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Distilling large quantities of acetone for reuse
TortoiseWrath:
I am using acetone to remove water from silica gels used in the production of aerogels. With the system I am currently using, I am replacing the acetone four times for every gel. However, I am looking to increase my production dramatically on account of demand, and this would lead to the use of 200-liter drums of acetone instead of small bowls.
Consuming 800 liters of acetone for every batch seems inefficient to me, so I'm wondering if it would be possible to distill the used acetone and reuse it. Because the boiling point of acetone is 43 K lower than that of water, it seems to me that it would be feasible to use simple distillation for this purpose.
The problem I'm running into is how I could possibly distill 200 liters at a time of mostly acetone. Would the following procedure work?
* Have another drum on the ceiling above the drum containing the mixture
* Connect a pipe with a valve in it between the drums
* Heat the lower drum (or both drums?) to, say, 70°C
* Wait a while
* Close the valve to trap the acetone gas in the upper drum
* Turn off the heat
* Replace the lower drum, now hopefully containing just water, with an empty one
* Open the valve, allowing the acetone to flow back into the lower drum
This seems like it would be far too simple to work, so what would the problem be? It's been a while since I've done distillation and I'm terribly unfamiliar with equipment on this scale, so please explain like I'm five.
Enthalpy:
Water and acetone make no azeotrope at normal pressure so some distillation method will work. The purity you need decides the number of steps - hum.
http://www.solvent--recycling.com/azeotrope_1.html
To the very least, the setup you propose is far too dangerous. Acetone is highly flammable and its vapour shouldn't be breathed, so heating a drum is the wrong way, worse within a building.
Companies supply distillation apparatus, you should consult them. Or ask your acetone supplier if it would recycle the product.
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Until you have the distillation apparatus, you can save much acetone by using successive acetone baths for the silica gel batches. That is:
- Each silica batch passes through successive baths, the first acetone bath contains some water, only the last is very dry.
- Acetone will absorb humidity. Once the wettest bath gets unusable, discard or recycle it - but only this one.
- Introduce a new very dry acetone bath. Degrade all others one step: the previous very dry bath is the new almost-dry one, the previous almost-wet bath is the new wettest one.
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My preferred process would go a bit differently: I'd let acetone vapour dehydrate the silica gel, as is done with vapour degreasing, vapour cleaning...
Have the acetone at the bottom of a container where you heat gently. Put the silica gel at the top, outside the liquid, and keep it colder than the liquid - or cool the acetone vapour independently, above the silica gel.
That way, you can accept more water in the acetone, since evaporation favours acetone. The vapour, possibly after condensation, will catch water from the silica gel and fall back into the liquid bottom.
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The multistep scheme previously described applies here as well, and you can combine the successive dehydration stations of silica gel with a fractional distillation of acetone and water, in a single apparatus.
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Please be careful with that! My intuition tells you lack the necessary qualifications for the process. Ask a specialized company. To the very least, don't tinker within a building! Maybe you can adapt a dry cleaning machine
http://en.wikipedia.org/wiki/Dry_cleaning
but chances are that acetone destroys the seals, and you get vapour everywhere even before.
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Could dry nitrogen be good enough, instead of acetone? End users just put the silica gel in an oven to dry it. You could cycle the nitrogen, with a good heat exchanger, between a chilled end where water condensates away, and a hot end where the gas carries humidity away from the silica gel. A regenerative heat exchanger and a pulsating gas movement, like in a Stirling engine, would make it more compact.
http://en.wikipedia.org/wiki/Stirling_engine
TortoiseWrath:
--- Quote from: Enthalpy on May 26, 2013, 07:44:32 PM ---the setup you propose is far too dangerous
--- End quote ---
Yeah, that's about what I figured. Stupid chemicals, always having properties... ;)
--- Quote ---Or ask your acetone supplier if it would recycle the product.
--- End quote ---
This is not applicable, for reasons that will become evident below.
--- Quote ---let acetone vapour dehydrate the silica gel
--- End quote ---
I'll try this; I hadn't thought of that. I don't know how well it will work in my application.
--- Quote ---My intuition tells you lack the necessary qualifications for the process.
--- End quote ---
Indeed...
--- Quote ---Ask a specialized company.
--- End quote ---
...unfortunately, not indeed. I live in an incredibly rural area (not something I can easily change). "Incredibly rural" as in "the distance to the nearest people qualified to do this is about 500 km." Random Internet forums are about as close as I can get.
--- Quote ---To the very least, don't tinker within a building!
--- End quote ---
I don't intend to; I have dedicated outdoors tinkering sites.
--- Quote ---Could dry nitrogen be good enough, instead of acetone?
--- End quote ---
Alas, the application won't provide for this. I have some other ideas about acetone replacements; some experimentation will be necessary. The distillation idea is what I'm primarily thinking of at this time, however.
I'd previously been thinking that distillation apparatus were the way to go; I'd just been having trouble finding one with adequate volume capacity. Any recommendations?
curiouscat:
--- Quote from: Enthalpy on May 26, 2013, 07:44:32 PM ---
My preferred process would go a bit differently: I'd let acetone vapour dehydrate the silica gel, as is done with vapour degreasing, vapour cleaning...
Have the acetone at the bottom of a container where you heat gently. Put the silica gel at the top, outside the liquid, and keep it colder than the liquid - or cool the acetone vapour independently, above the silica gel.
That way, you can accept more water in the acetone, since evaporation favours acetone. The vapour, possibly after condensation, will catch water from the silica gel and fall back into the liquid bottom.
-----
--- End quote ---
Good idea. But it has the same hazards as distillation.
curiouscat:
Wonder if fractional freezing might be viable. They have a huge difference in Freezing Points.
Where are you located? In winter you might have an excellent, free freezing source.
If you adopt a modified stage-wise fractional freezing thawing cycle you might be able to get a large enhancement. With none of the dangers of heating acetone.
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