The variation of structural characteristics of macerals during pyrolysis

Vitrinite and inertinite were separated by DGC from Chinese Shenmu bituminous coal and the structural characteristics of the macerals, before and after pyrolysis, were analyzed by ultimate analysis, FTIR and ¹³C NMR. The results showed that vitrinite chars always had higher H and lower C content than inertinite char at the same pyrolysis temperature. The FTIR and ¹³C NMR indicated that vitrinite had more aliphatic C-H, hydrogen bonding and lower aromaticity. With increasing temperature, the aliphatic C-H decreased, aromatic C-H, aromaticity and H_ar/H_al ratio increased. At the same temperature, inertinite always had higher H_ar/H_al ratio than vitrinite, which is consistent with that inertinite had higher aromaticity than vitrinite. And the H_ar/H_al ratio was also related to the remainder volatile matter. With increasing H_ar/H_al ratio, the remainder volatile matter in vitrinite and inertinite decreased. The higher aromaticity and H_ar/H_al ratio and lower H content of the inertinite in all temperature range were correlated with its higher thermal stability and lower volatile yield than vitrinite.