DIFFUSION OF STRAIGHT-CHAIN AND BRANCHED-CHAIN LIQUID COMPOUNDS IN H-ZSM-5 ZEOLITE

Effect of chain length, chain branching, and polarity of sorbate molecule on its diffusion in H-ZSM-5 zeolite has been investigated by studying the sorption of liquid normal C2-C-8 alcohols, isobutanol, tert-butanol, n-butylamine, n-hexane, and isooctane in the zeolite at different temperatures (274-338 K) using the volumetric sorption method. The chain branching and the increase in chain length caused a large decrease in the diffusivity and also a large increase in the activation energy for the diffusion. For sorbates having same molecular critical size and chain length and close molecular weight, their diffusion is stronly affected by the polarity of sorbate. The diffusion of nonpolar sorbate is found to be much faster. For polar sorbates, diffusion depends not only on the polarity of sorbate molecules but also on their interactions with the acid sites and/or cations in the zeolite.