HYDROTHERMAL OXIDATION KINETICS OF ETHANOL IN HOT COMPRESSED WATER

摘要

Ethanol oxidation rate in sub-critical water needs to be investigated to estimate the processing capacity of subcritical water oxidation as a heat source. Various studies about hydrothermal oxidation of ethanol have been reported, which have been carried out with a single step reaction rate of reactants considering decomposition of ethanol into acetic acid. The desire for the more realistic numerical simulation requires a multiple step reaction rate of ethanol into carbon dioxide and water. The purpose of this work is to construct the multiple step reaction pathways and decide the oxidation rate. Ethanol oxidation in subcritical water was examined at 25 MPa in the temperature range of 260-350 °C with equivalence ratio of 0.6. Oxidation reactions by oxygen were accomplished in a flow reactor, which was operated at subcritical conditions. The liquid and gas samples obtained were analysed by gas chromatographs. The overall first-order decomposition reaction parameters were determined to be 102.9 ± 0.5 s-1 for the pre-exponential factor and 54.2 ± 4.9 kJ·mol-1 for the activation energy. The products obtained by the hydrothermal oxidation of ethanol were acetaldehyde, acetic acid and carbon dioxide, and a small amount of other intermediates. First-order kinetics was enough to capture the main characteristics of species concentration profiles. Consecutive reaction network: C2H5OH→CH3CHO→CH3COOH→CO2 qualitatively described wet oxidation of ethanol.