Measurements of Hydrate Dissociation Temperature of Methane, Ethane, and CO₂ in the Absence of Any Aqueous Phase and Prediction with the Cubic Plus Association Equation of State

Gas hydrate formation is undesired in processing and gas distribution. Therefore, it is important to have a thermodynamic model that predicts correctly gas hydrate formation. Hydrate formation is very well studied in the literature in the presence of liquid water, and hydrate thermodynamic models predict correctly its formation. However, only very little information can be found concerning gas hydrate formation without an aqueous phase. A new experimental procedure combining an equilibrium cell with a water measurement by a Karl Fischer coulometer was developed. The water content of the vapor phase is measured as a function of the temperature, and the hydrate dissociation temperature is determined by the slope change of the curve. In the first step, the dissociation temperatures of methane hydrate, ethane hydrate, and carbon dioxide hydrate were determined at different pressures and for different water amounts. In the second step, the obtained results were compared with the literature data and with the calculated values using the classical Platteeuw and van der Waals model associated with the Soave−Redlich−Kwong and the cubic plus association equations of state to calculate the water fugacity in the vapor phase.