Rotovap settings for evaporating water

Need a few tips on what vacuum pressure(torr please), chiller temp and bath temp to evaporate water from cbd oil in a rotovap. What works best for you?

Every time you drop the pressure by roughly 1/2 of atmosphere, your boiling point will be reduced by roughly 1/4.

Evaporative cooling will fight your bath temp - phase change absorbs energy to lift the molecules into vapor and you will need to set your bath temp to be atleast 20 degrees C higher than your boiling point- tbh your equipment will reach an equilibrium where it maintains its heat level to match the evaporation temp and rate so its not like you have to babysit it or keep it at a precise level.

ok so short story mode: run the bath hot and vacuum deep for harder to evaporate substances like water, which require a substantial amount of issue to give and receive energy.

Set your chiller temp to be atleast 60 degrees celcius colder than your evaporation temp which should make for an 80 degree difference between chiller and bath.


So bath temp 60C and chiller -4C and vacuum at 300 torr should work well for evaporating water?

more like 100 torr, and set the chiller as low as it will go. rotation speed matters too- don’t go full speed cause it tends to make it more difficult for the vapor to leave if its also being slung outward to the wall of the flask due to G force- towards the end slow it down a bit, raise the pressure a bit and up the heat- I have noticed that it helps to get that final last bit out


Cool, thanks. This helped a lot!

1 Like