2013/07/26 by K. S. Glavatskiy, Glavatskiy, K. S., Thijs J. H. Vlugt +3
Engineering · Environmental Science · Physics and Astronomy · #FOS: Physical sciences #Methane Hydrates and Related Phenomena #Scientific Research and Discoveries #Soft Condensed Matter (cond-mat.soft) #Spacecraft and Cryogenic Technologies
paper · pdf · doi:10.48550/arxiv.1307.6977
openalex publication_date 2013/07/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We determine thermodynamic stability conditions in terms of Helmholtz and Gibbs energies for sI clathrate hydrates with CH4 and CO2 at 278 K. Helmholtz energies are relevant for processing from porous rocks (constant volume), while Gibbs energies are relevant for processing from layers on the ocean floor (constant pressure). We define three steps leading to hydrate formation, and find Helmholtz energy differences from molecular simulations for two of them using grand-canonical Monte Carlo simulations at constant temperature and volume; while the third step was calculated from literature data. The Gibbs energy change for the same steps are also determined. From the variations in the total Helmholtz and Gibbs energies we suggest thermodynamic paths for exchange of CH4 by CO2 in the isothermal hydrate, for constant volume or pressure, respectively. We show how these paths for the mixed hydrate can be understood from single-component occupancy isotherms, where CO2, but not CH4, can distinguish between large and small cages. The strong preference for CH4 for a range of compositions can be explained by these.