Trade-offs in Azeotropic Distillation

For a simple distillation column separating a ternary system, once the feed composition has been fixed, three-product component compositions can be specified, with at least one for each product. The remaining compositions will be determined by colinearity in the ternary diagram. For a binary distillation only two product compositions can be specified independently, one in each product. Once the mass balance has been specified, the column pressure, reflux (or reboil ratio) and feed condition must also be specified. 

By contrast with nonazeotropic systems, for azeotropic systems there is a maximum reflux ratio above which the separation deteriorates16. This is because an increase in reflux ratio results in two competing effects. Firstly, as in nonazeotropic distillation, the relative position of the operating surface relative to the equilibrium surface changes to improve the separation. This is countered by a reduction in the entrainer concentration, owing to dilution by the increased reflux, which results in a reduction in the relative volatility between the azeotropic components, leading to a poorer separation16. 

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