Catalytically cracked products

Figure 6.16 Catalytic cracking product distribution of n-butane over zeolite catalysts with various heteroatoms. Reproduced with permission from [19], Copyright (2001) Elsevier, (a) H-AI-ZSM-5, (b) H-Fe-ZSM-5, (c) H-Ga-ZSM-5...

The complex then splits beta to the point of complexing to produce an olefin and a new hydrogen deficient entity. However, superimposed on this basic cracking reaction are the simultaneous and consecutive reactions which produce the characteristic catalytic cracking product distribution. The relative stability of carbonium ions is tertiary > secondary > primary. There is, then, either a preferential formation of tertiary and secondary ions, or else isomerization to these preferred forms. The property of beta fission results in the formation from secondary ions of no olefins smaller than propylene, and from tertiary ions of no olefins smaller than isobutylene. Cycli-zation and hydrogen transfer reactions result in the large amounts of aromatic hydrocarbon formed. The sum total of these described reactions lead to the desirable product distribution characteristic of catalytic cracking. 

The phenols appear in the effluents from an oil refinery in the stages of catalytic cracking, production of lubricants and solvents, and in the rinse water of the gasoline. According to a survey, the average concentration of phenol in the effluents was 154 mg L-i (Mariano, 2001). Another study foimd that the concentrations of phenolic effluents from a refinery were between 0.9 mg L-i and 60.0 mg L-i (Barros Junior, 2004). 

The percentage of sulfur in catalytically cracked products can be estimated from Figs. 4-37 and 4-38. Material balances indicate that very much of the feed sulfur appears in the flue gases and cracked gases. 

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