Methane general characteristics

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

Bartholomew and co-workers also measured the loss of catalytic activity with time of Ni and Co bimetallics (157, 194), Ni-molybdenum oxide (23, 113), and borided Ni and Co catalysts (161) during methanation in the presence of 10 ppm H2S. Typical activity versus time plots are shown in Figs. 25 and 26. Activity is defined as the ratio of the mass-based rate of methane production at any time t divided by the initial rate. The activitytime curves are generally characteristic of exponential decay some catalysts decay more slowly than others, but all catalysts suffer at least two orders of magnitude loss in activity within a period of 100-150 hr. Accordingly, it does not appear that other metals or metal oxides in conjunction with Ni significantly change the sulfur tolerance defined in terms of steady-state activity of Ni. These materials can, however, influence the rate at which the... 

Jupiter s general characteristics have been well known for some time. Unlike the inner planets, it has no distinct dividing line he tween an outer atmosphere and an inner core, mantle, and crust. Instead, Jupiter consists of elements, compounds, and other chemical species that are normally gaseous hut that may occur as liquids or solids the closer they are to the planet s center. As the diagram below shows, the outermost region of the planet, the "atmosphere" that is visible from Earth, consists of clouds of ammonia, methane, and water. The pressure within the cloud layer is about one atmosphere, and the temperature, about 165 K (about -100 °C). 

In general, each nomial mode in a molecule has its own frequency, which is detemiined in the nonnal mode analysis [24]- Flowever, this is subject to the constraints imposed by molecular synmietry [18, 25, 26]. For example, in the methane molecule CFI, four of the nonnal modes can essentially be designated as nonnal stretch modes, i.e. consisting primarily of collective motions built from the four C-FI bond displacements. The molecule has tetrahedral synmietry, and this constrains the stretch nonnal mode frequencies. One mode is the totally symmetric stretch, with its own characteristic frequency. The other tliree stretch nonnal modes are all constrained by synmietry to have the same frequency, and are refened to as being triply-degenerate. 

A methanogenic bacterium was isolated from oil reservoir brines by enrichment with trimethylamine. Methane production occurred only with trimethyl-amine compounds or methanol as substrates. Sodium ions, magnesium ions, and potassium ions were all required for growth. This organism appears to be a member of the genus Methanohalophilus based on substrate utilization and general growth characteristics [695]. 

Thus methyl radicals are consumed by other methyl radicals to form ethane, which must then be oxidized. The characteristics of the oxidation of ethane and the higher-order aliphatics are substantially different from those of methane (see Section HI). For this reason, methane should not be used to typify hydrocarbon oxidation processes in combustion experiments. Generally, a third body is not written for reaction (3.85) since the ethane molecule s numerous internal degrees of freedom can redistribute the energy created by the formation of the new bond. 

The C2 chemistry is more complex than the Ci chemistry, and it is less well examined. As was the case for methane, the C2 hydrocarbons are oxidized through different pathways at low and high temperatures. The low-temperature mechanism is even more complex than that of methane, and is not discussed in detail here. It shares characteristics both with the methane low-temperature mechanism and that for higher hydrocarbons, which we discuss in general terms in Section 14.3.3. ... 

The location of the CO peak indicates the temperature regime for onset of fast oxidation for each hydrocarbon. At the reaction conditions of the flow reactor, the characteristic temperature regime for oxidation differs widely between fuels. Compared to methane, the C2 hydrocarbons are consumed at much lower temperatures at a given reaction time. This is consistent with the general observation that the C2 hydrocarbons have quite different ignition characteristics compared to methane [427]. As a consequence the presence of ethane (C2H6) and higher hydrocarbons in natural gas has a considerable influence on induction times. 

Very recently, various DHB complexes were analyzed [39].12 The complexes of ammonia and hydronium ions were included in this analysis, in addition to the complexes with acetylene and methane, and their derivatives. Generally, in such complexes, lithium hydride and berylium hydride (and its fluorine derivative) act as the Lewis bases (proton acceptors) while hydronium ion, ammonia ion, methane, acetylene, and their simple derivatives act as the proton donors. Therefore, it was possible to investigate the wide spectrum of DHB interactions, starting from those that possess the covalent character and extending to the systems that are difficult to classify as DHBs (since they rather possess the characteristics of the van der Waals interactions). Figure 12.8 displays the relationship between H—H distance and the electron density at H—H BCP.13 One can observe the H—H distances close to 1 A, (as for the covalent bond lengths) and also the distances of about 2.2—2.5 A, typical for the van der Waals contacts. This also holds for the pc-values - of the order of 0.1 a.u. as for the covalent bonds and much smaller values as for the HBs and weaker interactions. 

Explosion characteristics include the values of average and maximum rate of pressure rise and maximum pressure produced by the explosion (Table 3.59). Effective explosion suppression requires getting sufficient amounts of chemical to the trouble area in a very short time. Water and C02 are not generally utilized for explosions. Halogenated compounds, mostly methane derivatives, are popular suppressants. The hardware for explosion suppression falls into three categories (1) detectors (2) control units, which initiate the corrective action and (3) the actuated devices, which blanket the protected area with the suppressant. 

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