Enhanced Ionic Liquids for Acidic Gases Solubility and Task Specific Ionic Liquid for SO₂ Absorption

Composite IL-based materials containing commercial ionic liquids and basic substances were prepared for enhanced CO₂, SO₂, and NO₂ solubility. An isochoric saturation setup was designed and built to measure and compare the acidic gas absorption. Most of the developed materials showed a significant improved performance over the raw ionic liquids, supposing a fast turnaround for a quick implementation. In order to further improve the solubility performance towards SO₂, several novel task-specific ionic liquids (TSIL) were synthesized for the first time with design constraints based on SO₂ absorption performance at low partial pressure, SO₂/CO₂ selectivity, thermal stability, water influence and cost. HDBU-Triz was selected as the best performing TSIL tested, with the highest performance at 5% SO₂ partial pressure (0.375, 0.348 and 0.331 g/g at 30, 40 and 50 °C respectively), excellent selectivity and negligible water influence. The absorption thermodynamics were successfully analyzed employing the Reaction Equilibrium Thermodynamic Model (RETM), which determined an exothermic, spontaneous process with a high absorption enthalpy (−76 kJ/mol) in line with previous reports that explain the excellent performance at low partial pressures, and a moderate Henry’s Constant responsible for the lesser dependence of partial pressure on solubility. Finally, the material was characterized, and the absorption mechanism was proposed based on FTIR, H-NMR, and C-NMR techniques, showing a multisite interaction between the IL molecules and SO₂, where a relatively strong chemical interaction binds the first SO₂ molecule, the second one in the realm between the physical and chemical nature, and the third one merely a physical interaction occurring at higher partial pressures.