DIFFUSION OF MONATOMIC., DIATOMIC AND SIMPLE POLYATOMIC SORBATES IN 5A AND 13X ZEOLITE CRYSTALS AS STUDIED BY THE ZLC METHOD

Abstract

Intracrystalline diffusivities for Ar, Kr, Xe, O2, N2, CO2, CH4 and C2H6 in 5A zeolite and for O2, N2and C2H6 in NaX zeolite have been determined, over the temperature range 190-273K, by the zero length column (ZLC) method using crystals in the size range 27-100 μm. Under these conditions desorption rates are relatively low and easily measured. The dominance of intracrystalline diffusion resistance was confirmed by varying the crystal size. The ZLC diffusivities for CH4 and C2H6 in 5A and for C2H6 in NaX are quite close to the NMR self-diffusivities but for Xe 5A the agreement is not as close. The diffusivities are compared with the predictions from transition state theory and tentative conclusions are drawn concerning the nature of the diffusion process.