Influencing Factors and Adsorption Process of N2/CH4/CO2 Competitive Adsorption in Coal

To investigate the influence of key factors (temperature, pressure, and particle size) on the competitive adsorption of N₂/CH₄/CO₂ on coal, a self-built multicomponent gas adsorption apparatus was used based on the breakthrough curve method to conduct competitive adsorption experiments under different conditions. The adsorption process was dynamically analyzed by combining adsorption kinetics models with the pore structure characteristics of the samples. The results showed that increasing the temperature promotes competitive adsorption and enhances the preferential adsorption of CO₂, while increasing the pressure and particle size mesh number inhibits competitive adsorption and weakens the preferential adsorption of CO₂. The experimental data fitted well with the Yoon-Nelson, Thomas, and Clark kinetic models, with R² values all above 0.9. The mass transfer rate constants followed the order k(N₂) > k(CH₄) > k(CO₂). As temperature and pressure increased or particle size mesh number increased, the k values for each component increased, enhancing the gas mass transfer rate. The adsorption capacities (q_T) and Clark constants (A) for each component showed the order CO₂ > CH₄ > N₂, indicating that the coal samples had the highest adsorption capacity and strength for CO₂, followed by CH₄ and then N₂. Lowering the temperature, increasing the pressure, or increasing the particle size mesh number all led to increases in q_T and A for each component. The samples exhibited good pore connectivity, with the most developed micropores having a diameter of 2.05 nm, and relatively large specific surface area and pore volume. During competitive adsorption, N₂ was initially adsorbed and then displaced by CH₄ and CO₂, with CH₄ subsequently displaced by CO₂. These conclusions provide some guidance for the study of competitive adsorption of multicomponent gases in coal, further improving the related theory of coal competitive adsorption.