Separation of CO2 and H2S using room-temperature ionic liquid [bmim][PF6]

We have developed a ternary equation of state (EOS) model for the CO2/H2S/1-butyl-3-methylimidazolium hexafiuorophosphate ([bmimj[PF6]) system in order to understand the separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a generic RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. These interaction parameters have been determined using our previously measured VLE (vapor-liquid equilibrium) data for CO2/[bmim][PF6] and literature data for H2S/[bmim][PF6] and CO2/H2S. VLLE (vapor-liquid-liquid equilibrium) measurements have been made and validate EOS model predictions which suggest that the CO2/[bmim][PF6] and H2S/[bmim][PF6] systems are Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model calculations has also been checked by conducting VLE experiments for the CO2/H2S/[bmim][PF6] system. With this EOS model, isothermal ternary phase diagrams and solubility (VLE) behavior have been calculated for various (T, P, and feed compositions) conditions. The CO2/H2S gas selectivity is nearly independent of the amount of ionic liquid addition and ranged from about 3.2 to 4.0. For large CO2/H2S mole ratios (9/1) at 298.15 K, the addition of the ionic liquid increases the CO2/H2S gas selectivity from about 1.2 to 3.7. For high temperature (333.15 K) and high CO2/H2S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO2/H2S binary system without the ionic liquid. (C) 2010 Elsevier B.V. All rights reserved.