Investigation into the Anticoking Performances of Sol–Gel-Derived SiO₂ and SiO₂–CeO₂ Coatings during Thermal Pyrolysis of Light Naphtha

Abstract

CeO2-based materials are widely applied in a three-way catalyst framework for catalytic combustion of diesel soot. For the application of CeO2 in coking inhibition during thermal cracking of hydrocarbons, SiO2–CeO2 and SiO2 coatings were prepared on HP40 alloy samples through sol–gel dip coating. The coatings were then characterized in terms of morphology and microstructure perspectives, and their anticoking performances were evaluated under conditions relevant to the practical applications during thermal cracking of naphtha. Results showed that the addition of ceria could improve the quality of the silica coating, which subsequently presented better anticoking properties by preventing formation of catalytic coking. Furthermore, thermogravimetric analysis (TGA) results of coke samples revealed that the ceria in the coating had the potential function as a coke oxidation catalyst. However, the silica–ceria coating lost its coking resistance after approximately ten repetitious coking/decoking cycles. Nevertheless, the combined application of anticoking coatings and addition of dimethyl disulfide (DMDS) into the naphtha feed could mitigate risks of coke formation more effectively compared with pure coatings only because of its preferential adsorption of sulfur-based radicals at the coating defects. In particular, the application of the SiO2–CeO2 coating combined with the addition of DMDS could still maintain a stable anticoking rate of above 60% throughout three cycles of coking/decoking operations.