Three-phase equilibrium curve shift for methane hydrate in oceanic conditions calculated from Molecular Dynamics simulations

摘要

This paper presents an analysis using molecular simulation of the phase equilibrium of methane hydrates under the oceanic crust conditions. Although there is a number of works dealing with computational simulation of gas hydrates, obtaining their phase diagrams using different techniques, simulations under realistic conditions and environments are not available yet. As the first step in this direction, we have added Na+ and Cl- ions to the water liquid phase in a model of the hydrate (S)-water (L)-methane (G) three-phase system, with the aim to simulate the system behaviour using classical Molecular Dynamics with the direct coexistence technique. The results are in good agreement with other simulations and experimental measurements reported in literature. Coexistence curves are well defined including a proper shift between water with and without NaCl. Additionally, water solvation of ions was found to interfere with crystallization process, slowing it down and preventing the incorporation of all liquid molecules to the hydrate phase. (C) 2018 Published by Elsevier B.V.