Selective adsorption mechanism of CO2/CH4/N2 multi-component gas mixtures by N/S atoms and functional groups in coal

The modification of coal samples will effectively enhance their selective adsorption properties for different gases. To investigate this phenomenon, the adsorption mechanism of CO2/CH4/N2 binary gas mixture by single benzene ring layer doped system and microporous system formed by N/S atoms with different functional groups in coal was investigated at microscopic level, and electrostatic potential, diffusion characteristics, fluid type, radial distribution function (g(r)) and coordination number (CN) were analyzed. The results showed that the interaction of N/S atoms with oxygen-containing functional groups in coal enhanced the electrophilic capacity of the system and enhanced the adsorption capacity of CO2 in the gas mixture, and the Freundlich adsorption capacity of CO2 in the N-doped system was higher than that in the S-doped system. The interaction between N atoms and oxygen-containing functional groups in coal will effectively enhance the adsorption selectivity of CO2 in the gas mixture, with the best capture effect between 80% and 70% of CO2 concentration. The high-energy adsorption sites in N/S-modified coal samples are more inclined to be occupied by CO2, and the fatty functional groups are more likely to trap CH4 and N2. These findings indicate that N-doped modification of coal samples with high oxygen content can lead to solid adsorbents with high adsorption capacity and strong selectivity, which provides theoretical guidance for the development of new and efficient adsorbents.