Degradation Of SF6 Research Articles

Efficient photocatalytic degradation of potent greenhouse gas SF6 at liquid-solid interface

Sulfur hexafluoride (SF6), widely used in industries, poses a significant threat as the strongest greenhouse gas. Current methods for degrading SF6 are hindered by high energy consumption and costs, thus there is an urgent need for a low-cost, convenient, and efficient solution. In response, we established a gas-liquid-solid three-phase (GLS) system for efficient photocatalytic SF6 degradation by Bi2O2CO3, whose efficiency was approximately 20 times that of traditional gas-solid systems. Further, possible degradation mechanisms were demonstrated through the detection of material changes in three phases, respectively. Detailed studies revealed Bi2O2CO3 can in-situ form Bi2S3 heterojunction during the reaction, facilitating carrier separation. Besides, O2 can transform to ·O2− and accelerate the photodegradation process. This approach offered a novel toolbox for SF6 degradation. We predict this method will have a wider range of applications in the field of solar-powered catalytic degradation of extremely stable fluorinated pollutants at lower costs in the future.

A plasma-catalytic system with MgO/NiO/Ni cathode for SF6 degradation

In this work, a plasma-catalytic system in DC discharge with MgO/NiO/Ni (MNN) cathode is proposed for the degradation of SF6 greenhouse gas. The discharge power with MNN cathode is significantly increased compared with Ni cathode due to its good electron emission characteristics, and an effective and stable SF6 degradation performance is achieved in this multi-needle plate discharge system. Besides, surface discharge occurs on the MNN cathode in addition to the needle tips, which is believed to be conducive to the catalytic decomposition of SF6 on the MgO surface. Nontoxic products of MgF2 and MgSO4 are detected on the MgO layer after discharge from various characterizations (XRD, XPS, FTIR and Raman, etc.), suggesting that there is a series of catalytic reactions between SF6/intermediates and MgO. The addition of appropriate O2 (O2:SF6 = 1:1) in the background is not only conducive to the defluorination decomposition of SF6 in ionization region, but also O atom generated from O2 discharge promotes the formation of MgF2 and MgSO4, thus resulting in an effective SF6 degradation performance. Then, the possible degradation mechanism of SF6 in gas phase and on the MgO layer is discussed and the possible degradation pathways are proposed. This research first demonstrates the effectiveness of enabling degrading SF6 gases in a plasma-catalytic system with MNN cathode.

Activation and Catalytic Degradation of SF6 and PhSF5 at a Bismuth Center.

In this work, we report the catalytic degradation of SF6 and PhSF5 using N,C,N pincer bismuthinidene complexes (1 and 5). Exposure of SF6 and PhSF5 to 1 results in the reduction of the S(VI) substrates and concomitant formation of Bi(III) and Bi(II) compounds, which were isolated and characterized. The oxidized bismuth-based products were demonstrated to undergo reduction with PMe3, recovering the starting complex 1. Having established a synthetic redox cycle, the catalytic degradation of SF6 and PhSF5 was developed through ligand optimization to 5, leading to a 528 TON for SF6 and the first reported TON for PhSF5 (3.2).

A Study on the Efficient Degradation of Sulfur Hexafluoride by Pulsed Dielectric Barrier Discharge Synergistic Active Gas

SF6 is a strong greenhouse effect gas, which is widely used in high-voltage electrical equipment such as circuit breakers and high-voltage switchgear because of its excellent insulation performance and arc extinguishing ability. In recent years, the use and emission of SF6 have been rising, and with the proposal of the dual carbon strategic goal, its harmless degradation has become an urgent problem to be solved. In this paper, SF6 was degraded by pulsed DBD plasma technology and O2. Studies have shown that the addition of O2 can effectively promote the degradation of SF6. With the increase in the added O2 content, the DRE and EY of SF6 first increased and then decreased. Under the conditions of the input power of 50 W, SF6 concentration of 2%, and gas flow rate of 50 mL/min, the reaction system obtained the highest DRE and EY of 58.40% and 5.24 g/kWh when the O2 content was 1%, respectively. In the SF6/Ar/O2/H2O system, the addition of H2O could improve the product selectivity of SO2F2, and when the O2 concentration was 1%, the highest selectivity of SO2F2 was 48.96%, and the concentration was 8006.76 ppm. The addition of O2 inhibited the production of SO2, and with the addition of the O2 system, SO2F2 and SOF4 were the main components of degradation products; however, there were also SOF2, SO2, SiF4, SF4, etc. In this paper, the decomposition path of O2 under SF6 was analyzed in detail according to infrared spectroscopy and decomposition products.

Thermal degradation of greenhouse gas SF6 at realistic temperatures: Insights from atomic-scale CVHD simulations

Sulfur hexafluoride (SF6), recognized as a potent greenhouse gas with significant contributions to climate change, presents challenges in understanding its degradation processes. Molecular dynamics simulations are valuable tools for understanding modes of decomposition while the traditional approaches face limitations in time scale and require unrealistically high temperatures. The collective variable-driven hyperdynamics (CVHD) approach has been introduced to directly depict the pyrolysis process for SF6 gas at practical application temperatures, as low as 1600 K for the first time. Achieving an unprecedented acceleration factor of up to 107, the method extends the simulation time scale to milliseconds and beyond while maintaining consistency with experimental and theoretical models. The differences in the reaction process between simulations conducted at actual and elevated temperatures have been noted, providing insights into SF6 degradation pathways. The work provides a basis for the further studies on the thermal degradation of pollutants.

Degradation of SF6 by dielectric barrier discharge cooperating with TiO2 photocatalysis: Insights into the reaction mechanism

Research into the degradation and conversion of SF6 is important for environmental protection. Dielectric barrier discharge (DBD) technology is recognized as a reliable method for processing industrial waste gases, such as SF6. This research introduces a dual approach, combining DBD with TiO2 photocatalysis, to enhance SF6 degradation. When operating at 90 W, the degradation removal efficiency (DRE) of 2 % SF6 reaches 99.99 %. Moreover, the energy efficiency, measured as G50, reaches 10.25 g/(kW·h) for the combined DBD and TiO2 photocatalysis system, is, surpassing the efficiency of the standalone DBD system. The introduction of 0.5 % H2O enables complete SF6 degradation at a reduced input power (70 W). This synergy promotes the generation of a more easily processed product, SO2. Density functional theory (DFT) studies indicate that the availability of active sites on TiO2(101) is a crucial factor affecting the degradation efficiency. Specifically, the pre-adsorption of H2O on TiO2(101) surfaces facilitates the initial bond dissociation of SF6, while these surfaces strongly adsorb crucial intermediates, thereby enhancing the degradation of SF6. Additionally, the selectivity of the products was related to the dissociation energy barriers, and the pre-adsorption of H2O reduces these barriers for key intermediates, thereby improving SO2 selectivity. This study provides new insights into SF6 degradation and conversion using DBD combined with photocatalysis and provides inspiration for the conversion of other greenhouse gases (CO2, CH4, etc.).

Theoretical study on the interaction between SF6 and TiO2(001) surface: A DFT+U study

The research on SF6 degradation and conversion is of great significance for environmental protection. Based on the density functional theory, the adsorption process of SF6 on the TiO2(001) and TiO2(101) surfaces was investigated. The results indicate a strong interaction between SF6 and the TiO2 surface. Significant structural changes in the SF6, such as elongation of the S-F bonds, were observed after adsorption, rendering the SF6 more prone to decomposition. According to Mulliken charge analysis, electron transfer occurs from the TiO2 surface to the SF6, revealing SF6 as an electron acceptor while TiO2 acts as an electron donor. Analysis of the density of states confirms a pronounced electronic orbital overlap between the S/F atoms of SF6 and the Ti/O atoms of TiO2, and the charge density distribution along the Z-axis further supports this charge transfer process. Additionally, experimental studies have demonstrated that TiO2 photocatalysis can accelerate the degradation of SF6 during DBD. This study demonstrates the catalytic potential of TiO2 in the degradation of SF6 insulating gas and provides theoretical support for the efficient and harmless treatment of SF6.

Removal of sulfur hexafluoride in molten-tin bubble column reactors: Kinetics parameter identification and scale-up studies

This study presents the degradation of sulfur hexafluoride (SF6), which is a greenhouse gas emitted from semiconductor industry, in a molten metal bubble column reactor (MMBCR) using tin. Experiments were conducted in a bench-scale MMBCR ranging from 468 °C to 668 °C using a mixture of N2 and 1000 ppm SF6 to estimate reaction kinetic parameters, where high-value solid product (SnS and SnF2) used in solar-cell devices were produced. A one-dimensional MMBCR model integrating reaction kinetics, axial dispersion, and heat transfer was formulated to investigate hydrodynamics and the performance of three pilot-scale multitubular MMBCRs at a feed flow rate of 300 LPM. At 650 °C, the SF6 removal efficiencies (η) of the pilot-scale MMBCRs with 80, 60, and 40 tubes at the same height (=0.5 m) and diameter (=0.1 m) were 85 %, 83 %, and 82 %, respectively. The pilot-scale MMBCR featuring 80 tubes exhibited the highest η owing to a low axial dispersion coefficient and high residence time. This study provides useful insights and guidelines for the design and upscaling of SF6 degradation processes utilizing MMBCRs in the semiconductor industry.

Experimental study on the effect of H2O and O2 on the degradation of SF6 by pulsed dielectric barrier discharge

SF6 has excellent insulation performance and arc extinguishing ability, and is widely used in the power industry. However, its global warming potential is about 23,500 times that of CO2, it can exist stably in the atmosphere, it is not easily degradable and is of great potential harm to the environment. Based on pulsed dielectric barrier discharge plasma technology, the effects of H2O and O2 on the degradation of SF6 were studied. Studies have shown that H2O can effectively promote the decomposition of SF6 and improve its degradation rate and energy efficiency of degradation. Under the action of a pulse input voltage and input frequency of 15 kV and 15 kHz, respectively, when H2O is added alone the effect of 1% H2O is the best, and the rate and energy efficiency of degradation of SF6 reach their maximum values, which are 91.9% and 8.25 g kWh−1, respectively. The synergistic effect of H2O and O2 on the degradation of SF6 was similar to that of H2O. When the concentration of H2O and O2 was 1%, the system obtained the best rate and energy efficiency of degradation, namely 89.7% and 8.05 g kWh−1, respectively. At the same time, different external gases exhibit different capabilities to regulate decomposition products. The addition of H2O can effectively improve the selectivity of SO2. Under the synergistic effect of H2O and O2, with increase in O2 concentration the degradation products gradually transformed into SO2F2. From the perspective of harmless treatment of the degradation products of SF6, the addition of O2 during the SF6 degradation process should be avoided.

DFT study of SF6 adsorption by Pd-doped hydroxyl-terminal modified Ti3C2Tx MXene.

SF6 gas has a strong greenhouse effect, and how to treat SF6 in an environmentally friendly way has been a hot topic of current research. In this paper, the adsorption behavior of SF6 on the surface of Pd-doped hydroxyl-terminated modified Ti3C2Tx (i.e., Ti3C2(OH)2) was investigated based on the density functional theory using two-dimensional MXene as the catalyst. The structures of different Pd-doped Ti3C2(OH)2 were analyzed and the most structurally stable doped structures were selected as the basis for subsequent calculations. A large number of adsorption configurations were constructed and geometrically optimized, and the adsorption energy, charge transfer, differential charge density, and density of states of the systems were calculated in order to analyze the gas-solid interactions and find the surface active sites; compared with the adsorption performance of undoped Ti3C2(OH)2 on SF6, it was found that Pd doping played a less inhibitory role in the adsorption of SF6 on the Ti3C2(OH)2 surface. The results of this study can provide theoretical support for the use of Pd-doped Ti3C2(OH)2 as a catalyst for the degradation of SF6. In this paper, simulations of SF6 adsorption on Ti3C2Tx surfaces are based on density functional theory and are carried out in the Dmol3 module of Material Studio. To better describe the non-uniform electron density of the actual system, the PBE functional in the generalized gradient approximation (GGA) was chosen for the optimization of the structure of the gas-solid interface system and the calculation of the relevant electronic properties, combined with the Grimme dispersion correction in the DFT-D dispersion correction for the electron exchange correlation term. Because both Pd and Ti are transition metal elements, the mode-conserving pseudopotential DNP basis set containing relativistic effects was chosen for the electronic wave function expansion. In this paper, an all-electron model is used for the inner core treatment of gas molecules and a density generalized semi-nuclear pseudopotential DSSP is used for the solid surface treatment.

Theoretical analysis of Ni atom-doped MXene for improving the catalytic degradation performance of SF6

The strong greenhouse effect of SF6 will directly affect the whole habitat. Finding a suitable catalyst for the efficient degradation of SF6 is one of the main means to reduce SF6 emissions. In this paper, two-dimensional MXene doped with Ni atoms was used as catalytic material, and Density Functional Theory (DFT) was combined to investigate the influence properties of different terminal modifications of Ti3C2Tx (T = F, OH, O) on the catalytic degradation of SF6. The adsorption and decomposition processes of SF6 gas molecules on the surface of Ni-doped Ni-MXene material were calculated, and the adsorption energy transferred electron number and density of states (DOS) of the adsorption system were analyzed. The results show that: the adsorption energy of SF6 gas molecules on the surface of Ni-MXene is −6 eV and the number of transferred electrons is more than 0.5 e, in which the adsorption energy under the F-terminal group increases by 1 eV and the number of transferred electrons increases by 0.5 e compared with the undoped case, and the catalytic effect is improved; the molecular structure of SF6 changes significantly during the adsorption process, and the S-F bond was elongated to 2 Å and the S-F bond length away from the material was elongated by 0.2 Å, which made the SF6 molecule easier to be decomposed; according to the results of DOS calculations, the F atoms in the SF6 molecule had obvious electronic orbital interactions with both the Ni atoms on the surface of the Ni-MXene material and the MXene material itself, indicating that both showed the catalytic activity for SF6 during the adsorption process. The conclusions of this paper have some theoretical guidance for the efficient catalytic degradation of SF6.

Adsorption study of SF6 molecules on Pt-doped two-dimensional material Ti3C2Tx Mxene

In this paper, the effects of transition metal atom Pt doping on the structural parameters and electronic properties of the two-dimensional material Ti3C2Tx MXene (T = OH, O or F) as well as the adsorption interaction between the doped material and SF6 are investigated based on density functional theory calculations. To investigate the SF6 adsorption mechanism, the adsorption structure, adsorption energy, charge transfer, and density of states of Pt atom-doped Ti3C2Tx after the adsorption of SF6 molecules were analyzed. The results showed that the electronic properties and chemical activity of the doped Ti3C2Tx changed significantly compared to those before doping. In addition, Pt-doped Ti3C2(OH)2 has good adsorption ability on SF6 molecules, and its adsorption type is chemisorption; in the relevant sites, SF6 undergoes chemical bond breaking, and the doping of Pt improves the catalytic effect of Ti3C2(OH)2. The adsorption capacity of Pt-doped Ti3C2O2 and Ti3C2F2 for SF6 molecules is much weaker than that of Pt-doped Ti3C2(OH)2, physical adsorption occurred, and there was almost no degradation of SF6; the doping of Pt did not improve the catalytic effect of Ti3C2O2 and Ti3C2F2.

Mechanochemical Degradation of SF6 for Realizing Simultaneous Disposal of Super Greenhouse Gas and Manufacture of Fluorinated Graphite Materials

As the most potent greenhouse gas, SF6 can cause persistent harm to the environment if discharged directly to the air. Therefore, it is necessary to develop an efficient approach for its disposal and resource utilization. Here, we discovered the mechanochemical degradation of SF6 by graphite under mild conditions, along with the formation of an S-containing fluorinated graphitic carbon material (SFGCM) with over 8% of sulfur and 12% of fluorine, being a “one-stone-two-birds” strategy. The unexpected reaction between SF6 and graphite with least reactivity may be ascribed to the intensive mechanical stress and grinding on graphite for its size miniaturization and radical formation at the cutting edges, as well as their synergistic activation for SF6. The resultant SFGCM is composed of few-layered graphite nanomaterial with rich porosity, high specific surface area (380 m2 g–1), good amphiphilicity, and excellent adsorptivity for heavy metals (Hg2+) from aqueous solution. This study provides a viable way for the resource utilization of SF6, and sheds light on the massive degradation of various greenhouse F-gases in the future.

SF6 Degradation in a γ-Al2O3 Packed DBD System: Effects of Hydration, Reactive Gases and Plasma-Induced Surface Charges

SF6 Degradation in a γ-Al2O3 Packed DBD System: Effects of Hydration, Reactive Gases and Plasma-Induced Surface Charges

Process optimization of nanosecond pulsed packed‐bed discharge plasma for SF6 degradation based on response surface methodology

AbstractIn this work, a nanosecond pulsed packed‐bed discharge (PBD) plasma was developed for SF6 degradation under different dilution gases. The discharge form transfers from filamentary discharge to the combination of surface discharge and microdischarge after introducing the packing material regardless of the dilution gas used, and the local electric field strength and SF6 degradation performance are promoted. The mean electron energy and rate coefficient for SF6 excitation in SF6/Ar system are significantly higher than those in SF6/N2 or SF6/air system, which results in higher SF6 degradation efficiency in SF6/Ar system. Moreover, the response surface methodology based on the Box–Behnken design model was constructed to optimize several key process parameters including pulsed voltage, gas flow rate, oxygen content, and relative humidity, as well as assess the contribution of each parameter to SF6 degradation. The proposed optimization model shows a satisfactory correlation between the predicted and the experimental results. The energy yield concerning SF6 degradation in nanosecond pulsed PBD plasma achieves approximately 75.3 g/kWh with nearly complete degradation. This work is expected to provide an efficient and energy‐saving plasma technique for SF6 degradation.

Simulation and experimental study on the degradation of the greenhouse gas SF6 by thermal plasma

SF6 gas is widely used on many occasions especially in the power equipment, but it has been restricted since Kyoto Protocol as the strongest greenhouse gas. To reduce the SF6 emission, several methods are now used such the recycling & purification and the SF6 degradation. Considering the huge market of SF6 and the recent demand in the field of power equipment, it is necessary to explore new ways to thoroughly destroy SF6. This work brought out the idea to degrade retired SF6 by thermal plasma. A simplified kinetic model was established to predict the feasibility of this idea as well as the degradation products of SF6, and then the prototype of SF6 degradation by thermal plasma was built and tested. In thermal plasma, SF6 gradually decomposed into atoms, and then H2 was added to capture the released F atoms to generate HF and also prevent the association reactions of SF6. In order to achieve the desired degradation effect, the reaction temperature and the mixing ratio of H2 should be sufficiently high. However, excessive H2 could generate the H2S, and excessive discharge power could decrease the energy yield. When the flow rate of SF6/H2 was set as 8/30 L/min and the discharge current was set as 100A, the destruction removal efficiency (DRE) of SF6 was 99.0% and the energy yield was 206 g/kWh. This work also discusses how to further treat the by-products such as HF and S from this prototype effectively.

SF 6 catalytic degradation in a γ‐Al 2 O 3 packed bed plasma system: A combined experimental and theoretical study

Effective abatement of the greenhouse gas sulphur hexafluoride (SF6) waste is of great importance for the environment protection. This work investigates the size effect and the surface properties of γ-Al2O3 pellets on SF6 degradation in a packed bed dielectric barrier discharge (PB-DBD) system. Experimental results show that decreasing the packing size improves the filamentary discharges and promotes the ignition and the maintenance of plasma, enhancing the degradation performance at low input powers. However, too small packing pellets decrease the gas residence time and reduce the degradation efficiency, especially for the input power beyond 80 W. Besides, lowering the packing size promotes the generation of SO2, while reduces the yields of S-O-F products, corresponding to a better degradation. After the discharge, the pellet surface becomes smoother with the appearance of S and F elements. Density functional theory calculations show that SF6 is likely to be adsorbed at the AlIII site over the γ-Al2O3(110) surface, and it is much more easily to decompose than in the gas phase. The fluorine gaseous products can decompose and stably adsorb on the pellet surface to change the surface element composition. This work provides a better understanding of SF6 degradation in a PB-DBD system.

Rectified SiC-Fe2O3 heterostructures for high efficient activation and degradation of sulfur hexafluoride in air atmosphere

Sulfur hexafluoride (SF6) has a global warming potential of 23,900 CO2 equivalent during 100 years and is the strongest greenhouse gas. Therefore, it is essential to develop a degradation method for SF6. The space charge region in heterojunctions can form charged active sites, thus facilitating the absorption and decomposition of SF6 molecules. Herein, rectified SiC-Fe2O3 heterostructures were designed and in-situ generated from SiC-FeOOH composites during the thermal degradation of SF6. The heterostructures can completely decompose 2 vol% SF6 in air atmosphere at 700 °C, and have a higher initial degradation ratio of 93.6% and a degradation amount of 99.0 mL g−1. Detailed characterizations reveal that electron donor SiC can facilitate the absorption of SF6 molecules via electrostatic attraction, and the electron acceptor Fe2O3 can offer electrons to SF6 molecules to break S-F bonds. The concept of such heterostructures makes it possible to deal with large-scale leaks of low-concentration SF6.

Theoretical study of the interaction of SF6 molecule on Ti3C2Tx surfaces

At present, searching for efficient methods to degrade sulfur hexafluoride (SF6) is a worldwide hotspot. Due to the abundant active groups on the surface, MXene is regarded as an ideal catalyst support. In this paper, the potential active sites of Ti3C2Tx (T = OH, F, O) for SF6 degradation were studied using density functional theory (DFT) method. The results show the adsorption of SF6 on Ti3C2(OH)2 is significantly stronger than that on Ti3C2F2 and Ti3C2O2. Among typical adsorption sites on Ti3C2(OH)2, SF6 exhibited the strongest interaction at OH-1 site. Complex electron orbital interactions occurred between SF6 and Ti3C2(OH)2. Adsorption energy reached −6.739 eV and about 1.414e transferred from Ti3C2(OH)2 to SF6. Structure of SF6 changed obviously and chemical adsorption occurred in this process. However, on Ti3C2F2 and Ti3C2O2, gas–solid interactions were weak and the structures had little change, which was mainly physical adsorption. Compared with common catalysts such as Ag, α‑Al2O3 and BaTiO3, Ti3C2(OH)2 showed better catalytic activity for SF6 degradation. By strong adsorption of the active site on the surface, the degradation products were separated from each other, which weakened SF6 recombination and promoted the further degradation. The results provide theoretical support for MXene acting as a catalyst to efficiently degrade SF6.

SF6 abatement in a packed bed plasma reactor: Role of zirconia size and optimization using RSM

This work describes plasma destruction of SF6 in a zirconia (ZrO2) packed bed plasma reactor (PBR). Electric signals, equivalent parameters, emission spectra and degradation results have been utilized to evaluate the influence of ZrO2 size on PBR discharge characteristics and SF6 degradation. The results present that the size of ZrO2 has a significant impact on PBR discharge characteristics due to its influence on physical parameters. Moreover, bigger ZrO2 beads packing shows a better performance in SF6 degradation because of longer gas residence time. In addition, the key operating parameters including flowrate, SF6 concentration, oxygen concentration, and water vapor concentration were optimized by response surface methodology (RSM) with Box-Behnken design (BBD). The proposed optimization model shows satisfactory correlation between the predicted and actual results. For energy yield (EY), the mutual effect of flowrate, SF6 concentration and water vapor concentration was significant. For SO2F2 selectivity, the mutual effect of SF6 concentration and water vapor concentration was significant. The optimum SF6 abatement was predicted from RSM as 14.64g/kWh and 14.42% for EY and SO2F2 selectivity at flowrate of 200mL/min, SF6 concentration of 3%, oxygen concentration of 0.83% and water vapor concentration of 1.89%.