Micropores are the primary sites of methane adsorption in coal, and the heterogeneous mesostructures of coal create the non-uniform distribution of the micropores in coal. Using a thermal infrared imager, the temperature distribution on the surface of an anthracite sample during methane adsorption/desorption was tested in this paper, and a new method is advanced to calculate methane adsorption capacity in coal based on its temperature increment. The results confirm the strongly non-uniform distribution of methane adsorption in coal. A X-ray CT scan test demonstrates that the volumetric zones of coal sample with a strong methane adsorption capacity have a lower average density. In these regions, the clay minerals with developed micropores also have a strong methane adsorption capacity. During the coal skeleton deformation of methane adsorption, the high density is hard to be squeezed, while low density areas are likely to be squeezed. Therefore, the complexity density distribution in coal leads to the incompatibility of deformation, which make the direct determination of regional uptake a challenge; From the SEM micrographs of the same coal sample with different densities determined by the X-ray CT scan, the mesostructures of cell cavity pores with non-compact packing of the clay minerals appear to be the primary sites of methane adsorption in coal, and the telocollinite with fewer pores has a lower methane adsorption capacity.

This study analyzes the microstructure and deformation rule after methane adsorption on coal by scanning electron microscopy (SEM) and computed tomography (CT) scanning of microscopic coal samples. Studies have shown that coal is a natural rock composed of vitrinite coal matrix and clay mineral. After methane adsorption, coal undergoes non-uniform expansion deformation. This occurrence prompts coal density to decrease and then increase, causing the density distribution of coal to become highly concentrated. During swelling after adsorption, the effects of deformation and expansion on coal structures become stronger than that of mutual squeezing. Under low adsorption pressure, coal expansion deformation are more likely to crack the pore structure of the original coal to acquire space for expansion. When the adsorption pressure increases, compression becomes mainly concentrated in the low-density region; as adsorption pressure continues to increase, expansion deformation occur from high-density to low-density regions. The methane adsorption properties of coal are related to its pore structure. Adsorption and swelling mainly occur in the region where the pore structure is unfilled or filled with clay minerals. Expansion deformation conforms to the Langmuir equation; the region without pore structure development exhibits no swelling; the deformation degree and range of the pore structure and clay mineral mixing zone exhibit increase volatility. Overall, results reveal a microstructural change after methane adsorption.

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