Isosteric heat of adsorption: Theory and experiment

The isosteric heats of adsorption of the components of a gas mixture are cr itical variables for design of adsorbers for gas separation. They can be un ambiguously defined by the Gibbsian Surface Excess (GSE) model of multicomp onent adsorption. These variables can be experimentally measured by multico mponent differential calorimetry (MDC) and directly used to describe noniso thermal behavior of practical adsorbers. There is no need to make simplifie d assumptions about the nature and size of the adsorbed phase, as required by conventional adsorption thermodynamic models, to define the isosteric he ats. Pure gas isosteric heats of adsorption of N-2 and CO2 on a pelletized silicalite sample were measured using a MDC and a data analysis algorithm b ased on the GSE model. The silicalite sample behaved like a homogeneous ads orbent for weakly polar N-2 adsorption. The presence of polar alumina binde r in the silicalite sample introduced significant heterogeneity for more po lar CO2 adsorption.