Molecular dynamics study on the influence mechanism of pore structure regulation on oxygen adsorption in coal samples at the mesoscale

• The pore structure in coal samples is the main adsorption area for oxygen molecules. • The distribution of pore structure directly determines the diffusion ability of pore oxygen. • The adsorption of oxygen molecules in the same pore is equivalent. • The oxygen-containing functional groups have a prominent physical adsorption effect on oxygen. As a transitional scale between molecular and particle scales, the mesoscale can explore the adsorption mechanism of coal and oxygen at the molecular level while preserving the structural properties of particles. To investigate the mechanism of the pore structure of coal samples on the physical adsorption of oxygen, a macromolecular model of C 302 H 175 O 13 N 3 S 2 was independently constructed by analyzing the characteristics of lean coal samples. Based on the macromolecular model, six mesoscale models with different pore densities (0.80, 0.95, 1.10, 1.25, 1.40, and 1.55) were constructed by adjusting the density distribution of molecular clusters. Using Materials Studio simulation software for grand canonical Monte Carlo calculations, the adsorption characteristics of oxygen in pore structures under mesoscale models were explored. Molecular dynamics simulations were conducted on the most stable coal–oxygen configuration during the above process to investigate the adsorption characteristics of pore oxygen. The results indicate that the pore structure in coal samples is the primary adsorption area for oxygen molecules, and the adsorption of oxygen molecules within the same pore is equivalent, with the same adsorption state in each pore. Changes in pore size directly affect the adsorption and aggregation of oxygen in the pore structure. There are significant differences in the density distribution of oxygen in mesoscale models with different pore structures. As the density increases, the oxygen density distribution decreases significantly. The distribution of pore structure directly determines the diffusion ability of pore oxygen. As the porosity of coal samples decreases, the diffusion coefficient of oxygen molecules continues to decrease, indicating that the binding ability of the pore structure to pore oxygen continues to increase. The adsorption mechanism of oxygen by the pore structure is also influenced by key functional groups in coal molecules. Research has shown that oxygen-containing functional groups are significantly more prominent, particularly O=C–OH and O=S=O, which demonstrate strong adsorption capacity, and –OH and O=C–H are relatively enhanced. However, the pore structure has a certain influence on the adsorption of different functional groups. As the porosity decreases, the binding ability of C6 and C–O–C weakens, whereas the binding ability of O=C–OH, O=S=O, O=C–H, and OH increases.