Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 3. Azeotropic Mixtures with Light Entrainer.

Abstract

This article shows how knowledge of the location of univolatility lines and residue curve analysis helps in assessing the feasibility of extractive distillation of minimum-boiling (minT) or maximum-boiling (maxT) azeotropic mixtures or low-relative-volatility (low-α) mixtures (A–B) by using a light-boiling entrainer (E), in accordance with the general feasibility criterion of Rodriguez-Donis et al. [Ind. Eng. Chem. Res. 2009, 48 (7), 3544−3559]. Considering all possible locations of the univolatility line αAB, three minT azeotropic mixtures with a light entrainer (1.0–2 class), namely, ethanol–water with methanol, ethanol–toluene with acetone, and methyl ethyl ketone–benzene with acetone; three maxT azeotropic mixtures with a light entrainer (1.0–1a class), namely, water–ethylenediamine with methanol, acetone–chloroform with dichlomethane, and propanoic acid–dimethyl formamide with methyl isobutyl ketone; and one low-α mixture with a light entrainer (0.0–1 class), namely, ethyl acetate–benzene with acetone, were studied in a stripping extractive column. For the 1.0–2 class, both A and B can be recovered as the bottom product, depending on the location of αAB = 1, which sets limiting values for the entrainer feed flow rate FE/LT for one of the product. In addition, the feasible region of the extractive distillation process is larger than for the azeotropic distillation process. For the 1.0–1a class, the product is either A or B, depending on the location of αAB = 1, which sets a minimum value of (FE/LT)min for one of the product. For the 0.0–1 class, feasibility depends on the existence αAB = 1. When it does not exist, B is the unique possible product. When it does, both A and B are products, with B below a maximum value of (FE/LT)max,B and A above a minimum value (FE/LT)min,A.