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Keywords:

  • 1-butyl-3-methylimidazolium hexafluorophosphate;
  • carbon dioxide;
  • trifluoromethane;
  • phase behavior;
  • binary systems;
  • ionic liquid;
  • experimental

Abstract

The phase behavior of binary mixtures consisting of two different supercritical fluids, one with no dipole moment and the other one with a strong dipole moment, and an imidazolium-based ionic liquid were studied experimentally. Carbon dioxide (CO2) and trifluoromethane (CHF3), and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) were the selected supercritical fluids and ionic liquid, respectively. A synthetic method was used to measure liquid–vapor (LV) and liquid–liquid–vapor (LLV) boundaries of these binary systems. Results for the LV boundaries are reported for CO2 concentrations ranging from 10.0 to 65.0 mol % and within temperature and pressure ranges of 293.29–363.54 K and 0.59–73.50 MPa, and for CHF3 concentrations ranging from 10.2 to 99.0 mol % and within temperature and pressure ranges of 303.20–363.42 K and 0.58–41.00 MPa, respectively. The LV boundaries of pure CO2 and CHF3 were measured up to their critical points. For the binary systems consisting of either CO2 or CHF3 with [bmim][PF6], the LLV boundaries were similarly measured up to their critical endpoints. The experimental results obtained in this work show that the binary systems of CO2 or CHF3 + [bmim][PF6] have Type III phase behavior according to the classification of Scott and Van Konynenburg. To the extent available, the experimental data obtained for the system CO2 + [bmim][PF6] were compared with literature data. In addition, comparisons were made with literature data of binary systems of either CO2 or CHF3 with other ionic liquids belonging to the same homologous family. © 2005 American Institute of Chemical Engineers AIChE J, 2005