Combined Experimental and Molecular Simulation Characterization of CO2 Adsorption Characteristics of Full Aperture in Bituminous Coal Pores

Adsorption characteristics of CO₂ in pores of different sizes were analyzed by the molecular simulation method, which provided theoretical guidance for the storage of CO₂ in coal seams. The pore structure parameters of bituminous coal were acquired by mercury injection, low-temperature N₂ adsorption, and low-pressure CO₂ adsorption experiments. The ultramicropores of bituminous coal were constructed by molecular simulation. The pore structure characterization of a full aperture section was obtained by combining the simulation results with parameters obtained from the experimental tests. Using coal molecules as a framework, a slit model was designed to represent pores. The adsorption pores of 0.63–100 nm were selected to construct the plate pore model, and adsorption data of CO₂ in this pore size range were obtained microscopically. The findings unequivocally demonstrate that the intricate pore structure encompassing the entire size range can be accurately characterized through a synergistic integration of the constructed ultramicropore models derived from molecular simulations and the experimental test-derived pore structure data. The interaction forces generated by the adsorption of CO₂ molecules in pores of smaller sizes are stronger, while in larger pores, the interaction forces are weaker; molecules were easier to enter the larger pores but not easy to adsorb. The CO₂ adsorption ratio and adsorption heat decrease with the increase of pore size. Larger pores can accommodate more molecules, but more free molecules. Distribution of adsorption sites on the same molecular species demonstrates uniformity across the distinct pore sizes.