Methane reactions atmosphere

The influence of electronegative additives on the CO hydrogenation reaction corresponds mainly to a reduction in the overall catalyst activity.131 This is shown for example in Fig. 2.42 which compares the steady-state methanation activities of Ni, Co, Fe and Ru catalysts relative to their fresh, unpoisoned activities as a function of gas phase H2S concentration. The distribution of the reaction products is also affected, leading to an increase in the relative amount of higher unsaturated hydrocarbons at the expense of methane formation.6 Model kinetic studies of the effect of sulfur on the methanation reaction on Ni(lOO)132,135 and Ru(OOl)133,134 at near atmospheric pressure attribute this behavior to the inhibition effect of sulfur to the dissociative adsorption rate of hydrogen but also to the drastic decrease in the... 

Reaction between carbon monoxide and dihydrogen. The catalysts used were the Pd/Si02 samples described earlier in this paper. The steady-state reaction was first studied at atmospheric pressure in a flow system (Table II). Under the conditions of this work, selectivity was 100% to methane with all catalysts. The site time yield for methanation, STY, is defined as the number of CH molecules produced per second per site where the total number of sites is measured by dihydrogen chemisorption at RT before use, assuming H/Pd = 1. The values of STY increased almost three times as the particle size decreased. The data obtained by Vannice et al. (11,12) are included in Table II and we can see that the methanation reaction on palladium is structure-sensitive. It must also be noted that no increase of STY occurred by adding methanol to the feed stream which indicates that methane did not come from methanol. 

A great number of catalysts have been tried in the oxidation of methane at atmospheric pressure with the hope of obtaining intermediate products of oxidation. It appears, however, that catalysts tend to carry the reaction to equilibrium, at which state methanol, formaldehyde and formic acid are present in only extremely minute traces. This is well illustrated by the work of Wheeler and Blair," who studied the influence of catalysts in connection with their work on the mechanism of combustion. When methane was oxidized in the presence of metallic and metallic oxide catalysts, no formaldehyde could be detected even at very short times of contact. The formaldehyde produced in the circulation experiments was in a concentration much greater than that required for equilibrium in the reaction ... 

MPa total pressure, and H2 CO equal to 1.9. This may be a conservatively low value, as all the cobalt on the support may not be metallic. The value of Nco ior methanation at atmospheric pressure obtained by Vannice (12) on a 2% C0/AI2O3 catalyst, D = 0.08, was 4.6 X 10 sec" after extrapolation to 197°C. Furthermore, Vannice (12) obtained a — 0.5 order dependence on CO pressure. The two values of Nco for FT and methanation seem to be close. However, when compared with other reactions such as hydrogenation of olefins, where N at ambient conditions is about 1 sec (13), the Fischer-Tropsch reaction can be seen to be quite slow. 

The concurrent formation of methanol and formaldehyde during the oxidation of methane at atmospheric pressme in a static quartz reactor (T = 440—450 °C, fr = 1.5—4.3 min) was observed in [24]. Under these conditions, the methanol-to-formaldehyde ratio increased monotonically with decreasing residence time (Fig. 2.4), which led the authors to suggest that, at atmospheric pressure, methanol is the primary product of the process. However, even at the shortest reaction time (fr = 1-5 min), the selectivity of methanol formation was only 4.6%. 

Another example of the combined effect of nitrogen oxides and a heterogeneous catalyst in the oxidation of methane at atmospheric pressure is given in [188]. In this paper, the authors demonstrated that, by using MgO and CaO, alkaline-earth metal oxides with a high adsorption capacity with respect to OH radicals, as catalysts, it is possible to increase the yield of Ci-oxygenates in the NOx-promoted process by 10%, evidently due to a decrease in the rate of consumption of formed oxygenates in reactions with radicals. 

Availability of methane determines quality of methanotrophic community. Soils incubated in the atmosphere enriched with methane (10% vol.) showed high capacity for methane oxidation but they do not show the ability to oxidize methane at atmospheric (ambient) concentration (Walkiewicz et al. 2012). This phenomenon can result from the presence of the type II methanotrophs in soils. Those methanotrophs have methanotrophic maximum activity and a low affinity to CH (high value of the Michaelis constant Kj ) (Bender Conrad, 1993). Both the parameters are determined on the base of Michaelis-Menten equation. K constant represents the substrate concentration at which the rate of an enzyme-catalysed reaction is half of the maximum value. The type II bacteria are isolated from the environments rich in methane (>1%) and poor in oxygen (about 1%) (Hanson Hanson, 1996), such as bog peat or landfill covers. They are less sensitive to the environmental changes than the type I bacteria which has a low value of and high affinity to methane (Henckel et al. 2000) proved by the low value... 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

Beryllium carbide slowly hydroly2es to beryllium oxide and methane in the presence of atmospheric moisture although months may be requited to complete the reaction. Any carbon contained in beryllium metal is present as the carbide because the solubiUty of carbon in beryllium is extremely low. 

In the CVD coating process, the tools are heated in a sealed reactor with gaseous hydrogen at atmospheric or lower pressure volatile compounds are added to the hydrogen to supply the metallic and nonmetaUic constituents of the coating. For example, TiC coatings are produced by reaction of TiCl vapors with methane (CH and hydrogen (H2) at 900 to 1100°C. The reaction is... 

Miscellaneous Reactions. Ethylene oxide is considered an environmental pollutant. A study has determined the half-life of ethylene oxide ia the atmosphere (82,83). Autodecomposition of ethylene oxide vapor occurs at - 500° C at 101.3 kPa (1 atm) to give methane, carbon monoxide, hydrogen, and ethane (84—86). 

Stable intermediates are those where concentration and lifespan are comparable to those of stable reactants and products. An example is the reaction between methane and oxygen in the gas phase at 700 K and 1 atmosphere. The overall reaction is ... 

Methane reacts with sulfur (an active nonmetal element of group 6A) at high temperatures to produce carbon disulfide. The reaction is endothermic, and an activation energy of approximately 160 KJ is required. Activated alumina or clay is used as the catalyst at approximately 675°C and 2 atmospheres. The process starts by vaporizing pure sulfur, mixing it with methane, and passing the mixture over the alumina catalyst. The reaction could be represented as ... 

Methane is the most difficult alkane to chlorinate. The reaction is initiated by chlorine free radicals obtained via the application of heat (thermal) or light (hv). Thermal chlorination (more widely used industrially) occurs at approximately 350-370°C and atmospheric pressure. A typical product distribution for a CH4/CI2 feed ratio of 1.7 is mono- (58.7%), di-(29.3%) tri- (9.7%) and tetra- (2.3%) chloromethanes. 

A promoted nickel type catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700-800°C and 30-50 atmospheres, respectively. The reforming reaction is equilibrium limited. It is favored at high temperatures, low pressures, and a high steam to carbon ratio. These conditions minimize methane slip at the reformer outlet and yield an equilibrium mixture that is rich in hydrogen. ... 

The composition of the planetary atmospheres is fairly constant. This is indeed surprising in view of the fact that molecules such as methane, ammonia, and carbon dioxide are easily decomposed by the ultraviolet radiation from the sun. Presumably other reactions regenerate those substances that are light sensitive. 

At elevated temperatures, methylene carbons cleave from aromatic rings to form radicals (Fig. 7.44). Further fragmentation decomposes xylenol to cresols and methane (Fig. 7.44a). Alternatively, auto-oxidation occurs (Fig. 1.44b ). Aldehydes and ketones are intermediates before decarboxylation or decarbonylation takes place to generate cresols and carbon dioxide. These oxidative reactions are possible even in inert atmospheres due to the presence of hydroxyl radicals and water.5... 

---