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Author: Subject: How dangerous are vacuum distillations really?
aromaticfanatic
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[*] posted on 29-8-2020 at 20:38
How dangerous are vacuum distillations really?


I am looking into getting myself a good vacuum pump since I have needed one for many experiments and subsequently failed most of the time when I omitted it. There have been plenty of times where I needed to do a vacuum distillation but lacked the equipment for it.

I have heard horror stories about vacuum distillations imploding out of nowhere. A lot of universities do them behind a blast shield. They tend to get a bad rep from what I've seen.

Are they seriously this dangerous? What do you think of vacuum distillations in an at home and amateur environment?


I've done some more research and saw that implosions are often caused by weakened glass with cracks, chips, and scratches. The website I found mentions to wrap the glass in as much tape as possible to prevent glass from flying everywhere. What kinds of tapes can withstand such heat and forces in the even of an implosion?

[Edited on 30-8-2020 by aromaticfanatic]
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monolithic
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[*] posted on 30-8-2020 at 09:06


I've done them a few dozen times with Chinese glassware between 250 ml and 1000 ml. Most recently was 750 ml of ethylene glycol which vacuum distilled for several hours. No implosions but I am very much aware of the risk. I inspect round bottom flasks before vacuum, and I have a bleed valve connected to my pump which I use to slowly reduce the pressure over a 1 minute period, to prevent any shock loading. If you're really concerned about implosion you could built a blast shield out of polycarbonate or just drape everything in a fireproof blanket.

[Edited on 8-30-2020 by monolithic]

[Edited on 8-30-2020 by monolithic]
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wg48temp9
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[*] posted on 31-8-2020 at 04:32


Excluding the chemical spill problems vacuum distillations are really only as dangerous as changing a 500W tungsten light bulb or a 6ft fluorescent light bulb.

Probably not as dangerous as a dropped 26in TV cathode ray tube especially if you drop it on your foot.




i am wg48 but not on my usual pc hence the temp handle.

Thank goodness for Fleming and the fungi.

Old codger' lives matters, wear a mask and help save them.
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Herr Haber
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[*] posted on 31-8-2020 at 11:27


I'd worry more about what I'm distilling spilling all over but that's discussed in another topic.

It can happen, so as Monolithic said, if you are aware of it you can mitigate risks. I'm not sure I could spot a piece of glassware that's about to fail but I certainly can see chips or cracks.

Checking your glassware *before* weighting your reagents is of course a good idea.

It would probably make you feel better to make a dry run with water. This, has the added bonus that you'll know how good a vacuum you're pulling.




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Fyndium
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[*] posted on 31-8-2020 at 11:49


Are larger glassware generally more prone to implosion than smaller ones? I've usually used my smallest 3 neck rbf for vacuum distillations which are 1 liter each, but I could have use for 2 liter one or even larger for sometime.

It would be generally good idea to proof all glassware intended for vacuum. I used my new 4 liter 3-neck flask for direct suction of reagents with vacuum pump and apprently the glass was subjected to full vacuum when the filtering was excessively slow. I have now turned into using hand pump because the vac pump is too powerful.

Wrapping the glassware with shrink wrap or even tape would be somewhat clumsy idea, instead I would just use plexiglass or some other impact resistant plastic. It doesn't have to stop the shrapnel, it just needs to slow them enough to be not dangerous. Glass shards raining around is less of an issue than glass shards impacting. Even 1mm polycarbonate shield would be well enough for protection, as similar thicknesses are used for airsoft and paintball shields and they protect easily from 3J energy, and the thin sheet has the ability to deflect, further reducing point impact force. In this matter, I'd be more worried about the contents of the flask blowing up, as it can be flammable/corrosive/blistering/toxic/carcinogenic/strong smelling or in the worst case, all of them at the same time, not forgetting that it'd probably be somewhat hot, even when under vacuum.
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aromaticfanatic
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[*] posted on 31-8-2020 at 14:13


Quote: Originally posted by Herr Haber  
I'd worry more about what I'm distilling spilling all over but that's discussed in another topic.

It can happen, so as Monolithic said, if you are aware of it you can mitigate risks. I'm not sure I could spot a piece of glassware that's about to fail but I certainly can see chips or cracks.

Checking your glassware *before* weighting your reagents is of course a good idea.

It would probably make you feel better to make a dry run with water. This, has the added bonus that you'll know how good a vacuum you're pulling.


That is a good idea. I like to use water to test my equipment before doing anything remotely dangerous so I like that idea of doing a water distillation and using that to figure out how good of a vacuum I am pulling.

Yea I think spilling whatever is being distilled would definitely be a problem depending on what I'm distilling but I think for the majority of things that I need vacuum distillations for, it'd be fine to have a spill. It'd be a pain in the butt to clean up especially with glass shards everywhere but still wouldn't be the end of the world.
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karlos³
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[*] posted on 31-8-2020 at 14:14


In short? Not very dangerous.
However if you jump into it like an idiot, you can hurt yourself.
But it is unlikely.
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aromaticfanatic
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[*] posted on 31-8-2020 at 14:29


Quote: Originally posted by karlos³  
In short? Not very dangerous.
However if you jump into it like an idiot, you can hurt yourself.
But it is unlikely.


Good point. What are some things that I could do to fall into the idiot group?
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[*] posted on 31-8-2020 at 23:13


I was thinking of vacuum distilling sulfuric acid. It's bp would come down to about 170C with my pump, which is pretty feasible compared to the ntp of 340C and I could use paraffin wax bath to heat it.

This is another option to buying it, but I need only pretty small amount and buying it would warrant a full 25L canister because the price of 1 liter, 5 liter and 25 liter are in the range of 30, 80 and 200 euros.
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aromaticfanatic
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[*] posted on 2-9-2020 at 00:20


Quote: Originally posted by Fyndium  
I was thinking of vacuum distilling sulfuric acid. It's bp would come down to about 170C with my pump, which is pretty feasible compared to the ntp of 340C and I could use paraffin wax bath to heat it.

This is another option to buying it, but I need only pretty small amount and buying it would warrant a full 25L canister because the price of 1 liter, 5 liter and 25 liter are in the range of 30, 80 and 200 euros.


I personally wouldn't distill sulfuric acid especially under vacuum unless absolutely necessary. Just buy the 1L SA. It's very useful and you'll find uses for it trust me.

Boiling the most acidic mineral acid is very very dangerous. Many people do it and get off just fine but I'm not a fan of it. I like to picture myself living with the consequences if things go wrong. Hot SA is an entirely different animal and while a room temperature acid spill on you is not too bad, a boiling hot acid spill has the potential to be lethal in terms of burns. Not very likely lethal but the defacing part is serious. So use some extreme PPE if you do it.

People like to give me shit for heeding warning to others but go ahead and bash me for it if you want.

Also something to consider is that the vacuum pump will likely fail or be heavily damaged. Pumping sulfuric acid vapors through it for the duration of an entire distillation is going to corrode the shit out of it.

On top of that SA already has bumping issues at atmospheric pressures. I am not too well versed in vacuum distillations but I think bumping is even more severe with them so that's something to consider. Too violent of bumping and you risk an over pressure. Confined pressure is not good. It'll likely either break your flask leading to an implosion if things get severe enough. I'd say to do some serious research before trying this. I have yet to see someone distill SA under vacuum so there must be a reason as to why.

Oh also I suggest using a sand bath or something. Typically hot concentrated sulfuric acid doesn't mix very kindly with hot organic liquids. I'm not sure how severe of a reaction there is but if shit hits the fan you already have hot sulfuric acid to deal with as well as an implosion so I don't think you'd want another issue to deal with on top of that. Just food for thought.
Best regards

[Edited on 2-9-2020 by aromaticfanatic]
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Fyndium
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[*] posted on 2-9-2020 at 11:14


I might consider distilling a small amount at first because I need it as a catalyst in mL quantity in a synthesis which I would not like to induce unnecessary impurities - and also to see how things run. I could run it with 250mL flasks outdoors and a short parth still to just merely push over the pre-concentrated acid to leave all the impurities behind. For vacuum, an aspirator eliminates the issues with pump corrosion. I was gonna heat the vacuum acid with paraffin wax bath, because it should boil at 170-180C and 200C bath will do just fine.

I've managed bumping very well in my recent tests. Activated carbon granules have basically eliminated bumping, and for vacuum I've used bleeder tube and gotta test the carbon as well. Prior to this, I actually did not do vacuum distillations because the bumping just prevented it. I also had serious bumping issues with sulfuric acid earlier when I concentrated it, but now I had totally zero bumps during the whole run, and I stripped off 3 liters of battery acid into concentrate.

For purchasing, I might just consider the 25L jug, just in case because in the future the supply chain may fluctuate. If I had the space, I'd just get a whole barrel of oleum, for the sake of it.
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