Hydrophobic task-specific ionic liquids: Synthesis, properties and application for the capture of SO2

The capture of SO 2 by ionic liquids (ILs) has drawn much attention all over the world. However, ILs can absorb not only SO 2 but also water from flue gas. The removal of water from ILs is necessary for reusing the absorbent. In order to reduce the energy costs of removing water, it would be helpful to weaken the interactions between ILs and water. In this work, two kinds of hydrophobic task-specific ILs, 1-(2-diethyl-aminoethyl)-3-methylimidazolium hexafluorophosphate ([Et 2 NEmim] [PF 6 ]) and 1-(2-diethyl-aminoethyl)-1-methylpyrrolidinium hexafluorophosphate ([Et 2 NEmpyr][PF 6 ]), were designed and synthesized. Thermal stability and physical properties of the ILs were studied. Furthermore, the application of the ILs for the capture of SO 2 and the absorption mechanism were systematically investigated. It has been found that both of the ILs are immiscible with water, and [Et 2 NEmim][PF 6 ] has much lower viscosity, much higher thermal stability and much higher SO 2 absorption rate than [Et 2 NEmpyr][PF 6 ]. [Et 2 NEmim][PF 6 ] shows high SO 2 absorption capacities up to 2.11   mol SO 2 per mole IL (pure SO 2 ) and 0.94   mol SO 2 per mole IL (3% SO 2 ) under hydrous conditions at 30   °C. The result suggests that [Et 2 NEmim][PF 6 ] is a promising recyclable absorbent for the capture of SO 2 .