Influence of group component distribution of coal tar pitch on mesophase structure development of needle coke

Group composition distribution of raw coal tar pitch is the key factor to determine quality of needle coke. The components of coal tar pitch were separated by ultrasonic solvent extraction. Effect of each group composition on mesophase characteristics was investigated. The group components were well blended to explore impact of different components on formation and development of mesophase structure. The results show that n-hexane soluble fraction (HS) is rich of aliphatic functional groups, and the excessive amount of HS fraction is not conducive in formation of large scale mesophase. Nevertheless, an appropriate amount of HS can maintain a proper lower viscosity in a long time range of the melting pitch system, which is significantly beneficial to growth and development of mesophase. Toluene insoluble substance (TI) is mainly consisted of dense cyclic aromatic hydrocarbon with high degree of polymerization. It can accelerate generation and development of mesophase sphere. However, excessive TI fraction can lead to generation of mosaic structure and reduce quality of needle coke. The green coke obtained from n-hexane insoluble and toluene soluble matters (HI-TS) demonstrate better optical anisotropy structure and is considered be the most suitable component for preparation of needle coke. The refined pitch with HS≈25%, HI-TS≈69%, and TI≈3%−8% can produce needle coke with well-developed mesophase structure and low thermal expansion coefficient.