A rotary evaporator (or rotavap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the use of this technique and equipment may include the phrase "rotary evaporator", though use is often rather signaled by other language (e.g., "the sample was evaporated under reduced pressure").
A simple rotary evaporator system was invented by Lyman C. Craig. It was first commercialized by the Swiss company Büchi in 1957, and patented in 1964. The Büchi Rotavapor continues to be the most widely used rotary evaporator, so much so that "Rotavap" has become a synonym for such instruments. Other rotary evaporator manufacturers include Heidolph, Yamato, IKA, Stuart, EYELA and INGOS. The most common form is the bench-top unit, though large scale (e.g., 20L-50L) versions are available and are used in pilot plants in commercial chemical operations.
Design of Rotary Evaporator
The main components of a modern rotary evaporator are:
a motor unit which rotates the evaporation flask or vial containing one's sample.
a vapor duct which acts both as the axis for sample rotation, and as vacuum-tight conduit for the vapor being drawn off of the sample.
a vacuum system, to substantially reduce the pressure within the evaporator system.
a heated fluid bath, generally water, to heat the sample being evaporated.
a condenser with either a coil through which coolant passes, or a "cold finger" into which coolant mixtures like dry ice and acetone are placed.
a condensate-collecting flask at the bottom of the condenser, to catch the distilling solvent after it re-condenses.
a mechanical or motorized mechanism to quickly lift the evaporation flask from the heating bath.
The vacuum system used with rotary evaporators can be as simple as a water aspirator with a trap immersed in a cold bath (for non-toxic solvents), or as complex as a regulated mechanical vacuum pump with refrigerated trap. Glassware used in the vapor stream and condenser can be simple or complex, depending upon the goals of the evaporation, and any propensities the dissolved compounds might give to the mixture (e.g., to foam or "bump", see below). Various commercial instruments are available that include the basic features, and various designs of traps are manufactured to insert between the evaporation flask and the vapor duct. In addition, modern equipment often adds features such as digital control of vacuum, digital display of temperature and rotational speed, and even vapor temperature sensing.