Phase equilibria, solubility and modeling study of CO2/CH4+tetra-n-butylammonium bromide aqueous semi-clathrate systems

Interest has grown in tetra-n-butylammonium bromide (TBAB) semi-clathrates due to their formation at lower pressures and higher temperatures than conventional gas hydrates. This study focuses on TBAB semi-clathrates formed with carbon dioxide and methane and is to our knowledge the first study to re...

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Bibliographic Details
Published in:Fluid phase equilibria 2015-02, Vol.388, p.160-168
Main Authors: Verrett, Jonathan, Renault-Crispo, Jean-Sébastien, Servio, Phillip
Format: Article
Language:English
Subjects:
Bromides
Carbon dioxide
Equilibrium conditions
Liquids
Mathematical models
Methane
Modeling
Phase equilibria
Semi-clathrate hydrate
Solubility
TBAB
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Summary:Interest has grown in tetra-n-butylammonium bromide (TBAB) semi-clathrates due to their formation at lower pressures and higher temperatures than conventional gas hydrates. This study focuses on TBAB semi-clathrates formed with carbon dioxide and methane and is to our knowledge the first study to report and model semi-clathrate former solubility under hydrate–liquid–vapor equilibrium conditions. A thermodynamic model was developed using the Trebble–Bishnoi equation of state to calculate vapor and liquid phase fugacity. Liquid activity was determined using the electrolyte non-random two liquid model (eNRTL). The solid semi-clathrate phase was modeled using a modified van der Waals–Platteeuw model (vdW–P), with parameters re-optimized based on the data obtained in this study. Equilibrium conditions were successfully modeled over the temperature range of 281–294K, pressure range of 377–11,000kPa and TBAB composition range of 5–40wt%. The model functioned well for carbon dioxide with an average absolute relative error (AARE) of 4.7% for pressure prediction and an AARE of 17.5% for solubility. Methane was more difficult to model and yielded AAREs of 21.6% for pressure and 32.5% for solubility. Further understanding of semi-clathrate crystal structure and interactions between methane and TBAB would aid in improving the model.
ISSN:0378-3812
1879-0224
DOI:10.1016/j.fluid.2014.12.045