Kinetics of wet oxidation of propionic and 3-hydroxypropionic acids

Oxidation of aqueous solutions of 3-hydroxypropionic (3-HPA) and propionic acids (PA) was studied in a titanium high-pressure reactor at 280-310 degre es C using oxygen partial pressures between 10 and 45 bar. Oxidation of bot h acids was found to obey first-order kinetic with respect to their concent rations as well as to their lumped TOC concentrations. Oxidation rate revea led a half order dependence with respect to oxygen for oxidation of both ac ids. In the case of 3-HPA oxidation, the activation energy was found to be 135 kJ/mol, and it was 140 kJ/mol when lumped concentration TOC was used. T he activation energy for PA oxidation is 150 kJ/mol, and it is slightly hig her, 158 kJ/mol, for TOC reduction. Almost complete conversion of S-HPA was achieved at 300 degrees C after 1 h, whereas 95% conversion of PA acid was obtained at 310 degrees C after 3 h. During oxidation of 3-HPA, 3-oxopropi onic and acetic acids were identified as intermediate products. Oxidation o f PA yielded acetic and formic acids as intermediates; at oxygen partial pr essures above 25 bar and 310 degrees C, the formation of acetic acid was ap preciably reduced. In both cases, however, direct oxidation to carbon dioxi de and water was found to be the main reaction route.