Study of Adsorption Characteristics of CO2, O2, and N2 in Coal Micropores and Mesopores at Normal Pressure

At present, there are few studies on the adsorption laws of multicomponent gases in different pores of coal. This study takes AW (gas coal), YH (long-flame coal), and HL (lignite) coal samples as the research objects, and their molecular models are constructed by means of elemental analysis, 13C NMR, and X-ray. The experimental results of low-pressure nitrogen gas adsorption experiment were used to analyze the pore size distribution characteristics of coal and serve as the basis for establishing the corresponding micropore and mesopore structures. At 303 K and 0.1 MPa, the adsorption characteristics of coal in the ternary system of CO2, O2, and N2 were studied by the breakthrough experiments and gas adsorption simulations in different pores. The adsorption breakthrough curves and kinetic characteristics of the three gases were analyzed from a macroscopic point of view; the adsorption potential energy, adsorption density, adsorption amount, isosteric heat, and diffusion coefficient of the three gases in different pores of coal were compared from a microscopic point of view. It is found that the adsorption capacity of CO2 in the pores of the three types of coals is far greater than that of N2 and O2. The specific surface area and volume of pores have a significant effect on the displacement of CO2 and N2 on O2. The change of pore size has a significant effect on gas adsorption. In 0.4–5 nm pores, with the expansion of pore size, the value of gas adsorption and adsorption potential energy first decreases and then increases, the isosteric heat and the maximum adsorption density gradually decrease, and the self-diffusion coefficient shows an upward trend. The simulation results display a good agreement with the experimental results. This study is expected to provide some theoretical support for CO2 and N2 injection to prevent coal spontaneous combustion.