Energy & Fuels, Vol.32, No.2, 1223-1229, 2018
Relationship between Coking Behavior in Hydrocarbon Fuel Pyrolysis and Surface Roughness
The pyrolysis of hydrocarbon fuels can give rise to the formation of coke on metal substrate surfaces. Until now, there are few research reports about how the nature of these surfaces affects the formation of coke, especially the effect of surface roughness. A series of samples of different surface roughnesses was obtained by mechanical polishing, and the coking property with changed surface roughness was evaluated by cyclohexane cracking under 1 atm at 730-810 degrees C. The coke obtained was then analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and temperature-programmed oxidation (TPO). The results showed that reducing the surface roughness can effectively decrease the amount of coke in different ranges of cracking temperatures and cracking times, especially in high-temperature ranges (above 770 degrees C). The polishing process reduced the metal catalytic activity of coking to inhibit coke formation without changing the mechanism of cyclohexane cracking. Surface roughness could significantly affect the morphology of coke. The filamentous coke exhibited a cylindrical cross section with small amounts of amorphous carbon on its outer surface. The coke on the surface of the unpolished substrate had a higher degree of graphitization than that on the polished substrate, and the degree of graphitization gradually reduced as the surface roughness decreased. Generally, the decreased surface roughness was not only unfavorable to coke adhesion but also changed the properties of coke in the coking process.