Browsing by Author "Carvalho, Pedro J."
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- Densities, viscosities and derived thermophysical properties of water-saturated imidazolium-based ionic liquidsPublication . Martins, Mónia A.R.; Neves, Catarina M.S.S.; Kurnia, Kiki A.; Carvalho, Pedro J.; Rocha, Marisa A.A.; Santos, Luís M.N.B.F.; Pinho, Simão; Freire, Mara G.In order to evaluate the impact of the alkyl side chain length and symmetry of the cation on the thermophysical properties of water-saturated ionic liquids (ILs), densities and viscosities as a function of temperature were measured at atmospheric pressure and in the (298.15 to 363.15) K temperature range, for systems containing two series of bis(trifluoromethylsulfonyl)imide-based compounds: the symmetric [C n C n im][NTf2] (with n = 1-8 and 10) and asymmetric [C n C1im][NTf2] (with n = 2-5, 7, 9 and 11) ILs. For water-saturated ILs, the density decreases with the increase of the alkyl side chain length while the viscosity increases with the size of the aliphatic tails. The saturation water solubility in each IL was further estimated with a reasonable agreement based on the densities of water-saturated ILs, further confirming that for the ILs investigated the volumetric mixing properties of ILs and water follow a near ideal behaviour. The water-saturated symmetric ILs generally present lower densities and viscosities than their asymmetric counterparts. From the experimental data, the isobaric thermal expansion coefficient and energy barrier were also estimated. A close correlation between the difference in the energy barrier values between the water-saturated and pure ILs and the water content in each IL was found, supporting that the decrease in the viscosity of ILs in presence of water is directly related with the decrease of the energy barrier.
- The impact of oligomeric anions on the speciation of protic ionic liquidsPublication . Martins, Mónia A.R.; Carvalho, Pedro J.; Santos, Luís M.N.B.F.; Pinho, Simão; Coutinho, João A.P.The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being straightforward, is actually challenging and must be carefully addressed. This review discusses the importance of oligomeric anions, in particular those based on carboxylates, in the behavior and nature of protic ionic liquids. There is strong evidence in the literature that the synthesis, and subsequent purification, of protic ionic liquids involving carboxylic acids, leads to structures in the liquid phase with an acid:base proportion different from the expected 1:1 stoichiometry. The formation of the oligomeric anions, mostly dependent on the proton transfer from the Brønsted acid to the Brønsted base, may lead to a higher ionicity that suggests the formation of true ionic liquids. It is here stressed the relevance of deepening the understanding of the interactions between the species and the speciation of the liquid phase, combining experimental and theoretical approaches to establish foundations for insightful advances in the area.
- Infinite dilution activity coefficients in the smectic and isotropic phases of Tetrafluoroborate-based ionic liquidsPublication . Martins, Mónia A.R.; Vilas-Boas, Sérgio M.; Cordova, Isabella Weber; Carvalho, Pedro J.; Domańska, Urszula; Ferreira, Olga; Coutinho, João A.P.; Pinho, SimãoInverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ13∞) of several organic solutes and water in the thermotropic ionic liquid crystal phases of both [C12mim][BF4] and [C14mim][BF4] and their isotropic phases. In the smectic to isotropic transition, a change in the linear representation of the natural logarithm of γ13∞ with the reciprocal temperature was observed for [C14mim][BF4], and was more evident for alkanes, alkylbenzenes, esters, and alcohols, that can be related to structural modifications of the stationary phase. Results are interpreted in terms of the enthalpic and entropic contributions of solute-IL interactions. Selectivities and capacities of important separation problems, such as octane/benzene and cyclohexane/benzene, were calculated and compared with literature values for separating agents such as N-methyl-2-pyrrolidinone, sulfolane, and ionic liquids presenting the [BF4]- anion combined with several imidazolium-based cations. It is shown that to achieve maximum separation efficiency, imidazolium cations with short alkyl chain lengths such as [C2mim][BF4] should be used, whereas high capacities require larger alkyl chain lengths.
- Selecting Critical Properties of Terpenes and Terpenoids through Group-Contribution Methods and Equations of StatePublication . Martins, Mónia A.R.; Carvalho, Pedro J.; Palma, André M.; Domańska, Urszula; Coutinho, João A.P.; Pinho, SimãoThe knowledge of critical properties is fundamental in engineering process calculations for the estimation of thermodynamic properties and phase equilibria. A literature survey shows a large number of methods for predicting critical properties of different classes of compounds, but no previous study is available to evaluate their suitability for terpenes and terpenoids. In this work, the critical properties of terpenes and terpenoids were first estimated using the group-contribution methods of Joback, Constantinou and Gani, and Wilson and Jasperson. These were then used to calculate densities and vapor pressure through the equations of state Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) and then compared with the experimental values. On other hand, density and vapor pressure experimental data were used to estimate the critical properties directly by the same equations of state (EoSs), allowing a comparison between the two estimation procedures. For this purpose densities for 17 pure terpenes and terpenoids were here measured at atmospheric pressure in the temperature range (278.15 to 368.15) K. Using the first approach, the best combination is the Joback's method with the Peng-Robinson EoS, despite the high relative deviations found for vapor pressure calculations and difficulties to predict density at low temperatures. Following the second approach, the set of critical properties and acentric factors estimated are able to adequately correlate the experimental data. Both equatio ns show a similar capability to correlate the data with SRK EoS presenting a global %ARD of 3.16 and 0.62 for vapor pressure and density, respectively; while the PR EoS presented 3.61 and 0.66, for the same properties, both giving critical properties estimates also closer to those calculated by the Joback method, which is the recommended group-contribution method for this type of compounds.
- Selection and characterization of non-ideal ionic liquids mixtures to be used in COPublication . Martins, Mónia A. R.; Sharma, Gyanendra; Pinho, Simão; Gardas, Ramesh L.; Coutinho, João A.P.; Carvalho, Pedro J.Due to the costs involved, the capture of CO2 in post-combustion is not currently seen as economically viable. Aiming at changing the perception of post-combustion CO2 from a costly and non-profitable process to a valuable commodity and fostering the development of the next-generation of technologies, novel solvents and their mixtures have been investigated. In this work, mixtures of non-volatile ionic liquids were screened by COSMO-RS aiming to find mixtures with positive excess volumes that could present an increased CO2 capture by physical sorption. The most promising mixtures identified by COSMO-RS, [C4C1im][DMP] or [C4C1im][NTf2] þ carboxylate-based protic ILs were characterized through the measurement of their thermophysical properties, namely density and viscosity. Both properties were measured for pure ILs and their binary mixtures at different temperatures and compositions. The temperature dependence of density of pure ILs was described using the Gardas and Coutinho model while viscosity was accurately described using the Vogel Tammann Fulcher equation. The Redlich-Kister equation was used to predict the excess molar volumes and the non-ideality of the mixtures’ viscosity was assessed using the Grunberg and Nissan mixing law. The excess molar volumes for mixtures containing [C4C1im][DMP] show large positive values all over the range of compositions and temperatures, making them good candidates for CO2 capture. To the best of our knowledge, the excess molar volumes obtained in this work were the highest reported so far. COSMO-RS was able to correctly predict the trend of the experimental excess molar volumes for these mixtures. Regarding viscosity, mixtures of [C4C1im] [DMP] with the carboxylate-based protic ILs led to the desired viscosity decrease compared to the pure aprotic IL, and large deviations from ideality were observed. The mixing of ILs is thus an efficient way to fine-tune the properties, in this case decreasing the viscosity while increasing the sorption capacity.
- Surface crystallization of ionic liquid crystalsPublication . Martins, Mónia A.R.; Carvalho, Pedro J.; Alves, Douglas; Dariva, Cláudio; Costa, Mariana C.; Ferreira, Rute A.S.; André, Paulo S.; Morgado, Pedro; Pinho, Simão; Filipe, Eduardo J.M.; Coutinho, João A.P.The evidence for surface crystallization in ionic liquids is scarce. The existing reports seem to be contradictory as for its driving forces, since in the two compounds investigated in the literature, the contribution of coloumbic and van der Waals forces is very different. In this work 1-dodecyl-3- methylimidazolium tetrafluoroborate was studied and its surface crystallization characterized by surface tension, ellipsometry and optical microscopy. The results obtained seem to reconcile previous observations, and it was further shown, using the same techniques, that this phenomenon is prevalent in other ionic liquids. MD simulation results illustrate the different possibilities of organization, providing reasonable models to rationalize the experimental observations.