(583d) A Combined Volumetric and FTIR Apparatus for the Measurement of Adsorption Kinetics

The measurement of adsorption kinetics in zeolites is challenging due to the combined heat and mass transfer mechanisms involved in the process. In the case of a volumetric apparatus it is possible to reduce thermal effects by modifying the thermal mass of the sample, but for strongly adsorbed and rapid uptake systems this may not achieve near isothermal behaviour.

In this contribution we present an approach based on performing a volumetric experiment with an uptake cell that can be inserted in an FTIR instrument. In the first instance a sample of ZSM-5 powder is pressed into a thin pellet and the FTIR is used in transmission mode. With this configuration both the external pressure and the average adsorbed phase concentration are measured simultaneously. The results obtained using n-hexane and toluene indicated that heat effects were not negligible. A thermal imaging camera was added in order to measure also the surface temperature of the pellet.

The system in this configuration provides a direct measurement of total pressure, average adsorbed phase concentration and surface temperature of the solid. These experimental signals are matched to the theoretical non-isothermal volumetric model and provide information that can be used to determine both heat transfer and mass transfer coefficients.