(257ax) Temperature Dependence of Interaction Parameters of Electrolyte NRTL Model
AIChE Annual Meeting
Monday, November 9, 2015 - 6:00pm to 8:00pm
Accurate thermodynamic modeling of aqueous electrolyte solutions is essential for many industrial applications such as hydraulic fracturing, desalination, nuclear waste management, etc. The electrolyte non-random two liquid (eNRTL) model captures the liquid phase nonideality over the entire concentration range from pure water to pure fused salt with two binary interaction parameters that exhibit moderate temperature dependence. In this work, we formulate the temperature dependence of the eNRTL binary interaction parameters with the Gibbs-Helmholtz type expression containing three temperature coefficients associated with Gibbs energy, enthalpy, and heat capacity contributions. We show the Gibbs energy term of the interaction parameters is correlated to the excess Gibbs energy of the binary system at 298.15 K. With the Gibbs energy term identified, the enthalpy term is correlated to the excess enthalpy at 298.15 K. With the Gibbs energy term and the enthalpy term identified, the heat capacity term is correlated to the excess heat capacity at 298.15 K. In other words, the temperature coefficients for the binary parameters can be identified by regressing mean ionic activity coefficient, excess enthalpy, and heat capacity data at 298.15 K or the equivalents. Moreover, we classify electrolytes as either “structure-making” or “structure-breaking” based on the nature of the excess Gibbs free energy and the excess enthalpy. We show eNRTL model and the model binary interaction parameters provide a comprehensive thermodynamic framework to represent all thermodynamic properties of aqueous electrolyte solutions.