A rotary evaporator (or rotavap/rotovap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation.

The purpose of distillation is to separate a given mixture into its components based on their respective volatilities, through the process of evaporation and condensation (liquid-gas-liquid).

The purpose of using the rotary evaporator

We use the rotary evaporator (rotovap) for two main purposes:

1.to concentrate non-volatile components in a mixture (for example, concentrating the purest and freshest flavors from a blood orange by removing the water);

2. to extract the volatile aroma and flavor molecules from mixtures gently and at low temperatures (for example, extracting the desired flavors from a blend of alcohol, herbs, and fruit without heating the mixture up).

The key to understanding any distillation is to remember that it is a separation. Sugars, acids, colors, and most bitter compounds are separated from aromas, alcohols, water, and small flavor molecules, etc. What is phenomenal about rotovap distillation, as opposed to standard distillation, is that it can separate food compounds from one another without altering them.

Two key components of the rotovap allow for a gentle, precise, and efficient distillation not found in conventional distilling apparatuses: 1) the solvent is removed under vacuum, which lowers its boiling point, eliminating the need for high-temperature distillation, and 2) the rotation of the evaporating flask, immersed in a heated water bath, increases the surface area of the product, greatly speeding distillation and also, through forced convection, keeping the mixture evenly mixed and heated to promote stable, even evaporation.

An additional benefit of laboratory-type stills is that laboratory condensers, being sealed and made of glass, are easy to visually monitor and adjust. We can, therefore, recover almost 100% of the solvent.

A rotary evaporator works by the general assumption that at each given time, the boiling point of the solvent in question is much lower than the boiling point of the liquid surrounding it. As the boiling point of liquids slowly reduces when you decrease their pressure, it allows the solvent to be vaporized at lower temperatures than their standard boiling point at normal pressure. The other assumption is that the components in the liquid are usually thermally sensitive.

The working principle of a rotary evaporator is not a complicated one; it works by first creating a vacuum space in the rotary glass flask. The vacuum system is essential in the whole process of evaporation as it accomplishes the entire process that is why it is highly recommended to use a highly improved vacuum pump if you want to enhance evaporation efficiency. The work of the condenser at the other end is to aid in converting the gas back to a liquid form that needs lower temperatures.

So as to achieve an efficient cooling effect, there’s a need to use dry ice, liquid, or water nitrogen. The evaporation vessel is set to evaporate so that to increase the surface area, the boiling liquids continuously. The centrifugal force that is created keeps the liquid in the evaporator to stick in the walls of the vessel; this exposes a larger surface area for Carter evaporation.

Temperature and pressure are linearly related to each other, so when that temperature is doubled on a Kelvin or absolute zero scales, it will force the temperature to double so long as the volume area is kept constant. Also when the presided is reduced when you turn on the vacuum, it lowers the boiling point in the process to allow the volatile solvent to evaporate. And the evaporated solvent is, in turn, captured on a cooled surface where the gas molecules condense upon.

The most common way to create a condensation area is to mix dry ice and isopropyl alcohol. You can add dry ice continuously, but it should not be cold enough to freeze the alcohol content. Along with this process, a flask is placed in a heated bath that is kept in rotation. This is aimed at creating a thin film in the flask that increases the surface area for gas molecules to evaporate. It also helps to conduct heat directly into the system to keep the temperatures constant as the molecules evaporate off.

When the vacuum is created, the gas molecules will begin to condense on the cold surface. The required conditions are such that evaporations continue simultaneously from the whole surface, including from inside the liquid. The result is bubbling, which is another reason why a rotary motor is used in evaporation.

Using a rotary evaporator is not complicated of a process, it follows the following procedure:

The setup of a rotary evaporator

1. The first step is to pour the solvent mixture and the compound you want to work on in a round bottom flask. It is advisable to fill the flask less than a half if you want to get the desired results.
2. The second step is to fill the rotary evaporator cold traps using dry ice
3. After filling the cold traps, you then have to attach a glass bump trap to prevent the solution from entering into the main part of the rotary evaporator. This is made firm by securing it with a Keck clip.
4. After attaching a Keck clip, attach the pump trap and the flask to the adaptor of your rotary evaporator.
5. The fifth step is to lower your flask into a water bath. This aims at preventing your flask from disconnecting.

The operation of a rotary evaporator

1. The first step is to start that rotation, check on the correct speed for your volume as different volumes require different speeds.
2. Start increasing the vacuum owly by slowly. A vacuum is at a proper strength when it is possible to see the condensation of the solvent in the receiving flask or when the solvent starts to bubble.
3. The next step on the operation of a rotary evaporator is to turn on the heat for your water bath. As we all know, vacuum reduces that boiling point, so this will significantly the temperature needed to evaporate your solvent.
4. Make the adjustment needed for that vacuum.
5. After the whole solvent has been removed, the next thing is to turn your vacuum off and return the flask to the normal pressure, atmospheric pressure and immediately stop the rotation.
6. Remove the flask from the water bath and the flask from the adaptor.

Something you need to pay attention when using a rotary evaporator

When using a rotary evaporator, you need to pay attention to the rotation rate, make sure you rotate the flask moderately, preferably one- third of the maximum allowable value.

A rotary evaporator is a very important apparatus that is used to carry our important tests and extraction of a substance from a solution. It is important always to remember to remove the algae gunk from the coiled water condenser so increase its life span.