In the thermochemical cycles such as the SI (sulfur-iodine) cycle, the Westinghouse process, and Ispra Mark 13 process, SO(2) needs to be separated and purified to enhance system efficiency. As novel absorbents with non-volatility, thermal stability and high SO(2) absorption capability, the characteristics of ionic liquids (ILs) as SO(2) absorbents were investigated to separate SO(2) in SO(2)/O(2) gaseous mixtures from the sulfuric acid decomposer. SO(2) absorption and desorption experiments showed that SO(2) solubility and absorption rate in ILs were influenced mainly by anions of ILs. [BMIm][Cl] and [BMIm][OAc] (1.40-1.69 SO(2) gmol/lLs gmol) showed the highest SO(2) solubility among the tested ILs at 50 degrees C and 0.67 atm P(SO2). Interestingly, [BMIm][OAc] showed irreversibility in the cycle of absorption and desorption. [BMIm][MeSO(4)] showed moderate SO(2) solubility and good reversible cycles of absorption and desorption. The dependency of temperature and pressure on SO(2) solubility of [BMIm][MeSO(4)] was scrutinized. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.