Methane first-order kinetics

The presence of the intermediate methane in the ethane and propane oxidation experiments, coupled with failure to detect ethane or ethene intermediates in the propane experiments constitutes indirect evidence that the reaction rate constants are in the order k >k >k, This order is confirmed by comparing Tablls°5fnlo tVlan t s rate constants calculated on the assumption of first order kinetics, decrease with percent reaction. This is presumably the consequence of the closed reactor conditions and for this reason, rate constants are not given in the tables. However, on average, the assumption of first order kinetics with respect to... 

Effectiveness factors calculated in this way are of the order of 0.02-0.04 for both reactions. Van Hook (1 9) and Rostrup-Nielsen (20) published values which are of the same order of magnitude, but the latter were obtained assuming first order kinetics for the methane conversion and equilibrium for the watergas shift. The corresponding reaction layer amounts to 0.65-1.3 10 A, and to a surface area still exceeding Sp by a factor IOOO. 

The work by Wei and Iglesia [516] confirmed the first-order kinetics with respect to methane (Figure 3.29), but with no impact on the rate of other reactants. 

A second possibility to arrive to a similar first-order kinetics is starting from a dual site Langmuir-Hinshelwood model with oxygen adsorbed strongly in dissociative form while methane is adsorbed weakly ... 

Kinetic studies on the nitration of nitrobenzene by nitronium borofhioride in the polar solvents sulphuric acid, methane-sulphuric acid, and acetonitrile show the reaction to be first-order in both nitronium salt and aromatic110. With the first two solvents, the rate coefficients are similar for nitration by nitric acid and by the nitronium salts, indicating a common nitrating entity. With acetonitrile the rate coefficients are very much lower, consistent with a much lower concentration of free nitronium ions in this medium and thus with the nitronium salts existing as ion pairs in organic solvents (see Table 25). 

The rate is near first order in methane and zero order in oxygen for oxygen to methane ratios higher than 1. Also, the reaction kinetics remain unaffected upon polarization conditions. The kinetic data indicate weak bonding of methane and strong bonding of oxygen on the catalyst surface. 

Figure 7.8 Equilibrium curves (dotted lines) for the WGS reaction with or without methanation reaction for feed gas composition with 50% H2. The filled squares and circles are CO conversions over G-66 A and Cu02Ce08O2 y, catalysts, respectively. The solid lines are model fits assuming first-order reversible kinetics. (Reprinted from [51], With permission from Elsevier.)...

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