Modeling water vapor adsorption/desorption cycles

Abstract

This modeling work deals with the adsorption of water vapor on different porous materials where it undergoes capillary condensation and its adsorption/desorption isotherms exhibit hysteresis. The focus is on the description of the so called scanning curves, i.e. the adsorption/desorption isotherms observed when such an adsorbent is repeatedly loaded and unloaded in a range of conditions where hysteresis is observed, and on the simulation of fixed bed adsorption/desorption cycles. We use an approach originally developed by Štěpánek et al. (Chem Eng Sci 55(2):431–440, 2000), and expand it so as to include more general isotherms (not only the Dubinin–Radushkevich and Dubinin–Astakhov model, but also the Guggenheim–Anderson–de Boer model and the Do and Do model) and to allow for less than infinitely fast heat transfer, so as to consider non-isothermal situations. From a modeling point of view the results are satisfactory and highlight the need for better experimental data on water vapor adsorption, which need to be measured in enhanced experimental set-ups, capable to tightly control the relative humidity of the gas phase.