Kinetics and Mechanism of Methanol Oxidation in Supercritical Water

Abstract

We oxidized methanol in supercritical water at 246 atm and temperatures between 500 and 589 °C. Pseudo-first-order rate constants calculated from the data led to Arrhenius parameters of A = 1021.3±5.3 s-1 and Ea = 78 ± 20 kcal/mol. The induction time for methanol oxidation decreased from 0.54 s at 525 °C to 0.093 s at 585 °C and the reaction products were formaldehyde, CO, and CO2. Formaldehyde was a primary product, while CO and CO2 were secondary products. Formaldehyde was more reactive than methanol and its yield was always less than 24%. The temporal variation of the CO yield exhibited a maximum, whereas the CO2 yield increased monotonically. The experimental data were consistent with a set of consecutive reactions (CH3OH → CH2O → CO → CO2) with pseudo-first-order global kinetics. The experimental data were also used to validate a detailed chemical kinetics model for methanol oxidation in supercritical water. With no adjustments, this elementary reaction model quantitatively predicts the product distr...