Kinetics of hydrolysis of benzaldehyde dimethyl acetal over Amberlite IR-120

Abstract

The kinetics of the hydrolysis of benzaldehyde dimethyl acetal has been studied using a circulated batch reactor in dioxane. Amberlite IR-120, in its acidic form, was used as a heterogeneous catalyst. Kinetic expression for the formation of acetal was also determined since the reaction is reversible. In the temperature range 298-328 K, the equilibrium constant for hydrolysis of benzaldehyde dimethyl acetal was found to be K-e = exp(8.67 - 1880/T) mol center dot L-1 where T is the absolute temperature in Kelvin. In the presence of catalyst, the reaction has been found to occur between an adsorbed water molecule and a molecule of acetal in the bulk phase (Eley-Rideal model). It was also observed that benzaldehyde adsorbed by the catalyst has an inhibiting effect on the reaction rate. From this model it was concluded that the reaction is a "surface reaction control" and its rate will be given by the expression -r(W) = [k(m/V)(CACW - ((CBACM2)/K-e))]/[1 + KBACBA + KWCW] where concentrations are in the unit of mol center dot L-1. It was shown that temperature dependency of the hydrolysis rate constant can be given by k = exp(9.4 - 4915/T) L-2 center dot(g-dry resin)(-1)center dot mol(-1)center dot min(-1). The adsorption equilibrium constants related to benzaldehyde and water were also calculated to be K-BA = exp(7292/T - 24.9) L center dot mol(-1), K-W = exp(1296/T - 4.4) L center dot mol(-1), respectively.