Absorption of SO2 in Simulated Flue Gas by Functional Deep Eutectic Solvents Based on Imidazole and H2O with High Mass Capacities

In this work, we designed three kinds of functional deep eutectic solvents (DESs) to capture SO2 in simulated flue gas. The DESs were composed of imidazole (Im), 2-methylimidazole, and 2-ethylimidazole as the hydrogen-bond acceptor (HBA) and H2O as the hydrogen-bond donor (HBD). The absorption results showed that the mole absorption capacities of 2.1 vol % SO2 by the three DESs at 40 °C were all about 1 mol of SO2/mol of HBA. Im–H2O DES (nHBA/nHBD = 1:4) shows a mass absorption capacity of 0.331 g of SO2/g of DES, which is the highest value reported in the literature. The mole ratio of HBD/HBA, flow rate of flue gas, and other acid gases in flue gas did not influence the absorption capacity of SO2. The absorption capacity decreased when the temperature increased. The absorption capacity of SO2 was almost the same after absorbing and desorbing 5 times. Furthermore, the results of 1H nuclear magnetic resonance and Fourier transform infrared analyses showed that SO2 was interacted with Im by forming Im sulfite.