Efficient SO₂ Absorptions by Four Kinds of Deep Eutectic Solvents Based on Choline Chloride

Four kinds of deep eutectic solvents (DESs) based on choline chloride (ChCl) with ethylene glycol (EG), malonic acid (MA), urea, and thiourea as hydrogen bond donors were prepared and characterized. All these DESs show good thermal stability and can be stable at 363 K, which is beneficial for the application in flue gas desulfurization. Then, SO₂ absorption capacities of these DESs were determined at different temperatures and SO₂ partial pressures. The absorption results demonstrate that ChCl–EG (1:2) and ChCl–thiourea (1:1) DESs exhibit excellent absorption performances, and the absorption capacities are 2.88 and 2.96 mol SO₂ per mol DES at 293 K and 1 atm, respectively. In addition, the SO₂ absorption and regeneration experiments were conducted. All solvents can be regenerated at 343 K with N₂ bubbling, and the absorption capacities of DESs remain without a significant loss after six absorption and desorption cycles. What’s more, the absorption mechanism of SO₂ in these DESs were investigated by IR and ¹H NMR