Spectra response from macromolecular structure evolution of tectonically deformed coal of different deformation mechanisms

Coals with different deformation mechanisms (brittle deformation, brittle-ductile deformation, and ductile deformation) represent different ways in macromolecular structure evolution based on the metamorphism. The evolution of coal structure could affect the occurrence condition of coalbed methane (CBM) because the nanopore structure affected by macromolecular structure is the most important reservoir for CBM. This paper analyzes the evolutions and mechanisms of structure and functional group of tectonically deformed coals (TDCs) collected from Huainan-Huaibei coalfield using X-ray diffraction (XRD), Raman spectroscopy, and Fourier Transform Infrared (FTIR) spectroscopy methods. The results show that the macromolecular structure evolutions of TDC are different from the primary structure coal as a result of the different metamorphic grade and deformation mechanisms. The different deformation mechanisms variously affect the process of functional group and polycondensation of macromolecular structure. Furthermore, the tectonic deformation leads to secondary structural defects and reduces the structure stability of TDC. The coupled evolution on stacking and extension caused by the changes of secondary structural defects results from different deformation mechanisms. We consider that the changes of chemical structure and secondary structural defects are the primary reasons for the various structure evolutions of TDC compared with primary structure coal.