Influence of combining rules on the cavity occupancy of clathrate hydrates using van der Waals-Platteeuw-theory-based modelling

In the current study, we report an extensive series of thermodynamic calculations using continuum-level models based on the van der Waals-Platteeuw theory. The calculations are performed along the three phase hydrate-liquid water-vapor (H-L-W-V) or hydrate-ice-vapor (H-I-V) equilibrium curve for a number of gases of industrial interest (e.g., methane, ethane, propane, nitrogen and carbon dioxide). We examine the effect of deviations from the classical Lorentz-Berthelot combining rules on the hydrate equilibrium conditions as well as the cavity occupancy of the hydrates and work towards quantifying it. Hydrate equilibrium predictions have a very strong sensitivity to deviations, while cavity occupancies exhibit a weaker sensitivity. Furthermore, the sensitivity is stronger on the small cavities compared to the case of the large cavities. Model calculations are compared against experimental data for selected systems with reasonable agreement. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.