KINETICALLY DRIVEN INSTABILITIES ACID SELECTIVITIES IN METHANE OXIDATION

Ignitions, extinctions, and Hopf bifurcations in methane oxidation wer e studied as a function of pressure and inlet fuel composition. A cont inuous stirred-tank reactor was modeled with numerical bifurcation tec hniques, using the 177 reaction/31 species mechanism. Sensitivity and reaction pathway analyses were performed at turning points to identify the most important reactions and reactive species. Then, simulations were compared with experimental data. Multiple ignitions and extinctio ns as well as oscillations that are purely kinetically driven were fou nd. Ignition to a partially ignited state with considerable reactivity of methane indicates possible narrow operation windows with high sele ctivities to partial oxidation products. At 0.1 atm, we found a select ivity of up to 80% to CO at 70% CH4 conversion. The ignition to a full y ignited branch is associated with high selectivity to CO2 and H2O. T he C2 chemistry inhibits the ignition of methane to the partially igni ted branch. The methane ignition temperature exhibits two branches wit h respect to pressure, with only the low-pressure branch being dominan t. Reaction path analysis at ignition conditions shows that the prefer red pathway of CH4 oxidation is to form CO and CO2 through CH2O and CH 2(s) intermediates. However, at intermediate to high pressures, the re combination of CH3 to C2H6 also becomes quite significant.