Measurement and modelling of ternary solid-liquid phase equilibrium of (DL-malic acid + maleic acid + water) from 283.15 K to 333.15 K

Abstract The solid–liquid phase equilibrium data of (DL-malic acid + maleic acid + water) in binary and ternary systems were measured by high performance liquid chromatography (HPLC) method at 283.15 K, 293.15 K, 303.15 K, 313.15 K, 323.15 K and 333.15 K under atmospheric pressure, and then six isothermal ternary phase diagrams were established. Each isothermal ternary phase diagram included one co-saturated point (invariant), two saturated boundary curves, and three crystallization regions (DL-malic acid, maleic acid, and mixture of both). For extending the application of measured solid–liquid phase equilibrium data, the Wilson model and NRTL model were used for correlation and prediction, and the relative average deviation (RAD) and root-mean-square deviation (RMSD) were applied to assess the calculation precision. The maximum values of RAD and RMSD were 2.61 × 10−2 and 1.87 × 10−3 with Wilson model, 3.31 × 10−2 and 1.86 × 10−3 with NRTL model, respectively, which demonstrated that the calculated data were close to the experimental data, and accurate theoretical data under other experimental conditions were able to acquire through the two models in DL-malic acid + maleic acid + water system. The study provided reliable and accurate data for separating the mixture of DL-malic acid and maleic acid in water.