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.