STRUCTURAL EFFECT ON MOLECULAR SIMULATIONS OF TIGHT-PORE SYSTEMS

Adsorption of benzene and p-xylene on silicalite at infinite dilution at 20-degrees-C has been investigated via direct integration and Monte Carlo techniques. A small uncertainty in crystal structure causes a v ery large difference in the values of the Henry constants, while the i nternal energy of adsorption is less sensitive to this uncertainty. Th e sensitivity of the Henry constant to structural detail is magnified in these systems due to the tight fit of these molecules in the silica lite pore structure. This high sensitivity casts a shadow of doubt on the applicability of the common practice of determining potential para meters from data at infinite dilution while assuming that the structur e is rigid and completely defined. The calculations reveal that the pr eferential adsorption sites for both benzene and p-xylene are the chan nel intersections. Benzene is somewhat mobile between straight channel s and intersections while p-xylene is almost completely localized at t he intersections at 20-degrees-C. In tight-pore systems the most prefe rred adsorption site Is not necessarily the location with the highest adsorption potential, contrary to adsorption on flat surfaces and in l arge pores.