Phase equilibria of L-Valine/L-Leucine solid solutions

Modeling and experimental determination of Solid Liquid Equilibria (SLE) and the related phase diagrams are challenging in the presence of solid solutions. In this work, the ternary phase diagram of t-valinefi.leucine in water is measured and theoretically modelled at 298.15 K. The two similar molecules, L-valine and L-leucine form solid solutions as confirmed by Powder X-Ray Diffraction (PXRD) experiments. In addition, the concentrations of both equilibrated phases are determined using High Performance Liquid Chromatography (HPLC). Nonidealities are described using Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) and Non-Random Two-Liquid (NRTL) models for the liquid and solid phases, respectively. The models work well to describe the solubility curve, except some extreme points. Finally, a graphical separation method based on the Lippmann plot is derived and its potential use will be expanded for the separation of organic compounds forming solid solutions. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study measured and theoretically modeled the ternary phase diagram of t-valine and leucine in water, showing the formation of solid solutions between L-valine and L-leucine. Different models were used to describe the solubility curve, with a graphical separation method based on the Lippmann plot proposed for potential use in separating organic compounds forming solid solutions.