Based on the hypothesis that ionic liquids should show a similar behaviour as surfactants in membrane filtration, this research work analyses the potential of aggregation control to improve the performance of downstream membrane separations, applied to the system 3-octyl-1-methylimidazolium chloride (OMIM-Cl), water and iron(III) chloride (FeCl3). It was obtained that the addition of FeCl3 has an important effect on CAC value and its increase has consequences on the design of the corresponding membrane filtration system.