Devolatilization behaviour and pyrolysis kinetics of coking coal based on the evolution of functional groups

Knowledge of the mechanism of coking coal can improve coke and tar production in the coking industry. The evolution of six main functional groups in two coking coals with different ranks was investigated by in situ Fourier Transform Infrared Spectroscopy (FTIR) during non-isothermal pyrolysis in nitrogen gas flow. Different stages in various temperature ranges were proposed based on the evolution of functional groups during coking coal pyrolysis. The evolution of aromatic groups and C=O between the two coking coals had the largest difference because of the different coal ranks. The correlations among the evolution of the six functional groups during pyrolysis were also investigated to identify the possible reaction mechanism of coking coal pyrolysis. There were three processes, including evaporation of small molecules, decomposition of oxygen-containing groups, and devolatilization of aliphatic groups during pyrolysis. One-way transport and n th-order chemical reaction models were the main kinetic models of decomposition of the aliphatic groups, C=O, C-O, and OH. The activation energies of the functional group decomposition in two coking coals were in the range of 25.1-219.4 kJ/mol and 12.3-167.0 kJ/mol. The results that describe the pyrolysis process of coking coals with respect to functional groups can improve the understanding of the pyrolysis mechanism of coking coal and facilitate the development of clean coal technology.