Separation of CO 2 and H 2S using room-temperature ionic liquid [bmim][PF 6

Abstract

We have developed a ternary equation of state (EOS) model for the CO 2/H 2S/1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6]) 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 CO 2/[bmim][PF 6] and literature data for H 2S/[bmim][PF 6] and CO 2/H 2S. VLLE (vapor–liquid–liquid equilibrium) measurements have been made and validate EOS model predictions which suggest that the CO 2/[bmim][PF 6] and H 2S/[bmim][PF 6] 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 CO 2/H 2S/[bmim][PF 6] 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 CO 2/H 2S gas selectivity is nearly independent of the amount of ionic liquid addition and ranged from about 3.2 to 4.0. For large CO 2/H 2S mole ratios (9/1) at 298.15 K, the addition of the ionic liquid increases the CO 2/H 2S gas selectivity from about 1.2 to 3.7. For high temperature (333.15 K) and high CO 2/H 2S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO 2/H 2S binary system without the ionic liquid.