Experimental evidence of the influence of sorption-heat release processes on the sorption kinetics of benzene in NaX zeolite crystals

Abstract

Under constant-volume–variable-pressure conditions the sorption uptake of benzene by NaX zeolite crystals has been investigated with respect to the influence of external thermal conditions on the uptake rate. The information obtained permits quantitative conclusions concerning the influence of the sorption heat generated on the uptake rate, i.e. the decrease in apparent diffusivities calculated under the erroneous presumption of the isothermicity of the sorption process considered. A corresponding tentative mechanism which takes into account the generation of thermal interface barriers is proposed. Furthermore, there are experimental conditions for which the uptake of benzene by NaX zeolite crystals should be considered as an isothermic process. Within that parameter region agreement was obtained between the sorption diffusion data (corrected by the Darken equation) and the n.m.r. self-diffusivities, as reported earlier.