This paper reports the results of a new experimental study of two-liquid phases equilibria as a function of temperature and one-liquid phase thermodynamic magnitudes (densities, refractive indices and speeds of sound), covering the composition diagrams for the mixtures acetone + methanol + n-alkane (C-9-C-12). The obtained coexistence curves were very asymmetrical with respect to equimolar alcohol + n-alkane composition, such effect increasing with the length of the aliphatic chain and temperature. A comparative analysis was performed by application of different methods to predict experimental liquid-liquid equilibria (LLE) behaviour and thermodynamics of these ternary mixtures. The obtained experimental results let us know the potential role of the linear aliphatic alkanes as separation agents for heterogeneous modified distillation of the azeotrope acetone + methanol.