(179d) Hydrogen Storage in Hydrates: Evaluation of Different Force-Fields Used in Monte Carlo Simulations

Clathrate hydrates have been examined as storage materials for hydrogen or other “energy-carrier” gases such as methane, as a result of having a number of advantages compared to other materials, including among others: operating at moderate temperatures, low cost, complete reversibility of the formation/dissociation process, minimal environmental hazards, having mainly water as a by-product. Initially the pure and binary hydrogen hydrates with structure II were experimentally confirmed [1], followed by the binary hydrate with structure H [2], and finally the structure I was obtained experimentally [3].

A requirement that needs to be met for a solid material to be suitable for practical applications in gas storage is high gravimetric and volumetric gas content. Therefore, in addition to performing experimental measurements for confirmation, it is essential to develop accurate theoretical/ numerical methods for the storage-capacity calculation of hydrates.

By assuming a fixed geometry for the hydrate lattice it allows the hydrate formation to be described as a process of gas storage in a solid material. Grand Canonical Monte Carlo (GCMC) methods have been used extensively to simulate gas adsorption in solid materials [4]. Therefore, the hydrate cavity occupancies, could be calculated from the GCMC simulations at various temperatures and pressures, and the results can be fitted to Langmuir-type functions [5].

In this study, an extensive series of GCMC simulations for the case of all the known hydrate structures, sI, sII, and sH that hydrogen is known to form, will be performed. During the simulations a number of water force-fields will be examined regarding their effect on the storage capacity of hydrates. In particular, the following popular water force-fields will be considered: SPC/E, TIP4P, TIP4P/Ice, and TIP5P. The Langmuir constants for each type of cavity and hydrate structure will be reported as a function of temperature and pressure (i.e., fugacities). Therefore, the storage-capacity of the different hydrate structures can be calculated. 

References

[1] Mao, W. L.; Mao, H. K.; Goncharov, A. F.; Struzhkin, V. V. Guo, Q.; Hu, J.; Shu, J.; Hemley, R. J.; Somayazulu, M.; Zhao, Y. Science 2002, 297, 2247.

[2] Duarte, A. R. C.; Shariati, A.; Rovetto, L. J.; Peters, C. J. J. Phys. Chem. B 2008, 112, 1888.

[3] Grim, R. G.; Kerkar, P. B.; Shebowich, M.; Arias, M.; Sloan, E. D.; Koh, C. A.; Sum, A. K. J. Phys. Chem. B 2012, 116, 18557.

[4] Allen, M. P.; Tildesley, D. J. Computer Simulation of Liquids, Oxford University Press: New York, 1987.

[5] Papadimitriou, N. I.; Tsimpanogiannis, I. N.; Papaioannou, A. Th.; Stubos, A. K. J. Phys. Chem. B 2008, 112, 10294.