A reduced mechanism for methanol oxidation in supercritical water

We reduced the complexity of a previously reported 151 reaction, 22 species, free-radical reaction mechanism for the oxidation of methanol in supercritical water by using a net rate analysis and sensitivity analysis. The reduced mechanism contains only 17 reactions and 14 chemical species, yet the model based on this mechanism predicts concentrations of methanol, formaldehyde, CO and CO2 that are essentially indistinguishable from those of the complete mechanism under the range of reaction conditions of interest. The successful development of such a reduced mechanism points to the possibility of using mechanism-based kinetics models, rather than empirical global models, in supercritical water oxidation reactor engineering studies. We used the reduced mechanism to assess the effect of the uncertainty in the rate constants on the model predictions. This uncertainty analysis employed a Monte Carlo approach wherein the value of the rate constant for each elementary reaction was chosen randomly from within the range of values encompassed by the confidence interval for that rate constant. The results of this uncertainty analysis revealed the approximate ranges of the products' molar yields that would fall within the model's uncertainty for a given set of reaction conditions. By assessing the uncertainties in both the reduced mechanism-based model and in previous experimental results, we show that the reduced mechanism reported herein provides an accurate description of the reaction rates and product selectivities for methanol oxidation in supercritical water. (C) 1998 Elsevier Science Ltd. All rights reserved.