Azeotropic Separation: Playing with the Ionicity of Ionic Liquids

摘要

In modern chemical industry, the separation of solvent mixtures into their pure compounds is mandatory not only to prevent their accumulation, but also for that their reusability may assure a sustainable overall process. However, the presence of azeotropes or close boiling point mixtures constitute one of the most challenging tasks in industrial processes in the separation of solvent mixtures, since their separation by simple distillation is basically impossible. The processes designed for the efficient separation of azeotropic mixtures usually require the use of a separation agent.;Separation agents can range from an organic solvent, to an inorganic salt (IS), or even combinations of both. More recently, ionic liquids (ILs), deep eutectic solvents (DES) and hyperbranched polymers have also been successfully tested. ISs are known for their high separation efficiencies, due to their ionic character, and ILs for their liquid state and negligible vapour pressures. So, the next natural step is to combine the advantages of both these classes of compounds.;This thesis explores the separation of azeotropic mixtures using a combination of an IL and an IS as separation agent. The work presented herein starts by studying different IL-IS mixtures in terms of their physical and chemical properties, which allowed the determination of their ionicity or ionic character (Chapter 2 and 3). Afterwards, the studied IL-IS mixtures are tested in the separation of one specific azeotropic mixture, n-heptane + ethanol that will serve as test model (proof-of-concept) for the application of IL-IS mixtures as separation agents for breaking azeotropes (Chapter 4 and 5). In addition, deep eutectic solvents (DES), viewed as greener analogues of ILs, are also tested as potential azeotrope breakers (Chapter 6).;The obtained results enable the establishment of relationships between the thermophysical properties of IL-IS mixtures and their ionicity, and about the chemical structures of the ILs and ISs required to produce mixtures with increased ionicity. Furthermore, the work presented in this thesis shows that IL-IS mixtures can surpass neat ILs as efficient separation agents, allowing the establishment of a link between ionicity and extraction efficiency in the separation of azeotropic mixtures.