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Originally published in Science Express on 8 October 2009
Science 20 November 2009:
Vol. 326. no. 5956, pp. 1095 - 1098
DOI: 10.1126/science.1174010
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Reports

Microsecond Simulations of Spontaneous Methane Hydrate Nucleation and Growth

Matthew R. Walsh,1 Carolyn A. Koh,1 E. Dendy Sloan,1 Amadeu K. Sum,1,* David T. Wu1,2,*

Despite the industrial implications and worldwide abundance of gas hydrates, the formation mechanism of these compounds remains poorly understood. We report direct molecular dynamics simulations of the spontaneous nucleation and growth of methane hydrate. The multiple-microsecond trajectories offer detailed insight into the process of hydrate nucleation. Cooperative organization is observed to lead to methane adsorption onto planar faces of water and the fluctuating formation and dissociation of early hydrate cages. The early cages are mostly face-sharing partial small cages, favoring structure II; however, larger cages subsequently appear as a result of steric constraints and thermodynamic preference for the structure I phase. The resulting structure after nucleation and growth is a combination of the two dominant types of hydrate crystals (structure I and structure II), which are linked by uncommon 51263 cages that facilitate structure coexistence without an energetically unfavorable interface.

1 Center for Hydrate Research, Department of Chemical Engineering, Colorado School of Mines, Golden, CO 80401, USA.
2 Department of Chemistry, Colorado School of Mines, Golden, CO 80401, USA.

* To whom correspondence should be addressed. E-mail: asum{at}mines.edu (A.K.S.); dwu{at}mines.edu (D.T.W.)

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Hydrate Molecular Ballet.
P. G. Debenedetti and S. Sarupria (2009)
Science 326, 1070-1071
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