Metal-organic framework synthesis and node modification with adsorption and separation of C6 alkane isomers

Abstract

This invention discloses a method for synthesizing metal-organic frameworks (MOFs) and modifying their nodes, and their application in the adsorption and separation of C6 alkane isomers. By selecting suitable acid modifiers, this invention modifies the nodes on the MOFs, thereby adjusting the pore size of the framework. The node-modified MOF materials possess suitable pore sizes, with Zr-TSS(BA) exhibiting excellent C6 alkane isomer separation performance. The MOF materials of this invention are stable and exhibit excellent performance, making them suitable as alternatives or supplementary technologies for industrial alkane isomer separation.

Description

Technical Field

[0001] This invention relates to the field of new materials, specifically to a method for synthesizing and modifying metal-organic frameworks and their application in the adsorption and separation of C6 alkane isomers. Background Technology

[0002] The chemical separation and purification of mixed chemical components is an energy-intensive process, accounting for 10-15% of global energy consumption. Therefore, developing more energy-efficient separation methods is crucial for reducing energy use and curbing carbon dioxide emissions.

[0003] Separating alkane isomers with different degrees of branching still faces certain technical challenges in the petrochemical industry. During the refining process, light naphtha fractions (mainly straight-chain C5 and C6) undergo catalytic isomerization, producing a mixture of straight-chain, monobranched, and dibranched isomers.

[0004] Isomers with higher branching degrees typically have higher research octane numbers (RONs). For example, 3-methylpentane (75) and 2,2-dimethylbutane (94) have much higher RONs than their straight-chain isomer, n-hexane (25). Therefore, in order to produce high-RON gasoline, it is necessary to remove low-RON alkane isomers from the mixture and recycle them back into the catalytic reactor.

[0005] Distillation is a traditional process for separating alkane isomers, but it is energy-intensive. Adsorption separation, a more energy-efficient method, is used as an alternative or supplementary technology for the separation of alkane isomers.

[0006] The emergence of metal-organic frameworks (MOFs) has provided new opportunities for industrially challenging chemical separations due to their highly tunable pore size, pore shape, and surface functionality.

[0007] In fact, MOFs have shown great advantages in CO2 capture, propane / propylene separation, and acetylene / ethylene separation. Extensive research on MOFs also shows that they have potential in separating alkane isomers.

[0008] Inert alkanes mean that the thermodynamically driven process is primarily controlled by van der Waals interactions, and slight differences in binding affinity are insufficient to provide good separation performance. In contrast, molecular sieving shows unique advantages in the separation of C6 isomers.

[0009] Although MOFs are difficult to precisely control pore size to achieve complete sieving performance, C6 alkane isomer separation focuses more on coarse separation of isomers using RON to improve gasoline quality. For coarse separation, the pore size range should be appropriately broadened to reduce the difficulty of pore size control. Adjusting the appropriate pore size through node modification on the metal-organic framework is a promising strategy.

[0010] Patent specification CN116410475A discloses a zirconium-based metal-organic framework material, its preparation method and application, and an adsorption separation device and method. The chemical structural formula of this zirconium-based metal-organic framework material is [C]. 18 H6O 16 Zr3] n The material includes zirconium and an organic ligand that forms a coordinate bond with zirconium. The organic ligand is ethynylbiphenyl-3,3',5,5'-tetracarboxylic acid. The adsorption priority order of this zirconium-based metal-organic framework material for hexane isomers is as follows: n-hexane, monobranched hexane, and dibranched hexane. Summary of the Invention

[0011] In a first aspect, the present invention provides a method for synthesizing metal-organic frameworks, wherein an organic ligand and ZrOCl2 are added to a mixed solution of DMF (N,N-dimethylformamide) and HOAc (acetic acid) for a solvothermal reaction to obtain the metal-organic framework Zr-TSS (HOAc);

[0012] The organic ligand has the following chemical structure:

[0013]

[0014] The preparation method of the organic ligand may include: adding 1,1,2,2-tetra(thiophen-2-yl)ethylene to tetrahydrofuran under anhydrous and oxygen-free conditions, adding butyllithium at -75 to -80°C, mixing and reacting thoroughly at -80°C to room temperature, then introducing carbon dioxide gas at -75 to -80°C and stirring continuously for a period of time, then quenching the reaction with hydrochloric acid, and extracting with dichloromethane. The resulting organic phase is washed with saturated brine, dried with anhydrous sodium sulfate, and the organic solvent is evaporated to obtain the organic ligand.

[0015] 1,1,2,2-tetratetra(thiophen-2-yl)ethylene can be prepared by referring to existing technical literature Chem. Sci., 2017, 8, 2629-2639.

[0016] In the preparation method of the organic ligand, the ratio of 1,1,2,2-tetra(thiophen-2-yl)ethylene to tetrahydrofuran can be 0.5-1.5 g: 100 mL.

[0017] In the preparation method of the organic ligand, the molar ratio of 1,1,2,2-tetra(thiophene-2-yl)ethylene to butyllithium can be 0.5 to 1.5:10.

[0018] In the preparation method of the organic ligand, the butyllithium can be added in the form of a butyllithium n-hexane solution.

[0019] In the method for preparing the organic ligand, the concentration of butyllithium in the hexane solution of butyllithium can be 2-3 M.

[0020] In the preparation method of the organic ligand, an excess of carbon dioxide gas may be introduced.

[0021] In the method for preparing the organic ligand, the temperature of the continuously stirred reaction can be -80℃ to room temperature.

[0022] In the method for synthesizing the metal-organic framework, the mass ratio of ZrOCl2 to the organic ligand can be no less than 2:1.

[0023] In the method for synthesizing the metal-organic framework, the ratio of organic ligand to DMF can be 20 mg: 0.5–2 mL.

[0024] In the method for synthesizing the metal-organic framework, the volume ratio of DMF to HOAc can be 1:0.5 to 2.

[0025] In the method for synthesizing the metal-organic framework, the temperature of the solvothermal reaction can be 115–135°C, and the time can be 48–72 h.

[0026] In the method for synthesizing the metal-organic framework, after the solvothermal reaction is completed, the following post-processing operation can be performed: take the solid product, wash and soak it with DMF, then wash and soak it with acetone, and dry it to obtain the metal-organic framework Zr-TSS(HOAc).

[0027] Secondly, the present invention provides a metal-organic framework Zr-TSS(HOAc) synthesized by the synthesis method described in the first aspect.

[0028] Thirdly, the present invention provides a method for modifying the nodes of a metal-organic framework, comprising the steps of:

[0029] (1) Organic ligands and ZrOCl2 were added to a mixed solution of DMF and FA (formic acid) for a solvothermal reaction to obtain metal-organic framework Zr-TSS (FA);

[0030] (2) The metal-organic framework Zr-TSS(FA) and BA (benzoic acid) were added to DMF and subjected to a solvothermal reaction to obtain the metal-organic framework Zr-TSS(BA);

[0031] The organic ligand has the following chemical structure:

[0032]

[0033] The organic ligand can be prepared as described in the first aspect.

[0034] In step (1), the mass ratio of ZrOCl2 to the organic ligand may be no less than 2:1.

[0035] In step (1), the ratio of the organic ligand to DMF can be 30 mg: 1 to 3 mL.

[0036] In step (1), the volume ratio of DMF to FA can be 1:0.2 to 0.4.

[0037] In step (1), the temperature of the solvothermal reaction can be 115-135°C and the time can be 36-72h.

[0038] In step (1), after the solvothermal reaction is completed, the following post-processing operations can be performed: take the solid product, wash and soak it with DMF, then wash and soak it with acetone, and dry it to obtain metal-organic framework Zr-TSS (FA).

[0039] In step (2), the mass ratio of BA to Zr-TSS (FA) can be no less than 10:1.

[0040] In step (2), the ratio of Zr-TSS(FA) to DMF can be 20 mg: 1 to 3 mL.

[0041] In step (2), the temperature of the solvothermal reaction can be 65-75°C and the time can be 36-72h.

[0042] In step (2), after the solvothermal reaction is completed, the following post-processing operations can be performed: take the solid product, wash and soak it with DMF, then wash and soak it with acetone, and dry it to obtain metal-organic framework Zr-TSS (BA).

[0043] Fourthly, the present invention provides a metal-organic framework Zr-TSS(BA) synthesized by the node modification method described in the third aspect.

[0044] Fifthly, the present invention provides the application of the metal-organic framework Zr-TSS (HOAc) described in the second aspect or the metal-organic framework Zr-TSS (BA) described in the fourth aspect in the adsorption and separation of C6 alkane isomers.

[0045] In a sixth aspect, the present invention provides the application of metal-organic framework Zr-TSS (FA) in the adsorption and separation of C6 alkane isomers, wherein the metal-organic framework material is formed by the substitution coordination linking of organic ligands with Zr6 metal clusters (Zr6cluster);

[0046] The organic ligand has the following chemical structure:

[0047]

[0048] The Zr6 metal clusters have the following chemical structures:

[0049]

[0050] In the process of substitution coordination, the organic ligand forms a coordination link with the Zr6 metal cluster by substituting the OCO in the Zr6 metal cluster with the same structure using its carboxyl group.

[0051] The preparation method of metal-organic framework Zr-TSS(FA) can be as described in step (1) of the third aspect.

[0052] Due to the addition of different acid modifiers, the nodes on Zr6 are benzoic acid (BA), acetic acid (HOAc), or formic acid (FA). Specifically, the Zr6 nodes of the metal-organic framework Zr-TSS (FA) are formic acid, those of Zr-TSS (HOAc) are acetic acid, and those of Zr-TSS (BA) are benzoic acid. The node connection methods can be found in [reference needed]. Figure 1 .

[0053] This invention modifies the nodes on a metal-organic framework by selecting a suitable acid modifier, thereby adjusting the pore size of the framework. The node-modified metal-organic framework material has a suitable pore size, among which Zr-TSS(BA) exhibits excellent C6 alkane isomer separation performance. The described metal-organic framework material is stable and has excellent performance, and can be used as an alternative or supplementary technology for alkane isomer separation in industry.

[0054] The metal-organic framework of the present invention is preferably activated before being used for the adsorption and separation of C6 alkane isomers. The activation operation may include vacuum heating the metal-organic framework at 115-125°C for more than 6 hours, which is beneficial for better adsorption and separation of C6 alkane isomers.

[0055] The metal-organic frameworks Zr-TSS(FA), Zr-TSS(HOAc), and Zr-TSS(BA) in this invention all exhibit the ability to adsorb and separate C6 alkane isomers, wherein:

[0056] Zr-TSS(FA) has similar adsorption capacity for 3-methylpentane (3MP) and n-hexane (n-Hex), which is significantly better than that for 2,2-dimethylbutane (22DMB). When used for the adsorption and separation of C6 alkane isomers, it can preferentially adsorb 3MP and n-Hex to obtain high-purity 22DMB.

[0057] The adsorption capacity of Zr-TSS(HOAc) for C6 alkane isomers is as follows: 3MP > n-Hex > 22DMB; therefore, Zr-TSS(HOAc) can be used for any two-component or three-component separation among 3MP, n-Hex, and 22DMB.

[0058] Zr-TSS(BA) exhibits the highest adsorption selectivity for n-Hex among 3MP, n-Hex, and 22DMB, and shows similar almost non-adsorption properties for 3MP and 22DMB. It can be used for the efficient separation of n-Hex from other C6 alkane isomers such as 3MP and 22DMB, thereby improving the octane number.

[0059] Compared with the prior art, the beneficial effects of this invention are as follows:

[0060] 1. This invention creatively designs and synthesizes a novel metal-organic framework material, which can control the pore size by simply modifying the nodes.

[0061] 2. The preparation method of the metal-organic framework material provided by the present invention is simple, easy to operate, uses inexpensive materials, and is suitable for mass production.

[0062] 3. The framework material designed and preferred in this invention has excellent adsorption and separation performance of C6 alkane isomers.

[0063] 4. The metal-organic framework material provided by this invention has high stability and reusability, and has potential practical application value. Attached Figure Description

[0064] Figure 1 A schematic diagram showing the connection of different nodes in Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc).

[0065] Figure 2 X-ray powder diffraction (PXRD) patterns (left) and N2 adsorption / desorption plots (right) of Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc).

[0066] Figure 3 Pore ​​size distribution diagrams for Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc).

[0067] Figure 4 Adsorption diagrams of Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc) for n-hexane (n-Hex), 3-methylpentane (3MP), and 2,2-dimethylbutane (22DMB). Detailed Implementation

[0068] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0069] Synthesis of the organic ligand TSS:

[0070] 1 g of 1,1,2,2-tetra(thiophene-2-yl)ethylene was weighed into a 250 mL flask with a side arm. The system was purged under a nitrogen atmosphere and 100 mL of anhydrous tetrahydrofuran was introduced under anhydrous and oxygen-free conditions. The flask was then placed in a cryogenic bath at -78 °C. 11.2 mL of a 2.5 M butyllithium solution in n-hexane was slowly added dropwise. After the addition was complete, the mixture was stirred at -78 °C for 30 min. The system was then transferred to room temperature and stirred for 3 h to promote complete lithiation. The system gradually became a turbid liquid. The system was then transferred back to -78 °C, and carbon dioxide (CO2) gas was continuously introduced. The cryogenic refrigeration was turned off, and the mixture was stirred overnight. The reaction was quenched with 2 M hydrochloric acid, and the mixture was extracted twice with dichloromethane. The combined organic phases were washed with saturated brine, and then dried over anhydrous sodium sulfate. The organic solvent was evaporated to obtain product TSS (1.46 g, 98% yield). 1 H NMR (600MHz, DMSO-d6): δ13.31(s,4H),7.61(d,4H),7.01(d,4H).

[0071] Example 1

[0072] Preparation method of metal-organic framework material Zr-TSS(FA):

[0073] Weigh 600 mg of TSS and 1200 mg of ZrOCl2 into a 100 mL blue-capped reagent bottle (Shuniu), add 40 mL of DMF, and sonicate for 10 min until homogeneous. Add 12 mL of FA, then place in a 120 °C oven for a solvothermal reaction for 48 h. After cooling to room temperature, remove the mother liquor and wash twice with fresh DMF. Then soak in DMF for two days, replacing the DMF three times, followed by soaking in acetone for two days, replacing the acetone three times. Dry in air at room temperature to obtain the metal-organic framework material, named Zr-TSS(FA).

[0074] Example 2

[0075] Preparation method of metal-organic framework material Zr-TSS(BA):

[0076] 600 mg of Zr-TSS(FA) obtained in Example 1 was placed in a 100 mL blue-capped reagent bottle (Shuniu brand), along with 6 g of BA and 60 mL of DMF. The mixture was then placed in a 70 °C oven for a solvothermal reaction for 48 h. After cooling to room temperature, the mother liquor was removed, and the mixture was washed twice with fresh DMF. It was then soaked in DMF for two days, replacing the DMF three times, followed by soaking in acetone for two days, replacing the acetone three times. The resulting metal-organic framework material was obtained by air drying at room temperature and named Zr-TSS(BA).

[0077] Example 3

[0078] Preparation method of metal-organic framework material Zr-TSS(HOAc):

[0079] Weigh 600 mg of TSS and 1200 mg of ZrOCl2 into a 100 mL blue-capped reagent bottle (Shuniu brand), add 30 mL of DMF, and sonicate for 10 min until homogeneous. Add 30 mL of HOAc, then place in a 120 °C oven for a solvothermal reaction for 60 h. After cooling to room temperature, remove the mother liquor and wash twice with fresh DMF. Then soak in DMF for two days, replacing the DMF three times, followed by soaking in acetone for two days, replacing the acetone three times. Air-dry at room temperature to obtain the metal-organic framework material, named Zr-TSS(HOAc).

[0080] The metal-organic framework materials obtained in Examples 1-3 were characterized in a series of ways, and the PXRD, nitrogen adsorption-desorption (BET) curves, and pore size distributions are shown in the figures below. Figure 2 and Figure 3 As shown in the figure. The PXRD plots show that the three materials have similar curves, indicating that the overall framework structure has not changed significantly; the nitrogen adsorption-desorption curves show that the BET specific surface area of ​​the three materials is Zr-TSS(FA)>Zr-TSS(HOAc)>Zr-TSS(BA); the pore size distribution plots show that the pore size of the three materials is Zr-TSS(FA)>Zr-TSS(HOAc)>Zr-TSS(BA).

[0081] Example 4

[0082] Adsorption experiments of C6 alkane isomers in metal-organic framework materials Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc):

[0083] Three materials, Zr-TSS(FA), Zr-TSS(BA), and Zr-TSS(HOAc), were fully activated by vacuum heating at 120℃ for 8 hours. Adsorption experiments were then conducted on n-hexane (n-Hex), 3-methylpentane (3MP), and 2,2-dimethylbutane (22DMB), respectively. Taking Zr-TSS(FA) as an example, after vacuum activation at 120℃, n-hexane adsorption was performed at room temperature. Desorption followed by 3-methylpentane adsorption was then performed at room temperature and vacuum, without further activation. Adsorption of 2,2-dimethylbutane was then performed after desorption.

[0084] Adsorption experiment results are as follows Figure 4 As shown:

[0085] Zr-TSS(FA) has similar adsorption capacity for 3MP and n-Hex, which is significantly better than that for 22DMB. When used for the adsorption and separation of C6 alkane isomers, it can preferentially adsorb 3MP and n-Hex to obtain high-purity 22DMB.

[0086] The adsorption capacity of Zr-TSS(HOAc) for C6 alkane isomers is as follows: 3MP > n-Hex > 22DMB; therefore, Zr-TSS(HOAc) can be used for any two-component or three-component separation among 3MP, n-Hex, and 22DMB.

[0087] Zr-TSS(BA) does not adsorb 3-methylpentane and 2,2-dimethylbutane, but has a significant adsorption effect on straight-chain n-hexane. It can be used for the efficient separation of n-Hex from other C6 alkane isomers such as 3MP and 22DMB, and improve the octane number.

[0088] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for synthesizing metal-organic frameworks, characterized in that, Organic ligands and ZrOCl2 were added to a mixed solution of DMF and HOAc for a solvothermal reaction to obtain the metal-organic framework Zr-TSS(HOAc); The organic ligand has the following chemical structure:

2. The method for synthesizing metal-organic frameworks according to claim 1, characterized in that, The method for preparing the organic ligand includes: under anhydrous and oxygen-free conditions, adding 1,1,2,2-tetra(thiophen-2-yl)ethylene to tetrahydrofuran, adding butyllithium at -75 to -80°C, mixing and reacting thoroughly at -80°C to room temperature, then introducing carbon dioxide gas at -75 to -80°C and continuously stirring the reaction for a period of time, then quenching the reaction with hydrochloric acid, and extracting with dichloromethane. The resulting organic phase is washed with saturated brine, dried with anhydrous sodium sulfate, and the organic solvent is evaporated to obtain the organic ligand. In the preparation method of the organic ligand: The ratio of 1,1,2,2-tetra(thiophene-2-yl)ethylene to tetrahydrofuran is 0.5–1.5 g: 100 mL; The molar ratio of 1,1,2,2-tetra(thiophen-2-yl)ethylene to butyllithium is 0.5–1.5:10; The butyllithium was added in the form of a butyllithium n-hexane solution; The concentration of butyllithium in the hexane solution is 2-3 M; Excessive carbon dioxide gas was introduced; The temperature of the continuously stirred reaction is -80℃ to room temperature.

3. The method for synthesizing metal-organic frameworks according to claim 1, characterized in that, The mass ratio of ZrOCl2 to the organic ligand is not less than 2:1; The ratio of the organic ligand to DMF is 20 mg: 0.5–2 mL; The volume ratio of DMF to HOAc is 1:0.5 to 2; The solvothermal reaction is carried out at a temperature of 115–135°C for a duration of 48–72 h. After the solvothermal reaction is completed, the following post-processing operations are performed: the solid product is washed and soaked in DMF, then washed and soaked in acetone, and dried to obtain the metal-organic framework Zr-TSS (HOAc).

4. The metal-organic framework Zr-TSS(HOAc) synthesized by the synthetic method according to any one of claims 1 to 3.

5. A method for modifying the nodes of a metal-organic framework, characterized in that, Including the following steps: (1) Organic ligands and ZrOCl2 were added to a mixed solution of DMF and FA for a solvothermal reaction to obtain metal-organic framework Zr-TSS(FA); (2) The metal-organic framework Zr-TSS(FA) and BA were added to DMF and subjected to a solvothermal reaction to obtain the metal-organic framework Zr-TSS(BA); The organic ligand has the following chemical structure:

6. The method for modifying the nodes of a metal-organic framework according to claim 5, characterized in that, The method for preparing the organic ligand includes: under anhydrous and oxygen-free conditions, adding 1,1,2,2-tetra(thiophen-2-yl)ethylene to tetrahydrofuran, adding butyllithium at -75 to -80°C, mixing and reacting thoroughly at -80°C to room temperature, then introducing carbon dioxide gas at -75 to -80°C and continuously stirring the reaction for a period of time, then quenching the reaction with hydrochloric acid, and extracting with dichloromethane. The resulting organic phase is washed with saturated brine, dried with anhydrous sodium sulfate, and the organic solvent is evaporated to obtain the organic ligand. In the preparation method of the organic ligand: The ratio of 1,1,2,2-tetra(thiophene-2-yl)ethylene to tetrahydrofuran is 0.5–1.5 g: 100 mL; The molar ratio of 1,1,2,2-tetra(thiophen-2-yl)ethylene to butyllithium is 0.5–1.5:10; The butyllithium was added in the form of a butyllithium n-hexane solution; The concentration of butyllithium in the hexane solution is 2-3 M; Excessive carbon dioxide gas was introduced; The temperature of the continuously stirred reaction is -80℃ to room temperature.

7. The method for modifying the nodes of a metal-organic framework according to claim 5, characterized in that, In step (1): The mass ratio of ZrOCl2 to the organic ligand is not less than 2:1; The ratio of the organic ligand to DMF is 30 mg: 1-3 mL; The volume ratio of DMF to FA is 1:0.2 to 0.4; The solvothermal reaction is carried out at a temperature of 115–135°C for a duration of 36–72 h. After the solvothermal reaction is completed, the following post-processing operations are performed: the solid product is washed and soaked with DMF, then washed and soaked with acetone, and dried to obtain metal-organic framework Zr-TSS(FA); In step (2): The mass ratio of BA to Zr-TSS(FA) is not less than 10:1; The dosage ratio of Zr-TSS(FA) to DMF is 20 mg: 1-3 mL; The solvothermal reaction is carried out at a temperature of 65–75°C for a duration of 36–72 h. After the solvothermal reaction is completed, the following post-processing operations are performed: the solid product is washed and soaked with DMF, then washed and soaked with acetone, and dried to obtain metal-organic framework Zr-TSS (BA).

8. The metal-organic framework Zr-TSS(BA) synthesized by the node modification method according to any one of claims 5 to 7.

9. The application of the metal-organic framework Zr-TSS (HOAc) according to claim 4 or the metal-organic framework Zr-TSS (BA) according to claim 8 in the adsorption and separation of C6 alkane isomers.

10. The application of metal-organic framework Zr-TSS (FA) in the adsorption and separation of C6 alkane isomers, characterized in that, The metal-organic framework material is formed by the substitution coordination linking of organic ligands with Zr6 metal clusters; The organic ligand has the following chemical structure: The Zr6 metal clusters have the following chemical structures:

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