Crystallite Structure Characteristics and Its Influence on Methane Adsorption for Different Rank Coals

The ability of coal to adsorb methane depends on the coal microstructure; however, the research on its exploration is still underway. In this paper, a new method was adopted to investigate the evolution characteristics of the crystallite structure of eight different rank coals and its influence on the methane adsorption capacity. The crystallite lattice parameters, including d 002 , L c , L a , N ave , and f a , were determined by curve fitting analysis of X-ray diffraction (XRD) spectra. The methane adsorption experiments were carried out through a static capacity method, and the methane adsorption parameters ( V L , P L ) were measured. Correlations were established for the crystallite lattice parameters and the methane adsorption parameters. From the results obtained, there is a good negative linear relationship between V L and d 002 and a good exponential relationship between P L and d 002 , indicating that the increasing d 002 can weaken the methane adsorption capacity. V L displays an exponential increase with increasing L c and N ave , while P L presents a linear decrease, but reverse variations are emerged in the process of change for both, and the methane adsorption capacity is weaken temporarily. V L presents a lognormal distribution with increasing L a , and the minimum value appears at L a = 1.85-1.9 nm. V L and P L both obey lognormal distribution with increasing L a / L c , but their trends are completely opposite, and the methane adsorption capacity is the strongest at L a / L c = 0.85-0.9. As f a increases, V L and P L present an overall exponential increase and an overall exponential decrease, respectively, but reverse changes also emerge. The methane adsorption is related to the crystallite structure characteristics of coal. Finally, the influence mechanism of the crystallite structure evolution on the methane adsorption capacity was analyzed, which has great significance for prevention of gas disasters in underground coal mines.