Competitive Adsorption of Carbon Dioxide/Methane in Coal: First-Principles Quantum Mechanical Investigations

Sequestration of CO$_{\mathrm{2}}$ into geological formations has been suggested to mitigate the effect of the increasing of the atmospheric CO$_{\mathrm{2}}$ concentration on global warming. Coalbeds are investigated as one of the attractive storage sites since the cost of CO$_{\mathrm{2}}$ sequestration can be offset by the enhanced coalbed methane (ECBM) recovery. Extensive experimental studies have been performed for the competitive adsorption of CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$ into coalbeds. However, the atomic-level understanding for the interaction between the adsorbate (CO$_{\mathrm{2}}$/CH$_{\mathrm{4}})$ and the adsorbent (coal) has not been fully explored. We report first-principles density-functional calculations for the competitive adsorption between CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$ in the coal network. In particular, we report results of atomic structures, bonding characteristics, energetics, as well as electronic structures of the CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$-coal systems.