Fast development of computation techniques for electrolyte activities contributed recently to introduction of a few substantial programmes for thermodynamic computing of multiphase systems. The presented study comprises useful information for practical computing using selected thermodynamic models of aqueous electrolyte solutions. Those models enable quantitative description of both phase and ionic equilibria and provide values of activity coefficients. The carried out analysis of individual models involved a comparison of their practical effectiveness features along with problems encountered in evaluation of the coefficients. The authors conclude that for the Solvay soda system the exUNIQUAC model for an in-house code or the MSE model for a commercial one can be used.

The main objective of this work was to verify the mixed solvent electrolyte (MSE) thermodynamic model for the prediction of the liquid-solid equilibrium in the soda system. The full quaternary system NaCl-NaHCO3-Na2CO3-H2O and its three subsystems were considered. Validation of the thermodynamic model was based on experimental data from literature. Phase diagrams for the soda system are plotted for isotherms of 45°C. Good agreement of the MSE results with those from experiments was found at 45°C. Similar phase diagrams for other temperature levels can be constructed based on the validated MSE model.

A Comparative Study of Two Thermodynamic Models Applied to Solutions of the NH3-H3PO4-H2O and NH3-CO2-NaCl-H2O Systems -[32 refs.]. -(JAWORSKI, Z.; CZERNUSZEWICZ, M.; GRALLA, L.; Inz. Chem. Procesowa 31 (2010) 4, 789-811 ; Inst. Chem. Eng. Environ. Protect. Processes, West Pomeranian Univ. Technol., PL-70-322 Szczecin, Pol.; Eng.) -Schramke 51-168

Simplified relationships for the equilibrium partial pressure of the gas phase components were presented for the crystallization conditions of sodium bicarbonate in the NaCl–NH3–CO2–H2O system. Based on the partial pressures computed from the validated mixed-solvent-electrolyte (MSE) model, the regression equation coefficients were derived for explicitly correlating the partial pressures with the liquid phase concentrations and temperature in the range of (308.15 to 338.15) K. A good agreement was found between pressures calculated from the algebraic equations and compared with corresponding values computed from the MSE model. The obtained exponential equations can be directly used for the estimation of the equilibrium partial pressures in the process conditions of carbonation columns.