Two-way coupling dynamics of CH4 4 adsorption and coal matrix deformation: Insights from hybrid GCMC/MD simulations

QL Yang and JH Xue and HF Lin and ZH Jin, CHEMICAL ENGINEERING JOURNAL, 498, 155321 (2024).

DOI: 10.1016/j.cej.2024.155321

CH4 4 adsorption can deform coal microporous structures, subsequently altering adsorption isotherms. To unravel this intricate interplay at a microscopic level, we use a hybrid Grand Canonical Monte Carlo/Molecular Dynamics (GCMC/MD) simulation at 313.15 K and pressures up to 500 bar on five independent amorphous coal matrix models. Our results reveal that CH4 4 adsorption increases pore volume and porosity primarily by generating additional pores of similar sizes to those present in coal matrices, thereby maintaining a consistent average pore size across different pressures. The volumetric strain has a linear correlation with CH4 4 loading, with volumetric swelling amount approximating the expansion of CH4-occupiable 4-occupiable pore volume, but less than He- occupiable pore volume which results in increased matrix skeletal density. Local radial density distribution of carbon atoms indicates that the immediate environment around carbon atoms remains unchanged. In a flexible matrix, the energy released during CH4 4 adsorption is partially absorbed by matrix deformation, resulting in a lower isosteric heat of adsorption compared to a rigid matrix, which suggests easier desorption. This study provides new insights into the mutual relationship between CH4 4 adsorption and coal matrix deformation, shedding lights on the complex interactions of various hydrocarbons with geomaterials.

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