ADSORPTION OF N-ALKANES ON SILICALITE CRYSTALS - A TEMPERATURE-PROGRAMMED DESORPTION STUDY

The adsorption mechanism of n-alkanes on silicalite has been studied b y a modified temperature-programmed desorption (TPD) technique. These experiments are performed by thermogravimetry at constant hydrocarbon partial pressure and at slow heating rate. This work establishes the r eversibility of the adsorption equilibrium, and it is demonstrated tha t TPD experiments occur under conditions that are very close to equili brium. A quasi-chemical approach taking into account different adsorpt ion sites provides a good modeling of the TPD curves. Sorption enthalp y and entropy variations of n-alkanes are obtained. The sorption data for n-butane to n-octane are in good agreement with adsorption literat ure data. Moreover, they provide relevant information on the adsorptio n mechanism and show that entropic effects are predominant.