Isobaric Vapor–Liquid Equilibrium for Binary Systems of <i>n</i>‑Butyric Acid with Water, Isopropyl Acetate, <i>n</i>‑Propyl Acetate, and <i>n</i>‑Methylpyrrolidone

Isobaric vapor–liquid equilibrium (VLE) data for the four binary systems of n-butyric acid with water, isopropyl acetate, n-propyl acetate, and n-methylpyrrolidone were measured experimentally by a modified Rose still at the local atmospheric pressure of 99.8 kPa. All of the experimental VLE data for the four binary systems passed the Van Ness thermodynamic consistency test. Two activity coefficient models, namely, the NRTL and Wilson models, were selected to correlate the VLE data, and the binary interaction parameters were regressed with the two models. The result indicates that a homogeneous azeotropic behavior can be found for the two binary systems of water + n-butyric acid and n-butyric acid + n-methylpyrrolidone, and the obtained VLE data correlate well with the two models. There is no binary azeotropic behavior between n-butyric acid and isopropyl acetate/n-propyl acetate, indicating that isopropyl acetate and n-propyl acetate can be used as extractants and azeotropic agents for the extraction–azeotropic distillation separation of n-butyric acid and water