Carbon Structure Evolution during the Pyrolysis and Coking Process of Two Fat Coals

A deep understanding of the chemical structure evolution during coal pyrolysis and coking is crucial for expanding coking coal resources and developing more rational coal blending schemes. Two samples of fat coal at different pyrolysis stages were prepared by using a thermogravimetry-plastometer-swelling pressure apparatus and a muffle furnace. The samples were characterized by FTIR, 13C NMR, XRD and Raman spectroscopy to systematically investigate the evolution of the carbon structure during pyrolysis. The results indicate that the Feibei sample, which contains a higher content and longer length of aliphatic side chains, exhibits a slower formation rate of aromatic ring systems with≥6 rings in the later stages of pyrolysis. During the pyrolytic coking process of both coal samples, the content of aliphatic structure groups initially increased and subsequently decreased. Meanwhile, the aromatic ring systems underwent three distinct stages: initial longitudinal stacking dominated by 3-5 rings, followed by lateral expansion into larger systems comprising≥6 rings, and subsequent vertical growth centered on≥6 ring architectures, accompanied by a continuous reduction in the d002 of the carbon microcrystals. This study elucidates the evolution pathway of aromatic carbon structures during the pyrolytic coking of the tested coal samples.