Water/Hydrocarbon Phase Equilibria Using the Thermodynamic Perturbation Theory

Abstract

Two equations of state, the cubic plus association (CPA) and the statistical associating fluid theory (SAFT), which account explicitly for the effect of hydrogen bonding on the thermodynamic properties of associating fluids using the perturbation theory of Wertheim (J. Stat. Phys. 1986, 42, 459, 477), are applied to predict the phase equilibrium of pure water, n-alkanes, and 1-alkenes as well as the low- and high-pressure phase equilibrium of water/hydrocarbon mixtures. The pure compound parameters for the two equations are estimated by fitting experimental vapor pressure and saturated liquid density data that cover a very wide temperature range from approximately the triple point to very close to the critical point. One temperature-independent binary interaction parameter is calculated for each of the mixtures examined. The analysis of the results shows that the increased complexity of SAFT over CPA does not offer any improvement in modeling highly nonideal fluid behavior, at least for the systems examined here.