Density and phase equilibrium for ice and structure I hydrates using the Gibbs–Helmholtz constrained equation of state |
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| Affiliation: | 1. Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Cracow, Poland;2. Institute of Solid State Physics, Russian Academy of Sciences, Ac. Ossipyan str. 2, 142432 Chernogolovka, Russia;3. Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;4. Moscow Institute of Physics and Technology (State University), Institutskii per. 9, 141700 Dolgoprudny, Russia;5. Laboratory of Hybrid Nanomaterials, National University of Science and Technology “MISIS”, Leninskii prosp. 4, 119049 Moscow, Russia;6. AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, 30 Mickiewicza Av., 30-059 Crakow, Poland;7. Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, 30 Mickiewicza Av.,30-059 Crakow, Poland |
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| Abstract: | A new, rigorous framework centered around the multi-scale GHC equation of state is presented for predicting bulk density and phase equilibrium for light gas–water mixtures at conditions where hexagonal ice and structure I hydrate phases can exist. The novel aspects of this new framework include (1) the use of internal energies of departure for ice and empty hydrate respectively to determine densities, (2) contributions to the standard state fugacity of water in ice and empty hydrate from lattice structure, (3) computation of these structural contributions to standard state fugacity from compressibility factors and EOS parameters alone, and (4) the direct calculation of gas occupancy from phase equilibrium. Numerical results for densities and equilibrium for systems involving ice and/or gas hydrates predicted by this GHC-based framework are compared to predictions of other equations of state, density correlations, and experimental data where available. Results show that this new GHC-based EOS framework accurately predicts the densities of hexagonal water ice and structure I gas hydrates as well as phase equilibrium for methane–water and CO2–water mixtures. |
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| Keywords: | Hexagonal ice Methane gas clathrate hydrates Multi-scale Gibbs–Helmholtz Constrained equation Lattice structure contributions to standard state fugacity of water Gas hydrate occupancy Structure 1 clathrate hydrates |
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