Water solubility and dynamics of CO2 capture ionic liquids having aprotic heterocyclic anions

A computational study was carried out to investigate the solubility and dynamics of water in five different ionic liquids capable of chemically reacting with CO2. All the ionic liquids have a common tetrabutylphosphonium cation paired with five different aprotic heterocyclic anions. These ionic liquids have properties that make them attractive candidates for use in CO2 capture applications, but the impact of water on their properties is unknown. The simulations show that the ionic liquid having a 2-cyanopyrrolide anion is the most hydrophobic of all the liquids studied, but that upon reaction with CO2 it becomes much more hydrophilic. The other ionic liquids investigated show little change in water solubility upon reaction with CO2. Henry's Law constants, enthalpies and entropies of water absorption, liquid structure, hydrogen bonding and self-diffusivities were computed and found to correlate well with the strength of interaction between water and the anions and the relative hydrophobicity of the liquids.