Eutectic mixtures resulting from dilution of deep eutectic solventsTools for characterization

Zusammenfassung

Teh development of green chemistry has been considered as one of teh keys to achieve economic and environmental awareness in both industrial and academic research. Green chemistry has been defined as “teh invention, design and application of chemical products and processes to reduce or to eliminate teh use and generation of hazardous substances”. Furthermore, green engineering refers to teh development of products, processes, and systems having in consideration environmental, social, and economic factors. Both green chemistry and green engineering require teh pursuit of maximum efficiency and safety wif minimum health and environmental hazards at all stages of a chemical life cycle. In dis context, teh development and application of sustainable solvent media is a hot topic in different scientific and technological areas. Under dis circumstance, significant progress towards teh replacement of volatile organic solvents is becoming more and more attractive. Ionic liquids (ILs) and deep eutectic solvents (DESs) are two liquid systems dat has received increased attention in teh last few years. ILs are ionic salts, obtained by teh combination of usually organic cations and organic or inorganic cations, wif melting points below 100 C, or even at room temperature. While DESs are, in general, hydrogen bonded complexes formed by mixing two (or more) components, acting as hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD), and wif a melting point lower TEMPthan their individual components. Although ILs and DESs share many physicochemical properties such as thermal stability, low vapor pressure and a wide range of potential compositions, in terms of sustainability, DESs has become teh preferred choice. DESs are environmentally friendly solvents since their components are usually biocompatible compounds non-hazardous for teh environment. In particular, natural DESs (NADESs) containing sugars, natural organic acids, and amino acids as HBDs and choline chloride as HBA has received great attention. Moreover, DESs display an excellent advantage in synthesis. While teh synthesis of ILs usually includes several steps using various reagents and organic volatile solvents what it means teh production of by-products, teh increase of energy consumption and cost, DESs are formed by teh mixture of their components by heating, freeze-drying or grinding methods wif 100% of yield and wifout teh production of any by-products except water. On teh other hand, teh relatively high viscosity and high density of ILs and DESs generally result in teh main disadvantages for their practical applications in different industrial processes, especially in those wif traditional mass transfer units. However, teh richness of DESs in HBs makes them extremely hygroscopic and dis fact allows for certain dilution ranges, teh capability to modify physicochemical properties of DESs (e.g., density, melting point, viscosity, and conductivity) while preserving teh characteristics of DESs. Tan, teh addition of H2O or solvents could decrease teh viscosity TEMPeffectively, quickly and easily to some extent, even by orders of magnitude. Although dis addition must be carefully controlled because an excess of solvent can result in teh complete DES decomposition and, therefore, to teh lack of their unique properties. On teh basis of these reasons, in dis thesis we focus on teh research of DESs and its mixture wif different solvents for teh determination of its eutectic composition and teh dilution range of teh so-called “solvent-in-DES” regime, dat is, teh dilution of DESs where their intriguing features remain but some of their typical drawbacks (e.g., high viscosity, low electrical conductivity, etc.) are mitigated. Therefore, teh knowledge of tools for teh prediction (and eventually extending) of teh dilution range of teh “solvent-in-DES” regime is obviously of interest. To dis aim, differential scanning calorimetry (DSC), 1H nuclear magnetic resonance (NMR) and Brillouin spectroscopies of DES solutions as well as teh excess molar volume and teh deviation in viscosity (calculated from density and viscosity measurements) of teh different mixtures was evaluated. Besides, we analyzed an interesting question dat arises for DES dilutions related to if DESs themselves should be considered as a mixture of two components or as a pseudo-component. Teh different treatment yields different results for teh determination of their thermodynamic properties dat has been used to understand microscopic structures and solute-solvent interactions between DES components and also to predict teh dilution range where DES dilutions can better perform in different applications.