Effect of changes in the structure and composition of medium-low-temperature coal tar pitch on the quality of needle coke

The structure and composition of coal tar pitch are critical in the production of superior needle coke. We used high-temperature refined coal tar pitch (HRCTP) to modify medium-low-temperature refined coal tar pitch (MLRCTP) for needle coke preparation. Various characterization techniques were applied to evaluate the effects of the HRCTP addition on the MLRCTP's structure and composition, and to investigate the microstructural and crystallographic differences in needle coke from different feedstocks. We identified the optimal HRCTP addition level and assessed how carbonization reaction conditions influenced needle coke quality. The findings indicated that HRCTP addition increased the aromatic hydrocarbons content while reducing the heterocyclic compounds and excess alkanes, leading to enhanced structure and composition, which supported the structured development of carbon-based structures during the thermal polycondensation process. Notably, higher HRCTP amounts did not equate to better outcomes. With a 25% HRCTP additive level, the needle coke's microstructure showed a highly ordered fibrous texture with optimal orientation, the greatest degree of graphitization, and a mature graphite crystal content of 24.84%. Further optimization of the carbonization process demonstrated that very high temperatures might cause the formation of numerous mosaic structures due to disordered radical cross-linking. Properly reducing pressure at high temperatures could promote adequate directional airflow and apply shear force during orderly stacking of the mesophase, thus enhancing the carbon lamellae's streamline and orientation. Following the carbonization process optimization, the mature graphite crystal content in the needle coke increased from 24.84% to 39.87%.Graphical abstractFor table of contents only