The facilitated separation of CO2 and SO2 in a series of supported ionic liquid membranes (SILMs) impregnated with carboxylate-based Ifs (including monocarboxylates and dicarboxylates) was investigated systematically under humidified condition. The effects of transmembrane pressure difference and temperature on the permeability of acidic gases and permselectivity of gas pairs were studied. It is found that dicarboxylate-based ILs are a class of tunable media for the selective separation of acidic gases. When the anions of dicarboxylate-based ILs are fully deprotonated, they could be used as effective carriers for the selective separation of CO2. The permeabilities of CO2 in triethylbutylammonium malonate ([N-2224](2)[malonate]) and triethylbutylammonium maleate ([N-2224](2)[maleatep under the partial pressure of 0.1 bar range from 2147 to 2840 barrens and the permselectivities of CO2/N-2 and CO2/CH4 in them approach to 178-265 and 98-221, respectively. However, when the anions of dicarboxylate-basecl ILs are half deprotonated, they are efficient solvents for the selective separation of SO2. Triethylbutylammonium dimalonate ([N-2224][climalonatel) could facilitate the permeation of SO2 with a permeability of 7208 banners under the transmembrane pressure difference of 0.05 bar, and the permselectivities of SO2/N-2, SO2/CH4 and SO2/CO2 are 585, 271 and 18, respectively. The mechanism of facilitated separation is explained successfully from the reversible reactions of CO2 and SO2 with different forms of dicarboxylate-basecl ILs. (C) 2014 Elsevier By. All rights reserved.