# Reducing NOx Maybe!



## jeneje (Mar 3, 2013)

Hey guys, got a chemical question here, Why researching NOx - i found a post from GSP he posted back in 2007 http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=39&t=4284 where he talked about using NaOH + H202 + H20 to scrubb NOx.

Noxx wrote,
*Hey Chris, I think I figured the order of the scrubbers correctly. 

First, your NOx go through NaOH. NO2 will dissolve in the aqueous solution and make nitric acid:

2 NO2 + H2O => 2 NO + HNO3 

The nitric acid is then neutralized by the NaOH but the NO does not dissolve in the solution.

Then it goes through the H2O2 solution which oxidizes the NO into NO2. 

Final scubbing is in water. The release of NO at this point should be very minimal.*

Using this formula i setup this system for testing, I used Ag to create the NOx. Now to my question, the container with the NaOH is now changing color to a yellow tint. Could this be changing the NOx to HNO3? Like Noxx has wrote and can it be re-used. 

The H202 and H20 have no change as of 24 hours of use. Also if adding NaOH to the solution bringing the PH up again this should neutralize the HNO3, Is this a correct assumption.

Thanks
Ken


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## Geo (Mar 3, 2013)

im not a chemist at all but i think i understand that as the fumes pass the the solution and are converted to HNO3, it is then neutralized by the NaOH. you may be able to reclaim a certain portion of the nitric if you allowed the fumes to pass through the H2O2 solution first and then through the NaOH last.


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## jeneje (Mar 3, 2013)

Thanks Geo, so i have the setup backwards, need to re-think what i read. Being able to reclaim some HNO3, i could use that for help with base metal digesting maybe.
Thanks again,
Ken


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## butcher (Mar 3, 2013)

jeneje,
When dissolving metals in nitric acid sever gases can be formed we call these NOx gas for short, these can be a mix of several of the nitrogen oxide based gases, the two most common are nitric oxide NO, and NO2 nitrogen dioxide, although there are actually other these two we will focus on here.

Nitrous oxide (NO) is a clear gas, is also called nitrogen monoxide (NO)
nitrogen monoxide (NO) is not easily absorbed into water.
but if mixed with oxygen (or air) it becomes Nitrogen dioxide (NO2),
2NO + O2 -->2 NO2

NO2 nitrogen dioxide much more easily dissolved in cold water and will form nitric acid HNO3,

If you were using a similar set up as your other thread, where you were forcing air into your reaction chamber.
the air (oxygen) and the nitrogen oxide would combine, to form nitrogen dioxide:
2NO + O2 -->2 NO2

Another way to help convert NO into NO2 is with dissolved oxygen in water, here is where Hydrogen peroxide comes in handy in converting NO to NO2 which can be dissolved easier into the cold water forming nitric acid HNO3 and nitrous acid HNO2:
2H2O2 --> 2H2O + O2 
2NO + O2 --> 2NO2
3NO2 + H2O --> 2HNO3 + NO
4NO2 +2 H2O + O2 --> 4HNO3

Of course there are actually several other reactions to explain the process like NO2 is actually in equilibrium with N2O4 dinitrogen tetroxide:
NO2 <--> N2O4
but it still works out about the same:
2NO2/N2O4 + H2O --> HNO2 + HNO3

A few other formula's just encase you want more here:

HNO2 nitrous acid will only be found in cold dilute solutions, if warmed or concentrated it forms nitric acid HNO3:
2HNO2 --> HNO3 + 2NO + H2O

so we see if we have oxygen we can convert the colorless NO to the red brown gas NO2 which will dissolve in water to form nitric acid, we would want to this in the first portion of our scrubber.

Because if we had caustic soda or sodium hydroxide in our first vessel we would be making sodium 
If we did not add air, oxygen, or H2O2 the nitogen monoxide NO would not convert to NO2 nitrogen dioxide, so the gas would pass on through,but if oxygen was involved it would form NO2 gas, the NO2 in water would form nitric acid in the water but since the water is caustic with NaOH sodium hydroxide we would form sodium nitrate NaNO3, and if nitrous acid HNO2 was in the reaction it could form sodium nitrite NaNO2. so we see we want these soluble salts in out last vessels to make these salts dissolved in solution and if crystallized we could make nitric acid with them and sulfuric acid.

HNO2 + NaOH --> NaNO2 + H2O

HNO3 + NaOH --> NaNO3 + H2O

2NaNO3 + H2SO4 --> 2HNO3 + Na2SO4

And of coarse even after scrubbing NOx fumes as we see some are not easily detectible but can be harmful for us to breath, and some of these gases can escape our scrubber system, so we still need to rely on fresh air (working out doors) or fresh air from outdoors interring the lab and the gases moving quickly out of the lab or fume hood and venting these gases outdoors away from what air we need to breath.


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## butcher (Mar 3, 2013)

Beside the jars being backwards that is one nice little setup. :lol:


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## jeneje (Mar 4, 2013)

butcher said:


> Beside the jars being backwards that is one nice little setup. :lol:


Thanks Butcher, i have changed the jars and put them in the right order :lol: thank you for explaining the process it now make better sence to me what is going on with it.
Ken


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## butcher (Mar 6, 2013)

·	I think you could add some universal pH indicator to your sodium hydroxide jar, the color change would give you a visual indication of what is going on, and could let you know when to change the solution, or when it is less effective, or you could also just take samples every now and then during down times and test the pH that way.
·	
·	I was trying to find a way to detect NO gas (nitric oxide being the hardest for the system to scrub), without buying a meter, if you had an ozone generator or made one this may work?
·	
·	I have been wondering if you had an ozone generator, or made an ozone generator using two fiber circuit boards with a lot of needles and using car coil to generate the high voltage arc, a 555 timer circuit or other oscillator circuit with a transistor driver and relay could work to trigger the car coil, generating the primary current in your high voltage transformer (car coil), the high voltage arching across the needles generating ozone, the ozone rich atmosphere in an empty jar at the end of your vessel of scrubbers passing the exhaust gases through the ozone, if nitric oxide made it through your scrubber, you would see it changing to Nitrogen dioxide a brown gas in the jar of ozone gas, telling you, that you have NO getting through your system
·	
·	Thus possibly being able to detect NO passing through your scrubber system without having the expense of a fancy meter.
At work I have a gas meter for boiler flue gases that can detect O2, CO, CO2, and NOx gases, but these meters are expensive, and the sensors for them are also expensive and have to be replaced about once a year
Chemiluminescence
·	http://en.wikipedia.org/wiki/Chemiluminescence
·	
·	Another gas phase reaction is the basis of nitric oxide detection in commercial analytic instruments applied to environmental air-quality testing. Ozone is combined with nitric oxide to form nitrogen dioxide in an activated state.
NO+O3 → NO2[◊]+ O2
The activated NO2[◊] luminesces broadband visible to infrared light as it reverts to a lower energy state. A photomultiplier and associated electronics counts the photons that are proportional to the amount of NO present. To determine the amount of nitrogen dioxide, NO2, in a sample (containing no NO) it must first be converted to nitric oxide, NO, by passing the sample through a converter before the above ozone activation reaction is applied. The ozone reaction produces a photon count proportional to NO that is proportional to NO2 before it was converted to NO. In the case of a mixed sample that contains both NO and NO2, the above reaction yields the amount of NO and NO2 combined in the air sample, assuming that the sample is passed through the converter. If the mixed sample is not passed through the converter, the ozone reaction produces activated NO2[◊] only in proportion to the NO in the sample. The NO2 in the sample is not activated by the ozone reaction. Though un-activated NO2 is present with the activated NO2[◊], photons are emitted only by the activated species that is proportional to original NO. Final step: Subtract NO from (NO + NO2) to yield NO2[4]

Or just get a canary like the old miners did :lol:


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## Marcel (Mar 6, 2013)

Nice experiments!
Is there any way to make use of a common catalitic converter to reduce the NOx gases? I mean that is what it is designed for, but can it be used without the controlling circuit?


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## Geo (Mar 6, 2013)

Marcel, im not 100% on this but i think for the catalyst to work properly, it has to be heated.


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## jeneje (Mar 6, 2013)

*I think you could add some universal pH indicator to your sodium hydroxide jar, the color change would give you a visual indication of what is going on, and could let you know when to change the solution, or when it is less effective, or you could also just take samples every now and then during down times and test the pH that way.*

Butcher i found this little PH 600 probe at the aquarium store where i got the black scrubber balls. It ranges up to +14. I calibrated it with M10007 buffer solution to test the PH in the jars. They also have a metered probe made by milwaukee for $150.00 i am going to get for my main scrubber to monitor it.

This little probe should work well for now since i only use this setup for silver at this time.
Ken


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## butcher (Mar 8, 2013)

I have a pH probe I love it, I find it is especially handy when treating waste.


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