Mixtures of acetone, butanol, and ethanol (ABE) are common intermediate products in the production of biofuels via biomass fermentation. Their separation to yield, for example, bio-butanol, is still difficult due to the lack of a fundamental understanding of these mixtures at the molecular level. In order to bridge this gap, a detailed analysis of characteristic features of the vibrational spectrum is carried out. A systematic study of the binary solutions of acetone with ethanol and butanol does not only reveal a universal behaviour at the molecular level when acetone is mixed with short-chain alcohols, it also shows that the phenomena at a length scale between the molecules and in the macroscopic solution need to be taken into account to understand the structure-property relationships. The size of self-associated molecule clusters seems to determine whether or not a system exhibits an azeotrope. When a second alcohol is added to an acetone/alcohol solution, no additional non-idealities are induced, which is advantageous for modelling ternary ABE mixtures and for improving their processing in the production of biofuels.
Keywords: azeotropes; binary solutions; excess spectroscopy; infrared spectroscopy; molecular interactions.
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