THERMODYNAMICS OF METHANOL + FREON 113 - EXPERIMENTAL-DATA AND APPLICATION OF ASSOCIATION MODELS

Vapour-liquid equilibrium at 308.15 K, heats of mixing, heat capacities and densities at 298.15 K have been measured for methanol + 1,1,2-trichlorotrifluoroethane (Freon 113). In addition to the clearly dominant role of alcohol self-association, there are also indications of a weak specific interaction between methanol and Freon molecules. Three simple models of athermal association, which exclude lower multimers, have been used to predict gE, hE, cEP and the apparent heat capacity of methanol, φc,1: (1) Mecke-Kempter and (2) Kretschmer-Wiebe type models of continuous association of the alcohol starting with the tetramerization, and (3) a model considering only the tetramerization. The models perform reasonably well for methanol + Freon 113 and methanol + n-hexane mixtures. However, it appears that the continuous association models systematically overestimate the chemical part of hE, whereas the tetramerization-only model underestimates the chemical part of gE. When the models are extended to include complex formation between methanol and Freon, some of the experimental indications of the non-inert behaviour of Freon 113 can be predicted. The importance of the physical contribution to the excess functions is discussed and the magnitude of gE(phys) is estimated independently of the association models used. If amended by the physical contribution, both continuous association models yield an excellent prediction of gE. © 1990.