Improved Reversible and Selective SO<sub>2</sub> Absorption by a Stable Phosphonium Carboxylate Ionic Liquid
Nicolas Scaglione, Luke Wylie, Agı́lio A. H. Pádua, Margarida Costa Gomes
Abstract
The ionic liquid tetrabutylphosphonium 1H-tetrazole-1-acetate, [P 4,4,4,4 ][TetrazC 1 COO], appears as promising for the selective and reversible absorption of SO 2 at low pressures and in the presence of CO 2 . The ionic liquid reversibly reacts with SO 2 and to a minor extent with CO 2 as shown by high-pressure NMR analysis. High absorption capacities were measured for SO 2 at pressures below 1 bar using an isochoric saturation technique, the CO 2 being measured in a gravimetric microbalance. We could calculate one of the highest SO 2 /CO 2 selectivity reported so far. Contrary to previously reported ionic liquids, the solutions have lower viscosities, as inferred by the diffusivities measured by NMR, than that of the pure absorbent─a clear advantage for practical usages. Molecular dynamics simulations using validated polarizable force fields allow for a molecular understanding of the physical absorption of both acidic gases and how they impact of the microscopic structure of the liquid. Ab initio calculations provide estimates of the energetics of chemical absorption in line with the experiments confirming that the regeneration of the absorbent can be done at mild conditions of temperature and pressure.