Evaporators and evaporation systems are a key part of the sample prep process in many laboratories and industries. In particular, rotary evaporators have been crucial in materials, forensics, life science, environmental, and chemical industries for decades. In industry, evaporators are employed to improve the storage life of a product or to reduce its volume, as well as to remove water before drying. Rotary evaporators are made up of a vacuum source, collection flask, condenser, rotating flask, and a temperature bath. Dry evaporators, on the other hand, use a dry heat block instead of a bath to evaporate samples quickly under a gentle stream of nitrogen. Concentrators, as their name suggests, are used to concentrate samples and are particularly important in the water treatment and food and beverage industries.
What is a Rotary Evaporator?
A rotary evaporator is an indispensable equipment for the processes of evaporation, concentration, crystallization, drying, separation, and solvent recovery in many fields, and it is mainly used for continuous distillation of large amounts of volatile solvents under reduced pressure. It can be said that a rotary evaporator has a great number of applications. Not only can it be used in the small and pilot experiments, but it can be applied in the production in the biological, pharmaceutical, chemical and even food-making industries.
Working Principle of a Rotary Evaporator
A rotavap evaporates solvents from samples by utilizing the principle that the solvent will have a lower boiling point at a reduced pressure. Specifically speaking, the stepless speed regulation is adopted to make the evaporation flask rotate at a constant speed. By the rotation, materials can form a large area of uniform thin film on the inner wall of the flask. The evaporation flask is heated evenly by a water or oil bath, and materials, with a lower boiling point, is evaporated rapidly under the vacuum condition. The solvent steam is recycled in the receiving flask after being cooled by the high efficiency glass condenser.
The main components of a rotary evaporator?
- A motor unit that rotates the evaporation flask or vial containing the user’s sample.
- A vapor duct that is the axis for sample rotation, and is a vacuum-tight conduit for the vapor being drawn off 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 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”).
How does a Rotary Evaporator work?
Rotary evaporation is the process of reducing the volume of a solvent by distributing it as a thin film across the interior of a vessel at elevated temperature and reduced pressure. This promotes the rapid removal of excess solvent from less volatile samples. Most rotary evaporators have four major components: heat bath, rotor, condenser, and solvent trap. Additionally an aspirator or vacuum pump needs to be attached, as well as a bump trap and round bottom flask containing the sample to be concentrated.
Flask, Bump Trap, and Bath Temperature
Selecting a flask that accommodates approximately twice the starting volume. If proper caution is exercised, the volume of the bump trap is irrelevant, but one should always be used as it prevents you from having to recover your sample from the condenser and solvent trap if bumping occurs. A low-vac pump or sink aspirator and temperatures between 25 and 50°C suffice for most common lab solvents. Lower temperatures make for a slower process but reduce the likelihood of bumping. Use common sense when selecting a temperature unless you lack common sense or are crippled with self doubt. In such a case a manometer and distillation nomograph can be utilized.
How to Commence a Rotary Evaporation
- Let the heat bath get hot and the condenser get cold. The inverse situation often yields suboptimal results. Empty the solvent trap given that the previous user almost certainly did not. Take care when the trap is filled with unknown solvent as almost invariably the previous user left it brimming with pyridine or trifluoroacetic acid.
- Secure the bump trap and sample flask using clamps. Alternatively, see the page on how to extract 5 mg of advanced intermediate from several liters of algae-infested hard water.
- Activate the rotor. It should spin fast enough to create an even coating on the inner surface of the flask. Use this time to study the effects of coriolis force.
- Activate the vacuum pump. Close the stopcock on the condenser to the point where you can no longer hear it whistling, but that there is an audible “pop” if you cover and release it with your thumb. Allow the sample to spin under vacuum for approximately a minute. Very likely it will soon begin to boil. Don’t panic. Boiling is not the same as bumping. As long as the bubbles do not reach the neck of the flask it may be allowed to boil. If the bubbles do reach the neck you have allowed it to bump: congratulations. If the bubbles seem to be in danger of reaching the neck, repressurize the system by fully opening the stopcock to cease boiling. Repeat until boiling has ceased and solvent is steadily streaming from the condenser; only then do you fully close the stopcock. When condensation begins to form on the exterior surface of the flask, lower it into the heat bath approximately half way.
- Continue to monitor the situation for another minute or two. If there is danger of bumping, open the stopcock. Once again, repeat until boiling has ceased and solvent is steadily streaming from the condenser. At this point it is safe to leave the rotary evaporator unattended.
- Occasionally check to ensure nothing has gone heinously wrong.
How to Halt a Rotary Evaporation
- Remove the flask from the heat bath.
- Open the stopcock.
- Halt the rotor.
- Turn off the vacuum/aspirator.
- Disconnect the flask.
- Drop flask in heat bath.
- Hope that you serendipitously extract the cure for cancer from the crud in your heat bath.
Omission of any of these steps may result in an undesired outcome, e.g: filling the rotary evaporator with tap water when turning off the aspirator before opening the stop cock, bulk transport of your sample into the deepest recesses of the rotary evaporator when disconnecting the flask before opening the stopcock, and broken glassware as well as lacerations and the derision of fellow lab members when attempting to remove the flask before halting the rotor.
If at any point in this process bumping occurs, remove the flask and bump trap as a unit and rinse the interior with several mL of solvent. If your trap has drain holes the sample will flow back into the flask. Depending on the configuration of you trap, if it lacks drain holes you may have a Gordian monstrosity on your hands.
When you have finished your rotary evaporation do not empty the solvent trap, that is for suckers. So is washing and drying the bump trap.
Applications of a Rotary Evaporator
As an essential separation equipment, a rotary evaporator can remove a volatile solvent from a liquid mixture through evaporation and condensation.
In industrial field, people use rotary evaporators to extract cbd, which is the main component of mariguana. And cbd is usually used to be made into medicine in pharmaceutical field.
In people’s daily life, rotary evaporators are used at home for extracting water from all kinds of juices, which makes juices have a better taste.
In chemical and biochemical labs, rotary evaporators are used by professors to extract chemical substances, which will be further applied for other chemical purposes.
In recent years, the application of rotary evaporator has been extended to the cooking industry. Molecular cooking is a science that applies the principles of chemistry and physics to cooking. To some extent, molecular cooking has been promoted to be a proper term for describing innovative cooking styles. It is synonymous with cutting-edge technology and even psychology. The use of a rotary evaporator to non-heat evaporate liquid, thus retaining volatile aromatics that are easily lost by heating, is a perfect combination of modern culinary and experimental instruments.
Because of so many applications, a rotary evaporator has been quite well-received these days.
How to Clean Your Rotary Evaporator?
A rotary evaporator is a complex piece of equipment with multiple components. As such, it’s definitely not the simplest item in the lab to clean. However, it’s important to clean your rotary evaporator properly. Leaving residue in its components could pose safety risks or affect the outcome of subsequent applications.
There are two main ways to clean your rotary evaporator glassware, both of which we’ll discuss further below, including their pros and cons:
- The “quick and dirty” method: This involves a quick flush with acetone or another solvent.
- Thorough cleaning of glassware: In this case, you need to dismantle the apparatus before cleaning.
In either case, you should aim to clean the rotovap soon after you finish using it. This avoids residue drying onto the glassware and making it more difficult to clean.
The “Quick and Dirty” Method
You may have heard about a fast and simple method to clean your rotary evaporator glassware using a quick flush with acetone. The video below illustrates how this is done, but here are the general steps:
- Fill a small to medium-sized two-neck round-bottom flask about halfway with acetone. (A three-neck flask with a stopper in one socket will work too.)
- Connect one socket to the rotovap (where the evaporation flask would usually go). You can secure it in place or hold it with one hand. Note, the flask should not be set to spin during this process.
- Use your thumb to close the second socket of the two-neck flask.
- Set the vacuum pump to around 250 mbar and switch it on. You should start to see the acetone boil as a result of the reduced pressure.
- Quickly remove your thumb from the socket and you’ll see acetone shoot through the rotovap.
- Close the socket with your thumb again and repeat the flush if needed.
The obvious advantage to this method is that it’s very fast. You don’t even need to dismantle your setup. However, it could potentially cause problems. The rapid suction of the solvent into the system means you could up with solvent in your vacuum pump. If this gets into the oil of an oiled pump, it will decrease the time you’ll have between oil changes. If you’re using an oil-free pump such as a membrane pump, it could become flooded with solvent. If this happens, you’ll need to keep it running to help clear the solvent and dry it out.
In either case, in the long run, you’re better off skipping this cleaning method altogether and dismantling your setup for cleaning instead.
Thorough Cleaning of Glassware
The proper way to clean your rotary evaporator is to take it apart and wash each piece separately. Removable and washable parts include the evaporation flask, condenser, collection flask, and vapor tube.
Many manufacturers will provide advice about cleaning a specific rotary evaporator’s components, but these are the basic steps:
- Ensure parts are adequately cooled (chilled condensers should be at room temperature).
- Remove the component and dispose of its contents according to regulations.
- Flush the component with an appropriate solvent. If necessary and suitable as per manufacturer specifications, you can use a brush to remove more stubborn residue.
- Allow components to dry before reassembly.
Depending on your application, you may wish to sterilize your glassware using an autoclave. Just bear in mind that if you’re using safety-coated glassware, there may be some restrictions on what settings you use and how long you autoclave for. In particular, you should avoid sudden changes in pressure as this can cause the coating to come away from the glassware, leaving folds and creases in the coating once the glassware cools.
Cleaning Other Parts of a Rotary Evaporator
Aside from the glassware, you need to keep up with regular cleaning of other parts of the rotary evaporator.
- The exterior of the rotovap unit: Cleaning the outside of the rotary evaporator is relatively straightforward. You can wipe it with a cloth moistened with water and a mild detergent, but you should avoid using a flammable cleaning agent such as ethanol on the outside of the unit.
- The heating bath: This should also be cleaned with an appropriate solvent or water and a mild detergent. Note that some manufacturers advise not to use solvents on a bath, particularly those with Teflon coatings. Be sure that the bath is switched off before cleaning and that the evaporation flask, if still attached, is in the upper stop position.
- Protective covers: These can be removed and cleaned, but note that they may scratch easily, so avoid using abrasive materials for cleaning. Covers made of protective glass may be sensitive to certain solvents, so it’s best to stick with water and a mild detergent.
Primary Advantage of a Rotovap over Traditional Distillation
Higher efficiency, together with better accuracy, is the primary advantage of using a rotary evaporator over traditional distillation.
Decreased Pressure Within the System
The presence of a vacuum decreases the pressure within the system. This decreases the vapor pressure required for boiling to occur, thus lowering the boiling point of the solvent. This means less heat energy is needed for it to evaporate.
Aside from lowering the boiling point, a lower pressure can speed up the rate of evaporation. That is, a solvent will evaporate quicker when it is close to its boiling point. Pressure pushing down on a solvent makes it difficult for molecules to escape as vapor. A lower pressure means those molecules can enter the atmosphere at a faster rate.
Many standard distillation setups include the use of a vacuum, so pressure can be controlled in these systems. As such, rotary evaporation and standard distillation could be considered comparable in this manner.
Increased Temperature of the Solvent
An increase in temperature will increase the vapor pressure, leading to evaporation. However, whether you’re using increased temperature in a rotary evaporation or standard distillation setup, it takes time and energy to heat a bath. This reduces the efficiency of using increased temperature to evaporate the solvent.
Water takes a lot of energy to heat, and heating a bath from room temperature (usually 20 – 25°C) to, for example, 80°C, will take a lot more time than heating it from room temperature to 30°C (a common target vapor temperature for rotary evaporation). Oil baths may take even longer to heat, as they can go as high as 180°C.
What’s more, at higher temperatures, more heat is lost to the ambient environment and less heat is added to the bath, as the difference in temperature between the bath liquid and internal heating elements decreases. This makes operating at higher temperatures slower and less energy efficient.
Both standard distillation and rotary evaporation setups use increased temperature, so this factor does not necessarily make rotary evaporation more efficient than standard distillation. The key is in the rotation.
Rotation of the Flask
The rotation of the flask plays an important role in a rotary evaporation setup for two major reasons: increased surface area of the solvent and agitation of the water bath liquid.
In a static setup, as is seen in standard distillation, the surface area of the solvent is limited. In a rotating flask, the solvent forms a thin film around the sides of the flask, greatly increasing the surface area and speeding up evaporation.
Top 5 Questions You Should Ask When Buying Rotary Evaporator
1.What are your sample sizes?
Microtiter plates and micro centrifuge tubes work best in a centrifugal vacuum concentrator. For large samples up to 450mls, a vortex evaporator is recommended.
2. What are your samples?
Acids require an acid resistant system. Solvents damage plastic and rubber components, an appropriate system to prevent damage is recommended. A -50C cold trap is ideal for aqueous based samples, a -85C cold trap traps most solvents and a -105C cold trap is recommended for alcohols.
3. Are your samples heat sensitive?
Even at ambient set point, vacuum concentrators add heat through friction. A concentrator that has refrigeration built into it will give you the temperature control recommended to maintain the viability of heat liable samples.
4.What safety features are available?
Due to the nature of heating up aqueous samples, acids, and solvents, a variety of safety accessories can be used to ensure the safety of the operators. As glassware is under extreme pressure due to the vacuum pump as well as being heated, coated glassware can be used to ensure flasks don’t shatter during operation. Shields and protective hoods with ventilation can also help ensure operator safety. Some manufacturers offer advanced options, such as motorized lifts and shutoff procedures for power outages or if the heating bath goes dry.
5.What environmentally friendly options are available?
For the condensing and collection of samples, many options exist. Condenser coils or cold fingers are generally paired with circulating tap water or dry ice. While these methods are adequate for the purpose, constant changing of water to prevent algae buildup can get wasteful, along with a constant need for dry ice. Many manufacturers now offer circulating chillers which can be attached to evaporators, allowing for highly efficient condensation without the waste associated with using tap water or dry ice.
Operators should make sure their rotary evaporator is designed and set up for the intended application. For example, if using acids, the system needs to be properly coated to protect the internal components and the pump from damage.
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