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Showing papers on "Methane published in 2001"


Journal ArticleDOI
TL;DR: In this article, the anaerobic zones of submerged soils by methanogens and methanotrophs are oxidised into CO2 in the aerobic zones of wetland soils and in upland soils.

1,743 citations


Journal ArticleDOI
TL;DR: In this article, an extensive literature review of the three main groups of catalysts, which have been evaluated for the elimination of these hydrocarbons, are dolomite, alkali metals and nickel.

1,126 citations


Journal ArticleDOI
TL;DR: In this article, a review of the conversion of methanol, methane, propane, and octane to hydrogen is presented, and it is shown that indirect partial oxidation is the preferred process for all fuels.
Abstract: Increasingly stringent legislation controls emissions from internal combustion engines to the point where alternative power sources for vehicles are necessary. The hydrogen fuel cell is one promising option, but the nature of the gas is such that the conversion of other fuels to hydrogen on board the vehicle is necessary. The conversion of methanol, methane, propane, and octane to hydrogen is reviewed. A combination of oxidation and steam reforming (indirect partial oxidation) or direct partial oxidation are the most promising processes. Indirect partial oxidation involves combustion of part of the fuel to produce sufficient heat to drive the endothermic steam reforming reaction. Direct partial oxidation is favored only at high temperatures and short residence times but is highly selective. However, indirect partial oxidation is shown to be the preferred process for all fuels. The product gases can be taken through a water–gas shift reactor, but still retain ∼2% carbon monoxide, which poisons fuel-cell ca...

563 citations


Journal ArticleDOI
TL;DR: Different aspects of catalysis by the MMO proteins are examined, including the mechanisms of dioxygen activation at the diiron site and substrate hydroxylation by the activated oxygen species.
Abstract: Methanotrophic bacteria are capable of using methane as their sole source of carbon and energy. The first step in methane metabolism, the oxidation of methane to methanol, is catalyzed by a fascinating enzyme system called methane monooxygenase (MMO). The selective oxidation of the very stable C-H bond in methane under ambient conditions is a remarkable feat that has not yet been repeated by synthetic catalysts and has attracted considerable scientific and commercial interest. The best studied MMO is a complex enzyme system that consists of three soluble protein components, all of which are required for efficient catalysis. Dioxygen activation and subsequent methane hydroxylation are catalyzed by a hydroxylase enzyme that contains a non-heme diiron site. A reductase protein accepts electrons from NADH and transfers them to the hydroxylase where they are used for the reductive activation of O(2). The third protein component couples electron and dioxygen consumption with methane oxidation. In this review we examine different aspects of catalysis by the MMO proteins, including the mechanisms of dioxygen activation at the diiron site and substrate hydroxylation by the activated oxygen species. We also discuss the role of complex formation between the different protein components in regulating various aspects of catalysis.

555 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the kinetics of the methane steam reforming, accompanied by the reverse water gas shift reaction over a commercial Ni/α-Al2O3 catalyst in an integral reactor under conditions of no diffusion limitation.

543 citations


Journal ArticleDOI
TL;DR: In this article, anaerobic digestion of energy crops and organic wastes is used to produce a clean fuel from renewable feedstocks, which would replace fossil fuel-derived energy and reduce environmental impacts including global warming and acid rain.

491 citations


Journal ArticleDOI
03 Aug 2001-Science
TL;DR: Expected irreversible oxidation (∼1012 to 1013 moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized.
Abstract: The low O2 content of the Archean atmosphere implies that methane should have been present at levels ∼102 to 103 parts per million volume (ppmv) (compared with 1.7 ppmv today) given a plausible biogenic source. CH4 is favored as the greenhouse gas that countered the lower luminosity of the early Sun. But abundant CH4 implies that hydrogen escapes to space (↑space) orders of magnitude faster than today. Such reductant loss oxidizes the Earth. Photosynthesis splits water into O2 and H, and methanogenesis transfers the H into CH4. Hydrogen escape after CH4 photolysis, therefore, causes a net gain of oxygen [CO2 + 2H2O → CH4 + 2O2 → CO2 + O2 + 4H(↑space)]. Expected irreversible oxidation (∼1012 to 1013 moles oxygen per year) may help explain how Earth9s surface environment became irreversibly oxidized.

459 citations


Journal ArticleDOI
TL;DR: In this paper, the pore pressure at isothermal conditions between 242 and 271 K preserves up to 93% of the hydrate for at least 24 h, reflecting the greatly suppressed rates of dissociation that characterize this regime.
Abstract: Direct measurement of decomposition rates of pure, polycrystalline methane hydrate reveals a thermal regime where methane hydrate metastably “preserves” in bulk by as much as 75 K above its nominal equilibrium temperature (193 K at 1 atm). Rapid release of the sample pore pressure at isothermal conditions between 242 and 271 K preserves up to 93% of the hydrate for at least 24 h, reflecting the greatly suppressed rates of dissociation that characterize this regime. Subsequent warming through the H2O ice point then induces rapid and complete dissociation, allowing controlled recovery of the total expected gas yield. This behavior is in marked contrast to that exhibited by methane hydrate at both colder (193−240 K) and warmer (272−290 K) test conditions, where dissociation rates increase monotonically with increasing temperature. Anomalous preservation has potential application for successful retrieval of natural gas hydrate or hydrate-bearing sediments from remote settings, as well as for temporary low-pre...

420 citations


Journal ArticleDOI
01 Nov 2001-Tellus B
TL;DR: In this article, the atmospheric global warming potential of methane (GWP M ) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near-subtropics.
Abstract: Carbon fixation under wetland anaerobic soil conditions provides unique conditions for long-term storage of carbon into histosols. However, this carbon sequestration process is intimately linked to methane emission from wetlands. The potential contribution of this emitted methane to the greenhouse effect can be mitigated by the removal of atmospheric CO 2 and storage into peat. The balance of CH 4 and CO 2 exchange can provide an index of a wetland's greenhouse gas (carbon) contribution to the atmosphere. Here, we relate the atmospheric global warming potential of methane (GWP M ) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near-subtropics. This relationship permits one to determine the greenhouse carbon balance of wetlands by their contribution to or attenuation of the greenhouse effect via CH 4 emission or CO 2 sink, respectively. We report annual measurements of the relationship between methane emission and net carbon fixation in three wetland ecosystems. The ratio of methane released to annual net carbon fixed varies from 0.05 to 0.20 on a molar basis. Although these wetlands function as a sink for CO 2 , the 21.8-fold greater infrared absorptivity of CH 4 relative to CO 2 (GWP M ) over a relatively short time horizon (20 years) would indicate that the release of methane still contributes to the overall greenhouse effect. As GWP M decreases over longer time horizons (100 years), our analyses suggest that the subtropical and temperate wetlands attenuate global warming, and northern wetlands may be perched on the “greenhouse compensation” point. Considering a 500-year time horizon, these wetlands can be regarded as sinks for greenhouse gas warming potential, and thus attenuate the greenhouse warming of the atmosphere. DOI: 10.1034/j.1600-0889.2001.530501.x

414 citations


Journal ArticleDOI
01 Oct 2001-Fuel
TL;DR: In this paper, the feasibility of using Fe 2 O 3 as an oxygen carrier has been investigated in a fixed bed quartz reactor, where the iron oxide was exposed to repeated cycles of air and methane at 950 ° C, with the outlet gas concentrations measured.

404 citations


Journal ArticleDOI
TL;DR: In this article, the results of a one-cylinder CFR engine test with mixtures of hydrogen in methane of 0, 20, 40 and 60% by volume were presented.

Journal ArticleDOI
01 Sep 2001-Geology
TL;DR: In this paper, gas hydrates were observed to form within the center of pore spaces, rather than on grain surfaces, and clathrates formed from a soluble liquid hydrate former (tetrahydrofuran, C 4 H 8 O), from free gas (CH 4 ), and from dissolved gas (CO 2 ).
Abstract: Visual observation of gas hydrates at the microscopic scale in synthetic porous media provides unequivocal visual evidence that clathrates can form in systems without the presence of a free-gas phase. Hydrates were formed from a soluble liquid hydrate former (tetrahydrofuran, C 4 H 8 O), from free gas (CH 4 ), and from dissolved gas (CO 2 ). Clathrates were found to form within the center of pore spaces, rather than on grain surfaces. Cementation of grains only occurred in regions of a small grain size, or where a large proportion of pore space was filled with hydrate. However, even at high clathrate saturations, a thin film of free water persisted on grain surfaces. The results have important implications for the potential cementing effect of hydrates on sediments, and thus for sediment permeability, slope stability, and seismic interpretation of hydrate-bearing sediments.

Journal ArticleDOI
TL;DR: In this article, an experimental study of the reaction of dissolved CO2 in the presence of olivine under hydrothermal conditions (300°C, 350 bar) was conducted, and the results indicated that the potential for abiotic formation of hydrocarbons during serpentinization may be much more limited than previously believed.

Journal ArticleDOI
TL;DR: In this paper, a single-step decomposition of methane and other hydrocarbons over carbon-based catalysts in an air/water free environment is discussed, where clean carbon is produced as a valuable byproduct of the process.

Journal ArticleDOI
05 Apr 2001-Nature
TL;DR: In this article, the authors report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behavior of methane hydrate at pressures up to 10 GPa.
Abstract: Methane hydrate is thought to have been the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons formed. It accordingly plays an important role in formation models of Titan, Saturn's largest moon. Current understanding assumes that methane hydrate dissociates into ice and free methane in the pressure range 1-2 GPa (10-20 kbar), consistent with some theoretical and experimental studies. But such pressure-induced dissociation would have led to the early loss of methane from Titan's interior to its atmosphere, where it would rapidly have been destroyed by photochemical processes. This is difficult to reconcile with the observed presence of significant amounts of methane in Titan's present atmosphere. Here we report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behaviour of methane hydrate at pressures up to 10 GPa. We find structural transitions at about 1 and 2 GPa to new hydrate phases which remain stable to at least 10 GPa. This implies that the methane in the primordial core of Titan remained in stable hydrate phases throughout differentiation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mantle. This layer is a plausible source for the continuing replenishment of Titan's atmospheric methane.

Journal ArticleDOI
TL;DR: In this article, the role of water column methanotrophy (microbial methane oxidation) as a control on methane release was quantified by measuring water column methane profiles (concentration and δ13C) and oxidation rates at eight stations in an area of active methane venting in the Eel River Basin, off the coast of northern California.

Journal ArticleDOI
TL;DR: In this article, the authors presented results for the catalytic decomposition of undiluted methane into hydrogen and carbon using nanoscale, binary, Fe−M (M = Pd, Mo, or Ni) catalysts supported on alumina.
Abstract: Traditionally, hydrogen is produced by reforming or partial oxidation of methane to produce synthesis gas, followed by the water-gas shift reaction to convert CO to CO2 and produce more hydrogen, followed in turn by a purification or separation procedure. This paper presents results for the catalytic decomposition of undiluted methane into hydrogen and carbon using nanoscale, binary, Fe−M (M = Pd, Mo, or Ni) catalysts supported on alumina. All of the supported Fe−M binary catalysts reduced methane decomposition temperature by 400−500 °C relative to noncatalytic thermal decomposition and exhibited significantly higher activity than Fe or any of the secondary metals (Pd, Mo, and Ni) supported on alumina alone. At reaction temperatures of approximately 700−800 °C and space velocities of 600 mL g-1 h-1, the product stream was comprised of over 80 volume % of hydrogen, with the balance being unconverted methane. No CO, CO2, or C2 and higher hydrocarbons were observed in the product gas. High-resolution SEM and...

Journal ArticleDOI
TL;DR: In this article, a process-based model that derives methane emissions from natural wetlands as a function of soil temperature, water table, and net primary productivity is used to investigate the response of methane emissions of natural wetlands to climate variations, and the sensitivity of the hydrologic model to changes in precipitation is examined.
Abstract: Methane is an important greenhouse gas which contributes about 22% to the present greenhouse effect. Natural wetlands currently constitute the biggest methane source and were the major source in preindustrial times. Wetland emissions depend highly on the climate, i.e., on soil temperature and water table. To investigate the response of methane emissions from natural wetlands to climate variations, a process-based model that derives methane emissions from natural wetlands as a function of soil temperature, water table, and net primary productivity is used. For its application on the global scale, global data sets for all model parameters are generated. In addition, a simple hydrologic model is developed in order to simulate the position of the water table in wetlands. The hydrologic model is tested against data from different wetland sites, and the sensitivity of the hydrologic model to changes in precipitation is examined. The global methane- hydrology model constitutes a tool to study temporal and spatial variations in methane emissions from natural wetlands. The model is applied using high-frequency atmospheric forcing fields from ECMWF reanalyses of the period from 1982 to 1993. We calculate global annual methane emissions from wetlands to be 260 Tg yr -. Twenty-five percent of these methane emissions originate from wetlands north of 30oN. Only 60% of the produced methane is emitted, while the rest is reoxidized. A comparison of zonal integrals of simulated global wetland emissions and results obtained by an inverse modeling approach shows good agreement. In a test with data from two wetlands the seasonality of simulated and observed methane emissions agrees well.

Journal ArticleDOI
TL;DR: In this paper, the authors measured in situ CH4 emission and CH4 oxidation in an Italian rice field in 1998 and 1999, and studied CH4 production in soil and root samples.
Abstract: Summary Irrigated rice fields are an important source of atmospheric methane. In order to improve our understanding of the controlling processes, we measured in situ CH4 emission and CH4 oxidation in an Italian rice field in 1998 and 1999, and studied CH4 production in soil and root samples. The CH4 emission rates were correlated with diurnal temperature variations and showed pronounced seasonal and interannual variations. The contribution of CH4 oxidation to total CH4 flux, determined by specific inhibition with difluoromethane, decreased from 40% at the beginning to zero at the end of the season. The stable carbon isotopic composition of the emitted CH4 also decreased. The CH4-oxidizing bacteria probably became limited by nitrogen as indicated by the seasonal decrease of NH4+. Thus, CH4 oxidation had little effect on CH4 emission. Methane production on rice roots was relatively constant over the season. Methane production in soil slowly increased after flooding and was highest in the middle of the season. Pore water concentrations of CH4 showed a similar seasonal pattern. In 1999, CH4 production increased later in the season and reached lower rates than in 1998. An additional drainage in 1999 resulted in higher ferric iron concentrations, higher soil redox potentials and lower acetate concentrations. As a result, acetate-utilizing methanogens were probably out-competed by iron-reducers so that a larger percentage of [2–14C]acetate was converted to 14CO2 instead of 14CH4. The residual CH4 production was relatively low and was mainly due to H2/CO2-dependent methanogenesis. Experiments with radioactive bicarbonate and with methyl fluoride as specific inhibitor showed that the theoretical ratio of 7:3 of methanogenesis from acetate vs. H2/CO2 was only reached later in the season when total CH4 production was at the maximum. In conclusion, our results give a mechanistic explanation for the intraseasonal and interannual differences in CH4 emission.

Journal ArticleDOI
01 Aug 2001
TL;DR: In this paper, the authors measured sulfate reduction rates with SO, and the rates were compared with results of two fusion-reaction models, and the results showed that, even in these non-bioirrigated sediments without sul"de reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface.
Abstract: Beyond the shelf break at ca. 150 mwater depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate}methane transition at 2} 4m depth. Sulfate reduction rates were measured experimentally with SO , and the rates were compared with results of two di!usion-reaction models. The results showed that, even in these non-bioirrigated sediments without sul"de reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface. A hybrid modeling approach, in which experimentally measured rates in the upper sediment layers force a model that includes also the deeper layers, probably provides the most realistic estimate of sulfate reduction rates. Areal rates of sulfate reduction were 0.65}1.43 mmol SO m d, highest in sediments just below the chemocline. Anaerobic methane oxidation accounted for 7}11% of the total sulfate reduction in slope and deep-sea sediments. Although this methane-driven sulfate reduction shaped the entire sulfate gradient, it was only equivalent to the sulfate reduction in the uppermost 1.5 cm of surface sediment. Methane oxidation was complete, yet the process was very sluggish with turnover times of methane within the sulfate}methane transition zone of 20 yr or more. 2001 Elsevier Science Ltd. All rights reserved.

Journal ArticleDOI
TL;DR: It is suggested that there is a direct association between microbes and gas hydrate, a finding that may have significance for hydrocarbon flux into the Gulf of Mexico and for life in extreme environments.
Abstract: Although there is significant interest in the potential interactions of microbes with gas hydrate, no direct physical association between them has been demonstrated. We examined several intact samples of naturally occurring gas hydrate from the Gulf of Mexico for evidence of microbes. All samples were collected from anaerobic hemipelagic mud within the gas hydrate stability zone, at water depths in the ca. 540- to 2,000-m range. The delta 13C of hydrate-bound methane varied from -45.1per thousand Peedee belemnite (PDB) to -74.7per thousand PDB, reflecting different gas origins. Stable isotope composition data indicated microbial consumption of methane or propane in some of the samples. Evidence of the presence of microbes was initially determined by 4,6-diamidino 2-phenylindole dihydrochloride (DAPI) total direct counts of hydrate-associated sediments (mean = 1.5 × 109 cells g-1) and gas hydrate (mean = 1.0 × 106 cells ml-1). Small-subunit rRNA phylogenetic characterization was performed to assess the composition of the microbial community in one gas hydrate sample (AT425) that had no detectable associated sediment and showed evidence of microbial methane consumption. Bacteria were moderately diverse within AT425 and were dominated by gene sequences related to several groups of Proteobacteria, as well as Actinobacteria and low-G + C Firmicutes. In contrast, there was low diversity of Archaea, nearly all of which were related to methanogenic Archaea, with the majority specifically related to Methanosaeta spp. The results of this study suggest that there is a direct association between microbes and gas hydrate, a finding that may have significance for hydrocarbon flux into the Gulf of Mexico and for life in extreme environments.

Journal ArticleDOI
TL;DR: A mixed-conducting perovskite-type Ba0:5Sr 0:5Co0:8Fe0:2O3 (BSCFO) membrane reactor with high oxygen permeability was applied for the activation of methane as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, a numerical model was developed to predict the volume and distribution of gas hydrate in marine sediments, where sedimentation adds organic material to the region of hydrate stability.
Abstract: We develop a numerical model to predict the volume and distribution of gas hydrate in marine sediments. We consider the environment of a deep continental margin where sedimentation adds organic material to the region of hydrate stability. Conversion of the organic material to methane by bacteria promotes hydrate formation and depletes the supply of organic carbon. We derive mass balance equations for the volume of hydrate and gas bubbles in the sediments and account for the changing concentration of dissolved methane and salts in the pore fluid. The effects of sediment compaction and the associated fluid flow are explicitly modeled. Allowances for deeper sources of fluid are also described, though we focus on the case of an idealized passive margin where carbon is input solely through sedimentation. The numerical calculations indicate that the key parameters in this model are the rate of sedimentation, the quantity and quality of the organic material, and a rate constant that characterizes the vigor of biological productivity. Model predictions for conditions that are representative of the Blake Ridge are compared with observations from Ocean Drilling Program Leg 164. We obtain a very good match to the observed chlorinity profile, including the region below the stability zone, without invoking any extraneous sources of freshening. We also predict that hydrate is unlikely to occupy more than 7% of the pore volume, in good agreement with observed estimates.

Journal ArticleDOI
TL;DR: In this paper, the effect of ethanol addition to gasoline on regulated and unregulated emissions is studied using a 4-cylinder OPEL 1.6 L internal combustion engine equipped with a hydraulic brake dynamometer.

Journal ArticleDOI
TL;DR: In this article, the authors investigated how gaseous evasion of carbon from the stream surface compared with downstream carbon transport at three locations on a Scottish headwater stream, and found that the evasion represented a loss of 14.1 g C m 22 yr 21, which equals 28% of the estimated net carbon accumulation rate for such peatlands.
Abstract: Peatland streams potentially represent important conduits for the exchange of gaseous carbon between the terrestrial ecosystem and the atmosphere. We investigated how gaseous evasion of carbon from the stream surface compared with downstream carbon transport at three locations on a Scottish headwater stream. Carbon dioxide was consistently above atmospheric saturation in the stream, with mean concentrations of 159.1, 81.8, and 29.5 mmol L 21 at the lower, middle, and upper sites, respectively (i.e., 7.6, 3.9, and 1.2 times in excess of atmospheric equilibrium concentrations). Methane concentrations in stream water were much lower but showed a similar pattern. Rates of gaseous evasion from the stream surface to the atmosphere, determined experimentally using direct measurement of dissolved gas concentrations in conjunction with coinjection of conservative solute and volatile gas tracers, also declined downstream. Combined stream losses of all forms of carbon from the entire catchment (i.e., degassing from the stream surface and exports downstream) totaled 54,140 kg C yr 21 . Evasion of carbon dioxide from the stream surface accounted for 34% of this total, compared to 57% lost as dissolved organic carbon via export downstream. When expressed per unit area of watershed, the gaseous C evasion from the stream represents a loss of 14.1 g C m 22 yr 21 , which equals 28‐70% of the estimated net carbon accumulation rate for such peatlands. This study shows that gaseous carbon loss from the surface of temperate headwater streams can be both spatially variable and significant in terms of rates of net annual land surface‐atmosphere exchange at the catchment scale.

Journal ArticleDOI
TL;DR: A review of the recent approaches to the partial oxidation of methane into useful oxygenates with an emphasis on the selective formation of methanol in the presence of H 2 can be found in this article.
Abstract: Direct conversion of methane into useful chemicals remains as a big challenge in catalysis in the 21st century. A large number of studies have contributed to the direct conversion of methane in the past decade. Although there is still no direct process with commercial viability at this moment, many new methods and catalysts have been developed for the direct activation and conversion of methane. This review highlights the recent novel approaches to the partial oxidation of methane into useful oxygenates with an emphasis on the selective formation of methanol in the presence of H 2 .

Journal ArticleDOI
TL;DR: Gas hydrates are crystalline solids that form from mixtures of water and light natural gases such as methane, carbon dioxide, ethane, propane and butane.

Journal ArticleDOI
TL;DR: In this paper, Catalytic properties of substituted lanthanum chromites were investigated for their use as anode materials for direct methane oxidation in solid oxide fuel cell (SOFC) anode material.

Journal ArticleDOI
TL;DR: In this article, the dependence of the type of carbon formed and the amount of CO evolved on the nature of the support was highlighted, and the CO formation rates showed a common trend for all the catalysts: high initial rates followed by lower stabilized rates.

Journal ArticleDOI
TL;DR: In this paper, the volumetric changes of the coal matrix were monitored for four different gases (methane, nitrogen, carbon dioxide and helium) on a sample from the South Island, New Zealand.