Prediction of multiphase equilibrium using the PC-SAFT equation of state and simultaneous testing of phase stability

This work employs the PC-SAFT equation of state to illustrate how to compute phase equilibria and stability of multiphase systems. The proposed computation scheme is based on the methodology of Gupta et al. (1991) but with modifications. Phase equilibria and stability are computed simultaneously and without the need to modify the exact stability equation. This approach does not encounter difficulty when the phase fraction approaches zero. A simple initialization strategy is utilized. In addition, this work tests the predictive capability of PC-SAFT in multiphase systems of water-hydrocarbon containing systems at different pressure–temperature conditions. The dipole and quadrupole interactions were included in the PC-SAFT equation and the binary interaction parameters (kij) were set to zero. The work has demonstrated the ability of PC-SAFT to successfully predict vapour–liquid–liquid equilibrium of systems containing water, hydrocarbons and ethylene glycol with or without carbon dioxide.