Kinetic modelling of benzyl alcohol selective oxidation in aqueous mixtures of nitric and sulfuric acids

Benzyl alcohol oxidation by means of nitric acid or mixed acids for benzaldehyde production is a very attractive process enabling quantitative conversion and high purity. However, a number of discrepancies can be found in the past literature about the reaction mechanism and the kinetic behaviour of the system. In the present investigation, by running the reaction in a batch system under homogenous conditions, a radical mechanism was ruled out and experimental evidence of an ionic reaction network was provided. No induction period was found possibly due to a low amount of nitrous acid produced by dissociation of concentrated nitric acid. The reaction rate is significantly increased by the addition of sulfuric acid. A mathematical model is proposed based on benzyl nitrite as the key intermediate which is in equilibrium with benzyl alcohol and irreversibly decomposes with a significant yield of benzaldehyde. The model is capable to predict the behaviour of the reacting homogeneous phase system at varying initial conditions. The estimated kinetic and thermodynamic parameters are reported. The kinetic modelling carried out in this work would also be relevant to run the selective oxidation of benzyl alcohol in other reactor schemes, such as continuous flow (micro) reactors.