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Author: Subject: Problem boiling down sulfuric acid
NedsHead
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[*] posted on 9-3-2016 at 04:19


I once made that mistake to ave, towards the end of the distillation there would be long periods of calm in the boiling flask followed by an eruption of boiling and bumping that would shake the table, lucky for me my wife broke her favourite porcelain dish and the porous pieces are perfect as boiling chips
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Refinery
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[*] posted on 10-7-2020 at 12:53


Has anyone tested an ordinary bleeder tube with air pump to induce bubble stream into sulfuric acid?
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Fyndium
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[*] posted on 30-8-2020 at 07:04


FYI, I concentrated sulfuric acid today. I used a teaspoon of activated carbon granules as boiling stones and it worked flawlessly. I still need to concentrate the rest of them, and I consider vacuum distilling the acid itself to obtain higher concentration and purity. It would need approximately 180C with my vacuum pump, and it should do with paraffin wax bath at 200C. When concentrating sulfuric acid, I use bare propane gas heater because no reasonable heating bath is capable of providing enough heat and being inert for boiling sulfuric acid at the same time in case of cracking. Being not flammable, it is an exception in this matter for me.

I've introduced activated carbon into all distillations recently. I got a shot of acetone and styrene oxide from boiling flask when it bumped violently because apparently the reaction was too clean to introduce any nucleation. Bumping is not just absolutely detrimental to distillation, but also very dangerous, since spilling anything flammable is a call for disaster and it saved me from not getting a fire in my lab due to moving into using induction heater and calcium chloride baths and spillage of acetone was only a call for cleanup and ventilation until resume. After letting it cool down a little and adding - VERY carefully - even a few granules of carbon(it causes extreme frothing and it will easily foam over even bottoms from boiling flask even when introduced into a hot liquid, and into a boiling it will just cause it to basically blow up, so it must be done at room temp prior to heating, and even still gradually), it boiled absolutely flawlessly. Quarter of a teaspoon is very enough for 1 liter of liquid, since even few singular granules were capable of holding a smooth boil. Carbon has the benefit of being one of the most porous substance in existence, but still heavy enough to submerge in most forms of liquids we face in the lab for distillation, and of course, being inert for most stuff, exceptions being few. It may also has the very minor effect of absorbing coloured impurities in some instances, and if this effect is desirable, increasing the amount of granules is easy.

Not sure how it works at vacuum, but gonna test it out because I need a method to vacuum distill air sensitive stuff without bleeder tube and I do not have magstir that is sufficient at heating anything above micro scale. My bleeder was apparently blocked last time, but there was enough nucleation impurities to warrant a smooth boil anyways, so I see there is a chance carbon will do the job as well. I believe bleeder tube would work well with air pump at ntp as well in bump prevention.

[Edited on 30-8-2020 by Fyndium]
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Sulaiman
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[*] posted on 30-8-2020 at 07:34


Quote: Originally posted by hissingnoise  
I've ever only used pyrex jugs on a hotplate and have never seen acid being ejected - slight bumping, yes, but nothing to worry about.

I'm surprised that a Pyrex jug on a hotplate survived,
maybe the inside bottom is scratched a lot relative to a typical rbf, giving lots of nucleation points?




CAUTION : Hobby Chemist, not Professional or even Amateur
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KarelV
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[*] posted on 1-4-2021 at 16:21


Kyeliny sírové zkoncentrujeme destilací
až na 98,7%ní*) a pak ochladíme pod 0°. Co vypadne, jsou krystaly
H2S04, kdežto voda zbude v matečném podílu kapalném, jejž prostě
slijeme nebo odstranime v odstředivce.

Edit(woelen): Next time please in english instead of Czech.

Translation: Concentrate sulfuric acid up to 98.7% *) by distillation and then cooling down below 0 °. What falls out are crystals of H2SO4, while the water remains in the mother liquor, which simply can be drained or removed in a centrifuge.



[Edited on 2-4-21 by woelen]
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rockyit98
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[*] posted on 2-4-2021 at 07:07


Concentrating H2SO4 without distillation (with flask ans some PTFE )



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Aloesci
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[*] posted on 2-4-2021 at 17:35


OP also mentioned the problem of the Sulfuric Acid / SO3? fumes which start to come off well before coming close to 98%. When I went for the simple 'Boil away the water' approach, I was attempting to doing it outside with a cheap hotplate and 500ml beaker (least expensive option in case something went wrong).

I started with about 35% conc sulfuric and once the volume had reached just below half it's original, it started to fume slightly. I came back 5 minutes later (doorbell went or something) and the whole 5m radius surrounding the beaker was just a thick cloud of acid and death. I turned off the heat and carefully put a plank of wood over the beaker to stop the fumes before retreating because i was worried the neighbors would notice (i had full PPE). Afterwards the acid was still only about 87%.

Has anyone figured out a way to safely and easily scrub the vapors so the azeotrope can be reached without requiring a huge open space? Even if it results in substantial losses of acid?
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Fyndium
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[*] posted on 4-4-2021 at 13:09


Use a still. It will condense all the liquid coming over, effectively turning SO3 into H2SO4 with water and the little sulfuric acid that comes over with it. People have successfully done this. I still recommend the ebulliator with aquarium air pump to agitate the boiling liquid to prevent bumping.

Any fumes that come through receiver flask, can be led to water/base trap, for example simple inverted funnel to prevent suckback.

Chinese 1L flasks, erlenmeyers and others cost about 10$ apiece, so using those to boil it off risks only that amount of your capital. The stillhead and other parts will remain intact in case of flask failure.
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