APPLICATION OF THERMAL-ANALYSIS FOR EXPLAINING THE SORPTION OF BENZENE AND N-HEXANE ON SILICALITE

The origin of kinks (steps) on sorption isotherms was examined for the sorption of benzene and n-hexane on silicalite-1. In both cases sorpt ion revealed the existence of two different binding sites. There was n o equilibrium (or a very slow one), between molecules bound at differe nt sites. Sorption energies within particular centres display more or less wide overlapping distributions leading to a single resultant isot herm. Depending on differences in binding energies and degree of overl apping, the resulting isotherms exhibit steps (benzene) or no steps (n -hexane). In fact, the sorption isotherm of benzene being a sum of two elemental isotherms (Omega(1) and Omega(2)) of different shapes is ch aracterized by a 'kink', in contrast to n-hexane the elemental isother ms of which are of the same shape.