Effect of Carbonaceous Precursors on the Structure of Mesophase Pitches and Their Derived Cokes

Using six representative feedstocks as carbonaceous precursors, various mesophase pitches and their derived cokes were obtained by a heat-soaking method at a temperature range of 400-450 degrees C and a pyrolysis treatment at 900 degrees C, respectively. The optical texture and microstructure of the different mesophase pitches and their derived cokes were characterized by polarized-light microscope, scanning electron microscope, and X-ray diffraction. The results show that the formation and development abilities of liquid crystalline mesophase are obviously different for the various feedstocks. C-9 aromatic hydrocarbons and petroleum-derived paving pitch possess relatively high thermo-chemical reactivity due to the existence of low molecular substances and aliphatic groups, leading to form liquid crystalline mesophase easier and faster than those of naphthalene synthetic pitch and coal tar-based impregnating pitch under a similar condition, which however is undesirable to develop a bulk mesophase. Anthracene possesses a characteristic of forming a homogeneous bulk mesophase with a streamline texture under a suitable condition. The liquid crystalline transformation behavior of C-5-C-9 aromatic hydrocarbons is unexpectedly similar to that of naphthalene synthetic pitch and markedly different from that of C-9 aromatic hydrocarbons. Carbonaceous precursors have a significant effect on the anisotropic content and the optical texture of the mesophase pitch products, which leads to the microstructure variety of the resultant cokes. Fine-grained and coarse-grained mosaic textures are, respectively, present in the cokes derived from C-9 aromatic hydrocarbons and petroleum-derived paving pitch. The cokes derived both from coal tar-based impregnating pitch and from C-5-C-9 aromatic hydrocarbons possess a supra mosaic texture mingled with a local flow-induced orientation domain. A well-oriented lamellar texture is clearly found in the cokes derived from anthracene and naphthalene synthetic pitch.