Kinetics and dynamic behaviour of toluene desorption from ZSM-5 using in situ high-temperature synchrotron powder X-ray diffraction and chromatographic techniques

In situ high-temperature (HT) synchrotron X-ray powder diffraction (XRPD), was used in this study as a tool to understand the adsorption/desorption process features of toluene adsorbed in organophilic ZSM-5 zeolite (SiO2/Al2O3 ∼280), as well as framework structural modifications upon thermal treatment from room temperature to 600 °C. Rietveld refinements showed that toluene release starts in the 75 °C< T < 200 °C temperature range. Furthermore, extraframework structural changes take place when toluene removal starts. Significant internal pressure is developed with the composition product diffusion causing a corresponding transient expansion in the 10-ring channels. Our results clearly demonstrated that ZSM-5 regeneration is effective when it is thermally treated at about 400 °C. Above this temperature, when all the organic have been ejected, non-equilibrium distortions in the framework are relaxed and channel apertures become more circular. ZSM-5 shows no significant difference in saturation capacity once regenerated after toluene reloading, thus demonstrating that thermal regeneration under mild conditions appears to be both very effective even after several cycles of adsorption/desorption.