General Model for Studying the Feasibility of Heterogeneous Extractive Batch Distillation

By extending our former model for batch heteroazeotropic distillation, a general model is developed for the batch heterogeneous extractive distillation. An entrainer-rich and an entrainer-lean phase are present in the decanter, where the holdup of both phases can be reduced, kept constant, or increased, thanks to batch operation mode. Any fraction of both phases can be refluxed or withdrawn as distillate. The entrainer is fed continuously either onto one of the plates of the column, or into the decanter. The still path equation is derived for both cases. A discussion is given on the literature occurrence and practical applicability of the 16 possible operational policies, and the effect of continuous entrainer feeding on the still path direction of all operational policies is determined. The still path directions are validated by rigorous simulations for multiple operational policies for the mixture of ethanol, water, and n-butanol.