Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

Excess molar enthalpies, HE m, at 298.15K and atmospheric pressure, have been measured, over the entire mole fraction range, by means of a Tian Calvet microcalorimeter, for the systems: dipropylamine (DPA), or dibutylamine (DBA) + 2-propanone, + 2-butanone, + 2-pentanone, or + 2-heptanone. These data, together with those available in the literature for aniline or N-methylaniline + 2-alkanone systems, or for 2-alkanone, or amine + heptane mixtures have been used to determine HN CO, the enthalpy of the amine ketone interactions. For solutions with a given aromatic amine, HN CO values are large and decrease with the increasing of the ketone size. The corresponding HE m values are large and negative. Mixtures with DPA or DBA are characterized by much weaker interactions between unlike molecules and HN CO is nearly independent of the ketone. The HE m values are positive and decrease when the chain length of the 2-alkanone is increased, which has been ascribed to a decreasing positive contribution to HE m from the disruption of the ketone ketone interactions upon mixing. Excess molar internal energies at constant volume, UE Vm, have been obtained from HE m data using our previous volumetric measurements for the studied mixtures. Similar trends that for HE m are observed. Differences between UE Vm and HE m are about 15% for DPA or DBA solutions and are ranged between 35% and 45% for mixtures with aromatic amines. The excess molar volume, VE m, changes in line with HE m and both magnitudes are usually of the same sign, which reveals that the main contribution to the former is the interactional one. In systems including linear secondary amines, structural effects increase with the chain length of the ketone. Amine + 2-alkanone systems have been also investigated in terms of the DISQUAC, UNIFAC and ERAS models. DISQUAC and ERAS interaction parameters are reported. As in other many applications, the quasichemical interchange coefficients for l = 1 (Gibbs energy), 3 (heat capacity) remain constant along each homologous series considered. DISQUAC improves meaningfully ERAS results on HE m, while UNIFAC results are slightly better. This suggests that physical interactions are more relevant than those related to association/solvation effects. (C) 201