Vacuum distillation is a method of distillation whereby the pressure above the solution to be distilled is reduced to less than one Atmosphere (unit) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points.) Vacuum distillation is used with or without heating the solution; some distillation processes use both vacuum and thermal action.
Vacuum distillation works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure (atmospheric pressure above it or pressure in the distillation apparatus.) In standard thermal distillation, the vapor pressure is increased. In vacuum distillation, the ambient pressure is decreased.
The process is used when liquids to be distilled have high boiling points or chemically change at temperatures near their boiling points. Temperature sensitive materials such as complex caratenoids (Beta Carotene) also require vacuum distillation to remove solvents from the mixture while at the same time not damaging the product.