Solvent-membrane-solute interactions in organic solvent nanofiltration (OSN) for Grignard functionalised ceramic membranes: Explanation via Spiegler-Kedem theory

• Extensive study of the OSN performance of Grignard grafted ceramic membranes.
• Unravelling of the solvent-solute-membrane interactions influencing the performance.
• At high solvent polarity size exclusion rules and the retention is maximal.
• At low solvent polarity, retentions are lower and solute affinity plays a role.
• Spiegler-Kedem theory elegantly explains all results including pressure effects.

Amphiphilic Grignard modified ceramic nanofiltration membranes have been demonstrated to perform well for a wide range of solvents in organic solvent nanofiltration (OSN). The purpose of this study is to obtain a better understanding of the influence of the solvent-membrane-solute interactions governing the OSN membrane performance. This was achieved by performing an extensive retention study on two types of Grignard functionalised membranes, in many different solvents with a wide variety of polarity, and choosing three PEG molecules and polystyrene as solutes, all with almost the same size but different polarities. To unravel the transport mechanism properly, also the pressure effect on flux and retentions was thoroughly investigated.The retention results showed in general a very different behavior in different ranges of solvent polarity: at low solvent polarity, retentions are relatively low, varying with pressure and solvent polarity; at high solvent polarity, retentions are relatively high, and independent of pressure and solvent polarity. The Spiegler-Kedem theory, taking into account both diffusion and convection transport mechanisms, appears to be a very good basis for a fundamental explanation of all results. This knowledge shows also how membrane-solvent-solute interactions can be manipulated to enhance the membrane performance.