Breaking the Acetone-Methanol Azeotrope with Different Extraction Solvents

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Separation of a binary mixture composed of acetone (b.p. ) and methanol (b.p. ) using a distillation column is difficult because of the existence of a positive or minimum-boiling azeotrope (b.p. , composition ). For this reason, one has to use more complex distillation methods such as extractive distillation, which employs various kinds of entrainers or extraction solvents such as water or chlorobenzene.

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The Demonstration shows the VLE (vapor-liquid equilibrium) behavior of the ternary system composed of acetone, methanol, and the solvent. In particular, solvent-free acetone mole fraction in the vapor phase is plotted versus its counterpart in the liquid phase.

It is clear that for both water and chlorobenzene the binary azeotrope disappears. In addition, volatility inversion is observed for the case of chlorobenzene. The practical implication of this observation is that the heavier methanol will exit the extractive distillation column at the top, while the light acetone will exit as a bottom product mixed with the extrainer.

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Contributed by: Housam Binous and Naim Faqir (August 2012)
Open content licensed under CC BY-NC-SA


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Details

The vapor-liquid equilibrium (VLE) behavior is described by the modified Raoult’s law with activity coefficients predicted by the Wilson model [2].

References

[1] W. L. Luyben and I.-L. Chien, Design and Control of Distillation Systems for Separating Azeotropes, Hoboken, NJ: Wiley, 2010.

[2] G. M. Wilson, "Vapor-Liquid Equilibrium XI: A New Expression for the Excess Free Energy of Mixing," Journal of the American Chemical Society, 86(2), 1964 pp. 127–130. pubs.acs.org/doi/abs/10.1021/ja01056a002.



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