(80c) Al-based Coating for Coke Reduction during Ethane Steam Cracking

Surface engineering to suppress coke formation in cracking furnaces is one of the key research topics in the ethylene industry. Alumina containing coatings have been claimed as being a major step to improve furnace run lengths. Therefore, in this work a commercial coating CoatAlloy^TM has been compared to the uncoated Fe-Ni-Cr base alloy. First, the effect of the coating pretreatment was evaluated in an electrobalance set-up during ethane steam cracking under industrially relevant conditions (T_gasphase = 1173 K, P_tot = 0.1 MPa, X_C2H6 = 70 %, dilution δ= 0.33 kg_H2O/kg_HC). Addition of nitrogen proved to be detrimental for the anti-coking performance of the coating. Additionally, the effect of presulfiding with 500 ppmw DMDS/H₂O, continuous addition of 41 ppmw S/HC of DMDS, and combinations thereof were evaluated. The tested samples were examined using online thermogravimetry, scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis together with X-ray photoelectron spectroscopy and wavelength-dispersive X-ray spectroscopy for surface analysis. The passivating coating performed substantially better than the reference Fe-Ni-Cr alloy while no effect on the product distribution was observed.