Controlling mechanisms in benzene oxidation

Abstract

The vapour-phase oxidation of benzene has been the subject of several previous studies, but the controlling mechanisms in this reaction have not been fully elucidated. In the present work, based on a scheme in which benzene is simultaneously and consecutively (through maleic anhydride) oxidised to the final products of combustion (carbox dioxide and water), suitable first-order equations have been set up for the three reactions on a molybdenum-vanadium catalyst. The experimental results indicate that there is a definite shift in the controlling mechanism at about 350°C as evidenced by the change in the activation energy from about 20 kcal/g mole in the lower temperature range to about 2 kcal/g mole in the higher temperature range. A detailed analysis of the reaction in the higher temperature region has, however, shown that neither pore diffusion nor external mass transfer is controlling. It has therefore been postulated that this change is probably due to a change in chemical mechanism and not to a shift from the chemical to a diffusion regime.