Phase equilibria modeling of polar systems with Cubic-Plus-Polar (CPP) equation of state

Abstract

In this study, an equation of state (EoS), Cubic-Plus-Polar (CPP), has been constructed to model phase equilibria of polar and practical systems in a wide range of temperatures and pressures. In the proposed model, Soave-Redlich-Kwong (SRK) EoS takes into account dispersive forces while a set of polar terms was employed to account for dipolar and quadrupolar interactions. By applying these terms, dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions were directly taken into consideration. The CPP EoS with four pure-compound parameters could accurately correlate both vapor pressure and saturated liquid molar volume of studied pure compounds (water, methanol, ethanol, propanol, 2-propanol, 2-butanol, acetone, N-methyl-2-pyrrolidone (NMP), CO2, and H2S). By utilizing two temperature-dependent binary interaction parameters (BIPs), the phase equilibria of binary mixtures including water-CO2, water-H2S, CO2–H2S, methanol-CO2, ethanol-CO2, propanol-CO2, acetone-CO2, water-acetone, ethanol-acetone, water-NMP, 2-propanol-NMP, and 2-butanol-NMP were satisfactorily calculated by the model. Moreover, the proposed model is sufficiently efficient which is capable of representing minimum water mole fraction in the nonaqueous phase of water-CO2 and water-H2S mixtures. Additionally, the CPP EoS accurately predicted the saturated and single phase mixtures densities of water-CO2 mixture. Finally, the solubility values of CO2 and H2S mixtures in water were reasonably predicted by the model.