Vapor-liquid-liquid equilibria of hydrofluorocarbons+1-butyl-3-methylimidazolium hexafluorophosphate

In recent reports, we measured the vapor-liquid-liquid equilibria (VLLE) of trifluoromethane (R-23) and pentafluoroethane (R-125) with a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], using a volume-mass measurement method along various isotherms. In the present work, we complete similar investigation of VLLE for the methane and ethane series of hydrofluorocarbons (HFCs) in [bmim][PF6]. Compounds studied here are fluoromethane (R-41), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), and fluoroethane (R-161) in [bmim][PF6]. Observed VLLE behaviors are consistent with the earlier predictions by our equation-of-state (EOS) model, which showed partial immiscibilities in the HFC-rich side solutions, indicating type-III or type-V mixtures according to the Konynenburg-Scott classification. Thus, the present study as well as those with R-23 and R-125 reasonably validate our EOS model. In addition, very large negative excess molar volumes have been observed for all the studied systems, similar to that observed for mixtures with R-23 and R-125.