Equilibrium and fixed bed adsorption of 1-butene, propylene and propane over 13X zeolite pellets

Propylene-propane separation is one of the most difficult and demanding energetic operation currently practiced using cryogenic distillation. Extensive studies on various alternatives showed that cyclic adsorption processes, and particularly pressure swing adsorption (PSA), might be an option to replace the traditional distillation. In spite of the promising results of the PSA process, much attention is currently being paid to the simulated moving bed technology (SMB) for gas-phase separations. The ingenious principle of this process is based on the choice of an adequate adsorbent-desorbent couple. Thus, in the present work 1-butene has been studied as an interesting desorbent to displace adsorbed propylene-propane mixture on 13X zeolite. The measurements of pure 1-butene adsorption isotherms over 13X zeolite were performed with a gravimetric experimental device for pressure ranging from 0 to 110kPa and at temperature of 333, 353, 373, and 393K. The experimental adsorption data were correlated using Toth model. The heat of adsorption at zero coverage and the maximum loading capacity of 1-butene were found to be 54.4kJ/mol and 2.10mol/kg, respectively. The adsorption and desorption of 1-butene on 13X zeolite packed on a fixed bed initially saturated either by a propane-propylene mixture or a pure C3 hydrocarbon has been studied. The performance of 1-butene has been compared with isobutane that was previously proposed to be a highly effective desorbent for C3H6/C3H8 separation. A model based on a double LDF approximation for the mass transfer combined to a heterogeneous energy balance taking into account a variable velocity of the gaseous bulk phase, has been used to describe the breakthrough curves obtained experimentally at 373 K and 110 kPa. Copyright © Taylor & Francis Group, LLC.