As CO₂ emissions increase year by year, the climate and environmental problems caused by CO₂ are gradually intensifying. The porous nature of the coal seam itself and its strong adsorption of carbon dioxide are the keys to sequestering carbon dioxide. However, as to how coal seams can effectively store CO₂, the process and mechanism of coal seams storing CO₂ still need further research. Based on the device independently developed and designed by the research group, the author carried out an experiment of injecting CO₂ into a coal cylinder to replace N₂. Based on the comparison of FTIR and ¹³C NMR experiments with computer molecular design calculation spectral results, 2D and 3D models of anthracite macromolecules were created. At the same time, based on the 3D coal molecule model, Giant Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were used to conduct molecular simulations of the CO₂ and N₂ adsorption and replacement processes. The results show that the macroscopic process of the displacement process and the microscopic performance of molecular simulation have good mutual verification. The CO₂ production at the end of the coal pillar shows three stages: early accumulation, rapid displacement, and stable generation. The greater the CO₂ pressure or the pressure difference between CO₂ and N₂, the faster the CO₂ stored in the coal pillar can reach saturation, that is, the shorter the time required for the terminal gas components to reach equal percentages. Injecting CO₂ at a relatively low pressure is more conducive to the adsorption of CO₂ in the micropores and the full competitive adsorption of CO₂ and N₂ in the mixed components. In addition, molecular simulation further confirmed that coal seams have stronger adsorption capacity for CO₂ than N₂, and the pore size has a significant control on the adsorption and diffusion of CO₂ and N₂ molecules. For example, in 1 nm pores, the diffusion coefficient ratio of N₂ to CO₂ ranges from 14.14 to 20.98. The CO₂ injection pressure was 6 MPa, and more CO₂ molecules could be stored in the 2 nm and 3 nm pores. The research results explain the transport mechanism of CO₂ and N₂ in coal from a microscopic perspective, and provide a reference for CO₂ storage in coal seams.

CO2 displacement N2,Molecular Structure,Molecular Dynamics Simulation,Diffusion,CO2 Storage