The dominant role of surface chemistry on coking resistance of passivating coating

Abstract

Passivation coatings with excellent coking inhibition performance play an important role in active cooling technology and ethylene cracking furnace. However, different coating types possess different coking resistance, and the dominant factor remains unclear. Herein, a novel strategy of isolative analysis for coke in coating underwent RP-3 supercritical cracking is proposed to account for the role of carburization and surface chemistry. The carburization amount of TiN coating after cracking experiment was obtained from the model constructed by artificial carburization of standard TiN-coated samples. Introduced TiN/SiO2 coating owned different surface chemistry contrast to the TiN coating, additive of density-functional-theory calculations to reveal the correlation between surface chemistry and coke amount. The results indicated that carburization contributed little to the total coke amount of TiN coating, and non-negligibly, the coke diffused rapidly along the grain boundaries, threatened the integrity of coating. More importantly, the main coke belonged to the part that adhered to the coating surface. The strongly adsorbed 3d-4σ*/2π*bonded coking precursors (C2H2), were presented on the TiN surface, while the great flexibility of amorphous SiO2 made it non-adsorbent to C2H2, leading to weak coke adhesion on the TiN/SiO2 surface and strongly adherent coke on TiN surface. These results reveal that surface chemistry influenced coke adhesion and dominated coking resistance of coating.