A separation adsorbent for SF6 / N2 mixtures and its preparation method

Abstract

The application provides a kind of SF6 / N2 mixture separation adsorbent and its preparation method, belongs to industrial waste gas treatment technical field.The preparation method is: nickel nitrate hexahydrate and 1H-pyrazole-4-carboxylic acid are added to organic solvent, stirring until ligand is completely dissolved, to obtain mixed solution;1,4-diazabicyclo [2.2.2] octane is added to the mixed solution and stirred evenly, after reaction, green product is collected by centrifugation;The green product is washed with methanol to remove impurities, then vacuum dried to obtain adsorbent precursor;The adsorbent precursor is activated to obtain the separation adsorbent.The adsorbent synthesis method is simple, low in cost, is a kind of three-dimensional columnar layered metal organic framework material with reasonable distribution of cooperative supramolecular interaction sites, has high SF6 / N2 separation selectivity, so it can more effectively separate SF6 / N2 mixture under dynamic conditions.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste gas treatment technology, and particularly relates to a separation adsorbent for SF6 / N2 mixtures and its preparation method. Background Technology

[0002] Sulfur hexafluoride (SF6) is a synthetically produced inert fluorine-containing gas with excellent arc-quenching and dielectric properties, widely used in microelectronics, non-ferrous metal smelting and casting, and air pollution measurement. However, as one of the six common greenhouse gases, its global warming potential is 23,900 times that of carbon monoxide, and its impact on global climate change cannot be ignored. In current industrial production, SF6 is often mixed with nitrogen impurities and emitted directly. Direct emission of this untreated mixture not only wastes this valuable gaseous resource but also exacerbates the greenhouse effect. Therefore, effectively separating SF6 gas from low-concentration SF6 mixtures is crucial.

[0003] Currently, industrial technologies for separating SF6 / N2 mainly include cryogenic distillation, liquefaction, cryogenic freezing, SF6-hydrate, adsorbents, and membrane separation. Among these, cryogenic distillation and liquefaction are not economically feasible under low concentrations of sulfur hexafluoride, cryogenic freezing consumes far more energy than other separation methods, and the separation method using SF6-hydrate is still difficult to apply on a large scale, and the separated sulfur hexafluoride gas will still contain moisture impurities.

[0004] Compared with the separation processes mentioned above, adsorbent separation exhibits advantages such as low energy consumption, simple operation, environmental friendliness, and low cost. Adsorbents used for the separation of sulfur hexafluoride (SF6) and nitrogen mainly utilize the differences in polarity and kinetic diameter between their molecules, allowing them to achieve ideal separation results without undergoing a phase transition, thus showing promising development prospects. However, most adsorbents are still synthesized in powder form, requiring molding for industrial applications, which leads to performance degradation. Furthermore, adsorbent synthesis methods are difficult, their structures are unstable, their selectivity and adsorption capacity are low, and their costs are high. All these factors still limit the industrial application of adsorbents.

[0005] Therefore, it is necessary to develop an adsorbent with good SF6 adsorption capacity and SF6 / N2 selectivity, excellent structural stability, low cost, and simple synthesis method for SF6 / N2 mixtures to achieve efficient separation of SF6 / N2 mixtures.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a separation adsorbent for SF6 / N2 mixtures and its preparation method. The synthesis method is simple and low in cost. The adsorbent is a three-dimensional columnar layered metal-organic framework material with a reasonable distribution of synergistic supramolecular interaction sites, which has high SF6 / N2 separation selectivity and can therefore more effectively separate SF6 / N2 mixtures under dynamic conditions.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a separation adsorbent for SF6 / N2 mixtures:

[0010] Nickel nitrate hexahydrate and 1H-pyrazole-4-carboxylic acid were added to an organic solvent and stirred until the ligands were completely dissolved to obtain a mixed solution.

[0011] 1,4-diazabicyclo[2.2.2]octane was added to the mixed solution and stirred until homogeneous. After the reaction, the green product was collected by centrifugation.

[0012] The green product was washed with methanol to remove impurities, and then vacuum dried to obtain the adsorbent precursor.

[0013] The separation adsorbent is obtained by activating the adsorbent precursor.

[0014] Secondly, the present invention also provides a separation adsorbent for an SF6 / N2 mixture prepared by the aforementioned preparation method, the chemical formula of which is Ni(pca)(ted).

[0015] Compared with the prior art, the present invention has the following technical effects:

[0016] 1. The separation adsorbent of the present invention has good separation ability for SF6 / N2, and exhibits high adsorption capacity for SF6, good SF6 / N2 adsorption ratio and high SF6 / N2 separation selectivity under low pressure.

[0017] 2. The separation adsorbent used in this invention has a simple preparation method, mild synthesis conditions, and does not require acid-base adjustment, making it energy-saving and environmentally friendly; the raw materials are readily available and low in cost (PCA 0.1 kg). -1 0.04 kg -1 It is easy to scale up and synthesize.

[0018] 3. The separation adsorbent of the present invention has a stable structure, which is beneficial for transportation and storage in practical applications. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 The image shows the PXRD pattern of the separation adsorbent prepared in Example 1 of this invention.

[0021] Figure 2 The adsorption isotherms of SF6 and N2 at 298 K for the separation adsorbent prepared in Example 1 of this invention.

[0022] Figure 3 The SF6 / N2 selectivity of the separation adsorbent prepared in Example 1 of this invention is predicted by the ideal solution adsorption theory at 298K.

[0023] Figure 4 This is a comparison of the adsorption ratio of SF6 / N2 and the SF6 / N2 (10 / 90, v / v) selectivity between the separating adsorbent prepared in Example 1 of this invention and other high-performance adsorbents at 25°C and 0.1 bar.

[0024] Figure 5 The XRD pattern of the separation adsorbent prepared in Example 1 of this invention after acid and alkali treatment is compared with the simulated PXRD pattern. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0027] A method for preparing a separation adsorbent for an SF6 / N2 mixture according to an embodiment of the present invention may include the following steps:

[0028] (1) Add nickel nitrate hexahydrate and 1H-pyrazole-4-carboxylic acid to an organic solvent and stir until the ligands are completely dissolved to obtain a mixed solution.

[0029] Further, the ratio of the amount of nickel nitrate hexahydrate added to the organic solvent is 0.024-0.05 mol:1 L. Preferably, the ratio of the amount of nickel nitrate hexahydrate added to the organic solvent is 0.04 mol:1 L.

[0030] Furthermore, the organic solvent comprises a mixture of N,N-dimethylformamide and methanol. Even further, the volume ratio of N,N-dimethylformamide to methanol is 1:(0.8-1.2).

[0031] (2) Add 1,4-diazabicyclo[2.2.2]octane to the mixed solution and stir until homogeneous. After the reaction, collect the green product by centrifugation.

[0032] Further, the molar ratio of nickel nitrate hexahydrate, 1H-pyrazole-4-carboxylic acid and 1,4-diazabicyclo[2.2.2]octane is 1:(0.8-1.2):(0.8-1.2).

[0033] Furthermore, the reaction is carried out at 90-100°C for 20-40 hours. Preferably, the reaction is carried out under closed conditions; generally, the stirred reactants can be placed in a sealed container, and then the sealed container can be placed in an oven for the reaction.

[0034] The use of 1,4-diazabicyclo[2.2.2]octane further reduces the pore size of the material, which can form a strong constraint interaction with SF6 molecules and provide more N atom interaction sites for SF6 adsorption, thereby strengthening the interaction force on SF6 gas.

[0035] (3) The green product is washed with methanol to remove impurities, and then vacuum dried to obtain the adsorbent precursor. The washing may be repeated multiple times, and the drying temperature is generally 80-110°C.

[0036] (4) The adsorbent precursor is activated to obtain the separation adsorbent.

[0037] Furthermore, the activation is performed under vacuum at 70-90°C for 10-15 hours.

[0038] Embodiments of the present invention also provide a separation adsorbent for an SF6 / N2 mixture prepared by the aforementioned preparation method.

[0039] The separation adsorbent has a microstructure in which each Ni ion forms a six-coordinate system with two O atoms from the carboxyl group of the PCA ligand, two N atoms from the pyrazoles of two different PCA ligands, and two N atoms from two different TED rings. The pore surface is covered with a large number of O sites and N-rich TED rings, which greatly enhances the adsorption of SF6.

[0040] The present invention will be further illustrated by the following examples.

[0041] Example 1

[0042] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 2.4 mmol of 1H-pyrazole-4-carboxylic acid to a 60 mL mixture of N,N-dimethylformamide and methanol (volume ratio 1:1), stirring for 5 min until the ligands are completely dissolved, then adding 2.4 mmol of 1,4-diazabicyclo[2.2.2]octane to the above solution and stirring for 5 min. The mixture is then placed in a sealed reactor and reacted in a 90 °C oven for 36 hours. A green sample is collected by centrifugation, washed three times with methanol to obtain the material after impurity removal, dried under vacuum at 80 °C to obtain the adsorbent precursor, and activated under high vacuum at 80 °C for 12 hours to obtain the final product.

[0043] See Figure 1 The powder X-ray diffraction (PXRD) pattern matches the simulation results well, indicating that the synthesized separation adsorbent Ni(pca)(ted) has high purity.

[0044] See Figure 2 The separating adsorbent Ni(pca)(ted) showed a concentration of 45.96 mL g at 298 K and 1 bar. -1 (2.05mmolg -1) High SF6 adsorption capacity and 7.67 mL g -1 (0.34mmol g -1 It has a much lower N2 adsorption capacity than SF6, and a very high SF6 / N2 adsorption ratio.

[0045] See Figure 3 The separation selectivity of the separation adsorbent Ni(pca)(ted) for the SF6 / N2 (v / v, 10 / 90) mixture was evaluated by IAST, indicating that the separation adsorbent completes the molecular sieving of the gas for the separation of SF6 and N2.

[0046] See Figure 4 The separation adsorbent Ni(pca)(ted) has a high SF6 adsorption capacity and high IAST selectivity, which surpasses most common MOF materials. Moreover, its cost is very low, and it is expected to become a high-performance, low-cost gas adsorbent for the separation of SF6 / N2.

[0047] See Figure 5 The separation adsorbent Ni(pca)(ted) exhibits considerable stability under acidic and alkaline conditions and can be applied to SF6 feed gas containing small amounts of acidic and alkaline gases in industrial production.

[0048] Example 2

[0049] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 2.88 mmol of 1H-pyrazole-4-carboxylic acid to 80 mL of a mixed solution of N,N-dimethylformamide and methanol (volume ratio 1:0.8). After stirring for 5 min until the ligands are completely dissolved, 2.88 mmol of 1,4-diazabicyclo[2.2.2]octane is added to the above solution and stirred for 5 min. The solution is then placed in a sealed reactor and reacted in an oven at 90 °C for 36 hours. A green sample is collected by centrifugation, washed three times with methanol to obtain the material after impurity removal, dried under vacuum at 80 °C to obtain the adsorbent precursor, and activated under high vacuum at 80 °C for 12 hours to obtain the final product.

[0050] Example 3

[0051] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 2.88 mmol of 1H-pyrazole-4-carboxylic acid to 80 mL of a mixed solution of N,N-dimethylformamide and methanol (volume ratio 1:0.8). After stirring for 5 min until the ligands are completely dissolved, 2.88 mmol of 1,4-diazabicyclo[2.2.2]octane is added to the above solution and stirred for 5 min. The solution is then placed in a closed reactor and reacted in an oven at 95 °C for 30 hours. A green sample is collected by centrifugation, washed three times with methanol to obtain the material after impurity removal, dried under vacuum at 80 °C to obtain the adsorbent precursor, and activated under high vacuum at 85 °C for 10 hours to obtain the final product.

[0052] Example 4

[0053] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 1.92 mmol of 1H-pyrazole-4-carboxylic acid to 100 mL of a mixed solution of N,N-dimethylformamide and methanol (volume ratio 1:1.2). After stirring for 5 min until the ligands are completely dissolved, 1.92 mmol of 1,4-diazabicyclo[2.2.2]octane is added to the above solution and stirred for 5 min. The solution is then placed in a closed reactor and reacted in an oven at 100 °C for 20 hours. A green sample is collected by centrifugation, washed three times with methanol to obtain the material after impurity removal, dried under vacuum at 80 °C to obtain the adsorbent precursor, and activated under high vacuum at 75 °C for 15 hours to obtain the final product.

[0054] Example 5

[0055] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 1.92 mmol of 1H-pyrazole-4-carboxylic acid to 100 mL of a mixed solution of N,N-dimethylformamide and methanol (volume ratio 1:1.2). After stirring for 5 min until the ligands are completely dissolved, 1.92 mmol of 1,4-diazabicyclo[2.2.2]octane is added to the above solution and stirred for 5 min. The solution is then placed in a closed reactor and reacted in an oven at 90 °C for 36 hours. A green sample is collected by centrifugation, washed three times with methanol to obtain the material after impurity removal, dried under vacuum at 80 °C to obtain the adsorbent precursor, and activated under high vacuum at 80 °C for 12 hours to obtain the final product.

[0056] Example 6

[0057] A method for preparing a separation adsorbent for an SF6 / N2 mixture involves adding 2.4 mmol of nickel nitrate hexahydrate and 2.4 mmol of 1H-pyrazole-4-carboxylic acid to a 60 mL mixture of N,N-dimethylformamide and methanol (volume ratio 1:1). The mixture is stirred for 5 min until the ligands are completely dissolved. Then, 2.4 mmol of 1,4-diazabicyclo[2.2.2]octane is soaked in 10 mL of N,N-dimethylacetamide for 10 min and added to the above solution. The mixture is stirred for 5 min and then placed in a sealed reactor and reacted in a 90 °C oven for 36 hours. A green sample is collected by centrifugation, washed three times with methanol to remove impurities, and dried under vacuum at 80 °C to obtain the adsorbent precursor. This precursor is then activated under high vacuum at 80 °C for 12 hours to obtain the final adsorbent. The resulting adsorbent exhibits an SF6 adsorption capacity of 43.76 mL g at 298 K and 1 bar. -1 The N2 adsorption capacity is 5.57 mL g. -1 It can have a higher SF6 / N2 adsorption ratio. It can be seen that after 1,4-diazabicyclo[2.2.2]octane is soaked in N,N-dimethylacetamide, its polarity will be enhanced, and it will interact more strongly with the easily polarized SF6 molecules, which is conducive to increasing the activity of the adsorbent.

[0058] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a separation adsorbent for an SF6 / N2 mixture, characterized in that, Nickel nitrate hexahydrate and 1H-pyrazole-4-carboxylic acid were added to an organic solvent and stirred until the ligands were completely dissolved to obtain a mixed solution. 1,4-diazabicyclo[2.2.2]octane was added to the mixed solution and stirred until homogeneous. After the reaction, the green product was collected by centrifugation. The green product was washed with methanol to remove impurities, and then vacuum dried to obtain the adsorbent precursor. The separation adsorbent is obtained by activating the adsorbent precursor. The molar ratio of nickel nitrate hexahydrate, 1H-pyrazole-4-carboxylic acid, and 1,4-diazabicyclo[2.2.2]octane is 1:(0.8-1.2):(0.8-1.2); The organic solvent includes a mixture of N,N-dimethylformamide and methanol; The volume ratio of N,N-dimethylformamide to methanol is 1:(0.8-1.2); The reaction was carried out at 90-100℃ for 20-40 hours. The reaction is carried out under closed conditions; The activation process involves treating the sample in a vacuum at 70-90°C for 10-15 hours. Before adding 1,4-diazabicyclo[2.2.2]octane to the mixed solution, the 1,4-diazabicyclo[2.2.2]octane was first soaked in N,N-dimethylacetamide.

2. The method for preparing the separation adsorbent for the SF6 / N2 mixture according to claim 1, characterized in that, The ratio of the amount of nickel nitrate hexahydrate added to the organic solvent is 0.024-0.05 mol: 1 L.

3. The method for preparing the separation adsorbent for the SF6 / N2 mixture according to claim 2, characterized in that, The ratio of the amount of nickel nitrate hexahydrate added to the organic solvent is 0.04 mol: 1 L.

4. A separation adsorbent for an SF6 / N2 mixture prepared by the preparation method according to any one of claims 1-3.

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