High-temperature rheological behavior and non-isothermal pyrolysis mechanism of macerals separated from different coals

It is a challenge to accurately characterize the caking behavior of coal after thermal softening and its reaction mechanism. In this work, the formation behavior of metaplast during coal macerals coking was investigated using high-temperature confocal laser scanning microscopy and high-temperature small-amplitude oscillatory shear rheometer, the source of diversities in thermal fluidity of coal was revealed by thermogravimetric-mass spectrometry analysis and kinetic-thermodynamic theory calculations. The results showed that although vitrinite was the generator of metaplast in the thermoplastic stage, the expansion rate of vitrinite from coking coal is more than 70% greater than that from gas coal for two consecutive times. Moreover, the total weight loss of vitrinite from gas coal was about 1.262 times higher than that from coking coal, but the latter exhibited more generous aliphatic groups in pyrolysis products. In the thermal flow interval, the reaction activation energy of vitrinite and inertinite from coking coal and gas coal was 271.0 ± 0.7, 302.0 ± 1.5, 241.0 ± 0.1 and 300.25 ± 1.55 kJ/mol, respectively. Eventually, the kinetic and thermodynamic mechanism parameters of raw coal and macerals had favorable correspondence regularity, and macerals with the most prominent parameters would be dominant in the overall thermal properties of raw coal.