Questions for people who decarb in rotovap

So I’ve been decarbing at atmospheric pressure for a while now, but as we scale up, I’m looking for a better method. Dealing with the “muffin” at atmospheric pressure is kind of a pain, even with rapid stirring if I am not standing close by ready to stir/break the muffin, I risk the oil spilling over the beaker.

My question is, how difficult (or not) is it to control the muffin when decarbing in a rotovap? When evaporating ethanol on the rotovap, it’s possible to “break the muffin” or prevent bumping by adding a bit of air into the system. Does it work the same when decarbing? I feel like it wouldn’t have the same effect because when you’re just evaporating ethanol, adding air prevents further boiling. But unless I am mistaken, that’s not true for decarbing - if it’s at a high enough temperature, it will decarb at any pressure. So I guess my question is how do you control the muffin when decarbing in rotovap?

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Generally while in a rotovap, you can use an oil bath to hit like 110°C and you’re viscosity will be low enough as to not muffin horribly. Modulate your vacuum level if you’re still getting muffins. Less vacuum equals less muffin in general.


It’s a hell of a alot easier to decarb in a boiling flask. The trick is to allow a inert gas bleed. This prevents that muffin effect.


So it is possible to control muffin by modulating vac pressure? I get that that is the case when simply boiling ethanol as less vacuum results in higher vapor pressure and less boiling. But is that actually the case for decarboxylation? Does vapor pressure have an effect on decarboxylation? I thought no. Is it just a matter of vacuum pulling off CO2 faster which effects “muffining”?

So a procedure for decarbing on the rotovap would look something like bring oil to 110C in oil bath and slowly pull vacuum? What kind of range of vac pressures are common for decarbing on roto? Do you slowly work your way down to full vac?

Thanks for the info!

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Interesting. I’ll give that a shot too. Thanks!

My hesitation for decarbing in either a rotovap or a boiling flask is the inability to really do much if the muffin gets out of control. With a beaker or similar type design, I can pour some out or break the muffin with a spatula or something.

Yeah you have the right idea, slowly work your way to full vac till you can hold that without any gas evolution from your oil. By doing this you never let the oil get to the point of muffining

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I run mine til about 65-70c then dump alcohol and dont keep anymore that comes off it will have alot of terps. I then ramp my temps to 145c full vac fast rotation. Only had it bump once in 5 yrs from there being a ton of water in the alcohol


Cool thanks for the info, that’s reassuring! Do you save the condensate that collects past ~70C? Or are those terps more similar to terps from SPD and not too useful? I would guess the latter.

I use it to clean or whatever, i just dont want to compound the terps in tbe etho i will be using again. You’ll see the vac start to go up from the decarb and itl look like smoke especially in rhw condenser. I can roto about 10-12 liter in a 20l no problem. It will all basically pour right out when its that hot, mine holds about 35 grams but only happens once. Tip a 20l roto fits perfectly in a 12 gallons trash can from wal mart and will start to form around it.


I must learn this trick. Got nitrogen already in the lab. Just need some adapters now?

I’ve done a lot of reactions under inert gas. It’s nice to have a bubbler so that you can know that nitrogen is flowing and at what rate. Something like this, usually filled with some kind of oil (vac oil or simillar). If nitrogen is flowing, you’ll see bubbles in the oil, and you can have some idea of the rate by how vigorously it’s bubbling.

As for introducing gas to your flask, you can a vacuum adapter which is basically just a joint with a hose barb. Nicer ones have stop cocks or similar. You can also just use a septum with a needle. Cut a 1mL syringe in half and stick some tubing over it and stick the needle thru the septum. Makes me miss my Schlenk line.

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Thanks for this tip, never seen it before but it makes a hell of a lot more sense than sticking your ear on the N2 regulator to confirm your gas is running

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@Concentrated_humbold same here…I decarb in the 20L and 50L rotos at 80-90C. I just switch to a stronger vacuum pump once the condensation activity is clearly minimal in my condenser. I keep the RPMs and vacuum full throttle at all times. I used to do a couple hundred kgs of desolventizing this way daily.


If you wouldn’t mind lending the spoon, how long do you have to decarb at 90C? I’d really like to avoid switching the bath back and forth between water and oil to exceed 100C


Its the only way to do it, saves a ton of time and strips volitales as a bonus.


Depending on volume of boiling flask and volume of material the time varies but your primary indications are a lack of reactivity when releasing and pulling vacuum and slowing and speeding up rpms. Once there are insignificant visual delineations between the aforementioned variables you have achieved everything possible in your roto


I’ve used rotovap for this off and on, had to use an oil bath over water to go over 100c but doing it around 110c-120c in a 5-20L roto never gave me any muffin issues personally YMMV