The formation of nitrogen oxides (NO x ) during the regeneration of fluid catalytic cracking (FCC) catalyst can be attributed to oxidation of nitrogen in coke. Thermal NO x does not occur to any significant extent at FCC regenerator temperature. NO x is primarily comprised of nitric oxide (NO) with only a small concentration of NO2 detected. Under typical FCC regenerator conditions, only 10% of the nitrogen in coke evolves from the regenerator as nitric oxide with flue gases. Our findings show that ∼90% of nitrogen in coke is converted to dinitrogen (N2) in the regenerator. The authors suggest that dinitrogen is a secondary product produced by the reduction of NO with carbon and/or carbon monoxide in the regenerator. NO x emissions are lower in controlled burn regenerators where exposure to excess oxygen is minimized. Two-stage regeneration was found to lower NO x emissions by conversion to N2 during recontacting of flue gases and catalyst in the dense bed.

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