Modeling thermodynamic properties of electrolytes: Inclusion of the mean spherical approximation (MSA) in the simplified SAFT equation of state

Abstract

In this work, an equation of state has been utilized for thermodynamic modeling of aqueous electrolyte solutions. The proposed equation of state is a combination of simplified statistical associating fluid theory (SAFT) equation of state (similar to simplified PC-SAFT) to describe the effect of short-range interactions and mean spherical approximation (MSA) term to describe the effect of long-range interactions. In this model, the salt- based approach or restricted primitive model has been used to adjust the four parameters of the model. The salt (ion) parameters have been estimated through simultaneous fitting to experimental mean ionic activity coefficient and liquid density data of strong electrolytes. Four strong electrolytes, three 1:1 and one 1:2 electrolytes have been used. Using adjusted ion parameters, osmotic coefficient of solvent has been predicted with 0.79% average relative deviation (ARD%). Results show that simplified SAFT, in combination with the MSA term has ARD% about 1% and less for correlating of density and mean ionic activity coefficient of electrolyte solutions.