The oxidation rate of methanol in supercritical water at 253 bar and temperatures between 673 and 773 K is investigated using an isothermal, isobaric plug-flow tubular reactor and GC/FID and GC/TCD chromatographic methods. Experiments are conducted at a nominal methanol feed concentration of 0.88 mol % (1.53 wt %) using H2O2 as an initial oxidant. In some experiments, the O2MeOH molar ratios are varied from 1.5 to 3.0 and show that the rate of methanol oxidation is independent of the oxygen initial feed concentration. Overall first-order rate constants calculated from the data lead to Arrhenius parameters of A = 1011.8 s-1 and Ea = 178 kJ/mol (42.5 kcal/mol). The identified reaction products are mainly CO and CO2. The temporal variation of the CO yield exhibits a maximum at temperatures of 723 and 748 K, whereas the CO2 yield increases monotonically over the experimental range of residence time (3-50 s). The experimental data are consistent with a set of consecutive first-order reactions CH3OH → CO → CO2. The global rate-controlling step in the complete oxidation of methanol is the conversion of CO to CO2. The first-order rate constants calculated for CO oxidation to CO2 lead to A = 1010.8 s-1 and Ea = 172 kJ/mol (41.0 kcal/mol). Kinetics of this system may be useful to study supercritical water oxidation (SCWO) of polychlorinated biphenyls (PCBs) dissolved in methanol.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering