Phase equilibrium modeling of mixtures of long-chain and short-chain alkanes using Peng–Robinson and SAFT

Peng–Robinson and selected implementations of the Statistical Associating Fluid Theory (SAFT) equation of state (EoS) were evaluated for their ability to correlate and predict vapor–liquid equilibrium for highly asymmetric mixtures of n-alkanes. Peng–Robinson is surprisingly accurate for fitting such mixtures, but only if the pure component parameters are regressed with vapor pressure and liquid density data, as is normally done with SAFT. Furthermore, these parameters were found to be well-behaved and to increase monotonically with carbon number. In spite of its deficiencies in modeling the near-critical and critical regions, PC-SAFT is recommended for predicting the phase behavior of asymmetric mixtures of n-alkanes for which no data are available. For example, with a binary interaction parameter of zero, PC-SAFT accurately predicts liquid-phase compositions for n-alkane mixtures of C6+C16, C6+C24 and C6+C36 over a wide range of temperatures and pressures.