Methane recent measurements

Older IR-imwstigalions by Kolbel et at. led to the assumption of surface formyl or hydroxycarbene groups [113]. More recent measurements on supported ruthenium under synthesis conditions showed absorptions for mr ecularly adsorbed CO and for formate and CH species. As a result of deuieration experiments, however, the latter were concluded not to be reaction intermediates (113. 106], It was also shown that the production of methane and ethane continued for a significant period after CO had been removed from tlic reaction mixture and after the disappearance of all IR-observable COads species [106J. It was concluded that product formation occurs via carbidic intermediates. /n-situ IR studies at higher pressures (3 bar) revealed formation of CHjf species with absorptions in the 3000 cm region (114). 

Yes, there is no question that the handling of cattle, and the kinds of cattle, have changed at the same time that the numbers are changing. As far as I know, there are no recent measurements of the methane production per animal, nor any measurements which would allow comparison of the methane yield per animal from one country to another. There have been large differences in the way in which cattle have been treated from one continent to another for a long time. There is very little information about the methane release from different kinds of cattle, for different types of feed, for any of the many variables that obviously can be considered. The methane release estimate per head of cattle is a measured figure, but it is certainly crude to apply any of the measured releases for all types of cattle, on all types of feed, in every location in the world. However, they are the only data available and provide a crude estimate for the world release. 

Recent work indicates that it may be possible to discriminate between hydrate methane and diage-netic methane with measurements of If... 

Recent measurements (1980) Indicate that the atmospheric methane is about -47.0 0.3 /oo (48). The average isotopic fractionation associated with the sink process is -2.5 1.5°/oo, and there is a +0.3°/oo Isotope effect resulting from the nonsteady state increasing methane concentrations (48). This implies that the average for all sources is about... 

The discovery of methane in the atmosphere is due to Migeotte (1948). He observed the characteristic absorption features of CH4 in the infrared spectrum of the sun and estimated a mixing ratio of 1.5 ppmv. The majority of all recent measurements since the late 1960s have employed gas chromato-... 

Table 4-6. Recent Measurements of the Average Tropospheric Mixing Ratio m of Methane and the Ratio m /msfor the Mixing Ratios in the Northern and Southern Hemispheres...

Significant uncertainties have been associated with the dissociative recombination rate of Hj. However, recent measurements have shown that the rate is rapid, even if the ion is in its lowest vibrational state. The main primary ions in the topside ionosphere can be rapidly lost by reactions with upfiowing methane. However, the importance of this process depends on the rate at which methane is transported up fi om lower altitudes, which in turn depends on the eddy diffusion coefficient, which is not well known. Direct photoionization of hydrocarbon molecules at the lower altitudes can lead to a relatively thin, about 50 km broad, hydrocarbon ion layer around 300 km. 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

Recently, the CH4+-CH4 reaction has been investigated (9) by measuring the CH4 + disappearance cross-section rather than CH5 + formation cross-sections. Results of this work are shown in Figure 9. Two mechanisms cause a loss of CH4 + ions from the total ion yield in the methane mass spectrum. There are loss processes in the ion source which generate new ions, CH5 +, and possibly other products. Other loss... 

Figure 1. Atmospheric methane increases over the last 300 years. Points are annual averages the concentrations before 1960 are from ice core analyses more recent data from atmospheric measurements. From Khalil and Rasmussen (40).

Oilfields in the North Sea provide some of the harshest environments for polymers, coupled with a requirement for reliability. Many environmental tests have therefore been performed to demonstrate the fitness-for-purpose of the materials and the products before they are put into service. Of recent examples [33-35], a complete test rig has been set up to test 250-300 mm diameter pipes, made of steel with a polypropylene jacket for thermal insulation and corrosion protection, with a design temperature of 140 °C, internal pressures of up to 50 MPa (500 bar) and a water depth of 350 m (external pressure 3.5 MPa or 35 bar). In the test rig the oil filled pipes are maintained at 140 °C in constantly renewed sea water at a pressure of 30 bar. Tests last for 3 years and after 2 years there have been no significant changes in melt flow index or mechanical properties. A separate programme was established for the selection of materials for the internal sheath of pipelines, whose purpose is to contain the oil and protect the main steel armour windings. Environmental ageing was performed first (immersion in oil, sea water and acid) and followed by mechanical tests as well as specialised tests (rapid gas decompression, methane permeability) related to the application. Creep was measured separately. 

Reported flame speed results for most fuels vary somewhat with the measurement technique used. Most results, however, are internally consistent. Plotted in Fig. 4.21 are some typical flame speed results as a function of the stoichiometric mixture ratio. Detailed data, which were given in recent combustion symposia, are available in the extensive tabulations of Refs. [24-26], The flame speeds for many fuels in air have been summarized from these references and are listed in Appendix F. Since most paraffins, except methane, have approximately the same flame temperature in air, it is not surprising that their flame speeds are about the same (—45 cm/s). Methane has a somewhat lower speed (<40 cm/s). Attempts [24] have been made to correlate flame speed with hydrocarbon fuel structure and chain length, but these correlations... 

Bordwell (Bordwell and Bausch, 1986) has developed a method to determine C—H BDEs from a combination of p ha values and oxidation potentials (E ) of the corresponding anions in dimethyl sulphoxide solution. These acidity-oxidation potentials (AOP) are taken as measures for BDEs and are related to the stabilization of the radicals formed. This procedure has been recently applied to the subject of captodative stabilization (Bord-well and Lynch, 1989). Values of ABZ) relative to the C—H BDE in methane are calculated according to (13). These values are set equal to the... 

In Fig. 15.4, the measured turbulent flame speeds, normalized with mixture-specific laminar flame velocities obtained recently by Vagelopoulos et al. [14], are compared with experimental and theoretical results obtained in earlier studies. Also shown in the figure are the measurements made by Abdel-Gayed et al. [3] for methane-air mixtures with = 0.9 and = 1 a correlation of measured turbulent flame speeds with intensity obtained by Cheng and Shepherd [1] for rod-stabilized v-flames, tube-stabilized conical flames, and stagnation-flow stabilized flames, Ut/Ul = l + i.2 u /U ) a correlation of measured turbulent flame... 

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