Highly efficient and reversible SO2 capture by halogenated carboxylate ionic liquids

Because of the unique properties of ionic liquids, it has been suggested that ionic liquids, especially functionalized ionic liquids, could be used as good solvents for the capture of acidic gases such as SO2. In this work, a kind of carboxylate ionic liquid with a halogen atom on the alkyl chain of the carboxylate anion was developed for highly efficient and reversible capture of SO2 through multiple-site interactions. It was found that these halogenated carboxylate ionic liquids improved SO2 capture performance as well as being reversible. Spectroscopic investigations and quantum chemical calculations show that the enhancement in SO2 capacity originated from the halogen sulfur interaction between the halogen group on the carboxylate anion and SO2. Furthermore, the captured SO2 was easy to release by heating or bubbling N-2 through the SO2-saturated ionic liquids. This highly efficient and reversible process using halogenated carboxylate ionic liquids through adding a halogen group to the carboxylate anion provides an excellent alternative to current SO2 capture technologies.