Reaction Mechanism of Catalytic Cracking Reactions

The typical feeds to catalytic cracking units shown in Table 5.2 are mixtures of paraffins, naphthenes, alkyl chain substituted aromatics, and more comphcat-ed molecules. These undergo the series of complex cracking reactions, includ- 

TABLE 5.2. Typical FCC Unit Feed and Operating Conditions. 

Paraffins Branched paraffins and olefins mainly in C3-C10 range. Olefins crack and isomerize and are also satiwated by hydrogen transfer to give paraffins. Olefins also cyclize to naphthenes. 

Naphthenes Crack to olefins. Dehydrogenate to cyclic olefins. Isomerize to smaller rings. Furdier dehydrogenation to aromatics, by hydrogen transfer. 

Aromatics Alkyl groups crack at ring to form olefins. Dehydrogenation and condensation to polyaromatics. Furdier dehydrogenation and condensation forms coke. 

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