Molecular Mechanisms of Gas Diffusion in CO2 Hydrates

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• 作者：Shuai Liang ; Deqing Liang ; Nengyou Wu ; Lizhi Yi ; Gaowei Hu
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 4, 2016
• 年：2016
• 卷：120
• 期：30
• 页码：16298-16304
• 全文大小：346K
• 年卷期：0
• ISSN：1932-7455

文摘

Gas diffusion is considered a rate-limiting step in the formation of gas hydrates, yet its molecular mechanisms remain unclear. In this work, we present the molecular mechanisms of the CO₂ cage-to-cage transport in gas hydrates, as directly observed from molecular dynamics simulations performed at elevated temperatures. We found that at least one water vacancy is required for the CO₂ molecules to pass through five-membered water rings, while only the distortion of the local ring structure is required for the CO₂ molecules to pass through the six-membered water rings. We used the transition-state theory to estimate the relevant kinetic parameters associated with the CO₂ diffusion in gas hydrates. The calculated free energy of activation is about 44 ± 6 kJ/mol, and the diffusion coefficient is in the range of 1.0 × 10^–16∼2.0 × 10^–14 m²/s, for the CO₂ diffusion at 270 K, in close agreement with previous experiments. This work suggests that the presence of empty cages is crucial for the CO₂ cage-to-cage transport in gas hydrates.