Correlation between Computed Ion Hydration Properties and Experimental Values of Sugar Transfer through Nanofiltration and Ion Exchange Membranes in Presence of Electrolyte

Abstract

The widespread use of nanofiltration and electrodialysis membrane processes is slowed down by the difficulties in predicting the membrane performances for treating streams of variable ionic compositions. Correlations between ion hydration properties and solute transfer can help to overcome this drawback. This research aims to investigate the correlation between theoretically evaluated hydration properties of major ions in solution and experimental values of neutral organic solute fluxes. In particular, ion hydration energies, coordination and hydration number and the average ion-water distance of Na+, Ca2+, Mg2+, Cl− and SO42− were calculated at a high quantum mechanics level and compared with experimental sugar fluxes previously reported. The properties computed by simple and not computationally expensive models were validated with information from the literature. This work discusses the correlation between the hydration energies of ions and fluxes of three saccharides, measured through nanofiltration and ionic-exchange membranes. In nanofiltration, the sugar flux increases with the presence of ions of increasing hydration energy. Instead, inverse linear correlations were found between the hydration energy and the sugar fluxes through ion exchange membranes. Finally, an empirical model is proposed for a rough evaluation of the variation in sugar fluxes as function of hydration energy for the ion exchange membranes in diffusion experiments.

Why Are Saccharides Dehydrated in the Presence of Electrolytes? Insights from Molecular Modeling and Thermodynamic Measurements

“…The structural parameters of the ions hydration shell, i.e., the ion coordination number, its optimized coordinated water structure, and the average distance between the ion and the water molecules, are listed in Table . For comparison, other results from molecular modeling are also reported. − One can state that our values are consistent with the literature, indicating the validity of our approach and assumptions.…”

Investigation of ions hydration using molecular modeling

“…Concerning Mg 2+ , experimental [53,54] and simulation [55] works established that its coordination number includes six water molecules. The early X-ray diffraction [53] studies, Raman spectroscopy [56], and Extensive X-ray diffraction studies [54] showed that Mg 2+ had a CN of 6 in aqueous solutions of different concentrations, containing chlorides, nitrates, perchlorates, and sulfate ions.…”