Using the modified Pitzer model to analyze the solubilities of sodium and potassium halides in aqueous mixtures of amides (Formamide, N-methylformamide and N-Methylacetamide) at T = 298.15 K

Abstract

• Solubility of potassium halides (KCl, KBr, and KI) in aqueous mixtures of amides (Formamide, N-Methylformamide, and N-Methylacetamide) were determined experimentally at 298.15 K. • The experimental solubility data of potassium halides along with sodium halides (NaF, NaCl, NaBr, and NaI) from the literature were successfully correlated with the modified Pitzer model. • Solid-liquid phase diagrams were predicted for 6 ternary systems Amida-NaCl-H 2 O and Amida-KCl-H 2 O at 298.15 K as application examples of the model. • The performance of extractive crystallization processes with the amides were simulated using the modified Pitzer model for the 21 ternary systems of this study. In this work the solubilities of the potassium halides (KCl, KBr, and KI) in solvent mixtures water-amide (Formamide, N-Methylformamide, and N-Methylacetamide), were measured at temperature T = 298.15 K. These data along with those previously measured in another work for the corresponding sodium halides (NaF, NaCl, NaBr, and NaI), in the same solvent mixtures and at the same temperature, were correlated using the modified Pitzer model. The calculated solubility data are in good agreement with the experimental data for all systems over a wide range of co-solvent concentration. The solubility of a given potassium (or sodium) halide decreases with the weight percentage of the co-solvent due to the solventing-out effect. For all ternary systems, it was found that by changing the amide in the order (FA, NMF, and NMA), the dielectric constant increases and the density decreases, influencing these properties with a decrease in the solubility of the salt. The maximum crystallization yields were determined for an extractive crystallization process with different amides at T = 298.15 K, which also demonstrated the usefulness of the modified Pitzer model in the simulation of separation processes of inorganic salts.