Kinetics Experiments and Molecular Dynamics Simulations on the Effect of Montmorillonite on C2H6 Hydrate Formation

Abstract

C₂H₆ has a higher global warming potential than CO₂, and its release from natural gas hydrates would exacerbate climate change. However, the mechanism by which clay minerals affect hydrates remains unclear. This study focused on the effect of calcium montmorillonite (Ca-Mnt) on the nucleation and growth of C₂H₆ hydrate, using Ca-Mnt suspensions at different concentrations. Through kinetic experiments and molecular dynamics simulations, microscopic mechanisms of Ca-Mnt’s influence on C₂H₆ hydrate nucleation and growth were revealed. The key findings are as follows: Ca-Mnt has a dual effect on C₂H₆ hydrate nucleation in that it promotes nucleation by reducing the hydrogen bonding strength but inhibits nucleation due to the increase in interfacial tension, with the interfacial tension playing a dominant role. The kinetic experiments showed that 0.05 wt % Ca-Mnt shortened the induction time by 90.2%, whereas higher Ca-Mnt concentrations prolonged the induction time and reduced C₂H₆ hydrate yield. At lower Ca-Mnt concentrations, downward growth forms gas channels that disrupt the gas–liquid interface, whereas at higher concentrations, growth occurs above the interface. C₂H₆ hydrate is a structure-I hydrate, comprising empty 5¹² cages and 5¹²6² cages occupied by C₂H₆. Molecular dynamics simulations indicated that the heterogeneous nucleation of C₂H₆ hydrate occurred in regions away from the external surface of Ca-Mnt. Under high gas-to-water ratios, an uneven gas distribution led to bubble formation, which in turn slowed C₂H₆ hydrate growth. This study provides a scientific basis for designing environmentally sustainable hydrate reservoir management strategies and reducing greenhouse gas emissions.