Relationship between volumetric properties and mass transfer through NF membrane for saccharide/electrolyte systems

Recent studies have shown that unexpected performances can be obtained with NF membranes, when applied to the treatment of solutions containing significant amount of electrolyte. This study deals with the investigation of the mechanisms governing the mass transfer of neutral species through NF membranes with a focus on the role of ions. More precisely, it consists to determine the apparent molar volume of saccharides, which characterizes the hydration state of solutes in presence of electrolyte, and to assess the relationship between these parameters and those characterizing the mass transfer. The transfer of saccharides of increasing molecular weights (xylose, glucose and sucrose) through a NF membrane is studied in a diffusion regime. Different electrolytes (NaCl, Na2SO4, CaCl2, MgCl2) are chosen with respect to their hydration level. A specific procedure was developed to dissociate the flux variation due to the modifications of the solute properties and of the membrane material induced by the electrolyte. The results show that the mass transfer modification is mainly due to the influence of the electrolyte on the solute properties. Then, the mass transfer parameters are put in parallel with the apparent molar volume of saccharides measured in solutions of different ionic compositions.