Methane Gas Hydrates Viewed through Unified Solid–Liquid–Vapor Equations of State

Abstract

The phase behavior of methane gas hydrates (clathrates) has been investigated with unified equations of state for solid-liquid-vapor phases. This is a new way to look at the clathrate-containing system, being radically different from the traditional statistical thermodynamic model for clathrates. The present paper includes modifications and refinements of the previously published method with the unified equations of state. The univariant three-phase equilibrium lines containing clathrates have been successfully predicted with the present equation-of-state model for a wide temperature and pressure range. Particularly, the phase behavior in very high-pressure regions has been modeled for the first time by the present work. Although the present results at high pressures are still tentative, they will shed some light on the unsettled problem of high pressure phases as reported in the literature.

Phase equilibria of carbon dioxide and methane gas-hydrates predicted with the modified analytical S-L-V equation of state

“…In the modified S-L-V EoS, the pure component parameters a to d were taken from Yokozeki [9] for CO 2 and from Yokozeki [11] for H 2 O and CH 4 . Values for the reduced parameters, coefficients, and exponents in equations (2) to (4) can be found in the original articles by Yokozeki [9,11].…”

“…Values for the reduced parameters, coefficients, and exponents in equations (2) to (4) can be found in the original articles by Yokozeki [9,11]. Mixtures can be treated with a help of the van der Waals / Lorentz-Berthelot mixing rules [9] in the S-L-V EoS.…”

“…This EoS can simultaneously model all three phases and can be extended to simple mixtures such as CO 2 + CH 4 . In the following two studies [10,11], Yokozeki demonstrated that his EoS may also be used for gas-hydrates modeling. The S-L-V EoS provided qualitatively good prediction for CH 4 -and CO 2 -hydrate formation conditions.…”

“…The Yokozeki's EoS is therefore a relatively simple alternative to much more complicated hydrate models based on the vdWP theory. In this study, we modified the original Yokozeki's [9]- [11] S-L-V EoS to improve its predictive ability for CH 4 -and CO 2 -hydrate phase equilibria. Moreover, there were found several small discrepancies in the Yokozeki's articles [9]- [11] which we also tried to fix in this work.…”

“…In this study, we modified the original Yokozeki's [9]- [11] S-L-V EoS to improve its predictive ability for CH 4 -and CO 2 -hydrate phase equilibria. Moreover, there were found several small discrepancies in the Yokozeki's articles [9]- [11] which we also tried to fix in this work. The modified S-L-V EoS models quite accurately the formation conditions for both gas-hydrates over relatively wide ranges of temperature and pressure.…”