Transfer of neutral organic solutes during desalination by electrodialysis: Influence of the salt composition

• Organic solute diffusion and convection depend on ion hydration.
• Reversed trends are found for diffusion and convection contributions.
• Both membrane swelling and solute dehydration are involved.
• Same trend is found for hydrophilic and hydrophobic solutes.

Electrodialysis is a promising process to treat saline water containing organic solute. The desalination performances are fixed by the transfer of salts and organic solutes. On the contrary to the transfer of salts, few results were reported regarding that of organic compounds. This is the objective of this work to investigate the transfer of neutral organic solutes (acetic acid, phenol, glucose) through ion-exchange membranes, focusing on the influence of the salt (NaCl, MgCl2, Na2SO4). Results show that the water transfer due to electroosmosis depends on the salt composition following the ion hydration. Two contributions, diffusion and convection, are pointed out for the transfer of organic solutes. Both are important and mainly fixed by steric effect. Concerning the influence of the ion hydration, reverse trends are found for both contributions. Decreasing diffusion flux is observed for increasing membrane counter-ion hydration showing the influence of the membrane structural properties. Increasing convection flux is observed for increasing ion hydration showing the influence of the solute hydration.