Sciencemadness Discussion Board

Using a vacuum filtration flask in vacuum distillation?

KoiosPhoebus - 22-6-2023 at 09:30

Hi everyone, I have a question about the use of Erlenmeyer flasks in vacuum distillation where heating is involved.

Specifically, I'm referring to heavy-wall Erlenmeyer flasks designed for use in vacuum filtration. I've been told in the past that Erlenmeyer flasks should not be heated; however I noticed in this video (https://www.youtube.com/watch?v=eSIIp4Hnr6U) that NurdRage was able to both heat and pull a vacuum on the flask used. Would a flask designed for use in vacuum filtration be able to perform the same role? And would anyone happen to know whether thicker walls would make it less likely to implode or would it simply increase the risk of heat-induced implosion?

The reason I ask is because I have a hotplate which I could use for vacuum distillation, but I don't have a heating mantle. As far as I can tell, a heating mantle would be more expensive than the full vacuum distillation glassware set and it would be way cheaper if I could use conical vacuum filtration flasks in the setup.

Thanks in advance for any suggestions!

Sulaiman - 22-6-2023 at 15:59

I would not risk heating a filter flask under vacuum on a hotplate.

Most 'distillation kit' offerings have two RBFs
so I suggest an rbf in an oil bath.
(cooking oil in a metal cooking pot)

Below 100oC you could use a water bath instead of oil
- but I don't like condensing water vapour everywhere.
Above 200oC you would need a sand bath
- but thermal conductivity is poor so you may overheat your hotplate.
A transparent glass pot for the heating bath allows you to see more clearly
and maybe more easily allows the use of a stirbar
- but it adds the risk of dumping hot oil (water, sand) on your hotplate, and beyond.

PS although one clamp and stand is do-able, I suggest two stands and clamps.
Although stands and clamps are not cheap,
they are very useful for MANY purposes in chemistry
and general use as a third hand for all kinds of purposes.

Clamps and boss heads are not easy to diy
but I wish I'd diy'd my stands... taller, safer, cheaper.

[Edited on 23-6-2023 by Sulaiman]

Sir_Gawain - 22-6-2023 at 18:00

Or you could use a flat bottom flask like this. It would probably be stronger than an erlenmeyer flask. Other than that, your best bet is an oil bath.

KoiosPhoebus - 22-6-2023 at 23:36

Thanks for the info! Wouldn't a flat bottom flask experience the same issue as conical flasks, in that heating would be uneven?

Additionally, should I look for a heavier wall flask for heated vacuum distillation? I've been told that thicker walls mean greater risk of heat-induced cracks (due to uneven expansion) but thinner walls run a greater risk of vacuum implosion. Would anyone be able to advise on the optimal wall thickness of heated vacuum distillation? Thanks for everyone's help!

Dr.Bob - 29-6-2023 at 09:39

Thicker flask walls make the flask stronger, but much more prone to breakage from quick heating and cooling, as the glass does not evenly heat. Thick walled flasks are ideal for oil baths and heating mantles with gentle, slow heat. Thinner walled flasks are better for uneven heating. Erlenmeyers and flat bottom flasks are not great for heating under vacuum, as the edges and corners make them weaker. Filter flasks are thick to be able to withstand vacuum, but the thickness makes them much less safe under heat and vacuum. I would use a standard thickness (eg, Pyrex brand or Kimble brand) round bottom flask for most heating under vacuum work, as they are thick enough to withstand a vacuum, but not as thick as Chemglass and some other thick-walled brands.

Lionel Spanner - 5-7-2023 at 14:46

If vacuum distillation is something you're planning to do frequently, a heating mantle is definitely a worthwhile investment, as it's more efficient than either a water or oil bath.

I got a mantle with a stirrer (very handy for vacuum distillation) for £100 from a Chinese supplier, and it's proved to be a lot more robust than the £40 second-hand ones from UK-based ebay suppliers, which both developed electrical shorts after a few uses and blew the fuses in their plugs.

KoiosPhoebus - 9-7-2023 at 23:34

Quote: Originally posted by Dr.Bob  
Thicker flask walls make the flask stronger, but much more prone to breakage from quick heating and cooling, as the glass does not evenly heat. Thick walled flasks are ideal for oil baths and heating mantles with gentle, slow heat. Thinner walled flasks are better for uneven heating. Erlenmeyers and flat bottom flasks are not great for heating under vacuum, as the edges and corners make them weaker. Filter flasks are thick to be able to withstand vacuum, but the thickness makes them much less safe under heat and vacuum. I would use a standard thickness (eg, Pyrex brand or Kimble brand) round bottom flask for most heating under vacuum work, as they are thick enough to withstand a vacuum, but not as thick as Chemglass and some other thick-walled brands.


Thanks for the info!
Quote: Originally posted by Lionel Spanner  
If vacuum distillation is something you're planning to do frequently, a heating mantle is definitely a worthwhile investment, as it's more efficient than either a water or oil bath.

I got a mantle with a stirrer (very handy for vacuum distillation) for £100 from a Chinese supplier, and it's proved to be a lot more robust than the £40 second-hand ones from UK-based ebay suppliers, which both developed electrical shorts after a few uses and blew the fuses in their plugs.


Yeah, after reading everyone's contributions on the thread, I bought myself a new heating mantle on discount. Frustratingly, my hotplate/stirrer has now gone and broken down, so I'm in the market for a new hotplate/stirrer. If anyone in Australia knows where to find a reasonably-priced hotplate/stirrer do let me know!

greenlight - 10-7-2023 at 01:36

If your looking reasonably priced there is plenty of cheap chinese models on ebay but these can be prone to problems.

Australia sells IEC hotplate stirrers and they do cost upwards of $500 dollars new but they often pop up on ebay in aus for around $200 second hand.
I have one that still works fine after more than 10 years of use so dont let the second hand bit worry you. They are great plates, really reliable and well worth the money if you have the patience for one to pop up.

IKA is another expensive, reliable brand that can be found much cheaper second hand online too if you search.




[Edited on 10-7-2023 by greenlight]

Texium - 10-7-2023 at 05:45

Quote: Originally posted by greenlight  
IKA is another expensive, reliable brand that can be found much cheaper second hand online too if you search.
I wouldn’t consider IKA to be reliable. Their devices generally seem a bit too delicate for use in a typical chemistry lab, and every one I’ve encountered has been at least slightly broken (usually impossible to repair electrical issues). I greatly prefer simpler, more robust designs with fewer points of failure. The ThermoFisher Cimarec+ series are my favorite when it comes to fancy hot plate stirrers.

greenlight - 11-7-2023 at 18:27

Quote: Originally posted by Texium  
I wouldn’t consider IKA to be reliable. Their devices generally seem a bit too delicate for use in a typical chemistry lab, and every one I’ve encountered has been at least slightly broken (usually impossible to repair electrical issues). I greatly prefer simpler, more robust designs with fewer points of failure. The ThermoFisher Cimarec+ series are my favorite when it comes to fancy hot plate stirrers.


Wow I did not know that the IKA plates had problems, especially for their high price.
I have an IKA overhead stirrer and I haven't had any issues yet but it doesn't get used often though to say the least and there's no heating plate involved.

Ooh yes the thermofishers are nice indeed. I have a favourite fancy one too, the corning pc hotplate stirrers. I have a pc420d digital that mostly stays in the box often too because it's too nice to use almost.


B(a)P - 11-7-2023 at 19:29

Quote: Originally posted by KoiosPhoebus  
If anyone in Australia knows where to find a reasonably-priced hotplate/stirrer do let me know![/size][/font]


You could try Tech Trader
They often have reasonably priced second hand units. They also have auctions on grays online every 3 to 6 months, where you would likely get a very good deal. Their new hotplate stirers are no cheaper than any other laboratory supply company in Australia.