Methane dependent ratios

A representative comparison of the effect of the catalyst bed geometry on methane conversion and product selectivity over a range of methane/air ratios is shown in Fig 4 Unlike typical supported catalysts, where the catalyst is well-dispersed and submicrometer-sized, the noble-metal catalysts in these methane oxidation reactions were basically films with micrometer-sized surface features (Other tests on both extruded cordiente and alumina foam monoliths with lower catalyst loading resulted in similar carbon monoxide production but lower hydrogen yields than those illustrated in the figure, which provided evidence that the reaction is catalyst-dependent and not initiated by the monoliths or gas... 

FIGURE 9.20 Dependence of the selectivity of methanol formation on the methane/oxygen ratio for the oxidation of methane in SCW (70% HzO-SOX CH4) [224],... 

Instead of conversion, some producers prefer to use other identifications of severity, including coil outlet temperature, propylene to methane ratio, propylene to ethylene ratio, or cracking severity index (33). Of course, all these definitions are somewhat dependent on feed properties, and most also depend on the operating conditions. 

The chemical reactions that occnr in flames transform an initial reactant mixtnre into final reaction prodncts. In the case of fnel-oxygen combns-tion, the final prodncts are principally water vapor and carbon dioxide, althongh nnmerons other prodncts snch as carbon monoxide may be formed, depending on the reactant composition and other factors. If the ratio of fnel-to-oxygen is stoichiometric, the final reaction prodncts, by definition, contain no excess fnel or oxygen. Theoretically, this means that partial oxidation prodncts snch as CO (itself a fnel) are not formed. In reality, partial oxidation prodncts snch as CO or OH are formed by high tem-peratnre reactions. For example, the molar stoichiometric reaction of methane is written ... 

Figure 9. Dependence of the ratio of CH + ions to total ions in the methane mass spectrum on the pressure of methane in the mass spectrometer ion source for different values of source repeller voltage...

Kinetic examination of the methane yield shows behavior quite similar to that of methyl radical a pressure dependent yield of 0.406 molecule/100 e.v., a pressure independent yield of 0.126 molecule/100 e.v., and a rate constant ratio of kq/kf = 1.5 X 106 mole-1 cc. for the competing steps. 

One notes that the coverage of Cads depends on two important parameters the ratio p of the rate of hydrogenation of Cads to give methane and the rate constant of CO dissociation ... 

The catalyst performance depends on the H2 to CCI2F2 feed ratio. The selectivities to CH2F2 and CHCIF2 are influenced by the H2 to CCI2F2 feed ratio, while the selectivity to methane is independent of this ratio. We have previously proposed a reaction mechanism with serial reactions on the catalyst surface and minor readsorption of the intermediate products, which is depicted in figure 8 [4,5]. Thus the kinetics of the reaction follows mainly parallel reaction pathways, in which the selectivities are not influenced by the conversion, and a... 

The reason for this lies in the relatively high cost of gas compression, which depends on the ratio of the inlet and outlet pressures. The methane feed to the reformer will probably be available at a pressure much above 1 bar and similarly with the steam. Le Chatelier s principle indicates also that excess steam, as used in practice, will favour a higher conversion of methane compared with the stoichiometric proportions of the reactants. The same conclusion follows quantitatively from Kpi for which the equation involves the total pressure P. 

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