Transport and sorption studies in beta and USY zeolites via temporal analysis of products (TAP)

Abstract

Single pulse TAP experiments were chosen for obtaining estimates of intra-particle diffusion coefficients and better insight into adsorption–desorption dynamics and equilibria for isobutane and n-butane in commercially available beta and USY zeolite. This technique provides a unique way of directly estimating transport and sorption processes at extremely low surface coverage ( θ i → 0), in the absence of an inert carrier stream, with no external mass transfer resistance, and with a negligible thermal effect. The use of a thin zone TAP reactor configuration enables the use of small zeolite particles without causing high bed resistance. A theoretical model that considers transport and adsorption–desorption phenomena in the inter-particle and intra-particle space is developed and numerically solved. Numerical experiments demonstrate the ability of the model to represent the actual experimental response curves. It is shown that reliable values of intra-particle diffusivity and adsorption–desorption constants can be obtained from the TAP single pulse experiments when the three dimensionless constants of the model τ p i (the ratio of characteristic diffusion time in the micro-reactor to characteristic diffusion time in zeolite pore), K eq i (the ratio of characteristic desorption time to characteristic adsorption time), and k d i ∗ (the ratio of characteristic diffusion time in the micro-reactor to characteristic desorption time) fall within a prescribed range.