Hi I have a question regarding Cleaning H2SO4 with H2O2
I don't require a solution of H2SO4 over 90% so i wasn't going to finish by "evaporating off the water in open air" as suggested by numerous sources,
however I am worried about storing my H2SO4 before all the H2O2 has degraded/reacted, it appears after 24 hours stirring at room temperature that
bubbling has ceased although this could this simply be because there are no organics left in my now clear drain cleaner...
Is its safe to evaporate H2O using a regular distillation setup as opposed to open air? this should ensure that there is no piranha solution left in
my sulphuric acid correct?
also how safe is a complete distillation of sulphuric under vacuum? I have done the reading, but i lack the real world experience on this so... safety
first.
Thanks in advance.clearly_not_atara - 6-6-2018 at 18:40
IIRC H2O2 is stabilized by oxoacids, so it may have a much longer halflife as a dilute sol'n in vitriol. Not sure how to boil it safely although
venting H2O2 is little concern as its atmospheric halflife is very low.DoctorPhilosophy - 7-6-2018 at 05:19
First test for peroxide or persulfate presence, then say something. No need for doubt.zed - 7-6-2018 at 14:41
Well, Sulfuric acid, under high vacuum, may be distilled at ~100 C.
Still, it is HOT Boiling Sulfuric Acid. Albeit, not at its usual Super-Hot boiling point.
It is still plenty dangerous, if something goes wrong.
There are some good demonstrations on Youtube, I'll try to find one and attach it.
Fortunately, for many purposes, it appears that plumbing type H2SO4, needn't be purified.
Folks often use it as-is, to generate HCl, or Nitric Acid.
O.K., I checked. The "Vacuum Distillation of H2SO4" video, is no longer present on YouTube. Regrets.
[Edited on 7-6-2018 by zed]Assured Fish - 7-6-2018 at 22:07
Caros acid e.g. H2SO5 decomposes at temperatures above 55*C, i do not recall where i read this but i have made more than enough sulfuric acid before
and heating the caros solution up to around that temperature does in fact tend to increase the rate of oxygen being expelled from the solution.
I dont see why simply heating up your acid to around 100*C is such a problem, while i wouldn't advise it, i have heated up H2SO4/peroxide mixtures
indoors in a poorly ventilated area to well above 200*C before with little issues.
As for vacuum distillation of sulfuric acid, im pretty sure a few people have tried it and failed.
The major issue being a good source of vacuum, without some serious gas scrubbing, using a vacuum pump would likely lead to the destruction of the
pump and an aspirator would only likely be able to pull the BP of the acid down to maybe 250*C tops.
So my advice, either heat up your acid to 150*C to destroy any peroxides or distill it to purity. Aqua-regia - 8-6-2018 at 04:06
Purification with H2O2 is a bad way. A considerable part of impurities staying in oxidised form. Buy a cheap water vacuum pump like this.
If you have enough cold tap water (in winter is okay) you can do it. Use a vacuum distilling apparatur with air condenser, not water cooled one!
Magnetical stirring + electric heating mantle is advisable . If you dont have a chemical cabine do it in outside far from people in the yard.
XeonTheMGPony - 8-6-2018 at 04:06
I use peroxide often as a pre-cleaning stage, I then heat it with a rectifier column and let it boil the water off to atmosphere (Well vented to
remove the ozone (By product as the O2 off gassing, I have noticed how ever ozone tends to be a potent product )
Once the top of the rectifier begins to go well above 100c I terminate that phase and reset for simple distillation.
I have found this method offered the smoothest distillations, in the end you will be left with a pile of clear cubic crystals in the bottom! I filter
these off mechanically with glass frit, then store the tails for reactions where I want very concentrated acid that doesn't need to be pure (Now I'll
be making SO3 with it)12thealchemist - 8-6-2018 at 05:03
NurdRage did post a video where he mentioned at the end that he had attempted vacuum distillation of sulphuric acid, but to no avail. I believe his
distillation attempts suffered from too much foaming to be viable. However, he was attempting distillation of the raw untreated acid, which is a
little different to what was discussed here, as I understand it. It's probably worth bearing this in mind; it would appear one cannot short-cut to
vacuum distillation without first going through some form of purification. zed - 9-6-2018 at 11:54
Ummm. If you can acquire this product, it is of a better quality.
Battery electrolyte H2SO4 might exceed "Reagent Grade" in purity.
Only 30% H2SO4, but only needs evaporation/concentration, to become the good stuff.
Problem is, Home Depot is dicking around; no store within a hundred miles of me, has any in stock. Gotta order it.aga - 9-6-2018 at 13:23
In actual practice, just boil the acid until it starts to fume.
Add 3% H2O2 and stir if there is any colour.
All very dangerous to do, yet yields conc sulphuric.
The "acid-to-water" myth doesn't apply in my experience - it didn't explode or even spatter the few times i did this.
If "safety first." is a primary concern, do not attempt to make it - buy it instead, and deal with the impurities later. TheVoid - 9-6-2018 at 18:30
The acid I acquired was about $50 for 30 liters from a retired plumber. I could buy it new for 35 per 5liters. However this old acid was very black.
So before moving it to new glass bottles I decided to clean it.
I used 35% peroxide the first batch I stirred in a heating mantle during addition, the cleanup occurred very quickly but the temp rose to 80c and was
a bit nerve racking.
The second batch I stirred on a hotplate ir took 3 days but was not the least bit scary or bubbly and I used much less h202 as it didn't decompose as
fast.
I think given the information you guys provided that I will distill off water using simple distillation long condenser, the only thing i was worried
about was water vapour dripping back into the hot acid during distillation and assumed this was why it was recommended to dry in open air, however on
you tube people distil H2SO4 to 98% using a simple setup...
i will hold temp at 55c for an hour to help decompose the remaining H2O2
If it does not stay clear I will distill under vacuum using flask only 1/4 full
Pretty sure all organics that were oxidized became h20 and Co2.
Thanks for the input.
[Edited on 10-6-2018 by TheVoid]TheVoid - 9-6-2018 at 18:49
Might create a marquis reagent to test it outLearnedAmateur - 10-6-2018 at 02:08
The "acid-to-water" myth doesn't apply in my experience - it didn't explode or even spatter the few times i did this.
It’s not so much a myth but a general lab guideline due to the dehydrating properties of H2SO4 and the subsequent exothermic dissolution. I’ve
added water to 96% acid (only to make a <50mL solution with 10mL acid) and if done quickly it will generate steam bubbles and make a roaring sound
as the water begins to boil. Probably won’t splatter/explode unless you dump a few hundred mils + of water into the same amount of acid, but
regardless it will easily reach 90 degrees C and the vessel will of course be far too hot to touch.
