Thermodynamic models for determination of the solubility of dl-malic acid in methanol plus (acetonitrile, N,N-dimethylformamide, isopropyl alcohol) binary solvent mixtures

The solubility of dl-malic acid in binary solvent mixtures consisting of (methanol + acetonitrile); (methanol + N,N-dimethylformamide); and (methanol + isopropyl alcohol) was measured at temperatures ranging from (278.15 to 328.15) K by gravimetric method. Values of the solubility were fitted using modified Apelblat equation and Buchowski-Ksiazaczak λh model. Computational results showed that the modified Apelblat equation was superior to the other equation. In addition, the thermodynamic properties of the solution process, including the Gibbs free energy, enthalpy, and entropy were calculated by the van't Hoff analysis. This study provides valuable data for the dl-malic acid purification by the preferential crystallization procedure.