A Kinetic Study of Methanol Oxidation in Supercritical Water

Abstract

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 H 2 O 2 as an initial oxidant. In some experiments, the O 2 /MeOH 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 ) 10 11.8 s -1 and E a ) 178 kJ/mol (42.5 kcal/mol). The identified reaction products are mainly CO and CO 2 . The temporal variation of the CO yield exhibits a maximum at temperatures of 723 and 748 K, whereas the CO 2 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 CH 3 OH f CO f CO 2 . The global rate-controlling step in the complete oxidation of methanol is the conversion of CO to CO 2 . The first-order rate constants calculated for CO oxidation to CO 2 lead to A ) 10 10.8 s -1 and E a ) 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.

Decomposition of monochlorobiphenyl isomers in supercritical water in the presence of methanol

“…The experimental apparatus, described in detail elsewhere (Anitescu et al, 1999), consists of three major modules: pumps and preheaters, reactor, and cooling and separation. Several modifications are operated to improve its functionality and the quality of the data.…”

Kinetic analysis on alcohol concentration and mixture effect in supercritical water oxidation of methanol and ethanol by elementary reaction model

“…For instance, Vogel et al in their review [1] compared methanol conversion data as function of initial concentration reported by various research groups and concluded that higher concentrations of methanol in the feed gave a higher conversion, due to the short induction time by the calculations performed with a modified GRI mechanism. Rice et al [3] and Anitescu et al [4] also suggested that the apparent pseudo first order kinetics was sometimes not an accurate description of the rate behavior. However, detailed kinetic analysis of a wide feed concentration range of methanol was not found in the reported review.…”

SCWO of salt containing artificial wastewater using a transpiring-wall reactor: Experimental results

“…Methanol (Synopharm, Schweizerhalle, Basel, Switzerland, purity > 99.8%) is chosen as model organic compound, since it is widely used in model systems when performing SCWO studies [65][66][67][68][69][70][71][72]. The electric conductivity of the desalinated water at ambient conditions is 0.6-0.9 S. Technical grade oxygen (PanGas, Dagmersellen, Switzerland, purity > 99.5%) is used as oxidizer.…”