Guest–Host Interactions in Mixed CH4–CO2 Hydrates: Insights from Molecular Dynamics Simulations

Abstract

Classical molecular dynamics simulations of mixed CH4–CO2 gas hydrates provide a thorough analysis of the energetics of both pure CH4 and CO2 hydrates and three intermediate compositions along the (CH4)1–x(CO2)x·5.75(H2O) solid solution. The energy is broken into guest–guest, guest–host, and host–host contributions. Radial distribution functions and three-dimensional density distributions provide insight into the changes in guest orientation and interactions with the host framework as a function of guest composition. Both energetic and structural analyses provide complementary information to previous experimental studies of the system. The experimentally observed isotropic orientation of CH4 molecules in both small and large cages is confirmed and the description of the anisotropic orientation of CO2 molecules in the large cage is confirmed and further enhanced. In mixed hydrates, the presence of CH4 alters the orientation of CO2, an indication that the interactions between guests, either direct (guest–gu...