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.

A new formulation for the thermodynamic properties of nitrogen has been developed. Many new data sets have become available, including high accuracy data from single and dual-sinker apparatuses which improve the accuracy of the representation of the pT surface of gaseous, liquid, and supercritical nitrogen, including the saturation states. New measurements of the speed of sound from spherical resonators yield accurate information on caloric properties in gaseous and supercritical nitrogen. Isochoric heat capacity and enthalpy data have also been published. Sophisticated procedures for the optimization of the mathematical structure of equations of state and special functional forms for an improved representation of data in the critical region were used. Constraints regarding the structure of the equation ensure reasonable results up to extreme conditions of temperature and pressure. For calibration applications, the new reference equation is supplemented by a simple but also accurate formulation, valid only for supercritical nitrogen between 250 and 350 K at pressures up to 30 MPa. The uncertainty in density of the new reference equation of state ranges from 0.02% at pressures less than 30 MPa up to 0.6% at very high pressures, except in the range from 270 to 350 K at pressures less than 12 MPa where the uncertainty in density is 0.

Gaseous absorption measurements of hydrofluorocarbons (trifluoromethane, difluoromethane, pentafluoroethane, 1,1,1,2‐tetrafluoroethane, 1,1,1‐trifluoroethane, and 1,1‐difluoroethane) in l‐n‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF4]) were performed using a gravimetric microbalance at various isothermal conditions (temperatures between 283.15 and 348.15 K) and at pressures < 2 MPa. This report shows for the first time the solubility and diffusivity data for the hydrofluorocarbons in room‐temperature ionic liquids and surprisingly large differences in the solubility among the hydrofluorocarbons. Experimental gas solubility data were successfully correlated with well‐known solution models (Margules, Wilson, and NRTL activity coefficient equations). Diffusivities obtained from the time‐dependent absorption data were well analyzed using a diffusivity model developed in this study. The present solubility and diffusivity data are also compared with those of CO2, studied in our previous study. © 2005 American Institute of Chemical Engineers AIChE J, 2006