Organic ligands, metal-organic framework materials, methods of making the same, and applications thereof in adsorbing natural gas

Abstract

The application relates to the field of natural gas adsorption technology, in particular to an organic ligand, a metal organic framework material, a preparation method of the metal organic framework material and application of the metal organic framework material in adsorbing natural gas. The organic ligand has a structural formula as shown in formula (I). The organic framework material has good chemical stability and can be used for a long time; the organic framework material also has porosity and has more excellent natural gas adsorption performance than most common adsorption materials on the market such as activated carbon. Meanwhile, the synthesis condition is mild, the cost is low, and the organic framework material has certain commercial application potential.

Description

Technical Field

[0001] This invention relates to the field of natural gas adsorption technology, and in particular to organic ligands, metal-organic framework materials, their preparation methods, and their applications in the adsorption of natural gas. Background Technology

[0002] Natural gas has a high carbon-to-hydrogen ratio, and its combustion efficiency is generally higher than that of traditional fossil fuels such as oil and coal. Furthermore, the byproducts of natural gas combustion are water and carbon dioxide, making it a clean fuel that is environmentally friendly. Currently, there are three main methods for storing natural gas: liquefied natural gas (LNG), compressed natural gas (CNG), and adsorbed natural gas. LNG liquefies natural gas at extremely low temperatures, requiring a large amount of energy to maintain the cryogenic environment and carrying the risk of leakage. CNG compresses natural gas at pressures exceeding 80–100 bar, placing high demands on the pressure resistance and safety performance of the containers. Both of these methods consume significant amounts of energy, are complex to operate, and pose safety hazards. These issues limit the transportation and use of natural gas. Adsorbed natural gas utilizes adsorbents to adsorb and store natural gas under low temperature and pressure (30–80 bar) conditions. Traditional adsorbents include molecular sieves and activated carbon. Molecular sieves have an adsorption capacity of up to 100 cm³ / s for natural gas. 3 / cm 3 The following is far below the requirements of the U.S. Department of Energy for the development of adsorbents; and the pore structure and pore size of activated carbon are difficult to adjust. Therefore, the development of materials with high adsorption capacity for natural gas is of great significance and promising for energy utilization.

[0003] Metal-organic frameworks (MOFs) are crystalline materials with high specific surface area and regular channels, assembled from metal ions or metal clusters linked to organic ligands via coordination bonds. They can possess an infinitely repeating network structure on a three-dimensional scale. The structure and pore size and shape of MOFs can be modified by adjusting the structure of the organic ligands and the diversity of metal ions. The pore surface can also be further modified to control the physicochemical properties of MOFs. These modified MOFs can be applied to gas storage and separation, drug delivery, catalysis, and other fields. Methane, the main component of natural gas, has a strong interaction with the internal surface of MOF pores. Currently, a considerable number of MOF materials are used for natural gas adsorption and storage, but there is still room for improvement in the adsorption capacity of publicly disclosed MOF materials for natural gas. Therefore, the synthesis of MOFs with high natural gas adsorption capacity is of great significance. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides an organic ligand, a metal-organic framework material, a method for preparing the same, and its application in natural gas adsorption. The material is synthesized under mild conditions and at low cost. When used as a natural gas adsorbent, it exhibits advantages such as high adsorption capacity and long lifespan.

[0005] Based on this, the present invention has the following technical solution:

[0006] In a first aspect, the present invention provides an organic ligand for a metal-organic framework material, said organic ligand having the structural formula as shown in formula (I):

[0007]

[0008] Secondly, the present invention provides a method for preparing organic ligands of the aforementioned metal-organic framework material, comprising:

[0009] S1: 2,6-Dibromoazine, 3,5-dimethoxycarbonylphenylboronic acid, catalyst, first solvent and weak base are mixed under a nitrogen atmosphere to obtain a first mixed solution. The first mixed solution is subjected to a coupling reaction at 95-105℃. After the reaction is completed, the azurite ester derivative is obtained by purification.

[0010] In this invention, the structural formula of the azurite ester derivative is as follows:

[0011]

[0012] Preferably, the first solvent comprises a mixture of 1,4-dioxane and water.

[0013] S2: The azurite ester derivative obtained in S1, the second solvent, and the strong base are mixed to obtain a second mixed solution, and the second mixed solution is subjected to a hydrolysis reaction at 95-105°C.

[0014] Preferably, the second solvent comprises a mixture of 1,4-dioxane, ethanol, and water.

[0015] Preferably, the catalyst comprises tetra(triphenylphosphine)palladium; more preferably, the amount of the catalyst is 3 to 8 moles, based on the molar amount of bromine in 2,6-dibromoazine.

[0016] Preferably, the method for preparing the organic ligands of the metal-organic framework material includes:

[0017] S1: 2,6-Dibromoazine and 3,5-dimethoxycarbonylphenylboronic acid were added to a mixed solution of 1,4-dioxane and water. Tetra(triphenylphosphine)palladium was then added under a nitrogen atmosphere, followed by a weak base. The coupling reaction was carried out at 95–105 °C for more than 12 hours. After the reaction was completed, the reaction solution was diluted with water, extracted with dichloromethane, and the resulting organic layer was washed with water, dried with anhydrous sodium sulfate, and purified by column chromatography to obtain the ester derivative of azurite.

[0018] S2: The azurite ester derivative obtained in S1 is added to a mixed solvent of dioxane, ethanol and water, and then a strong base is added. The hydrolysis reaction is carried out at 95-105°C for 15-20 hours. After the reaction is completed, all solvents are removed and the product is dissolved in water again. The pH value is adjusted to 2-3. The precipitated solid is filtered, washed and dried in sequence. The solid obtained is the organic ligand.

[0019] Preferably, in S1, the molar ratio of 2,6-dibromoazine and 3,5-dimethoxycarbonylphenylboronic acid is 1:(2-2.5); and / or the volume ratio of 1,4-dioxane and water is (3.5-4.5):1.

[0020] Preferably, in S2, the volume ratio of dioxane, ethanol and water is (1-2):(1-2):(1-2).

[0021] In this invention, the weak base that can be used in S1 includes one or more of potassium carbonate, potassium phosphate, potassium acetate, cesium carbonate, and sodium carbonate, and the amount added is at least three times the molar amount of bromine in 2,6-dibromoazine.

[0022] Strong bases that can be used in S2 include potassium hydroxide and / or sodium hydroxide, etc., to hydrolyze the ester by adding strong bases; the amount of strong base added is 8 to 12 times the molar amount of bromine in 2,6-dibromoazine.

[0023] Thirdly, the present invention provides a metal-organic framework material (hereinafter also referred to as "Azu-MOF"), which is a three-dimensional crystalline porous material assembled by the organic ligands and copper ions through coordination bonds.

[0024] Preferably, the metal-organic framework material has a (4,4)-connected NbO configuration topology.

[0025] More preferably, in the metal-organic framework material, two adjacent copper ions are bridged by four carboxyl groups, and each copper ion is also coordinated with a water molecule to form a paddle-shaped secondary structural unit. The secondary structural unit is constructed to form a three-dimensional periodic network structure through bridging by organic ligands. The molecular formula of the secondary structural unit is Cu2(COO)4(H2O)2.

[0026] Preferably, the metal-organic framework material has two types of cage-like cavities in its structure: one with a diameter of... The two types of spherical cavities consist of six secondary structural units connected by twelve ligands; the other type is an olive-shaped cavity, the size of which is... It consists of 12 secondary structural units and 6 ligands connected together.

[0027] Fourthly, the present invention provides a method for preparing the metal-organic framework material, comprising:

[0028] S3: Mix the organic ligand, copper nitrate trihydrate and N,N-dimethylformamide, then add a mixture of 1,4-dioxane and water, and add acid as a regulator to obtain a third mixed solution; keep the third mixed solution sealed at 70-80°C for 1-2 days.

[0029] In this invention, dioxane is used as a nonpolar solvent, and water is used as a coordinating small molecule to regulate the synthesis rate of MOF together with DMF, thereby obtaining crystals of better quality. Acid is used as a regulator to inhibit the crystallization rate of MOF, which helps to obtain MOF with better crystallinity. The acid used can be concentrated hydrochloric acid and / or nitric acid, etc.; the concentration of nitric acid is 3-4M.

[0030] In the specific implementation process, the amount of acid is adjusted according to the amount of N,N-dimethylformamide used. Specifically, the relationship between the amount of N,N-dimethylformamide and the amount of acid is that 1 to 2 drops of the acid are added per milliliter of N,N-dimethylformamide.

[0031] Preferably, the mass ratio of the organic ligand to copper nitrate trihydrate is (0.5-1):(1-2).

[0032] Preferably, in S3, the volume ratio of 1,4-dioxane to water is 1:(1.5-2.5).

[0033] S4: After removing the reaction solution obtained in S3, remove the supernatant and wash with dry DMF to obtain dark blue crystal particles, which are the metal-organic framework material.

[0034] Fifthly, the present invention provides the application of the metal-organic framework material in the adsorption of natural gas.

[0035] Current patent research on adsorption-based gas storage mainly focuses on the development of high-efficiency adsorbents and devices. Conventional ambient-temperature adsorption-based gas storage technologies primarily address the adsorption, storage, and application of gases under environmental conditions, and have not yet met the requirements for industrial applications. The metal-organic framework material, its preparation method, and its applications provided by this invention offer advantages such as mild synthesis conditions, low cost, and high adsorption capacity and long lifespan when used as a natural gas adsorbent.

[0036] The specific surface area of ​​the metal-organic framework material Azu-MOF for natural gas adsorption of the present invention can reach 2000-2500 m². 2 / g, with a pore volume of 0.8–1.2 cm³. 3 / g. The synthesized metal-organic framework material exhibits good thermal stability and a simple preparation process. This material demonstrates a high room-temperature natural gas adsorption capacity, far exceeding the US Department of Energy's target (180 cm⁻¹). 3 / cm 3 It is also easy to desorb.

[0037] At the same time, the methane adsorption of this MOF far exceeds that of coconut shell activated carbon, one of the high specific area activated carbons sold on the market. Its volume adsorption capacity at 159K / 8bar is 1.8 times that of coconut shell activated carbon.

[0038] Preferably, the method for adsorbing natural gas using the metal-organic framework material includes: activating the metal-organic framework material and then adsorbing natural gas at room temperature and 0-80 bar; the activation includes replacing N,N-dimethylformamide in the metal-organic framework material with a third solvent; preferably, the third solvent includes one or a mixture of several low-boiling-point solvents such as acetone, dichloromethane, methanol, ethanol, chloroform and tetrahydrofuran.

[0039] In this invention, the organic framework material can be widely used in scenarios such as BOG processing at LNG receiving / satellite stations, natural gas recovery in marginal gas fields, and gas storage in distributed energy systems.

[0040] Based on this, the technical solution of the present invention has the following beneficial effects:

[0041] 1. The organic framework material described in this invention has good chemical stability and can be used repeatedly for a long time.

[0042] 2. The organic framework material described in this invention is porous and has superior natural gas adsorption performance compared to most commercially available adsorption materials such as activated carbon.

[0043] 3. The organic framework material provided by this invention has mild synthesis conditions, low cost, and certain commercial application potential. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a characterization diagram of the organic ligand H4L in Example 1 provided by the present invention.

[0046] Figure 2 This is a ball-and-stick model structural diagram of the metal-organic framework material Azu-MOF in Embodiment 2 of the present invention.

[0047] Figure 3 The X-ray powder diffraction results are those of the metal-organic framework material Azu-MOF in Example 2 of this invention.

[0048] Figure 4 This is a nitrogen adsorption curve of the metal-organic framework material Azu-MOF in Example 2 of the present invention.

[0049] Figure 5 The results are the cycle stability test results of the metal-organic framework material Azu-MOF in Example 2 of this invention.

[0050] Figure 6 This is a test diagram of the metal-organic framework material Azu-MOF in Example 2 of the present invention under LNG-ANG conditions for methane storage.

[0051] Figure 7 This is the adsorption test curve of methane for the metal-organic framework material Azu-MOF in Example 2 of the present invention at 298K. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0054] Example 1

[0055] This embodiment provides an organic ligand H4L, the preparation method of which includes the following steps:

[0056] 2,6-Dibromoazine and 3,5-dimethoxycarbonylphenylboronic acid were added at a molar ratio of 1:2.2 to a mixed solution of 1,4-dioxane and water at a volume ratio of 4:1. Then, 5 mol% tetra(triphenylphosphine)palladium was added as a catalyst under a nitrogen atmosphere, followed by 4 mol equivalents of potassium carbonate. The reaction was carried out at at least 95–105°C for at least 12 hours. After the reaction was complete, the reaction solution was diluted with water, extracted with dichloromethane, and the resulting organic layer was washed with water, dried with anhydrous sodium sulfate, and purified by column chromatography to obtain the azurite ester derivative.

[0057] The obtained product was added to a mixed solvent of dioxane, ethanol, and water in a ratio of 1:1:1, followed by the addition of 10 molar equivalents of potassium hydroxide. The mixture was reacted at 100°C for 15–20 hours. After the reaction was complete, all solvents were removed, and the product was redissolved in water. The pH was adjusted to 2–3 by adding hydrochloric acid. The precipitated solid was filtered and washed with distilled water until the filtrate was neutral. The solid was then dried to obtain the organic ligand H4L.

[0058] Its characterization diagram is shown below. Figure 1 Hydrogen spectrum data: 1 H NMR(600MHz,DMSO-d6)δ13.47(s,4H),8.76(s,2H),8.54(d,J=10.2Hz,2H), 8.53(s,1H),8.46(s,1H),8.45(s,2H),7.99(s,2H),7.56(d,J=10.2Hz,2H).

[0059] Example 2

[0060] This embodiment provides a metal-organic framework material, Azu-MOF, whose preparation method includes the following steps:

[0061] Copper nitrate trihydrate (60 mg) and the organic ligand H4L (30 mg) from Example 1 were added to a 40 mL glass bottle. N,N-dimethylformamide (10 mL) was added, and the mixture was sonicated to dissolve. Then, 5 mL of H2O and 2.5 mL of 1,4-dioxane were added. After thorough mixing, 10–20 drops of concentrated hydrochloric acid were added dropwise. The glass bottle was sealed and placed in a 75°C drying oven for 2 days. The mixture was then removed and cooled to room temperature. The supernatant was removed, and the mixture was washed with dry DMF to obtain a deep blue crystalline solid, which is the metal-organic framework material.

[0062] The structure of the obtained blue crystalline solid was characterized, and the ball-and-stick model structure is as follows: Figure 2As shown, the X-ray powder diffraction results are as follows: Figure 3 As shown, the nitrogen adsorption curve is as follows: Figure 4 As shown.

[0063] Example 3

[0064] This embodiment provides a metal-organic framework material, Azu-MOF, whose preparation method includes:

[0065] 2,6-Dibromoazine and 3,5-dimethoxycarbonylphenylboronic acid were added at a molar ratio of 1:2 to a mixed solution of 1,4-dioxane and water at a volume ratio of 4.5:1. Then, 8 mol% tetra(triphenylphosphine)palladium was added as a catalyst under a nitrogen atmosphere, followed by 3 mol equivalents of potassium phosphate. The reaction was carried out at 95–105°C for at least 12 hours. After the reaction was complete, the reaction solution was diluted with water, extracted with dichloromethane, and the resulting organic layer was washed with water, dried with anhydrous sodium sulfate, and purified by column chromatography to obtain the azurite ester derivative.

[0066] The obtained product was added to a mixed solvent of dioxane, ethanol, and water in a 1:1:1 ratio, followed by the addition of 10 molar equivalents of sodium hydroxide. The mixture was reacted at 100°C for 15–20 hours. After the reaction was complete, all solvents were removed, and the product was redissolved in water. The pH was adjusted to 2–3 by adding hydrochloric acid. The precipitated solid was filtered and washed with distilled water until the filtrate was neutral. The solid was then dried to obtain the organic ligand H4L.

[0067] Copper nitrate trihydrate (60 mg) and the organic ligand H4L obtained above (40 mg) were added to a glass bottle, followed by N,N-dimethylformamide (10 mL). After sonication to dissolve, 5 mL of H2O and 3 mL of 1,4-dioxane were added, and the mixture was thoroughly mixed. Then, 10–20 drops of concentrated hydrochloric acid were added dropwise. The glass bottle was sealed and placed in a 75°C drying oven for 2 days. After drying, the mixture was removed and cooled to room temperature. The supernatant was removed, and the mixture was washed with dry DMF to obtain a deep blue crystalline solid, which is the metal-organic framework material.

[0068] Experimental Example

[0069] The natural gas adsorption performance of the metal-organic framework Azu-MOF obtained in Examples 2 and 3 was tested.

[0070] Specifically, the following steps are included:

[0071] (a) The metal-organic framework material synthesized in Example 2 was washed with acetone and then immersed in 5 mL of acetone for three days, with the acetone being replaced every 12 hours. The blue solid containing acetone was added to the adsorption tube, and the acetone was gradually dried with nitrogen gas. Then, it was dried at 100°C under vacuum for 6 hours to obtain the activated sample.

[0072] (b) The activated sample was transferred to a high-pressure adsorption instrument to test the adsorption-desorption performance of the metal-organic framework for natural gas at room temperature, 159 K, 0-10 bar, and 298 K, 0-80 bar. Figures 5-7 As shown in the figure, the metal-organic framework material synthesized in this invention exhibits good adsorption capacity for natural gas at room temperature and 65 bar, with an adsorption capacity of 180 cm⁻¹ at 65 bar. 3 / cm 3 These results indicate that the metal-organic framework material possesses certain stability and porosity, demonstrating its potential for application in natural gas adsorption and storage.

[0073] Meanwhile, the experimental results show that the metal-organic framework materials prepared in Example 3 and Example 2 have comparable effects on natural gas adsorption and storage.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An organic ligand for a metal-organic framework material, characterized in that, The organic ligand has the structural formula as shown in formula (I): 。 2. The method for preparing the organic ligands of the metal-organic framework material according to claim 1, characterized in that, include: S1: 2,6-Dibromoazine, 3,5-dimethoxycarbonylphenylboronic acid, catalyst, weak base and first solvent are mixed under a nitrogen atmosphere to obtain a first mixed solution. The first mixed solution is subjected to a coupling reaction at 95-105°C. After the reaction is completed, the azurite ester derivative is obtained by purification. S2: The azurite ester derivative obtained in S1, the second solvent, and the strong base are mixed to obtain a second mixed solution, and the second mixed solution is subjected to a hydrolysis reaction at 95-105°C.

3. The method for preparing organic ligands of the metal-organic framework material according to claim 2, characterized in that, The first solvent comprises a mixture of 1,4-dioxane and water.

4. The method for preparing organic ligands of the metal-organic framework material according to claim 2, characterized in that, The second solvent comprises a mixture of 1,4-dioxane, ethanol, and water.

5. The method for preparing organic ligands of the metal-organic framework material according to claim 2, characterized in that, include: S1: 2,6-Dibromoazine and 3,5-dimethoxycarbonylphenylboronic acid were added to a mixed solution of 1,4-dioxane and water. Tetra(triphenylphosphine)palladium was then added under a nitrogen atmosphere, followed by a weak base. The coupling reaction was carried out at 95–105 °C for more than 12 hours. After the reaction was completed, the reaction solution was diluted with water, extracted with dichloromethane, and the resulting organic layer was washed with water, dried with anhydrous sodium sulfate, and purified by column chromatography to obtain the ester derivative of azurite. S2: The azurite ester derivative obtained in S1 is added to a mixed solvent of dioxane, ethanol and water, and then a strong base is added. The hydrolysis reaction is carried out at 95-105°C for 15-20 hours. After the reaction is completed, all solvents are removed and the product is dissolved in water again. The pH value is adjusted to 2-3. The precipitated solid is filtered, washed and dried in sequence. The solid obtained is the organic ligand.

6. The method for preparing the organic ligand of the metal-organic framework material according to any one of claims 2-5, characterized in that, In S1, the molar ratio of 2,6-dibromoazine to 3,5-dimethoxycarbonylphenylboronic acid is 1:(2-2.5); and / or the volume ratio of 1,4-dioxane to water is (3.5-4.5):1; In S2, the volume ratio of dioxane, ethanol and water is (1-2):(1-2):(1-2).

7. A metal-organic framework material, characterized in that, It is a three-dimensional crystalline porous material assembled from the organic ligands and copper ions as described in claim 1 through coordination bonds.

8. The metal-organic framework material according to claim 7, characterized in that, The metal-organic framework material has a (4,4)-connected NbO configuration topology.

9. The metal-organic framework material according to claim 8, characterized in that, In the metal-organic framework material, two adjacent copper ions are bridged by four carboxyl groups, and each copper ion is also coordinated with a water molecule to form a paddle-shaped secondary structural unit. The secondary structural unit is constructed into a three-dimensional periodic network structure through bridging by organic ligands. The molecular formula of the secondary structural unit is Cu2(COO)4(H2O)2.

10. The metal-organic framework material according to any one of claims 7-9, characterized in that, The metal-organic framework material has two types of cage-like cavities: one is a spherical cavity with a diameter of about 15 Å, which is composed of 6 secondary structure units and 12 ligands; the other is an olive-shaped cavity with a size of 13 × 29 Å, which is composed of 12 secondary structure units and 6 ligands.

11. A method for preparing the metal-organic framework material according to any one of claims 7-10, characterized in that, include: S3: The organic ligand, copper nitrate trihydrate, and N,N-dimethylformamide are mixed, and then a mixture of 1,4-dioxane and water is added, along with an acid as a regulator, to obtain a third mixed solution; the third mixed solution is kept in a sealed environment at 70-80°C for 1-2 days. S4: After removing the reaction solution obtained in S3, remove the supernatant and wash with dry DMF to obtain dark blue crystal particles, which are the metal-organic framework material.

12. The method for preparing the metal-organic framework material according to claim 11, characterized in that, The mass ratio of the organic ligand to copper nitrate trihydrate is (0.5-1):(1-2).

13. The application of the metal-organic framework material according to any one of claims 7 to 10 or the metal-organic framework material prepared by the preparation method according to claim 11 or 12 in the adsorption of natural gas.

14. The application of the metal-organic framework material according to claim 13 in the adsorption of natural gas, characterized in that, The metal-organic framework material is activated and then natural gas is adsorbed at room temperature and 0–80 bar; the activation includes replacing N,N-dimethylformamide in the metal-organic framework material with a third solvent.

15. The application of the metal-organic framework material according to claim 14 in the adsorption of natural gas, characterized in that, The third solvent includes one or more of acetone, dichloromethane, methanol, ethanol, chloroform, and tetrahydrofuran.

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