Isobaric Vapor−Liquid Equilibria for the Systems Propionic Acid + Butyric Acid, Isobutyric Acid + Butyric Acid, Butyric Acid + Isovaleric Acid, and Butyric Acid + Hexanoic Acid at 14 kPa

Isobaric vapor-liquid equilibria were measured at 14 kPa for the binary systems propionic acid + butyric acid, isobutyric acid + butyric acid, butyric acid + isovaleric acid, and butyric acid + hexanoic acid. The experimental data were modeled using the γ-φ approach as discussed by Raal and Muhlbauer. The proposed model uses the NRTL equation for correlation of the liquid-phase activity coefficient. The vapor-phase fugacity coefficient was calculated by the chemical theory, which treats binary mixtures containing associating species. The data were deemed thermodynamically consistent using a test proposed by Van Ness.