Adsorption and purification of biogas inside graphitic nanopores: molecular dynamics simulation approach

Biogas is one of the most common sources of biomass energy. Due to the associated environmental pollution and costs, desulfurization, and purification are the most important challenges of biogas power generation. Using all-atom molecular dynamics (MD), we systematically simulated the isothermal adsorption behavior of biogas (comprising CH 4 , CO 2 , H 2 O, H 2 S, and H 2 ) in graphite (Gr) slit nanopores. The impact of slit width, system temperature, and moisture content on the adsorption energy, adsorption ratio, and diffusion coefficient of biogas molecules was investigated. Simulation results revealed that due to strong interactions between graphite and H 2 S, graphite slits of width d = 48 ~ 80 Å displayed significant selective adsorption of H 2 S molecules. At temperatures between 300 and 500 K, Gr slits can effectively separate H 2 S in biogas. Moreover, as the moisture content of biogas (vol%) increases from 0 to 20%, the formation and interactions of hydrogen bonds between water molecules create H 2 O films accumulating on the Gr surface and taking up the adsorption sites, which reduces the amount of hydrogen sulfide that can be adsorbed. Our findings provide important insights into the material design for biogas purification. Graphical Abstract A schematic representation of molecular interactions between adsorbates and the wall for biogas mixtures (comprising CH 4 , CO 2 , H 2 O, H 2 S, and H 2 ) inside graphitic nanopores.