Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Chemical Engineering

First Advisor

Michael D Amiridis

Abstract

Fluid Catalytic Cracking (FCC) is the primary process used to convert crude oil into a variety of higher-value products in modern petroleum refineries. Some portion of the nitrogen present in crude oil feeds is transported - as part of the coke formed during the cracking process - into the FCC regenerator unit and is eventually released from this unit in the form of NOx and NH3. Among the different technologies currently employed to control these pollutants, the use of catalytic additives is the most attractive one, as it is simple, cost-effective, and applicable to existing FCC units without the need for equipment retrofit. Most of the modern refineries already use catalytic promoters to accelerate the oxidation of CO. For example, Pt-containing combustion promoters are commonly used as additives to the circulating catalyst inventory in FCC units for this purpose. However, in the presence of these promoters N-containing coke species are also converted to NOx. As a result, these materials are not effective for the combined reduction of CO-NOx emissions and new formulations have to be developed. Moreover, it is not clear why CO combustion promoters increase the formation of NOx under FCC regenerator conditions. As a result, developing a better understanding of the surfaces chemistry taking place in the presence of NO, CO, NH3, CxHy and O2 during the operation of such additives is crucial for the rational design of a new generation of low NOx/CO combustion promoters.

The main goal of this work is to understand on a fundamental level how surfaces of M/Cen+/Na+/Al2O3 (where M=Pt, Pd, Rh) CO emission control additives facilitate chemical reactions involving NO, CO, NH3, CxHy and O2 under conditions approaching those existing in FCC regenerators. Noble metal-based CO emission control additives are expected to be involved in reaction schemes leading to the formation and/or reduction of NOx. This work also shows the relative contribution of each reaction in NOx formation/reduction over the M/Cen+/Na+/Al2O3 family of CO emission control additives. This work has led to a working understanding of the mechanism of NOx reduction/formation over commercial additives in FCC regenerators. Such an understanding can assist in the further improvement of catalysts used commercially, with substantial benefits to this industrial sector and the environment.

Rights

© 2012, Behnam Bahrami

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