Extractive and Azeotropic Distillation

Although nonidealities in vapor and liquid phases complicate the separation of components from mixtures, a knowledge of these nonidealities can be applied to design an extractive distillation step. Ethylene glycol is added to an aqueous ethanol mixture to produce the overhead separation of ethanol from water. Methods published earlier by one of the authors are applied to calculate phase equilibria in a computer calculation of the separation. The extractive distillation results are tabulated, represented graphically, and discussed to illustrate extractive distillation as a method for dehydrating aqueous ethanol mixtures. The results are compared with corresponding results obtained by azeotropic distillation with n-pentane as entrainer. They show extractive distillation with ethylene glycol is more expensive than azeotropic distillation with n-pentane.