Study on coal molecular structure characteristics on methane adsorption performance under pyrolysis treatment

To reveal the effect of the molecular structure of coal on the gas adsorption ability of coal seams, this paper selects the high-quality bituminous coal in the Shenmu mining area of Shaanxi Province, China, as the research object. We changed the molecular structure of coal through pyrolysis experiments and studied the effect of changing coal molecular structure on methane adsorption capacity based on Langmuir adsorption equations, Infrared spectroscopy, X-ray diffraction, scanning electron microscopy and liquid nitrogen adsorption. The findings of the experiments reveal that d002 reduces as pyrolysis temperature rises, but La, Nave, and Lc increase overall. The molecular structure of coal is restructured and layered, and the degree of polycondensation in-creases. Simultaneously, heating decomposes the active functional groups inside the coal sample, AC-O/Aar, ACH(2) / ACH(3) and A(al)/A(ar )decrease with the increasing pyrolysis temperature, and the aromatization degree of coal also deepens. The adsorption Langmuir constant a is well connected with d002, La, Nave, Lc, AC-O/Aar, ACH2 /ACH3 and A(al)/A(ar). After high-temperature pyrolysis, A variety of chemical bonds in the coal sample are broken, resulting in the release of a substantial amount of light hydrocarbon, and then a large number of holes and cracks appear in the coal body, and the micropores are reduced, thus reducing the overall adsorption capacity of the coal. The findings of this study provide theoretical guidance for the development of new technologies to recover coal seam gas during mining.