Sciencemadness Discussion Board

Nitric Acid Failure...Please Help

jharmon12 - 27-2-2013 at 07:09

Hello group.

I am new here and wanted to introduce myself. My name is Joel and I have a 17 year background in fireworks manufacture on a hobbyist scale. I am a member of the Pyrotechnics Guild International and have won numerous rocket and aerial shell competitions. With that said, I just wanted to establish that I have exposure to energetic materials and hazardous substances. I don't want anyone to think I am a total "newb".

I obtained a 1000 ml retort for the purposes of making nitric acid to produce flash paper and flash cotton. I used this retort last night to attempt to produce nitric acid, but things didn't turn out as I had hoped. I want to describe what I did, and then present questions on what I might need some clarification on.

I put 85 grams of sodium nitrate prill into the retort. I added 147 grams of H2SO4, which I determined to be between 93 and 95% concentration using the specific gravity approach. These gram amounts are what I thought would be optimal based on some research I have done on stoichiometry of H2SO4 and NaNO3 to produce HNO3. I stirred it with a glass stirring rod to get it as mixed as possible. I placed the retort in a lab stand and set it on my flameless mantle that had a round ceramic fitting to fit the bottom of the round retort. I turned on the heating mantle and let it gently start warming up.

While this was warming up, I put a 1000 ml graduated cylinder in a 2000 ml beaker, and surrounded the cylinder with cracked ice. I brought this back into the lab and put the iced beaker/cylinder at an angle so that I could slide the long arm of the retort into it. The retort arm was into the cylinder about 3-4 inches.

The mixture slowly started to bubble and then the mass raised up in the retort, so I turned the heat down slightly so as not to use too much heat. I could clearly see red fumes in the retort and in the retort arm. The mixture was bubbling away. Fumes started to come out of the cylinder and get into the air, so I used a few layers tape to seal the area between where the retort arm went into the glass cylinder. This worked, as the fumes quit coming out. This kept the fumes in the retort, retort arm, and cylinder.

The red fumes went on for about an hour, then I turned the heat off after the reaction seemed to be done (no more red fumes). I was left with some liquid and coarse salt cake in the retort. When I pulled my cylinder out from the ice, I had a very small amount of nitric acid. I weighed it and I had only made 3 grams of nitric acid from 85 grams of NaNO3!!!! An hour wasted!

Some thoughts and other comments:

1. The retort was only 1/8th full. This possibly could have contributed to the low yield because all the nitric somehow got destroyed before it could even move out of the retort.
2. I didn't have ice around the arm of the retort. This could have contributed to the low yield because the nitric vapour couldn't condense.
3. I noticed that red vapour stayed in the retort and in the retort arm, but I never really saw it in the cylinder, so I assumed that it was condensing. It obviously wasn't, since I only got a few grams of material. Looking back, it appears as though the nitric vapour never condensed. It just floated around and I don't know where it went. This part is a mystery.
4. The mixture bubbled gently, but I did not let it boil hard at all.
5. I didn't have a vacuum. I have heard that you can increase yield by doing this whole process under a vacuum.

So here are my questions:

1. First, let's establish this: What is the optimal amount of sodium nitrate to use with 147 grams of concentrated H2SO4, in order to maximize yield and minimize waste (in grams)? Am I right that it is around 85 grams of NaNO3?
2. What is the right amount of heat to use to minimize waste and maximize yield, based on your experience?
3. Using those numbers from question 1, what should my actual yield of fuming nitric acid be, based on everyone's experience? I know that theoretical yield is going to be higher than the actual yield that one should expect using a relatively inefficient home lab.
4. Did I somehow destroy my nitric by using too much heat? Did I reduce my yield by not using enough heat? It was bubbling gently, but not boiling.
5. Is using a vacuum necessary to get a reasonable yield?
6. Should I have used more concentrated H2SO4? I could have concentrated it, but didn't think it was necessary since it was about 93%.
7. Why does it seem that the vapour is not going over to the cylinder? It's like the vapour just stays in one place and doesn't do anything. It's as if I need to apply suction or airflow to keep the vapour moving from one part of the retort to the end of the retort.
8. Do I have to have ice around the retort arm?
9. Should I have filled the retort up to the very top with H2SO4 and NaNO3 so the vapour has literally nowhere to go but out?

Thanks for your patience in this. I know I am asking a lot of questions, but I just can't figure out where I have gone wrong on this. I hope that you guys can help me with this problem.

Regards,

Joel

hissingnoise - 27-2-2013 at 07:54

You really need a proper condenser to condense HNO3 vapour . . .
The side-arm of the retort quickly becomes too hot for purpose!

Equal weights of acid and nitrate can be used if H2SO4 is ~98% but with lower conc. acid upping the nitrate helps for RFNA!

jharmon12 - 27-2-2013 at 07:59

Actually, the side arm on my retort was not getting hot, or even warm. I felt the part of the retort arm that wasn't in the cylinder periodically throughout the process, and it stayed at room temperature during the whole process. I think this is probably because the retort was so large that the heat didn't really have a chance to get the arm warm.

I know that retorts have been used throughout history to make nitric acid. I would hate to think that I can't effectively make nitric acid with a retort.

Thanks for the tips on the quantities of acid/nitrate. And thanks for the response.

Regards,

Joel

plante1999 - 27-2-2013 at 09:15

I think you are heating too much the nitrate and sulphuric acid, slight 80-85 degree Celsius is recomended for the distillation, or you will get nitrogen oxides and water decomposition product, try it back at lower temperature, use a sand bath and thermometer if nessecery.

hissingnoise - 27-2-2013 at 09:56

Quote:
I think you are heating too much the nitrate and sulphuric acid, slight 80-85 degree Celsius is recomended for the distillation.

Sulphuric acid/nitrate mixtures boil @~120°C, as does the HNO3 azeotrope.
Below this temp. the rate of vaporisation is too low for efficient distillation!

And a small water-cooled RBF should be a better receiver than a cylinder!
Quick and efficient cooling is the key!

plante1999 - 27-2-2013 at 09:58

Well, I think the low vaporisation is a good rate, at least for me. Better than overpowering air condensor, or destroying your product.

jharmon12 - 27-2-2013 at 10:44

I do have plenty of florence flasks. I could immerse one of them in ice water and see if I get a better result. Perhaps add salt to the ice water....

Would it be helpful to somehow pack ice around the retort's arm to get it as cold as possible, or would that just be a waste of time?

Also, if I am using a 1,000 ml retort and am only using 85 g of NaNO3 and 147 g of H2SO4, is that too little of an amount of material to try and react in such a large vessel? I guess I am asking if I need to react a larger quantity in order to minimize the amount of vapor in the retort's body.

It's as if the vapor lingers in there and never makes it to the "other side".

Thanks for the help so far!

Joel

[Edited on 27-2-2013 by jharmon12]

MrHomeScientist - 27-2-2013 at 10:51

First, I'll direct you to a video I posted on my YouTube channel on how I made my own nitric acid: http://www.youtube.com/watch?v=PYDFplw8iKg
I used ammonium nitrate and ~98% sulfuric acid. Watching that should give you a frame of reference for my comments below.


1) NaNO3 + H2SO4 == HNO3 + NaHSO4
Let's assume the low end and say your acid was 93%. That means your 147g of acid equates to 136.71g H2SO4. Stoichiometry then tells us that you need to use 118.6g NaNO3, which would be the minimum you should use based on your acid strength.

2) I never measured the temperature of mine all that accurately, but close to 100C I think is the goal.

3) Theoretically you should get 87.9g HNO3 using that amount of sulfuric acid. In practice you get quite a bit less because some of the acid inevitably decomposes. I think I got something like 50mL. I didn't really keep track of yield, but it's about time I make more so if I do that anytime soon I'll keep better records.

4) Overheating can definitely destroy your product, producing NOx gases (NO2 caused the brown haze you saw). "Bubbling gently" is how I would describe my run.

5) Vacuum isn't required, but it certainly improves yield by preventing thermal decomposition of the product. That's the only way to produce white fuming (WFNA) rather than red fuming nitric acid (RFNA).

6) Your concentration of acid should be fine for this. Try a titration to see exactly how strong it is, then you can make accurate stoichiometry calculations.

7 - 9) Agree with the others - it sounds like you had insufficient cooling in your condenser. As long as you're boiling, the gases will find their way to the outlet of your system; there's no need for any sort of blower setup. Edit: It may appear that the vapors linger in the retort bulb, but that's because there's more space there and it is easier to see the brown color of NO2. In the thinner portions the vapor is still there but is much less visible, in my experience.

Hope that helps!

[Edited on 2-27-2013 by MrHomeScientist]

hissingnoise - 27-2-2013 at 11:00

Quote:
I could immerse one of them in ice water and see if I get a better result. Perhaps add salt to the ice water....

Place your receiver in a sink so that cold water can be run onto the main body of the flask!
The side-arm should go in far enough to be close to the bottom of the receiver so that vapour leaving the retort immediately impinges on the cooled glass of the receiver . . .
If this fails, a condenser and some way of attaching it to the retort side-arm would seem called for!

jharmon12 - 27-2-2013 at 11:34

Goddamn! Thanks Mr. Home Scientist. I really was wondering about those numbers you have just posted. I really want to minimize the use of H2SO4. I don't care about the nitrate. I have plenty of that. These numbers also help me to have something to shoot for for yields. :-)

I watched your video and have actually never seen it before. I thought I had seen all the nitric acid videos on youtube, but I apparently haven't, and this one was very good. I like the idea of wrapping the flask with Al foil to keep the heat as consistent spread out as possible.

I also like the idea of using AN to make nitric. I have many, many pounds of it and got it very cheap! All I have seen in my searches have been people poo-pooing the use of AN because it is more trouble than it is worth for making nitric. This video seems to prove them wrong.


Thanks,

Joel

jharmon12 - 27-2-2013 at 11:37

The side-arm should go in far enough to be close to the bottom of the receiver so that vapour leaving the retort immediately impinges on the cooled glass of the receiver
------------------
This makes a lot of sense. I will do this next time as well. This gives the vapor less time to "rattle around" in the receiving container.

Thanks,

Joel

hissingnoise - 27-2-2013 at 11:58

Quote:
I also like the idea of using AN to make nitric.

I used AN for HNO3 with a slight excess of H2SO4 (to bind-up any remaining moisture) just once . . .
I found that as distillation progressed, the acid coming over was becoming diluted due to oxidation of NH4 by hot H2SO4!
Well dried alkali metal nitrates are, IMO, capable of producing a stronger product!


hissingnoise - 27-2-2013 at 12:04

Quote:
but with lower conc. acid upping the nitrate helps for RFNA!

Ooops! That should be; "lowering the nitrate content helps for RFNA!"

MrHomeScientist - 27-2-2013 at 13:42

No problem! Glad you liked the video :) I'd heard the negativity about AN as well, with I think the main complaint being it tends to decompose at higher temperatures. Seemed to work out fine for me though, I've never had any problems with the acid I made. Hissingnoise's experience sounds like a plausible outcome as well.

The amount of sulfuric you need will remain the same no matter what nitrate salt you use - the stoichiometry stays the same at a 1:1 ratio between the acids. Edit: Actually, an exception would be if you use calcium nitrate, then it's 1:2 H2SO4:HNO3.

You could always convert your ammonium nitrate to sodium, potassium, or calcium nitrate, if you prefer, by mixing it with the corresponding hydroxide:

NH4NO3 + KOH == KNO3 + NH3 + H2O

This produces copious amounts of ammonia gas, though, so be careful and do that outside! You can either mix solutions together, or if you want to collect ammonia for other experiments a better way is to mix the solid chemicals together, and drop a very small amount of water onto the mix. Since the reaction produces water, it should keep itself going, producing moist ammonia gas.
KNO3 is also found in some types of stump remover.

[Edited on 2-27-2013 by MrHomeScientist]

jharmon12 - 27-2-2013 at 14:22

Thanks for the tips, Mr. Home. Thanks to hissing as well for his comments on RFNA.

I actually have lots of sodium and potassium nitrate as well. So I really don't need to do any conversions. But when the sh*t hits the fan, it's good to know how to be entirely self sufficient. :-)

The difference is that I paid for the sodium and potassium nitrate, but I got a lot of the AN for free and some for .35/lb from a co-op. So if I can, it would be ideal to use AN for conversion to nitric, but it is not necessary.

I first want to perfect my process with NaNO3 and then maybe I'll try it with NH4NO3.

Thanks,

Joel

jharmon12 - 5-3-2013 at 14:13

Success. I followed some of the advice I got here and ended up with 240 ML of RFNA, which ended up being 348 grams (specific gravity 1.450) at 60 degrees F.

Here is what I did: All my sodium nitrate is used up and I have to get more at my storage location, so I loaded the retort with 355 grams of milled KNO3 and 410 grams of H2SO4, based on the info provided by Mr Home Scientist.

I stirred it up, covered it with Al foil, and put the heat on. The receiving container was a 500 ML florence flask in a metal bowl full of ice water. I covered the neck of the flask with ice and snow as much as I could.

It heated up and appeared to be making acid, so I walked away after I knew the heat was sufficient to NOT BOIL OVER.

I came back and there wasn't any acid coming across. It took about an hour. This indicated to me that it was done. I pulled the florence flask up and it only had maybe 5 ML! I couldn't believe I had the same problem again with such a sh*tty yield!

So I put a ring of Al foil around the retort arm where it entered the florence flask to make sure vapours were not getting out. I added another 210 grams of KNO3 and more acid. I turned it on again and gave it more heat this time. I figured that if it wasn't going to work, I can at least see what more heat will do.

I made sure it wasn't going to boil over and left it bubbling away. I came back and noticed that there was a lot of clear liquid going down the arm, almost like air was blowing it down the arm. So I waited and this eventually stopped. The material started to rise in the retort, as if it had gotten too hot suddenly. So I turned the heat down and no more acid could be had. I pulled out my florence flask and this time I had a lot of acid in there....it was half full.

So I measured it and my numbers are listed above. 565 grams of total nitrate and I ended up with 348 grams of acid. That's not theoretical yield, but it is closer.

I am not sure if more heat was the secret, or having a fuller retort so the vapor didn't have anywhere else to go but down the arm, or if the Al foil ring helped to keep any vapor from escaping. I am just not sure what helped the process this time since I changed so many things at once.

Just wanted you guys to know.

Thanks for the help so far and I am still open to suggestions, if you all have any.

Regards,

Joel

Bot0nist - 5-3-2013 at 14:45

Congradulations! I remember my first nitric acid run. Grab some jointed glass and a real, water cooled condensor if you want to get a little more efficiant and safe.

Not saying you dont know, but be careful with that stuff. Its fuming horrible clouds of insidious death (only a little hyperbole). Becareful with any possible nitrations for this, and other reasons too.

If you havent read the sticky "life after detonation," its a good read.

Have fun. The journey into chemistry is life enrichening.

cyanureeves - 5-3-2013 at 16:12

i also have been plagued by rising mixtures and dont know what is going on but i think i will try the ammonium nitrate method.the last time i made nitric i just let it all rise out into the condensor then i redistilled and lost an incredible amount of yield.the only thing different that i have done in my failure attempts seems to be the mixing of reagents thoroughly.since i have more reagents now i haven't bothered to mix properly and prills always saturated very easily without mixing.the only prills i have is ammonium nitrate so AN is what i will use now but i swear it's like gremlins sneak in my shed and put a pinch of soap in the mixture.good thing you got good nitric now jharmon12.

[Edited on 3-6-2013 by cyanureeves]

Bot0nist - 5-3-2013 at 16:38

Possible solutions to foaming;

A larger excess of sulfuric acid.
Very dry nitrate salt.
Gradual, consistant heating.
Larger RBF, or reaction vessle.
Anti foaming drops (possible compatibility issues?)

Just some brain storming.

Magpie - 5-3-2013 at 19:33

Quote: Originally posted by cyanureeves  
i also have been plagued by rising mixtures and dont know what is going on...


I found that crappy tree stump removal KNO3 had some kind of oil that increased the amount of foam. This subsided greatly when I switched to pottery grade KNO3. Also I use a Claisen adaptor to help deal with foam as shown below:


Attachment: nitric acid.doc (93kB)
This file has been downloaded 404 times

Also, slowing down the heating helps IIRC.

jharmon12 - 6-3-2013 at 08:33

Botonist, that was my third nitric acid run. The first one was 185 grams of NaNO3 and yielded me only five drops of nitric. The second one was making nitric well using two flasks taped together, but the mixture boiled up and shot across to the other florence flask and ruined the batch. This third yield also started boiling up, but I was able to stop it before it became a problem. I think this stuff boils up when you get less nitric acid content in the retort mixture as you are making it, but I am not sure. It seems to be able to handle high heat for a while, then when the nitric acid coming across starts to slow down, it starts boiling up.

I plan on getting a water cooled condenser to continue my experiments.

I just love this and wonder why I never tried it before. Oh, I know...because it involves fuming nitric acid! But seriously, I do think this is an excellent hobby. I have my nitric stored in a bucked, in a black trash bag, in a glass stopped glass bottle. It is cold outside and the stuff won't even fume outside. In other words, it is very tame right now. When it starts getting hot outside, I hope to have some amber bottles and PTFE lids and plan to store the stuff in a hole in the ground.

I also nitrated some tissue paper and cotton with it and man is that shit hot! The cotton balls were the third nitration with the same acid mix I used for two previous paper nitrations. Since I had acid mix left over from my previous two tissue paper nitrations, I figured I would try some "guncotton". I washed the cotton and the paper three times and also used ammonium hydroxide for a fourth soaking for same. Then water washing again for two more times. Then checked with litmus paper and it is reading a 7 or 8. You touch the cotton with a burning joss stick, and it literally burns like anitmony sulfide/Al/perchlorate flash powder (very, very fast...fooomp!). The tissue burns like I expected, but it seems faster than commercial.
------------------------------------------
cyanureeves, I think that you can get nitric acid yield faster with granular crystal nitrate rather than prills. Ball milled powder is hard to mix with the sulfuric acid, and I think the unmilled prills (I used NaNO3 prills) take too long to make the acid. Also, someone mentioned here or somewhere else that AN is okay to use to make nitric acid when you have a condenser and use a vacuum. I guess it is really efficient using this method. Otherwise, it is recommended to use an alkali metal nitrate.
------------------------------------------
Magpie, Nice picture. Is the stopper on top of the mixture vessel with the thermometer in it made of teflon? I can't see PTFE holding up really well to HOT nitric acid fumes, but maybe it does? Also, please forgive my ignorance, but what is the clear tube coming out of the receiving vessel for? In regard to stump remover, I have never used it. It seems like most of my luck came after I started using granular crystal. I use Haifa brand 13.75-0-46 KPN ratio greenhouse grade potassium nitrate. It comes in 50 lb bags and you can get these from farm supply stores and hydroponics suppliers. I plan on milling NaNO3, 2000 grams at a time, for about 15 minutes to get a granular crystal that is NOT a powder. This should be ideal, based on my experience so far.

Regards,

Joel

hissingnoise - 6-3-2013 at 09:05

Quote:
Also, please forgive my ignorance, but what is the clear tube coming out of the receiving vessel for?

It's to connect the adapter to a vacuum source!
The lower temp. used for vacuum distillation produces WFNA . . .

Magpie - 6-3-2013 at 09:11

Quote: Originally posted by jharmon12  
Is the stopper on top of the mixture vessel with the thermometer in it made of teflon? I can't see PTFE holding up really well to HOT nitric acid fumes, but maybe it does? Also, please forgive my ignorance, but what is the clear tube coming out of the receiving vessel for?


Yes, that's an Ace ptfe thermometer adaptor. It holds up fine in the hot nitric acid vapor. That's what I bought it for. Even the rubber o-ring holds up, which I suspect is made of Viton.

That clear tube is just a Tygon tube directing any escaping NOx/HNO3 vapors to the suction of my fume hood.

FYI there's a nice U-tube video on making fuming nitric acid, by MA Bakken, IIRC.