Isobaric vapour-liquid equilibrium for systems of propionic acid, butanoic acid and 1,4-butyrolactone at 15.0 kPa

Isobaric vapour-liquid equilibrium (VLE) data for binary systems containing propionic acid (PA) + 1,4-butyrolactone (GBL), butyric acid (BA) + GBL, and PA + BA at 15.0 kPa were measured by using a modified Othmer still. VLE data show that these binary systems are all positive deviation solutions unlike the ideal system. The Herington area test was conducted to confirm the thermodynamic consistency of these binary systems, and positive results were obtained. The interaction energy (E-inter) between these components was calculated by molecular simulation to explain the VLE behaviors. Simulation results showed that strongly interacting dihydrogen bonds can form between these acids, which indicated that stable dimer should be present in the vapour phase. In addition, the associating behavior in vapour was corrected using chemical theory, and the activity coefficients of liquid were correlated by the Wilson, the NRTL, and the UNIQUAC models. The correlated results agree well with the experimental values.