Heterogeneous extractive batch distillation of chloroform–methanol–water: Feasibility and experiments

Abstract

A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform -methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike to well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform -water is obtained at the column top, condensed and further split into the liquid -liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol.

Optimisation of heterogeneous batch extractive distillation

“…Optimisation problem formulation concerns to the separation of azeotropic mixture chloroform -methanol which is widely used for separating bioactives substances from biological sources. Water was shown to be an effective heterogeneous entrainer [1]. Thermodynamic and topological features of the resulting ternary system are shown in Figure 1 including the univolatility curve chloroform -methanol ( 12 ).…”

“…Thermodynamic calculations were done by using Simulis®Thermodynamics, a thermodynamic property server available in Microsoft Excel [3]. NRTL was chosen as thermodynamic model with literature binary coefficients [1]. As explained [1], because the univolatility line  12 =1 ends at the chloroform -water edge, the saddle binary hetero-azeotrope chloroform -water can be drawn as a vapour overhead at the column if water is fed continuously at the column top generating two liquidliquid phases into the decanter after condensation.…”

“…NRTL was chosen as thermodynamic model with literature binary coefficients [1]. As explained [1], because the univolatility line  12 =1 ends at the chloroform -water edge, the saddle binary hetero-azeotrope chloroform -water can be drawn as a vapour overhead at the column if water is fed continuously at the column top generating two liquidliquid phases into the decanter after condensation. The heavy chloroform-rich phase (x II = x D ) can be drawn as distillate product whereas the water -rich phase (x I ) or a mixture composed by both decanted liquid phases can be refluxed toward the column top.…”

“…Azeotropic and extractive distillation processes are the most used processes for separating azeotropic or close boiling mixture, always involving the addition of an auxiliary entrainer. Although heterogeneous entrainer has been widely used in batch azeotropic distillation, it has only been recently considered for batch heterogeneous extractive distillation (BHED) of the chloroformmethanol mixture with water [1]. Continuous feeding of the heterogeneous entrainer allows the residue curve map saddle binary heteroazeotrope to be drawn at the top of the column.…”

Generalised model for heteroazeotropic batch distillation with variable decanter hold-up

“…The batch heteroazeotropic distillation with continuous entrainer feeding (also known as heterogeneous batch extractive distillation) was investigated by Modla et al [55,56], Rodriguez-Donis et al [57], Van Kaam et al [58] and Barreto [26].…”