Insight into the Performance of Acid Gas in Ionic Liquids by Molecular Simulation

In this work, seven kinds of ionic liquids (ILs) composed of different cations and anions and their mixtures with SO2 and CO2 were studied by all-atom molecular dynamics simulations and ab initio calculations. The analysis of radial distribution functions, coordination numbers, spatial distribution functions, and interaction energies demonstrated that both the cations and the anions play an essential role in SO2 absorption. The cations mainly provide space for accommodating SO2, while the anions offer interaction sites to attract SO2. The free volume and interaction energy results suggested that, unlike CO2 absorption, the dissolution of SO2 is primarily dominated by the interaction energy of SO2-ILs. Moreover, the dynamic property changes of ILs during SO2 absorption were further investigated. It was found that the diffusion of ILs is dramatically enhanced and the viscosity is greatly reduced, which is mainly attributed to two aspects. One is that the big aggregation of cations is broken into small aggregations after SO2 absorption, which is favorable for the quick diffusion of cations and anions. The other is the high charge transfer from the anions to SO2, which leads to the obvious decrease of the electrostatic interaction between cations and anions.