Improving biogas separation and methane storage with multilayer graphene nanostructure via layer spacing optimization and lithium doping: a molecular simulation investigation.

Methane is a desirable alternative to conventional fossil fuels, and also a main component of biogas from anaerobic fermentation of organic wastes. However, its relatively lower purity and poor storage by existing adsorbent materials negatively affect its wide application. Thus, efficient, cost-effective, and safe adsorbent materials for methane purification and storage are highly desired. In this study, multilayer graphene nanostructures (MGNs) with optimized structure are investigated as a potential adsorbent for this purpose. The effects of layer distance and Li doping on MGN performance in terms of methane storage and acid gas (H(2)S and CO(2)) separation from biogas are examined by molecular simulations. The mechanisms for the interactions between gas molecules and substrates are elucidated by analyzing the binding energy, geometric structures, and charge distribution from the first-principles calculations. The results show that nonhydrocarbons in biogas can be effectively separated using Li-doped MGNs with the optimal layer distance of 0.68 nm, and then the pure methane gas can be stored in MGNs with capacity satisfying the DOE target. This work offers a molecular-level insight into the interactions between gas molecules and MGNs and might provide useful information for development of new materials for methane purification and storage.