I don't see urea forming NOx by thermal pyrolysis because of the pathway that urea pyrolysis follows
There is a good thread on thermal decomposition of urea on here somewhere, use google's site search. There's also a nifty review paper on the topic on
"cyanurates" that will give you ABSOLUTELY everything you want to know about it. If you don't find it, PM me.
Basically if you mix the appropriate amount of slaked lime and urea and heat, you will first produce copious amounts of ammonia and ultimately if you get to red heat, calcium cyanamide with the evolution of lots
of CO2. Note: Without the lime, you will release toxic isocyanic acid in large amounts!
The calcium cyanamide can be converted to melamine in theory (by acidification with a calcium precipitating weak acid, eg. CO2 and boiling down the
resulting cyanamide solution after filtering off the carbonate) though all in all, this is no trivial matter.
As I see it at the moment, there's two possibilities with urea:
(1) The hypothetical low-temperature oxidation with some super oxidant.
(2) Making ammonia from it and then catalytically oxidising the ammonia at high temperature with oxygen.
The second option is tough to execute, hence only option (1) seems plausible in practical terms, though whether the chemistry will play along is
[highly] suspect at this stage.
[Edited on 28-6-2015 by deltaH] |