Effects of olefins on mesophase pitch prepared from fluidized catalytic cracking decant oil

Olefin as one of the most important product molecules of fluidized catalytic cracking (FCC) process is widely distributed in FCC decant oil (DO), and drastically affects DO's thermal stability and the preparation of mesophase pitch due to its high reactivity. Mild hydrogenation was performed on a low-sulfur DO to stabilize the unstable molecules, i.e., olefins. Several selected olefins (including monoolefinic and conjugated) were added to the hydrotreated DO to investigate their effects on thermal stability and mesophase pitch preparation. Bromine number, diene value, proton magnetic resonance (H-1 NMR), Fourier transform infrared spectroscopy (FTIR) and two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) were used to characterize DO before and after hydrotreatment, and X-ray diffraction (XRD) and polarized optical microscope were used to detect the structure of mesophase pitch. Thermal stability of raw material was significantly enhanced through hydrotreatment where macromolecular aromatic hydrocarbons underwent partial hydrogenation, without over-hydrogenation. Influence of 1-octene, styrene and trans-stilbene on thermal stability of oil samples was enhanced successively due to the electron delocalization of conjugated olefins, and the effect of the amount of olefins added were significant. Olefins added to hydrotreated DO had different degrees of degradation on the crystal structures of mesophase pitch, and conjugated olefins had a much stronger effect on the development of mesophase pitch where the domain structures appeared in advance, with coarse-grained mosaic structure also interspersed in them.