Runic7 - 15-9-2021 at 04:36
Reposting this here cause it fits the specific board better:
Hello all, I'm looking to perform a reaction involving liberation of quite a lot of nitrogen dioxide. How can I efficiently neutralize this toxic gas?
I've looked into multiple methods from the use of bubbling it through a 20% NaOH solution and a solution of sodium sulfite. I also found some have
found success using a solution of 35% hydrogen peroxide. Another way to do it that came up was the use of drying agents to absorb the gas such as
Drierite or silica gel. So now I have a couple questions left unanswered. Would the first possibly produce nitrogen monoxide? Just another poisonous
gas that defeats the whole purpose of neutralization.. Do the drying agents actually work, and have any of you found personal success with them?
Finally, which of these methods is most efficient? If I've missed a method that may be worth exploring, please let me know. Thanks! 
teodor - 15-9-2021 at 10:42
NO gas (which is not possible to absorb by water) could be absorbed with an aqueous solution of acidic FeSO4. It forms Fe(NO)SO4 complex. I didn't try
that but I already posted references where this method was studied.
For NO2 I see no problems if you have water.
DBX Labs - 15-9-2021 at 13:44
From my experience, bubbling NO2 through a 10% ammonium hydroxide solution will capture almost all of the NO2. The drawback with a simple single
bubbler like this is that the air bubbles that do surface are saturated with aerosolized ammonium nitrate. This can be visible as small white clouds
of "smoke" that are carried up by each neutralized bubble.
Runic7 - 15-9-2021 at 16:17
Thanks teodor and DBX for the responses. I'll attempt to try both methods to the best of my ability. Possibly the iron sulfate could be used in
combination with water.
j_sum1 - 15-9-2021 at 16:39
NO reacts readily with oxygen to form NO2.
My suggestion is to draw off your gases with a vacuum pump but have a hole in the hose so that you draw excess air in as well. That will ensure you
are working with NO2 only. Then bubble through a solution of NaOH. You could either calculate the NaOH so that it is stiochiometric with your
synthesis or you could add an indicator so that you know when it is depleted.
Runic7 - 15-9-2021 at 19:40
Update: It worked! For anyone else that needs this information in the future, I found success in bubbling the reaction by-products (NO2, and NO) first
through a cold 20% solution of NaOH, then bubbling the NO through a solution of Iron(II) sulfate. In the Iron sulfate solution, a brown participate
formed when the gas rushed into the flask. I was left with what I can only assume is a complex ion of [Fe(H2O)5(NO)]2+.
Thanks again for all the help! -Runic
[Edited on 9-16-2021 by Runic7]
Johnny Cappone - 16-9-2021 at 18:30
Quite interesting thread. I've been thinking about NOx absorption/neutralization last week. By the way, I know that when distilling nitric acid from a
nitrate and H2SO4 some NO2 inevitably forms; would some NO also be formed? If so, would a solution of H2O2 oxidize it to HNO3/NO2? I know atmospheric
air does a good job.
teodor - 12-12-2021 at 08:52
I was thinking about a more stable binding of NO than [Fe(H2O)5(NO)]2+ anion and eventually, I found
"There is, however, another
absorbent for nitric oxide which leaves nothing to be desired, whose
use and value have remained unknown. This is a strong solution of
either sodium or potassium sulphite to which a little alkali hydroxide
has been added. It quickly absorbs every trace of nitric oxide, which
it fixes in the form of hyponitrososulphate, Na2N2O2SO3"
Attachment: divers1899.pdf (52kB)
This file has been downloaded 327 times
I believe somebody (probably woelen) mentioned this method before, but I think it should be mentioned in this thread because, according to the
article, it is far better absorbent than Fe(2+) salt.
Now I am curious, could be Na2N2O2SO3 isolated in a crystalline form.