THE INFLUENCE OF GAS-PHASE FUGACITY AND SOLUBILITY ON CORRELATION OF GAS-HYDRATE FORMATION PRESSURE

The dissociation pressure for single gas-hydrate systems is correlated by van der Waals and Platteeuw's model with a Kihara spherical-core potential for the interaction between water and the guest molecule. By fitting to dissociation pressures along the hydrate-ice-gas-line, Kihara parameters are obtained independent of the mutual solubility of the gas and water. Further, the fugacity coefficients in that region are close to unity so that the Kihara parameters are rather insensitive to the choice of equation of state. By fitting to the ice-line only, we can investigate to what extent the equation of state fugacities influence the calculated dissociation pressures along the hydrate-water gas and hydrate-water-condensate equilibrium lines. By comparing the calculated equilibrium data to the experimental data we can conclude that an accurate prediction of hydrate dissociation pressures requires an equation of stat which gives an accurate correlation of fugacities rather than densities, and that it is necessary to take gas solubility into account even for non-polar gases like nitrogen and methane. Such investigation has not been reported previously. The Kihara parameters for the single gas-hydrate systems are estimated using the thermodynamically stable hydrate structure.