A Kinetic Study of the Simultaneous Dealkylation and Disproportionation of Cumene over Silica–Alumina

Abstract

Abstract Cumene has been passed over a silica–alumina bed at low temperature (210 to 254 °C) and at cumene pressures of 0.003 to 0.023 atm. Both dealkylation and disproportionation occurred simultaneously and independently of each other. The disproportionation/dealkylation ratio increased with decrease in temperature and/or an increase in cumene pressure. The dealkylation and disproportionation reactions followed a Langmuir-Hinshelwood model with inhibition by the reactant. The dealkylation has been interpreted in terms of a unimolecular surface reaction, while the disproportionation reaction in terms of a bimolecular surface reaction. The heat of adsorption of cumene and the entropy loss of cumene on adsorption were much larger for the dealkylation sites than for the disproportionation sites. These results indicated that dealkylation was catalyzed by strong acid sites, while disproportionation by weak acid sites. The dealkylation had a much higher activation energy than the disproportionation reaction. The activation energy for dealkylation (33.5 kcal mol−1) was in good agreement with that predicted on the assumption that the previously reported LFER (linear free-energy relationship) in the alcohol dehydration holds for alkylbenzene dealkylation.