Replacement mechanism of methane hydrate with carbon dioxide from microsecond molecular dynamics simulations
Replacement mechanism of methane hydrate with carbon dioxide from microsecond molecular dynamics simulations
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DOI：
10.1039/c2ee21189k
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发表时间：
2012-05-01
影响因子：
32.5
通讯作者：
Wang, Wenchuan
中科院分区：
文献类型：
--
作者：
Bai, Dongsheng;Zhang, Xianren;Wang, Wenchuan
用CO2置换水合物形式的CH4是从其水合物中回收CH4气体并储存CO2的候选者。本文采用微秒级分子动力学模拟方法研究了CO2分子置换CH4水合物的机理。置换过程受客体分子的化学势、“记忆效应”和传质的协同控制。置换途径包括水合物表面附近CH 4水合物的熔化以及随后形成无定形CO2水合物层。CH4水合物熔化后残留的大量水合物残环促进了CO2水合物的成核，增强了动力学过程，表明存在所谓的“记忆效应”。在动力学方面，置换过程更容易发生在水合物表面附近。然而，随着置换过程的进行，CO2水合物的无定形层的形成为客体CH4和CO2分子的传质提供了显著的屏障，这防止了CH4水合物进一步解离并减慢了置换速率。
Replacement of CH4 in hydrate form with CO2 is a candidate for recovering CH4 gas from its hydrates and storing CO2. In this work, microsecond molecular dynamics simulations were performed to study the replacement mechanism of CH4 hydrate by CO2 molecules. The replacement process is found to be controlled cooperatively by the chemical potentials of guest molecules, "memory effect'', and mass transfer. The replacement pathway includes the melting of CH4 hydrate near the hydrate surface and the subsequent formation of an amorphous CO2 hydrate layer. A large number of hydrate residual rings left after the melting of CH4 hydrate facilitate the nucleation of CO2 hydrate and enhance the dynamic process, indicating the existence of so-called "memory effect''. In the dynamic aspect, the replacement process takes place near the surface of CH4 hydrate rather easily. However, as the replacement process proceeds, the formation of the amorphous layer of the CO2 hydrate provides a significant barrier to the mass transfer of the guest CH4 and CO2 molecules, which prevents the CH4 hydrate from further dissociation and slows down the replacement rate.