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jackchem2001
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I have not done this hazardous procedure so these are just my speculations on some of the posts in this thread:
I do not think that using a quartz boiler and having the rest of the setup be borosillicate is advisable - the difference in thermal shock resistances
of these glasses is due to the different coefficients of thermal expansion. I think it would be dangerous to have a male borosillicate joint inserted
into a female quartz joint at high temperature.
I don't think teflon stir bars/tape is advisable either. The operating temperature of teflon is 260 degrees, and its decomposition occurs around 350
degrees. I think ordinary stir bars would also demagnetize at the high temperature.
As for clips, I have found plastic clips to be a bit useless in general and they only have an operating temperature of around 140 degrees. I would use
metal. They will survive just fine in a well designed setup. Sulfuric acid is a perfectly sufficient joint grease and will probably wick its way into
the joints during the distillation.
Finally, if you plan to use foil to create an air bath around the flask, be absolutely certain to avoid direct foil-glass contact. I had a flask crack
like this during cooling - https://www.sciencemadness.org/whisper/viewthread.php?tid=61...
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macckone
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It seems most have not done this procedure.
I use a 1L quartz RBF with a quartz air condenser (one piece L type 75 degree).
I had the condenser custom made so it wasn't cheap.
If you mix borosilicate and quartz you need to be careful of the differing expansion rates.
I use steel keck clips. No sealant as there is only one joint with sulfuric acid vapor.
Teflon tape can become glue at these temperatures but the joint can be cooler than the vapor so mileage may vary.
Instead of a stir bar, use a piece of steel wire sealed in a glass tube.
You can magnetize it if you want. But most hot plate stirrers don't go hot enough.
Too many boiling chips act as an insulator. loose glass thread can work. I use regular glass chips but not a lot. My setup doesn't accommodate it
but an air bubbler would be ideal.
Expect bumping. Plan for it. Mixing a sodium carbonate with the sand and then a top layer of just sand in a steel pan helps prevent disasters. To
understand why sulfuric acid bumps so badly, the temperature that 96% sulfuric acid boils at is higher than 98% due to boiling point elevation and the
surface loses water faster than the bottom. So you have a layer of higher boiling liquid under a layer of lower boiling liquid just like oil and
water only the layers in this case can mix if stirred.
One trick to avoid full scale boiling of sulfuric acid is to use a beaker with a fiberglass sheet over it. This won't remove metal contaminants
(usually not relevant for many reactions) but organics will be removed. Heating it to 200C and bubbling air through it will destroy any organics that
don't boil off. water will come off above 290C but it is slow. Think evaporation rather than boiling.
The primary reason to purify sulfuric acid by distillation is to remove iron and lead contaminants. Those tend to occur due to process equipment.
Removing organics is easier, see above. Removing the water doesn't require distillation. It comes off before the sulfuric acid via evaporation. You
have to get it much hotter to boil off acid water mix, see above about bumping.
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ManyInterests
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Personally I have never distilled sulfuric acid and I never will. My setup for boiling has worked to produce very pure and (close) around 95-98%
concentration all the time. I put everything on my balcony and close the door (the power lines are controlled from inside my apartment, and the door
to my balcony is an excellent shield).
For bumping it was always hard to control, even with large quantities of boiling chips, but it hasn't destroyed my mantle yet. Maybe as others have
said that that too much boiling chips aren't necessarily better. As for VEVOR brand distillation equipment, is it available on amazon? Does it say
that it is a lab supply store? I do believe it is what they say it is, almost all my glassware is from Chinese lab supply and despite what you might
hear, they are top notch quality and I trust them fully. Vevor is much more expensive then them and I think if their boiling flasks and distillation
setups aren't up to the task then something has gone terribly wrong.
Those are my two cents.
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metalresearcher
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What I miss in this topic is that why TO does not use and nobody suggests an electric heating mantle instead of a Bunsen open flame. That is much
safer, temperature better to control. Amazon has enough such devices for a reasonable price.
https://www.amazon.com/s?k=mantle%2Bheater%2Blab&crid=1S...
Anyways, do it outdoors and use gloves and a face shield.
[Edited on 2024-8-25 by metalresearcher]
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jackchem2001
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Quote: Originally posted by metalresearcher  | What I miss in this topic is that why TO does not use and nobody suggests an electric heating mantle instead of a Bunsen open flame. That is much
safer, temperature better to control. Amazon has enough such devices for a reasonable price.
[Edited on 2024-8-25 by metalresearcher] |
That would certainly be safer, but do they get hot enough? You need to go a bit above the b.p so probably 350+ degrees. Is it bad for the mantle to be
at that temperature for a long time as well?
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metalresearcher
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| Quote: Originally posted by jackchem2001 | | Quote: Originally posted by metalresearcher | What I miss in this topic is that why TO does not use and nobody suggests an electric heating mantle instead of a Bunsen open flame. That is much
safer, temperature better to control. Amazon has enough such devices for a reasonable price.
[Edited on 2024-8-25 by metalresearcher] |
That would certainly be safer, but do they get hot enough? You need to go a bit above the b.p so probably 350+ degrees. Is it bad for the mantle to be
at that temperature for a long time as well? |
These Amazon samples are elivgible to 450 C and probably other labware suppliers do sell them. So not an issue for distilling H2SO4.
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