Kinetics of Hydrolysis of Benzaldehyde Dimethyl Acetal over Amberlite IR-120

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 Ke = exp(8.67 − 1880/T) mol·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 −rW = [k(m/V)(CACW − ((CBACM2)/Ke))]/[1 + KBACBA + KWCW] where concentrations are in the unit of mol·L-1. It was shown that temperature dependency of the hydrolysis rate constant can be given by k = exp(9.4 − 4915/T) L2·(g-dry resin)-1·mol-1·min-1. The adsorption equilibrium constants related to benzaldehyde and water were also calculated to be KBA = exp(7292/T − 24.9) L·mol-1, KW = exp(1296/T − 4.4) L·mol-1, respectively.