Sorption of Light Paraffins in Type-A Zeolites: Analysis and Interpretation of Equilibrium Isotherms

Abstract

Equilibrium data for the sorption of light paraffins in 4A and 5A zeolites are interpreted in terms of a simple idealized model isotherm. Henry’s law constants and isosteric heats of sorption, calculated from the model, agree well with published experimental values and (for CH4) with the values calculated theoretically. The observed increase in the isosteric heat of sorption with sorbate concentration arises primarily from the effect of sorbate-sorbate repulsion (finite size of sorbate molecules) and, for the systems considered, the effect of sorbate-sorbate attraction is relatively minor. Entropies of sorption are calculated and compared with the values for ideal Langmuir adsorption and the limitations of the Langmuir plot as a method of extracting Henry's law constants and saturation concentrations from experimental equilibrium data are discussed.