Methane Destruction Research Articles

(Invited) Applications of an AI-Powered, Iot-Based Electrochemical Sensor Platform

Emissions are a significant contributor to climate change [1-2]. Low-cost sensor platforms are needed to understand the levels of emissions and the types of emissions [3]. In addition, sensors are needed to help determine the impact levels of what soon-to-be prominent gases, like hydrogen, will have on the environment [4]. Mixed potential electrochemical sensors are a promising technology for the foundation of the sensor platform [5].Our group has developed an AI-powered, IoT-driven sensor platform capable of measuring and differentiating sources of methane, hydrogen, carbon monoxide, ammonia and oxides of nitrogen [6]. The sensor platform has been field tested at Colorado State University’s Methane Emission Technology Evaluation Center (METEC). Embedded in the system are machine learning methods that are applied to a training dataset collected in the laboratory to quantify the concentration and identify sources of emissions [6]. These results serve as a first demonstration that a low-cost mixed potential electrochemical sensor system can successfully detect underground pipeline emissions and quantify CH4 concentrations that are in agreement with previously published results [7] collected using more complex and costly methods.This talk will focus on the applications of the sensor platform including leak detection, emissions monitoring, tailpipe emissions for transportation, flare management optimization and even methane destruction - all of which support the ability to measure and confirm net-zero strategies.This work was supported by US Department of Energy Award DE-FE0031864.

Quantifying flare combustion efficiency using an imaging Fourier transform spectrometer

ABSTRACT Mid-wavelength infrared (MWIR) imaging Fourier transform spectrometers (IFTSs) are a promising technology for measuring flare combustion efficiency (CE) and destruction removal efficiency (DRE). These devices generate spectrally resolved intensity images of the flare plume, which may then be used to infer column densities of relevant species along each pixel line-of-sight. In parallel, a 2D projected velocity field may be inferred from the apparent motion of flow features between successive images. Finally, the column densities and velocity field are combined to estimate the mass flow rates for the species needed to calculate the CE or DRE. Since the MWIR IFTS can measure key carbon-containing species in the flare plume, it is possible to measure CE without knowing the fuel flow rate, which is important for fenceline measurements. This work demonstrates this approach on a laboratory heated vent, and then deploys the technique on two working flares: a combustor burning natural gas at a known rate, and a steam-assisted flare at a petrochemical refinery. Analysis of the IFTS data highlights the potential of this approach, but also areas for future development to transform this approach into a reliable technique for quantifying flare emissions. Implications: Our research is motivated by the need to assess hydrocarbon emissions from flaring, which is a critical problem of global significance. For example, recent studies have shown that methane destruction efficiency of flaring from upstream oil may be significantly lower than the commonly assumed figure of 98%; work by Plant et al., in particular, suggest that this discrepancy amounts to CO2 emissions from 2 to 8 million automobiles annually, considering the US alone. Similarly, the international energy agency (IEA) estimates a global flare efficiency of 92%,which translates in 8 million tons of CH4 emitted by flares in 2020. Highlighted by these studies and supported by the World Bankinitiatives toward zero routine flaring emissions, there is an urgent need for oil and gas industry to assess their flare methane emission, and overall hydrocarbon emissions. At the very least, it is critical to identify problematic flare operating conditions and means to mitigate flare emissions. Focusing on remote quantification of plume species, the measurement technique and quantification method presented in this paper is a considerable step forward in that direction by computing combustion efficiency and key components for destruction efficiency.

Measuring methane destruction efficiency in gas flares with dual comb spectroscopy

Gas flaring is used as an alternative to venting when waste gases cannot be captured from industrial processes such as oil and natural gas production, chemical processing, and waste management. In the oil and natural gas production sector alone, an estimated 3.5 % of total global natural gas production is flared. Survey studies have shown that the methane destruction efficiency (DE) of flares is lower than expected due to real-world conditions (weather and equipment malfunction) and estimate that improving flare efficiency is a 0.5 Tg/yr methane emissions reduction opportunity. Continuous monitoring of flare DE would provide the opportunity for feedback to lower emissions; however, there are currently no technologies used at scale that can provide such a measurement. Here we present a method for measuring the operational methane DE from flares by monitoring methane levels in flares using dual-frequency comb spectroscopy. This method leverages the temperature-dependent absorption fingerprint of methane to differentiate heated and ambient methane. We assess the capabilities of this technique through a set of laboratory-based experiments utilizing a partially premixed methane flame. We estimate the limit of detection (LOD) and sensitivity of the measurements for directly monitoring a flame, and monitoring a flame from a distance of 1 km in the presence of ambient methane. For our configuration, a targeted monitoring scenario (direct flame measurement) results in the ability to distinguish methane DE up to 99.9 %; whereas in the presence of a 1 km background methane signal, the approach is able to quantify methane DE to 97.5 %. These performance metrics could be improved through an updated high-temperature spectral absorption database for methane, however the current estimated performance could already substantially impact flare emissions by closing the gap between the flare design specifications and what research studies estimate from actual in-field performance.

Correction to: 'Is the destruction or removal of atmospheric methane a worthwhile option?' (2021) by Nisbet-Jones etal.

Correction to: 'Is the destruction or removal of atmospheric methane a worthwhile option?' (2021) by Nisbet-Jones etal.

Study of the anaerobic destruction of post-alcohol distillery waste by mateen

Post-alcohol distillery waste is an environmental pollutant, which determined the relevance of its disposal. One of the ways to utilise post-alcohol distillery waste is through its anaerobic methane destruction in biogas plants. The research aims to determine the optimal amount of post-alcohol distillery wastes to be added to the substrate to achieve maximum biomethane yield. The research was conducted on a laboratory biogas plant consisting of a 30-litre digester and a gas holder in a mesophilic mode at a substrate temperature of 40°C with a periodic substrate loading mode. It was found that the highest biogas yield of 5.369 l/(h×kg DOM) was obtained by anaerobic methane mono-degradation of post-alcohol distillery waste. However, the methane content in the biogas is in the range of 48-52%. During the anaerobic methane destruction of a mixture of post-alcohol distillery waste with cow manure, the methane content in biogas increases to 70-76%, but the biogas yield is lower and is 4.577 l/(h×kg DOM) at 36% post-alcohol distillery waste content in the substrate, 3.294 l/(h×kg DOM) at 27%, 2.960 l/(h×kg DOM) at 18%, 1.538 l/(h×kg DOM) at 9%. The optimum content of post-alcohol distillery waste in the substrate, at which the biomethane yield will be maximum (3.821 l/(h×kg DOM)), is 46.7% of the substrate content and 100% of the organic part of the substrate. The results of this study can be used in planning the composition of the substrate of biogas plants and designing and building new biogas plants near distilleries

Inefficient and unlit natural gas flares both emit large quantities of methane.

Flaring is widely used by the fossil fuel industry to dispose of natural gas. Industry and governments generally assume that flares remain lit and destroy methane, the predominant component of natural gas, with 98% efficiency. Neither assumption, however, is based on real-world observations. We calculate flare efficiency using airborne sampling across three basins responsible for >80% of US flaring and combine these observations with unlit flare prevalence surveys. We find that both unlit flares and inefficient combustion contribute comparably to ineffective methane destruction, with flares effectively destroying only 91.1% (90.2, 91.8; 95% confidence interval) of methane. This represents a fivefold increase in methane emissions above present assumptions and constitutes 4 to 10% of total US oil and gas methane emissions, highlighting a previously underappreciated methane source and mitigation opportunity.

Chain destruction of methane–hydrogen explosion in utility tunnel to adjacent space

Abstract Hydrogen is clean energy possible be transported in pipelines under utility tunnels in the future. Current research about gas explosions in the utility tunnel ignored the damage in the adjacent zones, the fire-proof wall, the above ventilated mezzanine and the escape room. The numerical simulation of methane–hydrogen explosion considering the chain destruction is conducted. The results show that the maximum overpressure peak is 6 MPa under 100% H2, and the fire-proof wall will increase the explosive intensity, so the length of one gas compartment should increase to 400 m or 600 m. The maximum overpressure sometimes presents in the adjacent zone rather than the explosive center, and the shock wave will not influence the ventilated mezzanine much. However, the flame will influence ventilated mezzanine, even the ground, so the adjacent zones, ventilated mezzanine and escape room are also dangerous. Therefore, a novel emergency system should be discussed for high-proportion-hydrogen transportation in utility tunnels.

Is the destruction or removal of atmospheric methane a worthwhile option?

Removing methane from the air is possible, but do the costs outweigh the benefits? This note explores the question of whether removing methane from the atmosphere is justifiable. Destruction of methane by oxidation to CO2 eliminates 97% of the warming impact on a 100-yr time scale. Methane can be oxidized by a variety of methods including thermal or ultraviolet photocatalysis and various processes of physical, chemical or biological oxidizers. Each removal method has energy costs (with the risk of causing embedded CO2 emission that cancel the global warming gain), but in specific circumstances, including settings where air with high methane is habitually present, removal may be competitive with direct efforts to cut fugitive methane leaks. In all cases however, great care must be taken to ensure that the destruction has a net positive impact on the total global warming, and that the resources required would not be better used for stopping the methane from being emitted.This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

Paleoclimate Evolution on Titan After Episodic Massive Methane Outgassing Simulated by a Global Climate Model

AbstractTitan's paleoclimate after the onset of the putative last major methane outgassing event 700 Myr ago is simulated by a global climate model. If the atmosphere was methane‐depleted prior to outgassing, outgassed methane initially causes warming due to increased greenhouse effect. Further outgassing leads to methane snowfall, which in turn cools the troposphere and surface by an ice‐albedo feedback and thereby initiates a lengthy ice age. Formation of ice sheets begins in the polar region, but with increasing methane inventory the entire globe is eventually covered by surface methane frost as thick as 100 m, with local accumulation on elevated terrains. Among various time‐dependent input parameters the methane inventory by far exerts the greatest control over the climate evolution. As Titan's climate transitions from a dry state via a partially ice‐covered state to a globally ice‐covered state, the circulation and precipitation pattern change profoundly and the tropospheric temperature further decreases. Globally ice‐covered snowball Titan is characterized by weak meridional circulation, weak seasonality and widespread snowfall. Frost ablation begins after the end of outgassing due to photochemical destruction of atmospheric methane. It is conceivable that Titan's polar seas resulted from melting of the polar caps within the past 10 Myr and subsequent drainage to the polar basins. Surface methane frost could only melt when the frost retreated to the polar region, which led to global warming by lowering of the surface albedo at low latitudes and increased greenhouse effect.

Day-night differences in Mars methane suggest nighttime containment at Gale crater

We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean in situ value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.

Dust devils on Mars

Whirlwinds, familiar on Earth, can be informative probes of the Martian surface environment.

METHANE IN THE SURFACE LAYER OF THE ATMOSPHERE: CURRENT CONTENT, LONG-TERM TRENDS, AND INTRA-ANNUAL VARIABILITY

The article deals with the empirical analysis of series of monthly mean concentrations of methane in the near-surface layer of the atmosphere from the global network of monitoring stations. They operate within the Global Atmosphere Watch (GAW) under the auspices of the World Meteorological Organization (WMO). The data is freely available at the World Data Center for Greenhouse Gases GAW/WMO (WDCGG) on its website https://gaw.kishou.go.jp/. The temporal coverage is from the 1980s. Data series from 69 stations are considered, of which 22 stations represent global background conditions. The rest of the stations are regional. Long-term trends in concentrations and the intra-annual (inter-monthly) deviations of monthly mean concentrations from long-term trends were studied. The multi-year trend was estimated using a series of 12-month running averages. To exclude systematic differences in methane concentrations, these series were adjusted to the series for the high-latitude Arctic station Alert (82° 30' N, 62° 21' W). The analysis showed that long-term trends are non-linear (in particular, a known pause in the growth of methane levels in 1999-2006 is observed), but are similar at most stations under consideration. Exceptions are six regional stations classified as “abnormal” in terms of methane. Possibly, this abnormality is due to the influence of certain sources of methane (anthropogenic or natural). Long-term trends at the rest of the stations just slightly differ from the average trend for the global stations. The series of intra-annual (inter-monthly) deviations of monthly mean concentrations from long-term trends for many stations (even those located at very significant distances from each other) show high correlative similarity. However, this similarity manifests itself at an optimal time shift from 5 months towards earlier dates up to 6 months towards later dates. The results of the analysis are consistent with the assumption that the intra-annual variability in methane concentration is largely driven by seasonal factors that are significantly related to latitude, such as vertical mixing in the atmosphere and destruction in the troposphere in reactions with hydroxyl. The root-mean-square values of intra-annual (inter-monthly) fluctuations in methane concentration depend significantly on latitude. In general, the higher the latitude is, the greater is the value. The maximum values are reached in the latitudinal belt within 45-50° N, and further to the North the values decrease. This feature of intra-annual fluctuations in the level of methane content may be explained, among other things, by significant inter-seasonal fluctuations in anthropogenic methane emissions occurring at the indicated latitudes in the countries with developed economies located in North America and Western Europe. The correlations of the series of intra-annual (inter-monthly) fluctuations of the monthly mean concentrations of CH4 and CO2 were estimated as rather high, about 0.8, at optimal time shifts, which is observed both at some polar stations and at tropical ones. This confirms the assumption that natural seasonal biogeochemical and geophysical processes play a significant role in the formation of intra-annual (inter-monthly) deviations of methane and carbon dioxide content in the near-surface layer from long-term trends. These processes include vertical mixing of air, CO2 absorption on the Earth’s surface, and destruction of methane in the troposphere in reactions with hydroxyl.

МЕТАН В ПРИПОВЕРХНОСТНОМ СЛОЕ АТМОСФЕРЫ: СОВРЕМЕННОЕ СОДЕРЖАНИЕ, МНОГОЛЕТНИЕ ТРЕНДЫ И ВНУТРИГОДОВАЯ ИЗМЕНЧИВОСТЬ

The article is devoted to the empirical analysis of series of monthly mean concentrations of methane in the near-surface layer of the atmosphere from the global network of monitoring stations. They operate within the Global Atmosphere Watch (GAW) under the auspices of the World Meteorological Organization (WMO). The data is freely available at the World Data Center for Greenhouse Gases GAW/WMO (WDCGG) on its website https://gaw.kishou.go.jp/ . The temporal coverage is from the 1980s. Data series from 69 stations are considered, of which 22 stations represent the global background conditions. The rest of the stations are regional. Long-term trends in concentrations and intraannual (inter-monthly) deviations of mean monthly concentrations from long-term trends were studied. The multi-year trend was estimated using a series of 12-month running averages. To exclude systematic differences in methane concentrations, these series were adjusted to the series for the high-latitude Arctic station Alert (82° 30' N, 62° 21' W). The analysis showed that long-term trends are non-linear (including with a known pause in the growth of methane levels in 1999-2006), but are similar at most of the stations under consideration. Exceptions are 6 regional stations classified as ‘abnormal’ for methane. A possible cause of the abnormality is being under the influence of certain sources of methane (anthropogenic or natural). Long-term trends at the rest of the stations are just slightly differ from the average trend for global stations. The series of intra-annual (inter-monthly) deviations of mean monthly concentrations from long-term trends for many stations, even those located at very significant distances from each other, show high correlative similarity. However, it manifests itself at an optimal time shift from 5 months. towards earlier dates up to 6 months. towards later dates. The results of the analysis are consistent with the assumption that the intra-annual variability in methane concentration is largely driven by seasonal factors that are significantly related to latitude, including vertical mixing in the atmosphere and destruction in the troposphere in reactions with hydroxyl. The root-mean-square values of the intra-annual (inter-monthly) fluctuations in methane concentration significantly depend on latitude. The higher the latitude, the greater the overall value. Maximum values are reached in the latitudinal belt 45-50° N, and further, to the north, the Кузовкин В.В., Семенов С.М. 20 values decrease. This character of intra-annual fluctuations in the level of methane content may be explained, among other things, by significant inter-seasonal fluctuations in anthropogenic methane emissions at the indicated latitudes in countries with developed economies located in North America and Western Europe. The estimates of correlations of the series of intra-annual (inter-monthly) fluctuations of the average monthly concentrations of CH4 and CO2 showed that at optimal time shifts, they are rather high, about 0.8. Moreover, this is observed both at some polar stations and at tropical ones. This confirms the assumption that natural seasonal biogeochemical and geophysical processes play a significant role in the formation of intra-annual (inter-monthly) deviations of the methane and carbon dioxide content in the near-surface layer from long-term trends, namely, vertical mixing of air, CO2 absorption on the Earth's surface, destruction of methane in the troposphere in reactions with hydroxyl.

Experimental modeling of subsurface gas traps on Mars

Methane seasonal variation observable by MSL mission and possible variations of atmospheric mass on timescale (105-106 years) are among the most intriguing problems in Mars exploration. These variations are connected with hypothetical biosphere activity in the subsurface Martian soil and existence of liquid water on the Martian surface within modern era. Stability of liquid water on surface request higher atmospheric pressure in comparing to modern value. CO2 cannot loss with known mechanisms of atmospheric escape. Therefore, the main part of necessary CO2 must be buried in upper layers of the Martian soil. Local and seasonal time variable sources and fast methane destruction are needed to explain high seasonal variations of methane concentration in air at the Martian surface. Gas reservoirs, containing biogenic or abiogenic methane could be possible seasonal sources of methane as well. In this work we experimental study stability of the gas reservoirs covered of mixture of regolith and water ice with perchlorates. Thickness of covered regolith layer was about 10mm. In experimental runs we increased a temperature of gas traps and monitored a possible diffusion of gases through the isolated layer with mass spectrometer. The gas traps stay stable at gas pressure up to 1 bar. We did not discover any diffusion process before mechanical destruction of reservoirs at gas pressure over 1 bar. In this work we show that the big subsurface gas reservoirs can exist for a long time before cracking due to slow process of the water ice sublimation by climate and seasonal variation of subsurface temperature.

Light on windy nights on Mars: A study of saltation-mediated ionization of argon in a Mars-like atmosphere

Laboratory experiments show that sand grain saltation in a Mars-like environment can result in the ionization of argon. This suggests that saltation can be a mechanism for the destruction of methane (CH4) on Mars given the ionization energy of argon is higher than the energy required to ionize methane to a reactive cation. The ionization energy is also higher than the energy to dissociate methane to highly reactive species like CH3, CH2, and CH. The feasibility of capturing the resulting emission glow on a windy Martian night is discussed.

Application research of low concentration methane oxidation heat supply for underground refrigeration

In order to solve the problem of low concentration coal mine methane (CMM) emission and low utilization rate in coal mine and the underground refrigeration demand of coal mine, this paper puts forward a technology of regenerative thermal oxidation (RTO) to provide waste heat vapor for lithium bromide refrigeration unit, which can effectively solve the problem of low concentration CMM utilization and provide stable heat source output for the refrigeration unit. The integrated process of oxidizing heat supplying to refrigerating unit includes low concentration CMM transportation security system, CMM RTO system and waste heat utilization system. The designed methane concentration is 1.2%, with flow rate 100, 000 Nm3/h, and steam heat of 7537kW. The expected effect of project operation is analyzed, and the economy of the project is demonstrated. The technology of CMM RTO supplying steam for underground refrigeration, through the destruction of methane, and the output of heat for underground refrigeration, has multiple meanings of energy saving and emission reduction, improving the utilization efficiency of coal bed gas in coal mine area, and promoting the safe production of coal mine.

Properties of carbon black produced by the thermal decomposition of methane in the products of premixed flames

The thermal decomposition of methane is a technique used to manufacture hydrogen gas and carbon black. The physical properties of carbon black produced by the thermal decomposition of methane (TDM) in the O2-deficient gas products of two premixed flames (propane- or methane-air) were investigated under different flow rates of decomposing methane injection (0.5–5 SLPM). An inverted burner was designed to provide a fuel-rich, laminar premixed flame, to produce hot gas into which methane was injected to thermally decompose inside a reactor. Particles from TDM were extracted by a nitrogen dilution system at the immediate exit of the reaction chamber, where another branch of the exhaust was dried and directed to a gas chromatograph. The carbon black particles were characterized by size resolved number concentration, mass concentration, effective density, volatility, and internal mixing state using different arrangements of a differential mobility analyzer, catalytic denuder, centrifugal particle mass analyzer, and condensation particle counter, as well as by morphology and primary particle size using transmission electron microscopy. A bimodal number-size distribution was observed at all conditions with count median diameters (CMDs) less than 58 nm and 21 nm when using propane- or methane-air premixed flames as the heat source, respectively. Higher number concentrations and mass concentrations with larger CMDs were achieved under lower flow rates of decomposing methane injection. For a given flow rate of decomposition methane, mass concentration and CMD increased significantly when using propane as the fuel, compared to the methane fuel. The size segregated mass fraction of internally mixed volatile content in particles was similar for both heat sources, showing a roughly constant fraction of volatile material in particles produced by the decomposition of 0.5 and 5 SLPM of methane (10%–30%) but a measurably larger fraction (55%–30%) with a decreasing trend as a function of particle size from the decomposition of 1 SLPM of methane. The effective density of denuded particles was similar, but slightly higher, than the effective density of soot from a wide range of internal combustion engines. A higher denuded effective density was observed in the particles with higher volatile contents (particles from decomposition of 1 SLPM of methane), suggesting the restructuring of carbon black into more compact clusters due to excessive volatile condensation. TEM analysis revealed some similarity between the produced carbon black and engine soot in terms of morphology and primary particle diameter (both below 40 nm). Beside the carbon black properties, the efficiency of TDM in this configuration was also investigated by evaluation of methane destruction efficiency, as well as carbon black and hydrogen production efficiencies, based on the product gas composition and the particle mass concentration. It was found that longer residence times corresponding to lower flow rates resulted in higher conversion efficiencies in terms of methane destruction efficiency (maximum of ∼95%), hydrogen production efficiency (maximum of ∼80%), and carbon black production efficiency (maximum of ∼1%). It was concluded that the significantly low efficiency of carbon black production is due to the high amount of CO formation, likely through the gasification process.

Studying the influence of design and operation mode parameters on efficiency of the systems of biochemical purification of emissions

A procedure for evaluating efficiency of the systems of biological elimination of soluble and insoluble in water harmful gaseous substances as well as dissolved in water contaminants has been devised. The procedure is based on previously developed mathematical models of the corresponding non-stationary bio oxidation processes. Based on the analysis of 27 design versions, real capabilities of biological purification facilities were shown, the effect of design and operation mode parameters on efficiency of the systems of biological destruction of methane, hydrogen sulfide and formaldehyde were assessed. In quantitative terms, the results obtained in numerical experiments indicate the necessity of taking into account variation of the rate of pollutant inflow in the process of vessel filling. It was established that an increase in the facility efficiency in terms of the volume of the gas-air mixture, N, causes a decrease in methane concentration at the bioreactor entry and a reduction of the purification degree to 62 %. An increase in the rate of hydrogen sulfide inflow to the reactor leads to a reduction of the purification degree from 98 to 95 %. An increase in the initial concentration of biomass by a factor of 1.7 causes a decrease in concentration of hydrogen sulfide in water from 2.5 to 1.1 g/m 3 . A significant decrease in the average specific bio oxidative power with an increase in the working space in which the final stage of emission purification from formaldehyde takes place was also observed. The revealed regularities represent a tool for improving quality of design solutions and increasing effectiveness of bio oxidation modes in operation of the systems of biological gas purification.

Application of non-thermal plasma technology on fugitive methane destruction: Configuration and optimization of double dielectric barrier discharge reactor

Fugitive methane (CH4) from waste treatment facilities (landfill mining), power industries (oil and gas process plants) and coal mining etc. into atmosphere is an increasing environmental concern. In this study, CH4 conversion efficiency in double dielectric barrier discharge (DDBD) has been investigated at various operating parameters including input power, feed gas-mixture flow rate, CH4 initial concentrations, and discharge gap distance between two dielectrics. Increase in input power, decrease in the gas-mixture flow rate and discharge gap distance; results in increases of CH4 conversion efficiency. In plasma alone, maximum CH4 conversion efficiency of 76% was obtained using 3 mm plasma discharge gap distance at flow rates of 2 L/min, input power of 65.8 W and is limited by experimental conditions. In addition, CH4 conversion efficiency in plasma alone and plasma-catalytic is compared by introducing various catalysts includes Pt–Sn/Al2O3, BaTiO3 and HZSM-5 in single plasma discharge zone. Results revealed that plasma combined with Pt–Sn/Al2O3 showed higher CH4 conversion efficiency (84.93%) as compare to plasma alone (56.42%) using 6 mm plasma discharge gap distance at flow rates of 2 L/min, input power of 65.8 W. Moreover, maximum energy efficiency of CH4 conversion (limited by experimental conditions) was 27.24 × 10−12 mol/kJ at 32.6 W observed in plasma-catalyst. Analysis of the exhaust gas showed that DDBD is a promising alternative reactor not only to achieve high CH4 conversion efficiency, but also to overcome the drawbacks of formation of undesirable byproducts. Moreover, deposition of carbon residues on the surface of internal electrode is not observed, which is often occurred in single DBD reactors.

Methane bursts as a trigger for intermittent lake-forming climates on post-Noachian Mars

Lakes existed on Mars later than 3.6 billion years ago, according to sedimentary evidence for deltaic deposition. The observed fluvio-lacustrine deposits suggest that individual lake-forming climates persisted for at least several thousand years (assuming dilute flow). But the lake watersheds' little weathered soils indicate a largely dry climate history, with intermittent runoff events. Here we show that these observational constraints, while inconsistent with many previously-proposed triggers for lake-forming climates, are consistent with a methane burst scenario. In this scenario, chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate. Using numerical simulations, we find that outgassed methane can build up to atmospheric levels sufficient for lake forming climates, for past clathrate hydrate stability zone occupancy fractions >0.04. Such occupancy fractions are consistent with methane production by water-rock reactions due to hydrothermal circulation on early Mars. We further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake-forming climates to less than a million years, consistent with observations. We conclude that methane bursts represent a potential pathway for intermittent excursions to a warm, wet climate state on early Mars.