Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

Density measurements have been carried out by means of a vibrating tube densimeter for the ternary system ethanol (EtOH) + dimethylformamide (DMF) + tetrahydrofuran (THF) and for the binary mixturescontaining DMF. For the same ternary system and for the binary DMF + THF vapour-liquid equilibrium data have been collected by head-space gas-chromatographic analysis of the vapour phase directly withdrawn from an equilibration apparatus. All experiments have been conducted at 298.15 K. Molar excess Gibbs energies GE and volumes VE, as well as activity coefficients gamma_i and excess apparent molar volumes of the components, have been obtained from the measured quantities. Both binaries involving THF show positive deviations from ideality for GE, while slightly negative deviations are exhibited by EtOH + DMF. The GE's and ln (gamma_i) of the ternary system are positive almost throughout due to destruction upon mixing of H-bonding in EtOH and dipolar interactions in DMF and THF pure liquids. Feeble negative VE's are displayed by the binaries involving DMF, whereas EtOH + THF shows an S-shaped curve with very small VE values. As a consequence, the VE's and excess apparent molar volumes of the ternary system, differently from GEand ln (gamma_i),are negative nearly over the whole composition domain suggesting a more ordered structure in solution,namely that EtOH-DMF association prevails on EtOH and DMF self-association.