Douchermann
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Removing stubborn carbon from flask?
I used the method of paraffin and sulfur to generate hydrogen sulfide, so there is a lot of left over carbon stuck in my flask. I used a flask that I
don't exactly need, but I would like it back lol.
Does anyone have any ideas on how to remove this? Perhaps heating the bottom with a blow torch, while adding fresh air to it would oxidise it out, no?
I can only reach part of the bottom with a screw driver for manual removal, due to it's long and skinny neck.
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BromicAcid
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How is the carbon stuck in the flask? Is it in chunks? Physical methods of attack may be the best of this is the case. When I tried heating carbon
with sulfur to make CS<Sub>2</sub> I was left with a carbon mess in my flask. I heated it with all sorts of solvents to no effect and
some acids. Finally I took a pen and bent it and used it to scrape the inside walls and it broke off in pieces.
If that is not an option there are some things that eat elemental carbon such as hot Caro's Acid (Mixture of sulfuric acid and peroxide with both
reagents concentrated) but you probably already know how wicked that particular acid can be.
Strong nitric might have an effect on heating though to what extent is debateable. You could also try heating with KClO<sub>3</sub> until
it is molten and swirling it around though that is usually reserved for small spots since the reaction can run away. Or, going back to physical
methods, rock salt mixed with any solvent in which it is insoluble (ethanol, toluene, etc) can be swished around to try and polish the inside of the
glass (though this can scratch things up too) the process is much better with the flask on a rotovap.
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Douchermann
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It's in a suspension with the unreacted wax, however the amount of wax left in there is so trivial, I can't simply melt it and pour it out. I will
try hot caro's acid, or nitric acid and see what it does. Mechanical means are almost completely out of the question, it's a distilation flask with a
25-30cm long neck, about 3cm in diameter. Part of it cracked off, so it's unusable for its intended purpose, but it worked perfectly for this.
I'm wary about the KClO3, since there is quite a lot in there, but I will deffinitely try the other two proposed methods. Thanks!
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not_important
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edit - if it's in wax use a hot hydrocarbon solvent, xylene or paint thinner, to remove the wax. Do a couple of "extractions", fesh solvent each time,
then once with acetone to remove the solvent. After that:
The rock salt idea, although even a mush of salt and water would work, can be used to remove much of the looser carbon. Pour enough in to fill the
flask a bit more than half way, stopper it, turn in on its side and rotate it for some time. Making a jig so that it could be clamped to a rotisserie
drive, or some other slow rotating motor, would be ideal.
For what's left careful use of "piranha solution", strong sulfuric acid and hydrogen peroxide and painstakingly read documentation on this, can
be tried. Better than premixed piranha is put 50% H2SO4 in the flask and warming it, then adding H2O2 in small amount, a ml or so of 35%, swirling
it about, and adding another dose of H2O2 when bubbles stop might be better.
Another old method was to put a small amount of magnesium nitrate in the flask, heat it carefully until it melts, actually first forming a solution
from water of crystallisation, then keeping it hot while rotating the flask to reach all the interior, works. Keep adding another small amount of
magnesium nitrate after the first stops working, often becoming a grey coating on the interior, until all the carbon is gone, then use hot dilute HCl
to remove the magnesium salts.
Don't but too much of an oxidiser in at any one time, to avoid an overly energetic removal of carbon that could also remove the flask and bits of you.
Also don't heat the flask too hot, 500 C is about the limit; directly burning the carbon out is likely not too practical unless you're real careful.
[Edited on 24-2-2008 by not_important]
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Panache
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If it is purely carbon and hydrogen then flame is by far the best way, heat the area's of the flask where the carbon is deposited in a bunsen flame
(from the outside is fine), the carbon will combust into CO2 well before the glass begins to soften (i think around 550). You can tell it's working as
the carbon glows bright red momentarily.
Make sure you have rinsed it properly with distilled water first to remove as much minerisation as possible. If you are worried about over heating it
then take it home and put it on you stovetop flame, although this will take longer you run less of a risk of overheating it. If the flask has a very
small joint on it passing a stream of air into whilst heating it greatly quickens the process. If you do overheat it (you can tell because the glass
will begin to glow red as opposed to just the carbon on its surface), cooling it as slowly as possible is important, this can be achieved by cooling
it in the outer mantle of the bunsen flame before then cooling it further above the flame and finally in the ambient atmosphere.
That said if you're reasonably careful there's no chance you'll overheat it, its much safer than the chemical methods and cheaper!!
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StevenRS
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I have found that the best way to remove C deposits or hydrocarbons is a molten oxidizer. I have found that KNO3 is the best, as it does not react too
vigorously. Piranha Solution scares me, and direct heating never seems to work. Salt with a solvent also works well, but not for "gooey" things like
wax.
[Edited on 24-2-2008 by StevenRS]
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kmno4
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Small amounts of carbon (at the bottom and walls) can be removed with aid of warm chromate/dichromate/CrO3 + H2SO4 mixture. Time of cleaning strongly
depends on amount of C and temperature.Swirling of flask (with mixture) reduces time of removing.
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Panache
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Actually this may be a good place to ask i have long wondered how to tackle removing what can only be described as 'dirt/soil' from the inside of the
cooling water jackets of some condensers i have. I understand trial and error would always find something but as its such a hassle cleaning these
areas and its actually only makes for an aesthetic difference (well i guess there would be minor heat transfer losses) i never even bother.
But if someone has a wizz bang technique i'll give it a go. I imagine the deposit is silt or something of the like as it's very distinctly different
to the ordinarily rusty looking staining that is more common.
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StevenRS
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Try putting coarse rock salt in it with acetone or alcohol, and shaking it. I have found it works wonders on chemically inert deposits.
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Klute
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Using a base bath usually gets ride of the condenser stains. I use one for all my glassware in contact with dirty rxn mixtures:
Mix Nx100g NaOH/KOH with Nx120mL H2O, and add N liters of denaturated ETOH. STir for a few hours, add some water if need be to dissolve remaining
base. The solution will turn black after a while (denaturants reacting), but can be kept for very long periods. I use a solid 20L plastic tube, half
full of this solution, and leave the glassware soaking in there overnight. Next morning, transfert the glassware to a tube half full of water, and
rince with free water. The glassware usually comes out as new.
Don't leave glass frits or glass taps for more than a few hours, as the base can attack the frits. Some etching can accur if the glassware is left
in there for long periods of time.
Obviously, use thick, chemically-resistant adapted gloves, and full face protection when charging/uncharging glassware, and keep the bath closed
with a lid in a safe place. More EtOH needs to be added now and then as it evaporates. When the temp gets too cold, the alkali can crash out, making a
brown sludge, but that isn't problematic for the effectiveness.
It is better to get the glassware a clean as possible before, using acetone and some brush or sorts, as large amounts of organic waste can be harder
to get rid of. Anything remaining after such as wash can usually be removed with some aqua regia or pyranha.
Very effective in removing traces of silicon vacuum grease, and organic remains. The glass is usually uniformly "wetted" after rinsing, proof that
most of the contaminants are removed. Atw ork, we usually changes the baths every 6-10months or so, to avoid accumulation of metal salts and such, but
they can be kept much longer.
PS: multiple pyranha washes were effective in removing fine carbon particules from a glass frit, that remained even after prolonged soaking in aqua
regia. It takes time though.
[Edited on 27-2-2008 by Klute]
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