Understanding the influences of different associated gas impurities and the kinetic modelling of biogas hydrate formation at the molecular scale

The biological degradation of organic waste generates biogas that mostly comprises a mixture of CH4 and CO2. The separation of CO2 and other gas impurities from CH4 using a hydrate-based technique has recently gained interest as an option. The captured CO2 and impurities can then be sequestered in natural gas hydrate (NGH) geological sites leading to an exchange of the in situ CH4 hydrate over to CO2-dominated hydrate and a simultaneous CH4 release from these huge natural sources of energy in permafrost sediments. Consequently, the effects of associated gas impurities such as SO2, H2S, N2, and H2 on either hydrate-based biogas purification or residual sequestration in NGH deposits need to be well-understood. In this work, the influence of different biogas compositions on the process of clathrate hydrate formation using molecular dynamics (MD) simulations was investigated. Additionally, a kinetic model for predicting the progress of biogas crystal growth based on the formation of the number of hydrogen bonds as well as total energy is proposed. The results elucidate that the concentration of dissolved gas in liquid water at the solid-solution interface is one of the key controllers of the growth rate but it has less impact on the filling percentage of formed both types the clathrate hydrate cages. The presence of H2S and SO2 molecules was found to slightly increase the formation of biogas hydrate. On the other hand, N2, and H2 molecules reduce the rate of biogas hydrate generation.