Showing papers on "Methane published in 1984"

Partial oxidation of methane by nitrous oxide over molybdenum on silica

Abstract: Kinetic data are presented for the partial oxidation of methane to methanol and formaldehyde by nitrous oxide catalysed by molybdenum supported on silica when steam is present in the system. The data are used as evidence to show how the selective oxidation mechanism fits into an overall reaction scheme. Moreover, in support of this selective mechanism, spectroscopic evidence is given for the formation of methyl radicals and methoxide ions on the surface. 12 references, 7 figures, 1 table.

Atmospheric methane in the recent and ancient atmospheres Concentrations, trends, and interhemispheric gradient

Abstract: Rasmussen and Khalil (1981) have shown that the concentration of methane is increasing in the earth's atmosphere. A continuing increase of methane may perturb the global environment in the future by warming the earth and leading to more ozone and carbon monoxide in the atmosphere. It appears that the present concentration of methane may be more than twice as high as the natural levels of 150 years ago. An analysis of air bubbles buried long ago in polar ice makes it possible to deduce the concentrations of methane in the old and ancient atmospheres. The present investigation is concerned with the results of an analysis of more than 80 ice core samples, taking into account both polar regions of the earth. The samples range in age from about 100 to nearly 3000 years old. It is found that the concentration of methane started changing significantly about 150 years ago. These findings suggest that the increase of methane is probably indirectly caused by the rapid increase of human population.

Methane production in Minnesota peatlands.

Abstract: Rates of methane production in Minnesota peats were studied. Surface (10- to 25-cm) peats produced an average of 228 nmol of CH4 per g (dry weight) per h at 25°C and ambient pH. Methanogenesis rates generally decreased with depth in ombrotrophic peats, but on occasion were observed to rise within deeper layers of certain fen peats. Methane production was temperature dependent, increasing with increasing temperature (4 to 30°C), except in peats from deeper layers. Maximal methanogenesis from these deeper regions occurred at 12°C. Methane production rates were also pH dependent. Two peats with pHs of 3.8 and 4.3 had an optimum rate of methane production at pH 6.0. The addition to peat of glucose and H2-CO2 stimulated methanogenesis, whereas the addition of acetate inhibited methanogenesis. Cysteine-sulfide, nitrogen-phosphorus-trace metals, and vitamins-yeast extract affected methane production very little. Various gases were found to be trapped or dissolved (or both) within peatland waters. Dissolved methane increased linearly to a depth of 210 cm. The accumulation of metabolic end products produced within peat bogs appears to be an important mechanism limiting carbon turnover in peatland environments.

In situ methane production from acid peat in plant communities with different moisture regimes in a subarctic mire

Abstract: In situ methane production from acid peat in plant communities with different moisture regimes in a subarctic mire

Pyrolysis of methyl chloride, a pathway in the chlorine-catalyzed polymerization of methane

Abstract: The reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 - initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol):

Seasonal study of methane oxidation in lake washington.

Abstract: The distribution of methane and methane-oxidizing bacteria in the water column of Lake Washington was determined monthly for 1 year. The methane profiles were relatively constant, with little stratification and low concentrations (0.05 to 0.5 muM). The number of methane-oxidizing bacteria detected by a filter-plating method was routinely <1/ml throughout the water column, and no incorporation or oxidation of methane was detected by radioisotopic labeling, even after methane was added. However, samples taken from the sediment-water interface contained as much as 3 muM methane and 50 CFU of methane-oxidizing bacteria per ml and showed significant rates of methane oxidation and incorporation. To define the region of maximum activity more precisely, vertical profiles of the sediment were examined. The concentration of methane increased with depth to a maximum of 150 to 325 muM at 2.5 cm, and significant rates of methane oxidation were found within the top 2.5 cm. The apparent K(m)s for methane and oxygen were determined for samples from the top 1.0 cm of the sediment and found to be ca. 10 and 20 muM, respectively. Projected values for methane oxidation rates suggested that maximum methane oxidation occurred in the top 0.5 cm of the sediment.

Influence of pH on Terminal Carbon Metabolism in Anoxic Sediments from a Mildly Acidic Lake.

Abstract: The carbon and electron flow pathways and the bacterial populations responsible for transformation of H2-CO2, formate, methanol, methylamine, acetate, glycine, ethanol, and lactate were examined in sediments collected from Knaack Lake, Wis. The sediments were 60% organic matter (pH 6.2) and did not display detectable sulfate-reducing activity, but they contained the following average concentration (in micromoles per liter of sediment) of metabolites and end products: sulfide, 10; methane, 1,540; CO2, 3,950; formate, 25; acetate, 157; ethanol, 174; and lactate, 138. Methane was produced predominately from acetate, and only 4% of the total CH4 was derived from CO2. Methanogenesis was limited by low environmental temperature and sulfide levels and more importantly by low pH. Increasing in vitro pH to neutral values enhanced total methane production rates and the percentage of CO2 transformed to methane but did not alter the amount of 14CO2 produced from [2-14C]acetate (∼24%). Analysis of both carbon transformation parameters with 14C-labeled tracers and bacterial trophic group enumerations indicated that methanogenesis from acetate and both heterolactic- and acetic acid-producing fermentations were important to the anaerobic digestion process.

Methane from anaerobic fermentation.

Abstract: Conventional anaerobic digestion is an established technology for wastewater stabilization, but methane production rates and net energy yields are generally too low to make the process competitive as a source of methane. Numerous improvements are being developed to make conversion of plant biomass to methane and simultaneous waste stabilization-methane production practical. Among these improvements are innovative-digester designs and process configurations. Efforts to commercialize modern anaerobic digestion technology are progressing.

Different Temperature Optima for Methane Formation When Enrichments from Acid Peat Are Supplemented with Acetate or Hydrogen

Abstract: Laboratory studies of methane formation in peat samples from an acid subarctic mire in Sweden indicated the presence of a low-temperature-adapted methanogenic flora. Enrichment culture studies with ethanol, acetate, hydrogen, or a combination of these as substrate for methane formation provided evidence for the existence of two different methanogenic populations in the peat: one, unaffected by hydrogen and using acetate, with a temperature optimum at 20°C; the other, oxidizing hydrogen, with a temperature optimum at ca. 28°C.

Carbon and hydrogen isotopic composition of bacterial methane in a shallow freshwater lake

Abstract: Hydrogen and carbon isotopes measured in biogenic gas from a shallow freshwater lake indicate the acetate-reduction pathway to be responsible for over 70% of the methanogenesis in these sediments. Methane 6D was strongly depleted (up to 3079m) relative to the associated formation water (ca. - 259~ vs. SMOW) and was similar to fermentation methane from sewage sludge digesters. Although the methane PC ranged from -529~ to -619& relative to the porewater CO, it had a consistent fractionation about (Y, = 1.05. With the combination of H isotopes, we can interpret previously ambiguous methane P3C values (- 50 to - 609~) as being of biogenic origin.

Generation and migration of light hydrocarbons.

Abstract: Light hydrocarbons (containing from 1 to 14 carbon atoms) are formed from disseminated organic matter in sediments at the parts-per-billion level by biological and low-temperature ( 50°C) cracking reactions. The cooler reactions produce mainly branched hydrocarbons, whereas the hotter reactions yield more straight chains. Hydrocarbon generation zones in the subsurface can be recognized on the basis of hydrocarbon distribution patterns. Hydrocarbons with tertiary carbon atoms form at lower temperatures than those with quaternary carbons. Methane and ethane migrate vertically through fine-grained shales by diffusion and solution, whereas many of the C3+ hydrocarbons show little or no vertical migration. Concentrations of light hydrocarbons, including methane, in fine-grained source rocks decrease to low values in deep, high-temperature (>200°C) sediments. This decrease may be one reason why no economic accumulation of gas has been found to date deeper than 8.2 kilometers (27,000 feet).

Method and apparatus for separating carbon dioxide and other acid gases from methane by the use of distillation and a controlled freezing zone

Abstract: The invention relates to method and apparatus for separating carbon dioxide and other acid gases from methane by treating the feedstream in at least one distillation zone and a controlled freezing zone. The freezing zone produces a carbon dioxide slush which is melted and fed into a distillation section. The apparatus used to practice the process is preferably in a single vessel.

Geochemical Surface Exploration for Hydrocarbons in North Sea

Abstract: Approximately 350 sediment samples were taken in the central part of the North Sea, and hydrocarbon composition, methane (C1) and ethane (C2) yields, and carbon isotope composition of the methane (^dgr13C1) adsorbed in the sediment were determined. Methane generation or oxidation by bacterial activity can not be deduced from the analytical data. This fact is explained by the assumption of a threshold of methane concentration in sediments below which methane oxidizing bacteria are inactive, and that this threshold was not reached in the area investigated. Background gases in the surface sediments, characterized by low C1 yields and ^dgr13C1 > -37 ppt can be distinguished from thermal sediment g ses which are obviously derived from a hydrocarbon generating source rock in the subsurface. Source rock data, obtained from several wells situated on a cross section through the investigated area, were compared to the geochemical patterns of the sediment gases and used to define profile sections with "good" (^dgr13C1 ^approx -40 ppt, yield C1 ^approx 217 ppb) and "poor" source rock properties (^dgr13C1 ^approx -33 ppt, yield C1 ^approx 24 ppb). An assessment of the source rock potential of the whole area under investigation has been carried out using the geochemical data of the surface sediment gases and taking into account that the C1 and C2 yields are generally higher in clay sediments than in sand samples. The number of producing wells was related to the number of all wells (271) in the areas characterized by surface geochemistry as good or poor source rock areas. The comparison showed that the relative number of producing wells is higher in areas geochemically characterized as good. Hydrocarbons in surface sediments of "good" North Sea areas are not generated by bacteria at shallow depth; they are formed thermally from the organic carbon of deep source rocks and migrate to the surface. Therefore they are indicative of thermal hydrocarbon generation in the subsurface.

On the distributions of long‐lived tracers and chlorine species in the middle atmosphere

Abstract: A numerical model employing the residual Eulerian formulation and small eddy diffusivity coefficients is used to calculate the distributions of chemical tracers and chlorine species. The predicted densities of nitrous oxide, methane, and chlorocarbons are shown to be in good agreement with available observations and to exhibit strong latitude gradients. Computed spatial variations in methane produce large variations in the HCl and ClO densities. In particular, a pronounced local minimum in HCl is obtained near 40 km for certain latitudes and seasons, with a corresponding maximum in ClO, primarily as a result of transport of atmospheric methane. It is suggested that spatial and short-term temporal variability in methane has potentially important consequences for the HCl and ClO distributions in the atmosphere, and their variability, and for the chlorine-catalyzed destruction of stratospheric ozone.

Relative gas-phase acidities of the alkanes

Abstract: : In the gas phase alkyl trimethyl silanes are cleaved by hydroxide ions to siloxides with loss of methane or alkane. The alkane to methane loss ratio in this reaction is proposed as a measure of the relative acidity of RH and CH4. A linear correlation is established for loss of substituents of known acidity (CH4, H2, C2H4, C6H6). This relationship allows the acidity of several alkanes to be predicted, as well as the electron affinity of the corresponding alkyl radicals. Ethane and the secondary position in propane are predicted to be less acidic than methane, and the ethyl, isopropyl and t-butyl radicals are predicted to have negative electron affinities.

Method and apparatus for purification of high CO2 content gas

Abstract: Nitrogen and methane are separated in a nitrogen-methane cryogenic fractionator operating at a temperature between the boiling points of nitrogen and methane A distillative aid or absorbent is injected into the nitrogen-methane cryogenic fractionator for enhancing separation, for enabling an increase in operating pressure, and for enabling a high separation rate at relatively high temperature

Coalbed methane resources of the United States

Abstract: Methane has been observed in coalbeds since underground mining of that resource began. This gas, however, has only recently been recognized as an economically producible resource. Coal underlies approximately 360,000 sq mi of the conterminous United States but because of the paucity of data on coals deeper than 3,000 ft the size of the deep coal and therefore deep gas resource is not well known. Coal responds to increased temperature over time by increasing in rank or thermal maturity. During this maturation process increased volumes of methane are generated. Coal is identified as a humic, Type III, kerogen and as such yields methane as its primary hydrocarbon product and water, carbon dioxide, and nitrogen as nonhydrocarbon products. It is estimated that more than 7,000 cubic feet of methane is generated for each ton of coal during coalification from lignite to anthracite rank. Methane is found in coals either adsorbed on the coal surfaces, as free gas in fractures and large pores or dissolved in ground water in coalbeds. The amount of gas stored in the coals is influenced by depth of burial and its related pressure, rank of coal and its related porosity distribution, and a time-maturity relationship. Adsorption isotherm determinations show the maximum amount of methane that can be adsorbed on coals of various ranks. Desorption analyses of coal core samples indicate that for high rank coals adsorbed gas may exceed that predicted by isotherm analyses. Methane has been produced from coals since the early 1900s. Producibility is influenced by depth, rank, permeability, water saturation, and other hydrogeologic characteristics. Current commercial gas production from coalbeds has been documented in the Warrior Basin, Northern Appalachian Basin, and the San Juan Basin. One well in the San Juan Basin is producing at a rate in excess of 1.5 MMcfd from a 17-ft coalbed. Possible constraints to coalbed gas production involve completion technology and legal and institutional inconsistencies. Research is currently underway to enhance gas production from deep coals. Legal and regulatory constraints are being addressed through appropriate state and federal channels to resolve questions of gas ownership and price. Data indicate that the coalbed methane resource is producible at currently economic rates.

Initiating production of methane from wet coal beds

Abstract: Production of methane from an underground wet coal seam is initiated by drilling a well from the surface of the earth through the seam. Rather than pumping water to lower hydraulic head on the seam to permit desorption of methane within the coal, high pressure gas is injected into the seam to drive water away from the wellbore. Gas injection is terminated and the well is opened to flow. Initial gas production is return of injected gas, followed by a mixture of return injected gas and methane, followed by free methane from the fracture system of the coal, and then by methane desorbed from the coal. Upon return of displaced water to the wellbore, pumping operations remove water at rates that permit sustained production of desorbed methane.

The high‐resolution visible overtone spectrum of CH4 and CD3H at 77 K

Abstract: We have obtained visible overtone spectra with Doppler‐limited resolution of methane and trideuteromethane in the vicinity of six quanta of C–H stretch. At room temperature, the methane spectrum is unresolved. Upon cooling to 77 K in a specially designed photoacoustic cell, methane shows a complicated but rotationally resolved spectrum. The widths of all features in the spectrum are consistent with Doppler broadened linewidths at 77 K. Efforts to assign this spectrum are in progress. The overtone spectrum of CD3H has been recently studied by other workers at a resolution of 0.5 cm−1 [Perry, Moll, Kupperman, and Zewail (preprint)]. The spectrum in this region consists of two parallel bands, one at 16 156 cm−1 and another at 16 230 cm−1. These are assigned as arising from a Fermi resonance between the pure C–H overtone 6ν1 and a combination with the degenerate C–H bend, 5ν1+2ν5. A high resolution spectrum taken at 77 K shows nearly completely resolved K‐subband structure for both bands. The rotational const...