Coking effects

F. Garda-Ochoa, A. Santos 1996, (Coke effect in mass transport and morphology of Pt-AfiCfi and Ni-Mo-AfiCfi catalysts), AIChEJ. 42, 524. 

The effectiveness of coke as a heat barrier retarding heat transfer to the undecomposed polymer depends primarily on the thermophysical properties of coke. Semiempirical models of intumescent coatings > -i ) allow the coke effectiveness to... 

Under the fixed reaction conditions, neither CS2 nor Pyridine react with n-octane or its reaction products, but when added to the reactor feed stream they adsorb on the catalyst active sites taking them away fi-om the main reaction in an amount that depend with the time on run. Their effect adds to the coke effect on the catalyst activity and in order to take them into account, the kinetic expression is multiplied by a time dependent empirical fector... 

Zeolite catalysts are important in the catalytic cracking of heavy petroleum distillates. Their high selectivities and high rates of reactions, coupled with reduced coking effects, are major advantages over the activities of the alumina/silica... 

Coke Effect.- There is an element of arbitrariness in assigning some discussions to this section or the one preceding since, as mentioned in the previous paragraph, it is sometimes not possible to separate coking from sintering phenomena. The preference of coke for steps and planar surfaces on metal particles has been noted in Section 2.2. 

Barriocanal, C et al.. Reactive-inert interfaces in metallurgical cokes Effect of added inerts. Fuel, 72(2), 243-245 (1996). 

Depending on the H2S/CH4 ratio, hydrogen sulfide reforming occurs at a temperature higher than 850°C. At these temperatures, the elemental sulfur produced is in the vapor phase and cannot cause deactivation of metal sulfide-based catalysts. However, the formation of solid carbon can be harmful for the catalysts. To avoid coking effect, the molar ratio of H2S/CH4 must be greater than 4. As indicated by thermodynamic analyses [21], a higher H2S/CH4 ratio can reduce carbon formation to zero at lower temperatures. 

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