Isobutane oxidation in the liquid and supercritical phases: comparison of features

The liquid phase oxidation (LPO) of isobutane is normally carried out in industry at conditions close to critical, and much data is available under these conditions. This reaction therefore affords an opportunity for a comparative study between supercritical oxidation (SCO) and LPOs, under very similar conditions of temperature and pressure. While studies in the literature report higher rates and yields for the SCO, it is not clear whether the reported effects have to do with the supercriticality of the reaction mixture or merely the different conditions employed to cause the mixture to become supercritical. This paper aims to clarify this point through a careful analysis of the published data on supercritical and liquid phase oxidations. The analysis demonstrates that the features of SCO extrapolate directly from those of LPO. A kinetic model previously proposed for the oxidation of cyclohexane [1] has been extended to isobutane oxidation and shown to fit the data well, not only in the liquid phase region, but in the supercritical region as well. The conclusion that emerges is that the oxidation under supercritical condition offers higher rates and productivities than conventional LPO, because it makes it possible to obtain liquid phase-like reaction behaviour at temperatures not accessible to LPO. These findings are of significance in view of claims in the patent literature on the advantages of SCO, and make it possible to predict the rate and yield obtainable under supercritical conditions. (C) 199