Carbon dioxide solubilities and diffusivities in 1-Alkyl-3-methylimidazolium tricyanomethanide ionic liquids: an experimental and modeling study

The solubility and diffusivity of CO2 in a series of 1-alkyl-3methylimidazolium tricyanomethanide ionic liquids ([Cnmim][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).