Influence of the ionic composition on the diffusion mass transfer of saccharides through a cation-exchange membrane

Abstract

Recent studies have pointed out that the presence of salts can change significantly the membrane process performances because of the resulting modification of the neutral solutes transfer through the membrane. The influence of the ionic composition on the transfer of neutral solutes through membranes could be explained by a modification of the membrane properties, due to electrostatic effects, by a modification of the solute radius, likely due to its dehydration induced by the electrolyte, or more probably by a combination of both. This study deals with the investigation of the mechanisms governing the mass transfer of neutral species through an ion-exchange membrane used in electrodialysis, CMX, with a focus on the role of ions. The mass transfer of various saccharides (xylose,glucose and sucrose) as well as the solvent transfer in different electrolytic solutions (NaCl,NH 4Cl, CaCl 2 and MgCl 2) was studied in a diffusion regime. A specific procedure has been used to dissociate the solvent or solute fluxes variations due to the modifications of the solute properties and of the membrane material induced by the electrolyte. The results showed that the transfer modification is mainly due to the influence of the electrolyte on the membrane properties, which is fixed by the membrane soaking. A quantitative correlation has been established between the solvent and solute transfer and the hydration number of the membrane counterion. In presence of electrolyte, the saccharide mass transfer increased but the impact of the presence of electrolyte is much less than the one of membrane soaking. However, in this case, a relationship has been also established between the increase of the saccharide mass transfer and the cation hydration state.