Loss Of CH Research Articles

Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems

AbstractThe atmospheric methane (CH4) concentration, a potent greenhouse gas, is on the rise once again, making it critical to understand the controls on CH4 emissions. In Arctic tundra ecosystems, a substantial part of the CH4 budget originates from the cold season, particularly during the “zero curtain” (ZC), when soil remains unfrozen around 0 °C. Due to the sparse data available at this time, the controls on cold season CH4 emissions are poorly understood. This study investigates the relationship between the fall ZC and CH4 emissions using long‐term soil temperature measurements and CH4 fluxes from four eddy covariance (EC) towers in northern Alaska. To identify the large‐scale implication of the EC results, we investigated the temporal change of terrestrial CH4 enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiaġvik, AK, from 2001 to 2017 and their association with the ZC. We found that the ZC is extending later into winter (2.6 ± 0.5 days/year from 2001 to 2017) and that terrestrial fall CH4 enhancements are correlated with later soil freezing (0.79 ± 0.18‐ppb CH4 day−1 unfrozen soil). ZC conditions were associated with consistently higher CH4 fluxes than after soil freezing across all EC towers during the measuring period (2013–2017). Unfrozen soil persisted after air temperature was well below 0 °C suggesting that air temperature has poor predictive power on CH4 fluxes relative to soil temperature. These results imply that later soil freezing can increase CH4 loss and that soil temperature should be used to model CH4 emissions during the fall.

Biogas separation using a membrane gas separator: Focus on CO2 upgrading without CH4 loss

The CO2 in biogas could be utilized as a resource for industrial or agricultural application, even though it was treated as impurity in many previous studies for biogas upgrading. In this study, biogas was upgraded in terms of recovering highly concentrated CO2 without incurring CH4 loss. Tests under various conditions were conducted to enhance CO2 concentration and recovery efficiency. First, the effects of temperature and pressure on CO2 upgrading were investigated. 40°C and 7bar being selected as the optimal conditions that were then applied for further experiments. Separation tests under varying CO2 and CH4 compositions in a synthetic biogas were performed. The CO2 concentration in the permeate gas was upgraded to a maximum of 70.1%, 77.3% and 83.1% at feed gas compositions of 30%, 35%, and 40% CO2, respectively. Next, when applying a triple-stage separation configuration, a simultaneous improvement in both the CO2 concentration and CH4 loss were observed. These results indicate that an increase in CO2 concentration caused a reduction of CH4 loss. Finally, at biogas plant, CO2 was concentrated at 95.6% with 0.57% CH4 loss, which could be utilized in area to want the carbon source such as industrial and agricultural field.

Methane distributions and sea-to-air fluxes in the Pearl River Estuary and the northern South China sea

We measured dissolved methane (CH4) at various depths in the Pearl River Estuary and the shelf, slope, and basin of the northern South China Sea (SCS) during cruises from May to July 2014, October 2014, June 2015, and March 2017. High CH4 concentrations (9.4–430.3 nM) were observed in the Pearl River Estuary. There was a negative correlation between the CH4 concentration and the salinity in the surface waters of the Pearl River Estuary, indicating rapid CH4 loss via air-sea exchange and aerobic CH4 oxidation. The CH4 concentrations in the surface waters ranged from 1.7 to 5.4 nM in the shelf and slope region and from 2.2 to 3.0 nM in the basin of the northern SCS. The injection of a Pearl River plume rich in CH4 and driven by eddies had a profound impact on the CH4 distribution in the shelf and slope region in June 2015. The vertical profiles of CH4 showed spatial variations that can be attributed to complex interactions among physical, chemical, and biological processes. The subsurface CH4 maxima occurred ubiquitously in the euphotic zones, probably due to in situ CH4 production in anoxic microniches and aerobic CH4 formation from potential substrate precursors such as dimethylsulfoniopropionate (DMSP). The gross CH4 production rate in the mixed layer was estimated at 0.11 nM d-1 in the summer and -0.19 nM d-1 in the autumn. The surface waters of the Pearl River Estuary were oversaturated in CH4 with respect to atmospheric equilibrium having a saturation level of 5066±5908% (mean±SD) in early autumn and 6166±3611% in early summer. The CH4 fluxes (estimated using the W14 relationship) were estimated at 314.3±464.9 μmol m-2 d-1 in early autumn and 184.2±187.5 μmol m-2 d-1 in early summer. In the shelf and slope areas, the CH4 saturation was 178±37% in early autumn, 181±60% in early summer, and 129±14% in winter. The sea-to-air CH4 fluxes were 8.0±4.3 μmol m-2 d-1 in autumn, 4.1±5.2 μmol m-2 d-1 in summer, and 1.1±0.8 μmol m-2 d-1 in winter. The CH4 saturation ratio was less variable in the deep basin, ranging from 108% to 184% with an average of 140±16%. The CH4 flux in the deep basin area was 1.9±1.2 μmol m-2 d-1. Overall, we estimate the annual CH4 emission from the SCS as 9.9 × 109 mol yr-1. Hence the SCS is a net source of atmospheric CH4.

Integration of flash vessel in water scrubbing biogas upgrading system for maximum methane recovery

High CH4 purity in upgraded biogas concomitantly results in high CH4 loss during water scrubbing biogas upgrading process. In the current study, central composite design based on response surface methodology was used to recover maximum CH4 by optimizing a flash vessel integrated in a water scrubbing biogas upgrading system. Optimum CH4 recovery of 8.46% was achieved from flash vessel at 2 bar flash pressure and 90 second retention time with simultaneous bioCH4 recovery of 90.73% from the scrubbing column with 0.77% CH4 loss from the system. CCD predicted values were confirmed experimentally under the modelled optimum conditions and showed strong agreement with an R2 value > 0.98. Flash gas blended with biogas was recirculated into the water scrubbing column for upgrading. At 10 Nm3/h gas flow rate, pressure of 12 bar and 2.1 m3/h water flow rate, 91.3% CH4 in upgraded gas was obtained with energy consumption of 0.29 kWh/Nm3.

Structure affecting dissociation energy in polycyclic aromatic hydrocarbon ions

Steric interference of two bay-hydrogen atoms causes the benzo[c]phenanthrene radical cation to be non-planar. The energy required to remove one of these H atoms (2.8 ± 0.1 eV, from iPEPICO spectroscopy) is 1.5 eV lower than that required from the planar tetracene ion due to the formation of a new CC bond. This low dissociation energy precludes benzo[c]phenanthrene ions losing C2H2 (observed from tetracene with an energy of 4.2 eV). The B3-LYP/6-311++G(2d,p) reaction pathways to C2H2 loss are presented and found to be mediated by azulene-containing intermediates. The second IE of tetracene was measured to be 19.0 ± 0.2 eV.

Preparation and characterization of multilayer thin-film composite hollow fiber membranes for helium extraction from its mixtures

The unique and distinctive physico-chemical properties of helium make it an irreplaceable resource in a wide range of applications, including cryogenics. Commercially-produced helium is extracted from natural gas. For the use of a membrane to be viable for the helium extraction and enrichment process, the membrane-based process must be economically competitive against other conventional technologies, and therefore, developments in membrane and optimized process design are crucial. This work demonstrates the successful fabrication of a highly helium-selective multilayer thin-film composite hollow fiber membrane for the enrichment of helium from natural gas. An aromatic polyamide selective layer was formed on top of a mesoporous polyacrylonitrile support by interfacial polymerization, followed by a caulking process to plug defects on the polyamide layer. The permeation and separation properties of the multilayer thin-film composite hollow fiber membrane were characterized using pure and quaternary mixed gases. The effects of feed pressure (up to 300 psig) and stage-cut (1.5–20%) on helium purity and CH4 loss were systematically investigated.

The Sequence of Coronene Hydrogenation Revealed by Gas-phase IR Spectroscopy

Abstract Gas-phase coronene cations ( ) can be sequentially hydrogenated with up to 24 additional H atoms, inducing a gradual transition from a planar, aromatic molecule toward a corrugated, aliphatic species. The mass spectra of hydrogenated coronene cations show that molecules with odd numbers of additional hydrogen atoms (n H) are dominant, with particularly high relative intensity for “magic numbers” n H = 5, 11, and 17, for which hydrogen atoms have the highest binding energies. Reaction barriers and binding energies strongly affect the hydrogenation sequence and its site specificity. In this contribution, we monitor this sequence experimentally by the evolution of infrared multiple-photon dissociation (IRMPD) spectra of gaseous with n H = 3–11, obtained using an infrared free electron laser coupled to a Fourier transform ion cyclotron mass spectrometer. For weakly hydrogenated systems (n H = 3, 5) multiple-photon absorption mainly leads to loss of H atoms (and/or H2). With increasing n H, C2H2 loss becomes more relevant. For n H = 9, 11, the carbon skeleton is substantially weakened and fragmentation is distributed over a large number of channels. A comparison of our IRMPD spectra with density functional theory calculations clearly shows that only one or two hydrogenation isomers contribute to each n H. This confirms the concept of hydrogenation occurring along very specific sequences. Moreover, the atomic sites participating in the first 11 steps of this hydrogenation sequence are clearly identified.

Why Do Large Ionized Polycyclic Aromatic Hydrocarbons Not Lose C2H2?

The reaction mechanisms for the loss of C2H2 from the ions of anthracene, phenanthrene, tetracene, and pyrene were calculated at the B3-LYP/6-311++G(2d,p) level of theory and compared to that previously published for ionized naphthalene. A common pathway emerged involving the isomerization of the molecular ions to azulene-containing analogues, followed by the contraction of the seven-member ring into a five- and four-member fused ring system, leading to the cleavage of C2H2. The key transition state was found to be for this last process, and its relative energy was consistent going from naphthalene to tetracene. That for pyrene, though, was significantly higher due to the inability of the azulene moiety to achieve a stable conformation because of the presence of the three fused rings. Thus, C2H2 loss is discriminated against in pericondensed PAHs. For catacondensed PAHs, C2H2 loss also drops in relative abundance as the PAH gets larger due to the increase in the number of available hydrogen atoms, increasing the rate constant for H atom loss over that for C2H2 loss as PAH size increases. The unimolecular reactions of four cyano-substituted polycyclic aromatic hydrocarbon (PAH) ions were also probed as a function of collision energy by collision-induced dissociation tandem mass spectrometry. As the size of the ring system increases, HCN loss decreases in importance relative to other processes (H and C2H2 loss). 9-Cyanophenanthrene ions were chosen for further exploration by theory and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. The calculated reaction pathway and energetics for C2H2 loss were consistent with those found above. The calculations suggest that larger PAHs of interest in the interstellar environment will behave independently of a CN substituent.

CO2/CH4 separation by hot potassium carbonate absorption for biogas upgrading

In biogas upgrading to biomethane, the release of CO2 off-gas into the atmosphere is generally regarded as a carbon-neutral emission, but a significant loss of CH4 can occur in this step: considering the global warming potential of this latter compound, methane slip can worsen or even nullify the CO2 savings associated to biomethane. This study investigates a novel approach for biogas upgrading to biomethane, aimed at reducing the methane loss. A plant based on hot potassium carbonate was fed with 150–200 Nm3 h−1 of biogas from municipal waste. CO2 is removed in a K2CO3 absorption column, with negligible CH4 absorption. An assessment of biomethane quality was performed to check its compliance with recent National and European standard specifications. Results show that a methane slip below 0.1% can be achieved with this technology, thus significantly reducing the greenhouse gas emissions associated to biomethane industry. This leads to a lower capital expenditure because no off-gas post-treatment is required. Heat and electricity consumption were monitored, and operational expense resulted to be lower than membrane separation in the specific case study, by applying life cycle cost (LCC) methodology.

Methane loss from commercially operating biogas upgrading plants

Biogas technology is one of the widely applied anaerobic digestion approaches to harvest methane from different wastes. Recently, methane loss from biogas plants and its environmental and economic consequences have been underlined, but not thoroughly researched. In this investigation, process related CH4 loss from nine different commercially operating biogas upgrading plants such as water scrubber, amine, and membrane-based plants was examined. The result of the measurements showed an average of 0.81% methane loss with respect to supplied methane to the upgrading plants. A methane loss up to 1.97% was detected in water scrubber methane upgrading technology and up to 0.56% loss from membrane technology, while 0.04% methane loss was detected in amine based upgrading, thus the water scrubber has shown the most detrimental effect as regards methane loss. The regenerative thermal oxidizer was further applied to reduce CH4 emission by 99.5% of the amount of CH4 in the waste gas from the upgrading unit, which ensures the sustainable process of biogas production.

CO2 Separation by Using a Three-stage Membrane Process

ABSTRACT In this work, a three-stage membrane process for CO2 separation was proposed and optimized. The results of this study revealed that the proposed technology is a suitable process for the CO2 separation at higher concentrations. In addition, MATLAB was used to simulate and obtain the optimal operational parameters for a three-stage membrane process. A partial cycle was established, and the CO2 was recovered from the permeation side of the second-stage membrane, which enhanced the purity of the CO2 gas stream. The results of this study indicated that when the CO2 concentration was higher than 50% at a flow rate of 100000 Nm3 d–1, CO2 separation could be achieved under optimal operating conditions. Under conditions where the membrane areas were 2400, 3800, and 1800 m2 for the first-, second-, and third-stage membranes, respectively, and where the operational pressure at the first- and third stage membranes were 3.0 and 2.5 MPa, respectively, the CO2 separation fraction was higher than 90%, and the CH4 loss rate was less than 5%. The results of this study indicate a high potential for practical application.

New insights into the dissociation dynamics of methylated anilines.

Aniline, an important model system for biological chromophores, undergoes ultrafast H-atom loss upon absorption of an ultraviolet photon. By varying the number and position of methyl substituents on both the aromatic ring and amine functional group, we explore the ultrafast production of photofragments as a function of molecular structure. Both N-methyl aniline and 3,5-dimethyl aniline show altered H-atom loss behaviour compared to aniline, while no evidence for CH3 loss was found from either N-methyl aniline or N,N-dimethyl aniline. With the addition of time-resolved photoelectron spectroscopy, the photofragment appearance times are matched to excited state relaxation pathways. Evidence for a sequential excited state relaxation mechanism, potentially involving a valence-to-Rydberg decay mechanism, will be presented. Such a global, bottom-up approach to molecular photochemistry is crucial to understanding the dissociative pathways and excited state decay mechanisms of biomolecule photoprotection in nature.

SIMULATION OF CO2 AND H2S EXTRACTION PROCESSES FROM BIOGAS USING AMINE AND WATER ABSORPTION

The research of technological circuits of biomethane from biogas production with the use of the most widespread amine and water absorption processes of carbon dioxide and hydrogen sulfide removal from biogas is carried out. With the use of software modeling for the amine process, an effective absorbent MDEAmod — an aqueous solution of methyldiethanolamine and monoethanolamine is proposed. This absorbent can be effectively applied to a wide range of biogas and for a range of pressure practically from atmospheric to 0.28 MPa. At the same time, the heat load of desorber reboiler is less in 1.5–4 times compared with the use of monoethanolamine solutions.Comparison of energy costs for the production of biomethane using amine and water technology shows that taking into account the greater yield of biomethane in the amine process by 8–15 % than in water absorption (loss of CH4 due to dissolution in H2O), and the use of this difference to heat the amine desorber reboiler these costs are comparative. In the case of the need to produce carbon dioxide as a commodity product, the amine process has an advantage, since the CO2 achieved in this process has a concentration of 98 % versus 80 % when using water absorption. The obtained results of simulation of СО2 and H2S removal process by amine and water absorption can be used in technologies of biogas refining and production of biomethane - an analogue of natural gas, as well as carbon dioxide as a commercial product. Bibl. 24, Fig. 6, Tab. 4.

Identification and Characterization of Terpenoid Lactones and Flavonoids from Ethanolic Extract ofAndrographis Paniculata(Burm.f.) Nees Using Liquid Chromatography/Tandem Mass Spectrometry

AbstractAndrographis paniculatais traditionally used for the prevention and treatment of infectious diseases due to its bioactive terpenoid lactones and flavonoids. So, there is an urgent need to develop a liquid chromatography with tandem mass spectrometry method for identification and characterization of terpenoid lactones and flavonoids. The chromatographic separation of terpenoid lactones and flavonoids from crude extract was carried on Thermo Betasil C8 column (250 mm × 4.5 mm, 5 μm) using 0.1% formic acid in water and 0.1% formic acid in acetonitrile as a mobile phase by high‐performance liquid chromatography coupled with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry. Terpenoid lactones showed characteristic consecutive losses of H2O, HCHO and CO whereas flavonoids gave successive losses of CH3, CH4, CO and retro Diels Alder fragment ions. In total 68 compounds including 28 terpenoid lactones and 40 flavonoids were tentatively identified and characterized on the basis of their chromatographic and mass spectrometric features (molecular formula, exact mass measurements and tandem mass spectrometry). Andrographolide and wogonin were unambiguously identified by comparison with their authentic standards. The present method can be used for identification and characterization of terpenoid lactones and flavonoids.

Process Simulation and Cost Evaluation of Carbon Membranes for CO₂ Removal from High-Pressure Natural Gas.

Natural gas sweetening is required to remove the acid gas CO2 to meet gas grid specifications. Membrane technology has a great potential in this application compared to the state-of-the-art amine absorption technology. Carbon membranes are of particular interest due to their high CO2/CH4 selectivity of over 100. In order to document the advantages of carbon membranes for natural gas (NG) sweetening, HYSYS simulation and cost evaluation were conducted in this work. A two-stage carbon membrane process with recycling in the second stage was found to be technically feasible to achieve >98% CH4 with <2% CH4 loss. The specific natural gas processing cost of 1.122 × 10−2 $/m3 sweet NG was estimated at a feed pressure of 90 bar, which was significantly dependent on the capital-related cost. Future work on improving carbon membrane performance is required to increase the competitiveness of carbon membranes for natural gas sweetening.

Physical absorption of CO2 and H2S from synthetic biogas at elevated pressures using hollow fiber membrane contactors: The effects of Henry’s constants and gas diffusivities

The present study applies the mathematical model to investigate the physical absorption of CO2, H2S and CH4 from synthetic biogas at high pressure using hollow fiber membrane contactors. Henry’s constants are considered pressure and temperature dependent, while the polarity of H2S is included in the calculation of gas diffusivities. The model was validated with the experimental data using two hollow fiber membranes, i.e., polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE), to analyze membrane wetting. The effects of pressure and temperature on the CO2 and H2S absorption and CH4 loss were investigated. From the model validation, the experimental results using PVDF and PTFE at 1 bar are in good agreement with non-wetting mode. At elevated pressures, non-wetting mode results correspond with the experimental results using PTFE, while the partially wetting mode well predicts the results of PVDF. The modeling results also indicate that increasing pressure and reducing temperature improves the absorption fluxes of CO2 and H2S, while the CH4 losses in this work are lower than 5.5%.

Reversible Photoisomerization of the Isolated Green Fluorescent Protein Chromophore.

Fluorescent proteins have revolutionized the visualization of biological processes, prompting efforts to understand and control their intrinsic photophysics. Here we investigate the photoisomerization of deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone anion (HBDI-), the chromophore in green fluorescent protein and in Dronpa protein, where it plays a role in switching between fluorescent and nonfluorescent states. In the present work, isolated HBDI- molecules are switched between the Z and E forms in the gas phase in a tandem ion mobility mass spectrometer outfitted for selecting the initial and final isomers. Excitation of the S1 ← S0 transition provokes both Z → E and E → Z photoisomerization, with a maximum response for both processes at 480 nm. Photodetachment is a minor channel at low light intensity. At higher light intensities, absorption of several photons in the drift region drives photofragmentation, through channels involving CH3 loss and concerted CO and CH3CN loss, although isomerization remains the dominant process.

The effect of silage type on animal performance, energy utilisation and enteric methane emission in lactating dairy cows

The present study aimed to investigate the effect of silage type on dry matter (DM) intake, nutrient digestibility, energy utilisation and methane (CH4) emission. Six late lactating Holstein dairy cows were used in a replicated 3 × 3 Latin square design study with three treatments (grass silage (GS), maize silage (MS) and whole-crop wheat silage (WCWS)) and three periods (3 weeks/period). All animals were offered forage ad libitum and 5.55 kg/day of a concentrate supplement, which contained (DM basis) 66.0% rapeseed meal, 28.3% soyabean meal and 5.7% a mineral/vitamin supplement. During each period, animals were subject to digestibility, CH4 and heat production measurements during the final 6 days using calorimeter chambers. The results demonstrated that total DM intake for MS and WCWS diets were higher (P &amp;lt; 0.001) than for the GS diet. Faecal energy and heat production loss for the GS diet were lower (P &amp;lt; 0.01) than for MS and WCWS diets. In contrast, cows fed the GS diet had higher (P &amp;lt; 0.05) urine energy loss compared with MS and WCWS diets. In comparison with the GS and MS diets, WCWS diet produced a lower CH4 loss per kg DM and organic matter intake (P &amp;lt; 0.01), and CH4 energy output as a proportion of gross energy and metabolisable energy intake (P &amp;lt; 0.05). The present study demonstrates that choice of forage types affects energy utilisation and CH4 emission in dairy cows.

Plasma activation of methane for hydrogen production in a N2 rotating gliding arc warm plasma: A chemical kinetics study

In this work, a chemical kinetics study on methane activation for hydrogen production in a warm plasma, i.e., N2 rotating gliding arc (RGA), was performed for the first time to get new insights into the underlying reaction mechanisms and pathways. A zero-dimensional chemical kinetics model was developed, which showed a good agreement with the experimental results in terms of the conversion of CH4 and product selectivities, allowing us to get a better understanding of the relative significance of various important species and their related reactions to the formation and loss of CH4, H2, and C2H2 etc. An overall reaction scheme was obtained to provide a realistic picture of the plasma chemistry. The results reveal that the electrons and excited nitrogen species (mainly N2(A)) play a dominant role in the initial dissociation of CH4. However, the H atom induced reaction CH4 + H → CH3 + H2, which has an enhanced reaction rate due to the high gas temperature (over 1200 K), is the major contributor to both the conversion of CH4 and H2 production, with its relative contributions of >90% and >85%, respectively, when only considering the forward reactions. The coexistence and interaction of thermochemical and plasma chemical processes in the rotating gliding arc warm plasma significantly enhance the process performance. The formation of C2 hydrocarbons follows a nearly one-way path of C2H6 → C2H4 → C2H2, explaining why the selectivities of C2 products decreased in the order of C2H2 > C2H4 > C2H6.

Identification of the fragment of the 1-methylpyrene cation by mid-IR spectroscopy

The fragment of the 1-methylpyrene cation, C17H11+, is expected to exist in two isomeric forms, 1-pyrenemethylium PyrCH2+ and the tropylium containing species PyrC7+. We measured the infrared (IR) action spectrum of cold C17H11+ tagged with Ne using a cryogenic ion trap instrument coupled to the FELIX laser. Comparison of the experimental data with density functional theory calculations allows us to identify the PyrCH2+ isomer in our experiments. The IR Multi-Photon Dissociation spectrum was also recorded following the C2H2 loss channel. Its analysis suggests combined effects of anharmonicity and isomerisation while heating the trapped ions, as shown by molecular dynamics simulations.