Computational Study on the Absorption Mechanisms of SO2 by Ionic Liquids

A density functional theory study was conducted to explore the absorption mechanisms of SO2 by ionic liquids (ILs), including task specific ILs 1,1,3,3-tetramethylguanidinium lactate ([TMG][LAC]), and normal ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The strength of chemical absorption by [TMG][LAC] is stronger than physical absorption, and the physical absorption energy follows the order of [TMG][LAC] > [BMIM][BF4] > [BMIM][PF6]. Other than O center dot center dot center dot H hydrogen bonding, S center dot center dot center dot O interactions are important for [TMG][LAC] physical absorption of SO2, and S center dot center dot center dot F interactions are critical for SO2 absorption by [BMIM][BF4] or [BMIM][PF6]. Both anions and cations of ILs contribute to the physical absorption of SO2. [TMG](+) plays an important role in the chemical reaction between SO2 and [TMG][LAC]. The proton transfer reaction barrier between 1,1,3,3-tetramethylguanidine and lactic acid is 1.176 kcal/mol.