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, 13 C 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 CO 2 , O 2 , and N 2 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 CO 2 in the pores of the three types of coals is far greater than that of N 2 and O 2 . The specific surface area and volume of pores have a significant effect on the displacement of CO 2 and N 2 on O 2 . 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 CO 2 and N 2 injection to prevent coal spontaneous combustion.
In this paper, the physical adsorption characteristics of oxygen in coal pores were systematically investigated by the Grand Canonical Monte Carlo and the COMPASS force field. Firstly, coal pore structures of different sizes were constructed by graphite slit models and different groups. Secondly, the physisorption behavior of oxygen in graphite slit models of different sizes was simulated. Finally, the physisorption behavior of oxygen in graphite slit models at different pressures and temperatures was analyzed. The results showed that the physisorption density and excess physical adsorption of oxygen were divided into the rapidly decreasing stage (0.4-0.7 nm), the slowly decreasing stage (0.7-1.4 nm), and the stable stage (1.4 nm-5 nm) with the increase of coal pores, and the excess oxygen physisorption amount was more sensitive to the change of pressure. The O2 isosteric heat of physisorption decreased with increasing pore size of coal. Oxygen is more strongly adsorbed by hydroxyl and ether bonds than by methyl, carboxyl and carbonyl groups. Through this study, the mechanism of oxygen physical adsorption in coal pores and the characteristics influenced by temperature and pressure can be better understood.
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