Hydrophobic Amino Acids as a New Class of Kinetic Inhibitors for Gas Hydrate Formation

Sa et al. investigated the effects of amino acids as Kinetic Hydrate Inhibiters (KHIs) on the initial formation, the continued growth, and the structure of hydrate blockages in natural gas and oil pipelines. They found that hydrophobic amino acids were more effective KHIs than the more commonly used polyvinyl pyrrolidone (PVP). It was also observed that in general, amino acids with shorter alkyl chains were more effective KHIs than those with longer alkyl chains, with glycine and L-alanine being the most effective KHIs. Examining how various KHI’s impacted the rate of growth of hydrate blockages, it was found that both PVP and glycine as KHIs caused a decrease in the rate of formation of the hydrogen blockage. When comparing amino acids with varying alkyl chain lengths, it was observed that as the length of the alkyl chain increased, its ability to act as an effective KHI decreased. It was found that the crystal structure of hydrates formed did not change in the presence of the amino acid KHIs. However, it was found that all amino acids, regardless of their hydrophobicity, were effective in inhibiting hydrate blockages once the blockages had begun to form, as seen by the increased number of ice crystals in the hydrate in the presence of glycine.—Allison Kerley

Sa, J., Kwak, G., Lee, B., Park, D., Han, K., Lee, K., 2013. Hydrophobic amino acids as a new class of kinetic inhibitors for gas hydrate formation. Scientific Reports 3, 2428.

                  Using nucleation kinetics measurements to observe the onset of hydrate blockage formation, Sa et al. examined the effects of different amino acids and PVP on hydrate formation in fresh water and memory water. The “memory effect” of memory water is a phenomenon in which hydrates form more easily in gas and water that has formed hydrates in the past. While PVP did not display any effect on the inhibition of hydrates, glycine (at an increased concentration of 1.0% mol) slowed the formation of hydrates.
                  Synchrotron powder X-ray diffraction (PXRD) was used to identify the structure of the hydrate blockages, enabling Sa et al. to determine whether KHIs affected the structural makeup of hydrate blockages. It was found that in the presence of glycine, hydrate blockages displayed more ice crystals, which was attributed to water molecules freezing instead of forming hydrates.

Allison Kerley

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