Isosteric study of sorption thermodynamics of single gases and multi-component mixtures on microporous materials

Abstract

Abstract The isosteric sorption technique with minimum dead volume is a useful and effective tool to obtain highly accurate sorption thermodynamic data for microporous sorption systems, i.e. enthalpy, entropy and Gibbs free energy of sorption, as functions of sorption phase concentration up to its saturation value. The latter parameter is available without presupposing a sorption isotherm model. The present study shows by relevant examples, i.e. sorption of carbon dioxide and nitrogen–oxygen mixtures into faujasite-type zeolites and a micro-(meso)-porous carbonaceous sorbent, that from isosteric measurements those thermodynamic data as functions of sorbate concentration were obtained with high accuracy, and isotherms were calculated therefrom over any physically meaningful regions of temperature and pressure. The energetic heterogeneity of sorbents due to specific interactions between molecules of carbon dioxide and zeolitic cations is quantified by characteristic concentration dependences of the thermodynamic functions. The isosteric method can be utilized for measurement of sorption equilibria/thermodynamics of multi-component gas mixtures.