Methane hydrate formation in clay mineral suspensions containing glycine: Experimental study and molecular dynamics simulation

Understanding the effects of clay minerals and amino acids on methane hydrate (MH) formation is essential for elucidating the occurrence of MH in marine sediments. In this study, kinetic experiments and molecular dynamics simulations of MH formation in montmorillonite and kaolinite systems with the presence of glycine were investigated. The experimental results showed that the addition of 5 wt% montmorillonite and 5 wt% kaolinite inhibited and promoted MH formation, respectively. Adding 1.5 wt% glycine to the montmorillonite suspension shortened the nucleation time and reduced the amount of MH; it also weakened the facilitating effect of the kaolinite suspension. The simulation results showed MH nucleation in the bulk solution due to the hydration properties of Ca2+ on the external surface of montmorillonite. However, the addition of glycine reduced the inhibitory effect of Ca2+ on MH formation due to the electrostatic interaction between the Ca2+ and COO- groups. Adsorbed methane molecules on the kaolinite siloxane surface formed clathrate-like structures. In addition, glycine also abnormally incorporated into the MH structure to inhibit MH nucleation. These findings imply that the clay mineral had a significant effect on the distribution of amino acids, causing the formation of MH in clay mineral suspension to be different from pure water. Therefore, these interactions should be fully considered when studying the occurrence mechanism of natural gas hydrate when clay minerals and amino acids coexist in marine sediments.