A metal-organic framework adsorbent, its preparation method and application

Abstract

This invention provides a metal-organic framework adsorbent, its preparation method, and its application, belonging to the field of adsorption and separation technology. The invention utilizes a metal salt, a coordination compound, and ligands. First, the metal ions and cyano ligands in the coordination compound coordinate with the metal ions in the metal salt, forming a two-dimensional bimetallic nanosheet structure linked by cyano groups. Then, the two-dimensional bimetallic nanosheet structure in the metal salt solution continues to coordinate with the ligands, forming a three-dimensional structure. The resulting metal-organic framework adsorbent exhibits high selectivity for methane. Furthermore, the adsorbent possesses suitable porosity, a high density of open metal sites, and abundant methylene groups within the pores that provide a strong affinity for methane molecules, resulting in excellent methane adsorption capacity and higher separation selectivity.

Description

Technical Field

[0001] This invention belongs to the field of adsorption and separation technology, and particularly relates to a metal-organic framework adsorbent, its preparation method, and its application. Background Technology

[0002] Coalbed methane (CBM) is an unconventional natural gas discovered in coal seams during coal mining. Its main components are methane, carbon dioxide, and nitrogen. Methane, the most abundant gas in CBM, is a high-calorific-value clean energy source and chemical feedstock, but it is also the second largest greenhouse gas after carbon dioxide. During coal mining, CBM easily mixes with air, exacerbating the greenhouse effect; its greenhouse potential is 25 times that of carbon dioxide. Therefore, CBM needs to be recovered during mining. The presence of carbon dioxide and nitrogen in CBM reduces its calorific value and poses certain safety risks during transportation. Therefore, it is necessary to separate methane and other impurity gases from CBM.

[0003] Separating methane and carbon dioxide is relatively simple; they can be separated based on their solubility or by using conventional adsorbents. However, methane and nitrogen have very similar physical and chemical properties. In industry, they are mainly separated by the difference in boiling points, which is achieved through low-temperature distillation. However, low-temperature distillation is expensive and not suitable for distilling low-concentration components. Adsorption separation technology utilizes the selective adsorption of adsorbents on methane and nitrogen to separate them, achieving good separation results. Among these, metal-organic frameworks (MOFs) are commonly used adsorbents. For example, CN109107329B discloses a method for separating methane and nitrogen: using a metal-organic framework as an adsorbent, methane and nitrogen are separated or methane is purified from a mixture containing methane and nitrogen using adsorption separation. The metal-organic framework is a three-dimensional network structure formed by transition metal ions or alkaline earth metal ions and organic ligands (2,5-dihydroxy-1,4-benzoquinone) through coordination bonds or intermolecular forces. Water molecules are coordinated with the metal and have strong hydrogen bonding with oxygen atoms on the organic ligands.

[0004] However, conventional MOF adsorbents have poor selectivity and stability, low adsorption capacity, and difficult synthesis methods, which limits their industrial application. In particular, in high humidity environments, the selectivity of conventional MOF adsorbents for methane and nitrogen becomes even worse, making them difficult to apply.

[0005] In summary, adsorption is commonly used to separate methane and nitrogen. Most commonly used adsorbents are metal-organic frameworks (MOFs). However, conventional MOF materials are difficult to synthesize, and the poor selectivity of adsorbents for methane, low adsorption capacity, and inability to be used in humid environments are still problems that need to be solved. Summary of the Invention

[0006] To address the above problems, this invention provides a metal-organic framework adsorbent, its preparation method, and its application. The adsorbent is prepared by mixing a metal salt solution with a ligand solution, resulting in an adsorbent with high adsorption capacity, good selectivity, stable structure, high recognition ability, and the ability to separate methane and nitrogen in a humid environment.

[0007] This invention provides a metal-organic framework adsorbent, which is prepared by mixing a metal salt solution and a ligand solution, wherein the metal salt solution comprises a metal salt and a coordination compound; the metal-organic framework adsorbent has an average pore size of 0.5-0.7 nm and a pore volume of 0.1-0.15 cm³. 3 / g, specific surface area is 320-350cm² 2 / g; The metal-organic framework adsorbent has a three-dimensional structure, including one-dimensional channels;

[0008] In powder X-ray diffraction (PXRD) analysis, the metal-organic framework adsorbent exhibits characteristic peaks of the 001 face-centered cubic lattice at 2θ = 12.1° ± 0.02°, characteristic peaks of the (1, -1, 0) face-centered cubic lattice at 17.4° ± 0.02°, and characteristic peaks of the (1, 1, -1) face-centered cubic lattice at 21.2° ± 0.02°. After soaking in deionized water for 3 days and in solutions with pH values ​​of 2 and 13 for 1 day, the characteristic peak positions in the PXRD analysis did not shift, indicating stable properties.

[0009] Furthermore, the metal salt is one or more of the following: chloride salts, nitrate salts, acetate salts, carbonate salts, and perchlorate salts, which include metal ions.

[0010] Furthermore, the metal ions include one or more of cobalt, copper, zinc, iron, chromium, tin, magnesium, titanium, manganese, and nickel.

[0011] Furthermore, the coordination compound is one or more of potassium tetracyanonitrile monohydrate, potassium tetracyanoplatin(II) trihydrate, and potassium tetracyanopallate.

[0012] Furthermore, the ligand in the ligand solution is 1,4-diazabicyclo[2,2,2]octane.

[0013] The present invention also provides a method for preparing the metal-organic framework adsorbent, the method comprising the following steps:

[0014] Step 1: At room temperature, add the metal salt and coordination compound to deionized water and stir until completely dissolved to obtain a metal salt solution.

[0015] Step 2: At room temperature, add the ligand to methanol and deionized water, and sonicate until completely dissolved to obtain the ligand solution;

[0016] Step 3: Mix and stir the metal salt solution and the ligand solution to prepare a gel-like mixture;

[0017] Step 4: After centrifuging the mixture, a solid adsorbent precursor is obtained. The solid adsorbent precursor is washed with anhydrous ethanol and then dried to obtain the metal-organic framework adsorbent.

[0018] Furthermore, the metal salt in step 1 is one or more of the following: chloride salts, nitrate salts, acetate salts, carbonate salts, and perchlorate salts, which include metal ions.

[0019] Furthermore, the metal ions include one or more of cobalt, copper, zinc, iron, chromium, tin, magnesium, titanium, manganese, and nickel.

[0020] Furthermore, the metal ion is one or more of cobalt and nickel.

[0021] Further, the coordination compound in step 1 is one or more of potassium tetracyanonickelate monohydrate, potassium tetracyanoplatin(II)ate trihydrate, and potassium tetracyanopallate.

[0022] Furthermore, in step 1, the metal ions and cyano ligands in the coordination compound coordinate with the metal ions in the metal salt to form a two-dimensional bimetallic nanosheet structure linked by cyano groups.

[0023] Further, the molar ratio of the metal salt and the ligand compound in step 1 is (1:10) - (1:0.2).

[0024] Furthermore, the concentration of the metal salt in the metal salt solution in step 1 is 0.002-20 mol / L.

[0025] Furthermore, the stirring speed in step 1 is 100-800 r / min.

[0026] Furthermore, the ligand in step 2 is 1,4-diazabicyclo[2,2,2]octane.

[0027] Further, in step 2, the volume ratio of methanol to deionized water is (1:10) - (1:0.2).

[0028] Furthermore, in step 2, the concentration of the ligand in the ligand solution is 0.002-20 mol / L.

[0029] Furthermore, the frequency of the ultrasound in step 2 is 20-50Hz.

[0030] Further, in step 3, the molar ratio of the metal salt in the metal salt solution to the ligand in the ligand solution is (1:10) - (1:0.2).

[0031] Furthermore, in step 3, the two-dimensional bimetallic nanosheet structure in the metal salt solution continues to interact with the ligand to form a three-dimensional structure.

[0032] Furthermore, in step 3, the stirring speed is 100-800 r / min, the stirring temperature is 25-80℃, and the stirring time is 1-12 h.

[0033] Furthermore, in step 4, the centrifugation speed is 5000-12000 r / min, and the centrifugation time is 1-10 min.

[0034] Furthermore, the number of washing cycles in step 4 is 3-5 times.

[0035] Furthermore, the drying temperature in step 4 is 30-80℃, and the drying time is 6-48h.

[0036] This invention also provides a gas adsorbent comprising the aforementioned metal-organic framework adsorbent, used for separating a mixture of methane and nitrogen; the gas adsorbent, under conditions of 25°C and dry ambient humidity, has an adsorption capacity of 20-40 cm³ for methane in the mixture of methane and nitrogen. 3 / g, the adsorption capacity for nitrogen is 0.5-3.01cm. 3 / g; the methane / nitrogen adsorption ratio of the gas adsorbent is 7-10, and the selectivity of the gas adsorbent is 10-25;

[0037] Under conditions of 25℃ and 50%RH, the adsorption capacity of the gas adsorbent for methane is 20-40 cm³. 3 / g, the adsorption capacity for nitrogen is 0.5-3.01cm. 3 / g; the methane / nitrogen adsorption ratio of the gas adsorbent is 7-10; the selectivity of the gas adsorbent is 10-25.

[0038] Furthermore, the adsorption process of the gas adsorbent for separating the mixture of methane and nitrogen is as follows:

[0039] The gas adsorbent is activated by heating at 120-200℃ for 8-24 hours. The activated gas adsorbent is then loaded into an adsorption separation column, and the mixture of methane and nitrogen is passed into the adsorption separation column to separate the methane and nitrogen. The outflow time of methane and nitrogen is observed.

[0040] Furthermore, the condition of dry ambient humidity is as follows: after the gas adsorbent is loaded into the fixed bed of gas adsorbent, the gas adsorbent is purged with helium at room temperature for 30 minutes.

[0041] Furthermore, the volume ratio of methane to nitrogen in the mixture of methane and nitrogen is (1:9) to (5:5).

[0042] Furthermore, the one-dimensional channels in the gas adsorbent can match methane molecules well, and the pores contain abundant open metal sites, providing stronger affinity for methane molecules with high polarizability and large molecular size. The low-polarity methylene groups on the ligands in the pores can also interact strongly with the highly polarizable methane molecules. Therefore, the adsorption capacity of the gas adsorbent for methane and nitrogen is significantly different. During dynamic breakthrough, since the adsorption capacity of nitrogen is small, it can quickly flow out of the fixed bed, thereby achieving methane enrichment. At the same time, since there are abundant hydrophobic methylene groups in its channels, its water resistance can be enhanced, enabling the gas adsorbent to separate mixtures of methane and nitrogen in humid environments.

[0043] The beneficial effects of this invention are:

[0044] 1. This invention utilizes a metal salt, a coordination compound, and ligands. First, the metal ions and cyano ligands in the coordination compound coordinate with the metal ions in the metal salt to form a two-dimensional bimetallic nanosheet structure linked by cyano groups. Then, the two-dimensional bimetallic nanosheet structure in the metal salt solution continues to coordinate with the ligands to form a three-dimensional structure. The metal-organic framework adsorbent prepared in this way exhibits high selectivity for methane. Furthermore, the metal-organic framework adsorbent has suitable porosity, a high density of open metal sites, and abundant methylene groups in the pores that provide strong affinity for methane molecules, resulting in excellent methane adsorption capacity and higher separation selectivity. At the same time, the three-dimensional structure of the metal-organic framework adsorbent in this invention is stable.

[0045] 2. The simple preparation method of this invention involves complexing a metal salt and a ligand compound, followed by adding the ligand and reacting at a specific temperature to prepare a three-dimensional metal-organic framework adsorbent. The synthesis process of the metal-organic framework adsorbent in this invention requires only three reaction steps and centrifugal drying. The raw materials and solvents used in the synthesis process are all green and non-toxic substances, ensuring high safety and low cost. This invention prepares the metal-organic framework adsorbent using only specific raw materials and reaction conditions, resulting in a large pore size and moderate specific surface area. However, excessively high or low temperatures can affect the coordination mode of the metal salt and the linker during the adsorbent synthesis process, or lead to incomplete reactions, thereby affecting the pore conditions of the adsorbent and degrading its performance. Furthermore, the metal-organic framework adsorbent prepared by the method of this invention can undergo scale-up reactions. For example, in Example 7, even after multiplying the reactants, the prepared metal-organic framework adsorbent still maintains high selectivity and adsorption capacity, unaffected by the amount of feed.

[0046] 3. The metal-organic framework adsorbent prepared in this invention can not only separate methane and nitrogen under dry conditions, but also exhibit high selectivity and high adsorption capacity for methane and nitrogen under humid conditions. In humid environments, water vapor can significantly affect the adsorption of methane by the adsorbent. However, the ligands in the metal-organic framework adsorbent of this invention contain methylene groups, making the metal-organic framework adsorbent hydrophobic. Therefore, it is unaffected by humid conditions. Attached Figure Description

[0047] Figure 1 The PXRD images are of the metal-organic framework adsorbent described in Example 1 without soaking, the metal-organic framework adsorbent soaked in deionized water for 3 days, and the adsorbent soaked in solutions with pH values ​​of 2 and 13 for 1 day, respectively.

[0048] Figure 2 This is the adsorption isotherm diagram of the gas adsorbent described in Example 3 after adsorbing methane and nitrogen;

[0049] Figure 3 This is a breakthrough experiment diagram of the gas adsorbent described in Example 3 adsorbing methane and nitrogen.

[0050] Figure 4 This is a comparison chart of the selectivity of the gas adsorbents described in Examples 2 and 3 of this embodiment;

[0051] Figure 5 This is a breakthrough experiment diagram of the gas adsorbent described in Example 4 adsorbing methane and nitrogen.

[0052] Figure 6 The PXRD patterns of the metal-organic framework adsorbents described in Examples 1 and 5 are shown below.

[0053] Figure 7 This is a comparison chart of the selectivity of the metal-organic framework adsorbents described in Examples 1 and 5 with other adsorbents;

[0054] Figure 8 This is the adsorption isotherm diagram of the gas adsorbent described in Example 6 after adsorbing methane and nitrogen;

[0055] Figure 9 This is a selectivity diagram of the gas adsorbent described in Example 6;

[0056] Figure 10 This is a flowchart illustrating the preparation process of the metal-organic framework adsorbent described in Example 7.

[0057] Figure 11 This is the adsorption isotherm diagram of the adsorbent described in Comparative Example 2 after adsorbing methane and nitrogen.

[0058] Figure 12 This is a selectivity diagram of the adsorbent described in Comparative Example 2;

[0059] Figure 13 This is a three-dimensional structural diagram of the metal-organic framework adsorbent described in this invention. Detailed Implementation

[0060] The invention will be described in detail below with reference to the embodiments:

[0061] This invention provides a metal-organic framework adsorbent, its preparation method, and its application. This invention prepares an adsorbent with high methane adsorption performance, strong environmental adaptability, and high stability through a simple preparation process, which greatly expands its application range in the field of gas separation.

[0062] In the following embodiments,

[0063] Example 1 is a metal-organic framework adsorbent and its preparation method, which uses cobalt nitrate hexahydrate as the metal salt in the metal salt solution;

[0064] Example 2 is a gas adsorbent prepared from the metal-organic framework adsorbent described in Example 1, wherein the volume ratio of methane to nitrogen is 10:90, and the ambient humidity is dry;

[0065] Example 3 is a gas adsorbent prepared from the metal-organic framework adsorbent described in Example 1, wherein the volume ratio of methane to nitrogen is 50:50, and the ambient humidity is dry;

[0066] Example 4 is a gas adsorbent prepared from the metal-organic framework adsorbent described in Example 1, wherein the volume ratio of methane to nitrogen is 50:50 and the ambient humidity is 50%RH;

[0067] Example 5 is a metal-organic framework adsorbent and its preparation method, which uses nickel nitrate hexahydrate as the metal salt in the metal salt solution;

[0068] Example 6 is a gas adsorbent prepared from the metal-organic framework adsorbent described in Example 5, wherein the volume ratio of methane to nitrogen is 50:50, and the ambient humidity is dry;

[0069] Example 7 describes a metal-organic framework adsorbent, its preparation method, and its application. The volume ratio of methane to nitrogen is 50:50, the ambient humidity is dry, and cobalt nitrate hexahydrate is used as the metal salt in the metal salt solution. The variables are the content of the metal salt, ligand compound, and ligand.

[0070] Comparative Example 1 is an adsorbent and its preparation method and a gas adsorbent, wherein the volume ratio of methane to nitrogen is 50:50, the ambient humidity is dry, and cobalt nitrate hexahydrate is used as the metal salt in the metal salt solution, wherein the variable is the type of ligand;

[0071] Comparative Example 2 is a commercial adsorbent and its uses.

[0072] Example 1

[0073] This embodiment provides a metal-organic framework adsorbent, which is prepared by mixing a metal salt solution and a ligand solution. The metal salt solution includes a metal salt and a coordination compound. The metal-organic framework adsorbent has an average pore size of 0.63 nm and a pore volume of 0.125 cm³. 3 / g, specific surface area is 349cm³ 2 / g.

[0074] This embodiment also provides a method for preparing the metal-organic framework adsorbent, the preparation method comprising the following steps:

[0075] Step 1: At room temperature, add 5.5 mmol of cobalt nitrate hexahydrate and 5.5 mmol of potassium tetracyanide nickelate monohydrate to 10 mL of deionized water and stir at 300 r / min for 90 min until completely dissolved to obtain a metal salt solution.

[0076] Step 2: At room temperature, 5.5 mmol of 1,4-diazabicyclo[2,2,2]octane was added to 100 mL of methanol and 100 mL of deionized water, and sonicated at 20 Hz until completely dissolved to obtain the ligand solution.

[0077] Step 3: Mix and stir the metal salt solution and the ligand solution at 40°C and 300 r / min for 3 h to prepare a gel-like mixture;

[0078] Step 4: Centrifuge the mixture at 8000 r / min for 5 min to obtain a solid adsorbent precursor. Wash the solid adsorbent precursor three times with anhydrous ethanol and dry it at 50°C for 12 h to obtain the metal-organic framework adsorbent.

[0079] like Figure 1 The PXRD images of the metal-organic framework adsorbent described in Example 1 are shown below: before soaking, after soaking in deionized water for 3 days, and after soaking in solutions with pH values ​​of 2 and 13 for 1 day. As can be seen from the images, the metal-organic framework adsorbent showed almost no structural changes before and after soaking, which proves the stability of the metal-organic framework adsorbent.

[0080] In the figure, the horizontal axis (2Θ) represents the diffraction angle, and the vertical axis (relative intensity) represents the relative intensity.

[0081] Example 2

[0082] This embodiment provides a gas adsorbent prepared from the metal-organic framework adsorbent described in Embodiment 1, which is used to separate a methane-nitrogen mixture; the adsorption capacity of the gas adsorbent for methane in the methane-nitrogen mixture is 26 cm³. 3 / g, with an adsorption capacity of 3.01cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 8.64, and the selectivity of the gas adsorbent is 13.4.

[0083] In this embodiment, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 10:90, the ambient humidity is dry, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0084] The gas adsorbent was activated by heating at 150°C for 12 hours. 1g of the activated gas adsorbent was then loaded into an adsorption bed, and the methane-nitrogen mixture was introduced at a flow rate of 4cm. 3 A flow rate of / min was introduced into the adsorption fixed bed to separate methane and nitrogen. The outflow times of methane and nitrogen were observed, with methane outflow time being 5.89 min and nitrogen outflow time being 0 min.

[0085] Example 3

[0086] This embodiment provides a gas adsorbent prepared from the metal-organic framework adsorbent described in Embodiment 1, which is used to separate a methane-nitrogen mixture; the adsorption capacity of the gas adsorbent for methane in the methane-nitrogen mixture is 26 cm³. 3 / g, with an adsorption capacity of 3.01cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 8.6, and the selectivity of the gas adsorbent is 23.5.

[0087] In this embodiment, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 50:50, the ambient humidity is dry, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0088] The gas adsorbent was activated by heating at 150°C for 12 hours. 1g of the activated gas adsorbent was then loaded into an adsorption bed, and the methane-nitrogen mixture was introduced at a flow rate of 4cm. 3 A flow rate of / min was introduced into the adsorption fixed bed to separate methane and nitrogen. The outflow times of methane and nitrogen were observed, with methane outflow time being 5.5 min and nitrogen outflow time being 0.41 min.

[0089] like Figure 2 The figure shows the adsorption isotherm of the gas adsorbent described in Example 3 after adsorbing methane and nitrogen. As can be seen from the figure, the adsorption capacity of the gas adsorbent for methane is 26 cm⁻¹. 3 / g, the gas adsorbent has an adsorption capacity of 3.01cm³ for nitrogen. 3 / g, where the horizontal axis (Pressure) in the graph represents pressure and the vertical axis (gas uptake) represents adsorption amount.

[0090] like Figure 3 The figure shows the breakthrough experiment of the gas adsorbent described in Example 3 adsorbing methane and nitrogen. As can be seen from the figure, nitrogen quickly becomes saturated during the adsorption process. The nitrogen outflow time is 0.41 min, and the methane outflow time is 5.5 min. The horizontal axis (Time) in the figure represents time, and the vertical axis (C / C0) represents the relative concentration.

[0091] like Figure 4 This is a comparison chart of the selectivity of the gas adsorbents described in Examples 2 and 3. At 25°C and 1 bar, the selectivity of the gas adsorbent in Example 2 (10:90) is 13.4, and the selectivity of the gas adsorbent in Example 3 (50:50) is 23.5. In the chart, the horizontal axis (Pressure) represents pressure, and the vertical axis (CH4 / N2 selectivity) represents the selectivity of CH4 / N2.

[0092] Example 4

[0093] This embodiment provides a gas adsorbent prepared from the metal-organic framework adsorbent described in Embodiment 1, which is used to separate a methane-nitrogen mixture; the adsorption capacity of the gas adsorbent for methane in the methane-nitrogen mixture is 26 cm³. 3 / g, with an adsorption capacity of 3.01cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 8.6, and the selectivity of the gas adsorbent is 23.5.

[0094] In this embodiment, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 50:50, the ambient humidity is 50%RH, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0095] The gas adsorbent was activated by heating at 150°C for 12 hours. 1g of the activated gas adsorbent was then loaded into an adsorption bed, and the methane-nitrogen mixture was introduced at a flow rate of 4cm. 3 A flow rate of / min was introduced into the adsorption fixed bed to separate methane and nitrogen. The outflow times of methane and nitrogen were observed, with methane outflow time being 5.8 min and nitrogen outflow time being 0.51 min.

[0096] like Figure 5 The figure shows the breakthrough experiment of the gas adsorbent described in Example 4 adsorbing methane and nitrogen. As can be seen from the figure, the outflow time of nitrogen during the adsorption process is 0.51 min and the outflow time of methane is 5.8 min, which is similar to the outflow time under the dry conditions in Example 3. This proves that the adsorbent for separating methane-nitrogen mixtures described in this invention can still stably adsorb methane in a humid environment. In the figure, the horizontal axis (Time) represents time and the vertical axis (C / C0) represents the relative concentration.

[0097] Example 5

[0098] This embodiment provides a metal-organic framework adsorbent, which is prepared by mixing a metal salt solution and a ligand solution, wherein the metal salt solution includes a metal salt and a coordination compound.

[0099] This embodiment also provides a method for preparing the metal-organic framework adsorbent, the preparation method comprising the following steps:

[0100] Step 1: At room temperature, add 5.5 mmol nickel nitrate hexahydrate and 5.5 mmol potassium tetracyanide nickelate monohydrate to 10 mL of deionized water and stir at 300 r / min for 90 min until completely dissolved to obtain a metal salt solution.

[0101] Step 2: At room temperature, 5.5 mmol of 1,4-diazabicyclo[2,2,2]octane was added to 100 mL of methanol and 100 mL of deionized water, and sonicated at 20 Hz until completely dissolved to obtain the ligand solution.

[0102] Step 3: Mix and stir the metal salt solution and the ligand solution at 40°C and 300 r / min for 3 h to prepare a gel-like mixture;

[0103] Step 4: Centrifuge the mixture at 8000 r / min for 5 min to obtain a solid adsorbent precursor. Wash the solid adsorbent precursor three times with anhydrous ethanol and dry it at 50°C for 12 h to obtain the metal-organic framework adsorbent.

[0104] like Figure 6 The figures show the PXRD patterns of the metal-organic framework adsorbents described in Examples 1 and 5. As can be seen from the figures, Examples 1 and 5 both show characteristic peaks of the 001 crystal plane of the face-centered cubic lattice at a diffraction angle of 2θ of 12.1°±0.02°, characteristic peaks of the (1, -1, 0) crystal plane at 17.4°±0.02°, and characteristic peaks of the (1, 1, -1) crystal plane at 21.2°±0.02°.

[0105] In the figure, the horizontal axis (2Θ) represents the diffraction angle, and the vertical axis (relative intensity) represents the relative intensity.

[0106] like Figure 7 This is a comparison chart of the selectivity of the metal-organic framework adsorbents described in Examples 1 and 5 with other adsorbents. At 25°C and 1 bar, the chart shows that the selectivity of the metal-organic framework adsorbents described in Examples 1 and 5 is much higher than that of other adsorbents, namely Ni(ina)2, Al-CDC, Co3(C4O4)2(OH)2, SBMOF-1, ATC-Cu, NKMOF-8-br, Cu(INA)2, ZIF-94, PRC-850, ZK-5, and Ni-MOF-74. In the chart, the horizontal axis (CH4 / N2 selectivity) represents the CH4 / N2 selectivity, and the vertical axis (CH4 / N2 uptake ratio) represents the CH4 / N2 adsorption rate.

[0107] In this embodiment, the Ni(ina)2 is derived from […]. Angewandte ChemieInternational Edition In 2022, in Volume 134, Wang et al. published the paper "Nickel-Based Metal–Organic Frameworks for Coal-Bed Methane Purification with Record CH4 / N2 Selectivity", DOI: 10.1002 / anie.202201017;

[0108] The Al-CDC is derived from […]. Sustainable Energy & FuelsIn 2020, Volume 4, pp. 138-142, Chang et al. published the article "Methane-trapping metal–organic frameworks with an aliphatic ligand for efficient CH4 / N2 separation", DOI 10.1039 / C9SE00838A;

[0109] The Co3(C4O4)2(OH)2 is derived from […]. AIChE Journal In 2018, Volume 64, pp. 3681-3689, Li et al. published the article "Highly Efficient Separation of Methane from Nitrogen on a Square-Based Metal-Organic Framework", DOI: 10.1002 / aic.16335;

[0110] The SBMOF-1 mentioned is derived from […]. Chemical Engineering Journal In 2021, Volume 408, page 127294, Chang et al. published the article "A robust calcium-based microporous metal-organic framework for efficient CH4 / N2 separation", DOI: 10.1016 / j.cej.2020.127294;

[0111] The ATC-Cu is derived from […]. Angewandte ChemieInternational Edition The article “A Metal–Organic Framework Based MethaneNano-trap for the Capture of Coal-Mine Methane” by Niu et al., published in 2019, Volume 58, pp. 10138-10141, DOI: 10.1002 / anie.201904507;

[0112] The NKMOF-8-br is derived from […]. Journal of Chemical&Engineering DataIn 2022, Volume 67, Issue 7, pp. 1654-1662, Guo et al. published the article "A Stable Cu(I)-Based Ultramicroporous NKMOF-8-Br with High CH4Uptake for Efficient Separation of CH4 / N2 Mixtures", DOI: 10.1021 / acs.jced.1c00787;

[0113] The Cu(INA)2 is derived from […]. RSC Advances In 2016, Volume 6, pp. 64039-64046, Hu et al. published the article "Separation of CH4 / N2 mixtures in metal–organic frameworks with 1D micro-channels", DOI 10.1039 / c6ra12280a;

[0114] The ZIF-94 mentioned is derived from […]. Separation and Purification Technology In 2020, on page 115850 of Volume 230, Shi et al. published an article entitled "Effective CH4enrichment from N2 by SIM-1 via a strong adsorption potential SOD cage", with the DOI 10.1016 / j.seppur.2019.115850.

[0115] The PRC-850 is derived from […]. Chemical Engineering Journal In 2020, on page 123388 of Volume 384, Tang et al. published the paper "Synthesis of novel particle rice-based carbon materials and its excellent CH4 / N2 adsorption selectivity for methaneenrichment from Low-rank natural gas", with DOI 10.1016 / j.cej.2019.123388.

[0116] The ZK-5 is derived from […]. Chemical Engineering JournalIn 2021, Volume 406, page 126599, Yang et al. published the article "Down-sizing the crystal size of ZK-5 zeolite for its enhanced CH4 adsorption and CH4 / N2 separation performances", DOI: 10.1016 / j.cej.2020.126599;

[0117] The Ni-MOF-74 is derived from […]. Microporous and Mesoporous Materials In 2014, Volume 198, pp. 236-246, Li et al. published the article "Separation of CO2 / CH4 and CH4 / N2 mixtures by M / DOBDC: A detailed dynamic comparison with MIL-100(Cr) and activated carbon", DOI: 10.1016 / j.micromeso.2014.07.041.

[0118] Example 6

[0119] This embodiment provides a gas adsorbent prepared from the metal-organic framework adsorbent described in Embodiment 5, which is used to separate a methane-nitrogen mixture; the adsorption capacity of the gas adsorbent for methane in the methane-nitrogen mixture is 18 cm³. 3 / g, with an adsorption capacity of 2.5cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 7.2, and the selectivity of the gas adsorbent is 23.

[0120] In this embodiment, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 50:50, the ambient humidity is dry, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0121] The gas adsorbent was activated by heating at 150°C for 12 hours. 1g of the activated gas adsorbent was then loaded into an adsorption bed, and the methane-nitrogen mixture was introduced at a flow rate of 4cm. 3 A flow rate of / min is introduced into the adsorption fixed bed to separate methane and nitrogen.

[0122] like Figure 8 The figure shows the adsorption isotherm of the gas adsorbent described in Example 6 after adsorbing methane and nitrogen. As can be seen from the figure, the adsorption capacity of the gas adsorbent for methane is 18 cm⁻¹. 3 / g, the gas adsorbent has an adsorption capacity of 2.5cm for nitrogen.3 / g, where the horizontal axis (Pressure) in the graph represents pressure and the vertical axis (gas uptake) represents adsorption amount.

[0123] like Figure 9 This is a selectivity graph of the gas adsorbent described in Example 6. At 25°C and 1 bar, the selectivity of the gas adsorbent described in Example 6 (50:50) is 23. The horizontal axis (Pressure) in the graph represents pressure, and the vertical axis (CH4 / N2 selectivity) represents the selectivity of CH4 / N2.

[0124] Example 7

[0125] This embodiment provides a metal-organic framework adsorbent, which is prepared by mixing a metal salt solution and a ligand solution, wherein the metal salt solution includes a metal salt and a coordination compound.

[0126] This embodiment also provides a method for preparing the metal-organic framework adsorbent, the preparation method comprising the following steps:

[0127] Step 1: At room temperature, add 4 mol of cobalt nitrate hexahydrate and 4 mol of potassium tetracyanide nickelate monohydrate to 7 L of deionized water, and stir at 300 r / min for 90 min until completely dissolved to obtain a metal salt solution.

[0128] Step 2: At room temperature, 4 mol of 1,4-diazabicyclo[2,2,2]octane was added to 17.5 L of methanol and 17.5 L of deionized water, and sonicated at 20 Hz until completely dissolved to obtain a ligand solution.

[0129] Step 3: Mix and stir the metal salt solution and the ligand solution at 40°C and 300 r / min for 3 h to prepare a gel-like mixture;

[0130] Step 4: Centrifuge the mixture at 8000 r / min for 5 min to obtain a solid adsorbent precursor. Wash the solid adsorbent precursor three times with anhydrous ethanol and dry it at 50°C for 12 h to obtain 1.315 kg of the metal-organic framework adsorbent.

[0131] This embodiment also provides a gas adsorbent, which is the aforementioned metal-organic framework adsorbent, used for separating a methane-nitrogen mixture; the adsorption capacity of the gas adsorbent for methane in the methane-nitrogen mixture is 25.7 cm³. 3 / g, with an adsorption capacity of 2.94cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 8.7, and the selectivity of the gas adsorbent is 23.3.

[0132] In this embodiment, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 50:50, the ambient humidity is dry, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0133] The methane-nitrogen mixture was activated by heating at 150°C for 12 hours. 1 g of the gas adsorbent was loaded into an adsorption bed, and the activated methane-nitrogen mixture was then introduced into the bed at a flow rate of 4 cm⁻¹. 3 A flow rate of / min was introduced into the adsorption fixed bed to separate methane and nitrogen. The outflow times of methane and nitrogen were observed, with methane outflow time being 5.3 min and nitrogen outflow time being 0.32 min.

[0134] like Figure 10 This is a flowchart illustrating the preparation process of the metal-organic framework adsorbent described in Example 7.

[0135] Comparative Example 1

[0136] This comparative example provides an adsorbent prepared by mixing a metal salt solution and a ligand solution, wherein the metal salt solution comprises a metal salt and a coordination compound; the adsorbent has an average pore size of 0.54 nm and a pore volume of 0.25 cm³. 3 / g, specific surface area is 640cm² 2 / g.

[0137] This comparative example also provides a method for preparing the adsorbent, the method comprising the following steps:

[0138] Step 1: At room temperature, add 5.5 mmol of cobalt nitrate hexahydrate and 5.5 mmol of potassium tetracyanide nickelate monohydrate to 10 mL of deionized water and stir at 300 r / min for 90 min until completely dissolved to obtain a metal salt solution.

[0139] Step 2: At room temperature, 5.5 mmol of pyrazine was added to 100 mL of methanol and 100 mL of deionized water, and sonicated at 20 Hz until completely dissolved to obtain the ligand solution.

[0140] Step 3: Mix and stir the metal salt solution and the ligand solution at 40°C and 300 r / min for 3 h to prepare a gel-like mixture;

[0141] Step 4: Centrifuge the mixture at 8000 r / min for 5 min to obtain a solid adsorbent precursor. Wash the solid adsorbent precursor three times with anhydrous ethanol and dry it at 50°C for 12 h to obtain the adsorbent.

[0142] This comparative example also provides a gas adsorbent, prepared from the aforementioned adsorbent, used for separating a methane-nitrogen mixture; the gas adsorbent has an adsorption capacity of 24.9 cm³ for methane in the methane-nitrogen mixture. 3 / g, with an adsorption capacity of 5.01cm for nitrogen. 3 / g; the adsorption ratio of methane / nitrogen by the gas adsorbent is 4.97, and the selectivity of the gas adsorbent is 6.2.

[0143] In this comparative example, the volume ratio of methane to nitrogen in the methane-nitrogen mixture is 50:50, the ambient humidity is dry, and the adsorption process of the gas adsorbent on the methane-nitrogen mixture is as follows:

[0144] The gas adsorbent was activated by heating at 150°C for 12 hours. 1g of the activated gas adsorbent was then loaded into an adsorption bed, and the methane-nitrogen mixture was introduced at a flow rate of 4cm. 3 A flow rate of / min was introduced into the adsorption fixed bed to separate methane and nitrogen. The outflow times of methane and nitrogen were observed, with methane outflow time being 3.1 min and nitrogen outflow time being 0.31 min.

[0145] Comparative Example 2

[0146] This comparative example also provides a commercial adsorbent, MIL-53 (Al), used for separating methane-nitrogen mixtures; the adsorbent has an adsorption capacity of 16.5 cm³ for methane in the methane-nitrogen mixture. 3 / g, with an adsorption capacity of 5.5cm for nitrogen. 3 / g; the adsorbent has an adsorption ratio of 3 for methane / nitrogen and a selectivity of 3.2.

[0147] like Figure 11 The figure shows the adsorption isotherm of the adsorbent described in Comparative Example 2 after adsorbing methane and nitrogen. As can be seen from the figure, the adsorbent's adsorption capacity for methane is 16.5 cm⁻¹. 3 / g, the adsorbent has an adsorption capacity of 5.5cm for nitrogen. 3 / g, where the horizontal axis (Pressure) in the graph represents pressure and the vertical axis (gas uptake) represents adsorption amount.

[0148] like Figure 12The graph shows the selectivity of the adsorbent described in Comparative Example 2. At 25°C and 1 bar, the selectivity of the adsorbent described in Comparative Example 3 is 3.2. The horizontal axis (Pressure) in the graph represents pressure, and the vertical axis (CH4 / N2 selectivity) represents the selectivity of CH4 / N2.

[0149] The MIL-53(A1) mentioned in this embodiment is derived from […]. Chinese Journal of Chemical Engineering In the article "Separation of CO2 / CH4 and CH4 / N2 on Homogeneous Metal-Organic Framework Materials" published by Wang Xiaoqing et al. in Volume 24, Issue 12, 2016, pp. 1687-1694, DOI: 10.1016 / j.cjche.2016.05.013.

[0150] The dry environmental humidity condition described in this invention is as follows: after the gas adsorbent is loaded into the gas adsorbent fixed bed, the adsorbent is purged with helium at room temperature for 30 minutes.

[0151] Table 1 shows the properties of the metal-organic framework adsorbents described in Example 1 and Comparative Example 1.

[0152]

[0153] As shown in Table 1, the metal-organic framework adsorbent prepared in Example 1 has a large pore size but a small pore volume and a smaller specific surface area compared to Comparative Example 1. Compared to Comparative Example 1, the introduction of 3D linkers in Example 1 leads to a reduction in pore volume and enhances the contact area between the framework and guest molecules. Since the polarizability of methane is greater than that of nitrogen, the introduction of 3D linkers hinders the adsorption of nitrogen and promotes the adsorption of methane, thereby resulting in Example 1 having excellent methane-nitrogen separation selectivity.

[0154] Table 2 shows the adsorption performance in Examples 2-4, Examples 6-7, and Comparative Examples 1-2.

[0155]

[0156] As shown in Table 2, the gas adsorbents in Examples 2-3 and 6-7 have high adsorption capacity for methane and good selectivity, and can better separate methane and nitrogen. In contrast, the adsorbent prepared by using pyrazine as a ligand in Comparative Example 1 has a high adsorption capacity for methane, but poor selectivity. The adsorbent in Comparative Example 2 is a common commercial adsorbent, which has poor separation effect and poor selectivity for methane and nitrogen.

[0157] As can be seen from the above, the metal-organic framework adsorbent described in this invention has a wide range of applications, low cost, and a very high market prospect.

[0158] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. An application of a metal-organic framework adsorbent for separating methane and nitrogen, characterized in that, The metal-organic framework adsorbent is prepared by mixing a metal salt solution and a ligand solution, wherein the metal salt solution comprises a metal salt and a coordination compound; the metal-organic framework adsorbent has an average pore size of 0.5-0.7 nm and a pore volume of 0.1-0.15 cm³. 3 / g, specific surface area is 320-350cm² 2 / g; The metal-organic framework adsorbent has a three-dimensional structure, including one-dimensional channels; In powder X-ray diffraction (PXRD) analysis, the metal-organic framework adsorbent exhibits characteristic peaks of the 001 face-centered cubic lattice at 2θ = 12.1° ± 0.02°, characteristic peaks of the (1, -1, 0) face-centered cubic lattice at 17.4° ± 0.02°, and characteristic peaks of the (1, 1, -1) face-centered cubic lattice at 21.2° ± 0.02°. After soaking in deionized water for 3 days and in solutions with pH values ​​of 2 and 13 for 1 day, the characteristic peak positions in the PXRD analysis did not shift, indicating stable properties. The metal ions in the metal salt include one or more of cobalt, copper, zinc, iron, chromium, tin, magnesium, titanium, manganese, and nickel. The coordination compound is one or more of potassium tetracyanonitrile monohydrate, potassium tetracyanoplatin(II) trihydrate, and potassium tetracyanopallate. The ligand in the ligand solution is 1,4-diazabicyclo[2,2,2]octane.

2. The application of the metal-organic framework adsorbent according to claim 1 in separating methane and nitrogen, characterized in that, The metal salt is one or more of the following: chloride salts, nitrate salts, acetate salts, carbonate salts, and perchlorate salts, which contain metal ions.

3. The application of the metal-organic framework adsorbent according to claim 1 in separating methane and nitrogen, characterized in that, The preparation method of the metal-organic framework adsorbent includes the following steps: Step 1: At room temperature, add the metal salt and coordination compound to deionized water and stir until completely dissolved to obtain a metal salt solution. Step 2: At room temperature, add the ligand to methanol and deionized water, and sonicate until completely dissolved to obtain the ligand solution; Step 3: Mix and stir the metal salt solution and the ligand solution to prepare a gel-like mixture; Step 4: After centrifuging the mixture, a solid adsorbent precursor is obtained. The solid adsorbent precursor is washed with anhydrous ethanol and then dried to obtain the metal-organic framework adsorbent.

4. The application of the metal-organic framework adsorbent according to claim 3 in separating methane and nitrogen, characterized in that, The molar ratio of the metal salt and ligand compound in step 1 is (1:10) - (1:0.2).

5. The application of the metal-organic framework adsorbent according to claim 3 in separating methane and nitrogen, characterized in that, In step 3, the molar ratio of the metal salt in the metal salt solution to the ligand in the ligand solution is (1:10) - (1:0.2).

6. The application of the metal-organic framework adsorbent according to claim 3 in separating methane and nitrogen, characterized in that, The stirring speed in step 3 is 100-800 r / min, the stirring temperature is 25-80℃, and the stirring time is 1-12 h.

7. The application of the metal-organic framework adsorbent according to claim 1 in separating methane and nitrogen, characterized in that, The metal-organic framework adsorbent adsorbs 20-40 cm⁻¹ of methane in the mixture of methane and nitrogen at 25°C and in a dry environment. 3 / g, the adsorption capacity for nitrogen is 0.5-3.01cm. 3 / g; the adsorption ratio of methane / nitrogen by the metal-organic framework adsorbent is 7-10, and the selectivity of the metal-organic framework adsorbent is 10-25; Under conditions of 25℃ and 50%RH, the adsorption capacity of the metal-organic framework adsorbent for methane is 20-40 cm⁻¹. 3 / g, the adsorption capacity for nitrogen is 0.5-3.01cm. 3 / g; the methane / nitrogen adsorbent adsorption ratio of the metal-organic framework adsorbent is 7-10; the selectivity of the metal-organic framework adsorbent is 10-25.

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