Ludus
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Distilling Sulfuric Acid
Hello,
Some time ago I acquired a sizable amount of 90-93% sulfuric acid for very cheap; however, the downside is that, being drain cleaner, has dyes and
other junk in it. I have tried boiling it with H2O2 to some effect, although I’m still left with a slight yellow tinge. I shouldn’t worry about
it, but I’m one of those stubborn chemists who likes pure chemicals. I tried distilling a small amount (about 150mL) utilizing a sand bath and a
camp stove to try to prevent thermal shock. This process took about 4 hours of babysitting, but it worked, no more detritus. I want to do this again
although I’m scared to use other methods as I'd prefer not to have sulfuric acid spilling in my lab.
Maybe y’all could shed some light on your experiences or ideas.
Thanks,
-Lud
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draculic acid69
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If u found something that works well and isn't difficult stick with it.how much pure h2so4 do you need anyway? Most of what I use it for can be done
with it as it comes out of the bottle.only thing I'd need pure distilled h2so4 for is if I was making something I was going to ingest.like foodgrade
sodium sulfate
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woelen
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Sulfuric acid has a very high boiling point and in my opinion is at the border of what can be done with glass. I would not feel very comfortable
distilling sulfuric acid as it requires 300+ C temperatures.
I would distill a small amount, e.g. 250 ml and only use that for critical experiments, such as doing experiments with transition metal complexes or
for preparation of pure metal sulfates. For many other types of reactions (e.g. as catalyst for esterification reactions, for nitrating things, for
making HNO3) the other type of acid is perfectly fine. E.g. when you make HNO3, then the dyes and other crap remain behind and/or are destroyed and
only HNO3 distills over.
Your method of distilling sounds very reasonable and indeed I would stick with that method if it works for you and take the 4 hour babysitting for
granted. You won't need to do that very often. Take a good book, install yourself and make your chemistry hobby a relaxing one 
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draculic acid69
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Yeah like women said unless purity is critical I would not bother as your pushing the limits of the glass and if it does break imagine having to deal
with the boiling sulfuric fumes and the destruction of a spill.if u have a few litres of something and need it all pure I'd just do it as needed.
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Ludus
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So far most of my uses for H2SO4 don't require it to be pure, the drain cleaner stuff works just fine. I guess I'll find a day to set aside time
distill some so I wont have to do it again.
Relatively speaking I'm pretty new to amateur chemistry, and I have to take the waiting in stride.
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macckone
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Commercially pure 98% sulfuric acid is made by combining fuming sulfuric acid with distilled water obviously adding fuming to water. 30% Fuming
sulfuric (30% oleum) is made by adding up to 30% sulfur trioxide to 98% sulfuric acid. Higher percentage fuming is made by adding more sulfur trioxide
to 30% oleum.
One trick for a home chemist is placing distilled water and fuming in a drying or vaccum chamber and allowing the fuming to slowly absorb the water.
This can be done with sulfur trioxide which has a much lower boiling point but is extremely dangerous to work with. For a home chemist seeking very
high purity sulphuric acid, this is probably easier than distilling.
See this thread for making sulfur trioxide:
http://www.sciencemadness.org/talk/viewthread.php?tid=10217
[Edited on 4-3-2020 by macckone]
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Vosoryx
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I find that distilling sulphuric in a heating mantle under vacuum is easy, however it does take quite some time. Alternatively, you can purchase
quartz flasks that can take open flame.
"Open your mind son, before someone opens it for you." - Dr. Walter Bishop
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XeonTheMGPony
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I've don this a lot in my normal flasks after testing it.
I add to a 1L flask 500ml of H2SO4, a small amount of broken lab glass chips, 10ml of 35% peroxide.
Place this in a heating mantle and warm till the peroxide reaction kicks off and allow to react.
then standard simple distillation with joints sealed with H2SO4
Just have preparations if some thing does go wrong, so far I have don over 6+ L with out issue but I all ways monitor it and prepared for disaster.
[Edited on 8-3-2020 by XeonTheMGPony]
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Mush
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Quote: Originally posted by Vosoryx  | | I find that distilling sulphuric in a heating mantle under vacuum is easy, however it does take quite some time. Alternatively, you can purchase
quartz flasks that can take open flame. |
I just wanted to recommend the same.
Use vacuum or quarz flask.
If one needs analytical grade h2so4 recommended purification is distil. after h2o2 was added from a quartz distil. flask.
https://pubs.acs.org/doi/pdf/10.1021/ac60320a016
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ManyInterests
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I plan on purifying and distilling/boiling sulfuric acid. I realize that I don't need too distill/boil all my drain cleaner grade sulfuric acid, but I
would like to have some on the ready for experiments.
I have a question on storage though. My bottles of drain cleaner are not close to being empty (yet), but I do have lots of empty glass liquor bottles,
some thicker than others.
Is it safe to store 98% sulfuric acid and 68% to 90+% nitric acid in simple glass bottles? I know this is probably a yes, but I want to make 200% sure
of this before I do anything. I'm still fairly new and I am aware of how dangerous these chemicals can be.
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XeonTheMGPony
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For Acids like that you're best off getting a couple proper reagent bottles from eBay, H2SO4 behaves like an oil, and with out proper bottle very hard
to get a good clean pour that is easy to clean after using.
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Keras
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| Quote: Originally posted by ManyInterests | | Is it safe to store 98% sulfuric acid and 68% to 90+% nitric acid in simple glass bottles? I know this is probably a yes, but I want to make 200% sure
of this before I do anything. I'm still fairly new and I am aware of how dangerous these chemicals can be. |
98% sulphuric acid can be stored in a standard PET container. That’s what I get (or rather got, now that it’s officially forbidden to trade it
inside the EU), and in over 2 years I had no problem with it. The vapour pressure of H₂SO₄ is about nil at r.t. and it won’t eat away at
plastic, so you’re definitely safe.
Same goes for azeotropic nitric acid. I've got a bottle full of it, never touched it in 4 years, and it’s still pristine.
Fuming nitric acid, however, is another kettle of fish. It must be stored in a glass bottle with a teflon lid. I have a couple of tens of millilitres
of it that I stored in a Duran 100 ml bottle properly stoppered (teflon sealed lid), and last time I checked it had begun to discolour the teflon
seal. It will probably attack and eat everything that is not glass/teflon made, because it is a very strong oxidiser, so beware to store it in a well
ventilated area and away from any other reactant.
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Oxy
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| Quote: Originally posted by Keras |
Fuming nitric acid, however, is another kettle of fish. It must be stored in a glass bottle with a teflon lid. |
I kept mine for a short time in glass bottle with blue PP cap and just after one day after distilling it I saw that the cap is discoloured. There is
also another thing, pressure build up which is caused by acid decomposition. It have to vented from time to time.
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Keras
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| Quote: Originally posted by Oxy | | I kept mine for a short time in glass bottle with blue PP cap and just after one day after distilling it I saw that the cap is discoloured. There is
also another thing, pressure build up which is caused by acid decomposition. It have to vented from time to time. |
I’m not surprised. You need a red cap with inner teflon joint to keep it secure. I never noticed any noticeable pressure build-up inside my vial,
though every so often we I open it there’s a small 'pscht' sound which indicates a small overpressure, but it’s never more than a fizz.
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rockyit98
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Use HDPE and if only impurities are organic refluxing will oxidize organic additives to CO2 and water no distillation needed.
"A mind is a terrible thing to lose"-Meisner
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zed
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You're new to this? Use the impure Sulfuric acid that you have, to manufacture other acids.
Want some reagent grade Sulfuric acid? Just buy a little bit.
Distilling Sulfuric Acid is perilous.
Yeah. It can be done.
Would I do it? No! Not unless I really had to.
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LeLaborantin
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Hello,
I have already distilled sulphuric acid. (Quite a few times)
If you want to do it there are several rules to respect:
-Use the smallest flask possible. And never try to distil everything.
Indeed, if you do, each drop that falls back into the glassware during distillation will generate a quantity of sulphuric acid under pressure. And
it's not nice at all when it reaches the receiver. (Ultra corrosive white cloud that makes paper disappear in less than a second)
-Use as little glassware as possible and with as little rough angle as possible. Always with the idea that the acid does not return to the starting
flask. (If possible a 75° distillation head in one piece)
-Lubricate the joints with sulphuric acid and do not be afraid to use it. Lock the joints with metal fasteners.
-Leave the receiver balloon free.
So do not push it into the glassware connected to the condenser. Because there will be pressure and you don't want the receiving flask to explode.)
-Use a long air condenser or in the worst case a Liebig condenser but never with water circulating in it. (It would start boiling)
-Have a very good heating mantle.
If your heating system is not strong enough and especially with sulphuric acid to unclog the toilet (black). You risk getting sulphur dioxide! And
that is very very very unpleasant. My balloon heater goes up to 450°C and that's what it takes to get the 337°C boiling point of 98% sulphuric acid.
(You won't get the 100% from the azeotrope)
One more thing. Respect the sulphuric acid you are distilling. Otherwise it will kill you.
I put a leather apron over my lab coat. Goggles, a helmet with a visor and very thick gloves (Not the simple lab gloves. Because boiling acid digests
them easily)
Sorry for my English, I am Belgian.
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Tsjerk
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Wouldn't it be safer to just stay away from the distillation while hot, instead of making yourself unable to properly move and then manipulate it?
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LeLaborantin
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| Quote: Originally posted by Tsjerk | | Wouldn't it be safer to just stay away from the distillation while hot, instead of making yourself unable to properly move and then manipulate it?
|
At the beginning of the distillation process, the concentration of the sulphuric acid is not at its maximum.
So at some point you will have to get close to the apparatus.
But I certainly stay as far away as possible the rest of the time.
You have to be ready to react in case something goes wrong. And so be dressed accordingly. Moreover, being well protected reminds you that you are
playing with a highly dangerous product.
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macckone
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Boiling off the water in a beaker will lose some acid but is safer. You can get 93% to 98%.
Then if necessary, distill. It reduces water dripping into hot sulfuric.
A couple of other tips:
use fiberglass pipe wrap to keep the still head hot which reduces dripback.
I have silica glassware specifically for high temp distillations. Worth the money.
Set up a catch basin below the apparatus with sand and sodium carbonate.
This will absorb and neutralize the acid and cool it down to a reasonable temperature.
Allow plenty of expansion room and don't let the flask get too low.
You can wrap joints with fiberglass wood stove seals as well as metal keck clips.
In my setup, I use a water condenser after the air condenser and use the fiberglass rope
To seal the joint between the borosilicate and the silica.
Test run with ethylene glycol first. Mineral oil is also a good test best leaves gunk that is hard to clean.
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SWIM
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If you're worried about the power of your mantle keep an eye out for glas-col STS and STR series mantles.
They are a bit more expensive, but still not too bad to buy used, and have higher wattage than the standard mantles.
They also have a special high temperature cloth on the inside and are rated for somewhere around 600C.
This may even be overkill for sulfuric acid, but they'd sure be a godsend if you want to make your own pyrophosphoric acid to dehydrate sulfuric acid
to SO3.
Yukangquartzglass_5 on ebay used to have 24/40 jointed quartz distilling flasks (500 ml), for like 120 USD.
They don't have any listed right now, but it says they make custom quartzware on request so they'd probably be happy to make more.
A few people on here have bought those and reported good results.
I think JJay was one.
[Edited on 18-7-2021 by SWIM]
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Fyndium
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When using ground jointed qz with boro glassware, should any precautions be taken considering thermal expansion on joint? For sulfuric acid, using
sulfuric acid itself as joint lubricant was preferred somewhere.
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