Distillation is the most widely used separation process for liquids separation in the industry. Even when the volatilities of the mixture are not favorable, then enhanced distillation is used. Extractive distillation is the enhanced distillation most widely used that consists in introducing a large flow rate of a third compound called extractive agent with a high boiling point that it is collected at the column bottoms and recovered in another column and reused again. Some heuristics are available for distillation column design, e.g. the optimum reflux is around 1.2 to 1.35 times the minimum reflux (or 1.1-1.2 times for refrigerated systems). Unfortunately, there is not a similar heuristic to determine the optimum extractive agent flow rate. Based on a literature review of rigorous simulations of extractive distillation processes, a heuristic is proposed that indicates that the optimum extractive distillation flow rate is which provides a Distillation Sequence Efficiency at 78 % of its maximum value. The maximum value is calculated assuming infinite flow rate of extractive agent. The Distillation Sequence Efficiency is a shortcut method available for distillation columns sequencing.
