Counterdiffusion of liquid hydrocarbons in type Y zeolite: Effect of molecular size, molecular type, and direction of diffusion

This paper presents experimental results on the counterdiffusion of liquid hydrocarbons in the Y zeolite as determined by an unsteady state technique using the zeolite powder. The critical diameter of aromatic molecules counterdiffusing with respect to cyclohexane into NaY zeolite has a marked effect upon the counterdiffusion rate. For a given molecular type, the single parameter of critical molecular diameter correlates the size effect well. Molecular type, for example, toluene vs. phenol, also has a pronounced effect on the counterdiffusion rate. Those molecules showing stronger interactions with the zeolite have lower counterdiffusion rates. In both NaY and SK‐500, the diffusion coefficients for adsorptive counterdiffusion are an order of magnitude greater than the diffusion coefficients for desorptive counter‐diffusion indicating that factors other than simple intracrystalline diffusion as such are also important in zeolite counterdiffusion. Simple diffusion models do not account for the differences observed indicating that a more sophisticated approach is necessary.