Derivative enthalpies of adsorption of p-xylene and m-xylene onto NaY and BaY zeolites at 150 degrees C - Contribution to the prediction of adsorption selectivity

The derivative enthalpies of adsorption of m-xylene and p-xylene onto the N aY and BaY zeolites were measured at 150 degrees C, then compared with thos e obtained at 25 degrees C, and finally used to predict the selectivity of adsorption of xylene mixtures. Significant differences were observed as the temperature was elevated: for the NaY zeolite, the adsorbate-adsorbate int eractions became prevalent, in contrast with the BaY zeolite, between zeoli te and derivative interactions were stronger. The difference between the ad sorption derivative enthalpies of the two xylenes displayed an abrupt varia tion from 2 molec. alpha(-1) for both zeolites, the filling from which sele ctivity towards m-xylene for the NaY zeolite and towards p-xylene for the B aY zeolite appeared. The preferentially adsorbed xylene was closely connect ed with the sense of this difference, which changed with the zeolite.