The effect of boron trifluoride complex on the preparation of mesophase pitch from FCC decant oil fractions with different compositions and molecular structures

Abstract

The boron trifluoride complex catalyst can effectively facilitate the development of anisotropic structures in FCC decant oil (FCC-DO) through cationic polymerization reaction. However, the fractions of FCC-DO with different boiling points possess different molecular compositions and aromatic nuclei configurations. In this study, FCC-DO is separated into light fraction, middle fraction, and heavy fraction by vacuum distillation. The different carbonization reaction pathways and reactivity were systematically investigated for three narrow fractions with no or 5 wt% addition of boron trifluoride complex catalyst. The results show that the heavy fraction is dominated by 4 and 5 plus ring aromatics with short side chains and methylene-bridged bonds. The catalyst showed excellent catalytic activity for the heavy fraction, the resulting product (MP-HF-5) possessing a softening point of 307 °C and 3.06 wt% methylene-bridged hydrogen at 95.3 wt% mesophase content. However, the catalyst slightly facilitated the development of anisotropic structures in the middle fraction (rich in 3 and 4 rings aromatics with naphthenic structures), which provided mesogen molecules during the FCC-DO carbonization reaction. Finally, the 1 ∼ 3 ring aromatics with long alkyl side chains are mainly present in the light fractions. The catalyst did not show obvious catalytic activity for the light fraction, in contrast, the oxygen-containing functional groups in the catalyst reacted with the aromatic molecule to form a disordered oxidative cross-linked structure, resulting in an almost completely isotropic structure of MP-LF-5.