ADSORPTION OF AROMATIC-HYDROCARBONS IN NAX ZEOLITE .2. KINETICS

Kinetic data are reported for the sorption of a range of aromatic sorbates in unaggregated crystals of NaX zeolite. Diffusivities (at 600 K) range from order 10(-6)-10(-7) cm2.s-1 for benzene and p-xylene to 10(-14)-10(-15) cm2.s1 for hexamethylbenzene and anthracene. The diffusivities decrease with increasing sorbate size, but the relationship is complex and does not follow the sequence of either molecular weight or critical molecular diameter. Rather the correlation appears to be with the moment of inertia of the sorbate molecule, suggesting that restriction of the rotational freedom of the diffusing molecule is probably a major factor. For several of the sorbates the validity of the diffusion model was confirmed by replicate measurements with different crystal size fractions.