Predictions of Stepped Isotherms in Breathing Adsorbents by the Rigid Adsorbent Lattice Fluid

Abstract

Adsorbents that undergo structural changes in the presence of adsorbate molecules are an interesting new class of materials, which could offer enhanced selectivity, purity, and recovery in separation technology. To date, however, their application in such technology is hampered by the lack of a simple, consistent thermodynamic framework, which can effectively describe and predict their adsorption behavior under a range of conditions. This becomes especially true for their behavior in multicomponent adsorbate mixtures, for which experimental data are limited and cumbersome to obtain. Here, we present how the relatively simple rigid adsorbent lattice fluid model successfully and accurately predicts stepped isotherms in the breathing metal–organic framework, MIL-53 (Al), in the presence of CO2 and CH4. Breathing transitions are predicted solely on the basis of the different densities of the material’s two structural configurations and their associated Gibbs energies. Hysteresis effects can easily be included...