Influence of Si/Al ratio on hexane isomers adsorption equilibria

In this work we aim to have a better knowledge of the influence of silica/alumina ratio (SAR) on the adsorption equilibrium of hexane isomers on MFI zeolites. With a manometric set-up coupled with a micro-calorimeter we did address adsorption properties and heats of adsorption of n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane on three samples with different Si/Al ratio. The branched isomers all show a type I isotherm on the three samples, while n-hexane presents a dual site for SAR 1600 and 100, and type I for SAR 50. The Si/Al ratio has a large influence on the adsorption equilibrium properties, in addition the Henry's constant and initial heats of adsorption increase with aluminium content. The saturation loading decreases with the increasing aluminium content. The differential heat of adsorption of n-hexane increases slightly with loading, whereas the heat of adsorption of branched hexanes presents a decrease with loading. The three MFI zeolite samples present equilibrium selectivity towards n-hexane. (C) 2007 Published by Elsevier Inc.