Enthalpy of dissociation of methane hydrates at a wide pressure and temperature range

Abstract

We present a detailed overview of the calculation of the enthalpy of dissociation of methane hydrates, focusing primarily on methods that are based on either the Clapeyron equation or the direct calculation of the enthalpies of all the components that are involved in the dissociation reaction. Molecular dynamics simulations are used extensively in order to calculate the enthalpies and molar volumes of water, methane, and sI methane hydrate (with variant degree of occupancy) at pressure and temperature conditions along the three-phase (Hydrate – Liquid water – Vapor) equilibrium line. While for temperatures lower than 304 K there is a consensus that the enthalpy of dissociation is independent of temperature, the case for temperatures higher than 304 K is not that clear, particularly for the case when the Clapeyron equation is used. Therefore, new experimental measurements are required for the higher temperatures to shed light to the problem. In addition, the aqueous solubility of methane is calculated using the phase coexistence approach, resulting in accurate predictions when using the TIP4P/Ice water model and the OPLS-UA model for methane.