Showing papers on "Methane published in 1990"
TL;DR: In this article, an index of global warming potential for methane, carbon monoxide, nitrous oxide, chlorofluorocarbons and CFCs relative to that of carbon dioxide was proposed.
Abstract: IN the past few years, many workers have noted that the combined effect on climate of increases in the concentrations of a large number of trace gases could rival or even exceed that of the increasing concentration of carbon dioxide1–3. These trace gases, principally methane, nitrous oxide and chlorofluorocarbons, are present at concentrations that are two to six orders of magnitude lower than that of carbon dioxide, but are important because, per molecule, they absorb infrared radiation much more strongly than carbon dioxide. Indeed a recent study4 shows that trace gases are responsible for 43% of the increase in radiative forcing from 1980 to 1990 (Fig. 1). An index to compare the contribution of various 'greenhouse' gas emissions to global warming is needed to develop cost-effective strategies for limiting this warming. Estimates of relative contributions to additional greenhouse forcing during particular periods do not fully take into account differences in atmospheric residence times among the important greenhouse gases. Here we extend recent work on halocarbons5,6 by proposing an index of global warming potential for methane, carbon monoxide, nitrous oxide and CFCs relative to that of carbon dioxide. We find, for example, that methane has, per mole, a global warming potential 3.7 times that of carbon dioxide. On this basis, carbon dioxide emissions account for 80% of the contribution to global warming of current greenhouse gas emissions, as compared with 57% of the increase in radiative forcing for the 1980s.
1,332 citations
TL;DR: A rough analysis based on the use of currently accepted values shows that natural gas is preferable to other fossil fuels in consideration of the greenhouse effect as long as its leakage can be limited to 3 to 6 percent.
Abstract: The current concern about an anthropogenic impact on global climate has made it of interest to compare the potential effect of various human activities. A case in point is the comparison between the emission of greenhouse gases from the use of natural gas and that from other fossil fuels. This comparison requires an evaluation of the effect of methane emissions relative to that of carbon dioxide emissions. A rough analysis based on the use of currently accepted values shows that natural gas is preferable to other fossil fuels in consideration of the greenhouse effect as long as its leakage can be limited to 3 to 6 percent.
779 citations
TL;DR: In this article, it was shown that the partial oxidation of methane to synthesis gas can be carried out at temperatures of only ∼775 °C by using lanthanide ruthenium oxide catalysts.
Abstract: THE diminishing reserves of petroleum oil have focused attention on the possibility of making more efficient use of natural gas, reserves of which are at present considerably under-utilized. Methane is commonly used as a fuel, but it is also the starting material for the production, by steam reforming, of synthesis gas (carbon monoxide and hydrogen), which acts as a feedstock for the synthesis of ammonia and methanol, and can be converted to higher hydrocarbons, alcohols and aldehydes by Fischer–Tropsch catalysis1. The partial oxidation of methane to synthesis gas is also an established industrial process2 but operates at very high temperatures (> 1,200 °C). Here we report that this reaction can be carried out at temperatures of only ∼775 °C by using lanthanide ruthenium oxide catalysts.
591 citations
TL;DR: In this article, a model was constructed for conversion in a pellet by incorporating both the reverse reaction and the effect of external and internal diffusion, and the model was expanded to a large-scale packed bed with appropriate heat transfer parameters.
475 citations
TL;DR: In this article, the Vostok ice core has been used to reveal substantial changes over the past 160,000 years which are associated with climate fluctuations and also show that methane has probably contributed, like carbon dioxide, to glacial-interglacial temperature changes.
Abstract: Methane measurements along the Vostok ice core reveal substantial changes over the past 160,000 years which are associated with climate fluctuations. These results point to changes in sources of methane and also show that methane has probably contributed, like carbon dioxide, to glacial-interglacial temperature changes.
436 citations
TL;DR: In this article, a four-phase description of refuse decomposition with leachate recycle, including an aerobic phase, an anaerobic acid phase, accelerated methane production phase, and a decelerated production phase is proposed.
Abstract: Methane is recovered from about 100 municipal solid waste landfills in the U.S. in saleable volumes, although yields are 1 to 50% of the methane potential of refuse based on biodegradability data. Studies on the microbiology of refuse decomposition and efforts to enhance refuse methanogenesis are reviewed here. Results of studies on the effects of leachate recycle and neutralization, a reduction in refuse particle size, the addition of anaerobic sewage sludge or old refuse as a seed, nutrient addition, calcium carbonate addition, and moisture on methane production are examined in consideration of new findings on landfill microbiology. A four‐phase description of refuse decomposition with leachate recycle, including an aerobic phase, an anaerobic acid phase, an accelerated methane production phase, and a decelerated methane production phase, is proposed. Mass balances and pumping tests may be used to estimate the methane potential of a sanitary landfill. The use of empirical, zero, and first‐order models t...
379 citations
TL;DR: In this article, the authors investigated the relationship between the coal matrix shrinkage and the gas flow path in coalbeds and found that the coal volume shrinks by ≈ 0.4% when the gas pressure falls from 6.9 MPa to atmospheric pressure.
366 citations
TL;DR: In this paper, the flux of methane into the soil is calculated from the concentration gradient at the soil surface, which indicates that the methane flux is mainly controlled by the transport resistance in the soil rather than by the potential microbial decomposition rate.
Abstract: Quasi-continuous observations of the methane concentration in aerated soils of the temperate zone are presented. The flux of methane into the soil is calculated from the concentration gradient at the soil surface. Depending on the permeability of methane in soil air at an individual site, yearly mean uptake rates between 0.09 and 1.3 g CH 4 m -2 yr -1 have been observed in temperate forest soils. The methane flux from the atmosphere into the soil shows only a weak seasonality with an about 50% higher uptake rate in the summer than in the winter months. This indicates that the methane flux into the soil is mainly controlled by the transport resistance in the soil rather than by the potential microbial decomposition rate. DOI: 10.1034/j.1600-0889.1990.00002.x
350 citations
TL;DR: Rice roots could absorb methane gas in the gas phase without water uptake, suggesting that methane dissolved in the soil water surrounding the roots diffuses into the cell-wall water of the root cells, gasifies in the root cortex, and then is mostly released through the micropores in the leaf sheaths.
Abstract: To clarify the mechanisms of methane transport from the rhizosphere into the atmosphere through rice plants (Oryza sativa L.), the methane emission rate was measured from a shoot whose roots had been kept in a culture solution with a high methane concentration or exposed to methane gas in the gas phase by using a cylindrical chamber. No clear correlation was observed between change in the transpiration rate and that in the methane emission rate. Methane was mostly released from the culm, which is an aggregation of leaf sheaths, but not from the leaf blade. Micropores which are different from stomata were newly found at the abaxial epidermis of the leaf sheath by scanning electron microscopy. The measured methane emission rate was much higher than the calculated methane emission rate that would result from transpiration and the methane concentration in the culture solution. Rice roots could absorb methane gas in the gas phase without water uptake. These results suggest that methane dissolved in the soil water surrounding the roots diffuses into the cell-wall water of the root cells, gasifies in the root cortex, and then is mostly released through the micropores in the leaf sheaths.
346 citations
TL;DR: In this paper, the results of field and laboratory experiments on methane consumption by tundra soils are reported and it is concluded that lowering of the water table as a resulting from a warmer, drier climate will decrease methane fluxes and could cause these areas to provide negative feedback for atmospheric methane.
Abstract: The results of field and laboratory experiments on methane consumption by tundra soils are reported. For methane concentrations ranging from below to well above ambient, moist soils are found to consume methane rapidly; in nonwaterlogged soils, equilibration with atmospheric methane is fast relative to microbial oxidation. It is concluded that lowering of the water table in tundra as a resulting from a warmer, drier climate will decrease methane fluxes and could cause these areas to provide negative feedback for atmospheric methane.
341 citations
TL;DR: In this article, it was found that Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium.
Abstract: Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (∼92%) is obtained with a 4∶2∶1 N2∶CH4∶O2 ratio at 1050 K and atmospheric pressure, with a space velocity of 4×104 hour−1.
TL;DR: In this article, the authors investigated the process of methane production and emission in rice fields at the Texas A&M University Agricultural Research and Extension Center, Beaumont, Texas, during the summer of 1989.
Abstract: To refine estimates of source strengths from agricultural wetlands and to study the process of methane production and emission, this study was carried out in rice fields at the Texas A&M University Agricultural Research and Extension Center, Beaumont, Texas, during the summer of 1989. It focussed on two fields on different soil types (Lake Charles clay and Beaumont clay) and spanned a period from shortly after permanent field flooding (June 6, 1989) until field draining prior to harvest (August 28, 1989). Integrated methane emission over 75 days ranged from 4.5 to 15.9 g m−2 . Aboveground biomass, net primary production, and root biomass were determined. Methane emission was strongly related to aboveground biomass in one of two fields studied. Laboratory incubations of soil cores show that methane production by soil bacteria is highest near the soil surface in the rice row and decreases with depth and distance from the plant. Much of the seasonal increase in total methane production is due to increasing activity at intermediate depths and distances from the plants. The temporal and spatial distribution of methane production was found to be related to root biomass. Seasonally integrated emission was 42% of methane production in both fields. Soil pore water methane and plant stem gas composition are related to the distribution in the soil of methane production and root biomass. Methane production ceased with field draining prior to harvest, even following prolonged anaerobic incubation. Methanogenesis rapidly resumed with added acetate substrate.
TL;DR: In this paper, the authors estimate that about 11,000 Gt of carbon is stored in clathrates under permafrost regions and about 400 Gt under ocean sediments.
Abstract: Methane clathrates are stable at depths greater than about 200 m in permafrost regions and in ocean sediments at water depths greater than about 250 m, provided bottom waters are sufficiently cold. The thickness of the clathrate stability zone depends on surface temperature and geothermal gradient. Average stability zone thickness is about 400 m in cold regions where average surface temperatures are below freezing, 500 m in ocean sediments, and up to 1,500 m in regions of very cold surface temperature (<-15 °C) or in the deep ocean. The concentration of methane relative to water within the zone of stability determines whether or not clathrate will actually occur. The geologic setting of clathrate occurrences, the isotopic composition of the methane, and the methane to ethane plus propane ratio in both the clathrates and the associated pore fluids indicate that methane in clathrates is produced chiefly by anaerobic bacteria. Methane occurrences and the organic carbon content of sediments are the bases used to estimate the amount of carbon currently stored as clathrates. The estimate of about 11,000 Gt of carbon for ocean sediments, and about 400 Gt for sediments under permafrost regions is in rough accord with an independent estimate by Kvenvolden of 10,000 Gt. The shallowness of the clathrate zone of stability makes clathrates vulnerable to surface disturbances. Warming by ocean flooding of exposed continental shelf, and changes in pressure at depth, caused, for example, by sea-level drop, destabilize clathrates under the ocean, while ice-cap growth stabilizes clathrates under the ice cap. The time scale for thermal destabilization is set by the thermal properties of sediments and is on the order of thousands of years. The time required to fix methane in clathrates as a result of surface cooling is much longer, requiring several tens of thousands of years. The sensitivity of clathrates to surface change, the time scales involved, and the large quantities of carbon stored as clathrate indicate that clathrates may have played a significant role in modifying the composition of the atmosphere during the ice ages. The release of methane and its subsequent oxidation to carbon dioxide may be responsible for the observed swings in atmospheric methane and carbon dioxide concentrations during glacial times. Because methane and carbon dioxide are strong infrared absorbers, the release and trapping of methane by clathrates contribute strong feedback mechanisms to the radiative forcing of climate that results from earth's orbital variations.
TL;DR: Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen.
Abstract: Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of kLa, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen.
TL;DR: In this article, it has been shown that at high temperatures, at atmospheric pressure and at temperatures in excess of 650°C, combined ethane and ethylene (C2) yields of 20% have been achieved.
TL;DR: High atmospheric CO/CO2 ratios are possible if either: the climate was cool (like today's climate), so that hydration of dissolved CO to formate was slow, or the formate formed from CO was efficiently converted into volatile, reduced carbon compounds, such as methane.
Abstract: A one-dimensional photochemical model was used to examine the effect of bolide impacts on the oxidation state of Earth's primitive atmosphere. The impact rate should have been high prior to 3.8 Ga before present, based on evidence derived from the Moon. Impacts of comets or carbonaceous asteroids should have enhanced the atmospheric CO/CO2 ratio by bringing in CO ice and/or organic carbon that can be oxidized to CO in the impact plume. Ordinary chondritic impactors would contain elemental iron that could have reacted with ambient CO2 to give CO. Nitric oxide (NO) should also have been produced by reaction between ambient CO2 and N2 in the hot impact plumes. High NO concentrations increase the atmospheric CO/CO2 ratio by increasing the rainout rate of oxidized gases. According to the model, atmospheric CO/CO2 ratios of unity or greater are possible during the first several hundred million years of Earth's history, provided that dissolved CO was not rapidly oxidized to bicarbonate in the ocean. Specifically, high atmospheric CO/CO2 ratios are possible if either: (1) the climate was cool (like today's climate), so that hydration of dissolved CO to formate was slow, or (2) the formate formed from CO was efficiently converted into volatile, reduced carbon compounds, such as methane. A high atmospheric CO/CO2 ratio may have helped to facilitate prebiotic synthesis by enhancing the production rates of hydrogen cyanide and formaldehyde. Formaldehyde may have been produced even more efficiently by photochemical reduction of bicarbonate and formate in Fe(++)-rich surface waters.
TL;DR: Les mesures des donnees d'equilibre de phases sont effectuees a 313.4 and 333.4 K a l'aide d'un nouvel appareil statique as discussed by the authors.
Abstract: Les mesures des donnees d'equilibre de phases sont effectuees a 313.4 et 333.4 K a l'aide d'un nouvel appareil statique. L'appareillage est presente
TL;DR: In this paper, a steam reforming of methane was carried out in a reactor incorporating a hydrogen-permeable membrane, which consisted of a thin palladium film supported on a porous glass cylinder.
TL;DR: A series of palladium on alumina catalysts were prepared and tested for methane oxidation at 300°C, 50 Torr methane, 110 Torr oxygen, 900 Torr helium, and conversions less than 2%.
TL;DR: A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs.
Abstract: A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs. Rates of string. Emission rates from the 2 swamp sites were lower (< 20 mg CH4 m−2 d−1 ), except during the spring thaw and when the sites were saturated. The low water table ( < 80 cm depth) in abnormally dry years reduced emission rates; rates were also low from a swamp site which had been drained and cleared of vegetation for horticulture. Methane emission rates were also low (< 5 mg CH4 m−2 d−1) from 2 ombrotrophic bog sites. Laboratory measurements of rates of methane production under anaerobic conditions and methane consumption under aerobic conditions revealed that production rates were generally highest in the surface layers (0 to 2.5 cm depth); production was high in the fens and very low in the bogs. The swamp samples were able to produce methane under anaerobic conditions, but were also able to consume methane under aerobic conditions. Annual methane emission rates are estimated to be 1 to 10 g CH4 m−2 from the fens, 1 to 4 g CH4 m−2 from the swamps and <0.2 g CH4 m−2 from the bogs and drained swamp.
TL;DR: In this paper, seven lignocellulosic materials: corn stover, napier grass, wood grass, newspaper, white fir and wheat straw from two different crops; two pure cellulosics: Solka Floc BW200 and Whatman No 5 filter paper; and glucose, propionic and acetic acids were subjected to long-term batch methane fermentation.
TL;DR: In this paper, the authors investigated the methane oxidation activity and structure of a number of complex metal oxides with the objective of determining the relationship between catalytic and such solid-state parameters as the type of transition metal cation incorporated in the oxide crystal structure, the metalcation valence state, oxygen stoichiometry, and defect structure.
TL;DR: In this paper, in situ measurements of soil methane consumption in a moist forest area of central Panama indicate that the conversion of forests to agricultural lands diminishes the soil sink for atmospheric methane.
Abstract: Laboratory and in situ measurements of soil methane consumption in a moist forest area of central Panama indicate that the conversion of forests to agricultural lands diminishes the soil sink for atmospheric methane. Rates of microbial methane consumption in agricultural soils were one fourth those of undisturbed forest soils. This reduction in soil methane consumption may partially account for past and future increases in atmospheric methane concentrations.
TL;DR: In this paper, the magnitude of natural gas reservoirs and fluxes are put into perspective and some recent geochemical enigmas are presented for both the adventurous and skeptics, as well as artifacts such as hydrocarbons generated during drilling or analysis, and sampling contamination/alteration.
TL;DR: In this article, the distribution of gas in the hydrate and the liquid phases for two-phase systems was calculated as a function of hydrostatic pressure, and it was found that at hydrostatic pressures higher than the three-phase hydrate-liquid-gas equilibrium pressure, a two phase hydrate liquid equilibrium exists, in which the hydrates of increasingly higher cage occupancy are obtained at the expense of converting a small amount of hydrate to ice.
Abstract: The distribution of gas in the hydrate and the liquid phases for the two-phase systems methane hydrate-water and methane hydrate-seawater has been calculated as a function of hydrostatic pressure. It is found that at hydrostatic pressures higher than the three-phase hydrate-liquid-gas equilibrium pressure, a two-phase hydrate-liquid equilibrium exists in which the hydrate phase is increasingly enriched in and the liquid phase depleted of the gas as the hydrostatic pressure increases. At higher pressures, the methane content of water necessary to form and to stabilize the hydrate is much less than required for saturation with respect to the gas phase. Similar results are obtained for the methane hydrate-ice system where, at hydrostatic pressures above the three-phase hydrate-ice-gas equilibrium pressure, hydrates of increasingly higher cage occupancy are obtained at the expense of converting a small amount of hydrate to ice.
TL;DR: In this paper, nonlocal density functional theory and grand canonical Monte Carlo simulations are used to investigate the adsorption behavior of gases of simple spherical molecules in model carbon micropores at temperatures above the critical value for the gas.
Abstract: Nonlocal density functional theory and grand canonical Monte Carlo simulations are used to investigate the adsorption behavior of gases of simple spherical molecules in model carbon micropores at temperatures above the critical value for the gas. In most of the calculations the parameters are chosen to model methane as the adsorbed gas, but some calculations are reported for a model of ethylene. The excess adsorption isotherms (which measure the increased density in the pore, relative to that of the bulk fluid) show a maximum at a particular value of the bulk gas density (pressure). Near the capillary critical temperature these maxima have a cusplike nature, similar to that observed experimentally
TL;DR: In this article, the reaction of the hydroxyl radical (HO) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere through the use of carbon isotope measurements.
Abstract: The reaction of the hydroxyl radical (HO) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The measued ratio of the rate coefficients for reaction with (C-12)H4 relative to (C-13)H4 (k12/k13) was 1.0054 (+ or - 0.0009 at the 95 percent confidence interval), independent of temperature within the precision of the measurement, over the range studied. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere through the use of carbon isotope measurements.
TL;DR: The data collectively support the notion that the distribution and activity of methane oxidation have a major impact on the magnitude of atmospheric fluxes from the Everglades.
Abstract: Rates of methane emission from intact cores were measured during anoxic dark and oxic light and dark incubations. Rates of methane oxidation were calculated on the basis of oxic incubations by using the anoxic emissions as an estimate of the maximum potential flux. This technique indicated that methane oxidation consumed up to 91% of the maximum potential flux in peat sediments but that oxidation was negligible in marl sediments. Oxygen microprofiles determined for intact cores were comparable to profiles measured in situ. Thus, the laboratory incubations appeared to provide a reasonable approximation of in situ activities. This was further supported by the agreement between measured methane fluxes and fluxes predicted on the basis of methane profiles determined by in situ sampling of pore water. Methane emissions from peat sediments, oxygen concentrations and penetration depths, and methane concentration profiles were all sensitive to light-dark shifts as determined by a combination of field and laboratory analyses. Methane emissions were lower and oxygen concentrations and penetration depths were higher under illuminated than under dark conditions; the profiles of methane concentration changed in correspondence to the changes in oxygen profiles, but the estimated flux of methane into the oxic zone changed negligibly. Sediment-free, root-associated methane oxidation showed a pattern similar to that for methane oxidation in the core analyses: no oxidation was detected for roots growing in marl sediment, even for roots of Cladium jamaicense, which had the highest activity for samples from peat sediments. The magnitude of the root-associated oxidation rates indicated that belowground plant surfaces may not markedly increase the total capacity for methane consumption. However, the data collectively support the notion that the distribution and activity of methane oxidation have a major impact on the magnitude of atmospheric fluxes from the Everglades.