Prediction of the three-phase coexistence line of the ethane hydrate from molecular simulation

TL;DR

This study uses molecular dynamics simulations to accurately predict the three-phase coexistence line of ethane hydrate, demonstrating the effectiveness of the direct coexistence approach in modeling hydrate stability across a range of pressures.

Contribution

It introduces a molecular simulation method to determine the ethane hydrate three-phase coexistence line, aligning well with experimental data and filling a gap in computational hydrate research.

Findings

Predicted coexistence line agrees with experimental data

Method effectively models hydrate dissociation behavior

Simulations confirm the suitability of the direct coexistence approach

Abstract

We investigate the three-phase coexistence line of ethane (C$_2$H$_6$) hydrate through molecular dynamics simulations using the direct coexistence approach. In this framework, C$_2$H$_6$ sI hydrate, aqueous, and pure guest phases are constructed within a single simulation box, allowing us to monitor their mutual stability. From the temporal evolution of the potential energy, we identify the equilibrium temperature (T$_3$) at which all three phases coexist, across pressures ranging from 1000 to 4000 bar, in accordance with available experimental data. Simulations are performed with the GROMACS package (version 2016, double precision) in the $NPT$ ensemble. Water and C$_2$H$_6$ molecules are represented using the TIP4P/Ice and TraPPE-UA models, respectively, while unlike non-bonded interactions are computed with the Lorentz-Berthelot combining rule. Dispersive Lennard-Jones and Coulomb interactions are truncated at 1.6 nm, with long-range Coulombic contributions treated via Particle-Mesh Ewald summation. The predicted three-phase coexistence line shows excellent agreement with experimental measurements within the investigated pressure range. These results demonstrate the suitability of the direct coexistence methodology, combined with established molecular models, for reproducing hydrate dissociation behavior in systems that have received little prior computational attention.