Phase equilibria of l–Valine/l–Leucine solid solutions

Abstract

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 l–valine/l–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.