The effect of accumulation of polycyclic aromatics in FCC decant oil on subsequent pyrolysis behaviors

To control the liquid-phase carbonization of the petroleum residue, the transition of the aromatics in earlier stages of the thermal conversion and its effect on subsequent carbonization behavior were analyzed. It was found that more monocyclic and dicyclic aromatics was converted to polycyclic aromatics in a comparatively shorter time between 450 and 500 degrees C. The higher polycyclic aromatics content of the oil accelerated the formation of the anisotropic phase, thus the excessive carbonization of the system was prevented and the lamellar orientation of the pyrolysis product was modified (the time required to obtain a fully developed carbonaceous mesophase decreased by 2 h and the stacking height (Lc) increased from 18.58 angstrom to 21.18 angstrom when the polycyclic aromatics content increased by 14.92 wt%). The modified oil obtained by thermal pretreatment (HCTO-RF-B) was converted to a carbonaceous mesophase with a large domain texture and good lamellar orientation (d(002) = 3.4599 angstrom, Lc = 21.94 angstrom), as well as a low softening point (273 degrees C) in a short carbonization time (8 h), which is attributed to the higher polycyclic aromatics content (which accelerated the formation of an anisotropic phase) and fewer long side chains (which controlled an appropriate free radical concentration) of the thermal pretreated oil. The fully developed carbonaceous mesophase from HCTO-RF-B had a higher stabilization reactivity, which is attributed to the alkyl chains preserved in the system (C-H substitution indice (I-CHS) = 0.7513, alkyl indice (I-A) = 0.7690).