# Uses for Nitrogen Dioxide



## Irons (Feb 4, 2008)

Nasty stuff and anyone who does any refining generates a lot of it. It's that nasty reddish-brown gas that comes off digesting metals with Nitric Acid or Aqua Regia.

If you distill it into Sodium Hydroxide, it makes Sodium Nitrate.

Nitrogen Monoxide will form Sodium Nitrite.

If you let the Sodium Nitrite remain in contact with air, it will oxidize to Sodium Nitrate.

Another idea for those in a hurry would be to use Sodium Percarbonate giving Sodium Nitrate and Carbon Dioxide.

Sodium Percarbonate can be bought under the name Oxy Clean in the grocery store.

Everything but the squeal.


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## Lino1406 (Feb 8, 2008)

NO2+NaOH=NaNO2+?


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## Irons (Feb 8, 2008)

In dilute solution, in the absence of Oxygen, Nitrogen Monoxide is produced. If you allow air in, it will react with oxygen in the air to produce Nitrogen Dioxide which, when reacted with Sodium Hydroxide produces Sodium Nitrate.

If you keep out air, it will form sodium Nitrite.

http://www.freepatentsonline.com/3965247.html

It is well known that if nitrous gases, i.e. gases containing nitric oxide and nitrogen dioxide, are brought into contact with alkaline aqueous solutions, the nitric oxide and nitrogen dioxide will be absorbed with the formation of nitrites and nitrates. See U.S. Pat. Nos. 1,903,815 and 1,978,431. Such gases are typically obtained from a wide variety of sources, as for example, by the arc process of nitrogen fixation, by the air-oxidation of ammonia or as waste gases from an absorption process of which nitric acid is the primary product. By controlling the ratio of nitric oxide and nitrogen dioxide so that more nitric oxide than nitrogen dioxide is present in the gas feed, the amount of nitrates that is formed can be minimized, thereby allowing maximum conversion of the nitrogen oxide to the nitrites.

In such processes nitrous gases are contacted for absorption in one or more stages with a liquid medium maintained alkaline by the presence of suitable alkaline reacting agents, e.g. sodium hydroxide, sodium carbonate, sodium bicarbonate and mixtures thereof. The liquor, herein termed the "final absorption liquor", which is separated from the last absorption stage contains dissolved sodium nitrite together with sodium nitrate and minor amounts of unreacted alkaline reacting agent. Further, use of a nitrous gas feed containing carbon dioxide will also cause the finished absorption liquor to contain sodium carbonate/bicarbonate values due to the absorption of CO 2 in the aqueous medium. 

http://en.wikipedia.org/wiki/Nitrogen_oxide

--snip--

In the presence of excess oxygen (O2), nitric oxide (NO) will be converted to nitrogen dioxide (NO2), with the time required dependent on the concentration in air as shown below:[1]
NO concentration in air

(ppm)
Time required for half NO

to be oxidized to NO2 (min)
20,000 0.175
10,000 0.35
1,000 3.5
100 35
10 350
1 3500

--snip--


Mono-nitrogen oxides eventually form nitric acid when dissolved in atmospheric moisture, forming a component of acid rain. The following chemical reaction occurs when nitrogen dioxide reacts with water:
2NO2 + H2O → HNO2 + HNO3 (nitrogen dioxide + water → nitrous acid + nitric acid).
Nitrous acid then decomposes as follows:
3HNO2 → HNO3 + 2NO + H2O (nitrous acid → nitric acid + nitric oxide + water),
where nitric oxide will oxidize to form nitrogen dioxide that again reacts with water, ultimately forming nitric acid:
4NO + 3O2 + 2H2O → 4HNO3 (nitric oxide + oxygen + water → nitric acid).


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## Lino1406 (Feb 8, 2008)

According with the parameters you
gave it seems that simple bubbling
of NO2 through NaOH (Which gives
contact time of seconds) is not 
enough for a meaningful absorption?
Correct me if I'm wrong.


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## Irons (Feb 8, 2008)

Lino1406 said:


> According with the parameters you
> gave it seems that simple bubbling
> of NO2 through NaOH (Which gives
> contact time of seconds) is not
> ...



It's like a fractionating column problem. How many theoretical plates will it take to separate the components of the feed stream given a rate of flow, ratios of reactants, temperature and pressure.

If you make a column a given height, fill it with bits of unreactive material to increase the surface area of contact, spray NaOH from the top so that it filters down over the plates and feed air and NO2 at the bottom, you can adjust the flow rate of the air such that no NO2 exits the top of the column, then you will have a theoretically complete conversion to Sodium Nitrate which can be drawn off at the bottom of the column. If you have to, you can recirculate it as many times as needed to get complete conversion. This would allow a shorter column, or use 2 columns in series with the recovered Sodium Nitrate solution from the second column being fed into the first column column that gets the primary NO2 feed set up in a backflow arrangement. The remaining NO2 output from the first column goes to the inlet of the second column.


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## SilverNitrate (Feb 12, 2008)

the gases from aquaregia (AR) makes NOx and chlorine containing compounds. 

to keep down on these fumes do not allow the water (solvent) to become too saturated (supernadant) That is if you use concentrated HNO3 and HCl add in a an equal volume of water to it and your metals.

I runs my NOx gases thru a fritted glass column in baking soda.


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## Irons (Mar 1, 2008)

by adding H2O2 to your digestion flask. You oxidize it back to Nitric Acid before it can boil off.


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## Platdigger (Mar 1, 2008)

If you are adding hydrogen peroxide to your AR.

Is it just as easy to kill the nitric with urea, 
as when you do not add the H2O2?

Randy


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## Irons (Mar 1, 2008)

Platdigger said:


> If you are adding hydrogen peroxide to your AR.
> 
> Is it just as easy to kill the nitric with urea,
> as when you do not add the H2O2?
> ...



By using H2O2, you can get away with less Nitric to begin with since it is recycled through oxidation with H2O2. When the digestion is complete, you can collect the NO2 fumes in H2O2 and recover the Nitric for reuse later.

I don't think this is a good idea if there is Osmium or Ruthenium. They will distill over and should be captured in NaOH for safety reasons or reduced. You don't want those floating around the lab.


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## Platdigger (Mar 1, 2008)

As always, Great information Irons.

But, what about Urea? Will it work with H2O2 in the mix?

Randy


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## Irons (Mar 1, 2008)

Platdigger said:


> As always, Great information Irons.
> 
> But, what about Urea? Will it work with H2O2 in the mix?
> 
> Randy



If you want to recover the nitric, you can't use Urea, unless someone has a way to break down Urea Nitrate.


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