Wet oxidation of benzoic acid catalyzed by cupric ions: Key parameters affecting induction period and conversion

Abstract

The catalytic wet oxidation (CWO) of aqueous solutions of benzoic acid (BA) has been thoroughly investigated using various copper- and iron-containing catalysts with emphasis on cupric nitrate. The influence of BA concentration ranging from 50 to 150mg/L, catalyst loading varying between 50 and 150mg/L (i.e. 14 and 40mgCu/L), reaction temperature in the range 150–180°C and oxygen partial pressure in the range 10–30bar on the induction period of the reaction and BA conversion has been extensively studied. A factorial experimental design methodology has been implemented to assess the significance of the aforementioned parameters and a mathematical model has been proposed. The induction period observed during the CWO of BA is strongly affected by the reaction temperature and to a lesser extent by the initial BA concentration, the oxygen partial pressure, as well as by the second order interaction between initial BA concentration and oxygen partial pressure. Differences in chemical structure account for different reactivities: electron-donating substituents (i.e. methoxy- or hydroxyl-group) seem to increase the reactivity of benzoic acid, whereas the presence of electron-withdrawing substituents, such as nitro-group, decreases the reactivity of the molecule. Hydroxylation of the aromatic ring is an important pathway during the CWO of BA.