Sciencemadness Discussion Board

98,7% HNO3 without vacuum distillation

Hoffmann-LaRoche - 12-9-2002 at 16:32

i calculated that using the Ca(NO3)2/H2SO4-method, max 98,7% HNO3 could be obtained, if normal 98,3% (conc.) sulfuric acid is used.
Really a pain in the arse for everyone, who has tried this method, is that the resulting CaSO4/HNO3-slug is a thick paste, and not a liquid with some precipitated CaSO4.
What adds to the problem, is that this white paste cannot be pressed out very easily.
Acid resistant filters(which are very expensive) and vacuum sucking would have to be applied, which is not acceptable to me.
My next idea was then to dilute the HNO3 with an inert solvent, that could later be removed without distillation, so that i would able to carefully decant the liquid.
I had several tries with glacial acetic acid for diluting.
Once the HNO3/glacial acetic acid mix was decanted, i extracted the glacial acetic acid with toluene(also xylene works), which is not very inert(i did that quickly and with ice cooling) but naturally not miscible with HNO3.
The problem now was that this worked only if absolutely no contaminant anorganic salts are present, so no Ca(NO3)2 and no H2SO4 traces.

A much better method could possibly be the use of tetrachlormethane.
Tetra is an inert solvent that doesnt mix with polar solvents and is slightly more dense than 100% HNO3. Therefor it would push the HNO3 out of the paste and it the HNO3 could be decanted.
The tetrachlormethane could later be recovered by the addition of a heavy anorganic salt-solution, that sinks into the CaSO4 - paste.
Due to the fact, that i wasnt able to get Tetrachlormethane so far(in my country it needs a special permission to get substances like tetrachlormethane, formaldehyde, methanol, heavy metal salts and so on..), i couldnt test this idea.

Any better ideas?


vulture - 14-9-2002 at 00:55

You will not get your hands on CCl4 which is a HIGHLY restricted chemical these days.
A very similar method using dichloromethane is currently being discussed here:;f=1...

Hoffmann-LaRoche - 14-9-2002 at 15:05

Thanks for the link.
I also found the patent "preparation of anhydrous nitric acid", that was mentioned(US pat. nr. 3981975), and i was asking myself wether it could also be possible to make N2O5 containing nitric acid (>100% nitric acid) by this method of methylene extraction using oleum instead of normal 98,3% sulfuric acid.
One of the questions would be wether N2O5 is soluble in the methylene chloride phase(the patent sais HNO3 does, because a complex with methylene chloride is built.)
This would be of course a "sexy" method for N2O5, cause the use of precious P2O5 would not be necessary.


Few problemos

vulture - 15-9-2002 at 00:58

N2O5 forms very volatile crystals which have the tendency to explode without any external stimilus being applied.
Sublimes at 32,4°C.
IIRC, 100%+ nitric acid is 100% nitric acid with dissolved N2O4.

Hoffmann-LaRoche - 15-9-2002 at 02:42

>100% nitric acid can be used for the manufacture of TNGU(Tetranitroglycoluril) and also for HMX.
Check out US pat. 4,487,938, if u want, just for knowing .

Although the HMX process uses 98+% nitric acid, some N2O5 is generated during the process by the action of acetic anhydride, and N2O5 is the main nitrating compound in this reaction...

BLAST_X - 27-9-2002 at 00:12

Tetranitroglycoluril can be synthetisyzed with adding glycoluril to 107,2 % HNO3 (56 % HNO3 + 44 % N2O5) below 5 C.

Here a short desciption of simple >99% HNO3 distillation.

To a 1000 ml flask add 300 ml 99% H2SO4 and slowly with cooling and stirring add 555 g finely pulverized KNO3 until dissolving all. Let sit for 1 hour, add 1 g silver nitrate and stir again.
Set the flask for simple distillation with flame or hotplate at a temperature
>123 C. (oil-bad can be used)
When all distilled over and the raction mixture are stiffen, use a new 1000 ml flask, pour the delute nitric acid init
and add slowly 200 ml 99% H2SO4.
Set for distillation with hotplate and stirring at 83 C.
Be careful with to high pressure !
At 26 mbar – pure HNO3 can be
distilled at 38 C with a water-bad.
The distillation of pure HNO3 are finnished with forming of NO2.
(The red acid at begin and at end of the distillation should be collected specially. [red fuming acid with high NO2 content])
Yield of >99 % HNO3 should be ~ 100 ml.
To collect the rest of delute 85-90% HNO3 distil with higher temerature (below bp of H2SO4 !).
Yield of 85-90% HNO3 should be ~ 100 ml.
The remaining H2SO4 can be used again.

Here a short desciption of dinitrogen pentoxide preparation.

To a distillation-device with addition funnel and cooling add P4O10 and slowly (1 ml/min) drop >99% HNO3 init. Heat the flask simultaneous in a water-bad to 35 C and pump a poor stream of O3 init.
Cool the condenser with a water bad. N2O5 will form rigorous and goes over with the support of O2.
At end of the reaction collect N2O5 careful and store in a air-tight brown-flask at temperatures below 15 C.
N2O5 melt at >30 and decompose at ~ 47 C.
When it heat to strong, it can explode !
I must test this exactly at soon.
It`s possible the N2O5 should be dryed in a vacuum.

Can describe samebody something about the preparation of glycoluril.
I think, it can be prepared by heating a mixture of 40% glyoxal and urea at ~ 100 C ?

synthesis of nitric acid anhydride

BLAST_X - 1-10-2002 at 22:46

I`ve readed a description in a other forum,
N2O5 can be synthesized by cooling down a mixture of >99% H2SO4 and >99% HNO3
to very low temperatures by dry ice.
Somebody did heared this ?

Hoffmann-LaRoche - 3-10-2002 at 08:55

Interesting what you said about that N2O5-process.....only problem is you´ll need an ozonizator which has a good yield(ozonizator=some kind of spark gap apparatus).

Although i´m quite familiar with high voltage, i fear that such a self-built ozonizator will only generate very low amounts of O3 and some additional know how/experimenting would be necessary.


other extraction methods

Hoffmann-LaRoche - 3-10-2002 at 14:43

Here are 2 new proposals for "extracting" the nitric acid out of the CaSO4-"slug" followed by freezing out the diluting fluid to get (maybe with a negliable amount of impurities left, due to eutecticum).

1) mixing the slug with conc. H2SO4, decanting and freezing out the H2SO4 and decant again to get the purified HNO3. note: H2SO4 freezes at about +10°C, HNO3 at about -40°C

2) mixing with glacial acetic acid, decanting and freezing out the CH3COOH.
The ice crystals of acetic acid will swim on the surface, so a seperatory funnel would be necessary. note: glacial acetic acid freezes at about +16°C

cheap cooling mixtures are:
crushed(thats important!) ice + NaCl provides up to -20°C

Also ammonium nitrate does a good job.
I know several other salt mixtures which are able to provide cooling temp. from
-30°C to -60°C without needing dry ice.

Unfortunately i have absolutely no time to test these ideas...


BLAST_X - 3-10-2002 at 15:22

I think ozonized oxygen should are sufficient to transport the N2O5 to the condenser, produced chemically!

You mean the tetrachlormethane-method are digestible ?

Hoffmann-LaRoche - 4-10-2002 at 02:03

The tetrachlormethane method is obsolete...tetra is too hard to get and its density is not really much higher than 1,52.


I think ozonized oxygen should are sufficient to transport the N2O5 to the condenser, produced chemically!

? ?


BLAST_X - 4-10-2002 at 03:11

Can you synthesize better oxidizing O3 with this electric monster-madness ?
(or 1. = O2-O-uv-O-O2-O3; 2. = ... ?)

Hoffmann-LaRoche - 4-10-2002 at 04:11

no. just O3....and the yield of these apparatus is usually low...but i wonder why in your process for N2O5 P2O5 AND O3 is employed.
P2O5 alone should work pretty well.


BLAST_X - 4-10-2002 at 16:45

I need looking for, to say the correct reaction of HNO3 and the P4O10
formation with O3 !

ADP - 7-9-2005 at 17:46

I have some strontium nitrate which I am soon to employ in making nitric acid. I plan on mixing it with H2SO4. Also on the topic of removing water from HNO3. Can anhydrous salts such as MgSO4 be used to suck up the water and then the mixture be distilled?

praseodym - 9-9-2005 at 03:13

I think using magnesium sulphate as the drying agent for nitric acid should not be a problem.

vulture - 9-9-2005 at 07:04

Well, actually it's a bit tricky.

In theory, SO4 (2-) is a strong enough base to be protonated by nitric acid. However, I think HLR mentioned somewhere hydrogensulfates of earthalkalimetals do not exist.

The safest bet is to use magnesiumnitrate or even calciumnitrate (obviously not in combination with H2SO4).

simply RED - 10-9-2005 at 04:12

Calcium nitrate normally exists as chrystalohydrate.
Ca(NO3)2. 4H2O
Is it possible to dehydrate it by heating?

If you buy it from grocery shop it is more likely to be calcium - ammonium nitrate fertilizer (again chrystalohydrate)...

ADP - 10-9-2005 at 07:54

Yes they both can be dehydrated in a conventional oven simply. I'm not sure of the temps and duration however.