Feasible separations and entrainer selection rules for heteroazeotropic batch distillation

A feasibility analysis is presented for the separation of close-boiling and azeotropic (minimum- and maximum-boiling) binary mixtures into pure components by the addition of an entrainer introducing a heterogeneous azeotrope. The analysis is done for both the conventional batch rectifier and the multivessel batch column. The analysis is theoretical and based on the assumptions of total reflux/reboil ratios and infinite number of stages. Two feasibility conditions are formulated that make it possible to investigate feasibility based on information coming solely from the distillation line map along with the binodal curve of the ternary mixture. Serafimov's classification is used for classifying the azeotropic phase diagrams. The feasibility analysis provides the necessary background and information for formulating rules for entrainer selection for the process. Two simple rules are then proposed, which make it possible to “screen” entrainers for heteroazeotropic batch distillation with minimum efforts.