Novel Deep Eutectic Solvents for Highly Efficient and Reversible Absorption of SO₂ by Preorganization Strategy

Abstract

Deep eutectic solvents (DESs) have emerged as promising substitutes for SO2 capture. In this work, an effective preorganization strategy was implemented to design DESs, aiming at improving the SO2 desorption property while ensuring the SO2 absorption capacity in DESs. Several novel DESs with the preorganized multi-imides as hydrogen bond donors were synthesized and evaluated for SO2 capture. The results showed that the studied DESs exhibited high SO2 absorption capacities. In particular, the ethylenurea (EU)/1-butyl-3-methylimidazolium chloride (BmimCl) (1:2) could achieve up to 1.18 and 0.25 gSO2/gDESs at 293.15 K under 1 and 0.02 atm, respectively. Moreover, the DESs absorbent could be regenerated easily under mild conditions and the absorption capacity remained almost unchanged after several consecutive absorption–desorption cycles. On the basis of the spectroscopic investigations and quantum chemical calculations, the reversible absorption mechanism was illustrated, in which the synergism of hydrogen bond donors and hydrogen bond acceptors facilitated the SO2 capture, and the charge-transfer and hydrogen bond interactions between DESs and SO2 could be effectively tuned by the preorganization strategy, thus endowing DESs with excellent desorption performance.