Adsorption and differential heats of adsorption of normal and iso-butane on zeolite MFI

Adsorption of n- and i-butane on zeolite MFI (silicalite type) at different temperatures has been investigated using a manometric technique combined with a micro-calorimeter. The Langmuir model can describe the isotherms for both components. The derived thermodynamic properties are in agreement with the literature data from other techniques. The differential heats of adsorption when plotted against loading present an initial plateau; followed by a slow rise, which can be attributed to adsorbate–adsorbate interactions. For i-butane these adsorbate–adsorbate interactions give rise to a sharp peak in heat of adsorption versus loading, at 0.6 mmol/g. A decrease at higher loadings on the heat of adsorption is observed for both isomers, this is attributed to surface adsorption.