Distillation under Reduced Pressure

Lowering the Boiling Point by Lowering the Pressure

Liquids that either have a very high boiling point, or that decompose when heated to their normal boiling point, are purified by distillation under reduced pressure. Since a liquid's boiling point falls as the pressure above its surface is reduced, this technique makes the liquid boil at a temperature well below its normal boiling point simply by lowering the pressure — using a water pump or a vacuum pump — rather than by raising the temperature further. This protects heat-sensitive liquids from decomposing during distillation. A practical industrial examp …