Isobaric Vapor−Liquid Equilibria for Binary and Ternary Mixtures of Methanol, Ethanoic Acid, and Propanoic Acid

Vapor-liquid equilibrium (VLE) data for the strongly associating ternary system methanol + ethanoic acid + propanoic acid and three constituent binary systems: methanol + ethanoic acid, methanol + propanoic acid, and ethanoic acid + propanoic acid have been determined by different liquid-phase compositions using a novel pump ebulliometer at 101.3 kPa. The vapor-phase compositions y of these binary systems had been calculated from T-p-x according to the Q function of molar excess Gibbs energy by the indirect method. The experimental T-x data are used to estimate Wilson, nonrandom two-liquid (NRTL), Margules, and van Laar model parameters, and these parameters in turn are used to calculate vapor-phase compositions y. The activity coefficients of the solution were correlated with its composition by the Wilson, NRTL, Margules, and van Laar models through the least-squares method. The VLE data of the ternary system were well-predicted from these binary interaction parameters of the Wilson, NRTL, Margules, and van Laar model parameters without any additional adjustment to build the thermodynamic model of VLE for the ternary system and obtain the vapor-phase compositions y and the calculated bubble points. The calculated bubble points with the model parameters of activity coefficients were in good agreement with the experimental data.