Gibbs Free-Energy-Based Objective Function for Electrolyte Activity Coefficient Models

Karhan Özdenkçi, Jukka Koskinen, Golam Sarwar, Pekka Oinas
2017 Industrial & Engineering Chemistry Research  
This paper proposes Gibbs free energy-based objective functions in parameter fitting of 7 activity coefficient and specific heat capacity of ions. The activity coefficient parameters are fitted 8 through the averaged squared error between Gibbs free energy calculated by using the measured 9 activity coefficient data and that by using the model equation. The standard-state heat capacity 10 parameters of ions are fitted through the minimization of the average squared error between Gibbs 11 free
more » ... een Gibbs 11 free energy of dissolution calculated through the saturation activity over a temperature range and that 12 calculated through the standard state chemical potential as a function of temperature via standard state 13 specific heat. This methodology is tested with Bromley and Pitzer models. The proposed 14 methodology reduces the need of experiments and avoids the uncertainty of extrapolation to infinite 15 dilution when determining standard state specific heat of ions. The proposed methodology provides 16 more accurate solubility estimates than the common methodology, except for low temperatures in 17 Pitzer model where the common approach is somehow slightly more accurate. In addition, the 18 proposed methodology enables accurate modeling with limited data: solubility over temperature 19 range, activity coefficient data up to some concentrated range not covering saturation and no ionic 20 specific heat data. 21 22 keywords: thermodynamics, electrolyte system, aqueous thermodynamics, objective function, Gibbs 23 2 free energy, Bromley's method, Pitzer model 24 25 =
doi:10.1021/acs.iecr.7b01345 fatcat:qisfwbww2ffrblneqedh3r4ufm