and the PXRD pattern simulated based on crystal data verify that it has a high degree of crystallinity, and the two are in good agreement, with excellent phase purity. Figure 2 The N2 adsorption-desorption curve of Al-CH3 shows a completely reversible type I microporous adsorption curve, and the specific surface area is 962m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0050] Example 4

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

[0052] Weigh 2226mg (9.22mmol) of aluminum chloride hexahydrate and 556mg (3.07mmol) of 2-aminoterephthalic acid and add them to 40mL of a 1:1 methanol / acetonitrile mixed solution and mix them evenly by ultrasonication for 30min. Then add an appropriate amount of sodium hydroxide to adjust the pH to 9.0, and then perform a hydrothermal reaction (125℃, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12h, and the number of exchanges is 6 times. Then put it in a 60℃ vacuum drying oven for 24h to obtain an aluminum-based metal organic framework material, which is recorded as Al-NH2.

[0053] like Figure 1The PXRD pattern of Al-NH2 and the PXRD pattern simulated based on crystal data verify the phase purity, and the two are in good agreement, with high crystallinity. Figure 2 The N2 adsorption-desorption curve of Al-NH2 shows a completely reversible type I microporous adsorption curve, and the specific surface area is 1021m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0054] Example 5

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

[0056] Weigh 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, respectively, and add them to 40 mL of a methanol / acetonitrile mixed solution with a volume ratio of 1:1, and mix them evenly by ultrasonication for 30 minutes. Then, add an appropriate amount of sodium hydroxide to adjust the pH to 9.0, and then perform a hydrothermal reaction (125°C, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12 hours, and the number of exchanges is 6 times. Then put it in a 60°C vacuum drying oven for 24 hours to obtain an aluminum-based metal organic framework material, recorded as Al-(OH) 0.5 (NH2) 0.5 .

[0057] like Figure 1 , Al-(OH) 0.5 (NH2) 0.5 The PXRD pattern of the crystal data and the PXRD pattern simulated based on the crystal data verify that it has a high degree of crystallinity, and the two are in good agreement, with excellent phase purity. Figure 2 , Al-(OH) 0.5 (NH2) 0.5 The N2 adsorption-desorption curve shows a completely reversible type I microporous adsorption curve, and the specific surface area is 852m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0058] Example 6

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

[0060] Weigh 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, respectively, and add them to 40 mL of a methanol / acetonitrile mixed solution with a volume ratio of 1:1, and mix them evenly by ultrasonication for 30 minutes. Then, add an appropriate amount of sodium hydroxide to adjust the pH to 9.0, and then perform a hydrothermal reaction (125°C, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12 hours, and the number of exchanges is 6 times. Then put it in a 60°C vacuum drying oven for 24 hours to obtain an aluminum-based metal organic framework material, recorded as Al-(CH3) 0.5 (NH2) 0.5 .

[0061] like Figure 1 , Al-(CH3) 0.5 (NH2) 0.5 The PXRD pattern of the crystal data and the PXRD pattern simulated based on the crystal data verify that it has a high degree of crystallinity, and the two are in good agreement, with excellent phase purity. Figure 2 , Al-(CH3) 0.5 (NH2) 0.5 The N2 adsorption-desorption curve shows a completely reversible type I microporous adsorption curve, and the specific surface area is 839m 2 / g, pore size distribution is Allows small gas molecules to pass freely.

[0062] Comparative Example 1

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

[0064] Weigh 2226mg (9.22mmol) of aluminum chloride hexahydrate and 556mg (3.07mmol) of 2-aminoterephthalic acid and add them to 40mL of a 1:1 methanol / acetonitrile mixed solution and mix them evenly by ultrasonication for 30min. Then add an appropriate amount of sodium hydroxide to adjust the pH to 12.0, and then perform a hydrothermal reaction (125℃, 5h). After the reaction is completed, cool to room temperature, wash with water three times, and purify with methanol. During this period, fresh methanol is replaced every 12h, and the number of exchanges is 6 times. Then put it in a 60℃ vacuum drying oven for 24h to obtain an aluminum-based metal organic framework material, which is recorded as Al-NH2 (PH=12).

[0065] The aluminum-based metal organic framework material obtained in Comparative Example 1 was used for adsorption separation test, and it was found that there was basically no ethane and ethylene separation performance.

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

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

[0068] Figure 3 The adsorption curves of ethane / ethylene for the aluminum-based metal organic framework materials prepared in Examples 1, 5 and 6 at 298K are shown. The adsorption amount of C2H6 for all tests is always higher than that of C2H4. In addition, at 298K and 1 bar, the adsorption amounts of Al-(OH)2 for ethane and ethylene are 5.3mmol / g and 3.2mmol / g, respectively. The calculated IAST selectivity of Al-(OH)2 for ethane / ethylene (50 / 50, v / v) is 3.4. Al-(OH) 0.5 (NH2) 0.5 The adsorption amounts of ethane and ethylene are 4.8mmol / g and 2.4mmol / g respectively. 0.5 (NH2) 0.5 The IAST selectivity for ethane / ethylene (50 / 50, v / v) is 4.1, Al-(CH3) 0.5 (NH2) 0.5 The adsorption amounts of ethane and ethylene are 5.0mmol / g and 2.4mmol / g respectively. 0.5 (NH2) 0.5 The IAST selectivity for ethane / ethylene (50 / 50, v / v) is 4.2 respectively. This is because the MOF pores are rich in amino and hydroxyl or methyl groups, and there are no OMS (unsaturated sites) (if the metal has unsaturated sites, it will preferentially adsorb ethylene, which will lead to a decrease in ethane selectivity), so that the CH bonds in the ethane molecules can form more and stronger interaction forces with the MOF framework than ethylene molecules (such as CH...N, CH...O, CH...π, etc.), resulting in preferential adsorption of C2H6 over C2H4. In addition, its higher ethane adsorption capacity and separation performance are higher than many other ethane selective materials with excellent performance ( Figure 4 ).

[0069] Adsorption cycle test ( Figure 5 ) shows that Al-(OH) 0.5 (NH2) 0.5It has good reusability and regeneration performance. Thanks to the completely reversible adsorption and desorption process, C2H6 and C2H4 molecules can avoid aggregation and thus will not block the channel. This feature effectively circumvents the inherent defects of MOF materials with strong adsorption sites (such as OMS).

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

[0071] The adsorption sites of ethylene and ethane were studied by quantum chemical theoretical calculations. Figure 7 It can be seen that the interaction distance between ethylene molecules and the pores of the metal organic framework material obtained in Example 1 is Compared to ethane molecule Furthermore, it is shown that the metal organic framework material obtained in Example 1 has a stronger electrostatic effect on ethane, has a stronger force on ethane, and has the property of preferentially adsorbing ethane.

[0072] The above are only 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 in the protection scope of the present invention.

Claims

1. A method for preparing an aluminum-based metal organic framework material, characterized in that: The steps include: 1) adding a metal aluminum salt and an organic ligand to a solvent and uniformly mixing them, then adding a base to adjust the pH to 8-11 to obtain a precursor solution; wherein the solvent is a polar mixed solution of a monohydric alcohol and acetonitrile; 2) subjecting the precursor solution obtained in step 1) to a hydrothermal reaction at a temperature of 90-130° C. to obtain an aluminum-based metal organic framework material.

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

3. The preparation method according to claim 1, characterized in that: In the step 1), the organic ligand is at least one of 2,5-dihydroxyterephthalic acid, 2-hydroxyterephthalic acid, 2-methylterephthalic acid, and 2-aminoterephthalic acid.

4. The preparation method according to claim 3, characterized in that: 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.

5. The preparation method according to claim 1, characterized in that: In the step 1), the molar ratio of the metal aluminum salt to the organic ligand is 1-5:1; and the volume ratio of the monohydric alcohol to acetonitrile in the solvent is 1-3:

1.

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

7. The preparation method according to claim 1, characterized in that: In the step 2), the reaction time of the hydrothermal reaction is 5-12 hours.

8. An aluminum-based metal organic framework material prepared by the preparation method according to any one of claims 1 to 7.

9. The aluminum-based metal organic framework material according to claim 8, characterized in that: The pore size distribution of the aluminum-based metal organic framework material is Specific surface area is 800-1100m 2 / g.

10. Use of the aluminum-based metal organic framework material according to claim 8 as an adsorbent in ethane / ethylene gas separation.

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