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Author: Subject: Dealing with NO2 fume residues in vessels.
javert
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[*] posted on 20-7-2017 at 13:02
Dealing with NO2 fume residues in vessels.


Hi people.

I've recently acquired a microwave digestion system with a set of thin, long reaction vessels (3 cm diameter and 24 cm long) made of TFM. I've performed a couple of digestions using 0,25 g of plant material and 10 mL HNO3 as indicated by the manufacturer.

Even after letting the vessels cool to room temperature, a stream of red N2O gas can be seen escaping the gas vent as I open the vessel (inside a fume hood of course) and some N2O gas can be seen "spilling" when pouring the digestate to the final flask (expected since the gas is heavier than air).

The problem I have is that the residual N2O fumes are damn hard to get rid of! After several obligatory rinses of the vessel with DI water, I have made full rinses with soapy water and then kept them submerged for 6 hours and then, as I drain and dry them, the remaining drops of water still color a pH strip and the pungent smell still comes off them.

At this point I believe the nitrous oxide have been adsorbed into the surface of the liner, since it became yellowish in contrast with the original white color. There's nothing in the manufacturer instructions regarding getting rid of the N2O remains since all it says is to wash them with a mild detergent and hot water and doing a empty run with HNO3 after running dirty samples, but I expect HNO3 itself to contribute with more N2O gas.

Is there a liquid cleaner or reagent known to solubilize and react with N2O gas quickly?
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[*] posted on 20-7-2017 at 13:21


NaOH will quickly react with NO2, destroying it. There really shouldn't be any left after a few rinses, and especially after soaking for six hours. I've had reaction vessels filled with NOx and all I did to clean them was rinses with water. No smell or residue left. Also, most pH strips come with a color chart, don't just assume that yellow means acidic. I have some strips which will turn purple at a pH of two.



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Sulaiman
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[*] posted on 20-7-2017 at 13:43


If TFM is resistant to it then I would consider a dilute hydrogen peroxide rinse, then flush nitric acid produced ?



CAUTION : Hobby Chemist, not Professional or even Amateur
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[*] posted on 21-7-2017 at 18:29


Peroxide will give you nitric acid again from NO/NO2 mixtures (NOx) and helps control NOx. In industrial practices using lots of HNO3 to dissolve metals, usually the first scrubber is hydrogen peroxide solution and the second one is reducing (i.e. sodium hydroxide/sodium sulfite/dithionite).





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PirateDocBrown
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[*] posted on 21-7-2017 at 20:18


Just Na2CO3 solution will react with NO2, and it's cheap as dirt. Just make a bucketful, and put your glassware in it.
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javert
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[*] posted on 24-7-2017 at 08:32


Thanks for your comments, I'll be researching both the peroxide and hydroxide absorption methods to see whether I'll keep one or both.

Just another question: given NO2's ability to linger on the surface due to its higher density, can I trust a fume hood to vent the gas properly through an upper escape duct? Since the sash always leaves the opening on the bottom, I'm a little paranoid about the NO2 "spilling" through it. Is there a recommended face velocity to it? If you can give me a regulatory specification regarding fume hoods I'll be thankful.

I'll probably be scrubbing the bulk of it, but want to rely on the fume hood to deal with the remnants.
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Boffis
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[*] posted on 7-2-2018 at 08:15


This thread raised an interesting idea. When silver dissolves in strong nitric acid roughly half the acid is converted into NO2 roughly along the lines:

Ag + 2HNO<sub>3</sub> &rarr; AgNO<sub>3</sub> + H<sub>2</sub>O + NO<sub>2</sub>

There has been much discussion about absorbing liberated NO2 in hydrogen peroxide so generating nitric acid but is it possible to prevent the liberation and reduce nitric acid consumption by using a mixture of nitric acid and hydrogen peroxide? Has any one ever tried it? Basically:

2Ag + 2HNO<sub>3</sub> + H<sub>2</sub>O<sub>2</sub> &rarr; 2AgNO<sub>3</sub> + 2H<sub>2</sub>O

There are several threads dedicated to dissolving copper etc in acetic or hydrochloric acid with the assistance of hydrogen peroxide. Would the currently available 12% (all that's permitted by the Nanny State) H2O2 be adequate assuming the acid is azeotropic 68%?


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[*] posted on 7-2-2018 at 08:46


Cody's Lab has tried that in one of his silver metal refining videos, but the problem is silver catalytically decomposes H2O2 quickly, making it practically useless. With metals that don't catalyze this decomposition, it is possible.



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[*] posted on 7-2-2018 at 11:06


A mist of water does a pretty good job of getting nitrogen dioxide gas out of the airspace. I used a dilute baking soda solution in a spray bottle to "capture" NO2 that was getting out of a vapor trap. It works, but leaves residue. I went back to using water for my purpose.

That stuff is super creepy looking, how it just lingers, and the way it mixes with air.

It looks like poor quality special effects, to me
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[*] posted on 7-2-2018 at 11:42


an idea is to turn on a little humidifier inside your hood, plenty with backing soda solution to spray it around the hood as small vaporised droplets. This would neutralize any nitrogen dioxide fumes that escapes from the vessels quickly, affording only thin sodium nitrate particles, CO2 and water.
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AJKOER
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[*] posted on 7-2-2018 at 19:22


Yes, to address fumes of .NO2, use a spray of aqueous NaHCO3 or Na2CO3.

Radical reactions:

.NO2 + HCO3- = NO2- + .HCO3

.HCO3 = H+ + .CO3-

.CO3- + .NO2 = CO2 + NO3-

.CO3- + .CO3- = C2O6(2-) + O2

If a residue is a problem, consider ammonium bicarbonate, but will have a strong ammonia presence:o

No smell, but weaker, just spray carbonated water:D, which is an improvement over 'a mist of water'.

If you use a solution of SO2 (from wine making chemicals), a trace amount of a soluble cobalt salt, and perhaps optional light treatment, similar but advanced chemistry leading to a powerful bleaching product, if that is of any value here.

[Edited on 9-2-2018 by AJKOER]
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[*] posted on 15-2-2018 at 19:54


NOx gases will react with ammonia and water to form N2 and H2O. Just leave something that releases ammonia gas nearby, if the fumes start to become too much.

Ammonium nitrate can be added to a fuming solution to replace HNO2 (which is where NO2 comes from) with HNO3. It works because the ammonium ion and the nitrite ion react to form N2 and water, leaving behind an H+ ion and a NO3- ion.




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[*] posted on 16-2-2018 at 02:50


I got a vac chamber, I pull a vac on the chamber. I connect the glassware up to the chamber, via a wash bottle of whatever is to hand, then simply draw the Nox through the wash bottle via an open system. In other words I open the vac up so it pulls all the gas through the wash bottle.

Its much nicer to clean up once you got most it out, i find I can then wash at the sink no problem, you do get a little bleach type smell, but barely enough to detect.
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[*] posted on 16-2-2018 at 20:08


A range of solvents that cover the polarity scale, various acids and bases, substances that react and bubble like H2O2 or sodium bicarbonate, soft abrasive scrubbing and last but not least... Very hi temperature blue flame such as a jet lighter or an acetylene torch turned down very low.

You would be surprised what a flame will remove when nothing else will.




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