Hydrate-liquid-vapor equilibrium condition of N2 + CO2 + H2O system: Measurement and modeling

Hydrate dissociation equilibrium conditions for the mixture of carbon dioxide (CO2), nitrogen (N-2), and water (H2O) are measured in the temperature range of 274.15-280.15 K. The relative molar composition of carbon dioxide in the feed gas mixture varies between 0.05 and 0.25 which is the interesting range of composition when it comes to production of methane, and sequestration of carbon dioxide, from methane hydrate reservoirs. A thermodynamic model is presented based on the classical van der Waals and Platteeuw (vdW-P) solid solution theory for the hydrate phase combined with the Equation of State (EoS) for combustion gas and combustion gas-like mixtures (CG-EoS). The results of this model are compared to the dissociation data measured here, along with all available data from the experimental literature. The predicted results from two thermodynamic software programs, CSMGem, and Multiflash (which use Peng-Robinson (PR) and Cubic Plus Association (CPA) EoSs respectively), are also statistically evaluated. A Clausius-Clapeyron type equation was used to derive the enthalpy of dissociation at 279.15 K, and the values were found to converge for mixtures containing 0.1-0.25 mol fraction of carbon dioxide.