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Author: Subject: Concentrating nitric acid using sulfuric acid
LardmanAttack
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[*] posted on 16-1-2020 at 01:50
Concentrating nitric acid using sulfuric acid


I eventually need WFNA for the nitration of hexamine, and have been wondering about the logistics of doing so. I heard that you can concentrate acids by combining with sulfuric to dehydrate it, then distilling. How well would this work?

[Edited on 16-1-2020 by LardmanAttack]
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LardmanAttack
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[*] posted on 16-1-2020 at 01:59


Preferably, I'd want to concentrate the nitric acid to over 99% so it can perform well in the nitration.
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XeonTheMGPony
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[*] posted on 16-1-2020 at 04:39


it works fine but you lose a fair bit due to retention in the acid, especialy if you do not have vacuum ability.

If you got H2SO4, I'd recommend checking out some stump remover and seeing if you can get KNO3 and directly make the fuming Nitric by drying the nitrate salt then doing the usual reaction to liberate the nitric acid.

Alternatively you can check the various cold packs out there to find a nitrate one is possible, then purify, dry, then use that.

By purify, they poison the nitrate ones with calcium nitrate to prevent then from being used directly as an explosive, I dissolve in ammonia water then filter off the calcium hydroxide then evaporate to dryness, bake at a further 150c for an hour, then use that to make my Nitric acid.

If you plan to do allot with high test Nitric acid I would strongly recommend getting a vacuum source, it improves recovery with less decomposition.

the rest is down to procedure.
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greenlight
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[*] posted on 16-1-2020 at 10:20


I have a large amount of 62% nitric acid so using sulphuric acid is my preferred method to high conc. HNO3. I usually use a 1:2 ratio of nitric acid to concentrated sulphuric acid which after distillation results in yellow 90%+ concentration HNO3.

I recommend a vacuum source for a second distillation as you can obtain water white 99% nitric acid with it. I use a sodium hydroxide filled washing bottle between the receiver flask outlet and the vacuum pump to avoid destroying the internals on it. Under vacuum the acid pretty much just jumps straight over into the receiver no problem.

I am guessing your are making RDX from the hexamine which is what I used my WFNA for too. I advise making hexamine dinitrate first off with azeotropic nitric and then drying and nitrating that with the WFNA to obtain your desired product. Having two NO3 groups on there before hitting it with the WFNA helps alot and should improve the yield you would get compared to just nitrating straight hexamine with WFNA.



[Edited on 16-1-2020 by greenlight]




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Fulmen
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[*] posted on 16-1-2020 at 11:30


IIRC the optimum ratio (62% HNO3 / 98% H2SO4) is 1:1 v/v. Reducing the sulfuric acid too much would reduce the final concentration, and I vaguely remember something about reduced yields if too much is used.



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Justin Blaise
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[*] posted on 18-1-2020 at 09:18


I've never been successful at making WFNA in this way. I always got a lot of nitrogen oxides in the concentrated acid. I don't know if vacuum is strictly necessary for avoiding RFNA, but I imagine it helps immensely.
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greenlight
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[*] posted on 18-1-2020 at 13:03


The nitrogen oxides are from decomposition of the acid at its boiling point when distilling it I believe.
Under reduced pressure there is no decomposition so it does help alot and results in nice water white fuming acid.




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LardmanAttack
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[*] posted on 18-1-2020 at 13:31


Alright, thanks for the advice. I suppose I could try getting a vacuum distillation setup ready using an aspirator pump I have lying around. I think I might just distill drain cleaner acid to 98% and then use that with a dry nitrate salt. Otherwise id have to be trying to concentrate my nitric with just 90% sulfuric, which I doubt would work very well.
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XeonTheMGPony
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[*] posted on 18-1-2020 at 18:27


Quote: Originally posted by Justin Blaise  
I've never been successful at making WFNA in this way. I always got a lot of nitrogen oxides in the concentrated acid. I don't know if vacuum is strictly necessary for avoiding RFNA, but I imagine it helps immensely.


You're pushing it too hard then.

I add the nitrate salt and the H2SO4 then gently warm till it all dissolves then I hold it there with just enough heat to barely get it to reflux.

Then I allow to cool, pull vacuum then very gently heat till it starts to come over and that's where I leave it, slow but gives crystal clear acid.
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Fulmen
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[*] posted on 19-1-2020 at 08:40


"trying to concentrate my nitric with just 90% sulfuric, which I doubt would work very well"

It should work fine with some adjustments. Some quick calculations suggest that equal volumes 98 & 65% should produce a spent sulfuric acid of roughly 77%. Using 3 parts (by volume) 90% sulfuric acid and 2 parts nitric should give the same final concentration.




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artemov
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[*] posted on 20-1-2020 at 02:08


Not sure if this is useful. Magnesium nitrate works too!

Attachment: Nitric Acid Concentration.pdf (969kB)
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Fulmen
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[*] posted on 21-1-2020 at 04:43


I don't think magnesium nitrate has any real benefits compared to sulfuric acid. From what I could find it uses a 60-68% solution, this gives a very poor "volumetric efficiency". It might be less corrosive than sulfuric acid, but for a laboratory setup you're pretty much stuck with glass anyways.



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