Impact of pore structure on gas adsorption and diffusion dynamics for long-flame coal

The pore structure of coal has a “U-shaped” relation with coal rank. Adsorption pores (pore size smaller than 2 nm) and seepage pores (2 nm < pore size<50 nm) greatly influence gas adsorption and diffusion. Thus, the pore structure of five coal samples (Ro between 0.57% and 0.62%) from eastern China was investigated in this study. Scanning electron microscopy was used for the qualitative analysis of the pore structure. Additionally, mercury porosimetry and the adsorption of CO2 at 273 K were used for the quantitative analysis of the pore size distribution. #15 and #16 coal samples were used to study gas adsorption properties at different temperature, while #12, #13, #14 and #16 coal samples were used to study gas diffusion characteristics. The results show that the micropores of long-flame coal are well developed and that micropores (pore size smaller than 2 nm) greatly affect gas adsorption properties, whereas mesopores (2 nm < pore size<50 nm) affect gas diffusion characteristics. The adsorption ability of long-flame coal increases with the microinvasion capacity and specific surface area. From the perspective of adsorption dynamics, VL increases with temperature, whereas PL does not change appreciably. Methaneʹs effective diffusion coefficient, obtained from adsorption data based on Fickʹs laws of diffusion, was observed to increase with the development of mesopore structure and decrease with time. Initially, the effective diffusion coefficient decreased sharply and stabilized after 15 min. The results may have significant implications for the control of methane in coal.