The preferred method for solvent removal in the laboratory is by use of a rotary evaporator , also known as a “rotovap”. A rotary evaporator is essentially a reduced pressure distillation: a solution in a round bottomed flask is placed in the water bath of the apparatus, and rotated while the system is partially evacuated (by a water aspirator or vacuum pump). The reduced pressure in the apparatus causes the solvent to boil at a lower temperature than normal (see vacuum distillation), and rotating the flask increases the liquid’s surface area and thus the rate of evaporation. The solvent vapor condenses when it comes into contact with a water condenser and drips into a receiving flask . When the solvent is removed, the concentrated compound is left in the flask. One difference between distillation and rotary evaporation is that the distillate is most often retained in distillation while the residue is retained in rotary evaporation.
Advantages of rotary evaporator better than other distillation equipment
Rotary evaporator becomes more and more popular since it was invented. Because it dose have several advantages better than other distillation equipment, the contrast is as follows:
Speed -the rotary evaporator distillation is faster
The rotary evaporator is electronically controlled to rotate the flask at a constant speed, in order to increase the evaporation area at a constant speed. The evaporation flask was brought to a negative pressure by a vacuum pump. When the rotary evaporator is distilled under reduced pressure, the distillation speed is quite fast because of the large surface area of the solution.The reduced pressure distillation is much slower, and zeolite is added.
Rotary evaporator is more widely used
Rotary evaporators are generally used for the extraction and concentration of solid drugs, which can prevent the spray of chemicals, and the extraction of liquid mixture. What’s more, people also use rotary evaporator to concentrate liquid through removing water from it.
In the mean time, reduced pressure evaporator and traditional evaporator can only be used for drying of easily decomposable liquid medicines.