New insights on physico-chemical investigation of water adsorption isotherm into seed of dates using statistical physics treatment: Pore size and energy distributions

Abstract

In this work, equilibrium wet content isotherms of water vapor in date kernels are achieved at different temperatures for modeling analysis. The statistical physics formalism is used to treat and interpret the sorption mechanism by applying a real gas law that takes into consideration the interaction between the adsorbate molecules in the free state. The numerical fitting of experimental isotherms showed that the formulation of an infinite multilayer sorption model with two energy levels is confirmed to be appropriate to interpret the sorption process. By exploiting our best fitting model, we found that an aggregate till three water molecules are assembled on the kernel receptor site. It was also resulted that the thermal agitation effect caused a decrement in the density of receptor site and in the saturation sorption capacity which is explained by the exothermic nature of the sorption process. The specific sorption areas calculated via our adapted model were found close to the experimental value 1643 m2/g. The sorption energies calculated at three temperatures reflected that the interaction between water molecules and the date kernels occurs with a physisorption process. Energetic analysis and the study of the Van der Waals parameters a and b provided important information to elucidate the energy-releasing result of the sorption mechanism. The advanced multilayer model is additionally applied to determine the pore size distribution (PSD) and the sorption energy distribution (AED). It confirmed the physical characteristic of the sorption procedure.