Tuning Environmentally Friendly Chelate-Based Ionic Liquids for Highly Efficient and Reversible SO₂ Chemisorption

Because of lots of outstanding properties of ionic liquids (ILs), three kinds of environmentally friendly chelate-based ILs such as [Li­(TDA-1)]­[SCN], [Li­(TDA-1)]­[TFSI], and [Li­(G3)]­[TFSI] were designed and synthesized in this work with easy procedure and no byproduct generation. Ligands of the ILs are cheap, nontoxic, thermally stable, and highly active. Density and viscosity of the ILs were determined, and they decreased linearly with increasing temperature. With the lowest flow activation energy, the [Li­(TDA-1)]­[SCN], containing tertiary amine in the cation and thiocyanate as the anion, exhibited the highest absorption rate and remarkable SO₂ chemisorption capacity. The effect of SO₂ partial pressure and absorption temperature on the uptake performance of SO₂ were also investigated, where a high absorption capacity up to 2.36 and 2.01 mol SO₂ per mol IL can be achieved by [Li­(TDA-1)]­[SCN] under low partial pressure of SO₂ (10 vol % SO₂) or high absorption temperature (70 °C), respectively. Spectroscopic investigations and quantum mechanical calculations show that the chemical interactions between SO₂ and two active sites (N and S) in ILs resulted in the high SO₂ absorption capacities. Furthermore, the chelate-based ionic liquids can be regenerated and recycled several times without losing capacity.