Pyrolysis characteristics and kinetics of low rank coals by TG-FTIR method

- Pyrolysis characteristics of four low rank coals were studied by TG-FTIR.
- Functional groups in coal structure were investigated by curve-fitted FTIR method.
- TG and DTG results showed the pyrolysis process could be divided into five stages.
- The fast pyrolysis stage showed the largest activation energy and frequency factor.

The paper studied the pyrolysis characteristics and kinetics of four typical low rank coals selected from different mines of China using thermogravimetry coupled with Fourier transform infrared spectrometry (TG-FTIR). The chemical structures of the low rank coals were investigated by the FTIR measurements. The FTIR spectra of the low rank coals were divided into four zones and functional groups of the chemical structures were investigated by curve-fitted method. The thermogravimetric (TG) and differential thermogravimetric (DTG) curves of low rank coals indicated that the overall pyrolysis processes could be divided into five stages based on characteristic temperatures and each stage had its unique characteristics. The pyrolysis reactions mainly occurred in the fast pyrolysis stage. The activation energy E and frequency factor A were calculated by a single first-order reaction model using Doyle integral method. The results showed that the E and A of the fast pyrolysis stage were the largest, while the obtained E of the slow pyrolysis stage was close to that of the fast polycondensation stage. The emissions of CO2 and CH4 were detected during pyrolysis process. The results revealed that the evolutions of CO2 and CH4 were affected mainly by content of carboxyl groups and content of aliphatic chains in the low rank coals, respectively. The pyrolysis characteristics and kinetics of low rank coals were closely associated with their complex chemical structures.