Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

We have developed a ternary equation of state (EOS) model for the CO2/H2S/1-butyl-3-methylimidazolium methylsulfate ([bmim][MeSO4]) system to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a modified RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor-liquid equilibrium) data for H2S/[bmim][MeSO4] and literature data for CO2/[bmim][MeSO4] and CO2/H2S. Due to limited VLE data for H2S/[bmim][MeSO4], we have also used VLLE (vapor-liquid-liquid equilibrium) measurements to construct the EOS model. The VLLE for H2S/[bmim][MeSO4] is highly asymmetric with a narrow (mole fraction H2S between 0.97 and 0.99) LLE gap which is the first such case reported in the literature and exhibits Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model has been checked by conducting VLE experiments for the CO2/H2S/[bmim][MeSO4] system. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For large (9/1) and intermediate (1/1) CO2/H2S feed ratios, the CO2/H2S gas selectivity is high (10 to 13, compared with less than4.5 in the absence of ionic liquid) and nearly independent of the amount of ionic liquid added. For small CO2/H2S mole ratios (1/9) at 298.15 K, increasing the ionic liquid concentration increases the CO2/H2S gas selectivity from about 7.4 to 12.4. For high temperature (313.15 K) and large 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.