Effects of micro-mesopore structure characteristics on methane adsorption capacity of medium rank coal

The relationship between micro-mesoporous structure characteristics and gas adsorption capacity of medium-rank coal under different particle sizes was studied by physical adsorption method. The results showed that the capacity of adsorption nitrogen and carbon dioxide, specific surface area (SSA), BET SSA and micropore volume all increased with the decrease of particle size. The range of mesoporous aperture measured by BJH method was larger than that by DFT method, but the pore volume (PV) and SSA are relatively lower, which confirmed that the BJH method will underestimate part of the aperture. However, there was blank bands in the measurement of pore size in 2-4 nm by DFT method, which will also reduce the real value. The limiting gas adsorption volumes of 1#, 2#, 3# and 4# coal samples under different particle sizes were 17.19-20.76 m3/t, 14.11-19.3 m3/t, 17.17-19.14 m3/t and 12.11-15.59 m3/t, respectively, and the results gradually increased with the decrease of particle size. The linear correlation between BET SSA, mesoporous PV and Langmuir volume of coal was 0.43, 0.5-0.53 and 0.37-0.5, respectively, which was relatively low on the whole and slightly lower than the results in the literature. The linear correlation between Langmuir volume and micropore volume and SSA was 0.73 and 0.76, respectively, which was higher than mesoporous structure parameters and BET SSA. The control effect of microporous structure parameters on gas adsorption was significantly higher than mesoporous structure and BET SSA. The error between the calculated limit gas adsorption volume and the experimental limit gas adsorption volume was small, and the proportion of the microporous filling limit gas adsorption volume was as high as 99.7%. Multiple studies have proved that micropore is the main space of gas adsorption.