The oxidative demethylation of toluene, using bismuth uranate as oxidant

When brought into contact with various bismuth uranates in a stream of an inert gas at 400-500 °C, toluene is oxidized to benzene, CO2 and H2O. The best benzene yields are obtained using the compound Bi2UO6 with a high specific surface area. A fixed percentage of the oxygen atoms present in this compound gives rise to a rapid total combustion of the toluene. After the consumption of these atoms, toluene is converted into benzene with a selectivity up to 70%. During this process bismuth uranate can lose 60% of its oxygen atoms, corresponding to zero-valent bismuth and tetravalent uranium. The original activity is completely restored by oxidation with molecular oxygen. This opens the possibility of demethylating toluene by passing air and toluene alternately over bismuth uranate. The kinetics of the reaction between toluene and bismuth uranate, investigated in micropulse and microflow systems and in a thermobalance, are complicated. The surface reaction appears to be first order in toluene with an energy of activation of 30 kcal mole-1 at 480 °C, but the transport rate of oxygen from the bulk of the Bi2UO6 matrix to the surface also plays a role. The selective reaction is likely to occur via a benzoate-like intermediate. The reoxidation of reduced bismuth uranate with air is very fast, and even proceeds at 100 °C.