Observed effect of parameters

Carbon laydown increases as the hydrogen-to-hydrocarbon ratio (HHCR) decreases.47 The variation of ageing rate with HHCR is very steep for HHCR 10 molar (Fig. 6.5).27 Lowering the Weight-Hourly Space Velocity (WHSV) at constant HHCR increases carbon laydown.47 

The work of Sinfelt21 and Franck49 demonstrated that as pressure is reduced, the rate of dehydrocyclisation at first increases, and then decreases 

Five-ring naphthenes are more toxic than 6-rings, for example, cyclopentane is particularly toxic, probably because it is a precursor for the conversion of cyclopentadiene into polyaromatics by Diels-Alder chemistry. This reaction appears to have similar structure-sensitivity to hydrogenolysis and sulphiding.52 Barbier considers that there is electron transfer from Pt — S. The composition of coke appears to be independent of feed composition.53 

The concentration of these coke precursors reaches a plateau during line-out, where their rate of removal from metal sites is similar to their rate of deposition.27 Both the deposition rate and the rates of hydrogenation and hydrogenolysis will depend on temperature, pressure and Pt dispersion. 

8 Evolution of the relative activity in benzene hydrogenation with the time of coking.59 (Reprinted from Applied Catalysis, 13, Barbier et al., pp. 245—250, Copyright 1985 with permission from Elsevier.) 

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