Microscopic Simulation of Methane Adsorption in Organic Matter

Shale is rich in nanopores with organic matter, but few studies have researched them in combination with molecular simulation and quantum mechanics. The organic matter was simplified into graphite and the graphene structure, and Grand Canonical Monte Carlo and Molecular Dynamics methods have been used to study methane adsorption in the different apertures of graphite; then, adsorption characteristics were calculated and analyzed by Density Functional Theory. The simulation results show that methane molecules form a tight adsorption layer near the wall with different orientations. The density distribution shows an obvious adsorption layer, and the interaction distance is 1 to 6 A. The adsorption energy is distributed in the range of -0.2200 to -0.1080 eV, which states physical adsorption, and can be divided into two segments: 1-3 and 4-6 angstrom. Density of states (DOS) of systems are distributed within the range of -20 to 5 eV. II B5 and III B1 are different only at -5.0 to -3.6 eV, and DOS of adsorbents coincided before and after adsorption, while DOS of methane shift to the lower energy region after adsorption.