(513cf) A Novel Catalytic Coating for Reduced Coking Formation in Ethylene Thermal Cracking

Ethylene thermal cracking occurs in cracking coils with the temperature of about 800-900℃, coking deposition with iron and nickel occurs in the coils of cracking machine at this temperature. Coke is attached to the inner surface of the furnace tube by growth, which leads to the reduction of the inner diameter in the furnace tube and the reduction of the total device output. To minimize coke formation, a catalytic coating actively removing coke that is deposited on the coils was prepared on the Cr25Ni20 alloy by powder pack cementation processes. The obtained Al-Si-Cr-Ce coating possessed a thickness of about 150um and had a dense multiple layers structure, which consisting of an outer layer composed of Al-Ce rich compounds and an inner layer composed of Cr-Si-rich compounds through EDS Analysis. Compared to other coking inhabit coating, Ce is used as gasify catalytic. Taking naphtha as cracking raw material, the coking test and periodic coke removal test are carried out in the ethylene cracking simulation device, and the coking inhibition performance of the coating is analyzed. The result show that structure of Al-Si-Cr-Ce coating samples is different from that of non-coating samples. The latter shows large areas of uneven carbon deposition and filamentous coke deposition, while the former shows pyrolytic morphology without catalytic filaments through SEM patterns. Contrast with no-coating material, the inhibition rate of the coating can reach more than 80%, and the inhibition rate is still more than 70% after three times decoking cycles.