Water-Hydrocarbon Phase Equilibria with SAFT-VR Mie Equation of State

The study of water-hydrocarbon phase equilibria is very important for both scientific and industrial purposes. This work is a thorough investigation of the predictive capability of SAFT-VR Mie equation of state (EoS) for aqueous hydrocarbon phase equilibria, including n-alkanes, alkenes, cycloalkanes, branched alkanes, and aromatic hydrocarbons.

For alkenes and alkyl benzenes, induced association (solvation) with water is considered. The model is able to capture the correct phase equilibrium topology for mixtures of n-alkanes and alkyl-benzenes with water as type III according to Van Konynenburg and Scott, but it is not able to predict the barometric shift for alkanes longer than n-hexacosane due to the overshoot of the critical temperature of water.

Quantitative results for the solubility of water in light hydrocarbons such as methane, ethane, and ethylene, as well as the mutual solubility of hydrocarbons and water above the solubility minimum, are possible. The latter is not predicted with SAFT-VR Mie EoS similar to other EoSs in literature. Accurate predictions are also reported for the pressure of the three-phase equilibrium and the critical lines for the binary mixtures.

Henry's law constant is often used for the prediction of low-pressure vapor-liquid equilibrium due to the low mutual solubility of hydrocarbons and water. EoS calculations are in reasonable agreement with experimental data for Henry's constant, especially at higher temperatures. Qualitatively, SAFT-VR Mie captures the maximum of Henry's constant with temperature, as well as the shift with the carbon number at temperatures near critical to water.

SAFT-VR Mie is shown to be overall capable of straightforward prediction of phase equilibria of aqueous hydrocarbon mixtures.