BULK AND SURFACE-PROPERTIES OF THE HIGHLY NONIDEAL ASSOCIATED MIXTURES FORMED BY METHANOL AND PROPANAL

Bulk (vapour-liquid equilibrium and excess enthalpy data) and surface (surface tension) properties of the highly non-ideal associated mixtur es formed by methanol and propanal have been measured. The vapour-liqu id equilibrium data have been obtained at 288.15, 298.15, 308.15 and 3 18.15 K using a Gibbs-Van Ness type apparatus. These mixtures show neg ative deviations from ideality, including a negative azeotrope in the methanol-rich region. The calculated values for the excess Gibbs energ y are very large and negative, and their absolute value decreases shar ply with increasing temperature. The calculated values for the concent ration-concentration correlation function are lower than those corresp onding to an ideal mixture and exhibit a minimum in the middle of the concentration range. The excess enthalpy data have been obtained at 4. 00 MPa and 298.15 and 318.15 K by means of a high-pressure flow calori meter. Values for the excess enthalpies are very exothermic and in agr eement with those calculated from the excess Gibbs energies. The surfa ce tension has been measured at 298.15 K. Values for the relative surf ace adsorption calculated from the surface tension and the chemical po tentials indicate that the surface is significantly enriched in propan al for mixtures rich in methanol. A complex composition dependence of the concentration profiles can be inferred. The lattice-fluid and the lattice-fluid associated solution models have been used to describe th e bulk properties of the methanol-propanal mixtures.