<scp>l</scp> -Isoleucine as a Green Kinetic Promoter for Methane and Carbon Dioxide Hydrates: A Sustainable Alternative to SDS for Gas Storage Applications

Gas hydrates offer a compact and energy-efficient route for storing and transporting methane (CH4) and carbon dioxide (CO2), yet their practical deployment is hindered by slow formation kinetics and environmentally unfriendly additives such as sodium dodecyl sulfate (SDS). This study explores l-isoleucine, a naturally occurring, hydrophobic amino acid, as a green kinetic promoter for CH4 and CO2 hydrate formation under static, unstirred conditions. Comparative experiments using 0.5 wt % l-isoleucine, SDS, and pure water systems revealed that l-isoleucine promotes faster hydrate growth, lower subcooling requirements, and higher gas uptake for both gases, while avoiding foaming during dissociation. Notably, l-isoleucine enabled ∼80% methane hydrate yield when combined with aromatic l-phenylalanine, although this synergy was not observed in CO2 systems, highlighting the gas-specific influence of amino acid side chains. Multiple nucleation events were recorded in the formation of CO2 hydrate with l-isoleucine, suggesting dynamic growth behavior and consistent promotion. The study also challenges existing hydropathy-based promoter models, showing that molecular structure plays a more dominant role. By introducing a reproducible method for hydrate evaluation under realistic conditions, this work positions l-isoleucine as a promising, sustainable alternative to synthetic surfactants, contributing to the development of green gas storage and carbon management technologies.