Investigating competitive CO2/H2 sorption in coal through laboratory core flooding experiments and molecular dynamics modelling

The contrasting affinities of low absorbing H 2 and strongly absorbing CO 2 in coal are central to a nascent concept for simultaneous H 2 purification and CO 2 storage in depleted coalbed methane reservoirs. We perform experimental studies as well as molecular dynamics (MD) simulations to examine the underlying mechanisms driving the strong preferential adsorption of CO 2 over H 2 in a H 2 /CO 2 -coal system. MD simulations were performed at 308.5 K (35°C) and pressures up to 45 MPa to investigate pure and mixed-gas adsorption behavior of CO 2 and H 2 on a bituminous coal model. The results confirm strong preferential adsorption of CO 2 over H 2 across the entire pressure range. In addition, H 2 adsorption is strongly suppressed compared to the uptake predicted by its pure-gas isotherm, indicating deviation from ideal competitive adsorption. In contrast, CO 2 adsorption in the mixture closely follows its pure-gas isotherm, suggesting minimal interference from H 2 . Observations from a laboratory coreflooding test and from H 2 sorption experiments, performed at 35°C and 24 MPa, are qualitatively consistent with the MD simulation results. H 2 adsorption is suppressed by up to 80% in the presence of CO 2 , while CO 2 uptake remains largely unaffected. The findings from this study strongly support the potential use of coal seams for selective hydrogen purification and CO 2 storage. • Simulation and experiments reveal strong CO 2 preference over H 2 in coal adsorption • H 2 adsorption is suppressed up to 80% in CO 2 /H 2 mixture experiments • CO 2 adsorption largely follows its pure-gas isotherm in mixed gases • Results support CO 2 sequestration and H 2 purification in coal seams