EXCESS-ENTHALPIES, AND VAPOR-LIQUID-EQUILIBRIUM AND SURFACE-PROPERTIES OF THE HIGHLY NONIDEAL ASSOCIATED MIXTURES FORMED BY AN ALCOHOL AND PROPANAL

Excess enthalpies, vapor-liquid equilibrium data and surface tensions of the highly non-ideal associated mixtures formed by methanol or etha nol and propanal have been measured in the temperature range of 288.15 -318.15 K. These mixtures show negative deviations from ideality, incl uding a negative azeotrope for the methanol-propanal system in the met hanol-rich region. The values for the excess enthalpies are very exoth ermic and become less negative as temperature increases. Methanol-prop anal mixtures exhibit minima of approximately -8.6 and -8.0 kJ mol(-1) , at a mole fraction close to 0.5 and 298.15 and 318.15 K, respectivel y. The ethanol-propanal system exhibits minima of approximately -7.2 a nd -5.0 kJ mol(-1) at 298.15 and 318.15 K, respectively. The surface t ension has been measured at 298.15 K. Values for the relative surface adsorption calculated from the surface tension and the chemical potent ials indicate that the surface is significantly enriched in propanal f or mixtures rich in methanol. The calculated values for the concentrat ion-concentration correlation function are lower than those correspond ing to an ideal mixture and exhibit a minimum in the middle of the con centration range. A complex composition dependence of the concentratio n profiles can be inferred. The Lattice-Fluid Associated Solution, the UNIQUAC Associated Solution and the Extended Real Associated Solution models have been used to describe the bulk properties of the alcohol- propanal mixtures.