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Rotary Evaporator

What it is and how to use it

The rotary evaporator is an apparatus commonly used to remove solvents from a solution of a compound of interest.
It is also used for vacuum distillation, concentration of solutions, crystallization and other processes.


Rotavapor -

What is it?

The rotary evaporator (/rotovap) is a machine that is used to separate different components of a compound. It consists of the following parts: 

  1. Evaporation flask: Here the mixed compound (the solution which needs to be evaporated) is filled. Use the 1L pear-shaped flask. It looks like this.

  2. Water bath: It has heating coils on the bottom and a temperature gauge. Together they maintain the temperature that you specify. This way, no excess heat is given to the reaction. The evaporation flask is immersed in this. 

  3. Rotating arm: The evaporation flask is attached to this arm. The rotation causes the liquid in the flask to get coated on to the surface of the glass, making it faster and easier to evaporate the substance. 

  4. Condenser: The vapours travel through the system and meet the cooling condenser. There is water running through it constantly. The vapors touch it and turn back to liquid. This liquid collects until it is heavy enough to fall into the receiving chamber. This is what it looks like.

  5. Receiving chamber/collection flask: This is a large, round bottom flask with a conical mouth instead of a cylindrical one. 

  6. Vacuum pump: This creates a vacuum inside the system, which causes the boiling point of the liquid in the evaporation flask, to lower.

  7. Bump trap: The bump trap is fitted between the rotating arm and the evaporation flask. It helps to avoid foaming, splashing or bumping. 


How to use it? 


Step 0: Make sure you know (and have written down) the temperature and vacuum needed for the substance to be evaporated out.

i. Securely affix the collection flask to the bottom of the condenser. Remember to grease! Also securely affix the bump trap to the rotating arm. Grease! Clamp! 

ii. Ensure the pressure valve is open. You'll close this later. 

iii. Fill the evaporation flask with not more than half the max capacity. For our lab, that means 500ml of the solutions is the max you can fill it up to. Securely affix it to the bump trap. GREASE! CLAMP!

iv. Start the rotation. The recommended speed is 1/3rd the max speed. (40 rpm for us). Tip: towards the end of the evaporation, speed up the rotovap to 60-70 rpm to save time on the last bit of evaporation.

v. Turn on the vacuum pump and close the valve. 

vi. Set the appropriate temperature for the water bath. Remember the 20 - 40 - 60 rule!

vii. Check the temperature when you start to see distillate - this might not be the product you want. Throw it away! The temperature should be in the (corrected for pressure) range of boiling points when you see a distillate.