Retention of progesterone by four carbonaceous materials: Study of the adsorption equilibrium

The adsorption process of a natural steroid hormone (progesterone) by four carbonaceous adsorbents has been studied. The corresponding equilibrium isotherms have been analyzed according to a previously proposed model which establishes a kinetic law satisfactorily fitting the C versus t isotherms. The obtained equilibrium isotherms consist of three segments, which have been separately discussed. Different equations corresponding to each of the referred segments have been proposed, the experimental data being fitted to such equations. From the values of the kinetic equilibrium constant corresponding to the second—and more significant—of the above mentioned segments, values of standard average adsorption enthalpy (ΔH°) and entropy (ΔS°) have been calculated. Finally, information related to variations of differential adsorption enthalpy (ΔH) and entropy (ΔS) with the surface coverage fraction (θ) was obtained by using the corresponding Clausius-Clapeyron equations.