Kinetics of malonic acid degradation in aqueous phase over Pt/graphite catalyst

This work aims at describing quantitatively the catalytic decarboxylation of malonic acid over a 5.0 wt. percent Pt/graphite catalyst. The study was carried out using a slurry phase continuous flow stirred slurry reactor (CSTR) at a temperature range a 120-160 degreesC and at reactor pressure of 1.8 MPa. The conversion of malonic acid during catalytic oxidation was found to proceed via decarboxylation to CO2 and acetic acid, and also oxidation to CO2 and H2O. No indication of deactivation of the platinum catalyst was observed at a maximum residual oxygen pressure in the reactor up to 150 kPa. A reaction mechanism involving elementary steps has been suggested to explain the decarboxylation and oxidation of malonic acid. A kinetic model that accounts for both non-catalysed and catalysed decarboxylation of malonic acid has been developed and validated. The non-catalysed reaction is first order in malonic acid. The activation energies and adsorption enthalpies have been determined. The model is able to describe the experimental data adequately. (C) 2004 Elsevier B.V. All rights reserved.