How does a Rotary Evaporator work?
Rotary evaporators (rotavaps) employ the fact that the boiling points of liquids reduce with decreasing 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.
How does Soxhlet Extraction work?
A Soxhlet (“socks–let”) extractor works by boiling a solution that has a solute of limited solubility in a percolator, then cooling and collecting the condensate in a reservoir from which the concentrated solute can be extracted. A siphon connecting the percolator to the reservoir flushes excess solvent back into the reservoir. Thus, a small amount of solvent is recycled in order to dissolve a larger amount of material. This closed system can be left to run continuously for many hours without the need for constant monitoring.
How does Steam Distillation work?
Most essential oils are obtained from the plant material by a process known as steam distillation. The fundamental nature of steam distillation is that it enables a compound or mixture of compounds to be distilled (and subsequently recovered) at a temperature substantially below that of the boiling point(s) of the individual constituent(s). Essential oils contain substances with boiling points up to 200C or higher, including some that are solids at normal temperatures. In the presence of steam or boiling water, however, these substances are volatilized at a temperature close to 100C at atmospheric pressure. The mixture of hot vapors will, if allowed to pass through a cooling system, condense to form a liquid in which the oil and water comprise two distinct layers. Most (but not all) essential oils are lighter than water and form the top layer.
Generating steam in a chamber separate from the plant material produces higher quality oils compared to boiling water mixed directly with the plant matter.