Browsing by Author "Maximo, Guilherme J."
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- Greener terpene-terpene eutectic mixtures as hydrophobic solventsPublication . Martins, Mónia A.R.; Silva, Liliana P.; Schaeffer, Nicolas; Abranches, Dinis O.; Maximo, Guilherme J.; Pinho, Simão; Coutinho, João A.P.Natural products can be the basis for the development of green solvents, relevant for the advancement of new, more sustainable processes and products. In this work, 10 binary mixtures constituted by terpenes are prepared and characterized. Their solid−liquid phase diagrams show that room-temperature solvents can be prepared from solid terpenes in a wide composition range. These diagrams are accurately described by the conductor-like screening model for real solvents, showing it to be a useful predictive tool for the design of novel natural solvents. At the eutectic point, these mixtures possess low viscosities, densities lower than water, and high boiling temperatures. The low water solubility in the eutectic solvents together with its negligible impact on the properties measured is a strong indicator of the hydrophobic character of these mixtures. The tunable character of these mixtures is demonstrated by studying the solvatochromic parameters in the entire concentration region, the properties of the final solvents being tuned by simply varying the mole fraction of the terpenes. The high potential of this tunable character is shown in the selective extraction of dyes from their aqueous solutions. This work is expected to devise new insights concerning these solvents as well as to boost their application in green industrial processes.
- Measurement and PC-SAFT modeling of solid-liquid equilibrium of deep eutectic solvents of quaternary ammonium chlorides and carboxylic acidsPublication . Pontes, Paula V.A.; Crespo, Emanuel A.; Martins, Mónia A.R.; Silva, Liliana P.; Neves, Catarina M.S.S.; Maximo, Guilherme J.; Hubinger, Miriam Dupas; Batista, Eduardo A.C.; Pinho, Simão; Coutinho, João A.P.; Sadowski, Gabrielle; Held, ChristophIn this study the solid-liquid equilibria (SLE) of 15 binary mixtures composed of one of three different symmetrical quaternary ammonium chlorides and one of five different fatty acids were measured. The experimental data obtained showed extreme negative deviations to ideality causing large melting-temperature depressions (up to 300 K) that are characteristic for deep eutectic systems. The experimental data revealed that cross-interactions between quaternary ammonium salt and fatty acid increase with increasing alkyl chain length of the quaternary ammonium chloride and with increasing chain length of the carboxylic acid. The pronounced decrease of melting temperatures in these deep eutectic systems is mainly caused by strong hydrogen-bonding interactions, and thermodynamic modeling required an approach that takes hydrogen bonding into account. Thus, the measured phase diagrams were modeled with perturbed-chain statistical associating fluid theory based on the classical molecular homonuclear approach. The model showed very good agreement with the experimental data using a semi-predictive modeling approach, in which binary interaction parameters between quaternary ammonium chloride and carboxylic acid correlated with chain length of the components. This supports the experimental findings on the phase behavior and interactions present in these systems and it allows estimating eutectic points of such highly non-ideal mixtures.
- Tunable Hydrophobic Eutectic Solvents Based on Terpenes and Monocarboxylic AcidsPublication . Martins, Mónia A.R.; Crespo, Emanuel A.; Pontes, Paula V.A.; Silva, Liliana P.; Bülow, Mark; Maximo, Guilherme J.; Batista, Eduardo A.C.; Held, Christoph; Pinho, Simão; Coutinho, João A.P.Recently, some works claim that hydrophobic deep eutectic solvents could be prepared based on menthol and monocarboxylic acids. Despite of some promising potential applications, these systems were poorly understood, and this work addresses this issue. Here, the characterization of eutectic solvents composed of the terpenes thymol or l(-)-menthol and monocarboxylic acids is studied aiming the design of these solvents. Their solid-liquid phase diagrams were measured by differential scanning calorimetry in the whole composition range, showing that a broader composition range, and not only fixed stoichiometric proportions, can be used as solvents at low temperatures. Additionally, solvent densities and viscosities close to the eutectic compositions were measured, showing low viscosity and lower density than water. The solvatochromic parameters at the eutectic composition were also investigated aiming at better understanding their polarity. The high acidity is mainly provided by the presence of thymol in the mixture, while l(-)-menthol plays the major role on the hydrogen-bond basicity. The measured mutual solubilities with water attest to the hydrophobic character of the mixtures investigated. The experimental solid-liquid phase diagrams were described using the PC-SAFT equation of state that is shown to accurately describe the experimental data and quantify the small deviations from ideality.