Correlation of Mesophase Properties with Molecular Structures of Pitches from Different Sources

In this paper, the molecular structures of vacuum residue (VR), coal liquefaction pitch (CLP), and coal tar pitch (CTP) are presented in detail, in order to explore their connection with mesophase properties. It is found that the H/C atom ratio of VR is as high as 1.32 because of abundant aliphatic structures. Its average aromatic ring number (RA) is only 3.88, and some of its internal aromatic rings are connected by bridged bonds. The mesophase pitch from VR (MP-VR) has a low mesophase content of 28.28–40.7% and is mostly of fiber texture. CTP has a degree of aromaticity (fa) of 0.90 and an RA of 10.65. The polycyclic aromatic molecule has only a few alkyl substituents at the periphery, resulting in a low H/C atom ratio of 0.56. The mesophase pitch from CTP (MP-CTP) has a mesophase content of 31.5–53.9% and has a distinct mosaic texture. CLP has the largest average molecular structure unit size, with an RA of 12.33 and a large degree of condensation. It contained certain cycloalkane structure and methyl substituents. The mesophase pitch from CLP (MP-CLP) has a mesophase content of 43.3–54.4% and contains abundant fiber and flaky textures. The regular and compact lamellar arrangement of planar aromatic macromolecules gives MP-CLP better graphitization properties, thermal stability, and rheological properties than MP-VR and MP-CTP.