Kinetic modelling of phenol hydroxylation using titanium and tin silicalite-1s: Effect of tin incorporation

Effects of tin incorporation in titanium silicalite-1 (TS-1) on the kinetic modelling of phenol hydroxylation to dihydroxybenzenes with aqueous hydrogen peroxide have been investigated. The modelling of the hydroxylation reaction was from the results of a batch reactor, minimizing mass transfer conditions. The kinetic analysis indicates that under the same reaction conditions, titanium-tin silicalite-1 (Ti-Sn-S-1) gave a higher phenol conversion rate than TS-1. This was attributed to the Sn active sites. Incorporation of tin influences the initiation of intermediate reactions of products with hydrogen peroxide. Tin increases the rate of benzoquinone conversion to tar; however, it does not affect hydroquinone and catechol reactions. A Langmuir–Hinshelwood-type mechanism model was used to fit the proposed phenol hydroxylation and parallel reactions of products with the observed rate data. The intrinsic kinetic constants were found to be proportional to the concentration of reactants and the Ti and Sn active sites. The surface reaction yielded the best fit of the model for reactions in the system. It however failed to predict the outcome of the catechol reaction using TS-1, in which the catechol adsorption on the Ti active site was rate-limiting. The model fitted to the experimental data generated in this study was determined to provide the best values for the kinetic parameters. The effect of temperature on the hydroxylation rate is also documented in further detail.