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

Methane adsorption characteristics of six Chinese pulverized coals were analyzed systemically. The maximum vitrinite reflectance values of the coal samples are within the range of 0.59% to 2.35% with varying maceral composition. Textures of the coal samples were characterized by N2 adsorption method at 77K. Particle surface morphologies were measured by scanning electron microscopy (SEM). The fine chemical structures on coal surface were analyzed by FTIR and Raman spectra. Methane adsorption isotherms were measured at simulated ambient environment of underground coal mine (298K and 1atm) and the Langmuir model was used to fit the experimental data. From the results, it can be seen that the nature of the isotherms varied widely for the selected six coal samples. Langmuir model is of the correct qualitative form to represent methane adsorption isotherms on the pulverized coal at ambient pressure environment. Methane adsorption parameters (VL and PL) present significant non-linear correlations with the increasing of coal maceral and proximate compositions. Ash has a negative impact on methane adsorption for all coals. About 1% increase in ash contents may reduce the methane adsorption capacities of 1.46cm³/g on the average. With the increase of maximum vitrinite reflectance values (R0,max), the Langmuir volume (VL) present first a decreasing and then an increasing trend after the maximum vitrinite reflectance values (R0,max) exceed 1.2%. However, Langmuir pressure (PL) presents a decreasing trend with the increase of the maximum vitrinite reflectance, 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. Research results may have important significance for understanding the mechanism of coal and methane coupling interactions in hybrid mixtures.