Solubility, Diffusivity, and Phase Equilibria of Oxygen in Ionic Liquids

Abstract

The temperature-dependent solubility and diffusivity of oxygen were measured in five ionic liquids (ILs) with imidazolium- and pyrrolidinium-based cations and bis(trifluoromethylsulfonyl)imide and bis(fluorosulfonyl)imide anions. A gravimetric microbalance was used to measure the solubility of oxygen (O2) at temperatures ranging from 283.15 to 328.15 K and pressures up to 0.5 MPa. The Henry’s law constants, enthalpies, and entropies of absorption were calculated from experimentally measured O2 solubility in ILs as a function of temperature and pressure. The solubility of O2 increased with increasing alkyl-chain length in ILs with similar cations and anions. The ILs with the bis(trifluoromethylsulfonyl)imide anion have higher O2 solubility than the ILs with the bis(fluorosulfonyl)imide anion. The imidazolium-based IL was found to have higher O2 solubility than the pyrrolidinium-based IL. The solubility of O2 increases with a decrease in temperature and an increase in pressure. The diffusion coefficient of O2 increases with an increase in temperature and pressure. This study provides solubility and diffusivity data for O2 in ILs, applicable for energy storage, especially for lithium–air batteries and other applications.