Role of Presulfidation and H₂S Cofeeding on Carbon Formation on SS304 Alloy during the Ethane–Steam Cracking Process at 700 °C

Abstract

The influence of presulfidation and H2S cofeeding on the carbon formation on SS304 alloy in the ethane–steam cracker was investigated in a laboratory-scale quartz reactor setup. SS304H coupons and SS304L powder samples were exposed to ethane–steam and dry ethane in varying H2S content (0–50 ppm), and the SS304 samples were characterized by scanning electron microscopy. This study shows that H2S cofeeding decreases catalytic carbon formation; while it increases the pyrolytic carbon formation during ethane–steam cracking. Preoxidation, presulfidation, and addition of steam to ethane feed also reduces the amount of catalytic carbon formed on the SS304H surface in short-term experiments (4 h). Presulfidation and addition of H2S to ethane feed significantly influences the shape and size of the carbon formed on the surfaces of investigated metal alloys. Presulfidation and H2S cofeeding reduced spalling of the SS304H coupon surface during coking/decoking and thermal cycling.

The effects of sulfides and sulfur/phosphorus‐containing compounds on coke formation during thermal cracking of light naphtha

“…The formation of coiled filaments is mainly because that the metal particle has the angular shape. Because of the different diffusion path lengths in the carbide crystal, the carbon fiber would grow along the helical strands from the active crystal face 17,18 . The helical strands growth can further result in double helices when two adjoining crystal faces are active sites for coke formation, 17 which gives to the coiled filaments observed in this study.…”

“…Because of the different diffusion path lengths in the carbide crystal, the carbon fiber would grow along the helical strands from the active crystal face 17,18 . The helical strands growth can further result in double helices when two adjoining crystal faces are active sites for coke formation, 17 which gives to the coiled filaments observed in this study. In the case of the addition of DMDS, the diffusion rate of carbon through the particle is no longer rate‐limiting step of carbon formation because the active sites are poisoned at the edge of the metal particles by sulfur 18 .…”

“…Hence, no segmented filaments are formed in the presence of DMDS. The formation of rod‐like coke filaments might be due to the corrosion by H 2 S, and it has been reported in the literatures involving sulfur‐containing compounds in the thermal cracking process 16–18 . In the presence of H 2 S, grain‐boundary embrittlement can be caused by H 2 S attack on Ni‐Cr‐Fe alloy, leading to a decrease in tensile strength of the metal.…”

“…It is observed that large quantities of filamentous cokes are generated and intertwisted with each other in the absence of DMDS in a short cracking time. The presence of some bright points at the filament tips or in the structure of filaments is mainly owing to the extraction of metal particles by filamentous carbon 16–18 . When DMDS is added at the mass concentration of 200 ppmw, it is observed that the amount of filamentous coke is decreased and amorphous coke is increased.…”

“…Thus, graphite layers are formed periodically, which are paralleled to the transverse face of the metal particle. This will result in the filaments with the segmented shape 17 . The formation of coiled filaments is mainly because that the metal particle has the angular shape.…”