Molecular dynamics simulation of the effects of different thermodynamic parameters on methane hydrate dissociation: An analysis of temperature, pressure and gas concentrations
KH Li and BB Chen and YC Song and MJ Yang, FLUID PHASE EQUILIBRIA, 516, 112606 (2020).
Molecular dynamics (MD) simulation plays an important role in the microscopic analysis of the gas hydrate phase transition. This technology enables the feasible analysis of the effects of thermodynamic parameters (such as temperature, pressure and chemical potential) on the hydrate dissociation kinetics. Molecular dynamics simulations were performed in this study to analyze the effects of multiple factors on methane hydrate (MH) dissociation in an aqueous environment using NPT ensembles and to further understand the mechanism of hydrate dissociation at the microscopic level. Three thermodynamic factors, temperature (285-300 K), pressure (5-40 MPa) and the initial concentration of CH4 in the liquid phase (0-0.03125), were analyzed. Moreover, the potential energy, dissociation rates, and statistical analyses of concentrations, hydrogen bonds and molecule numbers in each phase were determined. The activation energy of hydrate was calculated to determine the effect of temperature on the dissociation of hydrate, and the activation energy of CH4 hydrate at 285-300 K was approximately 83.9 kJ/mol. Pressure variations exerted an obvious effect on hydrate dissociation when the pressure was less than 20 MPa. In contrast, little effect was observed when the pressure was greater than 20 MPa. The potential explanation is that an increase in the pressure will increase the solubility of CH4 and decrease the size of the gas phase, thus limiting the effect of pressure on the simulated system. Using simulations with different initial CH4 concentrations, an increase in the number of methane molecules in the surrounding aqueous phase decreased the dissociation rate when the initial methane concentration was less than 0.02 (molar fraction). However, it exerted the opposite effect when the initial concentration was greater than 0.02, due to the earlier appearance of gas bubbles. (C) 2020 Elsevier B.V. All rights reserved.
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