Relationship between Structural Modification of Aromatic-Rich Fraction from Heavy Oil and the Development of Mesophase Microstructure in Thermal Polymerization Process

In this study, the aromatic-rich fraction from heavy oil was modified by polyacrylic acid and oleic acid to obtain the modified raw materials which were used for producing mesophase pitch via polymerization reaction. First, the properties of modified feedstocks were analyzed by Fourier transform infrared spectrometry (FTIR), simulated distillation, and elemental analysis. The optical texture and molecular and microcrystal structure of the mesophase were characterized by the techniques of polarized optical microscopy, FTIR, H-1 nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy. The influence of alkyl structures contained in modified feedstocks on the preparation of the mesophase was studied. The results suggested that the amounts of alkyl chains in modified raw materials increased first and then decreased with raising the amount of the additives. The short and long alkyl chains in mesophase pitches from modified feedstocks were resulted by treatment of polyacrylic acid and oleic acid, respectively. In addition, the mesophase pitches with finer microcrystal structures, less crystalline imperfection, and high degree of graphitization were generated from modified raw materials. Moreover, an appropriate amount of short alkyl chains or a small number of long alkyl chains was favorable for the formation of a mesophase with a large domain structure, low softening point, high carbon residue, and fine microcrystal structure.