Browsing by Author "Silva, Liliana P."
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- Can cholinium chloride form eutectic solvents with organic chloride-based salts?Publication . Abranches, Dinis O.; Silva, Liliana P.; Martins, Mónia A.R.; Fernandez, Luis; Pinho, Simão; Coutinho, João A.P.The high melting point of a large number of organic salts with potential ionic liquid-like properties, hinders their applicability as solvents. Considering the success of cholinium chloride on lowering the melting temperature of several substances and its success on forming deep eutectic solvents, this work studies its mixing with organic chlorides to lower their melting points producing eutectic ionic liquids. The solid-liquid phase diagrams for binary mixtures composed of cholinium chloride and ten organic halides were experimentally measured. Surprisingly, cholinium chloride presented, for all these systems, significant positive deviations from ideal liquid behaviour that restricted its ability to lower the melting points of these mixtures. Only for mixtures with ammonium chloride, tetramethylammonium chloride, bis(2-hydroxyethyl)dimethylammonium chloride or cholinium bromide was cholinium chloride able to significantly lower the melting point of the mixture, but without reaching values close to room temperature (298 K). For a better understanding of the results obtained, the solid-liquid phase diagrams of four alkylammonium chloride-based mixtures were experimentally assessed and used to show that these compounds are better than cholinium chloride at inducing negative deviations from ideality, leading to greater melting point depressions.
- Characterization and Modeling of the Liquid Phase of Deep Eutectic Solvents Based on Fatty Acids/Alcohols and Choline ChloridePublication . Crespo, Emanuel A.; Silva, Liliana P.; Martins, Mónia A.R.; Fernandez, Luis; Ortega, Juan; Ferreira, Olga; Sadowski, Gabrielle; Held, Christoph; Pinho, Simão; Coutinho, João A.P.The solid-liquid equilibria phase diagrams of eight eutectic systems formed by choline chloride and fatty acids, or fatty alcohols, were measured to characterize the nonideality of the liquid phase of these systems, commonly reported in the literature as examples of type III deep eutectic solvents (DESs), and to evaluate the best modeling approaches to their description. Most of these systems are shown to present only slight deviations from ideal behavior, resulting from a fine balance of the hydrogen bonding between the hydroxyl/carboxylic groups with the chloride anion and the interactions present in the pure compounds. The phase diagrams measured were modeled with an associative equation of state (EoS) and a g E model. As an EoS, the perturbed-chain statistical associating fluid theory (PC-SAFT) was used, and this model was able to accurately describe the experimental data and to provide reliable estimates of the eutectic points using just a single binary temperature-dependent interaction parameter that often correlates with the acid/alcohol chain length. The performance of PC-SAFT was further compared with the g E model, a non-random two-liquid model (NRTL), and was found to provide a better description of the experimental data, especially for the more nonideal systems. Ultimately, the data gathered, and the molecular modeling, allowed the discussion of the behavior of fatty acids or fatty alcohols as hydrogen bond donors in choline chloride-based DESs.
- Design and Characterization of Sugar-Based Deep Eutectic Solvents Using Conductor-like Screening Model for Real SolventsPublication . Silva, Liliana P.; Fernandez, Luis; Conceição, João H.F.; Martins, Mónia A.R.; Sosa, Adriel; Ortega, Juan; Pinho, Simão; Coutinho, João A.P.Inspired by the lack of characterization of natural eutectic and deep eutectic (DES) systems, we studied the solid-liquid equilibria (SLE) of binary and ternary mixtures involving choline chloride and sugars. The densities, viscosities and solvatochromic parameters for the binary systems containing choline chloride, [Ch]Cl, were measured at the eutectic composition, and the water impact on these properties was also investigated in order to address the tailoring of their properties using water. Mixtures of sugars are shown to present an ideal behavior, while their binary mixtures with choline chloride present negative deviations to the ideality, particularly in the sugar solubility curve. Aiming to develop a predictive model to design new sugar based DES, the [Ch]Cl + sugars phase diagrams were used to tune the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) parameters, which was after applied in the estimation of the eutectic points of new ternary DES. The predictions quality was checked experimentally, proving that COSMO-RS can be a useful tool for the design of deep eutectic solvents.
- Eutectic mixtures based on polyalcohols as sustainable solvents: screening and characterizationPublication . Silva, Liliana P.; Martins, Mónia A.R.; Conceição, João H.F.; Pinho, Simão; Coutinho, João A.P.Despite some promising potential applications of eutectic systems containing choline chloride ([Ch]Cl) and a polyalcohol, a detailed investigation of the thermodynamic behavior of these systems is still missing. In this work, the solid-liquid equilibria phase diagrams of binary systems containing [Ch]Cl and one from six different polyalcohols (ethylene glycol (EG), 1,3-propanediol, glycerol (Gly), meso-erythritol, xylitol, and sorbitol) were measured in the full composition. Except for the mixtures with Gly or EG, a quasi-ideal behavior in the [Ch]Cl solubility curve is observed. In the polyalcohol solubility curve, the mixtures present small negative deviations from ideality, except for [Ch]Cl + EG, which is slightly positive. The solid-liquid phase diagrams show a large liquid composition window, and not a fixed stoichiometry for the eutectic points, where the mixtures can be used as solvents close to, or below, room temperature. Aiming at their application, viscosities and densities were measured at the eutectic point in the temperature range from 278.15 to 373.15 K. All systems present densities and viscosities higher than water, which is directly related to the strong interactions between the components. Solvatochromic parameters were measured to characterize the solvents, and they show that solvent tunability can be achieved by varying the polyalcohol mole fraction.
- 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.
- Indirect assessment of the fusion properties of choline chloride from solid-liquid equilibria dataPublication . Fernandez, Luis; Silva, Liliana P.; Martins, Mónia A.R.; Ferreira, Olga; Ortega, Juan; Pinho, Simão; Coutinho, João A.P.The temperature and enthalpy of fusion of choline chloride -[Ch]Cl- are not directly measurable since this compound decomposes upon melting. Yet, given the wide use of this compound in the preparation of deep eutectic solvents (DES), its thermophysical fusion properties are very important for a better understanding of these mixtures and the thermodynamic description of their solid-liquid phase diagrams. In this work, the fusion properties of choline chloride were estimated using the solubility curves of choline chloride in ten different ionic compounds, forming simple binary eutectic mixtures with quasi-ideal liquid phases. Experimental solid-liquid equilibria data for these systems -[Ch] Cl + ionic compounds- were measured, and the ideality of the systems assessed through the quantification of the activity coefficients and their comparison in each pair of binary solutions. The values estimated for the fusion properties of choline chloride are T fus,[Ch]Cl = 597 ± 7 K and Δ fus H [Ch]Cl = 4300 ± 600 J mol −1 . These were additionally checked by thermodynamic consistency tests and by the prediction of the solid-liquid curves with COSMO-RS model. The results obtained with both procedures allow us to guarantee the usefulness and robustness of the estimated data.
- Insights into the chloride versus bromide effecton the formation of urea quaternary ammonium eutectic solventsPublication . Martins, Mónia A.R.; Abranches, Dinis O.; Silva, Liliana P.; Pinho, Simão; Coutinho, João A.P.The intermolecular interactions of urea and quaternary ammonium salts relevant to their thermodynamic nonideality were here investigated by measuring the solid-liquid equilibria of their binary mixtures. The experimental data revealed that the anion transfer between the quaternary ammonium salt and urea increases with increasing alkyl chain lengths, leading to negative deviations from ideality in the urea-rich side for [N4,4,4,4]- based systems. However, the use of bromides instead of chlorides dampens the nonideality of urea because of larger size and lower electronegativity of the anion. The behavior of urea when mixed with ChCl or ChBr was found to be remarkably different, indicating that its nonideality in the ChCl/urea eutectic solvent is governed by urea-chloride rather than hydroxyethyl-urea interactions. The conclusions presented highlight the contribution of charge delocalization in the formation of deep eutectic solvents of type III.
- Liquefying Compounds by Forming Deep Eutectic Solvents: A Case Study for Organic Acids and AlcoholsPublication . Abranches, Dinis O.; Martins, Renato O.; Silva, Liliana P.; Martins, Mónia A.R.; Pinho, Simão; Coutinho, João A.P.The criterion to distinguish a simple eutectic mixture from a deep eutectic solvent (DES) lies in the deviations to thermodynamic ideality presented by the components in the system. In this work, the current knowledge of the molecular interactions in types III and V DES is explored to liquefy a set of three fatty acids and three fatty alcohols, here used as model compounds for carboxyl and hydroxyl containing solid compounds. This work shows that thymol, a stronger than usual hydrogen bond donor, is able to form deep eutectic solvents of type V with the fatty alcohols studied. This is particularly interesting, since these DES formed are hydrophobic. Regarding type III DES, the results suggest that the prototypical DES hydrogen bond acceptor, cholinium chloride, is unable to induce negative deviations to ideality in the model molecules studied. By substituting choline with tetramethylammonium chloride, it is shown that the choline hydroxyl group is responsible for the difficulty in forming choline-based deep eutectic solvents and that its absence induces strong negative deviations to ideality in the alkylammonium side. Finally, it is demonstrated that tetrabutylammonium chloride acts as a chloride donning agent, causing significant negative deviations to ideality in both fatty acids and alcohols and leading to the formation of deep eutectic solvents of type III.
- Liquefying flavonoids with terpenoids through deep eutectic solvent formationPublication . Teixeira, Gabriel; Abranches, Dinis O.; Silva, Liliana P.; Vilas-Boas, Sérgio M.; Pinho, Simão; Ferreira, Ana I.M.C. Lobo; Santos, Luís M.N.B.F.; Ferreira, Olga; Coutinho, João A.P.The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.
- 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.
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