NaCl溶液中CO_2置换CH_4水合物的分子动力学模拟

Molecular Dynamics Simulation of Methane Hydrate Replacement With Carbon Dioxide in Aqueous NaCl Solutions

本文采用分子动力学方法,研究NaCl溶液中CO_2置换CH_4水合物的过程。结果表明,模拟开始时,在Na^+、Cl^-离子作用下水合物/溶液相界面处CH_4水合物笼子扭曲形成裂孔,CO_2直接置换CH_4水合物中CH_4,裂孔较大时,CO_2-CH_4分子间发生多次置换;从笼中被置换出的CH_4分子在NaCl溶液中容易聚集成气泡,水合物相和溶液相形成CH_4浓度梯度,水合物开始发生分解;随着较多的CO_2分子进入水合物相中,界面处形成的CH_4-CO_2混合水合物较为稳定,阻碍了进一步置换。

The process of methane hydrate replacement with carbon dioxide in aqueous NaCl solutions is investigated using molecule dynamics simulation.The results show that at the beginning of the simulations,the cages near the hydrate/solution interface distort in the presence of Na＋,Cl- ions which causes the opening formation.CO2 molecules directly replace CH4 molecules from CH4 hydrates.Multiple swapping of CO2 and CH4 molecules occurs when the hole is larger.CH4molecules escaped from the cages readily accumulate to form a bubble in NaCl solution.The hydrates start to decompose due to the methane concentration gradient between the hydrate phase and liquid phase.With more CO2 molecules being trapped in hydrates phase,CH4-CO2 mixed hydrates formed near the interface are more stable,which hinders the further swapping process.