Highly Efficient and Reversible Absorption of SO2 from Flue Gas Using Diamino Polycarboxylate Protic Ionic Liquid Aqueous Solutions

Ionic liquid (IL) aqueous solutions (aq) have emerged as promising candidates for SO2 absorption. In this work, a new series of diamino polycarboxylate protic ionic liquids (DPPILs) aq with low viscosities and high stabilities were developed and used for SO2 capture. All of the prepared absorbents could efficiently absorb low-concentration SO2 in simulated flue gas. Among them, DPPILs aq based on citric acid (CA) presented the most excellent SO2 desorption performance; nearly all absorbed SO2 could be easily desorbed under mild conditions. Particularly, N,N-dimethylethylenediamine citrate [DMEDA][CA] showed the highest available absorption capacity toward 0.2 vol % SO2 (up to 0.51 molSO2/molILs and 0.058 gSO2/gabs in 50 wt % aq at 20 °C), which also presented satisfactory SO2/CO2 selectivity, reusability, and SO2 removal efficiency. Fourier transform infrared and nuclear magnetic resonance spectroscopic analyses revealed that the protonation of [DMEDA]+ and [CA]− promoted SO2 absorption. Overall, the studied DPPILs aq with excellent physical properties, SO2 absorption–desorption performance, and stability may have a great perspective in industrial SO2 removal.