Coadsorption of the gases p-xylene and m-xylene on BaY and NaY was studied at 150 °C in the range of pressure 10 -2 -3 hPa. For BaY coadsorption isotherms and single-component adsorption isotherms are perfectly superimposed in the whole range of investigated pressure. The capacity of adsorption of BaY is 3 molecules R -1 for each single component as well as for each mixture under 3 hPa. For NaY coadsorption isotherms lie between those of single p-xylene and m-xylene. The capacity of adsorption of NaY for mixtures is in proportion to the composition of the initial adsorptive mixture and varies from the capacity of adsorption for single p-xylene (3.3 molecules R -1 ) to that for single m-xylene (3.6 molecules R -1 ) under 3 hPa. The selectivity of the Y zeolite depends on the filling, the composition of the mixture, and the exchangeable cation. Two selective adsorption processes are discerned according to the filling of R-cages. For filling lower than 2 molecules R -1 , BaY and NaY exhibit the same behavior toward the coadsorption of p-xylene and m-xylene and adsorb preferentially the more abundant isomer in initial adsorptive mixture: the selectivity depends only on the composition of the mixture. For filling higher than 2 molecules R -1 as the last molecules of xylenes are adsorbed in the R-cages, BaY is selective for p-xylene whereas NaY is selective for m-xylene whatever the composition of the adsorptive mixture: the selectivity depends on the exchangeable cation. The dependence of the composition of adsorbate on the selectivity shows a nonideal behavior of the adsorbate.

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The adsorption mechanism of n-alkanes on silicalite has been studied by 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 reversibility of the adsorption equilibrium, and it is demonstrated that TPD experiments occur under conditions that are very close to equilibrium. A quasi-chemical approach taking into account different adsorption sites provides a good modeling of the TPD curves. Sorption enthalpy and entropy variations of n-alkanes are obtained. The sorption data for n-butane to n-octane are in good agreement with adsorption literature data. Moreover, they provide relevant information on the adsorption mechanism and show that entropic effects are predominant.