Bifurcation analysis of methyl radical oxidation in open systems. The low-pressure regime

Abstract

Domains of bistability and hysteresis in the isothermal oxidation of methyl radicals by O_2 in low-pressure flow reactors are identified by means of continuation algorithms using a mechanism based on experimental results. Control (unfold) parameters comprise the reactants' inflows, F, residence time τ, and the probabilities, γ, of chain carrier losses per collision with reactor walls. The effect of methane addition is also investigated. In the spanned ranges, the singular points detected correspond to single folds of stable into unstable branches, marking the onset of narrow hysteresis loops. Orbits of bistability were found by tracing out the folds in two parameters: (F,τ) or (F_i,F_j). This analysis discloses the rich kinetic behavior expected for this system, in which the “branching” reaction (H + O_2 → OH + O) produces an inert radical toward the reactant. It also predicts the existence of high- and low-oxidation regimes under certain conditions and provides the basis for process optimization, i.e., for minimizing methyl losses, or for maximizing methyl yields in the sensitized oxidation of added methane.