Methane hydrate formation in amino acids / sodium montmorillonite systems

To understand the occurrence of natural gas hydrates in seabed sediments, it is crucial to examine the mechanisms of methane (CH4) hydrate formation in sodium montmorillonite (Na-Mt) systems in the presence of amino acid. Accordingly, this study employed kinetics experiments and molecular dynamics simulations to investigate CH4 hydrate nucleation and growth in an -Na-Mt system containing alanine (Ala), leucine (Leu), and phenylalanine (Phe), respectively. Kinetics and Raman experiments showed that, compared with Ala, Leu and Phe enhanced hydrogen bonding between water molecules surrounding -Na-Mt. This enhancement was due to the long carbon chain of Leu and the phenyl ring of Phe and facilitated CH4 hydrate formation. Moreover, in the -Na-Mt system, Ala reduced CH4 consumption, whereas Leu and Phe increased CH4 consumption. Molecular dynamics simulations revealed that the strength of electrostatic interactions between the negatively charged -Na-Mt surface and the functional groups of amino acids affected the distribution of amino acids, thereby altering CH4 aggregation and CH4 hydrate nucleation processes. The strong interaction between -Na-Mt and Ala significantly disrupted interfacial interactions between -Na-Mt and water molecules. In contrast, the weaker interactions between -Na-Mt and Leu and Phe, respectively, meant that these amino acids affected CH4 hydrate nucleation in the bulk-like solution by influencing the arrangement of water molecules. These findings indicate that interfacial interactions between -Na-Mt and amino acids play a crucial role in CH4 hydrate formation. Overall, this study generated insights into the formation kinetics and nucleation properties of CH4 hydrates in clay mineral-amino acid complexes that may increase understanding about the occurrence of natural gas hydrates in marine sediments.