Methylbranched C5-C9 alkanes do not adsorb in the intracrystalline void space of ZSM-23, neither from the vapour nor the liquid phase, but are adsorbed in ZSM-22, if only from the liquid phase, and this despite the small difference in pore size.

In the present work, molecular competition effects in the hydroconversion of alkane mixtures in vapor and liquid phase were studied. The influence of the pore size was investigated by performing catalytic experiments with equimolar heptane/nonane mixtures on a series of bifunctional zeolite catalysts (Pt/H-Y, Pt/H-USY, Pt/H-Beta, Pt/H-MCM-22). Vapor phase catalytic experiments were performed at a total pressure of 4.5 bar, while a total pressure of 100 bar was applied in the liquid phase experiments. The experimental results were analyzed using a lumped adsorption-reaction model. In vapor phase, the longest chain is preferentially converted on all studied catalysts. In liquid phase, the differences in conversion rate were less pronounced. On Pt/H-MCM-22, with active pockets on the surface, and Pt/H-USY having large mesopores, the competition between short and long alkanes in liquid phase reflect the intrinsic reactivities of the reacting molecules. In zeolites with smaller pores (Pt/H-Y, Pt/H-Beta), an inversion of the reactivity order of alkanes of different chain length was observed when increasing the pressure from 4.5 bar and vapor phase to 100 bar and liquid phase. The inversion of apparent reactivity orders is due to changes in physisorption at high pressure, favoring uptake of the smallest molecules.

A calculation method for Henry constants of diatomic molecules in zeolite cages is proposed. The method is based on a molecular electrostatic potential approximation formulated within a density functional theory (DFT) context for the evaluation of interaction energies. This approach is compared with ab initio and "molecule-in-point-charge-field" calculations. The effect of wave function versus DFT methods and basis set is discussed. The influence of the integration grid is studied and the partitioning of the cage in different peels, depending on the level of calculation, is considered. An optimal "quality/cost" ratio for the Henry and separation constants for nitrogen, oxygen, and argon (included as reference) in an NaY zeolite α-cage is obtained using the B3LYP/6-31G * method for the evaluation of the interaction energies and a Van der Waals radii-based criterion for determining the integration grid. Including carbon monoxide as a fourth example, for which no experimental results were yet available, confirms the excellent results for the calculation of separation constants. Some further refinement for the evaluation of adsorption energies is necessary.

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