Showing papers on "Methane published in 2009"

Anaerobic Oxidation of Methane: Progress with an Unknown Process

Abstract: Methane is the most abundant hydrocarbon in the atmosphere, and it is an important greenhouse gas, which has so far contributed an estimated 20% of postindustrial global warming. A great deal of biogeochemical research has focused on the causes and effects of the variation in global fluxes of methane throughout earth's history, but the underlying microbial processes and their key agents remain poorly understood. This is a disturbing knowledge gap because 85% of the annual global methane production and about 60% of its consumption are based on microbial processes. Only three key functional groups of microorganisms of limited diversity regulate the fluxes of methane on earth, namely the aerobic methanotrophic bacteria, the methanogenic archaea, and their close relatives, the anaerobic methanotrophic archaea (ANME). The ANME represent special lines of descent within the Euryarchaeota and appear to gain energy exclusively from the anaerobic oxidation of methane (AOM), with sulfate as the final electron accept...

Molecular approaches to the photocatalytic reduction of carbon dioxide for solar fuels

Abstract: The scientific community now agrees that the rise in atmospheric CO2, the most abundant green house gas, comes from anthropogenic sources such as the burning of fossil fuels. This atmospheric rise in CO2 results in global climate change. Therefore methods for photochemically transforming CO2 into a source of fuel could offer an attractive way to decrease atmospheric concentrations. One way to accomplish this conversion is through the light-driven reduction of carbon dioxide to methane (CH4(g)) or methanol (CH3OH(l)) with electrons and protons derived from water. Existing infrastructure already supports the delivery of natural gas and liquid fuels, which makes these possible CO2 reduction products particularly appealing. This Account focuses on molecular approaches to photochemical CO2 reduction in homogeneous solution. The reduction of CO2 by one electron to form CO2•− is highly unfavorable, having a formal reduction potential of −2.14 V vs SCE. Rapid reduction requires an overpotential of up to 0.6 V, du...

The Economic Effects of Climate Change

Abstract: Greenhouse gas emissions are fundamental both to the world’s energy system and to its food production. The production of CO2, the predominant gas implicated in climate change, is intrinsic to fossil fuel combustion; specifically, thermal energy is generated by breaking the chemical bonds in the carbohydrates oil, coal, and natural gas and oxidizing the components to CO2 and H2O. One cannot have cheap energy without carbon dioxide emissions. Similarly, methane (CH4) emissions, an important greenhouse gas in its own right, are necessary to prevent the build-up of hydrogen in anaerobic digestion and decomposition. One cannot have beef, mutton, dairy, or rice without methane emissions. Climate change is the mother of all externalities: larger, more complex, and more uncertain than any other environmental problem. The sources of greenhouse gas emissions are more diffuse than any other environmental problem. Every company, every farm, every household emits some greenhouse gases. The effects are similarly pervasive. Weather affects agriculture, energy use, health, and many aspects of nature—which in turn affects everything and everyone. The causes and consequences of climate change are very diverse, and those in low-income countries who contribute least to climate change are most vulnerable to its effects. Climate change is also a long-term problem. Some greenhouse gases have an atmospheric life-time measured in tens of thousands of years. The quantities of emissions involved are enormous. In 2000, carbon dioxide emissions alone (and excluding land use change) were 24 billion metric tons of carbon dioxide (tCO2).

Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis

Abstract: New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than −0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At −1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane pro...

High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels

Abstract: Efficient solar conversion of carbon dioxide and water vapor to methane and other hydrocarbons is achieved using nitrogen-doped titania nanotube arrays, with a wall thickness low enough to facilitate effective carrier transfer to the adsorbing species, surface-loaded with nanodimensional islands of cocatalysts platinum and/or copper. All experiments are conducted in outdoor sunlight at University Park, PA. Intermediate reaction products, hydrogen and carbon monoxide, are also detected with their relative concentrations underlying hydrocarbon production rates and dependent upon the nature of the cocatalysts on the nanotube array surface. Using outdoor global AM 1.5 sunlight, 100 mW/cm(2), a hydrocarbon production rate of 111 ppm cm(-2) h(-1), or approximately 160 microL/(g h), is obtained when the nanotube array samples are loaded with both Cu and Pt nanoparticles. This rate of CO(2) to hydrocarbon production obtained under outdoor sunlight is at least 20 times higher than previous published reports, which were conducted under laboratory conditions using UV illumination.

Physical properties of hydrate-bearing sediments

Abstract: [1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

Application of metal–organic frameworks with coordinatively unsaturated metal sites in storage and separation of methane and carbon dioxide

Abstract: The metal–organic frameworks M2(dhtp)(H2O)2·8H2O (CPO-27-M, M = Ni, Mg) can be activated to give the empty framework compounds M2(dhtp) with a honeycomb analogous structure containing large micropores of 11–12 A diameter and a high concentration of open metal sites. These sites play a major role in the adsorption of methane and carbon dioxide, which was studied at pressures up to 100 bar and 50 bar, respectively, and various temperatures in the range of 179 to 473 K. Both gases are taken up by the material in significant amounts. The maximum excess adsorption of CO2 observed at 298 K was 51 wt.% for Ni2(dhtp) and 63 wt.% for Mg2(dhtp). A surprisingly large amount of CO2, in the range 25–30 wt.%, was still adsorbed at 473 K. Up to 18 and 22 wt.% methane were adsorbed at 179 K in the nickel and the magnesium compound, respectively. Congruent with this result is the high isosteric heat of adsorption observed, which was found to be in the range 38–43 kJ mol−1 for CO2 and 20–22 kJ mol−1 for CH4, initially. The heat of adsorption decreases significantly after the open metal sites have been occupied, which also is reflected in the shape of the adsorption isotherms. The vacant coordination site at the metal atom also imparts favorable properties in respect to gas separation onto the material. Breakthrough experiments using Ni2(dhtp) and gas mixtures of CO2–N2 and CO2–CH4 demonstrate the ability of the material to separate these gases. It is shown that carbon dioxide is preferentially adsorbed over methane or nitrogen. In the case of CO2–N2, the retention is quantitative within the precision of the detection system.

Strong Release of Methane on Mars in Northern Summer 2003

Abstract: Living systems produce more than 90% of Earth9s atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained ∼19,000 metric tons of methane, and the estimated source strength (≥0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.

Escape of methane gas from the seabed along the West Spitsbergen continental margin

Abstract: More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150-400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward-flowing West Spitsbergen current by 1°C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic continental margins, tens of Teragrams of methane per year could be released into the ocean.

Ni, Co and bimetallic Ni–Co catalysts for the dry reforming of methane

Abstract: Alumina supported Ni, Co and bimetallic Ni–Co catalysts (with 9 wt.% nominal metal content) have been prepared, characterized and tested for the dry reforming of methane. For catalysts characterization the following techniques have been used: Atomic Absorption Spectroscopy (ICP-AES), Transmission Electron Microscopy (TEM), Temperature Programmed Reduction (TPR-H2) and Temperature Programmed Oxidation (TPO). The dry reforming of methane was carried out at 973 K using a mixture CH4:CO2 (1:1). Among the catalysts studied, those with the highest cobalt content (Co(9) and NiCo(1–8)) are the most active and stable, but they produce a large amount of carbon. The higher activity exhibited by cobalt rich catalysts is related with the higher activity of this metal for methane decomposition, while their remarkable stability seems to be due to the presence of large particles involved in long-term conversion, because they produce non-deactivating carbon deposits.

Is Gas Hydrate Energy Within Reach

Abstract: Technological advances have opened up natural gas resources that were previously unobtainable, including deep-water areas (depths >305 m) and unconventional resources, such as coal-bed methane, and gas in shale, that do not readily release their gas to wells. The next resource poised to be delivered is gas hydrates, which form from methane and water at low temperatures and moderate pressures. Gas hydrates occur in permafrost ( 1 ), but most of this vast resource occurs in marine sediments on the outer continental shelves ( 2 ). Physical barriers posed by Arctic and deep-water settings, as well as a lack of proven extraction methods, have made them an unexploited resource. However, a series of international field programs in the last 5 years, in conjunction with experimental studies and numerical simulations, show that it should be possible to extract the most favorable gas hydrates—those enclosed in sandy sediments that lay at the apex of the gas hydrate resource pyramid (see the figure)—with existing technologies.

Ocean methane hydrates as a slow tipping point in the global carbon cycle

Abstract: We present a model of the global methane inventory as hydrate and bubbles below the sea floor. The model predicts the inventory of CH4 in the ocean today to be ≈1600–2,000 Pg of C. Most of the hydrate in the model is in the Pacific, in large part because lower oxygen levels enhance the preservation of organic carbon. Because the oxygen concentration today may be different from the long-term average, the sensitivity of the model to O2 is a source of uncertainty in predicting hydrate inventories. Cold water column temperatures in the high latitudes lead to buildup of hydrates in the Arctic and Antarctic at shallower depths than is possible in low latitudes. A critical bubble volume fraction threshold has been proposed as a critical threshold at which gas migrates all through the sediment column. Our model lacks many factors that lead to heterogeneity in the real hydrate reservoir in the ocean, such as preferential hydrate formation in sandy sediments and subsurface gas migration, and is therefore conservative in its prediction of releasable methane, finding only 35 Pg of C released after 3 °C of uniform warming by using a 10% critical bubble volume. If 2.5% bubble volume is taken as critical, then 940 Pg of C might escape in response to 3 °C warming. This hydrate model embedded into a global climate model predicts ≈0.4–0.5 °C additional warming from the hydrate response to fossil fuel CO2 release, initially because of methane, but persisting through the 10-kyr duration of the simulations because of the CO2 oxidation product of methane.

Secondary Organic Aerosol Formation from Acetylene (C 2 H 2 ): seed effect on SOA yields due to organic photochemistry in the aerosol aqueous phase

Abstract: . The lightest Non Methane HydroCarbon (NMHC), i.e., acetylene (C2H2) is found to form secondary organic aerosol (SOA). Contrary to current belief, the number of carbon atoms, n, for a NMHC to act as SOA precursor is lowered to n=2 here. The OH-radical initiated oxidation of C2H2 forms glyoxal (CHOCHO) as the highest yield product, and >99% of the SOA from C2H2 is attributed to CHOCHO. SOA formation from C2H2 and CHOCHO was studied in a photochemical and a dark simulation chamber. Further, the experimental conditions were varied with respect to the chemical composition of the seed aerosols, mild acidification with sulphuric acid (SA, 3

Anaerobic digestion of slaughterhouse by-products

Abstract: Anaerobic digestion of animal by-products was investigated in batch and semi-continuously fed, reactor experiments at 55 °C and for some experiments also at 37 °C. Separate or mixed by-products from pigs were tested. The methane potential measured by batch assays for meat- and bone flour, fat, blood, hair, meat, ribs, raw waste were: 225, 497, 487, 561, 582, 575, 359, 619 dm 3 kg −1 respectively, corresponding to 50–100% of the calculated theoretical methane potential. Dilution of the by-products had a positive effect on the specific methane yield with the highest dilutions giving the best results. High concentrations of long-chain fatty acids and ammonia in the by-products were found to inhibit the biogas process at concentrations higher than 5 g lipids dm −3 and 7 g N dm −3 respectively. Pretreatment (pasteurization: 70 °C, sterilization: 133 °C, and alkali hydrolysis (NaOH) had no effect on achieved methane yields. Mesophilic digestion was more stable than thermophilic digestion, and higher methane yield was noticed at high waste concentrations. The lower yield at thermophilic temperature and high waste concentration was due to ammonia inhibition. Co-digestion of 5% pork by-products mixed with pig manure at 37 °C showed 40% higher methane production compared to digestion of manure alone.

Carbon dioxide reforming of methane to synthesis gas over Ni-MCM-41 catalysts

Abstract: A series of nickel incorporated MCM-41 mesoporous molecular sieves (Ni-MCM-41) were prepared by direct hydrothermal synthesis. Nickel nitrate was used as the Ni precursor. The catalytic properties of the Ni-MCM-41 were studied for the reforming of methane with carbon dioxide. The catalysts were carefully characterized by X-ray diffraction (XRD), N2 physisorption, H2 temperature-programmed reduction (TPR), H2 chemisorption, thermogravimetry, and Raman spectra. The results indicated that the presence of a suitable amount of nickel in Ni-MCM-41 was beneficial for maintaining high catalytic activity and long-term stability. The improved catalytic performance was suggested to closely associate with both the amount of active centers on the pore wall surface and the stabilized dispersion of these active sites by the silica matrix and/or the surrounding unreduced nickel ions. This anchoring effect facilitated the formation of the active Ni nano-clusters with high dispersion under reaction conditions. Hence the reforming reaction is favored and the carbon formation is suppressed. Two types of carbon species: active carbon and graphite were produced over the spent catalysts. The Ni-MCM-41 catalysts provided good catalytic activity, high stability and reasonable CO/H2 ratios in the product. Thus, the Ni-MCM-41 catalyst prepared by the direct hydrothermal synthesis promised a novel and stable catalyst candidate for CO2 reforming of CH4.

Nanofaceted Pd ? O Sites in Pd ? Ce Surface Superstructures: Enhanced Activity in Catalytic Combustion of Methane

Abstract: An open superstructure: A Pd/CeO2 catalyst prepared by solution combustion synthesis is three to five times more active for CH4 combustion than the best conventional palladium-based systems. The catalyst contains an ordered, stable Pd-O-Ce surface superstructure (see picture; cyan arrow is a square-planar Pd site, red arrow is an undercoordinated O atom) and is an example of ultra-highly dispersed, stable PdO within an oxide carrier.

Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics

Abstract: Recent observations of methane on Mars suggest that methane concentrations are locally enhanced and change with season. Methane has a photochemical lifetime of several centuries, however, and it is therefore expected to have a spatially uniform distribution on the planet. Frank Lefevre and Francois Forget use a global climate model of Mars with coupled chemistry to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane. They find that photochemistry as currently understood does not produce measurable variations in methane concentrations and that the destruction of methane on the surface of Mars would have to be extraordinarily fast to explain the reported observations. We may need to wait for future Mars probes to make in situ measurements to discover exactly what is happening to Martian methane. Recent observations of methane on Mars suggest that methane concentrations are locally enhanced and change with the seasons. However, methane has a photochemical lifetime of several centuries, and is therefore expected to have a spatially uniform distribution on the planet. Here, using a global climate model of Mars with coupled chemistry reveals that photochemistry as currently understood cannot explain these variations in Martian methane. The detection of methane on Mars1,2,3 has revived the possibility of past or extant life on this planet, despite the fact that an abiogenic origin is thought to be equally plausible4. An intriguing aspect of the recent observations of methane on Mars is that methane concentrations appear to be locally enhanced and change with the seasons3. However, methane has a photochemical lifetime of several centuries, and is therefore expected to have a spatially uniform distribution on the planet5. Here we use a global climate model of Mars with coupled chemistry6,7,8 to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane. We find that photochemistry as currently understood does not produce measurable variations in methane concentrations, even in the case of a current, local and episodic methane release. In contrast, we find that the condensation–sublimation cycle of Mars’ carbon dioxide atmosphere can generate large-scale methane variations differing from those observed. In order to reproduce local methane enhancements similar to those recently reported3, we show that an atmospheric lifetime of less than 200 days is necessary, even if a local source of methane is only active around the time of the observation itself. This implies an unidentified methane loss process that is 600 times faster than predicted by standard photochemistry. The existence of such a fast loss in the Martian atmosphere is difficult to reconcile with the observed distribution of other trace gas species. In the case of a destruction mechanism only active at the surface of Mars, destruction of methane must occur with an even shorter timescale of the order of ∼1 hour to explain the observations. If recent observations of spatial and temporal variations of methane are confirmed, this would suggest an extraordinarily harsh environment for the survival of organics on the planet.

Influence of gas hydrate morphology on the seismic velocities of sands

Abstract: This paper reports the results of a series of resonant column tests on specimens where gas hydrate has been formed in sands using an “excess water” technique. In these specimens the amount of hydrate formed is restricted by the amount of gas in the specimen and with an excess of water being present in the pore space. Results of resonant column tests carried out to determine compressional and shear wave velocities suggest that gas hydrate formed in this way are frame supporting. In contrast, the behavior observed in sands where the hydrate is formed from finite water where the remaining pore space is saturated with methane gas, termed in this paper the “excess gas” method, exhibits a cementing behavior, while tetrahydrofuran-hydrate sands or where the hydrate is formed from dissolved methane within the pore water, exhibit a pore-filling behavior for hydrate saturations less than 40%. For sands where the hydrate is formed using the excess water method, much larger volumes of hydrate are required before a significant increase in shear wave velocity occurs, although increases in compressional wave velocity are seen at lower hydrate contents. These results suggest that hydrate interaction with the sediment is strongly dependent on morphology, and that natural hydrate may exhibit contrasting seismic signatures depending upon the geological environment in which it forms.

Methanation of carbon dioxide over nickel-based Ce0.72Zr0.28O2 mixed oxide catalysts prepared by sol–gel method

Abstract: Ni–Ce0.72Zr0.28O2 catalysts containing up to 15 wt% Ni were prepared, characterized and their catalytic activity was investigated in carbon dioxide methanation. The impact of the pre-treatment and the gas hourly space velocity were also studied. NiO dispersion and part of its incorporation into the mixed oxide lattice obviously increased the activity and stability of the catalysts. Very high CO2 conversions were achieved at 350 and 400 °C, together with extremely high selectivity to methane (>98%) for all catalysts. Finally, high stability on stream toward deactivation was observed up to 150 h at 350 °C. 10 wt%Ni–Ce0.72Zr0.28O2 was found to be the optimal catalyst.

Gas Hydrate Formation in a Variable Volume Bed of Silica Sand Particles

Abstract: Gas hydrate formation was studied in a new apparatus designed to accommodate three different size volume beds of silica sand particles. The sand particles have an average diameter equal to 329 μm. The hydrate was formed in the water, which occupied the interstitial space of the water-saturated silica sand bed. A bulk gas phase was present above the bed (gas cap). Gas uptake measurements were carried out during experiments at constant temperature. More than 74.0% of water conversion to hydrate was achieved in all experiments conducted with methane at 4.0 and 1.0 °C. An initial slow growth was followed by a rapid hydrate growth rate of equal magnitude for nearly all experiments until 43−53% of water was converted to hydrate. During the third and final growth stage, the final conversions were between 74 and 98% and the conversion dynamics changed. Independent verification of hydrate formation in the sand was achieved via Raman spectroscopy and morphology observations in experiments using the same sand/water ...

The indirect global warming potential and global temperature change potential due to methane oxidation

Abstract: Methane is the second most important anthropogenic greenhouse gas in the atmosphere next to carbon dioxide. Its global warming potential (GWP) for a time horizon of 100 years is 25, which makes it an attractive target for climate mitigation policies. Although the methane GWP traditionally includes the methane indirect effects on the concentrations of ozone and stratospheric water vapour, it does not take into account the production of carbon dioxide from methane oxidation. We argue here that this CO2-induced effect should be included for fossil sources of methane, which results in slightly larger GWP values for all time horizons. If the global temperature change potential is used as an alternative climate metric, then the impact of the CO2-induced effect is proportionally much larger. We also discuss what the correction term should be for methane from anthropogenic biogenic sources.