NO Reduction Studies in the FCC Process. Evaluation of NO Reduction Additives for FCCU in Bench- and Pilot Plant-Scale Reactors E. A. Efthimiadis, E. F. Iliopoulou, A. A. Lappas,* D. K. Iatridis, and I. A. Vasalos Chemical Process Engineering Research Institute and Department of Chemical Engineering, Aristotle University of Thessaloniki, P.O. Box 361, 57001 Thermi-Thessaloniki, Greece During FCC catalyst regeneration, part of the nitrogen in coke forms NO x , which makes up a significant part of the total NO x refinery emissions. The addition of a small percentage (e1 wt %) of catalytic additive(s) in the FCC inventory can reduce the NO x emissions from the flue gases of the FCC regenerator. In this paper, experimental techniques are considered for evaluating, in laboratory reactors, the performance of two commercially available NO x removal additives. It has been shown that in an FCC regenerator the gas residence time and the concentration of CO in the flue gases are key parameters in controlling NO x emissions. For example, pilot plant experiments showed that the addition of a CO oxidation promoter (CP-3) in the catalytic inventory decreases the CO emissions significantly and increases the NO x emissions about 4 times. Replacement of the active CO oxidation promoter (CP-3) with an additive (XNO x ) with moderate CO oxidation activity reduced the NO x emissions by 78%. Comparison of regeneration results performed in bench-scale reactors with those measured in our FCC pilot plant unit showed that it is possible to evaluate NO x reduction additives in bench-scale experiments. The proposed protocol for this evaluation is to mix spent FCC catalyst with the NO x reduction additive and to load this mixture in a fluidized bed reactor. The above mixture is then regenerated at 700 °C by 2% O 2 diluted in N 2 . 1. Introduction Nitrogen oxide (NO x ) emissions from the regenerator of a fluid catalytic cracking (FCC) unit make up to 50% of the total NO x emissions in a modern integrated refinery. Other NO x sources in a refinery are the process furnaces and the utility boilers. The NO x emissions in an FCC regenerator originate from the nitrogen con- taining species deposited on the catalyst during the cracking cycle. Depending on FCC operation conditions, about 5 wt % of the gas oil feed forms coke. It has been reported 1 that about 40% of the nitrogen contained in the FCC feed is deposited with the coke on the cracking catalyst. During catalyst regeneration, coke containing C, H, N, and S is burned off the catalyst and its activity is restored. In a simplistic way, the reaction scheme (1)- (4) can represent the coke burning reactions. 2 It has been mentioned 3 that CO and CO 2 are concur- rently formed during coke combustion. Subsequent CO oxidation (afterburning) occurs in the dilute phase of a regenerator 2 with the result of a significant temperature rise. It is believed that the presence of significant amounts of CO in the dense bed of the regenerator results in low NO x concentrations, because reaction 4 takes place. The high dilute phase temperatures and their nega- tive effect on cyclone life led Mobil researchers in the 1970s to patent the use of Pt promoters, 4 that is, compounds which accelerate the oxidation of CO (CO + 1 / 2 O 2 f CO 2 ) as soon as it is formed in the dense bed. Thus, the heat release from the CO oxidation is taking place inside the regenerator dense bed, where the catalyst serves as a heat sink. The net result is that the dilute phase temperature is significantly reduced. The introduction of CO promoters, however, brought a significant change in the extent of chemical reactions 1-4. In particular, reaction 4 can no longer take place to the extent of a nonpromoted regenerator operation with the net result of a significant increase in NO x emissions. 1,5-8 * Corresponding author. Telephone: +30-310-498305. Fax: +30-310-498380. E-mail: angel@cperi.certh.gr. 5401 Ind. Eng. Chem. Res. 2002, 41, 5401-5409 10.1021/ie020265h CCC: $22.00 © 2002 American Chemical Society Published on Web 09/28/2002