Methane hydrate formation in amino acids / sodium montmorillonite systems

Abstract

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.