Sulaiman
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Nitric Acid from Calcium Nitrate
Just because I wanted to test my new 500ml distillation kit,
I made some nitric acid from calcium nitrate and sulfuric acid.
I will update this thread when I have titrated the three fractions collected and distilled the now diluted pot remains.
My calcium nitrate source was relatively expensive, so I decided to use the cheap sulfuric acid in excess.
(This also makes the pot contents easier to boil.)
Stage 1 ... Preparation
200 ml 95% sulfuric acid (2.5 mole, drain unblocker grade)
was added to
164g anhydrous calcium nitrate (1 mole, from dehydration of technical grade tetrahydrate)
in a 500 ml rbf.
The mixing was mildly exothermic, with a hint of NO2 visible.
This mixture was then agitated once a day for one week.
After the first day, all colour due to the drain cleaner had gone.
Stage 2 ... Distillation
The above contents were transfered to a NS25 500ml rbf for simple distillation using an oil bath heater and Leibig condenser.
From the time that the contents began to heat until the end of the run, NO2 there was visible continuous NO2 low level
production.
Three fractions were collected, each containing NO2
#1 83C to 85C, 10ml
#2 85C to 88C to 84C, 21ml
#3 84C to 80C, 34ml
I made a video at this point https://www.youtube.com/watch?v=NPxxiwGL15Y
When cool, 100ml dH2O was used to wash the contents of the pot into a normal rbf for later.
IF the collected fractions are near to anhydrous HNO3 then the yield was 78% relative to the limiting reagent.
CAUTION : Hobby Chemist, not Professional or even Amateur
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hissingnoise
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Calcium nitrate is a poorer source for HNO3 than Na or K nitrates because the insoluble sulphate formed prevents the reaction from going to
completion.
And it's hygroscopic!
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Sulaiman
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True
I hoped to mitigate the insolubility problem by soaking for a week, agitating daily.
I have both NaNO3 and KNO3 but I wanted to try the less conspicuous Ca(NO3)2.4H2O
Although far from ideal, it seems to be a usable route to HNO3.
I may have 78% yield, from a rushed distillation
Due to the 2.5x excess H2SO4, the contents of the pot were still mobile at the end of the run.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Melgar
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I've done this plenty of times with calcium nitrate fertilizer, which the local hydroponics shop was kind enough to sell me in bulk. Calcium nitrate
is extremely soluble in water, so it helped to dissolve it in hot water first, then mix it with H2SO4. With the CaSO4 pulling water out of
solution as it formed, it never got to the point where it was diluted to the point water was coming over. The only really annoying part was cleaning
the CaSO4 out of my glassware.
Also, the higher vacuum you can pull, the less NO2 forms. I've distilled plenty of white fuming nitric acid with no observed color at all in the
vapors or the distillate. Of course, that's also a good way to ruin whatever is pulling your vacuum, but there are certainly ways around that
happening.
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BromicAcid
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The first time I tried to distill HNO<sub>3</sub> from nitrate salts and sulfuric acid I got greedy and used too much sulfuric acid. My
first cut was mostly nitrogen dioxide! I thought it was just red fuming nitric acid but when you put a drop in water it would sink straight to the
bottom and send out little tendrils of red as it 'dissolved'. Since that attempt I ran more dilute distillations and had much less of an issue with
nitrogen dioxide then I went back and cleaned up the fractions with a second distillation.
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Camroc37
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Quote: Originally posted by hissingnoise  | Calcium nitrate is a poorer source for HNO3 than Na or K nitrates because the insoluble sulphate formed prevents the reaction from going to
completion.
And it's hygroscopic!
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It will produce nice clear azeotropic HNO3 however
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ave369
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What if you vacuum filter the mixture, separating CaSO4, and then distill the remaining clear liquid?
Smells like ammonia....
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Metacelsus
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If you're going to distill it anyway, there's not much point in filtering (besides making the flask easier to clean out afterwards). The filtering
could not be done with filter paper, and would require a fritted funnel.
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Fulmen
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I tried that once, it's like trying to filter wet mud.
We're not banging rocks together here. We know how to put a man back together.
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careysub
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Just a thought - would it work to make copper nitrate from calcium nitrate using metathesis with copper sulfate, then make nitric acid by decomposing
the copper nitrate thermally?
Also, for filtering difficult precipitates in bulk - how about stainless steel mesh, available in many porosities rather than fritted glass?
About that which we cannot speak, we must remain silent.
-Wittgenstein
Some things can never be spoken
Some things cannot be pronounced
That word does not exist in any language
It will never be uttered by a human mouth
- The Talking Heads
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Fulmen
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You're barking up the wrong three. What you end up with is a mass of something much like clay. You can't filter that without extreme losses. Pressing
would probably be much more effective, but due to the nature of concentrated nitric acid it's not friendly to home setups. But hey, prove me wrong :-)
It might be possible to get mixed acids from this, basically by washing the material with sulfuric acid.
We're not banging rocks together here. We know how to put a man back together.
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Sulaiman
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It would be good if the calcium sulphate could be filtered out prior to distillation
as it appears to cause a significant temperature gradient in the pot,
causing excess NOx (I can only see NO2)
A stirrer would be very useful for this reaction.
I considered filtering but it is plaster of paris - very fine grained
my filter papers would not last long
I did not want to vacuum a column with glass wool etc.
Remember, the liquid is ideally concentrated dehydrating sulfuric acid and oxidising nitric acid
... less handling is best.
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Fulmen
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Exactly.
For more dilute HNO3 it's probably the simplest method, no distilling required. But separating the calcium sulfate from anhydrous NA isn't going to be
easy.
We're not banging rocks together here. We know how to put a man back together.
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yobbo II
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A centrifuge would do the job (I presume) assuming you can get one or have one.
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Maroboduus
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Have you considered converting the calcium salt to a sodium or potassium salt first?
The carbonates or sulphates needed are pretty easy to get, and then the filtering can be done on a neutral solution. if filtering is too inefficient
you can even leach the calcium precipitate to get the last of the nitrate out. (like eluting a chromatography column, but on a bigger, slower scale)
Or if the calcium nitrate is cheap enough you can just let it settle and decant the supernatant liquor.
BTW: Are you using your new 'cow'? I ask because I recognized the photo you posted and was thinking of buying a few items from the same manufacturer.
Just wanted to know if the quality is reasonable.
EDIT: the heat differential problem could be reduce quite a bit by using an oil bath or other heating medium which covers the flask at least 1/2 way.
Slightly higher than the fluid level in the flask is best, and if you're boiling something with a tendency to bump it will militate against that as
well.
Cool video. Is that a solder pot you're using? I'd been thinking about one of those for high temp work. Are they thermostatic?
[Edited on 11-11-2016 by Maroboduus]
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Sulaiman
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I have not ordered a 'cow', I hope to get a Perkin triangle later,
once I get some proper distillation experience.
The glassware is, I think, adequate.
Compared to quickfit it feels and looks inferior in every respect - but I have not enough experience yet for a verdict.
The solder pot has served me well,
the heating control is basically a lamp dimmer, choose a dial setting for a given power
but it is too narrow and shallow to recommend it as a 500ml rbf bath - good for 250ml or less.
One good thing, theoretically 2 moles of nitric acid produced per mole of calcium nitrate used.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Maroboduus
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Sorry,
I was confusing a post by j_sum1 for one of yours. He just ordered a cow.
Definitely getting one of those solder pots.
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Microtek
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I second the suggestion Maroboduus made: CaCO3 is MUCH easier to filter out, so just dissolve your calcium nitrate in water, add the calculated amount
of ammonium-, sodium-, or potassium carbonate and filter off the CaCO3. Then evaporate the filtrate to dryness, and use that in your distillation.
I've done this (the metathesis and evaporation operations) on a 10 kg scale with no problems at all.
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RogueRose
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Removing fluids from the CaSO4 can be done with something like a t-shirt. I've found that the ribbed "strechy" undershitrts that some call "wife
beaters..." seem to work well as the weave allows for very little material to pass through.
first allow material to settle for 30-60 mins (even longer is better) then pour off the liquid. The remaining material is probably 30-60% liquid.
Cut the shirt so it lays open and place the solids in the center. Fold the corners towards the center and pinch at the base as close to the CaSO4 as
possible. I'd use a zip tie or some cord to ties the 4 corners together at the base. Hold the folds right above the tied part and then twist the
CaSO4 as much as possible and every couple turns press down on the sulfate over the whole area - then squeeze the material that has moved from the
center back into the "ball" - then twist some more and keep repeating. I've never had the fabric break and almost no CaSO4 passes through but there
is some fine particulate that passes through. When done, open up fabric, scrape with a putty knife or spatula into center, tie back up and repeat.
When the filtrate is collected this can be filtered with a coffee filter allowing it to coat the filter (some CaSO4 will pass through) and then
re-filter 2-3 times. The coating of the filter will catch the finer particulate over the next 2-3 passes and the filtrate will be as clear as can be
expected from a non-micron filter (clear as water in almost all cases).
This has been done with a Ca(NO3)2 (NH4)2SO4 which gibes ammonium nitrate and calcium sulfate. With this, there is no nitric acid to dissolve the
filters and then nitric acid can be made from the ammonium nitrate. I think the same can be done with H2SO4 and Ca(NO3)2 but will have to act quickly
as the nitric acid will eat away at the filter medium.
I've found thrift stores (good will, salvation army, etc) to be great places to get fabric scraps for filters or buying clothing that is the correct
weave/material to act as a filter. The right kind of fabric can make filtering 100x easier. I've found that wetting the fabrics prior to adding the
medium to be filtered makes things MUCH easier for some reason as there seems to be a surface tension on most fabrics which can make the liquid just
sit on top and not pas through.
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