Sciencemadness Discussion Board - Failed distillation of HNO3 from KNO3 ??

Failed distillation of HNO3 from KNO3 ??

Gammatron - 22-3-2023 at 08:24

So this morning I attempted a distillation of HNO3 using 550g of KNO3 and 300ml of rooto H2SO4 in a 1000ml rbf. I mixed them together last night so I could be ready to run the reaction in the morning but as soon as I started heating the mixture it foamed up to the neck of the flask. I pushed it back down with a stir rod and continued heating and melted down into a liquid as usual except I never got any NO2 fumes, just thick pale yellow fumes and all the glassware that was in contact with it fumed profusely, looked like wfna except it has no reaction with copper even after diluting with water. I didnt get a steady flow of distillate until 180C and it topped at 210C at the still head before I finally quit. The distillate does not fume at all and has no smell, ph paper shows high acidity and it only reacts with Al foil after some delay.

I also checked my KNO3 with some sugar and it burned as expected with little leftover residue and I also know my H2SO4 is of good quality, so wtf is going on?

[Edited on 3-23-2023 by Gammatron]

clearly_not_atara - 22-3-2023 at 10:00

Pale yellow fumes? Sounds like your KNO3 is contaminated with KCl.

Gammatron - 22-3-2023 at 11:04

KCl has an immediate reaction with H2SO4 at room temp producing a lot of bubbles. There was no perceivable reaction when I combined the acid and KNO3 and I stoppered the flask to keep it from absorbing moisture over night and there was no pressure release when I opened it in the morning.

ave369 - 22-3-2023 at 12:50

What's the source of your KNO3? Are you sure it's KNO3 and not, for example, NH4NO3? NH4NO3 can decompose on heating and produce a lot of useless outgassing and no HNO3 at all, and your distillate would be a weak solution of H2SO4 in that case.

To check it, try to dissolve your nitrate in water. If it is very very soluble, as in hundreds of grams per 100 ml, and cools significantly when dissolving, it is definitely NH4NO3.

[Edited on 22-3-2023 by ave369]

Gammatron - 22-3-2023 at 13:16

I believe this particular batch came from a fireworks supply store but I also have a bunch that I bought on eBay, not sure which exactly i was using. I'm at work now so I will have to check it when I get back home. It did appear that most of the fumes I made were of SO2 so seems like I was just decomposing the sulfuric acid, especially at those high temps.

ave369 - 22-3-2023 at 13:41

Well, if my guess is correct, there could be some H2SO4 oxidizing the ammonium and getting reduced, it's not impossible. H2SO4 also tends to decompose a bit when it is distilled, especially together with some sort of reducer.

[Edited on 22-3-2023 by ave369]

UC235 - 22-3-2023 at 14:20

Ammonium nitrate is much easier to use for making nitric acid because the ammonium bisulfate melts instead of being a horrible slushy foaming crystalline mess. All of my nitric acid has been made from NH4NO3. Your ratios are all fucked up though. You've got 5.5mol of KNO3 and maybe 2.85mol of sulfuric acid. The second proton on the sulfuric is useless, you should be using at least equimolar quantities, preferably excess sulfuric to ensure the distillate is fairly dried and the reaction mixture remains slushy.

Gammatron - 22-3-2023 at 14:43

Honestly I didn't even check the ratio. I just had that in my notes that I copied from an old nile red video and it worked pretty well for him.

Rainwater - 22-3-2023 at 15:15

Quote: Originally posted by Gammatron

Honestly I didn't even check the ratio. I just had that in my notes that I copied from an old nile red video and it worked pretty well for him.

Bad... bad madscientest.
You got to learn from the demonstrations not just copy them.
Here use this.
Attachment: Acid calculator.xlsx (10kB)
This file has been downloaded 236 times
Just fill in the orange squares with what you want and read the results.
It will tell you exactly the weights of reagents needed, assuming they are dry.

Their is even a tid bit at the bottom to make triations easier
Low heat and reduced pressure give the best yields.
My rig routinely gets +95% yields using extra water

Gammatron - 22-3-2023 at 15:20

I know... I say this with shame "Honestly I didn't even check the ratio." Cause now I probably just wasted a bunch of valuable reagents, but maybe I can save it by correcting the ratio and restarting?

Thanks for sharing that!

B(a)P - 22-3-2023 at 16:14

Quote: Originally posted by UC235

Your ratios are all fucked up though. You've got 5.5mol of KNO3 and maybe 2.85mol of sulfuric acid.

Really? Isn't 300 mL of (assuming concentrated) sulfuric acid about 5.5 moles? While I agree that an excess of sulfuric acid helps I consider the mass of reagents used by the OP to be workable.

Gammatron - 22-3-2023 at 16:34

If I put a target of 250ml of 90% HNO3 into the calculator it gives me very close values to what I used so that rules out having the wrong ratio so I guess I'm back to square one...

Rainwater - 22-3-2023 at 16:37

So was the 180c the hot plat temp, solution temp, or head temp?

[Edited on 23-3-2023 by Rainwater]

Gammatron - 22-3-2023 at 16:42

Head temp. Meant to put that in the original post..

[Edited on 3-23-2023 by Gammatron]

Rainwater - 22-3-2023 at 16:44

The "target product volume" on line 9 is anhydrous product.
Line 18 "total volume of target" is how much distillate you can expect with 100% yield
Is your distillate water soluble?

[Edited on 23-3-2023 by Rainwater]

Gammatron - 22-3-2023 at 16:46

I was just trying to find a target that gave a KNO3 value similar to what I used to see how much H2SO4 it called for.

Rainwater - 22-3-2023 at 16:51

The 180c is throwing me way off. It should have been 80~120c.
It couldnt have been ethylene glycol you would have blown up by now. It and nitrates are not nice together.
Do you have the msds on the acid source?

[Edited on 23-3-2023 by Rainwater]

Gammatron - 22-3-2023 at 17:03

It's a popular source among amatures. I've used it for other experiments and it works great.

I tried attaching a link to the pdf but it didn't work. It lists the only ingredient as H2SO4 93%, thought I think its actually closer to 96% iirc.

Rooto Drain Opener Sulfuric Acid MSDS

[Edited on 3-23-2023 by Gammatron]

Rainwater - 22-3-2023 at 17:14

The byproduct, was it a water soluble salt? One of the reagents has to be at fault.

[Edited on 23-3-2023 by Rainwater]

Gammatron - 22-3-2023 at 17:29

I will have to check it when I get home from work in a couple hours.

Herr Haber - 22-3-2023 at 20:51

KNO3 for fireworks is usually mixed with an anti-caking agent such as SiO2.
It shouldnt do much with the H2SO4 though and your temperature is very high so you should observe some NOx

Gammatron - 22-3-2023 at 20:59

So the "KNO3" is barely soluable in water both before and after the reaction. I noticed the slurry gets quite hot when mixed with water and I think its because it is full of unreacted H2SO4, I tried using it to make a nitration mixture for nitrocellulose before and all the cotton just dissolved into the acid so its definitely not making any HNO3.

At the time that I purchased the KNO3 I also ordered a kg of KCLO4 and I fear that something got mixed up along the way. Either by the seller or when I bottled them. That would explain the high temp distillate and why I got such a clean burn with sugar and the low solubility.. Ill have to do some more tests in the morning, thats a little scary if I was distilling HClO4.. and im gonna be pissed if I wasted all my KClO4 ):<

[Edited on 3-23-2023 by Gammatron]

Texium - 22-3-2023 at 21:28

Yikes! I was wondering if that could have been what happened when I first read this. Fortunately you probably didn’t distill much perchloric acid, since it is an even stronger acid than sulfuric, and boils at 203°C.

ave369 - 22-3-2023 at 22:26

So it was KClO4 actually. This is an even more fabulous mixup than I thought.

Quote: Originally posted by Texium

Fortunately you probably didn’t distill much perchloric acid, since it is an even stronger acid than sulfuric, and boils at 203°C.

From my experience, volatility matters more than acid strength, I've distilled HBr and HI using phosphoric acid which is significantly weaker than both of them, but less volatile.

[Edited on 23-3-2023 by ave369]

B(a)P - 23-3-2023 at 00:37

Quote: Originally posted by Gammatron

At the time that I purchased the KNO3 I also ordered a kg of KCLO4 and I fear that something got mixed up along the way. Either by the seller or when I bottled them. That would explain the high temp distillate and why I got such a clean burn with sugar and the low solubility.. Ill have to do some more tests in the morning, thats a little scary if I was distilling HClO4.. and im gonna be pissed if I wasted all my KClO4 ):<

[Edited on 3-23-2023 by Gammatron]

This definitely fits. When you heated the mixture any formed perchloric acid would have immediately decomposed yielding a lot of hydrogen chloride, oxygen and chorine, the foaming you observed. The fuming on the glass is likely from hydrochloric acid. You probably distilled a mixture of water hydrochloric acid and perchloric acid. How much did you end up with out of curiosity?

Edit

Just a thought - You should contact the seller, this was potentially a dangerous situation and as you say, you have likely wasted a very useful reagent. I guess it depends how certain you are that the mistake was not yours.

[Edited on 23-3-2023 by B(a)P]

Rainwater - 23-3-2023 at 00:53

Be very, very careful with this reaction gone wrong.
5ml of perchloric acid 70% was added to a blob of vacuum grease while hot(100c ish). From a safe distance
Just to see what the fuss was about.
My ears are ringing just thinking about it.
Shrapnel was fast.
Detonation was delayed and initiated by bumping the table

Gammatron - 23-3-2023 at 07:28

I did a bunch of small scale tests which ended up leaving me even more confused...

These were done in mg quantities in test tubes, all heated over a bunsen burner to drive the reaction and I did multiple test with varying amounts of added water:

NH4NO3 + H2SO4 + Cu = Lots of NO2 and bubbling

"KNO3" + H2SO4 + Cu = Dense white fumes and slight blueing of mixture

"KClO4" + H2SO4 + Cu = Nothing at all

I tested two different batches of KNO3 from two different sellers and got the same result, the sulfuric acid does not react with it at all and I think the white fumes are just SO2.

I did a burn test with the KClO4 and both samples of KNO3 in 2:1 oxidizer to sugar, all 3 burned with a hot flame with a hint of purple as expected but the KClO4 burned noticeably more vigorous. Also both of my KNO3 samples are clumpy powder and the KClO4 is a free flowing powder which seems about right, so I don't actually think anything was mixed up at this point. Im at a loss... I just wanted to make some nitric acid and have fun ):

[Edited on 3-23-2023 by Gammatron]

ave369 - 23-3-2023 at 07:44

Your KNO3 is obviously not KNO3. The question is, what it is actually. It is not NH4NO3, it is not KClO4.

Let's sum up the known properties of this material:

* Sparsely soluble in water
* Produces fuming and foaming with H2SO4, fumes are yellow
* Is an oxidizer, burns vigorously with sugar, flame has a hint of purple

IDK.... Maybe Berthollet's salt (KClO3)?

What do the crystals look like? Are they needle-like or scale-like? Try to recrystallize it in hot water and tell us the shape of the crystals.

[Edited on 23-3-2023 by ave369]

Gammatron - 23-3-2023 at 07:59

Definitely not KClO3, that immediately reacts to form HClO3 which is unstable and yields bright yellow ClO2. I will do a recrystallization right now

Rainwater - 23-3-2023 at 08:44

I will suggest a flame test.
If it is not KClO₃ or KClO₄ then its not a potassium cation.
Then some basic reactions like showen in these videos.
H2SO4 https://youtu.be/HtCN_iDQdio
Cations part 1 https://youtu.be/F7cSlwKfoHw
Cations part 2 https://youtu.be/VAy76V4THlY
Anions https://youtu.be/GXCTABFPabM

Dont forget. Most them youtubers make it look easy by screwing up off camera

Gammatron - 23-3-2023 at 08:51

I should note that the white fumes did not evolve until after strong heating. At room temp there's no reaction.

I remembered that I had a small sample of KNO3 recrystalized from stump remover and when I added the acid to that with a piece of copper it started reacting without heating. I'm thinking that the KNO3 I got from the fireworks place all got put into storage because I thought I was well stocked with the stuff I got on ebay which is what I've been using all along.

It seems pretty hydrophobic and it won't even begin to dissolve until the water is near boiling. It recrystalized into a fine sand-like consistency. It is fairly dense and settles out quickly after being disturbed.

Doing a flame test causes it to melt and rapidly decompose into white smoke with almost no residue, didn't notice any color change of the flame.

[Edited on 3-23-2023 by Gammatron]

ave369 - 23-3-2023 at 10:43

Definitely not KNO3. I swear, if it's KNO3 then I'm a Chinese pilot. KNO3 forms distinctive long needle-like crystals. Like this

The thing about decomposition into white smoke with no residue makes me again think about ammonium. Not nitrate, maybe ammonium perchlorate?

Damn, this thread begins to look like a mystery novel...

Try a standard alkali test for ammonium? Add concentrated NaOH and take a whiff. If it smells like ammonia, then it's an ammonium salt.

[Edited on 23-3-2023 by ave369]

Texium - 23-3-2023 at 10:57

Quote: Originally posted by ave369

Not nitrate, maybe ammonium perchlorate?

Probably not, given the solubility characteristics. Though not as soluble as sodium perchlorate, it's still appreciably soluble in water, and it sounds like this stuff isn't.

Gammatron - 23-3-2023 at 11:41

No reaction with hot NaOH or NaOCl, not sure what other chemicals I have that I can test it with. I guess I could try making flash powder with it since it burns so well with sugar.

Of all the cheap and popular oxidizers, this stuff doesn't seem like it could be any of them. I mean maybe the purple hint in the sugar flame was just in my head cause I wanted to imagine it was there but it burned just like KNO3. Even tho I bought it for making HNO3 I am not so upset since it's still useful for pyrotechnics... I just want to know wtf it is lol

Gammatron - 23-3-2023 at 11:52

So I made some flash powder 5:3:2 - Ox:Al:S and hit a little pinch of it with a hammer and now my ears are ringing... It made a very bright flash and was about as loud as a 9mm, pretty impressive power actually!

But the mystery grows, as the powder cannot be lit with a flame, it just decomposes and melts.

[Edited on 3-23-2023 by Gammatron]

ave369 - 23-3-2023 at 12:24

I guess this significantly narrows down the search. Not all flash powders give very loud report on shock. I think that someone from Energetic Materials subforum could identify the oxidizer. The crystal shape made me think of potassium persulfate (I happen to have a sample on my shelf), solubility matches too, but the decomposition confuses me, potassium persulfate does not decompose with little or no residue.

[Edited on 23-3-2023 by ave369]

Gammatron - 23-3-2023 at 12:32

Should I start a new thread? Since this went from a failed distillation to figuring out a mystery oxidizer

ave369 - 23-3-2023 at 12:33

I think yes.

Texium - 23-3-2023 at 13:55

I’m going to close this thread now to prevent cross-posting, being as the answer to why the distillation didn’t work has been resolved. For future readers, the new thread is here: https://www.sciencemadness.org/whisper/viewthread.php?tid=15...