Influence of chemical properties on CH4 adsorption capacity of anthracite derived from southern Sichuan Basin, China

This study aimed to determine the effects of high-rank coal chemical properties on CH4 adsorption capacity. A total of 24 core samples of anthracite from 11 coalbed methane wells in southern Sichuan Basin (China) were examined systemically using maceral analysis, proximate and ultimate analyses, total sulfur content test, and CH4 isotherm adsorption experiment. Results show that vitrinite group macerals are the most abundant maceral group, followed by inertinite and inorganic mineral matter of these coals. Vitrinite- and inertinite-rich coals have the similar average Langmuir volume under dry ash-free basis (V-Ldaf), and no positive or negative correlation was found between V-Ldaf and vitrinite and inertinite content. In addition, there is a weakly negative relationship between inorganic mineral matter and CH4 adsorption capacity. Effects of coal elements by ultimate analysis, such as C element and the atomic ratios of H/C, O/C and N/C, on CH4 adsorption capacity were studied. CH4 adsorption capacity has positive correlation with C element content, H/C atomic ratio and N/C atomic ratio, respectively, but negative with O/C atomic ratio. Effects of four proximate analysis parameters (moisture, ash, fixed carbon and volatile matter content) on CH4 adsorption capacity were also studied. Moisture, ash and volatile matter content negatively affect CH4 adsorption, respectively, and fixed carbon content has exactly the opposite effect. Principle component regression analyses for the set of elements and proximate analysis parameters show that C, O, ash and fixed carbon content are the important influence factors on CH4 adsorption capacity.