Increasing CH4 Concentration Research Articles

Seasonal and trend variation of methane concentration over two provinces of South Africa using Sentinel-5p data

South Africa faces the urgency to comprehensively understand and manage its methane (CH4) emissions. The primary aim of this study is to compare CH4 concentrations between Eastern Cape and Mpumalanga regions dominated by cattle farming and coal mining industries, respectively. CH4 concentration trends were analyzed for the period 2019 to 2023 using satellite data. Trend analysis revealed significant increasing trends in CH4 concentrations in both provinces, supported by Mann–Kendall tests that rejected the null hypothesis of no trend (Eastern Cape: p-value = 8.9018e−08 and Mpumalanga: p-value = 2.4650e−10). The Eastern Cape, a leading cattle farming province, exhibited cyclical patterns and increasing CH4 concentrations, while Mpumalanga, a major coal mining province, displayed similar increasing trends with sharper concentration points. The results show seasonal variations in CH4 concentrations in the Eastern Cape and Mpumalanga provinces. High CH4 concentrations are observed in the northwestern region during the December-January–February (DJF) season, while lower concentrations are observed in the March–April-May (MAM) and June-July–August (JJA) seasons in the Eastern Cape province. In the Mpumalanga province, there is a dominance of high CH4 concentrations in southwestern regions and moderately low concentrations in the northeastern regions, observed consistently across all seasons. The study also showed an increasing CH4 concentration trend from 2019 to 2023 for both provinces. The study highlights the urgent need to address CH4 emissions from both cattle farming and coal mining activities to mitigate environmental impacts and promote sustainable development. Utilizing geographic information system (GIS) and remote sensing technologies, policymakers and stakeholders can identify and address the sources of CH4 emissions more effectively, thereby contributing to environmental conservation and sustainable resource management.

Effect of cubicle hood system on methane concentrations around the lying area in cold climate dairy cattle buildings

There is scarcity of data on methane (CH4) concentration levels and other gas compositions around animals in commercial cattle barns, especially for developing technology for gaseous CH4 treatment. Consequently, use of biofiltration and catalytic combustion strategies as alternative enteric CH4 mitigation techniques remain concepts yet to be validated in real cattle barns. One of the major barriers to implementing these techniques is that they require close buildings, which is not the case for most cattle barns. Open cattle barns are frequently associated with excessive ventilation, resulting in low CH4 concentrations, which can reduce the cost effectiveness of CH4 treatment techniques. With the development of low-cost, low-CH4-concentration enrichment technologies still in their infancy, developing local ventilation systems at the animal level capable of collecting breath CH4 from cows prior to air mixing could be an option. Therefore, the effect of a cubicle hood system (CHS) with different air extraction techniques on increasing CH4 concentrations at the lying area were evaluated in natural and mechanically ventilated dairy cattle buildings during the winter in Norway. In both barns, the use of CHS increased CH4 concentrations under the hood at the lying area by 14-25 % compared to without CHS. The results obtained depended on the height of the CHS from the floor and effect of outdoor temperature on air exchange rate in the barns. In the naturally ventilated barn, the hourly mean CH4 concentrations under the cubicle hood ranged from 14-225 ppm, and 31-322 ppm in the mechanically ventilated building.

The concentration of CH4, N2O and CO2 in the Pearl River estuary increased significantly due to the sediment particle resuspension and the interaction of hypoxia

Hypoxia and sediment particle resuspension (SPR) alter the biogeochemical cycle of estuarine and coastal seas, which in turn affects the production and emission of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) greenhouse gases (GHGs) in estuaries. Despite the importance of CH4, N2O and CO2 in estuarine ecosystems, little is known about their magnitude and spatiotemporal variation under the combined influence of hypoxia and SPR. This study utilized continuous mooring observations to investigate the temporal and spatial variations of GHGs before and after hypoxia in the Pearl River Estuary (PRE). The results showed that the concentration of GHGs in the water column increased significantly following hypoxia as compared to its absence. The synergistic effect of SPR and hypoxia significantly enhances GHGs production and accumulation in bottom water. Anaerobic mineralization of organic matter (OM) in an environment with severely low dissolved oxygen (DO) is the primary determinant for increased CH4 concentration, while OM and CH4 oxidation are the main drivers for maintaining high CO2 concentration in subsurface water. Hypoxic development enhanced denitrification N2O production in the water column. The presence of SPR enhanced oxygen-consuming coupled hypoxia significantly stimulated the increase of CH4, N2O and CO2 concentrations in the water column. Hypoxic development results in an increased water–air GHGs flux, but this effect may be masked by runoff plumes with high GHGs concentrations in the regions near the river outlets. This study highlights that hypoxia leads to significant increases in anaerobic GHGs production and subsequent emissions from estuarine water columns.

Intense methane diffusive emissions in eutrophic urban lakes, Central China

Urban lakes are hotspots of methane (CH4) emissions. Yet, actual field measurements of CH4 in these lakes are rather limited and our understanding of CH4 response to urban lake eutrophication is still incomplete. In this study, we measured dissolved CH4 concentrations and quantified CH4 diffusion from four urban lakes in subtropical China during wet and dry seasons. We found that these lakes were constantly CH4-saturated, contributing the greenhouse gas (GHG) to the atmosphere. Nutrient enrichment significantly increased CH4 concentrations and diffusive fluxes. Average CH4 flux rate in the highly-eutrophic lake zones (4.18 ± 7.68 mmol m−2 d−1) was significantly higher than those in the mesotrophic (0.19 ± 0.18 mmol m−2 d−1) and lightly/moderately-eutrophic zones (0.72 ± 2.22 mmol m−2 d−1). Seasonally, CH4 concentrations and fluxes were significantly higher in the wet season than in the dry season in the mesotrophic and the lightly/moderately-eutrophic lake zones, but an inverse pattern existed in the highly-eutrophic lake zones. CH4 concentrations and fluxes increased with elevated levels of nitrogen, phosphorus and dissolved organic carbon (DOC). The accumulation of nutrients provided autochthonous substrate for methanogenesis, indicated by a negative correlation between CH4 and the C:N ratio. Ammonium-nitrogen (NH4+-N) was the best predictor for spatial fluctuation of CH4 concentrations and diffusive fluxes in the mesotrophic and the lightly/moderately-eutrophic lake zones, while total nitrogen (TN) and total phosphorus (TP) levels showed the highest predictability in the highly-eutrophic lake zones. Based on the findings, we conclude that nutrient enrichment in urban lakes can largely increase CH4 diffusion, and that urban sewage inflow is a key concern for eutrophication boosting CH4 production and diffusive emission. Furthermore, our study reveals that small urban lakes may be an important missing source of GHG emissions in the global C accounting, and that the ratio of littoral-to-pelagic zones can be important for predicting lake-scale estimation of CH4 emission.

Effects of marine environments on methane hydrate formation in clay nanopores: A molecular dynamics study

In nature, CH4 hydrates are mainly buried in marine sediments. The complex marine environments on the seafloor continuously affect hydrate formation. Herein, systematic molecular simulations have been performed to investigate CH4 hydrate formation in clay nanopore, mainly affected by several marine environmental factors, including seawater salinity, pressure and temperature. Simulation results show that these factors exert different effects on hydrate formation in the nanopore and the outside bulk solutions by affecting the mass transfer and phase separation inside and outside of the nanopore. Specifically, high salinity hinders the diffusion of CH4 molecules from nanopores into the outside bulk solutions, promoting hydrate formation in nanopore and inhibiting hydrate formation in bulk solution; salinity has a dual effect on hydrate formation in the whole system by changing the local CH4 concentration via the formation of the hydration of salt ions. High pressure favors the diffusion of CH4 molecules from nanopore into outside bulk solutions, promoting hydrate formation in bulk solution and inhibiting hydrate formation in nanopore; high pressure promotes hydrate formation at the nanopore throats by increasing CH4 concentration and reducing ion concentration therein. In contrast, temperature significantly affects hydrate formation in the system by causing phase separation, i.e. high temperature promotes the aggregation of CH4 molecules to form nanobubbles and inhibits hydrate formation. Under high temperature conditions, the nanobubble in the nanopore gradually decomposes, while the nanobubble in the outside bulk solution grows an extra-large cylindrical nanobubble. These molecular insights into the formation behavior of CH4 hydrates in clay nanopores are helpful for understanding the formation process of natural gas hydrates in marine sediments and the development and utilization of CH4 hydrates.

A standardized and miniaturized method to investigate rhizosphere microorganisms, with a focus on methanogenic archaea and methanotrophic bacteria

Plant-microorganism interactions and associations play a fundamental role in terrestrial ecosystems and mainly occur in the rhizosphere, an interaction zone around plant roots. However, the definitions and handling strategies described in the literature differ considerably, and the aim of the present work was to develop a standardized and miniaturized experimental setup that enables a simple and comparable investigation of the rhizosphere. After methodological optimization steps, we applied and evaluated our method to examine the effects of plants and increased methane (CH4) concentrations on the abundance and activity of rhizosphere microorganisms engaged in the CH4-cycle.Seedlings of black radish (Raphanus sativus) and yellow mustard (Sinapis alba) were grown in soil-filled reaction tubes, and the growth conditions were adapted for optimal plant root development. Since plant roots pervaded the entire volume of the soil, we could assume the entire soil to be influenced by the plants and regarded it as rhizosphere soil. Additionally, the application of plant growth chambers allowed to investigate plant and microbial growth at defined headspace compositions. The results demonstrate that bulk and rhizosphere soil differed significantly regarding the dissolved carbon and nitrogen contents. The abundances of cultivable microorganisms (CFU) and of methanotrophic bacteria (type Ia) were significantly increased in rhizosphere soil. Growth under increased CH4 concentration in the headspace revealed an increased abundance of methanotrophic and methanogenic microorganisms in the rhizosphere. A higher capacity to oxidize CH4 in the rhizosphere compared with bulk soil was demonstrated, extending the effect of the influence of plants on microbial activity and confirming the suitability of this approach to study plant-soil-microbe interactions. Since the headspace composition in the plant growth chambers can easily be adjusted, the current setup is also suitable for investigating further gas cycles and the microorganisms involved.

The Influence of Above-Ground Herbivory on the Response of Arctic Soil Methanotrophs to Increasing CH4 Concentrations and Temperatures.

Rising temperatures in the Arctic affect soil microorganisms, herbivores, and peatland vegetation, thus directly and indirectly influencing microbial CH4 production. It is not currently known how methanotrophs in Arctic peat respond to combined changes in temperature, CH4 concentration, and vegetation. We studied methanotroph responses to temperature and CH4 concentration in peat exposed to herbivory and protected by exclosures. The methanotroph activity was assessed by CH4 oxidation rate measurements using peat soil microcosms and a pure culture of Methylobacter tundripaludum SV96, qPCR, and sequencing of pmoA transcripts. Elevated CH4 concentrations led to higher CH4 oxidation rates both in grazed and exclosed peat soils, but the strongest response was observed in grazed peat soils. Furthermore, the relative transcriptional activities of different methanotroph community members were affected by the CH4 concentrations. While transcriptional responses to low CH4 concentrations were more prevalent in grazed peat soils, responses to high CH4 concentrations were more prevalent in exclosed peat soils. We observed no significant methanotroph responses to increasing temperatures. We conclude that methanotroph communities in these peat soils respond to changes in the CH4 concentration depending on their previous exposure to grazing. This “conditioning” influences which strains will thrive and, therefore, determines the function of the methanotroph community.

Effect of supercritical CO2 extraction on CO2/CH4 competitive adsorption in Yanchang shale

Competitive adsorption characteristics of CO2/CH4 on shales before and after supercritical CO2 (ScCO2) extraction are closely related to CO2 injection in shale reservoir for CO2 sequestration and enhanced shale gas recovery (CS-ESGR). Using a self-developed PCTPro-type automatic high-pressure gas adsorption instrument, the adsorption behaviors of CH4, CO2 and their mixtures with different ratios were investigated on raw and ScCO2-treated (10 day/16 MPa/40 °C) shale collected from the Ordos Basin. The influences of ScCO2 extraction, pressure and CO2/CH4 cratios on adsorption capacity and selective adsorption factor of CO2/CH4 (SCO2/CH4) of shale have been analyzed. To interpret the experimental data, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, low-pressure gases adsorption and mercury intrusion were performed to evaluate the variations of mineral compositions and pore structure of shale exposure to ScCO2. It is found that SCO2/CH4 and the adsorption capacity of CO2/CH4 with different ratios decreased after ScCO2 extraction and are mainly attributable to the decrease of TOC, carbonates, clay minerals and specific surface area in ScCO2-treated shale. The feasibility of CS-ESGR cannot be affected by ScCO2 due to the values of SCO2/CH4 are always greater than 2.5 after ScCO2 extraction. Additionally, SCO2/CH4 decreased initially and then tended to be stable with increasing pressure, and it decreased slightly with increasing CH4 concentration in gas mixtures, suggesting that the reservoir pressure should be lowered before the injection of CO2 into shale reservoir, and the efficiency and engineering cost of CS-ESGR should be considered comprehensively. This study provides a reference for future optimization design of CS-ESGR.

Spatial and temporal patterns of methane and its influencing factors in the Jiulong River estuary, southeastern China

Estuaries are important sources of methane (CH4) to the atmosphere. However, the lack of adequate field studies for understanding the sources/sinks of CH4 in estuaries hampers global atmospheric budgeting. Therefore, more studies are needed to bridge this gap and improve our understanding of CH4 dynamics. This study investigated the impacts of tides on CH4 emissions along a salinity gradient of the subtropical Jiulong River estuary (JRE) during spring, neap tides and over 24 h tidal cycles in 2017 and 2018. Spatially, the CH4 concentrations increased from the lower reaches to the upper reaches, with values varying widely from 58 to 1726 (393 ± 336) nmol/L, which correspond to saturations of 2513–59,371 (15,549 ± 11,341)%. The CH4 concentration was inversely and significantly correlated with salinity, indicating the dilution and sulfate inhibition effects of the adjacent saline water. Temporally, the highest CH4 concentrations and fluxes were detected in the spring tide period, which can enhance the resuspension of particles and CH4 from sediments, and were accompanied by high turbidity values. Elevated CH4 concentrations were found during low tide, and horizontal advection of low salinity water could be the driver of the increased CH4 concentrations during low tide. Due to the lack of agreement among current diffusive models, three different parameterizations were used to assess the water-air fluxes of CH4 in this study. The flux range was estimated to be 193–18,585 (2793 ± 3812) μmol/m2/d, which is well above that reported for most estuaries worldwide.

Thermodynamic Study on Reduction of Iron Oxides by H2 + CO + CH4 + N2 Mixture at 900 °C

The reduction gas used in the gas-based direct reduction iron-making process contains CH4 in different concentrations, which has an important effect on the gas and heat needed for the reduction of iron oxide. To investigate the influence of CH4 on gas utilization rate and heat needed at 900 °C, the initial conditions are set as H2% + CO% = 90, CH4% + N2% = 10, gas pressure 1–9 atm, and 0.5 mol Fe2O3, and the equilibrium state composition is calculated using the minimum free energy method. The utilization rate of total gas can be improved, and gas demand can be decreased by increasing CH4 concentration or H2 concentration or reducing gas pressure. For the production of per ton of Fe from 25 °C to 900 °C, 6.08–7.29 m3 of reduction gas, and 7.338–8.952 MJ of gas sensible heat can be saved by increasing 1 m3 CH4, while 10.959–11.189 MJ of reaction heat is increased. Compared with 3390.828–3865.760 MJ of the total heat of per ton of Fe for the reduction by H2 + CO, 2.174–3.703 MJ of total heat is increased by increasing 1 m3 CH4, and the increase ratio is 0.065–0.096%. This study is helpful to improve the gas efficiency and lower the pursuit of higher concentration of H2 + CO in reduction gas.

Design and analysis of renewable hydrogen production from biogas by integrating a gas turbine system and a solid oxide steam electrolyzer

In this paper, design and performance analysis of a biogas (60%CH4 + 40%CO2) fueled gas turbine (GT) power generation system integrated with a flameless boiler for steam generation for hydrogen production in a solid oxide steam electrolyzer (SOSE) is reported. In this design, the exhaust gases from GT is conducted to a flameless boiler where diluted and preheated exhaust gases are employed as an oxidizer in this process. Using a small amount of biogas in the flameless boiler enables the hybrid system to produce required steam for SOSE process and the whole generated electrical power by GT is employed in SOSE as well to produce hydrogen. The effects of biogas blends and flowrate, turbine inlet temperature (TIT), steam temperature and the electrode characteristics on the performance of the hybrid system are evaluated. The results indicate that by purification of biogas and increasing CH4 concentration up to 80%, the generated electrical power and produced hydrogen of the hybrid system augment 24% and 20% respectively. In GT system, the TIT should be set at the temperatures higher than 1300 K to prepare a desirable circumstance for the operation of flameless mode in the boiler. At the constant electrical power, when steam temperature increases, the overall SOSE potential decreases and consequently the current of the SOSE enhances which result in the enhancement of the overall hydrogen production in high steam temperatures. To increase the steam temperature from 850 K to 1450 K, the rate of overall biogas consumption of the system increases 1% while the amount of overall hydrogen production from SOSE system augments from 0.01 to 0.052 mol/s. The presented analysis in this paper can be employed to perform more analyses to achieve insightful understanding of the green hydrogen production using hybrid systems.

Phase Transformation of Nanocrystalline Diamond Films: Effect of Methane Concentration

Ultra-nanocrystalline diamond films were prepared by a microwave plasma-enhanced chemical vapor deposition reactor using CH4/H2 gas mixture with a power as low as 650 W. The effects of CH4 concentration on nanostructure of the films and gas-phase species in plasma were investigated. The CH4 concentrations of 1.5%, 3.0%, 3.5%, and 4.0% were used and balanced with H2 to a total flow rate of 200 sccm. Morphology and composition of the films were characterized by SEM, Raman spectroscopy and Auger spectroscopy. The gas-phase species and electron density in the plasma were explored by optical emission spectroscopy and plasma-impedance measurement. The increasing CH4 concentration from 1.5% to 4.0% increased C2Hx species and decreased electron density. Phase of the film transform from nano- into ultranano- diamond phase but the growth rate revealingly decreased from 300 to 210 nm/h. Raman spectra indicate the higher CH4 concentration promted phase of the film transiton from NCD to UNCD. While Auger spectra revealed that UNCD film deposited with 4.0%CH4 was composed of 90.52% diamond phase but only 9.48% of graphite phase. The relation between phase transformation of the films and growth mechnism controlled by gas-phase species in the plasma will be dissused.

Wettability and Biocompatibility of TaCx Films Deposited on AISI316L Stainless Steel: Effect of Methane Concentration

The present study aimed at investigating the effect of various CH4 concentrations ranging from 0 to 30% on wettability and biocompatibility of TaCx films which was deposited on AISI316L SS by reactive magnetron sputtering. In this regard, the structure, topography, wettability and biocompatibility of films studied by means of FESEM equipped with EDS, RBS/NRA, Raman spectroscopy, FT-IR, GIXRD, water contact angle measurement, MTT assay and immunostaining methods. it was found that the chemical nature of the coatings strongly depends on CH4 concentration. The deposited films can be categorized into three distinguishable types, namely: metallic, ceramic and amorphous, depending on CH4 concentration during the deposition procedure. Moreover, surface morphology of the coatings changed from pyramidal to spherical by increment of CH4 concentration. In addition, the wettability of the coatings decreased by increasing carbon content. However, interestingly, the coatings with the same chemical nature showed almost the same wettability. Furthermore, the investigation of the biocompatibility of the films revealed that applying the TaC base films improves the cell viability of AISI316L SS by an average value of 22%. Moreover, viability test indicated that the increasing CH4 concentration leads to further enhancement of coatings biocompatibility.

Dissolved carbon, greenhouse gases, and δ13C dynamics in four estuaries across a land use gradient

Land use is a well known driver of nutrient dynamics in estuaries, however less is known about how land use may influence the coastal carbon (C) cycle. Here, we report dissolved carbon concentrations, δ13C isotopic signatures, and water–air CO2 and CH4 fluxes for four Australian estuaries with contrasting catchment land use ranging from 9 to 72% natural. Water samples were collected during dry and wet hydrologic extremes. Dissolved organic carbon (DOC) concentrations were highest and total dissolved nitrogen and dissolved phosphorous were lowest in the least impacted estuary (Pine Creek). The DOC δ13C signature was enriched for the estuary with 91% urban-agricultural land use (Coffs Creek), implying a shift in the source of DOC along the land use gradient. Low DOC and high nutrient availability decreased CO2 fluxes to the atmosphere in the impacted systems during both wet and dry conditions, and increased CH4 concentrations and fluxes during the wet conditions. Variability of CO2 and CH4 were influenced by multiple drivers including hydrologic forcing, dissolved nutrients, as well as shifts in the nature of allochthonous versus autochthonous sources within each estuary.

Low-temperature oxidation of free radicals and functional groups in coal during the extraction of coalbed methane

To analyze the low-temperature oxidation of coal in an air flow containing coalbed methane (CBM), the low-temperature oxidation of coal under different CH4 concentrations was analyzed based on the oxidation reaction of free radicals and functional groups. Based on the experimental platform for simulating the low-temperature oxidation of coal in different atmospheres, the experimental process was carried out by using the electron spin resonance (ESR) and Fourier transform infrared (FTIR) technologies. Furthermore, the influences of CH4 on the activity of coal during low-temperature oxidation and the oxidation reaction of functional groups on the surface of coal were explored. The results showed that, at different oxidization temperatures from 20 °C to 200 °C, the concentration of free radicals decreased with increasing CH4 concentration (0%–45%), and CH4 inhibited the oxidation activity of coal. Under the condition that the CH4 concentration was lower than 30%, CH4 showed a large inhibitory effect on the oxidation activity of coal. After the oxidization temperature was higher than 80 °C, the promotion effect of the oxidization temperature on the oxidation activity of coal was significant. Moreover, –CH2 and –CH3 exhibited high activities during low-temperature oxidation and were the major reactive groups. When the coal was oxidized in dry air, the contents of –CH2 and –CH3 constantly decreased at temperatures of 40 °C–110 °C until the CH4 concentration was higher than 25%. This finding implied that CH4 inhibited the consumptions of –CH2 and –CH3 in the oxidation process of coal. The –OH content generally decreased at first and then increased, showing high activity during low-temperature oxidation, and was considered the major reactive group. With increasing CH4 concentration in the oxidation atmosphere, the reduction amplitude of –OH decreased, indicating that CH4 can inhibit the consumption of –OH in the oxidation process. When the CH4 concentration was higher than 35%, CH4 influenced both the consumption and production processes of –OH, such that the consumption rate of –OH was gradually equal to its production rate. The content of –C–O increased overall, which implied that –C–O was the main product of low-temperature oxidation. As a relatively stable group, the –C–O group was not produced below a certain temperature in the oxidation process. Additionally, the unchanged stage disappeared when the CH4 concentration was higher than 25%, which indicated that CH4 promoted the production process of the –C–O functional group. –COOH showed high activity during low-temperature oxidation, and its content rapidly decreased at first and then increased quickly during coal oxidation in dry air, indicating that it was the main reactive group during low-temperature oxidation. With increasing CH4 concentration in the oxidation atmosphere, the reduction in the –COOH content gradually decreased, and then the –COOH content remained unchanged after the CH4 concentration was higher than 25%. This result indicated that CH4 inhibited the consumption of –COOH in the oxidation process.

Diamond nucleation and growth on WC-Co inserts with Cr2O3-Cr interlayer

Cr2O3-Cr interlayer was prepared by magnetron sputtering to restrict graphite formation on WC-Co before diamond nucleation. Continuous diamond coatings containing little graphite phase were successfully deposited on single Cr2O3 interlayered WC-Co substrates. For Cr2O3/Cr duplex interlayer, a low nucleation density was observed at a low CH4 concentration, but a continuous diamond coating was readily obtained with an increased CH4 concentration during nucleation stage. X-ray diffraction and X-ray absorption analysis reveal that the Cr top layer was carburized to Cr3C2 and Cr7C3 after diamond deposition while Cr2O3 layer kept unchanged. In addition, the indentation test shows that the diamond coating has poor adhesion to the substrate with a single Cr2O3 interlayer, while the adhesion was significantly enhanced with the Cr2O3/Cr duplex interlayer combined with a high CH4 concentration for nucleation.

Effect of light hydrocarbon solvents on the performance of CO2-based cyclic solvent injection (CSI) in heavy oil systems

Cyclic Solvent Injection (CSI) has gained significant interest as a viable method among solvent injection processes to increase recovery factor of heavy oil reservoirs. The type of solvent, operating pressure, and oil viscosity markedly affect the performance of CSI.In this study, series of cyclic injection tests of pure CO2, CH4-CO2, and C3H8-CO2 were conducted at various operating pressures and mixture compositions to different (in term of viscosity) heavy oil samples. Sand pack models with absolute permeability of kabs = 6–10 D and porosity of ø = 27–32% were used as representative of a typical heavy oil reservoir. In each cycle, the produced oil and pressured drop during soaking time were measured and CO2/solvent apparent solubility was calculated using the pressure decay method.Results showed that there is an optimum pressure in cyclic CO2 injection process in heavy oil systems; the pressure beyond which the ultimate oil recovery factor (RF) did not notably improve (near 4.82 MPa in this study). Higher concentration of C3H8 in the CO2 stream improved the oil recovery during cyclic injection. However, ultimate RF was not noticeably increased when C3H8 concentration in the mixture exceeded a certain value (near 50% in this study). Although C3H8 showed effective role on the performance of CSI, it was found that the recovery factor reduces with increased CH4 concentration in the CO2 stream. The highest recovery factor of RF = 73.8% was obtained by injecting mixture of 50% C3H8 - 50% CO2 under the operating pressure of Pinj = 1.72 MPa. The results of CSI tests on the heavy oil with viscosity of 6 430 mPa s were lower by almost 20% since the solvent solubility was noticeably lower. No oil production was observed after conducting the first cycle injection of optimum quantified solvents on oil with the viscosity of 22 000 mPa s. Small values of SUF, relatively high values of SOR, and low quality of the produced oil suggested that higher cycle numbers of CSI in heavy oil reservoirs is depending on the economic limits and might be conducted cautiously.

Methane gas sensing properties of Pd-doped SnO2/reduced graphene oxide synthesized by a facile hydrothermal route

In this paper, palladium (Pd)-doped tin oxide (SnO2)/partially reduced graphene oxide (PRGO) and Pd-doped SnO2/reduced graphene oxide (rGO) nanocomposites are synthesized via a simple hydrothermal route. Field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) are used to characterize the structure, morphology and composition of the crystalline phases of the prepared gas sensitive materials. The FESEM images confirm the existence of homogeneous dispersion of Pd-doped SnO2 nanoparticles anchored onto the rGO/PRGO nanosheets. Then the application of these nanocomposites is investigated as methane (CH4) gas sensor and compared with each other. The performance of sensors is studied toward CH4 gas concentrations ranging from 800 to 16000 part per million (ppm) at room temperature. The fabricated sensors show an enhancement in the electrical conductivity with increasing CH4 concentration. The synthesized Pd-doped SnO2/rGO nanocomposite in comparison with Pd-doped SnO2/PRGO, exhibits better sensitivity, excellent selectivity and relatively short response time to CH4 at room temperature. The excellent sensing performance of sensor could be ascribed to the presence of Pd nanoparticles and rGO nanosheets in the sensing nanocomposite.

Methane oxidation in a landfill cover soil reactor: Changing of kinetic parameters and microorganism community structure

ABSTRACTChanging of CH4 oxidation potential and biological characteristics with CH4 concentration was studied in a landfill cover soil reactor (LCSR). The maximum rate of CH4 oxidation reached 32.40 mol d−1 m−2 by providing sufficient O2 in the LCSR. The kinetic parameters of methane oxidation in landfill cover soil were obtained by fitting substrate diffusion and consumption model based on the concentration profile of CH4 and O2. The values of (0.93–2.29%) and (140–524 nmol kgsoil-DW−1·s−1) increased with CH4 concentration (9.25–20.30%), while the values of (312.9–2.6%) and (1.3 × 10−5 to 9.0 × 10−3 nmol mL−1 h−1) were just the opposite. MiSeq pyrosequencing data revealed that Methylobacter (the relative abundance was decreased with height of LCSR) and Methylococcales_unclassified (the relative abundance was increased expect in H 80) became the key players after incubation with increasing CH4 concentration. These findings provide information for assessing CH4 oxidation potential and changing of biological characteristics in landfill cover soil.

Etch characteristics of Ru thin films using O2/Ar, CH4/Ar, and O2/CH4/Ar plasmas

The etch characteristics of Ru thin films patterned with TiN hard masks in O2/Ar, CH4/Ar and O2/CH4/Ar gas mixtures were studied using inductively coupled plasma reactive ion etching. When the Ru films were etched in O2/Ar gas, the etch rates of the Ru films and TiN hard masks decreased but the etch selectivity of the Ru films to the hard mask increased with increasing O2 concentration. The etch profiles of Ru films at various O2 concentrations were very similar, showing high etch slopes of >80° with uneven sidewalls. In the case of CH4/Ar gas, as the CH4 concentration increased, the etch rates of the Ru films and TiN hard masks and the etch selectivity of Ru films decreased. The etch profile of Ru films etched in 20% CH4/Ar showed the etch slope of approximately 60° and the etch slopes became worse with increasing CH4 concentration. The addition of O2 to the CH4/Ar gas resulted in a significant improvement in the etch profile, but both etch rates decreased slightly. Optical emission spectroscopy of O2/CH4/Ar plasma showed that O species could oxidize the Ru films to RuOx, and that inhibition layers containing C or CHx were formed, which protected the pattern sidewalls. X-ray photoelectron spectroscopy also identified the formation of RuOx and C or CHx compounds on the film surface. These findings indicated that Ru etching in O2/CH4/Ar gas chemistry could provide a good etch profile without redeposition or etch residues.