Equilibrium solubility determination, modeling and thermodynamic analysis of isophthalic acid in aqueous co-solvent mixtures of propylene glycol, ethylene glycol and glycerol

Solubility profile for isophthalic acid (IPA) in the mixtures of propylene glycol (PG), ethylene glycol (EG) or glycerol (Gly) as co-solvents and water was determined by a shake-flask method at 293.15–313.15 K under ambient pressure (≈ 85 kPa). Considering to the presence of many factors that can be changed the experimental results, this work focused mainly on temperature, chemical structure of co-solvent and water content as the main independent variables. The measured IPA solubilities were positively enhanced with enhancing temperature in a certain co-solvent composition; however, that decreased when the water content was gradually increasing and the maximum solubility in mole fraction terms was observed in neat mono-solvents of PG (0.0084), EG (0.0053) and Gly (0.0035) at 313.15 K. It seems that the solubilization power of each co-solvent was affected by their dipole moments and especially dielectric constants; so that, PG with the lowest values of dipole moment and dielectric constant (2.27 D, 32.0) presented the highest solubilization power for IPA in compared to the EG (2.27 D, 37.0) and Gly (2.56 D, 47.0). By representation the derived equilibrium solubilities with models of Jouyban-Acree and its two versions, the modified Wilson and its combined version of van’t Hoff, the mixture response surface, the combined nearly ideal binary solvent/Redlich–Kister and the Buchowski-Ksiazczak, a maximum overall average relative deviation of 9.4% was achieved. Furthermore, the thermodynamic functions of dissolution and mixing were determined from the solubility data using the modified van't Hoff equation. The results demonstrated that the dissolution process was an endothermic process and enthalpy-driven in all investigated systems.