Li Kehan, Chen Bingbing, Yang Mingjun, Song Yongchen, Sum Amadeu K
Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian, China.
Phases to Flow Laboratory, Chemical & Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA.
J Chem Phys. 2023 Dec 28;159(24). doi: 10.1063/5.0174705.
Natural gas hydrates, mainly existing in permafrost and on the seabed, are expected to be a new energy source with great potential. The exploitation technology of natural gas hydrates is one of the main focuses of hydrate-related studies. In this study, a large-size liquid aqueous solution wrapping a methane hydrate system was established and molecular dynamics simulations were used to investigate the phase equilibrium conditions of methane hydrate at different methane concentrations and interfacial geometries. It is found that the methane concentration of a solution significantly affects the phase equilibrium of methane hydrates. Different methane concentrations at the same temperature and pressure can lead to hydrate formation or decomposition. At the same temperature and pressure, in a system reaching equilibrium, the size of spherical hydrate clusters is coupled to the solution concentration, which is proportional to the Laplace pressure at the solid-liquid interface. Lower solution concentrations reduce the phase equilibrium temperature of methane hydrates at the same pressure; as the concentration increases, the phase equilibrium temperature gradually approaches the actual phase equilibrium temperature. In addition, the interfacial geometry of hydrates affects the thermodynamic stability of hydrates. The spherical hydrate particles have the highest stability for the same volume. Through this study, we provide a stronger foundation to understand the principles driving hydrate formation/dissociation relevant to the exploitation of methane hydrates.
天然气水合物主要存在于永久冻土带和海底，有望成为一种极具潜力的新能源。天然气水合物的开采技术是水合物相关研究的主要重点之一。在本研究中，建立了一个包裹甲烷水合物系统的大尺寸液体水溶液，并利用分子动力学模拟研究了不同甲烷浓度和界面几何形状下甲烷水合物的相平衡条件。研究发现，溶液中的甲烷浓度显著影响甲烷水合物的相平衡。在相同温度和压力下，不同的甲烷浓度会导致水合物的形成或分解。在相同温度和压力下，在达到平衡的系统中，球形水合物簇的大小与溶液浓度相关联，溶液浓度与固液界面处的拉普拉斯压力成正比。较低的溶液浓度会降低相同压力下甲烷水合物的相平衡温度；随着浓度的增加，相平衡温度逐渐接近实际相平衡温度。此外，水合物的界面几何形状会影响水合物的热力学稳定性。对于相同体积的情况，球形水合物颗粒具有最高的稳定性。通过本研究，我们为理解与甲烷水合物开采相关的水合物形成/分解原理提供了更坚实的基础。
