Phase equilibria modeling of methanol-containing systems with the CPA and sPC-SAFT equations of state

Proper representation at various conditions of phase equilibria of methanol-containing mixtures (with hydrocarbons, water, etc.) is important for oil flow assurance purposes.In this work two association equations of state, CPA and sPC-SAFT, are applied to methanol-containing mixtures. The purpose of this work is to investigate which association schemes (e.g. two-site, three-site) should be used for methanol which will result in successful representation of methanol–water–hydrocarbon phase equilibria. Parameters from the literature as well as newly estimated parameters based on vapor pressure, liquid density, enthalpy of vaporization and compressibility factor data are used. Methanol–alkane vapor–liquid equilibrium (VLE) and liquid–liquid equilibrium (LLE) data, water–methanol VLE as well as water–methanol–hydrocarbon LLE are considered.It is concluded that the two association equations of state perform overall similarly, with the two-site association scheme being a better choice than the three-site scheme, for phase equilibrium calculations. Use of the additional properties (enthalpy of vaporization and compressibility factor) in the parameter estimation has a larger effect on the performance of sPC-SAFT compared to CPA.