FCC Reactions

Whether thermal or catalytic, cracking of a hydrocarbon means the breaking of a carbon to carbon bond. But catalytic and thermal cracking proceed via different routes. A clear understanding of the different mechanisms involved is beneficial in areas such as  

Naphthenes (cyclo-paraffins) cracked to olefins and smaller ring compounds 

Normal olefins to iso-olefin Normal paraffins to iso-paraffin Cyclo-hexane to cyclo-pentane 

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Riser is a vertical pipe where virtually all FCC reactions take place. 

By avoiding the acid catalysis mechanism of the conventional FCC zeolite catalyst (optimized over the years for high octane gasoline), the novel MAB catalyst will produce substantially lower aromatics in the liquid products than is possible by less extreme FCC catalyst adaptations. By changing the FCC reaction system, it is possible to overcome the MAB catalyst low activity drawback and achieve slurry yields compatible with those observed in maximum distillate operation in today s FCC units. 

Hershkowitz et al. (3,10,11) measured adsorption and coke deposition on zeolite catalysts as well as catalytic cracking activity of FCC catalysts in short-contact-time interactions with decane at 573 K. They used 5 pi liquid decane injections to the catalyst bed to simulate FCC reaction conditions. Hershkowitz et al. focused on the measurement of adsorption and coke formation during the flow of the pulses. 

Firstly, for the FCC reaction, in which the coke formation kinetics is the same order of magnitude as the kinetics of the main reactions,... 

Tubular fixed bed reactors for studying FCC reactions are also somewhat limited by large temperature gradients due to the highly endothermic nature of cracking and pressure drops across extremely fine fluid catalyst beds. These deficiencies can be eased to some degree by using a micro-reactor with catalyst dilution (Nace, 1969 Collyer, 1987 Larocca, 1988). 

The last step in catalyst configuration is to specify the Activity section of the Catalyst Tab in the FCC Reaction Section Window as shown in Figure 4.64. The Activity of the catalyst essentially refers to the effect of metals on catalyst deactivation. We can either maintain a constant level of metals on the catalyst or keep adjust the feed metals content to match makeup rates and equilibrium activity. We recommend the using Constant Beat Metals option since the information required is available from routine equilibrium catalyst analysis of the FCC catalyst... 

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