Surface properties of pulverized coal and its effects on coal mine methane adsorption behaviors under ambient conditions

Methane adsorption characteristics were analyzed for six Chinese coals with the maximum vitrinite reflectance ranging from 0.59% to 2.35%. Textures of the coal samples were characterized by N2 adsorption method at 77 K. Particle surface morphologies were measured by SEM. FTIR and Raman spectra were used for the measurement to the fine chemical structures of coal. All methane isotherms were measured at simulated ambient environment of underground coal mine (298 K and 1 atm) and the Langmuir model was used to fit the experimental data. Results show that methane adsorption parameters present significant non-linear correlations with coal maceral and proximate compositions. With the increasing of maximum vitrinite reflectance (R0,max), the Langmuir volume (VL) present a first decreasing and then increasing trend after the R0,max exceed 1.2%. However, Langmuir pressure (PL) presents a decreasing trend with the increasing of R0,max, which indicates that methane seems to show a faster adsorption rate and higher affinity to the surface of coal with higher vitrinite contents. Furthermore, coals with larger specific surface area and richer-aromatic structures always have higher methane adsorption capacities.