Degradation kinetics of p-nitrophenol ozonation in water

Abstract

The degradation of p-nitrophenol with ozone in water has been studied. The influence of pH and ozone partial pressure on p-nitrophenol conversion has been observed. The kinetic regime of ozone absorption has been shown to be highly dependent on both variables. Thus, at pH 2 the kinetic regime corresponds to a slow reaction regardless of the ozone partial pressure applied. At pH 6.5 the absorption of ozone develops in the fast kinetic regime the reaction being of pseudo first-order with respect to ozone at ozone partial pressures lower than 500 Pa. Finally, at higher pH (8.5 and 12.4) and ozone partial pressures higher than 2000 Pa, the reaction becomes instantaneous. Under conditions of slow and instantaneous kinetic regimes the liquid phase volumetric mass transfer coefficient, k L a, was calculated. The results are in agreement with those obtained from the absorption of ozone in organic-free water at similar pHs. On the other hand, under the situation of fast pseudo first-order reaction the rate constant for the p-nitrophenol-ozone direct reaction was determined to be 4.5 × 10 6 M −1 s −1. The ozone decomposition reaction develops to some extent only at pH 12.4.