Oxide film prepared by selective oxidation of stainless steel and anti-coking behavior during n-hexane thermal cracking

Abstract

In order to reduce coke formation on the substrate surface, selective oxidation pre-treatments were systematically assessed for 316L stainless steel under H2-H2O atmospheres at 650 °C–950 °C and 0.1 MPa for 10 h. The phase constitution, elemental composition and surface morphology of oxide films were characterized by a combination of SEM, XRD, and EDS. The results showed that the oxidation temperature had a great influence on the morphology and microstructure of oxide films. The Mn and Cr content on the metal surface gradually increased with the increasing exposure temperature. The element composition was mainly associated with MnCr2O4 and Cr2O3. Thickness of oxide films was evaluated in various conditions. The anti-coking performance was evaluated by the n-hexane thermal cracking. It was found that the amount of the coke deposited on the oxidized tube was much smaller than that on the untreated tube, with an average anti-coking ratio of 83.2%. Moreover, the morphologies of carbon deposits were mainly filamentous on the inner surface of untreated tube, but granular for the case of the oxidized tubes.