Interfacial Assembly of Surfactants Drives the Promotion of Gas Hydrate Formation for Energy Storage

Gas hydrates have garnered significant attention as an environmentally friendly technology for natural gas storage and transportation. However, the large-scale application of this technology is hindered by the slow kinetics of gas hydrate formation. Surfactants have been identified as the most effective promoters for gas hydrate formation, playing a pivotal role in enhancing both the rate of hydrate formation and the storage capacity. Nevertheless, the mechanisms by which surfactants promote gas hydrate formation remain inconclusive. Understanding these mechanisms is crucial for optimizing surfactant-based gas hydrate technologies and harnessing their full potential in energy storage and transportation. In this study, a series of molecular dynamics (MD) simulations were conducted to investigate the promotion mechanisms of various surfactants in gas hydrate formation, with a specific focus on their behavior and effects in the liquid phase. While surfactants are known to influence gas-liquid interfacial properties, such as reducing interfacial tension and facilitating gas transport into the liquid phase, these effects are beyond the scope of the present study. The selected surfactants represented diverse chemical structures, charges, and hydrophobic-hydrophilic balances, enabling a comprehensive examination of their effects on gas hydrate formation. The simulations at the liquid phase revealed that surfactants promote gas hydrate formation primarily through two mechanisms: surface adsorption on hydrates and micelle or aggregate formation. While surface adsorption is a common characteristic of surfactants, the balance between hydrophobic effects and hydrogen bonding interactions with water molecules or hydrate surfaces is pivotal in determining their efficacy. The foaming capabilities of various surfactants were observed to be the highest in anionic surfactants. Noteworthy, branched anionic surfactants have emerged as highly promising candidates for gas hydrate-based methane storage technology due to their promoting ability and nonfoaming characteristics during the gas recovery stage. These findings contribute to advancing the understanding of hydrate promotion theory and provide a new direction for surfactant design and selection in gas hydrate-based technologies, including methane storage, hydrogen storage, desalination, and CO₂ capture.