The liquid-phase adsorption of C5-C24 linear alkanes in zeolite 5A at room temperature was studied using the configurational bias Monte Carlo molecular modeling technique and the batch experimental method. Up to C16, a highly discontinuous variation of the saturation capacity with the carbon number occurred. Whereas the shortest chains remain as a whole within the cage, longer chains are distributed in a more bent configuration over adjacent cages or even adopt highly coiled configurations within one cage. For alkanes greater than C16, a sharp, unexpected drop in adsorption capacity with a minimum at C18-C19 was observed experimentally. The almost complete exclusion of these alkanes was not observed in the molecular simulation under equilibrium conditions and is explained by an extremely slow diffusion of C18-C19 because of "cage nestling", i.e., an imperturbable adsorption of tightly fitting highly coiled n-alkanes in the first supercage they enter. The competitive adsorption and counterdiffusion of alkane mixtures is strongly affected by the differences in adsorption mechanism for alkanes of different chain length.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films