Is Amino Acid a Promoter or Inhibitor to Hydrate Kinetics? A Mini-Review

Methane hydrates are considered a promising alternative for natural gas storage and transportation owing to their high gas storage capacity, safety, and environmental advantages. However, their industrial application is limited by slow nucleation, sluggish growth kinetics, and incomplete gas conversion. Amino acids have recently emerged as environmentally benign additives capable of influencing hydrate formation by modifying gasliquid interfacial interactions and water structure. This minireview critically evaluates studies published between 2016 and 2025 on the role of amino acids in methane hydrate formation kinetics, with emphasis on molecular structure, hydrophobicity, concentration effects, and underlying promotion or inhibition mechanisms. The reviewed literature demonstrates that hydrophobic amino acids such as L-leucine, L-valine, L-methionine, and L-cysteine generally exhibit superior kinetic promotion by reducing induction time, enhancing methane uptake, and facilitating porous hydrate growth. In contrast, hydrophilic or charged amino acids often display weaker promotional effects or thermodynamic inhibition due to stronger interactions with water molecules. The findings reveal a strong correlation between amino acid hydrophobicity and hydrate promotion tendency, although factors such as aromaticity, sidechain structure, solubility, and concentration also significantly influence performance. Despite promising laboratory-scale results, challenges related to mechanistic understanding, recyclability, and process scalability remain unresolved. Future studies integrating molecular simulations and large-scale experimental investigations are essential for advancing amino acid-assisted hydrate technologies toward practical natural gas storage and repeat transportation applications.