Extractive Distillation: A Review

Abstract

Extractive distillation is more and more commonly applied in industry, and becomes an important separation method in chemical engineering. This paper provides an in‐depth review for extractive distillation. Separation sequence of the columns, combination with other separation processes, tray configuration and operation policy are included in process of extractive distillation. Since the solvent plays an important role in the design of extractive distillation, such conventional and novel separating agents as solid salt, liquid solvent, the combination of liquid solvent and solid salt, and ionic liquid are concerned. The prominent characteristics of extractive distillation is that one new solvent with high boiling‐point, i.e. separating agent, is added to the components to be separated, so as to increase their relative volatility. Selection of a suitable solvent is fundamental to ensure an effective and economical design. CAMD as a useful tool is applied for screening the solvents and thus reducing the experimental work. Theories from molecular thermodynamics, which can interpret the microscale mechanism of selecting the solvents, are also collected. To accurately describe the extractive distillation process, mathematical model is necessary. There are two types of mathematical models to simulate extractive distillation process, i.e. equilibrium (EQ) stage model and non‐equilibrium (NEQ) stage model. The EQ stage model as an old method is widely used, but the NEQ stage model should be pay more attention. In the end comparison of extractive distillation and adsorption distillation, both of which belong to special distillation suitable for separating close boiling point or azeotropic components, is done, and it is shown that extractive distillation is more advantageous.