Effect of supercritical conditions on the oxidation of isobutane

The paper examines the kinetics of isobutane oxidation in the liquid phase and under supercritical conditions. Isobutane oxidation has gained importan ce because of the applications of the oxidation products such as tert-butyl hydroperoxide and tert-butyl alcohol in the manufacture of the important c hemicals like propylene oxide and MTBE. An interesting aspect of this react ion is that, the reaction conditions can be conveniently manipulated in suc h a way that isobutane exists in supercritical state. The influence of supe rcritical conditions on the rate and selectivity of the reaction is investi gated and this permits a comparison of liquid phase and supercritical phase oxidation. The reactions were also performed in a glass-lined continuous r eactor. This mode of operation allows kinetic studies without an interventi on of gas-liquid mass transfer and in addition eliminates the catalytic eff ect, if any, of the stainless-steel walls. The reaction is autocatalytic an d the selectivity towards the hydroperoxide decreases with an increase in o verall conversion. Under supercritical conditions, the rates and selectivit y were significantly high compared to those obtained in liquid phase oxidat ion. In both, subcritical and supercritical oxidations, temperature has an adverse effect on selectivity towards tert-butyl hydroperoxide. A proposed kinetic model successfully explains the kinetic data and allows the rate co nstants and the activation energy to be determined. It is shown that the su percritical-phase oxidation shows all features present in the liquid-phase oxidation. Thus, this work provides a unified treatment for the supercritic al- and the liquid-phase oxidation of isobutane. (C) 1999 Elsevier Science Ltd. All rights reserved.