Absorption and Conversion of SO 2 in Functional Ionic Liquids: Effect of Water on the Claus Reaction.

The absorption of SO 2 from flue gas and its conversion to chemicals is important in the industry. Functional ionic liquids (ILs) have been broadly used to absorb SO 2 in flue gas, but seldom convert it to chemicals. As we know, water is inevitable in a desulfurization process. In this work, three functional ILs (monoethanolaminium lactate-[MEA][Lac], 1,1,3,3-tetramethylguanidinium lactate-[TMG][Lac], tetraethylammonium lactate-[N 2222 ][Lac]) with or without water were used as absorbents to absorb SO 2 in flue gas, and then the absorbed SO 2 in the absorbents was converted to sulfur via a Claus reaction. The result shows that the three ILs can efficiently absorb SO 2 and convert it to sulfur. But the addition of water in the ILs can reduce the conversion of absorbed SO 2 , and the conversion increases with increasing the acidity of absorbents. To explain this phenomenon, we studied the Claus reaction in H 2 SO 3 , NaHSO 3 and Na 2 SO 3 aqueous solutions. It turns out that the conversion of the Claus reaction is related to the species of S (IV) in the order of the oxidability: H 2 SO 3 > HSO 3 - > SO 3 2- , and their proportions dependent on the pH of solutions. On the basis of the absorption mechanism of SO 2 in functional ILs aqueous solution, H 2 S reacts with HSO 3 - and SO 3 2- with weaker oxidability, resulting in the lower conversion. Importantly, we found that the addition of lactic acid could increase the conversion of SO 2 via the Claus reaction.