CaliusOptimus
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Understanding reactions between NOx and NaOH
I've been wondering, what are the possible reactions between an NOx mixture and NaOH? These questions are related mainly to the scrubbing of NOx from
other processes.
According to wiki:
NO + NO2 + 2NaOH (or Na2CO3) → 2NaNO2 +H2O ( or CO2)
Basically what I was thinking was to scrub the gases with a KMnO4 soln to oxidize the NO to NO2, then to scrub the pure NO2 with a base. Will pure
NO2<->N2O4 react with bases like NaOH (or Na2CO3) in solution?
Also, I was distilling some nitric acid (from KNO3 and H2SO4) a few days ago, and I was using a wash bottle with NaOH soln to scrub the NOx
outgassing. I noticed a white oily liquid was forming near the frit, and some of it also made it's way to the walls of the bottle. It wouldn't wash
out with hot water, but it did wash out with acetone. Any idea what this may be? Possibly an impurity from the garden grade nitrate or drain cleaner
acid?
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woelen
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If you have pure NO, then it will not react with a solution of NaOH, it just bubbles through. Pure NO2 does react, it gives a mix of nitrite and
nitrate in a 1 : 1 ratio.
When a mix of NO and NO2 is bubbled through a solution of NaOH, then part of the NO will react as well. It first reacts with NO2, giving N2O3 and this
in turn can react with NaOH to NaNO2. I'm quite sure though that quite some NO also makes it to the surface and simply bubbles through. This is
because NO+NO2 is in equilibrium with N2O3.
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The oily liquid you describe almost certainly must be some organic material, possibly highly nitrated. Fertilizer KNO3 sometimes consists of "waxed"
prills, which have the nice property that they do not stick to each other. I have a bag of fertilizer KNO3 and if I add these prills to water, then a
large amount of greasy scum is produced and a turbid liquid is obtained. This most likely is from the "wax" on the prills.
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AndersHoveland
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2 NaOH + 2 NO2 --> NaNO3 + NaNO2 + H2O
2 NaOH + NO2 + NO --> 2 NaNO2 + H2O
NaNO2 + NO2 --> NaNO3 + NO
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CaliusOptimus
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Thank you Anders and woelen!
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AJKOER
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My research indicates a possible refinement to the answers provided so far. First, in an aqueous environment, the products are either nitrite and
nitrate ions or just nitrite ions depending on pH at room temperature. To quote (source: "Mechanism of the NO2 conversion to NO2- in an alkaline
solution" by Chen X, Okitsu K, Takenaka N, Bandow H. at the Department of Applied Materials Science, Graduate School of Engineering, Osaka Prefecture
University):
"The reaction of NO2 and NaOH aqueous solution at room temperature was studied for elucidating the behavior of gaseous NO2 in an alkaline solution.
Experimental runs related to NO2 absorption have been carried out in various pH solutions. The nitrite and nitrate ions formed in these absorption
solutions were quantitatively analyzed. In the case of pH 5-12, both of the nitrite and nitrate ions were formed simultaneously. On the other hand,
only the nitrite ion was formed when the pH of the absorption solution was higher than 13. In this paper, a new reaction mechanism was proposed to
explain the selective formation of nitrite ion in the 10 M alkaline solution. In order to confirm the new reaction mechanism, H2(18)O was used as part
of the absorption solution for detecting oxygen gas production. The amounts of reaction products: (18)O(18)O, (18)O(16)O and (16)O(16)O, were
quantitatively determined. It was confirmed that the new reaction proceeds mainly in the 10 M alkaline solution."
Link: http://www.ncbi.nlm.nih.gov/pubmed/15636532
Also, per Wiki on Dinitrogen trioxide (link http://en.wikipedia.org/wiki/N2O3 ) to quote:
"This deep blue liquid is one of the binary nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the
mixture below −21 °C (−6 °F):[1]
NO + NO2 is in equilibrium with N2O3."
So this is not a reaction product expected at room temperature and the following reaction, per Wiki, will not occur either:
N2O3 + 2 NaOH → 2 NaNO2 + H2O
Now, if solid NaOH is exposed to moist air and treated with NO2, in this high pH condition, I suspect that some and primarily NaNO2 may form.
However, this study using Soda Lime ("Elimination of nitrogen dioxide and nitric oxide by soda lime and its components", original in Chinese by Zhang
D, Hu X, Liu J at the Department of Anesthesiology, Fu Wai Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College) for scrubbing
gases notes that NaOH or KOH by themselves are not effective in removing NO and NO2 unless Ca(OH)2 is present. Link: http://www.ncbi.nlm.nih.gov/pubmed/9772493
Per this study, I would consider adding Ca(OH)2 to your scrubbing process.
[Edited on 12-1-2013 by AJKOER]
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Nicodem
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Admittedly this is less known, but NO also disproportionates in its reaction with hydroxides. With solutions of NaOH it reacts to give N2O
and NO2-. For example, see DOI: 10.2478/v10216-011-0004-0 (just because it is the first google hit for nitrogen(II) oxide disproportionation)
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
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scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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woelen
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This must be a very slow reaction. I have tried bubbling NO through a solution of NaOH in water and I saw no visible reaction. I kept the gas above
the solution in an inverted test tube. A small amount of absorbed NO (e.g. 1% or even less) of course remains unnoticed in such a crude experiment.
On the other hand, reaction of NO2 with water (and even more so with a solution of NaOH) is very fast. The brown color of NO2 disappears within
seconds when it is shaken with water and it disappears even faster when it is shaken with an alkaline liquid.
[Edited on 12-1-13 by woelen]
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