I've dry distilled nitric acid from sodium bisulfate and knk3 many times but I always wonder if my flask is going to break, is it? I know the glass
that makes up the flask is quite thick and probably holds to a great extent under pressure. But I feel that when letting the salt mixture melt when
done is a great point in time for everything to break apart! When melting salts and letting them hsrden I've broken many non lab glass containers but
will this apply to this scenario?
What is there to be done if anything needs to be done? jackchem2001 - 12-7-2025 at 16:43
First of all welcome to SM, I don't know much about rockets. But acids, hell yea. Radiums Lab - 13-7-2025 at 07:16
Ok here are the dangers and suggestions:-
- Increase the temperature slowly as rapid increase in temperature will crack your glass(and you mentioned it was very thick so heat should be
increased slowly).
-This will give lower yields because HNO3 decomposes at high temperatures.
-Remember both are not in solution so they should be mixed well for higher yields.
- I would synthesize it by using H2SO4 method instead because I'll use lower temperatures and the yield will be more in comparison and lesser NO2.
-In your method lots of NO2 fumes will be produced in comparison so make sure you set a trap for dilute acid.
-Cover the glass with Al foil to reduce decomposition and loss of heat.
- Because of high temperatures use a sand bath for even heating and it even prevents the glass cracking. In case the vessel breaks the acid and salts
are contained in the sand bath.
-Na2SO4 is a pain to clean...
-After the reaction is done make sure you cool the glassware even slowly because there is Na2SO4 layer now and you might end up cracking your glass.
[Edited on 13-7-2025 by Radiums Lab]Radiums Lab - 13-7-2025 at 07:58
Anyway, what are you planning to do with fuming HNO3?WD40_enjoyer - 13-7-2025 at 08:14
I'm mostly doing it cause hno3 is such a viable acid for so many purposes. I prefer making it by nahso4 since h2so4 is very hard for me to aquire
cause of regulations in the EU even though it should be better.
Fuming hno3 is good for many things but sometimes it's easier to make a large batch of fuming and then dilute then to do an azeotropic distillation.
A good tip I've seen is to cool down and reheat the flask to minimise the amount of decomposition.MrDoctor - 14-7-2025 at 02:32
Not to be that guy that says 'just use that thing you are doing this to avoid using' but have you considered making sulfuric acid from bisulfate?
a few new methods exist now for making sulfuric acid rather easily.
a new method doing the rounds by nurdrage seems to involve oxalic acid, as i believe its copper, iron or magnesium oxalate that is so insoluble that
dilute sulfuric acid can be displaced out by oxalic acid, which i think can be recycled efficiently. Magnesium sulfate regenerated using bisulfate
somehow, also is rather easy to pull off and only requires a clay pot seperator and i believe works fine with a lead anode.
then you just boil down the crude acid to where it needs to be to efficiently liberate nitric acid. If you can get bisulfate to hand over a sulfate to
iron, it can be electrolyzed very easily with a lead anode, or better yet, lead dioxide coated lead anode, protected by just a fairly rudimentary
membrane, possibly including just casting it in plaster. Or it can be used for the oxalic acid method since iron oxalate is quite insoluble.
i believe i have seen a writeup someone did once using bisulfate to produce an alcohol-sulfate ester, for the purpose of hydrolyzing it back to the
acid repeatedly. If using ethanol however, production of diethyl ether and diethyl sulfate might be unavoidable which isnt great to have fuming off
large amounts of solid waste, or just to be exposed to repeatedly on low yielding batch reactions, and i think other alcohols like butyl or isopropyl
might be more toxic.
If the temperatures and danger boiling sulfuric are a concern, nurdrage demonstrated that, with a reliable higher-temp magnetic stir bar, bumping is
eliminated when sulfuric acid is heated under strong stirring.
Someone on the forum also found that dry HCl under some condition can azeotropically remove water from sulfuric acid to quite a high concentration, i
think like 80 or 90% with only mild heating below 150C, which is weird given how sulfuric acid is used to dry gases including HCl, i guess nobody ever
did it at an elevated temperature sufficient for the equillibrium to shift and render the acid useless.
Otherwise, that same method that can get sulfuric acid from certain sulfates, can also molar yield 75% of dilute nitric acid, just using the right
nitrate salt and oxalic acid, which helps if you were also trying to avoid ever having sulfuric over the legal limit as this bypasses the need fur
sulfuric acid entirely, or bisulfates too. the only catch is that it doesnt work with sodium or potassium nitrate, you need an insoluble oxalate, so
calcium, magnesium, manganese or iron nitrate are required. https://www.youtube.com/watch?v=1x8oXCBjHFY
In the event oxalic acid is restricted where you are, as some places for some reason have done so, it can be made from spinach, rhubarb bagesse or
sugar, and recycled in a somewhat roundabout way.
If your nitrate and bisulfate is cheap enough however, why not just go with the wet-process, and instead focus on concentrating the dilute acid you
get. i think silica gel can be used to push it to azeotropic or higher, as might polyphosphoric acid or pyrophosphoric acid which can at times,
including dehydrating sulfuric to SO3/oleum, perform comparably to phosphorous pentoxide.
ignoring the fact it contains more water and requires quite a bit more labor, the dry distillation methods dont really yield an awful lot more than
the wet methods do, and cant be scaled up like they can either.
the key to saving your flask during dry distillation seems to be avoiding thermal stress, as well as having calcium precipitate on the surface of the
glass, as this causes damage that adds up.
As far as that goes, i do have two thoughts, firstly, if using the lower melting calcium nitrate eutectic, if one were to also add in sand, and/or
silica or a more alkaline sodium-glass or mineral, might that favor the silica or other mineral, over the borosilicate? or at least just prevent large
crystals from forming due to the abundance of nucleation sites.
the other is, can borosilicate be annealed as a form of preventative maintenance? or, is there a method for observing the buildup of stress indicating
it needs to be annealed? i believe that theres some method to make the stress in glass nakedly visible via diffraction.
WD40_enjoyer - 14-7-2025 at 02:50
Good points, I've tried the oxalic method aswell as electrolysis and some obscure methods like so3 in water and such but nothing is as cheap as
nahso4.
I have tried the wet method and it works great except for the fact that I can't go over azeotropic concentration. Not that pure hno3 is required for
everything but it's better to have and not need then to need and not have . MrDoctor - 14-7-2025 at 03:35
desiccants might be able to solve that one. coupled with a vacuum distillation perhaps. silicate gel, anhydrous magnesium sulfate, or copper sulfate
off the top of my head should be strong enough. idk what solvents are safe in conc nitric acid but using a dean stark to boil off a lower azeotrope
might be an idea too.
once you break the azeotrope, you end up with some high conc + more azeotrope, rinse and repeat.
vacuum might allow you to boil the solution below the decomposition temperature of the formed hydrate, if you used a hydrate for this purpose. I dont
know if it would work for an adsorbent like silica however, though silica also requires fairly high temps to release moisture fully.
As for how high you can get the conc? who knows.
another thing though is, i think vacuum is needed to keep the temp low enough to distill nitric properly at above-azeotropic conc.
SO3 is an anhydride, as is pyrophosphoric acid, and polyphosphoric acid, well kinda, but another one you should consider, is boric anhydride, and any
other inorganic acid-anhydrides you might have access to. anhydrides should be able to scavenge water chemically rather than just lock it away. Boric
acid i would think is not well soluble in conc nitric acid, certainly not enough to drive it out either, it might slowly produce higher conc fuming
nitric without any need for further distillation even if it does leave a bit of boric acid dissolved. Radiums Lab - 14-7-2025 at 06:31
MgSO4 to H2SO4 was demonstrated by scrap science.MrDoctor - 15-7-2025 at 07:56
if you make a split cell, im pretty sure you could then also go on to feed it SO2 at the same time and increase your yields. Scrap science i believe
blundered their sulfurous acid oxidation by not dividing the cell, because SO2 reduces at the cathode as readily as it oxidizes at the anode, but very
few things are immune to hydrogen sulfide, sulfurous acid and also sulfuric acid, even platinum isnt happy.
sulfuric acid is a great oxidizer for elemental sulfur, it produces pure SO2, though you do have to deal with sulfur sublimating out and clogging
things up down the line. Though if your chamber can handle being cycled hot enough the sulfuric acid forms a fog/fumes, that fog would contain enough
SO3 to just oxidize sulfur at room temperature (according to what ive read), its finely dispersed and high surface area, so it should work, so your
reactor can in principle, self clean.
Speaking of reactors though, provided you can cheaply produce the initial chlorine, you can make sulfuric acid by immediately hydrolyzing sulfuryl
chloride, which condenses readily and forms at room temp on simple activated carbon catalyst.
feeding the HCl from the hydrolysis into another reaction chamber loaded with manganese dioxide, additional chlorine is produced, allowing for 50%
re-use. you get way more using KMnO4 but you probably cant get that readily either. By using a hydro-lock (sideways S tube, like in drains so sewer
gas doesnt float into homes), or just using a stopcock or something restricted enough a couple centimeters of liquid back up to include some nice
forward pressure, you can drip the acid into a MnO2 chlorine generator, and send it back to some other section of the reactor via a tube, or bubble
it, because pressure from the chlorine would have to overcome the height of the S bend, or, pushing a bubble up a narrow tube with great resistance
without enough time to overcome gravity and water tension. since distillate drips in inconsistently, this doesnt stall out and you end up with 1-way
flow as long as something is condensing, its a hydrostatic check valve.
WD40_enjoyer - 15-7-2025 at 13:08
Not to seem negative but nahso4 is immensely cheap for me (~1.5€ per kg) so any way I could use that to make hno3 (and possibly h2so4 through
decomp) is gonna ne the best for me. However I'm very mich open to know which desicants will work best and of there is a way to get for example 30%
hno3 to anhydrous or close to anhydrous and then distill I'm all open to hear.
With that said all methods for making hno3 and h2so4 is welcomed by me since they may have advantages that my current process lacks. Radiums Lab - 15-7-2025 at 13:43
Anhydrous Na2SO4 and MgSO4 work fine but not upto fuming HNO3 conc.MrDoctor - 15-7-2025 at 13:53
what about nitrate? the wet method is meant to leave a fair bit of nitrate unreactedRadiums Lab - 16-7-2025 at 03:41
@Mr Doctor can you please eloborate your question.chloric1 - 17-7-2025 at 03:57
There are a few Youtubers doing this reaction and it does work. Two points I’d like to make:
1. From my observations, I’ve deduced this is something done over time to build up reserves as the acid generated, quite diluted and contaminated.
2. On concentration, most of the impurities, magnesium sulfate and possibly ferric sulfate from the clay pot, are insoluble and will precipitate. It
would better to concentrate acid in stages. Perhaps to specific gravity if 1.66 or 73% for example. At that point it will need to be filtered hot to
reduce viscosity through a glass wool plug in a glass funnel. For good acid, it should be distilled with a torch/gas burner and sand bath.
Although I can buy crude 93% sulfuric acid at hardware stores for $30 a gallon, I should start trying this just in case.
Radiums Lab - 17-7-2025 at 08:54
@chloric1 yea the impurities are truly a pain to remove.CuriousOnlooker - 23-7-2025 at 07:03
Not to seem negative but nahso4 is immensely cheap for me (~1.5€ per kg) so any way I could use that ...
Just to throw my hat into the ring, I would encourage you to employ what MrDoctor has suggested, particularly using a sand bath and
adding some inert substance into your boiling flask to break-up the solid mass as it cools down -- broken glass from a vehicle perhaps, or pieces of
broken porcelain, anything inert to break up the mass.
NaHSO4 may be cheap where you are but a couple of precautions may save your flask -- not to mention the mess, stress, and price of
replacing the flask, only to start over from scratch.
. 