Showing papers on "Methane published in 1983"

Genetic characterization of natural gases

Abstract: Natural gases can be characterized genetically using four properties: C2+ concentration, carbon and hydrogen isotope variations in methane, and carbon isotope variation in ethane. Three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters. In these diagrams, compositional fields have been defined for primary gases (biogenic, thermogenic associated, and thermogenic nonassociated) and for gases which result from mixing of these gases. These fields are strictly empirical and comprise compositional variations found in about 500 natural gases. The isotopic and compositional variations in natural gases can be described in terms of (1) processes during formation of the gases such as bacterial fermentation or maturation of organic matter, and (2) processes during secondary migration. Mixing of primary gases is an important and common process. Migration of gases predominantly affects the C2+ concentration, whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged, allowing an assessment of the origin of migrated gases and properties of their source rocks. The formation of gas from humic organic matter and coals is not yet clear from published data. The diagrams use data from various basins and areas. Interstitial gases from the Gulf of California are entirely of bacterial origin: traces of thermogenic gases are formed only in the vicinity of dolerite sills; gases in the south German Molasse basin and in the Vienna basin are of bacterial, mixed, and thermogenic origins. Data from the north Italian Po basin provide examples for genetic characterization of migrated gases.

Sources, sinks, and seasonal cycles of atmospheric methane

Abstract: It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.

Ethane ocean on Titan

Abstract: It is proposed that Saturn's satellite Titan is covered by an ocean one to several kilometers deep consisting mainly of ethane. If the ocean is in thermodynamic equilibrium with an atmosphere of 3 percent (mole fraction) methane, then its composition is roughly 70 percent ethane, 25 percent methane, and 5 percent nitrogen. Photochemical models predict that ethane is the dominant end product of methane photolysis so that the evolving ocean is both the source and sink for continuing photolysis. The coexisting atmosphere is compatible with Voyager data.

Methane and other Hydrocarbon Gases in Marine Sediment

Abstract: Hydrocarbon gases are common in marine sediment accumulating in present-day oceans. Such gases originate from the decomposition of organic matter by biochemical and chemical processes. We consider seven hydrocarbon gases that occur in marine sediment (Table 1). In addition, inorganic gases such as nitrogen (N2), argon (Ar), carbon dioxide (C02), and helium (He) are present, but usually as minor or trace components in natural gas. These will not be discussed here. Methane (C1) is almost always the dominant component of the natural gas mixtures. Usually accompanying C1 are other hydrocarbon gases, including ethane (C2), propane (C3), isobutane (i-C4), and normal butane (n­ C4), that are present in variable amounts from traces to 30-40 percent collectively. Marine sediments also contain volatile hydrocarbons of higher molecular weight, e.g. Cs through at least C7 (Hunt 1975), but our discussion is confined to permanent gas hydrocarbons C1 through C4. In addition to gaseous alkanes, the alkenes, ethene (C2;) and propene (C3;), are found also, but mainly in sediment near the seafloor and in the overlying water column. There are three main stages of natural gas formation during the burial history of sediment. The earliest stage is biological C1 formation, which

Methane, Hydrogen and Helium in Hydrothermal Fluids at 21°N on the East Pacific Rise

Abstract: Methane in 350°C hydrothermal fluids at 21°N on the East Pacific Rise occurs in concentrations greater than 1.1 cc (STP)/kg. Hydrogen concentrations vary from 8 to 38 cc(STP)/kg, showing a considerable range between different vent fields. Helium concentrations exceed 0.021 cc(STP)/kg. The injection rates of methane and hydrogen into the deep ocean indicate replacement times of the order of 30 years, implying that consumption of methane and hydrogen in the water column must be very rapid. Variations of end-member concentrations of methane, hydrogen and possibly helium, as well as δ13C(CH4), among vent fields suggests either chemical control of reactive gas abundances and/or variations in gas contents of ridge crest basalts. Measurements of methane and helium in basalt glass from the EPR show CH4/3He ratios of 2.5 × 106, compared to 3.5 × 106 in hydrothermal fluid from the same area. Carbon isotope evidence, CO2 CH4 isotope geothermometry, the lack of suitable thermocatalytic sources of organic carbon, and the similarity between CH4/3He ratios in these hydrothermal fluids and mid-ocean ridge basalts, point to an abiogenic origin of hydrothermal methane, extracted directly from basalt by circulating seawater.

Seasonal variation of methane flux from a California rice paddy

Abstract: To allow increased understanding of the global budget of atmospheric methane, individual methane sources require investigation. We have measured methane emissions from a California rice paddy during the entire 1982 growing season. A very strong seasonal dependence was observed. Methane emissions were highest in the last 2–3 weeks before harvest; daily emissions reached 5 g CH4/m2. Over the 100-day season, daily emissions averaged about 0.25 g CH4/m2, higher than our previously reported values. Attempts to estimate global rice paddy emissions must recognize the possibility of seasonal variations. Soil temperature at 10-cm depth correlated poorly with our measured fluxes; soil redox potential was a more reliable indicator.

Activation of methane by iridium complexes

Abstract: Addition oxydante du methane a un complexe carbonyle de pentamethylcyclopentadienyl-iridium

Methane Oxidation by Nitrosococcus oceanus and Nitrosomonas europaea

Abstract: Chemolithotrophic ammonium-oxidizing and nitrite-oxidizing bacteria including Nitrosomonas europaea, Nitrosococcus oceanus, Nitrobacter sp., Nitiospina gracilis, and Nitrococcus mobilis were examined as to their ability to oxidize methane in the absence of ammonium or nitrite. All ammonium oxidizers tested had the ability to oxidize significant amounts of methane to CO2 and incorporate various amounts into cellular components. None of the nitrite-oxidizing bacteria were capable of methane oxidation. The methane-oxidizing capabilities of Nitrosococcus oceanus and Nitrosomonas europaea were examined with respect to ammonium and methane concentrations, nitrogen source, and pH. The addition of ammonium stimulated both CO2 production and cellular incorporation of methane-carbon by both organisms. Less than 0.1 mM CH4 in solution inhibited the oxidation of ammonium by Nitrosococcus oceanus by 87%. Methane concentrations up to 1.0 mM had no inhibitory effects on ammonium oxidation by Nitrosomonas europaea. In the absence of NH4-N, Nitrosococcus oceanus achieved a maximum methane oxidation rate of 2.20 × 10−2 μmol of CH4 h−1 mg (dry weight) of cells−1, which remained constant as the methane concentration was increased. In the presence of NH4-N (10 ppm [10 μg/ml]), its maximum rate was 26.4 × 10−2 μmol of CH4 h−1 mg (dry weight) of cells−1 at a methane concentration of 1.19 × 10−2 mM. Increasing the methane concentration above this level decreased CO2 production, whereas cellular incorporation of methane-carbon continued to increase. Nitrosomonas europaea showed a linear response throughout the test range, with an activity of 196.0 × 10−2 μmol of CH4 h−1 mg (dry weight) of cells −1 at a methane concentration of 1.38 × 10−1 mM. Both nitrite and nitrate stimulated the oxidation of methane. The pH range was similar to that for ammonium oxidation, but the points of maximum activity were at lower values for the oxidation of methane.

Methane oxidation by Nitrosomonas europaea.

Abstract: Methane inhibited NH4+ utilization by Nitrosomonas europaea with a Ki of 2mM. O2 consumption was not inhibited. In the absence of NH4+, or with hydrazine as reductant, methane caused nearly a doubling in the rate of O2 uptake. The stimulation was abolished by allylthiourea, a sensitive inhibitor of the oxidation of NH4+. Analysis revealed that methanol was being formed in these experiments, with yields approaching 1 mol of methanol per mol of O2 consumed under certain conditions. When cells were incubated with NH4+ under an atmosphere of 50% methane, 50 microM-methanol was generated in 1 h. It is concluded that methane is an alternative substrate for the NH3-oxidizing enzyme (ammonia mono-oxygenase),m albeit with a much lower affinity than for methane mono-oxygenase of methanotrophs.

Effects of reactor severity on the gas-phase pyrolysis of cellulose- and kraft lignin-derived volatile matter

Abstract: Yields of permanent gases evolved by the gas-phase pyrolysis of cellulose- and lignin-derived voltatile matter cannot be correlated with a commonly used kinetic severity function. Instead, engineers explained the dependence of gas yields on temperature and residence time by a global mechanism composed of two competing reactions. The first creates permanent gases by cracking the volatile matter, whereas the second creates refractory condensable materials. For cellulose, the cracking reaction has an apparent activation energy of 49 kcal/g-mol, and the competing reaction 15 kcal/g-mol. The gas-phase cracking of cellulosic volatile matter involves competition between the dehydration (resulting in methane and ethylene formation) and decarboxylation reactions; the fraction of carbon atoms dedicated to carbon monoxide formation by the cracking reaction is not influenced by temperature. For lignin, competition exists between ethylene and carbon dioxide formation; the fraction of carbon atoms dedicated to carbon monoxide and methane formation is not influenced by temperature.

Methane release from Gulf coast wetlands

Abstract: A seasonal study of methane release from adjoining salt, brackish and fresh marsh sediment andthe adjacent open water areas in Louisiana’s Barataria Basin indicates that methane emission isa significant process in the carbon and energy flow of the ecosystem. Methane emission wasinversely related to salinity and sulfate concentration, with methane increasing and salinity andsulfate decreasing with increasing distance from the coast. The annual amounts of methaneevolved were 4.3, 73 and 160 g C m -2 for the salt, brackish and fresh marshes, respectively. Invitro experiments show that methane production is sensitive to the addition of sulfate, highconcentrations (10 mM SO,) inhibiting methane evolution. DOI: 10.1111/j.1600-0889.1983.tb00002.x

Numerical Modeling of Flame Inhibition by CF3Br

Abstract: A numerical model is used to investigate the properties of laminar flames inhibite d by CF3Br. Fuels include hydrogen, methane, methanol, and ethylene, with both oxygen and air as the oxidizers. A detailed chemical kinetic reaction mechanism for the fuel oxidation is combined with a mechanism describing reactions of CF3Br and its halogenated products. The effects of CF3Br on the flammability limits and burning velocity of laminar flames are predicted by the model, and the effects of variations in pressure, unburned gas temperature, and equivalence ratio on inhibition efficiency are examined.

Methanogenesis from methanol and methylamines and acetogenesis from hydrogen and carbon dioxide in the sediments of a eutrophic lake.

Abstract: 14C-tracer techniques were used to examine the metabolism of methanol and methylamines and acetogenesis from hydrogen and carbon dioxide in sediments from the profundal and littoral zones of eutrophic Wintergreen Lake, Michigan. Methanogens were primarily responsible for the metabolism of methanol, monomethylamine, and trimethylamine and maintained the pool size of these substrates below 10 μM in both sediment types. Methanol and methylamines were the precursors for less than 5 and 1%, respectively, of the total methane produced. Methanol and methylamines continued to be metabolized to methane when the sulfate concentration in the sediment was increased to 20 mM. Less than 2% of the total acetate production was derived from carbon dioxide reduction. Hydrogen consumption by hydrogen-oxidizing acetogens was 5% or less of the total hydrogen uptake by acetogens and methanogens. These results, in conjunction with previous studies, emphasize that acetate and hydrogen are the major methane precursors and that methanogens are the predominant hydrogen consumers in the sediments of this eutrophic lake.

Molecular dynamics studies of ice Ic and the structure I clathrate hydrate of methane

Abstract: Computer simulations are used to compare and contrast the dynamical behavior of structure I clathrate hydrates with that of ice Ic (cubic lattices). The calculations are based on recently proposed pairwise additive intermolecular potentials for the water molecules. The phonon densities of states of ice Ic and the hydrates are found to be broadly similar, not withstanding their different crystal structures. This fact explains the similarity of the observed heat capacity and infrared data. In the case of the methane hydrate the simulation predicts a distinct dynamical (localized-mode) behavior for methane molecules trapped in each type of cage. 10 figures, 4 tables.

Spatial and temporal fluctuations of methane production in anoxic coastal marine sediments

Abstract: In vitro rates of net methane production and sulfate reduction were measured at various depths from October 1979 to November 1981 in anoxic coastal marine sediments from Cape Lookout Bight, N.C. In sulfate-rich surface sediments at l-4 cm, calculated methane production rates were within the experimental error of 0.011 mM CH,.d-‘. The depth of maximum methane production rate varied from 7-30 cm from summer to winter with summer maxima at the shallower depth. A maximum rate of 0.305 mM CH,*d-’ was measured at 7-10 cm during July 1981. At intermediate depths low rates of methane production were observed in the presence of low concentrations of dissolved sulfate; however, these rates were near or within experimental error. Integrated rates of sediment column methane production ranged from 20 pmol*m+*hin April to 2,000 in August. These rates compared well with previously measured CH, sedimentwater fluxes measured in sediments from the same field site in 1977. The total methane flux then ranged from 50 to 2,600 pmol CH4.m-2*h-1

Distillative separations of gas mixtures containing methane, carbon dioxide and other components

Abstract: Distillative separations of hydrocarbon feed mixtures containing at least methane and carbon dioxide, as well as other components, such as ethane, higher hydrocarbons, and hydrogen sulfide are disclosed. In the separations described, methane is preferably separated from an acid gas under conditions of composition, temperature and pressure which would normally produce acid gas solids. Acid gas solids are prevented by adding a liquid solids-preventing agent into this distillation column. A second distillation column is subsequently employed to further separate the feed gas mixture. The second distillation column is operated under conditions which an azeotrope would normally form between the light hydrocarbon and carbon dioxide, which azeotrope would limit the carbon dioxide overhead composition. The azeotrope is prevented by introducing an agent for preventing azeotrope formation. Alternatively, the second distillation column may be operated to separate carbon dioxide from hydrogen sulfide. In this case, a liquid agent is added to the second distillation column to increase the relative volatility of carbon dioxide to hydrogen sulfide. All liquid agents preferably comprise a C 3 -C 6 alkane, such as butane, or a mixture of such alkanes.

Hard diamondlike carbon films deposited by ionized deposition of methane gas

Abstract: Very hard diamondlike carbon films have been prepared with the aid of an ionized deposition technique. The growth mechanism of films deposited in the presence of methane gas is discussed. The properties of these carbon films are as follows: The concentration of hydrogen atoms contained in the films is almost negligible. Micro‐Vickers hardness changes depended largely on the deposition conditions, but some of the values obtained were larger than that of sapphire. The 111, 220, and 311 reflections can be observed clearly in the electron diffraction patterns. Moreover the crystal structure obtained from these rings is very close to that of diamond.

Seep oil and gas in gulf of Mexico slope sediment.

Abstract: Concentrations in Gulf of Mexico slope sediment of material soluble in methanol and benzene as high as 4.5 percent are shown to be attributable to biodegraded petroleum. Associated carbonate deposits and organic sulfur are the products of the microbial oxidation of petroleum and sulfate reduction. The results of chemical and carbon isotope analyses indicate that high concentrations of hydrocarbon gases, from methane to pentane, are petroleum rather than microbiologically derived. These hydrocarbons, believed to have been produced thermally at depth, probably reached the surface through faults and fractures associated with salt diapirs.

Upper water column methane geochemistry in the eastern tropical North Pacific1

Abstract: Upper water column (~400 m) profiles of methane, suspended matter, biological indicators, and hydrographic parameters were obtained from nine stations in the eastern tropical North Pacific Ocean. Methane was consistently supersaturated with respect to atmospheric eguilibrium and displayed a subsurface maximum containing about 2-3 times near-surface conccntrations associated with the upper part of the pycnocline. Correlations between methane and the particulate and biological parameters at all nine stations taken together were low, although several stations individually exhibited significant correspondences. The methane distribution was largely controlled by physical oceanographic processes, Microbial activity associated with suspended particles, possibly recycled by repetitive zooplankton grazing, is believed most likely responsible for the excess methane.

An exploratory study of the thermal conductivity of methane hydrate

Abstract: Recent discoveries of natural gas hydrates in permafrost and sub-oceanic environments have led us to measure the thermal conductivity of methane hydrate. A guarded hot-plate cell was constructed and tested with various ice specimens. We find the conductivity of methane hydrate near −60°C is 0.45 W/mK, a value close to that obtained for other clathrate hydrates by us and others. It is much lower than for ice (by a factor of about 5), so that a logging tool based on this property should prove to be of use in identification of gas hydrates in permafrost zones.

Method of separating acid gases, particularly carbon dioxide, from methane by the addition of a light gas such as helium

Abstract: A method of separating acid gases, particularly carbon dioxide, from methane by cryogenic distillation. The method includes the step of adding helium to the stream to be separated to increase the critical pressure of the methane-carbon dioxide present. The cryogenic distillation tower may then be operated at a higher pressure and without the formation of solid carbon dioxide.

Mass spectrometric measurements of methane and oxygen utilization by methanotrophic bacteria

Abstract: A mass spectrometer with membrane inlet was used to measure methane and oxygen utilization rates at various methane concentrations in Methylosinus trichosporium and a locally isolated strain of a methane-oxidizing coccus (OU-4-1). The apparent Km for methane was found to be 2 μM for M. trichosporium and 0.8 μM for strain OU-4-1. These Km-values are 10–30 times lower than most previously reported values. The ratio of oxygen to methane utilization rates was 1.7 for M. trichosporium and 1.5 for strain OU-4-1 corresponding to a growth yield of 0.38 and 0.63 g dry weight/g methane, respectively.