Understanding the molecular dynamics of the ethanol/water azeotrope using magnetic resonance

Azeotropes are constant boiling mixtures that cannot be separated by fractional distillation. Components in an azeotropic mixture evaporate together at a boiling point that is different to the individual pure substances.[1] Separating azeotropes is a challenging process. Common methods of separation such as pressure-swing-distillation and the addition of entrainers, require either large amounts of energy or the addition of other components. These methods are sub-optimal and result in a high economic and/or environmental burden. Azeotropes impact a wide range of processing sectors from biofuel production to pharmaceutical manufacturing. In contrast to their common occurrence, there is a considerable gap in the understanding of their molecular dynamics. Investigating the molecular level origins of azeotropes may lead to the development of improved separation techniques. Nuclear Magnetic Resonance (NMR) relaxation and diffusion measurements are well suited to provide this information. Previous diffusion studies of the ethanol-water system have reported that both ethanol and water molecules have the same diffusion coefficients at the azeotropic point, alluding to the formation of complex solution structuring where both water and ethanol are somehow behaving as a single entity.[2] To further understand the molecular dynamics and the diffusion results of this azeotropic system, longitudinal and transverse relaxation time measurements on the samples with varying mole fraction of ethanol in water, at different temperatures and magnetic field strengths will be presented. This presentation will also discuss how they relate to the reported diffusion results and what they reveal about the molecular dynamics of this azeotropic system.