Reaction engineering investigations of the heterogeneously catalyzed partial oxidation of o-xylene in the explosion regime using a microfixed bed reactor

The heterogeneously catalyzed selective gas phase oxidation of o-xylene was investigated, using a microstructured fixed bed reactor, inside of the explosion regime. The reaction was carried out with high amounts of o-xylene in air and stoichiometric with oxygen using a V2O5/TiO2-catalystV2O5/TiO2-catalyst prepared through grafting. There were no significant losses in the selectivity to phthalic anhydride observable, during the measurements in the explosion regime, with feed compositions of up to 7 vol% o-xylene. Also the space-time yield was up to 2.3 times higher in comparison to conventional reaction conditions. An increase of the selectivity to total oxidation products was observed at higher o-xylene concentrations between 10 and 25 vol% o-xylene, which possibly was caused by the formation of a hotspot. The investigation of the used catalyst revealed a thermally induced deactivation due to phase transition of anatase into rutil and formation of crystalline vanadium oxide. Despite that expected hotspot at high o-xylene concentrations, there was no ignition or explosion of the gas mixture observable.

► O-Xylene gas phase oxidation to phthalic anhydride inside of the explosion regime. ► V2O5/TiO2 grafting catalyst was used in a microstructured fixed bed reactor. ► High selectivities to phthalic anhydride were obtained up to 7 vol% o-xylene. ► Selectivity to phthalic anhydride decreased at higher o-xylene concentrations. ► Possibility of a hotspot was estimated at high o-xylene concentrations.