Energy and Power Department, Shandong University of Science and Technology, Qingdao 266590, Shandong, China.
Energy and Power Department, China University of Petroleum, Qingdao 266580, Shandong, China.
Langmuir. 2023 May 23;39(20):7122-7131. doi: 10.1021/acs.langmuir.3c00421. Epub 2023 May 11.
Herein, several molecular systems are simulated by molecular dynamics to study the decomposition process and fluctuation-dissipation characteristics of spherical methane hydrates under different conditions. The spherical radius and the movement of the hydrate-liquid water interface during decomposition are measured. Different fitted formulas of the variation of methane numbers are obtained from the decomposition of spherical and bulk methane hydrates. Fluctuation-dissipation characteristics for spherical methane hydrates with different radii are analyzed, which show that increasing the scale of hydrates can increase the relaxation time and slow down the fluctuation process. The variations of the hydrogen bond and hydrogen-bond lifetime are calculated. For hydrate phase water, the peak of the hydrogen-bond lifetime lies between 8 and 10 ps. After complete decomposition, the hydrogen-bond lifetime mainly distributes in 0 and 2 ps and the peak disappears. The effects of temperature, cage occupancy, liquid phase environment, and spherical hydrate scale are explored. The decomposition activation energy for the spherical hydrate with a radius of 20 Å is calculated to be 52.23 kJ/mol. It can speed up the decomposition rate as well as the diffusion of methane and water molecules with a lower cage occupancy. For the effect of the liquid phase environment, it is found that the number of liquid water rarely affects the decomposition. However, when the Na and Cl concentrations change from 0 to 10%, the decomposition time reduces from ∼511 to ∼369 ps, which indicates that there is an obviously positive impact on decomposition.
在此，通过分子动力学模拟了几种分子体系，以研究不同条件下球形甲烷水合物的分解过程和涨落耗散特性。测量了水合物-液相界面在分解过程中的球形半径和运动。从球形和块状甲烷水合物的分解中得到了不同拟合形式的甲烷数变化。分析了不同半径的球形甲烷水合物的涨落耗散特性，结果表明，增加水合物的尺度可以增加弛豫时间并减缓涨落过程。计算了氢键和氢键寿命的变化。对于水合相水，氢键寿命的峰值位于 8 到 10 ps 之间。完全分解后，氢键寿命主要分布在 0 和 2 ps 之间，峰值消失。探讨了温度、笼占有率、液相环境和球形水合物尺度的影响。计算了半径为 20 Å 的球形水合物的分解活化能为 52.23 kJ/mol。较低的笼占有率可以加速甲烷和水分子的扩散以及分解速率。对于液相环境的影响，发现液态水的数量很少影响分解。然而，当 Na 和 Cl 浓度从 0 增加到 10%时，分解时间从约 511 ps 减少到约 369 ps，这表明分解有明显的积极影响。
