can i just freeze the water out of iso?

As I was adding iso to the dry ice around my recovery tank I wondered if I could just freeze the water out of iso. If I put a gallon of iso in a dry ice bath for a few hours would all the water turn to ice allowing me to pour off near 100% iso?

Dry ice doesn’t turn into water, it turns into CO2, hence why it’s “dry” ice. Iso does grab water from the air, though.

Unless there’s a significant amount of water in it, you won’t be able to freeze any out. Salt, however, will create a separation.

Sorry for the confusion, I’m asking if cryo temps will turn the water in isopropyl alcohol into ice thus separating the water from the alcohol if i were to pour off the liquid and leave the ice behind.

Pretty sure that’s going to be dependent on the ratio of iso/water. Alcohol and water create an azeotrope that’s kinda hard to break, which is why they have to use benzene to get ethanol to 200 proof.

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I have a related question:

Yesterday I had operator error while running my rotovap. I have a circulating water vacuum pump, and we ended up sucking water into our solvent (etoh denatured w/heptane). How can I get the water out?


My recommendation would be salt and a sep funnel, unless anyone can chime in with a better idea, haha.

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Answer is No
If your iso freezes iT has a lot of water in iT at least 40%
If You really want to freeze iso You Need to be able to go down to the 140C range
But that still won t separate your water
If there is Some water in molecularsieves Will reproof your iso

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that’s what i would try if i was in that boat.

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The man for this anwser is beaker
My guess is Ad more heptane equal amount as ethanol and water Maybe even Some more water trying to get the ethanol and water about even
Your cannabinoids Will jump to the heptane and ethanol water later can be discarted in a seperatory funnel.
Or You yust Evaporate etho/heptane and water of and start again

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For water mixed with ethanol you can dry the tincture using 200 proof EtOH in the rotovap. If you introduce 200 proof it will form an azeotrope at 5% concentration and take the water with it to the receiving flask. I have used this process successfully many times to dry out wet oil/ethanol solutions.

You start by adding an excess of 200 proof to the tincture in the roto under vac and then roto per usual. You will want to repeat this until the tincture is no longer cloudy when purged down to a loose syrup consistency. The down side of this process is that it takes a lot of 200 proof to clean up a lot of water. At a 5% azeotrope you are removing 50 ml of water for every liter of 200 proof. But, as far as non-invasive ways to dry out an alcohol/cannabinoid solution this is about as good as it gets.

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distillation with a column.

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That’s a no, the reason is: isopropyl alcohol and water are pretty miscible (meaning they mix into a homogenous solution), the miscibility is certainly affected by temperature but not enough for them to separate at such a high ratio of alcohol to water.

If you had a LN2 source you might be able to separate them, but I really doubt it.

Your best bet is distillation to get up to 95% isopropyl—otherwise the most effective method (posted above) is going to be using a dessicant salt. Hope this helps.

Can we take this topic in a little different direction???

Would this be the same for trying to separate Ethanol from Isopropyl Alcohol. Seems like the only way to break the bond is ethyl benzene?

I see some extremely cheap 95% ethanol on ebay with 5% iso and denatonium benzoate. I know the alcohols can be distilled from denatonium benzoate but how can i seperate the 2 alcohols after? seems like they are too close in temp to distill or fractionally distill? is chemical the only other way?

Or does it really matter if i have the 2 alcohols together if i plan to distil it anyways?

This is the magic of denaturents, hard to seporate mixtures courtasy of the tax man! A spinning band type apparatus might be the solution, they were origianlly developed to seporate close boiling points.
Any thing I missed @BR-Instrument?

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Water and ethanol are azeotropic.

You can read more about how to break the AZ at Azeotropic distillation - Wikipedia


Get a separatory funnel put your solution in. Add more heptane. Then salted water. Shake a few times and let rest. The water and heptane aren’t miscible. So the water trapped in your solution will grab ontothe salt water and leave your mix clean.


It isn’t because they boil too close. If they are an azeotrope they are boiling at the same temperature. No amount of theoretical plates will separate that.

Azeotropes are a constant boiling point and constant concentration mixture. 95% ethanol 5% water boils at 78.2 C where as pure ethanol boils at 78.4 C. Because of that water will always be distilling over.

One way to view this graph quickly is to see how far apart those lines are. One “up” and one “over” is one plate. Basically, if the lines are really close together, the separation is more difficult. If they touch, it is impossible, UNLESS you can somehow get to the other side of the the pinch point.

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