Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation, 1. Azeotropic Mixtures with a Heavy Entrainer

Abstract

Feasibility assessment of batch homogeneous extractive distillation for the separation of an A−B mixture feeding entrainer E traditionally relies on the systematic computation of rectifying and extractive composition profile maps under various reflux ratio and entrainer flow-rate conditions. This is a well-settled methodology for determining the product sequence and the corresponding column configuration. However, we show that all related literature examples can be simply explained using the thermodynamic insights of residue curve maps, in particular, the unidistribution and univolatility curves. A general feasibility criterion at infinite reflux is proposed and finite reflux operation is also discussed. Illustration is provided for the most common cases, namely, the separation with a heavy entrainer of minimum boiling (class 1.0-1a) and maximum boiling azeotropes (class 1.0-2). New cases that have not been published yet are presented, and operating conditions are also discussed. These results demonstrate the obligatory incorporation of the univolatility lines for explaining the unexpected behavior of some particular ternary mixtures to be separated by the homogeneous extractive distillation process.