Solubilities and Diffusivities of Carbon Dioxide in Ionic Liquids: [bmim][PF6] and [bmim][BF4]

Abstract

Gaseous carbon dioxide (CO 2 ) absorption measurements in l- n -butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) and l- n -butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]) were made using a commercial gravimetric microbalance at temperatures of 283.15, 298.15, 323.15, and 348.15 K and at pressures under 2 MPa. Gas solubilities were determined from absorption saturation (equilibrium) data at each fixed temperature and pressure. The experimental solubility data of CO 2 in ionic liquids have been successfully correlated for the first time using a simple cubic equation of state (EOS). Some phase behaviors of CO 2 and ionic liquid mixtures as well as Henry's law constants and the volume change of solutions are predicted well with the present EOS model. From time-dependent absorption data, binary diffusion coefficients of CO 2 in the ionic liquids have been obtained for the first time by the use of a simple diffusion model. Magnitudes in the observed diffusion coefficients are 10 -10 to 10 -11 m 2 s -1, which are about 10−100 times lower than typical values, found in various organic liquids.