Capillary condensation and sorption hysteresis of toluene, methylcyclohexane and neopentane on MCM-41 and MCM-48

Abstract

In this work, the adsorption of toluene, methylcyclohexane and neopentane was measured at several temperatures on MCM-41 and MCM-48 silica of similar pore size. The MCM-41 has a hexagonal array of uniform cylindrical pores while MCM-48 has a three-dimensional pore system consisting of two interwoven channels separated by a continuous pore walL The aim of this work is to investigate the effect of the pore structure ofMCM-48 on the capillary condensation and adsorption hysteresis ofthe hydrocarbons. It was found that the MCM-41 and MCM-48 silicas adsorb similar amounts of toluene and methy1cyclohexane at pressures below capillary condensation, despite the latter having a higher pore volume. This was not observed for the adsorption of nitrogen and neopentane. The adsorption behaviour of nitrogen and neopentane on MCM-48 compared to that on MCM-41 is identical and distinct from that of toluene and methy1cyclohexane. The hysteresis behaviour of toluene and methy1cyclohexane was found to be significantly affected by the pore structure of the MCM-48 material, with that of methylcyc1ohexane being the most affected. While adsorption hysteresis is observed at identical or slightly higher temperature on the methy1cyc1ohexane isotherms of MCM-41 materials, the Tch of toluene adsorbed on MCM-48 is 20 K higher.