Solvent Removal Questions (How to know its finished?)

How do you know when you are finished removing solvent? Would anyone share what parameters I should use to fully remove solvent using a Rotovap?

Only way to know for certain is analytical equipment. like a gas chromatograph.

We run our rotovap until the condensers arent dripping anymore and the drain the recovery flask and run the rotovap usually for another 3-4 hours before our solvent is no longer detectable on the GC.

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Thanks for the advice. Any chance you would share your roto-bath temp with me?

  1. Start rotovap.
  2. Do something else for a few hours.
  3. Send for solvent testing at a third party lab.
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Not unless you share which solvent you’re referring to…

Removing residual CO2 in a rotovap is way easier than removing residual limonene.

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My bad, I suppose I need to be more specific. I am removing ethanol from winterized CO2 oil. Thank you for your help clarifying my post.

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damn straight :wink:

then you’ll need to know your regulatory target…

OR for instance currently has no limit on residual ethanol.
some states are looking for 5000ppm, others for 500ppm.

if your state is looking for 50ppm, you’re not going to get there in a rotovap. Even 500 might be problematic.

where are you going after solvent removal?

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When removing residual Methanol we do the final 3-4 hours at 80c and our vac is around -0.09.

I dont work with Ethanol at all but it does have a bit higher boiling point than methanol.

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It’s gonna take a minute getting used to your new avatar

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The limit for residual EtoH in my state is 5000ppm. Afterward it goes to our sales team.

That should be relatively easy…and should even pour at 75C without too much loss

asking what your desired end point is…

Shatter? pens?
in jars for edibles?

why? because finishing in a vac oven vs decarbing and finishing in a beaker or the rotovap…

Its going for pens.

Decarbing to reduce viscosity might help with that goal. And make getting your extract out of the boiling flask easier.

Were you planning on adding terps back?

We actually use a cold trap oven to decarb before we extract. Will this change how I can recover solvent?

Weigh it. Plot it. Constant weight = done.

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Yes and no. If your material is decarbed, it’s viscosity will be lower, so it will be easier to move around at any given temp. So you can recover more solvent in the rotovap without losing more material to the inside of your flask.

If you’re going to pens, without added terps, your ideal finish temp in the rotovap is probably fairly similar to that at which you fill your pens.

If you’re adding terps to reduce viscosity, you may want to leave a little more solvent in your material, and remove it right before you stir in your terpenes.

@WiAlchemy What size Rotovap do you have? How much oil are you yielding when you pour it off?

I ended up figuring it out. I basically just ran a batch at a few different lengths of times and temps and sent them away for testing. Initially I was worried about the viscosity of my crude after I was done removing solvent. Figured out I was already testing way under my threshold.

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This is with a basic 20L rotovap with anywhere from 1-5kg of finished oil in it.