Self-diffusion of simple alcohols in heteroionic forms of LTA zeolites

Radiotracers have been used to follow molecular diffusion of ethyl and n-butyl alcohols in LTA zeolite crystallites under the conditions of liquid phase sorption. Evidence of a two-stage process has been observed. In the case of ethyl alcohol movement this prevented the estimation of energy barriers to molecular migration. Estimates were possible when n-butyl alcohol was the labelled species. The effect of the presence of Mg, Ca, Sr, Zn, Na, Li, K, and H cations was studied. It was concluded that the mobility of unbound alcohol molecules contributed to the initial diffusion process and that the second process was associated with alcohol molecules in some form of solvation shield round the cations present in the larger zeolite cages. Comparisons to literature data for molecules moving in the gaseous phase through zeolites were made, and this enabled suggestions of the mechanism for movements of molecules through zeolites in the liquid phase. (C) 2001 Elsevier Science B.V. All rights reserved.