Vapor–Liquid Equilibrium Data for 1-Methyl-2-Pyrrolidone + (1-Butanol or 1-Hexene or Water) Binary Mixtures

The unusual properties of 1-methyl-2-pyrrolidone or N-methyl-2-pyrrolidone (NMP) make it a solvent of interest in industrial extractive distillation processes. To augment available data, vapor–liquid equilibrium (VLE) measurements were made for NMP + 1-hexene at (313.15, 335.15, and 363.15) K, for NMP + water at (343.15, 363.15, and 380.15) K, and for NMP + 1-butanol at (10, 25, and 50) kPa using a dynamic recirculating apparatus. Limiting activity coefficients are reported for water and n-hexene as solutes in NMP. Activity coefficient minima were found for 1-butanol as solvent in NMP in the very dilute regions at (10 and 25) kPa. All systems were modeled satisfactorily with the nonrandom two-liquid (NRTL) equation for the Gibbs excess energy with a variable alpha parameter. Thermodynamic consistency testing of the isothermal data with the Van Ness (Van Ness, H. C. Pure Appl. Chem. 1995, 67, 859–872) direct test is discussed.