Influence of ion size on the prediction of nanofiltration membrane systems

The major ion partitioning effect may be due to steric, Donnan and dielectric exclusion which are collectively described by the Donnan steric pore model and dielectric exclusion (DSPM-DE). The effect of various ion size on charged solute rejection was studied using the DSPM-DE model. Sodium chloride, sodium sulphate and magnesium chloride were used as model solute. Born solvation energy was used to investigate dielectric exclusion. The effect of variation of physical properties such as viscosity and dielectric constant inside the nanopore was evaluated using the various ionic sizes. Stokes-Einstein, Born’s effective, cavity and Pauling radii were used as ionic size throughout the simulation. It was found that these radii predict the physical properties differently and hence have profound effect on the model predictions. There is a significant variation in the prediction of charge density present in the surface of the membrane using the various ionic radii. The effect of pore size distribution of each ion was studied using log- normal probability density function for both positive and negative charge density, which also showed variation in the prediction. The increase of upper limit of truncated pore size distribution (rmax) has significant influence on decreasing the solute rejection.