Strain Effects on the Mechanical Properties and Gas Adsorption and Diffusion Characteristics of Anthracite

Abstract

The coal matrix is subjected to complex strain conditions during exploration. Pore structural evolution, gas adsorption, and diffusion characteristics of high-rank coal matrix under uniaxial compressive and tensile strain conditions are investigated through molecular simulation in this study. The specific surface area and pore volume increase continuously when the strain increases from −0.09 (compression) to 0.09 (tension). Mechanical properties including the Lamé constants, Young’s modulus, bulk modulus, and shear modulus generally decrease with strain value while the compressibility increases with strain. The Langmuir–Freundlich equation is used to fit the adsorption isotherm, and the adsorption capacity is found to increase significantly with strain. Tensile strain has a larger influence on the diffusion coefficient due to the increase in pore volume. CO2 has a larger adsorption capacity and heat compared with CH4 due to its higher affinity with the coal matrix, while its diffusion coefficient is smaller than that of CH4, resulting from the larger molar mass and higher interactions. The high-density gas area is located in the pore center and increases with strain, while small gas density occurs at the pore boundary due to the rough surface and repulsive force. Oxygen-containing functional groups have a larger influence on gas adsorption, and the peak radial distribution functions of C, O, and H atoms reduce with the increase of strain.