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Title: Prediction of the phase equilibria of methane hydrates using the direct phase coexistence methodology

The direct phase coexistence method is used for the determination of the three-phase coexistence line of sI methane hydrates. Molecular dynamics (MD) simulations are carried out in the isothermal–isobaric ensemble in order to determine the coexistence temperature (T{sub 3}) at four different pressures, namely, 40, 100, 400, and 600 bar. Methane bubble formation that results in supersaturation of water with methane is generally avoided. The observed stochasticity of the hydrate growth and dissociation processes, which can be misleading in the determination of T{sub 3}, is treated with long simulations in the range of 1000–4000 ns and a relatively large number of independent runs. Statistical averaging of 25 runs per pressure results in T{sub 3} predictions that are found to deviate systematically by approximately 3.5 K from the experimental values. This is in good agreement with the deviation of 3.15 K between the prediction of TIP4P/Ice water force field used and the experimental melting temperature of ice Ih. The current results offer the most consistent and accurate predictions from MD simulation for the determination of T{sub 3} of methane hydrates. Methane solubility values are also calculated at the predicted equilibrium conditions and are found in good agreement with continuum-scale models.
Authors:
; ;  [1] ; ;  [2]
  1. Chemical Engineering Program, Texas A and M University at Qatar, P.O. Box 23847, Doha (Qatar)
  2. Environmental Research Laboratory, National Center for Scientific Research NCSR “Demokritos,” Aghia Paraskevi, Attiki GR-15310 (Greece)
Publication Date:
OSTI Identifier:
22416051
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 4; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BUBBLES; DISSOCIATION; GAS HYDRATES; ICE; MELTING POINTS; METHANE; MOLECULAR DYNAMICS METHOD; PHASE DIAGRAMS; PHASE STABILITY; PHASE STUDIES; SCALE MODELS; SOLUBILITY; SUPERSATURATION; WATER