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Imran
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Nitric acid by thermal decomposition of Ca(NO3)2
Has anyone produced nitric acid by thermal decomposition of Ca(NO3)2?
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Endimion17
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It is possible, but there's a problem. The stuff comes as a hydrate and it will first melt, and then sputter water and blobs of the salt. Then the
anhydrous salt melts at high temperatures, while decomposing to calcium oxide, nitrogen(IV) oxide, oxygen and nitrogen. I think it might depend on the
temperature because some sources don't mention nitrogen and/or oxygen.
Anyway, you have the melt from which gasses evolve, and solid calcium oxide precipitates. It can trap the nitrate melt that's evolving gases, which
might cause bumping. It might(!), in extreme cases, cause mild explosion, if the vessel is larger.
The melt is very hot, so you don't want any bursts or stresses and cracks in the vessel.
It's easy when you have products that are in liquid state at the given temperature, but CaO will precipitate out as a solid that will leave a hard
residue that you'll have to dissolve in hydrochloric acid. I'd try this with gram amounts first.
However, the fact it liberates oxygen is helpful because that way nitrogen dioxide will be converted to nitric acid in contact with water more easily.
As with all nitrates, don't apply pressure. Let the apparatus be at 1 atm for the sake of safety.
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hissingnoise
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No ─ short answer . . .
Decomposition temp is likely to be high, and NO<sub>2</sub> <i>still</i> needs some kind of absorption tower!
Distilling HNO<sub>3</sub> from Ca(NO<sub>3</sub> <sub>2</sub>/H<sub>2</sub>SO<sub>4</sub> is the way to go . . .
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bbartlog
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An alternative route if you insist on pyrolysis (or don't have H2SO4) is to react your Ca(NO3)2 with CuSO4 (in aqueous solution), filter
out the resulting CaSO4, and decompose the copper nitrate with heat. I would still expect it to be messy but at least the temperatures would be low
enough that you could do it in glass.
The less you bet, the more you lose when you win.
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Endimion17
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Quote: Originally posted by hissingnoise  | No ─ short answer . . .
Decomposition temp is likely to be high, and NO<sub>2</sub> <i>still</i> needs some kind of absorption tower!
Distilling HNO<sub>3</sub> from Ca(NO<sub>3</sub><sub>2</sub>/H<sub>2</sub>SO<sub>4</sub> is the way to go . . .
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Yeah, it's very hot.
http://www.sciencedirect.com/science/article/pii/S0040603196...
It would be a tricky, dangerous, and expensive (heat!) procedure. Not to mention the borosilicate glass would start sagging. Quartz glass wouldn't,
but if he has the money for such vessels, he can buy the goddamn nitric acid, too. 
But hey, he insists on pyrolysis.
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Eddygp
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Pyrolysis would be too difficult if you start with calcium nitrate. Try to react it to form iron o copper nitrate, which will be easier to manage.
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
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tetrahedron
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pour a stoichiometric amount of conc H2SO4 into a saturated soln of Ca(NO3)2, most of the calcium will precipitate as the sulfate, filter..for many
practical purposes it won't even be necessary to distill
i did the math for the molarity, and it boils down to:
[HNO3] = 2 / ( 1/[Ca(NO3)2] + 1/[H2SO4] )
assuming (as found in some other thread) 121.2g Ca(NO3)2 dissolves in 100ml of solution at 20°C, which corresponds to 7.386M, and taking 18M H2SO4,
this results in 10.47M HNO3. higher temperatures probably afford a higher concentration of Ca(NO3)2, and it might be possible to reach the 15M of 68%
HNO3 or even higher in just one step.
in terms of purity, you'll fare even better if you start with barium nitrate instead of the calcium salt (the Ca precipitates almost
quantitatively)..unfortunately Ba(NO3)2 is not as soluble, and your product concentration will suffer in return.
question. does anyone have data on the solubility of calcium of barium nitrate in the presence of HNO3? if this was reasonable, then
one could start over with the solution from step 1 instead of water and reach even higher concentrations =D
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hissingnoise
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If strong nitric is required, it's more efficient to convert Ca(NO<sub>3</sub><sub>2</sub> to NaNO<sub>3</sub> using Na<sub>2</sub>SO<sub>4</sub> before distilling!
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vmelkon
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| Quote: Originally posted by hissingnoise | If strong nitric is required, it's more efficient to convert Ca(NO<sub>3</sub><sub>2</sub> to NaNO<sub>3</sub> using Na<sub>2</sub>SO<sub>4</sub> before distilling!
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Why? I don't see what difference it makes using Ca(NO3)2 or NaNO3 if you are just going to throw it in with conc H2SO4 and distill.
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hissingnoise
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When Ca(NO<sub>3</sub><sub>2</sub> is added to conc.
H<sub>2</sub>SO<sub>4</sub>, insoluble CaSO<sub>4</sub> forms as a coating on the granules, which locks in nitrate
and prevents further reaction.
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tetrahedron
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what granules? you're supposed to dissolve the calcium nitrate first.
Edit: nvm, not for your distillation procedure
[Edited on 30-9-2012 by tetrahedron]
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vmelkon
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| Quote: Originally posted by hissingnoise | | When Ca(NO<sub>3</sub><sub>2</sub> is added to conc.
H<sub>2</sub>SO<sub>4</sub>, insoluble CaSO<sub>4</sub> forms as a coating on the granules, which locks in nitrate
and prevents further reaction. |
But if you use NaNO3, then Na2SO4 forms a coating on the NaNO3 crystals. (assuming 98% H2SO4 and dry NaNO3).
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plante1999
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sodium hydrogen sulphate is soluble in hot H2SO4 but CaSO4 isn't, by the way I would like that someone try to make nitric acid using copper nitrate
thermal decomposition. I'm still working on ammonia by the Ostwald process but I need more ammonia, when it will be done I will make a prepublication
of the process.
I never asked for this.
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hissingnoise
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| Quote: | | . . . what granules? you're supposed to dissolve the calcium nitrate first. |
Yes, but that will give dilute acid!
Sodium bisulphate's solubility is sufficient to react smoothly giving a full yield of fuming HNO<sub>3</sub>!
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tetrahedron
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| Quote: Originally posted by plante1999 | | I'm still working on ammonia by the Ostwald process but I need more ammonia, when it will be done I will make a prepublication of the process.
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i saw your post with the pics of your prototype Ostwald process and i was impressed, can't wait to read your writeup
at any rate, since this thread is all about generating HNO3 from nitrate salts, do you think copper is the best cation as far as pyrolysis goes?
what if the only source of nitrate available is NaNO3, and no conc H2SO4? is there a way to metathesize that to a more useable reagent? (even
potassium can be precipitated with bitartrate, or cobaltinitrite, but what about sodium?)
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plante1999
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I don't know if it is the best but many aspect make it a very good candidate. First all old procedure to generate nitrogen dioxide use it. Second
copper have a low decomposition temperature and copper salts are pretty cheap and easy to work with. lead nitrate decompose too but temperature is
higher and lead salt are toxic.
Sodium nitrate mixed with copper sulphate and heated will make nitrogen dioxide and oxygen at a low temperature.
I never asked for this.
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tetrahedron
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it should also be possible to regenerate this copper nitrate by absorbing nitrogen oxides (coming e.g. from Ostwald or Birkeland-Eyde) in the leftover
CuO..although this sounds circuitous given the end purpose
OTOH 'homemade' copper nitrate will be heavily hydrated so you'd be distilling diluted acid
[Edited on 30-9-2012 by tetrahedron]
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shannon dove
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One time I melted potassium nitrate in a small stainless steel cup, then I connected the negative electrode to the cup, and I connected the positive
electrode to a stainless steel spoon. As soon as I touched the spoon into the fused KNO3, it made copious amounts of brown gas I assume was nitrogen
dioxide. And KNO3 melts easy at low temperature.
I know it's probably not very efficient, I guess a lot of the NO2 reacts with the stainless steel, and like has already been said, the NO2 needs an
absorption tower to make nitric acid.
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Imran
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Can you make absorbtion column youself? Would a plastic bucket full of glass shards work?
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hissingnoise
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It'd work to some extent but some NO<sub>2</sub> would still escape, requiring a fume-cupboard since the gas is toxic . . .
See the wiki for NO<sub>2</sub>.
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tetrahedron
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shannon, how did the spoon hold up?
with proper cooling the N2O4 can be liquefied and subsequently reacted with ice cold water in a controlled way.
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Imran
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Yes below 21°C NO2 should be liquid which would be much easier to dissolve in water.
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SM2
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I always thought Ca(NO3)2 would be a better NO3- **BANG** for your buck than Chili Saltpeter. Don't even see Chili Saltpeter in the local landscaping
stores (next to the dried blood, etc.) I guess Na is just not the best thing for crops< Or was NaNO3 targeted as well.
So dry distillation of Ca(NO3)2 w/ bisulphate will give good results? No gypsum plug? Dry disassociation ^ of Ca(NO3)2 just seems very brute, it,
never really occurred to me. Maybe a solar concentrator to get things going.
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shannon dove
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I only put the spoon into the fused KNO3 for about 5 seconds, just long enough to test the idea. I abandoned the idea, and never did any further test.
At the time, my plan was to make liquid NO2/N2O4 and use it like liquid oxygen. Mix it with gasoline or maybe charcoal. But I abandoned the idea
after determining the the explosives would be too sensitive, too poisonous and not store able.
I have read somewhere that take liquid NO2 /N2O4 and vigorously mix it with diluted nitric acid, then let it set, two layers will form, one of those
layers will be almost 100% nitric acid.
I have tried to find that book again, but I can't. I think it was written in 18 hundreds.
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plante1999
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Actually RFNA can make energetic mix with liquid or solid fuel, this summer I had made 20ml of RFNA using 5 time theoretical excess of 96% sulphuric
acid. Before I diluted it I tried few experiments I had absorbed half a milliliter in a charcoal piece and lighted it, it burned extremely vigorously.
I also dropped 1 drop on nitril glove and it self ignited.
Nitrogen dioxide dissolve really well in water but 1/3 of it is lost as nitrogen monoxide, but if Nitrogen monoxide is oxygen rich, 4 gas absorption
flask are present and gas chamber between each gas absorption flask is used less than 1% nitrogen dioxide is lost.
I never asked for this.
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