Combustion promoters are required to ensure smooth regenerator operation, control of afterburning and reduction of CO emissions. Afterburning occurs when carbon monoxide reacts exothermically with oxygen in the regenerator dilute phase. Because of the lack of catalyst to absorb the heat of CO combustion the dilute phase experiences a large increase in temperature – the most common constraint in FCC unit operations. A CO promoter is be used to accelerate this reaction in the regenerator dense phase (catalyst bed) where the heat of reaction is readily absorbed by catalyst particles leading to much lower temperature rises.
CO promoters employ platinum group metals (pgm) as their active component supported on high surface area alumina to ensure high dispersion for maximum activity and retard deactivation via sintering.
The physical properties of Johnson Matthey’s INTERCATTM CO promoters, including particle size distribution, attrition resistance and bulk density, have been optimised to be fully compatible with all commercially available FCC unit designs and catalyst technologies. Independent testing has shown that INTERCAT CO promoters have the highest CO conversion efficiency on the market.
Platinum based promoters
Platinum based combustion promoters, COPTM-250, 375, 550, and COP-850, containing various levels of platinum provide a range of additives with varying activity. For units requiring higher levels of promotion the higher activity grades are recommended. For refiners requiring very little additive it is usually more effective to add a greater amount of a lower activity FCC additive for optimal control of afterburning.
Non-platinum based promoters
An undesired side effect of platinum based CO promoters is that they may increase the formation of NOx in some FCC regenerators. For this reason non-platinum CO promoters were developed. In cases where platinum based promoters lead to increased NOx their substitution with non-platinum CO promoters reduces NOx emissions at comparable levels of CO oxidation. COP-NPTM is an EPA approved non-platinum CO promoter that is commercially proven to effectively promote CO oxidation and control afterburn while reducing NOx emissions by over 70% relative to platinum based CO promoters.