In situ FT-IR spectroscopic studies on thermal decomposition of the weak covalent bonds of brown coal

•Curve-fitted analysis of in situ FT-IR spectra during pyrolysis of coal is studied.•The functional groups show different behaviors with increasing the temperature.•The release of CO2 and CH4 is found to be related to the decomposition of carboxyl group and alkyl group.

In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) was used to characterize the thermal decomposition of the functional groups in Huolinhe brown coal. The PeakFit program for curve fitting was used to analyze the overlapped IR bands. The formation and decomposition of the functional groups show different trends during the heat treatment. The methyl and carboxyl groups decomposed with increasing the temperature, which is closely related to the release of CO2, CH4. The amounts of ester and anhydride groups rise reach a maximum then fall. Different types of OH hydrogen bonds were also observed after the absorbed water was removed at high temperature. The results indicate that the curve-fitting analysis well represents the change in the chemical bonds in coal.