Optimizing light and heavy aromatic ratios in fluid catalytic cracking slurry oil for mesophase pitch with wide-area optically anisotropic texture

Abstract

Aromatics are the preponderant component of fluid catalytic cracking (FCC) slurry oil, with notable differences in molecular structure between the light and heavy aromatics. The effect of these differences on the formation and optically anisotropic texture of mesophase remains elusive, impeding the preparation of high-quality mesophase pitch. This paper aims to regulate the ratio of light to heavy aromatics in the FCC slurry oil for optimizing the optically anisotropic texture of mesophase pitch. The results show that the heavy aromatics possess higher aromaticity, longer alkane side chains, larger molecular size and more reactive structures (methylene bridges, n-alkane structures) compared with the light aromatics. As an “accelerator”, heavy aromatics can form mesophase quickly. Light aromatics not only served as a “diluent,” but also assumed the function of a “lubricant”, which facilitated the orderly arrangement of aromatic molecular lamellar. The system exhibits moderate reactivity that inhibits excessive condensation and modifies the structural orientation of pyrolysis products with the 2/5 ratio of light to heavy aromatics. Under these conditions, a high-quality mesophase pitch (d002 = 3.485 Å, Lc = 19.832 Å) with wide-area optically anisotropic texture, suitable softening point (262 °C) and short polymerization time (t = 5.5 h) was obtained. This work provides theoretical support for the preparation of high-quality mesophase pitch by regulating the components of slurry oil.