Molecular dynamics simulation on the decomposition of type SII hydrogen hydrate and the performance of tetrahydrofuran as a stabiliser

Abstract

Molecular dynamics simulation is used to study the decomposition and stability of SII hydrogen and hydrogen/tetrahydrofuran (THF) hydrates at 150 K, 220 K and 100 bar. The modelling of the microscopic decomposition process of hydrogen hydrate indicates that the decomposition of hydrogen hydrate is led by the diffusive behaviour of H₂ molecules. The hydrogen/THF hydrate presents higher stability, by comparing the distributions of the tetrahedral angle of H₂O molecules, radial distribution functions of H₂O molecules and mean square displacements or diffusion coefficients of H₂O and H₂ molecules in hydrogen hydrate with those in hydrogen/THF hydrate. It is also found that the resistance of the diffusion behaviour of H₂O and H₂ molecules can be enhanced by encaging THF molecules in the (5¹²6⁴) cavities. Additionally, the motion of THF molecules is restricted due to its high interaction energy barrier. Accordingly, THF, as a stabiliser, is helpful in increasing the stability of hydrogen hydrate.

Keywords:

• gas hydrate
• molecular dynamics
• stability
• decomposition
• clathrate

Acknowledgements

The authors gratefully appreciate the financial support from the Natural Science Foundation of China (No. 20821092). The authors also acknowledge the generous computational services provided by the Shenteng 6800 workstation referred by the Computer Network Information Center, Chinese Academy of Sciences.