Recovery of the chloroform – methanol mixture by heterogeneous extractive batch distillation process

Abstract

A systematic study of the separation of the azeotropic mixture chloroform – methanol by heterogeneous extractive distillation process is addressed in this work by using a batch rectifying column. Water was selected as an effective heavy entrainer adding to the resulting ternary system one unstable heterogeneous ternary azeotrope and one saddle heterogeneous binary azeotrope with chloroform. Unlike to well-known heteroazeotropic distillation process, the saddle binary heteroazeotrope chloroform – water can be drawn as a top condensed vapour thanks to the feeding of water at the first tray of the column. Therefore, the splitting of two liquid phases occurs into the top decanter and the chloroform-rich phase can be drawn as distillate product. The zeotropic mixture methanol – water left in the still can be separated in a further conventional batch distillation step. First, the process performance was determined by using rigorous simulation with the batch process simulator ProSim Batch taking into the technical features of the real bench batch distillation column. Experimental validation of the computed operating conditions for the extractive distillation step (reflux ratio and entrainer flowrate) was performed in the bench rectifying distillation column. One litre of the organic waste mainly composed by chloroform and methanol was separated adding continuously 20 mol/h of water at 25°C in the column top. Two constant reflux ratios, R=1.4 and R=10, was kept in the extractive distillation step during 1h and 20 minutes, respectively. Good agreement was obtained between simulation and experimental results. More than 85% of recovery yield can be obtained of each original component with a molar purity higher than 0.99 by using the proposed heterogeneous extractive distillation processes. This novel technology can be implemented at industrial scale for treatment of this organic waste and both azeotropic components can be reused in the genuine process.