Acetylcholine-based deep eutectic solvents for highly efficient SO2 absorption, selective separation from CO2 and their mechanism

The development of deep eutectic solvents (DESs)-based absorbents for selective uptake of SO2 from CO2 (SO2/ CO2, g/g) is of interest to flue-gas desulfurization (FGD). In this work, a series of DESs are designed through acetylcholine chloride (ACC) as hydrogen bond acceptor (HBA) and ethylene glycol (EG), 1,3-propylene glycol (1, 3-PDO), glycerol (Gly), polyethylene glycol 200 (PEG200) and triethylene glycol (TG) as hydrogen bond donors (HBDs). All the DESs display good thermal stability under 150 degrees C and competitive capacities of SO2. ACC/ PEG200 (1:1) is remarkable due to their absorption capacity of SO2 to 3.5 mol/mol (P = 1.0 bar, T = 303.2 K). All DESs show excellent selectivity separation of SO2 from CO2 more than 100, for example, up to 335 in ACC/TG (1:1). In this work, the relative mechanism reveals that DESs absorption of SO2 combining physisorption and chemisorption via a reaction equilibrium thermodynamic model and theoretical calculation. Furthermore, ACC/ TG (1:1) maintains the reversible absorption capacity of SO2 after five absorption/desorption cycles. Considering high SO2 absorption capacity, desired selectivity, and excellent recyclability, DESs in this study are considered recyclable green absorbers, which can be potentially applied to SO2 capture towards CO2 mixture.