Inorganic Membrane Reactors for the Gas Phase Partial Oxidation of Toluene

The gas phase oxidation of toluene was studied as an alternative way to obtain benzaldehyde and benzoic acid. A traditional support (TiO2) and a new mixed Al2O3–TiO2 support for the active catalyst element, vanadium, was used. The oxidation process was investigated by either using a packed bed reactor or inorganic membrane reactors. Vanadium was deposited on the supports (powder or inorganic membranes) through either ion exchange or impregnation from a solution of ammonium metavanadate. The catalysts were characterized in terms of vanadium content and distribution, morphology, specific surface area and porosity. The reaction runs quantified catalytic activity of the catalysts prepared. The effect of the temperature and of the hydrocarbon=oxygen ratio was investigated. Selectivity to intermediate oxygenated products was higher for vanadium supported by Al2O3–TiO2 and when the hydrocarbon to oxygen ratio was higher, the formation of carbon oxides was lowered. Finally inorganic membrane reactors were explored using different reactor configurations (i.e. both the reactants, toluene and oxygen, were flowed inside a inorganic membrane tube with catalytic walls, or were forced through the membrane from the internal side to the outer side).