Observation and Investigation of Increasing Isosteric Heat of Adsorption of Ethane on Zeolite-Templated Carbon

Ethane adsorption was measured on zeolite-templated carbon (ZTC) and compared to superactivated carbon MSC-30. Isotherms measured at temperatures between 252 and 423 K were fitted using a superposition of two Langmuir isotherms, and thermodynamic properties were assessed. Unlike typical carbon adsorbents, the isosteric heat of adsorption on ZTC increases by up to 4.6 kJ/mol with surface coverage. This increase is attributed to strong adsorbate–adsorbate intermolecular interactions, a hypothesis that is shown to be consistent with fundamental estimates of intermolecular interactions. Furthermore, the molar entropy of the adsorbed phase was measured and compared to an estimate derived from statistical mechanics. While the measured and estimated entropies of the adsorbed phase of ethane on MSC-30 are in agreement, they differ significantly on ZTC at high coverage, indicative of the atypical properties of ethane adsorption on ZTC.