n-Octane with Branched Pentanol Isomers: Isobaric Binary Vapor–Liquid Equilibria Measurements and Thermodynamic Modeling with NRTL, UNIFAC, and Modified UNIFAC (Dortmund)

Abstract

This work presents newly measured low-pressure isobaric vapor–liquid equilibrium data for four binary mixtures of n-octane with a branched pentanol isomer at atmospheric pressure. The pentanol isomers considered were 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-1-butanol, and 3-methyl-2-butanol. All systems were measured by using a dynamic recirculating Gillespie-type still, and the molar composition of each phase was determined via gas chromatography. Each of the binary mixtures exhibited a temperature-minimum azeotrope, indicating strong positive deviations from Raoult’s law. Consistent with previous works on n-alkane/alcohol phase equilibrium, the composition of the azeotrope was found to shift toward the center of the compositional space with decreasing boiling point difference between the binary mixture’s constituent components. The measured binary vapor–liquid equilibrium (VLE) data were modeled with the NRTL, UNIFAC, and modified UNIFAC (Dortmund) models. The NRTL model and its newly regressed parameters provided accurate correlations of the n-octane/pentanol isomer VLE data sets. The modified UNIFAC (Dortmund) model provided robust predictions of the VLE data, but predictions with the original UNIFAC model were poor. Modified UNIFAC (Dortmund) likely outperforms UNIFAC due to its additional temperature-dependent parameters, as well as its unique hydroxyl-group (“OH”) parameters for primary, secondary, and tertiary alcohols, respectively.