kilowatt
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Practical NOx Chemistry.
I produced a crude NO2/N2O4 by thermal decomposition of calcium nitrate in a stainless vessel placed inside my melting furnace with a propane burner
at moderate heat. The decomposition is said to begin around 500°C. The calcium nitrate started as tetrahydrate, so I simply ran the furnace to drive
off steam until the vapor began running red, then hooked it up to the condenser.
I used a Graham condenser supplied by eutectic KCl brine off a block of frozen brine. This has a melting point of -10.6°C, just above the freezing
point of N2O4 to keep that vapor pressure as low as possible. Considerable fumes were evolved despite this. The condensate was dripped into a
stainless jar packed in dry ice to collect solid bulk product.
Throughout the decomposition process, liquid periodically collected in the Teflon line running from the decomposition vessel to the condenser. This
was periodically unhooked and dumped out. It leads me to believe that some moisture is still present in the calcium nitrate even at high temperatures.
Thus there would be considerable moisture in the product.
Once the collection jar was sealed with a dip and vent tube in the lid, and thawed out, the product could be observed. The raw product was a dark
nearly opaque blueish liquid. Presumably this consisted of some mixture of N2O4 and nitric/nitrous acids, which are formed when NO2/N2O4 reacts with
water, or possibly some N2O3 which is also a blue liquid anhydride of nitrous acid. I do not fully understand the equilibrium process at play here and
what exactly would be in this raw product.
I oxygenated the raw product with pressurized oxygen at 20psi for 2 days, hoping to convert any HNO2/N2O3 into HNO3/N2O4, in preparation for
redistillation of the product to obtain purified N2O4 for further rocket propellant experiments.
After the oxygenation, the product became a dark almost opaque red or black liquid, still able to be fully frozen in the deep freeze. Distillation
using a setup with a variable flow reflux condenser and main Graham condenser using the same eutectic KCl brine resulted in roughly 50% purified N2O4,
coming over as an opaque red or black liquid at 21°C, and 50% of some grade of red fuming nitric acid, transparent red with an unknown density. Based
on reading around this forum, it would seem like this acid should not be anhydrous but possibly as little as 70% in strength, but again I am not sure.
The acid exhibits a strong reaction with turpentine leaving some embers, but does not appear readily hypergolic as good RFNA is.
In the future I will be measuring density of the byproduct acid to determine whether these processes are a viable route to useful grades of fuming
nitric acid, perhaps with redistillation from sulfuric acid or something.
The mind cannot decide the truth; it can only find the truth.
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woelen
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Interesting experiment. Good to see that this material can be condensed at temperatures like -10 C.
Getting pure N2O4 is quite difficult. I have tried many times with all kinds of NO2-generators, but I always ended up with mixes of NO2, NO (and
possibly a little water as well). I tried collecting the dark brown gas mix in a big glass bottle and when I put this in a freezer, I always had a
little amount of dark blue liquid with pale brown gas mix above it.
One good method (at least on paper) for making pure NO2/N2O4 seems to be heating of perfectly dry Pb(NO3)2. This gives PbO, O2 and NO2. No NO is said
to be formed. I tried once with a little Pb(NO3)2, but the reaction is very scary. The crystals make loud crackling noises and jump around violently.
I quit the reaction when it become too violent. Some people add filler materials (e.g. perfectly dry fine white sand), but still, the reaction is not
really smooth. Another disadvantage is the nasty and toxic waste you get from this process. The PbO, which remains is not pure. It also will contain
some higher oxides of lead and some unreacted nitrate and nitrite. If you have access to HNO3, then you might use that to regain lead nitrate from
this waste.
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kilowatt
Hazard to Others
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Interesting. Sounds like you came pretty close. Just need to oxygenate and distill.
I actually have some lead nitrate, probably not perfectly dry though. But the economics of my situation is such that I would be making nitric acid
from N2O4 not the other way around. The calcium nitrate is available so cheaply from ceramics suppliers. I have used the crude N2O4 product to make
25% nitric acid before but I'd like to be able to make fuming grades and even WFNA, without using precious nitrate salts and large amounts of sulfuric
acid.
In the future I would like to replace the calcium nitrate method with the Berkeland Eyde process. Running air in through a dessicant and collecting
the product either in a tube immersed in my liquid nitrogen tank (which stays cold for months) or bubbling it into lime in water to make my own
calcium nitrate.
The mind cannot decide the truth; it can only find the truth.
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AJKOER
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Per Wikipedia on Mg(NO3)2 (see https://en.wikipedia.org/wiki/Magnesium_nitrate ), to quote:
"Since magnesium nitrate has a high affinity for water, heating the hexahydrate does not result in the dehydration of the salt, but rather its
decomposition into magnesium oxide, oxygen, and nitrogen oxides:
2 Mg(NO3)2 → 2 MgO + 4 NO2 + O2.
The absorption of these nitrogen oxides in water is one possible route to synthesize nitric acid. Although inefficient, this method does not require
the use of any strong acid. "
I have prepare Mg(NO3)2 by aqueous mixing of MgSO4 + KNO3 and freezing out the K2SO4.
Note: Working with MgSO4 is completely safe, and in sharp contrast to Pb (where even vapors of Lead salts will induce 'brain fog', especially in
younger adults). Fumes of NO2, however, are not safe so appropriate safety measures required.
[Edited on 19-8-2020 by AJKOER]
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WGTR
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I did a small experiment here to obtain pure N2O4:
https://www.sciencemadness.org/whisper/viewthread.php?tid=93...
Nitrogen oxides, in the absence of oxygen, can be bubbled through water to produce NO and water vapor. The water vapor can be removed with silica gel
and the gasses can be collected in a bag, etc. Then, the dry NO can be mixed with dry oxygen to form NO2/N2O4, which
can then be condensed out with sufficient cooling.
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