Oxidation of methane at the CH4/H2O-(CO2) transition zone in the external part of the Central Alps, Switzerland: Evidence from stable isotope investigations

With the aim of understanding the mechanisms that control the metamorphic transition from the CH4- to the H2O-(CO2)-dominated fluid zone in the Helvetic domain of the Central Alps of Switzerland, fluid inclusions in quartz, illite ``crystallinity'' index, vitrinite reflectance, and the stable isotope compositions of vein and whole rock minerals and fluids trapped in quartz were investigated along four cross-sections. Increasing temperature during prograde metamorphism led to the formation of dry gas by hydrocarbon cracking in the CH4-zone. Fluid immiscibility in the H2O-CH4-(CO2)-NaCl system resulted in cogenetic, CH4- and H2O-dominated fluid inclusions. In the CH4-zone, fluids were trapped at temperatures <= 270 +/- 5 degrees C. The end of the CH4-zone is markedby a sudden increase of CO2 content in the gas phase of fluid inclusions. At temperatures > 270 +/- 5 degrees C, in the H2O-zone, the total amount of volatiles within the fluid decreased below 1 mol% with no immiscibility. This resulted m total homogenization temperatures of H2O-(CO2-CH4)-NaCl inclusions below 180 degrees C. Hydrogen isotope compositions of methane in fluid inclusion have delta D values of less than -100 parts per thousand in the CH4-zone, typical for an origin through cracking of higher hydrocarbons, but where the methane has not equilibrated with the pore water. delta D values of fluid inclusion water are around -40 parts per thousand., in isotopic equilibrium with phyllosilicates of the whole rocks. Within the CH4 to H2O(CO2) transition zone, delta D(H2O) values in fluid inclusions decrease to -130 parts per thousand interpreted to reflect the contribution of deuterium depleted water from methane oxidation. In the H2O-zone, delta D(H2O) values increase again towards an average of -30 parts per thousand which is again consistent with isotopic equilibrium with host-rock phyllosilicates. delta C-13 values of methane in fluid inclusions from the CH4-zone are around -27 parts per thousand in isotopic equilibrium with calcite in veins and whole rocks. The delta C-13(CH4) values decrease to less than -35 parts per thousand at the transition to the H2O-zone and are no longer in equilibrium with the carbonates in the whole rocks. delta C-13 values of CO, are variable but too low to be in equilibrium with the wall rock fluids, compatible with a contribution of CO2 from closed system oxidation of methane. Differences in isotopic composition between host-rock and Alpine fissure carbonate are generally small, suggesting that the amount of CO2 produced by oxidation of methane was small compared to the C-budget in the rocks and local pore fluids were buffered by the wall rocks during precipitation of calcite within the fissures. (c) 2006 Elsevier B.V. All rights reserved.

Selective catalytic oxidation of alkylaromatic molecules by nanosize water droplets containing Co2+ species in supercritical carbon dioxide fluid

Stabilized nano-sized water droplet carrying water-soluble Co2+ species is employed as a new catalyst system for the oxidation of the alkyl aromatics in the presence of a fluorinated surfactant. This stable system contains no labile C-H structure and can facilitate excellent mixing of catalytic Co(II)/NaBr species, hydrocarbon substrates and oxygen in supercritical carbon dioxide fluid, which is demonstrated to be an excellent alternative solvent system to acetic acid or nitric acid for air oxidation of a number of alkyl aromatic hydrocarbons using Co(II) species at mild conditions. As a result, potential advantages of this 'greener' catalytic method including safer operation, easier separation and purification, higher catalytic activity with selectivity and without using corrosive or oxidation unstable solvent are therefore envisaged.

Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

Study of the effect of biodiesel fuel on passive oxidation in a catalyzed particulate filter

A 2007 Cummins ISL 8.9L direct-injection common rail diesel engine rated at 272 kW (365 hp) and 317 kW (425 hp) was used to load the filter to 2.2 g/L and passively oxidize particulate matter (PM) within an aftertreatment system consisting of a diesel oxidation catalyst (DOC) and catalyzed particulate filter (CPF). The tests conducted with the engine rated at 365 hp used a 2007 DOC and CPF. The tests conducted with the engine rated at 425 hp used a 2010 DOC and 2007 CPF. Understanding the passive NO2 oxidation kinetics of PM within the CPF allows for reducing the frequency of active regenerations (hydrocarbon injection) and the associated fuel penalties. Modeling the passive oxidation of accumulated PM in the CPF will lead to creating accurate state estimation strategies. The MTU 1-D CPF model will be used to simulate data collected from this study to examine differences in the PM oxidation kinetics when soy methyl ester (SME) biodiesel is used as the source of fuel for the engine, and when the engine is operated at a higher power rating. A test procedure developed by Hutton et al. [1, 2] was modified to improve the ability to model the experimental data and provide additional insight into passively oxidized PM in a partially regenerated CPF. A test procedure was developed to allow PM oxidation rates by NO2 to be determined from engine test cell data. An experimental matrix consisting of CPF inlet temperatures from 250 to 450 °C with varying NOX/PM from 25 to 583and NO2/PM ratios from 5 to 240 was used. SME biodiesel was volumetrically blended with ULSD in 10% (B10) and 20% (B20) portions. This blended fuel was then used to evaluate the effect of biodiesel on passive oxidation rates. Four tests were performed with B10 and four tests with B20. Gathering data to determine the effect of fuel type (ULSD and biodiesel blends) on PM oxidation is the primary goal. The engine used for this testing was then configured to a higher power rating and one of the tests planned was performed. Additional testing is scheduled to take place with ULSD fuel to determine the affect the engine rating has on the PM oxidation. The experimental reaction rates during passive oxidation varied based upon the average CPF temperature, NO2 concentrations, and the NOX/PM ratios for each engine rating and with all fuels. The data analysis requires a high fidelity model that includes NO2 and thermal oxidation mechanisms and back diffusion to determine the details of the PM oxidation process.

Hydrocarbon concentrations from pressurized cores in the northern Gulf of Mexico

Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct-Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg**-1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.