Kinetic analysis of the oxidation of ascorbic acid in an open reactor with gas bubbling

Abstract

An open reactor with gas bubbling with various oxygen partial pressure was applied to investigate the role of oxygen in the oxidation of ascorbic acid (AA). The reaction kinetics was described well by the zero-th order mechanism and the rate constant was exactly propor tional to the oxygen partial pressure but no effect of initial AA concentration was observed. The reaction rate increased with an increase in pH and decreased by the addition of EDTA as a chelating agent to trace metals suggesting the involvement of metals in the AA oxidation process. The temperature dependence of the kinetics was measured from 0 to 70°C and the activation energy was obtained to be 62.1 kJ/mol. On the contrary, the AA oxidation was described by the 1-st order kinetics in a closed reactor system because of the limiting oxygen supply. From these results, the aerobic AA oxidation scheme was estimated with the reaction between molecular oxygen and AA as a limiting step.