The process of distillation is one of the most important separation techniques practiced worldwide and is used in petroleum refining, liquid gas production, desalinization of sea water for drinking, and in other industrial and research processes. Distillation is a practical application of a rather simple principle of physical chemistry. When a liquid is heated, its molecules begin to escape from its surface. If enough heat is applied, the liquid boils away. If the vapor which escapes from a boiling vessel is collected and then cooled or condensed so that it becomes a liquid, the process is known as distillation.

Around 350 b.c., the Greek philosopher Aristotle described a method of evaporating sea water to collect drinking water. Both Romans and Egyptians in Alexandria distilled oil of turpentine from pine resin. These early procedures used air-cooled outlets from the boiling vessel to condense the liquid product. Most likely the...