In situ synchrotron diffuse reflectance infrared fourier-transform spectroscopy study on functional group evolution during coal pyrolysis: Effect of temperature and inherent minerals

• In situ synchrotron DRIFTS maps functional group evolution during coal pyrolysis. • Minerals hinder aliphatic cleavage, raising hydrocarbon reaction temp 150 °C. • Demineralization boosts oxygen structures and aromatic condensation. • Fivefold CH 2 /CH 3 ratio surge via mineral removal. • Aromatic condensation peaks at 100 °C–250 °C in demineralized coal. Inorganic minerals in coal can influence the migration of functional groups during pyrolysis. In situ synchrotron diffuse reflectance infrared Fourier-transform spectroscopy was employed to investigate the influence of temperature and inherent minerals on the evolution of functional groups during pyrolysis at 50 °C–500 °C. In situ spectroscopy observed that during the pyrolysis process, the organic molecular structure in coal underwent cleavage and reorganization, leading to the gradual release of functional groups originally embedded within the coal, which then diffused to the surface. The inherent minerals in coal impeded the cleavage of aliphatic chains, increasing the initial temperature of cleavage reaction for the formation of hydrocarbons from methyl and methylene groups by 150 °C. Additionally, the removal of minerals introduced more oxygen-containing structure and enhanced the aromatization of aliphatic hydrocarbons and the condensation of aromatic compounds. The maximum increase in the degree of condensation of aromatic rings during the pyrolysis of acid-washed coal occurred between 100 °C and 250 °C, rising from 0.35 to 0.58.