EUTECTIC MIXTURES RESULTING FROM DILUTION OF DEEP EUTECTIC SOLVENTS: TOOLS FOR CHARACTERIZATION
[EN] The development of green chemistry has been considered as one of the keys to achieve economic and environmental awareness in both industrial and academic research. Green chemistry has been defined as “the invention, design and application of chemical products and processes to reduce or to elimi...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/259119 |
| Acceso en línea: | http://hdl.handle.net/10261/259119 |
| Access Level: | acceso abierto |
| Palabra clave: | Deep eutectic solvents Brillouin Spectroscopy Solvent-in-DES regime Excess properties Aqueous binary mixtures NMR Spectroscopy |
| Sumario: | [EN] The development of green chemistry has been considered as one of the keys to achieve economic and environmental awareness in both industrial and academic research. Green chemistry has been defined as “the invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazardous substances”. Furthermore, green engineering refers to the development of products, processes, and systems having in consideration environmental, social, and economic factors. Both green chemistry and green engineering require the pursuit of maximum efficiency and safety with minimum health and environmental hazards at all stages of a chemical life cycle. In this context, the development and application of sustainable solvent media is a hot topic in different scientific and technological areas. Under this circumstance, significant progress towards the replacement of volatile organic solvents is becoming more and more attractive. Ionic liquids (ILs) and deep eutectic solvents (DESs) are two liquid systems that have received increased attention in the last few years. ILs are ionic salts, obtained by the combination of usually organic cations and organic or inorganic cations, with 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 with a melting point lower than 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 have become the preferred choice. DESs are environmentally friendly solvents since their components are usually biocompatible compounds non-hazardous for the environment. In particular, natural DESs (NADESs) containing sugars, natural organic acids, and amino acids as HBDs and choline chloride as HBA have received great attention. Moreover, DESs display an excellent advantage in synthesis. While the synthesis of ILs usually includes several steps using various reagents and organic volatile solvents what it means the production of by-products, the increase of energy consumption and cost, DESs are formed by the mixture of their components by heating, freeze-drying or grinding methods with 100% of yield and without the production of any by-products except water. On the other hand, the relatively high viscosity and high density of ILs and DESs generally result in the main disadvantages for their practical applications in different industrial processes, especially in those with traditional mass transfer units. However, the richness of DESs in HBs makes them extremely hygroscopic and this fact allows for certain dilution ranges, the capability to modify physicochemical properties of DESs (e.g., density, melting point, viscosity, and conductivity) while preserving the characteristics of DESs. Then, the addition of H2O or solvents could decrease the viscosity effectively, quickly and easily to some extent, even by orders of magnitude. Although this addition must be carefully controlled because an excess of solvent can result in the complete DES decomposition and, therefore, to the lack of their unique properties. On the basis of these reasons, in this thesis we focus on the research of DESs and its mixture with different solvents for the determination of its eutectic composition and the dilution range of the so-called “solvent-in-DES” regime, that is, the 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, the knowledge of tools for the prediction (and eventually extending) of the dilution range of the “solvent-in-DES” regime is obviously of interest. To this aim, differential scanning calorimetry (DSC), 1H nuclear magnetic resonance (NMR) and Brillouin spectroscopies of DES solutions as well as the excess molar volume and the deviation in viscosity (calculated from density and viscosity measurements) of the different mixtures was evaluated. Besides, we analyzed an interesting question that arises for DES dilutions related to if DESs themselves should be considered as a mixture of two components or as a pseudo-component. The different treatment yields different results for the determination of their thermodynamic properties that have been used to understand microscopic structures and solute-solvent interactions between DES components and also to predict the dilution range where DES dilutions can better perform in different applications. |
|---|