Molecular Simulation of H2O, CO2, and CH4 Adsorption in Coal Micropores

Based on the chemical model of coal, slit micropores with different pore sizes are established and structures are optimized in the software of materials studio. As the temperature rises, absolute adsorption capacities of H 2 O are slightly affected, while absolute adsorption capacities of CO 2 and CH 4 gradually decrease. As the fugacity rises, excess adsorption curves of CO 2 experience increase-decrease-gentle three stages, while the curves of CH 4 gradually decrease. With the increase of pore size, adsorption capacities of H 2 O increase, while adsorption capacities of CO 2 and CH 4 gradually decrease. H 2 O firstly adsorbs on the oxygen-containing functional group, so the walls of pore are the preferential area for H 2 O, while CO 2 and CH 4 choose to adsorb on–C–C–, therefore the walls are the primary area for CO 2 and CH 4 . Strong potential in micropores and hydrogen bond among water molecules will promote the water adsorption, while the adsorptions of CO 2 and CH 4 are only induced by the Van der Waals interaction, but the difference between adsorption density and bulk density of CO 2 and CH 4 decides the change of excess adsorption capacity.