Analysis of methanol extraction from aqueous solution by n-hexane: Equilibrium diagrams as a function of temperature

This paper contains the results of a new experimental study of liquid-liquid equilibrium (LLE) as a function of temperature for the ternary mixture n-hexane + methanol + water under atmospheric conditions. The computed coexistence curves were very asymmetrical with respect to n-alkane + water composition at low operation temperature. A comparative analysis was performed by application of group contribution methods to predict the experimental equilibria behaviour of this ternary mixture. The experimental tie lines data were correlated to test consistency with the Othmer-Tobias equation. The obtained results point out the strong interaction by hydrogen bonds forming the so-called iceberg clusters of hydroxylated molecules at low concentration of n-hexane, a slight influence of temperature being observed. As a result of this intense interaction, sharp separations of n-hexane + methanol mixtures by extraction are possible at low temperature and small quantities of solvent. Extraction process simulation confirms n-hexane as an adequate medium for diluted methanol concentration.