Concentrating HNO3 - Archive File

[megalomania]

Tony Montana
Frequent Poster
Posts: 145
From: Australia
Registered: JUN 2001
posted 07-13-2001 09:58 PM
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I know this topic is covered a fair bit, because I have just been reading olpd posts. But I dreamed of having 70% HNO3 and wanted to concentrate it. The way I am pretty much going to go about it is:
Pouring 100ml HNO3 70% into a flask, then pouring 200ml H2SO4 98% into the same flask. Then Basically condensing the HNO3/H2SO4 with no vacuum, at a temperature of 80*-90*C hopefully collecting HNO3 90%-100% in the collecting flask? And dilute H2SO4 in the distilling chamber?
Does anyone know how successful this method will be?


mongo blongo
Frequent Poster
Posts: 175
From: I live in a Creosote Bush!
Registered: JUN 2001
posted 07-13-2001 10:48 PM
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Im with u until the "diluting the h2so4" ?
As far as i know to concentrate your HNO3,
well yes that's how evrybody does it as far as i know!
I would try to use a vacum pump to avoid nitric dioxides, Usally it is prefered that your HNO3 is white for most stuff (EG.RDX)
Watch those temps!
too much heat will decompose your HNO3!


John456
Frequent Poster
Posts: 105
From:
Registered: MAR 2001
posted 07-13-2001 11:50 PM
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HNO3 ive distilled from 1 part H2SO4 and one part 70% or so HNO3 has only been around 85% or so. Ive found that adding about 3g of NaNO3 per 5ml HNO3 ensures the concentration of your acid and increases your yield. Ive been able to distill HNO3 with that method (without a vacuum) with densities up to 1.522 after being freed of NOx. I should also mention that afterwards the sulfuric acid removed can be cooled and the sodium sulfate removed, and then reboiled to concentrate it, for 200mL of 98% sulfuric i usually get about 120mL back.

[froot]

I dreamt the following:
After setting up a basic distilling appauratus I added 1 part 55% NA to 2 parts 99% H2SO4 into the distilling flask. I used a basic straight condenser. The receiver was immersed in ice water. So I fired this baby up and here's what happened.
Nothing happened until about 90 degrees C. The solution then became slightly yellow and feint traces of brown NOx gas appeared in the distilling flask. The bubbling only started at about 120 degrees C, which then slowed to almost nothing and the brown gas cleared up. Droplets of a pale yellow liquid was runnung into the receiver. At about 130 deg. the bubbling started again and soon slowed again. This pattern continued until about 170 degrees C. The liquid runnung into the receiver cleared up and the yellowed again towards the end of the burn. The volume of liquit that left the distilling flask and is now sitting in the receiver is equivalent to 55% of the volume of dilute NA i started with. I'm not too worried about the H2O in the acid because H2SO4 maintains it's boiling point even if diluted to a certain point.
It seems that the yellow liquid I've ended up with is a very high concentration of NA with a bit of NOx. There is brown NOx gas present in the bottle above the 'acid' and the 'acid' fumes profusely in open air with that typical choking smell.
I speculate that during distillation tha NA is formed not only from NA vapours but also from a loop type reaction involving NOx, H2O, and O2.
Check this link: URL=http://www.cheresources.com/azeotrop.pdf (section 3).
Tonight I'll dream about adding a little AN and hexamine.

Off the topic; There is this chemical 'tris-hydroxymethyl aminomethane' C4H11NO3
Is there a use for this stuff in the spirit of this forum? Can it be used to make something that can be useful?

[grandyOse]

In another thread on this topic, someone suggested anhydrous epson salts as a drying agent for HNO3. I distilled some red/yellow fuming nitric acid that I estimate to be 75%. I carefully weighed and dried some epson salts and figured that the dry salt would absorb 55% it's weight in water. I added 7.38 grams of acid and 6.57 grams of salt. Now I have a wet yellow salt. It is not sepparating, probably due to the similar densities of pure nitric and wet salt. I could filter it, but the loss of evaporation and filter absorption will probably be too great. On a larger scale this may work OK. Any suggestions on how to separate the mixture?


Also, during the distilation, I had to keep the water bath to a boil to maintain distillation temp. inside the retort. Having to keep adding water, plus alerting the neighbors with clouds of steam is a pain. Next time, I think I will use dilute sulfuric acid for the bath and kill two birds. Any ideas about this?

[Anthony]

Use cooking oil instead!

H2SO4 would be:

1) more expensive
2) less obtainable
3) A hazard, especially when hot
4) would still steam (possibly boil) as you mentioned using dilute stuff.

[grandyOse]

Originally posted by Anthony
Use cooking oil instead!

H2SO4 would be:

1) more expensive
2) less obtainable
3) A hazard, especially when hot
4) would still steam (possibly boil) as you mentioned using dilute stuff.

Since I am concentrating my sulfuric acid anyway, many of your points are moot. BUT I think the cooking oil is a supurb idea! Without having to add to the bath, I can maintain a steady temp of 85C or so in the retort and have a more uniform and reliable process. This stuff will probably only splatter when a bug flies into it and I won't have water condensation on the ouside of all my glass. Wesson, it is. Thanks.

[me234]

What about using anhydrous sadium sulphate to absorb the water from dilute HNO3?, This has been used to dehydrate esters after their formation, any opinions on how well this would work?

[knowledgehungry]

You would end up with a mixture of Na2SO4 H2O and HNO3, unless you are suggesting using it as a dessicant. In that case i would doubt the Na2SO4 would work very well either.

[Mendeleev]

I have read in numerous threads that a very good process for getting 100% HNO3 is by adding to potassium nitrate to 98% sulfuric acid. The reaction would be:
2KNO3 + 1H2SO4 ---> 2HNO3 + 1K2SO4
This is great and everything except that sulfates are soluble unless they are either lead, mercury, calcium, or barium sulfates. However the other product of the reaction K2SO4 contains an alkali metal, and alkali metal compounds are always soluble. This is where the problem arises. How can one have 100% HNO3 (I am trying to make RDX) if you have large quantities of soluble K2S04 in it? I have read the potassium nitrate method in so many threads and other sources that it greatly puzzles me. Any reply or clarification would be helpful. Furthermore if you added calcium nitrate, wouldn't the product, CaSO4 be insoluble and thus precipitate out of the solution, creating pure nitric acid???

Thanks :D

[knowledgehungry]

:rolleyes: It's called distillation, also CaNO3+H2SO4--> sludge. More like a syrup than a precipitate and liquid.

[Dhzugasvili]

I have found throughout my experience with Nitric Acid that the best way of concentrating is by simple distillation of 2 parts 98% sulfuric to 1 part 60-75% nitric acid. Temperature was always regulated to keep the still going at anywhere from 1-2 drops per second, depending on the phase of the reaction (towards the end it slows down). The acid collected from this was found, using a density meter/hydrometer, to be of density 1.52. However, it was always impure from NOx fumes. Urea removes some of them but not all. I am looking to build a vacuum pump for vacuum distillation. This would give me white nitric. This red fuming nitric i have used to make rdx, hmx, and a whole bunch of other shyt. It has worked fine, but i would like to perfect the method.

I have also tried simple distillation with CaNO3 and H2SO4. Product was of equal density but slightly more NOx fumes.

I have also tried with KNO3 + H2SO4 , all these reactions giving red fuming nitric acid of 1.52 density...which is suitable for many reactions i have found. but it seems there is only one way to get white nitric acid that is completely pure, being a density of >1.5 and free of NOx fumes....vacuum distillation with any of the above processes - making an aspirator for vacuum distillation is not too hard it seems. Comments, reactions, suggestions, pretty much appreciated. Do you guys agree vacuum distillation is the way to go for white nitric acid?? I don't think there are any shortcuts.

[rooster]

Hey there dhzuga;) , mail me about news!
You are right about the 1-2drops per second thing. I have done several distillations of nitric acid, including too fast ones. I got about 5-8 drops per second at most, and was happy seeing that my product was yellow. I thought is was 95%+. When measuring afterwards, the density was 1,45:( . And after all that work. This was with a 2-L distillation bottle, 2:1 sulfuric:nitric. Of course I had too high temperature, so most of the nitric decomposed.

With 2-3 drops per second, you can't make many liters at a time, but hey, its 95%+!

This acid is suitable for almost all reactions where high percentage HNO3 is needed.

[Dhzugasvili]

ROOSTER ;)

Will mail you about news!! Good to see you posting! You're right your temps were too high and acid must have decomposed. You should take a look at the thread on vacuum distillation and what they say about an aspirator and simple construction of one... i think this would be strong enough for vacuum distillation. Then you can start cranking out the white nitric acid, which is under my impression as pure as you can get it w/out NOx fumes. Will keep ya posted :D

[SantasL.Helper]

What are you guys measuring the temperatures of? The evolving gas or the fluid in the starter flask?

[grandyOse]

Santa;

good question. I am using a retort with a condesner, and put the thermoter bulb at the same level as the retort output port (sorry about the nomenclature, if wrong). If possible, I think it would be helpful to also measure the temp inside the reacting fluids (to keep down the NOx) and also the vapor out of the condenser to make sure you are cooling it enough. It seems to me, if you can only measure at one point, it should be the excaping vapor.

[SantasL.Helper]

So you only need to make sure the Gas temperature is around the boiling point of nitric acid and don't need to mind the other temperatures? I got 2 thermometers, one for the gas and one for the fluid. Can anyone tell me what to monitor?

+
I'm using a spiral condensor that is hanging vertical, instead of the normal classic cooler. Last time when i tried distilling nitric i only got a verrrrrrry small amount of acid (+-5 drops total). Now i'm wondring, will my condensor cool enough to condensate all the nitric acid gasses? The water is about 8 degrees i gues and is constantly being refreshed (connected it to our garden hose, let my parents pay all the water ;) ).

And what will give me better yields? Distilling concentrated sulfuric acid with 60% Nitric acid or ammonium nitrate?

[Marvin]

Santa, define yeild. Both synths use up different chemicals. If the 60% nitric is cheep, this could well be the best for you.

According to orgsyn a good way to produce 95%+ acid is to distill 70% twice from an equal quantity of conc sulphuric, I'm not sure how doing it once from twice the amount of sulphuric would change things.

Its unlikley to matter much which you measure, the gas or the liquid unless you have something to compair against. The liquid will probably be a lot hotter than the boiling point of nitric acid when it comes off, ideally you should do fractions as the temperature of the liquid rises and compair that temperature with the strength of nitric acid being produced. The results will only be valid for the specific process you use, method, concentration of reagents, but it would give you a reliable indication of how strong the acid was in future attempts simply from the temperature of the liquid. I would not have thought under the circs that the temperature of the gas would be a reliable indicator. This is completely the oppasite as to how organic distillations are done.

[grandyOse]

marvin; I am not one to doubt you, but I have seen many diagrams showing the thermometer bulb at the outlet of the reaction vessel. I have in front of me a college organic chem textbook that shows the thermometer at this position in every distillation diagram. In fact it states that the bulb should be slightly below the outlet tube. Perhaps the theory states that the boiling liquid, the vapor, and the condensing vapor are all at the same temperature. Perhaps my old textbook is so far out of date that their methods are wrong, now. It seems sensible to me, though.

[SantasL.Helper]

But in order to get as pure nitric acid as possible from my 60% nitric and somewhere round 95% sulfuric acid: at what temperature should i keep the mixture or the gasses that evolve?? Bp of nitric? Remember, i'm NOT using a vacuum (don't have a pump, nor an adapter).

PS, i got one of those thermometers in my setup :rolleyes: