NOx Emissions in Fluid Catalytic Cracking Catalyst Regeneration

The formation of nitrogen oxides (NOx) during the regeneration of fluid catalytic cracking (FCC) catalyst can be attributed to oxidation of nitrogen in coke. Thermal NOx does not occur to any significant extent at FCC regenerator temperature. NOx 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. NOx emissions are lower in controlled burn regenerators where exposure to excess oxygen is minimized. Two-stage regeneration was found to lower NOx emissions by conversion to N2 during recontacting of flue gases and catalyst in the dense bed.