Addition Of Methane Research Articles

Nucleation in Liquid Ethane with Small Additions of Methane

The method of measuring the lifetime of a liquid in a metastable (superheated) state has been used to investigate the kinetics of spontaneous boiling-up of ethane–methane solutions. The temperature dependence of the solution mean lifetime has been traced at two values of methane concentration (2.1 and 6.0 mol %) and two pressures (1.0 and 1.6 MPa). The results of experiments are compared with classical homogeneous nucleation theory. For pure ethane at small (<8.9 s) lifetimes, one can observe a systematic “under-heating” (∼0.5–0.7 K) of the solution against theoretical values of the limiting superheating temperature. Dissolution of 6 mol % of methane in ethane results in a solution “superheating” of ∼0.7 K in excess of the theoretical value. The slopes of experimental curves at small (<8.9 s) lifetimes are in satisfactory agreement with theory. When the mean lifetimes exceed the value of 8.9 s, one can observe considerable deviations of experimental curves from theoretical lines. The discrepancies are discussed in the context of models of heterogeneous and initiated nucleation.

Potential Energy Surface for Anaerobic Oxidation of Methane via Fumarate Addition

Microbially mediated anaerobic oxidation of methane (AOM) is an important sink in the global methane cycle, but the mechanism and microorganisms responsible for this oxidation are not fully known. Using quantum chemical calculations, fumarate addition to methane was examined to determine if it could be an energetically feasible mechanism for AOM. A potential energy surface (PES) for the initial reaction was created and the results suggest the reaction is exothermic, with a calculated overall energy change between -9.8 and -11.2 kcal/mol. The addition of methane to fumarate is calculated to be the highest point on the surface, 25.0-25.3 kcal/mol above the reactants. Of the three possible molecular configurations of fumarate considered, the one that presents the least steric obstacles to the addition reaction with methane yields the greatest energy gain. While 11.2 kcal/mol may support growth under energy limited conditions it is unknown if enzymes can mediate an energetic barrier of 25 kcal/mol. These calculated energies provide values for what could be one of the least reactive substrates to undergo fumarate addition, making methane a model substrate in defining the limits of energy barriers and minimal energy requirements for growth in reactions activated by glycyl radical-containing enzymes.

Cathodic cage nitriding of AISI 409 ferritic stainless steel with the addition of CH4

AISI 409 ferritic stainless steel samples were nitrided using the cathodic cage plasma nitriding technique (CCPN), with the addition of methane to reduce chromium precipitation, increase hardness and wear resistance and reduce the presence of nitrides when compared to plasma carbonitriding. Microhardness profiles and X-Ray analysis confirm the formation of a very hard layer containing mainly ε-Fe3N and expanded ferrite phases.

Reduction of acid effects on trace element determination in food samples by CH4 mixed plasma-DRC-MS

A robust method for trace element determination in food samples by addition of methane to the plasma of a dynamic reaction cell mass spectrometer (CH4 mixed plasma-DRC-MS) was developed. Addition of 3mLmin−1 methane to Ar-plasma eliminates the signal suppressions of various elements (As, Se, Hg, etc.) due to the high concentration of nitric acid (10%, v/v). The CH4–Ar mixed plasma may compensate for the plasma cooling effects due to the highly concentrated nitric acid. The interfering polyatomic ions 40Ar12C+, 40Ar35Cl+ and 40Ar40Ar+ on 52Cr+, 75As+ and 80Se+ determination were removed effectively using the DRC with CH4 as the reaction gas. The limits of quantification (LOQ, 10σ) were 0.35ngg−1, 0.07ngg−1, 0.35ngg−1, 0.07ngg−1, 0.15ngg−1, and 0.07ngg−1 for As, Cd, Cr, Hg, Pb and Se, respectively. The proposed method was applied to the determination of these trace elements in four food standard reference materials (NIST1577b, GBW10018, NIST1570a and GBW10016), and the results were in good agreement with the certified values.

The Effect of Nitrogen Enrichment on C1-Cycling Microorganisms and Methane Flux in Salt Marsh Sediments

Methane (CH4) flux from ecosystems is driven by C1-cycling microorganisms – the methanogens and the methylotrophs. Little is understood about what regulates these communities, complicating predictions about how global change drivers such as nitrogen enrichment will affect methane cycling. Using a nitrogen addition gradient experiment in three Southern California salt marshes, we show that sediment CH4 flux increased linearly with increasing nitrogen addition (1.23 μg CH4 m−2 day−1 for each g N m−2 year−1 applied) after 7 months of fertilization. To test the reason behind this increased CH4 flux, we conducted a microcosm experiment altering both nitrogen and carbon availability under aerobic and anaerobic conditions. Methanogenesis appeared to be both nitrogen and carbon (acetate) limited. N and C each increased methanogenesis by 18%, and together by 44%. In contrast, methanotrophy was stimulated by carbon (methane) addition (830%), but was unchanged by nitrogen addition. Sequence analysis of the sediment methylotroph community with the methanol dehydrogenase gene (mxaF) revealed three distinct clades that fall outside of known lineages. However, in agreement with the microcosm results, methylotroph abundance (assayed by qPCR) and composition (assayed by terminal restriction fragment length polymorphism analysis) did not vary across the experimental nitrogen gradient in the field. Together, these results suggest that nitrogen enrichment to salt marsh sediments increases methane flux by stimulating the methanogen community.

A system for incubations at high gas partial pressure.

High-pressure is a key feature of deep subsurface environments. High partial pressure of dissolved gasses plays an important role in microbial metabolism, because thermodynamic feasibility of many reactions depends on the concentration of reactants. For gases, this is controlled by their partial pressure, which can exceed 1 MPa at in situ conditions. Therefore, high hydrostatic pressure alone is not sufficient to recreate true deep subsurface in situ conditions, but the partial pressure of dissolved gasses has to be controlled as well. We developed an incubation system that allows for incubations at hydrostatic pressure up to 60 MPa, temperatures up to 120°C, and at high gas partial pressure. The composition and partial pressure of gasses can be manipulated during the experiment. To keep costs low, the system is mainly made from off-the-shelf components with only very few custom-made parts. A flexible and inert PVDF (polyvinylidene fluoride) incubator sleeve, which is almost impermeable for gases, holds the sample and separates it from the pressure fluid. The flexibility of the incubator sleeve allows for sub-sampling of the medium without loss of pressure. Experiments can be run in both static and flow-through mode. The incubation system described here is usable for versatile purposes, not only the incubation of microorganisms and determination of growth rates, but also for chemical degradation or extraction experiments under high gas saturation, e.g., fluid–gas–rock-interactions in relation to carbon dioxide sequestration. As an application of the system we extracted organic compounds from sub-bituminous coal using H2O as well as a H2O–CO2 mixture at elevated temperature (90°C) and pressure (5 MPa). Subsamples were taken at different time points during the incubation and analyzed by ion chromatography. Furthermore we demonstrated the applicability of the system for studies of microbial activity, using samples from the Isis mud volcano. We could detect an increase in sulfate reduction rate upon the addition of methane to the sample.

Experimental investigation of alumina and quartz as dielectrics for a cylindrical double dielectric barrier discharge reactor in argon diluted methane plasma

Non-oxidative conversion of methane into higher hydrocarbons was studied under argon, at atmospheric pressure, in the non-equilibrium environment of the dielectric barrier discharge (DBD). In this study, two concentric dielectric barriers, a short plasma zone with a wide discharge gap have been used to investigate methane conversion in reactors employing alumina and quartz as dielectrics. As energy transfer to the plasma in a DBD system is determined by the capacitive properties of the dielectrics, discharge energy varies between quartz and alumina reactors at the same applied voltage and the conversion of methane and yield of hydrogen therefore also varies between quartz and alumina reactors. Although the dielectric strength of alumina is lower than that of quartz, this disadvantage is offset by increased dielectric permittivity resulting in greater dielectric capacity, in turn leading to increased gap voltage and associated higher conversion rates. Methane conversion was performed in a majority argon carrier. The addition of methane in low concentrations results in a modified argon discharge, one operating in the transition region between homogeneous glow and filamentary discharge regimes. Under these conditions, methane conversion rates were observed to vary with methane concentration, applied voltage and residence time. Experimental results are presented and interpreted in terms of ionization phenomena, metastable species activity and discharge power.

Properties of hydrogenated DLC films as prepared by a combined method of plasma source ion implantation and unbalanced magnetron sputtering

Abstract

Improved measurement of microbial activity in deep‐sea sediments at in situ pressure and methane concentration

A robust and convenient method was developed to evaluate rates of microbial activity in gas‐charged deepsea sediments at in situ hydrostatic pressure, temperature, and gas concentration. The method used a hydrostatic chamber to maintain high pressures of 50 bar and greater, and a modified Hungate tube and plunger to contain samples. This technique can be easily applied to quantifying rates of microbial processes sensitive to dissolved gas concentration (e.g., sulfate reduction, anaerobic methane oxidation, and methanogenesis) in high pressure, gas‐rich environments. Here, the method was used to determine rates of microbial activity in cold seep sediments from the Gulf of Mexico and the California coast. We measured rates of sulfate reduction (SR), anaerobic oxidation of methane (AOM), and methanogenesis (MOG) using radiotracer techniques. We compared in situ pressure and elevated methane concentration assays to traditional ex situ incubations at 1 bar using recovered (degassed) sediment. Methane concentrations were elevated in ex situ incubations to assess a substrate level effect. Upon the application of pressure, rates of AOM, SR, and MOG increased. AOM and MOG rates were more sensitive to methane addition than SR. Our results show that measuring rates of deep‐sea microbial activity at in situ pressure and gas concentrations is essential to quantify carbon flow in these environments accurately.

Measurements of propagation speeds and flame instabilities in biomass derived gas–air premixed flames

Three biomass derived gases (BDGs, named GG-H, GG-L and GG-V), which are derived from industry facilities and can be useful for reducing CO 2 and the application to combustors, are studied and examined for some basic flame characteristics such as unstretched laminar burning velocity, Markstein length, and cell formation over the entire flame surface. Experiments were conducted in a constant volume combustion chamber using a schlieren system. A better agreement between the measured and predicted unstretched laminar burning velocities is obtained using a suggested reaction mechanism modified from the GRI-Mech 3.0 mechanism. Additionally, cell formations on flame surfaces of the three mixtures were also analyzed and compared using high-speed schlieren images. It is shown that the GG-H–air flames and the GG-L–air flames have similar flame wrinkled surfaces, while the GG-V–air flames shows a stronger cellularity behavior. The effects of each fuel component in mixtures to cellularity are also evaluated by varying the concentration of each fuel in the reactant mixtures. The cellular instability is promoted (diminished) with hydrogen enrichment (methane addition); meanwhile the similar behavior is obtained for carbon monoxide addition.

Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-β-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh) 3) 2] and [Rh(FcCOCHCOR)(P(OPh) 3) 2(CH 3)(I)], with Fc = ferrocenyl and R = Fc, CH 3 and CF 3, have been synthesized. The reactivity of complexes of the type [Rh(β-diketonato)(P(OPh) 3) 2] increase in the order: β-diketonato = (CF 3COCHCOCF 3) − < (CF 3COCHCOPh) − < (CF 3COCHCOCH 3) − < (PhCOCHCOPh) − < (CF 3COCHCOFc) − < (CH 3COCHCOPh) − < (CH 3COCHCOCH 3) − < (CH 3COCHCOFc) − < (FcCOCHCOFc) −, giving linear relationships between the kinetic parameter ln k 2 and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the β-diketonato side groups ( χ R + χ R′) and the p K a of the uncoordinated β-diketone RCOCH 2COR′. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF 3)(P(OCH 3) 3) 2] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.

Rate determination of the catalytic oxidation of methane and propane in an electrochemical solid-electrolyte reactor

The possibility of using a solid-electrolyte reactor in kinetic studies of the catalytic oxidations of hydrocarbon with molecular oxygen was investigated. A theoretical analysis of processes in a catalytically asymmetric gas-diffusion cell in N2 + O2 + CH4 and N2 + O2 + C3H8 gas mixtures was performed. Analytical expressions are presented for calculating the oxygen, methane, and propane concentrations and the methane and propane oxidation rates in the inner space of the cell from the emf of the latter. The potentiometric response was studied experimentally after the addition of methane and propane in the gas mixture in a reactor with silver electrodes and samples with applied catalytic materials. The concentrations of the components in the inner space of the reactor and the oxidation rates of hydrocarbons were calculated from the experimental data.

Vapor−Liquid Equilibria Measurements of the Methane + Pentane and Methane + Hexane Systems at Temperatures from (173 to 330) K and Pressures to 14 MPa

New pTxy data are reported for methane + pentane and methane + hexane at pressures up to 14 MPa over the temperature range (173 to 333) K using a custom-built vapor−liquid equilibria apparatus. For methane (1) + pentane (2), a mixture with overall mole fraction z2 ≈ 0.02 was prepared gravimetrically, and measurements were performed along an isochoric pathway. For the methane (1) + hexane (3) mixture, liquid hexane was pumped into the evacuated cell using an HPLC pump, and then after the addition of methane, isothermal measurements were made at 11 temperatures. Two liquid phases were observed close to the bubble point in the methane + hexane mixture at (183.15 and 233.15) K at pressures of (3.31 and 12.99) MPa, respectively. Our data are compared with previous literature data and with the predictions of the Groupe European de Recherche Gaziere (GERG-2004 XT08) multiparameter equation of state (EOS) and the Peng−Robinson and Advanced Peng−Robinson cubic equations of state implemented in commercial process s...

Experimental study on cellular instabilities in hydrocarbon/hydrogen/carbon monoxide–air premixed flames

To investigate cell formation in methane (or propane)/hydrogen/carbon monoxide–air premixed flames, the outward propagation and development of surface cellular instabilities of centrally ignited spherical premixed flames were experimentally studied in a constant pressure combustion chamber at room temperature and elevated pressures. Additionally, unstretched laminar burning velocities and Markstein lengths of the mixtures were obtained by analyzing high-speed schlieren images. In this study, hydrodynamic and diffusional-thermal instabilities were evaluated to examine their effects on flame instabilities. The experimentally-measured unstretched laminar burning velocities were compared to numerical predictions using the PREMIX code with a H 2/CO/C 1–C 4 mechanism, USC Mech II, from Wang et al. [22]. The results indicate a significant increase in the unstretched laminar burning velocities with hydrogen enrichment and a decrease with the addition of hydrocarbons, whereas the opposite effects for Markstein lengths were observed. Furthermore, effective Lewis numbers of premixed flames with methane addition decreased for all of the cases; meanwhile, effective Lewis numbers with propane addition increase for lean and stoichiometric conditions and increase for rich and stoichiometric cases for hydrogen-enriched flames. With the addition of propane, the propensity for cell formation significantly diminishes, whereas cellular instabilities for hydrogen-enriched flames are promoted. However, similar behavior of cellularity was obtained with the addition of methane, which indicates that methane is not a candidate for suppressing cell formation in methane/hydrogen/carbon monoxide–air premixed flames.

Green house gas emissions from termite ecosystem

Methanogenic archaea (methanogens) that inhabit the gut of termites generate enormous amount of methane that adds to the global atmospheric methane (CH4). Methane is an important trace gas in the atmosphere, contributing significantly to long wave absorption and bringing in variations into the chemistries of both the troposphere and the stratosphere. In the troposphere, methane acts as a sink for hydroxide (OH) and as a source for carbon monoxide (CO). While in the stratosphere, methane is a sink for chlorine (Cl) molecules and a source of water vapor, which is a dominant greenhouse gas. Analysis has shown that atmospheric concentrations of methane have increased by about 30% over the last 40 years. Such an increase may greatly affect future levels of stratospheric ozone and hence, the climate of the earth. Recent estimates of the total annual source strength of CH4 vary from 400 to 1200 Tg. Activities such as rice cultivation, cattle production, mining, use of fossil fuels and biomass burning is believed to be the cause of increasing methane levels in the atmosphere. To add to this list is the source from termites, which contributes measurable quantities of CH4 ranging from 2 to 150 Tg per year. However, data indicate that while there are large variations in the amount of CH4 produced by different species, the total methane addition due to termites is probably less than 15 Tg per year, thus making a contribution of less than 5% to global CH4 emissions. Furthermore, the review addresses questions related to the biological aspects of termite harboring groups of bacteria that participate in methanogenesis and various other biotechnological potential of unique microbiota as well as possible strategies to mitigate methanogenesis by termite. Key words: Macrotermes, methane, carbondioxide, GHG, methanobacteria, methanosarcina.

Green house gas emissions from termite ecosystem

Methanogenic archaea (methanogens) that inhabit the gut of termites generate enormous amount of methane that adds to the global atmospheric methane (CH 4 ). Methane is an important trace gas in the atmosphere, contributing significantly to long wave absorption and bringing in variations into the chemistries of both the troposphere and the stratosphere. In the troposphere, methane acts as a sink for hydroxide (OH) and as a source for carbon monoxide (CO). While in the stratosphere, methane is a sink for chlorine (Cl) molecules and a source of water vapor, which is a dominant greenhouse gas. Analysis has shown that atmospheric concentrations of methane have increased by about 30% over the last 40 years. Such an increase may greatly affect future levels of stratospheric ozone and hence, the climate of the earth. Recent estimates of the total annual source strength of CH 4 vary from 400 to 1200 Tg. Activities such as rice cultivation, cattle production, mining, use of fossil fuels and biomass burning is believed to be the cause of increasing methane levels in the atmosphere. To add to this list is the source from termites, which contributes measurable quantities of CH 4 ranging from 2 to 150 Tg per year. However, data indicate that while there are large variations in the amount of CH 4 produced by different species, the total methane addition due to termites is probably less than 15 Tg per year, thus making a contribution of less than 5% to global CH4 emissions. Furthermore, the review addresses questions related to the biological aspects of termite harboring groups of bacteria that participate in methanogenesis and various other biotechnological potential of unique microbiota as well as possible strategies to mitigate methanogenesis by termite. Key words: Macrotermes, methane, carbondioxide, GHG, methanobacteria, methanosarcina.

Influence of methane addition on selenium isotope sensitivity and their spectral interferences

The measurements of stable selenium (Se) isotopic signatures by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) are very challenging, due to the presence of spectral interferences and the low abundance of Se in environmental samples. We systematically investigated the effect of methane addition on the signal of Se isotopes and their interferences. It is the first time that the effect of methane addition has been assessed for all Se isotopes and its potential interferences using hydride generator multi-collector inductively coupled plasma mass spectrometry (HG-MC-ICP-MS). Our results show that a small methane addition increases the sensitivity. However, the response differs between a hydride generator and a standard introduction system, which might be related to differences in the ionization processes. Both argon and hydrogen-based interferences, the most common spectral interferences on selenium isotopes in HG-MC-ICP-MS, decrease with increasing methane addition. Therefore, analyte-interference ratios and precision are improved. Methane addition has thus a high potential for the application to stable Se isotopes ratios by HG-MC-ICP-MS.

Effect of thermal stabilizers composed of zinc barbiturate and calcium stearate for rigid poly(vinyl chloride)

Zinc barbiturate [Zn(H2L)2·2H2O, abbreviated as ZnL2] was synthesized by a precipitation method in aqueous solution, and investigated as a co-stabilizer with calcium stearate (CaSt2) for rigid poly(vinyl chloride) (PVC) by the discoloration test and the dehydrochlorination test at 180 °C. ZnL2 exhibits high stabilizing effect with excellent initial colour of PVC films. In comparison with the synergistic effect of CaSt2/ZnSt2 stabilizers, the CaSt2/ZnL2 stabilizers in mass ratios ranging from 0.3/1.2 to 0.6/0.9 exhibit better synergistic effect. Moreover, PVC films stabilized by CaSt2/ZnL2 show better initial colour with the addition of dibenzoyl methane as an auxiliary stabilizer. The mechanism of stabilizing action of ZnL2 is also proposed. ZnL2 may replace the labile chlorine atoms to interrupt the formation of conjugated double bonds in PVC chains, and act as the absorber of hydrogen chloride to restrain the self-catalytic dehydrochlorination.

Experimental Study in H&lt;sub&gt;2&lt;/sub&gt;/CO/CH&lt;sub&gt;4&lt;/sub&gt;–Air and H&lt;sub&gt;2&lt;/sub&gt;/CO/C&lt;sub&gt;3&lt;/sub&gt;H&lt;sub&gt;8&lt;/sub&gt;–Air Premixed Flames. Part 2: Cellular Instabilities

Experiments in a constant pressure combustion chamber at room temperature and elevated pressures using schlieren system were conducted to investigate the cellular instabilities in hydrogen/carbon monoxide/methane (or propane)–air premixed flames. In the present study, hydrodynamic and diffusional-thermal instabilities were evaluated to elucidate their effects to flame instabilities. Effective Lewis numbers of premixed flames with methane addition decrease for all of the cases. Meanwhile, the effective Lewis numbers with propane addition increase for lean and stoichiometric conditions, but they increase for rich and stoichiometric cases for hydrogen-enriched flames. With propane addition, the propensity for cells formation is significantly diminished whereas the cellular instabilities for hydrogen enriched flames are promoted. With methane addition, the similar behavior of cellularity is obtained, indicating that methane is not a candidate for suppressing cells formation in hydrogen/carbon monoxide/methane–air premixed flames.

Enantioselective organocatalytic asymmetric allylic alkylation. Bis(phenylsulfonyl)methane addition to MBH carbonates

The highly enantioselective asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates with bis(phenylsulfonyl)methane is presented. The reaction is simply catalyzed by cinchona alkaloid derivatives affording the final alkylated products in good yields and enantioselectivities.