Comparison of the first stage of the thermal decomposition of Polish coals by diffuse reflectance infrared spectroscopy

Diffuse reflectance Fourier transform infrared spectroscopy was applied to study the decomposition of hard and brown coal during mild pyrolysis. The pyrolysis of investigated samples was conducted with a heating rate of 10 K/min up to 673 K under ambient pressure and a nitrogen flow of 4 L/h. Curve-fitting analysis was employed to characterise the coal structures evolving in temperatures ranging from 323 to 673 K. This study gives the information about the degradation of hydrogen bonds and oxygen structure. The comparison of the calculated structural parameters shows that bonds assigned to Car in hard coal are more stable at the investigated temperature range than the bonds in brown coal. The same phenomenon was observed for the CH bonds in aromatic formations. It was noted that during the pyrolysis the first changes in the structural parameters of lignite are visible at temperatures above 423 K and in case of hard coal above 473 K.