Rotovap Distillation: What Is A Rotary Evaporator? | BVV
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What Is A Rotovap?

by BVV |

 Table of Contents

What Is A Rotary Evaporator?

A rotary evaporator or rotovap is an essential tool in a processing facility. Its primary use is in the recovery of ethanol after a winterization or extraction process. Although we’ll be focusing on how a rotovap operates during a basic ethanol recovery, know that it can be applied in the recovery of many other solvents that are compatible with the gasket materials.

Understanding Rotovap Distillation

Before learning about rotovap setup and operation, you must have a clear picture of the physical change happening inside of the rotary evaporator. Consider how a mixture containing extract and ethanol must first be separated before rotovap distillation can occur.

To separate the mixture, heat is applied while simultaneously pulling your vacuum. This significantly drops the boiling point of the ethanol. As the evaporation flask turns, the mixture creates a thin film that spreads across the interior of the flask. This helps force the ethanol to vaporize at a faster rate. That vapor is pulled into the path of the condenser by the vacuum pump.

As the ethanol vapor enters the condensation path, it re-condenses back into a liquid and drops into the collection flask. In the end—the original extract remains in the evaporation flask while the ethanol moves into the collection flask. This ethanol can then be re-used for winterization or extraction.

Components Of A Rotovap

Before you learn how to successfully use a rotovap for evaporation, you should understand what components make it up. You can refer to our rotovap turnkey setups for specific component combinations.

Rotovap

The rotovap size depends on how many liters you need to recover. That being said, the most common sizes are 5L, 10L, 20L, and 50L. The size refers to the size of the evaporating flask. It’s important to note that the flask is not loaded at max capacity during operation, but usually around 20-40% capacity.

Chiller

Rotovap chillers are specially designed. They have a much higher cooling capacity compared to refrigerated circulators. However, they usually don’t have as large of a temperature range. That’s because you won’t need extremely cold temperatures for evaporation: just a higher cooling capacity. The solvent vapor is warm when it hits the condenser. The increased cooling capacity is meant to keep your chiller at a stable temperature.

Vacuum Pump

For best results, a chemical-resistant, oil-less diaphragm pump should be used with your rotovap. These pumps don’t have as much depth as rotary vane (oil) pumps but they are much more resistant to contamination. Don’t use an oil pump with a rotovap or you’ll find it destroyed in no time.

Cold Trap

The cold trap is placed between your vacuum pump and rotovap to protect the pump from further contamination. Cold traps are essential for rotovaps because they catch any vapors that pass through the condenser. The cold trap will be the coldest point in the system. This means that any vapors pulled into it will recondense in the trap, leaving your vacuum pump dry and contaminant-free.

How to Use a Rotovap

This operating procedure is meant to be a basic starting point for anyone new to rotary distillation and evaporation. Once mastered, you can adjust the parameters to suit your specific needs.

Continuous Feed Operating Procedure

  1. Lightly grease all joints and inspect components to ensure everything is in working order.

  2. Connect chiller output to condenser top and chiller input to condenser bottom. Set to 0°C (32°F) and fill from top-down.

  3. Connect vacuum pump to cold trap and cold trap to rotovap vacuum port.

  4. Turn on heat bath and set to 40°C (113°F).

  5. Once heat bath and coil have reached the desired temperature, turn on rotovap motor and set speed to approximately 100 RPM.

  6. Start vacuum pump and allow it to pull down for a few minutes before beginning injection.

  7. Prime the rotovap: once the vacuum has been pulled and displays a low reading; inject 20% total volume of liquid  in the rotovap valve and close it. It should evaporate as the chiller rises in temperature by 1-3 degrees.

  8. Once the temperature stops rising/drops down, slowly open the injection valve so that a small amount of liquid enters the rotary flask. Match the input speed to the output speed by injecting the same amount of liquid dropping off the coil (into the receiving flask) into the rotovap.

    1. The input speed and output speed are matched when the chiller maintains a stable temperature. If the chiller temperature rises: you’re injecting too much liquid. Dial back the valve until the chiller stabilizes.

  9. Once everything is stable: the rotovap can complete evaporation without supervision.


Rotovap FAQ

What’s a J-KEM DVR-200 Used For?

The J-KEM DVR-200 is a digital vacuum regulator. It maintains a specified vacuum level throughout the evaporation process. This pinpoints the specific solvent boiling points, speeds up processing, and prolongs the vacuum pump lifespan. It also allows you to data log the vacuum level over time.

What Kind of Tubing Do I Need?

Gum rubber is recommended for all vacuum tubing. Meanwhile, silicone or PVC tubing should be used for chiller tubing. We suggest supplementing these with tubing insulation to provide the most stable temperatures possible. 

Can I Use an Oil Vacuum Pump With a Rotovap?

You can… but you really shouldn’t. Any oil vacuum pump used will quickly become ruined.

Diaphragm vacuum pumps are lined with PTFE on the inside so they’re highly chemically resistant. If you use an oil vacuum pump with a rotovap, the pump oil will turn black and start to smell like ethanol. That’s because the vapors are getting trapped in the oil case and contaminating the inside of the pump. This dramatically decreases the lifespan of the pump and forces you to change oil too frequently. 

Do I Need a Cold Trap? How Does it Work?

Yes: a cold trap is always recommended when using a rotovap. Because ethanol is an alcohol, it’s very difficult to re-condense. Some ethanol vapor will pass through the condenser during evaporation. A cold trap is needed to capture the vapor before it reaches the vacuum system. This considerably prolongs the lifespan of the vacuum pump.

Cold traps also trap extremely volatile compounds like Terpenes. CT80 is fantastic for this, but the CT40 can get the job done too. A 1.5 G cold trap could also work, but it must be fed dry ice to stay cold.