Three dihydrogen phosphate-based (H2PO4-,) ionic liquids (ILs) with different cations, i.e., 1-methylimidazolium ([HMIM]), 1-butyl-3-methylimidazolium ([BMIM]), 1-methyl-3-(3-sulfopropyl)-imidazolium ([MIMPS]), are synthesized and investigated to determine their properties on the denitrification from simulated oil that compose of quinoline and n-heptane. Experimental results show that the mechanism of denitrification is not only liquid-liquid extraction, the acidity of ILs also contribute denitrification. With the increase of acidity, ILs show a high selectivity to quinoline. When ILs ([BMIM]H2PO4, [MIMPS]H2PO4) are used, under ambient conditions: temperature is 25 degrees C, time is 30 min, mass ratio of IL/oil is 1:10 and IL/H2O is 2:1, the rate of denitrification can reach more than 99%. They can be recycled for 6 times without significant decrease in activity. (C) 2013 Elsevier B.V. All rights reserved.