Sulfur hexafluoride (SF6) emission estimates for China: an inventory for 1990-2010 and a projection to 2020

Ag Modified SnS2 Monolayer as a Potential Sensing Material for C4F7N Decompositions: A Density Functional Theory Study

As the field of 2D materials rapidly evolves, substances such as graphene, metal dichalcogenides, MXenes, and MBenes have garnered extensive attention from scholars in the gas sensing domain due to their unique and superior properties. Based on first-principles calculations, this work explored the adsorption characteristics of both intrinsic and silver (Ag) doped tin disulfide (SnS2) toward the decomposition components of the insulating medium C4F7N (namely, CF4, C3F6, and COF2), encompassing the adsorption energy, charge transfer, density of state (DOS), band structure, and adsorption stability. The results indicated that Ag-doped SnS2 exhibited an effective and stable adsorption for C3F6 and COF2, whereas its adsorption for CF4 was comparatively weaker. Additionally, the potential for Ag-SnS2 in detecting C3F6 was highlighted, inferred from the contributions of the band gap variations. This research provides theoretical guidance for the application of Ag-SnS2 as a sensing material in assessing the operational status of gas-insulated equipment.

Construction of Hierarchical Porous UiO-66-Br2@PS/DVB-Packed Columns by High Internal Phase Emulsion Strategy for Enhanced Separation of CF4/N2 and SF6/N2

Recovery and separation of anthropogenic emissions of electronic specialty gases (F-gases, such as CF4 and SF6) from the semiconductor sector are of critical importance. In this work, the hierarchical porous UiO-66-Br2@PS/DVB-packed column was constructed by a high internal phase emulsions strategy. UiO-66-Br2@PS/DVB exhibits a superior selectivity of CF4/N2 (2.67) and SF6/N2 (3.34) predicted by the IAST due to the diffusion limitation in the micropore and the gas-framework affinity. Especially, UiO-66-Br2@PS/DVB showed significant CF4 and SF6 retention and enabled the successful separation of CF4/N2 and SF6/N2 with a resolution of 2.37 and 8.89, respectively, when used as a packed column in gas chromatography. Compared with the Porapak Q column, the HETP of the UiO-66-Br2@PS/DVB-packed column decreased and showed good reproducibility. This research not only offers a convenient method for fabricating a hierarchical porous MOF-packed column but also showcases the prospective utilization of MOFs for the separation of the F-gas/N2 mixture.

Revealing the global emission gaps for fully fluorinated greenhouse gases

In response to the global trend of climate change, it is important to accurately quantify emissions of fully fluorinated greenhouse gases (FFGHGs, referring to SF6/NF3/CF4/C2F6/C3F8/c-C4F8 here). Atmospheric observation-based top-down methods and activity-based bottom-up methods are usually used together to estimate FFGHG emissions at the global and regional levels. In this work, emission gaps at global and regional levels are discussed among top-down studies, between the top-down and bottom-up FFGHG emissions, and among bottom-up emissions. Generally, trends and magnitudes of individual FFGHG emissions among top-down estimates are close to each other within the uncertainties. However, global bottom-up inventories show discrepancies in FFGHG emissions among each other in trends and magnitudes. The differences in emission magnitudes are up to 93%, 90%, 88%, 83%, 87%, and 85% for SF6, NF3, CF4, C2F6, C3F8, and c-C4F8, respectively. Besides, we reveal the insufficient regional TD studies and the lack of atmospheric observation data/stations especially in areas with potential FFGHG emissions. We make recommendations regarding the best practices for improving our understanding of these emissions, including both top-down and bottom-up methods.

Sustained growth of sulfur hexafluoride emissions in China inferred from atmospheric observations

Sulfur hexafluoride (SF6) is a potent greenhouse gas. Here we use long-term atmospheric observations to determine SF6 emissions from China between 2011 and 2021, which are used to evaluate the Chinese national SF6 emission inventory and to better understand the global SF6 budget. SF6 emissions in China substantially increased from 2.6 (2.3-2.7, 68% uncertainty) Gg yr-1 in 2011 to 5.1 (4.8-5.4) Gg yr-1 in 2021. The increase from China is larger than the global total emissions rise, implying that it has offset falling emissions from other countries. Emissions in the less-populated western regions of China, which have potentially not been well quantified in previous measurement-based estimates, contribute significantly to the national SF6 emissions, likely due to substantial power generation and transmission in that area. The CO2-eq emissions of SF6 in China in 2021 were 125 (117-132) million tonnes (Mt), comparable to the national total CO2 emissions of several countries such as the Netherlands or Nigeria. The increasing SF6 emissions offset some of the CO2 reductions achieved through transitioning to renewable energy in the power industry, and might hinder progress towards achieving China's goal of carbon neutrality by 2060 if no concrete control measures are implemented.

A two-dimensional metal-organic framework assembled from scandium-based cages for the selective capture of sulfur hexafluoride

Herein, we report the synthesis of a two-dimensional metal-organic framework (MOF), assembled from octahedral metal-organic cages featuring phenanthroline-based carboxylate linkers and μ3-oxo-centered trinuclear Sc(III) inorganic building blocks. We study the performance of this MOF towards the capture of sulfur hexafluoride (SF6). On account of its structural features and porous nature, this MOF displays an SF6 uptake capacity of 0.92 mmol g-1 at 0.1 bar and an isosteric heat of adsorption of about 30.7 kJ mol-1 for SF6, illustrating its potential application for the selective capture of SF6 from N2. In addition, we study the adsorptive binding mechanism of SF6 and N2 inside this MOF via molecular simulations.

Non-CO2 greenhouse gas separation using advanced porous materials

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.

Monitoring SF6 Gas Leakage Based on a Customized Binocular System

Sulfur hexafluoride (SF6) gas is extensively utilized as an insulating and arc-quenching medium in the circuit breakers and isolating switches of electrical equipment. It effectively isolates the circuits from the atmosphere and promptly extinguishes arcs. Therefore, the issue of SF6 gas leakage poses a significant threat to the related application fields, and the detection of SF6 gas leakage becomes extremely important. Infrared imaging detection offers advantages including non-contact, high precision, and visualization. However, most existing infrared detection systems are equipped with only one filter to detect SF6 gas. The images captured contain background noise and system noise, making these systems vulnerable to interference from such noises. To address these issues, we propose a method for monitoring SF6 gas leakage based on a customized binocular imaging (CBI) system. The CBI system has two filters, greatly reducing the interference of system noise and background noise. The first filter features the absorption resonant peak of SF6 gas. The second filter is used to record background noise and system noise. One aspect to note is that, in order to avoid the interference of other gases, the central wavelength of this second filter should keep away from the absorption resonant peaks of those gases. Accordingly, the central wavelengths of our customized filters were determined as 10,630 nm and 8370 nm, respectively. Then, two cameras of the same type were separately assembled with a customized filter, and the CBI prototype was accomplished. Finally, we utilized the difference method using two infrared images captured by the CBI system, to monitor the SF6 gas leakage. The results demonstrate that our developed system achieves a high accuracy of over 99.8% in detecting SF6 gas. Furthermore, the CBI system supports a plug-and-play customization to detect various gases for different scenarios.

Recent progresses, challenges and proposals on SF6 emission reduction approaches

The increasing utilization and emission of sulfur hexafluoride (SF6) pose severe threats to the climate and the environment, owing to its potent greenhouse gas properties. In this paper, we comprehensively review the recent progresses of SF6 emission reduction approaches. Currently, the use and emission of SF6 are still on the rise, and mainly concentrated in the power industry. Restrictive use and emission reduction policies are fundamental step in guiding SF6 emission, but they are poor promoted in developing economies. More specific policies and regulations are needed in conjunction with timely and accurate assessments of SF6 atmospheric properties and emissions. SF6 recovery is the direct emission reduction approach, but defects in recovery methods and equipment limit its applications. The development of SF6 purification technologies and optimizations in recovery devices and processes are needed for its treatment of different regions and SF6 volumes. SF6 degradation is the final step of waste gas treatment, and its development needs to better balance the degradation rate and product selectivity, as well as to improve their multi-scenario responsiveness. SF6 substitution is a necessity for future large-scale SF6 emission reduction. Improvements in SF6-free applications and its long-term stability are critical via new gas design, gas mixture optimization and equipment updates. Finally, all the emission reduction approaches are closely related, and promoting their synergistic development and complementarity is the ultimate way to realize SF6 lifecycle management.

Mitigation of Fully Fluorinated Greenhouse Gas Emissions in China and Implications for Climate Change Mitigation

Fully fluorinated greenhouse gases (FFGHGs), including sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), and perfluorocarbons (PFCs), have drawn attention because they have long atmospheric lifetimes (up to thousands of years) and high global warming potential. Targeting SF6, NF3, and four PFCs (CF4, C2F6, C3F8, and c-C4F8), this study projects future FFGHG emission patterns in China, explores their mitigation potential, and evaluates the effects of FFGHG emission reduction on the achievement of the country's carbon neutrality goal and climate change. FFGHG emissions are expected to increase consistently, ranging from 506 to 1356 Mt CO2-eq yr-1 in 2060 under the business-as-usual (BAU) scenario. If mitigation strategies are sufficiently employed, FFGHG emissions under three mitigation scenarios: Technologically Feasible 2030, Technologically Feasible 2050, and Technologically Feasible 2060, will eventually decrease to approximately 49-78, 70-110, and 98-164 Mt CO2-eq yr-1 in 2060, respectively, compared to the BAU scenario. Extensive implementation of FFGHG emission mitigation technologies will curb temperature rise by 0.008-0.013 °C under the slowest mitigation scenario, compared to 0.013-0.026 °C under the BAU scenario. Well-coordinated policies and reforms on FFGHG emission mitigation are recommended to prevent potential adverse effects on the climate to a certain extent.

Sulfur hexafluoride in the marine atmosphere and surface seawater of the Western Pacific and Eastern Indian Ocean

Sulfur hexafluoride (SF6) is a powerful greenhouse gas with a high global warming potential. While SF6 emissions from urban areas have been extensively studied, our knowledge about SF6 concentrations in the oceanic atmosphere and its air-sea exchange remains limited. Herein, the concentrations of SF6 in the atmosphere and surface seawater of the WPO (Western Pacific Ocean) and EIO (Eastern Indian Ocean) were comprehensively characterized from 2019 to 2022 in the first long-term study. The mean mixing ratios of SF6 over the WPO and EIO during 2019-2020 (2021-2022) were 10.9 (11.2) and 10.9 (11.1) ppt, respectively. The atmospheric SF6 concentration over the WPO and EIO increased at rates of 0.40 ± 0.06 and 0.58 ± 0.28 ppt yr-1, respectively, surpassing previously reported annual growth rates. The faster growth was primarily attributed to the influence of polluted air masses originating from eastern Asian countries, particularly Japan, Northeast China, and India. This might explain why the radiative forcing caused by SF6 in the study region was higher than the global average. The concentrations of SF6 in the surface seawater of the WPO and EIO ranged from 0.33 to 2.54 fmol kg-1, and the distribution was affected by atmospheric concentrations and ocean currents. Estimated air-sea fluxes revealed that the ocean acted as a significant sink of atmospheric SF6, and the preliminary estimation suggested oceanic uptake accounts for about 7% of annual global SF6 emissions. Based on these findings, we tentatively suggest that the strength of the ocean as a sink of SF6 may warrant reassessment. The global oceanic uptake of SF6 has the potential to reduce its global abundance and environmental impacts.

In Situ Observations of Halogenated Gases at the Shangdianzi Background Station and Emission Estimates for Northern China

Halogenated gases include ozone-depleting substances and greenhouse gases, such as chlorofluorocarbons, halons, hydrochlorofluorocarbons, hydrofluorocarbons, and perfluorinated gases. In situ atmospheric observations of major halogenated gases were conducted at the Shangdianzi (SDZ) background station, China, from October 2020 to September 2021 using ODS5-pro, a newly developed measurement system. The measurement time series of 36 halogenated gases showed occasional pollution events, where background conditions represented 25% (CH₂Cl₂) to 81% (CF₃Cl, CFC-13) of the measurements. The annual mean background mole fractions of most species at SDZ were consistent with those obtained at the Mace Head station in Ireland. The background conditions were distinguished from pollution events, and the enhanced mole fractions were used to estimate the emissions of four categories of fluorinated gases (F-gases) from northern China using a tracer ratio method. The CO₂-equivalent (CO₂-equiv) emission of F-gases from northern China reached 181 ± 18 Tg year^-1 during 2020-2021. Among the four categories of F-gases estimated, SF₆ accounted for the highest proportion of CO₂-equiv emissions (24%), followed by HFC-23 (22%), HFC-125 (17%), HFC-134a (13%), NF₃ (10%), CF₄ (5.9%), HFC-143a (3.9%), HFC-32 (3.4%), and HFC-152a (0.2%).

Room-Temperature Detection of Perfluoroisobutyronitrile with SnO2/Ti3C2Tx Gas Sensors

Ti₃C₂T_x MXene is an emerging two-dimensional transition-metal carbide/nitride with excellent properties of large specific surface and high carrier mobility for room-temperature gas sensing. However, achieving high sensitivity and long-term stability of pristine Ti₃C₂T_x-based gas sensors remains challenging. SnO₂ is a typical semiconductor metal oxide with high reaction activity and stable chemical properties ideal for a dopant that can comprehensively improve sensing performance. Ti₃C₂T_x and SnO₂ are investigated for the first time in this study as functional materials for hybridization and room-temperature detection of the gas insulating medium fluorinated nitrile (C₄F₇N) with microtoxicity. A Ti₃C₂T_x-SnO₂ nanocomposite sensor exhibits superior sensitivity, high selectivity, strong anti-interference ability, and excellent long-term stability. The enhanced sensing mechanism is ascribed to the synergistic effect between SnO₂ and Ti₃C₂T_x and the strong adsorption ability of SnO₂ to C₄F₇N similar to bait for fish. We also established an actual leakage scene and demonstrated the feasibility of the Ti₃C₂T_x-SnO₂ sensor to provide distribution rules with high sensing efficiency for actual engineering applications. The results of this work can expand the gas sensing application of Ti₃C₂T_x MXene and provide a reference for maintaining C₄F₇N-based eco-friendly gas-insulated equipment.

Repurposing of F-gases: challenges and opportunities in fluorine chemistry

Fluorinated gases (F-gases) are routinely employed as refrigerants, blowing agents, and electrical insulators. These volatile compounds are potent greenhouse gases and consequently their release to the environment creates a significant contribution to global warming. This review article seeks to summarise: (i) the current applications of F-gases, (ii) the environmental issues caused by F-gases, (iii) current methods of destruction of F-gases and (iv) recent work in the field towards the chemical repurposing of F-gases. There is a great opportunity to tackle the environmental and sustainability issues created by F-gases by developing reactions that repurpose these molecules.

Toxic Study on the New Eco-Friendly Insulating Gas Trifluoromethanesulfonyl Fluoride: A Substitute for SF6

It has been proven that the gas trifluoromethanesulfonyl fluoride (CF3SO2F) has good dielectric performance and the potential to replace the potent greenhouse gas sulfur hexafluoride (SF6), which is the most commonly used insulating gas in high-voltage electrical equipment. However, there are many key biochemical properties, such as toxicity, that the new eco-friendly insulating gas will need to obtain. It could protect the operator and equipment and help the chemical engineering development of this gas in the power grid industry. In this study, according to Horn’s method, an acute toxic gas inhalation test was carried out. The results showed that the lethal concentration of 50% (LC50) for female rats was 27.1 g/m3, and that for male rats was 23.3 g/m3. The behavioral and vital sign changes in the rats were recorded. Pathological sections of the main organs revealed that the heart, lungs, spleen, and eyes suffered the most damage from the gas. This research also provides scientific suggestions for the protection of electrical workers exposed to the insulating gas CF3SO2F.

Low-Temperature Detection of Sulfur-Hexafluoride Decomposition Products Using Octahedral Co3O4-Modified NiSnO3 Nanofibers

Sulfur hexafluoride (SF₆) is widely used in electrical equipment because of its excellent insulating properties. The type of internal fault in the power system can be identified by detecting SF₆ decomposition products. In this manuscript, we report a novel sensing material based on octahedral Co₃O₄-modified NiSnO₃ nanofibers synthesized via a two-step process based on electrospinning followed by a hydrothermal method for detecting the SF₆ decomposition products. From the evaluation of various characterization techniques, it was determined that the Co₃O₄ octahedra adhered inflexibly to the surface of the NiSnO₃ nanofibers, which consist of smaller particles and provide a huge surface area for the adsorption of an enormous amount of gas species. Planar-type chemical gas sensors were devised, and their gas detecting performance against SF₆ decomposition products was systematically investigated. A comparison of the sensitivity properties of different amounts of charged Co₃O₄ octahedra in NiSnO₃ nanofibers shows that the S-2-based Co₃O₄@NiSnO₃ composite has a high selectivity for 100 ppm SO₂F₂ gas with a high sensing response of 22.5 at a relatively low temperature of 50 °C with a moderate response/recovery interval (∼200/∼268 s) and a low detection limit (5 ppm) over other interfering gases, such as SOF₂, SO₂, and H₂S. Interestingly, the sensing properties of the fabricated sensors based on the Co₃O₄@NiSnO₃ composites for the SO₂F₂ gas were improved in terms of lower operating temperatures, higher gas responses, and mild response/recovery intervals, which could be attributed to the unique microstructure effect, the catalytic influence of Co₃O₄ octahedra, and the creation of p/n junctions to increase the charge transfer and diffusion rate within the catalytic assembly of the sensor materials. This work highlights the importance of the heterostructure design in the construction of high-performance gas sensors for the real-time detection of SF₆ decomposition products.

SnO2 nanoparticles based highly sensitive gas sensor for detection of C4F7N: A new eco-friendly gas insulating medium

As a novel eco-friendly gas insulation medium, perfluoroisobutyronitrile (C₄F₇N) has been utilized in various gas insulated equipment. Considering the biological toxicity of C₄F₇N, it is of great engineering significance to develop highly sensitive sensors for leakage detection scenarios. Herein, we fabricated the first SnO₂ nanoparticles based highly sensitive C₄F₇N gas sensor that realized a superior response of 65.01% within 21 s for 50 ppm C₄F₇N exposure and a detection limit of 0.25 ppm. Meanwhile, successive response-recovery tests were performed to confirm its durability and stability. We also explored the sensing mechanism of SnO₂ nanoparticles towards C₄F₇N and explained the superior sensing performance compared with other gases based on the density functional theory. It was found that the O vacancy demonstrates strong interaction with the -CN group in C₄F₇N that promotes the detection response, which was also confirmed by sensing experiments for SnO₂ with different O vacancy density. We believe this paper provides convincing support for lowering the potential operation risk brought by C₄F₇N in electrical engineering and the application scenarios of SnO₂ based gas sensors.

Acute toxicity and health effect of perfluoroisobutyronitrile on mice: a promising substitute gas-insulating medium to SF6

Perfluoroisobutyronitrile (C₄F₇N) is a new eco-friendly gas insulation medium that has potential to replace the most greenhouse gas sulfur hexafluoride (SF₆) used in power industry. In order to ensure the engineering application safety, an in-depth assessment of the acute inhalation toxicity of C₄F₇N gas mixture is required. This article revealed gender differences in male and female mice after exposure to C₄F₇N and the physiological recovery characteristics of surviving mice by means of 4 h acute inhalation toxicity tests, hematological determinations and histopathological examination. Comparative analysis on the toxicity of C₄F₇N on mice and rats is also evaluated. We find that the LC₅₀ of C₄F₇N for male and female mice is 1175 ppm (4 h), 1380 ppm (4 h) and female ones are more tolerant to C₄F₇N. Mice that exposed to 1000 ppm C₄F₇N for 4 h could survive and return to their normal state after the 14-day observation period without irreversible damage. The toxic effect duration of C₄F₇N on rats is longer than that of mice. Relevant results revealed the acute inhalation toxicity of C₄F₇N systematically and provided fundamental reference for inhalation safety protection and engineering application.

Theoretical and experimental investigation on decomposition mechanism of eco-friendly insulation gas HFO1234zeE

Decomposition experiments under corona discharge and theoretical calculations using the density functional theory (DFT) method were accomplished to clarify the dissociation behavior and decomposition mechanism of HFO1234zeE (trans-1,3,3,3-tetrafluoropropene), an eco-efficient SF₆ alternative gas. The discharge decomposition products of HFO are mainly fluorocarbon, unsaturated hydrocarbon and saturated hydrocarbons, which are containing no more than three carbons. Free radicals, CF₃·, F· and H·, generated via bond-cleavage reaction are important structures to promote the decomposition, and HFO is more likely to dissociate with them by abstraction reaction to form CF₄ and CF₃H. Long-chain radicals, such as CF₃CHCF·, CF₃CHCH· and CF₃CCHF·, will be decomposed into CF₃CCH and CF₃CCF, and small intermediates would be easier to combine to form HF, C₂F₆, C₂F₄, C₂HF₅, CF₃HCF₃H and C₃F₈. It is also likely to be converted to Z-isomer. Due to the high discharge intensity and ion bombardment, solid by-products appeared on the electrode surface may contain carbon dust and metal compounds. The solid attached to the surface has little effect on the electric field distribution, and most gas decomposition products still maintain the insulation strength, so the air-gap breakdown voltage only dropped by about 6.2% after long-term corona discharge. The obtained results not only reveal the decomposition mechanism in a comprehensive way, but also present useful reference for exploring the application potentials of HFO1234zeE.

Sustainable and Tunable Mg/MgO Plasmon-Catalytic Platform for the Grand Challenge of SF6 Environmental Remediation

Sulfur hexafluoride (SF₆) is one of the most harmful greenhouse gases producing environmental risks. Therefore, developing ways of degrading SF₆ without forming hazardous products is increasingly important. Herein, we demonstrate for the first time the plasmon-catalytic heterogeneous degradation of SF₆ into nonhazardous MgF₂ and MgSO₄ products by nontoxic and sustainable plasmonic magnesium/magnesium oxide (Mg/MgO) nanoparticles, which are also effective as a plasmon-enhanced SF₆ chemometric sensor. The main product depends on the excitation wavelength; when the localized surface plasmon resonance (LSPR) is in the ultraviolet, then MgF₂ forms, while visible light LSPR results in MgSO₄. Furthermore, Mg/MgO platforms can be regenerated in few seconds by hydrogen plasma treatment and can be reused in a new cycle of air purification. Therefore, this research first demonstrates effectiveness of Mg/MgO plasmon-catalysis enabling environmental remediation with the concurrent functionalities of monitoring, degrading, and detecting sulfur and fluorine gases in the atmosphere.

Influence of Oxygen on the Thermal Decomposition Properties of C4F7N-N2-O2 as an Eco-Friendly Gas Insulating Medium

The C₄F₇N (fluorinated nitrile) gas mixture has been recognized as the most potential substitute gas to SF₆ used in gas-insulated equipment. In this paper, we explored the thermal stability and decomposition properties of the C₄F₇N-N₂-O₂ gas mixture. The influence mechanism of oxygen content and temperature on the byproduct generation was obtained and analyzed. It was found that thermal decomposition of the C₄F₇N-N₂-O₂ gas mixture mainly produces CO, C₃F₆, C₃F₈, CF₃CN, (CN)₂, and COF₂. The addition of oxygen could accelerate the decomposition of C₄F₇N. The content of C₃F₆ and (CN)₂ decreases, while the yield of CF₄, CO, C₃F₈, and COF₂ increases with the oxygen content. Thermal decomposition of the C₄F₇N-N₂-O₂ gas mixture at temperatures lower than 425 °C results from the interaction between C₄F₇N and the metal heating element, while the bond cleavage reactions occur at higher temperature. As for engineering application, the oxygen added in the 6%C₄F₇N-94%N₂ gas mixture should not exceed 6% to avoid the negative effect of oxygen on the thermal stability of C₄F₇N.

Can China Peak Its Non-CO2 GHG Emissions before 2030 by Implementing Its Nationally Determined Contribution?

Non-CO₂ greenhouse gas (GHG) emissions account for about ¹/₄ of global GHG emissions, and the trend of these emissions, as well as their mitigation potential and abatement cost, are of interest to both scientific researchers and decision makers. We present an integrated model, China Multigas Optimal Reduction Evaluation model (China-MORE), of the nitrous oxide (N₂O), methane (CH₄), and fluorinated gases (F-gases) emissions of China, with which we analyze the non-CO₂ emission reduction implications of China's Paris pledges. We find that China's non-CO₂ emissions can peak before 2030 under its Paris pledges, where the cobenefit of coal control policy is the largest contributor to this emissions trajectory due to reduction of CH₄ from coal mines. Based on the mitigation cost curve, we show that while the non-CO₂ emission reductions are cost-effective at a lower reduction rate, they can only be reduced up to 60-70% due to physical constraints of the reduction technologies, leaving 1.4 Gt CO₂-eq of residual emissions in 2050. The growth of non-CO₂ emissions in China is largely driven by household consumption of cooling technologies, vehicles, and food. Our findings imply that deep reductions can only be achieved through the deployment of mitigation technologies at a reasonable cost, along with policies to induce behavioral change.

Long-term entrapment and temperature-controlled-release of SF6 gas in metal-organic frameworks (MOFs)

In this work, a metal-organic framework (MOF), namely MFU-4, which is comprised of zinc cations and benzotriazolate ligands, was used to entrap SF₆ gas molecules inside its pores, and thus a new scheme for long-term leakproof storage of dangerous gasses is demonstrated. The SF₆ gas was introduced into the pores at an elevated gas pressure and temperature. Upon cooling down and release of the gas pressure, we discovered that the gas was well-trapped inside the pores and did not leak out - not even after two months of exposure to air at room temperature. The material was thoroughly analyzed before and after the loading as well as after given periods of time (1, 3, 7, 14 or 60 days) after the loading. The studies included powder X-ray diffraction measurements, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, ¹⁹F nuclear magnetic resonance spectroscopy and computational simulations. In addition, the possibility to release the gas guest by applying elevated temperature, vacuum and acid-induced framework decomposition was also investigated. The controlled gas release using elevated temperature has the additional benefit that the host MOF can be reused for further gas capture cycles.

A Structural Decomposition Analysis of China’s Consumption-Based Greenhouse Gas Emissions

The trends of consumption-based emissions in China have a major impact on global greenhouse gas (GHG) emissions. Previous studies have only focused on China’s energy-related consumption-based emissions of CO2 or specific non-CO2 GHGs without taking overall consumption-based non-CO2 GHG emissions into account. Based on a constructed global non-CO2 GHG emissions database, combined with CO2 emissions data, this paper fills this gap through an examination and analysis of China’s GHG emissions using a global multi-regional input–output (MRIO) model for 2004, 2007 and 2011, and identifies the major factors driving changes in consumption-based emissions through a structural decomposition analysis (SDA). The results show that compared with CO2 emissions, CH4, N2O and F-gases emissions all increased more rapidly. Among consumption-based non-CO2 GHG emissions, investment-based emissions experienced the fastest growth, but the net exports of non-CO2 GHG emissions dropped drastically in recent years. While investment in total final consumption demand is the most influential factor for CO2 emissions, household consumption most significantly affects the growth in consumption-based non-CO2 GHG emissions.

Improvement on Fluorine Migration from SF6 to SiF4 by an Efficient Mediator of Fe2O3/Cr2O3 Composites

An economic and facile method was urgently required for the degradation of SF₆ to replace the high-energy excitation treatment. Both theoretical calculations and experimental observations were conducted to reveal the synergy of Cr/Fe/Si composites on a new technique of SF₆ degradation through reacting silicon dioxide. Density functional theory (DFT) calculations show that strong adsorption of SF₆ on Cr₂O₃, and then the fast F/O exchange between CrF₃ and Fe₂O₃ (energy barrier was 1.45 eV) as well as FeF₃ and SiO₂ (energy barrier was 1.69 eV) enhanced mediated efficiency from SF₆ to SiF₄. The fluorine (F) migration between solid interfaces in Cr₂O₃&Fe₂O₃@SBA15 was responsible for efficient SF₆ removal. The F migration route was composed of SF₆ to CrF₃, CrF₃ to FeF₃, and FeF₃ to SiF₄ with the lowest thermodynamic driving. Enhanced specific accumulative converted amount (SACA) of SF₆ on Cr₂O₃&Fe₂O₃@SBA15 was achieved and the highest SACA was 13.98 mmol/g within 7 h, significantly higher than that on Fe₂O₃@SBA15 (5.74 mmol/g) and Cr₂O₃@SBA15 (2.71 mmol/g). Moreover, X-ray diffractometry and X-ray photoelectron spectroscopy were performed to support DFT calculations, including ion intensities detected using mass spectroscopy and composition analysis of the mediator during the reaction. Therefore, our work put forward a novel approach for economic and efficient SF₆ decomposition through reacting with silicon dioxide under the mediation of Cr₂O₃&Fe₂O₃. This method was also potentially used in effective degradation of refractory non-metal halides.

Assessment on the toxicity and application risk of C4F7N: A new SF6 alternative gas

C₄F₇N (fluorinated nitrile) gas mixture has been utilized as the gas insulating medium to replace the most greenhouse gas SF₆ (sulphur hexafluoride). Nowadays, there are few reports on the toxicity mechanism of C₄F₇N and studies on the application risk of C₄F₇N is insufficient. In this paper, we carried out acute toxicity tests for C₄F₇N gas systematically. The changes of vital signs of rats after exposure to C₄F₇N were analyzed and the influence of C₄F₇N on the main organs of rats was revealed for the first time. It was found that rats developed symptoms of respiratory rate decrease, respiratory mucosa damage, movement systems impairment and abnormal blood cell count after exposure to C₄F₇N. Pathological section results showed that 1.5% C₄F₇N could damage the lung, kidney, intestine and brain tissues of rats to a certain extent, but has little influence to the eye, skin, heart and liver. The LC50 (rat, 4 h) of C₄F₇N gas is in the range of 15,000 ppm (1.5%) and 20,000 ppm (2%). Relevant research results not only reveal the acute toxicity mechanism of C₄F₇N, but also provide important reference for the safety protection of scientific researcher, equipment production, engineering operation and maintenance personnel.

Alternative Environmentally Friendly Insulating Gases for SF6

Sulfur hexafluoride (SF6) shows excellent insulation performance as an insulating gas. It is suitable for various climate conditions due to its low boiling point (−64 °C). Therefore, it has been widely used in power grid equipment. However, its global warming potential (GWP) is 23,500 times higher than that of CO2. Thus, it is imperative to find an environmentally friendly insulating gas with excellent insulation performance, lower GWP, and which is harmless to equipment and workers to replace SF6. In this review, four possible alternatives, including perfluorocarbons, trifluoroiodomethane, perfluorinated ketones, and fluoronitrile are reviewed in terms of basic physicochemical properties, insulation properties, decomposition properties, and compatibility with metals. The influences of trace H2O or O2 on their insulation performances are also discussed. The insulation strengths of these insulating gases were comparable to or higher than that of SF6. The GWPs of these insulating gases were lower than that of SF6. Due to their relatively high boiling point, they should be used as a mixture with buffering gases with low boiling points. Based on these four characteristics, perfluorinated ketones (C5F10O and C6F12O) and fluoronitrile (C4F7N) could partially substitute SF6 in some electrical equipment. Finally, some future needs and perspectives of environmentally friendly insulating gases are addressed for further studies.

A Priori Theoretical Model for Discovery of Environmentally Sustainable Perfluorinated Compounds

Since SF₆ is the most potent greenhouse gas, the search for a viable alternative is taking on great urgency for several decades but without success. The demanding combination of performance, safety, and environmental properties for the new chemistry superior to SF₆ was thought to be nearly impossible to achieve. In contrast to the commonly used mixtures with two or three individual gases, a hybrid model has been proposed to create the new perfluorinated compounds with multiple unsaturated chemical bonds by means of full or partial integration of the parent molecules. A unique combination of a series of paradoxical properties that is high in dielectric strength and stability, low in boiling point, and significantly lower in global warming potential is achieved for the first time. The present a priori theoretical predictions shed new lights on the rational molecular design of the perfluorinated compounds and will greatly inspire experimental synthesis and field tests on the new chemistry for dielectric use.

Optimizing critical source control of five priority-regulatory trace elements from industrial wastewater in China: Implications for health management

Anthropogenic emissions of toxic trace elements (TEs) have caused worldwide concern due to their adverse effects on human health and ecosystems. Based on a stochastic simulation of factors' probability distribution, we established a bottom-up model to estimate the amounts of five priority-regulatory TEs released to aquatic environments from industrial processes in China. Total TE emissions in China in 2010 were estimated at approximately 2.27 t of Hg, 310.09 t of As, 318.17 t of Pb, 79.72 t of Cd, and 1040.32 t of Cr. Raw chemicals, smelting, and mining were the leading sources of TE emissions. There are apparent regional differences in TE pollution. TE emissions are much higher in eastern and central China than in the western provinces and are higher in the south than in the north. This spatial distribution was characterized in detail by allocating the emissions to 10 km × 10 km grid cells. Furthermore, the risk control for the overall emission grid was optimized according to each cell's emission and risk rank. The results show that to control 80% of TE emissions from major sources, the number of top-priority control cells would be between 200 and 400, and less than 10% of the total population would be positively affected. Based on TE risk rankings, decreasing the population weighted risk would increase the number of controlled cells by a factor of 0.3-0.5, but the affected population would increase by a factor of 0.8-1.5. In this case, the adverse effects on people's health would be reduced significantly. Finally, an optimized strategy to control TE emissions is proposed in terms of a cost-benefit trade-off. The estimates in this paper can be used to help establish a regional TE inventory and cyclic simulation, and it can also play supporting roles in minimizing TE health risks and maximizing resilience.

Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF6

Gases for electrical insulation are essential for the operation of electric power equipment. This Review gives a brief history of gaseous insulation that involved the emergence of the most potent industrial greenhouse gas known today, namely sulfur hexafluoride. SF₆ paved the way to space-saving equipment for the transmission and distribution of electrical energy. Its ever-rising usage in the electrical grid also played a decisive role in the continuous increase of atmospheric SF₆ abundance over the last decades. This Review broadly covers the environmental concerns related to SF₆ emissions and assesses the latest generation of eco-friendly replacement gases. They offer great potential for reducing greenhouse gas emissions from electrical equipment but at the same time involve technical trade-offs. The rumors of one or the other being superior seem premature, in particular because of the lack of dielectric, environmental, and chemical information for these relatively novel compounds and their dissociation products during operation.

Decomposition Mechanism of C5F10O: An Environmentally Friendly Insulation Medium

SF₆, the most widely used electrical-equipment-insulation gas, has serious greenhouse effects. C₅F₁₀O has attracted much attention as an alternative gas in recent two years, but the environmental impact of its decomposition products is unclear. In this work, the decomposition characteristics of C₅F₁₀O were studied based on gas chromatography-mass spectrometry and density functional theory. We found that the amount of decomposition products of C₅F₁₀O, namely, CF₄, C₂F₆, C₃F₆, C₃F₈, C₄F₁₀, and C₆F₁₄, increased with increased number of discharges. Under a high-energy electric field, the C-C bond of C₅F₁₀O between carbonyl carbon and α-carbon atoms was most likely to break and generate CF₃CO•, C₃F₇• or C₃F₇CO•, CF₃• free radicals. CF₃•, and C₃F₇• free radicals produced by the breakage more easily recombined to form small molecular products. By analyzing the ionization parameters, toxicity, and environmental effects of C₅F₁₀O and its decomposition products, we found that C₅F₁₀O gas mixtures exhibit great decomposition and environmental characteristics with low toxicity, with great potential to replace SF₆.

Theoretical Investigation of Mono- and Di-Chloro-Substitient Effects on the Insulation and Greenhouse Properties of Octafluorocyclobutane

Octafluorocyclobutane, c-C₄F₈, and its derivatives are regarded as promising replacements of insulation gaseous SF₆, which are currently widely used in electric equipment but suffer greatly from its greenhouse effect. Based on the recent finding that the dielectric and thermodynamics properties of insulating gases are greatly dependent on the molecule's microscopic electronic and vibrational parameters, in this work, we use density functional theory (DFT) to study the molecular structures, electron affinities, and IR-active vibrational frequencies as well as thermodynamic properties for c-C₄F₈ and a series of mono-, di-substituted c-C₄F₈ compounds. It is shown that DFT calculation of perfluoro-compounds is sensitive to the chosen functional. Although all chloro-substituted c-C₄F₈ molecules are found to have much larger electron affinities, only part of them have less IR intensity in the atmospheric IR "window" than c-C₄F₈. Such a study provides useful guideline for the pre-screening search for new insulation gases via electronic structure calculations.

Porous Organic Cages for Sulfur Hexafluoride Separation

A series of porous organic cages is examined for the selective adsorption of sulfur hexafluoride (SF6) over nitrogen. Despite lacking any metal sites, a porous cage, CC3, shows the highest SF6/N2 selectivity reported for any material at ambient temperature and pressure, which translates to real separations in a gas breakthrough column. The SF6 uptake of these materials is considerably higher than would be expected from the static pore structures. The location of SF6 within these materials is elucidated by X-ray crystallography, and it is shown that cooperative diffusion and structural rearrangements in these molecular crystals can rationalize their superior SF6/N2 selectivity.

Highly selective polymer electrolyte membranes consisting of poly(2-ethyl-2-oxazoline) and Cu(NO3)2 for SF6 separation

Polymer electrolyte membranes consisting of Cu(NO₃)₂ and poly(2-ethyl-2-oxazoline) (POZ) were prepared for SF₆/N₂ separation. It was anticipated that repulsive forces would be operative between the negative charge of water and the F atoms of SF₆ when Cu(NO₃)₂ in the composite was solvated by water, and that the barrier effect of Cu²⁺ ions would be activated. In fact, Cu(NO₃)₂ solvated by water in the POZ membrane was observed to have more higher-order ionic aggregates than free ions or ion pairs, as confirmed by FT-Raman spectroscopy. Thus, when Cu(NO₃)₂ solvated by water was incorporated into the POZ matrix, the N₂/SF₆ selectivity increased to 28.0 with a N₂ permeance of 11.2 GPU at a POZ/Cu(NO₃)₂ mole ratio of 1:0.7. The coordinative interaction of Cu(NO₃)₂ with the carbonyl group in POZ was confirmed by FT-IR spectroscopy and TGA, and the film thickness of the membrane was determined from SEM analysis.

Wide Carbon Nanopores as Efficient Sites for the Separation of SF6 from N2

SF₆ and SF₆-N₂ mixed gases are used widely as insulators, but such gases have high greenhouse gas potential. The separation of SF₆ from SF₆-N₂ mixed gases is an inevitable result of their use. Single-walled carbon nanohorns (CNHs) were used here for a fundamental study of the separation of SF₆ and N₂. The diameters of the interstitial and internal nanopores of the CNHs were 0.7 and 2.9 nm, respectively. The high selectivity of SF₆ over N₂ was observed only in the low-pressure regime in the interstitial 0.7 nm nanopores; the selectively was significantly decreased at higher pressures. In contrast, the high selectivity was maintained over the entire pressure range in the internal 2.9-nm nanopores. These results showed that the wide carbon nanopores were efficient for the separation of SF₆ from the mixed gas.

Atmospheric sulfur hexafluoride in-situ measurements at the Shangdianzi regional background station in China

We present in-situ measurements of atmospheric sulfur hexafluoride (SF6) conducted by an automated gas chromatograph-electron capture detector system and a gas chromatography/mass spectrometry system at a regional background site, Shangdianzi, in China, from June 2009 to May 2011, using the System for Observation of Greenhouse gases in Europe and Asia and Advanced Global Atmospheric Gases Experiment (AGAGE) techniques. The mean background and polluted mixing ratios for SF6 during the study period were 7.22 × 10⁻¹² (mol/mol, hereinafter) and 8.66 × 10⁻¹², respectively. The averaged SF6 background mixing ratios at Shangdianzi were consistent with those obtained at other AGAGE stations located at similar latitudes (Trinidad Head and Mace Head), but larger than AGAGE stations in the Southern Hemisphere (Cape Grim and Cape Matatula). SF6 background mixing ratios increased rapidly during our study period, with a positive growth rate at 0.30 × 10⁻¹² year⁻¹. The peak to peak amplitude of the seasonal cycle for SF6 background conditions was 0.07 × 10⁻¹², while the seasonal fluctuation of polluted conditions was 2.16 × 10⁻¹². During the study period, peak values of SF6 mixing ratios occurred in autumn when local surface horizontal winds originated from W/WSW/SW/SWS/S sectors, while lower levels of SF6 mixing ratios appeared as winds originated from N/NNE/NE/ENE/E sectors.