(290b) Design of Distillation System for Separating Azeotrope: Heterogeneous Azeotropic Distillation Vs. Extractive Distillation

A common way for separating azeotrope in industry is to add a light entrainer into the system to help the separation. The advantage of this separation system is to utilize a natural liquid-liquid separation in a decanter. A two-column system can be designed for separating the azeotrope. However, in a certain heterogeneous azeotropic distillation system, large recirculation rate will occur in the distillation system resulting in high total annual cost as well as high operating cost. This unfavorable situation can easily be predicted with the aid of residual curve maps and material balance lines of the feasible design flowsheet. For this separation system, it is advisable to explore the possibility of using another separation method called extractive distillation.

In the extractive distillation system, a heavy entrainer is added into the system causing the relative volatility of the original two components (with azeotrope) to be enhanced so that one original component can go overhead of the extractive distillation column and the other component will go with the heavy entrainer to the column bottoms. Another entrainer recovery column is needed to separate the entrainer with the other component so that entrainer can be recycled back to the extractive distillation column. Since the ability of the entrainer for the enhancement of the relative volatility is crucial to the success of the separation task, a very simple procedure is developed to quickly compare alternative entrainer candidates before rigorous process simulation is conducted.

Two industrial-relevant separation systems will be used to illustrate the findings. One system is to separate isopropyl alcohol (IPA) and water and the other one is to separate propylene glycol monomethyl ether (PM) and water. For each system, the designs using heterogenous azeotropic distillation and extractive distillation will be compared.