Microporous-mesoporous hierarchical carbon molecular sieves with low concentration SF6 capture, their preparation and application

Abstract

The present application belongs to the technical field of special gas capture and recovery, and discloses a microporous-mesoporous hierarchical carbon molecular sieve for low-concentration SF6 capture and its preparation and application, aiming to solve the technical problem that low-concentration sulfur hexafluoride (SF6) is difficult to be efficiently recovered indoors. The method comprises the following steps: impregnating a biomass hard-shell material with a zinc salt aqueous solution; performing a medium-temperature pre-carbonization treatment under an inert atmosphere; and performing a physical activation under a high-temperature carbon dioxide atmosphere to obtain a microporous-mesoporous hierarchical carbon molecular sieve with an ordered distribution. The carbon molecular sieve adsorbent prepared by the present application is mainly microporous and contains a certain proportion of mesopores conducive to gas diffusion, and exhibits excellent adsorption and separation performance for low-concentration sulfur hexafluoride. When the volume fraction of SF6 is 1000 ppm and 3000 ppm, the adsorption capacity is 0.11 mmol / g and 0.29 mmol / g, respectively, which is more than twice that of a commercial molecular sieve.

Description

Technical Field

[0001] This invention belongs to the field of special gas capture and recovery technology, specifically relating to microporous-mesoporous hierarchical carbon molecular sieves for capturing low concentrations of SF6, their preparation and application. Background Technology

[0002] Sulfur hexafluoride (SF6) has become a core dielectric in high-voltage electrical equipment such as substation circuit breakers and gas-insulated switchgear (GIS) due to its excellent electrical insulation and arc-quenching properties, and is widely used in power systems. However, SF6 is also a highly controlled greenhouse gas internationally, with an extremely high global warming potential (GWP) and a long atmospheric residence time. While possessing significant resource recovery and utilization value, it also faces stringent emission control standards.

[0003] In substation indoor environments, SF6-containing equipment such as circuit breakers and GIS systems are highly susceptible to minute SF6 leaks during their entire lifecycle, including long-term operation, maintenance, and repair. These leaks are caused by factors such as aging seals, mechanical vibration, and human error. The leaked gas continues to dissipate, exhibiting low concentrations at single leak points and long release times, easily accumulating gradually in enclosed or semi-enclosed indoor spaces. When the SF6 concentration in the environment exceeds the occupational exposure control limit of 1000 ppm, the exposure risk to on-site maintenance personnel increases significantly. Furthermore, fugitive SF6 emissions not only waste valuable gas resources but also exacerbate greenhouse gas emission pressures, contradicting current dual-carbon goals and environmental policies.

[0004] Existing sulfur hexafluoride (SF6) capture and recovery technologies are mostly developed and designed for high-concentration SF6 operating conditions, and generally employ techniques such as cryogenic condensation and absorption to recover SF6 gas. However, these technologies have significant adaptability limitations for the unique low-concentration, large-space, and continuous operation conditions of substations: SF6 in substations is mostly present in trace concentrations at the ppm level, with extremely low gas partial pressures, resulting in insufficient separation driving force and low recovery efficiency.

[0005] In contrast, adsorption methods are considered one of the preferred technologies for capturing and recovering low-concentration SF6 in substations due to their ability to operate under normal temperature and pressure conditions, simple process flow, and ease of modular integration. Adsorption materials are the core of adsorption technology. Existing research has reported numerous studies on the use of adsorbents such as activated carbon, molecular sieves, and metal-organic frameworks for SF6 capture. Among these, carbon materials, with their wide availability of raw materials, low preparation cost, and excellent chemical stability, possess outstanding potential for engineering applications. Chinese invention patent document CN121198237A discloses a method for preparing microporous carbon materials through KOH chemical activation, yielding microporous carbon materials with a specific surface area of ​​1100~1700 m². 2The adsorption capacity of SF6 can reach 2.83 mmol / g at 25℃ and 0.1 bar; Chinese patent document CN118598131A discloses a method for preparing lignin-based porous carbon by chemical activation with KOH, and its SF6 adsorption capacity reaches a maximum of 2.66 mmol / g. -1 (25℃, 0.1 bar) This method can be used to recover SF6 from SF6 / N2 mixed gases. Chinese invention patent document CN120943253A discloses a method for preparing activated carbon using staged physical activation with steam and carbon dioxide to increase the micropore ratio and improve SF6 adsorption performance. The above research focuses on the recovery of 10% SF6 concentration in electrical equipment, achieving certain adsorption and separation effects under specific experimental conditions or higher concentration systems. However, the following technical bottlenecks still exist when applying this method to low-concentration SF6 (ppm level) applications in substations:

[0006] (1) Although chemical activation can form rich microporous structures, it is often completed under high temperature and strong etching in a single step. The connectivity and structural strength of the carbon skeleton pores formed need to be optimized. Under low partial pressure conditions, the diffusion kinetics of SF6 molecules into the internal micropores are slow, which affects the dynamic adsorption efficiency. In addition, the evolution behavior of the pore structure of the carbon skeleton obtained by this strong activation method is difficult to control precisely in subsequent high temperature treatment, and it is not suitable as an ideal precursor for forming specific hierarchical pore structures.

[0007] (2) Introducing a larger pore structure through physical activation is beneficial to the diffusion of gas molecules, but its adsorption force on trace SF6 is weak, making it difficult to achieve efficient capture of trace SF6.

[0008] (3) The efficient capture of SF6 (kinetic diameter of about 0.55 nm) is not simply about pursuing the highest specific surface area or total pore volume. The best adsorption performance depends on the precise matching between the micropore size and the SF6 molecule (the strongest adsorption potential is provided in the range of 0.5~1.0 nm), and the effective synergy of mesopores (2~50 nm) as high-speed diffusion channels. Existing single activation methods or disordered combinations are difficult to achieve such ordered integration and optimization of the spatial distribution and ratio of "strong adsorption micropores" and "fast diffusion mesopores".

[0009] Therefore, it is evident that existing technologies still struggle to achieve an effective balance between the advantages of microporous adsorption and the diffusion rate of mesoporous channels in controlling pore structure for the low concentration, normal pressure, large space, and complex operating conditions of trace SF6 in substations. This results in problems such as low adsorption site utilization and insufficient dynamic operating efficiency in the process of capturing low-concentration SF6. Therefore, for the low concentration, normal pressure, and continuous operation conditions of trace SF6 in substations, it is necessary to develop a porous material preparation approach that can synergistically control the pore structure evolution process. This approach would maintain the advantages of microporous adsorption while introducing pore structures that facilitate gas diffusion, overcoming the limitations of single activation methods and improving the adaptability and operational stability of adsorbent materials in the process of capturing and recovering low-concentration SF6. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a microporous-mesoporous hierarchical carbon molecular sieve prepared through chemical-physical synergistic activation and its applications. This invention utilizes natural biomass hard-shell materials as a carbon source and employs a chemical-physical synergistic activation method and application. By introducing chemical and physical activation at different stages to generate a synergistic effect, a hierarchical porous structure is formed and its direction is controlled. In the chemical activation process, zinc salts with relatively mild etching properties (such as zinc chloride, zinc nitrate, and zinc acetate) are used as chemical activators. Through dehydration, cross-linking, and structural rearrangement of the carbon precursor, a primary carbon framework structure dominated by micropores is formed, thus providing a strong adsorption potential for sulfur hexafluoride molecules. The subsequent physical activation process utilizes the more mild reaction and more controllable gasification process of CO2 to react with the carbon framework. This allows for selective etching, widening, or connection of some micropores without significantly damaging the microporous framework formed in the chemical activation stage, thereby introducing mesoporous channels that facilitate gas diffusion. The resulting carbon molecular sieve material possesses both high adsorption driving force and good mass transfer performance under low partial pressure conditions. Through an orderly and controllable path of "first forming a matching microporous framework and then optimizing the diffusion channels", its adsorption efficiency and operational adaptability in the capture and recovery process of low-concentration sulfur hexafluoride are improved.

[0011] The objective of this invention is achieved through at least one of the following technical solutions.

[0012] This invention provides a method for preparing microporous-mesoporous hierarchical carbon molecular sieves with low concentration SF6 capture, comprising the following steps:

[0013] (1) First, mix zinc salt, water and biomass hard shell material, heat and stir to impregnate, and dry to obtain impregnated material;

[0014] (2) The impregnating material is then pre-activated at a medium temperature of 450~550℃ under an inert atmosphere to dehydrate, cross-link and preliminarily activate the biomass hard shell material to form a carbon skeleton structure dominated by micropores, thus obtaining pre-activated carbon material.

[0015] (3) The pre-activated carbon material is then subjected to acid washing, water washing and drying to obtain purified pre-activated carbon material;

[0016] (4) The purified pre-activated carbon material is then heated in an inert atmosphere, followed by physical activation at 700℃~800℃ in a CO2 atmosphere. The pore structure of the carbon framework is etched and connected by CO2. After activation, the inert atmosphere is switched to protection and cooled to obtain a microporous-mesoporous hierarchical carbon molecular sieve.

[0017] Preferably, the biomass hard-shell material in step (1) is one or more of peach shells, apricot shells, and macadamia nut shells, and the particle size range of the biomass hard-shell material is 10~20 mesh.

[0018] Preferably, in step (1), the mass ratio of biomass hard-shell material to zinc salt is 1:0.8~1.2.

[0019] Preferably, the zinc salt in step (1) is one or a combination of zinc chloride, zinc acetate, and zinc nitrate.

[0020] Preferably, the solid-liquid ratio of biomass hard-shell material to water in step (1) is 1:0.8~1.2 in g / mL.

[0021] Preferably, the immersion in step (1) is carried out at 60~80°C for 3~5 hours.

[0022] Preferably, in step (2), the inert atmosphere is nitrogen or argon, the gas flow rate is 20~60mL / min, and the medium-temperature pre-activation time is 1~2h.

[0023] Preferably, in step (3), the pickling is performed using a 1.0~2.0 mol / L hydrochloric acid solution for 1~2 h.

[0024] Preferably, in step (4), the inert atmosphere is nitrogen or argon, the inert atmosphere gas flow rate is 20~60mL / min, and the heating rate is 5~15℃ / min.

[0025] Preferably, the physical activation time in step (4) is 60 min to 120 min, and the CO2 gas flow rate is 20 to 60 mL / min.

[0026] This invention also provides a microporous-mesoporous hierarchical carbon molecular sieve with low-concentration SF6 capture, prepared by the above-described method. Its BET specific surface area is 1300~2000 m².2 / g, micropore volume 0.46~0.73 cm³ 3 / g, mesoporous pore volume 0.12~0.49cm³ 3 / g, and the main peak of the micropore size distribution is located in the range of 0.68±0.1 nm.

[0027] This invention also provides the application of the aforementioned microporous-mesoporous hierarchical carbon molecular sieve for capturing low-concentration SF6 in the capture of low-concentration SF6 or the separation of SF6 / N2, under the following conditions: 273K~313K; SF6 volume fraction of 1000ppm~1000000ppm.

[0028] Preferably, the SF6 volume fraction is 1000ppm to 100000ppm.

[0029] Preferably, the application includes the capture of low concentrations of sulfur hexafluoride in substation rooms.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) This invention employs a chemical-physical synergistic activation process. Zinc salt is used as a chemical activator to chemically activate and construct a primary carbon framework structure dominated by micropores. Carbon dioxide is then used as an activation gas for physical activation to etch and regulate the pore structure. The resulting material maintains a high microporosity while possessing a suitable mesopore ratio, forming a hierarchical pore system conducive to the adsorption and diffusion of low-concentration SF6. This achieves a structural balance between micropore adsorption capacity and pore mass transfer performance. Compared to the single KOH strong chemical activation method (Comparative Example 3), a stable framework dominated by 0.68 nm micropores can be formed at 450~550℃, avoiding excessive etching. Subsequent CO2 activation selectively widens some micropore walls and connects pores through a mild gasification reaction, introducing mesopore channels without damaging the strongly adsorbing micropores. This synergistic mechanism of first defining the structure and then regulating the pores allows the resulting material to possess both high adsorption potential and fast diffusion kinetics at low partial pressures (0.001~0.1 bar), significantly improving the capture efficiency of low-concentration SF6 (see Table 2). Figure 4 ).

[0032] (2) This invention provides a controllable and repeatable preparation method. By adjusting parameters such as the amount of zinc salt, the medium-temperature pre-activation temperature, and the physical activation temperature and time, the pore size distribution of the material can be adjusted within a certain range to meet the stringent requirements of different low-concentration SF6 capture for adsorption kinetics and capacity. The micropores of this material have a strong adsorption force for low-concentration sulfur hexafluoride, and can also reduce the diffusion resistance of gas molecules through mesoporous channels, thereby significantly improving its effective capture efficiency and adsorption site utilization rate for sulfur hexafluoride under low partial pressure conditions.

[0033] (3) The present invention constructs a stable carbon skeleton structure in the medium-temperature pre-activation stage, which effectively avoids the problems of skeleton collapse and excessive gasification caused by direct high-temperature activation, and improves the structural stability of the material while ensuring the controllability of the pore structure.

[0034] (4) The preparation method of microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 capture provided by the present invention has a clear process route, controllable parameters, good repeatability, wide range of raw material sources, low cost, and does not rely on complex equipment or harsh conditions, and has good engineering feasibility and large-scale application potential.

[0035] (5) The microporous-mesoporous hierarchical carbon molecular sieve prepared in this invention exhibits good capture performance and application adaptability for sulfur hexafluoride gas under low concentration conditions. At 25°C, a total pressure of 1 bar, and an SF6 volume fraction of 1000 ppm (corresponding to a partial pressure of 0.001 bar), the SF6 adsorption capacity is 0.11 mmol / g; at an SF6 volume fraction of 3000 ppm (corresponding to a partial pressure of 0.003 bar), the SF6 adsorption capacity is 0.29 mmol / g; at a partial pressure of 0.1 bar, the highest SF6 adsorption capacity reaches 2.19 mmol / g; at a partial pressure of 1 bar, the highest SF6 adsorption capacity reaches 6.77 mmol / g; and under SF6 / N2 (10:90, v / v) conditions, the dynamic adsorption capacity of SF6 is approximately 2.01 mmol / g. This demonstrates a high adsorption capacity for low-concentration SF6, making it suitable for the capture, recovery, and emission reduction of low-concentration sulfur hexafluoride tail gas in substations, with significant application value and promising prospects for promotion. Attached Figure Description

[0036] Figure 1 The 77K N2 adsorption-desorption isotherms of the microporous-mesoporous hierarchical carbon molecular sieves with low concentration SF6 captured by Examples 1-5 of this invention are shown.

[0037] Figure 2 This is a typical pore size distribution diagram of the microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 captured by Example 1 of the present invention.

[0038] Figure 3 The adsorption isotherms of pure SF6 by the microporous-mesoporous hierarchical carbon molecular sieves with low concentrations of SF6 prepared in Examples 1-5 at 25°C.

[0039] Figure 4 The graph shows the dynamic breakthrough experiment curve of the microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 captured by Example 1 against the SF6 / N2 (10:90, v / v) mixed gas at 25°C and 1 bar total pressure. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0041] Example 1

[0042] (1) Weigh 5.0g of cleaned and dried macadamia nut shells, crush and sieve them to obtain biomass hard-shell material with a particle size of 10-20 mesh. Weigh 5.0g of anhydrous zinc chloride, mix it with the above biomass hard-shell material, and add 5mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 70℃ for 4h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry, and obtain the impregnated material;

[0043] (2) Place the impregnating material obtained in step (1) into a ceramic boat, and place the ceramic boat into a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), heat the material from room temperature to 500°C at a heating rate of 5°C / min, and hold it at 500°C for 1.5 h. Then, allow it to cool naturally to room temperature to obtain the pre-activated carbon material.

[0044] (3) The pre-activated carbon material obtained in step (2) was placed in a 1.5 mol / L hydrochloric acid solution and acid-washed at 60°C for 1.5 h to remove residual zinc chloride and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain purified pre-activated carbon material;

[0045] (4) The purified pre-activated carbon material obtained in step (3) was placed back into the ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), the temperature was increased from room temperature to 750°C at a rate of 10°C / min. Then, the atmosphere was switched to carbon dioxide, with a CO2 gas flow rate of 40 mL / min, and the carbon was activated at 750°C for 1.5 h. After activation, the atmosphere was switched to nitrogen protection and cooled to room temperature to obtain a microporous-mesoporous hierarchical carbon molecular sieve with low concentration of SF6 capture.

[0046] Example 2

[0047] (1) Weigh 5.0g of cleaned and dried macadamia nut shells, crush and sieve them to obtain biomass hard-shell material with a particle size of 10-20 mesh. Weigh 4.0g of zinc nitrate, mix it with the above biomass hard-shell material, and add 4mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 60℃ for 3h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry, and obtain the impregnated material;

[0048] (2) Place the impregnating material obtained in step (1) into a ceramic boat, and place the ceramic boat into a tube furnace. Under an argon atmosphere (flow rate 20 mL / min), heat the material from room temperature to 450°C at a heating rate of 5°C / min, and hold it at 450°C for 1 hour. Then, allow it to cool naturally to room temperature to obtain the pre-activated carbon material.

[0049] (3) The pre-activated carbon material obtained in step (2) was placed in a 1.0 mol / L hydrochloric acid solution and acid-washed at 60°C for 1 h to remove residual zinc nitrate and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain purified pre-activated carbon material;

[0050] (4) The purified pre-activated carbon material obtained in step (3) was placed back into the ceramic boat and put into the tube furnace. Under nitrogen atmosphere (flow rate 20 mL / min), the temperature was increased from room temperature to 700℃ at a heating rate of 5℃ / min. Then the carbon dioxide atmosphere was switched to CO2 atmosphere with a CO2 gas flow rate of 20 mL / min. The carbon was activated at 700℃ for 1 h. After activation, the carbon was switched to nitrogen protection and cooled to room temperature to obtain microporous-mesoporous hierarchical carbon molecular sieve with low concentration of SF6.

[0051] Example 3

[0052] (1) Weigh 5.0g of cleaned and dried macadamia nut shells, crush and sieve them to obtain biomass hard-shell material with a particle size of 10-20 mesh. Weigh 6.0g of zinc acetate, mix it with the above biomass hard-shell material, and add 6mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 80℃ for 5h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry, and obtain the impregnated material;

[0053] (2) Place the impregnating material obtained in step (1) into a ceramic boat, and place the ceramic boat into a tube furnace. Under a nitrogen atmosphere (flow rate 60 mL / min), heat the material from room temperature to 550°C at a heating rate of 5°C / min, and hold it at 550°C for 2 hours. Then, allow it to cool naturally to room temperature to obtain the pre-activated carbon material.

[0054] (3) The pre-activated carbon material obtained in step (2) was placed in a 2.0 mol / L hydrochloric acid solution and acid-washed at 60°C for 2 h to remove residual zinc acetate and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain purified pre-activated carbon material;

[0055] (4) The purified pre-activated carbon material obtained in step (3) was placed back into the ceramic boat and put into the tube furnace. Under nitrogen atmosphere (flow rate 60 mL / min), the temperature was increased from room temperature to 800℃ at a rate of 15℃ / min. Then the carbon dioxide atmosphere was switched to CO2 atmosphere with a flow rate of 60 mL / min. The carbon was activated at 800℃ for 2 hours. After activation, the carbon was switched to nitrogen protection and cooled to room temperature to obtain microporous-mesoporous hierarchical carbon molecular sieve with low concentration of SF6.

[0056] Example 4

[0057] (1) Weigh 5.0g of washed and dried peach shell raw material, crush and sieve to obtain biomass hard-shell material with a particle size of 10~20 mesh. Weigh 5.0g of anhydrous zinc chloride, mix it with the above biomass hard-shell material and add 5mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 70℃ for 4h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry to obtain impregnated material;

[0058] (2) Place the impregnating material obtained in step (1) into a ceramic boat, and place the ceramic boat into a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), heat the material from room temperature to 500°C at a heating rate of 5°C / min, and hold it at 500°C for 1.5 h. Then, allow it to cool naturally to room temperature to obtain the pre-activated carbon material.

[0059] (3) The pre-activated carbon material obtained in step (2) was placed in a 1.0 mol / L hydrochloric acid solution and acid-washed at 60°C for 1 h to remove residual zinc chloride and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain purified pre-activated carbon material;

[0060] (4) The purified pre-activated carbon material obtained in step (3) was placed back into the ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), the temperature was increased from room temperature to 750°C at a rate of 10°C / min. Then, the atmosphere was switched to carbon dioxide, with a CO2 gas flow rate of 40 mL / min, and the carbon was activated at 750°C for 1.5 h. After activation, the atmosphere was switched to nitrogen protection and cooled to room temperature to obtain a microporous-mesoporous hierarchical carbon molecular sieve with low concentration of SF6 capture.

[0061] Example 5

[0062] (1) Weigh 5.0g of washed and dried apricot shell raw material, crush and sieve to obtain biomass hard shell material with a particle size of 10~20 mesh. Weigh 5.0g of anhydrous zinc chloride, mix it with the above biomass hard shell material and add 5mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 70℃ for 4h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry to obtain impregnated material;

[0063] (2) Place the impregnating material obtained in step (1) in a ceramic boat, put it into a tube furnace, and heat it from room temperature to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere (flow rate 40 mL / min), and keep it at 500°C for 1.5 h. Then cool it naturally to room temperature to obtain the pre-activated carbon material;

[0064] (3) The pre-activated carbon material obtained in step (2) was placed in a 1.0 mol / L hydrochloric acid solution and acid-washed at 60°C for 1 h to remove residual zinc chloride and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain purified pre-activated carbon material;

[0065] (4) The purified pre-activated carbon material obtained in step (3) was placed back into the ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), the temperature was increased from room temperature to 750°C at a rate of 10°C / min. Then, the atmosphere was switched to carbon dioxide, with a CO2 gas flow rate of 40 mL / min, and the carbon was activated at 750°C for 1.5 h. After activation, the atmosphere was switched to nitrogen protection and cooled to room temperature to obtain a microporous-mesoporous hierarchical carbon molecular sieve with low concentration of SF6 capture.

[0066] Comparative Example 1

[0067] (1) Weigh 5.0g of cleaned and dried macadamia nut shells, crush and sieve them to obtain biomass hard-shell material with a particle size of 10-20 mesh. Weigh 5.0g of anhydrous zinc chloride, mix it with the above biomass hard-shell material, and add 5mL of deionized water to make the solid-liquid ratio 1:1 (g:mL). Place the mixture under magnetic stirring at 70℃ for 4h. After impregnation, place the obtained material in an oven at 105℃ for 12h to dry, and obtain the impregnated material.

[0068] (2) Place the impregnating material obtained in step (1) into a ceramic boat, and place the ceramic boat into a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), heat the material from room temperature to 500°C at a heating rate of 5°C / min, and keep it at 500°C for 1.5 h. Then cool it naturally to room temperature to obtain the pre-activated carbon material.

[0069] (3) The pre-activated carbon material obtained in step (2) was placed in a 1.0 mol / L hydrochloric acid solution and acid-washed at 60°C for 1 h to remove residual zinc chloride and its derivative inorganic substances; then it was repeatedly filtered and washed with deionized water until the pH of the washing solution was close to neutral. The resulting filter cake was dried in a vacuum drying oven at 105°C for 10 h to obtain chemically activated carbon material.

[0070] Comparative Example 2

[0071] 5.0 g of washed and dried macadamia nut shells were weighed, crushed, and sieved to obtain biomass hard-shell material with a particle size of 10-20 mesh. The biomass hard-shell material was placed in a ceramic boat and then placed in a tube furnace. Under a nitrogen atmosphere (flow rate 40 mL / min), the temperature was increased from room temperature to 750 °C at a rate of 10 °C / min. Subsequently, the atmosphere was switched to carbon dioxide, with a CO2 gas flow rate of 40 mL / min, and the material was activated at 750 °C for 1.5 h. After activation, the atmosphere was switched back to nitrogen protection and cooled to room temperature to obtain CO2 physically activated carbon material.

[0072] Comparative Example 3

[0073] Weigh 5.0g of washed and dried macadamia nut shells, crush and sieve them to obtain biomass hard-shell material with a particle size of 200-300 mesh. Mix 5.0g of KOH with the above biomass hard-shell material in a ceramic boat and place it in a tube furnace. Then, under a nitrogen atmosphere of 40mL / min, raise the temperature to 750℃ at a heating rate of 5℃ / min and hold for 90min. After naturally cooling to room temperature, place the high-temperature activated product into a reaction vessel containing 50mL of water and wash it with water at 100℃ for 6h. Then, replace the water with 0.1mmol / L hydrochloric acid solution and acid wash it at 100℃ for 6h. Then, wash it with water at 80℃ for 6h. Finally, dry the washed product at 150℃ under a vacuum of -0.08Mpa ~ -0.1Mpa for 6h to obtain KOH chemically activated carbon material.

[0074] Comparative Example 4

[0075] 200 mg of commercial NaX molecular sieve was weighed and placed in a muffle furnace, and calcined at 450 °C for 6 hours to obtain pretreated NaX molecular sieve.

[0076] Performance testing:

[0077] The N2 adsorption-desorption isotherms at 77 K of the low-concentration SF6-captured microporous-mesoporous hierarchical carbon molecular sieves obtained in Examples 1-5 were determined using a Micromeritics ASAP2460 multi-station fully automated surface area and pore size analyzer to characterize their pore structure. Figure 1As shown in Table 1, the pore structure data and pore size distribution are as follows: Figure 2 As shown. Before testing, the sample was degassed under vacuum at 150°C for 6 hours to remove impurities from the material pores.

[0078] Depend on Figure 1 The results in Table 1 show that the BET specific surface area of ​​the low-concentration SF6-captured microporous-mesoporous hierarchical carbon molecular sieve prepared in this invention is mainly distributed in the range of 1300~2000 m². 2 The range of / g indicates that the material has a relatively well-developed porous structure. Combined with Figure 2 The pore size distribution results show that the microporous-mesoporous hierarchical carbon molecular sieve captured by low-concentration SF6 is predominantly microporous, with the main peak of the pore size distribution located at approximately 0.68 nm. Simultaneously, a certain proportion of mesoporous structures exist within the larger pore size range, exhibiting a hierarchical pore structure characterized by synergistic microporous-mesoporous interaction. This structural feature is beneficial for balancing adsorption driving force and gas mass transfer efficiency under low partial pressure conditions, providing a structural basis for the material's high adsorption capacity and high diffusion rate during the capture of low-concentration SF6.

[0079] Table 1 Summary of Pore Structure Parameters

[0080]

[0081] Using a Micromeritics 3Flex three-station gas adsorption analyzer (USA), the adsorption-desorption isotherms of high-purity SF6 captured by microporous-mesoporous hierarchical carbon molecular sieves obtained in Examples 1-5, Comparative Examples 1-2, and NaX molecular sieves were measured under a constant temperature of 25℃ in the pressure range of 0-100 kPa. Before testing, the samples were activated under vacuum at 150℃ for at least 4 hours. The test results are shown in Table 2 and... Figure 3 As shown.

[0082] The microporous-mesoporous hierarchical carbon molecular sieve with low-concentration SF6 capture prepared in this invention exhibits the following adsorption capacities: 0.11 mmol / g at an SF6 volume fraction of 1000 ppm (corresponding to a partial pressure of 0.001 bar); 0.29 mmol / g at an SF6 volume fraction of 3000 ppm (corresponding to a partial pressure of 0.003 bar); 2.19 mmol / g at a partial pressure of 0.1 bar; and 6.77 mmol / g at a partial pressure of 1 bar. Under all concentration conditions, the microporous-mesoporous hierarchical carbon molecular sieve with low-concentration SF6 capture prepared in this invention demonstrates higher adsorption capacities than the porous carbon materials with single activation methods in Comparative Examples 1-3 and the commercial NaX molecular sieve in Comparative Example 4.

[0083] The microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 capture prepared in Example 1 showed significantly higher SF6 adsorption capacity than that of Comparative Examples 1-4 under ppm-level low concentration (1000ppm, 3000ppm) SF6 conditions. The SF6 adsorption capacity increased by 83%~175% at 1000ppm and by 53%~383% at 3000ppm, demonstrating that the microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 capture prepared in this invention has excellent adsorption effect under ppm-level low concentration SF6 conditions.

[0084] Table 2 Summary of Adsorption Capacity of Single SF6 Components

[0085]

[0086] Adsorption-breakthrough experiment:

[0087] 0.3 g of the low-concentration SF6-captured microporous-mesoporous hierarchical carbon molecular sieve prepared in Example 1 and 0.3 g of KOH-activated activated carbon material prepared in Comparative Example 3 were respectively packed into stainless steel adsorption columns with an inner diameter of 7 mm. Before the experiment, the adsorbent was activated by purging with high-purity He at 150 °C for 0.5 h. At the start of the experiment, a standard gas mixture of SF6 / N2 (10:90, v / v) with a total flow rate of 3 mL / min was introduced into the adsorption column. The gas composition at the adsorption column outlet was analyzed online in real time by a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD).

[0088] Experimental results are as follows Figure 4 The graph shows the relationship between time (min) and the ratio of SF6 concentration (C) in the outlet gas to the inlet concentration (C0) (C / C0). As can be seen from the graph, in Example 1, SF6 was undetectable in the outlet gas for a long period after the experiment began (C / C0≈0), indicating that SF6 was completely captured by the adsorbent. N2, due to its extremely weak adsorption, penetrated the adsorption column at 0 min. The breakthrough time of SF6 (defined as the moment C / C0=0.05) was approximately 231.7 min / g, resulting in a calculated dynamic adsorption capacity of 2.01 mmol / g. In contrast, although the material in Comparative Example 3 had a relatively high static adsorption capacity, its adsorption kinetics were slow due to fewer mesopores, resulting in poor dynamic adsorption performance. The breakthrough time of SF6 (defined as the moment C / C0=0.05) was approximately 170.4 min / g, resulting in a calculated dynamic adsorption capacity of only 1.49 mmol / g. This result intuitively demonstrates that the microporous-mesoporous hierarchical carbon molecular sieve with low concentration SF6 capture prepared in this invention can achieve dynamic adsorption and separation of SF6 and N2 to a great extent.

[0089] As can be seen, the present invention achieves a synergistic effect of optimized pore size distribution and enhanced mass transfer performance through the synergistic effect of activator selection, activation temperature gradient and strict sequence, so that the obtained material has both high adsorption potential and fast adsorption kinetics at low partial pressure, and is particularly suitable for capturing low concentrations of SF6 at the ppm level.

Claims

1. The application of microporous-mesoporous hierarchical carbon molecular sieves for low-concentration SF6 capture in SF6 capture or SF6 / N2 separation, characterized in that, The application conditions are: 273K~313K; the volume fraction of SF6 is 1000ppm~3000ppm; the preparation method of the microporous-mesoporous hierarchical carbon molecular sieve captured by the low concentration of SF6 includes the following steps: (1) First, mix zinc salt, water and biomass hard shell material, stir and impregnate at 60-80℃, and dry to obtain impregnated material; (2) The impregnating material is then pre-activated at a medium temperature of 450-550°C under an inert atmosphere to obtain pre-activated carbon material; (3) The pre-activated carbon material is then acid-washed and dried to obtain purified pre-activated carbon material; (4) The purified pre-activated carbon material is then heated in an inert atmosphere and then physically activated at 700℃~800℃ in a CO2 atmosphere to obtain microporous-mesoporous hierarchical carbon molecular sieves with low concentration of SF6 capture.

2. The application according to claim 1, characterized in that, The biomass hard-shell material is one or more of peach shells, apricot shells, and macadamia nut shells, and the particle size range of the biomass hard-shell material is 10-20 mesh; the solid-liquid ratio of the biomass hard-shell material to water is 1:0.8-1.2 by mass-volume ratio g / mL.

3. The application according to claim 1, characterized in that, The zinc salt mentioned in step (1) is one or a combination of zinc chloride, zinc acetate, and zinc nitrate; the mass ratio of biomass hard-shell material to zinc salt is 1:0.8 to 1.

2.

4. The application according to claim 1, characterized in that, The stirring and soaking time in step (1) is 3 to 5 hours.

5. The application according to claim 1, characterized in that, The inert atmosphere mentioned in step (2) is nitrogen or argon, the gas flow rate is 20-60 mL / min, and the medium-temperature pre-activation time is 1-2 h.

6. The application according to claim 1, characterized in that, The pickling in step (3) uses a 1.0-2.0 mol / L hydrochloric acid solution and the pickling time is 1-2 h.

7. The application according to claim 1, characterized in that, The inert atmosphere mentioned in step (4) is nitrogen or argon, the inert atmosphere gas flow rate is 20-60 mL / min, the heating rate is 5-15 °C / min, the physical activation time is 60 min-120 min, and the CO2 gas flow rate is 20-60 mL / min.

8. The application according to claim 1, characterized in that, The application includes the capture of low concentrations of sulfur hexafluoride in substation rooms.

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