Sciencemadness Discussion Board

Distillation of Ethylene Glycol from Antifreeze Toubleshooting

Melkor333 - 2-4-2021 at 13:46

I am attempting to recover ethylene glycol via simple distillation from antifreeze. The distillation was performed under atmospheric pressure and I added a claisen adapter to the setup so I could easily add more antifreeze when necessary. I started the distillation and the temperature steadily rose up to ~85C. It stabilized around that temperature and I had some distillate come over. I figured this was just some additive junk, so I waited until that distilled over and I reached the boiling point of ethylene glycol and collect that. However, instead of increasing; the temperature dropped quite rapidly to ~20-25C and is staying there. I'm not sure what is going on. I measured the temperature just above the boiling flask and it is ~75-80C, so the problem seems the be that the vapors aren't climbing the column. The setup was already wrapped in aluminum foil when the temperature reached ~85C, so I don't think wrapping anymore will help and it's not that windy. Any ideas would be much appreciated.

[Edited on 2-4-2021 by Melkor333]

RustyShackleford - 2-4-2021 at 14:25

remove the column or do it under vacuum

digga - 2-4-2021 at 16:33

Use a short distillation path and insulate with aluminum foil. Watch out for the foam monster.

zed - 3-4-2021 at 20:05

What are you using for heat?

Antifreeze is typically Ethylene Glycol, plus a little water. Or, in some cases, a lot of water.

The water should distill off at ~100C or less.

Then, you are left with Ethylene Glycol, which boils at ~200C. At less than ~200 C, it isn't boiling, there isn't much vapor, and hot vapor isn't going to reach the thermometer.

You need more heat, or a shorter path, or you need to use vacuum, to lower the boiling point.

Many stir-plates and hot plates, struggle at 200C.. Either a "Bare" filament, Kitchen Stove type hot plate, or a heating mantle, can distill things at 200C+.

Melkor333 - 7-4-2021 at 16:34
Quote:

What are you using for heat?

Antifreeze is typically Ethylene Glycol, plus a little water. Or, in some cases, a lot of water.

The water should distill off at ~100C or less.

Then, you are left with Ethylene Glycol, which boils at ~200C. At less than ~200 C, it isn't boiling, there isn't much vapor, and hot vapor isn't going to reach the thermometer.

You need more heat, or a shorter path, or you need to use vacuum, to lower the boiling point.

Many stir-plates and hot plates, struggle at 200C.. Either a "Bare" filament, Kitchen Stove type hot plate, or a heating mantle, can distill things at 200C+.


As I was doing it I realized that the vapors were not reaching the thermometer because the ethylene glycol was not boiling yet. I was able to get a long thermocouple probe into the boiling flask to measure the temperature, and it was rising. Eventually the ethylene glycol did begin to boil and I was able to distill some for a few minutes but it then was no longer distilling over. I suppose that it was a bit too chilly outside so I will try again as it gets warmer.

As for doing it under a vacuum, I would like to although I have never done it. I have a 12V mini vacuum pump and its specifications say that the negative pressure is -500 mmHg and vacuum degree of 66 kPa (I do not know if those 2 stats are the same thing). I do not know if that is a strong enough vacuum. Also, I assume I would keep the vacuum on throughout the distillation.

Bezaleel - 8-4-2021 at 01:34

1013 hectopascal ~ 760 mm Hg
So you are at around 101.3 * (760-500)/760 = 34.6 kPa. (This is the same as an under pressure of ~66 kPa.)
I don't expect miracles at this pressure, but it should help a bit. (I find that e.g. tap water boils at around 15C at 1mBar ~ 0.1kPa.)

mekanochemical - 23-4-2021 at 16:10

first of all, make sure that you bought the right antifreeze. It has 2 main types in market, one labeled as "organic" and other labeled as "ethylene based"

in both cases you could buy in concentrated version and ready for use (diluted) version... look for the concentrated and you just need to distill to remove some colorant and anticorrosive additives.

Swinfi2 - 24-4-2021 at 01:26

Cold condenser water could also be an issue, if the cold water keeps the glass below ~200c before the bend you'll never get any distillate.

I used a circulating pump and let it get hot, had no issues even with a Vig column, but I have a good mantle and plenty of insulation. I was doing a different thing but EG was still the bulk of the liquid.