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nbk2000
April 10th, 2002, 07:23 AM
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This is part of an article on nitric acid production that I'm writing for my PDF. What I need is peer review as to anything that has been left out, and suggestions for things to include.



This is the part dealing with the distillation of nitric. I'm also including the acid/nitrate decanting method, solvent concentration, catalytic conversion of ammonia, and some others.



Articel begins below.
<HR>
<CENTER><H1><FONT FACE="COMIC SANS MS" >NITRIC ACID</FONT></H1></CENTER>
Nitric acid is THE most important single chemical for explosives manufacture. Without it, virtually every high explosive in existance would be either impossible, or extremely expensive, to make.



And because nitric acid is of such great importance, it's either tightly regulated, or extremely expensive, to buy. This is why it is of vital importance that you know how to make it yourself.
<HR>
<H3><FONT FACE="Comic Sans MS">Nitrates</FONT></H3>
Regardless of which method you use, you'll need a supply of nitrate to make nitric acid from. Common chemical fertilizers are the source of the nitrate radical (NO3) needed to make nitric acid.



The nitrates that can be used are listed in order of preference:



<UL TYPE="DISC">(Chemical Name / CAS # / Molecular Weight)
Potassium Nitrate / 7757-79-1 / 101</LI>
Sodium Nitrate / 10124-37-5 / 85</LI>
Calcium Nitrate / 10124-37-5 / 164</LI>
Ammonium Nitrate / 10124-37-5 / 80</LI>
[/list]



It may be possible to use other nitrates, but they're likely to be difficult to obtain, or too expensive for making useful quantities.



Most agricultural grade nitrates come in the form of "prills". These are little BB sized pellets that need to be treated before they can be used.



You'll first dissolve the prills in the minimum amount of boiling water possible. This will remove the coating that some fertilizers have, and save you the hassle of grinding them to powder.



Once the prills are dissolved, filter while hot, and allow to cool while covered. The solution will precipitate out crystals of pure nitrate. The longer it takes to cool down, the larger and purer the crystals.



Filter the crystals and wash with a small amount of cold acetone or 99% isopropyl alcohol to remove the last traces of contaminants.



After letting the crystals dry out, you now put them in an oven to remove the water of crystallization. This is the water that is molecular bound to the nitrate.



To remove it, you place the nitrate is glass or ceramic casserole dish so that it's spread out in a thin layer.



Turn the oven on to 250&deg;F (120&deg;C) and occasionally stir it till it no longer steams and falls apart into a fine powder.



Remove from the heat and immediately place it in pre-heated jar or can to keep it dry.



<H3><FONT FACE="Comic Sans MS">Sulfuric Acid</FONT></H3>
In order to make nitric acid with nitrates, you'll also need sulfuric acid. This is most commonly available as battery acid or drain cleaner.



The battery acid is approximately 30% concentration, and is too weak to be used as is. You'll have to concentrate it by removing the water. The simplest way to do this is to boil it off.



You'll be wanting to use fresh battery acid from the container. Don't use battery acid that's been in a battery if you have any choice as there's bound to be lots of contaminates in it.



Take a glass or ceramic pot, pan, jar, flask, etc, and fill it a quarter ways full of your dilute acid. Have the boiling container sitting in a shallow pan filled with sand to prevent cracking.



Using an electric hot plate or burner, gradually heat the acid till dense white fumes come off.



Do this outdoors as the fumes are HIGHLY DANGEROUS! Stay upwind at all times.



Once the fumes are coming off, turn off the heat and immediately cover the container with a glass lid or plug. Don't use rubber or cork as it will be destroyed.



Once the acid has cooled off, pour it into a dark glass soda bottle which works well. You can also use polyethylene bottles which are safer from breakage.



<H3><FONT FACE="Comic Sans MS">Distillation</FONT></H3>



The most frequently cited method of preparing nitric acid in a laboratory or field enviroment is heating of a nitrate with concentrated sulfuric acid. So we'll start with this method first.



The reaction that takes places between an alkaline nitrate (R = alkali metal ion) and sulfuric acid is as follows.
<H3><CENTER>2RNO<sub>3</sub> + H<sub>2</sub>SO<sub>4</sub> = 2HNO<sub>3</sub> + R<sub>2</sub>SO<sub>4</sub></CENTER></H3>
When you react the alkali nitrate with sulfuric acid, it decomposes in nitric acid and alkali sulphate.



To determine the proper amount of nitrate to use with any given amount of acid, you divide the weight of the acid by 98. Multiply the results by twice the molecular weight of the nitrate that you are using.



For instance, you have 98 grams of sulfuric acid. You also have potassium nitrate. Potassium nitrate has a molecular weight of 101. So, double 101 = 202. Thus, you'd use 202 grams of potassium nitrate with the 98 grams of sulfuric acid.



Though, in actual practice, you'd want to use a slight excess of acid to ensure a complete reaction.



Ideally, when distilling the acid, you'd be using laboratory grade glassware, but even 2 beer bottles could be used in dire circumstances.



To start, place the concentrated sulfuric acid in the container that's going to be heated. Next, add with swirling or stirring with a glass/plastic rod, the dry powdered nitrate. If there's any visible fuming, STOP! Get upwind and wait a few minutes for it to stop. Then continue until all the nitrate is added and well wetted by the acid. There should be no clumps.



If you have lab glass, you already know what to do for a distillation. If you're using a beer bottle still, place the bottle with the nitrate/acid paste in a larger can with a layer of sand on the bottom. Fill the remaining space with more sand the filled, and slide the cut out lid with a hole for the bottles neck over the can. Wire the lid in place.



(The purpose of the sand can is to prevent the glass bottle from shattering from uneven heating.)



Now lay the can on it's side. If you've measured it correctly, then no paste will come out the neck. If any does, catch it in a bowl or such and save it for your next batch.



Now line up the second bottle exactly parrallel to the first one, and seal them together using teflon tape (if possible) or damp cotton cloth (bandages work). The second bottle is the condenser that the nitric acid will be collected in. If using tape, poke a very small hole in the gap between the two bottles to provide pressure relief so the tape doesn't rupture.



Keep this second bottle well cooled. You can do this by wrapping it in a small towel and having a constant stream of cold water from a hose flowing over it. Or wrap it in ice. However you do it, keep it as cold as possible.



Proceed to gently heat the bottle using a gas or charcoal fire. You don't want to overheat the paste which would cause some to carry over into the receiving bottle.



You'll know the reaction is done when no more fumes are seen to be in the bottles.


At this point, remove the heat and allow the assembly to cool down while keeping the receiver cool.



Carefully seperate the two bottles, being careful to wear acid resistant gloves and staying upwind of the assembly.

Mr Cool
April 10th, 2002, 07:59 AM
Two things, one very minor and one quite important: there are no nitrate radicals in metal nitrates, only ions.
The important thing is: unless you get it very hot (well above the decomposition temp. of HNO3), the reaction will be XNO3 + H2SO4 --> XHSO4 + HNO3, so you need one mole of nitrate, plus one mole of sulphuric acid, to get one mole of nitric acid.

Apart from that, it all seems good.

stanfield
April 10th, 2002, 08:13 AM
hum... I found an equation different from your own... (more sulfuric acid)
3 NaNO3 + 2 H2SO4 -> 3 HNO3 + ...
I use this one to produce my own nitric acid and it works well...

I use :
- 1000 mL of sulfuric acid @ 95%
- 2378 g of sodium nitrate
for more than 1 L of nitric acid (1167 mL theory)

and I don't need to purify the nitrate and to place it in my oven, I just open the fertilizer bag, put my 2.3 Kg of nitrate in my boiling flaks and 1 bottle of sulfuric acid... works pretty well !

At the end of the distillation, I have a solid (NaSO4) and no more sulfuric acid (maybe a bit...)

see ya !

<small>[ April 10, 2002, 07:18 AM: Message edited by: stanfield ]</small>

nbk2000
April 10th, 2002, 08:21 AM
So if I use one mole of (say) sodium nitrate with one mole acid, I'll get one mole nitric and one mole sodium bisulfate?

I thought that 2 moles nitrate to 1 mole acid was required? And that the nitric would boil off before being decomposed.

nbk2000
April 10th, 2002, 08:26 AM
Stanfield, you may wish to try an experimetn if you have an accurate scale.

Weigh the nitrate from the sack as usual. Then crush and dry in an oven. What's the weight loss? That's water in your reaction diluting your acid.

Mr Cool
April 10th, 2002, 09:57 AM
NBK: IIRC, if you use 2 moles of NaNO3 and 1 mole of H2SO4, then you heat it and one mole of HNO3 boils off at 80*C or whatever it is. Then you're left with NaHSO4 and NaNO3, no HNO3, so the temperature rises and gets much higher. At a certain point, HNO3 is made again, but the temperature is so high that it immediately decomposes. Some will re-form in the condenser, but you'll still have a lot of NO2 and H2O, which you don't want.

nbk2000
April 10th, 2002, 10:54 AM
No reason can't have it both ways.

1 to 1 if acid is freely available. 2 to 1 if acid is scarce.

But either way, it does work, correct? Also, you say you get a bisulfate and nitrate mix that breaks down at high temperature into nitric with lots of NOx and water. Well, what about that as an acid free method of nitric?

Bisulfate is available as a toilet cleaner IIRC. Then, using the solvent extraction process, you'll get pure anhydrous nitric anyways.

stanfield
April 10th, 2002, 11:17 AM
I have a densimeter and witout putting my nitrate in the oven, my nitric acid has a density of 1.50 1.51 g-cm-3, so, I think the oven way for nitrate is unusefull... Maybe the excess of H2SO4 absorb the water from my nitrate... I don't know !

see ya !

Zambosan
April 10th, 2002, 12:27 PM
How useful oven-drying is will depend upon which nitrate you start with, methinks. Sodium nitrate is more hygroscopic than potassium nitrate, and ammonium nitrate even more so. I've never had problems with KNO3 prills absorbing much water... but that's just observation, not density calculations so take it for what it's worth.

Oh yes, and post your decanting method whenever you get a chance to, if you would be so kind. I'd be awfully interested in a no-heat method, even if the yield suffers a bit.

<small>[ April 10, 2002, 11:28 AM: Message edited by: Zambosan ]</small>

Anthony
April 10th, 2002, 12:33 PM
Minor, possibly questionable points:

H2SO4 from batteries - there's a problem besides contaminants if extracting from a battery. Any battery that you can get for a reasonable price (cheaper than buying new electrolyte) is likely to be scrap. Scrap batteries are discharged and usually refuse to accept a charge. The electrolyte in a discharged battery is mostly H2O as the H2SO4 has been decomposed into PbSO4 and electrons liberated during the discharging process.

Plugging the hot H2SO4 container after boiling - Could this cause a vacuum to develop inside the container as it cools? Just wondering if it's an improvised container (i.e silica glass) whether it might be a safety hazard.

"add with swirling or stirring with a glass/plastic rod, the dry powdered nitrate. If there's any visible fuming, STOP! Get upwind and wait a few minutes for it to stop."

You might need to be specific here on what "fuming" is. In my experience no matter how slowly you add the nitrate you will always get white HNO3 vapour being emitted, although it's not pleasant to breathe I presume it's the red/brown N2O that you're warning against. I get this image of someone adding a milligram of nitrate at a time and then waiting 30minutes for the HNO3 formed to stop fuming :)

Zambosan
April 10th, 2002, 02:16 PM
You also have not mentioned anything about cooling the H2SO4 prior to nitrate addition. IIRC, a low inital temperature will help dissipate the heat during addition, minimizing the amount of HNO3 disintegration to NOx that occurs.

stanfield
April 10th, 2002, 02:45 PM
this is pretty hard to cool big amount of chemical... (see my amounts above)

see you

Zambosan
April 10th, 2002, 05:14 PM
Why couldn't you just place it in the freezer for a bit?

<small>[ July 18, 2002, 01:22 AM: Message edited by: Zambosan ]</small>