Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 4. Azeotropic Mixtures with Intermediate Boiling Entrainer

Abstract

This paper shows how knowledge of the univolatility and unidistribution lines location and residue curve analysis help assessing the feasibility of batch extractive rectifying or stripping distillation of azeotropic mixtures by using an intermediate boiling entrainer. We consider five minimum boiling (minT) azeotropic mixtures AB with entrainer E, namely acetone – heptane with benzene; methanol – toluene with triethylamine; methyl acetate – cyclohexane with carbon tetrachloride; dichloromethane – ethanol with acetone, and ethyl acetate – heptane with benzene (E); and one maximum boiling (maxT) azeotropic mixture, namely chloroform – ethyl acetate with either 2-chlorobutane, isobutylchloride, bromopropane or bromocloromethane. All ternary diagrams A-B-E belong to the 1.0-1b class, for which all three possible univolatility AB, BE and AE and unidistribution lines KA, KB and KE can exist. Applying the general feasibility criterion of Rodriguez-Donis et al. (Ind. Eng. Chem. Res., 48(7), 3544–3559, 2009), both azeotropic components (A) or (B) accomplish the criterion and they can be recovered, (A) in an extractive rectifier and (B) in an extractive stripper. The process efficiency of each alternative depends strongly on the location of the AB univolatility line interception with the triangle edge, and also depends on the BE (resp. AE) in the minT (resp. maxT) case and of the unidistribution line KE closeness to the (E-B) (resp. A-E) edge. Besides, choice of the rectification of (A) instead of the stripping of (B) is set by the ratio of AE/BE, the ratio of relative volatility variation of the binary mixtures between (A) or (B) with (E).