Adsorption mechanism of inhibitor and guest molecules on the surface of methane hydrate
Gas hydrates are crystalline solids which consist of water and guest molecules such as methane. Gas hydrate ‘plugs’ sometimes occur in gas and oil pipelines. This is a serious industrial problem because the pipeline must be shut down until the hydrate plugs are removed. A common way to avoid the plugging is by using a dosage of a type of water-soluble polymers called ‘kinetic hydrate inhibitors’ (KHIs).
KHIs bind to the hydrate/water interface and inhibit the crystal growth of gas hydrates. Scientists believe KHI adsorbs on the hydrate surface mainly due to hydrogen bonding between the amide groups of the KHI and water molecules on the hydrate surface.
Takuma Yagasaki, Masakazu Matsumoto, and Hideki Tanaka at Okayama University, Japan, performed molecular dynamics simulations on KHI binding, demonstrating that the conventional picture of the adsorption mechanism of KHIs is incorrect.
The team calculated the free energy profiles of various molecules using an umbrella sampling technique with the weighted histogram analysis method. They discovered that the adsorption of nonpolar or weakly polar molecules, including KHIs, on the hydrate surface is largely due to entropic stabilization arising from the presence of cavities on the hydrate surface. The amide-hydrogen bonding makes no contribution to the adsorption affinity.
The researchers believe the mechanism found in this study will help in the development of new KHIs in the future.
・Authors: Takuma Yagasaki, Masakazu Matsumoto, and Hideki Tanaka.
・Title of original paper: Adsorption mechanism of inhibitor and guest molecules on the surface of gas hydrates.
・Journal, volume, pages and year: J. Am. Chem. Soc. 137, 12079 (2015).
・Digital Object Identifier (DOI): 10.1021/jacs.5b07417
・Journal website: http://pubs.acs.org/doi/abs/10.1021/jacs.5b07417
・Affiliations: Department of Chemistry, Faculty of Science, Okayama University.
・Department website: http://chem.okayama-u.ac.jp/index.html
OKAYAMA UNIV. e-Bulletin. Theoretical physics: Demystifying the molecular mechanisms of the initial stages of how ice melts. Vol.4, Sep, 2013.