Absorption of SO2 in aqueous solutions of mixed hydroxylammonium dicarboxylate ionic liquids

Three new hydroxylammonium dicarboxylate ionic liquids (ILs) dimethylethanolammonium dimalonate ([DMEAH][dimalonate]), dimethylethanolammonium dimalate ([DMEAH][dimalate]) and dimethylethanolammonium diglutarate ([DMEAH][diglutarate]) were synthesized and mixed with free DMEA and water to form novel hybrid solvents for SO2 absorption. The mixed absorbents exhibited low viscosity in the range of 6-13 mPa s at 313.2 K, favoring the transfer performance of SO2 absorption. Significantly, they reached SO2 absorption equilibrium in less than 50 s, and their absorption capacities were as high as 0.1-0.6 mol SO2 per mol IL at 313.2 K and 0.004 bar SO2 partial pressure. SO2 solubility increased with increasing DMEA/IL molar ratio, whereas desorption efficiency decreased. pH significantly affected SO2 absorption and desorption performance in the mixed absorbents. The optimal pH for desulfurization was approximately 4.5-5.5, a compromise between absorption and desorption ability. Compared with pure task-specific ILs for SO2 absorption, which are too expensive and viscous for flue gas desulfurization, the mixed absorbents described in this study have more practical applications. (C) 2012 Elsevier B.V. All rights reserved.