Distillation, Azeotropic, and Extractive

Abstract

Many industrial processes depend on efficient methods for separating azeotropic, close‐boiling, or other low relative volatility mixtures. Ordinary distillation is typically either uneconomical or impossible in these cases. However, by adding specially chosen separating agents, the separation can generally be accomplished. The principal distillation‐based techniques employed for separating such mixtures are discussed: extractive or homogeneous azeotropic distillation, where a completely miscible liquid separating agent is added to alter the relative volatilities; heterogeneous azeotropic distillation, where the agent, known as the entrainer, forms one or more azeotropes and causes immiscibility; distillation in the presence of ionic salts that alter the relative volatilities of the components; and pressure‐swing distillation, wherein some azeotropes can be circumvented using a series of columns operating at different pressures. Residue curve maps, material balance lines, and column sequences are given for several example systems. Methods for identifying feasible separating agents are also discussed.

Process Designs for Separating R-410A, R-404A, and R-407C Using Extractive Distillation and Ionic Liquid Entrainers

“…Extractive distillation is the most widely used technology for the separation of homogeneous azeotropic mixtures or solvents with similar boiling points . Extractive distillation separations include organic/water, olefin/paraffin (alkene/alkane), aliphatic/aromatic hydrocarbons, and aromatic/aromatic hydrocarbons . Extractive distillation uses an additional solvent, an entrainer, to alter the liquid phase properties and modify the volatility of each component, resulting in a more efficient separation.…”

COSMO-RS-Based Ionic-Liquid Selection for Extractive Distillation Processes

“…Extractive distillation (ED) is a widely used technology in the chemical industry for separating azeotropic, close-boiling, and low-relative-volatility mixtures . In this technology, a solvent is used in order to interact with the components and increase their relative volatilities by modifying their activity coefficients.…”

Extension of Thermodynamic Insights on Batch Extractive Distillation to Continuous Operation. 1. Azeotropic Mixtures with a Heavy Entrainer

“…The search for limiting values of the reflux ratio and entrainer flow rate has been more systematized by the use of an algebraic criterion or of mathematical approaches such as bifurcation theory, interval arithmetics, or the combined bifurcation–shortcut rectification body method …”