Sciencemadness Discussion Board

Nitric acid stills

madscientist - 20-5-2002 at 17:03

I think it would be useful to others if everyone here who possesses or had at one point a working nitric acid still to share images, diagrams, or written descriptions of it. I will do my best to describe my most recent revision to my design, which will be tested later tonight.

I use a single burner propane camping stove. I use sodium nitrate and sulfuric acid to make my nitric acid. The ratios are 55ml of concentrated H2SO4 for every 85g of NaNO3. The NaNO3 is powdered; if it is left in pellet form, yields will be very low. I use glass tubing that was originally straight, but I heated and bent it using my propane burner. To seal the connection between the flask containing the sodium nitrate / sulfuric acid and the glass tubing, I use sheets of teflon. I do not purchase the teflon in sheet form. I buy rolls of telfon ribbon, lay out many strips overlapping on top of each other, and melt them together using a soldering iron. This results in a sheet of telfon. I wrap the teflon tightly around the connection between the flask and the glass tubing. To further tighten the seal, I then wrap aluminum foil around that (aluminum is resistant to attack from nitric acid; I would use that instead of the teflon, except the sulfuric acid vapors corrode the aluminum). Then to tighten the seal further I apply duct tape. At the other end is the collection flask. This flask is in an ice bath. The seal for this flask is similar to the other flask, except it is only loosely sealed. If it is tightly sealed, then pressure will build inside the two flasks and the glass tube until leaks spring in places not of your choosing. About halfway down the tube is a ziplock baggie filled with a mixture of sodium chloride and crushed ice; this baggie is wrapped around the tube; this condenses the nitric acid. This is about the best description I can offer. Right now I am not on my computer and so I cannot draw a diagram in MS Paint. I do not own a digital camera. However, if I can borrow one in the near future, I will not hesitate to photograph my still and upload images onto a website.

Polverone - 20-5-2002 at 17:03

I use nitric acid only rarely. I don't use it for nitrations (I have no convenient place to enjoy any nitrated materials at this time). Therefore I have invested very little effort in my setup. I put powdered potassium nitrate and sulfuric acid in a glass soda bottle and turn it on its side. The tapering glass mates nicely with a glass teriyaki sauce bottle's mouth. The first time I padded the joint with teflon tape but there's very little loss of product even without it. The sauce bottle is wrapped in plastic bags of crushed ice/water. The whole setup is balanced on a couple of cinder blocks so that the rear half or so of the soda bottle is suspended in the air. This I heat with a bunsen burner held with metal tongs (to save my hands should the crappy glass suddenly shatter). This setup is low- yield and low-effort, perfectly adequate for my current needs. I can even throw away my distilling vessel afterward should I so desire. It's not like I'm not going to be drinking more soda. I don't even bother with precise measurements for the materials. Compared to other lab supplies, sulfuric acid and KNO3 from consumer sources are dirt cheap. I don't know exactly how pure the acid I produce is. It's definitely yellowish (almost orange when still hot), so there's probably considerable free nitrogen oxides in it. I also wonder how much sulfuric I'm distilling over with the nitric. Next time I make some I'll test it for sulfuric with barium chloride.

If I wanted to make more acid I would probably invest in a setup like that detailed in Pyro500's PDF on nitric acid production. But right now it's not worth it. I don't want to invest $100+ in a vacuum distillation setup (despite the numerous uses) at the moment. Besides, my relatively small rental room is already crammed with gear and chemicals. I wouldn't have a good place to store it.

madscientist - 20-5-2002 at 17:06

I finally got around to testing that still design I suggested earlier in this thread. I am pleased to announce yields indistinguishable from 100% yields. I am using dried sodium nitrate and a pyrosulfuric acid / sulfuric acid mix (oleum) as the reactants; this insures that no water is released. The nitric acid produced is indistinguishable from 100% concentration.

Polverone - 20-5-2002 at 17:08

Where do you get 100% nitric to serve as your reference sample (when you say your nitric is indistinguishable from 100%)? And for that matter, where are you getting oleum from? Are you making your own sulfur trioxide and dissolving it in conc. sulfuric? If so, I'm impressed. But for 100% nitric I would think it would still be easier to distill under reduced pressure using ordinary conc. sulfuric. Have you used it to nitrate anything interesting yet?

madscientist - 20-5-2002 at 17:09

Sorry, I now realize how poorly worded and confusing my previous post in this thread was... What I meant by "indistinguishable" is that with my analytical techniques, the nitric acid is concentrated, as far as I know. The density is 1.5g/cm3, and it reacts violently with oxidizable organic compounds. For example, I recently poured about 10ml of my nitric acid onto frozen mud, temperature of the acid was around 50 degrees Celcius; there was several loud *crack* sounds, and the mud foamed up instantly, forming a sponge- like chunk of carbon. Yes, I did make the oleum by bubbling sulfur trioxide gas into concentrated sulfuric acid. I created the sulfur trioxide by jetting sulfuric acid vapors over anhydrous magnesium sulfate; the magnesium sulfate absorbs some of the water that composes the sulfuric acid vapors, leaving an excess of sulfur trioxide. The sulfur trioxide was then bubbled into concentrated sulfuric acid. Something key that I forgot: nitric acid is broken down by light into nitrogen oxides and water. My 60ml of nitric acid is now an orangish color, just from spending around an hour in dim light. I also am encountering problems with the above still design; the seal seems to enjoy springing leaks. The problem is I cannot use anything except glass, teflon, and aluminum to make the seal; this does not make for a tight seal. Recently I was producing nitric acid, and a large leak must have been sprung, for my backyard was engulfed in a fog of nitric acid vapors. This fog rapidly turned yellowish then reddish as the floodlight outside broke down the nitric acid; I did not dare go outside to go attempt to fix the hole in the still, for I did not have chemical warfare protection gear, or an oxygen tank. The snow outside now possesses a yellowish tinge. Any suggestions on how to tighten the seal are welcome. I have not attempted to nitrate anything yet. I have never had any pentaerythol, and I am out of hexamethyltetramine and phenol. I am thinking of a way to produce phenol on my own, though... soon I will start a thread on that subject.

[Edited on 22-5-2002 by madscientist]

Polverone - 20-5-2002 at 17:09

Interesting. Can you build any sort of framework to keep the pieces of your apparatus tightly connected at the joints? I just moved cinderblocks into appropriate positions to keep my vessels from moving. Nobody has an unlimited budget, but it sounds like you should be saving your pennies for some real ground glass joint labware and an aspirator. And once you have those items, there are many interesting things you can try apart from nitric acid as well.

Polverone - 20-5-2002 at 17:10

Quote:
Why not try attaching the still to a vertical peg-board. Just use some sort of tie to hold each part to the peg board and I imagine it should keep the still in place.

By the way, what does creating a vacuum in the still do for the distillation process?


A partial vacuum lowers the boiling point of the acid. Being able to distill the acid at a lower temperature means higher yields and less contamination with nitrogen oxides (since heat breaks the acid down).

[Edited on 22-5-2002 by Polverone]

Coen - 20-5-2002 at 17:11

I must say I have quite some experience with destillations of nitric acid.

I distill one part of 40% HNO3 with two parts conc H2SO4, and this is repeated two times with the obtained destillate. The obtained product is nearly pure nitric acid with a density of 1,56-1,58 g/cm^3 and usually has a concentration of 98,5-99,5%. The best way of determing the exact concentration is titration.

Also it is not really necessary to destillate under vaccuum although a lot of (also scientific) sources claim this. But in practice it seems that it doesn't matter that much.

Years ago I still made my nitric acid using H2SO4 and KNO3, but since you can recycle your H2SO4 with the method a described above, which is off course a lot more economical, I don't do this anymore.

PHILOU Zrealone - 20-5-2002 at 17:11

I must say that I have a glass rod distillator and that it is a good way to get nearly pure white fuming HNO3!To control wel the T, I use a stirred oil bad in wich my reactor is diving to about half height! The oil bad is heated electrically to avoid any fire/ hot spot!

The problem with NaNO3/KNO3 /concH2SO4 process, is that it renders the solution very viscous and terribly bubbling due to the number of nucleation site of the solid nitrate suspended in it; agitation is hard and distillation is low; with this high viscosity, you need to heat stronger to "evaporate" HNO3; higher heat means decomposition of the HNO3 into NOx; the resulting HNO3 is red; and upon standing in dry air flow turns deep orange-yellow.If you have no other alternative, use this process with NaNO3 (dried); NaNO3 is more soluble than KNO3 so does NaHSO4 vs KHSO4!
Also not to say that to manipulate the original flask after reaction, you have to wait it cools down; a lot of HNO3 is stil in there and the NaHSO4 or KHSO4 cakes. NaHSO4 is easier to wash away by heating with H2O; KHSO4 being less soluble is more of a trouble.
A good way if you have no alternative is to use this process under vaccuum; HNO3 will be taken off the viscous matrix at lower T and you should end with a nearly white conc HNO3.

Another way that has been mentionned is HNO3 conc + H2SO4 conc codistillation (I have used with success HNO3 40% and H2SO4 96%); after a first distillation HNO3 has an average concentration of 80%; after a second distillation you have 98-99%HNO3. The acid is pale yellow without any vaccuum.
Here being more fluid the acid volatilise much faster from the mix; but the speed is not that high for the distillation since there is a lack of nucleation sites.; The original flask is easy to wash after cooling and the dilluted H2SO4 with a little HNO3 can be recycled if needed!

A final way to make this is an hybrid version of the two:
NaNO3 + conc HNO3 + conc H2SO4
This combination offers the advantages of both processes, high yield, moderate T, low viscosity, and a few nucleation sites from tiny NaNO3 cristalls but (much more controlable than in the first process where the heat is critical on bubbling rate; here it is constant); this allows faster distillation.NaHSO4 is almost fully dissolved and doesn't cake when cooled down.
Typical first distillation gives HNO3 of 90%; second distillation provides HNO3 99%.

Ratios are:
Process 1:
2 V NaNO3/3 V H2SO4
Process 2:
1 V HNO3/2 V H2SO4
Process 3:
1 V NaNO3/2 V HNO3 /3 V H2SO4

NaNO3 is oven dried at 120°C
H2SO4 is 96%-98%
HNO3 is 40-69% (yield and % increases with %!)

For Madscientist:
I have some ideas that you will for sure likevery much:
After all, I'm not chemical engineer for nothing ;-)

MgSO4 and CuSO4 can catch a lot of water!
MgSO4 + 7 H2O --) MgSO4.7H2O
CuSO4 + 5 H2O --) CuSO4.5H2O
I would prefer CuSO4 since the effect is visual (CuSO4 anhydrous is white amorphous powder; when hydrated, it is deep blue; while MgSO4 is amorphous when anhydrous and white transparent when hydrated).
Anyway:
HNO3 diluted will concentrate upon exposure to the anhydrous salts.
Add the powderous salts into the diluted acid, stir a little, warm a little to dissolve the salt and oversaturate the solution; then place in the fridge or the freezer; cristalls will appear; vaccuum filter when cold on glass paper filter (normal paper is eaten by HNO3).Recycle the cristalls by dehydrating over a flame for MgSO4 and in the oven at 120°C for the CuSO4; some nitrous fumes will appear since there is always a little HNO3 in the cristals. CuSO4 is more sensitive to heat than MgSO4 since it decompose at 200°C when anhydrous; but it has the advantage to show when it is completely free of water.
Do this a few times to concentrate even more your HNO3!
My original idea was to use gypsum since CaSO4 catches water and is unsoluble; it is also easily recovered by heating.
Only drawback, there must remain traces of Mg(2+) or Cu(2+) in your acid eather as Cu or Mg nitrates or sulfates; CaSO4 has this disavantage too but on a much lower extand; the only problem is its ability to cake --) contains a lot of HNO3 trapped --) vaccuum filtrate on glass filter paper!

Another:
Very good idea is to use a completely made of Al metal distillator; you use Al2(SO4)3 as the drying agent or MgSO4 (not CuSO4!!!! due to eletro potential it would dissolve Al and deposit Cu); then you would be able to distill HNO3 without troubles, even under vaccuum without risk of corrosion of Al reactor; distillates several times the HNO3 to get it anhydrous; here vaccuum is very wise since viscosity can be very high --) overheating --) red HNO3!

PH Z

madscientist - 24-5-2002 at 19:32

Latest yield: 76%. I was not able to complete the distillation due to time constraints, enforced by the much-feared Punctuality Gestapo. The density of the HNO3 yielded was approximately 1.51g/cm3. The HNO3 is a strong yellow; not orange or red.

My still

mr.evil - 1-6-2002 at 03:15

Okay, my first post on this forum (í'm coming from the E&W forum)

Here you can see my pictures(and my still)

http://www.geocities.com/tshadowpp/Pictures.html



leopard - 20-1-2003 at 08:22

I too have made nitric acid using h2so4 and kno3 using a 500ml flask, glass tubing and a cast lead stopper. The glass tube exited inside a graduated cylinder in an ice bath. This works well except the lead stopper forms a thick white layer (lead nitrate?)where it is exposed inside the flask. I can buy Teflon tape cheaply in rolls from plumbing stores. I wonder if this tape might be a solution to the problem of sealling the top of the flask to the glass tubing? Just a thought.

Mongo Blongo - 20-1-2003 at 10:58

Dude, that is Lead Nitrate and it is very toxic! If I were you I would use something else like cast glass or Teflon.
For some reason I have never been able to find Teflon.
I use a home made still made out of glass and polypropylene. I also have a setup using two glass bottles. One bottle on a inverted iron and the other in an ice bath. The mouth of both bottles are fitted together with a PP cap that they screw into. I found this setup to be much quicker and needs less heating than conventional means.
Now I use solvent extraction from NaNO3 and 96% H2SO4 with Dichloromethane. I then distill it at 40 deg C and obtain white 98% HNO3.

menchaca - 30-3-2003 at 15:27

i dont know what i did when i was child or how i did it but this is what happened to me:

i took a large bottle and i added quantity of ammonia and a large quantity of comercial H2O2(3%) suddenly it´s colour turned red and white fumes appeard in the mouth of the bottle. Could that generate nitric acid? i dont know what to to think because nitric acid isnt easy to obtain oxidying ammnia but this was what happened to me and.........
well that´s all, i hope somebody can help me