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Ionic liquids in the water can be divided into two-phase through the liquid-liquid extraction process using refrigerant to aqueous layer (under 300 ppm ILs) and ionic liquids (99.9% ILs) layer.Trace ionic liquid in aqueous layer can be concentrated using the membrane capacitive deionization (MCDI) process.MCDI is salt removal or concentrated technology.MCDI uses the principles of ionic adsorption on the electrode surface due to electrostatic force (Fig.1).When the electrode is charged,ions with opposite electric charge move to the electrode and from an electric double layer (EDL).When the electrode is discharge,ions are desorbed from the electrode surface and move back into bulk solution.In this study,we investigated the feasibility of the MCDI process for the concentration of trace hydrophilic ionic liquid in aqueous solution.MCDI experiments were carried out with various operating conditions.The size of the carbon electrode was 100 × 100 mm.A MCDI cell that employed an ion exchange membrane (IEM) was also constructed.In this cell,the carbon electrode was coated with cation-exchange polymer to the cathode carbon electrode and anion-exchange polymer to the anode carbon electrode.The feed solution was 300 ppm BMImBF4 supplied continuously at a flow rate of 20 ml/min.A conductivity meter was placed at the outlet of the cell to monitor the changes in conductivity of the effluent during the sorption and desorption periods.The potential of the cell was controlled by a potentiostat (WPG100HP,WonA Tech Corp.) connected to a personal computer for monitoring electrode potential and electrode current over time (Fig.2).The experimental results have demonstrated that the MCDI system could be applied successfully process for the concentrated of trace hydrophilic ionic liquid in aqueous solution.