Insights into the Ethyl Lactate + Water Mixed Solvent

Abstract

The mixed green solvent ethyl lactate + water is studied from macro- and microscopic viewpoints using a wide collection of experimental and computational tools. High-pressure thermophysical data, density, and dynamic viscosity provide valuable information on the macroscopic behavior of the mixed fluid, which is of remarkable importance for industrial purposes, and through the analysis of the derived excess and mixing properties lead to relationships with molecular level properties. Large deviations from ideality are obtained, which are related to the development of strong intermolecular hydrogen bonding between both molecules upon mixing. Computational studies, using the density functional theory, both in gas phase and water solution, allow to characterize, from energetic and structural viewpoints, the different ethyl lactate/water association complexes. The use of atoms in a molecule and natural bond orbital methods sheds light into the properties of ethyl lactate/water hydrogen bonding. Classical molecular dynamics simulations are carried out for the whole composition range, and as a function of pressure and temperature. Force field validation is done by comparison of predicted thermophysical properties with measured ones. Structural features are inferred from the analysis of radial distribution functions and their evolution with composition, pressure, and temperature, and dynamic aspects are inferred from the calculated self-diffusion constants and mean square displacements. The whole study points to a highly structured fluid, in which hydrogen bonding is developed both for water-rich and ethyl-lactate-rich solvents, showing a remarkable effect in the fluid structure upon the addition of the second component for both pure compounds, even more important for the effect of ethyl lactate on water hydrogen bonding network