Influences of alkyl group on the formation of needle coke

Needle coke was prepared through the co-carbonization of toluene soluble fraction (TS) of coal tar pitch and waste polystyrene (WPS) in a tube bomb. The effects of the content of alkyl groups in the mesophase pitches on the properties of needle coke were investigated. By adding WPS into TS, the alkyl content in the mesophase pitches is increased from 12.0% to 33.3%; the resultant needle coke exhibits lower coefficient of thermal expansion (CTE) and better anisotropic orientation. The anisotropic indices of average length of vectors parallel to the CTE axis and average length of anisotropic unit vectors increase from 20.8μm and 23.4μm to 28.4μm and 28.8μm, respectively, while the CTE value decreases from 0.8×10^-6 /K to 0.1×10^-6 /K. The increase of alkyl content can reduce the viscosity of the carbonization system, which is beneficial to the development of flow texture and uniaxial orientation. Moreover, the sufficient gas evolution during the carbonization may also force the uniaxial arrangement of bulk mesophase molecules at the solidification stage.