Grupo Especializado en Termodinámica de los Equilibrios entre Fasesenglish versionGETEF emblema


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Año 2005

1-Alkanol + linear alkanoate mixtures have been investigated in the framework of the DISQUAC model. The interaction parameters for the OH/COO contacts are reported. The quasichemical parameters are independent of the mixture compounds. The dispersive parameters change with the molecular structure of the components. The same behaviour is observed for the OH/CO (carbonyl) and OH/OCOO ( carbonate) contacts. DISQUAC represents well the molar excess Gibbs energies, coordinates of azeotropes and molar excess enthalpies. Using binary parameters only, DISQUAC improves meaningfully predictions on this property from the UNIFAC model for 1-alkanol + linear alkanoate + hydrocarbon systems. In contrast, the Nitta - Chao and the DISQUAC models yield similar results for the thermodynamic properties of the binary and ternary mixtures considered. 1-Alkanol + linear alkanoate mixtures are characterized by strong dipolar interactions between like molecules. In 1-alkanol + CH3COO(CH2)u-1CH3 systems, dipole-dipole interactions between ester molecules are more important for u ≤ 7. For u ≥ 8, the more important contribution to the excess molar enthalpy comes from the disruption of the alkanol - alkanol interactions. For systems containing a polar compound such as alkanone, alkanoate or linear organic carbonate, dipolar interactions increase in the order: alkanone< alkanoate< carbonate.
Vapor pressures of the 1-propanol + di-n-propylamine (DPA) system at six different temperatures between 293.15 and 318.15 K were measured by a static method. The reduction of the experimental data to obtain molar excess Gibbs energies, GmE was carried out according to Barker's method, assuming that GmE is represented by a Redlich-Kister equation. In the temperature range considered, the mixture shows azeotropic behaviour and negative deviation from the Raoult's law. DISQUAC describes better than the ERAS or UNIFAC (Dortmund version) models the experimental data. The analysis of the mixture structure in terms of the so-called concentration-concentration structure factor, Scc(0) reveals that interactions between unlike molecules occur in such a way that several molecules of amine interact with one molecule of alcohol.
Vapor-liquid equilibria (VLE; P-x1 measurements) for the 1-methylpyrrolidin-2-one (NMP) + 2-propanol system at 353.15 and 373.15 K and for the NMP + 2-butanol mixture at 373.15 K are determined by an ebulliometric method. The data are reduced using Barker's method. The systems show negative deviations from Raoult's law. NMP or N,N-dialkylamide + 2-alkanol mixtures are treated in terms of the DISQUAC, UNIFAC (Dortmund version), and ERAS models. The corresponding interaction parameters for the DISQUAC and ERAS models are reported. In the framework of UNIFAC, parameters available in the literature are used. DISQUAC represents fairly well VLE and excess molar enthalpies, HE, of the binary mixtures investigated. In addition, DISQUAC correctly predicts VLE of the ternary N,N-dimethylformamide + 2-propanol + 1-butanol system using binary parameters only. UNIFAC provides very poor results for systems with NMP, probably because the database used when fitting the required interaction parameters was rather limited. ERAS calculations are carried out taking into account that the considered amides are not self-associated. The symmetry of the excess functions is, in general, poorly described by ERAS. This is attributed to the existence of strong dipole-dipole interactions in the mixtures under study.
Isothermal vapour-liquid equilibrium data, (VLE) have been measured by an ebulliometric method for four binary mixtures of N-methyl-2-pyrrolidinone (NMP) with dipropyl ether at T= 353.15 K and T= 373.15 K, or dibutyl ether at T= 373.15 K, or methyl 1, 1-dimethylethyl ether (MTBE) at T= 333.15 K, or methyl 1,1-dimethylpropyl ether (MTAE) at T= 353.15 K, in the pressure range from P = 0 kPa to P = 135 kPa.
The experimental VLE results have been correlated using a three parameter Redlich-Kister expansion. All these systems present positive deviations from Raoult's law.
Binary mixtures of NMP with dipropyl ether, dibutyl ether, MTBE and MTAE have been investigated in the framework of the Modified UNIFAC (Do) and DISQUAC models. The reported new interaction parameters for the NMP-group (N-CO) and the ether group (-O-) give much better results than known from literature predictions of the thermodynamic properties, including vapour-liquid equilibrium, excess molar Gibbs energy, molar excess enthalpies and solid-liquid equilibrium. Our experimental data and literature data for binary mixtures containing NMP and ethers were compared to the results of predictions with the Mod. UNIFAC (Do) and DISQUAC models.
Mixtures formed by linear alkanoates and CHCl3 or 1,1,2,2-tetrachloroethane, which show strongly negative deviations from the Raoult's law, have been studied in the framework of the dispersive-quasichemical (DISQUAC) model. Systems involving CH2Cl2; CCl4, Cl3C-CH3 or ClCH-CH2Cl have also been briefly considered in order to carry out a more complete study. The corresponding interaction parameters are reported. As in other previous applications, the first (Gibbs energy) and third (heat capacity) quasichemical interaction parameters do not depend on the mixture components. DISQUAC represents fairly well vapor-liquid equilibria, VLE, and molar excess enthalpies, HE, of the systems considered. VLE of the methyl ethanoate+CHCl3+benzene mixture is also well described by the model neglecting ternary interactions. UNIFAC (universal functional activity coefficient) fails when representing HE of systems containing very long alkanoates. The mixture structure is investigated using the concentration-concentration structure factor, Scc(0). Heterocoordination is prevalent even at very high temperatures.
Binary mixtures of aniline with benzene, toluene, alkane, alkanol, or N,N-dialkylamide have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regularly with the molecular structure of the mixture components. The model consistently describes a set of thermodynamic properties including liquid-liquid equilibria, vapor-liquid equilibria, and molar excess enthalpies. The two latter properties for ternary systems are well-represented by DISQUAC using binary parameters only (i.e., neglecting ternary interactions). A comparison of DISQUAC results and those obtained from the UNIFAC (Dortmund version) and ERAS models is also shown. The experimental molar excess enthalpies for binary and ternary mixtures are better described by DISQUAC than by UNIFAC. ERAS fails when representing molar excess enthalpies of those binary systems including methanol or ethanol. This may be due to the existence of strong dipolar interactions among aniline molecules as well as to effects related to the equation of state term, evaluated comparing molar excess enthalpies, and molar excess internal energies at constant volume. The study of the aniline systems in terms of the concentration-concentration structure factor also underlines the importance of dipolar interactions in solutions with alkanes or alcohols, which may be due to the high polarizability of the aniline molecule.



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