Wednesday 28 October 2015

Rotary Evaporator

Rotary evaporator

The rotary evaporator is a piece of equipment that is designed to allow you to distill a liquid under conditions of reduced pressure. Since the pressure within the system is reduced, it means that the liquid can be distilled at a lower temperature than it would at atmospheric pressure.

This is a very safe and fast method of distilling flammable solvents like dichloromethane. Dichloromethane normally boils at 40 deg C at atmospheric pressure.

Round bottom flask
The sample to be “rotovapped” is added into the round bottom (RB) flask. The sample RB flask should never be more than half-full with liquid when it is attached to the rotary evaporator. The sample RB flask is connected to the trap and is secured using a circular clip. The clip has two sides. It is always oriented with the smaller circle on top.

Open positionThe stopcock that is fitted at the top of the condenser needs to be in the closed position. To close, turn the stopcock such that it is crosswise (90 degrees) to the air inlet. Turn on the water aspirator to evacuate the system.

Ensure that the condenser has cold water running through the glass coil.

cold water circulating

When the vapour enters the distillation tube inside the condenser, it will be in a cooled environment for the vapour to condense and drip into the large round collection flask to which it is attached.

dripping condense solvent

There is a splash trap at the end of the distillation tube to prevent unwanted sample from splashing up into the condenser

To speed up the rate of evaporation, the liquid sample can be warmed with hot water. Lower the flask by sliding the “Push” knob below the water bath. The temperature can be set using the dial on the side of the water bath.

RB flask immerse in hot water

To ensure even heating of the sample RB flask, turn the rotary dial to spin the sample RB flask that is immersed in the hot water bath.

Observe the condensation of vapour near the condenser. As the solvent condenses, you will see dripping of the condensed vapour collecting in the collection flask. Once the dripping stops, wait another minute and stop the rotary evaporator.

To remove the sample RB flask, disassemble by reversing the steps. Raise the sample RB flask from the hot water bath. Turn the rotary dial to stop the sample RB flask from spinning. Turn the stopcock that is fitted at the top of the condenser so that it is in-line with the air inlet. This will let air back into the system, and you should hear the sound of air rushing into the system. Turn off the water to the aspirator and the condenser. Remove the clip that is used to secure the sample RB flask. Gently give the neck of the sample RB flask a twist and remove the flask from the rotary evaporator.

Steps in operating the rotary evaporator

1. Turn power switch on. Turn water bath on. Adjust water bath to desired temperature.

2. Turn on water to condenser (slow to moderate flow).

3. Turn on aspirator full counterclockwise.

4. Attach the splash trap to the vapour tube and secure with clip.

5. Attach the sample RB flask to the splash trap and secure with clip.

6. Adjust rotational speed of the flask.

7. Turn the air inlet valve to the closed position to obtain a vacuum.

8. Slide the "Push" knob down to unlock the lift mechanism to lower the sample RB flask into the bath.

9. Watch for the dripping of the condensed solvent into the collection flask at the condenser. After the dripping stops, wait another minute to ensure that the evaporation has finished.

10. To disassemble, slide the "Push" knob to raise the flask.

11. Turn the rotational speed knob to the off position.

12. Turn the air inlet valve to the open position to re-establish atmospheric pressure.

13. Remove the clip and the sample RB flask.

14. Remove the clip and the splash trap.

15. Turn off aspirator, water to the condenser, water bath and the power switch.

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