Role of the Solution Environment in Nanofiltration for the Recovery of Ionic Liquids from Water

In this work,experiments to examine the recycling of ionic liquids（ILs） from aqueous solution by nanofiltration（NF） were conducted.The influences of pH,ionic strength,and macromolecular organic matter on filtration performance metrics including the volume flux（Jv） and observed rejection(Robs) were systematically studied.Aqueous solutions of three widely studied ILs,specifically 1-butyl-3-methylimidazolium chloride（[C4 mim]Cl）,1-decyl-3-methylimidazolium chloride([C10mim]Cl),and 1-buty 1-3-methylimidazolium tetrafluoroborate（[C4 mim]BF4）were selected for this study. The mechanisms of interaction between the ILs and the NF membrane under different pH and ionic-strength conditions were revealed by quantum chemical calculations and molecular simulations.The results showed that with increasing pH,the Jv and Robs values of the [C4 mim] Cl and [C10mim] Cl aqueous solutions increased,while for the [C4 mim]BF4 aqueous solution the Jv value increased and the Robs value decreased.Furthermore,with increasing ionic strength,the Jv values of the [C4 mim]Cl and [C4 mim]BF4 aqueous solutions decreased,and their Robs values increased;conversely,for the [C10mim]Cl aqueous solution,the Robs value decreased,and the Jv vale first increased and then decreased.In addition,it was found that the presence of macromolecular organic matter tends to cause membrane fouling and has a great influence on the separation of aqueous solutions of ILs by NF.In general,membrane fouling leads to an increase in the Robs value but a decrease in the Jv value.