Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation, 2. Low-Relative-Volatility Binary Mixtures with a Heavy Entrainer

Abstract

All former studies reported that the separation of the low relative volatility binary mixture by using a heavy entrainer in a batch rectifier imposed the obligatory withdrawal of the most volatile original component. In this paper, we demonstrate that this does not always happen and that the product sequence can be unambiguously determined from the sole analysis of thermodynamic properties of residue curve maps and the occurrence of unidistribution lines and univolatility lines, following the general feasibility criterion enounced in part I for the separation of azeotropic mixtures using heavy or light entrainers. For low relative volatility mixtures, the original component having an intermediate boiling temperature can be also drawn as the first distillate product. Cases concerning 94% of statistically occuring zeotropic ternary mixtures are investigated, allowing to define the product sequence without any previous calculation of the liquid composition profile inside the column. Preliminary feasibility results are confirmed by computing maps of extractive and rectifying liquid composition profiles using a simplified mass balance. Final validation is done via rigourous simulation using ProSim Batch software.