Performance of stabilized zirconia nanofilters under dynamic conditions

The nanofiltration performance of stabilized zirconia nanofilters was tested under dynamic conditions in an electrolytic solution. Interaction between nanostructured materials and solutes may modify the rejection properties of such membranes in the dynamic range of the experiments. Optimal filtration performance can only be realized by a proper understanding of these interactions. At high pressures, a decrease in electrolyte rejection is observed and the membranes show a reduction in hydraulic permeability. Two approaches (one thermodynamic and the other electrokinetic) are considered to explain these phenomena, i.e. the concentration polarization model and the electroviscosity model. A combination of these two approaches is successfully developed to explain the observed nanofilter behaviour at high pressures in the case of electrolytes. Further investigations were performed using an uncharged solute (vitamin B₁₂) in an electrolyte buffer. Although a reduction in permeability was observed at high pressures, there was no important decrease in vitamin B₁₂ rejection because the optimal transmembrane pressure (where the rejection reaches a maximum) was above the pressure range studied experimentally or did not allow the rejection reducing effects of the concentration polarization layer to be observed more clearly.