Formation of CO from reaction with stainless steel

[eeprom]

Hello,
I am not a chemist. I am working on a heating device which converts NH3 to NOx. The heater is a cylinder filled with stainless steel BBs. The BBs are heated to 1600F, and a mixture of atmospheric air and NH3 is passed through this at a rate of about 10-20 SCFM. The heater is supposed to break down the NH3 and form NO or NO2.

In my tests, I keep running into a significant amount of CO in the gas. There is no carbon in the input mixture. All of the tubing, with the exception of the heater, is plastic. The amount of CO goes up with heater temperature, and also with gas flow.

My question is...can the hot gas react with the stainless to produce CO? If not, can someone explain where this might be coming from?

Any references to journal papers or articles would be appreciated.

thanks,
EE

 

[moltenmetal]

You are not transmuting elements from one to another. You don't need a journal article to know that.

Either the CO is an analytical artifact (i.e. it shows up in your analysis but isn't really there), or you are feeding some carbon-containing species that is reacting with oxygen to form CO. Either there's carbon in your feed gas that you don't know about, or you're pyrolyzing something (cutting oil/grease, your feed or more probably your discharge tubing etc.) to produce CO.

If you suspect the former, do better analysis using another method.

 

[eeprom]

Thanks for your reply. It sounds like I can rule out the stainless steel as the possible source of carbon.

I believe the CO exists because it behaves predictably with temperature and flow changes. I have considered both possibilities, grease and plastic tubing as two sources of carbon. The tubing is supposedly chemically inert. I'm not sure that means it is immune to thermally affects.

This morning I will put an additional heat source directly on the plastic tubing to see if this causes an increase in CO.

 

[Latexman]

Atmospheric air contains at least three sources of carbon that I know of - carbon dioxide, methane, and carbon monoxide. See:

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

Good luck,
Latexman

 

[eeprom]

Well, thank you both for your help. We borrowed a second test unit and the second unit detected 1-4 ppm CO, while our unit was detecting 100-150 ppm. As it turns out, the CO sensor can be fooled by NOx. The CO sensor has a NOx filter on it, and when the CO sensor goes bad, this is usually the first sign. So, we just need a new filter.

EE

 

[moltenmetal]

So you had an analytical artifact. Very common problem.