Evolution of Structure Properties during Zhundong Coal Pyrolysis

Pyrolysis is the first stage reaction in the processes of coal thermochemical conversion. In this study, Zhundong coal is pyrolyzed in an electric heated horizontal tube furnace. The combustion and gasification of coal and char are affected by the surface area, pore structure and chemical factors. The structure properties of Zhundong coal and chars are characterized with X-ray diffraction (XRD), CO2 adsorption isotherm, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM). XRD results indicate that, with pyrolysis temperature and time increasing, the stacking height (Lc) increases and then decreases, and the size of aromatic layer (La) of chars increases while the lattice plane spacing (d002) almost stays unchanged. The specific surface area, pore volume, and average pore width are calculated, and the results show that the chars present more developed pore structure. FT-IR study reveals the presence of -OH, C=O, -CH, and C=C. The intensity of band of -OH group (3100-3600 cm-1), C=O group (1700 cm-1), C=C group (1600 cm-1), and C-H group (2800-3100 cm-1) decreases with the increase in the pyrolysis temperature and time. The above results indicate that the structure properties of chars are strongly dependent on heat treatment conditions, which is essential for the utilization of Zhundong coal.