Coke Formation on Preoxidized Iron and Nickel in a CH₄-H₂ Gas Atmosphere at 1,000°C

Coke formation on preoxidized iron (Fe) and nickel (Ni) specimen was studied in a 15% methane-hydrogen gas (CH₄-H₂) atmosphere at 1,00°C by thermogravimetry. Ground specimen of different surface finish were investigated also. An accelerated heterogeneous reaction resulted when the Fe specimen were preoxidized, resulting in a heavy coke deposition. This resulted from formation of an active “metallic” surface generated by the reduction of preoxidized scales. For Ni specimen, acceleration resulting from preoxidation was small. The different surface activities between the preoxidized Fe and Ni specimen were not attributed to the different surface areas. Based on the test results, a practical remedy to alleviate deposition of coke in high-temperature cracking environments was proposed.