Prediction of vapor-liquid equilibria for mixtures of low boiling point compounds using Wong-Sandler mixing rule and EOS/GE model

Vapor-liquid equilibrium (VLE) of low boiling point components occurs at low-temperature and usually at high pressure. A proper method for computing the fugacity coefficient is to use a cubic equation of state with mixing rules. However, empirical mixing rules include one adjustable parameter and cannot predict VLE of some mixtures accurately. An alternative that could be used for non-ideal mixtures is the Wong-Sandler mixing rule, which is derived based on the excess Gibbs energy (GE). In this research, VLE of light gaseous mixtures was calculated at low temperatures and medium to high pressures using the Peng-Robinson equation of state (PR EOS), the Wong-Sandler mixing rule, and the NRTL equation as a GE model. This introduces an additional adjustable parameter. Assuming the adjustable parameters as a function of temperature, the results show that this thermodynamic model is an appropriate method to predict VLE of low boiling point materials at wide range of temperatures.