Distillation – An Introduction

Distillation is defined as:

a process in which a liquid or vapour mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat.

Distillation is based on the fact that the vapour of a boiling mixture will be richer in components that have lower boiling points. When this vapour is cooled and condensed, the condensate contains more volatile components, while the original mixture contains more less-volatile material.

Distillation columns are designed to achieve this separation efficiently.

Important manufacturing considerations are:

• It is the most common separation technique.
• It consumes enormous amounts of energy for cooling and heating.
• It can contribute to more than 50% of plant operating costs.

The best way to reduce operating costs of existing units is to improve their efficiency and operation through process optimisation and control. Understanding distillation principles and system design is essential.

What these notes cover

This introduction provides basic terminology used in distillation practice and introduces:

• types of columns
• basic distillation equipment and operation
• column internals
• reboilers
• distillation principles
• vapour–liquid equilibria
• distillation column design
• factors affecting column operation