Binary distillation partially miscible liquids

Figure 13.11 Temperature-composition phase diagrams of binary systems with partially-miscible liquids exhibiting (a) the ability to be separated into pure components by fractional distillation, (b) a minimum-boiling azeotrope, and (c) boiling at a lower temperature than the boiling point of either pure component. Only the one-phase areas are labeled two-phase areas are hatched in the direction of the tie lines.

Mass transport in distillation and fractionation towers can sometimes be adversely affected by the generation of unwelcome, but transient, foam, which is a product of the intrinsic properties of the relevant liquids rather than any inadvertent contaminant. Ross and coworkers have drawn attention to the role played by partial miscibility of those liquids in determining that foam behavior (see, e.g., references [134-137]). Their studies concerned both binary and ternary mixtures of low molecular weight molecules, most of which were non-aqueous. Unlike the aqueous eth-oxylated and propoxylated non-ionic surfactant and polymer systems considered in Section 4.6.3.2, these binary systems often exhibit higher critical temperatures so that miscibility occurs with increasing temperature. 

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