Investigation of Highly Efficient and Reversible Absorption of SO2 Using Ternary Functional Deep Eutectic Solvents

The efficient and reversible capture of low-concentration SO2 in flue gas has attracted increasing attention. In this work, a series of novel ternary functional deep eutectic solvents (DESs) based on 1-butyl-3-methylimidazolium chloride (BmimCl) as a hydrogen bond acceptor and ethylene urea (EU) along with azole derivatives as hydrogen bond donors were prepared to investigate the low-concentration SO2 absorption. Results demonstrated that the studied ternary DESs exhibited superior SO2 capture performance at low concentration. Of note, EU/4-methylimidazole (4-CH3-Im)/BmimCl (1:2:1) and EU/4-CH3-Im/BmimCl (1:1:1) exhibited high SO2 available absorption capacity (0.259 and 0.209 g(SO2)/g(DES) at 0.2 vol % SO2 and 20 degrees C) and satisfactory desorption efficiency. Furthermore, the ternary DESs showed high thermostability, outstanding reusability, and reversibility during the five-cycle absorption-desorption experiments. Moreover, combining spectroscopic investigations with quantum chemical calculations, it can be concluded that 4-CH3-Im in DESs chemically interacted with SO2 to effectively capture SO2, and EU could tune the reactivity of the active site in 4-CH3-Im to improve the desorption capability of DESs. Overall, these ternary DESs with distinguished desulfurization performance (high SO2 available absorption capacity and improved desorption capability) have promising prospects in flue gas desulfurization.