Modeling the temperature-dependent solubility of salts in organic solvents

Abstract

The temperature-dependent solubility of salts in organic solvents is of particular interest in nearly water-free multi-component systems, such as chemical reactions at extreme conditions, e.g., carboxylation reactions or Suzuki-Miyaura reactions. In this work, a novel modeling approach is proposed, which utilizes the correlative Pitzer model and the equation of state ePC-SAFT advanced to model the temperature-dependent solubility of salts in organic solvents. The proposed approach was applied to model the temperature-dependent solubility of CsCl in the organic solvents methanol, ethanol, and N-methyl-2-pyrrolidone (NMP) over a temperature range from T = 273.15 K to T = 333.15 K. The Pitzer model was used to correlate accurately temperature-dependent osmotic coefficients (OC). Pitzer was then used to determine ePC-SAFT binary interaction parameters and to determine the thermodynamic solubility product KSP of the salts over the temperature. Missing OC data were measured in this work using vapor-pressure osmometer for Na2CO3 and Cs2CO3. The resulting KSP values do not depend on the solvent, and they were used as an input into ePC-SAFT to model the temperature-dependent solubility of salts in organic solvents. Excellent agreement was achieved for CsCl, and the approach was then transferred to carbonate salts (Na2CO3 and K2CO3), which form multiple hydrates with water. Hypothetical KSP values of the anhydrous form were determined via the van ’t Hoff equation and successfully allowed modeling of the solubility of (anhydrous) Na2CO3 and K2CO3 in methanol, ethanol, and NMP. To conclude, a combination of accurate KSP values together with a robust thermodynamic model, such as ePC-SAFT advanced, can help to reduce the experimental burden in screening the solubility of salts in organic solvents over the temperature.