A rotary evaporator, or rotavap, works by heating liquids under low pressure, vaporizing them and condensing that gas in a separate vessel, just like many other distillation apparatus. However, a rotavap uses both temperature and pressure changes in its functionality.
A rotavap’s main principle is that the boiling points of liquids reduces on decreasing their pressure, allowing solvents to be vaporized at much lower temperatures than their boiling points at normal pressure. This is accomplished by a vacuum system composed of a vacuum pump and a vacuum controller. The controller controls the vacuum pump, which in turn stabilizes the vacuum in maintaining a particular pressure, enabling only the intended solvent to evaporate. The pressure can then be lowered further and stabilized to vaporize other solvents.
A condenser at the other end converts the gas back to liquid, which requires lowered temperatures. Liquid nitrogen, dry ice or water is used in achieving the cooling effect, after which the condensed liquid is collected in a separate vessel.
The evaporation vessel constantly rotates. This tactic aims to increase the surface area of the liquids. The centrifugal force keeps the liquid sticking to the inner surface of the vessel, exposing a larger surface area and causing faster evaporation.