Applicability research of thermodynamic models of gas hydrate phase equilibrium based on different equations of state

Abstract

Choosing an appropriate equation of state and thermodynamic model is very important for predicting the phase equilibrium of a gas hydrate. This study is based on statistical thermodynamics, considering the changes in water activity caused by gas dissolution, and deriving and summarizing four thermodynamic models. Based on the 150 collected experimental data points, the accuracy of the four thermodynamic models in predicting the phase equilibrium of methane hydrate, ethane hydrate, and carbon dioxide hydrate were compared. In addition, the influence of five equations of state on each thermodynamic model's phase equilibrium prediction accuracy is compared. The analysis results show that in the temperature range of 273.40–290.15 K, the Chen–Guo model is better than other thermodynamic models in predicting the phase equilibrium of methane hydrate by using the Patel–Teja equation of state. However, in the temperature range of 290.15–303.48 K, the John–Holder model predicts that the phase equilibrium of methane hydrate will perform better. In the temperature range of 273.44–283.09 K, the John–Holder model uses the Peng–Robinson state to predict the phase equilibrium of carbon dioxide hydrate with the highest accuracy. In the temperature range of 273.68 K to 287.6 K, the Chen–Guo model is selected to predict the phase equilibrium of ethane hydrate with the highest accuracy. However, as the temperature increases, the predicted values of the vdW–P model and the Parrish–Prausnitz model deviate further from the experimental values.