What is a Rotary Evaporator?
A rotary evaporator is a device used in laboratories for the efficient and gentle removal of solvents from samples by evaporation. Scientists often talk about a sample being evaporated under reduced pressure – ie in a rotary evaporator.
Rotary evaporators are also used in molecular cooking for the preparation of distillates and extracts.
The main components of a rotary evaporator are:
- A motor unit that rotates the evaporation flask or vial containing the user’s sample.
- A vapour duct that is the axis for sample rotation, and is a vacuum-tight conduit for the vapour 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.
- A condenser with either a coil passing coolant, or a “cold finger” into which coolant mixtures such as 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 motorised 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 vapour 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”).
Commercial instruments are available that include the basic features, and various traps are manufactured to insert between the evaporation flask and the vapour duct. Modern equipment often adds features such as digital control of vacuum such as the KNF SC950 unit shown below, digital display of temperature and rotational speed, and vapour temperature sensing.
Users of rotary evaporators must take precautions to avoid contact with rotating parts, particularly entanglement of loose clothing, hair, or necklaces. Under these circumstances, the winding action of the rotating parts can draw the users into the apparatus resulting in breakage of glassware, burns, and chemical exposure. Extra caution must also be applied to operations with air reactive materials, especially when under vacuum. A leak can draw air into the apparatus and a violent reaction can occur. Care must also be taken to avoid implosions resulting from use of glassware that contains flaws, such as star-cracks. Explosions may occur from concentrating unstable impurities during evaporation.
What would it be like… if you could just disappear from the daily lab routine? As easily and quickly as liquid escapes from the rotary evaporator? This is the fantasy in the IKA image video above.
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