Discrimination among gas translation, surface and Knudsen diffusion in permeation through zeolite membranes

Gas translation diffusion is proposed to compete with surface diffusion for describing the permeation of light gases (He, H-2, CO2 and CO) through zeolite membranes. The analysis for both DD3R and NaY zeolite membranes shows some differences in H-2, CO and CO2 permeation for both binary/ternary gas mixture and single gas. The permeation description through gas translation of weakly adsorbed species such as, e.g., H-2, specifically at low temperatures, is more accurate than that obtained by Knudsen diffusion in a previous work. Gas translation paired to surface diffusion well reproduces the maximum in H-2 flux, which was missed by the Knudsen diffusion (Caravella et al., 2016) [13]. The strongly adsorbed species are less dependent on gas translation or Knudsen diffusion since the surface diffusion is very significant in the whole temperature range investigated. The gas translation was demonstrated to reproduce the permeation through zeolite membranes better than Knudsen diffusion. This paper attempts to discriminate the operating mechanisms among gas translation, surface and Knudsen diffusion in gas mixture permeation through zeolite membranes.