Study on the Solid–Liquid Equilibrium and Thermodynamic Model of l-Histidine + dl-Methionine + Water System

The solubility of amino acids is a fundamental characteristic that needs to be determined in order to better understand the design of the production and purification processes. In this study, the solid–liquid equilibrium data of the ternary system of 288.15–328.15 K l-histidine + dl-methionine + water at atmospheric pressure were obtained using the isothermal solution saturation method. Subsequently, these data were utilized to develop five precise ternary phase diagrams, each detailing the phase relationships at a specific composition range, in addition to a comprehensive variable-temperature phase diagram that captured the phase behavior across the entire temperature range of 288.15–328.15 K. Based on experimental data, a semiempirical model was employed to derive the thermodynamic equation that described the solid–liquid equilibrium within this system. The model predicted solid–liquid equilibrium data for ternary systems over a wide range of temperatures. The resulting phase diagram exhibited three distinct crystallization zones, two cosaturation solubility curves, and a single cosaturation point. This comprehensive representation of the mutual solubility data and ternary phase diagram holds immense significance in optimizing the purification process of l-histidine and dl-methionine, ultimately leading to improved industrial applications and product quality.