ie7b02479_si_001.pdf (2.21 MB)
Impact of Initial Surface Roughness and Aging on Coke Formation during Ethane Steam Cracking
journal contribution
posted on 2017-10-16, 00:00 authored by Stamatis
A. Sarris, Steffen H. Symoens, Natalia Olahova, Kim Verbeken, Marie-Françoise Reyniers, Guy B. Marin, Kevin M. Van GeemAlloy
composition and morphology of the inner wall of steam cracking
reactors are well-known key factors that affect their coking tendency.
The effect of surface roughness on the coking tendency remains uncharted
to date and has been studied here for a 35/25 Ni/Cr wt % alloy in
a quartz jet stirred reactor equipped with an electro-balance under
coil outlet industrially relevant ethane steam cracking conditions: Tgas phase = 1173 K, Ptot = 0.1 MPa, and XC2H6 = 70%. Up to 6 times higher initial coking rates have been
observed during cyclic aging in an Rα surface roughness range of 0.15–7 μm, and cyclic aging
proved to have an effect mainly on the catalytic coking behavior.
No effect was observed on the asymptotic coking rates. Scanning electron
microscopy, energy diffractive X-ray surface analysis, and cross section
elemental mappings suggest that the effect of surface roughness and
aging on the catalytic coking rate derives mainly from changes in
the metal surface composition. The amounts of metallic Ni and Fe show
an increasing tendency with increasing surface roughness, explaining
the pronounced coke deposition. Using Ekvicalc, thermodynamic calculations
were performed proposing that the amount of Cr2O3 gradually decreases followed by an increase of manganese chromite,
MnCr2O4.