ISOSTERIC STUDY OF SORPTION THERMODYNAMICS OF SINGLE GASES AND MULTICOMPONENT MIXTURES ON MICROPOROUS MATERIALS

The isosteric sorption technique with minimum dead volume is a useful and effective tool to obtain highly accurate sorption thermodynamic da ta 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 rel evant examples, i.e. sorption of carbon dioxide and nitrogen-oxygen mi xtures into faujasite-type zeolites and a micro-(meso)-porous carbonac eous sorbent, that from isosteric measurements those thermodynamic dat a as functions of sorbate concentration were obtained with high accura cy, and isotherms were calculated therefrom over any physically meanin gful regions of temperature and pressure. The energetic heterogeneity of sorbents due to specific interactions between molecules of carbon d ioxide and zeolitic cations is quantified by characteristic concentrat ion dependences of the thermodynamic functions. The isosteric method c an be utilized for measurement of sorption equilibria/thermodynamics o f multicomponent gas mixtures. (C) 1998 Elsevier Science B.V. All righ ts reserved.