Efficient SO₂ Capture and Fixation to Cyclic Sulfites by Dual Ether-Functionalized Protic Ionic Liquids without Any Additives

The capture of SO₂ with ionic liquids (ILs) has attracted much attention in recent years; however, the examples involving SO₂ capture and utilization (SCU) in the same medium are scarce. Here, we demonstrated an innovative strategy for SO₂ capture and fixation to cyclic sulfites in dual ether-functionalized protic ionic liquids (PILs) for the first time. These dual ether-functionalized PILs exhibited low viscosities and remarkable SO₂ loading capacities (up to 6.12 mol of SO₂ per mol of IL and 1.34 g of SO₂ per g of IL at 1.0 bar) that is conducive to conversion of SO₂ absorbed in situ. The mechanism of absorption was proposed which includes both chemical and physical absorptions from the spectral results and theoretical calculations. Particularly, the SO₂ absorbed in the PILs was directly transformed into cyclic sulfites without any additives; meanwhile, these PILs were also used as efficient catalysts for the synthesis of a series of cyclic sulphites using equimolar SO₂ and epoxides. Good to excellent yields of cyclic sulfites were obtained for varied substrates. The dual roles of PILs as both absorbents and catalysts as well as the recyclability of the PILs are examined in detail in this paper. This innovative strategy not only eliminated the traditional intensive energy input for SO₂ desorption but also enabled the production of value-added cyclic sulfites

Cyano-Containing Protic Ionic Liquids for Highly Selective Absorption of SO₂ from CO₂: Experimental Study and Theoretical Analysis

The solubility of SO₂ and CO₂ in four cyano-containing protic ionic liquids (PILs) was experimentally measured at temperatures from 303.2 to 333.2 K and pressures up to 3.0 bar. Their physical properties, such as density, viscosity, and decomposition temperature, were also determined. It is found that [DMPANH]­[MOAc] and [DMAPNH]­[EOAc] have the best selective absorption of SO₂ from CO₂ at 303.2 K and 1.0 bar among the investigated PILs, and the ideal selectivities (119 and 107, respectively) of SO₂/CO₂ are significantly higher than those reported in literature for other ILs. The temperature-dependent Krichevsky–Kasarnovsky (K–K equation) and PR-NRTL equations are used to calculate the solubility data of SO₂ and CO₂, and the interactions between PILs and acid gases are analyzed thermodynamically. Quantum chemical calculations are also done to obtain the interaction configurations and energies. It is shown from the themodynamic analysis and the quantum chemical calculations that the interaction between SO₂ and PILs is more energy favorable than that between CO₂ and PILs, primarily due to the existence of the cyano group on the cation of PILs. The protic ionic liquids were reused for five absorption–desorption cycles without obvious loss in the absorption capacity, showing their potential as selective absorbents of SO₂