Grupo Especializado en Termodinámica de los Equilibrios entre Fasesenglish versionGETEF emblema


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Año 2006

Binary mixtures containing pyridine (PY), or 2-methylpyridine (2MPY) or 3-methylpyridine (3MPY) or 4-methylpyridine (4MPY) and an organic solvent as benzene, toluene, alkane, or 1-alkanol are investigated in the framework of DISQUAC. The corresponding interaction parameters are reported. The model describes accurately a whole set of thermodynamic properties: vapor-liquid equilibria (VLE), liquid-liquid equilibria (LLE), solid-liquid equilibria (SLE), molar excess Gibbs energies, GE, molar excess enthalpies, HE, molar excess heat capacities at constant pressure, CPE, and the concentration-concentration structure factor, Scc(0). It is remarkable that DISQUAC correctly predicts the W-shaped curve of the CPE of the pyridine + n-hexadecane system. The model can be applied successfully to mixtures with strong positive or negative deviations from the Raoult's law. DISQUAC improves the theoretical results from UNIFAC (Dortmund version). The replacement of pyridine by a methylpyridine leads to a weakening of the amine-amine interactions, ascribed to the steric effect caused by the methyl group attached to the aromatic ring. This explains that for a given solvent (alkane, 1-alkanol) HE(pyridine) > HE(methylpyridine).
The coexistence curves of the liquid-liquid equilibria (LLE) for systems of dimethylformamide (DMF) with hexane, heptane, octane, or nonane and of dimethylacetamide (DMA) with heptane have been determined visually. All the curves show an upper critical solution temperature (UCST) and have a rather horizontal top. The measured LLE curves for DMF mixtures show that their symmetry depends on the size of the alkane. For a given alkane, the UCST is higher for systems with DMF. This reveals that dipole-dipole interactions between amide molecules are stronger in such solutions. The DISQUAC model represents fairly well the LLE curves.



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