Optimizing your RotoVap


What temp are you using for the bath?


running hotter is better. i dont get your comment


46-47c Is my sweet spot on my buchi Frankenstein setup. Its pretty slow and I lose about 1/4 to 1/3 my etoh somehow. My cold finger condenser stays -20 to -30c


What’s your vac at?


To be fair to my equipment I’m using a Welch 2585b and I have a few small leaks in the system. Vacuum isn’t getting very deep but my guage is currently broken lol. I’m guessing im getting around 27 in mg

Is anyone using propylene glycol for their water bath liquid? I’ve got a bunch of food grade PG and it’s boiling point is 188 degrees Celsius which would be perfect to decarb my oil in the rotovap


So you don’t use a vac regulator? I found that to high vac with too high temp can lead to vapor/etho loss, but it’s down to how fast you want to recover vs how much you’re prepared to lose. I found that increasing my temp from 42c to 45c at 20-30 torr lead to some etho coming out the evac port of my diaphragm pump. But i was running at 58 for a while, but i lost so much etho that in the end it wasn’t worth the time saved.


No regulator here just the Welch pump going continuous. It’s not a high vacuum capable pump. Specs show it capable of going to 60 torr or 27.6" I think it’s achieving less since I have some slight leaks at non greased joints

I can see the vapor cloud condensing in the cold finger. I run the heat of the bath hot enough to keep the vapors a few inches from the vacuum take off port of the roto. If I go too hot in will see some etoh condensing in the vacuum line. Less than 45c bath and the etoh drips off the cold finger at such a slow pace it would take all day just to recover 1 liter. I’m losing etoh somehow and I figured it was either the inefficiency of the Dewar design over the much greater surface area of a coil type or it was too low of vacuum.


how stupid would i be for buying a cracked condenser not knowing if it still holds a vacuum for my rotovap its a few hundred dollar gamble?


I returned the condenser i got that had such a crack on arrival. Not worth the risk in my opinion. Just my 2 cents. A new one shouldn’t be that much more, i think.


Meh a new one is about 1200 this one is 200


I know a few glass blowers that have fixed worse for me. Pm me if you want some reccomendations.

btw, that looks like a really easy reapir.


Pm sent. I would be interested to see if one of these plastic coated pieces can be repaired easily or at a minimum I could just use some epoxy to cover the crack if it leaks lol.

It would be nice to have the ability to try out a coil condenser versus the Dewar style.

Do you guys know if the diagonal condensers are more efficient at solvent collection since the etoh drips off each coil versus dripping all the way down the entire coil assembly. Are there any numbers to base the different collection rates of condenser types?




The angled condenser is designed to be low profile for fume hoods.Longer condensers have more cooling ability, so naturally you can run your rotobath hotter without having carryover to the cold trap.


Ya that makes sense I just looked at the path of condensed etoh as it travels all the way down the rings versus one single ring before it drips down. Thinking about it now it probably doesn’t do much.


I have made my roto run continuously without the need to stop it to empty the flask. Used the same components as my previous post in this thread, but instead of connecting the 20l chamber to the vac i left the vac pulling from the receiving 5l flask. I then connected another vac pump to the port of the 20l. Now when the 5l is full i just open the valve and start the other vac pump and pull everything into the 20l, then close the valve. This way the roto runs until you don’t need it too. Might not work for everyone, works for me.

Edit: it made the recovery go from 5l/h to 8-9l/h. Quite the increase, i must say.


Is anyone purging etoh completely in their roto?


Yes. Why?


Just wondering if ppl were able to completely purge their crude in the roto.


I’m letting it go till no more etho drops in the condenser, then i push the heat to 85-90c. Then i dump that in my pot and decarb it directly.


I am trying to come up with a method to fully purge then decarb in the roto. Just want to see if others are successfully purging and fully decarbing in their rotos