(246c) Naturally Occurring Amino Acids As a New Class of Gas Hydrate Inhibitors

Despite a worldwide attention to gas hydrates as clean energy sources and their environmental implications, the principle of hydrate inhibition phenomenon, controlling the crystallization of gas and water to form hydrate, is not well understood yet. Herein, we propose naturally occurring amino acids as a new class of inhibitors for gas hydrate formation, and their mechanisms of action were investigated using them as a model system. CO₂ hydrate phase (water-hydrate-vapor) equilibira with 0.1-3.0 mol% aqueous amino acid solutions were obtained measured in the temperature and pressure range of 273.05-281.45 K and 14.1-35.2 bar. By comparing the inhibition performances, their thermodynamic inhibition mechanisms were illustrated by "hydrogen bond" and "hydrophobic effect" between water and amino acid molecules. Along with this, heterogeneous nucleation and growth kinetics of CO₂ hydrates in the presence of 0.01-1.0 mol% amino acids were measured to evaluate their kinetic inhibition performances. The clear differences in the inhibition performances were attributed to the competition between the charged or hydrophilic and hydrophobic parts of the molecules. This result provides experimental evidence in support of the hypothesis that perturbation of water structure plays a critical role in kinetic inhibition. In addition, synchrotron (Pohang Light Source) powder X-ray diffraction patterns of CO₂ hydrates with amino acid systems were obtained for the structural identification. One distinct advantage of the application of amino acids as inhibitors is their environmentally friendly nature. It may, therefore, lower the damage to the environment significantly. These findings will advance the better control of gas hydrate crystallization and the development of hydrate inhibitors with enhanced biodegradability.