Hydrogenation of coal tar pitch for improved mesophase pitch molecular orientation and carbon fiber processing

Abstract

The high softening point and mosaic optical textures of coal tar pitch (CTP)-derived mesophase pitches are the main factors limiting their application in high performance carbon fibers. Spinnable mesophase pitch was prepared using CTP hydrogenation process, and the effect of hydrogenation process on the preparation of mesophase pitch and the crystal structure of carbon fibers was investigated. Molecular structure characterization results show that the naphthenic structures and the aliphatic groups in hydrogenated CTP were generated by the hydrogen addition reaction of aromatic rings and the subsequent naphthenic cracking reactions, respectively. The naphthenic structures and aliphatic groups introduced during the CTP hydrogenation process of CTP have a significant effect on improving the homogeneity of anisotropic textures, molecular weight distributions and the molecular stacking heights of mesophase pitches. The prepared mesophase pitch has lower viscosity and enhanced flowability, significantly improving its spinning stability and the molecular orientation of their as-spun pitch fibers. Benefits from this, the optimized carbon fibers present distorted graphite lamellar structures and possess a larger crystal size than commercial coal tar-based carbon fibers K13D2U. The work provides some valuable insights for enhancing crystal structures of carbon fibers via molecular structure regulations of their precursors.