Nuclear magnetic resonance self-diffusion studies of methanol–water mixtures in pentasil-type zeolites

Abstract

Molecular self-diffusion data of methanol–water mixtures sorbed in pentasil-type zeolites of two different Si/Al ratios are reported. At medium loading and room temperature, the self-diffusion coefficients of sorbed methanol and water are found to be of the order of 10^–9 m² s^–1. For both sorbate molecules intracrystalline mobility is greater for the higher Si/Al ratio. While water self-diffusion is only slightly affected by sorbate concentration, in the case of methanol a decrease of approximately one order of magnitude with increasing loading has been observed. In contrast to the liquid state, the sorbed state of binary mixtures exhibited no minima of the self-diffusion coefficients. The molecular mobilities observed can be correlated with structural features of the pentasils determined from ¹H n.m.r. measurements.