Catalysis Today 20 ( 1994) 541-554 Dynamics of desorption with supercritical fluids: prediction of regeneration times of spent packed beds J. Puiggenk”, A. Adivinacih, E. Velo, F. Recasens ETSEIB. Universitat Pohtbzica de Catalunya. Barcelona, Spain zyxwvutsrqponmlkjihgfe Abstract Regeneration kinetics for an integral bed of spent adsorbent using a supercritical fluid (SCF), is studied. A heterogeneous model that uses the linear-driving force concept and the local equilibrium assumption is used to describe the regeneration history. The solution to the mathematical model allows the calculation of the desorbed fraction vs. time for the case of activated carbon loaded with toluene. If the solute irreversibly held on the solid is considered in the regeneration fractions predicted by the model, the values of the fluid-to-particle mass transfer coefficient are near those calculated from existing correlations. 1. Introduction High-performance extraction processes have been developed during recent years by using supercritical fluids. Working at conditions not far above the critical, fluid properties can be adjusted so that solubilities and diffusional rates are higher than those in the liquid or gas phase. Compared with a low pressure gas, a supercritical fluid (SCF) has a higher density, and similar viscosity. Molecular diffusion coefficients are about 10 times larger than those of liquids, with Schmidt numbers in the range of 5 to 15. The application of SC solvents to the elucidation of catalyst coking and reactivation mechanisms, are also an important contribution [ 1,2]. Moreover, regeneration of porous adsorbents with supercritical carbon dioxide is economically attractive because it can be carried out at much lower temperatures (50 to 6O”C, compared to 800°C in the Herreshof furnace process and 150°C in the steam process). Additionally, carbon losses due to gasification do not occur. Experimental data and simple kinetic descriptions of desorption rates of organics from an adsorbent, have recently appeared [ 3,4]. Published data also include adsorption equilib- *Corresponding author. 0920-5861/94/$07.00 0 1994 Elsewer Science B V. All rights reserved SSDIO920-5861(94)00051-3