Ti-Base Alloy Coking Behavior during Steam Cracking of Ethane

Reactor material technologies are in the core of the research around anti-coking technologies. In an effort to evaluate the coking performance of a Ti-base Alloy under ethane steam cracking conditions, a thermogravimetric experimental study was performed in a jet stirred reactor under industrially relevant conditions (T_gasphase = 1173 K, P_tot = 0.1 MPa, X_C2H6 = 70 %, dilution δ= 0.33 kg_H2O/kg_HC). As a first step, the optimal pretreatment for Fe-Ni-Cr Alloys was applied and compared with a pretreatment at increased temperature, aiming at a better oxidation of the surface and thus coking behavior of the material. The results indicated decreased coking rates of the Ti-Alloy at the expense of the pronounced formation of carbon oxides. Additionally, the tested coupons showed crack propagation after application of cyclic aging and cooling down back to ambient conditions. Therefore, the tested Ti-Alloy cannot be considered an industrially interesting steam cracking reactor alloy. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy was used to characterize the metal surface and cross section morphology of the studied samples and the coke morphology. Thus suggested that the rapid and disorderly oxidation of the surface and bulk made the alloy brittle leading to observable crack initiation and propagation.