Carbon Dioxide Solubilities and Diffusivities in 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids

Abstract

The solubility and diffusivity of CO₂ in a series of 1-alkyl-3methylimidazolium tricyanomethanide ionic liquids ([C_nmim][TCM] with n = 2, 4, 6, 7, 8; ILs) was studied using a magnetic suspension balance at temperatures ranging from 298 to 353 K and pressures up to 2 MPa. The effects of temperature, pressure, and alkyl chain length on CO₂ solubility and diffusivity were examined. The electrolyte PC-SAFT (ePC-SAFT) equation of state was used to describe the solubility of CO₂ in the ILs. The Henry's law constant and the excess properties of solvation (Gibbs free energy, enthalpy, and entropy) were calculated. A series of equations derived from Fick's second law were evaluated, and a Fourier expansion of Fick's second law of diffusion was found to be the most suitable model for deriving diffusivities from gravimetric data. The diffusivities range from 10^-10 to 10^-9 m²·s^-1 in the temperature and pressure ranges applied. The activation energies for CO₂ diffusion (12-16 kJ·mol^-1) were found to be in the range of traditional solvents. (Graph Presented).