Homogeneous azeotropic distillation: Comparing entrainers

TLDR

The study aims to determine the optimal entrainer and feasible separation sequence for separating a binary azeotrope into pure components. This is achieved by analyzing heavy, intermediate, and light entrainer effects using equivolatility, isovolatility, and local volatility order diagrams to design separation flowsheets. The analysis shows that a good entrainer readily breaks the azeotrope, produces high relative volatilities, and can be identified and compared via equivolatility diagrams, with the method validated and its limits illustrated by examples.

Abstract

Abstract In this article, we present practical solutions (in the case of entrainers which add no azeotropes) to two problems of industrial relevance: Given a binary azeotrope which we want to separate into pure components, and a set of candidate entrainers, how do we determine which one is the best? Also, for each of these entrainers, what is the flowsheet of the feasible separation sequence(s)? We obtain these solutions by analyzing in details the mechanisms by which heavy, intermediate and light entrainers make separation feasible, using the new notions of equivolatility curves, of isovolatility curves and of local volatility order. We show that the second question finds an easy solution from the volatility order diagram. This analysis shows that a good entrainer is a component which “breaks” the azeotrope easily (i.e., even when its concentration is small) and yields high relative volatilities between the two azeotropic constituents. Because these attributes can be easily identified in an entrainer from the equivolatility curve diagram of the ternary mixture azeotropic component #1 — azeotropic component #2 — entrainer, we can easily compare entrainers by examining the corresponding equivolatility curve diagrams. Finally, we demonstrate the validity and limits of this method with examples.