Compressibility of zeolite 4A is dependent on the molecular size of the hydrostatic pressure medium

Abstract

Unit-cell parameters of synthetic zeolite 4A were determined at several pressures to 4.0 GPa in four different hydrostatic pressure media: ethanol, methanol, glycerol, and an organofluorine compound, C8F16O (FC-75). These data, when combined with previously published results on zeolite in water and a water-bearing 4 : 1 methanol : ethanol mixture, reveal that compression of zeolite depends on the relative sizes of the hydrostatic fluid molecules compared with the structural channels in the zeolite framework. Zeolite 4A is most compressible (ΔV/VΔP =β=0.046 GPa−1) in glycerol and FC-75, which have molecular dimensions that are larger than the zeolite channels. Zeolite is least compressible ( β=0.007 GPa−1) in water, which has a maximum molecular dimension that is significantly smaller than the channel diameter. In methanol and ethanol alcohols, which have intermediate molecular diameters, zeolite 4A also has intermediate compressibility. This zeolite in alcohols, furthermore, progressively undergoes a series of transitions to more compressible states as pressure is raised.