Selective oxidation of p-cymene catalyzed by VPO catalyst: Process performance and kinetics studies

The catalyzed liquid phase oxidation process of p-cymene to tertiary cymene hydroperoxide (TCHP) by vanadium phosphorous oxide (VPO) catalysts was studied in a well-stirred batch reactor. It was found that the VPO compounds improve the p-cymene oxidation rates and selectivity towards TCHP. In particular, the process gave around 85% TCHP selectivity with conversion of about 30% achieved within 4 h when compared to long oxidation times (8–12 h) in non-catalyzed industrial-scale p-cymene oxidation process. Although catalysts material containing the vanadyl pyrophosphate phase ((VO)2P2O7) are more active and selective, there is no evidence that this phase is the solely required active phase for this type of oxidation reaction based on the results of the tested different VPO catalyst phases. The results indicated the active participation of the catalyst in the initiation of the oxidation process, thus, reducing the long induction period. In the presence of only initiator added (ROOH), the reaction initiation showed typical long induction period of about 5–6 h to form only about 1% conversion. The observed improved TCHP selectivity displayed by the VPO catalyst during normal oxidation reaction can be explained by the slow or insignificant influence of the catalyst on the decomposition rate of the formed TCHP to by-products at substrate conversions of 35% or less. A kinetic model was determined that fitted the experimental results to predict the performance of the p-cymene liquid phase oxidation rates and conversion.