Methane Adsorption Capacity of Deep-Buried Coals Based on Pore Structure in the Panji Deep Area of Huainan Coalfield, China

Pore structure characterization of deep-buried coals and its implications on methane adsorption capacity are of great significance for further understanding the adsorption mechanism of methane molecules by pores in deep strata. In this study, a series of several experiments, including high-pressure mercury intrusion porosimetry, N-2/CO2 adsorption, field emission scanning electron microscopy, and methane adsorption, were used to investigate the pore structure and methane adsorption capacity of deep-buried coals from the Panji Deep Area in Huainan Coalfield, China. The methane adsorption capacity of coal samples was obtained by experiment and correction based on the results by tests, and molecular simulation; the latter one adopted the pore filling and monolayer coverage theories. Results show that deep-buried coals developed with multiple types of pores and microfractures. Micropores provide the majority of the specific surface area, whereas the pore volume of deep-buried coals is dominated by macropores. On the basis of experiments, the measured methane adsorption capacity of deep coals shows a medium to high value compared with the adjacent coalmines, and the corrected methane adsorption capacity is in the range of 14.56-24.07 cm(3)/g with an average of 18.91 cm(3)/g. The number of methane molecules adsorbed as a state of micropore filling is (32.98-59.83) x 10(19) pcs, whereas in a form of monolayer coverage it is (0.51-2.05) x 10(19) pcs; the former is the primary contributor and accounts for 94.98-98.46% of the total. Notably, molecular simulated volume is close to that of measured methane adsorption volume, and both of them are significantly and positively correlated with volume and specific surface area of micropores. Methane adsorption capacity is dependent on the micropore volume and external surface area, and the adsorption process consists of a majority of micropore filling and a small amount of monolayer coverage.

Automated summary

Characterizing the pore structure and methane adsorption capacity of deep-buried coals is crucial for understanding the adsorption mechanism in deep strata. The presence of multiple pore types and microfractures in deep-buried coals was observed, with micropores contributing to a majority of the specific surface area. The measured methane adsorption capacity was found to be closely correlated with the volume and specific surface area of micropores, indicating that the adsorption process primarily involves micropore filling.