Extension of Cubic-Plus-Polar (CPP) equation of state (EoS) for application in aqueous electrolyte solutions

Abstract

In this study, an extension of Cubic-Plus-Polar (CPP) equation of state (EoS), i.e. electrolyte CPP (eCPP), was proposed to study various aqueous binary electrolyte solutions as well as water-CO2-NaCl, water-CO2-Na2SO4, and water-H2S-NaCl ternary systems. To avoid complexity, polar (dipole-dipole, quadrupole-quadrupole, and dipole-quadrupole) interactions were only considered for water, CO2, and H2S components, not for the studied ionic species in electrolyte solutions. In this work, the long-range electrostatic contribution was taken into account by Pitzer-Debye-Huckel equation. The proposed model has three adjustable parameters for each electrolyte, which were determined by fitting to experimental mean activity coefficient and liquid molar volume data of 79 aqueous strong electrolyte solutions at 0.1 MPa and 298.15 K. The overall average absolute relative deviation (AARD) between model-calculated values and experimental data were 1.05% and 1.44% for liquid molar volume and mean activity coefficient, respectively, while this value was 1.27% for predicted results of osmotic coefficient. Moreover, eCPP EoS predicted the liquid molar volumes of 15 different electrolyte solutions with an overall AARD of 0.6% in a wide range of pressure, temperature, and electrolyte concentration. The reliability of the proposed EoS (eCPP) was verified by the obtained AARDs.