ADSORPTION EQUILIBRIUM OF BENZENE-P-XYLENE VAPOR MIXTURE ON SILICALITE

Adsorption equilibrium of benzene-p-xylene vapor mixture on silicalite is measured at 70-degrees-C with a specially designed cyclic volumetr ic apparatus at pressure levels of 2.53 and 1.20 kPa. The isobaric iso therms are S-shaped, and selectivity curves at different pressures cro ss over; the p-xylene selectivity at 2.53 kPa is higher than that al 1 .20 kPa over a certain composition range. The heterogeneous ideal adso rbed solution (HIAS) model implemented on two patches qualitatively pr edicts these highly unusual behavior. The observed extraordinary pheno mena are attributed to structural heterogeneity, a result of the tight -fit of sorbate molecules in silicalite pores. The success of HIAS att ests to the paramount importance of adequate representation of heterog eneity in adsorption models.