Three-phase equilibria of hydrates from computer simulation. III. Effect of dispersive interactions in the methane and carbon dioxide hydrates

TL;DR

This study uses molecular dynamics simulations to examine how the range of dispersive interactions influences the three-phase coexistence temperature of methane and carbon dioxide hydrates, revealing that cut-off distance significantly affects hydrate stability, especially at lower pressures.

Contribution

It provides a detailed analysis of the impact of dispersive interaction cut-off distances on hydrate stability, including effects of long-range corrections and guest molecule variations.

Findings

Dispersive interaction cut-off distance affects hydrate dissociation temperature.

Lower pressure amplifies the effect of cut-off distance on hydrate stability.

Long-range corrections influence the predicted stability conditions.

Abstract

In this work, the effect of the range of the dispersive interactions in the determination of the three-phase coexistence line of the CO$_2$ and CH$_4$ hydrates has been studied. In particular, the temperature ($T_3$) at which solid hydrate, water, and liquid CO$_2$/gas CH$_4$ coexist has been determined through molecular dynamics simulations using different cut-off values (from 0.9 to 1.6 nm) for the dispersive interactions. The $T_3$ of both hydrates has been determined using the direct coexistence simulation technique. Following this method, the three phases in equilibrium are put together in the same simulation box, the pressure is fixed, and simulations are performed at different temperatures $T$. If the hydrate melts, then $T>T_3$. Contrary, if the hydrate grows, then $T<T_3$. The effect of the cut-off distance on the dissociation temperature has been analyzed at three different pressures for CO$_{2}$ hydrate, namely, $100$, $400$, and $1000\,\text{bar}$. Then, we have changed the guest and studied the effect of the cut-off distance on the dissociation temperature of the CH$_{4}$ hydrate at $400\,\text{bar}$. Also, the effect of long-range corrections for dispersive interactions has been analyzed by running simulations with homo- and inhomogeneous corrections and a cut-off value of 0.9 nm. The results obtained in this work highlight that the cut-off distance for the dispersive interactions affects the stability conditions of these hydrates. This effect is enhanced when the pressure is decreased, displacing the $T_{3}$ about $2-4\,\text{K}$ depending on the system and the pressure.